GB1588467A - Method of utilizing an apparatus for the production of coagulated polymer latex - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO A METHOD UTILIZING AN APPARATUS FOR THE PRODUCTION OF COAGULATED POLYMER LATEX (71) We, KANEGAFUCHI KAGAKU Ko GYO KABUSHIKI KAISHA, a Japanese Com- pany of 3, 3-chome, Nakanoshima, Kita-ku, Osaka, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method of utilizing an apparatus for the production of coagulated polymer latex.

High molecular weight polymeric material, contained in a polymer latex obtained by an emulsion polymerization or by a suspension polymerization is usually recovered as a solid resinous product, mixed with polymer particles of various sizes. The procedure generally followed is that the polymer latex is coagulated by adding an aqueous solution of a suitable coagulating agent such as an inorganic salt or acid, to the latex or conversely, adding the latex to the solution, where-upon the coagulated latex is converted into slurry by heat treatment; then dehydration and drying are carried out. The result of such a process is however to form particles of irregular shape and size and the particle size distribution of the resultant powder becomes so broad that the powder contains too high a proportion of fine particles. This results in many other difficulties during the recovery of polymer from the latex. For example dusting of such fine particles leads to a significant loss of resin during processing and the fine particles further tend to cause frequent interruption of operations by blocking passages of the processing equipment. Furthermore there is often considerable contamination of the environment in the operating room by the airborne powder leading to a danger of explosion as the powder content of the atmosphere increases.

At the present time it is not possible to obtain a polymer powder having large bulk density by conventional procedures and in consequence the expense of packaging storage and transportation are inevitably increased. Moreover, since the latex coagulated by conventional procedures is inferior in dehydrative, drying, fluidity and anti-blocking properties, it has been necessary to provide expensive apparatus for finishing the latex coagulate during dehydration and drying.

In our British Patent No: 1,516,476 there is described and claimed a method for the production of coagulated synthetic polymer latex capable of being recovered as a resinous powder, which method comprises a) dispersing said latex of a resinous polymer obtained by an emulsion or a suspension polymerization whose concentration of solid matter is 15 to 50 weight % as a spray of substantially spherical liquid drops whose diameters are 5 microns to 5 millimeters into a coagulating atmosphere containing a coagulating gas and/or a liquid coagulating spray each of which has the ability to coagulate said spray of liquid drops of the polymer latex, b) coagulating said drops in said atmosphere to form particles having a substantially spherical configuration, c) allowing said particles to fall into a liquid recovery medium, formed from an aqueous medium or an organic solvent in which the particles retain their substantially spherical configuration, and d) recovering the so formed particles therefrom. An apparatus for use therein is also disclosed and claimed.

According to the present invention, there is provided a method of utilizing an apparatus for the production of a coagulated polymer latex in an apparatus comprising means for dispersing said latex in a spray of droplets, means for generating and maintaining a coagulating atmosphere, and a receiving container which method comprises: dispersing a polymer latex prepared by emulsion or suspension polymerization as a spray of droplets coagulating said droplets during passage thereof through said atmosphere, receiving said particles in a liquid recovery medium which is chemically distinct from said coagulating atmosphere, in said container and recovering the so formed particles therefrom.

One embodiment of the present invention relates to a method carried -out in an apparatus for the production of coagulated polymer latex which is particularly applicable to the method of production of coagulated polymer latex set out in out British Patent No: 1,516,476 and for convenience the invention will be described with reference thereto.

The dispersion of the polymer latex may be -effected by a high pressure nozzle or a two fluid nozzle or using any other suitable device such as a rotating disc. The drops so formed form substantially spherical shapes quickly by action of surface tension and are dispersed into an atmosphere (hereafter referred to as the "coagulating atmosphere") containing a gas (hereafter, referred to as the coagulating gas) such as hydrogen chloride, which has an ability to coagulate the liquid drops of the polymer latex such 'that 'they ;retain their natural configuration ie: nearly spherical. Alternatively the drops may be dispersed into a coagulating atmosphere, -containing a spray of a solution hereafter referred to as a coagulating spray), of a compound having an ability to coagulate the liquid drops of the polymer latex. Such a coagulating spray may be sodium chloride fed into the coagulating atmosphere with or without said coagulating gas, as super fine droplets using any suitable super fine droplet generator such as a spray gun, an ultra-sonic nozzle, a high-pressure nozzle or a high frequency electric droplet generator, said coagulating spray may be fed from the top of a coagulating chamber or from the upper side-wall of the chamber, so as to make liquid drops of the polymer latex which are intimately in contact with the coagulating gas and/or with the coagulating spray contained in the said coagulating atmosphere.

This allows the liquid latex drops to absorb the coagulating gas and/or the compound having an ability to coagulate the polymer latex contained in the coagulating spray sufficiently to stiffen them into coagulated particles which can retain their original spherical configuration acquired upon the forming of drops in the coagulating atmosphere, even after the falling into a liquid recovery medium. The liquid recovery medium may be an aqueous organic solventj situated at the lower portion of the chamber.

The polymer particles which have sufficiently coagulated while falling downwardly through the chamber are therefore received in the liquid recovery medium. On entering the medium the particles retain their sphere cal diameter and the resultant polymer parti- cles have a distribution almost equal to the diameter of each liquid drop produced on dispersion of the polymer latex.

In order to obtain polymer particles of coagulated latex which have sufficient stiffness during the coagulation process such that they are not deformed on impact with the liquid recovery medium it is of course necessary to adjust those conditions properly, Thus, the coagulating agent, the amount of the coagulating agent to be absorbed by the unit volume of liquid drops of the polymer latex being coagulated, the mean diameter of the liquid drops, the particle size distribution, the concentration of solid matter in the liquid drops of the polymer latex, the temperature of polymer latex and the temperature of coagulating atmosphere, are all parameters which must be correctly adjusted in the apparatus used in the invention. In particular the amount of coagulating agent absorbed into the coagulated particles should be greater than the amount required for minimun coagulation. The amount is mainly determined by the concentration of the coagulating agent in the coagulating atmosphere and the length (height) of the chamber containing the coagulating atmosphere.

When a rotating disc is used for dispersion, the desired mean diameter of liquid drops can be obtained by the regulation of the feed ratio of the polymer latex and the speed of revolution of the disc. When a high pressure nozzle is used for dispersion the desired mean diameter of the liquid drops can be realized by the selection of a nozzle orifice of the correct diameter and the spraying pressure. When a two-fluid nozzle is utilized, desired means particle size can be realised by selecting a feed ratio of the polymer latex and the flow rate of the gaseous component such as air or nitrogen. Further, a combination of at least two types of spray devices makes it possible to obtain a spray having any,desired particle size distribution.' The temperature of operation of the apparatus is preferably within the range of 0 C to 120 C whereby the liquid drops of the polymer latex are held within the range of 0'Cto 100 C.

Furthermore, the operating pressure of the chamber accommodating the coagulating atmosphere should be between 50 tor and 2 atm abs. Thus, if any possibility of boiling the liquid drops of the polymer latex or the liquid recovery medium by virtue of their boiling points the operating pressure may be raised accordingly.

In the present invention, it is desirable to provide a third liquid as a sealing liquid; to prevent the direct contact of the aqueous recovery medium with the coagulating atmosphere. The third liquid has a poor reactivity both to the coagulating atmosphere and to the aqueous medium, and negligible solubility and affinity to the both phases. Moreover having lower specific gravity than that of aqueous medium, at the operating temperature and pressure it will float thereon. Examples are hexane, heptane, octane, nonanej decane, and mixtures thereof.

After an extensive study on the apparatus for the production of coagulated polymer latex based upon the method of production of the coagulated polymer latex explained above, the present inventors have found that the particular apparatus shown by way of illustration in the following description, is most advantageous.

In the accompanying drawings Figure 1 shows a diagrammatic vertical cross-section of an apparatus according to the invention, and Figure 2 shows a diagrammatic vertical cross-section of another apparatus of the invention.

Figure 1 shows an apparatus for the production of coagulated polymer latex, comprising a device 2, for dispersing the polymer latex as liquid drops. The device 2 has a single nozzle, at least two types of high pressure or low-pressure nozzles or a centrifugal disc, provided at the top or in the side wall (not shown) of a coagulating chamber.

An inlet 5 provides a coagulating atmosphere 4 for coagulating the said liquid drops of the polymer latex, by feeding a coagulating gas or spraying a solution 3 containing a coagulating agent as fine particles into the coagulating chamber 6. Consequently the liquid drops of the polymer latex coagulate during their downward fall through the coagulating atmosphere until they reach a liquid recovery medium 7, situated at the bottom of the chamber.

At this point the liquid drops are sufficiently stiff to retain their spherical configuration almost completely without any deformation on impact with the liquid recovery medium. A receiver for holding the said liquid medium is provided at the bottom of the chamber or at the side-wall thereof and an outlet 9 is provided to remove the polymer particles of the coagulated latex from the receiver.

In figure 2, an apparatus for use in the present invention is additionally provided with means for providing a sealing liquid 10 (for example, hexane) between the coagulating atmosphere 4 and the recovering aqueous medium 7 in the receiver 8 in order to prevent the direct contact of the coagulating atmosphere with the aqueous recovery medium 7. The sealing liquid 10 has very low reactivity with the medium 7 and the atmosphere 4 at the temperature and at the pressure obtaining. Further the specific gravity of the sealing liquid 10 is lower than that of the aqueous recovery medium 7.

Additional washing device 12 is also provided for the washing down of the coagulated latex adhering at the inner wall of the coagulating chamber 6, by washing it out with a liquid 11 flowing down the inner wall of the chamber from the top thereof. The liquid 11 may conveniently be the same as the aqueous recovery liquid 7. Circulation of said liquid may then be repeatedly effected by a device 13.

An additional separation device 14 may also be provided for separation the polymer particles of the coagulated latex from the liquid recovery medium.

Further, the apparatus can be provided with an inlet 15 for the addition of components for maintaining the composition of the recovering liquid medium at a constant value. Such a solution may comprise a regulating agent for pH value, a stabilizer, or a coagulating agent.

The apparatus may also have an inlet 17 for supplying a gas 16 at a controlled temperature to retain the temperature of the coagulating atmosphere at a desired value ie: in the range of 0 C. to 120 C.

Similarly an inlet 19 may be provided to supply a diluent 18 to assist in the coagulation of the liquid drops of the polymer latex under the most desirable conditions by supplying a diluent 18 (for example water) as a super fine spray, thus controlling the concentration of coagulating agent in the coagulating atmosphere.

Figure 2 also shows a coil 20 for heating or cooling the liquid recovery medium 7 in the receiver 8 to make it possible to treat the coagulated polymer particles at a desired temperature within the range of 0 C. to 120 C. Further, a solution containing a desired amount of a coagulating agent may be added to the liquid recovery medium 7 in the receiver 8 via an inlet 21. Said receiver 8 may also be provided with an agitator, a bubbler or a circulation pump shown diagrammatically at 22 in order to prevent the coalesence of the polymer particles of the coagulated latex into a block in the receiver 8.

A third substance such as dye or stiffening agent, may be added to the apparatus by spraying a solution 23 containing the third substance via inlet 24.

Finally the apparatuas for use in the present invention can have an additional device 26 to prevent the blockage of the nozzle end 2.

Claims (12)

WE MAKE NO CLAIM TO ANY THING CLAIMED IN BRITISH PATENT NO: 1516476 ALLUDED TO HEREINBE FORE, BUT SUBJECT TO THE FORE GOING DISCLAIMER: WHAT WE CLAIM IS:-

1. A method for the production of a coagulated polymer latex in an apparatus comprising means for dispersing said latex in a spray of droplets, means for generating and maintaining a coagulating atmosphere, and a receiving container which method comprises: dispersing a polymer latex prepared by emulsion or suspension polymerization as a spray of droplets, coagulating said droplets during passage thereof through said atmosphere, receiving said particles in-a liquid recovery medium which is chemically distinct from said coagulating atmosphere, in said container and recovering the so formed particles therefrom.

2. A method as claimed in claim 1 wherein the dispersing means includes a nozzle.

3. A method as claimed in claim 1 or 2 wherein the dispersion means includes a rotating disc.

4. A method as claimed in any one of claims 1 to 3 wherein said means for maintaining the coagulating atmosphere includes a coagulating chamber and wherein -the dispersing means is located at or near the top or-a side wall of said chamber.

5. A method as claimed in any one of claims 1 to 4 which includes providing a -sealing liquid between the coagulating atmo sphere .and the liquid recovery medium in the receiver, wherein the sealing liquid has a low solubility in, affinity for, or reactivity to, both said atmosphere and said recovery medium at the temperature and pressure obtaining and wherein said sealing liquid has a specific gravity lower than that of the liquid recovery medium.

6. A ,method as claimed in either of claims 4 or 5 which comprises providing a downward liquid flow on the inner surface of the coagulating chamber from the top thereof thereby to wash off any coagulated latex adhering to said inner surface.

7. A method as claimed in any one of claims 1 to 6 which comprises mechanically removing a slurry of the polymer particles of -the coagulated latex from said receiver.

8. A method as claimed in any one of claims 1 to 7 which includes supplying gas at a controlled temperature into the coagulating chamber

9. A method as claimed in any one of claims 1 to 8 which comprises supplying a diluent for the coagulating agent contained in the coagulating atmosphere by spraying said diluent into the chamber to control thereby the concentration of the coagulating agent in the coagulating atmosphere.

10. A method as claimed in any one of claims 7 to 9 wherein the recovery means includes means ,for -heating or cooling the liquid medium in the receiver thereby to control the temperature thereof.

11. A method as claimed in any preceding claim comprising supplying a solution .containing a coagulating agent to the "liquid recovery medium in the receiver.

12. A method as claimed in any one of claims 1 to 11 comprising agitating the liquid recovery medium held in the receiver, to prevent the -coalesence of polymer particles collected therein.