DE3238173C2 - - Google Patents

Description

Elastic polyurethane foams made from toluene diisocyanate (TDI) have been manufactured for many years, especially for use with upholstery and mattresses. It has However, it has been shown that in the manufacture of hydrophilic Foams for medical purposes or for the Application in health care is desirable, the TDI exchange in the foams for diphenylmethane diisocyanate (MDI), because the TDI has a high vapor pressure and relative is highly toxic, which is why special precautions should be taken during the manufacture and use are required. Further can use foams based on TDI during sterilization or storage in a wet package due to hydrolysis be affected. For example, hydrophilic Foams based on TDI after just a few cycles be liquefied in a steam autoclave at 120 ° C. Such Hydrophilic foams can also be extraordinary when wet swell strongly, in the order of magnitude of more than 100% by volume.

Conventional MDI polyurethane foams are already known. These foams are rigid or semi-rigid because of the MDI gives the foams a certain crystallinity becomes. From GB-PS 8 74 430 are elastic polyurethane foams known by the reaction of polyether polyols with at least 2 hydroxyl groups and a polyisocyanate mixture from diarylmethane diisocyanate and 5 to 10 wt .-% one Polyisocyanate with a functionality greater than 2 in the presence  a small amount of water. Possibly a catalyst can also be used. These known foams have the disadvantage that they are not hydrophilic and do not contain sufficient amounts of Water is produced, which is the transport of large quantities on fibers, fillers, antiseptic agents or others water-dispersible components, such as those used for medical purposes Allow purposes and used in healthcare. The term "hydrophilic" is used in this context used in the sense that the foam in the It is able to absorb 15 to 20 times its weight in water. Another disadvantage is that for the If a catalyst is used, catalyst residues may be left behind, which is not desirable.

From US-PS 41 37 200 is a method for producing a cross-linked hydrophilic polyurethane foam known in which a hydrophilic polyoxyethylene diol with an ethylene oxide content of at least 40 mol%, e.g. B. those with a molecular weight from 200 to 20,000, and a polyol with functionality from 3 to 8, for example trimethylolpropane, glycerol or Pentaerythritol, in an amount of 1 to 20 wt .-%, based on the Polyol blend, with a polyisocyanate with functionality from 2 to 2.8, for example with polyarylpolymethylene polyisocyanate with a functionality greater than 2, in an amount of 1.8 up to 1.9 NCO equivalents per OH equivalent, all Cap hydroxyl groups of the polyol mixture. This NCO terminated prepolymers is additionally polyisocyanate with a Functionality from 2.0 to 2.8 in an amount from 0.1 to 0.3 NCO equivalents are added per initially present OH groups and then 6.9 to 390 moles of water per mole of unreacted Isocyanate added to the mixture. You can do this that the prepolymer is made by essentially doing that linear polyol with a polyol which is at least 3 and particularly preferably has 3 to 4 hydroxyl groups, mixed and then reacting the mixture with the polyisocyanate.  

In US-PS 42 37 240 the production of elastic MDI-based foams with a high load-bearing capacity and high energy absorption capacity through implementation of diphenylmethane diisocyanates with polyester polyols or Mixtures of polyester polyols and polyether polyols with a polyester polyol content of at least 60% by weight described on the polyol mixture, as well as small amounts of water. From the claims it appears that a catalyst is used. These foams have the same Disadvantages like the products described in GB-PS 8 74 430, including undesirable catalyst residues in the foams; Furthermore the polyester polyols are more expensive than polyether polyols.

According to GB-PS 12 09 058 elastic hydrophilic polyurethane foams can by reacting a polyisocyanate with Polyether polyols containing at least 10% by weight of a block copolymer made of ethylene oxide with propylene oxide protective groups is provided, so as the stability against hydrolysis to be made to improve. The procedure requires  at least the use of a divalent tin salt Fatty acid and / or at least one tertiary amine as a catalyst. The foams produced by this process have, although they are hydrophilic, the disadvantage that they are made only with small amounts of water. Further require the use of block copolymers. In addition, this GB-PS does not use the intrinsically hydrophobic MDI for the production of hydrophilic Foams taught, and the foam obtained contains again undesirable catalyst residues.

The object of the present invention is to provide an improved to create elastic polyurethane foam, from one Prepolymer system containing a diphenylmethane diisocyanate Isocyanate product with a functionality greater than 2.0 as the sole one Source of isocyanate.

Another object of the present invention is to create an improved elastic polyurethane foam, the large amount of fibers, fillers, antiseptics or other water-dispersible components can. Furthermore, an elastic hydrophilic foam is said be made of white paint so that the foam used for medical purposes and in health care can be.

Another object of the present invention is to manufacture a polyurethane prepolymer with an MDI-containing isocyanate product with a functionality greater than 2.0 than the sole source of isocyanate. The prepolymer obtained can can be stored for an unlimited time and still results when mixed with an approximately equal amount of water used as a carrier for water-dispersible ingredients can be a hydrophilic foam.

In addition, the polyurethane prepolymer is said to last over the retention period also have good viscosity stability.  

After all, the polyurethane prepolymer is said to be less than 50 % By weight of isocyanate product and become an elastic Have foam processed.

This object is achieved by an elastic Polyurethane foam according to claim 1 and a polyurethane Prepolymer according to claim 10.  

The elastic foams according to the invention that are water-absorbent are and therefore for medical purposes as well as in health care can be applied accordingly from a prepolymer provided with isocyanate groups using an MDI-containing isocyanate product produced as the sole isocyanate.  

The elastic polyurethane foams according to the invention are produced in two embodiments. In the procedure designated as embodiment A, a monomeric polyol crosslinking agent is used, while in the procedure designated as embodiment B, a polymeric poly (oxy-C _2-4 alkylene) polyol crosslinking agent is used.

In embodiment A, the foams are produced from a certain composite prepolymer which contains at least one poly (oxy-C _2-4 alkylene) diol with a molecular weight of at least 1100 and at least 50% by weight of oxyethylene groups, and also a monomeric polyol Crosslinking agent with 3 or 4 hydroxyl equivalents per mole, such as trimethylolpropane, and an isocyanate product based on diphenylmethane diisocyanate, abbreviated MDI, having a functionality greater than 2.0, such as. B. the product sold under the trademark Isonate®143-L by Upjohn Polymer Chemicals, which has a functionality of approximately 2.1 and which is produced from a mixture of MDI and isocyanate-containing derivatives of MDI.

In embodiment B, the foams are produced from a prepolymer which contains at least one poly (oxy-C _2-4 -alkylene) diol with a relatively low molecular weight of less than 2000 and with at least 50% by weight of oxyethylene groups, preferably of has at least 80 wt .-% oxyethylene groups and further a polymeric poly (oxy-C _2-4 alkylene) polyol crosslinking agent with 3 or 4 hydroxyl equivalents per mole with an average molecular weight of at least 500, such as. B. a poly (oxyethylene) triol with a molecular weight of about 900, or the product sold under the trademark Poly G®76-120 by the company Olin, a poly- (oxypropylene) -triol provided with oxyethylene protective groups with a Molecular weight of about 1400, and an isocyanate product based on MDI with a functionality of greater than 2.0, which is prepared from a mixture of MDI and isocyanate-containing derivatives of MDI, such as. B. Isonate®143-L. With these formulations, white foams are obtained which are aesthetically pleasing and are of a desirable nature for medical purposes and applications in health care.

One of the essential features of these prepolymer formulations is that the amount of isocyanate product containing diphenylmethane diisocynate, for example Isonate®143-L, is restricted so that it is less than 50% by weight, generally 38 to 46% by weight. % of the prepolymer in embodiment A and 37 to 48% by weight of the prepolymer in embodiment B. The reduction in the amount of isocyanate is made possible in embodiment A by increasing the average molecular weight of the poly (oxy-C _2-4 -alkylene) diol component to more than 1100. When trimethylolpropane is used as the monomeric polyol crosslinking agent, the preferred diol molecular weights are from 1200 to 1400 and the diol contains at least 80% by weight of oxyethylene groups. The diol used in a preferred embodiment consists of a mixture of 2 diols with different molecular weights. For example, one diol can have a molecular weight of 1000 and the other diol can have a molecular weight of 1450.

In embodiment B, the amount of isocyanate is reduced by increasing the average molecular weight of the polymeric poly (oxy-C _2-4 -alkylene) polyol crosslinking agent to over 500. If the poly (oxy-C _2-4 alkylene) diol used is one with a molecular weight of about 1000, the preferred polymeric poly (oxy-C _2-4 alkylene) polyol crosslinking agent is a triol with a molecular weight of about 1400.

The actual content of free MDI can be found in this Isocyanate product regulated up or down as long as the functionality is greater than 2.0 remains. For example, additional pure MDI could be added will.

It has now been found that in embodiment A with MDI-containing isocyanate products containing a poly (oxy-C _2-4 alkylene) diol and z. B. trimethylolpropane as a monomeric polyol crosslinking agent, the isocyanate products can advantageously be reduced to a value greater than 1100 by increasing the average molecular weight of the poly (oxy-C _2-4 alkylene) diol components. These diols preferably contain at least 80% by weight of ethyleneoxy groups. The elastic foams obtained retain their physical properties even when exposed to steam in an autoclave at 120 ° C for 5 hours, and the foams have a substantial reduction in swellability compared to foams containing TDI. Hydrophilic foams based on TDI swell by more than 100% by volume when wet, while the foams of embodiment A according to the invention swell only by 30 to 60% by volume when wet.

It was further found that in embodiment B according to the invention in the MDI-containing isocyanate products with relatively low molecular weight poly (oxy-C _2-4 -alkylene) diols, the molecular weight of which is less than 2000, the isocyanate product is advantageous by increasing the molecular weight of the poly- (oxy-C _2-4 alkylene) polyol crosslinking agent can be reduced. Instead of using trimethylolpropane with a molecular weight of 134, higher molecular weight poly- (oxy-C _2-4 -alkylene) -triols or -tetraols with molecular weights in the range of 500 to 2000 are used. A preferred example of this is POLY G®176-120. The elastic foams obtained retain their physical properties even when exposed to steam in an autoclave at 120 ° C. for 5 hours, and the foams show a significant drop in swelling capacity compared to TDI foams. Hydrophilic foams based on TDI swell to a volume of more than 100% by volume in the wet, while the foams according to the invention of embodiment B only swell by 30 to 75% by volume when they are wet.

The reduced content of isocyanate product, such as isonates ®143-L, in the two embodiments A and B.  the production of foams that are elastic and springy are, compared to the foams that have a content of Isonate®143-L of more than 50% by weight and semi-rigid and are not resilient. The increase in the molecular weights of the Diols allow the required amount to be reduced to Isonate®143-L to such an extent that the ratio the functional isocyanate groups to the functional hydroxyl groups (known as the so-called isocyanate index) from 3.5: 1 can be reduced to about 3: 1. This change contributes to the flexibility of the foam product.

Although the flexibility is best with the help of the bending module is characterized in the present case as an approximation Classification of these foams into soft and elastic (Modules below 0.14 N / mm²), firm but elastic (modules between 0.14 and 0.27 N / mm²) and semi-rigid or rigid (Modules over 0.27 N / mm²) the more easily measurable tensile strength applied at 1% extension.

For the isocyanate product containing diphenylmethane diisocyanate with a functionality greater than 2.0 it is a modified diphenylmethane diisocyanate with a high percentage on pure diphenylmethane diisocyanate and a lower one Amount of carbodiimides and trifunctional carbodiimide cycloadducts. A corresponding commercial product is that under the trademark Isonate®143-L product sold by Upjohn Polymer Chemicals, which is converted into a carbodiimide by converting MDI and further implementation of this material to a trifunctional Cycloadduct is produced. The MDI mix, the carbodiimide and the cycloadduct are in mutual Balance. A mixture of the following Components A and B represent the Isonate®143-L system:

The prepolymer technology for the production of foams requires mixing the prepolymer with about the same Volume of water. The prepolymer must be hydrophilic for whatever reason at least a small amount of Diol containing poly (oxyethylene) units for the preparation of the prepolymer must be used. The one for a good mix and foaming with water suitable viscosity is in the range from 10,000 to 35,000 mPa · s at 25 ° C, preferably at of about 20,000 mPa · s. Both the viscosity and the hydrophilicity of the prepolymers are selected by appropriate selection of Polyol type and molecular weight controlled. The prepolymers must not thicken noticeably during storage. It it has been found that adequate storage stability is achieved  if the viscosity does not exceed 100,000 mPa · s (measured at 25 ° C) after a 2-week rapid storage test rises at 80 ° C.

An elastic suitable for most uses Foam should have a tensile strength of at least 0.14 N / mm², a foam density of about 0.048 to 0.096 g / cm³ and one Elongation at break of at least 100%, preferably higher Values. In an example according to embodiment A was an elongation at break of 200% and in one example obtained an elongation at break of 250% according to embodiment B.

The poly (oxy-C _2-4 alkylene) diol has at least 50% by weight of oxyethylene groups. If it contains oxypropylene and / or oxybutylene groups, then the aforementioned minimum amount of oxyethylene groups must also be present. The preferred diols in embodiment A have at least 80% by weight of oxyethylene groups.

In one of the preferred embodiments A, it has proven to be satisfactory to use, as poly (oxy-C _2-4 -alkylene) diol, a mixture of products sold by Union Carbide Chemicals under the trademark Carbowax®1000 and Carbowax®1450 , although other combinations of the particularly preferred poly (oxyethylene) diols with an average molecular weight of 1000 to 2000, but preferably in the range of 1200 to 1400, are also suitable. In these cases, the average molecular weights of all the diols used are at least 1100. By using a mixture of these two diols in approximately equimolar amounts, foams are obtained which advantageously have a low swelling volume and a low density.

In embodiment A according to the invention, poly (oxy-C _2-4 -alkylene) polyol crosslinking agents which have 3 or 4 hydroxyl equivalents per mole are used as crosslinking agents. These include trimethylolpropane, trimethylolethane, glycerin, triethanolamine, pentaerythritol and mixtures of these polyols. Trimethylolpropane (TMOP) of the formula is particularly preferred

It has also been found that in preferred embodiments B satisfactory results when using Carbowax®1000 or Carbowax®1450 can be obtained as diols, though for this embodiment of the invention, any polyoxyethylene diol with an average molecular weight from 1000 to 2000, but preferably in the range from 1000 to 1500, can be used.

In embodiment B according to the invention, polymeric poly (oxy-C _2-4 -alkylene) -polyol crosslinking agents which have 3 or 4 hydroxyl equivalents per mole and an average molecular weight of at least 500, or mixtures of these polymeric polyols, are used as crosslinking agents. POLY G®76-120 is very particularly preferred. It is believed that the oxyethylene portion contains blocks of oxyethylene units attached to a central polyoxypropylene core. However, the poly (oxy-C _2-4 alkylene) polyol crosslinking agent can also consist of a copolymer with a random distribution of these units.

The density and physical properties of the foams according to embodiments A and B appear to be sensitive to the polyol content. If a low density foam is desired that is firm and less rubbery, then the amount of polyol must be increased. Accordingly, the amount of polyol must be reduced in the case of a desired foam with higher density and greater elasticity. The operational amount of polyol crosslinking agent with a hydroxyl functionality of 3 or 4 is measured so that 2 to 35% of the hydroxyl content of the diol and polyol mixture comes from the polyol. The preferred range for a foam with good elasticity is 10 to 30% hydroxyl content from the polyol. In embodiment B, a polymeric poly (oxy-C _2-4 alkylene) polyol crosslinking agent is used as the polyol, generally a relatively small amount of the polymeric polyol being used to keep the prepolymer in a liquid state. If the amount of polyol crosslinking agent is based on the amount of diol present, then the diol and the polyol crosslinking agent in embodiment A are in a molar ratio of 4: 1 to 8: 1, and the amount of polymeric polymer is (oxy-C _2-4 alkylene) polyol crosslinking agent on the larger amount of the present poly (oxy-C _2-4 alkylene) diol in embodiment B, then the poly (oxy-C _{2- 4-} alkylene) polyol crosslinking agent in such an amount that the hydroxyl equivalents 5 to 35 mol% of the total hydroxyl equivalents in the poly (oxy-C _2-4 alkylene) diol and poly- (oxy-C _2- Make up _4- alkylene) polyol crosslinking agents.

In embodiment A, the Carbowax®1000 has an equivalent weight of 500 per hydroxyl group while using TMOP a molecular weight of 134 an equivalent weight of 45 per hydroxyl group. Since the Isonate®143-L is used so that it binds to the hydroxyl groups the required amount of isocyanate becomes very sensitive address the TMOP amount, which is why the TMOP amount is proportional is carefully controlled.  

If in embodiment B the molecular weight of the polyol is too high, it means that the hydroxyl concentration is so low that it takes too long for the raw materials react with each other. On the other hand, if the molecular weight of the polyol is too low and diols with low Molecular weight are used, then are larger Amounts of isocyanate product required with the consequence that stiff Foam products can be obtained.

In embodiment B, the Carbowax®1000 has an equivalent weight of 500 per hydroxyl group, while POLY G® 76-120 with a molecular weight of 1400 an equivalent weight of 467 per hydroxyl group. Since the Isonate® 143-L in turn is used to attach it to the hydroxyl groups is bound, the required amount of isocyanate also very sensitive to the amount of POLY G®76-120, which is why its amount is proportional is carefully controlled.

The operational amount of Isonate®143-L is in both Embodiments A and B so that the isocyanate index at 2.5 to 3.5, preferably 2.8 to 3.2, and with very good ones Results is 3.1. Higher ratios lead to a lower viscosity of the polymer, a lower Foam density and less swelling, however, they are also more expensive and reduce the softness and elasticity of the polyurethane foams. One reacts during the preparation of the prepolymer Isocyanate group of the polyisocyanate component with a hydroxyl group, with the remaining isocyanate group not is implemented. These free isocyanate groups in the prepolymer then react with water to form polyurea bonds, while the molecular weight increases at the same time and CO₂ is released, which in the formation of contributes to the foamed product.  

In the implementation of the components for the preparation of the prepolymer according to embodiments A and B it has The isocyanate concentration after one hour proved to be helpful Measure implementation by titration. Thereby and subsequent titrations can increase the additional reaction time be determined, which is required to determine the isocyanate concentration towards the theoretically required value lower, in which all hydroxyl groups with the isocyanate will have reacted. Put the reaction above it further away, so that the isocyanate concentration continues reduced, then the prepolymer viscosity increases with the As a result, it becomes more difficult, then the prepolymer to mix with water. The implementation of the Prepolymer ingredients also result in foam density increases and the ability of the foam obtained to water to absorb decreases.

Surfactants are selected so that they have a foam of good quality Appearance with the correct cell size and shape as well as durability against insufficient foaming or splitting. Such surfactants can be used Suitability for the production of polyurethane foams already is known. Examples of preferred surfactants are block copolymers with oxyethylene and oxypropylene units, such as those under the trademark Pluronic® polyol surfactants sold by Wyandette Chemicals Corporation. A preferred surfactant is Pluronic®L-62.

The preferred method of making the polyurethane foam is that about an equal amount of the aqueous Suspension added to the prepolymer mixture and then the two components are mixed together. The Composition of the aqueous suspension can also on the Based on 100 parts of the prepolymer expressed will. So 100 phr water means that 100 parts water 100 parts of prepolymer come. The quantitative ratio of prepolymer mixture  too aqueous suspension can be used in a wide range can be varied. However, if the amount of aqueous suspension is too large, the strength of the foam obtained drops from. On the other hand, if the amount of the aqueous suspension increases is greatly reduced, then it will not be possible to get one add sufficient amount of fibers and fillers that introduced into the prepolymer via the aqueous suspension will.

The preferred method for foaming the prepolymer is in that the aqueous suspension, e.g. B. a 2nd % solution of Pluronic®L-62, and the prepolymer on a Temperature of about 35 ° C warmed. Then the Components cast or pumped in one Ratio of about 100 parts by weight of aqueous suspension to about 80 parts by weight of the prepolymer, and then immediately to stirred for 30 s using a mechanical stirrer. During this time, complete mixing is made possible without any noticeable chemical conversion takes place. This mixture is immediately poured into a mold in which the swelling and curing of the polyurethane foam he follows.

To get additional structural rigidity, can the aqueous phase for introduction into the foam composition Fibers are added. Particularly advantageous are polyester fibers that are up to a length of about 1.27 cm or less can be cut. The fibers can be added to the aqueous suspension in various amounts be added, though preferably no more than about Should make up 10% by weight, otherwise the suspension is too difficult to pump.

A high molecular weight suspension or thickening agent can also be used be added for the purpose of  Keep ingredients suspended so that no water from the fibers flow and the fibers do not float. The thickener acts as a lubricant for the fibers, so that they do not become matted, do not drain and themselves Do not build up when passing through the mixing pump. Examples for thickeners are water-soluble non-ionic polyethylene oxide, water-soluble hydroxyethyl cellulose, xanthan gum and polyacrylamides, that have high molecular weights of about 1 million.

Preferred suspension or thickening agents are acrylic acid polymers, which neutralizing agents, e.g. B. sodium or Ammonium hydroxide, can be added. If you have ammonium hydroxide Adds to the acrylic acid polymer as a neutralizing agent the viscosity of the aqueous phase increases more advantageously Way. Furthermore, since ammonium hydroxide is less expensive than that Acrylic acid polymers is a more economical one Formulation for the same amount of thickener produce a smaller amount of acrylic acid polymers is needed.

Which are the most suitable surfactants depends on any fibers, fillers, antiseptic Agents, dyes, thickeners or others water-soluble or water-dispersible components that can be incorporated. Therefore, these surfactants for example, highly hydrophobic silicones, such as B. Pluronic®L-520 or other silicone surfactants, however also highly hydrophilic compounds be. For general use, non-ionic ones surface-active substances, such as the Pluronics®, in particular L-62, L-72, L-92, P-75 or P-85,  prefers. The use of these surfactants is for one in the formulation of polyurethane foams knowledgeable expert.

The water adsorption test is cut with rectangular Foam samples measuring 2.54 x 7.62 x 12.70 cm performed. The sample is immersed in water and then held up until it no longer drips. The ratio of wet weight to dry weight of the The sample is the water absorption ratio.

The invention is further elucidated below with the aid of examples explained, in the examples 1 to 4 different configurations of embodiment A and in the examples 5 to 9 specific embodiments of embodiment B. to be discribed.

Example 1

A mixture of 174 g (0.174 mol) of Carbowax®1000, 249 g (0.172 mol) Carbowax® 1450 and 6.1 g (0.045 mol) trimethylol propane was by heating to 70 ° C for two hours reduced pressure (2.7 mbar) dried. To this dried one and degassed polyol blend were 365 g (2.56 equivalents of the isocyanate) Isonate®-143 L added. The temperature was held at 70 ° C for 70 minutes to complete the reaction to end. It became a light yellow liquid with a Isocyanate content of 2.18 meq / g and with a viscosity at 25 ° C obtained from 23,000 mPa · s. After two weeks of storage Sample at 80 ° C, the product still had a viscosity of 40,000 mPa · s at 25 ° C, had therefore only thickened relatively little. When 80 g of the product heated to 35 ° C with 100 ml a 2% non-ionic surfactant solution (Pluronic®L-62) were stirred, a foam with a density was obtained of 0.066 g / cm³, which was soft, elastic and hydrophilic and had the properties summarized in Table II.  

Table I

Prepolymer composition

Table II

Physical properties of polyurethane foams

Examples 2 to 3 and Comparative Experiment I

Various prepolymers were made using the compositions given in Table I. The properties of the polyurethane foams obtained are summarized in Table II.

In Example 2, a diol mixture with an increased average Molecular weight used, making the use enables less isocyanate and a foam product with higher density and greater water absorption capacity has been.

In Comparative Experiment I, the amount of TMOP was reduced. The ratio of diol to triol was however outside the scope of the invention. A rigid foam was obtained, but no water soaked up and did not get wet, so it was not possible was to determine a water adsorption ratio.

In Example 3, a single diol, namely Carbowax®1450, used together with TMOP as a crosslinking agent. Here became a soft, hydrophilic foam product with high elongation, and still good water retention and good Preserve steam resistance.

Example 4

A mixture of 412 g (0.412 mol) Carbowax®1000 and 28 g (0.02 mol) Poly G®176-120 was under at 70 ° C for 2 hours reduced pressure (2.7 mbar). Then 349 g (2.45 isocyanate equivalents) Isonate®143-L to the dried one and degassed polyol mixture added. The temperature was held at 70 ° C for 80 minutes to complete the reaction  to end. It became a light yellow liquid with a Isocyanate content of 1.96 meq / g and with a viscosity of Obtained 27,000 mPa · s at 25 ° C. After two weeks of storage one Sample at 80 ° C was a thickening to only 43,000 mPa · s 25 ° C occurred. When 80 g of the prepolymer heated to 35 ° C with 100 ml of a 2% non-ionic surfactant solution (Pluronic®L-62) were stirred, a foam with a Density of 0.062 g / cm³, which is soft, elastic and hydrophilic and had the properties given in Table IV.  

Table III

Prepolymer composition

Table IV

Physical properties of polyurethane foams

Examples 5 to 7

Foams were made using different prepolymer compositions, which are given in Table III, produced. The properties of the foams obtained are summarized in Table IV.

In example 5, the amount of triol and as a balance the isocyanate index increases to a product with lower Viscosity and lower foam density and lower To get swelling factor.

In Example 6, the amounts of triol and isocyanate were further enlarged, maintaining the good foaming properties remained.

In Example 7 the molecular weight of the Carbowax® diol increased to 1450, which enabled the crowd of isocyanate to only 37% by weight, based on the total composition, to reduce, the good foaming properties of the product obtained remained.

Claims (20)

1. Elastic polyurethane foam, obtainable by mixing and reacting an aqueous phase consisting of water and a conventional surfactant with either

• A) a prepolymer
  • a) a poly (oxy-C _2-4 alkylene) diol with at least 50% by weight of oxyethylene groups and with a nominal average molecular weight of at least 1100 and nominally 2 hydroxy equivalents per mole,
  • b) an isocyanate product containing diphenylmethane diisocyanate with a functionality greater than 2.0, which is a modified diphenylmethane diisocyanate with a high percentage of pure diphenylmethane diisocyanate and a smaller amount of carbodiimides and trifunctional carbodiimide cycloadducts, and
  • c) a monomeric polyol crosslinking agent with 3 or 4 hydroxyl equivalents per mole,
• the isocyanate product (b) making up less than 50% by weight of the prepolymer, the poly (oxy-C _2-4 alkylene) diol and the polyol crosslinking agent in a molar ratio in the range from 4: 1 to 8: 1 are present and the ratio of the isocyanate equivalents to the total hydroxyl equivalents is 2.5: 1 to 3.5: 1, or
• B) a prepolymer
  • a) a poly (oxy-C _2-4 alkylene) diol with at least 50% by weight of oxyethylene groups and a nominal average molecular weight of less than 2,000 and nominally 2 hydroxyl equivalents per mole,
  • b) an isocyanate product containing diphenylmethane diisocyanate with a functionality greater than 2.0, which is a modified diphenylmethane diisocyanate with a high percentage of pure diphenylmethane diisocyanate and a smaller amount of carbodiimides and trifunctional carbodiimide cycloadducts, and
  • c) a poly (oxy-C _2-4 alkylene) polyol crosslinking agent with 3 or 4 hydroxyl equivalents per mole and with an average molecular weight of at least 500,
• wherein the isocyanate product b) is less than 50% by weight of the prepolymer, the poly (oxy-C _2-4 alkylene) polyol crosslinking agent is present in an amount such that the hydroxyl equivalents are 5 to 35 mol% of the total hydroxy equivalents in the poly (oxy-C _2-4 alkylene) diol and poly (oxy-C _2-4 alkylene) polyol crosslinking agent, and the ratio of the isocyanate equivalents to the total hydroxyl equivalents being 2.5: 1 to 3 , Is 5: 1.

2. Elastic polyurethane foam according to claim 1, obtainable by using a prepolymer A, in which the nominal average molecular weight of the poly (oxy-C _2-4 alkylene) diol is in the range from 1100 to 2000 and the diol at least 80 wt. -% has oxyethylene groups. 3. Elastic polyurethane foam according to claim 2, obtainable by using a prepolymer A, in which the nominal average molecular weight of the poly (oxy-C _2-4 alkylene) diol is in the range from 1200 to 1500. 4. Elastic polyurethane foam according to claim 1, obtainable by using a prepolymer B, in which the nominal average molecular weight of the poly (oxy-C _2-4 alkylene) diol is in the range from 600 to 2000 and the diol at least 80 wt. -% has oxyethylene groups. 5. Elastic polyurethane foam according to claim 4, obtainable by using a prepolymer B, in which the nominal average molecular weight of the poly (oxy-C _2-4 alkylene) diol is in the range from 950 to 1500. 6. Elastic polyurethane foam according to claim 1, obtainable by using a prepolymer A, in which the poly (oxy-C _2-4 alkylene) diol comprises a mixture of at least 2 diols, each of the diols having a different nominal average molecular weight . 7. Elastic polyurethane foam according to claim 6, in which a Mixture of a diol with a molecular weight of 1000 and another diol with a molecular weight of 1450 is used. 8. Elastic polyurethane foam according to claim 1, obtainable by using a prepolymer B in which the poly (oxy-C _2-4 alkylene) polyol crosslinking agent is a poly (oxyethylene) triol with a molecular weight of 900 and / or is a 1400- molecular weight poly (oxypropylene) triol provided with oxyethylene protecting groups. 9. Elastic polyurethane foam according to claim 8, obtainable by using a poly (oxy-C _2-4 alkylene) polyol crosslinking agent in which blocks of oxyethylene and oxypropylene units are present. 10. prepolymer for the production of an elastic foam according to claim 1, consisting of the reaction product A)

• a) a poly (oxy-C _2-4 -alkylene) diol with at least 50% by weight of oxyethylene groups and a nominal average molecular weight of at least 1100, and nominally two hydroxyl equivalents per mole,
• b) an isocyanate product containing diphenylmethane diisocyanate with a functionality greater than 2.0, which is a modified diphenylmethane diisocyanate with a high percentage of pure diphenylmethane diisocyanate and a smaller amount of carbodiimides and trifunctional carbodiimide cycloadducts, and
• c) a monomeric polyol crosslinking agent with 3 or 4 hydroxyl equivalents per mole,

wherein the isocyanate product makes up less than 50% by weight of the propolymer, the poly (oxy-C _2-4 alkylene) diol and the polyol crosslinking agent are present in a molar ratio in the range from 4: 1 to 8: 1 and that Ratio of the isocyanate equivalents to the total hydroxyl equivalents is from 2.5: 1 to 3.5: 1,
or from the reaction product B)

• a) a poly (oxy-C _2-4 -alkylene) diol with at least 50% by weight of oxyethylene groups and a nominal average molecular weight of less than 2000, and nominally 2 hydroxyl equivalents per mole,
• b) an isocyanate product containing diphenylmethane diisocyanate with a functionality greater than 2.0, which is a modified diphenylmethane diisocyanate with a high percentage of pure diphenylmethane diisocyanate and a smaller amount of carbodiimides and trifunctional carbodiimide cycloadducts, and
• c) a poly (oxy-C _2-4 alkylene) polyol crosslinking agent with 3 or 4 hydroxyl equivalents and with a nominal average molecular weight of at least 500,

wherein the isocyanate product makes up less than 50 wt .-% of the prepolymer, the poly (oxy-C _2-4 alkylene) polyol, crosslinking agent is present in such an amount that the hydroxyl equivalent 5 to 35 mol .-% of the total hydroxyl equivalent in Make up poly (oxy-C _2-4 alkylene) diol and poly (oxy-C _2-4 alkylene) polyol crosslinking agents, and the ratio of the isocyanate equivalents to the total hydroxyl equivalents is from 2.5: 1 to 3 , 5: 1. 11. Prepolymeres according to claim 10, consisting of the reaction product A), for the preparation of which uses a poly (oxy-C _2-4 alkylene) diol with a nominal average molecular weight between 1100 and 2000 and at least 80 wt .-% oxyethylene groups has been. 12. Prepolymer according to claim 11, consisting of the reaction product A), for the preparation of which a poly (oxy-C _2-4 alkylene) diol with a nominal average molecular weight between 1200 and 1500 has been used. 13. Prepolymeres according to claim 10, consisting of the reaction product B), for the preparation of which uses a poly (oxy-C _2-4 -alkylene) diol with a nominal average molecular weight of 600 to 2000 and at least 80 wt .-% oxyethylene groups has been. 14. Prepolymeres according to claim 13, consisting of the reaction product B), for the preparation of which a poly (oxy-C _2-4 alkylene) diol with a nominal average molecular weight of 950 to 1500 has been used. 15. A prepolymer according to claim 10, consisting of the reaction product A), for the preparation of which a poly (oxy-C _2-4 alkylene) diol mixture of at least 2 diols has been used, each of the diols having a different nominal average Has molecular weight. 16. A prepolymer according to claim 15, consisting of the reaction product A), for the preparation of which a poly (oxy-C _2-4 alkylene) diol mixture of a diol with a molecular weight of 1000 and a diol with a molecular weight of 1450 has been used. 17. Prepolymer according to claim 10, consisting of a reaction product B), for its production as a poly (oxy-C _2-4 - alkylene) polyol crosslinking agent a poly- (oxyethylene) - triol with a molecular weight of 900 and / or a poly- (oxypropylene) -triol with a molecular weight of 1400 and provided with oxyethylene protective groups has been used. 18. Prepolymeres according to claim 17, consisting of a reaction product B), for the preparation of which a poly (oxy-C _2-4 alkylene) polyol crosslinking agent with blocks of oxyethylene and oxypropylene units has been used.