WO2018077799A1

WO2018077799A1 - Sintered refractory roofing granules

Info

Publication number: WO2018077799A1
Application number: PCT/EP2017/076996
Authority: WO
Inventors: Johan Pierre LORICOURT; Benoit LECACHEUX; Alexander Hirsch
Original assignee: Imerys Technology Center Austria Gmbh
Priority date: 2016-10-31
Filing date: 2017-10-23
Publication date: 2018-05-03
Also published as: DE102016120776A1

Abstract

The present invention relates to sintered refractory roofing granules and a method for making such granules. Disclosed are white granules of increased total solar reflectance (TSR). A method including the step of calcining pure clays without adding any flux or other sintering additives is disclosed.

Description

SINTERED REFRACTORY ROOFING GRANULES

The present invention relates to sintered refractory roofing granules and a method for making such granules. Disclosed are white granules of increased solar reflectance.

BACKGROUND OF THE INVENTION

Asphalt based roofing products today are designed to last 30 to 40 years by using mineral roofing granules. The roofing granules are typically embedded in the asphalt coating on the surface of an asphalt-impregnated felt base material. The mineral granules are employed to provide a protective layer on asphaltic roofing materials and to add simultaneously aesthetic values to a roof. For this reason, colored pigments are used for coatings ordinarily applied to the base mineral granules. Thus, most of the roofing materials are provided with a granular coating to reduce weathering, provide aesthetics, and add fire resistance.

In recent years, interest in mineral-surfaced roofing of increased solar reflectance has enormously gained as a way to reduce summer cooling costs and to mitigate smog-producing urban "heat island" effects. Due to increased interest in energy conservation, the USEPA has developed standards under its Energy Star® program for increased magnitude and retention of solar reflectance of roofing materials. A greater reflectance leads to less heat absorption by roofing materials and lowered temperature control costs for buildings. Some states and large cities in the United States are considering or beginning to require "cool roof" technologies to reduce energy costs and the "heat island" effect, in which cities are several degrees warmer than the surrounding land.

Conventional asphalt based roofing products are known to have low solar heat reflectance, because the mineral particles typically used for making roofing granules, such as talc, slag limestone, granite, syenite, diabase, slate, trap rock, basalt, greenstone, andesite, porphyry, rhyolite, and greystone, generally have low solar reflectance. Furthermore, the absorption of solar heat will still increase as the granules covering the surface of the roofing materials become dark in color. For this reason, the granules are sometimes coated with a ceramic coating to make them white enough for obtaining an acceptable solar reflectance.

U.S. Patent No. 8,361 ,597 B2 discloses solar reflective roofing granules having improved solar heat resistance, which granules are formed by coating colored mineral particles with a coating composition including titanium dioxide nanoparticles.

U.S. Patent No. 8,865,303 B2 discloses a cool roofing system including highly reflective white calcined kaolin particles that can be applied to a substrate to increase solar reflectance of a roofing system to equal to or greater than 70%.

U.S. Patent Application Publication No. 2010/0203336 discloses uncalcined kaolin dispersed with binder and solar reflective particles, such as ΤΊΟ2, to provide roofing granules revealing high solar reflectance.

Ultrawhite granules for use in roofing compositions are disclosed in international Patent Application Publication No. WO 2015/1 12590 A1 . The composition includes aluminosilicate and a flux, wherein the aluminosilicate and the flux are calcined to form calcined granules. The aluminosilicate may include kaolin and/or chamotte. The flux may include a salt, sodium silicate, or potassium feldspar.

International Patent Application Publication No. WO 2013/192336 A1 discloses hyperbright white roofing granules with high solar reflectance. The bright white refractory granules are synthesized by forming a mixture comprising clay (e.g. kaolin clay), sintering material (e.g. feldspar), and optionally one or more additional ingredients selected from silica particles, pigments, fillers, lightning agents, porosity enhancers, and mixtures thereof. The mixture is formed into aggregates which are subsequently fired. However, due to the fact that energy conservation and environmental aspects become more and more important, there is still a continuing need for equivalent or improved roofing granules providing increased solar heat reflectance to reduce the solar absorption of roofing materials and to mitigate "heat island" effects. SUMMARY OF THE INVENTION

The present invention provides sintered refractory roofing granules having a chemical composition comprising, in percentages by weight:

The above sintered refractory roofing granules according to the present invention have a mineralogical composition comprising, in percentages by weight:

- 45% to 65% mullite;

less than 4.5% quartz;

less than 10% cristobalite; and

- 20% to 50% amorphous phases.

Furthermore, the roofing granules of the present invention have an open porosity of at most 35% per volume, preferably at most 20% per volume, and more preferably at most 15% per volume. The average pore diameter is of less than 0.75 μηπ, preferably less than 0.5 μηπ, and more preferably less than 0.3 μηι.

In some preferred embodiments, the mineralogical composition comprises less than 5% by weight cristobalite, more preferably less than 3% by weight cristobalite In one embodiment of the present invention, the chemical composition of the sintered refractory roofing granules may furthermore comprise between 0.01 and 3.0 percent by weight K2O.

The total solar reflectance (TSR) of the sintered refractory roofing granules of the present invention is at least 0.75 (75%), preferably at least 0.80 (80%), prior to any added surface treatment. After application of the granules to the asphalt or modified bitumen substrate, the final roofing product reflectance (3-year aged reflectance) is at least 0.65 (65%) in conformance to Low-Slope Energy Star® standards, preferably at least 0.70 (70%). In some preferred embodiments of the present invention, the sintered refractory roofing granules have a Mohs hardness of at least 3.5, preferably at least 5.0. In another embodiment of the present invention, the base clays for making roofing granules have a LOI (Loss of Ignition) of at least 10 percent by weight.

In another embodiment, the roofing granules according to the present invention may be coated with a hydrophobic coating.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a bar graph illustrating the relationship of total solar reflectance (TSR) and sintering temperature.

Figure 2 is a bar graph illustrating the relationship of total solar reflectance

(TSR), sintering temperature, and open porosity.

Figure 3 is bar graph illustrating the direct relationship of total solar reflectance

(TSR) and open porosity.

Figure 4 is a bar graph illustrating the relationship of total solar reflectance and particle size distribution.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the finding that calcined aluminosilicate clays may have some desired properties that may predestine roofing material in acting as "cool roof". Therefore, some selected kaolin clays were tested for making roofing granules. The mineralogical and chemical compositions of the raw materials which were used for the present disclosure are summarized in tablel . Table 1

The above mentioned raw materials come from different sources in England, USA, and Brazil. The product designations are internal identifications of Imerys Filtration and Performance Additives.

In some embodiments, also blends of different clay types were used for making roofing granules. Generally, the clays used for the experiments had a loss of ignition (LOI) of more than 10% by weight, preferably of about 13% by weight.

The general procedure for making roofing granules of the present invention comprises the steps:

- milling a base clay to obtain a starting material having an average particle size - moistening the clay or a respective blend of clays by adding 20% to 35% by weight of water;

- extruding the moistened clay mixture using a piston press to form a green body;

- sintering the obtained green bodies in a temperature range of 1200°C to

1500°C; and

- crushing and screening the sintered bodies to from granules having a particle size of 0.5 and 3.0 mm.

The starting materials, which were prepared by milling the base clay, had an average particle size dso of less than 10 μηπ, preferably less than 5 μηπ, more preferably less than 3 μηι. The milling itself was performed using conventional equipment.

It was generally found that the finer the particle size distribution of the starting material the higher is the solar reflectance of the final calcined roofing granules.

However, the sizing step of the starting material was limited to a particle size distribution with an average particle size dso of 2.7 μηι. This limitation had not only economic aspects, it rather appeared that still finer particle size distributions will lead to enhanced compaction during extrusion and therewith to an undesired lowered porosity of the final product.

The influence of the particle shape is not that clear. However, an angular grain shape seems to promote the formation of roofing granules with a high percentage of open porosity, whereby high levels of open porosity generally lead to high bulk solar reflectance.

Because some preliminary pilot tests with additions of titania or methylcellulose to the moistened mixture of the starting material resulted in decreasing solar reflectance, only pure clays moistened with 10% to 35% by weight of water were used. With respect to the state of the art, it has to be pointed out that no sinter material and/or flux are used according to the present invention. Furthermore, it's preferably abstained from using other additives, such as e.g. pigments, fillers, or lightening agents. Particularly, for environmental reasons, the use of finely ground silica, wherewith the amount of quartz in the final product could be enhanced, is avoided. The inhalation and adsorption of quartz dust is considered to be a potential cause of lung cancer. It can't be excluded that the handling of quartz containing roofing granules could release quartz dust. Therefore, it is one objective of the present invention to provide roofing granules having quartz portions as low as possible. All samples were extruded using a piston press to form rods with a diameter of about 10 mm. The extrusion speed and the extrusion pressure were varied in a range of between 8 and 40 bar (pressure) and between 1 and 3 mm/s (speed). The influence of the extrusion speed on the total solar reflectance of the final product seems to be insignificant while the extrusion pressure and the moisture of the extrusion mixture significantly influence the product quality. The solar reflectance of the roofing granules increases with increasing moisture of the extrusion mixture and decreasing extrusion pressure.

The green bodies obtained from extrusion were sintered at different temperatures between 1200 °C and 1500 °C. It was found that the total solar reflectance of the final product increases with decreasing sintering temperature. However, because the hardness is another important criterion for roofing granules, a minimum sintering temperature is necessary to reach the desired hardness of at least 3.5 Mohs. Thus, sintering temperatures between 1200 °C and 1350 °C were usually used for sampling. Different sintering cycles were tested. For all samples, a long cycle with a run-time of 55 to 68 hours (depending on the sintering peak temperature) yields the desired high total solar reflectance.

After sintering, the rods were crushed and sieved to form roofing granule fractions having a particle size distribution of 0.5 mm to 3.0 mm. Various fractions with different particle size distributions has been investigated with the result that the finer the particle size the higher is the total solar reflection of the final roofing granules.

The total solar reflectance (TSR) of the final roofing granules may be measured using any relevant commercially available instrument, such as D&S Reflectometer, Model SSR-ER (Devices & Services Company), and by following the instrument

manufacturer's instructions. For example, TSR may be measured in accordance with ASTM C1549-09. The total solar reflectance indicates the portion of incident solar radiation reflected by the roofing granules. The extent to which solar radiation effects surface temperatures depends on the solar reflectance of the exposed surface. A total solar reflectance of 1 .00 would mean that 100% is reflected and no effect on surface temperature is observed while a total solar reflectance of 0.00 (none reflected) would result in the maximum absorption.

Within the present works, it was found that the open porosity and the pores size play an important role for obtaining high solar reflectance. The explanation may be that internal pores scatter incident light enhancing therewith the solar reflectance. As usual, the porosity is determined by mercury intrusion porosimetry while the pore size is determined by optical measurements of SEM-images of polished sections of respective roofing granules.

Aging of untreated aluminosilicate based roofing granules usually results in a significant reduction of the total solar reflectance. In this context, a reduction of more than 20% was observed within 21 days for uncoated materials. Such deactivating may be prevented by coating the granules with a hydrophobic substance, for example, silane or siloxane. In some preferred embodiments, the amount of hydrophobic coating relative to the weight of the calcined granule may comprise about 1 % by weight silane or siloxane. Suitable silanes or siloxanes are disclosed in WO 2015/1 12590 A1 which is incorporated herein by reference.

While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the detailed description and the following exemplary selected samples. Accordingly, the drawings and the detailed examples are to be regarded as illustrative in nature and not restrictive.

Examples

The examples summarized in table 2 were produced using the raw materials described in table 1 . Firstly, the clays were milled by means of a ball mill to obtain a starting material having an average particle size dso of about 2.7 μηι. Subsequently, the clays were moistened with 30.6 wt.-% water. The moistened mixtures were extruded using a piston press to obtain strands having a diameter of 10 mm. The green bodies such obtained were sintered at different temperatures using sintering cycles of about 55 to 68 hours. After sintering, the rod-like sintered bodies were crushed and screened to obtain sintered roofing granules having a particle size distribution of 0.5 to 2.5 mm.

Porosity, average pore size, Mohs hardness, total solar reflectance (TSR), mineralogical composition, and chemical composition of the sintered refractory roofing granules were measured and the results are summarized in tables 2 to 4.

Table 2

As evident from table 2, the total solar reflectance decreases with increasing sintering temperature. Also the open porosity decreases with increasing sintering temperatures. Simultaneously, the hardness of the roofing granules increases. The higher the hardness the better is the abrasion resistance of the roofing granules. A Mohs hardness of at least 3.5 is sufficient to comply with the actual requirements of the market. Thus, it can be summarized that all the above granules fulfill the requirements with respect to hardness.

The Mohs hardness was measured according to the SC-T-7-method. Starting with the number nine mineral in the Mohs Hardness Kit, the mineral aggregate being tested will be scratched and visually inspected for a scratch mark made by the Mohs mineral. If this mark cannot be rubbed off, the number eight mineral has to be used and the procedure has to be repeated. Continuing in descending order of the other minerals until a mineral is found that the scratch on the surface of the aggregate rubs off. The number of the stone that allows the scratch to be rubbed off will be the Mohs Hardness Scale Value.

Table 3

Example Mineralogical Composition (wt.-%)

Mullite Quartz Cristobalite Amorphous Others

1 56 4 0 40 0

1 ^* 58 1 2 39 0

2 74 0 6 18 2

2^* 72 0 2 25 1

3 63 1 8 27 1

3^* 61 0 2 37 0

4 49 1 1 41 8

4^* 47 0 0 46 7

5 66 1 15 16 2

5^* 64 0 8 27 1

6 64 1 1 1 23 1

6^* 63 1 5 31 0

7 68 1 19 1 1 1

7^* 65 0 8 27 0

8 66 1 14 18 1 8^* 65 0 9 22 1

9 61 1 9 28 1

9^* 61 0 4 35 0

Generally, for environmental reasons, quartz and cristobalite are undesired components of roofing granules. However, an increased amount of cristobalite may not be too critical as far as there are no airborne particles in the final product.

Likewise fibrous silicates, such as asbestoform minerals, should be absent. From the above table 3 it is evident that the amount of cristobalite decreases with increasing temperature, indicating that the amount of cristobalite may be reduced by increasing temperature if necessary. However, it has to be assumed that in this case the total solar reflectance will simultaneously decrease.

Table 4

Table 4 shows the chemical compositions of the sintered refractory roofing granules. The chemical composition is affected by the fact that no flux is used for the manufacturing process. Some general interrelations of the most important parameters used for the production and the product quality are additionally illustrated by means of the enclosed figures.

Figure 1 is a bar graph illustrating the relationship between the total solar reflectance (TSR) and the sintering temperature. In this specific case, the total solar reflectance decreases from 84 to 45 with increasing sintering temperature from 1200°C to 1500°C. However, this strong decline is rather anomalous. As evident from table 2, the total solar reflectance of the most investigated samples is still more than 0.75 even up to sintering temperatures of 1400°C. The above example was selected because of its strong decline clearly showing the influence of the sintering

temperature to the total solar reflectance. In this special case, CCTP was used as mineral source.

Figure 2 is a bar graph illustrating the relationship between the total solar reflectance (TSR), the open porosity and the sintering temperature. A sample based on CCTP as mineral source was sintered at different temperatures between 1250°C and 1400°C. The open porosity was measured by mercury intrusion porosimetry. Similar to figure 1 , the total solar reflectance decreases with increasing temperature. Additionally, the graph shows that the open porosity simultaneously decreases with increasing temperature.

The relationship between open porosity and the total solar reflectance is furthermore illustrated in figure 3 which is a bar graph illustrating the direct relationship between the total solar reflectance (TSR) and the open porosity at defined temperature.

Different samples were sintered at 1300°C. The respective mineral sources are specified in parentheses behind the porosity values. Particularly, the different CCTP- samples make evident that the total solar reflectance increases with increasing open porosity independent from the sintering temperature. Figure 4 is a bar graph illustrating the relationship between the total solar reflectance and the particle size distribution. It is obvious that the fine fractions perform better than the coarse ones. An explanation for this effect may be that the surface is better covered with granules having fines. In this case there may be less or smaller voids between the particles. Also in this case, CCTP was used as mineral source. However, with regard to the above summarized relationships between the total solar reflectance and the open porosity, it has to be considered that finally the 3-year aged reflectance is the critical value for the suitability the roofing granules. The 3-year aged reflectance depends on further parameters which are subject matter of subsequent investigations. For example, it was found in line with some preliminary investigations that - contrary to the above described relationships - the 3 year-aged solar reflectance of roofing material may decrease with increasing open porosity of the roofing granules.

Claims

1 . Sintered refractory roofing granules formed from a mixture comprising at least one ceramic-forming clay, wherein said mixture does not comprise any additional sinter material nor flux, said roofing granules having a chemical composition comprising, in percentages by weight:

and a mineralogical composition comprising, in percentages by weight:

- 45% to 65% mullite;

- less than 4.5% quartz;

- less than 10% cristobalite; and

- 20% to 50% amorphous phases,

wherein said roofing granules have an open porosity of at most 35% per volume and an average pore diameter of less than 0.75 μηι.

2. The roofing granules according to claim 1 ,

wherein the roofing granules have a total solar reflectance (TSR) of at least 0.75.

3. The roofing granules according to claim 1 or 2,

wherein the chemical composition comprises between 0.01 % and 3.0% by weight K2O.

4. The roofing granules according to any preceding claims,

wherein the mineralogical composition comprises less than 5% by weight, preferably less than 3% by weight, cristobalite.

5. The roofing granules according to any preceding claims,

wherein the roofing granules have an open porosity of at most 20% per volume, preferably at most 15% per volume.

6. The roofing granules according to any preceding claims, wherein the roofing granules have an average pore diameter of less than 0.5 μηπ, preferably less than 0.3 μηι.

7. The roofing granules according to any preceding claims,

wherein the roofing granules have a Mohs hardness of at least 3.5, preferably at least 5.0.

8. The roofing granules according to any preceding claims,

wherein the roofing granules are coated with a hydrophobic coating.

9. The roofing granules according to any preceding claim,

wherein the roofing granules are suitable for obtaining a subsequent roofing product having a 3-year aged reflectance of at least 0.65, preferably at least 0.70, in conformance to Low-Slope Energy Star® standards.

10. A method of making sintered refractory roofing granules, comprising the steps:

- milling a base clay to obtain a starting material having an average particle size dso of less than 10 μηπ;

- moistening the pure clay or a respective blend of pure clays by adding between 20% and 35% by weight of water;

- sintering the green bodies in a temperature range between 1200°C and 1500°C; and

- crushing and screening the sintered bodies to form granules having a particle size between 0.5 and 3 mm,

whereby the roofing granules are manufactured without using any sinter material or flux.

1 1 . A method according to claim 10, whereby the roofing granules are

subsequently coated with a hydrophobic coating.