RU2655805C1 - Epoxy binder, prepreg based thereon and article made therefrom - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of producing melt epoxy binders for structural polymeric composite materials (PCM) based on fibrous fillers obtained by prepreg technology, with energy-efficient curing modes, which can be used in the aviation, helicopter, machine, auto, shipbuilding and other industries. Epoxy binder includes the following components in the following ratio in wt%: epoxy polyfunctional resin 22.0–38.0; epoxy resin based on bisphenol A 40.0–50.0; thermoplastic 7.0–13.0; latent curing agent – dicyandiamide 3.0–7.0; hardener – 4,4'-diaminodiphenylsulphone 4.7–15.0; accelerator – asymmetrically disubstituted urea 0.3–3.0. Prepreg comprises said epoxy binder and fibrous filler in the following ratio, wt%: epoxy binder 30.0–50.0, fibrous filler 50.0–70.0. Product is produced by vacuum moulding of the prepreg.

EFFECT: developed epoxy binder and prepreg, made therefrom, demonstrates improved technological characteristics, which simplifies the process of obtaining PCM, and also makes it possible to obtain products with a higher level of preservation of physical and mechanical properties (compression strength at temperature 20 °C) after exposure to negative operational factors, characterised by low porosity and a slight spread in strength values, which reduces the coefficient of variation of physical and mechanical properties of PCM (ultimate strength at interlayer shear at temperature 20 °C).

7 cl, 3 tbl, 1 ex

Description

The invention relates to the field of creating melt epoxy binders for structural polymer composite materials (PCM) based on fibrous fillers obtained by prepreg technology, with energy-efficient curing modes that can be used in the aviation, helicopter, machine, auto, shipbuilding industry and others branches of technology.

The prior art epoxy binder for preparing prepregs containing epoxytriphenol resin, low molecular weight and high molecular weight epoxy resins, hardeners dicyandiamide (DCDA) and bis (N, N'-dimethylcarbamide) diphenylmethane, solvent (a mixture of ethyl, isopropyl alcohol and isopropyl alcohol) silicon. The prepreg obtained by mortar technology includes 30-42 wt. % epoxy binder and 58-70 wt. % fibrous filler. Oversized products, such as helicopter blade spars and the like, are obtained from the created prepreg by molding. (RU 2263690 C1, November 10, 2005).

The main disadvantage of this epoxy binder is the content in its composition of a large amount of inert volatile organic solvent (up to 40%), which complicates the technology for producing PCM from it and contributes to the deterioration of the environmental and fire safety of the process of its processing. The removal of volatile products usually leads to the formation of strong porosity in products from PCM, which is accompanied by a drop in elastic-strength properties.

PCM is formed at high temperatures (the last step up to 180 ° C), which makes the process of their manufacture quite energy-intensive.

Another prepreg epoxy binder is known containing a high molecular weight epoxy resin, hardeners dicyandiamide and 2-methylimidazole, a nitrogen containing epoxy resin and a polyester resin. The prepreg made on the basis of this binder, includes 55-65 wt. % fibrous filler and 35-45 wt. % binder. From the obtained prepreg, a three-layer honeycomb panel is made of PCM for aircraft and other vehicles (RU 2559495 C1, 08/10/2015).

The indicated epoxy binder and prepregs based on it, due to the presence of UP-610 grade nitrogen-containing epoxy resin, characterized by increased reactivity, and also hardener 2-methylimidazole sufficiently active at room temperature, have a low viability at a temperature of 25 ° C for no more than 5 days, which complicates the process of their processing and requires the use of refrigeration equipment to increase the shelf life.

The closest analogues adopted for the prototype are:

- epoxy composition, which is a mixture of epoxy resins: multifunctional based on tetraglycidyl diaminodiphenylmethane: 46.7 mass. % and difunctional based on bisphenol A: 20.0 mass. %, thermoplastic - polyethersulfone: 6.7 wt. %, latent curing agent of dicyandiamide (DCDA): 2.0 wt. %, hardener 4,4'-diaminodiphenylsulfone (DADFS): 20.0 wt. % and accelerator asymmetric disubstituted urea: 4.6 mass. %;

- unidirectional prepreg containing the specified epoxy binder and carbon fiber brand T700G-12K-31E (manufacturer Toray K.K.), with a ratio of components: binder - 35 mass. %, carbon fiber filler - 65 mass. %;

- the prepreg product is obtained by vacuum molding at a vacuum of 0.095 MPa in a two-stage mode: increasing the temperature at a speed of 1.5 ° C / min to 90 ° C, holding at a temperature of 90 ° C - 1.5 hours; raising the temperature at a rate of 1.5 ° C / min to 130 ° C, holding at 130 ° C for 2 hours (US 2013217283 A1, working example 8, 08/22/2013).

The disadvantages of the prototype materials are:

- a low level of technological characteristics of an epoxy binder (a low degree of preservation of rheological characteristics and viability in the prepreg at a storage temperature of 25 ° C);

- the formation of a cured polymer structure with a low degree of conversion of oligomers to a polymer (reduced curing degree) during PCM formation, which does not provide their reliable operational stability after exposure to negative factors (elevated temperature and moisture) and can lead to the creation of materials characterized by low moisture resistance with low preservation of strength characteristics after moisture saturation;

- low manufacturability of prepregs, since they are based on an epoxy binder with increased viscosity and reduced fluidity, have reduced stickiness and drape (flexibility and elasticity), which complicates and increases the complexity of the process of processing them in PCM and can lead to the formation of products with high rates porosity and a large coefficient of variation of physical and mechanical characteristics.

The technical task and the technical result of the claimed invention is the creation of an epoxy binder with improved technological characteristics (high levels of preservation of rheological characteristics and its viability in the prepreg at a storage temperature of 25 ° C), which provides a high degree of curing and an increase in the degree of preservation of strength characteristics (compressive strength at 20 ° C) obtained by PCM after exposure in a heat-moist chamber at a temperature of 70 ° C and 85% humidity for 30 days, as well as akterizuyuschegosya optimal viscosity and fluidity, which will enable to obtain high-tech prepregs based on it, suitable for molding FRP with low porosity and a low coefficient of variation of physical and mechanical properties (tensile strength, interlaminar shear at 20 ° C).

To solve this problem and achieve a technical result, an epoxy binder is proposed, including a mixture of polyfunctional and difunctional based on bisphenol A epoxy resins, thermoplastic, latent curing agent - dicyandiamide (DCDA), hardener - 4,4'-diaminodiphenylsulfone (DADFS), accelerator - asymmetric disubstituted urea, characterized in that one polyfunctional epoxy resin or a mixture thereof is used as a polyfunctional epoxy resin, and is used as a thermoplastic according to iarilsulfon, polyethersulfone or phenoxy, or mixtures thereof, with the following component ratio, wt. %:

epoxy polyfunctional resin 22.0-38.0 bisphenol A epoxy 40.0-50.0 thermoplastic 7.0-13.0 latent curing agent - dicyandiamide 3.0-7.0 hardener - 4,4'-diaminodiphenylsulfone 4.7-15.0 accelerator - asymmetrically disubstituted urea 0.3-3.0

A prepreg is also proposed, including the specified epoxy binder and a fibrous filler, in the following ratio of components, mass. %:

epoxy binder 30.0-50.0 fiberfill 50.0-70.0

As the fibrous filler can be used fibrous glass or carbon fillers.

Products are obtained by vacuum molding a prepreg based on the claimed epoxy binder.

To create an epoxy binder:

- as a polyfunctional epoxy resin in the invention, one of the resins selected from the groups can be used: polyfunctional epoxy resins based on phenols of grades UP-643, EN-6 (manufactured by LLC Doros), nitrogen-containing epoxy resins (amino-epoxy) of brands EMDA, ECD (manufacturer ZAO Himex Limited), Araldite MY9655 (manufacturer Huntsman Advanced Materials), etc., or mixtures thereof;

- as a difunctional epoxy resin based on bisphenol A, epoxy resins of the brands Araldite LY1556 (manufacturer Huntsman Advanced Materials), ED-22, ED-20 (GOST 10587-93) or D.E.R. can be used. 330 or D.E.R. 331 (manufactured by Dow Chemical Company) and others;

- as the latent curing agent of DCDA in the invention, the following can be used: DYHARD 100S, DYHARD 100SF (manufacturer AlzChem), DICY 7 (manufacturer Japan Erohu Resins), etc .;

- as a hardener, 4,4'-diaminodiphenylsulfone (DADFS) grades ARADUR 9664-1 or ARADUR 976-1 (manufacturer Huntsman Advanced Materials), etc. can be used;

- as an accelerator of asymmetrically disubstituted urea, for example, 2,4-toluilidene bisdimethyl urea (brand Omncure U-24, manufacturer CVC Thermoset Specialties), 3- (3,4-dichlorophenyl) -1,1 dimethyl urea (brand DYHARD UR-200, manufacturer AlzChem), 1,3-bis- (N, N-dimethylcarbamide) -4-methylbenzene (brand DYHARD UR-500, manufacturer AlzChem); DYHARD UR-800 brand (manufacturer AlzChem) and others;

- as a thermoplastic, one of the brands of polyarylsulfone, for example, grade PSFF-30, PSFF-70 (manufactured by JSC Institute of Plastics named after G. Petrov, JSC), one of the brands of polyethersulfone, for example grade PSK-1, (manufacturer of JSC “G. Petrov Institute of Plastics”), brand PES5003P (manufacturer Sumitomo Chemical KK), brand Ultrason E 2020 Р (manufacturer BASF Corporation) and one of the phenoxy resin brands, for example RKNV, RKNN (manufacturer Gabriel Phenoxies Inc) and others or mixtures thereof.

It was found that the presence of a large amount of the active hardener of 4,4'-diaminodiphenyl sulfone (20.0 wt.%) And an epoxy resin based on tetraglycidyl diaminodiphenylmethane (46.7 wt.%) Containing a tertiary amine in its molecular structure catalytic activity, contributes to the accelerated activation of the curing process even at room temperature, which leads to a rapid increase in the viscosity of the binder and a decrease in its viability in the prepreg during storage at a temperature of 25 ° C, which is significant venno worsens their technological properties. In contrast to the prototype, the proposed binder contains a smaller amount of 4,4'-diaminodiphenyl sulfone (up to 15.0 wt.%) And an epoxy resin based on tetraglycidyl diaminodiphenylmethane (up to 38.0 wt.%), Due to which the synergistic effect of the influence of these components on the activity The curing process at room temperature manifests itself to a lesser extent and the epoxy binder is characterized by improved technological properties: a high degree of preservation of rheological characteristics and long viability in the prepreg storage temperature 25 ° C.

It was experimentally established that the use of a complex curing system with an optimally balanced amount of latent curing agent dicyandiamide (3.0 ÷ 7.0 wt.%), A curing accelerator of asymmetrically disubstituted urea (0.3 ÷ 3.0 wt.%) In the composition of the proposed epoxy binder ) and hardener 4,4'-diaminodiphenylsulfone (4.7 ÷ 15.0 wt.%), due to its high activity at elevated temperatures, leads to the fact that the beginning of the curing process is observed at temperatures of 90 ÷ 100 ° C, which is characterized by a rapid P swelling and is accompanied by a significant heat release in a narrow temperature range (the width of the exothermic peak of the differential scanning calorimetry (DSC) curve is 40 ÷ 60 ° C) for a short period of time at which the released heat does not have time to dissipate into the environment and the temperature in the reaction zone begins to exceed the temperature supplied from the outside, which helps to achieve a high degree of conversion of reactive groups and a more complete cure of the developed binder (curing degree 96.5 ÷ 98.7%) with high temperatures (not higher than 130 ° C) for a short curing period (within 2 hours).

Selected as a prototype epoxy binder with a comprehensive curing system containing 2.0 mass. % latent curing agent of dicyandiamide, 4.7 wt. % accelerator curing asymmetrically disubstituted urea and 20.0 mass. % hardener 4,4'-diaminodiphenylsulfone, provides the beginning of the curing process only at temperatures above 108 ° C and is also accompanied by a significant exothermic effect, but the thermal effect is fixed in a wider temperature range (width of the exothermal peak of the DSC-80 ° C curve) for a longer a period of time, which does not make it possible to achieve a sufficiently deep degree of conversion of reactive groups at low temperatures (not higher than 130 ° C) in a short period of time (no more than 2 hours). A cured polymer structure, with a low degree of conversion of oligomers to a polymer (cure rate of 94%), does not provide reliable stability of plastics after exposure to negative operational factors (elevated temperature and moisture) and leads to the creation of PCMs with reduced moisture resistance and low retention of strength characteristics (strength when compressed at 20 ° C) after moisture saturation during exposure in a heat-moist chamber (T = 70 ° C, ϕ = 85%) for 30 days. The used ratio of the components in the complex curing system of the present invention promotes the formation of polymer structures and products based on them, more resistant to moisture and elevated temperature and is characterized by a higher degree of preservation of strength characteristics (compressive strength at 20 ° C) after moisture saturation.

The prototype binder contains a large number of components (20.0 wt.% Hardener 4,4'-diaminodiphenylsulfone and 46.7 wt.% Polyfunctional epoxy), which when combined with other components lead to the formation of a composition with a sufficiently high viscosity ( viscosity at a temperature of 40 ° C - 4751 Pa⋅s, the minimum viscosity of the composition - 12.0 Pa⋅s) and low fluidity, due to its poor flowability with increasing temperature. At the stage of production of prepregs in the manufacture and application of a film of a binder on the surface of the filler, it is necessary that the melt of the binder has optimal rheological characteristics, due to which it is possible to obtain a defect-free surface of the prepreg, namely, with uniform application of the binder and the absence of unimpregnated areas. To achieve such a fluidity of the highly viscous binder-prototype, the prepreg is manufactured at a temperature of 120 ° C, which contributes to the formation of a partially cured polymer system (the beginning of the curing of the binder begins at a temperature above 108 ° C) and leads to the creation of prepregs with low processability, characterized by reduced drapeability and stickiness, which makes it difficult to lay them on a snap of any complexity so that they take the desired shape without forming cracks and creases, tears When removing them after curing from a snap. As a result of the reduced technological characteristics of the used prepregs based on the prototype binder, unformed sections and other defects can be present in the formed material, which lead to the formation of products with high porosity (up to 2.1%) and a large coefficient of variation in physical and mechanical characteristics (tensile strength with interlayer shear at 20 ° C).

In contrast to the prototype, the proposed epoxy binder contains fewer thickening components (hardener 4,4'-diaminodiphenylsulfone - 4.7 ÷ 15.0 wt.%, Polyfunctional epoxy resin - 22.0 ÷ 38.0 wt.%), Due to which makes the composition less viscous (viscosity at a temperature of 40 ° С - 1030 ÷ 1100 Pa⋅s, and the minimum viscosity - 3.5 ÷ 4.5 Pa⋅s). The low viscosity of the proposed epoxy binder contributes to good flowability with increasing temperature, which makes it possible to manufacture the prepreg at temperatures of 75 ÷ 85 ° C. Under these conditions, there are no significant changes in the characteristics of the polymer composition and due to the uniformly applied film of the distributed binder, the appearance of the prepreg improves, there is no variation in the mass content of the binder over the entire area of the filler impregnation, and as a result, the technological parameters of the prepreg, such as drape and stickiness, are optimized. The prepreg made using the proposed epoxy binder makes it possible to obtain a defect-free and uniform polymer structure characterized by low porosity (0.9 ÷ 1.5%) and maximum physicomechanical properties of PCM with a minimum coefficient of variation of strength characteristics (tensile strength at interlayer shear at 20 ° C).

Examples of implementation

Preparation of the claimed epoxy binder

Example 1 (table. 1)

In a clean and dry reactor load 22 mass. % polyfunctional epoxy based on phenols UP-643 brand, 50 wt. % of a difunctional epoxy resin based on bisphenol A grade ED-20 and with a working stirrer is heated to a temperature of 100 ° C. The mixture is stirred at a speed of 250 rpm at a temperature of 100 ° C for a complete combination of resins. Then raise the temperature to 150 ° C and increase the speed of rotation of the mixer to 300 rpm

In small portions with a working stirrer at a temperature of 150 ° C, 7.0 wt. % thermoplastic phenoxysmol brand RKNV and mix until a homogeneous mass.

The temperature of the reaction mixture was reduced to 110 ° C, loaded in small portions with a working stirrer 15.0 mass. % hardener ARADUR 976-1 and mix until a homogeneous mass.

When the stirrer is operating at a speed of 300 rpm, 3.0 mass are charged. % dicyandiamide brand DYHARD 100S, while increasing the speed of the mixer to 600 rpm Stir until a homogeneous mass.

Reduce the temperature to 80 ° C and add in small portions of 3.0 mass. % curing accelerator asymmetrically disubstituted urea Omncure U-24 with stirring at a speed of 250 rpm for 60 minutes to obtain a completely homogeneous mass. Turn off the mixer and drain the finished binder through the drain fitting.

The manufacturing technology of epoxy binders according to examples 2-12 (table. 1) was used analogously to example 1.

Obtaining the declared prepreg

Example 1 (table. 2)

Obtaining a prepreg is carried out by applying 30 mass. % epoxy binder prepared according to the recipe of example 1 (table. 1) by means of an impregnation machine at a temperature of 80 ° C on a carbon tow T700S-12K-50C in an amount of 70 wt. %

The prepregs for examples 3, 5, 7, 9, and 11 were made using a T700S-12K-50C carbon tow, for examples 2, 4, 6, 8, 10, and 12 using a glass roving RVMPN 10-400,

Manufacture of the claimed product

Example 1 (table. 3)

A prepreg based on a binder and carbon fiber T700S-12K-50C, obtained on an impregnation machine according to the formulation of Example 1 (Table 2), is cut into ribbons 6.35 mm wide, which are laid out on an automated laying machine with adjustable rolling force (about 1, 0 MPa) and temperature (of the order of 85 ° C (short-term). The manufacture of the product is carried out by vacuum molding the prepreg obtained at a pressure of 0.095 MPa, according to the temperature regime: 2 hours at a temperature of 130 ° C, in this way structurally similar car-like samples are obtained ace fuselage.

Based on the prepared prepregs according to Examples 2-12 (Table 2) using a technology similar to Example 1, structurally similar product samples were made by vacuum molding: according to Examples 3, 5 and 8, such as the fuselage frame, according to Examples 2, 4, 6, 7 and 9 - type stabilizer, according to examples 10, 11 and 12 - type spar stabilizer.

The compositions of the binders according to the invention and the prototype are shown in table 1, the compositions of the prepregs according to the invention and the prototype are shown in table 2, the properties of the binders according to the claimed invention and the prototype, prepregs and PCM made on their basis are shown in table 3.

Comparative data from table 3 show that the proposed epoxy binder provides advantages compared with the prototype:

- is more technologically advanced, because it is characterized by more stable indicators of viscosity conservation, as a result of its storage for 30 days at a temperature of 25 ° C, there is no increase in viscosity compared to the initial value (coefficient of increase in viscosity of the binder is 1.0), the prototype but there is an increase in the viscosity index up to 50% (coefficient of increase in viscosity of the binder is 1.5). Such a high chemical stability of the claimed epoxy binder at room temperature and the absence of a rapid increase in viscosity simplifies the technological process of its processing in PCM, and also makes it possible to manufacture prepregs with a long pot life of at least 60 days at room temperature, in contrast to the prototype, whose viability at room temperature is only 15 days. Such technological characteristics of the claimed epoxy binder make it possible to create technologically advanced and long-lived prepregs based on it, which can provide a reduction in energy consumption during transportation and storage until processing by eliminating the use of refrigeration equipment, which in turn affects the economic performance of production;

- characterized by a higher degree of conversion of oligomers to polymer (cure degree 96.5 ÷ 98.7%) than the binder-prototype (cure rate 94.0%). This provides increased moisture resistance of polymer structures and products based on the proposed binder after a 30-day heat and moisture exposure in a heat and humidity chamber (T = 70 ° C, ϕ = 85%), since they are characterized by lower moisture saturation - 0.3 ÷ 0.9%, in comparison with the prototype material, in which the moisture saturation is up to 1.0%, and demonstrate a higher degree of preservation of strength characteristics (tensile strength at compression at a temperature of 20 ° C) after moisture saturation - 72 ÷ 85% (of the value of compressive strength at temperature 20 ° С to saturation), in comparison with the prototype material in which the degree of preservation of strength characteristics (compressive strength at a temperature of 20 ° C) after moisture saturation is not higher than 65% (from the value of compressive strength at a temperature of 20 ° C to moisture saturation). Characteristics of materials based on the developed epoxy binder confirm the possibility of creating PCMs based on it, which have increased moisture resistance, and their reliable operation after exposure to negative operational factors (elevated temperature and moisture);

- provides the creation of more technological prepregs, characterized by optimal drape and stickiness at room temperature compared to prepregs based on a prototype binder, in which these technological characteristics are significantly lower. This makes it possible to produce defect-free PCMs based on the proposed epoxy binder, characterized by lower porosity (not more than 1.5%) compared to PCMs based on the prototype binder (2.1% porosity) and exhibiting a slight variation in physical and mechanical properties (tensile strength) when the interlayer shear at a temperature of 20 ° C), which helps to reduce the coefficient of variation of the strength properties of PCM by about 2 times compared with the value of PCM based on a binder-prototype (K _{coefficient of variation of the} prototype = 9, 9; K _{coefficient of variation of the} developed binder = 4.7 ÷ 5.0).

Thus, the claimed epoxy binder and prepreg, made on its basis, demonstrate improved technological characteristics, which simplifies the process of obtaining PCM and reduces the cost of their manufacture, transportation and storage, and also makes it possible to obtain products with a higher level of preservation of physico-mechanical properties (tensile strength at compression at a temperature of 20 ° C) after exposure to negative operational factors, characterized by low porosity and a small spread strength values, which reduces the coefficient of variation of physical and mechanical properties of FRP (tensile strength, interlayer shear at a temperature of 20 ° C).

Claims (9)

1. An epoxy binder comprising a mixture of polyfunctional and difunctional based on bisphenol A epoxy resins, thermoplastic, latent curing agent - dicyandiamide (DCDA), hardener - 4,4'-diaminodiphenylsulfone (DADFS), an accelerator - asymmetrically displaced by urea, as a multifunctional epoxy resin, one multifunctional epoxy resin or a mixture thereof is used, and as a thermoplastic polyarylsulfone, polyethersulfone or phenoxy resin or a mixture thereof is used, in the following solutions of components, mass. %: epoxy polyfunctional resin 22.0-38.0 bisphenol A epoxy 40.0-50.0 thermoplastic 7.0-13.0 latent curing agent - dicyandiamide 3.0-7.0 hardener - 4,4'-diaminodiphenylsulfone 4.7-15.0 accelerator - asymmetrically disubstituted urea 0.3-3.0 2. The epoxy binder according to claim 1, characterized in that as a polyfunctional resin using one epoxy resin selected from the groups: nitrogen-containing epoxy resins based on phenols or mixtures thereof. 3. The epoxy binder according to claim 1, characterized in that as a thermoplastic use one thermoplastic polyarylsulfone, polyethersulfone, phenoxy resin or mixtures thereof. 4. A prepreg, including an epoxy binder and a fibrous filler, characterized in that as the epoxy binder use a binder according to one of paragraphs. 1-3. 5. The prepreg according to claim 4, characterized in that it contains components in the following ratio, mass. %: epoxy binder 30.0-50.0 fiberfill 50.0-70.0 6. Prepreg according to one of paragraphs. 4, 5, characterized in that as the fibrous filler contains fibrous carbon filler. 7. Prepreg according to one of paragraphs. 4, 5, characterized in that as the fibrous filler contains a fibrous glass filler.