Low-free polyurethane prepolymer composition

Abstract

The present invention provides a cured polyurethane having physical properties equivalent to or better than those of a polyurethane prepolymer having high NCO functionality, such as tear strength, or adhesive properties, such as high shear strength. [Solution] The present invention provides a polyurethane prepolymer composition comprising more than 0% by mass and less than 1.0% by mass of free diisocyanate monomer, wherein the polyurethane prepolymer comprises a composition comprising less than 80% by mass of a 2:1 stoichiometric adduct (complete prepolymer) of diisocyanate and at least one polyol, a curable composition comprising these polyurethane prepolymer compositions, and the use of these polyurethane prepolymer compositions as an adhesive.

Description

Technical Field

[0001] The present invention relates to a polyurethane prepolymer composition containing a free diisocyanate monomer of more than 0% by mass and less than 1.0% by mass, wherein the polyurethane prepolymer contains less than 75% by mass of a 2:1 stoichiometric adduct (complete prepolymer) of a diisocyanate and at least one polyol, a curable composition containing these polyurethane prepolymer compositions, and use of these polyurethane prepolymer compositions as adhesives.

Background Art

[0002] Isocyanate-terminated polyurethane prepolymers are commonly used in the production of polyurethane products such as elastomers, foams, coatings, adhesives, sealants, and binders. However, in the production process of polyurethane prepolymers, the residual concentration of the polyisocyanate monomer used in prepolymer synthesis usually becomes high. Residual polyisocyanate may pose health and safety problems and may also have an adverse effect on the performance and properties of the end-use product. For example, residual polyisocyanate may cause an undesirable loss of open time, product instability, increased moisture sensitivity, and decreased adhesiveness as these molecules migrate to the interface. Polyurethane prepolymers containing residual diisocyanate at a low level of less than 1.0% by mass, preferably less than 0.1% by mass, based on the total mass of the polyurethane prepolymer can reduce health and safety risks and improve the performance of the final product.

[0003] Since residual polyisocyanate may pose significant health and safety risks as well as a decrease in product performance, many products and processes with reduced residual polyisocyanate levels have been introduced. JP08176252 discloses the reaction of MDI with a linear molecule having two active hydrogen atoms and Mw = 250 to 4,000 in an equivalent ratio of 2.5 to 10:1 (NCO:OH). The amount of free MDI is less than 1% by mass by vacuum distillation. Examples include polytetramethylene glycol (PTMEG) and ethylene glycol adipate.

[0004] US-B-4,786,703 discloses a process for producing reaction products containing TDI prepolymers, in which at least about 90% of such prepolymers consist of a prepolymer of 2 moles of TDI per mole of long-chain diol, and the level of unreacted TDI is less than about 0.15%. This document teaches the advantages of using large quantities of complete prepolymers exceeding 90% by mass.

[0005] US-A-4,888,442 discloses a process for reducing the free monomer content of a polyisocyanate adduct, comprising treating the adduct in a stirred thin-layer evaporator with 2-30% by mass of an inert solvent under conditions sufficient to reduce the free monomer content of the polyisocyanate adduct mixture to a level lower than that obtained in the absence of the solvent. There are no examples demonstrating the use of MDI as a diisocyanate suitable for the preparation of polyisocyanate adducts.

[0006] US-A-4,892,920 discloses a method for producing a cyclohexane diisocyanate (CHDI)-based prepolymer that does not contain unreacted CHDI and is essentially free of oligomeric CHDI byproducts.

[0007] US-A-5,202,001 discloses the preparation of polyurethane prepolymers having low levels of residual organic diisocyanates. This example shows prepolymers made from toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylene-bis[(4-cyclohexyl)-diisocyanate] (CHDI).

[0008] US-A-5,703,193 discloses a process for reducing the amount of residual organic diisocyanate monomer in a polyurethane prepolymer reaction product, which involves distillation in the presence of an inert solvent blend having boiling points higher and lower than the monomer. A comparative example shows the removal of MDI monomer from a PTMEG 1000 / MDI prepolymer reaction product.

[0009] US-A-6,133,415 discloses a countercurrent extraction method for producing polyurethane prepolymers. This example shows MDI / PTMEG treated to obtain low free MDI. US-B-6,174,984 discloses a prepolymer of at least one diisocyanate and at least one polyether polyol selected from the group consisting of ethylene oxide homopolymers, propylene oxide homopolymers, and copolymers of ethylene oxide and propylene oxide, wherein the free diisocyanate is reduced to a level of less than 1% of the prepolymer.

[0010] EP-A-0827995 discloses a hot-melt adhesive comprising a polyisocyanate prepolymer prepared by reacting a polyisocyanate having at least two functionalities with a polyol having at least two functionalities, wherein the reaction product comprises at least 90% by mass of "complete" prepolymer and less than 2% by mass of unreacted isocyanate monomer, and the prepolymer has 0.2 to 8% by mass of free NCO functionality. This document teaches the advantages of using a large amount of complete prepolymer, more than 90% by mass.

[0011] US-B-6,866,743 discloses a prepolymer composition that essentially consists of at least 80% by mass of a complete prepolymer and less than 2% by mass of free MDI monomers, and is MDI or TDI based, and is suitable for use in non-structural polyurethane adhesive compositions.

[0012] US-B-6,884,904 discloses an MDI / polypropylene polyether prepolymer composition suitable for use in polyurethane adhesive compositions, comprising essentially at least 80% by mass of a complete prepolymer and less than 2% by mass of free MDI monomers. No polyurethane prepolymer composition containing less than 75% by mass of a complete prepolymer and less than 1.0% by mass of residual diisocyanate monomers is disclosed.

[0013] US-B-6,943,202 discloses a polyurethane prepolymer having an NCO content of at least 70% of the theoretical NCO content for a pure ABA structure, preferably at least 80% of the theoretical NCO content for a pure ABA structure.

[0014] WO-A-01 / 040340 discloses that polyurethane compositions having low levels of monomeric diisocyanate can be prepared in a two-step process, in which a diol component having a molecular weight of less than 2000 and a monomeric diisocyanate having a molecular weight of less than 500 are reacted in the first step. The molar ratio of MDI to polyol is preferably 5:1 to 10:1, which is advantageous for forming a final prepolymer (after removal of solvent and free MDI monomer) having an NCO content of at least about 80% of the theoretical NCO content for a pure ABA structure. The resulting low monomeric polymeric diisocyanate is reacted with a polyol in the second step to form a reactive prepolymer having isocyanate-terminated groups. Such polyurethane compositions are described in this document as useful as binders for reactive one- or two-component adhesives / sealants, which may contain solvents, and are also described as useful for preparing reactive hot melts, provided that the polyol is appropriately selected.

[0015] US-A-2004 / 259968 discloses a composition comprising a polyol and at least one reaction product of a stoichiometric excess of a mixture of an asymmetric polyisocyanate having a molecular weight of 500 or less and NCO functionality of 1.75 to 2.5 and a high molecular weight polyisocyanate. A comparative example not relating to the present invention discloses a prepolymer based on 4,4'-MDI and PPG-750 in a 5:1 ratio, wherein the monomeric MDI residue is <0.1%.

[0016] US-A-2005 / 154172 discloses a polyurethane prepolymer that is a reaction product of IPDI with polypropylene glycol (PPG) at Mw=4200 g / mol and PPG at Mw=6300 g / mol, containing 0.05% by mass of residual IPDI, having an oligomeric adduct content of 44%, and an NCO content of 1.5% by mass. This document does not describe the adhesive properties of the disclosed prepolymer, nor does it describe the use of MDI as a diisocyanate.

[0017] EP-A-1746117 discloses a polyurethane prepolymer that is a reaction product of 4,4'-methylenediphenyl diisocyanate (4,4'-MDI) and a trifunctional polyether polyol (PPO; Lupranool® 2095; prepared by the addition reaction of polypropylene oxide and ethylene oxide with glycerol as the initiator molecule) with Mw = 4350 g / mol, containing 0.083% by mass of unreacted monomer (residual MDI), having a maximum of 80% by mass of complete ABA structure, and having a 2% by mass NCO content.

[0018] US-A-2007 / 060731 discloses that when a defined ABA structure of isocyanate and polyol is constructed, such a defined structure has a favorable effect on the property profile of compact elastomers such as thermoplastic polyurethanes or injectable elastomers, and thus the formation of oligomeric polyurethanes is not desirable. Asymmetric diisocyanates, such as 2,4'-MDI, react with PPG-450 to provide prepolymers with more than 80 area% of diurethanes measured by gel permeation chromatography (GPC). Such asymmetric diisocyanates have low reactivity. 2,4'-MDI is also not easily available on an industrial scale.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Patent Document 13

[0020] In view of the prior art, it is clear that a polyurethane prepolymer with a large amount of "complete" prepolymer and a small amount of oligomer is preferred.

[0021] [[ID=))0]]There has been a long-standing desire to provide a cured polyurethane having a small amount of free diisocyanate monomer and, nevertheless, physical properties equivalent to or better than those of a polyurethane prepolymer having a high NCO functionality, such as tear strength, or adhesive properties, such as high shear strength. Here, surprisingly, in contrast to the long-standing teachings in the prior art, a small amount of residual free diisocyanate monomer of more than 0% by mass and less than 1.0% by mass based on the total mass of the polyurethane prepolymer, and less than 75% by mass of a 2:1 stoichiometric adduct (complete prepolymer) of a diisocyanate and at least one polyol, has been found to exhibit desirable performance significance with respect to a polyurethane prepolymer containing a small amount of residual diisocyanate monomer and at least 75% by mass of a 2:1 stoichiometric adduct of a diisocyanate and at least one polyol. [Means for Solving the Problems]

[0022] The present invention relates to an isocyanate-terminated polyurethane prepolymer composition comprising a polyurethane prepolymer which is a reaction product of the reaction of an excess diisocyanate with at least one polyol, and a free diisocyanate monomer in an amount greater than 0% by mass and less than 1.0% by mass, preferably less than 0.5% by mass, and more preferably less than 0.1% by mass, based on the total mass of the polyurethane prepolymer, wherein the polyurethane prepolymer comprises less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, preferably less than 73% by mass, and more preferably less than 70% by mass, based on the total mass of the polyurethane prepolymer.

[0023] The present invention includes the following embodiments. [Aspect 1] A polyurethane prepolymer composition, (a) A polyurethane prepolymer which is a reaction product of the reaction of an excess diisocyanate with at least one polyol, and (b) Based on the total mass of the polyurethane prepolymer, it contains more than 0% by mass and less than 1.0% by mass of free diisocyanate monomer, Herein, the polyurethane prepolymer has an NCO content of 0.2 to 15% by mass, and the polyurethane prepolymer composition contains less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, based on the total mass of the polyurethane prepolymer, wherein the at least one polyol comprises two types of polypropylene glycol with different molecular weights. [Aspect 2] The polyurethane prepolymer composition according to Embodiment 1, wherein at least one polyol comprises a primary polypropylene glycol having a weight-average molecular weight Mw of 200 to 600 g / mol and a secondary polypropylene glycol having a weight-average molecular weight of 800 to 12,000 g / mol. [Aspect 3] The polyurethane prepolymer composition according to embodiment 1 or 2, wherein the diisocyanate is methylenediphenyl diisocyanate (MDI), paraphenylenedi diisocyanate (PPDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), cyclohexyl diisocyanate (CHDI), isophorone diisocyanate (IPDI), or toluene diisocyanate (TDI). [Aspect 4] The polyurethane prepolymer composition according to embodiment 1 or 2, wherein the diisocyanate is 4,4'-methylenediphenyl diisocyanate (4,4'-MDI). [Aspect 5] The polyurethane prepolymer composition according to embodiment 1 or 2, wherein the prepolymer contains more than 30% by mass and less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol. [Aspect 6] The polyurethane prepolymer composition according to embodiment 1 or 2, wherein free diisocyanate monomers are present in an amount greater than 0% by mass and less than 0.5% by mass based on the total mass of the polyurethane prepolymer. [Aspect 7] A curable polyurethane prepolymer composition comprising the polyurethane prepolymer composition described in Embodiment 1 or 2 and a curing agent. [Aspect 8] The curable polyurethane prepolymer composition according to embodiment 7, wherein the curing agent is a diamine, a polyol, or a blend thereof. [Aspect 9] A method for adhesively joining or sealing two substrates, (1) A step of applying the curable polyurethane prepolymer composition described in Embodiment 7 onto a substrate, and (2) A method comprising the step of bringing a curable polyurethane prepolymer composition applied to a substrate into contact with a second substrate so that bonds are formed. [Aspect 10] An adhesive comprising the curable polyurethane prepolymer composition described in Embodiment 7. [Aspect 11] An adhesive composition comprising the curable polyurethane prepolymer composition described in Embodiment 7.

[0024] The present invention relates to a polyurethane prepolymer composition that has low residual diisocyanate monomer content and high oligomer content, based on the reaction of an excess diisocyanate with at least one polyol.

[0025] The polyurethane prepolymer composition is a product obtained from the reaction of at least one polyol containing "n" (at least 2) OH groups with an excess of diisocyanate. The polyurethane prepolymer reaction product includes an oligomer and a so-called "complete" prepolymer. The high oligomer content required for this prepolymer composition may be expressed as the content of a 2:1 stoichiometric adduct of diisocyanate and polyol, which should be greater than 20% by mass or, conversely, less than 75% by mass, based on the total mass of the prepolymer composition.

[0026] 2:1 stoichiometric adducts (complete prepolymers) of diisocyanates and at least one polyol, as well as methods for preparing them, are widely known and described in the art, for example, in EP-A-0288823, EP-A-0370408, EP-A-0370392, EP-A-0827995, EP-A-1237967, EP-A-1237971, EP-A-1249460, EP-A-1253159, EP-A-1499653, and EP-A-1553118.

[0027] The 2:1 stoichiometric adduct of a diisocyanate and at least one polyol according to the present invention is a stoichiometric end-encapsulation product of one polyol molecule (B) and two diisocyanate molecules (A). The stoichiometric ratio of diisocyanate to polyol in the reaction product is 2:1 in the case of a diol (a bifunctional polyol (B)). The complete prepolymer is essentially an adduct containing only one molecule of polyol (B) in each prepolymer molecule A:B:A (or A2B).

[0028] The oligomer of the present invention, in the case of the bifunctional polyol (B) (n=2), is any species having a composition greater than the perfect 2:1 molecular ratio (A:B:A; diurethane), for example, 3:2 (A:B:A:B:A; triurethane) or 4:3 (A:B:A:B:A:B:A).

[0029] The present invention requires that the polyurethane prepolymer composition, based on the total mass of the polyurethane prepolymer, (1) contains less than 75% by mass, preferably less than 73% by mass, and more preferably less than 70% by mass, a 2:1 stoichiometric adduct of diisocyanate and polyol, and (2) contains more than 0% by mass and less than 1.0% by mass, unreacted, but free, diisocyanate monomer. In a preferred embodiment, the present invention requires that the diisocyanate prepolymer reaction product contains (1) more than 30% by mass, a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, and less than 75% by mass, preferably less than 73% by mass, and more preferably less than 70% by mass, a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, and (2) contains more than 0% by mass and less than 1.0% by mass, unreacted diisocyanate monomer.

[0030] The polyurethane prepolymer reaction product contains 0.2 to 15% by mass, preferably 0.5 to 8% by mass, and more preferably 5 to 7% by mass, of free prepolymer NCO functional groups. The free NCO content is typically determined as mass% according to ASTM D1638-70.

[0031] In one embodiment, the polyurethane prepolymer composition of the present invention contains 0.2 to 15% by mass, preferably 0.5 to 8% by mass, more preferably 5 to 7% by mass of free prepolymer NCO functional groups, and contains more than 0% by mass and less than 1% by mass of unreacted diisocyanate monomer, preferably less than 0.5% by mass, more preferably less than 0.1% by mass.

[0032] In preferred embodiments of the present invention, the polyurethane prepolymer comprises, based on the total mass of the prepolymer, at least 30% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, and less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, preferably less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, more preferably less than 70% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, even more preferably less than 65% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, or conversely, at least 20% by mass of oligomer, preferably at least 25% by mass of oligomer, more preferably at least 30% by mass of oligomer, and even more preferably at least 35% by mass of oligomer. [Modes for carrying out the invention]

[0033] Diisocyanate The diisocyanates of the present invention are not particularly limited. Suitable diisocyanates of the present invention include aliphatic diisocyanates, alicyclic diisocyanates, polycyclic diisocyanates, aromatic diisocyanates, and aliphatic-aromatic diisocyanates.

[0034] In a preferred embodiment, the diisocyanate of the present invention is methylenediphenyl diisocyanate (MDI), paraphenylenedi diisocyanate (PPDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), cyclohexyl diisocyanate (CHDI), isophorone diisocyanate (IPDI), or toluene diisocyanate (TDI).

[0035] In a more preferred embodiment, the polyurethane prepolymer is prepared using a symmetric diisocyanate. In a more preferred embodiment, the polyurethane prepolymer is prepared using 4,4'-methylenediphenyldiisocyanate (4,4'-methylene-bis-(phenylisocyanate)); 4,4'-diphenylmethanediisocyanate (4,4'-MDI).

[0036] polyol The present invention is not limited by the use of a specific polyol, and may use more than one polyol. Suitable polyols for the present invention may be selected from any polyols known in the art. Polyols include compounds having one or more hydroxyl groups. The formation of such polyols is well known in the art.

[0037] In many embodiments, to avoid an increase in viscosity, a diol (with a hydroxyl functionality of 2.0) is preferred over a triol or a polyol having a higher hydroxyl functionality. In some embodiments of the present invention, the polyol includes at least one polyester polyol, at least one polyether polyol, at least one polycaprolactone polyol, at least one polycarbonate polyol, or a combination thereof.

[0038] Preferred polyols are polypropylene oxide-based polyether polyols, also known as polypropylene glycol (PPG), which include, but are not limited to, polypropylene polyether polyols having two or more functionalities and an average equivalent weight of 100 to 8,000. Also included are ethylene oxide-capped PPGs and low-monool-containing PPGs.

[0039] Further polyols that may be used include alkylenediols, such as diethylene glycol (DEG), other bifunctional or polyfunctional alkylene ether polyols, such as poly(tetramethylene ether) glycol (PTMEG), and polyethylene oxide, polyester polyols, polycaprolactone, and polyester polyols derived from terminally hydroxyl-grouped polybutadienes.

[0040] The polyether polyols and polyester polyols described above are commonly used in the production of polyurethane prepolymers. The polyols used in the production of the prepolymer can be blended so that at least one polyol (either a single polyol or a blend) has a weight-average molecular weight (Mw) in the range of about 50 to 16,000 g / mol, preferably 250 to 4,000 g / mol, and preferably 500 to 1,200 g / mol. In another preferred embodiment, at least one polyol comprises two polypropylene glycols having different molecular weights. The average molecular weight can be determined using gel permeation chromatography (GPC).

[0041] In a preferred example, at least one polyol of the polyurethane prepolymer composition of the present invention comprises a primary polypropylene glycol having a weight-average molecular weight Mw of 200 to 800 g / mol, preferably 200 to 600 g / mol, more preferably 400 to 600 g / mol, and a secondary polypropylene glycol having a weight-average molecular weight of 800 to 12,000 g / mol, preferably 800 to 4,000 g / mol, more preferably 800 to 2,000 g / mol.

[0042] Preparation process for polyurethane prepolymers The polyurethane prepolymer according to the present invention is prepared by the reaction of an excess of diisocyanate with at least one polyol. In a preferred embodiment, the polyurethane prepolymer of the present invention is prepared by reacting at least one polyol with an excess of MDI, preferably 4,4'-MDI.

[0043] In some embodiments, the polyurethane prepolymer is prepared by reacting an excess of diisocyanate, preferably MDI, more preferably 4,4'-MDI, with at least one polypropylene glycol.

[0044] The polyurethane prepolymer of the present invention can be prepared by heating a reaction mixture of a polyol and a diisocyanate at 50°C to 150°C for 10 minutes to 24 hours, preferably at 60°C to 100°C for 2 hours to 6 hours.

[0045] Methods for synthesizing polyurethane prepolymers are generally known in the art. Generally, the polyurethane prepolymers of the present invention are produced using standard industrial reaction processes and conditions that are generally known in the art for the production of polyurethane prepolymers.

[0046] In a preferred embodiment, the addition of at least one polyol to the diisocyanate is carried out in a batch rather than dropwise.

[0047] The polyurethane prepolymer of the present invention is typically prepared using an excess of diisocyanate monomer, resulting in a polyurethane prepolymer composition containing unreacted monomers, e.g., unreacted or "free" diisocyanate. The level of free diisocyanate monomer can reach 20% by mass or more based on the polyurethane prepolymer composition.

[0048] In preferred embodiments, the prepolymer reaction is uncatalyzed. The use of a catalyst may result in trace amounts of catalyst residue in the polyurethane prepolymer reaction product, which could affect the curing process.

[0049] The polyurethane prepolymer of the present invention is a "low free monomer" polyurethane prepolymer (also known as "low free," "LF," or "low isocyanate" = "LNCO").

[0050] Those skilled in the art will understand that it has fewer "free" monomer isocyanate groups than conventional polyurethane prepolymers; that is, the polyurethane prepolymer composition of the present invention has less than 1.0% by mass of free diisocyanate monomer based on the total mass of the polyurethane prepolymer.

[0051] Unreacted diisocyanate monomers in the prepolymer reaction product are removed to a concentration of more than 0% by mass and less than 1% by mass, preferably less than 0.5% by mass, and most preferably less than 0.1% by mass, based on the total mass of the polyurethane prepolymer. A polyurethane prepolymer without residual free diisocyanate monomers will have an undesirably high viscosity.

[0052] The amount of free diisocyanate monomer in the prepolymer composition can be determined by common measurement methods, such as HPLC (high-performance liquid chromatography). Furthermore, the amounts of adducts and oligomers can be determined by MALDI-MS.

[0053] Any suitable process can be employed to reduce the amount of free diisocyanate monomer in the polyurethane prepolymer composition to the low levels of the present invention. Various methods are known to reduce and minimize the residual isocyanate content of the polyisocyanate monomer, such as wiped film evaporation, solvent-assisted distillation / co-distillation, molecular sieving, and solvent extraction. Vacuum distillation is preferred, and in particular, thin film evaporation under vacuum or stirred thin film evaporation is preferred.

[0054] Curable polyurethane prepolymer composition The present invention further relates to a curable polyurethane prepolymer composition comprising the polyurethane prepolymer composition of the present invention and at least one curing agent.

[0055] hardening agent Suitable curing agents for the curable polyurethane prepolymer composition of the present invention include diamines, polyols, or blends thereof. Examples of diamines include aromatic and aliphatic diamines, primary and secondary amine-terminated polyether polyols, and bifunctional, trifunctional, and high molecular weight amines.

[0056] Examples of polyols include polyester or polyether polyols, which may be diols, triols, and tetrols having primary, secondary, and / or tertiary alcohol groups. Preferred polyol curing agents are 1,4-butanediol (BDO) or hydroquinone bis(2-hydroxyethyl) ether (HQEE). These polyols may be mixed with diamines.

[0057] The ratio of prepolymer to curing agent is typically in the range of 0.5:1 to 1.5:1, preferably 0.7:1 to 1.2:1, and more preferably 1.1:1 to 0.90:1.

[0058] additives The curable polyurethane prepolymer composition of the present invention optionally comprises further additives, such as catalysts; thickeners; tackifying resins, such as abietic acid, abietic esters, terpene resins, terpene phenol resins, or hydrocarbon resins; fillers, such as silicates, talcanes, calcium carbonate, clay, or carbon black; plasticizers, such as phthalates; thixotropic agents, such as bentone, calcined silica, urea derivatives, fibrillated or pulped short fibers; colorants, such as color pastes and pigments, or desiccants.

[0059] Any catalysts include tertiary amine catalysts and suitable organometallic catalysts, such as catalysts derived from tin, zirconium, and bismuth.

[0060] glue The present invention also provides a method for adhesively joining or sealing two substrates, (1) A step of applying the curable polyurethane prepolymer composition of the present invention onto a substrate, and (2) The method also includes the step of bringing a curable polyurethane prepolymer composition applied to a substrate into contact with a second substrate so that bonds are formed.

[0061] In one embodiment, the polyurethane adhesive composition used in the method of the present invention includes the polyurethane prepolymer reaction product, which can be prepared by reacting a diisocyanate, preferably 4,4'-MDI, with a polypropylene polyether polyol having an average molecular weight of 500 to 1,100 g / mol.

[0062] Substrates that can be bonded with adhesives include cold-rolled steel, aluminum, glass fiber reinforced polyester (FRP), sheet molded compounds (SMC), plastics, wood, and glass.

[0063] Accordingly, the present invention also relates to the use of the curable polyurethane prepolymer composition of the present invention as an adhesive. In a preferred embodiment, the polyurethane prepolymer composition comprises a polyurethane prepolymer obtained by the reaction of excess 4,4'-MDI with at least one polypropylene glycol, and comprises, based on the total mass of the polyurethane prepolymer, more than 0% by mass and less than 1.0% by mass, preferably less than 0.5% by mass, and more preferably less than 0.1% by mass, free 4,4'-MDI monomer, wherein the polyurethane prepolymer comprises, based on the total mass of the polyurethane prepolymer, less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, preferably less than 73% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, and more preferably less than 70% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol.

[0064] In a preferred embodiment, the amount of ABABA oligomer is 25% by mass or more based on the total mass of the polyurethane prepolymer. The present invention also includes the use of the polyurethane prepolymer composition of the present invention for preparing a curable polyurethane prepolymer composition.

[0065] The present invention also includes the use of the polyurethane prepolymer composition of the present invention as a one-component foam (OFC). The present invention also includes the use of the curable polyurethane prepolymer composition of the present invention as an adhesive at room temperature or as a hol-melt adhesive.

[0066] By using the polyurethane prepolymer composition of the present invention in an adhesive composition, an adhesive is provided that, after curing at room temperature for 1 or 7 days, exhibits superior shear strength compared to adhesive compositions based on polyurethane prepolymers not of the present invention having a small amount of oligomer, or conventional polyurethane prepolymers not of the present invention having a large amount of residual diisocyanate monomer, and also exhibits health and safety advantages related to a lower level of volatile diisocyanate monomer, less than 1.0% by mass based on the total mass of the polyurethane prepolymer. [Examples]

[0067] The following materials were used in the examples. [Table 1]

[0068] Adhesion experiment [Table 2]

[0069] method: Free NCO content (%NCO) Free NCO content was measured according to ASTM D1638-70.

[0070] Residual monomer content The amount of free 4,4'-MDI monomer in the polyurethane prepolymer reaction product is measured by HPLC (high-performance liquid chromatography).

[0071] Oligomer content The oligomer content of the polyurethane prepolymer composition is measured using MALDI-MS. The strengths of each structural type are summarized, and the relative amounts are shown in Table 2a. The sample is prepared from a mixture of 20 mg / mL of DCTB (trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile) in THF, 10 mg / mL of the sample in THF, and 20 mg / mL of NaTFA in THF, in a ratio of 10:10:1. Data acquisition is performed in linear mode (positive ions, mass range 300-30000). Data analysis is performed using baseline subtraction (smooth SG7 points, Centroid 0.3 width S / N 1).

[0072] Example 1 (The present invention) 6046 g of 4,4'-methylenediphenyl diisocyanate (4,4'-MDI) was added to a reactor and heated to 50°C. Then, 2896 g of PPG-500 and 1646 g of PPG-1100 were added. The reaction temperature was maintained at 80°C for 4 hours. Excess residual 4,4'-MDI monomer was removed from the reaction product by thin-film distillation under reduced pressure, resulting in a residual 4,4'-MDI level of less than 0.1% by mass and a total NCO content of 6.05% by mass.

[0073] Example 2 (The present invention) 2880g of 4,4'-MDI was added to the reactor and heated to 50°C. Then, 603g of PPG-500 and 1017g of PPG-1100 were added. The reaction temperature was maintained at 80°C for 4 hours. Excess residual 4,4'-MDI monomer was removed from the reaction product by thin-film distillation under reduced pressure, resulting in a residual 4,4'-MDI level of less than 0.1% by mass and a total NCO content of 6.10% by mass.

[0074] Example 3 (Comparative Example) 4,4'-MDI was added to a reactor at 4182 g and heated to 50°C. Then, 443 g of PPG-500 and 1500 g of PPG-1100 were added. The reaction temperature was maintained at 80°C for 4 hours. Excess residual 4,4'-MDI monomer was removed from the reaction product by thin-film distillation under reduced pressure, resulting in a residual 4,4'-MDI level of less than 0.1% by mass and a total NCO content of 5.87% by mass.

[0075] Example 4 (Comparative Example) 1584 g of 4,4'-MDI was added to a reactor and heated to 50°C. Then, 900 g of PPG-500 and 1516 g of PPG-1100 were added. The reaction temperature was maintained at 80°C for 4 hours. The %NCO content of the reaction product was 5.90% by mass. The residual 4,4'-MDI monomer is over 5% by mass. Table 1 shows the %NCO, residual free 4,4'-MDI, and oligomer content of the MDI / PPG polymers of Examples 1-4.

[0076] [Table 3]

[0077] The oligomer content was calculated based on the measured mass percentage of free NCO groups and the molecular weights of the MDI monomer and polyol used, and the results are shown in Table 1a. The calculation of oligomer content is based on the assumption that the oligomers with higher molecular weights are mainly ABABA, and that the amount of even higher molecular weight oligomers, such as ABABABA, is negligible.

[0078] However, the prepolymer compositions were further analyzed using MALDI MS to determine the exact amounts of ABA adducts, as well as ABABA and ABABABA oligomers (where A represents 4,4'-MDI and B represents PPG).

[0079] [Table 4]

[0080] Table 2a shows the amounts of ABA adducts and oligomers from Examples 1-4 as measured by MALDI mass spectrometry. Examples 1 and 2 of the present invention exhibit a residual 4,4'-MDI content of less than 0.1% by mass and an oligomer content of more than 25% by mass based on the total mass of the polyurethane prepolymer. Therefore, the amount of the 2:1 stoichiometric adduct of 4,4'-MDI and PPG is less than 75% by mass based on the total mass of the prepolymer composition in Examples 1 and 2 of the present invention.

[0081] Example 5 The prepolymer compositions of Examples 1 to 4 were evaluated in the following structural adhesive compositions by curing them at room temperature on an aluminum coupon.

[0082] [Table 5]

[0083] The adhesive composition was prepared by mixing parts A and B in an NCO:OH ratio of 1:0.9 while adding 1% by mass of microbeads. The substrate was prepared according to the following substrate preparation process steps.

[0084] (1) Polishing An aluminum coupon was partially polished with 20 / 40 crushed glass at a distance of 6 inches using an 80 psi nozzle. The expected profile on the aluminum coupon was 2–3 mm.

[0085] (2) Solvent cleaning The surface was cleaned with acetone and then air-dried. Then, the adhesive composition is applied to one side of a 2.54 × 12.7 cm aluminum coupon, and then to a length of at least 3.23 cm. 2 It covers the area, and then joins with the second base material coupon, for a total of 3.23 cm 2The lap shear strength was obtained. The samples were cured at room temperature and 50% humidity. The samples were prepared and tested after 1 day and 7 days according to ASTM D10002-10 (Standard test method for determining the apparent shear strength of metal specimens bonded by simple lap with tensile load (intermetallic)). All tests were performed at room temperature.

[0086] [Table 6]

[0087] The results in Table 3 show that adhesive compositions based on the polyurethane prepolymer Examples 1 and 2 of the present invention have higher shear strength after curing for 1 day and 7 days compared to adhesive compositions based on a prepolymer that does not conform to the present invention (Example 3) with a low amount of oligomer, or a conventional product that does not conform to the present invention (Example 4) with a high amount of free diisocyanate monomer.

[0088] Example 6 The adhesive test procedure described in Example 5 was repeated, except that as the third step in the substrate preparation process, the binder was applied to the polished and cleaned surface of the aluminum coupon before applying the adhesive composition, as follows.

[0089] (3) Binder A binder was prepared consisting of a 50:50 blend of methyl ethyl ketone (MEK) and Chemlok® 218 adhesive. Aluminum coupons were immersed in this binder and dried by hanging them vertically. The results of the shear strength test are shown in Table 4.

[0090] [Table 7]

[0091] The data in Table 4 shows that equivalent shear strength can be achieved between the prepolymer composition of the present invention and adhesive compositions based on prepolymer compositions other than those of the present invention, only by employing a process step of applying an additional, undesirable, binder.

[0092] Example 7 Cast elastomers were prepared using the prepolymers of Examples 1-4 by conventional techniques. The polyurethane prepolymer compositions were cured stoichiometrically with 98% 1,4-butanediol (BDO) or hydroquinone bis(2-hydroxyethyl) ether (HQEE), followed by post-curing at 115°C for 16 hours. Physical properties were determined using the following ASTM test methods: hardness (ASTM D2240), split tear (ASTM D-470), trouser tear (ASTM D-1938), die-C tear (ASTM D-624), modulus, breaking strength, and elongation (ASTM D638). The data are shown in Tables 5 and 6.

[0093] [Table 8]

[0094] [Table 9]

[0095] Examples 1 and 2 of the present invention, which are low monomer and high oligomeric prepolymers, exhibit superior split tear, trouser tear, and die-C tear strength compared to Examples 3 and 4, which are not part of the present invention.

[0096] [Table 10]

[0097] Examples 1 and 2 of the present invention, which are low monomer and high oligomer prepolymers, exhibit a higher modulus compared to Examples 3 and 4, which are not part of the present invention.

[0098] [Table 11]

[0099] Example 1 of the present invention, which is a low monomer and high oligomer prepolymer, exhibits a higher modulus compared to Examples 3 and 4, which are not part of the present invention.

Claims

1. A polyurethane prepolymer composition, (a) A polyurethane prepolymer which is a reaction product of the reaction of an excess diisocyanate with at least one polyol, and (b) Based on the total mass of the polyurethane prepolymer, comprising more than 0% by mass and less than 1.0% by mass of free diisocyanate monomers, Herein, the polyurethane prepolymer has an NCO content of 0.2 to 15% by mass, and the polyurethane prepolymer contains less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol, based on the total mass of the polyurethane prepolymer, wherein the at least one polyol comprises two types of polypropylene glycol with different molecular weights.

2. The polyurethane prepolymer composition according to claim 1, wherein at least one polyol comprises a primary polypropylene glycol having a weight-average molecular weight Mw of 200 to 600 g / mol and a secondary polypropylene glycol having a weight-average molecular weight of 800 to 12,000 g / mol.

3. The polyurethane prepolymer composition according to claim 1 or 2, wherein the diisocyanate is methylenediphenyl diisocyanate (MDI), paraphenylenedi diisocyanate (PPDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), cyclohexyl diisocyanate (CHDI), isophorone diisocyanate (IPDI), or toluene diisocyanate (TDI).

4. The polyurethane prepolymer composition according to claim 1 or 2, wherein the diisocyanate is 4,4'-methylenediphenyl diisocyanate (4,4'-MDI).

5. The polyurethane prepolymer composition according to claim 1 or 2, wherein the prepolymer contains more than 30% by mass and less than 75% by mass of a 2:1 stoichiometric adduct of diisocyanate and at least one polyol.

6. The polyurethane prepolymer composition according to claim 1 or 2, wherein free diisocyanate monomers are present in an amount greater than 0% by mass and less than 0.5% by mass based on the total mass of the polyurethane prepolymer.

7. A curable polyurethane prepolymer composition comprising the polyurethane prepolymer composition according to claim 1 or 2 and a curing agent.

8. The curable polyurethane prepolymer composition according to claim 7, wherein the curing agent is a diamine, a polyol, or a blend thereof.

9. A method for adhesively joining or sealing two substrates, (1) A step of applying the curable polyurethane prepolymer composition described in claim 7 onto a substrate, and (2) A method comprising the step of bringing a curable polyurethane prepolymer composition applied to a substrate into contact with a second substrate so that bonds are formed.

10. An adhesive comprising the curable polyurethane prepolymer composition described in claim 7.

11. An adhesive composition comprising the curable polyurethane prepolymer composition described in claim 7.

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