US3040948A

US3040948A - Molded pulp article

Info

Publication number: US3040948A
Application number: US789433A
Authority: US
Inventors: Wells Roger
Original assignee: Diamond National Corp
Current assignee: Diamond National Corp
Priority date: 1959-01-27
Filing date: 1959-01-27
Publication date: 1962-06-26
Anticipated expiration: 1979-06-26
Also published as: DK100346C; BE584277A

Description

Filed Jan. 27, 1959 eeeoooooo oooo oooboo SDOOOOOOOGOO o o 0 o 0 0 o o o o o o 0 o o o o o 0 o o o o o o o o o o o o o o o o o o o o o 0 o o o o o o o o o o 0 o o o o o o o o o o o o o o o 0 o 0 o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 0 o o 0 o 0 o o o o o o o o o o o o o o o o o 0 Q o o o o o o o o o o o o 0 o o o o o o o o o o o o o o o o o o o o o o o o o o o o 0 o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 0 0 0 0 0 0 0 0 o o o o 0 @w 7%@ "(A QJU Ll). i LOC ATTORNEY United States Patent Ofiice $,d-' i@,948 Patented June 26, 1962 1 3,040,948 MOLDED PULP ARTICLE Roger Wells, Stamford, Conn, assignor to Diamond National tlorporation, a corporation of Delaware Filed Jan. 27, 1959, Ser. No. 789,433 2 tClaims. (til. mans This invention relates to molded pulp articles, and methods of molding such articles. More particularly the invention relates to molded pulp containers especially suitable for packaging foods, and to methods of making such containers.

Containers made of molded pulp are customarily used in most retail food markets today for packaging fresh meat, poultry, fish or other commodities from which some natural juices are likely to exude. These containers are usually in the form of a shallow, generally rectangular tray, and a transparent covering sheet of cellophane or polyethylene may be Wrapped around the tray and heat-sealed to the bottom surface thereof. Such containers present an attractive display While providing adequate protection during the sale and temporary storage of foodstuffs, particularly for naturally juicy fresh poultry and the like, from which some blood may exude.

It is desirable to absorb any exuded blood or other juices to prevent such fluids from being free to run around the inside of the sealed package during normal handling by the customers or prospective purchasers. For this purpose the entire body of the molded pulp tray has sometimes been made of an unsized grade of pulp to render it inherently absorbent. However, when the amount of fluid present is excessive, this type of tray may 7 become soggy and weakened, resulting in an unattractive appearance and possible leakage from the package. It has been proposed that certain wet strength resins could be incorporated into the molded pulp to prevent weakness caused by sogginess, but the resulting tray may still show blood stains on the outer surfaces of its bottom and side walls. Furthermore, a significant disadvantage of this type of tray is that it exhibits a tendency to dehydrate the meat or poultry contained in the package.

Another instance in which great quantities of containers are used and similar problems are encountered is in the packaging of freshly killed chickens at the wholesale terminal level. The freshly killed and dressed chickens are taken directly from the tubs of crushed ice, they are cut into sections, and while they are still wet they are packed into containers for shipment to retail markets. It would be desirable if the Wholesale packers at the terminals could package the chickens directly into individual containers suitable for retail sale, but one of the major reasons this procedure has seldom been practiced is the fact that so much free water and exuded juice drains off the chicken by the time it reaches the retail store that the package becomes W612 and unsightly. Efforts have been made to absorb such fluids by inserting loose blotting sh but this has not always provided adequate protection. Furthermore, these blotters constitute an extra expense, and they involve added handling, inventory and labor costs.

One suitable container structure designed to trap any freely flowable fluids without dehydrating the packaged food, is described and claimed in copending application Serial No. 750,495, filed July 23, 1958, for Food Container, naming as inventors Richard F. Reiiers and the present inventor. The structure covered by said copending application comprises a molded pulp tray having the upper surface of its bottom wall provided with a multiplicity of uniformly distributed cup-shaped depressions possessing certain critical dimensions. The

sets into the bottom of the containers,

body of this tray may be non-absorbent or only slightly absorbent, and instead of becoming absorbed the liquid is mechanically trapped in the cup-shaped depressions due to their particular size, shape and arrangement.

The present invention relates to an improved construction for food containers designed to overcome the abovementioned problems associated with the presence of excess fiuid drained from packaged foods. This is accomplished, in accordance With the invention, by providing molded pulp trays and other containers, which may be molded from a non-absorbent grade of pulp, with an integrally molded layer of absorbent pulp on the upper surface of its bottom wall. This absorbent layer may be provided with a multiplicity of uniformly distributed cup-shaped depressions adapted to trap any excess liquid which then becomes absorbed into the sides of said depressions. Thus, the invention is embodied in containers which are of two ply construction in their bottom portion and single ply elsewhere, such as their side walls. Another important aspect of the invention relates to new methods of manufacturing molded pulp articles which are two ply in specific areas.

It is therefore an object of this invention to provide new and improved molded pulp articles and methods of molding such articles.

A specific object of the invention is to provide new and improved molded pulp containers for packaging foods and methods of molding such containers.

Another object of the invention is to provide new and improved food containers, particularly suitable for packaging fresh poultry or other naturally wet or juicy food, which containers are provided with means for trapping any excess freely flowable fiuids drained from the packaged r'ood.

Still another object of the invention is to provide new and improved food containers having integral means for absorbing excess fluids without dehydrating food packaged therein.

Yet another object of the invention .is to provide molded pulp trays, dishes and other types of containers with an integral highly absorbent portion limited to the upper surface of the inside bottom wall thereof, and to provide new methods of molding such containers.

Other objects and the nature and advantages of the instant invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a top plan view of a molded pulp tray embodying the invention;

FIG. 2 is an enlarged vertical section taken along the line 22 of FIG. 1;

FIG. 3 is a sectional view corresponding to FIG. 2 but showing a modification of the invention;

FIG. 4 is a vertical section of a portion of the bottom wall of a molded pulp tray representing another embodiment of the invention; and

FIG. 5 is a sectional view of a suction mold shown at one stage of a molding method embodying the invention.

in order to illustrate the principles of the invention as applied to a typical Widely used article of commerce, the molded pulp trays embodying the invention shown in the drawings appear relatively shallow and generally rectangular in overall configuration, and it should be understood that this configuration may be varied as desired. The illustrated trays are particularly suitable for packaging fresh meat, poultry or fish for sale. in retail food markets.

The tray shown in FIGS. 1 and 2 comprises a gen erally flat horizontal bottom wall 10 from the edges of which project integral upstanding inclined sidewalls 12 terminating in a peripheral lip 14. of the bottom well ill on the inside of the tray is provided with a multiplicity of cup-shaped depressions l6 uniformly distributed over the entire area of this surface.

In accordance with the present invention, the entire bottom wall lit of the tray is composed of two integrally united layers of molded pulp, constituted by an upper layer 18 and a lower layer Ztl, resulting in a composite two-ply construction. The upper layer 18 is intended to be highly absorbent, and for this purpose it may be molded from unsized sulphite pulp stock. On the other hand, the lower layer 2i? as well as the integral sidewalls 12 and the peripheral lip 14 are preferably nonabsorbent or only slightly absorbent in character, and they may be molded from highly sized groundwork stock. The sidewalls 12 and the lip 14 are preferably of singleply homogeneous construction, and none of the highly absorbent pulpstock employed to form the upper layer 18 of the bottom wall should be allowed to extend elsewhere.

(The cup-shaped depressions to may be limited in depth to extend only partially through the upper layer 18, or they may extend completely through the layer 18, and they may also extend partially through the thickness of the lower layer 20 of the bottom wall it The depressions 16 when properly constructed in size, shape and arrangement serve to provide traps for mechanically holding any freely flowable fluid, and these depressions also impart a distinctive attractive appearance to the trays. Any fluid trapped within the depressions 16 eventually becomes absorbed into the cylindrical side walls thereof. However, primarily the absorbency of the entire upper layer 1% is relied upon to control the excess fluid, and the provision of the depressions 16 to serve as fluid traps is optional.

FIG. 3 shows an embodiment of the invention wherein'such depressions have been omitted. In this embodiment, the tray is provided with a bottom wall Tall, integral upstanding sidewalls 32, and a peripheral lip 34, which are related to each other in the same manner as the corresponding parts described for the tray shown in FIGS. 1 and 2. The bottom wall is composed of two integrally united layers of molded pulp, namely, an

'irnperforate upper layer 36 of highly absorbent pulp and a similarly imperforate lower layer 38 of non-absorbent or slightly absorbent pulp.

In the aforesaid copending application Serial No. 750,- 495, details are given of the required size, shape and arrangement, as well as the critical dimensions, for the depressions to serve effectively as fluid traps. It is disclosed therein that due to the surface tension of the fluid, drops will enter the depressions without running out when the container is inverted, if the diameter of the depressions is in the critical size range of about to 7 The preferred depth of the depressions is in the range of about 0.06" to 0.125 but is not limited thereto. In spacing they may be centered about apart in alternately staggered parallel rows and columns, and in aggregate areas the depressions may occupy from about one-fifth to one-third of the total surface area of the bottom wall inside the container.

In order to achieve maximum effectiveness as fluid traps, the cup-shaped depressions should have smooth cylindrical sidewalls and sharply defined upper edges. They may be formed with such characteristics simultaneously with the formation of the main body of the molded pulp tray, by providing the usual drainage screen on the surface of the mold with a plurality of uniformly spaced and distributed solid projecting nubbins made of metal, rubber or a plastic. It has been observed that the pulp fibers which deposit in the vicinity of these nubbins assume an irregular or heterogeneous pattern, whereasrthe pulp fibers deposited on the perforate other portions of the mold appear felted in a regular symmetrical pattern. This results in the production of an The upper surface irregular deposition pattern around the cylindrical side walls of the cup-shaped depressions, and a regular pattern on the upper surface of the bottom wall of the tray between these depressions. Pulp deposited in the irregular pattern exhibits greater absorbency than the pulp deposited in the regular pattern. Consequently, the side walls of the depressions are inherently more absorptive than the upper surface of the bottom of the tray between the depressions. Due to this construction, most of the free liquid is trapped and absorbed Within the depressions rather than elsewhere on the bottom of the tray, and the tendency to dehydrate the packaged food resting on the surface between the depressions is minimized.

The embodiment of the invention illustrated in FIG. 4 represents a modification of the tray shown in FIGS. 1 and 2, wherein an extra protective coating is employed to assist in preventing any tendency to dehydrate food packaged in the tray. This tray is provided with a bottom wall 40, of which only a portion is shown in FIG. 4, and the sidewalls and rim of this tray which do not appear in this view are identical in structure and in function to the corresponding sections of the trays depicted in FIGS. 1, 2 and 3. The bottom wall 4t) includes a lower layer 42 of non-absorbent or slightly absorbent molded pulp, a highly absorbent pulp layer 44 is superimposed upon and integrally united with the lower layer 42, and the entire area of the bottom wall 4@ is provided with a multiplicity of cup-shaped depressions 46 which correspond to the depressions 7.6 of the tray disclosed in FIGS. 1 and 2. However, the tray shown in FIG. 4 is equipped with a thin liquid impervious protective coating 43 covering the entire upper surface of the highly absorbent layer 44. The protective coating 48 may be formed by spraying a suitable sizing composition onto the layer 44, or

' by bonding a sheet of wax paper thereto, or in any other suitable fashion. Of course, the protective coating 43, whether formed by spraying or by a bonded sheet or otherwise, must not extend down into the depressions 46. It is intended that any free fluid trapped within the depressions as should become absorbed into the portions of the layer 44 constituting the cylindrical side walls of these depressions. Whatever food is packaged in the tray rests upon the protective coating 48, and due to the liquid impervious nature of this coating the normal tendency of the absorbent layer 44 to cause dehydration of the packaged food is prevented.

It is evident that the tray illustrated in FIG. 4 offers the greatest protection against possible dehydration of food packaged therein, but that some measure of protection is provided in all of the disclosed containers embodying the invention, due to the confinement of the highly absorbent pulp layer to the upper inside surface of the bottom of the tray while the upstanding sidewalls of the tray are made non-absorbent or only very slightly absorbent. Moreover, due to the previously described deposition pattern of the pulp fibers, the surfaces possessing the greatest powers of absorption are located down inside of the cup-shaped depressions, and this fact also contributes to the prevention of dehydration of the packaged food.

The preferred method molding containers embodying the invention involves the successive deposition of two different layers of pulp from two different grades of pulp stock onto a specially constructed suction mold. In FIG. 5 there is shown a portion of such a mold with the two different layers of pulp deposited thereon at an intermediate stage of the molding operation. This mold is provided with a tubular body 59 adapted to be connected to a suitable source of suction. Covering the open end of the tubular body 50 is a perforated forming plate 52 contoured to produce a generally rectangular shallow tray. A foraminous wire straining screen 54 is secured over the forming face of the plate 52 by means of a peripheral retaining ring 56. The straining screen 54 may be of the ordinary well known type for production of imperforate articles similar to the tray shown in FIG. 3, and for the production of trays having the

cupshaped depressions

16 or 46, this screen could be provided with the previously described spaced solid project ing nubbins.

The perforated forming plate 52 is provided with a plurality of spaced transverse perforations 58, and it is important to notice that the perforations 58 are present only in areas of the forming face where the molding of a two-ply structure is desired. When the mold is submerged first in a thin slurry of sulphite stock and then is dipped into a thick slurry of groundwood stock, a two-ply structure is formed directly over the area of the forming plate 52 where the perforations 58 are located, and elsewhere over this forming plate a single ply structure is deposited. The thin sulphite stock has such a high drainage rate that the slurry passes through the first fibers deposited above the perforations and gradually builds up a relatively thick layer 60 of absorbent molded pulp, but no fibers are deposited elsewhere on the mold from this dilute slurry. When the partially coated mold, having the layer 60 coated thereon only above the perforations 58 is then submerged in the thick slurry of groundwood pulp stock, the fibers deposited from the slurry accumulate on top of the layer 60 until a natural barrier against further drainage is formed, and then deposition occurs over the remainder of the forming face of the plate 52 resulting in the formation of a layer 60. The length of immersing and the degree of suction applied to the mold in the two different slurries can be so controlled that the wall thickness in the single ply portions is substantially the same as that in the two-ply portions of the tray. Thus, even though two successive deposits form the bottom of the tray, no extra thickness need be created thereby, and the finished article may have the same dimensions and proportions as a conventional tray.

The thin sulphite pulp stock contemplated should preferably contain about A by weight of unsized pulp fibers in water, and this percentage should not be greater than about 1%. The relatively thick slurry of groundwood stock is preferably kept at about 1% by weight of pulp fibers in water, which is approximately the consistency usually employed for molding simple pulp articles such as trays. However, somewhat thicker slurries of the groundwood stock, up to about 3%, may be employed if desired. A small quantity of a suitable sizing composition may be incorporated into the groundwood slurry. The consistency of both the sulphite stock and the groundwood stock may be varied slightly to regulate the thickness of the deposited layers of pulp fibers. Sulphite stock possesses a higher drainage rate than that of groundwood stock at the same percentage of pulp fibers, and advantage is taken of this dilference to produce molded pulp articles in accordance with the present invention.

Molds having perforations limited to areas where the molding of a two-ply structure is desired, such as the mold illustrated in FIG. 5, may be dipped successively into two separate vats of slurry, or this mold may be placed on a rotary drum type molding machine adapted to advance the mold through a vat divided vertically into two sections containing the two different slurries, in a manner well known to those skilled in the art. Of course, more than two layers may be deposited in this fashion if desired.

Following these suction molding operations, the usual drying and finishing steps are performed to complete the fabrication of the molded pulp articles.

Although the invention has been illustrated and described with particular reference to the production of food containers, and especially to containers having an integral absorbent inside bottom portion adapted to trap free fluids, the principles of the invention may be applied advantageously in other types of molded pulp articles. For example, pocketed molded pulp containers for packaging industrial or electronic parts may be provided with pockets of two-ply construction including a cushioning lining of one grade of pulp, while the main body of the container may be made more rigid and strong by a different grade of pulp in a single ply.

It will be obvious to those skilled in the art that various changes may be made without departing from the spirit of the invention, and therefore the invention is not limited to what is shown in the drawings and described in the specification, but only as indicated in the appended claims.

What is claimed is:

l. A food container of pulp material adapted for the packaging of meat and poultry comprising a tray having a bottom wall and upstanding side Walls, said bottom wall having three plies of material extending therethrough, the lower ply being relatively non-absorbent, the intermediate ply being relatively absorbent and the upper ply being an impermeable film, depressions extending downwardly from the upper surface of said bottom wall through the upper ply and at least partially through the intermediate ply, said depressions being of such shape and size as to be capable of mechanically trapping any juices therein due to the surface tension of said juices, whereby any juices resulting from any food products stored therein will pass into said depressions from whence they will be absorbed by said intermediate ply.

2. A food container in accordance with claim 1, wherein the depressions are in the shape of cylindrical cups, each said cup having a sharply defined vertical side wall and upper lip.

References Cited in the file of this patent UNITED STATES PATENTS 1,848,056 Chaplin Mar. 1, 1932 1,974,898 Rutledge Sept. 25, 1934 2,081,740 Farnham May 25, 1937 2,515,113 Chaplin July 11, 1950 2,629,533 Chaplin Feb. 24, 1953 2,974,843 Reifers Mar. 14, 1961 FOREIGN PATENTS 1,086,193 France Feb. 10, 1956