Method for enveloping pellets of foamed poly-styrene suitable for producing lightened manufactured articles of cement

The present invention relates to a method and device for: depositing coatings on polystyrene foam pellets · suitable for the manufacture of profiled parts or other lightweight concrete products, and further relates to a particularly economical composition usable in said process.

It is known in the field of the manufacture of elements based on cement that a light product can be obtained which has special thermal and acoustic insulation properties, by incorporating foam pellets into the part material. of polystyrol previously covered with a layer of synthetic resin. One of the known methods of obtaining a preliminary coating proposes to introduce said pellets into a basin provided with an agitator together with doses of epoxy resins which are of high cost, as well as 'cement or lime. At the outlet of the basin, a wet product is obtained in which the resin which covers the core of the pellet is not polymerized. This results in the disadvantage that during storage or during transport, lumps or agglomerates of pellets are formed, which are detrimental to the quality of the final product. According to another proposal of the prior art, an adhesive of the type used in agriculture is used in place of the epoxy resins to adhere the anticryptog / amic or fungicidal products to the foliage. However, such adhesives are at least partially soluble in water following an incomplete polymerization of the resins so that when the pellets are brought into contact with water during the manufacture of the product the coating is somehow washed by water which leaves the pellet in the initial state and leads to poor quality of the final product. During the research which led to the present invention, it has been found that the cement or lime present in the coating layer react chemically in the presence of water and the various other chemicals used by degrading. This degradation propagates in the mass of the finished products and negatively influences the resistance of the latter. On the other hand, it should be noted that all the coating methods of the prior art are of the discontinuous type and work by successive fixed loads. This is a great disadvantage when the coating is deposited directly on the site of use. In fact, the installations downstream of the coating station work at a much faster and faster rate.

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tinu. The processes of the prior art therefore have the consequence of costly downtime. Another drawback lies in the absence of suitable and rapid drying following the polymerization, which imposes an additional delay before the use of the pellets.

The present invention proposes to provide a process, a device for its implementation as well as a composition which can be used in the process which allow rapid, continuous and economical operations, while avoiding the drawbacks of the prior art. I

I

The method according to the invention is characterized in that it substantially takes the following continuous steps: it

After the admission into a mixer of a continuous stream of pellets to another compartment of the mixer into which is also introduced continuously a proportionate amount of water and ¹resin ^ the pellets thus wetted are then transported to a second compartment of the mixer where they are added with an inert filler in proportionate amount and metered, before being subjected in a last compartment to a drying and polymerization operation.

Another characteristic of the present invention consists in that the device for carrying out the process comprises a mixer preferably consisting of a double cylinder body open at its connection center and provided with conveyors to ^!rotating shafts. in which the introduction of water, resins as well as the inert load takes place, in the transverse direction with respect to the axis of advance of the material, through various feeding points which extend throughout the blender.

According to another characteristic of the invention, for coating the pellets, water with resin and an inert filler is used instead of the cement or lime used in the processes of the prior art. According to a preferred variant, the invention proposes the use of low-cost vinyl resins with the addition of a synthetic complexing agent to promote the dispersion of the resin in water and to reduce the percentage of water required.

The object of the invention will be explained and other advantages, and characteristics will appear in the light of the description · 'i which follows in which the invention is illustrated in a nonlimiting manner by reference to the appended drawings, where:

FIG. 1 shows a diagram of the entire device, for carrying out the coating method according to the invention, FIG. 2 shows an end view of the mixer (mixer with double shaft) according to FIG. 1, I i I i

J Figure 3 shows · a detail of the device for introducing the charII. '

I j inert according to Figure 1, j ί Figure 4 shows an alternative embodiment with respect to the!

Figure 1, with a mixer comprising a first comi i vertical part

On these drawings and in particular in FIGS. 1, 2 and 3, the reference mark indicates a reservoir for the pellets made of · polystyrol foam, intended to be coated; by 2 and 2 ′ are identified reservoirs for mixing water with the synthetic resin, said reservoirs being provided in duplicate in order to ensure continuity in the process even if one of said reservoirs was empty. In fact, if one of the reservations »* i voïrs was already empty (the 2 for example) the selection tap>

i automatic 5 allows the flow of the basin 2 '; by 5' is identified a pump for delivering the liquid containing the resin. Par 3 is indicated ·· a tank for the inert filler intended to be incorporated during the coating process. The polystyrene foam pellets, the resin mixture plus water and the inert filler are introduced into a mixer 7 respectively at the points A, B and C. The mixer 7 is preferably a tubular body comprising in; its interior two shafts provided with paddles 8 in opposite rotation¹ used to transport the material introduced. In the area placed in i

downstream of the introduction points, the unit 7 comprises a drying compartment 10 with reheating which will be described later. From the outlet end of the unit 7, there is a zone 11 with a raised bottom I • I, which constitutes a temporary obstacle for the pellets which therefore pile up before passing said obstacle,¹ which results in an extended holding time in the drying compartment. Zone 11 is surmounted by a hood for the aspi! vapor ration. The admission of the polystyrol foam pellets i ί into A can be carried out either by descent or by means of a screw-carrying transI J which makes it possible to dose the quantities introduced. The last variant is shown diagrammatically by the reference 4. The polystyrene foam peljets after their introduction into unit 7, are driven by ro- ',

... 4 rejation of the trees in reverse 8, to the right. The shafts are connected by means of a transmission 9 to a variable speed motor unit. The pellets then arrive below the point JB where the admission by the pump 5 'of water takes place with the synthetic resins. The admission does so through a transverse pipe fitted with a sprinkler so as to promote humidification. The dispensing device, fitted with a metering tap, can be one type! any suitable, spraying or even atomizing. The; humidified pellets then advance to point C where the inert filler is incorporated using the metering device.

6. Said metering device 4 'better shown in Figure 3, com-i essentially takes an Arch'imëde screw with geared motor | adjustable speed 13, the screw is placed 1 inside an element! tubular or of a housing 14, the base of which has a slit-shaped hopper 12, in transverse direction relative to the axis of the unit,⁷· I

The different materials introduced respectively in A, B, and C i.e. the pellets now provided with a coating arrive in a reheating compartment 10 where takes place in complete drying. Drying in 1? compartment 10 can be carried out for example by injecting hot air, by heating the mixer casing and / or with elements with infrared rays (the use of infrared rays is advantageous since these rays are also used for rapid polymerization of resins). The treated pellets then arrive at the outlet 16 where they meet the aforementioned obstacle 11 and pile up before exceeding said obstacle this makes it possible to extend the holding time in the drying zone 10 and to take full advantage of the effect of the water vapor extractor hood.

With reference to FIG. 4, a variant will be described with respect to FIG. 1. In this one, the similar parts bear the same references provided with an accent. The difference with respect to FIG. 1 consists in that the first compartment of the unit 7 in FIG. 1, is constituted by a vertical element 17, having substantially the appearance of a tubular tower inside. which in A and B takes place, respectively starting from the base, the feeding of the pellets in polystyrol and in the mixture of water with the resins. Said materials entrained by means of a paddle shaft 18 actuated by a geared motor 19 rise inside the tower 17 and are transferred at its top towards the horn jmparj5 J

I timent horizontal 7 '. The introduction of the inert charge is carried out at C according to the methods already described in FIG. 1; | the same applies to the reheating zone and! drying 10 '. j

As described above, the invention also relates to a particular composition which can be used in the process according to the invention. It has already been said that the components used to obtain the coating of the pellets consist of a mixture of {i!

i resins and water as well as an inert filler in place of the cement j or lime used according to the prior art. In particular, the inj vention proposes using instead of epoxy resins of the prior art which are of a high price, vinyl resins of lower cost price, said resins being suitably added with a synthetic reaction complexing t J to facilitate their dispersion in water. We found a good day

I yield by using per m of polystyrol foam pellets a mixture of water and resin having the following composition:

water: 10 liters;

! ¹polyacetovinyl resin with a high degree of polymerization:

I 2 kg ·!

! i agent improving water retention (methylcellulose): i 20-40 gr (i.e. 0.1 to 0.2¾ relative to the amount of resin) component having the function of anti-slip agent (i.e. to roughen the surface of the polystyrol pellets) and which makes it possible to adjust the load by weight while being inert with respect to the other products of the mixture, such as barium dioxide (ventilated) diatomaceous earth (disaggregated)

I soapstone (ventilated, dolomite (ventilated) and the like

- 40 gr (i.e. 0.1 to 0.2 I based on the amount of resins).

j A test conducted has shown that the lightweight concrete product! î comprising pellets coated according to the aforementioned compositions ij has better resistance to compression and! iij bending of the finished object with respect to the characteristics obtained by the known methods.

_J ______ While the best results are obtained with the ___. 6 ...... · compositions described above, the process according to the invention also has advantages with the types of resin from the prior art, for example with epoxy resins, since jl

the coated pellets are already dry at the outlet of the mixer and that they are therefore free from the drawbacks which the prior art presents by the formation of lumps and agglomerates.

The invention is not limited to the details of embodiment previously illustrated and / or described; on the contrary, it includes all the variants and all the equivalents which are within the reach of those skilled in the art.