RU2575456C2 - Epoxy composite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method for making an epoxy composite. In the present method an epoxy prepolymer, a curing agent and particulate filler are combined to form a curable mixture. The mixture is then agitated under a non-air atmosphere to render it substantially homogeneous, and pressure is applied to the mixture to reduce or eliminate gas pockets in the mixture and is maintained until the curable mixture is cured to form the epoxy composite.

EFFECT: forming an epoxy composite.

36 cl, 17 dwg, 2 tbl

Description

Technical field

The present invention relates to a method for producing an epoxy composite.

BACKGROUND OF THE INVENTION

The author of the present invention needed syntactic foam with extremely high and uniform strength for flotation and as a structural element for deep sea applications. Various commercial foams were tested and all did not meet the requirements of a suitable FofS (safety factor). It was considered that the failure of these materials is partly due to the heterogeneity of the materials, leading to unstable strength characteristics in different parts of the material. Commercial foams tended to weaken first on one side and / or to develop dangerous cracks. Since a rather large piece of foam was needed to provide flotation and structural integrity for use, the present inventor considered the low FofS and the non-uniform strength of commercial foams, which are the main disadvantages.

Epoxy composites can be prepared by combining an epoxy prepolymer, curing agent and filler and curing the resulting mixture. A filler may serve one or more of a number of purposes, including increasing stiffness, increasing strength, improving crack resistance, and decreasing density in a cured composite. If a low filler level is used, the improvement in properties may be less than was necessary. Also, the uncured mixture may have a relatively low viscosity. This may allow partial separation of the filler (due to the excellent densities of the filler and epoxy prepolymer), resulting in a cured composite with heterogeneous properties.

These problems can be resolved by increasing the level of filler in the mixture. However, this leads to new problems. An increase in the level of filler leads to an increase in the viscosity of the uncured mixture. Stirring this mixture in order to achieve a homogeneous product can lead to the inclusion of large amounts of air, which can form voids in the cured composite. These voids can adversely affect the physical properties (strength, etc.) of the cured composite. The use of vacuum during mixing can partially eliminate this problem, however, the high viscosity of the uncured composite together with the high loading of the filler can make it difficult to remove all air bubbles.

Because of this, there is a need for a method for producing epoxy composites that reduces or eliminates voids, while at the same time assuming a relatively high loading of filler.

The purpose of the present invention

The aim of the present invention is mainly to overcome or at least mitigate one or more of the above disadvantages. An additional objective is to at least partially satisfy the above need.

A brief description of the present invention

In a first aspect of the present invention, there is provided a method for producing an epoxy composite comprising combining an epoxy prepolymer, a curing agent and a particulate filler to form a curable mixture, shaking the mixture to become substantially uniform, and applying pressure to the mixture to reduce or eliminate gas bubbles in the mixture. In the present context, the expression “reduce” refers to a decrease in the size (eg, volume) of gas bubbles. The pressure must be maintained until the curable mixture cures to form an epoxy composite. The agitating step, and optionally also combining, can be carried out in an airless atmosphere.

Embodiments may be used in combination with the first aspect, either individually or in any suitable combination.

The pressure applied to the mixture may be at least about 7000 kPa or may be from about 7000 to about 15000 kPa. It may alternatively be from about 2000 to about 7000 kPa. Lower pressures can be used to produce composites for use at lower pressures than those obtained using higher pressures. Pressure can be applied isostatically. It can be applied hydrostatically. The prepolymer and curing agent may be such that the working time of the curable mixture at 20 ° C. is at least about 1 hour, or at least about 6 hours, or at least about 1 day. They can be such that the curable mixture does not cure at about 20 ° C, or such that it does not cure at about 20 ° C for at least about 1 day or at least about 1 week.

The combination may be accompanied or preceded by cooling of one or more components of the curable mixture. It may, for example, include cooling the prepolymer and then adding a curing agent and a particulate filler. Cooling may be to a temperature of from about 0 to about 10 ° C, for example to about 3 ° C.

The airless atmosphere in which shaking is carried out, and optionally also combining, can be one which has a solubility in the curable mixture higher than the solubility of air in the curable mixture at the same temperature. An airless atmosphere may contain at least about 50% molar-based argon. It can be welding gas. It may contain approximately 93% argon and approximately 5% carbon dioxide. It may contain approximately 2% oxygen. It may contain approximately 93% argon and approximately 7% carbon dioxide.

The pressure application step may be carried out so that the mixture is not exposed to air. It can be carried out in an airless atmosphere as described above. It can be carried out surrounded by a protective layer or insulating material that impedes or prevents the access of air and / or airless atmosphere to the mixture. It may be applied isostatically to the surrounding fluid (liquid or gas), and the protective layer or insulating material may impede or prevent the access of the surrounding fluid to the mixture.

The particulate filler may have a lower density or absolute density than the prepolymer. It may have a lower density or absolute density than the curable mixture. It may have an absolute density of less than about 0.5 g / cm ³ . The particulate filler may be from or may contain hollow microspheres. Hollow microspheres can be hollow glass microspheres (glass microbubbles). Hollow microspheres can be such that (for example, they can have a wall thickness such that) no more than about 10% of the microspheres are destroyed during the stage of applying pressure to the mixture. The particulate filler may in some cases contain more than one class of hollow microspheres. One class can be a class with high strength. Another class may be a low density class.

The combining step may comprise combining an epoxy prepolymer, a curing agent, a particulate filler, and a second filler to form a curable mixture. The second filler may contain from about 0.1 to about 1% by weight or volume of the curable mixture.

The method may include heating the curable mixture in order to initiate or accelerate curing to form an epoxy composite. This step may be useful in cases where the curable mixture has a working time of more than about 6 hours at about 20 ° C. If the heating step is used to initiate or accelerate curing, the heating may be to a temperature of less than 90 ° C or to a temperature of from about 40 to about 90 ° C. It can be up to a temperature at which the working time is less than about 1 hour. Heating (if applicable) can be started at a point in time (referred to herein as holding time) after the application of pressure to the mixture has begun. The exposure time may be at least about 1 hour. If a heating step is used to cause or accelerate curing, the epoxy composite may be cooled before depressurizing. In this context, the expression “heating to” a specific temperature refers to the placement of the mixture in the environment at a specific temperature, and there is no need to relate the actual temperature obtained by the cured mixture in that environment. The actual temperature of at least parts of the mixture may exceed a specific temperature due to the exothermic curing effect.

The method can be used to obtain an epoxy composite according to the second aspect (below).

In an embodiment, a method for producing an epoxy composite is provided, comprising:

- combining an epoxy prepolymer, a curing agent and a particulate filler consisting of glass microspheres to form a curable mixture, said prepolymer and curing agent being such that the curable mixture has a working time of more than about 6 hours at about 20 ° C,

- shaking the mixture in an atmosphere containing argon and carbon dioxide in sufficient volume to turn the mixture into almost uniform,

- applying isostatic pressure from about 7000 to about 15000 kPa to the mixture in order to reduce or eliminate gas bubbles in the mixture,

- heating the mixture under pressure to a temperature of not more than 90 ° C, and the specified temperature is sufficient to cause the curing of the mixture,

- providing the mixture with the ability to cure under high pressure with the formation of an epoxy composite,

- allowing the epoxy composite to cool to approximately ambient temperature, and

- return of the epoxy composite to approximately atmospheric pressure.

In another embodiment, a method for producing an epoxy composite is provided, comprising:

- combining an epoxy prepolymer, a curing agent, a particulate filler consisting of glass microspheres and a fibrous filler to form a curable mixture, said prepolymer and curing agent being such that the curable mixture has a working time of more than about 6 hours at about 20 ° C ,

- shaking the mixture in an atmosphere containing argon and carbon dioxide in sufficient volume to turn the mixture into almost uniform,

- wrapping the mixture in an elastic insulating material;

- applying isostatic pressure from about 7000 to about 15000 kPa to the mixture in order to reduce or eliminate gas bubbles in the mixture,

- heating the mixture under pressure to a temperature of not more than 90 ° C, and the specified temperature is sufficient to cause the curing of the mixture,

- providing the mixture with the ability to cure under high pressure with the formation of an epoxy composite,

- allowing the epoxy composite to cool to approximately 60 ° C,

- return of the epoxy composite to approximately atmospheric pressure; and

- allowing the epoxy composite to cool to ambient temperature at atmospheric pressure for more than at least 1 day.

In a second aspect of the present invention, there is provided an epoxy composite comprising a particulate filler and having a compressive stress of greater than or equivalent to 100 MPa. The composite may have a density of less than about 0.7 g / cm ³ .

Embodiments may be used in combination with the second aspect, either individually or in any suitable combination.

An epoxy composite can be obtained by the method of the first embodiment.

The epoxy composite may be syntactic foam.

The epoxy composite may have such a modulus of elasticity in compression such that the compressive strain of 110 MPa is less than or equal to approximately 0.9%. It may exhibit a linear distortion of less than or equivalent to approximately 0.9% under a hydrostatic compression pressure of 110 MPa.

It may have low water absorption. It may have equilibrium water absorption of less than about 0.5% volume / volume or less than about 0.1% volume / volume.

The density of the particulate filler may be less than about 0.5 g / cm ³ . The particulate filler may be hollow microspheres or may contain hollow microspheres. Hollow microspheres can be hollow glass microspheres. A particulate filler may be present in the composite at a rate of about 60% or more by volume.

The epoxy composite may further comprise a second filler. The second filler may be a fibrous filler. The second filler may comprise aramid fibers and / or e-glass fibers. Fibers can be from about 0.2 to about 2 mm on average in length. A second filler may be present in the composite at a rate of from about 0.1 to about 1% v / v. An epoxy composite may in some cases contain one or more additional fillers.

The epoxy composite of the second aspect can be obtained by the method of the first aspect.

In an embodiment, an epoxy composite is provided comprising a particulate filler consisting of hollow glass microspheres, said composite:

- has an ultimate compressive stress greater than or equivalent to 100 MPa,

- exhibits a linear distortion of less than or equivalent to approximately 0.9% under a hydrostatic compression pressure of 110 MPa; and

- has a density of less than about 0.7 g / cm ³ .

In a third aspect of the present invention, there is provided the use of an epoxy composite according to the second aspect or a method of the first aspect obtained as a structural component in compression.

Embodiments may be used in combination with the third aspect, either individually or in any suitable combination.

Application may take place in a device for use under water. In this context, the use of "in" the device means the use as part of the device, both inside the device and on the surface of the device, or both. The device may be suitable for use at a depth of at least about 10 km below the surface of the water. The application may be at a depth of at least about 10 km below the surface of the water. The device may be a deep-sea habitable vehicle. It can be a deep-sea automatic vehicle. The epoxy composite may form at least a portion of the outer surface of said device. It may be a structural or load bearing part of the outer surface of the device. It can function as an element of the buoyancy of the device. It can be either a buoyancy element, or a structural or load-bearing part of the outer surface or department of a device. An application may include any one or more of the additional steps:

- Forming, or cutting, or grinding the epoxy composite into a suitable shape, for example blocks, tiles or plates;

- The distribution of the composite (for example, in the form of blocks, tiles or plates) in order to form a profile material (for example, a two-tare profile) suitable for use as a structural part of an underwater vehicle or other device or part thereof;

- Filling the intervals between the parts (for example, blocks, tiles or plates) of the composite by filling, capable of withstanding the conditions of use of the apparatus or other device.

A brief description of the graphic materials

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, where:

figure 1 is a flowchart showing a method for producing a cured composite of the present invention;

figure 2 shows electron micrographs of a) a local section and b) a polished section of a cured composite filled with glass microspheres and obtained according to the present invention;

figure 3 shows a typical temperature profile of the method of the present invention;

4 shows the properties of various epoxies that have been seated and cured by compression: a) stress strain curves under compression; b) modulus of elasticity in compression; c) Poisson's ratio;

figure 5 is a graph showing the density (g / cm ³ ) relative to the hydrostatic crushing pressure of the NDS (MPa) for various commercial glass microspheres;

figure 6 shows data for a series of composites with filler particles according to the present invention;

figure 7 shows a curve of the dependence of deformation on the pressure of the composite of syntactic foam under hydrostatic pressure;

Figure 8 shows the compression properties of the composite used in Figure 7: a) stress strain curves under compression; b) modulus of elasticity in compression; c) Poisson's ratio;

figure 9 shows a fragment of the actual sample of the composite used in figure 8, after fracture in compression;

figure 10 shows the results of a bending test for a composite of the present invention;

figure 11 shows a photograph of the destruction of the surface of the sample of the cured composite after bending tests; and

Figure 12 is a drawing of a bending test apparatus showing the location of strain gauges on a sample.

Detailed Description of Preferred Embodiments

In the present description, the following expressions apply:

Epoxy: an oxirane ring or particles containing oxirane groups, or a cured material obtained from such particles.

Prepolymer: oligomeric or polymer particles capable of crosslinking to form a cured resin. The degree of polymerization will usually be greater than about 3. The prepolymer is usually a liquid, which may be highly viscous or may be relatively inviscid. Viscosities ranging from about 100 to about 100,000 cps are common. Prepolymers can be called resins.

Curing agent: particles capable of reacting with an epoxy prepolymer to react with epoxy groups in an epoxy prepolymer to crosslink the prepolymer to form a cured epoxy resin. The curing agent may contain thiol and / or amino groups and may contain a catalyst for the crosslinking reaction. Curing agents can be called hardeners.

Composite: a crosslinked polymer having filler particles dispersed in the polymer. Crosslinking can be physical, chemical and / or physico-chemical. In the present invention, the filler is a particulate filler, optionally supplemented with a second filler.

Working hours: time after mixing the curable mixture (prepolymer and curing agent) during which the mixture remains liquid.

Filler: A solid additive introduced into the polymer (in this case, epoxy) in order to change its properties. This definition refers to a particulate filler and a second filler. These expressions are used simply to distinguish between different fillers. It will be understood that the second filler, if present, may be particulate in nature, although different from the particulate filler.

Airless atmosphere: An atmosphere that is different from air. The particular airless atmosphere typically used in the present invention may have a solubility in the curable mixture higher than the solubility of air in the curable mixture at the same temperature. The airless atmospheres used in the present invention may, for example, contain at least about 50% molar-based argon. A specific example is a welding gas. A suitable airless atmosphere may, for example, contain about 93% argon and about 5% carbon dioxide. It may contain approximately 2% oxygen. It may contain approximately 93% argon and approximately 7% carbon dioxide.

Isostatic pressure: pressure applied to the body equally on all sides.

In the preparation of the epoxy composite of the present invention, the epoxy prepolymer, curing agent and particulate filler are combined to form a curable mixture. Typically, even if not necessary, commercial epoxy prepolymers and curing agents are used. Appropriate ratios of such components will then be provided by the supplier. The ratio is usually within about 10% of the stoichiometric ratio (i.e., such a ratio where the molar ratio of epoxy groups and groups, such as amines, which can react with epoxy groups). Thus, the molar ratio of prepolymer to curing agent (based on functional groups) can be from about 0.9 to about 1.1, or from about 0.9 to 1, from 1 to 1.1, or from 0.95 to 1.05, for example, approximately 0.9, 0.95, 1, 1.05, or 1.1. The actual weight (or volume) ratio will depend on the density of the functional groups in the prepolymer and the curing agent. Typically, the weight or volume ratio is from about 10: 1 to about 1:10 based on weight or volume, or about 5: 1-1: 5, 2: 1-1: 2, 3: 2-2: 3, 5: 1-1: 1, 5: 1-3: 1, 2: 1-1: 1, 3: 2-1: 1, 1: 1-1: 5, 1: 1-1: 2, 1: 1- 2: 3, 1: 1-1: 10 or 10: 1-1: 1, for example, approximately 10: 1, 9: 1, 8: 1, 7: 1, 6: 1, 5: 1, 4: 1 , 3: 1, 2: 1, 3: 2, 1: 1, 2: 3, 1: 2, 1: 3, 1: 4, 1: 5, 1: 6, 1: 7, 1: 8, 1 : 9 or 1:10. The amount of particulate filler may be sufficient to achieve a volume ratio in the curable mixture of from about 60 to about 70%, or about 60-65, 65-70, 63-68, or 66-67%, for example about 60, 61, 62, 63 , 64, 65, 66, 67, 68, 69, or 70%, although in some cases it may be more or less, for example, about 20, 30, 40, 50, 75, or 80%. In the case where the particulate filler includes hollow microspheres, the amount of particulate filler can be selected so that the bulk density is not high enough to result in a high content of hollow microspheres destroyed by physical contact when isostatic pressure is applied. Epoxy must be sufficient (i.e., a sufficiently low amount of particulate filler) so that isostatic pressure is applied to each hollow microsphere and there is little or no direct contact between the microspheres. Such mixtures are usually viscous enough to avoid movement / separation of the components. The amount of particulate filler may be sufficient to provide a curable mixture that practically does not separate upon settling. It may be sufficient to provide a curable mixture that has a yield strength sufficient so that it practically does not separate upon settling. It may be sufficient to provide a curable mixture with a non-zero yield strength. It can have a plastic flow stress of at least about 100 Pa, or at least about 200, 300, 400, 500, 600, 700, 800, 900 or 1000 Pa, or have a yield strength of from about 100 to about 2000 Pa, or approximately 100-1500, 100-1000, 100-500, 100-200, 200-2000, 500-2000, 1000-2000, 200-500, 200-300, 300-500 or 500-1000 Pa, for example, approximately 100 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000 Pa. In some cases, a lower yield stress may be suitable, for example at least about 10, 20, 30, 40, 50, 60, 70, 80, or 90 Pa, or about 10-100, 10-50, 50-100, 10-30 or 30-50 Pa, for example, approximately 10, 20, 30, 40, 50, 60, 70, 80 or 90 Pa. A non-zero yield strength or high viscosity or the quasi-solid nature of the curable mixture serves to ensure that particulate filler particles do not separate before the mixture cures. This, in turn, contributes to the fact that the cured composite is uniform in composition and, therefore, uniform in physical properties. In particular, since the presence of filler particles affects the strength of the cured composite, regions with different densities of filler particles can have different strength properties, which leads to an overall composite with reduced strength with respect to a fully uniform composite (such as that described herein) with such the same macroscopic composition, and therefore should be avoided.

As already noted, epoxide (prepolymer and curing agent) may be a commercial product. It may alternatively be a target obtained for a particular application. Basically, it can be chosen because of its high strength properties. As indicated elsewhere, the present invention finds its main application in high-strength, lightweight syntax foams for use in underwater applications. The epoxide can be chosen so that it, being cured, is very resistant to hydrolysis, for example, to hydrolysis with sea water under high pressure. It can be selected so that it has low or minimal water absorption when cured. It can be chosen so that it has a low density when cured. It can be chosen so that the optimum mixing ratio of the prepolymer to the curing agent is suitable. It can be chosen so that the viscosities of the curing agent and prepolymer are suitable for preparing a mixture with a particulate filler that has the corresponding rheological properties (as indicated above). It can be selected so that the working time of the curable mixture at 20 ° C. is at least about 1 hour or at least about 2, 3, 4, 5, 6, 9, 12, 15, 18 or 24 hours, or is approximately from 1 to about 24 hours, or about 1-12, 1-6, 6-24, 12-24, or 18-24 hours or 1-7 days. It can be chosen so that the curable mixture does not cure at about 20 ° C, or so that it does not cure at about 20 ° C for at least about 1, 2, 3, 4, 5, 6, or 6 days. It can be chosen so that at a suitable elevated temperature below about 90 ° C, the curable mixture cured in less than about 5 hours or less than about 5, 3, 2, 1 or 0.5 hours, for example, cured in about 0.5, 1, 1 5, 2, 2,5, 3, 3,5, 4, 4,5 or 5 hours. The combination of long working hours at approximately room temperature and relatively fast curing at elevated temperatures is taken into account to control curing, i.e. cure on demand, so that the curable mixture can be processed, molded, etc. at room temperature without premature curing, and then curing is started by simply raising the temperature. Curing temperatures below approximately 90 ° C are suitable since they impose less stringent requirements on equipment used to hold and process the material. Additionally, hazard levels according to AS4343 are reduced when temperatures are below 90 ° C. The curing temperature may be less than about 65 ° C. This can further reduce associated hazards. Additionally, in some cases, the epoxy mixture may cure exothermically, leading to a further increase in temperature. If the temperature causing the curing is too high, then the exothermic effect can increase the internal temperature of the curing mixture to the point where the cured composite is damaged, for example, leading to a decrease in strength.

The inventor has found that when large amounts of the curable mixture are mixed, an exothermic effect can occur suddenly, leading to cure rates that are faster than required. Premature curing can prevent or inhibit the elimination of voids in the mixture (since the application of pressure before curing will not be sufficient), leading to a defective product. To prevent or reduce this effect, one or more of the components of the curable mixture can be cooled, either before or during the combining step. Since it is usually easier to cool when the viscosity is lower, it is generally accepted to cool before adding particulate filler, since adding particulate filler usually results in a paste-like mixture. Thus, the epoxy prepolymer can be cooled before other components are added. In the case where a second filler is used, it is usually used at relatively low concentrations and, thus, usually has a small effect on viscosity. Accordingly, the epoxy prepolymer can be mixed with the second filler before cooling or simultaneously with cooling. Thus, one or more components can be delivered at a low temperature (i.e., at the cooling temperatures described below) or can be cooled as part of the process. Cooling may be to a temperature of from about 0 to about 10 ° C, or about 0-5, 5-10, or 2-6 ° C, for example, about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 ° C. For large batches of epoxy composite, this may take some time, for example, all night.

A suitable method of forming a curable mixture, therefore, is as follows:

a) combining an epoxy prepolymer and optionally a second (e.g. fibrous) filler;

b) cool the mixed prepolymer / second filler, for example, by mixing in a cold chamber at about 3 ° C overnight;

c) add a curing agent and continue mixing;

d) add a particulate filler, optionally in several batches, and continue mixing until uniform;

e) placing the resulting mixture in a shell made of a waterproof elastic insulating material, and placing the mixture in a shell in a heating bath inside the pressure vessel;

f) increase the pressure of the heating bath and the shell containing the mixture to the desired pressure and maintain the pressure for a suitable holding time to allow the mixture to absorb gases;

g) heating the heating bath to approximately 80 ° C for approximately 8 hours, while also maintaining pressure in order to harden the mixture to the cured composite;

h) turn off the heat in order to allow the cured composite to cool; and

i) relieve pressure. Pressure relief may occur when the temperature of the unit is approximately 60 ° C. Pressure relief can occur in stages in 2, 3, 4, 5 or more than 5 stages. Alternatively, it may be continuous for a period of from about 5 to about 60 minutes, or about 5-30, 5-15, 15-60, 30-60, or 15-30 minutes, for example, for about 5, 10, 15 , 20, 25, 30, 40, 50 or 60 minutes. The above method may be suitable for mixtures of up to about 80 kg or even more.

The author of the present invention noted that in the absence of externally applied heating, a large temperature gradient can be established in the cured material. It is assumed that this is due to heat generation due to the curing method, which can be released more easily from the outer regions of the mixture than from its inner regions. This large temperature gradient can lead to variable properties due to the resulting cured material block, possibly leading to cracking. An external application of heat to the cured block can serve to facilitate a more even distribution of temperatures within the cured block and, consequently, more uniform properties. In a typical curing profile, therefore, the addition of a curing agent to the epoxy prepolymer results in a slow exothermic effect, which continues as particulate filler is added. Once this is completed and the final curable mixture is placed in a heating bath / pressure vessel, heating produces a faster exothermic effect. Heating is continued above the exothermic peak of the curable mixture. Once the heating is turned off, the unit is allowed to cool slowly. The unit will typically be cooled to about 60 ° C before depressurizing, or from about 50 to about 70 ° C. At these temperatures, the variability within the block is usually less than about 20 degrees Celsius. When depressurizing, the unit can be removed from the pressure vessel, usually still at elevated temperature. Final cooling to room temperature can usually take several days.

The resulting cured block can be machined to have smooth, even orthogonal faces with the required dimensions. Typical dimensions are approximately 300 mm × 300 mm × 1300 mm. The width may be from about 100 to about 500 mm, or about 100-300, 300-500 or 200-400 mm, for example, about 100, 150, 200, 250, 300, 350, 400, 450 or 500 mm. The height may be from about 100 to about 500 mm or about 100-300, 300-500 or 200-400 mm, for example about 100, 150, 200, 250, 300, 350, 400, 450 or 500 mm. The length can be approximately 500-2000 mm, or approximately 500-1500, 500-1000, 1000-2000 or 1000-1500 mm, for example, approximately 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400 , 1500, 1600, 1700, 1800, 1900 or 2000 mm. The block may not have cracks visible from the outside. It may not have internal cracks or voids. Typically, in the previous methods, it was difficult to obtain blocks without cracks with dimensions greater than about 0.02 m. In comparison, using this method, it is easy to obtain blocks without cracks larger than approximately 0, 1 m ³ .

The curable mixture may have an accelerator, or a catalyst, or a moderator to change the cure rate. This may be a component of the curing agent, or it may be added separately. Suitable accelerators / catalysts are typically trisubstituted amino compounds. Accelerators / catalysts can be, for example, substituted guanidines, piperazines, imidazoles and phenolic compounds. The accelerator / catalyst may be present in the mixture in sufficient quantity to achieve the desired cure profile, as described above.

The particulate filler may be any suitable filler that provides the desired properties in the cured composite containing the filler. It can be a bulking filler. It can be a reinforcing filler. It can be both increasing the volume and reinforcing. It can be a filler to improve the buoyancy of the cured composite. It can be a buoyancy enhancing and reinforcing filler. There may be more than one filler, each independently having any one or more of an increase in volume, reinforcement, and improved buoyancy. The filler particles can be spherical, or they can be in any other shape, such as oval, ellipsoid, cubic, rhomboid, prismatic, parallelepipedal (for example, a rectangular parallelepiped), oblate spherical, needle-shaped, fibrous, in the form of a torus, polyhedral (with from about 6 to about 50 sides), lamellar, diamond-shaped, or may be irregular in shape, or may be a mixture of particles of any two or more such shapes. The particulate filler may be suitable for increasing strength (under stress, shear, bending and / or compression), increasing toughness, increasing elasticity, increasing elongation at break, increasing stiffness, increasing modulus (stress, shear, bending and / or compression ), a decrease in the density of the cured composite, a decrease in water absorption, an increase in the viscosity of the uncured mixture, or for any combination of such effects. The nature and loading of the particulate filler may be selected to achieve the desired properties of the cured composite. Mixtures of particulate fillers can be used to achieve such properties.

For use in deep-sea applications, the desired effect is a decrease in density (i.e., an increase in buoyancy), and a preferred additional effect is an increase in compressive strength (and also preferably in bending). Hollow microspheres are particularly suitable for this application. Microspheres may differ in part in their absolute density. It can be considered as a mass of liquid with a density of 1.00 g / cm ³ displaced by the microsphere completely immersed in this liquid divided by the volume of the microsphere. It will be seen from this definition that the absolute density is not affected by the spaces between the microspheres, but will be affected by the spaces enclosed in the microspheres. The absolute density of the microspheres will depend on the material from which the walls are made, the thickness of the walls and the diameter of the microspheres. The microspheres can be polymeric (for example, styrene, optionally crosslinked with divinylbenzene, acrylic, for example, polymethylmethacrylate, etc.), or they can be ceramic, or they can be glass, i.e. they may be hollow glass microspheres, or may be hollow polymer microspheres, or may be hollow ceramic microspheres. In some cases, mixtures of two or more of them may be used.

Glass microspheres are preferred in the present invention. The absolute density of the microspheres for use in the present invention may be less than about 0.85 g / cm ³ or less than about 0.8, 0.7, 0.6 or 0.5 g / cm. It can be approximately 0.1-0.85 g / cm ³ or approximately 0.1-0.8, 0.1-0.5, 0.1-0.3, 0.3-0.8, 0 5-0.8, 0.33-0.43 or 0.3-0.7, for example, approximately 0.1, 0.15, 0.2, 0.25, 0.3, 0.31, 0 , 32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44 , 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.8 g / cm ³ . They can be essentially monodisperse, or they can be polydisperse, or they can have a multimodal (for example, bimodal, trimodal, etc.) particle size distribution. Monodisperse microspheres may have a more uniform crushing strength, while polydisperse microspheres may have improved bulk properties, contributing to increased particulate filler loads in the curable mixture. In this context, “substantially monodisperse” may refer to a dispersion in which less than about 10% of the microparticles (in terms of particle number) differ by more than about 10% in diameter from the average particle diameter. Mixtures of different categories (for example, particles of different sizes, densities, etc.) of microspheres can also be used. This may be applicable in improving bulk density by providing an increased content of microspheres to be used in the curable mixture. This may reduce the density of the resulting cured composite. The microspheres may have crush strengths of from about 35 to about 200 MPa (from about 5,000 to about 30,000 psi) or from about 35-150, 35-100, 100-200, 100-150, 150-200, 50- 150, 55-110, 35-70, 35-50, 50-100, 75-100 or 50-75 MPa, for example approximately 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 , 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200 MPa. In some cases, lower crush strengths than these values can be used, for example, from about 5 to about 35 MPa or about 5-20, 5-10, 10-35, 20-35, 10-25 or 15-25 MPa (e.g., approximately 5, 10, 15, 20, 25, or 30 MPa). Such microspheres are not allowed due to the high curing pressure (since at high pressures, most will crush during curing) and will only be suitable for foams for use at lower compression pressures. In this context, crush strength is the pressure required to crush approximately 10% of the microspheres. It can be hydrostatic crushing pressure (NDS). Microspheres can have an average diameter of from about 10 to about 200 microns, or about 10-100, 10-50, 10-20, 20-200, 50-200, 100-200, 20-100, 20-50, 50- 100 or 1-30 microns, for example, approximately 10.15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 microns. They can have average wall thicknesses from about 0.1 to about 5 microns, or about 0.1-2, 0.1-1, 0.1-0.5, 0.5-5, 1-5, 2- 5, 0.5-2, 1-2 or 0.5-1 microns, for example, approximately 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 microns. Preferred microspheres may have a crushing strength of from about 55 to 110 MPa and an absolute density of from about 0.3 to about 0.45 g / cm ³ . They may have a ratio of wall thickness to diameter of from about 0.5 to about 10%, or from about 0.5-5, 0.5-2, 0.5-1, 1-10, 2-10, 5-10, 1-5, 1-2 or 2-5, for example, approximately 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4,5, 5, 6, 7, 8 9 or 10%. Suitable microbubbles include, for example, 3M ™ S42XHS glass vials, which have an absolute density of approximately 0.42 g / cm ³ and an isostatic crush strength of approximately 8000 psi. inch (approximately 55 MPa). It is believed that brittle hollow microspheres (i.e., those that would be damaged in the determination of NDS) can weaken the cured epoxy composite if they survived the method of obtaining the mixture. Therefore, it is considered preferable that such microspheres be crushed in order to become a solid (incomplete) filler in the curable mixture. It should be noted that the ratio of wall thickness / diameter is likely to determine the NDS microspheres. Fragile microspheres can be of any size and can be those that have lower sphericity or have thinner walls. Higher-density microspheres may simply have thin walls.

Microspheres can be sorted. Thus, sorting, you can remove the microspheres larger than the selected size, or you can remove the microspheres smaller than the selected size. Smaller microspheres may have a reduced portion of the void volume, thereby weakening the properties of density reduction, while larger microspheres may have lower crush strength. They can be crushed during production, thereby weakening the properties of density reduction.

In some cases, with microspheres, the surface may be machined or the surface may be coated. This can improve the interaction between the epoxy matrix and the microspheres. This can improve the adhesion between the epoxy matrix and the microspheres. This can increase the strength and / or resilience and / or toughness of the composite. Suitable surface treatments include epoxysilane treatments (e.g., using glycidoxypropyltrimethoxysilane CH ₂ (O) CHCH ₂ OC ₃ H ₆ -Si (OCH ₃ ) ₃ to bond epoxy groups to the surface of the microspheres), or aminosilane treatments (e.g., using aminopropyltriethoxysilane NH ₂ C ₃ H ₆ -Si (OC ₂ H ₅ ) ₃ ) to bind the amino groups to the surface of the microspheres). In other cases, the surface of the microspheres is not processed or the surface of the microspheres is not coated.

In the present invention, there may be more than one type of microspheres used. For example, for improved strength, higher density microspheres can be used in combination with lower density microspheres to reduce the density of the epoxy composite.

This may be applicable for the use of a second filler and optionally additional fillers. Any of them independently may be fibrous or may be non-fibrous. Suitable non-fibrous fillers include polyolefin (e.g. polypropylene) granules or macrospheres (hollow or solid). They can have a diameter of from about 1 to about 20 mm, or about 1-10, 1-5, 1-2, 2-20, 5-20, 10-20, 15-20, 5-15, 2-5, 5 -10 or 10-15 mm, for example, approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 mm . Macrospheres can be made from epoxy resin reinforced with carbon fiber or fiberglass over polystyrene spheres that are made using rotational casting. Suitable macrospheres are available from dimming Corporation or Matrix Composites and Engineering Ltd. They have the following typical properties: density less than 0.4 g / cm ³ , compressive strength above 17 MPa, modulus of elasticity under compression above 0.8 GPa. Tests for the NDS (hydrostatic crushing pressure) of the foam of the present invention show that it is able to withstand a hole with a diameter of 16 mm 12 mm below the surface without crushing. It is clear that macrospheres can be safely added to the curable material, ensuring that they have the corresponding curable material around them (i.e. that there is sufficient distance between the macrospheres), and they also get a cured product that can withstand isostatic pressure, for which it was developed and / or strong enough to maintain the required hydrostatic crush strength of the syntactic foam, while it becomes generally less dense. Suitable fibrous fillers may be aramid fibers (e.g. Kevlar® fibers) or e-glass fibers. E-glass is an aluminoborosilicate glass with less than about 1 wt.% Alkaline oxides commonly used for fiber reinforcement. The second and optional additional fillers may each individually or in combination be present in from about 0.1 to about 1% by weight of the curable mixture or in about 0.1-0.5, 0.1-0.2, 0.2- 1, 0.5-1 or 0.2-0.5%, for example, in approximately 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0, 8, 0.9 or 1% w / w. Fibers (if the second filler is fibrous) can have an average fiber length of from about 0.2 to about 2 mm, or about 0.2-1, 0.2-0.5, 0.5-2, 1-2, or 0, 5-1.5 mm, for example, approximately 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1, 2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 mm, or in some cases may be more than 2 mm. The second filler can improve the tensile strength of the cured epoxy composite. This can improve its rigidity. This can improve its cracking resistance. This can improve any one or more, not necessarily all, of such properties by at least about 5% or at least about 10%, for example, by about 5, 6, 7, 8, 9, 10, 11, 12, 13 , 14 or 15% relative to the same material without a second filler. The benefit of using aramid or other organic (e.g. polymer, aramid, etc.) fibers as a second filler is to improve properties with relatively little, or in some cases no, effect on the density of the final composite.

Once the components of the curable mixture are combined, the resulting mixture is shaken properly, for example, mixed (i.e. for a sufficient time and at a sufficient speed) to turn it into a substantially uniform one. This can be accomplished, for example, with a mixer or mixer. The combination (described above) and also optionally mixing can be carried out in an airless atmosphere. The inventor has found that a small amount of carbon dioxide in an airless atmosphere can have a beneficial effect on the strength of the resulting cured composite. The concentration of carbon dioxide may be from about 1 to about 10%, or about 1-5, 1-2, 2-10, 5-10, or 3-8% based on volume, or about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10% by volume. In some cases, increased concentrations can be used, for example, from about 10 to about 50% (or about 10-40, 10-30, 20-50, 30-50, or 20-40%), for example, about 10, 15, 20, 25, 30, 35, 40, 45 or 50% by volume. It has been hypothesized that the presence of carbon dioxide affects the gas / mixture interface so that it reduces the size of the included gas bubbles. It has also been hypothesized that carbon dioxide can inhibit or retard (the approval of the epoxy resin, thereby providing a longer time to reduce or reduce voids (gas bubbles) in the mixture before curing (see below). This may be the result of the action of carbon dioxide on the curing agent The author of the present invention, however, found that if the concentration of carbon dioxide in the airless atmosphere is too high (for example, 100%), the density of the cured composite is higher than it It would be a disadvantage for deep-sea applications or other applications that benefit from the low density of the composite, although the use of 100% carbon dioxide may be suitable in cases where the low density of the composite is not critical. carbon by other gases that perform a similar function, for example, sulfur dioxide, nitrogen oxides, or mixtures of such gases. The remainder of the airless atmosphere or most of the remainder may be a gas that has a higher solubility in the curable mixture than air. Such a suitable gas is argon. You can also use krypton, xenon or other chemically inert gases. A preferred gas may be heavier than a combustible mixture of air and gasoline vapors. In some cases, instead of argon, gases can be used lighter than air, for example, helium. Mixtures of gases (e.g. helium / argon / carbon dioxide, neon / argon / carbon dioxide, etc.) can also be used. In some cases, mixtures with nitrogen may be used. Nitrogen may be in a smaller amount than in air, for example, less than about 70, 60, 50, 40, 30, or 20% by volume, or may be about 10, 20, 30, 40, 50, 60, or 70% airless atmosphere by volume. A preferred gas is one that has relatively high solubility in the curable mixture (e.g., higher solubility than air) and relatively low solubility in the cured composite (to allow it to exit the cured composite and thereby reduce the density of the composite). This can be useful in facilitating the preparation of a gas solution in the mixture before curing, so that any voids that are present in the mixture must be reduced or eliminated. It is believed that the reduction and / or elimination of gas bubbles can occur partly due to a simple decrease in the size of the gas in the cavity due to increased pressure (according to Boyle's law) and partly due to the absorption of gas in the cavity into the surrounding matrix due to the increased solubility of the gas in the matrix under increased pressure. According to the hypothesis, after curing, at least some dissolved gas diffuses from the composite. This can help reduce the density of the composite without introducing voids. An airless atmosphere can be heavier than air, although if suitable protective equipment is used, gas can be used lighter than air. The gas may have a density with respect to air at the same pressure of at least about 1.05 or at least about 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45 or 1.5, or approximately 1.05-2, 1.05-1.8, 1.05-1.5. 1.05-1.3, 1.1-2, 1.2-2, 1.5-2 or 1.1-1.5, for example, approximately 1.05, 1.1, 1.2, 1 , 3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2. The airless atmosphere may include, for example, 90-95% argon (or other suitable gas, as described above) ) or 90-93 or 92-95% of argon or other suitable gas, for example about 90, 91, 92, 93, 94 or 95% of argon or other suitable gas by volume. It may include both argon and carbon dioxide. It may include carbon dioxide as a side component (e.g., about 1-10%) and argon as a main component (e.g., about 90-95%). It can be, for example, welding gas. To mix under a heavier than airless airless atmosphere, it may be sufficient to have a stream of gas flowing through the mixture that is already mixed, however, the gas may alternatively or additionally be sparged / sprayed into the mixture. A suitable gas flow rate will depend on the volume of the mixture, however, typical costs are from about 1 to about 10 l / min or about 1-5, 1-2, 2-10, 5-10, 2-5 or 2-3 l / minute, for example about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 l / min for about 2-3 kg of the curable mixture. For large quantities of curable mixture, the flow rate may be proportionally higher. Mixing is usually carried out at ambient temperature or lower to avoid premature curing of the mixture. It can be carried out, for example, at from about 15 to about 30 ° C or about 15-25, 15-20, 20-30, 25-30 or 20-25 ° C, for example, about 15, 20, 25 or 30 ° C. As described elsewhere, it may be lower than temperatures such as about 0 ° C, for example. To achieve an acceptable degree of uniformity in the curable mixture, mixing may be required for at least about 30 minutes or at least about 1, 2, 3, 4, 5, or 6 hours, however, this will depend to some extent on the viscosity of the mixture. In some cases, shorter mixing can be effectively applied, for example, from about 1 to about 30 minutes, or from about 1-15, 1-10, 1-5, 1-2, 2-30, 5-30, 10-30, 20 -30, 2-15, 2-10, 2-5, 5-10 or 10-20 minutes, for example, approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 25 or 30 minutes.

Once the mixture reaches a suitable degree of uniformity, increase pressure to reduce or eliminate gas bubbles in the mixture. In this case, “reduce” refers to a decrease in the size or volume of gas bubbles (voids). “Eliminate” refers to the disappearance of gas bubbles (voids). It is assumed that this is at least partially due to gas in gas bubbles (voids) that are absorbed / dissolved in the curable mixture. This step is preferably carried out in such a way that the mixture is not exposed to gas (other than that which is trapped or dissolved in the mixture). This avoids the addition of additional gas to the mixture, which will reduce the ability of the mixture to absorb gas present in the voids. Pressure can be applied almost isostatically. Suitable methods of applying pressure to the gas are to envelop it with a protective material and immerse the wrapped mixture in a liquid and apply the required pressure to the liquid. A simple way to envelop the mixture is to place it on / on a thin layer of protective material, wrap the protective material around the mixture so as to completely surround it, and secure the ends of the protective material, for example, twisting and / or tying (for example, a collar, rope or some other suitable method). In this method, the curable mixture can be wrapped cylindrically with a protective material. The ends can then be twisted (like a sausage), and then clamps or other suitable fasteners are used to secure the ends. Alternatively, the enveloping can be performed cylindrically, and the additional end is attached to the end windings in at least two directions, as well as to the additional cylindrical windings. The insulating material may be a single layer insulating material or may be multilayer (for example 2-, 3-, 4- or 5-layer) in order to improve the insulating properties. The insulating material may be shrouded around the curable material in order to form an approximately rectangular parallelepiped. In some cases, the sealing material can be used to seal the insulating material. This can be a pressure-resistant adhesive, such as butyl mastic. In other cases, the insulating material may be densified by heating. The insulating material may be in the form of a hexagonal bolted box, sealed at 4 ribs with a sealant and having a partition at the top and bottom. The baffle allows the applied pressure to compress the mixture inside. An additional option is the use of an enveloped polypropylene box sealed with sealing material, for example, double-sided black tape with butyl mastic, with one or more external layers (for example, 1, 2, 3, 4 or 5) of PVC film, welded as a tank lining and again sealed double-sided black tape with butyl mastic. The PVC sheathing and polypropylene box can then be placed in a hexagonal bolted box that is no longer sealed. In a further embodiment, the curable mixture can be placed in an open tray and sealed with an elastic membrane that can be fixed to the upper faces of the tray. In this embodiment, the release agent may optionally be applied to the bottom and / or sides of the pallet. Suitable release agents include, for example, silicone release agents. Alternatively, the tray may have a non-stick surface, for example, a surface of a fluorocarbon polymer. The winding may be a single layer winding. It can be multilayer (for example, 2, 3, 4, 5, 6, 7, 8, 9 or 10-layer winding). Accordingly, the curable mixture can be introduced in a bag of insulating material. It can then be sealed, for example, sealed by heating so as to impede the access of the liquid in which it is compressed. The seal may be configured to include as little gas as possible inside the insulating material (i.e., inside the bag). In some cases, the mixture can be wrapped first and then sealed in a bag. The pressure in the liquid will then flow almost isostatically to the mixture. A suitable insulating material will be flexible in order to absorb pressure changes in the mixture and to transfer pressure from the surrounding liquid to the mixture. It should be practically impervious to liquids. It can be strong enough to withstand the forces they are subjected to during use. It should also be capable of (i.e., having a suitable softening and / or melting temperature) to withstand the temperature during curing of the curable mixture. Suitable insulating materials include polymer films, for example, polyethylene film, PVC film, latex film, polyurethane film, EPDM rubber, and the like. In the case of multilayer insulating materials, the different layers may be of the same material or may differ. The winding should be such that, under applied pressure, the liquid does not penetrate (or penetrate in small amounts) into the mixture, at least until the curable mixture cures to form a cured composite. In some cases, examples of the insulating material may be damaged at below about 90 ° C (for example, they may shrink, become brittle and / or fray). However, while the mixture and insulating materials reach this temperature, the mixture will be cured to a large extent (and will easily pass through the final transition phase, effective after curing, to further increase strength) and will therefore be impervious to liquid so that some penetration fluid did not cause problems. The fluid may be aqueous (e.g., water), or may be non-aqueous (e.g., silicone fluid, mineral oil, etc.), or may be some other type of fluid. The fluid may have a viscosity of from about 0.5 to 200 centistokes, or from about 1 to 200, 10-200, 50-200, 0.5-100, 0.5-50, 0.5-10, 0.5- 2, 1-100, 1-50, 50-100, 1-20 or 20-50 centistokes, for example, approximately 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4 5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180 or 200 centistokes. In some embodiments, the implementation of the wrapped curable mixture may be compressed by gas instead of liquid. In this case, the insulating material will be practically impermeable to gas. It should be noted that in some cases, the insulating material is not completely impervious to the surrounding liquid, and some liquid may leak into the mixture located here.

The pressure applied to the curable mixture may be approximately equal to or may be less than that which is designed to withstand use. It can be from about 5% to about 100% of the pressure expected to be applied, or from about 5 to 50, 5-20, 5-10, 10-100, 20-100, 50-100, 10-50, 10-20 or 5-20%, for example, approximately 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100% of the pressure to be applied. In specific embodiments, the implementation will be approximately 10% of the expected application pressure. It may be a pressure sufficient to break from about 5 to about 15% of the microsphere filler particles, or from about 5 to 10, or from 10 to 15%, for example, about 5, 10, or 15%. A small portion of the microspheres that collapse can then act as a filler to give strength to the resulting cured composite. The pressure may be a pressure of at least about 7000 kPa (approximately 1000 psi), although in some cases pressures below this value may be effective, for example, pressures of approximately or at least approximately 3000, 3500 (approximately 500 psi). inch), 4000, 4500, 5000, 5500, 6000 or 6500 kPa, or approximately 3000-7000, 3000-5000, 5000-7000, 4000-6000 or 4000-5000 kPa. Lower pressures can be used to produce composites with lower design depths. Such foams may have lower strength and / or lower density than cured at higher pressures. The pressure can be at least about 7500, 8000, 8500, 9000, 9500 or 10000 kPa, or can be from about 7000 to about 15000 kPa, or 7000-10000, 7000-8000, 8000-15000, 10000-15000, 8000- 12000 or 8000-10000 kPa, for example approximately 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000, 12000, 13000, 14000 or 15000 kPa. If the pressure is too low, the required degree of elimination of voids can not be achieved, leading to a cured composite, which has insufficient crushing strength (or compression). If the pressure is too high, excessive amounts of microspheres or particles of another particulate filler may be crushed or destroyed, in the case where the particulate filler particles are capable of crushing or collapsing. This may result in a cured composite that has a greater than desired density and may cause other undesirable physical properties (although this may increase the strength of the cured composite). This suggests that a pressure of approximately 7000 kPa will reduce the void size by at least about 70 times, and that since the gas in the void dissolves in the curable mixture, the void can decrease almost more than this value and can completely disappear.

In some cases, pressure may first be applied at a temperature at which the curable mixture does not cure rapidly (for example, does not cure for about 2 hours or for about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 hours). This initial compression phase may occur at approximately room temperature. It can occur at from about 15 to about 30 ° C, or from about 15 to 25, 15-20, 20-30, 25-30, or 20-25 ° C, for example, about 15, 20, 25, or 30 ° C. This allows time to reduce or eliminate gas voids in the mixture before curing. The curable mixture can be compressed at the above temperature for from about 1 to about 20 hours, or from about 1 to 10, 1-5, 5-20, 10-20, 15-20, or 10-15 hours, for example, about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 hours. This time can be regarded as the exposure time. In some cases, the temperature during this phase (holding period) may be below 15 ° C, for example from about 0 to about 15 ° C or from about 0 to 10, 0-5, 5-10 or 5-15 ° C, for example approximately 0, 5, 10, or 15 ° C. Compression at lower temperatures may be advantageous since the curable mixture will cure more slowly at lower temperatures, providing a longer time to reduce or eliminate voids (e.g., absorption). Additionally, since gases are usually more soluble at lower temperatures, the dissolution of gases in compression voids is provoked at lower temperatures, providing a greater reduction in the volume of voids.

After the initial stage of low temperature compression, the temperature can be raised to the curing temperature so as to harden the curable mixture. The temperature can be increased, for example, by increasing the temperature of the liquid into which the curable mixture was immersed (preferably wrapped in a protective material as described above). The curing temperature may be less than about 90 ° C, or less than about 80, 70 or 60 ° C. It can be above about 40 ° C, or above about 50, 60 or 70 ° C, or it can be from about 40 to 90, from 40 to 80, from 40 to 65, from 40 to 60, from 50 to 90, from 70 to 90 or from 50 to 80 ° C, for example approximately 40, 45, 50, 55, 60, 65, 70, 75. 80, 85 or 90 ° C. A curing temperature of about 90 ° C or higher can be applied in some cases, for example up to about 170 ° C, or up to about 160, 150, 140, 130, 120, 110 or 100 ° C, for example about 95, 100, 105, 110 , 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165 or 170 ° C. The curable mixture can be heated to the curing temperature and maintained without decreasing, i.e. maintaining pressure as described above. Thus, after mixing, optionally in an airless atmosphere, and subsequent wrapping in a protective material, if necessary, the pressure is increased to the required pressure and maintained until the curable mixture has cured to form a cured composite. In some cases, the pressure can be further increased before or during the high-temperature curing phase or slightly reduced, but it should be maintained in the desired range (described above). Typically, elevated pressures are kept substantially constant during curing of the curable composite. The curing temperature can be maintained for a sufficient time to cure the curable mixture. It can be maintained for at least about 2 hours, or at least about 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours, or from about 2 to 12, from 4 to 12 , from 6 to 12, from 8 to 12, from 2 to 10, from 2 to 6 or from 6 to 10 hours, for example, approximately 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 hours. The cure time will depend on the origin and proportions of the components of the curable composite (particulate filler, epoxy prepolymer and curing agent), as well as the origin, presence or absence and quantity of other components, such as a catalyst. The curing temperature may be such that the curing time or production time of the curable mixture is less than about 1 hour or less than about 2, 3, 4, 5, 6. 7, 8, 9, 10, 11, 12, 13, 14 , 15, 16, 17, 18, 19 or 20 hours. For example, the curing temperature may be such that the operating time or curing time is approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. 12, 13, 14, 15, 16, 17, 18, 19 or 20 hours. In some cases, it is possible to carry out post-cure either before or after pressure reduction (i.e., with a return to approximately ambient pressure). Post curing can be carried out under conditions (temperature, time), as set forth above for curing. These may be the same conditions as during curing or under various other conditions.

As described above, heating can be carried out by means of a heated liquid bath. In this case, the liquid in the bath can be recycled through a temperature controller that maintains the desired temperature. As well as providing the necessary heating to raise the temperature of the bath to the desired curing temperature, this can also serve to remove excess heat generated by the exothermic effect of the curing reaction so as to prevent overheating of the cured mixture. Additionally or alternatively, the heating can be carried out by means of an electric heating coil or some other suitable methods.

If a heating step is used to begin curing, the epoxy composite can be cooled until the pressure is released. Cooling can be accomplished by removing the cured composite from the liquid into which it was immersed for heating, or by cooling the liquid into which it was immersed. The cured composite can be cooled to room temperature before depressurizing, or it can be cooled to a temperature of less than or approximately equal to 40, 35, 30, 25, or 20 ° C, or to a temperature of approximately 40, 35, 30, 25, or 20 ° C. In some cases, it can be cooled to a temperature of 45, 50, 55, 60, 65 or 70 ° C until the pressure is released. The latter ranges are the most common with large samples of the product, since the time required for cooling is significantly longer for such large samples.

In a summary of the invention, a method for producing an epoxy composite of the present invention includes the following steps. The time indicated below is suitable for producing about 1-2 kg of a cured epoxy composite, but for large batches it may take a different time (for example, longer) and a slightly modified method.

- The epoxy prepolymer and curing agent were mixed in an airless atmosphere (for example, sparging with an airless atmosphere), usually about 3-4 minutes.

- Then, hollow glass microspheres were added to the combined prepolymer / curing agent. This may include the addition of two or more kinds of microspheres. In this case, the microspheres of increased (highest) strength or increased (highest) absolute density are the first to add. The resulting final cured mixture was then mixed in an airless atmosphere for 5 minutes until uniform. The total time for this and the previous mixing step, including the addition time, can be approximately 10-15 minutes.

- Then the cured mixture was wrapped in a polymer film. This may include wrapping the mold with a film, adding a curable mixture to the wrapped mold, and then completing the wrapping. Then, the wrapped mixture can be placed in a cooking bag made of a heat-sealable polymer film, which is then heat sealed to further protect the mixture. Wrapping and sealing in the bag should be done with the least possible filling with gas (air or airless atmosphere) of the wrapped or sealed bag.

- Then the wrapped mixture was immersed in a liquid, such as water or low viscosity liquid silicone, and then hydrostatically squeezed to the required pressure (from about 7 to about 15 MPa). This pressure is maintained for about 6-8 hours at or below ambient temperature (typically from about 10 to about 25 ° C).

- Then the temperature is raised to the desired curing temperature (usually approximately 50-90 ° C) while maintaining pressure. The temperature rise time can be approximately 4-6 hours. Then, the elevated temperature and pressure were maintained for about 6-8 hours to cure the mixture to form a composite. A post-cure step at 120 ° C. for approximately 1-3 hours is optional.

- Then, the cured composite was cooled to approximately room temperature (typically approximately 20-40 ° C) while maintaining elevated pressure.

- Once the composite temperature returns to approximately room temperature, the pressure can be relieved.

After the manufacture of the epoxy composite, as described above, it can be formed, for example, cut, saw, machine, grind, grind, grind, etc., to the desired shape. It can be formed in the form of blocks, bricks, plates or other suitable shape. It can be formed, for example, in a suitable form for the construction of a structural part or component for deep-sea marine vehicles. Alternatively, the curable mixture can be pressed into the desired shape before curing so that it cures to form pieces of a curable composite of the desired shape. When used, blocks or other forms of composite can be glued together, for example, for the construction of building beams. The adhesive may be epoxy adhesive. It can be high strength epoxy adhesive. It can be filler epoxy. It can be epoxy adhesive with microspheres as a filler. The microspheres can be polymer, glass or ceramic microspheres. If glass microspheres are used as filler for the epoxy adhesive, the epoxy and / or microspheres may be as described elsewhere in this document. The epoxide and / or microspheres may independently be as used in the preparation of the composite, or may be different. When used, the structural shell of the composite may have a shell or coating. It can be a plastic shell or coating. It can be a textile sheath or coating. It may be a protective sheath or coating. It may include, for example, a polymer sheath or a filler coating (for example, boron fiber, Kevlar® fiber and / or carbon fiber filler). It may include, for example, a fibrous textile sheath or coating, for example, including boron fiber, Kevlar® fibers and / or carbon fibers or polyester or polypropylene fabrics. The shell or coating may be in the form of a flexible film. The shell or coating can be layered on an epoxy composite. It can be flexible enough not to delaminate easily when used. The shell or coating may help to maintain the integrity of the composite at high pressures that occur during use.

The epoxy composite according to the present invention is subjected to an ultimate compressive stress (or crush strength) of greater than or equal to 100 MPa (approximately 14,500 psi), or greater than or equal to approximately 105, 110, 110 or 120 MPa, or from approximately 100 up to about 120 MPa, or from about 100 to 110, from 100 to 105, from 105 to 120, or from 105 to 110 MPa, for example, about 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119 or 120 MPa. The stress limit described above refers to the applied voltage at which the composite breaks. Usually this is a catastrophic destruction, in which the sample breaks. The composite has such a modulus of elasticity in compression such that at a pressure of 110 MPa (or at a crushing strength limit that is in any case less), it exhibits a deformation of less than or equal to about 3%, or less than or equal to about 2.5, 2, 1.5, 1, 0.95, 0.9, 0.85, 0.8, 0.75, 0.7, 0.65, 0.6, 0.55 or 0.5%. It can exhibit linear distortion of less than or equal to approximately 1.3% at a hydrostatic compression pressure of 110 MPa, or less than approximately 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6 or 0.5, for example, linear distortion of approximately 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1, 2 or 1.3%. In comparison, commercial syntactic foams typically exhibit compression deformation (or linear distortion) of approximately 1.4% or more under similar conditions. When using suitable microspheres as a particulate filler (as described previously), a density of less than about 0.8 g / cm ³ can be achieved with the strength and modulus values described above, or a density of less than about 0.75, 0.7 , 0.65 or 0.6 g / cm ³ , or from about 0.5 to about 0.8 g / cm ³ , or from about 0.5 to 0.7, from 0.5 to 0.6, from 0.6 to 0.8, or from 0.6 to 0.7 g / cm ³ , for example, approximately 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0, 8 g / cm ³ . An epoxy composite may have low water absorption. Its equilibrium water absorption may be less than about 0.5% weight / weight or less than about 0.1% weight / weight. It can be measured at approximately atmospheric pressure, or at a pressure of approximately 100 MPa, or at a pressure of approximately 110 MPa, or at a pressure of approximately 125 MPa. Water absorption may be less than about 0.4, 0.3, 0.2, 0.1, 0.05, 0.02 or 0.01%, or may be about 0.01, 0.02, 0.03 , 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0 , 4, 0.45 or 0.5% w / w. In comparison, previously known syntactic foams may have water absorption of about 3% by weight at about 18,000 ft / sq. inch (approximately 125 MPa). The above water absorption values are measured at room temperature, for example at approximately 20 or 25 ° C. The cured composite may have a tensile strength of more than about 20 MPa, or more than about 25, 30, 35, or 40 MPa, or from about 20 to about 50 MPa, or from about 20 to 40, from 30 to 50, or from 30 to 40 MPa, for example about 20, 25, 30, 35, 40, 45, or 50 MPa.

For a cured composite, the compression module may be at least about 2 GPa, or at least about, or from about 2 to about 9 GPa, or from about 2 to 8, from 2 to 6, from 2 to 4, from 3 to 8.5, 5 to 8.5, 7 to 8.5, 4 to 8, 6 to 8, 4 to 6, 2 to 3, 3 to 4, 2.5 to 4, or from 2.5 to 3.5 GPa. It can have a modulus of approximately 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or 8.5 GPa. This module can be deformed to about 3%, or to about 2.5, 2, 1.5, 1, 0.5, or 0.1%.

An important aspect of the composite described herein is the combination of high crush strength (i.e., compressive modulus) with low density, which makes it suitable for use in deep-sea building applications. Other properties that can be combined with this combination include high crack resistance, low compressibility (i.e., high modulus of compression), high rigidity and uniformity of physical properties throughout the large block of the composite. Important aspects of the process for producing these products include:

- selection of appropriate raw materials, in particular low density fillers and optionally a second (usually fibrous) filler: a particular grade of raw material may be important to obtain suitable properties;

- the use of appropriate component ratios so that the uncured mixture has sufficient viscosity to prevent separation of the components (specific fillers);

- the use of a combination of prepolymer and curing agent, which allows you to greatly slow down curing at ambient temperatures and relatively quick curing at elevated temperatures. In certain cases, this allows curing on demand. In large blocks, the mixture can be cured without external heating due to the very slow rise in temperature that was observed before rising to about 50 ° C. There is reason to believe that the cause of this may be the insulating properties of glass or simply epoxy. For smaller blocks, heat loss from the mixture can overcome the exothermic effect, which requires external heating to cure the mixture, providing curing on demand;

- mixing in a suitable airless atmosphere so that any entrained gas bubbles / inclusions can decrease in size and / or adsorb into the mixture upon compression;

- compression of the curable mixture at a temperature at which curing is very slow, this compression is used for a sufficient time to ensure the absorption of gases into the mixture before curing;

- external use of heating to accelerate curing and to reduce temperature gradients within the curable mixture. The use of external heating also provides post-curing of the resin. An epoxy resin usually takes 8 hours at 80 ° C to achieve its optimum HDT (temperature allowable deformation), which, according to the author of the present invention, is best carried out at elevated pressure. Thus, the use of external heating can start / accelerate curing, reduce temperature gradients and provide a post-cure cycle for the cured mixture.

The cured composite of the present invention, in particular when formulated with hollow microspheres as a particulate filler, may be suitable for use in deep sea applications. It may be able to withstand operating pressures in the deepest parts of the ocean (approximately 11,000 m). It may be able to resist hydrolysis in seawater at operating pressures at these depths. It can be floating in seawater. It may be suitable for use as a flotation element and / or as a structural element at this depth. For example, it may be suitable for use as the outer surface of an underwater vehicle, which is used in the deepest parts of the ocean, and may additionally provide buoyancy in this application. It may be suitable for use as a casing for deepwater risers of an oil pipeline. It may have thermal and / or acoustic properties suitable for deep sea applications. It may possess any combination of the above properties suitable for the applications in which it will be used.

For use in aquatic environments, low water absorption may be an advantage. The composite of the present invention may have a water absorption of less than about 0.5% under application conditions (for example, to a water depth of 11,000 m), or less than about 0.4, 0.3, 0.2, or 0.1% by weight, or approximately 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5%. At a depth of approximately 11,000 m in seawater, the pressure is approximately 16,500 psi. inch (approximately 114 MPa). At these pressures, the water absorption of the cured composite described herein may be zero or may be negligible. There is reason to believe that a specific production method in which the composite is cured at high pressure, combined with a highly active particulate filler (which leaves relatively small amounts of an organic matrix that absorbs water), provides this exceptional water absorption property.

The use of microspheres, in particular glass microspheres, as a filler in the form of particles in the cured composite can also increase the heat-insulating and / or sound-insulating properties of the composite, which may be an advantage in some applications.

In a specific embodiment, the epoxy composite of the present invention is produced using hollow glass microspheres with an epoxy resin. But unlike other syntactic materials, the real composite is “isos” or of equal strength (iso as a prefix from the Greek word “isos” meaning equal). Equal (or identical) properties are achieved by mastering a special production method that differs from the prior art. The following is a guide for a suitable method for producing the epoxy composite of the present invention:

For the epoxy resin, glass microspheres with high-density packaging were selected so that the mixture became plastic or semi-solid. Light hollow glass microspheres that would normally move and float to the surface in a liquid are less capable of moving as fast in a plastic or highly viscous mixture.

Hollow glass microspheres and an epoxy mixture were mixed and packaged in a mold in an artificial environment. An atmosphere of 5% CO ₂ with argon is suitable since both gases are readily available (individually and / or previously mixed as a welding gas). In addition, since both gases are heavier than air, using simple equipment it is easy to create an artificial environment above the microsphere / resin mixture, for example, a flow meter and an open pipeline. Similar results were expected with other gases and / or a mixture of other gases, including gases that are lighter than air, with special chambers for stuffing and mixing in order to retain the artificial medium (s).

Then the packaged mixture was sealed in air and sealed. Successfully used wrapping in several layers of "sticky" film, sealed plastic bags or special flexible liners packages.

The sealed mixture was placed in a pressure vessel and compressed with a liquid. A safe thermally conductive fluid such as water is suitable, although other fluids may also be used. The pressure was selected depending on a number of factors, such as NDS (hydrostatic crushing pressure) of hollow glass microspheres, packing density, etc. Ideal pressure will destroy the fragile hollow glass microspheres that are undesirable without breaking the overpack so that the strong, hollow glass microspheres are crushed by physical contact with each other.

Slow curing of the epoxy is more preferable, which allows the amount of gas involved in the mixture to be absorbed into the liquid epoxy (pre-mixed with the curing agent). Hydrostatic pressure is maintained throughout the curing of the resin and any additional post-curing cycle, including cooling to room temperature before depressurizing.

The various properties of the method described above, including selecting the correct packing density, type of hollow glass microspheres, epoxy systems, artificial gases, applied hydrostatic pressure, curing temperature and number of curing cycles, are all important for the present method. Rather, it is a collaborative process that allows syntaxing with the best results.

The author of the present invention suggests that CO ₂ can change the surface tension of the epoxy resin and / or can act as a moderator to allow the epoxy to remain liquid longer. Both of these effects will allow more gas to be absorbed into the liquid epoxy resin before it thickens or becomes solid. Argon acts as a CO ₂ solvent, since the present inventor has found that the presence of a large amount of CO ₂ on an epoxy resin can have an adverse effect and can be more absorbed than air into a liquid epoxy resin.

In prior art methods, hollow glass microspheres and epoxy are typically mixed to form a suspension, then poured into curing molds. High-quality foams are mixed under vacuum to minimize air entrainment, and carefully poured to prevent additional air from entering the mixture. Trapped or entrained air is undesirable since it reduces the NDS (hydrostatic crushing pressure) and stiffness (measured during deformation), but does not increase the buoyancy and insulating properties, therefore, a certain amount of air / gas in the mixture was usually allowed.

Hollow glass microspheres / epoxy system were considered as potentially suitable for use, however, mixing the ingredients in a vacuum was considered difficult and undesirable. Other low-density fillers and hollow fillers have been considered, but hollow glass microspheres provide a ratio of the highest crush strength to density than other types. Other binders were considered in the same way, but epoxy systems have the distinctive advantage of having the best ratio of compressive strength to density and are practically impervious to water penetration.

To overcome the need to mix in a vacuum, the inventor of the present invention has developed a method comprising mixing the ingredients at significantly higher packing densities, and then compressing the mixture in an isostatic pressure vessel and curing it under pressure. It was believed that this would create a practically airless foam (or at least a foam with reduced amounts of air), since any air spaces would decrease during compression (Boyle's law) and would be absorbed into the liquid epoxy resin before it cured (Henry's law). It should be recognized that the “airless” in this case refers to air outside the microspheres, since obviously the process does not affect the air inside the microspheres. The present inventor contemplates that any compressed / absorbed air will be decompressed from the cured composite and will not cause problems. There is no direct evidence that this is actually happening, but air was not a problem.

A large number of cured composites were obtained with different packing densities of hollow glass microspheres in epoxy resin, following recommended curing cycles using various isostatic pressures. It was found that increased packing densities of the filler in the form of particles provide a more uniform foam, since hollow glass microspheres are not able to move in mixtures of high packing density if the mixture was mixed to a paste-like consistency. This is an important step in obtaining a foam of uniform density and strength.

The initially obtained foams (mixing in air) seemed to be free of voids, however, it became apparent that large air inclusions were not absorbed into the epoxy and became trapped in the foam. Bending tests revealed specimens destroyed by stress near the explosive pockets of trapped air that were under pressure in the cured composite. The voids were distinguished by a brownish mark so that any light brown mark was detected when the treatment was considered as suspicious voids (although not obvious to the eye). It seemed that there were more voids than was considered desirable, despite the fact that the results of the NDS tests (hydrostatic crushing pressure) were suitable. It was found that these foams had poor stress properties.

In order to solve the problem of voids of compressed gas, the components were mixed in environments of various gases, which were heavier than air. This was relatively easy to achieve since the only equipment needed was a gas source, a flow meter and a short pipeline. It was assumed that the gas would remain in the mixing tank under the condition of current and further retention. The mixture, which was mixed in airless media, was then isostatically compressed in a high-pressure chamber similarly to samples "mixed in air".

The following effects were observed using various gases:

- mixing in an atmosphere of CO ₂ gave a foam without voids, but an undesirable reaction to the curing agent was noted in the epoxy system: the samples mixed in the medium of this gas were denser than expected, although good NDS was maintained;

- when mixing 100% argon mixed in a medium, finer voids were obtained, identified by finer brown marks, again with good HCP;

- tested welding gas with 5% CO ₂ , 2.5% O ₂ by volume and the remainder of argon.

The results so far have been foam without voids, and no significant increase in density has been observed.

From the above mixtures in various gases, it is obvious that low concentration of CO ₂ can slow down the curing of the epoxy resin (not at high concentrations) and / or it can change the surface tension of the liquid epoxide enough to provide a large absorption of gas (or rapid gas exchange) into the epoxy resin before curing. During these tests, it was found that the ongoing curing temperature delay also reduces voids. Obviously, this can provide more time for the gas, which is absorbed until the epoxy is fully cured.

Thus, the present invention includes the use of gas to change the properties and / or cure of the epoxy resin to facilitate absorption of the entrained gas into the mixture, which is then placed under isostatic pressure conditions until completely cured.

Figure 1 summarizes a suitable method in accordance with the present invention, as described previously.

Figure 2 shows electron micrographs of both rough and smooth sections of the composite. In the rough fragment (Fig. 2a), voids can be seen where the microspheres came out during the destruction.

Figure 3 shows a characteristic temperature profile during the high pressure stages of the method described here. The initial slight increase in temperature may be due to a weak exothermic effect during curing, however, in the absence of external heating, the temperature remains mainly constant around 22-25 ° C. After approximately 6 hours, external heating begins, and approximately 5-6 hours are required to reach a final temperature of about 80 ° C. Fluctuations in temperature may be due to changes in the temperature of the bath, due to the “oscillation” of the thermostat, and / or may be due to other reasons, such as instability due to the weak exothermic effect during curing. After approximately 6 hours of high temperature curing, the composite is cooled to a temperature of about 30 ° C, which takes about 4 hours. From this point on, the cured composite is ready for pressure reduction.

Selection of hollow glass microspheres

Hollow glass microspheres can be purchased from any suitable manufacturer. It was found that those microspheres that were produced by 3M ™ were particularly suitable. 3M uses the expression “glass bubbles” for hollow glass microspheres. Figure 5 shows a graph showing suitable 3M glass balls showing NDS (hydrostatic crushing pressure) versus natural bubble density. From figure 5 it is clear that the increase in the NDS occurs due to the increased density - the dependence appears sharply linearly up to the NDS about 80 MPa, although it seems possible to increase the NDS without a significant increase in density. The ideal microsphere for deepwater applications would be in the lower right-hand side of the graph (low density / high NDS), however, these products are not currently available for purchase. The table below provides the data from FIG. 5 along with identification of specific grades of tested microspheres.

Glass Bubbles (Type 3M) HCP (MPa) Density (g / cm ³ ) NDS (psi) A16 / 500 3.45 0.16 500 A20 / 1000 6.89 0.2 1000 D32 / 4500 31.03 0.32 4500 H20 / 1000 6.89 0.2 1000 H50 / 10000 EPX 68.95 0.5 10,000 iM30K 206.84 0.6 30000 K1 1.72 0.125 250 K15 2.07 0.15 300 K20 3.45 0.2 500 K25 5.17 0.25 750 K37 20.68 0.37 3000 K46 41.37 0.46 6000 S22 2.76 0.22 400 S32 13.79 0.32 2000 S35 20.68 0.35 3000 S38 27.58 0.38 4000 S38hs 37.92 0.38 5500 S38XHS 37.92 0.38 5500 S42XHS 55.16 0.42 8000 S60 / 10000 68.95 0.6 10,000 S60XHS 124.11 0.6 18000 XLD3000 20.68 0.23 3000 XLD6000 41.37 0.3 6000

From figure 5 and the table above, it is apparent that the most effective glass vials for low pressure applications are K1, for slightly higher pressure applications the XLD3000 and XLD6000, and for iM30K ultrahigh pressure applications. While the iM30K is not specifically designed for use in syntactic foam production, they are nonetheless effective glass bubbles for use in this application. A suitable material would be a glass vial of FIG. 5 (possibly individual production) with a density of 0.4 g / cm ³ and a crush strength of approximately 12,000 psi. inch (approximately 83 MPa). Glass vials XLD6000, iM30K and S42XHS were selected for testing.

Selection of a suitable epoxy system

Pure samples of the following types of epoxy resins were tested for density and compression resistance:

- KINETIX® R118 Epoxy R118 from ATL Composites with H103 Hardener

- KINETIX®R246 Epoxy R246 from ATL Composites with H128 Hardener

- KINETIX®R240 epoxide R240 from ATL Composites with hardener H341

- Epiglass® HT9000 Epiglass® HT9000 with standard hardener HT9002

- L285 Epoxy L285 from Hexion Chemicals with a curing agent L285

- 862L6 Hexion Chemicals Epon® 862 with Lindau® Lindride® 6 hardener

- 862LS-81K Hexion Chemicals Epon® 862 with Lindau LS-81K curing agent.

The stress-strain curves under compression are shown in FIG. Thus, FIG. 4 illustrates the properties of various epoxies that have cured under elevated pressure. Fig. 4a shows stress-strain curves, indicating that the materials withstood compression stress of more than 80 MPa and in one case more than 120 MPa. Fig. 4b shows the modulus values obtained from the curves of Fig. 4a. The initial modulus was between about 3 and 4 GPa, but decreased when the voltage was more than about 2% (corresponding to a voltage of about 60-80 MPa). From these values it is obvious that the region in which these materials are sufficiently elastic is at least about 2% stress. Fig. 4c shows the ratio of the Poisson ratio to the curves of Figs. 4a and 4b. An increase in the Poisson's ratio was observed approximately linearly upwards to at least approximately 4%, and the linearity of the Poisson's ratio manifests itself with an increase with decreasing maximum strain. The following densities were measured:

- R118 1,130 g / cm ³ - R246 1,136 g / cm ³ - R240 1.185 g / cm ³ - NT9000 1,166 g / cm ³ - L285 1.172 g / cm ³ - 862L6 1.235 g / cm ³ - 862LS-81K 1.217 g / cm ³

Sample making

In the present method, the recommended ratio of epoxy to curing agent was mixed with glass microspheres to obtain a microsphere concentration of approximately 66-67% by volume in the mixture. Mixing was carried out in a flow of welding gas containing 2% oxygen, 5% carbon dioxide and 93% argon, for a sufficient time to achieve a homogeneous mixture of a paste-like consistency. The mixture was wrapped with a flexible plastic film and immersed in a liquid at room temperature. Pressure is approximately 1,500 psi. an inch (approximately 10,300 kPa) was applied to the liquid to increase the pressure of the mixture. The pressure was maintained for about 15 hours and then the temperature was raised (while maintaining the same pressure) to about 80 ° C. This temperature and pressure were maintained for approximately hours, after which the final cured composite was cooled to approximately room temperature before the pressure was released.

While increased epoxy compression resistance can increase the NDS of syntactic foam, the effect of increasing the strength of epoxy is negligible when the syntactic HCP is higher than epoxy compression resistance. A disadvantage of the increased compression resistance of the epoxy resin is that it usually coincides with an increase in the density of the epoxy resin. The densities of the epoxy resins described above are in the range of less than 0.105 g / cm ³ . The syntactic buoyancy effect of the tested resins may be more than 2 pounds / cubic foot (0.032 g / cm ³ ) in a high density glass bubble.

6 shows a graph on which NDS and the density of syntactic foam are applied, which was made using different glass bubbles with different packing densities with different epoxies. From these results it is obvious that the packing density of the glass bubble and various epoxies change the density of the syntactic foam and HCP, but mainly the NDS of the glass bubbles determines the NDS of the syntactic foam. The table below shows the data (HCP, density and deformation) for FIG. 6, which identify the foams (by the ratio of the microspheres, the origin of the microspheres and the origin of the epoxy).

% glass bubbles, type of bubbles and type of epoxy HCP (MPa) Density (g / cm ³ ) µε at 114 MPa% 68 iM30K R118 206.8427 0.795297 -0.84 60 XLD R240 124,1056 0.672658 -1.03 60 XLD R240 132,3793 0.680128 -1.09 33 iM30K 33 S42 R118 166.8531 0.725107 -0.84 62 S42 XHS R118 137.8951 0.697111 -0.94 66 S42 XHS R246 150,9952 0.671396 -0.96 32 iM30K 32 XLD R246 144.7899 0.698383 -0.86 61 XLD R246 131,0004 0.684823 -one 9 iM30K 54 XLD R240 130.3109 0.653948 -1.05 61 XLD R118 109,6266 0.62063 -1.12 63 XLD R118 105,4898 0.609826 -1.12 65 XLD R118 97.21608 0.596809 -1.12 61 XLD R240 129,3456 0.663678 -1.05 63 XLD R240 122,7267 0.67249 -1.05 61 XLD L285 115.8319 0.638555 -1.17 63 XLD L285 115.8319 0.663587 -1.17 61 XLD R246 116.5214 0,603609 -1.29 59 XLD R246 121.3477 0.643174 -1.15 59 XLD R118 116.5214 0.643878 -1.13 58 XLD R118 117.4867 0.647853 -1.11 59 XLD L285 128.5872 0.65742 -1.14 58 XLD L285 131.6899 0.665804 -1.13 10 iM30K 57 S42 R118 147.3754 0.689103 -0.87 10 iM30K 57 S42 R118 149.2853 0.690064 -0.81 20 iM30K 47 S42 R118 167,846 0.703526 -0.8 30 iM30K 37 S42 R118 177.3469 0.721154 -0.89 10 iM30K 57 S42 R118 Argo 160,1169 0.697596 -0.92

Key findings include:

- XLD6000 — Syntactic foam made with XLD6000 glass vials matched to target densities. Foams were made with HCP varying from about 96 MPa to 132 MPa. Although sufficient for limited depth applications, these HCP values do not meet FofS for the depth requirements required for deepwater applications.

- S42XHS - syntactic foams made with S42XHS glass bubbles do not meet target densities up to 0.024 g / cm ³ . This makes them even less effective than claimed. However, foam samples were made with HCP 151 MPa at a density of 0.67 g / cm ³ . While FofS within these limits may be acceptable, its density is less than desired.

- iM30K is a syntactic foam sample made with iM30k glass bubbles and has a widely acceptable density. He also retained the highest packing density of all other mixtures. Despite the exceptionally high HCP (206.8 MPa), it is too heavy to use for general buoyancy. However, it can be used in other areas of deep-sea vehicles that require lightweight and durable material.

With reference to FIG. 6 and the accompanying table, a class of glass bubbles between the XLD6000 and iM30k appears to be preferred. Lying on the same line between the two products, the “bottom target” would be a glass bubble with an HCP of 10,000 psi. an inch (68.9 MPa) at a density of 0.35 g / cm ³ , while a “high target” would be a bubble with an HCP of 16,000 psi. inch (110.3 MPa) at a density of 0.425 g / cm ³ . It was envisaged that the use of such microspheres could not only meet the FofS HCP requirements, but also lightweight floating material for use at any depth could be produced. Even one class between the two goals could help fill the void and allow manufacturers of syntactic foam to meet the requirements of a customer who wants a higher strength, more efficient foam.

Figure 7 shows the characteristics of a composite prepared using iM30K glass microspheres together with S42XHS glass microspheres under hydrostatic pressure. The iM30K microspheres provide improved strength, while the S42XSH microspheres provide lower density. Deformation meters were attached at the top and bottom to the sample. You can see that the difference between the curves is very small, which indicates a significant symmetrical compression, and thus a significant uniformity of the sample. The execution of compression causes a linear change in deformation with an increase in pressure up to 160 MPa, which is significantly higher than the created requirements for materials used at great depths.

Fig. 8 shows a compression test of the sample that was used in Fig. 7. Thus, Fig. 8a shows a stress-strain curve under compression, indicating a significant linear change (increase) to approximately 100 MPa / 1.5% strain, with a corresponding increase in characteristics to approximately 110 MPa / 2% strain. Fig. 8b shows a characteristic of a module. Even up to about 2%, the modulus is more than 5 GPa and up to 1% remains above 7 GPa. Fig. 8c shows the nature of the change in Poisson's ratio. It increases approximately linearly, but even at 2% strain, it is only approximately 0.4.

Fig.9 shows a fragment of a valid sample of the composite used in Fig.8 after fracture in compression. It is seen that no visible voids were detected in the sample. As noted earlier, voids in the cured composite can act as sites of initiation of fracture of the sample, leading to a decrease in the tensile strength during deformation.

Figure 10 shows the results of a bend test on a sample made using 10% iM30K glass microspheres and 57% S42XHS glass microspheres with R118 / H103 epoxy. 11 shows a sample after breaking, showing a clean fracture. You can see that the sample can withstand bending forces of up to about 24 kN. Linear curves indicate that during the test the material remains elastic in the bending mode. The fact that compression strains (curves that slope down to the right) are almost similar to those under tension (those that slope up to the right) is encouraging, since it indicates that the material behaves the same when squeezed and stretched. The sample used in this test was made using low pressure, and other samples were made using higher pressure, returning better results in bending mode.

As a test for shrinkage of the curable mixture before hardening, a batch of the curable mixture consisting of 10% iM30K glass microspheres, 57% S42XHS glass microspheres with R118 / H103 epoxy, was stirred at 20 ° C into a cylindrical shape approximately 110 mm in diameter and length 380 mm. 31.2 kg was added to a flat sheet to shape the pancake (within a few minutes). After this period, the amount of shrinkage was minimal. The width of the flattened cylinder was reduced to 85 mm. The contact surface of the flat sheet and the mixture was approximately 110 mm wide × 390 mm long oval. According to estimates, this amounted to a plot of approximately 33150 mm ² using a force of 0.306 kN, which corresponds to 9.227 kPa.

Test reports

The following test protocols were used for the experiments described above.

Pressure test

A sample of 100 mm × 100 mm × 100 mm was used as the sample and strain gauges were placed centrally on four surfaces or on two opposite surfaces. For the hysteresis test, the pressure was increased from 0 to 125 MPa and back with a cycling frequency of 5 times. The rate of change was 10 MPa / min. After cycling, the sample was brought to failure. For the fracture test, pressure was recorded at the onset of fracture.

4-point bending test

Used the apparatus as shown in Fig.12. Centrally, three parallel 120 ° notches were made in the sample, as shown in FIG. Used rollers with a diameter of 20 mm and a length of 75 mm. The 0 ° / 90 ° strain gauges were placed centrally and 10 mm to the side and duplicated at the bottom of the sample, or alternatively one 0 ° / 90 ° was placed centrally at the top and bottom. The force was increased until the destruction of the sample.

A 4-point bending test was considered preferable for testing these materials. The widely used 3-point bending test does not necessarily result in failure at the most fragile point of the specimen. Therefore, they took a 4-point test, as this allowed the defective sample to collapse at the point of weakness.

Applications

The present invention has been developed for use as a structural component in areas of very high pressure, such as ocean depth. However, other applications where the epoxy of the present invention can be used include hairpin winches, diffusers, explosion protection in both cylinders and pistons.

Claims (36)

1. A method of obtaining an epoxy composite in the form of syntactic foam, including:
- combining an epoxy prepolymer, a curing agent and a particulate filler to form a curable mixture, wherein the particulate filler is hollow microspheres;
- shaking the mixture in an airless atmosphere to turn it into almost uniform, where the solubility of the airless atmosphere in the curable mixture is higher than the solubility of air in the curable mixture;
- applying a pressure of at least about 3000 kPa to the mixture to reduce or eliminate gas bubbles in the mixture; and
- maintaining a pressure of at least about 3000 kPa until the curable mixture becomes cured to form an epoxy composite,
wherein the epoxy prepolymer is oligomeric or polymer particles capable of crosslinking to form a cured resin and containing oxirane groups, and the curing agent is particles capable of reacting with an epoxy prepolymer to react with oxirane groups in an epoxy prepolymer to crosslink the prepolymer to form cured epoxy. 2. The method of claim 1, wherein the pressure applied to the mixture is at least about 7000 kPa. 3. The method of claim 1, wherein the pressure applied to the mixture is from about 2000 to about 7000 kPa. 4. The method according to any one of paragraphs. 1-3, where the prepolymer and curing agent are such that the working time of the curable mixture at 20 ° C is at least about 1 hour. 5. The method according to any one of paragraphs. 1-3, where the combining step is accompanied or precedes the cooling of one or more components of the curable mixture. 6. The method according to p. 5, where the cooling is carried out to a temperature of from about 0 to about 10 ° C. 7. The method according to any one of paragraphs. 1-3, where the stage of Association is carried out in an airless atmosphere. 8. The method according to any one of paragraphs. 1-3, where the airless atmosphere contains at least about 50% molar-based argon. 9. The method of claim 8, wherein the airless atmosphere contains about 5% carbon dioxide and about 93% argon. 10. The method according to any one of paragraphs. 1-3, where the stage of applying pressure is carried out so that the mixture is not exposed to air or airless atmosphere. 11. The method according to any one of paragraphs. 1-3, where the particulate filler has a lower density than the prepolymer. 12. The method according to p. 11, where the density of the filler in the form of particles is less than approximately 0.5 g / cm ³ . 13. The method of claim 1, wherein the hollow microspheres are hollow glass microspheres. 14. The method of claim 1, wherein the hollow microspheres are such that no more than about 10% of the microspheres are destroyed during the stage of applying pressure to the mixture. 15. The method according to any one of paragraphs. 1-3, where the combining step involves combining an epoxy prepolymer, a curing agent, a particulate filler, and a second filler to form a curable mixture. 16. The method of claim 15, wherein the combining step is such that the second filler comprises from about 0.1 to about 1% by weight of the curable mixture. 17. The method according to any one of paragraphs. 1-3, including heating the curable mixture so as to start or accelerate curing to form an epoxy composite. 18. The method according to p. 17, where the heating is carried out to a temperature of less than 90 ° C. 19. The method according to p. 17 or 18, where the heating is started at the point in time (referred to in this document as the exposure time) after the start of applying pressure to the mixture. 20. The method according to p. 19, where the exposure time is at least about 1 hour. 21. The method according to p. 17, where the epoxy composite is cooled before depressurization. 22. An epoxy composite in the form of a syntactic foam containing a filler in the form of particles and having an ultimate compressive stress greater than or equal to 100 MPa, and a density less than about 0.7 g / cm ³ ,
where the particulate filler is a hollow microspheres, the specified epoxy composite is obtained from:
an epoxy prepolymer representing oligomeric or polymeric particles capable of crosslinking to form a cured resin and containing oxirane groups, and
a curing agent, which is particles capable of reacting with an epoxy prepolymer to react with oxirane groups in an epoxy prepolymer to crosslink the prepolymer to form a cured epoxy resin. 23. The epoxy composite according to claim 22, which exhibits a linear distortion of less than or equal to approximately 0.9% under a hydrostatic compression pressure of 110 MPa. 24. The epoxy composite of Claim 22 or 23, wherein the particulate filler density is less than about 0.5 g / cm ³ . 25. The epoxy composite according to claim 22, where the hollow microspheres is a hollow glass microspheres. 26. An epoxy composite according to claim 22 or 23, wherein the particulate filler is present in the composite at a rate of about 60% or more by volume. 27. An epoxy composite according to claim 22 or 23, further comprising a second filler. 28. The epoxy composite of claim 27, wherein the second filler is a fibrous filler. 29. The epoxy composite of claim 27, wherein the second filler comprises aramid fibers and / or e-glass fibers. 30. The epoxy composite of claim 28 or 29, wherein the fibers of the fibrous filler are from about 0.2 to about 2 mm on average in length. 31. The epoxy composite of claim 28 or 29, wherein the second filler is present in the composite from about 0.1 to about 1% w / w. 32. The use of the epoxy composite according to any one of paragraphs. 22-31 as a structural component in compression. 33. The application of claim 32, wherein said application takes place in a device for use under water. 34. The application of claim 33, wherein said application is at a depth of at least about 10 km below the surface of the water. 35. The application of claim 33 or 34, wherein said device is a deep-sea habitable vehicle. 36. The application of claim 33 or 34, wherein the epoxy composite forms part of the outer surface of said device.

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