Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02470193 2004-06-30
TIME RELEASED CURING SYSTEM
FIELD OF THE INVENTION
[0001] The present invention relates to a curable urea formaldehyde binder
composition
useful in coated abrasive and engineering wood products. The composition
includes a
curable urea formaldehyde resin and an aryl phosphite.
BACKGROUND OF THE INVENTION
[0002] This invention relates to abrasive articles in which a thin layer or,
more usually, a
single layer of abrasive grit is adhesively bonded to a backing. Such products
are coated
abrasives, more commonly referred to as "sandpaper," and fibrous abrasive
pads, for
example. Conventionally, glue or thermosetting resins such as phenol
formaldehyde resins
("PF resins") and urea formaldehyde resins ("UF resins") have been used in
coating
formulations. UF resins, which are less expensive than phenolic resins, have
been used to
reduce the cost in abrasive products. However, current UF resin systems used
in the
manufacture of coated abrasive products do not provide desirable working times
and curing
times under ambient or near ambient conditions. The coated abrasive industry
is seeking
time released curable urea formaldehyde binder compositions in order to have
enough
working time, yet faster curing to provide a sharp image and non-curled sand
paper.
[00031 Phenolic resin compositions are known that can cure at ambient
temperatures with
rapid cure at modestly higher temperatures. Such resins, as in U.S. Patent No.
5,296,520 to
Gerber, provide controlled work time for hardening phenolic resins at ambient
temperature
using aryl phosphite latent acid catalysts. However, Gerber found that urea
and other amide
compounds were very effective retarders of ambient temperature hardening of
the resin with
the aryl phosphite hardening agents.
100041 Nevertheless, UF resins are different from phenolic resins and each
have vastly
different chemistry and methods of manufacture. UF resins are prepared by a
condensation
whereby the nitrogen of urea reacts with the carbonyl group of formaldehyde.
In contrast, an
exemplary phenolic polymer is a phenol formaldehyde resin prepared by aromatic
substitution of the multiple activated sites of a phenol, initially by
formaldehyde, followed by
reaction with other reactive intermediates. In the preparation of phenolic
resins, catalysts
such as strong base, zinc acetate, and borates can be used to provide phenolic
resoles, while
strong acid can be used to provide phenolic novolacs. UF resins can be
prepared using a
strong acid catalyst, such as, for example, sulfuric acid. Structurally,
phenolic resins are
CA 02470193 2008-07-24
highly aromatic, and contain aromatic end groups. In contrast, UF resins are
amino
resins and essentially non-aromatic. Regarding curing properties, phenolic
polymers
range from thermosetting resoles to thermoplastic novolacs. UF resins are
thermosetting
resins. Accordingly, PF resin chemistry is not predictive of UF resin
chemistry, as shown
by Gerber, op. cit.
[0005] UF precondensates can be blended with liquid phenolic resin systems.
However, such systems are catalyzed by providing a basic environment (pH above
7), in
contrast to the acid catalyst used for unblended urea formaldehyde
prepolymers.
[0006] Accordingly, curable urea formaldehyde binder compositions employing a
latent acid hardening component are needed that will provide desirable working
times
and curing times under ambient or near ambient conditions. The results
presented below
provide surprising and unexpected improvements in urea formaldehyde based
binder
compositions.
SUMMARY OF THE INVENTION
[0007] In one embodiment of the present invention, there is provided a curable
binder
composition, including a urea formaldehyde resin and an aryl phosphite.
In another embodiment of the present invention, there is provided a curable
binder composition, including a urea formaldehyde resin; and an aryl phosphite
in an
amount ranging from about 0.05% by weight to about 15% by weight, based on the
total
weight of the resin.
The invention also provides a coated abrasive article including the cured
binder
of the invention; and an engineered wood article including the cured binder of
the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] There is provided in accordance with one embodiment of the present
invention
a curable binder composition using varying concentrations of aryl phosphites.
The
unique advantages of the curing system include: improvement in the color of
the urea
formaldehyde binder to enhance the final product appearance, such as in sand
paper; and
faster curing to save energy in the engineering wood products industry. The
color
improvement is largely due to the aryl phosphite component. Aryl phosphites,
acting as
anti-oxidants, are known as stabilizers in a wide range of polymers.
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CA 02470193 2004-06-30
`} v
100091 In another embodiment of the present invention there is provided a time
released
curable urea formaldehyde binder composition. It has been discovered that aryl
phosphites,
for example triphenyl phosphite, act as accelerators in the pre-formulated
curable binder, but
in a time released fashion, wherein the determining parameter is temperature.
For example,
the curing system is stable under about 70 F (about 21 C), but the curing
reaction
accelerates above about 80 F (about 27 C). Working times range from about
0.5 hours to
over 100 hours. The aryl phosphites of the present invention can be used in an
amount
ranging from about 0.05% by weight based on the total weight of the resin to
about 15% by
weight based on the total weight of the resin. Urea formaldehyde resins are
particularly
useful in the binder compositions. Thus, this time released curable binder
composition is
useful for coated abrasive products and engineering wood applications.
[00101 The terms "hardening" and "curing" are used interchangeably herein.
100111 The aryl phosphite hardeners of this invention are esters of
phosphorous acid
which have: two aromatic organic ester groups and an acid hydrogen, three
aromatic ester
groups, or two aromatic ester groups and one alkyl group. Illustratively, the
hardener can be
a disubstituted phosphorous acid ester such as diphenyl hydrogen phosphite
("DPP") or a
trisubstituted phosphorous acid ester such as triphenyl phosphite ("T.PP").
[001.21 In the presence of water, the aryl phosphites of this invention
hydrolyze in a
controllable manner over a period of time to stronger acidic products and
eventually to
phosphorous acid. Phosphorous acid is a strong acid having an ionization
constant pKa of
1.20. Phosphorous acid is sufficiently acidic to provide ambient temperature
hardening or
near ambient temperature hardening of urea formaldehyde resins,
[00131 The aryl phosphite hardening agents of this invention can be
represented by the
general formula (I)
(Ar-O)2-P-OX
(I)
wherein Ar is aryl and X is selected from hydrogen, aryl, or alkyl. The aryl
phosphites
having two ester groups and a hydrogen atom, e.g. diphenyl hydrogen phosphite,
are also
referred to herein and in the literature as simply by the name of the ester
groups and omit the
hydrogen, e.g., diphenyl, phosphite ("DPP"). Useful aryl phosphite hardeners
include:
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diphenyl hydrogen phosphite (DPP); dicresyl (preferably meta or para) hydrogen
phosphite;
phenyl p-cresyl hydrogen phosphite; phenyl m-cresyl hydrogen phosphite;
dinaphthyl
hydrogen phosphite; diphenyl isopropyl phosphite; diphenyl methyl phosphite,
di(p-cresyl)
hexyl phosphite, triphenyl phosphite (TPP), tri(m-cresyl) phosphite, diphenyl
isooctyl
phosphite, diphenyl 2-ethylhexyl phosphite, diphenyl isodecyl phosphite,
diphenyl
cyclohexyl phosphite, 2-chloroethyl diphenyl phosphite, and the like. One
useful commercial
DPP solution is DOVERPHOS'213, available from Dover Chemical Corp., Dover,
Ohio.
One useful commercial TPP solution is DOVERPHOS'*10, available from Dover
Chemical
Corp., Dover, Ohio.
100141 The work time of the resin can vary over a broad range by varying the
total water
content, the use of retarder or accelerator additives, the specific phosphite
hardening agent,
and its quantity, and temperature. The room or ambient temperature hardening
compositions
of this invention can have a working time of about 15 minutes up to about 20
hours. The
Shore D hardness can be measured by use of a Durometer Type D of the Shore
Instrument &
Manufacturing Company located in New York. Another test for ambient
temperature
hardening is measured by use of a stick applicator wherein the composition
consisting of the
urea formaldehyde resin, aryl phosphite and water is "stick hard" as described
in the
Qualitative Flow Procedure set forth hereafter within 24 hours or less after
mixing. The
ambient temperature hardening compositions are preferably those having either
a diaryl
hydrogen phosphite, a triaryl phosphite or a diaryl monoalkyl phosphite. The
triaryl
phosphite or diary] monoalkyl phosphite can be pre-hydrolyzed with from about
I% to 10%
of water based on the weight of the aryl phosphite. The phosphites having 3
organic
substituents can be pre-solvolyzed with water, alkanol, glycol, and mixtures
thereof. The aryl
phosphites of the present invention can be formulated with accelerators.
However, these pre-
treatments would dampen the time release aspect of the present invention.
[0015] Aryl phosphites having three organic substituents, such as triaryl
phosphites or
diaryl monoalkyl phosphites, are preferably used as latent hardeners to
provide extended
periods of stability at ambient temperature for the hardenable compositions
and rapid
hardening at moderately elevated temperatures such as those not above 60 C,
e.g., about 35
C to 50 C. Thus, such hardeners can remain fluid for a period of 5 hours or
more at a
temperature of about 23 C, but cure rapidly at the higher temperatures,
depending on the
level of the aryl phosphite. However, by use of low concentrations of diaryl
hydrogen
phosphites, or small concentrations of water or with retarders, diaryl
hydrogen phosphites as
well as triaryl phosphites or diary] monoalkyl phosphites can also have
extended periods of
* trade-mark
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ambient temperature stability and then be rapidly hardened at moderately
elevated
temperatures.
10016] The viscosity of the basic ingredients, i.e., urea formaldehyde resin,
aryl
phosphite, and water, is capable of remaining flowable at ambient temperature
for a period of
several hours up to over 100 hours, based on the concentration of aryl
phosphite.
100171 The quantity of the aryl phosphite used in this invention can vary over
a wide
range. For example, in the curable urea formaldehyde binder of the present
invention, a
preferred range of aryl phosphite can be present in an amount ranging from
about 0.05% by
weight to about 15% by weight, based on the total weight of the resin. When
DPP is used, a
more preferred range is from about 0.1 % by weight to about 2% by weight,
based on the total
weight of the resin; and a most preferred range is from about 0.30% by weight
to about 2%
by weight, based on the total weight of the resin. When TPP is used, a more
preferred range
is from about 0.25% by weight to about 5% by weight, based on the total weight
of the resin.
100181 The urea formaldehyde resins ("UF resins") of the present invention are
aqueous
resins and are hardenable using hardeners or accelerators. For example, useful
UF resins
have a U:F molar ratio ranging from about 1:1 to about 1:3.5. The UF resins of
the present
invention can have a pH range of from about 4 to about 9. In the present
invention,
formaldehyde scavengers can be employed, e.g. urea, that can be back-added to
a urea-
formaldehyde resin. Modified OF resins can be used in the binders of the
present invention.
100191 Urea-aldehyde resins employed in the coatable binder precursor
compositions
useful in the invention may be comprised of urea or any urea derivative and
any aldehyde
which are capable of being rendered coatable, have the capability of reacting
together at an
accelerated rate in the presence of a catalyst, and which afford an abrasive
article with
abrading performance acceptable for the intended use. The resins comprise the
reaction
product of an aldehyde and a urea. Urea-formaldehyde resins are preferred in
the abrasive
industry, as noted above, because of their thermal properties, availability,
low cost, and. ease
of handling. The urea-aldehyde resins preferably are 30-95% solids, more
preferably 60-80%
solids, with a viscosity ranging from about 125 to about 1500 cps (Brookfield
viscometer,
number 3 spindle, 30 rpm, 25° C.) before addition of water and catalyst
and have
molecular weight (number average) of at least about 200, preferably varying
from about 200
to 700.
CA 02470193 2010-10-05
[0020] A preferred urea-aldehyde resin for use in the present invention is
that
known under the trade designation"AL3029R"from Borden Chemical, Inc.,
Columbus, OR This is an unmodified (i. e. contains no furfural) urea-
fonnaldehyde
resin, 65% solids viscosity (Brookfield, #3 spindle, 30 rpm, 25 C) of 325
cps, a free
formaldehyde content of 0.1-0. 5 weight percent.
[0021] Lowering the pH of the urea formaldehyde resins to about 4 or above by
use
of acids that are as acidic or more acidic than phosphorous acid, i. e. ,
acids having a
pKa of 1.20 or less increases the hardening rate of the resin with the aryl
phosphite in
comparison to the use of acids having a higher pKa. Illustrative of acids
which have a
pKa of 1.2 or less there can be mentioned: sulfamic, oxalic, dichloroacetic,
trichloroacetic, methanesufonic, sulfuric, hydrochloric and phenol sulfonic
acids.
Ammonium chloride can be used as a source of hydrochloric acid and/or a buffer
solution component. Lowering the pH with acids which are less acidic than
phosphorous, such as acetic, fonnic, benzoic, and salicylic acids leads to
lower
reactivity with the phosphite than when the acid is equal to or greater in
acidity than
phosphorous acid.
[0022] Catalysts can also be used in the curable binders of the present
invention.
Examples of useful catalysts include but are not limited to Lewis acids, for
example,
aluminum chloride and the like. Preferred are those Lewis acids selected from
the
group consisting of aluminum chloride, iron (III) chloride, and copper (II)
chloride.
Particularly preferred is the Lewis acid aluminum chloride in either its non-
hydrated
form (Aids) or hexahydrate form (AIC13. 6H20). Useful catalysts also include
aqueous
organic amine salt or ammonium ion salt. If an ammonium ion salt is used it is
preferably a salt of ammonium ion (NH4+) and a halide ion such as chloride ion
(Cl-),
fluoride ion (F-), bromide ion (Br-), and the like. A particularly preferred
ammonium
ion salt is ammonium chloride (NH4C1).
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CA 02470193 2010-10-05
Ammonium sulfate ((NH4) 2SO4), ammonium peroxydisulfate ((NH4) 2S203),
ammonium thiosulfate ((NH4) 2S203), and ammonium nitrate (NH4NO3) are deemed
suitable for use in the invention as useful ammonium ion salts when used
specifically
in combination with A 1 C 13 as cocatalyst. Mixtures of inorganic and organic
salts are
typically, and in some cases, preferably utilized.
In a particular embodiment of the invention there is provided a curable binder
composition, comprising: a urea formaldehyde resin having a urea to
formaldehyde
ratio ranging from 1:1 to 1:3.5; a 25% ammonium chloride solution in an amount
ranging from 2% to 10% by weight based on the total weight of the resin; a 28%
aluminum chloride solution in an amount ranging from 0.1 % to 2% by weight,
based
on the total weight of the resin; water in an amount ranging from 5% to 20% by
weight, based on the total weight of the resin; and an aryl phosphate in an
amount
ranging from 0.05% to 15% by weight, based on the total weight of the resin.
[0023] The hardening reaction of this invention requires water in order to
hydrolyze
the aryl phosphite, e. g. , eventually to phosphorous acid. The total water
content in
the composition, i. e. water available for hydrolyzing the phosphite, can vary
over a
broad range such as that of about 0.15 to 5 parts of water by weight for each
part by
weight of the aryl phosphite, preferably from about 0.3 to 3 parts of water by
weight
for each part of the
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phosphite. The requisite total water content can come from any of the
ingredients in the
composition, e.g., the urea formaldehyde resin, or additional water can be
added to the
composition.
[00241 The compositions of this invention can include fillers, modifiers, and
aggregates
which are conventionally used with urea formaldehyde resins. The aggregate
material may
be a particulate material such as that in granular, powder, or flake form.
Suitable aggregate
materials include but are not limited to: sand, alumina, zirconia, silica,
zircon sand, olivine
sand, silicon carbide, silicon nitride, boron nitride, bauxite, quartz,
chromite, and corundum
and. mixtures thereof. For certain applications, low density aggregate
materials such as
vermiculite, perlite, and pumice are preferred. For other applications,
preferable high density
aggregates include: quartz sand, gravel, crushed rock, and broken brick.
Fillers such as mica,
kaolin, wollastonite, and barites can be used. The compositions of the present
invention can
be used to make coated abrasive articles, for example, sand paper.
[0025] Coatable binder compositions useful in the present invention can
contain fillers,
fibers, lubricants, grinding aids, antistatic agents, wetting agents, and
other additives such as
surfactants, pigments, dyes, coupling agents, plasticizers, dispersants, and
suspending agents.
The amounts of these materials are selected to give the properties desired,
for example
improvement of the wettability of abrasive grains. Alternatively, useful
binder precursor
compositions may be formulated without these additives, and the additives
mixed into the
binder precursor just prior to coating onto a substrate.
100261 The binder compositions of the present invention can include
formaldehyde
scavengers such as, for example, urea and ammonium compounds.
(0027] Fillers are frequently used in abrasive articles to reduce cost and
improve
dimensional stability and other physical characteristics. Fillers can be
selected from any filler
material that does not adversely affect the rheological characteristics of the
binder precursors
or the abrading performance of the resulting abrasive article. Preferred
fillers include
calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite,
magnesia, kaolin, quartz,
and glass. Fillers that function as grinding aids are cryolite, potassium
fluoroborate, feldspar,
and sulfur. Fillers can be used in varying amounts limited only by the proviso
that the
abrasive article retains acceptable mechanical properties (such as flexibility
and toughness)
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[00281 Coated abrasive articles of the invention may be produced by
incorporating cured
versions of the coatable binder precursor compositions described above. The
backing may
either be a polymeric film, paper sheet, or laminate.
[00291 For wood engineering applications, e.g. composite panels and the like,
lignocellulosic materials can be used. Examples of lignocellulosic materials
include, but are
not limited to, wood fiber, wood flake, wood strands, wood chips and wood
particles, straw,
bagasse, wood bark, recycled wood fiber, recycled paper fiber, and mixtures
thereof. The
composite panels produced are known as fiberboard, waferboard, strandboard,
oriented
strandboard, fakeboard, particleboard and the like.
[00301 Several comparison experiments illustrate the utility of the present
invention.
These experiments were designed for abrasive and wood applications; therefore,
co-catalysts
were introduced into the binder formulations. The units for the components of
Curable
Binders A - B were based on the UF resin being set to a given mass and all
other components
were then set to parts per mass of given OF resin. The hardening experiments
using Curable
Binders A - B with viscosity measurements and observations are presented in
Table 1.
Viscosity readings were determined using a Brookfield Viscometer, Model DV-
11+, #18
Spindle, 20 rpm, and the viscosity units are in centipoises (cps). All
reaction times are
calculated from the time of initial mixing of all the components.
Comparison Binder A
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 5 hours from initial mixing, the viscosity of the
reaction mixture
was 116.8 cps. After 5 hours, 30 minutes, the mixture was placed in a 32 C
oven. After 6
hours, 10 minutes, the viscosity of the reaction mixture was 136.5 cps.
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Curable Binder Al
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVCRPIiOS 10 0.84
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 55 minutes from initial mixing, the
viscosity of the
reaction mixture was 122.7 cps. After 5 hours, 20 minutes, the mixture was
placed in a 32 C
oven. After 6 hours, 5 minutes, the viscosity of the reaction mixture was
149.4 cps.
Curable Binder A2
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOV ERPI IOS 10 1.26
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 50 minutes from initial mixing, the
viscosity of the
reaction mixture was 128.3 cps. After 5 hours, 10 minutes, the mixture was
placed in a 32 C
oven. After 6 hours, the viscosity of the reaction mixture was 159.2 cps.
Curable Binder A3
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVERPIIOS 10 3.5
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 1.5 - 20 C bath. 4 hours, 50 minutes from initial mixing, the
viscosity of the
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reaction mixture was 156.3 cps. After 5 hours, 5 minutes, the mixture was
placed in a 32 C
oven. After 6 hours, the viscosity of the reaction mixture was 208.2 cps.
Curable Binder A4
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVLRPIIOS 213 0.21
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 45 minutes from initial mixing, the
viscosity of the
reaction mixture was 188.2 cps. After 4 hours, 55 minutes, the mixture was
placed in a 32 C
oven. After 6 hours, the viscosity of the reaction mixture was 456.5 cps. The
viscosity
continued to rise at about 3.5 cps/second.
Comparison Binder B
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 15 minutes from initial mixing, the
viscosity of the
reaction mixture was 116 cps. After 4 hours, 30 minutes, the mixture was
placed in a 32 C
oven. After 5 hours, 10 minutes, the viscosity of the reaction mixture was
125.4 cps.
Curable Binder B 1
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVBRPITOS 213 0.07
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The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 10 minutes from initial mixing, the
viscosity of the
reaction mixture was 121.8 cps. After 4 hours, 20 minutes, the mixture was
placed in a 32 C
oven. After 5 hours, the viscosity of the reaction mixture was 139.2 cps.
Curable Binder B2
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVERPHOS 213 0.14
The components were mixed thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 4 hours, 10 minutes from initial mixing, the
viscosity of the
reaction mixture was 130.1 cps. Then the mixture was placed in a 32 C oven.
After 4 hours,
50 minutes, the viscosity of the reaction mixture was 164.3 cps.
Curable Binder B3
AL3029R 70
Water 7
25% ammonium chloride 3.64
28% aluminum chloride 0.49
DOVERPHOS 213 0.84
The components were mixed. thoroughly in the order above at ambient
temperature, then
placed in a 15 - 20 C bath. 2 hours, 40 minutes from initial mixing, the
reaction mixture had
gelled, and was still soft.
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TABLE 1. VISCOSITY MEASUREMENTS AND OBSERVATIONS
Binder/ Tine / Temperature Phosphite level Viscosity (cps) `%, Increase /
NO ' Control
A/ 5 hours/ 15 C -- 116.8
A/ 6 hours, 1.0 minutes/ 32 C -- 136.5
A1/ 4 hours, 55 minutes/ 15 C 1.2 (TPP) 122.7
Al! 6 hours, 5 minutes/ 32 C 1.2 (TPP) 149.4 9.4
A2/ 4 hours, 50 minutes/ 15 C 1.8 (TPP) 128.3
A2/ 6 hours / 32 C 1.8 (TPP) 1.59.2 16.6
A3/ 4 hours, 50 minutes/ 15 C 5.0 (TPP) 156.3
A3/ 6 hours/ 32 C 5.0 (TPP) 208.2 52.5
A4/ 4 hours, 45 minutes/ 15 C 0.3 (DPP) 188.2
A4/ 6 hours/ 32 C 0.3 (DPP) 456.5 334
B/ 4 hours, 15 minutes/ 15 C -- 116
B/ 5 hours, 10 minutes/ 32 C -- 124.5
B1/ 4 hours, 10 minutes/ 15 C 0.1 (DPP) 121.8
B1/ 5 hours/ 32 C 0.1 (DPP) 139.2 11.8
132/ 4 hours, 10 minutes/ 15 C 0.2 (DPP) 130.1
B2/ 4 hours, 50 minutes/ 32 C 0.2 (DPP) 164.3 32.0
B3/ 2 hours, 40 minutes/ 15 C 1.2 (DPP) Not measurable,
Gelled
Based on resin weight; Phosphite is indicated as DPP or TPP
2 Time is cumulative for each example
100311 As shown in Table 1 above, the binder compositions of the present
invention can
be engineered to cure in a time released fashion useful for making, for
example, coated
abrasive products. The curing properties of binders having different levels of
aryl phosphite
are compared. Unexpected improvements in viscosity were observed at relatively
low levels
of aryl phosphite in the binder. For example, for DPP levels of 0.2 to 0.3%,
viscosity
increased. 32% and 334%, respectively. At higher DPP levels, hardening was
even more
rapid. Additionally, for TPP levels of 1.8 and 5.0%, viscosity increased 17%
and 52%,
respectively. Increasing the temperature along with an effective amount of
aryl phosphite can
also accelerate curing in the binders of the present invention.
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[0032] There has been disclosed in accordance with the principles of the
present
invention a curable urea formaldehyde binder composition including an aryl
phosphite
hardener that acts as an accelerator in a time released fashion. The time
released curable urea
formaldehyde binder composition is useful, for example, in coated abrasive
articles.
Although the above examples are intended to be representative of the
invention, they are not
intended to limit the scope of the appended claims. It will be apparent to
those skilled in the
art that modifications may be made therein without departing from the spirit
of the invention
and the scope of the appended claims.
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