NO134060B - - Google Patents

Description

The invention relates to a pencil, consisting of a pencil of a graphite-containing or other coloring material in a

-binding agent, as well as an enveloping sheath of foam plastic with volume-

weight 0.3 - 0.7 g/cm^, the pencil being characterized by the fact that the plastic in the sheath consists of a) 5-60 wt% of a butadiene polymer containing up to 50 wt% copolymerized styrene, isoprene,

acrylonitrile or a lower alkyl ester of acrylic

acid or methacrylic acid and

b) 95-^0% by weight styrene or methylstyrene, copolymerized with acrylic or methacrylonitrile, where the weight ratio between the styrene monomer and nitrile mono-

the mer is from 95:5 to 50:50, which monomers may be fully or partially replaced with methyl methacrylate,

with at least 10% by weight of the monomers (b) being grafted onto the butadiene polymer (a), and the possible remainder of (b) being present as a separate copolymer.

Pencils, such as ordinary pencils and colored pencils, are usually made by providing a regular pencil lead with a cover a-v wood. This process involves considerable work and many special conditions and individual operations. These can be summarized as follows: 1. Only first-class wood material can be used. The number of suitable wood species is limited, for good qualities only cedar can be used. 2. Before processing, the wood must be dried under suitable conditions. The content of resin and essential oils must neither exceed nor fall below certain limits 3. The pre-treated wood is cut up with special saws into thin enins, which are subjected to the following operations: Staining, milling, insertion of staples, gluing together, rough grinding and division into rough pencils followed by further grinding

to the final form.

4. The subsequent polishing and varnishing involves a lot of work and a number of individual operations.

Attempts have already been made to simplify the sheathing of pencils, e.g. by using extrusion processes, with the wood material being replaced in whole or in part with other materials.

From German utility model no. 1,709,581 (excluded

27 October 1955) it is known to produce pencils with a foam plastic casing, as the foam plastic sleeve can be extruded and the pin is attached by gluing or shrinking.

German patent no. 839,092 with supplementary patent no.

914.555 shows sheathing of wires and cables with foam plastic during extrusion.

From "Modern Plastics Encyclopedia", Volume 45,

No. IA (September 1967) it is known to produce ABS foam plastic which is like wood to the touch and also resembles wood in sound and appearance.

From US patent no. 2,988,784, it is known to provide good adhesion between the pencil lead and the sleeve by choosing the binder in the pencil from a material that is related to the binder in the sleeve. The sleeve material here essentially consists of wood flour, but it is indicated as advantageous to extrude the pin and the sleeve at the same time, so that the two parts are combined in a single process (column 9, lines 64-73).

It has now been found that pencils of which

any shape and length can be formed continuously from foamable thermoplastic with a volume weight after foaming of 0.3 to 0.7 g/cm^, as sleeve material. There is no difference between the sharpening of pencils obtained in this way and pencils with wooden sleeves.

The pencils according to the present invention can be given

any cross-sectional shape and length using a nozzle connected to a conventional extruder.

They can be cut by machines in any way, manufactured by semi- or fully continuous processes. Polishing and varnishing can be simplified to an immersion in a conventional solvent. The pencils can also be lacquered using conventional methods and embossed after colouring. A conventional single-screw or double-screw extruder is used for the production of pencils in accordance with the invention. An extruder head of the type described, for example, in German patent no. 940,492, can be used as an extruder mold for this purpose.

In another preferred embodiment, the extruder head is designed in such a way that it is provided with an appropriate cooling or heating medium, so that the temperature inside the mold can be regulated as needed. When using these preferred embodiments, the expansion process can be influenced in such a way that the volume weight of the obtained foam varies from the outside to the inside.

The outer opening (nozzle) of the extruder head

is identical to the shape of the pencil to be produced. E.g. a nozzle of round, hexagonal, triangular or oval cross-sectional shape can be used. The diameter of the opening is usually from 5 to 15 mm and suitably approx. 7 mm. It is possible to use pencils of any shape and diameter, e.g. round pins with a diameter of 1.5 to approx. 3 mm, triangular or rectangular staples.

The thermoplastic itself is produced according to known methods. Conventional plastic can be used. E.g. British Patent No. 79,400 relates to the manufacture of ABS polymers.

Materials with an antistatic finish, e.g. of

the kind described in German specification no. 1,244,398 and Austrian patent specification no. 282,939 are suitable ABS polymers. In this way, the shavings that are removed will fall directly into the collection container, with the result that the milling machine parts will be free.

The expanding agents can be added according to known methods. When a granulated thermoplastic is used as starting material, it has been found advantageous to use a small amount of an adhesion accelerator, e.g. 0.5% by weight (based on the whole mixture) of butyl stearate or of a higher alkyl sulfonic acid ester of phenol or a substituted phenol. If powdered thermoplastic is used, it is not necessary to use such an agent.

The expansion agent can be incorporated, for example

by means of a drum mixer in the case of a granule, and by means of a mixer at high speed in the case of a powder being used. If you want to achieve a foam material with the desired volume weight,

must the finished mixture have an expansion agent content of

about 0.7 to 1 weight#, although the volume weight of the foam as well. is influenced by the manufacturing conditions. Azodicarbonamide and sulfohydrazide-based agents can be used as expansion agents. IN

Mixtures containing the expanding agent can be conventionally processed in a conventional single or twin screw extruder in a temperature range of from 150 to 200°C. Single-screw extruders are suitable when a granule is used as starting material. Twin-screw extruders are used above all when an expandable thermoplastic powder is used.' Although the granules may be coloured, it is also possible to add suitable pigments or colors to the powder during the mixing process in mixers at high speed, and thus obtain a colored product. Other additives such as e.g. lubricants, antistatic agents and stabilizers can be used.

The pencil leads are encased with the foam in a reversal type extruder head attached to the extruder. It contains two nozzles, one inside the other; the inner nozzle is used to guide the pin, while the outer one is used to guide and shape the enveloping expandable thermoplastic, which moves in the same direction as the pin. An extruder nozzle which allows the temperature inside the nozzle to be regulated is preferably used.

The extruded length of the pencil can be subtracted, e.g. using guides and conveyor belts. To achieve

a high-gloss surface, the strands are allowed to pass through a suitable solvent, e.g. methyl ethyl ketone, while they are carried away.

The endless string is then divided into pencil lengths and embossed.

In accordance with the invention, the hitherto extremely complicated and mostly batch-wise production of ordinary pencils and colored pencils is simplified to a fully continuous and efficient extrusion process. The pencils produced have the same advantages as wooden pencils. The multi-layer varnishing and polishing used is replaced by an immersion in a solvent.

The pencils thus obtained are particularly suitable for use as writing pencils, and have no disadvantages whatsoever when compared with conventional pencils made of wooden materials.

The invention is illustrated in the following examples,

where parts and percentages are weight indications where nothing else is stated.

Example 1.

The following components are mixed in a mixer with

high speed: 1000 parts of an ABS graft polymer of the following composition:

a) 25% of a graft polymer of 35% styrene and 15% acrylonitrile and 50% polybutadiene, b) 75% styrene/acrylonitrile copolymer 70:30, 7i=0.60, c) 4 parts of a linear polypropylene glycol with an average molecular weight of 2000 and OH number

of 56±1,

10 parts azodicarbonamide,

2.0 parts titanium dioxide,

0.4 parts iron oxide brown, and

0.04 parts carbon black.

After everything has been homogenized, this mixture is introduced into a twin-screw extruder fitted with a reversing type injection head. The outlet opening of this head is at right angles to the insertion opening. The head is designed in such a way that another material can be introduced between the inlet and the outlet. This inlet leading to the center of the outlet opening of the mold is known as the mantle. The outlet opening of the extruder head itself is in this case a regular hexagon with a corner-to-corner diameter of 7 mm. It corresponds to the cross-section of a normal hexagonal pencil. If the plastic is extruded through this extruder head at 150°C, and if a ceramic bonded graphite pin of 2 mm in diameter is simultaneously introduced through the jacket of the extruder head, a continuous length of pencil is obtained where the pin is embedded in ABS foam of the above composition. The average volume weight of the foam is 0.5 g/cm 2 . In the longitudinal direction, the pencil thus obtained is brown in colour. The surface is smoothed by brief immersion in methyl ethyl ketone. It is then cut

in pencils of standard length, which can be sharpened as easily as a pencil sheathed in wood.

Example 2.

The following masses are mixed together in a mixer at high speed:

1000 parts of graft polymer of

20% polybutadiene,

50% methyl methacrylate,

30% styrene/acrylonitrile in a weight ratio of 70:30, 10 parts azdicarbonamide and

0.3 parts carbon black.

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

Example 3-

This example shows the fully continuous production of pencils: A pencil of the following composition is extruded from a single screw extruder connected to a 2 mm extruder die (hole die):

180 parts of one graft polymer of

h0% of vinyl chloride,

23% vinyl acetate and

37% ethylene,

20% graft polymer of

a) 30% graft polymer of 35% styrene and 15% acrylonitrile and 50% polybutadiene, and b) '70% of styrene/acrylonitrile copolymer (weight ratio 70:30, °?i = 0.60),

10 parts of an alkyl sulfonic acid ester of phenol with

an alkyl radical with 15 carbon atoms,

10 parts barium/cadmium laurate,

40 parts of bis-stearylamide of ethylenediamine, and 750 parts of graphite.

A continuous string of pencil lead is obtained.

The hole nozzle is arranged so that it simultaneously functions as a core or mandrel for an extruder nozzle of the type described in example 1. The extruder head itself is, connected to another extruder (a twin-screw extruder), arranged vertically on the first process unit. An expandable moldable composition is extruded through the outer extruder head. This plastic composition is identical to that described in example 1, except that the styrene/acrylonitrile copolymer is replaced by an equivalent amount of an α-methylstyrene/acrylonitrile copolymer with the same intrinsic viscosity. The extrusion of both mixtures

is regulated so that as soon as it emerges from the hole nozzle,

the thermoplastic staple is surrounded by plastic foam. This foam has a regular hexagon shape and dimensions, like a normal pencil.

The resulting continuous-length pencil is passed through a methyl ethyl ketone bath for surface finish, and after rapid drying is cut into standard lengths.

The pencil, produced by this fully continuous process, has the same properties as ordinary pencils.

Example 4.

The method of manufacture is as in example 3. The pencil has the following composition:

120 parts of a graft polymer of 80% vinyl chloride,

2 3% vinyl acetate and 37% ethylene,

80 parts of a mixture of

a) 30% of a graft polymer of 35% styrene and 15% acrylonitrile and 50% butadiene/styrene copolymer

with the ratio 90:10, and

b) 70% styrene/acrylonitrile copolymer with weight ratio 70:30, ^ i =0.60,

10 parts of barium/cadmium laurate,

400 parts of a red dye,

10 parts of an alkyl sulfonic acid ester of phenol with an alkyl radical of 15 carbon atoms and

400 parts talc.

In this case too, the manufacturing process is completely continuous. The manufactured colored pencils have excellent writing properties and can be sharpened with normal pencil sharpeners.

Claims (3)

!• Pencil, consisting of a stick of a glue-containing or other coloring material in a binder, as well as an enveloping sheath of foam plastic with a volume weight of 0.3 - 0.7 g/cm-<5>, characterized in that the plastic in the sheath is of a) 5-60% by weight of a butadiene polymer containing up to 50% by weight copolymerized styrene, isoprene, acrylonitrile or a lower alkyl ester of acrylic acid or methacrylic acid and b) 95-40% by weight styrene or methylstyrene, copolymerized ... with acrylic -, or methacrylonitrile,!. where the weight ratio between the styrene monomer and the nitrile monomer is from 95 = 5 to'50:50, which monomers can be whole or partially replaced with methyl methacrylate, wherein at least 10% by weight of the monomers (b) is grafted onto the butadiene polymer (a), and the possible remainder of (b) is present as a separate copolymer. 2. Pencil according to claim 1, characterized in that the plastic is a mixture of 25% by weight of a graft polymer of 35 parts by weight styrene and 15 parts by weight acrylonitrile on 50 parts by weight polybutadiene, and 75% by weight of a styrene/acrylonitrile copolymer with a weight ratio of styrene and acrylonitrile at 70:30. 3. Pencil according to claim 1, characterized in that the binder of the pencil consists of a mixture of I. 1-100 parts by weight of a polymer of a) 25-100% by weight ethylene/vinyl acetate copolymer with a vinyl acetate content from 20 to 70% by weight and b) up to 75% by weight grafted vinyl chloride and II. 99-0 parts by weight of a graft polymer of a) 5-60% by weight of a butadiene polymer, containing up to 30% by weight of copolymerized styrene, isoprene, acrylonitrile or a lower alkyl ester of acrylic or methacrylic acid and b) "95-40% by weight of styrene or methylstyrene, copolymerized with acrylic or methacrylonitrile, where the weight ratio between the styrene monomer and the nitrile monomer is from 95:5 to 50:50, which monomers can be completely or partially replaced with methyl methacrylate, wherein at least 10% by weight of the monomers (b) is grafted onto the butadiene polymer (a), and the possible remainder of (b) is present as a separate copolymer, as the choice of this thermoplastic staple binder allows the pencil to be manufactured in a fully continuous process.