MXPA98000353A - Elements retrorreflejan - Google Patents

Abstract

A process and retroreflective elements are provided. The process for preparing a retroreflective element includes the steps of: (a) combining a bed of optical elements and one or more core elements comprising a thermoplastic material, and (b) shaking the combination of optical core elements for a sufficient period of time and at a sufficient temperature to coat the optical elements on the core elements to form retroreflective elements

Description

RETRORREFLEJANTES ELEMENTS BACKGROUND DB THE INVENTION Markings on the pavement in different ways (for example, paints, tapes and individually assembled items) are well known for guiding and directing drivers as they travel along a highway. In the daytime period, the marks, which are only of selected distinctive colors, may be sufficiently flexible under ambient light to effectively indicate to guide the driver. However, at night, especially when the main source of illumination are the headlights of the driver's vehicle, the colors of the markings are generally insufficient to guide the driver properly. For this reason, pavement markings with retroreflective properties have been used. Many retroreflective pavement markings, such as lane or road lines, are made by dropping retroreflective elements, such as glass spheres, onto the line while it is still sticky so that the elements are partially embedded therein. Others are made by fixing retroreflective elements to a rubber base sheet REF: 26546 which contains pigments and fillers either by embedding them in the base sheet or by fixing them or securing them to the base sheet with a binder. Pigments and fillers are typically dispersed throughout the base sheet for various reasons, including cost reduction, improved durability and to provide adaptation. The pigments can also be placed in the bonding material to improve the visibility of the marks on the pavement and as part of the retroreflective mechanism. The light that falls on the retroreflective mark on the pavement is retroreflected as follows. First, the incident light passes through the retroreflective elements so that it impinges on the pigments in the base sheet or in the bonding material. The pigments subsequently disperse the incident light and the retroreflective elements redirect or change a portion of scattered light back in the direction of the light source. If retroreflective elements are too embedded within the base sheet or material forming the rail line, for example, retroreflection typically decreases. Thus, for an effective retroreflection for marking the pavement, the retroreflective elements preferably rise to some extent above the pavement surface.

This can be carried out using a base sheet with a pattern or pattern and selectively applying a bonding material to the protuberances with a pattern so that the retroreflective elements are fixed exclusively on the protuberances where they are most effective. Examples of such pavement markings are described in U.S. Patent Nos. 5,227,221; 4,988,555; and 4,988,541. This can also be carried out by using retroreflective elements having a core material that is coated with a multiplicity of reflectors, such as glass spheres. Examples of such elements (referred to as aggregates or particles) are described in EP Application No. 565,765 A2; and the US patents NOS. 3,043,196; 3,171,827; 3,175,935; 3,274,888; 3,418,896; 3,556,637; and 4,983,458. In some of these retroreflective elements, the reflectors (i.e., the optical elements) are also in the body of the elements. Although many of these elements are extremely useful, some do not use an effective means of joining the reflectors to the core material. In addition, some can not be easily manufactured. Therefore, there is still a need for other retroreflective elements.

BRIEF DESCRIPTION DB THE INVENTION The present invention provides a process for preparing a retroreflective element comprising: (a) combining a bed of optical elements and one or more core elements comprising a thermoplastic material; and (b) shaking the combination of optical elements and core elements for a sufficient period of time and at a temperature sufficient to cover the optical elements on the core elements to form retroreflective elements. Preferably, the stirring step is carried out for a sufficient period of time at a temperature sufficient to embed the optical elements in the core elements at an average depth of at least about 50% of the average diameter of the optical elements . In particularly preferred embodiments, the core elements additionally comprise a thermoset resin. Another embodiment of the present invention is a retroreflective element comprising: (a) a core element comprising an elastic thermoplastic material; (b) optical elements applied as a coating on the core element in which more than about 50% of the projected surface area of the core element is covered with optical elements. Preferably, the optical elements are embedded in the numbering element to an average depth of at least about 50% of the average diameter of the optical elements. Yet another embodiment of the present invention is a retroreflective element comprising: (a) a core element comprising a thermoplastic material selected from a group consisting of a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid , and combinations thereof; and (b) • optical elements applied as a coating on the core element in which more than about 50% of the projected surface area of the core element is coated with optical elements. The core elements used to prepare the retroreflective elements of the present invention are particularly advantageous because they are capable of undergoing shape changes during processing.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a representation of two exemplary shape changes experienced by the core elements of the retroreflective elements of the present invention during the application of the optical elements.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides shaped retroreflective elements and a method for forming them. Retroreflective elements include a layer of optical elements (also referred to herein as reflectors), such as glass spheres, partially embedded in the core surface of a thermoplastic resin, optionally in combination with a hardened thermoplastic resin and / or a pigment . These elements are formed by combining solid core elements consisting of a thermoplastic resin and optical elements. Preferably, this is carried out by adding the core elements to a moving bed of optical elements. The moving bed of optical elements can be formed in various ways. For example, a moving bed of optical elements can be formed in a fluidizing chamber or in a rotary kiln. The optical elements are preferably heated to a temperature at least approximately at the adhesion temperature of the core elements. Preferably, the core elements are at room temperature (i.e., 20-30 ° C) and the optical elements are at a temperature at least about 10 ° C higher than the adhesion temperature of the core elements. This method allows the substantially immediate bonding of the optical elements of most of the surface area (preferably substantially throughout the surface area) of the thermoplastic elements of the core. The additional heating allows the optical elements to be immersed at an appropriate level in the thermoplastic elements. The covering of the optical element around the core thermoplastic elements provides free movement within the moving bed of optical elements. In addition, this process allows the formation of various shaped retroreflective elements, based on the choice of thermoplastic resin, pigment and / or processing conditions established during extrusion and cooling of the core resin. Among the possible shaped retroreflective elements are the substantially spherical, disc and cylindrical shapes which can be produced using the method of the present invention. The core material of a retroreflective element of the present invention can change shape by coating the optical elements on its surface. Alternatively, based on the choice of materials, processing conditions, etc., the core material does not substantially change in shape. Fig. 1 is a representation of two exemplary shape changes in which the core elements of the retroreflective elements of the present invention may experience during the coating of the optical elements. For example, a core element (1) of substantially cylindrical core can be "flattened" and made substantially similar to a disk (2) or simply "rounded" and becomes substantially spherical (3) when coated with optical elements . As used herein, "coating" refers to simply joining the optical elements to the surfaces of the core elements without much encrustation, as well as the joining and embedding of optical elements on the surface of the core elements. Each of the forms can be used for a specific advantage in specific applications. For example, a retroreflective element in the form of a flat disc, when used with a ceramic optical element is very durable and resistant to wear and is considered to be useful in brands with liquid maintenance. The retroreflective spherical elements can be incorporated into oven-coated tapes used as pavement markings by dropping them as ribbon products and heating them until they form a dome shape. The retroreflective elements of the present invention are substantially covered by optical elements. This is, the surface of the retroreflective elements does not contain main portions that are composed or empty of optical elements, although the optical elements do not necessarily need to be closely packed. That is, for any retroreflective element, more than about 50% of the projected surface area of the core element is coated by optical elements. Preferably, more than about 60% of the projected surface area is covered, and more preferably more than about 90% is covered. More preferably, the optical elements are packed tightly on the surface of the core elements. As used herein, a "projected" surface area refers to an apparent area of the surface that remains perpendicular to the retroreflective element.

The core elements of the present invention include a thermoplastic material. This thermoplastic material can be any of a wide variety of materials having functional groups capable of interacting with the optical elements for effective binding. Examples of such functional groups include acids, amides, amines and the like. The thermoplastic material is preferably one that is elastic. That is, under the melting conditions in the process, the core elements made of the thermoplastic material are elastic so that the shape of the resulting retroreflective elements can be controlled by process conditions, eg, extrusion temperature, Cooling and cooling temperature established during the extrusion and cooling of the core resin. By this, it is meant, for example, that the thermoplastic material is one that is elastic when combined with the optional materials described herein, for example, pigments, at the melting temperature of the combination. Typically, the shape of the retroreflective elements results from a balance of melt elasticity and surface energy. That is, for a material to form a rounded element, the conditions for forming the core element must be chosen to relax substantially completely before it comes into contact with the optical elements. When heating again in the presence of the optical elements, the surface tension will cause the granule to be rounded. Therefore, little internal polymer memory is generated during extrusion and cooling of the strip. To form a material in a disc-shaped or flattened element, the formation conditions of the core element must be chosen so that there is some memory accumulated in the material. When re-heating in the presence of the optical elements, the elasticity of fusion will cause the granule to flatten. This can typically be accomplished by pumping the material faster through a longer extensional flow field to induce more orientation of the molecules, and cool more rapidly. Typically, a material with a higher molecular weight will have a higher melt elasticity. Preferred thermoplastic materials include ethylene / acrylic acid copolymers ("EAA") and ethylene / methacrylic acid copolymers ("EMAA"), and mixtures of EAA and EMAA. These materials can be processed to form granules that undergo a transformation of forms. For example, the granules manufactured from EMAA are rounded as a result of surface energy during the application of the optical elements. In contrast, the granules manufactured from a mixture of EMAA and EAA are flattened and acquired in disk form during the application of the optical elements, as a result of the accumulated memory of the material during extrusion and cooling. The EMAA copolymers are commercially available under the trade name NUCREL from E.I. DuPont de Nemours and Company, Wilmington, DE. The EAA copolymers are commercially available under the tradename PRIMACOR from the Dow Chemical Company, Midland, MI. Other thermoplastic materials that may be used include, but are not limited to, ethylene n-butylacrylate, ethylene vinyl acetate, urethane, and mixtures thereof. Certain retroreflective elements of the present invention also include reactive monomers, ie, thermosetting resins in the thermoplastic elements of the core. These materials contribute to the formation of retroreflective elements that are generally more resistant. Typical reactive materials that are usable in the core thermoplastic elements of the present invention include their systems commonly used in powder coating formulations. Powder coatings are described in Oraanic Coatincrs. Science and Technolosy. chapter 31, by Zeno Wics, Jr. et al., John Wiley and Sons, Inc., 1994. Examples of such systems include epoxy, polyester, acrylic, epoxy-functional acrylics, blocked isocyanates in combination with polyols or amines. Such materials may be included within the core thermoplastic elements in an amount that does not interfere with the formation, e.g., extrusion and cooling, of the core elements that do not detrimentally alter the embedding of the optical elements.

Optical Elements A wide variety of optical elements can be used in the retroreflective elements in the present invention. Typically, optical elements having a refractive index of about 1.5-2.6 are used. The optical elements preferably have a diameter compatible with the size, shape, spacing and geometry of the core thermoplastic element. Typically, optical elements, for example microspheres or spheres of approximately 50-1000 micrometers in diameter can be used appropriately. Preferably, the ratio of the diameter of the optical elements to the diameter of the core elements is no greater than about 1: 2. Preferably, the optical elements use a relatively narrow size distribution for an effective coating. Other factors that alter the size of the elements are the number of rows of spheres that are desired to be available for the headlights of the vehicle and the particle size of the core material. Suitable optical elements include glass microspheres (also known as retroreflective spheres or spheres) formed of glass materials, preferably having refractive indices of from about 1.5 to about 1.9. Preferred optical elements are described in U.S. Patent Nos. 4,564,556 and 4,758,469, which are incorporated herein by reference. These optical elements generally described as non-vitreous, transparent and solid ceramic spheroids comprise at least one crystalline phase containing at least one metal oxide. The ceramic spheroids may also have an amorphous phase, such as silica. The term "non-vitreous" means that the spheroids have not been derived from the fusion or mixture of raw materials capable of carrying liquid state at elevated temperatures, such as glass. The spheroids are resistant to scraping and wear, with relatively hard, (hardness greater than about 700 Knopp) and are manufactured to have a relatively high refractive index. These optical elements may comprise zirconia-alumina-silica and zirconia-silica.

To improve the joining of the optical elements to the core thermoplastic elements, the optical elements can be treated with a coupling agent, such as a silane, titanate, zirconate and the like. A particularly suitable coupling agent is an aminosilane coupling agent, such as the coupling agent A1100 Silane, which is available from Union Carbide Company, Danbury, CT.

Optional additives Other materials may be included within the retroreflective elements of the present invention. These can be materials added to the resin during the formation of compounds, they can be added to the resin by the supplier and / or they can be added to the retroreflective elements during the coating with the optical elements. Examples of such materials include pigments, UV stabilizers, heat stabilizers, antioxidants, processing aids and slip resistant particles, for example. If desired, a suitable pigment is added to the thermoplastic resin to impart reflection to the resin as well as color and opacity. Typically, approximately 8-50 weight percent (% by weight) is used in the core elements. The core elements of the retroreflective elements may include mirror reflective pigments, diffuse reflective pigments, or both. Diffuse pigments are generally fine particles that have a relatively uniform size. The light that hits the diffuse pigment particles is reflected back at many angles, which include the return along the trajectory of the incident light. An example of a diffuse pigment is titanium dioxide. For lane strips on a road, for example, white rutile titanium dioxide or anatase titanium dioxide is typically used. Specular pigments are generally similar to thin plates. The light that falls on the specular pigment particles is reflected back at an equal angle, but opposite that is, as an image to the mirror of the normal one, of the angle in which it enters. Examples of plate-like pigments include, for example, crosslinking aluminum, mica, pearlescent and opalescent pigments. Such pigments can be used to help maintain the shape of the core element during the application of the optical elements. Other pigments may be used to produce a white, yellow or other color mixture including aluminum oxide, iron oxide, silicon carbide, antimony oxide, lead oxide, lead chromate, zinc chromates, cadmium pigments , siennas, ochres, inorganic or organic reds, chrome yellows, chrome oranges, chrome greens, etc., as well as organic yellows such as those described in U.S. Patent No. 5,286,682. The pigments can be spread with suitable natural or manufactured granular materials. It is also desirable to include a stabilizing agent in the core thermoplastic element in order to improve the resistance to UV light and / or heat of the thermoplastic material, pigment and / or thermoset material. Preferred stabilizing agents are hindered amine light stabilizers (HALS) and may be present at concentrations of up to about 5%. Exemplary HALS stabilizing agents are CHIMASSORB 944 available from Ciba-Geigy Corp., Additives Division, Hawthorne, N.Y., and CRYASORB UV 3346 available from American Cyanamid Co., Wayne, NJ. Other stabilizing agents. suitable include, for example, antioxidants such as IRGANOX 1010 and IRGAFOS 168, both of which are available from Ciba Geigy. Processing aids may also be used in the retroreflective elements of the present invention. Typically, these are added to the core element to improve processing. That is, when other optional additives are combined with the thermoplastic material in the core element, a processing aid improves dispersion or mixing. Examples of such processing aids include low molecular weight ethylene acrylic acids, such as those available under the trademark AC540 from Allied Signal and low molecular weight polyethylene resins, such as those available under the trademark AC16 from Allied Signal. Typical anti slip particles do not play a role in retroreflectivity, instead they are placed on the marks in the retroreflective and non retroreflective pavement to improve the dynamic friction between the mark and a vehicle tire. The anti-slip particles can be, for example, ceramic parts such as quartz or aluminum oxide or similar abrasive media. Preferred slip particles include calcined ceramic spheroids having a high alumina content such as that described in U.S. Patent Nos. 4,937,127; 5,053,253; 5,094,902; and 5,124,178, the descriptions of which are incorporated herein by reference. The particles are preferred because they do not crumble before impact such as the crystalline abrasive medium such as A1203 and quartz.

The slip resistant particles typically have sizes of about 200 to 800 microns. The slip resistant particles can be combined with the optical elements and can be applied as a coating on the core thermoplastic elements in the same way as described below to apply the optical elements. Alternatively, the slip resistant particles can be applied to the core thermoplastic elements without the optical elements. In this modality, the formed product will not be retroreflective. In addition, the core element does not necessarily include a pigment. The retroreflective elements of the present invention also include a thermoplastic core material laminated to the retroreflective laminate material. This combination can then be applied as a coating with the optical elements in the same manner as described herein.

The technique of adding solid core elements to a moving bed of optical elements, preferably hot optical elements, allows the substantially immediate bonding of the optical element to most of the surface area of the core thermoplastic elements. By this it is meant that before visual inspection, either with or without amplification, more than about 50% of the projected surface area of a core element is covered by the optical elements. Preferably, more than about 60% of the projected surface area is covered, and more preferably, more than about 90% of the projected surface area is covered. An additional heating allows the optical elements to be immersed at an appropriate level in the core elements and to be joined, i.e. embedded firmly therein. More preferably, the optical elements and core elements are mixed together for a time and at a temperature sufficient to embed the optical elements in the core elements in a generally closely packed arrangement. The layer of optical elements together with the movement of the core elements within the moving bed reduces the tendency of the core elements to melt and fuse with each other or with the container during this process. This problem is further reduced if the optical elements are heated and the core elements are at a temperature near or below the ambient temperature before they are in contact. This allows the hot optical elements to coat the cold core elements before the heat of the optical elements causes the core elements to become sticky. Once the core elements are coated with the optical elements, they are highly mobile within the bed of optical elements. This allows an additional hardening time in the bed of optical elements for heat transfer and obtain an effective incrustation. The coated core elements, ie the retroreflective elements, are then removed from the bed of optical elements and allowed to cool and thereby fix the embedded particles to the desired level of embedding on the surface. Effective incrustation typically results from submergence or wetting and / or capillarity. Capillarity is the term used to describe the action of light ascension by capillarity of the core material around each optical element. This capillarity is important because the core material forms a receptacle-like structure around each optical element and holds it in place. Preferably, for effective bonding, the topical elements are embedded in the core element on average to a depth of at least about 50% of their average diameter.

That is, for an optical element with a diameter of x is embedded in the surface of a core element to a depth of at least about x / 2. More preferably, the optical elements are incrusted on average to a depth of at least about 60%. Typically, they are not embedded to a depth of more than about 80% of their average diameter. Although for any retroreflective element it is desirable to have all the optical elements with an incrustation of at least 50%, it is not a necessary requirement. Preferably, to the extent that at least about 50% of the optical elements are embedded in the core element to a depth of at least about 50% of its average diameter, the retroreflective elements are within the range of the present invention. If the retroreflective elements of the present invention are used in applications in which they are heated to a temperature that will melt or taint the core element, the optical elements can simply be applied as a coating on the surface of the core elements without obtaining a effective incrustation. Subsequent heating conditions should be effective to cause embedding of the optical elements to a depth of at least about 50%. The retroreflective elements are manufactured by forming small pieces, eg granules, of the core thermoplastic material, which optionally contains one or more types of thermosetting resins and / or pigments. Preferably, this is done by combining the core thermoplastic material, which can be a combination of different thermoplastic materials if desired, the optional thermosetting resins and the optional pigment in an extruder and forming a strip or strip of well-mixed material which will be used as the core of the retroreflective elements. The pigment can be premixed with one or more thermoplastic materials and can be added as granules of a pigmented thermoplastic material if desired. The strip is extruded at a temperature above the melting temperature of the thermoplastic material, cooled and then cut into small pieces. That is, the "core thermoplastic elements" or simply the "core elements". Preferably, the extrusion temperature is not much above the melting temperature of the thermoplastic material so that it is flowable and does not form a self-supporting strip. If a granule former is used below the water to form the grains of this strip, higher extrusion temperatures can be used because lower viscosities can be tolerated. Generally, the choice of temperature and time in the extruder depends on the materials that are combined and the desired shape of the resulting retroreflective elements. These conditions can be easily determined by a person familiar with the art. For preferred thermoplastic materials used herein, the extrusion is carried out at a temperature of about 93-316 ° C (200-600 ° F). The extrusion can be carried out in a single screw or double screw extruder, for example. Typically, the extrusion rate is about 5-200 revolutions per minute (rpm) to obtain the desired pumping speed. The strip can be cooled by air or in a water bath or by any kind of heat transfer mechanism. Preferably, it is cooled in a water bath to a temperature of less than about 30 ° C. The cooled strip is then cut into small pieces for coating with the optical elements. These pieces of core elements can be of a wide variety of shapes and sizes. Preferably, they have a "size" of no more than about 10 cm (4 inches). By this, it is meant that the largest dimension is no greater than about 10 cm. That is, the length is no more than about 10 cm. Preferably, they are in the form of small, cylindrical granules of a length of about 0.16 cm (0.06 inches) to about 10 cm (4 inches), more preferably from about 0.16 cm (0.06 inches) to about 2.54 cm (1 inch) and more preferably from about 016 cm (0.06 inches) to about 0.32 cm (0.13 inches). Granules can be made by a wide variety of techniques such as cutting, granulation under water, etc. These pieces of thermoplastic elements with a dry solid core (ie not sticky) are subsequently fed through a moving bed of optical elements. These optical elements are preferably at a temperature above the adhesion temperature of the solid core thermoplastic elements in the initial contact. That is, the optical elements are preferably at a temperature, initially, which causes the surface adhesion of the solid core thermoplastic material to produce effective bonding and embedding of the optical elements. This can be easily determined by a person familiar with the technique based on knowledge of the melting temperature of the thermoplastic material in the core elements. For the preferred materials used in the solid core thermoplastic elements of the present invention, the optical elements are preferably heated initially to a temperature approximately 10 ° C higher than the adhesion temperature of the core elements for bonding, in a more efficient manner. preferable, at least about 25 ° C more for an effective scale, and more preferably, at least about 50 ° C more for effective embedding, in a reasonable amount of time. U.S. Patent No. 3,418,896 (Rideout) discloses that retroreflective elements can be formed by extruding or otherwise molding a plastic material in the form of a bar and applying glass spheres to the outer surface of the bars before the material hardens. . The bar is then cut into pieces that form elements that are empty of optical elements at the ends. During the application stage, the glass spheres are at a temperature below the temperature of the extruded bars. This method does not provide good embedding as defined herein, although the coverage is generally adequate. In addition, the Rideout process is difficult to perform on a large scale. For example, a hot, partially melted strip of core material is generally too weak and breaks during processing.

The core thermoplastic elements are typically in contact with the moving bed of the optical elements for a time sufficient to coat the optical elements on the surface of the core elements. Typically, this lasts at least about 30 seconds. Preferably, the core thermoplastic elements are in contact with the moving bed of the optical elements for a time sufficient to produce effective embedding of the optical elements. This typically lasts at least about two minutes, and preferably at least about four minutes. The optical elements are generally in contact with the core thermoplastic elements for no more than about 10 minutes. If the hardening time is too long, deformation, melting, agglomeration, etc., of the core elements may occur. The ratio of the optical elements compared to the core thermoplastic elements is preferably at least about 100: 1 by weight, more preferably at least about 40: 1 by weight, and much more so preferable of at least about 10: 1. Generally, the greater the ratio of the optical elements to the core thermoplastic elements, the easier the process is. However, there should not be a large excess of optical elements that are wasted or damaged with the result of repeated recycling. What is needed is a sufficient amount of optical elements to prevent the core thermoplastic elements from agglomerating and / or merging with the equipment. The process of joining and embedding the optical elements in the core elements can be carried out through a batch process or a continuous process. Such processes can be carried out using a rotary kiln, a fluidizing chamber, a mixer, a rotating drum, etc. Preferably, the process of joining and embedding the optical elements in the core elements is carried out in a continuous manner. This can be done using a rotary kiln. The conditions of rotation, elevation of the oven temperature, air flow, etc. they can be altered by a person familiar with the technique to produce the appropriate hardening times for the materials used.

Applications The retroreflective elements of the present invention can be dropped or cascaded onto the liquid by applying coatings such as wet paint, thermosetting materials or hot thermoplastic materials. Thermoplastic brands applied by heat of fusion are described in U.S. Patent Nos. 3,849,351; 3,891,451; 3,935,158; and 3,988,645, the descriptions of which are incorporated herein by reference. Other applied liquid coatings are described in U.S. Patent Nos. 2,043,414; 2,440,584; 4,203,878; and 4,856,931, the descriptions of which are incorporated herein by reference. In these applications, the paint or thermoplastic material forms a matrix which serves to retain the retroreflective elements in a partially incised and partially protruding orientation. The matrix can be formed of two durable component systems such as epoxy or polyurethane materials, or from thermoplastic polyurethanes, alkyd materials, acrylics, polyesters and the like. Alternative coating compositions that serve as a matrix and include retroreflective elements described herein are also presented within the scope of the present invention. Typically, the retroreflective elements of the present invention are applied to a path or other surface by the use of conventional marking or delineation equipment. The retroreflective elements are dropped from a random position on the surface, and each element is placed with one of its faces placed in a downward direction so that it is embedded in the paint, the thermoplastic material, etc. If different retroreflectors of different sizes are used, they are typically distributed randomly on the surface. When the paint or other film-forming material hardens completely, the retroreflective elements are firmly held in position to provide an extremely effective reflective marker. The retroreflective elements of the present invention can also be used on preformed tapes used as pavement markings. The following examples illustrate various features, advantages and other specific details of the invention. However, it should be understood that the particular ingredients and amounts used as well as other conditions and details are not considered to unduly limit the scope of this invention in any way. The percentages are given by weight. gjffl lQg l___i Granules of the following materials are mixed by rotating drum placement: 400 g of ethylene / methacrylic acid copolymer NUCREL 699 ("EMAA" available from DuPont Company, Polymer Products Department, Wilmington, DE), 250 g of a color concentrate that includes 50% rutile Ti02 in 40.8% NUCREL 699 with 8.9% AC540, a low molecular weight acrylic acid processing aid (available from Allied Signal), 0.2% CHIMASORB 944, and 0.1% IRGANOX 1010; 250 g of a color concentrate that includes 30% yellow pigment 191 in 60.8% NUCREL 699 with 8.9% AC540, 0.2% CHIMASORB 944, and 0.1% IRGANOX 1010; 100 g of a color concentrate that includes 25% yellow pigment 110 in NUCREL 699 with approximately 10% AC16, a low molecular weight polyethylene resin (available from Allied Signal) and approximately 0.05% of IRGAFOS 168 (available from Allied Signal).

The mixed granules are fed through a small twin screw extruder (Baker-Perkin Model No. 60007 that has screws 30.5 cm (12 inches) long by 2.5 cm (1 inch) in diameter), and through a die with an opening of approximately 0.3 cm (0.12 inches) in diameter to mix the materials and form a strip of material. The strip is extruded at a temperature of about 130 ° C and 25 revolutions per minute (rpm), cooled in a water bath to a temperature of about 50 ° C, and rolled onto a reel at a speed that matches the extrusion speed. The strip is then granulated to approximately 0.3 cm (0.12 in.) Long in cylindrical granules using a Conair Jetro Model 304 Granulator. The granules are fixed through a rotary kiln at approximately 185 ° C with a large number of yellow ceramic spheres ( which are generally manufactured in accordance with Example 4 of U.S. Patent No. 4,564,556, which is incorporated herein by reference, with the addition of 1% Fe203 using ferric nitrate as the zirconium sol stabilized by nitrate) it has a refractive index of approximately 1.75. Initially, the ceramic spheres are at room temperature; however, they are applied as a coating on the core thermoplastic elements (ie, the granules) more effectively if the ceramic spheres are at a temperature higher than the temperature of the core thermoplastic elements. In this example, the ceramic spheres are finally heated to a temperature of about 205-215 ° C. The spheres which have been previously treated with an aminosilane coupling agent (A1100 Silane available from Union Carbide Company), as described in U.S. Patent Nos. 5,124,178 and 5,094,902, which are incorporated herein by reference, to assist in their union to the resin. The rate of feed rate of ceramic spheres in comparison with the resin granules is 40: 1 by weight, which is a sufficient amount of spheres to prevent the thermoplastic elements from agglomerating / or melting / melting together or with the equipment. The granules are in the rotary kiln for about 4 minutes. The rotary kiln is tilted at an angle of approximately 5.5 degrees with respect to the horizontal to maintain a sufficient resistance time (at least 2 minutes): The excess spheres are collected and reused. The resulting retroreflective elements are rounded, but they are not perfect spheres with ceramic spheres that cover the entire surface of each element.

E-example 2 Granules of the following materials are mixed by rotating drum placement: 600 g of NUCREL 699 and 400 g of color concentrate including 50% TiO- in NUCREL 699 listed in Example 1. Granules are fed through an extruder small double screw and through a die, as in Example 1. The extruded strip is fed directly to a granulator after advancing through a cooling bath. The granules are subsequently fed through a rotary kiln at 205-215 ° C together with transparent ceramic spheres (which are generally manufactured according to Example 4 of the US Pat. No. 4,564,556) having a refractive index of about 1.75. These spheres have been pretreated with an aminosilane coupling agent to improve the bonding of the surface of the sphere to the resin, as described in Example 1. Initially the spheres do not heat, but thermoplastic elements coated more completely once are produced that are hot. The ratio of the ceramic sphere feed rate compared to the resin granules ranges from about 40: 1 to about 10: 1, all of which produces well-coated thermoplastic elements. The oven is tilted approximately 5.5 degrees with respect to the horizontal and the excess spheres are collected and reused. The thermoplastic elements are in contact with the optical elements for approximately 4 minutes. The resulting retroreflective elements have a rounded shape.

EjfflPlQ 3 Granules of the following materials are mixed by rotating drum placement: 50% by weight of PRIMACOR 3440 ethylene / acrylic acid copolymer ("EAA", available from Dow Chemical Company, Midland, MI), 50% by weight of a concentrate colored including 50% by weight of rutile Ti02, 12.5% by weight of a low molecular weight polyethylene (available under the tradename AC16 from Allied Signal) 0.05% by weight of an antioxidant (available under the trade name IRGAFOS 168 from Ciba Geigy) and 37.45% by weight of PRIMACOR 3440. The blended granules are further compounded as described in Example 1 using the small twin screw extruder and formed into a strip. The strip is then granulated and the granules are coated with ceramic spheres using the rotary kiln, but using a temperature of approximately 275 ° C (± 15 degrees) to adapt the submerging or embedding of spheres in the resin with higher melting point used in this example. The granules change immediately when heated in the furnace from a narrow cylindrical shape to a flattened disk shape. The proportions by weight of the granules and spheres are the same as in Example 2, and the spheres used are also of the same time and have the same treatment as those used in Example 2; the angle of the oven is also the same and the excess of spheres is again collected and reused. The resulting retroreflective elements are generally flat discs.

E-jgfplg 4.

A small amount of NUCREL 699 resin and outer opalescent fine pearl pigment MEARLIN (containing mica, titanium dioxide, tin oxide and chromium hydroxide) obtained from Mearle Corporation, New York, NY, is mixed in a metal container in a ratio of 90% resin to 10% pigment. The metal container in its contents is heated in a convection oven until the resin melts. The pigment and the resin are subsequently mixed with a stirrer and punched on a release coating. The resin solidifies rapidly at room temperature. Some time later (several days), the resin is cut into small pieces of random and irregular shapes that vary from approximately 0.31-0.95 cm at its widest point. Each piece is approximately 0.16 cm thick. These pieces are then placed in a rotary kiln with ceramic spheres of a refractive index of approximately 1.92, as described in US Pat. No. 4,772,511. These elements, based on the NUCREL 699 resin which typically tends towards a rounded shape when formulated with other pigments, maintains the shape in which it has been cut when prepared with this combination of resin and pigment and with this method. It is also much brighter than other granules.

IrPO $ EJCT This example contains a core granule of 35% Ti02 and 65% EMAA (NUCREL 699) prepared by mixing in a rotating drum of 1200 g of NUCREL granules 699 and 2800 g of color concentrate used in Example 1 ( 50% Ti02 in NUCREL 699) followed by extrusion of the mixture with a 3.2 cm (1.25 inch) Killion single screw extruder (available from Killion, Verona, NJ) having a temperature profile of 104 ° C (220 ° C) F, zone '1), 110 ° C (230 ° F, zone 2), 121 ° C (250 ° F, zone 3), 127 ° C (260 ° F, zone 4), 138 ° C (280 ° F) , zone 5), to form a strip 0.3 cm (0.12 inches) in diameter using a winding speed of 5.2 meters per minute 17 fpm, (feet per minute) and a screw speed of 30 rpm. Subsequently the strip is cut into granules of 0.3 cm (0.12 inches). These granules are then added at room temperature to a fluidized bed of hot (approximately 170 ° C) VISI glass spheres of 1 mm in diameter having a refractive index of 1.5 (available from Potter Industries, Hasbrouck, NJ). The resulting retroreflective elements are slightly rounded. These spheres are generally too large for them to embed themselves well in the core element.

Eiemolo 6 This sample contains a core granule containing 35% of Ti02 and 65% of EMAA prepared as described in Example 5. These granules are added at room temperature to a fluidized bed of a hot mixture (approximately 170 ° C) of spheres FLEX-O-LITE glass having a refractive index of 1.9 (available from Flexolite, Paris, TX) and slip resistant ceramic particles (which are manufactured in accordance with Example 1 of U.S. Patent No. 5,094,902). The mixture contains 95% glass spheres having a diameter of about 250-400 micrometers and 5% slip resistant particles having a diameter of about 250-400 micrometers. The ratio of glass spheres to core granules is approximately 100: 1. The spheres and the granules are in contact for approximately 30 seconds to form slightly rounded retroreflective elements with a monolayer of spheres and particles resistant to slip, firmly packed.

Example 7 This sample contains a core granule containing 35% Ti02 and 65% EMAA prepared as described in Example 5. These granules are added at room temperature to a fluidized bed of hot FLEX-O-LITE glass spheres (approximately 170 ° C) described in Example 6, but without the slip resistant particles. The resulting elements are slightly rounded with a monolayer of closely packed spheres. 9 This example contains a core material of cut pieces of a laminate containing a retroreflective validation sheet or laminate (commercially available from 3M Company, St. Paul, MN under the trademark SCOTCHLITE) pre-laminated on one side with a pigmented extruded film with a 0.13 cm- (50 mils) extruder containing 20% Ti02 and 80% EMAA (prepared from NUCREL 699 and the 50% color concentrate of Ti02 used in Example 1). During the coating process with spheres as defined in Example 7, the hot spheres are attached to all exposed surfaces of the pigmented film while the reflective laminate remains free of spheres due to the thermosettable top film in the laminate. Based on the shape of the pieces that are cut, they are reformed as the thermoplastic pigmented core element shrinks under heat downstream from its previous film extrusion process. This results in an element that takes on the form of a dome. This combination of exposed sphere / embedded or included lens has certain advantages over daytime color in addition to providing an effective reflective element in wet conditions.

EJ3Bflp 9 This example contains a core granule of 35% Ti02, 35% EMAA (NUCREL 699) and 30% EAA (PRIMACOR 5980). This is done using the 50% Ti02 color concentrate described in Example 1. These granules are added at room temperature to a fluidized bed of hot glass spheres (approximately 170 ° C) with an index of 1.9, with an approximate diameter of 250-400 micrometers. The technique of cold-adding the solid thermoplastic elements to a moving bed of hot spheres allows immediate embedding or partial bonding of the spheres to any available surface that is thermoplastic. The additional heating (almost 30 seconds) allows the spheres to immerse or embed at an appropriate level in the resin and bond firmly to it. The monolayer of spheres together with the movement of the elements within a fluidized bed prevents the elements from fusing together during this process. The core granule produces a flat disk shape with a tightly packed general monolayer of spheres that is partially embedded in the surface of a thermoplastic or pigmented core. This disc shape is the result of shrinkage of the granule under heat in the downstream direction of its previous strip extrusion operation.Example 10 A mixture consisting of 35% of Ti02, 30% of NUCREL 699 EMAA, and 35% of PRIMACOR 3150 EAA is extruded using a Killion extruder of 3.1 cm (1.25 inches) in diameter of 24 1 / d (length with respect to diameter) with the temperature profile described in Example 5). This is carried out using the 50% Ti02 color concentrate described in Example 1. The diameter of the extruded strip is set to approximately 0.3 cm (0.12 inches) when setting the winding speed at 5.1 meters / minute (17 fpm) and the screw speed at 30 rpm. The strip is cut into granules of approximately 0.3 cm (0.12 inches) in length. A fluidized bed of ceramic spheres used in Example 2, treated on the surface with aminosilane A-1100 (α-aminopropyltriethoxysilane available from Union Carbide, Danbury, CT) is heated to a temperature of about 77-82 ° C (170-180). F). The granules are introduced into the heated fluidized bed (approximately 170 ° C) of spheres and allowed to remain in the rotating drum for about 1 minute to join and embed the spheres to the surface of the granules. The granules undergo a transformation forming disk-like spheroid elements. The "diameter" is greater than about 3 times the height of the granule.

EJCTP Q A blend of approximately 90% PRIMACOR 3440 Dow and 10% MEARLIN opalescent pigment, fine pearlizing, is formed in a Baker-Perkin twin screw extruder model 60007. The extruded mixture is formed as a strip but part of the material is driven in flattened and random shapes while the resin is still plastic. The melting temperature is about 210 ° C during the formation of the compound. Samples of the material are cut into various shapes. Then they are coated with spheres using a fluidized bed of surface treated spheres, ceramics, at approximately 80 ° C. The longitudinal dimension of the elements is shortened slightly, but the flattened strips remain flat and the pieces are cut into triangular shapes and other shapes and these shapes are maintained.

Example 13 By using a Baker-Perkin double screw extruder, model 60007, the following materials are composed together: 21% of glass beads treated on the VOLAN surface of approximately 60 micrometers in diameter and having a refractive index of 1.9; 39% resin PRIMACOR 3440 EAA; 39% PRIMACOR 3440 EAA resin preconstituted with Ti02 in a ratio of approximately 50:50. The speed of the extruder screw is 42 rpm and the melting temperature of the materials in the extruder is about 210 ° C. A single die with a hole of approximately 2.5 mm is used and the strip is wound at a speed of 5.5 meters per minute (18 feet per minute). The strand containing spheres is subsequently granulated using a Conair JETRO model 304 granulator. The spherical coating is performed using a rotary kiln inclined at approximately 5.5 degrees with respect to the horizontal. The oven temperature is set to approximately 275-280 ° C. The residence time in the oven is approximately 4 minutes. The spheres are surface-treated ceramic spheres, such as those used in Example 2 having a refractive index of 1.75 and a diameter of about 170-230 microns. The proportion by weight of the spheres that are applied as a coating with respect to the granules used is approximately 12: 1.

Example 13 A retroreflective element is made using the thermosetting resin in combination with a thermoplastic resin by extruding a strip of 25% ethylene / methacrylic acid copolymer NUCREL 699, 50% color concentrate used in Example 1 including 50% Ti02 in 40.8% NUCREL 699, 19% blocked diisophorone diisocyanate BF1540 (available from Huís America) and 6% tris-2-hydroxyethyleneisocyanurate (available from BASF). A Perkin-Elmer twin screw extruder at 25 rpm and a temperature of approximately 130-140 ° C. is used, the strips are cooled in a water bath and granulated using a JetAir granulator.The subsequently formed granules are fed into an oven rotary with the ceramic spheres used in Example 2 in a weight ratio of 12: 1 (spheres: granules) The oven temperature is about 210 ° C. The curing time in the oven is about 4 minutes. Cylindrical granules are rounded by the application of the spheres Various modifications and alterations will be evident to those familiar with the technique without departing from the spirit and scope of this invention., the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (28)

1. A process for preparing a retroreflective element, characterized in that it comprises: (a) combining a bed of optical elements and one or more core elements comprising a thermoplastic material, wherein the ratio of the diameter of the optical elements to the diameter of the core elements is no greater than about 1: 2; and (b) shaking the combination of optical elements and core elements for a sufficient period of time and at a temperature sufficient to coat the optical elements on the core elements to form one more retroreflective elements.

2. The process according to claim 1, characterized in that the stirring step is carried out for a time and at a temperature sufficient to embed the optical segments in the core elements at an average depth of at least about 50% of the average diameter of the optical elements.

3. The process according to claim 2, characterized in that the optical elements are heated to a temperature at least approximately the adhesion temperature of the core elements before the combining step.

4. The process according to claim 3, characterized in that the optical elements are heated to a temperature at least about 10 ° C higher than the adhesion temperature of the core elements.

5. The process according to claim 1, characterized in that the core elements additionally comprise a thermosetting resin.

6. The process according to claim 1, characterized in that the optical elements and the core elements are combined in a weight ratio of at least about 100: 1.

7. The process according to claim 1, characterized in that the core elements comprise substantially cylindrical granules that acquire a substantially disk shape when coated with the optical elements.

8. The process according to claim 7, characterized in that the core elements comprise a copolymer of ethylene and acrylic acid.

9. The process according to claim 7, characterized in that the core elements comprise a copolymer of ethylene and methacrylic acid.

10. The process according to claim 1, characterized in that the core elements comprise substantially cylindrical granules that become spherical by the coating with the optical elements.

11. The process according to claim 10, characterized in that the core elements comprise a copolymer of ethylene and acrylic acid.

12. The process according to claim 10, characterized in that the core elements comprise a copolymer of ethylene and methacrylic acid.

13. The process according to claim 1, characterized in that the core elements additionally comprise a pigment.

14. The process according to claim 1, characterized in that it comprises: (a) heating a moving bed of optical elements; and (b) adding one or more core elements comprising a thermoplastic material to the moving bed of optical elements; wherein the optical elements are initially heated to a temperature which is at least about the adhesion temperature of the core elements.

15. The process according to claim 14, characterized in that the temperature of the optical elements is at least about 25 ° C higher than the adhesion temperature of the core elements.

16. The process according to claim 14, characterized in that it is carried out in a continuous manner.

17. The process according to claim 16, characterized in that the moving bed of the optical elements forms a rotating element.

18. The process according to claim 14, characterized in that the moving bed of optical elements is formed in a fluidizing chamber.

19. The process according to claim 1, characterized in that the core elements change shape by the coating by the optical elements.

20. The process according to claim 1, characterized in that the core elements do not substantially change shape by the coating with the optical elements.

21. The process according to claim 20, characterized in that the core elements additionally comprise plate-like pigment particles.

22. The process according to claim 1, characterized in that the core elements are prepared by a process comprising: (a) extruding the thermoplastic material into a strip, - (b) cooling the strip of thermoplastic material; (c) cutting the strip of thermoplastic material into core elements.

23. A retroreflective element, characterized in that it comprises: (a) a core element comprising an elastic thermoplastic material and a thermosetting resin; and (b) optical elements that cover the core element with more than about 50% of the projected surface area of the core element covered with optical elements.

24. The retroreflective element according to claim 23, characterized in that the optical elements are embedded in the core element at an average depth of at least about 50% of the average diameter of the optical elements.

25. The retroreflective element according to claim 23, characterized in that the core element additionally comprises plate-like pigment particles.

26. A retroreflective element, characterized in that it comprises: (a) a core element comprising a thermoplastic material that is selected from the group consisting of a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid and combinations thereof; and (b) optical elements that cover the core element more than about 50% of the projected surface area of the core element covered with optical elements.

27. A slip resistant element, characterized in that it comprises: (a) a core element made of a thermoplastic material and a thermosetting resin; and (b) slip resistant particles that coat the core element, wherein more than about 50% of the projected surface area of the core element is covered with the slip resistant particles.

28. A slip resistant element, characterized in that it comprises: (a) a core element comprising a thermoplastic material selected from the group consisting of a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid and combinations thereof; and (b) slip resistant particles that coat the core element, wherein more than about 50% of the surface area projected on the core element is covered with slip resistant particles.