PROCESS FOR PREPARING MULTIHARDNESS FOAMED ARTICLESThe present invention relates to a process for preparing multihardness foamed articles. In particular the present invention relates to a process for making foamed articles comprising layers of polyurethane foam of differing hardness.
The concept of preparing multihardness polyurethane foam, eg for automobile and furniture seating, is now well established. A number of different approaches to preparing multihardness foam has been described in EP 67870, US 4190697 and EP 251689 and using these technologies a range of multihardness layered or encapsulated foams can be prepared.
The process described in EP 251689 is particularly suitable for the manufacture of multilayer foams having layers of differing hardness. This process involves pouring sequentially two or more foam formulations, designed to produce two or more foam formulations of differing hardness, onto a given point in the bottom of a seat mould and thereafter allowing them to rise and cure. The seat mould is inclined slightly to the horizontal (preferably 5-12 degrees) and the point of pouring is located at or near the top of the inclined bottom surface of the mould. It is a feature of the process described that the formulations are poured sequentially without any waiting time between, hence in general little or no foaming of any of the formulations takes place on the time scale on which pouring occurs.Although, according to the patentee, it would be expected that under such conditions, the formulations would mix, this does not however occur and, after curing, a foam seat comprising discrete layer of the various foams is produced. The discrete layers are founded to be bound to one another.
An improvement on this process is described in United Kingdom patent application. Because the process described in EP 251689 involves dispensing the various formulations at the same point near the top of the incline, it can be difficult in certain circumstances the ensure uniform coverage of the seat mould. Furthermore for large seat moulds it is necessary to use formulations having long cream times. These problems are solved by dispensing each formulation from its own outlet moving in a strip across the mould at or near the top of the incline. In this particular application the outlets are arranged in a line and the outlets move across the mould along the line defined by the outlets.By this means each subsequently dispensed foam can be poured directly into each previously dispensed foam in a way equivalent to the point pouring procedure described in EP 251659 without a significant time delay.
whilst this technology represents an improvement over that described in EP 251659 there is still a disadvantage in that thickness of each layer is not uniform in the direction of the incline.
A further improvement to the process described in EP 251659 is now provided which produces layered foam articles in which the thickness of each layer is more uniform in the direction of the incline.
According to the present invention there is provided a process for preparing a multihardness or multidensity foamed article, comprising layers of foams having differing hardness by reacting two or more foam formulations of differing hardness or density in a mould arranged so that the bottom surface is inclined up to 40 degrees to the horizontal characterised in that the process comprises the following steps:: (a) dispensing a first foam formulation from an outlet onto the bottom surface of the mould whilst the first outlet is moved relative to the mould along a line substantially perpendicular to the incline at or near the top of the incline, (b) allowing the first foam formulation to expand by an amount in the range + 100Z to + 2300Z of its original volume, (c) thereafter dispensing a second foam formulation from an outlet onto the first foam formulation whilst the outlet is moved relative to the mould along the line defined in step (a).
The present invention solves the problem defined above by pouring each foam formulation in a strip across the top of the incline and by introducing a delay between the dispensings of the formulations. This is to be compared with EP 251659 which teaches that there should be no substantial time interval between the dispensings. By introducing a significant delay it is found that the second foam formulation flows under the expanding first foam formulation.
The process of the present invention is suitably operated so that the bottom surface of the mould be inclined from between 0.1 to 40 degrees to the horizontal. This may be achieved by actually tilting the mouldd or by employing a mould which has been manufactured with an inclined bottom surface. In fact, for most conventional automobile seat moulds, the incline in the mould running from the front to the back of the seat is sufficient for the purposes of this invention. Preferably, the angle of incline is 4 to 20 degrees, most preferably 5 to 12 in agreement with the teaching of EP 0251659.
In step (a) of the process of the present invention the first foam formulation is dispensed from a first outlet onto the bottom surface of the mould. The first outlet is suitably mounted on the movable arm of a robot. The first outlet is suitably fed by a mixing head in which the components of the foam formulation are mixed. It is preferred that the first outlet and associated mixing head is computer controlled so that the dispensing of the formulation can be matched to the movement characteristics of the robot arm. The outlet is moved along a line substantially perpendicular to the incline at or near the tope of the incline.
Although the term perpendicular is used here small deviations of up to 5% are entirely acceptable.
During step (b) of the process the first foam formulation is allowed to expand by an amount in the range + 100% to + 2300X of its original volume preferably in the range + 300Z to + 1000%. For most practical polyurethane foam formulations used this will correspond to a delay of between 10 and 25 seconds.
As regards step (c), the second foam formulation is dispensed from the second outlet in a strip along the line defined by the relative motion of the first outlet. The second foam formulation can be dispensed from a second outlet if desired. However in view of the delay between dispensing a single outlet connected to two mixing heads can be used.
After step (c) the mould is closed and the contents are allowed to expand and cure. After curing the final foam article can be demoulded in the usual way. It is of course possible to repeat steps (a) to (c) if desired to build up a succession of layers. If this is done then the foam formulation used in the repeat of step (a) can either be the original first foam formulation or a further different foam formulation.
The process can be effected either by moving the outlet(s) relative to a fixed mould or by moving the mould relative to fixed outlet(s).
The process of the present invention is applicable to automobile seat mould especially those moulds having a divider running across the middle of the incline. In such moulds there is the additional problem that the divider holds up the flow of the first foam formulation if the original technology described in EP 251689 is employed. Using the technology herein the liquid second foam formulation can be used to lift the expanding first foam formulation over the divider thereby ensuring that the expanding foam formulation is spread evenly across the whole mould.
The foam formulations to be used in the present invention are suitably polyurethane foam formulations, although it is envisaged that the technique could be applicable to other polymer foam systems. Polyurethane foams are well known in the art and comprise the product obtained by mixing a polyfunctional isocyanate with a polyfunctional active hydrogen containing compound (e.g. a polyether polyol) in the presence of a blowing agent. In the process of the present invention, such mixtures are generated in the mixing head and then poured into the mould through the outlet before the mixture has started to rise, i.e. whilst the foam formulation is still in an essentially liquid state.
The process of the present invention can be used with any type of polyurethane foam formulation including 'hot-cure' and 'cold-cure' formulations. Preferably the foam formulations used are of the 'cold-cure' type.
In general the polyfunctional active hydrogen containing compound can be any one of polyether polyols, polyester polyols, polycarbonates, polycaprolactones, poly THF, saturated polybutadienes and the like. Preferably the polyfunctional hydrogen containing compound is a polyether polyol in which the active hydrogens are those on primary and/or secondary hydroxyl groups. These compounds are generally known in the art as polyols; 'hot-cure' foams employing polyols having more secondary than primary hydroxyl groups and 'cold-cure' foams using polyols having more primary than secondary.
The preferred polyurethane foam formulations to be used in the present invention however are those producing flexible foam, most preferably flexible HR (high resilience) foams. In such a case, two streams are fed to the mixing head; one comprising a formulated polyol, i.e. some or all of polyols, polymer polyols, blowing agent, catalysts, silicone surfactants, blowing agents and other additives; the other comprising the polyisocyanate.
Examples of preferred polyols for HR foams are those having the following additional characteristics: (a) an average primary hydroxyl content of at least 40 mole percent(or no more than 60 mole percent of the less reactive secondaryhydroxyl groups); and (b) an average molecular weight of from about 2000 to about 12000.
Preferably, such polyether polyols for use as components ofHR foam formulations contain from about 60 to about 90 mole percent of primary hydroxyl groups and have an average molecular weight of from about 4000 to 7000.
Consistent with their polyfunctionality and the aforesaid respective ranges of molecular weights, such polyether polyols have hydroxyl numbers from 84 to 21, preferably from 42 to 24. These highly reactive polyether polyols are provided by oxyalkylation of a polyfunctional alcohol starter such as glycerol, sorbitol and the like, with propylene oxide and ethylene oxide. Usually, the total ethylene oxide content of the polyether polyol is between about 7 and about 20 weight percent, expressed on the basis of total alkylene oxide fed during the oxyalkylation reaction. The high primary hydroxyl content is introduced by capping of the polyoxyalkylene chains with at least a portion of the total ethylene oxide feed.
For both high resilience flexible foam and hot cure foams, the polyether polyols may be employed in combination with other polyols to control the degree of softness or hardness of the foam and to vary the load bearing properties.
In particular, the formulated polyol may contain polymer polyols which in turn contain finely dispersed or grafted organic or inorganic material to provide improved load bearing properties.
Examples of such polymer polyols are graft polymer polyols prepared by polymerising ethylenically unsaturated monomers e.g.
acrylonitrile and/or styrene in a polyether polyol or the so calledPHD or PIPA dispersion polymer polyols. The polyether polyol in which the polymerisation takes place preferably has the characteristics indicated above in the case of polyols for HR foam.
Other conventional blowing agents can be used in place of water.
The catalysts used are known per se, e.g. tertiary amines such as triethylamine, tributylamine, N-methyl-morpholine, N-ethylmorpholine, N,N,N',N'-tetramethyl-ethylene-diamine, 1,4-diazabicyclo-(2,2,2)-octane, N-methyl-N' -dimethyl-amino-ethylpiperazine, N,N-dimethyl benzylamine, bis-(N,N-diethylamino-ethyl)adipate,N,N-diethylbenzylamine, pentamethyl diethylene-triamine, N,N-dimethylcyclohexylamine, N,N,N',N'-dimethyl-phenyl-ethylamine, 1.2-dimethyl imidazole and 2-methyl-imidazole, triethylene diamine, bis(2-dimethylamino ethyl) ether.
Tertiary amines which contain hydrogen atoms capable of reacting with isocyanate groups may also be employed, e.g.
triethanolamine, triisopropanolamine, N-methyldiethanolamine,N-ethyldiethanolamine, N,N-dimethylethanolamine or their reaction products with alkylene oxides such as propylene oxide and/or ethylene oxide.
Organic metal compounds may also be used as catalysts according to the invention, especially organic tin compounds. The organic tin compounds used are preferably tin (II) salts of carboxylic acids such as tin (II)-acetate, tin (If) octoate, tin (II)-ethylhexonoate and tin (II)-laurate and the dialkyl tin salts of caroboxyic acids such as dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate or dioctyl tin diacetate.
The catalysts are generally used in a quantity of between 0.002 and 10Z by weight, based on the total quantity of polyol.
In producing flexible polyurethane foam in accordance with the method of this invention, a minor amount of an organosilicone surfactant may also be present as an additional component of the polyurethane-forming reaction mixture. When used, such surfactants are usually present in amounts up to about 5 parts by weight per 100 parts by weight of total polyol reactant. Suitable classes of silicone surfactants are poly(dimethylsiloxane) oils and the polysiloxane-polyoxyalkylene block copolymers wherein the respective blocks are joined through silicon-to-carbon or silicon-to-oxygen-to-carbon bonds and the respective polyoxyalkylene blocks are bonded to different silicon atoms of the polysiloxane backbone to form a comb-like or branched structure. Usually, the polysiloxane blocks are trialkylsiloxy end blocked. In addition to the siloxy units to which the pendant polyoxyalkylene chains are bonded, the polysiloxane backbone is formed of difunctional siloxy units wherein the respective two remaining valences of silicon are satisfied by bonds to organic radicals. Illustrative of such organic radicals are the hydrocarbyl groups having from 1 to 12 carbon atoms including alkyl, aryl, aralkyl, bicycloheptyl and halogen substituted derivatives of such groups. The polyoxyalkylene blocks are usually constituted of oxyethylene units, oxypropylene units or a combination of such units, and the polyoxyalkylene chains are hydroxyl-terminated or capped with a monovalent organic group such as alkyl, aryl, aralkyl, acyl, carbamyl and the like.
The organosilicone component is preferably present in formulations in an amount between about 0.025 and about 2 parts by weight per 100 parts by weight of total polyol.
Generally, the blowing agent is employed in an amount from about 1 to about 15 parts by weight per 100 parts by weight of polyol, the particular blowing agent and amount thereof depending upon the type of foam product desired. Flexible foam formulationsusually contain no more than about 6 pphp of water. The selection and amount of blowing agent in any particular foam formulation is well within the skill of those skilled in the polyurethane foam art. Suitable organic blowing agents are halogenated alkanes, such as methylene chloride, chloroform, ethylidene chloride, vinylidene chloride, monofluorotrichloromethane, chlorofluoromethane or dichlorodifluoremethane, carbon dioxide or other inert gases.A blowing effect can also be obtained by adding compounds which decompose at temperatures above room temperature to liberate gases, e.g. azo compounds such as azoisobutyric acid nitrile which liberate nitrogen.
Other ingredients may also be included optionally. They include chain extenders, crosslinkers, colouring agents, fillers, flame retardants and the like.
Chain extenders are difunctional compounds containing active hydrogen (i.e. hydrogen which will react with isocyanate groups under the conditions used in foaming). Examples of suitable compounds containing active hydrogen are compounds containing hydroxyl or amines groups.
Cross-linkers are compounds containing more than 2 active hydrogen atoms per molecule, preferably more than 3. Examples of such cross-linkers are diethanolamine, triethanolamine,N,N,N'N'-tetrakis-(2-hydroxypropyl) ethylene diamine, and phenol/formaldehyde/aniline condensation products.
The active hydrogen content of the cross-linker or chain extender is preferably relatively high so as to allow a significant effect on hardness to be obtained without requiring an excessive amount of additive. The active hydrogen content may for- example correspond to a hydroxyl number as low as 50, particularly when a chain extender is used. The cross-linker or chain extender preferably has an active hydrogen content corresponding to a hydroxyl number of at least 100, more preferably 600 to 1500.
Where the cross linker or chain extender is fed as an additive to one of the main reaction streams it is preferably used at the rate of 2 to 10 parts by weight per 100 parts of polyol.
It is also sometimes desirable to include various additives in the reaction mixture such as colouring agents, fillers, flame retardants and the like. Suitable colouring agents are, for example carbon black, titanium dioxide, methyl blue, chromium red and the like. Suitable fillers are vermiculite, saw dust, synthetic plastics including vinyl polymers such as, polyvinyl chloride, polystyrene and the like. Suitable flame retardants are antimony oxide, tris (chloroethyl) phosphate, tricresyl phosphate, triphenyl phosphate, melamine and the like.
The isocyanate component employed in this invention for mixing with active hydrogen compounds are those having the general formula: Q(NCO)i wherein i is an integer of two or more and Q is an organic radical having the valence of i. Q can be a substituted or unsubstituted hydrocarbon group (e.g. an alkylene or an arylene group). Examples of such compounds include hexamethylene diisocyanates, phenylene diisocyanates and tolyene diisocyanates.
Q can also represent a polyurethane radical having a valence or i in which case Q(NCO)i is a composition conventionally known as a pre-polymer. Such pre-polymers are formed by reacting a stoichiometric excess of a polyisocyanate with an active hydrogen-containing component, especially polyhydroxyl containing materials or polyols.
More specifically, the polyisocyanate component employed in this invention also includes the following specific compounds as well as a mixture of two or more of them, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, crude tolylene diisocyanate, bis(4-isocyanatophenyl) methane, polyphenylmethylene polyisocyanates that are produced by phosgenation of aniline formaldehyde condensation products.
The polyurethane foam formulations used in the process of the present invention are preferably chosen such that they differ in hardness from each other. It is further preferred that such formulations differ in hardness by virtue of their content of one or more of the following: 1. polymer polyols, 2. isocyanate with a functionality greater than two, i.e. withmore than two isocyanate groups per molecule, e.g. the contentof polyphenylmethylene polyisocyanate inbis(4-isocyanatophenyl)methane 3. active hydrogen containing compound which may be chain extenderor cross-linker 4. blowing agent.
In the case of a typical automobile seat it is preferable, where two foam formulations are used, that the foam formulation added first yields a harder foam than that added second.
The invention defined above will now be illustrated with reference to the following Examples.
Example 1An automobile front seat cushion mould, as shown in Figure 1, was used. The bottom surface of the mould was inclined by 6* to the horizontal.
Foam formulations were dispersed from two outlets mounted on the arm of a Asea 90 Robot. The outlets were connected to a KraussMaffei RIM star 40/20 mixing head (soft foam formulation) and aKrauss Maffei KK 10-5/5 mixing head (hard foam formulation) respectively. The formulations used are given in Tables 1 and 2.
The mould was located beneath the robot arm and the hard foam formulation was dispersed along an upper line as shown in Figure 1 (dispensing time a 2 seconds). Thereafter the soft foam formulation was poured in the lower part of the mould so as to fill the side rolls and the lower part of the mould (1.3 seconds). These foams were then allowed to cream and rise.
15 seconds after the hard foam formulation had been dispensed, the soft foam formulation was dispensed stripwise along the same upper line (2 seconds). When dispensing was complete, the mould was closed and the foams were allowed to rise and cure in the usual way. After a further five minutes the cushion was demoulded. The cushion was cut across the centre to reveal a cross-section as shown in Figure 2.
Example 2The same mould, formulations and apparatus as described inExample 1 were used. In this example the hard foam formulation was poured from the right side roll along an upper line of the mould to the left side roll (2.4 sec). Thereafter the soft foam formulation was poured onto a point in the centre of the lower part of the mould: 0.3 sec. Fifteen seconds after the first hard foam formulation was poured, the soft foam formulation was poured along the same line from the right to the left side roll (2.2 sec). After demoulding the cushion a hard/soft distribution as in Fig. 3 was obtained.
Example 3The same mould, formulations and apparatus as described inExample 1. In this example the hard foam formulation was poured from the right side roll along an upper line of the mould to the left side roll (2.4 sec). Thereafter the soft foam formulation was poured onto a point in the lower centre of the mould (0.3 sec).
15 seconds after the first hard foam formulation was poured the soft foam formulation was poured along the same line but in this case only in the central seating part of the mould, thus omitting the side rolls (2 sec).
After cure and demoulding and crossectioning the cushion's hard/soft distribution was as shown in Fig. 4.
TABLE 1Soft Foam Formulations
Polyol Stream Parts by Weight U1315 Polyol (ex BPCI) 100 Water 3 Niax Al Catalyst (ex UCC) 0.1 Dabco 33LV Catalyst (ex UCC) 0.6 Y10366 Silicone Surfactant (ex UCC) 0.7 Polyol Stream Output into mixing head - 225g.sec'1 Isocyanate stream : I 1317 Index 100(80/20 TDI/MDI) ex BPCIIsocyanate stream output into mixing head - 83g.sec'l Ratio Polyol stream :Isocyanate Stream - 2.7Temperature - 25*C Cream Time - 5 secsRise Time - 80 secsGel Time - 50 secsTABLE 2Hard Foam Formulation
Polyol Steam Parts by Weight RP-1490 (polymer polyol 100 ex BPCI - 35Z styrene acrylonitrile copolymer) Water 2.8 Niax Al 0.1 Dabco 33LV 0.7 Y10366 2.4 Polyol steam output into mixing head - 120g sec~ Isocyanate stream : as Table 1Isocyanate steam output into mixing head - 40g.sec-1Ratio Polyol Stream : Isocyanate Stream - 3.04Temperature I 350C (polyol)25 C (isocyanate)Cream time - 3-4 secsRise time - 50 secsGel time - 40 secs.