Methods to produce gel sheets

TECHNICAL FIELD [0001] This invention relates to the continuous production of solvent filled gel sheets. Such gel sheets are used to make airgel layers, airgel composites, airgel monoliths or other airgel based products.

DESCRIPTION OF RELATED TECHNICAL BACKGROUND [0002] Aerogels are a class of material based on their structure, namely low-density structures with open pores, large surfaces (often 900 m²/ g or more) and with a subnanometer scale of pores. Supercritical and subcritical fluid extraction technologies are often used to extract fluid from delicate material cells. Many airgel compositions are known and may be inorganic or organic. Inorganic aerogels are generally based on metal alkoxides and contain materials such as silica, carbides and alumina. Organic aerogels include, but are not limited to, urethane aerogels, resorcinol-formaldehyde aerogels, and polyimide aerogels.

[0003] Low density airgel materials (0.01-0.3 g / cm³) are widely regarded as the best solid thermal insulators, better than the best rigid foams with a thermal conductivity of 10-15 mW / mK and less at 38 ° C (100 ° F) and atmospheric pressure. Aerogels act as heat insulators mainly by minimizing conduction (low density, winding path of heat transport through a solid nanostructure), convection (very small pore size limiting convection to a minimum), and radiation (IR absorbing or scattering admixtures are easily dispersed in an airgel matrix ). Depending on the composition, they can work well in the range from cryogenic temperature to 550 ° C and above. Airgel materials also have many other interesting acoustic, optical, mechanical and chemical properties that make them very useful.

[0004] Low density insulation materials have been developed to solve a number of thermal insulation problems in applications where core insulation experiences significant compressive forces. For example, polymeric materials have been combined with hollow glass microspheres to produce syntactic foams, which are usually very rigid and compressive. Syntactic materials are well known as insulators for underwater oil and gas pipes and for support equipment. Syntactic materials are relatively inelastic and have a high thermal conductivity compared to flexible airgel composites (fiber reinforced airgel matrices). Aerogels can be made from flexible gels precursors. Various flexible layers, including fiber-reinforced flexible aerogels, can easily be combined and shaped to form prefabricated components that, when mechanically compressed along one or more axes, form compression-resistant bodies along all these axes. Airgel bodies that are compressed in this way show significantly better thermal insulation values ​​than syntactic foams. Methods for the rapid production of these materials will facilitate the large-scale use of these materials in underwater oil and gas pipelines as external insulation.

[0005] Conventional methods for making gel sheets and / or fiber-reinforced composite gel sheets, using sol and gel chemistry, described in the patent and scientific literature invariably include batch casting. Batch casting is defined here as catalyzing one full volume of sol to induce gelation simultaneously in that volume. Gel forming techniques are well known to those skilled in the art: examples include adjusting the pH and / or temperature of the diluted metal oxide sol to the point where gelation occurs (RK Iler, Colloid Chemistry of Silica and Silicates, 1954, Chapter 6; RK Iler, The Chemistry of Silica, 1979, chapter 5, CJ Brinker and GW Scherer, Sol-Gel Science, 1990, chapter 2 and 3).

[0006] US Patent No. 6,088,882 (Ryu) discloses an example of a fiber reinforced aerogel composite material that can be implemented with embodiments of the present invention. Preferred precursor materials for an airgel composite are such as Cryogel^®, Pyrogel^®or Spaceloft^™ , sold commercially by Aspen Aerogels, Incorporated. U.S. Patent No. 5,306,555 (Ramamurthi et al.) Discloses an airgel matrix composite, an airgel with fibers dispersed in an airgel mass, and a method for producing an airgel matrix composite. WO 00/10789 A1 discloses a method of continuously casting a gradient or non-gradient electrophoretic gel plate comprising tubular cylindrical blocks that are emptied into nozzles that provide a gel solution for a primer passing between two belts, where the belts are sealed by pressure plates having UV transparent windows , wherein the gel solution is carried through the belts, passes through a UV light source that initiates gel polymerization. However, the boards produced are not continuous sheets. WO 02/052086 A2 discloses a batch process for producing aerogel composite materials having fluffy fibrous reinforcement in the form of a cotton sheet preferably in combination with one or both of individual short randomly oriented microfibers and conductive layers. However, this process is not continuous.

SUMMARY OF THE INVENTION [0007] According to claims 1 to 3 and 5, the present invention describes continuous and semi-continuous sol-gel casting methods that are significantly improved compared to conventional periodic sol-gel casting methods for gel sheets, fiber reinforced flexible gel sheets. and rolls of composite gel materials. [0008] In particular, the invention describes methods for continuously combining a solution with a low viscosity sol and an agent (thermal catalyst or chemical catalyst) that causes the formation of a gel sheet on a moving element, such as a conveyor belt with edges that determine the volume of the formed gel sheet by applying the catalyzed sol at a fixed speed to allow effective gelation on the moving element. The sol contains inorganic, organic, or a combination of hybrid inorganic / organic materials. Inorganic materials include zirconia, yttrium oxide, hafnium oxide, alumina, titanium oxide, cerium oxide and silica, magnesium oxide, calcium oxide, magnesium fluoride, calcium fluoride and any combinations thereof. Organic materials include polyacrylates, polyolefins, polystyrenes, polyacrylonitriles, polyurethanes, polyimides, poly furfuryl alcohol, phenol-furfuryl alcohol resins, melamine-formaldehyde resins, resorcinol-formaldehyde resins, cresol-formaldehyde resins, phenol-polyhydric polyhydric alcohols various epoxides, agar and agarose and any combinations of the above ingredients. According to the invention, the methods describe the formation of monolithic gel sheets or fiber-reinforced gel composites having two parts, namely reinforcing fibers and a gel matrix, in which the reinforcing fibers are in the form of a fluffy fiber structure (e.g., a wadding sheet), preferably based on either thermoplastic polyester or fibers silica, and preferably in combination with single, randomly distributed short fibers (microfibers) in a continuous manner. Fibrous material in the form of cotton wool or mat is introduced onto the moving element for connection with the catalyzed sol before gelation.

[0009] Furthermore, according to the invention, when the gel matrix is ​​reinforced with a fluffy wadding material, in particular a continuous nonwoven wadding sheet consisting of very low denier fibers, the resulting composite material when dried to form an airgel or xerogel product by solvent extraction, maintains similar thermal properties as a monolithic airgel or xerogel in a much stronger, more durable form. The diameter of the fibers used is in the range of 0.1-10,000 microns. In some cases, nanofibers in the range 0.001 to 100 microns are used to strengthen the gel. In addition to fibrous wadding, crimped fibers can be spread in the gel structure.

[0010] Even more specifically, the methods describe methods for the continuous production of gel composites by introducing an energy dissipation zone on a moving conveyor apparatus. The gelation of the catalyzed sol can be enhanced by a chemical process or an energy dissipation process. For example, a controlled stream of electromagnetic radiation (ultraviolet, visible, infrared, microwave), acoustic (ultrasound) or corpuscular radiation can be introduced across the width of the moving volume of the sol contained on the conveyor belt to cause sufficient cross-linking of the polymers contained in the sol to reach a point gelling. The stream, point and area of ​​radiation can be adjusted along the conveyor apparatus to achieve optimized casting speed and desired gel properties until the end of the conveyor is reached for a given gel section. In this way, the properties of the gel can be adjusted in a new way as much as possible with periodic casting methods. In addition, another moving element rotating in the opposite direction may be used to provide the shape of the top of the gel sheets.

[0011] Even more specifically, a roll of composite gel material that is coiled or rolled up with a porous flowing layer that facilitates solvent extraction using supercritical fluid processing methods can be made in a very small space using the method of the present invention. This is accomplished by pouring a certain amount of catalyzed sol into a coiled precast fiber roll together with an impermeable release layer, gelation of the flooded roll, followed by the development of a composite gel product, removal of the impermeable layer and re-rolling of the incompletely cured solid flexible gel composite with a porous release layer. The method described in this invention provides greater benefit from increasing the production rate of composite gel materials in as small a surface as possible.

[0012] Even more specifically, a method of producing gel sheets in a continuous manner is described, wherein the gel sheets are produced by any of the above-mentioned methods and rolled into multiple layers. This is a new and effective method of producing gel sheets for effective drying operations. As another feature, any release material is rolled together with gel sheets. Such release material may be permeable or impermeable by nature. Depending on the permeability of the separation material, an advantageous flow system can be obtained for subsequent drying. The separation material also provides flow paths for easy passage of subsequent silylating (aging) fluids. They also help during drying by providing flow paths that effectively reduce the thickness of the gel sheet extracted in the radial direction.

[0013] These and further embodiments of the present invention are described in more detail below. There are many advantages of the methods described in this invention regarding the processing of monolithic sheets and fiber reinforced composite sheets in a continuous or semi-continuous manner compared to the previously described methods. For example, gel products can be shaped in a continuous or semi-continuous manner, assuming that all ingredients are fed into the apparatus at the appropriate speed. Therefore, large volumes of material can be processed on a smaller production area than in traditional batch casting, requiring molds that must be filled and allowed to solidify for maturation before solvent extraction to produce airgel or xerogel materials. Very long continuous sheets of fiber-reinforced, flexible gel material are easily produced using the methods of the present invention, because the combined casting and rolling processes allow the continuous use of a single forming surface in a small production area. When the gel coils are cast periodically, followed by scrolling the coil onto a coil to place porous flowing layers between layers of gel material, the production space is further reduced, increasing production capacity and potentially reducing production costs relative to periodically casting flat sheets.

[0014] Embodiments of the invention are as follows:

1. A continuous method of casting solvent-filled continuous sheets of fiber-reinforced flexible gel material, including:

continuously combining the sol (11) and the gel inducing agent (12) to form a catalyzed sol;

providing a first moving element (18) and a second moving element (18), the second moving element moving in the same direction as the first moving element;

providing a cotton sheet (17) as layers or sheets of fibrous materials between the first (18) and the second moving element (18); combining the catalyzed sol with a cotton sheet (17); and forming a gel sheet from the joint having a first surface and a second surface by dispensing the catalyzed sol such that the first surface of the catalyzed sol contacts the first moving element (18) and the second surface of the catalyzed sol contacts the second moving element (18), wherein the first moving element (18) and the second moving element (18) move at a predetermined speed enabling effective gelation of the catalyzed sol on the first moving element (18) and the second moving element (18).

2. A continuous method of casting solvent-filled continuous sheets of fiber-reinforced flexible gel material, including:

providing a first moving element (18) and a second moving element (18), the second moving element (18) moving in the same direction as the first moving element (18);

providing a cotton sheet (17) as layers or sheets of fibrous materials between the first (18) and the second moving element (18); dispensing the sol (11) onto the first moving element (18) and connecting it to the cotton sheet (17);

forming a sol sheet from a joint having a first surface and a second surface by dispensing and joining the sol (11) so that the first surface of the sol (11) contacts the first moving element (18) and the second surface of the sol (11) contacts the second moving become element (18); and inducing gelation of the sol sheet in a process selected from the group consisting of (a) a chemical process, and (b) dispersion of a specified amount of energy from the energy source into the cross-sectional area of ​​the sol.

3. A continuous method of casting solvent-filled continuous sheets of fiber-reinforced flexible gel material, including:

continuously forming a gel sheet by dispensing the catalyzed sol onto a moving element (28; 77) at a predetermined speed and combining it with a cotton sheet (27; 75) provided as layers or sheets of fibrous materials; and inducing gelation in combination in the moving member (28; 77) in a process selected from the group consisting of (a) a chemical process, and (b) dispersing a specified amount of energy from the energy source into the sol cross-sectional area.

4. The method of Item 1, 2 or 3, in which a cotton wool sheet (17; 27; 75) is provided by unwinding from a roll.

5. A continuous method of casting solvent-filled continuous sheets of fiber-reinforced flexible gel material, including:

continuously combining the sol (21; 70) and the gel inducer (22; 71) to form a catalyzed sol; and forming a gel sheet by dispensing the catalyzed sol onto the moving element (28; 77) at a specified effective speed and combining it with a cotton sheet (27; 75) provided as layers or sheets of fibrous materials to allow gelation of the joint to occur on the moving element (28 ; 77).

6. The method of Item 5, wherein the cotton wool sheet (17; 27; 75) is provided by unwinding from a roll.

7. The method of Item 1, 2, 5 or 6, in which the moving element comprises edges.

8. The method of Item 1, 2, 5 or 6, wherein the sol comprises a material selected from the group consisting of inorganic materials, organic materials, and a combination of inorganic materials and organic materials.

9. The method of Item 8, wherein the inorganic materials are selected from the group consisting of zirconia, yttrium oxide, hafnium oxide, alumina, titanium oxide, cerium oxide and silica, magnesium oxide, calcium oxide, magnesium fluoride, calcium fluoride and combinations thereof.

10. The method of Item 8, wherein the organic materials are selected from the group consisting of polyacrylates, polyolefins, polystyrenes, polyacrylonitriles, polyurethanes, polyimides, polyfurfuryl alcohol, phenol-furfuryl alcohol resins, melamine-formaldehyde resins, resorcinol-formaldehyde resins, cresol-formaldehyde resins formaldehyde, polyvinyl alcohol dialdehyde, policyanurates, polyacrylamides, various epoxides, agar and agarose, and combinations thereof.

11. The method of Item 4 or 6, wherein the fibrous wadding or matting material comprises fibers selected from the group consisting of inorganic materials, organic materials, and a combination of inorganic materials and organic materials.

12. The method of Item 4 or 6, wherein the fibrous material in the form of a cotton sheet or mat comprises fibers having a diameter in the range of 0.1 μm to 1000 μm or in the range of 0.001 μm to 10 μm.

13. The method of Item 5 or 6, further comprising the step of:

the arrangement of crimped fibers in a gel sheet.

14. The method of Point 2 or Point 3, wherein the energy source is selected from the group consisting of an electromagnetic energy source, an infrared energy source, an X-ray energy source, a microwave energy source, an energy source in the form of gamma rays, an acoustic energy source, an ultrasonic energy source, and energy sources in the form of a particle beam, an energy source in the form of an electron beam, an energy source in the form of beta particles, an energy source in the form of alpha particles and their combinations.

15. The method of Item 1, 2, 3 or 5, wherein the at least one moving element is a conveyor belt.

BRIEF DESCRIPTION OF THE DRAWINGS [0015]

FIG. 1 illustrates a method of producing fiber reinforced gel sheets using an opposingly rotating conveyor belt.

FIG. 2 illustrates a method of producing fiber reinforced gel sheets using a single rotating conveyor belt.

FIG. 3 (for reference only) illustrates a method for producing fiber reinforced gel sheets using an opposingly rotating conveyor belt with an additional cut.

FIG. 4 (for reference only) illustrates a method of producing fiber reinforced gel sheets using a single rotating conveyor belt with additional cutting.

FIG. 5 illustrates the overall flow diagram of mixing the catalyst with the sol before casting.

FIG. 6 illustrates an additional embodiment of spreading the catalyzed sol onto a pre-formed roll containing release layers.

FIG. 7 illustrates an additional embodiment for producing a gel sheet by inducing a gelation zone.

FIG. 8 illustrates an additional embodiment for producing gel sheets with one or more release layers.

DETAILED DESCRIPTION OF THE INVENTION [0016] The invention described herein relates to the preparation of a solvent-filled nanostructured gel monolith and flexible coating composite sheet materials. Nanoporous airgel bodies are obtained from these materials after extraction of all mobile phase solvents using hypercritical solvent extraction (supercritical fluid drying). For example, the methods described in this invention will offer much better production capacity for forming monolithic gel sheets or coiled gel composite articles with a shape factor that will facilitate solvent removal in the subsequent supercritical fluid extraction procedure. The first method relates to a conveyor-based system that uses a low-viscosity catalyzed sol mixture at one end and a system for cutting and handling formed monolithic sheets (defined herein only as a polymer or ceramic matrix, without the addition of fibers) of a solvent-filled gel material to the system for further chemical treatment. The second method describes a conveyor-based system that utilizes the delivery of a low-viscosity catalyzed sol mixture at one end and a system for cutting and transferring solvent-filled fiber-reinforced gel composite sheets to a winding system (with or without a porous separating flow layer) to produce a coefficient shape ready for further processing before supercritical fluid extraction. The third method describes the direct roll-roll transfer process between two containers, the first containing a direct "gel-in-roll" reaction environment followed by developing and rolling the gel with a flowing layer of a porous separator to prepare the shape factor for further processing before supercritical extraction. These three methods can be used in conjunction with controlled energy supply methods to facilitate good alignment during gelation and the strength of the formed raw bodies. Energy in the form of ultrasound, heat and various forms of radiation can be used to induce gelation from the prepared sol mixture in addition to classical chemical catalysis methods (such as changing the pH from a stable pH sol to pH, which facilitates gelation).

[0017] The matrix materials described in this invention are best derived from sol-gel processing, preferably consist of polymers (inorganic, organic or hybrid inorganic / organic) that define a structure with very small pores (on the order of one billionth of a meter). Fibrous materials added prior to the polymer gelation point reinforce the matrix materials described in this invention. The preferred fibrous reinforcement is preferably a fluffy fibrous structure (wadding or web), but may also comprise single randomly oriented short microfibers, and woven or nonwovens. In particular, preferred fibrous reinforcements are based on or organic fibers (e.g. thermoplastic polyester, high-strength carbon, aramid, oriented high-strength polyethylene), low-temperature inorganic fibers (variously metal oxide glass such as E glass), or refractory fiber (e.g. silica, alumina, aluminum phosphate or aluminosilicate) . The thickness or diameter of the fibers used in embodiments of the present invention are in the range from 0.1 to 10,000 microns, preferably in the range from 0.1 to 100 microns. In another preferred embodiment, nanostructured fibers of only 0.001 microns are used to strengthen the gel. Typical examples include carbon nanofibers and carbon nanotubes as small as 0.001 microns in diameter. Solvent-filled gel sheets combining a ceramic solid (e.g. silica) and a mobile solvent phase (e.g. ethanol) can be formed on the conveyor by continuously injecting the catalytic phase into the sol phase and spreading the catalyzed mixture on a moving conveyor. Such materials will find use in transparent insulation materials, such as double-glazed windows in buildings. Since these gel materials are normally rigid and inflexible, when they are composed of a ceramic or cross-linked polymer matrix material with an inclusion solvent (gel solvent) in the absence of fibrous reinforcement, such materials must be manipulated in a molded form when cast continuously. When the conveyor has formed edges that retain volume, the gel can be poured directly onto the surface of the conveyor. When the conveyor contains molds placed thereon, the mold volumes can be continuously filled with fresh catalyzed sol.

[0018] Suitable materials for forming inorganic airgels are oxides of most metals that can form oxides such as silicon, aluminum, titanium, zirconium, hafnium, yttrium and vanadium. Especially preferred are gels formed mainly from alcohol solutions of hydrolyzed silicate esters due to their easy availability and low cost (algogel). Organic aerogels can be made from polyacrylates, polystyrenes, polyacrylonitriles, polyurethanes, polyimides, polyfuryl alcohol, phenol-furfuryl alcohol resins, melamine-formaldehyde resins, resorcinol-formaldehyde resins, cresol-formaldehyde resins, cresol-formaldehyde resins, polyol-phenol resins, polyacrylamides, various epoxides, agar or agarose (see for example CS Ashley, CJ Brinker and DM Smith, Journal of NonCrystalline Solids, vol. 285, 2001).

[0019] In one preferred embodiment of the methods of the present invention, energy dissipation over a portion of the sol volume is used at the specific position of the conveyor apparatus used for casting the gel. By regulating the surface of the catalyzed sol that is exposed to heat or a specific radiation flux (e.g. ultrasonic, X-ray, electron beam, ultraviolet, visible, infrared, microwave, gamma rays), gelation can be induced at a given point in the conveyor apparatus. It is preferred to control the timing of the gelation point relative to the conveyor speed so that the material has sufficient time to mature and strengthen before any mechanical manipulation at the end of the conveyor apparatus. Although the diffusion of polymer chains and subsequent growth of the solid network are much slower in the sticky structure of the gel after the gelation point, for obtaining an airgel that has the best thermal and mechanical properties it is important to keep the original gel liquid (mother liquor) for some time after gelation. This time at which the gel "matures" without interference is called "syneresis." Syneresis conditions (time, temperature, pH, solids concentration) are important for the quality of the airgel product.

[0020] Gels are a class of materials formed by introducing a mobile interstitial solvent phase into the pores of a solid structure. Solid structures may consist of inorganic, organic or hybrid inorganic / organic polymeric materials in which pore morphology develops in direct relation to the gelation method, solvent-polymer interaction, polymerization and crosslinking rate, solids content, catalyst content, temperature and a number of other factors. It is preferred that the gel materials are made of precursor materials, including various fibrous reinforcing materials that give flexibility to the formed composite, in a continuous or semi-continuous manner in the form of sheets or rolls of sheets, so that the interstitial solvent phase can be easily removed by fluid extraction supercritical to form an airgel material. By maintaining the solvent phase above critical pressure and critical temperature throughout the process or at least at the end of the solvent extraction process, high capillary forces generated by the evaporation of liquid from very small pores that cause shrinkage and collapse of pores are not achieved. Aerogels usually have low bulk densities (0.15 g / cm³ or less, preferably 0.03 and 0.3 g / cm³), a large area (generally from 300 to 1,000 m²/ g and more, preferably 700 to 1000 m²/ g), high porosity (90% and higher, preferably higher than 95%) and relatively large pore volume (3 ml / g, preferably 3.5 ml / g and more). The combination of these properties in the amorphous structure ensures the lowest values ​​of thermal conductivity (9 to 16 mW / mK at 37 ° C at 1 atmosphere) for any coherent solid material. [0021] The methods of casting the monolithic and composite gel material described in the present invention comprise three distinct phases. The first phase is the mixing of all constituent substances (solid precursor, admixtures, additives) to form a low viscosity sol that can be dosed continuously. The second phase may also involve dispensing the mixed sol onto a moving conveyor mold, which may also include a synchronized counter-rotating upper belt forming a formed upper surface. The second phase may also involve applying heat or radiation to the non-gelatinized sol in a specific area of ​​the moving conveyor device to induce gelation or modify gel properties, such as gel modulus, tensile strength or density. The third phase of the method of the invention involves cutting the gel and transferring monolithic gel sheets to the post-treatment area or co-winding a flexible, fiber-reinforced gel composite with a flexible, porous flowing layer to form a particularly favorable material aspect ratio. The formed coils of the composite gel material and the flowing layer are in particular susceptible to removal of interstitial solvent using supercritical processing methods. An example of a preferred gel casting method is shown in Figure 1, in which a conventional chemically catalyzed sol-gel process is used in conjunction with a moving conveyor apparatus with the option of being molded in the opposite direction. The fiber-reinforced nanoporous gel composite can be mechanically wound, with or without a porous flowing layer, as shown in Figure 1. Figure 2 shows the same process using a moving conveyor belt with only one forming surface (continuously rotating bottom belt with shaped sides). Figure 3 shows how monolithic gel sheets formed from a polymer sol (without added fiber reinforcing structures) can be formed continuously by depositing a sol-catalyzed solution on a moving conveyor, and Figure 4 illustrates the same procedure except that the forming strategy is shown with the conveyor rotating in the opposite direction. The sols used in this invention are mixed and prepared, often by mixing together with a chemical catalyst, before being deposited on a moving conveyor, as shown in the block diagram of Figure 5. A similar but alternative form of the process according to the invention is shown in Figure 6, in which the pre-formed roll of fibers and the separation layer is soaked in a sol, and after the initial gelation occurs, it is developed to separate the gel composite from the impermeable layer and then rolled up again with a permeable layer to prepare for further chemical treatment.

[0022] The gel matrix of preferred precursor materials for the present invention may be organic, inorganic or a mixture thereof. Sols can be catalyzed to induce gelation by methods known to those skilled in the art: examples include adjusting the pH and / or temperature of the diluted metal oxide sol to the point where gelation occurs (RK Iler, Colloid Chemistry of Silica and Silicates, 1954, Chapter 6; RK Iler , The Chemistry of Silica, 1979, chapter 5, CJ Brinker and GW Scherer, Sol-Gel Science, 1990, chapters 2 and 3). Suitable materials for the production of inorganic aerogels are oxides of most metals that can form oxides such as silicon, aluminum, titanium, zirconium, hafnium, yttrium and vanadium. Especially preferred are gels made mainly from alcohol solutions of hydrolyzed silicate esters (algogel) due to their easy availability and low cost.

[0023] It is also well known to those skilled in the art that organic aerogels can be made from organic polymeric materials including solutions of polyacrylates, polystyrenes, polyacrylonitriles, polyurethanes, polyamide, EPDM and / or polybutadiene rubber, polyimides, polyfuryl alcohol, phenol alcohol furfuryl resins , melamine-formaldehyde resins, resorcin-formaldehyde resins, cresol-formaldehyde resins, phenol-formaldehyde resins, polyvinyl alcohol dialdehydes, policyanurates, polyacrylamides, various epoxides, agar and agarose (see for example CS Ashley, CJ Brinker and DM Smith, Journal of Non-Crystalline Solids, vol. 285, 2001).

[0024] Various forms of sources of electromagnetic radiation, acoustic radiation or corpuscular radiation can be used to cause gelation of sol precursor materials on a moving conveyor apparatus. There are many examples in the literature where heat, ultrasound energy, ultraviolet light, gamma radiation or electron beam radiation can be directed to a sol material to cause gelation. The use of energy dissipation (thermal, acoustic, radiation) in a fixed zone of the conveyor apparatus, so that the moving sol container interacts with the controlled energy flow for a set time, is beneficial for controlling the properties of the gel as well as the dried airgel or xerogel material. This process is illustrated in Figure 7.

[0025] Generally, the basic synthesis route for the production of the inorganic airgel is the hydrolysis and condensation of the corresponding metal alkoxide. The most suitable metal alkoxides are those having 1 to 6 carbon atoms, preferably from 1-4 carbon atoms, in each alkyl group. Specific examples of such compounds include tetraethoxilane (TEOS), tetramethoxysilane (TMOS), tetra-n-propoxysilane, aluminum isopropoxide, aluminum sec-butoxide, cerium isopropoxide, hafnium tert-butoxide, magnesium aluminum isopropoxide, yttrium isopropanolate, and titanium isopropanolate. In the case of silica precursors, these materials can be partially hydrolyzed and stabilized at low pH as polymers of polysilicic acid esters, such as polydiethoxysiloxane. Such materials are commercially available in alcohol solution. Prepolymerized silica precursors are particularly preferred for processing the gel materials described in this invention. In this disclosure, the induction of gelation of metal oxide sols in an alcoholic solution is referred to as an algogel process.

[0026] It is understood by those skilled in the art that gel materials made using the sol-gel process may be derived from a wide variety of metal oxides or other polymer forming forms. It is also well known that sols can be doped with solid substances (substances that absorb IR radiation, sintering retardants, microfibers) that affect the physical and mechanical properties of the gel product. Suitable amounts of such admixtures generally range from 1 to 40% by weight of the finished composite, preferably 2 to 30% using the casting methods of the present invention.

[0027] The main variables in the inorganic airgel forming process include the type of alkoxide, pH of the solution, and the alcoholate / alcohol / water ratio. Variable control can allow control of the growth and aggregation of matrix forms by transitioning from the "sol" state to the "gel" state. Although the properties of the resulting airgels are strongly influenced by the pH of the precursor solution and the molar ratio of the reagents, any pH and any molar ratio that allow the formation of gels can be used in the present invention.

[0028] Generally, the solvent will be a lower alcohol, i.e. an alcohol having 1 to 6 carbon atoms, preferably 2 to 4, although other liquids may be used, as is known in the art. Examples of other useful liquids include: ethyl acetate, ethyl acetoacetate, acetone and dicholoromethane.

[0029] For convenience, the algogel pathway for the production of inorganic silica gels and composites is used below to illustrate how to make the precursors used according to the invention, although it is not intended to limit the present invention to any particular type of gel. The invention is useful for other gel compositions.

[0030] Alternatively, other sol preparation and gelation methods can be used to make the precursor gel product using the processing methods of the present invention, but chemical approaches that allow products with the lowest density and / or best thermal insulation to be obtained are preferred . For example, the water-soluble precursor in the form of a basic metal oxide can be neutralized continuously with an aqueous acid solution, deposited on a moving conveyor belt as shown in Figures 1 and 2, and induced the formation of a hydrogel on the moving conveyor. Sodium silicate is widely used as a hydrogel precursor. Salt by-products can be removed from the silicic acid precursor by ion exchange and / or by washing subsequent gels with water after the gel has been manufactured and machined.

[0031] After identifying the gel material to be produced using the methods of the present invention, a solution of the appropriate metal alkoxide in alcohol is prepared. The preparation of solutions forming aerogels is well known in the art. See, for example, SJ Teichner et al., Inorganic Oxide Aerogel, Advances in Colloid and Interface Science, vol. 5, 1976, pp. 245-273, and LD LeMay, et al., LowDensity Microcellular Materials, MRS Bulletin, vol. 15, 1990, p. 19. For the production of silica gel monoliths and fiber reinforced silica gel composites useful for the production of silica airgel materials, typical preferred ingredients are tetraethoxysilane (TEOS), water and ethanol (EtOH). The preferred ratio of TEOS to water is 0.2-0.5: 1, the preferred ratio of TEOS to EtOH is 0.02-0.5: 1, and the preferred pH is 2 to 9. The natural pH of the solution of the ingredients is 5. Although any acid can be used to achieve a lower solution pH, the preferred acids are currently HCl, H2SO4 or HF. To achieve higher pH, NH4OH is the preferred base.

[0032] For the purposes of this patent specification, a fluffy cotton sheet is defined as a fibrous material that exhibits large volume and some elasticity (with or without full volume recovery). The preferred form is a soft web of this material. The use of material reinforced in the form of a fluffy cotton sheet minimizes the volume of the deposited airgel, while avoiding a substantial deterioration in the thermal properties of the airgel. The wadding sheet preferably refers to layers or sheets of fibrous material commonly used as quilt liners or for stuffing or packing or as a thermal insulation blanket.

[0033] Cotton sheet materials having a certain tensile strength are preferred for introduction into the conveyor casting system, but are not necessary. Load transfer mechanisms can be used in the process to introduce delicate materials in the form of cotton wool to the conveyor area before supersaturation through the prepared sol flow.

[0034] Suitable fiber materials for forming both fluffy cotton wool layers and xy oriented tensile reinforcement layers are any fiber-forming materials. Particularly suitable materials include: glass fibers, quartz, polyester (PET), polyethylene, polypropylene, polybenzimidazole (PBI), polyphenylene benzobisazoxazole (PBO), polyether ether ketone (PEEK), polyarylate, polyacrylate, polytetrafluoroethylene (PTFE), polymethylene phenylenediamine (Naphthalene). Kevlar), ultra-high molecular weight polyethylene (UHMWPE) e.g. SpectraTM, novoloid resins (Kynol), polyacrylonitrile (PAN), PAN / carbon and carbon fibers.

[0035] FIG. 1 illustrates a method of producing fiber reinforced gel sheets in a continuous or semi-continuous manner using a sol dispensing system and mixing of a catalyst and a forming apparatus with an opposingly rotating conveyor belt. Gel composite sheets can be made in a rolled form when they are wound mechanically at the end of the tape. The internal numbers of the figure correspond to the following markings: 11 means a stable sol precursor solution, 12 means a catalyst for inducing gelation of the sol, after adding it in the right amount under controlled conditions, 13 indicates the position of flow control, 14 means a static mixer, 15 means a position in the fluid mixing system in which the sol has been thoroughly mixed with the catalyst , 16 means a scraper / lubrication device (optional), 17 means a fiber material in the form of cotton wool (may appear in separate sheets or coils, which are fed into the kit), 18 means two tape sets moving in the opposite direction, which form the forming surfaces along the length at which gelation occurs, before the winding kit marked 19.

[0036] FIG. 2 illustrates a method of producing fiber reinforced gel sheets in a continuous or semi-continuous manner, utilizing a sol dosing and catalyst mixing system and a forming apparatus with a single conveyor belt. Gel composite sheets can be produced in a rolled form when they are mechanically wound at the end of the tape. The internal numbers of the figure correspond to the following markings: 21 means a stable sol precursor solution, 22 means a catalyst to induce gelation of the sol when it is added in the right amount under controlled conditions, 23 means flow control positions, 24 means a static mixer, 25 means a position in the fluid mixing system in which the sol has been thoroughly mixed with catalyst, 26 means scraper / lubrication device (optional), 27 means fibrous wadding (may be in separate sheets or coils that are fed into the kit), 28 means a conveyor belt kit that forms a forming surface along the length at which gelation occurs before the winding kit designated 29.

[0037] FIG. 3 (for reference only) shows a method of producing gel sheets in a continuous or semi-continuous manner using a sol dispensing system and mixing of a catalyst and forming apparatus with an opposingly rotating conveyor belt. The internal numbers of the figure correspond to the following markings: thirty means a stable sol precursor solution, 31 means a catalyst to induce gelation of the sol when it is added in the right amount under controlled conditions, 32 means flow control positions, 33 means a static mixer, 34 and 35 means two belt sets rotating in the opposite direction, which they form the forming surfaces along the length where gelation takes place before the gel sheet cutting set indicated by 36. Separate gel sheets (37) are then ready for further processing. [0038] FIG. 4 (for reference only) shows a method of producing gel sheets in a continuous or semi-continuous manner using a sol distribution and catalyst mixing system as well as a forming apparatus with a conveyor belt. The internal numbers of the figures correspond to the following markings: 40 means a stable sol precursor solution, 41 means a catalyst for inducing gelation of the sol when it is added in the right amount under controlled conditions, 42 means flow control positions, 43 means a static mixer, 44 means a form in the form of a tape along the conveyor length along which gelation takes place before the gel sheet cutting set indicated by 45. Separate gel sheets (46) are then ready for further processing.

[0039] FIG. 5 is a general flow diagram for mixing sol and catalyst in a mixing zone prior to pouring (settling) at a controlled rate onto a conveyor apparatus continuously.

[0040] FIG. 6 shows an alternative casting method that includes a roll (60) of a pre-formed fibrous and separating layer in a sol-quenching tank (61), which after initial gelation (63) is developed (64) to separate the gel composite from the impermeable layer (65) and then is re-coiled with a permeable layer (66) to form a gel composite / flowing web (67) in preparation for further chemical treatment. Alternatively, the sol-impregnated pre-formed roll can be dried directly with the separating layer present therein, and can be unwound.

[0041] FIG. 7 shows a method of producing fiber reinforced gel sheets in a continuous or semi-continuous manner, using a sol dispensing system and a forming apparatus with a single conveyor belt. Gelation is induced in the designated area of ​​the conveyor apparatus by exposing the sol to heat or radiation. The internal numbers of the figure correspond to the following markings: 70 means a stable sol precursor solution, 71 means a catalyst to induce gelation of the sol when added in the right amount under controlled conditions, 72 means a flow control position, 73 means a static mixer, 74 means a position in a fluid mixing system where the sol has been thoroughly mixed with the catalyst , 75 stands for fibrous wadding (can be supplied as separate sheets or coils that are fed into the kit), 76 stands for device, which dissipates energy in a sol or gel to change its properties (e.g., cause cross-linking), 77 means a conveyor belt set that forms a forming surface along the length of gelation in front of the roll set indicated as 78.

[0042] FIG. 8 shows another embodiment of the present invention in which the sol is applied to the conveyor belt and allowed to gel it once the conveyor belt has traveled a certain distance (corresponding to a specified residence time) and is wound onto a mandrel. When the gel sheet is wound, the permeable separation layer is wound together with the gel sheet so that the two layers of gel sheets are separated by the separation layer. Optionally, this separation element could be impermeable. The set of wound gel sheet is further dried in a supercritical dryer. The separation layer provides effective flow paths during supercritical extraction / drying. When an impermeable release layer is used, it forms channels for the extraction fluid in the axial direction. a permeable separation layer is used, and an additional radial flow form is obtained. Depending on the requirements of the composition of the gel sheet, an impermeable or permeable release layer is used to provide the necessary flow forms in the supercritical extractor / dryer.

[0043] Further details and explanation of the present invention can be found in the following specific examples, which describe the preparation of the mechanically compacted airgel composites of the present invention and the test results obtained for them. All parts and percentages are mass, unless otherwise stated.

Example 1 (reference example) [0044] Twenty gallons (75.7 l) of a silica sol obtained by hydrolysis of a 20% TEOS solution in ethanol (at pH 2 at room temperature for 24 hours) are fed into a stainless steel tank equipped with a bottom drain connected to fluid pump and flow meter. A separate tank also equipped with a bottom drain, pump and flow meter is filled with excess ethanol containing ammonia (1%). Two separate liquids are combined in a fixed ratio using flow meters in a static mixer and are deposited through the embedding head on a flat surface of a moving conveyor. The conveyor belt has flexible edges welded to the surface (in this example a 38 "(96.5 cm distance) is used, but it can be practically almost any width), so that the distributed sol is included in the volume. The pressure roller contacting the front surface of the moving conveyor belt prevents low viscosity back diffusion of the sol. The belt speed is adjusted so that the gel front in the mixed sol (defined as a fixed position on the conveyor table where the sol no longer flows freely, assuming a gummy character) appears in the middle of the table length. The ratio of gelation time to syneresis time 1: 1 is preferred, but it can be easily changed between 2: 1 and 1: 5. When the gelled sol reaches the end of the table, each silica gel plate is cut to a specific size across the width and is transferred to the load transfer plate into the alcohol bath for further processing.

Example 2 [0045] Twenty gallons (75.7 L) of the silica sol obtained by hydrolysis of a 20% TEOS solution in ethanol (at pH 2 at room temperature for 24 hours) are introduced into a stainless steel tank equipped with a bottom drain connected to a fluid pump and flow meter. A separate tank also equipped with a bottom drain, pump and flow meter is filled with excess ethanol containing ammonia (1%). Two separate liquids are combined in a fixed ratio using flow meters in a static mixer and are deposited through the embedding head on a flat surface of a moving conveyor (38 "(96.5 cm) distance between flexible edges). A roll of polyester wadding sheet (38 "wide) and about 0.5" (1.27 cm) thick is fed into the conveyor assembly at the same linear speed as the belt. The pressure roller contacting the front surface of the moving conveyor belt prevents low viscosity reverse diffusion of the sol, and another pressure roller at the front of the sol deposition point is used to assist the sol saturation of the cotton wool material. The belt speed is adjusted so that the gel front in the mixed sol (defined as a fixed position on the conveyor table where the sol no longer flows freely, assuming a gummy character) appears in the middle of the table length. The preferred ratio of gelation time to syneresis time is 1: 1, but it can be easily changed between 2: 1 and 1: 5. When the gelled sol reaches the end of the table, the flexible gel composite is wound on a cylindrical axis. Perforated polyethylene mesh is used to maintain the tension of the coil when it is formed. The shaft is then ready for further chemical treatment and can be moved using the mandrel as a load transfer tool.

Example 3 [0046] Twenty gallons (75.7 L) of the silica sol obtained by hydrolysis of a 20% TEOS solution in ethanol (at pH 2 at room temperature for 24 hours) are introduced into a stainless steel tank equipped with a bottom drain connected to a fluid pump and flow meter. The silica sol is pumped at a fixed speed through the dosing head onto the flat surface of the moving conveyor (38 "(96.5 cm) wide between flexible edges). A roll of polyester wadding sheet (38 inches (96.5 cm wide)) with a thickness of about 0.5 "(1.27 cm) is fed into the conveyor assembly at the same linear speed as the belt, before the sol dosing point. A pressure roller in contact with the front surface of the moving conveyor belt prevents low diffusion back diffusion of the sol, and another pressure roller at the front of the sol deposition point is used to assist the sol with material wool wadding. The ultrasonic transducer systems connected to the bottom of the belt through a lubricating gel are located halfway through the conveyor apparatus. The belt speed as well as the power and frequency of the ultrasound are adjusted so that the gel front in the mixed sol appears approximately in the middle of the table length. When the gelled sol reaches the end of the table, the flexible gel composite is wound on a cylindrical axis. Perforated polyethylene mesh is used to maintain the tension of the coil when it is formed. The shaft is then ready for further chemical treatment and can be moved using the mandrel as a tool for carrying the load.

Example 4 (reference example) [0047] Twenty gallons (75.7 L) of a silica sol prepared by hydrolysis of a 20% solution of tetramethyl orthosilicate (TEOS) in methanol (at pH 2 at room temperature for 4 hours) is introduced into a stainless steel tank equipped with a bottom drain connected to a fluid pump and flow meter. A separate tank also equipped with a bottom drain, pump and flow meter is filled with excess ethanol containing ammonia (1%). Two separate liquids are combined in a fixed ratio using flow meters in a static mixer and are deposited through the embedding head on a flat surface of a moving conveyor. The silica sol is pumped at a constant speed through the dosing head onto the flat surface of the moving conveyor (38 "(96.5 cm) wide between the flexible edges). The pressure roller contacting the front surface of the moving conveyor belt prevents low diffusion viscosity of the sol. The speed of the conveyor belt and the flow rate of the deposited sol are such that the gel front of the (monolithic) silica gel sheet occurs approximately in the middle of the conveyor length. The belt speed is kept constant during the process so that the ratio of syneresis time and gel time is approximately 1: 1. When the mature silica gel sheet reaches a favorable length behind the end of the conveyor belt (on the supporting surface to prevent the delicate gel structure from cracking), a cutting apparatus is used to separate the separate pieces from the continuously moving gel. The new gel sheet is transferred to the load-bearing plate and removed to another area for further processing. This action is repeated until all the sol is deposited on the table. This process can continue continuously as long as the properly formed sol is topped up in the dispensing apparatus.

Example 5 [0048] Twenty gallons (75.7 L) of silica sol obtained by hydrolysis of a 20% TEOS solution in ethanol (at pH 2 at room temperature for 24 hours) are introduced into a stainless steel tank equipped with a bottom outlet connected to a fluid pump and flow meter. Ethanol containing ammonia (1%) is added while stirring at a rate that maintains an almost constant temperature until the pH of the sol reaches between 4 and 7. A sol with adjusted pH ("catalysed") is introduced into the tank through a roller of polyester wadding (38 inches (96.5 cm) wide) with a thickness of about 0.5 (1.27 cm), which was wound on a stainless steel stem polyethylene separation layer. The introduction is carried out in a manner that prevents excessive bubble formation in the fiber volume, and extruded resin forming techniques or vacuum impregnation techniques known to those skilled in the art can be used successfully. After gelation takes place, the gel shaft is developed before excessive stiffening (a ratio of gelation time to syneresis time greater than 1: 1 is preferred), where the impermeable plastic layer is removed and the elastic gel is re-wound with the permeable layer flowing with appropriate stress to a separate container (Figure 6). The gelled roller is then ready for further maturation and chemical treatment before supercritical drying.