US2016807A - Improved black writing pencil leads - Google Patents

Description

. photographic printing.

Patented Oct. 8, 1935 FA'E'ENT OFFICE August Schwarz and Karl Kreutzer, Nuremberg,

Germany, berg, Germany, a firm assignor to J. S. Staedtler, Nurem- No Drawing. Application March 14, 1933, Serial 2 Claims.

This invention relates to the production of leads for writing and drawing pencils to be used for preparing documents and drawings which are intended to be directly reproduced by means of The pencil leads, composed of graphite and clay, are saturated with fatty material (tallow, stearin, wax and the like), for the purpose of improving their writing capability. This fatty material is mix-ed with a fatsoluble colouring material or dyestufi in order to raise the light opacity of the lead that is making the writing or printing dense to light.

This invention consists on the one hand in using a colouring material or dyestufi which is soluble in the agent for fixing the marks and on the other hand in preliminarily impregnating the leads with the dyestufi or coloring material.

The first part of the invention is carried out as follows;

A colouring material or dyestuii is added to the fatty mass used for making the lead, which is soluble in an ordinary agent for fixing the marks, e. g. a solution of shellac in alcohol, for the purpose of producing a black lead mark on tracing paper which is light opaque like an India ink mark. This effect is obtained by the dye-stun forming one constituent of the lead mark being made to flow under the action of the fixing agent and to distribute itself in the mark so as to make the latter uniformly black, that is dense to light.

The so-called Sudan dyestuffs of the I. G. Farbenindustrie A. 6%., more particularly Sudan yellow, are adapted as colouring materials or dyestuffs for use in accordance with this invention.

The second part of the invention is carried out as follows:

A fat-soluble dyestuff, e. g. Sudan yellow, is first of all dissolved in a solvent which is thinly liquid at ordinary temperature, e. g. alcohol, benzine, and so forth. The leads are soaked in this dye solution. The solvent is then removed by dry- In Germany April 11, 1932 ing, whereupon the dyestuff previously present in the solvent now remains behind in the lead. The leads preliminarily dyed in this way are then prepared by means of a fatty mass to which is added a similar dyestufi. Particularly, however, dyestuffs are used which are soluble in the fixing agent.

The preliminary colouring of the lead ensures that the latter takes up substantially more dyestuff and consequently the blackness or density 10 of the marks produced with the leads with reference to light is enhanced. Moreover, the process enables fat masses to be employed having smaller solvent capability for dyestuffs.

The term writing in the claims is intended to also include drawing and printing.

Having now particularly described and ascertained the nature of this invention and in What manner the same is to be performed, we declare that what we claim is:

1. A method of increasing the opaqueness to light of the black Writing from a lead pencil, which consists in impregnating an ordinary pencil lead with a fat soluble dyestui'i dissolved in a substance which is thinly liquid at ordinary temperature, said substances being selected from a group consisting of alcohol and benzine whereby, upon such writing coming in contact with a fixing agent containing such substances the writing becomes substantially impenetrable to light, then drying the lead leaving the dyestufi therein.

2. A black writing pencil comprising as main constituent a lead and a substance impregnated in said lead adapted to make the writing substantially impenetrable to light for photographic 35 printing; said substance consisting of a fat soluble dyestuff dissoluble in a shellac solution in alcohol used as fixing agent for the writing.