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Description  |
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This invention is directed to a dust free heat fusible improved injection
moldable phenol-aldehyde composition in pellet form and more particularly
to such pellets having a coating thereon.
BACKGROUND OF THE INVENTION
Phenolic molding compositions have been available for many years and
generally consist of phenol-formaldehyde resin blended with various
fillers. The molding compositions are prepared by blending a one-stage or
two-stage phenol-formaldehyde resin with fillers and then working the
material between differential hot rolls in order to soften the resin and
obtain a more uniform blend of the constituents. The composition is then
cooled, crushed, screened for some degree of uniformity of particle size.
Unfortunately, such molding compositions are dusty, lack uniform size, and
do not lend themselves readily to the new method of injection molding of
thermosettable resins. The time of contact with the hot rolls is critical,
and the process does not result in a uniform blend of all the constituents
as well as being costly because of the many steps to the final molding
composition.
While it has been disclosed in patent application Ser. No. 500,113 filed
Aug. 23, 1974 of Thornton R. Calkins titled AN INJECTION MOLDABLE
THERMOSETTABLE COMPOSITION AND PROCESS, filed on the same day as the
instant application which in turn is a continuation-in-part of patent
application Ser. No. 303,844, filed Nov. 6, 1972 and now abandoned, that
injection moldable thermosettable compositions can be prepared in pellet
form having in admixture with the pellets certain materials, the
compositions lacked the critical feature of being dust free. As is known,
the dusting of materials is becoming a critical feature within the various
industries because of the health situation arising through dust that may
occur in the various manufacturing operations.
DESCRIPTION OF THE INVENTION
It has now been surprisingly discovered that an improved heat fusible
thermosettable phenol aldehyde molding resin composition can be prepared
which is essentially completely dust free, is suitable for injection
molding in apparatus used for the injection molding of thermoplastics, is
generally glossy in appearance but not essential, has a high density, has
uniform pellet size and has extreme ease in molding and handling. The
pellets employed in the practice of this invention are those prepared in
accordance with and described in Applicant's co-pending patent application
Ser. No. 500,113 filed Aug. 23, 1974 of Thornton R. Calkins titled AN
INJECTION MOLDABLE THERMOSETTABLE COMPOSITION AND PROCESS, filed on the
same day as the instant application which in turn is a continuation in
part of patent application Ser. No. 303,844 filed Nov. 6, 1972 and now
abandoned, which discloses the pellets prepared in accordance therewith
for use in injection molding apparatus.
It has now been discovered that these pellets can be made dust free with
excellent molding characteristics as described above. The pellets are
prepared and made dust free by blending the pellets with a particular
composition which in turn uniformly coats the pellets to provide pellets
which are dust free and may be glossy and are injection moldable. The
composition applied to the pellets may be applied by any of the known ways
of mixing or blending ingredients. The resulting pellets are essentially
coated with the composition and are thus dust free.
The particular coating employed in the practice of this invention comprises
a mixture of (1) a metallic salt of a long chain fatty acid of 8-20 carbon
atoms and (2) a particular material which may be either an alkyl ester of
an aromatic acid, or an alkyl ester of an aliphatic acid, either of which
may be used alone or in combination with a polyglycol or a polyglycol
ester, or mixtures of the polyglycol and polyglycol ester. It has been
discovered that the use of either one of these component parts does not in
itself provide a dust free pellet for injection molding.
It is the combination of these ingredients that is necessary to provide the
dust free injection moldable thermosettable pellets of the instant
invention.
PREFERRED EMBODIMENT OF THE INVENTION
The following examples are set forth to illustrate more clearly the
principle and practice of this invention to those skilled in the art and
unless otherwise specified, where parts or percentages are mentioned, they
are parts or percentages by weight.
EXAMPLE I
A phenol-formaldehyde resin is prepared by reacting about 0.7 moles of
formaldehyde per mole of phenol in the presence of an acid catalyst, which
is subsequently neutralized, to form a novolac.
The novolac is ground to a fine particle size with about 16 weight percent
of hexamethylenetetramine based on the weight of novolac. The resin
mixture is then blended with about 35 weight percent of asbestos fibers
and about 15 percent weight of wood flour to form a 50/50 mixture. The
blend is then compounded in a screw extruder at about 220.degree.F which
is sufficient to melt the resin. The molten mixture is advanced through
the screw extruder and extruded through a die orifice of about one-eighth
inch in diameter. The extrudate is then comminuted into pellets of about
one-eighth inch long. The pellets are cooled rapidly to prevent
advancement in molecular weight of the resin and to prevent coagulation of
the pellets. The pellets are essentially uniform in size.
The pellets are then blended in a container on rolls with a composition
consisting of 0.3 part of dibutyl phthalate and 0.1 part of zinc stearate
per 100 parts of the pellets. The material is blended for about 10
minutes.
The resulting pellets are free flowing, completely dust free with a glossy
surface. After standing for 3 months, the pellets are still free flowing,
dust free and have a glossy surface.
EXAMPLE II
Example I is repeated except that the pellets are blended with a
composition consisting of 0.2 part of dibutyl phthalate, 0.1 part of
polyethylene glycol monooleate and 0.1 part of zinc stearate.
The results obtained are the same as in Example I.
EXAMPLE III
Example I is repeated except that the pellets are blended with only 0.3
part of dibutyl phthalate.
The resulting pellets are damp, have a dull coating, but are dust free.
After one (1) month of standing, the pellets are extremely dusty.
EXAMPLE IV
Example I is repeated except that the pellets are blended with 0.1 part of
zinc stearate alone.
The resulting pellets are dusty and dull in appearance.
EXAMPLE V
Example I is repeated except that the pellets are blended with the
following compositions:
a.
0.3 part of dibutyl phthalate
0.1 part of calcium stearate
b.
0.3 part of dibutyl phthalate
0.1 part of lithium stearate
c.
0.7 part of diethyl phthalate
0.25 part of calcium stearate
d.
0.25 part diisooctyl phthalate
0.25 part of zinc stearate
0.25 part of glycerol
e.
0.5 part of dioctyl adipate
0.1 part of zinc stearate
f.
0.5 part of diisooctyl sebacate
0.1 part of zinc stearate
The results obtained with all of the above compositions are the same as in
Example I.
The instant application is directed to an improved heat fusible
thermosettable injection moldable phenol-aldehyde composition in pellet
form having a diameter of at least one-sixteenth inch. The improvement in
the composition consists of the pellets having a particular coating on the
surface thereof. The particular coating comprises in admixture (1) a
metallic salt of a long chain fatty acid of 8-20 carbon atoms and (2) a
material which may be either (a) an alkyl ester of an aromatic acid, or
(b) an alkyl ester of an aliphatic acid. In addition, (a) or (b) may be
used alone or in admixture with each other or in admixture with a
polyglycol, or a polyglycol ester, or with mixtures of the polyglycol and
the polyglycol ester. The composition of the coating may be added to the
pellets by any known conventional means such as blending in a jar on
rolls, merely stirring in a container, a ribbon blender, etc. The coating
ingredients may be added to the pellets either as a paste or as a hot
liquid mixture or as a hot liquid solution or as a hot slurry or
individually. For example, a paste may be made by dissolving the
ingredients of the coating composition at an elevated temperature of about
120.degree.C, which temperature is not critical, and then cooling to form
a paste, which is then blended with the pellets. Alternatively, the
coating composition may be left as a hot liquid and added to the pellets
in that manner. The method of applying the coating composition of the
instant invention is not critical. The preferred characteristic of the
coating composition of this invention is such as to result in either the
wetting of or the dissolving of, partially or completely, the metallic
salt of the long chain fatty acid component. The coating composition must
further be one which has a low volatility at room temperature and must be
one which has a low rate of absorption into the pellet. While the
resulting pellets generally have been found to be glossy in surface
appearance, this is not always a necessary feature of the instant
invention. For example, the pellets with a suitable coating of the instant
invention can be dull in appearance.
In the practice of the instant invention the metallic salts of long chain
fatty acids that can be employed herein in place of the zinc stearate used
in the examples with the same results occurring are lithium, sodium,
potassium, manganese, calcium, barium, zinc, cadmium, and aluminum salts
of saturated or unsaturated monobasic or dibasic, branched or straight
chain fatty acids of 8-20 carbon atoms. Such acids that may be included
within the practice of this invention but are not limited thereto are
palmitic, stearic, lauric, oleic, pimelic, sebacic, adipic, ricinoleic,
and palmitoleic.
The amount of the coating to be employed can vary anywhere from 0.05 to 2.0
parts per 100 parts of the pellets. The component parts of the coating
composition may vary from 0.5 to 10 parts of the alkyl ester of an
aromatic acid or alkyl ester ester of an aliphatic acid or a mixture of
these per one part of the metallic salt of a long chain fatty acid.
Obviously, part of the ester portion of the coating composition can
consist of the polyglycol or the polyglycol ester or mixture thereof. This
portion can preferably be 20-50 weight percent of the ester part of the
coating composition.
In the practice of this invention, some of the alkyl esters of aromatic
acids and alkyl esters of aliphatic acids that can be employed herein are:
diethyl phthalate
diethyl isophthalate
dibutyl phthalate
diamyl isophthalate
di-2-ethoxyethyl phthalate
butyl benzoate
hexylbenzoate
ethyl-2-chlorobenzoate
ethyl-3-methoxy benzoate
methyl-3-methyl benzoate
dibutoxyethyl phthalate
butyl octyl phthalate
dioctyl adipate
diisooctyl sebacate
butyl oleate
dibutyl sebecate
diisodecyl adipate
di(2 ethyl hexyl) adipate
dibenzyl sebacate
and combinations or mixtures thereof. In addition, some of the polyglycols
and polyglycol esters that can be employed in the practice of this
invention are:
glycerine
glycerol esters of fatty acids of 8-20 carbon atoms
polyethylene glycol
polypropylene glycol
glyceryl monooleate
polyethylene glycol dioctoate
polyethylene glycol monooleate
The pellets of the instant application are prepared by feeding to a screw
extruder a thermosettable phenol-aldehyde composition, which composition
consists of a phenol-aldehyde resin, a cross linking agent, and fillers.
The composition is advanced through the screw extruder while being
subjected to a temperature of less than 290.degree.F and preferably
200.degree.F to 240.degree.F which must be sufficient to render the
phenol-aldehyde resin molten. The composition is advanced through the
screw extruder and extruded through a die orifice of at least
one-sixteenth inch in diameter and preferably about one-eighth inch in
diameter. The extrudate is then comminuted into pellets and can be, if
necessary, rapidly cooled to prevent advancement of the phenol-aldehyde
resin and to prevent pellet agglomeration.
The term "pellet" herein means a solid of any shape including spherical,
cylindrical, ellipsoidal, etc. and any variations of these shapes.
However, the pellet must have one dimension of at least one-sixteenth
inch.
The phenol-aldehyde resin employed in the practice of this invention can be
any phenol-aldehyde resin which is prepared by reacting from less than one
mole to more than one mole of an aldehyde per mole of phenol under certain
conditions to provide a resin. If less than one mole of an aldehyde is
used, the resin so produced is commonly called a novolac. The novolac
resin is generally the type that can be finely ground and requires
blending thereof with an external crosslinking agent such as
hexamethylenetetramine in order to provide a thermosettable resin which
can be advanced to an infusible state upon exposure to elevated
temperatures. While any external crosslinking agent can be employed
herein, the preferred external crosslinking agent is
hexamethylenetetramine. Generally, the preferred range of aldehyde
employed herein to provide the novolac is 0.5-0.9 moles thereof per mole
of phenol and preferably 0.6-0.8 moles thereof. While any aldehyde can be
employed herein such as formaldehyde, paraformaldehyde, acetaldehyde,
butyraldehyde, furfuraldehyde, etc., the preferred aldehyde to be employed
herein is formaldehyde.
When employing more than one mole of aldehyde per mole of phenol, a
one-stage resin is produced which can be advanced to an infusible state by
the mere application of elevated temperatures. The one-stage resin which
can be employed herein is one prepared by reacting more than one mole of
an aldehyde per mole of phenol and preferably 1.3-3.0 moles thereof.
Again, the preferred aldehyde is formaldehyde. The one-stage resin best
suited for the preparation of molding compounds is in the powdered form.
The fillers that can be employed herein are well known in the phenolic
molding compound art. These fillers include such materials as asbestos
fibers, wood flour, cotton flock, cellulose flock, wool flock, aluminum
silicate, calcium carbonate, talc, glass fibers, etc., and any combination
of these or other known fillers employed in the phenolic molding
composition art. In addition, there is also employed such additives as
lime, stearic acid, etc.
It will thus be seen that the objects set forth above among those made
apparent from the preceding description are efficiently attained and since
certain changes may be made in carrying out the above process and in the
composition set forth without departing from the scope of this invention,
it is intended that all matters contained in the above description shall
be interpreted as illustrative and not in a limiting sense.
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