Abstract:
A process for the production of a blocked urea group-containing polyisocyanate from a partially blocked polyisocyanate and polyamine, comprising the steps of: 
     (i) reacting a partially blocked polyisocyanate, said polyisocyanate being made substantially free of monomeric polyisocyanate, by vacuum thin layer evaporation with a primary polyamine, secondary polyamine, or mixtures thereof, in relative proportions such that the ratio of isocyanate groups to amino groups is in the range from about 1:1 to 1.3:1, and 
     (ii) isolating said urea group-containing polyisocyanate by wherein the vacuum boiling point of said polyisocyanate is lower than the deblocking temperature of said urea group-containing polyisocyanate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a process for manufacturing blocked, urea group-containing polyisocyanates from semi-blocked polyisocyanates and polyamines. 
     2. Discussion of Background 
     The reaction of polyisocyanates with polyamines is so violent that &#34;it has priority over all other isocyanate reactions&#34; (cf. Houben-Weyl, Methoden der Organischen Chemie. Vol. XIII, p. 132). This high reactivity may also be the reason for the fact that for a long time little research has been done on the direct reaction between polyamines and polyisocyanates to the corresponding urea derivatives. 
     Of course, in principle symmetrical urea derivatives can be obtained through direct conversion of polyisocyanates and water according to the process designated in DE-OS No. 23 41 065, but with this process one must accept the fact that gaseous reaction products, which must be carefully removed, are produced during the formation of urea. Furthermore, the reaction between water and isocyanate has the drawback that there is limited variability and in using the stoichiometric method, oligomeric urea will form, leaving monomeric polyisocyanate. In addition to this, DE-OS No. 23 41 065 teaches that frequently an excess of polyisocyanate-isophorone-diisocyanate is added or that due to viscosity reasons, solvents must be used. 
     Another disadvantage is that the high reactivity of the reaction between a polyamine and polyisocyanate results in a reaction that can be controlled only with difficulty, and results in a wide range of molecular weights. 
     This reaction is also observed in the preparation of biuret polyisocyanates and represents there an undesired secondary reaction (cf. DE-OS No. 22 61 065, OS No. 26 09 995 and U.S. Pat. No. 3,903,126). 
     Finally, in the DE-OS No. 31 43 060 a process for preparing blocked, urea group-containing isophoronediisocyanate adducts is described. Such compounds are obtained by converting 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, also called isophorone diisocyanate (IPDI), that are partially blocked with epsilon-caprolactam, and diamines having two sterically feasible primary and/or secondary amino nitrogens. The reaction is performed neat and, for viscosity reasons, must occur above 130° C. and, as demonstrated in the examples, even at 160° C. If the partial blocking of IPDI is carried out according to the directives in DE-OS No. 31 43 060, then as the reaction equation shows and it would be desirable, ##STR1## not only the partially-blocked IPDI adduct but also completely blocked IPDI is obtained while retaining from 15 to 17% by weight non-reacted, thus unblocked monomeric IPDI. This high monomer content has a very grave disadvantage, since during the reaction with diamines, it is responsible for the formation of undesired polymeric urea compounds. 
     According to DE-OS No. 31 43 60, further reactions of the partially blocked polyisocyanates with polyamines are unsuitable for producing urea compounds that are interesting for polyurethane chemistry. 
     SUMMARY OF THE INVENTION 
     Therefore, one object of the present invention is a process for producing blocked urea group-containing polyisocyanates from partially-blocked polyisocyanates and polyamines. 
     This and other objects which will become apparent from the following specification have been achieved by the process for the production of blocked urea group-containing polyisocyanates from a partially blocked polyisocyanate and a polyamine, comprising the steps of: 
     (i) reacting a partially blocked polyisocyanate, said polyisocyanate being made substantially free of monomeric polyisocyanate, by vacuum thin layers evaporation with a primary polyamine, secondary polyamine, or mixtures thereof, in relative proportions such that the ratio of isocyanate groups to amino groups is in the range from about 1:1 to 1.3:1, and 
     (ii) isolating said urea group-containing polyisocyanate by wherein the vacuum boiling point of said polyisocyanate is lower than the deblocking temperature of said urea group-containing polyisocyanate. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Formulas I and II illustrate the type of polyamines that may be used in the present process: ##STR2## in which R is --(CH 2 )-- 2-36 , or C 2-36  branched alkyl, ##STR3## in which R 1  is the same as or different from R 3  =H, straight chain or branched alkyl, cycloalkyl-, aryl-, aralkyl, R 2  is --CH 2  -- or if desired, a branched alkyl group, in which the polyamine contains from 2 to 36 carbon atoms, and m=2 to 8, X=0 to 6, and n=2 to 8. 
     The polyisocyanates to be added according to the invention are described for example in &#34;Methoden der Organischen Chemie,&#34; Houben-Weyl, Vol. 14/2, 4th edition, Georg Thieme Verlag Stuttgart, 1963, pp. 61-70 and in W. Siefken, Liebigs Ann. Chem. 562, pp. 75-136. 
     By using a partially blocked polyisocyanate containing 6.5% by weight of monomeric polyisocyanate, preferably up to 3.5% by weight and in particular up to 2.5% by weight, it is possible to obtain an additional reaction. These partially blocked polyisocyanates may be produced by reacting a large excess of polyisocyanate (5 to 20 mole) with the blocking agent (1 mole) at temperatures ranging from 50° C. to 130° C., preferably from 70° C. to 100° C., and subsequently separating the excess polyisocyanate by means of conventional thin-layer evaporation. This process is disclosed in U.S. application Ser. No. 07/243,605, filed Sept. 13, 1988 incorporated herein by reference. 
     Only those polyisocyanates whose boiling points under vacuum are below the deblocking temperature of the blocking agent added are suitable and thus those which can be separated by means of thin-layer evaporation. 
     Particularly preferred aliphatic, (cyclo)aliphatic and aromatic polyisocyanates are those which are technically readily accessible such as 1,6-hexamethylene diisocyanate (HDI), 2,2,4,(2,4,4)-trimethylhexamethylene diisocyanate (TMDI), 2-methylpentane-1,5-diisocyanate (DI51), and 2,4- or 2,6-toluylene diisocyanate, and in particular 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (IPDI) and their mixtures of isomers. 
     For manufacturing polyisocyanate-urea-adducts according to the invention, polyamines having primary and/or secondary amino groups are suitable. They preferably have from 2 to 36 carbon atoms and can be aliphatic or have one or more cycloaliphatic, aromatic or heterocyclic rings having from 5 to 8 substituents. The polyamines that can be added can also carry tertiary amino groups. Non-limiting examples of suitable polyamines include: 
     (i) non-branched primary alkylene diamines, such as ethylene diamine, trimethylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, dodecamethylene diamine and the C 36  -diamine, 
     (ii) branched primary alkylene diamines, such as 2-methyl-pentamethylene diamine, 2,2,4(2,4,4)-trimethylhexamethylene diamine and 5-methylnonamethylene diamine, 
     (iii) cycloaliphatic primary diamines such as 1,4(1,2)-diaminocyclohexane, 2,4(2,6)-diamino-1-methylcyclohexane, 4,4&#39;-diaminodicyclohexylmethane, 4,4&#39;-diamino-3,3&#39;-dimethyldicyclohexylmethane, and 4,4&#39;-diamino-3,3&#39;5,5&#39;-tetramethyldicyclohexylmethane, 
     (iv) cycloaliphatic/aliphatic primary or secondary diamines, such as N-cyclohexyl-1,3-propylene diamine, bis-(1,4-aminomethyl)-cyclohexane and 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophorone diamine IPD), 
     (v) aliphatic primary and secondary polyamines such as diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, dipropylene triamine, dihexamethylene triamine, dioctamethylene triamine, and bis-(3-aminopropyl)ethylene diamine, 
     (vi) aromatic primary diamines such as 3,5-diethyl-toluylene diamine, 2,4(2,6)-toluylene diamine, 1,4-diamino-2,3,5,6-tetramethylbenzene and 4,4-diaminodiphenylmethane, 
     (vii) aliphatic secondary diamines such as 1,1,6,6-tetraisopropyl-2,5-diazahexane and N,N&#39;-diisobutyl isophorone diamine, 
     (viii) heterocyclic diamines such as 4-(3-aminopropyl-amino)- 2,2,6,6-tetramethylpiperidine and 4[(bis-3-aminopropyl)amino]-2,2,6,6-tetramethylpiperidine, 
     (ix) and their mixtures. 
     Melamine and water may also be used. 
     The addition of the aforementioned heterocyclic compounds is of a great interest since the manufacture of permanent ultraviolet-stable plastics, and in particular paint systems, are then feasible. In this method they function not only as an additive but rather they are incorporated directly into the macromolecule. 
     According to the invention, suitable blocking agents are those which deblock at curing conditions, i.e. between 140° and 220° C. This includes alcohols, e.g. methanol, ethanol, ispropanol, cyclohexanol; oximes such as acetone oxime, methylisobutyl ketoxime; mercaptans; lactams, for example lauryl lactam, acetoacetic ester, malonic ester, and especially epsilon-caprolactam and methyl ethyl ketoxime (cf. &#34;Methoden der Organischen Chemie,&#34; Houben-Weyl, Vol. 14/2, 4th edition, Georg Thieme Verlag Stuttgart, 1963, p. 61 ff.). 
     In the process of the invention, the curing agent is manufactured in the solvent and in particular such that the partially blocked polyisocyanate is present in the solvent and the polyamine is added dropwise either neat or also dissolved in a solvent. Suitable solvents are, on the one hand, those that can be readily removed such as toluene, xylene, cyclohexane, special benzene with less than 1% by vol. of aromatics (a mixture of mainly aliphatic, cycloaliphatic and aromatic hydrocarbons with a boiling point between 60°-96° C.), acetic ester and acetone, in order to isolate the polyisocyanate-urea-adducts of the invention; on the other hand, such solvents as toluene, xylene, SOLVESSO® 100 and 150 (mixture of aromatics produced by Esso), tetraline, cumene, methylisobutyl- and diisobutyl ketone, hexyl acetate, butyl acetate, ethylene glycol diacetate (EGA), methoxypropyl acetate (MOP-acetate), butylene glycol diacetate etc., which in industry are added for solvent-containing paint systems. 
     The aforementioned compounds can also be used as mixtures. The concentrations of polyisocyanate-urea-adducts can vary widely. Concentrations ranging from 30 to 70% by weight have proven to be advantageous. 
     According to the invention, the reaction takes place between room temperature and 80° C., preferably between room temperature and 70° C. Following successful addition of polyamine it is preferable to heat the reaction mixture to, if desired, a temperature ranging from 100° to 120° C. If the reaction product is to be liberated from the solvent, this can be done by simply applying a vacuum. Melt extrusion in an evaporation screw is especially suitable for removing the solvent. 
     The use of special benzenes having less than 1% by vol. of aromatics or cyclohexane as solvent has proven to be an especially advantageous process for manufacturing permanent, blocked polyisocyanate-urea-adducts according to the invention. In this process the reaction is carried out at room temperature, and in particular such that the partially-blocked polyisocyanate is dissolved in special benzene or cyclohexane and with intensive stirring, the polyamine is added dropwise in such a manner that the reaction temperature does not exceed 70° C. The reaction product precipitates out during the dropwise addition. Following completion of the amine addition, stirring is continued from 30 to 45 minutes and the solvent is subsequently removed. 
     In the conversion process of the invention, the reaction partners--polyisocyanate and polyamine--are added in such proportions as to give a ratio of isocyanate groups to amino groups of 1-1.3:1, preferably one isocyanate group per primary and/or secondary amino group. In general, the adducts of the invention have an NCO content ranging from 4 to 20%, preferably from 6 to 15% by weight. The free isocyanate content ranges from about 0.7% by weight to 5% by weight. The polyisocyanate addition products have a melting range from 90° to 210° C. They are especially suitable as curing agents for highly functional compounds having Zerewitinoff active hydrogen atoms. Combined with such compounds having Zerewitinoff active hydrogen atoms, above 140° C., preferably from 180° to 220° C., the polyaddition products result in systems that cure to high-grade plastics. Probably the most important application area for such systems is their use as linkers for PUR powder paint and solvent-containing single component-PUR-varnish. 
     The compounds of the invention are suitable as intermediate products for manufacturing plastics, in particular paints. Therefore, they are especially valuable because they also facilitate, in a simple manner, the manufacture of PUR varnish having a reduced degree of gloss. 
     Other features of the invention will become apparent according to the following descriptions of the exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. 
    
    
     EXAMPLES 
     Example 1 
     A. Preparation of partially blocked polyisocyanates General preparation 
     One mole of blocking agent was added in proportions of from 5 to 20 moles of polyisocyanate at temperatures ranging from 70° to 80° C. with stirring. After the completed addition of the blocking agent, the reaction mixture was then heated at 100° C. for another hour and subsequently the non-reacted polyisocyanate was removed via thin-layer evaporation at temperatures ranging from 90° to 140° C. and at 0.0133 mbar. The chemical and physical characteristic values of the reaction product (=residue) were determined and compiled in the following table. 
     
         __________________________________________________________________________Partially blocked polyisocyanatesStarting Materials            NCO content                    PolyisocyanateExamplespolyiso-     blocking            in % by weight                    monomer Viscosity in mPa&#39;sA    cyanate     agent  free                total                    % by wt.                            25° C.                                 30° C.                                     40° C.                                         50° C.                                             70° C.__________________________________________________________________________1    IPDI caprolactam            12.4                24.8                    &lt;1.0    1250000                                 410000                                     63500                                         13700                                             12502    IPDI caprolactam            11.5                24.5                    2.2     1145000                                 397000                                     61250                                         12530                                             10703    IPDI caprolactam            11.6                24.4                    3.5     1120000                                 360000                                     59500                                         11500                                             9804    IPDI caprolactam            11.8                24.5                    4.6     660000                                 194000                                     34000                                         8550                                             6805    IPDI caprolactam            11.85                24.6                    6.4     451000                                 101000                                     22000                                         4500                                             4506    IPDI MEK-oxime            12.8                26.5                    2.8     571000                                 152000                                     27500                                         5500                                             4207    HDI  caprolactam            15.3                29.4                    0.5     100  80  50  30  &lt;308    HDI  MEK-oxime            15.8                32.4                    2.5     70   60  50  30  &lt;309    DI51 caprolactam            14.8                29.3                    0.7     160  120 60  45  &lt;3010   DI51 MEK-oxime            15.7                31.5                    0.8     190  150 80  60  3011   DI51 MEK-oxime            16.5                32.9                    7.5     110  70  40  &lt;30 &lt;30__________________________________________________________________________ 
    
     B. Preparation of blocked polyisocyanate-urea-adducts according to the invention 
     With respect to the free NCO content, the equivalent quantities of a 50 to 70% solution in toulene of a diamine or polyamine or their mixtures were added in such a manner to a 50 to 70% solution in toluene of a partially blocked polyisocyanate, with intensive stirring, at a temperature ranging from 55° to 65° C. such that the reaction temperature does not exceed 70° C. Following completion of amine addition, the reaction mixture was then heated for a period ranging from 30 to 45 minutes. During this time, the temperature was slowly increased to from 100° to 120° C. Then the toluene was removed from the reaction product under vacuum at 0.133 mbar. The following table lists the chemical and physical characteristics of the reaction products. 
     (a) IPDI-urea-adducts according to A 2 and amine component 
     (b) IPDI-urea-adducts according to A 1 and amine component 
     (c) HDI-urea-adduct according to A 7 and amine component 
     (d) DI51-urea-adducts according to A 9 and amine component 
     (e) IPDI-urea-adducts according to A 3, A 4, A 5 and amine component 
     (f) IPDI-urea-adducts according to A 2 in such proportions as to give a ratio of NCO to NH 2  ranging from 1.05 to 1.3:1 and amine component 
     (g) IPDI-urea-adducts according to A 2 and amine component, prepared at a temperature ranging from 40° and 110° C. 
     (h) IPDI-urea-adducts according to A 2 and amine component, prepared in acetone or acetic ester 
     (i) IPDI-urea-adducts according to A 2 and water 
     (j) IPDI-urea-adducts according to A 2 and amine component, prepared in special benzene and cyclohexane 
     
         __________________________________________________________________________                   NCO content    glass transition                   (% by weight)                           melting range                                  temperature  amine component  latent                       Free                           °C.                                  (DTA) °C.__________________________________________________________________________Example B a 1     1,6-hexamethylene diamine                   10.8                       0.15                           120-122                                  51-66 2     1,8-octamethylene diamine                   10.5                       0.5 101-103                                  41-61 3     1,12-dodecamethylene diamine                   9.6 0.3 93-96  32-56 4     2-methyl-pentamethylene-                   10.5                       0   106-108                                  35-47  1,5-diamine 5     2,2,4(2,4,4)-trimethyl-                   10.0                       0   107-109                                  30-44  hexamethylene 1,6-diamine (TMD) 6     1,4-diaminocyclohexane                   10.3                       0.3 120-130                                  53-85 7     4,4&#39;-diamino-dicyclohexyl-                   9.9 0.25                           148-150                                  39-58  methane - solid 8     4,4&#39;-diamino-dicyclohexyl-                   10.0                       0.3 146-149                                  40-57  methane - liquid 9     3,3&#39;-dimethyl-4,4&#39;-diamino-                   9.3 0   149-155                                  37-85  dicyclohexylmethane10     N-cyclohexyl-propylene                   10.8                       0.3 142-145                                  43-80  1,3-diamine11     bis-(1,4-aminomethyl)-                   10.9                       0.5 133-140                                  50-80  cyclohexane12     isophorone diamine (IPD)                   10.5                       0.1 160-165                                  60-8713     90 parts by weight IPD                   9.9 0   146-157                                  49-72  10 parts by weight TMD14     70 parts by weight IPD                   9.9 0   138-148                                  38-61  30 parts by weight TMD15     50 parts by weight IPD                   10.2                       0.1 125-127                                  34-58  50 parts by weight TMD16     diethylene triamine                   11.1                       0.4 162-165                                  45-8817     triethylene tetramine                   11.5                       0.5 140-145                                  40-8018     tetraethylene pentamine                   12.0                       0.3 120-123                                  40-7519     pentamethylene hexamine                   12.1                       0.4 113-115                                  36-7020     dipropylene triamine                   11.8                       0.4 153-155                                  40-6521     bis-(3-aminopropyl)-                   11.6                       0.5 152-155                                  42-68  ethylene diamine22     3,5-diethyl-toluylene-                   10  0   203-205                                  70-80  diamine23     1,4-diamino-2,3,5,6-                   10  0   175-177                                  55-72  tetramethyl benzene24     4,4&#39;-diaminodiphenyl-                   10  0.3 178-182                                  58-74  methane25     1,1,6,6-tetraisopropyl-                   9.7 0.45                           120-122                                  47-65  2,5-diazahexane26     N,N&#39;-diisobutyl-isophorone-                   9.4 0.3 130-132                                  45-65  diamine27     4-(3-aminopropyl-amino)-                   10.1                       0.5 125-129                                  35-49  2,2,6,6-tetramethylpiperidine28     4-[(bis-3-aminopropyl)-amino]-                   9.6 0.5 138-140                                  40-53  2,2,6,6-tetramethylpiperidine29     melamine         10.3                       0.5 197-200                                  75-9030     N-(3-aminopropyl)glucamine                   9.5 0   124-126                                  33-95Example B b1      4,4&#39;-diamino-dicyclohexyl-                   10.2                       0.1 144-147                                  41-59  methane - liquid2      bis-(1,4-aminomethyl)cyclo-                   10.8                       0.3 136-141                                  53-75  hexaneExample B c1      4,4&#39;-diaminodicyclohexyl-                   10.7                       0   124-126                                  26-52  methane - liquidExample B d1      4,4&#39;-diaminodicyclohexyl-                   10.6                       0.1 105-111                                  24-52  methane - liquid__________________________________________________________________________ 
    
     Example B e 
     According to the general preparation B, the partially blocked IPDI adducts according to A 3, A 4 and A 5 underwent a reaction with 4,4&#39;-diaminodicyclohexylmethane. The following table shows the chemical and physical characteristics of the product: 
     
         ______________________________________Exam-            NCO content                       melting                              glass transitionple   IPDI adduct            % by weight                       range  temperatureB e   according to            latent  free °C.                                (DTA) °C.______________________________________1     A 3        10.3    0.3  148-150                                38-722     A 4        10.2    0.1  155-161                                37-783     A 5        10.25   0.2  155-157                                40-96______________________________________ 
    
     Example B f 
     According to the general preparation B, the partially blocked IPDI adducts according to A 2, were reacted with 4,4&#39;-diaminodicyclohexylamethane, not in equivalent proportions, but rather in such proportions as to give a ratio of NCO to amine of X:1. The following table shows the chemical and physical characteristics for the product: 
     
         ______________________________________         NCO content                    melting                           glass transitionExample       % by weight                    range  temperature (DTA)B f    X      latent  free °C.                             °C.______________________________________1      1.05   9.9     0.4  145-148                             35-582      1.1    10.7    0.8  140-142                             33-593      1.2    11.5    1.4  138-140                             35-584      1.3    12.0    1.95 131-136                             33-55______________________________________ 
    
     Example B g 
     According to the general preparation for the blocked polyisocyanate-urea-adducts, at X °C., the partially blocked IPDI adducts according to Example A 2, underwent a reaction with 4,4&#39;-diaminodicyclohexylmethane and in the following table the chemical and physical characteristics of the inventive and comparative reaction products are shown. 
     
         ______________________________________          Reaction   NCO content                              glass transitionExample        Temperature                     % by weight                              temperature inB g            X °C.                     latent                           free °C. (DTA)______________________________________1              40         10.27 0.2  36-592              50         10.25 0.3  38-583        I     60         10.1  0.2  40-574              70         10.3  0.25 40-595              80         10.0  0.15 40-566              90         10.3  0.1  28-817        II    100        10.2  0    19-908              110        10.15 0.2  17-125______________________________________ Remarks: I = invention II = comparison 
    
     Example B h1 
     With respect to the free NCO content, 210 parts by weight of 4,4&#39;-diamino- dicyclohexylmethane were added to 730 parts by weight of a partially blocked IPDI of a A 2, dissolved in 506 parts by weight of acetone with intensive stirring, at a temperature ranging from 55° to 65° C. in such a manner that the reaction temperature does not exceed 65° C. Following completion of diamine addition, the reaction mixture was then stirred for a period ranging from 30 to 45 minutes urea NCO content has dropped to 0.5% by weight. Then the acetone was removed from reaction product under a vacuum at 0.133 mbar. The reaction product had the following chemical and physical characteristics: 
     NCO content (latent): 10.3% by weight 
     NCO content (free): 0.3% by weight 
     melting range glass transition: 147°-149° C. 
     temperature (DTA) 40°-59° C. 
     Example B h2 
     According to Example B h1, the reaction was carried out in acetic ester. The reaction product had the following chemical and physical characteristics: 
     NCO content (latent): 10.4% by weight 
     NCO content (free): 0% by weight 
     melting range glass transition: 146°-148° C. 
     temperature (DTA) 46°-59° C. 
     EXAMPLE B i 
     With respect to the free NCO content, Z parts by weight of water were added to X parts by weight of a partially blocked IPDI of A 2 and 0.15% by weight of DBTL, with respect to the partially blocked IPDI added, dissolved in Y parts by weight of acetone with intensive stirring, at a temperature ranging from 50° to 60° C. in such a manner that the reaction temperature does not exceed 65° C. Following completion of water addition, the reaction mixture was then heated with stirring until the calculated CO 2  quantity had been evolved. Then the reaction was analyzed by volumetric analysis of NCO by titration and the acetone was removed from the reaction product under a vacuum at 0.133 mbar. The quantities and the corresponding chemical and physical characteristics were compiled in the following table: 
     
         __________________________________________________________________________                NCO content                       meltingExample in % by wt.    range  DTA*B i   X  Y  Z  CO.sub.2 (l)                total                    free                       °C.                            °C.__________________________________________________________________________1     359    146       9  11.3-12                12.5                    0.3                       105-107                            45-652     185    120       3.45          4.3-4.6                15.2                    2.1                       94-96                            38-56__________________________________________________________________________ *glass transition temperature 
    
     Example B j 
     With respect to the free NCO content, the calculated quantity of amine component was added dropwise to 730 parts by weight of a partially blocked IPDI of A 2, dissolved in from 500 to 550 parts by weight of special benzene (contains 3% by vol. of aromatics) or cyclohexane with intensive stirring, at room temperature in such a manner that the reaction temperature does not exceed 70° C. During the addition of diamine the polyisocyanate-urea-adduct precipitated out. Following completion of the diamine addition, the reaction mixture was then stirred for a period ranging from 30 to 45 minutes and then following volumetric analysis of NCO by titration, freed of the solvent. The following table gives the chemical and physical characteristics of the product: 
     
         __________________________________________________________________________           NCO content                  melting                       glass transitionExampleamine      % by weight                  range                       temperature (DTA)B j  component  total               free                  °C.                       °C.__________________________________________________________________________Ratio of NCO to amine = 1:11    4-4&#39;-diaminodi-           9.5 0.4                  146-149                       36-63cyclohexylmethane-liquid2    bis-(1,4-aminomethyl-           10.2               0.4                  134-136                       45-95cyclohexane3    isophorone diamine           10.0               0.4                  154-159                       56-844    pentaethylene-           11.3               0  123-127                       37-65hexaneRatio of NCO to amine 1.1:1.2:1.3:15    4,4&#39;-diaminodi-           10.9               0.8                  137-141                       37-60cyclohexylmethane6    4,4&#39;-diaminodi-           11.2               1.5                  140-141                       33-59cyclohexylmethane7    4,4&#39;-diaminodi-           12.1               1.9                  133-135                       32-56cyclohexylmethane__________________________________________________________________________ 
    
     C. Preparation of blocked polyisocyanate-urea-adducts according to the invention in conventional paint solvents 
     With respect to the free NCO content, the equivalent quantities (dissolved or neat) of a diamine or polyamine or their mixtures were added to a from 30 to 50% conventional paint solvent solution of a partially blocked polyisocyanate with intensive stirring, at a temperature ranging from 50° to 60° C. in such a manner that the reaction temperature does not exceed 70° C. Following completion of amine addition, the reaction mixture was then heated urea NCO content has dropped to zero. The following table lists the chemical and physical characteristics of the product: 
     
         __________________________________________________________________________           concentration  NCO content                                 ViscosityExample         of urea        (latent)                                 DIN-4-cup                                       mPa&#39;sC a  amine component           adduct solvent % by weight                                 20° C. (sec)                                       25° C.__________________________________________________________________________1    2,2,4(2,4,4)-trimethyl-           40     S* 100  4.2    116   330hexamethylene-1,6-           50     E*/S                     100                        1:2                          5.3    345   1,040diamine (TMD)2    pentaethylene-           40     S  100  4.6     32   90hexamine (PEHA)           50     E/S                     100                        1:2                          5.8    200   6443    bis-(1,4-aminomethyl)-           40     E/S                     100                        1:2                          4.3    --    7,000cyclohexane (HXDA)4    isophorone diamine           30     E/S                     100                        1:2                          3.1    151   410           40     E/S                     100                        1:2                          4.1    --    15,6005    HXDA/PEHA 2:1           30     E/S                     100                        1:2                          3.4    190   489           40     E/S                     100                        1:2                          4.2    190   4906    IPD/PEHA 2:1           40     E/S                     100                        1:2                          4.2    166   4727    HXDA/TMD 1:1           30     E/S                     100                        1:2                          3.1     72   177           40     E/S                     100                        1:2                          4.1    754   2,086__________________________________________________________________________ S* = SOLVESSO ®, E* = EGA 
    
     Example C b 
     With respect to the free NCO content, Z parts by weight of water were added to X parts by weight of a partially blocked IPDI of example A 1 and 0.15% by weight of DBTL, with respect to the partially blocked IPDI added, dissolved in Y parts by weight of conventional paint solvent with intensive stirring, at a temperature ranging from 55° to 60° C. in such a manner that the reaction temperature does not exceed 65° C. Following completion of water addition, the reaction mixture was then heated with stirring urea calculated CO 2  quantity has been evolved. The reaction was then analyzed via volumetric analysis of NCO by titration. The quantities and the corresponding chemical and physical characteristics were listed in the following table: 
     
         ______________________________________                               time ofExam-              NCO content                      outflow inple   CO.sub.2     in % by wt.                      DIN-4-cupC b   X      Y      Z    (l)   total free 20° C. in______________________________________                                     sec1     185    120    3.45 4.2-4.6                           9.4  1.6  2152     183.3  120    2.3  2.8-3.0                          10.9  3.4  503     181.6  120    1.15 4.2-4.5                          12.8  5.0  20______________________________________ 
    
     D. I. Comparison examples - General preparation (partially blocked polyisocyanates without thin-layer evaporation) 
     One mole of blocking agent was added in such a manner to one mole of polyisocyanate at a temperature ranging from 90° to 110° that the temperature of the reaction mixture does not exceed 120° C. After completion of the addition of blocking agent, the reaction mixture was heated urea NCO content of the reaction mixture has reached the calculated value. The following table shows the chemical and physical characteristics of the reaction products: 
     
         __________________________________________________________________________            NCO content                   PolyisocyanateExamplepolyiso-     blocking            % by weight                   monomer Viscosity in mPa&#39;s at °C.DI   cyanate     agent  free               total                   % by wt.                           25  30  40  50 70__________________________________________________________________________1    IPDI caprolactam            12.4               24.85                   15.8    381,000                               142,000                                   27,800                                       6,650                                          6902    IPDI MEK-oxime            12.4               26.0                   15.3    27,000                               14,750                                   3,390                                       1,100                                          1953    HDI  caprolactam            14.7               29.75                   14.5    90  70  60  40 &lt;304    HDI  MEK-oxime            16.4               31.5                   14.5    75  55  35  30 &lt;305    DI51 caprolactam            14.5               29.0                   14.3    190 140 70  40 &lt;306    DI51 MEK-oxime            16.2               31.7                   17.7    110 85  45  30 &lt;307    HMDI caprolactam            10.9               21.9                   17.0    880,000                               300,000                                   60,000                                       9,000                                          1,100__________________________________________________________________________ 
    
     D. II. Comparison examples (polyisocyanate-urea-adducts) 
     According to the general preparation B for the blocked polyisocyanate-urea-adducts, the partially blocked polyisocyanates of D I underwent a reaction with the amine component. The chemical and physical characteristics were compiled in the following table: 
     
         __________________________________________________________________________             NCO content                    melting                         glassExamplepolyiso-      amine  % by weight                    range                         transitionD II cyanate      component             total                 free                    °C.                         (DTA) °C.__________________________________________________________________________1    1     4,4&#39;-diamino-             9.4 0.2                    158-160                          19-110      dicyclohexyl-      methane2    3     4,4&#39;-diamino-             10.6                 0.1                    102-104                         17-38      dicyclohexyl-      methane3    5     4,4&#39;-diamino-             10.8                 0  90-92                         14-34      dicyclohexyl-      methane4    7     4,4&#39;-diamino-             8.5 0  160-162                         26-85      dicyclohexyl-      methane5    1     IPD    9.9 0  141-145                         20-83__________________________________________________________________________ 
    
     In all of the examples more or less severe incompatibilities (agglomeration) occurred as early as during the amine addition so that the course of the reaction between NCO and amino groups was not without problems. The polyisocyanate-urea-adducts still exhibit weak basicity. 
     D. III Comparison examples (Polyisocyanate-urea-adducts in conventional paint solvents) 
     If according to the general preparation C, the partially blocked polyisocyanates of D I undergo reaction with the amine component, the polyisocyanate-urea-adducts precipitate out already during the amine addition and cannot be used for manufacturing solvent-containing paint systems. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Accordingly, the invention may be practiced otherwise than as specifically described herein.