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The invention pertains to viscous mixtures or pastes of a cellulose ester,
a binder resin, and water, and optionally a plasticiser, an organic
solvent, an emulsifier, and/or a thickener, and to coating compositions
incorporating such mixtures or pastes.
BACKGROUND OF THE INVENTION
Mixtures or pastes based on cellulose esters have earlier been proposed in
EP-B-076 443 and EP-B-184 127.
The products described in these documents are used to a large extent for
varnishing wood, metal, synthetic material, paper, leather, glass, and
plastic films, all surfaces where great value is placed on solventless
coating compositions.
A drawback to the coats obtained using the known coating compositions is
their poor hardness and comparatively low resistance to various liquids
such as alcohol, red wine, coffee, and the like.
The invention now provides a coating composition with markedly enhanced
properties such as greater hardness and improved resistance to chemicals.
The invention consists in that in the mixtures or pastes of the known type
mentioned in the opening paragraph wherein at least a portion of the
binder resin is functionalized with an amino-functional acetal.
"Amino-functional" means an amino group is present.
It should be noted that it is known in itself from EP-B-255 608 that a
thermosetting coating composition can be obtained by mixing hydroxyl
group-containing compounds with a non-volatile acetal-functional
cross-linking agent which can be obtained by converting a compound having
a free isocyanate group with a hydroxyl-functional acetal. A possible
drawback to the coating compositions described in this document is that
when they are applied as coats, they have to be cured at a comparatively
high temperature. A further drawback is the limited availability in
industrial quantities of the hydroxyacetal used in these coating
compositions.
EP-A-744 449 also describes mixtures or pastes based on cellulose esters
and a binder resin in coating compositions. The use of a polysiloxane
compound is required to achieve enhanced stability in water, while the use
of an aqueous polyisocyanate dispersion as cross-linking is necessary to
obtain a coating with markedly enhanced properties.
For that reason it must be considered extremely surprising that the now
proposed coating compositions can be cured in a comparatively short time
even at ambient temperature. This is of major significance for industrial
coating processes of heat sensitive substrates like, e.g., wood which is
used in the furniture industry. The use of coatings curable only at high
temperatures would not only require unacceptably high investments in that
branch of industry, but also result in higher costs (e.g. energy).
SUMMARY OF THE INVENTION
The invention is, in one embodiment, a mixture comprising cellulose ester,
binder resin, and water, wherein at least a portion of the binder resin is
functionalized with an amino-functional acetal.
In other embodiments, the mixture further comprises a plasticizer, an
organic solvent, an emulsifier and/or a thickener.
In another embodiment, the mixture is in the form of a paste.
The mixture or paste is preferably used in coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
Among the cellulose esters eligible for use according to the invention are
the known nitrate esters, as well as esters based on acetobutyrate and
acetopropionate.
According to the invention, it was found that very favorable results can be
obtained when at least a portion of the resin is functionalized by
converting the amino group of the amino-functional acetal with a free
isocyariate, (meth)acrylate, ester or epoxy group present in the binder
resin, or with an at least difunctional compound having at least one free
isocyariate, (meth)acrylate, ester or epoxy group and a group which is
reactive towards one or more of the groups present in the resin to be
functionalized. Usually, this means hydroxyl groups, which exhibit a high
reactivity towards, e.g., isocyanate or epoxy groups.
Examples of at least difunctional isocyanate compounds include aliphatic,
cycloaliphatic or aromatic di-, tri- or tetraisocyanates which may be
ethylenically unsaturated or not, such as: 1,2-propylene diisocyanate,
trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene
diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate,
2,2,4-trimethyl hexamethylene diisocyariate, 2,4,4-trimethyl hexamethylene
diisocyanate, dodecamethylene diisocyariate, .omega.,.omega.'-dipropyl
ether diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane
diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate,
4-methyl-1,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate,
dicyclohexyl methane-4,4'-diisocyanate, 3,3'-dimethyl dicyclohexyl
methane-4,4'-diisocyanate, a toluene diisocyanate,
1,3-bis(isocyanatomethyl)benzene, a xylene diisocyanate,
1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene,
1,5-dimethyl-2,4-bis(2-isocyanatoethyl)-benzene,
1,3,5-triethyl-2,4-bis(isocyanatomethyl)-benzene,
4,4'-diisocyanatodiphenyl, 3,3'-dichloro4,4'-diisocyanatodiphenyl,
3,3'-diphenyl-4,4'-diisocyanatodiphenyl,
3,3'-dimethoxy-4,4'-diisocyanatodiphenyl, 4,4'-diisocyanatodiphenyl
methane, 3,3'-dimethyl-4,4'-diisocyanatodiphenyl methane, a
diisocyanatonaphthalene, the adduct of 2 molecules of a diisocyanate, e.g.
hexamethylene diisocyanate or isophorone diisocyanate, to a diol such as
ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate
to 1 molecule of water (available under the trade designation
Desmodur.RTM.N of Bayer.RTM.), the adduct of 1 molecule of trimethylol
propane to 3 molecules of toluene diisocyanate (available under the trade
designation Desmodur.RTM.L of Bayer.RTM.), the adduct of 1 molecule of
trimethylol propane to 3 molecules of isophorone diisocyanate, compounds
such as 1,3,5-triisocyanatobenzene and 2,4,6-triisocyanatotoluene, and the
adduct of 1 molecule of pentaerythritol to 4 molecules of toluene
diisocyanate. Preferably, an aliphatic or cycloaliphatic di- or
triisocyariate having about 8 to about 36 carbon atoms is employed.
Typical examples of compounds containing at least 2 acryloyl or
methacryloyl groups include the (meth)acrylic esters of di-, tri- or
polyvalent polyols, including polyester polyols and polyether polyols;
adducts of, on the one hand, a hydroxyl group-containing (meth)acrylic
ester of a polyol to, on the other hand, an at least difunctional
isocyanate compound; and adducts of (meth)acrylic acid to an at least
difunctional epoxy compound.
Ester compounds suitable for use are esters of polycarboxylic acids and
low-boiling alcohols. Examples of these are methyl, ethyl, n-propyl,
isopropyl, n-butyl, sec-butyl, and tert-butyl esters of di-, tri- or
tetracarboxylic acids such as malonic acid, adipinic acid, dimeric fatty
acids, maleic acid, fumaric acid, cyclohexane-1,2-dicarboxylic acid,
phthalic acid, isophthalic acid, cyclohexane-1,3-dicarboxylic acid,
cyclohexane-1,4-dicarboxylic acid, thiophene-1,5-dicarboxylic acid,
trimellitic acid, ethylene tetracarboxylic acid, acetylene dicarboxylic
acid, and propane-1,1,2,3-tetracarboxylic acid.
Examples of suitable at least difunctional, solid or liquid epoxy compounds
include the di- or polyglycidyl ethers of (cyclo)aliphatic or aromatic
hydroxy compounds such as ethylene glycol, glycerol, cyclohexane diol,
mononuclear di- or polyvalent phenols, bisphenols such as Bisphenol-A and
Bisphenol-F, and polynuclear phenols; glycidyl ethers of fatty acids
having about 6 to about 24 carbon atoms; glycidyl(meth)acrylate;
isocyanurate group-containing epoxy compounds, an epoxydised
polybutadiene; hydaritoin epoxy resins; epoxy resins obtained by
epoxydising aliphatic and/or cycloaliphatic alkenes, such as dipentene
dioxide, dicyclopentadiene dioxide, and vinylcyclohexene dioxide, and
glycidyl groups-containing resins such as polyesters or polyurethanes
containing one or more glycidyl groups per molecule, or mixtures of the
aforesaid epoxy resins.
So far, optimum results have been obtained using 1-amino-4,4-dialkoxybutane
having 1 to 4 carbon atoms per alkoxy group as the amino-functional
acetal.
Eligible binder resins are all resins which are compatible with the
cellulose esters employed. Examples of eligible resins according to the
invention are polyesters, epoxy resins, polyethers, polyurethanes, amino
resins such as melamine formaldehyde and urea formaldehyde resins, resins
having blocked isocyanate groups, and acrylic or vinyl polymers.
According to the invention, preference is given to mixtures or pastes where
the functionalized portion of the binder resin is an alkyd resin. Also,
the other aforementioned resins are eligible to be functionalized in
principle. According to the invention, the binder resin is regarded as
functionalized not only when the amino-functional acetal is covalently
bonded to this resin, but also when the resin is mixed with a compound
obtained by converting the aminoacetal compound with a difunctional
compound such as a diisocyanate, a diacrylate ester, a diester or a
diepoxide, and the resulting diacetal is incorporated into one of the
aforesaid resins. Included in "difunctional compounds" are both compounds
wherein the functional groups are the same and those where the functional
groups are different.
Preferred are mixtures or pastes where the binder mix is made up of an at
least partially functionalized alkyd resin. The alkyd resin can be made up
of a single resin or form part of a mixture of several alkyd resins,
including functionalized resins.
Optionally, a portion of the alkyd resins dries oxidatively by
incorporating unsaturated aliphatic compounds, at least a portion of which
is polyunsaturated. The unsaturated aliphatic compounds preferably are
unsaturated aliphatic monocarboxylic acids, more particularly
polyunsaturated aliphatic monocarboxylic acids. Examples of
mono-unsaturated fatty acids are myristoleic acid, palmitoleic acid, oleic
acid, gadoleic acid, erucic acid, and ricinoleic acid. Preferably, use is
made of fatty acids containing conjugated double bonds, such as dehydrated
ricinus oil fatty acid and/or wood oil fatty acid. Other monocarboxylic
acids suitable for use include tetrahydrobenzoic acid and hydrogenated or
non-hydrogenated abietic acid or isomer thereof. If so desired, the
above-envisaged monocarboxylic acids may be employed wholly or in part as
triglyceride, e.g. as vegetable oil, in the preparation of the alkyd
resin. Optionally, mixtures of two or more of such monocarboxylic acids or
triglycerides may be used, if so desired in combination with one or more
saturated, (cyclo)aliphatic, or aromatic monocarboxylic acids, e.g.,
pivalic acid, 2-ethyl hexanoic acid, lauric acid, palmitic acid, stearic
acid, 4-tert.butyl benzoic acid, cyclopentane carboxylic acid, naphthenic
acid, cyclohexane carboxylic acid, 2,4-dimethyl benzoic acid, 2-methyl
benzoic acid, and benzoic acid.
Optionally, there may be incorporated into the alkyd resin also acids
suitable for forming dendrimers such as dimethylol propionic acid, or
polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic
acid, 5-tert. butyl isophthalic acid, trimellitic acid, pyromellitic acid,
succinic acid, adipic acid, 2,2,4-trimethyl adipic acid, azelaic acid,
sebacic acid, dimerised fatty acids, cyclopentane-1,2-dicarboxylic acid,
cyclohexane-1,2-dicarboxylic acid, 4-methylcyclohexane-1,2-dicarboxylic
acid, tetrahydrophthalic acid, endomethylene cyclohexane-1,2-dicarboxylic
acid, butane-1,2,3,4-tetracarboxylic acid, endoisopropylidene
cyclohexane-1,2-dicarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic
acid, and butane-1,2,3,4-tetracarboxylic acid. If so desired, the
above-envisaged carboxylic acids may be used as anhydride or in the form
of an ester, e.g., an ester of an alcohol having 1-4 carbon atoms.
In addition, the alkyd resin may be composed of di- or polyvalent hydroxyl
compounds. Examples of suitable divalent hydroxyl compounds are ethylene
glycol, 1,3-propane diol, 1,6-hexane diol, 1,12-dodecane diol,
3-methyl-1,5-pentane diol, 2,2,4-trimethyl-1,6-hexane diol,
2,2-dimethyl-1,3-propane diol, and 2-methyl-2-cyclohexyl-1,3-propane diol.
Examples of suitable triols are glycerol, trimethylol ethane, and
trimethylol propane. Suitable polyols having more than 3 hydroxyl groups
are pentaerythritol, sorbitol, and etherification products of the
above-envisaged compounds, such as di- and trimethylol propane and di-,
tri-, and tetrapentaerythritol. Preferably, use is made of compounds
having 3-12 carbon atoms, e.g., glycerol, pentaerythritol and/or
dipentaerythritol.
The alkyd resins can be obtained via direct esterification of the
constituent components, possibly with a portion of these components
already having been converted into ester diols or polyester diols.
Alternatively, the unsaturated fatty acids can be added in the form of a
drying oil, such as linseed oil, tunafish oil, dehydrated castor oil,
coconut oil, and dehydrated coconut oil. The final alkyd resin is then
formed by means of transesterification with the other added acids and
diols. This transesterification generally is performed at a temperature in
the range of about 115 to about 250.degree. C., possibly with solvents
such as toluene and/or xylene also being present. The reaction generally
takes place in the presence of a catalytic amount of a transesterification
catalyst. Examples of transesterification catalysts suitable for use
include acids such as p-toluene sulphonic acid, a basic compound such as
an amine, or compounds such as calcium oxide, zinc oxide, tetraisopropyl
orthotitanate, dibutyl tin oxide, and triphenyl benzyl phosphonium
chloride.
The functionalized resin should be capable of binding at least such a
number of acetal groups as corresponds to the desired weight percentage of
acetal groups in the binder resin. This weight percentage, calculated as
dimethoxyacetal, e.g. as 1-amino4-4'dimethoxybutane, preferably is in the
range of about 1 to about 20 wt. %, more preferably of about 1 to about 15
wt. %.
The eligible cellulose esters according to the invention are cellulose
nitrate, cellulose acetobutyrate, cellulose acetopropionate, and cellulose
acetate, as well as mixtures thereof.
In addition to the aforementioned synthetic resins the binder resin may
comprise natural resins, such as colophonium resin, balsam resin, shellac,
copal resin and/or dammar resin.
Optionally, a plasticiser may be incorporated into the mixtures or pastes.
Suitable plasticisers include the esters of phthalic acid such as dibutyl
phthalate, diisobutyl phthalate, di-2-ethylhexyl phthalate, diisononyl
phthalate, dibutyl glycol phthalate, esters of adipic acid, sebacic acid,
and fatty acids, epoxydised fatty acids, esters of phosphoric acid, and
vegetable oils which may be modified or not.
Optionally, the preparation of the mixtures or pastes according to the
invention may be carried out in the presence of one or more solvents.
These can be removed wholly or in part after the preparation. Suitable
solvents; are esters of acetic acid, such as n-butyl acetate, isobutyl
acetate, methoxypropyl acetate, ethoxypropyl acetate, butyl glycol
acetate, 3-methoxy-n-butyl acetate, ethyl lactate,
ethyl-(3-ethoxy)propionate; ketones, such as methylisobutyl ketone,
diisobutyl ketone, cyclohexanone; alcohols, such as n-butanol, isobutanol,
3-methoxybutanol; aromatic hydrocarbons, such as toluene, xylene, and
mixtures of these solvents.
Examples of suitable emulsifiers are dodecyl benzene sulphonate, butyl
naphthalene sulphonate, lauryl stearyl sulphate, dioctyl disodium
succinate, and the oxethylates of octyl phenol or nonyl phenol having a
degree of oxethylation of about 4 to about 60.
Furthermore, advantageous properties can be achieved using a polymeric
dispersant (see e.g. WO 97/19120) or a polysiloxane, above all a
polyethermodified polysiloxane.
If so desired, a thickener may also be present. One example of a suitable
thickener is a polyurethane resin.
Mixtures or pastes according to the invention preferably contain the
aforementioned constituents in the following concentrations:
about 2.0--about 60 wt. % of cellulose ester,
about 2.0--about 60 wt. % of binder resin, at least a portion of which is
functionalized,
about 1.0--about 80 wt. % of water,
0.0--about 40 wt. % of plasticiser,
0.0--about 20 wt. % of emulsifier,
0.0--about 20 wt. % of thickener, and
0.0--about 45 wt. % of organic solvent, with the sum total of the weight
percentages always being 100.
The invention further pertains to coating compositions based on cellulose
esters in which the binder resin is functionalised with an
amino-functional acetal. When these are incorporated into the coating
composition, a small amount of an acid catalyst can be added prior to the
application of the lacquer. Examples of suitable acids are p-toluene
sulphonic acid, dodecyl benzene sulphonic acid, dinonyl naphthalene
disulphonic acid, and other acid catalysts. The amount of acid catalyst to
be incorporated corresponds to 0,05 to 1 wt. %, calculated on the solids
content of the mixtures or pastes.
The invention will be elucidated with reference to the following examples.
These are intended to illustrate the invention but are not to be construed
as limiting in any manner the scope thereof. Unless otherwise indicated,
"parts" stands for "parts by weight" and "%" for "weight per cent"
hereinafter. The solids content SC was calculated or determined in
accordance with ISO 3251-1993 after 1 hour of heating at 120.degree. C.
and is given in wt. %. The viscosity was determined at 23.degree. C. using
a viscometer as specified by Brookfield (spindle 4 and motor set at 30)
and is given in cPa.s. The acid value and hydroxyl number value are given
in mg KOH per gram of resin. The molecular weights were determined with
the aid of GPC (THF as mobile phase and polystyrene as standard). Unless
otherwise indicated, "hardness" stands for "Pendulum hardness according to
Persoz".
EXAMPLE I
Preparation of hydroxyl-functional alkyd resin
32.6 parts of tall oil fatty acid, 17.7 parts of trimethylol propane, 16.6
parts of pentaerythritol, and 33.1 parts of phthalic anhydride were mixed
and heated for 50 minutes at 185.degree. C. with continuous stirring. At
240.degree. C. xylene was added, and the water of reaction was removed
with refluxing until an acid value of <7 was reached. After cooling, an
alkyd having the following properties was obtained, the listed values
being related to a solids content of 100%. Next, the product was diluted
with butyl acetate to a solids content of 70.+-.1.5%.
Oil length 33%
Hydroxyl number (of theory) mg KOH/g 145
Number average molecular weight Mn 2470
Weight average molecular weight Mw 13860
EXAMPLE II
Three solutions (E1, E2, and E3) were prepared of the alkyd resin of
Example I functionalized with 1-amino-4,4-dimethoxybutane (ABAA). The
quantities by weight (in g) used in the preparation, the reaction times,
and the temperatures are listed in the table below.
E1 E2 E3
alkyd resin of Ex. I 367 367 550
butyl acetate 257 257 200
dibutyl tin laureate 1.8 1.8 2.0
isophorone diisocyanate (IPDI) 71.7 71.7 59.8
10 min. residence at room temp. " " "
number of minutes heated to 60.degree. C. 40 " 30
temperature of 60.degree. C. for 2 " 90 minutes
hours at 55.degree. C.
cooling to room temperature " " "
feeding of ABAA for 15 min. at 38.6 38.6 36.1
temp. <30.degree. C.
1 hour of stirring " " "
3 hours of stirring at 80.degree. C. 60.degree. C. 60.degree. C.
wt. % of ABAA calculated on solids 10.5 10.7 7.5
content
EXAMPLE Ill
Three oil-in-water emulsions were prepared by combining the following
components (in parts by weight)
III-1 III-2 III-3
functionalised alkyd resin solution E2 from 34.5 44.0 48.5
Example II
dibutyl phthalate 3.0 3.0 3.0
methoxypropyl acetate 2.5 2.5 2.5
emulsifiers 4.5 4.5 4.5
nitro-cellulose (Standard 24 E (65 wt. % dry 27.0 17.5 13.0
solids)
Each mixture was homogenised at 45.degree. C. and with slow stirring 28.5
parts of water were added dropwise. The obtained oil-in-water emulsions
had a alkyd resin to nitro-cellulose ratio based on solids of 1:1, 2:1,
and 3:1, respectively. To prepare lacquers out of these emulsions, 100
parts of each emulsion was mixed at room temperature with 5 parts of a
non-ionic wax dispersion, 8 parts of a silica-premix, 2 parts of
butylglycol acetate, and 15 parts of water.
The lacquers were applied to a wooden substrate and the hardness of the
lacquer was measured one night and 2 days after application. The following
results were found:
hardness of the lacquer hardness of the lacquer
Example after one night after two days
III-1 150 185
III-2 90 100
III-3 60 60
Example IV (Comparative example)
An oil-in-water emulsion was prepared by combining the following components
(in parts by weight)
IV-1
alkyd resin solution from Example I 33.0
dibutyl phthalate 3.0
methoxypropyl acetate 3.0
emulsifiers 4.5
nitro-cellulose (Standard 24 E (65 wt. % dry solids) 18.5
butylglycol acetate 10.0
This mixture was homogenised at 45.degree. C. and with slow stirring 38.0
parts of water were added dropwise. The obtained oil-in-water emulsion had
a alkyd resin to nitro-cellulose ratio based on solids of 2:1. To prepare
lacquers out of these emulsions, 100 parts of each emulsion was mixed at
room temperature with 5 parts of a non-ionic wax dispersion, 10 parts of a
silica-premix, and 7 parts of water.
The lacquers were applied to a wooden substrate and the hardness of the
lacquer was measured one night and 2 days after application. The following
results were found:
hardness of the lacquer hardness of the lacquer
Example after one night after two days
IV-1 55 55
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