US2917777A

US2917777A - Manufacture of pencils

Info

Publication number: US2917777A
Application number: US445477A
Authority: US
Inventors: Pischel Paul
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-07-23
Filing date: 1954-07-23
Publication date: 1959-12-22
Anticipated expiration: 1976-12-22

Description

United States atent MANUFACTURE OF PENCILS Paul Pischel, Hanuover, Germany No Drawing. Application July 23, 195 Serial No. 445,477

Claims. (Cl. 18-475) The invention relates to a method of manufacturing writing cores and is particularly useful in preparing writing cores for use in mechanical pencils or for enclosure in wooden sheaths and the like.

In the general common manufacture of writing cores, a pasty mass of high consistency is extruded under high pressure through a nozzle in the form of a strand and the strand-like core still having a high content of moisture is laid out on boards or like supports in the desired straight form. The moist and still soft strand upon emerging from the extrusion press is still capable of being molded by hand and this characteristic is taken advantage of in the final shaping of the strand hereinafter also referred to as straightening the core.

The freshly extruded strand has usually a moisture content of to 30% by weight, depending upon the nature of the core mass and other factors or production. In order to remove or reduce this high moisture content the strand has to undergo a drying process while in its final form intended for use to reach a state of final dryness. Such drying step is time consuming and required careful handling of the boards in an effort to move the cores when they are still susceptible to deformation. The problem of drying can be alleviated only to a certain extent as the core must undergo a slow drying for days and sometimes weeks in order to be break-resistant. An accelerated drying produces a core that may readily split. Furthermore, when straightening the freshly extruded strand or core by hand, the core is often flattened or otherwise deformed by manipulation and such deformities when reaching 3% of the diameter of the core make the core unsuitable for use in mechanical pencils in which inaccuracies in diameter of the core should not approximate 2%.

Manual operations have been found of advantage in the production of colored writing cores as distinguished from graphite cores commonly referred to as lead. In the manufacture of colored cores the strand emerging from the press is guided and supported by hand to minimize deformation and tearing particularly when producing cores having a diameter of l to 0.6 millimeter. Great skill is required in laying out such extra thin cores on boards.

It is common practice to pass the straightened core through various drying chambers or drying stages and to expose the cores to drying air of less moisture content.

A uniform and careful drying process of the cores while lying straight on the boards is advisable in order to avoid crumpling, chipping or breaking of the core during writing. The straightening operation, especially for small sized cores, requires at least two thirds of the time of extruding the strand and forming the straight moist core. Also, the experience has been made that, after the manual straightening, final drying and cutting, up to 30% of the cores are defective and form scrap, particularly when small sized cores are involved.

According to a prior method cores have been produced from a composition including principally clay, color pigment (which may be graphite) and a binder. A suitable binder is a water-soluble cellulose ether or derivative thereof, such as methyl cellulose. The binding agent is contained in the composition mass in a pasty state, and in order to thicken the mass by evaporation of excessive moisture before extrusion of the mass it has been proposed to heat the mass. The cores produced from such a composition are very hard and do not give up sufficient -material when passed over a writing surface. Therefore,

the straight and already dried cores of a length in which they are to be sold are impregnated with wax or fat by submerging the cores in a molten bath of such wax or fat.

Cores having indelible writing characteristic do not re quire the latter treatment.

According to a more common practice, the wax or fat is added to the mass before its extrusion to form the core,

and the invention, in its preferred form, is particularly concerned with this mode of producing the core.

It has been discovered that the dried, hard and rigid cores containing a Water-soluble cellulose ether or derivative thereof, can regain their pliability by heating the dried core and this can be made use of to re-shape the dried core. The thus re-shaped core, upon cooling, becomes rigid again without having lost any of its previous qualities, including break-resistance.

It is the broad object of the invention to take advantage of this discovery and to improve on the manufacture of writing cores which due to the inclusion of a watersoluble cellulose ether or a derivative thereof, become re-shapable by the application of heat.

It is a further object of the invention to postpone the step of straightening the freshly extruded strand until after the drying step and thereby permit a continuous operation of the extrusion press and storing of the freshly extruded strand for the drying process in a more convenient form, for instance in coils.

It is a still further object of the invention to heat the dried strand immediately before its use in a machine for wrapping a composition sheath about the core.

Other objects and features of the invention will become apparent from the following description.

A preferred method of carrying out the invention will now be described. A suitable composition mass containing, for example, by dry Weight, 20% china clay, 20% Ca stearate, 20% coloring matter or pigment, 20% wax or fat (Japan wax, stearic acid, petrol wax), and 20% methyl cellulose or a mixture thereof with tragacanth and sufficient water (ti. 7 parts of water to one part of the cellulose content) to form a. pasty mass, is extruded continuously and the strand thus formed is coiled in spiral or 8-form or collected in any other suitable manner for storing and drying. According to the invention, the dried strand of great length is heated to become soft and pliable again and in its pliable state is straightened preferably by a suitable machine whereupon the thus straightened strand or core is permitted to cool and harden again.

Although the previously mentioned binding agent as such does not exhibit the characteristic of melting or being thermoplastic under heat, it appears that the extruded and dried strand becomes thermoplastic. Whatever the explanation may be, the thermoplastic characteristic of the already dried core of a suitable composition such as mentioned above has heretofore not been taken advantage of and, to my knowledge, was not expected.

The method of the invention just described permits an extrusion of any desired length of strand at great speed unhampered by conditions imposed by short lengthproduction. The thus produced strand has a uniform density and therefore an improved quality. An extrusion nozzle can be conveniently placed in an opening preferably at the top of a container which is relatively moved for coiling the strand therein.

The container may be constructed as a drying chamber for receiving and circulating therein drying air, or as a heating vessel for drying the strand by convection, if desired, with the assistance of vacuum, by high-frequency electric current or infrared heat, or the container as such may be placed with other containers in a drying chamber.

When heating again the dried and cooled strand to make the strand pliable again the container may serve as suitable means for submerging or exposing the strand to a heating medium. The heating may be carried out in stages so that the strand will have an optimum degree of pliability during uncoiling and during the subsequent straightening operation. Cooling of the straightened core can be accelerated to shorten the cooling period to a few seconds.

It has been found that heating the strand to about 50 C. or more causes sutficient pliability and softening for the straightening operation which can be combined with cutting the core to desired lengths. The time of heating the strand can be reduced to two to three seconds by using higher temperatures, for instance of 70 to 80 C.

It has also been found that the step of heating the dried coil can be combined with the impregnation of Wax in the previously mentioned method according to which cores produced from a composition mass not containing the wax are dried and the dried cores are impregnated with wax. The aforementioned advantages remain.

It is also a feature of the present invention to combine the re-heating of the already dried core with a manufacture of sheath pencils substantially as disclosed and described in US. Patent 1,937,104. According to this disclosure a pliable moisture-containing strand is fed through a nozzle forming a mandrel in the outlet of an extrusion press, the cross section of the outlet determining the form of the pencil sheath. A composition mass, f.i. of the self-hardening type, is pressed through the outlet while the core advances through the nozzle to form a sheath pencil in a single operation. The invention is not concerned with the mode of manufacture itself and, therefore, an illustration of the machine is not considered necessary.

The pencil stock thus produced is still in a plastic state and hardening of the encased core tends to a shrinkage of the core diameter which differs from the shrinkage of the sheath. The result of drying the sheath and core simultaneously invariably results in a loosely encased core. This disadvantage is avoided by the invention by feeding a dried core in a state of final dryness made pliable by heating, through the internal nozzle, whereby shrinkage of the composition during drying of the plast1c pencil stock causes a firm grip of the sheath on the already dry core.

While I have described a preferred form of the invention, I do not wish to be limited thereby; various changes may be made in the mode of operation, as disclosed and defined in the appended claims.

I claim:

1. In the method of producing writing cores for pencils from a pasty composition mass consisting essentially of water, materials which in kind and amount are incapable of imparting pliability to a dried pencil core under heat, and a water-soluble cellulose ether as binding agent which causes a finally dried rigid core to become pliable upon the application of heat, in combination with the steps of extruding the composition mass, collecting the extruded strand, and finally drying the strand to rigidness, the steps of heating the thus dried strand to make said strand pliable, straightening the pliable strand and permitting the straightened strand to cool and to form a rigid pencil core.

2. In the method of producing writing cores for pen cus from a pasty composition mass consisting essentially of water, materials which in kind and amount are incapable of imparting pliability to a dried pencil core under heat and a water soluble cellulose ether having the characterteristics of methyl cellulose as binding agent in the dried core, water-soluble cellulose ether or a derivative thereof having the characteristic of methyl cellulose as binding agent in the dried core, the steps, in the sequence stated, of extruding the composition mass, collecting the extruded strand, finally drying the strand to rigid hardness, heating the finally dried strand to make said strand pliable, straightening the pliable strand and permitting the straightened strand to cool to form a rigid pencil core.

3. The method as defined in claim 2, in which the freshly extruded strand is collected and finally dried in coiled form.

4. The method as defined in claim 2, in which the freshly extruded strand is stored and finally dried in a container.

5. The method as defined in claim 2, in which the freshly extruded strand is finally dried while stored in a container, and the finally dried strand while in said container is heated prior to removing said finally dried strand from said container. 7

6. In the method of producing pencil cores from pasty composition mass consisting essentially of water, materials which in kind and amount are incapable of imparting pliability to a dried pencil core under heat, and a finely dispersed water-soluble cellulose ether as binding agent and the dried, extruded mass having the characteristic of being pliable upon the application of heat, the steps of extruding the composition mass, collecting the extruded strand, finally drying the strand to rigid hardness, heating the finally dried strand to make said strand pliable, straightening the pliable strand and permitting the straightened strand to cool to form a rigid pencil core.

7. The method as defined in claim 6, in which the freshly extruded strand is finally dried while stored in a container, and the finally dried strand while in said container is heated prior to removing said finally dried strand from said container.

8. A method of producing sheath pencils by extruding a pasty composition mass adapted to form the encasing pencil sheath upon setting of the mass about a simultaneously advanced pencil core, including the steps of forming a supply of said pencil core in form of a strand by extruding a pasty composition mass consisting essentially of water, materials which in kind and amount are incapable of imparting pliability to a finally dried pencil core under heat, and a water-soluble cellulose ether or a derivative thereof as binding agent, collectmg the extruded strand in coil form, finally drying the coiled strand to rigid hardness, heating said dry coiled strand to make the strand pliable and feeding the pliable strand through a nozzle in the outlet of an extrusion press while extruding said sheath composition about said finally dried strand, said strand being straightened by passing through said nozzle to form the pencil core.

9. The method of producing writing cores for pencils from a pasty composition mass consisting essentially of water, materials which in kind and amount are incapable of imparting pliability to a finally dried pencil core under heat, a water-soluble cellulose ether, the binding agents being of a nature causing a core dried to hardness materials which in kind and amount are incapable of imparting pliability to a finally dried pencil core under heat, and water-soluble methyl cellulose as binding agent including the following steps in the stated sequence, extruding the composition mass, collecting the extruded strand and drying the extruded strand in the absence of any straightening operation to slowly reduce the moisture content and to thereby obtain an extruded strand having the dryness and rigidness of a finished core, subsequently heating the strand to a temperature at which the strand becomes pliable and finally straightening and cooling the straightened strand.

References Cited in the file of this patent UNITED STATES PATENTS Loomis Mar. 19, 1940 OTHER REFERENCES Cellulose and Cellulose Derivatives, by Emil Ott, pp. 790491, 2nd (revised) Printing, 1946. Interscience Publishers, Inc., New York, NY.