WAX CRAYON COMPRISING ZRO2

Abstract

The present disclosure relates to a writing instrument comprising a lead, wherein the lead comprises at least about 0.5 wt.-% ZrO.sub.2, relative to the total weight of the lead, in particular wherein the lead comprises less than about 0.5 wt.-%, more specifically less than about 0.2 wt.-% and in particular substantially no or no TiO.sub.2.

Claims

1. A writing instrument comprising a lead, wherein the lead comprises at least about 0.5 wt.-% ZrO.sub.2, relative to the total weight of the lead.

2.-15. (canceled)

16. The writing instrument according to claim 1, wherein the lead comprises less than about 0.5 wt.-% of TiO.sub.2, relative to the total weight of the lead.

17. The writing instrument according to claim 1, wherein the lead comprises 1) substantially no TiO.sub.2 or 2) no TiO.sub.2.

18. The writing instrument according to claim 1, wherein the lead comprises between about 1 wt.-% to about 25 wt.-% of ZrO.sub.2, relative to the total weight of the lead.

19. The writing instrument according to claim 1, wherein an external surface of the lead has an L*-value of at least 40 and wherein the lead comprises between about 11.0 wt.-% to about 20 wt.-% of ZrO.sub.2, relative to the total weight of the lead.

20. The writing instrument according to claim 1, wherein the external surface of the lead has an L*-value of less than 40 and wherein the lead comprises between about 0.5 wt.-% to about 10.9 wt.-% of ZrO.sub.2, relative to the total weight of the lead.

21. The writing instrument according to claim 1, wherein the lead comprises the ZrO.sub.2 in the form of particles.

22. The writing instrument according to claim 21, wherein the ZrO.sub.2 particles have a D.sub.50 between about 0.1 m to about 17 m.

23. The writing instrument according to claim 21, wherein the ZrO.sub.2 particles have a D.sub.50 between about 0.2 m to about 10 m.

24. The writing instrument according to claim 21, wherein the ZrO.sub.2 particles have a D.sub.50 between about 0.5 m to about 50 m.

25. The writing instrument according to claim 21, wherein the ZrO.sub.2 particles have a BET-value between about 0.5 m.sup.2/g to about 22 m.sup.2/g measured according to DIN ISO 9277:2014-01.

26. The writing instrument according to claim 21, wherein the ZrO.sub.2 particles have a BET-value between about 2.5 m.sup.2/g to about 20 m.sup.2/g, measured according to DIN ISO 9277:2014-01.

27. The writing instrument according to claim 1, wherein the lead has a diameter between about 5 mm to about 35 mm.

28. The writing instrument according to claim 1, wherein the lead comprises about 0.005 wt.-% to about 3.45 wt.-% of one or more metal oxides or transition metal oxide from the second, third, fourth and/or thirteenth group of the periodic table, relative to the total weight of the lead.

29. The writing instrument according to claim 1, wherein the lead comprises between about 10 wt.-% to about 90 wt.-% of one or more waxes, relative to the total weight of the lead.

30. The writing instrument according to claim 1, wherein the lead comprises between about 10 wt.-% to about 45 wt.-% of one or more waxes, relative to the total weight of the lead.

31. The writing instrument according to claim 1, wherein the lead comprises between about 1 wt.-% to about 20 wt.-% of a fatty acid or salt thereof, relative to the total weight of the lead.

32. The writing instrument according to claim 1, wherein the lead comprises between about 5 wt.-% to about 30 wt.-% of a hydrous aluminum phyllosilicate relative to the total weight of the lead.

33. The writing instrument according to claim 1, wherein the lead comprises between about 0.05 wt.-% to about 10 wt.-% of one or more pigments, relative to the total weight of the lead.

34. The writing instrument according to claim 1, wherein the lead comprises between about 3 wt.-% to about 50 wt.-% of a binder relative to the total weight of the lead.

Description

DETAILED DESCRIPTION

[0044] Hereinafter, a detailed description will be given of the present disclosure. The terms or words used in the description and the aspects of the present disclosure are not to be construed limitedly as only having common-language or dictionary meanings and should, unless specifically defined otherwise in the following description, be interpreted as having their ordinary technical meaning as established in the relevant technical field. The detailed description will refer to specific embodiments to better illustrate the present disclosure, however, it should be understood that the presented disclosure is not limited to these specific embodiments.

[0045] Writing instruments such as pencils, wax crayons or chalks comprise or consist of a solid pigment core, also referred to as a lead. The writing instruments comprising a lead are used to create markings by rubbing the lead against a substrate, such as a piece of paper. To adjust the lightness of a lead and its deposit, TiO.sub.2 is typically used as an effective whitening pigment.

[0046] However, recently concerns have emerged that TiO.sub.2 dust may possible be carcinogenic to humans. During the production of leads comprising TiO.sub.2, in particular during the mixing of the structural component with the TiO.sub.2, TiO.sub.2 dust may be generated, which may be harmful to manufacturing personnel. Further, in some jurisdictions TiO.sub.2 in powder form has been banned to be used above certain concentration due to concern about a carcinogenic risk by inhalation. For example, the EU has placed a limit on the use of TiO.sub.2 powder at 1 wt.-% or the product must be labelled as comprising possible carcinogens, even if the TiO.sub.2 cannot become airborne from the product. As a result, an alternative for TiO.sub.2 to adjust the lightness of leads is required.

[0047] However, exchanging TiO.sub.2 for other white colorants, in particular pigments, is not straightforward since white colorants cannot be used interchangeably. Alternative white colorants may not be equally effective in improving the lightness of the lead and/or the lead's deposit. Further, alternative white colorants may lead to other discoloration, in particular a yellowish tinge, of the lead and/or the lead's deposit. To make matters worse, TiO.sub.2 is an almost ideal white colorant since it is effective in providing leads, in which the lead's color is perceived very similar to the formed deposit. This may make it easier for users to choose between different colors and predicting how the markings will look. Alternative white colorants can result in leads, where the perceived color of the lead varies strongly from the lead's deposit. Surprisingly, it has been found that zirconium dioxide, ZrO.sub.2, may be an effective white pigment to increase the lightness of leads, in particular in comparatively low amounts. Further, ZrO.sub.2 may not lead to a significant other discoloration. Additionally, ZrO.sub.2 may allow producing leads, wherein the perceived color of the lead does not strongly vary from the color perceived from the lead's deposit on e.g. paper.

[0048] Accordingly, in a first aspect, the present disclosure relates to a writing instrument comprising a lead, wherein the lead may comprise at least about 0.5 wt.-% ZrO.sub.2, relative to the total weight of the lead, in particular wherein the lead may comprise less than about 0.5 wt.-%, more specifically less than about 0.2 wt.-% and in particular substantially no or no TiO.sub.2.

[0049] In some embodiments, the lead may comprise between about 1 wt.-% to about 25 wt.-%, more specifically between about 2 wt.-% to about 20 wt.-%, even more specifically between about 5 wt.-% to about 20 wt.-%, and in particular between about 11 wt.-% to about 15 wt.-% ZrO.sub.2, relative to the total weight of the lead. A higher proportion of ZrO.sub.2 may result in a lighter lead.

[0050] The lightness and the color of the lead in general may be defined as per the CIELAB or CIELCh color space. The CIELAB color space, also referred to as L*a*b*, is a color space defined by the International Commission on Illumination. The color space is designed to approximate human vision. The CIELAB color space defines color in term of three coordinates L*, a* and b*. L* represents the lightness of the color. An L*=0 yields black and an L*=100 indicates diffuse white. Specular white may attain L* values above 100. a* defines a color's position between red and green. A negative a* value indicates green and positive values indicate red. b* defines a color's position between blue and yellow. A negative b* value indicates blue and positive values indicate yellow.

[0051] The CIELCh color space is based on the CIELAB color space. In the CIELCh color space the lightness L* remains unchanged. However, the a* and b* are converted into the polar coordinates C*, for chroma/relative saturation, and h for hue angle/angle of the hue in the CIELAB color wheel. The term chroma within this disclosure is well-known in the art and attributed its common meaning in this technical field. In some embodiments, the term chroma may refer to colorfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears white or highly transmitting.

[0052] The C* may be derived from a* and b* by formula I:

[00001]$\begin{array}{cc}{C}^{*}=\sqrt{a^2+b^2}& \left(I\right)\end{array}$

[0053] The h may be derived from a* and b* by formula II:

[00002]$\begin{array}{cc}{h}^{}=\mathrm{atan}\left(\frac{b^{*}}{a^{*}}\right)& \left(\mathrm{II}\right)\end{array}$

[0054] Further, based on the L*, a* and b* value a color-difference E.sub.00* can be calculated based on ISO/CIE 11664-6:2014Colorimetry Part 6: CIEDE2000 Colour-difference formula. The ISO/CIE 11664-6:2014Colorimetry Part 6: CIEDE2000 Colour-difference formula, in particular the Colour-difference formula, are incorporated herein by reference.

[0055] A protocol for measuring the L*, a* and b* value is provided in the experimental section.

[0056] In some embodiments, an external surface of the lead may have an L*-value of at least 40 and wherein the lead comprises between about 11.0 wt.-% to about 20 wt.-%, more specifically between about 11 wt.-% to about 18 wt.-% and in particular between about 12 wt.-% to about 15 wt.-% ZrO.sub.2, relative to the total weight of the lead.

[0057] In some embodiments, the external surface of the lead may have an L*-value of less than 40 and wherein the lead comprises between about 0.5 wt.-% to about 10.9 wt.-%, more specifically between about 1 wt.-% to about 9 wt.-% and in particular between about 2 wt.-% to about 8 wt.-% ZrO.sub.2, relative to the total weight of the lead.

[0058] In some embodiments, the lead may comprise the ZrO.sub.2 in the form of particles.

[0059] In some embodiments, the ZrO.sub.2 particles may have a D.sub.50 between about 0.1 m to about 17 m, more specifically between about 0.2 m to about 10 m and even more specifically between about 0.3 m to about 7 m, in particular between about 0.3 m to about 5 m, in particular between about 0.4 m to about 5 m, and in particular between about 0.4 m to about 2 m. D.sub.50 is a measure for the particle size. Of a given sample, 50% of the particles have a particle size above the D.sub.50 and 50% have a particle size below D.sub.50. It has been surprisingly found that the particle size may influence the color of the lead. In particular, ZrO.sub.2 of a smaller particle size may lead to an increased L*-value of the lead compared to ZrO.sub.2 of a greater particle size. Hence, ZrO.sub.2 of a smaller particle size may produce leads of lighter colors compared to ZrO.sub.2 of greater particle size or ZrO.sub.2 of a smaller particle size may be used in smaller amounts compared to ZrO.sub.2 of greater particle size. Often leads are significantly darker compared to their deposit, in particular as the lightness of the deposit may be aided by the white color of the paper the deposit is formed upon. However, it may be preferable to produce leads of lighter colors as these more closely resemble the color of the final deposit. Further, the color of leads with a low L* may be harder to distinguish from other colors compared to leads with a higher L*. For example, two wax crayons may both produce a blue deposit of the same color, but a first wax crayon appears darker than a second wax crayon. It may be difficult for a user to distinguishing the first darker wax crayon from for example a black wax crayon.

[0060] It has been further surprisingly found, that for leads comprising ZrO.sub.2 particles of a smaller particle size the color difference quantified as E.sub.00 may be smaller between the lead and the deposit created by the lead. A smaller color difference E.sub.00 may make it easier for a user to determine the color of a deposit a lead will produce by looking at the lead. Wax crayons are commonly supplied without a casing and may not even comprise a wrapping or the wrapping may be removed. As a result, the only way to distinguish wax crayons from one another and/or to determine which color the deposit may create, may be by looking at the surface of the wax crayon.

[0061] In some embodiments, the ZrO.sub.2 particles may have a D.sub.90 between about 0.5 m to about 50 m, more specifically between about 0.5 m to about 15 m, in particular 1 m to about 3 m. D.sub.90 is a measure for the particle size. Of a given sample, 10% of the particles have a particle size above the D.sub.90 and 90% have a particle size below D.sub.90.

[0062] In some embodiments, the D.sub.50 and D.sub.90 may be measured according to ISO 13320:2020.

[0063] In some embodiments, the ZrO.sub.2 particles may have a BET-value between about 0.5 m.sup.2/g to about 22 m.sup.2/g, more specifically between about 2.5 m.sup.2/g to about 20 m.sup.2/g, in particular about 4 m.sup.2/g to about 20 m.sup.2/g, and in particular about 4 m.sup.2/g to about 18 m.sup.2/g, measured according to DIN ISO 9277:2014-01. The BET-value is a measure for the specific surface area of a material, for example for ZrO.sub.2 particles. It has been surprisingly found, that leads comprising ZrO.sub.2 particles of an increased BET-value the hue h* may be similar between the lead and an otherwise equal lead comprising TiO.sub.2 in the amount of weight. Hence, it may be easier for suppliers to adjust their lead compositions by exchanging TiO.sub.2 with the same amount of ZrO.sub.2 particles.

[0064] In some embodiments, the lead may have a coefficient of friction between about 0.414 to about 0.5, more specifically between about 0.420 to about 0.48 and in particular between about 0.43 to about 0.46. An increased coefficient of friction may result in a greater deposit per area when marking a substrate. A greater deposit per area may increase the visibility and/or color intensity of the made marking. The coefficient of friction may be measured as described in the Experimental Section.

[0065] In some embodiments, the writing instrument may be a wax crayon.

[0066] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may have a diameter between about 5 mm to about 35 mm, more specifically between about 6 mm to about 20 mm and in particular 7 mm to about 12 mm.

[0067] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 10 wt.-% to about 90 wt.-% of one or more waxes, relative to the total weight of the lead.

[0068] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 50 wt.-% to about 95 wt.-%, more specifically, between about 60 wt.-% to about 90 wt.-% and in particular between about 70 wt.-% to about 85 wt.-% of one or more waxes, relative to the total weight of the lead.

[0069] In some further alternative embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 10 wt.-% to about 45 wt.-%, more specifically, between about 15 wt.-% to about 40 wt.-% and in particular between about 20 wt.-% to about 30 wt.-% of one or more waxes, relative to the total weight of the lead.

[0070] The term wax, in the present disclosure is intended to be used as is well-established in the field of writing instruments and is, in particular, meant to refer to a lipophilic (fatty) compound that is solid at e.g. room temperature (e.g. about 25 C.) with a reversible solid/liquid change of state. The method of measuring the melting point of the wax is not particularly limited and may be measured using a differential scanning calorimeter (DSC), in some embodiments, the calorimeter sold under the name DSC 3 by the company Mettler Toledo.

[0071] Amongst the aforementioned waxes, the present disclosure relates to waxes having a melting point of at least about 40 C. and a solubility water at about 25 C. of less than about 1000 mg/L. These properties may help in providing a relatively water-insoluble solid base matrix for the writing instrument, in particular for a wax crayon, for the dispersion of the pigment therein. In some embodiments, the one or more waxes may have a melting point of at least about 35 C., more specifically at least about 50 C. and in particular at least about 75 C. In some embodiments, the wax may have a melting point range of between about 35 C. and about 200 C., more specifically between about 55 C. and about 180 C., and in particular between about 75 C. and about 150 C.

[0072] In some embodiments, the wax may have a solubility in water at about 25 C. of less than about 100 mg/L, more specifically a solubility of less than about 10 mg/L, and in particular a solubility of less than about 1 mg/L. In some embodiments, the wax may be substantially insoluble or insoluble in water at about 25 C. The method of determining the solubility of the wax is not particularly limited and may be performed by any suitable means, for instance using a USP Dissolution Apparatus 2 (paddle type).

[0073] In some embodiments, the one or more waxes may comprise one or more apolar waxes. In some embodiments, such apolar waxes include paraffin waxes, microcrystalline waxes, ozokerine and Fisher-Tropsch waxes. Apolar waxes may be hydrocarbon-based and may be substantially free or free of polar groups.

[0074] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 10 wt.-% to about 45 wt.-%, more specifically, between about 15 wt.-% to about 35 wt.-% and in particular between about 18.5 wt.-% to about 27 wt.-% of a polymer, more specifically a thermoplast even more specifically an olefine and in particular polyethylene or polypropylene, relative to the total weight of the lead. The polymer may increase the leads resistance to breaking. The addition of the polymer may increase the leads modulus of elasticity and/or hardness.

[0075] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 1 wt.-% to about 20 wt.-%, more specifically, between about 3 wt.-% to about 17 wt.-% and in particular between about 5 wt.-% to about 15 wt.-% of a fatty acid or salt thereof, relative to the total weight of the lead.

[0076] In some embodiments, in particular wherein the writing instrument is a wax crayon, the fatty acid or salt may comprise a monovalent linear or branched saturated or unsaturated carboxylic acid salt having between about 8 to about 24 carbon atoms, more specifically a monovalent linear saturated carboxylic acid salt having between about 16 to about 20 carbon atoms, and in particular stearic acid, calcium stearate, zinc stearate or mixtures thereof. The fatty acid and/or fatty acid salts may improve the smoothness of writing and/or drawing, in particular by improving the glide. Moreover, the fatty acid and/or fatty acid salt may increase the laydown and thereby the quality of the deposit. Fatty acids may migrate to the surface of the lead, which may lead to the formation of a fatty film, which may be unpleasant to the user. Fatty acid salts may be in some instances advantageous as they have a reduced tendency to migrate to the surface of the lead.

[0077] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise a filler, in particular a hydrous aluminum phyllosilicate and/or an alkali and/or earth alkali carbonate.

[0078] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 10 wt.-% to about 50 wt.-%, more specifically, between about 17 wt.-% to about 40 wt.-% and in particular between about 23.5 wt.-% to about 32 wt.-% of the filler, relative to the total weight of the lead. Some fillers, in particular kaolinite, may comprise a layered structure. As a result, filler, such as kaolinite, may improve the laydown of a lead by providing surfaces where along shearing action may occur. Additionally, the fillers may decrease the price of the lead.

[0079] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 5 wt.-% to about 30 wt.-%, more specifically, between about 10 wt.-% to about 25 wt.-% and in particular between about 15 wt.-% to about 20 wt.-% of the hydrous aluminum phyllosilicate, more specifically a layered hydrous aluminum phyllosilicate and in particular kaolinite, relative to the total weight of the lead. In some embodiments, the hydrous aluminum phyllosilicate may be at least partly or fully substituted in mica and/or talc.

[0080] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 5 wt.-% to about 20 wt.-%, more specifically, between about 7 wt.-% to about 15 wt.-% and in particular between about 8.5 wt.-% to about 12 wt.-% of the alkali and/or earth alkali carbonate, more specifically an earth alkali carbonate and in particular calcium carbonate, relative to the total weight of the lead.

[0081] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 0.5 wt.-% to about 5 wt.-%, more specifically between about 1 wt.-% to about 3.5 wt.-% and in particular between about 1.5 wt.-% to about 2.5 wt.-% of a plasticizer, more specifically of a phthalic acid ester and in particular of C.sub.7-C.sub.9 alkyl benzyl phthalate, relative to the total weight of the lead. The plasticizer may soften the lead and thereby increase the laydown of the lead, which in turn may improve the visibility and/or intensity of the deposit.

[0082] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 2 wt.-% to about 20 wt.-%, more specifically between about 4 wt.-% to about 15 wt.-% and in particular between about 7 wt.-% to about 11 wt.-% of a processing aid, more specifically a lubricant and in particular tetrastearate pentaerythritol. The processing aid may improve manufacturing efficiency of the lead. In particular, as the ZrO.sub.2 has been shown to lead to a higher coefficient of friction, the manufacturing may be improved by adding processing aids, more specifically a lubricant and in particular tetrastearate pentaerythritol.

[0083] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 0.05 wt.-% to about 10 wt.-%, more specifically between about 0.05 wt.-% to about 7 wt.-% and in particular between about 0.1 wt.-% to about 5 wt.-% of one or more colorants, relative to the total weight of the lead.

[0084] In some embodiments, in particular wherein the writing instrument is a wax crayon, the lead may comprise between about 0.05 wt.-% to about 10 wt.-%, more specifically between about 0.05 wt.-% to about 7 wt.-% and in particular between about 0.1 wt.-% to about 5 wt.-% of one or more pigments, relative to the total weight of the lead. The one or more colorant and/or pigments may adjust the color of the lead. For example, the addition of a blue pigment may lead to a blue lead. The term pigment and colorant used within this disclosure are well known in the art. Within this disclosure the proportions attributed to pigments and colorants shall not apply to ZrO.sub.2 or TiO.sub.2.

[0085] In some embodiments, in particular wherein the writing instrument is a pencil, the writing instrument may comprise a casing and the lead may be comprised within the casing.

[0086] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may have a diameter of between about 2.0 mm to about 4.5 mm, more specifically between about 2.3 mm to about 4.2 mm and in particular between about 2.8 mm to about 4.0 mm.

[0087] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 5 wt.-% to about 80 wt.-%, more specifically, between about 5 wt.-% to about 60 wt.-%, more specifically, between about 10 wt.-% to about 55 wt.-% and in particular between about 15 wt.-% to about 50 wt.-% of a hydrous aluminum phyllosilicate, more specifically a layered hydrous aluminum phyllosilicate and in particular kaolinite, relative to the total weight of the lead. In some embodiments, the hydrous aluminum phyllosilicate may be at least partly or fully substituted in mica and/or talc.

[0088] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 1 wt.-% to about 20 wt.-%, more specifically, between about 3 wt.-% to about 17 wt.-% and in particular between about 5 wt.-% to about 15 wt.-% of a fatty acid or salt thereof, relative to the total weight of the lead.

[0089] In some embodiments, in particular wherein the writing instrument is a pencil, the fatty acid or salt may comprise a monovalent linear or branched saturated or unsaturated carboxylic acid salt having between about 8 to about 24 carbon atoms, more specifically a monovalent linear saturated carboxylic acid salt having between about 16 to about 20 carbon atoms, and in particular stearic acid, calcium stearate, zinc stearate or mixtures thereof.

[0090] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 5 wt.-% to about 30 wt.-%, more specifically, between about 10 wt.-% to about 25 wt.-% and in particular between about 13 wt.-% to about 17 wt.-% of one or more colorants, relative to the total weight of the lead.

[0091] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 5 wt.-% to about 30 wt.-%, more specifically, between about 10 wt.-% to about 25 wt.-% and in particular between about 13 wt.-% to about 17 wt.-% of one or more pigments, relative to the total weight of the lead.

[0092] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 3 wt.-% to about 50 wt.-%, more specifically, between about 10 wt.-% to about 50 wt.-%, more specifically, between about 15 wt.-% to about 45 wt.-% and in particular between about 20 wt.-% to about 40 wt.-% of a binder, more specifically a polymeric binder, and in particular styrenic polymers such as polystyrene and/or acrylonitrile butadiene styrene, relative to the total weight of the lead.

[0093] In some embodiments, in particular wherein the writing instrument is a pencil, the lead may comprise between about 0.5 wt.-% to about 10 wt.-%, more specifically between about 2 wt.-% to about 8 wt.-% and in particular between about 3.5 wt.-% to about 6.5 wt.-% of a plasticizer, more specifically of a benzoate ester.

[0094] In some embodiments, the writing instrument may be a chalk.

[0095] In some embodiments, the lead may comprise about 0.005 wt.-% to about 3.45 wt.-% of one or more metal oxides or transition metal oxide from the second, third, fourth and/or thirteenth group of the periodic table, relative to the total weight of the lead.

[0096] In some embodiments, the lead may comprise about 1.0 wt.-% to about 14.6 wt.-% of one or more metal oxides or transition metal oxides from the second, third, fourth and/or thirteenth group of the periodic table, relative to the total weight of the ZrO.sub.2.

[0097] In some embodiments, the lead may comprise Y.sub.2O.sub.3, HfO.sub.2, MgO, CaO and/or Ce.sub.2O.sub.3, in particular HfO.sub.2 and/or Y.sub.2O.sub.3, and in particular Y.sub.2O.sub.3. The aforementioned metal oxides and/or transition metal oxides may be used to increase the mechanic properties of the ZrO.sub.2. For writing instruments, in particular chalks or pencils, this may be useful as the ZrO.sub.2 may not only constitute the pigment, but also a structural component. As a result, the mechanical stability of the lead may be increased. The ZrO.sub.2 may be stabilized prior to the addition of the pigment to the lead or the process may occur during manufacturing of the lead, in some embodiments, during the calcination.

[0098] In some embodiments, the lead may be devoid, or substantially devoid of MgO and/or CaO.

[0099] In some embodiments, the lead may comprise less than 0.05% of SiO.sub.2, more specifically less than 0.04% of SiO.sub.2, and even more specifically less than 0.03% of SiO.sub.2, relative to the total weight of the lead.

[0100] In some embodiments, the lead may comprise ZnO and/or ZnS. ZnO and ZnS may further increase the colorimetric properties of the lead, in particular the L*-value.

EXPERIMENTAL SECTION

[0101] Experiments to determine the influence of different ZrO.sub.2 compositions on the colorimetric values and coefficient of friction of leads were performed. The results were also compared to a TiO.sub.2 composition. Wax crayon compositions were used for the tests. The compositions are provided in Table 2.

Manufacturing of Test Specimen:

[0102] The following steps were performed to manufacture the test specimen with a composition according to Table 2: [0103] 1) Mix all components. [0104] 2) Set a thermostatic bath (For example, AMETEK Brookfield TC-202) to a temperature of 150 C. and add a mixing vessel into the thermostatic bath. [0105] 3) Add the mixture to the mixing vessel in the thermostatic bath. [0106] 4) Stir the mixture of neutral base and colorant at 2000 rpm with a butterfly tool attached to the DISPERMAT CV3 Plus by VMA-Getzmann GmbH for 2 hours. [0107] 5) Remove butterfly tool and fill molten mixture into a cubic mold of the dimensions: 25 mm100 mm10 mm. [0108] 6) Let mixture cool and subsequently remove the finished specimen from the mold.

[0109] Table 1 shows the properties of different types of ZrO.sub.2 and TiO.sub.2 used to manufacture the Test specimen according to Table 2.

TABLE-US-00001 TABLE 1 Properties of ZrO.sub.2 powders. ZrO.sub.2 ZrO.sub.2 ZrO.sub.2 ZrO.sub.2 ZrO.sub.2 TiO.sub.2 powder for powder for powder for powder for powder for powder for Composition Composition Composition Composition Composition Composition A B C D E F D50 0.5 m 0.5 m 4.0 m 6.9 m 16.5 m 0.484 m D90 <2.0 m <2.0 m 7.6 m 20.5 m <100 m 1.069 m BET-value 14-18 m.sup.2/g 4-8 m.sup.2/g 3-5 m.sup.2/g <3 0.5-4 4.4 m.sup.2/g

TABLE-US-00002 TABLE 2 Compositions of Test Specimen for Tests Comp. A Comp. B Comp. C Comp. D Comp. E Comp. F Component [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] Wax 27.10 27.10 27.10 27.10 27.10 27.10 Polyolefine 23.50 23.50 23.51 23.51 23.50 23.50 Fatty Acid Salt 7.2 7.2 7.2 7.2 7.2 7.2 Plasticizer 2.00 2.00 2.00 2.00 2.00 2.00 Pigment (PV23) 0.15 0.15 0.15 0.15 0.15 0.15 Pigment (PR 57:1) 0.02 0.02 0.02 0.02 0.02 0.02 ZrO.sub.2 A 11.99 ZrO.sub.2 B 11.99 ZrO.sub.2 C 11.99 ZrO.sub.2 D 11.99 ZrO.sub.2 E 11.99 TiO.sub.2 11.99 Fillers QSP 100% QSP 100% QSP 100% QSP 100% QSP 100% QSP 100%

Colorimetry of DepositsTest Setup:

[0110] All colorimetric measurements on deposits have been performed on deposits created on a white paper AURORA ISO-12757.

[0111] To create the deposit a Writing apparatus HST 10 by the company HUTT Maschinenbau from Germany was used under the conditions described in Table 3. Further, to measure the colorimetric data in the CIE L*a*b* color space, e.g. L*, a* and b*a KONICA MINOLTA CM-3610 A spectrophotometer was used. The following setting were applied for the KONICA MINOLTA CM-3610 A spectrophotometer: [0112] illuminant: D65, [0113] angle: 10, [0114] specular components: included.

TABLE-US-00003 TABLE 3 Parameters for producing the deposits for colorimetry. Parameters for producing the deposits Article type Composition According to Table 2 Paper feed (mm/min) 20 Writing speed 4.5 m/min Writing angle 70 Total weight support/additional 340 +/ 5 weight (g) Writing length for axial rotation 7 of the article (m) Writing length (m) in a spiral 25 pattern

[0115] The test for the deposit's colorimetric measurement was carried out by the following protocol: [0116] 1. Place the writing article in the appropriate supports; [0117] 2. Produce a deposit according to the parameters specified in Table 3; [0118] 3. Measure the colorimetric data of the deposit with the KONICA MINOLTA CM-3610 A spectrophotometer with an opening of measurement at 25.4 mm.

Colorimetry of DepositsTest Setup:

[0119] All colorimetric measurements done on a surface of a crayon were performed using a KONICA MINOLTA CM-3610 A spectrophotometer with an opening of measurement at 4 mm. For colorimetric measurements of the surface of a crayon, the crayon's surface is placed in direct contact with the lens of the spectrophotometer.

Friction Tests Setup:

[0120] All coefficient of friction measurements have been performed on a white paper AURORA ISO-12757. A TriboLab UMT by the company Bruker Corporation with a sensor DFH-5.0 was used to measure the coefficient of friction.

TABLE-US-00004 TABLE 4 Parameters for measuring the coefficient of friction. Parameters for producing the deposits Article type Composition According to Table 2 Writing speed 4.5 m/min Writing angle 70 Total weight support/additional 350 +/ 5 weight (g) Writing length (m) 3 Spiral Step (mm) 0.8 r max 47 mm

Results of the Tests

TABLE-US-00005 TABLE 5 Results of Colorimetry Tests Evaluated Colorimetric data Composition Surface L* a* b* C* h* E.sub.00* Composition A Surface of 50.51 14.21 31.16 34.24 294.51 crayons Deposit after 89.29 7.67 16.79 18.46 294.54 scriptmeter Evaluation 38.78 6.54 14.37 15.78 0.03 30.90 Delta Composition B Surface of 52.56 15.92 30.18 34.12 297.81 crayons Deposit after 90.16 6.94 16.06 17.5 293.36 scriptmeter Evaluation 37.6 8.98 14.12 16.62 4.45 29.58 Delta Composition C Surface of 40.58 14.99 27.57 31.38 298.54 crayons Deposit after 89.15 7.73 17.05 18.72 294.38 scriptmeter Evaluation 48.57 7.26 10.52 12.66 4.16 40.46 Delta Composition D Surface of 47.01 15.32 33.17 36.53 294.78 crayons Deposit after 89.93 7.24 16.19 17.73 294.09 scriptmeter Evaluation 42.92 8.08 16.98 18.8 0.69 34.79 Delta Composition E Surface of 37.34 14.61 25.31 29.23 299.99 crayons Deposit after 91.31 5.96 14.82 15.97 291.9 scriptmeter Evaluation 53.97 8.65 10.49 13.26 8.09 45.31 Delta Composition F Surface of 61.66 12.79 28.87 31.58 293.89 crayons Deposit after 88.41 7.80 16.65 18.39 295.11 scriptmeter Evaluation 26.75 4.99 12.22 13.19 1.22 20.57 Delta

[0121] The results Table 5 shows that a smaller particle size may lead to an increased L*-value. Further, the results show that a smaller particle size may lead to a lower E.sub.00 value. Additionally, the results in Table 5 show, that a higher BET-value may result in a lead with a hue h closer to that of TiO.sub.2.

Results of the Friction Tests

TABLE-US-00006 TABLE 6 Results of Friction Tests Composition Coefficient of Friction Composition B 0.432 Composition C 0.413 Composition D 0.416 Composition E 0.392 Composition F 0.413

[0122] The results Table 6 shows that a smaller particle size and increased BET-value may lead to an increased Coefficient of Friction. The coefficient of friction of ZrO.sub.2 may surpass that of TiO.sub.2 compositions. In particular, ZrO.sub.2 of smaller particle sizes may lead to a higher coefficient of friction compared to TiO.sub.2, which in turn may increase the laydown of the writing instrument.

[0123] The present disclosure furthermore relates to the following aspects.

Aspects

[0124] 1. A writing instrument comprising a lead, wherein the lead comprises at least about 0.5 wt.-% ZrO.sub.2, relative to the total weight of the lead, in particular wherein the lead comprises less than about 0.5 wt.-%, more specifically less than about 0.2 wt.-% and in particular substantially no or no TiO.sub.2.

[0125] 2. The writing instrument according to aspect 1, wherein the lead comprises between about 1 wt.-% to about 25 wt.-%, more specifically between about 2 wt.-% to about 20 wt.-%, even more specifically between about 5 wt.-% to about 20 wt.-%, and in particular between about 11 wt.-% to about 15 wt.-% ZrO.sub.2, relative to the total weight of the lead.

[0126] 3. The writing instrument according to any one of aspects 1 or 2, wherein an external surface of the lead has an L*-value of at least 40 and wherein the lead comprises between about 11.0 wt.-% to about 20 wt.-%, more specifically between about 11 wt.-% to about 18 wt.-% and in particular between about 12 wt.-% to about 15 wt.-% ZrO.sub.2, relative to the total weight of the lead.

[0127] 4. The writing instrument according to any one of aspects 1 or 2, wherein the external surface of the lead has an L*-value of less than 40 and wherein the lead comprises between about 0.5 wt.-% to about 10.9 wt.-%, more specifically between about 1 wt.-% to about 9 wt.-% and in particular between about 2 wt.-% to about 8 wt.-% ZrO.sub.2, relative to the total weight of the lead.

[0128] 5. The writing instrument according to any preceding aspect, wherein the lead comprises the ZrO.sub.2 in the form of particles.

[0129] 6. The writing instrument according to aspect 5, wherein the ZrO.sub.2 particles have a D.sub.50 between about 0.1 m to about 17 m, more specifically between about 0.2 m to about 10 m and even more specifically between about 0.3 m to about 7 m, in particular between about 0.3 m to about 5 m, and in particular between about 0.4 m to about 2 m.

[0130] 7. The writing instrument according to aspect 5 or 6, wherein the ZrO.sub.2 particles have a D.sub.90 between about 0.5 m to about 50 m, more specifically between about 0.5 m to about 15 m, in particular 1 m to about 3 m.

[0131] 8. The writing instrument according to any preceding aspect, the wherein ZrO.sub.2 particles have a BET-value between about 0.5 m.sup.2/g to about 22 m.sup.2/g, more specifically between about 2.5 m.sup.2/g to about 20 m.sup.2/g, in particular about 4 m.sup.2/g to about 20 m.sup.2/g and in particular about 4 m.sup.2/g to about 18 m.sup.2/g, measured according to DIN ISO 9277:2014-01.

[0132] 9. The writing instrument according to any preceding aspect, wherein the lead has a coefficient of friction between about 0.414 to about 0.5, more specifically between about 0.420 to about 0.48 and in particular between about 0.43 to about 0.46.

[0133] 10. The writing instrument according to any preceding aspect, wherein the writing instrument comprises a casing and the lead is comprised within the casing.

[0134] 11. The writing instrument according to any preceding aspect, wherein the lead has a diameter of between about 2.0 mm to about 4.5 mm, more specifically between about 2.3 mm to about 4.2 mm and in particular between about 2.8 mm to about 4.0 mm.

[0135] 12. The writing instrument according to any preceding aspect, wherein the lead has a diameter between about 5 mm to about 35 mm, more specifically between about 6 mm to about 20 mm and in particular 7 mm to about 12 mm.

[0136] 13. The writing instrument according to any preceding aspect, wherein the lead comprises about 0.005 wt.-% to about 3.45 wt.-% of one or more metal oxides or transition metal oxide from the second, third, fourth and/or thirteenth group of the periodic table, relative to the total weight of the lead.

[0137] 14. The writing instrument according to any preceding aspect, wherein the lead comprises about 1.0 wt.-% to about 14.6 wt.-% of one or more metal oxides or transition metal oxides from the second, third, fourth and/or thirteenth group of the periodic table, relative to the total weight of the ZrO.sub.2.

[0138] 15. The writing instrument according to any preceding aspect, wherein the lead comprises Y.sub.2O.sub.3, HfO.sub.2, MgO, CaO and/or Ce.sub.2O.sub.3, in particular HfO.sub.2 and/or Y.sub.2O.sub.3, and in particular Y.sub.2O.sub.3.

[0139] 16. The writing instrument according to any preceding aspect, wherein the lead is devoid, or substantially devoid of MgO and/or CaO.

[0140] 17. The writing instrument according to any preceding aspect, wherein the lead comprises less than 0.05% of SiO.sub.2, more specifically less than 0.04% of SiO.sub.2, and even more specifically less than 0.03% of SiO.sub.2, relative to the total weight of the lead.

[0141] 18. The writing instrument according to any preceding aspect, wherein the lead comprises between about 10 wt.-% to about 90 wt.-% of one or more waxes, relative to the total weight of the lead.

[0142] 19. The writing instrument according to any preceding aspect, wherein the lead comprises between about 50 wt.-% to about 95 wt.-%, more specifically, between about 60 wt.-% to about 90 wt.-% and in particular between about 70 wt.-% to about 85 wt.-% of the one or more waxes, relative to the total weight of the lead.

[0143] 20. The writing instrument according to any preceding aspect, wherein the lead comprises between about 10 wt.-% to about 45 wt.-%, more specifically, between about 15 wt.-% to about 40 wt.-% and in particular between about 20 wt.-% to about 30 wt.-% of the one or more waxes, relative to the total weight of the lead.

[0144] 21. The writing instrument according to any preceding aspect, wherein the lead comprises between about 10 wt.-% to about 45 wt.-%, more specifically, between about 15 wt.-% to about 35 wt.-% and in particular between about 18.5 wt.-% to about 27 wt.-% of a polymer, more specifically a thermoplast even more specifically an olefine and in particular polyethylene or polypropylene, relative to the total weight of the lead.

[0145] 22. The writing instrument according to any preceding aspect, wherein the lead comprises between about 1 wt.-% to about 20 wt.-%, more specifically, between about 3 wt.-% to about 17 wt.-% and in particular between about 5 wt.-% to about 15 wt.-% of a fatty acid or salt thereof, relative to the total weight of the lead.

[0146] 23. The writing instrument according to any preceding aspect, wherein the lead comprises a fatty acid salt, wherein the fatty acid or salt comprises a monovalent linear or branched saturated or unsaturated carboxylic acid salt having between about 8 to about 24 carbon atoms, more specifically a monovalent linear saturated carboxylic acid salt having between about 16 to about 20 carbon atoms, and in particular stearic acid, calcium stearate, zinc stearate or mixtures thereof.

[0147] 24. The writing instrument according to any preceding aspect, wherein the lead comprises a filler, in particular a hydrous aluminum phyllosilicate and/or an alkali and/or earth alkali carbonate.

[0148] 25. The writing instrument according to aspect 24, wherein the lead comprises between about 10 wt.-% to about 50 wt.-%, more specifically, between about 17 wt.-% to about 40 wt.-% and in particular between about 23.5 wt.-% to about 32 wt.-% of the filler, relative to the total weight of the lead.

[0149] 26. The writing instrument according to aspect 24 or 25, wherein the lead comprises between about 5 wt.-% to about 30 wt.-%, more specifically, between about 10 wt.-% to about 25 wt.-% and in particular between about 15 wt.-% to about 20 wt.-% of a hydrous aluminum phyllosilicate, more specifically a layered hydrous aluminum phyllosilicate and in particular kaolinite, relative to the total weight of the lead.

[0150] 27. The writing instrument according to any one of aspect 24 to 26, wherein the lead comprises between about 5 wt.-% to about 20 wt.-%, more specifically, between about 7 wt.-% to about 15 wt.-% and in particular between about 8.5 wt.-% to about 12 wt.-% of an alkali and/or earth alkali carbonate, more specifically an earth alkali carbonate and in particular calcium carbonate, relative to the total weight of the lead.

[0151] 28. The writing instrument according to any preceding aspect, wherein the lead comprises between about 2 wt.-% to about 20 wt.-%, more specifically between about 4 wt.-% to about 15 wt.-% and in particular between about 7 wt.-% to about 11 wt.-% of a processing aid, more specifically a lubricant and in particular tetrastearate pentaerythritol.

[0152] 29. The writing instrument according to any preceding aspect, wherein the lead comprises between about 0.5 wt.-% to about 5 wt.-%, more specifically between about 1 wt.-% to about 3.5 wt.-% and in particular between about 1.5 wt.-% to about 2.5 wt.-% of a plasticizer, more specifically of a phthalic acid ester and in particular of C.sub.7-C.sub.9 alkyl benzyl phthalate, relative to the total weight of the lead.

[0153] 30. The writing instrument according to any preceding aspect, wherein the lead comprises between about 0.05 wt.-% to about 10 wt.-%, more specifically between about 0.05 wt.-% to about 7 wt.-% and in particular between about 0.1 wt.-% to about 5 wt.-% of one or more pigments, relative to the total weight of the lead.

[0154] 31. The writing instrument according to any one of aspects 24 or 28 to 30 when dependent on aspect 22, wherein the lead comprises between about 5 wt.-% to about 80 wt.-%, more specifically, between about 10 wt.-% to about 60 wt.-%, more specifically, between about 15 wt.-% to about 55 wt.-% and in particular between about 15 wt.-% to about 50 wt.-% of a hydrous aluminum phyllosilicate, more specifically a layered hydrous aluminum phyllosilicate and in particular kaolinite, relative to the total weight of the lead.

[0155] 32. The writing instrument according to any one of aspect 1 to 29 or 31, wherein the lead comprises between about 5 wt.-% to about 30 wt.-%, more specifically, between about 10 wt.-% to about 25 wt.-% and in particular between about 13 wt.-% to about 17 wt.-% of a pigment, relative to the total weight of the lead.

[0156] 33. The writing instrument according to any preceding aspect, wherein the lead comprises between about 3 wt.-% to about 50 wt.-%, more specifically, between about 10 wt.-% to about 50 wt.-%, more specifically, between about 15 wt.-% to about 45 wt.-% and in particular between about 20 wt.-% to about 40 wt.-% of a binder, more specifically a polymeric binder, and in particular styrenic polymers such as polystyrene and/or acrylonitrile butadiene styrene, relative to the total weight of the lead.

[0157] 34. The writing instrument according to any preceding aspect, wherein the lead comprises ZnS or ZnO.