Note: Descriptions are shown in the official language in which they were submitted.
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TDI POLYISOCYANATES CONTAINING ~ETEROALLOPIIANATE
GROUPS
S BACKGROUND OF THE ~NVENTION
Field of the Invention
The present invention relates to a process for the production of polyisocyanatescnnt~ining allophanate groups and having aromatically bound isocyanate groups,
and to their use as binders in coating compositions.
Description of the Prior Art
Polyisocyanates cont~inin~; allophanate groups and having highly reactive,
aromatically bound isocyanate groups and coatings produced therefrom are known
(c.~ GB-A 994,980, US-A 3,769,318, 5,283,311, DE-A 2,009,179, 4,040,645 and
2,725,318). These polyisocyanates are produced by reacting excess quantities of
15 aromatic diisocyanates with mono- or polyfunctional alcohols or polymer alcohols.
The properties of the resultant products may be varied within a wide range
depending upon the diisocyanate and alcohol used. A disadvantage of prior art
allophanate polyisocyanates is their poor thermal stability, such that the
alloph~n~te groups decompose and release the incorporated diisocyanates during
20 thin film tli.ctill~tion, which makes it impossible to completely remove excess
diisocyanate following the alloph~n~ti7~tion reaction. However, if excess diiso-cyanate is not removed, then the resulting products have an elevated content of
volatile isocyanates, which is not acceptable for reasons of occupational hygiene.
The "co-allophanates" produced by reacting hydroxyl components with a mixture
25 of aromatic or aliphatic and aromatic diisocyanates and described in the previously
mentioned publications also do not exhibit the required thermal stability. Another
disadvantage of these polyisocyanates is their multi-stage drying and cro.~linking
mech~ni~m brought about by the presence in the polyisocyanate of isocyanate
groups having different reactivities. This is particularly evident in co-allophanates
30 produced from mixtures of aromatic and aliphatic diisocyanates. In coating
formulations these co-allophanates exhibit a relatively short pot life due to the
highly reactive aromatic isocyanate groups, but complete drying of the resulting
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coatings and the attainment of final properties are greatly retarded by the presence
of the sparingly reactive aliphatic isocyanate groups.
An object of the present invention is to provide a process for the production ofhighly reactive polyisocyanates cont~inin~ allophanate groups, which have uniform
5 reactivity and a low monomer content and exhibit sufficient thermal stability.
This object may be achieved in accordance with the process of the present
invention, which is described in greater detail below. Thermally stable poly-
isocyanates having alloph~n~te groups are produced by using a linear aliphatic
isocyanate component for the initial urethanization reaction and tolylene
10 diisocyanate for the subsequent alloph~n~ti7~ion. The resulting polyisocyanates
contain different isocyanate groups in chemically incorporated form and are
described below as "heteroalloph~n~tçs". Such polyisocyanates contain free
(unreacted) aromatic isocyanate groups and thus do not exhibit the difference inreactivity known from HDI/TDI co-allophanates.
SUMMARY OF TIIE INVENTION
The present invention relates to a process for the production of polyisocyanatescont~ining heteroallophanate groups and aromatically bound isocyanate groups by
reacting
a) a di- and/or polyurethane component which is substantially free from
isocyanate groups and is based on the reaction product of
al) a linear aliphatic isocyanate component and
a2) a hydroxyl group-cont~ining component having an average OH
functionality of 1 to 1.75
with
b) an isocyanate component cont~ining at least 90 wt.% of 2,4- and/or 2,6-
diisocyanatotoluene
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to form allophanate groups at a ratio of NCO groups to urethane groups of 3 :1 to
l00:1 and removing excess distillable isocyanate component b) to a content below0.5%.
The present invention also relates to the use of the polyisocyanate compounds as5 binders for coating, adhesive, sealant and polymer molding compositions.
DETAILED DESCRIPTION OF TI~E INVENTION
Compounds a) c~-nt~inin~; urethane groups are substantially free from isocyanategroups. This means that the NCO content of compounds a) is at most 2%,
preferably at most 0.5 and more preferably at most 0.2%. These levels are
10 achieved by reacting starting components al) and a2) to form compounds a) at an
NCO/OH equivalent ratio of 1:1.201 to 1:2, preferably 1:1.4 to 1:1.9. Urethane
formation reaction is generally performed at a temperature of 20 to 140~C,
preferably 50 to 120~C and more preferably 70 to 90~C, preferably as a bulk
reaction.
15 Isocyanate component al) is selected from linear aliphatic isocyanates having an
average molecular weight of 110 to 1000, preferably of 140 to 340; an NCO
content of 8 to 75, preferably 22 to 60 and more preferably 40 to 60 wt.%; and an
average NCO functionality of 1.8 to 4.0, preferably 2.0 to 3.0 and more preferably
2Ø Preferably, isocyanate component al) exclusively contains diisocyanates.
20 Examples of linear aliphatic diisocyanates include 1,2-diisocyanatoethane, 1,4-
diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocy~n~tohex~ne (HDI), 1,11-diisocyanatoundecane, dodecamethylene diisocyanate, trimethyl- 1 ,6-diisocyanato-
hexane and mixtures thereof.
Diisocyanates cc nt~ining ester or ether groups may also be used, although this is
25 less preferred.
It is also possible, but not preferred, to use monoisocyanates, such as hexyl
isocyanate, 2-ethylhexyl isocyanate and other monoisocyanates having 4 to 18
carbon atoms.
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Also suitable as starting isocyanates al) are modification products of the preceding
di- and monoisocyanates, which contain biuret, uretidione, isocyanurate, allopha-
nate and/or carbodiimide groups.
1,6-diisocyanatohexane and/or 1,4-butane diisocyanate are preferably used as the5 isocyanate component al); 1,6-diisocyanato-hexane is most preferably used.
Alcohol component a2) have an average functionality of 1 to 1.75, preferably 1 to
1.5 and more preferably 1 and is selected from alcohols having a number average
molecular weight of 32 to 4000, preferably of 60 to 2000 and more preferably of
70 to 300. Examples of suitable compounds include saturated monoalcohols such
10 as methanol, ethanol, n-propanol, isopropanol, metho~yplopanol, isomeric buta-
nols, pentanols, hexanols, n-heptanols, n-octanols, n-nonanols, n-decanols, n-
dodecanols, n-octadecanol, Lorol alcohols (Henkel KGaA) and saturated fatty
alcohols (for example Stenol and Guerbitol alcohols, Henkel KGaA); highly
-functional polyalcohols such as ethylene glycol, 1,2- and 1,3-propanediol, 1,4 and
1 ,3-butanediol, 1,6-hexanediol, 1 ,8-octanediol, 1 ,9-nonanediol, 1,1 0-decanediol,
1,12-dodecanediol, 1,12-octadecanediol, neopentyl glycol, 1,4-bis-hydroxymethyl-cyclohexane, 2-methyl- 1,3 -propanediol, 2,2,4-trimethyl- 1,3 -pentanediol, 2-ethyl-
1,3-hexanediol, dimer fatty alcohols, trimer fatty alcohols, glycerol, trimethylol-
propane, trimethylol-ethane, isomeric hexanetriols, pentaerythritol and sorbitol; and
20 mixtures thereof.
It is also possible to use unsaturated alcohols such as allyl alcohol, trimethylol-
propane diallyl ether, butenediol, and monofunctional alcohols derived from
corresponding acids or acid mixtures cont~ining unsaturated synthetic and natural
fatty acids (for example HD-Ocenol alcohols, Henkel KGaA). Naturally occurring
25 fatty acid mixtures include the acids derived from castor oil, peanut oil, cottonseed
oil, safflower oil, tung oil, soya oil, sunflower oil, linseed oil, rapeseed oil, tall oil,
sperm oil and herring oil.
In addition to these unsaturated monofunctional alcohols, reaction products
prepared from the previously described unsaturated fatty acids and epoxy
30 compounds such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide
and 2-ethylhexyl oxide may also be used as the alcohol component a2).
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Prior art polymer polyols having ether, ester and/or carbonate groups may also be
used. Of these polymer polyols, hydroxy-functional polyethers based on propyleneoxide and/or ethylene oxide are preferably used.
If the alcohol component a2) is selected from alcohol having a number average
molecular weight of 901 to 4000 the NCO/OH equivalent ratio of starting
component al) to a2) should be 1,2:1 to 1:2 preferably 1,1:1 to 1:1,9 and more
preferably 1:1.
Most preferably, only monofunctional alcohols are used, especially alcohols
having an average chain length of 12 to 22 carbon atoms.
As previously set forth, component a) is produced by reacting individual
components al) and a2) to form urethane groups. It is also possible, although not
preferred, to use compounds a), which were produced by a different method, for
example, by using a known "phosgene-free urethane synthesis", as described, for
example, in EP-A 27,940, EP-A 27,952, EP-A 27,953, EP-~ 323,514 and EP-A
355,443.
2,4- or 2,6-diisocyanatotoluene or mixtures thereof are used as the aromatic
diisocyanate component b). Preferably, mixtures c~-nt~ining a minimllm of 65% of2,4-diisocyanatotoluene are used.
In order to achieve certain properties, up to 10 wt.% of other known aromatic oraliphatic mono-, di- or polyisocyanates may be added to diisocyanate component
b). However, this is not preferred.
Urethane component a) is reacted with the diisocyanate component b) at an
NCO/urethane equivalent ratio of 3:1 to 100:1, preferably 4:1 to 60:1 and more
preferably 6:1 to 30:1 at a temperature of 20~C to 149~C, preferably 50~C to
120~C and more preferably 60~C to 90~C. Known catalysts for accelerating the
alloph~n~ti7~tion reaction are also preferably used. Examples of usable catalysts
include tetraalkyl-ammonium hydroxides and arylalkylammonium hydroxides.
Also suitable are metal salts such as iron(III) chloride; potassium octoate; zinc
compounds such as zinc stearate, zinc octoate, zinc naphthenate and zinc acetyl-acetonate; tin compounds such as tin(II) octoate, tin(II) ethylhexanoate, tin(II)
laurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin
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dilaurate, dibutyltin maleate and dioctyltin diacetate; aluminum tri-
(ethylacetoacetate); and m~ng~nese, cobalt and nickel compounds, together with
mineral acids such as trifluoroacetic acid, sulphuric acid7 hydrogen chloride,
hydrogen bromide, phosphoric acid and perchloric acid; and mixtures of these
5 catalysts. When reacting urethane groups with isocyanate compounds, strong
acids, such as those described in EP 000 194, are less preferred. Preferably, zinc
compounds are used to catalyze allophanate formation.
The catalysts may be added before the alloph~n~ti~tion reaction or before the
ureth~ni7~tion reaction. They are used in concentrations of 0.001% to 5%,
preferably of 0.004% to 1%, based on the weight of the reaction components. The
catalyst may, if possible, be removed from the reaction mixture by (li.~till~tion.
The catalytic action may also be t~rmin~ted by the addition of catalyst poisons,such as acid chlorides or alkylating agents.
After the reaction excess, distillable starting diisocyanate b) is preferably removed
15 by thin film distillation to a residual content in the product of the at most0.5 wt.%, preferably at most 0.2 wt.%.
Depending upon the viscosity of the products obtained according to the invention,
it may be appropriate to dilute them with inert solvents to a solids content of
approximately 50%, preferably 80%. Suitable solvents include toluene, xylene,
20 cyclohexane, chlorobenzene, butyl acetate, ethyl acetate, ethylene glycol mono-
ethyl ether acetate, pentyl acetate, hexyl acetate, methoxypropyl acetate, tetra-
hydrofuran, dioxane, acetone, methyl ethyl ketone, mineral spirits, higher
substituted aromatics (such as Solvent Naphtha, Solvesso, Shellsol, Isopar, Nappar
and Diasol solvents), crude benzene, Tetralin solvent, Decalin solvent, alkanes
25 c~-nt~ining more than 6 carbon atoms and mixtures of these solvents. The products
produced according to the invention are preferably used in solvent-free form.
The isocyanate compounds according to the invention are valuable binders for
coating compositions, which may be cured under the action of atmospheric
moisture and optionally atmospheric oxygen.
30 The polyisocyanates according to the invention may also be used as a cro.c.~linking
component in two component coatings in combination with known compounds
cont~ining two or more isocyanate-reactive groups, preferably hydroxyl groups.
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Examples include polyols such as hydroxy-functional polyethers, polyesters,
polycarbonates, polyacrylates, polyamides or mixtures thereof.
The compounds produced according to the invention may also be used in blocked
form in heat curing coating compositions.
The coating compositions may also contain other additives such as wetting agents,
levelli~g agents, anti-~kinnin~ agents, anti-~oaming agents, Iqatting agents (such as
silica, alllmimlm silicates and high-boiling waxes), viscosity-controlling sub-
stances, pigments, dyes, W absorbers and stabilizers against thermal or oxidative
degradation.
The coating compositions may be used for coating any desired substrates such as
wood, plastics, leather, paper, textiles, glass, ceramics, rendering, masonry, metals
or concrete. They may be applied using conventional application methods such as
spraying, brushing, flow coating, pouring, dipping or roller application. The
coating compositions may be either clear or pigmented.
The products produced using the process according to the invention are
distinguished by low viscosities and good thermal stability. The thermally stable
polyisocyanates have aromatic isocyanate groups and uniform reactivity. The
polyisocyanates may be used as crosslinkers in one- and two-component coating
compositions, which may be cured without a multi-stage curing mech~ni.~m
In the following examples all parts and percentages are by weight, unless
otherwise indicated.
EXAMPLES
ExamPle 1
815.4 g (3.0 moles) of an unsaturated alcohol (HD-Ocenol 110/130, product of
Henkel KGaA, OH number: 200-220, iodine value: 110-130, approx. 95%
hydrocarbon chains having 18 carbon atoms) were introduced into a stirred
apparatus purged with nitrogen and combined at 70~C with 168 g (1.0 mole) of
1,6-hexamethylene diisocyanate. After reacting for approximately 3 hours at a
temperature of 90~C, the NCO content of the resulting urethane component had
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fallen to below 0.1%. The alloph~n~ti7~tion reaction was then initiated at 88~C by
the addition of 1740 g (10.0 moles) of tolylene diisocyanate (TDI, 2,4-:2,6-isomer
ratio = 80:20) and subsequent catalysis with 140 mg of zinc stearate. After 9
hours, the reaction was termin~ted at an NCO content of 24.2% by adding 140 mg
5 of isophthaloyl dichloride. The excess tolylene diisocyanate was then removed by
thin film distillation under a high vacuum (0.1-0.3 mbar) at a temperature of
1 SO~C.
Product data:
Yield: 1536 g
Viscosity: 3300 mPa-s at 23~C
Free TDI content: 0.04%
NCO content: 9.1%
Example 2
325 g (2.5 moles) of 2-ethylhexanol were introduced into a stirred apparatus
purged with nitrogen and combined at 70~C with 168 g (1.0 mole) of 1,6-
hexamethylene diisocyanate. After reacting for approximately 3 hours at a
temperature of 90~C, the NCO content of the resulting urethane component had
fallen to below 0.1%. The alloph~n~ti~tion reaction was then initiated at 88~C by
the addition of 1914 g (11.0 moles) of tolylene diisocyanate (TDI, 2,4-:2,6-isomer
ratio = 80:20) and subsequent catalysis with 100 mg of zinc acetylacetonate. After
9 hours, the reaction was t~rmin~ted at an NCO content of 29% by adding 100 mg
of isophthaloyl dichloride. The excess tolylene diisocyanate was then removed bythin film distillation under a high vacuum (0.1-0.3 mbar) at a temperature of
150~C. When dissolved in butyl acetate, the highly viscous product had the
following properties:
Solids content: 85%
Viscosity: 400 mPa s at 23 ~C
Free TDI content: 0.04%
NCO content: 10.68%
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Example 3
203.3 g (1.0 mole) of a monofunctional alcohol (Lorol, product of Henkel KGaA,
OH number: 265-275, iodine value: < 0.5, hydrocarbon chains having 12 to 18
carbon atoms) were introduced with 500 g (0.125 moles) of a polyether produced
5 by the propoxylation of propylene glycol and subsequent ethoxylation of the
propoxylation product (PO/EO ratio 79/21, OH number: 28.5) into a stirred
apparatus purged with nitrogen and combined at 70~C with 105 g (0.625 moles) of
1,6-hexamethylene diisocyanate. After reacting for approximately 13 hours at a
temperature of 100~C, the NCO content of the resulting diurethane had fallen to
below 0.2%. The alloph~n~ti7~tion reaction was then initiated at 85~C by the
addition of 652.5 g (3.75 moles) of tolylene diisocyanate (TDI, 2,4-:2,6-isomer
ratio = 80:20) and subsequent catalysis with 73 mg of zinc stearate. After 9 hours,
an NCO content of 17.3% was obtained and the reaction was t~rrnin~ted with
70 mg of isophthaloyl dichloride. The excess TDI was then removed by thin film
distillation under a high vacuum (0.1-0.3 mbar) at a temperature of 140~C.
Product data:
Yield: 995 g
Viscosity: 7500 mPa s at 23~C
Free TDI content: < 0.03%
NCO content (i): 5.4%
Example 4 (Comparison)
1392 g (16 equiv) of tolylene diisocyanate (TDI, 2,4-:2,6-isomer ratio = 80:20)
were introduced into a stirred apparatus purged with nitrogen and combined at
60~C with 158 g (1 equiv) of dodecanol. After reacting for approximately 2 hours25 under a nitrogen atmosphere, the reaction temperature was raised to 120~C and the
reaction was catalyzed with 150 ppm of tin(II) octoate. After an alloph~n~ti7~ion
period of approximately 16 hours, an NCO content of 37.5% was achieved. The
excess diisocyanate was then removed by thin i~llm distillation under a high
vacuum (0.1-0.3 mbar) at a temperature of 150~C.
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- 10 -
Product data:
Yield: 364 g
NCO content: 9.4%
Viscosity: 400,000 mPa-s
5 Free l'L)I content: 1.7%
The resulting homoallophanate groups exhibited inadequate thermal stability
during removal of the excess monomer by distillation and partially dissociated into
urethane groups and free monomer. This was detected by l3C-NMR spectroscopy.
Despite a relatively high monomer content, which diluted the polyisocyanate, the10 final product was a highly viscous resin.
Even if a renewed attempt was made to remove monomeric diisocyanate by thin
film distillation, the TDI content could not be reduced below 0.5%.
Example 5 - Use of the products produced according to the invention as one-
component clear composition
15 The polyisocyanate from Example 2 was applied in combination with 0.22% of
dibutyltin dilaurate as catalyst as a 120 llm wet film onto a cleaned glass sheet
and dried at room temperature. The resulting high gloss film exhibited the
following properties:
Sand dry 40 min
Touch dry 180 min
Pendulum hardness after 1 day (s) 154
Pendulum hardness after 7 days (s) 172
Although the invention has been described in detail in the foregoing for the
purpose of illustration, it is to be understood that such detail is solely for that
25 purpose and that variations can be made therein by those skilled in the art without
departing from the spirit and scope of the invention except as it may be limited by
the claims.
