WO2013095876A1

WO2013095876A1 - Method for measuring polymer foam expansion and apparatus for use therein

Info

Publication number: WO2013095876A1
Application number: PCT/US2012/066735
Authority: WO
Inventors: Seth Thomas STEWART; Paul R. VAN RHEENEN
Original assignee: Rohm & Haas Company
Priority date: 2011-12-22
Filing date: 2012-11-28
Publication date: 2013-06-27
Also published as: CN103175832A; CN103175832B; JP2013136751A; TW201333468A; KR102130175B1; TWI569015B; KR20130079201A; JP6016614B2

Abstract

A method of measuring polymer foam expansion comprising extruding a free foaming polymer formulation which comprises one or more blowing agents; feeding the extruded formulation through a right angle die (12) to produce a formed foam having a foam front at an exit of the die; measuring a thickness of the formed foam (16) at the die nozzle (14), using a laser thickness measuring device comprising a laser (18), a vertical positioner (20) driven by a motor drive (22) wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser; adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and recording the foam thickness, wherein the thickness of the formed foam is measured every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time is provided. Also provided is an apparatus for executing the inventive method.

Description

METHOD FOR MEASURING POLYMER FOAM EXPANSION

AND APPARATUS FOR USE THEREIN

Field of Invention

The instant invention relates to a method for measuring polymer foam expansion and apparatus for use therein.

Background of the Invention

Creating a foamed polymer product is a very difficult procedure that is on the edge of control. Many factors are involved in keeping this process in a controlled state. For example, for a PVC foamed product, such factors include PVC K-value, processing aids used, lubricant type and level, and identity of the chemical blowing agent. Prediction of the expansion profile of polymer formulations containing test additives and levels would be useful in controlling the foamed polymer product production. Currently available methods provide foam expansion for only one point in time.

Summary of the Invention

The instant invention is a method for measuring polymer foam expansion and apparatus for use therein.

In one embodiment, the instant invention provides a method of measuring polymer foam expansion comprising: extruding a free foaming polymer formulation which comprises one or more blowing agents; feeding the extruded formulation through a right angle die to produce a formed foam having a foam front at an exit of the die; measuring a thickness of the formed foam at the die nozzle, using a laser thickness measuring device comprising a laser, a vertical positioner driven by a motor drive wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser; adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and recording the foam thickness, wherein the measuring the thickness of the formed foam is repeated every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time.

In an alternative embodiment, the instant invention further provides an apparatus for the measurement of free foam expansion of polymers comprising: an extruder for extruding and forming a foamed polymer formulation resulting in a formed foam; wherein the extruder comprises a right angle die having a die nozzle; a laser measuring head attached to a vertical positioning device for measuring a thickness of the formed foam at or near the die nozzle; a motor drive unit attached to the vertical positioner for adjusting a vertical displacement of the laser measuring head so as to synchronize the rate of vertical displacement of the foam exiting the die with the rate of vertical displacement of the laser measuring head; a means for controlling the motor drive unit speed; and a recording device to record a thickness of the formed foam as a function of time.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the measuring the thickness of the formed foam is repeated at least one hundred times.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the method further comprises determining the maximum foam thickness from the foam thickness as a function of time.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the free foaming polymer formulation comprises polyvinyl chloride and one or more blowing agents.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the die has a shape selected from the group consisting of circle, oval, square, and rectangle.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the method further comprises measuring the location of the foam front as a function of time, determining a rate of the vertical displacement of the foam front and automatically adjusting the speed of the motor drive such that the laser moves at the same vertical displacement rate as the determined vertical displacement rate of the foam front.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the expansion of the foam, for a circular die opening, measured as the foam diameter squared divided by the die nozzle diameter squared, is from 1 to 50.

In an alternative embodiment, the instant invention provides a method of measuring polymer foam expansion and an apparatus for the measurement of free foam expansion of polymers, in accordance with any of the preceding embodiments, except that the apparatus further comprises a sensor for measuring the vertical location of a front of the formed foam as a function of time, means for determining the vertical displacement rate of the formed foam front, and a control loop between the means for determining the vertical displacement of the formed foam front and the means for controlling the motor drive unit.

In another embodiment, the instant invention provides a method of measuring polymer foam expansion consisting essentially of: extruding a free foaming polymer formulation which comprises one or more blowing agents; feeding the extruded formulation through a right angle die to produce a formed foam having a foam front at an exit of the die; measuring a thickness of the formed foam at the die nozzle, using a laser thickness measuring device comprising a laser, a vertical positioner driven by a motor drive wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser; adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and recording the foam thickness, wherein the measuring the thickness of the formed foam is repeated every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time.

In another embodiment, the instant invention provides an apparatus for the measurement of free foam expansion of polymers consisting essentially of: an extruder for extruding and forming a foamed polymer formulation resulting in a formed foam; wherein the extruder comprises a right angle die having a die nozzle; a laser measuring head attached to a vertical positioning device for measuring a thickness of the formed foam at or near the die nozzle; a motor drive unit attached to the vertical positioner for adjusting a vertical displacement of the laser measuring head so as to synchronize the rate of vertical displacement of the foam exiting the die with the rate of vertical displacement of the laser measuring head; a means for controlling the motor drive unit speed; and a recording device to record a thickness of the formed foam as a function of time. Brief Description of the Drawings

For the purpose of illustrating the invention, there is shown in the drawings a form that is exemplary; it being understood, however, that this invention is not limited to the precise

arrangements and instrumentalities shown.

Fig. 1 is schematic diagram illustrating one embodiment of the apparatus;

Fig. 2 is a graph of cross sectional expansion ratio versus time for PVC formulations using three different mixed endothermic/exothermic blowing agents;

Fig. 3 is a graph of cross sectional expansion ratio versus time for PVC formulations using three different endothermic blowing agents;

Fig. 4 is a graph of cross sectional expansion ratio versus time for PVC formulations using three different exothermic blowing agents; and

Fig. 5 is a graph of cross sectional expansion ratio versus time for PVC formulations using three different blowing agents.

Detailed Description of the Invention

The method of measuring polymer foam expansion according to the present invention comprises: extruding a free foaming polymer formulation which comprises one or more blowing agents; feeding the extruded formulation through a right angle die to produce a formed foam having a foam front at an exit of the die; measuring a thickness of the formed foam at the die nozzle using a non-contact measuring device comprising a laser, a vertical positioner driven by a motor drive wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser; adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and recording the foam thickness as a function of time, wherein the thickness of the formed foam is measured every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time.

As used herein, "at the die nozzle" means a location from 0 to 1 mm from the die nozzle.

The extruding a free foaming polymer formulation may be accomplished using any appropriate extruder provided the extruder may be fitted with a right angle die for forming a formed foam. Such extruders include, for example, single and multiple screw extruders. One appropriate extruder for use in the extruding step is a HAAKE POLYLAB conical twin screw extruder. As used herein free foaming polymer formulations include any polymer formulation which freely expands/foams upon exiting the die. Examples of such polymer formulations include polymers selected from the group consisting of styrenated polymers, acrylates, polyolefms, polyesters, polyamides, polyvinyl chloride (PVC), chlorinated PVC, and fluoropolymers and one or more physical or chemical blowing agents. The chemical blowing agent can be any of a variety of chemical blowing agents which release a gas upon thermo decomposition. The blowing agent or mixtures of agents can be selected from chemicals containing decomposable groups such as azo, N- nitroso, carboxylate, carbonate, heterocyclic nitrogen-containing and sulfonyl hydrazide groups. Generally, they are solid materials that liberate gas(es) when heated by means of a chemical reaction or upon decomposition. Representative compounds include azodicarbonamide and derivatives, bicarbonates, hydrazine derivatives, semicarbazides, tetrazoles, benzoxazines, and borohydrates as outlined in Plastic Additives Handbook, eds. R. Gachter, H. Muller, and P.P. Klemchuk, Hanser Gardner Publishers, Cincinnati, 1996, Ch. 16. Examples of these blowing agents are:

azodicarbonamide, 4,4-oxybis(benzenesulfohydrazide), diphenylsulfone-3,3-disulfohydrazide, trihydrazinotriazine, p-toluylenesulfonyl semicarbazide, 5-phenyltetrazole, isatoic anhydride, sodium bicarbonate, and sodium borohydride. In addition, foaming can be generated by physical blowing agents that are injected into the extruder. Exemplary physical blowing agents include liquefied carbon dioxide, nitrogen, hydrocarbons, chlorinated fluorocarbons, hydrochlorofluorocarbons and water.

The right angle die attached to the extruder and used in forming a formed foam may have any appropriate opening, or nozzle, shape. Such cross sectional shapes may include, for example, circle, oval, square and rectangle. The extruded polymer formulation exits the die thereby taking on a cross sectional shape of the die opening. In the instance of a die having a circular opening, the thickness of the formed foam refers to the diameter of the resulting circular formed foam. In the instance of a die having a square opening, the thickness of the formed foam refers to the length of one side of the square formed foam. In the instance of a die having an oval opening the thickness of the formed foam may refer to either the short or long axis of the oval. Likewise, in the instance of a die having a rectangular opening the thickness of the formed foam may refer to either the short or long side of the rectangle. A multiaxis thickness measuring device can also be used to measure all axis dimensions simultaneously. In this way the cross sectional expansion ratio (cross sectional area at any given time divided by the cross section area of the die opening) can be determined for any die geometry.

The adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die may be accomplished manually or may be automated. In the case of manual adjustment, either or both of the vertical displacement rates of the laser and that of the foam front exiting the die may be manually monitored. In this case, the vertical motor drive is started when foam is even with the bottom of the laser measuring device. The speed is adjusted manually with a variable autotransformer (e.g., VARIAC) so that the foam front stays even with the bottom of the laser device. This normally can be done with 2 or 3 adjustments of the transformer. Likewise, in the case of automatic adjustment, either or both of the vertical displacement rates of the laser and that of the foam front exiting the die may be automatically monitored by electronics and/or sensors well known in the art. For example, the vertical foam front speed and the vertical laser speed can be measured by separate laser Doppler velocimeters and the speeds of both can be synchronized by a control loop. Any type of non- contact velocimeter, such as a laser Doppler velocimeter, may be used to measure the vertical speed of the formed foam front. Exemplary laser Doppler velocimeters include those available from POLYTECH (Irvine, CA) and ZUMBACH ELECTRONIC AG (Orpund, Switzerland).

Multiple thickness measurements are made on the formed foam front over a period of time from exiting the die to at least a time at which maximum expansion is reached. The measurements may be made at intervals from every 0.05 seconds to every 0.15 seconds. The total time period of measurement may range from 1 second to 10 minutes.

All individual values and subranges from 0.05 to 0.15 seconds are included herein and disclosed herein; for example, the thickness measurement can be made from a lower limit of every 0.05, 0.07, 0.09, 0.11, or 0.13 seconds to an upper limit of 0.07, 0.09, 0.11, 0.13, or 0.15

seconds. For example, the thickness may be measured at intervals in the range of from every 0.05 to 0.15 seconds, or in the alternative, of from every 0.07 to 0.13 seconds, or in the alternative, of from 0.09 to 0.11 seconds.

In some embodiments, the method further comprises calculating the rate of foam expansion from the foam thickness as a function of time. As the method measures multiple thickness as a function of time, the rate of foam expansion may be readily calculated by dividing the change in thickness over a defined period of time by the defined period of time. In some embodiments, the method of measuring the thickness of the formed foam is repeated at least one hundred times.

In one embodiment of the method, the free foaming polymer formulation comprises polyvinyl chloride and one or more blowing agents.

In some embodiments, the method further comprises measuring the location of the foam front as a function of time, calculating a rate of the vertical displacement of the foam front and

automatically adjusting the speed of the motor drive such that the laser moves at the same vertical displacement rate as the calculated vertical displacement rate of the foam front. For example, the vertical foam front speed and the vertical laser speed can be measured by separate laser Doppler velocimeters and the speeds of both can be synchronized by a control loop. Control loops and components thereof are well known and examples thereof are described at

ttp://en.wikipedia.org/wiki/Control_loop, the disclosure of which is incorporated herein by reference.

In some embodiments of the inventive method, the expansion of the foam, measured as the foam diameter squared divided by the die opening diameter squared is from 1 to 50. All individual values and subranges from 1 to 50 are included herein and disclosed herein; for example, the expansion of foam can be from a lower limit of 1, 10, 20, 30 or 40 to an upper limit of 10, 20, 30, 40 or 50. For example, the foam expansion may be in the range of from 1 to 50, or in the alternative, the foam expansion may be in the range of from 10 to 40.

In an alternative embodiment, the instant invention further provides an apparatus useful in the inventive method comprising an extruder for extruding and forming a foamed polymer formulation resulting in a formed foam; wherein the extruder comprises a right angle die having a die nozzle; a laser measuring head attached to a vertical positioning device for measuring a thickness of the formed foam at or near the die nozzle; a motor drive unit attached to the vertical positioning device for adjusting a vertical displacement of the laser measuring head so as to synchronize the rate of vertical displacement of the foam exiting the die with the rate of vertical displacement of the laser measuring head; a means for controlling the motor drive unit speed; and a recording device to record a thickness of the formed foam as a function of time.

Extruders and dies useful in embodiments of the inventive apparatus include those discussed above. Vertical positioners may be any mechanism for vertically displacing items. For example, a vertical positioner may comprise a threaded rod rotated by a motor drive unit which comprises a rotary device, such as a brushed DC motor (example electric drill or stepper motor).

Laser measuring heads useful in the apparatus are devices which project a laser onto the formed foam and the cast shadow is detected electronically and converted into an electrical signal. It is possible to have two or three axis heads where more than one dimension is measured

simultaneously. An alternate device uses two or more lasers to measure thickness by triangulation.

The means for controlling the motor drive may include any method and/or device for adjusting the speed of the motor drive, including for example rheostats and variable

autotransformers. A description of various devices for controlling the speed of electric motors can be found at www.en.wikipedia.org/motor controller.

Referring to Fig. 1, one embodiment of an apparatus useful in the inventive method is shown. The apparatus for measuring the foam expansion of polymers is shown. The apparatus includes an extruder 10, a right angle die 12 having a die nozzle 14. Polymer is extruded in extruder 10, passes through right angle die 12 and die nozzle 14. Upon exiting the die nozzle 14, the formed foam 16 takes on the shape of the die nozzle 14. A laser measuring head 18 is attached to a vertical positioner 20. The vertical positioner 20 is driven by a motor drive 22. As shown in Fig. 1, the means for controlling the motor drive is a VARIAC 24. The recording device shown in Fig. 1 is a computer 26 with requisite input cables 28.

Examples

The following examples illustrate the present invention but are not intended to limit the scope of the invention.

The equipment used in the exemplary methods was a HAAKE POLYLAB conical twin screw extruder (available from THERMO FISHER SCIENTIFIC, INC.) with a right angle die.

Table 1 shows the zone settings for the extruder.

Table 1

Free foam polymer formulations run in the exemplary method was a PVC foam masterbatch (MBl) having the composition shown in Table 2. The processing aid, which was kept constant in all testing (SURECEL T-55 (available from The Dow Chemical Company, 10 PHR), and the blowing agent were bag mixed with the masterbatch prior to extrusion. Table 3 contains a list of the chemical blowing agents used in the various exemplary methods. A ZUMBACH USYS IPC-1 controller with a ZUMBACH ODAC laser gauge (i.e., laser measuring head) (available from

ZUMBACH ELECTRONIC AG, Orpund, Switzerland) was used to measure the thickness of the formed foam.

Table 2

The ZUMBACH ODAC laser gauge was attached to a stand that moves parallel to the formed foam via a threaded support. A rotary drill controlled by a VARIAC autotransformer was used to raise and lower the laser gauge attached to the threaded support. The speed of the rotary drill was matched to the linear output of the formed foam by adjusting the VARIAC.

In order to better center the formed foam for higher expansion samples, a piece of Teflon was attached with hook and loop tape to the bottom of the laser gauge. Such optional hook and loop tape is shown as element 30 in Fig. 1. A measurement of the thickness of the formed foam was collected every 0.1 seconds. The thickness measurements were collected from the ZUMBACH controller and graphed and analyzed using Excel software. Table 3

The maximum thickness and time to maximum thickness along with the Cross Sectional Expansion Ratio (CSER), as defined below, and density values were recorded. The density values were obtained by following the ASTM standard D792 "Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement." The maximum thickness values are given in Table 4. Cross Sectional Expansion Ratio (CSER), is a unitless measurement which is defined by the following equation: circular cross sectional area at time t

Cross Sectional Expansion Ratio = &^{e cross} sectional area where D_t is the diameter of the formed foam at time t and D₀ is the diameter of the die nozzle. The graphs were broken into the different blowing agent types (Exothermic (Exo), Endothermic (Endo), and Mixed Endo and Exo) with the Experimental Sample 1 plot being on all graphs for comparison purposes. Figs. 2-5 illustrate the expansion curves for samples of the polymer formulation using each of the blowing agents shown in Table 3.

Fig. 2 illustrates cross sectional expansion ratio of PVC compositions containing chemical blowing agents composed of a mixture of exothermic and endothermic components as a function of time after the foam exits the die opening. Such mixed exo/endo blowing agents are the most common blowing agents found in PVC foam due to the combination of positive properties of each blowing agent type.

Fig. 2 shows that a mixture of exothermic and endothermic blowing agents gives a quick expansion with a relatively high level of expansion. The TRAMACO TSE3140 has a slightly lower slope in the initial expansion section.

As Fig. 3 shows, the endothermic blowing agents have a much higher maximum expansion than the blowing agents composed of a mixture of Exo and Endo. While the endothermic samples have a much greater overall expansion, the initial rate of expansion is much less than a compound containing exothermic material and density is slightly higher.

Fig. 4 shows the comparison of the exothermic blowing agents with experimental sample 1 for reference. The overall expansion is lower than experimental sample 1 but the initial rate of expansion is similar. The K-198 gives more expansion than the HRVPOl, which corresponds to its higher gas evolution number (221 cc/g vs.190 cc/g).

Fig. 5 shows the best of each type of blowing agent in one graph so that a direct comparison in expansion characteristics can be viewed.

Table 4

The present invention may be embodied in other forms without departing from the spirit and the essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

We Claim:

1. A method of measuring polymer foam expansion comprising:

extruding a free foaming polymer formulation which comprises one or more blowing agents;

feeding the extruded formulation through a right angle die to produce a formed foam having a foam front at an exit of the die;

measuring a thickness of the formed foam at the die nozzle, using a laser thickness measuring device comprising a laser, a vertical positioner driven by a motor drive wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser;

adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and

recording the foam thickness,

wherein the measuring the thickness of the formed foam is repeated every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time.

2. The method according to Claim 1, further comprising determining the maximum foam thickness from the foam thickness as a function of time.

3. The method according to any one of the preceding Claims, wherein the free foaming polymer formulation comprises polyvinyl chloride and one or more blowing agents.

4. The method according to any one of the preceding Claims, wherein the die has a shape selected from the group consisting of circle, oval, square, and rectangle.

5. The method according to any one of the preceding Claims, further comprising measuring the location of the foam front as a function of time, determining a rate of the vertical displacement of the foam front and automatically adjusting the speed of the motor drive such that the laser moves at the same vertical displacement rate as the determined vertical displacement rate of the foam front.

6. The method according to any one of the preceding Claims, wherein the expansion of the foam, measured as the foam diameter squared divided by the die nozzle diameter squared is from 1 to 50.

7. The method according to any one of the preceding Claims, wherein a cross Sectional Expansion Ratio of the polymer foam is from 1 to 50.

8. An apparatus for the measurement of free foam expansion of polymers comprising: an extruder for extruding and forming a foamed polymer formulation resulting in a formed foam; wherein the extruder comprises a right angle die having a die nozzle;

a laser measuring head attached to a vertical positioning device for measuring a thickness of the formed foam at or near the die nozzle;

a motor drive unit attached to the vertical positioner for adjusting a vertical displacement of the laser measuring head so as to synchronize the rate of vertical displacement of the foam exiting the die with the rate of vertical displacement of the laser measuring head;

a means for controlling the motor drive unit speed; and

a recording device to record a thickness of the formed foam as a function of time.

9. The apparatus according to Claim 8, further comprising a sensor for measuring the vertical location of a front of the formed foam as a function of time, means for determining the vertical displacement rate of the formed foam front, and a control loop between the means for determining the vertical displacement of the formed foam front and the means for controlling the motor drive unit.