US2686141A

US2686141A - Preparation of resin-bearing fibrous pulp

Info

Publication number: US2686141A
Application number: US234273A
Authority: US
Inventors: Edith F Sawyer
Original assignee: Keyes Fibre Corp
Current assignee: Keyes Fibre Corp
Priority date: 1951-06-29
Filing date: 1951-06-29
Publication date: 1954-08-10
Anticipated expiration: 1971-08-10

Description

1954 E. E. sAvWER 2,686,141

PREPARATION OF RESIN-BEARING FIBROUS PULP Filed June 29, 1951 2 Sheets-Sheet 1 VV'VVVVVV INVENTOR EB. Sanger BY A; ATTORNE Aug. 10, 1954 E. E. SAWYER PREPARATION OF RESIN-BEARING FIBROUS PULP Filed June 29, 1951 2 Sheets-Sheet 2 INVENTOR. E. E. SAWYER HI AT T04? Patented Aug. 10, 1954 PREPARATION OF RESIN-BEARING FIBROUS PULP Edward E. Sawyer, Water-ville, Maine; Edith F. Sawyer, administratrix of said Edward E. Sawyer, deceased, assignor to Keyes Fibre Company, Portland, Maine, a corporation of Maine Application June 29, 1951, Serial No. 234,273

'7 Claims. 1

The present invention relates to resin-bearing fibrous pulp, more particularly to methods and apparatus for preparing such pulp mixtures so that they can be used to make molded pulp articles.

Among the objects of the present invention is the provision of novel methods and apparatus for preparing resin-bearing fibrous pulp mixtures without the usual difficulties and losses characteristic of the normal wet-felting.

The above as well as further advantages of the present invention will be more completely understood from the following description of several of its exemplifications, reference being made to the accompanying drawings wherein:

Fig. 1 is a schematic showing of the essential elements of one form of apparatus for preparing the resin-bearing pulp according to the present invention;

Fig. 2 is a schematic showing similar to Fig. 1 of a different form of apparatus embodying the present invention; and

Figs. 3, 4 and 5 are diagrammatic illustrations of electric circuit details for the construction of Fig. 1.

According to the present invention finely-di vided resin particles are given an electrical charge, and a mass of pulp fibres is given an oppositely polarized electrical charge, and the two charged materials are brought together, causing the electrical attraction between the oppositely polarized charges to bring the resin particles in intimate commingled relationship with the pulp. This produces a resin-bearing pulp that is Well suited for direct molding into articles having good strength and rigidity, such as cafeteria trays, china-dike dishes, etc.

Fig. l of the drawings shows one form of apparatus for producing the desired pulp mixtures. A hammermill H3 is hopper H and is connected by means of duct !2 with a mixing chamber or reactor 20. A blowing arrangement such as an internally mounted fan (not shown) fastened to rotate with the hammer shaft of the mill, can be used to blow the disintegrated fibres out of the mill. Where the hammers themselves create a sufiicient amount of air movement, no auxiliary blowers are needed. Another hammermill I4 having the same or a separate blower is connected to the same reactor through duct !6. In the modification shown in, this figure the mixing chamber is provided with electrical charging structure indicated by the

screens

22, 23 connected to suitable sources of high D. C. voltage as by means of the

leads

24, 25

provided with a receiving suitably insulated from each other as well as from intervening structures, by

insulators

26, 27. The mixing chamber 20 has an outlet 36 leading to a separator 34 which can conveniently be in the form of a cyclone or centrifugal settler. Solid particles settling from separator 34 are permitted to drop onto a support 36, a belt conveyor for example, for transport to the molding apparatus, not shown.

Duct I5 is shown as also provided with. a sprayer for atomizing resins that are supplied in the form of dispersions in a liquid in which the resin is either dissolved or suspended in finely-divided form.

In use the hammermills ill, I 4 are provided with screens to limit the sizes of the particles which they discharge. One of the hammermills is supplied with sheet pulp or pulp lap and, under the beating action of the mill, this pulp is fluifed and disenfibered to produce finely-divided pulp fibres that are easily suspended in the air or other atmosphere of the mill in the form of a cloud. Under the influence of the blower, a suspension or cloud of pulp fibres passes through the exit screen, through duct I2 and into the mixing chamber 20. A corresponding cloud or suspension of resin particles is formed in hammermill l4 and delivered through duct IE to this reaction chamber. Upon passage of the respective particles through the

screens

22, 23, they become electrically charged to oppositely polarized potentials. As a result the resin and fibre particles in chamber 29 are electrically attracted toward each other and move toward each other till they come together or coalesce in intimate commingled relationship. This coalescence increases the weight of the individual particles that remain, and this together with the concomitant neutralization of electrical charges results in the production of resin-bearing particles that are relatively rapid settling. The blowing action under which the particles are brought together, along with the above settling, causes the resin-- bearing pulp fibres to drop into separator 34 where the propelling air or other atmospheric medium is separated out in conventional manner leaving the resin-bearing fibres to drop onto support 36.

The resin-bearing particles so formed can be permitted to accumulate to a substantial layer, or delivered to a container where they are collected.

In place of a hammermill, finely. divided pulp fibres suitable for use with the present invention can be provided by shredding, grinding as by a ball or rod mill, or any other mechanical disintegrating device.

The collected mass of resin-bearing pulp can then be dry molded or formed into reforms of the types shown in Patent 2,343,330, granted March 7, 1944 or Patent 2,274,095, granted February 24, 1942. The resulting preforms suitable for use in final hot molding of the desired articles as described in these above patents. The final cured and molded articles are comparable in every way to corresponding articles made from resin-bearing pulp formed by the conventional wet process. A feature of the invention is that the pulp and resin losses which are unavoidable in the Wet-forming process, are substantially completely avoided. This is particularly significant in the case of resins which are more water soluble and cannot ordinarily be used in the wet process. For example melaminedormal lehyde resins, which impart very desirable characteris tics to molded pulp articles, heretofore have had to be limited to impregnation into the fibrous structure of preformed articles, since these resins are too soluble in water unless condensed to such a state that most of their advantages are not obtainable. Furthermore, the awkward and delicate handling of wet limp pre-forrns that are made by the wet process is also avoided. Another feature of the present invention is that it enables the use of two-stage thermo-sett-ing res-- ins rather than being restricted to the singlestage resins required in the wet process by reason of the relative solubility of the accelerator normally present in the resinifying ingredients of the two-stage resin as it is prepared for use.

The resin supplied for reduction to finely-divided particles can be of any suitable type al though thermosetting resins, such as phenol-aldehydes, urea-aldehydes, amine-aldehydes, phenol amine-aldehydes, melamine-aldehydes, alkyds, glyptals, etc., are preferred. These thermosetting resins are conveniently supplied in solid form, so that they can be melted in the final molding step to bond together and rigidity the fibres in the final article. Thermo-plastic resins such as cellulose acetate, polyvinyl chlorides and acetates and polystyrene can also be used.

Alternatively the resin can be supplied in liquid form either undiluted or dispersed in a carrier liquid as pointed out above. With this type of feed the spray structure fill is used instead. of the hammermill Hi to atoinize the resin particles. This atomization also causes volatile types of solvents or suspending liquids to at least partially evaporate, thereby assuring that the electrically commingled particles dropping on support 35 are not unduly moist. Suitable solvents in accord ance with the present invention are or the water repellent, non-inflammable types such as halogenated hydrocarbons. Other types of solvents can also be used with adequate provision to insure that they are not ignited by the electric fields and do not provide sufficient electrical conductivity to prevent the electric field from build ing up to the desired extent.

The

charging screens

22, 23 are preferably made adjustable in position and coarse enough in mesh to freely pass the particles supplied for charging. In fact the charging screen need only be a series of spaced parallel bars or wires mechanically free of crossing wires. A specific form of such type charging screen is illustrated in 3 of the drawings as including a support bar 328 from which depends a plurality of spaced ver tical wires 323. The bar may be structurally suspended and electrically energized from a lead wire 325 afiixed to bar 328. For supplying the electrical charging currents, each screen can be connected to the respective terminals of a single or common D. C. power supply. This connection may be made as shown in Fig. 4 of drawings in which a single D. C. generator #29 is connected via separate lead wires 42 325 to respective screens Q22 and $23. It will, of course, be understood that two different power supplies can be used with the screens connected respectively to the positive terminal of one supply and the negative terminal of the other. With either type or construction, one of the screens can be grounded to the earth as by means of a connection to some electrically conductive portion of the apparatus that is secured to the ground. Alternatively if the power supply is in the form of a multiplicity of units the shell or chambers 20 can be grounded through the power supply at a potential differ ence, with respect to both screens, suitable for practical application to maintain the electric fields around the screens. This form of the invention is schematically illustrated in 5 of the drawings where a pair of

D. C. generators

529 and 529 are connected to a common ground 539 at a suitable potential with respect to the screens 522 and 523. To reduce the accumula tion of particles on the chamber walls, these walls may also be coated on their internal surfaces with a suitable lining 52L Effective charging potentials at the screens are in the range of 5 to 100,000 or more volts for each charging field.

By arranging for any ground connection to be to a positively polarized portion of the power sup ply, adjacent electrically conductive structures that are also grounded can be advantageously subjected to some degree of cathodic protection to reduce their corrosion. However, the ground ing of a negatively polarized portion will operate to substantially completely prevent corrosion of the ground connection itself, and is particularly desirable where the ground connection is provided by a portion of the apparatus.

Fig. 2 shows a diiferent apparatus and method for preparing the resin-bearing pulp material in accordance with the invention. Here a layer of pulp lap or loosely deposited pulp fibres ital is carried as by means of conveyor belt Hi2 through a depositing chamber iill. Conduit H2 leading into the chamber is provided for the reception of a supply of suspended resin particles that can be prepared as indicated above in connection with the apparatus of Fig. 1. Within the chem-- ber lid are electrical charging elements shown in the form of a combination of conveyor-backing conductor iZG and pointed ionizing type electrode [33, each connected to high potential electric supply. The backing E20 need not be used where the conveyor belt is itself electrically conductive and suitably connected as by contact brushes to the power supply.

The apparatus and method of Fig. 2 are generally similar to those of Fig. 1. Plate 21? acts as a charging electrode for the fiber mass it that is carried over it, and pointed electrode 138 efiects an electrical charging of the suspended resin particles. Under the influence of their charges these suspended particles are brought into intimate engagement with the fibres in mass i Mi as it moves through the chamber. The emerging resin-bearing fibrous mass can then be sent to the final molding equipment, and can if desired, be sectioned or divided into portions shaped to fit or provide a suitable amount of molded mixture for individual molding processes. The final molded article is substantially identical with that produced from the resin-bearing fibrous mass prepared by the apparatus of Fig. 1.

By having the fibres on conveyor I 02 moistened with about or more of water based on their dry weight, they can be made sufiiciently conductive to electricity to effect good resin deposition without the presence of a fibre-contacting electrode in the chamber H0, or to improve the depositions where such an electrode is present.

The form of the charging electrodes can be subjected to considerable variations. Thus the pointed electrode I 30 of Fig. 2 can be used in place of the screens 22 and/ or 23 of the construction of Fig. 1 and conversely a screen can be used as the charging electrode in the construction of Fig. 2.

The resin content of the fibrous mixture prepared according to the present invention, can be varied from as little as '1% resin by weight to about 50% resin by weight or even more. Control of the resin content is effected by adjustment of the blowers, hammermill operating speeds or spray feed in the apparatus of Fig. 1,

and in addition the conveyor velocity and fibre deposit in the apparatus of Fig. 2. In general with the higher resin contents more of the resin is deposited at the surface portions of the fibre layer I00 in the apparatus of Fig. 2, and less resin makes its way into the interior of this layer. However, suitable controls such as increasing the strength of the electric field, reduction of the electrical conductivity of the fibres, or increasing the distance between the charging electrode and the fibres, will tend to make the resin depositions more uniform throughout the thickness of the fibre layer. The resin-bearing product can accordingly be controlled to vary the resin from one that is much richer at the surface, as sometimes desired with certain types of articles such as cafeteria trays, to one that is substantially uniform Where this is preferred.

Either type of resin-bearing layer can be cold compacted, with or without punching out of special shapes, to directly make preforms such as the multi-layer preforms described in the abovementioned patents. Any scrap left by reason of the punching can be readily disintegrated to make a uniform mixture that is suitable for use in the flow type of molding described in the above identified Patent 2,343,330. Any of the cold compacting in accordance with the present invention can be preformed with the fibres moistened somewhat with water or any other lubricating liquid such as the resin dispersants described above. This enables a reduction in the cold compacting forces that are required and at the same time produces a preform that is more readily handled. Such moistening need not be sufficient to cause the moistening liquid to drain or drip from the moistened mass.

The charged fibres provided in accordance with the present invention can be any kind of cellulosic fibres such as are used in ordinary paper making processes. Asbestos or synthetic fibres such as rayon, casein, cellulose acetate, nylon are suitable.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof, except as defined in the appended claims.

What is claimed is:

1. A method of forming a resin-bearing molded pul preform, which method comprises electrically charging a mass of cellulosic pulp, preparing a cloud of finely-divided solid resin particles having an electrical charge opposite to that of the pulp, bringing the electrically charged pulp and resin particles together to cause them to become attracted to each other and cause the resin particles to become intimately but loosely commingled with the pulp, removing a portion of the resulting loose mass and cold molding this portion of resin-bearing pulp into the desired preform shape.

2. A method of forming a resin-bearing pulp molding mixture, which method comprises electrically charging a mass of dry cellulosic pulp, preparing a cloud of finely divided solid resin particles having an electrical charge opposite to that of the pulp, and bringing the electrically charged pulp and resin particles together to cause them to become attracted to each other and cause the resin particles to become intimately but loosely commingled with the pulp.

3. The combination as defined by claim 2 in which the mass of electrically charged pulp is a suspension of finely divided pulp in air.

4. The combination as defined by claim 2 in which the mass of electrically charged pulp is alayer of uncompacted pulp held on a support.

5. A method of forming a resin-bearing molded pulp article, which method comprises preparing a fluffy mass of dry cellulose pulp fibres, electrically charging these fibers to a high D. C. voltage, preparing a cloud of finely-divided solid dry particles of incompletely cured thermosetting resin, which particles are electrically charged oppositely to that of the pulpfibres, bringing the electrically charged pulp and resin particles together to cause them to become attracted to each other and cause the resin particles to become intimately commingled with the pulp, and pressure molding the resulting mass of resin-bearing pulp into the desired shape at a temperature high enough to cure the resin.

6. The method as defined by claim 1, in which the fibres have less than 10% moisture by weight when they are electrically charged.

7. The method as defined by claim 1 in which the fibres have at least 10% moisture by Weight when they are electrically charged.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,173,032 Wintermute Sept. 12, 1939 2,174,328 Meston et al Sept. 26, 1939 2,270,341 Ransburg Jan. 20, 1942 2,336,745 Manning Dec. 14, 1943 2,411,660 Manning Nov. 26, 1946 2,466,906 Miller Apr. 12, 1949 2,493,194 Heino Jan. 3, 1950 2,564,397 Duddy Aug. 14, 1951 2.569.169 Heritage e ..s Sept. 25, 1951

Claims

1. A METHOD OF FORMING A RESIN-BEARING MOLDED PULP PREFORM, WHICH METHOD COMPRISES ELECTRICALLY CHARGING A MASS OF CELLULOSIC PULP, PREPARING A CLOUD OF FINELY-DIVIDED SOLID RESIN PARTICLES HAVING AN ELECTRICAL CHARGE OPPOSITE TO THAT OF THE PULP, BRINGING THE ELECTRICALLY CHARGED PULP AND RESIN PARTICLES TOGETHER TO CAUSE THEM TO BECOME ATTRACTED TO EACH OTHER AND CAUSE THE RESIN PARTICLES TO BECOME INTIMATELY BUT LOOSELY COMMINGLED WITH THE PULP, REMOVING A PORTION OF THE RESULTING LOOSE MASS AND COLD MOLDING THIS PORTION OF RESIN-BEARING PULP INTO THE DESIRED PREFORM SHAPE.