Composition of blocked polyisocyanates, use of said composition, and method of preparation

Abstract

A composition comprising or, alternatively, consisting of: - isocyanates blocked by means of a blocking agent; - optionally one or more technological additives; said isocyanates being polyisocyanates, wherein said polyisocyanates have a molecular weight distribution (MWD) as follows: more than 50% by weight of said polyisocyanates comprise a number of isocyanate units ≥ 3, said isocyanate units being covalently bonded with each other; and less than 50% by weight of said polyisocyanates comprises molecules of identical molecular weight; said MWD being determined by means of SEC-MALS-DRI.

Description

[0001] Composition of blocked polyisocyanates, use of said composition, and method of preparation

[0002] The present invention relates to a composition comprising or, alternatively, consisting of isocyanates blocked by means of a blocking agent and, optionally, one or more additives (e.g., technological additives).

[0003] Furthermore, the present invention relates to an adhesive material or a coating varnish for a substrate comprising said composition and at least one resin containing hydroxyl or amine groups, for example polyesters, polyols, or polyacrylates.

[0004] Furthermore, the present invention relates to a use of said composition as a cross-linking agent, preferably for a resin containing hydroxyl or amine groups, for example polyesters, polyols, or polyacrylates.

[0005] Furthermore, the present invention relates to a method for preparing said composition.

[0006] Methyl ethyl ketoxime (or 2-butanone oxime, CAS No. 96-29-7; in short, “MEKO”) is a colourless liquid that is the oxime derived from methyl ethyl ketone.

[0007] MEKO is mainly used as an anti-skinning agent for oil and latex paints and coatings, as it is able to prevent the formation of solid skins above said paints and said coatings. The functioning of MEKO takes place through a bond with drying agents (in particular metal salts) that catalyse the oxidative cross-linking of the oils contained in the paints and in coatings. Once the paint or the coating is applied to a surface, MEKO evaporates, thus allowing the drying process to proceed.

[0008] MEKO is also widely used as an isocyanate blocking agent in automobile electrodeposition coating, in painting works, as a curing agent for silicone rubber due to its outstanding water and heat resistance, in fabric treatment in combination with a non-fluorinated resin due to the water repellency properties or in combination with a fluorinated resin due to the water repellency and / or oil repellency properties, and in the printing industry as a fixative.

[0009] However, MEKO presents several significant hazards to human health. It has in fact been the subject of the evaluation process (SEv; Substance Evaluation process) whose outcome, reported in the Substance Evaluation Report, led to the drafting of a proposal for harmonized classification (CLH) for the substance.

[0010] On the basis of this proposal, ECHA's Risk Assessment Committee (RAC) in September 2018 adopted the opinion to classify MEKO as Care. 1 B, H350: may cause cancer.

[0011] The same process has also led to the attribution of the following hazards: Acute Tox. 3, H301 : toxic if swallowed; Acute Tox. 4, H312: harmful in contact with skin; Skin Sens. 1 , H317: may cause an allergic skin reaction. 1 , H318: Causes serious eye damage; Skin Irrit. 2, H315: causes skin irritation; STOT SE 3, H336: may cause drowsiness or dizziness; STOT SE 1 , H370 (upper respiratory tract): causes organ damage; and STOT RE 2, H373 (blood system): may cause organ damage in case of prolonged or repeated exposure.

[0012] The corresponding inclusion in Annex VI of Regulation (EC) No. 1272 / 2008 (CLP) entered into force with the 15th ATP in August 2020. As of March 2022, the obligation of classification and labelling as Care. 1 B (H350) for mixtures containing the substance MEKO in concentrations exceeding 0.1 % will therefore come into force.

[0013] US 11 ,091 ,584 B2, US 2013 / 190437 A1 , JP 2 975950 B2, WO 2015 / 025776 A1 , US 2008 / 033086 A1 and US 2022 / 267636 A1 belong to the prior art.

[0014] The Applicant, after long and intense research and development activity, has identified some blocking agents that might be used as an alternative to MEKO and that could provide an adequate response to the existing limitations, drawbacks and problems.

[0015] In particular, the compounds identified in the present invention possess significantly lower toxicity characteristics with respect to MEKO, exhibit similar and in some cases superior properties to the currently used compounds, and are obtained from precursors that are normally available on the market in large amounts and at an acceptable cost, even if - at least at present - higher than that of MEKO.

[0016] Therefore, the subject matter of the present invention is a composition comprising or, alternatively, consisting of isocyanates blocked by a blocking agent and, optionally, one or more additives (e.g., technological additives), having the characteristics as defined in the accompanying claims.

[0017] It is further the subject matter of the present invention an adhesive material or a coating varnish for a substrate comprising said composition and at least one resin containing hydroxyl or amine groups, e.g., polyesters, polyols, or polyacrylates, having the characteristics as defined in the accompanying claims.

[0018] It is further the subject matter of the present invention a use of said composition as a cross-linking agent, preferably for a resin containing hydroxyl or amine groups, e.g., polyesters, polyols, or polyacrylates, having the characteristics as defined in the accompanying claims.

[0019] Furthermore, the present invention relates to a method for preparing said composition.

[0020] Preferred embodiments of the present invention will be described hereinafter by way of example, and therefore not by way of limitation with the aid of the figures, wherein:

[0021] - Fig. 1 : overlapping of MALS (90°) and DRI detector signals of the sample LAB 290323;

[0022] - Fig. 2: calibration curve Log(M) = f(V) for the sample LAB 290323;

[0023] - Fig. 3: differential molecular weight distribution (MWD) of the sample LAB 290323;

[0024] - Fig. 4: Cumulative MWD of the sample LAB 290323.

[0025] Therefore, the subject matter of the present invention is a composition comprising or, alternatively, consisting of: - isocyanates blocked by means of a blocking agent;

[0026] - optionally one or more additives (e.g., technological additives); said isocyanates being polymers of isocyanate units (polyisocyanates), wherein said isocyanate units are joined together by one or more urea bonds (-NH-CO- NH-), and wherein said polyisocyanates have a molecular weight distribution (MWD) as follows:

[0027] - more than 50% by weight of said polyisocyanates comprise a number of isocyanate units > 3, said isocyanate units being covalently bonded with each other; and

[0028] - less than 50% by weight of said polyisocyanates comprises molecules of identical molecular weight; said MWD being determined by SEC-MALS-DRI, wherein SEC is size exclusion chromatography connected to a multi-angle light scattering (MALS) detector and to a differential refractometer (DRI).

[0029] It should be specified that knowledge of the dispersity (D) of a polymer alone - defined as D = Mw / Mn- is not sufficient information to assess whether polyisocyanates have a molecular weight distribution as indicated above. In fact, to understand if more than 50% by weight of polyisocyanates comprise a number of isocyanate units > 3, and whether less than 50% by weight of said polyisocyanates comprise molecules of identical molecular weight, it is necessary to know the entire molecular weight distribution (cumulative MWD) from which the content of oligomers up to trimer and the content of macromolecules of identical molecular weight are then calculated.

[0030] It should further be noted that a determination by SEC-MALS-DRI provides absolute values, and thus independent of an external calibration with a standard.

[0031] In terms of performance, the composition which is the subject matter of the present invention envisages the presence of a plurality of isocyanate groups (- NCO) which ensure better surface adhesion. In fact, a single polyisocyanate polymer molecule comprises a series of distinct anchoring points which increase the adhesion thereof with respect to single isocyanate molecules (monomers) which have a single anchoring point -NCO.

[0032] With regard to the methodology for determining said MWD, it should be noted that a MALS signal depends on molecular weight and concentration. Therefore, in order to calculate the molecular weight of each polyisocyanate molecule, it is necessary to determine a concentration of said molecule in each fraction (slice) of the chromatogram. Said concentration can be calculated from each DRI signal.

[0033] Preferably, said MWD is calculated from a cumulative MWD.

[0034] The isocyanate unit is preferably the repeating unit of the polyisocyanate. Said isocyanate units are preferably monomers or oligomers, more preferably dimers or trimers.

[0035] Preferably, said composition comprises said blocked isocyanates in an amount comprised from 10% to 90% by weight, more preferably comprised from 30% to 85% by weight, even more preferably comprised from 50% to 80% by weight, with respect to the total weight of said composition.

[0036] More preferably, said polyisocyanates are either bio-based or comprise biobased isocyanate units. "Bio-based" means that the polyisocyanates are obtained from biomass, preferably through bio-refining and fermentation processes.

[0037] Said size exclusion chromatography is preferably HPLC / SEC, where HPLC is high-performance liquid chromatography.

[0038] Said DRI is preferably a detector preceding or following the MALS detector, more preferably said DRI is placed in series with and after said MALS detector.

[0039] By way of example, the SEC system used is an "Alliance 2695" separation module from Waters Corporation (USA), equipped with a "MALS Heleos II" photometer from Wyatt Technology Corp. (USA) and with a "Waters 2414" DRI detector from Waters Corporation (USA), in an Alliance 2695 - MALS Heleos II - Waters 2414 series set-up. The flow accuracy of the Alliance 2695 separation module pump is < 0.1 %.

[0040] Experimental methodologies that can be used for SEC-MALS determinations are, for example, illustrated in:

[0041] - R. Mendichi, A. Giacometti Schieroni; “Use of a multi-detector size exclusion chromatography system for the characterization of complex polymers", TransWorld Research Network, S. G. Pandalai Ed., Trivandrum, India, Current Trends in Polymer Science, Vol. 6, p. 17-32 (2001 ); and - P. J. Wyatt; “Light Scattering and absolute characterization of macromolecules" ,

[0042] Anal. Chim. Acta, 1993, 272, 1 -40.

[0043] Preferred experimental conditions of the size exclusion chromatography (SEC) are summarised in Table A below.

[0044] Table A

[0045] Preferred experimental conditions of the multi-angle light scattering (MALS) detector are summarised in Table B below.

[0046] Table B

[0047] A MALS detector coupled to a DRI detector allows to obtain the absolute molecular weight (M) and the size of the polyisocyanates (i.e. , the mean square radius <s2>1 / 2), hereafter referred to as the radius of gyration (Rg), of each eluted fraction. The MALS calibration constant can be calculated with ultrapure toluene solvent assuming a Rayleigh factor R(0) = 1.406-1 O’5cm-1. The normalisation of the 18 photodiodes can be performed by measuring the angular scattering intensity of a narrow MWD standard of polystyrene (PS) (Mp= 9.6 kg / mol, Rg= 2.0 nm; Mw / Mn< 1 .03), which is assumed to act as an isotropic scatterer.

[0048] With regard to the differential refractometer detector (DRI), the increase in the specific refractive index, dn / dc, with respect to the solvent (preferably THF) is measured - preferably off-line - by means of a Chromatix KMX-16 differential refractometer. Said blocking agent is preferably selected from the group consisting of:

[0049] (i) optionally 2-pentanone oxime (CAS No. 623-40-5);

[0050] (ii) 4-methylpentane-2-one oxime (CAS No. 105-44-2);

[0051] (iii) 5-methyl-3-heptanone oxime (CAS No. 22457-23-4); and

[0052] (iv) a mixture of two or more of (i)-(iii).

[0053] Within the present description, the term “blocked isocyanates” means the reaction products between an isocyanate and said blocking agent, such that at least one isocyanate function is blocked (non-reactive). Similarly, a "blocked polyisocyanate" is a reaction product between a polyisocyanate and a blocking agent, such that at least one isocyanate function of said polyisocyanate is blocked (non-reactive).

[0054] Preferably, said 2-pentanone oxime is not obtained by means of an ammoxidation reaction.

[0055] More preferably, said mixture (iv) comprises (iii) 5-methyl-3-heptanone oxime in combination with:

[0056] (i) 2-pentanone oxime; and / or

[0057] (ii) 4-methylpentane-2-one oxime.

[0058] Preferably, in said mixture (iv):

[0059] - a (iii):(i) or (iii):(ii) by weight ratio is comprised from 20:1 to 1 :20, preferably comprised from 10:1 to 1 :10, more preferably comprised from 5:1 to 1 :5; or

[0060] - a [(iii)]:[(i)+(ii)] by weight ratio is comprised from 20:1 to 1 :20, preferably comprised from 10:1 to 1 :10, more preferably comprised from 5:1 to 1 :5.

[0061] Said isocyanates are preferably selected from the group consisting of:

[0062] (a) 1 ,5-pentamethylene diisocyanate (PDI) and polymers thereof, preferably trimers, optionally bio-based;

[0063] (b) toluene diisocyanate (TDI) and adducts thereof, preferably TDI trimers; (c) polyisocyanates derived from hexamethylenediisocyanate (HDI) obtained by means of trimerization, biuretization and / or allophanatization process / es;

[0064] (d) polyisocyanates derived from isophorone diisocyanate (IPDI) obtained by means of trimerization, biuretization and / or allophanatization process(es);

[0065] (e) 4,4'-methylene dicyclohexyl diisocyanate (H12MDI);

[0066] (f) trimethyl hexamethylene diisocyanate (TMDI);

[0067] (g) 1 ,4-cyclohexyl diisocyanate (CHDI);

[0068] (h) tetramethyl xylene diisocyanate (TMXDI);

[0069] (i) hexamethylene-1 ,6-diisocyanate; and

[0070] (i) any mixture of two or more selected from (a)-(h).

[0071] Preferably, said (d) polyisocyanates derived from isophorone diisocyanate (IPDI) obtained by trimerization, biuretization and / or allophanation process(es) comprise or, alternatively, consist of oligomerization products of 3- isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate and butane-1 -ol and pentane-1 -ol and 2-ethylhexane-1-ol, of allophanate type.

[0072] More preferably, said (d) comprise the product EC I List no.: 933-047-9, comprising or consisting of the mixture of compounds illustrated in the following general formula (II): wherein R is an alcoholic residue of butane-1 -ol and pentane-1 -ol and 2- ethylhexane-1 -ol. Said isocyanates are more preferably selected from the group consisting of:

[0073] (a) 1 ,5-pentamethylene diisocyanate (PDI) and polymers thereof, preferably trimers, optionally bio-based;

[0074] (b) adducts, preferably trimers, of toluene diisocyanate (TDI) obtained from the reaction between trimethylolpropane and toluene diisocyanate, isocyanurate from hexamethylene diisocyanate (HDI) and isocyanurate from isophorone disocyanate (IPDI), more preferably a reaction product between trimethylolpropane and a mixture of isomers 2,4 toluene diisocyanate and 2,6 toluene diisocyanate, even more preferably said isomers being in a ratio comprised from 90:10 to 70:30, from 85:15 to 75:15 by weight, for example of 80:20 by weight;

[0075] (c) hexamethylene-1 ,6-diisocyanate or oligomers thereof (e.g. , dimers or trimers); and

[0076] (j) a mixture of (a)-(c).

[0077] Said composition comprising or alternatively consisting of blocked isocyanates and optionally one or more additives is preferably a solution, a suspension or a dispersion in an organic solvent.

[0078] More preferably, said organic solvent is an aromatic or aliphatic hydrocarbon solvent, optionally aprotic.

[0079] In accordance with various embodiments, said organic solvent comprises or consists of a naphtha, preferably the compound identified by CAS No. 64742-95- 6, or a butoxyethyl acetate, preferably 2-butoxyethyl acetate (i.e. , the compound identified by CAS No. 112-07-2), or mixtures thereof.

[0080] Preferably, when said organic solvent comprises or consists of a mixture of said naphtha and said butoxyethyl acetate, said butoxyethyl acetate is present in an amount > 10% by weight with respect to the total weight of said organic solvent, for example in an amount > 20% by weight, > 50% by weight, or > 80% by weight.

[0081] Said composition is preferably devoid of methyl ethyl ketoxime (MEKO). In accordance with an embodiment, said blocking agent is at least one imidazole compound of the following general formula (I): wherein:

[0082] R1 = H or CH3;

[0083] R2 = H, CH3, CH2CH3or CH(CH3)2.

[0084] In this description the expression “at least one imidazole compound” means that said composition may comprise a single imidazole compound of general formula (I), or a mixture of two or more imidazole compounds of general formula (I) having R1 and / or R2 different from each other.

[0085] Preferably, said imidazole compound or an imidazole compound of said mixture is 2-isopropyl-1 H-imidazole (CAS No. 36947-68-9) or 2-ethyl-4-methylimidazole (CAS No. 931 -36-2).

[0086] More preferably, said composition comprises a mixture of 2-isopropyl-1 H- imidazole and 2-ethyl-4-methylimidazole.

[0087] Even more preferably, said imidazole compound or an imidazole compound of said mixture is 2-ethyl-4-methylimidazole.

[0088] According to other embodiments, said blocking agent is s-caprolactam and / or dimethyl malonate and / or 3,5-dimethyl pyrazole (DMP).

[0089] Furthermore, the subject matter of the present invention is an adhesive material or a coating varnish for a substrate comprising said composition and at least one resin containing hydroxyl or amine groups, for example polyesters, polyols, or polyacrylates.

[0090] Preferably, said substrate is selected from the group consisting of: paper, cardboard, natural fabrics, synthetic fabrics, non-woven fabric, carpets, leather, artificial leather, sheet metal, wood, glass, polymeric materials (e.g., PVC), building materials, bricks, tiles, natural stone, reconstituted stone, ceramics, plasters, concrete, cement, mortar, metals and plastics.

[0091] Said adhesive material or said coating varnish are used - by way of non-limiting example - in the automotive industry, for coil coatings, for making industrial enamels, in the packaging industry (such as cans, glass containers, etc.).

[0092] It is further the subject matter of the present invention a method for preparing said composition. Said method comprises the following steps:

[0093] (I) contacting isocyanate units (monomers or oligomers, e.g., dimers or trimers) with an organic solvent to give a liquid mixture;

[0094] (II) adding a polymerisation catalyst, e.g., 1 ,4-diazabicyclo[2.2.2]octane, to the liquid mixture of step (I);

[0095] (III) heating the product of step (II) to a temperature equal to or greater than 50 °C, preferably equal to or greater than 65 °C, and then adding water as a reagent - i.e., in a stoichiometric amount - to give polyisocyanates and carbon dioxide; wherein, in said polyisocyanates, said isocyanate units are joined together by one or more urea bonds (-NH-CO-NH-);

[0096] (IV) reacting at least one blocking agent with the polyisocyanates of step (III) to give polyisocyanates blocked by the blocking agent; preferably said blocking agent being as described in any one of the preceding embodiments (an oxime, and / or an imidazole compound, and / or s- caprolactam, and / or dimethyl malonate, and / or 3,5-dimethyl pyrazole);

[0097] (V) optionally adding one or more additives to the blocked polyisocyanates obtained from step (IV).

[0098] Preferably, said water is demineralised, deionised or distilled water. More preferably, said water as a reagent is present in a stoichiometric amount to form, in the presence of the polymerisation catalyst, polyisocyanates having a molecular weight distribution (MWD) according to the present invention.

[0099] By way of example, a technological additive that can be used in step (V) could be or comprise an organic solvent, e.g., to dilute said polyisocyanates blocked by the blocking agent.

[0100] Preferably, step (III) comprises the following sub-steps:

[0101] (III. A) reaction (1 ) between an isocyanate group of an isocyanate unit Ri and a water molecule to give an amine and carbon dioxide:

[0102] Ri-NCO + H2O R1-NHCO-OH R1-NH2 + CO2 (1 )

[0103] (III.B) reaction (2) between said amine of step (III. A) and an isocyanate group of another isocyanate unit R2 to give said one or more urea bonds:

[0104] R2-NCO + R1-NH2 R2-NHCO-NH-R1 (2)

[0105] The isocyanate units R1 and R2 can be independently selected, whereby they may be the same or different according to different embodiments.

[0106] Some examples of the present invention are provided below by way of nonlimiting example.

[0107] EXAMPLES.

[0108] The blocking agents illustrated below were reacted with the following commercially available isocyanates:

[0109] - Desmodur® CQ ultra N 7300 (produced by Covestro Deutschland AG): a biobased 2-ethyl-1 -hexanol blocked 1 ,5-pentamethylene-diisocyanate homopolymer, i.e. , obtained from biomass. Desmodur® CQ ultra N 7300 contains the compound identified by CAS No. 1976005-08-9 (1 ,5-pentamethylene- diisocyanate homopolymer (trimer)) in an amount comprised from 99% to 100% by weight, preferably about 100% by weight (apart from unavoidable impurities); - Polurgreen MT 100 (produced by S.A.P.I.C.I. S.p.A., which is part of Sun Chemical DIC Group): a hexamethylene-1 ,6-di isocyanate homopolymer (identified by CAS No. 28182-81-2), more precisely hexamethylene-1 ,6- diisocyanate oligomer in an amount comprised from 80% to 100% by weight, and hexamethylene-1 , 6-diisocyanate (identified by CAS No. 822-06-0) in an amount < 0.1 % by weight;

[0110] - Desmodur® Ultra N 3300 (manufactured by Covestro AG): a homopolymer (trimer) of hexamethylene 1 , 6-diisocyanate (CAS No. 28182-81 -2; EC I List No.: 931 -274-8);

[0111] - Polurgreen AD 01 (produced by S.A.P.I.C.I. S.p.A., which is part of the Sun Chemical DIC Group): a toluene diisocyanate (TDI) adduct, in particular a reaction product of trimethylolpropane and toluenediisocyanate (mixture of the isomers 2,4 and 2,6 in an 80:20 weight ratio).

[0112] The polyisocyanates according to the invention were obtained by polymerising Polurgreen MT 100 in a controlled manner, and blocking the polyisocyanates with blocking agents. Polyisocyanates blocked with 2-pentanone oxime (LAB 070623A)

[0113] In a 4-neck flask provided with a mechanical stirrer, coolant and thermometer, 50 g Polurgreen MT 100, 0.1 g 1 ,4-diazabicyclo[2.2.2]octane (TEDA; CAS 280-57- 9) as catalyst, and 12 g Solvesso 100 as solvent are loaded under nitrogen flow.

[0114] The solution is heated to 70°C and then 0.38 g of demineralised water is added drop by drop. The development of CO2 is observed. Titration after 3.5 hours of reaction at 70°C shows a weight percentage of isocyanate groups (-NCO) of 14.928% (theoretical value: 14.8%).

[0115] At a temperature comprised from 68 °C to 74 °C, 21 .95 g of 2-pentanone oxime is added drop by drop. Once the addition of the oxime is complete, a 10-minute reaction is carried out at 70 °C. IR analysis confirms the completion of the reaction with disappearance of the isocyanate group peak. It is cooled to about 50 °C, diluted with 11 .08 g of Solvesso 100 solvent to obtain a concentration of 75%.

[0116] Examples 2-5: Polyisocyanates blocked with other blocking agents

[0117] Proceed as in Example 1 , loading the following substances into the flask in the amounts (expressed in grams (g)) indicated in Table 1 below. For the sake of completeness, information on the previous Example 1 (LAB 070623A) is also given.

[0118] Table 1

[0119] Reference examples 6-8: Blocked isocyanates corresponding to Examples 1 -5. Isocyanates corresponding to the previous examples were further prepared with the difference that the isocyanates are non-polymerised isocyanate units, whereby the reactions are conducted in the absence of a catalyst (TEDA) and demineralised water. Experimentally, proceed by loading the amounts of isocyanate and solvent indicated in Table 2 below (amounts in grams (g)) into a 4-neck flask provided with a mechanical stirrer, coolant and thermometer, under nitrogen flow. The solution is heated to 68 °C and then the amount of blocking agent is added drop by drop over a period of one hour - maintaining a temperature range comprised from 68 °C to 74 °C. Once the addition of the blocking agent is complete, a 10- minute reaction is carried out at 70 °C. The IR analysis confirms the completion of the reaction. It is cooled to 50 °C, and finally diluted with the indicated amount of solvent to obtain a 75% concentration.

[0120] Table 2

[0121] Examples 9-13: Blocked isocyanates corresponding to Examples 6-8 using biobased isocyanates falling within the scope of the present invention.

[0122] Isocyanates corresponding to Examples 6-8 were further prepared, with the difference that the isocyanates are bio-based, i.e. , obtained from biomass. Experimentally, the amounts of bio-based isocyanate and solvent indicated in Table 3 below (amounts in grams (g)) into a 4-neck flask provided with a mechanical stirrer, coolant and thermometer, are loaded under nitrogen flow. The solution is heated to 68 °C and the indicated amount of blocking agent is added drop by drop in about one hour. IR analysis confirms the completion of the reaction. It is cooled to about 50 °C and finally diluted with the specified amounts of solvent.

[0123] Table 3

[0124] Other tests were also conducted in which a mixture of Solvesso 100 and ethyl 2- butoxy acetate (50:50 by weight) or ethyl 2-butoxy acetate alone were used as reaction solvents and in the same amounts. In dilution, either Solvesso 100 or 2- butoxyethyl acetate was used. The results of such tests are in line with those illustrated in this disclosure.

[0125] Example 14: Experimental verification of the number of isocyanate units and polyisocyanate molecules with identical molecular weight

[0126] The experimental conditions of the size exclusion chromatography (SEC), the multi-angle light scattering detector (MALS) and the differential refractometer detector (DRI) are as illustrated in the disclosure above (Table A, Table B, etc.).

[0127] LAB sample 290323 according to the invention comprises polyisocyanates blocked with 5-methyl-3-heptanone oxime. It is calculated that the isocyanate unit used (repetitive unit: hexamethylene-1 ,6-di isocyanate) has a molecular weight of 479 g / mol. The data reported are evaluated on three different sample solutions and three independent analyses.

[0128] Fig. 1 shows an overlapping of the MALS (90°) and DRI detector signals of the product LAB 290323.

[0129] The chromatogram of sample LAB 290323 consists of eleven components (peaks or shoulders), identified by a progressive number from (1 ) to (11 ). The MALS signal depends - inter alia - on molecular weight and concentration; the DRI signal depends only on concentration and it is straightforward to assign the components of the chromatogram to the polymer, low molecular weight oligomers and foreign components or "other chemicals". From a preliminary qualitative analysis of the chromatogram of the sample LAB 290323, the following assignments can be made: - Components (1 ) to (7): polymers and oligomers;

[0130] - Components (8) to (9): residues of reagents and / or additives and / or solvents;

[0131] - Components (10) to (11 ): system peaks related to the THF mobile phase without interest in the sample analysis. Preliminarily, the composition of the sample LAB 290323 was obtained by integration of nine chromatogram components. Table 4 below shows the composition of such a sample obtained from chromatogram integration. On the basis of previous assignments, it was deduced that such a sample consists of approximately 75.5% by weight of polymeric and oligopolymeric components, and approximately 24.5% by weight of residues and / or additives and / or solvents.

[0132] Table 4

[0133] The DRI curve of Fig. 1 shows that the polymeric components (1 ) to (5) and oligopolymeric components (6) to (7) are well separated from the low molecular weight foreign components ('Others') (8) to (9). Consequently, it is believed that an accurate characterisation of MWD is possible using an absolute calibration curve of the MALS detector of the type:

[0134] Log(M) = f(V) wherein M is the molecular weight, and V is the elution volume.

[0135] The calibration curve for the sample LAB 290323, constructed from external standards, is shown in Fig. 2.

[0136] In addition to molecular weight and concentration, the MALS signals also depend on the increase in the specific refractive index in accordance with the following equation (I):

[0137] Hi = KLS ■ (dn / dc)2■ M, ■ c, (I) wherein: Hi is the height of the scattered light signal of each eluted fraction i; KLS is a constant containing all the instrumental and physical-chemical parameters; dn / dc is the specific refractive index increment; Mi is the molecular weight of the eluted fraction i (expressed in g / mol); is the concentration of the eluted fraction i. For the sample LAB 290323 dissolved in THF dn / dc = 0.106 mL / g.

[0138] Table 5 below summarises the most important findings of the sample LAB 290323 obtained by means of SEC-MALS. Table 5 shows: molecular weight of the chromatogram peak (Mp); three molecular weight averages (numerical average molecular weight Mn, weight average molecular weight Mw, weight average molecular mass Mz); polydispersity indices (Mw / Mnand Mz / Mw), and the value "Rec. Mass", the latter being the mass of the sample (polymers and oligomers) recovered from the SEC columns, calculated from the area of the DRI chromatogram after calibration and expressed as a percentage of the injected mass. The relative standard deviation of the sample LAB 290323, calculated from three independent SEC-MALS-DRI characterisations, was found to be: 2.5% for the mean Mn, 2.4% for the mean Mw, and 2.5% for the mean Mz.

[0139] Table 5 From Table 5 above, it can be seen that the MWD of the sample LAB 290323 is large, and that the recovered sample mass is substantially complete by virtue of the foreign component content (see Table 4 above).

[0140] The differential MWD and cumulative MWD of the sample LAB 290323 are respectively shown in Fig. 3 and Fig. 4: Fig. 3 shows the molecular weight peaks (Mp) of seven polymer components; Fig. 4 shows the limit M = 1 .437 g / mol which corresponds to polyisocyanate trimer (number of isocyanate units = 3).

[0141] Table 6 below summarises the composition of the sample LAB 290323 (polymers and oligomers). For each component, Table 6 shows: i) type of component; ii) molecular weight (M); iii) normalised relative content (%) excluding residues and additives (peaks (8)-(9) of Fig. 1 ; (iv) degree of polymerisation DP(n) assuming repeating units with molecular weight M = 479 g / mol.

[0142] Table 6

[0143] The sample LAB 290323 has a molecular weight distribution (MWD) according to the present invention in that:

[0144] - the dimer content (n = 2) of isocyanate calculated from the cumulative MWD is 35.6% by weight, whereby more than 50% by weight of said polyisocyanates comprise > 3 isocyanate units;

[0145] - the amount of molecules of identical molecular weight, calculated from the cumulative MWD, is approximately 37.7% by weight, viz., less than 50% by weight of all the polyisocyanate molecules.

[0146] Example 15: Experimental determination of the deblocking temperatures (T deblocking) of isocyanates and polyisocyanates blocked with imidazole compounds

[0147] A DSC (Differential Scanning Calorimetry) study was performed on the blocked isocyanates and blocked polyisocyanates to determine the deblocking temperatures thereof. The instrument used is Discovery DSC25AUTO TA INSTRUMENTS (WATERS CORPORATIONS) Serial No. DSC2A-01063.

[0148] The proposed DSC method consists of preparing the blocked isocyanates in a nitrogen atmosphere and then performing the following temperature ramps:

[0149] - a first temperature ramp from 25 °C to 250 °C at 10 °C / min, thanks to which a change in slope of the profile can be observed which represents the beginning of the deblocking temperature;

[0150] - cooling the sample to 25 °C;

[0151] - a second temperature ramp from 25 °C to 250 °C at 10 °C / min, thanks to which a complete deblocking of the isocyanates can be observed. The results are illustrated in Table 7 below. Reference samples are shown in this table.

[0152] Table 7

[0153] In general, the reactions between isocyanates and imidazoles result in good reaction kinetics, and the deblocking temperature for both imidazoles tested is comprised in the range from 89.9°C to 98°C.

[0154] With regard to the appearance of the blocked isocyanates, the samples LAB 220621 and LAB 230621 are slightly yellowish.

[0155] The deblocking temperatures of the blocked polyisocyanates - the subject matter of the present invention - corresponding to those shown in Table 7 are lower than those of the corresponding isocyanates.

[0156] Example 16: Experimental determination of the deblocking temperatures (T deblocking) of isocyanates and polyisocyanates blocked with oximes

[0157] Proceed as in Example 15 to determine the deblocking temperatures. The results are illustrated in Table 8 below. Reference samples are shown in this table. Table 8

[0158] In all the products obtained, the colouration was white. The reactivity of all oximes with both isocyanates tested is high.

[0159] From the above data it emerges that the three oximes (i), (ii), (iii) have very promising characteristics to be used as blocking agents in isocyanates due to their classification, reactivity, and due to the colouration of the final products obtained.

[0160] The temperature values in Table 8 suggest that the three oximes (i), (ii), (iii) may also be used in combination in a single composition to modulate the deblocking temperatures as a function of contingencies, so as to allow flexibility necessary to optimize the processes of use of such compositions. Furthermore, as can be noted, the deblocking temperatures are not particularly high. This aspect is particularly important with a view of optimizing energy consumption and improving process productivity.

[0161] The deblocking temperatures of the blocked polyisocyanates - the subject matter of the present invention - corresponding to those shown in Table 8 are lower with respect to those of the corresponding isocyanates.

[0162] Table 9 below shows the temperatures of the deblocking start for the samples LAB 050623A and LAB 290323 - according to the invention - indicated above.

[0163] Table 9

[0164] Table 9 shows that, in the presence of polyisocyanates, the application efficiencies of the compositions are improved, and there is further evidence of lower deblocking temperatures. This last aspect is particularly important with a view to optimising energy consumption. Example 17: Experimental determination of the deblocking temperatures (T deblocking) of polyisocyanates blocked with oximes

[0165] Proceed as in Example 15 to determine the deblocking temperatures.

[0166] The results are illustrated in Table 10 below. Table 10

[0167] In all the products obtained, the colouration was white. The reactivity of all the oximes with the tested polyisocyanate is high.

[0168] The results obtained are in line with the previous tests. It should be noted that the tests carried out on bio-based PDI reveal relatively low deblocking temperatures, with important consequences with a view to optimizing energy consumption and improving process productivity. With the same isocyanate, lower deblocking temperatures are achieved by increasing the chain length of the oxime blocking agent. Example 18: Experimental tests related to the viscosity of the polyisocyanates which are the subject matter of the present invention

[0169] The viscosities determined by means of rheometer for some samples are shown in Table 11 below. LAB 110423 is a reference sample (ref.), while LAB 290323 and LAB 050623A are according to the invention (inv.). Table 11

[0170] The samples LAB 290323 and LAB 050623A show a higher viscosity with respect to the corresponding reference sample, but regardless of the same order of magnitude.

[0171] Table C below shows the rheometer model and analytical parameters used for the viscosity determination.

[0172] Table C The analytical method used is shown in Table D below.

[0173] Table D

[0174] Advantageously, from a regulatory perspective, the compounds of the present invention are considered polymers in the REACH classification, and therefore have a simplified market placement procedure.

[0175] Advantageously, for all the compounds which are the subject matter of the present invention, the deblocking temperatures are not particularly high.

[0176] This aspect is an application advantage and is particularly important with a view to optimising energy consumption and improving process productivity.

[0177] Advantageously, for all the compounds which are the subject matter of the present invention, the presence of differentiated deblocking temperatures allows to obtain a series of flexibilities, for example necessary to optimise the processes of use of such compositions. Advantageously, the composition which is the subject matter of the present invention is capable of generating products with neutral colours (i.e., tending to white or soft yellow). Advantageously, the composition which is the subject matter of the present invention has reaction kinetics comparable to the corresponding products blocked by MEKO.

[0178] Advantageously, the composition which is the subject matter of the present invention has a viscosity of the same order of magnitude as the isocyanates of the prior art. Since it is preferably a liquid phase composition, the viscosity of such a composition can therefore be adjusted to meet the requirements of sufficient surface adhesion, sufficient substrate wettability, and cost of the composition and process. Advantageously, and quite unexpectedly, the locked polyisocyanates which are the subject matter of the present invention have markedly lower deblocking temperatures with respect to the corresponding isocyanates. Such an aspect is particularly important with a view to optimising energy consumption.

[0179] Advantageously, the composition which is the subject matter of the present invention can be formulated so as not to be flammable.

Claims

CLAIMS1 ) A composition comprising or, alternatively, consisting of:- isocyanates blocked by means of a blocking agent;- optionally one or more additives; said isocyanates being polymers of isocyanate units (polyisocyanates), wherein said isocyanate units are joined together by one or more urea bonds (-NH-CO-NH-), and wherein said polyisocyanates have a molecular weight distribution (MWD) as follows:- more than 50% by weight of said polyisocyanates comprise a number of isocyanate units > 3, said isocyanate units being covalently bonded with each other; and- less than 50% by weight of said polyisocyanates comprises molecules of identical molecular weight; said MWD being determined by SEC-MALS-DRI, wherein SEC is size exclusion chromatography connected to a multi-angle light scattering (MALS) detector and to a differential refractometer (DRI); wherein said composition is a solution, a suspension or a dispersion in an organic solvent.2) The composition according to the preceding claim, wherein said organic solvent is an aromatic or aliphatic hydrocarbon solvent, optionally aprotic.3) The composition according to claim 1 or 2, wherein said organic solvent comprises or consists of a naphtha, preferably the compound identified by CAS No. 64742-95-6, or a butoxyethyl acetate, preferably 2-butoxyethyl acetate, or mixtures thereof.4) The composition according to any of the preceding claims, wherein said isocyanate units are oligomers, preferably dimers or trimers.5) The composition according to any of the preceding claims, comprising said blocked isocyanates in an amount comprised from 10% to 90% by weight, preferably comprised from 30% to 85% by weight, more preferably comprised from 50% to 80% by weight, with respect to the total weight of said composition.6) The composition according to any of the preceding claims, wherein said polyisocyanates are bio-based or include bio-based isocyanate units.7) The composition according to any of the preceding claims, wherein said blocking agent is selected from the group consisting of:(i) 2-pentanone oxime, preferably not obtained by an ammoxidation reaction;(ii) 4-methylpentane-2-one oxime;(iii) 5-methyl-3-heptanone oxime; and(iv) a mixture of two or more of (i)-(iii); preferably wherein said mixture (iv) comprises (iii) 5-methyl-3-heptanone oxime in combination with (i) 2-pentanone oxime; and / or (ii) 4- methylpentan-2-one oxime.8) The composition according to claim 1 , wherein said blocking agent is at least an imidazole compound of the following general formula (I):wherein:R1 = H or CH3;R2 = H, CH3, CH2CH3or CH(CH3)2; preferably wherein said imidazole compound is 2-isopropyl-1 H-imidazole or 2-ethyl-4-methylimidazole; more preferably wherein said imidazole compound is a mixture of 2- isopropyl-1 H-imidazole and 2-ethyl-4-methylimidazole.9) The composition according to claim 1 , wherein said blocking agent is s- caprolactam, and / or dimethyl malonate, and / or 3, 5-dimethyl pyrazole.10) The composition according to any one of the preceding claims, wherein said composition is devoid of methyl ethyl ketoxime (MEKO).11 ) An adhesive material or a coating varnish for a substrate comprising the composition according to any one of the preceding claims and at least one resin containing hydroxyl or amine groups, for example, polyesters, polyols, or polyacrylates.12) A use of the composition according to any one of claims 1 -10 as a crosslinking agent for a resin containing hydroxyl or amine groups, for example, polyesters, polyols, or polyacrylates.13) A method for preparing a composition according to any one of claims 1 -10; wherein said method comprises the following steps:(I) contacting isocyanate units with an organic solvent to give a liquid mixture;(II) adding a polymerisation catalyst to the liquid mixture of step (I);(III) heating the product of step (II) to a temperature equal to or greater than 50 °C and then adding water as a reagent to give polyisocyanates and carbon dioxide; wherein, in said polyisocyanates, said isocyanate units are joined together by one or more urea bonds (-NH-CO-NH-);(IV) reacting at least one blocking agent with the polyisocyanates of step (III) to give polyisocyanates blocked by the blocking agent; preferably said blocking agent being as described in any one of claims 4-9;(V) optionally adding one or more additives to the blocked polyisocyanates obtained from step (IV).14) The method according to claim 13, wherein said step (III) comprises the following sub-steps:(III. A) reaction (1 ) between an isocyanate group of an isocyanate unit (Ri) and a water molecule to give an amine and carbon dioxide:Ri-NCO + H2O R1-NHCO-OH R1-NH2 + CO2 (1 )(III.B) reaction (2) between said amine of step (III. A) and an isocyanate group of another isocyanate unit (R2) to give said one or more urea bonds:R2-NCO + R1-NH2 R2-NHCO-NH-R1 (2)15) The method according to claim 13 or 14, wherein said polymerisation catalyst of step (II) is 1 ,4-diazabicyclo[2.2.2]octane.16) The method according to any one of claims 13 to 15, wherein said isocyanate units of step (I) are oligomers, preferably dimers or trimers.

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