MXPA99010545A - Polyurethane foams - Google Patents

Abstract

The present invention relates to a polyurethane foam composition comprising:a hydrogenated polydiene diol having a number average molecular weight from 1,000 to 20, 000;an aliphatic or cycloaliphatic polyisocyanate;a stabilizer;and a blowing agent. The present invention further relates to a process for preparing the polyurethane foam and to articles containing the polyurethane foam.

Description

OE POLYUTHANE FOAMS BACKGROUND OF THE INVENTION: This invention relates to polyurethane foams, in particular flexible polyurethane foams resistant to ambient conditions, containing a polyol and aliphatic or cycloaliphatic isocyanates. The invention also relates to a process for preparing polyurethane foams and articles containing polyurethane foams. Polyurethane foams having high resilience are typically produced from a polyether triol and an isocyanate. The polyether triols typically have an average molecular weight number of 4,500 to 6,000 and an average functionality of 2.4 to 2.7 hydroxyl groups per molecule. Toluene diisocyanate, diphenyl di-isocyanate, mixtures of toluene diisocyanate / diphenyl diisocyanate, and modified versions of toluene diisocyanate or diphenyl diisocyanate methane diisocyanate are used to produce foams with ample processing freedom. The functionality of the isocyanate is typically 2.0, and in most cases no higher than 2.3 isocyanate groups per molecule. Polyether triols form resilient foams when combined with isocyanates having from 2.0 to 2.3 isocyanate groups per molecule under REF .: 31904 conditions that promote foam formation. However, polyethers are degraded when exposed to ultraviolet light and the polyesters are degraded by hydrolysis under conditions of heat and humidity. U.S. Patent No. 4,939,184 describes the production of polyurethane foams from polyisobutylene triols and diols, which were prepared cationically. The polyisobutylenes are premixed with an isocyanate, ie an isocyanate which is a mixture of meta- and para-toluene diisocyanate isomers having a functionality of 2.0. Then water was added as a gas injection agent to form the polyurethane foam. The foams obtained were of low resilience and were useful in energy absorption applications. The international application (PCT) WO 97/00902 discloses a high resilience polyurethane foam produced from a polydiene diol. The resilience of the foam was achieved by adding an aromatic polyisocyanate having a functionality of 2.5 to 3.0 isocyanate groups per molecule to ensure adequate crosslinking. The polydiene diol foams produced showed excellent moisture aging properties in comparison to conventional polyurethane foams. U.S. Patent No. 5,710,192 discloses a high resilience, high tear resistance polyurethane foam produced from a polydiene diol. The resilience of the foam was achieved by selecting an appropriate amount of an aromatic polyisocyanate having a functionality of 1.8 to 2.5 isocyanate groups per molecule to ensure adequate crosslinking. The polydiene diol foams produced showed excellent tear resistance and were almost white in color. In some applications of the foams described above, they will be exposed to environmental conditions and the foams will degrade under prolonged exposure to heat, moisture and sunlight. It is desirable to have a resilient, flexible, light-stable foam that can withstand degradation under prolonged exposure to ambient conditions. Surprisingly, it has been found that a foam made of a hydrogenated polydiene diol and an aliphatic or cycloaliphatic isocyanate is resistant to degradation by ultraviolet light. Therefore, the present invention relates to a polyurethane foam composition comprising: a hydrogenated polydiene diol having an average molecular weight number from 1,000 to 20,000; an aliphatic or cycloaliphatic polyisocyanate; a stabilizer; and a gas injection agent. The foams present excellent stability to light and resistance to ultraviolet light. The present invention is preferably a durable resilient polyurethane foam containing 100 parts by weight (pep) of a hydrogenated polydiene diol having an average molecular weight number of 1., 000 to 20,000, more preferably from 1,000 to 10,000, more preferably from 3,000 to 6,000. To this is added from 20 to 60 pbw of an aliphatic or cycloaliphatic polyisocyanate, a stabilizer, and a gas injection agent. In a more preferred embodiment, the hydrogenated diol polydiene has a functionality of 1.6 to 2, more preferably 1.8 to 2, hydroxyl groups per molecule. Preferably the polyisocyanate used has a functionality of 2.0 to 3.0 isocyanate groups per molecule. The isocyanate is preferably added in a concentration giving almost an equal number of isocyanate groups and hydroxyl groups. Preferably, the molar ratio of NCO: OH is in the range of "0.9 to 1.2." The foam exhibits excellent resistance to ultraviolet light.

The polydiene diols used in this invention are typically prepared anionically. Anionic polymerization is well known to those skilled in the art and has been described e.g. in U.S. Patents Nos. 5,376,745, 5,391,663, 5,393,843, 5,405,911 and 5,416,168. The polymerization of the polydiene diols begins with a monolithium initiator containing a protected hydroxyl group or initiator. of dilithium that polymerizes a conjugated diene monomer at each lithium site. Due to cost advantages, the conjugated diene is typically 1, 3-butadiene or isoprene, although other conjugated dienes will also work well in the invention. When the conjugated diene is 1,3-butadiene and when the resulting polymer will be hydrogenated, the anionic polymerization could be controlled with structure modifiers such as diethyl ether or 1,2-diethoxyethane to obtain the desired amount of 1.4 addition. The anionic polymerization is terminated by the addition of a functionalization agent before termination. The functionalization agents used are known to those skilled in the art and are described in U.S. Patents 5,391,637, 5,393,843 and 5,418,296. The preferred functionalizing agent is ethylene oxide. The polydiene diols are preferably hydrogenated to improve the stability, so that at least 90%, preferably at least 95%, of the carbon-carbon double bonds in the diols are saturated. The hydrogenation of these polymers and copolymers could be carried out by means of a variety of well-established processes including hydrogenation in the presence of such catalysts as RANEY® Nickel, noble metals such as platinum, soluble transition metal catalysts and titanium catalysts. , as described in the US Patent 5,039,755., The hydrogenated polydiene diols provide stable, resilient foams. The polydiene diols have from 1.6 to 2, more preferably from 1.8 to 2 terminal hydroxyl groups per molecule. An average functionality of, for example, 1.8 means that approximately 80% of the molecules are diols and about 20% of the molecules are mono-ols. Since most of the product molecules have two hydroxyl groups, the product is considered a diol. The polydiene diols of the invention have an average molecular weight number between 1,000 and 20,000, more preferably from 1,000 to 10,000, more preferably from 3,000 to 6,000. Hydrogenated polybutadiene diols are preferred, in particular those having a 1, 2 addition between 40% and 60%. Diene microstructures are typically determined by nuclear magnetic resonance (NMR) of 13 C in chloroform. It is desirable for polybutadiene diols to have at least about 40% addition of 1,2-butadiene because, after hydrogenation, the polymer will be a waxy solid at room temperature if it contains less than about 40% addition of 1. , 2-butadiene. Preferably, the 1,2-butadiene content is between 40 and 60%. The isoprene polymers typically have at least 80% addition of 1,4-isoprene to reduce the glass transition temperature (Tg) and the viscosity. The polydiene diols used in the invention typically have hydroxyl equivalent weights between about 500 • and about 10,000, more preferably between 500 and 5,000, more preferably between 1,500. and 3,000. Thus, for the polydiene diols, the appropriate average molecular weight number will be between 1,000 and 20,000, more preferably between 1,000 and 10,000, more preferably between 3,000 and 6,000. The numbers of average molecular weights referred to herein are weight numbers Molecular molecules measured by gel permeation chromatography (CPG) calibrated with polybutadiene standards having known average molecular weight numbers. The solvent for the CPG analysis is tetrahydrofuran. The isocyanates used in this invention are aliphatic or cycloaliphatic polyisocyanates. Since the saturated polydiene diol has a functionality of approximately 2 hydroxyl groups per molecule, a polyisocyanate having a functionality of 1.8 to 3, preferably 2.5 to 3.0, is used to achieve a crosslink density resulting in a stable foam, high load resistance and high resilience. Using isocyanates of lower functionality results in less stable foams having lower load bearing capacity and having reduced resilience. The higher isocyanate functionality will result in foam having a very high closed cell content, which will negatively influence the physical properties. Examples of suitable aliphatic or cycloaliphatic polyisocyanates include the DESMODUR® series of isocyanates (Bayer). These include DESMODUR® Z-4370, a triisocyanate based on isophorone diisocyanate (70% p in xylene) having a functionality of 3.0-, DESMODUR® N-3400, a di / triisocyanate based on hexane diisocyanate which has 2.5 functionality. , and DESMODUR® W, a cycloaliphatic dicyclohexylmethane diisocyanate having a functionality of 2.0. One or more stabilizers, such as antioxidants and ultraviolet stabilizers, are also added to further increase the heat and light stability of the foam. • As used herein, the antioxidant / stabilizer combination will be referred to as a stabilizer package. The main component of the antioxidant portion of a stabilizer package is typically an antioxidant-type blocking phenol. Examples of commercially available antioxidants of this type are ETHANOX® 330 (from Albemerle Corporation), CYANOX® 2246 (from American Cyanamid), and IRGANOX® 1010 and IRGANOX® 1076 (from Ciba Geigy). A wide variety of secondary antioxidants and synergists can also be included in the formulation. Examples include dialkyl zinc dithiocarbamates such as ZIMATE® butyl (from RT Vanderbilt), phosphite esters such as WESTIN ™ 618 (from General Electric), and sulfur-containing compounds such as dilaurylthio-dipropionate, CYANOX® LTDP (from American Cyanamid) ). Antioxidants are typically used in the formulation at concentrations of 0.1 to 2 percent by weight (% p), the basis of the total formulation. The UV inhibitor portion of a stabilizer package will typically be composed of a combination of a UV light absorber-type compound and an obstruction amine light stabilizer. The combinations of stabilizers are often more effective, due to the different degradation mechanisms to which several polymers are subjected. A combination of an ultraviolet light absorber and an obstruction amine light stabilizer has been found to provide good resistance to sunlight degradation in the foams of the invention. Typical absorbents of the UV inhibitor type include the benzophenone type such as CYASORB® UV 531 (from American Cyanamid) and the benzotriazole type such TINUVIN® P and TINUVIN® 328 (Ciba Geigy). Typical obstruction amine light stabilizers include TINUVIN® 770 and TINUVIN® 123 (Ciba Geigy) and SANDUVOR® 3056 (American Cyanamid). UV inhibitors containing a metal can also be used, such as the nickel-containing UV inhibitor, CYASORB® UV 1084 (American Cyanamid). These UV inhibitors will generally be included in the formulation at concentrations of 0.5 to 6% p, the basis of the total formulation. The essential components of the polyurethane foams of this invention are the polydiene diol, the aliphatic or cycloaliphatic polyisocyanate, a stabilizer, and a gas injection agent such as water. The concentration of the gas injection agent could be varied to alter the density of the foam.

A variety of gas injection agents could be used. Suitable gas injection agents include halogenated hydrocarbons, aliphatic alkanes and alicyclic alkanes, as well as water which is often referred to as a chemical gas injection agent. Due to the ozone depletion effect of chlorinated or fully fluorinated alkanes (CFC), the use of this type of gas injection agent is not preferred, although it is possible to use them within the scope of the present invention. Halogenated alkanes in which at least one hydrogen atom has not been replaced by a halogen atom (so-called HCFC) have a lower ozone depletion potential, and are therefore preferred halogenated hydrocarbons for use in inflated foams physically. A very suitable HCFC type gas injection agent is 1-chloro-1,1-difluoroethane. Even more preferred as gas injection agents are the hydrofluorohydrocarbons which are indicated to have a ozone depletion potential of zero. The use of water as a gas (chemical) injection agent is also well known. The water reacts with the isocyanate groups according to the well-known reaction NCO / H20, thus releasing carbon dioxide which causes the injection of gas to occur. Aliphatic and alicyclic alkanes, finally, were developed as alternative gas injection agents to CFCs. Examples of such alkanes are n-pentane, isopentane and n-hexane (aliphatic), and cyclopentane and cyclohexane (alicyclic). It will be understood that the above gas injection agents could be used alone or in mixtures of two or more. Of the aforementioned air injection agents, water and cyclopentane have been found to be particularly suitable as a gas injection agent for the purpose of the present invention. The quantities in which the gas injection agents are to be used are those conventionally applied, i.e. in the range of 0.1 to 5 pep per 100 parts of polydiene diol in the case of water and in the range of about 0.1 to 20 pep per 100 parts of polydiene diol in the case of halogenated hydrocarbons, aliphatic alkanes and alicyclic alkanes. Preferably, the gas injection agent is water. The water is preferably added in an amount of 0.5 to 3.5 parts by weight (pep) per 100 parts of polydiene diol. Preferably, distilled or demineralized water is used, since the impurities could affect the reaction of the foam. Typically, a catalyst and a surfactant are needed in the preparation of the foams. Surfactants are often added to improve the miscibility of the components, which in turn promote the hydroxyl / isocyanate reaction. In addition, the surface tension of the mixture is reduced, which influences the nucleation of the cell and stabilizes the expansion of the foam, leading to a fine cell structure. Preferably, the surfactant is a silicone oil. An example of a commercially available suitable silicone oil is TEGOS -B8404 (TEGOSTAB is a registered trademark). As the preferred silicone surfactant is DABCO® DC-5160. The surfactant, if present, is usually added in an amount of 0.05 to 5 parts by weight per 100 pb of the polydiene diol (0.05-5 phr). In principle, any known catalyst could be used to catalyze one or more foaming reactions in the system. Examples of suitable catalysts are described in European Patent Specification No. 0 358 282 and include amines such as tertiary amines, salts of carboxylic acids and organometallic catalysts. The amine catalysts found useful in the manufacture of polyurethane foams of polydiene diols are the DABCO® 33-LV amine catalyst and the DABCO® DC-1 delayed-action amine catalyst, both from Air Products and Chemicals. Examples of suitable tertiary amines are triethylene diamine, N-methylmorpholine, N-ethylmorpholine, diethyl ethanolamine, N-co-morpholine, l-methyl-4-di-methyl-amino-ethylpiperazine, 3-methoxypropyl-dimethylamine, N, N, N'-tri-methyl-isopropyl-propylenediamine, 3-diethylamino-propyl-diethylamine , dimethyl ilbenzylamine and dimethylcyclohexylamine. An example of a useful carboxylic acid salt or a catalyst is sodium acetate. Suitable organometallic catalysts include stannous octoate, stannous oleate, stannous acetate, stannous laureate, lead octoate, lead naphthenate, nickel naphthenate, cobalt naphthenate and dibutyl tin dichloride. Further examples of organometallic compounds useful as a catalyst in the production of polyurethanes are described in U.S. Patent Specification. No. 2,846,408. Of course, mixtures of two or more of the above catalysts could also be applied. The amount in which the catalyst, or mixture of catalysts, is used normally falls in the range of 0.01 to 5.0 pbw, preferably in the range of 0.2 to 2.0 pbp per 100 parts of polydiene diol. If desired, flame retardants (fire), fillers and other additives could be added. It belongs to the practice of the average expert in this field to select the appropriate additional compounds that are to be added to the composition to be foamed. Resins and sticky oils can also be added to modify the adhesion and hardness of the foams. However, to maintain the good durability of the foams, only sticky hydrogenated resins and highly saturated oils should be used. Polyurethane foams are preferably prepared by mixing all the components except the polyisocyanate. The polyol mixture is preferably preheated to reduce the viscosity before mixing. After mixing, the polyisocyanate is added quickly and stirred briefly before pouring the mixture into a mold to keep the foam expanding. The polyurethane foam could be subjected to a curing treatment by heating the foam to an elevated temperature, usually between 100 and 160 ° C for a certain period of time, typically in the range of 10 minutes to 96 hours, preferably 30 minutes to 48 hours. hours. Usually, however, the heat generated by the exothermic reaction of polyurethane formation is sufficient to ensure complete curing, and the process is carried out adiabatically.

Thus, according to a further aspect, the present invention relates to a process for preparing a polyurethane foam composition comprising (i) mixing a hydrogenated polydiene diol, having an average molecular weight number of 10,000 to ,000, with a stabilizer and gas injection agent to obtain a mixture, and (ii) mixing an aliphatic or cycloaliphatic polyisocyanate with the mixture to obtain a mixture, and (iii) leaving the mixture to foam to obtain the mixture. Polyurethane foam composition.

According to a more preferred embodiment, the present invention relates to a resilient polyurethane foam comprising 100 parts by weight of a hydrogenated polydiene diol having an average molecular weight number of 3,000 to 6,000 and a functionality of 1.8 to 2.0 groups hydroxyl per molecule, from 0.5 to 3.5 parts by weight of water, 0.1-6% by weight of a stabilizer, an aliphatic or cycloaliphatic polyisocyanate having a functionality of 2.0 to 3.0 isocyanate groups per molecule at a concentration that will give an almost equal number of isocyanate and hydroxyl groups (NCO: OH = 0.9-1.2), from 0.4 to 0.8 parts by weight of an amine catalyst, from 0.3 to 0.6 parts by weight of a delayed action amine or a tin catalyst, and from 0 to 0.06 parts by weight of a silicone surfactant. The foam shows superior strength for degradation compared to conventional foams made with polyether or polyester polyols and aromatic isocyanates. According to a further preferred embodiment, the present invention relates to a polyurethane foam produced by a process comprising the steps of: combining a hydrogenated polydiene diol having an average molecular weight number from 1,000 to 20,000 and a functionality of 1.6 2 hydroxyl groups per molecule with an aliphatic or cycloaliphatic polyisocyanate having a functionality of 2.0 to 3.0 isocyanate groups per molecule; and foaming "the polydiene diol and aliphatic or cycloaliphatic polyisocyanate combined to form a polyurethane foam having stability upon exposure to sunlight." According to a more preferred embodiment, the present invention relates to a polyurethane foam produced by a process comprising the steps of: mixing 100 parts by weight of a hydrogenated polydiene diol having a number average molecular weight of from l000 to 10,000 and a functionality of 1.8 to 2.0 hydroxyl groups per molecule with from 1 to 2 parts by weight of water, from 0.4 to 0.8 parts by weight of an amine catalyst, from 0.3 to 0.5 parts by weight of a delayed-action amine or a tin catalyst, from 0.02 to 0.04 parts by weight of a silicone surfactant, of 0.1 to 6% by weight of a stabilizer, and add an aliphatic or cycloaliphatic polymeric isocyanate, wherein the isocyanate has a functionality of 2.5 to 3.0 isocyanate groups per molecule and is added in a Concentration giving an almost equal humerus of isocyanate groups and hydroxyl groups (NCO: OH = 0.9-1.2). The polyurethane foams of the present invention are useful for the manufacture of articles such as seat cushions and gaskets and long lasting seals for use in exposure to harsh environments. According to a further aspect, the present invention relates to articles containing the polyurethane foam according to the present invention. The following examples are not intended to limit the present invention to specific embodiments, although each example could support a separate claim "which ensures that it is a patentable invention.

Examples' • Seven foams were prepared using polydiene hydrogenated diol, isocyanate, catalyst and surfactant. Six of the foams were made with an aliphatic or cycloaliphatic isocyanate, producing white foams. One of the seven polydiene foams was made with an aromatic isocyanate, producing a cinnamon brown foam, and is presented as a comparative example. Three foams also contained a stabilizer package. An eighth foam, also used as a comparative example, was prepared using a polyether triol and an aromatic isocyanate. The formulations of the foams are shown in Table 1.

The hydrogenated polydiene diol of the Examples has an average molecular weight number of 3300, a functionality of 1.92 and a 1,2-butadiene content of 54%. The polymer was hydrogenated to remove more than 99% of the carbon-carbon double bonds. The triol used was CARADOL ™ 36-03, a polypropylene oxide polyether triol with a hydroxyl number of 36 and a functionality of 2.7 (from Shell Chemicals International). In the typical preparation, the polymer was preheated to 80 ° C. All components in the formulation except the isocyanate were weighed into a dry container and mixed using a CAFRAMO® stirrer equipped with a regular 5.1 cm (2 in) spacer impeller. The isocyanate was then added and mixing was continued for about 45 seconds. During this time the dough would begin to foam and was poured into a paper cube. After the foam stabilized and a film formed, the foam was post-hardened in an oven for ten (10) minutes at 110 ° C. The cube-shaped specimens, 50 mm on each side, were cut from the block for the measurement of foam density and compression hardness. After testing the initial property, the foams were placed in wire cages and exposed to outdoor environmental conditions in Houston, Texas, USA, for approximately 7-1 / 2 months, beginning in August. After the exposure, the foam specimens were recovered and the compression hardness tests were repeated.

Density The density was determined by the weight of a block and its dimensions. The results are given in Table 2.

Compression Hardness Compression hardness (ASTM D3574) was measured in the cube specimens both before and after exposure to environmental conditions. The cubes were compressed twice up to 25% of their initial dimensions and then compressed up to 50% of their initial dimensions. An INSTRON® test machine was used. After 1 minute at 50% compression, the load was • measured and the compression hardness was calculated. The results are given in Table 2.

Table 1. Foam formulations 1 a polyisocyanate based on diphenyl methane diisocyanate (MDI), with a functionality of 2.6 (from Shell International Chemicals) Table 2. Foam Properties a) Obvious surface degradation. The surface, especially the surface facing the sun, was brittle and brittle when scratched. b) An indication of some degradation was not evident. c) Very slightly sticky on the surface facing the sun. d) Completely sticky on all surfaces, especially the surface facing the sun.

The eight foams presented good elasticity and resilience. However, after aging, conventional Foam 1 showed obvious signs of degradation. The surface was fragile and when it was scraped with a finger it left a residue of dust on the finger. The surfaces facing the sun suffered the greatest fragility. The degradation seems to be limited to the surface, since the compression hardness increased only slightly. The replacement of the polyether triol with a polydiene diol (Foam 2) substantially improved the durability on the outside of the polyurethane foams based on the aromatic isocyanate. Foams 3, 5 and 6, which were made with aliphatic or cycloaliphatic isocyanates and without stabilizer, became sticky. These three foams also suffered approximately a 40% drop in compression hardness. Foams 4, 7 and 8, based on aliphatic or cycloaliphatic isocyanates and containing the stabilizer package, showed excellent stability, showing almost no change in properties. Qualitatively, there was no change in the surfaces and the compression hardness values changed very little with aging. While this invention has been described in detail for purposes of illustration, this was not constructed as a limit but as an attempt to cover all changes and modifications within the spirit and scope thereof.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (8)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A process for preparing a polyurethane foam composition, characterized in that it comprises (i) mixing a hydrogenated polydiene diol, having an average molecular weight number of 1, 000 to 20,000, with a stabilizer and gas injection agent to obtain a mixing, and (ii) mixing an aliphatic or cycloaliphatic polyisocyanate with the mixture to obtain a mixture, and (iii) leaving the mixture to foam to obtain the polyurethane foam composition.

2. A process as claimed in claim 1, characterized in that in step (ii) an aliphatic polyisocyanate is mixed with the mixture to obtain a mixture.

3. A process as claimed in claim 1 or 2, characterized in that the gas injection agent is water.

4. A process as claimed in any of claims 1 to 3, characterized in that the polydiene diol has a functionality of 1.6 to 2 hydroxyl groups per molecule, and wherein the polyisocyanate has a functionality of 1.8 to 3.0 isocyanate groups per molecule.

5. A process as claimed in any of the preceding claims, characterized in that the polydiene diol is a polybutadiene diol.

6. A process as claimed in claim 5, characterized in that the polybutadiene diol has from 40% to 60% 1,2-butadiene addition.

7. A process as claimed in any of the preceding claims, characterized in that the molar ratio NCO: OH is in the range of 0.9 to 1.2.

8. A polyurethane foam composition, characterized in that it comprises: a hydrogenated diol polydiene having an average molecular weight number from 1,000 to 20,000; an aliphatic polyisocyanate; a stabilizer; and a gas injection agent.