Low-flammability epoxy resin, prepreg, fiberglass, spherical plastic and products made from them

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to melt epoxy binders with reduced flammability and smoke emission for the production of structural materials. An epoxy binder is proposed for the production of prepregs and spheroplastics, comprising, in parts by weight: a polyfunctional epoxy novolac resin 59.0-75.9; a low-molecular epoxy resin 3.5-5.9; a latent hardener dicyandiamide 3.3-5.1; a phosphorus-comprising fire retardant triphenyl phosphate 7.2-28.2; a deaerating additive based on a mixture of glycidyl derivatives of fatty alcohols or saturated hydrocarbons with a number of carbon atoms in a molecule of up to 25, selected from the group: BYK A-500, BYK A-501, BYK A-525, BYK A-530, BYK A-535, BYK P 9920 0.6-2.1. Also proposed are a prepreg consisting of the proposed binder and a woven glass filler; fiberglass made from the proposed prepreg using pressing, autoclave, or vacuum-furnace methods; spherical plastic comprising the proposed epoxy binder, glass microspheres, and a thixotropic additive, and a multilayer honeycomb panel made from the proposed prepreg and spherical plastic.EFFECT: increase in the technological window for processing the binder due to an increase in the time of its gelation at a temperature of 80°C, achieving a shelf life of the binder and semi-finished products made from it (prepreg or spheroplastic) at room temperature of at least 90 days, ensuring high indicators of physical and mechanical characteristics, such as tensile strength and compressive strength, while maintaining low porosity, as well as flammability and smoke formation.7 cl, 4 tbl, 7 ex

Description

[0001] The invention relates to the field of melt epoxy binders with reduced flammability and smoke emission for the production of structural materials that can be used in the aviation sector of transport engineering, in the radio engineering and radio-electronic industry, as well as other areas of the national economy where low-smoke, low-flammability materials based on epoxy resins are in demand.

[0002] Epoxy binders for polymer composite materials (PCMs) with reduced flammability are produced in various ways, but most commonly by incorporating halogen-containing epoxy resins or flame retardants into the binder. The addition of halogens not only significantly increases smoke emission during combustion but also increases the toxicity of the resulting pyrolysis gases, which consist of toxic halogen-containing compounds.

[0003] Another approach to creating low-flammability epoxy binders is the use of phosphorus-containing epoxy resins or fire retardants, which, when burned, form a porous phosphorus-containing coke that prevents oxygen from entering the combustion zone and promotes self-extinguishing of the polymer matrix.

[0004] In order to reduce smoke emission and the overall flammability of epoxy binders, finely dispersed metal hydroxides are widely used in synergy with the above-mentioned fire retardants. Under the influence of temperature, they release water molecules, absorbing a large amount of heat and reducing the heating temperature of the material in the combustion area.

[0005] A low-flammability melt epoxy binder for aircraft floor panels is known (RU 2486217 C1, C08L 63 / 00, 27.06.2013), containing, in parts by weight:

[0006] epoxy novolac resin 16-38 tetrabromodiane-based epoxy resin 26-32 low molecular weight epoxy resin 20-40 high molecular weight epoxy resin (Diaplast) 0,5-7 polysulfone 0,5-7 bis(N,N'-dimethylurea)diphenylmethane 0,5-1,5 dicyandiamide 4,2-5,3

[0007] The disadvantages of this low-flammability hot melt epoxy binder include its lengthy production process, due to the use of four different epoxy resins, including the expensive high-molecular-weight resin Diaplast. Fiberglass reinforced plastics based on this binder meet AP-25 fire safety requirements, and these fire-safe properties are achieved by adding a halogen-containing tetrabromodiane-based epoxy resin to the binder. This increases smoke emission during combustion and the toxicity of the resulting pyrolysis gases. Furthermore, binder preparation requires lengthy dissolution of the high-molecular-weight resin and polysulfone at high temperatures (90 minutes at 145-155°C).

[0008] An epoxy binder is known for the production of self-extinguishing fiberglass (RU 2614701 C1, C08L 63 / 00, 03 / 28 / 2017), containing, in parts by weight:

[0009] bromine-containing epoxy resin 67-75 tetrafunctional chlorine-containing epoxy resin 9-25 bismaleimide-modified epoxy resin 7-25 active diluent - 3-glycidyloxypropyl-trimethoxysilane 0,9-8,7 hardener - isomethyltetrahydrophthalic anhydride 58-73 curing accelerator 0,1-2 targeted supplements 0,5-3

[0010] Fiberglass-based composites based on this binder are characterized by AP-25 as difficult to burn and self-extinguishing. However, to achieve fire-safe properties, the authors use large amounts of halogenated epoxy resins in the binder, which leads to increased smoke emission during combustion and also the toxicity of the resulting pyrolysis gases. Another drawback of the binder is the use of an expensive epoxy resin modified with bismaleimide (ED-BM-20).

[0011] A low-flammability adhesive binder is known (RU 2676634 C1, C08L 63 / 00, 09.01.2019), containing, in parts by weight:

[0012] epoxy resin 10-23 epoxidized brominated resin 25-35 epoxyimide resin 19,1-30 bromine-containing polyhydroxyether (bromoplast) 3-8 low molecular weight rubber with terminal carboxyl groups 2,4-6,5 latent amine hardener 3,5-7,7 bis-(N,N'-dimethylurea)-diphenylmethane 4,0-7,3 sebacic acid polyanhydride 1,5-5,8 polysulfone 1,5-2,5

[0013] Fiberglass reinforced plastics based on this binder meet the fire safety requirements of AP-25, but the "slow-burning" fire resistance class is achieved by incorporating not only brominated epoxy resin but also a poorly soluble brominated polyhydroxyether (bromoplast) into the binder. Consequently, the binder production process must be carried out at high temperatures (170-180°C). Furthermore, this binder is expensive due to the presence of epoxyimide resin and bromoplast.

[0014] The closest analogue of the proposed binder is a halogen-free melt epoxy composition (RU 2797591 C1, C08L 63 / 00, 07.06.2023), including, by weight %:

[0015] polyfunctional epoxy resin 20,0-26,5 fire-resistant epoxy resin 6,6-11,0 low molecular weight epoxy resin 28,3-37,0 thermoplastic - polysulfone 4,0-7,0 curing accelerator - unsymmetrically disubstituted urea 0,3-1,0 latent hardener dicyandiamide 3,0-4,3 aromatic diamine hardener 6,5-8,2 phosphorus-containing flame retardant 7,0-15,4 fire retardant alkaline earth metal hydroxide 4,0-9,9

[0016] Prepreg based on the prototype binder contains, wt. %:

[0017] epoxy binder 30,0-50,0 fiberfill 50,0-70,0

[0018] Various aircraft parts, including honeycomb panels, are manufactured from this prepreg using direct compression, vacuum or autoclave molding methods.

[0019] The disadvantages of the composition taken as a prototype are the presence of expensive phosphorus-containing epoxy resins and mixtures of phosphorus-containing fire retardants, some of which (Phosporen-3, DOPO and FR-100), moreover, are not widely available.

[0020] Furthermore, the presence of dissolved aromatic diamine reduces the shelf life of the binder and prepreg at room temperature, thereby negating the benefits of using a latent curing system consisting of dicyandiamide and asymmetrically disubstituted urea, which ensures a long shelf life for semi-finished products. As a result, semi-finished products based on the above-described compositions require special conditions for transportation and storage at low temperatures, as well as conditioning measures before use.

[0021] Despite the presence of a large number of dispersed particles of hardeners and fire retardants (10.5-23.6 wt.%), the prototype composition does not use deaerating additives that promote the release of entrained air from the dispersed-filled binder, preventing increased porosity and a decrease in the physical and mechanical properties of PCMs based on them.

[0022] The technical objective of the invention is to develop a technologically advanced melt thermosetting binder, prepreg, fiberglass and spherical plastic, as well as products made from them with reduced flammability and smoke emission from available components, reducing costs during their storage and transportation to the place of further use.

[0023] The technical result of the claimed invention is to increase the technological window for processing the binder by increasing the time of its gelation at a temperature of 80°C, achieving a shelf life of the binder and semi-finished products made from it (prepreg, spheroplastic) at room temperature of at least 90 days, ensuring high indicators of the physical and mechanical characteristics of the PCM (tensile strength, compressive strength) while maintaining low porosity, as well as flammability and smoke formation.

[0024] The technical result of the claimed invention is achieved due to the fact that the proposed epoxy binder for the production of prepregs and spheroplastics includes a mixture of polyfunctional and low-molecular epoxy resins, a latent hardener - dicyandiamide and a phosphorus-containing fire retardant, while it also contains a deaerating additive based on a mixture of glycidyl derivatives of fatty alcohols or saturated hydrocarbons with a number of carbon atoms in a molecule of up to 25, selected from the group: BYK A-500, BYK A-501, BYK A-525, BYK A-530, BYK A-535, BYK P 9920, contains epoxy novolac resin as a polyfunctional epoxy resin, contains triphenyl phosphate as a phosphorus-containing fire retardant, with the following ratio of components, parts by weight:

[0025] polyfunctional epoxy novolac resin 59,0-75,9 low molecular weight epoxy resin 3,5-5,9 latent hardener - dicyandiamide 3,3-5,1 phosphorus-containing flame retardant - triphenyl phosphate 7,2-28,2 deaerating additive 0,6-2,1

[0026] The binder for the production of prepregs preferably also contains 4.0 - 8.0 parts by weight of thermoplastic polysulfone, 0.5 - 1.0 parts by weight of curing accelerator - asymmetrically disubstituted urea and 11.5 - 16.4 parts by weight of mineral fire retardant - finely dispersed aluminum hydroxide.

[0027] Also proposed is a prepreg containing, in parts by weight:

[0028] the proposed thermosetting binder 25-55 fiberfill 75-45

[0029] It may contain woven glass filler as a fiber filler.

[0030] Fiberglass made from the proposed prepreg using pressing, autoclave or vacuum-furnace methods is also offered.

[0031] Fiberglass can be produced as a monolayer with a thickness of 0.05 to 0.3 mm.

[0032] Also proposed is a spherical plastic containing, in parts by weight:

[0033] thermosetting binder 72-82 glass microspheres 16-27,5 thixotropic additive 0,5-2

[0034] Also proposed is a product that can be manufactured from a honeycomb core, the proposed prepreg and spheroplastic filling parts of the honeycomb core, in one technological cycle by joint molding, or manufactured by separate molding of the proposed fiberglass and then a product from it in the form of a honeycomb panel.

[0035] from a honeycomb filler, the proposed prepreg and spheroplastic filling parts of the honeycomb filler, in one technological cycle by joint molding or separate molding of the proposed fiberglass and honeycomb filler.

[0036] The product can be multi-layered.

[0037] Unlike the prototype composition, the claimed binder does not use expensive phosphorus-containing epoxy resins and fire retardants, in addition, the total number of components for its production has been reduced, which reduces the time and material costs for its production.

[0038] The use of epoxy derivatives based on novolac oligomers as a resin base positively impacts the fire safety properties of the binder due to their reduced total hydrogen content per epoxy group. Furthermore, the polyfunctional nature of epoxy novolac epoxy resin facilitates the production of a highly cross-linked polymer matrix with an elevated degradation temperature, which is particularly advantageous for the creation of low-flammability polymer composites.

[0039] The absence of dissolved hardeners such as aromatic diamine in the melt binder allows the advantages of the latent curing system based on dicyandiamide and asymmetrically disubstituted urea to be utilized in terms of long shelf life at room temperature and its pot life at processing temperature.

[0040] To reduce pore formation and achieve a high level of physical and mechanical properties of the resulting PCM, a deaerating additive based on a mixture of glycidyl derivatives of fatty alcohols or saturated hydrocarbons with a number of carbon atoms in a molecule of up to 25, selected from the group: BYK A-500, BYK A-501, BYK A-525, BYK A-530, BYK A-535, BYK P 9920 is introduced into the proposed binder. The most preferable is the use of additives with glycidyl derivatives of fatty alcohols, which react with the hardener during the curing process, increasing the content of the gel fraction of the binder and have the greatest positive effect on the physical and mechanical properties of the PCM. Thus, the introduction of the proposed deaerating additive promotes the effective removal of air from the dispersed-filled binder, reducing its foaming during the preparation process and pore formation during the production of PCM from prepregs based on it.Low pore formation allows obtaining polymer composite materials with a high level of physical and mechanical characteristics.

[0041] The deaerating additive in some variants (BYK A-500, BYK A-501, BYK A-525) additionally contains 1-methoxy-2-propyl acetate as a surface activity modifier.

[0042] Triphenyl phosphate effectively reduces the viscosity of epoxy resin, so that less low molecular weight epoxy resin is required to adjust the viscosity, which helps to reduce the flammability and smoke generation of the cured resin.

[0043] The use of widely available and inexpensive triphenyl phosphate as a phosphorus-containing plasticizer-flame retardant not only reduces the flammability of the epoxy binder but also improves the physical and mechanical properties of the polymer composite materials based on it due to its plasticizing effect on the highly cross-linked filled polymer matrix. Furthermore, triphenyl phosphate, in synergy with the aforementioned deaerating additive, promotes complete wetting of the finely dispersed particles of the inorganic flame retardant.

[0044] To reduce smoke formation during combustion and pyrolysis, an inorganic flame retardant, aluminum hydroxide, is added to the prepreg binder. Under the influence of temperature, it decomposes into aluminum oxide and water, absorbing a large amount of heat and reducing the heating of the material in the combustion zone and the release of pyrolysis gases. The use of a finely dispersed filler reduces the negative impact on the strength properties of the cured binder by more uniformly distributing the dispersion throughout the polymer matrix.

[0045] The introduction of thermoplastic polyarylsulfone grade PSFF-30 increases the mechanical strength of the cured dispersed-filled binder and PCM based on it, and the presence of phenolphthalein fragments in its structure causes its reduced flammability, in comparison with basic polysulfones containing only bisphenol A fragments.

[0046] The combination of the above-described characteristics of the starting components allows us to obtain a technologically advanced melt epoxy binder with reduced flammability and smoke emission, an extended processing window, a long shelf life at room temperature for prepregs based on it, and characterized by the availability of components and low cost.

[0047] To obtain the claimed epoxy binder with low flammability, epoxy novolac resins of the following grades were used as a polyfunctional epoxy resin: EN-6, UP-643 or their analogues.

[0048] EA grade epoxy resin or its equivalent is used as a low-molecular epoxy resin.

[0049] The curing system consists of a latent hardener, dicyandiamide, and a curing accelerator. The latent hardener used is dicyandiamide of any of the following grades: Dyhard 100S, Dyhard 100SF, Dycure 10, or their equivalents, and the curing accelerator is an asymmetrically disubstituted urea, bis-(N,N'-dimethylurea)-diphenylmethane (Omicure U-52) or an equivalent.

[0050] The following brands of products can be used as a deaerating additive: BYK A-500, BYK A-501, BYK A-525, BYK A-530, BYK A-535, BYK P 9920 or their analogues.

[0051] Powdered polyarylsulfone grade PSFF-30, polysulfones PSFF-40K or PSFF-70K or PSK-1 can be used as thermoplastic.

[0052] Phosphorus-containing fire retardant triphenyl phosphate is used in the form of powder or flakes with a melting point of 48-50°C.

[0053] Finely dispersed aluminum hydroxide of the FRAMIAL 01 brand or an equivalent is used as an inorganic fire retardant.

[0054] Fiberglass can be produced from the proposed prepreg using pressing, autoclave or vacuum oven methods.

[0055] Spheroplastic can be produced by dispersing glass microspheres in the proposed binder at a temperature not exceeding 60°C.

[0056] Products such as three-layer honeycomb panels used in aviation technology can be manufactured from the proposed prepreg, spherical plastic and honeycomb core in one technological cycle using pressing, autoclave or vacuum oven methods, or manufactured by gluing the honeycomb core with pre-fabricated fiberglass and filling the end or other required parts of the honeycomb core with spherical plastic.

[0057] Examples of implementation.

[0058] Polyfunctional and low-molecular-weight epoxy resins were loaded into a clean, dry reactor and heated to 135°C. Thermoplastic was then added in portions, and the mixture was maintained at this temperature until the polyarylsulfone was completely dissolved. The mixture was then cooled to 120°C, and triphenyl phosphate, a deaerating additive, and a mineral fire retardant (finely dispersed aluminum hydroxide) were added successively. The mixture was then mixed until a homogeneous melt was achieved. The mixture was then cooled to 70°C, and a latent curing system was added, continuing to stir until the dispersed particles were completely distributed throughout the binder melt. Upon completion of the process, the prepared binder was poured into clean, dry trays lined with release paper.

[0059] The ratio of binder components for the examples is shown in Table 1.

[0060] From the binders obtained in Examples 1-4 (Table 1), prepregs were produced using a Coatema BL-2800 impregnation machine.

[0061] The following grades of glass fabric were used as reinforcing fillers: T-10-14 (examples 1-2), T-15(P)-76 (example 3) and Ortex 120 (example 4).

[0062] Fiberglass was manufactured from the obtained prepregs. Gel time tests were conducted in accordance with GOST R 57779-2017. Tensile strength tests were conducted in accordance with GOST R 56785-2015. Compressive strength tests were conducted in accordance with GOST R 56812-2015. Porosity was determined in accordance with GOST R 56682-2015.

[0063] The properties of the obtained binder, prepreg and fiberglass are shown in Table 2.

[0064] A spheroplastic filler was produced from the binders according to examples 5-7 by dispersing in them finished glass microspheres of the MS-VP-A9 group 5 brand and a thixotropic additive - aerosil A-380.

[0065] Made from prepreg based on T-15(P)-76 fiberglass and binder according to example 3 (table 1), honeycomb filler grade PSP-1-2.5-48 with a density of 48 kg / m3 3and a spheroplastic filler according to example 5, a three-layer honeycomb panel was produced.

[0066] All the above examples are not exhaustive in the implementation of the proposed invention.

[0067] As can be seen from the presented data, the proposed epoxy binder, compared to the prototype binder, is characterized by an extended processing window for prepreg processing and a long shelf life at room temperature. The binder does not use expensive phosphorus-containing epoxy resins and flame retardants, while containing fewer raw materials.

[0068] The presence of a fire retardant-plasticizer and a deaerating additive in the composition reduces the negative impact of the dispersed mineral fire retardant and allows for the production of PCM with low porosity and high strength characteristics.

[0069] Based on the test results of fiberglass (Table 3) and three-layer honeycomb panel (Table 4), it was found that they comply with the requirements of AP-25 Appendix F Part I in terms of flammability and smoke formation, and can be used in interior composite structures of aircraft equipment.

[0070]

[0071]

[0072]

Claims

1. An epoxy binder for the production of prepregs and spheroplastics, comprising a mixture of polyfunctional and low-molecular epoxy resins, a latent hardener - dicyandiamide and a phosphorus-containing fire retardant, characterized in that it also contains a deaerating additive based on a mixture of glycidyl derivatives of fatty alcohols or saturated hydrocarbons with a number of carbon atoms in a molecule of up to 25, selected from the group: BYK A-500, BYK A-501, BYK A-525, BYK A-530, BYK A-535, BYK P 9920, contains epoxy novolac resin as a polyfunctional epoxy resin, contains triphenyl phosphate as a phosphorus-containing fire retardant, in the following ratio of components, wt. h: polyfunctional epoxy novolac resin 59,0-75,9 low molecular weight epoxy resin 3,5-5,9 latent hardener - dicyandiamide 3,3-5,1 phosphorus-containing flame retardant - triphenyl phosphate 7,2-28,2 deaerating additive 0,6-2,1 2. The binder according to paragraph 1, characterized in that it additionally contains 4.0-8.0 parts by weight of thermoplastic polyarylsulfone grade PSFF-30, 0.5-1.0 parts by weight of a curing accelerator - asymmetrically disubstituted urea and 11.5-16.4 parts by weight of a mineral fire retardant - finely dispersed aluminum hydroxide.

3. A prepreg containing an epoxy binder and a woven glass filler, characterized in that it contains an epoxy binder according to paragraph 2 in the following ratios of components, in parts by weight: epoxy binder 25-55 woven glass filler 75-45 4. Fiberglass, characterized in that it is made from prepreg according to paragraph 3 using pressing, autoclave, or vacuum-furnace methods.

5. Fiberglass according to paragraph 4, characterized in that it is a monolayer with a thickness of 0.05 to 0.3 mm.

6. A spheroplastic characterized in that it is made from an epoxy binder according to paragraph 1, glass microspheres and a thixotropic additive with the following component content, in parts by weight: epoxy binder 72-82 glass microspheres 16-27,5 thixotropic additive 0,5-2 7. A multilayer honeycomb panel, characterized in that it is made from a honeycomb filler, a prepreg according to paragraph 3 and a spherical plastic according to paragraph 6, filling parts of the honeycomb filler, in one technological cycle by joint molding or made by separate molding of the fiberglass according to paragraph 4 and then a multilayer honeycomb panel from it.

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