Interlayer material for glass sheets

Abstract

According to a first aspect, the invention relates to a glass plate interlayer material comprising a cellulose powder, wherein the cellulose powder is purified and at least 95 wt% of the cellulose powder particles have a diameter, the diameter being determined by sieving, of at most 80 µm, preferably at most 75 µm, preferably at most 70 µm. The invention also relates, according to a second aspect, to a stack of glass sheets comprising at least two glass sheets spaced apart by a layer of interlayer material according to the invention. According to a third aspect, the invention relates to a method for spacing glass sheets with respect to one another during the stacking of the glass sheets, the method comprising the application, between two adjacent glass sheets, of an interlayer material according to the invention. Finally, according to another aspect, the invention relates to the use of an interlayer material according to the invention for stacking glass sheets, for example for the transport or storage of a stack of glass sheets.

Description

Description Title of the invention: Interlayer material for glass sheets. TECHNICAL FIELD

[0001] The invention relates to the field of interlayer materials for glass sheets, intended to be placed between sheets of glass, particularly large ones. More specifically, the present invention relates to an interlayer material in powder form, the use of this material for spacing glass sheets, and a method for spacing glass sheets. TECHNOLOGICAL BACKGROUND

[0002] During transport or storage, large sheets of glass may be stacked face-to-face, for example, horizontally, vertically, or at an angle. Interlayer materials have been used for decades to facilitate the separation of the sheets by preventing them from sticking together, which can be caused by various physical phenomena, including capillary condensation. Furthermore, these interlayer materials aim to protect the surface of the glass sheets from damage and degradation, specifically by preventing corrosion, scratches caused by friction between the sheets, or other surface alterations that can occur during the transport, handling, or storage of the stacked glass sheets.

[0003] To overcome these problems, separation sheets can be inserted between the glass plates. However, these separation sheets generate significant waste.

[0004] Other conventional solutions include powdered interlayer materials, most often composed of polymethyl methacrylate (PMMA) or polystyrene (PS), depending on the application. These generally spherical particles can range in size from 50 to 150 µm. These particles can withstand very high loads and resist crushing or conditions that could compromise their integrity. For example, in a stack of 20 large-format glass plates (PLF, i.e., 3.21 m x 6 m with a thickness of 4 mm) tilted at a 4° angle, the first glass plate must withstand over 5500 kg, or approximately 2800 Pa, without breaking, sticking, or being marked by the ground powder. The interlayer materials are generally sprayed onto the surface of the glass plates using machines at the end of the manufacturing process. The adhesion of these materials is generally sufficient to withstand handling and transport, and at the same time, the particles can be easily removed by conventional washing operations in preparation for subsequent glass processing stages (coating or laminate manufacturing). However, these materials are microplastics, and their removal by washing creates environmental pollution problems.

[0005] Therefore, less environmentally impactful alternative solutions are being proposed. For example, natural cellulosic materials such as wood or coconut powders are known. Document WO 2022 / 180222 describes, for instance, a natural composite material made from plant fibers or fruit kernels.

[0006] However, the adhesion of these types of particles to the glass surface is insufficient, leading to problems with sheet removal with this type of material, as well as particle accumulation on the floor, making it slippery for personnel. Good adhesion is therefore essential for safety on manufacturing sites. Furthermore, the applicant discovered that the use of these new raw materials created an environment conducive to bacterial growth in the glass washing water basins, a problem that did not exist with conventional synthetic raw materials. Indeed, when the glass is washed to remove the powder, the powder ends up in retention basins where it is collected, while the wash water is filtered and reused. However, on coating application lines, the wash water is not treated with biocides in order to avoid negatively impacting the quality of the glass surface.These bacterial growth problems in wash water are not only detrimental to the quality and efficiency of subsequent glass processing stages (lamination, coatings, etc.) but also increase health risks in the presence of pathogens, which can then develop rapidly and spread when the retention basins are periodically washed in turn.

[0007] Therefore, there is still a need for durable or biodegradable interlayer materials that allow for efficient separation of glass sheets, adhere sufficiently to the plates to overcome problems of glass plate depilation and powder dispersion in glass pile formation areas, exhibit the required performance in terms of resistance to compression, humidity or various stress storage conditions, and can be easily disposed of while minimizing both glass corrosion and impacts on the entire glass manufacturing and / or processing process (glass surface quality, safety, etc.).

[0008] It is to the applicant's credit that she proposed a solution which, surprisingly, resolves all of these problems. SUMMARY OF THE INVENTION

[0009] According to a first aspect, the invention relates to an interlayer material for glass plates comprising a cellulose powder, wherein the cellulose powder is purified and at least 95% by mass, preferably at least 97% by mass, more preferably at least 99% by mass, of the cellulose powder particles have a diameter, determined by sieving, of at most 80 µm, preferably at most 75 µm, more preferably at most 70 µm. In other words, at least 95% by mass, preferably at least 97% by mass, more preferably at least 99% by mass, of the purified cellulose powder particles pass through a sieve with a mesh size of 80 µm, preferably 75 µm, more preferably 70 µm. The mesh size corresponds to the size of the sieve openings through which the particles can pass. The "diameter" of the particles is preferably determined by sieving.

[0010] Surprisingly, the inventors highlighted that the specific interlayer material according to the invention made it possible to combine good adhesion properties, while limiting bacterial growth and maintaining resistance properties to very high loads.

[0011] According to another aspect, the invention relates to an interlayer material for glass plates comprising a cellulose powder, wherein the cellulose powder is purified and at least 95% by mass, preferably at least 97% by mass, more preferably at least 99% by mass of the cellulose powder particles have a minimum Feret diameter of at most 80 pm, preferably at most 75 pm, more preferably at most 70 pm. The minimum Feret diameter is the smallest distance between two parallel tangents framing the contours of the particle. The minimum Feret diameter can be determined by dynamic image analysis.

[0012] The invention also relates, according to another aspect, to the use of a cellulose powder as an intercalating material between two glass substrates, preferably between two sheets of glass, said cellulose powder being purified and at least 95% by mass of the cellulose powder particles having a diameter, determined by sieving, of at most 80 pm, preferably at most 75 pm, preferably at most 70 pm.

[0013] The invention also relates, according to another aspect, to a stack of glass sheets comprising at least two glass sheets separated by a layer of intercalated material according to the invention.

[0014] According to another aspect, the invention relates to a method of spacing glass sheets from one another when stacking said glass sheets, the method comprising the application of an intercalary material according to the invention between two adjacent glass sheets.

[0015] According to another aspect, the invention relates to the use of an interlayer material according to the invention for stacking glass sheets, for example for transporting or storing a stack of glass sheets. DETAILED DESCRIPTION

[0016] The general terms used in this text are defined below.

[0017] The expression "comprising" is equivalent to "including" and encompasses the expression "consisting of".

[0018] The expression "from ... to ..." should be understood to include the boundaries.

[0019] For the purposes of this invention, "purified cellulose powder" refers to a powdery material, particularly one that is insoluble in water, consisting almost entirely of cellulose. Specifically, cellulose powder is considered "purified" if it comprises at least 95% cellulose by mass. Preferably, purified cellulose powder comprises at least 97% cellulose by mass, preferably at least 98% by mass, and more preferably at least 99% by mass. Purified cellulose powder may, in particular, be obtained through fractionation processes that isolate the cellulose from the other constituents of a cellulosic material, especially one of plant origin. Indeed, a cellulosic material may be of animal or plant origin and comprises, in addition to cellulose, other constituents such as hemicellulose, lignin, and possibly proteins, oils, waxes, or various impurities such as mineral residues or dirt.Cellulose insulation processes from cellulosic materials are well known and are described for example in document WO2014 / 105997. Generally, cellulosic material can be pre-ground and washed with water to remove dirt and soluble residues. Then, more or less extensive chemical treatments are used to remove the lignin and hemicellulose constituents (alkaline treatments, acid treatments, oxidative bleaching, etc.). Finally, the material is washed with water and dried. Spectroscopic or chemical methods are used to quantify the residual components. Depending on specific needs, certain steps can be repeated or intensified to achieve a higher degree of purity. Non-limiting examples of cellulosic materials include fruit kernels (olive, peach, apricot, etc.), fruit shells (almond, pistachio, walnut, coconut shells), and flours (corn cob flour, wood flour, fruit kernel flour, etc.).Preferably, the purified cellulose powder is obtained through a chemical denaturation treatment process in an acidic or basic medium, for example in an alkaline medium.

[0020] Preferably, the cellulose powder comprises less than 1% by mass of constituents selected from hemicellulose, lignin, proteins, oils, waxes, or a mixture of these compounds. More preferably, the cellulose powder comprises less than 1% by mass of impurities.

[0021] In the context of the present invention, cellulose powder provides structural rigidity to the interlayer material, such that it possesses sufficient compressive strength to withstand the load applied by several sheets of glass when stacked, particularly between several large-format glass sheets (PLF). In other words, the cellulose powder serves as the interlayer powder. Preferably, the cellulose powder has a compressive strength of at least 3 MPa, preferably at least 4 MPa, and more preferably at least 5 MPa, at 25 °C. It is also understood that, in the context of the present invention, the interlayer material is free of cellulose powder other than purified cellulose powder.

[0022] Preferably, the interlayer material is free of interlayer powder other than purified cellulose powder.

[0023] Preferably, the interlayer material is free of inorganic particles.

[0024] Advantageously, purified cellulose powder is insoluble in water, in particular it has a solubility of less than 0.01 g / L.

[0025] Purified cellulose powder can be microcrystalline cellulose powder. In other words, in addition to being separated from components such as lignin and hemicellulose, cellulose can be purified to remove the amorphous cellulose portion, for example by acid hydrolysis. Indeed, in biomass or plant matter, cellulose is present in the form of bundles of microfibrils, part of which is composed of amorphous cellulose (that is, whose chains are arranged in a disordered manner) and another part of which is made up of crystalline cellulose (that is, whose chains are ordered in such a way as to form crystals).

[0026] Alternatively, the purified cellulose powder may be non-crystalline or include a portion of amorphous cellulose. For example, the cellulose powder may comprise at least 30% by mass of amorphous cellulose, preferably at least 40% by mass of amorphous cellulose, and more preferably at least 50% by mass of amorphous cellulose.

[0027] At least 95% by mass of purified cellulose powder particles have a diameter, determined by sieving, of no more than 80 pm, preferably no more than 75 pm, and more preferably no more than 70 pm. Preferably at least 97% by mass, and more preferably at least 99% by mass, of purified cellulose powder particles have a diameter, determined by sieving, of no more than 80 pm, preferably no more than 75 pm, and more preferably no more than 70 pm. By "Diameter" in the context of the present invention means a particle size determined by sieving. In other words, at least 95% by mass, preferably at least 97% by mass, more preferably at least 99% by mass of the cellulose powder particles pass through a sieve with a mesh size of 80 µm, preferably 75 µm, more preferably 70 µm.

[0028] Alternatively or concomitantly, at least 95% by mass, preferably at least 97% by mass, more preferably at least 99% by mass of purified cellulose powder particles have a minimum Feret diameter of at most 80 pm, preferably at most 75 pm, more preferably at most 70 pm.

[0029] Preferably, at least 90% by mass, preferably at least 95% by mass, of the purified cellulose powder particles have a diameter, determined by sieving, of at least 20 µm, preferably at least 30 µm. In other words, at least 90% by mass, preferably at least 95% by mass, of the purified cellulose powder particles do not pass through a sieve with a 20 µm mesh, preferably 30 µm mesh.

[0030] Alternatively or concomitantly, at least 90% by mass, preferably at least 95% by mass of the purified cellulose powder particles have a minimum Feret diameter of at least 20 pm, preferably at least 30 pm.

[0031] Preferably, at least 95% by mass, more preferably at least 97% by mass, and even more preferably at least 99% by mass, of purified cellulose powder particles have a diameter, determined by sieving, of 20 µm to 80 µm, preferably 30 µm to 80 µm, more preferably 30 µm to 75 µm, or even 30 µm to 70 µm. This allows, in particular, for optimized adhesion properties while limiting dust clouds during spraying.

[0032] Alternatively or concurrently, at least 95% by mass, more preferably at least 97% by mass, and even more preferably at least 99% by mass, of purified cellulose powder particles must have a minimum Feret diameter of 20 pm to 80 pm, preferably 30 pm to 80 pm, more preferably 30 pm to 75 pm, or even 30 pm to 70 pm. The minimum Feret diameter is determined, in particular, by dynamic image analysis.

[0033] Purified cellulose powder particles can advantageously have an average projection surface area of ​​less than 5000 pm 2 , preferably less than 4000 pm 2 This allows, in particular, for the optimization of adhesion properties. The average projection surface (S m ) denotes the average value of the projected surfaces of a set of particles. The "projected surface" of a particle is defined as the two-dimensional area obtained by orthogonally projecting the outer silhouette of said particle onto an observation plane perpendicular to the optical axis of the measuring device. This surface corresponds to the apparent area of ​​the particle as observed along this direction and constitutes a representative measure of its size in the plane considered. The average projection surface (denoted here as S) m ) can notably be determined by dynamic image analysis. To determine the average projection area Sm A statistically representative sample of particles is analyzed using an image analysis technique, specifically dynamic image analysis, which allows for the individual measurement of the projected surface area of ​​each particle. Among the known techniques that can be used is a binocular microscope equipped with a camera, coupled with software for calculating the average projection surface area, such as Microvision Ellix. The average projection surface area S m is then obtained as the arithmetic mean of the projected areas measured for all the particles in the lot examined.

[0034] Preferably, the purified cellulose powder has an absolute density of 0.8 to 1.8 g / cm³ 3 , preferably 1.2 to 1.6 g / cm³ 3 . Absolute density represents the density of matter and can be measured using a pycnometer, for example according to ASTM D6226-21.

[0035] The purified cellulose powder particles can be of any shape, for example irregular, elongated, granular or substantially spherical, preferably substantially spherical.

[0036] Preferably, purified cellulose powder particles have an aspect ratio of 1 to 1.5, for example 1 to 1.3. The aspect ratio is the ratio between the largest dimension of the particle and the shortest perpendicular dimension.

[0037] The interlayer material according to the invention may further comprise at least one additive. Indeed, one or more additives may be added to the powder to improve certain properties, such as the fluidity or flow of the cellulose powder. Preferably, the additive is a flow-enhancing agent, for example, an anti-caking agent and / or a lubricant. The additive may, for example, be in powder form or as a liquid sprayed onto the cellulose powder. Non-limiting examples of additives include additives based on fumed silica, precipitated silica, or fumed metal oxides (aluminum oxide, titanium oxide). The mass content of additive(s), in particular flow agent(s), in the interlayer material may be, for example, less than 5% by mass, for example from 0% to 3% by mass, preferably from 0.1% to 1% by mass, preferably from 0.2% to 0.5% by mass, relative to the mass of the interlayer material.

[0038] Advantageously, the interlayer material according to the invention may comprise a corrosion inhibitor, preferably an acid, particularly in powder form, preferably a carboxylic acid. This improves the corrosion protection of the glass. Preferably, the acid is an aliphatic dicarboxylic acid, for example, having an alkyl chain comprising 1 to 18 carbon atoms, preferably 3 to 10 carbon atoms. Non-limiting examples of acids include adipic acid, succinic acid, etc. The mass content of the acid in the interlayer material is preferably less than 80% by mass, for example, 5% to 80% by mass, for example, 5% to 70% by mass, preferably 8% to 60% by mass, more particularly 10% to 50% by mass, relative to the mass of the interlayer material.

[0039] Advantageously, the interlayer material according to the invention may comprise, preferably consists of: - 15% to 100% by mass, preferably 30% to 95% by mass, of purified cellulose powder, - from 0% to 80% by mass, preferably 5% to 70% by mass of corrosion inhibitor, and - 0 to 5%, preferably 0% to 3% by mass, of flow agent.

[0040] The particle size of powders other than cellulose powder is of little importance, as these particles do not necessarily possess the mechanical strength required to withstand heavy loads. Powder particles other than cellulose powder may, for example, have a diameter of no more than 150 µm, or for example, no more than 100 µm, preferably no more than 80 µm. Preferably, the interlayer material is free from any other powder in which more than 5% by mass of the particles has a diameter, determined by sieving, greater than 80 µm.

[0041] Preferably, the interlayer material is free of additives other than an acid as defined above.

[0042] For the purposes of this invention, "exempt" means a mass content of less than 0.5%, preferably less than 0.2%, more preferably less than 0.1%, relative to the total mass of the intercalated material.

[0043] According to a particular embodiment, the interlayer material according to the invention consists of purified cellulose powder, and optionally an acid as defined above, in particular in powder form.

[0044] According to another embodiment, the interlayer material according to the invention consists of purified cellulose powder.

[0045] The present invention also relates, according to a second aspect, to a stack of glass sheets comprising at least two glass sheets separated by a layer of intercalated material according to the invention.

[0046] More specifically, the interlayer material is formed by a monolayer of purified cellulose powder. In other words, the interlayer material is placed between two plates so that there is only one layer of purified cellulose particles.

[0047] In the stacking of glass sheets according to the invention, two sheets can be spaced apart from each other by a distance of 20 to 80 pm, preferably 30 to 80 pm, more preferably 30 to 75 pm, even more preferably 30 to 70 pm.

[0048] The present invention also relates, according to a third aspect, to a method of spacing glass sheets from one another when stacking said glass sheets, the method comprising the application, preferably by spraying, of an intercalary material according to the invention on a first glass sheet and then the positioning of a second glass sheet opposite the first glass sheet, against the face comprising the intercalary material.

[0049] According to another aspect, the present invention also relates to the use of an interlayer material according to the invention for stacking glass sheets, for example for the transport or storage of a stack of glass sheets.

[0050] The invention is illustrated in more detail by the non-limiting examples presented below. Examples

[0051] The tests below were carried out to evaluate the adhesion of various powdered interlayer materials and their impact on the contamination of glass plates, particularly by the bacterial growth they generate.

[0052] Various powdered materials are being evaluated: - Sample 1 is a commercially available PMMA powder, having a particle size distribution of approximately 50 to 70 pm; - Sample 2 is another commercially available PMMA powder, having a particle size distribution of approximately 50 to 70 pm - Sample 3 is a commercially available cellulose powder, having a particle size distribution of approximately 20 to 200 pm; - Sample 3a is prepared by purifying sample 3 according to the purification method described below; - Sample 3b is prepared by sieving sample 3, so as to obtain particles passing through a sieve with a mesh size of 80 pm; - Sample 3c is prepared by sieving sample 3, so as to obtain particles with a diameter greater than 80 pm; - Sample 3d is prepared by purifying sample 3 according to the purification method described below and by sieving to obtain particles passing through a sieve with a mesh size of 80 pm; - Sample 4 is a commercially available starch powder, with a particle size of approximately 20 to 140 pm.

[0053] Samples 3a and 3d of purified cellulose powder were obtained using the following purification method: Approximately 2 g of cellulose powder (commercially available powder sample 3) was dispersed in 100 mL of an aqueous NaOH (IM) solution, and the solution was heated to 90°C under stirring and reflux for 2 hours. The mixture was filtered using a Buchner funnel, and the powder was rinsed several times with distilled water. The powder was then dispersed in an aqueous mixture of 50 mL of a 3% NaOH solution and 50 mL of a 2% H₂O₂ solution. The dispersion was heated to 70°C for 90 minutes under stirring. The mixture was filtered using a Buchner funnel, and the powder was rinsed with distilled water. Redispersion in a NaOH / H₂O₂ mixture was repeated a second time (or until the resulting powder turned white). The powder is then rinsed with ethanol and then dried at 80°C for one hour.

[0054] The sieving of the samples is carried out using a Retsch AS200 digit sieve shaker with 80 pm sieve from VWR, with continuous vibration at 70% amplitude for 10 minutes.

[0055] Adhesion tests are performed using the following method: for each interlayer powder tested, four measurements are taken by spraying the powder with a powder sprayer (similar to a barber's sprayer) onto four 15x15cm glass plates, laid flat and preheated to 100°C for 10 minutes. Each glass plate is then placed vertically approximately 1 cm above a surface and dropped onto this surface (still vertical), causing the interlayer powder particles that did not adhere to the glass to fall. For each glass plate, an adhesion measurement of the interlayer powder on the glass surface is taken using an Ellix device (and its image analysis software), which allows for the evaluation of the average particle projection area "S". m » (in PM) 2 ) : - in its initial state (i.e., just after spraying: Smo), and - after impact (i.e. after a vertical fall: Smœ). The results obtained are listed in Table 1 below and in Figures 1 and 2.

[0056] [Table 1] 1 2 3 3a 3b 3c 3d 4 Sm(i) 2284 2996 5870 5296 4509 8912 3951 3307 Sm(f) 2304 2064 3223 4714 3285 3463 3417 1215 T (%) 100 45 31 92 52 15 78 25

[0057] Figure 1 represents the average projection surface of the particles in the initial state (or before impact "S m (i)") and the average projection surface of the particles in the final state (or after impact "S m (f)") depending on the samples. Figure 2 represents the residual recovery rate "T", which corresponds to the percentage of particles remaining on the glass after the impact.

[0058] The results show that powders with a diameter greater than 80 pm tend to adhere less well to glass, as is the case for cellulose powder 3c, with a diameter greater than 80 pm, compared to cellulose powder 3b. Surprisingly, the purified powder 3d according to the invention, with a diameter of at most 80 pm, exhibits even better adhesion to glass with a synergistic effect compared to purified powder 3a and unpurified powder 3b sieved with the same 80 pm mesh.

[0059] Bacterial growth tests are performed according to the method described below. Approximately 500 mg of the interlayer powder to be tested is introduced into 20 mL of unsterilized deionized water. The suspensions are incubated at 45°C in 25 cm³ cell culture flasks. 2Bacterial enumeration is performed at t0 (i.e., immediately after suspension), at t7j (i.e., after 7 days of incubation), and then at t14j (i.e., after 14 days of incubation). Each bacterial enumeration is performed by loading onto a so-called "minimum" medium (growth conditions on a synthetic medium "R2A") at 30°C for 68 hours. The results are expressed in CFU (Colony Forming Units) per mL of sample. These bacterial enumeration tests are also performed on a sample "E" without intercalated powder (initial water). The results obtained are shown in Figure 3. The limit "D" represents the detection threshold for bacterial colonies.

[0060] The results show that commercially available natural powders no. 3 (cellulose powder) and no. 4 (starch powder) promote bacterial growth. This problem was not known with previous synthetic powders such as PMMA (sample no. 1) and can be detrimental to subsequent glass treatments, as well as posing health risks in the event of the presence and development of pathogens. In contrast, the purified cellulose powder sample according to the present invention (3d) limits bacterial growth with results equivalent to those of the synthetic powders.

[0061] In conclusion, the 3d sample according to the invention comprising the purified cellulose powder surprisingly exhibits improved adhesion to the surface of the glass and protects the wash water against bacterial growth.

Claims

Demands 1. Glass plate interlayer material comprising a cellulose powder, in which the cellulose powder is purified, at least 95% by mass of the cellulose powder particles have a diameter, determined by sieving, of not more than 80 pm, preferably not more than 75 pm, preferably not more than 70 pm, and at least 90% by mass of the cellulose powder particles have a diameter, determined by sieving, of not more than 20 pm.

2. Interlayer material according to claim 1, in which the cellulose powder comprises at least 97% by mass of cellulose, preferably at least 98% by mass, more preferably at least 99% by mass of cellulose.

3. Interlayer material according to any one of the preceding claims, the interlayer material being free of interlayer powder other than said cellulose powder.

4. Interlayer material according to any one of the preceding claims, wherein at least 97% by mass, more preferably at least 99% by mass of the cellulose powder particles have a Feret diameter of at most 80 pm, preferably at most 75 pm, more preferably at most 70 pm.

5. Interlayer material according to any one of the preceding claims, wherein at least 95% by mass, more preferably at least 97% by mass of the cellulose powder particles have a diameter, determined by sieving, of 30 pm to 80 pm, more preferably of 30 pm to 75 pm, or even of 30 pm to 70 pm.

6. Interlayer material according to any one of the preceding claims, wherein the cellulose powder particles have an average projection surface area of ​​less than 5000 pm 2 preferably less than 4000 pm 27. Interlayer material according to any one of the preceding claims, wherein the cellulose powder has an absolute density of 0.8 to 1.8 g / cm³ 3 , preferably 1.2 to 1.6 g / cm³ 3 .

8. Interlayer material according to any one of the preceding claims, wherein the cellulose powder particles have an aspect ratio of 1 to 1.5, preferably 1 to 1.

3.

9. Interlayer material according to any one of the preceding claims, comprising an acid, in particular in powder form.

10. Interlayer material according to any one of the preceding claims, comprising, preferably, of: - from 15% to 100% by mass, preferably 30% to 95% by mass, of said cellulose powder, - from 0% to 80% by mass, preferably 5% to 70% by mass of corrosion inhibitor, and - 0 to 5%, preferably 0% to 3% by mass, of flow agent.

11. Interlayer material according to any one of the preceding claims, the interlayer material being free from any other powder of which more than 5% by mass of the particles has a diameter, determined by sieving, greater than 80 pm.

12. Interlayer material according to any one of the preceding claims, consisting of said cellulose powder, and optionally an acid, in particular in powder form.

13. Use of a cellulose powder as an interlayer material between two glass substrates, said cellulose powder being purified and at least 95% by mass of the cellulose powder particles having a diameter, determined by sieving, of at most 80 pm, preferably of at most 75 pm, preferably of at most 70 pm.

14. Stacking of glass sheets comprising at least two glass sheets separated by a layer of interlayer material according to any one of claims 1 to 12.

15. Method for spacing glass sheets from one another when stacking said glass sheets, the method comprising applying, preferably by spraying, an interlayer material according to any one of claims 1 to 12 on a first glass sheet and then positioning a second glass sheet opposite the first glass sheet, against the face comprising the interlayer material.

16. Use of an interlayer material according to any one of claims 1 to 12 for stacking glass sheets, for example for transporting or storing a stack of glass sheets.

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