PROCESS FOR THE PRODUCTION OF LUBRICATING, STABILISING ADDITIVE MIXTURES IN THE FORM OF POWDER-FREE FLAKES

Abstract: A process for producing lubricating, stabilising additive mixtures in the form of powder-free flakes with good flowability and dispersibility characteristics comprises com­ pressing and heating a pulverulent mixture of additives to obtain a dense, ductile mix which is then extruded, cold or hot-rolled, then reduced to flakes, and finally blown counter-­ currently in order to separate the powder from the flakes. A plant for implementing the process comprises a screw extruder (3, 4, 5) provided with successive heating elements (T₁, T₂, T₃, T₄) operating at increasing temperatures, a cold roller mill (7) arranged to reduce into strips (66) the filaments (6) produced by the extruder (3, 4, 5), a device (8) for crushing the strips (66) into flakes, and a powder-separation cyclone (11) which eliminates the powder from the finished product.

Description: PROCESS AND PLANT FOR THE PRODUCTION OF LUBRICATING, STABILISING ADDITIVE MIXTURES IN THE FORM OF POWDER-FtEE FLAKES WITH GOOD FLOWABILITY AND DISPERSIBILITY CHARACTERISTICS Halogenated vinyl p-lyxers in general and polyvinyl chloride - PVC in particular are known to be widely used for the production of ehd EMI1.1 EMI1.2 <tb> prefabricated <SEP> components, <SEP> <tb> for example in the form of sheets, panels, EMI1.3 EMI1.4 <tb> sections <SEP> for <SEP> windows <SEP> <tb> roll shutters and others, which are usually exposed ts tospheric agents and light during their use. It is also known that in order to prevent degradation of the polymer, mixtures ore added to it which comprise stabilising products, nti- oxidant products, products for filtering the ultraviolet rays, lubricant products, and alse pigments if necessary. Because these additives are highly toxic, and because they are often in the form f fine powders which are difficult to handle, the corresponding stabilising mixtures have to be reduced to granules or flakes which together with the absence f powder possess good flowability and dispersibility in the resin for which they are intended. In general, in order to give the stabilising fixtures ne of the aforesaid foras, processes are used which operate on a molten lass having good fluidity, and of which the formulation comprises both the eatable products and the non-meltable products to be processed. Consequently, in order to obtain the required fluidity the ratio of the quantity of meltable products to the quantity of non-meltable products wust be at least 1:4 for products which are of low viscosity in the molten state, and up to at least 1:2 for products which are viscous in the molten state, otherwise if the values are lower the molten mass cannot be worked by known systems. In a first known system, for example that described in Italian patents 762,268 and 788,040, stabilisers which are not eatable below the PVC softening point, for example tribasic Pb sulphate, are dispersed in a molten lass of meltable components, for example neutral Pb stearate, with the possible addition of other low-melting products for making the molten mass fluid. This latter is then transformed in a cold environient, for example by means of spraying, to obtain granules, flakes r or another convenient form. The molten stabilising mixture lass obtained by this process wust be fluid and lovable when hot, and thus said system is suitable only for those formulations in which the ratio of eatable products to non-meltable products is greater than 1:4, u stated. In anther known process, described in Italian patent 803,002, pulverulent stabilising mixtures are mixed with low melting point organic products, such os waxes and esters, by means of rapid mixers. The result is a product in the f.rm of granules of various sizes, of diameter between 0.1 and 10 ma, which have the tendency to aggloberate and are net free from powder. Again, in order to transform the additives into granules, Italian patent 867,139 suggests the use of extruder devices in which the stabilising mixture is compressed under cold conditions in order to force it through a convenient die, for example a perforated plate or drui. It has however been found that the granules obtained by this latter known system have their interior friable, whereas their outer surface is excessively compact, with the result that they are often poorly dispersible, particularly in plasticised PVC. Moreover. said granules have relativelv low flowabilitv and are EMI3.1 therefore difficult to ensile and to EMI3.2 <tb> proporttonl <SEP> <tb> automatically. Again, Italian patent 916,928 in the Mme of the present applicant teaches how to obtain a stabilising mixture granulate possessing good flowability and thus suitable for automatic ensiling without the aid of complex and costly plant, but for certain formulations the presence of finely divided texic powders is not completely eliminated, and these create sone problems especially in those plants without automatic weighing systems. A further known system is that described in Italian patent applica tion 49,948 A/78 which relates to a process for obtaining small flakes of stabilising mixtures by keeping a fluid molten mass agitated with the aid of electrical resistance heaters, and then cooling the product on a belt. This process is also suitable only for certain formulations, and cannot be used in those cases in which the percentage of eatable products is low compared with that of the non-meltable products. A drawback conon to all known processes of this type is that if the eatable products used are not soluble in each ether, it is difficult to keep them mixed in the form of a homogeneous molten muss, and there is thus a strong tendency to generate undesirable stratification. A further limitation of said known processes is the need to use large quantities of meltable components in the addictive formulation, in order to always obtain at one stage of the process a nass which is fluid and flowable under hot conditions. The present patent provides and protects a process and plant by means of which it is possible to obtain flakes of additive mixtures of any formulation, in the presence of very small quantities of oeltable components, the flakes being practically free from powder and possessing good flowability and dispersibility characteristics. In other words, the ratio of meltable products to non-meltable products is no longer important, because according to the invention the component mixtures do not have to be transformed into a mass which under normal conditions is naturally fluid and flowable when hot. In this respect, it has been surprisingly found that if a pulverulent mass containing at least one meltable component in a very small quantity is mixed and compressed simultaneously at a temperature higher than the softening point of said meltable component, it becomes sintered and can be extruded te give a dense or pasty mass which can be easily transformed without generating powder. The process according to the present invention therefore comprises treating the powder mixture in an extruder with screws of variable nitch and having sections temperature-controlled at temperatures EMI4.1 which increase from'downstream EMI4.2 <tb> stO <SEP> up8traRlJ <SEP> <tb> then rolling the extruded product, and crushing the sheet thus obtained. The finial product is collected absolutely free from powder by conveying it in a stream of air through successive cyclone separators, the small quantity of powder recovered being recycled. By this means, according to the process of the invention, flakes of stabilising mixtures are obtained having a size of the order of - few millimetres, which are free from powder, very flowable, and thus easy to store, for example through a pneumatic conveying line. Said flakes have good dispersibility in halogenated vinyl polymers in general. As heretofore stated, the stabilising mixtures can comprise a wide range of formulations, and according to the invention comprise the products of the classes listed hereinafter, obviously mixed to form compositions which depend on their application and on the characteristics required for the corresponding polymer to which they are to be added. A. Non-meltable products such as basic Pb salts, for example the sulphuric, sulphurous, phosphorous, phthalic, maleic and carbonic acid derivatives. B. Partly meltable products such as neutral or basic metal soaps deriving from organic acids with 8 - 24 C atoms, for example Ba or Cd laurates, Ca, Zn. Pb or Mg stearate, dibasic and one basic Pb stearate, Li and Ca hydroxystearate. C. Meltable lubricant products such as synthetic and natural waxes of the stearyl stearate type, glyceryl monostearate, montan wax, paraffin, high-melting point synthetic paraffin, stearyl phthalate. D. Stabilising products in the form of organnetal derivatives of tin and antimony. E. Antioxidants, phenolic derivatives such as bisphenol A: ditertiary butylparacresol EMI5.1 <tb> ;andcalciumnonylphenoland <SEP> <tb> nonylphenates; organic phosphites such as diphenylisodecyl phosphite, stearylpentaerythritolphosphite; organic inhibitors such as pentaerythritol and trimethylolpropane. F. Other products normally used in PVC transformation such as plasticisers, fillers, UV filters and pigments. As stated heretofore, the process is applicable to any stabilising mixture formulation or composition, the only condition being that it comprises at least a small quantity of one of the low-melting products stated under point C of the aforesaid list, in order to obtain said ductile mix. According to the invention, the quantity of low-melting product is at least 3X of the total weight of the stabilising mixture. Correspondingly, the sections of the screw extruder temperature- controlled at different temperatures, in which the stabilising mixtures are compressed and mixed, have temperatures which increase from 500C, to 900C in proximity to the outlet. A particular preferred embodiment of the plant suitable for imple- mending the process of the invention is described hereinafter by way of non-limiting example Figure 1 is a diagrammatic representation of the plant. It comprises o hopper 1 for receiving the stabilising mixture in pulverulent forts, and which can be prepared either at the place of manufacture of the coaponents or immediately upstream of the plant. The hopper 1 comprises a lower discharge screw 2 which feeds the powdered mixture into the chamber of an extruder 3 provided with two side-by-side screws of variable pitch 4, one being right handed and the other left handed, and with a transformation head or die 5 comprising a series of uniformly distributed holes. The various longitudinal portions of the extruder 3 and die 5 are surrounded by respective jackets which contain electrical resistance heaters, indicated by T1, T2, T3, and T4, of which the operating temperatures, which can be adjusted according to the stabilising mixture being processed, increase EMI6.1 <tb> from <SEP> # <SEP> downstream <SEP> ## <SEP> # <SEP> upstream <SEP> to# <SEP> <tb> These temperatures lie between 500C and gO*C, and the speeds of the discharge screw 2 and extrusion screws 4 are also varied according to the mixture being processed. The combined action of the compression, the mixing induced by the screws 4 and the heating means that at the outlet of the extruder 3 the mixture is in the form of a mix which is sufficiently plastic and ductile for subsequent extrusion and rolling. This mix leaves in the form of continuous filaments 6 from the die 5, said filaments 6 then being inserted into an underlying roller mill 7 in which the rollers are cooled and the gap between them can be adjusted. At the outlet of the roller mill 7, rigid sheets 66 are obtained having a thickness of between 0.1 and 2 mm, according to the compo- sition of the mixture, and are then reduced to flakes by means of a toothed-roller crushing device 8. The flakes have a surface area of ap to 15 ma2 and are fed, together with the small powder residues originating from the crushing, to a pneumatic conveying line 9 which is served by a blower 10. The line 9 discharges into a powder-separating cyclone 11, in which the flakes fall freely into an underlying collection silo 12 for the finished product. The air stream which passes through the cyclone 11 in counter-current with the falling path of the flakes separates the fine powder from the flakes and feeds it te a collection vessel 13 under vacuum, and from which the powder can be withdrawn for recycling. The finished product is therefore free from powder, has good flowability and possesses good dispersibility in halogenated vinyl polymers in general, as will be apparent from the examples given hereinafter. The same plant was used for all the examples, and consisted of a BANDERA double-screw extruder Type MBBlO0 with a three-phase 380 V motor, disposed upstream of a BATTAGION roller mill type MCC 150 x 300, with a roller diameter of 150 mm and an average roller temperature of 150C. The crusher was of the usual type. The characteristic data of each example are given hereinafter. EXAMPLE 1 The extruder is fed with the follewing powder mixture (percentages by weight) Tribasic Pb sulphate 25X Dibasic Pb stearate 50% Paraffin of M.P. 70 C 10% Stearin 15X The extruder is driven at 6 r.p.m. with an absorbed current of 10 A. The temperatures in the various sections are T1 - 60 C, T2 " 690C, T3 - 71 C, T I 710C. 4 The hourly production rate was 100 kg/hour. The final product characteristics are: good dispersibility, particle thickness 0.65 ma, apparent density 720 g/l. EXAMPLE 2 The mixture fed to the extruder is as follows (percentages by weight) Dibasic Pb phosphite 60X Ba-Cd stabiliser 20X Calcium stearate 5X RLI05 Paraffin 5X Hydroxystearic acid 5% Stearyl phthalate 5% The extruder is driven at 6 r.p.m. with an absorbed current of 10 A. The temperatures in the various sections are T1 ^ 40 C, T2 = 400C, T3 - 40"C, T4 L 40"C. The hourly production rate was 105 kg/hour. The final product characteristics are: good dispersibility, particle thickness 0.85 mm, apparent density 700 g/l. EXAMPLE 3 The mixture fed to the extruder is as follows (percentages by weight): Barium stearate 63Z Cadmium stearate 252 Bisphenol A 9X Stearyl phthalate 3Z The extruder is driven at 40 r.p.m. with an absorbed current of 25 A. The temperatures in the various sections are T1 " 70 C, T2 = 700C, T a 800C, T - 800C. 3 4 The hourly production rate was 95 kg/hour. The final product characteristics are: good dispersibility, particle thickness 0.65 n, apparent density 450 g/l. EXAMPLE 4 Barium stearate 50Z Neutral Pb stearate 30Z Stearin 12Z Bisphenol A 8Z The extruder is driven at 40 r.p.m. with an absorbed current of 24 A. The temperatures in the various sections are T1 - 50 C, T2 - 530C, T3 s 60 C, T4 - 600C. The hourly production rate was 120 kg/hour. The final product characteristics are: good dispersibility, particle thickness 0.85 mm, apparent density 500 g/l EXAMPLE 5 Cadmium laurate 48X Barium laurate 30X Pentaerythritol 12Z Bisphenol A 7X Stearyl phthalate 3X The extruder is driven at 40 r.p.m. with an absorbed current of 25 A. The temperatures in the various sections are T1 - 700C, T2 = 700C, T3 - 80 C, T4 - 80 C. As can be seen, the melting point, which for Cd laurate is about lOOµC, is never reached. The hourly production rate is 110 kg/hour The final product characteristics are: good dispersibility, particle thickness 0.6 -, apparent density 520 g/l. EXAMPLE 6 The extruder is fed with the following mixture Tribasic Pb sulphate 95X Paraffin of melting point 700C 5X The extruder is driven at 40 r.p.m. with an absorbed current of 20 A. the temperatures in the various sections are T1 G 650C, T2 = 70°C, T3 - 70 C, T4 - 75 C. The final product characteristics are: good dispersibility, particle thickness 0.8 mm, apparent density 950 g/l. EXAMPLE 7 The extruder is fed with the following mixture Sulphate 90X Stearyl stearate 10% The extruder is driven at 40 r.p.m. with an absorbed current of 18 A. The temperatures in the various sections are T1 - 50 C, T2 = 55eC, T3 = 55 C, T4 - 58eC The final product characteristics are: good dispersibility, particle thickness 0.6 mm, apparent density 850 g/l. All the aforesaid obtained products have a dispersibility such that the prefabricated PVC component to which they are added has no EMI11.1 EMI11.2 <tb> "dimple" <SEP> <tb> defects noticeable at a magnification of 10 times. The invention is not limited only to the aforesaid embodiments, and modifications and improvements can be made thereto without leaving the scope of the inventive idea, the basic characteristics of which are summarised in the following claims.

Claims: PATENT CLAIMS 1. A process for the production of flakes from a mixture of lubricating, stabilising additives which contains a product having a melting point less than the PVC softening point, characterised by comprising the following operations: - continuously mixing a pulverulent mixture of additives, while simultaneously subjecting it to increasing pressure and temperature; - extruding the ductile mix thus obtained into at least one continuous filament of constant size; - cold-rolling said at least one filament to obtain a uniformly compacted continuous strip; - crushing said strip into flakes; and - blowing the flakes in counter-current before being stored, in order to separate therefrom any powder generated by the crushing. 2. A process as claimed in claim 1, characterised in that the product of melting point less than the PVC softening point which is present in the initial pulverulent mixture is a product of melting point between 500C and 900 C, chosen from synthetic and natural waxes of the stearyl stearate type, glyceryl monostearate, montan wax, paraffin, high-melting point synthetic paraffin, and stearyl phthalate, and is present in a quantity exceeding 3Z by weight of the initial pulverulent mixture. 3. A process as claimed in the preceding claims, characterised in that the heating of the compressed mixture increases gradually from the beginning to the end of the mixing and compression operation, within the temperature range of between 400C and 900 C. 4. A plant for implementing the method claimed in the preceding claims, characterised by comprising, in cascade, a variable pitch double-screw extruder device (3, 4, 5) fed continuously with a pulverulent mixture of additives, its consecutive longitudinal portions being surrounded by electrical heating jackets (T1, T2, T3, T4) of temperatures which increase from upstream to downstream; a cold-rolling device (7) arranged to reduce into strips (66) the continuous filaments (6) of material leaving the extruder (3, 4, 5); a crushing device (8) for reducing said strips (66) into flakes; and a powder separation cyclone (11) arranged to remove the powder from the flakes before their storage. 5. A plant as claimed in claim 4, characterised in that the gap between the active surfaces of the rollers of the rolling device (7) is between 0.1 and 2 mm.

Inventors: AMBU, IGNAZIO, DR., NANNI, AUGUSTO, SCALORBI, ENEA, DR.
Applicants: REAGENS S.P.A. INDUSTRIA CHIMICA
Application year: 1984
Main classification: C08K9
IPC codes: B29B9, C08K9