U.S. patent application number 12/519466 was filed with the patent office on 2010-01-21 for coating compositions with high scratch resistance and weathering stability.
This patent application is currently assigned to BASF COATINGS AG. Invention is credited to Matthijs Groenewolt, Simone Hesener, Gunter Klein, Manuela Niemeier, Andreas Poppe, Wilfried Stubbe, Elke Westhoff.
Application Number | 20100015344 12/519466 |
Document ID | / |
Family ID | 39199992 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100015344 |
Kind Code |
A1 |
Groenewolt; Matthijs ; et
al. |
January 21, 2010 |
COATING COMPOSITIONS WITH HIGH SCRATCH RESISTANCE AND WEATHERING
STABILITY
Abstract
Disclosed are coating compositions comprising (a) at least one
hydroxyl-containing compound (A), (b) at least one compound (B)
having free and/or blocked isocyanate groups, and (c) at least one
catalyst (D) for the crosslinking of silane groups, where (i) one
or more constituents of the coating composition contain
hydrolyzable silane groups and (iii) the coating composition can be
finally cured to a coating which has statistically distributed
regions of an Si--O--Si network. The finally cured coating obtained
from the coating composition has a post-crosslinking index (PCI) of
less than 2, wherein (PCI) is defined as the ratio of the storage
modulus E'(200) at 200.degree. C. to the minimum of the storage
modulus E'(min) at a temperature above the measured glass
transition temperature Tg.
Inventors: |
Groenewolt; Matthijs;
(Munster, DE) ; Poppe; Andreas; (Sendehorst,
DE) ; Klein; Gunter; (Munster, DE) ; Niemeier;
Manuela; (Drensteinfurt, DE) ; Westhoff; Elke;
(Steinfurt, DE) ; Stubbe; Wilfried; (Greven,
DE) ; Hesener; Simone; (Munster, DE) |
Correspondence
Address: |
Mary E. Golota;Cantor Colburn LLP
201 W. Big Beaver Road, Suite 1101
Troy
MI
48084
US
|
Assignee: |
BASF COATINGS AG
Munster
DE
|
Family ID: |
39199992 |
Appl. No.: |
12/519466 |
Filed: |
December 19, 2007 |
PCT Filed: |
December 19, 2007 |
PCT NO: |
PCT/EP07/11191 |
371 Date: |
September 21, 2009 |
Current U.S.
Class: |
427/407.1 ;
524/588 |
Current CPC
Class: |
C08G 18/6254 20130101;
C09D 175/04 20130101; C08G 18/289 20130101; C08G 18/778 20130101;
C09D 175/14 20130101; C08G 18/809 20130101 |
Class at
Publication: |
427/407.1 ;
524/588 |
International
Class: |
B05D 1/36 20060101
B05D001/36; C09D 175/00 20060101 C09D175/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2006 |
DE |
10 2006 059 951.9 |
Claims
1. A coating composition comprising (a) at least one
hydroxyl-containing compound (A), (b) at least one compound (B)
having free and/or blocked isocyanate groups, and (c) at least one
catalyst (D) for the crosslinking of silane groups, wherein (i) one
or more constituents of the coating composition contain
hydrolyzable silane groups, (ii) the coating composition can be
finally cured to a coating which has statistically distributed
regions of an Si--O--Si network, and the finally cured coating
obtained from the coating composition has a post-crosslinking index
(PCI) of less than 2, where the post-crosslinking index (PCI) is
defined as the ratio of the storage modulus E'(200) of the finally
cured coating, measured at 200.degree. C., to the minimum of the
storage modulus E'(min) of the finally cured coating, measured at a
temperature above the measured glass transition temperature Tg, the
storage moduli E'(200), E'(min), and the glass transition
temperature Tg are measured on free films with a thickness of 40
.mu.m.+-.10 .mu.m by dynamic-mechanical thermo-analysis (DMTA) at a
heating rate of 2 K per minute and at a frequency of 1 Hz, and the
DMTA measurements on free films with a thickness of 40 .mu.m.+-.10
.mu.m which have been cured for 20 minutes at an article
temperature of 140.degree. C. and stored at 25.degree. C. for 8
days after curing.
2. The coating composition of claim 1, wherein the finally cured
coating obtained from the coating composition has a
post-crosslinking index (PCI) of less than or equal to 1.8.
3. The coating composition of claim 1, wherein the catalyst (D)
comprises phosphorus.
4. The coating composition of claim 3, wherein the catalyst (D) is
selected from the group of substituted phosphoric monoesters,
substituted phosphoric diesters, the corresponding amine-blocked
phosphoric esters, and mixtures thereof.
5. The coating composition of claim 4, wherein the catalyst (D) is
blocked with a tertiary amine.
6. The coating composition of claim 4, wherein the catalyst (D) is
selected from the group of amine-blocked phosphoric acid ethylhexyl
partial esters and amine-blocked phosphoric acid phenyl partial
esters.
7. The coating composition of claim 1, wherein the finally cured
coating obtained from the coating composition has a storage modulus
E'(200), measured at 200.degree. C., of less than 4*10.sup.8
Pa.
8. The coating composition of claim 1, wherein one or more
constituents of the coating composition comprise at least partly
one or more identical or different structural units of the formula
(I) --X--Si--R''.sub.xG.sub.3-x (I) where G=identical or different
hydrolyzable groups, X=organic radical, R''=alkyl, cycloalkyl, aryl
or aralkyl, it being possible for the carbon chain to be
interrupted by nonadjacent oxygen, sulfur or NRa groups, with
Ra=alkyl, cycloalkyl, aryl or aralkyl, x=0 to 2.
9. The coating composition of claim 1, wherein one or more
constituents of the coating composition comprise between 2.5 and
97.5 mol %, based on the entirety of structural units (II) and
(III), of at least one structural unit of the formula (II)
--N(X--SiR''.sub.x(OR').sub.3-x).sub.n(X'--SiR''.sub.y(OR').sub.3-y).sub.-
m (II) where R'=hydrogen, alkyl or cycloalkyl, it being possible
for the carbon chain to be interrupted by nonadjacent oxygen,
sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl,
X,X'=linear and/or branched alkylene or cycloalkylene radical
having 1 to 20 carbon atoms, R''=alkyl, cycloalkyl, aryl or
aralkyl, it being possible for the carbon chain to be interrupted
by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl,
cycloalkyl, aryl or aralkyl, n=0 to 2, m=0 to 2, m+n=2, x=0 to 2,
and y=0 to 2, and between 2.5 and 97.5 mol %, based on the entirety
of structural units (II) and (III), of at least one structural unit
of the formula (III) -Z-(X--SiR''.sub.x(OR').sub.3-x) (III), where
Z=-NH--, --NR--, --O--, with R=alkyl, cycloalkyl, aryl or aralkyl,
it being possible for the carbon chain to be interrupted by
nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl,
cycloalkyl, aryl or aralkyl, x=0 to 2, and X, R', R'' have the
meaning given in formula (II).
10. The coating composition of claim 9, wherein one or more
constituents of the coating composition contain between 5 and 95
mol %, based in each case on the entirety of the structural units
(II) and (III), of at least one structural unit of the formula
(II), and between 5 and 95 mol %, based in each case on the
entirety of the structural units (II) and (III), of at least one
structural unit of the formula (III).
11. The coating composition of claim 9, wherein the structural
elements (II) and (III) are present in fractions of 2.5 to 97.5 mol
%, in each case based on the sum of the functional groups critical
for crosslinking in the coating composition, formed from the
fractions of the hydroxyl and isocyanate groups and from the
fractions of the structural elements (II) and (III).
12. The coating composition of claim 8, wherein the polyisocyanate
(B) comprises the respective structural units (I) or (II) or
(III).
13. The coating composition of claim 12, wherein, in the
polyisocyanate (B), between 2.5 and 90 mol % of the isocyanate
groups in the core polyisocyanate structure have undergone reaction
to structural units (II) and between 2.5 and 90 mol % of the
isocyanate groups in the core polyisocyanate structure have
undergone reaction to structural units (III) and/or the total
fraction of the isocyanate groups in the core polyisocyanate
structure that have undergone reaction to structural units (II)
and/or (III) is between 5 and 95 mol %.
14. The coating composition of claim 12, wherein the core
polyisocyanate structure is selected from the group of
1,6-hexamethylene diisocyanate, isophorone diisocyanate, and
4,4'-methylenedicyclohexyl diisocyanate, the biuret dimers of the
aforementioned polyisocyanates, the isocyanurate trimers of the
aforementioned polyisocyanates, and mixtures thereof.
15. The coating composition of claim 1, wherein the polyol (A)
comprises at least one poly(meth)acrylate polyol.
16. A multistage coating method which comprises applying a
pigmented basecoat film to an uncoated or precoated substrate and
thereafter applying a film of the coating composition of claim
1.
17. The multistage coating method of claim 16, wherein, following
the application of the pigmented basecoat film, the applied
basecoat material is first dried at temperatures from room
temperature to 80.degree. C. and, following the application of the
coating composition of claim 1, the system is cured at temperatures
from 30 to 200.degree. C. for a time of 1 min up to 10 h.
18. The coating composition of claim 1 that is a clearcoat material
for automotive OEM finishing or automotive refinish.
19. The coating composition of claim 2, wherein the finally cured
coating obtained from the coating composition has a
post-crosslinking index (PCI) of less than or equal to 1.5.
20. The coating composition of claim 7, wherein the finally cured
coating obtained from the coating composition has a storage modulus
E'(200), measured at 200.degree. C., of less than or equal to
3*10.sup.8 Pa.
Description
[0001] The present invention relates to thermally curable coating
compositions, based on aprotic solvents and comprising polyols and
polyisocyanates with hydrolyzable silane groups which lead to
coatings which combine a high scratch resistance with high gloss
and high weathering stability.
[0002] WO-A-01/98393 describes 2K (2-component) coating
compositions comprising a polyol binder component and a
polyisocyanate crosslinker component partly functionalized with
alkoxysilyl groups. These coating compositions are used as primers
and are optimized for adhesion to metallic substrates, especially
aluminum substrates. Over these coating compositions, as part of an
OEM finish or a refinish, it is possible to apply
basecoat/clearcoat systems. In terms of scratch resistance and
weathering stability, the coating compositions of WO 01/98393 are
not optimized.
[0003] EP-A-0 994 117 describes moisture-curable mixtures
comprising a polyol component and a polyisocyanate component which
may partly have been reacted with a monoalkoxysilylalkylamine that
has undergone reaction preferably to an aspartate. Although
coatings formed from such mixtures do have a certain hardness, they
are nevertheless of only limited suitability for OEM applications
in terms of their weathering stability and, in particular, their
scratch resistance.
[0004] US-A-2006/0217472 describes coating compositions which can
comprise a hydroxy-functional acrylate, a low molecular mass polyol
component, a polyisocyanate, and an amino-functional alkoxysilyl
component, preferably bisalkoxysilylamine. Such coating
compositions are used as clearcoat material in basecoat/clearcoat
systems and lead to scratchproof coatings. Coating compositions of
this kind, however, have only very limited storage qualities, and
the resulting coatings have low weathering stability, particularly
with respect to UV radiation in a wet/dry cycle.
[0005] WO 2006/042585 describes clearcoat materials which are
suitable for OEM finishing and which as their main binder component
comprise polyisocyanates whose isocyanate groups, preferably to an
extent of more than 90 mol %, have undergone reaction with
bisalkoxysilylamines. Clearcoat materials of this kind combine
excellent scratch resistance with high chemical and weathering
resistance. But there is still a need for a further improvement in
the weathering stability, particularly with respect to cracking
under UV irradiation in a wet/dry cycle, with retention of the high
level of scratchproofing.
[0006] EP-A-1 273 640 describes 2K coating compositions composed of
a polyol component and of a crosslinker component consisting of
aliphatic and/or cycloaliphatic polyisocyanates, 0.1 to 95 mol % of
the free isocyanate groups originally present having undergone
reaction with bisalkoxysilylamine. These coating compositions can
be used for OEM finishing and, after their curing is complete,
combine good scratch resistance with effective resistance to
environmental influences. Nevertheless, these coating compositions
have a particularly strong propensity toward post-crosslinking,
which--straight after final thermal curing--results in only
inadequate scratch resistance of the coatings. The strong
post-crosslinking also has a negative impact particularly on the
weathering stability as it entails an increased risk of tearing
under tension.
[0007] In the as yet unpublished German patent application
P102007013242 there are coating compositions described which
comprise surface-actively modified, silane-containing compounds.
These coating compositions lead to finally cured coatings which in
the near-surface coating zone--owing to the accumulation of the
surface-actively modified, silane-containing compounds prior to
thermal cure--have a higher density of Si atoms of the Si--O--Si
network than in the bulk. This accumulation of the Si--O--Si
network at the surface, in contrast, is specifically not exhibited
by the coatings of the invention; instead, the regions of the
Si--O--Si network of the finally cured coating of the invention are
distributed statistically.
[0008] Problem and Solution
[0009] It was an object of the present invention to provide coating
compositions, particularly for the clearcoat film in OEM finishes
and automotive refinishes, that lead to a network with a high
degree of weathering stability, the unwanted formation of moieties
unstable to hydrolysis and weathering being very largely
suppressed, in order to ensure high acid resistance. In addition,
the coating compositions ought to lead to coatings which already
have a high degree of scratchproofing straight after thermal curing
and in particular a high retention of gloss after scratch exposure.
Moreover, the coatings and coating systems, especially the
clearcoat systems, ought to be able to be produced even in film
thicknesses>40 .mu.m without stress cracks occurring. This is a
key requirement for the use of the coatings and coating systems,
particularly of the clearcoat systems, in the technologically and
esthetically particularly demanding field of automotive OEM
finishing.
[0010] The intention in particular was to provide clearcoat systems
featuring high resistance, particularly to cracking, under
weathering with UV radiation in a wet/dry cycle, in combination
with outstanding scratch proofing.
[0011] Furthermore, the new coating compositions ought to be
preparable easily and with very good reproducibility, and ought not
to present any environmental problems during application of the
coating material.
[0012] Solution to the Problem
[0013] In the light of the above objectives, coating compositions
have been found comprising [0014] (a) at least one
hydroxyl-containing compound (A), [0015] (b) at least one compound
(B) having free and/or blocked isocyanate groups, [0016] (c) at
least one catalyst (D) for the crosslinking of silane groups,
[0017] where [0018] (i) one or more constituents of the coating
composition contain hydrolyzable silane groups and [0019] (ii) the
coating composition can be finally cured to a coating which has
statistically distributed regions of an Si--O--Si network,
[0020] wherein the finally cured coating obtained from the coating
composition has a post-crosslinking index (PCI) of less than 2,
where [0021] the post-crosslinking index (PCI) is defined as the
ratio of the storage modulus E'(200) of the finally cured coating,
measured at 200.degree. C., to the minimum of the storage modulus
E'(min) of the finally cured coating, measured at a temperature
above the measured glass transition temperature Tg, [0022] the
storage moduli E'(200) and E'(min) and also the glass transition
temperature Tg having been measured on free films with a thickness
of 40 .mu.m.+-.10 .mu.m by dynamic-mechanical thermo-analysis
(DMTA) at a heating rate of 2 K per minute and at a frequency of 1
Hz, and [0023] the DMTA measurements on free films with a thickness
of 40 .mu.m.+-.10 .mu.m which have been cured for 20 minutes at an
article temperature of 140.degree. C. and stored at 25.degree. C.
for 8 days after curing were carried out before the DMTA
measurements.
[0024] In light of the prior art it was surprising and
unforeseeable for the skilled worker that the objects on which the
present invention was based could be achieved by means of the
coating composition of the invention.
[0025] The components of the invention can be prepared particularly
easily and with very good reproducibility, and do not cause any
significant toxicological or environmental problems during
application of the coating material.
[0026] The coating compositions of the invention produce new
coatings and coating systems, especially clearcoat systems, which
are highly scratchproof and, in contrast to common, highly
crosslinked scratchproof systems, are acid-resistant. Moreover, the
coatings and coating systems of the invention, especially the
clearcoat systems, can be produced even in film thicknesses>40
.mu.m without stress cracks occurring. Consequently the coatings
and coating systems of the invention, especially the clearcoat
systems, can be used in the technologically and esthetically
particularly demanding field of automotive OEM finishing. In that
context they are distinguished by particularly high carwash
resistance and scratchproofing. The high scratch resistance
straight after the final curing of the coatings is given such that
the coatings can be handled without problems straight after the
final curing. In addition, the resistance of the coatings of the
invention to cracking under UV radiation and wet/dry cycling in the
CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2
November 00), in combination with a high scratch resistance, is
outstanding.
DESCRIPTION OF THE INVENTION
[0027] The Post-Crosslinking Index (PCI)
[0028] In order to achieve the coatings with the requisite high
scratch resistance--even directly after thermal curing--in
conjunction with good weathering stability it is essential to the
invention that the coating compositions cure as far as possible
under the applied curing conditions, in other words exhibit low
post-crosslinking after the coating has been cured. This low
post-crosslinking is expressed through the post-crosslinking index
(PCI).
[0029] The post-crosslinking index (PCI) is defined as the ratio of
the storage modulus E'(200) of the finally cured coating, measured
at 200.degree. C., to the minimum of the storage modulus E'(min) of
the finally cured coating, measured at a temperature directly above
the measured glass transition temperature Tg, i.e., E'(min) is the
minimum of the storage modulus which occurs during the DMTA
measurement when the measuring temperature is greater than Tg and
less than 200.degree. C. By finally cured coating is meant a
coating which is cured for 20 minutes at an article temperature of
140.degree. C. and stored at 25.degree. C. for 8 days after curing
before the DMTA measurements are carried out. It will be
appreciated that the coating compositions of the invention can also
be cured under other conditions, differing in accordance with the
intended use. Furthermore, it will be appreciated that the coating
compositions of the invention can also be stored for less than 8
days after final curing before the storage moduli are measured.
Naturally, in that case, generally speaking, the post-crosslinking
index in the case of shorter storage of, say, just 1 day at
25.degree. C. will be somewhat higher than in the case of storage
at 25.degree. C. for 8 days. To determine the post-crosslinking
index by means of DMTA measurements with the objective of
ascertaining whether the coating compositions in question are in
accordance with the invention, however, it is necessary to cure and
store the coating under the reproducible, precisely specified
conditions.
[0030] The storage moduli E'(200) and E'(min) and also the glass
transition temperature Tg, which are required for the determination
of the post-crosslinking index, are measured by dynamic-mechanical
thermo-analysis (DMTA) at a heating rate of 2 K/min and at a
frequency of 1 Hz.
[0031] Dynamic-mechanical thermo-analysis is a widely known
measurement method for determining the viscoelastic properties of
coatings and is described for example in Murayama, T., Dynamic
Mechanical Analysis of Polymeric Material, Elsevier, N.Y., 1978 and
Loren W. Hill, Journal of Coatings Technology, vol. 64, no. 808,
May 1992, pages 31 to 33.
[0032] The measurements can be carried out, for example, using the
DMTA V instrument from Rheometrics Scientific at a frequency of 1
Hz and an amplitude of 0.2%. The heating rate is 2 K per
minute.
[0033] The DMTA measurements are carried out on free films with a
thickness of 40 .mu.m.+-.10 .mu.m. For this purpose the coating
composition of the invention is applied to substrates to which the
coating obtained does not adhere. Examples of suitable substrates
include glass, Teflon, polyethylene terephthalate and
polypropylene. The resulting coating is cured for 20 minutes at an
article temperature of 140.degree. C. and stored at 25.degree. C.
for 8 days after curing, before the DMTA measurements are carried
out.
[0034] A further feature of the coating compositions of the
invention is that they can be finally cured to a coating which has
statistically distributed regions of the Si--O--Si network. This
means that there is no deliberate accumulation or depletion of the
Si--O--Si network in particular regions of the coating, including,
in other words, the near-surface coating zone accumulation that is
described in the as yet unpublished German patent application
P102007013242.
[0035] It is essential to the invention that the finally cured
coating obtained from the coating composition has a
post-crosslinking index (PCI) of less than 2, preferably of less
than or equal to 1.8, more preferably less than or equal to 1.7,
and very preferably less than or equal to 1.5.
[0036] In this context it is first noted that, generally speaking,
the smaller the fraction of silane crosslinking as a proportion of
the crosslinking overall, the smaller the post-crosslinking and
hence the smaller the post-crosslinking index (PCI). At the same
time, however, as the proportion of silane crosslinking goes down,
there is also a decrease in the scratch resistance, with the
consequence that, for the purpose of achieving the desired very
high scratch resistance, a relatively high proportion of silane
crosslinking is desired.
[0037] The low post-crosslinking index (PCI) to be set in
accordance with the invention, of less than 2, preferably less than
or equal to 1.8, more preferably less than or equal to 1.7, and
very preferably less than or equal to 1.5, can be set by means of a
multiplicity of measures, which are elucidated in more detail
below. Hence it is possible in accordance with the invention to
provide coating compositions having the high proportions of silane
crosslinking that are needed for setting a very high scratch
resistance, which, owing to the low degree of post-crosslinking
(measured by way of the post-crosslinking index), do not have the
disadvantages typically associated with high proportions of silane
crosslinking. More particularly it is possible, through the setting
of the low post-crosslinking index, to provide coating compositions
which have a high scratch resistance directly after the final
thermal curing of the coating and at the same time exhibit good
weathering resistance. Furthermore, the coating compositions of the
invention are distinguished at the same time by very good
resistance properties on the part of the coatings of the invention
with respect to cracking under UV radiation and wet/dry cycling in
the CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO
4892-2 November 00), a high gloss, and high gloss retention after
weathering.
[0038] The Catalyst (D) for the Crosslinking of the Silane
Groups
[0039] One preferred measure for controlling the post-crosslinking
index (PCI) is the catalyst (D) for the crosslinking of the silane
groups. As catalyst for the crosslinking of the silane groups
and/or the alkoxysilyl units and also for the reaction between the
hydroxyl groups of the compound (A) and the free isocyanate groups
of the compound (B) it is possible to use compounds that are known
per se, if at the same time the low post-crosslinking index is
ensured by virtue of the other measures specified further below.
Examples of such known catalysts are Lewis acids (electron
deficiency compounds), such as, for example, tin naphthenate, tin
benzoate, tin octoate, tin butyrate, dibutyltin dilaurate,
dibutyltin diacetate, dibutyltin oxide, lead octoate, and also
catalysts as described in WO-A-2006/042585.
[0040] In order to set a low post-crosslinking index, however, it
is preferred as catalyst (D) to employ phosphorus-containing, more
particularly phosphorus- and nitrogen-containing, catalysts. In
this context it is also possible to use mixtures of two or more
different catalysts (D).
[0041] Examples of suitable phosphorus-containing catalysts (D) are
substituted phosphonic diesters and diphosphonic diesters,
preferably from the group consisting of acyclic phosphonic
diesters, cyclic phosphonic diesters, acyclic diphosphonic diesters
and cyclic diphosphonic diesters. Catalysts of this kind are
described for example in German patent application
DE-A-102005045228.
[0042] More particularly, however, use is made as catalyst of
substituted phosphoric monoesters and phosphoric diesters,
preferably from the group consisting of acylic phosphoric diesters
and cyclic phosphoric diesters, more preferably amine adducts of
the phosphoric acid monoesters and diesters.
[0043] The acyclic phosphoric diesters (D) are selected more
particularly from the group consisting of acyclic phosphoric
diesters (D) of the general formula (IV):
##STR00001##
[0044] where the radicals R.sub.10 and R.sub.11 are selected from
the group consisting of:
[0045] substituted and unsubstituted alkyl having 1 to 20,
preferably 2 to 16, and more particularly 2 to 10 carbon atoms,
cycloalkyl having 3 to 20, preferably 3 to 16, and more
particularly 3 to 10 carbon atoms, and aryl having 5 to 20,
preferably 6 to 14, and more particularly 6 to 10 carbon atoms,
[0046] substituted and unsubstituted alkylaryl, arylalkyl,
alkylcycloalkyl, cycloalkylalkyl, arylcycloalkyl, cycloalkylaryl,
alkylcycloalkylaryl, alkylarylcycloalkyl, arylcycloalkylalkyl,
arylalkylcycloalkyl, cycloalkylalkylaryl, and cycloalkylarylalkyl,
the alkyl, cycloalkyl, and aryl groups present therein each
containing the aforementioned number of carbon atoms, and
[0047] substituted or unsubstituted radical of the aforementioned
kind, containing at least one, more particularly one, heteroatom
selected from the group consisting of oxygen atom, sulfur atom,
nitrogen atom, phosphorus atom, and silicon atom, more particularly
oxygen atom, sulfur atom and nitrogen atom,
[0048] and being able additionally to be hydrogen as well (partial
esterification).
[0049] With very particular preference use is made as catalyst (D)
of the corresponding amine-blocked phosphoric esters, and more
particularly here amine-blocked phosphoric acid ethylhexyl esters
and amine-blocked phosphoric acid phenyl esters, especially
amine-blocked bis(2-ethylhexyl)phosphate.
[0050] Examples of amines with which the phosphoric esters are
blocked are, more particularly, tertiary amines, an example being
triethylamine. For blocking the phosphoric esters it is
particularly preferred to use tertiary amines, which ensure high
efficacy of the catalyst under the curing conditions of 140.degree.
C.
[0051] Certain amine-blocked phosphoric acid catalysts are also
available commercially (e.g., Nacure products from King
Industries). Mention may be made for example of Nacure 4167 from
King Industries as a particularly suitable catalyst on the basis of
an amine-blocked phosphoric acid partial ester.
[0052] The catalysts are used preferably in fractions of 0.01% to
20% by weight, more preferably in fractions of 0.1% to 10% by
weight, based on the nonvolatile constituents of the coating
composition of the invention. The amount of catalyst used also has
a certain influence on the post-crosslinking index, since a
relatively low catalyst efficacy can be compensated in part by
correspondingly higher amounts employed.
[0053] The Structural Units with Hydrolyzable Silane Groups
[0054] It is essential to the invention that one or more
constituents of the coating composition comprise hydrolyzable
silane groups. These hydrolyzable silane groups lead to the
construction of the Si--O--Si network which is distributed
statistically in the finally cured coating.
[0055] Suitable more particularly here are coating compositions in
which one or more constituents of the coating composition contain
at least partly one or more identical or different structural units
of the formula (I)
--X--Si--R''.sub.xG.sub.3-x (I)
[0056] where
[0057] G=identical or different hydrolyzable groups,
[0058] X=organic radical, more particularly linear and/or branched
alkylene or cycloalkylene radical having 1 to 20 carbon atoms, very
preferably X=alkylene radical having 1 to 4 carbon atoms,
[0059] R''=alkyl, cycloalkyl, aryl or aralkyl, it being possible
for the carbon chain to be interrupted by nonadjacent oxygen,
sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl,
preferably R''=alkyl radical, more particularly having 1 to 6 C
atoms,
[0060] x=0 to 2, preferably 0 to 1, more preferably x=0.
[0061] The structure of these silane radicals also has an influence
on the reactivity and hence also on the maximally extensive
reaction during the curing of the coating, in other words on the
setting of a maximally low post-crosslinking index (PCI).
[0062] In terms of the compatibility and the reactivity of the
silanes, preference is given to using silanes having 3 hydrolyzable
groups, i.e., x=0.
[0063] The hydrolyzable groups G may be selected from the group of
halogens, more particularly chlorine and bromine, from the group of
alkoxy groups, from the group of alkylcarbonyl groups, and from the
group of acyloxy groups. Particular preference is given to alkoxy
groups (OR').
[0064] The alkoxy radicals (OR') that are preferred in each case
may be alike or different; critical for the structure of the
radicals, however, is the extent to which they influence the
reactivity of the hydrolyzable silane groups. Preferably R' is an
alkyl radical, more particularly having 1 to 6 C atoms. Particular
preference is given to radicals R' which increase the reactivity of
the silane groups, i.e., which represent good leaving groups. With
that aim in mind, a methoxy radical is preferred over an ethoxy
radical, which is preferred in turn over a propoxy radical. With
particular preference, therefore, R'=ethyl and/or methyl, more
particularly methyl.
[0065] Furthermore, the reactivity of organofunctional silanes may
also be influenced considerably by the length of the spacers X
between silane functionality and organic functional group that
serves for reaction with the modifying constituent. As examples of
this, mention may be made of the "alpha" silanes available from
Wacker, in which a methylene group is between the Si atom and the
functional group, rather than the propylene group that is present
in the case of "gamma" silanes. For illustration it is stated that
methacryloyloxymethyltrimethoxysilane ("alpha" silane, e.g.,
commercial product Geniosil.RTM. XL 33 from Wacker) is used with
preference over methacryloyloxypropyltrimethoxysilane ("gamma"
silane, e.g., commercial product Geniosil.RTM. GF 31 from Wacker)
in order to introduce the hydrolyzable silane groups into the
coating composition.
[0066] In very general terms, spacers which increase the reactivity
of the silanes are preferred over spacers which reduce the
reactivity of the silanes.
[0067] In addition, the functionality of the silanes also has an
effect on the post-crosslinking index. By functionality in this
context is meant the number of radicals of the formula (I) per
molecule. A monofunctional silane is therefore a silane of the kind
which for each silane molecule introduces one radical of the
formula (I) into the constituent that is to be modified. A
difunctional silane is a silane of the kind which for each silane
molecule introduces in each case two radicals of the formula (I)
into the constituent.
[0068] Particular preference is given in accordance with the
invention to coating compositions in which the constituents have
been modified with a mixture of a monofunctional silane and a
difunctional silane. Difunctional silanes used are more
particularly the amino-functional disilanes of the formula (IIa)
that are described further below, and monofunctional silanes used
are the silanes of the formula (IIIa) that are described further
below.
[0069] In general, then, for a given level of silanization, the
post-crosslinking index (PCI) decreases as the proportion of
monofunctional silane goes up, but at the same time there is also a
decrease in the scratch resistance. Generally speaking, moreover,
as the proportion of difunctional silane goes up, there is an
increase in the post-crosslinking index (PCI), but at the same time
there is also an increase in the scratch resistance. With high
proportions of difunctional silane, therefore, correspondingly
different measures must be taken in order to reduce the
post-crosslinking index in order to provide the coating
compositions of the invention. By way of example, the degree of
silanization overall can be lowered; in other words, in the case of
the below-described modification of the polyisocyanate component
(B) with a (bis-silyl)amine of the formula (IIa), the fraction of
isocyanate groups reacted overall with a silane can be chosen to be
correspondingly low. Moreover, as the degree of silanization goes
up (i.e., as the overall proportion of the isocyanate groups
reacted with the compounds (IIa) and (IIIa) goes up) and as the
proportion of difunctional silane (IIa) goes up, the influence of
the catalyst on the post-crosslinking index becomes increasingly
great, with the consequence that, in that case, it is preferred to
employ phosphorus-containing catalysts, and more particularly
amine-blocked phosphoric acid-based catalysts.
[0070] Finally, it is also possible for nonfunctional substituents
on the organofunctional silane that is used to introduce the
structural units (I) and/or (II) and/or (III) to influence the
reactivity of the hydrolyzable silane group. This may be
illustrated by way of example taking as an example bulky,
voluminous substituents on the amine function, which can reduce the
reactivity of amine-functional silanes. Against this background,
N-(n-butyl)-3-aminopropyltrimethoxysilane is preferred over
N-cyclo-hexyl-3-aminopropyltrimethoxysilane for the introduction of
the structural units (III).
[0071] Very generally, the radicals which increase the reactivity
of the silanes are preferred over radicals which lower the
reactivity of the silanes.
[0072] There are different ways in which the structural units of
the formula (I) can be introduced into the constituents of the
coating composition. Common to the various ways, however, is that
the introduction of the structural units takes place via a reaction
of the functional groups of the constituents to be modified with
complementary functional groups of the silane. Set out below by way
of example, therefore, are various possibilities for the
introduction of the structural units (I) into the
hydroxyl-containing compound (A)--which, where appropriate, also
contains further reactive groups--and/or into the compound (B)
containing isocyanate groups.
[0073] Use is made, more particularly in the context of Michael
additions, of, for example, primary aminosilanes, such as
3-aminopropyltriethoxysilane (available for example under the trade
name Geniosil.RTM. GF 93 from Wacker Chemie),
3-aminopropyltrimethoxysilane (available for example under the
trade name Geniosil.RTM. GF 96 from Wacker Chemie),
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (available for
example under the trade name Geniosil.RTM. GF 9 and also
Geniosil.RTM. GF 91 from Wacker Chemie),
N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (available for
example under the trade name Geniosil.RTM. GF 95 from Wacker
Chemie), and the like.
[0074] Use is made, more particularly in the context of additions
to isocyanate-functional compounds, of, for example, secondary
aminosilanes, such as, for example,
bis(2-trimethoxysilylethyl)amine, bis(2-triethoxysilylethyl)amine,
bis(3-triethoxysilylpropyl)amine (available under the trade name
Dynasylan.RTM. 1122 from Degussa),
bis(3-trimethoxysilylpropyl)amine (available under the trade name
Dynasylan.RTM. 1124 from Degussa), bis(4-triethoxysilylbutyl)amine,
N-(n-butyl)-3-aminopropyltrimethoxysilane (available under the
trade name Dynasylan.RTM. 1189 from Degussa),
N-(n-butyl)-3-aminopropyltriethoxysilane,
N-cyclohexyl-3-aminopropyltrimethoxysilane (available under the
trade name Geniosil.RTM. GF 92 from Wacker Chemie),
N-cyclohexyl-3-aminopropyltriethoxysilane,
N-cyclohexylaminomethylmethyldiethoxysilane (available from Wacker
Chemie under the trade name Geniosil.RTM. XL 924),
N-cyclohexylaminomethyltriethoxysilane (available from Wacker
Chemie under the trade name Geniosil XL 926),
N-phenylaminomethyltrimethoxysilane (available from Wacker Chemie
under the trade name Geniosil XL 973), and the like.
[0075] Epoxy-functional silanes can be used more particularly for
addition to compounds with carboxylic acid or anhydride
functionality. Examples of suitable epoxy-functional silanes are
3-glycidyloxypropyltrimethoxysilane (available from Degussa under
the trade name Dynasylan.RTM. GLYMO),
3-glycidyloxypropyltriethoxysilane (available from Degussa under
the trade name Dynasylan.RTM. GLYEO), and the like.
[0076] Anhydride-functional silanes can be used more particularly
for addition to epoxy-functional compounds. An example that may be
mentioned of a silane with anhydride functionality is
3-(triethoxysilyl)propylsuccinic anhydride (available from Wacker
Chemie under the trade name Geniosil.RTM. GF 20).
[0077] Silanes of this kind can be used in the context of Michael
reactions or else in the context of metal-catalyzed reactions.
Those exemplified are 3-methacryloyloxypropyltrimethoxysilane
(available for example from Degussa under the trade name
Dynasilan.RTM. MEMO, or from Wacker Chemie under the trade name
Geniosil.RTM. GF 31), 3-methacryloyloxypropyltriethoxysilane,
vinyltrimethoxysilane (available, among others, from Wacker Chemie
under the trade name Geniosil.RTM. XL 10),
vinyldimethoxymethylsilane (available, among others, from Wacker
Chemie under the trade name Geniosil.RTM. XL 12),
vinyltriethoxysilane (available, among others, from Wacker Chemie
under the trade name Geniosil.RTM. GF 56),
(methacryloyloxymethyl)methyldimethoxysilane (available, among
others, from Wacker Chemie under the trade name Geniosil.RTM. XL
32), methacryloyloxymethyltrimethoxysilane (available, among
others, from Wacker Chemie under the trade name Geniosil.RTM. XL
33), (methacryloyloxymethyl)methyldiethoxysilane (available, among
others, from Wacker Chemie under the trade name Geniosil.RTM. XL
34), methacryloyloxymethyltriethoxysilane (available, among others,
from Wacker Chemie under the trade name Geniosil.RTM. XL 36).
[0078] Silanes with isocyanato function or carbamate function are
employed in particular in the context of reactions with
hydroxy-functional compounds. Examples of silanes with isocyanato
function are described in WO 07/03857, for example.
[0079] Examples of suitable isocyanatoalkyltrialkoxysilanes are
isocyanatopropyltrimethoxysilane,
isocyanatopropylmethyldimethoxysilane,
isocyanatopropylmethyldiethoxysilane,
isocyanatopropyltriethoxysilane,
isocyanatopropyltriisopropoxysilane,
isocyanatopropylmethyldiisopropoxysilane,
isocyanatoneohexyltrimethoxysilane,
isocyanatoneohexyldimethoxysilane,
isocyanatoneohexyldiethoxysilane,
isocyanatoneohexyltriethoxysilane,
isocyanatoneohexyltriisopropoxysilane,
isocyanatoneohexyldiisopropoxysilane,
isocyanatoisoamyltrimethoxysilane,
isocyanatoisoamylmethyldimethoxysilane,
isocyanatoisoamylmethyldiethoxysilane,
isocyanatoisoamyltriethoxysilane,
isocyanatoisoamyltriisopropoxysilane, and
isocyanatoisoamylmethyldiisopropoxysilane. Many isocyanatoalkyltri-
and -di-alkoxysilanes are available commercially, for example,
under the designation SILQUEST.RTM. from OSi Specialties, Inc., a
Witco Corporation company.
[0080] The isocyanatopropylalkoxysilane used preferably has a high
degree of purity, more particularly a purity of at least 95%, and
is preferably free from additives, such as transesterification
catalysts, which can lead to unwanted side reactions.
[0081] Use is made more particularly of
(isocyanatomethyl)methyldimethoxysilane (available from Wacker
Chemie under the trade name Geniosil.RTM. XL 42),
3-isocyanatopropyltrimethoxysilane (available from Wacker Chemie
under the trade name Geniosil.RTM. XL 40), and
N-dimethoxy(methyl)silylmethyl O-methylcarbamate (available from
Wacker Chemie under the trade name Geniosil.RTM. XL 65).
[0082] More particular preference in accordance with the invention
is given to coating compositions comprising at least one
hydroxyl-containing compound (A) and at least one
isocyanato-containing compound (B), wherein one or more
constituents of the coating composition comprise, as additional
functional components, between
[0083] 2.5 and 97.5 mol %, based on the entirety of structural
units (II) and (III), of at least one structural unit of the
formula (II)
--N(X--SiR''x(OR')3-x)n(X'--SiR''y(OR')3-y)m (II)
[0084] where
[0085] R'=hydrogen, alkyl or cycloalkyl, it being possible for the
carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa
groups, where Ra=alkyl, cycloalkyl, aryl or aralkyl, preferably
R'=ethyl and/or methyl X,X'=linear and/or branched alkylene or
cycloalkylene radical having 1 to 20 carbon atoms, preferably
X,X'=alkylene radical having 1 to 4 carbon atoms,
[0086] R''=alkyl, cycloalkyl, aryl or aralkyl, it being possible
for the carbon chain to be interrupted by nonadjacent oxygen,
sulfur or NRa groups, where Ra=alkyl, cycloalkyl, aryl or aralkyl,
preferably R''=alkyl radical, in particular having 1 to 6 carbon
atoms,
[0087] n=0 to 2, m=0 to 2, m+n=2, and x,y=0 to 2,
[0088] and
[0089] between 2.5 and 97.5 mol %, based on the entirety of
structural units (II) and (III), of at least one structural unit of
the formula (III)
-Z-(X--SiR''x(OR')3-x) (III),
[0090] where
[0091] Z=-NH--, --NR--, --O--, with
[0092] R=alkyl, cycloalkyl, aryl or aralkyl, it being possible for
the carbon chain to be interrupted by nonadjacent oxygen, sulfur or
NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl,
[0093] x=0 to 2
[0094] X, R', R'' have the meaning given in formula (II).
[0095] Very particular preference is given to coating compositions
wherein one or more constituents of the coating composition contain
between 5 and 95 mol %, more particularly between 10 and 90 mol %,
more preferably between 20 and 80 mol %, and especially between 30
and 70 mol %, based in each case on the entirety of the structural
units (II) and (III), of at least one structural unit of the
formula (II), and between 5 and 95 mol %, more particularly between
10 and 90 mol %, more preferably between 20 and 80 mol %, and
especially between 30 and 70 mol %, based in each case on the
entirety of the structural units (II) and (III), of at least one
structural unit of the formula (III).
[0096] The Hydroxyl-Containing Compound (A)
[0097] As hydroxyl-containing compound (A) it is preferred to use
both low molecular mass polyols and also oligomeric and/or
polymeric polyols.
[0098] Low molecular mass polyols used are, for example, diols,
such as, preferably, ethylene glycol, neopentyl glycol,
1,2-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol,
1,6-hexanediol, 1,4-cyclohexanedimethanol, and
1,2-cyclohexanedimethanol, and also polyols, such as, preferably,
trimethylolethane, trimethylolpropane, trimethylolhexane,
1,2,4-butanetriol, pentaerythritol, and dipentaerythritol. Low
molecular mass polyols of this kind are preferably admixed in minor
proportions to the oligomeric and/or polymeric polyol component
(A).
[0099] The preferred oligomeric and/or polymeric polyols (A) have
mass-average molecular weights Mw>500 daltons, as measured by
means of GPC (gel permeation chromatography), preferably between
800 and 100 000 daltons, in particular between 1000 and 50 000
daltons. Particularly preferred are polyester polyols, polyurethane
polyols, polysiloxane polyols, and, in particular, polyacrylate
polyols and/or polymethacrylate polyols, and their copolymers,
referred to as polyacrylate polyols below. The polyols preferably
have an OH number of 30 to 400 mg KOH/g, in particular between 100
and 300 KOH/g. The glass transition temperatures, as measured by
DSC (differential thermoanalysis), of the polyols are preferably
between -150 and 100.degree. C., more preferably between
-120.degree. C. and 80.degree. C.
[0100] Suitable polyester polyols are described for example in
EP-A-0 994 117 and EP-A-1 273 640. Polyurethane polyols are
prepared preferably by reacting polyester polyol prepolymers with
suitable di- or polyisocyanates and are described in EP-A-1 273
640, for example. Suitable polysiloxane polyols are described for
example in WO-A-01/09260, and the polysiloxane polyols recited
therein can be employed preferably in combination with further
polyols, especially those having relatively high glass transition
temperatures.
[0101] The polyacrylate polyols that are very particularly
preferred in accordance with the invention are generally copolymers
and preferably have mass-average molecular weights Mw of between
1000 and 20 000 daltons, in particular between 1500 and 10 000
daltons, in each case measured by means of gel permeation
chromatography (GPC) against a polystyrene standard. The glass
transition temperature of the copolymers is generally between -100
and 100.degree. C., in particular between -50 and 80.degree. C.
(measured by means of DSC measurements). The polyacrylate polyols
preferably have an OH number of 60 to 250 mg KOH/g, in particular
between 70 and 200 KOH/g, and an acid number of between 0 and 30 mg
KOH/g.
[0102] The hydroxyl number (OH number) indicates how many mg of
potassium hydroxide are equivalent to the amount of acetic acid
bound by 1 g of substance during acetylation. For the
determination, the sample is boiled with acetic anhydride-pyridine
and the acid formed is titrated with potassium hydroxide solution
(DIN 53240-2). The acid number here indicates the number of mg of
potassium hydroxide consumed in neutralizing 1 g of the respective
compound of component (b) (DIN EN ISO 2114).
[0103] The selection of the hydroxyl-containing binders as well may
be used to influence the post-crosslinking index. Generally
speaking, indeed, as the OH number of component (A) goes up, it is
possible to lower the degree of silanization, i.e., the amount of
structural units of the formula (I) and/or (II) and/or (III), which
in turn results in a lower post-crosslinking index.
[0104] Hydroxyl-containing monomer units used are preferably
hydroxyalkyl acrylates and/or hydroxyalkyl methacrylates, such as,
in particular, 2-hydroxyethyl acrylate, 2-hydroxyethyl
methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl
methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl
methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate,
and, in particular, 4-hydroxybutyl acrylate and/or 4-hydroxybutyl
methacrylate.
[0105] Further monomer units used for the polyacrylate polyols are
preferably alkyl methacrylates and/or alkyl methacrylates, such as,
preferably, ethyl acrylate, ethyl methacrylate, propyl acrylate,
propyl methacrylate, isopropyl acrylate, isopropyl methacrylate,
butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl
methacrylate, tert-butyl acrylate, tert-butyl methacrylate, amyl
acrylate, amyl methacrylate, hexyl acrylate, hexyl methacrylate,
ethylhexyl acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl
acrylate, 3,3,5-trimethylhexyl methacrylate, stearyl acrylate,
stearyl methacrylate, lauryl acrylate or lauryl methacrylate,
cycloalkyl acrylates and/or cycloalkyl methacrylates, such as
cyclopentyl acrylate, cyclopentyl methacrylate, isobornyl acrylate,
isobornyl methacrylate, or, in particular, cyclohexyl acrylate
and/or cyclohexyl methacrylate.
[0106] Further monomer units which can be used for the polyacrylate
polyols are vinylaromatic hydrocarbons, such as vinyltoluene,
alpha-methylstyrene or, in particular, styrene, amides or nitriles
of acrylic or methacrylic acid, vinyl esters or vinyl ethers, and,
in minor amounts, in particular, acrylic and/or methacrylic
acid.
[0107] In a further embodiment of the invention the
hydroxyl-containing compound A, as well as the hydroxyl groups,
comprises structural units of the formula (I) and/or of the formula
(II) and/or of the formula (III).
[0108] Structural units of the formula (II) can be introduced into
the compound (A) by incorporation of monomer units containing such
structural units, or by reaction of polyols containing further
functional groups with a compound of the formula (IIa)
HN(X--SiR''x(OR')3-x)n(X'--SiR''y(OR')3-y)m (IIa),
[0109] where the substituents are as defined above. For the
reaction of the polyol with the compound (IIa), the polyol,
correspondingly, has further functional groups which react with the
secondary amino group of the compound (IIa), such as acid or epoxy
groups in particular. Inventively preferred compounds (IIa) are
bis(2-ethyltrimethoxysilyl)amine,
bis(3-propyltrimethoxysilyl)amine,
bis(4-butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine,
bis(3-propyltriethoxysilyl)amine and/or
bis(4-butyltriethoxysilyl)amine. bis(3-Propyltrimethoxysilyl)amine
is especially preferred. Aminosilanes of this kind are available
for example under the trade name DYNASILAN.RTM. from DEGUSSA or
Silquest.RTM. from OSI.
[0110] Monomer units which carry the structural elements (II) are
preferably reaction products of acrylic and/or methacrylic acid or
of epoxy-functional alkyl acrylates and/or methacrylates with the
abovementioned compounds (IIa).
[0111] Structural units of the formula (III) can be introduced into
the compound (A) by incorporation of monomer units containing such
structural units or by reaction of polyols containing further
functional groups with a compound of the formula (IIIa)
H-Z-(X--SiR''x(OR')3-x) (IIIa),
[0112] where the substituents are as defined above. For the
reaction of the polyol with the compound (IIIa) the polyol,
correspondingly, has further functional groups which react with the
functional group -ZH of the compound (IIIa), such as acid, epoxy or
ester groups in particular. Inventively preferred compounds (IIIa)
are omega-aminoalkyl- or omega-hydroxyalkyltrialkoxysilanes, such
as, preferably, 2-aminoethyltrimethoxysilane,
2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane,
3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane,
4-aminobutyltriethoxysilane, 2-hydroxyethyltrimethoxysilane,
2-hydroxyethyltriethoxysilane, 3-hydroxypropyltrimethoxysilane,
3-hydroxypropyltriethoxysilane, 4-hydroxybutyltrimethoxysilane, and
4-hydroxybutyltriethoxysilane. Particularly preferred compounds
(IIIa) are N-(2-(trimethoxysilyl)ethyl)alkylamines,
N-(3-(trimethoxysilyl)propyl)alkylamines,
N-(4-(trimethoxysilyl)butyl)alkylamines,
N-(2-(triethoxysilyl)ethyl)alkylamines,
N-(3-(triethoxysilyl)propyl)alkylamines and/or
N-(4-(triethoxysilyl)butyl)alkylamines.
N-(3-(Trimethoxysilyl)propyl)butylamine is especially preferred.
Aminosilanes of this kind are available for example under the trade
name DYNASILAN.RTM. from DEGUSSA or Silquest.RTM. from OSI.
[0113] Monomer units which carry the structural elements (III) are
preferably reaction products of acrylic and/or methacrylic acid or
of epoxy-functional alkyl acrylates and/or methacrylates, and also,
in the case of hydroxy-functional alkoxysilyl compounds,
transesterification products of alkyl acrylates and/or
methacrylates, especially with the abovementioned hydroxy- and/or
amino-functional alkoxysilyl compounds (IIIa).
[0114] The Isocyanato-Containing Compounds (B)
[0115] As component (B) the coating compositions of the invention
comprise one or more compounds having free, i.e., nonblocked,
and/or blocked isocyanate groups. Preferably the coating
compositions of the invention comprise compounds (B) having free
isocyanate groups. The free isocyanate groups of the
isocyanate-group-containing compounds B may also, however, be used
in blocked form. This is preferably the case when the coating
compositions of the invention are employed in the form of
one-component systems.
[0116] The di- and/or polyisocyanates which serve as parent
structures for the isocyanato-containing compounds (B) used with
preference in accordance with the invention are preferably
conventional substituted or unsubstituted aromatic, aliphatic,
cycloaliphatic and/or heterocyclic polyisocyanates. Examples of
preferred polyisocyanates are as follows: 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, diphenylmethane 4,4'-diisocyanate,
diphenylmethane 2,4'-diisocyanate, p-phenylene diisocyanate,
biphenyl diisocyanates, 3,3'-dimethyl-4,4'-diphenylene
diisocyanate, tetramethylene 1,4-diisocyanate, hexamethylene
1,6-diisocyanate, 2,2,4-trimethylhexane 1,6-diisocyanate,
isophorone diisocyanate, ethylene diisocyanate, 1,12-dodecane
diisocyanate, cyclobutane 1,3-diisocyanate, cyclohexane
1,3-diisocyanate, cyclohexane 1,4-diisocyanate, methylcyclohexyl
diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene
2,6-diisocyanate, hexahydrophenylene 1,3-diisocyanate,
hexahydrophenylene 1,4-diisocyanate, perhydrodiphenylmethane
2,4'-diisocyanate, 4,4'-methylenedicyclohexyl diisocyanate (e.g.,
Desmodur.RTM. W from Bayer AG), tetramethylxylyl diisocyanates
(e.g., TMXDI.RTM. from American Cyanamid), and mixtures of the
aforementioned polyisocyanates. Additionally preferred
polyisocyanates are the biuret dimers and the isocyanurate trimers
of the aforementioned diisocyanates.
[0117] Particularly preferred polyisocyanates PI are hexamethylene
1,6-diisocyanate, isophorone diisocyanate, and
4,4'-methylenedicyclohexyl diisocyanate, their biuret dimers and/or
isocyanurate trimers.
[0118] In a further embodiment of the invention the polyisocyanates
are polyisocyanate prepolymers containing urethane structural units
which are obtained by reacting polyols with a stoichiometric excess
of aforementioned polyisocyanates. Polyisocyanate prepolymers of
this kind are described for example in U.S. Pat. No. 4,598,131.
[0119] The isocyanato-functional compounds (B) that are especially
preferred in accordance with the invention, functionalized with the
structural units (II) and (III), are prepared with particular
preference by reacting the aforementioned di- and/or
polyisocyanates with the aforementioned compounds (IIa) and (IIIa),
by reacting
[0120] between 2.5 and 90 mol %, preferably 5 to 85 mol %, more
preferably 7.5 to 80 mol %, of the isocyanate groups in the core
polyisocyanate structure with at least one compound (IIa) and
[0121] between 2.5 and 90 mol %, preferably 5 to 85 mol %, more
preferably 7.5 to 80 mol %, of the isocyanate groups in the core
polyisocyanate structure with at least one compound (IIIa).
[0122] The total fraction of the isocyanate groups reacted with the
compounds (IIa) and (IIIa) in the polyisocyanate compound (B) is
between 5 and 95 mol %, preferably between 10 and 90 mol %, more
preferably between 15 and 85 mol % of the isocyanate groups in the
core polyisocyanate structure. Particularly in the case of a high
degree of silanization, i.e., if a high proportion of the
isocyanate groups, more particularly at least 50 mol %, has been
reacted with the compounds (IIa)/(IIIa), the isocyanate groups are
advantageously reacted with a mixture of the compounds (IIa) and
(IIIa).
[0123] Particularly preferred compounds (IIa) are
bis(2-ethyltrimethoxysilyl)amine,
bis(3-propyltrimethoxysilyl)amine,
bis(4-butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine,
bis(3-propyltriethoxysilyl)amine and/or
bis(4-butyltriethoxysilyl)amine. bis(3-Propyltrimethoxysilyl)amine
is especially preferred. Aminosilanes of this kind are available
for example under the trade name DYNASILAN.RTM. from DEGUSSA or
Silquest.RTM. from OSI.
[0124] Preferred compounds (IIIa) are 2-aminoethyltrimethoxysilane,
2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane,
3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane,
4-aminobutyltriethoxysilane, 2-hydroxyethyltrimethoxysilane,
2-hydroxyethyltriethoxysilane, 3-hydroxypropyltrimethoxysilane,
3-hydroxypropyltriethoxysilane, 4-hydroxybutyltrimethoxysilane, and
4-hydroxybutyltriethoxysilane.
[0125] Particularly preferred compounds (IIIa) are
N-(2-(trimethoxysilyl)ethyl)alkylamines,
N-(3-(trimethoxysilyl)propyl)alkylamines,
N-(4-(trimethoxysilyl)butyl)alkylamines,
N-(2-(triethoxysilyl)ethyl)alkylamines,
N-(3-(triethoxysilyl)propyl)alkylamines and/or
N-(4-(triethoxysilyl)butyl)alkylamines.
N-(3-(Trimethoxysilyl)propyl)butylamine is especially preferred.
Aminosilanes of this kind are available for example under the trade
name DYNASILAN.RTM. from DEGUSSA or Silquest.RTM. from OSI.
[0126] Especially preferred isocyanato-containing compounds (B) are
reaction products of hexamethylene 1,6-diisocyanate and/or
isophorone diisocyanate, and/or their isocyanurate trimers, with
bis(3-propyltrimethoxysilyl)amine and
N-(3-(trimethoxysilyl)propyl)butylamine. The reaction of the
isocyanato-containing compounds (B) with the compounds (IIa) and
(IIIa) takes place preferably in inert gas at temperatures of not
more than 100.degree. C., preferably at not more than 60.degree.
C.
[0127] The free isocyanate groups of the isocyanato-containing
compounds B can also be used in blocked form. This is preferably
the case when the coating compositions of the invention are used as
one-component systems. For the purpose of blocking it is possible
in principle to use any blocking agent which can be used for
blocking polyisocyanates and which has a sufficiently low
unblocking temperature. Blocking agents of this kind are very
familiar to the skilled worker. It is preferred to use blocking
agents as described in EP-A-0 626 888 and EP-A-0 692 007.
[0128] The Combination of Components A and B, and Further
Components of the Coating Composition
[0129] The weight fraction of hydroxyl-containing compounds A to be
employed, based on the weight fraction of the isocyanato-containing
compounds B, is dependent on the hydroxy equivalent weight of the
polyol and on the equivalent weight of the free isocyanate groups
of the polyisocyanate B.
[0130] It is preferable that in the coating composition of the
invention there is one or more constituents between 2.5 to 97.5 mol
%, based on the sum of structural units (II) and (III), of at least
one structural unit (II) and between 2.5 to 97.5 mol %, based on
the sum of structural units (II) and (III), of at least one of
structural units (III).
[0131] The coating compositions of the invention contain preferably
between 2.5% and 97.5%, more preferably between 5% and 95%, very
preferably between 10% and 90%, and in particular between 20% and
80%, by weight, based on the amount of nonvolatile substances in
the coating composition, of the hydroxyl-containing compounds (A),
and preferably between 2.5% and 97.5%, more preferably between 5%
and 95%, very preferably between 10% and 90%, and in particular
between 20% and 80%, by weight, based on the amount of nonvolatile
substances in the coating composition, of the isocyanato-containing
compounds (B).
[0132] Based on the sum of the functional groups critical for
crosslinking in the coating composition of the invention, formed
from the fractions of the hydroxyl and isocyanate groups and also
the fractions of the structural elements (I) and/or (II) and/or
(III), the structural elements (I) and/or (II) and/or (III) are
present preferably in fractions of 2.5 to 97.5 mol %, more
preferably between 5 and 95 mol %, and very preferably between 10
and 90 mol %.
[0133] In order to ensure further-improved, very good resistance
properties on the part of the coatings of the invention toward
cracking under UV radiation and wet/dry cycling in the CAM180 test
(to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2 November 00)
in combination with a high scratch resistance directly following
the final thermal cure, a high gloss, and high gloss retention
after weathering, it is additionally preferred to choose the level
of structural units (I) and/or (II) and/or (III) to be at most such
that the coating compositions of the invention in the finally cured
state have a storage modulus E' (200.degree. C.), measured at
200.degree. C. in accordance with the method described above in
connection with the description of the PCI, of less than 4*10.sup.8
Pa, more particularly of less than or equal to 3*10.sup.8 Pa.
[0134] It is particularly preferred, in addition, to select the
amount of structural units (I) and/or (II) and/or (III) to be at
most such that the coating compositions of the invention contain
less than 6.5% by mass of Si of the structural units (I) and/or
(II) and/or (III), very preferably not more than 6.0% by mass of Si
of the structural units (I) and/or (II) and/or (III), based in each
case on the solids content of the coating compositions. The silane
content in % by mass of Si is determined arithmetically from the
amounts of the compounds with the structural unit (I) and,
respectively, the compounds (IIa) and/or (IIIa) that are used.
[0135] In a further embodiment of the invention the structural
elements (I), (II) and/or (III) may additionally also be part of
one or more further components (C), different than the components
(A) and (B), in which case the criteria to be applied are those
specified above. By way of example it is possible as component (C)
to use oligomers or polymers containing alkoxysilyl groups, such
as, for example, the poly(meth)acrylates specified in patents and
patent applications U.S. Pat. No. 4,499,150, U.S. Pat. No.
4,499,151 or EP-A-0 571 073, as carriers of structural elements
(III), or to use the compounds specified in WO-A-2006/042585, as
carriers of structural elements (II). Generally speaking,
components (C) of this kind are used in fractions of up to 40%,
preferably up to 30%, more preferably up to 25%, by weight, based
on the nonvolatile constituents of the coating composition. The
weight fractions of the polyol A and of the polyisocyanate B are
preferably selected such that the molar equivalent ratio of the
unreacted isocyanate groups of the isocyanate-containing compounds
(B) to the hydroxyl groups of the hydroxyl-containing compounds (A)
is between 0.9:1 and 1:1.1, preferably between 0.95:1 and 1.05:1,
more preferably between 0.98:1 and 1.02:1.
[0136] Where the compositions are one-component coating
compositions, a selection is made of the isocyanato-containing
compounds (B) whose free isocyanate groups have been blocked with
the blocking agents described above.
[0137] In the case of the inventively preferred 2-component (2K)
coating compositions, a coating component comprising the
hydroxyl-containing compound (A) and also further components,
described below, is mixed conventionally with a further coating
component, comprising the isocyanato-containing compound (B) and,
where appropriate, further of the components described below, this
mixing taking place shortly before the coating composition is
applied; generally speaking, the coating component that comprises
the compound (A) comprises the catalyst and also part of the
solvent.
[0138] Solvents suitable for the coating compositions of the
invention are in particular those which, in the coating
composition, are chemically inert toward the compounds (A) and (B)
and also do not react with (A) and (B) when the coating composition
is being cured. Examples of such solvents are aliphatic and/or
aromatic hydrocarbons such as toluene, xylene, solvent naphtha,
Solvesso 100 or Hydrosol.RTM. (from ARAL), ketones, such as
acetone, methyl ethyl ketone or methyl amyl ketone, esters, such as
ethyl acetate, butyl acetate, pentyl acetate or ethyl
ethoxypropionate, ethers, or mixtures of the aforementioned
solvents. The aprotic solvents or solvent mixtures preferably have
a water content of not more than 1%, more preferably not more than
0.5%, by weight, based on the solvent.
[0139] Besides the compounds (A), (B), and (C) it is possible
additionally to use further binders (E), which preferably are able
to react and form network points with the hydroxyl groups of the
compound (A) and/or with the free isocyanate groups of the compound
(B) and/or with the alkoxysilyl groups of the compounds (A), (B)
and/or (C).
[0140] By way of example it is possible to use amino resins and/or
epoxy resins as component (E). Suitable amino resins are the
typical, known amino resins, some of whose methylol and/or
methoxymethyl groups may have been defunctionalized by means of
carbamate or allophanate groups. Crosslinking agents of this kind
are described in patents U.S. Pat. No. 4,710,542 and EP-B-0 245 700
and also in the article by B. Singh and coworkers,
"Carbamylmethylated Melamines, Novel Crosslinkers for the Coatings
Industry" in Advanced Organic Coatings Science and Technology
Series, 1991, Volume 13, pages 193 to 207.
[0141] Generally speaking, such components (E) are used in
fractions of up to 40%, preferably up to 30%, more preferably up to
25%, by weight, based on the nonvolatile constituents of the
coating composition.
[0142] The coating composition of the invention may further
comprise at least one typical, known coatings additive in effective
amounts, i.e. in amounts preferably up to 30%, more preferably up
to 25%, and in particular up to 20% by weight, in each case based
on the nonvolatile constituents of the coating composition.
[0143] Examples of suitable coatings additives are: [0144]
particularly UV absorbers; [0145] particularly light stabilizers
such as HALS compounds, benzotriazoles or oxalanilides; [0146]
free-radical scavengers; [0147] slip additives; [0148]
polymerization inhibitors; [0149] defoamers; [0150] reactive
diluents, of the kind which are common knowledge from the prior
art, and which are preferably inert toward the --Si(OR)3 groups;
[0151] wetting agents such as siloxanes, fluorine compounds,
carboxylic monoesters, phosphoric esters, polyacrylic acids and
their copolymers, or polyurethanes; [0152] adhesion promoters such
as tricyclodecanedimethanol; [0153] flow control agents; [0154]
film-forming assistants such as cellulose derivatives; [0155]
fillers such as, for example, nanoparticles based on silicon
dioxide, aluminum oxide or zirconium oxide; for further details
refer to Rompp Lexikon "Lacke und Druckfarben" Georg Thieme Verlag,
Stuttgart, 1998, pages 250 to 252; [0156] rheology control
additives, such as the additives known from patents WO 94/22968,
EP-A-0 276 501, EP-A-0 249 201 or WO 97/12945; crosslinked
polymeric microparticles, as disclosed for example in EP-A-0 008
127; inorganic phyllosilicates such as aluminum-magnesium
silicates, sodium-magnesium and sodium-magnesium-fluorine-lithium
phyllosilicates of the montmorillonite type; silicas such as
Aerosils; or synthetic polymers containing ionic and/or associative
groups such as polyvinyl alcohol, poly(meth)acrylamide,
poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic
anhydride copolymers or ethylene-maleic anhydride copolymers and
their derivatives, or hydrophobically modified ethoxylated
urethanes or polyacrylates; [0157] and/or flame retardants.
[0158] In a further embodiment of the invention the coating
composition of the invention may additionally comprise further
pigments and/or fillers and may serve for producing pigmented
topcoats. The pigments and/or fillers employed for this purpose are
known to the skilled worker.
[0159] Because the coatings of the invention produced from the
coating compositions of the invention adhere excellently even to
electrocoats, surfacer coats, basecoat systems or typical, known
clearcoat systems that have already cured, they are outstandingly
suitable not only for use in automotive OEM finishing but also for
automotive refinish or for the modular scratchproofing of
automobile bodies that have already been painted.
[0160] The coating compositions of the invention can be applied by
any of the typical application methods, such as spraying, knife
coating, spreading, pouring, dipping, impregnating, trickling or
rolling, for example. In the course of such application, the
substrate to be coated may itself be at rest, with the application
equipment or unit being moved. Alternatively the substrate to be
coated, in particular a coil, may be moved, with the application
unit at rest relative to the substrate or being moved
appropriately.
[0161] Preference is given to employing spray application methods,
such as compressed-air spraying, airless spraying, high-speed
rotation, electrostatic spray application (ESTA), alone or in
conjunction with hot spray application such as hot-air spraying,
for example.
[0162] The applied coating compositions of the invention can be
cured after a certain rest time. The rest time serves, for example,
for the leveling and devolatilization of the coating films or for
the evaporation of volatile constituents such as solvents. The rest
time may be assisted and/or shortened by the application of
elevated temperatures and/or by a reduced humidity, provided this
does not entail any damage or alteration to the coating films, such
as premature complete crosslinking, for instance.
[0163] The thermal curing of the coating compositions has no
peculiarities in terms of method but instead takes place in
accordance with the typical, known methods such as heating in a
forced-air oven or irradiation with IR lamps. The thermal cure may
also take place in stages. Another preferred curing method is that
of curing with near infrared (NIR) radiation. The thermal cure
takes place advantageously at a temperature of 30 to 200.degree.
C., more preferably 40 to 190.degree. C., and in particular 50 to
180.degree. C. for a time of 1 min up to 10 h, more preferably 2
min up to 5 h, and in particular 3 min to 3 h, although longer cure
times may be employed in the case of the temperatures that are
employed for automotive refinish, which are preferably between 30
and 90.degree. C.
[0164] The coating compositions of the invention produce new cured
coatings, especially coating systems, more particularly clearcoat
systems; moldings, especially optical moldings; and self-supporting
films, all of which are highly scratchproof and in particular are
stable to chemicals and to weathering. The coatings and coating
systems of the invention, especially the clearcoat systems, can in
particular be produced even in film thicknesses>40 .mu.m without
stress cracks occurring.
[0165] For these reasons the coating compositions of the invention
are of excellent suitability as decorative, protective and/or
effect-imparting, highly scratchproof coatings and coating systems
on bodies of means of transport (especially motor vehicles, such as
motor cycles, buses, trucks or automobiles) or parts thereof; on
buildings, both interior and exterior; on furniture, windows, and
doors; on plastics moldings, especially CDs and windows; on small
industrial parts, on coils, containers, and packaging; on white
goods; on films; on optical, electrical, and mechanical components;
and on hollow glassware and articles of everyday use.
[0166] The coating compositions and coating systems of the
invention, especially the clearcoat systems, are employed in
particular in the technologically and esthetically particularly
demanding field of automotive OEM finishing and also of automotive
refinish. With particular preference the coating compositions of
the invention are used in multistage coating methods, particularly
in methods where a pigmented basecoat film is first applied to an
uncoated or precoated substrate and thereafter a film with the
coating compositions of the invention is applied. Not only
water-thinnable basecoat materials but also basecoat materials
based on organic solvents can be used. Suitable basecoat materials
are described for example in EP-A-0 692 007 and in the documents
cited there in column 3 lines 50 et seq. The applied basecoat
material is preferably first dried, i.e., at least some of the
organic solvent and/or water is stripped from the basecoat film in
an evaporation phase. Drying is accomplished preferably at
temperatures from room temperature to 80.degree. C. Drying is
followed by the application of the coating composition of the
invention. Subsequently the two-coat system is baked, preferably
under conditions employed for automotive OEM finishing, at
temperatures from 30 to 200.degree. C., more preferably 40 to
190.degree. C., and in particular 50 to 180.degree. C., for a time
of 1 min up to 10 h, more preferably 2 min up to 5 h, and in
particular 3 min to 3 h, although longer cure times may also be
employed at the temperatures employed for automotive refinish,
which are preferably between 30 and 90.degree. C.
[0167] The coats produced with the coating composition of the
invention are notable in particular for an especially high chemical
stability and weathering stability and also for a very good carwash
resistance and scratchproofing, in particular for an excellent
combination of scratchproofing and weathering stability with
respect to UV radiation in a wet/dry cycle.
[0168] In a further preferred embodiment of the invention, the
coating composition of the invention is used as a transparent
clearcoat material for coating plastics substrates, especially
transparent plastics substrates. In this case the coating
compositions include UV absorbers, which in terms of amount and
type are also designed for effective UV protection of the plastics
substrate. Here as well, the coating compositions are notable for
an outstanding combination of scratchproofing and weathering
stability with respect to UV radiation in a wet/dry cycle. The
plastics substrates thus coated are used preferably as a substitute
for glass components in automobile construction, the plastics
substrates being composed preferably of polymethyl methacrylate or
polycarbonate.
Examples
[0169] Preparation of Inventive Component B
Preparation Example B1
Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol
% of IIIa: Conversion c=30 Mol %)
[0170] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, 21.8 parts by weight of
N-[3-(trimethoxysilyl)propyl]butylamine (IIIa) (Dynasilan.RTM. 1189
from Degussa) are metered in at a rate such that 50 to 60.degree.
C. are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 70 mol %.
[0171] The solution of the partly silanized polyisocyanate has a
solids content of 47.1% by weight.
Preparation Example B2
Preparation of a Partly Silanized Polyisocyanate (HDI with 70 Mol %
of IIIa and 30 Mol % of IIa: Conversion c=30 Mol %)
[0172] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, a mixture of 14.8 parts
by weight of N-[3-(trimethoxysilyl)propyl]butylamine
(Dynasilan.RTM. 1189 from Degussa) (IIIa) and 9.2 parts by weight
of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan.RTM. 1124
from Degussa) is metered in at a rate such that 50 to 60.degree. C.
are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 70 mol %.
[0173] The solution of the partly silanized polyisocyanate has a
solids content of 53.9% by weight.
Preparation Example B3
Preparation of a Partly Silanized Polyisocyanate (HDI with 30 Mol %
of IIIa and 70 Mol % of IIa: Conversion c=30 Mol %)
[0174] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, a mixture of 6.4 parts
by weight of N-[3-(trimethoxysilyl)propyl]butylamine
(Dynasilan.RTM. 1189 from Degussa) (IIIa) and 21.5 parts by weight
of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan.RTM. 1124
from Degussa) is metered in at a rate such that 50 to 60.degree. C.
are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 70 mol %.
[0175] The solution of the partly silanized polyisocyanate has a
solids content of 55.0% by weight.
Preparation Example B4
Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol
% of IIa: Conversion c=30 Mol %)
[0176] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, 30.7 parts by weight of
bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan.RTM. 1124 from
Degussa) are metered in at a rate such that 50 to 60.degree. C. are
not exceeded. After the end of the metered addition, the reaction
temperature is held at 50 to 60.degree. C. until the isocyanate
mass fraction as determined by titration is at the theoretically
calculated 70 mol %.
[0177] The solution of the partly silanized polyisocyanate has a
solids content of 63.0% by weight.
Preparation Example B5
Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol
% of IIIa: Conversion c=70 Mol %)
[0178] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, 49.4 parts by weight of
N-[3-(trimethoxysilyl)propyl]butylamine (IIIa) (Dynasilan.RTM. 1189
from Degussa) are metered in at a rate such that 50 to 60.degree.
C. are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 30 mol %.
[0179] The solution of the partly silanized polyisocyanate has a
solids content of 54.8% by weight.
Preparation Example B6
Preparation of a Partly Silanized Polyisocyanate (HDI with 70 Mol %
of IIIa and 30 Mol % of IIa: Conversion c=70 Mol %)
[0180] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, a mixture of 34.6 parts
by weight of N-[3-(trimethoxysilyl)propyl]butylamine
(Dynasilan.RTM. 1189 from Degussa) (IIIa) and 21.5 parts by weight
of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan.RTM. 1124
from Degussa) is metered in at a rate such that 50 to 60.degree. C.
are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 30 mol %.
[0181] The solution of the partly silanized polyisocyanate has a
solids content of 61.9% by weight.
Preparation Example B7
Preparation of a Partly Silanized Polyisocyanate (HDI with 30 Mol %
of IIIa and 70 Mol % of IIa: Conversion c=70 Mol %)
[0182] A three-neck glass flask equipped with a reflux condenser
and a thermometer is charged with 57.3 parts by weight of
trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from
BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux
cooling, nitrogen blanketing, and stirring, a mixture of 14.8 parts
by weight of N-[3-(trimethoxysilyl)propyl]butylamine
(Dynasilan.RTM. 1189 from Degussa) (IIIa) and 50.2 parts by weight
of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan.RTM. 1124
from Degussa) is metered in at a rate such that 50 to 60.degree. C.
are not exceeded. After the end of the metered addition, the
reaction temperature is held at 50 to 60.degree. C. until the
isocyanate mass fraction as determined by titration is at the
theoretically calculated 70 mol %.
[0183] The solution of the partly silanized polyisocyanate has a
solids content of 58.2% by weight.
[0184] Preparation of the Polyacrylate Polyol A
[0185] In a steel tank reactor equipped with monomer inlet,
initiator inlet, thermometer, oil heating, and reflux condenser,
29.08 parts by weight of a commercial aromatic solvent mixture
(Solventnaphtha.RTM. from DHC Solvent Chemie GmbH) are heated to
140.degree. C. Then a mixture a1 of 3.39 parts by weight of solvent
naphtha and 2.24 parts by weight of tert-butyl
peroxy-2-ethylhexanoate is added with stirring, at a rate such that
the addition of the mixture a1 is concluded after 6.75 h. 15 min
after the beginning of the addition of the mixture a1, a mixture a2
consisting of 4.97 parts by weight of styrene, 16.91 parts by
weight of tert-butyl acrylate, 19.89 parts by weight of
2-hydroxypropyl methacrylate, 7.45 parts by weight of n-butyl
methacrylate, and 0.58 part by weight of acrylic acid is added at a
rate such that the addition of the mixture a2 is concluded after 6
h. After the addition of the mixture a1, the reaction mixture is
held at 140.degree. C. for a further 2 h and then cooled to below
100.degree. C. Subsequently the reaction mixture is diluted
additionally with a mixture a3 of 3.70 parts by weight of
1-methoxyprop-2-yl acetate, 3.06 parts by weight of butyl glycol
acetate, and 6.36 parts by weight of butyl acetate 98/100.
[0186] The resulting solution of the polyacrylate polyol A has a
solids content of 52.4% (1 h, 130.degree. C., forced-air oven), a
viscosity of 3.6 dPas (ICI cone/plate viscometer, 23.degree. C.), a
hydroxyl number of 155 mg KOH/g, and an acid number of 10-13 mg
KOH/g.
[0187] Formulation of the Coating Compositions
[0188] The coating compositions were formulated as follows:
[0189] Component 1, containing component A (polyol) and commercial
additives and catalyst and solvent, is combined shortly before
application with component 2, containing component B (modified
polyisocyanate), and the components are stirred together until a
homogeneous mixture is formed.
[0190] Application takes place pneumatically at 2.5 bar in three
spray passes. Thereafter the coating is flashed off at room
temperature for 5 minutes and subsequently baked at 140.degree. C.
for 22 minutes.
[0191] Table 1 lists all of the inventive coating compositions B1
to B7 in terms of the proportions of the components:
TABLE-US-00001 TABLE 1 Formulation of inventive coating
compositions Example B1 B2 B3 B4 B5 B6 B7 Component B B1 B2 B3 B4
B5 B6 B7 Parts by weight of 45.0 45.0 45.0 45.0 45.0 45.0 45.0
polyacrylate polyol A of example Parts by weight of 52.0 47.2 48.3
43.7 144.9 133.0 153.0 component B Parts by weight of 2.1 2.2 2.3
2.4 6.9 7.2 7.8 catalyst.sup.1 (Nacure 4167, King Industries)
nonvolatile fraction 25% Parts by weight of BYK 0.2 0.2 0.2 0.2 0.2
0.2 0.2 301 (flow control agent, Byk Chemie) Parts by weight of 0.9
0.9 0.9 0.9 0.9 0.9 0.9 Tinuvin 384.2 (Ciba) Parts by weight of 0.8
0.8 0.8 0.8 0.8 0.8 0.8 Tinuvin 292 (Ciba) Parts by weight of 20.0
20.0 20.0 20.0 20.0 20.0 20.0 Solventnaphtha (DHC Solvent Chemie
GmbH) Equivalent ratio of free 1.00:1.00 1.00:1.00 1.00:1.00
1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 isocyanate groups in
component B to hydroxyl groups in polyacrylate polyol A Si content
in % by 1.5 1.8 2.5 2.9 3.9 4.5 5.9 mass.sup.2) .sup.1catalyst
based on amine-blocked phosphoric acid partial ester .sup.2)Si
content calculated from the amounts of (IIa)/(IIIa) employed, based
on the solids content of the coating compositions
[0192] The storage moduli E'(200) and E'(min) and also the glass
transition temperature Tg of the respective cured coating are
measured by dynamic-mechanical thermo-analysis (DMTA) at a heating
rate of 2 K/min using the DMTA V instrument from Rheometrics
Scientific at a frequency of 1 Hz and an amplitude of 0.2%. The
DMTA measurements are carried out on free films with a thickness of
40 .mu.m.+-.10 .mu.m. For this purpose the coating composition
under test is applied to substrates to which the coating obtained
does not adhere. Examples of suitable substrates include glass,
Teflon, polyethylene terephthalate and polypropylene. The resulting
coating is cured for 20 minutes at an article temperature of
140.degree. C. and is stored at 25.degree. C. for 8 days after
curing, before the DMTA measurements are carried out.
[0193] The scratchproofing of the surfaces of the resultant
coatings was tested by means of the Crockmeter test (in general in
accordance with EN ISO 105-X12, with 10 double rubs and an applied
force of 9 N, using 9 .mu.m abrasive paper (3M 281Q, using
wetordry.TM.production.TM.), with subsequent determination of the
residual gloss at 20.degree. using a commercially customary gloss
meter), and by means of the hammer test (10 or 100 double rubs with
steel wool (RAKSO.RTM.00(fine)) with an applied weight of 1 kg,
implemented with a hammer. Subsequently, again, the residual gloss
at 20.degree. is determined with a commercially customary gloss
meter) and the weathering stability is investigated by means of the
CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2
November 00). The results are listed in Table 2.
TABLE-US-00002 TABLE 2 Properties of the clearcoat films produced
with the inventive coating compositions Example B1 B2 B3 B4 B5 B6
B7 E' (200.degree. C.) in Pa 2.74 * 10.sup.7 3.58 * 10.sup.7 3.27 *
10.sup.7 6.73 * 10.sup.7 5.94 * 10.sup.7 1.68 * 10.sup.8 2.99 *
10.sup.8 E' (min) in Pa 2.36 * 10.sup.7 3.23 * 10.sup.7 2.99 *
10.sup.7 5.47 * 10.sup.7 5.33 * 10.sup.7 1.01 * 10.sup.8 1.85 *
10.sup.8 Post-crosslinking 1.2 1.1 1.1 1.2 1.1 1.7 1.6 index PCI
Crockmeter test 41 53 58 63 75 88 95 (residual gloss in %) Hammer
test 10 DR 38 49 60 64 79 88 93 (residual gloss in %) Hammer test
100 DR 0 1 18 28 65 81 92 (residual gloss in %) Gloss 82 85 85 85
86 86 86 CAM 180 test (h) 5500 5250 5000 4500 5250 5000 4000 until
appearance of cracks
[0194] Table 2 shows the properties of the coatings of examples B1
to B7, prepared from the inventive coating compositions comprising
an isocyanurate adduct B originating from the reaction of the HDI
isocyanurate with, in each case, a mixture of a component IIa and a
component IIIa (Examples B2, B3, B6 and B7), in comparison to
coating compositions comprising an isocyanurate adduct B
originating from the reaction with the HDI isocyanurate, referred
to as HDI for short below, and exclusively one component IIa
(example B4) or IIIa (examples B1 and B5).
[0195] In all of examples B1 to B7, coatings with the low degrees
of post-crosslinking, in accordance with the invention, and the
corresponding good scratch resistance and weathering resistance
properties are obtained. It is noted first of all that, generally
speaking, the smaller the fraction of the silane crosslinking as a
proportion of the crosslinking overall, the lower the
post-crosslinking in general and hence the smaller the
post-crosslinking index (PCI). For instance, in the case of
examples B1 and B2, with a very low proportion of silane
crosslinking (conversion of the isocyanate groups of the HDI of 30
mol % and high fraction of monofunctional silane structural units
of 100 mol % structural units III in example B1 and 70 mol %
structural units III in example B2) lower degrees of
post-crosslinking are obtained than in example 7, with a high
proportion of silane crosslinking (conversion of the isocyanate
groups of the HDI of 70 mol % and high fraction of difunctional
silane structural units of 70 mol % structural units II in example
B7). At the same time, however, as the fraction of silane
crosslinking goes down, there is also a decrease in the scratch
resistance, with the consequence that, in order to achieve very
high scratchproofing values, relative high fractions of silane
crosslinking are desired, as is likewise shown by a comparison of
examples B1 and B2 with B7.
[0196] With a conversion of the isocyanate groups of the HDI of 30
mol %, B1 (containing only structural units III) as against B4
(containing only structural units II), exhibit a much longer time
in the CAM180 test until cracks appear. Correspondingly, for a
degree of conversion of the isocyanate groups of the HDI of 70 mol
%, example B5 (containing only structural units III) as against B7
(containing 70 mol % structural units II) exhibits a significantly
longer time in the CAM 180 test before the appearance of cracks.
The situation with the scratchproofing is the inverse of this: with
a conversion of the isocyanate groups of the HDI of 30 mol %, B1
(containing only structural units III) as against B4 (containing
only structural units II), exhibit a much weaker scratchproofing in
the various scratch tests. Correspondingly, for a conversion of the
isocyanate groups of the HDI of 70 mol %, example B5 (containing
only structural units III) as against to B7 (containing 70 mol %
structural units II) shows a significantly weaker scratchproofing
in the various scratch tests. Since the relative fraction of the
structure II hence shows itself to be responsible for the
scratchproofing, and the fraction of the structure III for the
weathering resistance, a careful blending of the amounts used of
both siloxane amines IIa and IIIa allows a fine-tuned balance to be
struck between weathering time and scratchproofing.
[0197] By way of example, B1 and B4 may be contrasted with B2 and
B3 in the group with 30 mol % conversion of the isocyanate
functions. B1 achieves high weathering values, but the
scratchproofing is moderate. B4 has good scratchproofing values,
but is weaker in weathering. Both examples B2 and B3 have better
scratchproofing than B1 and better weathering times than B4.
[0198] Similar comments apply to B5 contrasted with B6 and B7 in
the group with 70 mol % conversion of isocyanate, although here
both scratchproofing and weathering resistance are influenced more
strongly, as a result of the high relative fraction of the siloxane
functions. In addition it is clear that, with a high conversion of
the isocyanate functions, the relative fraction of the structure
III influences the weathering resistance significantly more
strongly than structure II influences the scratchproofing, as can
easily be seen from comparing the values of B6 and B7. In general,
the scratchproofing value correlates with the conversion of the
isocyanate groups with the compounds II and III, and in this
context a higher conversion of the isocyanate groups is also
necessary for the attainment of very high scratchproofing.
Comparative Examples 1 to 7
[0199] Examples 1 to 7 were repeated, albeit with the sole
difference that this time, instead of the catalyst based on
amine-blocked phosphoric acid partial esters, blocked
para-toluenesulfonic acid was used as the catalyst.
[0200] Table 3 lists all of the coating compositions of the
comparative examples, in terms of the proportions of the
components:
TABLE-US-00003 TABLE 3 Formulation of the coating compositions of
the comparative examples Example VB1 VB2 VB3 VB4 VB5 VB6 VB7
Components B B1 B2 B3 B4 B5 B6 B7 Parts by weight of 45.0 45.0 45.0
45.0 45.0 45.0 45.0 polyacrylate polyol A of example Parts by
weight of 52.0 47.2 48.3 43.7 144.9 133.0 153.0 component B Parts
by weight of 1.1 1.1 1.2 1.2 3.5 3.6 3.9 catalyst.sup.3 (Dynapol
1203, Degussa), nonvolatile fraction 50% Parts by weight of BYK 0.2
0.2 0.2 0.2 0.2 0.2 0.2 301 (flow control agent, Byk Chemie) Parts
by weight of 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Tinuvin 384.2 (Ciba) Parts
by weight of 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Tinuvin 292 (Ciba) Parts
by weight of 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Solventnaphtha (DHC
Solvent Chemie GmbH) Equivalent ratio of free 1.00:1.00 1.00:1.00
1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 isocyanate groups
in component B to hydroxyl groups in polyacrylate polyol A Si
content in % by 1.5 1.8 2.5 2.9 3.9 4.5 5.9 mass.sup.4)
.sup.3catalyst based on blocked p-toluenesulfonic acid .sup.4)Si
content calculated from the amounts of (IIa)/(IIIa) employed, based
on the solids content of the coating compositions
TABLE-US-00004 TABLE 4 Properties of the clearcoat films produced
with the coating compositions of the comparative examples Example
VB1 VB2 VB3 VB4 VB5 VB6 VB7 E' (200.degree. C.) in Pa 3.08 *
10.sup.7 4.13 * 10.sup.7 4.05 * 10.sup.7 7.39 * 10.sup.7 6.03 *
10.sup.7 1.80 * 10.sup.8 2.79 * 10.sup.8 E' (min) in Pa 1.08 *
10.sup.7 1.13 * 10.sup.7 0.99 * 10.sup.7 1.54 * 10.sup.7 1.73 *
10.sup.7 3.39 * 10.sup.7 4.23 * 10.sup.7 Post-crosslinking 2.9 3.6
4.1 4.8 3.5 5.3 6.6 index PCI Crockmeter test 14 6 7 13 35 56 78
(residual gloss in %) Hammer test 10 DR 16 23 32 36 44 67 79
(residual gloss in %) Hammer test 100 DR 0 0 0 7 20 53 58 (residual
gloss in %) Gloss 82 85 84 84 84 85 85
[0201] The comparison of the inventive examples 1 to 7 with the
comparative examples VB1 to VB7 shows that the inventive coatings
of examples B1 to B7 exhibit good scratchproofing directly after
final curing, whereas the corresponding coatings of the comparative
examples VB1 to VB7, with a high post-crosslinking index PCI>2,
all exhibit a significantly poorer scratchproofing after the final
20-minute 140.degree. C. cure. More particularly, therefore, the
coatings of comparative examples VB1 to VB4, with a low degree of
silanization, must be given an additional thermal aftertreatment
following the cure, in order to obtain the good scratchproofing
that is required in the field of OEM finishing; to do so, however,
is very costly and inconvenient and therefore impracticable.
Without this aftertreatment, owing to the low scratchproofing, the
coatings can be handled to a limited extent at best, given the risk
of damage. Even the polishability of the resulting coatings, as is
required for line refinishing, is present only conditionally for
the coatings of the comparative examples.
[0202] As the silane content goes up, the inventive coatings, more
particularly those of examples B3 to B7, also exhibit a better
gloss than the coatings of the corresponding comparative
examples.
[0203] Furthermore, as the degree of silanization goes up and the
proportion of difunctional silane (IIa) goes up, in other words
from B1 to B7 and from VB1 to VB7, the effect of the catalyst on
the post-crosslinking index becomes increasingly great. At a low
degree of silanization, with 30 mol % degree of conversion of the
isocyanate groups, the inventive example B1, using the
high-activity catalyst based on the amine-blocked phosphoric acid
partial ester, exhibits a PCI of 1.1, whereas the corresponding
comparative example, using the corresponding amount of the
substantially less effective catalyst based on blocked
p-toluenesulfonic acid, has an excessively high PCI of 2.9. Owing
to this excessively high PCI, the coating of comparative example
VB1 has the aforementioned completely inadequate scratchproofing.
As the amount of silane increases in series via VB2, VB3, up to
VB7, the post-crosslinking index, PCI, of the comparative examples,
and hence the post-crosslinking, increases drastically to reach a
PCI value of 6.6 in the case of a high degree of silanization, with
70 mol % degree of conversion of the isocyanate groups, in
comparative example VB7, in comparison to the only slightly
increased post-crosslinking index of PCI=1.6 in the corresponding
inventive example B7. Post-crosslinking, however, proceeds in a
less controlled manner than curing during the thermal treatment,
and the final hardness of the resulting coatings after
post-crosslinking has taken place is very much more difficult to
set, if indeed it can be set at all. This leads, in general, to
properties of poor reproducibility in the resultant coatings. Above
all, however, the comparative examples, with high to very high
post-crosslinking, as in comparative examples VB6 and VB7, exhibit
a very high risk of the occurrence of stress cracks, so making them
unsuitable for the demanding sector of automotive OEM
finishing.
* * * * *