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Insulation Composition

This invention relates to an insulation composition in the form of a paste and including an aerogel. The invention further relates to a method of forming such a paste and to the application of such a paste to a substrate to provide thermal insulation, s

Many insulation composites are known to incorporate aerogels in order to provide optimum thermal conductivity ratings. Aerogel has an extremely low density, which results in low thermal conductivity. The use of aerogel as an insulator tends to be restricted to certain solid forms, such as in aerogel blankets and aerogel boards. This type of product can be difficult to apply, particularly to uneven and non-planar substrates and results in wastage.

Efforts have been made to produce aerogel-based insulation compositions in spray forms; one such aerogel insulation composition is described in European Patent No. EP1515796. This patent covers the use of aqueous binders and the mixing of aerogel. Aerogel insulation pastes have also been produced. There are difficulties in applying existing aerogel insulation composites externally to substrates as they tend to be too soft and thus friable and, following application to a substrate, disintegrate when exposed to water. To gain a lower thermal conductivity the amount of aerogel has to be increased or the binder reduced, both of which have been found to reduce the mechanical strength of the combined product.

Efforts to address the softness and water resiliency issues by mixing an aerogel insulation paste with render or plaster causes dilution of the aerogel and thus an increase in the thermal conductivity rating of the product.

In view of the above, it would be advantageous to produce an aerogel paste which can be applied to a substrate and which has increased strength once dried with greater resistance to water and without compromise on thermal conductivity.

It is a principal aim of the present invention to provide an insulation composition that addresses at least one of the above-identified problems.

According to a first aspect of this invention, there is provided an insulation composition in the form of a paste that will harden after application, the paste comprising: a binder, an aerogel and a hardener, wherein the dispersion of the aerogel within the paste is such that the paste has a thermal conductivity of 30mW/m2k or below.

Any suitable aerogel can be used in conjunction with the invention. Suitable aerogels are commercially available, and methods for preparing such aerogels are well known. The aerogel may be a supercritically dried aerogel (SCDA) as this may provide an even lower thermal conductivity than standard aerogels. The use of a SCDA may result in a paste having a very low thermal conductivity, possibly as low as 20mW/m2k.

It should be appreciated that hardening of the paste after application occurs due to natural drying of the paste, in a similar way that paint dries after application, rather than any additional curing process; additional drying processes could however be used and this would not depart from the present invention.

The composition, after drying, will have a thermal conductivity of about

30mW/m2k or less. The composition is preferably formulated so as to have a density of about 180-190 kg/m3, or less, after drying. Preferably, the density of the paste is not substantially different to the density of the aerogel prior to mixing. The aerogel, prior to mixing, may have a density of approximately 180-190 kg/m3 or preferably even less. The aerogel particles may be spherical in shape with an average particle diameter within the range 1 mm - 5mm.

Preferably, the binder comprises an aqueous binder. Any suitable aqueous binder or combination of binders can be used in conjunction with the invention, for example, acrylic binders, silicone-containing binders, phenolic binders, vinyl acetate binders, ethylene-vinyl acetate binders, styrene-acrylate binders, styrene-butadiene binders, polyvinyl alcohol binders, and polyvinylchloride binders, and acrylamide binders, as well as mixtures and copolymers thereof. The term aqueous binder, as used herein, refers to a binder that, prior to being dried, is water-dispersible or water-soluble. Preferably the aqueous binder is an aqueous acrylic binder. Suitable aqueous acrylic binders are commercially available, for example WorleeCryl CH-X 2158 or WorleeCryl CH-X 2159™ (manufactured by Worlee-Chemie GmbH).

The binder can be used alone or in combination with suitable cross-linking agents. Various types of suitable crosslinking agents are commercially available, including, for example, WorleeAdd 8905 Alkaline ZnO solution (manufactured by Worlee-Chemie GmbH).

The binder preferably further comprises a foaming agent. The foaming agent serves to assist binding of the aerogel with the binder. The foaming agent produces a generally foamed product, thus ensuring that the density of the composition is low; this assists with the maintenance of a low thermal conductivity rating when the binder and aerogel are mixed. Any suitable foaming agent can be used in the insulation composition. Suitable foaming agents include, but are not limited to, foam-enhancing surfactants (e.g., non-ionic, cationic, anionic, and zwitterionic surfactants), as well as other commercially available foam enhancing agents, or mixtures thereof. Many types of suitable foaming agents are commercially available; one such example is Hostapur ® which is marketed as having a low tendency to build up viscosity. The foaming agent should be present in an amount sufficient to enable the aqueous binder to be slightly foamed.

The binder may further comprise strengthening fibres. The strengthening fibres may provide additional mechanical strength to the insulation composition. The fibres can be a suitable length for example between 1 - 3 mm. Fibres of any suitable type can be used, but preferably, the strengthening material is chopped glass fibres. Fibres of any suitable type can be used, such as fiberglass, alumina, calcium phosphate mineral wool, wollastonite, ceramic, cellulose, carbon, cotton, polyamide, polybenzimidazole, polyaramid, acrylic, phenolic, polyester, polyethylene, PEEK, polypropylene, and other types of polyolefins, or mixtures thereof. Preferred fibres are heat and fire resistant, as are fibres that do not have respirable pieces. The fibres also can be of a type that reflects infrared radiation, such as carbon fibres, metallized fibres, or fibres of other suitable infrared-reflecting materials.

The hardener advantageously ensures that the paste, when dried, produces a structurally stable product, which is not soft or friable. Surprisingly, and unexpectedly, the Applicant's have discovered that the presence of a hardener also serves to protect the paste from water damage; in effect the

hardener protects the binder from breaking down when submerged in water or other liquid. This result is a remarkable breakthrough in the industry. The hardener may be a single component added to the paste. The mixing of a single component hardener with the paste will initiate a curing process resulting in hardening of the paste. As such, preferably, the hardener comprises two components, a resin and an activator. Generally, the resin may be mixed with the paste initially and then packaged and supplied separately to the activator. In this way, the activator may be added to the paste immediately prior to the application process to avoid premature hardening of the paste. The hardener may comprise a water based epoxy coating, such as that supplied by Antel Limited.

A proportional increase in the amount of aerogel in the composition will cause the thermal conductivity of the composition to decrease, thereby resulting in highly desirable insulation characteristics. However, with increased proportions of aerogel the mechanical strength and integrity of the composition decreases; this is as a result of the relative amount of binder used. Similarly, a proportional increase in the amount of binder results in a decrease in the proportion of aerogel and thus an increase in the thermal conductivity of the composition. It is thus, desirable to use as little of the binder as needed to attain a desired amount of mechanical strength whilst maintaining a good thermal conductivity rating. Accordingly, the insulation composition preferably comprises the following components:

56%-59% by weight of binder;

35%-38% by weight of aerogel;

5%-7% of by weight of hardener.

Even more preferably, the insulation composition comprises the following components:

56.34%-58.3% by weight of binder;

35.87%-37.56% by weight of aerogel;

5.83%-6.1 % by weight of hardener.

As discussed above, the hardener may comprise two parts, namely a resin and an activator. Preferably, the hardener comprises between 76% - 77% resin

and between 23%-24% activator. Even more preferably, the hardener comprises 76.92% resin and 23.08% activator. The binder may comprise a range of components, in addition to the acrylic binder, such as foaming agent, water and/or strengthening material. Preferably, the binder comprises the following components:

61 %-67% by weight of acrylic binder;

3%-5% by weight of foaming agent;

1 1 %-13% by weight of water;

1 1 %-13% by weight of strengthening material;

3%-5% by weight of flame retardant;

0%-3% by weight of crosslinker; and

0%-3% by weight of pigment.

Even more preferably, the binder comprises the following components:

61 .54%-66.66% by weight of acrylic binder;

3.85%-4.17% by weight of foaming agent;

1 1 .53%-12.5% by weight of water;

1 1 .53%-12.5% by weight of strengthening material;

3.85%-4.17% by weight of flame retardant;

0%-3.85% by weight of crosslinker; and

0%-3.85% by weight of pigment.

The insulation composition may include a flame retardant to enable use of the composition under high temperature conditions. Suitable flame retardants are commercially available and include, for example WorleeAdd FR5000™ (manufactured by Worlee-Chemie GmbH). The values indicated above may be adjusted to enable an increase in the quantity of flame retardant, depending on the flame retardant requirements of the intended application. This may be achieved by adjusting the quantity of other components within the binder.

The binder, aerogel and hardener can be combined by any suitable method to form a composition in the form of a paste, which then can be applied to a substrate by spreading on the substrate. It is important that the method used does not compromise the final thermal conductivity properties of the paste. Accordingly, in a second but related aspect of this invention, there is provided a method for forming an insulation composition, in the form of a paste, the method comprising the following sequential steps:

a) mixing a binder with a foaming agent to form a foamed product; b) mixing the foamed product with an aerogel and water to form a paste; and

c) mixing the paste with a hardener.

The binder may be an acrylic binder and may be used in combination with a cross-linking agent and, in this case, step a) of the method further comprises mixing a crosslinker with the binder and foaming agent.

To increase the mechanical strength of the insulation composition and/or to provide flame retardant properties, in step a) of the method a strengthening material and/or a flame retardant may be mixed with the acrylic binder and foaming agent.

The mixing of the paste with a hardener may be achieved in a two-step process involving the introduction of a resin and an activator. In this way, step c) may comprise the following sequential steps:

ci. mixing the paste with a resin; and

cii. mixing the combined paste and resin with an activator.

Following step ci, the paste with mixed resin may be packaged for supply such that a purchaser of the product may be provided with the paste and the activator as separate products. When the paste is to be applied to a substrate, step cii may be carried out, to ensure that hardening of the paste occurs shortly thereafter. The introduction of the hardener ensures that the fully dried paste remains intact once submerged in water or if water simply contacts the dried paste. The introduction of the resin and activator prevents the binder from being affected by the introduction of water and thus provides a water-resistant paste.

In order to provide a visual indication of sufficient mixing, in a preferred arrangement, a pigment may be added to the mix in one more of steps a), b) or c). The pigment may be, for example a coloured pigment added to the mix to ensure that sufficient mixing has been effected.

The time taken to mix the components and the speed of mixing may have an influence on the density of the final paste product and thus on the consistency of the paste and the resultant thermal conductivity rating. It has been identified that, if mixed too vigorously and/or for too long, over volumizing of the paste occurs; this results in much lower levels of aerogel density and an increased thermal conductivity. Obviously, the time taken to mix and the speed of mixing will depend on the quantity of the components used to form the paste. An example defining the mixing time and speed for a set of particular quantities of components is discussed hereinafter and it will be appreciated that the skilled person should be able to manipulate this information to account for larger and smaller scales with relative ease.

As an example, a suitable selection and quantity of components appropriate for producing an insulation composition according to the present invention is shown in the table below:

A method of forming an insulation composition of the present invention using the above components and quantities will now be discussed.

The method may comprise a first step (step a) involving the mixing of the following components: the acrylic binder, the strengthening fibres, the foaming agent, the flame retardant, the H2O and optionally, the crosslinker. A pigment may also optionally be included in the mix in order to obtain a visual indication that full mixing has occurred. The components are mixed in step a) for 60

seconds with a mechanical mixer at around 95 - 140 rpm to provide a base binder which has a generally creamy consistency.

The next step (step b) requires the base binder to be mixed with the aerogel for 60 seconds at a lower revolution to produce a paste. The mixing may be carried out by hand or with a mixer at approximately 60-80 rpm to ensure full mixing of the aerogel. Next, in step ci. the resin is added to the paste and mixed by hand or with a mixer at approximately 60 - 80 rpm for 120 seconds. A pigment may be included with the mix, along with the resin or the resin may be pigmented to provide a visual indication of sufficient mixing.

The final step, step cii, may be carried out immediately prior to application of the paste to a surface. In step cii. the activator is added to the mixture and mixed by hand or with a mechanical mixer at 60 - 80 rpm for a period of 120 seconds. As with the resin, the activator may be pigmented or a coloured pigment may be applied to the mix with the activator in order to provide confirmation that the activator is fully combined with the paste.

The paste of the present invention is ideally suitable as an insulation composition for use in the building industry, though it is not limited to such use. Indeed, the insulation composition can be used for all industries and applications, including for example shipping or automotive industries. Preferably, the insulation composition, is used by mixing the paste with the activator and then immediately applying the paste to a substrate by spreading on the substrate; and then allowing the paste to dry. The drying of the paste may be carried out naturally at room temperature. The time taken fully to cure may vary depending on the quantity of paste applied and the ambient conditions such as air temperature. The paste discussed in the above method would take approximately 5 to 7 days at room temperature. The substrate to which the paste is to be applied may be any surface which requires insulative properties and this surface may need to be prepared in order to receive the paste.

The present invention provides an insulation composition which allows for the mixing of aerogel to a paste, addresses the softness and water resiliency issues of the prior art whilst also maintaining a low thermal conductivity rating.