GB1593302A

GB1593302A - Method for continuous production of slabs of polyurethane foam

Info

Publication number: GB1593302A
Application number: GB4080677A
Authority: GB
Original assignee: Toyo Rubber Chemical Industrial Co Ltd
Current assignee: Toyo Quality One Corp
Priority date: 1976-10-04
Filing date: 1977-09-30
Publication date: 1981-07-15
Also published as: DE2744492A1; FR2366117A1; FR2366117B1

Description

(54) METHOD FOR CONTINUOUS PRODUCTION OF SLABS OF POLYURETHANE FOAM (71) We, TOYO RUBBER CHEMIC AL INDUSTRIAL CORPORATION, a Japanese corporation, of 1-1, 2-chome, Nihonbashi Muromachi, Chuo-ku, Tokyo, Japan, 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: This invention relates to a method for the continuous production of a slab of polyurethane foam.

Conventionally, a method for the continuous production of a porous material is known which comprises feeding a foamable material continuously to a horizontally moving hollow mold and allowing the material to foam freely for a predetermined period of time. By this method, however, the height of both lateral edges of the molded material or foamed mass is made smaller than the mean height thereof due to the friction produced between the foaming mass and the sidewalls of the mold. In order to obtain a final product having a flat top surface, therefore, the raised portion of the foamed mass must be cut off. This necessarily causes a heavy material loss.

U.S. Patent 3,091,811, issued June 4, 1963, relates to an improvement in the above-described method and discloses the conception of installating a means for positively elevating both shoulders of the foaming mass within the vertical sidewalls of the advancing trough and thereby making flat the top surface thereof. By this latter method, however, the forcedly elevated portions of the foaming mass tend to have a lower density than the remaining portions thereof, so that variations in quality may occur among the resulting final products.

Moreover, the latter method as well as the former one causes a thick and hard film to be formed on the top surface of the mold mass because the top surface of the foaming mass remains in contact with air. This film must be cut off from the molded mass and discarded.

When slabs of polyurethane foam, are made in accordance with the prior art including the above-described two methods, a huge mass of polyurethane foam generally measuring about 2,000 mm(W) x 900mm(H) x 2,000 mm(L) is provided and sliced into a plurality of slabs having a desired thickness of, for example, 100 mm.

In order to cure such a mass completely, it must be allowed to stand for about 24 hours after the completion of foaming. During this cure cycle, the mass accumulates therein a sufficient amount of heat of reaction to raise its temperature to about 150-170"C. This not only incurs the risk of fire, but also tends to cause yellowing of the polyurethane foam due to the internal heat build-up and thereby diminish the commercial value of the product. In order to dissipate such a large amount of heat of reaction as efficiently as possible, a well-ventilated storehouse of fire-proof structure having accommodation for huge porous masses as described above is required, which necessarily raises the cost of equipment.

Furthermore, if the final product has a sheet of, for example, fabric laminated to a surface thereof, the manufacturing process requires a number of additional steps, such as applying an adhesive to the surface of a slab sliced off from the above-described huge mass and then laminating a sheet to the surface.

It is an object of this invention to provide a method for producing, at low cost, a slab of polyurethane foam having a flat top surface and showing no local variation in density.

It is another object of this invention to provide a method for the continuous production of a slab of polyurethane foam which causes only a small material loss.

It is an object of a preferred embodiment of this invention to provide a method for the continuous production of a slab of polyurethane foam having formed on the top surface thereof a thin and soft film which need not be discarded.

it is an object of another preferred embodiment of this invention to provide a method for the continuous production of a slab of polyurethane foam which enables one to laminate a sheet to the top surface or under surface thereof or both, without resort to any additional step.

It is still another object of this invention to provide a method for the continuous production of a slab of polyurethane foam which does not incur the risk of fire due to the heat of reaction accumulated during the cure cycle after the completion of foaming.

It is still another object of this invention to provide a method for the continuous production of a slab of polyurethane foam which permits one to increase the rate of expansion without incurring the risk of fire.

In accordance with this invention, there is provided a method for the continuous production of a slab of polyurethane foam comprising the steps of providing a creamy foamable polyurethane-forming material which the chemical reaction has been initiated, feeding a horizontally moving trough continuously with said foamable material to form a foaming mass, and using pressure means to press the top surface of said foaming mass only over a zone extending for 3 to 7 metres from a point which is virtually the point of completion of foaming and thereby make flat the top surface thereof, said pressure means moving horizontally in synchronism with and in the same direction as said trough, and the method being arranged so that a slab of polyurethane foam having a thickness of 40 to 250 mm is produced.

The bottom of the horizontally moving trough may be composed of a conveyor comprising a travelling endless belt, and each of the sidewalls thereof may be composed of a travelling endless belt having a vertical belt surface. Preferably, each of the sidewalls of the trough is composed of a vertical sheet or strip moving horizontally in synchronism with and in the same direction as the conveyor.

In one embodiment of this invention, a sheet is continuously fed between the pressure means and the foaming mass. This sheet may be stripped from the top surface of the foaming mass after the foaming mass has been fabricated, or may be bonded to the top surface of the foaming mass so as to constitute a part of the final product.

Another sheet is continuously fed between the foaming mass and the conveyor of which the bottom of the trough is composed. This sheet may be stripped from the under surface of the foaming mass after the foaming mass has been fabricated, or may be bonded to the under surface of the foaming mass so as to constitute a part of the final product. The vertical sheets, of which the sidewalls of the trough are composed, may be bonded to the sides of the foaming mass so as to constitute a part of the final product. However, they are preferably stripped from the sides of the foaming mass after the foaming mass has been fabricated.

The pressure means is preferably composed of a travelling endless belt.

The foamable material polyurethaneforming which is useful in the practice of this invention is a creamy, or highly viscous, fluid of which the chemical reaction has been initiated. If the foam able polyurethane-forming material is a fluid having lower viscosity, it will be necessary to prevent leakage of the fluid by composing the bottom of the trough of, for example, a U-shaped sheet having both lateral edges bent upward. In accordance with this invention using a highly viscous fluid, however any leakage is prevented in spite of the presence of a small gap or space created between the sidewalls and bottom of the trough. Moreover, if the foamable polyurethane-forming material has lower viscosity, it is probable that a freshly fed fluid penetrates between the previously fed and thickened fluid and the bottom of the trough and thereby interferes with uniform foaming. In contrast to this, the creamy fluid used in the invention forms into a good foaming mass without developing the above-described troubles. The top surface of the foaming mass must be pressed only over a zone extending for 3 to 7 metres from a point which is virtually the point of completion of foaming. Pressing at earlier stages of foaming should be avoided because the foaming reaction is unduly inhibited to cause undesirable collapse of cells.

The magnitude of the pressing force exerted by the pressure means should be great enough to make flat the top surface of the foaming mass. However, unnecessarily great pressing forces are undesirable because they interfere with uniform foaming.

If desired, an oven may be used to heat the foaming mass after the completion of foaming. This can not only accelerate drying of the surfaces thereof but also reduce the time required for cure thereof.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figure 1 is a perspective view of an exemplary apparatus for carrying out the method of this invention; Figure 2 is a perspective view of a modification of the apparatus of Figure 1; and Figure 3 is a perspective view of an example of the final product made by means of the apparatus of Figure 2.

Some preferred embodiments of this invention will be described below with reference to the accompanying drawings.

In Figure 1, a conveyor is shown at 1. This conveyor comprises a pair of rollers 2 rotated by suitable drive means, not shown, and an endless belt 3 stretched thereon. Belt 3 is made of a releasable or strippable material such as polytetrafluoroethylene fabric or stainless steel sheet. At both lateral edges of the top surface of conveyor 1, a pair of vertical reinforcing plates 4 are longitudinally located in opposed and spaced relationship and fixed by suitable fastening means, not shown. On the inside of each reinforcing plate 4, a vertical sheet or strip 5 made of, for example, paper having a release agent applied thereto is arranged so that it travels in synchronism with and in the same direction as conveyor 1, and then wound on a take-up roller, not shown. Thus, the horizontally moving trough is composed of conveyor 1 and a pair of strips 5. More specifically, conveyor 1 forms the bottom of the trough while a pair of strips 5 form the sidewalls thereof.

Alternately, the sidewalls of the trough may be composed of a pair of endless belts having a vertical belt surface, instead of a pair of strips 5. These belts are made of a releasable material. Shown at 6 is a nozzle for feeding the trough continuously with a creamy foamable polyurethane-forming material of which the chemical reaction has been initiated. Nozzle 6 can be moved in a reciprocating way across the top surface of conveyor 1. The foamable polyurethane forming material is prepared by agitating a composition comprising, in this embodiment, a hydroxy compound, an isocyanate compound, water and a catalyst. The viscosity of the foam able polyurethane-forming material can be easily enhanced, for example, by increasing the amount of the catalyst or by increasing the length of feed nozzle 6.

In addition, the thickness of the final product or slab can be controlled by changing the feed rate of the foamable material. The creamy foamable material is carried by conveyor 1 travelling in the direction of the arrow, during which its volume gradually increases to form a foaming mass 7. Shown at 8 is pressure means, such as an endless belt, for pressing the top surface of foaming mass 7 over a zone extending for 3 to 7 metres from a point which is virtually the point of completion of foaming and thereby making flat the top surface of foaming mass 7. Pressure means 8 is designed to move horizontally at the same speed and in the same direction as conveyor 1.

The foaming mass 7 of which the top surface has been made flat by pressure means 8 is carried by an another conveyer, not shown, during which it is cured completely and finally cut into slabs of the desired length. Thus, the thickness of the final product corresponds to that of the foaming mass after the completion of foaming. In accordance with this invention, therefore, the need of slicing a thick slab of porous material into a plurality of pieces as was the case in the prior art is obviated. The thickness of the slab of soft polyurethane foam made by the method of this invention is 40 to 250mm. In the prior art, slabs having a thickness of 40 to 250mm were made by producing a slab of about 900 mm thickness and then slicing it to the desired thickness.

The reason for this is that the top surface of the foaming mass always had a thick and hard film formed thereon and this had to be cut off. Therefore, as the thickness of the initially produced slab was decreased, the film became more difficult to cut off and the material loss increased. In accordance with this invention, the top surface of foaming mass 7 which has been made flat by pressure means 8 has a thin and soft film formed thereon, so that this film may be utilized as a part of the final product, instead of being cut off. More-over, the slab made by the method of this invention shows no local variation in density. That is, a uniformly foamed porous mass can be obtained.

Furthermore, fire and yellowing which were liable to occur during the cure of thick slabs in the prior art is completely prevented in accordance with this invention.

Generally, the rate of expansion of soft polyurethane foam increases in proportion to the amount of the blowing agent, such as water, contained in the starting composition. However, as the amount of the blowing agent increases, the heat of reaction accumulated during the cure cycle tends to increase and becomes more liable to cause a fire. In the prior art, the rate of expansion of the foam had to be limited to a maximum of about 70 in order to avoid the internal heat build-up during the cure cycle. In contrast to this, a much thinner slab is cured and then utilized directly as final product in accordance with this invention, so that the rate of expansion of the foam may be increased to a maximum of about 200 without incurring the risk of fire.

Figure 2 show the essential parts of an apparatus for carrying out another form of the method of this invention. In Figures 1 and 2, like parts are given like reference characters. In the apparatus shown in Figure 2, a sheet 11 is continuously fed between pressure means 8 and foaming mass 7. and another sheet 12 is continuously fed be tween conveyor l and foaming mass 7. Both sheets 11 and 12 are arranged so that they move horizontally in synchronism with and in the same direction as conveyor 1. Sheet 11 may be stripped from the top surface of foaming mass 7 after foaining mass 7 has been fabricated. or may be bonded to the top surface of foaming mass 7 so as to constitute a part of the final product. Similarly to sheet 11. sheet 12 may be stripped from the under surface of foaming mass 7 after foaming mass 7 has been fabricated, or may be bonded to the under surface of foaming mass 7 so as to constitute a part of the final product. When constituting a part of the final product, sheets 11 and 12 are beneficial in preventing the porous mass from yellowing under the action of ultra violct rays. If sheets 11 and 12 are to be stripped, it is desirable to use a sheet of releasible material such as paraffin paper and Kraft paper. If sheets 11 and 12 are to constitute a part of the final product, no particular limitation is placed on the material thereof. When sheets 11 and 12 are made of watcr-soluble resin such as polyvinyl alcohol. the thickness thereof is preferably about 0.02 to O. 1 mm. When sheets 11 and 12 are made of woven fabric, unwoven fabric, or foamed or unfoamed synthetic rcsin, the thickness thereof is preferably 0.1 to 1.0 mm. When sheets 11 and 12 are bonded to foaming mass 7 so as to constitute a part of the final product, there is no need of using an adhcsive because the stickiness of the surfaces of foaming mass 7 is useful for this purpose.

Figure 3 shows an example of the final product made by means of the apparatus of Figure 2. This is a slab 21 of soft polyurethane foam having two sheets of fabric 22 and 23 laminated to the top surface and under surface thereof, respectively.

WllAT WE CLAIM IS- l. A method for the continuous production of a slab of polyurethane foam comprising the steps of providing a creamy foamable polyurethane-forming material of which the chemical reaction has been initi ated. feeding a horizontally moving trough continuously with said foam able polyurethane-forming material to form a foaming mass, and using pressure means to press the top surface of said foaming mass only over a zone extending for 3 to 7 metres from a point which is virtually the point of completion of foaming and thereby make flat the top surface thereof. said pressure means moving horizontally in synchronism with and in the same direction as said trough. and the method being arranged so that a slab of polyurethane foam having a thickness of 40 to 250 mm is produced.

2. A method as claimed in claim l wherein the bottom of said trough is composed of an endless belt conveyer and each of the sidewalls of said trough is composed of a vertical sheet moving horizontally in synchronism with and in the same direction as said conveyer.

3. A method as claimed in claim 1 comprising the additional step of feeding a sheet continuously between said conveyer and said foaming mass and wherein said sheet is stripped from the under surface of said foaming mass after said foaming mass has been fabricated.

4. A method as claimed in claim 1 comprising the additional step of feeding a sheet continuously between said conveyor and said foaming mass and wherein said sheet is bonded to the under surface of said foaming mass so as to constitute a part of the final product.

5. A method as claimed in claim 2 wherein said vertical sheet is stripped from each of the sides of said foaming mass after said foaming mass has been fabricated.

6. A method as claimed in claim 1 comprising the additional step of feeding a sheet continuously between said pressure means and said foaming mass and wherein said sheet is stripped from the upper surface of said foaming mass after said foaming mass has been fabricated.

7. A method as claimed in claim 1 comprising the additional step of feeding a sheet continuously between said pressure means and said foaming mass and wherein said sheet is bonded to the top surface of said foaming mass so as to constitute a part of the final product.

8. A method as claimed in claim 1 wherein said pressure means is composed of a travelling endless belt.

9. A method for continuous production of slabs of polyurethane foam, substantially as hereinbefore described with reference to the accompanying drawings.

10. A slab of polyurethane foam when produced by the method as claimed in any

Claims

preceding claim.