GB2145376A

GB2145376A - Marking or erasing implement

Info

Publication number: GB2145376A
Application number: GB08420936A
Authority: GB
Inventors: Werner Handl
Original assignee: JS Staedtler GmbH and Co KG
Current assignee: JS Staedtler GmbH and Co KG
Priority date: 1983-08-20
Filing date: 1984-08-17
Publication date: 1985-03-27
Also published as: GB2145376B; GB8420936D0; DE3330119A1; DE3330119C2

Abstract

A marking or erasing implement consists of a casing and a rod of marking or erasing material firmly connected therewith, wherein the connection of the rod with the casing, as well as optionally also the connection of parts of the casing with each other, is effected by an adhesive substance which contains the product of a poly-reaction of an isocyanate with compounds containing reactive hydrogen.

Description

SPECIFICATION Marking or erasing implement The present invention relates to a marking or erasing implement, in particular an implement having a casing in which a rod of marking or erasing material is encased, a connection between the casing and the rod, and also between individual parts of the casing in the instance of a multi-part casing, being effected by an adhesive substance. The invention also relates to methods of manufacturing implements of that kind. The term marking or erasing implement embraces writing pencils, painting pencils, cosmetic pencils, erasing pencils, other types of correcting pencils, scribing pencils and similar pencils, and crayons with solid shanks or grips.

Writing or painting pencils manufactured with the use of glue are known from, for example, German (Federal Republic) published specification No. 19 53 985, In this case, a polyvinylacetate dispersion glue is employed for gluing a writing or painting rod in a two-part shank and a melting glue for the gluing together of the shank halves in order to be able to dispense with heating for setting of the latter glue.

In a method disclosed in United Kingdom patent specification No. 956 119, a pencil lead and pencil shank parts are glued together by a vinyl resin glue, for example polyvinylacetate, under heating.

According to German (Federal Republic) patent specification No. 28 45 078, gluing together of pencil shanks with leads is carried out in such a manner that the glue connection between lead and shank is provided by an emulsifier contained in the lead and a copolymer of methylvinylether and maleic acid anhydride. The shank parts themselves are glued together by a dispersion of polyvinylacetate. The gluing process as a whole takes place under the influence of heat, preferably through use of a high-frequency or microwave heating system.

These known methods have the disadvantage that it is necessary for the grooves for the leads to be kept within narrow tolerance limits and for the grooves to be formed cleanly and with uniform and relatively smooth surfaces, as the employed adhesive substances are otherwise not applied in sufficient quantity and thereby do not result in a sufficiently firm connection between lead and shank or on the other hand are applied in too thick a layer and form a relatively hard layer around the lead. Both can impair repointing of the pencils and during use lead to frequent lead breakage.

In addition, it is necessary to use either heating systems for the setting of the glue or two different adhesive substances in order to achieve solidification of the adhesive layers in an economically acceptable time.

In the gluing of water-soluble marking rods in casings, for example in watercolour pencils, insulation of the rod, or use of special adhesive substances and heating installations, is necessary to prevent the rod from being partially dissolved or attacked during the gluing phase by polyvinylacetate dispersion glue, which as a rule is very watery, or by softening agents contained therein. In some circumstances, a firm gluing of the rod to the casing cannot be achieved and a relatively hard adhesive layer is created.

It would thus be desirable to avoid or minimise these disadvantages, so that inexpensive but high quality implements can be produced with the marking or erasing rods securely anchored in the casing and without using protective insulation. In addition, grooves for such rods should be capable of production in a relatively wide tolerance range and possibly with rough surfaces without thereby impairing the security of the gluing or the quality of the implement in respect of pointing and breakage strength. It would also be desirable for the gluing to be carried out with an adhesive substance which can be modified within wide limits and which can result in a relatively soft adhesive layer yet provide good adhesion to casing and the rod.

According to a first aspect of the present invention there is provided a marking or an erasing implement comprising an elongate casing and a rod of marking or erasing material encased in the casing and secured thereto by an adhesive substance comprising a poly-reaction product of an isocyanate with at least one compound containing reactive hydrogen.

It is indeed known to use polyurethane, a synthetic material formed by poly-addition of isocyanate and functional hydroxyl groups, for the manufacture of adhesive substances (see Kunststoff-Handbuch, Vol.

VII, "Polyurethane", Carl Hanser Verlag, Munich 1966, pages 24 and 719 to 735). Adhesive substances of that kind are used in the furniture industry for the gluing together of wood or for the connecting of wood to parts of plastics or ceramic material. It was not, however, apparent that products of poly-reactions of isocyanate and compounds containing reactive hydrogen would be suited for use in gluing in writing or marking implements. The layer provided by such an adhesive substance is, within certain limits, present as a foam structure and consequently was regarded as insufficiently rigid, especially since, in the pointing of writing or erasing implements, appreciable demands are made on the strength of the glue connection between casing and rod.The prevailing opinion was thus that gluing together of rods and casings required a relatively hard or rigid layer and that a resilient or even porous adhesive substance film was not suitable for this purpose.

Contrary to these views and In spite of the known problems, adhesive substances comprising the reac tlon products of isocyanate and compounds containing reactive hydrogen have now been found to result In a very good gluing together of implement casings and marking or erasing rods, the gluing effect being variable within wide limits.

Reaction products which have proved to be particularly suitable are those resulting from moisture-reactive isocyanate, from isocyanate and compounds having functional hydroxyl groups and from blocked isocyanate compound and a plastics material dispersion, for example an aqueous polyvinylacetate dispersion, preferably a prepolymer, with a diphenylmethandiisocyanate.

If a moisture-reactive isocyanate is used, then the quantity of water required for polymerisation can be contained in the marking or erasing rod or in the casing material or can be provided by an impregnating medium. If the casing consists of wood, then the wood can have an increased residual moisture. Similarly, the marking rods, for example colour leads, can be in a "green" state, i.e. not predried or incompletely predried, or can contain impregnating medium which includes water or emulsion.

If polyurethane, as poly-reaction product of functional hydroxyl groups and corresponding isocyanate, is used, then the hydroxyl groups can be present as a component of the rod or of the casing material or as an impregnating medium or can be added separately. Preferably, polyetherpolyol or polyesterpolyol is used as a component of that kind, preferably with a hydroxyl number between 20 and 400.

Aiternatively, poly-reaction products of isocynate and polyaminotriazole, polyethylamine, polycarboxylic acid, polyesteramide and/or polyetheramine, each containing reactive hydrogen, can be used as the adhesive substance.

The isocyanate component preferably has an isocyanate content of 8 to 55% by weight. Particularly suitable components are, 4,4'-diphenylmethandiisocyanate, toluylendiisocyanate, napthylene-1 -5-diiso- cyanate and 4,4',4"- triphenylmethantriisocyanante.

Depending on the kind of isocyanate and the processing conditions, a metallo-organic compound, a metal salt and/or an amine or a compound with acidic hydrogen, or other catalyst or accelerator, can be added to the reaction mixture to controi the polymerisation time. If blocked isocyanate compounds are used, the substance preventing or delaying the access of water to the isocyanate, for example a slowly evaporating solvent, can be selected in accordance with or adjusted to the reaction conditions.

According to a second aspect of the present invention there is provided a method of manufacturing marking or erasing implements, comprising the steps of providing two blanks each provided in a mating surface thereof with a row of spaced grooves, the row of grooves of one blank corresponding to the row of grooves of the other blank, introducing into the grooves an isocyanate and at least one compound containing reactive hydrogen, coating the mating surface of at least one of the blanks with an adhesive substance, placing a rod of marking or erasing material in each of the grooves of one of the blanks, disposing the blanks in mutual contact at the mating surfaces thereof, pressing the blanks together while causing or allowing the adhesive substance to cure and the isocyanate to react with the or each said compound thereby to join the blanks together and secure the rods thereto, and cutting the joined blanks into portions each encasing a respective one of the rods.

According to a third aspect of the invention there is provided a method of manufacture of marking or erasing implements, comprising the steps of providing two blanks each provided in a mating surface thereof with a row of spaced grooves, the row of grooves of one blank corresponding to the row of grooves of the other blank, introducing an isocyanate into the grooves, coating the mating surface of at least one of the blanks with an adhesive substance, placing a rod of marking or erasing material in each of the grooves of one of the blanks, the blanks, the rods, or the blank and the rods comprising as a constituent or impregnant thereof at least one compound containing reactive hydrogen, disposing the blanks in mutual contact at the mating surfaces thereof, pressing the blanks together while causing or allowing the adhesive substance to cure and the isocyanate to react with the or each said compound thereby to join the blanks together and secure the rods thereto, and cutting the joined blanks into portions each encasing a respective one of the rods.

If, however, at least the blanks have said at least one compound as a constituent or impregnant, the mating surface of the at least one blank can be coated with an isocyanate rather than an adhesive substance.

Preferably, the gluing of the rods to the blanks and of the blanks to each other is undertaken with the same adhesive substance. The choice of the most suitable procedure depends mainly on the requirements of the production method or on the available equipment.

When merely the rods are to be glued to the blanks by the reaction adhesive, the isocyanate is introduced in metered quantity into the grooves of the blanks, for example boards, the rods are laid in the grooves, and the two blanks are pressed together until the adhesive is solid. In this case, the mating surfaces of the blanks are coated separately with a different adhesive substance, for example polyvinylacetate glue, before pressing of the blanks together.

Heating can be optionally used during the setting process so as to influence this phase of the production, generally by shortening it. Basically, however, heating for solidification of the adhesive is not required, as the particular amenability to reaction of the isocyanate with reactive hydrogen, with functional hydroxyl groups or simply with water effects a complete and relatively rapid polymerisation.

In the case of a polyurethane adhesive, the adhesive results from the following reaction: HO-R-OH + OCN-R'-NCOo + R-O-CO-NH-R'-NH-CO-O+ wherein: R = residue of the hydroxyl group compo nent R' = residue of the isocyanate HO or OH = hydroxyl group NCO or OCN = isocyanate group O-CO-NH = urethane group (N = nitrogen; C = carbon; 0 = oxygen).

(N = nitrogen; C = carbon; O = oxygen).

If a moisture-reactive isocyanate and water are used, then the polymerisation and setting of the adhe sive layer takes place, after the isocyanate has been applied, through moisture in the rods and/or the blanks. In order to control the reaction time so that the rods can be laid in the grooves, the moisture content is appropriately set.

In addition, a decelerator or an accelerator can be admixed to the isocyanate in order to obtain the most suitable reaction time. The reaction moisture, the reactive hydrogen groups or the functional hy droxyl groups for reaction with the isocyanate can be present in the rods, in the blank material or in a suitable impregnating medium for the rods or the blanks.

Alternatively, the moisture or hydrogen or hydroxyl groups can be applied with the isocyanate. A ho mogeneous mixture can then be produced from the two components prior to application, or the two components can be applied separately from each other.

Reaction times can be adapted to requirements, for example through selection and/or modification of the isocyanate or the operating conditions, or through use of appropriate additives.

Embodiments of the implement and example of the methods of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an implement's blank, in which leads have been placed and to which an adhesive substance is being applied; Figure 2 is a perspective view of a further implement's blank to be glued to the blank of Figure 1 with leads sandwiched therebetween; and Figure 3 is a perspective view of the joined blanks and encased leads, the blanks being pressed to gether while the adhesive substance sets.

Referring now to the drawings, a number of examples of methods of manufacturing implements are described in the following, each method having general reference to the manufacturing steps shown in Figures 1 to 3: Example 1 4,4'-diphenylmethandiisocyanate as an adhesive substance component 7 is introduced by means of nozzles 13 into preformed grooves 3 in a blank 1 in the form of a wooden board containing moisture, the grooves being present in a mating surface 5 of the blank. The parts of the surface 5 between the grooves are then coated with aqueous polyvinylacetate dispersion glue, as an adhesive substance 8, by means of a roller 14.

Leads 11 are then laid into the grooves 3 of the blank 1 and covered by a second such blank 2, in the mating surface of which are grooves 4 in which the component 7 is also present. The blanks 1 and 2 are now pressed against each other by press elements 15 and the formation and setting of a reaction adhe sive substance 9, through the polymerisation of the isocyanate by the moisture contained in the wood and the polyvinylacetate dispersion glue, takes place. The leads 11 are thereby firmly glued in place and the battens are joined by the polyvinylacetate adhesive which forms a layer 10. This results in an article 12, which is cut or sawn into individual portions in known manner, each portion containing one of the leads 11 and constituting a pencil. Such pencils can then be shaped as well as, if so desired, lacquered and pointed.

Example 2 4,4'-diphenylmethandiisocyanate as adhesive components 7 and 8 is introduced into the grooves 3 and 4 of the blanks 1 and 2 and coated on their surfaces 5 and 6 between the grooves 3 and 4. After insertion of the leads 11 into the grooves 3 of the blank 1 and placing of the correspondingly treated blank 2 thereon, the blanks are pressed together to produce the article 12.

The formation of both adhesive layers 9 and 10 in this case takes place through the reaction of the isocyanate with moisture contained in the wood of the blanks and/or in the leads 11.

Further processing can take place as in Example 1.

Example 3 The manufacture of the articles 12 is carried out according to Example 2. The leads 11, however, are impregnated before insertion with a polyetherpolyol, which has a viscosity of 800 to 1000 millipascal seconds and an OH-number of 160.

The formation of the adhesive layer 9, between the leads 11 and the blanks 1 and 2 in this case takes place through the reaction of the isocyanate with the hydroxyl groups of the polyetherpolyol, while the formation of the layer 10 between the blanks takes place through the reaction of the moisture in the wood with the isocyanate. A particular advantage of this method of gluing is that the hardness of the glue layer together is variable within wide limits through the choice of appropriate impregnating media.

Consequently, the hardness of the layer 9 and 10 can be adapted to the kind or hardness of the lead and/ or of the blank material.

Example 4 From two different containers, toluylendiisocyanate and polyesterpolyol having a viscosity of 700 to 900 millipascal seconds and an Oh-number of 90 are pumped by way of separate ducts into a two-component low-pressure mixing head and intimately mixed therein. The resulting mixture is introduced into the grooves 3 and 4 of the blanks 1 and 2 and coated on the surfaces 5 and 6 as adhesive substances 7 and 8.

Formation of the adhesive layers, under pressing together of the blanks, takes place through reaction of the isocyanate with the functional hydroxyl groups of the polyester.

Example 5 90 parts by weight of a 50% aqueous polyvinylacetate dispersion with a viscosity of 6000 millipascal seconds are mixed under stirring with 10 parts by weight of a blocked diphenylmethandiisocyanate prepolymer. The resulting mixture is applied and processed as in Example 2 or 3. Formation of the adhesive layer in this case takes place through the reaction of the prepolymer and through the setting of the polyvinylacetate.

Example 6 80 parts by weight of a 20% aqueous polyacrylic acid solution are mixed under stirring with 20 parts by weight of an inhibited 4,4',4"-triphenylmethantriisocyanate prepolymer.

Further processing takes place as in Example 2, wherein the formation of the adhesive layers 9 and 10 takes place through the reaction of the prepolymer with the acrylate and the water of the polyacrylic acid solution.

Example 7 For the manufacture of pencils as in Example 3, the leads 11 are impregnated with a polyethylenimine which has a viscosity of 600 to 1000 millipascal seconds.

In this case, the setting of the reaction adhesive substance takes place through reaction of the isocyanate with the imine groups of the impregnating medium.

Example 8 The blanks 1 and 2 are impregnated with a saturated solution of polyaminotriazole. After application of isocyanate as adhesive components 7 and 8 and after insertion of the lead 11, the formation of the layers 9 and 10, under pressing together of the blanks, takes place through the reaction of the isocyanate with the amino-groups of the impregnating medium.

As a result of carbon dioxide separation, which usually takes place during the reaction, the adhesive substances used in the aforesaid Examples has a microporous foam structure. As a result, the set layer of adhesive remains relatively soft and eiastic within certain limits. For this reason, the grooves in the blanks can, if desired, be produced to be larger than required, i.e. in greater tolerance ranges than hitherto, without resulting in unduly hard adhesive layers around the marking or erasing rods or between the casing parts. Through the affinity of the reaction adhesive substance to the casing material and the rods and of the urethane molecules to each other, the resulting porous adhesive layer has good or adequate strength and effects a secure connection between the rod and the casing.

Apart from wood, plastics material or metal can be used as the casing material.

Equally, the casings can be formed by methods other than gluing blanks together. For example, cas ings can be extruded or injection-moulded from thermoplastic plastics material. In this case, the adhesive substance components can be applied separately or together to the rod or into the casing bore.

Equally well, of course, the casings can be produced from more than two parts. The reaction adhesive used in implements embodying the invention can be part of an adhesive mixture, which may contain only a certain proportion of the reaction adhesive.

For adjustment of the hardness of the reaction adhesive, otherwise than by any impregnating medium that is present, the choice of the reaction component for the isocyanate is of particular importance.

Equally, the particular type of isocyanate can influence the hardness of the adhesive layer.

In the case of blocked prepolymers, the isocyanate component and the hydrogen-containing component of the adhesive substance can be present already mixed and, if so desired, as an aqueous dispersion. In that case, the wetting usually arises only as a result of additional heating or through the addition of a third component, which in some circumstances may contain isocyanate.

If the adhesive components are present separately, then the mixing ratio of the isocyanate component and a reaction component containing functional hydroxyl groups should be such that an excess of isocyanate is always present so that all hydroxyl groups are bound with certainty. The excess isocyanate can react with moisture in the air.

Casings of metal can in some circumstances be formed as pure grip elements, for example for thick leads or for crayons, in which case repointing is not envisaged.

Embraced by the expression marking or erasing implements are, apart from all writing pencils, painting pencils, cosmetic pencils and crayons provided with colour-delivering rods, also pencils having rods which do not include a colour-delivering substance. These include erasing pencils, in which a strand of plastics material, rubber or similar is glued into a shank of wood or plastics material, and pencils having rods constructed as, for example marking needles of metal or other hard material, or rods which contain a chemically acting correcting substance bound in solid material.

In certain cases, rods can have only a coating layer of the reaction adhesive substance, in which case part of this layer represents the casing of the rod.

Claims

1. A marking or an erasing implement comprising an elongate casing and a rod of marking or erasing material encased in the casing and secured thereto by an adhesive substance comprising a poly-reaction product of an isocyanate with at least one compound containing reactive hydrogen.

2. An implement as claimed in claim 1, wherein the adhesive substance comprises a poly-addition product of an isocyanate with at least one of water, an imino compound, an amino compound, a carboxy compound and a hydroxy compound, each such compound containing reactive hydrogen.

3. An implement as claimed in claim 1, wherein the adhesive substance comprises a poly-condensation product of a reactive isocyanate with water.

4. An implement as claimed in claim 2, wherein the adhesive substance comprises a poly-reaction product of an isocyanate and a functional hydroxyl group which is present before the reaction as a constituent or an impregnant of one of the casing and the rod.

5. An implement as claimed in claim 2, wherein the adhesive substance comprises a poly-addition product of an isocyanate with at least one of polyaminotriazole, polyethylenimine, polycarboxylic acid, polyetherpolypol, polyesterpolypol, polyesteramide and polyesteramine, each such polymer compound containing reactive hydrogen.

6. An implement as claimed in claim 5, the compound or compunds reacted with the isocyanate having a hydroxyl number of 20 to 400.

7. An implement as claimed in either claim 1 or claim 2, wherein the adhesive substance comprises a poly-reaction product of a blocked isocyanate compound and an aqueous plastics material dispersion.

8. An implement as claimed in claim 7, wherein the isocyanate compound is a prepolymer.

9. An implement as claimed in claim 8, wherein the isocyanate of the prepolymer is diphenylmethandiisocyanate.

10. An implement as claimed in any one of the preceding claims, wherein the isocyanide is a compound having an isocyanate content of 8 to 55 percent by weight.

11. An implement as claimed in any one of claims 1 to 6 and 10, wherein the isocyanate is one of 4,4'- diphenylmethandiisocyanate, toluylendiisocyanate, naphthylene-1-5-diisocyanate and 4,4',4"-triphen ylmethantriisocyanate.

12. An implement as claimed in any one of the preceding claims, wherein the isocyanate is reacted with said at least one hydrogen-containing compound in the presence of one of a catalyst and an accelerator.

13. An implement as claimed in claim 12, wherein the catalyst or accelerator is one of a metallo-or ganic compound, a metal salt, an amine and a compound containing acidic hydrogen,

14. An implement as claimed in any one of the preceding claims, wherein the casing comprises a plurality of parts secured together by the adhesive substance.

15. A marking or an erasing implement substantially as hereinbefore described with reference to any one of Examples 1 to 8.

16. A method of manufacturing marking or erasing implements, comprising the steps of providing two blanks each provided in a mating surface thereof with a row of spaced grooves, the row of grooves of one blank corresponding to the row of grooves of the other blank, introducing into the grooves an isocyanate and at least one compound containing reactive hydrogen, coating the mating surface of at least one of the blanks with an adhesive substance, placing a rod of marking or erasing material in each of the grooves of one of the blanks, disposing the blanks in mutual contact at the mating surfaces thereof, pressing the blanks together while causing or allowing the adhesive substance to cure and the isocyanate to react with the or each said compound thereby to join the blanks together and secure the rods thereto, and cutting the joined blanks into portions each encasing a respective one of the rods.

17. A method as claimed in claim 16, wherein the step of introducing comprises introducing a homogeneous mixture of an isocyanate and at least one of polyaminotriazole, polyethylenimine, polycarboxylic acid, polyetherpolypol, polyesterpolypol, polyesteramide and polyesteramine, each such polymer compound containing reactive hydrogen.

18. A method as claimed in claim 16, wherein the step of introducing comprises introducing an isocyanate dispersion system, the isocyanate thereof being caused or allowed to react with the moisture of the dispersion compounds.

19. A method as claimed in any one of claims 16 to 18, wherein said adhesive substance comprises an isocyanate and at least one compound containing reactive hydrogen.

20. A method of manufacture of marking or erasing implements, comprising the steps of providing two blanks each provided in a mating surface thereof with a row of spaced grooves, the row of grooves of one blank corresponding to the row of grooves of the other blank, introducing an isocyanate into the grooves, coating the mating surface of at least one of the blanks with an adhesive substance, placing a rod of marking or erasing material in each of the grooves of one of the blanks, the blanks, the rods, or the blank and the rods comprising as a constituent or impregnant thereof at least one compound containing reactive hydrogen, disposing the blanks in mutual contact at the mating surfaces thereof, pressing the blanks together while causing or allowing the adhesive substance to cure and the isocyanate to react with the or each said compound thereby to join the blanks together and secure the rods thereto, and cutting the joined blanks into portions each encasing a respective one of the rods.

21. A method of manufacture of marking or erasing implements, comprising the steps of providing two blanks each provided in a mating surface thereof with a row of spaced grooves, the row of grooves of one blank corresponding to the row of grooves of the other blank, introducing an isocyanate into the grooves, coating the mating surface of at least one of the blanks with an isocyanate, placing a rod of marking or erasing material in each of the grooves of one of the blanks, the blanks or the blanks and the rods comprising as a constituent or impregnant thereof at least one compound containing reactive hydrogen, disposing the blanks in mutual contact at the mating surfaces thereof, pressing the blanks together while causing or allowing the isocyanate to react with the or each said compound thereby to join the blanks together and secure the rods thereto, and cutting the joined blanks into portions each encasing a respective one of the rods.

22. A method as claimed in either claim 20 or claim 21, wherein said at least one compound is water.

23. A method as claimed in either claim 20 or claim 21, wherein said at least one compound is a hydroxyl group.

24. A method as claimed in any one of claims 16 to 23, comprising the step of initially heating the blanks to promote curing of the adhesive substance and reaction of the isocyanate and said at least one compound.

25. A method as claimed in any one of claims 16 to 24, comprising the step of shaping the cut portions of the joined blanks.

26. A method as claimed in any one of claims 16 to 25, comprising the step of forming a point at each cut portion of the joined blanks.

27. A method as claimed in any one of claims 16 to 26, comprising the step of coating the cut portions of the joined blanks with lacquer.

28. A method of manufacturing marking or erasing implements, the method being substantially as hereinbefore described with reference to any one of Examples 1 to 8.

29. A method of manufacturing marking or erasing implements, the method being substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

30. A marking or erasing implement when manufactured by a method as claimed in any one of claims 16 to 29.