POLYOL COMBINATION
The present invention concerns a polyol combination, a formulation for preparing foam with the help of the polyol combination and a process of preparing foam from this polyol. In particular, the present invention concerns a polyol combination for preparing high resilience viscoelastic foam. Background of the Invention
Polymers like polyurethanes tend to exhibit both viscous and elastic behaviour. High resilience polyurethanes predominantly exhibit elastic behaviour which means that they change shape when force is applied but return nearly instantaneously to their initial shape when the applied' force is removed. Viscoelastic polyurethanes show viscous behaviour in that mechanical energy is converted into heat and molecular motion when the polyurethane is deformed. It takes some time (the recovery time) before viscoelastic foams have returned to their initial shape. High resilience and viscous behaviour seem incompatible. However, the frequency used for testing the viscoelastic and the resilience properties is markedly different. Therefore,, viscoelastic high resilience foams are possible, and are also called slow recovery foams.
Flexible viscoelastic polyurethane foam generally is produced at low isocyanate index. The isocyanate index is 100 times the mole ratio of isocyanate groups to isocyanate-reactive groups in the formulation. Usually, the isocyanate index for preparing viscoelastic polyurethane foam is less than 90. Unfortunately, low- index foam formulations are extremely sensitive to small changes in catalyst and surfactant amounts, so the
processing window is undesirably narrow. Special, expensive silicones are often needed to avoid shrinkage or foam collapse. Moreover, when toluene diisocyanate (TDI) is used to make viscoelastic foam at low index, the 5. foams can contain undesirably high levels of toluene- diamines, particularly after the normal curing process.
US-A-6, 391, 935 discloses a method for preparing flexible viscoelastic foam at an isocyanate index of from about 95 to about 110 with the help of a mixture that 0 includes a polyester or polyoxyalkylene polyol and from about 15 to about 70 %wt of a polyester or polyoxyalkylene monol. The foams obtained have a low resilience, i.e. less than 15% 'as measured in the standard ball rebound test. US-A-6, 391, 935 contains no information on 5 how to manufacture viscoelastic foams which have high resilience .
Furthermore, the polyol formulations used in US-A-6, 391, 935 have the disadvantage that a large amount of monol is to be used. The presence of large amount of 0 monols can easily lead to a substantial amount of unreacted monol in the final product. A substantial amount of unreacted monol gives an unpleasant hand feel.
It has now been found possible to prepare flexible polyurethane foam having both high resilience and 5 viscoelastic properties with the help of a limited amount of monols . Summary of the Invention
Accordingly, the present invention relates to a polyol combination comprising up to a total of 100 parts 0 by weight of
(1) 1 to 15 parts by weight of a polyalkoxylated monol having a number average molecular weight in the range of from 400 to 4000,
(2) 50 to 97 parts by weight of a polyalkoxylated diol having a number average molecular weight in the range of from 1000 to 7000, and
(3) 2 to 40 parts by weight of a polyoxyalkylated polyol having solid polymer particles stably dispersed therein
(hereinafter referred to as "polymer polyol") , which polyoxyalkylated polyol has a nominal functionality of at least 3. Detailed description of the Invention The monol for use in the present invention has one hydroxyl group per polyalkyoxylated molecule. The diol for use in the present invention has two hydroxyl groups per polyalkyoxylated molecule. The polyol for use in the present invention contains, on number average, of from 2.2 to 6 hydroxyl groups per molecule.
Polyoxyalkylated compounds are prepared by reacting a hydroxyl containing compound with an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide and/or mixtures thereof. Preferably, the alkylene oxide is propylene oxide, optionally together with one or more other alkylene oxides like ethylene oxide or butylene oxide. Suitable hydroxyl containing starting compounds include polyfunctional alcohols, generally containing of from 2 to 8 hydroxyl groups. Examples of such alcohols comprise glycols, glycerol, pentaerythritol, trimethylolpropane, triethanolamine, sorbitol and mannitol. Usually a strong base like potassium hydroxide or a similar metal hydroxide salt is used as a catalyst in this type of reaction. However, catalysts such as double metal cyanide complex catalysts can also be used. The monol for use in the present invention can be prepared separately from the diol for use in the present invention such as with the help of hydroxyl containing starting compounds such as methanol, ethanol and/or phenols. In order to prepare monols in this way, it can
be preferred to use a double metal cyanide complex catalyst.
An efficient and attractive method for preparing the relatively small amount of monol required by the present invention, comprises the use of a diol containing a substantial amount of monol and/or the use of a polymer polyol containing monol. Such mixtures are more easily prepared and more readily available than monols per se. Combinations of polyoxyalkylated monol and poly- oxyalkylated diol which contain a substantial amount of monol can be prepared by reacting starter containing 2 hydroxyl groups at process conditions which favour the formation of a substantial amount of polyoxyalkylated compounds containing a single hydroxyl group. Such process conditions comprise the use of a potassium hydroxide catalyst and process conditions such as a relatively high catalyst concentration, a relatively high reaction temperature and/or a relatively high alkylene oxide, such as propylene oxide, pressure.. Suitable starters comprise ethylene glycol, propylene glycol, alkoxylated ethylene glycol, alkoxylated propylene glycol, and mixtures thereof. Although monols prepared in this way tend to have a substantial amount of unsaturation, this unsaturation has not been found to lead to problems. Commercially available diols containing a substantial amount of monols are diols commercially available under the trade name of CARADOL ED diols, such as CARADOL ED56-07, CARADOL ED56-10 and CARADOL ED52-01 (CARADOL is a trade mark) . The monol for use in the present invention has a number average molecular weight in the range of from 400. to 4000, more preferably of from 500 to 3000, most preferably of from 500 to 2000. The primary hydroxyl content of the monol generally will be of from 0 to 98%,
preferably of from 50 to 98%, most preferably of from 60 to 95%.
The diol for use in the present invention has a number average molecular weight in the range of from 1000 to 7000, more preferably of from 1000 to 5000, most preferably of from 1500 to 4800. The primary hydroxyl content of the diol generally will be of from 0 to 98%, preferably of from 50 to 98%, most preferably of from 60 to 95%. In addition to the monol and diol, the present invention comprises a polyoxyalkylated polyol having solid polymer particles stably dispersed therein, also called polymer polyol. In general, a polymer polyol is a dispersion of a solid polymer in' a liquid polyol. Such systems are well known in the art and are normally prepared by polymerising one or more ethylenically unsaturated monomers in the presence of a free radical catalyst.' Examples of such polymer polyol systems and methods for their preparation are disclosed in, for instance, EP-A-076,491, EP-A-343,907 and EP-A-495, 551. Polyurea or polyurethane polymers are also known to be useful as the dispersed polymer in polymer polyols instead of the polymers based on ethylenically unsaturated monomers. For the purpose of the present invention, the base polyol used is not critical. The nominal functionality makes that the polyoxyalkylated polyol is prepared from a hydroxyl containing starting compound containing 3 or more hydroxyl groups. Preferably, the nominal functionality is of from 3 to 6, which means the use of a starting compound containing of from 3 to 6 hydroxyl groups. The polyoxyalkylated polyol generally has a number average functionality of from 2.2 to 6. Usually, the polyol will contain monol in addition to polyols of higher functionality. If any, diols are generally present in a limited amount. Any monol and diol which is present in the
polyoxyalkylated polyol is considered to be part of the monol content (1) and the diol content (2) , respectively. These monols and diols are not considered to be part of the polymer polyol . The number average molecular weight of the polyoxyalkylated polyol generally will be in the range of from 1000 to 13000, more specifically of from 2000 to 10,000, more preferably of from 3000 to 7000. The primary hydroxyl content of the base polyol generally will be of from 0 to 98%, preferably of from 50 to 95%, most preferably of from 60 to 95%. The number average functionality preferably is of from 2.4 to 5, more specifically of from 2.5 to 4.5. The amounts • indicated for the present invention are based on 100 parts by weight of polyol. For these calculations, the polymer present in the polyol is also considered to be part of the polyol.
The polymer dispersed in the base polyol, may in principle be any such polymer known to be applicable for this purpose. Thus, suitable polymers include the polymers based on ethylenically unsaturated monomers and particularly polymers of vinyl aromatic hydrocarbons, like styrene, alpha-methyl styrene, methyl styrene and various other alkyl-substituted styrenes . Of these, the use of styrene is preferred. The vinyl aromatic monomer may be used alone or in combination with other ethylenically unsaturated monomers, such as acrylonitrile, methacrylonitrile, vinylidene chloride, various acrylates and conjugated dienes like 1, 3-butadiene and isoprene. Preferred polymers, however, are polystyrene and styrene- acrylonitrile (SAN) copolymers . Another suitable class of polymers are the polyurea and polyurethane polymers . Particularly the condensation products of primary amines or polyhydric alcohol amines and aromatic diisocyanates are very useful in this respect. A very much preferred polymer is the condensation product of triethanolamine and toluene
diisocyanate (TDI) . The dispersed polymer is generally present in an amount of from 5 to 40% by weight based on total weight of polymer polyol. In case the polymer is polystyrene or SAN polymer, preferred solids amounts are in the range of from 5 to 35% by weight, whilst in case of polyurea polyurethane polymers the preferred amount of polymer is from 5 and 20% by weight.
The amount of polymer present added via the polymer polyol preferably is such that the final polyol combination comprises of from 1 to 10 %wt of solid polymer particles, more preferably of from 2 to 7 %wt .
Examples of some commercially available polymer polyol compositions which may be applied as polymer polyol include the polyurethane polyols CARADOL SP50-01 and DESMOPHEN 7652, and also the polystyrene polyols CARADOL MD25-02 and CARADOL MD30-02 and the styrene-acrylonitrile polymer polyols CARADOL MD22-40, CARADOL MD22-02 and CARADOL SP33-03 (CARADOL and DESMOPHEN are trade names) . The polyoxyalkylated monol, diol and' polyol for use in the present invention can have been capped with poly (oxyethylene) moieties. This can be attained by adding ethylene oxide only at the end of the alkylene oxide, normally propylene oxide, polymerization reaction. This is also sometimes referred to as "tipping" with ethylene oxide. Tipping gives an increased primary hydroxyl content such as a primary hydroxyl content of at least 50%. The polyoxylalkylated compounds for use in the present invention preferably have been tipped.
The polyol combination according to the present • invention specifically comprises, up to a total of
100 parts by weight, of from 6 to 13 parts by weight of monol, of from 65 to 91 parts by weight of diol and of from 3 to 25 parts by weight of polymer polyol.
The present invention also relates to a formulation for preparing a foam comprising, based on total amount of polyol,
(a) 100 parts by weight of the polyol combination according to the present invention;
(b) 0.1 to 6 parts by weight of blowing agent;
(c) 0.1 to 5 parts by weight of crosslinking agent (s);
(d) 0.01 to 2.5 parts by weight of polyurethane catalyst (s) ; and optionally (e) further usual auxiliaries.
It has been found possible to reliably prepare high resilience, viscoelastic foams with the help of the above formulations. Therefore, the present invention further relates to the process of preparing viscoelastic high resilience foam by reacting the above formulation with one or more polyisocyanates .
The use of water as a (chemical) blowing agent is well known. Water reacts with isocyanate groups according to the well known NCO/H2O reaction, thereby releasing carbon dioxide which causes the blowing to occur. Other blowing agents, such as carbon dioxide, can be used as well either per se or in combination with water. Preferably, water' is the blowing agent in the formulation according to the present invention. The use of cross-linking agents in the production of polyurethane foams is well known. Polyfunctional alkanol amines are known to be useful for this purpose. Preferred amines which may be included in the polyol formulation to aid or maintain the miscibility of the first and second polyols include diethanolamine, often abbreviated as DEOA, triethanolamine, often abbreviated as TEOA, and glycerol. Most preferably, diethanolamine is used in the polyol formulation of the present invention.
Polyurethane catalysts are known in the art and include many different compounds. An extensive list of
polyurethane catalysts is, for instance, given in US-5, Oil, 908. A preferred catalyst is an amine, especially a tertiary amine, catalyst. Preferred amine catalysts include an amine group substituted by at least two optionally-substituted, preferably unsubstituted, lower alkyl groups which may be the same or different, but are preferably the same. A lower alkyl group may have up to 8, preferably up to 6, more preferably up to 4, carbon atoms, with methyl and ethyl groups being especially preferred. A tertiary amine catalyst may be selected from bis (2, 2 ' -dimethylamino) ethyl ether, trimethylamine, triethylamine, triethylenediamine, dimethylethanolamine, N,N' , N' -dimethylaminopropylhexa- hydrotriazine and N,N-dimethylcyclohexylamine. Examples of commercially available tertiary amine catalysts are those sold under the trade names NIAX, TEGOAMIN, JEFFCAT and DABCO (all trademarks) . Within the polyurethane catalysts and even within the tertiary amine catalysts a distinction can be made between gellation catalysts and blowing catalysts. Gellation catalysts are catalysts which predominantly promote the gellation of the foaming mixture, i.e. which promote the reaction between polyols and polyisocyanate. Typical gellation catalysts are stannous octoate and dibutyltindilaurate. Blowing catalysts predominantly promote the NCO/H2O reaction, whereby carbon dioxide is released which causes the blowing to occur. Typical blowing catalysts are dimethylaminoethylether and urea.
Other usual auxiliaries may include fillers, flame retardants, foam stabilisers (surfactants) and colourants. Organosilicone surfactants are most conventionally applied as foam stabilisers in polyurethane production. A large variety of such organosilicone surfactants is commercially available. A preferred compound is compound L2100 commercially
available from Osi. Usually, such foam stabiliser is used in an amount of up to 5% by weight based on the reaction mixture of polyol reactant and polyisocyanate reactant. In a further aspect the present invention relates to the preparation of a viscoelastic high resilience polyurethane foam by reacting 100 parts by weight of the polyol combination according to the present invention, 0.1 to 6 parts by weight of blowing agent, 0.1 to 5 parts by weight of crosslinking agent (s) and a polyisocyanate component at an isocyanate index in the range of from 80 to 120 in the presence of from 0.01 to 2.5 parts by weight of polyurethane catalyst (s) and optionally further usual auxiliaries.
The above process is preferably carried out by intimately mixing all components but the polyisocyanate, then adding the polyisocyanate and mixing this with the polyol formulation. The foams are subsequently allowed to form. The foam can be manufactured either batch-wise, or continuously such as with the help of a conveyor. Mixing of the various components is preferably carried out at ambient temperature, suitably in the range of from 10 to 40 °C, preferably of from 20 to 25 °C.
Polyisocyanates that may be used are those conventionally applied in the production of polyurethane foams. Useful polyisocyanates should contain at least two isocyanate groups and include both aliphatic (usually alkylene) and aromatic di-, tri-, tetra- and higher isocyanates known in the art to be suitably applied in the production of flexible polyurethane foams. Mixtures of two or more of such aliphatic and/or aromatic polyisocyanates may also be applied. Examples of suitable polyisocyanates, include 2,4-toluene diisocyanate (2,4-TDI), 2,6-TDI, mixtures of 2,4-TDI and 2,6-TDI, 1, 5-naphthene diisocyanate, 2, 4-methoxyphenyl diisocyanate, 4,4'-di- phenylmethane diisocyanate (MDI) , 4, 4 ' -biphenylene diiso-
cyanate, 3, 3 ' -dimethoxy-4, 4 ' -biphenylene diisocyanate, 3, 3 ' -dimethyl-4, ' -biphenylene diisocyanate and 3,3'-di- methyl-4, 4 ' -diphenylmethane diisocyanate, 4,4',4"-tri- phenylmethane triisocyanate, 2, 4, 6-toluene triisocyanate, 4, 4 ' -dimethyl-2, 2 ', 5,'5 ' -diphenylmethane tetraisocyanate, polymethylene-polyphenylene polyisocyanate, carbodiimide modified isocyanates, MDI prepolymers and mixtures of two or more of these. Polymeric MDI, a mixture of polyisocyanates with MDI as the main component, may also be used. For the purpose of the present invention the use of TDI is preferred. Polyisocyanates are commercially available.
An advantage of the present invention is that a wide range of polyisocyanate indices can be used. The polyisocyanate can be used in such amount that the isocyanate index is in the range of from 80 to 120. Especially good results are obtained with polyisocyanate indices in the range of from 85 to 110, most specifically in the range of from 95 to 105. The density of the foam prepared with the help of the present invention is relatively high. Generally, the foam obtained will have a density of at least 40
preferably at least 50 kg/m^. The density can be as high as 200 kg/m.3, more specifically up to 150 kg/m^. The high resilience, viscoelastic foam prepared with the help of the present invention is especially suitable for preparing mattresses, pillows and shock-absorbing parts for shoes.
The present invention makes it possible to manufacture high resilience, visco-elastic foam. The resilicience of foam is measured with the help of the standard ball rebound test (ASTM D 3574-95, Test H) . A preferred high resilience comprises that the ball bounces back at least 20%, preferably at least 25%, more
preferably at least 30%, more preferably at least 35%, most preferably at least 40%.
The visco-elasticity of foam is measured by the DIN 7003- flexible - Verecoti method. A preferred viscoelastic foam has a recovery time of from 3 to 20 seconds.
The invention is further illustrated by the following examples without limiting the scope of the invention to these particular embodiments. Examples
In the examples the following polyols were used. Polyol A
CARADOL ED56-7 polyol, monopropyleneglycol reacted with propylene oxide which is subsequently reacted with ethylene oxide (EO tipped) resulting in a polyol comprising 6 %wt monol having a number average molecular weight of 700 and 94 %wt of diol having a number average molecular weight of 2100. Polymer polyol B CARADOL MD30-02 polymer polyol containing 15 %wt of polystyrene particles in a liquid polyol having a number average functionality of 2.5 and a number average molecular weight of 5000, containing 25 pbw of monol and 75 pbw of triol. Polymer polyol C
CARADOL MD22-02 polymer polyol containing 45 %wt of polystyrene particles in a liquid polyol having a number average functionality of 2.5 and a number average molecular weight of 5000, containing 25 pbw of monol and 75 pbw of triol With the exception of the isocyanate, the compounds described in Tables 1 and 2 were blended into one stream. The isocyanate formed another stream. The amounts indicated as "php" are based on 100 pbw of polyols. Both streams were mixed and allowed to react. The amine catalyst is dimethylamino-ethylether.
The surfactant is L2100 silicone surfactant available from Osi.
CARADATE 80 is a mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate. The resilience was measured according to
ASTM D 3574-95 Test H.
The recovery time of the foam was measured according to the DIN 7003-flexible-Verecoti method. '
Wet and dry compression sets were measured according to ASTM 3574-86.
The tensile and elongation at break were measured according to ASTM 3574.
The compression load deflection, which is a measure ■for hardness, was measured according to DIN 53577. The results of the foam evaluation are indicated in
Tables 1 and 2.
The good elongation and break properties for foams according to the present invention are especially advantageous as such values can generally not be attained at low isocyanate indices.
Table 1
Table 1 (cont'd)
Table 2