GB2174800A - Colour stability measuring device - Google Patents

Abstract

A device for the determination of color stability during thermal degradation, e.g. a P.V.C. sample 10, comprises a heating block 1, insulating case 4, 5, light source 7, optical system 8 conveying light to a monochromator and detector such as an AAS spectrophotometer 11; and a heating system such as heated oil pumped through connections 2 and 3. Alternatively the lower case 4 may contain an electric heater, and heated carrier gas may pass through passages in the upper case 5 for measurement of evolved HCI. C.I.E. tristimulus values and other properties such as electrical conductivity may also be measured. <IMAGE>

Description

SPECIFICATION Color stability measuring device This invention relates to a measuring device for the determination of color stability during thermal degradation, which can be used for studies of PVC thermal degradation or other related studies.

PVC thermal degradation studies are conducted based on the measurement of sample color change, evolved HCI, electrical conductivity measurement and mechanical strength change. The amount of HCI evolved during thermal degradation is the most frequently used method in both industry and research laboratories, yet it does not measure the most essential factors for the preservation of the initial quality of polymer, with regard to either mechanical strength or color. This is attributable to the sensitivities of presently known methods. The situation is further complicated by the fact that there is no correlation between the amount of evolved HCI and the color stability of the sample.

In studies on PVC thermal stabilization, the color retention is regarded as the most important fact used to control the suitability of stabilizer formulation. At the moment, two methods are in common use; both involve the heating of test samples at known temperatures for varying times. In one method, samples are visually inspected and compared with those of other formulations. In a modernized technique, the color of samples is measured by adaptation of CIE tristimulus values method and given in a numerical form, allowing for comparison. The latter method, although the best technique now available, has a few serious deficiencies. It does not allow for kinetic measurements, since samples are prepared by the periodic heating and measured externally. Periodic heating disturbs isothermic conditions; therefore, the method cannot be used for studying changes of 'early color'.Finally, it is not possible to perform other test (HCI emission, electric conductivity measurement) simultaneously for the same sample.

With the present invention, the above disadvantages of the method of PVC color change measurement are no longer crucial. The sample is heated and the light reflected from the sample is measured continuously without the necessity of its manipulation. This allows a study of the sample under stable conditions. Measurements performed by this invention allow for early color studies. Also, it is possible to perform color studies, HCI emission, and electrical conductivity measurement for one test sample.

The measuring device is comprised of a heating block, insulation, a source of white light, a light pipe, monochromator and a light intensity measuring system.

The heating block which maintains the temperature of the sample, can be heated either by oil pumped from an external ultrathermostate or by a regulated electrical heating element. The upper surface of the heating block should be gold-plated in order to avoid corrosion by evolved HCI. The insulation should sufficiently protect the isothermal conditions, and in our design a PTFE insulating block is preferred, although any other material, such as glass wool, asbestos, etc. can be used.

Incoming and outcoming light beams are at a 45" angle to each other in order to measure only the light dispersed on the sample surface. The outgoing beam is taken from the measuring device by light pipes to a monochromator and then a detector. The latter allows the use of either an opticalelectronic system designed for this particular measurement, or of other existing equipment, such as atomic absorption spectrophotometer, fluorimeter, thereby decreasing the equipment cost.

A specific embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 shows the cross-section of the oilheated device; and Figure 2 shows the device with electric heating element for simultaneous measurement of color change, HCI emission and electrical conductivity.

The measuring device shown in Figure 1 is comprised of a heating element (1), equiped with an oil inlet (2) and outlet (3), bottom insulating cover (4), upper insulating cover (5) containing light pathway (6) a halogen lamp (7) with a current stabilizing circuit up to 0.01 V (in order to obtain stable beam intensity) and a set of light pipes (8) mounted in a water-cooled mounting (9) in order to protect them. Light from the halogen lamp, dispersed on sample (10) is normally conveyed to an AAS spectrophotometer (11), and measured at 500 nm, converted to reflectance, and continuously recorded, resulting in a graph of reflectance versus time.

The measuring device shown in Figure 2 is comprised of a metal block (1) with a heating element (2), a thermocouple (3), which measures and regulates temperature, a carrier gas heating channel (4), lower insulating case (5), gas-tight gasket (6), in order to maintain the atmosphere of gas (air, N2, etc.) and to allow for HCI measurement, carrier gas sample outlet (7), upper insulating case (8), containing the light pathway and part of the optical system (9). Light signal from the lamp (13) dispersed on the sample (10) is conveyed through an optical system to a monochromator and converted to an electrical signal by the detector. The color of sample is expressed in ClE-tristimulus values. The evolved HCI is measured by conductivity of water, through which outlet gas is percolated. Electric conductivity of sample (10) is measured continuously between upper sensor ring (11) and metal block (1). Electric signal is taken from electrodes (12). The upper part of metal block, made of brass, is gold-plated like the upper cylinder (11) in order to protect it against the corrosive action of HCl.

1. Color stability measuring device for solid, non-transparent samples, comprising a sample heating element and an attached optical system which allows conveyance of a light signal to a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Color stability measuring device This invention relates to a measuring device for the determination of color stability during thermal degradation, which can be used for studies of PVC thermal degradation or other related studies. PVC thermal degradation studies are conducted based on the measurement of sample color change, evolved HCI, electrical conductivity measurement and mechanical strength change. The amount of HCI evolved during thermal degradation is the most frequently used method in both industry and research laboratories, yet it does not measure the most essential factors for the preservation of the initial quality of polymer, with regard to either mechanical strength or color. This is attributable to the sensitivities of presently known methods. The situation is further complicated by the fact that there is no correlation between the amount of evolved HCI and the color stability of the sample. In studies on PVC thermal stabilization, the color retention is regarded as the most important fact used to control the suitability of stabilizer formulation. At the moment, two methods are in common use; both involve the heating of test samples at known temperatures for varying times. In one method, samples are visually inspected and compared with those of other formulations. In a modernized technique, the color of samples is measured by adaptation of CIE tristimulus values method and given in a numerical form, allowing for comparison. The latter method, although the best technique now available, has a few serious deficiencies. It does not allow for kinetic measurements, since samples are prepared by the periodic heating and measured externally. Periodic heating disturbs isothermic conditions; therefore, the method cannot be used for studying changes of 'early color'.Finally, it is not possible to perform other test (HCI emission, electric conductivity measurement) simultaneously for the same sample. With the present invention, the above disadvantages of the method of PVC color change measurement are no longer crucial. The sample is heated and the light reflected from the sample is measured continuously without the necessity of its manipulation. This allows a study of the sample under stable conditions. Measurements performed by this invention allow for early color studies. Also, it is possible to perform color studies, HCI emission, and electrical conductivity measurement for one test sample. The measuring device is comprised of a heating block, insulation, a source of white light, a light pipe, monochromator and a light intensity measuring system. The heating block which maintains the temperature of the sample, can be heated either by oil pumped from an external ultrathermostate or by a regulated electrical heating element. The upper surface of the heating block should be gold-plated in order to avoid corrosion by evolved HCI. The insulation should sufficiently protect the isothermal conditions, and in our design a PTFE insulating block is preferred, although any other material, such as glass wool, asbestos, etc. can be used. Incoming and outcoming light beams are at a 45" angle to each other in order to measure only the light dispersed on the sample surface. The outgoing beam is taken from the measuring device by light pipes to a monochromator and then a detector. The latter allows the use of either an opticalelectronic system designed for this particular measurement, or of other existing equipment, such as atomic absorption spectrophotometer, fluorimeter, thereby decreasing the equipment cost. A specific embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 shows the cross-section of the oilheated device; and Figure 2 shows the device with electric heating element for simultaneous measurement of color change, HCI emission and electrical conductivity. The measuring device shown in Figure 1 is comprised of a heating element (1), equiped with an oil inlet (2) and outlet (3), bottom insulating cover (4), upper insulating cover (5) containing light pathway (6) a halogen lamp (7) with a current stabilizing circuit up to 0.01 V (in order to obtain stable beam intensity) and a set of light pipes (8) mounted in a water-cooled mounting (9) in order to protect them. Light from the halogen lamp, dispersed on sample (10) is normally conveyed to an AAS spectrophotometer (11), and measured at 500 nm, converted to reflectance, and continuously recorded, resulting in a graph of reflectance versus time. The measuring device shown in Figure 2 is comprised of a metal block (1) with a heating element (2), a thermocouple (3), which measures and regulates temperature, a carrier gas heating channel (4), lower insulating case (5), gas-tight gasket (6), in order to maintain the atmosphere of gas (air, N2, etc.) and to allow for HCI measurement, carrier gas sample outlet (7), upper insulating case (8), containing the light pathway and part of the optical system (9). Light signal from the lamp (13) dispersed on the sample (10) is conveyed through an optical system to a monochromator and converted to an electrical signal by the detector. The color of sample is expressed in ClE-tristimulus values. The evolved HCI is measured by conductivity of water, through which outlet gas is percolated.Electric conductivity of sample (10) is measured continuously between upper sensor ring (11) and metal block (1). Electric signal is taken from electrodes (12). The upper part of metal block, made of brass, is gold-plated like the upper cylinder (11) in order to protect it against the corrosive action of HCl. CLAIMS

1. Color stability measuring device for solid, non-transparent samples, comprising a sample heating element and an attached optical system which allows conveyance of a light signal to a measuring unit, including a monochromator and a detector.

2. Color stability measuring device, as claimed in Claim 1, wherein an gas-heating system is provided in a metal block, allowing maintenance of a continuous gas flow over the sample.

3. Color stability measuring device as claimed in Claim 1 or Claim 2, wherein electric conductivity sensors are provided for the continuous measurement of the electric conductivity of the sample.