U.S. patent application number 09/770034 was filed with the patent office on 2001-11-15 for uv-curable coating compositions and their use for coating polycarbonate molded articles.
Invention is credited to Fischer, Wolfgang, Meixner, Jurgen, Pedain, Josef.
Application Number | 20010041785 09/770034 |
Document ID | / |
Family ID | 25933786 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041785 |
Kind Code |
A1 |
Meixner, Jurgen ; et
al. |
November 15, 2001 |
UV-curable coating compositions and their use for coating
polycarbonate molded articles
Abstract
UV-curable coating compositions containing urethane acrylates
prepared from hydroxyalkyl acrylates and low-viscosity
polyisocyanates having isocyanurate groups, low-viscosity acrylic
ester components as reactive diluents, initiators, and optionally
solvents and/or other known additives, and their use for coating
molded articles of thermoplastic polycarbonates.
Inventors: |
Meixner, Jurgen; (Krefeld,
DE) ; Fischer, Wolfgang; (Meerbusch, DE) ;
Pedain, Josef; (Koln, DE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
25933786 |
Appl. No.: |
09/770034 |
Filed: |
January 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09770034 |
Jan 25, 2001 |
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08383328 |
Feb 3, 1995 |
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6232360 |
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Current U.S.
Class: |
528/412 |
Current CPC
Class: |
C08G 18/672 20130101;
C08J 7/046 20200101; C08J 7/0427 20200101; C08J 2369/00 20130101;
C08J 2433/00 20130101; C09D 175/16 20130101; C08G 18/792 20130101;
C09D 4/00 20130101; Y10T 428/31507 20150401; C09D 4/00 20130101;
C08F 222/1065 20200201 |
Class at
Publication: |
528/412 |
International
Class: |
B32B 027/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 1994 |
DE |
P 4404616.2 |
Claims
What is claimed is:
1. An UV-curable coating composition containing A) 20 to 75 wt %,
based on the total weight of components A), B) and C), of a
reaction product, which is essentially free from hydroxyl and
isocyanate groups and is prepared from A1) one or more hydroxyalkyl
acrylates having 2 to 4 carbon atoms in the alkyl group, optionally
mixed with up to 30 hydroxyl equivalent %, based on the total
weight of component A1), of one or more other alcohols, and A2) an
polyisocyanate component comprising an aliphatic polyisocyanate
which contains isocyanurate groups, is based on
1,6-diisocyanatohexane and has an NCO content of 22 to 23.5 wt %
and a viscosity at 23.degree. C. of 800 to 1400 mPa.s, B) 5 to 80
wt %, based on the total weight of components A), B) and C), of a
low-viscosity acrylic ester component containing B1) at least 80 wt
% of one or more bis-acrylates having a molecular weight of less
than 350 and based on an alkane diol which may contain ether oxygen
atoms and B2) up to 20 wt %, based on the weight of component B),
of one or more acrylic esters other than B1), C) 0 to 80 wt %,
based on total weight of components A), B) and C), of a solvent or
solvent mixture and D) 0.1 to 10 wt %, based on the total weight of
components A), B) and C), of one or more photoinitiators.
2. The coating composition of claim 1 wherein component A1)
exclusively contains 2-hydroxyethyl acrylate.
3. The coating composition of claim 1 wherein component A2)
exclusively contains said aliphatic polyisocyanate.
4. The coating composition of claim 2 wherein component A2)
exclusively contains said aliphatic polyisocyanate.
5. A molded article of thermoplastic polycarbonate coated with an
UV-curable coating composition containing A) 20 to 75 wt %, based
on the total weight of components A), B) and C), of a reaction
product, which is essentially free from hydroxyl and isocyanate
groups and is prepared from A1) one or more hydroxyalkyl acrylates
having 2 to 4 carbon atoms in the alkyl group, optionally mixed
with up to 30 hydroxyl equivalent %, based on the total weight of
component A1), of one or more other alcohols, and A2) an
polyisocyanate component comprising an aliphatic polyisocyanate
which contains isocyanurate groups, is based on
1,6-diisocyanatohexane and has an NCO content of 22 to 23.5 wt %
and a viscosity at 23.degree. C. of 800 to 1400 mPa.s, B) 5 to 80
wt %, based on the total weight of components A), B) and C), of a
low-viscosity acrylic ester component containing B1) at least 80 wt
% of one or more bis-acrylates having a molecular weight of less
than 350 and based on an alkane diol which may contain ether oxygen
atoms and B2) up to 20 wt %, based on the weight of component B),
of one or more acrylic esters other than B1), C) 0 to 80 wt %,
based on total weight of components A), B) and C), of a solvent or
solvent mixture and D) 0.1 to 10 wt %, based on the total weight of
components A), B) and C), of one or more photoinitiators.
6. The molded article of claim 5 wherein component A1) exclusively
contains 2-hydroxyethyl acrylate.
7. The molded article of claim 5 wherein component A2) exclusively
contains said aliphatic polyisocyanate.
8. The molded article of claim 6 wherein component A2) exclusively
contains said aliphatic polyisocyanate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the use of special
UV-curable coating compositions based on urethane-modified acrylate
resins for coating molded articles of thermoplastic
polycarbonates.
[0003] 2. Description of the Prior Art
[0004] Polycarbonate molded articles are used in a variety of ways
because of their excellent properties, such as transparency, impact
or shock resistance and tensile strength. However, the properties
of the surface of the material, such as its low abrasion and
scratch resistance and the low resistance to solvents, are
inadequate for many areas of application.
[0005] In the past, very different solutions have been proposed for
the removal of this drawback (cf e.g. PCT Applications WO 80/00968
and 86/04592, U.S. Pat. No. 3,968,305, EP-A 0,274,595 and EP-A
0,274,596). These publications are primarily directed to the
coating of molded articles with UV-curing lacquer systems. The
processes of these prior publications, however, have a number of
serious disadvantages. In particular, the adhesion of the lacquers
or the scratch resistance obtained with the lacquers, as the case
may be, is not completely satisfactory. The coating compositions of
the two last-mentioned prior publications cure only under nitrogen
as a deactivating medium.
[0006] The coating compositions based on polyacrylate resins having
urethane groups according to EP-A 0,020,344 or according to
PCT-Application WO 80/00942 also lead to coatings that still do not
fully satisfy the practical requirements with regard to scratch
resistance and stability to weathering.
[0007] The coating compositions according to DE-OS 3,134,157
contain fairly large amounts of N-vinyl derivatives of linear or
cyclic amides. A disadvantage of these compositions is the need to
carry out the UV irradiation several times in order to obtain good
scratch resistance. Furthermore, a low viscosity can be obtained in
this case only by using large amounts of N-vinyl pyrrolidone.
However, this reduces the resistance to scratching and to solvents
as well as the stability to weathering. In addition, if fairly
large amounts of N-vinyl pyrrolidone are used, the risk exists of
the partial solution, whitening and stress cracking of the
polycarbonate, as long as the coating is not yet cured.
N-vinyl-pyrrolidone is also undesirable with regard to job
hygiene.
[0008] The urethane acrylates according to DE-OS 3,819,627 also are
used in combination with N-vinyl compounds, which leads to the
disadvantageous consequences already mentioned.
[0009] The urethane acrylates according to DE-OS 4,021,109 are used
in combination with tri- to hexafunctional (meth)acrylates as
reactive diluents in order to avoid the said disadvantages of the
aforementioned solvents. However, the stability to weathering of
the resulting lacquer films is insufficient. This becomes
recognizable as a loss of adhesion even after a relatively short
time.
[0010] Finally, DE-OS 3,318,147 is concerned with special urethane
acrylates without any connection to the special problem of coating
polycarbonate molded articles.
[0011] It is an object of the present invention to provide coating
compositions for coating thermoplastic polycarbonates which do not
suffer from the disadvantages of the coating compositions of the
prior art.
[0012] This object may be achieved with the coating compositions of
the present invention which are described in more detail below. The
coating compositions to be used according to the invention differ,
e.g. from the coating compositions according to DE-OS 4,021,109 by
the use of a selected low-viscosity polyisocyanate component having
isocyanurate groups for the manufacture of the urethane acrylates
as well as by the use of mainly linear bis-acrylates as reactive
diluent B).
SUMMARY OF THE INVENTION
[0013] The present invention relates to UV-curable coating
compositions containing
[0014] A) 20 to 75 wt %, based on the total weight of components
A), B) and C), of a reaction product, which is essentially free
from hydroxyl and isocyanate groups and is prepared from
[0015] A1) one or more hydroxyalkyl acrylates having 2 to 4 carbon
atoms in the alkyl group, optionally mixed with up to 30 hydroxyl
equivalent %, based on the total weight of component A1), of other
alcohols, and
[0016] A2) an polyisocyanate component containing an aliphatic
polyisocyanate which contains isocyanurate groups, is based on
1,6-diisocyanatohexane and has an NCO content of 22 to 23.5 wt %
and a viscosity at 23.degree. C. of 800 to 1400 mPa.s,
[0017] B) 5 to 80 wt %, based on the total weight of components A),
B) and C), of a low-viscosity acrylic ester component
containing
[0018] B1) at least 80 wt % of one or more bis-acrylates having a
molecular weight below 350 and based on an alkanediol which may
contain ether oxygen atoms and
[0019] B2) up to 20 wt %, based on the weight of component B), of
one or more acrylic esters other than B1),
[0020] C) 0 to 80 wt %, based on total weight of components A), B)
and C), of a solvent or solvent mixture and
[0021] D) 0.1 to 10 wt %, based on the total weight of components
A), B) and C), of one or more photoinitiators.
[0022] The present invention is also directed to the use of the
coating compositions for coating molded articles of thermoplastic
polycarbonates.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The coating compositions to be used according to the
invention preferably contain 25 to 60 wt % of component A), 10 to
75 wt % of component 8) and 10 to 75 wt % of component C),. wherein
these percentages are based on the total weight of components A),
B) and C). The content of initiator component D) is preferably 1 to
5 wt %, based on the total weight of components A), B) and C).
[0024] Component A) is selected from reaction products of at least
70% by weight of component A1) and optionally up to 30% by weight
of component A2), wherein these percentages are based on the weight
of component A). Component A) is "essentially free from hydroxyl
and isocyanate groups" which means that in the production of the
reaction products, components A1) and A2) are used at an NCO/OH
equivalent ratio of 0.9:1 to 1.1:1, preferably about 1:1.
[0025] Starting compounds A1) are hydroxyalkyl acrylates with 2 to
4 carbon atoms in the hydroxyalkyl group or, less preferably,
mixtures of such hydroxalkyl acrylates with other compounds having
alcoholic hydroxyl groups. Suitable hydroxyalkyl acrylates include
2-hydroxyethyl acrylate, the isomer mixture formed by the addition
of propylene oxide to acrylic acid, or 4-hydroxybutyl acrylate.
2-hydroxyethyl acrylate is preferred.
[0026] Other suitable hydroxyl compounds include mono- to trihydric
aliphatic alcohols having molecular weights of 32 to 400, such as
methanol, ethanol, n-hexanol, isooctanol, isododecanol, benzyl
alcohol, ethylene glycol, diethylene glycol, propylene glycol,
glycerol and alcohols obtained from these alcohols by
alkoxylation.
[0027] Component A2) is selected from polyisocyanates having
isocyanurate groups, which are based on 1,6-diisocyanatohexane
(hexamethylene diisocyanate, HDI) and have an NCO content of 22 to
23.5 wt % and a viscosity at 23.degree. C. of 800 to 1400 mPa.s.
These polyisocyanates are obtained in a known manner by the
trimerizing HDI until the reaction mixture has an NCO content of 42
to 45, preferably 42.5 to 44.5 wt %, subsequently terminating the
reaction and removing unreacted HDI by distillation to a residual
content of less than 0.5 wt %.
[0028] The manufacture of component A) by reacting starting
components A1) and A2) can be carried out by known methods,
optionally by using suitable urethane catalysts. As previously
indicated, the reaction is carried out at an NCO/OH equivalent
ratio of 0.9:1 to 1.1:1, preferably about 1:1.
[0029] Suitable catalysts for this reaction include tin(II)
octanoate, dibutyltin dilaurate and tertiary amines such as
dimethylbenzylamine. The reaction can be carried out in the absence
of the other components or also in the presence of reactive diluent
component B) and/or solvent component C), provided that these
components do not contain H atoms reactive with isocyanate groups,
i.e., isocyanate-reactive groups.
[0030] Urethane acrylate A) can be protected from premature and
undesirable polymerization before the manufacture of the coating
compositions according to the invention by the addition of suitable
inhibitors and antioxidants, such as phenols and/or hydroquinones,
in amounts of 0.001 to 0.3 wt % each, based on the weight of the
urethane acrylate. A very suitable inhibitor is phenothiazine,
which is used in the examples. This inhibitor can be added before,
during and/or following the reaction of components A1) and A2).
[0031] Component B) is selected from bis-acrylates of alkanediols,
optionally containing ether oxygen atoms, provided that the
bis-acrylates have a molecular weight of less than 350. These
bis-acrylates may be mixed with up to 20 wt %, based on the total
weight of component B), of other acrylic esters of tri- to
hexafunctional alcohols. Suitable bis-acrylates include dipropylene
glycol diacrylate, tripropylene glycol diacrylate, 1,4-butanediol
diacrylate and 1,6-hexanediol diacrylate. Suitable acrylic esters
of higher alcohols include trimethylolpropane triacrylate,
pentaerythritol tetraacrylate or sorbitol hexaacrylate. Component
B) preferably exclusively contains 1,6-hexanediol diacrylate.
[0032] Suitable solvents C) include C.sub.5-C.sub.8 aliphatic
compounds or cydo-aliphatic compounds, fluorinated/chlorinated
hydrocarbons, C.sub.1-C.sub.6 aliphatic or cycloaliphatic alcohols
and solvent systems containing
[0033] a) 50 to 95 wt % of C.sub.1-C.sub.6 aliphatic alcohols, such
as methanol, ethanol, propanol, 1-propanol, n-butanol, and
1-butanol, and
[0034] b) 5 to 50 wt % of aliphatic esters, such as ethyl acetate
or butyl acetate.
[0035] Photoinitiators D) are known and include those described in
"Methoden der organischen Chemie" (Houben-Weyl), Volume E 20, pages
80 ff, Georg Thieme Verlag, Stuttgart 1987. Preferred are benzoin
ethers such as benzoin isopropyl ether, benzil ketals such as
benzil dimethylketal, and hydroxyalkylphenones such as
2-hydroxy-2-methyl-1-phen- yl-1-propan-1-one.
[0036] The coating compositions according to the invention can be
mixed with known additives E) such as UV absorbers, fillers,
pigments, dyes, thixotroping agents, smoothing agents, flatting
agents and levelling agents, which can be used in the customary
amounts.
[0037] Components A), B), C), D) and E) can be mixed by customary
methods, e.g., at room temperature or slightly elevated
temperatures, preferably with exclusion of the direct action of
light.
[0038] The polycarbonate articles can be coated with the coating
compositions according to the invention by known methods such as by
spraying and dipping processes.
[0039] The curing of the coatings is initiated by UV-irradiation,
for which purpose commercial UV radiation sources are preferably
used.
[0040] Thermoplastic polycarbonates, their manufacture and their
use for the manufacture of molded articles are described for
example in "Chemistry and Physics of Polycarbonates", Polymer Rev.
Vol. 9, Interscience Publishers.
[0041] Examples of molded articles of thermoplastic polycarbonates
which can be coated according to the invention are all types of
articles of daily use, wherein abrasion and scratch resistance as
well as stability to weathering are required to a particular
degree. Examples include electrical articles, cover plates, sight
screens, safety discs and solid slabs.
[0042] In the following examples all parts and percentages are
percentages by weight, unless otherwise indicated.
EXAMPLES
[0043] The following polyisocyanates are used in Table 1:
[0044] Polyisocyanate 1
[0045] A polyisocyanate prepared by trimerizing hexamethylene
diisocyanate at 60 to 65.degree. C. using trimethylbenzylammonium
hydroxide as the catalyst, terminating the trimerization reaction
with dibutyl phosphate at an NCO content of 43.6 to 44% and
removing excess hexamethylene diisocyanate in the short-path
evaporator to a residual content of<0.5%.
1 NCO content: 23% Viscosity: 1000 mPa .multidot. s (23.degree.
C.)
[0046] Polyisocyanate 2--Polyisocyanate from mixture M1 of DE-OS
4,021,109
[0047] An HDI-based biuret polyisocyanate available form Bayer AG
as Desmodur N 3200.
2 NCO content: 23% Viscosity: 3100 mPa .multidot. s (23.degree.
C.)
[0048] Polyisocyanate 3--Polyisocyanate from mixture M2 of DE-OS
4,021,109
[0049] An HDI-based, isocyanurate group-containing polyisocyanate
available from Bayer AG as Desmodur N 3300.
3 NCO content: 22% Viscosity: 3100 mPa .multidot. s (25.degree.
C.)
[0050] Preparation of urethane acrylates (Component A)
[0051] The polyisocyanates set forth in Table 1 were dissolved in
1,6-hexanediol diacrylate. After the addition of 0.02% of
dibutyltin dilaurate and 0.01% of phenothiazine, based on the total
weight of polyisocyanate and 2-hydroxyethyl acrylate,
2-hydroxyethyl acrylate was added while passing through dry air at
50 to 60.degree. C. The temperature was maintained until the NCO
content had fallen below 0.1%.
4TABLE 1 Solutions of urethane acrylates A) in acrylic ester B)
Solution 2 Solution 3 Starting components (%) Solution 1 (Comp)
(Comp) Polyisocyanate 1 (A2) 46.0 -- -- Polyisocyanate 2 -- 46.0 --
Polyisocyanate 3 -- -- 47.1 2-Hydroxyethyl acrylate (A1) 29.0 29.0
27.9 1,6-Hexanediol diacrylate (B) 25.0 25.0 25.0 Viscosity (mPa
.multidot. s) / 23.degree. C.) 4500 6500 8700
[0052] The solutions of urethane acrylates according to Table 1
were processed to spraying lacquers according to the formulation
given in Table 2 and sprayed in one operation at 20 g/m.sup.2 on
plates (145.times.65.times.3 mm) of bisphenol A homopolycarbonate
(Makrolon AL 2443, Bayer AG). After a flash-off time of 3 minutes
at room temperature the coatings were cured by means of a UV
irradiation plant available from IST (1 mercury high-pressure UV
radiation source, 80 W/cm, 1 m/min belt speed).
[0053] To determine the scratch resistance, the increase in
haziness after spraying the sample with quartz sand was measured
according to DIN 52348.
[0054] The weathering resistance was tested by means of accelerated
weathering tests (DIN 53231, Xenotest 1200).
[0055] To evaluate the adhesion of the coating and its weathering
resistance, a cross-cut test was carried out by scratching a grid
of 6 by 6 lines, each at a distance of 1 mm, in the coating,
followed by pressing on and rapidly peeling off an adhesive
tape.
[0056] The test results of the coatings are set forth in Table
3.
5TABLE 2 Comparative Comparative Coating Composition (%) Example 1
Example 2 Example 3 Solution 1 36.0 Solution 2 36.0 Solution 3 36.0
1,6-Hexanediol diacrylate (B) 34.9 34.9 34.9 Solvent Mixture* (C)
25.0 25.0 25.0 2-Hydroxy-2-methyl-1-phenyl-1- 2.0 2.0 2.0
propane-1-one (photoinitiator) Light protective agent** 1.4 1.4 1.4
Light protective agent*** 0.7 0.7 0.7 *A solvent mixture containing
27.3% ethanol, 36.3% isopropanol, 27.3% ethyl acetate and 9.1%
n-butanol. **Tinuvin 350, available from Ciba-Geigy. ***Tinuvin
292, available from Ciba-Geigy.
[0057]
6 TABLE 3 Comparative Comparative Example Example Example 1 2 3
Scratch Resistance good good good Loss of adhesion after >3000
<1500 <1500 weathering (hours)
[0058] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *