GB2028214A - Process and mould for the manufacture of polyurea foam articles. - Google Patents

Abstract

The process comprises covering at least part 16 of a mould surface with an impervious material 37, introducing into the mould cavity 20 a polyurea foam-forming mixture, allowing the mixture to expand to fill the mould cavity and, before the foam so formed cures, puncturing or otherwise rupturing the foam while it is still in the mould to release the gas pressure and prevent blistering. Apparatus suitable for carrying out the process comprises a mould 11 and a foam rupturing device consisting of a set of regularly spaced rigid pins 27, 29 and 31 attached to an outer casing 19 and passing through a former 17 into the mould cavity 20. Channels in the former, through which the pins pass, have grooves for the relief of pressure in the mould when the pins are retracted. The process and apparatus find particular application in the making of roof liners for cars. <IMAGE>

Description

SPECIFICATION Process and mould for the manufacture of polyurea foam articles This invention relates to the production of moulded articles composed of polyurea foam and faced with impervious material.

Processes are already known for producing shaped articles comprising a shaped body of a foamed plastics material, for example polyurethane foam, and an adherent facing material.

One process is to apply a polyurethane foam-facing mixture to a facing material in a suitable mould so that the foam is formed in contact with the facing material. When this process is used for moulding an article from a polyurea foam and an impervious facing material, we have found that it is unsatisfactory as the material blisters.

According to the present invention we provide a process for the manufacture of a shaped article which comprises covering at least part of a mould surface with an impervious material, introducing into the mould a polyurea foam-forming mixture, allowing the mixture to expand to fill the mould cavity and, before the foam so formed cures, puncturing or otherwise rupturing the foam while it is still in the mould. The invention also includes shaped articles so formed.

By "impervious material", we mean a material which cannot be penetrated by the foam-forming mixture during the process of the invention. Suitable materials include polyvinylchloride and polyethylene coated textiles and other plastics coated fabrics. In particular we would mention 'brushed nylon' and "Cambrelle" (Registered Trade Mark).

The polyurea foam-forming mixture used in the invention comprises an organic polyisocyanate, water and, usually, a catalyst.

Organic polyisocyanates which may be used include those aromatic polyisocyanates that have already been described in the literature for use in the manufacture of polyurea foams. Mention may be made of diphenylmethane diisocyanate and tolylene diisocyanate in their various forms and, in particular, diphenylmethane diisocyanate, especially diphenylmethane-4,4'-diisocyanate, which may be in admixture with isomeric or other related polyisocyanates or may have been modified in known manner to introduce a significant iscoyanurate, carbodiimide, uretonimine or biuret content. Polyisocyanate components comprising diphenylmethane diisocyanate include the crude diphenylmethane diisocyanates that have been fully described in the prior art.

The amount of water used will normally be at least chemically equivalent to the isocyanate groups present in the polyisocyanate and possibly ten times that amount. Preferably 1.5 to 5 times, and especially 2 to 4 times, the chemically equivalent amount is used.

The catalyst may be any known polyurea foam catalyst. Particularly useful are the imidazole compounds described in OLS 2627 719.

Other ingredients and additives may be used. The inclusion of an organic polyol, polymeric or otherwise, may improve the stability of the foam. Suitable polyols are those well known to the skilled man in the polyurethanes field and are catalogued in the literature.

Additives which may be used are those conventionally employed in the production of poiymeric foams from organic polyisocyanates and include plasticisers, fire-retardants, surfactants, thickeners, dyes, pigments and fillers. Conventional blowing agents may also be included, if desired, although the carbon dioxide generated by the reaction between the polyisocyanate and water will itself act as a blowing agent.

While not wishing to be bound by any particular theory, it is believed that the problem of blistering of the impervious material is related to the development of high gaseous pressure in the mould during the reaction of the polyurea foam-forming mixture. This is caused by the formation of carbon dioxide and steam. The carbon dioxide is formed as already described. Excess water in the reaction mixture is turned to steam by the heat of reaction.

In the process of the invention the expanded foam is punctured or otherwise ruptured by, for instance, tearing, piercing, lacerating or perforating the foam, or in any other way which will release the pressure within the mould.

The amount of rupturing necessary will depend on the size and shape of the mould, but because the foams have predominantly open cells it need not be excessive. To avoid damage to the facing material, the foam is preferably ruptured, if possible, where it is not faced. In the manufacture of car furnishings, such as roof liners, door panels and cappings, where the invention is of particular value, a substantial part of the article may be unfaced.

The foam is ruptured after the foam has expanded and before it cures. The best time for doing this will depend on the particular foam formulation used and configuration of the mould cavity and will necessarily be found by trial and error. For the skilled worker in the field, this will not be difficult. If the foam is ruptured too early it may start to collapse; if too late gas will only be released in the immediate vinicity of the ruptured area and blistering will not be eradicated.

In carrying out the moulding process of the invention, the impervious material is stretched by the high gas pressures generated to take up the form of the mould.

According to a further aspect of our invention we provide apparatus suitable for carrying out the process of the invention which comprises a mould having therewithin a mould surface which defines a mould cavity, the mould, which can be opened to permit the mould surface to be covered, at least in part, with an impervious material, being provided with means for introducing a foam-forming mixture into the mould cavity while the mould is in a closed position, a rupturing device which can be moved within the mould cavity from an inoperative position to a foam-ruptured position by means external to the mould while the mould is in the closed position, and a pressure relief device operative when or after the rupturing device is moved to the foam-ruptured position.

For most purposes the mould is conveniently a two-part mould having a standard foam injection point, and in this respect is similar to any conventional foam mould.

One type of rupturing device consists of one or more rods which pass through channels into the mould cavity, the rods being in gas-tight contact with and moveable longitudinally within the channels from an inoperative position to a foam-rupturing position by means external to the mould.

In their simplest form the rods are rigid pins or wires. These may be in an inoperative position when they are retracted from the mould cavity and moved to a foam- ruptured position by sliding them into the cavity so that they rupture by piercing the foam. Retraction may then assist pressure release. Alternatively they may be in an inoperative position when they protrude into the cavity and are moved to a foam-ruptured position by retraction from the cavity. In this case the foam expands and forms around the rods and is ruptured by their retraction.

The rods may be fitted with foam-cutting or tearing devices inside the mould cavity to assist their penetration of the foam or with other devices to assist tearing the foam or with both.

The means external of the mould by which the rods are moved in their channels, preferably in unison, may be, for example, a simple handle for manual or automatic operation or a screw drive or a series of pneumatic or hydraulic cylinders.

The pressure relief device is a means by which gas can be released from the mould cavity when or after the foam has been ruptured.

In its simplest form it comprises one or more passages by which the mould cavity can be vented, the passages having closure members which can be opened when or after the rupturing device is moved to the foam-ruptured position.

The passages may enter the mould cavity at any suitable position but preferably they are near to the rupturing device and therefore near to a ruptured foam site. Conveniently the pressure relief device works in co-operation with the rupturing device.

Thus, in a preferred embodiment of the apparatus of the invention, the rupturing device comprises one or more rods which pass through channels into the mould cavity and the pressure relief device comprises one or more passages each of which is associated with a rod and channel of the rupturing device, the rods being in gas-tight contact with and movable longitudinally within the channels from an inoperative position to a foam-ruptured position and providing closure members for the associated passages of the pressure relief device.

In one aspect of this embodiment the rods open the passages of the pressure relief device as they move from the inoperative position to the foam-ruptured position.

In another aspect the rods open the passages of the pressure relief device on being moved from the foam-ruptured position to a pressure relief position.

By way of example only, the invention will now be further described with reference to the accompanying drawings in which Figures 1, 2, and 3 are cross sections of a mould in different positions during its operation, the mould being fitted with a foam rupturing device which tears foam formed in the mould when closed; Figures 4 and 5 are details from Figures 1 and 2 respectively; Figure 6 is a perspective view of a part of the foam-rupturing device; Figure 7 is a cross-section of a different mould fitted with a foam-rupturing device which punctures foam formed in the mould when closed; Figure 8 is a detail from Figure 7; Figure 9 is a perspective view of a mechanism for operating a rupturing device of yet another mould which both punctures and tears foam formed in the mould when closed;; Figure 10 is a diagrammatic illustration of part of the foam-rupturing device used with the mould referred to in Figure 9; Figure 11 is a perspective view of a part of Figure 10; and Figure 12 is a view of the part of Figure 11 in the direction 'X'.

In the drawings, a two-part metal mould 11, for a car roof liner, consists of parts 13 and 15 and has therewithin a mould surface comprising faces 12, 14, 16 and 18 defining a mould cavity 20. The mould cavity 20 measures approximately 100 cm by 60 cm by 1 cm deep. Part 15 has a former 17 slidable within an outer casing 19 and a retractable constraining plate 21 which has guide bars 23 and 25 screwed into the outer casing 19 and passing slidably through former 17. A chamber 10 (shown in Figures 2 and 3) is formed when the casing 19 is pulled away from the former 17.

A foam rupturing device consists of rigid pins 27, 29 and 31, screwed at one end into former 17 and having at the other end a foam-tearing device 22,24 or 26 respectively. The pins are in gas-tight contact with and moveable longitudinally within their respective channels 28,30 and 32 (see Figures 2 and 3).

Pins 27, 29 and 31 are three of a series of regularly spaced pins placed at the corners of imaginary squares having sides of approximately 20 cm.

The tearing device 22, shown in detail in Figure 6, is a solid frusto-cone having diametrically opposite segments cut away. The other tearing devices 24 and 26 are similar.

The channel 28, part of which is shown in detail in Figures 4 and 5, is formed within a sleeve 33 securely fitted in former 17. The sleeve 33 has a groove 35 for the passage of gas which terminates before it reaches the mould cavity 20. The pin 27 acts as a closure member for the groove 35. Both of the channels 30 and 32 are similar, each having associated sleeves with grooves.

A layer of impervious material 37 covers face 16 of the mould surface. In Figures 2,3 and 5 a foam layer 39 is shown formed in cavity 20. A ruptured foam site 38 left by tearing device 22 is shown in Figure 5.

In operation, parts 13 and 15 of mould 11 are clamped together with the layer of impervious material 37 covering face 16 of the mould surface. The decorative side of the material faces towards the mould surface.

Figure 1 shows the mould in this closed position. The pins 27,29 and 31 are in an inoperative position.

A polyurea foam-formed mixture prepared as described below is introduced into the mould cavity 20, by means not shown, and the foam expands to fill the mould cavity encapsulating tearing devices 22, 24 and 26.

The mould is pre-heated to 50 C. The amount of foam-forming mixture used is such that, without being constricted by the mould. the foam would expand to fill a volume slightly greater than the mould cavity.

The polyurea foam-forming mixture is prepared by mixing together a high molecularweight 67.5 parts by weight; poly(propylene/ethylene) oxide polyol of OH value 32 mg KOH/g water 6.5 parts by weight; dimethylimidazole 2.0 parts by weight; and diphenylmethane-4,4'- 100 parts by weight.

diisocyanate The mixture is dispensed into the mould by high pressure impingement mixing and has a 'cream' time of 10 seconds and 'end of rise' time of 30 seconds.

Before the foam cures, within 55 to 65 seconds after injection of the foam, the outer casing 19 is pulled by means not shown, away from the former 17 which is held in position by the constraining plate 21. Pins 27,29 and 31 are retracted from the mould cavity 21 with the casing 19 to a foam-ruptured position, rupturing the foam by tearing it as they retract. Figure 2 shows the casing 19 pulled away from the former and the pins 27, 29 and 31 retracted in the foam-ruptured position.

As the pins retract, groove 35 and the grooves associated with pins 29 and 31 are opened to the mould cavity 21 allowing gas to escape to chamber 10, thereby relieving pressure from the mould cavity. At the same time, gas also escapes from the sides of the foam formed against mould faces 12 and 14 which are removed with the outer casing 19.

When the foam has cured, the mould is opened, as shown in Figure 3, and the roof liner is removed.

By way of comparison, a roof liner is produced in the same way as described above except that the casing 19 is not pulled away from the former 17 and hence the pins 27, 29 and 31 are not retracted to a foam-ruptured position. When the mould is opened the impervious material is found to be blistered.

In Figure 7, a two-part mould 41 consists of parts 43 and 45. Pins 47,49 and 51 are attached at one of their ends to pistons 53, 55 and 57 respectively, housed in pneumatic cylinders 54, 56 and 58 and have at their other ends foam puncturing devices 59, 61 and 63 respectively. The pins are in gas-tight contact with and longitudinally moveable within channels, one of which, 60, is shown more clearly in Figure 8 in conjunction with its associated pin 47. Figure 8 also shows more clearly the puncturing device 59 of pin 47. The channel 60 is formed within a sleeve 65 (see Figure 8) fitted in mould part 45. The sleeve 65 has a groove 67 for the passage of gas which vents to atmosphere by ducting not shown. The groove 67 terminates before it reaches mould cavity 40. The other channels are similar, having associated sleeves with grooves.

In its operation the mould is similar to that shown in Figures 1 to 6 except that in their inoperative positions the pins 47, 49 and 51 are retracted from the mould cavity 40 (see Figures 7 and 8) while, in their foam-ruptured positions, they extend into the cavity and into the foam. The foam is punctured as the pins are moved by the pneumatic cylinders 54, 56 and 58 from their inoperative positions to their foam-ruptured positions. Immediately the foam is punctured the pins are retracted, by reversing the operation of the pneumatic cylinders, to a pressure relief position in which the grooves in the sleeves are allowed to communicate with the cavity, thereby allowing gas to escape to atmosphere.

Figures 9 to 12 show features of a mould similar to that shown in Figures 7 and 8 except that instead of being operated by pneumatic cylinders, the pins, one of which, 71, is shown in Figure 10, have multi-start threads and sprockets and are driven by a chain 77 and motor 79. The multi-start thread 73 and sprocket 75 of pin 71 are shown in Figure 10. The other pins are similar.

The puncturing device fitted to pin 71 is a cutting edge 81 shown best in Figure 11. The tearing device is a bar 83 fitted inside the puncturing device.

This mould operates in a similar way to that of Figures 7 and 8 except that the pins are moved spirally within their respective passages by the multi-start drive assembly. The spiralling movement of the pins from the inoperative position to the foam-ruptured position assists puncturing of the foam by the cutting edge and enables the bar 83 to tear the foam.

Claims (7)

1. Process for the manufacture of a shaped article which comprises covering at least part of a mould surface with an impervious material, introducing into the mould a polyurea foam-forming mixture, allowing the mixture to expand to fill the mould cavity and, before the foam so formed cures, puncturing or otherwise rupturing the foam while it is still in the mould.

2. Process as claimed in claim 1 in which the impervious material is a plastics coated fabric.

3. Process substantially as herein described with reference to the accompanying drawings.

4. A shaped article when obtained by the process claimed in claim 1.

5. Apparatus suitable for carrying out the process claimed in claim 1 which comprises a mould having therewithin a mould surface which defines a mould cavity, the mould, which can be opened to permit the mould surface to be covered, at least in part, with an impervious material, being provided with means for introducing a foam-forming mixture into the mould cavity while the mould is in a closed position, a rupturing device which can be moved within the mould cavity from an inoperative position to a foam-ruptured position by means external to the mould while the mould is in the closed position, and a pressure relief device operative when or after the rupturing device is moved to the foam-ruptured position.

6. Apparatus as claimed in claim 5 in which the rupturing device comprises one or more rods which pass through channels into the mould cavity and the pressure relief device comprises one or more passages each of which is associated with a rod and channel of the rupturing device, the rods being in gas-tight contact with and movable longitudinally within the channels from an inoperative position to a foam-ruptured position and providing closure members for the associated passages of the pressure relief device.

7. Apparatus substantially as herein described with reference to the accompanying drawings.