Epoxy binding agent and pre-impregnated fibrous filler based on it

Abstract

Invention relates to the field of producing melt epoxy binders for structural polymeric composite materials based on fibrous fillers obtained by prepreg technology. Epoxy binder includes the following components in the following ratio in wt.%: difunctional epoxy resin 8.6-14.8, mixture of polyfunctional nitrogen-containing epoxy resins 34.8-47.4, rubber-containing component 15.7-20.9, thermoplastic resin - polyethersulfone 8.0-13.1, curing agent, aromatic diamine 10.5-16.5, blocked curing agent - dicyandiamide 3.0-4.3, latent curing accelerator - asymmetrically substituted urea 0.4-2.0. Prepreg comprises said epoxy binder and fibrous filler in the following ratio, wt. %: epoxy binder 24-55, fibrous carbon filler 45.0-76.0. EFFECT: developed epoxy binder and prepreg, made therefrom, demonstrates improved technological characteristics and makes it possible to obtain products with a higher level of preservation of physical and mechanical properties.

Description

[0001] EPOXY BINDING AGENT AND PRE-IMPREGNATED

[0002] FIBROUS FILLER BASED ON IT

[0003] The invention relates to the field of creating melt epoxy binders and prepregs based on them, for obtaining structural polymer composite materials (PCM) based on fibrous reinforcing fillers, which can be used to obtain composite structures used in the automotive, aviation, shipbuilding, wind energy, sports, electronic and construction industries, as well as for new process solutions.

[0004] In the production of polymer composite materials, the technology of molding prepregs (fibrous fillers pre-impregnated with a binder) occupies a key place. It is this technology that ensures the production of high-strength polymer composite materials with reduced porosity and stable physical and mechanical properties.This technology allows for strict control over the orientation of the reinforcing fibers and offers a high degree of freedom in designing the configuration of the composite structure being created.

[0005] The method for producing fiber-reinforced composite materials involves heating and molding the prepreg under pressure using an autoclave. However, this molding method has a number of problems: high cost and energy consumption, as well as limitations on the size of the structures being formed due to the small dimensions of the equipment.

[0006] An energy-efficient and inexpensive molding method is also known, which is often used in the production of large composite integrated structures. The method of vacuum molding of prepreg allows molding using only a vacuum pump and a heating cabinet, without using an expensive autoclave.

[0007] In the composition of the formed composites, epoxy compositions are used as matrix binders in most cases, which are a combination of epoxy resins and amine curing agents. Such systems have excellent heat resistance, elastic modulus, moisture resistance and .minimal shrinkage during curing. To achieve large-scale production of composite structures using the nonautoclave process of prepreg molding, their curing temperature should be relatively low, approximately 100-150 °C, for approximately 1-3 hours. To solve this problem, active curing systems based on the blocked curing agent, dicyandiamide, and latent- catalysts, asymmetrically substituted ureas, are most often used in the prepreg binder. These systems provide rapid curing at low temperatures. Binders for prepregs with energy-efficient curing modes created on their basis have become widespread for the production of products from polymer composite materials. When using them, the cost of the process is significantly reduced due to a decrease in temperature and simplification of the process equipment.

[0008] An epoxy composition is known from the prior art (see EP2623533A1, published 07.08.2013) containing a mixture of epoxy resins selected from a series of resins based on bisphenol A and F, amine-type epoxy resins based on tetraglycidyldiaminodiphenylmethane, triglycidyl-para-aminopheiiol and / or 3,3’- tetraglycidyldiam.inodip.henylsulibne, phenol-type epoxy -novolac resin, as well as a blocked curing agent - dicyandiamide, a latent curing accelerator - asymmetrically substituted urea 3 -(3 ,4-dichlorophenyl)« 1,1 “dimethylurea, and an impact modifier - block copolymer selected from a series including block copolymers SBM, BM and MBM. Prepregs containing 10 -M0 wt.% of the created epoxy composition and 60 -*• 90 wt.% of reinforcing carbon fiber T700SC-24K are also known. The optimal ratio in the used curing system of the blocked curing agent, dicyandiamide, and the latent curing accelerator, asymmetrically substituted urea, provides the possibility of molding composite materials from prepregs at low temperatures (temperature 130°C for 1.5 hours). The main disadvantage of the known composites is their very low heat resistance (glass-transition point Tgdsy ” 87-112 °C). This is the upper limit of their heat resistance, ensuring the operating temperature of the created composite materials Top < 60-80 °C and guaranteeing the preservation of strength characteristics only below these temperature values.

[0009] Sometimes, a curing agent based on an aromatic diamine is included in the composition of a curing system based on a blocked curing agent, dicyandiamide (DCDA), and latent curing accelerators, asymmetrically substituted ureas, for prepreg composites in order to increase heat resistance and improve performance characteristics.

[0010] Also known from the prior art is an. epoxy composition used to produce a prepreg and a fiber-reinforced composite material (see EP2637860A1, published 08, 11.2010). The known composition contains at least 60.0-95.0 wt, parts of a tetraglycidylamine-type epoxy resin, 5.0-40.0 wt. parts of at least one resin or mixture thereof selected from the group: phenol-volac epoxy resin, diglycidylaniline, and bisphenol A-based epoxy resin, 3.0 wt. parts of the blocked curing agent, dicyandiamide, 5.0-10.0 wt. parts of the curing agent 4,4‘- diaminodiphenylsulibne, and also 3.0-8.0 wt. parts of latent curing accelerator - one of the asymmetrically substituted ureas: 2,4-toluenebis-dimethylurea or 3-(3,4- dichlorophenyl)- 1,1 “dimethylurea, and 6.0-26.0 wt. parts of thermoplastic resin - polyethersulfone. Also known from the document is a prepreg based on carbon fiber T700G-12K-31E, containing 30-95 wt.% of the developed epoxy composition. The presence of the aromatic amine curing agent 4,4 -diaminodiphenyIsulfone in the curable system contributes to the formation of heat-resistant composite materials with Tgdry-150-165 °C. rhe disadvantages of tills invention include the high rigidity of the cured matrix (modulus of elasticity B ~ 4.0-4.3 GPa) due to the significant content of tetrafunctional epoxy resin of the ietraglycidy lamine type. This leads to a significant decrease in the impact resistance of the final composite product. In addition, the curing system of this composition includes a large amount of latent curing accelerator, asymmetrically substituted urea, in relation to other curing agents. This leads to a significant decrease in thermomechanical characteristics after exposure to elevated temperatures and humidity.

[0011] The closest analogues adopted as a prototype (see JP7206993B2; implementation example 2, published 18.01.2023) are:

[0012] - an epoxy composition comprising (in wt.%) a mixture of epoxy resins, including diftmctional low molecular weight epoxy resin, based on bisphenol A, JER 828 - 5.0, and epoxy resin based on bisphenol F, JER 807 - 34.0; polyfunctional epoxy resin based on tetraglycidyidiaminodiphenylmethane JER 604 - 21.6, and epoxy resin based on triglycidyl-para-'aminophenol, Araldite MY0510 - 3.1; thermoplastic resin polyethersulfone, Sumika Excel PES5003MP ■••• 8.0; curing agent 4,4’"diaininodiphenylsulfone, Seikacure-S ~ 26.7; blocked curing agent, dicyandiamide, DICY 7 - 1.0; latent catalyst, asymmetrically substituted urea 3~ (3,4“diclophenyl)-l,.l-dimethyhirea, DCMU 99 ■- 0.6;

[0013] - prepregs based on unidirectional carbon fiber TR50S, obtained by impregnation with 30-40 wt% melt of the developed epoxy binder.

[0014] The disadvantages of the specified prototypes are:

[0015] - low level of processing characteristics of the epoxy binder, namely, short process viability at room temperature, due to the use of a large amount of 4,4'“ diaininodiphenylsulfone curing agent, high viscosity, reduced stickiness and elasticity, as well as significant structural rigidity of the binder film at room temperature;

[0016] - low processability of the prepreg, since it is created on the basis of an epoxy binder with a short process viability at room temperature, with increased viscosity and fluidity, possessing reduced stickiness and drapeability (flexibility and elasticity ), which complicates and increases the labor intensity of its processing into composite structures and leads to the formation of a fiber-reinforced composite material with high porosity indices and a high coefficient of variation of physical and mechanical characteristics;

[0017] - reduced moisture resistance of the cured epoxy prepreg binder;

[0018] - energy-intensive mode of forming polymer composite materials based on the proposed prepreg.

[0019] The epoxy binder known from the prototype contains a fairly large amount (26.7 wt.%) of a powdered substance of an aromatic diamine curing agent, which, when combined with other components, leads to the formation of a composition with a high viscosity at room temperature (qso^c: ™ 5000.0 Pa.s). However, when heated, the viscosity decreases significantly (minimum viscosity at a temperature of 130°C Pa.s) and ensures high fluidity of the binder with an increase in temperature (the fluidity of the binder in the prepreg during curing is 14,2%),

[0020] In addition to the critical effect of the powdered component on the rheological characteristics of the known binder, it also imparts increased structural rigidity to the uncured binder film, reducing its stickiness, elasticity and flexibility, The formed structure of the uncured binder film has reduced plasticity properties, wh ich leads to the formation of a prepreg known from the prototype, based on it with low processing characteristics: reduced elasticity and flexibility , as a result of which its drapeability at the workshop temperature (25°C ± 3°C) worsens. The use of a ’’dry ” rigid prepreg prototype with low drapeability and stickiness indicators, due to high viscosity and rigidity of the impregnating binder prototype, reduces the efficiency of laying out the prepreg on the tooling, especially on a curved one with a complex profile. When manually laying out in a three-dimensional form, the personnel must apply additional efforts and professional skills so that it takes and holds the required shape. And also maintains its integrity, does not form cracks, folds, tears when removing it from the tooling. AH this complicates and increases the process cycle of obtaining the final composite product. Sometimes, to facilitate the draping process, prepreg laying operators use hot air guns, heat guns or heaters. This reduces the viscosity of the binder in the prepreg, increases its flexibility and elasticity, but will definitely complicate the process of creating a composite product using a prepreg. prototype.

[0021] Reduced stickiness of the prepreg prototype also complicates the placement of unidirectional tapes and strips based on it, and reduces adhesion during automated laying processes using robotic or gantry devices (Automated Tape Laying (ATL) and Automated Fiber Placement (AFP)). Reinforcement material used in automated laying, obtained from the prepreg prototype, cannot be held on the tooling in the desired position, leading to manufacturing defects in the formed structure, such as gaps, overlaps and folds, each of which can significantly worsen the mechanical properties of the final composite part. An effective process method for controlling the stickiness of the prepreg in this situation is to change the temperature. Modem laying machines are equipped with infrared heaters or hot air guns for local heating before placing the reinforcing material. However, due to the presence of a large amount of active aromatic diamine curing agent (26.7 wt.%) containing active reactive primary amino groups, a small increase in temperature can contribute to partial localized curing of the prototype binder in the reinforcing material. In addition, the high fluidity of the prototype binder in the prepreg with an increase in temperatu re wi ll cause the matrix binder to spread, which leads to a loosening of the reinforcing component. In this case, a large number of pores will form, in the interlayer structures of the formed composite material, due to an insufficient amount of binder for adhesion to the previously laid layer. It will be quite difficult to remove air contained in the closed space of the formed pores when the prepreg tape does not fully adhere to the tooling or the adjacent layer during non-autoclave molding of the composite material.

[0022] As a result of the reduced processing characteristics of the used prototype prepregs based on the prototype binder, unimpregnated areas and other defects may be present in the formed material. Such, defects may lead to the formation of porous products (porosity m - 2.7%) with a large coefficient of variation of physical and mechani cal characteristics.

[0023] For curing the prototype epoxy binder under consideration, a curing system is used consisting of' 26.7 wt.% of the curing agent, aromatic diamine 4,4’- diaaiinodipheny Isul fone, 1 ,0 wt.% of the blocked curing agent, dicyandiamide, and 0.6 wt.% of the latent catalyst, asymmetrically substituted urea. Usually, to ensure effective “cross-linking” of the epoxy resin by the curing agent according to the reaction of the polycondensation type for curing of epoxy binders, a ratio of the number of functional amine groups in the curing agents and epoxy groups in the resins is used, theoretically equal to I .0:1.0, Le. during the curing process, the interaction of equimolar (stoichiometric) quantities of the resin and curing agent is optimal. The known prototype binder contains an equivalent amount of the aromatic diamine curing agent 4,4’-diaminodiphenylsulfone in relation to the amount of epoxy groups in the resin mixture used (1,0: 1.0). This ratio of reactive components makes 4,4'-diaminodiphenylsulfone the main curing agent, due to which the curing of the prototype binder occurs by a polycondensation reaction in an energy-intensive mode: increasing the temperature from room temperature to 180°C at a rate of 1.7°C / min, holding at 180°C for 2 hours.

[0024] Such high energy consumption of the process is explained by the peculiarity of the chemical structure of the curing agent of this chemical class - delocalization of the unshared electron pair of the nitrogen atom in the conjugated system of the aromatic ring, and the resulting stabilization and decrease in the activity of the amino group at a certain stage of curing.

[0025] Thus, duri ng the synthesis of the prototype binder, during the combination of epoxy resins and the aromatic diamine curing agent at an. elevated temperature, along with the dissolution processes, the first stage of the chemical reaction of epoxy resin curing is initiated. It continues at room temperature until the primary amine groups of the curing agent are completely consumed. Due to the higher content of the aromatic diamine curing agent 4,4'-diaminodiphenylsulfone (26.7 wt.%) in the prototype binder, this process occurs quite actively. Therefore, even with short-term storage of the prepreg prototype at room temperature, an increase in the viscosity of the binder can be observed, leading to the appearance of britleness and cracking of the binder film. The processes taking place significantly worsen the processing characteristics of the prepreg prototype, completely reducing its stickiness and drapeability. These characteristics are significant in the process of prepreg laying out, limiting i ts process viability at a temperature of 25°C to a short period - no more than 10 days. Such a low viability of the prepreg prototype requires the mandatory use of refrigeration equipment at the stage of its storage and transportation.

[0026] To further initiate the curing process of the prototype binder, it is necessary to increase the temperature. The activity of "hot” curing of epoxy resins with aromatic diamine 4,4 -diaminodiphenylsulfone at the initial stage (temperature 80-100 °C) is usually quite high, but subsequently (the second and subsequent stages) there is a decrease in the rate and activity of curing. This occurs due to the observed decrease in the nucleophilicity of the amino group of the aromatic curing agent. Curing agents of this type usually slowly provide complete curing of epoxy binders and for this reason the curing of the prototype binder and prototype prepreg based on it is canned out for a sufficiently long time and at high temperatures (temperature 180°C for 2 hours). This makes it possible to achie ve a high degree of curing and the formation of heat-resistant materials (Tgdry= 164 °C).

[0027] At the same time, in the composition of the curing system of the prototype binder, along with a large amount of the main curing agent, aromatic diamine (26.7 wt.%), there are small concentrations of the blocked curing agent, dicyandiamide (0.1 wt.%), and the latent curing accelerator, asymmetrically substituted urea (0.6 wt.%). This leads to a superstoichiometric amount of amine curing agents in the composition of the prototype binder. Such a ratio of components in the curing system of the prototype binder cannot promote acceleration and reduction of its curing temperature and suppression of leakage from the prepreg, but provides an excess of unreacted amine curing agent. Since latent components are active at certain temperatures, they enter into competing curing reactions by the mechanisms of cationic polymerization and polyaddition. The reaction system selected in this way leads to the formation of a cured polymer epoxy structure with a large number of unreacted terminal amine elements. Unreacted hydrophilic amine groups are capable of creating connections between the formed polymer network and water molecules through hydrogen bonds. As a result, interchain hydrogen bonds can be destroyed, causing swelling and plasticizing the epoxy polymer. 'Thus, the use of excess amine curing components in the prototype binder helps to reduce its resistance to heat and moisture exposure, increasing the penetration of moisture into the cured epoxy system. The content of unbound moisture leads to an increase in the weight of the composite material based on the prototype binder. This limits the use of prototype materials for the creation of aircraft structures.

[0028] The technical problem that this invention is intended to solve is the insufficient quantity of epoxy binders and prepregs based on them, which ensure the production of moisture-resistant, low-porosity fiber-reinforced composite materials with the same (uniform) physical and mechanical properties in all areas. Moreover, such products can be manufactured using both manual and automated laying. At the same time, they are capable of curing in energy-efficient modes.

[0029] The technical result achieved by solving the technical problem consists in increasing the viability of the binder at room temperature, increasing moisture resistance, optimizing the stickiness and drapeability of the binder film, and reducing the curing temperature. At the same time, porosity is reduced and the coefficient of variation of physical and mechanical characteristics is reduced. Simultaneous, the possibility of using composite materials based on the binder at elevated temperatures is preserved.

[0030] The technical problem is solved and the technical result is achieved due to the fact that the epoxy binder for structural polymeric materials includes a mixture of a difonctional epoxy resin based on bisphenol A and poly functional nitrogencontaining epoxy resins, a thermoplastic resin - poly ethersulfone, a curing agent - djd'-diaminodiphenylsulfone, a blocked curing agent - dicyandiamide, a latent catalyst ■■ asymmetrically substituted urea, characterized in that it includes a rubbercontaining component consisting of rubber nanoparticles of the ’’core-shell” type distributed in an epoxy resin selected from the series: a difonctional epoxy resin based on bisphenol A, a poly functional nitrogen-containing epoxy resin from a mixture of polyfunctional nitrogen-containing epoxy resins, wherein the ratio of the components is as follows, wt.%: difonctional epoxy resin - 8.6-14.8 mixture of poly functional nitrogen-containing epoxy resins - 34.3-47.4 rubber-containing component - 15,7-20.9 thermoplastic poly ethersulfone - 8.0- 13.1 curing agent, aromatic diamine - 10.5-16.5 blocked curing agent, dicyandiamide - 3.0-43 latent curing accelerator, asymmetrically substituted urea -■ 0.4-2.0 Polyfunctional nitrogen-containing epoxy resins can be selected from the following series: nitrogen-containing epoxy resin based on triglycidyl-para- aminophenol, nitrogen-containing epoxy resin based on triglycidyl-meta- aminophenoi, nitrogen-containing epoxy resin based on tetraglycidyldiaminodiphenyhnethane.

[0031] To achieve the technical result, a prepreg is also proposed, including the said epoxy binder and fibrous filler, with the following ratio of components, wt%:

[0032] - epoxy binder 24.0-55.0

[0033] - fibrous filler 45.0-76.0.

[0034] Fibrous glass and carbon fillers can be used as fibrous filler.

[0035] The ratios of the components in the epoxy binder are selected experimentally, The composition of the proposed epoxy binder has an optimal balanced amount of components used, provides for improvement of its processing characteristics and characteristics of prepregs based on it, and also contributes to an increase in their viability at room temperature, an increase in moisture resistance, the formation of heat-resistant polymer composite materials in energy-efficient non-autoclave modes with minimal porosity and low coefficients of variation of strength characteristics.

[0036] The following components can be used to create the declared epoxy binder and prepreg based on it:

[0037] -■ difunctional low-molecular (epoxy equivalent weight EEW~ 170-220 g / eq) epoxy resin selected from the following series: bisphenol A resin YD- 128 (manufactured by K.UKDO Chemical Co., Ltd), AR- 101 (manufactured by Atul LTD), .1ER 828 (manufactured by Mitsubishi Chemical Corporation), etc.;

[0038] ~ polyfimctional epoxy resins selected from a homologous series of nitrogen- containing epoxy resins, for example: epoxy resin based on tetraglycidyldiaminodiphenylmethane, JER 604 (manufactured by .Mitsubishi Chemical Corporation) or grade ARTF-23 (manufactured by Atul LTD), epoxy resin based on ethyl-substituted tetraglycidylmethylene dianiline, ARTF-33 (manufactured by Atul LTD), epoxy resin based on triglycidyl-para-aminophenoi, ARTF-36 or ARTF-35 (manufactured by Atul LTD), Araldite MY0510 or Araldite MY0500 (manufactured by Huntsman Advanced Materials), epoxy resin based on triglycidyl-meta-aminophenol, Araldite MY0610 (manufactured by Huntsman Advanced Materials), etc.;

[0039] - as a rubber-containing component, one of the following compositions can be used; Kane Ace MX125 (manufactured by Kaneka Corporation), etc., consisting of 25 wt.% of rubber nanoparticles of the «core~shell» type, distributed in a. di functional low molecular weight epoxy resin based on bisphenol A, Kane Ace MX45 1 (manufactured by Kaneka Corporation), etc., consisting of 25 wt.% of rubber nanoparticles of the «core“S.hell» type, distributed in an epoxy resin based on triglycidyl-para-aminophenol, Kane Ace MX416 (manufactured by Kaneka Corporation),- etc., consisting of 25 wt.% of rubber nanoparticles of the «core~sheU» type, distributed in an epoxy resin based on tetraglycidyldianiinodiphenylmethaiie, or a premix prepared (Table 1 ) by dispersing 25 wt.% of core-shell rubber nanoparticles consisting of a core of a butadicne-styrene copolymer and a shell of an alkyl methacrylate polymer, Clearstrength XT100 (manufactured by Arkema). Paraloid EXL-2655 or Paraloid EX.L-2691 (manufactured by Dow Chemicals), etc., in a difunctional low-molecular (epoxy equivalent weight EEW™170-220 g / eq) epoxy resin based on bisphenol A or nitrogen-containing epoxy resins based on triglycidyl-para-aminophenol, triglycidyl-meta-aminophenol, tetraglycidyldiaminodiphenylmethane, etc.;

[0040] - one of the polyethersulfones, such as Sumika Excel PES5003MP or Sumika Excel P'ES 3600P (manufactured by Sumitomo Chemical Co., Ltd.), Ultrason E 2020 P (manufactured by BASF Corporation), etc., can be used as a thermoplastic;

[0041] - an amine-type curing agent, dicyandiamide, selected from the group of components with the trade marks Dyhard 100S (manufactured by AlzChem), DJ.CY 7 (manufactured by Japan Epoxy Resins), etc., can be used as a blocked curing agent in the proposed binder;

[0042] - asymmetrically substituted urea selected from the group of components: Omicure U-24 (2,4~toluylidene bisdimethyl urea manufactured by CYC Thermoset Specialties), DCMU-99 (1 , l~dimethyl-3-(3 ,4-dichlorophenyl) urea manufactured by Hodogaya Chemical Industry Co), Toluene Bis (Dimethyl Urea) (3~[5~ (dim ethylcarbamoylamino)-2 -methylphenyl]- 1 , 1 -dimethylurea manufactured by Ataman Klmya Ltd), DYHARD UR-500 (l,3-bis-(N,N~dimethylurea)~4~ methylbenzene manufactured by AlzChem), etc., can be used as a latent curing accelerator in the proposed binder;

[0043] - the curing agent 4f4’-diaminodiphenylsulfbne, ARADUR 9664-1 (manufactured by Huntsman Advanced Materials), Seikacure-S (manufactured by Wakayama Seika Kogyo Co., Ltd.), etc. can be selected as an aromatic diamine;

[0044] ■- the following can be selected as a fibrous filler: carbon fiber filler TR50S, carbon fiber filler lK-50k, carbon fiber filler lK-3k, carbon fiber filler 12k~50K, carbon fiber filler 3K-6K, glass fiber filler based on type E glass, glass fiber filler based on type S2 glass.

[0045] In order to modify the binder in order to improve its processability and processability of prepregs based on it, the composition of the claimed invention includes a rubber-containing component with core-shell nanoparticles, which imparts stickiness and elasticity to the binder film. In addition, this component reduces the britleness of the formed composite material, increases elasticity, and also contributes to increased resistance to dynamic loads. However, a significant increase in the content of core-shell nanopmticles makes the binder film too soft and sticky. To avoid this drawback, it is effective to combine rubber-containing components with high-molecular polymer modifiers - heat-resistant thermoplastic resins containing rigid aromatic, heterocyclic and organoelement structures in their structure. The use of polyethersulfone thermoplastic resins in the composition of the claimed epoxy binder contributes to the formation of film properties, makes it possible to reduce excessive stickiness, regulate the elastic properties of the film and reduce shrinkage stresses. The combined use of processing characteristic modifiers, 15.7-20.9 wt.% of a ru bber-containing component with core-shell nanoparticles and 8.0- 13.1 wt.% of a thermoplastic poly ethersulfone resin, contributes to the formation of a c omposition with optimal processing characteristics. This is the viscosity of the binder at room temperature - rptpc 1100.0-1200 Pa.s, which decreases upon heating (minimum viscosity at temperatures of 125-130°C “ 3.9-4.4 Pa.s) and ensures low binder fluidity with increasing temperature (binder fluidity in the prepreg during curing is 5.2-7.7%). This helps to optimize the film stickiness level at room temperature and improve the processing characteristics of the developed binder. In addition, the binder in the prepreg has significant flow resistance. This prevents its spontaneous leakage from the reinforcing fibrous filler during the manufacturing, storage and lay ing out of the prepreg. The optimal level of stickiness and elasticity of the binder film makes prepregs and unidirectional tapes and strips based on it high-tech materials for both manual and automated laying out when forming a fiber-reinforced composite material using non-autoclave technology. This ensures better drapeability, effective adhesion of the reinforcing material to the tooling or adjacent layer and good compaction of the fibrous reinforcing filler with maximum removal of gas impurities and air bubbles, In addition, it allows to get a composite with low porosity and a coefficient of variation of physical and mechanical characteristics.

[0046] As a complex curing system in the composition of the declared epoxy binder, a mixture is used that includes 10.5-16.5 wt.% of a curing agent, aromatic diamine, capable of starting- a slow curing process already at room temperature, 3.0-4.3 wt.% of a blocked curing agent, dicyandiamide. Such a system is activated only at a temperature above 154°C, and 0.4-2.0 wt.% of a latent curing accelerator, asymmetrically substituted urea, capable of actively starting the curing process only when the temperature rises above 80°C. The ratio of epoxy and amine functional groups of the curing agent reactive at room temperature, aromatic diamine 4,4’- diaminodiphenylsulfone, in the samples of the proposed binder is 1.0: (0.35-0.55), which makes it less active in comparison with the prototype binder at a temperature of 25°C. Such ratios of components in the curing system ensure stability during storage, slow down the process of viscosity increase, decrease in elasticity and increase in brittleness of the epoxy composition. This contributes to an increase in the duration of the process viability of the binder and prepregs based on it during their storage at a temperature of 25°C for at least 30 days. It is known that the curing of epoxy systems is an autocatalytic and highly exothermic process.

[0047] When a bond is formed between the fonctional epoxy groups and the active amine groups of the curing agent, heat is released, accompanying the initial process of reactive crosslinking. This generated heat accelerates the curing reaction, which then forms additional thermal energy, accelerating the reaction further, and so on. It has been experimentally established that the presence in the composition of the proposed epoxy binder of an optimally balanced curing system consisting of curing agents of different types (aromatic diamine (10.5-16.5 wt.%), blocked curing agent, dicyandiamide (3.0-4.3 wt.%), and latent curing accelerator, asymmetrically substituted urea (04-2.0 wt.%)), capable of initiating active curing already at a temperature above 80eC, makes it possible to use exothermic energy. This energy is created by a reaction occurring at a low temperature to activate the next energetically inaccessible reaction at this stage of curing, for the initiation of which a higher temperature is required. The use of such a chemical technique helps to obtain, with minimal energy costs, a cured polymer matrix comparable in strength and thermoinechanical properties (glass transition temperature) with matrices formed at a higher temperature. Thus, the curing process of the proposed binder and prepreg based on it becomes energy-efficient and energy-saving.

[0048] The optimal ratio of the components of the curing system was selected experimentally. The ratio of the components in the curing system was selected so that there is no excess of curi ng components, since the ratio of the functional groups of the epoxy resin mixture and the amine functional groups o f the curing agent of the aromatic diamine 44’-diaminodiphenylsulfone in the samples of the proposed binder is 1.0: (0.35-0.55). It is this ratio that allows obtaining more densely crosslinked molecular structures of the cured epoxy binder with a high degree of conversion of reacti ve groups, Such a densely cross-linked cured polymer structure is characterized by higher heat resistance and also provides increased moisture resistance of the created epoxy binder. The polyfunctional nitrogen-containing epoxy resins used in the composition of the claimed epoxy binder make it possible to increase heat resistance and moisture resistance; due to their increased functionality and high concentration (34.8-47.4 wt.%X highly cross-linked compositions with increased moisture resistance (moisture saturation W-l.86~2.10 wt.%) and heat resistance (Tgdry =450-153 °C) are formed in the epoxy binder.

[0049] Examples of implementation.

[0050] Production of a premix of a rubber-containing component for the claimed epoxy binder.

[0051] Example 1-1 (Table 1).

[0052] To obtain a premix of a rubber-containing component, 75.0 Wt. % of low- molecular epoxy resin based on bisphenol A, JER 828 is loaded .into a clean and dry heated mixer and heated to a temperature of 100°C with the mixer running. 25.0 wt.% of Paraloid EXL-2691 core-shell rubber nanoparticles are introduced in small portions with the mixer running at a temperature of l()0°C. The mixture is stirred at a speed of 250 rpm at a temperature of 100°C to completely combine the components. The mixer is turned off and the finished premix of the rubbercontaining component is drained through the drain nipple into a dry, clean container.

[0053] The production of the premix of the rubber-containing component according to examples 1-2, 1-3, 1-4, 1-5, 1-6, 1-7 is carried out similarly to example 1 , but with other components listed in Table 1 ,

[0054] Production of the declared epoxy binder

[0055] Example 1 (Table 2).

[0056] A clean and dry reactor is loaded with 14.8 wt.% of a di functional low- molecular epoxy resin based on bisphenol A, JER 828, 34.8 wt.% of a mixture of polyfunctional nitrogen-containing epoxy resins (19.6 wt.% of a polyfunctional nitrogen-containing epoxy resin based on tetraglycidyldiaiiiinodiphenylmethane, JER 604, and 15,2 wt.% of a polyfunctional nitrogen-containing epoxy resin based on triglycidyhpara-aminophenok ARTF-36) and heated to a temperature of W0°C with the stirrer running. The mixture is stirred at a speed of 250 rpm at a temperature of 100°C until the resins are completely combined. Then the temperature is raised to 150°C and the stirrer rotation speed is increased to 300 rpm.

[0057] In small portions, with the mixer running at a temperature of 150°C, 8.0 'wt. % of thermoplastic polyethersulfone PES 3600P is added and mixed until a homogeneous mass is obtained.

[0058] Then, with the mixer running, 20.9 wt. % of the rubber-containing component Kane Ace MX451 is loaded in small portions and mixed at a speed of 350 rpm at a temperature of 130°C until a homogeneous mass is obtained.

[0059] After this, the temperature is reduced to 80°C, 16.5 wt.% of the curing agent, aromatic diamine A.RADUR 9664-1, 3,0 wt.% of the blocked curing agent, dicyandiamide DY.HARD 100S, 2.0 wt.% of latent curing accelerator, asymmetrically substituted urea Omicure U~24, are mixed at a speed of 150 rpm for at least- 60 minutes until a completely homogeneous mass is obtained. Turn off the mixer and drain the finished binder through the drain nipple into a dry and clean container.

[0060] The production of epoxy prepreg binders according to examples 2-10 (Table 2) is carried out at the ratio of components indicated m die table using the technology similar to Example 1 .

[0061] Obtain ing the declared prepreg.

[0062] Example 1 (Table 3).

[0063] The prepreg is manufactured by applying 24 wt.% of epoxy binder prepared according to the rec ipe of Example 1 (Table 2) using an impregnation machine at a temperature of 80°C onto fibrous carbon filler of composition 1K-50E in an amount of 76 wt,%.

[0064] Prepregs for Example 7 are manufactured using l K-50k. carbon fiber filler, for Examples 2, 6 using lK~3k carbon fiber filler, for Examples 3, 5, 9 using 12k-50K carbon fiber filler, for Examples 4, 8 using 3K-6K carbon fiber filler, for Examples 11, 13 using E-type glass fiber filler, for Examples 12, 14 using 82-type glass fiber fi ller, with the ratio of components indicated in Table 3. Manufacturing of fiber-reinforced composite material

[0065] Example 1 (Table 3).

[0066] From the cut prepreg obtained according to the recipe of Example 1 (Table 3 ) based on a binder and fibrous carbon filler of composition IK-SOk, a process package is formed, from which a fiber-reinforced composite material is obtained by vacuum molding at a pressure of 0.095 MPa, according to the temperature regime: 180 minutes at a temperature of (130±5)°C.

[0067] Also, a fi ber-reinforced composite m aterial is made of the prepregs according to Examples 2-14 (Table 3).

[0068] The recipes for making the premix of the rubber-containing component are given in Table 1 , the compositions of the epoxy prepreg binders according to the invention and the prototype are given in Table 2, the compositions of the prepregs according to the invention and the prototype are given in Table 3, the properties of the binders according to the claimed invention and. the prototype, prepregs and composite materials made on their basis are given in Table 4.The invention is not limited to the given examples.

[0069] Table I . Recipe for the production of a premix of a rubber-containing component

[0070] Table 2. Composition of the proposed epoxy binder and the prototype binder.

[0071] Table 3. Composition of the prototype prepreg and prepregs of the claimed invention.

[0072] Table 4. Properties of the binder of the claimed invention and prototype, prepregs and fiber-reinforced composite material mad on their basis

[0073] Table 4 (continued)

[0074] Comparative data from Table 4 show that the proposed epoxy binder provides advantages over the prototype:

[0075] - it is more advanced, since it is characterized by low viscosity at room temperature (rpw c — 1100.0-1200 Pa.s), which decreases upon heating to the optimal minimum value = 3.9-4.4 Pa.s) due to its low fluidity (binder fluidity in the prepreg during curing is 5.2-77%), helps to optimize the level of elasticity and stickiness of the binder film at room temperature and improve the processing characteristics of prepregs based on it in comparison with the known binder, which is characterized by increased structural rigidity of the uncured film due to the high viscosity of the binder at room temperature (rjjo’c ~ 5000.0 Pa.s). The viscosity of the prototype binder is significantly reduced by heating .9 Pa.s) and ensures high flowability of the prototype binder with increasing temperature (the flo wability of the binder in the prepreg during curing is 14.2%), This can lead to its spontaneous leakage from the reinforcing fibrous taller during the production, storage and laying out of the prepreg;

[0076] - ensures the creation of more advanced prepregs with optimal drapeability and stickiness at room temperature. This facilitates the ease of laying out and assembling prepreg packages and comfortable work with them both during manual and automated laying out, compared to prepregs based on the prototype binder, which have significantly lower processing characteristics. This allows for the production of defect-free composite materials based on the proposed epoxy binder using non-autoci ave technology, characterized by lower porosity (porosity m = 1 ,4- 1.6%) compared to the composite material based on the prepreg prototype (porosity m = 2.7%) and demonstrating a sl ight spread of physical and mechanical properties (three-point bending strength), which helps to reduce the coefficient of variation of the strength properties of composite samples by approximately 2 times compared to the value of the polymer composite material (PCM) based on the prototype binder: Kj ~ 9.1 > K.;i ~ 4.6-5.0 (Ki is the coefficient of variation of the strength properties of the composite sample based on the prototype binder; K2 is the coefficient of variation of the strength properties of the composite sample based on the developed binder);

[0077] - provides increased moisture resistance of cured polymer structures after heat-moisture aging (keeping at a temperature of 70°C in a water bath for 14 days) since they are characterized by lower moisture saturation W~1.86%-2.10% in comparison with the prototype material, which has a moisture saturation of up to W“3>58%. The characteristics of materials based on the developed epoxy binder confirm the possibility of creating composites based on it, which have improved moisture resistance, ensuring their reliable operation after exposure to negative operational factors (high temperature and moisture);

[0078] - the created prepregs have increased process viability, since when stored for more than 30 days at a temperature of 25CC, they are characterized by more stable indicators of stickiness, elasticity and drapeability in comparison with the prototype prepreg, the viability of which at a temperature of 25 °C does not exceed .10 days. Such high stability of the declared epoxy bi nder in the prepreg leads to the absence of a rapid increase in viscosity and the appearance of brittleness, long-term preservation of elasticity, which simplifies the process of working with it. The optimally balanced composition of the curing system interacts very slowly with the epoxy system at room temperature, and the created binder is able to retain its processing properties for a long time (at least 30 days). Such processing characteristics of the declared epoxy binder are a competitive advantage and make it possible to create long-lived prepregs on its basis (process viability of at least 30 days). They can reduce energy costs during their transportation and storage until use by eliminating the use o f special industrial freezing equipment. In turn, this has a positive effect on the economic indicators of production;

[0079] - they are more cost-effective materials. Thus, their curing process is earned out according to an energy-efficient temperature-time regime: duration. 3 hours, curing temperature no more than I30°C. The formation of heat-resistant materials with Tgdfy - 150-153 °C is ensured (for the prototype, the duration is 2 hours, curing temperature Thus, the claimed epoxy binder and prepreg made on its basis demonstrate improved processing characteristics. This provides the possibility of obtaining composite materials using non-autoclave technology, simplifies the process and reduces the costs of their production, transportation and storage. It also makes it possible to obtain products using energy-efficient molding modes that are resistant to the impact of negative operational factors (high temperature and humidity), characterized by low porosity and insignificant variation in strength under three- point bending. In addition, it provides a decrease in the variation coefficient of the physical and mechanical properties of the created composite materials. The set of achieved processing and operational characteristics in the developed binder and prepregs based on it make these materials promising for use in the creation of structural composite aviation materials operating at temperatures from -60 to -H00oC,

Claims

Claims1. An epoxy binder for structural polymeric materials, comprising a mixture of a difunctional epoxy resin based on bisphenol A and poly functional nitrogen-containing epoxy resins, a thermoplastic resin - polyethersulfone, a curing agent - 4>4’-diaminodiphenylsulibne, a blocked curing agent - dicyandiamide, a latent catalyst - asymmetrically substituted urea, characterized in that it additionally includes a rubber-containing component consisting of rubber nanoparticles of the ’’core-shell” type, distributed in the epoxy resin, with the following ratio of components, wt.%: difunctional epoxy resin ■ • 8.6-14.8 mixture of poly functional riitrogen-containing epoxy resins - 34.8-47.4 rubber-containing component - 15.7-20.9 thermoplastic polyethersulfone - 8.0- 13.1 curing agent, aromatic diamine ~ 10.5-16.5 blocked curing agent, dicyandiamide - 3.0-4.3 latent curing accelerator, asymmetrically substituted urea - 0.4-2.

02. The epoxy binder according to claim 1, characterized in that the epoxy resin in which the core-shell rubber nanoparticles are distributed is a di functional epoxy resin based on bisphenol A.

3. The epoxy binder according to claim 1, characterized in that the epoxy resin in which the «core-shell» rubber nanoparticles are distributed, is a mixture of poly functional nitrogen-containing epoxy resins,4. The epoxy binder according to claim 1, characterized in that the polyfunctional nitrogen-containing epoxy resins are selected from the series: a nitrogen-containing epoxy resin based on trigiycidyl-pmx?- aminophenol, a nitrogen-containing epoxy resin based on triglycidyl-meta-amiiiopheriol, a nitrogen-containing epoxy resin based on tetraglycidyidiatninodiphenylniethane.

5. A prepreg comprising an epoxy binder and a fibrous filler, characterized in that the epoxy binder is a binder according to any of claims 1-4, in the following ratio, wt.%: epoxy binder 24.0-55.0 fibrous filler 45.0-76.0.

6. A prepreg according to claim S, characterized in that it contains fibrous carbon filler as the fibrous filler.

7. A prepreg according to claim 5, characterized in that it contains fibrous glass filler as the fibrous filler.

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