CERAMIC GRANULES WITH HIGH UV OPACITY AND HIGH SOLAR REFLECTANCE

Abstract

The invention relates to ceramic granules with a high UV opacity and high solar reflectance, which is produced by forming a calcined clay mineral powder into green body and re-calcining, featured with a water absorption of 15-35%; ≥97% crystalline content and 90-100% UV opacity. The invention further relates to a method for preparing ceramic granules with a high UV opacity and high solar reflectance and the use thereof for reflectance-improving application on building surface for the purpose of energy conservation.

Claims

1. Ceramic granules having a high UV opacity and high solar reflectance, produced by forming a calcined clay mineral powder and re-calcining, wherein the ceramic granules are characterized by: 15-35% water absorption; ≥97% crystalline content; 90-100% UV opacity; and a solar reflectance of between 82% and 90%.

2. The ceramic granules according to claim 1, which have a water absorption of between 20% and 30%.

3. The ceramic granules according to claim 1, which have a crystalline content of between 97% and 100%.

4. The ceramic granules according to claim 1, which have a crushing index of from 15% to 35%.

5. The ceramic granules according to claim 1, which have a UV opacity of between 92% and 100%.

6. The ceramic granules according to claim 1, wherein the clay comprises dickite, kaolin, montmorillonite, pyrophyllite, halloysite, allophane, ammonium illite or a mixture of one or more thereof.

7. The ceramic granules according to claim 1, wherein the calcined clay powder has a particle size D.sub.50 of between 0.01 μm and 8 μm.

8. The ceramic granules according to claim 1, wherein the calcined clay powder has an L* between 85 and 100, a* between −3 and +3 and b* between 1 and 9.

9. The ceramic granules according to claim 1, wherein the forming of the calcined clay mineral powder is conducted by casting, pressure moulding or rolling granulation.

10. The ceramic granules according to claim 1, wherein the ceramic granules have a particle size of 0.1 to 3.5 mm.

11. The ceramic granules according to claim 1, wherein the ceramic granules are surface treated, and the surface treatment is selected from inorganic coating, organic coating, water repellent or a combination of more than one above treatment thereof.

12. A system, comprising: a substrate formed of an asphaltic substrate, a polyurethane foam substrate, cement substrate or a coated metal substrate; and the ceramic granules of claim 1 applied to the top surface of the substrate.

13. Ceramic granules having a high UV opacity and high solar reflectance, produced by forming a calcined clay mineral powder and re-calcining, wherein the ceramic granules are characterized by: 15-35% water absorption; ≥97% crystalline content; 90-100% UV opacity; and the resultant ceramic granules have a solar reflectance of from 75% to 85% when applied to asphaltic substrate at a coverage of 90% or more.

14. The ceramic granules according to claim 13, wherein the ceramic granules have a particle size of 0.1 to 3.5 mm.

15. The ceramic granules according to claim 13, wherein the ceramic granules are surface treated, and the surface treatment is selected from inorganic coating, organic coating, water repellent or a combination of more than one above treatment thereof.

16. Ceramic granules having a high UV opacity and high solar reflectance, produced by forming a calcined clay mineral powder and re-calcining, wherein the ceramic granules are characterized by: 15-35% water absorption; ≥97% crystalline content; 90-100% UV opacity; and the resultant ceramic granules have a solar reflectance of between 80% and 90% when applied to the surface of a polyurethane foam substrate at a coverage of 90% or more.

17. The ceramic granules according to claim 16, wherein the ceramic granules have a particle size of 0.1 to 3.5 mm.

18. The ceramic granules according to claim 16, wherein the ceramic granules are surface treated, and the surface treatment is selected from inorganic coating, organic coating, water repellent or a combination of more than one above treatment thereof.

Description

DESCRIPTION OF DRAWINGS

[0017] FIG. 1 shows a flow chart for preparing highly reflective ceramic granules in accordance with one aspect of the present invention.

[0018] FIG. 2 shows an X-ray diffraction spectrum of ceramic granules according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The preparation of highly reflective ceramic granules in accordance with one aspect of the present invention is illustrated below referring to FIG. 1.

[0020] The Calcined clay powders, to which water is added, are mixed homogeneously and then formed into green bodies. The green bodies are calcined at high temperature in kiln. The calcined material is crushed and sieved to obtain highly reflective ceramic granules.

[0021] FIG. 2 shows an X-ray diffraction spectrum of ceramic granules obtained according to Experiment No. 1 of the present invention. As can be seen from the figure, the ceramic granules have a crystalline content of 100%.

Definitions

[0022] The following definitions are used herein to further define and describe the present disclosure. Unless otherwise defined in specific instance, these definitions apply to the terms as used throughout the present disclosure.

[0023] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. In case of conflict, the present specification, including the definitions given herein, shall prevail.

[0024] Unless otherwise indicated, all percentages, parts, ratios, and the like amounts used herein are defined by weight.

[0025] In the present invention, the UV opacity is used to indicate the opacity of an object to light within the ultraviolet range.

[0026] In the present invention, solar reflectance (SR) is used to characterize the ability of a material to reflect back solar radiation incident on its surface.

[0027] In the present invention, D.sub.50 representing an average particle size of the granules is a median diameter of the 50% cumulative volume in a particle size distribution curve measured by the laser diffraction scattering method.

[0028] The crushing index indicates the ability of the granules to resist crushing, which may be used to evaluate the corresponding strength of the granules indirectly.

[0029] The water absorption of mineral materials depends mainly on their porosity. In the present invention, the water absorption is used to indicate the porosity of the ceramic granules.

[0030] According to one embodiment, clay suitable for the invention comprises halloysite, dickite, kaolin, montmorillonite, allophane, ammonium illite, pyrophyllite or a mixture of one or more thereof. Calcined clay is commercially available from suppliers including, for example, Hebei Chida Manufacture and Trade Co., Ltd.

[0031] According to one embodiment, the calcined clay powder is selected to have a particle size D.sub.50 of between 0.01 and 8 μm, preferably between 0.1 and 6 μm, more preferably between 0.5 and 5 μm.

[0032] The color space is a color system represented by L*, a*, and b*. In the present invention, the standard used by the L*a*b* color system is the CIE color model, where L* represents the lightness, with L*=0 indicating black and L*=100 indicating white. The a* value represents the red-green component of the color, with green in the negative direction and red in the positive direction. The b* value represents the yellow-blue component of the color, with blue in the negative direction and yellow in the positive direction. According to one embodiment, the color values of the calcined clay powder are selected such that L* is between 80 and 100, a* is between −5 and +5, and b* is between 1 and 10. According to one embodiment, the color values of the calcined clay powder are: L* of between 85 and 100, a* of between −3 and +3, and b* of between 1 and 9. According to another aspect of the present invention, the color values of the calcined clay powder are: L* of between 88 and 100, a* of between −1 and +1, and b* of between 2 and 8. The powder material thus selected has a small content of light absorbing material.

[0033] According to one embodiment, the crushing index of the ceramic granules is between 15% and 35%, preferably between 20% and 30%.

[0034] According to one embodiment, the solar reflectance of the ceramic granules is between 82% and 90%.

[0035] According to one embodiment, the ceramic granules have a solar reflectance of from 75% to 85% when being applied to an asphaltic substrate at a coverage of 90% or more. According to another embodiment, the ceramic granules have a solar reflectance of 80% to 90% when being applied to a foam (such as polyurethane) substrate at a coverage of 90% or more.

[0036] According to one embodiment, no flux/fluxing agent is needed in the course of the re-calcination.

[0037] According to one embodiment, the calcined clay powder is formed to green body and then calcined to obtain granules having a certain strength and retaining a certain amount of pores.

[0038] The amount of water required for the forming step itself is known by those skilled in the art. The amount of water added may be 0% to 100%, preferably 5% to 60%, more preferably 10% to 50% relative to the weight of the calcined clay powder.

Forming Pressure and Forming Method

[0039] The forming/moulding pressure has influence on the strength and porosity of the ceramic granules. High pressure leads to high strength and low porosity of the granules.

[0040] The forming/moulding pressure for the green body to be calcined is in the range of 0-1000 MPa.

[0041] High pressure sets forth a high requirement on the forming/moulding equipment, rendering a higher equipment investment and a more serious wear. On the other hand, it is difficult to obtain suitable strength of the ceramic granules when the moulding pressure is too low.

[0042] Generally, the forming/moulding pressure can be selected between 50 to 200 MPa.

[0043] The forming/moulding of the powder can be conducted, for example, by casting, pressure moulding or rolling granulation.

Green Body Calcination

[0044] The green body can be calcined with heat sources such as electricity, coal, natural gas, fuel oil, etc. The calcining kiln can be a shuttle kiln, a tunnel kiln, a roller kiln, a rotary kiln and the like. If the calcination temperature is too low, the strength of the prepared granules is insufficient. If the calcination temperature is too high, the number of pores is gradually reduced, which impacts the reflection of the granules to solar radiation. According to one aspect of the invention, the green body is calcined at a temperature from 1100 to 1400° C., preferably from 1150 to 1350° C.

Crushing and Sieving

[0045] The calcined material obtained by calcining the green body can be crushed with a jaw crusher, a hammer crusher, a cone crusher, a roll crusher, an impact crusher, a mill, or a combination thereof. The ceramic granules obtained by crushing can be sieved to adjust their particle size distribution. As for the sieving device, a fixed sieve, a movable sieve, a vibrating sieve or a combination thereof can be used. In order to make the ceramic granules suitable for roofing material, they are processed into granules having a particle size of from about 0.1 to 3.5 mm, preferably from about 0.3 to 2.3 mm, more preferably from about 0.5 to 2 mm

Surface Treatment

[0046] According to one embodiment, the ceramic granules can be further surface treated to obtain functions such as water repellency, stain resistance and algae resistance. The surface treatment generally includes surface treatment selected from inorganic coating, organic coating, water repellent or a combination of more than one above treatment thereof.

[0047] According to one embodiment, the inorganic coating is a liquid inorganic coating selected from at least one of silicate, aluminum phosphate, silica sol, and aluminum sol. The silicate is selected from the group consisting of sodium silicate, potassium silicate, aluminum silicate, lithium silicate or a mixture of one or more thereof.

[0048] According to one embodiment, the organic coating is selected from the group consisting of acrylics and silicone-acrylic coating. The water repellent may be selected from the group consisting of silanes, silicones, and fluorine-containing water repellents.

[0049] The inorganic coating, the organic coating or the water repellent may further comprise one or more selected from the group consisting of pigments, algaecides, insecticides, self-cleaning agents, viscosity modifiers, fluxing agents, flame retardants, surface tension modifier and anti-aging agents.

[0050] According to one embodiment, the ceramic granules further comprise an additional coating obtained by secondary coating with an organic coating and/or a water repellent, wherein the organic coating is a resin coating or an emulsion coating, and the water repellent is a silicon-containing water repellent or a fluorine-containing water repellent.

Applications

[0051] According to one embodiment, the ceramic granules can be applied to the surface layer of a roofing material with substrate made of cement, asphalt, polyurethane foam or coated metal, so as to increase the roof reflectance to solar radiation. The ceramic granules have a solar reflectance of 75% to 85% when applied on asphaltic substrate at a coverage of 90% or more. According to another embodiment, the ceramic granules have a solar reflectance of 80% to 90% when being applied to foam substrate (such as polyurethane foam) at a coverage of 90% or more.

[0052] According to one embodiment, the ceramic granules can also be used in stone texture coating for buildings to produce a highly reflective coating layer, which has the same effect as white granules.

Examples

[0053] The following examples are provided to describe the invention in more detail. These examples, illustrating the specific embodiments and preferred technique for implementing the present invention, are intended to illustrate but no to limit the invention.

General Description of the Testing Methods

Whiteness

[0054] The color value was measured with a colorimeter (Model SC-100, manufactured by Beijing Kangguang Optical Instrument Co., Ltd.).

[0055] Take a certain amount of a sample and put into a tablet machine (an accessory of the colorimeter, Model SC-100, manufactured by Beijing Kangguang Optical Instrument Co., Ltd), to be pressed into a tablet. The tablet is measured for its whiteness with the colorimeter at the flatter side of the tablet. The values of L*, a* and b* were measured for three times and an average value was calculated.

Particle Size D.SUB.50

[0056] The particle size D.sub.50 was measured with a laser particle size analyzer (Model BT-9300H, manufactured by Dandong Bettersize Instrument Co., Ltd.)

Water Absorption

[0057] Take 50 g ceramic granules, and place it in a beaker with water, and stirred the mixture with a glass rod for 10 s. A piece of cotton cloth was immersed in water, wringed until no water dripping and then unfolded on a table. The granules immersed in water were removed from the beaker and laid on the cotton cloth. The granules were wiped back and forth with the cotton cloth until no water stains on the surface of the granules can be observed (the granules shall be loose and not sticky). Weigh approximately 5-10 g (m1) of the wiped ceramic granules with a scale accurate to 0.1 mg and place into a beaker. The granules were dried in a 105° C. oven to constant weight. The weight (m2) of the ceramic granules after drying was measured. The water absorption is calculated according to the following equation: Water absorption=(m1−m2)/m2*100%.

Crystalline Content

[0058] The crystalline content was measured with an X-ray diffractometer (Model D/MAX 2500, Rigaku Corporation, Japan), and calculated.

Crushing Index

[0059] The crushing index was measured on ceramic granules with size between 1.7 mm and 1.18 mm according to the Part 6.12.2 of GB/T 14684-2001.

UV Opacity

[0060] UV opacity was measured similar to ASTM D1866-79.

[0061] Instruments: flood lamp box, standard photographic step tablets (Kodak photographic step tablets, No. 2, calibrated), filter (UV-light transparent and visible-light absorbing glass, model ZWB1, Nantong Ruisen Optical Element Technology Co., Ltd), camera (Panasonic DMC-GF5), template (a perforated board with 110 holes).

Procedure

[0062] The flood lamp box consists of a box and a flood lamp (PHILIPS, Model: RVP350 L 1XHPI-T 400W IC220V50 Hz SP SY) installed in the box. There was a square opening on the top of the box, and the light emitted from the flood lamp was illuminated upward through the square opening. The filter was fixed above the square opening with a filter slide, and the template was placed above the filter. Turn on the flood lamp for 10 minutes to warm up the apparatus.

[0063] Screen the ceramic granules using a Tyler 10 mesh and Tyler 12 mesh screen and take 5 g sample of 10-12 mesh. Place one granule in each space of the template with tweezers. Adjust the granule to make sure each hole is completely covered and there was no light transmit. Then, place the upper template and check for light transmission. If there was light transmitted, adjusted the granule until there was no light transmitting through the hole.

[0064] A standard graphical step tablets was carefully cut lengthwise down the center to produce two equal tablets. One tablet was laid on the other one so that the 14th step of the bottom tablets was situated below the 1st step of the upper tablets (Note: Don't count the clear area. The dark steps of both step tablets should on the left side. Secure the two step tablets with two tapes on both ends). The combined step tablets was placed on the 10 holes at the bottom of the lower template. Make sure the 14.sup.th step of the bottom tablet and the 1st step of the upper tablet are squarely over the 5.sup.th hole from the left. Secure the tablets with tapes. Make sure all the holes are completely covered by the step tablets and that the tape does not block the holes.

[0065] Fix a camera right above the square opening with a camera holder. Turn off the room lights and make sure it is in completely darkness. Take photos with the camera.

[0066] Open the photos with Photoshop software in a computer. Adjust the contrast of the photos so that the brightness of the 5th hole from the left of the step tablets is barely seen, and count the number of bright spots on the photo (the number of holes n). Calculate UV opacity according to the following equation:

UV opacity=(number of granules placed−number of bright spots)/100*100%=(100−n)/100*100%.

Solar Reflectance (Ceramic Granules)

[0067] The solar reflectance was measured in accordance with the ASTM-C1549 standard. The reflectance of the sample was measured with a solar spectrum reflectometer (model SSR-ER, A&D, USA). Set the reflectometer in b891 output mode for measurement. 50 g granules sample was placed in a flat sample tray, and then levelled and smoothed with a ruler. Solar reflectance was measured on three points randomly selected on the surface.

Solar Reflectance (after being Applied to Asphalt Substrate)

[0068] The solar reflectance was measured in accordance with the ASTM-C1549 standard. The reflectance of the sample was measured with a solar spectrum reflectometer (model SSR-ER, A&D, USA). Adjust the reflectometer to the b891 output mode for measurement. A sufficient amount of granules were evenly spread on the low-melting sticky asphalt board, flattened, and the loose granules on the surface were removed. Solar reflectance was measured on three points randomly selected on the surface of the asphalt substrate.

Experiment Series 1

[0069] Calcined clay powders, uncalcined powder and raw ore from China Hebei Chida Manufacture and Trade Co., Ltd. were employed, the properties of which are summarized in Table 1.

TABLE-US-00001 TABLE 1 Properties of raw materials employed Calcined clay Powder powder D.sub.50 value, whiteness whiteness whiteness number Mineral μm L* a* b* 1 Calcined 0.5 μm 93 0 3 ammonium illite powder 2 Calcined 4.0 μm 93 0 3 ammonium illite powder 3 Calcined 10 μm 93 0 3 ammonium illite powder 4 Calcined 4.0 μm 93 1 3 kaolin powder  .sup. 1a ammonium 0.5 μm 50 0.7 3.4 illite powder (uncalcined)  .sup. 2a ammonium 4.0 μm 50 0.7 3.4 illite powder (uncalcined)  .sup. 3a ammonium 10 μm 50 0.7 3.4 illite powder (uncalcined)  1b ammonium / 45 0.8 3.6 illite ore (uncalcined)

[0070] The preparation of Ceramic granules from calcined clay powder was as follows.

Place 10 kg calcined clay powders listed in the table 1 and 2 kg water into a mixer [Gongyi City Zhanjie Wandu Machinery Factory, Model 000] to mix evenly. The mixed powders were pressed into 240*115*53 mm green bodies with a 100 tons press [Beijing Zhongcai Jianke Industry & Trade Co., Ltd., model ZCY-200]. The green bodies were then calcined in a high temperature furnace at 1250° C. [Luoyang Hengli Kiln Co., Ltd., model HLX17C] for 10 h. After cooling, the calcined materials were crushed with a crusher [Hebi city Three Long Electronic Technology Co., Ltd., Model CP-180×150] to granules with the size of about 0.5-2 mm. The granules were tested with respect to their UV opacity, SR (ceramic granules), and SR (after applied to asphalt substrate).

[0071] The preparation of Ceramic granules from uncalcined clay powder is as follow.

The preparation of ceramic granules from uncalcined clay powder was the same as with calcined clay powder, except the calcining time of the former is about 30 hr. The purpose of extending the calcination time is to turn the uncalcined clay powder into white.

[0072] Ceramic granules were prepared from raw mineral ore according to the following procedure:

[0073] About 10 kg of the ore were weighed and put into a high temperature furnace[Luoyang Hengli Kiln Co., Ltd., Model HLX17C]. The ore were heated therein at 1250° C. for 30 h. After cooling, the ore was crushed with a crusher [Hebi City Three Long Electronic Technology Co., Ltd., Model CP-180×150] to about 0.5-2 mm granules. The granules were tested with respect to their UV opacity, SR (granules as produced), and SR (after applied to asphalt substrate).

TABLE-US-00002 TABLE 2 Properties of the ceramic granules Granules on the Powder/ asphalt Experiment ore UV Granules, substrate, Crystalline No. used opacity % SR % SR % content % 1 1 100 90 83 100 2 2 99 89 81 100 3 3 85 88 74 100 4 4 99 88 81 100 5  .sup. 1a 100 83 74 100 6  .sup. 2a 99 80 73 99 7  .sup. 3a 82 80 70 99 8  1b 78 82 67 99

[0074] As can be seen from the above table, even with different UV opacity, the granules have similar SR values. However, when applied to asphalt substrate, the granules of higher UV opacity tend to result in higher solar reflectance.

Experiment Series 2

[0075] Procedure for preparing the ceramic granules:

Place 10 kg of calcined clay powder listed as No. 1 in table 1 and 2 kg water into a mixer [Gongyi City Zhanjie Wandu Machinery Factory, Model 000] and mix evenly. The mixed powders were pressed into 240*115*53 mm green bodies with a 100 tons press [Beijing Zhongcai Jianke Industry & Trade Co., Ltd., Model ZCY-200]. The green bodies were then heated in a high temperature furnace [Luoyang Hengli Kiln Co., Ltd., Model HLX17C] for 10 h at temperature of 1050° C., 1150° C., 1280° C. and 1450° C., respectively. After cooling, the bodies were crushed with a crusher [Hebi city Three Long Electronic Technology Co., Ltd., Model CP-180×150] to granules with the size of about 0.5-2 mm. The granules were tested for UV opacity, SR (ceramic granules), SR (granules on asphalt substrate) and the crushing index to evaluate the influence of the calcination temperature.

TABLE-US-00003 TABLE 3 Properties of the ceramic granules Granules Calcination Water UV Granules on the asphalt Crushing Crystalline temperature absorption % opacity % SR % substrate, SR % index % content % 1050 50 100 90 82 40 95 1150 30 100 90 82 30 98 1280 25 99 88 80 20 100 1450 10 80 88 70 15 100

[0076] As can be seen from the above table, a low calcination temperature tends to result in low granule strength, while a high calcination temperature tends to result in low UV opacity.