US1970603A

US1970603A - Pencil lead and method of making same

Info

Publication number: US1970603A
Application number: US644270A
Authority: US
Inventors: Grossman Harold
Original assignee: American Lead Pencil Co; EBERHARD FABER PENCIL CO
Current assignee: American Lead Pencil Co; EBERHARD FABER PENCIL Co
Priority date: 1932-11-25
Filing date: 1932-11-25
Publication date: 1934-08-21
Anticipated expiration: 1951-08-21

Description

l 'atentecl Aug. 21, 1934 PENCIL LEAD nn METHOD F MAKING l sAME r Harold Grossman, Newark, N. Lassignor of one half to The American lLead Pencil Company,

Hoboken, N. 5., a corp oration of New York, and one-half to Eberhard Faber Pencil 00.,

Brooklyn, N. iii, a corporation of New York No Drawing. Application November 25 1932;

Serial No. 644,270

8 Claims. (01.106-5).

This invention relates to the manufacture of pencil leads, crayons and similar products which are used for marking upon surfaces, and has for its object the improvement of such products and "5 the method of preparing them, and particularly the treatment of crystallized graphites whereby these materials may be reduced to a finely divided condition, thereby permitting'the manufacture of improved pencil leads and thelike 10 therefrom.

In'the manufactureof black pencil leads and the preparation of graphite for use in such leads and in crayons and similar products used for marking, it is essential that the constitu cuts of the mixture used be in a very finely divided condition, in order that the marking element may be smooth. The usual practice heretofore requires the selection of the materials clay and graphite for purity, and the use preferably of an amorphous variety of graphite. The clay is washed to remove as much sand as possible, and is dried. The graphite is ground and air floated to ensure the desired fineness. The clay and graphite are then mixed in the desired proportions with water, and the mixture is again ground. The grinding is an extremely tedious operation, and the quality of the product depends to a large extent upon the time devoted to grinding. The time must, in any event, be prolonged to ensure an homogeneous and smooth-writing product. In the preparation of high grade products, grinding frequently consumes weeks. When the grinding is completed, the mass is filter pressed to remove surplus moisture and is worked into the desired shape and baked.

It is the object of the present invention primarily to avoid the tedious grinding for prolonged periods, and especially to permit the use .of crystallized graphites in the manufacture of pencil leads, crayons and the like.

When crystallized graphites are subjected to a grinding operation, the graphite is broken down or fractured across the planes of cleavage, thus exposing a multitude of rough edges. Consequently, in the attempt to increase the fineness of such graphite the proportion of smooth sliding surfaces to the rougher fracture surfaces is reduced. The smooth-writing quality of the leads produced from such material is correspondingly lessened, so that a large part of the benefit which should be secured from the grinding is lost. Improvement of the quality of the leads by grinding is limited, therefore, when crystallized graphites are employed.

In carrying out the present invention, the

difficulty is avoided by subjecting the graphite to chemical'oxidation in which the graphite i's converted into graphitic acid. Upon reduction, the graphitic acid is converted into graphite in a colloidal condition. This colloidal graphite *-beno cause of its fineness, is admirably adapted for use in the preparation or" pencil leads, crayons and the like. It maybe combined withclay of suitable fineness or other materials pressedfinto leads and the like, and baked. The graphite can be added to clay or other-suitable fillers, with'ap prcpriate binders, such as gums, resins, -etc., similar to the practice followed in making colored leads. In this case, it is not necessary to bake the leads. The resulting product affords a smooth- {0, i writing element of a quality surpassing any obtainable by the simple grinding of the graphite in the manner hereinbefore described.

For the purpose of the present invention, the graphite is treated with strong oxidizing agents, '15 for example a mixture of concentrated sulphuric acid (H2804) and potassium permanganate (KMnOl). Other strong oxidizing agents such as the bichromates, perchromates, chromates, perchlorates and chlorates of the alkali metals inja'o concentrated sulphuric acid may be used. The treatment of graphite with any of these oxidizing agents in the manner described produces graphite in the form of ultramicroscopic particles, that is to say, in a colloidal condition which may be defined for the purpose of the invention as that condition in which the product in the aqueous suspension passes completely through the pores of a standard filter paper or shows no sediment after it has been permitted to stand for considerable periods.

Chemical oxidation of graphite in the manner described affords a product which is most favorable structurally for the manufacture of pencil leads and similar marking elements. The 001- loidal graphite produced consists of minute scales or flakes which are split from the raw material in planes parallel to the plane of cleavage. Consequently, the product affords a maximum of sliding surfaces. When the colloidal product is .100 mixed with clay or the like and baked, the resulting leads, because of the sliding surfaces of the graphite, provide a smooth-writing element of uniform quality and consistency.

As hereinbefore noted, the invention is pari ticularly adapted for the treatment of graphites, which have a distinctly crystallized structure, such as Ceylon graphites. Such materials may be subjected to the method as herein described and thereby reduced to a colloidal condition. After 0 production of satisfactory pencil leads in a shorterv time and with material savings with respect to the initial cost and maintenance and the space required for the complicated and bulky grinding machine.

The invention as herein described and claimed relates particularly to the production of pencil leads and similar marking elements, and involves the application in this art of the chemical oxidation of graphites to reduce them to a colloidal condition, followed by admixture of clay or other materials of suitable quality, the pressing of the mixture into strands, and thefinal baking of the strands to provide finished leads. Various changes may be made in the details of the invention without departing therefrom or sacrificing any of the advantages thereof.

7 I claim:

l. The method of producing marking elements which consists in subjecting graphite to chemical oxidation to reduce it to a colloidal condition, mixing clay therewith, pressing the mixture into strands and then burning the strands.

pencils consisting 2. The method of manufacturing lead for pencils consisting in chemically converting crystalline graphite by oxidation into a colloidal form, admixing with thecolloidal graphite clay and/ or other additions, pressing the mixture into strands and subsequently burning the strands.

3. The method of manufacturing lead for in chemically converting graphite byoxidation into a colloidal form, admixing clay and binders with the colloidal graphite and pressing the mixture into strands.

4. Pencil leads manufactured by the process set forth in claim 1.

5'. Pencil leads manufactured by the process set forth in claim 2.

5. A pencil lead comprising crystalline graphite transformedby oxidation into colloidal state so as to have a crystalline structure especially fit for pencil leads.

7. The method of making pencil leads, consisting in converting crystalline graphite by oxidation into colloidal state, mixing the colloidal graphite ai -w are