COMPOSITION OF RETROREFLECTIVE AQUEOUS PSEUDOPLASTIC GEL FOR INDUSTRIAL SPRAYING.

Abstract

The invention relates to an aqueous pseudoplastic gel composition having a first viscosity η1 at a shear rate of 0.01 s-1 of between 5 and 200 Pa·s and a second viscosity η2 at a shear rate of 100 s-1 that is between 10 and 1000 times lower than the first viscosity, wherein the aqueous pseudoplastic gel contains, based on the total weight of the composition: • from 15 to 60% by weight of water; • from 20 to 60% by weight of spherical glass beads having a mean particle diameter D50, as measured by laser diffraction, of between 5 and 150 µm, and a refractive index, measured at a wavelength λ of 589 nm, of between 1.8 and 2.8; • from 0.15 to 1.5% by weight of a thickener; and • from 0 to 50% by weight of one or more additional ingredients. The invention also relates to procedures for its preparation.The invention further relates to a process for coating a substrate with a retroreflective layer using said aqueous pseudoplastic gel composition and to substrates coated with a retroreflective layer that can be obtained by said process.

Description

COMPOSITION OF AQUEOUS RETROREFLECTIVE PSEUDOPLASTIC GEL FOR INDUSTRIAL SPRAYING FIELD OF INVENTION The invention relates to an aqueous pseudoplastic gel composition and processes for its preparation. The invention further relates to a process for coating a substrate with a retroreflective layer using said aqueous pseudoplastic gel composition and to substrates coated with a retroreflective layer obtainable by said process. BACKGROUND OF THE INVENTION Retroreflective paints, inks, and coatings are used in a variety of applications. For example, they improve the visibility of traffic signs, road markings, textiles, automobiles, and so on, in low-light conditions. Paints, inks, and coatings typically achieve retroreflective properties through the addition of spherical glass beads with a specific refractive index. Retroreflection occurs through the combined action of incident light refracting through the top surface of a spherical glass bead, internal reflection from the lower lateral surface of the bead, and subsequent refraction of the light as it exits the top surface of the bead, traveling back in the direction from which the incident light originated. WO2004 / 017104A2 discloses retroreflective compositions comprising retroreflective microspheres, a binder system, and a thixotropic mixture comprising at least two thixotropic agents in an amount of approximately 2 to approximately 5% by weight, based on the retroreflective composition. The composition may include water. The retroreflective compositions are intended for use as paints, inks, and coatings and are applied to a substrate using aerosol applicators with a propellant. Table 1 of WO2004 / 017104A2 discloses typical and preferred amounts of the ingredient classes in the compositions.Example 1 of WO2004 / 017104A2 discloses a composition in which the solvent is an undefined aliphatic or aromatic naphtha, the solid resin granules are of an undefined acrylic type, the first thixotrope is of an undefined polyurea type, and the second thixotrope is an undefined calcium sulfonate complex. The accompanying viscosity of the composition in Example 1, measured with a Brookfield No. 3 spindle at 25 °C, would be between 9,000 and 30,000 cps at 0.5 rpm and between 600 and 1,900 cps at 20 rpm. Document WO01 / 16223A1 refers to retroreflective inks for printing on textiles. The only example in WO01 / 16223A1 discloses a screen printing ink. This screen printing ink consists of: • 3 parts of base 409 AG Reflective Clear LF (comprising water and spherical glass beads and a matrix material); • 1 part of Grancill PWX binder and finish (containing water as a volatile component); and • 2% by volume of CX100 crosslinker, based on the combined volume of base 409 AG Reflective Clear LF and Grancill PWX. The viscosity of the 409 AG Reflective Clear LF base is described as being approximately 0.090 to 0.110 centistokes. The kinematic viscosity v [cSt] is related to the dynamic viscosity μ [Pa-s] as follows: v [cSt] = 1.10+6μ [Pa-s] / p [kg / m3] Given a realistic estimate of the density ρ of 409 AG Reflective Clear LF base of 1300 g / m³, the dynamic viscosity μ of 409 AG Reflective Clear LF base is between 0.12 and 0.14 mPa·s. As experts will appreciate, a viscosity more than seven times lower than that of water is simply not possible for a mixture of water, a considerable amount of glass beads, a binding agent, a finishing agent, and other volatile components. The viscosity of the final screen printing ink is not disclosed in the example in WO01 / 16223A1. Screen printing is a printing technique in which a mesh is used to transfer paste-like ink onto a substrate, except in areas made impervious to ink by means of a blocking stencil.A blade or squeegee is moved across the screen to fill the open mesh openings with ink, and then a reverse motion causes the screen to momentarily touch the substrate along a contact line. This causes the ink to wet the substrate and flow out of the mesh openings as the screen snaps back after the blade has passed. As is generally known to printing experts, the properties of screen printing inks and professional or industrial (high-speed) spray inks are fundamentally different due to the distinct techniques used to apply them to a substrate. Screen printing inks are not suitable for professional or industrial (high-speed) spraying. Document WO00 / 42113A1 relates to retroreflective inks comprising microbeads in a liquid carrier medium. The liquid carrier medium may be water. The inks are intended for screen printing on textiles. Document WO00 / 42113A1 discloses that the viscosity of a screen printing ink is 10 to 30 Pa·s at room temperature, measured with a Brookfield viscometer using a No. 5 spindle rotating at 10 rpm. The inks disclosed in Tables 1 to 4 and 6 comprise water, a thickening agent, and glass beads. The viscosities are between 12.3 and 32 Pa·s at room temperature, measured with a Brookfield viscometer using a No. 5 spindle rotating at 10 rpm.As explained above, in the context of document WO01 / 16223A1, those with experience in the field of printing generally know that the technical characteristics of screen printing inks and professional or industrial (high speed) spray inks are fundamentally different due to the fundamentally different techniques used to apply them to a substrate. Developing retroreflective compositions that have good stability and sprayability is challenging because the rheology modifiers needed to keep the retroreflective particles, such as spherical glass beads, which generally have a substantially higher density than the fluid vehicle, distributed homogeneously throughout the fluid vehicle generally negatively affect the rheological behavior during spraying. There is a need for retroreflective inks, coatings, and paints that are shelf-stable and can still be easily applied to a variety of substrates, preferably by professional or industrial (high-speed) spraying, resulting in good quality retroreflective layers or coatings. Accordingly, an object of the invention is to provide aqueous retroreflective compositions that can be applied professionally or industrially, such as paint, ink, or coating, to a variety of substrates, wherein said aqueous retroreflective compositions can be applied to the substrate by means of spraying, such as professional or industrial (high-speed) spraying, and wherein said aqueous retroreflective compositions have sufficient stability or shelf life. A further object of the invention is to provide aqueous retroreflective compositions that can be applied professionally or industrially, as paint, ink, or coating, to a variety of substrates by means of spraying, such as professional or industrial (high-speed) spraying, to result in good or improved print or coating quality, such as good or improved layer homogeneity and wide-angle retroreflectivity, and preferably good or improved layer smoothness and cleanability. DESCRIPTION OF THE INVENTION The inventors have unexpectedly established that one or more of the objectives can be met by using an aqueous retroreflective composition that is an aqueous pseudoplastic gel composition, having a first viscosity η\ at a shear rate of 0.01 s'1 of between 5 and 200 Pas and a second viscosity / 72 at a shear rate of 100 s'1 that is between 10 and 1000 times lower than the first viscosity. Thus, in a first aspect, the invention relates to an aqueous pseudoplastic gel composition, preferably for professional or industrial (high-speed) spraying, having a first viscosity η1 at a shear rate of 0.01 s⁻¹ of between 5 and 200 Pa-s, and a second viscosity η2 at a shear rate of 100 s⁻¹ that is between 10 and 1000 times lower than the first viscosity, wherein the aqueous pseudoplastic gel contains, on a total weight basis, the following: • 15 to 60% water by weight; • 20 to 60% by weight of spherical glass beads having a median particle diameter D50, as measured by laser diffraction, of between 5 and 150 pm, preferably between 20 and 150 pm, and a refractive index, measured at a wavelength λ of 589 nm, of between 1.8 and 2.8, wherein optionally at least some of the spherical glass beads are coated in a semi-spherical manner with a light-reflecting coating; • 0.15 to 1.5% by weight of a thickener; and • 0 to 50% by weight of one or more additional ingredients; in which viscosity is measured with a rheometer with plate-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C. The inventors have established that this aqueous pseudoplastic gel composition can be applied, for example, by high-speed industrial spraying, to various substrates, resulting in retroreflective coating layers with excellent print or coating quality, such as homogeneity and wide-angle retroreflectivity. If the retroreflective coating is provided with one or more additional transparent coating layers, a retroreflective layer with high smoothness and good cleanability can be obtained. Unexpectedly, these results can also be achieved when the aqueous pseudoplastic gel composition is applied to the surface of a vertically positioned substrate. Secondly, a process for the preparation of the aqueous pseudoplastic gel composition is provided in accordance with the definition in this document, said process comprising the following steps: (i) add water, the spherical glass beads as defined herein, the thickener as defined herein and one or more optional additional ingredients as defined herein to a container; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (iii) optionally adjusting the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. Thirdly, a process is provided for the preparation of the aqueous pseudoplastic gel composition as defined in this document, said process comprising the following steps: (i) adding water, the spherical glass beads as defined herein, at least part of the thickener as defined herein and optionally part of one or more additional ingredients as defined herein to a container; (ii) stir or homogenize the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; (iii) optionally adjust the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11; (iv) add at least part of one or more additional ingredients as defined herein to the composition obtained in step (ii) or (iii), optionally add part of the thickener as defined herein and optionally add water; (v) stirring or homogenizing the mixture obtained in step (iv), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (vi) optionally adjusting the pH before or after step (v), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. In a fourth aspect of the invention, a process is provided for the preparation of the aqueous pseudoplastic gel composition as defined herein, said process comprising the steps of: (i) adding water, the spherical glass beads as defined herein, at least part of the thickener as defined herein and optionally part of one or more additional ingredients as defined herein to a container; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 5 and 30 °C, preferably for a period of between 5 and 15 minutes, to obtain an intermediate aqueous pseudoplastic gel composition having the composition and properties of the aqueous pseudoplastic gel composition as defined herein; (iii) optionally adjust the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11; (iv) adding at least part of one or more additional ingredients as defined herein to the intermediate aqueous pseudoplastic gel composition obtained in step (ii) or (iii), optionally adding part of the thickener as defined herein and optionally adding water; (v) stirring or homogenizing the mixture obtained in step (iv), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes, to obtain the aqueous pseudoplastic gel composition; and (vi) optionally adjusting the pH before or after step (v), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. In a fifth aspect, the invention relates to a process for coating a substrate with a retroreflective layer, said process comprising the steps of: a) providing a substrate; b) optionally apply a primer coat to the substrate of step (a); c) spraying the aqueous pseudoplastic gel composition as defined herein onto the substrate of step (a) or onto the primed substrate of step (b) to provide a substrate coated with a retroreflective layer; d) optionally drying the substrate coated with the retroreflective layer obtained in step (c); and e) optionally coating the substrate coated with the retroreflective layer obtained in step (c) or the dry substrate coated with the retroreflective layer obtained in step (d) with one or more transparent coating layers followed by drying or curing. In a sixth aspect, the invention relates to substrates coated with a retroreflective layer that can be obtained by means of the process for coating a substrate as defined herein. DEFINITIONS The term “pseudoplastic gel” as used in this document refers to gels that exhibit shear thinning behavior and have no elastic limit. The term “shear thinning behavior” in the context of the pseudoplastic gel of the present invention refers to a reduction in viscosity when the pseudoplastic gel, initially in a static state, is subjected to a shear rate. The term “tan(δ)”, where δ is the phase change, is defined by the ratio G” / G, according to common understanding in the field of rheology. G” represents the loss modulus and characterizes the viscous or liquid behavior of the sample. G represents the storage modulus and characterizes the elastic or solid behavior of the sample. If a sample exhibits purely viscous behavior and no elastic behavior, then δ = 90°, G’ = 0, and tan(δ) = 0. If a sample exhibits purely elastic behavior and no viscous behavior, then δ = 0°, G” = 0, and tan(δ) = 0. If the sample has a non-zero phase change δ less than 45°, tan(δ) is less than 1, G is greater than G”, and the sample exhibits gel-like behavior in the sense that elastic behavior dominates viscous behavior. BRIEF DESCRIPTION OF THE FIGURES Figure 1 represents a viscosity versus shear rate profile of aqueous pseudoplastic gel compositions according to the invention. Figure 2 represents the thixotropic behavior of the aqueous pseudoplastic gel compositions of Figure 1. Figure 3 represents the tan(<5) profiles as a function of the oscillatory frequency of the aqueous pseudoplastic gel compositions according to the invention. DETAILED DESCRIPTION In a first aspect, the invention relates to an aqueous pseudoplastic gel composition, preferably for professional or industrial (high-speed) spraying, having a first viscosity 71 at a shear rate of 0.01 s'1 of between 5 and 200 Pa-s and a second viscosity 72 at a shear rate of 100 s'1 that is between 10 and 1000 times lower than the first viscosity, wherein the aqueous pseudoplastic gel contains, on a total weight basis of the composition: • 15 to 60% water by weight; • 20 to 60% by weight of spherical glass beads having a median particle diameter D50, as measured by laser diffraction, of between 5 and 150 pm, preferably between 20 and 150 pm, and a refractive index, measured at a wavelength λ of 589 nm, of between 1.8 and 2.8, wherein optionally at least some of the spherical glass beads are coated in a semi-spherical manner with a light-reflecting coating; • 0.15 to 1.5% by weight of a thickener; and • 0 to 50% by weight of one or more additional ingredients; in which viscosity is measured with a rheometer with plate-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C. In preferred embodiments, the aqueous pseudoplastic gel composition is stable for at least 1 day, more preferably at least 2 days, at least 5 days, at least 10 days, at least 1 month, at least 2 months, at least 6 months, at least 1 year, at least 2 years, wherein the composition is considered stable if, upon visual and tactile inspection, no sedimentation, syneresis, or separation can be observed. The aqueous pseudoplastic gel composition as defined in this document is preferably an ink, paint, or coating formulation. Spherical glass beads According to what has been previously defined in this report, the refractive index of spherical glass beads, measured at a wavelength λ of 589 nm, is between 1.8 and 2.8. The term “glass” in “spherical glass beads,” as used herein, refers to a transparent, amorphous, non-crystalline solid material made of oxides. The refractive index of spherical glass beads is closely related to the density of the glass, although the relationship is not linear. Due to the nature of glass, density is approximately an additive function of its composition. The densities of spherical glass beads with refractive indices between 1.5 and 2.8 typically range from 2.5 to 4.5 g / cm³. The oxides that can be used in glass are oxides of silicon, boron, aluminum, sodium, barium, vanadium, titanium, lanthanum, strontium, zirconium, potassium, magnesium, iron, calcium, zinc, lithium, barium and lead. Spherical glass beads can comprise, for example, different combinations of silica (S1O2), boric oxide (B2O3), phosphorus pentoxide (P2O5), vanadium pentoxide (V2O5), arsenic trioxide (As2O3), germanium oxide (GeO2), calcium oxide (CaO), sodium oxide (Na2O), magnesium oxide (MgO), zinc oxide (ZnO), aluminum oxide (Al2O3), potassium oxide (K2O), iron oxide (Fe2O3), lead oxide (PbO), barium oxide (BaO), barium titanate (BaTiCF), titanium oxide (T1O2), lithium oxide (L12O), strontium oxide (SrO), lanthanum oxide (La2O3), and zirconium oxide (ZrO2). Silica and boric oxide are generally the least dense.Therefore, glasses containing high weight percentages of these oxides generally result in glass beads with low refractive indices. Refractive indices can be increased by adding oxides with higher molecular weights. Preferably, spherical glass beads do not contain PbO. Glass beads having refractive indices in the range of 1.5 to 2.51 and their composition in terms of oxides are disclosed in WO2014 / 109564A1, which is incorporated herein by reference in its entirety. Transparent, lead-free glass beads with refractive indices above 2.15 are disclosed in US 4,082,427, which is incorporated herein by reference in its entirety. Spherical glass beads can be colored spherical glass beads, provided they remain transparent. The invention encompasses both colored spherical glass beads made of colored transparent glass and spherical glass beads provided with a concentric transparent colored coating. The color can be the natural color resulting from the composition of the oxides or can be deliberately selected by adding ingredients that have a specific color. Colored glass beads with high refractive indices and high transparency are disclosed in WO2014 / 109564A1. Accordingly, in one embodiment, at least some of the spherical glass beads are spherical glass beads made of colored transparent glass and / or at least some of the spherical glass beads are provided with a concentric transparent colored coating. Spherical glass beads have a median particle diameter D50, as measured by laser diffraction. Consequently, the median particle diameter D50 is a volume median, based on a volume distribution. The median particle diameter D50 is the diameter below which half of the population of spherical glass beads lies. This diameter of MA / a / ¿U¿¿ / UUO l ¿l volume median particle in the art is often referred to as Dv50 or Dvo,5In a preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 25 and 100 pm, preferably between 30 and 75 pm, with greater preference between 35 and 50 pm. In another preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 5 and 100 pm, such as between 5 and 75 pm, between 5 and 50 pm, between 5 and 45 pm, between 5 and 40 pm, or between 5 and 35 pm. In yet another preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 25 and 150 pm, such as between 50 and 150 pm, between 75 and 150 pm, between 100 and 150 pm, between 110 and 150 pm, or between 115 and 150 pm. The DIO and D90 diameters in the technique are often referred to as DvlO or Dvo,iy and Dv90 or Dvo.9, respectively. The DIO diameter is the diameter below which 10% of the spherical glass bead population lies. Similarly, the D90 diameter is the diameter below which 90% of the spherical glass bead population lies. The span, as measured by laser diffraction, of the particle size distribution of spherical glass beads is defined by: D90 — DIO D50 In further preferred embodiments, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 25 and 100 pm and a span between 0 and 1, preferably between 0 and 0.7, more preferably between 0 and 0.5, even more preferably between 0 and 0.2, and even more preferably between 0 and 0.1. In a more preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 30 and 75 pm and a span between 0 and 1, preferably between 0 and 0.7, more preferably between 0 and 0.5, even more preferably between 0 and 0.2, and even more preferably between 0 and 0.1. In an even more preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 35 and 50 pm and a span between 0 and 1, preferably between 0 and 0.7, with greater preference between 0 and 0.5.even more so between 0 and 0.2, even more so between 0 and 0.1. In another more preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 5 and 35 pm and a span between 0 and 2, such as between 0 and 1.8, between 0 and 1.5, between 0 and 1.25 and between 0 and 1, or such as between 0.5 and 2, between 1 and 2 and between 1.25 and 2. In another, even more preferred embodiment, the spherical glass beads have a median particle diameter D50, as measured by laser diffraction, between 10 and 25 pm and a span between 0 and 2, such as between 0 and 1.8, between 0 and 1.5, between 0 and 1.25 and between 0 and 1, or such as between 0.5 and 2, between 1 and 2 and between 1.25 and 2. As those experienced in the technique will appreciate, lapso = 0 corresponds to monodisperse spherical glass beads. In a preferred embodiment, at least some of the spherical glass beads are coated hemispherically with a light-reflecting coating. An example is a hemispherical aluminum coating. Although this is possible, it is not essential to provide the effects described herein. Accordingly, in one embodiment, the spherical glass beads are not coated hemispherically with a light-reflecting coating. In a preferred embodiment, the amount of spherical glass beads is 25 to 55% by weight, more preferably 26 to 52% by weight, even more preferably 27 to 50% by weight, based on the total weight of the aqueous pseudoplastic gel composition. In embodiments, the amount of spherical glass beads is 20 to 55% by weight, 20 to 50% by weight, 20 to 45% by weight, 20 to 40% by weight, 20 to 35% by weight, 20 to 30% by weight or 20 to 25% by weight, based on the total weight of the aqueous pseudoplastic gel composition. In other embodiments, the amount of spherical glass beads is 22 to 60% by weight, 25 to 60% by weight, 30 to 60% by weight, 35 to 60% by weight, 40 to 60% by weight, 45 to 60% by weight, 50 to 60% by weight or 55 to 60% by weight, based on the total weight of the aqueous pseudoplastic gel composition. The specific application of the aqueous pseudoplastic gel composition determines the optimum refractive index of the spherical glass beads. If the composition is to be applied in a dry environment or on a substrate that will exhibit retroreflectivity under dry conditions, and where the applied layer of retroreflective spherical glass beads is not coated with an additional layer, the refractive index of the spherical glass beads, measured at a wavelength λ of 589 nm, may be between 1.8 and 2.8. In one embodiment, the aqueous pseudoplastic gel composition as defined herein comprises spherical glass beads having a refractive index, measured at a wavelength λ of 589 nm, between 1.8 and 2.0. If, on the other hand, the composition is to be applied in a humid environment or on a substrate that will exhibit retroreflectivity under humid conditions, or if the applied layer of retroreflective spherical glass beads is coated with one or more additional transparent layers, the refractive index of the spherical glass beads, measured at a wavelength λ of 589 nm, is preferably between 2.0 and 2.8, with greater preference between 2.2 and 2.4. Compositions that are to exhibit retroreflectivity under both dry and humid conditions, and in which the applied layer of retroreflective spherical glass beads is or is not coated with one or more additional transparent layers, may comprise different types of glass beads having different refractive indices and, optionally, different sizes.In one embodiment, the aqueous pseudoplastic gel composition as defined herein comprises spherical glass beads having a refractive index, measured at a wavelength λ of 589 nm, between 2.0 and 2.8, preferably between 2.2 and 2.4. In another embodiment, the aqueous pseudoplastic gel composition as defined herein comprises at least two types of spherical glass beads, wherein at least one type of spherical glass beads has a refractive index, measured at a wavelength λ of 589 nm, between 1.8 and less than 2.0, and at least one other type of spherical glass beads has a refractive index, measured at a wavelength λ of 589 nm, between 2.0 and 2.8. Thickener The aqueous pseudoplastic gel composition includes a thickener. Without intending to be bound to any particular theory, it is believed that the thickener limits or prevents the settling and / or sedimentation of the spherical glass beads and, optionally, other particles within the aqueous pseudoplastic gel composition. Furthermore, again without intending to be bound to any particular theory, it is believed that the thickener imparts shear-thinning behavior to the gel composition. In one embodiment, the thickener comprises mixtures of different thickeners. In preferred embodiments, the thickener consists of a single thickener. A preferred group of thickeners are ASE polymers (Alkaline Swellable Emulsions; these polymers are produced using emulsion polymerization). ASE polymers are based on an equilibrium of hydrophilic (meth)acrylic acid monomers and hydrophobic (meth)acrylate ester monomers and can be supplied in liquid form with a high volume of solids. ASE polymers rely on a change from low to high pH (neutralization) to trigger thickening. The "trigger" is built into the polymer by creating an approximately 50:50 ratio of water-soluble (meth)acrylic acid and a water-insoluble (meth)acrylate ester. When the acid is not neutralized (low pH), the polymer is water-insoluble and does not thicken. When the acid is fully neutralized (high pH), the polymer becomes soluble and thickens.ASE polymers are supplied at a low pH (< 5) and maintain a low viscosity as supplied (< 100 cP) with up to 35% solids. When subjected to a pH of approximately 7 or higher, ASE polymers solubilize, swell, and thicken the composition by volume exclusion. The degree of thickening is related to the polymer's molecular weight. Because their performance depends on water absorption and swelling, ASE polymers tend to have a very high molecular weight, allowing them to thicken efficiently. The thermal profiles created by ASE polymers typically exhibit pronounced shear thinning (pseudoplasticity), and therefore, ASE polymers are well-suited for generating high viscosity at very low shear rates. In one embodiment, the hydrophilic monomers of the ASE polymer are selected from the group consisting of (meth)acrylic acid, maleic acid, and combinations thereof. In another embodiment, the hydrophobic monomers of the ASE polymer are selected from the group consisting of (meth)acrylic acid esters with C4 C1 alcohols, in particular ethyl acrylate, butyl acrylate, and methyl methacrylate. In another further preferred embodiment, the hydrophilic monomers of the ASE polymer are selected from the group consisting of (meth)acrylic acid, maleic acid and combinations thereof, and the hydrophobic monomers of the ASE polymer are selected from the group consisting of esters of (meth)acrylic acid with C1 to C4 alcohols, in particular ethyl acrylate, butyl acrylate and methyl methacrylate. In one embodiment, the ASE polymer is a copolymer consisting of 10 to 90 wt%, based on the weight of the ASE polymer, of repeating units based on one or more hydrophilic monomers A and 10 to 90 wt% of repeating units based on one or more hydrophobic monomers B, wherein the amounts of monomers A and B sum to 100 wt%: (A) (B) wherein Ri and R? are independently hydrogen or methyl and wherein R3 is C4 alkyl. Another preferred group of thickeners are HASE polymers (hydrophobically modified alkaline swellable emulsions; these polymers are produced using emulsion polymerization). HASE polymers are copolymers based on ASE polymer chemistry through the addition of one or more hydrophobic associative monomers, such as an acrylic ester and / or vinyl ester monomer, to the ASE polymer composition. HASE polymers retain the pH-dependent behavior of their ASE equivalents, but in addition to absorbing water, HASE polymers also thicken by hydrophobic association. This mechanism is known as associative thickening (i.e., association with any hydrophobic moiety in the composition). The hydrophilic and hydrophobic monomers of HASE polymers can be the same as those described for ASE polymers. The preferred hydrophobic associative monomers are (meth)acrylic ester monomers of (meth)acrylic acid and Cs-C22 alcohols and / or vinyl ester monomers of (substituted) vinyl alcohols and Cs-C22 alkyl acids. In another preferred embodiment, one or more hydrophobic associative monomers are selected from the group consisting of steareth-20 methacrylate, beheneth-25 methacrylate, vinyl neodecanoate, and combinations thereof. In one embodiment, the HASE polymer is a copolymer consisting of 10 to 90 wt%, based on the weight of the HASE polymer, of repeating units based on one or more hydrophilic monomers A as defined above in this specification, 10 to 90 wt% of repeating units based on one or more hydrophobic monomers B as defined above in this specification, and 0.01 to 2 wt% of repeating units based on one or more hydrophobic associative monomers C and / or D, wherein the amounts of monomers A, B, C and D sum to 100 wt%: (C) (D) wherein R4 is hydrogen or methyl, wherein R5 is Cs to C22 alkyl, wherein n is an integer from 0 to 50, wherein Ró is hydrogen or methyl and wherein R7 is Cs to C22 alkyl. Another preferred group of thickeners is hydrophobically modified ethoxylated urethane (HEUR) polymers. Unlike ASE or HASE thickeners, HEUR polymers are non-ionic and soluble at any pH. This solubility is due to the polymer's ethylene oxide backbone, which is water-soluble and constitutes the majority of the polymer's structure. Therefore, HEUR polymers require a hydrophobic moiety in their composition to interact with the ethylene oxide backbone and impart structure. Examples of ASE polymers include Rheovis® 1125 (available from BASF Corporation), ACULYN™ 33; ACULYN™ 38, ACUSOL™ 810A, ACUSOL™ 830, ACUSOL™ 835, ACUSOL™ 842 (all available from DOW Chemical) and Carbopol® Aqua 30 polymer (from Lubrizol Corporation). Examples of HASE polymers include ACULYN™ Excel, ACRYSOL™ TT615, ACULYN™ 22; ACULYN™ 88, ACUSOL™ 801S, ACUSOL™ 805S, ACUSOL™ 820 and ACUSOL™ 823 (all available from DOW Chemical). Examples of HEUR polymers include ACUSOL™ 880, ACUSOL™ 882, ACULYNTM 44 and ACULYNTM 46N (all available from DOW Chemical). In another embodiment, the thickener is selected from the group consisting of acrylate crosspolymers, crosslinked polyacrylic acid polymers, and crosslinked polyacrylic acid copolymers, in particular from Lubrizol Corporation's Carbopol® Polymer products, such as Carbopol® AQUA SF-1 Polymer, Carbopol® AQUA SF-1 OS Polymer, and Carbopol® Aqua SF-3 Polymer. In yet another embodiment, the thickener is selected from the group consisting of liquid dispersions of acrylics or crosslinked copolymers. In another embodiment, the thickener is selected from non-ionic aqueous emulsions of a modified ethylene vinyl acetate copolymer wax, such as Aquatix 8421, available from BYK. In yet another embodiment, the thickener is selected from modified urea or urea-modified polyamides, such as Rheobyk-420, available from BYK. In one embodiment, the thickener is selected from the group consisting of ASE polymers, HASE polymers, HEUR polymers, liquid dispersions of acrylics or crosslinked copolymers, acrylate crosslinked polymers, crosslinked polyacrylic acid polymers, crosslinked polyacrylic acid copolymers, non-ionic aqueous emulsions of a modified vinyl acetate ethylene copolymer wax, modified urea or urea-modified polyamides, and combinations thereof. In another embodiment, the thickener is selected from the group consisting of ASE polymers, HASE polymers, HEUR polymers, liquid dispersions of acrylics or crosslinked copolymers, acrylate crosslinked polymers, crosslinked polyacrylic acid polymers, crosslinked polyacrylic acid copolymers, non-ionic aqueous emulsions of a modified vinyl acetate ethylene copolymer wax, and combinations thereof. In another embodiment, the thickener is selected from the group consisting of ASE polymers, HASE polymers, HEUR polymers, liquid dispersions of acrylics or crosslinked copolymers, crosslinked polyacrylic acid polymers, crosslinked polyacrylic acid copolymers, and combinations thereof. In another embodiment, the thickener is selected from the group consisting of ASE polymers, HASE polymers, and combinations thereof. In one embodiment, the thickener is selected from the group consisting of ASE polymers and combinations thereof. In another embodiment, the thickener is selected from the group consisting of HASE polymers and combinations thereof. In a preferred embodiment, the amount of thickener is 0.20 to 1.4% by weight, more preferably 0.25 to 1.3% by weight, even more preferably 0.30 to 1.2% by weight, based on the total weight of the aqueous pseudoplastic gel composition. In various embodiments, the amount of thickener is 0.15 to 1.4% by weight, 0.15 to 1.3% by weight, 0.15 to 1.2% by weight, 0.15 to 1.1% by weight, 0.15 to 1.0% by weight, 0.15 to 0.9% by weight, 0.15 to 0.8% by weight, 0.15 to 0.7% by weight, 0.15 to 0.6% by weight, 0.15 to 0.55% by weight, of 0.15 to 0.5% by weight or 0.15 to 0.45% by weight, based on the total weight of the aqueous pseudoplastic gel composition. In other embodiments, the amount of thickener is 0.20 to 1.5% by weight, 0.25 to 1.5% by weight, 0.30 to 1.5% by weight, 0.35 to 1.5% by weight, 0.40 to 1.5% by weight, 0.45 to 1.5% by weight, 0.50 to 1.5% by weight, 0.55 to 1.5% by weight or 0.6 to 1.5% by weight, based on the total weight of the aqueous pseudoplastic gel composition. The amount of water in the aqueous pseudoplastic gel composition is specified separately. If a thickener is applied in the form of, for example, a water dispersion, the amount of thickener, as defined above in this document, refers to the dry weight of the thickener. Other ingredients In a preferred embodiment, one or more additional ingredients are selected from the group consisting of humectants, preservatives, colorants, luminescent agents such as phosphorescent and fluorescent agents, pigments, UV absorbers, binders and resins, mica flake pigments and metallic flakes or powders. Non-limiting examples of humectants that can be used are 2,3-propanediol, ethylene glycol, and butylene glycol. Examples of binders and resins that can be used are water-based binders and resins, such as aqueous dispersions of binders and resins. Metallic flakes or powders can be used as reflective pigments. Examples include flakes of aluminum, bronze, copper, gold, silver, tin, and nickel, with aluminum flakes being preferred. The size of the flakes is usually substantially smaller than that of spherical glass beads. Mica flake pigment can also be used as a reflective pigment, such as pearlescent pigments based on mica flake. In embodiments, the amount of one or more additional ingredients is 0 to 45% by weight, 0 to 40% by weight, 0 to 35% by weight, 0 to 30% by weight, 0 to 25% by weight, 0 to 20% by weight, 0 to 15% by weight, 0 to 10% by weight or 0 to 5% by weight, based on the total weight of the aqueous pseudoplastic gel composition. In other embodiments, the amount of one or more additional ingredients is 5 to 50% by weight, 10 to 50% by weight, 15 to 50% by weight, 20 to 50% by weight, 25 to 50% by weight, 30 to 50% by weight, 35 to 50% by weight, 40 to 50% by weight or 45 to 50% by weight, based on the total weight of the aqueous pseudoplastic gel composition. The amount of water in the aqueous pseudoplastic gel composition is specified separately. If one or more additional ingredients are applied in form or, for example, as a dispersion in water, the amount of one or more additional ingredients defined above in this specification refers to the dry weight, i.e., the weight without water, of one or more additional ingredients. Rheological behavior Aqueous gel composition exhibits pseudoplastic behavior, meaning it undergoes shear thinning without reaching an elastic limit. This means the composition is gel-like but still flowable under static / stable conditions (without shear) and also gel-like (and capable of flow) at increasing shear rates. In other words, aqueous gel composition is gel-like but pourable. Furthermore, viscosity decreases when the static / stable condition is disturbed by subjecting the gel to a certain increased shear rate (shear thinning behavior). The aqueous pseudoplastic gel compositions according to the invention are preferably characterized by tan(<5) values, measured with a rheometer with plate-to-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C, that are less than 1 at oscillation frequencies between 10 and 0.1 Hz. In preferred embodiments, the tan(d) values, measured with a rheometer with plate-to-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C, are between 0.1 and 0.9, more preferably between 0.2 and 0.8 at oscillation frequencies between 10 and 0.1 Hz. As those experienced in the technique will appreciate, the values ​​of tan(u) are measured at suitable shear strains in the linear viscoelastic range. As previously defined in this specification, the aqueous pseudoplastic gel composition has a first viscosity η1 at a shear rate of 0.01 s⁻¹ of between 5 and 200 Pa·s and a second viscosity η1 at a shear rate of 100 s⁻¹ that is between 10 and 1000 times lower than the first viscosity. In a preferred embodiment, the first viscosity is between 10 and 190 Pa·s, more preferably between 14 and 180 Pa·s, more preferably between 16 and 150 Pa·s, more preferably between 18 and 120 Pa·s, and more preferably between 20 and 80 Pa·s. In another preferred embodiment, the second viscosity is between 0.05 and 2 Pa-s, more preferably between 0.08 and 1 Pa-s, more preferably between 0.1 and 0.8 Pa-s, more preferably between 0.12 and 0.7 Pa-s, more preferably between 0.15 and 0.6 Pa-s, and more preferably between 0.2 and 0.5 Pa-s. In another embodiment, the aqueous pseudoplastic gel composition has a first viscosity ηι at a shear rate of 0.01 s-1 between 5 and 50 Pa- s and a second viscosity ηη at a shear rate of 100 s'1 which is between 10 and 200 times lower than the first viscosity. In another embodiment, the aqueous pseudoplastic gel composition has a first viscosity 71 at a shear rate of 0.01 s1 between 5 and 50 Pa-s and a second viscosity 72 at a shear rate of 100 s'1 between 0.15 and 0.6 Pa-s, preferably between 0.2 and 0.5 Pa-s. In another embodiment, the aqueous pseudoplastic gel composition has a first viscosity 71 at a shear rate of 0.01 s'1 of between 100 and 200 Pa-s and a second viscosity 72 at a shear rate of 100 s1 that is between 200 and 1000 times lower than the first viscosity. In another embodiment, the aqueous pseudoplastic gel composition has a first viscosity 71 at a shear rate of 0.01 s-1 of between 100 and 200 Pa-s and a second viscosity 72 at a shear rate of 100 s-1 that is between 0.15 and 0.6 Pa-s, preferably between 0.2 and 0.5 Pa-s. The gel structure and first viscosity of the aqueous pseudoplastic gel composition, determined at a shear rate of 0.01 s⁻¹, are sufficient to keep spherical glass beads and other optional particulate materials in suspension for an extended period. The shear rate of 100 s⁻¹ is typical for (industrial) spraying conditions under which the aqueous pseudoplastic gel composition can be applied to a substrate. The second viscosity, measured at 100 s⁻¹, is sufficiently low to provide aqueous pseudoplastic gel compositions that can be easily sprayed. The inventors have established that aqueous pseudoplastic gel compositions according to the invention regain their initial viscosity in a relatively short time after applying a shear rate of 100 s⁻¹ (thixotropy test). This phenomenon is highly advantageous for obtaining smooth, homogeneous layers that do not exhibit sagging behavior. Accordingly, in a preferred embodiment, the aqueous pseudoplastic gel composition as defined herein has a third viscosity 773 at a shear rate of 0.1 s1, wherein the aqueous pseudoplastic gel composition recovers at least 20%, preferably at least 30%, more preferably at least 50%, and even more preferably at least 70% of the third viscosity value >73 within 10 s, preferably within 5 s, more preferably within 2 s from the reduction of the shear rate in step (iii) of the following process comprising the consecutive steps of: (i) subject the aqueous pseudoplastic gel composition to a shear rate of 0.1 s'1 for at least 30 seconds and measure the third viscosity 773; (ii) subjecting the aqueous pseudoplastic gel composition to a shear rate of 100 s1 for 30 seconds; (iii) reduce the shear rate to 0.1 s'1; and (iv) measure the viscosity of the aqueous pseudoplastic gel composition as a function of time and compare it with the value of the third viscosity 773; in which viscosity is measured with a rheometer with plate-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C. The expression “recover at least x% of the value of the third viscosity η3 within a certain time” as used in the context of the present invention means that the viscosity actually reaches a value xpd 100 within that time. This embodiment can also be formulated as set forth below. In a preferred embodiment, the aqueous pseudoplastic gel composition as defined herein has a third viscosity 773 at a shear rate of 0.1 s⁻¹, wherein the aqueous pseudoplastic gel composition achieves, exhibits, or has a fourth viscosity 774 of at least 20%, preferably at least 30%, more preferably at least 50%, and more preferably at least 70% of the value of the third viscosity 773 within 10 s, preferably within 5 s, more preferably within 2 s from the reduction of the shear rate in step (iii) of the following process comprising the consecutive steps of: (i) subject the aqueous pseudoplastic gel composition to a shear rate of 0.1 s1 for at least 30 seconds and measure the third viscosity 773; (ii) subjecting the aqueous pseudoplastic gel composition to a shear rate of 100 s'1 for 30 seconds; (iii) reducing the shear rate to 0.1 s1; and (iv) measuring a fourth viscosity ^4 of the aqueous pseudoplastic gel composition as a function of time; in which viscosity is measured with a rheometer with plate-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C. In embodiments, the aqueous pseudoplastic gel composition recovers at least 20%, preferably at least 30%, more preferably at least 50%, even more preferably at least 70%, and even more preferably at least 90% by weight of the third viscosity value / 73 within 10 s from the reduction of the shear rate in step (iii). In embodiments, the aqueous pseudoplastic gel composition recovers at least 20%, preferably at least 30%, more preferably at least 50% of the third viscosity value ηi within 5 s from the reduction of the shear rate in step (iii). In embodiments, the aqueous pseudoplastic gel composition recovers at least 20%, preferably at least 30% of the value of the third viscosity 773 in 2 s from the reduction of the shear rate in step (iii). As will be evident from the accompanying examples, aqueous pseudoplastic gel compositions according to the present invention can recover approximately 100% of the value of the third viscosity ^3 after a period of time from the reduction of the shear rate in step (iii). Process for preparing the aqueous pseudoplastic gel composition. In general, the ingredients of the aqueous pseudoplastic gel composition can be added in any order. After mixing all the ingredients, the composition is stirred or homogenized, preferably at a temperature between 15 and 30 °C, for a period of 5 to 15 minutes. In a preferred embodiment, the thickener is added after mixing water, spherical glass beads, and any other ingredients. Stirring or homogenization is preferably carried out at low shear rates to avoid the inclusion of air bubbles in the aqueous pseudoplastic gel composition. As explained previously, the thickening effect of the thickener may depend on the pH value. Consequently, the process for preparing the aqueous pseudoplastic gel composition may include a pH adjustment step, for example, adjusting the pH to a value between 6.0 and 11, such as between 7.0 and 11, between 7.0 and 9.5, or between 7.4 and 7.9. The pH can be appropriately adjusted using dilute NaOH or aminomethyl propanol neutralizers, such as AMP Ultra® PC 2000. Accordingly, in a second aspect of the invention, a process is provided for the preparation of the aqueous pseudoplastic gel composition as defined herein, said process comprising the steps of: (i) adding water, the spherical glass beads as previously defined in this document, the thickener as previously defined in this document and one or more optional additional ingredients as previously defined in this document to a container; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (iii) optionally adjusting the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. The pH in stage (iii) is preferably adjusted to a value between 7.0 and 9.5. However, the addition of the different ingredients can also be carried out at different stages of the process. Accordingly, in a third aspect of the invention, a process is provided for the preparation of the aqueous pseudoplastic gel composition as defined herein, said process comprising the steps of: (i) add water, the spherical glass beads as previously defined in this document, at least part of the thickener as previously defined in this document and optionally part of one or more additional ingredients as previously defined in this document to a container; (ii) stir or homogenize the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; (iii) optionally adjust the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11; (iv) add at least a portion of one or more additional ingredients as defined above in this document to the composition obtained in step (ii) or (iii), optionally add a portion of the thickener as defined above in this document and optionally add water; (v) stirring or homogenizing the mixture obtained in step (iv), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (vi) optionally adjusting the pH before or after step (v), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. The pH in stage (vi) is preferably adjusted to a value between 7.0 and 9.5. In terms of implementation, the time between the implementation of stages (i) to (iii) on the one hand and stages (iv) to (vi) on the other hand can be days or months or even longer. The process for preparing the aqueous pseudoplastic gel composition may also encompass the production of an intermediate aqueous pseudoplastic gel composition having the composition and properties as defined above in this document, followed by the addition and mixing of another composition to obtain a final aqueous pseudoplastic gel composition, provided that the final aqueous pseudoplastic gel composition still has a composition and properties as defined above in this document. Accordingly, in a fourth aspect of the invention, a process is provided for the preparation of the aqueous pseudoplastic gel composition as defined above in this specification, said process comprising the steps of: (i) adding water, the spherical glass beads as defined above in this document, at least part of the thickener as defined above in this document and optionally part of one or more additional ingredients as defined above in this document to a container; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes to obtain an intermediate aqueous pseudoplastic gel composition having the composition and properties of the aqueous pseudoplastic gel composition as defined above in this specification; (iii) optionally adjust the pH before or after step (ii), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11; (iv) adding at least a portion of one or more additional ingredients as defined above in this specification to the intermediate aqueous pseudoplastic gel composition obtained in step (ii) or (iii), optionally adding a portion of the thickener as defined above in this specification and optionally adding water; (v) stirring or homogenizing the mixture obtained in step (iv), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes to obtain the aqueous pseudoplastic gel composition; and (vi) optionally adjusting the pH before or after step (v), preferably to a value between 6.0 and 11, more preferably to a value between 7.0 and 11. The pH in stage (vi) is preferably adjusted to a value between 7.0 and 9.5. In terms of implementation, the time between the implementation of stages (i) to (iii) on the one hand and stages (iv) to (vi) on the other hand can be days or months or even longer. Process for coating a substrate. In a fifth aspect, the invention relates to a process for coating a substrate with a retroreflective layer, said process comprising the steps of: a) providing a substrate; b) optionally apply a primer coat to the substrate of step (a); c) spraying the aqueous pseudoplastic gel composition as defined above in this specification onto the substrate of step (a) or onto the primed substrate of step (b) to provide a substrate coated with a retroreflective layer; d) optionally drying the substrate coated with the retroreflective layer obtained in step (c); and e) optionally coating the substrate coated with the retroreflective layer obtained in step (c) or the dry substrate coated with the retroreflective layer obtained in step (d) with one or more transparent coating layers followed by drying or curing. Step (c) of spraying the aqueous pseudoplastic gel composition may comprise spraying a single layer in one step or multiple layers on top of each other in subsequent spraying steps. In one embodiment, step (b) is carried out. The primer layer applied in step (b) can be, for example, a colored primer layer comprising mica flake pigments or metallic flakes or powders. The geometry of the substrate to be coated is not limited in any way, provided that it can be coated by spraying, i.e., provided that the droplets of the aqueous pseudoplastic gel composition can reach the substrate surface. In one embodiment, the substrate is flat. In other embodiments, the substrate is curved. In further embodiments, the substrate comprises both flat and curved parts. The inventors have established that the aqueous pseudoplastic gel composition can be applied, for example, by high-speed industrial spraying, to various substrates, resulting in retroreflective coating layers with excellent print or coating quality, such as homogeneity and wide-angle retroreflectivity. If the retroreflective coating layer is provided with one or more additional transparent coating layers (i.e., step (e) of the process is carried out to coat a substrate as previously defined herein), a retroreflective layer with high smoothness and good cleanability is obtained. Unexpectedly, these results can also be obtained when the aqueous pseudoplastic gel composition is applied to the surface of a vertically positioned substrate. In preferred embodiments, the substrate is selected from textiles, leather, metal, concrete, rubber, plastics, carbon fibers, and combinations thereof. Textiles, as used herein, include woven or knitted fabrics such as cotton, polyester, nylon, silk, wool, viscose, and acrylics. Regardless of the type of material the substrate is made of, the substrate can be selected from the group consisting of clothing, traffic signs, car chassis, bicycle frames, roads, sidewalks, and railings. A substrate provided with a retroreflective coating according to the present invention may be provided in step (e) with one or more additional transparent coating layers. These additional transparent coating layers may serve to protect the retroreflective layer against abrasion and / or moisture. Furthermore, they may be used to provide the substrate coated with the retroreflective layer with a specific matte or glossy / glossy appearance. The additional transparent coating layers may be colored. The additional transparent coating layers applied in the optional step (e) may comprise layers of MA / a / ¿u¿¿ / uuo r ¿ r liquid coatings, powder coating layers or combinations thereof, which are subsequently cured or dried. The spraying in step (c) is preferably carried out using a spray gun. In one embodiment, the spraying is carried out using a propellant. In a preferred embodiment, the spraying is carried out without using a propellant. The drying in optional step (d) and the drying or curing in step (f) can be carried out under ambient conditions. Alternatively, they can be carried out at elevated temperature and / or reduced pressure. In preferred embodiments, the aqueous pseudoplastic gel composition is applied in step (c) in an amount of 60 to 250 g per m² of substrate, more preferably in an amount of 80 to 225 g per m² of substrate, and even more preferably in an amount of 90 to 205 g per m² of substrate. These amounts can be sprayed as a single layer in one step or as multiple layers one on top of the other in subsequent spraying steps. In a sixth aspect, the invention relates to substrates coated with a retroreflective layer that can be obtained by the process as previously defined herein. The substrate coated with the retroreflective layer can have a matte or glossy appearance. In a preferred embodiment, the substrate coated with the retroreflective layer, preferably coated with one or more additional transparent coating layers (i.e., step (e) of the process for coating a substrate as previously defined herein is carried out), exhibits retroreflection of the retroreflective layer at any angle between 0 and 80°, such as between 0 and 78°, between 0 and 75°, between 0 and 70°, between 0 and 65°, between 0 and 60°, between 0 and 55°, between 0 and 50°, between 0 and 45°, and between 0 and 40°, from the perpendicular of the coated substrate. This retroreflection of the retroreflective layer is determined by directing the beam of a flashlight at the retroreflective layer, where the line of sight of the eyes substantially coincides with the flashlight beam, and by visually determining whether retroreflection is observed.The experiment begins at a zero angle to the perpendicular of the coated substrate, after which the angle is gradually increased until no retroreflection is observed. MA / a / ¿U¿¿ / UUO l ¿ l Thus, the invention has been described with reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those skilled in the art. Furthermore, for a proper understanding of this report and its claims, it should be understood that the verb “to understand” and its conjugations are used in their non-limiting sense to indicate that elements following the word are included, but elements not specifically mentioned are not excluded. In addition, reference to an element by means of the indefinite article “a” or “an” does not preclude the possibility that more than one of the elements may be present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” generally means “at least one.” ινΐΛ / a / zuzz / uuo i ¿ i EXAMPLES Example 1 Five aqueous pseudoplastic gel compositions according to the invention were prepared by adding the following ingredients at room temperature (-20 °C) in the following order to a container: (1) demineralized water, (2) spherical glass beads, (3) additional ingredients, and (4) thickener. When necessary, AMP Ultra PC 2000 (an additional ingredient) was added to adjust the pH. The resulting mixtures were blended for approximately 10 minutes, again at room temperature. The quantities of the different ingredients are listed in Table 1. The following ingredients were used. Spherical glass beads: SFX 2.2, obtained from Jianxi Sunflex Light Retroreflective Material Co., Ltd., has a refractive index of approximately 2.2, measured at a wavelength λ of 589 nm, a median particle diameter D50 of 40.37 pm, a DIO diameter of 37.32 pm, and a D90 diameter of 44.11 pm, as measured by laser diffraction, and a specific gravity of approximately 4.5 g / cm3. These spherical glass beads comprise T1O2, BaO, ZnO, and CaO. Other ingredients Kuncai Gold Finch 10-60 pm, obtained from Kuncai; mica Syntran KL219 CG, obtained from Interpolymer; film-forming polymer Optiphen, obtained from Ashland Specialty Ingredients; preservative Syntran 5778, obtained from Interpolymer; film-forming polymer Citrofol, obtained from Jungbunzlauer; plasticizer Worlee Color Yellow, obtained from Worlee; pigment AMP Ultra PC 2000, obtained from Angus Chemical Company; neutralizer Glitsa® Normaal Gebruik Parketlak Kleurloos, obtained from Akzo Nobel; water-based parquet varnish Ceta Bever® Schuur & Tuinhuis Beits, Blank Transparant Zijdeglans, Akzo Nobel; water based stain Sikkens AutowaveTM MM 2.0, derived from Akzo Nobel, a water-based base coat for automobiles MBL actic acid, obtained from Thor; preservative Thickeners Carbopol® Aqua SF-1, obtained from Lubrizol, crosslinked acrylate copolymer thickener; Aquatix 8421, obtained from B YK; thickener, non-ionic aqueous emulsion of a modified ethylene vinyl acetate copolymer wax Rheobyk-420, obtained from BYK, modified urea thickener Rheovis® AS 1152, obtained from BASF, thickener ASE ACULYNTM Excel, obtained from DOW Chemical, HASE thickener Table 1 ινΐΛ / a / zuzz / uuo Sample T00340 T00345 T00395 T00382 T00397 Ingredients Quantity [% by weight] Quantity [% by weight] Quantity [% by weight] Quantity [% by weight] Quantity [% by weight] Water Water(1) 34.55 46.54 48.12 49.17 53.10 Spherical Glass Beads SFX 2.2 47.35 29.96 30.98 30.46 28.48 Other ingredients*2' Kuncai Gold Finch 10-60 pm 5.27 6.66 Butylene glycol 0.53 0.67 Syntran KL219 CG 0.57 0.73 Optiphen 0.32 0.40 Syntran 5778 9.26 11.91 Citrofol 1.62 2.00 Worlee Color Yellow 0.07 0.11 AMP ultra 0.10 0.14 Glitsa® Normaal Gebruik Parketlak 20.24 Sikkens Autowave™ MM 2.0 19.12 Ceta Bever® Schuur and Tuinhuis Beits 17.59 MBL Acticide 0.01 AMP Ultra PC 2000 0.24 0.21 A-methylpyrrolidone*3' 0.60 Subtotal other ingredients*2' 17.74 22.62 20.48 19.72 17.80 Thickener Carbopol Aqua SF-1 0.36 Aquatix 8421 0.88 Rheovis AS 1125 0.42 Rheobyk-420(3) 0.65 ACULYN Excel 0.62 Thickener Subtotal*4' 0.36 0.88 0.42 0.65 0.62 Total Composition 100.00 100.00 100.00 100.00 100.00 (1) Demi-water + water from other ingredients (2) The concentration of other ingredients is based on dry weight. Water is listed separately. (3) N-methylpyrrolidone is a solvent for Rheobyk-420. (4) The concentration of thickeners is based on the dry weight. Non-aqueous solvents are listed under 'other ingredients'; water is listed separately. Example 2 The stability of the five aqueous pseudoplastic gel compositions provided in Table 1 was assessed by visual and tactile inspection to determine whether the sample exhibited sedimentation, syneresis, or separation (phase or otherwise). A sample was considered stable if no sedimentation, syneresis, or separation was observed after visual and tactile inspection. The pH of the five compositions immediately after synthesis and their subsequent stability are listed in Table 2. Table 2 Sample T00340 T00345 T00395 T00382 T00397 pH 7.77 7.73 8.84 8.60 8.1 Stability > 49 days > 43 days 1 day 11 days 4 days Example 3 The rheological behavior of the five compositions given in Table 1 was measured using a Malvern Kinexus rheometer with a plate-to-plate geometry (PL40 plate) and a separation distance of 0.5 mm at a temperature of 25.0 °C. A viscosity-shear rate profile was measured for the five aqueous pseudoplastic gel compositions according to the invention at shear rates ranging from approximately 0.0001 s⁻¹ to 1000 s⁻¹ with 10 samples per decade. The viscosity-shear rate profiles are presented in Figure 1. As can be deduced from Figure 1, all the aqueous pseudoplastic gel compositions exhibit shear-thinning behavior. The shape of the viscosity-shear rate profile at the zero shear rate limit suggests that the compositions have no yield strength. All five aqueous pseudoplastic gel compositions were pourable. A thixotropy test was performed by applying three shear rate regimes and measuring viscosity over time. In the first regime, a shear rate of 0.1 s⁻¹ was applied for approximately 30 to 60 seconds, and viscosity was measured at a 2-second sampling interval. In the second regime, the shear rate was increased to 100 s⁻¹, and viscosity was measured for 30 seconds at a 2-second sampling interval. In the third regime, the shear rate was reduced to 0.1 s⁻¹, and viscosity was measured for 600 seconds at a 1-second sampling interval. Figure 2 illustrates the thixotropic behavior of the five aqueous pseudoplastic gel compositions shown in Figure 1.Based on what can be deduced from Figure 2, all aqueous pseudoplastic gel compositions recover at least 50% of the viscosity measured in the first regime within a few seconds of the start of the third regime. Furthermore, the aqueous pseudoplastic gel compositions are capable of recovering approximately 100% of the viscosity value from the first regime. In addition, frequency sweep tests were performed to evaluate the viscoelastic behavior of four of the aqueous pseudoplastic gel compositions. The loss modulus G₁, storage modulus G₂, and tan(θ) were measured at appropriate shear strains in the linear viscoelastic range and at oscillatory frequencies ranging from 10 Hz to 0.1 Hz, with 10 samples per decade. The results are presented in Figure 3. The tan(θ) values ​​are all below 1 in the oscillatory frequency range, indicating gel-like behavior in that elastic behavior dominates viscous behavior. Example 4 The five aqueous pseudoplastic gel compositions described in Example 1 were applied to flat metal test plates (10 x 15 cm), positioned vertically, using a spray gun (DeVILBISS HVLP, DV1-C1 Plus) with a 1.3 mm nozzle at a pressure of 2.2 bar, at a rate of approximately 130 g per m² of substrate. The sprayed layers were air-dried at room temperature. After drying, visually appealing retroreflective coatings with excellent smoothness and homogeneity were obtained. Consequently, industrial spraying onto vertically positioned substrates is possible without the occurrence of, for example, sagging or uneven coatings. Metal test plates coated with the five aqueous pseudoplastic gel compositions were further coated with a two-component Sikkens® Aerodry reactive clear lacquer (Akzo Nobel) and then cured. The retroreflection of the resulting retroreflective layers was determined by directing a flashlight beam at the retroreflective layer, ensuring that the line of sight of the eyes substantially coincided with the flashlight beam, and by visually determining whether retroreflection was observed. The experiment began at zero angle to the perpendicular of the coated substrate, after which the angle was gradually increased until no retroreflection was observed. Substrates coated with the retroreflective layers showed clear retroreflection of the retroreflective layer at all angles between 0 and 80° from the perpendicular of the coated substrate. Example 5 The viscosities of the compositions in Table 1 of Example 1 were measured with a Brookfield viscometer using a No. 5 spindle rotating at 10 rpm. The results are presented in Table 3. Table 3: Brookfield viscosity using a No. 5 spindle rotating at 10 rpm at approximately 20 °C ινΐΛ / a / zuzz / uuo i ¿ i Sample Viscosity T00340 2.4 Pa-s T00345 2.0 Pa-s T00395 1.4 Pa-s T00382 5.8 Pa-s T00397 6.0 Pa-s The Brookfield viscosities resulting from the use of a No. 5 spindle rotating at 10 rpm are between 1.4 and 6 Pa-s, which is well below the lowest value required for screen printing (ink) as disclosed in document WO00 / 42113A1.

Claims

1. An aqueous pseudoplastic gel composition, having a first viscosity ηι at a shear rate of 0.01 s'1 of between 5 and 200 Pas and a second viscosity / 72 at a shear rate of 100 s'1 that is between 10 and 1000 times lower than the first viscosity, wherein the aqueous pseudoplastic gel contains, based on the total weight of the composition: • from 15 to 60% by weight of water; • 20 to 60% by weight of spherical glass beads having a mean particle diameter D50, as measured by laser diffraction, of between 5 and 150 pm, and a refractive index, measured at a wavelength λ of 589 nm, of between 1.8 and 2.8, wherein optionally at least some of the spherical glass beads are semi-spherically coated with a light-reflecting coating; • 0.15 to 1.5% by weight of a thickener; and • 0 to 50% by weight of one or more additional ingredients;in which viscosity is measured with a rheometer with plate-to-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C.; 2. An aqueous pseudoplastic gel composition according to claim 1, having a third viscosity η73 at a shear rate of 0.1 s⁻¹, wherein the aqueous pseudoplastic gel composition recovers at least 20%, preferably at least 30%, more preferably at least 50%, and more preferably at least 70% of the third viscosity value η73 within 10 s, preferably within 5 s, more preferably within 2 s from the reduction of the shear rate in step (iii) of the following process comprising the consecutive steps of: (i) subjecting the aqueous pseudoplastic gel composition to a shear rate of 0.1 s⁻¹ for at least 30 seconds and measuring the third viscosity η73; (ii) subjecting the aqueous pseudoplastic gel composition to a shear rate of 100 s⁻¹ for 30 seconds; (iii) reduce the shear rate to 0.1 s1;and (iv) measuring the viscosity of the aqueous pseudoplastic gel composition as a function of time; wherein the viscosity is measured with a rheometer with plate-to-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C.; 3. Aqueous pseudoplastic gel composition according to claim 1 or 2, wherein the tan(c>) values, measured with a rheometer having plate-plate geometry and a separation distance of 0.5 mm at a temperature of 25 °C, at oscillatory frequencies between 10 and 0.1 Hz are less than 1, preferably between 0.1 and 0.9, more preferably between 0.2 and 0.

8.

4. Aqueous pseudoplastic gel composition according to any of claims 1 to 3, wherein the spherical glass beads have a refractive index, measured at a wavelength λ of 589 nm, of between 2.0 and 2.8, preferably between 2.2 and 2.

4.

5. Aqueous pseudoplastic gel composition according to any of claims 1 to 4, comprising from 0.20 to 1.4% by weight of the thickener, more preferably from 0.25 to 1.31% by weight, even more preferably from 0.30 to 1.2% by weight, based on the total weight of the aqueous pseudoplastic gel composition.

6. Aqueous pseudoplastic gel composition according to any of claims 1 to 5, wherein the thickener is selected from the group consisting of ASE polymers, HASE polymers, HEUR polymers, liquid dispersions of acrylics or crosslinked copolymers, acrylate crosslinked polymers, crosslinked polyacrylic acid polymers, crosslinked polyacrylic acid copolymers, non-ionic aqueous emulsions of a modified vinyl acetate ethylene copolymer wax, modified urea or urea-modified polyamides, and combinations thereof.

7. Aqueous pseudoplastic gel composition according to any of claims 1 to 6, which is stable for at least 1 day, wherein the composition is considered stable if, after visual and tactile inspection, no sedimentation, syneresis, or separation is observed.

8. Aqueous pseudoplastic gel composition according to any of claims 1 to 7, which is an ink, paint or coating formulation.

9. A process for preparing the aqueous pseudoplastic gel composition according to any one of claims 1 to 8, said process comprising the steps of: (i) adding water, spherical glass beads, thickener and one or more optional additional ingredients to a container; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (iii) optionally adjusting the pH before or after step (ii), preferably to a value between 6.0 and 11.

10. A process for preparing the aqueous pseudoplastic gel composition according to any one of claims 1 to 8, said process comprising the steps of: (i) adding to a container water, the spherical glass beads, at least part of the thickener and optionally part of one or more additional ingredients; (ii) stirring or homogenizing the mixture obtained in step (i), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; (iii) optionally adjusting the pH before or after step (ii), preferably to a value between 6.0 and 11; (iv) adding at least part of the one or more additional ingredients to the composition obtained in steps (ii) or (iii), optionally adding part of the thickener and optionally adding water;(v) stirring or homogenizing the mixture obtained in step (iv), preferably at a temperature between 15 and 30 °C, preferably for a period of between 5 and 15 minutes; and (vi) optionally adjusting the pH before or after step (v), preferably to a value between 6.0 and 11.

11. A process for coating a substrate with a retroreflective layer, said process comprising the steps of: a) providing a substrate; b) optionally applying a primer layer to the substrate of step (a); c) spraying the aqueous pseudoplastic gel composition according to any one of claims 1 to 8 onto the substrate of step (a) or onto the primed substrate of step (b) to provide a substrate coated with a retroreflective layer; d) optionally drying the substrate coated with the retroreflective layer obtained in step (c); and e) optionally coating the substrate coated with the retroreflective layer obtained in step (c) or the dried substrate coated with the retroreflective layer obtained in step (d) with one or more transparent coating layers, followed by drying or curing.

12. Process according to claim 11, wherein the aqueous pseudoplastic gel composition is applied to the substrate in step (c) by using a spray gun.

13. Substrate coated with a retroreflective layer that can be obtained by the process according to claims 11 or 12.

14. Substrate coated with a retroreflective layer according to claim 13 having a matte or glossy appearance.

15. Substrate coated with a retroreflective layer according to claim 13 or 14, wherein the substrate coated with the retroreflective layer is preferably coated with one or more additional transparent coating layers, exhibiting retroreflection of the retroreflective layer at any angle from 0 to 80° from the perpendicular of the coated substrate.