Bulk materials comprising solid diisocyanates and urethane-group-containing prepolymers obtainable therefrom

Abstract

This invention relates to a bulk material comprising a solid diisocyanate, particularly naphthalene 1,5-diisocyanate or p-phenylene diisocyanate, a method for producing the same, and a method for preparing isocyanate prepolymers using the bulk material of this invention, the isocyanate prepolymers themselves, and their use in the preparation of polyurethane elastomers, particularly cast polyurethane elastomers.

Description

Technical Field

[0001] The present invention relates to a bulk material comprising a solid diisocyanate, in particular naphthalene-1,5-diisocyanate or p-phenylene diisocyanate, to a method for producing the same, and to a method for preparing an isocyanate prepolymer using the bulk material of the present invention, to the isocyanate prepolymer itself and to its use for preparing a polyurethane elastomer, in particular a cast polyurethane elastomer. Background Art

[0002] Cast polyurethane elastomers are usually used to produce porous or solid moldings. They are usually prepared by reacting an isocyanate component with a component having hydrogen atoms reactive toward isocyanate groups. The latter component usually contains polyfunctional alcohols, amines and / or water.

[0003] In principle, there are two possible processes for the preparation of cast polyurethane elastomers, which differ in the order in which the co-reactants are added. In the so-called one-shot process, all components are mixed simultaneously after gravimetric or volumetric metering and reacted while undergoing shaping. The disadvantage here is that, in particular when high-melting-point isocyanates are used, only inferior elastomers are obtained, since the intermediates formed from short-chain polyols (chain extenders) and isocyanates partially precipitate out of the reaction melt and are therefore excluded from any further reaction, which disrupts the further orderly increase in molecular weight. A further disadvantage of the one-shot process is the rapid release of high reaction heat, which often cannot be removed sufficiently. The high temperatures generated promote side reactions, such as isocyanurate formation or carbodiimidization, which further impair the properties of the elastomer.

[0004] For these reasons, a large number of prepolymer processes for producing cast elastomers have been established, in which the long-chain diol component is first reacted with an excess of diisocyanate to give a liquid NCO prepolymer, which is then subsequently reacted with a short-chain diol, such as butane-1,4-diol, or an amine, such as methylenebis(o-chloroaniline) (MOCA) or diethyltoluenediamine (DETDA), and / or water. This has the advantage that some of the heat of reaction is already released and removed beforehand in the prepolymerization, and the reaction in the actual polymer formation is easier to control. This promotes a more regular increase in molar mass and allows longer casting times, which facilitates blister-free filling of even complex shapes.

[0005] The long-chain diol components used are polyether polyols, polycarbonate polyols and preferably polyester polyols, more preferably poly-ε-caprolactone polyols. The isocyanate components used for particularly high-quality cast elastomers are high-melting diisocyanates, such as p-phenylene diisocyanate (PPDI), 3,3-dimethyl-4,4'-biphenyl diisocyanate (TODI), and especially naphthalene-1,5-diisocyanate (NDI).

[0006] The use of the prepolymer process for these high-quality cast elastomers is not without problems, since the prepolymers prepared initially with a suitable NCO content still contain a certain amount of free, i.e. monomeric, diisocyanates which then have a tendency to crystallize at low storage temperatures, while storage at elevated temperatures leads to undesirable reactions and an associated increase in viscosity.

[0007] EP1918315A1 describes a process for preparing NDI prepolymers, in which polyols are mixed with solid NDI at a temperature of 80-240° C. The temperature is selected so that the solid isocyanate melts during the exothermic reaction. After a transparent homogeneous melt is obtained, the resulting prepolymer is cooled rapidly.

[0008] WO02081537A1 describes a process for preparing NDI prepolymers, wherein a polyol is initially charged at 140° C. and then mixed and reacted with solid NDI under vigorous stirring.

[0009] DE10060473A1 describes the preparation of prepolymers based on naphthalene-1,4-diisocyanate or, for comparison, naphthalene-1,5-diisocyanate. The polyol is initially charged and dehydrated at 120° C. and 20 mbar, and then the corresponding diisocyanate is added while stirring. The reaction mixture is then stirred at 20 mbar and 125-130° C. for 15 minutes.

[0010] WO2015185659A1 describes a continuous process for preparing NDI prepolymers, in which a melt of a diisocyanate and a polyol are reacted in a tubular reactor at 80-175°C. This application, like EP1918315A1, also discusses chemical engineering problems in the metering of diisocyanates. For a controlled reaction with a uniform increase in molecular weight, it is therefore first necessary to heat so that the NDI can melt rapidly and then to cool rapidly after reaching the clearing point so that the reaction temperature cannot rise significantly above 127°C during the exothermic reaction. Although the continuous process can avoid some of the problems of the batch process, it is ultimately less flexible and has not yet been established due to the inherently higher chemical engineering complexity.

[0011] In the inverse prepolymer processes already described, which are carried out in a batchwise manner, i.e. those processes in which the polyol component is initially added and then the isocyanate is added, the reactor with each batch undergoes a change in the OH- to NCO-functional content. This leads to a more pronounced tendency for the process to fluctuate than in regular prepolymer processes, in which no such change occurs. In these regular prepolymer processes, it can be ensured, for example by gradually metering in insufficient reactants, that the latter are always oversupplied with a large excess of reactants, which leads to a very uniform reaction. In the inverse prepolymer process, there is no such option for reaction control, in which a varying excess is inevitably present. In order to minimize this problem, the change from the OH-dominated state to the NCO-dominated state must be carried out as quickly as possible, which means that the excess component, i.e. in this case the isocyanate, must be supplied to the reaction very quickly. However, as is evident from the prior art, the inverse prepolymer process has become an intermediate step in the production of high-quality cast elastomers. This is especially because solid isocyanates are used. If the structured prepolymer process is used, these solid isocyanates must be initially charged and first melted at elevated temperatures, whereby undesirable isocyanate side reactions already occur.

[0012] A simple measure that can be used to determine the extent to which side reactions occur during the prepolymer formation is the NCO content of the prepolymer, i.e. the mass percentage of isocyanate groups based on the total mass of the prepolymer. The stoichiometric relationship of the main reaction of the two components can be used to determine a theoretical value for the NCO content of the prepolymer, assuming complete conversion of the component reactive toward NCO groups present in insufficient amounts. The further the NCO content of the prepolymer deviates from this theoretical value, i.e. the lower it is, the more frequently the NCO groups participate in other reactions, for example reactions with urethane groups to form allophanates, reactions with other isocyanate groups to form uretdiones, isocyanurates or 1-nylons, or reactions with urea groups to form biuret substances. Summary of the invention

[0013] The problem to be solved by the present invention is to prepare prepolymers from solid diisocyanates in a simple and cost-effective manner with low by-product formation.

[0014] Surprisingly, it has now been found that NCO prepolymers based on solid diisocyanates can be prepared in a simple and cost-effective manner with good quality and low levels of by-products by using a bulk material consisting predominantly of solid diisocyanate particles having a particle size of 0.1 mm to 4 mm as the diisocyanate component.

[0015] The present invention provides a bulk material containing or consisting of a diisocyanate which is solid at room temperature (25° C.), characterized in that, in a sieve analysis of the bulk material carried out in a known manner using a double sieve device with mesh sizes of 0.1 mm and 4 mm, at least 90% by weight, preferably at least 95% by weight, of the bulk material is obtained in a particle size fraction of 0.1 mm to 4 mm.

[0016] The sieve analysis was performed according to ASTM 1921-89, with the sieving time reduced to 5 minutes compared to the standard.

[0017] The particles obtained by this sieve size fraction are particularly suitable for preparing prepolymers by the inverse batchwise process established in industry. As mentioned above, the equivalence point is crossed in the inverse batchwise process, and it is known that this must be crossed very quickly to avoid the formation of long polymer chains and the generation of viscosity increase until gelation. However, the rapid addition of isocyanate alone is not enough to achieve this goal. On the contrary, it is also necessary to ensure that the isocyanate groups are truly available to the coreactants through melting, dissolving and mixing operations. In larger particles, in the absence of the required coreactants, as the temperature rises, there may already be side reactions of the isocyanate groups with each other. In contrast, the upper limit of the particle size in the bulk of the present invention leads to rapid melting and mixing of the isocyanate in the reaction mixture, and thus quickly reaches the clearing point and the molecular weight increases uniformly. The lower limit of the size is used to significantly avoid dust, which is firstly undesirable due to occupational hygiene reasons and secondly also creates technical problems. The large surface area of ​​the dust particles in turn promotes side reactions. For example, the usually hygroscopic isocyanate may react with moisture to form slightly soluble urea. On an industrial scale and with regard to the handling of solids, complete exclusion of air and therefore of air humidity is hardly achievable. In particular, in some cases, the dust fraction can only be dispersed completely into the reaction mixture with difficulty and is more likely to adhere to the surface or remain as airborne suspensions in the gas space above the liquid surface for a period of time. This affects the stoichiometry of the reaction and also promotes undesirable side reactions.

[0018] The bulk material is preferably free-flowing. This is understood to mean a bulk material with an angle of repose of ≤55°, preferably ≤50°, measured with a Granu Heap (from Granutools). The reason why the bulk material according to the invention has a high degree of fluidity is essentially the claimed particle size or particle size distribution. Preferably, the bulk material contains not more than 5% by weight, preferably not more than 3% by weight, and more preferably not more than 2% by weight of particles obtained in a particle size fraction of <0.1 mm in a sieve analysis. Due to its good fluidity, such a bulk material enables optimal emptying of transport containers and simple pneumatic conveying of the bulk material.

[0019] Preferably, the bulk material according to the invention is a bulk material containing or consisting of a diisocyanate which is solid at room temperature, characterised in that in a sieve analysis of the bulk material carried out in a known manner with a double sieve device having mesh sizes of 0.2 mm and 3 mm, at least 90% by weight, preferably at least 95% by weight of the bulk material is obtained in a particle size fraction of 0.2 mm to 3 mm. The term "undersize" is to be understood as meaning particles which are smaller than those specified in the lower limit of the respective particle size fraction. They therefore have a shape such that they fall through a finer sieve in the sieve analysis or can fall through a finer sieve. Correspondingly, the term "oversize" is to be understood as meaning particles which are larger than those specified in the upper limit of the respective particle size fraction. In the sieve analysis, they therefore remain on the coarser upper sieve.

[0020] If 90% by weight of the bulk material is obtained in a particle size fraction of 0.1 to 4 mm in the case of an analysis with mesh sizes of 0.1 and 4 mm, or in a particle size fraction of 0.2 to 3 mm in the case of an analysis with mesh sizes of 0.2 and 3 mm, the bulk material preferably contains not more than 5% by weight of oversize and not more than 5% by weight of undersize.

[0021] In a further preferred embodiment, the bulk material contains ≥98% by weight, preferably ≥99% by weight, and more preferably ≥99.5% by weight of solid diisocyanates, based on the total mass of the bulk material. Other components may be, for example, by-products from the preparation of diisocyanates, in particular monoisocyanates, solvent residues or chlorinated by-products.

[0022] Suitable solid diisocyanates are those which are solid at room temperature, i.e. have a melting point above 25° C. These are, for example, methylene 2,2-diisocyanate, methylene 2,4-diisocyanate, methylene 4,4-diisocyanate, naphthalene 1,4-diisocyanate, naphthalene 1,5-diisocyanate, naphthalene 1,8-diisocyanate, phenylene 1,3-diisocyanate, phenylene 1,4-diisocyanate, isomers of tetralin 2,3-diisocyanate, tetralin 2,4-diisocyanate, tetralin 2,5-diisocyanate, tetralin 3,4-diisocyanate, o-toluidine diisocyanate, durene diisocyanate, benzidine diisocyanate and / or anthracene 1,4-diisocyanate. Particular preference is given to those diisocyanates having a melting point ≥80° C. Very particular preference is given to naphthalene 1,5-diisocyanate or phenylene 1,4-diisocyanate.

[0023] The present invention also provides a method for producing a bulk material according to the invention. To this end, the diisocyanate is first prepared in a known manner by phosgenating the corresponding amine. Phosgene-free methods, such as thermal cleavage of carbamates, are also conceivable, but these methods have not yet been established on an industrial scale for various reasons for preparing solid diisocyanates. An option for high-melting diisocyanates, such as naphthalene 1,5-diisocyanate or phenylene 1,4-diisocyanate, is suspension phosgenation as described in WO2014044699. Methods that can be used to separate the diisocyanate from the solvent and for further purification include those known to those skilled in the art, such as crystallization, sublimation or distillation, optionally with the addition of, for example, seed crystals or entrainers. In the context of the present invention, the term "crystallization" is also understood to mean a simple solidification operation. Therefore, it is not absolutely necessary to obtain a crystalline material; for example, even precipitation of an amorphous solid satisfies the requirements.

[0024] In a first embodiment, the method for producing bulk materials of the present invention comprises a crystallization operation (i) and at least one step (ii) selected from classification, agglomeration and pulverization. Preferably, step (ii) is agglomeration and / or pulverization; more preferably, step (ii) is pulverization.

[0025] In a preferred embodiment of the process, the crystallization step (i) is carried out by crystallizing the melt of the solid diisocyanate on a cold surface, preferably on a chill belt or a rotating drum flaker, more preferably on an internally cooled drum flaker, and scraping it off after solidification.

[0026] The layer thickness of the crystallized solid diisocyanate on the cold surface can be adjusted here by the operating parameters during the crystallization operation, in particular by the temperature of the melt and the cold surface and the advance speed of the cold surface. Preferably, the layer thickness is in the range of ≥0.1 mm and ≤4.0 mm, more preferably in the range of ≥0.2 mm and ≤3.0 mm, and most preferably in the range of ≥0.5 mm and ≤2.5 mm. In this way, particles are obtained at a later stage which already have a favorable extent in one dimension, which firstly has a positive influence on the melting properties of the finished bulk material and secondly also simplifies the further processing to obtain the bulk material according to the invention.

[0027] Preferably, the crystallized diisocyanate is removed from the cold surface with a scraper. Here too, the shape of the particles can be influenced by the positioning and shape of the blade.

[0028] In the crystallization operation (i), only some particles are already obtained in the shape and size required for the bulk material according to the invention. Therefore, in the process according to the invention, at least one further step selected from classification, agglomeration and comminution is required.

[0029] In the embodiment of the selective classification as step (ii) of the method according to the invention, this is preferably carried out by a dry process, i.e. by screening or by windsifting, using a gas, preferably nitrogen or air, more preferably nitrogen as a separation medium. The classification is preferably carried out by screening. Here, the particles are separated into various particle size fractions by a sieve in a manner known per se, so that one or more particle size fractions for producing the bulk material according to the invention can be selected subsequently. During the screening process, it is not possible to exclude that a certain proportion of particles will have a high aspect ratio and will therefore be larger than the mesh size of the sieve used in each case in at least one dimension. This is not important for the bulk material of the invention, because such particles only slightly impair the melting and mixing characteristics in the reverse prepolymer process. Oversized or undersized particles, i.e. those particles that are not obtained with a sieve particle size fraction of 0.1 mm to 4 mm, can be recycled into the method and recrystallized. As an alternative or in addition, oversized particles can be crushed in a comminution device.

[0030] In the embodiment of the method according to the invention in which agglomeration is selected as step (ii), this is preferably carried out in dry form by sintering or compression molding. This embodiment is particularly advantageous when a high proportion of primary particles, i.e. particles obtained after the crystallization operation, have a particle size that is too small to be used in the bulk material according to the invention. Alternatively, this embodiment is also advantageous in combination with a screening or comminution step, in which small particles are obtained in a controlled manner and then agglomerated back to the desired size. In this way, a very defined bulk material can be produced. Compression molding methods, such as granulation or tableting, are preferred, which produce very uniform particles, resulting in a bulk material consisting of them having good flowability.

[0031] In the preferred embodiment of the method according to the invention, the crushing is carried out in a crushing device as step (ii). Preferably, those crushing facilities designed for dry operation in the prior art are suitable for this purpose. For example, a crushing facility consisting of two or more rotating rollers can be used, and the two or more rotating rollers together form a roller gap, in which the particles applied are crushed. It is also possible to use a so-called screw roll comminutor, in which the particles are crushed by a counter-rotating screw. If necessary, the discharged crushed bulk material can be at least partially introduced back into the crushing device, which optionally has a smaller grinding gap to obtain a desired particle size.

[0032] The preferred comminution facility is a hammer mill or a knife mill. A standard knife mill usually has a cylindrical grinding space. The stator blades extend into it from the outside, and a rotating drum equipped with a cutting blade pointing outward rotates therein. A screen, preferably a perforated plate screen, is preferably provided in the periphery of the grinding space, through which the crushed particles leave the grinding space, while the oversized particles are retained and further crushed. The material to be crushed can be introduced into the grinding space axially or radially. It is particularly preferred to use a hammer mill as a comminution facility. The rotor rotates in the grinding chamber here, and the rotor is equipped with a movable hammer or a fixed hammer. The impact of the hammer on the blocks of the grinding material crushes them and throws them to the grinding wall, where further crushing occurs. As has been described for the knife mill, a screen, preferably a perforated plate screen, is also provided in the periphery of the grinding space, through which particles less than the maximum particle size can leave the grinding space. Since this comminution step only includes the particle upper limit, if necessary, a dust removal operation is subsequently performed by air sorting or screening the bulk material.

[0033] In another preferred embodiment of the process, any oversize or undersize present is at least partially removed from the bulk material obtained in step (ii) by classification in step (iii), preferably by sieving or wind sorting, more preferably by sieving, and the oversized and / or undersized particles are at least partially recycled into the process, i.e. melted or dissolved and subjected to crystallization operation (i) again. If step (ii) comprises comminution, the oversized particles can optionally be recycled to the comminution device.

[0034] The invention further provides for the use of the bulk material described above for preparing NCO-terminated prepolymers.

[0035] The present invention further provides a process for preparing NCO-terminated prepolymers, which comprises or consists of the reaction of at least one component (A) which comprises or consists of an isocyanate which is solid at room temperature, with at least one isocyanate-reactive component (B), characterised in that component (A) corresponds to a bulk material as described above.

[0036] The isocyanate-reactive component (B) preferably comprises a polyol.

[0037] Suitable polyols for preparing the prepolymers have, for example, a number average molecular weight M of 400 to 8000 g / mol, preferably 600 to 6000 g / mol, and more preferably 1000 to 3000 g / mol. n Their hydroxyl value is 22-400 mg KOH / g, preferably 30-300 mg KOH / g and more preferably 40-250 mg KOH / g, and their OH functionality is 1.5-6, preferably 1.7-3 and more preferably 1.9-2.2.

[0038] The polyol used to prepare the prepolymer is an organic polyhydroxy compound known in polyurethane technology, such as standard polyester polyols, polyacrylate polyols, polyurethane polyols, polycarbonate polyols, polyether polyols, polyester polyacrylate polyols and polyurethane polyacrylate polyols, polyurethane polyester polyols, polyurethane polyether polyols, polyurethane polycarbonate polyols, polyester polycarbonate polyols, phenol / formaldehyde resins, individually or in a mixture. Preferred polyester polyols, polyether polyols, polyacrylate polyols or polycarbonate polyols, particularly preferred polyether polyols, polyester polyols and polycarbonate polyols. Most preferred is polyester polyol.

[0039] Polyether polyols include, for example, polyaddition products of styrene oxide, ethylene oxide, propylene oxide, tetrahydrofuran, butylene oxide, epichlorohydrin and mixed addition and graft products thereof, as well as polyether polyols obtained by condensation of polyols or mixtures thereof, and those obtained by alkoxylation of polyols, amines and amino alcohols. Suitable hydroxy-functional polyethers have an OH functionality of 1.5 to 6.0, preferably 1.7 to 3.0, more preferably 1.9 to 2.2, an OH value of 22 to 400, preferably 30 to 300, more preferably 40 to 250 mg KOH / g, and a molecular weight M n The alkoxylation products of hydroxy-functional starter molecules are 400 to 8000, preferably 600 to 6000, more preferably 1000 to 3000 g / mol. These are, for example, alkoxylation products of hydroxy-functional starter molecules such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, trimethylolpropane, glycerol, pentaerythritol, sorbitol or mixtures of these and other hydroxy-functional compounds with ethylene oxide, propylene oxide or butylene oxide.

[0040] Examples of polyester polyols with good suitability are the known polycondensates of di- and optionally tri- and tetraols with di- and optionally tri- and tetracarboxylic acids or hydroxycarboxylic acids or lactones. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic acid esters of lower alcohols can also be used to prepare the polyesters. Examples of suitable diols are ethylene glycol, butanediol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, and propane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butane-1,4-diol, hexane-1,6-diol and isomers, neopentyl glycol or neopentyl glycol hydroxypivalate, preferably the latter three compounds. In order to achieve a functionality > 2, a certain proportion of polyols with a functionality of 3 can optionally be used, for example trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate. Available dicarboxylic acids include, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, suberic acid, 2-methylsuccinic acid, 3,3-diethylglutaric acid, 2,2-dimethylsuccinic acid. The anhydrides of these acids are also available when they exist. Therefore, for the purposes of the present invention, anhydrides are covered by the expression "acid". Monocarboxylic acids, such as benzoic acid and hexanecarboxylic acid, can also be used, provided that the average functionality of the polyol is ≥2. Saturated aliphatic or aromatic acids, such as adipic acid or isophthalic acid are preferred. An example of a polycarboxylic acid optionally used additionally in a smaller amount is trimellitic acid. Examples of hydroxycarboxylic acids that can also be used as coreactants in the preparation of polyester polyols with terminal hydroxyl groups include hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid, hydroxystearic acid, etc. Useful lactones include ε-caprolactone, butyrolactone, and homologues. Polyester polyols based on butanediol and / or neopentyl glycol and / or hexanediol and / or ethylene glycol and / or diethylene glycol with adipic acid and / or phthalic acid and / or isophthalic acid are preferred. Polyester polyols based on butanediol and / or neopentyl glycol and / or hexanediol with adipic acid and / or phthalic acid are particularly preferred. Also particularly preferred are linear polyester diols based on ε-caprolactone.

[0041] Useful polycarbonate polyols are obtainable by reaction of carbonic acid derivatives, such as diphenyl carbonate, dimethyl carbonate or phosgene, with diols. Useful diols of this type include, for example, ethylene glycol, propane-1,2- and 1,3-diols, butane-1,3- and 1,4-diols, hexane-1,6-diol, octane-1,8-diol, neopentyl glycol, 1,4-dihydroxymethylcyclohexane, 2-methylpropane-1,3-diol, 2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A, tetrabromobisphenol A, and lactone-modified diols. Preferably, the diol component comprises 40% to 100% by weight of hexane-1,6-diol and / or hexanediol derivatives, preferably those having not only OH end groups but also ether groups or ester groups, such as products obtained by the reaction of 1 mol of hexanediol with at least 1 mol, preferably 1 to 2 mol, of ε-caprolactone, or by etherification of hexanediol with itself to give di- or trihexylene glycol. Polyether polycarbonate polyols can also be used. Polycarbonate polyols based on dimethyl carbonate and hexanediol and / or butanediol and / or ε-caprolactone are preferred. Polycarbonate polyols based on dimethyl carbonate and hexanediol and / or ε-caprolactone are very particularly preferred.

[0042] Suitable polyacrylate polyols are obtained, for example, by free radical polymerization of ethylenically unsaturated monomers having hydroxyl groups or by free radical copolymerization of ethylenically unsaturated monomers having hydroxyl groups with optionally different ethylenically unsaturated monomers, such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, styrene, acrylic acid, acrylonitrile and / or methacrylonitrile. Suitable ethylenically unsaturated monomers having hydroxyl groups are especially 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, a hydroxypropyl acrylate isomer mixture obtainable by adding propylene oxide to acrylic acid, and a hydroxypropyl methacrylate isomer mixture obtainable by adding propylene oxide to methacrylic acid. Suitable free radical initiators are those selected from azo compounds, such as azobis(isobutyronitrile), or those selected from peroxides, such as di-tert-butyl peroxide.

[0043] The polyols mentioned may be used alone or in mixture.

[0044] The above isocyanate-reactive compounds of component (B) are reacted with the isocyanate of component (A) using an excess of isocyanate groups over the isocyanate-reactive groups to obtain an NCO-terminated prepolymer containing urethane groups. The quantitative ratio here is such that the isocyanate component is in excess so that the calculated (theoretical) NCO content is preferably 2.5% to 6.0%, preferably 3.0% to 5.0%.

[0045] In the preparation of the prepolymers, additives may additionally be used. Suitable additives are catalysts, emulsifiers, UV and hydrolysis stabilizers, preferably stabilizers customarily used in polyurethane chemistry. An overview can be found, for example, in “Kunststoff Handbuch [Plastics Handbook], Vol. 7, G. Oertel, 1983, Carl Hanser Verlag, Munich, Vienna”.

[0046] Examples of the catalyst are trialkylamines, diazabicyclooctane, dibutyltin dilaurate, N-alkylmorpholine, lead octoate, zinc octoate, calcium octoate and magnesium octoate, and the corresponding naphthenates, p-nitrophenolates and the like.

[0047] Examples of suitable UV and hydrolysis stabilizers are 2,6-di-tert-butyl-4-methylphenol and carbodiimides.

[0048] Examples of suitable stabilizers are Bronsted and Lewis acids, such as hydrochloric acid, benzoyl chloride, dibutyl phosphate, adipic acid, malic acid, succinic acid, pyruvic acid, citric acid, etc., and alkyl- and arylsulfonic acids, such as p-toluenesulfonic acid and preferably dodecylbenzenesulfonic acid.

[0049] The process is preferably a reverse prepolymer process, in which - as described above - the isocyanate-reactive component (B) is initially charged and the isocyanate component (A) is metered in. Here, the isocyanate-reactive component (B) is initially charged in liquid form, i.e. in the form of a solution or melt, while component (B) is charged in bulk form, i.e. in solid form and mixed with the polyol component, preferably while stirring. This causes the bulk to melt and react with the polyol component. The reaction temperature here is preferably in the range from 80 to 160° C., more preferably in the range from 100 to 150° C.

[0050] More preferably, the NCO-terminated prepolymer is prepared batchwise in a reverse prepolymer process.

[0051] The NCO prepolymers prepared by the process of the invention have an NCO content of 2.5% to 6.0%, preferably 3.0% to 5.0%, and a viscosity of 1000 to 12000 mPas / 70° C., preferably 2000 to 10000 mPas / 70° C., according to DIN EN ISO 3219, and can advantageously be used to produce solid or porous elastomers. DETAILED DESCRIPTION

[0052] Example

[0053] raw materials:

[0054] COVER TM 2161A: Poly-ε-caprolactone diol from PERSTORP having a molecular weight of 1600 Da and an OH functionality of 2 (OH value 70 mg KOH / g).

[0055] The theoretical NCO content of each prepolymer described hereinafter is 4.07%.

[0056] Example 1 (not the present invention, the particles are too small):

[0057] First, a representative sample of a bulk material containing 99.7% by weight of naphthalene 1,5-diisocyanate was graded into three particle size fractions by a double sieve device (mesh size of 4 mm and square mesh of 0.1 mm), and their weight ratios were determined. The particle size fraction of 0.1 mm to 4 mm accounted for 88% by weight of the total mass of the bulk material, the particle size fraction greater than 4 mm had a proportion of 1% by weight, and the particle size fraction less than 0.1 mm had a proportion of 11% by weight.

[0058] Under nitrogen atmosphere, 100 g of CAPA was initially added to a glass flask. TM 2161A and heated to 125° C. in an oil bath. Then, 25.94 g of the bulk material analyzed in the sieve analysis were added in advance while stirring. During the exothermic reaction, the reaction mixture reached a maximum temperature of 135° C. After 30 minutes, the still turbid mixture was cooled rapidly. The NCO content of the resulting prepolymer was 3.82%.

[0059] Embodiment 2 (the present invention):

[0060] First, a representative sample of a bulk material containing 99.7% by weight of naphthalene 1,5-diisocyanate was graded into three particle size fractions by a double sieve device (mesh size of 4 mm and square mesh of 0.1 mm), and their weight ratios were determined. The particle size fraction of 0.1 mm to 4 mm had a proportion of 96.6% by weight of the total mass of the bulk material, the particle size fraction greater than 4 mm had a proportion of 1% by weight, and the particle size fraction less than 0.1 mm had a proportion of 2.4% by weight.

[0061] Under nitrogen atmosphere, 100 g of CAPA was initially added to a glass flask. TM2161A and heated to 125°C by oil bath. Then, 25.94 g of bulk material analyzed in the sieve analysis were added in advance while stirring. During the exothermic reaction, the reaction mixture reached a maximum temperature of 134°C, and the reaction mixture became completely clear. After 30 minutes, the solution was cooled rapidly. The NCO content of the obtained prepolymer was 3.90%.

[0062] Example 3 (not according to the present invention, 10% oversized particles):

[0063] First, a representative sample of a bulk material containing 99.7% by weight of naphthalene 1,5-diisocyanate was graded into three particle size fractions by a double sieve device (mesh size of 4 mm and square mesh of 0.1 mm), and their weight ratios were determined. The particle size fraction of 0.1 mm to 4 mm had a proportion of 88% by weight of the total mass of the bulk material, the particle size fraction greater than 4 mm had a proportion of 10% by weight, and the particle size fraction less than 0.1 mm had a proportion of 2% by weight.

[0064] Under nitrogen atmosphere, 100 g of CAPA was initially added to a glass flask. TM 2161A and heated to 125° C. in an oil bath. Then, 25.94 g of the bulk material analyzed in the sieve analysis were added in advance while stirring. The reaction mixture reached a maximum temperature of 134° C. during the exothermic reaction. After 30 minutes, the reaction mixture still contained solid flakes and cooled rapidly. The NCO content of the prepolymer was 3.79%.

[0065] Embodiment 4 (the present invention):

[0066] From a bulk material containing 99.7% by weight of naphthalene-1,5-diisocyanate, a particle size fraction of 0.2 mm to 3 mm was fractionated by a double sieve device (mesh sizes of 3 mm and 0.2 mm square mesh) to obtain a bulk material in which more than 99% of the particles belonged to this particle size fraction. This was used to prepare a prepolymer as in Example 2. The NCO content of the obtained prepolymer was 3.91%.

Claims

1. A bulk material containing a diisocyanate which is solid at room temperature of 25° C., characterized in that: In a sieve analysis of the bulk material using a double sieve device with mesh sizes of 0.1 mm and 4 mm, at least 90% by weight of the bulk material is obtained in a particle size fraction of 0.1 mm to 4 mm, wherein the sieve analysis is carried out in accordance with ASTM 1921-89 and wherein the solid diisocyanate is a diisocyanate with a melting point ≥80°C.

2. Bulk material according to claim 1, characterized in that It contains not more than 5% by weight of particles which were obtained in a particle size fraction of <0.1 mm.

3. Bulk material according to claim 1 or 2, characterized in that: In a sieve analysis with a double sieve device having mesh sizes of 0.2 mm and 3 mm, at least 90% by weight of the bulk material is obtained in a particle size fraction of 0.2 mm to 3 mm.

4. Bulk material according to any one of claims 1 to 2, characterized in that: It contains at most 5% by weight of oversize and at most 5% by weight of undersize.

5. Bulk material according to any one of claims 1 to 2, characterized in that: The content of solid diisocyanate in the bulk material is ≥98% by weight.

6. A process for producing a bulk material comprising a crystallization operation (i) and at least one step (ii) selected from classification, agglomeration and comminution, wherein the bulk material contains a diisocyanate which is solid at room temperature of 25° C., characterized in that In a sieve analysis of the bulk material using a double sieve apparatus having mesh sizes of 0.1 mm and 4 mm, at least 90% by weight of the bulk material is obtained in a particle size fraction of 0.1 mm to 4 mm, wherein the sieve analysis is carried out in accordance with ASTM 1921-89.

7. The method according to claim 6, characterized in that The bulk material contains not more than 5% by weight of particles obtained in a particle size fraction of <0.1 mm.

8. The method according to claim 6 or 7, characterized in that: In a sieve analysis with a double sieve device having mesh sizes of 0.2 mm and 3 mm, at least 90% by weight of the bulk material is obtained in a particle size fraction of 0.2 mm to 3 mm.

9. The method according to any one of claims 6 to 7, characterized in that: The bulk material contains at most 5% by weight of oversize material and at most 5% by weight of undersize material.

10. The method according to any one of claims 6 to 7, characterized in that: The content of solid diisocyanate in the bulk material is ≥98% by weight.

11. The method according to any one of claims 6 to 7, characterized in that: The solid diisocyanate is a diisocyanate with a melting point of ≥80°C.

12. The method according to claim 6, characterized in that In the crystallization operation (i), the melt of the solid diisocyanate is crystallized on a cold surface and scraped off after solidification.

13. The method according to claim 12, characterized in that In the crystallization operation (i), the melt of the solid diisocyanate is crystallized on a cooling belt or a drum flaker and scraped off after solidification.

14. The method according to claim 6, characterized in that As step (ii), comminution of the crystallized diisocyanate is carried out in a comminution apparatus.

15. The method according to claim 14, characterized in that As step (ii), comminution of the crystallized diisocyanate is carried out in a hammer mill or a knife mill.

16. The method according to claim 6, characterized in that In step (iii), the bulk material obtained in step (ii) is at least partially separated into oversize material and undersize material by classification.

17. The method according to claim 16, characterized in that The classification is carried out by sieving or pneumatic sorting, and the oversized and / or undersized particles are at least partially recirculated into the process.

18. A process for preparing NCO-terminated prepolymers, comprising or consisting of the reaction of at least one component (A) with at least one isocyanate-reactive component (B), wherein the component (A) comprises or consists of an isocyanate which is solid at room temperature, characterized in that Component (A) corresponds to a bulk material according to any one of claims 1 to 5 or a bulk material obtained by a process according to any one of claims 6 to 17.

19. The process of claim 18 which is a reverse prepolymer process.

20. The process of claim 18 or 19, wherein the process is batch-wise.

21. NCO-terminated prepolymer obtainable by the process according to any one of claims 18 to 20.

22. Polyurethane elastomer obtainable using the NCO-terminated prepolymer according to claim 21.