Control over polymer surface modification

FIELD: process engineering.

SUBSTANCE: invention relates to modification of polymer material surface. Control over polymer surface modification in low-temperature HV discharge plasma at lower pressures of the medium is performed by varying the discharge power. Here, discharge power is continuously measured, its current magnitude being used for calculation in real time of temperature field in discharge area. Modification termination time is defined automatically when polymer surface reaches the preset temperature (70°C for polyethylene).

EFFECT: reproducibility of the surface adhesive properties, i.e. interfacial angle and work of adhesion, as well as stable surface hydrophysics.

1 dwg, 3 tbl

 

The invention relates to a process of modification (change properties) of the surface of polymeric materials (films), in particular polyethylene, more precisely, to the optimization of process modification.

Closest to the present invention is a method of inoculation (process control method of surface modification of polymer materials), carried out in low-temperature plasma frequency (RF) discharge at low pressure environment by changing the discharge power. [Encyclopedia of low temperature plasma. Introductory volume IV/ Ed. by Fortov C. E. - M.: Nauka, 2000. - S. 401, PL. XI.5.23, 4ththe line above]. The input parameters of the process in the method prototype is: current frequency (f=1 kHz - 40 MHz), specific discharge power (W=0.1 to 1 W/cm2), the residual air pressure (F=1,33-500 PA). The time duration of the process is not specified. Accordingly, according to this method, the process of plasma modification is carried out for different time under different for each material and each of its thickness asked specific discharge capacity. In other words, the control process carried out by disconnection discharge (reset power to zero) based on pre-experimental matching operational parameters - specific discharge power and BP is the seed processing.

This method of control does not allow to achieve reproducibility of the (wetting angle, the work of adhesion), because the input process parameters of plasma modification (electric field strength, current or discharge power) does not remain fixed, but depend in a complex way from the surface of the processed material (so-called "boot"). By the "effect download" the inverse relationship between the chemical composition of the plasma and its physical properties is manifested in a time-dependent parameters of the discharge power or the discharge current [Kutepov, A. M., Maximov, A. I., Nikiforov A. Y., Titov, C. A. the Effect of foods plasma-chemical reactions on the properties of the plasma and its dynamic behavior // Tiora. fundamentals of chem. technology, 2003. - So 37. No. 4. - S. 365-373].

This explains the difference between the results of the modification observed on the experience with the same input parameters process - pressure plasma gas, the density of the discharge current, the power density of the discharge. Even more significant disadvantage of the known control method is the instability of the surface properties elasmobranch films subsequent storage in air. Indeed, when the time dependence of operating parameters of the process, as a result, a different value is of acquire not only its surface properties, but the final temperature of the surface. Meanwhile, this parameter has a determining impact on the weakening effect of aging modified (elasmobranch) films (RF Patent 2443558, IPC VS 59/14, 2010). It should be noted that direct measurement of the surface temperature of the film material in the process of modifying the plasma RF discharge is technically impossible.

The task of the invention is the provision of reproducibility and stability acquired by the modification of surface properties of polymeric materials, including subsequent storage in air.

The solution of this problem is achieved by the fact that in the process control method of surface modification of polymeric materials in low-temperature plasma of high-frequency discharge at low pressure environment by changing the discharge power produce continuous measurement of discharge power, the current value which is used to calculate in real time the temperature field in the discharge zone, and the end of the process of modifying the determined automatically on reaching the surface of the polymer material of the set temperature.

Application of the proposed method ensures the reproducibility acquired as a result of the modification of the properties is poverhnosti polymers - wetting angle and work of adhesion. In addition, due to the possibility of a precise selection of the optimum final temperature of the surface is ensured by the stability of the surface properties of the films subsequent storage in air, as it significantly reduces the aging effect. Thus the conditions for the successful implementation of the process of film metallization and other processes involving the time intervals between operations, for example, the process of obtaining composite materials with polymeric fillers.

A block diagram of a device that implements the proposed method, shown in Fig.1.

The control object 1 is a plasmachemical reactor installed inside the bit capacitor connected to an RF generator. Between the electrodes of the discharge capacitor placed the film processed polymer material. Controlled object parameters are the voltage at the electrodes and the discharge current I. the phase Shift between current and voltage cosφ continuously measures the phase detector 2. Simultaneously, in block 3, the calculated total power S chain. In the result of the addition of the two signals in the block 4 is the calculation of the current active discharge power P(τ). The signal R(τ) is fed to the input of block 5 carrying out the calculation of the rate is Turnovo field in the material in real-time. At the moment of reaching the surface of the film of the predetermined final temperature Trot=TKonthe comparator 6 in the feedback circuit produces a disable bit in block 1.

The proposed solution is new, involves an inventive step and is industrially applicable.

Examples of the method.

Example 1. Conducted surface modification of samples of polyethylene films with thickness of 200 μm in the low-temperature plasma of RF discharge at a standard frequency f=27,12 MHz above described method comprising measuring the current of the discharge power. Regime (input) the process parameters are given in table.1. Here F is the residual air pressure in the discharge reactor; RI- set (input) the power density of the discharge; τ - time processing; GKon- set the value of the final temperature of the sample surface.

The change in the surface properties of the samples characterized by the boundary values of the angles θ wetting with distilled water (bidistillate) defined the goniometric method according to standard methods. The work of adhesion of the surface of the sample W was calculated by the formula Dupre-Jung: W=σW(1+cosθ). Here σW- the surface tension of the working fluid. In each cycle of measurement of the contact angle θ on the sample was applied three drops, and the results were averaged. For the doctrine of comparative data the surface modification of the same samples were assayed by the method prototype. The surface temperature of the sample as implemented in the prototype method, measured remotely using the IR thermometer immediately after turning off the discharge. The results of the experiments are presented in table.1.

Analogously to example 1, involving the processing of 3 samples in the same conditions, the proposed method was carried out in examples 2, 3 when the changed mode parameters of the process (samples 3, 4, 5, 6, 7, 8). The results of the experiments are summarized in table.2 and 3.

The proposed method provides reproducible results - parameters θ and W. in Addition, due to the automatic disconnection of the discharge at the moment of reaching the sample surface the predetermined final temperature can significantly weaken the effect of aging elasmobranch films. After 3 days after plasma treatment the values of the wetting angle is almost stabilized. Thus the steady hydrophilicity surface.

When implementing the process according to the method prototype is similar (or lower) indicators of sustainable hydrophilization achieved only one of the three samples (table.1, 2), have given a sufficiently large process has provided heating the surface of the film to the optimal (or close to it), the temperature (for polyethylene: TKon=70°C). Each of the other two exemplary is, modified in various modes according to the method prototype, sustainable hydrophilicity is achieved no earlier than 10 days. Thus, the resulting process indicators (wetting angle θ, the adhesion work surface W) worsen (table.1, 2).

In example 3, implements the method-prototype at the maximum value of power density discharge (table.3), to find in advance to set the time duration of the process is not possible. In the end, all three samples 6, 7, 8 sustainable hydrophilicity is achieved only within 10 days after plasmablade with reduced significantly the resulting indicators.

The process control method of surface modification of polymeric materials in low-temperature plasma of high-frequency discharge at low pressure environment by changing the discharge power, characterized in that produce continuous measurement of discharge power, the current value which is used to calculate in real time the temperature field in the discharge zone, and the end of the process of modifying the determined automatically on reaching the surface of the polymer material to a predetermined temperature.



 

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