CN1980967B - flexible polyurethane foam - Google Patents

Abstract

The present invention prepares flexible polyurethane foams by mixing a prepolymer with foam-forming components that include an isocyanate that reacts with water to form carbon dioxide. The prepolymer is a hydroxyl-terminated prepolymer prepared by reacting a polyol with less than the theoretically required isocyanate to react with all of the available hydroxyl groups of the polyol. The prepolymer is a novel storage-stable raw material for preparing polyurethane foam, and the foam prepared from the prepolymer has favorable performance in hydrolysis resistance. By suitably selecting the proportion of isocyanate reacted with the polyol, the prepolymer produced can be made to be of low or high viscosity. At high viscosities, the pore structure can be advantageously controlled by appropriate gassing or degassing during foaming.

Description

flexible polyurethane foam

The present invention relates to flexible polyurethane (PU) foams.

Methods for producing flexible polyurethane foams (flexible PU foams) are known in the art, for example in Plastic Manual (Plastic Manual), Volume 7, Polyurethanes (Polyurethanes), Becher/Braun, 2nd Edition, Carl Hanser Verlag Publishing, pp. 170-235.

Usually flexible PU foams can be prepared by reacting polyols with multifunctional isocyanates, so that NCO and hydroxyl groups form urethane bonds through addition reactions, and then foam polyurethane with carbon dioxide generated in situ by the reaction of isocyanates with water.

This conventional method can be carried out in the so-called "one-step process", where the polyol, isocyanate and water are mixed together so that the polyurethane is formed and foamed in the same step.

However, it is also known to use a two-stage process, the first reaction of the polyol with the isocyanate to obtain a so-called "prepolymer", and the second step of foaming by reaction of the isocyanate with water to generate carbon dioxide.

Both GB870119 and GB929371 describe the reaction of polyols with toluene diisocyanate (TDI) to give a viscous prepolymer which is then mixed with water and a catalyst to generate foam.

However, these prior publications describe prepolymers prepared by reacting sufficient TDI with all available hydroxyl groups of polyols, the resulting prepolymers being NCO-terminated; these are so-called "isocyanate prepolymers", free of available hydroxyl. The NCO groups of the prepolymer can react with water to form PU foam without adding other isocyanates.

So-called "polyol prepolymers" are also known in the production of PU materials. As described in "Polyurethane Handbook", Dr. Günter Oertel, Hanser Publishers, p. 76, polyol prepolymers are converted by reacting polyether and polyester polyols with a stoichiometrically deficient isocyanate, leaving residual Oligomeric adducts made from hydroxyl groups. As described in the literature, these prepolymers are urethane-modified polyols with higher viscosity than unmodified polyols and are used in the field of lacquers, paints, coatings and sealants. For example heat activated hard coatings (baking coatings) can be prepared by reacting polyol prepolymers with blocked or blocked polyisocyanates. This field of application is different from the field of flexible PU foams to which the present invention relates.

In the field of flexible PU foams, hydrolysis is known to cause foam aging, especially softening. Foam aging is undesirable in various applications as aging changes the properties of the material in the application.

It is an object of the present invention to provide a flexible PU foam with significantly improved resistance to hydrolysis.

The present invention therefore provides a process for the preparation of PU foams from a mixture of prepolymers and foam-forming components, wherein said prepolymers are prepared by reacting at least one polyol with at least one polyfunctional isocyanate, which It is characterized in that the prepolymer is an unfoamed polyol prepolymer containing available hydroxyl groups, the foam-forming component comprising at least one polyfunctional isocyanate and water.

It was found that according to the method described PU foams can be produced which have a surprising resistance to hydrolytic aging.

As mentioned above, the use of polyol prepolymers is known to produce, for example, stoving hardcoats and has surprisingly been found useful for the production of flexible PU foams with advantageous properties.

Contrary to the teaching of the above prior publications describing the use of isocyanate-terminated prepolymers to make foams, the present invention uses isocyanate/polyol prepolymers with available hydroxyl groups, thus requiring additional addition of isocyanates to make PU foams, and it was found that it is possible to obtain Surprisingly hydrolysis-resistant foam.

While not wishing to be bound by any mechanism of hydrolysis resistance, we believe that the use of prepolymers results in PU foams that contain urea linkages and are not readily chemically reactive with water.

The isocyanate reacts with the polyol through an addition reaction to give a urethane linkage.

I.R-NCO+HO-R'→R-NH-CO-O-R'

Isocyanates react with water to give amines and carbon dioxide.

II.R-NCO+H ₂ O→RNHCOOH→RNH ₂ +CO ₂

Amines react with isocyanates to give urethane linkages.

III.R-NCO+RNH ₂ →R-NH-CO-NH-R

The urethane bond is hydrolyzed stepwise to give the amine and carbon dioxide.

IV.R-NH-CO-NH-R+H ₂ O→2RNH ₂ +CO ₂

Since the above reactions I, II, and III occur simultaneously, NCO, OH, and H ₂ O react with each other to obtain PU chains with urea bonds.

Usually flexible PU foam has a block structure consisting of long flexible polyol chains connected by polyurethane and polyurea aromatic hard segments, polar groups (such as NH of urea and urethane linkages) and carbonyl) are linked by hydrogen bonds.

Water can attack this structure by hydrolyzing the urea bonds causing dissociation, i.e. splitting the chains according to reaction IV, also changing the hydrogen bonds by penetrating the structure causing chain slippage within the structure, thus causing the foam to change its physical properties, especially softening.

It is believed that due to the formation of the PU chain network, there is little opportunity for urea bond formation via isocyanate/water reaction, so urea bond formation is minimized when using prepolymers that have undergone partial isocyanate/polyol reaction prior to foaming.

It is also believed that when the isocyanate reacts with both water and available hydroxyl groups on the prepolymer, those urea linkages that do form during foaming are better "organized" in the network of PU chains, making them less reactive with water. As mentioned above, one possible explanation is that the PU groups act as urea-forming species, resulting in a more structured or heterogeneous system, making water less permeable to hydrolyze urea bonds causing cleavage, or altering hydrogen bonds causing slip. Increasing the isocyanate in the prepolymer increases the level of texturization, but, as described below, increasing the viscosity of the prepolymer can alter the physical and chemical properties of the foam.

In the case of PU foams prepared by reacting isocyanate, polyol and water together in a so-called "one-step process", or by reacting an isocyanate-terminated prepolymer with water, urea linkages can be incorporated in a more "random" two-phase system , making it more susceptible to “structural reorganization” of the PU chain network through hydrolysis or chain slippage. This "restructuring" results in softening or a decrease in hardness.

In the context of the present invention, the prepolymers may be storage-stable materials prepared by reacting isocyanates with polyols in the complete or substantial absence of water. The prepolymer is prefabricated and foamed in a subsequent step by exposure to carbon dioxide produced by the reaction of isocyanate with water, and this step may be carried out in the same or a different apparatus shortly after the preparation of the prepolymer, or at In cases where the storage-stable prepolymers are prepared or supplied entirely independently, sometimes using different apparatus, if desired.

The term "prepolymer" as used herein refers to a urethane-modified polyol in its general sense, that is, a polymer material containing urethane linkages prepared by reacting a polyol with an isocyanate and used to prepare the end product polyurethane Material. Likewise, "unfoamed prepolymer" as used herein refers to a prepolymer substantially free of any foam generation. In fact, there may be negligible or slight degree of foaming due to the unavoidable presence of traces of water (eg contained in the base polyol) which can react with the isocyanate. Preferably, however, no purposeful or deliberate addition of water is made during the preparation of the prepolymer, and the reaction conditions and components are selected to inhibit or minimize the generation of carbon dioxide from the isocyanate/water reaction.

It is also understood that the method of the present invention may involve the use of a single prepolymer, i.e. a polymeric material prepared by reacting a single polyol with a single multifunctional isocyanate, or that the method of the present invention may involve the use of multiple prepolymers. The use of multiple prepolymers, that is, a variety of different prepolymers and/or one or more copolymers obtained by reacting a variety of polyols with a variety of multifunctional isocyanates.

The prepolymer can be formed by mixing a polyol or mixture of polyols with an isocyanate or mixture of isocyanates in the presence of one or more other components, such as a catalyst. The mixing can be carried out batchwise (for example with stirring) or continuously by mixing top feeds. Mixing may be at room temperature and may be maintained for any suitable time (eg, 24 hours), but may be other temperatures and times depending on the nature of the reactants and any other components.

Polyols can be of any suitable kind. Usually polyether and polyester polyols are used for the production of PU foams, it is preferred according to the invention that the polyols are entirely or at least predominantly polyether polyols. PU foams made with polyether polyols are less sensitive to hydrolysis than PU foams made with polyester polyols. When polyether polyols are used, those derived entirely or mainly from propylene oxide (PO) are preferred, but it is also possible to use ethylene oxide (EO) instead of PO, or to use EO and PO. EO derived polyols are more susceptible to hydrolysis than PO. However, it is also possible to use polyester polyols or mixtures of polyethers and polyester polyols. Suitable polyols may have an OH functionality of 2-6, especially 2-4, and a molecular weight (MW) of about 400-10,000.

The use of mixed polyols to modify the reactivity of the system or to impart desired properties to the resulting PU foam is well known in the art, and while PO derived polyether polyols are generally preferred for this invention, other polyols or Mixture of various polyols.

Examples of polyether polyols which can be used according to the invention are described, for example, in Plastic Manual (Plastic Manual), Volume 7, Polyurethanes (polyurethane), Becher/Braun, 2nd edition, published by Carl Hanser Verlag, pages 44-54 and 75- 78 pages.

Thus, polyols may for example be as follows:

I. A polyol derived from PO and propylene glycol with a viscosity (25° C.) of 250-350 mPa·s and a hydroxyl value of 56±3.

II. Polyols derived from EO, PO and trimethylolpropane with a viscosity (25° C.) of 750-900 mPa·s and a hydroxyl number of 35±2.

III. A polyol derived from PO and trimethylolpropane, with a viscosity of 600-700 mPa·s and a hydroxyl number of 380±25.

IV. Derived from PO and glycerol, the viscosity is 450-550mPa·s, and the hydroxyl value is 56±3.

All viscosity measurements (in mPa·s) were performed using a Brookfield viscometer. Viscosities are measured at 25°C unless otherwise stated. The hydroxyl value is a conventional parameter, which is the concentration of NCO-active hydroxyl groups per unit weight, in mg KOH/g.

Hydroxyl value (OH)=[(56.1×functionality)/molecular weight of polyol]×1000

It is also possible to use those polyether polyols which already contain an embedded catalyst, for example those described in WO03/016373A1. Mixtures of the aforementioned polyether polyols may also be used.

3008(Dow ChemicalCompany)或DESMOPHEN20WB56(Bayer)。Preferred polyols are triols which are propylene oxide adducts of glycerol with molecular weights on the order of 3,000. Commodity example is Voranol

3008 (Dow Chemical Company) or DESMOPHEN 20WB56 (Bayer).

As polyfunctional isocyanates, preference is given to diisocyanates, especially TDI (toluene diisocyanate). However, polyfunctional isocyanates preferably having a functionality of 2-5 may be used alone or in any suitable combination. The same isocyanate may be used to prepare the prepolymer and subsequently to prepare the foam, or different isocyanates may be used.

Therefore, the polyfunctional isocyanate can be any one or more of the following:

TDI (toluene diisocyanate all isomer blends)

MDI (diphenylmethane-4,4'-diisocyanate),

Can be pure substances or polymer variants (hence the name aromatic isocyanates).

T80(Shell)或VoranateT80和T65(DowChemicals)。还可使用4，4′-二苯基甲烷-二异氰酸酯(＝4，4′-亚甲基双(苯基异氰酸酯)；MDI)以及TDI和MDI的混合物。但是还可使用基于TDI或MDI和多元醇的异氰酸酯预聚物。还可使用改性或混合的异氰酸酯(例如Desmodur

MT58，购自Bayer)。脂族异氰酸酯的实例有1，6-六亚甲基二异氰酸酯或三异氰酸酯，例如Desmodur

N1000或N3300，购自Bayer。More specifically, polyfunctional isocyanates are polyisocyanates comprising two or more isocyanate groups, usually standard commercial diisocyanates and/or triisocyanates are used. Examples of suitable polyisocyanates are aliphatic, cycloaliphatic, arylaliphatic and/or aromatic isocyanates, for example mixtures of the 2,4- and 2,6-isomers of commercial toluene diisocyanate (TDI), so The product name is Caradate

T80 (Shell) or Voranate T80 and T65 (Dow Chemicals). It is also possible to use 4,4'-diphenylmethane-diisocyanate (=4,4'-methylenebis(phenylisocyanate); MDI) and mixtures of TDI and MDI. But it is also possible to use isocyanate prepolymers based on TDI or MDI and polyols. Modified or mixed isocyanates (e.g. Desmodur

MT58, available from Bayer). Examples of aliphatic isocyanates are 1,6-hexamethylene diisocyanate or triisocyanate, e.g. Desmodur

N1000 or N3300, available from Bayer.

The relative proportions of polyol and isocyanate reacted to form the prepolymer and the MW (molecular weight) of the polyol can be selected as desired. The proportion of isocyanate can be from 0.1 to 99%, preferably from 0.1 to 50%, of the amount theoretically required to react with all available hydroxyl groups. As the proportion of isocyanate increases, the viscosity increases, and the upper limit depends on the needs of processing. In fact, the hydroxyl value of the prepolymer can be determined by the following relationship:

OH(prepolymer)=OH(polyol)-(php(NCO)×561/EW(NCO))

OH (polyol) is the hydroxyl value of the raw material polyol, usually 56. php(NCO) is the proportion by weight of NCO per hundred parts of polyol, EW(NCO) is the equivalent weight of isocyanate, which is 87 for TDI (ie molecular weight divided by theoretical functionality).

The proportion of isocyanate can be high and, if desired, the MW of the polyol can be high, so the prepolymer can be very viscous, with a viscosity of about 30,000 mPa·s or higher. Alternatively a smaller proportion of isocyanate can be used, and if desired, the polyol MW can be lower, so less hydroxyl groups react and the viscosity can be lower. Lower viscosity prepolymers are more suitable for continuous production of PU foam. Thus, the viscosity may be less than 20,000 mPa·s, may be less than 7,000 mPa·s, be as low as about 700 mPa·s and/or be close to or substantially equal to the viscosity of the base polyol. The MW of the polyol can range from 400-10,000.

It was found that the advantageous foams of the present invention (i.e. foams with good hydrolysis resistance) can be prepared from both low viscosity prepolymers (only a few hydroxyl groups react with isocyanate) and higher viscosity prepolymers (a larger proportion of hydroxyl groups react with isocyanate) . Foams prepared from higher viscosity prepolymers can also have advantageous properties, such as control of cell structure, if desired, as described below.

The viscosity of the higher viscosity prepolymer may be greater than 5,000 mPa·s, preferably greater than 7,000 mPa·s, the upper limit may be about 50,000 mPa·s, preferably 35,000 mPa·s. More specifically, the favorable viscosity is 9,000-35,000 mPa·s, especially 15,000-35,000 mPa·s.

The lower viscosity prepolymers may overlap with the higher viscosity range of less than 20,000 mPa s, especially less than 7,000 mPa s, although the preferred range is less than 5,000 mPa s down to a viscosity close to that of the base polyol, It can be 600 or 700mPa·s.

Viscosity is determined by the ratio of isocyanate used to the theoretical weight of isocyanate required to react with all available hydroxyl groups of the polyol, and also by the initial viscosity of the polyol or mixture of polyols used to form the prepolymer . In general, as mentioned above, this proportion may range from 0.1 to 99%. For low-viscosity prepolymers, this proportion can be 0.1-30% or 0.1-23% or 25%, especially 0.1-12%, such as 3-12%, and for high-viscosity prepolymers, this proportion can be 30% -99%, especially 30-50%.

The isocyanate addition reaction can be carried out using any suitable catalyst. These catalysts may be tin compounds such as stannous dioctoate, dibutyltin dilaurate or tertiary amines such as 1,4-diaza[2,2,2]bicyclooctane, or other compounds used in the art. Substances such as zinc octoate, etc. Two or more different catalysts can also be used simultaneously if desired. However, prepolymers can also be prepared in the absence of catalyst, if desired, depending on heating or other reaction initiating conditions.

Any added catalyst is typically used in minor amounts, such as 0.004% of a tin salt (eg, dibutyltin dilaurate, stannous octoate, or higher homologues), although the amines and other catalysts may also be used. The catalyst is usually mixed with the polyol, followed by the slow addition of the isocyanate, and then the resulting mixture is fully reacted, followed by foaming. Thus the initial mixing can be carried out for about 15 minutes and the further reaction can be carried out for about 24 hours.

It is also possible to incorporate other components as auxiliaries or additives when forming the prepolymer.

More specifically, these components include various adjuvants such as chain extenders, crosslinkers and chain terminators.

Low molecular weight isocyanate reactive difunctional compounds such as diethanolamine or water or higher functional compounds such as triethanolamine, glycerol or sugar alcohols such as sorbitol can be used as chain extenders and/or crosslinkers.

Isocyanate-reactive monofunctional compounds such as monoalcohols, primary and secondary amines can be used as chain terminators.

Other auxiliaries known in the art, such as flame retardants, pigments or fillers, may also be added.

Prepolymers can be incorporated or mixed with other materials prior to foaming. For example unreacted polyols of the same or different kind can be added, for example to dilute the prepolymer, make the viscosity lower or modify the reactivity of the system or the properties of the resulting foam.

Conventional devices can be used to foam prepolymers by conventional methods, such as PlasticManual (Plastic Handbook), Volume 7, Polyurethanes (Polyurethane), Becher/Braun, 2nd Edition, published by Carl Hanser Verlag, pages 171-178 Described method, and use conventional foam preparation, for example Plastic Manual (plastic handbook), the 7th volume, Polyurethanes (polyurethane), Becher/Braun, 2nd edition, published by Carl Hanser Verlag, described in the page 187-193 foam preparation.

Typically, to prepare foams, the prepolymers may be mixed with water and/or other blowing agents, isocyanates, one or more catalysts, and one or more other components such as foam stabilizers.

Batch method or continuous method can be used for foaming, and the mixture can be aerated with nitrogen.

In more detail, the foaming component may include one or more of the following:

T80(购自Shell)、VoranateT80和T65(购自DowChemicals)。还可使用4，4′-二苯基甲烷二异氰酸酯(＝4，4′-亚甲基双(苯基异氰酸酯)；MDI)以及TDI和MDI的混合物。a) Isocyanates, for example aliphatic, cycloaliphatic, arylaliphatic and/or aromatic isocyanates. Examples are commercially available mixtures of the 2,4- and 2,6-isomers of toluene diisocyanate (TDI). The product name is Caradate

T80 (available from Shell), Voranate T80 and T65 (available from Dow Chemicals). It is also possible to use 4,4'-diphenylmethane diisocyanate (=4,4'-methylenebis(phenylisocyanate); MDI) and mixtures of TDI and MDI.

MT58，购自Bayer)。脂族异氰酸酯的实例有二异氰酸1，6-六亚甲基二异氰酸酯或三异氰酸酯，例如Desmodur

N1000或N3300，购自Bayer。Other isocyanate prepolymers based on TDI or MDI and polyols can also be used. Modified or mixed isocyanates (e.g. Desmodur

MT58, available from Bayer). Examples of aliphatic isocyanates are 1,6-hexamethylene diisocyanate or triisocyanates such as Desmodur

N1000 or N3300, available from Bayer.

The isocyanate may be the same or different from the isocyanate used to prepare the prepolymer.

b) Water, preferably from 0.5 to 10 parts by weight of water per 100 parts by weight of polyol or prepolymer or polyol/prepolymer mixture.

c) Liquid _CO2 can also be used as an additional blowing agent.

33LV(叔胺，购自Air Products)和/或金属有机化合物例如锡催化剂例如KOSMOS29(辛酸亚锡)或其他催化剂例如辛酸锌；本领域已知的泡沫稳定剂，例如聚硅氧烷表面活性剂，例如Tegostab

类(购自Goldschmidt)或Silbyk类(购自BYK-Chemie)；扩链剂和/或交联剂，例如二乙醇胺、甘油、山梨糖醇；以及阻燃剂；填料。可使用任何组合的与常规发泡方法相关的本领域已知的那些添加剂和其他物质。d) Other additives may optionally be used, especially those known in the field of PU foams, such as catalysts, especially amines, such as DMEA (dimethylethanolamine), DABCO

33LV (tertiary amine, available from Air Products) and/or organometallic compounds such as tin catalysts such as KOSMOS29 (stannous octoate) or other catalysts such as zinc octoate; foam stabilizers known in the art, such as silicone surfactants , such as Tegostab

Class (purchased from Goldschmidt) or Silbyk (available from BYK-Chemie); chain extenders and/or crosslinkers such as diethanolamine, glycerin, sorbitol; and flame retardants; fillers. Any combination of those additives and other materials known in the art associated with conventional foaming methods may be used.

e) Nitrogen for entrainment and control of cell structure (pore size and pore size distribution).

Regarding foaming, it can also be carried out under reduced pressure or overpressure if necessary; the processing conditions thereof are disclosed in US Pat. No. 5,194,453, for example.

Very fine cells can be obtained by adding a finely divided gas to the base material to be foamed (for example a prepolymer or a liquid mixture of various base components). The gas is preferably nitrogen, or air may be used.

As described below, for high viscosity prepolymers, eg, prepolymers with viscosities greater than 5,000 mPa·s, air entrainment is particularly useful for controlling cell structure.

In addition to prepolymers, it is also possible to use mixtures of prepolymers with polyether polyols and/or polyester polyols or other polyols. Diols to hexols containing any amount of ethylene oxide can be used.

It was found that a secondary feature of the present invention is the possibility to control the parameters related to the number of cells and the viscosity of the prepolymer, resulting in PU foams with advantageous properties, which is another particular advantage of using said prepolymer.

Thus, in one embodiment, flexible PU foams are produced with a particularly regular or, where appropriate, irregular cell structure, in which the pore size can vary from very fine (cell number greater than 80 ppi) to very coarse ( hole count down to 6ppi). The term "ppi" is a measure of cell (pore) size, determined by the number of cells per inch (per 2.54 cm) of length of the foam surface. This embodiment adopts a large-scale industrial production method to produce the above-mentioned flexible PU foam, and the prepared foam has a predetermined desired pore size or pore number and/or pore size distribution.

In this regard, flexible polyether-polyurethane foams with very fine cells (greater than 80 ppi) have hitherto not been industrially produced using raw materials generally available on the market. On the other hand, it is known that if polyester polyols are foamed to produce polyester-polyurethane foams, very fine cells can be obtained.

However, in the present invention, as described below, using the prepolymers of the invention, preferably the highly viscous prepolymers described herein, it has surprisingly been shown that polyether polyols (generally considered very Low-viscosity materials) are processed into very fine-celled PUR foams.

Unless otherwise stated, the term "highly viscous" refers to a material or mixture of materials having a viscosity equal to or greater than 5,000, especially greater than 7,000 mPa·s.

The resulting flexible foams are often distinguished by the following properties, hitherto unattainable in the field of polyether polyol-based PU foams:

- By controlling the structure and thus the viscosity of the prepolymer, the number of pores and the structure (fine/coarse number of pores and regular/irregular structure) can be controlled.

- excellent hydrolytic aging resistance properties; and

- a density of 10-100, preferably 14-70 kg/m ³ .

A particular advantage of the production method according to the invention is that it facilitates purposeful presetting of the pore size or number of pores and the regularity or irregularity of the pore size or pore structure. Depending on the desired foam quality, for example for foaming, this advantage is achieved mainly by varying the entrainment with air or nitrogen, if necessary with a more or less degassing of the base material or at least part of the base material.

The term "cell structure" is understood to mean the structure of the foam matrix in terms of pore size, distribution and number and type of cells contained herein. A uniform or regular pore structure means that the majority of the pores are the same or about the same size.

Since it is assumed that high viscosity may depend on the structure of the prepolymer and thus vary with the polymer, the possibility of diffusion and especially the diffusion rate of gas bubbles is significantly reduced compared to low viscosity reaction mixtures, so that gas bubbles or water vapor bubbles can polymerize knots, forming larger structures less rapidly. In particular the ability to increase the viscosity of foaming systems based on polyether polyols, which are generally low viscosity systems, makes the control and precise determination of the pore size a surprising feature of the present invention.

Surprisingly, it is also possible to produce foams with very large cells by deliberately limiting the entrainment of air to the foam or, on the other hand, even by carrying out a controlled degassing of the isocyanate and/or prepolymer. In this case, a greater degree of degassing increases the pore size and reduces the pore number of the final product. Degassing can be performed, for example, in a closed-circuit system under vacuum.

The high viscosity prepolymer has a viscosity greater than 5,000 mPa·s, especially greater than 7,000 mPa·s, preferably 15,000-35,000 mPa·s, or even up to about 50,000 mPa·s.

In order to better illustrate the present invention, the present invention is further described with reference to the following examples.

Example 1

The prepolymers were prepared using a batch process.

96.24% polyether polyol [DESMOPHEN 20WB56 (Bayer)], hydroxyl value: 56, viscosity: about 700mPa s (20°C);

3.75% Toluene Diisocyanate 80/20 (TDI 80/20)

0.00385% dibutyltin dilaurate (DBTL)

The polyether polyol was placed in a mixing vessel at room temperature and then dibutyltin dilaurate was added with stirring. Toluene diisocyanate was slowly stirred into the mixture.

After about 24 hours, the resulting prepolymer had a viscosity (25° C.) of about 30,000 mPa·s.

However, the prepolymers can also be prepared analogously in a continuous process.

Example 2

Preparation and properties of the foams according to the invention compared to conventional products known from the prior art.

Foams were prepared in a standard industrial flexible foam board workshop (Messrs. Hennecke, Germany) using a one-step process. In this example, the raw materials are metered according to the recipe with a pump (for example a piston pump or a gear pump) from a storage container directly into a mixing chamber equipped with a stirrer and a discharge tube.

The ingredients are metered and mixed using methods known in the art. In this example, the temperature of the feedstock was adjusted to 25±3°C.

The overall discharge rate of prepolymer or polyol is 50 kg/min. For additional nucleation (that is to say additional nucleation of gas bubbles), nitrogen is metered into the mixing chamber. Foaming is performed at a stirring speed not exceeding 6,000 rpm, preferably below 6,000 rpm, and a pressure in the mixing chamber not exceeding 2.5 bar, preferably below 2.5 bar.

Use each component described in following table 1 as foaming raw material, prepare the prepolymer that is used for the present invention according to embodiment 1, the polyether polyol of reference embodiment is identical with embodiment 1, and its viscosity is about 700mPa. s.

Table 1

^* php = parts by weight per 100 parts by weight of polyol (or prepolymer or prepolymer/polyol mixture).

The flexible PU foam prepared under these conditions was subjected to the following tests:

a) decrease in compression hardness due to accelerated aging tests, and

b) Determination of pore structure (ppi).

The compressive hardness was measured before and after the accelerated aging test, and the unit is kPa·s. Measured at 40% strain according to EN ISO3386-1. Accelerated aging test (wet aging) in an autoclave with saturated vapor pressure according to EN ISO 2440 at 120°C for 5 hours (one aging cycle).

The pore structure is determined by counting the number of pores lying on the line. Units are ppi (pores per linear inch or 2.54 cm).

Table 2 Test results

Compressive hardness before accelerated aging test [kPa] Compressive hardness after accelerated aging test [kPa] Decrease in compression hardness [%] Number of holes (ppi) foamed prepolymer 3.37 3.37 0% 92 Foamed polyether polyol (reference example) 3.67 3.41 7.08% 45

From this comparison (table 2) it can be seen that the flexible PU foams prepared according to the invention have a density of about 25 kg/m ³ and not only have cells of significantly finer diameter, but at the same time have the same Denser foam is more resistant to aging.

It has also been found that all of the various foam articles prepared hitherto according to the method of the invention are significantly more resistant to wet aging than those foams having the same or substantially the same formulation prepared under comparable conditions by methods known from the prior art (according to the above-mentioned accelerated aging test standard).

While foams prepared according to known methods exhibited compression hardness reductions of up to 35%, for formulations prepared according to the present invention with the same or substantially the same principal isocyanate and polyol components, the compression hardness of the foams did not decrease by more than 15%. In the case of foams with a cell count greater than 80 ppi, and a density of 20-30 kg/m ³ , the drop in compressive hardness is even only 0-5%.

Typically the reduction in compressive hardness of the products prepared according to the invention is at least 10-50% lower than that of reference products prepared according to the prior art. This strongly demonstrates that the foams produced according to the invention have significantly improved resistance to aging, in particular resistance to wet aging.

In this context, the formulation of the reference product is chosen such that the density and hardness properties are substantially the same as those of the product prepared according to the invention.

More specifically, the formulation of the reference product was chosen such that the apparent density and hardness of the foam prepared according to the invention were approximately the same, within a tolerance of ±10%.

Example 3

Preparation of coarse-celled flexible foams by reducing bubble nucleation.

Prepare another reaction preparation according to Example 2, adopt the same formula to use the prepolymer to prepare flexible foam by degassing the raw material (mainly the isocyanate used), the density of this flexible foam is 18kg/m ³ , and the number of cells is 8ppi.

These and other examples are given with reference to Table 3 below, where columns A and B are the same as Table 1, column C is Example 3 above, and the other columns are other examples using the same formulation and method as Table 1, except that Instead of machine mixing as in Table 1, processing was carried out in each case in a laboratory mixer.

Table 3A Examples (based on 200g polyol mix), all amounts in php

(parts per hundred parts by weight polyol and/or prepolymer)

A B C D E F G H I J Polyol.OH＝56 100 100 100 prepolymer 100 100 100 100 100 100 100 TDI 80/20 47.8 17.8 24.2 23.2 23.2 22.8 48 47.7 46.9 TDI 65/35 17.8 45.2 24.2 23.2 23.2 22.6 water 3.8 3 4.2 3.8 3.8 3.8 3.8 3.8 3.8 3.8 Dabco 33lv 0.05 0.05 0.05 0.05 0.05 Niax A1 0.12 0.12 0.12 0.12 0.12 Stannous octoate 33% 0.18 0.2 0.2 0.3 0.3 0.3 Tegoamln ZE-1 0.3 0.3 0.3 0.3 Kosmos EF 1.5 1.5 1.5 1.5 Polysiloxane Surfactant 1.05 1.05 1.05 1.5 1.5 1.5 1.5 1.05 1.05 1.05 Amount of isocyanate in prepolymer, php nll 3.89 3.89 nil 0.5 1 2 nil 1 2 Viscosity of polymer or prepolymer, mpa 700 30.000 30.000 700 800 1.440 2.000 700 1.450 2.010 Density, Kg/M3 24.8 25 18 22.7 22.6 22.5 twenty three 23.6 23.9 26 CLD 40% (Kpa) 3.67 3.37 3.9 3.31 2.46 3.03 2.98 3 3.44 3.91 CLD decrease after wet aging (%) 7.08 0 2.5 19.3 12.1 6.6 14.4 twenty one 9.3 9.8 Aperture (ppi) 45 92 8 54 48 50 55 55 52 56

Table 3B Examples (based on 200g polyol mix), all amounts php (as above)

K L M N O P Q R Polyol, OH=56 100 50 prepolymer 100 100 100 100 100 100 50 TDI 80/20 20.2 18.3 18.2 18.2 18.2 18.8 20 20 TDI 65/35 20.2 18.2 18.2 18.2 18.2 19.8 20 20 water 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 Dabco 33lv Niax A1 Stannous octoate 33% Tegoamin ZE-1 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Kosmos EF 1.5 0.8. 1.5 1.5 1.5 1.5 1.5 1.5 Polysiloxane Surfactant 1.5 1 1.5 1.5 1.5 1.5 1.5 1.5 Amount of isocyanate in prepolymer.php nil 3.5 2 1 3.9 0.8 0.27 1 Viscosity of polymer or prepolymer, mpa 700 17.000 2.000 1.440 8.850 750 700 1.440 Density.kg/m ³ 28.6 30.9 28.3 29.3 27.1 29.2 28 27.5 CLD 40% (Kpa) 2.76 4.4 2.88 2.37 4.65 3.34 3.1 2.8 CLD decrease after wet aging (%) 24.5 12.6 9 0.8 11.6 11.1 11 10.4 Aperture (ppi) 52 49 51 48 53 50 49 47

Table 3C Examples (based on 200g polyol mix), all amounts php (as above)

S T   Polyol, OH＝56 100   Prepolymer 100 TDI 80/20 15.2 14.5 TDI 65/35 15.2 14.5 water 2.3 2.3 Tegoamin ZE-1 0.3 0.3 Kosmos EF 1.5 1.5   Polysiloxane 1 1 Amount of isocyanate in prepolymer.php 2 Viscosity of polymer or prepolymer, mPa 600 3.700 Density, kg/ ^m3 34.8 37.6   CLD 40% (Kpa) 2.31 4.13   Decrease in CLD after wet aging (%) 19.5 11.1 Aperture (ppi) 46 46

Tegoamin ZE-1 and KOAMOS EF are amine and tin catalysts respectively, different from Dabco33lv and Niax A1, but have the required low fogging properties.

Interpretation of Table 3

Columns A and B are Example 1 above, and Column C is Example 3. That is, columns B and C are machine produced foams made according to the invention (using a high viscosity prepolymer) and column A is conventional foam made with the same base polyol used to make column B prepolymer The reference machine produces foam formulated to the same density as column B foam.

Significantly improved hydrolytic aging resistance is shown, with a controlled fine and coarse pore structure (columns B and C).

Columns D-G are foams prepared with similar densities and similar water contents in the foaming stage. Prepolymers were prepared using the same isocyanate and catalyst (TDI and DBTL), but with different ratios of isocyanate, resulting in prepolymers with different viscosities. The base polyol was the same as used in Example 1 (MW=3,000). The blowing catalyst, unlike the catalyst used in Example 1, is a low-fogging catalyst preferably used for the production of foam for the automotive industry.

Compared to reference column D, the inventive foams (columns E-G) have improved aging resistance.

Columns H-J are similar to Column A (same polyol, same isocyanate and catalyst were used to make the prepolymer), but the ratio of isocyanate used to make the prepolymer was different and was lab mixed, not machine mixed. Compared with the reference column H, the inventive foam (column I,

J) Has improved aging resistance.

Columns K-R are other examples (using the same polyol as in Example 1), but with different proportions of isocyanate used to prepare the prepolymer, lower water content for foaming than in Example 1, and the following parameters varied as follows:

i) Isocyanates/catalysts used to prepare prepolymers:

K-N, Q, R: TDI+DBTL

O: TDI+ stannous octoate

P: polymeric MDI (eg Voranate M220, available from Dow Chemical)+DBTL

ii) K is a reference example, the base polyol is not converted to a prepolymer; L-Q have the same amount of the same base polyol converted to a prepolymer; half the amount of the same base polyol in P is converted to a prepolymer, Dilute with an equal amount of the same base polyol that does not convert to prepolymer.

Compared to reference column K, the inventive foams (columns L-R) have improved aging resistance.

Columns S and T are different from Example 1, especially the polyols are EO/PO polyols (rather than the specific PO polyols in Example 1), which can be trifunctional polyether polyols containing a large number of secondary hydroxyl groups, MW =3,500, specifically LUPRANOL 2084 (BASF). The isocyanate/catalyst used to make the prepolymer was TDI/DBTL.

The inventive foams (column T) have improved aging resistance compared to the reference (column S).

From Table 3, partly the same as Tables 1 and 2 (repeating columns A and B of Table 3), the formulations of the invention have significantly improved hardness reduction compared to reference formulations that do not use the prepolymer of the invention.

The proportions of isocyanate used to prepare the prepolymers were varied and the resulting prepolymers had viscosities ranging from a relatively low viscosity of 700 mPa·s to high viscosity levels (30,000 mPa·s). In each case, however, there was a surprisingly significant improvement in hardness reduction compared to the corresponding reference formulation, suggesting that the use of hydroxyl-terminated isocyanate/polyol prepolymers was an important factor. The results also indicated that viscosity increase could also be a contributing factor in some cases. High quality usable foams are available over a wide range of prepolymer viscosities.

As noted above, higher isocyanate content results in a higher prepolymer viscosity and a slightly higher final foam density.

The foams of the present invention, especially foam boards produced on an industrial scale, can have a wide variety of uses. Its use extends to electrical, acoustic and thermal insulation systems, e.g. in construction and civil engineering and in automotive production, in the production of cleaning products for cleaning sponges or cleaning tools equipped with cleaning sponges, for the production of cosmetic sponges and comfort foams, e.g. for beds Pad and upholstery foams, especially as carrier foams for inks or as printing pads in recording devices or printing presses.

It is to be understood, of course, that the invention is not limited to the details of the formulations of the foregoing examples, which are given by way of illustration only.

As stated above, the present invention, in addition to providing a process for the preparation of polyurethanes, also provides novel storage-stable prepolymers for the preparation of said foams.

Claims (5)

1. A method for preparing flexible polyurethane foam from a mixture of prepolymers and foam-forming components, wherein said prepolymers are prepared by reacting at least one polyol with at least one polyfunctional isocyanate, said prepolymers The polymer is an unexpanded polyol prepolymer having a viscosity of less than 20,000 mPa·s and having available hydroxyl groups, said viscosity being measured at a temperature of 25°C using a Brookfield viscometer, said prepolymer being obtained by mixing with said All available hydroxyl groups of the polyol are prepared by reacting 0.1 to 30% by weight of the theoretically required isocyanate of isocyanate, and the foam-forming component comprises at least one polyfunctional isocyanate and water. 2. Process according to claim 1, characterized in that the polyol is at least predominantly a propylene oxide derived polyether polyol. 3. A method for preparing flexible polyurethane foam from a mixture of prepolymers and foam-forming components, wherein said prepolymers are prepared by reacting at least one polyol with at least one polyfunctional isocyanate, said prepolymers The polymer is an unfoamed polyol prepolymer having a viscosity of 7,000-50,000 mPa·s and having available hydroxyl groups, the viscosity measured at a temperature of 25° C. using a Brookfield All available hydroxyl groups of the polyols are prepared by reacting 30-99% of the theoretically required isocyanate weight isocyanate, and the foam-forming component comprises at least one polyfunctional isocyanate and water. 4. The method of claim 3, wherein the polyol is at least predominantly a propylene oxide derived polyether polyol. 5. The method of claim 3 or 4, wherein the prepolymer is an unfoamed polyol prepolymer having a viscosity of 15,000-35,000 mPa·s and available All available hydroxyl groups of alcohols are prepared by reacting 30-50% of the isocyanate weight theoretically required.