U.S. patent application number 12/206681 was filed with the patent office on 2009-01-08 for aqueous polyurethane compositions for low gloss coatings.
This patent application is currently assigned to DSM IP Assets B.V.., Heerlen, The Netherkands. Invention is credited to Richard G. COOGAN, Nikos J. Georgakakis, Anthony D. Pajerski.
Application Number | 20090012226 12/206681 |
Document ID | / |
Family ID | 9950709 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090012226 |
Kind Code |
A1 |
COOGAN; Richard G. ; et
al. |
January 8, 2009 |
AQUEOUS POLYURETHANE COMPOSITIONS FOR LOW GLOSS COATINGS
Abstract
An aqueous coating composition having a 60.degree. gloss of
.ltoreq.40 upon drying comprising a self-crosslinkable polyurethane
obtained by the reaction of: (A) an isocyanate-terminated
pre-polymer formed from components which comprise (i) 5 to 65 wt %
of at least one organic polyisocyanate; (ii) 0.8 to 4 wt % of at
least one polyol containing ionic or potentially ionic
water-dispersing groups, having two or more isocyanate-reactive
groups and having a molecular weight in the range of from 100 up to
500 g/mol; (iii) 0 to 30 wt % of at least one polyol containing
water-dispersing groups, having two or more isocyanate-reactive
groups and having a molecular weight in the range of from 500 to
6000 g/mol; (iv) 10 to 80 wt % of at least one polyol containing
crosslinkable groups, having two or more isocyanate-reactive groups
and having a molecular weight in the range of from 150 to 6000
g/mol; (v) 10 to 70 wt % of at least one polyol not comprised by
(iii) or (iv) having two or more isocyanate-reactive groups and
having a molecular weight in the range of from 500 to 6000 g/mol;
(vi) 0 to 50 wt % of at least one component not comprised by (i),
(ii), (iii), (iv) or (v); where (i), (ii), (iii), (iv), (v) and
(vi) add up to 100 wt %; and where the NCO:OH ratio is in the range
of from 1.1:1.0 to 10.0:1.0; and (B) at least one active-hydrogen
chain extending compound.
Inventors: |
COOGAN; Richard G.;
(Wilmington, MA) ; Georgakakis; Nikos J.;
(Wilmington, MA) ; Pajerski; Anthony D.;
(Wilmington, MA) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DSM IP Assets B.V.., Heerlen, The
Netherkands
|
Family ID: |
9950709 |
Appl. No.: |
12/206681 |
Filed: |
September 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10540914 |
Oct 25, 2005 |
7439299 |
|
|
PCT/GB2003/005465 |
Dec 16, 2003 |
|
|
|
12206681 |
|
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Current U.S.
Class: |
524/500 ;
524/591 |
Current CPC
Class: |
C08G 18/0823 20130101;
C08G 18/12 20130101; C09D 175/14 20130101; C08G 18/3231 20130101;
C08G 18/61 20130101; C08G 18/12 20130101; C08G 18/6659 20130101;
Y10T 428/31551 20150401 |
Class at
Publication: |
524/500 ;
524/591 |
International
Class: |
C08L 75/04 20060101
C08L075/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2003 |
GB |
0300225.0 |
Claims
1. An aqueous coating composition having a 60.degree. gloss of
.ltoreq.40 upon drying comprising a self-crosslinkable polyurethane
obtained by the reaction of: (A) an isocyanate-terminated
pre-polymer formed from components which comprise (i) 5 to 65 wt %
of at least one organic polyisocyanate; (ii) 0.8 to 4 wt % of at
least one polyol containing ionic or potentially ionic
water-dispersing groups, having two or more isocyanate-reactive
groups and having an average molecular weight in the range of from
100 up to 500 g/mol; (iii) 0 to 30 wt % of at least one polyol
containing water-dispersing groups, having two or more
isocyanate-reactive groups and having an average molecular weight
in the range of from 500 to 6000 g/mol; (iv) 10 to 80 wt % of at
least one polyol containing crosslinkable groups, having two or
more isocyanate-reactive groups and having an average molecular
weight in the range of from 150 to 6000 g/mol; (v) 10 to 70 wt % of
at least one polyol not comprised by (iii) or (iv) having two or
more isocyanate-reactive groups and having an average molecular
weight in the range of from 500 to 6000 g/mol; (vi) 0 to 50 wt % of
at least one component not comprised by (i), (ii), (iii), (iv) or
(v); where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %;
and where the NCO:OH ratio is in the range of from 1.1:1.0 to
10.0:1.0; and (B) at least one active-hydrogen chain extending
compound.
2. An aqueous coating composition according to claim 1 having a
85.degree. gloss of .ltoreq.60.
3. An aqueous coating composition according to any one of the
preceding claims containing <5% by weight of flattening agent by
weight of the self-crosslinkable polyurethane.
4. An aqueous coating composition according to claim 1 additionally
comprising component (ia) 0 to 20 wt % of at least one organic
polyisocyanate with an isocyanate functionality .gtoreq.2.2, where
(i), (ii), (iii), (iv), (v), (vi)+(ia) add up to 100 wt %.
5. An aqueous coating composition according to claim 1 wherein
component (vi) comprises a polysiloxane polyol.
6. An aqueous coating composition according to claim 1 wherein the
self-crosslinkable polyurethane has an average particle size in the
range of from 500 nm to 5000 nm
7. An aqueous coating composition according to claim 1 additionally
comprising a reactive diluent.
8. An aqueous coating composition comprising: I) 40 to 80 wt % of
water, II) 0 to 30 wt % of co-solvent; III) 20 to 60 wt % of the
self-crosslinkable polyurethane according to claim 1; IV) 0 to 10
wt % of hydrophobe modified ethylene oxide urethane; V) 0 to 16 wt
% of surfactants; VI) 0 to 10 wt % of thickeners; and VII) 0 to 3
wt % of alkyd drying agent, accelerator and/or activator; where I),
II), IiI), IV), V), VI) and VII) add up to 100%.
9. A coating obtained from an aqueous coating composition according
to claim 1.
10. A coated substrate having a coating comprising an aqueous
coating composition according to claim 1.
11. A method of coating a substrate using an aqueous coating
composition according to claim 1, comprising (a) application of the
aqueous coating composition to a substrate and (b) removal of the
water and any co-solvent.
12. A process for preparing an aqueous coating composition
according to claim 1 comprising the following steps: a) reaction of
components (i) to (vi) to form an isocyanate-terminated prepolymer
(A); b) forming an aqueous dispersion of the isocyanate-terminated
prepolymer (A) in water; c) optionally neutralising the
isocyanate-terminated prepolymer (A) after and/or during step a)
and/or step b); d) chain extension of the isocyanate-terminated
prepolymer (A) by reaction with the active-hydrogen chain extending
compound (B); and e) optionally adding crosslinker.
Description
[0001] This application is a continuation of commonly owned
copending U.S. application Ser. No. 10/540,914, filed on Oct. 25,
2005, which is the national phase application under 35 USC .sctn.
371 of PCT/GB2003/005465, filed Dec. 16, 2003 and claims the
benefit of priority from GB 0300225.0, filed Jan. 4, 2003, the
entire content thereof being hereby expressly incorporated by
reference in this application.
[0002] The present invention relates to an aqueous coating
composition having a 60.degree. gloss of .ltoreq.40 upon drying, a
process for preparing such a composition and a coating obtained
from such a composition.
[0003] Coating compositions have long been used to produce coatings
having desired coating characteristics. For example coating
compositions are used to protect surfaces from the environment, to
conceal surface irregularities, to provide a surface which is more
receptive further treatment, or to enhance the surface appearance,
such as providing high gloss or low gloss.
[0004] Gloss is associated with the capacity of a surface to
reflect more light in some directions than in others. High gloss
surfaces reflect a high proportion of light directed at them and
low gloss surfaces reflect a low proportion of light directed at
them. The directions associated with mirror (or specular)
reflection normally have the highest reflectances. Measurements by
such a test method (as described for example in ASTM D 523-89
correlate with the visual observations of surface shininess made at
roughly the corresponding angles. Low gloss coatings that produce
less image impairment are often more pleasing aesthetically.
[0005] Traditionally low gloss coating compositions are obtained by
the addition of flattening agents such as silicone dioxide.
Flattening agents are well known in the art and traditionally
comprise materials ground into minute particles of irregular shape
which are used in compositions such as paints and varnishes to
disperse incident light rays so that a low gloss effect is
achieved. Standard flattening agents include but are not limited to
silica (for example amorphous silicon dioxide), diatomaceous earth,
heavy metal soaps, talcum and chalk. To obtain for example low
gloss in clear coats, typically more than 6 wt % of flattening
agent based on the weight of the coating composition has to be
added. Such compositions are disclosed in for example U.S. Pat. No.
6,284,836 B1 and EP 1186641 A1.
[0006] The disadvantages resulting from the addition of flattening
agents to reduce gloss include coagulation of the composition
resulting in a seedy appearance; increased brittleness of the
resultant coating; settling out of the flattening agents often
resulting in inconsistent mixing before application resulting in
variation in gloss throughout the coating; and a decrease in
burnish resistance as well as reducing the general resistance and
performance properties of the coating. Burnish is the change in
appearance of a coating as a result of rubbing the coating with a
different material. The change in appearance may be measured as a
change in the gloss level of a coating.
[0007] Low gloss coating compositions have been described in for
example U.S. Pat. No. 6,331,582 B1 which discloses a thermally
activated coating composition comprising an acrylic or polyester
solvent based binder resin, colorant and a polyvinyl acetal matting
agent. EP 0841992 A2 discloses a low gloss coating composition
comprising acrylic polymer particles containing at least one void
and pigments. U.S. Pat. No. 6,410,147 discloses a low gloss solvent
based crosslinkable coating composition comprising a combination of
a polar polymer, a non-polar polymer and a crosslinking agent. U.S.
Pat. No. 5,744,522 discloses a low gloss coating powder composition
comprising an acrylic copolymer, an aromatic polyester and a
specific isocyanurate curing agent.
[0008] These all describe ways of avoiding the use of silicone
dioxide flattening agents, however they appear to be providing
complex and costly solutions, including a preference for the use of
solvents and powders.
[0009] The aqueous coating composition of the present invention
provides a low gloss coating preferably without the use of
flattening agents. Furthermore the coating obtained from the
aqueous coating composition of the present invention has a warmer
look when compared with a conventional urethane coating using
flattening agents. The look is very subjective and there do not
appear to be any specific instrumental measurements available,
however warmth may be measurable by colour tones, a cooler look may
appear bluer while a warmer look may appear more white.
[0010] According to the present invention there is provided an
aqueous coating composition having a 60.degree. gloss of .ltoreq.40
upon drying comprising a self-crosslinkable polyurethane obtained
by the reaction of:
(A) an isocyanate-terminated pre-polymer formed from components
which comprise [0011] (i) 5 to 65 wt % of at least one organic
polyisocyanate; [0012] (ii) 0.1 to 6 wt % of at least one polyol
containing ionic or potentially ionic water-dispersing groups,
having two or more isocyanate-reactive groups and having a
molecular weight in the range of from 100 up to 500 g/mol; [0013]
(iii) 0 to 30 wt % of at least one polyol containing
water-dispersing groups, having two or more isocyanate-reactive
groups and having a molecular weight in the range of from 500 to
6000 g/mol; [0014] (iv) 10 to 80 wt % of at least one polyol
containing crosslinkable groups, having two or more
isocyanate-reactive groups and having a molecular weight in the
range of from 150 to 6000 g/mol; [0015] (v) 10 to 70 wt % of at
least one polyol not comprised by (iii) or (iv) having two or more
isocyanate-reactive groups and having a molecular weight in the
range of from 500 to 6000 g/mol; [0016] (vi) 0 to 50 wt % of at
least one component not comprised by (i), (ii), (iii), (iv) or (v);
where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %; and
[0017] where the NCO:OH ratio is in the range of from 1.2:1.0 to
10.0:1.0; and (B) at least one active-hydrogen chain extending
compound.
[0018] Gloss measurements are made with 60.degree., 20.degree. or
85.degree. geometry of angles and apertures. The 60.degree.
geometry is used for comparing most samples and for determining
when the 20.degree. geometry may be more applicable. The 20.degree.
geometry is advantageous for comparing samples having a 60.degree.
gloss value higher than 70. The 85.degree. geometry is advantageous
for comparing samples having 60.degree. gloss values lower than
10.
[0019] Preferably the 60.degree. gloss of the aqueous coating
composition of the invention upon drying is .ltoreq.30, more
preferably .ltoreq.20, most preferably .ltoreq.10, especially
.ltoreq.5 and most especially .ltoreq.3.
[0020] Preferably the 85.degree. gloss of the aqueous coating
composition of the invention upon drying is .ltoreq.60, more
preferably .ltoreq.40, more preferably .ltoreq.30, especially
.ltoreq.20 and most especially .ltoreq.10.
[0021] The self-crosslinkable polyurethane is crosslinkable without
the requirement for added compounds which react with groups on the
polyurethane to achieve crosslinking, although these can still be
employed if desired. Optionally the aqueous coating composition of
the present invention comprises at least one post-added crosslinker
in the range from 0 to 35 wt % based on solids of the
self-crosslinkable polyurethane.
[0022] The self-crosslinkable polyurethane may crosslink at ambient
temperature by a number of mechanisms including but not limited to
autoxidation, Schiff base crosslinking and silane condensation. By
crosslinking by autoxidation is meant that crosslinking results
from an oxidation occurring in the presence of air and usually
involves a free radical mechanism and is preferably metal-catalysed
resulting in covalent crosslinks.
[0023] Suitably autoxidation is provided for example by fatty acid
groups containing unsaturated bonds (by which is meant the residue
of such fatty acids which have become incorporated into the
polyurethane by reaction at their carboxylic acid groups) or by
(meth)allyl functional residues, .beta.-keto ester groups or
.beta.-keto amine groups. Preferably autoxidation is provided at
least by fatty acid groups containing unsaturated bonds.
[0024] By Schiff base crosslinking is meant that crosslinking takes
place by the reaction of a carbonyl functional groups, where by a
carbonyl functional group herein is meant an aide or keto group and
includes an enolic carbonyl group such as is found in an
acetoacetyl group with a carbonyl-reactive amine and/or hydrazine
(or blocked amine and/or blocked hydrazine) functional group.
[0025] By silane condensation is meant the reaction of alkoxy
silane or --SiOH groups in the presence of water, to give siloxane
bonds by the elimination of water and/or alkanols (for example
methanol) during the drying of the aqueous coating composition.
[0026] Other crosslinking mechanisms known in the art include those
provided by the reaction of epoxy groups with amino, carboxylic
acid or metcapto groups, the reaction of mercapto groups with
ethylenically unsaturated groups such as fumarate and acyloyl
groups, the reaction of masked epoxy groups with amino or mercapto
groups, the reaction of isothiocyanates with amines, alcohols or
hydrazines, the reaction of amines (for example ethylenediamine or
multifunctional amine terminated polyalkylene oxides) with
.beta.-diketo (for example acetoacetoxy or acetoamide) groups to
form enamines. The use of blocked crosslinking groups, such as
blocked isocyanate groups, may be beneficial.
[0027] Preferably the self-crosslinking is by autoxidation of
unsaturated functional groups, such as conjugated unsaturated
functional groups, and Schiff base crosslinking optionally in
combination with other crosslinking mechanisms as discussed
herein.
[0028] Methods for preparing polyurethanes are known in the art and
are described in for example the Polyurethane Handbook 2.sup.nd
Edition, a Carl Hanser publication, 1994, by G. Oertel; and these
methods are included herein by reference. The self-crosslinkable
polyurethane may be prepared in a conventional manner by reacting
at least one organic polyisocyanate with at least one
isocyanate-reactive compound by methods well known in the prior
art. Isocyanate-reactive groups include --OH, --SH, --NH--, and
--NH.sub.2. Usually an isocyanate-terminated polyurethane
prepolymer is first formed which is then chain extended with an
active hydrogen containing compound.
[0029] Component (i) comprises any suitable organic polyisocyanates
including aliphatic, cycloaliphatic, araliphatic and/or aromatic
polyisocyanates. Examples of suitable polyisocyanates include
ethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI),
isophorone diisocyanate (IPDI), cyclohexane-1, 4-diisocyanate,
4,4'-dicyclohexylmethane diisocyanate (4,4'-H12 MDI), p-xylylene
diisocyanate, p-tetramethylxylene diisocyanate (p-TMXDI) (and its
meta isomer m-TMXDI), 1,4-phenylene diisocyanate, hydrogenated
2,4-toluene disocyanate, hydrogenated 2,6-toluene diisocyanate,
4,4'-diphenylmethane diisocyanate (4,4'-MDI), polymethylene
polyphenyl polyisocyanates, 2,4'-diphenylmethane diisocyanate,
3(4)-isocyanatomethyl-1-methyl cyclohexyl isocyanate (IMCI) and
1,5-naphthylene diisocyanate. Preferred organic polyisocyanates are
IPDI and/or H.sub.12MDI which provide improved low yellowing and
ease of processing of the self-crosslinkable polyurethane. Mixtures
of polyisocyanates can be used and also polyisocyanates which have
been modified by the introduction of urethane, allophanate, urea,
biuret, carbodiimide, uretonimine, urethdione or isocyanurate
residues.
[0030] Preferably component (i) comprises 20 to 60 wt %, more
preferably 30 to 50 wt % of the isocyanate-terminated
prepolymer.
[0031] Preferably component (i) comprises organic polyisocyanates
with a functionality of 2 (i.e. diisocyanates), however the
polyurethane prepolymer may also be formed from additional
component (ia) comprising 0 to 20 wt % of at least one organic
polyisocyanate with an isocyanate functionality .gtoreq.2.2, more
preferably in the range of from 2.5 to 4.0.
[0032] Preferably component (ia) comprises 3 to 15 wt %, more
preferably 4 to 10 wt % of the isocyanate-terminated
prepolymer.
[0033] The effect of component (ia) is to allow a degree of
pre-crosslinking in the prepolymer, however too much
pre-crosslinking may result in an unacceptable increase in
viscosity.
[0034] Component (ii) comprises any suitable polyol, preferably
diol, containing ionic or potentially ionic water-dispersing
groups.
[0035] Preferred ionic water-dispersing groups are anionic
water-dispersing groups. Preferred anionic water-dispersing groups
are carboxylic, phosphoric and/or sulphonic acid groups. Examples
of such compounds include carboxyl containing diols and triols, for
example dihydroxy alkanoic acids such as 2,2-dimethylol propionic
acid (DMPA) or 2,2-dimethylolbutanoic acid (DMBA). The anionic
water-dispersing groups are preferably fully or partially in the
form of a salt. Conversion to the salt form is optionally effected
by neutralisation of the self-crosslinkable polyurethane with a
base, preferably during the preparation of the self-crosslinkable
polyurethane and/or during the preparation of the aqueous coating
composition of the present invention.
[0036] If the anionic water-dispersing groups are neutralised, the
base used to neutralise the groups is preferably ammonia, an amine
or an inorganic base. Suitable amines include tertiary amines, for
example triethylamine or N,N-dimethylethanolamine. Suitable
inorganic bases include alkali hydroxides and carbonates, for
example lithium hydroxide, sodium hydroxide, or potassium
hydroxide. A quaternary ammonium hydroxide, for example
N.sup.+(CH.sub.3).sub.4(OH), can also be used. Generally a base is
used which gives counter ions that may be desired for the
composition. For example, preferred counter ions include Li.sup.+,
Na.sup.+, K.sup.+, NH.sub.4.sup.+ and substituted ammonium
salts.
Cationic water dispersible groups can also be used, but are less
preferred. Examples include pyridine groups, imidazole groups
and/or quaternary ammonium groups which may be neutralised or
permanently ionised (for example with dimethylsulphate).
[0037] Preferably component (ii) comprises 0.8 to 4.0 wt %, more
preferably 1.9 to 3.0 wt % of the isocyanate-terminated
prepolymer.
[0038] Component (iii) may contain ionic water-dispersing groups as
discussed above and/or may also contain non-ionic water-dispersing
groups. Preferably component (iii) contains anionic and/or
non-ionic water-dispersing groups.
[0039] Preferred non-ionic water-dispersing groups are polyalkylene
oxide groups, more preferably polyethylene oxide groups. A small
segment of the polyethylene oxide group can be replaced by
propylene segments and/or butylene oxide segments, however the
polyethylene oxide group should still contain ethylene oxide as a
major component. When the water-dispersible group is polyethylene
oxide, preferably the polyethylene oxide group has a molecular
weight from 175 to 5000 g/mol, more preferably from 350 to 2200
g/mol and most preferably from 660 to 2200 g/mol.
[0040] Examples of such compounds containing non-ionic
water-dispersing groups include methoxy polyethylene glycol (MPEG)
with molecular weights of for example 550, 750, 1000 and 2000
g/mol. Examples of such compounds containing ionic water-dispersing
groups include polyether, polyester and polycarbonate polyols
containing carboxylic acid groups.
[0041] Preferably component (iii) comprises 5 to 25 wt % and more
preferably 8 to 20 wt % of the isocyanate-terminated prepolymer.
This is especially preferred when levels of component (ii) are kept
to the minimum.
[0042] The self-crosslinkable polyurethane preferably contains a
sufficient concentration of ionic and/or non-ionic water-dispersing
groups via components (ii) and (iii) capable of rendering the
polyurethane self-water-dispersible (i.e. dispersible in water
without the requirement to use added dispersing agents) but the
concentration of such groups is preferably not so great that the
polyurethane has an unacceptably high water solubility in order to
not compromise the water sensitivity of the final coating.
[0043] Moreover, the strength of the ionic and/or non-ionic
water-dispersing groups or their efficiency as a dispersing and/or
stabilising group may also influence the optimal amounts
required.
[0044] The crosslinkable groups contained in component (iv) may be
any as discussed above which allow self-crosslinking, including but
not limited to autoxidisable groups; carbonyl functional groups;
carbonyl reactive amine and/or hydrazine groups; alkoxysilane or
SiOH groups; epoxy groups; mercapto groups; isothiocyanate groups;
hydroxy groups, blocked isocyanate groups and ethylenically
unsaturated groups. Preferably component (iv) has
self-crosslinkable groups selected from ethylenically unsaturated
groups, carbonyl functional groups, alkoxysilane groups, epoxy
groups, amino groups, mercapto groups, isothiocyanate groups and
hydrazine groups. Preferably the molecular weight of component (iv)
is in the range of from 150 to 4000 g/mol and more preferably in
the range of from 200 to 2000 g/mol.
[0045] Preferably component (iv) comprises 15 to 60 wt % and more
preferably 20 to 50 wt % of the isocyanate-terminated
prepolymer.
[0046] Component (v) comprises polyols containing neither ionic or
non-ionic water-dispersing groups, or crosslinker groups.
[0047] The polyols particularly include diols and triols and
mixtures thereof but higher functionality polyols may be used, for
example as minor components in admixture with diols. The polyols
may be members of any of the chemical classes of polyols used or
proposed to be used in polyurethane formulations. In particular the
polyols may be polyesters, polyesteramides, polyethers,
polythioethers, polycarbonates, polyacetals, polyolefins or
polysiloxanes. Preferred molecular weights are from 600 to 4000,
more preferably from 700 to 3000 g/mol. Preferably component (v)
comprises 15 to 60 wt %, more preferably 15 to 45 wt % of the
isocyanate-terminated prepolymer.
[0048] For component (vi) low molecular weight organic compounds
containing at least one (preferably at least two)
isocyanate-reactive groups and having a weight average molecular
weight up to 500, preferably in the range of 40 to 250 can also be
used. Preferably component (vi) comprises a diol having a molecular
weight of 40 to 500 g/mol. Examples include ethyleneglycol,
di-ethylene glycol, tri-ethylene glycol, tetra-ethylene glycol and
similarly poly-glycols made from propylene glycol up to a molecular
weight of 500, neopentyl glycol; 1-propanol, bis(hydroxyethyl)
teraphthalate, furan dimethanol, glycerol, 1,4-cyclohexyldimethanol
and the reaction products of these examples with propylene and/or
ethylene glycol up to a molecular weight of 500 g/mol. Preferably
component (vi) comprises a polysiloxane polyol.
[0049] Preferably component (vi) comprises 0 to 40 wt %, more
preferably 0 to 30 wt % of the isocyanate-terminated
prepolymer.
[0050] The acid value of the self-crosslinkable polyurethane may
vary considerably depending on the hydrophobicity of the
polyurethane and the degree, if any, of pre-crosslinking.
[0051] The self-crosslinkable polyurethane preferably has an acid
value in the range of from 0.3 to 25.1 mg KOH/g, more preferably in
the range of from 0.4 to 16.7 mg KOH/g and most preferably in the
range of from 0.5 to 11.7 mg KOH/g.
[0052] The Tg of a polymer herein stands for the glass transition
temperature and is well known to be the temperature at which a
polymer changes from a glassy, brittle state to a rubbery state. Tg
values of polymers may be determined experimentally using
techniques such as Differential Scanning Calorimetry (DSC) or
calculated theoretically using the well-known Fox equation where
the Tg (in Kelvin) of a copolymer having "n" copolymerised
comonomers is given by the weight fractions "W" and the Tg values
of the respective homopolymers (in Kelvin) of each comonomer type
according to the equation "1/Tg=W.sub.1/Tg.sub.1+W.sub.2/Tg.sub.2+
. . . W.sub.n/Tg.sub.n". The calculated Tg in Kelvin may be readily
converted to .degree. C.
[0053] The self-crosslinkable polyurethane has at least one glass
transition temperature (Tg) as measured by modulated differential
scanning calorimetry (DSC), preferably being in, the range of from
-100 to 250.degree. C., more preferably -80 to 150.degree. C., most
preferably -70 to 130.degree. C. and especially -70 to 30.degree.
C.
[0054] The self-crosslinkable polyurethane preferably has a
particle size in the range of from 500 to 5000 nm, more preferably
in the range of from 900 to 3500 nm and most preferably in the
range of 1000 to 2500 nm.
[0055] Not wishing to be bound to this theory, however it appears
that the larger the particle size, the greater the gloss reduction
when compared with a conventional particle size of around 40 to 150
nm. However an increase in particle size may also result in a
decrease in stability of the polyurethane when in a dispersed
state.
[0056] The self-crosslinkable polyurethane preferably has a
molecular weight in the range of from 15,000 to 50,000, more
preferably in the range of from 15,000 to 40,000 and especially in
the range from 18,000 to 30,000 g/mol. The molecular weight may be
measured by Gel Permeation Chromatography (GPC) using
tetrahydrofuran as a solvent and polystyrene standards. It appears
that the use of very low molecular weight polyurethanes may affect
tack and hence film formation resulting in an increase in
gloss.
[0057] The isocyanate-terminated polyurethane prepolymer is
conventionally formed by reacting a stoichiometric excess of the
organic polyisocyanate with the isocyanate-reactive compounds under
substantially anhydrous conditions at a temperature between about
30.degree. C. and about 130.degree. C. until reaction between the
isocyanate groups and the isocyanate-reactive groups is
substantially complete; the reactants for the prepolymer are
generally used in proportions corresponding to a ratio of
isocyanate groups to isocyanate-reactive groups of from about 1.2:1
to about 6:1, preferably from about 1.4:1 to 3:1.
[0058] If desired, catalysts such as dibutyltin dilaurate and
stannous octoate, zirconium or titanium based catalysts may be used
to assist the isocyanate-terminated prepolymer and/or polyurethane
formation. An organic solvent may optionally be added before or
after prepolymer formation or final polyurethane formation to
control the viscosity. Examples of solvents include water-miscible
solvents such as N-methylpyrrolidinone, dimethyl acetamide, glycol
ethers such as butyldiglycol, methyl ethyl ketone and alkyl ethers
of glycol acetates or mixtures thereof. The solvent may also
include reactive diluents such as olefinically unsaturated
monomers. Optionally no organic solvents are added.
[0059] The aqueous polyurethane composition may be prepared by
dispersing isocyanate-terminated polyurethane prepolymer
(optionally carried in an organic solvent medium) in an aqueous
medium and chain extending the prepolymer with at least one active
hydrogen-containing chain extender in the aqueous phase.
[0060] Active hydrogen-containing chain extenders which may be
reacted with the isocyanate-terminated polyurethane prepolymer
include amino-alcohols, primary or secondary diamines or
polyamines, hydrazine, and substituted hydrazines.
[0061] Examples of such chain extenders useful herein include
alkylene diamines such as ethylene diamine and cyclic amines such
as isophorone diamine. Also materials such as hydrazine, azines
such as acetone azine, substituted hydrazines such as, for example,
dimethyl hydrazine, 1,6-hexamethylene-bis-hydrazine,
carbodihydrazine, hydrazides of dicarboxylic acids and sulphonic
acids such as adipic acid mono- or dihydrazide, oxalic acid
dihydrazide, isophthalic acid dihydrazide, hydrazides made by
reacting lactones with hydrazide such as gammahydroxylbutyric
hydrazide, bis-semi-carbazide, and bis-hydrazide carbonic esters of
glycols may be useful. Water itself may be effective as an indirect
chain extender. Preferably the active-hydrogen chain extending
compound is selected from the group comprising water,
amino-alcohols, primary or secondary diamines or polyamines,
hydrazine, substituted hydrazines and substituted hydrazides.
[0062] Where the chain extender is other than water, for example, a
polyamine or hydrazine, it may be added to the aqueous dispersion
of the isocyanate-terminated polyurethane prepolymer or,
alternatively, it may already be present in the aqueous medium when
the isocyanate-terminated polyurethane prepolymer is dispersed
therein. The isocyanate-terminated polyurethane prepolymer may also
be chain extended to form the polyurethane while dissolved in
organic solvent (usually acetone) followed by the addition of water
to the solution until water becomes the continuous phase and the
subsequent removal of the solvent by distillation to form an
aqueous dispersion.
[0063] The chain extension may be conducted at convenient
temperatures from about 5.degree. C. to 95.degree. C. or, more
preferably, from about 10.degree. C. to 60.degree. C.
[0064] The total amount of active-hydrogen chain extending compound
employed (apart from water) should be such that the ratio of active
hydrogens in the chain extender to isocyanate groups in the
polyurethane prepolymer preferably is in the range from 0.1:1 to
2.0:1 more preferably 0.80:1 to 1.7:1.
[0065] In another embodiment of the present invention there is
provided a process for preparing the aqueous coating composition
comprising the following steps: [0066] a) reaction of components
(i) to (vi) to form an isocyanate-terminated prepolymer (A); [0067]
b) forming an aqueous dispersion of the isocyanate-terminated
prepolymer (A) in water; [0068] c) optionally neutralising the
isocyanate-terminated prepolymer (A) after and/or during step a)
and/or step b). [0069] d) chain extension of the
isocyanate-terminated prepolymer (A) by reaction with the
active-hydrogen chain extending compound (B); and [0070] e)
optionally adding crosslinker.
[0071] The process may additionally comprise step f) the addition
and subsequent polymerisation of a reactive diluent.
[0072] Steps b), c), d), e) and f) may be in any order.
[0073] Surfactants and/or high shear can be utilised in any order
to any assist in the dispersion of isocyanate-terminated prepolymer
or the polyurethane in water (even if it is self-dispersible).
Suitable surfactants include but are not limited to conventional
anionic, cationic and/or nonionic surfactants such as Na, K and
NH.sub.4 salts of dialkylsulphosuccinates, Na, K and NH.sub.4 salts
of sulphated oils, Na, K and NH.sub.4 salts of alkyl sulphonic
acids, Na, K and NH.sub.4, alkyl sulphates, alkali metal salts of
sulphonic acids; fatty alcohols, ethoxylated fatty acids and/or
fatty amines, and Na, K and NH.sub.4 salts of fatty acids such as
Na stearate and Na oleate. Other anionic surfactants include alkyl
or (alk)aryl groups linked to sulphonic acid groups, sulphuric acid
half ester groups (linked in turn to polyglycol ether groups),
phosphonic acid groups, phosphoric acid analogues and phosphates or
carboxylic acid groups. Cationic surfactants include alkyl or
(alk)aryl groups linked to quaternary ammonium salt groups.
Non-ionic surfactants include polyglycol ether compounds and
polyethylene oxide compounds. The amount of surfactant used is
preferably 0 to 15% by weight, more preferably 0 to 8% by weight,
still more preferably 0 to 5% by weight, especially 0.1 to 3% by
weight, and most especially 0.3 to 2% by weight based on the weight
of the self-crosslinkable polyurethane.
[0074] In a further embodiment of the present invention if a
reactive diluent is employed, in particular where the reactive
diluent comprises olefinically unsaturated monomers (also known as
vinyl monomers) these may be polymerised in-situ to prepare a vinyl
polymer. Suitable vinyl monomers include but are not limited to
(meth)acrylic acid, fumaric acid, itaconic acid, 1,3-butadiene,
isoprene, styrene, .alpha.-methyl styrene, divinyl benzene, indene,
acrylonitrile, methacrylonitrile, vinyl halides such as vinyl
chloride, vinyl esters such as vinyl acetate, vinylpropionate,
vinyl laurate, vinyl esters of versatic acid, heterocyclic vinyl
compounds, alkyl esters of mono-olefinically unsaturated
dicarboxylic acids (such as di-n-butyl maleate and di-n-butyl
fumarate) and, in particular, esters of (meth)acrylic acid of
formula CH.sub.2.dbd.CR.sup.1--COOR.sup.2 wherein R.sup.1 is H or
methyl and R.sup.2 is optionally substituted alkyl or cycloalkyl of
1 to 20 carbon atoms (more preferably 1 to 8 carbon atoms) examples
of which are methyl (meth)acrylate, ethyl (meth)acrylate,
trifluorethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate,
and hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl
(meth)acrylate, 2-hydroxypropyl (meth)acrylate and 4-hydroxybutyl
(meth)acrylate.
[0075] Preferably the reactive diluent comprises vinyl monomers
selected from at least one member of the group containing free
vinyl acids, esters of (meth)acrylic acid, hydroxy alkyl
(meth)acrylates and styrene.
[0076] All of the vinyl monomers may be present at the commencement
of the preparation of the isocyanate-terminated prepolymer or some
or all of the vinyl monomers may be added during the course of the
preparation.
[0077] Preferably the vinyl monomers are not polymerised until
after chain extension has been carried out.
[0078] The polymerisation of any vinyl monomer will require the use
of a free-radical-yielding initiator to initiate the vinyl
polymerisation. Suitable free-radical-yielding initiators include
inorganic peroxides such as ammonium persulphate hydrogen peroxide,
organic peroxides, such as benzoyl peroxide, alkyl hydroperoxides
such as t-butyl hydroperoxide and cumene hydroperoxide; dialkyl
peroxides such as di-t-butyl peroxide; peroxy esters such as
t-butyl perbenzoate and the like; mixtures may also be used. The
peroxy compounds are in some cases advantageously used in
combination with suitable reducing agents (redox systems) such as
iso-ascorbic acid. Azo compounds such as azobisisobutyronitrile may
also be used. Metal compounds such as Fe.EDTA (EDTA is ethylene
diamine tetracetic acid) may also be usefully employed as part of
the redox initiator system. The amount of initiator or initiator
system to use is conventional, e.g. within the range of 0.05 to 6
wt % based on the weight of vinyl monomer used.
[0079] Such an aqueous vinyl polymerisation normally would need to
be performed in the presence of an external stabilising and/or
dispersing material such as the surfactants discussed above and the
amount used is usually 0.1 to 5% by weight based on the total vinyl
monomer used.
[0080] The theoretical glass transition temperature, calculated
using the Fox equation, of the resultant vinyl polymer may vary
within a wide range, a preferred range being from -50 to
120.degree. C., preferably from -20 to 80.degree. C.
[0081] After polymerisation, the free vinyl monomer content in the
aqueous composition of the invention is preferably less than 500
ppm, more preferably less than 300 ppm and more preferably less
than 100 ppm.
[0082] If a reactive diluent comprising vinyl monomers is used, the
ratio of resultant vinyl polymer to self-crosslinkable polyurethane
is preferably in a weight ratio in the range of from 10:90 to
90:10, more preferably 20:80 to 60:40 and most preferably 30:70 to
50:50.
[0083] The aqueous composition of the present invention typically
has a solids content of from about 20 to 60% by weight, more
preferably from 25 to 55% by weight.
[0084] The aqueous composition of the present invention may contain
other conventional ingredients including coalescing organic
solvents, pigments, dyes, emulsifiers, surfactants, thickeners,
heat stabilisers, levelling agents, anti-cratering agents, fillers,
sedimentation inhibitors, UV absorbers, antioxidants and the like
introduced at any stage of the preparation process or subsequently.
It is possible for example to include an amount of antimony oxide
in the dispersions to enhance the fire retardant properties.
[0085] Typically a flattening agent when added at 5% by weight of
the self-crosslinkable polyurethane reduces the gloss at 60.degree.
by .gtoreq.30%. Preferably the aqueous composition of the invention
contains <5% by weight of flattening agent, more preferably
.ltoreq.4.5%, most preferably .ltoreq.4%, especially .ltoreq.2%,
more especially .ltoreq.1% and most especially contains in the
range of from 0 to 0.5 wt % of flattening agent by weight of the
self-crosslinkable polyurethane.
[0086] In particular the aqueous composition of the invention if
comprising autoxidisable groups on the self-crosslinkable
polyurethane advantageously includes at least a drier salt. Drier
salts are well known to the art for further enhancing autoxidation
in unsaturated fatty acid residue containing film-forming
substances. Generally speaking, drier salts are metallic soaps,
that is salts of metals and long chain carboxylic acids or metal
naphthanates. It is thought that the metallic ions effect the
curing action in the film coating and the fatty acid components
confer compatibility in the coating medium. The most important
drier metals are cobalt, manganese, zirconium, lead and calcium.
The level of drier salt in the composition is typically that to
provide an amount of metal within the range of from 0.01 to 0.5% by
weight based on the weight of the self-crosslinkable
polyurethane.
[0087] Drier salts are conventionally supplied as solutions in
common organic solvents. They may, however, be used quite
satisfactorily in aqueous coating composition since they can
normally be dispersed in such systems fairly easily. The drier salt
may be incorporated into the composition at any convenient
stage.
[0088] Other useful ingredients in the aqueous composition include
rheology modifiers and urethane associative thickeners such as
hydrophobe-modified ethylene oxide urethane (HEUR) which provides
stabilisation and modifies the rheology by acting as a thickener. A
potential disadvantage of such materials (HEUR) however is that
they may contribute to water-sensitivity in the final coating.
[0089] Thus in a further embodiment of the present invention there
is provided an aqueous coating composition comprising: [0090] I) 40
to 80 wt %, preferably 50 to 70 wt % of water; [0091] II) 0 to 30
wt %, preferably 0 to 20 wt % of co-solvent; [0092] III) 20 to 60
wt %, preferably 30 to 50 wt % of the self-crosslinkable
polyurethane defined above; [0093] IV) 0 to 10 wt %, preferably 0
to 7 wt % of hydrophobe modified ethylene oxide urethane; [0094] V)
0 to 16 wt %, preferably 0 to 10 wt %, more preferably 0 to 5 wt %
of surfactants; [0095] VI) 0 to 10 wt %, preferably 0.5 to 4 wt %
of thickeners; and [0096] VII) 0 to 3 wt %, preferably 0 to 1 wt %
of alkyd drying agent, accelerator and/or activator; where I), II),
III), IV), V), VI) and VII) add up to 100%.
[0097] The aqueous coating composition of the present invention is
particularly useful as a coating composition or for providing the
principle component of coating compositions (e.g. protective or
decorative coating compositions) for which purpose they may be
further diluted with water and/or organic solvents, or they may be
supplied in more concentrated form by evaporation of water and/or
organic components of the liquid medium. As coating compositions,
they may be applied to a variety of substrates including wood,
board, metal, stone, concrete, glass, cloth, leather, paper,
plastics, foam and the like, by conventional methods including
brushing, dipping, flow coating, spraying, and the like. They are,
however, particularly useful for providing coatings on wood and
board substrates. The aqueous liquid medium usually comprising
water and any co-solvent is removed by natural or accelerated (by
heat) drying to form a coating.
[0098] There is further provided according to the present invention
a coating obtained from an aqueous composition according to the
present invention.
[0099] There is also provided a coated substrate having a coating
comprising an aqueous coating composition according to the present
invention; and a method for coating a substrate using an aqueous
coating composition according to the present invention comprising
a) application of the aqueous coating composition to the substrate
and b) removal of the water and any co-solvent.
[0100] The present invention is now illustrated by reference to the
following example. Unless otherwise specified, all parts,
percentages and ratios are on a weight basis.
EXAMPLES
Abbreviations Used
[0101] Millester 9-55 Hexane diol-neopentyl glycol adipate
polyester polyol available (average molecular weight 2000 g/mol)
from Polyurethane Specialties Company Inc. [0102] U7380 Proprietary
alkyd self-crosslinking diol (average molecular weight 970 g/mol)
available from NeoResins Inc. [0103] DMPA Dimethylol propionic
acid. [0104] DC 1248 fluid Polyhydroxyl polydimethylsiloxane polyol
(Data sheet data: average molecular weight 2000 g/mol) available
from Dow Corning. [0105] NMP N-methylpyrrolidinone. [0106] IPDI
isophorone diisocyanate. [0107] F-820 Di-butyl tin dulaurate
catalyst available from Ferro Corporation. [0108] Desmodur.TM.
N-3200 A polyisocyanate based on the biuret of hexamethylene
diisocyanate available from Bayer. [0109] TEA Triethyl amine.
[0110] H.sub.2O Deionised water. [0111] DSX-1514 A proprietary
urethane associative thickener available from Henkel Corporation.
[0112] Triton.TM. X-405 A proprietary non-ionic surfactant
available from Union Carbide/Dow. [0113] Dapro 7007
Catalyst/accelerator for alkyd cure available from Elementis
Specialties. (Dapro is a trade name of Elementis Specialties).
[0114] NeoRez.TM. R-9403 A self-crosslinking uralkyd dispersion (to
promote film formation) available from NeoResins Inc. [0115]
N.sub.2H.sub.4 (64%) Hydrated hydrazine solution available from
Aldrich Co. [0116] NCO Isocyanate group. [0117] OH Hydroxyl group.
[0118] NeoRez.TM. R-9637 Commercially available polyurethane
dispersion from NeoResins Inc. [0119] SLS Sodium Lauryl Sulphonate
available from Rhodia as Rhodapon SB-8208/5. (Rhodapon is a trade
name of Rhodia). [0120] Silica Acematt.TM. TS 100 available from
Degussa Corporation, particle size 4 .mu.m.
Example 1 and Example 2
[0121] The components used to prepare the isocyanate terminated
prepolymer and to subsequently prepare the aqueous composition of
the invention are listed in Table 1 below.
TABLE-US-00001 TABLE 1 Prepolymer Example 1 Example 2 Item No.
Material Wt (g) Wt % Wt (g) Wt (%) 1 Millester 9-55 109 29.2 109
27.6 2 U7380 109 29.2 109 27.6 3 DMPA 8.7 2.3 8.7 2.2 4 DC 1248
fluid 20 5.3 20 5 5 NMP 34 -- 34 -- 6 IPDI 106 28.4 106 26.8 7
F-820 0.2 -- 0.2 -- 8 Desmodur N-3200 21 5.6 42 10.6 9 TEA 10.5 --
10.5 10.5 Prepolymer (Items 1 to 7) 2.0 2.0 NCO:OH ratio
Theoretical NCO % 5.18% 5.18% (prior to adding items 8 & 9)
Theoretical final adjusted NCO % 5.95% 6.78% (after adding items 8
& 9) Aqueous self-crosslinkable polyurethane Item No. Material
Wt (g) Wt (g) 10 H.sub.2O 520 520 11 DSX-1514 9.2 2 12(a) Triton
.TM. X-405 6.2 7.2 12(b) SLS -- 1 13 Dapro 7007 2 2 14 NeoRez .TM.
R9403 116 116 15 Prepolymer 320 320 16 N.sub.2H.sub.4 (64%) 8.6
8.6
Example 3 and Example 4
[0122] The components used to prepare the isocyanate terminated
prepolymer and to subsequently prepare the aqueous composition of
the invention are listed in Table 2 below.
TABLE-US-00002 TABLE 2 Prepolymer Example 3 Example 4 Item No.
Material Wt (g) Wt % Wt (g) Wt (%) 1 Millester 9-55 109 30.8 109
28.9 2 U7380 109 30.8 109 28.9 3 DMPA 8.7 2.5 8.7 2.3 4 DC 1248
fluid 20 5.6 20 5.3 5 NMP 34 -- 20 -- 6 IPDI 107 30.3 110 29.1 7
F-820 0.2 -- 0.2 -- 8 Desmodur .TM. N-3200 0 -- 21 5.5 9 TEA 10.5
-- 9.8 -- prepolymer (Items 1 to 7) 2.0 2.05 NCO:OH ratio
Theoretical NCO % 5.21% 5.64% (prior to adding items 8 & 9)
Theoretical final adjusted NCO % 5.07% 6.41% (after adding items 8
& 9) Aqueous self-crosslinkable polyurethane Item No. Material
Wt (g) Wt (g) 10 H.sub.2O 520 520 11 DSX-1514 5 9 12(a) Triton .TM.
X-405 7 2 12(b) SLS 0 6 13 Dapro 7007 2 0.7 14 NeoRez .TM. R9403
116 58 15 Prepolymer 320 320 16 N.sub.2H.sub.4 (64%) 9.1 11.5
Comparative Example 5
[0123] The components used to prepare an isocyanate prepolymer with
more than 6 wt % of a polyol with ionic water-dispersing groups and
to subsequently prepare the comparative aqueous composition are
listed in Table 3 below:
TABLE-US-00003 TABLE 3 Prepolymer Comparative Example 5 Item No.
Material Wt (g) Wt % 1 Millester 9-55 109 20.5 2 U7380 109 20.5 3
DMPA 50 9.4 4 DC 1248 fluid 20 3.8 5 NMP 34 -- 6 IPDI 243.5 45.8 7
F-820 0.2 -- 8 Desmodur .TM. N-3200 0 -- 9 TEA 60.2 -- Prepolymer
(Items 1 to 7) 2.0 NCO:OH ratio Theoretical NCO % 8.14% (prior to
adding items 8 & 9) Theoretical final adjusted NCO % 7.36%
(after adding items 8 & 9) Aqueous self-crosslinkable
polyurethane Item No. Material Wt (g) 10 H.sub.2O 520 11 DSX-1514 5
12(a) Triton .TM. X-405 7 12(b) SLS 0 13 Dapro 7007 2 14 NeoRez
.TM. R9403 116 15 Prepolymer 320 16 N.sub.2H.sub.4 (64%) 13.2
Procedure for Examples 1 to 4, Comparative Example 5
Stage 1:
[0124] The isocyanate-terminated prepolymer was prepared in the
following manner: items 1 to 5 were loaded into the reactor and the
temperature adjusted to 55 to 60.degree. C. while stirring/mixing
was applied. At 55 to 60.degree. C. item 6 was loaded into the
reactor containing items 1 to 5 and the temperature adjusted to 80
to 82.degree. C. and held for 45 minutes at which time item 7 was
then added. The reaction was allowed to proceed for an additional
1.75 hours at 80 to 82.degree. C., or until the theoretical NCO %
was reached (as determined by a wet analysis of the prepolymer).
(Typically the actual NCO % when the prepolymer is "finished" is 92
to 98% of theoretical when measured by wet analysis). After
reaching the theoretical NCO % the prepolymer cooling was started
to bring the temperature of the prepolymer to 68 to 70.degree. C.
During this cooling process item 8 was added to the prepolymer
reactor and homogenised with stirring. When the prepolymer reached
68 to 70.degree. C. item 9 was added to the prepolymer and
homogenised with mixing. Items 10 to 14 were placed in a dispersion
vessel sequentially and homogenised with adequate stirring and the
temperature adjusted to 18 to 20.degree. C. The prepolymer (item
15) was then dispersed into the homogenised mixture adjusting the
stir/shear rate to improve dispersing of the prepolymer if
necessary while maintaining the temperature at .ltoreq.28.degree.
C. After the given amount of prepolymer was dispersed stirring was
continued for an additional 3 to 5 minutes after which item 16 was
added to the dispersion to provide the chain extended
self-crosslinkable polyurethane. Item 16 was allowed to react with
stirring over a period of 45 to 60 minutes before the polyurethane
was then packaged.
[0125] The final dispersion of Examples 1 and 2 typically had a
solids level of about 31% by weight, a viscosity of 300 to 700 mPas
and a pH of 7.5 to 8.5.
[0126] The final dispersion of Examples 3 and 4 had a solids level
of about 33 to 34% by weight, a viscosity of 300 to 600 mPas and a
pH of 7.5 to 8.5.
[0127] Comparative Example 5 had a solids level of 33% by weight, a
viscosity of 160 mPas and a pH of 9.7.
Example 6
[0128] The prepolymer prepared in Example 3 was dispersed into
water containing just the hydrazine (item 17) and not items 11 to
15, to give Example 6 comprising a self-crosslinkable aqueous
polyurethane, with a solids level of 33.1% by weight, a viscosity
of 150 mPas and a pH of 8.3.
Example 7
[0129] Example 3 was repeated with 40 g instead of 20 g of item 4
(DC 1248), with a resultant solids level of 33.1% by weight, a
viscosity of 1500 mPas and a pH of 8.8.
Example 8
[0130] Example 3 was repeated with 125.4 g instead of 109 g of item
1 (Millester 9-55) with a resultant solids level of 33.4% by
weight, a viscosity of 1170 mPas and a pH of 8.6.
Particle Sizes:
[0131] The particle sizes of the resultant self-crosslinkable
polyurethane in Examples 1 to 8 and Comparative Example 5 were in
the range of from 1000 to 2000 nm.
Gloss Measurements
[0132] Gloss measurements were carried out on a BYK Gardner
micro-TRI-gloss 20-60-85 glossmeter in accordance with ASTM
0523-89, the results are shown in Table 4 below, and confirm that
the use of sufficient flattening agent to obtain low gloss values
in conventional systems such as NeoRez.TM. R9637 (comparative
examples 9 to 11) may lead to a lack of stability and ease of
handling of the composition, when compared with the composition of
the present invention.
TABLE-US-00004 TABLE 4 60.degree. Gloss 85.degree. Gloss Stability
Example 1 1.0 34.2 Example 2 1.1 3.1 Example 3 1.1 11.5 Example 4
0.8 24 Comparative Example 5 91.1 96.5 Example 6 1.5 1.2 settled
Example 7 2.9 9.3 Example 8 1.7 9.5 Comparative Example 9 90.6 98.6
NeoRez .TM. R9637 Comparative Example 10 10.9 30.5 NeoRez .TM.
R9637 + 5% silica Comparative Example 11 7.7 41.1 X NeoRez .TM.
R9637 + 25% silica key: -- = not measured
* * * * *