IE48877B1 - Process and apparatus for continuous production of polyurethane foam - Google Patents

Abstract

A process and apparatus for the continuous production of polyurethane foam are directed to the use of a laterally translating mold 13, the first portion of which has divergent side walls, including a "V"- shaped mold (12) having divergent straight vertical side walls (14). A polyurethane reaction mixture is deposited via conduit (11) at or near the mold apex the angle of which is 10 DEG to 120 DEG . Typically, the mixture is permitted to substantially complete its rise after being conveyed past the extremities of the divergent side walls (14) of the first mold portion. The invention contemplates use of a ratio of conveyor velocity to foam product height lower than those of the prior art. Both rectangular and circular cross sectional products can be produced.

Description

The present invention relates to the continuous production of cast polyurethane foams, such as rigid, semirigid and flexible polyurethane foams.

Polyurethane foams are widely used as materials-from which articles such as mattresses, seat cushions, and thermal insulators are fabricated. Such polymeric foam materials are ordinarily manufactured by a casting process in which a mixture of liquid polyurethane-foamgenerating reactants are deposited in a mold. As used herein, the term mold includes both stationary molds for batch casting and translating or otherwise movable molds for continuous casting. Evolution of a gas causes the reactants to foam. For some foam formulations, the reactants themselves react to evolve sufficient gas; in others a blowing agent is mixed with the reactants to provide gas evolution. Continued gas evolution causes the foam to expand to fill the mold. The foam, initially a partially expanded fluid mixture, becomes increasingly viscous as the reactants polymerize, ultimately curing into a polyurethane foam casting shaped by the mold.

Slabs of polyurethane foam approximately rectangular or circular in cross section are conventionally cast in a translating channel-shaped mold. Such molds typically include a belt conveyor forming the bottom of the mold and a pair of spaced-apart, opposing -side walls, which can be fixed or translatable at the speed of the conveyor. The mold sides and bottom are generally lined with one or more sheets of flexible-web such as kraft paper or polyethylene film. The sheets of mold liner are ordinarily withdrawn from rolls and continuously translated along the mold channel at the same speed as the belt of the conveyor. Liquid-foam-generating reactants are deposited on the mold bottom in a zig-zag pattern from a pouring nozzle positioned above the mold which is reciprocated back and forth across the width of the mold. Typically, after the reactants flow together, they expand and form a uniform slab of foam. Conventional production of foam products having rectangular and circular cross sections is taught in U. S. Patent No. 3,325,823 and U.S.

Patent No. 3,325,573, respectively. The disclosures of those patents are incorporated by reference.

If fresh reactant mixture is deposited on top of foam generated from previously deposited reactants, the re15 suiting cured foam will have an uneven surface and nonuniform density, which is undesirable for most applications. By continuously translating the mold liner, the reactant mixture is continuously carried away from the pouring area below the pouring nozzle, which reduces the tendency for fresh reactant mixture to cover that previously deposited.

Propitious selection of conveyor velocity can prevent production of undesirable foam products. A range of velocities can be established for a particular reactant mixture formulation. Minimum velocity is achieved when liquid reactant mixture is evenly distributed on the bottom of the mold and does not flow in a direction opposite to that of the mold and conveyor. Maximum velocity is achieved when the deposited liquid mixture begins to flow in the same direction as the conveyor.

Selection of a velocity within the mentioned range requires consideration of the chemical reaction occuring subsequent to the depositing of liquid mixture in the mold. During residence in the mold, liquid mixture foams and cures.

The height of the foam is affected by conveyor velocity. Because economy necessitates maximum product height, lower velocities are preferred during the foaming portion of the reaction to attain such heights. The ratio of dists/jce travelled by the conveyor per minute to product height is a useful criterion for evaluating process efficiency, i.e. the lower the ratio, the more efficient the process. According to the process of this invention, that ratio can be reduced to the range of about 1 to about 3.

To reduce further the tendency.of the liquid reactants to flow back under the pouring nozzle and to assist the zig-zags of reactant mixture to merge uniformly, it is customary to incline a pouring board, the surface trader the nozzle, from horizontal so that the bottom liner slopes downward in the direction of translation. However, the angle of inclination of the pouring board cannot be greater than about 4.5° from horizontal for typical flexible polyether polyurethane-foam formulations without causing the reactant mixture to flow forward under previously deposited mixture, which leads to undesirable nonuniform foam. The angle of inclination is different for different foam formulations, such as polyester polyurethane foams.

Problems arise if the mold bottom slopes downward along its entire length. Conventional continuous slab molds are quite long, typically in excess of 60 feet, to provide for the long curing time of the foam. Building a translatable mold of this length inclined from hori30 zontal is significantly more expensive than building a translatable mold of the same length which is horizontal, because, for example, the building housing the inclined mold would be required to have higher than normal ceilings.

Moreover, it is expensive to change the angle of inclination of the entire mold to compensate for differing viscosities among various foam formulations. Thus, some continuous slab molds have horizontal belt conveyors for most of the length of the mold bottom, but have relatively short inclined pouring boards located beneath the pouring nozzles. The expansion and rise of the foam generally takes place on the sloping pouring board.

A second reason for providing a pouring board which makes 10 an angle with respect to the belt conveyor relates to the cross-sectional shape of the slab cast in the mold. As the foam expands and rises in the mold, it encounters the sides of the mold. If the mold-side liners are being translated substantially parallel to the mold bottom, the expanding foam experiences a shear force which resists its rise along the sides. This shear force results in a rounding of the top of the slab to form a crown or crest of convex shape, much like a loaf of bread. For most applications, such rounded portions are unusable and must be discarded as scrap. Thus, the more nearly rectangular the cross section of the slab, i.e., the flatter the top, the more economical is the casting process.

If, over the length the foam expands, the mold bottom liner and the two mold side liners are translated at an angle with respect to one another, the mold side liner can have a velocity component relative to the mold bottom in the direction of the expansion of the foam. This velocity component can compensate for the shear force which resists the rise of the foam. Guiding the mold bottom linor across an inclined pouring board, which intersects an inclined mold-bottom conveyor can provide such a compensating velocity component when foam expansion occurs over the length of the pouring board and when mold5 side liners are translated parallel to the mold-bottom conveyor. The angle of intersection, which ordinarily leads to polyurethane foam slabs having the most nearly rectangular cross sections, is about 10° for typical 5 foam formulations and production conditions. Unfortunately, if the pouring board is sloped 10° from horizontal freshly deposited reactant mixture tends to flow forward, as discussed above, leading to foam slabs of non-uniform density or other imperfections.

Although it is possible to construct a continuous slab mold with a pouring board inclined from horizontal by an angle of 4.5° and intersecting the belt conveyor at 10°, the belt conveyor in such a case must be inclined upward by an angle of 5.5°. See, for example, the apparatus of u.S. Patent No. 3 325 823. As noted above, however, inclined translatable molds are more expensive than comparable horizontal molds.

United States Patent No. 3,786,122 discloses a process tor producing polyurethane foam slabs which employs a horizontal, channel-chaped mold having at its forward end an inclined fall plate which makes an angle of significantly greater than 4.5° from horizontal. The problem of reactant mixture flowing down the inclined fall plate is obviated by prereacting the reactant mixture prior to introducing it onto the fall plate. The prereacting step is carried out in a trough which opens onto the upper edge of the fall plate. Liquid foam reactants are introduced onto the bottom of the trough and the foam which is generated is allowed to expand upwards in the trough and spill over onto the fall plate. The foam continues to expand as it is carried down along the fall plate by a translating bottom sheet. Because the prefoamed reactant mixture exiting the trough is more viscous than the initial liquid reactant mixture, the fall plate can be inclined at a greater angle from horizontal than a pouring board in a conventional polyurethane foam slab mold.

An additional result of introducing prefoamed reactant mixture into the mold is that relatively high foam slabs can be produced as compared with conventional processes. Economies result from producing high slabs because, the thicker the foam slab, the less is the loss from discarding rind which generally coats polyurethane foam castings.

With a conventional slab mold, if the rate of introduction of reactant mixture is kept constant and the rate of translation of the mold liner is reduced, the height of the foam slab tends to increase because more foam-generating reactant is deposited per unit length. However, if the rate of translation is slowed sufficiently, the expanding foam, particularly the youngest and most fluid portion, becomes unstable and tends to slip and shift, which results in cracks and other imperfections in the cured foam.

This problem of instability of rising foam is reduced in the process of U.S. Patent No. 3 786 122 by introducing into the translating mold pre foamed reactant mixture which is sufficiently viscous as to be able to sustain a relatively steep slope of the pouring board as it completes its expansion. Thus, the height of the foam can be increased.

In addition to permitting higher foam slabs to be cast by reducing the translation speed of the mold liner, this process permits the use of slab molds shorter than those of conventional processes, because the slab moves a shorter distance during the curing time.

Certain problems attend the use of the open trough of U.S.

Patent No. 3 786 122. For example, changing the width of the trough is difficult because foam deposits interfere with re-establishing fluid-tight seals. Moreover, the trough opening is subject to partial blockage by deposits of cured foam along the back and sides where the flow of prefoamed reaction mixture stagnates. Such deposits break free from time to time and are swept over the weir into the rising foam, thereby causing objectionable non-uniformities in the foam slab. A further difficulty is encountered when air bubbles are introduced into the bottom of the trough with the liquid reactants. These air bubbles generally remain entrained in the foam, leading to voids and other defects in the cured material.

United States Patent No. 3 870 441 discloses an apparatus for producing polyurethane foam slabs which uses a horizontal, channel-shaped mold similar to the apparatus disclosed in U.S. Patent No. 3 786 122. Likewise, liquid foam reactants are introduced into the bottom of the trough and allowed to expand upward eventually spilling over onto a fall plate. The expanding foam moves across the fall plate to a conveyor via a translating bottom sheet. The improvements of U.S. Patent No. 3 870 441 is directed to a means for assisting the expanded foam in spilling over the fall plate. That flow assisting means comprises translating sheets, substantially perpendicular to the bottom sheet, which continuously move around the periphery of the channel-shaped mold including the periphery of the trough. However, that improvement to U.S. Patent No. 3 786 122 does not alleviate all of the drawbacks noted above for U.S. Patent No 3 876 122.

According to the present invention, there is provided a process for continuously molding polyurethane foam in a continuous, laterally translating open top mold at a given bottom conveyor velocity by depositing a polyurethane foam-forming mixture of reactants at a given feed rate on a pouring board, comprising increasing the height of the so molded flexible polyurethane foam product/Obtained by (i) depositing said polyurethane foam forming mixture of reactants near the apex of a first mold portion of the laterally translating mold, which first portion of said laterally translating mold has divergent first side walls which form an angle therebetween of 10° to 120° and which join, at their extremities, the parallel second side walls of a second portion of said translating mold, and (ii) allowing said polyurethane foam forming mixture of reactants to substantially complete its rise after traversing past said first portion of the translating mold.

According to a further aspect of the present invention there is provided apparatus for producing polyurethane foam including: (a) means for mixing liquid polyurethane foam-generating reactants; (b) means for depositing the mixed reactants in a laterallytranslating mold; and (c) a continuous, open top mold, which includes: (1) a bottom belt conveyor extending laterally for translating a foam product; (2) a laterally translating mold whose bottom surface is adjacent the belt conveyor; and (3) a pouring board disposed between side walls of the mold having an elevated edge adjacent said depositing means which extends to the mould bottom surface; . . wherein a stationary deposis employed iting means/to deposit the mixture of polyurethane foam-forming reactants near the apex of a first open top mold portion having divergent first side walls which form an angle therebetween of 10° to 120° and which join, at their extremities, parallel second side walls of a second portion of said translating mold.

The invention contemplates the use of a unique laterally translating mold arrangement having the ability to achieve high block heights or greater diameter round block foams. Specifically, that mold arrangement contains a first mold portion with diverging side walls, particul arly a V'-shaped mold portion with diverging straight vertical side walls.

The angle of the diverging side walls is not critical, but should be less than about 120°, preferably within the range of 10° to 90°. The angle referred to is defined by imaginery lines from the apex of the first mold portion to the point of intersection of the diverging side walls with the parallel second side wall portions of the mold. Reaction mixture is deposited at the apex of the V" and substantially completes its expansion shortly past the extremities of the V which join parallel side walls of a conventional mold arrangement. A centrifuge, as described in U.S. Patent No. 4 158 132 can advantageously be employed to deposit a partially-expanded prefoamed mixture of reactants. The mixture can be deposited on a segmented pouring board. Use of the present invention results in low ratios of conveyor velocity to product height as compared with substantially higher ratios used in prior art processes and apparatus.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of an apparatus of the present invention used for producing polymeric foam products utilizing a mold having a V shape; Figure 2 is an elevation and partial section of the embodiment of Figure 1 wherein a conventional mixing head is used to deposit 3θ poly urethane reactants on a pouring board inclined at an angle a from horizontal near the apex of the V portion of the mold; Figure 3 is also an elevation and partial section of a modification of Figure 1 wherein the segmented pouring board is depicted having a first horizontal segment followed by a second segment inclined at an angle a from horizontal; Figure 4 is also an elevation and partial section of a modification of Figure 1 wherein the polyurethane foam reactants are passed from a conventional mixing head into a prefoaming means and then deposited on a device depicted in great detail in ' Figure 4A. which device is suspended below the mixing head and above the pouring board to receive the polyurethane foam-forming reactants as a partially-expanded prefoamed mixture of reactants; Figure 4A is a frontal view of the device in Figure 4 on which the partially-expanded prefoamed mixture of reactants is deposited; Figure 5 is also an elevation and partial section of a modification of Figure 4 wherein a segmented pouring board is depicted having a first and second segment inclined at angles and from horizontal, respectively; Figure 6 is a frontal view of the modification of Figure 1, wherein the polyurethane foam-forming reactants are passed into a cone-shaped bottom prefoaming means and then deposited on the pouring board by flowing out of the cone-shaped prefoaming means as a partially-expanded prefoamed mixture of reactants; and Figure 6Λ is a frontal view of the cone-shaped prefoaming means utilized in the apparatus depicted in Figure C used in conjunction with an upstream or bottom centrifuge.

Referring now to Figure 1, and apparatus 10 for producing products of free-rising polyurethane foam is illusurated. The foam product will have a substantially rectangular cross-section (see U.S. Patent No. 3 325 823); however this apparatus could be modified to make a foam product with a substantially circular cross section according to the teachings of U.S. Patent No. 3 325 573. Such apparatus is suitable for use with the process of the present invention. The apparatus includes a conduit 11, which can be stationary or can reciprocate, depending upon the neces10 sity for distributing the premixed reactants near the apex of the V shaped first portion 12 of a continuously translating mold 13. The latter second portion of mold 13 includes a conventional arrangement for producing a product having the desired shape with a conventional bottom convey15 or means to translate the expanding and curing polyurethane foam and parallel side walls which can be either .moving or stationary. The V-shaped portion includes the first mold portion side walls 14 which diverge and cannot be parallel or convergent. Those first mold portion side 2q walls of the V-shaped portion join at their extremities the second mold portion parallel side walls 15 comprising the latter second portion of the mold 13.

Fig 2 shows conduits 16 and 17 which simultaneously convey a mixture of polyurethane foam forming reactants to a conventional mixing head 18 connected to conduit 11 for depositing premixed reactants on pouring board 19. A mold bottom liner 20 made of a flexible-wob, such as Kraft paper, is supplied from a roll shown in the drawing and ic guided over pouring board 19 onto a mold bottom surface 21 of a bottom belt conveyor 22.

First and second side mold-side liners 23 and 23Λ, also made of a flexible-web, such as Kraft paper, are guided past opposing guide means 24 and then translate across the first portion mold side-walls 14 of the V" shaped first mold portion 12 and then past second mold portion side walls 15 of mold 13. Mold side liners 23 are positioned flat against mold side walls 14 and 15 by the pressure of the expanding, premixed polyurethane foam forming reactants. The mold side liners and mold bottom liner define a channel-shaped mold for casting foam products, which can have substantially rectangular or substantially circular cross sections. Means are provided for guiding and translating the side liners and bottom liner in a parallel relationship. Of course, the rate of translation of the three liners should be substantially equal to the rate of translation of belt conveyor 22.

Pouring board 19 can be substantially flat or curved and makes an angle a from the horizontal. The angle of inclination a can be adjusted to accommodate variations in the viscosity of the mixture being deposited thereon.

Although a one angle pouring board 19 is illustrated in Figures 1 and 2, in certain applications it can be advantageous to employ pouring boards having more than one segment such as that shown in Figure 3, each segment being inclined at a different angle from horizontal, or, as in Figure 3 with a first segment horizontally arranged. Figure 3 shows a pouring board consisting of two segments, a first horizontal segment 25 located adjacent conduit 11 and a second inclined segment 26 abutting first segment 25 and adjacent to belt conveyor 22 inclined at an angle a from horizontal. Such a pouring board arrangement has been used to make foam products of substantially rectangular and substantially circular cross sections. Other segmented pouring boards „ 48877 are of course within the bounds of the instant invention.

Figure 4 depicts a further modification of Figure 1 employ ing a prefoaming means 27 used in making a partially expanded prefoamed mixture of polyurethane foam forming reactants to be deposited on pouring board 19. Prefoaming means 27 is illustrated as a top centrifuge such as those described in U.S. patent No. 4,158,132Other prefoaming means useful in the practice of the present invention are the cone-shaped prefoaming means alone or in conjunction with the bottom centrifuge depicted in Figures 6 and 6A; in this regard reference is made again to U.S. patent No. 4,158,132.

As previously described, conduits 16 and 17 15 simultaneously transport polyurethane foam reactants into nixing head 18. Premixed reactants exit mixing head 18 through conduit 11 which comprises the inlet for prefoaming means 27, which is illustrated in this instance as a top centrifuge.

When prefoaming means 27 includes a top centrifuge, a variable speed electric motor 28 is used to rotate container 29 by way of a pully drive 30. A motor speed control 31 varies the speed of motor 28. Accordingly, mixed reactants enter through inlet tube 11 to rotating pressurized container 29 to form a partially-expanded polymeric raixture 32.

A gas atmos[jhere can be maintained over mixture 32. -,0 The pressure of that atmosphere is controlled at a predetermined value by a conventional gas pressure controller 33 which is connected to container 29 by conduit 34.

That pressure propels the partially-expanded mixture through flexible conduit 35 to a dispensing nozzle 36.

Flexible conduit 35 directs the partially-expanded' mixture from the interior of the container 29 to the apex of the "V-shaped portion 12 of mold 13. Nozzle 36 is positioned above pouring board 19 near the apex of the V-shaped portion of the mold. Advantageously, a circular reservoir 37 and a weir 38 combination is positioned below nozzle 36; this combination is depicted in greater detail by Figure 4A. The nozzle can be stationary or be reciprocated cross-wise of mold 13 across the width of the apex of the V-shaped portion 12 by conventional reciprocation means. An edge of the pouring board 19 abuts a surface of a conventional belt conveyor 22, which is used to form a mold bottom surface 21. That surface is preferably substantially horizontal. Otherwise, the apparatus operates in a manner previously described with regard to Figure 1.

The circular reservoir 37 and weir 38 combination depicted by Figure 4A is employed to further control the spread of the partially-expanded prefoamed mixture of reactants onto the pour board 19. That combination also contains a lip 39 over which the partially-expanded prefoamed mixture of reactants passes before running onto the pouring board 19.

Although a one segment pouring board 19 is depicted in Figure 4, in certain applications it can be advantageous to employ a multi-segmented pouring board such as that shown in Figure 5', each segment being inclined at a different angle from horizontal. Figure 5 shows a pouring board consisting of two segments, a first segment 40 located adjacent to pouring nozzle and having an angle from horizontal and a second segment 41 abutting first segment 40 and adjacent belt conveyor 22, having an angle a2 from horizontal. Again, further multiple-segmented pouring boards are within the scope of the instant invention.

Figure 6 shows a frontal view of the modification of the apparatus depicted by Figure 1, wherein a cone5 shaped bottom prefoaming means 42 is employed to deposit the partially-expanded prefoamed mixture of reactants onto the pouring board 19. In that cone-shaped bottom prefoaming means (depicted separably by Figure 6A), the partially-expanded prefoamed mixture of reactants is introduced from below the pouring board 19 through conduit 43; thereafter the mixture exits from the opening 44 and flows into the reservoir 45 formed by the back and side wall 46 and the front weir 47. Thereafter the partially-expanded prefoamed mixture of reactants moves onto pouring board 19, above which a mold bottom liner 20 made of a flexible web, such as Kraft paper, passes.

The first and second side wall liners 23 and 23a, also made of a flexible web such as Kraft paper, are guided past opposing guide means 24 and 24a. The bottom mold liner and first and second side wall liners 23 and 23a thereafter pass over the surface 21 of the bottom belt conveyor 22.

Figure 6Λ depicts separably the cone-shaped bottom pre foaming means employed in Figure 6. Figure 6A also contains reference to a bottom centrifuge 48 which has been employed advantageously in combination therewith.

Ir. accordance with the process of the subject invention, a first component Λ and a second component B enter mixing head 18 simultaneously. These components are premixed using a conventional mixing head and can either be deposited directly on pouring board 19 by conduit 11 or can enter prefoaming means 27 where a partially16 expanded prefoamed mixture 32 is formed and then be subsequently deposited via nozzle 36 on the pouring board. Conduit 11 and nozzle 36 can either be stationary or be reciprocated. The mixture is normally deposited at a constant rate near the apex of the V shaped portion 12 of mold 13. The components of the mixture continue to react, expand and cure to form a polyurethane foam product. The deposited mixture continuously translates along with the mold liners and the conveyor. The conveyor normally translates at a constant velocity. Typical foam formulations used in the subject invention are exemplified hereinafter.

EXAMPLES The following examples are illustrative of the ease with which polyurethane foam products can be produced in accordance with the process of the present invention.

EXAMPLE I 2Q A slab of polyurethane foam was cast continuously using a conventional mixing head illustrated in Figure 1. The following formulation was mixed in the head and deposited near the apex of the V-shaped portion of the mold: EXAMPLE I weight % weight % Component A Dow Polyol CP 3140 (3700 MV copolymer of ethylene oxide and propylene oxide, made by Dow Chemical Company) Master Batch I: Dow Polyol CP 3140 BF 2370 (Silicone surfactant made by Goldschmidt Chemical Company) Via ter A-l (70¾ solution of bis (di methylaminoethyl) ether in di propylene glycol, made by Onion Carbide Company) Master Batch II: Dow Polyol CP 3140 20 C-6 (33-1/3% T-9) (33-1/3% solution of stannous octate in D.O.P. made by VJitco Chemical Company) Component B TD-80 (Toluene diisocyanate 80/20 2,4/2,6 isomer ratio, made by Mobay Chemical) The ingredients of component component, were premixed and 65.05 65.05 g/min 3,470 32.45 0.75 4.00 0.10 37.30 37.30 1,990 2.50 0.75 3.25 3.25 173 50.00 50.00 2,667 155.60 8,300 (18.26 lb/min) A, comprising the polymer pumped by a single stream into the mixing head. Component B, comprising the toluene diisocyanate component, was separately and simultaneously pumped into the head. The two components were mixed at ambient temperature. The feed rate of the blended components was 8,300 grams/minutc or 18.26 pounds/minute. The resulting mixture was deposited at a constant rate near the apex of the V-shaped portion of the mold. The f irst mold side walls of the V-shaped portion were 44 inches in length and were spaced apart 25 inches at the point where they joined second mold side walls. The angle between the divergent side walls in this instance is therefore about 33°. The expanded mixture moved down a segmented pouring board similar to that depicted in Figure 3. The first segment of the pouring board was inclined at an angle 0° from the horizontal while the second segment was inclined at an angle 17° from the horizontal. The segmented pouring board abutted a conveyor inclined upwardly at an angle 3° from the horizontal.

The constant velocity of the conveyor was 4.29 ft/min. Consonant with Figure 3, the mold was channel-shaped with parallel side walls lined with Kraft paper which paper moved at the same velocity as the conveyor. A substantially rectangular polyurethane foam product was produced having a density of 1.65 pounds/cubic foot and having a height of 19.2 inches. The ratio of conveyor velocity to product height was about 2.7.

EXAMPLE II Example I was repeated using a lower feed rate and a different reactant formulation: Component A weight % weight % g/min Dow Polyol CP 3140 77.13 77.13 3,470 Master Batch I: Dow Polyol CP 3140 20.37 BF-2370 0.75 Water 4.00 Λ-1 0.10 25.22 25.22 1,135 Master Batch II: Dow Polyol CP 3140 2.50 C-6 (33-1/33 T-9) 0.75 3.25 3.25 146 Component B TD-80 50.00 50.00 2,249 155.60 7,000 (15.4 lb/min) The feed rate of the reactants was 15.4 pounds/minute, and the velocity of the conveyor was 3.41 feet/minute. A quality foam product was produced having a rectangular cross section and having a height of 15.9 inches. The ratio of conveyor velocity to product height was about 2.6 EXAMPLE III A slab of polyurethane foam was cast continuously using a centrifugal prefoaming means similar to that illustrated in Figure 4. The following formulation was mixed in the 10 prefoaming means: Component A weight % weight % g/min Dow Polyol CP 3140 75.00 75.00 7,160 Master Batch I: 15 Dow Polyol CP-3140 BF 2370 Water A-5 ( 22.50 0.80 4.00 20 Master Batch II: 0.03 27.33 27.33 2,609 Dow Polyol CP-3140 C-6 (33-1/3 T-9) 2.50 0.57 3.07 . 3.07 293 Component B 25 TD-30 50.00 50.00 4,773 155.40 14,835 (32.6 lb/min) Tile ingredients of component A, comprising the polyol component, were premixed and pumped as a single stream into a conventional mixing head. Component B, comprising the toluene diisocyanate component, was separately and simultaneously pumped into that head. Then the two components were mixed at ambient temperature. The mixed components were then fed into a centrifugal prefoaming means to form a partially-expanded polyurethane foam mixture. That mixture was deposited near the apex of the V-shaped portion of the mold at a constant feed rate of 14,835 grams/minute. First mold side walls of the V were 60 inches in length and were spaced 46 inches apart; the angle between the side portions of the "V'-shaped mold is, therefore, about 45°. The pouring board, upon which the partially-expanded mixture was deposited, contained 3 segments: a first segment inclined at 15°, a second segment inclined at 0° and a third segment inclined at IQ 13°. The pouring board abutted a conveyor which was upwardly inclined at an angle of 3°. The latter portion of the mold was channel-shaped with parallel side walls spaced apart about 46 inches. The mold was lined with Kraft paper which translated at a constant velocity.

Utilizing the formulation and feed rate mentioned above, a number of experiments were conducted wherein the velocity of the conveyor was varied. The results are tabulated below: TABLE Experiment Number Conveyor Velocity (V , ft/min J Product Height (H) Ratio inches (V X c 12J/H 1 2.75 17.2 1.92 2 2.93 16.15 2.18 3 3.02 16.65 2.IS 4 3.02 16.10 2.25 5 3.34 16.5 2.43 6 3.34 16.95 2.36 7 3.34 16.15 2.43 8 3.61 16.55 2.62 9 4.10 17.6 2.79 10 4.38 18.0 2.92 The ratio ' varied from about 1.9 to about 2.9.

EXAMPLE IV Experiment I was repeated using a similar polyurethane formulation with an increased feed rate of 32.6 pounds per minute: Component A Dow Polyol CP 3140 Master Batch I: Dow Polyol CP-3140 BF 2370 Water A-5 Master Batch II: Dow Polyol CP-3140 C-6 (33-1/3-1 T-91) Comoonent B TD-80 weight I 75.00 weight 75.00 g/min 7,160 22.50 0.80 4,00 0.07 27.37 27.37 2,613 2.50 0.57 3.07 3.07 299 50.00 50.00 155.44 4,773 14,845 (32.6 lb/ min) First mold side walls of the V-shaped portion of the mold were 60 inches in length and spaced apart 46 inches at the point where they joined the latter portion of the mold (i.e. a = about 45°). The expanded mixture moved down a segmented pouring board:' a first segment inclined at 15°, a second segment inclined at 0°, a third segment inclined at 3°, and a fourth segment inclined at 13°. The segmented pouring board abutted a conveyor inclined upwardly at an angle of 3°. The velocity of the conveyor was 4.0 feet/minute, and the height of the rectangular foam slab was 15.5 inches, which resulted in a ratio of the conveyor velocity to the product height of about 3.2.

EXAMPLE V Exanple III was repeated for round block production using a tunnel-shaped portion for the latter portion of the mold.

The following polyether formulation was mixed in the prefoaming means : Component A weight % weight % g/min Dow polyol CP-3140 Master Batch I: 64.968 64.968 3,470 Dow Polyol CP-3140 BF 2370 Water A-5 32.522 0.800 4.000 0.030 37.352 37.352 1,995 Master Batch II; Dow Polyol CO-3140 C-6 (33-1/3¾ T-91) 2.50 0.57 3.070 3.070 164 Component B TD-80 50.000 50.000 2,671 155.390 8,300 (16.2 lb/min) First mold side walls had length of 44 inches and were spaced 23 inches apart. The pouring board was i segmented having a first segment inclined at 60, and a second segment inclined at 15°. The pouring board abutted the conveyor which was inclined upwardly at an angle of 3°. Circular foam products were obtained having a diameter of 22 inches. The velocity of the conveyor varied from 2.13 feet/minute to 4.19 feet/minute with attendant ratios of about 1.1 and about 2.2, respectively.

Overall, it should be noted that certain free-rising polyester-derived polyurethane foam formulations may be too sensitive to mechanical stresses to be employed in the present invention.

Claims (23)

1. A process for continuously molding polyurethane foam in a continuous, laterally translating open top mold at a given bottom conveyor velocity by depositing a polyurethane foam-forming mixture of reactants 5 at a given feed rate on a pouring board, comprising increasing the height of the molded flexible polyurethane foam product so obtained by (i) depositing said polyurethane foam forming mixture of reactants near the apex of a first mold portion of the laterally translating mold, which first portion of said laterally translating 10 mold has divergent first side walls which form an angle therebetween of 10° to 120° and which join, at their extremities, the parallel second side walls of a second portion of said translating mold, and (ii) allowing said polyurethane foam forming mixture of reactants to substantially complete its rise after 15 traversing past said first portion of the translating mold.

2. A process as claimed in Claim 1 wherein the ratio of the distance travelled by the conveyor per minute to the foam product height is from 1 to 3.

3. A process as claimed in Claim 1 or 2 wherein said polyurethane 20 foam-forming mixture of reactants is deposited in partially-expanded, prefoamed form between the divergent vertical side walls of the first mold portion.

4. A process as claimed in Claim 3 wherein said polyurethane foamforming mixture of reactants is deposited in a partially-expanded, 25 prefoamed form from a centrifuge, prefoaming means.

5. A process as claimed in Claim 3 wherein said polyurethane foam fonning mixture of reactants is deposited in a partially-expanded, prefoamed form from a cone-shaped prefoaming means.

6. Λ process as claimed in any preceding claim, wherein said polyurethane foam is a polyester-derived polyurethane foam.

7. A process as claimed in any preceding claim, wherein the deposited mixture of reactants translates across a segmented pouring 5 board having a horizontal first segment.

8. A process as claimed in any preceding claim, wherein the deposited mixture of reactants translates across a pouring board having at least one segment downwardly inclined toward the second portion of the translating mold. 10

9. A process as claimed in any preceding claim, wherein a continuous slab is molded having a substantially rectangular cross section.

10. A process as claimed in any preceding claim, wherein a continuous slab is molded having a substantially circular cross section.

11. A process as claimed in Claim 1 for continuously molding 15 polyurethane foam substantially as hereinbefore described.

12. A process for continuously molding polyurethane foam, substantially as hereinbefore described with reference to Figures 1 and 2; Figure 3; Figures 4 and 4A; Figure 5; or Figures 6 and 6A of the accompanying drawings. 20

13. A process for continuously molding polyurethane foam, substantially as hereinbefore described with reference to any one of the foregoing Examples I to V.

14. Polyurethane foam when produced by the process as claimed in any preceding claim.

15. Apparatus for producing polyurethane foam including: (a) means for mixing liquid polyurethane foam-generating reactants; (b) means for depositing the mixed reactants in a laterallytranslating mold; and (c) a continuous, open top mold, which includes: (1) a bottom belt conveyor extending laterally for translating a foam product; 2. (2) a laterally translating mold whose bottom surface is adjacent the belt conveyor; and (3) a pouring board disposed between side walls of the mold having an elevated edge adjacent said depositing means which extends to the mold bottom surface; wherein a stationary depositing means is employed to deposit the mixture of polyurethane foam-forming reactants near the apex of a first open top mold portion having divergent first side walls which form an angle therebetween of 10° to 120° and which join, at their extremities, parallel second side walls of a second portion of said translating mold,

16. Apparatus as claimed in Claim 15 wherein a prefoaming means is employed in combination with the depositing means so that, when deposited, the mixture of polyurethane foam-forming reactants is in the partially-expanded pre-foamed state.

17. Apparatus as claimed in Claim 16 wherein the prefoaming means is a centrifuge.

18. Apparatus as claimed in Claim 16 wherein the prefoaming means is a cone-shaped bottom foaming means.

19. Apparatus as claimed in any of Claims 15 to 18, wherein the pouring board is segmented.

20. Apparatus as claimed in Claim 19, wherein the pouring board has a first horizontal segment adjacent said depositing means followed by an inclined second segment.

21. Apparatus as claimed in any of Claims 15 to 20, wherein the second mold portion is rectangular in cross-section. 10

22. Apparatus as claimed inanyof Claims 15 to 20, wherein the second mold portion is circular in cross-section.

23. Apparatus for continuously molding polyurethane foam substantially as hereinbefore described, with reference to Figures 1 and 2; Figure 3; Figures 4 and 4A; Figure 5; or Figures 6 and 6A of the 15 accompanying drawings.