Retroreflective materials and use thereof in horizontal road markings DESCRIPTION

The present invention refers to a coating film for horizontal road marking consisting of a paint composition layer and a mixture comprising glass beads and plastic or thermoplastic particles over-deposited (drop-on) on said layer, as well as to a method for obtaining said coating film.

State of the art

One of the main causes of traffic accidents is failure to identify the road.

Since driving belongs to visual input-dependent cognitive processes, a clearly visible travel path should lead to fewer errors by drivers and thus to greater safety. To this end, horizontal road markings, which guide drivers and help them keep their vehicles within a pre-set route, are commonly used to achieve road safety purposes.

In fact, since the first line was implemented in 1911 , horizontal markings have become present on most roads.

Nearly half of all traffic accidents that occur are reported to have occurred between dusk and dawn. Mortality rates are significantly higher at night than during the day, and the accidents severity is higher [Plainis S, Murray I J, Pallikaris IG. Road traffic casualties: understanding the night-time death toll. Injury Prev. 2006; 12(2): 125-128\.

For this purpose, retroreflecting elements, most frequently glass beads, are embedded into the coating film to improve the poor visibility of road markings in the dark.

Research has shown that during night driving the retroreflectance (RL) of road markings becomes a natural focal point for all drivers [Zwahlen H, Schnell T. Visibility of road markings as a function of age, retroreflectivity under low- beam and high-beam illumination at night. J Transport Res Board 1999, 1692: 152- 163\.

The brightness value reflected by the horizontal road marking coating, when hit by the light projected by vehicle headlights (RL), is therefore one of the main reference parameters for the qualitative classification of horizontal road markings.

Horizontal road markings are normally made up of a coating layer containing or over-deposited with (drop-on) reflective materials, most frequently glass beads.

WO2016/051354 discloses glass beads coated with natural and organically modified montmorillonite. Such coated beads are compatible with water-based paints for horizontal road marking and have high wear resistance and reflectance.

US9222230 discloses a water-based paint with improved durability and retroreflectance. The paint composition consists of a water-based paint, retroreflective glass beads, porous silica, and optionally an acrylic emulsion in water.

WO99/57076 discloses cementitious material formulations which contain a redispersible polymer and retroreflective/reflective materials.

WO98/56862 discloses yellow, hot melt alkyd traffic marking compositions.

GB2357985 discloses road markings and methods of producing the same.

The “coating” can in turn be made of paint products based on the following organic polymers: polymers in a solvent solution or aqueous dispersion/emulsion, radical curing unsaturated polymers, thermoplastic polymers, multi-component mixtures of polymers with different reactive functionalities.

Among these, water-based (waterborne) paint products are the preferred ones due to their reduced impact on human health and environment compared to other materials such as, for example, solvent-based coatings.

It is known that the paint coating layer can contain polymeric particles which can adsorb water.

In this context, US5947632 and US6132132 disclose a waterborne paint for horizontal road marking characterized in that particles of a solid polymer or an inorganic compound, commonly ion exchange resins, which are capable of adsorbing the water, are incorporated in the paint.

It is therefore clear the need to make horizontal markings with a high RL available, but at the same time with a long-lasting retro reflectance, to improve the safety and confidence of road users, especially elderly drivers who tend to rely almost exclusively on the roadside horizontal marking line to detect the end of the road pavement.

The duration of the horizontal marking coating, combined with the persistence of its reflective capacity over time, represents a performance factor but also an eco- sustainable one, because the extension of the “average life” of the marking line will reduce the need for restoration operations (repainting). Every painting, rolling, or spreading operation for making the marking coating, in fact, represent a potentially impacting factor for the environment.

In addition, a marking coating that abrades more easily, releases more particles (residual microplastics) due to surface wear into the surrounding environment.

Summary of the invention An object of the present invention is to provide a marking coating having a high retroreflectance which is durable over time.

A further object of the present invention is to make available new marking coatings which have a low environmental impact.

The inventors have surprisingly found that the main objects described above are achieved with a coating film for horizontal road marking according to claim 1 and with a method for obtaining said coating film according to claim 12.

Description of the Figures

Figure 1. Theoretical principle of retroreflectance induced to the marking coating strip by glass beads (Reference);

Figure 2. Dosage percentage of the glass/thermoplastic mixture in the respective samples;

Figure 3. Drying times of the different samples tested at 15°C;

Figure 4. Retroreflectance (RL) expressed by the various coatings applied;

Figure 5. Coating weight loss after abrasion test;

Figure 6. Retroreflectance of the coating before and after the abrasion test.

Definitions

Unless otherwise defined, all terms of the art, notations and other scientific terminology used herein are intended to have the meanings commonly understood by those skilled in the art to which this disclosure pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and/or for ready reference; thus, the inclusion of such definitions in the present disclosure should not be construed to represent a substantial difference over what is generally understood in the art.

The terms “approximately” and “about” used in the text refer to the range of the experimental error that is inherent in the execution of an experimental measurement.

The terms “comprising”, “having”, “including” and “containing” are to be intended as open-ended terms (/.e., meaning “comprising, but not limited to”), and are to be considered as a support also for terms such as “consist essentially of”, “consisting essentially of”, “consist of”, or “consisting of”.

The terms “consist essentially of”, “consisting essentially of” are to be intended as semi-closed terms, meaning that no other ingredients affecting the novel features of the invention are included (optional excipients may therefore be included).

The terms “consists of”, “consisting of” are to be intended as closed terms.

The term “bead” refers to a generally spherical structure.

The term “quick-set technology” is intended to indicate that ammonia is introduced into the polymer forming the binding portion of waterborne paint products. Drop of pH occurs as ammonia evaporates and, as a result, the polymer irreversibly solidifies.

Detailed description of the invention

The inventors have surprisingly identified a mixture of glass beads and plastic or thermoplastic particles which can be used as a retroreflective material in horizontal road markings.

An object of the present invention is represented by a coating film for horizontal road marking consisting of a paint composition layer and a mixture comprising glass beads and plastic or thermoplastic particles, preferably of an acrylic nature, over-deposited (drop-on) on said layer, wherein said glass beads and said plastic or thermoplastic particles are at least partially embedded into said layer. The glass beads are preferably spherical in shape and have a smooth surface. Recycled glass is preferably used.

Glass beads have been used as a reflective element in horizontal road markings for many years.

The theoretical principle of retroreflectance induced on the marking coating stripe by glass beads was already extensively and thoroughly described in 1952 by Pocock B.W., Rhodes C.C.: Principles of glass-bead reflectorization. Highway Research Board Bulletin, 57, 1952, 32-48.

Further theoretical analyses have shown that a glass bead of refractive index (Rl) equal to 1 .5, having 59% of its diameter embedded in the paint, allows the highest retroreflection if the angle between the incident and reflected light is comprised between 0 and 3 degrees.

In a preferred embodiment, the glass beads have a refractive index comprised between 1 .45 and 2.2, preferably between 1 .5 and 2.

In a further preferred embodiment, the glass beads have an average diameter comprised between about 100 and 850 pm.

In a further preferred embodiment, between 50% and 80%, preferably between 50% and 60%, of the glass beads diameter is embedded in the coating.

Glass beads are usually prepared in vertical furnaces by flame quenching at about 1200°C starting from ground recycled window glass (refractive index Rl equal to1 .5) and can give white marking coatings with an initial RL of about 350 350 med / m ² / lx.

With high Rl glass beads it is easy to obtain a high RL that may reach even 2000 mcd/m ² /lx, for example beads with Rl equal to about 1.9 (high index beads) are used for special applications, such as airport marking. However, their use is limited to specific marking applications, firstly because of their prohibitive cost and secondly because of their surface which is poorly resistant to abrasion thus leading to rapid dulling and RL loss during normal use [Burghardt, T. E., Babic, D., Babic, D., Application of waterborne road marking paint in Croatia: Two years of road exposure. In Proceedings of International Conference on Traffic and Transport Engineering; Belgrade, Serbia, 24-25 November 2016: 1092-1096\.

Examples of glass beads available on the market and usable for the purposes of the present invention are the products Echostar®: 63-212, 125-710, 125-850, 125-1180, 212-1180, 212-1400, 300-600.

The plastic or thermoplastic particles according to the invention are preferably spherical in shape, more preferably in the form of beads.

In a preferred embodiment, the plastic or thermoplastic particles have an average diameter of between about 100 and 500 pm.

Preferably, the plastic or thermoplastic particles are soluble in a solvent selected from glycol ethers, ethers, or alcohols.

Examples of plastic or thermoplastic particles, preferably in the form of beads, available on the market and usable for the purpose of the present invention are the products NeoCryl® B-775, NeoCryl® B-725, Elvacite® 2016.

In a preferred embodiment, the amount of plastic or thermoplastic particles in the mixture is comprised between 2 and 25% by weight, preferably between 10 and 20% by weight, more preferably between 5 and 15% by weight, with the remaining balance to 100% being made of glass beads.

The particle size “distribution” of the plastic or thermoplastic particles can have minimum or maximum values that are lower, equal, or higher than that of the glass beads. In a preferred embodiment, plastic or thermoplastic particles with a particle size distribution range being on average lower than that of the glass beads are used.

The coating compositions which can be used in the present invention are based on polymers in solvent solution, polymers in aqueous dispersion/emulsion, radical curing unsaturated polymers, thermoplastic polymers, or multi-component mixtures of polymers with different reactive functionalities, preferably polymers in emulsion or aqueous dispersion.

Preferably, waterborne paint products for horizontal road marking, are formulated using polymeric materials in emulsion or aqueous dispersion, coalescence driers and/or self-crosslinking curing agents or are formulated using polymeric materials in emulsion or aqueous dispersion using a quick-set technology or a technology in agreement with the International Patent Application No. WO2022/112958 in the name of Team Signal S.r.l..

The painting systems for horizontal road markings which can be used in the present invention are selected from two-component materials of an epoxy, polyurethane or unsaturated acrylic nature, which cure due to the chemical reaction occurring at the application site, thermoplastic powders based on hydrocarbon or alkyd resins that require heat for application onto road, solventborne paints that dry upon evaporation of the dissolving solvent medium, and waterborne paints that cure at the application site due to water evaporation, and in the case of the so-called “quick-set” technology, the evaporation of the neutralizing agent (for example ammonia).

To obtain coatings for horizontal road markings, the relative paint products are applied with methods known in the field (spraying, roller, dripping, pouring (street box) etc.) and immediately afterwards they subjected to drop-on with the mixture of glass beads and plastic or thermoplastic particles according to the present invention.

The thickness of the applied coating is normally inversely proportional to its drying time but directly proportional to the duration of the same coating.

The abrasion resistance of the complete coating (coating + drop-on) is a direct function of the chemical-physical capacity of the paint product to keep the glass bead anchored to itself, in the final coating.

Although the inventors do not wish to be limited by any theory of interpretation, the coating is believed to provide the desired color, surface for retroreflection and retain the glass beads; while the suitably incorporated glass beads provide retroreflectance (RL), and at the same time protect the paintwork from abrasion caused by the passage of vehicle tires or snow plows.

A complete coating is more resistant to abrasion, and it keeps longer the retroreflectance necessary to perform the marking task.

Advantageously, the horizontal marking coating of the present invention allows to obtain a substantial performance benefit which was unpredictable based on the current technical knowledge (state of the art).

The final characteristics of the coating for horizontal marking thus obtained prefigure an improvement in performance both in terms of retroreflectance and resistance to abrasion.

These characteristics have a strong impact on road safety, both in terms of performance and improvement of the environmental impact (higher persistence of the marking line).

A further object of the present invention is represented by a method of obtaining the coating film for horizontal road markings according to the present invention, comprising:

- a first step of applying the paint composition to a road surface,

- a second step of applying the mixture comprising glass beads and plastic or thermoplastic particles, preferably of an acrylic nature, over said paint composition.

In a particularly preferred embodiment, the paint formulation comprises:

1.1 ) The use of a binder (L) (resin or polymer) in the form of an aqueous dispersion/emulsion, able to provide the coating with the performance characteristics of the final coating, required by its use.

1.2) One or more pigments, (P) essential for the color required for the final coating. The pigment should be selected based on both its characteristics for formulation use and its behavior/performance once in the final coating. Examples of inorganic pigments are Titanium Dioxide, Iron Oxides, Bismuth Vanadates, etc. Examples of organic pigments are Azo yellow, Isoindoline, Benzimidazolone; Naphthol Red, Quinacridone; Phthalo Blue, Phthalo Green.

1 .3) Extenders of various nature (F), selected to optimize the rheology, the physical performance of the coating and possibly to contain the costs determined by the pigmentation. Extenders suitable for rheological adjustment are micronized minerals with low oil absorption. The specific gravity and particle size will affect the settling of the product in the tin and the abrasion resistance. Other extenders which can positively influence the duration of the coating are micronized silicates which partially intervene in the polymer film formation. Examples of extenders are Calcium Carbonate, Barium Sulfate, various Silicates: Kaolin, Talc, Quartz, Cristobalite, Nepheline syenite, etc.

1.4) Specific additives (A), aimed at optimizing the paint product both in the production process phase and in its behavior during application and drying phase, such as for example dispersant additives, antifoam additives, anionic and non-ionic surfactants and rheological additives.

In the first production phase, pigment and extenders should be dispersed in the same aqueous vehicle which supports the organic polymer in colloidal form. To facilitate this heterogeneous “incorporation”, it is necessary to introduce dispersants capable of helping the pigmentary extender to rapidly and effectively break up until reaching its minimum particle size, without the need of excessive shearing effort.

The dispersion phase of the pigmentary extender causes the incorporation of a large amount of air. Due to its nature and surface tension, the aqueous vehicle easily tends to stabilize this air in the form of a foam. For this reason, an antifoam should be included in the “production” additives.

The heterogeneous equilibrium obtained by the incorporation of the inorganic material (pigments/extenders) in the same medium in which the organic colloid is suspended, may require the support of a surfactant. The addition of this type of additive should be evaluated with caution due to the influence it generates on foam stabilization, drying rate and residual sensitivity to humidity.

The behavior of the paint product should also be seen from the point of view of storage and application thereof. Storage stability is determined by the chemistry of the organic binder and by the rheological characteristics of the formulation. The addition of a rheological additive acts on viscosity and the type of fluidity, consequently influencing the sedimentation of the inorganic portion and the application characteristics.

1 .5) Coalescents, specific to aid film formation (coalescence) of the polymer in colloidal form and to adequately regulate the drying time of the applied coating.

Once the product is applied to the substrate, water evaporation generates the aggregation of the organic colloid particles. To optimize this aggregation, a solvent that favors the process is needed: the “film coalescent” (CF).

To regulate the water evaporation phase, and consequently the drying of the coating film, drying coalescent (CE) can be added. The latter, when mixed with the water contained in the product, form minimal azeotropes, accelerating the evaporation thereof.

1.6) Neutralizing agents (N), suitable for maintaining the pH in the range predicted for the polymeric dispersion stability.

The preferred neutralizing agent in a system that requires rapid drying is ammonia.

1 .7) Antibacterial agents (B), are additives that have the purpose of preventing the development of bacterial pollution (molds, etc.). The choice of the suitable additive must be made on the basis of the binder nature and tested in the stability tests of the tin product over time.

The following examples are intended to further illustrate the invention without however limiting it.

EXPERIMENTAL PART

Materials

A series of mixtures containing glass beads and increasing weight percentages of thermoplastic beads of an acrylic nature to be used in the drop-on phase were tested.

A series of different paint products for horizontal road markings were applied on a road surface substrate, and all these applications were subjected to drop-on with common glass beads (standard) and with mixtures of glass beads and thermoplastic beads according to the present invention.

The coatings thus obtained were evaluated in terms of retroreflectance, initially at the end of the drying and complete curing period, and subsequently after an intensive cycle of accelerated abrasion.

The result obtained from the retroreflectance readings of the coatings before the intensive abrasion cycle was surprisingly unexpected.

In the coatings obtained with drop-on of glass/thermoplastic mixture according to the invention, an increase in retroreflectance values was found, when compared to the standard with simple glass drop-on, which reached extraordinarily high values (approximately > 35-40%).

Tables 1-3 show the sampling scheme and related parameters resulting from application tests concerning different paint products for horizontal road markings used as basecoat, for example the product Aquaerapid TOP formulated with a technology according to International Patent Application No. WO2022/112958 in the name of Team Segnal S.r.L, or other commercially available paint products subjected to drop-on with the various bead mixtures object of the present invention.

Formulation of tested paint products

FORMULATION 1

DR = % of dry residue FORMULATION 2

DR = % of dry residue FORMULATION 3

FORMULATION 4 FORMULATION 5

FORMULATION 6

FORMULATION 7

FORMULATION 8

Methods

Standard test for measuring the drying rate of the applied paint product film (ASTM D711 - 89 (1998), Standard Test Method for No-Pick-Uo Time of Traffic Paint}

A calibrated weight, cylindrical in shape, with two rubber rings placed on the circumference at a precise distance, is allowed to roll through a guide (slide) on a panel coated with the paint product to be tested.

The time (minutes) required for the film to leave no marks on the rubber rings surrounding the cylinder is measured.

Standard test for abrasion resistance of paint products with the TABER apparatus (ASTM D4060, Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser). The paint product is applied to special panels which, after having undergone the complete drying process, are placed on a machine which carries out controlled abrasion with C17 type abrasive wheels (coarse abrasive) with the addition of a total additional weight of 500 g on the horizontal axis.

Each abrasive test had a duration of 5000 revolutions.

The weight loss found after testing each sample was reported as a percentage with respect to the standard coating (glass beads).

RETROREFLECTANCE (RL) (EN 1436 Standard, ASTM E 1710)

The retroreflectometer simulates the nocturnal retro reflectance (RL) condition of horizontal road markings which occurs to drivers of motor vehicles when the available lighting is provided by the vehicle headlights, i.e. of the nocturnal type. The instrument is able to measure the nocturnal retroreflectance (RL) of horizontal road markings in perfect scale.

The observation angle of 2.29° corresponds to a vehicle observation distance of 30 m, under normal conditions. The illumination angle is 1.24°.

Table 1 : Application tests on Aquaerapid TOP paint product (FORMULATION 1). Drying times and retroreflectance detected

Table 2: Application tests on Aquaerapid paint product (FORMULATION 2). Drying times and retro reflectance detected

Progressing with a graphical analysis of the values reported in Tables 1 and 2, Figure 2 shows the dosage percentage of the glass/thermoplastic mixture in the respective samples; Figure 3 shows the drying times of the different samples tested at 15°C; Figure 4 shows the retroreflectance (RL) expressed by the various coatings applied.

Table 3: Application tests on paint products (FORMULATIONS 3-8). Drying times and retroreflectance detected The coatings according to the present invention show an improvement in the retroreflectance immediately after the complete drying and curing cycle, ranging from a minimum of 5% higher than the standard, up to values that exceed the standard value by 40%, where standard means the coating obtained by drop-on of the paint product with glass beads only.

A series of samples of complete marking coatings, made with Aquaerapid TOP paint product (FORMULATION 1) and mixtures of beads according to the invention in various ratios, were then prepared to be used in the evaluation of the anti-abrasive performance expressed by this technological solution.

These samples were tested:

• according to the “ASTM D4060” standard for assessing the loss of coating due to the abrasive action.

• with equipment comparable to that set out in the BS EN 13197:2011+A1 :2014 standard for assessing the loss of reflectance as a function of the abrasive action exerted by the passage of the full-weight tire of a road vehicle.

The weight loss detected after the test carried out on each sample was reported as a percentage with respect to the standard coating (glass beads) in Figure 5.

The retroreflectance of the coating before and after the abrasion test was represented in Figure 6. Table 4: Coating samples for abrasion tests

In all coatings obtained with drop-on of the glass/thermoplastic mixture according to the present invention, the improvement in terms of resistance to abrasion compared to standard coatings (glass only) was considerable and directly proportional to the percentage of thermoplastic material added in the drop-on mixture (Figure 5).

The reflectance measurement after abrasion reveals a surprisingly different behavior with respect to standard. The retroreflectance improvement is not directly proportional to the amount of thermoplastic beads introduced in the drop- on mixture, but shows an ideal concentration curve (Figure 6).