DE19947563A1 - Transesterification polyols for polyurethane prepolymers with specifically adjustable viscosity - Google Patents

Abstract

The invention relates to transesterification polyols which are produced from ricinus oil and native trigycerides that are free of OH-groups and which are suitable for use as polyols for producing polyurethane prepolymers. Conversion products of transesterification polyols of this type with polyisocyanates also have a low, constant viscosity in the form of solvent-free or water-free compositions. They are suitable for producing single or multiple component adhesives, sealants, casting compounds or coating agents.

Description

The invention relates to the production and use of low-viscosity, in essential solvent-free polyurethane prepolymers based on Transesterification products of castor oil.

Polyurethanes are due to their high specific adhesion to numerous Materials as well as flexibility and cold resistance for years as adhesives, Sealants, potting compounds or coating agents in one or multi-component form applied. Castor oil as a polyol from renewable Raw materials is an ecologically advantageous polyurethane raw material, under also for the aforementioned areas of application.

Already very early was for the production of polyurethane coatings Castor oil with hydroxyl numbers of about 160 mg KOH / g used as polyol, see "Polyurethanes: Chemistry and Technology" Part I (1962), Pages 6, 9, 48 to 54 from the series "High Polymers", Vol 16.

Because of its relatively high hydroxyl number and low molecular weight however, castor oil is not the sole polyol for many applications suitable because the cured polyurethane binders prepared in this way have mechanically unsatisfactory properties. From GB 671368 are dehydrated oils of castor oil having hydroxyl numbers between about 17 and 40 which is already known several times for use as a polyol in the Polyurethane chemistry have been proposed.  

Thus, DE-A-41 14 022 describes the use of partially dehydrated Ricinusölen with hydroxyl numbers between 80 and 135 mg KOH / g as Reactive constituent of a polyol mixture with the concomitant use of further 2-, 3- and / or polyhydric alcohols. It is proposed to use this polyurethane Compositions as two-component solvent-free adhesives or Use casting compounds. About the amount of dehydrated castor oil can the open time and the pot life of the adhesives are extended. A lesson to Production of low-viscosity, solvent-free, storage-stable, one-component Polyurethane compositions with free isocyanate groups may be the font not be removed.

WO 95/23172 proposes to produce low viscosity, at least predominantly solvent-free polyurethane adhesives with good storage stability the use of polyol mixtures of dehydrated castor oil, polypropylene glycols (Diols) and at room temperature liquid monoalcohols having a hydroxyl value under 250 before.

EP-A-709414 describes the use of partially dehydrated Ricinusölen as a polyol component for the production of aqueous Polyurethane dispersions and their use as coatings. It will it said that the partially dehydrated castor oil as the sole Polyol component or used to a considerable percentage can. It is further disclosed that the use of partially dehydrated castor oil in the production of aqueous Polyurethane dispersions causes a lowering of the prepolymer viscosity. Low viscosity one-component, essentially solvent-free and Non-aqueous polyurethane prepolymers are not disclosed in this document.

The main object of the present invention is to be on or multicomponent reactive polyurethane compositions based on  To provide castor oil derivatives which reproducibly low Have viscosity, so that they are particularly good for use as Adhesives, sealants, potting compounds or coating materials are suitable. there are said to be based on the well-known good properties of polyurethane systems of castor oil like good adhesion to numerous materials, adequate Tensile, tensile shear and peel strength, good setting behavior and good Storage stability.

The achievement of the object of the invention can be taken from the claims, It consists essentially in the polyol as a transesterification of the Ricinusöls with OH-free triglycerides to use.

A particularly preferred use of the invention produced Polyurethane prepolymers are moisture-curing adhesives for use in Holzverklebungen and in the panel production. The panels will become one Schaumschoff- or Rockwoolkern preferred with plywood, chip and Glued fiberboard, plastic or primed metal topcoats.

For these applications are dependent on production methods Solvent and anhydrous adhesives with viscosities between 1,000 and 15,000 mPa.s used, these adhesives are preferably between viscosities Have 3,000 and 12,000 mPa.s. With dehydration polyols of castor oil in GB 671368, which have hydroxyl numbers, as described in DE-A-44 06 211 are disclosed, can not be prepolymers with constant viscosity produce. Occasionally arise when using the polyols according to DE-A-44 06 211 even cloudy products, which then phase separation during prolonged storage or have other inhomogeneities. The dehydration of the castor oils according to The state of the art takes place at temperatures of over 230 ° C in the presence of acid catalysts. This method has the disadvantage that by Side reactions, for example by transesterification, polymerization and Hydrolysis easily products with comparatively high or very low  Molar masses can arise. Also, it is rather difficult to increase the hydroxyl number to reproducibly limit a very small specification area. Molar mass fluctuations, however, lead in particular Polyurethane prepolymers for one-component systems too strong Viscosity changes. These viscosity fluctuations cause problems the processing of such products. Lead OH number fluctuations, especially in the case of two-component polyurethane systems, to reactivity and Strength changes.

Another object of the present invention is the preparation of such transesterified castor oils using castor oil and substantially OH-free native triglycerides. Although for the OH-group-free oils A variety of native oils can be used, which are rapeseed oil Sunflower oil or soybean oil particularly preferably usable oils. By the Specification of the mixing ratio of castor oil to the or the OH group-free oils, the OH number can be exactly predetermined. Especially It is surprising that in the inventive Transesterification reaction does not work as well as dehydrating molecules with strong form deviating higher or lower molecular weights. This is special advantageous, because thereby according to the predetermined destination a very high Viscosity constant paired with an OH number in a narrow Specification window is achievable.

Castor oil products produced according to the invention have hydroxyl numbers of less than 160 mg KOH / g in accordance with DIN 53240. A particularly preferred range is between 20 and 130, most preferably values between 30 and 100 mg KOH / g. These polyols have an average functionality between about 0.3 and 3.

Another advantage is that according to the inventive method reproducibly produce clear prepolymers with defined viscosity range  to let. In this case, the range of viscosity of the polyurethane prepolymer by the functionality or OH number of the transesterification polyol, the functionality of the used polyisocyanate and the ratio of polyisocyanate to Transesterification polyol are set.

Suitable transesterification catalysts are in principle all of the organic Chemistry known esterification or transesterification catalysts such. B. acid Catalysts, organotin compounds, organotitanates and especially alkali metal or alkaline earth metal hydroxides. Lithium hydroxide, since it has surprisingly been found that this transesterification catalyst in the polyol can remain in the preparation of the polyurethane prepolymer without to negatively influence the storage stability of the polyurethane prepolymer.

Although the polyurethane prepolymers of the invention are preferably based on the dehydration polyol are constructed as the sole polyol, more can used in polyurethane chemistry di- or trifunctional polyols be z. B. polyethylene glycols, polypropylene glycols, polytetraethylene glycols, Polybutylene glycols and / or their copolymers and polyester polyols on the Based on aliphatic or aromatic dicarboxylic acids and low molecular weight di- or triols, furthermore, hydroxy-functional polycaprolactones with be used.

Examples of such polyols to be used are di- and / or trifunctional Polypropylene glycols in the molecular weight range from 200 to 6000, preferably in the range of 400 to 3000. Statistical and / or Block copolymers of ethylene oxide and propylene oxide are used. A Another group of preferably used polyethers are the Polytetramethylene glycols, the z. B. by the acidic polymerization of Are made of tetrahydrofuran, while the molecular weight range of Polytetramethylene glycols between 200 and 6000, preferably in the range of 400 to 4000.  

Furthermore, as polyols, the liquid polyesters are suitable by Condensation of di- or tricarboxylic acids, such as. B. adipic acid, sebacic acid, Glutaric acid, azelaic acid, suberic acid, 3,3-dimethylglutaric acid, terephthalic acid, Isophthalic acid, hexahydrophthalic acid or dimer fatty acid with low molecular weight Diols or triplets such. As ethylene glycol, propylene glycol, diethylene glycol, Triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, Dimer fatty alcohol, glycerol or trimethylolpropane can be prepared. Another group of polyols to be used according to the invention are the Polyester based on ε-caprotactone, also called "polycaprolactone". However, it is also possible to use polyester polyols of oleochemical origin become. Such polyester polyols, for example, by complete Ring opening of epoxidized triglycerides of one at least partially olefinic unsaturated fatty acid-containing fat blends with one or more Alcohols with 1 to 12 carbon atoms and subsequent partial transesterification of Triglyceride derivatives to alkyl ester polyols having 1 to 12 carbon atoms in the alkyl radical getting produced. Other suitable polyols are polycarbonate polyols and Dimer diols (Henkel). Also, the hydroxy-functional polybutadienes, like them z. B. under the trade name "poly-bd" are available for the Compositions of the invention are used as polyols.

In principle, all polyisocyanates known in polyurethane chemistry and can be used industrially produced polyisocyanates, but particularly preferred liquid products of 4,4'-diphenylmethane diisocyanate (MDI). In principle, can Even the solid pure MDI can be used, even with this obtained low-viscosity prepolymers. But its use includes additional Reaction steps before prepolymer formation, in particular the melting the fixed MDI, this also has a significantly higher price than that so-called "raw MDI" on. It also makes little sense to use liquid MDI Qualities with a high proportion of 2,4'-isomers, as described in the DE-A- 42 36 562 are proposed. The use of the 2,4'-isomer of MDI  Although also causes low viscosities of the thus prepared Prepolymers. However, low adhesives also result in such adhesives Strengths of bonding. According to the invention can therefore be particularly with great advantage to use the so-called raw MDI. This technical MDI Composed primarily of a mixture of homologues and isomers of 4,4'-diphenylmethane diisocyanate and usually has a Isocyanate functionality above 2, namely about 2.2 to 2.7.

For the preparation of the polyurethane prepolymer with free isocyanate groups is while the transesterification polyol or its mixture with other polyols with the polyisocyanate reacted so that a stoichiometric excess of Isocyanate groups to hydroxyl groups. This stoichiometric Excess of the isocyanate groups is in the range between 1.3 and 7, preferably between 2 and 5. For prepolymer formation can be in in itself known manner, a conventional polyurethane catalyst can be added.

Examples of such catalysts are those which in particular the Can catalyze isocyanate / polyol and the isocyanate / water reaction: organometallic compounds such as tin (II) salts of carboxylic acids, eg. Tin (II) acetate, ethylhexoate and diethylhexoate or strong bases such as alkali metal Hydroxides, -alcoholates and phenolates can be used. A preferred Class of compounds represent the dialkyl-tin (IV) carboxylates. The carboxylic acids have 2, preferably at least 10, in particular 14 to 32 C-atoms. It Dicarboxylic acids can also be used. As acids are express called: adipic acid, maleic acid, fumaric acid, malonic acid, succinic acid, Pimelic acid, terephthalic acid, phenylacetic acid, benzoic acid, acetic acid, Propionic acid and 2-ethylhexane, caprylic, capric, lauric, myristic, palmitic and stearic acid. Concrete compounds are dibutyl and dioctyltin diacetate, maleate, bis (2-ethylhexoate), dilaurate, tributyltin acetate, bis (β-methoxycarbonyl ethyl) tin dilaurate and bis (β-acetyl-ethyl) tin dilaurate.  

Tin oxides and sulfides and thiolates are also useful. Concrete compounds are: bis (tributyltin) oxide, bis (trioctyltin) oxide, dibutyl and dioctyltin bis (2-ethylhexylthiolate) dibutyl and dioctyltin dodecylthiolate, bis (β-methoxycarbonyl-ethyl) tin dodecylthiolate, bis (β-acetyl-ethyl ) tin bis (2-ethylhexylthiolate), dibutyl- and dioctyltin dodecylthiolate, butyl- and octyltin tris (thioglycolic acid 2-ethylhexoate), dibutyl- and dioctyltin-bis (thioglycolic acid 2-ethylhexoate), tributyl- and trioctyltin (thioglycolic acid). 2-ethylhexoate) and butyl- and octyltin tris (thioethylene glycol-2-ethylhexoate), dibutyl- and dioctyltin bis (thioethylene glycol-2-ethylhexoate), tributyl- and trioctyltin (thioethylene glycol-2-ethylhexoate) having the general formula R _{n + 1} Sn (SCH ₂ CH ₂ OCOC ₈ H ₁₇ ) _3-n , wherein R is an alkyl group having 4 to 8 C atoms, bis (β-methoxycarbonylethyl) tin bis (thioethylene glycol 2-ethylhexoate), bis (β-methoxycarbonyl ethyl) tin bis (thioglycolic acid 2-ethylhexoate), and bis (β-acetyl-ethyl) tin bis (thioethylene glycol-2-e ethylhexanoate) and bis (β-acetyl-ethyl) tin bis (thioglycolic acid 2-ethylhexoate.

Also suitable are aliphatic tertiary amines, in particular with cyclic structure. Among the tertiary amines, those are also suitable which, in addition to the isocyanates, still carry reactive groups, in particular hydroxyl and / or amino groups. Specifically named are:
Dimethylmonoethanolamine, diethylmonoethanolamine, methylethylmonoethanola min. Triethanolamine, trimethanolamine, tripropanolamine, tributanolamine, trihexanolamine, tripentanolamine, tricyclohexanolamine, diethanolmethylamine, diethanolethylamine, diethanolpropylamine, diethanolbutylamine, diethanolpentylamine, diethanolhexylamine, diethanolcyclohexylamine, diethanolphenylamine and their ethoxylation and propoxylation products, diaza-bicyclo-octane (Dabco), Triethylamine, dimethylbenzylamine (Desmorapid DB, BAYER), bis-dimethylaminoethyl ether (Calalyst AI, UCC), tetramethylguanidine, bis-dimethylaminomethylphenol, 2,2'-dimorpholinodiethylether, 2- (2-dimethylaminoethoxy) ethanol, 2-dimethylaminoethyl 3-dimethylaminopropyl ether, bis (2-dimethylaminoethyl) ether, N, N-dimethylpiperazine, N- (2-hydroxyethoxyethyl) -2-azanorborane, Texacat DP-914 (Texaco Chemical), N, N, N, N-tetramethylbutane 1,3-diamine, N, N, N, N-tetramethylpropane-1,3-diamine and N, N, N, N-tetramethylhexane-1,6-diamine.

The catalysts may also be in oligomerized or polymerized form lie, z. B. as N-methylated polyethyleneimine.

For the cross-linking of the polyurethane framework two-component systems can also the trimerization reaction of the isocyanate groups with itself or with Urethane and urea groups used to allophanate or biuret groups become. For this purpose, trimerization catalysts can be used. When Trimerization catalyst is DABCO TMR-2, etc. from Air Products mentioned, which are dissolved in ethylene glycol quaternary ammonium salts is.

The advantages of the inventively particularly preferred prepolymers based on crude products of MDI and transesterification polyols of castor oil are:

• - The preparation of the prepolymer is possible without additional heating.
• The prepolymer has a very good storage stability in the absence of Moisture on.
• It is a high adhesive strength with very good resistance to hydrolysis of Bonding achieved.
• - The products have a weaker odor than products that high temperatures of 100 ° C and higher were made.
• Due to the absence of solvents, the prepolymers have one lower odor than solvent-based products.
• - They have a lower toxic potential than pure MDI products, As the crude MDI has a significant fraction of higher functional tri and polynuclear homologues of MDI, thus, these prepolymers a lower proportion of monomeric (2-nuclear) MDI.

The adhesives, sealants, potting compounds and coating compositions according to the invention generally contain a significant proportion of fillers in addition to the abovementioned binder constituents. In addition to the usual in polyurethane chemistry fillers such as calcium carbonate in the form of precipitated or ground chalk or as limestone flour and dolomite (CaMg (CO ₃ ) ₂ ), barium sulfate (baryte), alumina, alumina hydrate and quartz sand, dried stone abrasive, wood chips, cellulose Fibers, foam wastes, rubber powder, rubber chips, foam glass granules or ground glass. The proportion of filler depends on the purpose of use, it can make up to 85 wt .-% of the polyurethane binder. At high water contents of the fillers, it may be necessary to dry them in a known manner prior to mixing with the prepolymers.

The invention will now be described with reference to the following embodiments The selection of examples is not limited to the Scope of the subject invention represents. Unless otherwise stated, are all quantities in the following examples weight% or Parts by weight based on the total composition.

Example 1 (comparative example) Dehydrated castor oil with OH number 60

1000 kg of castor oil were placed in a stirred tank, mixed with 5 kg of phosphorous acid and heated under vacuum (15-20 Torr) for 6-8 hours at 240 ° C. The reaction was controlled by comparison with the refractive index of the specification-compliant product and OH-number determination. When the required OH number was reached, it was cooled rapidly and the product was bottled as a pale yellow liquid.

product parameters OH number ~ 65 mg KOH / g acid number <2.0 mg KOH / g saponification ~ 190 mg KOH / g iodine ~ 120 g J / 100 g

Example 2 (according to the invention) Transesterified castor oil with OH number 60

In a dry stirred tank 647 kg rapeseed oil raffinate (rapeseed oil raffinate erucaarm) and 380 kg castor oil were filtered as preheated products (75 ° C) mixed and then mixed with 185 g of LiOH.H ₂ O. The reaction was purged with nitrogen three times and finally heated to 240 ° C with stirring. The reaction control was carried out by comparison with the refractive index of the specification-compliant product. When the desired index of calculation was reached, the mixture was cooled rapidly and the product was bottled as a light yellow liquid.

product parameters OH number ~ 65 mg KOH / g acid number <2.0 mg KOH / g saponification ~ 190 mg KOH / g iodine ~ 100 g J / 100 g

The 3 figures according to FIG. 1 show a comparison of the gel permeation chromatograms of the dehydrating and the transesterification polyol with castor oil. It can clearly be seen that the transesterification polyol has significantly fewer higher and lower molecular weight fractions than the dehydration polyol. Consequently, the gel permeation chromatogram of the transesterification polyol does not differ as much as that of the dehydration polyol from the castor oil chromatogram.

Example 3 (comparative example)

In a reactor were under inert gas 380 kg of crude MDI having a viscosity of 280 mPas submitted at 20 ° C. This was dehydrated with stirring Castor oil according to Example 1 with an OH number of 63 mgKOH / g. The Amount of this product was 227 kg. Subsequently, the succession took place Addition of 0.5 kg dibutyltin dilaurate and 0.65 kg DABCO 33 LV to the strong stirred product. After the temperature of the mixture no longer increased, 389 kg of polypropylene glycol having a molecular weight of about 4000 were added. The last addition of 0.5 kg of benzoyl chloride, and it was 10 minutes touched.

The prepolymer produced had a brown color and was slightly cloudy. The Viscosity of the product was 18,500 mPas and the NCO content was 10.0%.

Example 4 (according to the invention)

The dehydrated castor oil of Example 3 was replaced by a transesterification polyol replaced according to Example 2 with an OH number of 61 mg KOH / g. The remaining Products and the manufacturing process did not differ from Example 3.

This prepolymer was brown and not cloudy. The viscosity was 7100 mPas and the NCO content at 10.2%.

Claims (6)

1. Polyol, prepared by transesterification of mixtures of castor oil and native, substantially OH-free triglycerides selected from Rapeseed oil, sunflower oil, New Sunflower oil, soybean oil or theirs Mixtures. 2. Polyol according to claim 1, characterized in that the Transesterification product an OH number of less than 160 mg KOH / g according to DIN 53240. 3. Polyol according to claim 1 or 2, characterized in that as Transesterification catalyst an alkali or Erdalkalilydroxid for transesterification was used. 4. Low-viscosity, essentially solvent-free polyurethane Compositions with reactive isocyanate groups obtainable by Reaction of polyols according to claim 1 to 3, wherein the stoichiometric Excess of the isocyanate groups over the sum of the hydroxyl groups 1.3: 1 to 7: 1. 5. Polyurethane composition according to claim 4, characterized in that that as further polyols di- or trifunctional polyethylene glycols, Polypropylene glycols, polytetraethylene glycols, polybutylene glycols and / or their copolymers and / or polyester polyols and / or polycaprolactones be used. 6. Use of the polyurethane composition according to at least one of Claims 4 to 5 optionally with the concomitant use of plasticizers, fillers, Rheological aids, pigments, anti-aging agents and other auxiliary and additives as one- or multi-component adhesives, sealants, Potting compounds or coating agents.