WO2021107908A1

WO2021107908A1 - Sprayable insulation coating formulation having a low thermal conductivity that provides resistance against aerodynamic heating through erosion

Info

Publication number: WO2021107908A1
Application number: PCT/TR2020/051181
Authority: WO
Inventors: Yasemin ALTUN; Olcay ELMALI MEÇO; Hüseyin ÇİÇEK
Original assignee: Roketsan Roket Sanayi̇i̇ Ti̇caret A. Ş.
Priority date: 2019-11-29
Filing date: 2020-11-27
Publication date: 2021-06-03
Also published as: TR201918742A1

Abstract

The present invention relates to an ablative insulation coating formulation that can be applied through a spraying method on at least one exterior surface of metal components of missile systems and features a low thermal conductivity. Said formulation comprises at least one solvent; at least one epoxy-novolac based resin; at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder, phenolic micro balloon and/or combinations thereof, at least one flame-retardant material comprising the mixture of ammonium polyphosphate and/or boric acid; a hardening agent; at least one diluting agent and at least one bonding silicone resin.

Description

SPRAYABLE INSULATION COATING FORMULATION HAVING A LOW THERMAL CONDUCTIVITY THAT PROVIDES RESISTANCE AGAINST AERODYNAMIC HEATING

THROUGH EROSION

Technical Field

The present invention relates to an ablative insulation coating formulation that can be applied through a spraying method on at least one exterior surface of metal components of missile systems and features a low thermal conductivity.

Prior Art

Missile and rocket systems that can fly at supersonic speeds a couple of times faster than sound are exposed to aerodynamic heating resulting from the friction with the dense atmosphere layer and the exterior surface temperatures thereof may increase up to 2000°C in certain areas. Significantly high surface temperatures affect electronic and mechanical components in the utility load and prevent them from operating their tasks. Therefore, ablative heat insulation coatings with low thermal conductivity and thermal stability are used on the exterior surfaces of such systems.

It is known that it is necessary for an ablative layer so as to dissipate/remove the energy affecting on its surface in order to protect this component from high thermal energy. The term "ablation" may be defined as releasing and dispersing combustion products in the gas form resulting from the combustion of the coating, before the energy occurring due to the aerobic friction on the ablative material causes excessive temperature rises. Therefore, the ablative insulation material experiences mass loss in small particles from its surface in a controlled manner and leaves from the surface with other erosive effects. Portions that, on the one hand, experience the mass loss through disintegration and on the other hand, cannot be gasified due to the effect of erosive loads resulting from the thermo-chemical reactions, form an ash layer on the material surface. Various heat and mass transfer mechanisms occur simultaneously on the insulation material surface during the endothermic decomposition. Thus, it is prevented that the temperature of the system rises over the critical values during the operation period, thereby protecting the insulation lower layers and the critical components such as electronic and mechanical pieces on the application area. In the state of the art, various types of epoxy resins with favorable structural features are mainly used as a matrix in ablative heat insulation coating materials applied on the exterior surface. Such resin matrices are disclosed in the patent document no. CN106467699. In this document, silica fiber, glass, or phenolic microspheres and a set of flame-retardant materials are used as a filler and auxiliary material. Low thermal conductivity value requiring thermal insulation cannot be provided through the flame-retardant materials used in this document. Furthermore, the use of fiber constitutes a significant technical problem in terms of applying the prepared coating mixtures in a sprayable form. In particular, it becomes significantly troublesome to spray the mixture through a gun, as the length of fiber increases.

Brief Description of the Invention

The object of the invention is to provide an ablative insulation coating formulation that can be applied to metal components by using and spraying light and easily accessible materials.

In order to achieve the object, the present invention relates to an sprayable ablative insulation coating formulation for missile systems comprising at least one insulating filler material selected from a group that comprises at least one solvent; at least one epoxy-novolac based resin; vermiculite, fumed silica, a dried mushroom powder, phenolic micro balloon and/or the combinations thereof. The formulation comprises at least one flame-retardant material containing a mixture of ammonium polyphosphate and boric acid; a hardening agent; at least one diluting agent and at least one bonding silicone resin. It is ensured surprisingly by means of the formulation to provide an ablative insulation coating formulation that can be cured in the thickness of 0.5 mm at a single layer and that does not crack due to the thermal stress during maturing and to apply said formulation at least one exterior surface of metal components in missile systems by way of spraying. It is required an ablative layer with low thermal conductivity so as to dissipate/remove the energy affecting on its surface in order to protect this component from high thermal energy. That said insulation material is sprayable is technically advantageous and the desired effect. Studies conducted in the art are insufficient in terms of the need for sprayable ablative insulation with low thermal conductivity. Therefore, via the present invention, it is developed an ablative insulation coating formulation with thermal conductivity of 0.20 - 0.25 W/m°C that can be applied on at least of one exterior surface of metal components in missile systems through a spraying method, and a method for applying said formulation on at least one surface of a metal component by means of spraying. Metal components in missile systems herein referto metal sub-component and metal components such as a nose cone, missile guidance portion, warhead section, wing, control drive surfaces comprising electronic and mechanical components of said missile.

The ablative insulation coating formulation developed by the present invention comprises at least one solvent; an epoxy-novolac based resin; at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder (preferably dried oyster mushroom powder, oak mushroom powder), phenolic micro balloon and combinations thereof; a flame-retardant material comprising the mixture of ammonium polyphosphate and boric acid, at least one anhydride-based hardening agent, at least one diluting agent and a bonding silicone resin.

In the formulation developed by the present invention, it is used as an insulating filler material selected from a group comprising vermiculite, fumed silica, mushroom powder, phenolic micro balloon instead of silica or glass fiber used commonly in the art. Thus, it is provided an ablative insulation coating formulation in a sprayable form, thereby overcoming technological drawbacks. Furthermore, it is achieved by coating features that provide ablative insulation by means of ingredients contained in said formulation of the present invention. The mixture of ammonium polyphosphate and boric acid in the flame-retardant material constitutes importance in terms of its synergistic effect caused by said two compounds together. It is ensured controlled combustion by means of the use of ammonium polyphosphate and boric acid together, thereby contributing to the thermal insulation. It is aimed to achieve higher thermal insulation through obtaining the highest level of ash efficiency by way of changing in the rates of boric acid/ammonium polyphosphate. As a result of the combustion reaction of boric acid; dehydration of boric acid forms metaboric acid at 130°C and glass-like B₂0₃ (boron oxide) layer at 169°C and the layer causes an increase in the viscosity of the layer in a melt form at 350°C and prevents the resulting gas from being leaked to outside. Gas molecules, which cannot escape easily, mainly causes the carbon-containing layer to be porous through expansion and the thermal insulation to increase. Ammonium polyphosphate has a flame-retardant feature. Ammonium polyphosphate being a phosphate source causes an ammonia gas discharge after reaching up to 200°C as a result of the reaction of the phosphoric acid formed through the combustion reactions with the polymeric matrix. The resulting ammonia gas both allows for cooling the coating and the heat insulation due to the formation of the porous structure, while the resulting gases pass through the melt upper layers. It is achieved an insulation coating with a significantly low thermal conductivity (0.20 - 0.25 W/m°C) by means of the flame-retardant components, namely boric acid and ammonium polyphosphate.

In the present invention, it is used at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder (preferably, oyster mushroom powder), phenolic micro balloon, and combinations thereof so as to increase the thermal insulation feature of the coating. Vermiculite, fumed silica, dried mushroom powder, and phenolic micro balloon should be of particle size of 100 m or smaller so that they are suitable for the spraying process. Bigger particle sizes may cause clogging at the gun during the spraying process. Vermiculite is a mineral that is available naturally and is not reactive, highly absorbent, compressible, non-flammable, and is a mica group with a thermal insulation feature with an original layered structure. In a preferred embodiment of the invention, the vermiculite added in the ablative insulation coating formulation is vermiculite that is initially ground, preferably sieved through a sieve of 100 m and preferably subjected to a thermal treatment at 900°C. Subjecting the vermiculite to the thermal treatment at 900°C increases its thermal insulation feature. The use of mushroom powder in a composite structure increases the thermal erosion feature of the material. Phenolic micro balloon (preferably, the particle size of 90 pm) is added into the coating mixture since it can be combusted at higher temperatures and forms a proper ash layer when combusted. The phenolic micro balloon has a variety of application fields as well as is a substance allowing for lightening in the final product in liquid resin systems. Fumed silica has a high surface area at minimal masses, wherein it contributes to the developed formulation in terms of viscosity improver, thickener, and supplementary filler features. It is ensured to decrease the thermal conductivity of the ablative insulation coating formulation by means of the epoxy resin with higher thermal and structural resistance and the insulation-promoting filler substance.

In a preferred embodiment of the present invention; said formulation comprises a thermal conductivity of 0.20 - 0.25 W/m°C. Thus, it is ensured that the thermal conductivity is low.

In a preferred embodiment of the present invention; the dried mushroom powder is a dried oyster mushroom powder. In a potential embodiment; the dried mushroom powder is an oak mushroom powder.

In a preferred embodiment of the present invention; the dried mushroom powder has a particle size of 50-100 m. In a preferred embodiment of the present invention; the vermiculite has a particle size of 50-100 m.

In a preferred embodiment of the present invention; the vermiculite is subjected to the thermal treatment at 900°C.

In a preferred embodiment of the present invention; the particle size of the phenolic micro balloon is 50-90 m.

In a preferred embodiment of the present invention, said bonding silicone resin comprises preferably an amine functional group. Partial flexibility is provided to the final product with the ablative insulation coating formulation developed by means of said bonding silicone resin and it also increases chemical, thermal, corrosion, and damp resistance.

In a preferred embodiment of the present invention; the solvent comprises ethanol at the rate of 1-5%, methyl ethyl ketone at the rate of 1-5%, and acetone at the rate of 1-5% based on the total weight. In a preferred embodiment of the present invention; it comprises an epoxy novolac-based resin at the rate of 15-50 % based on the total weight.

In a preferred embodiment of the present invention; said insulating filler material comprises vermiculite at the rate of 15-50%, fumed silica at the rate of 5-10%, dried oyster mushroom powder at the rate of 1-10%, and the phenolic micro balloon at the rate of 5-10% based on the total weight of the formulation.

In a preferred embodiment of the present invention; said flame-retardant material comprises the mixture of ammonium polyphosphate at the rate of 1-10% and boric acid at the rate of 1-10% based on the total weight of the formulation.

In a preferred embodiment of the present invention; it comprises at least one anhydride-based hardening agent at the rate of 5-30% based on the total weight of the formulation.

In a preferred embodiment of the present invention; it comprises epoxy resin diluting agents at the rate of 1-10% based on the total weight of the formulation. The diluting agent in the formulation developed by the present invention is added in the formulation so as to decrease the viscosity of the ablative insulation coating formulation. The formulation developed is cured with an anhydride- originated hardening agent to prevent the absolute curing process until the final curing process between layers.

In a preferred embodiment of the present invention; the formulation comprises a bonding silicone resin at the rate of 1-10% based on the total weight.

In a preferred embodiment of the present invention; the hardening agent is anhydride-based.

In a preferred embodiment of the present invention; it is a production method of a sprayable ablative insulation coating formulation for missile systems and comprises the process step of stirring the ablative insulation coating formulation, which comprises at least one solvent, at least one epoxy-novolac-based resin, at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder, phenolic micro balloon and/or combinations thereof; at least one solvent; at least one flame-retardant material comprising the mixture of ammonium polyphosphate and boric acid; at least one diluting agent and at least one bonding silicone resin, in a container for at least 30 min. until it becomes homogeneous; spraying the resulting homogeneous formulation on at least one exterior surface of said metal component, such that its thickness is of 0.10-0.50 mm.

By means of the present invention, it is achieved an sprayable ablative insulation material with low thermal conductivity and the operation process, wherein it is ensured to coat surfaces of metal or composite components in a complex or uniform geometry at desired thickness by means through the spraying method by means of the present invention.

An embodiment of the present invention comprises the process steps of keeping and airing the coated metal component at room temperature for at least one hour and forming a coating with a thickness of 3-5 mm by repeating the coating process for 1-3 times; achieving a semi-product through semi-curing the coating by means of keeping the component with a coating thickness of 3-5 mm for 30 min. at 70-110°C.

An embodiment of the present invention comprises the steps of fully curing the metal component coated with the semi-cured coating for 1-2 hours at 100 °C and 8-10 hours at 150 °C. A preferred embodiment of the present invention comprises the process step of coating at least one surface of the metal component with an epoxy primer with three components comprising an epoxy resin component, curing agent, and thinner before applying said ablative insulation coating formulation.

An embodiment of the present invention is a missile system comprising at least one metal component coated through the production method described above.

Detailed Description of the Invention

In this detailed description, the subject matter of the invention is disclosed through references with examples such that it does not construe any limiting meaning, but to provide a better understanding of the invention.

In an embodiment of the present invention, the interlaminar shear strength of the ablative insulation coating formulation is of 5-10 MPa. Furthermore, a sanded metal surface (preferably aluminum and/or steel surface) is coated with an epoxy primer with three components comprising epoxy resin component, curing agent, and thinner before applying the ablative insulation coating formulation.

The mixture formulation of the above-mentioned materials is shown in Table 1. Accordingly, in a preferred embodiment of the present invention, the ablative insulation coating formulation comprises ethanol at the rate of 1-5% based on the total weight of the solvent coating formulation, methyl ethyl ketone at the rate of 1-5% based on the total weight and acetone at the rate of 1-5% based on the total weight. Furthermore, the ablative insulation coating formulation comprises an epoxy novolac-based resin at the rate of 15-50% and vermiculite at the rate of 15-50% based on the total weight of the formulation. The insulating filler material in the formulation comprises fumed silica preferably at the rate of 5-10% based on the total weight of the formulation, dried oyster mushroom powder at the rate of 1-10% based on the total weight of the formulation, and the phenolic micro balloon at the rate of 5-10% based on the total weight of the formulation.

Flame-retardant material mentioned in the embodiment comprises a mixture of ammonium polyphosphate at the rate of 1-10% based on the total weight of the formulation and boric acid at the rate of 1-10% based on the total weight of the formulation. The ablative insulation coating formulation comprises at least one anhydride-based hardening agent at the rate of 5-30% based on the total weight of the formulation; epoxy resin diluting agent at the rate of 1-10% based on the total weight of the formulation and bonding silicone resin at the rate of 1-10% based on the total weight of the formulation. TABLE 1

Firstly, an epoxy primer with three components comprising epoxy resin component, curing agent, and thinner is applied on the sanded metal surface (preferably aluminum and/or steel surface), on which the ablative coating is to be applied so that the coating is able to adsorb on the surface. The metal surface coated with the primer is cured preferably at 70-110°C. Afterward, the coating process is performed.

It is developed by means of the present invention a coating method by spraying the ablative insulation coating formulation on at least one exterior surface of the metal components in missile systems, wherein said method comprises the process steps of stirring the developed formulation in a container for at least 30 min. until it becomes homogeneous; achieving a component, at least one surface of which is coated with the ablative insulation coating formulation, as a result of spraying the resulting homogeneous formulation on at least one surface of the metal component, such that the coating thickness is in the range of 0.10-0.50 mm; keeping and airing the component at room temperature for at least one hour; repeating these steps until the coating reaches to the thickness of 3-5 mm (preferably 1-3 times); semi-curing the coating by keeping the component with a thickness of 3-5 mm for 30 min. at 70-110°C; fully curing the component coated with the semi-cured coating for 1-2 hours at 100 °C and for 8-10 hours at 150 °C.

In a preferred embodiment of the present invention, the method developed can be applied on at least one surface of the component for 1-3 times. The component is aired at the room temperature for at least one hour subsequent to each application. Considering the curing periods, it is achieved a coating thickness of approximately 1 mm per day.

In a preferred embodiment of the method developed by the invention; said method comprises the process steps of grinding vermiculite and dried mushroom powder into a particle size of 50-100 m through a grinder, achieving materials in particle size of 50-100 m by sieving the ground vermiculite and dried mushroom powder through a sieve of 100 m and subjecting vermiculite to thermal treatment at preferably 900°C.

By means of the present invention, it is achieved a sprayable ablative insulation material with low thermal conductivity and the operation process, wherein it is ensured to coat surfaces of metal or composite components in a complex or uniform geometry at desired thickness by means through the spraying method by means of the present invention.

Claims

1 . Sprayable ablative insulation coating formulation for missile systems, comprising at least one solvent; an epoxy-novolac based resin; at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder, phenolic micro balloon and/or combinations thereof, characterized by comprising at least one flame- retardant material comprising the mixture of ammonium polyphosphate and/or boric acid; a hardening agent; at least one diluting agent and at least one bonding silicone resin.

2. Ablative insulation coating formulation according to Claim 1, characterized in that said formulation has a thermal conductivity of 0.20 - 0.25 W/m°C.

3. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the dried mushroom powder is a dried oyster mushroom powder.

4 . Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the dried mushroom powder is an oak mushroom powder.

5. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the particle size of the dried mushroom powder is 50-100 m.

6. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the particle size of the vermiculite is 50-100 m.

7 . Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the vermiculite is subjected to a thermal treatment at 900°C.

8 . Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the particle size of the phenolic micro balloon is 50-90 pm.

9. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that said bonding silicone resin comprises an amine functional group.

10. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that said solvent comprises ethanol at the rate of 1-5%, methyl ethyl ketone at the rate of 1-5%, and acetone at the rate of 1-5% based on the total weight.

11. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that it comprises epoxy novolac-based resin at the rate of 15-50% based on the total weight.

12 . Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that said insulating filler material formulation comprises vermiculite at the rate of 15-50%, fumed silica at the rate of 5-10%, dried oyster mushroom powder at the rate of 1 -10%, and the phenolic micro balloon at the rate of 5-10% based on the total weight.

13. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that said flame-retardant material formulation comprises the mixture of ammonium polyphosphate at the rate of 1-10% and/or boric acid at the rate of 1-10% based on the total weight.

14. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the formation comprises at least one anhydride-based hardening agent at the rate of 5-30% based on the total weight.

15. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the formation comprises epoxy resin diluting agent at the rate of 1- 10% based on the total weight.

16. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the formation comprises a bonding silicone resin at the rate of 1-10% based on the total weight.

17. Ablative insulation coating formulation according to any one of the preceding Claims, characterized in that the hardening agent is anhydride-based.

18. A production method of an sprayable ablative insulation coating formulation for missile systems according to any one of the preceding Claims, characterized by comprising the process step of stirring the ablative insulation coating formulation, which comprises at least one solvent, at least one epoxy-novolac-based resin, at least one insulating filler material selected from a group comprising vermiculite, fumed silica, a dried mushroom powder, phenolic micro balloon and/or combinations thereof; at least one solvent; at least one flame- retardant material comprising the mixture of ammonium polyphosphate and boric acid; at least one diluting agent and at least one bonding silicone resin, in a container for at least 30 min. until it becomes homogeneous; spraying the resulting insulation coating homogeneous formulation on at least one exterior surface of said metal component, such that its thickness is of 0.10-0.50 mm.

19 . A production method according to Claim 18, characterized comprising the process steps of keeping and airing the coated metal component at room temperature for at least one hour and forming a coating with a thickness of 3-5 mm by repeating the coating process for 1-3 times; achieving a semi-product through semi-curing the coating by means of keeping the component with a coating thickness of 3-5 mm for 30-40 min. at 70-110°C.

20 . A production method according to Claim 19, characterized by comprising the steps of fully maturing the metal component coated with the semi-cured coating for 1-2 hours at 100 °C and 8-10 hours at 150 °C.

21. A production method according to Claim 17, characterized in that at least one surface of the metal component is coated with an epoxy primer with three components comprising an epoxy resin component, curing agent, and thinner before applying said ablative insulation coating formulation.

22. Missile system comprising at least one metal component coated through a production method according to Claim 18-21.