Gum powder containing kaolin

Abstract

The present invention relates to a rubber powder consisting of ground inner rubber particles from tires, which rubber powder comprises kaolin. The rubber powder improves the tear resistance of rubber compositions containing the powder.

Description

Title of the invention: Gum powder containing kaolin

[0001] The invention relates to gum powders derived from tire rubber compositions.

[0002] Indeed, it is of interest today for tire manufacturers to encourage the recycling of end-of-life tires into new tires or other new rubber articles with a view to reducing the environmental impact of their activity.

[0003] It is also of interest to manufacturers to find solutions to reduce the costs of rubber compositions without penalizing the performance of tires or other rubber articles using these compositions.

[0004] One possible way of addressing these two points of interest is to incorporate rubber crumbs from the grinding or micronization of vulcanized rubber compositions into rubber compositions for tires or rubber articles. Tires from this type of process are described in the prior art, for example in document WO2020 / 128255.

[0005] Tire manufacturers have sometimes also incorporated gum powders from the recycling of tires or curing membranes into compositions for tire inner rubber, as described in documents KR100943526, EP1612242 and US6730732.

[0006] However, rubber articles, in particular inner rubbers for tires, must also have good mechanical resistance properties, including after aging. However, very surprisingly, the Applicant has discovered that the use, in rubber compositions, of specific rubber crumbs in that they contain kaolin, makes it possible to improve the tear resistance properties after aging of the compositions thus obtained.

[0007] Thus, a first object of the invention is a gum powder consisting of particles of crushed inner tire rubber comprising kaolin. The invention also relates to a rubber composition comprising a gum powder in accordance with the invention. Another subject of the invention is a tire comprising a rubber composition or a rubber powder in accordance with the invention. The invention also relates to a rubber article comprising a rubber composition or a gum powder in accordance with the invention. Detailed description

[0008] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from more than a to less than b (i.e., excluding the limits a and b) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict limits a and b).

[0009] The abbreviation "pce" means parts by weight per hundred parts of elastomers present in the elastomer matrix. The term "elastomer matrix" means all the elastomers present in a rubber composition.

[0010] The compounds mentioned in the description (typically the polymers, fillers, plasticizers, coupling agents, the vulcanization system, other additives, etc.) may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned may also come from the recycling of materials already used, that is to say they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0011] The invention described in more detail below has as its object at least one of the objects defined according to any one of the following listed embodiments: 1. Gum crumb consisting of crushed tire inner rubber particles, which gum crumb includes kaolin. 2. Gum powder according to embodiment 1 having a median particle size by volume of between 50 and 500 pm, preferably between 100 and 400 pm. 3. Gum powder according to any one of the preceding embodiments comprising at least 40% by mass of a halogenated butyl rubber. 4. Gum powder according to any one of the preceding embodiments comprising from 0 to 20% by mass of a polyisoprene elastomer, the polyisoprene elastomer preferably containing more than 90% by mole of 1,4-cis bond. 5. Gum crumb according to any one of the preceding embodiments wherein the halogenated butyl rubber is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of the two. 6. Gum powder according to any one of the preceding embodiments comprising a reinforcing filler. 7. Gum powder according to embodiment 6 in which the mass percentage of the reinforcing filler ranges from 10 to 40%, preferably initially 20 to 30%. 8. Gum powder according to one of embodiments 6 or 7 in which the reinforcing filler comprises a carbon black representing more than 50% by mass, preferably more than 80% by mass, even more preferably 100% by mass of the total mass of the reinforcing filler. 9. Gum powder according to any one of the preceding embodiments in which the mass percentage of kaolin in the gum powder ranges from 3 to 30%, preferably from 5 to 20%. 10. Gum powder according to any one of the preceding embodiments comprising a vulcanization system. 11. A rubber composition comprising a gum crumb according to any one of the preceding embodiments. 12. A tire comprising a rubber composition according to embodiment 11 or a gum powder according to any one of embodiments 1 to 10. 13. A rubber article comprising a rubber composition according to embodiment 11 or a gum crumb according to any one of embodiments 1 to 10. Gum powder

[0012] The first subject of the invention is a gum powder.

[0013] It is recalled that rubber crumbs are generally in the form of granules (or aggregates), possibly put in the form of a rubber plate. Most often, rubber crumbs are a product of recycling materials: they come from grinding, in particular micronization, of cooked rubber compositions already used for a first application, for example as tire curing membranes (as in document US6730732) or as tires that have reached the end of their life (as in document KR100943526). Any method or process that does not degrade the rubber during grinding may be suitable as a method of grinding rubber compositions.For example, a grinding method in the presence of water may be chosen such as those described in documents US4374573, US4714201, US5238194 and US5411215: such a method makes it possible to keep the temperature of the gum at a sufficiently low level to avoid reversion, i.e. the degradation of the crosslinking network of the gum. A cryogenic grinding method may also be used. Depending on the object size distribution obtained, the gum powder obtained by the processes cited may undergo an additional sieving step so as to control this distribution. The sieving may be carried out by different technologies (vibration, centrifugation, suction) known to those skilled in the art. The gum powders from the . grinding process are generally in the form of microparticles. By "microparticles" we mean particles which have a size, namely their diameter in the case of spherical particles or their largest dimension in the case of anisotropic particles, of a few tens or hundreds of microns.

[0014] According to one embodiment of the invention, the gum powder in accordance with the invention is in the form of microparticles preferably having a median size by volume of between 50 and 500 μm, preferably between 100 and 400 μm. These particle size ranges can be applied to any of the embodiments of the invention. Inner tire rubber

[0015] An essential characteristic of the rubber crumb according to the invention is that it is made up of particles of crushed inner tire rubber. In other words, the constituent elements of the rubber crumb are particles of inner tire rubber. The rubber crumb useful for the purposes of the invention can then be manufactured by a process which consists of recovering inner tire rubber, then grinding or micronizing this inner rubber by means of a process as described above.

[0016] The composition of a gum powder useful for the purposes of the invention is typically a vulcanized rubber composition constituting an inner gum.

[0017] In a well-known manner, a rubber composition for the inner rubber of a tire, hereinafter referred to as a rubber composition for the inner rubber, comprises a halogenated butyl elastomer. The halogenated butyl elastomer typically represents from 40% to 75% by mass, preferably from 50% to 75% by mass of the total mass of a rubber composition for the inner rubber. A rubber composition for the inner rubber may also contain natural rubber. The natural rubber then represents less than 20% by mass of the total mass of elastomer in a rubber composition for the inner rubber.

[0018] A rubber composition for interior rubber also contains a reinforcing filler which contains carbon black, the reinforcing filler then typically representing from 10% to 50% by mass of the total mass of a rubber composition for interior rubber.

[0019] A rubber composition for an interior rubber also contains a vulcanization system, i.e., a system based on sulfur (or a sulfur donor) and a primary vulcanization accelerator. In a rubber composition for an interior rubber, sulfur is used at a preferred level of between 0.5 and 5 parts by weight per 100 parts by weight of the composition for an interior rubber. The primary vulcanization accelerator is used at a preferred level between 0.5 and 5 pce. Various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or known vulcanization retarders may be added to this basic vulcanization system. Mention may be made, as a (primary or secondary) vulcanization accelerator, of any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. The vulcanization system of a rubber composition for inner rubber does not include a curing resin, such as phenolic resins.

[0020] Since the rubber composition of the constituent particles of the gum powder useful for the purposes of the invention is a rubber composition of an inner gum, it also does not contain any curing resin, such as phenolic resins. Consequently, it should not be confused with a rubber composition for an expandable curing membrane (in English bladdef) which contains as crosslinking agent a curing resin, in particular phenolic. Kaolin

[0021] The gum powder in accordance with the invention has the essential characteristic of containing kaolin. Kaolin (A12O3 2SiO2 2H2O) is a non-reinforcing lamellar mineral filler belonging to the family of natural phyllosilicates.

[0022] According to one embodiment of the invention, the kaolin represents from 3 to 30% by mass, preferably from 5 to 20% by mass of the total mass of the gum powder in accordance with the invention. These ranges of mass percentage of kaolin in the gum powder in accordance with the invention can be applied to any of the embodiments of the invention. Elastomer

[0023] Usually, the terms “elastomer” and “rubber” are used interchangeably in the text.

[0024] According to one embodiment of the invention, the gum powder according to the invention contains a halogenated butyl rubber. The halogenated butyl rubber can be used alone or in a mixture with one or more other diene elastomers.

[0025] Butyl rubber means a copolymer of isobutylene and a 1,3-diene, in particular a copolymer of isobutylene and isoprene, as well as the halogenated derivatives, in particular generally brominated or chlorinated, of these copolymers.

[0026] Butyl rubbers are well known to those skilled in the art, particularly for their air-impermeability property. Generally, copolymers of isobutylene and of a 1,3-diene, in particular isoprene, contain 1 to 5 mol% of diene units, in particular isoprene, and have a Mooney viscosity (ML 1+8 at 125°C) of 30 to 60. Halogenated copolymers of isobutylene and a 1,3-diene, in particular isoprene, generally have a halogen content of 1 to 4% by mass of the copolymer mass.

[0027] Examples of halogenated butyl rubbers which are particularly suitable for carrying out the invention include bromobutyl rubbers such as brominated isobutylene and isoprene copolymer (BIIR), chlorobutyl rubbers such as chlorinated isobutylene and isoprene copolymer (CIIR) and mixtures of these rubbers.

[0028] According to any one of the embodiments of the invention, the halogenated butyl rubber is preferably a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of the two.

[0029] By "diene" elastomer, whether natural or synthetic, is meant in a known manner an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not). As diene elastomers which may be suitable, mention will be made in particular of the diene elastomers usually used in rubber compositions intended for the manufacture of tires, such as polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers such as copolymers of butadiene and styrene.

[0030] According to one embodiment of the invention, the gum crumb in accordance with the invention comprises from 0 to 20% by mass of a diene elastomer other than a halogenated butyl rubber and chosen from the group consisting of polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and their mixtures, mass percentage calculated relative to the total mass of the gum crumb. Preferably, the diene elastomer is a polyisoprene elastomer and, even more preferably, the diene elastomer is a polyisoprene elastomer which contains more than 90% by mole of 1,4-cis bond. These preferred ranges of mass percentage of elastomer in the gum powder in accordance with the invention and of molar percentage of 1,4-cis bond in the polyisoprene elastomer as well as these preferential choices of diene elastomer can be applied to any of the embodiments of the invention.

[0031] According to any one of the embodiments of the invention, the mass percentage of halogenated butyl rubber in the gum crumb in accordance with the invention is preferably greater than or equal to 40%, mass percentage calculated relative to the total mass of the gum crumb. Preferably, the only other rubber present in the gum crumb useful for the purposes of the invention is natural rubber. Charge

[0032] According to one embodiment of the invention, the rubber crumb in accordance with the invention comprises at least one reinforcing filler. Any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition which can be used in particular for the manufacture of tires, may be used, for example a reinforcing organic filler such as carbon black, a reinforcing inorganic filler such as silica or a mixture of these two types of fillers.

[0033] According to one embodiment of the invention, the mass percentage of the reinforcing filler in the gum powder in accordance with the invention ranges from 10 to 40%, preferably from 20 to 30%, mass percentage calculated relative to the total mass of the gum powder.

[0034] According to one embodiment of the invention, the reinforcing filler comprises carbon black. Suitable carbon blacks include all carbon blacks, in particular the blacks conventionally used in tires. These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for certain of the rubber additives used.

[0035] According to an embodiment of the invention where the reinforcing filler comprises carbon black, the carbon black represents more than 50% by mass, preferably more than 80% by mass, even more preferably 100% by mass of the reinforcing filler of the gum crumb according to the invention. In this even more preferred embodiment, the reinforcing filler is composed solely of carbon black, which is the only reinforcing filler present in the gum crumb. Vulcanization system

[0036] According to one embodiment of the invention, the gum powder according to the invention comprises a vulcanization system, i.e. a crosslinking system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. Various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders may be added to this basic vulcanization system. Mention may be made, as a (primary or secondary) vulcanization accelerator, of any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithio- phosphates, thioureas and xanthates. Sulfur is used in the gum crumb at a preferred level of between 0.5 and 12% by mass of the total mass of elastomer in the gum crumb, in particular between 0.5 and 5% by mass of the total mass of elastomer in the gum crumb. The primary vulcanization accelerator is used in the gum crumb at a preferred level of between 0.5 and 10% by mass, more preferably between 0.5 and 5.0% by mass of the total mass of elastomer in the gum crumb. These preferred ranges relating to the sulfur and accelerator levels can apply to any of the embodiments. Other additives

[0037] The gum powder in accordance with the invention may also comprise all or part of the usual additives normally used in rubber compositions intended for the manufacture of tires, such as, for example, plasticizers, lubricants, pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants, anti-fatigue agents and mixtures of such compounds. Other objects of the invention

[0038] The rubber composition in accordance with the invention has the essential characteristic of comprising the gum crumb in accordance with the invention, for example in an amount of 5 to less than 40 phr. It can be manufactured in suitable mixers, generally using two successive preparation phases well known to those skilled in the art: a first phase of thermomechanical working or kneading at high temperature, up to a maximum temperature of between 90°C and 150°C, preferably between 100°C and 130°C, followed by a second phase of mechanical working down to a lower temperature, typically below 110°C, for example between 40°C and 100°C, a phase of finishing and homogenization of the rubber composition. The rubber composition in accordance with the invention can be in the raw state (before crosslinking or vulcanization) as well as in the cured state (after crosslinking or vulcanization).

[0039] The invention also relates to a tire or any other rubber article comprising a rubber composition or a gum powder in accordance with the invention, which tire or rubber article is both in the raw state and in the cured state. In the present invention, the term "tire" means a pneumatic or non-pneumatic bandage. A pneumatic bandage usually comprises two beads intended to come into contact with a rim, a crown composed of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. A non-pneumatic bandage, for its part, usually comprises a base, designed for example for mounting on a rigid rim, a crown reinforcement, ensuring the connection with a tread and a deformable structure, such as spokes, ribs or cells, this structure being arranged between the base and the crown. Such non-pneumatic bandages do not necessarily comprise a sidewall. Non-pneumatic bandages are described for example in documents WO 03 / 018332 and FR2898077. According to any one of the embodiments of the invention, the tire according to the invention is preferably a pneumatic bandage.

[0040] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes. Examples Measures and tests used

[0041] Determination of tear resistance properties of rubber compositions

[0042] The tear breaking force per unit thickness (hereinafter referred to as F^z and expressed in N / mm of thickness) and the tear breaking elongation (hereinafter referred to as Ardz and expressed in %) are measured on a specimen stretched at 500 mm / min to cause the specimen to break on a dynamometric machine for tensile tests, equipped with a system for measuring and acquiring the force and the displacement of the moving crosshead. The tensile specimen consists of a parallelepipedal rubber plate, with a thickness equal to 2.5 mm, a length equal to 145 mm and a width equal to 10 mm. Before starting the test, three very fine notches perpendicular to the length of the test piece are made using a razor blade to a depth of 3 mm, on one edge of the test piece, one in the middle and the other two on either side of the first and 6 mm apart from it.FRDz is determined as the force (expressed in N per mm of specimen thickness) to be exerted to obtain rupture and Ardz is measured as the elongation (expressed in %) to be applied to the specimen to obtain rupture. The test was carried out in air at a temperature of 100°C. The tear coefficient (expressed in N / mm) is calculated as the product of FRDz and ARI) / . High values ​​indicate good cohesion of the rubber composition although there are crack initiations. In the examples below, the measurements were carried out both on "new" tensile specimens, i.e. those which had not undergone any prior aging, and on specimens which had been subjected to thermo-oxidative aging. for 21 days in air at 77°C before traction. The results are given in base 100: an arbitrary value of 100 is given for the tear coefficient of the control, a result greater than 100 indicates improved tear resistance properties compared to the control.

[0043] Determination of the particle size of gum crumbs

[0044] The volume distribution of the size of the gum crumb particles can be measured by laser granulometry, on a mastersizer 3000 type device from Malvern. A 1 minute ultrasonic treatment is carried out prior to the measurement in order to guarantee good dispersion. The measurement is carried out in a liquid process: the gum crumb particles are dispersed in alcohol. The measurement is carried out in accordance with the ISO-13320-1 standard and allows, from the determination of the diffraction angles of the laser by the gum crumb particles, to determine in particular the D10 and the D50, that is to say the diameter below which respectively 10% by volume and 50% by volume of the total particle population is present. Preparation of rubber compositions

[0045] Four rubber compositions C1, C2, C3 and C4 are prepared. The formulations (in phr) of these compositions are described in Table 1.

[0046] Rubber compositions C3 and C4 are in accordance with the invention; rubber compositions C1 and C2 are not in accordance with the invention. Rubber compositions C1, C2, C3 and C4 all contain a rubber crumb consisting of ground inner rubber from a tire. Rubber compositions C1 and C2, not in accordance with the invention, comprise respectively 10 and 30 phr of a rubber crumb of composition A (given in Table 2) which does not contain kaolin and is therefore not in accordance with the invention; rubber compositions C3 and C4, in accordance with the invention, comprise respectively 10 and 30 phr of a rubber crumb of composition B (given in Table 2) which contains kaolin and is in accordance with the invention.

[0047] The results are considered by comparing the properties of C1 (not in accordance with the invention) and C3 (in accordance with the invention) on the one hand, and those of C2 (not in accordance with the invention) and C4 (in accordance with the invention) on the other hand.

[0048] The tests are carried out as follows: the halogenated butyl rubber is first introduced into an internal mixer, filled to 70% by volume and with an initial tank temperature of approximately 40°C, followed by the reinforcing filler, the rubber crumb, the vulcanization system and the other additives of the rubber composition. A single-stage thermomechanical process is then carried out, lasting a total of approximately 3 to 4 minutes, until a maximum "drop" temperature of 115°C is reached.

[0049] The mixture thus obtained is recovered, cooled on an external mixer (roller tool) to 30°C, mixing everything in order to homogenize the mixture for an appropriate time (for example between 5 and 12 min). The compositions thus obtained are then calendered in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties after vulcanization for 20 min at 150 °C. Properties of rubber compositions

[0050] The properties of rubber compositions C1, C2, C3 and C4 are given on a basis of 100 relative to C1 in Table 3.

[0051] Rubber composition C3 contains the same level of gum crumb as rubber composition C1, but the gum crumb included in C3 contains kaolin (gum crumb of composition B), unlike that of rubber composition C1 which does not contain it (gum crumb of composition A). C3 is therefore in accordance with the invention and has a tear resistance 17% higher than that of rubber composition C1, which is not in accordance with the invention. Similarly, rubber composition C4 contains the same level of gum crumb as rubber composition C2, but the gum crumb included in C4 includes kaolin (gum crumb of composition B) unlike that of rubber composition C2 which does not include it (gum crumb of composition A). C4 is therefore in accordance with the invention and has a higher tear resistance than that of rubber composition C2, which is not in accordance with the invention.

[0052] The results obtained therefore show that the rubber crumb in accordance with the invention makes it possible to solve the technical problem here, in that it makes it possible to obtain rubber compositions with tear resistance properties after aging which are much better than those of the rubber compositions comprising a crumb not in accordance with the invention. This result is all the more surprising since, before aging, the rubber compositions comprising crumbs in accordance with the invention do not have tear resistance properties which are better than those of the rubber compositions comprising crumbs not in accordance with the invention. [Tables 1] Cl C2 C3 C4 Elastomer (1) 100 100 100 100 Carbon black (2) 40 40 40 40 Kaolin (3) 20 20 20 20 Stearic acid (4) 1.5 1.5 1.5 1.5 Zinc oxide (5) 1.5 1.5 1.5 1.5 Lubricant (6) 2 2 2 2 Accelerator (7) 1.2 1.2 1.2 1.2 Sulphur 1.5 1.5 1.5 1.5 Gum powder 1 (8) 10 30 0 0 Gum powder 2 (9) 0 0 10 30 1. Brominated butyl X-ButylTM BB2030 from ARLANXEO 2. N770 ASTM grade from ORION company 3. Natural kaolin grade Argirec B24 from the company IMERYS 4. Stearic acid from UMICORE 5. Zinc oxide from UMICORE 6. Struktol 40MS from STRUKTOL company 7. 2-Mercaptobenzothiazole Disulfide Accelerator (“MBTS”) from Solutia 8. Microparticles of vulcanized internal rubber of composition A with an average size of 280 pm 9. Microparticles of vulcanized internal rubber of composition B with an average size of 280 pm [Tables 2] AB Elastomer (1) 100 100 Carbon black (2) 50 40 Kaolin (3) 0 20 Stearic acid (4) 1.5 1.5 Zinc oxide (5) 1.5 1.5 Lubricant (6) 2 2 Accelerator (7) 1.2 1.2 Sulphur 1.5 1.5 [Tables 3] Cl C2 C3 C4 Tear coefficient when new [N / mm] 100 92 100 89 Tear coefficient after aging [N / mm] 100 117 119 130

Claims

Claims

1. Gum crumb consisting of crushed tire inner rubber particles, which gum crumb comprises kaolin.

2. Gum powder according to claim 1 having a median particle size by volume of between 50 and 500 pm, preferably between 100 and 400 pm.

3. A gum powder according to any preceding claim comprising at least 40% by mass of a halogenated butyl rubber.

4. Gum powder according to any one of the preceding claims comprising from 0 to 20% by mass of a polyisoprene elastomer, the polyisoprene elastomer preferably containing more than 90% by mole of 1,4-cis bond.

5. A gum crumb according to any preceding claim wherein the halogenated butyl rubber is a brominated copolymer of isobutylene and isoprene, a chlorinated copolymer of isobutylene and isoprene, or a mixture of the two.

6. Gum powder according to any one of the preceding claims comprising a reinforcing filler.

7. Gum powder according to claim 6 in which the mass percentage of the reinforcing filler ranges from 10 to 40%, preferably from 20 to 30%.

8. Gum powder according to one of claims 6 or 7 in which the reinforcing filler comprises a carbon black representing more than 50% by mass, preferably more than 80% by mass, even more preferably 100% by mass of the total mass of the reinforcing filler.

9. Gum powder according to any one of the preceding claims in which the mass percentage of kaolin in the gum powder ranges from 3 to 30%, preferably from 5 to 20%.

10. Gum powder according to any one of the preceding claims comprising a vulcanization system.

11. A rubber composition comprising a gum crumb according to any one of the preceding claims.

12. A tire comprising a rubber composition according to claim 11 or a gum crumb according to any one of claims 1 to 10.

13. A rubber article comprising a rubber composition according to claim 11 or a gum crumb according to any one of claims 1 to 10.