US20080277617A1

US20080277617A1 - Granular Fibre-Free Microporous Thermal Insulation Material and Method

Info

Publication number: US20080277617A1
Application number: US11/885,718
Authority: US
Inventors: Oras Khalid Abdul-Kader; Mark Daniel Mortimer; Takashi Yamamuro
Original assignee: Microtherm Ltd
Current assignee: Microtherm Ltd
Priority date: 2005-03-15
Filing date: 2005-11-23
Publication date: 2008-11-13
Also published as: GB0505270D0; WO2006097668A1; EP1858823A1; CN101128404A; CA2595785A1; JP2008533402A; KR20070112472A

Abstract

A granular fibre-free microporous thermal insulation material, having a thermal conductivity less than 0.05 W/mK and a shrinkage of not more than 10%, which is free flowing and consists of granules of an intimate mixture of: 30-95% dry weight microporous insulating material; 5-70% dry weight infrared opacifier material; 0-50% particulate insulating filler material; and 0-5% binder material. The material is made by mixing together the microporous insulating material and the infrared opacifier material to form an intimate aerated mixture with a first density; conveying the intimate mixture at a first volumetric flow rate to an extrusion means (5); extruding the intimate mixture as a compressed material with a second density greater than the first density at a second volumetric flow rate lower than the first volumetric flow rate; venting a proportion of air from the aerated intimate mixture through a porous membrane to relieve pressure generated within the intimate mixture due to the change from the first volumetric flow rate to the second volumetric flow rate; and granulating the compressed material.

Description

The present invention relates to granular fibre-free microporous thermal insulation material. The invention also relates to a method of manufacturing granular fibre-free microporous thermal insulation material.
The term “microporous” is used herein to define porous or cellular materials in which the ultimate size of the cells or voids is less than the mean free path of an air molecule at NTP, i.e. of the order of 100 nm or smaller. A material which is microporous in this sense will exhibit very low transfer of heat by air conduction (that is, collisions between air molecules). Such microporous materials can be obtained from controlled precipitation from solution, the temperature and pH being controlled during precipitation to obtain an open lattice precipitate. Other equivalent open lattice structures include pyrogenic (fumed) and electro-thermal types in which a substantial proportion of the particles have an ultimate particle size less than 100 nm. Any of these materials, based for example on silica, alumina or other metal oxides, may be used to prepare a composition which is microporous as defined above.
In order to provide insulation for certain high temperature applications which restrict the use of sheets or blocks of insulating material (for example pipe-in-pipe insulation, such as for exhaust pipe systems, furnace cavities, double skin linings, areas over arched roofs, open joints and for levelling furnace bottoms and hearths) loose filled thermal insulation material can be used.
In order for loose filled thermal insulation material to be efficient, it is necessary for the insulation material to be relatively free flowing such that the individual pieces of insulation material do not undergo cohesion and bridge across gaps. Pieces of free flowing thermal insulation material need to be able to move past each other to enable the insulation material to settle into the most dense packing arrangement possible and thus avoid uninsulated areas being formed. Granulation is well known to make materials made from fine particles flow relatively more easily.
Sheets or blocks of microporous insulation materials are known to have substantially superior thermal conductivity properties than other insulation materials due to the size of the voids as described hereinbefore.
Granular insulations contain relatively large voids (greater than microporous voids as defined hereinbefore) between successive granular pieces of the insulation which causes the thermal conductivity of the granular material to be high relative to large continuous bodies of comparable insulation. As such, granular microporous thermal insulation materials are not generally available as any thermal insulation advantage gained by the individual granules of microporous insulation having the microporous voids is lost due to the large voids between the granules. The large voids in granular microporous thermal insulations are caused in part by the presence of reinforcing fibres within the granules. The fibres make the granules “hairy” and as such the ability to close pack the granules is reduced.
Granular microporous aerogel materials are known, for example grade IN01 beads from Cabot sold under the registered trademark NANOGEL. However, such thermal insulation materials undergo relatively high shrinkage on heating. For example the height of the NANOGEL granular aerogel material within a crucible, measured before and after heating for 24 hours, decreases by 12 percent following heating at 600 degrees Celsius and by 24 percent following heating at 800 degrees Celsius.
Granular forms of non-microporous thermal insulation material with good free flowing properties are known.
Vermiculite granules, for example exfoliated fine grade vermiculite supplied by Skamol of Denmark, have a relatively high thermal conductivity at a density of nominally 150 to 180 kg/m³, for example 0.105 W/mK at a mean temperature of 200 degrees Celsius and 0.145 W/mK at a mean temperature of 400 degrees Celsius.
Other forms of granular free flowing thermal insulation material are based on granulated mixtures of clay and calcined diatomaceous earth, for example Moler 05 aggregate supplied by Skamol of Denmark. These insulation materials also have relatively high thermal conductivity, for example 0.2 W/mK at a mean temperature of 200 degrees Celsius.
It is an object of the present invention to provide a granular fibre-free microporous thermal insulation material, and a method of manufacture thereof, which is free flowing, resistant to high temperatures and which has relatively low thermal conductivity.
According to one aspect of the present invention there is provided a granular fibre-free microporous thermal insulation material, having a thermal conductivity less than 0.05 W/mK and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from an intimate mixture of:

- 30-95% dry weight microporous insulating material,
- 5-70% dry weight infrared opacifier material,
- 0-50% particulate insulating filler material, and
- 0-5% binder material.

According to another aspect of the present invention there is provided a method of manufacturing a granular fibre-free microporous thermal insulation material, having a thermal conductivity of less than 0.05 W/mK and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from a mixture of 30-95% dry weight microporous insulating material, 5-70% dry weight infrared opacifier material, 0-50% particulate insulating filler material, and 0-5% binder material comprising the steps of:

- mixing together the microporous insulating material and the infrared opacifier material to form an intimate aerated mixture with a first density;
- conveying the intimate mixture at a first volumetric flow rate to an extrusion means;
- extruding the intimate mixture as a compressed material with a second density greater than the first density at a second volumetric flow rate lower than the first volumetric flow rate;
- venting a proportion of air from the aerated intimate mixture through a porous membrane to relieve pressure generated within the intimate mixture due to the change from the first volumetric flow rate to the second volumetric flow rate; and
- granulating the compressed material.

The first volumetric flow rate may be in a range from 2.0 to 4.5 times the second volumetric flow rate.
The first volumetric flow rate may be in a range from 100 to 300 litres/hour, preferably in a range from 125 to 280 litres/hour.
The second volumetric flow rate may be in a range from 20 to 90 litres/hour, preferably in a range from 25 to 90 litres/hour.
The intimate mixture may be screw conveyed to the extrusion means.
The intimate aerated mixture may be extruded by at least one roller, preferably a pair of opposing rollers.
A pressure in a range from 2.5 to 20 bar, preferably in a range from substantially 5 to substantially 10 bar, may be exerted on the intimate aerated mixture.
The porous membrane may be metallic and may have pores with nominal diameters in a range from 5 to 50 microns, preferably substantially 15 microns.
The compressed material may be in the form of a sheet of compressed material.
The compressed material may be broken up into smaller pieces prior to being granulated, for example by rotary chopping.
Granulation of the compressed material may include the step of forcing material through apertures in a mesh, preferably a metal mesh, using a rotor.
The granular fibre-free microporous thermal insulation material may have substantially the following composition:

- 40-85% dry weight microporous insulating material,
- 15-60% dry weight infrared opacifier material,
- 0-50% particulate insulating filler material, and
- 0-5% binder material.

The granule size of the granular fibre-free microporous thermal insulation material may be in a range from 0.25 mm to 2.5 mm.
The bulk density of the granular fibre-free microporous thermal insulation material may be in a range from 180 to 350 kg/m³.
The tap density of the granular fibre-free microporous thermal insulation material may be in a range from 250 to 450 kg/m³.
The opacifier material may be selected from titanium dioxide, iron titanium oxide, zirconium silicate, zirconium oxide, iron oxide, silicon carbide, and mixtures thereof.
The microporous insulating material may comprise silica, for example fumed and/or precipitated silica.
The fumed silica may have a BET specific surface area in a range from 180 m²/g to 230 m²/g, more preferably nominally 200 m²/g.
The fumed silica may have a hydrophobic surface treatment.
The particulate insulating filler material may be selected from vermiculite, perlite, flyash, volatilised silica, and mixtures thereof.
The binder may be an organic binder, for example polyvinylalcohol, or may be an inorganic binder, for example selected from sodium silicate, potassium silicate, aluminium orthophosphate, and mixtures thereof.
For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made to the following examples, and to FIG. 1 which is a schematic illustration of a method of producing a granular fibre-free microporous thermal insulation material in accordance with the present invention.

EXAMPLE 1

A series of three granular fibre-free microporous thermal insulation materials (Mix Nos. 1 to 3) were made by mixing together a mixture of nominally 60% dry weight of a microporous insulating material in the form of fumed silica material available from Degussa AG under the Registered Trade Mark AEROSIL A200, and 40% dry weight of infrared opacifier in the form of rutile (titanium dioxide), available from Eggerding Group, Amsterdam to form intimate, homogenous aerated mixtures. The aerated mixes had a bulk density of 80 kg/m³.
The fumed silica had a nominal (BET) specific surface area of 200 m²/g. The opacifier material had a nominal particle size such that 100% of the material passed through a 9 micron sieve.
As illustrated in FIG. 1, each aerated mixture 2 formed in a mixer 4 was introduced into a feed hopper 1 of a roller compactor apparatus 3, for example a model FR compactor available from Turbo Kogyo Co. Ltd. of Japan.
The roller compactor apparatus 3 comprised the feed hopper 1, an extrusion means in the form of a pair of opposed compression rollers 5, and screw conveyor means 7 for moving each mixture from the hopper to the compression rollers. The walls of the screw conveyor means were provided with metallic porous membranes having pores with nominal diameters approximately 15 microns.
The roller compactor apparatus also comprised a rotary chopper 9 and a granulator 11.
Each mixture was fed through a rotary valve (not shown) from the hopper 1 to the screw conveyor means 7. The screw conveyor means 7 conveyed each mixture at a first volumetric flow rate to the roller (shown in Table 1 hereinafter).
The screw conveyed mixtures were passed through the pair of compression rollers. Each roller rotated about a substantially horizontal axis and the rollers were arranged such that one roller was positioned parallel to, and vertically above, the other. The rollers were separated by a gap of nominally 1 mm. The pressure generated by the rollers on the mixtures was selected to be either 5, 10 or 20 bar. The passage of each mixture from the hopper through the gap between the rollers resulted in the mixtures being densified, compressed and extruded in the form of substantially planar sheets of compressed thermal insulation material. The densified materials exited the rollers at the second volumetric flow rates shown in Table 1.

TABLE 1

		First	Second	Ratio of
	Roller	volumetric	volumetric	First to
Mix	Pressure	flow rate	flow rate	Second flow
No.	(bar)	(litres/hour)	(litres/hour)	rate

1	5	275	87	3.2:1
2	10	275	79	3.5:1
3	20	225	55	4.1:1

The action of the compression rollers on the mixtures caused the air present within the aerated mixtures to be forced out of the mixtures, potentially increasing the air pressure within the screw conveyor means. The potential increase in pressure in the screw conveyor means was substantially prevented by means of the porous membranes provided in the walls which allowed air to be vented out of the screw conveyor means.
Each planar sheet of compressed thermal insulation material was then passed from the rollers 5, via deflecting means 15, through the rotary chopper 9 in which blades 17 provided on the rotary chopper 9 caused the compressed material to be broken up into smaller pieces with a nominal diameter in a range from 2 to 5 mm and a nominal thickness of 1 mm.
The smaller pieces of each thermal insulation material were passed into the granulator 11. The granulator comprised a metal screen mesh 19 and a rotor 21 positioned relative to the screen mesh. The screen mesh had a nominal aperture size of 2.5 mm. The relative motion of the rotor to the screen mesh caused the broken pieces of each thermal insulation material provided between the rotor and the mesh to be forced though apertures of the mesh to produce granular fibre-free microporous thermal insulation material. Each granular fibre-free microporous thermal insulation material 25 was retained in a collecting means 23. A sieve was used to remove granules of collected granular fibre-free microporous thermal insulation material with a nominal size of less than 0.6 mm.
The granule size of each of the granular fibre-free microporous thermal insulation materials was measured by sieve analysis, as known to a person skilled in the art. The range of granule size for each mix was from 0.25 mm to 2.5 mm.
Granular fibre-free microporous thermal insulation materials with a granule size of less than 0.6 mm were detected by the sieve analysis as the granules of the materials underwent some break up due to handling and the process of the sieve analysis itself.
The bulk density of each of the granular fibre-free microporous thermal insulation materials was measured using apparatus known to a person skilled in the art. The bulk densities are shown in Table 2 hereinafter.
The tap density (otherwise known as the optimally settled density) of each of the granular fibre-free microporous thermal insulation materials was determined by repeat tapping of a known mass of a sample of each of the insulation materials in a container of predetermined volume using an automated tapping machine, known to a person skilled in the art, until the density of each of the materials underwent no further change. The density at which no further change occurred following continued tapping corresponded to the tap density of the material. The measured tap density of each of the granular fibre-free microporous thermal insulation materials is shown in Table 2 below.
Each granular fibre-free microporous thermal insulation material was tested for thermal conductivity at a mean temperature of 400 degrees Celsius and at the tap density of the material, as determined by the above method, using cylindrical cell thermal conductivity methods as known by a person skilled in the art and as described in European Fuel Cell News, volume 8, number 2, July 2001. The results are shown in Table 2 below.
The effect of temperature on each of the granular fibre-free microporous thermal insulation materials was also tested. A straight sided alumina crucible was filled with a granular fibre-free microporous thermal insulation material. Vibration was applied to the crucible during the filling to produce a substantially consistent packing density of the granular fibre-free microporous thermal insulation material within the crucible. The granular fibre-free microporous thermal insulation material was then heated at nominally 900 degrees Celsius for 24 hours. The height of the granular fibre-free microporous thermal insulation material within the crucible was measured before and after heating and the percentage difference in height was noted (see Table 2 below).
A negative value for the change in height indicates that the height of the granular fibre-free microporous thermal insulation material within the crucible after heating was less than the height before heating.

TABLE 2

				Change in
				height of
	Bulk	Tap	Thermal	heated
Mix	Density	Density	Conductivity	material
No.	(kg/m³)	(kg/m³)	(W/mK)	(Percent)

1	253	350	0.0387	−1.4
2	277	406	0.0418	−1.8
3	325	450	0.0473	−1.6

EXAMPLE 2

Two granular fibre-free microporous thermal insulation materials (Mix Nos. 4 and 5) were made by mixing together mixtures of the microporous insulating material and infrared opacifier described in Example 1.
Mix 4 was made by mixing together a mixture of nominally 50% dry weight of the microporous insulating material and 50% dry weight of infrared opacifier.
Mix 5 was made by mixing together a mixture of nominally 40% dry weight of the microporous insulating material and 60% dry weight of infrared opacifier.
Each mix was mixed to form an intimate, homogenous aerated mixture. The aerated mixes had a bulk density of 80 kg/m³.
The mixes were introduced into the roller compactor apparatus as described in Example 1 to produce granular fibre-free microporous thermal insulation materials essentially as described in Example 1.
The mixtures were conveyed by the screw conveyor 7 to the roller at the volumetric flow rates shown in Table 3.
The pressure generated by the rollers on the mixtures was bar.
The densified material exited the rollers at the volumetric flow rates shown in Table 3.

TABLE 3

		First	Second	Ratio of
	Roller	volumetric	volumetric	First to
Mix	Pressure	flow rate	flow rate	Second flow
No.	(bar)	(litres/hour)	(litres/hour)	rate

4	5	275	82	3.4:1
5	5	188	59	3.2:1

The bulk density, tap density, thermal conductivity and effect of temperature were determined and measured as described in Example 1.

TABLE 4

				Change in
				height of
	Bulk	Tap	Thermal	heated
Mix	Density	Density	Conductivity	material
No.	(kg/m³)	(kg/m³)	(W/mK)	(Percent)

4	269	390	0.0357	−1.8
5	256	420	0.0373	−1.7

EXAMPLE 3

A granular fibre-free microporous thermal insulation material (Mix No. 6) was made by mixing together a mixture of nominally 85% dry weight of a microporous insulating material, as described in Example 1, and 15% dry weight of infrared opacifier in the form of silicon carbide, grade F1200D, available from ESK of Germany to form an intimate, homogenous aerated mixture. The aerated mix had a bulk density of 80 kg/m³.
The mix was introduced into the roller compactor apparatus as described in Example 1 to produce a granular fibre-free microporous thermal insulation material essentially as described in Example 1.
The mixture was conveyed by the screw conveyor 7 to the roller at a volumetric flow rate of 125 litres/hour.
The pressure generated by the rollers on the mixture was 5 bar.
The densified material exited the rollers at a volumetric flow rate of 56 litres/hour. Consequently the ratio of first to second volumetric flow rates was 2.2:1.
The bulk density of the granular fibre-free microporous thermal insulation material was measured to be 180 kg/m³.
The tap density of the granular fibre-free microporous thermal insulation material was determined, as described in Example 1, to be 250 kg/m³.
The granular fibre-free microporous thermal insulation material was tested for thermal conductivity as described in Example 1 and measured to be 0.0374 W/mK.
The effect of temperature on the granular fibre-free microporous thermal insulation material was also tested as described in Example 1. The percentage change in height of material following heating at nominally 900 degrees Celsius for 24 hours was −1.6 percent.

EXAMPLE 4

A granular fibre-free microporous thermal insulation material (Mix No. 7) was made by mixing together a mixture of nominally 35% dry weight of a microporous insulating material, as described in Example 1, 25% dry weight of a microporous insulating material in the form of a hydrophobic fumed silica material available from Degussa AG under the Registered Trade Mark AEROSIL R974 and 40% dry weight of infrared opacifier, as described in Example 1, to form an intimate, homogenous aerated mixture. The aerated mix had a bulk density of 80 kg/m³.
The mix was introduced into the roller compactor apparatus as described in Example 1 to produce a granular fibre-free microporous thermal insulation material essentially as described in Example 1.
The mixture was conveyed by the screw conveyor 7 to the roller at a volumetric flow rate of 188 litres/hour.
The pressure generated by the rollers on the mixture was 5 bar.
The densified material exited the rollers at a volumetric flow rate of 54 litres/hour. Consequently the ratio of first to second volumetric flow rates was 3.5:1.
The bulk density of the granular fibre-free microporous thermal insulation material was measured to be 276 kg/m³. The tap density of the granular fibre-free microporous thermal insulation material was determined, as described in Example 1, to be 420 kg/m³.
The granular fibre-free microporous thermal insulation material was tested for thermal conductivity as described in Example 1 and measured to be 0.0337 W/mK.
The effect of temperature on the granular fibre-free microporous thermal insulation material was also tested as described in Example 1. The percentage change in height of material following heating at nominally 900 degrees Celsius for 24 hours was −1.3 percent.

EXAMPLE 5

Two granular fibre-free microporous thermal insulation materials (Mix Nos. 8 and 9) were made by mixing together mixtures of the microporous insulating material and infrared opacifier described in Example 1 along with a particulate insulating filler material in the form of micron grade exfoliated vermiculite available from Hoben International.
Mix 8 was made by mixing together a mixture of nominally 57.5% dry weight of the microporous insulating material, 37.5% dry weight of infrared opacifier and 5% dry weight of vermiculite.
Mix 9 was made by mixing together a mixture of nominally 55% dry weight of the microporous insulating material, 35% dry weight of infrared opacifier and 10% dry weight of vermiculite.
Each mix was mixed to form an intimate, homogenous aerated mixture. The aerated mixes had a bulk density of 80 kg/m³.
The mixes were introduced into the roller compactor apparatus as described in Example 1 to produce granular fibre-free microporous thermal insulation materials essentially as described in Example 1.
The mixtures were conveyed by the screw conveyor 7 to the roller at the volumetric flow rates shown in Table 5.
The pressure generated by the rollers on the mixtures was 5 bar.
The densified material exited the rollers at the volumetric flow rates shown in Table 5.

TABLE 5

		First	Second	Ratio of
	Roller	volumetric	volumetric	First to
Mix	Pressure	flow rate	flow rate	Second flow
No.	(bar)	(litres/hour)	(litres/hour)	rate

8	5	188	65	2.9:1
9	5	200	66	3.0:1

TABLE 6

				Change in
				height of
	Bulk	Tap	Thermal	heated
Mix	Density	Density	Conductivity	material
No.	(kg/m³)	(kg/m³)	(W/mK)	(Percent)

8	230	335	0.0382	3.0
9	242	342	0.0372	5.0

It was noted that with the addition of vermiculite, the height of the granular fibre-free microporous thermal insulation materials made from Mix Nos. 8 and 9 increased following heating at nominally 900 degrees Celsius for 24 hours. The expansion of a granular fibre-free microporous thermal insulation material on heating has the beneficial effect of causing the insulation to more adequately fill any potential spaces within an area to be insulated which could provide a through-path for heat.

EXAMPLE 6

A granular fibre-free microporous thermal insulation material (Mix No. 10) was made by mixing together a mixture of nominally 48% dry weight of a microporous insulating material, 12% dry weight of a particulate insulating filler material in the form of a volatilised silica material, grade VAW, available from RW Fuller of Germany Degussa AG and 40% dry weight of infrared opacifier to form an intimate, homogenous aerated mixture.
The microporous insulating material and the infrared opacifier were as described in Example 1.
The aerated mix had a bulk density of 80 kg/m³.
The mix was introduced into the roller compactor apparatus as described in Example 1 to produce a granular fibre-free microporous thermal insulation material essentially as described in Example 1.
The mixture was conveyed by the screw conveyor 7 to the roller at a volumetric flow rate of 250 litres/hour.
The pressure generated by the rollers on the mixture was 5 bar.
The densified material exited the rollers at a volumetric flow rate of 70 litres/hour. Consequently the ratio of first to second volumetric flow rates was 3.6:1.
The bulk density of the granular fibre-free microporous thermal insulation material was measured to be 286 kg/m³.
The tap density of the granular fibre-free microporous thermal insulation material was determined, as described in Example 1, to be 395 kg/m³.
The granular fibre-free microporous thermal insulation material was tested for thermal conductivity as described in Example 1 and measured to be 0.0397 W/mK.
The effect of temperature on the granular fibre-free microporous thermal insulation material was also tested as described in Example 1. The percentage change in height of material following heating at nominally 900 degrees Celsius for 24 hours was −5.5 percent.

EXAMPLE 7

A granular fibre-free microporous thermal insulation material (Mix No. 11) was made by mixing together a mixture of nominally 48% dry weight of a microporous insulating material (described in Example 1), 12% dry weight of a microporous insulating material in the form of a precipitated silica material, grade LS500, available from Degussa AG and 40% dry weight of infrared opacifier (described in Example 1) to form an intimate, homogenous aerated mixture. The aerated mix had a bulk density of 80 kg/m³.
The mix was introduced into the roller compactor apparatus as described in Example 1 to produce a granular fibre-free microporous thermal insulation material essentially as described in Example 1.
The mixture was conveyed by the screw conveyor 7 to the roller at a volumetric flow rate of 238 litres/hour.
The pressure generated by the rollers on the mixture was 5 bar.
The densified material exited the rollers at a volumetric flow rate of 69 litres/hour. Consequently the ratio of first to second volumetric flow rates was 3.4:1
The bulk density of the granular fibre-free microporous thermal insulation material was measured to be 276 kg/m³.
The tap density of the granular fibre-free microporous thermal insulation material was determined, as described in Example 1, to be 380 kg/m³.
The granular fibre-free microporous thermal insulation material was tested for thermal conductivity as described in Example 1 and measured to be 0.0405 W/mK.
The effect of temperature on the granular fibre-free microporous thermal insulation material was also tested as described in Example 1. The percentage change in height of material following heating at nominally 900 degrees Celsius for 24 hours was −7.1 percent.
Granular fibre-free microporous thermal insulation material according to the present invention has been described in which the infrared opacifier material is either rutile (titanium dioxide) or silicon carbide. It should be appreciated that the infrared opacifier material could also be selected from other suitable materials, for example iron titanium oxide (for example ilmenite or leucoxene), zirconium silicate (zircon), zirconium oxide (zirconia), iron oxide (for example hematite), and mixtures thereof.
The fumed silica can have a specific surface area in a range from 50 m²/g to 400 m²/g, preferably in a range from 180 m²/g to 230 m²/g.
In addition to the compositions described in the examples, it should be appreciated that granular fibre-free microporous thermal insulation material in accordance with the present invention could consist of fumed silica material in a range from 30 to 95% dry weight, infrared opacifier in a range from 5 to 70% dry weight, particulate insulating filler material in a range from 0 to 50% dry weight, and binder material in a range from 0 to 5% dry weight.
The binder can be an organic binder, for example polyvinylalcohol, or can be an inorganic binder, for example sodium silicate, potassium silicate and/or aluminium orthophosphate.
Although Example 5 describes the addition of a particulate insulating filler material in the form of vermiculite, it should be appreciated that the particulate insulating filler material could be perlite, flyash and/or volatilised silica (otherwise known as arc silica or silica fume).
The bulk density of granular fibre-free microporous thermal insulation material in accordance with the present invention can be in a range from 180 to 350 kg/m³.
The tap density of the granular fibre-free microporous thermal insulation material can be in a range from 250 to 450 kg/m³.
Although the examples have described the use of a roller compactor apparatus, it should be appreciated that any apparatus which enables air to be vented from an aerated mixture to provide a compressed material which is granulated can be used.
Although the examples describe the extrusion means of the roller compactor apparatus exerting a pressure on the intimate aerated mixture in a range from 5 to 20 bar, it should be appreciated that a pressure in a range from 2.5 to 20 bar could be applied. The preferred range of pressure is from substantially 5 to substantially 10 bar.
Although the diameters of the pores of the porous membrane are described as being approximately 15 micron, it should be appreciated that the pores could have diameters in a range from 5 to 50 micron.
It should be appreciated that the first volumetric flow rate can be in a range from 2.0 to 4.5 times the second volumetric flow rate. The first volumetric flow rate can be in a range from 100 to 300 litres/hour, preferably in a range from 125 to 280 litres/hour. The second volumetric flow rate can be in a range from 25 to 90 litres/hour, preferably in a range from 50 to 90 litres/hour.
Although in the examples the means of compacting the material is described as a pair of opposed rollers, it should be appreciated that other compression means can be used, for example compression between a single roller and a substantially flat substrate or between a pair of substantially parallel compression faces.
The compacted material has been described as being in sheet form. It should be appreciated that the compacted material used to form the granular fibre-free microporous thermal insulation can be of other laminar forms, for example strips.
Although a rotary chopper has been described in the examples to break up the compressed material prior to granulation, it should be appreciated that other means, for example slicing means, could be used to break up the material. It should also be appreciated that the compressed material can be fed directly into the granulator without first being broken up into smaller pieces.
Granular fibre-free microporous thermal insulation made in accordance with the present application has a thermal conductivity which is considerably lower than vermiculite or granulated mixtures of clay and calcined diatomaceous earth.
At a mean temperature of 400 degrees Celsius, granular fibre-free microporous thermal insulation in accordance with the present invention has a thermal conductivity lower than expanded vermiculite at its tap density.
Granular fibre-free microporous thermal insulation made in accordance with the present application has a height shrinkage which is considerably lower than granular microporous aerogel materials.

Claims

1. A granular fibre-free microporous thermal insulation material, having a thermal conductivity less than 0.05 W/mK, when measured at a mean temperature of 400 degrees Celsius and at the tap density of the material, and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from an intimate mixture of:

30-95% dry weight microporous insulating material;

5-70% dry weight infrared opacifier material;

0-50% particulate insulating filler material; and

0-5% binder material.

2. A thermal insulation material as claimed in claim 1, wherein the thermal insulation material has substantially the following composition:

40-85% dry weight microporous insulating material;

15-60% dry weight infrared opacifier material;

0-50% particulate insulating filler material; and 0-5% binder material.

3. A thermal insulation material as claimed in claim 1, wherein a granule size of the granular fibre-free microporous thermal insulation material is in a range from 0.25 mm to 2.5 mm.

4. A thermal insulation material as claimed in claim 1, wherein a bulk density of the granular fibre-free microporous thermal insulation material is in a range from 180 to 350 kg/m³.

5. A thermal insulation material as claimed in claim 1, wherein the tap density of the granular fibre-free microporous thermal insulation material is in a range from 250 to 450 kg/m³.

6. A thermal insulation material as claimed in claim 1, wherein the opacifier material is selected from titanium dioxide, iron titanium oxide, zirconium silicate, zirconium oxide, iron oxide, silicon carbide, and mixtures thereof.

7. A thermal insulation material as claimed in claim 1, wherein the microporous insulating material comprises silica.

8.-12. (canceled)

13. A thermal insulation material as claimed in claim 1, wherein the particulate insulating filler material is selected from vermiculite, perlite, flyash, volatilised silica, and mixtures thereof.

14. A thermal insulation material as claimed in claim 1, wherein the binder comprises an organic binder.

15. A thermal insulation material as claimed in claim 14, wherein the organic binder comprises polyvinylalcohol.

16. A thermal insulation material as claimed in claim 1, wherein the binder comprises an inorganic binder.

17. A thermal insulation material as claimed in claim 16, wherein the inorganic binder is selected from sodium silicate, potassium silicate, aluminium orthophosphate, and mixtures thereof.

18. A method of manufacturing a granular fibre-free microporous thermal insulation material, having a thermal conductivity of less than 0.05 W/mK, when measured at a mean temperature of 400 degrees Celsius and at the tap density of the material, and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from a mixture of 30-95% dry weight microporous insulating material, 5-70% dry weight infrared opacifier material, 0-50% particulate insulating filler material, and 0-5% binder material comprising the steps of:

mixing together the microporous insulating material and the infrared opacifier material to form an intimate aerated mixture with a first density;

conveying the intimate mixture at a first volumetric flow rate to an extrusion means (5);

extruding the intimate mixture as a compressed material with a second density greater than the first density at a second volumetric flow rate lower than the first volumetric flow rate;

venting a proportion of air from the aerated intimate mixture through a porous membrane to relieve pressure generated within the intimate mixture due to the change from the first volumetric flow rate to the second volumetric flow rate; and

granulating the compressed material.

19. A method according to claim 18, wherein the first volumetric flow rate is in a range from 2.0 to 4.5 times the second volumetric flow rate.

20. A method according to claim 18, wherein the first volumetric flow rate is in a range from 100 to 300 litres/hour.

21. (canceled)

22. A method according to claim 18, wherein the second volumetric flow rate is in a range from 20 to 90 litres/hour.

23. (canceled)

24. A method according to claim 18, wherein the method includes the step of conveying the intimate mixture to the extrusion means (5) by means of a screw conveyor (7).

25. A method according to claim 18, wherein the method includes the step of extruding the intimate aerated mixture by at least one roller (5).

26. A method according to claim 25, wherein the intimate aerated mixture is extruded by a pair of opposing rollers (5).

27. A method according to claim 18, wherein a pressure in a range from 2.5 to 20 bar is exerted to extrude the intimate aerated mixture.

28. (canceled)

29. A method according to claim 18, wherein the porous membrane is metallic and has pores with nominal diameters in a range from 5 to 50 microns.

30. (canceled)

31. A method according to claim 18, wherein the compressed material is in the form of a sheet of compressed material.

32. A method according to claim 18 and including the step of breaking up the compressed material into smaller pieces prior to granulation.

33. A method according to claim 32, wherein the compressed material is broken up by rotary chopping.

34. A method according to 18, wherein granulation of the compressed material includes the step of forcing material through apertures in a mesh (19) using a rotor (9).

35.-51. (canceled)