US2100396A - Hydro-pneumatic pulp molding - Google Patents

Description

R. D. HEYMANN HYDROPNEUMATIC PULP MOLDING Novf 30, 1937.

Filed March 9, 1955 NNNNN INVENTOR Zay J2 /fglfmlzm ATTORNEYS BY @wn-M Patented Nev. 30, 1937 PATENT OFFICE HYDRO-PNEUMATIC` PULP MOLDING l Roy D; Heymann, Woodbridge, Conn., assignor, by mesne assignments, to Pulp Products Company, Inc., New York Delaware Application March 9,

9 Claims.

This invention relates generally to molded pulp 'articles and a process for making such articles by the utilization of hydrostatic and pneumatic forces.

More specifically the invention relates to the manufacture of molded pulp articles by forming them in a foraminous mold wherein the article may be completed, or alternatively, partially completed, so as to require only a relatively small additional treatment to give to the article many varied and desirable characteristics, depending upon the ultimate purpose for which the article is to be used.

By way of introduction, and for the purpose of -explanation and not of limitation, it may be assumed that molded pulp containers are desired which will be sturdy in construction, cheap in manufacture cost, impervious to oil or water, and safe to use in dispensing liquids, such as, for example, motor oils, in relatively small amounts. If such molded pulp containersare required for milk or other llquid,`or for any other of the commodities which lend themselves to packaging in individual containers, they may require different characteristics, not only as to size and shape, but further .as to qualities giving resistance to loss and deterioration which may be inherent in the material intended to be packaged, or by reason of some effect which may result from contact between the material packaged and the contain- 'er which encloses it. The invention hereinafter more fully described contemplates the manufacture of containers or articles which, when made in accordance therewith, will have such characteristics as may be necessary to meet the requirements for which the container or article is intended.

The particular treatment of the pulp to produce such articles and to accomplish these de- 40 sirable results will, in many, if not all instances,

depend upon the use for which the Aarticle is designed. It is a major purpose of this invention, in its broader aspects, to produce a container in a foraminous mold by the utilization of hydrostatic and pneumatic forces in successive stages whereby separate and distinct layers of pulp and other materials may be built up in the form of an integral wall orwalls and in such manner that the inner or outer layer, or both, of said wall or falls may be easily and economically treated in situ to render the container suitable for the purpose for which it is ultimately to be used.

It has been common practice to form containers of pulp in foraminous molds. Efforts have tbeen made with limited success to mii; with the N.' Y., a corporation of 1935, serial No. 10,219

pulp suspension, materials commonly known as sizes for the purpose of rendering the walls of. the containers, waterand grease-proof, but difficulties have been encountered in the actual molding operations when suilicient size is added 5 to the pulp suspension to accomplish the desired results. The disadvantages under these conditions have been so great as to make this method impractical if a water-proof and grease-proof article is desired. It is well known in the art that 10 a certain minimum freeness of the suspension is necessary. to successful commercial molding. The addition of most sizes or materials to the pulp suspension reduces the "freeness. Generally, the quantity of size or other material added l5 to the pulp suspension has a direct functional relation to this characteristic known as freeness, hence the amount which may be added directly to the pulp suspension itself is limited by the practical difiiculties encountered in the molding operation. In other words, if suicient sizing material is added to the pulp suspension to render the article when completed grease and waterproof, the freeness of the suspension is reduced to an extent which makes it impractical to mold on a commercial scale, inasmuch as the water or other carrying liquid of the pulp cannot readily free itself from the suspension to find its way to the outside of the foraminous mold.

The present invention overcomes the foregoing difiiculties and broadly contemplates the use of a pulp suspension whichhas sufcient freeness to mold easily, and, in addition, the injection ofv a material into .the mold after the pulp suspension has freed itself of the major portion of its carrying liquid.

Further, the invention relates to a process of making containers comprised of a wall made up of distinct layers, one of which layers is paper pulp and another is material of diiferent characteristics but capable of being introduced into the mold in liquid suspension and capable of being intermatted with the paper pulp layer in such manner as to produce an integral wall. The vsecond material is laid upon the pulp layer in` such manner as to be capable of further treatment in situ, to form, if desired, a continuous, homogeneous and impervious lm on the pervious pulp layer.

Still more specically the invention contemplates the introduction of a pulp suspension into av foraminous mold where it is partially molded byhydrostatic pressure into a wall or layer having the general contour lof the inner surface of the mold, after which a second suspension of finely divided material is introduced into the mold under hydrostatic pressure and laid upon the pulp layers to form an inner layer. Then, as further steps, air under predetermined pressure and temperature is introduced in successive stages for reasons described later herein and finally the container thus formed is removed from the mold and treated, if desired, to render the completed container suitable for its ultimate purpose, all of which will more fully appear hereinafter.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it maybe carried out, may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in whichg Fig. 1 is a schematic or flow diagram to illustrate various steps of the process;

Fig. 2 is a diagrammatic illustration of a heating and drying step;

Fig. 3 is a diagrammatic illustration of one method of treatment of the container after the molding operation; and

Fig` 4 is a diagrammatic illustration of a modifled form of treatment of the container after the molding operation.

To facilitate description, certain preferred methods of utilizing the invention will be described with reference in part to the accompanying drawing, but it will be understood that the terms herein employed are intended to be interpreted as broadly and as generically in their connotation as the present state of the art will.."

permit.

Referring now to the drawing which as hereinbefore specified is diagrammatic, I0 represents a pulp suspension tank containing a suspension I I of pulp fibers in a carrying liquid such as water. It will be understood that the process may be conveniently carried out by machinery, the moving parts of which are timed or otherwise controlled by cam movements or the utilization of other principles known in the art of machine designing.

The paper pulp which may be prepared by the sulphite or sulphate process and which is commonly known as chemical pulp is treated in a beater and charged into the pulp suspension tank I0 through charging port I2. If mechanical pulp is'used, the fibers of lengths ranging from 1 mm.'to 3 mm. should predominate and 1% to 2% of Apulp is maintained in water suspension in which the hydrogen ion concentration may be controlled. .A pH value of 4.2 to 4.5 has been found to be satisfactory, although a wide latitude is permissible. It is preferable to maintain the suspension well on the acid side to insure what appears to be a better laid fiber, suitable for molding. The pulp suspension may be constantly agitated by the blades I3 mounted on the shaft I4 which in turn is movably mounted in the tank and may be revolved by a belt (not slwn) on a pulley I9 keyed to said shaft.

The pulp suspension is introduced into the mold by gravity through a conduit I5. A valve I6 is timed with reference to its opening and closing and is kept open only long enough to allow sufficient pulp suspension to gravitate into the separable foraminous mold II to form a container which will have a wall of the desired thickness when completed. The amount of suspension required may be determined initially by trial and error and will depend on the type, nature and percent of pulp and on the hydrogen ion concentration.

When this predetermined amount of pulp suspension has been introduced into the mold I1 the hydrostatic head will exert its pressure toward the outside of the mold and cause the suspended pulp fibers to be built up within the mold in a loosely formed matted layer or wall assuming the contour of the inner surface of the mold. In the manufacture of quart containers, for example, of the general shape shown in the diagram at I8, and having a wall thickness when completed of about I?, of an inch, and a dry finished weight of approximately 51 grams, there would be required about 3.6 quarts of suspension containing 1.5% fibers.

Immediately following the hydrostatic molding step under gravitational pressure, valve 20 is opened. This permits the suspension 2l, hereinafter described, to flow through conduit 22 from tank 23 which latter may be charged through port 26. The suspension 2| in tank 23 may be comprised of a suspension of nitrocellulose fibers in suitable concentration. A 1/2 of 1% suspension of 1/2 to 1 second cotton has been found to be satisfactory. In some instances, a different concentration of nitrocellulose suspension may be preferable and other types of fibers may be used.

A pressure of from 10 pounds'to 30 pounds per square inch is maintained upon the nitrocellulose suspension. Valve 20 is held open for a time sufficient. to allow the desired quantity of nitrocellu- ,lose suspension to flow through conduit 24 and finally through the nozzle 25 into the mold and interiorly of the loosely formed pulp layer mentioned in the foregoing. This step will ordinarily require, in the case of the formation of a quart bottle being presently described, from 2 to 5 seconds, although in some instances it may be more or less and will depend upon the nature of the materials being worked. "The flow of this suspension interiorly of the pulp layer already partially formed in the mold I 'I tends to flush the inside of said pulp layer, redepositing the pulp fibers as a smooth interior surface while at the same time building up on the pulp layer a layer of nitrocellulose particles which become intermatted withthe pulp fibers. This step, for purposes of-description, may be termed the flushing step, although it will be apparent that in addition to the flushing action there is being formed, simultaneously, an innermost layer of nitrocellulose fibers alone. It will further be apparent that the two layers will form an integral matted or felted wall which may be described as being progressively less predominant in nitrocellulose particles in a direction toward the outside of the container. Conversely, the outside of the container will predominate in pulp fibers and the wall will be progressively less predominant in pulp fibers in a direction toward the inside of the container. i

Immediately following the flushing or inner layer formingstep, air at atmospheric temperature and under a constant predetermined pressure is introduced into the mold interiorly of the container walls. Compressed; air is maintained in the receiver 26a and the pressure kept constant by a regulator or relief valve 21 which discharges into co'nduit 26 leading into tank 23.

It will be observed that a regulator or relief valve 36 is installed in conduit 29 leading from tank 23 content in the container and serves to maintain a predetermined constant pressure upon the nitrocellulose suspension in said tank 23. A pressure which has vbeen found to be satisfactory in receiver 26 ranges from 20 pounds to 45 pounds per square inch. 'This low pressure air passes through valve 30, the operation of -which likewise is vtimed and ordinarily will require from 2 to 5 seconds. The amount of time and pressure may vary, depending upon the shape, ,Size of container and the type of pulp being worked. This low pressure air or pneumatic step drives excess or free water from the interior of the container walls in a direction toward the outside of the foraminous mold, and at the same time tends further to compact the pulp and nitrocellulose layers. It will be observed that, by reason of the first layer of pulp forming a felted orilltering wall, the nitrocellulose particles are caught and withheld on the inner surface of the pulp except for those particles which become intermatted with the pulp fibers.

Following immediately after the low pressure pneumatic step, or preferably slightly overlapping it, a blast of high pressure, high temperature air is introduced into the partially formed container in the mold il. For this purpose ccmpressed air is maintained in a receiver 3i under a predetermined constant pressure o approximately 65 poundslper square inch. The high pressure air may pass through conduit 32. A relief or regulator valve 3d is installed in conduit 33 which leads from said receiver Si. Relief valve 34 discharges into receiver 23 through conduit 35. The pressure vmaintained on the high pressure receiver may likewise be varied and will depend upon operating conditions.

The highl pressure air may pass through a heater represented conventionally at 37 where the temperature is raised to approximately '700 F.

and maintained constant by thermostatic control 38 connected with the heating elements 39 and the hot air receiver 40. Avalve 4i in the high pressure, high temperature air condut 42 which is connected with conduit I5 is likewisetimed,

and is kept open only sucient time to permit the heated air to compact the pulp and nitrocellulose layers, and to drive the free Water from the container walls. This ordinarily will require from l0 to 15 seconds, and will reduce the water walls to from 40% to 60% by weight. The pressure then built up within the mold is relieved through escape valve 43 which is likewise timed, it being necessary to reduce the pressure within the container before the mold is opened lest the container be ruptured when the mold is separated. It will be understood that, due to the cooling of the air by the expansion thereof as it enters the mold and due to contact with the wet Wall., the temperature of the wall is never raised suillciently to scorch the wall or appreciably deteriorate the bers.

The internal pressure having been relieved, the mold is opened as indicated by dotted lines 44, and the container is removed. Themold is then closed and the same cycle requiring not more than 25 to 30 seconds is repeated ad infinitum.

Compressed air is supplied by the compressor 45 and the discharge from valve 36 is led into the intake side of the compressor through conduit 46. Check valve 41 prevents escapement of air under pressure to the atmosphere, and check valves 48 and 49 prevent ilow of air or liquid in' sa reverse direction.

At this stage of the operations the container is of suillcient rigidity to be handled readily although itis still moist and contains from 40% to 60% of moisture. The hot air blast might be continued forsuillcient time to completely dry the walls of the container, but it has been found more economical to dry the containers in a drier su'ch as diagrammatically illustrated at 50. The containers are transported continuously through the drier maintained at any desirable temperature. The temperature, however, should be maintained low enough to prevent scorching of the container, and preferably below 212 tion, and have a sturdy construction capable of withstanding rough handling and hard usage.

` treated to coalesce or flux the nitrocellulose par ticles of the inner layer by spraying or otherwise wetting the nitrocellulose-particles with sumcient quantity of a suitable solvent to dissolve the particles and ilux them into a continuous homogeneous and impervious 111m. This step is -diagrammatically illustrated in Fig. 3 in which 5'@ represents a tank, 5l a bath of solvent, 52 a pump and 53 aspray nozzle.

The action of the solvent should be rapid and an excess should be avoided. Otherwise the nitrocellulose will be dissolved and carried into the container wall or drained oil instead of remaining on andl near the interior surface. The nature of the solvent should be such that the film which is formed thereby shall have the property of drying to a continuous, tough, in iperviousv film. For this purpose a mixture oi' solvents and plasticizers may be used such as is customarily used in lacquer manufacture. As solvents, acetone, ellosolve, butyl, methyl and amyl alcohols, etc., may serve, while, as a plasticizer, dibutyl phthalate may be used, but the use of other materials will be apparent to those skilled in the art.y In some instances, the iluxing operation may be carried out by dipping the container into the solvent, although this method does notiend itself so readily to eflicient and economical rel suits. Other nethods of uxing will now readily `suggest themselves. After the nitrocellulose particles of the inner layer have been iiuxed,y or coalesced into an impervious lm, the excess solvent is permitted orL caused to evaporate and the container is ready for use.

A modified form of procedure may comprise substitution of other types of suspension in 'the inner layer forming step. For example, instead of charging a nitrocellulose suspension into tank 23, a suspension of parailin particles may be used. A preferred form of paramn suspension may comprise an emulsion of paramn made in accordance with the following formula; 4 parts 11n-` l F. The containers come from the drier in a dry condihereinbefore described. It will be apparent that the container removed from the mold in this case will have an inner layer of paraffin starch particles. To coalesce or flux the parafiin, the container after being molded may be heated to drive out excess water from the container walls. and then further heated sufficiently high to melt and coalesce the paramn into a film. r, if the container is of such shape as to lend itself, it may be subjected to a mechanical pressure while simultaneously applying heat as shown diagrammatically in Fig. 4 in which 54 represents a female mold, 55 a molded pulp container, and 56 a male die which may be heated, It will be obvious that only containers having proper draft to insert and remove the die are well adapted to this operation.

While certain specific substances have been disclosed herein as being susceptible and adaptable to the inner layer forming step, it is within the contemplation of the invention to encompass other substances such as lacquer in suspension, finely divided gums land resins and other substances which may be carried into the mold in suspension, uxing or coalescing operations, whether the last mentioned Ioperation be performed by heat, solvents or otherwise. K y

While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, vsubstitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A process of forming a hollow pulp article having an impervious wall which comprises establishing a layer of loosely matted pulp fibers uponthe inner surface of a hollow foramlnous mold, depositing on and intermatting with said first loosely matted layer, a second layer of soluble nitrocellulose fibers, compacting said layers within said mold and contacting said second layer with a solvent for said soluble fibers whereby to coalesce said second layer of fibers into an impervious solidy coating adhering to said layer of pulp fibers. y

2. A hollow molded pulp article identical with one formed by depositing on a felt of loosely laid pulp fibers a layer of nitrocellulose fibers, com

pacting said felt of pulp fibers and layer of nitrocellulose fibers, applying to said nitrocellulose fibers a solvent for said nitrocellulose fibers whereby to dissolve said nitrocellulose flbersand drying to f orm an impervious solid coating on the felt.

3. A hollow molded pulp article identical with one formed by depositing from a liquid suspension a layer of felted pulp fibers, depositing on said layer from a liquid suspension a layer of nitrocellulose fibers, compressing said layers to compact the same, and contacting said second layer with a nitrocellulose solvent and plasticizer whereby to dissolve and plasticize said fibers and drying to form a pulp wall having a closely adhering, impervious solid coating.

4. A composite, two-layer container comprising a layer of molded compressed pulp bers and a and which lend themselves to thel closely adhering layer of coalesced, nitrated cellulosic fibers forming a hard, glossy, waterand oilinsoluble coating penetrating partially into the inner surface of said layer of compressed pulp fibers.

5. A composite molded pulp container comprising a layer of relatively long pulp fibers, a second layer of relatively short nitrocellulose fibers compressed against said first layer and filling the depressions in the surface thereof, said fibers of said second layer being coalesced to constitute a substantially smooth, impervious solid coating covering the surface of said container.

6. A hydro-pneumatic process of forming coated, molded pulp articles which comprises introducing into a hollow foraminous mold pulp fibers in liquid suspension causing hydrostatic deposition of the pulp fibers on the walls of said mold whereby to form a loosely matted layer, contacting at least one face of said layer with a liquid suspension of nitrocellulosic fibers under pressure by a iiushing action whereby to smooth' the surface fibers of said layer and form a second layer intermatted therewith, compacting said layers by the introduction into said mold of air under pressure and combining with the fibers of said second layer a volatile solvent therefor to form a coalesced impervious coating on the surface of said first layer.

'7, The process of forming a molded pulp article which comprises introducing .under gravimetric pressure a liquid suspension of pulp fibers into a perforated mold to deposit a matted layer of pulp fibers having substantially the shape of the article to beformed, subsequently introducing into the mold under higher pressure a liquid suspension of comminuted nitrocellulose particles whereby to deposit a layer of said particles overlying said layer of pulp fibers, compressing said layers, at least partially drying said layers, and contacting said second layer with a solvent for said particles whereby to form a continuous, impervious coating adhering to the first layer of fibers.

8. The method of forming a molded pulp container which comprises forming a wall of pulp fibers by hydrostatic pressure, depositing on at least one surface thereof fibers of a nitrocellulosic material, compacting said fibers by gaseous pressure., contacting said second-named fibers with a solvent to coalesce said second-named fibers into a film, and drying said film to form a solid, impervious coating adhering to said wall.

9. The process of forming molded pulp articles which comprises depositing pulp fibres from a vliquid suspension to form a matted layer, contacting a surface of said layer with a liquid suspension, under pressure, of finely divided particles vof nitrocellulose to deposit thereon a layer of said particles, compacting said layers with a gaseous medium under pressure to express free liquid therefrom, further compacting said layers with a heated gaseous medium under pressure to at least partially dry said layers, and contacting said second-named layer with a solvent for said particles to coalesce said particles into an'impervious coating, adhering to and penetrating said matted layer of pulp fibres.

ROY D. HEYMANN.

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