HK1002660B - Process for making flexible foams - Google Patents

Description

Process for producing flexible foam

The production of flexible polyurethane foams by reacting organic polyisocyanates, such as Toluene Diisocyanate (TDI) or diphenylmethane diisocyanate (MDI), with polyether polyols and blowing agents is well established. Polyethers are generally polyoxypropylene polyols derived from propylene oxide or poly (oxypropylene-oxyethylene) polyols derived from various mixtures of propylene oxide and ethylene oxide. Ethylene oxide-capped polyoxypropylene polyols in which the oxyethylene groups comprise a small proportion of the total oxyalkylene groups are particularly important because of their enhanced reactivity towards polyisocyanates.

Polyols having a high oxyethylene content, for example 50% or more by weight of oxyethylene are often used as minor additives to ensure that the foam has an open cell structure. It is not uncommon to use these high concentrations of polyethers with conventional isocyanates because closed cell foams are formed without the open cell effect.

In co-pending application PCT/EP94/01659 it has been found that flexible foams having valuable properties can be successfully produced from formulations containing high concentrations of polyhydroxy compounds having a high ethylene oxide content if a blowing agent comprising substantially pure 4, 4' -MDI or a derivative thereof as polyisocyanate and water is used. The preparation of hydrophilic flexible foams is further described in USP 4137200 and USP 4828542.

Surprisingly, it has now been found that hydrophilic foams can be obtained when prepolymers prepared from polyisocyanates and polyhydroxyl compounds having a high oxyethylene content are reacted with water at different temperatures.

Thus, according to the present invention there is provided a process for the preparation of a flexible foam by reacting with water a prepolymer having an NCO value of 3 to 15% by weight of the reaction product obtained by reacting an excess of a polyisocyanate with a polyether polyol or mixture thereof having an average nominal hydroxyl functionality of 2 to 6 and preferably 2 to 4, an average hydroxyl equivalent weight of 500 to 5000 and preferably 1000 to 5000 and an ethylene oxide content of at least 50% by weight, the water content being 15 to 500 parts by weight per 100 parts by weight of prepolymer, characterised in that the temperature of the prepolymer at the start of the reaction is 10 to 50 ℃, preferably 15 to 30 ℃ and most preferably the temperature of the room temperature and water is 10 to 50 ℃ above the temperature of the prepolymer, preferably 20 to 45 ℃ above the temperature of the prepolymer. The water temperature is 25-90 ℃, preferably 40-70 ℃, and most preferably 55-65 ℃.

A preferred embodiment of the present invention is a process for preparing a flexible polyurethane foam by reacting with water an excess of a prepolymer having an NCO value of 3 to 10% by weight, which prepolymer comprises the reaction product of a polyisocyanate containing at least 65%, preferably at least 90%, and more preferably at least 95% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof, and a polyether polyol or mixture thereof having an average nominal hydroxyl functionality of 2.5 to 3.5, an average hydroxyl equivalent weight of 1000 to 3000 and an ethylene oxide content of 50 to 85% by weight, the water content being 30 to 300 parts by weight per 100 parts by weight of prepolymer, characterized in that the prepolymer is at a temperature of 10 to 50 ℃, preferably 15 to 30 ℃ and most preferably room temperature at the start of the reaction, the water temperature is 25 to 90 ℃, preferably 40-70 ℃ and most preferably 55-65 ℃ and the water temperature is 10-50 ℃ higher than the temperature of the prepolymer, preferably 20-45 ℃.

Surprisingly, it has been found that high-quality hydrophilic foams having a low density and hardness can be obtained, the density and hardness of the foam being less or hardly dependent on the amount of water used than in the case where the prepolymer and the water both have the same or similar temperature at the start of the reaction. For convenience, unless otherwise specified, the word "average" is used in this application to mean the number of indices.

The polyisocyanates used for preparing the prepolymer may be selected from aliphatic, cycloaliphatic and araliphatic polyisocyanates, especially diisocyanates, such as hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1, 4-diisocyanate, 4' -dicyclohexylmethane diisocyanate and m-and p-tetramethylxylene diisocyanate, and especially aromatic polyisocyanates such as Toluene Diisocyanate (TDI), benzene diisocyanate, most preferably methylene diphenyl diisocyanate (MDI) and its homologues with an isocyanate functionality greater than 2, such as crude MDI and polymeric MDI.

Preferred polyisocyanates are methylene diphenyl diisocyanates selected from pure 4, 4 '-MDI, isomeric mixtures of 4, 4' -MDI and 2, 4 '-MDI and less than 10% by weight of 2, 2' -MDI, and modified variants thereof containing carbodiimide, allophanatimide, isocyanurate, urethane, allophanate, urea or biuret groups, such as allophanate imide and/or carbodiimide modified MDI having an NCO content of at least 25% by weight and urethane modified MDI obtained by reacting excess MDI with low molecular weight polyols (MW up to 1000) and having an NCO content of at least 25% by weight.

Mixtures of the abovementioned isocyanates can be used if desired. The polyisocyanate may contain dispersed urea particles and/or urethane particles prepared in a conventional manner, for example by adding small amounts of isophorone diamine to the polyisocyanate.

The most preferred polyisocyanates for use in preparing the prepolymer are those containing at least 65%, preferably at least 90% and more preferably at least 95% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof. It consists essentially of pure 4, 4 ' -diphenylmethane diisocyanate or a mixture of this diisocyanate with one or more other organic polyisocyanates, in particular other diphenylmethane diisocyanate isomers, for example any combination of the 2, 4 ' -isomer and the 2, 2 ' -isomer. The most preferred polyisocyanate may also be an MDI variant derived from a polyisocyanate composition containing at least 65% by weight of 4, 4' -diphenylmethane diisocyanate. MDI variants are well known in the art and are used in the present invention and include in particular the liquid products obtained by introducing ureidoimide and/or carbodiimide groups to said polyisocyanates, such carbodiimide and/or ureidoimide modified polyisocyanates preferably having an NCO value of at least 25% by weight and/or by reacting such polyisocyanates with one or more polyhydroxyl compounds having a hydroxyl functionality of from 2 to 6 and a molecular weight of from 62 to 1000 to obtain modified polyisocyanates preferably having an NCO value of at least 25% by weight.

The polyether polyols or mixtures thereof used to prepare the prepolymers of the present invention preferably have an average nominal hydroxyl functionality of 2 to 4 and most preferably 2.5 to 3.5 and an average hydroxyl equivalent weight of 1000 to 3000 and an ethylene oxide content of 50 to 85% by weight.

Polyether polyols include products obtained by polymerization of ethylene oxide, optionally with other epoxides such as tetrahydrofuran and preferably propylene oxide, optionally in the presence of polyfunctional initiators. Suitable initiator compounds contain a number of active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethanolamine, diethanolamine, triethanolamine, toluene diamine, diethyl toluene diamine, phenylene diamine, diphenylmethane diamine, ethylene diamine, cyclohexane dimethanol, resorcinol, bisphenol A, glycerol, trimethylolpropane, 1, 2, 6-hexanetriol, pentaerythritol and sorbitol. Mixtures of initiators may be used.

If other epoxides are used, the polyol may be obtained by the simultaneous or subsequent addition of ethylene oxide and other epoxides as is well described in the art.

To obtain the preferred polyols having an average nominal hydroxyl functionality of 2.5 to 3.5, polyols having a nominal hydroxyl functionality of 3 or mixtures of polyols having an average nominal hydroxyl functionality of 2 to 6 may be used, provided that the mixture is in the above functionality range of 2.5 to 3.5.

Generally, mixtures of polyols can be used, provided they have the desired functionalities, equivalent weights and oxyethylene content as described above.

The term "average nominal hydroxyl functionality" as used herein refers to the average functionality (number of hydroxyl groups per molecule) of the polyol composition, assuming herein that the average functionality of the polyoxyalkylene polyol is the same as the average functionality (number of active hydrogen atoms per molecule) of the initiator used in its preparation, although in fact it is often somewhat lower due to some terminal unsaturation.

If desired, the polyether polyol or mixture of polyols may contain dispersed polymer particles. Such polymer-modified polyols have been fully described in the prior art and include products obtained by the in situ polymerisation of one or more vinyl monomers, such as acrylonitrile and styrene, in polyoxyalkylene polyols or by the in situ reaction between a polyisocyanate and an amino-or hydroxy-functional compound, such as triethanolamine, in polyoxyalkylene polyols.

In general, the prepolymers are prepared by reacting polyisocyanates with polyhydroxyl compounds at a temperature of preferably 40 to 90 ℃ in relative amounts so as to give NCO values of 3 to 15% by weight, preferably 3 to 10% by weight. The prepolymer so prepared is liquid at ambient conditions. If desired, small amounts (up to 30% by weight) of further polyisocyanates, in particular MDI, can be added to the prepolymer thus prepared. An organic acid or Lewis acid may be added to improve the stability of the prepolymer.

The prepolymer preferably has a viscosity of up to 10,000mpa.s at 25 ℃.

In preparing the prepolymer, it should be avoided that both the isocyanate functionality of the polyisocyanate and the average hydroxyl functionality of the polyol or mixture of polyols are 2.0, and if one of these functionalities is 2.0 the other is preferably at least 2.2.

The prepolymer is reacted with water in an amount of from 15 to 500 parts by weight, preferably from 30 to 300 parts by weight, most preferably from 40 to 250 parts by weight, per 100 parts by weight of prepolymer.

The foaming reaction mixture may contain one or more additives used in the preparation of flexible foams. Such additives include catalysts such as tertiary amines and tin compounds, surfactants and foam stabilizers such as siloxane-oxyalkylene copolymers and polyoxyethylene/polyoxypropylene copolymers and polyoxyethylene polymers, chain extenders such as low molecular weight diols or diamines, crosslinkers such as triethanolamine, glycerol and trimethylolpropane, flame retardants, organic and inorganic fillers, pigments, agents which inhibit the so-called boiling foaming effect such as polydimethylsiloxanes, internal mold release agents, anticeptics, biocides and pharmaceuticals. However, valuable flexible foams can be obtained without using any of these additives. Preferably, no additives are used, except for up to 10 parts by weight and preferably up to 5 parts by weight of the polyoxyethylene/polyoxypropylene copolymer and polyoxyethylene polymer described above per 100 parts by weight of prepolymer. If used, such additives are preferably pre-mixed with water.

As regards the use of these (co) polymers, surprisinglyIt was found that a foam exhibiting good wicking properties and capable of absorbing and retaining water in an amount several times the weight of the foam and/or having reticulated cells can be obtained when the prepolymer is reacted with water in the presence of from 0.01 to 10 parts by weight per 100 parts by weight of the prepolymer of a polyol having an average molecular weight of 500-10000 and an average nominal hydroxyl functionality of from 2 to 6, the polyol being a polyoxyethylene polymer or a polyoxyethylene/polyoxypropylene block copolymer having an oxyethylene content of at least 30% by weight. The polyol is preferably used in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the prepolymer. These polyhydroxy compounds are known in the art and are commercially available. An example is Synperonic^TMPE L44, L64, F68, P75, P84, P85 and F87, all of which are commercially available from Imperial Chemical Industries PLC.

Wicking properties are particularly obtained when these polyols are used, in particular when the polyols used have an oxyethylene content of 35 to 70% and especially 40 to 70% by weight; preferably, these polyols have an average nominal hydroxyl functionality of 2. When these polyols are used, web-forming properties are obtained in particular when the polyols used have an oxyethylene content of 70 to 100% and preferably 100% by weight; preferably, at least 40 parts by weight of water per 100 parts by weight of prepolymer are used to prepare such foams in web-formed structure.

Preferably, the polyol is premixed with water before the prepolymer is reacted with water in the presence of the polyol.

Furthermore, the process according to the invention using water at a temperature higher than the temperature of the prepolymer can be carried out in the presence of superabsorbent polymers, as will be explained in more detail below. The type, amount and method of use of the super absorbent polymer will be described below.

This reaction method is used to manufacture hydrophilic flexible foams having good properties in a very simple manner. The preferred prepolymers have low viscosity which improves delivery and processability when making flexible foams having a desired color (white), having open cells or being crushable and capable of compression set values of less than 20% (ASTM D3574-77, test D, dry 50%), especially when surfactants are not used. The purity and simplicity of the chemicals used to make the prepolymer ensures that the flexible foams made therefrom have minimal leachables, no releasable mono-, di-, or polyols, before the foam is contacted with water or aqueous solutions. This makes the flexible foam particularly suitable for applications in contact with the human body such as medical and hygienic applications.

The foams can be formed into panels, molded articles, and the like and can be used for vibration damping, hand towels, foams, bandages, tampons, cosmetic pads, drug delivery products, plant growth media, food pan absorbents, and the like.

Furthermore, the present invention relates to a process for the manufacture of hydrophilic flexible foams by reacting a prepolymer as defined above with from 15 to 500 parts by weight of water per 100 parts by weight of prepolymer in the presence of a superabsorbent polymer.

Superabsorbent polymers (SAPs) are well known per se. SAPs or water-absorbing polymers or hydrogels are water-insoluble hydrophilic polymers that swell and absorb up to 10-100 times their own weight in water, saline solution, physiological fluid or body fluid. They are composed of polyelectrolytes or other highly hydrophilic polymer matrices, often with crosslinking sites along the macromolecular chain in order to avoid dissolution. They may be natural SAPs like guar gum, other natural gums and starches and, preferably, include synthetic SAPs based on acrylic or methacrylic acid, esters, nitriles, amides and salts thereof, polysaccharides, maleic anhydride polymers, polyvinyl alcohol, poly (N-vinyl-pyrrolidone) and diallyl dialkyl quaternary ammonium salts. For summary SAP we refer to riccarado PO at j.m.s-rev.macromol.chem.phys.; c34(4), 607-662(1994) "Water-absorbing Polymer: review of patents. The superabsorbent polymers disclosed in this article are useful in the present invention.

SAPs based on acrylic or methacrylic acid monomers are prepared by reacting acrylic or methacrylic acid, esters, nitriles, amides and/or their salts, optionally with other unsaturated monomers like derivatives of maleic, fumaric or itaconic acid, vinyl-substituted sulfonates or ammonium salts, olefinic and styrenic monomers, hydroxyalkyl or alkyl acrylates and methacrylates, unsaturated sulfonates, acrylamide alkylsulfonates, vinyl sulfonates, styrene sulfonates, vinylbenzyl sulfonates, N, n' -methylenebisacrylamide, dialkylaminoalkyl acrylates and methacrylates, carbonyl-containing heterocyclic N-vinyl monomers such as N-vinyl-2-pyrrolidone, N-vinyl-2-caprolactam, and N-vinyl-2-morpholinone. The polymers may be prepared by methods known in the art using, if desired, initiators, crosslinkers and surfactants known in the art; see, e.g., PO, pages 610-632. Crosslinking can be carried out by free-radical copolymerization of small amounts of polyvinyl comonomers or by reaction of the pendant carboxylic acid esters or carboxyl groups of the polymer with polyepoxides, haloepoxides and/or polyhydroxy compounds.

The polysaccharide-based superabsorbent polymer may be selected from, for example, starch graft copolymers and modified cellulose polymers. Such SAPs are obtained by grafting unsaturated monomers such as acrylonitrile, acrylic acid or acrylamide onto polysaccharides such as starch or cellulose, followed by optional saponification. These polysaccharide-based superabsorbent polymers are known in the art and can be prepared by methods known in the art; see PO, page 632-638.

SAPs based on maleic anhydride polymers are prepared by reacting maleic anhydride with hydrophobic comonomers such as olefins or vinyl ethers according to methods known in the art; see PO, pages 638 and 642.

Additional SAPs that may be used are those obtained by the reaction of diallyl: dialkyl quaternary ammonium salts are prepared by polymerization in the presence of a multifunctional divinyl compound and/or a crosslinking agent such as triallylmethylammonium chloride; prepared by polymerizing a polyalkylene oxide, such as polyethylene oxide, which has been crosslinked with, for example, formaldehyde and glutaraldehyde, in the presence of sulfuric acid; are prepared by polymerization of poly (N-vinylpyrrolidone) and poly (N-methyl, N-vinylacetamide) which have been crosslinked with, for example, divinylbenzene, diacrylate or diethylene glycol divinyl ether. These SAPs and their preparation are known in the art; see pages PO 642 and 647.

Preferred SAPs are selected from superabsorbent polymers based on acrylic or methacrylic acids, esters, nitriles, amides and/or salts thereof; a polysaccharide-based superabsorbent polymer and a maleic anhydride-based superabsorbent polymer.

The SAP may be used in polyurethane foam. There are three ways to incorporate SAPs into polyurethane foams:

1. mixing together components for preparing the SAP and components for preparing the polyurethane foam while forming the SAP and the polyurethane foam; see, for example, US 4731391 and EP-163150. The product is an interpenetrating network. The disadvantage of this method is that the presence of relatively large amounts of reactive chemicals makes the process cumbersome and difficult to control, and the monomers used for SAP preparation are often hazardous and toxic, requiring additional measures by the flexible foam manufacturer to protect the safety and health and the environment of employees.

2. SAP is incorporated by impregnation into polyurethane foam by using a liquid as a carrier for the SAP, see EP-41934. The disadvantage of this process is that the manufacture of SAP-containing foams requires a number of additional steps which make it economically less attractive; in addition, the requirement that the cell size of the flexible foam is larger than the size of the expanded SAP particles means a severe limitation on the size of the SAP particles.

3. The SAP particles are mixed with the components for the preparation of the flexible foam.

EP-453286 discloses a superabsorbent foam material based on polyurethane foam and containing a superabsorbent material. The superabsorbent material may be selected from known materials, it is mixed with a conventional polyurethane formulation and the mixture is then used to make a polyurethane foam. Such formulations contain a polyol, a catalyst, a polyisocyanate and a small amount of water.

US 5336695 describes hydrophilic foams based on polyurethane gels obtainable from polyhydroxy compounds, diisocyanates, superabsorbers, catalysts and small amounts of water.

US 4201846 discloses the use of fibres made of polyvinyl alcohol polymers in hydrophilic foams to reduce expansion of the foam. Polyurethanes are prepared by reacting prepolymers with water in the presence of fibers and exhibit improved tensile and tear resistance and reduced volume increase due to water absorption.

US3900030 discloses hydrophilic foams for tamponade containing finely divided, water-swellable polymers. It is important to avoid leaking the polymer content. The foams are prepared by reacting a mixture of a polymer and a polyol with a diisocyanate in the presence of a catalyst and a small amount of water.

US 4603076 discloses the preparation of hydrophilic foams by foaming MDI based prepolymers with a non-aqueous blowing agent and polyoxyethylene polyols in the presence of a hydrophilic compound and a catalyst. This prepolymer is based on a mixture of MDI and polymeric MDI.

US 4985467 discloses the preparation of hydrophilic foams by reacting a polyisocyanate, a polyol and water in the presence of a superabsorbent material followed by heat-reticulation.

EP-547765 and WO 94/29361 disclose the preparation of flexible foams using prepolymers prepared from 4, 4' -MDI and a polyether polyol having an oxyethylene content of 50 to 85% by weight and water.

Surprisingly, we have found that hydrophilic flexible foams can be prepared using the superabsorbent polymers discussed above by reacting the above prepolymers with large amounts of water in the presence of such superabsorbent polymers (SAP). Such foams can be made without the need for thermal reticulation.

The SAP can be premixed with the prepolymer, which makes the production process very simple for the foam producer: only water needs to be added.

The present foams are also attractive from an environmental point of view. No further additives, in particular no catalyst, are required in addition to the prepolymer, the SAP and the water.

The foam has very desirable properties: they exhibit limited shrinkage, have open pores, are stable, do not scorch and have very good water absorption and water retention, very good wicking and mechanical properties such as (dry and wet) tear strength and elongation. In addition, the foams produced using the above-mentioned polymers and copolymers, if they are not reticulated, also have a soft hand.

The invention therefore also relates to a process for the preparation of a flexible foam by reacting a prepolymer having an NCO value of 3-15% by weight with water, the prepolymer being the reaction product obtained by reacting an excess of a polyisocyanate with a polyether polyol or a mixture of such polyols, the polyol or mixture thereof having an average nominal hydroxyl functionality of 2-6 and preferably 2-4, an average hydroxyl equivalent weight of 500-5000 and preferably 1000-5000 and an ethylene oxide content of at least 50% by weight, and a water content of 15-500 parts by weight per 100 parts by weight of prepolymer, characterized in that the reaction of the prepolymer with water is carried out in the presence of a superabsorbent polymer. More particularly, the present invention relates to a composition comprising a prepolymer having an NCO value of 3-15% by weight, the prepolymer being the reaction product obtained by reacting an excess of a polyisocyanate with a polyether polyol or a mixture of such polyols, the polyol or mixture thereof having an average nominal hydroxyl functionality of 2-6, an average hydroxyl equivalent weight of 1000-5000 and an ethylene oxide content of at least 50% by weight, and a superabsorbent polymer.

The superabsorbent polymer is generally used in an amount of 1 to 100 parts by weight (pbw) and more preferably 5 to 80 parts by weight and most preferably 10 to 70 parts by weight per 100 parts by weight of the prepolymer.

The prepolymers useful in the process of the present invention and the process for making foams are the same as described above. The amount of water used is preferably as described above.

In particular, in addition to the aforementioned polyoxyethylene polymers and polyoxyethylene/polyoxypropylene copolymers, the foams are preferably prepared in the absence of additives, especially the aforementioned catalysts.

The same measures as described above can be taken when a particularly good wicking properties are desired or when a foam exhibiting a reticulated structure is desired.

The SAP class may be selected from those described in the aforementioned PO article. More specifically, they may be chosen from crosslinked polyacrylates and polyacrylamides and their salts. Such SAP's are commercially available, e.g., SANWET from Hoechst/Cassella^TMIM 3900G, IM 3746/1, and E394-95. Additional SAPs may be selected from starch or cellulose grafted SAPs using, for example, acrylonitrile, acrylic acid or acrylamide as unsaturated monomers. Such SAP class is also available on the market, for example from Hoechst/Cassella available SANWETIM 7000.

Different SAP classes may be used in combination. The SAP may be mixed with the prepolymer and water as they are mixed, or the SAP may be premixed with the prepolymer. Preferably the SAP-like is not pre-mixed with water. Mixing can be carried out by hand mixing or under typical mechanical or high shear mixing conditions.

In addition, the invention relates to absorbent articles, such as towels, sponges, bandages and tampons, comprising a catalyst-free, hydrophilic, flexible polyurethane foam containing superabsorbent polymers, the core density of which foam is at most 154kg/m³. Preferably the foam is based on diphenylmethane diisocyanate.

The invention is further illustrated by the following examples.

Example 1

Polyol 1 is a polyether (triol-initiated) having random oxyethylene and oxypropylene groups, an oxyethylene content of 77% and a molecular weight of about 4000.

The prepolymer was prepared by reacting 70 parts by weight of polyol 1 with 30 parts by weight of 4, 4' -MDI. The prepolymer was thus prepared by reacting it with a variable amount of water containing 0.4% by weight of Pluronic PE 6200 (EO/PO surfactant from BASF-Pluronic, trade name). The prepolymer had an NCO value of 7.85% by weight and a viscosity of 6000 mPas at 25 ℃. The temperature of the prepolymer before the reaction was room temperature (22 ℃ C.). The temperature and amount of water before reaction and the density and hardness of the foam produced are given in table 1 below. The density and hardness were measured after drying the foam in an oven at 60 ℃ to a constant weight.

TABLE 1

Test of	1★	2★	3★	4★	5	6	7	8
									Parts by weight of water per 100 parts by weight of prepolymer	30	110	30	110	30	110	30	110
Water temperature, DEG C	10	10	25	25	45	45	65	65
									Core Density, kg/m3	75	170	72	144	68	91	64	74
Hardness, CLD 40% (kPa) ISO 3386	9.1	17.1	7	14.5	5	6.4	3.6	4.3

Compare test-

Example 2

The following Synperonic surfactants were used.

TABLE 2

	EO content,% (by weight)	Molecular weight
			Synperonic PE L 43	30	1900
L 44	40	2200
			L 64	40	2900
P 84	40	4200
			P 85	50	4650
F 87	70	7700
			F 38	80	4800

A flexible foam was prepared from 100 parts by weight of the prepolymer used in example 1 by reacting it with 70 parts by weight of water containing 0.56 parts by weight of Synperonic polyol. The temperature of the prepolymer before the reaction was 22 ℃. The temperature of the water before reaction, the type of Synperonic used and the results of the wicking test are given in table 3.

TABLE 3

Test of	Synperonic PE type	Wicking test (seconds)	Water temperature (. degree.C.)
				1	L43	53	45
2	L44	11	45
				3	L64	8	45
4	P84	2	45
				5	P85	1	45
6	F87	5	45
				7	F38	130	45
8★	L64	238	20
				9★	P84	254	20
10★	P85	267	20

Compare test-

The foams obtained from runs 8-10 had a predominant number of closed cells.

Wicking test:

a sample of dry foam having dimensions of 9 x 1cm was placed on the surface of water (one of the two large surfaces of the sample was placed on the water) and the time until complete wetting of the upper surface of the sample was seen was recorded.

A foam was made from the above prepolymer (100pbw, 22 ℃), water and surfactant (0.8% by weight in water). The amount and temperature of water (per 100pbw of prepolymer) and the type of surfactant are listed in Table 4, along with whether the resulting foam is reticulated.

TABLE 4

Test of	Surface active agent	Amount of water	Water temperature, DEG C	Foam plastic with net structure
					11★	G26	70	25	Is not
12	G26	70	60	Is totally that
					13	F68	70	80	Is totally that
14★	F87	110	25	Is not
					15	F87	110	45	The majority of the cells are
16★	P75	110	25	Is not
					17	P75	110	45	A small proportion of the cells are

Compare test-

G26 is a polyoxyethylene triol having a molecular weight of 1200.

F68 is Synperonic PE F68: EO content 80% by weight and MW 8350.

P75 is Synperonic PE P75: EO content 50% by weight and MW 4150.

Example 3

100 parts by weight of the prepolymer of example 1 were reacted with 70 parts by weight of water containing 0.8% by weight of Synperonic L64. The temperature of the prepolymer and water before the reaction were room temperature (22 ℃ C.) and 45 ℃ C, respectively. In thatThe SAP is added to the prepolymer and mixed before the water is mixed with the prepolymer. The type (per 100 parts by weight of prepolymer) and amount of SAP used are given in Table 5, runs 1-10 and results: core Density (kg/m) of the resulting foam³) Is determined according to ASTM 3574/A; the maximum amount of 0.9% NaCl solution in water (physiological saline solution) which can be absorbed by the foam was determined (in terms of per dm)³Solution grams of foam); when the pressure is 1psi (4.5kg/64 cm)²) The solution retention was measured when applied for 15 minutes on a foam containing the above measured amount of solution and calculated according to the following formula:

wherein A is_mIs the maximum amount of solution that can be absorbed by the foam and A_pIs the amount of solution remaining in the foam after pressurization. The pressure is applied after allowing the foam to stand for 1, 10, 20 or 30 minutes. The retention numbers in table 5 are given for the optimum resting time (seconds).

The maximum absorption was determined by drying the foam at room temperature for 24 hours, completely immersing the foam in the solution for 15 seconds, removing the foam from the solution and measuring the amount per dm of foam before and after immersion³The weight difference of the foam.

The above experiment was repeated using water at 22 ℃. The results are given in table 5, runs 11 and 12 (30 minutes of standing).

TABLE 5

Test of	SAP type/SAP amount	Maximum absorption, g/dm3	Retention,%/optimum standing time, min	Core Density, kg/m3
					1	-	1370	53/1-30	65
2	1/15	1470	61/1-10	96
					3	1/30	1350	57/1-10	99
4	1/50	1280	79/20	133
					5	2/15	1240	67/10	90
6	2/30	1410	95/10	105
					7	2/50	990	98/30	102
8	3/15	1480	64/10	80
					9	3/30	1330	71/10	102
10	3/50	1250	99/10	128
					11	1/50 (Water temperature 22 degree)	1460	97	154
12	2/30 (Water temperature 22 degree)	1360	94	124

SAP type 1: polyacrylamide-based SAP having a molecular weight of about 5.10⁶

2: starch grafted sodium polyacrylate SANWET IM7000

3: sodium polyacrylate SANWET IM 3900G

Example 4

Example 3, run 4 was repeated except that the SAP was added in a different manner. The cells of the resulting foam were visually inspected for open cells and the shrinkage of the foam was determined according to the formula:

wherein S_bIs the diameter of the cup in which the foam was made and Sa is the diameter of the foam obtained after 12 hours of standing at room temperature.

The results of tests 1-5 are listed in Table 6.

TABLE 6

Test of	Addition of SAP	Opening holes	Shrinkage rate
				1	Adding the prepolymer immediately to water	Is free of	18
2	Adding the prepolymer to water after 150 seconds	Is free of	65
				3	To the prepolymer, followed immediately by addition of water	Is that	14
4	To prepolymerizationTo this, water was then added after 150 seconds	Is that	13
				5	The SAP, prepolymer, and water are mixed together	Is that	13
6 and 7	To the prepolymer, water was added after 2 hours	Is that	13

Test 4 was repeated, except that water was added not after 150 seconds but after 2 hours and that the amounts of SANWET IM7000 and SANWET IM 3900G were 30 parts by weight. The results of tests 6 and 7 are listed in table 6.

Example 5Comparative example

Example 3, run 3 was repeated except that water was used in an amount of 5 parts by weight. The foam collapses.

Claims (22)

1. A process for producing a flexible foam by reacting a prepolymer having an NCO value of 3 to 15% by weight of the NCO value of the reaction product obtained by reacting an excess of a polyisocyanate with a polyether polyol or a mixture thereof having an average nominal hydroxyl functionality of 2 to 6, an average hydroxyl equivalent of 500 to 5000 and an oxyethylene content of at least 50% by weight, with water in an amount of 15 to 500 parts by weight per 100 parts by weight of the prepolymer, the temperature of the prepolymer at the start of the reaction being 10 to 50 ℃ and the water temperature being 10 to 50 ℃ higher than the temperature of the prepolymer, with water.

2. The process for producing a flexible foam according to claim 1, wherein the temperature of water at the start of the reaction is 25 to 90 ℃.

3. The process according to claim 1, wherein the temperature of the prepolymer is 15 to 30 ℃, the water temperature is 40 to 70 ℃ and the water temperature is 20 to 45 ℃ higher than the temperature of the prepolymer.

4. A process according to claim 1, wherein the prepolymer is a reaction product having an NCO value of 3 to 10% by weight obtained by reacting an excess of a polyol containing at least 65% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof, and having an average nominal hydroxyl functionality of 2.5 to 3.5, an average hydroxyl equivalent weight of 1000 to 3000 and an ethylene oxide content of 50 to 85% by weight, or a mixture thereof, and water in an amount of 30 to 300 parts by weight per 100 parts by weight of the prepolymer.

5. A process as claimed in claim 1, wherein the reaction between the prepolymer and water is carried out in the presence of from 0.01 to 10 parts by weight, per 100 parts by weight of prepolymer, of a polyhydroxyl compound (2) having an average molecular weight of from 500-10000 and an average nominal hydroxyl functionality of from 2 to 6, which polyhydroxyl compound is a polyoxyethylene polymer or a polyoxyethylene/polyoxypropylene block copolymer having an oxyethylene content of at least 30% by weight.

6. A process according to claim 5, wherein the average nominal hydroxyl functionality of the polyhydroxyl compounds (2) is 2 and the oxyethylene content is from 35 to 70% by weight.

7. A process according to claim 5, wherein the polyol (2) has an oxyethylene content of at least 70% by weight and the amount of water used is at least 40 parts by weight per 100 parts by weight of prepolymer.

8. A process according to any one of claims 1 to 7, wherein the reaction between the prepolymer and the water is carried out in the presence of the superabsorbent polymer.

9. A process according to claim 8, wherein the amount of superabsorbent polymer used is from 10 to 70 parts by weight per 100 parts by weight of prepolymer.

10. A process according to claim 8, wherein the superabsorbent polymers are selected from the group consisting of superabsorbent polymers based on acrylic or methacrylic acids, esters, nitriles, amides and/or salts thereof; a polysaccharide-based superabsorbent polymer and a maleic anhydride-based superabsorbent polymer.

11. Process for the manufacture of flexible foams by reacting a prepolymer having an NCO value of 3-15% by weight of the NCO value of the reaction product obtained by reacting an excess of a polyisocyanate with a polyether polyol or mixture thereof having an average nominal hydroxyl functionality of 2-6, an average hydroxyl equivalent weight of 500-5000 and an oxyethylene content of at least 50% by weight, with water in an amount of 15-500 parts by weight per 100 parts by weight of prepolymer, characterized in that the reaction between the prepolymer and water is carried out in the presence of a superabsorbent polymer.

12. A process according to claim 11 wherein the prepolymer is a reaction product having an NCO value of 3 to 10% by weight obtained by reacting an excess of a polyol containing at least 65% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof, with an average nominal hydroxyl functionality of 2.5 to 3.5, an average hydroxyl equivalent weight of 1000 to 3000 and an oxyethylene content of 50 to 85% by weight, or a mixture thereof, in an amount of 30 to 300 parts by weight per 100 parts by weight of prepolymer.

13. A process as claimed in claim 11, wherein the reaction between the prepolymer and water is carried out in the presence of from 0.01 to 10 parts by weight, per 100 parts by weight of the prepolymer, of a polyhydroxyl compound (2) having a number average molecular weight of from 500-10000 and an average nominal hydroxyl functionality of from 2 to 6, which polyhydroxyl compound is a polyoxyethylene polymer or a polyoxyethylene/polyoxypropylene block copolymer having an oxyethylene content of at least 30% by weight.

14. A process according to claim 13, wherein the amount of the polyhydroxyl compound (2) is from 0.05 to 3 parts by weight per 100 parts by weight of the prepolymer.

15. A process according to claim 13, wherein the average nominal hydroxyl functionality of the polyhydroxyl compounds (2) is 2 and the oxyethylene content is from 35 to 70% by weight.

16. A process according to claim 13, wherein the polyol (2) has an oxyethylene content of at least 70% by weight and the amount of water used is at least 40 parts by weight per 100 parts by weight of prepolymer.

17. A process according to any one of claims 11 to 16, wherein the amount of superabsorbent polymer used is from 10 to 70 parts by weight per 100 parts by weight of prepolymer.

18. A process according to any one of claims 11 to 16, wherein the superabsorbent polymers are selected from the group consisting of superabsorbent polymers based on acrylic or methacrylic acids, esters, nitriles, amides and/or salts thereof; a polysaccharide-based superabsorbent polymer and a maleic anhydride-based superabsorbent polymer.

19. A flexible foam obtained by the production process according to any one of claims 1 to 18.

20. An absorbent article comprising the flexible foam of claim 19, wherein the flexible foam is catalyst-free, hydrophilic, superabsorbent-containingFlexible polyurethane foam of a polymer having a core density of at most 154kg/m³。

21. An absorbent article comprising the flexible foam of claim 19 wherein the flexible foam is a catalyst-free, hydrophilic polyurethane flexible foam which is free of releasable mono-, di-or polyols prior to contacting the foam with water or an aqueous solution.

22. An absorbent article according to claim 20 or 21, wherein the foam is a diphenylmethane diisocyanate based foam.