US2988784A

US2988784A - Manufacture of pencils and other shaped articles

Info

Publication number: US2988784A
Application number: US600236A
Authority: US
Inventors: Lorenian Zareh
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-06-28
Filing date: 1956-07-26
Publication date: 1961-06-20
Anticipated expiration: 1978-06-20
Also published as: BE489862A; NL80121C; FR989587A

Description

Z. LORENIAN June 20, 1961 MANUFACTURE OF PENCILS AND OTHER SHAPED ARTICLES Filed July 26, 1956 United States Patent I 2,988,784 h MANUFACTURE OF PENCILS AND OTHER SHAPED ARTICLES Zareh Lorenian, Arnold Heise Str. '17, Hamburg, Germany Filed July 26, 1956, Ser. No. 600,236

Claims priority, application Italy June 28, 1948 8 Claims. (Cl. 18-59) My invention relates to the manufacture of pencils and components thereof, such as pencil sheaths and pencil cores, and other shaped articles from thermoplastic compositions and is herein disclosed as a continuation-inpart of my copending application Serial No. 100,822, filed June 23, 1949, now abandoned.

In one of its more specific aspects, my invention relates to writing pencils of the scissible type, that is pencils which can be sharpened by a knife or pencil sharpener like ordinary wood-sheathed pencils.

For that reason, the invention is hereinafter mainly described with reference to writing, drafting, coloring or copying pencils, although it should be understood that my invention, in its broader aspects, applies generally to shaped articles made by shaping a thermoplastic mixture in dry condition under heat and pressure.

Heretofore the sheaths of pencils have ordinarily been made of wood. The wood must be of special quality since the finished pencil must not only be capable of being easily sharpened but the sheath must also form the support for the relatively fragile core. Moreover, the process of manufacturing pencils with conventional wooden sheaths and lead, including twelve to twentyfour operations, is expensive and time-consuming, and a large quantity of wood is wasted. The wood is first cut into small slabs which are then grooved. The lead is inserted in the groove of oneslab, a second grooved slab is placed upon the first one to enclose the lead, and the two grooved slabs are then glued together. Furthermore, in order to obtain satisfactory cutting capacity the grooved wooden slabs in the course of manufacture must undergo special treatment. Pencils are exposed to varying temperatures and varying degrees of humidity. The wooden sheath of the conventional pencil tends to expand or to dry out, causing the lead to loosen in the sheath and to slip out or break in the pencil particularly if the two slabs of the sheath have different fibrilliation or grain.

Another disadvantage of the wooden sheath is that the grain of the wood tends to guide the knife when sharpening the pencil so that a person sharpening a pencil manually cannot always control the direction of cutting in the desired manner. Furthermore, when sharpening a conventional pencil, a certain minimum thickness of chip must be cut. As a result the pencil is prematurely used up. When the pencil is sharpened by pencil sharpening apparatus, the sharpened portion of the wood is left rough because the knives or cutting blades of the pencil sharpener operate across the grain. This roughness may be disagreeable when using the pencil.

In the conventional pencil, moreover, the lead or core is a mixture of clay and graphite, the clay serving as a binder. The hardness of the lead is controlled by varying the proportion of clay in the mixture. The clay also influences the shade of the lead. Moreover, the clay, particularly in a hard pencil, scratches the paper; and when the paper is erased the scratches are not removed. If the proportion of clay is reduced, the breaking strength of the lead is reduced too, and the rate of wear of the pencil is increased; and the pencil is prematurely used up.

a ceramic lead. Therefore, hydrophile binders, such as tragacanth are used. These leads or cores are very sensitive to atmospheric influence.

Because of the disadvantages with lead and sheaths as previously made, there have been prior suggestions that artificial, synthetic materials be used for sheaths, or cores, or for both sheaths and cores. Thus, it has been proposed to manufacture pencil sheaths by extrusion and subsequent drying of an aqueous pulp of wood or paper; but all attempts in this direction have been unsuccessful because of the necessity of expelling large amounts of water from the extruded strand and the low quality of the finished pencils in which the lead or other marking core is apt to be loosened in the sheath due to shrinkage and expansion of the moisture-sensitive sheath material.

As will be more fully set forth below, my invention requires the dry shaping, under heat and pressure, of a thermoplastic composition comprising a water-insoluble synthetic thermoplastic resin. Now, such thermoplastic synthetic resins, used as a binder, have generally a relatively small binding capacity as compared with natural resins and thermosetting resins such as phenolic resins. Water-insoluble synthetic thermoplastic resins, therefore, when used in small quantity as a binder for a large quan-- tity of comminuted and voluminous material, such as wood flour or other cellulosic fibres, do not bind such materials in such a manner as to impart to the shaped article the resistance and strength needed for the intended use of the particular article. Besides, comminuted wood, such as wood flour and other fibrous materials, as well as a number of comminuted mineral substances such as kaolin, are sensitive to moisture, and a small proportion of synthetic water-insoluble thermoplastic resin, even if moisture-insensitive as such, does not have the capacity of rendering the composition practically insensitive to moisture. e

Furthermore, some of the mixed substances, notably wood flour, rice or straw and other particulate materials of organic origin, tend to decompose or become -carbonized or otherwise imp-aired when subjected to the plasticizing temperature and pressure required for the thermoplastic binder when the mixed composition is being shaped into an article, especially if some delay in the extrusion press or other heated molding equipment is encountered.

It is an object of my invention to produce thermoplastic pencil components such as pencil sheaths and pencil cores, or complete pencils and other shaped articles that, aside from having all desired qualities of the corresponding conventional articles, afford being made at low cost and have the advantage of being practically insensitive to moisture and dryness and preferably also fire retardent, and which possess the resistance and rigidity or flexibility as required for the intended use of the panticular article. Relative to pencil sheaths and similar articles, it is a conjoint object to obtain superior and more uniform scissibility, and as to pencil marking cores and similarly composed articles, it is a conjoint object to obtain improved mark-depositing and sliding ability to minimize scratching the paper, thus generally achieving advantages which the conventional pencils do not have and cannot attain because of the properties of their structural material and because of their method of manufacture. p

To achieve these objects, and in accordance with my invention, I produce the pencil components or complete pencils and other shaped articles by shaping, in dry condition under heat and pressure, a homogeneously mixed composition of three basic components, namely:

(1) A major quantity of a comminuted main ingredient, such as wood flour and/or the other particulate sub- 3 stances mentioned below, which determines the character of the finished shaped article;

(2) A minor quantity of waxy substance such as chlorinated naphthalene and/ or the other substances mentioned below; and

(3) A minor quantity of a binder consisting essentially of substantially water-insoluble and practically moistureinsensitive thermoplastic synthetic resin such as polyvinyl chloride and/orthe other synthetic thermoplastic resins mentioned below.

All quantities and percentages herein referred to are by weight.

I have found that, as a general rule, the desired superior results are obtained only if the quantity of the binder is smaller than that of the particulate main ingredient, and if the quantity of waxy substance is always smaller than that of the binder in order to preserve the desired binding capacity of the binder needed for mechanical resistance and strength and stability of the article. For best results in most cases, particularly for pencils and pencil components such as scissible pencil sheaths and leads or cores, it is preferable to have the quantity of main ingredient larger than the sum of the respective quantities of the two other basic ingredient-s.

A suitable range of composition, relating to 100 parts by weight of main ingredient, is about 1 to about 70 parts, preferably more than 5 parts, of waxy substance, and about to about 90 parts of the specified binder, the latter quantity being in each case larger than that of the waxy substance. Under such conditions, the character of the finished article is substantially determined by the particulate main ingredient, as contrasted to wax crayons in which waxy and/ or fatty substances predominate and occur in a quantity as large as, or larger than, that of the binder.

It will be understood that each of the three basic ingredients may comprise more than one individual substance and that the usual plasticizer, coloring agents or the like auxiliary additions may be present depending upon the intended use or appearance of the article, as will be more fully described below. The composition after being prepared into a homogeneous mixture, is not suitable for aqueous or wet shaping methods but must be shaped in dry condition under heat and pressure whereafter the shaped articles are immediately ready for use. The shaping may be done by extrusion, injection molding, compression molding, pressing or calendering. I have found that extrusion of the composition by means of a screw press is particularly favorable for making pencils, pencil components, as well as profiled, tubular or fiat articles in general.

When mixing the three basic ingredients together, it is necessary to follow a certain sequence or course of mixing operation so that the waxy substance can become fluid or liquid and thus can coat or impregnate the individual particles of the main ingredient before the thermoplastic resin can have a bonding effect upon the waxy substance or the main ingredient. This will be further explained in a later place as the necessity for proper mixing will best be understood from the more detailed description of the basic ingredients and their mutual coaction given presently.

(a) As mentioned, the particulate main ingredient may consist of, or comprise, comminuted wood such as wood flour. This material, preferably used in pencil sheaths, is sensitive to moisture and dryness; and it is one of the outstanding advantages of the invention that such materials, used as herein disclosed, do not impart such detrimental sensitivity to the finished article. Other main ingredients of the same type, i.e. sensitive to moisture and dryness, are various forms of wood dust, wood fibres and such other cellulosic fibre materials as straw meal, rice flour and paper flour, all subject to Working when exposed to moisture or dryness.

(b) Also suitable as main ingredients for the purpose of the invention are particulate substances that are practically sensitive to moisture but insensitive to dryness,

namely such mineral or organic substances as kaolin, lithopone, clay, barium sulphate, bone fiour, cotton, wool, asbestos fibre and similar materials.

(c) Comminuted substances that are virtually insensitive to moisture and dryness are likewise applicable as main ingredients and, as in the case of pencil leads, may have to be used for special purposes. Such substances, for example, are graphite, glass meal, glass fibre or glass wool, metal dust, and the like. Excepting the use of graphite for graphite leads, these insensitive ingredients, in general, are not suitable for scissible pencils; but they can be used as main ingredients for the manufacture of pencil sheaths to be used with sliding leads or cores, that is for sheaths that need not be sharpened, and for other shaped articles not requiring scissibility.

The various substances that form the main ingredient may be used in any desired mixture with one another. It is apparent that the main ingredient must be stable and compatible with the other two basic ingredients, waxy substance and binder, under the conditions obtaining during the shaping operation. Ihe above-specified particulate substances meet this requirement, but I have found that comminuted cork used as a main ingredient produces inferior results because when a mixture of cork particles, waxy substance and thermoplastic binder is heated to a temperature of about C. or more and is mixed or worked under heat and pressure in a closed container, such as in an extruder, the cork particles, despite the waxy coating, commence to decompose and evolve gas which sometimes causes explosions. Besides, comminuted cork, due to its structural constitution, does not impart to the shaped article the strength and resistance obtained, for instance, with wood flour or wood dust. A pencil sheath made with comminuted cork is too yielding to permit satisfactory sharpening by means of a knife or pencil sharpener. For these reasons, the use of comminuted cork is not favorable for the purposes of the invention.

The water-insoluble thermoplastic resin used as a binder is preferably practically insensitive to moisture and may consist essentially of polyvinyl chloride (preferably made by the suspension process), copolymers of vinyl chloride, polyethylene (preferably low-pressure polyethylene), ethyl cellulose, cellulose acetate, cellulose butyrate, polyvinyl butyrate, and other water-insoluble thermoplastic synthetic resins. The preferred choice in each case is determined by the fact that the binder must have a bonding effect upon the two other basic ingredients and must be compatible with the waxy ingredient. Conventional plasticizers, stabilizers and/or lubricants may be added to the binder, as well as small quantities of water-insoluble natural resins and/ or thermosetting resins as further described below.

The waxy substance, practically insensitive to moisture, used as the third basic ingredient of the composition, may consist of any water-insoluble waxy substance of mineral, vegetable, animal or synthetic origin such as parafiin, ceresin, bees wax, osokenite, carnauba wax, Chinese or Japan wax, montan wax, chlorinated naphthalene, chlorinated paraffin or other chlorinated waxy substances, as well as fatty materials similar to wax, for instance, spermacetti. I prefer using waxy substances, such as those mentioned, which are practically insensitive to moisture. An essential criterion for all such substances for the purpose of the invention is the fact that they are water-insoluble and become liquid or fluid when heated in dry condition at a temperature not higher than the softening or molding temperature of the thermoplastic-resin ingredient of the composition, so as to form a coating or impregnation on the particulate main ingredient. The waxy substance must be compatible with the main ingredient and, particularly, also with the binder which is used in a larger quantity than the waxy substance. Some of the waxy substances, such as chlorinated naphthalene, are preferable because of their fire-retarding or fire-proofing quality. For economical reasons,

I further prefer using a waxy Substance lower in' cost than the therr'noplasticbi'nder as is also the case with chlorinated naphthalene, although the more expensive waxy substances are likewise economically applicable in compositions containing a relatively small proportion of such substances in comparison with the larger amount of binder and, above all, with the larger amount of main ingredient.

If the comminuted main ingredients of the composition are sensitive to moisture and dryness as is the case, for instance, with wood flour, then the waxy substances, which are liquid when heated, cover and impregnate the individual particles of the main ingredients; and if the main ingredients are porous the waxy substances penetrate into the pores of the particles of main ingredients thus making them practically inert and insensitive to moisture and dryness. Besides, if the waxy substances are fireresistant, as is the case with chlorinated naphthalene, the coated or impregnated particles of the main ingredients are made fire retarding or practically fire-proof.

Furthermore, since the waxy substances are compatible with the thermoplastic synthetic binders, they also have the effect of increasing and/or extending the over-all binding capacity; that is, the quantity of the binder which generally is not liquid when heated to the molding temperature can be kept smaller than otherwise required. In

' finished particles a smoother and more agreeable surface,

-nnd, as the case may be, it also improves the scissibility of the product.

The waxy substance also acts as a lubricant when the articles are being shaped under heat and pressure so that the usual addition of supplemental lubricant to the mixture can be reduced or omitted.

When making pencil sheaths from the composition, the waxy substances greatly contribute to improved scissibility. When the composition is used for making graphite dead .and colored cores for pencils, the waxy substance improves the mark-depositing and gliding ability as well as the scissibility of such leads or cores. As a result, scratching of the paper by the tip of the marking core is greatly minimized or eliminated, even with relatively hard grades of the marking core. These advantages and qualities due to the presence in the mixed composition of water-insoluble and compatible waxy substance is important even if the main ingredient is not sensitive to moisture or dryness as is the case where the main ingredient consists of graphite and article made of the composition consists of a graphite lead for pencils.

As briefly mentioned above, it is an essential requirement for achieving the desired result of the invention that the three basic ingredients be mixed in a manner that permits the waxy substance to become liquefied under heat and to become incorporated or impregnated into the particular main ingredient before the thermoplastic synthetic binder can become effective to bond either the main ingredient or the waxy substance. This requirement will be understood if one considers that the waxy substance becomes liquefied more readily and at lower temperature than the thermoplastic synthetic resin and requires only heat but no pressure to thus change its consistency. In contrast, the water-insoluble thermoplastic synthetic resin not only requires a higher temperature as well as pressure but it also does not become as fluid as a dry waxy substance Consequently, when the preparation of the composition is so conducted that the waxy substance can liquefy without being bonded by, or incorporated in, the thermoplastic binder, then the good dispersion ability of the wax takes careof having the particles of the main ingredient covered or preferably impregnated by the liquid wax, before the binder, becoming plastic or viscous under heat and pressure, can bond the coated particles together.

There are several ways of properly preparing the mixed composition. The first and preferable way is to first mix the waxy substance in dry condition, that is without solvent, with the particulate main ingredient while the waxy substance is heated and liquefied. In this manner, the particles of the main ingredient are first covered or impregnated with the waxy substance. The next step is to mix the wax-coated or impregnated main ingredient with the binder.

A second, generally less satisfactory or less reliable way, is to mix the comminuted main ingredient at once with the waxy substance and with the binder. In this case, when heat and pressure are applied, the waxy substance will liquefy more rapidly and at a temperature below the plasticizing point of the binder so that the liquefied waxy substance can cover, or enter into, the main ingredient before the binder becomes plastic under heat and pressure to provide the necessary bonding between the coated particulate main ingredients.

In contrast, I have found that no satisfactory results are obtained under otherwise the same conditions if the waxy substance is first mixed with the binder and thereafter the mixture of waxy substance and binder is mixed together with the main ingredient. I believe the reason for the failure of producing the desired result in the lastrnentioned manner is the fact that when the waxy substances are first combined with, or incorporated into, the thermoplastic binder, the waxy substances are no longer readily liquefied at low temperature but become plastic together with the binder, so that they do no longer have the above-mentioned dispersion capacity and are pre vented from covering or impregnating the comminuted, voluminous main ingredient. As a result, much larger proportionate quantities of binder are necessary, and the article shaped from the. mixed composition, aside from being generally more expensive, do not have the same physical characteristics as those produced with the above-mentioned proper methods of preparation.

It will be recognized from the foregoing that three general conditions are essential for the invention: v

In the first place, the composition must comprise the above-described three basic ingredients, namely a comminuted or particulate main ingredient, a water-insoluble waxy substance, and a water-insoluble thermoplastic synthetic resin, the quantity of waxy substance being smaller than that of the resin; secondly, the three basic ingredients mus-t be mixed together in such a manner that the waxy substance can liquefy and cover or impregnate the main ingredient before the bonding effect of the thermoplastic resin takes effect; and, ultimately, the composition must be shaped under heat and pressure in dry condition, as it is not applicable for use in a wet method such as the above-mentioned processes involving aqueous suspension or pulp masses.

The particular physical properties of the articles made according to the invention depend upon various factors to be chosen in accordance with the particular purpose for which the articles are to be used. One of these factors, for instance, is the proportion of the waxy substance relative to the proportion of the binder as compared with the amount of the comminuted main substance. Another factor is the quantity of the conventional plasticizers which are added to the water-insoluble thermoplastic resin and which generally determines the degree of rigidity or flexibility of the shaped articles. It will of course also be understood that any desired coloring agents may be added to the main ingredients, the waxy substance and/or the binder. The conventional lubricants and stabilizers, if desired, are also applicable.

While, as described above, the quantity of comminuted main ingredients according to the invention, in principle, is larger than the quantity of each of the two other basic ingredients or larger than the sum of both other basic ingredients, I have found that there exists an exception to this general principle in those cases Where the main ingredient consists of comminuted wood or other cellulosic materials that are sensitive to moisture and dryness. In such cases, results satisfactory for some purposes can also he obtained if the quantity of the Water-insoluble thermoplastic synthetic resin is made somewhat larger than the quantity of the main ingredient, provided the quantity of the waxy substance remains smaller than the individual quantities of main ingredient and thermoplastic binder. Such compositions, comprising a thermoplastic binder in a quantity of up to about 20% larger than the quantity of the main ingredient, afiford the production of shaped articles of great mechanical resistance and strength and improves insensitivity to dryness and moisture. On the other hand, such increase in quantity of binder relative to the main ingredient has the disadvantage that the cost of the shaped article made of such a composition is higher and that the scissibility of the shaped articles, particularly those of pencil sheaths, is impaired or, if the composition is used for pencil leads or marking cores, the marking ability is likewise impaired.

The invention will be more fully understood from the examples described in the following. It should be understood that the examples are not presented in a limited sense but that various modifications are applicable in accordance with the foregoing explanations and within the scope of the claims annexed hereto. All proportions and percentages given in the examples are by weight.

Example 1 The following composition is suitable for the manufacture of scissible pencil sheaths and other shaped articles that are woodlike in general character and/or appearance:

100 parts wood flour (main ingredient) About 20-40 parts chlorinated naphthalene (waxy substance) About 30-55 parts polyvinyl chloride, preferably made by the suspension process (binder) 320%, relative to the amount of binder, of dibutyl phthalate (plasticizer) l-3%, relative to the amount of binder, of lead stearate (stabilizer) lparts of cedar brown mixed with orange dyestuff and mixed with 5-10 parts titanium white (coloring substance) It will be understood that the specific composition to be chosen from the indicated ranges depends upon the desired degree of scissibility, rigidity or other physical properties which the shaped article is supposed to possess. For instance, I have found the following specific compositions to be particularly useful for scissible wood sheath of pencils and other woodlike articles of similar appearance and rigidity:

100 parts wood flour (main ingredient) 30 parts chlorinated naphthalene (waxy substance) 45 parts polyvinyl chloride (binder) relative to the amount of P.V.C., of dibutyl phthalate (plasticizer) 2%, relative to the amount of binder, of lead stearate (stabilizer), 4% relative to the total composition, of zinc stearate (lubricant) 2 parts of cedar brown and 1 part of orange dyestuff mixed with 5 parts of titanium white to serve as a coloring substance Regardless of the specific composition chosen for the particular shaped article to be produced, I prefer preparing the above-described combination of ingredients in the following manner:

The wood flour is to be used in dry condition. For this purpose the wood flour is placed into a mixer and heated under vacuum to a temperature of about 130 C. to C. The mixer is maintained under vacuum so that the moisture of the main ingredient is withdrawn. Then, a mixture of the waxy substance with the abovementioned coloring substances is sprayed dry, in heated and melted form, onto the particles of the main ingredient while the main ingredient is still contained in the mixer and kept under vacuum. The mixing is continued until the mass is substantially homogeneous. The thermoplastic binder is mixed with the plasticizer and stabilizer and, as the case may be, also with the lubricant, to form a separate batch. Then the mixture of binder and auxiliary additions is added to the impregnated main ingredient. This is also done in the mixer and preferably While the mixer is kept under heat and vacuum. The vacuum in the mixer during the above-described operations may be kept, for instance, at 5-10 m. Hg, and the temperature maintained during the mixing operation and while the binder is being added may be kept, for example, between about 130 and 160 C. After the mixture is made homogeneous, it is discharged from the mixer and thereafter calendered under heat and pressure, for instance at a temperature of 120 to C. Thereafter the calendered composition is milled and is subjected in dry condition to shaping under heat and pressure. The preferred shaping operation for the manufacture of pencil sheaths and various other shaped articles is by means of an extrusion screw press and at a temperature preferably between about 120 and about C. It is also possible to shape the composition as it comes out of the mixer without calendering, but I prefer adding the calendering step because it results in a better compacted and homogenized material. The shaped articles thus produced are woodlike in appearance and general character and are readily scissible, the main ingredient, namely the wood flour, determining the overall character of the product.

Another method is to dry the wood by any other method than vacuum in this case. Then the wood flour may simply be impregnated in hot condition with the liquefied waxy substance without the use of a vacuum, and the binder may thereafter be added likewise without the use of a vacuum. However, for best results and best uniformity of the products, I prefer preparing the composition under vacuum as described above. As mentioned, there is also the possibility of mixing the main ingredient with the waxy substance and at the same time with the binder, but I consider the latter method less preferable to those described in the foregoing. In any case, the waxy substance must not be permitted to become combined with, or incorporated into, the thermoplastic binder before the waxy substance is joined with the main ingredient.

Example 2 The following composition is suitable for the manufacture of scissible colored cores for pencils and other shaped articles of distinctive color:

100 parts kaolin 15-45 parts chlorinated naphthalene (waxy substance) to which are added 2-15 parts Sudan red (main ingredient) 30-50 parts polyvinyl chloride (binder) 3-15%, relative to the amount of P.V.C., of tricresyl phosphate (plasticizer) l-3%, relative to the amount of binder, of lead stearate (stabilizer) 2-8 parts of calcium stearate (lubricant) This composition is prepared and fabricated in accordance with one of the methods described above with reference to Example 1.

The particular proportion of substances to be chosen within the ranges above indicated, as well as the particular coloring substance added to the main ingredient, depend upon the desired physical characteristics and color of the colored marking core or other shaped article to 100 parts kaolin to which are added parts Prussian blue and parts titanium white (main ingredient) 40 parts chlorinated naphthalene (waxy substance) 45 parts of polyvinylchloride, made by suspension process (binder) v 12% of dioctyl phthalate, relative to the weight of the polyvinylchloride (plasticizer) 1.5% lead stearate (stabilizer), relative to the weight of the polyvinylchloride 3 parts of calcium stearate (lubricant) Example 3 The following composition is suitable for the manufacture of graphite leads for pencils and other shaped articles in which graphite is the main ingredient and determines the character and appearance of the finished article:

100 parts graphite powder, preferably mixed in equal proportions of crystalline graphite and amorphous graphite 2-15 parts lamp black, which forms part of the main ingredient but also contains waxy substances 20-35 parts chlorinated naphthalene (waxy substance) 25-45 parts polyvinylchloride (binder) 2-15% dioctyl phthalate (plasticizer), relative to the weight of the binder 1-3% lead stearate (stabilizer) relative to the weight of the binder 2-10 parts of zinc stearate (lubricant) As in the previous examples the specific composition best to be chosen from the indicated ranges depends upon the desired specific character, for instance hardness, of the product. One of the specific compositions which I have found preferable is the following:

50 parts amorphous graphite 50 parts crystalline graphite 5 parts lamp black 30 parts chlorinated naphthalene 40 parts polyvinylchloride (suspension process) 10% tricresyl phosphate (plasticizer), relative to the weight of the P.V.C.

2% lead stearate (stabilizer), relative to the weight of the binder 4 parts zinc stearate (lubricant) The composition according to this example may be prepared and fabricated in accordance with the methods described with reference to Example 1. However, since graphite is not water-sensitive, it is not necessary to work under vacuum, and the other methods referred to under Example 1 are less objectionable. However, I prefer spraying and dispersing the waxy substance onto the graphiteparticles under vacuum to obtain a more uniform coating of the particles.

It will be noted that in all foregoing examples the waxy substance consists of chlorinated naphthalene and the binder consists of polyvinylchloride. The use of the same waxy ingredient and the same binder ingredient in these examples serves the following purpose. While articles according to the respective examples, such as pencil sheaths and pencil cores, can be manufactured individually and separately from one another, it is advantageous in the manufacture of pencils to extrude the sheath material onto and around a marking core material which is being extruded simultaneously within the same extrusion device, so that the pencil core and the sheath are manufactured and combined with each other within one single operation. As a result, the shaped sheath composition and the shaped core composition emerge at the same rate from a single nozzle at the end of the extrusion ma- '10 chine, preferably an extrusion screw press. While details of this manufacturing method are not essential to the present invention proper, reference may be had, if desired,

to the methods and extrusion devices illustrated and de-- scribed in my copending applications Serial No. 100,323, filed June 23, 1949, now Patent No. 2,769,201, and Serial No. 279,496, filed March 31,- 1952, now Patent No. 2,790,202. When using for such simultaneous extrusion of pencil sheaths and pencil cores such compositions as exemplified by Example 1 on the one hand, and Example 2 or 3 on the other hand, the similarity of the thermoplastic binders and waxy substances in the sheath and core compositions has the result that the extruded core becomes tightly bonded or welded together with the pencil sheath so tthat the core in the finished pencil will never become loose from the sheath and will not break in the pencil when the pencil is dropped onto a hard floor or otherwise subjected to impact. When such a pencil is sharpened by a knife or pencil sharpener, each individual chip shows that the graphite or other core material is coalesced with the sheath material into one integral body. It should be understood, however, that other waxy substances or other binders that are mutually compatible may readily be used instead of those given in the foregoing examples. Thus, paraffin may serve as a waxy substance with a binder consisting of ethyl cellulose with which it is compatible. In other words, the particular binder and the particular waxy substance should be chosen from the viewpoint of compatibility relative to each other.

Example 4 The following composition is suitable for manufacturing pencil sheaths and other shaped articles:

250 parts wood flour 5-25 parts chlorinated naphthalene 0.1-3 parts coloring substances These materials are intimately mixed together in hot condition. Then the following materials are intimately admixed also at elevated temperature:

This dry blend is formed at l10-130 C. under pressure in accordance with one of the methods mentioned in.

Example 1.

Example 5 Another composition for manufacturing pencil sheaths:

and other shaped articles consists of:

300 parts wood flour 5-30 parts water-insoluble waxes with an addition of 2 to 10 parts of water insoluble fats This group of materials is intimately mixed together. To the mixed group are added the following materials:

parts ethylcellulose or celluloseacetatebutyrate (binding agent) 2-8 parts zinc stearate (lubricant) 0.5-3 parts coloring substances These materials are mixed together. To the binding agent may be added as additional binder:

2-40 parts of thermosetting synthetic resins, and/or 2-40 parts of thermoplastic natural resins To this blend may be added 2-10 weight parts of ammonium bicarbonate or similar gas-producing agent. The dry blend is formed at -140 C. under pressure. The mixing and shaping can be done as in the Example 1.

T1 Example 6 For manufacturing of graphite-leads for pencils and other shaped articles, the. following materials in proportions as follows are intimately mixed together:

100 parts graphite (main ingredient) l-l5 parts carbon black (which form part of the main ingredient but also contains waxy substances) 5-20 parts water-insoluble waxes with an addition of 2 to 10 parts water-insoluble fats After these materials are mixed together, the following materials are added:

20-50 parts polyvinylchloride or copolymer of vinylchloride (binding agent) -10 parts orthonitrodiphenyl 1-30 parts cadmium ricinoleate (lubricant) All these materials are mixed together. To the binding agent may be added as additional binder:

2-40 parts of thermosetting synthetic resins, and/or 2-40 parts of thermoplastic natural resins This dry blend is formed at 120-160 C. under pressure as described with reference to Example 1.

Example 7 For manufacturing colored leads for pencils and other shaped articles the following materials are intimately mixed together in hot condition:

100 parts clay or similar materials -50 parts coloring substances 2-10 parts water-insoluble fats 5-20 parts waxes After these materials are mixed together, the following materials are added:

20-35 parts ethylcellulose or cellulose acetatebutyrate (binding agent) 0-15 parts paratoluol sulphonamide or triphenylphosphate 5-30 parts barium ricinoleate (lubricant) 1 -3 parts coloring substances All these materials are mixed together. To the binding agent may be added as additional binder:

2-40 parts of thermosetting synthetic resins, and/ or 2-40 parts of thermoplastic natural resins This dry blend is formed at 100-120 C. under pressure as described in Example 1.

Example 8 The following composition is suitable for pencil sheaths and other shaped articles of woody character that have a lesser degree of scissibility than the product resulting from Example No. 1:

100 parts cellulose acetate (of the kind suitable for injection molding or extrusion) are dissolved in 400 parts acetone This solution is kneaded together with:

100 parts wood dust 50 parts straw meal 50 parts rice flour 40 parts dibutyl phthalate 10 parts parafiine 3 parts zinc stearate 1 part titanium white After or while preparing a homogeneous mixture of all ingredients, the solvent is evaporated by heating, preferably in vacuum, so that a completely dry mass is obtained. This dry mass is shaped, preferably by extrusion in a screw press, in dry condition under heat and pressure as described earlier in this specification.

12 Example 9 Composition for colored leads and other colored shaped articles:

100 parts barium sulphate and 3-20 parts chrome yellow (main ingredient) 15-45 parts carnauba wax 30-50 parts ethylcellulose (binder) 3-15 parts ricinoleate (plasticizer) The composition is prepared and shaped, preferably extruded, as in Example 1.

Example 10 Composition for copying or indelible marking cores:

70 parts kaolin and 30 parts talcum (main ingredient) 5-20 parts methyl violet 20-60 parts chlorinated naphthalene 40-90 parts low-pressure polyethylene The mixture is prepared and shaped as described with reference to Example 1.

Example 11 As mentioned, the rigidity or flexibility of the shaped article depends upon the proportion of the conventional plasticizer added to the water-insoluble thermoplastic synthetic resins that form the binder of the combination of ingredients. Accordingly, the following example relates to a composition for the production of comparatively rigid articles, such as the sheaths of slidable-core pencils, which need not be sharpened and need not be scissible:

40 parts paper flour 30 parts cotton flour 30 parts comminuted glass fibres 2-10 parts Prussian-blue coloring substance (all forming together the main ingredient) 10-30 parts ceresin (waxy substance) 40-60 ethylcellulose (binder) 0-20 tricresyl phosphate (plasticizer) The above ingredients are to be prepared as in Example 1.

Example 12 This example also relates to the manufacture of pencil sheaths and other shaped articles which, like the sheaths of slidable-core pencils, need not be scissible:

The above ingredients are to be prepared as described for Example 1.

Example 13 This composition is given as exception to the abovementioned general rule of proportioning of main ingredient and binder, and is suitable for making sheaths for slidable-core pencils or other shaped articles, preferably by extrusion in a screw press:

parts wood flour 20 parts cotton flour, and

2-10 parts coloring substances (all forming together the main ingredient) 20-30 parts montan wax 5-10 parts paraflin, and

10-15 chlorinated naphthalene (waxy substances) T13, 70-80 parts ethylcellulose, and 30-40 parts cellulose butyrate (binders) To the binder is added; 2-20 parts dibutyl phthalate (plasticizer).

Ihis combination of ingredients is prepared and shaped as described for Example 1.

It will be recognized that in Example 13, each of the three basic ingredients is composed of more than one component and that, while the quantity of the waxy substances is smaller than the respective quantities of main ingredient and hinder, the total quantity of binder is somewhat larger than the total quantity of the main ingredients. However, the total quantity of the main ingredient is still large enough in comparison to the binder quantity to determine the character of the shaped article. The articles made of such a combination of ingredients have greater mechanical resistance and strength than those made according to the other examples but, as explained, some disadvantages must be put up with.

Example 14 The following composition is suitable for pencils, and particularly other shaped articles, of greater flexibility than obtained with the compositions according to the preceding examples:

100 parts wood flour to which are added 2 parts of cedar brown, 2 parts of orange pigment and 4 to 20% titanium white, all forming part of the main ingredient and imparting a woody color to the product 35 parts chlorinated naphthalene (waxy substance) 60 parts polyvinylchloride, made by the suspension process (binder) 35% tricresyl phosphate (plasticizer) in proportion to the weight of the binder 2% lead stearate (stabilizer) in proportion to the weight of the binder 3% aluminum stearate (lubricant) in proportion to the weight of the total composition This composition is prepared and fabricated as described in the foregoing, particularly with reference to Example 1. s As is apparent from the examples, the water-insoluble thermoplastic synthetic resins used as binder may be admixed with conventional and compatible, preferably non-volatile plasticizers in order to impart to the finished product the desired degree of rigidity or flexibility. The amount of added plasticizer may range up to about 100% of the thermoplastic binder. The conventional stabilizers and/ or lubricants may also be added, as is apparent from the examples. The amount of such additions of stabilizers may beup to about 5% of the binder and the amount of the lubricant may be up to about to the amount of the whole composition. It will further be recognized from Examples 4, 5, 6 and 7 that the water-insoluble, plastic synthetic resins may be admixed with small quantities of compatible water-insoluble and preferably moisture-insensitive thermosetting resins such as phenol formaldehyde or urea resins, or those available under the trade name Desodur or Desmophen and other similar thermosetting resins and/or water-insoluble and preferably moisture-insensitive natural resins such as colophony,v copal resins, damar resins, kauri resins, and other similar natural resins. Such additional thermosett ing and natural resins have binding effect in addition to that of the main binder which is always formed by thewater-insoluble thermoplastic synthetic resins. The proportion of such additional thermosetting and natural 'resins may amount up to 40% of the total weight of the water-insoluble thermoplastic synthetic resin. It will be understood that such additional small quantities of natural or thermosetting resin may also be added to the binders of the other examples presented in the foregoing. I

If porosity of the pencil components or other shaped articles is desired, a small quantity of gas-producing agent such as ammonium bicarbonate, calcium carbonate or similar substances, as exemplified by Example 5, may be added to the composition. Such gas-producing agents have the eifect of reducing the density and weight of the articles by the resulting pores; they also impart better scissibility to pencil sheaths, pencil leads or other marking cores, and also improve the mark-producing ability of such marking cores. The proportion of the gas-producing agents may vary from 2 to 20% of the total amount of components. The gas-producing agent is mixed with the other ingredients and becomes efiective to evolve gas and to form a porous structure when the articles are being shaped in dry condition under heat and pressure. The gas-producing agent may be added to any of the compositions according to the above-pre sented examples.

As mentioned above, there are essentially the follow ing ways of preparing. the mixed compositions to be used according to the invention.

,The first Way, particularly important when the main ingredient is sensitive to moisture, is to first place the main ingredient under vacuum in a heated mixer so that practically all moisture is exhausted under heat and vacuum. Thereafter the dry waxy substance, in hot and liquid condition, is sprayed onto the particles of the main ingredient during continued mixing operation and during continued maintenance of vacuum so that the particles become impregnated or coated with the waxy substance. Thereafter, preferably always under vacuum and heat, the binder and any further components are introduced into the mixer; and after all components are mixed together to a homogeneous composition, the articles to be produced are shaped in dry condition under heat and pressure, preferably by extrusion with the aid of a screw press.

The second way of preparing the compositions is to calender, or mix under heat and pressure, the main ingredient with the waxy substances, whereby the moisture of the main ingredient is evaporated and the particles of main ingredient are covered or impregnated with the waxy substance. When this condition is reached, the binder and any supplementary materials are added while the calendering or mixing is continued under pressure until a homogeneous composition is obtained. This composition is then shaped in the dry state under heat and pressure, preferably by extrusion.

The third way is to mix all ingredients together under heat and thereafter apply pressure and to then shape the article from the homogeneous mixture in the same manner as mentioned above. p I have found that in most cases the first way of preparation afiords superior results in comparison with the second way, but that the second way of preparation is applicable with main substances that are not sensitive to moisture as in the case with graphite. The third way is the least preferable of the three methods and may have inferior results with moisture-sensitive main ingredients.

It will be understood that the physical characteristics of the shaped articles made according to the invention are, to some extent, also dependent upon the pressure applied to the composition during the shaping operation, preferably by extruding the material under heat and pressure in an extrusion screw press. This pressure is determined by the dimensions and length of the extrusion nozzle as well as by the normal operating pressure and temperature of the nozzle. The pressure conditions, in, general, can be modified to some extent in accordance withrthe desired density of the product.

Embodiments of pencils which can be made in accordance with the present invention are illustrated by way of example in .the accompanying drawing showing in FIG. 1 a partial and partly sectional view of a scissible 15 pencil, and in FIG. 2 a longitudinal section of a slidablecore pencil.

The pencil according to FIG. 1 comprises an extruded thermoplastic sheath 1 made, for instance, in accordance with Example 1, and a likewise extruded lead or marking core coalesced with the sheath material and made by extrusion of a thermoplastic material, for instance, according to Example 2 or 3. The sheath has a coating 3 of thermoplastic varnish which may be extruded onto the surface of the sheath simultaneously with the extrusion of sheath and core. An extrusion apparatus suitable for simultaneous production of pencil core, pencil sheath and coating is described in my copending application Serial No. 279,496, filed March 31, 1952, now Patent No. 2,790,202. The coating 3 may be made from a composition obtained by mixing 100 parts polyvinyl chloride, 40 parts tricresyl phosphate, 20 parts ochre, and parts titanium white. As mentioned, the yellow mass thus obtained is spread on the surface of the sheath in the same operation in which the sheath and core are produced. The pencil is scissible, i.e. can be sharpened, as shown at 4, by means of a knife or pencil sharpener.

The pencil shown in FIG. 2 is generally of the mechanical type. It comprises a rigid non-scissible sheath- 11 of plastic material made, for instance, according to Example 12. A lead 12 of the ceramic type, consisting of the usual mixture of graphite and clay, is enclosed within the sheath that the lead is immovable radially and can be displaced longitudinally only by application of axial pressure. One end 13 of the sheath is machined to a somewhat smaller diameter and is provided with a screw thread 14. The core channel 15 of the sheath is preferably widened at 16 to provide together with the interior of an interiorly threaded sleeve 17 a sufiiciently large space 58 for the reception of a hydraulic medium. The sleeve 17 is in tight threaded engagement with the end portion 14 of the sheath. The hydraulic medium fills the space 18 as well as the adjacent conical bore 16 of the channel 15. By turning the sleeve 17, the core 12 can be made to protrude more or less out of the conical portion of the sheath 11 and, if desired, may also be retracted into the sheath by turning the sleeve in the opposite direction and pressing the core back into the channel.

Various pencils of the type shown in FIG. 2, as well as methods and apparatus for manufacturing them, are disclosed in the copending application for Manufacture of Slidable-Core Pencils, Serial No. 595,454, filed July 2, 1956, now Patent No. 2,902,754, to which reference may be had if desired.

It will be apparent to those skilled in the art, upon a study of this disclosure, that my invention permits a large variety of modifications and hence may be embodied in a manner different from the particular embodiments described herein, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

I claim:

1. A shaped article formed of a mixture comprising a major quantity of a comminuted main ingredient consisting predominantly of wood flour, a minor quantity of chlorinated naphthalene waxy material and a minor quantity of polyvinyl chloride as binder, the quantity of chlorinated naphthalene being less than that of the polyvinyl chloride, the quantity of the main ingredient being greater than the sum of the quantities of chlorinated naphthalene and polyvinyl chloride.

2. A method of making a shaped article, comprising spraying a minor quantity of Water-insoluble, water insensitive waxy material in dry liquid condition and under vacuum onto a major quantity of a dry comminuted main ingredient consisting predominantly of cellulose, heating to disperse the waxy material into the comminuted ingredient, admixing a minor quantity of a water-insoluble, water-insensitive thermoplastic resin binder to form a 16 homogeneous mixture, the quantity of comminuted main ingredient being greater than the sum of the quantities of waxy material being less than that of the thermoplastic resin, the resin being one that is compatible with the waxy material, and shaping said mixture in dry condition under heat and pressure to produce the article.

3. A method of making a pencil sheath, comprising mixing a major quantity of a comminuted main ingredient consisting predominantly of cellulose, a minor quantity of water-insoluble, water-insensitive waxy material, heating to melt the waxy material to disperse it into the comminuted ingredient, admixing a minor quantity of a water-insoluble, water-insensitive thermoplastic resin to form a homogeneous mixture, the quantity of comminuted main ingredient being greater than the sum of the quantities of waxy material and thermoplastic resin, the quantity of waxy material being less than that of the thermoplastic resin, the resin being one that is compatible with the waxy material, and shaping said mixture in the substantial absence of moisture in the mixture and under heat and pressure to produce the pencil sheath.

4. A pencil sheath formed of a mixture comprising a major quantity of a comminuted main ingredient consisting predominantly of cellulose, a minor quantity of water-insoluble, water-insensitive waxy material and a minor quantity of water-insoluble, water-insensitive thermoplastic synthetic resin as binder, the quantity of waxy material being less than that of the thermoplastic resin, the quantity of the main ingredient being greater than the sum of the quantities of waxy material and the thermoplastic resin, the resin being one that is compatible with the waxy material.

5. The method defined in claim 3, employed for forming the pencil sheath about a marking core to make a pencil, the method further comprising mixing a homogeneous dry composition of a major quantity of a main core ingredient, a minor quantity of water-insoluble waxy substance and a minor quantity of binder, the main core ingredient consisting essentially of a comminuted marking material which determines the character of the finished article, the binder consisting essentially of water-insoluble, water-insensitive thermoplastic synthetic resin, the resin being one that is compatible with the waxy substance, the quantity of waxy substance being less than that of the binder; and extruding said composition in dry condition under pressure and heat to produce the core, the forming of the sheath also being by extrusion, the mixture forming the sheath being extruded onto and around said marking core as the latter is being extruded.

6. A method of making a pencil marking core comprising mixing a homogeneous dry composition of a major quantity of a main core ingredient, a minor quantity of water-insoluble waxy substance and a minor quantity of hinder, the main core ingredient consisting essentially of a comminuted marking material which determines the character of the finished article, the binder consisting essentially of water-insoluble, water-insensitive thermoplastic synthetic resin, the resin being one that is compatible with the waxy substance, the quantity of waxy substance being less than that of the binder; and extruding said composition in dry condition under pressure and heat to produce the core.

7. A method of making a shaped article, comprising mixing a minor quantity of water-insoluble, water-insensitive waxy material in dry condition with a major quantity of a dry comminuted main ingredient consisting predominantly of cellulose, heating to disperse the waxy material into the comminuted ingredient, admixing a minor quantity of a water-insoluble, water-insensitive thermoplastic resin binder to form a homogeneous mixture, the quantity of comminuted main ingredient being greater than the sum of the quantities of waxy material and thermoplastic resin, the quantity of waxy materialbeing less than that of the thermoplastic resin, the resin being one that is compatible with the waxy material, and shaping said mixture in dry condition under heat and pressure to produce the article.

8. The method defined in claim 7, said cellulose ingredient being wood flour.

References Cited in the file of this patent 18 Zuckert July 11, 1939 Chesler May 18, 1943 Mackey Feb. 22, 1944 Irvine et al. June 25, 1946 Johnson Oct. 1, 1946 Rubinstein Oct. 8, 1946 Brennan May 13, 1952 Roy Sept. 13, 1952

Claims

2. A METHOD OF MAKING A SHAPED ARTICLE, COMPRISING SPRAYING A MINOR QUANTITY OF WATER-INSOLUBLE, WATER INSENSITIVE WAXY MATERIAL IN DRY LIQUID CONDITION AND UNDER VACUUM ONTO A MAJOR QUANTITY OF A DRY COMMINUTED MAIN INGREDIENT CONSISTING PREDOMINANTLY OF CELLULOSE, HEATING TO DISPERSE THE WAXY MATERIAL INTO THE COMMINUTED INGREDIENT, ADMIXING A MINOR QUANTITY OF A WATER-INSOLUBLE, WATER-INSENSITIVE THERMOPLASTIC RESIN BINDER TO FORM A HOMOGENEOUS MIXTURE, THE QUANTITY OF COMMINUTED MAIN INGREDIENT BEING GREATER THAN THE SUM OF THE QUANTITIES OF WAXY MATERIAL BEING LESS THAN THAT OF THE THERMOPLASTIC RESIN, THE RESIN BEING ONE THAT IS COMPATIBLE WITH THE WAXY MATERIAL, AND SHAPING SAID MIXTURE IN DRY CONDITION UNDER HEAT AND PRESSURE TO PRODUCE THE ARTICLE.