SU953023A1 - Method of controlling forming of articles from cellulose triacetate - Google Patents

Description

(54) METHOD OF MANAGING THE FORMATION OF PRODUCTS FROM PULSID TRIACETATE

one

The invention relates to the production of molded articles and can be used, for example, in the molding of acetate films and fibers.

A known method of stabilizing the cooling mode of the melt-spun filaments, 5 consists in measuring the speed of the blowing and suction air streams and controlling the cooling mode by adjusting the difference between the speeds of the blowing and suction air streams JQ 1.

The disadvantage of this method is the unevenness of the properties of the filaments and films caused by fluctuations in the parameters of the molding process, such as, for example, the temperature of the blowing air, viscosity 15 and the temperature of the melt.

The closest in technical essence to the invention is a method for controlling the molding of products from cellulose triacetate, which consists in controlling the temperature of the vapor-gas mixture supplied to the ribbon mashing box by changing the flow rate of the coolant 2.

The disadvantage of this method is the heterogeneity of the properties of the films associated with the change in time of the conditions of the molding process. In particular, when using the method to control the mold of the triacetate base film films. made on belt casting machines, such conditions are changes in the composition of the vapor-gas mixture, the surface temperature of the cooled drums and, consequently, the carrier metal tape.

The aim of the invention is to improve the uniformity of the properties of the products.

This goal is achieved in that in the known method of controlling the molding of articles from cellulose triacetate. to control the temperature of the gas-vapor mixture, suppressing the box of the belt machine, changing the flow rate of the coolant, determine the temperature difference of the vapor-gas mixture at the inlet and outlet of the box of the belt machine and adjust the temperature of the vapor-gas mixture supplied to the box depending on the values of the difference obtained tape machine. ,

FIG. 1 shows a diagram of a tape casting machine for producing a base film and a control system, an implementation method; in fig. 2 is a graph for determining the value Atgj of the correction of the values of temperature tgjj of the gas-vapor mixture at the inlet to the duct depending on the change in temperature difference between the inlet and outlet of the mixture from the duct of the machine (for a typical process).

The machine contains drums 1, an endless metal tape 2, a spinneret 3, a sealed box 4, a base 5, a hydraulic lock 6, a drying part 7 of the machine, a winding unit 8, a condenser 9, a centrifugal fan 10, a preheater 11, a circuit 12 for circulating gas-vapor mixture, a meter of 13 temperature of the gas-vapor mixture supplied to the box of the machine, a controller 14 of the temperature of the gas-vapor mixture, an executive mechanism and a regulator on the steam supply line to the heater 15 of the vapor-gas mixture, a meter 16 of the temperature of the vapor-gas mixture leaving the machine box s, subtracting unit 17, scaling unit 18,

The tape casting machine (Fig. 1) consists of a casting part, a drying part and a coiling unit. The casting part of the machine consists of two drums 1, on which an infinite metal band 2 is tensioned. To apply a layer of film-forming solution to the surface of the tape 2, there is a slit of the die 3, into which the film-forming solution comes from the back-thermostat. The casting part of the machine is enclosed in an airtight duct 4, forming two other channels - for the upper and lower parts of the belt 2. Drying of the film-forming solution occurs due to the circulation of the drying agent - a vapor – gas mixture in the channels. With the continuous movement of the tape 2. Formed film (base) 5 removed from the tape 2 with some residual solvent content and through the hydraulic lock 6 enters the drying part 7 of the machine, where it is finally dried and with the help of the winding unit 8 rolls into a roll.

In the process of film formation and drying of the film in the channels of the casting part of the belt machine, a large amount of solvents evaporate from the solution. With a closed air exchange cycle, the vapor-gas mixture is recirculated in the circulation circuit 12. Coming out of the drying channels of the duct 4, the vapor-gas mixture enters the condenser 9, where it is subjected to cooling, as a result of which a part of the solvents condenses and is discharged through a siphon for regeneration. The cooled gas-vapor mixture using a centrifugal fan 10 is fed into the heater 11 and again enters the box 4 of the casting part of the machine. The fan 10 provides a constant flow rate of the vapor-gas mixture in a closed sealed loop-12 circulation. Heating of the vapor-gas mixture to a predetermined value is provided by the control system, which includes the measuring device 13, the controller 14 and the actuator 15.

The control method is implemented as follows.

At the first moment of time, the automatic control system, which includes the measuring device 13 of the gas-vapor mixture outlet temperature of the preheater II, the controller 14 and the operating mechanism 15 with the regulator on the steam supply line to the heater 11, stabilizes the predetermined temperature value of the vapor-gas mixture at the heater 11 output The stabilized value of the mixture temperature IB is selected based on the required evaporation rate of the solvents from the moldable base.

. Then, using the measuring device 16, the temperature of the vapor-gas mixture leaving the box of the belt machine is measured, and using the subtraction unit 17, the temperature difference () of the vapor-gas mixture at the inlet to the box and exit of the belt mash is calculated.

After that, according to the schedule (Fig. 2), the required value At-j, x of the change (correction) of the mixture temperature supplied to the machine box is determined depending on the deviation A () of the calculated temperature difference from its value set at the initial time (starting the system) and using the scaling unit 18 change the task to the controller 14 of the temperature of the gas-vapor mixture.

The essence and efficiency of the use of the method can be explained from physical considerations as follows.

When molding a base from a polymer solution, the rate and the physical and mechanical properties of the base (tensile strength, shrinkage, brittleness, etc.) are significantly affected by the rate of evaporation of solvents from the layer applied to the metal tape of the machine.

At the same time, the main parameters affecting the evaporation rate of solvents are the temperature and consumption of the vapor-gas mixture fed to the machine box. Increasing the temperature of the mixture increases the rate of solvent evaporation and vice versa. In addition, a number of other indicators of the process have a significant effect on the evaporation rate of solvents, such as, for example, vapor pressure

solvents in the mixture, which change as a result of the gradual freezing of condenser 9, the temperature of the polymer solution supplied to the spinneret of the machine, the surface temperature of water-cooled drums 1, and the surface temperature of the metal strip 4. Variations and changes over time of these indicators lead to the release of a base having a variation on structure and physicomechanical properties.

The speed of the substrate, i.e., the amount of solvents evaporated per unit of time, is proportional to the amount of heat produced by the layer of film-forming solution from the vapor-gas mixture supplied to the mash box. The amount of heat Q | introduced by the vapor-gas mixture in the box of the machine is Qj G-C-tex, where G and C are the consumption and heat capacity of the mixture, respectively.

The amount of heat Q carried away by the gas-vapor mixture from the box of the machine is Q2 GC tgbix In steady state at a constant flow of the mixture in circuit 12 and the mixture temperature stabilizes at the inlet to the duct the temperature difference (t (the inlet and outlet are proportional to the amount of heat (Qt- Q2) spent per unit of time for evaporation of solvents, i.e. evaporation rates. The sign and magnitude of the deviations of the temperature difference () characterize the sign and the amount of changes in the rate of evaporation of solvents. At the same time, the difference difference (t x-tebu indicates a decrease, and an increase indicates an increase in the rate of evaporation of solvents due to changes in the molding conditions of the base.

For a typical temperature mode of the band mask at t ,, 70 ° C, the temperature difference (t- - o) is about 22 ° C. The introduction of the correction of the stabilized value of the temperature of the vapor-gas mixture depending on the changes in the calculated value of the temperature difference () makes it possible to maintain a constant evaporation rate of solvents over time.

Thus, the disturbing effects on the process of forming the base, caused by changes in the partial pressure of solvent vapors in the mixture, the temperature of the film-forming solution, the temperature of the surfaces of the drums and the metal tape, will be compensated by a change in temperature 1) of the vapor-gas mixture supplied to the box. This will ensure the stabilization of the structure and physicomechanical indicators of the base produced.

The proposed method can be implemented using mass-produced technical means.

The introduction of the proposed method will significantly reduce the instability of the quality characteristics of the manufactured base, such as shrinkage, curl, tensile and impact strength, elongation, and increase production by reducing rejects.

According to the initial data, the stabilization of the conditions of the process of forming the triacetate base on casting tape machines will increase the yield of the base by 0.5%.

Claims (2)

1. USSR author's certificate number 525758, cl. D 01 D 5/04, 1975. 2. Author's Certificate of the USSR No. 577260, cl. D 01 D 5/04, 1975 (prototype). J x7