GB1602137A

GB1602137A - Process for the production of a powder of plyvinyl-chloride or a vinylchloride copolymerisate suitable for producing plastisols

Info

Publication number: GB1602137A
Application number: GB2552478A
Authority: GB
Original assignee: Niro Atomizer AS
Current assignee: GEA Process Engineering AS
Priority date: 1977-08-31
Filing date: 1978-05-31
Publication date: 1981-11-04

Description

(54) IMPROVEMENTS IN AND RELATING TO A PROCESS FOR THE PRODUCTION OF A POWDER OF POLYVINYLCHLORIDE OR A VINYLCHLORIDE COPOLYMERISATE SUITABLE FOR PRODUCING PLASTISOLS (71) We, A/S NIRO ATOMIZER, a company organized under the laws of Denmark, of No. 305 Gladsaxevej, 2860 Sdborg, Denmark, 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:- British Patent Specification No. 1,538,351 relates to a process for the production of a powder of polyvinylchloride or a vinylchloride copolymerisate suitable for the production of plastisols the process consisting in atomizing, via at least one twofluid nozzle, an aqueous dispersion of polyvinylchloride or a vinylchloride copolymerisate, if desired containing emulsifier and other auxiliary agents, into a substantially uniform flow of drying air within a drying tower, so that said process is carried out substantially as a co-current process, and grinding at least the coarsest fraction of the resulting powder, characterised in providing within said drying tower a controlled rotary motion of the particles produced by atomization and of the drying air about the longitudinal axis of said drying tower by injecting, via at least one injector member, pressurised air in a direction which, projected onto a plane at right angles to the longitudinal axis of the drying tower, forms an angle with a line through the centre of the drying tower and the injector outlet orifice, also projected onto said plane.

It has now turned out that the special desired effect which is achieved by providing the controlled rotary motion of the atomized particles of the dispersion and of the drying air around the longitudinal axis of the drying tower, which effect is explained in detail in the above patent specification, is not only achieved when the atomization is performed by means of twofluid nozzles, but also when the atomization is performed by means of pressure nozzles.

The term "pressure nozzle" is here used covering every nozzle which, without use of pressurized air, is able to atomize the dispersions in question when these are pumped to the nozzle under a suitable pressure. In contradiction thereto a twofluid nozzle requires a substantial supply of pressurized air to achieve the atomization.

Accordingly, the present invention relates to a modification of the process according to Claim 1 of Patent Specification No.

1,538,351 as specified above, which modification is that the aqueous dispersion is atomized by means of at least one pressure nozzle or by means of a combination of at least one pressure nozzle and at least one two-fluid nozzle, and the controlled rotary motion is provided either by injecting air via at least one injector member in the manner specified in the aforesaid claim, or by atomizing the dispersion through the pressure nozzle or at least one of the pressure nozzles in a direction which, projected onto a plane at right angles to the longitudinal axis of the drying tower forms an angle with a line through the center of the drying tower and the outlet orifices of said pressure nozzle, also projected onto said plane, or by using both these measures.

Accordingly, it is thus possible to provide the desired rotary motion solely by injecting air in the specified direction, while the pressure nozzles are directed so that they do not contribute to the achievement of any rotation.

However, the desired rotation can also be provided solely by a suitable adjustment of the pressure nozzles, although the effect on the rotation by injection of a certain quantity of dispersion in a certain injection direction by pressure nozzles will be substantially less than when two-fluid nozzles are used, for which reason either a greater number of pressure nozzles will be set in positions in which they enhance the rotary motion, or the nozzles will be adjusted in such a direction that their centre lines, projected onto a plane at right angles to the longitudinal axis of the drying tower, forms angles with lines through the centre of the drying tower and the outlets of the respective nozzles, also projected onto said plane, which are greater than they would have been if two-fluid nozzles had been used.

To achieve a good control of the rotation it is convenient to use an air injection in the direction defined in Claim 1 and at the same time to direct the pressure nozzles in such a way that the injection of atomized dispersion takes place in the direction defined in Claim 1.

Air injection can take place through a plain pipe but can, of course, also take place through a two-fluid nozzle, which means that a combination of pressure nozzles and two-fluid nozzles may be used in the process. In this last-mentioned embodiment especially good possibilities exist for obtaining such a grain size distribution which gives a particularly low viscosity of the plastisol, c.f. the main patent, page 3, lines 14 to 22.

Those advantages which the method according to the invention have in common with the method according to the main patent are the possibility of obtaining a powder which gives a plastisol having low and stable viscosity and at the same time obtaining a good heat economy by the drying of the dispersion and, moreover, to obtain a relatively easy grinding of the spray-dried powder. Moreover, a substantially greater flexibility for the process is obtained compared with drying methods in which no rotary motion is used in the drying tower. Besides, the method of the present invention has the advantage that it makes it possible to perform the drying process using substantially less energy, because the energy which is required for atomizing the dispersion by means of pressure nozzles is substantially smaller than the energy that is necessary when the atomization is performed by two-fluid nozzles, and because by using pressure nozzles a decrease in heat economy of the drying process caused by the injection of pressurized air through the two-fluid nozzles is avoided.

To obtain an improved heat economy a preferred embodiment of the method is characterized in that the temperature of the drying air when introduced into the drying tower is above 140"C. Preferably, the drying air is introduced at a temperature between 180 and 280"C, i.e. the same temperature range as when the atomization is performed by means of two-fluid nozzles.

In a preferred embodiment of the process in which use is made of a plurality of pressure nozzles, the directions of at least some of the pressure nozzles are adjusted so that the angle which is formed between the centre line of each nozzle and a line through the centre of the drying tower and the opening of the nozzle, projected onto a plane at right angles to the longitudinal axis of the drying tower, is different for each pressure nozzle or for groups of pressure nozzles. By this embodiment it is possible to obtain a very accurate control of the rotation.

When a drying tower having a great number of pressure nozzles is used, some of the pressure nozzles are preferably adjusted that the centre line of each forms an angle with a line through the centre of the drying tower and the opening of the nozzle, projected onto a plane at right angles to the longitudinal axis of the drying tower, while other pressure nozzles are adjusted so that the projected centre line of each of them passes through the centre of the tower, because thereby a more simple adjustment of the rotation is obtained than would be possible if a uniform adjustment of all pressure nozzles had been performed.

The modified process according to the invention is further illustrated with reference to the drawings, wherein:- Fig. 1 very diagrammatically and partly in section shows an embodiment of a drying tower, said section being taken on line 1-I in Fig. 2; Fig. 2 shows diagrammatically a section of the drying tower shown in Fig. 1, taken on line 11-11; Fig. 3 shows a single nozzle lever; Fig. 4 shows diagrammatically the upper portion of the drying tower, shown in Fig. 1, viewed on the slant from below, and displaying only one nozzle lever viewed from the rear, so that the angle between the nozzle tip and the vertical centre line, also called the longitudinal axis, of the drying tower is set off, Fig. 5 shows diagrammatically and partly in section another embodiment of a drying tower, and Fig. 6 shows diagrammatically a sectional view of the drying tower shown in Fig. 5, taken on line VI-VI.

In Figs. 1, 2 and 4, 1 is the drying tower as such. In the upper portion thereof hot drying air is supplied through pipe 2, and penetrates through one or more distributor plates 3 into the upper part of the drying chamber of the drying tower 1.

Pressure nozzle levers 4 and 5 are introduced into the upper portion of the drying tower. In the embodiment shown, as will appear from Fig. 1 and 2, these nozzle levers belong to two groups (a and b), of which the nozzle levers of group a are so set that centre line 6 of each nozzle, projected onto a plane at right angles to the longitudinal axis of the tower, forms an angle a with line 7 through the centre of the drying tower and the outlet orifice of the nozzle, thereby providing a rotary motion within said drying tower.

The nozzle levers of the other group bare, in the embodiment shown, directed horizontally towards the longitudinal axis or centre line of the tower. These lastmentioned nozzles do not contribute to the rotary or helical motion within the drying tower.

The outer ends of the nozzle levers are each connected with sources of latex under pressure (not shown).

As mentioned, Figures 1 and 2 show two groups each comprising uniformly set nozzle levers, and with such an arrangement excellent results have been achieved, but it is also possible to perform the process according to the invention with all the levers set uniformly, or with a further differentiated setting of these, so that the drying tower operates with three or more groups of nozzle levers, the setting of which may vary both as far as angle ,P, (or , ,') or angle y are concerned.

The major part of the powder produced by the process is discharged from the drying tower together with the drying gas through pipe 8, whereas the remainder is discharged from the bottom of the drying tower through pipe 9. The mixture of drying gas and powder from 8 is expediently directed to a cyclone or filtering unit, not shown, together with powder from pipe 9, where the product is separated from the gas.

As will appear clearly from Fig. 3, the centre line of the nozzle tip forms, in the embodiment illustrated, an angle a with the nozzle lever, which affords the special advantage that angle y, and consequently also angle , can be changed just be turning the nozzle lever on its longitudinal axis, as illustrated in Fig. 4. For the purpose of clearness this latter figures shows only a single nozzle lever belonging to group a.

The desired setting of a nozzle tip can, however, also be obtained even if the nozzle tip forms no angle with the axis of the nozzle lever.

In Figs. 5 and 6, references 11, 12 and are elements similar to those referred to in Figs. I and 2 as 1, 2 and 3, respectively.

This embodiment comprises a plurality of pressure nozzles, the nozzle tips of which are straight extensions of the nozzle levers, and centre line 16 of which, when projected onto a plane at right angles to the longitudinal axis 15 of tiXe drying tower, coincide with line 17 through the centre of the tower and the nozzle outlet orifice. Thus the pressure nozzles do not contribute to the establishment of any rotary motion.

Installed above nozzle level there is a pipe 18, the centre line of which forms an angle d' with a line from the pipe outlet at a right angles to the longitudinal axis of the tower.

Consequently, when injecting air through pipe 18, it is possible to achieve the desired rotation.

The process according to the invention will be further illustrated by means of comparison examples I and 2 and example 1 given below.

In the following examples use is made of polyvinyl chloride latex of another origin (from another supplier) than the polyvinylchloride latex used in the examples of British application 16887/77 (Serial No.

1538351). The solid matter content was approximately 45% by weight.

The viscosity at high shearing gradient was determined on a Burrell-Severs viscometer, A-120 (ASTM-D1823).

Comparison Example 1 Polyvinylchloride latex was dried in a pilot plant drying tower having a cylindrical diameter of 1.7 m and a height of the cylindrical part of 8 m. The atomization was performed by means of a single two-fluid nozzle mounted centrally and directed vertically downwards. The weight ratio of pressurized air to latex was 1.2:1. The pressure of the pressurized air was 3.2 kg/cm2 gauge. The tower had a perforated ceiling air distributor.

The drying air and the atomized latex were caused to perform a rotating motion by using a similar construction to that illustrated in Patent Specification No.

1,538,351 Figs. 5 and 6, pressurized air being injected through two pipes, both fixed in a similar way as the pipe 18 in Figs. 5 and 6.

A test was performed using drying air at an inlet temperature of 220"C. The outlet temperature of the drying air was 60"C.

The resulting product after grinding had a screen residue i.e. particles larger than 63 y of 0.8% by weight. The viscosity of a plastisol prepared from the product was measured to 4 100 cP (centipoise).

Example I The same polyvinylchloride latex and the same drying tower were used as in comparison example 1. The atomization was performed through a single high pressure nozzle. An atomization pressure of 160 kg/cm2 gauge was used. The drying air was rotated as in comparison example 1.

One test was performed with drying air at an inlet temperature of 220"C and an outlet temperature of 60"C. The resulting product after grinding had a screen residue of 0.8% by weight and a plastisol viscosity (the plastisol having the same solid content as the plastisol manufactured according to comparison example 1) of 4 700 cP.

Comparison Example 2 Polyvinylchloride latex of the same type as used in the example above was dried in a conventional spray dryer having rotary atomizer wheels. The inlet and outlet temperature of the drying air were 220"C and 60"C, respectively. The resulting product was analysed as above. The plastisol viscosity (at same solid content as in comparison example 1) was 9 200 cP and the screen residue after grinding 0.1% by weight.

The results obtained in the above comparison example 1, which illustrates the method according to the main patent, and in the above Example 1 which illustrates the modified process according to the invention are both satisfactory because a suitable low viscosity and an acceptable screen residue are obtained in both cases. This shows that the desired results which are obtained by using the rotary motion are not restricted to those cases in which the atomization takes place by means of two-fluid nozzles, but can also be achieved in connection with pressure nozzle atomization.

WHAT WE CLAIM IS: 1. The process according to Claim 1 of Patent Specification No. 1,538,351 for the production of a powder of polyvinylchloride or of a vinylchloride copolymerisate suitable for plastisols, modified in that the aqueous dispersion is atomized by means of at least one pressure nozzle or by means of a combination of at least one pressure nozzle and at least one two-fluid nozzle, and the controlled rotary motion is provided either by injecting air via at least one injector member in the manner specified in the aforesaid claim, or by atomizing the dispersion through the pressure nozzle or at least one of the pressure nozzles in a direction which, projected onto a plane at right angles to the longitudinal axis of the drying tower forms an angle with a line through the centre of the drying tower and the outlet orifice of said pressure nozzle, also projected onto said plane, or by using both these measures.

2. A process as claimed in Claim 1, in which the temperature of the drying air, when introduced into the drying tower, is above 140"C.

3. A process as claimed in Claim 2, in which the temperature of the drying air, when introduced into the drying tower, is between 1800 and 280"C.

4. A process as claimed in any of the preceding claims, in which a plurality of pressure nozzles is used, and the directions of at least some of the pressure nozzles are so adjusted that the angle formed between the centre line of each nozzle and a line through the centre of the drying tower and the orifice of the nozzle, projected onto a plane at right angles to the longitudinal axis of the tower, is different for the nozzles taken individually or in groups.

5. A process as claimed in Claim 4, in which some of the pressure nozzles are so adjusted that the centre line of each forms an angle with a line through the centre of the drying tower and the orifice of the nozzle, projected onto a plane at right angles to the longitudinal axis of the tower, whereas other pressure nozzles are so directed that the projected centre line of each passes through the centre of the drying tower.

6. A process for the production of powder according to Claim I and substantially as described with reference to Example 1.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. nozzle. An atomization pressure of 160 kg/cm2 gauge was used. The drying air was rotated as in comparison example 1. One test was performed with drying air at an inlet temperature of 220"C and an outlet temperature of 60"C. The resulting product after grinding had a screen residue of 0.8% by weight and a plastisol viscosity (the plastisol having the same solid content as the plastisol manufactured according to comparison example 1) of 4 700 cP. Comparison Example 2 Polyvinylchloride latex of the same type as used in the example above was dried in a conventional spray dryer having rotary atomizer wheels. The inlet and outlet temperature of the drying air were 220"C and 60"C, respectively. The resulting product was analysed as above. The plastisol viscosity (at same solid content as in comparison example 1) was 9 200 cP and the screen residue after grinding 0.1% by weight. The results obtained in the above comparison example 1, which illustrates the method according to the main patent, and in the above Example 1 which illustrates the modified process according to the invention are both satisfactory because a suitable low viscosity and an acceptable screen residue are obtained in both cases. This shows that the desired results which are obtained by using the rotary motion are not restricted to those cases in which the atomization takes place by means of two-fluid nozzles, but can also be achieved in connection with pressure nozzle atomization. WHAT WE CLAIM IS:

1. The process according to Claim 1 of Patent Specification No. 1,538,351 for the production of a powder of polyvinylchloride or of a vinylchloride copolymerisate suitable for plastisols, modified in that the aqueous dispersion is atomized by means of at least one pressure nozzle or by means of a combination of at least one pressure nozzle and at least one two-fluid nozzle, and the controlled rotary motion is provided either by injecting air via at least one injector member in the manner specified in the aforesaid claim, or by atomizing the dispersion through the pressure nozzle or at least one of the pressure nozzles in a direction which, projected onto a plane at right angles to the longitudinal axis of the drying tower forms an angle with a line through the centre of the drying tower and the outlet orifice of said pressure nozzle, also projected onto said plane, or by using both these measures.