US3263891A

US3263891A - Low density container for liquids

Info

Publication number: US3263891A
Application number: US354551A
Authority: US
Inventors: Jr Latane D Brugh
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-03-25
Filing date: 1964-03-25
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02

Description

g- 2, 1965 1.. D. BRUGH, JR 3,263,891

LOW DENSITY CONTAINER FOR LIQUIDS Filed March 25, 1964 2 Sheets-Sheet 1 INVENTOR.

LATANE E BRUQH ATTORNEY 2, 1966 L. D. BRUGH, JR 3,263,891

LOW DENSITY CONTAINER FOR LIQUIDS Filed maro h 25, 1964 I 2 sheets sheet 2 k k A v :2 -#-$4 m 1 FIG 2 m soooog E W i m I Z I i zsooog I i a a a a 5600- a i a m mo :50 290 250 30a 350i 400 Msas waaem' man-- INVENTOR. LATANE D. BRUGH ATTORNEY United States Patent 3,263,891 LOW DENSITY CONTAINER FOR LIQUIDS Latane I). Brugh, Jr., Rte. 1, Covington, Va. Filed Mar. 25, 1964, Ser. No. 354,551 7 Claims. (Cl. 2293.1)

The present invention pertains to a novel container of the type used for packaging of liquids.

At present, a large portion of the containers used in packaging liquids are formed of a stiff paper, generally referred to as paperboard or simply, board, with a moisture resistant coating. In the packaging of milk, for example, this type of container has, to a large extent, supplemented other types of containers, such as glass bottles.

In forming paper, liquid containers, certain criteria have heretofore dictated the use of a paper stock of relatively high basis weight and density; the term basis weight, as used herein, referring to the weight per 3,000 square feet of board, while the term density is expressed as the ratio of basis weight to caliper or thickness measured in thousandths of an inch.

Thus, since economic considerations require that the cartons be filled and sealed on high-speed, automatic packaging machinery and because of this, the cartons must possess a certain amount of stiffness, a fairly heavy, dense board has generally been felt necessary. Similarly, in handling and storage of the cartons subsequent to filling .and sealing, the necessity of rigidity and resistance to bulge has led the industry to require a paper stock of relatively high basis weight.

An additional consideration, which to a great extent has limited the type of paper stock usable in liquid containers, is the adaptability of the stock to coating with a moisture-proof material. For example, if the surface of the board is fairly rough or uneven, with fibers, or groups of fibers, extending away from the general surface of the board, the coating will be thin in some spots with many of the fibers and fiber groups extending through the coating.

This will usually result in an unacceptable carton since the thin spots are possible sources of subsequent carton failure and the discontinuities in the coating caused by protruding fibers provide paths for moisture to travel into the board.

In prior art cartons, this roughness has been overcome by passing the carton stock through a plurality of calender stacks; thereby forming a dense, smooth surfaced board. Of course, in producing this type of board, the cost will necessarily be 'higher than in the production of less dense board of comparable thickness since the fiber content will be proportionately greater.

Another manner in which unevenness of the board might be compensated for would be to increase the thickness of the moisture-proof coating to a point where all fibers were completely covered. However, since the cost of the coating material is relatively high, this approach,

for the most part, is impractical.

Closely related to these considerations is another which results from the construction of the cartons generally used in this type of packaging. Thus, in the formation of paper, liquid containers, a longitudinal seam is generally formed as a lap joint running the length of the carton; resulting in severed uncoated edge of a carton blank being placed on the inside of the carton in contact with the liquid product. Because of this, it had previously been thought that a comparatively high density board must be used to prevent absorption by this edge, or wicking, as it is referred to by those skilled in the art.

Therefore, for reasons of stiffness, good coatability and non-absorption, paper, liquid containers have, as noted supra, been heretofore formed from a fairly heavy, dense board. For example, in the construction of half- 7 3,263,891 Patented August 2, 1966 "ice gallon containers, a stock having a basis weight of approximately 286 pounds and a density, or ratio of basis weight to thickness, of 13 is most commonly used. With smaller cartons, such as quarts, while the same density is used, a thinner, lighter stock of 208 pounds per 3,000 square feet has been found acceptable.

While stock of this type, suitably coated with a moist-ure resistant covering such as polyethylene, provides a satisfactory carton, it would be, of course, desirable to reduce the basis weight of the container stock, and hence, its cost, if the characteristics of stiffness, smoothness and non-absorption present in more expensive container stock could be retained.

The present invention achieves these requirements and permits the construction of cartons having the desired stiffness, smoothness, and non-absorption of prior art cartons but with paperboard of much lighter weight, and hence, appreciably lower cost.

In achieving these results, applicant found that if the thickness of the stock used for the cartons was increased, the basis weight could be greatly reduced and the stiffness of the carton board retained or even slightly increased.

While this lighter, lower density board exhibited a rough or flulfed up surface, unsuitable as a coating base, it was found that if it was subjected to a limited amount of heat and pressure after formation, little change in the overall caliper or density and hence, stiffness resulted, but the surface so treated took on a smoothness heretofore found only in denser, more compact stock. Thus, a well-formed continuous coating comparable to that found on heavier more expensive cartons is attained with no increase in coat weight.

It was further discovered that, contrary to expected results, wicking or absorption by the uncoated raw edge of the uncompacted board forming the carton remained about the same as in cartons formed of denser, heavier board.

These, and other advantages and features of the carton of the present invention will become apparent from the following description and accompanying drawings where- FIGURE 1 is a crosssectional, comparison view through a carton wall of the prior .art and .a carton wall according to the present invention;

FIGURE 2 is a somewhat schematic representation of the manner in which the surface of the stock forming the carton of the present invention is smoothed;

FIGURE 3 is a graphical representation of the effect on stiffness caused by varying the basis weights of different caliper boards;

FIGURE 4 is a perspective view, with portions broken away, of a liquid-proof container; and

FIGURE 5 is a cross-sectional view taken on line 5--5 of FIGURE 4.

Turning to FIGURE 1 of the drawings, there is therein shown by way of contrast, a cross-sectional view through a wall of a carton of the prior art and a similar view of a wall of a carton of the present invention. From this figure it will be noted, that although paperboard core 11 of the prior art and core 12 of the present invention are both coated with polyethylene or a similar moistureproof coating 13, board 12 is less dense but appreciably thicker. 'This results from the fact that applicant has found that while the stiffness and endurance of a carton are to some extent governed by the density or weight of the board, a more significant factor is its caliper or thickness. Thus, considering that the stiffness of a homogenous body of material is proportional to its modulus of elasticity times its moment of inertia, and its moment of inertia is proportional to the cube of its thickness, it becomes apparent that if these relationships hold true for a body of paperboard, varying the thickness or .3 caliper of the board will have a much more pronounced effect than varying the density alone. For example, doubling the size or thickness would result in an increase in stiffness 8 times the original. It was determined, 'however, that in increasing the caliper or thickness of paperboard While decreasing its density the internal bonding of the fibers was slightly decreased. This resulted in a decrease of the modulus of elasticity, and to some extent, offset the gain in stiffness and endurance achieved by increasing the caliper. Thus, for paperboard a more exact definition in a case where the caliper is increased while density is decreased was found to be:

where S=stiffness, c=caliper in thousandths of an inch, d=density or basis weight divided by caliper and K is a constant which varies with the physical'properties of different boards. Or, since where W=basis weight,

It will, therefore, be seen that contrary to previous thoughts that a fairly dense board was necessary to obtain the required stiffness and endurance, the density of the board can be decreased appreciably if the caliper is slightly increased. Or stated somewhat differently, a board having a much lower basis weight and hence cost can be used if the caliper is increased and comparable bulge and endurance characteristics will be obtained.

This is illustrated graphically in FIGURE 3 wherein curves are plotted for the equation S=KW c for boards of constant calipers of 27 and 22 thousandths of an inch or points and varying basis weights. These two calipers are chosen for purposes of comparison since the former represents the caliper found satisfactory by applicant for his carton and the latter represents a common thickness of conventional cartons.

From this graph it will be noted that curve A, which represents a board having a caliper of 27 thousandths of an inch, rapidly increases in stiffness with small increases in basis weight. Curve B, on the other hand, increases much more slowly. The comparison of the curves can probably best be made by drawing a straight 'line parallel to the basis weight axis, which would represent a line of equal stiffness. If this line is drawn through curve B at a basis weight of 286 pounds, a commonly used weight for 22 point board, the point of intersection of this' line with curve A will represent the theoretical weight of 27 point board necessary to obtain the same stiffness. Thus, in FIGURE 3, line C represents a line of equal stiffness intersecting curve B at W=286 pounds. Considering next, the point where line C intersects curve A, it will be seen that whereas a basis weight of 286 pounds is' needed to obtain the required stiffness with 22 point board, a basis weight of less than 202 .pounds is theoretically needed for the same stiffness in a 27 point board.

Taking into account such factors as stock formation and surface smoothness, and allowing a generous factor of safety, applicant has found that, for half-gallon cartons, a container stock of 253 pounds per 3,000 square feet and a caliper of 27 thousandths of an inch is satisfactory; while for smaller sizes, such as quarts, stock having abasis weight of 184 pounds per 3,000 square feet and a thickness of 19.5 thousandths of an inch is more than adequate. In either case, it will be noted that the resulting density is less than 10 pounds per point.

In comparative tests made between cartonsconstructed according to the present invention and conventional cartons, the less expensive containers of the present invention proved at least comparable, and in most instances, superior to those formed of heavier, denser board. In the tests set forth below, cartons formed of stock having a basis weight of 286 pounds per 3,000 square feet, a caliper of 22 thousandths of an inch or 22 points and a density of 13 pounds per point were compared with cartons constructed according to the present invention of a stock having a basis Weight of 253 pounds per 3,000 square feet, a caliper of 27 thousandths of an inch or 27 points and a density of approximately 9.3 pounds per point. In the tabulations below the latter are referred to as L.D. cartons and the former, H.D. In all other re spects, the cartons were, as nearly as possible, identical.

The tests conducted are standard tests generally refered to as the 45-minute shake test, the 7-day bulge test, and the %-ll10h drop test.

In the 45-minute shake test, filled, sealed cartons are packed in all-wire, 4 /z-gallon case and placed on a mechanical shake table; The table is then shaken with one inch strokes at 210 cycles per minute for 45 minutes; the cartons being rotated each 15 minutes. At the end of 45 minutes, the cartons are checked for leakers and the results expressed as the percentage of good or non-leaking cartons remaining. The results of this test were as follows:

Number Number 0t of Number Percent Carton Cartons Leakers Good Good Tested H.D 18 7 11 61 L.D 1s 0 is In the 7-day bulge test the cartons are filled to their nominal capacity and their maximum dimension from front to back and side to side measured and totaled. The cartons are then stored for seven days at 45 F. and their maximum front to back and side to side dimensions again measured and totaled. The first measurement is then subtracted from that made after seven days and the result expressed as the total bulge occurring in the sevenday storage period. The average results of this test were as follows:

Carton Total bluge, inches H.D .05

The A-inch' drop test consists in dropping a filled, sealed carton inch onto a flat surface, 35 times a day. After each days drops, the carton isstored for one day at 40 F., after which it is placed under a 50% relative humidity for a one hour sweating period prior to commencing drop testing. This procedure is continued until leakage of the carton is detected and the result expressed as either the number of days or the number of drops to In summary, it Will be noted that the cartons of the present invention, although formed from stock 33 pounds lighter in basis weight than the comparison cartons, exhibited a total bulge after seven days only one onehundredth of an inch greater, while in endurance tests they proved superior. Since basis weight, as a single fact-or, is probably the most effective in determining carton costs, the savings in forming cartons of stock 33 pounds per 3,000 square feet lighter are obvious.

Thus, it will be seen that applicant has succeeded in producing a carton having endurance and bulge characte-ristics equal to cartons using much heavier and more expensive carton stock with a lower weight, and hence, cheaper paperboard. I

While endurance and bulge are primary considerations in the formation of papenboard liquid containers, yet another factor must be considered which would seem to indicate that low density paperboard is unsuitable for this purpose. Thus, while applicant found that, with regard to stiffness, cartons formed of lighter, cheaper board performed as well or better than conventional cartons if the caliper of the carton stock was increased, the rougher surface characteristic of the low density board resulted in coating discontinuities or pinholing when attempts were made to cover with conventional coat weights.

For example, when using polyethylene as a coating, standard industry practice is to apply a coat weight of approximately 18 pounds per ream on the inside of the container where intimate contact is made between the container and the stored product. Since the outside of the carton is normally not subject to the same amount of contact with moisture'as the inside, this surface need only have a coating sufficient to resist penetration of moisture from less intensive sources, such as from icing, condensate, and the like. Therefore, a coating of approximately pounds of polyethylene per ream of board is usually suflicient for the outside of the carton. However, even though the overall outside coat weight may be decreased appreciably from that used on the inside, it is still necessary that this coating be substantially continuous. Applicant found, however, that with the rough surfaced, low density stock, it would be necessary to use approximately 18 pounds of polyethylene per ream of board on both surfaces to decrease pinholing to an acceptable level. Therefore, even though the stock used in the carton of the present invention is much lower in cost, the higher weights of coating necessary to obtain a pinhole free surface would render its use impractical since the increased use of the relatively more expensive coating material would more than offset any savings made by using the lighter board.

Referring to FIGURE 2 of the drawings, the manner in which this problem is overcome will be described. At the left hand side of FIGURE 2 will be seen the untreated, rough surface board 12' having fibers and fiber groups, as at 14 and '15, extending away from the general plane of the surface. As the board 12 travels toward the right, as seen in FIGURE 2, it passes between a pair of

rollers

16 and 17, portions only of which are shown, where it is subjected to heat and a fairly light pressure.

Roller 16 is heated by steam or the like and may be conveniently made of a polished metal, such as steel, while roller 17 is formed of a fairly hard, yet resilient material, such as hard rubber. In practice it has been found that a pressure of between 400 and 500 pounds per lineal inch in the nip formed by

rolls

16 and 17 and a temperature of approximately 350 F. is satisfactory. As noted previously, while the heated roll 16 is conveniently formed from a relatively rigid material such as steel, roll 17 should be somewhat resilient to permit its deformation at the nip. For example, a material having a plastomer index of 35 to 40 when a temperature equilibrium is reached has proven satisfactory. This deformation of the roll 17 as the board passes through the nip results in a varying speed of the web across the nip. Since the amount of friction between the rubber roll 17 and the board is greater than that between the polished metal roll 16 and the board, the speed variation across the nip causes the board to slide against the polished roller, bufling or burnishing it, and producing the comparatively smooth surface 18 seen at the right hand side of FIGURE 2.

At the same time, the resilient roll 17 also tends to smooth the surface 19 of the board, although not to the extent that surface 18 is smoothed by roll 16. Of course, if it were desired to have both surfaces of the board equally smooth, both could be treated in the same manner by, for example, using two pairs of oppositely disposed rollers.

However, in the specific application contemplated here, i.e., liquid containers, this is generally unnecessary. This results because, as noted supra, even very rough textured board can be coated fairly satisfactorily with, for example, a polyethylene coating of 18 pounds per ream. Since, after treatment by the roller 17, the surface 19 of the board is much smoother than before treatment, the 18 pound coating is then more than adequate to provide a good continuous coating. Therefore, since a polyethylene coating of 18 pounds per ream is standard on the inside of conventional cartons, if the surface 6 is used as an inside carton surface, no increase in coat weight will be necessary when using the lighter board. At the same time, due to the burnishing by the roller 16 of the surface 18, a coating of polyethylene of 10 pounds per ream on that surface is sufiicient to prevent pinholing. This, as noted above, is the conventional coat weight used on the outside of liquid cartons. Thus, although both surfaces may be burnished if desired, it will be seen that by burnishing only one surface of the rough textured board, increases in coating are completely avoided.

It will be apparent, therefore, :that by treating the rough surface of the low density board in the manner described above, both surfaces are smooth, although to different degrees, allowing a pinhole free coating of 18 pounds per ream to be applied to the inside of the carton and a similarly continuous coating of only 10 pounds to the outside. It will thus be :seen that, although the weight of the board is decreased appreciably, no increase in coat weight is necessary to obtain'the degree of coating continuity previously obtainable only in the heavier, denser board.

Referring to FIGURE 4 of the drawings, the problem of raw edge absorption, or wicking, will now be considered. In FIGURE 4 is shown, for purposes of illustration, a carton 1 of fairly common configuration. In this type of carton, a one-piece blank is severed from a sheet of stock material suitably coated with a moisture resistant coating and folded to the configuration shown to form an upright side wall portion including side wall panels 25, a bottom wall 6, and a gable top 7. While the carton shown for purposes of illustration exhibits four distinct side wall panels, it will be apparent that the carton may take the form of any one of several different configurations commercially available, such as that wherein the side wall portion is formed as a truncated cone and a separate insert is secured in place as a bottom wall. Regardless of the particular configuration chosen, in most coated paper containers of this type, at least the side wall portion is formed from a single piece of stock and folded to form a tubular shape. The free ends of the blank are then lapped, as at 8, to form a longitudinal seam.

Referring now to FIGURE 5 of the drawings, a crosssectional view of the lap joint formed in the construction of the carton is shown in more detail. As therein shown, the two edges 9 and 10 of the carton blank are secured in overlapping relationship, with edge 9 overlying inwardly folded edge 10. Since the paperboard core is coated with a moisture resistant coating material 13, such as polyethylene, it will be apparent that the carton is, for the most part, liquid proof. However, since the carton blank is stamped from the sheet of stock material after coating, the edges thereof will be uncoated. This presents no problem with uncoated edge 9, since it lies outside of the carton. Edge 10, however, is in direct contact with the stored fluid, where it provides a possible means for liquid to penetrate into the material of the container. While a slight penetration is permissible, if the liquid tends to travel into the board or wick, delamination of the carton board will occur and carton failure will result.

Prior to the present invention it was thought that, in order to prevent substantial penetration through this uncoated portion, the board would have to be made relatively dense, that is, on the order of 13 pounds per point.

Applicant has found, however, that the density of the board may be reduced materially without substantial wicking. While the reason for this phenomenon has not yet been fully explained, one possible explanation is, that the suspended solids carried by many edible, liquid products, such as milk, are filtered out by the fibers at the raw edge and seal off the path therethrough. Of course, the surface tension of the liquids may also have an inhibiting effect on the natural tendency thereof to migrate through the minute interstices of the carton material. However, regardless of the reason, applicant has found that with cartons formed of board having a density of less than 10 and used for the storage of milk, for example, penetration through the raw edge, or wicking, is negligible as in cartons formed of heavier, denser stock.

It will be seen, therefore, that although the basis weight and density, and hence, the cost of the board are decreased by increasing the thickness of the board while decreasing the fiber content, raw edge absorption remains negligible, as in heavier, high density boards.

From the foregoing it will be apparent that applicant has devised a paperboard liquid container with characteristics of stiffness, adaptability for coating and raw edge absorption heretofore found only in heavier, denser, more expensive cartons but at appreciably lower costs.

While specific details of the invention have been described above, it will be apparent that changes may be made therein within the scope of the appended claims.

I claim:

1. A liquid-proof container comprising:

(a) An upright side wall portion,

(b) a bottom wall portion attached to said side wall portion at its lower edge,

(e) at least said side wall portion including a paperboard core,

(d) the ratio of the basis weight of said core in pounds per 3,000 square feet to the thickness of said core in thousandths of an inch being appreciably less than 13, and

(e) a moisture resistant coating laminated to both sides of said core.

2. The liquid-proof container of claim 1 wherein:

(a) Said basis weight is approximately 253 pounds per 3,000 square feet, and

(b) said thickness is approximately 27 thousandths of an inch.

3. The liquid-proof container of claim 1 wherein:

(a) Said basis weight is approximately 184 pounds per 3,000 square feet, and

(b) said thickness is approximately 19.5 thousandths of an inch.

4. The liquid-proof container of claim 1 wherein:

(a) Said ratio is less than 10.

5. The liquid-proof container of claim 1 wherein:

(a) Said carton is formed from a unitary blank folded into tubular form, and

(b) longitudinal edges of said tubularly formed blank are overlapped forming a joint extending longitudinally of said carton.

6. The liquid-proof container of claim 5 wherein:

(a) Said side wall portion is formed of substantially planar side wall panels.

7. The liquid-proof container of claim 1 wherein:

(a) The moisture-resistant coating laminated to one of said sides of said core weighs approximately 18 pounds per ream of said core, and

(b) the moisture resistant coating laminated to the vother side of said core weighs approximately 10 pounds per ream of said core.

References Cited by the Examiner UNITED STATES PATENTS 2,327,713 8/1943 Hunter 20662 3,094,432 6/ 1963 Meyer-Iagenberg 2293.1 X 3,107,837 10/1963 Graser 229-3.1 3,170,568 2/1965 Carter 229-3.1 X

GEORGE O. RALSTON, Primary Examiner.

Claims

1. A LIQUID-PROOF CONTAINER COMPRISING: (A) AN UPRIGHT SIDE WALL PORTION, (B) A BOTTOM WALL PORTION ATTACHED TO SAID SIDE WALL PORTION AT ITS LOWER EDGE, (C) AT LEAST SAID SIDE WALL PORTION INCLUDING A PAPERBOARD CORE, (D) THE RATIO OF THE BASIS WEIGHT OF SAID CORE IN POUNDS PER 3,000 SQUARE FEET TO THE THICKNESS OF SAID CORE IN THOUSANDTHS OF AN INCH BEING APPRECIABLY LESS THAN 13, AND (E) A MOISTURE RESISTANT COATING LAMINATED TO BOTH SIDES OF SAID CORE.