WO2016051354A1

WO2016051354A1 - Improvements in surface properties of the glass beads which are used as retrorefrective material in road markings by coating with natural clay

Info

Publication number: WO2016051354A1
Application number: PCT/IB2015/057487
Authority: WO
Inventors: Alican VATANSEVER; Tülay İNAN; Hacer DOĞAN; Murat Koral; Nuran KÖKER
Original assignee: Tubitak
Priority date: 2014-09-30
Filing date: 2015-09-30
Publication date: 2016-04-07
Also published as: JP6381793B2; JP2018501170A; TR201411519A2; RU2661511C1; CN107148405B; CN107148405A

Abstract

By means of this invention, glass beads are coated with natural and organically modified montmorillonite to be competed with commercial products, applied easily, compatible with environmentally friendly water-based road marking paints, have high wear resistance and retoreflectivity. Coated glass beads are spread on the water based paint that is applied on 10 x 50 cm briquettes, soon after the paint applying process. Ratio of glass beads to paint is 33 % by weight. After paint dries, in order to simulate the way, a wheel with 6 bars pressure shuttles on the paint. At the end of this process, night visibilities are measured. After 10.000 cycles of shuttling, night visibility of paint including water based montmorillonite coated glass bead is higher than the paints including commercial silane coated, uncoated and modified montmorillonite coated glass beads. Modified montmorillonite coated glass beads provide similar night visibility when compared to commercial silane based glass bead and higher night visibility than uncoated glass bead.

Description

IMPROVEMENTS IN SURFACE PROPERTIES OF THE GLASS BEADS WHICH ARE USED AS RETROREFRECTIVE MATERIAL IN ROAD MARKINGS BY

COATING WITH NATURAL CLAY Description

Technical Field

The invention relates to coating of glass beads, which will be used in water based road markings to increase night visibility, with natural montmorillonite and/or modified montmorillonite; as a result of this coating, obtaining cheap glass beads that provide increased retoreflectivity and wear resistance for road marking paints when compared to commercial glass beads.

Background Art

Glass beads are spread on the paint soon after the paint application. Glass beads with higher diameters will be seen on the surface whereas glass beads with low diameters will be embedded in the paint. Glass bead application is critical to obtain road paints having high retroreflectivity [1 ,2,3]. Dispersing glass beads in paint can be impossible if glass beads are not free flowing. Moisture may cause small glass beads to agglomerate due to the hydrophilic -OH group on the glass surface. Agglomeration can be prevented by modifying glass bead surface with hydrophobic coatings. However, the adhesion between the coating on the glass surface and the paint should be strong. Otherwise, glass beads could be easily removed under traffic due to the friction. So, retroreflectivity will decrease in case of coating glass beads with hydrophobic material. To overcome this problem, in some situations binding agents are being used. However, binding agent cause a thick coating on the glass surface and retroreflectivity decreases again. Moreover, binding agents cause agglomeration because of being hydrophilic [2].

At the beginning of paint and glass bead application, retroreflectivity is high since large glass beads could be easily seen on the paint surface. After the tracks roll over the paint, paint and glass beads begin to wear which causes the reflectivity to decrease. After the remove of glass bead from the paint surface, the gaps are filled with dust. As a result of this situation paint begins to brown out and both day and night visibilities reduce. If the surface of glass beads are not modified then the adhesion between glass and paint will be weak and glass bead will be removed from the paint surface easily. Thus, there are many studies in the literature that coats glass bead surface with polymeric materials.

US3253146 discloses that epoxy resins and pigments are used for glass bead coating [4]. US3222204 coats glass beads with fluorocarbons. Unfortunately, both these two applications are expensive and have low wear resistance. That means the more the the vehicles roll over road marking paint, the more the glass beads are removed from the surface [5].

US20050100709 discloses that poly urethane based polymeric material is obtained by using polyester polyols and aliphatic polyisocyanate. Then, glass bead are coated with this material. However, this method is expensive too and the results of the performance tests are not satisfying [1 ].

Mostly, silane compounds are being used in literature because of their hydrophobic structure. Silane coated glass beads are also popular in industrial applications (US4756931 , US5128203, S4305863, US4713295). Although coating glass bead with silane compounds is practical and cheaper compared to other coating materials, as can be seen in this study, much cheaper, green and natural material can be used.

[6,7,8,9].

US2005/0158461 uses a commercial silane compound for coating of glass beads.

[3].

WO01/42349 and GB2208078 glass beads are mixed with silane compounds with benzoyl peroxide. However, this method is a little bit complex and expensive due to high need for special attention [10,1 1 ]. In addition, benzoyl peroxide is a volatile and flammable material. Therefore, coating effect will reduce and flame risk will occur.

Unlike the studies in literature, WO01/42349 uses poly vinyl acetate as the coating material. After the coated glass beads were spread out the road paint, night visibilities are measured for a year. According to the results, adherence of poly vinyl acetate coated glass beads to paint is stronger than uncoated glass beads. However, no compare is available between poly vinyl acetate and silane coated glass beads. Poly vinyl acetate could be more expensive than silane compounds [10].

Aim of the present invention is to obtain coated glass beads that can be competitive with commercial glass beads, inorganic based, cheap, easily applicable, green and especially highly compatible with water based road paints and have high wear resistance as well as retroreflectivity.

Technical Problem

Road lines, easily visible during the day on the road, can be also visible in the dark night due to glass beads located on the paint surface. Owing to the global shape of the glass spheres and glass structure, glass beads reflect the light from the headlights back to the car driver, which make the road marking visible in night. By this way, drivers can have a more careful and proper trip according to the traffic rules. Glass beads; reflect light back to the headlights even in rainy weather, are important to ensure the safety of traffic at night. The situation that the incident light to be reflected back to the light source, is called as "retroreflectivity" (backward reflection). The chemical composition of the glass spheres, glass bead/paint ratio and the percentage of embedded volume of glass beads in paint surface is adjusted to make retroreflectivity at the highest level.

As vehicles roll over road marking paint, glass beads having larger sizes are removed from the surface due to the impact made by the friction of the vehicles. Small glass beads begin to appear on the paint surface due to the wear of paint over time. Consequently, night visibility decreases eventually. For longer night visibility there should be strong affinity between glass bead surface and paint. To ensure this affinity, the glass spheres are coated with different materials that can provide high compatibility between glass bead and paint [1 ,2,3]. In literature, to ensure the affinity generally polymeric structure with organic based materials were preferred. Such materials should be of a structure that is suitable with chemical structure of paint binding so as, at the end of the adhesion between glass beads and paint, some of the glass beads should locate on the paint surface and some of the glass beads should stay in the paint without sinking. Hence, the chemical structure of the coating material should be selected so as to adhere to the binder contained in the paint. Such organic coating materials could have yellowing problems caused by the sun and some organic-based components could diffuse into the paint depending on the increase of air temperature. Glass beads in the present invention, are coated with inorganic based, nano sized natural sodium montmorillonite (Na-montmorillonite) and montmorillonite modified with quaternary ammonium salt. Afterwards, performance of these glass beads are compared to uncoated glass beads or glass beads coated with silan based polymeric materials which are industrially most used glass beads in road marking paints. According to the performance tests, high wear resistance, thereby more durable paint is provided as well as durable high reflectivity. Moreover, due to inorganic based natural character of the coating, diffusion problems that may occur over time are prevented and cheaper coating cost is provided. This study also has a high importance on the aspect of adding value to the natural resources, since using this natural material for the glass bead coating is first in literature. Due to all the features mentioned above as well as the improved retroreflectivity and high wear resistance, the present invention differs from other patents.

Description of Drawings

Abbreviations used in the figures are defined as follows:

MMT-1 Montmorillonite modified by quaternary ammonium salt at a concentration equivalent to 1 cation exchange capacity (CEC) of Na- montmorillonite.

MMT-2 Montmorillonite modified by quaternary ammonium salt at a concentration equivalent to 2 CEC of Na-montmorillonite.

MMT-3 Purified sodium montmorillonite

CK-1 : Uncoated glass bead

CK-2 : Silane coated glass bead

CK-3 : MMT-1 coated glass bead

CK-4 : MMT-2 coated glass bead

CK-5 : MMT-3 coated glass bead Figure 1. In FT-IR spectra, O-H stretching peak of silicate layers is seen in 3700 - 3400 cm^"1. At 917.51 cm^"1 octahedral layer peak could be seen explicitly. These peaks are the sign of montmorillonite. IR spectras of MMT-1 and MMT-2 are in concordance and shows peaks at 2950-2850 cm^"1 and 1470-1370 cm^"1 which could not be seen for MMT-3. Peaks observed at 2950-2850 cm-1 represent methylene structure and peaks at 1470-1370 cm^"1 are assigned to H-C-H stretching. These peaks are the sign of quaternary ammonium salts within the montmorillonite structure.

Figure 2. In the TGA curve, decrease observed between 0-150 °C is due to the divergence of the water between the layers of clay minerals. At 650-850 °C OH ions and impurities such as MgCO3 and CaCO3 has removed from the structure. The decline observed at 200-400 °C for MMT-1 and MMT-2 indicates that ammonium salt is attached to montmorillonite and carbon is burned. Figure 3. In SEM (Scanning Electron Microscope) images, (a) CK-1 , (b) CK-3, (c) CK-4, (d) CK-5 glass beads coated with MMT can be seen. High brightness is seen in SEM of MMT2 coated glass beads due to the high proportion of quaternary ammonium salt.

Disclosure of Invention Coating Studies In the first step of coating glass beads with montmorillonite, a montmorillonite (MMT)- water suspension is prepared. MMT suspension with 0.5-2 % MMT content is prepared by dispersing purified and having cation exchange capacity (CEC) of 105 meq/100g montmorillonite at 30-80 °C. Afterwards, glass bead are added to the MMT suspension and mixed to have glass bead/MMT suspension ratios differing from 1 :1 to 1 :4. As a result of this mixing process coating thickness is 0.1 -0.5 pm. The mixture is transferred into a pan where glass bead could spread. Then, the mixture is dried between 80-100 °C. In order to separate agglomerated glass beads, glass beads are grinded very gently soon after drying. Glass beads should not be broken in this process.

In the coating process with modified montmorillonite, quaternary ammonium salts are added at 0.5, 1 and 2 CEC of MMT to the MMT suspension described above. After the suspension is mixed at 30-80 °C for 0.5-2 hours, coating process is conducted as described above.

The coated glass spheres are spread 33 % by weight to the road marking paint adsorbed onto briquettes. Glass beads are spread to water based road marking paint that consists of water based binder. Wet film thickness of the paint applied to the briquettes is 400-600 pm. Glass beads are in different gradation, that the particle sizes of glass beads range between 150-700 pm. After paint dries, in order to simulate the way, a wheel with 6 bars pressure shuttles on the paint. Each shuttle is considered one cycle, and this process has continued up to 10.000 cycles.

Characterization

FT-IR Infrared Spectroscopy

In order to specify natural montmorillonite and modified montmorillonite, FTIR of MMTs used to coat glass beads are taken on a Perkin Elmer Spectrum One FTIR Spectrometer (Figure 1 ) Thermal Gravimetric Analysis (TGA) In order to specify natural montmorillonite and modified montmorillonite, thermal gravimetric analysis of MMTs used to coat glass beads are taken Perkin Elmer Pyris 1 by heating the sample till 950 °C (Figure 2). Scanning Electron Microscope (SEM)

Morphology of the coated glass beads are observed by JEOL 6335F electron microscope (Figure 3).

Microscope images of the glass beads are given in figure 4 Glass Bead Performance Test

Wear test is performed under wheel to determine glass bead performance by measuring night visibility values of the paints that are worn at a certain level. At the end of this test simulating the way, night visibility values are measured. Glass beads used with water based paint are listed below ;

CK-1 : Uncoated glass bead

CK-2 : Silane coated glass bead (commercial product)

CK-3 : Glass bead coated with 2:1 modified montmorillonite

CK-4 : Glass bead coated with 1 :1 modified montmorillonite

CK-5 : Glass bead coated with 0,5: 1 modified montmorillonite

CK-6 : Glass bead coated with Na-montmorillonite

As in the road application, road marking paint is applied on the briquettes with 600 pm wet film thickness. Images of glass beads on road marking paint are given in figure 5. A wheel with 6 bars pressure shuttles on the paint. Each shuttle is considered one cycle. Night visibilities of the glass bead loaded paints are measured until 10.000 cycles of wheel shutting (Table 1 ). According to these results, at the end of the 1 .000 cycles the paints loaded with commercial glass bead CK-2 has the highest night visibility. However, at 3.000 cycles, the paint loaded with natural montmorillonite coated glass bead CK-5 has the same night visibility with CK-2 loaded paint and till 10.000 cycles night visibility of paint including CK-5 has higher night visibility than CK-2 loaded paint. This situation shows that adhesion of CK-5 is stronger than the commercial product CK-2. As the wheels shuttles on the paint, the paint begins to be worn and new glass beads appear from the bottom. As a result of wearing, glass beads other than CK-5 are removed from the paint surface. Till 8.000 cycles night visibilities increase for CK-5 loaded paint. Though night visibility decrease after 8.000 cycles, night visibility of CK-5 loaded paint is 1 ,5 times of CK-2 loaded paint. Though CK-3 and CK-4 loaded paints have lower night visibilities than CK-2, they have higher night visibilities than uncoated glass bead CK-1 . Table 1. Day and Night Visibility

* Rl : Day visibility ; Qd : Night visibility Industrial Applicability

Produced or purchased glass beads, will be mixed at ambient temperature in bentonite suspension. Coated glass beads will be dried after mixing.

In order to prevent glass beads sticking together, drying process can be performed by fluidized bed system or constant drying can be used if glass spheres can be separated from each other without breaking. This form of glass beads, are ready to use in road marking paint

References

1 . Retroreflective elements comprising a bonded resin core and pavement markings, US20050100709, 2005

2. A reflective road marking and a method of producing and applying a reflective road marking composition , WO2001042349, 2001

3. Methods of making reflectve elements, US20050158461 , 2005

4. Flourescent marker pigment for roadways, US53253146, 1966

5. Process of making beaded coatings and films from glass beads treated with oleophobic sizing agent US3222204, 1965

6. Retroreflective materials and methods for their production and use, US4756931 , 1988

7. Marking comprising glass beads in a matrix, US5128203, 1992

8. Glass bead-filled resin composition, US4305863, 1981 Method of modifying the wettability of glass beads, glass beads polymeric material incorporating such glass beads, and method of applying reflective markings to a surface, US4713295, 1987

A reflective road marking and a method of producing and applying a reflective road marking composition, WO0142349, 2001

Forming a polymeric matrix containing filler material, GB2208078, 1989

Claims

A method of spreading glass beads with different gradation onto the road marking paint soon after the paint application comprising the coating_of the glass beads with inorganic based natural clay and/or modified clay.

A method according to claim 1 characterized in that montmorillonite and/or modified montmorillonite is used for coating glass bead surface.

A method according to claim 1 characterized in that montmorillonite and/or modified montmorillonite used for glass bead coating is in nano size.

A method according to claim 1 characterized in that average particle size of montmorillonite and/or modified montmorillonite used for glass bead coating is 50-500 nm.

A method according to claim 1 characterized in that immersion method is used for coating glass bead surface with montmorillonite and/or modified montmorillonite.

A method according to claim 1 characterized in that the method of coating glass bead surface with montmorillonite is given below;

- Preparing montmorillonite (MMT) suspension

- Dispersion of MMT in water at 30-80°C with 0.5-2 % MMT/suspension ratio and obtaining a homogenous suspension

- Afterwards, adding glass beads to MMT/water suspension with 1 : 1 -1 :4 glass bead/MMT suspension ratio and mixing for a while

- Finally, the mixture is transferred into a pan where glass bead could spread and dried at 80-100°C.

A method according to claim 4 characterized in that glass bead surface is coated with montmorillonite and used montmorillonite is purified before being used to have a cation exchange capacity of 105 meq/100 g.

A method according to claim 4 characterized in that glass bead surface is coated with montmorillonite and after drying process in order to remove glass bead agglomeration, glass beads are grinded softly.

A method according to claim 1 characterized in that the method of coating glass bead surface with modified montmorillonite is given below;

- Preparing montmorillonite (MMT) suspension

- Adding quaternary ammonium salts to the suspension for the modification

- Afterwards, adding glass beads to modified MMT/water suspension with 1 : 1 -1 :4 glass bead/MMT suspension ratio and m ixing for a while

10. A method according to claim 7 characterized in that glass bead surface is coated with modified montmorillonite and quaternary ammonium salt used for modification is added to the suspension with amounts of half, equal and 2 times of the cation exchange capacity of montmorillonite.

1 1 . A method according to claim 1 characterized in that coated glass beads are used with varying gradation.

12. A method according to claim 1 characterized in that glass beads are spread on the pain as larges beads are on the paint surface, small beads lay on the bottom and glass bead ratio is 33 %.

13. A method according to claim 1 characterized in that binder used in the paint is water based.

14. A method according to claim 1 characterized in that binder is such a water based material that shows high affinity towards the coating of glass bead.

15. A method according to claim 1 characterized in that wet film thickness of the paint is 400-600 pm.

16. A method according to claim 1 characterized in that particle sizes of glass beads varies between 150-700 pm.

17. A method according to claim 1 characterized in that coating thickness of the glass beads is 0, 1 -0,5 pm.