JPH0545614B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for modifying the physical properties of materials, in particular shaping by vibration (mechanical or electrical) to enable control or modification of the physical properties, in particular mechanical and optical properties, of the shaped material. Regarding the method. Modern improvements in molding engineering include the control of certain production variables during or subsequent to molding in order to improve the end use performance of the final product. In various operations such as rotomolding, blow molding or thermoforming, the forming operation is performed on already preformed material. This technique combines methods of morphologically processing the structure of materials with the means to exhibit improved properties. Perhaps one of the most important factors influencing a material's end-use performance is the material's thermodynamic transition temperature, ie, the rate at which it is cooled past its melting point or its glass transition temperature. In crystalline and semi-crystalline materials, the number, size, type and distribution of crystallites formed under specific cooling conditions are
The degree of crystallinity, the density of defects, if any, significantly governs the overall morphology as well as the critical amorphous regions that determine the performance of the final product. For example, it is well known that crystallites act as fillers or physical crosslinks in polymers and therefore they play an important role in determining the shear modulus of the solidified product. Similarly, crystallinity is also well known to determine the optical properties of end-use products, controlling their transparency to light. Complete transparency is
For materials that can crystallize under cooling conditions, this is generally accomplished under certain conditions that avoid crystallization. It is therefore seen that the physical and physicochemical properties of a material depend on the rate of cooling of the material or variations in the rate of cooling while the material passes between the molten or viscous state and the solid state. . Amorphous, non-crystallizable materials are materials that condense into glass, which is structurally similar to liquids but kinetically indistinguishable from liquids. FIG. 1 shows the volume change as the glass-forming rubber is cooled through its glass transition temperature Tg. All glass-forming materials undergo a radical property change when passing through this region, the exact value of which depends on the cooling rate and other experimental factors such as pressure and time. The glassy state is a disequilibrium state and represents a frozen disordered condition with highly molecular mobility limitations. In FIG. 1, it can be seen that an amorphous material rapidly cooled through its Tg condenses at a higher temperature and that the specific volume of the rapidly cooled glass is greater than that of the slowly cooled material. The physical properties of amorphous thermoset resins in the glass state depend on the cooling rate through the Tg (alternatively for subsequent annealing below the Tg), as is well known for the impact resistance of polycarbonate. can vary considerably. Impact strength is the ability of impact energy to be dissipated by some mechanical loss process without causing material failure. It is not fully understood why untransformed amorphous polymers exhibit such a wide range of impact behavior, from tough polycarbonate to brittle polystyrene. Of all non-transforming amorphous polymers, polycarbonate has one of the highest values for impact strength. Moreover, it has been reported that polycarbonate completely loses its impact energy when it is strongly annealed below its glass transition temperature. This same complete loss of impact properties of polycarbonate will also be observed by gradual cooling past its Tg to allow stress relaxation under non-isothermal cooling conditions. The dependence of residual stresses in thermosets due to mold assembly processes and post-processing is a problem well known to design and application engineers. Residual stresses increase with rapid cooling and can be removed by annealing below Tg. Once a residual stress is created, the rate at which this stress relaxes is controlled by the material's ability to recover to its equilibrium state. Residual stress is closely related to the total stress level, which affects the optical and mechanical behavior of the product, and therefore knowledge of residual stress, and the means to control its level, is essential to reduce the maximum stress that can be applied to thermoset products. This is important when selecting the allowable external stress. Another important influence on cooling rate is shown in the formation of stable mixtures of materials. A polyblend is a mixture of two or more materials. For example, for macromolecular materials, polyblends are mixtures of chemically different powders, resins, or elastomers. From both thermodynamic considerations and experimental observations, when polymers of different compositions are mixed, they do not mix with each other down to the molecular level and therefore do not give a homogeneous single phase structure. The ultimate state of molecular mixing that can be achieved by molecular mixtures can only be reached to a certain extent by polymeric polyblends. Conceptually, stability is a measure of how close the polyblend approaches the ultimate state of molecular mixing. From this, stability can be best expressed by the degree of homogeneity of the polyblend, which can be measured and compared by the domain size of the dispersed phase. The finer the dimensions of the dispersed phase within the continuous phase, the better the stability of the polyblend. The stability of a molten blend of two or more polymers is a function of temperature. The higher the temperature,
Stability is good. The completeness of stability and its dependence on temperature and time is a rate or diffusion sensitive process that is a function of the cooling rate applied to the molten blend within the mold cavity while it is being cooled to room temperature. A supercooled blend, or a blend quenched at an infinite rate, would theoretically have the stability properties it had at the temperature at which the quenching began. Thus, this is another important consideration in the effect of cooling rate on the final properties of the final product. The thermal history during the forming operation plays an important role in determining the properties of the final product. Therefore, the ability to monitor the rate of temperature fluctuation while a material is being processed in order to change its properties is an important engineering objective. To date, research carried out in laboratories has been limited to working at constant hydrostatic pressure and determining the cooling rate of materials.
It consists of modifying the material either by thermally insulating it or by accelerating heat exchange to the outside. Known methods consisting of heat exchange between the material of the cooling process and the outside are limited by heat transfer (conduction, convection or radiation) constraints. Once the product reaches ambient temperature, it is not always possible to change the rate of heat exchange or temperature fluctuation significantly within sufficient limits to affect its physical properties. The classic method for obtaining unbalanced phases in metallurgy was the rapid removal of heat by convection.
Generally, the molten metal was dropped into a cooling fluid such as liquid nitrogen. Cooling rates on the order of 10,000 or 20,000 degrees per second were reached for samples several microns thick. Due to the low thermal conductivity of some non-metallic materials, such as polymeric materials, special attention had to be paid to simple dimensions and geometric considerations in cooling experiments. On the other hand, while the extremely high cooling rates used in metallurgy are not necessary to prepare fully polymeric samples of amorphous, this technique can only be used for extremely thin samples and is therefore Its application is in fact very limited. Today, many materials are transformed from their initial green state to finished or semi-finished products by forming operations. These materials are, for example, metals, glasses, ceramics, polymers, resins and rubbers; organic or inorganic; synthetic and natural materials. These materials may also be blends of several materials. Each of these materials is endowed with a set of mechanical and physical characteristics, which depend on its chemical nature, but also on its thermodynamic state after forming, especially the thermodynamic imbalance at the temperature of use. , which in turn depends to a large extent on its thermal history during molding. Various researchers have sought to modify and improve certain physical and mechanical properties of materials by controlling the parameters of the forming process. for example,
The effect of constant forming water pressure on amorphous and semicrystalline polymeric materials has been a strong research topic. It is known that constant hydrostatic pressure applied during cooling changes the state of the material, for example during the vitrification process. This effect is due to the glass transition temperature (Tg)
is a function of the constant hydrostatic pressure applied to the liquid material during cooling, as shown in FIG. The value of Tg represents the thermodynamic instability of the vitreous material or glass. It is theoretically possible to condense this material to a glassy state at any temperature, provided that sufficient constant hydrostatic pressure is applied to raise the glass transition temperature (Tg) at least to the temperature in question. This means that it is possible. These phenomena have been described experimentally in the literature. G. Allen et.
al., J, Polymer Sci., C, 23, 127 (1968),
W, C, Dale et al., J. Appl. Polymer. Sci.,
16, 21 (1972), and E. Jones Parry & D.
See Tabor, J. Materials Sci. 8, 1950 (1973). However, nowhere in these documents does the hydrostatic pressure during cooling of the material be controlled by variations in the material's own temperature in order to control the properties of the final product or to "tailor it" be made. There is no suggestion that it will. Bograski et al. patent (USP 3912480)
The glass is annealed to a temperature (below Tg), maintained at this temperature in a molten salt bath, and at the same time this molten salt (viscosity does not exceed 100 cp) is heated to the glass by a constant machine at 20-18000 Hz. describes a method for annealing glass by applying physical vibrations. This method is not intended to cause a change of state and, contrary to the present invention, is carried out at a constant frequency and temperature. Note that it does not mention any other materials; it is applied only to porcelain glass. USP 4150079 to Chang includes a method for controlling (suppressing or enhancing) crystallization of a crystallizing thermoplastic polymeric material by varying hydrostatic pressure during cooling. There is no suggestion in Chang of applying vibratory means (mechanical or electrical) superimposed on hydrostatic pressure effects to determine a specific cooling pattern. The present invention is a method for modifying the physical and physicochemical properties of a material, the rate of rate-sensitive change of the material from a state of physical equilibrium to a state of disequilibrium as a function of time of at least two rheological parameters. This is a method that involves controlling by simultaneously varying the values. The rate of change of the rheological parameters over time is controlled according to a predetermined relationship in order to achieve a final product with defined physical and/or physicochemical properties. At least one of the rheological parameters is mechanical vibration, shear stress, hydrostatic pressure, dielectric vibration for dielectric materials, or electromagnetic vibration for metallic materials. For crystalline materials, rheological variables include mechanical vibrations, shear stress, dielectric vibrations for dielectric materials, and electromagnetic vibrations for metallic materials. For amorphous materials, hydrostatic pressure is an additional rheological variable. The vibration (mechanical, dielectric or electromagnetic) variation may be due to frequency or amplitude (intensity). When changing temperature or other rheological variables, the material changes at a rate that includes changes in physical state, such as between solid, viscous, or molten (liquid) states, and the solid state, e.g., crystalline or amorphous upon cooling of the material. Pass through the sensitive transition point. This phase transition is velocity sensitive, meaning that passing through this point at a certain speed results in a certain unbalanced state. The present invention involves forming, heating with cooling, annealing,
or any combination of these tasks. One or more rheological parameters can be changed simultaneously with temperature. For example, vibration treatment can be overlapped with hydrostatic pressure action. The improved properties imparted to materials by using the present invention include stress and strain in tension or bending, modulus of elasticity, mechanical strength, flexibility, resistance to chemical attack, surface hardness, heat capacity, homogeneity. properties, impact strength, and thermal conductivity. moreover,
Use of the present invention results in improved crystallinity, modified crystal structure and reduced annealing time to stabilize the material. The pressure and vibration treatment of the present invention can be applied uniformly over the entire outer contour of the material being molded. In addition, the vibration treatment plus hydrostatic pressure can be applied at appropriate locations around the periphery of the material to be molded, through the bulges and cavities in the walls of the mold. The material to be treated may initially be in the form of particles, powders, mixtures, films, plates (layered or otherwise) or even "sandermanch"-shaped structures. This material can be polymers (synthetic or natural), ceramics, metals,
Glass, rubber, or other materials may be used. The invention can be implemented in a device characterized in that the material includes means capable of simultaneously being subjected to programmed cooling and vibration up to 3000 cycles.
This cooling may be accomplished by convection through cold glass or by wetting with water or other fluid. The regulating device for programming variations in the vibration characteristics of the device may apply a constant frequency, a frequency that varies logarithmically with respect to time, or a frequency that varies in a programmed manner in tune with variations in the temperature of the mold. . This regulating device controls the level of the vibratory force (sinusoidal amplitude) acting on the material according to a predetermined program that harmonizes the vibrational force fluctuations with the temperature of the mold. The apparatus may include means for subjecting the material to gas pressure or, conversely, high vacuum during the processing step. Furthermore, the apparatus may include means for applying a predetermined thermal gradient to the material during the processing step, the gradient being applied in the direction of the thickness of the material. Thus, the device may include means for subjecting the material to vibrations whose characteristics (frequency and amplitude) are programmed to achieve a specific improvement of the final product during the cooling process. The static (non-oscillatory) force applied to the material may be varied in a programmed manner. A vibratory treatment (with frequency and amplitude varied as programmed) may apply vibratory forces on either side of the average static stress. This oscillation is applied at least from the moment the temperature reaches its maximum value and at the latest until the moment when the material returns to the selected temperature, for example ambient temperature. The period and amplitude of the vibrations are programmed as a function of the cooling curve of the material, the rheological properties of the material, and the changes desired to be made to the treated material. Although vibrations can be imparted to the material in various ways, in particular by mechanical means, this general method, which is applicable in many cases, has the drawback of generating mechanical vibrations outside the machine. Vibrations in the frame of the device are troublesome. This is because it causes fatigue of the framework members and thus causes serious maintenance problems for the device. The invention also includes the modification of dielectric vibration for materials with dielectric properties. In such cases, this material is considered to be the dielectric of a capacitor (acting as a container), where the dielectric and the material are subjected to a sinusoidal electric field, the frequency and voltage strength of which are determined as a function of time by a specific program. be done.
In the case of dielectric materials, it is also possible to provide programmed variations in voltage and aperiodic electric field strength over time. This variation corresponds to temperature changes in the mold. Rather than proposing to release heat into the material to some extent, the idea is to vary the electrical excitation and the amplitude of the signal;
That is, by varying the magnitude of the current or voltage across the capacitor while cooling the material. In this way, an internal viscoelastic state is created, which introduces a special cooling pattern. In the case of materials with dielectric properties, the benefit of electrically applying vibrations is that the same modification of the physicochemical properties of the material as in the case of mechanical vibrations is guaranteed (because viscous - Corresponding to the elastic transition, og (Hz) is the reciprocal of the absolute temperature (1/T)
This is because the curve expressed as a function of is a single curve no matter what the nature of the frequency. The benefits of this feature of the method of the invention consist in better energy yield in operation, less fatigue of the equipment, reduced equipment costs, more precise control of the method as a function of the predetermined program (frequency and amplitude of vibration). . According to another feature of the invention, mechanically generated vibrations and electrically generated vibrations are applied simultaneously to adjust several viscoelastic transitions during cooling. This makes it possible to take into account secondary transitions that always appear. Finally, according to another feature of the invention, electrical vibration means are used to heat the dielectric material in situ at a constant frequency (resonant frequency) before applying the novel method of the invention. be done. The invention will now be explained in more detail with reference to the drawings. The graph in FIG. 1 shows the variation of specific volume versus temperature T for two different cooling rates under constant hydrostatic pressure. The obtained curve has two parts C ₁
and C ₂ , which join at the transition point M ₁₄ . If the cooling rate is accelerated, the change does not depend on curve C ₂ but on curve C ₃ starting from point M ₁₅ .
I'll leave it to you. Thus, this transition itself depends on variations in the cooling rate. The curves in Figure 2 show that the specific volume (the reciprocal of the density) of the material changes as a function of the temperature when the material is subjected to three different hydrostatic pressures P ₁ , P ₂ , P ₃ (P ₃ > _P 2 > P ₁ ). Expressed as a function. The three curves in FIG. 2 clearly show that the variation in specific volume is greater at high temperatures than at low temperatures. The two parts of each curve at constant pressure join at points M ₁₂ and M ₁₃ , respectively, defining transitions corresponding to transition temperatures Tg (P ₁ ), Tg (P ₂ ), Tg (P ₃ ). It is therefore possible to study the variation of the transition point as a function of one rheological parameter, in this case Tg, as a function of hydrostatic pressure. The graph in Figure 3 shows two physical phases E ₁ and E ₂
The transition temperature (Tg) between The "g" in "Tg" particularly refers to the case of a glass transition between phases E ₁ and E ₂ . This transition temperature is the solidification temperature in the case of crystalline materials that solidify based on their crystal structure. In the case of amorphous materials, this temperature is
It can also be the glass transition temperature. The transition temperature can also be any other transition of the second-order type in the case of materials that have distinct physicochemical specificities on both sides of the second-order transition. Curve C is plotted point by point, variable X is held constant and non-volume versus temperature is recorded to determine the transition temperature. According to the graph of FIG. 3, curve C separates two rheological states E ₁ and E ₂ . In the region above curve C the material is in state E ₁ and in the region below curve C the seat is in state E ₂ . To create the curve C, the passage between states E ₁ and E ₂ is made by keeping the value of the parameter X constant, i.e. by moving on a line (D ₁ ) parallel to the temperature axis. Ru. This line D ₁ corresponding to the parameter X ₁ is
Intersects curve C at point _M1 . At point M′ located above point M ₁ , the material is in state E ₁ ;
At point M _' ', which is located below point M1, the material is in state _E2 . The passage between states M' and M'' is influenced by lowering the temperature. The point M ₁ corresponding to the transition point itself depends on the cooling rate, i.e. the speed of moving through the distance M′, M″ (see FIG. 1). Therefore, in order to satisfactorily program the variables of the method of the invention, , it is necessary to include a family of curves corresponding to different cooling rates. In the majority of cases described in the literature, the rheological parameter is hydrostatic pressure. In the laboratory, the rheological parameter is vibration (mechanical, electrical or frequency (electromagnetic) and amplitude (or strength) of vibration
A study was conducted using . In these latter cases, the graph of transition temperature versus rheological parameters is of the same nature as in _{FIG .} To separate. In Figure 3,
It has been shown that the transition temperature increases as X increases. If this were not the case for a selected rheological variable, then X would represent the reciprocal of the rheological parameter. FIG. 4 shows how variations in the rheological variables can be programmed as a function of temperature variations to simulate the effects of special cooling patterns during molding of materials according to the invention. According to the invention, in order to change the rate of change of temperature in passing through the transition curve C, i.e. to change the speed of passing from state E ₁ to state E ₂ , it is possible to change the temperature T and its state change. Combining the variations of another rheological parameter X, which affects the transition temperature, in the vicinity and in between, according to functions such as F(T,X), G(T,X) and H(T,X). is provided. According to the prior art, lowering the temperature of the material initially in the state represented by point M' is carried out while keeping the parameter X constant at the value _X1 .
The change of state occurs at M ₁ along the vertical line D ₁ passing through point M'. The rate of temperature change, which strongly influences the properties of the final product, depends only on the heat transfer with the mold. According to the invention, the temperature T and the parameter X are changed simultaneously so that new physical properties arise due to the special thermal history that once reached ambient temperature. Variations in temperature and parameter X can be matched by function F. This is the first point N in Figure 4.
_x between the intersection points R of the transition curves C corresponding to
It is represented by a curve that decreases in the direction of increasing. The variations in temperature and parameter x can also be matched by the function G(T,x) in FIG. Point N
The corresponding curve starting at intersects the transition curve C at a point S above the horizontal line passing through point N, and intersects the curve C at a point L corresponding to x ₂ . the horizontal line
NL keeps the temperature constant and corresponds to the formation of state E ₂ by the action of the rheological parameter x alone. The variations in temperature and parameter x also pass through point N and intersect the transition curve C at point T, which lies below point M, ie corresponds to parameter x ₅ (x ₅ <x ₁ ) in FIG. It can be harmonized by the function H(T,x). In the first case curve [F(T,x)], the temperature of the material decreases before reaching the transition point at point R, and at the same time the parameter x increases, so that the state E ₂
It is an accelerated approach to. This case shows that the rate of approach to state E ₂ can be controlled by the level of variation of the temperature T due to heat transfer and by the rate of change of the rheological variable x, which can likewise be varied independently of this heat transfer. This case provides a simulation of the effect of faster quenching rates. In the case of curve G(T,x) in Fig. 4,
Both temperature and parameter x increase simultaneously.
This shows that the effect of increasing temperature can be compensated by a simultaneous increase in Tg due to variations in x. In the case of curve H(T,x) in Fig. 4,
The temperature decreases simultaneously with the decrease of x, and the rate of variation can be independently programmed. This is particularly useful when quenching effects, such as internal stresses, can be compensated for by simultaneous variations in x. In general, the parameter x may correspond to a physical size or an inverse of a physical size. Typically, the rheological parameter x is the stress (hydrostatic pressure or shear stress, oscillatory, non-oscillatory) to which the material is subjected while passing through its transition curve and/or the frequency of oscillation and/or the amplitude of oscillation. Mathematically, the method of the invention can be analyzed by partial differentiation. Experiment, if Tg is the transition temperature of the material, t is time, x is the first variable that can vary Tg, and y is the second variable that can also vary Tg, then The temperature fluctuation can be written as: dTg/dt=(∂Tg/∂x)y・dx/dt+(∂Tg/∂y)xd
y/dt Approximately, variables x and y near the transition point Tgo
Let xo and yo be the following equation: [∂dTg/∂dt] (x ₀ , y ₀ ) = ∂ [Tg (x ₀ , y ₀ )]/
∂x・Δx/Δt+∂[Tg(x ₀ , y ₀ )]/∂y・Δx/Δt Thus, in the vicinity of the selected point of the curve C (or of the surface in the case of variables x and y) The variation of Tg as a function is controlled by varying x and y as a function of time. The rate of approach to state E ₂ is a direct function of the variation in (dTg/dt) and the variation in (dT/dt) controlled by heat transfer. Now, for example, if x is a pressure variable with respect to time and y is a frequency variable with respect to time, then program their variations to obtain the desired state of (dTg/dt)E ₁ →E ₂ . It is sufficient to do so. If there is one variable, for example x, then (Δy/Δt) = 0 and dTg/dt
The formula giving becomes simple. The invention applies to any rheological parameter that can affect the transition temperature. Thus, the present invention can be applied to any parameter whose variation over time during the molding process can simulate the effect of cooling rate on the final properties. A vibrator assembly including a mold for carrying out the method of the invention is designated A in FIG. 5 and details thereof are shown in FIG.
As shown in the figure. A vibrator field source and vibration control device, for example a sine wave generator B, is connected to a power amplifier C (solid state). Control panel D
The average supply power, average deviation amount, temperature and degree of cooling can be monitored. Electrical energy is supplied from power amplifier C to vibrator assembly A via lead wire 1.
supply to. Leads leading to armature coil 101, field supply 102, and accelerometer 26 are designated 1, 2, and 3, respectively. The vibrator assembly A is connected to the air cooling blower 53 via a pipe 58. Also, connect vibrator assembly A to lead wires 4, 5, 6 and 1.
6 to a control panel D to enable monitoring and control of the measurements of mean force, force variation, phase difference between stress and strain, and displacement of the vibrating table 42 shown in FIG. The vibrator 13 of FIG. 6 is also connected to a cooling source, a belt driven blower 53, a coolant supply 54 to the amplifier and mold, and a fluid cooling drain 55, respectively. A regulated gas supply 57 (at A) that communicates with the mold a vacuum pump 56 containing a pressure gauge also communicates with the mold (at A). From vibrator assembly A, four connection leads are connected to a heating element (not shown, but are resistors or cartridges inserted into mold halves 21 and 32), a thermocouple 27, a load cell 28, and a displacement measuring element 30, respectively. , 5, 6, 16. Electric wire 7, 8,
10 indicates a connection to an external power source 51, respectively. line 9,
19 is used to convey the output to chart recorder 52 and frequency or amplitude-temperature function generator 103. Average force, peak force, average displacement, phase difference between force and displacement, temperature and frequency can be recorded. Two valves a and b control the cooling of the mold. Valve a makes it possible to thermally insulate the load cell and the enclosure of the mold to be heated, and valve b makes it possible to regulate the cooling of the mold. Valve c is a cooling fluid output valve. Valve d also makes it possible to regulate the cooling of the transistors of power amplifier c. In FIG. 6, two mold parts 21, 32 and a bellows 31 are provided between the load cell 28 and the support plate 41, and the support plate 41 is screwed to the vibrating table 42. Threaded rod 22 is threaded vertically through frame 29 into support plate 41 . Rotate the rod 22 to compress the set of springs 11;
A force is then applied to the mold with a speed change controlled by the rotational speed of rod 22. mechanical device 12
The controlled pressure can be adjusted manually or electrically as shown and disposed on a plate 41 holding down the spring 11. The cooling duct 23 is connected to the molds 21 and 32 through an inlet valve 24 (a and b in FIG. 5), and an outlet valve 25,
c in Fig. 5, it is opened toward the exit. Accelerometer 26 is connected to mold 3 to a thermocouple 27 and a heating element (not shown). One of the thermocouples 27 is connected to frequency-temperature generator B. Strain measurement element 30
is firmly attached to the vibrating table inside the vibrator 13, and its output is connected to the control panel D in FIG. 5 via the lead wire 16. The apparatus is designed and configured to apply processed variations in temperature, stress (prior to vibration application) and vibration (frequency or amplitude) to the material. A flexible metal bellows 31 allows a small relative movement between the upper and lower parts of the mold. The material to be treated is inserted between the two parts of this mold. An electrical heating element is also inserted between the two halves of this mold. Rapid or controlled cooling of the mold is made possible by introducing fluid into passages through the mold close to the material to be treated. An electromagnetic force energizer generates an oscillating motion, which determines the range of variation in the total pressure applied to the material. The operating principle of an electromagnetic energizer is the same as that used in high fidelity loudspeakers, but as used herein the components are much larger and more powerful than those in the loudspeaker. A load cell 28 is mounted on top of the mold 21 to provide direct reading from the force applied to the material placed within the mold. The other end of the load cell 28 is fixed to a frame 29 of the vibrator assembly A, and the frame 29 itself is screwed to the fixed armature of the vibrator 13. The output 43 of the load cell 28 is connected to a stress sensor to provide direct reading of the force applied to the material. A selector switch allows setting either the average force (mean value of the sine wave) generated on the specimen or the peak force corresponding to the maximum compressive stress. The frame 29 allows the armature of the vibrator assembly A to be connected to the upper part of the mold via the load cell 28. It resists the force of the armature of the vibrator 13 and exerts a retraction force on the body of the vibrator 13. The elasticity of the frame 29 is clearly greater than the material to be treated, so that the upper part of the mold remains stationary. A set of springs 11 can be mounted above the mold to provide a relatively constant stress on the mold so that the material can maintain a compressive stress despite the total vibratory stress applied by the vibrator. This constant force is larger than a half-wave of the sinusoidal force. The force exerted by the spring is read directly with a pressure gauge (located in D). Several thermocouples 27 are inserted into the mold as close as possible to the material (2 mm) so that the temperature of the two parts of the mold can be measured. The output of one of these thermocouples is amplified and becomes the input signal to the vibration frequency and amplitude generator 103. The output voltages of the other thermocouples are transmitted to automatic meters and y-t recorders that regulate the temperature of the mold.
The device comprises an electronic servo regulator (proportional strip regulator) of the electrons distributed to the heating resistor. The device is able to reach the desired temperature within the shortest possible time and stabilize at this temperature. Depending on the initial temperature, vibration frequency and amplitude in the mold, the material to be molded assumes a particular physical state. In an apparatus embodying the invention, the mold cavity is designed to compress plastic discs of various diameters and thicknesses from about 2 mm up to about 3.75 mm, with a maximum internal diameter of 70 mm. be. Assuming a 70mm diameter disc is used, the average pressure developed by the spring assembly is 4140Lbs (1878Lbs) on an average bellow area of 9.19in ² (5929mm ² ).
450psi (31.42Kg/
^cm2 ). The plastic can be heated to cause it to flow through the mold and bellows. Therefore, the method (vibrational molding) can even be carried out on flowing plastics or liquids. The mass to be inserted is PS with a thickness of 3.75mm, a diameter of 70mm, and a density of approximately 1gr/ ^cm3.
It is better not to exceed the mass of the disc. A flexible mechanical bellows allows the material to be treated to be heated to a temperature at which it can flow into the cavity and into the bellows. As a result, it was possible to perform vibration molding on molten resin and even various liquids. The amount of material charged into the mold must not exceed 8.85gr. The amount of variable pressure that can be generated by the force from the vibrator varies depending on the frequency at which the vibrator is operating. According to calculations, 225psi (15.8
Oscillating pressures of Kg/cm ² ) can be reached at frequencies up to 200Hz. Approximately 625psi (43.9Kg/ ^cm2 )
Peak pressures of should be achievable at frequencies up to about 200 Hz, and larger pressures can be reached with the use of smaller specimens. Maximum displacement amplitude (at lowest frequency) is 1.4mm
, which corresponds to 40% of the relative displacement of the original 3.75 mm thick sample. The vibrator could operate at frequencies from 5 to 3000Hz (up to 5000Hz possible). about
At frequencies above 300Hz, assuming a constant vibration amplitude, the force transmitted to the mold theoretically falls inversely proportional to approximately the square of the driving frequency (Newton's law of motion). The amplitude of the vibrations could be reduced to maintain constant output pressure even at higher frequencies. In fact, it has been found experimentally that the apparent moving mass of this device, ie the quotient of the force transmitted to the material divided by the acceleration, is frequency dependent. The logarithm of the moving mass was in fact linearly related to the logarithm of the frequency. (with negative slope). This result simply shows that the higher the frequency, the more difficult it is to transfer the vibrational energy to the material. The mold temperature could be set to work between 0° and 500°C. The temperature of the mold could be reached from room temperature to its maximum temperature of 500°C within about 15 minutes. The mold can be cooled under various cooling conditions, and the most severe cooling condition is to use water as a coolant and lower the mold temperature from 500°C to 60°C within 2 minutes. Molds have also been heated or cooled using hot water (20-70°C). The mold could also be cooled by forced draft of gas, for example air or nitrogen, which provided a wide range of slowing and controlled cooling rates. The total mass to be vibrated was approximately 60 pounds (27 Kg) including the vibrating table. The equipment used has a limited capacity of 3000 lbs (1363.64Kg), which is
Given by an acceleration of 3000/60=50g. (Gravity acceleration g=9.8m/s ₂ ). This mechanical bellows, acting as a vibrating enclosure, had insurmountable mechanical properties.
Specifically, the flange could not be compressed more than 1.4 mm (0.055 in) when it was not filled with material. On the other hand, when molten or liquid material fills the bellows flange, the material transmits its pressure and vibrations under pressure to the bellow wall, and in this case the compression limit is only 0.89 (0.035 in.)
It was nothing more than a simple thing. A fixed power amplifier was used as the main unit of the apparatus. This could output up to 8KW of arbitrary sine wave output from 5Hz to 3000Hz. The four output modules (transconductors) each had 60 power transistors. These were driven by a buffer and preamplifier to produce a 115V, 70A output from a low level signal source (60RMS max). The load on this amplifier was the vibrator armature. This is 3000 pounds (1361Kg)
It had a rated force of It was air cooled by a motor-driven centrifugal blower. The vibrator also required a DC power source due to the coil creating a strong magnetic field in the air gap. This was provided by field power. It had an output of 190V, 40A. The solid state power amplifier, field power supply and blower motor required 380V, 50Hz, 3-phase power.
The total demand was approximately 28.3KVA. This was supplied from the mains via a fused disconnector and three-pole AC contactor on the wall near the equipment. Power for low level amplifier stage and control circuitry is 110V, 50Hz,
Single phase and supplied from an externally mounted control power transformer. control gear network equipment, heaters,
The total 220V power required for the force and temperature instruments is approx.
It was heated at 3KVA. The amplifier control panel, which is integrally attached to the power amplifier, is equipped with pushbuttons, indicator lamps, safety interlocks, master gain controls, and other items necessary to control power to the device. The low level signal source was installed in the same cabinet as the field power supply. It included all the necessary circuitry for generating low-level AC signals and monitoring acceleration, velocity, amplitude, etc. Cooling water was supplied to the power amplifier transistor thermal tank at a rate of approximately 3 gpm (11.36 pm). Cooling water was also required for the mold on the vibrator. Approximately 38 psi (2.67 Kg/cm ² ) of air was required for the vibrator vibration isolator. The interconnections between the vibrator and the power amplifier and between the blower and the power amplifier are made using the blower cable (4
wire), for field (2 wire), for armature (2 wire),
For limit switches (3 wires) and for accelerometers (coaxial). Additional leads were required for the mold heater, thermocouple, load cell, LVDT and frequency generator. The frequency and amplitude of the vibrations are determined during the molding process.
It could be programmed by preset frequency-amplitude time patterns or by frequency-amplitude temperature conversion electronics. In the latter case, the millivolt source from one thermocouple was continuously amplified and cold-junction compensated before going to a "frequency-to-amplitude-to-temperature converter" (FATC). The current frequency-time pattern or settings for FATC depended on the chemistry of the material, its rheological behavior within the operating temperature range, and the selection of the macroscopic properties desired to be improved. The control cabinet included circuitry to provide power to the machine's mold heater, strip chart recording controller for mold temperature, and force measuring instruments used with the load cell. The system's controls were independent of the amplifier's controls, which were located in another cabinet. Main power was obtained from a three-phase 380V, 50Hz wire via a 100A main disconnect switch 1DISC. The power at this voltage is 1
Next, 3 HP for power supply source (for armature), field power source, and blower that cools the vibrator.
Used in motors. The control power for the coil of the large cutter that cuts off the line voltage power was 115V, 50Hz, single phase. This was achieved via a separate step-down transformer and fused stage. Most control circuits required 24VDC to drive small relays, fixed relay drivers (transistors), and indicator lights. It was obtained from a 115V power supply with a step-down transformer, diode rectifier and filter capacitor. Other circuits for solid state devices required three regulated ±15 VDC supplies, one +15 VDC Zener regulated supply, one unregulated 24 VDC, and one 5V Zener regulated supply.
There were thus six separate DC sources for each control. The power supply source for the power amplifier is 380V, 3 phase, 50
HzAC power was converted to ±115VDC. The field power supply is 380V, 3 phase, 50Hz AC at 40A.
Converted to 190VDC. Both of these sources used step-down transformers and silicon power diode direct feed full wave bridge rectifier circuits. The power amplifier power supply was particularly well filtered. In order to illustrate the numerous practical benefits of the method, some non-limiting methods according to the invention will now be described. The effect of the vibration treatment according to the invention on the physical properties of the molded material is illustrated by the attached measurement results of these physical properties. Example 1 A Dupont-990DSC cell was tested for the effect of vibration treatment on the heat capacity of general purpose polystyrene material (PS). FIG. 7 gives the results for two different types of processing. For each treatment, the reference curve corresponds to a specimen cooled under identical conditions except for vibration. This reference curve thus corresponds to a conventional compression molded specimen. The heating rate was kept constant at 20°C/min for all DSC samples. In the process shown in the top curve of Figure 7, the PS sample is initially a round piece of material sheet and is placed in a mold until the temperature is constant at (Tg + 30°C), i.e. 135°C. Heated. 215psi (15.12
A static pressure of Kg/cm ² ) was applied to the sample, and then vibration was started, the vibration wave was initially 15 Hz, and the peak-to-peak amplitude of deformation was 0.005 in (0.127 mm). When the mold was rapidly cooled to rapidly cool the specimen, the vibration frequency increased as (Hz) = 15e ^t/5 , but the amplitude of deformation remained constant. The vibration treatment was discontinued when the sample temperature reached 98°C. The specimen continued to cool, but the vibrations did not continue. The reference specimen in FIG. 7 (top curve) was cooled under the same conditions, but no vibrations were applied during cooling. The thermograms of treated and untreated specimens clearly show the difference in heat capacity of these two specimens. Although both treated and untreated samples exhibit conventional endothermic reactions at the glass transition temperature, their thermal behavior after the transition is quite different. The heat capacity of the treated sample is
After passing the Tg endotherm, it returned to a value approximately equal to the heat capacity (at the corresponding temperature) by extrapolation of low temperature (T<Tg) behavior. Thus, it is well known that the vibration-molded specimen has properties at room temperature (after processing), which are temperature properties obtained by extrapolation from the behavior after Tg, in which case the polymer is in equilibrium. It is. This means that at temperatures below Tg, the treated specimen behaves like a specimen that has reached equilibrium, ie, an extremely strongly annealed specimen. The heat capacity of the untreated sample (reference sample) deviated above the endotherm, showing a large difference in heat capacity between the glassy state (T<Tg) and the rubbery state (T>Tg). This behavior is further illustrated in the fourth diagram,
This is typical for quenched materials. In this figure, PS specimens are tested at three different cooling rates (80°C/ ^min ,
2°C/min, 0.5°C/min). The initial temperature of the rubber state was 135°C. Vibration in Figure 7-
It is clear that the molded swatch (top) behaves similarly to the slowly cooled swatch (bottom curve in Figure 8), but in fact it has been subjected to a severe rapid cooling process. Therefore, this specimen shows that the vibration treatment according to the invention applied during cooling controls and improves the equilibrium state. That is, the stability of the formed "glass" was obtained without losing the speed advantage of the quenching process. This method also eliminates lengthy and expensive post-quench temperature treatments (such as annealing). This is currently used to relieve internal stresses that have built up and frozen within the "glass" during quenching operations. Example 2 Effect on mechanical properties of treated sample The second treated sample in Figure 7 is another sample that was rapidly cooled from a rubber state at 80°C/min while being subjected to vibration.
This is a polystyrene sample. The static pressure acting on the sample was 217 psi (14.76 Kg/cm ² ), and the initial temperature was
It was 120℃. The vibration frequency during cooling is constant 100
Equal to Hz. The sinusoidal pressure is P=217±126sin(2π
×100t) (P=14.76±8.86sin(2π×100t)), where P is psi (Kg/cm ² ) and t is seconds. Vibration was discontinued when the sample temperature reached 80°C. FIG. 7 (lower curve) shows the thermograms of a vibration-molded specimen according to the invention and a reference specimen similarly cooled without vibration during cooling.
Once again, the treated and untreated samples behaved differently with respect to temperature. The endothermic characteristics at Tg were more complex for treated specimens than for untreated specimens. In particular, the endotherm is wide-ranging for treated materials, extending to over 40°C. Mechanical properties in tension and bending of treated and untreated specimens are ASTM
D790 () and ASTM D638-68 methods were used. 1 Bending result: Processed sample: Bending strength: 13635psi (958.7Kg/cm ² ) (Variation: 5%) Maximum strain%: (4.2±0.2)% Bending modulus of elasticity: 400350psi (28149Kg/cm ² ) (Variation: 5%) Untreated sample: Bending strength: 10096psi (709.9Kg/cm ² ) (Variation: 4%) Maximum strain %: (2.7±0.3)% Bending modulus of elasticity: 386000psi (27140Kg/cm ² ) (Variation: 6 %) 2 Tensile test Treated sample: Tensile force: 6100 psi (428 Kg/cm ² ) (Variation: 7%) Elongation at break %: (2.4-3)% Yield stress: 4540 psi (319 Kg/cm ² ) (Variation: 2 %) Elongation % at yield point: (1.6-2)% Elastic modulus in tension: 3.75×10 ⁵ psi (2.64×10 ⁴ Kg/cm ² ) (Variation: 5%) Untreated sample: Tensile strength: 5080 psi ( 357.2Kg/cm ² ) (Variation: 4%) Elongation at break: (1.5-2)% Yield stress: No yield point, ultimate stress Elongation at yield: No yield point, ultimate stress Elastic modulus in tension: 1.6× 10 ⁵ psi (1.12×10 ⁴ Kg/cm ² ) (variation: 5%) These results were obtained on a statistical population of four samples for the treatments. The dispersion was set as 100 times the ratio between the standard deviation and the mean value. The above results show that the mechanical properties of the vibro-formed specimens are excellent, especially in terms of tensile force and % elongation. For example, in bending, the bending strength of the vibration-formed sample is
35% higher, and the maximum strain is 50% higher than the corresponding value for the untreated sample. This was also true for the tensile results, although to a lesser extent. This example shows that specimens subjected to the vibration treatment described above during cooling are mechanically superior to untreated specimens, especially in terms of bending. Example 3 Effect on the deformability of the material The purpose of this example is to demonstrate that vibration treatment applied to a vitreous polymeric material below its glass transition temperature favorably softens the material. The material studied was general purpose polystyrene, which had already been cut into disk shapes from sheet material. Untreated swatches used as standards were tested at room temperature.
Pressurized to 9140 psi (642.6 Kg/cm ² ) plate pressure (swatches were free to flow laterally). Heat was applied to the mold to obtain a linear increase in sample temperature. The deformation parallel to the force axis was measured and plotted against temperature to characterize the softening behavior of the material under static loading. Treated specimens start at 50°C and are subjected to oscillating pressure P.
=6819±2311sin(2π ₀ t)(479±162.5sin(2π ₀
t) received. Here, P is psi (Kg/cm ² ), ₀ is frequency in Hz, t is time in seconds, and the heating rate was the same for each sample. FIG. 9 compares the deformation-temperature curves of statically and dynamically pressurized specimens. The maximum pressure was the same for all specimens, 9140 psi (642.6 Kg/cm ² ). The average pressure exerted on the treated specimen was 6819 psi (479
Kg/cm ² ), or 34% less than the standard pressure. Figure 9 shows the effect of vibration frequency on softening temperature (frequency remains constant during operation). It is clear from Figure 9 that the vibrations applied during heating have a significant effect on the ability of the loaded material to deform. For example, for a sample vibrated at 50Hz, the softening temperature is approximately 30°C lower. Therefore, a lower dynamic pressure is required to obtain the same deformation result. Figure 9 also shows that the frequency effect at a given average or maximum stress is not linear forward. The maximum breakdown appears to occur when the processing frequency is approximately 50-60Hz. Specifically, for mechanical processes involving low temperature thermoforming (T<Tg), the benefits of using vibration at selected frequencies during the process are quite clear. That is, lower total pressures or lower operating temperatures can be used. Example 4 Post-molding Birefringence and Thermal Stress Reduction The material used in this example was again general purpose polystyrene, cut into disc-shaped specimens from 2 mm sheets. The reference specimen was heated to 140° C. past the glass transition temperature. 8700psi (612Kg/
After a plate pressure of cm ² ) was applied at the corresponding temperature, the mold was quenched. During the processing process, the specimen changed dimensions, decreasing in thickness and increasing in diameter. Although it was optically clear, it was less transparent and the transmission of light was uneven. Examination of swatches between orthogonal polarizers showed a radially symmetrical birefringence pattern (Maltese cross conformal tilt and concentric isochromism)
(Maltesecross isoclinic and concentric
isochorome). The treated swatches were geometrically identical to the reference swatches. It has the same temperature 140℃ with no load
heated to ℃. 6525±2175sin (2π×100t)
After a motive plate pressure of psi (459±153 sin (2π×100 t) k) Kg/cm ² was applied, the mold was quenched as before.
Vibration was discontinued when the sample temperature reached 50°C. This sample was subjected to a total pressure of 8700 psi (612 Kg/cm ² ), the same as the reference pressure, for each cycle. The optical properties of these samples were excellent. There was no birefringence pattern in the deformed plane. The swatch was completely dark when viewed between crossed polarizers. It could be concluded that the vibration treatment during cooling provides relaxation and removal of thermal and/or directional stresses due to temperature-mechanical treatment. The optical properties were also improved by this vibration treatment. Example 5 Compression molding of granules with vibration The polystyrene granules used were obtained from the Dow Chemical Company (PS-otS-108). Reference specimen A was prepared according to the following sequence of steps. 1 8.85gr of granules were packed into the mold cavity at room temperature. 2 The mold was rapidly heated to 210°C in 7 minutes.
During this time, the mold cavity was evacuated to 4×10 ^-2 Torr. 3 A plate pressure of 435 psi (30.6 Kg/cm ² ) was applied to the mold (1 minute). 4 The mold was held at 120°C for 1 minute, 3 minutes, and 5 minutes, respectively. 5 Both halves of the mold were quickly cooled to room temperature with cold water. The pressure was removed when the sample temperature reached 50°C. Another reference sample B was prepared according to the following order. 1 and 2 are as described above. 3 When the mold temperature reaches 100℃, 435psi (30.6
A pressure of Kg/cm ² ) was applied and maintained as it was. 4 and 5 were as described above. Treated specimens were prepared according to the following conditions. 1 and 2 were as described above. Next, when the temperature of the sample reached 100°C, the mold was subjected to vibration treatment under the following conditions. - Lower limit of frequency: 5Hz - Upper limit of frequency: 3000Hz - Passage time from lower limit to upper limit: 30 seconds - Vibration frequency was changed back and forth between 5Hz and 3000Hz. The logarithm of the frequency was changed linearly with time.・The average pressure applied to the mold is 325psi (22.9Kg/cm ² )
And so. Next, when the temperature of the sample reaches 210℃, the mold is rapidly cooled, and when the temperature of the sample reaches 50℃, the application of vibration is stopped. In the following table, the total time spent in the mold and the final appearance of the swatches were recorded in terms of the presence of bubbles.

[Table] It is clear that the vibration treatment during molding enhances the diffusion of the bubbles to the periphery and subsequent suction from the molded article by the vacuum device. The total time in the mold is only a fraction of the time required to obtain a satisfactory sample when the process according to the invention is carried out. It is clear that the present invention may be modified without departing from its spirit and should not be limited to the embodiments described in the above specification.

[Brief explanation of the drawing]

Figure 1 is a graph showing the effect of variations in cooling rate on the final state of the material after cooling; Figure 2 is a graph showing the variation in specific volume as a function of temperature at various constant hydrostatic pressures; Figure 3 is the transition temperature. Graph giving the variation of as a function of rheological parameters, 4th
The figure illustrates the method according to the invention and shows the variation of Tg x
FIG. 5 is a schematic diagram of a preferred apparatus for carrying out the method of the invention;
Fig. 6 is a side view of part A of the apparatus shown in Fig. 5, Fig. 7 is a graph showing the effect of the vibration molding method according to the present invention on the heat capacity of polystyrene, and Fig. 8 is a graph showing the effect of the cooling rate on the temperature characteristics of polystyrene. FIG. 9 is a graph showing the effects that various vibration frequencies of constant amplitude have on polystyrene. 1 is a spring, 13 is a vibrator, 22 is a threaded rod, 23 is a cooling duct, 21, 32 are molds, 24 is an inlet valve, 25 is an outlet valve, 26 is an accelerometer, 27 is a thermocouple, 28 is a load cell, 29 is frame, 3
1 is a bellows, 41 is a support plate, 42 is a vibration table, 51
is a power supply source, 53 is a blower, 54 is a coolant supply, 55 is a drain, 58 is an air pipe, B is a sine wave generator, C is a power amplifier, and D is a control panel.

Claims (1)

[Scope of Claims] 1. Transformed from an initial green state into a finished or semi-finished product by a molding process, which has inherent properties and associated transition temperatures determined by its chemical nature and thermodynamic state after molding. 2. A method of changing the physical and physicochemical properties of a polymer having an equilibrium condition by simultaneously varying temperature and at least one other rheological parameter together as a function of time. in order to control the rate-sensitive rate of change of the physical state to, and thereby obtain a final product with defined physical and/or physico-chemical properties, the rate of change of said temperature with respect to time and the above-mentioned, etc. A method of changing the physical and physicochemical properties of a polymer using mechanical vibration as the other rheological parameter, in which the rate of change with respect to time of a rheological parameter is controlled according to a predetermined relationship. 2. The method of claim 1, wherein the change in mechanical vibration comprises a change in amplitude. 3. The method of claim 1, wherein the change in mechanical vibration comprises a change in frequency. 4. The method according to claim 1, wherein in addition to the vibration treatment described above, electrostatic stress is simultaneously applied. 5. The method of claim 1, wherein the modification of said properties occurs during said molding process.