US2100395A - Molding of pulp - Google Patents

Description

Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE MOLDING F PULP Delaware No Drawing. Application February 11, 1935, Serial No. 6,129

4 Claims. (Cl. 92-54) This invention relates to molding of pulp into finished shapes and particularly to the molding of receptacles and containers, such as bottles and the like which are intended to hold. liquid 5 or semi-liquid materials, and to have smooth interior surfaces.

Although the molding of pulp containers, such as bottles, has long been attempted, the results have not heretofore been altogether satisfactory. One reason for this has been the fact that the containers heretofore made by molding pulp have had rough, uneven interior surfaces, which not only were unsightly when inspected, but caused considerable loss of contents from clingage and failure to drain well when the containers were emptied. Such loss has been considerable in amount when a large volume of material such, for example, as lubricating oil, was dispensed in packages containing one quart or less.

The present invention consists primarily in a molding process which will produce a smooth,-

even, surface or layer on the interior of the container. To this end, the process is conducted in stages, in which the pulp supply used to form the inner lining is in a much finer state of subdivision than the pulp deposited within the Walls of the container. Also the pulp is hydrated more highly and should be free working, although this property may be varied within wide limits depending on the use for which the article is intended.

The invention further relates to means for controlling both the rate and the pressure at which the pulp particles are deposited in the outer portion of the body walls and in the interior surface or lining of the receptacle. This is accomplished preferably by the use of pulp of relatively thick consistency when building up the body walls and by the use of pulp in a highly diluted or attenuated state when finishing the interior surface.

The invention further relates to the intro- "duction of a dispersing medium in such a man- 45 ner that uneven deposits or lumps of pulp initially deposited on the wall near the inner surface will be broken up and dispersed sufiiciently to permit the particles to be redeposited and thereby form a distinct inner layer having the so desired characteristics with respect to fineness of pulp particles and smoothness of finish.

The invention further consists in the new and novel features of operation and the new and original arrangements and combinations of steps in the process and also in a product having the general characteristics, the new and useful applications, and the several features of utility hereinafter described and more particularly set forth in the claims.

In carrying out my improved process, the pulp is introduced in the form of a relatively thick suspension containing, for example, from 1% to 2% of pulp fibres. Water from the ordinary source of supply may be used, but preferably should be relatively free from suspended or dissolved substances such as mud or calcium or magnesium compounds. Substantially all the pulp fibres have length of approximately 0.5 mm. to 3 mm. (millimeters), although this may vary within wide limits, depending upon the type of article being molded.

The suspension is introduced into the mold, which may be perforated in the usual way, through an inlet, which may or may not project a certain distance into the mold. In the first stage, the pressure may vary from one to ten pounds per square inch, comparatively low pressure being desirable, so that only normal conditions will obtain as the pulp flows into the mold and the walls gradually build up from the outer to the inner portion, until at least three fourths of the normal thickness of the walls has been deposited.

After the desired wall thickness has been obtained, to form the main body of the receptacle wall, the supply of pulp is cut off leaving the interior of the mold filled with pulp suspension, with an appreciable quantity also of such suspension within the feed pipe from which it will drain only slightly because, although the pressure is cut off, the thickness of the walls is sufficient to prevent rapid drainage of the water. In this manner a layer of coarse pulp is laid against the mold walls.

Promptly upon the closing of the first pulptank valve there is introduced into the mold, under a pressure varying from 10 lbs. to lbs. per square inch, a /2% water suspension of fine pulp. This immediately causes quite rapid ebullition of the liquid Within the container and, at the same time, it causes a washing or scouring action to take place over the interior walls which,

at the pressure stated, is sufficient to loosen some of the pulp particles and to disperse through the mixture any nodules, clots or aggregations of pulp that may have accumulated on the interior walls during the preceding stages of the process.

This action dilutes the first pulp suspension and, as the draining and deposition take place,

the particles remaining in suspension and which were washed away from the surface tend to become finer and finer until eventually all of the pulp is deposited as a second layer and only clear Water remains. Generally speaking, the thinner pulp to form the second or inner layer is supplied to the mold for a period of approximately two to five seconds after it is first admitted so that loosening and redeposition of pulp takes place to a considerable extent. Since the liquid tends to escape through the walls at the points where they are thinnest, innumerable currents are automatically set up to deposit pulp particles at any point Where the liquid escapes and thus automatically the depressions and valleys are filled up to or almost to the level of the thickest part of the interior wall, thus providing the container with a smooth interior surface.

Not only are the walls of the containers produced by my process of more uniform thickness but the interior of the receptacle is smoother because of the selection that takes place automati cally with respect to pulp particles. Ordinarily, the coarser particles will be first to deposit and, unless they become imbedded and form projections or protuberances Where they are subjected to the washing action of the liquid currents, they tend to remain where placed by drainage. This causes the particles remaining in suspension to become progressively finer and finer until at last only the very fine particles are in suspension and are then deposited on the Walls while the liquid drains away.

By means of this process, I am enabled to produce a smooth, even, finely-textured layer on the interior surface of a container without resorting to secondary treatments or to mechanical manipulation of any kind. Hence, the invention is well adapted to the manufacture of molded pulp containers having restricted mouths or openings. The smooth walls in the finished containers drain much more evenly and with less clingage than walls having irregularities, such as projections and depressions, which tend to' withhold material even though it is not viscous in character. The steps of the operation follow immediately one after the other and very little more liquid is required than in the processes heretofore attempted.

By the process described, comprising the successive use of thicker and of thinner pulp suspensions, it has been possible to avoid the formation of rough interiors in molded pulp'containers and to cause the finer fibres to predominate there and to constitute a smooth felted inner lining which makes the container substantially free from clingage defect and consequent loss, and a new product in the molded pulp art.

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, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is 1. The herein described method of making molded paper pulp containers having substantially smooth interiors, which comprises successive introduction into a foraminous mold, of a pulp suspension containing 1%% to 2% of fibres, at a pressure of from one to 10 pounds, followed by a pulp suspension containing /4% to of fibres at a pressure of 10 lbs. to 30 lbs. per square inch, the duration of the flow of thick pulp suspension being shorter than that of the thin pulp suspension.

2. The method of making molded paper pulp containers having substantially smooth interiors,

which comprises successive introduction through a nozzle into a foraminous mold, of a series of pulp suspensions, the first containing 1%% to 2% of 0.5 mm. to 3 mm. pulp fibres, at a pressure not exceeding 10 lbs. per square inch and continuing for a period not exceeding five seconds, the next pulp suspension containing about 0.5% of pulp, and introduced under a higher pressure but not exceeding 30 lbs. per square inch for a period not exceeding ten seconds, whereby to agitate the second pulp suspension and disperse lumpy aggregations of fibres and finally to deposit said pulp in a layer having a smooth interior surface.

3. The method of making a molded pulp bottle having a restricted mouth in a foraminous mold having an interior shape like the desired exterior shape of the bottle to be formed, which comprises introducing into said mold a predetermined quantity of 1%% to 2% pulp suspension, under a pressure not to exceed 10 lbs. per square inch, whereby to form a layer of substantial thickness upon the interior of said mold, then introducing into the container thereby formed a predetermined quantity of approximately 0.5% suspension of finer pulp under a pressure exceeding 10 lbs. per

square inch whereby to disperse any lumps of fibre previously deposited in said layer and to lay the fibres of said pulp in a second layer having a relatively smooth interior surface.

4. The method of molding a container from pulp which includes introducing a liquid suspension of fibers into a foraminous mold under a pressure not substantially in excess of 10 pounds per square inch todeposit the fibers against the walls of the mold as a loosely molded layer, introducing a second suspension of finer fibers than said first fibers, under a pressure substantially in excess of 20 pounds per square inch to effect a compacting of the layer of fibers, and to cause sufficient circulation currents in and agitation of the suspension to entrain deposits of fibers projecting from the layer and continuing the introduction of said second suspension to smooth and level the layer and deposit the finer fibers and entrained fibers on and in intermatting relation with the fibers of said layer to form a smooth wall.

. ROY D. HEYMANN.