ITMI950766A1 - PROCESS AND EQUIPMENT FOR THE VERTICAL PRODUCTION OF PRE-EXPANDED POLYURETHANE FOAM BLOCKS - Google Patents

Abstract

A process and equipment for the continuous production of pre - expanded polyurethane foam blocks. The reactive polyurethane components are mixed, under pressure, with a low boiling expansion agent maintained in the liquid state; the resulting mixture is made to pre-expand by feeding it, continuously, into a frothization cavity through an elongated slit which opens at the bottom of the frothization cavity, transversely to the flow of the mixture. The frothization of the polyurethane mixture takes place at the bottom of a foam polymerization path that extends vertically upwards; the polymerized foam is continuously dragged upwards with a speed related to the expansion speed of the polyurethane mixture during the frothization phase, and is subsequently cut into blocks at the upper end of its vertical path.

Description

DESCRIPTION FOR INVENTION PATENT

The present invention relates to a process and an apparatus for the continuous vertical production of pre-expanded polyurethane foams, using in a new and advantageous way the innovative principles of a process of frothization of polyurethane mixtures which is the subject of a previous application for European Patent EP A 0645 226, in combination with a vertical production system.

In the continuous production of polyurethane foams in blocks, both flexible and rigid, horizontal systems characterized by large dimensions and high daily production are conventionally used, since a normal polyurethane foaming process requires high conveyor sliding speeds and a consequent long polymerization path of the foam, to avoid the undesirable phenomenon of reflux of the mixture still in the liquid state, below the polyurethane foam in the expansion phase or in the initial polymerization phase; conventional systems of this kind are described for example in US-A-3.325.B23 and DS-A-3.786.122.

In order to obviate this drawback, and with the aim also of creating smaller and smaller plants, such as to allow better results and a more economical management of the plant itself, the European Patent application EP-A- 0645 226 proposes a particular frothization process and a system for the continuous production of polyurethane foams in blocks, which uses a particular frothization equipment that makes it possible to mix reactive polyurethane components, with a low boiling expansion agent, in particular CO2 or other chemically inert blowing agent, under controlled pressure conditions, such as to maintain the blowing agent in a liquid state. In particular, according to this document, the frothization of the polyurethane mixture takes place according to a continuous process which involves a pressure equalization phase obtained by passing the mixture through an elongated pressure drop zone, which extends transversely to the flow direction of the mixture. which is then made to flow into a frothization cavity where the expanding agent is gradually released in the gaseous state in the same mixture that is expanding, before the chemical reaction between the chemical components and the polymerization of the polyurethane foam produced begins.

In the past, machines for the continuous production of polyurethane foams have also been proposed, according to traditional formulations in which the polyurethane foam was developed and dragged upwards, with relatively low speeds and flow rates, such as to reduce the overall dimensions of the entire plant. . Examples are found in various prior documents, for example in the French patent application 2.023.961 or in the corresponding German patent application 1.956.419, or in the patent application EP-A-0 058 553. Among the various proposals, for various reasons , very few have found a practical application.

In particular, both in the patent application FR-A-2.023.961 and in the European application EP-A-0058 553, the polyurethane mixture obtained by means of a conventional mixing device is fed in the liquid state into a channel located at the lower end of a foaming space, where the mixture expands by chemical reaction between the polyurethane components, polymerizing as it is dragged upwards; the height of the foaming space, the dragging speed of the foamed polyurethane material, as well as the length of the entire polymerization path, therefore depend on the mixing conditions and on the foaming conditions themselves.

In general, these prior documents therefore propose the use of conventional polyurethane blends in which the expansion of the foam is obtained exclusively by the effect of the carbon dioxide generated by the chemical reaction between water and isocyanate. Therefore, the height of the foaming space required to obtain a complete expansion of the mixture is still undesirably high; moreover, the physical characteristics of the polyurethane material produced, and of the plant itself, depend on the technology used. None of these documents therefore suggests or proposes a process and a plant that are suitable for an application of the frothization technique, in the continuous production of polyurethane foams in blocks.

Therefore, the object of the present invention is to provide a process and a plant for the continuous production of pre-expanded polyurethane foams, which advantageously use the frothization technology and a particular apparatus designed to allow mixing under pressure of the polyurethane components and of an inert expansion agent, in the liquid state, as well as such as to allow the controlled release of the expansion agent, as a gas, in a condition suitable to further favor the frothization of the mixture, so that the pre-expansion takes place in a comparatively small space .

In general, according to the invention, a process and relative plant have been provided for the continuous production of pre-expanded polyurethane foam blocks, comprising the steps of: preparing a mixture of reactive polyurethane components with a low boiling expanding agent, in particular liquid CO2, by subjecting the mixture to a pressure sufficient to keep the expanding agent in a liquid state; frothize the mixture under controlled pressure conditions by equalizing its pressure along an equalization chamber and through an elongated slot that extends transversely to the flow of the mixture itself, subsequently making the polyurethane mixture pre-expand and polymerize while it flows along a frothization cavity constituting part of a vertical path in which the mixture moves and is dragged upwards.

The process and the apparatus according to the present invention will be further illustrated below with reference to the attached drawings, in which:

Fig. 1 is a longitudinal section of the plant according to the invention;

Fig. 2 is a longitudinal section of the same plant, taken in a plane orthogonal to that of Fig. 1;

Fig. 3 is an enlarged perspective view of the frothization device;

Fig. 4 shows a variant of the frothization device;

The present invention starts from the premise of using, advantageously, the frothization technology in the continuous production of expanded polyurethane foam blocks, developed and described in the previous European patent application EP-A-0645226, adapting it to a vertical process, in in order to improve the frothization conditions as the pre-expansion of the mixture occurs in the same direction in which the gaseous frothization agent develops, all in an extremely limited space, while the polyurethane foam moves and is dragged at low speed , bottom up; in this way not only the frothization and pre-expansion conditions of the foam are improved, but it also allows to reduce the height of the entire foaming plant, compared to traditional plants.

Therefore, as shown in Figures 1 and 2, the plant substantially comprises a frothization apparatus 10 at the lower end of a path 11 for the polymerization of a polyurethane foam 12, which develops vertically, from the bottom upwards.

The frothization apparatus 10 in turn consists of a tubular bar 13 comprising a longitudinal chamber 14 connected, by means of ducts 15, to the outlet of a mixing apparatus 16, for example of the high-pressure type, into the chamber of which are fed and mixed under controlled pressure conditions, both the chemically reactive polyurethane components, such as a polyol and an isocyanate, with any additives, and an inert expansion agent, in the liquid state, of a low boiling type, for example liquid CO2 which will subsequently be released as gas to cause frothization or pre-expansion of the polyurethane mixture, before the chemical reaction between the polyurethane components and the polymerization of the foam thus obtained takes place.

The chamber 14 of the tubular bar of the frothization device 10 serves to equalize the pressure and to homogeneously distribute the mixture, extending longitudinally in a plane transversal to the direction of flow, substantially for the entire width of the blocks of polyurethane material to be produced.

In particular, as shown in Figure 1 and in the enlarged view of Figure 3, the distribution bar 13 has a narrow longitudinal slot 17 on one side of it which opens into a short horizontal duct 18 which in turn opens towards a cavity of frothization 19 facing upwards, delimited by diverging side walls 20 which extend in height by a divergent portion 19A constituting a sort of diffuser. The diverging section 19A of the diffuser partially penetrates between inclined side walls 20 which define an expansion zone or a laterally closed space that extends vertically, in which the frothization and expansion of the polyurethane mixture can take place in a controlled manner while the same mixture it grows and moves, that is, it is dragged from the bottom upwards.

In particular, the expansion space and the path 11 for polymerization of the foam are delimited, on the sides, by movable surfaces which accompany and laterally contain the polyurethane foam 12 while it moves or is dragged towards an upper cutting area 21.

As shown in Figures 1 and 2 of the drawings, the movable surfaces accompanying the polyurethane foam are defined by web material 22, for example a paper web or plastic film, which unwinds from a lower roll 23 and rewinds on an upper roller 24, said rollers 23 and 24 being suitably motorized and controlled so that the speed of each individual strip of material 22 corresponds to the speed of dragging or sliding upwards of the polyurethane foam 12, containing it in the frothization phase .

The upward dragging of the polyurethane foam 12 must therefore be carried out with a speed correlated to the expansion speed of the mixture in the frothization cavity 19, and is obtained by means of at least two conveyor belts 25 arranged on the two opposite sides of the apparatus, while on the other two sides, in the example described, rigid side walls 26 are provided which extend starting from the upper edge of the walls 20, along the path 11, for a length sufficient to allow dimensional and structural stabilization of the polyurethane foam 12 during the polymerization phase

As shown, the polyurethane foam 12 is dragged upwards, past the rollers 24 for rewinding the web of material 22, towards a transversal cutting device schematically indicated by 21, to form single blocks of pre-expanded polyurethane foam 27 which from time to time they are removed from the top of the equipment.

Figure 3 of the drawings shows on an enlarged scale a perspective section of the frothization apparatus 10, which constitutes a substantial part of the plant.

As can be seen from said figure, the elongated slot 17 defines a pressure drop zone delimited by parallel flat surfaces which extend substantially in the direction of the flow; in a plane parallel and laterally spaced from the longitudinal axis of the frothization cavity and of the vertical polymerization path 11, the width and thickness of the slot 17 must be such as to generate in the mixing device 10 a pressure sufficient to maintain the agent expansion in the liquid state. Purely by way of indication, the slot 17 can have a thickness between 1 and 10 tenths of a millimeter, a length in the direction of the flow between about 10 and 30 mm, as well as a width, measured in the direction transverse to the flow of the mixture, for example of about 2 meters and in any case equal to the width in the same plane of the polyurethane material 12.

In Figures 1 and 3 the slot 17 is arranged parallel to the axis of the vertical path 11, however it could be oriented differently or form any angle with said axis.

Also from figure 3, it can be seen that the slot 17 opens into a first horizontal duct 18 of the frothization cavity, delimited by an external surface of the distribution bar 13 itself, by a side wall 28 set back with respect to the slot 17 and by a wall upper 29 which extends beyond the slit mentioned.

The upward facing part of the frothization cavity 19 is in turn defined by a bottom wall 30 which preferably constitutes an extension of the upper surface of the distribution bar 13, as well as by the diverging side walls 19A and the head walls 19B previously defined.

It is important to note that the walls 19A and 19B penetrate into a frothization cavity which extends in height for a length sufficient to allow the complete expansion of the polyurethane mixture under the effect of CO2 or of the expansion agent which is gradually released. in the gaseous state while the polyurethane components do not yet chemically react with each other. Since the polyurethane mixture is instantaneously frothized, expanding when the CO2 is released, "assuming the appearance of a thick cream that fills the cavity 19, growing homogeneously in the same vertical direction of flow of the polyurethane material 12, thus obtaining a cellular structure of the polyurethane foam, fine and homogeneous, without bubbles or cavities, in a relatively small foaming space and with very low translation speed.

Therefore, the speeds of translation both of the material belts 22 accompanying the polyurethane foam 12 during its upward movement, and the speed of the conveyor belts 25, must be suitably correlated with the growth rate of the polyurethane foam which pre- expands in the frothization cavity 19, which must be substantially constant in order to avoid the formation of polyurethane foams with densities that are too high or inhomogeneous due to the presence of holes or cavities.

The controls of the various moving parts of the equipment must therefore be suitably correlated to each other, controlling the speeds at a constant and optimal value, by means of suitable adjustment and control means, not shown, establishing the most suitable speeds from time to time through appropriate tests. preventive, according to the estimated growth rate for the polyurethane foam in the frothization phase.

Tests were carried out with an apparatus according to the example of Figures 1 and 2 for the production of blocks of frothed polyurethane material with a rectangular section having dimensions of 2 by 1.20 m in width. The equipment developed in height for about 5 m, including the upper area for cutting and removing the blocks, and was equipped with two side conveyors that were operated at a constant speed of 0.9 m / minute. Frothization and expansion of the foam took place along a vertical section of about 1 m corresponding to about 1.2 minutes; the distribution bar had a 5/10 mm thick slot, and was delimited by parallel walls which extended in the direction of flow for 30 mm.

Kraft paper tapes were also used to define the movable surfaces 22 accompanying the polyurethane foam along the polymerization path 11.

A polyurethane blend formulated in three component parts was used;

PART Ai

load 24 kg / minute;

polyether polyol 3,500 mw = 100.00

water = 3.50

amino catalyst = 0.10

silicone = 1.20

PART B;

capacity 12.5 kg / minute

80: 20 TDI = 55.00

PART C:

load 0.05 kg / minute

Stannous octoate-based catalyst = 0.22 The quantities referred to above are defined as parts by weight on polyol.

Part A of the polyurethane mixture was also saturated with a certain quantity of carbon dioxide in the liquid state, in a quantity sufficient to reach a pressure of about 10 bar in the tank.

Once the equipment was started, the optimal speed of the conveyor belts was established, the polyurethane mixture frothized regularly, completing its expansion at the end of the diffuser, while continuing its upward stroke, along the polymerization path 11, dragged from the conveyors 25. At the end of its upward stroke, the polymerized polyurethane material was cut into blocks with a height of about 1.5 m, obtaining a polyurethane foam with a homogeneous density, measured in 15 kg / n »3.

The cell structure was fine, regular and did not contain large voids or bubbles, resulting in a commercially acceptable quality.

The tests were repeated several times, obtaining substantially homogeneous results which demonstrated the great advantages obtainable with the method and apparatus according to the invention.

Figure 4 shows a possible variant for the frothization apparatus, which allows in certain cases to improve the operation and characteristics of the polyurethane foam obtained; in said figure the same references as in the previous figures are used to indicate similar or equivalent parts.

The apparatus of Figure 4 differs from that of Figure 3 mainly in that the wall 28 which closes the end of the duct 18 constitutes a continuation of the analogous lateral surface of the slot 17; this continuity of the two surfaces tends to reduce the causes of the introduction of turbulence in the polyurethane mixture which comes out of the distribution bar 13 and which begins to froth, thus improving the qualities of the polyurethane foam obtained.

From what has been said and shown it is therefore evident that the invention is aimed at a new combination of a vertical plant for the continuous production of rigid or flexible polyurethane foam blocks, with a frothization device that allows an initial pre-expansion phase , thus improving the whole process and the quality of the foam produced.

Claims (12)

R IV E N D I CA C T IO N I 1. Process for the continuous production of pre-expanded polyurethane foams comprising the steps of: - a) preparing a mixture of reactive polyurethane components, with a low boiling gasifiable expansion agent, of inert type, by subjecting the mixture to a pressure sufficient to maintain the expansion agent in the liquid state; b) equalizing the pressure and pre-expanding the mixture under controlled pressure conditions by continuously feeding it into a frothization cavity through a pressure equalization chamber and an elongated pressure drop slot which extend transversely to the flow of the mixture, gradually releasing said gaseous agent in the polyurethane foam which is expanding in said frothization cavity before the chemical reaction between the polyurethane components begins, and in which the polyurethane foam moves along a polymerization path, characterized in that the pre-expansion phase of the polyurethane foam takes place in a frothization cavity that extends vertically, while the polyurethane foam moves along a vertical path that extends from the bottom up. 2. Process for the continuous production of pre-expanded polyurethane foams, according to claim 1, characterized by feeding said mixture to the bottom of said frothization cavity and to divert the flow of the mixture towards said frothization cavity, allowing the expansion as well as polymerization of the polyurethane foam as it moves along said vertical path and is drawn upward. ' 3. Process according to claim 1, characterized in that said polyurethane foam is contained on the sides and guided upwards, by means of sliding surfaces which move with the polyurethane foam. 4. Process according to claim 1, characterized in that it causes a deviation of the flow of the mixture which emerges from said pressure drop slot, and of guiding it by means of a lateral surface which constitutes a continuation of the corresponding lateral surface of the aforesaid elongated slot. 5. Process according to claim 1, characterized in that the flow of the polyurethane mixture which emerges from said pressure drop slot lies in a plane parallel to and spaced from the longitudinal axis of the frothization cavity and of the vertical polymerization path. 6. Process according to claim 1, characterized in that the flow of the polyurethane mixture which emerges from said pressure drop slot forms an angle with the longitudinal axis of the frothization cavity and of the vertical polymerization path. 7. Process according to claim 5 or 6, characterized in that it causes a first horizontal deviation of the flow which exits from said slot, laterally and in the direction of said upwardly oriented frothization cavity. 8. Process according to claim 1 characterized by the fact of maintaining the upward dragging speed of the polymerized polyurethane foam, at a speed constantly correlated to the expansion speed of the polyurethane mixture in said frothization cavity. 9. Plant for the continuous production of expanded polyurethane foam blocks comprising: a mixing device for mixing, under pressure, chemically reactive polyurethane components and an inert, low boiling expansion agent; a device for pre-expansion of the polyurethane mixture connected by means of supply lines to said mixing device; said pre-expansion device comprising an elongated pressure equalization chamber which opens towards a frothization cavity through a longitudinal slot, characterized in that said frothization cavity is oriented upwards and is arranged at the lower end of a path of polymerization of the polyurethane foam which extends vertically above said cavity, and by the fact of comprising sliding surfaces for containing the polyurethane foam, which move with the expanding foam itself. 10. Implant according to claim 9, characterized in that said frothization cavity has a longitudinal axis aligned with the longitudinal axis of the polymerization path, and in that said longitudinal slot is arranged in a parallel plane, laterally spaced from said axes of the frothization cavity and the polymerization path. 11. Implant according to claim 9 characterized by the fact that said frothization cavity has a longitudinal axis aligned with the longitudinal axis of the polymerization path, and by the fact that said longitudinal slot is arranged in a plane forming an angle with said longitudinal axes of the cavity of frothization and of the polymerization path. 12. Plant according to claim 9, characterized in that said frothization cavity has a lateral surface for guiding the mixture which constitutes a continuation of a corresponding lateral surface of the longitudinal slot of the pre-expansion device.