CA1056841A - Organic compounds which contain uretdione groups and blocked isocyanate end groups - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for producing polyisocyanates containing uretdione groups and blocked terminal isocyanate groups. Organic diisocyanates are dimerized, optionally in the presence of phosphine cata-lysts and then reacted with a blocking agent and optionally a chain lengthening agent. The proportions of blocking agent and chain lengthening agent are chosen such that less than all the isocyanate groups are reacted with chain lengthening agent and such that there are substantially no free isocyanate groups left. The invention also relates to latent polyisocyanate produced by this process, i.e.
those containing ?rethdione groups and blocked terminal isocyanate groups. The invention is also concerned with the use of such polyisocyanates to make polyurethane resins.

Description

Mo-1588-P
LeA 16,190 ORGANIC COMPOUNDS WHICH CONTAIN
URETDIONE GROUPS AND BLOCKED - . .
ISOCYANATE END GROUPS

This invention relates to a process ~or the pxepara-tion of new compounds which have a hicJh laten~ isocyanate content, the compounds obtained by this process and their use as starting materials fox the reaction with compounds which contain hydrogen atoms capable of reacting with iso-cyanate gxoups to produce polyurethane resins by the iso-cyanate polyaddition process. : -~.
Ba k~round of the Invention Masked isocyanates, also known as isocyanate , releasers, have been known for a long time. Among these .. -compounds, diisocyanates having uretdione groups, in which ::
two of the four isocyanate groups are present in a latent ~ :
form, take up a spPcial position. Polyurethanes which con- :
tain uretdione groups in the macromGlecule are also already :~ :
known (Kunststoff Handbuch, Volume VII, Polyurethanes, : ~ ~ published by Vieweg and ~ochtlen, Carl-Hanser-Verlagt Munich, 1966, pages 17, 37). ; .

It is also known tha~ whe~ compounds which contain ~:
uretdione groups are heated o elevated temperatures, the ~ ;~
; uretdione ring open up and isocyanate groups are liberated :~
(I.H. Saunders and K.C. Frisch "Polyurethanes: Chemistry and ~ :
~echnology", Part Il Interscience Publishers (1962), pages 113 et seq~. -.' -polyisocyaRates and polyisocyanate polyaddition ~ -products which contain uretdione groups and .in whiçh the isocyanate end groups are inactivated by blocking agents LeA 16,190 ' ~
. .
,, ~ . .

represent new types of polyisocyanates which can be activated by heat for the production of polyureth~ne resins by the iso-cyanate polyaddition process.

These latent polyisocyanates tthe term "la-tent" being used in this context to denote compounds containing uretdione groups and blocked isocyanate groups) differ advantageously from the blocked polyisocyanates already known in the art by the fact that only some of their isocyanate groups are blocked with blocking agents which can be split off by heat so that when the new compounds are reacted in combination with compounds which contain hydrogen atoms capable of reacting with isocyanate groups, the quantity of blocking agent liberated is only a fraction of the quantity which would be liberated from blocked polyisocyanates which contain a comparable quantity of latent isocyanate groups but in which all the isocyanate groups are blocked with blocking agents which can be split off. The new compounds differ advantageously from the known prior art diisocyanates which contain uretdione groups by the fact that all their isocyanate groups are in a latent, i.e. blocked form. The new compounds differ advantageously from the known polyurethanes which contain uretdione groups by their very substantially higher concentration of latent isocyanate groups.

Summary of the Invention The present invention therefore relates to a pro-cess for the preparation of organic compounds which contain uretdione groups and blocked isocyanate end groups, characterized in that an organic polyisocyanate is converted in known manner Le~ 16,190-C~ - 2 -',' ~

' :' . . ~ , . ~ . , , .
. - " , ,. . . :

into an intermediate product which contains uretdione groups and free isocyanate groups,and this intermediate product is converted into the corresponding compound which contains uretdione groups and blocked isocyanate end groups and optionally urethane and/or urea groups in the chain by reaction with a blocking agent which is monofunctional in the isocyanate poly-addition reaction, the reaction with the blocking agent being carried out, if desired, before and/or during and/or after a chain lengthening reaction with sub-equivalent quantities of a chain lengthening agent which has a molecular weight in the range of about 18 to 300 and which contains 2 to 3 groups which are reactive with isocyanate groups.

The present invention relates also to the compounds LeA 16,190 - CA 3 -~, .

obtained by this proces~, in particular to the preferred compounds which cons~itu~e la~en~ polyisocyanates c~arac-terized by having a molecular weight of from about 300 to 4,000 and containing about 2.5 to 10~ by weight of uret-dione groups (-N=(CO)2=N-3 and about 2 to 15% by weight of isocyanate end groups which are blocked.

Finally, the present invention also relates to the use of the compounds obtained by the process according to the invention as reactants for polyhydroxyl compounds in the production of polyurethane resins by the isocyanate poly-addition process.

Detailed DescriPtion of the Invention The starting materials used for the process according to the invention are polyisocyanates which contain uretdione groups, in particular diisocyanates, which can be obtained in known manner by the t~imeri~ation of organic di-i ocyanates ~see e.g. German Of~enlegungsschriften No.
1,670,720 and No. 1,934,763 or "ICunststoff-Handbuch", Vol.
VII, Polyurethane, Carl-Hanser-Verlag, Munich (1966), pages 16-17). These uretdione dii ocyanates can easily be obtained from the corresponding i~ocyanates by a catalytic reaction. The catalysts used for this reaction are pre- :
ferably tertiary phosphine~ which h~ve at least one ali-phatic substituent, e.g. triethylphosphine, tributylphos-phine, or phenyldimethylphosphine, but pyridine may al~o b~ u5ed.

~he dimeriæation may be carried out solvent-free or :
...
preferably in inert organic ~olvents. The preferred ~ol-vents are henzene, toluene, methyl or ethyl glycol acetate, :~
LeA 16,1gO -4- :: ~.

dimethylformamide, xylene and oth~r axomatic or aliphatic hydrocarbons includin~ also ketones such a~ acetone, me~hyl butyl ketone, methyl isobutyl keton~ and cyclohexanone, chlorinated aromatic hydrocarbons and any mixtures of these compounds and other inert organic solvents. Toluene and xylene are quit~ particularly preferred solvents or dimerization.

When carrying out the dimerization process, it is ~ :
essential to stop the reaction when the mixture reaches a :
given isocyanate content, preferably when about 25 to 53 and in particular about 26 to 47% of the NC0 yroups have undergone dimerization. `~

The reaction temperature employed varies according to the cataly~t used. For tertiary aliphatic or mixed ali-phatic aromatic phosphines, the optimum temperature i8 betwee~about 0C and 120C and temperatures of between about 0C
and 60C are preferably used. A; is well known, if higher temperatures and lower catalyst c:oncentrations are used, increasing quantities o other by-products such as carbadi-imides and uretimines are produced in addition to isocyanu-rates. Since the dimerization reaction in the presence of catalysts is an equilibrium reaction and the highest degree of dimerization is xeached at low te~perature~, the reac-tion is generally carried out at relatively low temperatures.

For thermal dimerization without catalysts, tempera-tures between about 120C and 150C are the most ~uitable.
At lower temperatures, the reaction take~ too long to reach a state of equilibrium whereas at higher temperatures a :~
considerable proportion of uretdione i5 converted into i~o-LeA 16,190 _5_ :

, . . .. ~ .
~, ' , . :
,.

cyanurate.

The quantity of catalyst required varies according to the nature and degree of purity of ~he isocyanate u~ed and the tempera~ure employed. Quantities of from about 0.1 to 5% by weight, based on the quantity of diisocyanate put into the reaction~ are gener~lly sufficient when using tertiary aliphatic pho~phines. Quantities of fro~ about 0.3 to 2% by weight are prPferably used.

If the reaction is carried out at a temperature of from about 0C to 25C in the presence of the above- :
mentioned catalysts, a free NCO group content which corres- -ponds to a conversion of about 26 to 47% of the isocyanate . ~ :
groups presPnt if aromatic dii~ocyanates are used becomes .:
establi~hed after a reaction time of about 0.5 to 6 hours.
The aromatic or mixed aromatic-ali.pha~i~ uretdione ~iiso-~yanate~ crys~allizo from the reac~tion mixture during dimeri zation. The dime~ization catalyst: is inacti~ated by the addition of a waxm 10~ ~olution of ~ulphur in tolu~ne.

The uretdioné diisocyanates prepared as de~cribed above can be used in the process according to the invention either a3 the sole isocyanate component or as a mixture with diisocyanates which are free from uretdione groups. The . :
:
addition of a diisocyanate which is free from uretdione groups provides a simple method of varying the properties of the products as desired, in particular their melting ~:
point, since the monomeric diisocyanate which is free from uretdione groups ls built into the p.roducts of the proce~
as a so-called interfering ~omponent. `.
."
It is particularly advantageous to use as the LeA 16,190 -6-::
' ~ ~

isocyanate component in the process accsrding to the invention ~he diisocyanate mixture described abo~e which is prepared in situ by partial dimerization of a suitable diisocyanate. When the mixture is subsequently reacted with its reaction partner, the monomeric diisocyanate still present in the reaction mixture functions as an "interfering component".

The reaction mixture is heated to a temperature of from about 90 to 100C after inactivation of the catalys~.
A clear solution of the uretdione diisocyanate/diisocyanate mixture is ~hereby obtained. No further change in the free isocyanate content or in the quantity of latent isocyanate present in the uretdione occurs during this heat treatment.

The diisocyanate~ free from uretdione groups which may be u~ed as "intexfering components" as well a~ for the preparation o the uretdione dii~ocyanates may be aliphatic, cycloaliphatic, araliphatic, ar~miatic or heterocyclic dii30-cyanates ~uah as those described, for example, by W~ Siefken in Justus ~iebigs Annalen der Che~ie, 562, pages 75-136.
The following are examples:
Ethylene dii~ocyanate, tetram~thylene-1,4-dii~ocyanate;
hexamethylene-1,6-diisocyanate, dodecane 1,12-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate and any mixtures of these isomers, 1-isocyanato~
3,3/5-trimethyl-5-isocyanatomethyl-cyclohexane (DAS No. ~ -1,202,785), hexahydrotolylene-2,4- and -2,6-diisocyanate and any mixturas o these isomers, hexahydrophenylene-1,3-and/or -1,4-diisocyanate, perhydrodiphenylm~thane-2,4'-an~/or 4,4'-diisocyanate, phenylene-1,3- and -1,4-diisocya-nate, tolylene-2,4- and -2,6-diisocyanate and any mixtures of LeA 16,190 _7_ .

' . : ,, . ' ,. ' ; ~ '; ' ':
;

these isomers, diphenylmethane-2,4'- and/or 4,4'-diisocyanate naphthylene-l~5-diisocyanate~ or p-~ylylenediisocya~ate~

It is generally preferred to use commercially :
readily available diisocyanates such as tolylene-2,4-diiso-cyanate, 1-isocyanato-~3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, hexahydrotolylene-2,4~ and -3,6-diisocyanate and any mixtures of these isomers, perhydrodiphenylmethane-

2,4' and/or 4,4'-diisocyanate and hexamethylene-1,6-diisocyanate.

:
The uretdione polyisocyanates obtained, preferably uretdione diisocyanates, or mixtures of these uretdione isocyanates with polyisocyanates which are free from ur t~
dione groups, preferably diisocyanates, constitute the ~ -intermediate product mentioned above which is a preliminary lS stage leading to the products of the process according to the invention. .

According to first m~thod of carrying out the pro- -~
ce~s of the invention, this intermediate product is con-verted directly without further modification into the pro~
duct according to the invention which contains uretdione : ~
groups and blocked isocyanate end groups, as will he described :~ :
~-:: .
below. According to a second method, the reaction with the blocking agent is combined wi~h a chain lengthening reaction so that the afore~aid intermediat~ product is modiied , ;~::
with a subequivalant quantity of a difunctional or trifunc- ;
tional chain lengthening agent~ This modification i5 ~ar~

ried out beor~ and~ox during and/or after the exces~ iso-cyanate groups are blocked with the blocking agent. This -~
modification of the intermediate product with a difunctional :.: :
LeA 16,190 -8- ~
: ;.

f~

or tri~unctional chain lengthening agent provides a simple me~hod of varying the proportion of uretdione groups to the isocyanate groups which are blocked with blocking agent and in addition, if trifunctional chain lengthening agents are used, it provides for the possibility of increasing the isocyanate functionality of the polyisocyanates which can be obt~ined by the action of heat on the products according to the invention. The difunctional or trifunctional chain lengthening agents are used in quantities of 0 to about 30%
by weight :in the process according to the invention, the quantities being based on the aforesaid interm~diate pro-duct. The difunctional or trifunctional chain lengthening agents are compounds having molecular weights ranging from abollt 18 to 300 which contain 2 to 3 groups capable of reacting with i~ocyanate groups, preferably hydroxyl and/or amino gxoups. . `

Water or alcohols of the formula . ' : ~ ' wherein m represent~ 2 or 3 and R represents an aliphatic or cycloaliphatic hydrocarbon group having 2 to 18 carbon atoms which may be interrupted by ether oxygen atoms, for example, are suitable chai~ lengthening agent~. :

Examples of such polyhydric alcohols include ethylene glycol, propylene-1,2- and -1,3-glycol, butylene- :
1,4- and -2,3-glycol, hexane-1,6-diol, octane~l,8-diol, neopentyl glycol, 2-methyl-1,3 propanediol, diethylenegly- ~ .
col, triethyleneglycol, tetraethyleneglycol, dipropylene-glycol, tripropyleneglycol, dibutylene glycol, 2-ethyl-hexane-1,3-diol, 1,4 bis-hydrox~methylcyclohexane, 2-L~A 16,190 -9- ~:
.

.
. . .

methyl-1,3-propane-diol, glycerol, trimethylolpropane, hexane-1,2,6-triol, butane~l,2,4-triol and trimethylolethane.

The chain lengthening agents having amino groups which are well known in the chemistry of isocyanates may also be used as linking components in the process according to the invention. Examples of such chain lengthening agents include hydrazine, ethylene diamine, triethylene dianine, hexamethylene diamine, diethylene triamine, dipropylene diamine and the like.

Chain lengthening agents which contain aromatic nuclei or ester group~ are also suitable e.g. terephthalic acid bis-ethylene glycol ester or 1,4-bis-(2-hydroxyethoxy) `-benzene.

If the reaction between ~he intermediate products and the chain lengthening agent i~ carried out before the :. ~ -blocking reaction, the reaction~ are brought together in the proportions mentioned above at temperatures of ~rom about 0 to lS0C and preferably about 80 to 120C, care being ~::
taken to ensure that the i~ocyanate groups are always pre~ent in excess over the groups which are capable of reacting with isocyanate groups. The molar ratio of iso-cyanate groups to group~ which are capable of reacting : .
with them is generally between 1 O and about 1 0.99 and preferably between 1 O p and about 1 : 0. 87 in the reactio~
between th~ above-mentioned intermediate product and ahain lengthening agent regardless of the ~tage at which the chain leng hening reaction i~ carried ou~, that i~
to ~ay al~o if it i5 carried out duxin~ and/or after the blocking reaction.
LeA 16,190 -10- :
...',.. '.,,'. .

- ' ~ ' ' : ,~ ' The reaction of the above-mentioned intermediate product with the chain lengthening agent may be carried out in the presenca of the solvents described below and of the known catalysts described below for accelera ing the diisocyanate polyaddition reaction.

The reaction of the aforesaid intermediate pro-duct with the chain lengthening agent is preferably carried out by using mixtures of chain lengthening agent and block-ing agent in the process according to the invention. In principle, the chain lengthening reaction could be carried out after the isocyanate groups of the said intermediate product have been partially blocked, or the diisocyanates used as starting material could be partly blocked and the chain lengthening reaction can then be carried out after dimerization.

~ locking agents suitable for the process according to the i.nvention are in particular c~mpounds which contain preferably one group capable of reacting with isocyanate groups and which enter into an adclition reaction with organic isocyanates at te~peratures above about 50~C and pre~erably between about 80 and 120C $o produce addition products which, when mixed with non-volatile polyols which contain primary hydroxyl groups at temperatures between 100 and ~00C, release the blocking agent and react with the non volatile polyols to produce urethane. Suitable blocking agents of this Xind include e.g. secondary or tertiary alcohols suah a~ i30propanol or tert.-butanol, oximes such as formaldoxime, acetaldoxime, methyl ethyl ketone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime or diethylglyoxime, lactams such as ~-caprolactam, LeA 16,190 -- ~ .. . , : . .. ;~ - , , .

~3~

~-valerolactam or y-hutyrolactam, phenols suoh as phenol or o-methylphenol, ~-alkylamides such as N-methyl-ac~t-amide~ imides such as phthalimide, imidazole or alkali metal bisulphites.

Particularly suitable blocking agents for the process according to the invention are compounds of the formula: :

X-~ :

in which X represents the following groups.

O ~: :
. . .

-N \ (CH2)n (n = 3 _ 7) ~ -~~ , '' ~ --o~

~ H3 . ' :' .

-O ~ or -O-N-C

CH \ R2 .

wherein Rl and R2 represent identical or different ali-phatic hydrocarbon groups containing 1 - 4 carbon atoms ..
or Rl and R2 t¢gether wi~h the carbon atoms which is attached to the nitrogen atom by a double bond form a cycloaliphatic hydrocarbon group containing 5 or 6 carbon atom~.
LeA 16,190 -12 ~ ~ -,: ~ -.. . . . . . . . . . . . . . . . ... .. . . .

In the process according to the invention, the blocking agents may be used in combina~ion with chain lengthen-ing agents, as already explained above. The compound which is reacted with the blocking agent may be either the inter-mediate produc~ mentioned above which is not modified wi~h chainlengthening agent or the chain lengthened intermediate product mentioned above. In the blocking reaction, the molar ratio of isocyanate groups : (groups in the blocking agent which are reactive with isocyanate groups plus groups in the chain lengthening agent optionally present with the blocking agent which are reactive with isocyanate groups) is between about 1 : 1 and about 1 : 2 and preferably between about 1 : 1.1 and about 1 : 2. The blocking reaction is generally carried out by intro-ducing the isocyanate component into the reaction vessel and adding the other reactant. The reaction may be carried out solvent-free or in ~he presence of suitable solvents, e.g~
benzene, toluene, methyl or ethyl glycol acetate, dimethyl-~ormamide, xylene or other aromatic or aliphatic hydrocarbon~
including also ketones such a acetone t methyl butyl ketone or methyl isobutyl ketone, ~clohexanone, chlorinated aromatic hydrocarbons and any mixtures of these and other inert organic solvents.

The blocking reaction is generally carried out at -temperatures of from aboutc50- 150C and preferably from about 80 - 120C. The products of the process generally crystalize during and after cooling of the reaction mixture. Catalysts which accelerate th~ isocyanate polyaddition reaction may also be used or this reaction, but not those catalysts which contain very strong basic centers because the latter, which are common7 y used as catalysts in polyisocyanate chemistry, are liable to bring about premature opening of the uretdlone ring in the LeA 16 ,190 -13-~.

process according to the invention.

On the other hand, organic metal compounds,particularly organic tin compounds, may be used as catalysts in the process according to the invention. -~

The organic tin compounds used as catalysts are preferably tin~ salts of carboxylic acids such as tin~
acetate, tin-(II~ oc~oate, tin-(II) e~hyl hexoate and ~in-(II) laurate as well as the dialkyl tin salts o carboxylic acids, e.g. dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate or dioctyl tin diacetate.

Other examples of catalysts which may be used for the process according to the invention and details about the action of these catalysts may be found in Kunststoff-Handbuch, Volume VII~ published by Vieweg and Hochtlen, Carl-Hanser-Verlag, ~unich (1966), e.g. on pages 96 - 102.
.
The catalysts are generally used in a quantity of between about 0.001 and 10% by weight, based on the quantity of compounds which contain hydrogen at~ms capable of reacting with isocyanates.

.. .. . ...

~ 20 Reaction retarders may also be used in the process ..;0~ ,... .. .
according to the invention, e.g. compounds which are acid in reaction such as hydrochloric acid or organic acid halides.

: ':
The reaction mixtures are generally worked up by ~reeing the polyuretdione poly~rethanes which are blocked at the end group~ rom any ~olvent uæed in the process. This can be achieved by suction filtration and/or by ~imply air drying the crystalline polyuretdione polyurethanes or by other known methods such as spray dr~ing or melt extrusion in an evaporation screw.
LeA 16,190 -14-.

The products obtained by the process according to the invention are generally compounds having molecular weights of from about 300 to 4000 and preferably about 400 to 3000.
They have a melting point of 30 to 240C and preferably from 70 to 180C. The preferred latent polyisocyanates according to the inven~ion are characterized by containing about 2O5 to 10% by weight and preferably about 3.5 to 8% by weight of uretdione groups (calculated as -N=(CO~2=N-) and about 2 to 15% by weight, preferably 4 to 10% by weight of blocked isocyanate end groups (calculated as -NCO). The products of the process are particularly suitable for use as hardeners for higher unctional thermoplastic compounds which contain Zerewitinoff hydrogen atoms. When used in combination with such :~
compounds, they form syRtems which c,an be hardened to form high ~uality resins at temperatures above 110C and preerably at abouk 160 to 220C. The most important field of application for such systems lies in their use as binders for powder lacquers. -;~

The compound~ which can be obtained ac~ording to ~he invention may also partly or completely replace the known polyisocyanates used for the production of polyurethane elastomexs, polyurethane leather coatings, polyure~hane foam~
or other polyurethane products.

In this way, polyaddition xeactions can be accompanied by cross-linking.

Suitable reactants which may be used with the products of the proces~ ~or producing such systems which ~a~
be cro~-linked by heat are compounds ~f the kind already known in the chemistry of polyurethanes which contain amino, 3p thiol, carboxyl, and/or hydroxyl groups. I~ is preferred to use polyhydroxyl compounds, in particular compounds which LeA 16,190 -15- :

f~
con~ain 2 to 8 hydroxyl groups and e~pecially tho~e having a molecular weight of about 400 to 10,000, preferably poly-esters, polyethers, polythioethers, polyacetal~, polycarbonate~, polyester amides, polyepo~ides and polyacrylate~ having 2 to 4 hydroxyl groups, of the kind which are already known for the prepaxation of polyurethanes.

Suitable polyesters having hydroxyl groups include, e.g. the reaction products of polyhydric alcohols, preferably dihydric alcohols with the optional addition of trihydric :-alcohols, with poly ~sic, preferably dibasic carboxylic acids.
Instead of free polycarboxylic acids, the corresponding polycarboxylic acid anhydrides or corresponding polycarboxylic acid esters of lower alcohol~ or mixtures thereof may be used : for preparing the polyesters. The polycarboxylic acidR may be aliphatic, cycloaliphatic, aromati.c and/or heterocyclio and they may be substituted, e.g. wi1:h halogen atoms, and/or unsaturated. The following are examples: succinic acid, adipic acid, suberic acid, azelaic acid, ~ebacic acid, phthalio acid, isophthalic acid, trimellitic acid phthalic acid anhydride, tetrahydrophthalic ~cid anhydride, hexahydrophthalic acid anhydride, tetrahydrophthalic a~id anhydride, hexahydro-phthalic acid anhydride, tetrachlorophthalic acid anhydride, endomethylenetetrahydrophthalic acid anhydride, glutaric acid anhydride, maleic acid, maleic acid anhydride, fumaric acid, dimeric and trimeric ~atty acids such as oleic acid, if desired mixed with monomeric fatty acid, dimethylterephthalate --or bis-glycol terephthalate. Suitable polyhydric alcohols include e.g., ethylene glycol, propylene-1,2- and -1,3-glycol, butylene-l, 4- and -2, 3-glycol, hexane-1,6-diol, octane-1,8-diol, neopentyl glycol, cyclohexanedimethanol (1,4-bis-hydrox~methyl- .-cyclohexane), 2-methyl-1,3-propanediol, glycerol. trimethylol- ~
propane, hexane-1,2,6-triol, butane-1,2,4-triol, trimethylol~ :

LeA 16,1gO -16- :

.: : , . - .

ethane, pentaerythri~ol, quinitol, mannitol and ~orbitol, methylglycoside, diethyleneglycol, triethyleneglycol, tetra-ethylene glycol, polyethyleneglycols, dipropylene glycol, poly-propylen~glycols r dibutyleneglycol and polybutyleneglycols.
The polyes~er~ may in part contain carboxyl end groups.
Polyesters of lactones such as -caprolactone or of hydroxy-carboxylic acid, e.g. ~-hydroxycaproic acid may also be used.

The polyethers which are suitable for the purpose of the invention, which contain a~ least two, generally 2 to 8 and pxeferably 2 or 3 hydroxyl groups, are known p r se and can be prepared e.g. by the polymerization of epoxides such as ethylene oxide, propylene oxide, butylene oxide, -tetrahydrofuran, styrene oxide or epichlorohydrin, either each on its own, e.g. in the presence of BF3, or by addition of these epoxides, i~ desired as mixtures or successively, to ~tarting components which contain reac~ive hydrogen atoms, such as water, alcohols or amines, 13.g. ethylene glycol, propylene-1,3- or -1,2-glycol, trimethylolpropane, 4,4'~dihy droxydiphenylpropane, anili~e, ammonia, etha~olamine or ethylenediamine. Sucrose polyethers of thP kind described in e.g. German Auslegeschriften No. 1jl76,358 and 1,064,938 may also be used according to the invention. In many eases it is preferred to use polyethers which contain predominantly primary O~ groups (up to 90% by weight, based on all the O~I
groups present in the polyether). Polyethers modified wi~h vinyl polymers, eOg. the polyethers which can be obtained by the polymerization of styrene or acrylonitxile in the presence of polyether~ (U.S. Patent Specification Nos. 3,383,351;

3,304,273; 3,523,033 and 3,110,695 and German Patent Specifica-tion No. 1,152,536) and polybutadienes which contain O~ group~
are al~o suitable.

LeA 16,190 -17-.: . ~ .:- . . .
',' . ~' ' ' ' ",' ' ' ' ,~ ' ' ' ' : ~, .
, Particular examples of the polythioethers are th~
condensation products obtained by conden~ing thiodiglycol on its o~n and/or with other glycols, dicarboxylic acid, formal-dehyde, aminocarboxylic acids or amino alcohols. The product~
obtained are polythio mixed ethers, polythio ether ester~ or polythioether ester amides, depending on the cocomponen~s.

Suitable polyacetals are e.g. the compounds which can ~e prepared from glycols such as diethylene glycol, triethylene glycol, 4,4'-dioxe~hoxy-diphenyldimethylmethane, hexane diol and ormaldehyde. Polyacetals suitable for the purpo~e of the in~ention can also be prepared by the polymerization of cyclic acetals.

Suitable polycarbonates having hydroxyl groups include those known per se which can be prepared e.g. by the reaction of diols such as propane-1,3-diol, butane-1,4-diol and/or hexane-1,6-diol or diethylene glycol or triethylene glycol with diaryl¢arbonates such as diphenylcarbonAte or phosgene. -:

Suitable polyester amides and polyamides include, for example, the predominantly linear condensates obtained rom polybasic saturated and unsaturated carboxylic acids or their anhydrides and polyvalent saturated and unsaturated amino alcohols, diamines, polyamines and mixtures thereof.

Suitable polyepoxides include e.g. the known -reaction products o~ bisphenol A with epichlorohydrin.

Suitable hydroxypolyacrylate~ include e.g. the known copolymer of olefines such as acrylonitrile and~or styrene with acrylic acid esters and/or mathacrylic acid e~ters in which the alcohol component consists at least partly ~:~
of a diol such as ethylene glycol or propane 1,2-diol. :

LeA 16,190 -18-~;

. . .

The reactants used with the products of the process for producing binders for powder lacquers are, of coursP, preferably solid representative~ of the compou~ds listed above as example~, in particular those having a softening point of between about 60 and 120C and preferably between about 80 and 100C. The mixture~ which are capable of being cro~s- . -linked generally contain about 0.5 to 1.5 and preferably about 0.8 to 1.2 hydroxyl groups per latent iso~yanate group, based on the polyhydroxyl compounds mentioned above. If the mixtures of reactants are to be used as powder lacquers, they preferably have a melting point of from about 50 to 150C and preferably from about 70 to 120C. Care must be taken to ensure that the melting point of the powder lacquer binder when ready for u~e is at least about 10 to 20C below the cross-linking temperatur~.

Th~ compounds described above which contain Zerewitinoff active hydrogen atoms may be mixed with poly-uretdione polyurethanes according to the invention immediately a~ter the latter have been synthesizecl, using the same reaction vessel. Homogeneous, clear, ~elf-cross-linking two-component resins are o~tained in this way after evaporation ~ :
of the solvent, e.g. using melt extruders. The resi~s may be -~ ~:
mixed in the usual manner, either at the same time or in a ~:
subsequent operation, with known dyes, pigments, fillers~ other resins, hardening catalysts and auxiliary agents such as flow 25 levelling agents, UV absorbents, matting agents, etcThe binders may, of course~ also be used unpigmented, for example as clear lacquers, or they may b~ dissolved in solvents and . ~ -used in this form e O g . for lacquering wires and as electro- .
insulating materials.

Summarizing, the process according to the invention ~ :
for the preparati.on of polyisocyanates or polyurethanes having ~:
uretdione groups and blocked end groups which are to be used as `.:
LeA 16,190 -19-, .:

starting materials for the produc-tion of polyurethane resins has the following advantages:

1. Physiologically inert, latent polyisocyanates having a high-po-tential isocyanate content are made available by a simple method of in situ preparation from diisocyanates after dimerization, if desired also after chain lèngthening, and addition of blocking agents 2. ~he simplicity of the method of preparing the new polyuretdione polyurethanes with blocked end groups as free flowing, physiologically inert reactive po~ders opens up new possibilities for the production of powder lacquers which can be kept in storage. The polyuretdion~-polyurethane cross-linking agents are compatible with n~lmerous hard, linear or branched polyhydroxyl compounds of various kinds and can be mixed with them in extruders without entering into preliminary reactions. The extruded resins obtained are hard and brittle and very suitable for grinding. Powclers applied to metal sheets by the known electros-tatic powder spray process have levelling temperatures of from about 80 to 120C and can be stoved within about 15 to 30 minutes at temperatures of from about 130 to 220C, preferably about 150 to 180C. High impact strength, elastic, weather-resistant metal coatings having a finish varying from matt to high gloss are obtained after stoving.

The reactive powders are stable in storage and non-blocking even under extreme conditions (presence of water storage at 60C). They have no tendency towards sel~-ignition or dust explosion.

3. Films~ sheets and leather-like materials having 16,190-CA - 20 -high tensile strength can be produced from the polyuretdione compounds having blocked end groups according to the invention.

4. The compounds according to the invention may also be used as mixtures with known polyisocyanates Eor the produc-tion of polyurethane foams, in which case the reactive systems according to the invention liberate their isocyanate groups only towards the end of the foaming process, when elevated tempera-tures have developed in the interior of the foam blocks, and thereby increase the degree of cross-linking.

The invention will now be described in more detail with the aid of the following examples. The parts mentioned are parts by weight unless otherwise indicated.

J LeA 16,1go-CA - 21 -J

~ I, 696 parts of tolylene-2,4-diisocyanate are dissolved in 2600 parts of toluene. The reac~ion mixture is then cooled to 10 - 15C and 14.4 parts of tri-n-butylphosphine are added wi~h vigorous stirring. ~imeric TDI is produced in a slightly exothermic reaction after only 3 to 5 minutes. It can easily be stirred and separates as a crystalline suspension. The mixture is stirred for 5 to 6 hours with cooling under nitrogen.
The mixture in the reaction vessel cools to 10 - 13C during this time. 27.4 parts of a 10% solution of sulphur in toluene heated to 90 - 100C are then added. The vessel i5 then heated to 100C and a clear solution is obta:Lned. A sample is removed from the solution to determine the isocyanate number. The isocyanate content of the mixture (free ~CO) is found to be 27 to 28% NCO. 523 parts of ~-caprolactam are then added gradually to the reactio~ mixture at !90 to 100C.
i When all the F-caprolactam has been added, the mix-ture is stirred for a further 2 to 3 hours at 90 to 100C.
About 1050 parts of finely crystalline, free-flowing powd~r having a melting point of 191 - 192C are obtained after cooling, suction filtration and drying. The cross-linking agent contains 5.9% by weight of uretdione groups and 15.6~
by weight of blocked NCO, and therefore a total of 27.4% by weight of latent NCO.

A mixture of 396 part~ ~4 OH e~uivalents) of 1,4- , `-bis-(2-hydroxyethoxy)-ben3ene and 452 parts (4 mol) of caprolactam is rapidly adcled to 1512 parts (8 NCO equiva-lents) of a polyisocyanate mixture consisting mainly of dimeric .
~ LeA 16,190 -22~ ~

hexamethylene diisocyanate at 100 to 120~C under nitrogen.
After a reaction time of 15 to 30 minutes, l part of tin-(II) octoate is added to the mixture. This causes the reaction temperature to rise to 130C. The highly viscous melt obtained is stirred for a further 30 to 60 minutes at 130 to 140C and poured out on to metal sheets while still hot. The resin solidifies to a solid product having a melting point of 120 to 123C which can easily be ground up. The cross-linking agent contains 4.75% of ure~dione groups -N=(CO)2=N- and 7.1% of blocked NCO and therefore a total of 16.6% of laten~ NCO.

Polyuretdione polyurethanes which are ~locked at their end ~roups and which-have been synthesized from uretdione diisocyana~e, diols and masking agent'3 according to ~he general lS method of preparation are summarized in the following Table (the quantities are also indicated in the Table)~ ;

n The uretdione diisocyanate, whi~h may have been prepared in situ, is introduced into the reaction vessel (optionally using ~oluene or xylene as solven~ and heate~ to 90 - 100C. The masking agent is added to the isocyanate mixture with vigorous stirring under nitrogen, and $he chain lengtheniny diol is added at the same time or subsequently.
Only a small quantity of free isocyanate can be dete~ted in the IR spectrum of the reaction mixture after a reaction time of 1 to 4 hollrs at 90 to 100C. The reaction mixture is left to stand at room temperature for l~ hours. No more free isocyanate can then be detected in the IR spectrum.

A very f.ine, free flowing powder is obtained after LeA 16,190 -23- -'. . . .

drying and if necessary size reducing the reaction products.
The IR spectra of the reactive powders have the characteristic intensive bands of the uretdione group at 1760-1780 cm 1, :

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.

348 parts of 2,4-diisocyanatotoluene ars di~solved in 1300 parts of toluene, and 7.2 parts of tributylphosphine are added under nitrogen with cooling. After a reaction time of 4 hours at 7 to 10C, 15.9 ml of a 10~ solution of sulphur in toluene are added to the reaction mixture. The crystalline suspension in toluene is heated to 100C wi~h stirring ~o form a clear solution. A sample is then removed from the reaction mixture to determine the NCO number. The polyisocyanate mixture :
is found to contain 29.7% of NCO (free NCO). 315 parts of aza-lactam (l-N-methylhexyhydro-1,4-diazepinone (see German Offen-legung~schrift 2,035,799)) are then added to the reactîon mixture and the mixture is heated to 100C for a further 4 hours. 670 parts of a finely crystalline compouncl having a melting point of 177-179C are obtained after coolirlg, suction filtration and drying. The cros~-linking agent contains 5.15% by weight of uretdione groups -N-(CO~2=N~ and 15.15% by w~ight of blocked NCO and therefore a total of 25~45% by weight of latent NCO.

EX~MPLE 18 Prepaxation_of a powder lacquer ready for use 1. Method:
The required components consisting of 100 parts of a branched chain terephthalate polye~ter of terephthalic acid, neopentyl glycol, hexanediol and trimethylolpropane -:~
(1,5% OH) and 13 parts of cross-linking agent from ~xample 3 are ~irst mixed with finely divided titanium dioxide pigment. A commerclal copolymer o~ butyl Acrylate and 2-methylhexalacrylate is used as levelling agent.
The levelling agent i~ incorporated in the form o a so-LeA 16,190 -28- ;
...
.' .

called master batch, i.e. 100 parts of the polyester and 10 parts of levelling agent are melted toge~her and size reduced when solidified.
The components are homogenized in a commercial two-shaft, self-cleaning extruder apparatus~ The temperature of ~he jacket of the extruder is adjusted so that the outlet temperature of the melt is approximately 125C. The melt cake may either be left to cool by itself or, as is ~.
more common in practice, it may be rapidly cooled by means ; -of a continuously operating squeezing and cooling device.
Ater it has cooled to a room temperature of 20 to 30C, it is first coarsely ground and then fine ground wh.ile being cooled with a blast of air. The fine powder obtained is then freed from coarser fractions with particles larger than about 90 ~m by wind sifting or mechanical sifting. ~ -The powder lacquer obtained in this way is subsequently applied by means of an electrostatic spray device, which may be any of the commercially available products.
The voltages applied may be positive or negative with respect to the workpiece and may lie within a range of about 20 to 100 kV.
To obtain homogen~ous, smooth, mechanically perfect films, the lacquer is melted and hardened in a stoving oven at temperatures of between 160 and 220C.
2. Lacquex technical properties of the combination described under 1 of terephthalate polyester and cross linking agent from Example 3: ~
The metal ~heet to which the la~u rs are applied are ~...... -in all ca~es steel sheets of quality St 14.05 with a thickness of 0.5 mm unless otherwise indicated. . ~.:
LeA 16,190 -29~
'',:..:' :: ;': ' , . : ,, ,: , The samples are tested after they have been stoved for 30 minutes at 180C or 10 minutes at 200C.

Elasticity tests_ 1. The elasticity is tested by Erichsen cupping according to DIN 53 156: 9 mm or until the sheet cracks.
2. Conical mandrel according to ASTM D 522 - 41: 37% (free from faults).
3. Grid section accordiny to DIN 53 151, appara~us Gt C : O
(free from faults, optimal). ~-10 4. Pencil hardness according to DIN 46 450* : 3 H
*Test method for wire lacquers. -The knife test shows that the chips cut from the sample are tough and elastic and it con~irms the excellent adherence in the grid section testing method.

The solvent res tance shows eviclence of good chemical cross-linking. The ~ac~uers are found to be resistant to tolu~ne J ethyl glycol a~etate and acetone when exposed to the~e solvents for several minutes until the surface begins ~ -~o soften. The coat does not dissolve but only swells Rlightly.

The corrosion xesistance is tested by the salt spray test according to DIN 53 167~ The sur~ace to which the lacquer is applied is pretreated with a zinc phosphate coating. Aft~r 400 hours, undersurface rusting is found to occur for at most 3mm from a cut made before the test. The best possible results ~5 are obtained with the adherence test in the grid section carried - -out immediately after the ~ample is removed, a~ well as with the test using a self~adhesive tap.

The test for detergent resistance which is also carried o~t on zinc phosphate treated steel sheet to test the rasistance ~o LeA 16,190 -30-';' :.

ordinary household detergents shows that he samples are resistantto the test solution for more than 40 hours at 100C without producing any faults.

The surface is in all cases very smooth with no signs of an orange peel effect and no shrinkage from ~he edges. ~he film is homogeneous and free from bubbles.

Example of use 19 .
Examples 19 and 20 serve to demonstrate that the polyuretdione polyurethanes according to the invention can also be used for the production of films and lether-like materials.

2.52 g of the cross-linking agent based on hexa-methylene diisocyanate described in Example 2 and 10 g of a h~xanediol polycarbonate having a molecular weight of 2000 and an OH number of 56 are mixed in the molten state at 100C. The molten mixture is then poured out on to a glass plate and ~toved for 30 minutes at 180C. A soft; tear-re~istant film is obtained. After 2 to 3 day~' storage at room temperature, it has high tensile strength and a dry handle.

Exam~le of use 20 2~52 g of the cross-linking agent described in Example 2 and 10 g of a polyester having a molecular weight of 2000 and OH number 56 which has been prepared from adipic acid ~ ; -and ethylene glycol are mixed in the molten state at 80 o 100C
The melt is then poured out on to a glass plate and stoved for 30 minutes at 180C. A clear, stretchable, tear-resistant, non-tacky film is obtained. ::

Example of use 21 This example serves to show that pulverulent polyuretdione polyurethane cross-linking agents can also be LeA 16,190 -31--~ , ~ , , ~ : : . . . .

~35~

used in formulations for foam resins since they have no deleterious effect on the formation of the foams but substantially increase the degree of cross-linking when the foam is reheated.
a) The polyether used in ~his example for the production of the foam was prepared as described below and has the following composition:
Polyaddition of propylene oxide to a mixture of trimethylolpropane and propylene glycol was first carried out in the presence of catalytic quantities of sodium alcoholate. Polyaddition of ethylene oxide was then carried out in a second phase. The liquid polyether contains primary and secondary hydroxyl groups and has an OH number of 49, an average molecular weight of 3200 and an average functionality of 2~78. ~ ;
~) Preparation of the foam:
100 parts of the polyether described under a), 4 par~s of water, 2 parts of a commercial polyethersiloxane stabiliz er, 0.2 parts of triethylene d.iamine, 0.25 parts of a tin-~II) salt of 2-ethylcaproic acid and Z.5 part~ of the cross-linking agent described in Example 1 are vigorously mixed.
50 parts of toIylane diisocyanate (80~ 2,4- and 20% 2,6-i~omer) are added to this mixture and the components are vigorously mixed with the aid of a high spe~d stirrer.
Foam formation begins after a starting time of 10 seconds ~5 and white, soft elastic, open celled polyurethane foam is :
obtained~ The foam is subsequently reheated at 160-170C -:
for 30 minutes. The resulting foam is more tear-resis~ant -~
than a comparison sample which has been produced without . ~-the additional cross~linking agent from Example 1.
.. . . . . .
Although the inv~ntion has been deqcribed in detail for the purpose of illustration, it is to be understood that LeA 16,1g0 -32-variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention excep~ as it may be limited by the claims.

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LeA 16,190 -33- ~:

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Claims (9)

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. Organic compounds which contain uretdione groups and blocked isocyanate end groups produced by a process charac-terized in that an organic polyisocyanate is converted in a known manner into an intermediate product which contains uret-dione groups and free isocyanate groups, and this intermediate product is converted into the corresponding compound which contains uretdione groups and blocked isocyanate groups and optionally also contains urethane and/or urea groups in the chain by reaction with a blocking agent which is monofunc-tional for the purpose of the isocyanate polyaddition reaction, optionally before and/or during and/or after the reaction with subequivalent quantities of a chain lengthening agent which has a molecular weight range of about 18 to 300 and contains 2 to 3 groups which are reactive with isocyanate groups.

2. Organic compounds produced according to Claim 1, characterized in that the proportions in which the reactants are used are chosen so that the products of the process con-tain about 2.5 to 10% by weight of uretdione groups -N=(CO)2=N-and, calculated as NCO, about 2 to 15% by weight of blocked isocyanate end groups.

3. Organic compounds produced according to Claim 1, characterized in that the blocking agents used are compounds of the formula X-H
wherein X represents (n = 3 - 7) or wherein R1 and R2 denote identical or different aliphatic hydrocarbon groups containing 1 to 4 carbon atoms or R1 and R2 together with the carbon atom which is attached to the nitrogen by a double bond represent a cycloaliphatic hydrocarbon group containing 5 to 6 carbon atoms.

4. Organic compounds produced according to Claim 1, characterized in that the organic polyisocyanate used is 2,4-diisocyanato-toluene, 1-isocyanato-3,3,5-trimethyl-5-isocyanato-methyl-cyclohexane, hexamethylenediisocyanate, 2,4-diisocyanato-perhydrotoluene or 4,4'-diisocyanatodicyclohexylmethane.

5. Organic compounds produced according to Claim 1, characterized by a molecular weight of from about 300 to 4000.

6. Latent polyisocyanates containing uretdione groups produced by a process comprising a) dimerizing an organic diisocyanate at temperatures be-tween about 0 and 120°C in the presence of ahout 0.1 to 5 wt. %, based on the weight of diisocyanate to be dimerized of a tertiary phosphine catalyst until about 25 to 50% of the NCO
groups present in said diisocyanate have been dimerized, b) inactivating said phosphine catalyst by the addition of elemental sulphur dissolved in an organic solvent, c) then adding 0 to 30 wt. %, based on the weight of isocyanate present of a chain lengthening agent having a molecular weight of about 18 to 300 and 2 to 3 groups per molecule capable of reacting with isocyanate groups, said chain lengthening agent being present in a subequivalent quantity, based on the free isocyanate groups chemically bound to uretdione rings, and d) reacting the free isocyanate groups present with a blocking agent which has one group per molecule reactive with an isocyanate group at temperatures between about 80 and 120°C.

7. A process for the production of polyurethane resins comprising reacting polyhydroxyl compounds with the organic compounds produced according to Claim 1 by the isocyanate polyaddition process.

8. A process for the production of polyurethane resins comprising reacting polyhydroxyl compounds with the organic compounds produced according to Claim 6 under conditions of temperature and catalysis sufficient to render both the uretdione groups and the blocked end groups reactive with said polyhydroxyl compounds.

9. Polyurethane resins produced by the process of either Claim 7 or 8.