WO2014184393A1

WO2014184393A1 - Insulation panels

Info

Publication number: WO2014184393A1
Application number: PCT/EP2014/060270
Authority: WO
Inventors: Victor BAILY; Davide DEI SANTI; Frederic Gubbels
Original assignee: Dow Corning Corporation
Priority date: 2013-05-17
Filing date: 2014-05-19
Publication date: 2014-11-20
Also published as: GB201309061D0

Abstract

Vacuum insulation panels (VIPs), their manufacture and utilisation in insulation applications with the VIPs having an insulation panel core composition, comprising (a) 40 to 93 weight (wt) % of fumed silica, silica aerogel or a mixture thereof, (b) 5 to 50 wt % of particles having a specific surface area, determined by the BET method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, talc fly ash, light weight aggregates, vermiculite, mica, ash, aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash, shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicon containing materials, aluminium powder, or any combination thereof, (c) 1 to 15 wt % of fibres, (d) 1 to 20 wt % of an opacifier, with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

Description

INSULATION PANELS

[0001] This relates to vacuum insulation panels (VIPs), their manufacture and utilisation in insulation applications.

[0002] The need for increasing the efficiency of thermal insulation in a wide variety of applications, such as construction in both new buildings and existing buildings as well as thermal insulation in the mobile, logistics and stationary sectors is becoming increasingly important because of the need for sustainable development and the increasing cost of energy, increasingly scarce resources and the desire to reduce C0₂ emissions.

[0003] A wide variety of thermal insulation materials have historically been used. These include, for example, organic insulation materials, such as foamed plastics, e.g.

polystyrene, polyurethane; wood fibre materials, such as wood wool and cork; vegetable or animal fibres, such as hemp, flax and/or wool; inorganic thermal insulation materials, such as mineral wool, glass wool, foamed glass, calcium silicate boards and gypsum

plasterboards; and mineral foams, such as porous concrete, pumice, perlite and

vermiculite. These conventional thermal insulation materials are mostly used in the form of foamed or pressed boards and mouldings. Thus, it is possible, for example, to introduce polyurethanes and polystyrenes as foams directly into hollow spaces in buildings.

However, these materials alone are not sufficiently effective in their provision of thermal insulation for today's increasingly demanding requirements as, for example; their thermal conductivities are all above 0.020 W/mK at room temperature.

[0004] Far superior insulation properties than the above are displayed by vacuum insulation panels (VIPs) which are effectively a core insulating material such as

polystyrene, polyurethane and/or silica enveloped in an air-tight filmic casing, e.g. a metal (aluminium) foil or a metalized plastic film which panel is evacuated by vacuum. These panels have a significantly lower thermal conductivity of from about 0.004 to 0.008 W/mK at room temperature (depending on the core material and the level of reduced pressure) and therefore provide significantly better thermal insulation than the aforementioned conventional thermal insulation systems resulting in the ability to be provided in

comparatively slimmer units (because of their improved thermal insulation).

[0005] As indicated above, the thermal conductivity value of the insulation materials used are significant with the lower the thermal conductivity value the lower the heat flow (energy) through the insulation material at any given temperature difference. Typically heat transfer in insulation occurs as a result of the sum of three components:

(i) solid phase conduction,

(ii) gas phase conduction and

(iii) radiation. [0006] Solid phase conduction is generally minimized by using a low-density material (e.g. a material comprising a high volume fraction of pores). Most insulation is between 80% and 98% porous. It is also advantageous to use a solid material that has a low inherent thermal conductivity (e.g. plastics and some ceramics/glasses are better than metals).

[0007] With control of radiation, use of low thermal conductivity materials and a highly porous solid matrix, the thermal conductivity of an insulation material approaches that of the gas contained within the pores of the insulation. There are at least two methods of lowering gas phase conduction in insulation, these are:-

(i) Trapping gases having a lower thermal conductivity than air (e.g. argon, carbon

dioxide, xenon and krypton) in the pores.

The thermal conductivity of insulation filled with such an inert gas may range from 0.009 to 0.018 W/mK at room temperature, dependent on the gas selected/utilised. In such cases, it is essential to select suitable gas-tight wrapping materials to prevent both the selected gas from leaking out of the pores and atmospheric gases (e.g. nitrogen, oxygen) being introduced into the insulation;

(ii) Reliance on the Knudsen effect.

Generally, gases transfer heat when gas molecules collide with each other. The mean free path of a particular gas is the average distance between collisions for the molecules of the gas. The Knudsen effect occurs when a gas is trapped within insulation which has a pore size approximately equal to or smaller than the mean free path of the gas molecules. When the mean free path of the gas approaches the pore size of the insulation, the gas phase conductivity is dramatically reduced. However, when the mean free path is much larger than the pore size, the gas phase conductivity approaches zero and the total effective thermal conductivity is the sum of only radiation and solid phase conduction. For example, the mean free path of air is approximately 60 nm at ambient temperature and pressure while the pore/cell size of polymer foams and fibrous materials are often greater than 10 μηι. In this situation it will be appreciated that the Knudsen effect cannot occur if such polymer foams and fibrous materials are used with air at or near ambient temperature and pressure.

[0008] However, a VIP system can utilise the Knudsen effect to lower gas phase conduction by encapsulating an insulation material within a barrier envelope and creating a partial vacuum in the insulation within the barrier envelope once sealed. This increases the mean free path of the gas by lowering the gas density which, in turn, lowers gas phase conduction. Hence VIP systems can achieve thermal conductivity values of less than 0.002 W/mK at ambient temperatures, which is an order of magnitude improvement over conventional insulation. Hence, the thermal insulation efficiency of evacuated microporous panels is a factor 5 to 10 higher than atmospheric panels.

[0009] US4159359 provides insulating materials having low thermal conductivity formed from pyrogenic (fumed) silica, precipitated silicas and silica aerogels which are formed into compacted panels wrapped in an air-tight skin. A low conductivity gas is provided in the system to replace air/nitrogen.

[0010] Currently, the two main core compositions utilised for core compositions in VIP systems are glass fibre based and/or silica based VIPs. The former have an average 15 year life time and are principally used in appliance to insulate refrigerators. The latter have a > 25 year life time and can be used in insulation of buildings.

[0011 ] There is provided herein a VIP panel core composition, comprising

(a) 40 to 93 weight (wt) % of fumed silica or silica aerogel,

(b) 5 to 50 wt % of particles having a specific surface area, determined by the BET

method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, talc fly ash, light weight aggregates, vermiculite, mica, ash, , aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash, shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicon containing materials, aluminium powder, or any combination thereof

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

[0012] In one embodiment the VIP panel core composition, consists of

(a) 40 to 93 wt % of fumed silica or silica aerogel,

method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, talc, fly ash, light weight aggregates, vermiculite, mica, ash, , aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicone materials, aluminium powder, or any combination thereof

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %. [0013] In another embodiment of the invention there is provided a VIP panel comprising a panel core composition as hereinbefore described in a vacuum inside a filmic barrier envelope.

[0014] For the avoidance of doubt:

In Component (a) - Fumed silica (sometimes referred to as pyrogenic silica), CAS Registry Number: 1 12945-52-5, is produced in a flame from the flame pyrolysis of silicon

tetrachloride or quartz sand vaporised in a high temperature (e.g. 3000 °C) electric arc. During the preparation process molten spheres of fumed silica (primary particles) collide and fuse with one another to form into branched chain-like 3-D particles (secondary particles), typically referred to as aggregates. As the aggregates cool below the fusion temperature of silica further collisions occur resulting in the formation of tertiary particles (agglomerates) which agglomerate. The resulting fumed silica powder has a particle size of from 5 to 50 nm, has an extremely low bulk density (35.00 to 40.00 kg/m³ e.g. about 36.85 kg/m³) and a high surface area of 50-600 m²/g. The particles are substantially non-porous.

[0015] Also in component (a) are silica aerogels, CAS Registry Number: 308075-23-2. A silica aerogel is a synthetic porous ultralight material derived from silica gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density (e.g. from 0.001 - 0.5 g cm^"3) and thermal conductivity of from 0.03 W/m K down to 0.004 W/rn- K. Silica aerogels are composed of silica nanoparticles which are interconnected in a complex framework, typically dependent on the chemistry used to prepare the aerogel precursor gel (e.g. via a base-catalyzed alkoxide sol-gel process which can produce for example nano-sized primary particles of silica 2-50 nm in diameter). These primary particles are then agglomerated into spherical secondary particles 50 - 2000 nm in diameter which are then, in turn, connected together in strands. However, in silica aerogels produced via acid-catalyzed sol-gel processes, the smaller primary particles tend not to agglomerate into secondary particles which can result in, e.g. a leaf like morphology.

[0016] Component (b) - particles having a specific surface area, determined by the BET method, of less than or equal to 100m²/g, alternatively less than or equal to 50 m²/g, alternatively less than or equal to 30 m²/g selected from clay, kaolin, metakaolin, talc, fly ash, light weight aggregates, vermiculite, mica, ash, aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ashes including perlite, pumice, shirasu balloons and zeolites, microsilica, geothermal silica, silicone materials, aluminium powder, or any combination thereof. In one embodiment component (b) may be microsilica. [0017] For the avoidance of doubt it is to be understood that any reference to microsilica herein is referring to the particulate form of silica (otherwise known as "Silica fume"), (CAS number 69012-64-2). Microsilica is an amorphous (non)crystalline polymorph of silica which is an ultrafine powder collected as a by product in the carbothermic reduction of high-purity quartz with carbonaceous materials in electric arc furnaces in the production of silicon and ferrosilicon alloys. Microsilica is an ultrafine material of spherical particles with an average particle diameter of 150 nm, a typical specific gravity of about 2.25 and a specific surface area in the range of from about 15,000 to about 30,000 m²/ kg and a densified bulk density of from 600 - 750 kg/m³ and an undensified bulk density of from 175 to 350 kg/m³.

[0018] Component (a) is typically present in an amount of 40 to 93 wt % of (a) + (b) + (c) + (d), alternatively from 40 to 85 wt % of (a) + (b) + (c) + (d), alternatively 40 to 75 wt % of (a) + (b) + (c) + (d), alternatively from 50 to 75 wt % of (a) + (b) + (c) + (d), given the total of (a) + (b) + (c) + (d) is 100 wt % in each instance.

[0019] Component (b) is typically present in an amount of 5 to 50 wt % of (a) + (b) + (c) + (d), alternatively from 10 to 50 wt % of (a) + (b) + (c) + (d), alternatively 20 to 50 wt % of (a) + (b) + (c) + (d), alternatively from 25 to 50 wt % of (a) + (b) + (c) + (d), given the total of (a) + (b) + (c) + (d) is 100 wt % in each instance.

[0020] Other essential ingredients in the core composition are:

Fibres as indicated as Component (c). The fibres which are utilised are used to provide reinforcement or strengthening, i.e. for mechanical reinforcement. These fibres can be of inorganic or organic origin. Examples of inorganic fibres are preferably glass wool, rock wool, basalt fibres, slag wool and ceramic fibres composed of melts of aluminium and/or silicon dioxide and also further inorganic metal oxides. Pure silicon dioxide fibres are, for example, silica fibres. Examples of organic fibres include polyester fibres and/or cellulosic, textile fibres or synthetic polymer fibres or any combination thereof. In one embodiment organic fibres are utilised, for example cellulosic fibres such as viscose fibres. Component (c) is typically present in an amount of from 1 to 15 wt % of (a) + (b) + (c) + (d),

alternatively from 1 to 10 wt % of (a) + (b) + (c) + (d), alternatively 1 to 7 wt % of (a) + (b) + (c) + (d), given the total of (a) + (b) + (c) + (d) is 100 wt % in each instance. Such fibres are all available commercially.

[0021] Component (d) is one or more infrared opacifiers, compounds which can absorb, scatter and reflect thermal radiation in the infrared range. These opacifiers preferably have a maximum absorption in the range of preferably from 1 .5 to 10 m in the infrared spectral range. The particle size of these particles is preferably in the range 0.5-15 μηι. Examples of such substances are preferably titanium oxides, zirconium oxides, ilmenites, iron titanates, iron oxides, zirconium silicates, silicon carbide, manganese oxides and carbon black or any combination thereof. In one embodiment silicon carbide is utilised as the opacifier. Component (d) is typically present in an amount of from 1 to 20 wt % of (a) + (b) + (c) + (d), alternatively from 1 to 15 wt % of (a) + (b) + (c) + (d), alternatively 2 to 12 wt % of (a) + (b) + (c) + (d), given the total of (a) + (b) + (c) + (d) is 100 wt % in each instance. Component (d) is available commercially.

[0022] It is generally recognized that the silica microstructure plays a significant role on the thermal insulation properties. The Brunauer-Emmet-Teller (BET) technique is commonly used in the powder industry to measure the specific surface area of solids. It is

demonstrated that a highly structured silica, i.e. having a high specific surface area measured by the BET method will improve thermal insulation properties in a VIP. It can be seen within this disclosure that the addition of a silica having low specific surface area measured by the BET method (ca 20 m²/g) i.e. microsilica in substitution for a silica having a high specific surface area measured by the BET method (300 m²/g) e.g. fumed silica or silica aerogel is leading to equivalent and in some cases better thermal insulation properties, which is totally unexpected. Besides the thermal insulation gain, the use of silica having a low specific surface area measured by the BET significantly reduces the raw material costs over the use of silica having a high specific surface area measured by the BET method silica.

[0023] Optional ingredients may be introduced into the composition if desired these may include, for example, one or more desiccants and/or one or more hydrophobing agents. Any suitable commercially available desiccants and hydrophobing agents, flocculants, thickeners, plasticizers, forming agents, polymeric resin emulsions or any combination thereof may be utilised if required. These may be added to the mixture in an amount of up to 10% by weight of the total weight of (a) + (b) + (c) + (d).

[0024] In one preferred embodiment there is provided herein a VIP panel core composition, comprising

(a) 40 to 75 wt % of fumed silica, silica aerogel or any combination thereof

(b) 10 to 50 wt % of particles having a specific surface area, determined by the BET

method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, , talc, fly ash, light weight aggregates, vermiculite, mica, ash, aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates,

microspheres, volcano ash shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicone materials, aluminium powder, or any combination thereof (c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier, and

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

[0025] In one alternative of the above, component (b) comprises and/or consists of microsilica, zeolite or calcium carbonate or any combination thereof and/or component (c) comprises and/or consists of cellulosic fibres in particular viscose fibres and/or component (d) comprises or consists of silicon carbide.

[0026] In an alternative embodiment there is provided herein a VIP panel core composition, comprising

(a) 50 to 75 wt % of fumed silica , silica aerogel or any combination thereof

method, of less than or equal to 100m²/g selected from clay, kaol'n, metakaolin, , talc, fly ash, light weight aggregates, vermiculite, mica, ash, aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicone materials, aluminium powder, or any combination thereof

(c) 1 to 15 wt % of fibres, ,

(d) 1 to 20 wt % of an opacifier, preferably composed of silicon carbide, and

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

[0027] In one alternative of the above component (b) comprises and/or consists of microsilica, zeolite or calcium carbonate or any combination thereof and/or component (c) comprises and/or consists of cellulosic fibres e.g. viscose fibres and/or component (d) comprises or consists of silicon carbide.

[0028] In order to form a vacuum insulated panel the core material is placed into a suitable filmic barrier envelope and the envelope is sealed and evacuated. Typically the filmic barrier envelope is moisture impermeable and/or substantially gas impermeable and can comprise or consist of a metallised film or a multi-layered laminate of metalised films, such as a metallized polyester or polyethylene terephthalate (PET) films. The filmic barrier envelope can be thermoplastic to facilitate heat-sealing of the core composition within said filmic barrier envelope after evacuation via a suitable vacuum means. Typically the filmic barrier envelope is sealed excepting an entrance to allow insertion of the core material. Once the core material has been inserted into the envelope said entrance is sealed and the filmic barrier envelope is evacuated. [0029] Often one or more inner liners or bags may be utilised intermediate between the core composition as hereinbefore described and the filmic barrier envelope. The inner liner may be made of polyolefin, polyester or glass fibres. The inner liner(s) may function as oxygen barrier(s) (e.g. containing cross-linked polyvinyl alcohol ("PVOH")).

[0030] The inner liner can be a plastic film and the plastic film can comprise a plastic material that is different than the filmic barrier envelope. The or each inner liner can also be thicker than the filmic barrier envelope. For example, an inner liner can have a thickness of at least about 0.025 mm but typically not greater than about 1 mm, and more preferably at least about 0.05 mm and not greater than about 0.5 mm. In one aspect, the inner liner can be a film of material such as polystyrene or polypropylene.

[0031] According to one aspect, the filmic barrier envelope can be evacuated via any appropriate method to a pressure of not greater than about 100 millibars (100 x 10⁵mPa), such as not greater than about 10 millibars (10 x 10⁵mPa), preferably lower than 5 millibars (5 x 10⁵mPa).

[0032] According to another embodiment, a method for making a vacuum insulation panel is provided which involves the following steps:-.

(A) mixing the constituents of the core material composition as hereinbefore described and (if required) pressing said mixture into a panel or shaped article;

(B) if required inserting the panel or shaped article resulting from step A into an inner liner

(C) if required, drying the panel or shaped article resulting from step (A) or (B) to reduce moisture content

(D) Insertion of the panel or shaped article resulting from step (A), (B) or (C) into a filmic barrier envelope

(E) evacuating and sealing the filmic barrier envelope to form a vacuum insulation panel.

[0033] The aforementioned vacuum insulation panels have a thermal conductivity of from 0.003 to 0.008 W/mK at room temperature when evacuated.

[0034] The vacuum insulated panels as hereinbefore described are typically used in the construction of new buildings and for insulating pre-existing buildings as insulation in refrigeration appliances and for insulation of pipes and/or machines in industry.

Examples

[0035] All samples of vacuum insulated panels (VIPs) utilised in the following examples were prepared in the following manner:

The fibres have been predispersed with a dynamic mixer (IKA RW 20) to facilitate their dispersion in the powders. The VIP core components were weighed out and in each instance were then introduced into a 20 litre pail in order to reach a total weight of 420g. Five stainless steel balls of dimension 17.5 mm diameter were added to each pail to facilitate fibre dispersion. The pail was closed with a standard lid and then placed in a Collomix^® biaxial mixer and shaken for 8 minutes. 302 g of the resulting core composition mixture was weighed and poured into a 300 x 300 mm² mold and progressively compressed until a thickness of 20 mm was achieved. The pressure was then released slowly over a period of 5 minutes.

The resulting panel or shaped article was then packaged in an inner liner in the form of biaxial oriented polyethylene films. The resulting product was then heated at 160^QC for 5 s and subsequently dried in a chamber at 100^QC for a period of 3 days.

[0036] Two Hanita^® MF3 metalized films (V08621 B) were placed on top of each other with their respective polyethylene side facing each other (i.e. facing inwardly). Two edges of the films were then sealed together at a temperature of about 140^QC for 6 sec, to form a filmic barrier envelope sized to be able to receive the compressed mixed core composition wrapped in biaxial oriented polyethylene film. The compressed mixed core composition wrapped in biaxial oriented polyethylene film was then placed inside envelope and was subsequently sealed at the third edge.

[0037] The filmic barrier envelope containing the compressed mixed core composition wrapped in biaxial oriented polyethylene film was evacuated using a VAC^® Company vacuum apparatus (HVV90500). The last edge of the envelope was heat sealed when the pressure applied in the chamber reached a value below 0.5 mbar (5 x 10⁴ mPa). Then the chamber was equilibrated at atmospheric pressure and the VIP was unloaded from the chamber.

[0038] A Heat Flow Meter Lasercomp^® Fox 314 was used to perform thermal conductivity measurements according to ISO 8301 : 1991 . A temperature of 0^QC on the upper plate and 20^QC at the lower plate was set until an equilibrium state is achieved. The thickness (s) of the sample was averaged from the 4 corners automatically by the equipment. The heat flow (q) at the upper and lower plate must be equal and is used in the following equation to measure the thermal conductivity (λ) of the sample,

λ = (q.s)/(A.AT).

in which

s= the average thickness of the panel

A= is the surface area of the panel, and

ΔΤ = temperature change (°C)

The error of measurement was estimated to about 4%.

[0039] Figure 1 depicts the increase in thermal conductivity of an unevacuated

compressed mixed core composition wrapped in biaxial oriented polyethylene film in a sealed envelope as discussed above. The composition comprised 3% by weight of silicon carbide (opacifier), 3% by weight of viscose fibres and a variable amount of microsilica substituting fumed silica (with the total weight % being equal to 100 wt% in each case). An increase of the atmospheric thermal conductivity is observed with the increase in microsilica content in the composition. This trend is expected from the current

interpretations of the Knudsen effect: as microsilica is denser and consists of spherical particles a more defined route for gases within the compressed composition is identified because of the gaps resulting from the spherical shape of the microsilica particles.

[0040] Figure 2 depicts the relationship between thermal conductivity (Y axis) of an evacuated (0.5 mbar (5 x 10⁴ mPa)) compressed mixed core composition wrapped in biaxial oriented polyethylene film in a sealed envelope as discussed above. The composition comprised 3% by weight of silicon carbide (opacifier), 3% by weight of fibres and a variable amount of microsilica substituting fumed silica (with the total weight % being equal to 100 wt% in each case). In the case of Figure 2 unexpectedly the thermal conductivity remains relatively constant (in the presence of polyester fibres and is actually seen to reduce with increasing amounts of microsilica when in the presence of viscose fibres. This behaviour is unexpected from current interpretations of the Knudsen effect.

[0041 ] Table 1 below details specific values of thermal conductivity for the specifically listed compositions and shows that the replacement of some of the fumed silica with microsilica, zeolite or calcium carbonate unexpectedly results in reduced thermal conductivities when rather than increasing the thermal conductivity values. The

composition values are given as % wt of the composition for each constituent.

Table 1

[0042] The Knudsen effect is actually due to the reduction of collisions in the gas due to its dilution. While pulling vacuum there is less gas molecules and therefore less collisions and finally less heat transfer from one side to another. Fumed silica is a highly structured particle, which is leading to a microporous core under compression. The average particle size of the pores is well below 1 μηι, which provides already a benefit in terms of atmospheric thermal insulation properties as the mean free path of the gas molecules (= path without collision) is about the size of the pores and already contributes to the excellent insulation properties of the core. From this point of view the microsilica does not contribute to increase the microporosity as it is a round shape particle. We actually see quite logically a significant increase of the thermal conductivity of the core at atmospheric pressure. It is then surprising to see that after evacuation we observe a reduction of thermal conductivity when microsilica, calcium carbonate and/or zeolite is present.

Claims

An insulation panel core composition, comprising

(a) 40 to 93 weight (wt) % of fumed silica, silica aerogel or a mixture thereof,

(b) 5 to 50 wt % of particles having a specific surface area, determined by the BET method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, talc fly ash, light weight aggregates, vermiculite, mica, ash, , aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash, shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicon containing materials, aluminium powder, or any combination thereof,

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

An insulation panel core composition in accordance with claim 1 consisting of

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

An insulation panel core composition in accordance with claim 1 or 2 characterised in that component (a) is present in the amount of from 40 to 85 wt % of (a) + (b) + (c) +

(d) or 40 to 75 wt % of (a) + (b) + (c) + (d) or from 50 to 75 wt % of (a) + (b) + (c) +

(d), given the total of (a) + (b) + (c) + (d) is 100 wt % in each instance.

An insulation panel core composition in accordance with any preceding claim characterised in that component (b) is typically present in an amount of from 10 to 50 wt % of (a) + (b) + (c) + (d), or from 20 to 50 wt % of (a) + (b) + (c) + (d), or from 25 to 50 wt % of (a) + (b) + (c) + (d), given the total of (a) + (b) + (c) + (d) is 100 wt %.

5. An insulation panel core composition in accordance with any of claims 1 , 2 or 3

comprising

(a) 40 to 75 wt % of fumed silica, silica aerogel or a mixture thereof,

(b) 25 to 50 wt % of particles having a specific surface area, determined by the BET method, of less than or equal to 100m²/g selected from clay, kaolin, metakaolin, talc fly ash, light weight aggregates, vermiculite, mica, ash, , aluminium oxide, alumina trihydrate, waterproofing agents, wollastonite, calcium carbonate, titanium dioxide, metal oxides pigments, colorants, diatomaceous earth and resins, plastic hollow materials, glass and ceramic materials, calcium silicate hydrates, microspheres, volcano ash, shirasu balloons and zeolites, microsilica, geothermal silica, particulate silicon containing materials, aluminium powder, or any combination thereof,

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

6. An insulation panel core composition in accordance with any of claims 1 , 2 or 3

comprising

(a) 50 to 75 wt % of fumed silica, silica aerogel or a mixture thereof,

(c) 1 to 15 wt % of fibres,

(d) 1 to 20 wt % of an opacifier,

with the sum of the constituents (a) + (b) + (c) + (d) being 100 wt %.

7. An insulation panel core composition in accordance with any preceding claim

characterised in that component (c) is selected from cellulosic fibres, polyester fibres or a mixture thereof.

8. An insulation panel core composition in accordance with claim 7 characterised in that the cellulosic fibres of component (c) are viscose fibres.

9. An insulation panel core composition in accordance with any preceding claim

characterised in that component (d) is silicon carbide.

10. An insulation panel core composition in accordance with any preceding claim

characterised in that component (b) is microsilica, zeolite, calcium carbonate or any combination thereof.

1 1 . A vacuum insulation panel comprising the insulation panel core composition of any preceding claim.

12. A method for making a vacuum insulation panel comprising the following steps:-.

(A) mixing the constituents of the insulation panel core composition in accordance with any one of claims 1 to 10 and (if required) pressing said mixture into a panel or shaped article;