KR19980025446A - Method and apparatus for monitoring latex quality of halogen-containing vinyl polymer - Google Patents

Abstract

A method for monitoring the quality of a halogen-containing vinyl polymer latex of an aqueous emulsion, wherein the luminescent radiation is emitted directly into the aqueous emulsion and scattered light reflected by the polymer particles of the latex in a spectral band located between 1100 and 2500 nm. The monitoring method of measuring by the intrinsic wavelength which forms a correlation equation with the intrinsic property of the latex which is captured, transmitted, and monitored by a spectrophotometer.

The measuring probe located in the reactor, the optical coupling of the probe with a near-infrared spectrophotometer equipped with means for capturing and scattering the reflected light and for emitting light, mainly comprising a computer with a correlation equation in memory during the polymerization. Device to monitor the quality of latexers.

Description

Method and apparatus for monitoring latex quality of halogen-containing vinyl polymer

The present invention relates to a method for monitoring the latex quality of halogen-containing vinyl polymers. In particular, the present invention relates to a method for monitoring the latex quality of such polymers during radical polymerization of halogen-containing vinyl monomer aqueous emulsions, and also to the apparatus for monitoring the quality of aqueous emulsions.

In addition to the aqueous polymerization medium, radical polymerization of aqueous emulsions, typically using emulsifiers and radical initiators, can be used to prepare aqueous emulsions of halogen-containing vinyl polymers, commonly referred to as latexes, for example polyvinyl chloride or vinylidene chloride copolymers. A polymerization method particularly suitable for is achieved. The resulting latex thus contains final polymer small particles with very small average diameters ranging from about 10 to about 4000 nm (nanometers). In some applications, for example in the field of paints or general coatings, these latexes are used directly without preferentially isolating polymers from these polymer media. In other applications, such as, for example, PVC-based plastisols, the polymers are isolated and dried from their polymerization medium before use. In all cases the quality of the product produced depends in particular on the average diameter of the polymer small particles of the latex and the diameter distribution of the particles. This has been the reason why it has been desired to find a way to effectively and quickly monitor the quality of latex in one treatment during the polymerization of aqueous emulsions in order to have the ability to make the reproducibility of the latex and the resulting polymer very high. By monitoring the polymerization progress by measurements reflecting the properties of the polymer formed, it is possible to prepare polymers with predetermined properties of improved reproducibility by practically adjusting the polymerization conditions.

The polymer's molecules, such as the viscosity index or density of the polymer, are measured by measuring the absorption spectrum of the near-infrared (hereinafter NIR) region in the polymer sample previously released in their polymerization medium taken during the polymerization, especially in powdered olefin polymers. Monitoring of structural properties has already been proposed. The method in question (European patent application EP-A-0328826) should control the polymerization by modifying the polymerization conditions if a predicted difference between the measured and the desired properties of the isolated polymer is to be achieved. The method according to document EP-A-0328826 requires regular collection and analysis of polymer samples previously separated from the polymerization medium and is therefore not suitable for in situ monitoring during polymerization.

Furthermore, in the near-infrared region having a range of 900-1200 nm, with light transmitted to a copolymer ratax of styrene and methyl acrylate having a solid content of 30% by weight containing polymer particles having an average diameter of about 60-80 nm. Measurements of spectral transmission reflections are described (see calibrated scales) (Pool. D. Gossen et al., Applied Spectroscopy, Vol. 47, No. 11, 1993, pp. 1852–1870). Several correlations can be established between some properties of styrene and methyl acrylate copolymer latex, such as average particle diameter and solids content. Such off-line calibration using photoluminescent light transmitted to such latexes is described as not suitable for latexes with polymer particles having an average diameter of about 150-200 nm (and more). Therefore, the more common diameter distribution and average of polymer particles in the monitoring of industrial latex, where concentration may exceed 50% at the end of the polymerization, or in an aqueous suspension consisting of one or several kinds of particles with a final average diameter of generally about 200 nm or more It cannot be suitable for measuring diameters.

It is an object of the present invention to provide a method for monitoring the quality of a halogen-containing vinyl polymer latex that does not exhibit any of the above drawbacks.

Accordingly, the present invention relates to a method for monitoring the quality of halogen-containing vinyl polymer latexes during radical polymerization of halogen-containing vinyl monomers in aqueous emulsions, which emits luminescent radiation to the aqueous emulsion and is located between 1100 and 2500 nm. The shot tube reflected by the polymer particles of the latex in the spectral band is captured by the near-infrared spectrophotometer and transmitted, reflected at any inherent wavelength located in the spectral band, and stored in memory to correlate with the intrinsic properties of the latex. Coal mines are measured, the measured values are injected into the memory and the monitored uniqueness is calculated.

The wavelength chosen to create a correlation between the intrinsic properties of the polymer latex and the reflected diffuse coal mine (hereinafter simply referred to as reflectance) generally depends on the polymerization conditions, the nature of the latex and the function of the halogen-containing vinyl polymer. Therefore, they must be measured in advance by experimentation, and such calibration is advantageously performed by statistical analysis with a large quantity of latex sample. The correlation is advantageously established by statistical regression. The correlation can then be injected into the memory of a computer coupled to the light spectrometer or into the light tourism system itself, and the properties can be calculated directly.

Non-limiting examples of latex properties that can be monitored during polymerization in accordance with the present invention are the average particle diameter, the total solid content and thus the degree of conversion (or progress of the polymerization reaction), the particle size distribution (by type) and thus The detection of other kinds of particles according to this, or the total surface area of the particles is mentioned.

For example, examples of wavelengths correlated by statistical regression of vinyl chloride homopolymer latex are as follows.

-In case of total solids content:

1602, 1610, 1692, 1714, 1886 and 2394nm

-For average particle diameter:

1332, 1328, 1390, 1816, 2102 and 2180nm

For particle types from 500 to 900 nm in diameter:

1394, 1402, 1410, 2094 and 2488nm

If the particle is the total surface area

1190, 1198, 1206, 1282, 1404 and 2230 nm

Measurement of the scattered light (reflectivity) reflected at the intrinsic wavelength is generally observed during the polymerization, e.g. at the beginning of at least close polymerization, in terms of initiation, and at the end of the polymerization before demonstrating the degree of conversion before degassing the reactor. At least several times.

According to a particular configuration of the process of the invention, monitoring of the halogen-containing vinyl polymer latex is carried out with a sample of the aqueous emulsion taken during the polymerization. Such sampling is performed in a bypass located in the polymerization remnant.

According to another preferred special arrangement, the monitoring process according to the invention is carried out in aqueous emulsion directly in the polymerization reactor. In this preferred configuration, no latex sampling is required, and the response to deviations in properties associated with the preestablished values is faster. Moreover, this configuration has the advantage of keeping the latex quality monitored during the polymerization.

Halogen-containing vinyl monomers, in the present invention, refer to any monomer capable of polymerizing by the radical method, having terminal olefin distribution and substituted by at least one halogen atom.

These monomers are selected from substituted derivatives of ethylene and propylene and preferably contain only two or three carbon atoms each.

The halogen atom is preferably selected from chlorine and fluorine atoms.

Such monomers include, but are not limited to, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, chlorotrifluoroethylene, tetrafluoro-ethylene and hexafluoropropalene. The present invention is particularly suitable for monitoring the aqueous emulsion radical polymerization of vinyl chloride, vinylidene chloride and vinylidene fluoride.

In the present invention, polymerization refers to homopolymerization of halogen-containing vinyl monomers and copolymerization with these monomers or with other monomers copolymerizable with them. Examples of these mentioned include vinyl esters such as vinyl acetate, acrylic esters such as methyl acrylate and methyl methacrylate, distributed nitriles such as acrylonitrile and methacrylonitrile, aryl esters such as aryl acetate, styrene derivatives and Alpha-olefins such as ethylene and propylene. However, the present invention is preferably applied to monitor latexes of polymers containing at least 50 mole percent, preferably at least 80 mole percent, units derived from halogen-containing vinyl monomers. In particular, the present invention is used to monitor the quality of vinyl chloride polymer latexes, moreover, vinyl chloride homopolymers, vinylidene chloride copolymers and vinylidene fluoride polymers, both homopolymers and copolymers.

Non-limiting examples of the vinylidene chlorides mentioned include copolymers consisting essentially of about 70-96% by weight of vinylidene chloride, the remainder being alkyl acrylates such as methyl acrylate, or vinyl chloride.

Non-limiting examples of the vinylidene fluoride copolymers mentioned are for example Chlorotrifluoroethylene containing at least 75% by weight of vinylidene fluoride, or copolymers with hexafluoropropylene.

In the present invention, aqueous emulsion radical polymerization refers to any radical polymerization method performed in an aqueous medium in the presence of an emulsifier and a radical initiator. This definition includes, in particular, micro-suspension polymerization, referred to as homogenous aqueous dispersions using oil-soluble initiators as well as so-called general aqueous emulsion polymerizations using water-soluble radicals, and emulsions of monomer droplets are characterized by Prepare in the presence.

The properties of the water-soluble and oil-soluble emulsifiers and initiators are not limited. The monitoring process according to the invention is therefore used as an aqueous emulsion process for radically polymerizing halogen-containing vinyl monomers in the presence of common initiators and emulsifiers in this type of polymerization. In particular it is suitable for monitoring general aqueous emulsion polymerizations using emulsifiers and water soluble initiators.

The process according to the invention is carried out during the polymerization, i.e. in the case of low rate of change (start of polymerization), when the latex has a low solids content and contains only very small sized particles, and in the case of high rate of conversion (end of polymerization) Has the advantage of allowing latex quality monitoring, for example, monitoring of the average size and / or conversion of polymer particles, when having a high solids content (tens of%) and especially containing large diameter particles.

The process according to the invention also has the significant advantage of directly measuring some properties of the latex during the polymerization without pre-isolating the polymer from the polymerization medium (in this case water). As a result, this is very fast in case of departure of latex properties in association with pre-established values in the polymerization parameters which control the polymerization which can ensure very high reproducibility of the latex produced by affecting the properties of falling off when necessary. That is, quick arbitration. Non-limiting examples of parameters that are well known to those skilled in the art and affect the properties of the polymer latex during polymerization, such as polymerization temperature, stirring speed of the polymerization mixture, molecular program of reactants such as emulsifiers and initiators, or during polymerization There is infusion of one or several other polymer latexes.

The present invention also relates to a device for monitoring the quality of halogen-containing vinyl polymer latex in a reactor during polymerization.

The device according to the invention consists mainly of a measuring probe located in the reactor, and an optical coupling between the probe and a near infrared spectrophotometer located outside the reactor, the spectrophotometer being scattered light reflected in a spectral band located between 1100 and 2500 nm. Is supplied to a means for capturing and emitting luminescent radiation, and to a computer having an equation in its memory that correlates the intrinsic properties of the latex and the value of the scattered light reflected at the intrinsic wavelength.

This type of measuring probe, known as the NIR probe, is available from your dealer. Optical coupling between the measuring probe and the near-infrared spectrophotometer is advantageously made of optical fiber.

The measurement immersion is located at the bottom of the reactor and moreover on the stirrer and the polymerization is initiated (ie it is located in the passage where it is immersed when the reactor contains the whole reaction charge)

Surveillance measurements performed under these conditions are typical of latex quality.

Probes located in the reactor need to be able to withstand the high pressure developed during the polymerization and the partial vacuum used prior to the polymerization to remove oxygen from the reactor. In addition, the probe is absolutely necessary to prevent leakage of the gas phase monomer.

For this purpose two leak barriers are used: a probe with the best leak barrier, eg a sapphire window on the side of the reactor and a second leak barrier, eg a 0-ring seal on the outside, and It is recommended to keep the inside of the probe under pressure.

This monitoring of pressure can detect failure of the reactor-side barrier as the pressure increases during polymerization (or pressure drop in the exhaust stage) and failure of the outer barrier as the pressure drop.

In order to ensure maximum stability and to be able to detect possible simultaneous failures of the two leak-proof barriers, a probe of monomers such as vinyl chloride can be supplied at the point where the probe enters the polymerization reactor. In simulating the simultaneous failure of these two leak-proof barriers, additional double protection can be provided, i.e. the closure of the stop cock valve, which cuts the optical fiber connected to the measuring probe and ensures leakage of the container branch, In order to additionally ensure the stability of complete leakage prevention, supply the closing device (after removal of the cutting fiber) of the control stopcock valve provided in series to the first stopcock valve.

The apparatus according to the invention can be adapted for monitoring the quality of the halogen-containing vinyl polymer latex of an aqueous emulsion in a polymerization reactor generally used for aqueous emulsion polymerization of such monomers.

These monomers are generally supplied to means for injecting reactants and releasing polymer latex and to jackets for removing heat of polymerization.

An example of the method and apparatus according to the present invention is as follows.

These relate to the homogeneous polymerization of vinyl chloride in aqueous emulsions that produce polyvinyl chloride latex while directly monitoring the change in the average diameter of the polymer particles in the reactor with the total solid content of the polyvinyl chloride latex and the polymerization process.

Measurement of reflectance in the spectral band between 1100 and 2500 nm at wavelengths particularly correlated to these two properties of vinyl chloride homopolymer latex (as described above) begins on the initial charge until the end of the polymerization and degassing of the residual vinyl chloride Every two minutes.

The practice is carried out in a 6, 6 liter laboratory reactor equipped with a conventional stainless steel stirrer with a jacket and paddle blades through which the heat transfer fluid is circulated. Furthermore, the reactor is supplied with a probe for near-infrared (NIR) area measurement mounted vertically through a jacket with measurement windows arranged in a plane on the reactor wall. This probe is located at the bottom of the reactor below the initial charge level. Correlation equations and calculators are incorporated into a computer connected to the spectrophotometer.

Example 1

This example relates to monitoring the total solids content and the average particle diameter during the non-micelic aqueous emulsion polymerization of vinyl chloride to produce a single shaped latex consisting of single crude oil particles having a final average diameter of about 300 nm. Non-micelic aqueous emulsion polymerization refers to a polymerization having a concentration that does not exceed the critical micelle concentration of the emulsifier at any time in the presence of a certain amount of emulsifier.

2675 g of demineralized water and 0.0075 g of copper sulfate pentahydrate (which is a 7.5 cm 3 solution containing 1 g / l) are continuously injected into the reactor at room temperature. Shut down the reactor and operate the stirrer at 225 rpm. The temperature of the reactor is raised to 30 ° C. and once it is stable, the vacuum is doubled (180 mm absolute mercury), and between the two operations, the reactor is purged with industrial nitrogen at a pressure of 600 mm mercury absolute. Inject 2180 g of vinyl chloride, then gradually raise the temperature of the reactor contents to 51 ° C. and immediately upon reaching 51 ° C., inject 1.30 g of ammonium persulfate, which is a 26 cm 3 solution containing 50 g / l. do. After 6 minutes, 2.16 g of ammonia (which is a solution of 6 cm 3) containing 135 g / l is injected, which is considered to be the zero time t0 of polymerization.

21.8 g of myristic acid is gradually injected (in ammonium form) between t0 + 0 hours 30 minutes and t0 + 4 hours 15 minutes (this is a 242 cm3 solution containing 90 g / kg of myristic acid)

After the pressure drop of 2 Baha the temperature is raised to 80 ° C. The stirring speed is reduced to 50 rpm and the residual vinyl chloride is degassed during boiling and removed by consumption.

Samples of polyvinyl chloride latex are taken starting at t0 + 0 hours 30 minutes at regular intervals of approximately 30 minutes, while monitoring the values obtained by reflectance measurements. Degassed and consumed during boiling from the sample taken to liberate the residual bean chloride. The solid content (using the density method) and the average particle diameter are measured on these samples using the photosettling method.

The total solid content of the monitored latex, expressed in%, is indicated in the cell coordinates in the accompanying Figure. The average diameter of the particles, expressed in micrometers (µm), is shown in ordinates in FIG. 2 attached. The time, expressed as minutes, starting with t0, is shown in abscissa in Figures 1 and 2.

In these figures, the open forward direction corresponds to the entire circumference of the measurements made every two minutes according to the invention and every 30 minutes with the blanks taken during polymerization.

Example 2

This example is directed to monitoring the total solids content and average particle diameter during the non-micelle type inoculated aqueous emulsion polymerization of vinyl chloride to produce a monolithic latex that constitutes a single type of particle having a final average diameter of about 600 nm. It is about.

2520 g of water, 0.0070 g of copper sulfate pentahydrate (which is a 7 g solution containing 1 g / l) and 295 g of polyvinyl chloride in the form of latex prepared in Example 1 are continuously injected into the reactor. Close the reactor and start the stirrer. From this moment, the process of Example 1 is repeated throughout, except that the following amounts of components (in g) are used.

Vinyl Chloride: 1975.00

Ammonium Persulfate: 0.70

Ammonium: 2.00

Myristic acid

(Salt form): 11.80

As in Example 1, the value of reflectance at the above-mentioned wavelength is measured every two minutes through a direct probe in an aqueous emulsion, and furthermore, a latex sample is taken regularly every 20 minutes, after degassing, and analyzed by monitoring.

The measurement results were repeated in FIGS. 3 and 4, where the abscissa represents the time calculated from t0, expressed in minutes. The total solid loss of the monitored latex, expressed in%, is shown in ordinates in FIG. 3 and the mean particle diameter in μm is shown in FIG.

Comparing the results shown in FIGS. 1 to 4 demonstrates the reliability and reproducibility of the method for monitoring the quality of the latex according to the invention.

Claims (10)

A method of monitoring the quality of a halogen-containing vinyl polymer latex during radical polymerization of a halogen-containing vinyl monomer of an aqueous emulsion, wherein the luminescent radiation is emitted to the aqueous emulsion and the polymer of the latex in a spectral band located between 1100 and 2500 nm. The scattered light reflected by the particles is captured and transmitted by a near-infrared spectrophotometer, and the scattered light having a correlation with the intrinsic properties of the latex is measured and measured by reflecting the intrinsic wavelength located in the spectral band and stored in memory. And injecting the calculated value into the memory and calculating the monitored uniqueness. The method of claim 1, wherein monitoring of the halogen-containing vinyl polymer latex is carried out on an aqueous emulsion sample taken from the reactor during the polymerization. The method according to claim 1, wherein the latex monitoring is carried out in an aqueous emulsion directly in the polymerization reactor. The method according to any one of claims 1 to 3, which is used for monitoring the polymer quality of the halogen-containing vinyl monomer selected from vinyl chloride, vinylidene chloride and vinylidene fluoride. 5. The method of claim 4, wherein the polymer of halogen-containing vinyl monomer is selected from vinyl chloride homopolymer, vinylladen chloride copolymer and vinylidene fluoride homopolymer and copolymer. The monitoring method according to any one of claims 1 to 5, which is used for radical polymerization of an aqueous emulsion in the presence of an emulsifier and a water-soluble radical initiator. A device for monitoring halogen-containing vinyl polymer latex in a reactor during aqueous emulsion polymerization, comprising a measuring probe located in the reactor and an optical coupling between the probe and a near-infrared spectrophotometer located outside the reactor, The spectrophotometer is supplied to a means for capturing scattered light reflected in a spectral band located between 1100 and 2500 nm and emitting emission radiation, and formulating an interrelation between the property of latex and the value of scattered light reflected at an intrinsic wavelength. Said device being supplied to a computer having in memory. 8. The apparatus of claim 7, wherein an optical coupling between the measurement probe and the near-infrared spectrophotometer is produced by the optical fiber. The device of claim 7 or 8, wherein the probe is located at the bottom of the reactor above the stirrer. 10. The apparatus of any of claims 7-9, wherein the probe is supplied with a first leak barrier on the side of the reactor and a second leak barrier on the outside and the inside of the probe is maintained under a predetermined pressure of inert gas.