WO2001042349A1

WO2001042349A1 - A reflective road marking and a method of producing and applying a reflective road marking composition

Info

Publication number: WO2001042349A1
Application number: PCT/DK2000/000684
Authority: WO
Inventors: Hans Abildgaard Thomsen
Original assignee: Abildgaard Roadvision Aps
Priority date: 1999-12-10
Filing date: 2000-12-08
Publication date: 2001-06-14
Also published as: AU1852401A

Abstract

A reflective road marking and a method for producing the same wherein beads are incorporated in a binder on polymer basis and coated with a cohesive coating material having a surface tension closer to the surface tension of the polymeric matrix than the surface tension of the beads.

Description

A reflective road marking and a method of producing and applying a reflect _ve road marking composition

The present invention relates to a reflective road marking composition comprising a thermoplastic binder and a filler m the form of beads. The invention also relates to a method of producing and applying a reflective road marking composition, a method of treating the beads for use m the composition, and the treated beads.

Reflective road marking compositions are well known m the art. In the preparation of road marking m the form of a melt, a solution or a dispersion, very often comprising a polymeric or polymenseable material, it is also a known technique to incorporate glass beads to the road marking m order to improve the light reflecting properties .

The present invention is principally concerned with the surface properties of beads, which are to be incorporated into a thermoplastic binder and which contact the polymeric material forming the matrix while that material is m the liquid or molten state. The material which is to form the matrix may be m the form of e.g. a melt, a solution or a dispersion and it may be polymeric or polymeπsable .

Beads may be incorporated into synthetic polymeric material for a variety of purposes, for example as fillers m thermoplastic materials and m thermosettmg resins m order to modify the properties of the material or to facilitate moulding, and m order to give light reflective properties to road markings. When used as filler m thermoplastics and thermosettmg materials, it is often desirable that the beads should be evenly distributed throughout the final product m order to give uniformity of properties, and this implies that the beads should be uniformly distributed m the liquid material from which the product is moulded or other ways prepared. It is also often desirable, that the glass beads does not affect the cohesive strengths of the cooled thermoplastic or thermosettmg materials compared to the pure polymeric material, and this implies a strong bonding between the surface of the glass beads and the respective polymeric material to which the glass beads are incorporated.

Certain analogous problems arise in connection with mixtures which may be applied to form road markings, for example to divide a carriageway into different traffic lanes or to indicate traffic priorities at road junctions. It is desirable that such markings should be highly visible at night, and one way of promoting high visibility is to incorporate glass beads into the markings to reflect light from a vehicle's lamps back to the driver of that vehicle. It will of course be appreciated that m order to exhibit this effect, at least some of the glass beads must be well exposed at the surface of the marking. If the beads are exposed, there is a risk that they may be removed as traffic is driven over the marking, with the result that during the course of time, more and more beads are removed so that the marking becomes less and less reflective and so less clearly at night. In relation to the last-mentioned there is also a risk, that the many craters at the surface of a marking, remaining after the removed glass beads, is filled with traffic dust resulting a grey surface of the marking which is reducing both the night and day visibility. As the adhesion between the untreated glass beads and the road marking is rather poor, there is also a risk, that the encapsulated beads works as break initiators resulting a promoted degradation of the total marking during the course of time. International Publication No. WO 93/18237 describes a thermoplastic road marking material containing partial embedded glass beads. The marking comprises a binder which fluoresces by irradiation with UV-light. European Patent No. 0 567 765 A2 describes light reflecting granulated thermoplastic bodies having very small glass beads partly embedded into its surface for use in road marking. European Patent No. 0 586 341 Al describes an equipment for simultaneous applying road marking material and glass beads. US Patent No. 3,746,425 describes a road marking where the voids between large uniform sized glass beads are filled with small also uniform sized glass beads. US Patent No. 4,301,050 describes a thermoplastic road marking, wherein glass beads eventually are incorporated. The road marking material is characterised that is has a particular heat resistance. All the road markings compositions described the above patent publications have certain disadvantages. When the composition is applied to a road and exposed to traffic wear and weathering, the glass beads which are partly embedded the surface, are easily peeled out of the marking if the intrusion depth of the glass beads is less than 50 of its diameter and especially if the marking is exposed to studded tyres or heavy traffic intensity. Furthermore the encapsulated beads works as break initiators resulting m an accelerated erosion of the total marking during the course of time. When the glass beads are removed from the surface of a marking, they are leaving many small craters which are filled with dark highway film resulting m an undesired discolouπsation of the marking causing both reduced night and day visibility.

US Patent No. 3,556,637 describes a light reflection spherical lens or aggregates of e.g. glass for use road marking material. The spherical aggregates are coated with a transparent binder e.g. a mixture of a fluorated elastomer, methylisobutyl ketone, xylol and polyethylmethacrylate, wherein uncoated glass beads are partial embedded. A road marking comprising such aggregates with embedded glass beads have the same disadvantages as the known road markings described above, namely that the glass beads easily slip out of the road marking leaving small craters which may causing both reduced night and day visibility.

US Patent No. 4,305,863 describes a thermoplastic polyurethane resin composition comprising ammosilane or epoxysilane, wherein microspherical ammosilane or epoxysilane coated glass beads may be incorporated. The coating on the glass beads serves as coupling agents to the resin. However, order to serve as a coupling agent it is necessary to use a resm containing a similar silane which render the resulting product to be very expensive. Furthermore, there is still a need for improving the bonding of the glass beads to the thermoplastic binder of the road marking.

US Patent No. 4,713,295 provides a method of improving the wettability properties of glass beads for use road marking paints order to improve the bonding of the glass beads to the marking paint and thereby achieve prolong the light reflecting properties when the paint is exposed to weathering and wear, describes coated glass beads for use m polymeπseable road marking paints, especially as drop-on beads, but also as coated beads incorporated the paint. The method comprises two step comprises a first step of coating the glass beads with a silane an organic solvent providing the surface of the glass beads with hydrophobic properties and a second step of coating the glass beads with a fluorocarbon compound an organic solvent providing the surface of the glass beads with both hydrophobic and oleophobic properties. This two-step method of coating glass beads is very inconvenient, expensive and require use of organic solvents .

The obiect of the present invention is to provide a road marking composition with incorporated beads, which beads have a good bonding strengths to the road marking composition.

A second object is to provide a road marking composition with incorporated beads, which road marking composition when applied on a road, has prolonged light reflecting properties when the marking is exposed to weathering and wear.

A third object is to provide a method of producing and applying a reflective road marking composition with partly embedded beads on a road, which method is simple and cheap and provides a marking on the road which has good and durable reflecting properties.

A fourth object is to provide a method of treating beads for use m a reflective road marking composition, which method is simple, fast and relatively cheap.

Yet a fifth object is to provide a method of treating beads for use m a reflective road marking composition, which method does not require the use of organic solvents

These and other object are provided with the invention as it is defined the claims.

The reflective road marking composition according to the invention may basically be any type of polymer based road marking composition wherein beads, preferably beads coated with a cohesive coating material having a surface tension closer to the surface tension of the thermoplastic binder than the surface tension of the beads, is incorporated.

Preferably the reflective road marking composition according to the invention comprises a binder on polymer basis and incorporated beads, the beads being coated with a cohesive coating material having a surface tension closer to the surface tension of the polymeric matrix than the surface tension of the beads and wherein the binder before hardening or curing is a solution, a dispersion, two-component or thermoplastic.

The binder for use m the thermoplastic road marking according to the present invention may be any type of thermoplastic binder normally used m road marking compositions. Useful thermoplastic binders are e.g. described US patent 4,301,050 and US patent 4,305,863.

Preferably the thermoplastic binder contains at least 50% by weight of binder of a hydrocarbon resm, a ketone res or a malemate resm. The thermoplastic binder preferably also contains modifying polymers and other rheological modifiers such as mineral oil, antioxidant, lubricants/plasticizer and other components, which are added order to improve the rheological properties of the resm for the particular use. Such rheological modifiers are generally known m the art. The resm provides the thermoplastic binder with adhesive properties for adhesion to the filler and the surface on which the thermoplastic road marking is applied.

Preferably the modifying polymers are selected between SBS or SIS block co-polymers, amorphous polyolefmes

(polypropylenes, polybutadienes ) , ethylenevmylacetate (EVA) or mixture thereof, and they are preferably added m the amount of op to about 40 % by weight, more preferably from 30 to 40 ^c by weight of the binder. The modifying polymers improve the cohesive strengths and the low-temperature properties of the binder.

Mineral oil preferably of the naphtenic or parafmic type may be added m an amount of up to about 15 % by weight, more preferably from 5 to 15 - by weight of the binder. The mineral oil compatibilise the resm and the polymers.

Heat stable antioxidants may preferably be added to the mixture m small amounts m order to prevent yellowing of the thermoplastic mixture in the molten state.

Lubricants/plasticizers may be added m an amount of up to about 10 o by weight, preferably m an amount from 5 to 7 weight percent of the binder. The lubricants/plasticizers reduce the application temperature and thereby reducing the preparation time. Lubricants/plasticizers are also responsible for the ability of the road marking to wet the surface on which it is applied.

The thermoplastic road marking composition according to the invention consist of 18 to 25, preferably about 20 o by weight thermoplastic binder, and 75 to 82, preferably about 80 % by weight of light or transparent and durable filler.

The filler of the thermoplastic road marking according to the invention comprises at least about 13 °, preferably about 25 % by weight of coated beads. Furthermore, the filler preferably comprise quartz, light granite, calcined flint and/or Danopal . These filler components preferably have gra sizes from 0.074 to 2.0 mm, determined according to BS 3262 : 1976 m order to induce light reflective properties, skid resistance and resistance to wear.

Furthermore, the filler may preferably comprise one or more of calcium sulphate, talc, calcium metasilicate, quartz powder, Danopal powder, calcined flint powder, clay, mica, calcium silicate glass fibres, pigments dyes. These filler components preferably have gram sizes less than 0.074 mm, determined according to BS 3262 : 1976 and may be added m order to improve the overall rheological properties of the thermoplastic road marking, and to prevent segregation of and to colour the road marking.

A preferred pigment dye for white thermoplastic road marking is titanium dioxide (rutile or anatas) , zinc oxide, magnesium oxide or mixture thereof, preferably m the amount of 4 to 10 weight percent of the filler, but the invention is not limited to this range.

The thermoplastic road marking according to the invention may be provided with other colour than white, i.e. yellow, blue or red. The type and content of the pigment dye is selected according to the specific purpose for the road marking. A person skilled m the art, will know how to select a pigment dye which is suitable for its purpose .

The beads used in the present invention may be of any suitably type including polymer based beads and glass beads. The mam requirement is that the beads is stable to heat applied under the preparation, mixing and application of the road marking, preferably the beads should be stable when subjected to a heat above at least 200 °C for a period of about 20 minutes. Beads prepared from polymers should preferably be able to withstand the pressure applied from normal traffic without breaking or crushing.

The most preferred type of beads is glass beads.

The beads should at least have an average size of 0.1 mm. The size of the beads is measured according to the British standard BS 6088 A981. The beads serves as reflecting agent m the road marking composition according to the invention.

Glass beads used as reflecting agent generally have a size m the range from 0.1 to 0.8 mm, but for special purposes larger beads may be used.

Generally non-spherical glass particles m the bead fraction are not preferred, as their ability to reflect light is rather poor, but beads with a sphericallity larger than about 70 ° is preferred. More preferred is beads with a sphericallity larger than about 80 %. Spherical beads with a sphericallity larger than about 90 ⁰ are particularly preferred. The sphericallity is measured by counting under microscope also according to BS 6088A981.

Glass having a refraction index of 1.44 to 2.02 is preferred. More preferred is glass having a refraction index of 1.45 to 1.65. Especially preferred is glass having a refraction index of 1.48 to 1.55. Glass with a refraction index larger than 1.60 is very often, dependent on the Abbe number of the glass, less durable than glass m the said range and is therefore more susceptible to traffic wear.

The beads preferably have a size between 0.1 and 3.0 mm measured as described above. More preferred the beads have a size between 0.1 and 2.0 mm. Even more preferably the beads have a size between 0.1 and 0.8 mm.

The beads m the thermoplastic binder according to the invention is coated with a cohesive coating material having a surface tension closer to the surface tension of the thermoplastic binder than the surface tension of the beads .

A coating material with a cohesion larger than 4 MPa at 25 °C, preferably larger than 10 MPa at 25 °C and particulary preferred is a coating with a cohesion larger than 20 MPa at 25 °C.

Preferably the coating material has a surface tension measured according to DIN 53364 Seπe B m a range of +/- 15 mN/m of the surface tension of the thermoplastic binder. More preferred the surface tension of the coating material is 2 to 10 mN/m larger than the surface tension of the thermoplastic binder.

The surface tension of the coating material may also be measured by visual means. The visual means designated "the water droplet method" for easurend surface tension includes treating an object glass for microscopy with a dispersion comprismg the coating material. The treated object glass is dried with a hair dryer (Braun type 4- 479) for 20 seconds and heated to 140 °C for 5 minutes on a heating surface and left to cool to room temperature. 4 separate droplets of destilled water are put on the coated glass surface and the average size of the droplets diameter is determined. Preferably the surface tension, expressed m the size of the diameter of a water droplet, of the coating material is 1 mm larger than the surface tension of the thermoplastic binder measured according to the above visually method. The coating material forms a proper uniform, cohesive layer on the surface of the beads which is significant reducing the surface tension of the beads. The coating material forms a strong bonding to the resm of the thermoplastic binder.

The coating material on the beads comprises at least 80 % by weight of polyvmyl compound. Preferred polyvmyl compounds is polyvmyls polyvmyl acetate, polyvmyl alcohol, polyvmyl amines, polyvmyl butyral, polyvmyl pyrrolidon, polyvmyl chloride and co-polymers thereof. The coating material may comprise one or more types of polyvmyl compounds or other suitable polymers.

The coating material preferably comprises 80 % by weight or more of polyvmyl acetate, which may be able to crosslink e.g. by applying heat. After coating the polyvmyl acetate is preferably at least partly cross- linked.

There are several suitable coating materials, which are commercial available, for example "Bostik 730 from Bostik DK, Sikabond 540 from Sika DK, Gludan G515 from Gludan DK or Cascol 3337 or Cascol 3339 from Casco DK", to name a few types. This preferred coating material is very cohesive and resistant to heat, and it is not melting, stripped of the beads or soluted m the binder of the road marking while heating and preparing the thermoplastic road marking according to the invention.

The coating material may preferably comprises small amounts e.g. up to about 6.0 _, preferably between 2.0 and 5.0 by weight of emulsifying agents which makes the coating partial water resistant. The emulsifying agent is very often polyvmyl alcohol, which also work as a cross- linking agent under the influence of a catalyst which may also be added to the coating material.

When the reflective road marking composition according to the invention comprises beads coated with a coating composition comprising a suitable amount of emulsifying agents, the part of coated beads, which sticks out from the road marking are cleaned by moisture and traffic, leaving them very reflective, meanwhile the part of the coated beads partial embedded in and inside the road marking remains unaffected until the traffic wear makes the embedded beads rises on the markings surface.

The thermoplastic binder and the coating on the coated beads according to the invention are bonded to each other by adhesive forces, and the strong bonding is responsible for a durable density of beads on the surface of the road marking. This causes a significant increase of the light reflective properties.

In preferred embodiments of the invention, the coating material comprises one or more of following additives: Cationic or non-ionic surfactants up to 1 %, preferably 0.25 % by weight, an antioxidant as Irganox 1010 from Ciba-Geigy up to 0.5 ^", preferably 0.2 _ by weight, a white pigment as titan dioxide (rutile type) up to 10 % preferably 5 % by weight, an phosphorescent

(afterglowing) pigment as Lumilux SN from Riedel-de Haen up to 30 % by weight, a luminescent pigment as Lumogen F from BASF up to 0.01 -s by weight and UV absorbers as Fe;θ3 up to 0.1 % by weight.

The coating is preferably applied in one single step and preferably it forms a proper layer e.g. a layer having an average thickness of at least 0.1 μ , preferably at least

0.4 μm on the surface of the beads. Coatings in the preferred thickness may preferably have incorporated pigments which improves the functional properties of the road marking further without reducing the bonding strengths between the coated beads and the thermoplastic road marking.

It is preferred that the coating on the beads is applied in one single step and includes one single layer. Thereby the cost of production is very reduced. Preferably the coating is applied without being dissolved or diluted m an organic solvent.

In a preferred embodiment of the invention, the coating is relatively transparent, which gives the fresh-laid road marking a satisfactory reflection. When traffic and moisture during the course of time removes the coating from the parts of the beads which sticks out from the road marking, the reflection significantly increases.

Generally the beads of the invention are incorporated into thermoplastic binders in order to maintain a satisfactory reflection during the course of time. When traffic wear and weathering removes the upper layer of the road marking including some of the beads, new beads are exposed to the surface. The larger amount of beads added to the composition, the larger becomes the reflection of the marking.

As the uncoated beads of the prior art are mostly physically entrapped m the composition, the beads works as break initiators. Therefore the higher the amount of beads prior art compositions is, the faster is the erosion of the total marking.

The beads according to the invention are preferably uniformly distributed m the composition and is thereby physically entrapped m the polymer matrix when it cool down after applying the road marking. Therefore the reflection is uniform during the course of time.

A preferred amount of beads m the thermoplastic binder is between 10 % and 60 % by weight of the composition. More preferably between 20 and 40 % by weight.

The reflective road marking composition according to the invention may be prepared by coating the beads with the coating material and mixing the components of the reflective road marking composition using ordinary methods known m the art.

A preferred method preparing a reflective road marking composition according to the invention comprises the step of preparing a pre-mix for forming a thermoplastic road marking or a pre-fab for forming prefabricated symbols.

Pre-mix is a mixture of predetermined amounts of binder and filler which is held into meltable plasticbags at room temperature. Generally the thermoplastic road marking is formed from the pre-mix by heating the pre-mix inclusive the plastic bag while stirring a chamber until the binder melts and the mixture becomes liquid and uniform. This resulting thermoplastic road marking is applied on the road by e.g. an extruder.

Pre-fab is thermoplastic road marking which has been applied on a non-tacky surface m lanes in a thickness of approx. 3 mm. After cooling down these lanes is cutted into different trafic symbols as e.g. triangles and arrows. The pre-fab is mounted on a dry road surface by placing the solid symbol on the road and heat it by e.g. a gas et until the symbol melts. After cooling down, the symbol is well bonded to the road surface. A preferred method is as follows: Predetermined amount of binder including resm and a predetermined amount of filler including coated beads and for example light quartz are mixed optionally with a polymers, mineral oil, antioxidant, lubricant, plasticizer pigment dyes and other components. The mixture is held into meltable plastic bags.

The pre-mix including the plastic bag is placed m a suitable tank and is heated to obtain a homogeneous mixture. Normally the mixture will be heated under stirring until the temperature reaches approx . 200 °C, and after approx. 20 minutes stirring at about 200 °C the mixture is molten, homogeneous and ready for the application. When the coating on the beads is subjected to high temperature under the mixing procedure when beads and binder is mixed, the cohesive strength will often increase .

The hot mixture or reflective road marking composition is applied on a suitable substrate.

The reflective road marking composition including the pre-mix for forming the thermoplastic road marking or the pre-fab for forming the prefabricated symbols may be manufactured and applied as known m the art except the usual beads are replaced or partly replaced with the said coated beads according to the invention.

The invention also relates to a "drop on" method of producing and applying a reflective road marking composition on a road. This method comprises the step of l) applying a pre-mix road marking composition comprising a thermoplastic binder and preferably beads on a road m a thickness of at least 0,3 mm, preferably at least 1 mm. 11) spreading beads coated with a cohesive coating material having a surface tension closer to the surface tension of the pre-mix composition than the surface tension of the beads.

Generally the beads sink into the molten thermoplastic marking by gravimetric force, but very often this application is carried out by means of an air-pressure- driven bead strewer which is provided with a mouth piece whereby the beads are speeded up, before they enter the road marking.

The beads being spread onto the road marking material while the road material is m a molten state.

Preferably the pre-mix road composition is a reflective road marking composition according to the invention.

Generally drop-on beads are added to the surface of a road marking to secure a satisfactory reflection of the new road marking until the traffic wear and weathering makes incorporated beads rise on the surface of the marking.

Immediately after applying the mixture to the substrate, beads are sprinkled over the melt, whereby the beads are embedded 50 to 75 of their diameter into the melt m order to improve the retro reflective properties of the road marking. After cooling down, the road marking is ready for traffic or for the manufacturing of the prefabricated symbols.

The invention also relates to a method of treating beads for use m a reflective road marking composition. This method comprises the step of 1) providing a partial water resistant, acidic dispersion of a coating mate: lal comprising one or more polyvmyl compound, the polyvmyl compound preferably being selected between polyvmyl acetate, polyvmyl alcohol, polyvmyl amines, polyvmyl butyral, polyvmyl pyrrolidon, mixtures and co-polymers thereof,

n) contacting the surface of dry beads with the dispersion at a temperature above 5 °C to avoid breaking of the dispersion,

m) drying the coating.

The coating may preferably be dried by removing the water m a hot air current or under reduced pressure until the beads no longer sticks to one another.

After the drying of the coating the coated beads may preferably be sieved through a vibratory screen and eventually formed agglomerates of coated beads may be passed through a soft double roller to loosen the agglomerates .

After the preparation the coated beads may be stored under dry condition until use of the beads.

The method of treating beads according to the invention is simple (one coating is sufficient) and without any environmental hazardous consequences to coat the beads. Further more, the coated beads provides a strong bonding to a thermoplastic road marking when incorporated or embedded m a such thermoplastic road marking.

The treated beads according to the invention bears a coating which is reducing the surface tension difference between the normal road marking material and the bead. Various preferred embodiments of the invention will now be described by way of examples.

EXAMPLES

Example 1.

Coating of glass beads:

Dry, untreated glass beads from Potters-Ballotmi Class A according to the British Standard BS 6088:1981, were while stirring added a fresh maid water diluted dispersion of polyvmyl acetate at room temperature as indicated the following Table I. A masterbatch of the water diluted dispersion was prepared as follows: Predetermined amount of the polyvmyl acetate dispersion, Sikabond 540 from Sika DK havmg a density of 1.1 g/cm³ at 25 °C, was while stirring at room temperature added the predetermined amount of postal water. The stirring was maintained until the diluted dispersion by visual inspection looked homogeneous . After addition of the diluted dispersion to the glass beads, the mixture was stirred further 1 minute to ensure a complete coating of all the glass beads. Still while stirring the water was removed from the mixture by a hair dryer (Braun type 4- 579). When the temperature of the mixture reaches approx. 80 °C, the polyvmylacetate sticked to the surface of the glass beads. The coated glass beads were then sieved to sort out eventually formed agglomerates of coated glass beads. The agglomerates were easily crushed by passing them through a soft double roller. After cooling down, the polyvmylacetate coated glass beads were transferred to suitable plastic bags and stored under dry condition. The thickness in μm (T) of the coating is arithmetical determined setting the mass in kg of diluted dispersion named M, the specific surface (S) of the glass beads, Potters-Ballotini Class A, to 3.8 iA/kg, the water content of the undiluted dispersion to 50 % by weight, the density (δ) of the coating to 1100 kg/m³ and the degree of dilution, the polyvinyl acetate dispersion content of the diluted dispersion, named F by following formula :

T = 1, 000, 000*M*0.5*F/ (δ*S)

Ex: T(A) = 1,000,000*0.010*0.5*0.33/(1100*3.8) = 0.4 μm

TABLE I

Water/Disper Glass Diluted Thickness of sion Beads dispersion coating weight ratio WT % WT % μm

66/33 99 1 0.4 A

50/50 98 2 1.2 B

50/50 96 4 2.4 C

Reference 100 0 0 D Example 2 .

Surface tension measurements by the droplet method:

In order to determine the heat influence on the coating material 6 object glasses with the dimension 76*26*1 mm were coated with two droplets of fresh maid 50 % water diluted polyvmyl acetate dispersion of the type Sikabond 540. The dispersion was distributed on the object glass by help of a cotton bud. After applying the diluted dispersions on the object glasses, the samples were dried with a hair dryer, Braun type 4-579, for approx. 20 seconds. The coated object glasses were stored at room temperature until next day. The coated object glasses were then heated on a heating surface for 5 minutes to respectively 60, 80, 100, 120 and 140 °C and afterwards cooled to room temperature. One of the coated glasses was kept unheated.

Further, object glasses for microscopy with the dimensions of 76 * 26 * 1 mm were coated with 2 droplets fresh maid 50 O water diluted polyvmyl acetate dispersion of the types Sikabond 540, Cascol 3337, Danalim B3 and Bostik 730. Two object glasses were coated with each dispersion. The dispersion was distributed on the object glass by help of a cotton bud. The tested dispersions were all of the type D3 according to DS/EN 204. A masterbatch of the water diluted dispersion was prepared as follows: Predetermined amount of the polyvmyl acetate dispersion of the named types was while stirring at room temperature added the predetermined amount of postal water. The stirring was maintained until the diluted dispersion by visual inspection looked homogeneous. After applying the diluted dispersion on the object glass, the samples were dried with a hair dryer, Braun type 4-579, for approx. 20 seconds. One of each sample and an obje;t glass without coating was heated to 140 °C for 5 minutes en a heating surface and afterwards cooled to room temperature.

In a similar way object glasses were coated with pigmented 50 % water diluted dispersion of the types Sikabond 540, Cascol 3337, Danalim B3 and Bostik 730. The pigment was rutile titan dioxide, Bayertitan RKB3, was added to the water diluted dispersion m the amount of 2.5 and 5 s by weight. Immediately after applying the diluted dispersion on the object glass it was dried by the hair dryer for approx. 20 seconds. All these coated surfaces were heated to 140 °C for 5 minutes and afterwards cooled to room temperature.

500 g of thermoplastic road marking of the type Hv 195 from Nordisk Vejmarkermg DK was while stirring, heated to 190 °C . After reaching the process temperature, the molten road marking material was stirred for further 20 minutes to ensure a homogenous blend. The molten road marking was poured on a non-sticky surface and cooled to room temperature .

The surface tension of the above fabricated surfaces was measured m the following way: 4 separated droplets of destilled water were put on each preparated surface at room temperature. One minute after, the average diameter of the droplets on each sample was determined finding following sizes m mm: TABLE II

Sample : Action: Diameter of droplet Glass (Uncoated, unheated 12 mm Glass (140 °C, 5 mm.) : 11 mm

Coated glass (room temperature) : 9 mm Coated glass (60 °C, 5 mm. ) : 9 mm Coated glass (80 °C, 5 mm.) : 9 mm Coated glass (100 °C, 5 mm. 8 mm Coated glass (120 °C, 5 mm. 7 mm Coated glass (140 °C, 5 mm. 7 mm Coated glass ( Pigmented, 140 °C , 5 mm : 7 mm Road marking Hv 195 , Nordisk Ve markermg 6 mm

From the above results, the following is concluded:

I) Heating an uncoated glass to 140 °C has no particular effect on its respective surface tension, n) the coating of glass surfaces by the water diluted polyvmyl acetate dispersion causes a significant reduction of the surface tension, m) the surface tension of the coating material is very dependent of the heat influence,

IV) titan dioxide m the tested concentrations does not affect the surface tension of the coating material and v) the surface tension of the coated object glass, which is heated to 140 °C, comprising whitening pigment or not, is much closer to the surface tension of the roadmarkmg than uncoated object glass.

Example 3.

Surface tension measurements

In order to determine the surface tension of two different surfaces m a scientific way, an object glass was treated with a diluted polyvinyl acetate dispersion, Sikabond 540, as described in example 2. The treated glass sheet was heated to 140 °C for 5 minutes and afterwards cooled to room temperature. Further, a thermoplastic roadmarking, Hv 195 from Nordisk Ve markering, DK, was applied on a non-sticky surface and afterwards cooled to room temperature. A drop of formamide, of which the surface tension is known under experimental conditions (58.2 mN/m), was placed onto the prepared surfaces, one at a time. The surface tension of the prepared surfaces were evaluated by measuring the angle theta between the surface of the drop and the respective prepared surface using the equation of Young and Dupre quoted in ^* Physical Chemistry of Surfaces" (second edition) by Arthur W. Adamson (Department of Chemistry, University of Southern California, Los Angeles, Calif.), published by ^w Interscience Publishers". The measurements were affected at 20 °C.

The surface tension measured by the above described method for the polyvinyl acetate treated surface and the thermoplastic roadmarking were 42.5 mN/m and 36.4, respectively.

Example 4.

Cohesion between polyvinyl acetate treated glass beads and thermoplastic roadmarkering:

Two glass discs with a diameter of 20 mm and a thickness of 3 mm were treated with a diluted polyvinyl acetate dispersion, Sikabond 540, as described in example 2. The treated discs were heated to 140 °C on a heating surface for 5 minutes and afterwards cooled to room temperature. A disc of thermoplastic roadmarking of the type Hv 195 from Nordisk Vejmarkermg with a diameter of approx. 2.2 mm and a thickness of approx. 4 mm was placed on the coating side of one of the treated glass discs. This system was heated to 190 °C on the heating platform. When the thermoplastic was molten, tne other treated glass disc was placed on the thermoplastic with the coating towards the thermoplastic. Immediately after, this sandwich was removed from the heating surface and cooled to room temperature. The excess of thermoplastic sticking out from the glass discs was removed by help of a hot knife. The glass discs were supplied with two nuts using Araldit as binder between the steel and the glass. Thereafter, the sandwich was placed m a tensiometer. The tensile strength or cohesion at 25 °C of the system was measured to 6.2 MPa. The speed of the tensiometer was 1 mm/s. The fracture was obtained mside the thermoplastic. The corresponding reference with untreated glass discs gave a cohesion of 0.7 MPa and the fracture was obtained between the glass and the thermoplastic.

Example 5.

Coated glass beads m premix or prefab for thermoplastic roadmarking:

When glass beads from Potters-Ballotmi Class A according to BS 6088:1981 i.e. untreated, silicone treated or silan treated glass beads, m premix for prefab or for thermoplastic roadmarking of i.e. the type Hv 195 from Nordisk Vejmarkermg I/S DK, having a surface tension at 6 mm, determined by the above droplet method, were replaced with the polyvmyl acetate coated glass beads, type A, B or C, the coating material having a surface tension at 7 mm determined by the droplet method, m the amounts of 20 to 40 - by weight, it did not cause any particular change the rheological properties as softening point, viscosity and density of the modified thermoplastic road marking compared to the corresponding unmodified or noriral thermoplastic road marking. Other physical properties of the last-named modified thermoplastic road marking as whiteness, durability, resistance to wear, adhesion and especially the cohesion would be promoted compared to the corresponding unmodified thermoplastic road marking because the coating of the invention induces a better contact between the glass beads and the thermoplastic matrix.

TABLE III

From the above results, the following is concluded: i) Generally, the polyvmyl acetate coated glass beads do not cause any particular change in the rheological properties, ii) the increase of the softening point as a function of the content of modified glass bead and the thickness of the polyvinyl acetate coating, is indicating that the modified glass beads have a promotive effect on the cohesion of the thermoplastic matrix. Example 6 .

Coated glass beads as drop-on beads m situ

Premix of the type Hv 195 from Nordisk Vejmarkermg DK for forming thermoplastic roadmarking was heated while stirring to the process temperature at approx. 200 °C . After reaching the process temperature, the mixture was stirred further 20 minutes to ensure a homogeneous blend. The molten thermoplastic was applied on an asphalt concrete as a plane traffic lane marking with dimension of 0.10 m width, approx. 10 m length of each sample and 3 mm m thickness. Immediately after applying the thermoplastic on the asphalt concrete, polyvmylacetate coated glass beads were sprinkled over the molten thermoplastic m an amount of approx. 500 g/m², so that the individual glass bead was partially embedded m the thermoplastic. The night visibility (specific luminance) of the marking was followed the next 17 months and compared with a thermoplastic marking sprinkled with 500 g/m² untreated glass beads, Class A according to BS 6088 : 1981 from Potters-Ballotmi. The measurements were carried out by using an apparatus under the trade mark LTL 800 Retrometer (geometry 1.24°/2.29°, equivalent to measurement distance of 30 m) to measuring the specific luminance R_L m mCd/m² Lx from DELTA Lys & Optik, Hjortekaersvej 99, DK-2800 Lyngby. The test results are indicated m the following Table III. This situ test was initiated 2 X May 1997. The average daily trafic (ADT) on the tested samples was m 1997 approx. 2000. TABLE IV

97.05.29 279 225 200 458 (new)

97.07.24 ;32 430 397 442 (2 months!

98.05.29 12 34i 324 302 266 months)

98.10.19 ^'17 401 375 243 151 months)

99.03.19 ^'22 248 212 227 136 months)

99.06.23 ^'25 180 155 168 81 months )

99.10.13 ^'29 172 152 156 105 months) Example 7 .

Test of coated beads on Rundlaufprufanlage, RPA (Turntable) , BAST, Germany:

The test was carried out as follows according to the proposal of the German Delegation of WG2 - TC226 regarding qualification tests for road marking materials on the turntable (RPA) .

Untreated glass beads from Potters-Ballotmi according to BS 6088: 1981 Class A m premix of the type Hv 195 from Nordisk Vejmarkermg, DK, for forming thermoplastic roadmarking, were replaced with polyvmyl acetate coated glass beads type A of the invention m the amount of 20 % by weight and the test on the Turntable was carried out as follows: The modified premix was heated to appr. 200 °C . The molten premix was transferred to the marking machine and 5 test specimen with dimensions of 0.40 x 0.20 m were applied on a bitumenous surface. Immediately after applying the thermoplastic on the bitumenous surface, polyvmylacetate coated glass beads type A were sprinkled over the molten thermoplastic m the amount of 350 g/m², so that the individual glass bead was partially embedded m the thermoplastic. It was checked, that the amount of drop-on material did not differ more than 10 % from the preferred quantity. 3 test specimens were used for the turntable test. 1 test specimen was necessary to establish the drying time, and finally, 1 test specimen was set aside m case of a damaged one had to be replaced.

The test was conducted under the following conditions: The turntable was equipped with 4 new tyres customary m trade, like Michelm XDX, 195/70 VR 14. The load on wheels was 3000 N and a tyre air pressure on 2.2 bar. The support angle was 0 ° and the steering (oblique) angle was ± 1 °. The daily driving cycle was 3 hours of specimens at disk speed of approx. 10 km/h, followed by roll-over of the specimens at a speed of 60 km/h, until 0.2 million roll-overs were carried out, whereby the turning direction was changed every hour. The test temperature was 5 to 10 °C .

After 0.2 million roll-overs and increases of roll-overs by 0.2 million at a time, the adjustment values was checked.

In each test cycle, two standard marking materials were included. The measurements of all other marking materials after 0.2; 0.4; 0.8 and 2.0 million roll-overs were only conducted after it was sure that the test values established in the standards did not differ more than 15 in wear resistance, 15 o in day- and night visibility and 10 ^cc in skid resistance.

From the results measured on the 3 test markings, the arithmetical mean value (test value) was calculated and rounded to an integral number. The test results are compared with test results from a turntable test on a thermoplastic roadmarking comprising 20 % by weight, and sprinkled with 350 g/m², untreated glass beads from Potters-Ballotini Class A according to BS 6088 : 1981. TABLE V

Beads Number of roll-overs in million

Properties 0.6 1.0 1.4 2.0

Night visibility, A 166 82 105 mCd/m² 'Lx

Night visibility, D 30! 44 44 44 46 mCd/m²'Lx, reference

Luminans factor, β, A 0.68 0.49 0.62 0.57 0.60 relative

Luminans factor, β, D 0.62 0.44 0.45 0.47 0.45 relative, reference

Wear resistance A 100 100 100 98 95

Wear resistance ., D 100 100 100 100 100 reference

Skid resistance, SRT A 49 47 47 55 49

Skid resistance, SRT, D 44 43 44 45 44 reference

By comparison the above test results from the road markings comprising untreated glass beads (N) and the corresponding modified road marking comprising polyvinyl acetate coated glass beads (M) , the following is concluded: i) M have significant promoted reflective properties

(night visibility) and luminans factor (day visibility) , meanwhile other physical properties tested according to this proposal as wear resistance, skid resistance are at the same level for N and M.

Example 8.

Coating of glass beads with polyvmylbutyral

995 g of dry untreated glass beads from Potters-Ballotini Class A according to BS 6088:1981 were coated with polyvmylbutyral . The glass beads were while stirred, heated to 170 °C and at this temperature slowly added 5 g of polyvmylbutyral (i.e. Mowital B 20 H from Clariant) m the form of a fine white powder. The stirring was maintained for 5 minutes to ensure a complete coating of all the glass beads. The hot coated glass beads were then still under stirring cooled to roomtemperature to avoid the formation of agglomerates and finally sieved through a 1,4 mm sieve .

Claims

C L A I S :

1. A reflective road marking composition comprising a binder on polymer basis and incorporated beads, the beads being coated with a cohesive coating material having a surface tension closer to the surface tension of the polymeric matrix than the surface tension of the beads, and wherein said binder before hardening or curing is a solution, a dispersion, two-component or thermoplastic.

2. A reflective road marking composition according to claim 1 comprismg a thermoplastic binder and incorporated beads, the beads being substantially heat stable to the temperature necessary for softening the thermoplastic binder, and the beads being coated with a cohesive coating material having a surface tension closer to the surface tension of the polymeric matrix than the surface tension of the beads.

3. A road marking composition according to claim 1 or 2 wherein the beads are glass beads.

4. A road marking composition according to claim 1, 2 or 3 wherein the coating material on the beads has a cohesion above about 4 MPa at 25 °C, preferably above about 10 MPa at 25 °C and particularly preferred above 20 MPa.

5. A road marking composition according to claim 1, 2, 3 or 4 wherein the coating material on the beads has a surface tension m a range of +/- 15 mN/m of the surface tension of the thermoplastic binder, preferably the surface tension of the coating material is 2 to 10 mN/m larger than the surface tension of the thermoplastic binder.

6. A road marking composition according to any one of the preceding claims wherein the coating material on the beads measured according to the water droplet method has a surface tension on 7 mm expressed m the diameter of a water droplet.

7. A road marking composition according to any one of the preceding claims wherein the coating material on the beads comprises at least 80 by weight of a polyvinyl compound, the polyvmyl compound preferably comprising one or more of the polyvmyls polyvmyl acetate, polyvinyl alcohol, polyv yl amines, polyvinyl butyral, polyvmyl pyrrolidon, polyvmyl chloride and co-polymers thereof .

8. A road marking composition according to any one of the preceding claims wherein the coating material on the beads comprises polyvmyl acetate, preferably at least 80 by weight of polyvinyl acetate, the polyvmyl acetate preferably being cross-linked,

9. A road marking composition according to any one of the preceding claims wherein the coating material comprises small amounts e.g. up to about 6 % by weight of emulsifying agents, preferably between 2 and 5 % by weight of emulsifying agent.

10. A road marking composition according to any one of the preceding claims wherein the coating material on the glass beads is provided in a layer having an average thickness of at least 0.1 μm, preferably at least 0.4 μm on the surface of the glass beads.

11. A road marking composition according to any one of the preceding claims wherein the coating material on the beads further comprises pigment dye, preferably titanium dioxide (rutile or anatas), zinc oxide, magnesium oxide or mixture thereof, more preferably m the amount of 4 to 10 weight percent of the filler.

12. A road marking composition according to any one of the preceding claims wherein the thermoplastic binder comprises a thermoplastic material or a thermosettmg resm, preferably at least 50% by weight of binder consisting of a hydrocarbon resm, a ketone resm or a malemate resm.

13. A road marking composition according to any one of the preceding claims wherein the thermoplastic binder comprises modifying polymers, preferably selected between SBS or SIS block co-polymers, amorphous polyolef es (polypropylenes, polybutadienes) , ethylenevmylacetate (EVA) or mixture thereof.

14. A road marking composition according to claim 13 wherein the modifying polymers are added m the amount of up to about 40 % by weight, preferably from 30 to 40 % by weight of the binder.

15. A road marking composition according to any one of the preceding claims wherein the thermoplastic binder comprises mineral oil, preferably of the naphtenic or parafmic type, more preferably m an amount of up to about 15 ° by weight.

16. A road marking composition according to any one of the preceding claims wherein the thermoplastic binder comprises lubricants/plasticizers, preferably m an amount of up to about 10 by weight, more preferably m an amount from 5 to 7 weight percent of the binder.

17. A road marking composition according to any one of the preceding claims wherein the composition substantially consist of 18 to 25, preferably 20 % by weight thermoplastic binder and 75 to 82, preferably 80 % by weight of filler, the filler includes the coated glass beads .

18. A road marking composition according to any one of the preceding claims wherein the filler of the thermoplastic composition comprises at least 13% by weight of coated glass beads.

19. A road marking composition according to any one of the preceding claims wherein the thermoplastic binder comprises as filler one or more of calcium sulphate, talc, calcium metasilicate, quartz powder, Danopal powder, calcined flint powder, clay, mica, calcium silicate glass fibres, pigments dyes.

20. A road marking composition according to any one of the preceding claims wherein the beads have a sphericallity larger than about 70 %, preferably larger than about 80 ^~ and more preferred a sphericallity larger than 90 ₀.

21. A road marking composition according to any one of the preceding claims wherein the beads have an average size of at least 0.1 mm, preferably a size between 0.1 and 3,0 mm and more preferred between 0,1 and 2.0 mm.

22. A road marking composition according to any one of the preceding claims wherein the glass beads have a refraction index of 1.44 to 2.02, preferably between 1.45 and 1.65 and more preferred between 1.48 and 1.55.

23. A road marking composition according to any one of the preceding claims wherein the amount of coated beads is between 10 ^c and 60 % by weight of the composition, preferably between 20 and 40 % by weight.

24. A method of producing and applying a reflective road marking composition on a road comprising the step of

l) applying a thermoplastic composition comprising a thermoplastic binder on a road in a thickness of at least 0,3 mm, preferably at least 1 mm,

n) spreading beads coated with a cohesive coating material having a surface tension closer to the surface tension of the pre-mix composition than the surface tension of the beads to obtain a reflective road marking composition, the beads being substantially heat stable to the temperature necessary for softening the thermoplastic binder,

said glass beads being spread onto the road marking material while the road material is m a molten state.

25. A method of treating beads for use m a reflective road marking composition comprising the step of

l) providing a partial water resistant, acidic dispersion of a coating material comprising one or more polyvinyl compounds, the polyvmyl compound preferably being selected between polyvinyl acetate, polyvmyl alcohol, polyvmyl amines, polyvmyl butyral, polyvmyl pyrrolidon, polyvmyl chloride, mixtures and co-polymers thereof, ii) contacting the surface of dry beads with the dispersion at a temperature sufficiently high to avoid breaking of the dispersion,

iii) drying the coating.

26. Coated glass beads obtainable by the method defined in claim 25.