US3704071A

US3704071A - Pencil having a formed abs polymer barrel

Info

Publication number: US3704071A
Application number: US755812A
Authority: US
Inventors: Karl-Heinz Muller; Harry Rohr; Karl-Heinz Ott
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1967-10-04
Filing date: 1968-08-28
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28
Also published as: GB1240852A; FR1588294A; DE1561767B1; AT296467B; JPS4813368B1; DK131277B; NL6814263A; DK131277C; BE721839A; NO134060B; SE346086B; NO134060C; CH523791A

Abstract

Pencils comprising a lead and a foamed thermoplastic moulding composition sheathed around this lead and having a density of from 0.3 to 0.7 g /cc.

Description

United States Patent Muller et a1. [45] Nov. 28, 1972 [5 PENCIL HAVING A FORMED ABS [56] References Cited POLMR BARREL UNITED STATES PATENTS [72] Inventors: Karl-Heinz Muller Levekusen;

Harry Rom. cologrle, KarLHeinz 1,937,104 11/1933 Thomsen .,.40l/96 X Ott, Leverkusen, all of Germany 2,960,967 11/1960 Bauserman.. ..401/96 2,988,784 6/1961 Lorenian ..401/96 X [73] Assignee: Bayer Aktiengesellschaft, Lever kusen, Germany FOREIGN PATENTS OR APPLICATIONS [22] Filed: Aug. 28, 1968 154,937 1/1954 Australia ..401/96 [21] AppL No: 755,812 969,976 6/1950 France ..401/96 579,860 7/1958 Ita1y. ..401/96 [30] Foreign Application Priority Data Primary Examiner-Lawrence Charles Oct. 4, 1967 Germany .F 1 5 1 767.1 Azrom yy and t [52] US. Cl ..401/96, 264/45 [57] ABSTRACT 51 I t. Cl ..B43k 02 d I581 F ield of Search .?.4?JZ/ 2 Pemfls mPriSing a lead and a famed hermplastic moulding composition sheathed around this lead and having a density of from 0.3 to 0.7 g lcc.

08m??? N0 D i PENCIL HAVING A FORMED ABS POLYMER BARREL This invention relates to a process for the production of pencils in which a lead, for example the lead of an ordinary pencil, a copying pencil or colored pencil, is surrounded in continuous process by a thermoplastic foam with a density of from 0.3 to 0.7 g/cc, and to the pencils obtained by this process.

Pencils, such as ordinary lead pencils or colored pencils, are conventionally manufactured by providing a suitable lead with a wooden sheath. This process, however, involves considerable work and many special conditions and individual operations. These may be summarized as follows:

1. Only wood that is first class and specially selected may be used. The number of suitable woods is limited, and it is only cedar wood that is normally used for high grade products.

2. Before it is processed, the wood has to be dried under suitable climatic conditions. The resin or essential oil content should neither exceed nor fall below certain limits.

3. The prepared wood is cut up with special saws into thin boards which are subjected to the following operations: staining, grooving, inserting the leads, glueing together, coarse sanding, and cutting into crude pencils followed by further sanding to give the final form.

4. The subsequent polishing and varnishing process again involves considerable work and a number of individual operations.

Attempts have already been made to simplify the sheathing of leads, for example by using different processes and by replacing the wood required for the sheath either wholly or in part by other materials. Attempts such as these are described for example in German Patent specifications Nos. 496,016, 496,017 and 496,018, all of which describe apparatus by means of which the leads are sheathed in a plastic cellulose composition.

German Patent specification No. 917,771 relates to a pencil comprising a tubular lead holder in the center of a pencil-like grip member with connections in the form of longitudinal strips between the lead holder and the grip member. The pencil is formed in one piece from a free-flowing injectable or extrudable, for example thermoplastic, plastics material.

Unfortunately, these processes have not met with success for the following reasons:

1. In view of the fact that cellulose-based compositions are used for sheathing, the pencils are sensitive to moisture. They have still to be painted and polished.

2. If different thermoplastic moulding compositions, for example, polyethylene, are used the pencils cannot be sharpened with a pencil sharpener of conventional design because the material cannot be cut like wood.

3. If moulding compositions of this kind are mixed with a suitable plasticizer in order thus to make them injectable, the problem of plasticizer migration occurs with the result that the quality of the leads in particular is detrimentally affected.

4. Conventional leads, either for ordinary pencils or for colored pencils, break very easily. For this reason, a continuous sheathing process is far from a practical proposition. Batch operation is more suitable.

It has now been found that writing leads of any shape and length can be continuously sheathed providing a foamable thermoplastic plastic with a density after foaming of 0.3 to 0.7 g/cc., is used for sheathing. There is no difierence in the sharpening properties of the pencils thus obtained and those of pencils sheathed in wood.

In the context of this invention, foamable thermoplastic plastics are moulding compositions which contain expanding agents and which, under the processing conditions, give a porous strand of any desired cross section having the aforementioned density on issuing from a nozzle attached to a conventional type of extruder. The following are examples of suitable thermoplastic plastics: expandable polystyrene; expandable copolymers of styrene with other vinyl or vinylidene monomers, for example acrylonitrile or methyl methacrylate; expandable polymethyl methacrylate; expandable polyvinyl chloride; expandable polyvinyl chloride modified with monomeric or polymeric plasticizers; expandable cellulose esters modified with plasticizers; and expandable rubbermodified polystyrenes with a styrene content of at least about 50 percent by weight.

In a preferred embodiment of the invention, the leads are sheathed in expandable thermoplastic moulding compositions comprising copolymer mixtures of polymers of acrylonitrile, butadiene and styrene (ABS- polymers) of the following composition:

A. 5 to 60 percent by weight of an elastomeric butadiene polymer with optionally up to 50 percent by weight of copolymerized styrene, isoprene, acrylonitrile or a low alkyl ester of acrylic acid or methacrylic acid, and

B. 95 to 40 percent by weight of polymerized styrene and acrylonitrile in a ratio by weight of 95 5 to 50 50 wherein these two monomer components may be replaced either wholly or in part by their respective alkyl derivatives, or alternatively one or both of them may be replaced either wholly or in part by methyl methacrylate; all or part of the styrene and acrylonitrile having been polymerized in the presence of the butadiene polymer, theresidual component of styrene and acrylonitrile having been added in separately copolymerized form during the course of a partial graft polymerization reaction.

In another preferred embodiment, the object of which is to make the process used to manufacture the pencils fully continuous, leads are used which contain as binder 99 to 0 parts by weight of the abovedescribed ABS-polymer and l to 100 parts by weight of a graft polymer of a. 25 to 85 percent by weight of an ethylene/vinyl acetate copolymer with a vinyl acetate content of from 20 to percent by weight and preferably from 30 to 55 percent by weight, and

b. to 15 percent by weight of grafted-on vinyl chloride; this graft polymer may be replaced either wholly or in part by copolymer (a). Leads of this kind are the subject of one of our own co-pending applications.

According to the present invention, leads of any length and cross section which may be machine cut in any way, can be produced by a semi-continuous or fully continuous process. The operation of polishing and lacquering may finally be reduced to straightforward immersion in a conventional solvent. The pencils produced by the process according to the invention may also be lacquered by conventional processes and embossed after coloring.

A conventional single-screw or twin-screw extruder is used to manufacturethe pencils according to the invention. An extruder head of the kind described for example in German Patent specification No. 940,492, may be used as the extrusion die for this purpose.

In another preferred embodiment of this invention, however, the extruder head is designed in such a way that, providing a suitable heating or cooling medium is used, the temperature prevailing inside the die may be controlled as required. By virtue of this preferred design, the process of expansion may be influenced in such a way that the density of the issuing foam varies from the outside towards the inside.

The outer outlet opening (nozzle) of the extruder head is identical in shape with the shape of the pencil to be produced. For example, a nozzle of round, hexagonal, triangular or oval cross section may be used. The diameter of the outlet is generally from to mm. and preferably around 7 mm. The cross section of the lead is governed by the shape of the die opening which can also be varied as desired. It is possible both to produce and to use leads-of any customary shape and diameter, for example round leads with diameters of from about 1.5 to about 3 mm., triangle or rectangular leads.

The thermoplastic plastics themselves are produced by known methods. Conventional thermoplastic plastics may be used to carry out the process according to the invention. For example, British Patent specification No. 794,400 relates to the production of ABS- polymers, as does German Patent application F 44 156 lVd/39c.

Materials with an anti-static finish, for example of the kind described in German Auslegeschrift No. 1,244,398 and in German Patent Application F 52753 Ive/39c, are preferably used as the ABS-polymers. In this way, the chippings removed when the pencils are sharpened are not electrostatically charged, with result that the outlet opening of a normal pencil sharpener cannot be blocked. Where a pencil-sharpening machine is used, the chippings which are milled off drop directly into the collecting container with the result that the milling unit remains free.

The expanding agents may be added by known methods. When a granular thermoplast is used as the starting material, it has proved to be of advantage to add a small quantity of an adhesive promoter, for example 0.5 percent by weight (based on the mixture as a whole) of butyl stearate or of a higher alkyl sulphonic acid ester of phenol or of a substituted phenol. When powdered thermoplasts are used as the starting materials, there is no need to add an adhesive promoter.

The expanding agentmay be worked in, for example, by means of a tumbler mixer in the case of a granulate, and by means of a high speed mixer in the case of a powder. In order to provide a foamed material of the required density, the finished mixture should have a content of expanding agent of from about 0.7 to 1 percent by weight, although the density of the foam is also influenced by the particular processing conditions. Substances whose decomposition temperature lies in the processing range of the thermoplastic moulding compositions, may be used as the expanding agents, examples of such substances being azodicarbonamide and sulphohydrazide-based expanding agents.

The moulding compositions containing the expanding agents may conveniently be processed in conventional single-screw or twin-screw extruders at temperatures in the range from 150 to 200C. Single-screw extruders are preferably used when an expandable thermoplast granulate is used for the foaming operation. Twin-screw extruders are used above all when an ex pandable thermoplast powder is used as the starting material. Although the granulate may already be colored, it is also possible to add appropriate pigments or dyes to the powder'during the process of mixing in the high speed mixer, and thus to obtain a colored foam. Similarly, other additives, for example, lubricants, anti-static agents, stabilizers and additional pigments may also be added.

The leads are sheathed in the thermoplastic foam in a reversal-type extruder head attached to the extruder which contains two nozzles arranged one inside the other, the inner nozzle being used to guide the lead, whilst the outer nozzle is used to guide and form the surrounding, expandable thermoplastic composition.

which movesin the same direction as the lead. An extruder head which enables the temperature inside the die to be controlled is preferably used.

' The extruded length of pencil may be drawn off, fo example, by means of former sleeves and conveyor belts. In order to obtain a high-gloss surface, the strand is passed through a suitable solvent, for example methyl ethyl ketone, as it is being drawn off. The endless strand is then cut into pencil lengths and embossed.

According to the invention, the hitherto extremely complicated and, for the most part, batch-type production of lead pencils and colored pencils is simplified into a fully continuous and efficient extrusion process. The pencils produced have all the advantages of wooden pencils. The multi-layer lacquering and polishing are replaced by straightforward immersion in a solvent.

The pencils thus obtained are eminently suitable for use as writing instruments and do not have any disadvantages at all when compared with conventional material, wood.

The process according to the invention is illustrated in the following Examples in which the parts and percentages are parts and percentages by weight unless otherwise indicated.

EXAIWPLE l The following components are mixed in a high speed mixer: 1,000 parts by weight of an ABS-graft polymer of the following composition:

a. 25 percent by weight of a graft polymer of 35 percent by weight of styrene and 15 percent by weight of acrylonitrile on by weight of polybutadiene,

b. 75 percent by weight of a styrene/acrylonitrile copolymer 30, n 0.60,

c. 4 parts of a linear polypropylene glycol with an average molecular weight of 2,000 and an 01-1 number of 56 i1, 1

10 parts by weight of azodicarbonamide,

2.0 parts by weight of titanium dioxide,

0.4 part by weight of iron oxide brown, and

0.04 part by weight of carbon black After it has been homogenized, this mixtureis introduced into a twin-screw extruder equipped with a reversal-type extruder head. The outlet opening of this extruder head is atright-angles to its inlet opening. The head is designed in such a way that another material can be' introduced through an additional inlet at the bend between the inlet and outlet. This inlet which leads into the middle of the outlet opening of the die, is known as the mandrel. The outlet-opening of the extruder head itself is in this instance a regular hexagon with a diameter from corner to corner of 7 mm. It thus corresponds to the cross section of a normal hexagonal pencil. If the thermoplastic material is extruded through this extruder head at 150C. and if ceramically bonded graphite leads 2 mm. in diameter are simultaneously introduced through the mandrel of the extruder head, a continuous length of pencil is obtained in which the lead is sheathed in the ABS-foam of the afore-mentioned composition. The average density of the form is 0.5 g/cc. The length of pencil thus obtained is brown in color. Its surface is smoothed off by brief immersion in methyl ethyl ketone. It is then cut into pencils of standard length which can be sharpened just as easily as a pencil sheathed in wood.

EXAMPLE 2 The following components are mixed together in a tumbler mixer: 1,000 parts by weight of polystyrene granulate,

5 parts by weight of butyl stearate, and

7 parts by weight of diphenyl sulphone-3,3-

disulphohydrazide.

The expandable granulate is fed through a metering unit to a single-screw extruder to which an angled extruder head of the kind described in Example 1 is connected as the die. The temperature at which the material is processed is in the range from 120 to 150C. If ceramically bonded graphite leads are simultaneously introduced through the mandrel of the extruder head, followed by extrusion of the thermoplastic material, a continuous length of pencil with a silk-smooth surface is obtained. It is then cut up into pencils of standard length which are sufficiently rigid and which are easily sharpened. The foam has an average density of 0.4

g/cc.

EXAMPLES 3 t0 6 The procedure is as in Example 2 with the following thermoplastic moulding compositions being used in granulate form:

Example 3:

styrene/acrylonitrile copolymer (weight ratio 70 1; 1.0 (as measured in dimethyl formamide at A rubber-modified polystyrene of the kindknown commercially as Polystyrene 475 (a registered trade mark of BASF). Example 6:

Polymethyl methacrylate, 'n 0.8 (as measured in dimethyl formamide at 20c.).

In contrast to Example2, the diphenyl sulphone- 3,3'-disulphohydrazide is replaced by azodicarbonamide in Examples 3 and 6 on account of the higher melt viscosity of the thermoplastic moulding compositions.

Even when these moulding compositions are used, pencils are obtained which are highly rigid and easy .to

sharpen.

7 EXAMPLE 7 The following components are mixed together in a high-speed mixer: Y 1,000 parts by weight of graft polymer of 20 percent by weight of polybutadiene,

50 percent by weight of methacrylate and 30 percent by weight of styrene/acrylonitrile in a weight ratio of 30,

10 parts by weight of azodicarbonamide, and 0.3 part by weight of carbon black.

The mixture is further processed as described in Example 1..The resulting pencil withits graphite lead is easy to sharpen.

EXAMPLE 8 EXAMPLE 9 This Example is intended to demonstrate the fully continuous production of pencils: I

A lead of the following'composition is extruded from a single-screw extruder attached to a 2 mm. extrusion die:' parts by weight of a graft polymer of 40 percent by weight of vinyl chloride, 23 percent by weight of vinyl acetate and 37 percent by weight of ethylene, 20 parts by weight of a graft polymer of a. 30 percent by weight of a graft polymer of 35 percent by weight of styrene and 15% by weight of acrylonitrile on 50 percent by weight of polybutadiene, and b. 70 percent by weight of a styrene/acrylonitrile copolymer weight ratio 70 30, 1; 0.60, 10 parts by weight of an alkyl sulphonic acid ester of phenol having an alkyl radical of 15 carbon atoms, 10 parts by weightof barium cadmium laurate, 40 parts by weight'of the bis-stearyl amide of ethylene diamine, and 750 parts by weight of graphite.

A continuous strand of lead 2 mm. in diameter is obtained. I

The extrusion die attached to the extruder is designed in such a way that it simultaneously acts as the mandrel of an extruder head of the kind described in Example 1. The extruder head itself is connected to a second extruder (a twin-screw extruder) arranged perpendicularly of the first processing unit. An expandable. moulding composition is extruded through the 'outer nozzle of the extruder head. This moulding composition is identical with that described in Example 1, ex cept that the styrene/acrylonitrile copolymer' is replaced by an equivalent quantity of an a-methyl styrene/acrylonitrile copolymer with the same intrinsic viscosity. Extrusion of both compositions is controlled in such a way that, as soon as it emerges from the man- 4 EXAMPLE 10 The procedure is as in Eitample 9. The lead composition used is made up as follows: 120 parts by weight of a graft polymer of 40 percent by weight of vinyl chloride, 23 percent by weight of vinyl acetate and 37 percent by weight of ethylene, 80 parts by weight of a graft co-polymer of 1. 30 percent by weight of a graft polymer of 35 percent lay-weight of styrene and 15% by weight of acrylonitrile on 50 percent by weight of a butadiene/styrene copolymcr in a weight ratio of 90 z l0, and b. 70 percent of a styrene/acrylonitrile copolymer weight ratio '70 30, 1; =0.60, 10 parts by weight of an alkyl sulphonic acid ester of phenol having an alkyl radical of 15 carbon atoms, l parts by weight of barium cadmium laurate, 400 parts by weight of Cadmopurrot (registered trade mark of Farbenfabriken Bayer AG), and 400 parts by weight of talc.

In this case, too, the manufacturing process is fully continuous. The colored pencils show outstanding chalking properties and can be sharpened with a conventional pencil sharpener. We claim l. A pencil having a sheath comprising a. foamed thermoplastic moulding composition of A. to 60 percent by weight of an elastomeric butadiene polymer with optionally up to 50 percent by weight of copolymerized styrene, isoprene, acrylonitrile or a lower alkyl ester of acrylic or .methacrylic acid; and

B. 95 to 40 percent by weightof polymerized styrene and acrylonitrile in a ratio by weight of from 95 z 5 to 50 50 wherein these two monomer components may be replaced either wholly or in part by their respective alkyl derivatives or alternatively one or both of them may be replaced either wholly or in part by methyl methacrylate; all or part of the styrene and acrylonitrile having been polymerized. in. the presence of the butadiene polymer andthe remainingcomponent of styrene and acrylonitrile added even in separately copolymerized form during the course of apartial graft polymerization reaction, the foam having a density of 0.3 to 0.7 g/cc.

2. A pencil comprising a central core of a graphitic or other coloring agent composition and a surrounding sheath, said sheath comprising a foamed thermoplastic moulding composition of a density of 0.3 to 0.7 g/cc and containing f A. 5 to 60 percent by weight of an elastomeric homopolymer of butadiene or a copolymer thereof with up to 50 percent by weight of copolymerized styrene, isoprene, acrylo'nitrile .or a lower alkyl ester of acrylic or methacrylic acid and B. 95 to 40 percent by weight of polymerized styrene or methyl styrene and acrylonitrile or methyl acrylonitrile in a ratio by weight of 95:5 to 50:50, said monomers having been polymerized either wholly or in part in the presence of component A).

.3. The pencil of claim 2 wherein up to 100 percent by weight of methyl methacrylate is employed for either or both of the monomers of component B).

4. The pencil of claim 1 wherein said sheath comprises a foamed thermoplastic moulding composition of 25 percent by weight of a graft polymer of 35 percent by weight of styrene and 15' percent by weight of acrylonitrile on 50 percent by weight of polybutadiene and 75% by weight of a styrene-acrylonitrile copolymer in a ratio by weight of :30.

5. The pencil of claim 1 wherein said central core comprises a graphite or other pencil coloring agent and, as a binder thereof, a mixture of C. l to 100 parts by weight of a graft polymer of a. 25 to 100 percent by weight of ethylene/vinyl acetate copolymer having a vinyl acetate content of from 20 to 70% by weight and b. to 0 percent by weight of grafted-on vinyl chloride and D. 99 to 0 parts by weight of a graft polymer of a. 5 to 60 percent by weight of a homopolymer of butadiene or a eopolymer of butadiene containing up to 30 percent by weight of copolymerized styrene, acrylonitrile, isoprene or a vloweralkyl ester of acrylic or methacrylic acid and l b. to 40 percent by weight of polymerized styrene or methyl styrene and acrylonitrile or methyl acrylonitrile .in a ratio by weight of 95:5 to 50:50, said monomers having been polymerized either wholly or in part in the presence of said butadiene polymer of component D).

6. A pencil as claimed in claim 5 wherein up to 100 percent by weight of methyl methacrylate is employed for either or both of the grafting monomers of component D).

Claims

2. A pencil comprising a central core of a graphitic or other coloring agent composition and a surrounding sheath, said sheath comprising a foamed thermoplastic moulding composition of a density of 0.3 to 0.7 g/cc and containing A. 5 to 60 percent by weight of an elastomeric homopolymer of butadiene or a copolymer thereof with up to 50 percent by weight of copolymerized styrene, isoprene, acrylonitrile or a lower alkyl ester of acrylic or methacrylic acid and B. 95 to 40 percent by weight of polymerized styrene or methyl styrene and acrylonitrile or methyl acrylonitrile in a ratio by weight of 95:5 to 50:50, said monomers hAving been polymerized either wholly or in part in the presence of component A).
3. The pencil of claim 2 wherein up to 100 percent by weight of methyl methacrylate is employed for either or both of the monomers of component B).
4. The pencil of claim 1 wherein said sheath comprises a foamed thermoplastic moulding composition of 25 percent by weight of a graft polymer of 35 percent by weight of styrene and 15 percent by weight of acrylonitrile on 50 percent by weight of polybutadiene and 75% by weight of a styrene-acrylonitrile copolymer in a ratio by weight of 70:30.
5. The pencil of claim 1 wherein said central core comprises a graphite or other pencil coloring agent and, as a binder thereof, a mixture of C. 1 to 100 parts by weight of a graft polymer of a. 25 to 100 percent by weight of ethylene/vinyl acetate copolymer having a vinyl acetate content of from 20 to 70% by weight and b. 75 to 0 percent by weight of grafted-on vinyl chloride and D. 99 to 0 parts by weight of a graft polymer of a. 5 to 60 percent by weight of a homopolymer of butadiene or a copolymer of butadiene containing up to 30 percent by weight of copolymerized styrene, acrylonitrile, isoprene or a lower alkyl ester of acrylic or methacrylic acid and b. 95 to 40 percent by weight of polymerized styrene or methyl styrene and acrylonitrile or methyl acrylonitrile in a ratio by weight of 95:5 to 50:50, said monomers having been polymerized either wholly or in part in the presence of said butadiene polymer of component D).
6. A pencil as claimed in claim 5 wherein up to 100 percent by weight of methyl methacrylate is employed for either or both of the grafting monomers of component D).