US 3120336 A
Description (OCR text may contain errors)
Feb. 4, 1964 FIG.I
A. WHATLEY, JR
POUCH Filed March 9. 1960 FIG.2
INVENTOR ALLAN WHATLEY, JR,
AGENT United States Patent 3,120,336 POUCH Allmi Whatley, Jr., Middletown, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Mar. 9, 1960, Ser. No. 13,808 1 Claim. (Cl. 229-66) This invention relates to a pouch formed by the heat sealing of a thermoplastic material and to the method of sealing the pouch. More particularly it relates to a moisture-impermeable pouch having an easily rupturable seal. Even more particularly, this invention relates to a pouch, as just described, which is light proof so as to be usetul in the packaging of photographic film.
Heat sealing of thermoplastic material is well-known in the packaging ar-t. However, it is difiicult to obtain a seal which, at the same time, is both impermeable to water vapor and easily opened. In packaging of certain types of material, such as photographic material which must be opened in darkness or serniarkness, it is considered particularly objectionable if the package is not readily opened or if any tools are required to open the package.
An object of this invention is to provide a thermallysealed pouch which is impermeable to moisture but which can be easily ruptured, without the use of tools, when it is desired to have access to the contents of the pouch. Another object is to provide a light-proof, moistureresistant pouch for packaging light-sensitive photographic film which will both provide maximum protection to the film when sealed and will also be capable of being opened quickly and easily in a photographic darkroom without the use of tools. Still other objects will be apparent from the [following description of the invention.
.These and other objects are accomplished by the pres ent invention which comprises a pouch of thermoplastic material having a high resistance to the transmission of water vapor, said pouch being permanently sealed on all sides but one, and further being closed on the remaining side with at least one easily rupturable seal at least a portion of which presents a wavy-line configuration to the interior of said pouch.
Pouches of thermoplastic material which are closed on all sides with straight line seals are not within the scope of this invention. Further, lbroad seals which may have a wavyline configuration for decorative or aesthetic purposes at their extreme end but nevertheless have a straight line configuration across the poition of the seal adjacent the interior of the pouch are likewise not within the scope of this invention since they do not embody the easy opening feature of the invention. To be within the scope of the present invention, the easily rupturable seal must present a wavy-line configuration to the interior of the pouch so that when the material of the pouch at the front and back of the pouch, above or below and near the seal line is pulled in opposite directions the stresses will be concentrated at the top or the bottom of the waves,
respectively, greatly facilitating the rupturing of the seal.
The easily rupturable seal of this invention can be up to about 0.1 inch wide but is preferably from about 0.02 to about 0.1 inch wide.
The detailed features of preferred embodiments of this pouch and method of forming same will be more readily understood with respect to the accompanying drawing wherein FIGS. 1, 2 and 3 are illustrations of preferred embodiments of pouches of this invention.
The easily ruptura'ble seal can be formed in diiferent ways; in one preferred embodiment shown in FIG. 1 it can consist of a seal 11 whose entire length is a wavy line. In another preferred embodiment shown in FIG. 2 it can consist of two substantially parallel wavy-line seals 12 and 13 in reasonably close proximity across one end.
In still another preferred embodiment shown in FIG. 3 the easily rupturable seal can have the configuration in which two straight-line portions 14 and 15 are connected with a wavy-line portion 16 said straight-line portions contacting the parallel sides of said pouch 17 and 18 at an oblique \angle. In all three figures the pouches shown have been made of a thermoplastic material, e.g., tubular polyethylene which has a permanent seal along the bottom. The pouch can also be made with thermoplastic sheets and have permanent seals along the bottom and sides. The tops of the pouches shown in the figures have not been cut off above the wavy-line seal, but it is possible to make satisfactory seals by cutting off the pouch tops down to the seal as will be described below.
The apparatus used for carrying out the process of this invention is essentially that described in A. Fener et al., U.S. Patent 2,796,913. The only significant difference between the apparatus of that patent and the apparatus of the present invention is the modification of the sealing band and its supporting members. U.S. Patent 2,796,913 shows a simple, tensioned cutting wire of Nichrome (No. 21 of FIG. 2) over which the thermoplastic material to be sealed is placed. In the present invention this wire is replaced by an appropriately designed sealing band under which is placed the thermoplastic material to be sealed. One particular sealing band is a Nichrome ribbon having a wavy configuration in the central portion while the end portions are straight. Other sealing bands can be used to obtain the particular configuration of the seal desired.
In all embodiments the wavy section or" the seal facilitates the seal opening by concentrating the stresses at the top or bottom of the waves when material of the pouch at the dront and back of the pouch near the seal line is pulled in opposite directions, e.'g., when force is applied above or below the seal line, respectively. In the pouch shown in FIG. 3 the ends of the straight portion of the seal provide a V on the sides of the pouch once the seal is opened. -By pulling the material of the pouch on either side of the V the sides of the pouch can be torn down to or below the contents of the pouch so that the contents can be easily removed. The straight line portions of the seal 14 and 15 make it possible for a single sealing apparatus to accommodate pouches having considerable variation in width and still make the desired type of seal which is at the same time moisture impermeable and yet easily rupturable.
The invention will be further illustrated by the following examples. They exemplify suitable types of pouches which can be heat sealed and cut off by the process of this invention but are not intended to limit the invention.
Example I Tubularly extruded black polyethylene, 6 mils (0.006 inch) (210%) in thickness, was chopped in 21 inch lengths, flattened, and heat sealed at one end by a conventional, straight bar, heat sealer to give a permanent, moisture-impermeable seal. Thus, open-ended pouches were formed, the diameter of the extruded polyethylene tube having been such as to give a width of 15.5 inches when flattened to form pouches. The black polyethylene was produced from a base resin having a density of 0.9200.923 and a melt index within the range 1.8-2.7. After addition of 6% by weight of carbon black the density increased to 0.934-0937.
One of these open-ended pouches was filled with sheets of 14 inch x 17 inch medical X-ray film and then closed by heat scaling in the apparatus described earlier. The heating band trimmed oil the excess material extending beyond the seal simultaneously with the formation of the seal itself. The sealing band was applied at a pressure of 10 lb./inch a temperature of about 310 F., and a heating period of 1.5 seconds followed by 4.5 second amazes cooling period before release of pressure. The molten thermoplastic material solidified during the cooling period so as to strengthen the seal and assure its moistureimpermeability.
The seal thus formed across the top of the pouch was one similar to that illustrated in FIG. 3 and was easily opened by an X-ray technician under darkroom conditions by simply pulling in opposite directions on the polyethylene at the front and back of the pouch near the seal. Once the seal was opened, the ends of the straight portion provided a V on either side of the pouch. By pulling the polyethylene on either side of these Vs, the sides of the pouch were torn down to points slightly below the sheets of film contained therein, thus permitting easy removal of the contents of the pouch.
An identical pouch, unfilled, was sealed as described above except that it was held in such a manner that it was partially inflated by the entrapment of a considerable volume of air. When this inflated pouch was gently submerged under water there was no evidence of escaping air bubbles. By sharply striking the sides of the submerged pouch, however, the wavy portion of the seal was ruptured and bubbles of air were seen escaping.
Example 11 Example I was essentially repeated except that a stack of 75 sheets of medical X-ray film, 8 inches x 10 inches in size and interleaved with sheets of black paper, were placed in a black polyethylene pouch which was 9.5 inches x 14 inches in size. The same sealing apparatus as used in Example I was used except with a sealing bar which gave a configuration of seal similar to that in FIG. 1. The seal was tested as described in Example I and found to produce a moisture-impermeable, easily rupturable seal.
Example 111 Example I was essentially repeated except that a stack of 100 sheets of medical X-ray film, 10 inches x 12 inches in size, were placed in a black polyethylene pouch which was 11.5 inches x 16 inches in size. The same sealing apparatus as used in Example I was used except with a sealing bar which gave a configuration of seal similar to that in FIG. 2. The seal was tested as described in Example I and found to produce a moisture-impermeable, easily rupturable seal.
Example IV Example I was essentially repeated except that a stack of 25 sheets of medical X-ray film, 11 inches x 14 inches in size and interleaved with sheets of black paper, were placed in a black polyethylene pouch which was 12.5 inches x 18 inches in size. The same sealing apparatus as used in Example I produced a similar seal which was tested as described in that example and found to produce a moisture-impermeable, easily rupturable seal.
Example V Example I was repeated as to pouch dimensions and contents thereof. The material of the pouch, however, was of mil i polyethylene. The sealing band was applied at a pressure of 8 lb./inch a temperature of about 275 F., and a heating period of 2 seconds followed by a 2 second cooling period before release of pressure. An excellent seal was produced, being at the same time moisture-impermeable and easily rupturable.
Example VI Example I was repeated as to pouch dimensions and contents thereof. The material of the pouch, however, was of 7 mil (i10%) polyethylene. The sealing band was applied at a pressure of 12 lb./inch a temperature of about 250 F., and a heating period of 1.5 seconds followed by a 1 second cooling period before release of pressure. An excellent seal was produced, being at the same time moisture-impermeable and easily rupturable.
4 Example VII Example I was repeated as to pouch dimensions and contents thereof. The material of the pouch, however, was of 8 mil (i10%) polyethylene. The sealing band was applied at a pressure of 10 lb./inch a temperature of about 225 F., and a heating period of 1.5 seconds followed by immediate release of pressure. An excellent seal was produced, being at the same time moisture-impermeable and easily rupturable.
Example VIII A commercially available open-ended pouch, formed from two superimposed 8 inch x 10 inch sheets of heat sealable polyester film, 2.5 mils in thickness, had been sealed along 3 of its 4 sides by conventional, straight-line seals. This transparent pouch, unfilled, was closed by the method of sealing described in Example I to form a moisture-impermeable seal which was easily ruptured by pulling the material at the front and back of the pouch near the wavy portion of the seal.
Example IX An open-ended, 18 inch x 25 inch, translucent pouch was made from two superimposed sheets of polypropylene, 4.5 mils in thickness, by using conventional, straight-line heat sealing to close 3 of the four sides. The pouch was sealed and tested as described in Example VIII.
Example X One hundred sheets of 14 inch x 17 inch medical X- ray film were packaged, according to conventional, commercial procedure, in a foil-paper laminate which was hand-wrapped and tape-sealed around the bundle of cutsheet film, then inserted into a cardboard box. Another one hundred sheets of film, cut from the same widestock film coating, were packaged in a 6 mil black polyethylene pouch as described in Example I, the sealed pouch then being inserted into a cardboard box like the one mentioned above.
The two boxes were placed side-by-side for one week in an accelerated aging oven maintained at 120 F. and 65% relative humidity. Then the boxes were opened under dark light conditions and the outside sheets from each box were placed between X-ray intensifying screens and given identical X-ray exposures through a squareroot-of-two aluminum step wedge, simulating the exposure normally used in radiography of the human chest.
After exposure, the films were developed for 5 minutes at 68 F. in a solution containing 3 g. monomethylp-amino phenol sulfate, 9 g. hydroquinone, 50 g. Na sO (anhydrous), 50 g. K CO 4.5 g. KBr and H 0 to make 1 liter. Processing was continued by fixing 'for 10 minutes at 68 F. in Du Pont 2-F (White Alum) Fixing Bath (p. 5-26, Photo Lab Index, 1959), and Washing for 10 minutes in tap water. Densities at the various exposure steps of the dried fil rns were read on a stroboscopic photoelectric densitometer similar to that described by D. R. White, J. Soc. Motion Picture Television Engrs. 33, October 1939, p. 403. Calculations based on these density readings gave the following results:
Conventional 6 ml. polylackage ethylene Pouch Relative Speed 113 G anuua 2. 27 2. 35 Fog 30 29 experimental data, to provide protection (particularly against penetration of moisture) equivalent to that of the foil-paper laminate.
Example XI A number of boxes containing 100 sheets of each of 14 inch X 17 inch medical X-ray film were packaged as described in Example X, some boxes having the foilpaper laminate and others having the sealed black polyethylene pouch. The boxes and their contents were placed for one hour on a vibrating machine which comprised a table moved by an eccentric in simultaneous back and forth and up and down motion. The vibration frequency was approximately 300 per minute and a force of approximately one G acted upon the packaged products. This vibration test was designed to simulate the effect of a moving truck base, i.e., to simulate the efiect of transporting the packaged product from point of manufacture to its ultimate destination. At the conclusion of the test it was found that the film packaged in the foil-paper laminate had an average of 28.5 detectable abrasion marks per box while the pouch packaged film had an average of 28.0 detectable abrasions per box. The resistance to abrasion was thus considered to be equivalent for the two methods of packaging.
Example XII A commercially available film is cast from a copolyester prepared by ester interchange polymerization of a mixture of 1 molar part of isophthalic acid, 3 molar parts of terephthalic acid and 4 molar parts of ethylene glycol. An open-ended pouch was formed from two superimposed, rectangular sheets of this copolyester film 7 inches x 9 inches in area and 2.2 mil-s in thickness, by conventional, straight-line, heat sealing along three of the four edges. This transparent pouch, unfilled, was closed by the method of sealing described in Example I to form a moisture-impermeable seal which was easily ruptured by pulling the material at opposite sides of the wavy portion of the seal.
Example XIII An open-ended pouch was formed from two superimposed, rectangular sheets of clear polyethylene film, 20 inches x 25 inches in area and 2 mils in thickness, by conventional, straight-line, heat sealing along three of the four edges. This pouch, unfilled, was closed by the method of sealing described in Example l to form a moisture-impermeable seal which was easily ruptured by pulling the material at opposite sides of the wavy portion of the seal.
Example XIV Example XIII' was essentially repeated except that the pouch was formed from clear polyethylene sheets, 9.5 inches x 11 inches in area and 2.5 mils in thickness.
Example XV Example XIII was essentially repeated except that the pouch was formed from clear polyethylene sheets, 10.5 inches x 12 inches in area and 3.5 mils in thickness.
Although the present invention has been applied specifically to the packaging of light-sensitive photographic sheet material, it is possible to visualize many other applications. For instance, such a pouch would be useful in the packaging of certain types of foods or any other materials which are moisture-damageable. The easyopening feature of the invention would be of advantage in the packaging of almost any type of commodity. The material from which the pouch is manufactured can be any thermoplastic material which is itself heat sealable, or any sheet material which can be coated or laminated with a thermoplastic material, e.g., polyethylene, so as to make the composite structure heat sealable. The pouch may be opaque to light as in the examples related specifically to the packaging of photographic products, or it may be transparent or translucent, depending upon the desired use. Preferably, the thickness of the material from which the pouch is manufactured may be from 1 mil to 10 mils or thicker depending upon the strength required of the pouch. In packaging of photographic products, adequate protection against moisture penetration requires a certain minimum thickness of packaging material, e.g., 3 to 5 mil polyethylene, depending upon its density. The size of the pouch itself is limited only by the intended use since this type of seal is operable over a very wide range of pouch sizes. The examples have illustrated the formation of the described seal by a hand operated apparatus. It is obvious that a seal of this type could be formed equally well in a partially or fully automatic apparatus. A Nichrome ribbon has been described as the heating and cutting element; also, a Nichrome wire has satisfactorily performed the heating and cutting function.
The seal is particularly advantageous in the photographic trade where the packaged product must be opened in the dark, or under safe light conditions, where it would be hazardous to use sharp tools for opening the package. The pouch herein described is ideally suited for being easily opened in the photographic dark room. The seal is advantageously unique in that it combines this requirement of being easily opened with moistureimpermeability. These same features of moisture impermeability and being easily opened would, of course, be advantageous in the packaging of other materials. This type of seal is rapid, simple and quite economical.
As many widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as defined by the claim.
What is claimed is:
A pouch of flattened, tubular, light-opaque polyethylene containing a light-sensitive, moisture-damageable material having at least one end closed by a pair of essentially parallel, easily rupturab'le, heat seals extending entirely across said end, both seals being spaced from one another in reasonably close proximity and both having the configuration of -a wavy line of from about 0.02 to about 0.1 inch in width.
References Cited in the file of this patent UNITED STATES PATENTS 2,133,946 Bloomer Oct. 25, 1938 2,468,517 Salfisbeng Apr. 16, 1949 2,751,074 Ringlen et all June 19, 1956 2,754,865 Moore July 17, 1956 2,796,913 Fener et 'al June 25, 1957 2,976,989 Wiesner Mar. 28, 1961 FOREIGN PATENTS 773,078 France Aug. 25, 1934