SE420582B - PROCEDURE FOR PREPARING POLYURETHANE FOAM BLOCK - Google Patents

Description

_f7900266-3 L ". 10 15 20 30 are the nature of the constituent components and their proportions. Among the properties that can be varied by the choice of components and proportions are the stiffness, density, resistance to degradation, tensile strength and cell size. The nature of the polyol and the polyisocyanate and the proportions of polyol, polyisocyanate, water and blowing agent are of particular importance among the parameters present.

Industrially, polyurethane foam is produced in the form of blocks. These blocks can have a length of more than 100 m, their width is normally 2 m and their height varies between 0.8 and 1.3 m.

The cross-sectional shape of the foam blocks obtained by the conventional method is shown in Figure 1 of the drawing, which is described in more detail below.

Regardless of the type of foam produced, a serious problem occurs in the manufacture of blocks, which has to do with the densification of the bottom layer. As a result of this densification, a significant part of the finished material must be discarded due to the fact that it has a significantly higher density and poorer mechanical properties than the rest of the block.

The densified area amounts to about 5% by weight and is sometimes up to 7% by weight of the entire block.

The disadvantages of forming foam blocks with a densified bottom are readily apparent when considering the following factors. (a) The amount of raw material lost may be significant, given that production in a medium-sized polyurethane foam plant may exceed 20 000 kg per day. b) It involves the cost of cutting off the densified foam layer, which may have a length of 100 m (block length), a width of 2 m and a thickness of 10 - 15 mm, by mechanical means, preferably specially designed saws. 7 c) It is difficult to sell the cut densified layer as a by-product. (d) Since a significant proportion of the components of the foam are of petrochemical origin, it is obviously desirable to save as much as possible on these materials, with Lanka on the high price of petrolcum and its derivatives.

It can be seen from the above that it is highly desirable to produce blocks without the lower densified area.

The above disadvantages are eliminated according to the present invention, which offers a block without densified area, thereby obtaining an excellent utilization of the raw materials and a significant reduction of the manufacturing costs.

The invention is described in more detail in connection with the accompanying drawings.

Figure 1 shows in cross section a foam block made by the conventional method.

Figure 2 is a schematic side view of a plant for producing polyurethane foam blocks according to the invention. Figure 3 is a graph showing the temperature (QC) of the ordinate and the time of the abscissa. The horizontal distance 00 'represents the time during which, with the endless conveyor belt in the foaming tunnel operating without feeding with the components of the foam, an articulated element therein goes from room temperature to a temperature T. The distance O'O "corresponds to the time during which the endless belt stands still. The distance 0" B 'corresponds to the time it takes for an element in the belt, whereupon foam is about to form, to pass through the foaming tunnel. Finally, the distance B'G 'corresponds to the time it takes for an element of the foam block to move from the end of the foaming tunnel to the end of the drying area.

In connection with Figure 2, the conventional process for producing polyurethane foam blocks is described. The plant comprises a foaming tunnel with an inclined conveyor belt 1 composed of conductive plates P., the upper part or transport part of which is formed by the bottom of the foaming tunnel. Otherwise, the tunnel is formed by side walls 5 and a roof T, in which, as can be seen from the figure, there are three lines for extraction of gases formed and / or released during the reaction, such as carbon dioxide and blowing agent. At the entrance end of the foaming tunnel there is a mixer and feeder head MA, in which the foam components are mixed in the right proportions and from where they are discharged to the conveyor belt.

At the exit end of the endless conveyor belt 1 there are several traction conveyors 2, 3, which pull the foam formed in the foaming tunnel into an arrangement of free-running rollers 6, where the foam string E is cut into blocks and from which these are discharged to a bearing.

A web, which moves over the surfaces of the conveyors 1, 2 and 3 and which has the same width as these conveyors, is interposed between the foam string fi and the conveyors. The web is fed from 7900266-3 10 15 20 25 30 35 a supply roll H, moves at the same speed as the conveyors 1, 2 and 3 and is led away to a take-up roll H '. The web can consist of paper, polyethylene film or other material with the required tensile strength, rigidity and explosive strength. The web Ci for the sake of simplicity ("paper web") is needed because the conveyor does not have a continuous surface, but is formed by articulated plates, which are arranged at intervals. It will be appreciated that it is imperative to use a web of paper or similar material, since the foam ingredients deposited at the entrance end of the tunnel are liquid in the mixture in the mixer head, so that the liquid mixture in the absence of the paper web would penetrate the gaps between the conveyor belts. 7 With respect to Figure 2, the following is to be noted.

First, the figure is only a schematic diagram, and it does not include all the necessary elements, such as tanks for the components, pumps and drive motors. Secondly, in the plant where the conventional process is carried out, there are no elements corresponding to the devices S1, S2 and S3 shown in the figure, which are included in the present invention and are described in more detail below. This means that the conveyors 1, 2, 3 and the roller table are arranged in immediate connection to each other without the spaces shown in figure 2.

In the operation of the conventional plant, the conveyors 1, 2, 3 and the devices 4, H 'operate for supply and take-up of the web at a predetermined speed. The liquid mixture of reactants is discharged in a suitable flow from the hlandar and maiar head MA and is deposited at the entrance end A of the foaming tunnel on the web moving along the bottom of the foaming tunnel. Upon deposition, the mixture of the reactants is a viscous liquid, which progressively reacts exothermically, expands and forms the foam block. This phase of the representation is shown in Figure 2 with an ascending curve, the position of which varies from one kind of foam to another, so that the point C in the tunnel, which corresponds to the end point of the ascending curve, can be moved to the right or to the left of the position in figure?, depending on the reactivity of the mixture. Since it has reached its maximum height, 2 the foam block grows progressively in the longitudinal direction, whereby it is pulled forward by the movement of the conveyors 1, 2 and 3. After the block has passed the last conveyor, i.e. the conveyor 3 in Figure 2, and after the paper web has been pulled away, the block is cut into pieces of varying size and stored after a curing time of 2H. hrs.

The cross section of the block is shown in Figure 1, from which it can be seen that it has a densified underlayer F, the underside of which is uneven.

It is therefore necessary to cut off the densified underlayer F in order to dispose of the densified area and the surface roughness, with consequent inconveniences, as indicated above.

The improved method of the invention includes the step of running the endless conveyor belt in the foaming tunnel without feeding it with the foam components and raising the temperature within the casing around the endless conveyor belt.

The result of the heating is that the temperature in the upper part of the belt, which forms the bottom of the foaming tunnel, is raised from a room temperature (Ta) to a temperature (TP) of about SOOC within a time of between D and 90 minutes. This temperature increase is represented by the leftmost part of Figure 3.

The movement of the conveyor belt is then interrupted for a certain time and the paper web is placed on the belt to insert it between the belt plates and the foam string and the supply of the mixture of the foam-forming reactants through the mixer and feeder head to the paper web begins in the upstream portion of the tunnel. During this time, while the conveyor belt is from the value TP to a value TR, the reaction temperature, which is determined for each foam. At this moment (point A in Figure 3) the conveyor belt is put in a bunch.

At the same time, the supply and peeling devices are also stopped, the temperature of the paper web drops.

From this moment on, the temperature in the upper part of the endless belt in the foaming tunnel is regulated (which temperature is substantially the same as the temperature of the continuous paper web and consequently substantially equal to the temperature in the lower part of the foam block resting on the paper web to be formed), so that in a first area (reaction area) the above-mentioned value TP is maintained and in a second area downstream of the first area (consolidation area) eti value TC is maintained, which is higher than TR.

In at least one area downstream of the foaming tunnel, the underside of the consolidated traveling block is exposed to a drying temperature TS while the block passes a drying area.

Figure 2 shows three drying areas S1, S2 and S3.

After drying, the paper web is picked up and wound on the receiving device H ', and a thin foam layer then adheres to the paper web. The block transferred to the roller table has a sub-zone without densification and a smooth and smooth underside, which does not require re-cutting, which has been an indispensable operation according to the state of the art.

During its formation, the foam runs through the first area, i.e. the reaction area located at the upstream portion of the conveyor belt, at a predetermined time, which varies from one foam to another. As stated above, the surface of the endless belt is kept in this area at a constant temperature TR, which also depends on the nature of the foam.

The time it takes for the foam to pass the consolidation zone depends on the predetermined time in the reaction zone.

The essential parameters for the process according to the invention are as follows. surface temperature in the reaction zone W surface temperature in the consolidation zone surface temperature in the drying zone the time of passage of an element of the conveyor belt of the PUUJO resting on the block thereon or an element of paper-coated underside through the reaction zone, i.e. from point A to point C in Figures 2 and 3. the time of passage of the above-mentioned element through the consolidation area, i.e. from point C to point B in Figs. 2 and 3. t the time of the passage of said element through the foaming tunnel, i.e. from point A to point B in Figures 2 and 3.

Since the bottom of the foaming tunnel passes through the reaction area and the consolidation area, it is understood that tT = tR + tc (1) and since the value of tR is given for each type of foam, it follows that t = t - t (2) 10 .A ¿-. Although the values tR and TR are determined for a given foam, they vary from one foam to another, since the exothermicity of the polyurethane-forming reaction varies with the nature of the main ingredients and with the ratio between them. The main ingredients are, as mentioned above, a polyol and a polyisocyanate. However, the water content of the mixture also plays an important role.

An important feature of the invention lies in the fact that the surface temperature in the three areas satisfies the relationship TR <TC <TS Usually the difference TC - TR = AT is between 10 and 1500, and about 10 ° C is preferred.

A temperature within the foaming line in the reaction zone above a certain limit can lead to decomposition (cracking) or combustion of the foam. This decomposition temperature varies from one composition to another and is usually between H5 and 8000, so you have TR <TC <so ° c The temperature TS in the drying range can go up to high values, e.g. between 100 and 250OC, for a short time. This does not contradict what has been said above with regard to decomposition and / or combustion, given that the drying temperature is generated in an area located outside the foaming tunnel, which is passed through the foam string in a very short time.

Although only one drying area is mentioned above, the invention is not limited to the use of only one such area.

Several may occur, but for practical reasons the number is usually limited to three. However, a single Turkish area is preferable.

Due to the differences between the three specified temperature levels, after the block's passage of the drying area and removal of the paper web, a block without a densified underlayer and with a smooth and even underside is obtained. A thin and even layer of foam with the same density as the rest of the block remains adhering to the paper web.

The distance of the band 1 which forms the reaction area is represented by AC, and CB is the longitudinal edge of the consolidation area. 795266-3 From the foregoing it appears that the position of point C is admittedly fixed for each given foam, but varies from one foam to another and may be offset to the right or left from the position shown.

Figure 2 shows three drying areas S1, S2 and S3 outside the foaming tunnel itself. The drying areas are usually shorter than the other two areas, and the length (or the time it takes a certain element of the consolidated block to pass the drying area) varies inversely with temperature. A fairly short drying area (or a short time for passing the drying area) requires a high temperature and vice versa.

Figure 3 shows the variation of the temperature in a surface element of the underside of the foam block with time. In the figure, O0 'is the time of the belt working in the foaming tunnel without feeding with the components of the foam, and O'0 "is the standstill time of the belt.

It will be appreciated that the transition of the temperature from the reaction zone to the consolidation zone does not occur suddenly, and therefore a sloping section has been given in Figure 3, and point C is at a temperature which can be considered to be midway between the values TR and TC. After a certain plate element in the conveyor belt has reached the turning point, the part of the underside of the block which has been in contact with this element undergoes a temperature increase to the value TS1, if the drying area S1 is present. If the drying area is further downstream, for example at Sé ~ or S3, the temperature of the block begins to fall, in that it tends to decrease to the air temperature. The broken line BF represents the variation of the temperature with time that would exist in the absence of drying areas. It is further apparent from the figure that the farther away from the foaming tunnel the drying area is, the higher the temperature therein must be in order to counteract the decrease in the consolidation temperature. After the drying area has been passed, the temperature of the block surface naturally drops from the value D, E or G according to Figure 3 to the ambient temperature.

The removal of the paper web is one of the most important features of the invention. Although the above is a web of paper, which is the material usually inserted between the foam block in formation and the articulated rectangular plates in the conveyor belt, others may be used; ~ 7900266-z web material that performs the same function.

The following is an example of the production of polyurethane foam with the improved process of the invention.

The example is illustrative, but not limiting. From the mixer head in a plant as above, a composition containing (in parts by weight) 100 parts of polyol, 51.3 parts of toluene diisocyanate, U, 1 part of water, 0.0 part of dimethylaminoethanol, 1 part of silicone, 6.5 parts is added. freon 11, 0.2 part tin octoate and 0.3 part dye. The temperature in the reaction zone is kept at a value TR = 41.5 in 100 and the temperature in the consolidation zone at a value TC = 51.5 in 100 with a time tR of 2 - 3 min in the reaction zone and a residence time tc of 3 - 2 min in the consolidation area.

Since the block has been exposed to 120 ° C in the drying area and the continuous paper web has been peeled from the underside, the block has a substantially uniform density of 20 kg / m 3 in its entire volume, i.e. without densification in the underlayer and without irregularities, so that it does not need to be trimmed.

The economic advantages of the process according to the invention appear from the following calculation.

A medium-sized factory produces foam plastic for 200 days a year and produces a continuous block of 20 tonnes for each foaming work. The annual production is thus 20 X 200 = 4000 tons or H 000 000 kg. When working according to the conventional procedure, if the densified sublayer is assumed to be on average U, 5% by weight, an annual production of dense foam of H 000 000 X 0.005 = 180 000 kg is obtained. The annual production of foam with a uniform density is thus 3,820,000 kg.

A factory of the same size, operating the process according to the invention, obtains, if the proportion of the thin foam layer adhering to the paper web is estimated at 0.5% by weight, an annual production of H 000 000 - H 000 000 X 0.005 = 3 980,000 kg foam of uniform density.

This means that when applying the invention, the annual production increases by 160,000 kg. This shows that the advantage of the system lies in a production of 160,000 kg of foam plastic without raw material costs. In addition to this saving, there are the savings, which are due to the fact that the costs of energy and labor for cleaning, storage and sales in the dense foam are eliminated.

Claims (4)

'7900266'3. 10 PATENT REQUIREMENTS A process for producing a polyurethane foam block, in which a mixture of polyurethane foam-forming reactants is fed to one end of a foaming tunnel and passed through it on an endless conveyor belt, which forms the bottom of the foaming tunnel, while the mixture reacts and forms foam, a web of material, preferably a paper web, being inserted between the endless conveyor belt and the foam, whereupon the foam is dried after exiting the foaming tunnel, characterized in that the temperature in the upper part of the endless belt, which forms the bottom of the foaming tunnel, is adjusted so that in a reaction area in the upstream portion of the belt gets a constant value TR and in a subsequent consolidation area another constant value TC, the time for maintaining the temperature being determined by the relationship tT = tR + tc, where tT is the total time for the stay of the foam in the foaming tunnel, tR is the time of passage of a foam element through the reaction zone and tc is the time of a foam passage of elements through the consolidation area, and that the block, after leaving the foaming tunnel, is subjected to drying of its lower part in a drying area kept at a constant temperature TS, which is significantly higher than TR and TC, after which said web of material is peeled off together with a thin foam film, leaving a polyurethane foam blanket without a thickened bottom and with a smooth surface, which does not need to be cleaned. Process according to Claim 1, characterized in that the temperature difference between the consolidation zone and the reaction zone is at most 15 ° C, preferably 10 ° C. 3. A method according to claim 1 or 2, characterized in that the web of material consists of paper or other material which resists the high temperature in the drying area and has the required strength. Method according to one of Claims 1 to 3, characterized in that the endless conveyor belt in the foaming tunnel is first operated for a period of suitably 15-90 minutes while the endless belt is heated, so that the surface temperature in the upper part of the belt, which forms the bottom of the tunnel, goes from room temperature to a temperature TP of suitably between _ '7900266-3 11 60 eeh 8UOC, that the endless belt is stopped and the web of material placed; on the belt to be introduced between the foam and the belt without the application of the ecum-forming reactants. The upstream portion of the belt is started, the temperature of the belt falling from a value TP to a value TR during the standstill period, and the endless belt being restarted when the value TR is reached, and devices for supplying and receiving the web covering the web of material are started.