Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-10-20
2001-11-13
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06316526
ABSTRACT:
The invention relates to a method for producing leads for color pencils, cosmetic pencils and colored chalks. As a rule, such leads contain a binding agent, e.g. a cellulose derivative, filler materials such as kaolin and coloring agents. For producing leads, the base materials are mixed with water, e.g. in a plasticizer, to form a lead mass. Raw leads are extruded from this lead mass and are dried at temperatures of approximately 110° C. The consistency or hardness of a lead is determined decisively by the binding agent used and its concentration. In addition, the mechanical stability and consistency of a lead depends on the additives, in particular also the filler materials. Traditional leads are dipped into liquid waxes, liquid fats or fatty acids following the drying to improve the downstroke behavior. A wax absorption of between approximately 15% and 25% of the total weight of the lead is necessary to change the downstroke behavior of the leads noticeably in the direction of a softer downstroke. Adding emulsifying agents, fats, waxes and fatty acids to the base materials already provides another option of improving the downstroke behavior of the raw leads. The improved downstroke behavior is thus always obtained with the aid of a relatively high share of fats, waxes, fatty acids or emulsifying agents. However, for some types of uses, such a high share of the aforementioned materials is not desirable. Reducing the share of binding agent provides another option for influencing the downstroke behavior. This is linked however to a reduction in the mechanical stability of the raw leads. There is an increased danger of breakage before the raw leads with little binding agent have reached their final stability, thereby resulting in increased rejection rates caused by lead breakage.
Based upon this, it is the object of the invention to propose a method for producing leads for color pencils, cosmetic pencils and colored chalks, which permits varying the mechanical qualities and in particular the downstroke behavior of the leads in a simple way through production technology.
The solution is with a method according to claim
1
. Based on this, the crushed base materials, having a somewhat powder-like or granular shape and containing a thermolabile, polymeric binding agent, inorganic filler materials, and coloring agents, are mixed with water. The resulting raw material mass is subsequently extruded into raw leads and these are heat-treated at a raised temperature, namely a decomposition temperature, until the binding agent is partially decomposed. The finished lead consequently contains a polymeric binding agent that is partially decomposed as a result of a thermal treatment step. In addition to the above-mentioned factors, such as weight share and type of binding agent, which influence the firmness and downstroke behavior, this provides another option of influencing the downstroke behavior in particular. That is, the binding agent matrix holding together the lead constituents can be changed through the degree of its thermal decomposition. Thus, varied consistencies and mechanical stabilities as well as a varied downstroke behavior can be achieved, for example, by changing only the thermal decomposition degree for leads having an otherwise comparable composition. In addition, leads are made available that display a soft downstroke with sufficient lead mass release to the underlying material, despite the lack of a high share of fat and wax, which normally determines the downstroke behavior. Depending on the respectively used binding agent, the consistency and the downstroke behavior of the lead are essentially determined by the temperature level and the duration of the treatment. As mentioned in the above, it is not easily possible to reduce the share of binding agent in the raw lead mass with the lead-production methods in question. A reduced share of binding agent would result in increased lead breakage owing to the mechanical drawbacks during the extrusion of the raw leads, as well as the subsequent transport to a drying station or a heat-treatment station. The method according to the invention is based on the idea of reducing, as it were, the share of binding agent in a finishing processing step, in which the leads are subjected to a heat-treatment without mechanical influencing, or of weakening, as it were, the effectiveness of the binding agent, thereby changing the downstroke behavior of the lead. It is thus possible to completely forego a modification of the downstroke behavior through dipping the finished lead into waxes or fats. However, such a measure can be useful if the heat-treated lead must be modified in the direction of a softer downstroke behavior. In that case, only small amounts of wax or fat are necessary.
It is preferable if biopolymers from the group of cellulose derivatives and alginates are used as binding agents. Alginates are understood to be salts and esters of the alginic acid. Such binding agents have a high binding power for the lead constituents. However, one essential advantage of these binding agents is their thermal decomposability, wherein the extent of the decomposition can be adjusted in fine degrees via the temperature level (in the following called decomposition temperature) and the duration of the heat treatment.
The following base materials (amounts given in percentages by weight) are preferably used: 0.5%-12.5% binding agent; 30%-90% filler material; 5%-96% coloring agent. If necessary, it is possible to add up to 2% of waxes, fats, fatty acids and/or emulsifying agents and up to 10% of auxiliary agents. The base materials are mixed with an amount of water that is sufficient to obtain an extrudable mass. It is preferable if enough water is added to the base materials, so that the mixture contains approximately 5 parts by weight of base material and 1 weight share of water. The finished leads contain less than 1% water owing to the heat treatment or the drying.
Natural magnesium silicates, kaolin, finely-ground quartz and pumice powder, talcum and mica are preferably used as filler materials. Mica in this case is understood to include alkali, hydroxyl and even fluorine-containing aluminosilicates, which belong to the phyllosilicates. Inorganic or organic pigments, colorants or pigmented colorants as well as coated or non-coated metal bronzes can be used as coloring agents. Coated metal bronzes are understood to be those, for which the metal particles have a coating of, for example, silicon dioxide. Traditional surfactants, glycols, alcohols, fats or fatty acids, waxes and emulsifying agents can be used as auxiliary agents. The fats, waxes, fatty acids and emulsifying agents can be added to the lead base mixture with a share of 2 weight %. Larger amounts of these materials are not retained by the lead matrix, owing to their liquefaction during the heat treatment, but can be added after the heat treatment with a share of up to 25 weight % through dipping into the liquefied waxes, fats, fatty acids and emulsifying agents. However, it is also conceivable that following their production in the standard way, the leads according to the invention are dipped into melted waxes, fats or fatty acids to further improve, if necessary, the soft downstroke behavior caused by the partially decomposed binding agent. However, a smaller share than for traditional leads is necessary for this.
The heat treatment for the method according to the invention can last up to 24 hours, depending on the base materials used, the level of the decomposition temperature, and the desired degree of decomposition of the binding agent.
The binding agent preferably is composed of at least one material selected from the group hydroxyethylcellulose, methyl hydroxyethylcellulose, ammonium carboxymethylcellulose, alkali carboxymethylcellulose and alginates.
With a method according to the invention, the raw leads produced are preferably dried at a drying temperature of 30° C. to 110° C. prior to the heat treatment that partially decomposes the binding agent. The heat treatment follows o
A.W. Faber-Castell Unternehmensverwaltung GmbH & Co.
Cain Edward J.
Kelemen Gabor J.
Venable
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