WO2018056845A1

WO2018056845A1 - Blocked polyisocyanates, a process for the manufacture thereof and use thereof

Info

Publication number: WO2018056845A1
Application number: PCT/PL2016/000108
Authority: WO
Inventors: Barbara PILCH-PITERA; Piotr Franciszek KRÓL; Łukasz Julian BYCZYŃSKI; Joanna Maria WOJTURSKA
Original assignee: Politechnika Rzeszowska im. Ignacego Łukasiewicza
Priority date: 2016-09-20
Filing date: 2016-09-23
Publication date: 2018-03-29
Also published as: PL418764A1; PL238230B1

Abstract

The present invention relates to blocked polyisocyanates, a process for the manufacture of the blocked polyisocyanates and use thereof as crosslinking agents for polyurethane powder systems. Blocked polyisocyanates obtained by the process according to the invention after crosslinking with typical resins for powder systems provide polyurethane coatings with higher hydrophobicity and oleophobicity, and better abrasion and scratch resistance than products crosslinked with typical polyisocyanates used for powder coatings.

Description

Blocked polyisocyanates, a process for the manufacture thereof and use thereof

The invention relates to blocked polyisocyanates, a process for the manufacture thereof and use thereof as crosslinking agents for the manufacture of polyurethane powder systems with higher hydrophobicity, oleophobicity, gloss and abrasion and scratch resistance, intended for use in the field of powder coatings, in particular for painting metal parts for outdoor use in various sectors of the industry.

Polyurethane powder coating systems are known and used in practice. A typical polyurethane powder system contains a solid polyisocyanate component with blocked isocyanate groups (PIC), a solid polyester or poly acrylic resin capped with hydroxy groups, a catalyst, auxiliary agents, such as compounds which facilitate the application of coatings, accelerate degassing and flow control agents, as well as various additives depending on use, such as pigments, fillers, corrosion inhibitors, biocides, flame retardants, antioxidants. All these components which comprise the powder products need to have solid consistency [Gillis de Lange P., Powder coatings chemistry and technology, Vincentz Network Gmbh. Hannover, 2004; Spyrou E., Powder coatings chemistry and technology, Vincentz Network Gmbh. Hannover, 2012]. The resin is blended with a blocked polyisocyanate in a quantity so that the molar ratio of hydroxy to isocyanate groups is between 1 :1 and 1 :1.05. The manufacturing process for the powder systems consists of the following stages: preparation of a premix, extrusion, cooling, grinding, pulverisation, screening and packaging. A finished product should have grain diameter in a range of 10 - 150 μιη. All the components must have melted before crosslinking (T_m approx. 110 - 120°C) to ensure that the gaps between the grains are completely filled. The powder is crosslinked as a result of the reaction between deblocked isocyanate groups and the hydroxy groups in the resin at a temperature above the temperature of polyisocyanate deblocking. However, the deblocking temperature must be higher than the melting points of the raw materials so that the blend is homogenised during extrusion, but with no uncontrolled crosslinking. The powder is applied on a substrate typically by dipping in a fluidized bed or using an electrostatic (Corona) or electrokinetic (Tribo) method by way of special guns. Blocked diisocyanates or polyisocyanates are used as crosslinking agents. The glass-transition temperature (T_g = 55 - 90°C), melting point (T_M - 80 - 110°C) and content of isocyanate groups (CNCO = 10 - 18 weight %) are important factors which directly determine whether a PIC is useful as a crosslinking agent [Chen A. T., Wojcik R. T., Metal Finishing 2000, 98, 143; US 2002095019]. PICs are usually prepared in order to increase the functionality of the isocyanate component. Polyisocyanates are most typically prepared in a reaction between diisocyanates and low molecular weight compounds containing two, three or four hydroxy groups (e.g., ethylene glycol, trimethylolopropane, triethanolamine [DE 3 004 876] or pentaerythritol), and less commonly amine groups, e.g., diamines [DE 3 143 060], These may also be prepared as a result of trimerisation [DE 19729242], biuretisation [PL/EP 1524284] and in a reaction between diisocyanates and urethanes with allophanate formation [US 4 177 342]. PICs may be externally blocked as a result of a reaction between -NCO groups with a blocking agent, most commonly ε-caprolactam, 2-butanone oxime, 3,5- dimethylpyrazole or 1,2,4-triazole or else internally blocked as a result of dimerisation, biuretisation or through allophanate moieties. When products containing an internally blocked PIC are cured, the blocking agent is emitted into the atmosphere. Therefore, such systems cannot be used for the formation of thick coatings (more than 60 μπι), because blisters left by the released blocking agent may form in such conditions. A small amount of the blocking agents invariably remains permanently trapped in the coating, which may result in yellowing over time. Curing of systems which contain internally blocked PICs is more environmentally friendly.

From a commercial perspective, most important are PICs synthesised from isophorone diisocyanate (IPDI) blocked by ε-caprolactam [Spyrou E., Powder coatings chemistry and technology, Vincentz Network Gmbh. Hannover, 2012]. As well as isophorone diisocyanate, aliphatic 1 ,6-hexamethylene diisocyanate (HDI) and trimethylhexamethylene diisocyanate (TMDI), cycloaliphatic 4,4'-dicyclohexylmethane diisocyanate (Hi₂MDI), l,4-bis(isocyanatomethylene)cyclohexane [US 4 375 539], l,3,5-tris(isocyanatomethylene)cyclohexane and aromatic tolylene 2,4- and 2,6- diisocyanate and 3,5-tris(isocyanatomethylene)benzene [DE 3 128 743] and m- and p- tetramethylxylylene diisocyanate (TMXDI) are used on an industrial scale. It is noted that in spite of their lower prices, aromatic diisocyanates are of limited use for coatings due to their lower resistance to environmental factors, and they can be used only for indoors application.

The process for the preparation of internally blocked PICs as a result of dimerisation involves two stages. The first stage is dimerisation of diisocyanate in the presence of tris(dimethylamino)phosphine, while the other stage involves reaction of the dimerised product with diols and/or monoalcohols or monoamines, e.g., butane- 1,4-diol and/or 2-ethylhexanol and/or dibutylamine [EP 0045996; Schmitt F., Wenning A., Weiss J.-V., Prog. Org. Coat. 1998, 34, 227]. IPDI only could be dimerised so far with satisfactory yield, and 99% of the dimer was obtained with respect to isocyanurate structures. Considerable quantities (25 - 50%) of compounds containing isocyanurate and oxadiazinetrione rings always form during the dimerisation of other diisocyanates (HDI, TMDI or H₁₂MDI) commonly used in powder systems due to the chemical equivalence of both isocyanate groups [Wenning A., WeiB J.-V., Grenda W., Eur. Coat. J. 1998, 4, 244]. Searching for highly selective dimerisation catalysts and optimisation of reaction conditions to increase yields of the formation of uretidione structures is one of the directions contemporary research and development.

Because the functionality of polyisocyanates containing uretidione groups is lower than 2, these compounds reveal lower reactivity during curing in the presence of commonly used organic tin catalysts (dibutyltin(IV) dilaurate, tin(II) octoate) compared to internally blocked PICs, while coatings formed using these compounds have lower resistance to solvents and other chemicals. The crosslinking reaction rate for systems which contain uretidione compounds can be increased in the presence of zinc(II) acetylacetonate [EP 1137689] or amidine derivatives, such as 1,2- dimethyltetrahydropyrimidine [EP 0803524].

Internal blocking through biuret or allophanate moieties occurs with higher yields, and the reactions are reversible at lower temperatures (temp. 150°C) compared to dimerisation (180°C), and the resulting PICs may have functionality of more than 2 [PL/EP 1524284, US 4 177 342].

Regardless of the area of their use, hydrophobic coatings are very important in practice as easier to clean, and they may be self-cleaning and additionally have increased mechanical, chemical, thermal and ageing resistance. Coatings based on polyurethane systems with increased hydrophobicity are prepared in a reaction between polyisocyanates with resins having incorporated siloxane or fluoroalkyl segments or as a result of crosslinking specially selected resins with polyisocyanates having fluoroalkyl or siloxane substituents [Wu W., Zhu Q., Qing F., Han C. C: Langmuir 2009, 25, 17; Wang L.-F.: Polymer 2007, 48, 894].

The application of a blocked PIC synthesised in a reaction between a perfluorinated alcohol with Ν,Ν-carbonylbiscaprolactam was one of the synthesis methods for hydrophobic polyurethane coatings. As a result of crosslinking a polyester resin with such a PIC, a hydrophobic coating formed, characterised by a water contact angle of 125° wit a fluorine content of 2%, while the contact angle for an unmodified coating was 87° [Van Ravenstein L., Ming W., Van de Grampel R. D., Van der Linde R., De With G., Loontjens T., Thune P. C, Niemantsverdriet J. W., Macromolecules 2004, 37, 408-413]. The use of polyisocyanates containing fluorinated substituents synthesised as a result of a reaction between polyisocyanurates with fluorinated alcohols provides another example of coating hydrophobisation [Ming W., Melis F., Grampel R. D., Ravenstein L., Tian M., Linde R.: Prog. Org. Coat 2003, 48, 316-321],

Perfluorinated alcohols have also been used for the preparation of thermoplastic polyurethane powder clear coatings in a reaction with FfDI and subsequently with hydroxyethyl aery late, hydrogenated bisphenol A and decane-l,10-diol as a chain extender [WO 2013/096195].

The incorporation of perfluorinated polyoxypropylene alcohol with a molecular weight of 757 g mol (30.9%) to polyisocyanates containing allophanate groups in a reaction with HDI (61.7 %) and butan-l-ol (7.4 %) in the presence of tin octoate in order to reduce the surface free energy (SFE) of coatings is disclosed in patent specification US 5541281. The SFE of coatings obtained from two-component high-solid solvent-based systems using polyisocyanates synthesised in this way and a polyacrylic resin containing hydroxy groups was 19.4 mJ/m , while that of an unmodified coating was 43.3 mJ/m . SFE reduction to the same value was also obtained for coatings formed as a result of crosslinking a polyacrylic resin with a polyisocyanate with allophanate moieties and with an incorporated fluorinated monoalcohol with a molecular weight of 452 g/mol [US 5576411].

Patent US 5747629 discloses a process for the preparation of high-solid polyurethane coatings formed as a result of crosslinking a polyester resin with polyisocyanate with allophanate moieties and with an incorporated fluorinated monoalcohol with a molecular weight of 570 g/mol. The SFE of resulting coatings was 16.8 mJ/m² when polyisocyanate synthesised from HDI was used, while the SFE of coatings for polyisocyanate synthesised from IPDI was 18.4 mJ/m with a fluorine content 0.1 %, and the SFE of a coating without fluorine was 31.5 mJ/m .

A process for the preparation of polyester resins containing carboxy groups and fluorinated substituents for powder clear coatings as a result of a polycondensation reaction between butane- 1,4-diol, isophthalic anhydride and a polyaddition product of 1H,1H,7H- dodecafluoro-l-heptanol with epichlorohydrin was described in a paper by Xiong and coworkers [Xiong J., Jin Y., Shentu B., Weng Z., J. Coat. Technol. Res. 10 (5) 621-629, 2013]. The SFE of coatings obtained as a result of crosslinking the resins using TGIC was reduced from 42 mJ/m² for coatings without fluorine to 22 mJ/m² for coatings with a fluorine content of 1%. Coatings with a fluorine content of more than 1% did not reveal SFE reduction below 22 mJ/m².

For coatings obtained from polyurethane ionomers, as well as fluorine diisocyanate derivatives or polyols, fluorinated chain extenders are used, such as 2,2,3,3- tetrafiuorobutane-l,4-diol [Krol P., Krol B., Pielichowska K., Pikus S., Colloid Polym Set 2011; 289(15-16): 1757-1767]. The SFE of cationomers synthesised from HDI, poly(oxyethylene) glycol with Mn = 600 g mol, N-methyldiethanolamine and butane- 1,4- diol was reduced from 40 mJ/m to 30 mJ/m when 15% of butane- 1,4-diol was replaced by 2,2,3 ,3 -tetrafluorobutane- 1 ,4-diol.

The method for the modification of blocked PICs containing biuret moieties with fluorinated polyols or their use as crosslinking agents for powder systems has not been disclosed in the literature so far.

It was unexpectedly found that a considerable increase in the hydrophobicity of powder coatings could be obtained by using blocked polyisocyanates containing biuret bonds and modified with fluorinated polyols as crosslinking agents.

The objective of the invention is to provide novel blocked polyisocyanates and a process for the manufacture thereof for use in the production of improved powder systems. Following crosslinking with typical commercially available resins used for coating systems, the blocked polyisocyanates can provide polyurethane coatings with higher hydrophobicity, good durability and other valuable properties, such as higher gloss, oleophobicity, better abrasion and scratch resistance and resistance to environmental factors, compared to products crosslinked by typical polyisocyanates used for powder coatings.

The subject matter of the invention includes blocked polyisocyanates characterised in that they contain a fluorinated polyol, an isocyanate component and a blocking agent.

As the fluorinated polyol, the blocked polyisocyanates preferably contain a linear polyol with side fluoroalkoxy groups and capped with hydroxy groups at both ends, with a molecular weight in a range between 500 and 15,000, preferably 800 to 12,000, especially preferably 1200 to 1950.

The isocyanate component is preferably selected from a group comprising isophorone diisocyanate (IPDI), 1 ,6-hexamethylene diisocyanate (HDI), 2,2,4- and 2,4₅4-trimethyl-l,6-hexamethylene diisocyanate (TMDI), 4,4'-dicyclohexylmethane diisocyanate (H₁₂MDI), l,4-bis(isocyanatomethylene)cyclohexane, 1,3,5- tris(isocyanatomethylene)cyclohexane, tolylene 2,4- and 2,6-diisocyanate, 3,5- tris(isocyanatomethylene)benzene and m- and p-tetramethylxylylene diisocyanate (TMXDI).

The blocking agent is preferably selected from a group comprising ε- caprolactam, diethyl malonate, oximes or 3,5-dimethylpyrazole.

The blocked polyisocyanates preferably contain the fluorinated polyol in an amount of 5 to 32 weight %, preferably 15 to 25 weight %, the isocyanate component in an amount of 45 to 65 weight %, preferably 53 to 57 weight %, and the blocking agent in an amount of 22 to 31 weight %, preferably 22 to 28 weight %.

The blocked polyisocyanates preferably contain 19.0 weight % of the fluorinated polyol, 55.2 weight % of isophorone diisocyanate and 25.8 weight % of ε-caprolactam.

The viscosity of the blocked polyisocyanates at a temperature of 140°C is preferably 20 to 25 Pa^s at a shear rate of 200 s^'1.

The subject matter of the invention also includes a process for the manufacture of the blocked polyisocyanates for polyurethane powder systems, which consists in that:

a) monomers of the isocyanate component are reacted in the presence of a biuretising agent to form a urea polyisocyanate, b) a biuretisation of the urea polyisocyanate formed in stage a) is conducted,

c) an addition of a fluorinated polyol with both ends capped with hydroxy groups to the isocyanate groups of the polyisocyanate is performed,

d) free isocyanate groups in the polyisocyanate are blocked using the blocking agent.

In stage a), the isocyanate component and at least two catalysts in an amount of

0.10 to 0.15 weight % are preferably placed into a reactor and the biuretising agent is slowly dispensed in an amount of 0.4 to 0.1 mol per 1 mol of the isocyanate component, preferably 0.3 to 0.2 mol per 1 mol of the isocyanate component.

In stage b), the mixture is preferably heated to a temperature not lower than 140°C, preferably 140 to 150°C, and maintained at that temperature until biuretisation of the isocyanate component is completed.

In stage c), the fluorinated polyol is preferably dispensed in an amount of 1 to 40 weight %, preferably 3 to 25 weight %. In stage d), the blocking agent is preferably incorporated at a temperature not lower than 65°C, preferably 80 to 90°C, until free isocyanate groups disappear.

The isocyanate component selected from a group comprising isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4- and 2.4,4-trimethyl- 1,6-hexamethylene diisocyanate (TMDI), 4,4'-dicyclohexylmethane diisocyanate (H₁₂MDI), l,4-bis(isocyanatomethylene)cyclohexane, 1 ,3,5- tris(isocyanatomethylene)cyclohexane, tolylene 2,4- and 2,6-diisocyanate, 3,5- tris(isocyanatomethylene)benzene and m- and p-tetramethylxylylene diisocyanate (TMXDI) is preferably used.

An organic phosphorus compound, an organometallic compound or an amine compound selected from a group comprising dibutyl phosphate, dibutyltin dilaurate, tin octoate, triethylamine and triethylenediamine is preferably used as the catalyst.

Water, formic acid or alcohols are preferably used as the biuretising agent.

A linear polyol with side fluoroalkoxy groups and capped with hydroxy groups at both ends, with a molecular weight in a range between 500 and 15,000, preferably 800 to 12,000, especially preferably 1200 to 1950, is preferably used as the fluorinated polyol.

An agent selected from a group comprising ε-capro lactam, diethyl malonate, oximes or 3,5-dimethylpyrazole is preferably used as the blocking agent.

The viscosity of the polyisocyanates at a temperature of 140°C is preferably 20 to 25 Pa-s at a shear rate of 200 s^"1.

The subject matter of the invention also includes blocked polyisocyanates manufactured by the process as defined above.

The subject matter of the invention also includes polyurethane powder systems containing the blocked polyisocyanates as defined above.

The subject matter of the invention also includes the use of the blocked polyisocyanates as defined above for the manufacture of polyurethane powder systems. According to the disclosure, the production of polyurethane powder clear coatings with increased hydrophobicity includes, therefore, the synthesis of a modified PIC and manufacture of a PIC-based powder clear coating.

The synthesis of the modified PIC includes the following stages: a) preparation of urea polyisocyanate, b) biuretisation of the resulting product, c) addition of a fluorinated polyol and d) blocking of the isocyanate end groups. All the stages of the synthesis process for the modified PIC are conducted in the same reactor intended for typical chemical synthesis and equipped with a stirrer, reflux condenser, thermometer, heating mantle and a nitrogen inlet.

In stage a), the diisocyanate and at least two catalysts in an amount of 0.10 to 0.15 weight % are placed into the reactor and the biuretising agent is slowly dispensed in an amount of 0.4 to 0.1 mole, preferably 0.3 to 0.2 mole, per 1 mole of the diisocyanate.

According to the proposed procedure, typical diisocyanates used in polyurethane powder coatings industry, such as: isophorone diisocyanate (IPDI), 1 ,6-hexamethylene diisocyanate (HDI), 2,2,4- and 2.4,4-trimethyl-l,6-hexamethylene diisocyanate (TMDI), 4,4'-dicyclohexylmethane diisocyanate (H₁₂MDI), 1 ,4-bis(isocyanatomethylene)- cyclohexane, l,3,5-tris(isocyanatomethylene)cyclohexane, tolylene 2,4- and 2,6- diisocyanate, 3,5-tris(isocyanatomethylene)benzene and m- and p-tetramethylxylylene diisocyanate (TMXDI) may be used as the isocyanate component.

As the catalysts, organometallic compounds, such as dibutyltin dilaurate, tin octoate, amines, e.g., triethylamine, triethylenediamine, or phosphorus compounds, e.g., dibutyl phosphate, may be used as being well known in polyurethane industry.

Water, formic acid or alcohols may be the biuretising agent. After the biuretising agent is introduced, reaction progress is monitored for example using an acidimetric titration procedure by determining the content of unreacted -NCO groups.

After the stage a) is completed, the mixture in the reactor in stage b) is heated to a temperature not lower than 140°C, preferably to a temperature of 140 to 150°C, and maintained at this temperature until biuretisation of the IC is completed. Biuretisation is a two-stage process. The first stage involves formation of urea bonds. Temperature at this stage may be lower than 140°C, and the lowest temperature is 60°C, while the duration of the stage is 2 hrs. The second stage is biuretisation proper. Temperature at this stage may not be lower than 140°C, because the reaction does not proceed below this temperature, and duration of the stage is 4 to 6 hrs. The total duration of the biuretisation process (stage one and stage two) is 6 to 8 hours.

In stage c), the fluorinated polyol is dispensed in an amount of 1 to 40 weight %, preferably 3 to 25 weight %. Linear polyols are preferably used with side fluoroalkoxy groups and capped with hydroxy groups at both ends, with a molecular weight in a range between 500 and 15,000, preferably 800 to 12,000, especially preferably 1200 to 1950. The use of a fluorinated polyol with a higher molecular weight is especially preferable, because the compound is incorporated in the polyisocyanate chain through urethane bonds formed in a reaction between hydroxy groups at the ends of the chain and, therefore, longer segments derived from the polyol have a greater chance for mobility and migration towards the surface of the coating being formed, thus giving it properties typical of fluorinated compounds.

In stage d), the free -NCO groups are blocked by introducing the blocking agent at a temperature not lower than 65°C, preferably 80 to 90°C, and that temperature is maintained until the -NCO groups disappear. Blocking agents well known in polyurethane powder coatings industry, such as: ε-caprolactam, diethyl malonate, typical oximes or 3,5-dimethylpyrazole may be used for blocking the -NCO groups.

The finished product in the resin form is discharged from the reactor while hot, cooled to room temperature and pulverised.

A particular advantage of the new powder systems of the invention is their processability and applicability using commercially available methods employed in the technology of powder coating application.

To obtain a powder clear coating, the modified PIC is blended with a typical polyester resin intended for polyurethane powder coatings with LOH in a range of 30 - 45, preferably 35 - 40 mg KOH g, T_g = 50 - 65°C, preferably 55 - 60°C, such as Rucote 102 or Sirales 6110, and degassing agents, catalysts and flow control agents. The raw materials are weighed and initially milled, e.g., using an electric grinder, and the resulting powder is extruded. The extruded mix is crushed and ground in a mill, and subsequently passed through a screen with mesh size in a range of 30 - 200 μπι, preferably 60 - 150 μπι, to eliminate too large particles. The finished powder clear coating may be used for painting various parts intended for outdoors use, such as using special guns based on CORONA or TRIBO methods or using other techniques. When the powder clear coating is applied using the TRIBO method, an additive improving the charging of the powder must be used. Painted parts are placed in an oven at a temperature of 140 - 190°C for 10 - 30 minutes for the coatings to cure.

The powder systems prepared according to the invention are transparent and colourless. When colouring is needed, typical pigments used in powder system industry can be added, such as rutile titanium white Ti0₂.

The invention will be specified in more detail by way of the following embodiments of the invention. Example 1

A process for the synthesis of polyisocyanate (comparative example)

To a three-necked flask fitted with a stirrer, reflux condenser, thermometer, dropping funnel and tube with a nitrogen inlet, isophorone diisocyanate was added (111.10 g; 0.500 mole) followed by catalysts: dibutyltin dilaurate and dibutyl phosphate (0.11 g each; 0.1 weight % as per the diisocyanate). Using the dropping funnel, formic acid was dispensed into the mixture over 0.5 hour (5.75 g; 0.125 mole) at 25°C. After the addition was completed, the reaction mixture was heated to 60°C and maintained at that temperature while being stirred vigorously until the content of isocyanate groups was reduced to 27 weight %. Temperature was increased at that time to 140°C. The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups in the reaction mixture was reduced to 19 weight %. After the mixture was cooled to 65°C, ε-caprolactam was added (49.74 g 0.440 mole) and it was maintained at 65°C while being stirred vigorously until isocyanate groups disappeared. When cooled to room temperature, a transparent straw yellow polyisocyanate with solid consistency and the following properties was obtained:

Content of NCO groups after deblocking - 19.0 weight %,

Mean functionality (determined using gel permeation chromatography (GPC)) -

3.87,

Viscosity at 140°C - 20 Pa^s at a shear rate of 200 s^'1.

Example 2

A process for the synthesis of polyisocyanate modified with a fluorinated polyol

To a three-necked flask fitted with a stirrer, reflux condenser, thermometer, dropping funnel and tube with a nitrogen inlet, isophorone diisocyanate was added (111.10 g; 0.500 mole) followed by catalysts: dibutyltin dilaurate and dibutyl phosphate (0.11 g each; 0.1 weight % as per the diisocyanate). Using the dropping funnel, formic acid was dispensed into the mixture over 0.5 hour (5.75 g; 0.125 mole) at 25°C. After the addition was completed, the reaction mixture was maintained at 60°C while being stirred vigorously until the content of isocyanate groups was reduced to 27 weight %. Temperature was increased at that time to 140°C. The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups was reduced to 19 weight %. In a subsequent stage, the reaction mixture was cooled to 80°C and a fluorinated polyol: PolyFox PF-6520 (from OMNOVA Solutions) was added (37.1 g). The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups in the reaction mixture was reduced to 12.9 weight %. After the mixture was cooled to 65°C, ε-caprolactam was added (50.18 g; 0.44 mole) and it was maintained at 65°C while being stirred vigorously until isocyanate groups disappeared. When cooled to room temperature, a transparent straw yellow polyisocyanate with solid consistency and the following properties was obtained:

Content of NCO groups - 12.9 weight %,

Mean functionality (GPC) - 3.41 ,

Viscosity at 140°C - 25 Pa-s at a shear rate of 200 s^"1,

Content of fluorinated polyol - 19.0 weight %.

According to the aforementioned description, the composition of the blocked polyisocyanate is as follows: IPDI - 55.2 weight %, fluorinated polyol - 19.0 weight %, ε-caprolactam - 25.8 weight %.

Example 3

To a three-necked flask fitted with a stirrer, reflux condenser, thermometer, dropping funnel and tube with a nitrogen inlet, isophorone diisocyanate was added (111.10 g; 0.500 mole) followed by catalysts: dibutyltin dilaurate and dibutyl phosphate (0.11 g each; 0.1 weight % as per the diisocyanate). Using the dropping funnel, formic acid was dispensed into the mixture over 0.5 hour (5.75 g; 0.125 mole) at 25°C. After the addition was completed, the reaction mixture was maintained at 60°C while being stirred vigorously until the content of isocyanate groups was reduced to 27 weight %. Temperature was increased at that time to 140°C. The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups was reduced to 19 weight %. In a subsequent stage, the reaction mixture was cooled to 80°C and a fluorinated polyol: PolyFox PF-6520 (from OMNOVA Solutions) was added (76.0 g). The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups in the reaction mixture was reduced to 10.9 weight %. After the mixture was cooled to 65°C, ε-caprolactam was added (53.68 g; 0.48 mole) and it was maintained at 65°C while being stirred vigorously until isocyanate groups disappeared. When cooled to room temperature, a transparent straw yellow polyisocyanate with solid consistency and the following properties was obtained:

Content of NCO groups - 10.9 weight %,

Content of fluorinated polyol - 32.0 weight %.

According to the aforementioned description, the composition of the blocked polyisocyanate is as follows: IPDI - 45.4 weight %, fluorinated polyol - 32.0 weight %, ε-caprolactam - 22.6 weight %.

Example 4

To a three-necked flask fitted with a stirrer, reflux condenser, thermometer, dropping funnel and tube with a nitrogen inlet, isophorone diisocyanate was added (111.10 g; 0.500 mole) followed by catalysts: dibutyltin dilaurate and dibutyl phosphate (0.11 g each; 0.1 weight % as per the diisocyanate). Using the dropping funnel, formic acid was dispensed into the mixture over 0.5 hour (5.75 g; 0.125 mole) at 25°C. After the addition was completed, the reaction mixture was maintained at 60°C while being stirred vigorously until the content of isocyanate groups was reduced to 27 weight %. Temperature was increased at that time to 140°C. The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups was reduced to 19 weight %. In a subsequent stage, the reaction mixture was cooled to 80°C and a fluorinated polyol: PolyFox PF-6520 (from OMNOVA Solutions) was added (8.4 g). The reaction mixture was maintained at that temperature while being stirred vigorously until the content of isocyanate groups in the reaction mixture was reduced to 16.3 weight %. After the mixture was cooled to 65°C, ε-caprolactam was added (51.0 g; 0.45 mole) and it was maintained at 65°C while being stirred vigorously until isocyanate groups disappeared. When cooled to room temperature, a transparent straw yellow polyisocyanate with solid consistency and the following properties was obtained:

Content of NCO groups - 16.3 weight %,

Content of fluorinated polyol - 5.0 weight %. According to the aforementioned description, the composition of the blocked polyisocyanate is as follows: IPDI - 64.5 weight ¾, fluorinated polyoi - 5.0 weight %, ε-caprolactam - 30.5 weight %.

Example 5

A process for the manufacture of powder clear coating

Powder clear coatings were prepared by blending the resulting powdered polyisocyanate (142.47 g prepared according to Example 2; 166.23 g prepared according to Example 3; 110.97 g prepared according to Example 4) with polyester resin Sirales 6110 (552.00 g), a flow control agent (Resiflow PH-240 (3%)) and degassing agents (WorleeAdd 902 (1.5 %) and benzoin (1%)). When blended, the components were initially milled and subsequently extruded in a co-rotating twin-screw extruder at a temperature of 125°C and at a screw rotational speed of 150 rpm and milled again in a disintegrating mill at a rotor rotational speed of 11000 rpm. The milled powder was screened using a vibrating screen with a mesh size of 100 μπι. Example 6

A process for obtaining cured coatings from powder clear coatings

Coatings were obtained by applying the screened powder fraction using an electrostatic method with a PEM X-1 hand gun with a built-in electrode and an EPG Sprint X controller onto normalised steel panels with curing at a temperature of 180°C over 20 min.

The percentage amounts of the fluorinated polyoi and fluorine in the cured coatings obtained using the powder clear coatings manufactured from the polyisocyanates prepared according to Examples 2, 3 and 4 are listed in Table 1 below.

Table 1

Samples of the powder clear coatings and cured coatings obtained according to the aforementioned embodiments of the invention had properties as listed below in Table 2 in which they are compared to the properties of a reference sample. The data in Table 2 confirm the more favourable properties of the coatings obtained from the powder clear coatings prepared using the polyisocyanate modified with the fluorinated polyoi compared to coatings obtained from typical polyisocyanates.

Table 2

The invention can be used in particular in automotive industry (painting vehicle bodies and parts, bicycle and motorcycle frames), construction industry (painting metal sheets intended for roofing materials, painting facades, metal construction structures, such as used in bridges, protection barriers), shipbuilding industry (painting bottom parts of ship hulls), machinery industry (painting machine parts), energy industry (painting gas pipelines and other transmission facilities, such as for crude oil), aircraft industry (painting external aircraft parts), defence industry (painting firearms), mining industry (painting long- wall mining machines) and agricultural industry (painting combine harvesters and other agricultural machines).

Claims

1. Blocked polyisocyanates characterised in that they contain a fluorinated polyol, an isocyanate component and a blocking agent.

2. Blocked polyisocyanates of claim 1 , characterised in that they contain a linear polyol with side fluoroalkoxy groups and capped with hydroxy groups at both ends, with a molecular weight in a range between 500 and 15000, preferably 800 to 12000, especially preferably 1200 to 1950, as the fluorinated polyol.

3. Blocked polyisocyanates of claims 1-2, characterised in that the isocyanate component is selected from a group comprising isophorone diisocyanate (IPDI), 1 ,6-hexamethylene diisocyanate (HDI), 2,2,4- and 2,4,4-trimethyI-l,6- hexamethylene diisocyanate (TMDI), 4,4'-dicyclohexylmethane diisocyanate (H₁₂MDI), l,4-bis(isocyanatomethylene)cyclohexane, 1,3,5- tris(isocyanatomethylene)cyclohexane, tolylene 2,4- and 2,6-diisocyanate, 3,5- tris(isocyanatomethylene)benzene and m- and p-tetramethylxylylene diisocyanate (TMXDI).

4. Blocked polyisocyanates of claims 1-3, characterised in that the blocking agent is selected from a group comprising ε-caprolactam, diethyl malonate, oximes or 3,5-dimethylpyrazole.

5. Blocked polyisocyanates of claims 1-4, characterised in that they contain the fluorinated polyol in an amount of 5 to 32 weight %, preferably 15 to 25 weight %, the isocyanate component in an amount of 45 to 65 weight %, preferably 53 to 57 weight % and the blocking agent in an amount of 22 to 31 weight %, preferably 22 to 28 weight %.

6. Blocked polyisocyanates of claims 1-5, characterised in that they contain 19.0 weight % of the fluorinated polyol, 55.2 weight % of isophorone diisocyanate and 25.8 weight % of ε-capro lactam.

7. Blocked polyisocyanates of claims 1-6, characterised in that a viscosity at a temperature of 140°C is 20 to 25 Pa s at a shear rate of 200 s^"1.

8. A process for the manufacture of the blocked polyisocyanates for polyurethane powder systems characterised in that:

a) monomers of the isocyanate component are reacted in the presence of a biuretising agent to form an urea polyisocyanate,

b) a biuretisation of the urea polyisocyanate formed in stage a) is conducted, c) an addition of a fluorinated polyol with both ends capped with hydroxy groups to the isocyanate groups of the polyisocyanate is performed,

9. The process of claim 8, characterised in that in stage a), the isocyanate component and at least two catalysts in an amount of 0.10 to 0.15 weight % are placed into a reactor and the biuretising agent is slowly dispensed in an amount of 0.4 to 0.1 mol per 1 mol of the isocyanate component, preferably 0.3 to 0.2 mol per 1 mol of the isocyanate component.

10. The process of claims 8-9, characterised in that in stage b), the mixture is heated to a temperature not lower than 140°C, preferably 140 to 150°C, and maintained at that temperature until biuretisation of the isocyanate component is completed.

11. The process of claims 8-10, characterised in that in stage c), the fluorinated polyol is dispensed in an amount of 1 to 40 weight %, preferably 3 to 25 weight %.

12. The process of claims 8-11, characterised in that in stage d), the blocking agent is introduced at a temperature not lower than 65°C, preferably 80 to 90°C, until free isocyanate groups disappear.

13. The process of claims 8-12, characterised in that the isocyanate component selected from a group comprising isophorone diisocyanate (IPDI), 1,6- hexamethylene diisocyanate (HDI), 2,2,4- and 2,4,4-trimethyl-l,6- hexamethylene diisocyanate (TMDI), 4,4'-dicyclohexylmethane diisocyanate (Ht2MDI), l,4-bis(isocyanatomethylene)cyclohexane₅ 1,3,5- tris(isocyanatomethylene)cyclohexane, tolylene 2,4- and 2,6-diisocyanate, 3,5- tris(isocyanatomethylene)benzene and m- and p-tetramethylxylylene diisocyanate (TMXDI) is used.

14. The process of claims 8-13, characterised in that an organic phosphorus compound, an organometallic compound or an amine compound selected from a group comprising dibutyl phosphate, dibutyltin dilaurate, tin octoate, triethylamine and triethylenediamine is used as the catalyst.

15. The process of claims 8-14, characterised in that water, formic acid or alcohols are used as the biuretising agent.

16. The process of claims 8-15, characterised in that a linear polyol with side fluoroalkoxy groups and capped with hydroxy groups at both ends, with a molecular weight in a range between 500 and 15,000, preferably 800 to 12,000, especially preferably 1200 to 1950, is used as the fluorinated polyol.

17. The process of claims 8-16, characterised in that an agent selected from a group comprising ε-caprolactam, diethyl malonate, oximes or 3,5-dimethylpyrazole is used as the blocking agent.

18. The process of claims 8-17, characterised in that the viscosity of the polyisocyanates at a temperature of 140°C is 20 to 25 Pa-s at a shear rate of 200 s^"1.

19. Blocked polyisocyanates manufactured by the process as defined in any one of claims 8 - 18.

20. Polyurethane powder systems containing the blocked polyisocyanates as defined in any one of claims 1 - 7 or 19.

21. Use of blocked polyisocyanates as defined in any one of claims 1 - 7 or 19 for the manufacture of the polyurethane powder systems.