U.S. patent application number 10/768345 was filed with the patent office on 2004-09-23 for aqueous dispersion of high molecular weight polyester for chip resistant primer.
Invention is credited to Kemp, Lisa Kay, Knight, Michael Charles JR., Nothnagel, Joseph Leo, Spilman, Gary Eugene.
Application Number | 20040186227 10/768345 |
Document ID | / |
Family ID | 26857269 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040186227 |
Kind Code |
A1 |
Spilman, Gary Eugene ; et
al. |
September 23, 2004 |
Aqueous dispersion of high molecular weight polyester for chip
resistant primer
Abstract
The present invention is directed to an aqueous dispersion of a
polyester salt and polymeric vehicles which include the aqueous
dispersions of a polyester salt. The polymeric vehicle is
particularly effective for providing coating binders in cured
primer coatings. The primer coating compositions are useful for
multilayer paint coating films which have at least two layers of
paint film including the cured primer coating composition film. The
use of the primer polymeric vehicles of the present invention in
conjunction with one or more additional overlaying top coating film
layers provide a multiple layer coatings having improved adhesion
and chip resistance.
Inventors: |
Spilman, Gary Eugene; (Lake
in the Hills, IL) ; Knight, Michael Charles JR.;
(McHenry, IL) ; Kemp, Lisa Kay; (Algonquin,
IL) ; Nothnagel, Joseph Leo; (Woodstock, IL) |
Correspondence
Address: |
FITCH EVEN TABIN AND FLANNERY
120 SOUTH LA SALLE STREET
SUITE 1600
CHICAGO
IL
60603-3406
US
|
Family ID: |
26857269 |
Appl. No.: |
10/768345 |
Filed: |
January 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10768345 |
Jan 30, 2004 |
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09952819 |
Sep 14, 2001 |
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09952819 |
Sep 14, 2001 |
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09161145 |
Sep 25, 1998 |
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6277953 |
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09952819 |
Sep 14, 2001 |
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09160843 |
Sep 25, 1998 |
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Current U.S.
Class: |
524/601 |
Current CPC
Class: |
C08J 3/02 20130101; C08J
3/03 20130101; C08J 2451/00 20130101; C08J 3/07 20130101; C08F
255/023 20130101; C09D 151/06 20130101; C08J 7/0427 20200101; C08J
2323/02 20130101; C08J 2351/00 20130101; C08F 255/023 20130101;
C08F 220/1806 20200201; C08F 220/14 20130101; C08F 220/1812
20200201; C08F 220/06 20130101 |
Class at
Publication: |
524/601 |
International
Class: |
C08K 003/00 |
Claims
What is claimed is:
1. A polymeric vehicle comprising an aqueous dispersion of a
polyester salt, wherein the polyester salt is a residue of a
polyester having an acid value of at least 30, a number average
molecular weight of at least 1500 and a hydroxyl value of not more
than 90, the aqueous dispersion effective for providing the
polymeric vehicle with less than about 5 weight percent organic
solvent.
2. The polymeric vehicle as recited in claim 1 wherein the
polyester salt is the residue of a polyester having an acid value
of from about 40 to about 50 and a hydroxyl value of from about 90
to about 50 and a number average molecular weight of from about
1500 to about 2800.
3. The polymeric vehicle as recited in claim 2 wherein the
polyester salt in the aqueous dispersion has a particle size of
less than 400 nm.
4. The polymeric vehicle as recited in claim 3 wherein the
polymeric vehicle is effective for providing a cured primer coating
composition film, the primer coating composition film, when part of
a multilayer coating having at least two layers inclusive of the
primer film effective for providing the multilayer paint coating
with a two pint chip number rating of at least about 5 and a two
pint chip size of at least about A.
5. The polymeric vehicle as recited in claim 2 wherein the
polyester includes --COOH groups which may be neutralized to form a
water dispersible salt.
6. The polymeric vehicle as recited in claim 1 wherein the
polyester includes --COOH groups which may be neutralized to form a
water dispersible salt.
7. The polymeric vehicle as recited in claim 3 wherein the
polymeric vehicle further includes a cross linker selected from the
group consisting of an amino resin, an isocyanate compound and
mixtures thereof.
8. An aqueous polymer dispersion formed by a process comprising:
forming a polyester having sufficient --COOH groups to provide the
polyester with an acid value of from about 30 to about 50, a number
average molecular weight of about 1500 to about 2800 and a hydroxyl
number of from about 50 to about 90, mixing the polyester in an
organic hydrophilic solvent, wherein the polyester polymer has a
solubility in the hydrophilic solvent of at least about 50 weight
percent, and the organic hydrophilic solvent has a solubility in
water of at least about 5 weight percent; neutralizing at least
about 30 percent of the ionizable groups of the polyester with an
amount of neutralizer effective to form a solution of neutralized
polymer salt; mixing the solution of neutralized polyester salt
with water to form a blend of water/organic solvent/neutralized
polyester; and stripping the organic from the blend of
water/organic solvent/neutralized polyester blend at not more than
about 65.degree. C. to form a dispersion of neutralized polyester
salt in water, the dispersion having a viscosity of less than about
10 poise at a temperature of about 25.degree. C.
9. The aqueous polymer dispersion according to claims 8 wherein the
neutralizer is selected from the group consisting of ammonia,
triethanol amine, 2-amino-2-methyl-1-propanol, and dimethyl ethanol
amine.
10. The aqueous polymer dispersion according to claim 8 wherein
water is added to the solution of the neutralized polyester in an
amount effective to provide an initial ratio of organic solvent to
water of from about 0.15 to about 0.45.
11. The aqueous polymer dispersion according to claim 10 wherein
organic solvent is removed without an inversion.
12. The aqueous polymer dispersion according to claim 8 wherein the
process is effective for providing the polyester salt in the
aqueous dispersion with a mean particle size of not more than about
400 nm.
13. An aqueous dispersion of a polyester salt, wherein the
polyester salt is the residue of a polyester having a number
average molecular weight in the range of from about 1500 to about
2800 and a hydroxyl value of from about 90 to about 50, and an acid
value of from about 40 to about 50, the polyester having --COOH
groups which are neutralizeable to form a water dispersible
polyester salt.
14. An aqueous dispersion of a polyester salt according to claim 13
wherein the polyester has a number average molecular weight of
about 1500 and a hydroxyl value of about 90.
15. An aqueous dispersion of a polyester salt according to claim 13
wherein the polyester has a number average molecular weight of
about 2800 and a hydroxyl value of about 50.
16. A multilayer paint coating having a two pint chip number rating
of at least about 5 and a two pint chip size of at least about A
which is provided by application of a polymeric vehicle to a
substrate, the polymeric vehicle comprising an aqueous dispersion
of a polyester salt, wherein the polyester salt is the residue of a
polyester having a number average molecular weight of at least 1500
and a hydroxyl value of not more than 90.
Description
[0001] The present application is a continuation-in-part
application of U.S. Ser. No. 09/161,145 filed Sep. 25, 1998 and of
U.S. Ser. No. 09/160,843 filed Sep. 25, 1998.
[0002] The present invention relates to stable aqueous polyester
dispersions useful as primers. More particularly, the aqueous
polyester dispersions balance relatively high molecular weights and
low hydroxyl numbers to provide a primer coating that effectively
improves chip resistance of paint coatings overlaying the primer
while maintaining adhesion and low levels of volatile organic
compounds and low viscosities.
BACKGROUND OF THE INVENTION
[0003] Automotive and other durable coatings are complex multilayer
systems which rely on certain performance criteria at each level
for overall success. The bulk of the responsibility for providing
improved chip resistance lies with the primer surface layer.
However, improving chip resistance properties of automotive
coatings or other types of protective or decorative durable
coatings is clearly a system-dependent task. For many systems,
there appears to be several key ingredients to achieving
incremental improvements. A chip-resistance test is by nature high
in stress, impact, and shear, which intuitively generates
hypotheses based on the softness, or rubber-like characteristics of
the primer layer. Any contributions from the primer to increase
brittleness eventually may lead to reduced chip performance. This
can be related to the degree of cross linking. Very low and very
high levels of cross linking in such systems lead to poor chip
resistance. In the case of low cross linking, the coating does not
possess the strength properties necessary to withstand the impact
and shear forces applied by the gravel. The base molecular weight
is usually too low to provide appropriate elastic properties
associated with light cross linking. The result is flow and
scission on gravel impact. An extremely high cross link density
affords large numbers of covalent cross links which impart
brittleness to the coating, and failure is based on the inability
of the coating to absorb and evenly distribute these concentrated
forces applied at the gravel impact. The material neither flows,
nor elastically deforms, but instead suffers brittle fracture.
Further, cross linkers often cause VOCs by virtue of VOC by product
release from the cross link reaction between the cross linkers and
polymeric resin. Also complicating systems which use separate cross
linking agents is the propensity for the cross linking agent to
react with itself. For example, self-condensation of melamine cross
linkers is a potential competing reaction, which may result in
local areas of high concentration of highly cross linked melamine
resin. This would produce localized brittleness which may result in
chip or adhesion failures. Another key contributor to successful
chip resistance is the adhesion of the primer to the substrate, and
the subsequent adhesion of another paint coating to the primer
(collectively intercoat adhesion). A major contributor to this
effect is the functionality of the primer resin-polar group
functionality including hydroxyl and carboxyl that play a key role
in interactions with the substrate and other paint layers.
[0004] In order to obtain the optimal chip-resistant properties,
the coatings overlying the primer and the primer base resin must
each deliver a balance of properties to the final coating. The
easiest way to maximize mechanical properties of the primer resin
is to increase molecular weight. Increases in molecular weight,
however, generally increase the viscosity of such resins. While
high viscosity resins may be cut with organic solvents, this
results in an undesirable increase in volatile organic compounds
(VOCs).
SUMMARY OF THE INVENTION
[0005] The present invention is directed to an aqueous dispersion
of a polyester salt and polymeric vehicles which include the
aqueous dispersions of a polyester salt. The polymeric vehicle is
particularly effective for providing coating binders in cured
primer coatings (the cured primer paint coating film). The primer
coating compositions (also known as formulated coating
compositions) are useful for multilayer paint coating films which
have at least two layers of paint film including the cured primer
coating composition film. The use of the primer polymeric vehicles
of the present invention in conjunction with one or more additional
overlaying top coating film layers provide a multiple layer coating
system having improved adhesion and chip resistance.
[0006] The primer polymeric vehicle of the invention permits the
use of less cross linker to cross link the polyester salt. The use
of less cross linker results in the release of less VOCs upon cross
linking and a lower cross linker density in the cured coating
binder film of in the cured primer coating composition. The reduced
cross link density with the relative high molecular weight of the
polyester salt provides improved chip resistance. While not
intending to be bound by a theory, the polyester salt of the
present invention has a higher molecular weight which enhances chip
resistance and needs less cross linker (which also enhances chip
resistance) to cure into a useable film than a polyester which is
compositionally the same (and is not a metal or ammonium salt), but
has a lower molecular weight. These lower molecular weight polymers
are used in high solids systems and are dispersed in an organic
solvent or mixed organic/water solvent system. Moreover, the
molecular weight of the polyester in the latter high solids system
can not be increased without also increasing the viscosity of the
polymer dispersion or solution (increasing molecular weight
inherently increases viscosity in such systems). Hence, the
polymeric vehicle of the present invention includes a water
dispersible polyester salt having unique combination of high
molecular weight, a relatively low hydroxyl value or number, a
unique ratio of hydroxyl value to number average molecular weight
and a polyester with an acid value which permits formation of the
water dispersible salt.
[0007] The polyester salt is cross linkable to form a cured coating
binder in a primer paint coating film which is chip resistant when
it is part of a multilayer paint coating system which has at least
two paint film layers including the cured primer paint coating film
layer. The cured coating binder of the primer of the invention also
renders the multilayer paint coating system chip resistant. Hence,
the polymeric vehicle of the primer coating composition balances
the hydroxyl value and number average molecular weight of the
polyester salt in the aqueous dispersion to provide VOC reduction
through the use of an aqueous system with reduced amount of cross
linker as well as improved chip resistance and adhesion for the
cured primer paint coating film of the primer coating
composition.
[0008] For enhancing chip resistance of coatings systems in which
primers of the invention are used, the desired hydroxyl number is
generally inversely related to the polyester molecular weight. By
way of example, the polymeric vehicle for the primer coating
composition or formulated coating comprises an aqueous dispersion
of a polyester salt which is the residue of a polyester having a
number average molecular weight of about 1500 Daltons and a
hydroxyl value of about 90. In such aspect, the polyester has a
hydroxyl equivalent weight of about 600. This aqueous dispersion is
effective for providing the polymeric vehicle with less than about
5 weight percent organic solvent. At a higher molecular weight, the
polymeric vehicle for the primer coating composition or formulated
coating comprises an aqueous dispersion of a polyester salt which
is the residue of a polyester having a number average molecular
weight of about 2800 Daltons and a hydroxyl value of about 50. In
such aspect, the polyester has a hydroxyl equivalent weight of
about 1100. This aqueous dispersion is effective for providing the
polymeric vehicle with less than about 5 weight percent organic
solvent.
[0009] The chip resistance of the multilayer paint coating system
which includes the coating binder of the primer of the invention,
is superior to the chip resistance of a multilayer paint coating
system which includes a primer which has compositionally the same
polyester which has a lower molecular weight and is not a salt. It
is these latter lower molecular weight polyesters which are
generally used with organic solvent or mixed organic/water solvent
systems. They are high in VOCs and generally require more cross
linker to cure than the polymeric vehicle of the present
invention.
[0010] In an important aspect of the invention, the polymeric
vehicle for the primer coating composition or formulated coating
comprises an aqueous dispersion of a polyester salt which is the
residue of a polyester having a number average molecular weight of
at least 1500 Daltons and a hydroxyl value of not more than 90. In
one aspect, the polyester has a hydroxyl equivalent weight of about
600 to about 1100. This aqueous dispersion is effective for
providing the polymeric vehicle with less than about 5 weight
percent organic solvent. In another important aspect, the salt of
the polyester in the aqueous dispersion has a particle size of less
than 400 nm.
[0011] In yet another aspect, the polyester salt is the residue of
a polyester having an acid value of at least 30, and in an
important aspect, from about 40 to about 50, the polyester salt
having a hydroxyl value of from about 90 to about 50 and the salt
having a number average molecular weight of from about 1500 to
about 2800 Daltons (not including the cationic portion of the salt,
that is the salt includes the residue of a polyester where the
polyester has a molecular weight of from about 1500 to about 2800
Daltons). The polymeric vehicle of the invention is effective for
providing a multilayer paint coating system and primer coating
binder with a two pint chip number rating of at least about 5 and a
two pint chip size of at least about A (using the Society of
Automotive Engineers Chip Test No. J400) when the polymeric vehicle
of the primer is cured and a part of a multilayer paint coating
system of at least two layers inclusive of the primer coating
binder. Despite the use of a relatively high molecular weight
polyester, the polymeric vehicle and the aqueous dispersion of the
present invention have a viscosity of less than about 10 poise at a
temperature of about 25.degree. C. using less than about 5 weight
percent organic solvent, and in an important aspect, less than
about 2 weight percent organic solvent.
[0012] As previously stated above, the polyester salt requires less
equivalent amounts of cross linker for cross linking than the same
lower weight polyester (which is not a salt) having molecular
weights of less than about 1500 Daltons, which polyester is
generally less than about 800 Daltons. Suitable cross linkers
include multifunctional amino resins and blocked isocyanate
compounds. The polymeric vehicles of the invention generally will
include from about 15 to about 25 weight percent crosslinker, based
on the weight of the polymeric vehicle. Polymeric vehicles which
use the low molecular weight polyesters previously described are
polyesters which are not salts and which are used in high solids
systems will generally require from about 35 to about 50 weight
percent crosslinker.
[0013] In accordance with the present invention, an ionic
functional polyester polymer is synthesized neat and subsequently
mixed with hydrophilic organic solvent. The aqueous polymer
dispersion is made by forming a polyester having sufficient
ionizable groups to provide the polyester with an acid value of
from about 30 to about 50. The polymer has a solubility in the
hydrophilic solvent of at least about 50 weight percent, and the
organic hydrophilic solvent has a solubility in water of at least
about 5 weight percent. As previously stated, the polyester prior
to neutralization reactions to form a salt, has a number average
molecular weight of at. least about 1500, and in an important
aspect, about 1500 to about 2800 and a hydroxyl number of from
about 50 to about 90. At least about 30 percent of the ionizable
groups of the polyester polymer in the solvent are neutralized with
an amount of neutralizer effective to form a solution of
neutralized polymer salt. Thereafter the solution of neutralized
polymer salt is mixed with water to form a blend of water/organic
solvent/neutralized polymer. The organic solvent then is stripped
from the latter blend at not more than about 65.degree. C. to form
a dispersion of neutralized polymer salt in water. This dispersion
has a viscosity of less than about 10 poise at a temperature of
about 25.degree. C. The neutralizer may be any salt-forming base
compatible with the ionizable functional polymer such as sodium
hydroxide or an amine. In a very important aspect the neutralizer
is an amine type which is selected from the group consisting of
ammonia, triethanol amine, dimethyl ethanol amine, and
2-amino-2-methyl-1-propanol. Not all of the ionizable groups on the
polymers need to be reacted with the base (or neutralized).
[0014] Depending on the type of ionizable groups present in the
polymer it may be important that the polymer is neutralized before
it is blended with water so that water dispersible neutralized
ionizable groups are generally evenly distributed throughout the
polymer. It is also important that the organic solvent and some
water are removed or stripped from the blend at a duration,
temperature and pressure effective for providing an aqueous
dispersion having a resin mean particle size of not greater than
about 400 nm. In an important aspect the the polymer salt
concentration is at least about 30 weight percent, the organic
solvent concentration of less than 5 weight percent, and even less
than 2 weight percent. In an important aspect, where the
neutralizer is an amine or ammonia, the mean particle size of the
resin is maintained with a stripping temperature of not more than
about 65.degree. C. at a pressure which permits such a stripping
temperature.
[0015] In another aspect, the invention provides formulated
coatings that include aqueous polymer dispersions of the invention
with co-solvents selected from the group consisting of butoxy
ethanol, diethylene glycol monobutyl ether, secondary butyl
alcohol, propylene glycol n-butyl ether, dipropylene glycol n-butyl
ether, propylene glycol n-propyl ether, propylene glycol t-butyl
ether, and mixtures thereof. These formulated coating compositions
generally will include rheology modifiers such as fumed silica and
bentonite clays.
DETAILED DESCRIPTION
Definitions
[0016] "Hydroxyl number" or "hydroxyl value" which is also called
"acetyl value" is a number which indicates the extent to which a
substance may be acetylated; it is the number of milligrams of
potassium hydroxide required for neutralization of the acetic acid
liberated on saponifying 1 g of acetylated sample. For purposes of
this application, hydroxyl number is based on solid polyester in
the system and not on solution.
[0017] "Hydroxyl equivalent weight" is calculated from the hydroxyl
number (OHN) per ASTM D1957 as follows.
[0018] Hydroxyl Equivalent Weight=56,100/OHN
[0019] The hydroxyl number units are mg KOH/gram of resin
solids.
[0020] "Polymeric vehicle" means all polymeric and resinous
components in the formulated coating, i.e., before film formation,
including but not limited to the water dispersible salt of a
polymer. The polymeric vehicle may include a cross linking
agent.
[0021] "Coating binder" means the polymeric part of the film of the
coating after solvent has evaporated and after crosslinking.
[0022] "Formulated coating composition" means the polymeric vehicle
and solvents, pigments, catalysts and additives which may
optionally be added to impart desirable application characteristics
to the formulated coating and desirable properties such as opacity
and color to the film.
[0023] The term "aqueous medium" as used herein means water and a
mixture of water and hydrophilic organic solvent in which the
content of water is at least 10% by weight. Examples of hydrophilic
solvents include alkylalcohols such as isopropanol, methanol,
ethanol, n-propanol, n-butanol, secondary butanol, tert-butanol and
isobutanol, ether alcohols such as methyl cellosolve, ethyl
cellosolve, propyl cellosolve, butyl cellosolve, methyl carbitol
and ethyl carbitol, ether esters such as methyl cellosolve acetate
and ethyl cellosolve acetate, dioxane, dimethylformamide, diacetone
alcohol, methyl ethyl ketone, acetone, and tetrahydrofurfuryl
alcohol.
[0024] "Ionizable group" refers to functional groups on the polymer
that effect water dispersibility of the polymer. An example of an
ionizable group includes --COOH.
[0025] "Neutralizer" refers to compositions which can react with
ionizable groups on the polymer to affect water dispersibility.
Examples of neutralizers useful in the present invention include
amines, ammonia, and metal hydroxides including NaOH and KOH. In an
important aspect of the invention, the neutralizers are amines and
ammonia.
[0026] "Residue of a polyester salt" refers to the reaction product
of an ionizable polyester with a neutralizer.
[0027] "Cross linker" or "cross linking agent" means a
polyfunctional compound capable of reaction with a hydroxyl of a
polyol or a phenol hydroxyl or both. These agents include a
compound having di- or polyfunctional isocyanate groups or a
polyfunctional amino resin. The isocyanate compound or amino resin
contains isocyanate or other cross linking functional groups that
are capable of forming covalent bonds with hydroxyl groups that are
present on the polyester polyol in the polymeric vehicle. The cross
linking agent may be a blend; hence, there may be more than one
substance which forms a blend of substances which form covalent
bonds with the hydroxyl groups of the polyester polyol. Amino reins
and polyisocyanates are such cross linking agents.
[0028] "Isocyanate compound" means a compound which when reacted
with an hydroxyl results in a carbamate linkage. The isocyanate
compound may be a blocked polyisocyanate, a blocked biuret, a
blocked uretdione and a blocked isocyanurate.
[0029] Diisocyanates which may be used in the invention additional
to HDI include isophorone diisocyanate (IPDI), tetramethylxylene
diisocyanate (TMXDI), and other aliphatic diisocyanates such as
trimethylene diisocyanate, tetramethylene diisocyanate,
pentamethylene diisocyanate, 1,2-propylene diisocyanate,
2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or
2,2,4-trimethylhexamethylene diisocyanate; cycloalkylene
diisocyanates such as 1,3-cyclopentane-diisocyanate,
1,4-cyclohexane-diisocyanate and 1,3-cyclohexane-diisocyanate; and
aromatic diisocyanates such as m-phenylene diisocyanate,
p-phenylene diisocyanate, 4,4'-diphenyldiisocyanate,
1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate,
2,4- or 2,6-tolulene diisocyanate.
[0030] "Polyisocyanate" can mean compounds with two or more
isocyanate groups [--N.dbd.C.dbd.O] which compounds may be biurets
and isocyanurates. The polyisocyanates may be dimerized or
trimerized diisocyanates such as trimerized HDI or IPDI and
triisocyanates such as triphenylmethane-4,4',4"-triisocyanate,
1,3,5-triisocyanatobenzene, 1,3,5-triisocyanatocyclohexane,
2,4,6-triisocyanatotoluene and
.omega.-isocyanatoethyl-2,6-diisocyanatocaproate; and
tetraisocyanates, such as
4,4'-diphenyldimethylmethane-2,2',5,5'-tetraisocyanate.
[0031] "Carbamate linkage" means --OC(.dbd.O)N(--H)-- which can be
a urethane linkage.
[0032] "Biuret" means an isocyanate reacted with water in a ratio
of three equivalents of isocyanate to one mole of water, such as
the biuret of HDI shown below: 1
[0033] An "isocyanurate" is a six-membered ring having nitrogens at
the 1, 3 and 5 positions and keto groups at the 2, 4 and 6
positions, the nitrogens being substituted with an isocyanate
group, such as shown below in the isocyanurate of HDI. 2
[0034] Methylol (alkoxymethyl) amino crosslinking agents are
suitable for use in the present invention and are well known
commercial products, and are generally made by the reaction of di
(poly) amide (amine) compounds with formaldehyde and, optionally, a
lower alcohol.
[0035] "Aminio resins" includes melamine resins amd may also be
referred to as "melamine-formaldehyde resins" or "alcoholated
melamine-formaldehyde resin." Examples of suitable
amino-crosslinking resins include one or a mixture of the following
materials:
[0036] Melamine Based Resins: 3
[0037] wherein R is the following:
[0038] R=CH.sub.2, (Cymel).RTM. 300, 301, 303);
[0039] R=CH.sub.2, C.sub.2H.sub.5 (Cymel.RTM. 1116);
[0040] R=CH.sub.2, C.sub.2H.sub.5 (Cymel.RTM. 1130, 1133)
[0041] R=C.sub.2H.sub.5 (Cymel 1156) ; or
[0042] R=CH.sub.2, H (Cymel.RTM. 370, 373, 380, 385).
[0043] The preferred melamine is hexamethoxymethyl melamine.
[0044] Benzoquanamine Based Resins: 4
[0045] wherein R=CH.sub.3, C.sub.2H.sub.5 (Cymel.RTM. 1123).
[0046] Urea Based Resins: 5
[0047] wherein:
[0048] R=CH.sub.3, H (Beetle.TM. 60, Beetle.TM. 65); or
[0049] R=C.sub.2H.sub.5 (Beetle.TM. 80).
[0050] Gycoluryl Based Resins: 6
[0051] wherein:
[0052] R=CH.sub.3, C.sub.2H.sub.5 (Cymel.RTM. 1171); or
[0053] R=C.sub.2H.sub.5 (Cymel.RTM. 1170).
[0054] "Polyester" means a polymer which has 7
[0055] linkages in the main chain of the polymer.
[0056] As used herein, the reaction product of an alkali metal base
or amine or ammonia with a carboxyl group or other ionizable group
which is part of a polyester produces a "salt".
[0057] "Substantially solventless" means a polymeric vehicle or
formulated coating composition having not more than about five
weight percent organic solvent.
[0058] "Solvent" means an organic solvent.
[0059] "Organic solvent" means a liquid which includes but is not
limited to carbon and hydrogen which liquid has a boiling point in
the range of not more than about 150.degree. C. at about one
atmosphere pressure.
[0060] "Hydrophilic solvent" means a solvent that has a solubility
in water of at least about 5 weight percent at room
temperature.
[0061] "Volatile organic compounds" (VOCs) are defined by the U.S.
Environmental Protection Agency at 40 C.F.R. 51.000 of the Federal
Regulations of the United States of America.
[0062] A "high solids" or "high solids formulated coating
composition" means an aqueous formulated coating composition
containing more than about 30 weight percent solids, and in an
important aspect of the present invention about 35 weight percent
to about 70 weight percent solids as per ASTM test D-2369-92.
"Film" is formed by application of the formulated coating
composition to a base or substrate, evaporation of solvent, if
present, and cross-linking if necessary.
[0063] "Baked formulated coating composition" means a formulated
coating composition that provides optimum film properties upon
heating or baking above ambient temperature.
[0064] "Dispersion" in respect to a polymeric vehicle, formulated
coating composition, or components thereof means that the
composition must include a liquid and particles detectable by light
scattering.
[0065] "Dissolved" in respect to a polymeric vehicle, formulated
coating composition or components thereof means that the material
which is dissolved does not exist in a liquid in particulate form
where particles larger than single molecules are detectable by
light scattering.
[0066] "Soluble" means a liquid or solid that can be partially or
fully dissolved in a liquid. "Miscible" means liquids with mutual
solubility. "Imbibe water" means a liquid is miscible with
water.
[0067] "Acid number" or "acid value" means the number of milligrams
of potassium hydroxide required for neutralization of or reaction
with ionizable groups present in 1 g of material, such as
resin.
[0068] "Substantially free of emulsifier" means a composition with
not more than about 0.5 weight percent emulsifiers. Aqueous
dispersions of the present invention are substantially free of
emulsifier.
[0069] As used herein the term "inversion" refers to a phase change
where a mobile phase becomes a disperse phase. For example, an
inversion takes place where sufficient oil is added to an oil in
water phase such that phases invert to change from a oil in water
phase to a water in oil phase. Conversely, in an "inversionless"
system, the mobile phase does not become the disperse phase and the
corresponding increase in viscosity associated with dispersions
does not occur. In an important aspect of the present invention,
the viscosity of the system during processing remains less than
about 20 poise, and in a very important aspect, less than about 10
poise at 25.degree. C.
Stage One: Preparation of Polyester
[0070] In accordance with stage one of the present invention, a
polyester polymer is synthesized neat and subsequently blended into
an organic hydrophilic solvent which has limited to infinite
solubility in water. Polyester polymers useful in the present
invention include those that provide a polyester salt where the
polyester salt is the residue of a polyester having a number
average molecular weight of from about 1,500 to about 2,800
Daltons. In an important aspect of the invention, the polyester
polymers have an acid value of less than about 50, and in a very
important aspect, about 30 to about 50.
[0071] The polyesters used herein are reaction products of
polyhydric alcohols and polycarboxylic acids. Examples of suitable
polyhydric alcohols include triols and tetraols such as
trimethylolpropane, trimethylolethane, tris(hydroxyethyl)
isocyanurate, glycerine, and pentaerythritol, and dihydric alcohols
or diols that may include neopentyl glycol, dimethylol hydantoin,
ethylene glycol, propylene glycol, 1,3-butylene glycol, diethylene
glycol, dipropylene glycol, 1,4-cyclohexane dimethanol, Esterdiol
204 (trademark of Union Carbide), 1,3-propane diol, 1,6-hexanediol,
and dimethylol propionic acid (DMPA). As can be seen from the
reference to DMPA, polyhydric alcohols may have --COOH groups.
[0072] Carboxylic acids utilized in the invention may be aromatic
carboxylic acids such as isophthalic acid, terephthalic acid,
phthalic acid, phthalic anhydride, dimethyl terephthalic acid,
naphthalene decarboxylate, tetrachlorophthalic acid, terephthalic
acid bisglycol ester, and benzophenone dicarboxylic acid; and
cycloaliphatic, aliphatic carboxylic acids, and polyacids such as
trimellitic anhydride (TMA). As can be seen from the reference to
TMA, diacids may have additional --COOH groups.
[0073] In another important aspect of the invention, the polyester
polymers that are synthesized neat are blended with a solvent
selected from the group consisting of alkylalcohols such as
isopropanol, methanol, ethanol, n-propanol, n-butanol, secondary
butanol, tert-butanol and isobutanol, ether alcohols such as methyl
cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve,
methyl carbitol and ethyl carbitol, ether esters such as methyl
cellosolve acetate and ethyl cellosolve acetate, dioxane,
dimethylformamide, diacetone alcohol, methyl ethyl ketone, acetone,
and tetrahydrofurfuryl alcohol. The polymers of the invention have
a solubility at processing temperatures in the hydrophilic solvent
of at least about 50 weight percent, more preferably at least about
80 weight percent, based on the total weight of the
composition.
[0074] Stage one provides a resin in a hydrophilic solvent which
can be stored, and which can be further processed in stage two. In
an important aspect, the resin provided in stage one has a storage
stability of at least about 6 months.
Stage Two: Polyester Dispersion
[0075] Neutralizing the Resin
[0076] The polyester salt is formed in situ in the organic solvent
with water being mixed with the polyester salt/organic solvent
combination. In accordance with the invention, neutralizer is added
to an organic solvent solution containing the polyester in an
amount effective for neutralizing the polyester to provide
sufficient salt to render the polyester dispersible in water.
Neutralizer useful in the present invention include but are not
limited to ammonia, triethanol amine, dimethyl ethanol amine,
2-amino-2-methyl-1-propanol, NaOH and KOH.
[0077] The amount of neutralizer added is dependent on acid value
and molecular weight. In one aspect, from about 30 to about 100
percent of the carboxyl groups are neutralized to obtain the solids
level and low VOC level of the dispersions of the invention. In
another aspect, neutralizer is mixed with the polyester polymer in
an amount effective to provide at least about 70 parts polymer salt
in less than about 30 parts solvent wherein with subsequent mixing
with water, the neutralized polymer will provide a dispersion which
comprises not more than about 70 weight percent water, based on the
weight of the dispersion.
[0078] In a very important aspect of the invention, where the
ionizable group is carboxyl, the polyester requires about 70% to
about 100% neutralization to stabilize the dispersion. In another
important aspect of the invention, the process provides a mean
particle size of not more than about 400 nm, with a typical mean
particle size in the range of about 40 nm to about 200 nm as
measured by laser light scattering.
[0079] The polyester polymer can be preneutralized by making the
polymer with metal, amine or ammonia salts of the ionizable groups
such as --COOH. The polymer made from these "preneutralized"
monomers would have an acid value, as measured by titration, of at
least about 30 if the ionizable groups which form part of the
polymer were not already neutralized. In this aspect of the
invention, monomers have a polyfunctionality such as a
difunctionality which permits them to form polymers that also have
the salt form of the ionizable groups.
[0080] An example of such a monomer is 8
[0081] where A and B are --OH and/or --COOH which can form a
polyester in a condensation reaction and C is --COOX, where X is an
alkali metal such as sodium or potassium.
[0082] Addition of Water
[0083] In the next step of stage two of the process, water having a
temperature of about 25.degree. C. to about 65.degree. C. is added
to the neutralized resin solution. Lower temperatures provide
smaller mean particle sizes.
[0084] In an important aspect of the invention, the initial ratio
of solvent to water (solvent/water) is from about 0.15 to about
0.45 for polyester polymer. The initial ratio of solvent to water
is important to ensure that inversion does not take place during
subsequent stripping of solvent. The amount of water to be added
may be greater than that required to obtain the desired solids of
the final dispersion. Some water loss typically occurs during
solvent distillation. The system requires sufficient solvent at the
beginning to solubilize the salt prior to water addition.
[0085] In an alternative aspect of the invention, polymer in
hydrophilic solvent is added to water that already contains a
neutralizer.
[0086] Removal of Solvent
[0087] In the next step of the process, the organic solvent and
water if required are removed or stripped from the neutralized
resin/water/solvent mixture. A reduced atmospheric pressure may be
applied to the mixture to aid in the removal of solvent and water.
In an important aspect, vacuum may range from about 22 inches to
about 29 inches of mercury gauge. With lower temperatures, a higher
vacuum must be used to remove solvent. Lower reaction temperatures
result in less foaming, as the higher vacuum coupled with the
surface tension of the bubbles helps to break the bubbles. In
another aspect of the invention, solvent/water is stripped with
heat being supplied through the use of a heat exchanger. Use of a
heat exchanger may reduce distillation times and temperatures and
further minimize destruction of the salt.
[0088] In a very important aspect of the invention, solids levels
of at least about 30 weight percent to about 45 weight percent can
be attained for polyesters.
[0089] In another aspect of the invention, solvent that is removed
can be purified and reused. A simple flash or multiple stage
distillation is sufficient to clean the solvent of any
contamination.
[0090] In an alternative aspect, the invention permits manufacture
of the water dispersion from the polymer using one reaction vessel.
The water dispersion of the invention does not require emulsifying
agents and does not have more than about 2 weight percent, based on
the weight of the composition, of organic solvent after the
distillation of the solvent. In an important aspect, the aqueous
dispersion contains from about 0.2 to about 2 weight percent
organic solvent.
[0091] The water dispersion of the invention includes the water
dispersible amine salt of the polymer as well as the unsalified
polymer, but in the aspect of the invention where the ionizable
group is a carboxyl, the aqueous dispersion of the invention does
not have less than 30 percent of the free carboxyl groups of the
polymer neutralized or converted into a salt. As the acid number of
the polymer goes down, the higher the percent of the carboxyl
groups on the polymer must be neutralized. Where the ionizable
groups are --COOH, to maintain the dispersion below an acid value
of about 15, about 100% of the carboxyl groups on the polymer
should be neutralized to the salt. In an important aspect of the
invention, about 100% of the carboxyl groups on the polymer are
neutralized to the salt and the dispersions of the invention do not
have more than about 1 pound per gallon of dispersion (120 g/l)
VOCs, and in a very important aspect the dispersion has about 0.2
pounds per gallon of dispersion VOCs. The water dispersion of the
invention with about 0.2 pounds per gallon VOC is stable through at
least about 1 freeze-thaw cycle, and up to about 4 freeze-thaw
cycles. Freeze-thaw cycles can be increased with small amounts of
solvents or glycols as is typically used for latex systems.
Formulated Coating Compositions
[0092] The polymeric vehicle is incorporated into a formulated
coating composition which upon heating provides a baked formulated
coating composition or cured composition. Baking is above ambient
temperatures with a cross linker to provide a coating binder. The
polymeric vehicle which includes the water dispersion of the
invention provides a formulated coating composition having VOCs of
less than 1 pound per gallon of formulated coating composition,
includes water dispersible polymers and salts thereof having the
above indicated molecular weights and not only eliminates a need
for, but is substantially free of emulsifiers, surfactants and
coalescents.
[0093] Water dispersion of such high molecular weight polymers
provide a coating binder and baked formulated coating compositions
with improved film performance characteristics which include, but
are not limited to improved chip resistance, adhesion which is just
as good as lower molecular weight higher VOC systems, improved lay
down performance of the wet film, enhanced film build of the film
per pass, faster dry times, improved corrosion resistant films per
pass, improved corrosion resistant films, harder films, more
abrasion resistant films, and improved humidity resistant films.
The polymeric vehicle of the invention also provides coating
binders for improved exterior "ultraviolet resistant" durable films
which are derived from an aqueous low VOC formulated coating
composition. Films provided from the invention are improved over
that of aqueous thermoplastic emulsions or water reducible systems
of low molecular weight thermoplastic or those thermosetting
polymers requiring cross linking.
[0094] The following examples illustrate methods for carrying out
the invention and should be understood to be illustrative of, but
not limiting upon, the scope of the invention which is defined in
the appended claims.
EXAMPLES
Example 1
Polyester Dispersion
[0095] A. Synthesis of Polyester Polymer:
[0096] 1. 218.9 grams of neopentyl glycol (NPG), 77.2 grams of
trimethylol propane (TMP), and 248.4 grams of 1,6-hexanediol (HDO)
were charged to a round bottom flask equipped with a packed column,
partial condenser, receiver, and nitrogen blanket.
[0097] 2. The flask was heated until the glycols were melted and
322.8 grams of Adipic acid (AA) and 322.8 grams of Isophthalic acid
(IPtA) were added with mixing.
[0098] 3. The temperature was steadily and gradually increased to
220 degrees centigrade and waters of esterification were
removed.
[0099] 4. When the acid value was 6.8, the temperature was reduced
to 170 degrees centigrade.
[0100] 5. 80 grams of trimellitic anhydride (TMA) was added to the
flask and the temperature was maintained at 170 degrees
centigrade.
[0101] 6. Waters of esterification were removed until an acid value
of 46.3 was reached.
[0102] 7. The temperature was reduced to 90 degrees centigrade and
the polymer was cut with methyl ethyl ketone (MEK).
[0103] Properties of the Polyester Solution:
1 Percent Solids (NVM) 70 Acid Value (Mg KOH/g) 45 Molecular Weight
(Mn) 2350 Hydroxy number (Mg KOH/g) 65
[0104] B. Preparation of Polyester Dispersion:
[0105] 1. 635 grams of the polyester solution in MEK and 26.4 grams
of AMP-95 were charged to a round bottom flask equipped with a
total condenser and receiver.
[0106] 2. The flask was heated to 40 degrees centigrade with
mixing.
[0107] 3. Upon reaching temperature, 666 grams of deionized water
was added over approximately 30 minutes.
[0108] 4. Vacuum was applied to the flask and slowly increased to a
maximum of 26 inches of mercury.
[0109] 5. Vacuum was continued until the desired percent solids of
the dispersion was reached.
[0110] 6. After the desired amount of distillate was removed, the
vacuum was broken and the resulting product analyzed.
[0111] Properties of the Polyester Dispersion:
2 Percent Solids (NVM) 41.0 Viscosity (cps) 45 pH (units) 6.0
particle size (nm) <80 weight/gal (lbs) 8.9
Example 2
Polyester Dispersion
[0112] A. Synthesis of Polyester Polymer:
[0113] 1. 1170.0 grams of nenopentyl glycol (NPG), 412.5 grams of
trimethyol propane (TMP), and 1687.5 grams of
butyl-ethyl-propanediol (BEPD) were charged to a round bottom flask
equipped with a packed column, partial condenser, receiver, and
nitrogen blanket.
[0114] 2. The flask was heated until the glycols were melted, and
1725.0 grams of Adipic acid (AA) and 1725.0 grams of Isophthalic
acid (IPtA) were added with mixing.
[0115] 3. The temperature was steadily and gradually increased to
220 degrees Celsius and waters of esterification were removed.
[0116] 4. When the acid value was 3.1, the temperature was reduced
to 170 degrees celsius.
[0117] 5. 427.5 grams of trimellitic anhydride (TMA) was added to
the flask and the temperature was maintained at 170 degrees
celsius.
[0118] 6. Waters of esterification were removed until an acid value
of 41.2 was reached.
[0119] 7. The temperature was reduced to 90 degrees centigrade and
the polymer was cut with isopropyl alcohol (IPA).
[0120] Properties of the Polyester Solution:
3 Percent Solids (NVM) 69.4 Acid Value (Mg KOH/g) 41.1 Molecular
Weight (Mn) 2050 Hydroxyl number (mg KOH/g) 65
[0121] B. Preparation of Polyester Dispersion:
[0122] 1. 1352 grams of the polyester solution in IPA and 26.4
grams of N,N-dimethylethanolamine (DMEA) were charged to a round
bottom flask equipped with a total condenser and receiver.
[0123] 2. The flask was heated to 40 degrees Celsius with
mixing.
[0124] 3. Upon reaching temperature, 1476 grams of deionized water
was added over approximately 30 minutes.
[0125] 4. Vacuum was applied to the flask and slowly increased to a
maximum of 26 inches of mercury.
[0126] 5. Vacuum was continued until the desired percent solids of
the dispersion was reached.
[0127] 6. After the desired amount of distillate was removed, the
vacuum was broken and the resulting product analyzed.
[0128] Properties of the Polyester Dispersion:
4 Percent Solids (NVM) 42.6 Viscosity (cps) 45 pH (units) 7.0
particle size (nm) <80 weight/gal (lbs) 8.9
Example 3
Paint Formulation with a Polyester Dispersion
[0129] Preparation of Paint:
[0130] The dispersed polyester from Example 1 was formulated into a
primer as follows:
[0131] 1. A 228 gram aliquot of resin dispersion prepared as
described in Example 1 was placed in a one liter stainless steel
mixing vessel.
[0132] 2. 9 grams of propylene glycol monobutyl ether and 36 grams
of deionized water were then added to the resin dispersion
[0133] 3. A vertical disperser was then inserted.
[0134] 4. 195 grams of TiO2 (R-960, DuPont) and 5 grams of Raven 16
were added under agitation.
[0135] 5. Approximately 300 grams of 3 mm glass beads were added to
the vessel, and the mixture was dispersed at high speed for 30
minutes to disperse the pigment to a 7 Hegman.
[0136] 6. The mill was slowed to mixing speed, and the following
let down ingredients were added under slow agitation:
[0137] 143 grams of polyester dispersion
[0138] 40 grams of Cymel 301
[0139] 7.2 grams of Nacure 3525
[0140] 0.5 grams of Surfynol 104BC
[0141] 7. After incorporation of these ingredients, the mixture was
filtered through a 25 micron filter cone to remove the glass beads.
The pH then adjusted to 8.2 to 8.5 with AMP-95, and then reduced to
34-36 seconds #4 Ford cup with deionized water.
[0142] The resulting paint had a calculated VOC of less than 2.0
pounds per gallon and 51% weight non-volatile.
[0143] Properties of the Paint:
[0144] The formulated paint was tested by spraying onto high edge
protection electrodeposition coated galvanized steel panels. Film
thickness of the primer was 1.0 mil dry. The painted panel was
flashed at room temperature for 5 minutes, and then flashed an
additional 10 minutes in 180 degrees F. oven. The painted panel was
baked 25 minutes at 330 degrees F. The top three inches of the
panel was masked off and the panel was then top coated with a
commercially available automotive waterborne base coat/clear coat
system and baked 20 minutes at 275 degrees F. Adhesion was then
checked with a 3 mm crosshatch of both the primer to electrocoat
only area and the top coated area of the panel. Excellent adhesion
was noted in both areas of the panel. The bottom half of the panel
was the chipped in a Q-Panel Gravelometer machine with 2 pints of
gravel at -20 degrees C. Excellent chip resistance was noted.
5 Adhesion Ratings: Gravelometer Rating: GM8 Primer only 0 topcoat
1 where 0 = no failure 1 = less than 5% failure
Example 4
Paint Formulation with Polyester Dispersion
[0145] Preparation of Paint:
[0146] The dispersed polyester from Example 2 was formulated into a
primer as follows:
[0147] 1. A 201 gram aliquot of resin dispersion prepared as
described in Example 2 was placed in a one liter stainless steel
mixing vessel
[0148] 2. 15 grams of butoxy ethanol and 26 grams of deionized
water were then added to the resin dispersion
[0149] 3. A vertical disperser was then inserted
[0150] 4. 151 grams of TiO2 (R-920, DuPont) and 3 grams of Raven 16
were added under agitation.
[0151] 5. Approximately 300 grams of 3 mm glass beads were added to
the vessel, and the mixture was dispersed at high speed for 30
minutes to disperse the pigment to a 7 Hegman.
[0152] 6. The mill was slowed to mixing speed, and the following
let down ingredients were added under slow agitation:
[0153] 106 grams of polyester dispersion
[0154] 56 grams of BL-3175
[0155] 5.4 grams of Cymel 303
[0156] 6.8 grams of Nacure 5528
[0157] 2.2 grams of DC-14
[0158] 7. After incorporation of these ingredients, the mixture was
filtered through a 25 micron filter cone to remove the glass beads.
The pH is then adjusted to 8.2 to 8.5 with DMEA, and then reduced
to 30-32 seconds #4 Ford cup with deionized water.
[0159] The resulting paint had a calculated VOC of less than 2.0
pounds per gallon, and 53%, weight non-volatile.
[0160] Properties of the Paint:
[0161] The formulated paint was tested by spraying onto
electrodeposition coated cold rolled steel panels. Film thickness
of the primer was 1.0 mil dry. The painted panel was flashed at
room temperature for 5 minutes, and then flashed an additional 10
minutes in a 180 degrees F. oven. The painted panel was then baked
25 minutes at 330 degrees F. The panel was the top coated with a
commercially available automotive waterborne basecoat/clearcoat
system and baked 30 minutes at 250 degrees F.
[0162] Adhesion was then checked with a 3 mm crosshatch of the top
coated area of the panel. Excellent adhesion was noted on the
panel. The bottom half of the panel was then chipped in a Erichsen
Chip tester machine with 1.0 kg of steel shot at room temperature.
Excellent chip resistance was noted.
6 Adhesion Rating: Erichsen Rating: 7 Topcoat 0 Where 10 best and 0
worst where 0 = no failure
Example 5
Adhesion Rating Results
[0163] Procedures were conducted in accordance with SAE J400.
7 Symbol Electrocoat Bake Primer Bake U/U 10 .times. 330 F. 25
.times. 275 F. U/T 10 .times. 330 F. 25 .times. 330 F. U/H 10
.times. 330 F. 60 .times. 375 F. T/U 10 .times. 360 F. 25 .times.
275 F. T/T 10 .times. 360 F. 25 .times. 330 F. T/H 10 .times. 360
F. 60 .times. 375 F. H/U 10 .times. 390 F. 25 .times. 275 F. H/T 10
.times. 390 F. 25 .times. 330 F. H/H 10 .times. 390 F. 60 .times.
375 F. U = under bake T = target bake H = over bake 10 .times. 330
F. = 10 minutes at 330 degrees F.
[0164] Polyester Hydroxyl
8 Type Number U/U U/T U/O T/U T/T T/O O/U O/T O/O NPG 118 9/4 3/4
5/9 9/8 9/8 1/1 7/4 1/3 0/1 NPG/HDO 73 1/2 0/1 0/0 3/1 1/1 0/1 0/1
0/1 0/1 NPG 55 0/0 0/1 3/0 0/1 0/1 0/0 0/1 0/1 0/1 Key: 0 = 0%
removed 2 = 5% removed 6 = 25% removed 7 = 45% removed 10 = 95%
removed
Example 6
Chip Rating Results
[0165] Procedures were conducted in accordance with ASTM D3359.
9 2 pint Polyester Hydroxyl chip 2 pint 3 pint 3 pint Type Number
no. chip size chip no. chip size comment NPG 118 5 B 4 rating B
lower end of standard rating hydroxyl range (100-200) BEPD 110 4 B
3 rating B lower end of standard rating hydroxyl range (100-200)
NPG/HDO 117 5 B 3 rating B lower end of standard rating hydroxyl
range (100-200) BEPD 117 4 B 4 rating B lower end of standard
rating hydroxyl range (100-200) NPG/BEP 66 5 A 4 rating A target
range-lower than rating average NPG/HDO 73 5 A 4 rating A target
range-lower than rating average NPG/BEP 72 5 A 4 rating A target
range-lower than rating average NPG 55 5 A 4 rating A target
range-lower than rating average BEPD 65 5 A 4 rating A target
range-lower than rating average NPG 38 5 A 4 rating A extremely low
hydroxyl rating Chip number ratings: 5 = 25-49 chips per standard
area
[0166] Numerous modifications and variations in practice of the
invention are expected to occur to those skilled in the art upon
consideration of the foregoing detailed description of the
invention. Consequently, such modifications and variations are
intended to be included within the scope of the following
claims.
* * * * *