MXPA06008202A - Methods of making reflective elements - Google Patents

Abstract

The invention generally relates to methods of embedding secondary particles onto the surface of a primary particle by means of a polymeric material and in particular to methods of making retroreflective elements.

Description

METHODS OF ELABORATION OF REFLECTIVE ELEMENTS Field of the Invention The invention generally relates to methods of accommodating secondary particles on the surface of a primary particle by means of a polymeric material, and in particular to methods of making retroreflective elements.

BACKGROUND OF THE INVENTION The use of pavement markers (eg, paints, tapes and individually assembled items) to guide and direct drivers traveling along a road is well known. During the day the markers can be sufficiently visible under ambient light, to effectively signal and guide a driver. At night, however, especially when the primary source of illumination is the headlights of the driver's vehicle, the markers are generally insufficient to guide a driver, because the light from the headlights hits the pavement and the marker at an angle of very low incidence, and is reflected mostly away from the driver. For this reason, pavement markers with improved retroreflective properties have been employed. Ref .: 174490 Retroreflection describes the mechanism where light incident on a surface is reflected, so that much of the incident beam is directed back towards the source. The most common retroreflective pavement markers, such as lane lines on roads, are made by casting transparent ceramic or glass optical elements onto one. line of freshly painted paint, such that the optical elements become partially housed in them. The transparent optical elements each act as a spherical lens, and thus, the incident light passes through the optical elements to the base paint or sheet, upon striking the pigment particles in them. The pigment particles scatter the light, by redirecting a portion of the light back to the optical element, such that a portion is then redirected back to the light source. Vertical surfaces tend to provide better orientation for retroreflection. Therefore, numerous methods have been made to incorporate vertical surfaces into pavement markers, typically by providing projections on the marking surface. Vertical surfaces can prevent the accumulation of a layer of water on the retroreflective surface during rainy weather, which may otherwise interfere with the retroreflective mechanism of optical elements exposed on the surface.

In order to increase the number of optical elements that are supplied in a vertical orientation, reflective elements have been developed in which the optical elements are joined to a core particle. See for example, - Patents of E.U.A. Nos. 3,175,935 (Vanstrum); 3,043,196 (Palmquist); and 3,252,376 (De Vries). Still another example, Patents of E.U.A. Nos. 5,772,265 and 5,942,280 describe retroreflective elements before they are - all of ceramic, which can be used in pavement markers comprising an opaque ceramic core and ceramic optical elements partially housed over the core (summary). Representative retroreflective elements of this nature are commercially available from 3M Company, St. Paul, MN under the trade designations "3M Liquid Pavement Marker Elements 1270" (white) and "3M Liquid Pavement Marker Elements 1271" (yellow). Such retroreflective elements have been used in pavement markers. Although such retroreflective elements provide adequate retroreflective properties in combination with adequate durability, the industry would find advantages in alternative methods of retroreflective element making, particularly methods related to the manufacture of retroreflective elements at a reduced cost.

Brief Description of the Invention The invention describes methods of making retroreflective elements that comprise providing a plurality of core particles., coating the particles with a non-solidified polymer composition that forms coated particles, combining the coated particles with optical elements such that the optical elements are housed in the non-solidified polymeric composition, and solidifying the polymeric composition that forms retroreflective elements. In one embodiment, the method comprises combining the coated particles with the optical elements in a continuous process. The particles of the core and / or polymer composition and / or optical elements can also be continuously supplied. In another embodiment, the method comprises providing a plurality of core particles having surfaces comprising a non-solidified polymer composition.; combining the core particles with optical elements by means of a device comprising at least one rotating mixing member selected from the group consisting of a disk, a helical extruder screw, co-rotating or counter-rotating blades, and polishing discs , such that the optical elements are housed in the non-solidified polymer composition; and solidifying the polymer composition that forms retroreflective elements.

. In each of these embodiments, the non-solidified polymer composition can be a molten thermoplastic resin or a bonded resin core precursor. An excess of optical elements is preferably supplied, the method further comprising separating the retroreflective elements from the non-housed optical elements. The core particles typically range in size from about 0.1 mm to about 3 mm. The core particles preferably comprise an inorganic material such as sand, roofing granules, and particles for sliding. The transparent microcrystalline beads are preferably used in combination with a polymer composition comprising at least one material for light scattering. Various types of optical elements can be supplied in parallel. In one aspect, the optical elements provided include first optical elements having a refractive index in the range from about 1.5 to about 2.0 and second optical elements having a refractive index in the range from about 1.7 to about 2.6. . The methods described herein may be related to the formation of other types of articles in which secondary (eg, smaller) particles are housed on the surface of a core particle by means of a polymeric composition.

Brief Description of the Figures FIG. 1 details a schematic diagram of an exemplary continuous method for housing small particles on the surface of a larger particle suitable for making retroreflective elements. FIG. 2 details enlarged cross-sectional views of the core particles, coated particles, and retroreflection elements of the invention.

Detailed Description of the Invention The invention generally relates to methods of accommodating secondary particles on the surface of a primary particle by means of a polymeric material and in particular to methods of making retroreflective elements. In methods of making retroreflective elements, the optical elements are partially housed within the core particle surface comprising a non-solidified polymer composition. The primary particle is referred to herein as the "core particle" since it is the innermost part relative to the housed secondary particles. The core particle typically comprises a single particle in the size range from about 0.1 mm to about 10 mm. Preferably, the particle size is greater than 300 microns and less than 2000 microns. Although the core particle may comprise a polymeric material (eg, crosslinked), the core particle typically comprises an inorganic material. The presence of the inner inorganic particle is assumed to aid in the prevention of particle deformation, during the process of accommodating the smaller particles (e.g., optical elements). Suitable inorganic particles include sand, roofing granules and slip particles such as those commonly used in pavement markers. In preferred embodiments, the core particle is coated with a non-solidified polymer composition. The non-solidified polymer composition is preferably a "bonded resin core precursor" which refers to a crosslinkable polymer resin. The agglutinated resin core precursor composition comprises monomeric, oligomeric, and / or polymeric components, and mixtures thereof, which are cross-linked upon exposure to heat (eg, thermosets), actinic radiation (eg, ultraviolet light, electron beam) or other chemical reaction (eg, catalyst). It is assumed, however, that the non-solidified polymeric material may alternatively comprise a molten resin. By "molten" it means that the thermoplastic resin is softened substantially such that secondary particles can be accommodated therein (e.g., optical elements). For the currently preferred core particle dimensions for retroreflective elements, which have a diameter in the range from about 0..2 (ie, 200 microns) to about 10 millimeters, the optical elements are typically in the range in size from about 30 to about 300 micrometers in diameter. In preferred embodiments, the secondary particles of the retroreflective element are smaller than the core particle. Typically, the secondary particles are less than half the diameter of the core particle. In preferred embodiments, the secondary particles (e.g., optical elements) are 100 to 300 times smaller than the core particle, resulting in a plurality of secondary particles (e.g., optical elements) housed on the surface of the particle of core. In alternative interstitial embodiments, the secondary particles may be larger than the primary particle, resulting in for example four secondary particles closely packed around the core particle. The secondary particles can be of any size also between the dimensions previously stated.

As used herein, "optical elements" refers to granules, flakes, fibers, beads, etc., that reflect light either independently or when combined with a core of diffuse reflection. The spheroidal transparent elements, also described herein as "beads", "glass beads" and "ceramic and glass beads" are typically preferred. Typically, the optical elements have a refractive index of about 1.5 to about 2.6. The optical elements comprise inorganic materials that are not easily susceptible to abrasion. The optical elements (e.g., transparent beads) may comprise an amorphous phase, a crystalline phase, or a combination thereof. The most widely used optical elements in pavement markers are made of soda lime and silicate glasses. Although the durability is acceptable, the refractive index is only about 1.5, which greatly limits its retroreflective brightness. The optical index glass elements of improved durability that can be used herein are taught in the U.S.A. No. 4,367,919. For increased resistance to grinding, the beads are preferably microcrystalline. Representative microcrystalline beads may be non-vitreous, as described in the U.S. Patent. 4,564,556 (Lange '), or the beads may comprise a ceramic and glass material, such as described in the US patent. Do not-. 6,461,988. Microcrystalline optical elements are also described in the Patents of E.U.A. Nos. 4,758,469 and 6,245,700. The optical elements are preferably resistant to scratching and chipping, are relatively hard (above a 700 Knoop hardness), and are made to have a relatively high refractive index. - Secondary particles (eg, optical elements) are typically housed to a depth sufficient to maintain the particles in the core during processing and use. The housing of at least 20% of the diameter, particularly in the case of spheroidal optical elements (e.g., microcrystalline beads), will typically effectively hold the optical element within the core. By 20% hosted, it means that about 80% of the total number of optical elements are housed within the core surface, such that about 20% of each bead sinks into the core and about 80% is exposed on the surface of the nucleus. If the optical elements are housed more than about 80%, the retroreflective properties tend to decrease substantially. In order to obtain a bonding balance between the optical elements and the core in combination with adequate retroreflectivity, typically more than about 90% of the total number of beads are housed to a depth of about 40% up to about 60%. Although the methods of the invention are described herein with reference to methods of making retroreflective elements, these same methods may also be suitable for other articles where secondary particles are attached to a core particle by means of a non-solidified polymeric material. . In one aspect, the method of making retroreflective elements comprises providing a plurality of core particles (eg, inorganic), coating the particles with a non-solidified polymer composition such as a bonded resin precursor, combining the coated particles with optical elements. in a continuous process such that the optical elements are accommodated in the non-solidified polymer composition, and solidify the polymeric composition that forms retroreflective elements.

With reference to FIG. 1, which details an exemplary continuous process, core particles (e.g., sand) 100 and optical elements 200 (e.g., ceramic and glass beads) are continuously fed to a mixing station 300. The core and secondary particles (for example example, optical elements) can be supplied in any way, such as by means of a first 101 and second 201 gravity feed hopper. Alternatively, the core and secondary particle can be measured at the mixing station. Various mass and measurement devices are known. Suitable representative measuring devices include helical screw conveyors and feeders such as can be found on the website www.ajax.co.uk. A non-solidified polymer composition 400 is coated on top of the core particles. The polymer composition may be contained in a container 401 that is pumped to the mixing station. Preferably, the non-solidified polymer composition is also measured. Provided that the non-solidified polymer composition is sufficiently low in viscosity, the composition can alternatively be fed by gravity to the mixing station. For embodiments, wherein the non-solidified polymer composition is a molten thermoplastic resin, the resin may be pre-melted or the containment vessel may be equipped with a heater to melt the resin. The ratio to which the core particles and the uncured polymer composition are supplied can vary depending on the particle size of the core particle as well as the desired thickness of the uncured polymer composition on the core particle. In a preferred embodiment, the ratio of the rate of delivery of non-solidified polymer composition to core particle (eg, inorganic) is about 1 to 10 by weight (eg, for core particles of a 20 mesh size). / 30). The non-solidified polymer composition is coated on the core particles in a coating station 500 equipped with a suitable mixing medium. Typically, the uncured polymer composition is relatively low in viscosity and thus can be easily coated on the surface of the core particles. For example, the core material and non-solidified polymer composition can both be measured at just described weight ratios in a continuous mixer such as commercially available from Ajax Equipment Limited, UK, under the trade designation "Ajax LynFlow Continuous Mixer". Such a mixer is equipped with a screw conveyor stop. When the appropriate amount of non-solidified polymer composition is supplied, there is typically no need to separate the excess uncured polymer composition from the output coated particles 525. Alternatively, even less convenient the core particle can be coated with an excess of precursor of bonded resin and the uncoated material separated from the coated particle. This can be achieved for example by transporting the mixture on a screen having a mesh adequately smaller than the core particles, so that it only allows the passage of the excess uncured polymer material. Other suitable means for coating the core particles with a non-solidified polymer composition include disk coaters such as described in US Patents. Nos. 5,447,565; 4,675,140; and 5,061,520; as well as grinding and extruders, as will be described later, and the like. The non-solidified polymeric material may optionally comprise other ingredients such as fillers (e.g., glass beads) and solvents). When present, these other ingredients can be combined prior to, (for example, continuously) or concurrently with the coating of the core particle. In a suitable method, a light scattering material (eg, pearlescent pigment) is combined with a bonded resin core precursor by means of a small secondary extruder. Regardless, however, the polymer composition, prior to solidifying (eg, curing), has a suitable viscosity for coating the core particles. It has been found that the Brookfield viscosity of a resin precursor composition bonded at 72 ° F (22.2 ° C) prior to curing and prior to the addition of the light scattering material typically have a viscosity of at least about 1000 cps. . In order to disperse relatively high concentrations of light scattering material, however, the Brookfield viscosity of the bonded resin composition at 72 ° F (22.2 ° C) is typically less than 10,000 cps (e.g., less than 9,000 cps). 8,000 cps, 7,000 cps, 6,000 cps, 5,000 cps). For example, the bonded resin precursor may have a Brookfield viscosity at 72 ° F (22.2 ° C) of about 1500 cps at 2500 cps. Coated core particles are combined with secondary particles (eg, optical elements). In preferred embodiments, these materials are combined in a continuous process. As used herein, the continuous process refers to a non-intermittent process. This is typically achieved by the mixing station 300 having an inlet for receiving the coated particles at a different location than the outlet 320 for the particle housed with the secondary particles (e.g., optical elements). Typically, the inlet and outlet of the mixing station are located at. opposite ends. For example, for gravity feeding methods, the inlet is placed above the mixer and the outlet is placed underneath. However, the entire apparatus or portions thereof can be configured in a horizontal rather than vertical configuration, as is often the case when an extruder is employed. The ratio of the rate of delivery of the secondary particle (eg, optical element) to the delivery rate of the coated core particle may vary depending on the particle size. The ratio of the delivery rate of the secondary particles (eg, optical element) to the delivery rate of the coated core particles are generally in the range of 0.2: 1 to 10: 1. (for example, for core particles of 20/30 mesh size). It is generally preferred to provide an excess of secondary particles (eg, optical element) (ie, even 20: 1). The non-housed secondary particles 200 can then be separated from the retroreflective elements for example by a 550 sieve and recycled if necessary. The mixing station is equipped with a suitable means of mechanical mixing. The applicant has found that mechanical mixing is advantageous in preventing the undesirable formation of agglomerations, that is, the joining of more than one core particle to one another. In preferred methods, retroreflective elements are formed comprising a single core housed with optical elements by means of the polymeric coating. During the continuous method described herein, the coated particles of the core and optical elements are preferably fed continuously into the mixing station. In addition, the mixing station preferably continuously forms retroreflective elements by housing the optical elements on the surface of the coated particles. The retroreflective elements 600 preferably also exit continuously from the mixing station. As used in the '"present, mechanical mixing refers to a device having at least one rotating mixing member. With the exception of the disc coater, the mixing device preferably comprises a pair of co-rotating or counter-rotating blades. Preferably, the surface area (cm2) of the mixing blades relative to the volume (ml) of material being mixed is in the range from about 1: 5 to 1:10 and preferably in ranges from about 1: 6 to 1: 8 The mixing device forces the coated core particles and secondary particles through at least one field of high shear stress. Preferably, the "dead space" is minimized by the radius of the mixing blade positioned such that it closely approaches (eg, within about 0.5 mm) the inner peripheral surface of the container 301 so that the unmixed material do not accumulate on the wall of the container. Alternatively, but typically less efficiently, the container can be equipped with one or more blades that scrape the wall of the container. Various mechanical mixing devices having at least one rotating mixing member have been determined as suitable by the applicant. The rotational speed of the mixing member (s) may vary depending on the equipment used. A suitable mixing device, as detailed in FIG. 1, comprises at least one pair of co-rotating or counter-rotating mixing blades 350. Any number of individual mixing blades may be present. The convenience of such a mixing device has been exemplified herein by the use of a manual mixer having four blades in each of the two "beaters". It is obvious to one of ordinary skill in the art that this mixing configuration can be scaled up to an industrial capacity. The co-rotation of the mixing blades forces the coated core particles and the optical elements to pass between the pair of blades. Typically this is done at high speeds in order to provide sufficient strength for a suitable housing as well as the separate breaking of some agglomerations that may be formed. In one embodiment, the rotary speed is typically at least about 1000 revolutions per minute ("rpm"), and more typically at least about 2000 rpm (eg, 2500), reaching up to around 4000 rpm. Another suitable mixing device comprising a rotating mixing element is a "grinding mill comprising at least one rotating milling plate." Mill mills are also referred to as "grinding mills", disk mills and attrition mills. Mill grinders typically include two metal plates that have small projections (ie, burins) Alternatively, abrasive stones can be used as in polishing discs One plate can be stationary while the others rotate or both can rotate Opposite directions In one embodiment, the rotating speed is about 80 rpm revolutions per minute Grinding takes place between the plates that can operate in a vertical or horizontal plane.For vertical configurations, the coated core particles, and secondary particles ( for example, optical element) would typically enter above the plates and reflective elements 600 emerge from l background, as detailed in FIG. 1. The distance (that is, space) between the plates is adjustable. In the present invention, the space is set such that it is greater than the size of the largest particle employed (e.g., core particle), although smaller in dimension than an agglomeration comprising two or more core particles joined one to the other. the other. By fixing the space in this way, the clumps are too large to pass through the space and so can not come out until they are broken by the grinding discs. Various industrial grinding mills are commercially available, such as can be found on the website page www. aaoofoods. com / graingrinders. A third suitable mixing device comprising at least one rotary mixing member is an extruder. Extruders generally include at least one helical screw within a cylindrical housing. The material is mixed during its course of travel through the helical channels defined by the path of the helical screws. Extruders generally have a range in dimension from 10 L / D (that is, length to diameter) up to 60 L / D. Preferably, a helical twin screw extruder having co-rotating and counter-rotating helical screws, including those referred to as extruders, is employed. A suitable helical twin screw extruder is commercially available from Baker Perkins, Saginaw, MI under the trade designation "Baker Perkins Continuous Mixer". The rotational speed of this striker is typically in the range from about 25 to 225 revolutions per minute. A proper fit for this extruder in order from the start of the extruder to the extruder outlet includes: (1) 5 inches (12.7 cm) of forward movement paths, (2) 1.5 inches (3.8 cm) of gear mixers inverse 1050-3LDE-FFR / 1.50-8, (3) 3"inches (7.6 forward travel strokes, (4) 3 inches (7.6 cm) forward gear mixer 1050-3LDE-RFL / 1.50-8 and (5) 8 inches (20.3 cm) of forward movement paths Suitable feed locations of the binder, sand, and optical elements relative to the beginning of the extruder with their proximity to the screw assembly may be for example (1). ) addition of sand to 3.5 inches (8.9 cm) with the resin precursor bonded through the same port at 4 inches (10.2 cm), (2) addition of optical elements to 10 inches (25.4 cm) (above the mixer assembly) of front gears) and (3) retroreflective elements that come out at 20 inches gadas (50.8 cm). The feeding location of the optical elements can be within 10 inches (25.4 cm) or less from the extruder outlet. In addition, the location of the start of the front gear mixer can be adjusted in this manner to match the location of the feed. Other suitable helical screw extruders are commercially available from various suppliers including for example Berstorff (Florence, KY), Coperion _ (Ramsey, NJ), JSW (Corona, CA) and Leistritz (Somerville, NJ). If desired, extruders having more than two tielicoidal screws can be used, for example, three or four helical screw extruders. As will be appreciated by those skilled in the art, the helical screw configuration and the operating conditions of the extruder can be optimized or adjusted depending on the materials and equipment used. Extruders and helical screws of representative extruders are shown in U.S. Patents. Nos. 4,875,847, 4,900,156, 4,911,558, 5,267,788, 5,499,870, 5,593,227, 5,597,235, 5,628,560 and 5,873,654. Simple helical screw extruders may also be suitable. Typically, single helical screw extruders differ from helical screw feeders and conveyors, either by the speed at which they operate (ie, helical screw rpm) and / or the surface area of the blades relative to the volume that it mixes. In view of these differences, helical screw feeders and conveyors typically can not mix and pump polymeric materials or melt polymeric material when desired. One type of single helical screw extruder is commercially available from Coperion Buss Kneader MKS, Ramsey, NJ under the trade designation "Modular Mixer System". This device has a simple reciprocating helical screw. The helical screw has three helical screw paths and rotates / oscillates in the mixing chamber. The camera is lined with bolts or teeth. Other single helical screw extruders are commercially available from Crompton, CT and Meritt-Davis, Hamden, CT. Each of the mechanically mixing means just described preferably comprises at least one pair of co-rotating or counter-rotating mixing elements (i.e., blades, helical screws, polishing discs). Another suitable mixing device comprises a simple rotating disk. Representative devices include rotary disc coating apparatus as described in US Patents. Nos. 5,447,565; 4,675,140; and 5,061,520. These patents, however, refer to the coating of solid particles with a liguid coating. The Applicant has found that a rotating disc coater is also suitable for housing solid particles on the coated core particle. A preferred rotary disc coater for this purpose is described in the pending U.S. Patent Application. Serial No. 10/762032, filed on January 21, 2004, entitled "RECYCLE DISC". The coater concludes a disk having a periphery, a motor that is coupled to the disk in order to be able to rotate the disk, and a choke mounted adjacent to the disk in order to provide a space for the output of the coated particles near the periphery of the disk. The choke may include a flange portion positioned above the disk, "so that the space between the choke and the disk extends over an important portion - of the radius of the disk.In addition, the choke may also have a portion adjacent to the portion thereof. with flange (eg, frusto-conical shape) so that the height of the space between the disc and the choke decreases with the radial distance from the center of the disc.This is supposed to uniformly measure the particles within the space. It fixes the space at a height only slightly greater than the maximum theoretical size of one of the core particles (eg sand) that has a single layer of the retroreflective beads.The rotating speed of this device is typically in the range of 300 revolutions per minute at 700 revolutions per minute The output ratio of elements retroreflect before the method (for example, continuous ) of the invention, is preferably at least 20 Ibs / hr (9.1 kg / hr), more preferably at least 50 lbs / hr (22.7 kg / hr), more preferably at least 100 lbs / hr (45.4 kg / hr) and even more preferably at least 150 Ibs / hr (68.1 kg / hr) and greater. Substantially greater productions can be achieved for example, by the use of a larger extruder than other means, as would be readily apparent to one of ordinary skill in the art. Various polymeric materials can be used to coat the core particle including various one- and two-part curable binders, as well as thermoplastic binders wherein the binder achieves a liquid state - by heating until it melts. Common binder materials include polyacrylates, methacrylates, polyolefins, polyurethanes, polyepoxide resins, phenolic resins, and polyesters. Preferred polymeric materials in view of their known durability include those materials that have been used as a binder in the manufacture of pavement markers. As an example, a two-part composition having an amine component including one or more aliphatic amines (e.g., aspartic ester) and optionally one or more amine-functional co-reactants, an isocyanate component including one or more polyisocyanates, and material selected from the group of fillers, diluents, pigments and combinations thereof may be employed such as compositions described in the US patent. No. 6,166,106. As another example, a suitable epoxy resin can be obtained from 3M Company, St. Paul, MN under the trade designation "3M Scotchcast Electrical Resin Product No. 5" Preferred bonded resins include certain polyurethanes including those derived from the reaction product of a trifunctional polyol, such as those commercially available from Dow Chemical, Danbury, CT under the trade designation "Tone 0301", with an adduct of hexamethylene diisocyanate (HDI), such as commercially available from Bayer Corp., Pittsburg, PA under the commercial designation "Desmodur N-100" at a weight ratio of about 1: 2. The physical properties of agglutinated resins, and in particular the agglutinated resins specifically described and exemplified herein, can further be characterized in accordance with various known techniques for determining the glass transition temperature (Tg), tensile strength, elastic modulus etc., as such, the physical properties are inherent properties of the agglutinated resin compositions described herein. It is appreciated that other agglutinated resin compositions having similar physical properties can contribute comparable results. Other polyol polyesters which may be employed in appropriate equivalent weights include "Tone 0305", "Tone 0310" and "Tone 0210". In addition, other polyisocyanates include "Desmodur N-3200", "Desmodur N-3300", "Desmodur N-3400", "Desmodur N-3600", as well as "Desmodur BL 3175A", a block polyisocyanate based on HDI, which it is assumed that it contributes substantially to an improved "receptacle life" as a result of minimal changes in the viscosity of the polyol / polyisocyanate mixture.The non-diffused reflecting core particle (e.g. to be used in combination with specular reflection optical elements, such as would be supplied by the glass beads described in the US Patents Nos. 3,274,888 and 3,486,952. In preferred embodiments, however, the coated core particle comprises at least one scattered light scattering material within the polymer coating. In this way, the optical elements are typically transparent and substantially free of mirror reflective properties (eg, metal-free). The reflection of the core material (eg, bonded resin or coated core particle) comprising one or more core materials. Light scattering can be conveniently characterized as described in the ANSI PH2.17-1985 standard. The measured value is the reflectance factor that compares the diffuse reflection of a sample, at specific angles, with that of a calibrated standard for a perfect diffuse reflection material. For retroreflective elements employing a diffuse reflection core, the reflectance factor of the core is typically at least 75% at a thickness of 500 micrometers for retroreflective elements with adequate brightness for markers on roads. More typically, the core has a reflectance factor of at least 85% at a thickness of 500 micrometers. Diffuse reflection is caused by the scattering of light within the material. The degree of scattering of the light is generally due to the difference in the refractive index of the dispersion phase compared to the base composition of the core phase. An increase in light scattering is typically observed when the difference in the refractive index is greater than about 0.1. Typically, the refractive index difference is greater than about 0..4. (for example, greater than 0.5, 0.6, 0.7 and 0.8). The light scattering can be provided by combining the uncured polymer composition with at least some diffuse reflection particles and / or at least some particles that are reflected specularly (for example, aluminum flakes, pearl pigment). Examples of useful fuzzy pigments include, but are not limited to, titanium dioxide, zinc oxide, zinc sulfide, lithophone, zirconium silicate, zirconium oxide, natural and synthetic barium sulfates, and combinations thereof. An example of a useful pigment-specular is a pearlescent pigment, such as pearlescent pigments commercially available from EM Industries, Inc., Hawthorne, NY under the trade designations "Afflair 9103" and "Afflair 9119" and commercially available from The EM Industries of Hawthorne, NY under the commercial designations "Mearlin Fine Pearl # 139V" and "Bright Silver # 139Z". The diffusely reflecting pigments are typically used at a concentration of at least 30% by weight. Specular mirror pigments are preferred and are typically used in an amount of at least 10% by weight (eg, 15% by weight, 20% by weight and any amounts between them). Other pigments can be added to the core material _ to produce a colored retroreflective element. In particular the yellow, it is a desirable color for pavement markers. In order to maximize the reflectance of the element, particularly in combination with transparent microspheres, it is preferred to maximize the concentration of pigment with the proviso that the coating viscosity is not compromised, and the physical properties of the cured binder. Typically, the maximum total amount of light scattering material is about 40 to 45% by weight. Typically, for an optimum retroreflective effect, the optical elements have a refractive index in the range from about 1.5 to about 2.0 for optimum retroreflectivity in dry, preferably in the range from about 1.5 to about 1.9. For optimal wet retroreflectivity, the optical elements have a refractive index in the range from about 1.7 to about 2.6, preferably in the range from about 1.9 to 2.6, and more preferably in the range from about 2.1 to about 2.3. Different types of optical elements that have the same or approximately the same refractive index can be used. The optical elements can have two or more refractive indexes. Typically, optical elements that have a higher refractive index work better when wet and optical elements that have a lower refractive index work better when they are dry. When a mixture of optical elements having different refractive indices is used, the ratio of optical elements of higher refractive index to optical elements with lower refractive index is preferably about 1.05 to about 1.4, and more preferably about 1.08. up to around 1.3. The optical elements can be colored to retroreflect a variety of colors such as color that matches binders of the pavement marker (e.g., paints) in which they will be housed. Techniques for preparing colored ceramic optical elements that can be used herein are described in U.S. Pat. No. 4,564,556. Dyes such as ferric nitrate (for red or orange) can be added in the amount of from about 1 to about 5 weight percent of the total metal oxide present. Color can also be imparted by the interaction of two colorless compounds under certain processing conditions (for example, Ti02 and Zr02 can interact to produce a yellow color). Regardless of the method, the optical elements (for example, beads) are preferably treated with at least one adhesion promoting agent and / or at least one flotation agent. In addition, the core particle (eg, inorganic) can also be treated with an adhesion promoting agent. Adhesion promoting agents, also referred to as coupling agents, typically comprise at least one functional group that interacts with the polymer composition and a second functional group that interacts with the optical element and / or core. In general, the adhesion promoting agent is chosen based on the chemistry of the polymer composition. For example, vinyl-terminated adhesion promoting agents are preferred for polyester-based agglutinated resins, such as polyester resins formed from addition reactions. In the case of agglutinated epoxies, adhesion promoters terminated in amines are preferred. Preferred adhesion promoting agents for polyurethanes, particularly for microcrystalline optical elements (e.g., glass and ceramic beads) and inorganic core materials (e.g., sand, gliding particles) are the amine-terminated silanes such as 3- aminopropyltriethoxysilane, commercially available from OSI Specialties, Danbury, CT under the trade designation "Silquest A-1100". Suitable flotation agents include various fluoroguimics such as described in the U.S.A. No. 3,222,204, patent publication of E.U.A. No. 02-0090515-A1 and patent publication of E.U.A. No. 03-0091794-Al. A preferred flotation agent includes a surface treatment based on polyfluoropolyethers such as (hexafluoropropylene) polyoxide having a carboxylic acid group located at the terminus of the chain, commercially available from Du Pont, Wilmington, DE under the trade designation "Krytox. " The "Krytox" 157 FS is available in three relatively broad molecular weight ranges, 2500 g / mol (FSL), 3500-4000 g / mol (FSM) and 7000-7500 g / mol (FSH), respectively for low molecular weights , medium and high. Medium and low molecular weight grades are preferred for the aqueous supply of the surface treatment. Other preferred flotation agents are described in WO 01/30873 (for example, Example 16). For use in pavement markers, the retroreflective elements may have virtually any size and shape, provided that the retroreflection coefficient (RA) is at least about 3 cd / lux / m2 in accordance with Procedure B of the standard. ASTM E809-94a using an input angle of -4.0 degrees and an observation angle of 0.2 degrees. The preferred size of the retroreflective elements, particularly for pavement marker uses, is in the range - from about 0.2 mm to about 10 mm and is more preferably around - 0.5 mm to about 3 mm. In addition, substantially spherical elements are more preferred. For most uses of pavement marker, RA is typically at least about 5 cd / lux / m2 (eg, at least 6 cd / lux / m2 at least 7 cd / lux / m2, at least 8 cd / lux / m2 and older). The methods described herein result in retroreflective elements having at least comparable retroreflective properties and often better in comparison to retroreflective elements having a ceramic core, although they can be manufactured at a substantially lower cost due to the invention described herein. Thus, pavement markers comprising retroreflective elements prepared from the method of the invention will show at least the same, and often better initial retroreflectivity when measured in accordance with ASTM E 1710-97. It is also assumed that the resulting retroreflective elements can exhibit comparable durability compared to retroreflective elements having a core of ceramics. "The same retroreflective elements" refers to retroreflective elements comprising the same optical elements with the main difference that the core comprises a different composition. The initial Retruereflected Luminance Coefficient of the pavement markers of the invention is at least 1000 milicandelas / m2 / lux and thus at least about the same initial RL as the same reflective elements having an opacified ceramic core. In preferred modalities, the pavement markers of the invention show improved retroreflective properties. For such modalities, the initial RL can be at least 1400 milicandelas / m2 / lux, at least 1600 milicandelas / m2 / lux, at least 1800 milicandelas / m2 / lux, and about 2000 milicandelas / m2 / lux or greater. By employing retroreflective elements having a higher initial luminance coefficient, the retroreflected luminance coefficient after the wear test is also higher, since the retroreflected luminance loss ratio may be around it. In this way, pavement markers that employ elements that have an upper initial RL, are advantageously more durable in that such a marker shows a minimum RL of at least 200 milicandelas / m2 / lux for a longer duration of time, (ie , 1 year, 2 years, 3 years, more than 5 years, and time intervals between them depending on environmental conditions). The retroreflective elements of the invention prepared from the methods described herein can be used to produce a variety of retroreflective products or articles, such as retroreflective coating and in particular pavement markers. Such products share the common feature that they comprise a binder layer and a multitude of retroreflective elements housed at least partially within the surface of the binder, such that at least a portion of the retroreflective elements are exposed on the surface. In the retroreflective article of the invention, at least a portion of the retroreflective elements will comprise the retroreflective elements of the invention and thus, the inventive elements may be used in combination with other retroreflective elements as well as with other optical elements (eg, transparent beads). ). The objects and advantages of the invention are further illustrated by the following examples, but the particular materials and amounts mentioned of the same examples, as well as other conditions and details, should not be constituted to unduly limit the invention. All percentages and ratios herein are by weight unless otherwise specified.

Examples Test Methods Retroreflection of Reflective Elements-Coefficient of Retroreflection (RA) The brightness was measured as the coefficient of retroreflection (RA) by placing sufficient elements in the bottom of a plate that was at least 2.86 cm in diameter, so that no part of the bottom of the plate was visible. Then Procedure B of the Standard ASTM Standard E809-94a was followed, using an input angle of -4.0 degrees and an observation angle of 0.2 degrees. The photometer used for the measurements is described in the defensive publication of E.U.A. No. T987,003.

Optical Elements The optical elements used in the Examples were ceramic and glass beads having a starting composition of oxide material by weight of 30.9% TiO2, 15.8% SiO2, 14.5% deZrO2, 1.7% MgO, 25.4% A1203 and 11.7% CaO. The beads were prepared according to the patent of E.U.A. No. 6,245,700 to supply beads that had a nominal refractive index of 1.9. The beads were treated on the surface first with "Silquest A-1100" adhesion promoting agent, by first diluting approximately 8% by weight of "Silquest A-1100" with water such that the amount was sufficient to coat the beads and provide 600 ppm on the dried pearls. The beads were then treated with a flotation promoting agent "Krytox 157 FSL" in the same manner, to provide 100 ppm of such treatment. Each surface treatment was applied by placing the beads in a stainless steel vessel and by splashing the diluted surface treatment solution onto the beads while mixing continuously to provide wetting of each bead. After each treatment, the optical elements were placed in an aluminum drying tray to a thickness of about 1.9 cm and dried in an oven at 66 ° C for about 30 minutes.

Agglutinated Resin Core Precursor A polyurethane precursor composition was prepared by hand-mixing the following ingredients to form a binder:% by weight 15.3% Polyester Polyol, available from Dow Chemical, Danbury, CT under the trade designation "TONE 0301" (Brookfield Viscosity = 2400 at 72 ° F (22 ° C)) 31% Aliphatic Polyisocyanate, available from Bayer Corp., Pittsburg, PA under the trade designation "DESMODUR N-100" (Brookfield Viscosity = 7500 to 72 ° F (22 ° C)) 37% pearl pigment, commercially available from EM Industries Corporation under the trade designation "AFFLAIR 9119" 5.9% methyl ethyl ketone solvent 5.9% acetone solvent 4.9% additives (dispersants, modifiers) Inorganic Core Particle Sand type sandblasting was used in the 20/30 (840/600 micron) mesh range commercially available from Badger Mining, Berlin, WI under the trade designation "BB2".

Example 1-Co-rotating Blade Mixer Method The sand was surface treated with 600 ppm of "Silquest A1100" (without "Krytox 157 FSL") in the same manner as previously described for the surface treatment of the beads. A portion of the bonded resin core precursor was added to 10 parts of treated sand. The sand and binder were mixed by hand with a spatula, until all the sand was completely covered with binder. The retroreflective elements were prepared by mixing 40 g of coated sand and 1200 g of optical elements in a 1000 ml polyethylene beaker. A manual kitchen blender obtained from Hamilton Beach under the commercial designation "Portfolio" equipped with dual four-knife beaters, each with a collar, was inserted into the beaker containing the optical elements and the coated sand. Each beater had a radius of 1.75 inches (4.4 cm), the width of each of the four blades was 1/4 inch (0.63 cm) and had a length of 3.25 inches (8.3 cm). The optical elements and the coated sand were mixed at maximum speed. The mixer and the 1000 ml beaker were turned so that the coated and grouted sand was removed through the co-rotating beaters in the presence of the excess optical elements. This was continued until most or all of the coated sand was in the form of discrete particles, resulting in a core of sand coated with a bonded resin core precursor and covered with optical elements. In order to solidify the precursor coating of the bonded resin, the sand-coated particles having surfaces substantially covered with housed optical elements were cured for 30 minutes in an oven at 80 ° C.

Example 2-Method of Co-rotating Blade Mixer The retroreflective elements were prepared in a mixing vessel, made by removing the bottom of a 1000 ml polyethylene beaker and by placing a three inch (7.6 cm) funnel. diameter of polyethylene with epoxy to obtain a container with a flared bottom. A 0.5 inch (1.3 cm) ball valve was placed at the bottom of the funnel with flexible tubing, so that the flow of material out of the mixing vessel could be controlled. The container was suspended with a ring holder. A pearl hopper was made by removing the bottom of a two gallon (7.6 liter) bottle of Nalgene. The bottomless bottle was suspended from top to bottom with the ring holder and placed directly above the mixing vessel. A 0.5 inch (1.3 cm) valve was also placed on the neck of the bottomless bottle with flexible tubing, so that the flow of material out of this hopper could be controlled. The Hamilton Beach kitchen manual blender was inserted into the mixing container. The optical elements were emptied into the suspended pearl hopper. The ball valves on the bead hopper and the mixing vessel were adjusted (opened), so that a constant level of optical elements was maintained in the vessel (1200g). A helical screw conveyor consisting of a series of propelling blades was adjusted to coat the sand with the binder composition and then the coated sand was fed into the mixing vessel containing the optical elements and the hand blender. The agglutinated resin precursor was added to a pressure vessel and air pressure was used to feed the binder into the helical screw conveyor. The feed ratio of the sand and binder was adjusted to produce a weight ratio of 10: 1 respectively. The sand precursor coated with agglutinated resin core was then thrown into the mixing vessel, where it was fragmented into discrete particles by the hand blender, in the presence of the optical elements in excess. The result was a sand core coated with a binder and covered with optical elements. The retroreflective elements were carried through the bottom of the beaker together with the optical elements in excess and collected in a 500 micron mesh. The excess optical elements were returned to the pearl hopper. In order to solidify the precursor coating of the bonded resin, the sand-coated particles having surfaces substantially covered with housed optical elements were cured for 30 minutes in an oven.

Example 3 - Grinding Plate Method The retroreflective elements were prepared by using a mill obtained from Quaker City Mili Philadephia, PA under the trade designation "Model F NO 4". The mill consisted of a four-bit slotted auger and 3.5-inch (8.9 cm) diameter grinding plates, model 4CS. The manual arm was replaced with a variable speed electric motor of 0.25 hp. The plates were spaced, so that the sand would pass right through the unmilled plates. The speed of the variable speed electric motor was set to. a maximum that generated a bit and grinding plate of 80 rpm. A portion of the bonded resin core precursor was added to 10 parts of the sand. The sand and binder were mixed by hand with a spatula until all the sand was completely coated with binder. The coated sand was gradually added to the mill hopper and formed auger through the grinding plates at a rate of 50 grams per minute. The optical elements were fed by gravity at the outlet end of the grinding hopper prior to the grinding plates at a rate of 1000 grams per minute. The grinding plates fragmented the sand coated with binder grouped in the presence of the optical elements in excess, resulting in a sand core coated with a binder and covered with optical elements. - In order to solidify the precursor coating of the bonded resin, the sand-coated particles having surfaces substantially covered with housed optical elements were cured for 30 minutes in an oven.

Example 4- Grinding Plate Method Retroreflective elements were prepared by using the procedure of Example 3 with the following exceptions. A tray was placed under the mill with a slope of about 30 degrees. The sand coated with the bonded resin precursor was fed only through the grinding plates at a rate of 50 grams per minute. The coated sand that left the mill surprisingly was in the form of discrete particles. The discrete particles were deposited on a sloping tray and covered immediately with an excess amount of optical elements that were emptied onto the particles in the tray. The result was a sand core coated with a binder and covered with optical elements. In order to solidify the precursor coating of the bonded resin, the sand-coated particles having surfaces substantially covered with housed optical elements were cured for 30 minutes in an oven at 80 ° C.

Example 5- Extruder Method A twin (smaller) helical screw secondary extruder, obtained from MAX Machinery, Healdsburg, CA under the trade designation "1.25 co-rotating subassembly, part 745-400-095" was used to mix a three component bonded resin polyurethane precursor composition. The first component was a pigmented polyol composition consisting of the following ingredients in parts per 100: 32.6 parts of Tone 0301, 31.9 parts of Afflair 9119, 12.5 parts of methyl ethyl ketone, 12.5 parts of acetone and 10. parts of additives ( dispersants, modifiers). The second component was Desmodur N-100. The third component was Afflair 9119. Two 2.5 gallon (9.4 liter) pressure vessels were used, obtained from Binks, Glendale Heights, IL, one contains the pigmented polyol and the other contains Desmodur N-100. The compositions in each of the two pressure vessels were measured inside the helical twin screw extruder by means of pumps, obtained from Zenith, Sanford, NC under the trade designation "BPB Series 0.297 cc / rev gear pump". Component three was fed by means of a powder feeder Model No. KCC-T20 K-TRON SODER obtained from K-TRON, Pitman, NJ and using double coiled flexible spiral cable screws, within a higher port open on the secondary extruder approximately two inches (5 cm) prior to the feed currents of Component one and Component two. The three components were fed into the secondary extruder at a fixed weight percent ratio of 47% by weight of the first component up to 31% by weight of the second component up to 22% by weight of the third component. The secondary extruder mixed and supplied the three components to the 50mm (10L / D) primary co-rotating twin helical screw extruder obtained from Baker Perkins, Saginaw, MI under the trade designation "Baker Perkins MPC / V-50 Continuous Mixer" . The sand was surface treated with 600 ppm "Silquest Al 100" (without "Krytox 157 FSL") in the same manner as previously described to treat the surface of the beads. The sand was fed into the extruder by means of a single connection flexible wire helical screw feeder Model 105-D obtained from ACRISON, Moonachi, NJ. The optical elements were fed into the extruder by means of a single connection flexible cable helical screw feeder obtained from ACCURATE, Whitewater, WI. The fit for the primary extruder was as follows, in order from the beginning of the extruder to the exit of the extruder: (1) 5 inches (12.7 cm) of forward travel paths, (2) 1.5 inches (3.8 cm) of " reverse gear mixers 1050-3LDE-RFL / 1.50-8, (3) 3 inches (7.6 cm) forward travel paths, (4) 3 inches (7.6 cm) forward gear mixer 1050-3LDE-FFR /1.50-8, and (5) 8 inches (20.3 cm) of forward travel routes. The feeding locations of the binder, sand, and optical elements relative to the beginning of the extruder with its proximity to the screw assembly were: (1) addition of sand to 3.5 (8.9 cm) inches with the resin precursor bonded therethrough port to 4 inches (10.2 cm), (2) addition of optical elements to 10 inches (25.4 cm) (on the front gear mixer assembly) and (3) retroreflective elements that come out at 20 inches (50.8 cm). In order to solidify the precursor coating of the bonded resin, the sand-coated particles having surfaces substantially covered with housed optical elements were cured for 30 minutes in an oven. Other suitable operating conditions are set forth in Table I as follows: Table I Example 6 - Rotary Disk Method A disk coater was generally constructed as detailed in Figure 1 of the U.S. patent application. pending Serial No. 10/762032, filed on January 21, 2004, entitled "RECYCLE DISC", with the following particulars. The disk coater had a disk having an outer diameter of 22.9 cm (9 inches). The disk was constructed of metal and had a layer of double-walled polyurethane (0.8 mm) thick polyurethane foam adhesive tape adhered to its top surface commercially available from 3M Company, St. Paul, MN under the commercial designation "Scotch 110 Mounting Tape". The choke was constructed of metal and had an outer diameter of 22.9 cm (9 inches) and an inner diameter of 10.2 cm (4 inches). The choke had a frusto-conical portion, sloping downward at an angle of 20 degrees from the horizontal from the inside diameter to the point where the diameter was 17.8 mm (7 inches). Peripheral to the frusto-conical portion of the throttle was a flange portion projecting horizontally from the end of the frusto-conical portion the rest of the path towards the outside diameter. The choke was mounted in an adjustable manner on the disk in a structure placed by helical screw fine spacing guide, and for the experiment described in this example, the flange portion was spaced so as to provide a gap of 1.3 mm (0.050 inch) . The disk coater was further supplied with a vibrating table dispenser, commercially available as Model 20A from Eriez Magnetics of Erie, PA, placed on top of the disk within the inner diameter of the choke. The bonded resin core precursor was supplied a. through a pair of commercially available gear pumps such as the Zenith gear pump model 'BPB from Zenith Pumps Division of Parker Hannifin Corporation, Sanford, North Carolina. The sand particles were dosed by an AccuRate Tuf-Flex feeder, model 304, from Schenk Accurate, Whitewater, Wisconsin, in a conventionally designed dynamic mixer. Within the same dynamic mixer the Afflair 9119 was dosed by spraying using an AccuRate Tuf-Flex ™ model 304 feeder. The primary particles, the powdered pigment, and the bonded resin core precursor were dosed into the dynamic mixer in a weight ratio of 47.62 / 1.06 / 3.70, and the dynamic mixer was operated at a speed of 100 rpm. The coated core particles of the dynamic mixer were directed on top of the vibration table of Example 1 at a ratio of 0.4 kg / minute. The optical elements were supplied by means of a solid feeder model KCL / T20, commercially available from K-Tron International, of Pittman, New Jersey, at a ratio of 0.36 kg / min. The contents of the vibration table were dosed on disk with the disc rotating and the speed '525 rpm, which results in the formation of discrete retroreflective particles.

Results of the RA Test The brightness of the resultant retroreflective elements produced from each of the methods of Examples 1-6 was measured as previously described. The value of RA using an input angle of -4.0 degrees and an observation angle of 0.2 degrees was measured for each example that averaged 25-35 candelas / lux / m2. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (20)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property 1. A retroreflective method of making elements previously characterized in that it comprises: providing a plurality of core particles; coating the particles with a non-solidified polymer composition which forms coated particles; combining the coated particles with optical elements in a continuous process such that the optical elements are accommodated in the non-solidified polymer composition; and solidifying the polymeric composition that forms retroreflective elements before.
2. 2. The method according to claim 1, characterized in that the combination of the coated particle and optical elements comprises mechanical mixing.
3. 3. The method according to claim 1, characterized in that the non-solidified polymer composition is selected from a molten thermoplastic resin and a bonded resin core precursor composition.
4. 4. The method according to claim 1, characterized in that an excess of optical elements are supplied and the method further comprises separating the retroreflective elements from the non-housed optical elements.
5. 5. The method according to claim 1, characterized in that the core particles have a size range from about 0.1 mm to about 3 mm.
6. 6. The method according to claim 1, characterized in that the core particles consist of an inorganic material.
7. 7. The method according to claim 6, characterized in that the particles consist of a material selected from sand, granules for roofs, and particles for sliding.
8. 8. The method according to claim 1, characterized in that mechanical mixing is achieved by means of at least one rotating mixing member.
9. 9. The method according to claim 8, characterized in that the mixing member comprises a rotating disk.
10. 10. The method according to claim 8, characterized in that the mixing member comprises an extruder helical screw.
11. 11. The method according to claim 8, characterized in that the mixing member comprises a grinding plate.
12. 12. The method according to claim 8, characterized in that the mixing member comprises at least two co-rotating or counter-rotating mixing members.
13. 13. The method according to claim 1, further comprising combining the uncured polymer composition with at least one light scattering material.
14. 14. The method according to claim 13, characterized in that the light-diffusing material is selected from the group comprising reflections pigments before diffuse form, specular refined pigment and combinations thereof. fifteen .
15. The method according to claim 1, characterized in that the optical elements consist of microcrystalline beads.
16. 16. The method according to claim 15, characterized in that the microcrystalline beads consist of ceramic and glass beads.
17. 17. The method according to claim 15, characterized in that the microcrystalline beads consist of non-vitreous pearls.
18. 18 The method according to claim 1, characterized in that the optical elements are treated on the surface with at least one adhesion promoting agent.
19. 19 The method according to claim 1, characterized in that the optical elements are treated on the surface with at least one flotation agent.
20. 20. The method according to claim 19, characterized in that the flotation agent is a fluorochemical.