WO2002040421A1

WO2002040421A1 - Photoluminescent plastic aggregates

Info

Publication number: WO2002040421A1
Application number: PCT/AU2001/001500
Authority: WO
Inventors: Barry Rogers
Original assignee: S.L.E. (Australia) Pty Ltd
Priority date: 2000-11-20
Filing date: 2001-11-20
Publication date: 2002-05-23
Also published as: AU2002214840A1; WO2002040421A8

Abstract

Plastic aggregates are disclosed that exhibit long-lasting photoluminescence, typically 4-15 mm in size and containing 4-20% of a long-lasting phosphor pigment, dispersed in a crosslinked or thermoset matrix that is preferably formed by the polymerisation of an unsaturated polyester resin/styrene solution. Particularly preferred photoluminescent pigments are inorganic phosphors such as strontium aluminate supported on low density (e.g. 0.2 1.5 g/l) inorganic substrates such as a porous ceramic, silica or glass. The plastic aggregate may be spread on the surface of a cementitious substrate before cure to embed the aggregate over the surface. After cure this substrate may be polished to provide a surface with long-lasting after-glow properties.

Description

PHOTOLUMINESCENT PLASTIC AGGREGATES

Technical Field

This invention relates to photoluminescent plastic aggregates and in particular to such aggregate suitable for use in cementitious or polymeric binders. The invention also relates to cured cementitious or polymeric binders that include the photoluminescent plastic aggregates. Background to the Invention

Cementitious binders are widely used to prepare decorative concrete finishes. An example is terrazzo material. This material includes stone chips set into the concrete. The material is commonly used as floors, steps and construction slabs as well as bench tops. The material may be cut into slabs and polished. Alternatively the material may be moulded into the desired shape and the surface may be polished. As well as cementitious binders polymeric resinous binders may be used with decorative chips or flakes. Examples include thermoplastic acrylic polymers as well as crosslinked styrene/polyester polymers or epoxy/polyamide polymers. In the case of thermoplastic polymers which are formed by extrusion type techniques the range of chips or flakes that may be used is limited as they must be capable of extrusion. These binders, whether cementitious or polymeric, form the matrix in which the stone chips or other decorative chips or flakes are embedded. The articles formed from the chips or flakes and the cementitious or polymer binder may be moulded or formed to the desired shape. One or more surfaces of the article may be finished with sanding and polishing to provide the desired decorative effect.

Fluorescence is a phenomenon where material emits visible radiation when the material is excited by an external excitation source. A fluorescent lamp and a cathode ray tube each emit fluorescence. A material which emits fluorescence is called a phosphor. When light emitted by a phosphor lasts after cessation of excitation for duration of time sufficient for the light to be perceived by the eye, i.e., i i about 0.1 second or longer, the light is called phosphorescence. A phosphor which has a long persistent phosphorescence lasting for several hours at room temperature is called a long-lasting phosphor or a light storage phosphor. As long-lasting phosphors, there are two types of prior art materials, namely a sulfide represented by ZnS:Cu and an Eu²⁺ activated alkaline-earth metal aluminate RA1₂ O₄ (R being an alkaline-earth metal). The ZnS:Cu sulfide long- lasting phosphors have been practically used for several decades but they have the disadvantage that their after-glow only lasts for a relatively short duration of time, typically about three hours at the longest. This short duration is significant as it means that with normal darkness periods extending to ten or more hours in a day, there is insufficient after-glow to be useful throughout the darkness period. Furthermore, this type of phosphor has a serious defect in that a decomposition reactions of ZnS+H₂0 and Zn+H₂S takes place from ultraviolet rays contained in sunlight and moisture contained in the air. This causes the phosphor to blacken and, as a result, the after- glow characteristics significantly deteriorate within a relatively short period of time. For this reason, this type of phosphor has only found limited applications such as a luminous watch display and a night-time display of a particular location in a house.

In order to improve the brightness and after-glow duration, radioactive luminescent materials were produced, in which some radioactive elements such as CO,Ra andH₃ were added. The addition of such elements can make the phosphor continuously emit light and has enabled the phosphor to be used in aircraft dashboards and clocks. However, due to the danger of radioactive contamination and high material cost, the application of these phosphors has been greatly restricted.

Recently developed Eu²⁺ activated alkaline metal aluminate long lasting phosphors (U.S. Pat. Nos. 5,376,303 and 5,424,006) exhibit higher phosphorescence brightness, longer lifetime as well as better chemical durability and light resistance than the previous ZnS:Cu phosphors. These aluminate phosphors are expected to have wide applications such as signage in addition to the existing applications for luminous watches and vehicle instruments.

Most of the known phosphor materials are subject to hydration when suspended in an aqueous solution and this causes them to suffer deterioration of performance. This in turn prevents the use of these materials in many applications such as in cementitious compositions because of the strongly alkaline nature of this binder in both uncured and partially cured form. Their use in these applications is further limited to varying degrees by other negative characteristics. For example, most phosphor materials tend to settle due to their high specific gravity. The specific gravity is typically in excess of 3 g/cm . In cementitious compositions if the pigments or aggregates of the phosphor pigments were spread onto the surface, the high density of the pigment material may lead to settlement below the surface. This would necessitate surface grinding and the use of higher levels of phosphors then desired. Because of settlement, a significant percentage of the phosphor would be buried below the surface where its phosphor properties would be unavailable.

It would be desirable to have a chip or aggregate that when included in a cementitious or polymeric binder provided a photoluminescent effect. The afterglow produced would be a significant safety advantage when used for example on parts of steps in the stairwells of buildings. It could also be used on paths, walkways and the marking of car parking bays. As well as safety benefits it may also produce an aesthetically pleasing or interesting effect. Phosphor pigments encapsulated in or coated by a polymeric matrix are known. Examples are described in US patent 5,607,621 and EP 542669. However, in such applications the polymeric matrix is required to be thermoplastic or heat flowable. The use of inorganic phosphors in a cementitious matrix has been proposed in US patent 5,314,536. However, the inorganic phosphor is not in a plastic aggregate form and hence is vulnerable to deterioration from the cementitious environment. Summary of the Invention

This invention provides in one form a photoluminescent plastic aggregate comprising a long lasting photoluminescent pigment dispersed within a thermoset or crosslinked polymeric binder.

Preferably the binder is polymerised by the addition polymerisation of ethylenically unsaturated monomers selected from (meth)acrylic esters, styrene, ethylene, propylene, vinyl acetate and acrylonitrile. Alternatively the polymeric binder may be a condensation type polymer selected from epoxy, polycarbonate, polyurethane, polyamide, phenol formaldehyde and urea formaldehyde.

The polymerised binder is thermoset or crosslinked and a particularly useful polymerised binder is formed from solutions of unsaturated polyester resin and styrene. This may be conventionally cured using peroxide type initiators. Suitable resins and initiators are well known and used in the fabricating and boat building industries where glass fibres are commonly used as reinforcement. Phenol formaldehyde and urea formaldehyde resins may also be used and these resins are also well known. They are usually cured with acids. Furfuryl alcohol may be also included as an additive to these formaldehyde resins.

As well as the addition polymerisable monomers described above minor amounts of functional monomers such as (meth)acrylic acid and acrylamide may be included. In addition multifunctional monomers are usually included to provide the required thermoset or crosslinked characteristics. With addition polymerisable monomers suitable monomers are trimethylol propane triacrylate and pentaerythritol tri and tetra acrylate. With condensation type polymers such as polyurethanes the thermoset character or cros slinking is achieved by using a triol or other multifunctional polyol in combination with the isocyanate component. Detailed Description of the Invention

In this specification the term aggregate means pieces of crushed material, in particular plastic material. The term is usually used with regard to crushed stone or gravel used in making concrete. However, in this specification, the term is not limited to the method of formation. The aggregate may be formed not only by crushing or size reduction but also by casting or moulding as well as extrusion. Size enlargement methods such as compaction moulding could also be used to form the aggregate.

While a wide range of long lasting photoluminescent pigments may be used it is preferred that the pigments comprise: 5 to 95 wt % of an inorganic phosphor pigment; 5 to 95 wt % of ceramic or silica particles wherein the ceramic or silica particles are bonded to the phosphor pigment.

Preferably the ceramic or silica particles are ceramic microspheres.

Preferably the ceramic microspheres are glass and more preferably they are borosilicate glass.

Preferably the wt % of inorganic phosphor pigment is 40 to 80% and the wt % of the ceramic or silica particles is 20 to 60%.

Preferably the silica particles are amorphous silica particles.

Preferably the density or specific gravity of the phosphor pigments is in the range 0.2 - 1.5 g/cm³ and more preferably 0.3 - 1.2 g/cm³ and even more preferably 0.4 - 1.0 g/cm³.

It is preferred that long lasting photoluminescent pigment formed within microspheres are used when the aggregates are formed by extrusion. They appear to cause less wear on the die surface of the extruder. Preferably the plastic aggregates containing the long lasting photoluminescent materials are relatively small, preferably in the range 2- 25 mm, more preferably 3-20 mm and most preferably 4-15 mm. This size allows them to be integrated into the top layer of cement or terrazzo surfaces. The size can be selected by appropriate well known sieving techniques. The aggregates may be formed by moulding processes or by size reduction after polymerisation.

The plastic aggregates are preferably evenly distributed into the cement or terrazzo surface whilst the composition is still wet and the aggregates become embedded in the surface of the cured cement matrix.

Once the substrate is completely set and hydrated sufficiently to be hard, the surface can then be sanded or ground level so as to expose the photoluminescent aggregates to light. As well as the photoluminescent aggregates of the present invention other conventional chips or flakes may be used in combination with the photoluminescent aggregates.

Preferably the substrate will contain 20-200g of plastic aggregate per square meter.

The amount of long lasting photoluminescent pigment used in the plastic aggregate is in the range of 2-80% w/w, more preferably 4-20% where the percentage is expressed as a percentage in the total.

The plastic aggregates of the present invention have exhibited good photoluminescent properties when added to cement or polymeric type compositions. The cementitious compositions suitable for use with the plastic aggregates of the present invention are those suitable for terrazzo type finishes. Typically they consist of sand and Portland cement. Polymeric binders suitable for use with these aggregates include unsaturated polyesters/styrene resins and epoxy/polyamide resins. The invention will be further described by reference to a preferred embodiment described in the following Examples. Example 1.

Preparation and use of long lasting photoluminescent plastic aggregate. Long lasting photoluminescent pigment was prepared as follows: soda lime borosilicate spheres* 300g strontium aluminate phosphor pigment + 700g hydrochloric acid 15% solution 40g

* Brand name "Scotchlite Glass Bubble K15". Particle size = 15 - 1255 μ , pH = 9, Specific Gravity = 0.15 g/cm³. Available from Zeelan Industries Inc., 3M Center Bldg, 220-8E-04, St. Paul, MN, USA.

+ Brand name "Lunbo G34-200-A1" or "Lunbo G35-200A", Particle size = 4.0 - 95 μm. pH = 10. Specific Gravity = 4.2 g/cm³. Available from Shandong Lunbo Ind. & Comm. Group Co Ltd, 3/86 Chaoshan Street, Jinan, Shandong, China. Into a plastic mixing vessel the following materials were added: Hydrochloric Acid (30% concentration) 500ml

De-ionised water 500ml

The soda lime borosilicate micro spheres were added to the tumbler mixer and then the above acid solution was added. The tumbler mixer was sealed and the contents agitated for 10 minutes. In the tumbler mixer, the strontium aluminate phosphor pigment was spread over the acid moistened soda lime borosilicate micro spheres. After this addition, the tumbler mixer was again sealed and mixing was commenced with an airflow being pumped into the mixture. Traces of hydrogen gas and water vapour that were generated during the tumbling action were evacuated. The tumbling mixing was continued for three hours or until the mixture was thoroughly dry to promote pigment density 0.45 g/cm .

To 900g of a crosslinkable unsaturated polyester/styrene resin lOOg of pigment prepared above was dispersed under high speed stirring. A peroxide curing agent was added together with a small amount of wax, and the composition was poured into a 300 x 300mm tray to provide a 10mm thick layer. The wax was then used to promote surface cure of the polymer.

After curing the slab was broken into aggregates of average size 15mm. This aggregate contained 10% w/w of pigment.

A concrete mixture consisting of 4 parts of 20mm basaltic aggregate, 2 parts of sand and 1 part of Portland cement was dry blended. Water was added to form a pourable mix which was formed into a block 200mm x 900mm in area and 100mm in thickness. The concrete was trowelled off and 20g of the above prepared plastic aggregate was spread on the surface. After curing the upper surface was polished to form a flat surface which produced the desired after-glow effect

Since modifications within the spirit and scope of the invention may be readily effected by persons skilled in the art, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, hereinabove.

Claims

I. A photoluminescent plastic aggregate comprising a long lasting photoluminescent pigment dispersed within a thermoset or crosslinked polymeric binder.

2. A photoluminescent plastic aggregate as defined in claim 1 wherein the weight percentage of long lasting photoluminescent pigment is in the range 2 - 80%.

3. A photoluminescent plastic aggregate as defined in claim 2 wherein the weight percentage of long lasting photoluminescent pigment is in the range 4 - 20%.

4. A photoluminescent plastic aggregate as defined in any one of claims 1 to 3 wherein the polymeric binder in polymerised from an unsaturated polyester resin and styrene monomer solution.

5. A photoluminescent plastic aggregate as defined in any one of claims 1 to 4 wherein the density of the long lasting photoluminescent pigment is in the range 0.2 - 1.5 g/cm³.

6. A photoluminescent plastic aggregate as defined in claim 5 wherein the density of the long lasting photoluminescent pigment is in the range 0.3 - 1.2 g/cm³.

7. A photoluminescent plastic aggregate as defined in claim 6 wherein the density of the long lasting photoluminescent pigment is in the range 0.4 - 1.0 g/cm³.

8. A photoluminescent plastic aggregate as defined in any one of claims 1 to 7 wherein the long lasting photoluminescent pigment comprises:

5 to 95 wt % of an inorganic phosphor pigment;

5 to 95 wt % of ceramic or silica particles wherein the ceramic or silica particles are bonded to the phosphor pigment.

9. A photoluminescent plastic aggregate as defined in claim 8 wherein the ceramic or silica particles are ceramic microspheres.

10. A photoluminescent plastic aggregate as defined in claim 9 wherein the ceramic microspheres are glass.

II. A photoluminescent plastic aggregate as defined in any one of claims 1 to 10 wherein the size of the aggregate is in the range 2 - 25 mm.

12. A photoluminescent plastic aggregate as defined in claim 11 wherein the size of the aggregate is in the range 4 - 15 mm.

13. A cementitious substrate having incorporated into the surface of the substrate photoluminescent plastic aggregate as defined in any one of claims 1 to 12 at the rate of 20 to 200 g per square metre of substrate surface.