RU2170745C2 - Method of hardening composite material - Google Patents

Abstract

FIELD: chemistry of polymers. SUBSTANCE: described is method of hardening composite materials by stepwise heating and maintenance till hardened composite material is formed (heating is carried out from room temperature to 1280132 C at rate of 0.8+1.2 C/min), is maintained at above-indicated temperature for 28-32 minutes and is thereafter heated to 175+1 C at rate of 1.8-2.2 C/min. During heating and maintenance operation at isotherm temperatures, values of electric conduction and loss tangent of dielectric are constantly measured, and hardening process is completed till above-indicated vales with respect to time are attained. Polymeric materials are visually homogeneous with respect to volume and have stable (99%) degree of hardening. EFFECT: simplified process, improved quality of materials due to attaining pore-free matrix which is ENFB binder and conducting hardening composite materials using method of preparing pore-free matrix. 3 ex, 4 tbl

Description

 The invention relates to the field of production of composite materials based on epoxyphenol binder grade ENFB, which may find application in the preparation of prepregs.

 The ENPB binder consists of a mixture of the following components: EN-6 epoxywoven resin, SF-341 A anilinophenol formaldehyde resin, EFU furfuryl glycidyl ether, UP-605/3 catalyst and alcohol-acetone mixture (Technological instruction TI 59-1004-82. Preparation, quality control and storage of binders 5-211B, ENFB. A copy of the statement is attached).

 The known mode of autoclave molding of carbon fiber KMU-4 on a binder ENFB / Technological instruction TI 59-1004-82. The autoclave molding mode of carbon fiber reinforced plastic KMU-4 on a binder ENFB p / A A-3396), which is the closest in technical essence to the method of curing a composite material based on epoxyphenolic binder ENFB by stepwise heating and holding until a cured composite material is obtained.

According to the known method, heating is carried out to (80 ± 1) ^o C in 20-30 minutes when creating a vacuum of 0.08-0.09 MPa (0.8-0.9 kgf / cm ² ), followed by turning off the vacuum pump and connecting the vacuum systems with the atmosphere, a further rise in temperature to a second temperature point (110 ± 7 ^o C) for 10-15 minutes when pressure reaches this time 0.6 MPa (6 kgf / cm ² ), a rise in temperature to a third temperature point, changing depending on the type of filler (165 ± 5 ^o C) for KMU-4 or (175 ± 5 ^o C) for KMU-43 with holding at this point for 6 hours. That is, heating in media it is carried out at a speed of 2-3 ^o C / min with turning off the vacuum in the range of 80-175 ^o C with a total heat treatment cycle of about 7 hours. Cooling is carried out at a speed of 0.5-1.0 ^o C / min to 40-50 ^o C at a pressure of at least 0.25 MPa (2.5 kgf / cm ² ).

The disadvantage of this method is the long curing cycle (about 7 hours) and the possibility of obtaining low-quality material due to its heating at a high technological speed in the gelation area in the temperature range of 80-175 ^o C with the vacuum turned off at increasing pressure, which can lead to the blocking of volatile formed during the curing reaction (polycondensation) inside the material, and their subsequent explosive exit, causing warping of the resulting PCM. In addition, different types of fillers use different maximum curing temperatures, which makes the mode unacceptable for other types of fillers, and a long heat treatment time at the maximum curing temperature can cause additional damage to the material due to thermal degradation.

 The present invention solves the following problems: the technology of obtaining composite materials based on the ENPB binder is simplified due to the possibility of curing using the same curing temperature for different types of fillers, halving the curing mode compared to the prototype. At the same time, the materials are obtained guaranteed without pores and air inclusions with a stable degree of cure of 99%. Reduced labor costs.

To achieve this technical result, in the method of curing composite materials based on epoxyphenol binder ENBF, carried out by stepwise heating and holding until a cured composite material is obtained, heating is carried out from room temperature to 128-132 ^o C at a speed of 0.8-1.2 ^o C / min, the material is kept at this temperature for 28-32 min, then heated to (175 ± 2) ^o C at a speed of 1.8-2.2 ^o C / min, kept at this temperature until a cured material is obtained, and heating progress and exposure of the material at these temperatures, a constant measurement of the electrical conductivity and the tangent of the dielectric loss angle is carried out, and the curing process is completed when constant values of these values are reached in time.

 The invention is illustrated by the following examples.

 Example 1. In a furnace with a viewing window, heated according to a given mode, a bottle with 1 ml of ENPB binder and an electrophysical cell in the form of a high glass tube with two copper electrodes inserted into it (diameter of the working electrode is 1 cm) are placed, the distance between the electrodes is 1 cm), where the binder ENFB is poured in an amount of 30 ml. The inspection window of the furnace allows you to visually observe the picture of the curing of the material. A thin layer of a binder in a box with an open surface allows you to simulate a layer of a binder on fiberglass, the type of product between the electrodes of the electrophysical cell is a thick layer of a binder in multilayer composites or monolithic thick-walled products.

The box and the cell with the ENBF binder sample are heated according to the regime: at a speed of 1.0 ^o C / min to 130 ^o C with holding at this temperature for 30 minutes, at a speed of 2.0 ^o C / min to a temperature of maximum cure of 175 ^o C holding at this temperature until constant values of electrical conductivity G are achieved, controlling the end of curing after reaching constant values of the dielectric loss tangent (tan δ). The curing product is visually homogeneous, monolithic, without air inclusions and pores. Data electrophysical analysis of the curing of the binder ENBF for this mode are presented in table 1.

As can be seen from the table, the values of G and tan δ stabilize after 192 minutes of heating. Further heating for 60 min did not change the readings of the electrophysical parameters, which indicates the complete course of curing at 192 min of heating. The change in electrical conductivity from its maximum value of 3.300 μS (65 ^o C) at the end of curing occurred by 3 orders of magnitude: 0.0036 μS (175 ^o C), which indicates a deep cure of the material and its high dielectric properties.

 The conditions for curing the binder ENBF in this mode are shown in table 2, experiment 5.

Similarly to this example of conducting the optimal curing regime of a binder, ENBF, a series of experiments was carried out to conduct a curing regime of a binder ENBF to treat conditions that did not cause visual damage to the material at the shortest heat treatment time, i.e. the optimal speed V _{1 of} raising the temperature to the temperature of the isothermal step T ₁ , the temperature of the isotherm T ₁ , ^o C, the exposure time τ ₁ on it, the heating rate V ₂ to the temperature of maximum curing of the temperature of the isotherm T ₂ .

From table 2 it is seen that a homogeneous material is obtained under the minimum boundary conditions of heat treatment (experiment 4): speeds V ₁ = 0.8 ^o C / min, T ₁ = 128 ^o C, τ ₁ = 38 min, V ₂ = 1.8 ^o C / min and at the maximum boundary conditions of heat treatment (table. 2, experiment 6): speeds V ₁ = 1.2 ^o C / min, T ₁ = 132 ^o C, τ ₁ = 32 min, V ₂ = 2.2 ^o C / min

As can be seen from the data in table 2 (experiments 2, 3, 7-10), the change in V ₁ ± 0.05 ^o C / min; the temperature of the first isotherm T ₁ ± 3 ^o C; V ₂ at ± 3 ^o C / min and the time of the isotherm τ ₁ at ± 3 min causes the formation of air inclusions and pores in the binder ENBF. Heating at a speed of 0.5 ^o C / min to T ₁ with holding on it for 30 minutes and a further rise in temperature at a speed of 2.0 ^o C / min to the temperature of maximum cure gives a homogeneous material, but the curing time is delayed.

Based on the foregoing, the following boundaries of the limiting values of the curing conditions were established: V ₁ = 0.8-1.2 ^o C / min, τ ₁ = 28-32 min, V ₂ = 1.8-2.2 ^o C / min, T ₁ = 128-132 ^o C. For the convenience of reference during the further experiment, the optimal parameters were selected (Table 2, experiment 5): V ₁ = 1.0 ^o C / min, T ₁ = 130 ^o C, τ ₁ = 30 min, V ₂ = 2.0 ^o C / min.

Example 2. On the basis of the binder ENFB (TI 59 1004-82) and carbon tape LUP-02 (TU 6-06-31-218-78), a prepreg blank is prepared. A strip of 50 cm long and 4 cm wide is cut out of the carbon tape. The strip is passed through an impregnation bath with an ENPB binder, connected to a fluoroplastic tape of the same size and passed through a control squeeze roller (tape tension 19 nm), after which at a speed of 2.0 m / min preform was drawn through three drying oven thermostated at lentotraktu zone whose temperature was 60-75-50 ^o C. Uglelenta impregnated binder ENFB density of 1.03 g / cm ^3, an initial concentration of 55% and dried in a three-zone furnace was analyzed for containing s binding: the volatile content in the soluble portion, which were, respectively, wt%: 36;. 2.0; 95, then a triple layer wound on a glass rod. A copper electrode was placed on it, placed between two layers of T-10-80 fiberglass (GOST 19170-73), also impregnated with ENPB and dried in the same zones of 60-75-50 ^o C of a three-zone furnace. Then, again, three layers of the LUP-02 carbon-based prepreg were wound in a triple layer over the copper electrode and T-10-80 fiberglass. From the copper electrode and from the prepreg itself, based on LUP-02 and ENFB, which is an electrical measuring cell, wires were stretched in a shielded and fluoroplastic sheath for their connection to an E-7-8 type meter. The T-10-80 fiberglass fabric served as an insulator of a copper electrode from LUP-02 filler-carbon tape, which itself has high electrical conductivity, which can distort the measurement of electrical parameters during curing of the binder or make them impossible if it is not isolated. Reliable insulation can only be achieved using at least 2 layers of T-10-80 fiberglass. With finer insulation, a short circuit between the metal electrode and carbon tape is possible. The manufactured cell is placed in the middle of the furnace, the heating is set from room temperature at a speed of 1.0 ^o C / min to 130 ^o C, kept at 130 ^o C for 30 minutes, then heated at a speed of 2.0 ^o C / min to 175 ^o C and they are kept at this temperature until, first, constant conductivity is reached, and then the dielectric loss tangent. The data of electrophysical measurements are presented in table 3.

 As can be seen from the data in Table 3, the prepreg based on LUP-02 and ENFB also cures three orders of magnitude lower in electrical conductivity from its maximum, i.e. the same as the binder itself: carbon fiber has high dielectric properties. However, the effect of the filler is on the cure time, which is 210 minutes, i.e. 18 min longer than the cure time of the pure ENPB binder. Thus, the introduction of non-destructive electrophysical control allows you to accurately determine the curing time and holding it at the curing temperature, not allowing you to overexposure or under-hold the material at the maximum curing temperature, and therefore to obtain high quality products. Plastic samples were examined to the depth of cure by extraction in an alcohol-acetone mixture (1: 2). Data from three parallels showed a steady degree of cure by weight of the prepreg, which was 99%. The plastic after curing is monolithic, without delamination.

Example 3. To assess the curing mode of the composite material on a binder ENFB with another filler - fiberglass T-10-80, i.e. the acceptability of the regime in the case of different fillers, prepreg sample is prepared on the basis of T-10-80 and ENPB. Fiberglass T-10-80 for 1 h is heated in a thermal furnace at 100 ^o C to remove traces of moisture. Then the glass fabric is impregnated for 10 minutes in the same ENPF binder, dried in air for 10 minutes, cut into 10x10 mm layers each, 4 layers are taken for 3 samples. One is placed between the electrodes of the pressure cell with a diameter of the working electrode of 4 mm, the other two are suspended in a free state next to the cell in the middle of the furnace. The wires from the cell are connected to a type E-7-8 meter and, under the control of the electrophysical method, the samples are heated according to the specified mode: from room temperature at a rate of 1.0 ^o C / min to 130 ^o C with a shutter speed of 130 ^o C for 30 min and further, heating the samples at a speed of 2.0 ^o C / min to 175 ^o C with holding at this temperature until first the constant conductivity values are reached, and then the dielectric loss tangent. The measurement data of the electrophysical parameters are presented in table 4.

 As can be seen from the data in table 4, the complete curing of the plastic based on T-10-80 and ENFB occurs after 196 minutes of heating according to the specified mode. The sample also undergoes curing three orders of magnitude lower from the maximum value of electrical conductivity. The degree of curing, measured by the extraction method in alcohol-acetone in the Soxhlet apparatus of three samples cured in this mode, as in the experiment in Example 3, showed a steady value of 99%. Fiberglass after curing is also monolithic, without delamination.

 Thus, the method for producing the cured composite material according to the invention, including a two-stage curing mode, allows, regardless of loading conditions, type of filler, to obtain visually uniform polymer materials: glass or carbon fiber with a stable degree of cure of the order of 99%, and also reduce almost twice the curing time upon receipt of the composite material, which in turn will significantly reduce labor and energy costs. At the same time, the technology for producing CMs based on ENFB is also simplified.

Claims (1)

The method of curing a composite material based on an epoxyphenol binder grade ENFB, comprising the stepwise heating of the components of the material from room temperature to the maximum curing temperature and holding on it until a cured material is obtained, characterized in that at first the components are heated to T ₁ = 128 - 132 ^o C with a speed V ₁ = 0.8 - 1.2 ^o C / min, incubated at T ₁ for τ ₁ = 28 - 32 min, and then heated to a maximum curing temperature (175 ± 1) ^o C with a speed of V ₂ = 1, 8 - 2,2 ^o C / min, wherein during the heating Provo ny continuous measurement of conductivity values and loss tangent, and the curing process is complete upon reaching constant time values of said quantities.

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