MXPA97005038A - Method to verify and control the limiteelast - Google Patents

Abstract

The present invention relates to a method for verifying and controlling a pressure drop which is proportional to the elastic limit of a polymeric material, the method is characterized in that it comprises: (a) flowing the material in a forward direction through a chamber that has an outlet through a restricted passage, to produce a positive pressure in the chamber, (b) stop the forward flow of material in the chamber and allow the residual positive pressure in the chamber to stabilize and reach a value, (c) record the residual positive pressure in the chamber under non-flowing conditions with respect to the value reached in step (b), (d) extract the material from the chamber to produce a negative pressure and initiate a reverse flow of the material in the chamber through the restricted passage, (e) stop the extraction of the material from the chamber and allow the negative pressure to stabilize and reach a value , (f) recording the residual negative pressure in the chamber under non-flowing conditions with respect to the value reached in step (e), and (h) determining half of the difference between the residual positive pressure and the residual negative pressure as a pressure drop proportional to the elastic limit of the material

Description

METHOD TO VERIFY AND CONTROL THE ELASTIC LIMIT Field of the Invention The present invention relates to a method for verifying and controlling the elastic limit in polymeric systems. The method was developed and demonstrated using a capillary rheometer connected directly on the line. Such method has utility in the test of security or guarantee connected directly to the line of the processes of production and is a suitable replacement for the test methods commonly used, made out of line.

Background of the Invention Rheology is the science of flow and the possible elastic deformation of matter. It is related to the response of materials to a mechanical force. The flow properties of a simple viscous liquid are defined by their resistance to flow, ie the viscosity and are measured by determining the flow velocity through a capillary. Such a simple viscous liquid continues to deform- Ref.025121 since it is subjected to a unit load of tensile break or a shear stress. The shear stress is a force applied tangentially to the material. In a liquid, the shear stress produces a sliding of one infinitesimal layer over another. For a liquid under shear stress, the rate of deformation or shear is proportional to the shear stress. This is true for ideal liquids or Neo tones, ie water, but the viscosity of many liquids is not independent of the shear rate. Non-Newtonian liquids are classified according to their viscosity behavior as a function of the shear rate. Some liquids exhibit a thinning of the cut, while others exhibit a thickening of the cut. Some liquids at rest appear to behave in a similar way to elastic solids until the shear stress exceeds a certain value, called the elastic limit (tauo), after which they flow easily. The elastic behavior as well as the viscous behavior is observed at the beginning or during the interruption of the flow when the applied stress or tension is insufficient to initiate or sustain the flow, respectively. A minimum voltage required to initiate the flow is referred to as the elastic limit, while the maximum voltage observed during the interruption of the flow is referred to as the residual voltage. The elastic limit and the residual tension are not necessarily equal. Their values are subject to considerations of flow velocity and flow history. However, on a reasonable time scale, their values are usually considered to be proportional and approximately equal for most materials. For the purposes of this invention, specific measurements of the residual stress are made, but the results have been reported generically in terms of the elastic limit. The shear stress is often plotted against the shear rate on graphs called flow curves which are then used to express the rheological behavior of liquids. The Newtonian flow is shown by a straight line, and the thinning of the shear or shear and the thickening of the shear or shear are shown by the curves. The elastic limit is an intercept or point on the tension axis (tau) of such graphs (see Figure 2 of the drawings, for example). The elastic limit, therefore, is a parameter which is very useful for characterizing materials. For example, water has an elastic limit of zero. A method to verify and control the elastic limit was discovered, while repeatedly trying to calibrate a capillary rheometer. It has been discovered that when the flow through the capillary was stopped for zero calibration, a positive (forward) residual back pressure, proportional to the elastic limit, remained inside the capillary rheometer. By manually inverting the dosing pump of the rheometer, a negative backpressure is observed (in reverse). The difference between the positive and negative residual pressures (forward and reverse) is proportional to twice the elastic limit, and is independent of the value of the zero calibration. This discovery was made while using a capillary rheometer connected directly to the line to verify a silicone sealant mixture. The mathematical rela- tion used to make the measurement is defined by the equation: Cutting Tension (With FIX on the Capillary Wall = where R is the capillary radius, L is the length of the capillary, and P is the pressure drop through the capillary.) Therefore, for a given system, the Pressure P is a proportional measurement of the residual voltage (s? n), below which the flow through the capillary will stop, the most common units for the shear stress (With flow)? the residual voltage, and the elastic limit (Sn flow) f are dynes per square centimeter (din / cm2), Pascal (10 din / cm2 = 1 Pa), newtons per square meter (1 N / m2 = 1 Pa) and barias (1 bar = 1 x) 105 Pa = 14.5 pounds / in.2).

Detailed description of the invention This invention is directed to a method for verifying and controlling the residual stress of a polymeric material. The method is carried out by practicing the following steps: (a) flowing a polymeric material in a forward direction through a capillary passage to produce a positive back pressure (i.e., 17.2 bar in Table I), (b) ) stop the flow of the polymeric material in the forward direction and allow the positive back pressure to stabilize and reach a constant value (ie, +0.20 bar in Table I), (c) to record the positive back pressure under non-flowing conditions with with respect to the constant value reached in step (b), (d) flowing the polymeric material in the reverse direction through the capillary passage to produce a negative back pressure, (e) stopping the flow of the polymeric material in the reverse direction and allow the negative back pressure to stabilize and reach a constant value (ie, -1.07 bar in Table I), (f) register the negative back pressure under non-flowing conditions with respect to to the constant value reached in step (e), (h) determine half of the difference between the positive back pressure (+0.20 barias) and the negative back pressure (-1.07 barias) as the pressure drop (0.635 barias) through of the capillary passage, and (i) calculate the residual stress for the polymeric material in accordance with the ratio Residual Tension (without fiU o) = RP / 2L where R is the radius of the capillary passage, L is the length of the capillary passage and P is the pressure drop through the capillary passage determined in step (h).

In other words, the present invention is a method for verifying and controlling a residual pressure drop and shear or shear stress which is considered to be proportional to the elastic limit of a polymeric material. The method comprises: (a) flowing the material in a forward direction through a chamber that has an outlet through a restricted passageway to produce positive pressure in the chamber, (b) stopping the forward flow of the material in the chamber and allow the residual positive pressure in the chamber to stabilize and reach a constant value, (c) register the residual positive pressure in the chamber under non-flowing conditions with respect to the constant value reached in step (b), ( d) extract the material from the chamber to produce a negative pressure and initiate a reverse flow of the material into the chamber through the restricted passage, (e) stop the extraction of the material from the chamber and allow the negative pressure to stabilize and reach a constant value, (f) register the residual negative pressure in the chamber under non-flowing conditions with respect to the constant value reached in step (e), (h) determine half of the difference between the residual positive pressure and the residual negative pressure as a pressure drop proportional to the residual stress of the material, and (i) calculate the residual stress (Without fi ux) of the material based on the equation to determine the shear stress (CO-. FIX) for the geometry of the restricted passage using the pressure drop in step (h). It was also noted that instead of requiring a constant value as in steps (b) and (e), the residual pressure or torque after a time or arbitrary change value (predetermined), will also provide an adequate measurement of the elastic limit. The term "polymeric material" is used herein to include any viscous stream such as a fluid, gum, rubber, paste, sealant, elastomer, caulking, adhesive, resin, coating, or personal care formulation (i.e. a lotion, cream, emulsion, or microemulsion, for example). To illustrate the method of the invention in the following example, a silicone sealant mixture was selected as the polymeric material. The silicone sealant materials typically contain a polydiorganosiloxane, a filler, a crosslinking agent, and a curing catalyst. These sealing agents are cured by exposure to moisture, and are viscous materials which are extruded from cartridges into cracks or slits that are to be sealed. The consistency of the silicone sealant is typically viscous and toothpaste-like. In applications such as building construction, silicone sealants are thixotropic and not flexible to stay in place until they are cured. When such sealants are used in the construction of buildings, aesthetic characteristics such as color are important. Therefore, silicone sealants of a variety of colors are used commercially. These sealing agents are made by mixing several ingredients in predetermined and defined weight or volume ratios. For room temperature vulcanizable silicone sealants (RTV), the polydiorganosiloxanes are blocked at the ends with silanol or similar "hydrolyzable groups." These polydiorganosiloxanes typically have a viscosity in excess of one Pa.s (1,000 centistokes) measured at 25 °. C, preferably 1 to 100 Pa.s (100,000 centistokes) When a filler is added to this polydiorganosiloxane, the mixture is called a "sealer base", since it constitutes a larger portion of the silicone sealant, since cause other ingredients are then added to arrive at a final composition.The useful fillers are (i) reinforcing fillers such as silica or carbon black; and (ii) non-reinforcing or semi-reinforcing fillers such as titanium dioxide, quartz, diatomaceous earth, calcium carbonate and alumina. To this "sealer base", the crosslinking agent and the catalysts are frequently added. The crosslinking agents are generally silanes or products of partial hydrolysis of the silanes. These silanes include acetoxy silanes, alkoxysilanes, ketoximosilanes, aminosilanes and amidosilanes. The crosslinking silanes have three to four hydrolysable groups per molecule, although the partial hydrolysis products have more than three. In addition to the crosslinking agents, the silicone sealants include chain extenders which are also silanes, but only with two hydrolyzable groups per molecule. The hydrolyzable group terminating the polydiorganosiloxane is frequently the same as the group of the silane crosslinking agent, but mixtures of the different types of the hydrolyzable groups may be present in the same silicone sealant composition. Catalysts for curing these sealant compositions depend on the type of the crosslinking agent and include compounds such as metal carboxylates, alkyl orthotitanates, titanate chelates and zirconium alkoxides or chelates. Since the polydiorganosiloxane in the silicone sealant base is clear and colorless, coloring agents are often necessary. Although these sealing agents can be clear, they are usually produced in five to eight standard colors, including black, white, and various shades of beige, brown or gray. Virtually any color or shade is possible, subject to the reproducibility of the pigment, the accuracy of the dosage, and the perfection of mixing. These coloring agents, commonly called pigments, include various categories of organic and inorganic pigments. For example, the most important inorganic coloring agents used in silicone sealants are derivatives of iron oxide pigments, such as yellow, brown, red and black iron oxides. Other synthetic inorganic pigments include cadmium orange, chromium oxide green, manganese violet and molybdenum orange. They are representative of numerous varieties of organic synthetic coloring agents for silicone sealants: Acid Red 52 (Acid Red 52), Benzidine Yellow HR (Benzidine Yellow HR), Methyl Violet (Methyl Violet), Green and Phthalocyanine Blue (Phthalocyanine Green and Blue), Pigment Brown 28 (Pigment Brown 28) and Victoria B Blue (Victoria Blue B). To facilitate processing, the coloring agent is added to the "sealer base" in the liquid state. These pigment dispersions, color concentrates and liquid colorants are easily achieved by the dispersion of a pigment in a liquid carrier or vehicle. In the past, the processes for coloring silicone sealants have been complicated by the fact that frequent alterations from one color to another are required. Accordingly, the "sealant base" was first compounded, catalyzed and packed in drums or containers for bulk material. Then, these containers were moved to a separate process area for pigmentation. Many different pigments are necessary to make or manufacture the variety of colors and shades "" required in the market. Therefore, the matching of a particular color frequently requires techniques for combining or mixing several pigments. Usually, production personnel load the "sealer base" and dose the necessary coloring agent into the mixer to produce the desired silicone sealant and color. The ingredients are mixed over a period of time to match the color using standard colorimetry technology. The addition of the pigment has to be carefully controlled, because the pigments can degrade the physical properties of the silicone sealant, when the amount of the pigment exceeds certain concentration levels. When the color of the sealing agent is determined to be correct, the silicone sealant is then moved to a proportioning machine where the silicone sealing agent is dosed into cartridges, drums or cubes, in a volumetric dosing system of one part . During dosing, production personnel measure various physical properties of the silicone sealant agent "off the line" to ensure its quality, and verify that the sealing agent meets product and manufacturing specifications. This requires the production staff to sample the silicone sealant, - send the sample to the laboratory for testing, and wait for the laboratory confirmation that the sealant meets the production specifications. Such "off-line" procedures are costly and time-consuming, contributing to an already lengthy production process and otherwise waste valuable manufacturing time.

This invention surprisingly can eliminate the "out of line" test for the elastic limit by providing a direct "on-line" measurement. For example, it can be used as a substitute for the "Standard Test Method for Sinking or Depressing Sealant Substances", Designation D 2202-93a (Annual Book of ASTM Standards Volume 04.07) of the American Society for Testing and Materials (ASTM), wherein the samples of the viscous material are placed on a flat horizontal surface having a graduated scale, the surface is raised to the vertical, and the distance of travel (or subsidence) of the viscous material descending on the vertical surface is measure then. The method of the invention can also replace the bending tests of the penetrometer used for the verification and control of the physical properties of the materials of the product. Figure 1 is a graphic representation of a type of capillary rheometer available that includes several system components necessary to carry out the method of the invention. Figure 2 is a graphical representation of the shear stress plotted against the shear rate for some common types of flow behavior referred to above. The elastic limit (tauo), where appropriate, is shown on the y-axis (ie, the coordinate of the shear stress). The viscosity is defined as the shear stress divided by the shear rate at any point. Figure 3 is another graphical representation, similar to that of Figure 2, but showing the flow behavior for some common food products. The Newtonian fluid of JARABE OSCURO KAROR (that is to say without elastic limit) has a higher viscosity at a high shear rate, while the MIRACLE WHIPR DRESSING and the TOMATO HEINZ 57R SAUCE, here later SYRUP, DRESSING and TOMATO SAUCE, they show a much higher yield strength and viscosity at low shear rates. Plastic materials similar to dressing and tomato sauce show a small deformation or no deformation up to certain levels of tension. Above this elastic limit, the material flows easily. For example, to exceed the elastic limit of tomato sauce on the neck of a bottle, the bottle should be frequently tapped. When the shear stress in the wall exceeds the elastic limit, the flow is fast. For the tomato sauce in figure 3, the elastic limit (tauy) is 200 dynes / cm2 (20 Pa). For the dressing in Figure 3, the elastic limit (tauy) is 600 dynes / cm2 (60 Pa). Accordingly, with reference to Figure 1, there is shown a form of capillary rheometer device suitable for practicing the claimed method. The device will be observed comprising a cylindrical WAKE that has a HEATING AREA. The HEATING AREA can be controlled to provide temperatures in the range of 60-350 ° C. A positive displacement ENGINE PUMP is placed inside the HEATING AREA, and is driven by a PULSE MOTOR (ie, a servomotor mounted on top of the ACCOMMODATION.) The impulse motor is capable of generating a speed of 0.1 -100 RPM The heated HOUSING contains a chamber that has a CAMERA OUTPUT The CHAMBER OUTPUT is in fluid communication with a CAPILLARY NOZZLE located in the lower portion of the heated HOUSING The CAPILLARY NOZZLE is removably mounted inside the HOUSING in the HEATING AREA Typically, the geometry of the CAPILLARY NOZZLE 'is provided for the lengths / diameters of 20/1, 20/2, 20/3, 20/4, 40/1, 40/2, 40/3 , and 40/4 (millimeters), respectively Some nozzles are available with lengths / diameters of 60/1 to 20/4 millimeters and are useful here The device in Figure 1 is specially designed to finish and compose p Processes in which there are frequent changes of the product. This allows easy access to the CAPILLARY NOZZLE, which is easily changed with a minimum of stop time. The process stream, i.e., a mixture of the silicone sealant, is removed from the main pressurized process stream, and is in fluid communication with the inlet of the GEAR PUMP by means of a FLOW CONTROL VALVE. A PURGE VALVE, located downstream of the FLOW CONTROL VALVE, is used to (i) ventilate or vent the air from the lines, (ii) extract samples of the material from the lines, (iii) supply the material from the process line up to the ENGINE PUMP more quickly for the test, or (iv) to purge the lines of materials previously pumped through the system. The temperature and pressure conditions existing within the CAMERA between the outlet of the ENGINE PUMP and the inlet of the CAPILLARY NOZZLE are easily verified by means of pressure and temperature sensors. A PRESSURE SENSOR such as a 50 bar transducer is typically employed. The TEMPERATURE SENSOR is a thermocouple to directly check and control the melting temperature in the melting channel. The materials that pass through the CAPILLARY NOZZLE are sent to be discarded as shown in Figure 1, or these materials are recycled back to the PROCESS CURRENT. The following example illustrates the invention in greater detail. The silicone sealant used as the PROCESS CURRENT in this example was a mixture containing polydiorganosiloxane blocked at the ends with silanol, a filler and an acetoxysilane. Such silicone sealant mixtures are described more fully in US Pat. Nos. 3,035,016; 3,077,465; 3,274,145 and 4,115,356. In general, sealing systems of this type are represented by the sequence of the reaction: --- SiOH + (AcO) 2RSi (OAc)? (AcO) 2RSiOSi = + HOAc where Ac is CH3CO-. These mixtures vary from viscous fluids to thick viscous pastes, and are curable to rubber or elastomeric materials when exposed to moisture.

Example I What led to this experiment was the problem of establishing an adjustment to the zero value, accurate and repeatable, of a capillary rheometer. It is assumed that the problem has been due to the residual pressure and the stress related to the elastic limit of the silicone sealant mixture contained in the capillary rheometer. In previous experiments, it has been noted that when the capillary was removed from the rheometer, or when the capillary was reinstalled in the rheometer, the procedure had an impact on the value of zero. This impact was in the direction, and of an approximate magnitude, expected for the elastic limit of the silicone sealing mixture that corresponds to a capillary nozzle with a diameter of one millimeter and a length of forty millimeters. It was decided that, in order to confirm the effect of the elastic limit, the pump could be stopped with the capillary nozzle in the rheometer, and the "zero" noted or indicated. Then it was decided to invert or manually reverse the pump in a small amount and signal a new "zero". The difference between these two values of "zero" must therefore correspond to two-thirds the elastic limit; and its average could be a true "zero" point for the system. This procedure of obtaining readings in the opposite directions of flow, takes into account and eliminates the drift factor found in the pressure sensors and the pressure meters. Therefore, under ideal conditions, measurements in empty pipes without flow are read 0.00. Under non-ideal conditions, however, measurements are often displaced or derived over time from a true zero value to a positive or negative value. Therefore, a true reading is obtained here without considering the displacement or drift, verifying and controlling the value which is half the difference between two readings taken in opposite directions. Accordingly, it has been found that this residual pressure within a GOETTFERTR Model WR Rheometer, shown schematically in Figure 1, after the stop of the gear pump, resulted from the elastic limit of the silicone sealant mixture. Verifying and controlling this residual stress, a calculation of the elastic limit based on the geometry of the capillary nozzle (ie, its configuration) was then made. The capillary nozzle used in the experiment had a length of forty millimeters and a diameter of one millimeter. The measurements were made at a temperature of 50 ° C. The data recorded during this experiment is shown in Table I. By way of explanation, the values of 17.2 bar in time 9:05 and 17.1 bar in time 9:37, are measurements of the flow voltage or the Cutting tension of the sealing material. The residual voltage on the other hand, is measured under conditions without flow and is reflected by the pressure sensor readings indicated as "No Flow".

TABLE I Sensor Reading Time Condition of the Pressure Pump (barias) 8: 43-8: 48 Flow in the forward direction at 2.0 cm3 / minute 8:53 No flow during + 0.15 5 minutes 8:54 Inverted back (0.05 cm3) 9:02 No flow during - 0.34 8 minutes 9: 05-9: 20 Running forward + 17.20 to 2.0 cm3 / minute 9:21 No flow for one minute + 0.20 9: 24-9: 30 Inverted one turn (0.2 cm3) 9:34 No flow for 4 minutes - 1.07 9 : 35-9: 39 Running forward to + 17.10 2.0 cm3 / minute 9:41 No flow for 3 minutes + 0.20 Residual stress, which is expected to be related to the elastic limit of the acetoxy silicone sealant mixture used in this example, it was calculated (i) by determining half the difference between the positive back pressure and the negative back pressure as the pressure drop (P) through the capillary passage, and (ii) calculating the residual stress of the polymeric material in accordance with the relationship Residual Tension (without Fiujo) = RP / 2L where R is the radius of the capillary passage, L is the length of the capillary passage, and P is the pressure drop through the capillary passage. Therefore, as a first example in the Table I, (0.5 mm) r + 0.15 - (-0.34) 1 2 Voltage = = 0. 0015 Residual (without FIU3O) 2 (40 mm) barias As a second example in Table I, (0.5 mm) r + 0.20 - (-1.07) 1 2 Voltage = = 0.0040 Residual (without FIRE) 2 (40 mm) barias Given the fact that the pressure sensor used in this experiment was a 50 bar (50 x 105 Pascal) transducer, these much smaller residual pressures and the resulting variations in residual stress are considered acceptable within the limits and capacity of the equipment used. An average of these values provides a good estimate of the elastic limit, even when additional readings were not obtained. The advantages of obtaining forward and reverse (double) readings are that (i) the rheometer system becomes insensitive to calibration errors, and (ii) the forward and reverse measurements have one more interval. Large than methods that use "forward (single) measurements." Although single and double methods lead to the measurement of residual stress (stress), forward and reverse (double) measurement provides greater precision and accuracy Although the method has been demonstrated here using a capillary nozzle, the rheometer can be modified to force the polymeric material through a thin rectangular channel or slot, a square nozzle or a tapered nozzle, for example, except for the numerical constants. , the equations for calculating the shear rate for the rheometry of the groove are the same as for capillary rheometry.The working equation for a rheometry of the groove pertinent to the invention is shown below: Residual Tension (Without FIU O) = HP 2 (1 + H / W) L where H is the thickness of the groove, P is the pressure drop through the groove, W is the width of the groove, and L is the length of the groove. In addition, the method of the invention is applicable in rheometers that record torque such as rheometers of the Couette type, rheometers of cone and plate, and rheometers of parallel plate.

It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following

Claims (7)

1. A method to verify and control a pressure drop which is proportional to the elastic limit of a polymeric material, the method is characterized in that it comprises: (a) flowing the material in a forward direction through a chamber having a exit through a restricted passage, to produce a positive pressure in the chamber, (b) stop the forward flow of material in the chamber and allow the residual positive pressure in the chamber to stabilize and reach a value, (c) record the residual positive pressure in the chamber under non-flowing conditions with respect to the value reached in step (b), (d) extract the material from the chamber to produce a negative pressure and initiate a reverse flow of the material in the chamber to through the restricted passage, (e) stop the extraction of the material from the chamber and allow the negative pressure to stabilize and reach a value, (f) record the pressure negative residual in the chamber under non-flowing conditions with respect to the value reached in step (e); and (h) determining half of the difference between the residual positive pressure and the residual negative pressure as a pressure drop proportional to the limit Elastic material.

2. A method according to claim 1, characterized in that the pressure drop is determined on the operating line while the material is a part of a process stream.

3. A method according to claim 2, characterized in that the material is selected from a fluid, gum, paste, sealing substance, elastomer, caulking substance, adhesive, resin, coating or formulation for personal care.

4. A method according to claim 2, characterized in that the restricted passage is a capillary passage, a rectangular channel, a slotted channel, a square channel or a tapered passage.

5. The method according to claim 1, characterized in that it further comprises: (i) calculating the residual voltage < Without FIU O) of the material based on the equation for the determination of the shear stress (C? N FIXED for the geometry of the restricted passage using the pressure drop in step (h).

6. A method according to claim 4, characterized in that the restricted passageway is a capillary, and the residual stress of the material is calculated according to the ratio Residual Tension (without Flow) = RP / 2L where R is the radius of the capillary passage, L is the length of the capillary passage and P is the pressure drop in step (h).

7. A method according to claim 4, characterized in that the restricted passageway is a rectangular channel or a slotted channel "- • '" - and the residual stress of the material is calculated according to the ratio Residual Tension (Without LIVE = HP 2 (1 + H / W) L where H is the thickness of the rectangular channel or grooved channel, P is the pressure drop in step (h), is the width of the rectangular channel or of the grooved channel, and L is the length of the rectangular channel or grooved channel.