The present invention concerns a polymer-based lead casing for pencil. The invention also concerns a method for manufacturing a pencil comprising a lead casing according to the invention. Finally, the invention relates to the use of a pencil comprising a lead casing for pencil according to the invention for writing, drawing, marking, plotting, and/or coloring.

Such polymer-based lead casings for pencil are intended to replace traditional lead casings made of wood, and may be referred to "synthetic wood" or "body/core synthetic". They allow the gripping of pencil and protect the lead against breakage. They must be resistant to deformation for not being bended or twisted, which would break the lead from inside. They must also be able to be cut by a traditional sharpener. They are generally made of polymer-based synthetic material whose density and sharpness are similar to those of wood and can be extruded. They can be expanded.

They also have no splinters if the pencil breaks because they are based on polymeric material.

Two main families of thermoplastic polymers are used today in synthetic lead casings for pencils: styrenics such as polystyrene (PS) and acrylonitrile butadiene styrene (ABS) and polyolefins such as polyethylene (PE) and polypropylene (PP). These polymers are all from the petroleum industry. For ecological reasons, it would be interesting to be able to replace such thermoplastic polymers with biorenewable polymers.

The patent application FR2988643 describes a pencil whose lead casing (called the envelope portion in the application) is based on expanded synthetic material. It teaches that the thermoplastic materials of the lead casing portion and the lead portion may be selected from styrenic polymers such as polystyrene, polyolefins and biopolymers. Polylactic acid (PLA) is thus the only biopolymer cited, although the only example of lead casing is based on a polymer matrix of the styrenic family.

The inventors have now observed that the use of PLA as the sole thermoplastic polymer in the lead casing for pencil did not make good mechanical properties in terms of resilience and impact resistance, which can cause problems in the manufacturing process and the sharpness of the final pencil. Thus, PLA "alone" does not make a good substitute for polymers derived from petroleum such as polystyrene in the manufacture of the lead casing for pencil.

The inventors, however, surprisingly observed that it was possible to manufacture a lead casing for pencil having better mechanical properties to polystyrene-based lead casings by using as a thermoplastic polymer a mixture of PLA with polybutylene adipate terephtalate (PBAT), another biopolymer, in specific proportions, in combination with an appropriate content of mineral fillers chosen in the group consisting of shellfish shells, preferably milled shellfish shells, more preferably oyster shells, and even more preferably milled (or crushed) oyster shells.

The present invention therefore relates to a lead casing for pencil which is made of a composition comprising (advantageously consisting essentially of, in particular consisting of), by weight relative to the total weight of the lead casing for pencil:

a) from 50 to 95%, advantageously from 60 to 95%, and more advantageously from 70 to 90%, of a mixture of PLA and PBAT in a weight ratio PLA/PBAT ranging from 60/40 to 90/10, and

b) from 5 to 40%, advantageously from 7 to 30%, of mineral fillers chosen in the group consisting of shellfish shells, preferably milled shellfish shells, more preferably oyster shells, and even more preferably milled (or crushed) oyster shells.

According to a preferred embodiment, the lead casing for pencil of the invention is made of a composition comprising (advantageously consisting essentially of, in particular consisting of), by weight relative to the total weight of the lead casing for pencil:

a) from 70 to 90% of a mixture of PLA and PBAT in a weight ratio PLA/PBAT ranging from 60/40 to 90/10, and

b) from 7 to 30% of mineral fillers chosen in the group consisting of shellfish shells, preferably milled shellfish shells, more preferably oyster shells, and even more preferably milled (or crushed) oyster shells.

According to a preferred embodiment, the lead casing for pencil of the invention is made of a composition comprising (advantageously consisting essentially of, in particular consisting of), by weight relative to the total weight of the lead casing for pencil:

a) from 80 to 90% of a mixture of PLA and PBAT in a weight ratio PLA/PBAT ranging from 65/35 to 85/15, and

b) from 10 to 20% of mineral fillers chosen in the group consisting of shellfish shells, preferably milled shellfish shells, more preferably oyster shells, and even more preferably milled (or crushed) oyster shells.

The lead casing for pencil of the invention thus comprises a mixture of PLA, for example commercially available from NaturePlast, and PBAT, for example commercially available from NaturePlast, in a weight ratio of PLA/PBAT ranging from 60/40 to 90/10, in particular from 65/45 to 80/20, more particularly from 70/30 to 80/20, and even more particularly in a weight ratio of 70/30.

This mixture of biodegradable thermoplastic polymers serves as a matrix for the lead casing for pencil of the invention and makes it possible to manufacture the lead casing by extrusion and to provide good mechanical properties such as resilience and impact resistance. It also makes it possible to bring the trimming to the lead casing for pencil of the invention. The content of the mixture of PLA and PBAT in the lead casing for pencil of the invention thus ranges from 50 to 95%, advantageously from 60 to 95%, more advantageously from 60 to 92%, more advantageously from 70 to 90%, and even more advantageously from 80 to 90%, by weight relative to the total weight of the lead casing for pencil.

The lead casing for pencil of the invention further comprises mineral fillers chosen in the group consisting of shellfish shells. The shellfish shells are preferably oyster shells or scallop shells, more preferably oyster shells, and even more preferably milled (or crushed) oyster shells. In particular, the mineral fillers are chosen in the group consisting of milled oyster shells, advantageously in the form of crushed shells, in particular commercially available from NaturePlast. The mineral fillers make it possible to improve the mechanical properties of the lead casing for pencil such as the flexural modulus (3 points).

Advantageously shellfish shells, preferably milled shellfish shell, and more preferably milled (or crushed) oyster shells, have a volume-average diameter (d50) ranging preferably from 10 to 160 pm, in particular from 20 to 100 pm, and more particularly from 30 to 80 pm, and still more particularly of 70 pm. The volume-average diameter (d50) can for example be measured by laser particle sizing with a Mastersizer 3000 type apparatus commercially available from Malvern.

More advantageously, the mineral fillers of the invention are combined with additional fillers, preferably different from shellfish shells, and more preferably different from milled (or crushed) oyster shells. Preferably, the additional fillers can be vegetable fillers, preferably wood fibers, more preferably in the form of powder, in particular commercially available from JRS Rettenmaier or CFF GmbFI &. Co. KG or Jelu-Werk or Rossow. The fillers can therefore consist of a mixture of oyster shells and wood fibers, in particular a mixture of milled (or crushed) oyster shells and wood fibers.

The total content of fillers (mineral fillers + additional fillers) in the lead casing for pencil of the invention may range from 5 to 50%, advantageously from 7 to 40%, more advantageously from 8 to 30%, more advantageously still from 9 and 20%, and in particular 10% by weight, with respect to the total weight of the lead casing for pencil.

The content of mineral fillers in the lead casing for pencil of the invention ranges from 5 to 40%, advantageously from 7 to 30%, more advantageously from 10 to 20%, and in particular 15%, by weight relative to the total weight of the lead casing for pencil.

The lead casing for pencil of the invention may further comprise an adhesion promoter. If the adhesion promoter is present, its content ranges from 0.1 to 10%, preferably from 1 to 5%, more preferably from 2 to 5%, and even more preferably from 1 to 3%, by weight relative to the total weight of the lead casing for pencil. The adhesion promoter makes it possible to improve the adhesion between the thermoplastic polymer (mixture of PLA and PBAT) and the mineral fillers.

Thus, in a particular embodiment, the lead casing for pencil of the invention comprises mineral fillers which consist of shellfish shells, in particular milled shellfish shells, preferably oyster shells, and more preferably milled (or crushed) oyster shells, alone or possibly mixed with vegetable fillers, preferably wood fibers, more preferably in the form of powder, the lead casing for pencil also comprising an adhesion promoter as defined according to the invention.

In a preferred embodiment, the adhesion promoter of the invention is a polylactic acid grafted with maleic anhydride (PLA-MA), for example commercialized by NaturePlast or NatureWorks.

The lead casing for pencil of the invention may comprise other additives, such as, for example, dyes and/or pigments, in particular in the form of a masterbatch, for example based on PLA, blowing agents, agents for use, lubricants, slip agents such as stearates (calcium stearate for example) and/or stearamide, performance modifiers of PLA (melt enhancer which improve the strength/consistency of the extrusion melt), in particular acrylics, and a mixture of these additives. The content of additive in the lead casing for pencil of the invention when present ranges from 0.1 to 10%, and preferably from 3 to 8% by weight, by weight relative to the total weight of the lead casing for pencil.

In particular, the lead casing for pencil of the invention may comprise a blowing agent, for example consisting of expandable and impervious particles, the wall of which is made of an extensible polymer material. Under the effect of temperature, a chemical or physical reaction occurs within said particles, causing an increase in the internal volume of said particles and their expansion. Thus, the blowing agent may be chosen from microspheres having a shell and enclosing a gas or a gas mixture. An increase in temperature causes an increase in the internal pressure of the microspheres that swell to a size that can be multiplied by five or more. Depending on the desired result of flexibility, weight, and any other property of the material in which the blowing agent is incorporated, the expansion is completed or not.

Preferably, the blowing agent is introduced into the composition of the lead casing in a content ranging from 0.1 and 1%, and more preferably from 0.5 and 1%, by weight relative to the total weight of the lead casing for pencil. The blowing agent is advantageously chosen in the group consisting of citric acid, sodium bicarbonate, or mixture thereof.

The lead casing for pencil of the invention may also comprise dyes and/or pigments (such as red iron oxide), in particular in the form of a masterbatch, more particularly based on PLA. The content of dyes and/or pigments preferably ranges from 0.1 to 10% by weight, in particular if the dye and/or the pigment is not in the form of a masterbatch, more preferably from 0.1 to 5% by weight, and even more preferably from 0.5 and 3% by weight, relative to the total weight of the lead casing for pencil of the invention. In a preferred embodiment, the dyes and/or pigments are capable of providing a color close to the wood to the lead casing for pencil of the invention. The lead casing for pencil of the invention may be made of a composition wherein the sum of weight % of component a) (mixture of PLA and PBAT), components b) (mineral fillers) and optional other component(s) such as additional fillers, adhesion promoters, dyes, pigments, blowing agents, agents for use, lubricants, slip agents, performance modifiers, etc., represents 100%.

The lead casing for pencil of the invention is advantageously extrudable. It is also advantageously shaped and can have in particular the density and the sharpness approximating those of wood. In particular, the pencil can be cut by a traditional pencil sharpener. Therefore, it is not the lead casing for pencil of a mechanical pencil.

The present invention further relates to a pencil for writing, drawing, marking, plotting, and/or coloring, comprising a lead casing for pencil according to the invention. The pencil of the invention is not a mechanical pencil.

In the pencil of the invention, the lead casing advantageously surrounds, in particular concentrically, the lead or a protective intermediate layer disposed between the lead and the lead casing of the invention. In a particular embodiment of the invention, the pencil of the invention comprises an additional layer of decoration, preferably varnish, surrounding, in particular concentrically, the lead casing of the invention. Advantageously, the decorative layer is made of a material compatible with that of the lead casing of the invention.

According to a preferred embodiment, the lead of the lead casing of the invention is a polymer-based lead, and not a calcined lead.

In a particular embodiment of the invention, the pencil of the invention is obtained by extrusion, in particular by coextrusion of the lead/optional protective layer/lead casing according to the invention/optional decorative layer. In a preferred embodiment, the coextrusion makes it possible to prepare in a single step a continuous ring consisting of the four aforementioned layers of the pencil, these being assembled in the chosen order lead/optional protective layer/lead casing according to the invention/optional decorative layer. For this, four single ^¬ screw extruders each delivering the material constituting a layer are connected in a coextrusion head tooling associating in the right order the layers between them. Multiple extrusion techniques are well known to the person skilled in the art. By way of example, such methods for continuously manufacturing pencils are described in document US 6,572,295.

According to a preferred embodiment, the pencil of the invention is a graphite pencil and/or a colored pencil. The formulation of the lead may vary depending on whether the pencil is a graphite pencil or a colored pencil. An example of formulation of a graphite lead is described in the application WO2016/097553. The formulation of a colored lead may exist in two forms: polyolefin-based erasable formulation as described in the application WO2016/097555 or styrenic-based standard formulation as described in the application WO2017/220914.

In a particular embodiment of the invention, the lead has a diameter of between 2 and 3.6 mm. In a graphite pencil, the diameter of the lead may advantageously vary from 2 to 2.5 mm. In a colored pencil, the diameter of the lead may advantageously vary from 3 to 3.5 mm.

In the case of a graphite pencil, carbon black may be added to the lead, and thus considered as a pigment. In this case, graphite may vary from 40 to 60% by weight and carbon black from 0 to 10% by weight, relative to the total weight of the lead.

The pencil of the invention advantageously has a hexagonal, round or triangular section, more advantageously round or hexagonal.

Advantageously, the pencil of the invention comprises means for erasing, such as an eraser, at the uncut end of the pencil. In addition to the above provisions, the invention also comprises other provisions which will emerge from the remainder of the description which follows. Examples:

Two compositions A and B of lead casing were prepared.

Composition A (invention) was a mixture of PLA/PBAT (NaturePlast PLE 005-1 and PBE 006) in a weight ratio of 80/20, added with 15% by weight of milled oyster shells (from NaturePlast).

Composition B (comparative) was a mixture of polylactic acid/polybutylene succinate PLA/PBS (NaturePlast PLE 005-1 and PBE 003) in a weight ratio of 70/30, added with 10% by weight of milled oyster shells (from NaturePlast).

Pencils with hexagonal section were manufactured by coextrusion with a color lead made of acrylonitrile-butadiene-styrene (ABS) (composition in % by weight relative to the total weight of the lead: 40% ABS copolymer, 12.5% kaolin, 27.5% calcium stearate, 20% additive), a sheath, a lead casing of composition A (invention) or of composition B (comparative), and a varnish. The thickness of the lead casing is 4.5 mm.

The performances of the pencils made of the lead casings of compositions A and B were tested according to the following tests:

The pencil flexural resistance test was carried out in order to check the strength and the crack resistance of the pencil.

The characteristics of the test were as follows: Equipment: Dynamometer LLOYD-AMETEK Instrument type, U- bracket span of 6 cm, Sensor ADAMEL DY20 Chatillon Instrument type TCD110 50 daN

Descent speed of sensor: 50 mm. min ¹

Operating method:

1. Turn on the dynamometer.

2. Locate the sensor in the up position.

3. Fix the pencil on the U-bracket.

4. Go down the needle.

5. Record the results expressed in daN.

The lead resistance at 45° was carried out with a Dynamometer Chatillon instrument type TCM 201-M.

Operating mode:

1. Position the pencil in a support with a 45° inclination, descend the pencil at a descent speed of 50 mm. min ¹ , and come into contact with a metal plate until the lead breaks.

2. Read the value of the result displayed on the dynamometer.

The result was the measure of the force required to break the mine, expressed in daN.

The performances of the pencils made of the lead casings of compositions A and B are summarized in the following Table 1: Table 1 :

The results presented in Table 1 show better flexural resistance and lead resistance at 45°, for the pencil according to the invention made of the lead casing of composition A with respect to the comparative pencil made of the lead casing of composition B. A higher pencil flexural resistance means that the pencil of the invention resists better to flexing forces, and is therefore more resistant to break during flexing.