US3236438A

US3236438A - Thermoplastic valved bags

Info

Publication number: US3236438A
Application number: US259708A
Authority: US
Inventors: Chester D Rhodes
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1963-02-19
Filing date: 1963-02-19
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22

Description

Feb. 22, 1966 c, RHODES 3,236,438

THERMOPLAS TIC VALVED BAGS Filed Feb. 19, 1963 CHESTER D. RHODES INVENTOR.

120mm 4,%/n /Juul ATTORNEY.

United States Patent Ofiice 3,236,438 Patented Feb. 22 1966 3,236,438 THERMOPLASTIC VALVED BAGS Chester D. Rhodes, Wilbraham, Mass., assignor to Monsanto Company, a corporation of Delaware Filed Feb. 19, 1963, Ser. No. 259,708 2 Claims. (Cl. 22962.5)

This application is a continuation-in-part of copending application S.N. 157,028, filed November 16, 1961, now Patent Number 3,087,670 which is a continuation of application Serial No. 788,970, filed January 26, 1959, and now abandoned.

The present invention relates to novel bags and to methods for preparing same.

In the copending application a novel valved thermoplastic bag is described wherein a valve sleeve member is heat sealed inside a corner portion of a tubular thermoplastic bag blank. The valve sleeve member of that bag is of substantially thinner gauge than the rest of the bag and consequently a novel selfc1osure effect is attained. It has now been found that the self-closure effect can be further improved by utilizing a plurality of sleeve members rather than the unitary valve member described in the copending application.

Accordingly, it is a primary object of the present invention to provide novel self-closing valved bags of substantial volumetric capacity which are fabricated from thermoplastic materials and methods for preparing same.

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

These and other objects are attained in a valved bag comprising, in combination, a tubular body of thermoplastic film that is heat sealed across its top, a top corner of said tubular body being folded into the bag and constituting a valve flap, and a plurality of valve sleeves of thermoplastic film which are heat sealed at one end to the valve flap and at a lengthwise portion thereof partially across the top of the bag.

The objects and advantages of the invention will be apparent from the following detailed description thereof when read in conjunction with the attached drawings in which:

FIGURE I is an elevation of a blank from which the valved bag is to be prepared;

FIGURE II is a plain view of the valve sleeves illustrated in FIGURE I before its attachment to the bag blank;

FIGURE III is a fragmentary top plan view illustrating the manner in which the valved sleeves and a contiguous corner of the tubular blank illustrated in FIGURE I are folded into the mouth of the bag blank prior to heat sealing the top of the bag;

FIGURE IV is a fragmentary perspective side view of the sealed valve bag from FIGURE III with parts broken away;

FIGURE V is a fragmentary perspective side view of an alternate embodiment of a sealed valve bag with parts broken away illustrating triangularly cut sleeve members.

Referring to FIGURE 1, is a tube of thermoplastic film which is heat sealed at its bottom 22 and which has a top peripheral edge 24. The upper left-hand corner of tube 20 (defined by side 26, top peripheral edge 24 and folded line 28) is designated as 30 and is destined to become the valve flap in the finished bag. The

valve sleeves

32 and 34 are heat sealed to tube 20 adjacent edge 24 at 36. The valve sleeve 32 is fabricated from thermoplastic film which is either equal to or thinner than the gauge employed for the fabrication of tube 20. Valve sleeve 34 is longer than the valve sleeve 32 and is fabricated from thermoplastic film having a substantially thinner gauge than that employed in tube 20. In general, valve sleeve 34 will be fabricated from 1-2 mil film which will be membrane-like in effect, whereas tube 20 Will be fabricated from 5-10 mil film with valve sleeve 32 lying in thickness somewhere between these two ranges. If desired, the number of valve sleeves may be increased with the longest sleeve member preferably being the thinnest in gauge. In FIGURE II

valve sleeves

32 and 34 are shown with a common center fold line designated as 38 and common vertical edges designated as 40 and 42 respectively.

In FIGURE III

valve sleeves

32 and 34 and corner 30 of tube 20 are folded into the mouth of tube 20 so that the

common sleeve edges

40 and 42 are positioned within and in juxtapositioned relationship with the peripheral edge 24 of tube 20. While in the position illustrated in FIGURE III, the edge assembly of 24, 40, 42 and 24 is heat sealed to form a unified top seal 44 as illustrated in FIGURE IV. It will be noted that the terminal end 46 of top seal 44 extends to the left of seal 36 which was employed to join

valve sleeves

32 and 34 adjacent and parallel to edge 24 of tubular blank 20 (see FIGURE I). This feature of the seal is an important element of the present invention and its significance is discussed in the next paragraph below. The valve of the finished bag consists of a valve flap 28,

valve sleeves

32 and 34 and a valve opening 48.

The manner by which the valve bags are filled may be described with reference to FIGURE IV. It will be noted that the major portion of the thinner gauge film of the valve sleeves lies to the right of the heat seal 36 and is supported at the area of seal by an underlying section of the higher gauge film from which the body of the bag is fabricated. When the bag is filled, the contents of the bag press the plurality of valve sleeves against the main top portion of the tube to effect a closure. By using more than one sleeve member, a multiple plugging or self-closure effect is attained which is superior to that obtainable with a unitary valve sleeve member. By fabricating the final or longest sleeve member of substantially thinner gauge to be membrane-like in effect, a tight closure will be effected. Consequently, the thickness of the longest valve sleeve member is very important. By the longest member is meant that member which projects furthermost laterally across and parallel to the edge 24 of the tube 20. Generally, tube 20 has to be extremely strong and therefore thick enough to support heavy loads. If the longest valve sleeve member were to be constructed of the same thickness film as tube 29, it may be possible to eliminate the heat seal 36 but to do this would greatly diminish, if not destroy, the valves unique self-closing feature. For example, the pressure of the contained material will immediately collapse the membrane-like valve sleeve member and plug up the valve opening regardless of the direction the bag may be turned. It is also desirable that valve sleeve 32 and any other intermediate sleeve be of thinner gauge than the body of the bag to increase the plugging or self-closing effect. In general, as the gauge or thickness of the valve sleeves is increased, their flexibility and self-closing effect tends to decrease. The preferable and optimum closure effect is obtained wherein the various valve sleeves decrease in gauge as their length increases, with the longer sleeve sections arranged to nest within the shorter sections, the final or longest member being of sufliciently thin gauge to be membrane-like in effect. It is, of course, possible to separately seal the thinner gauge sleeve members to the open end or ends of the heavier gauge sleeve members. However, this tends to increase the operational steps necessary to fabricate the bag.

As shown in FIGURE IV, the edges 50 and 52 of the valve member 34 are folded parallel to one another. It is sometimes desired and preferable to cut one of the edges, as shown in FIGURE V, triangularly with an apex at 54 to obtain a stronger and more uniform heat seal along the top of the bag. This may be similarly done with the other valve members making up the valve sleeve bag. In the subsequent discussion of the invention and in the claims, this geometric form will be referred to as a corner truncated rectangle. When the valve sleeve members are cut in this fashion, the assembly of layers of thermoplastic film change more gradually and more uniformly in thickness than the corresponding assembly illustrated in FIGURE III.

The valved thermoplastic bags can be fabricated from such heat-sealable plastic materials as polyethylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyisobutylene, polypropylene, polytetrafluoroethylene and the like.

The preferred material of construction is polyethylene, a solid, tough polymer of ethylene which can be manufactured in film-form in thicknesses less than one mil. It is light in weight, extremely low in water absorption and moisture permeability and consequently is an excellent material for packaging uses. In addition layers of polyethylene can be heat sealed or fused together to present a strong bond. It is also preferable to utilize the same material for the construction of both the bag and the various sleeve members since optimum fusion of two or more layers of film can only be accomplished if the fusion temperatures of the various joining layers are approximately within the same temperature range.

The valved bags of this invention ordinarily will have a substantial volumetric capacity, e.g., at least 1 cubic foot, and are designed primarily to carry from about 50 to about 100 pounds of such common pulver-ulent materials such as cement, flour, fertilizer, carbon black, chemicals and the like. The walls of the bag ordinarily will have a thickness of the order of 510 mils, although obviously the walls may be either thinner or thicker as indicated by the use to which the bags are to be put. If desired, the walls of the bag can be fabricated from a plurality of plies of thin thermoplastic film. The valve sleeves ordinarily will be thinner than the walls of the bag. In general, the longest sleeve will be fabricated from film which is about .5 to 4 mils thick depending on the strength and flexibility of the material, and in the case of polyethylene, thicknesses of 12 mils are generally sufficient to effect a membrane-like flexibility in the material.

The above descriptions and particularly the drawings are set forth for purposes of illustration only. Many variations and modifications thereof will be obvious to those skilled in the art and can be made without departing from the spirit and scope of the invention herein described.

What is claimed is:

1. A valve bag comprising, in combination, a tubular body of thermoplastic film that is heat sealed across its top, a top corner of said tubular body being folded into the bag and constituting a valve flap and a plurality of valve sleeves of thermoplastic film of various lengths which are thinner gauge than the thermoplastic film of said tubular body and which are heat sealed at one end to the valve flap and at a lengthwise portion thereof partially across the top of the bag, the longest sleeve being of minimum gauge and substantially thinner gauge than the gauge of said tubular body so as to be membrane-like in effect, the thickness of the tubular body in relation to the thicknesses of the various valve sleeves and the relative thicknesses and lengths of the various valve sleeves being such to effect multiple plugging thereby obtaining a tight closure.

2. A valve bag comprising, in combination, a tubular body of thermoplastic film that is heat sealed across its top, a top corner of said tubular body being folded into the bag and constituting a valve flap and a plurality of valve sleeves of thermoplastic film of various lengths which are of thinner gauge than the thermoplastic film of said tubular body and which are heat sealed at one end to the valve flap and at a lengthwise portion thereof partially across the top of the bag, the longest sleeve being of minimum gauge and substantially thinner gauge than the gauge of said tubular body so as to be membrane-like in effect; the unsealed edges of each valve sleeve being formed in triangular relationship to obtain a stronger and more uniform heat seal across the top of the bag.

References Cited by the Examiner UNITED STATES PATENTS 2,542,170 2/1951 Weeks.

2,708,067 5/1955 Paton 229-625 3,065,899 11/1962 Means 229-62.5 3,087,670 4/1963 Rhodes 269-625 FOREIGN PATENTS 1,025,255 2/1958 Germany.

FRANKLIN T. GARRETT, Primary Examiner.

EARLE I. DRUMMOND, Exam'iner. I

Claims

1. A VALVE BAG COMPRISING, IN COMBINATION, A TUBULAR BODY OF THERMOPLASTIC FILM THAT IS HEAT SEALED ACROSS ITS TOP, A TOP CORNER OF SAID TUBULAR BODY BEING FOLDED INTO THE BAG AND CONSTITUTING A VALVE FLAP AND A PLURALITY OF VALVE SLEEVES OF THERMOPLASTIC FILM OF VARIOUS LENGTHS WHICH ARE THINNER GAUGE THAN THE THERMOPLASTIC FILM OF SAID TUBULAR BODY AND WHICH ARE HEAT SEALED AT ONE END TO THE VALVE FLAP AND AT A LENGTHWISE PORTION THEREOF PARTIALLY ACROSS THE TOP OF THE BAG, THE LONGEST SLEEVE BEING OF MINIMUM GAUGE AND SUBSTANTIALLY THINNER GAUGE THAN THE GAUGE OF SAID TUBULAR BODY SO AS TO BE MEMBRANE-LIKE IN EFFECT, THE THICKNESS OF THE TUBULAR BODY IN RELATION TO THE THICKNESS OF THE VARIOUS VALVE SLEEVES AND THE RELATIVE THICKNESS AND LENGTHS OF THE VARIOUS VALVE SLEEVES BEING SUCH TO EFFECT MULTIPLE PLUGGING THEREBY OBTAINING A TIGHT CLOSURE.