Note: Descriptions are shown in the official language in which they were submitted.
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
TITLE
TOUGHENED NYLON COMPOSITIONS WITH IMPROVED FLOW
AND PROCESSES FOR THEIR PREPARATION
FIELD OF THE INVENTION
This invention relates to toughened polyamide compositions and processes
for their preparation. More specifically, this invention relates to such
compositions toughened with rubber or ionomer, which incorporate organic acids
to desirably decrease viscosity but without significantly reducing the
toughness
thereof, together with methods for their preparation.
BACKGROUND OF THE INVENTION
High flow (or low melt viscosity, as these terms are used interchangeably)
is a very desirable characteristic of an injection molding resin. A resin with
higher flow or lower melt viscosity can be injection molded with greater ease
compared to another resin which does not possess this characteristic. Such a
resin
has the capability of filling a mold to a much greater length at lower
injection
pressures and temperatures and greater capability to fill intricate mold
designs
with thin cross-sections. It is well known that the melt viscosity of a
polymer is
directly proportional to its molecular weight. It is also well known that the
melt
2o viscosity of a polymer, especially at low shear rates are much higher for a
branched polymer compared to a linear polymer at the same molecular weight. It
is also well known that polyamide polymers react with organic acids and amines
when added in the melt causing a reduction in its molecular weight. This
method
is sometimes used to increase the flow or lower the melt viscosity of a
polyamide
polymer.
The presence of a dispersed phase such as mineral and glass
reinforcements in a polymer results in increased melt viscosity. The presence
of a
dispersed phase of an incompatible polymer also results in an increase in the
melt
viscosity. To be able to form a stable dispersion, the toughener is generally
3o functionalized with for example, anhydride or epoxide. Thus, generally,
mbber-
toughened polyamides containing dispersed rubber have melt viscosities much
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
higher than the original polyamide polymer. It is also well known that to
obtain
good toughness and to optimize dispersion of incompatible polymers such as
olefin rubbers and/or ionomers with polyamides, the melt viscosities of the
two
polymers must be fairly close to each other.
The advantages of reduced viscosity resins are well known to those skilled
in the practice of injection molding. However, the most highly desirable
combination of properties was previously not available. For example,
tougheners
such as are disclosed in US 4,174,358, incorporated herein by reference, can
be
l0 utilized in improving the toughness of polyamide resins by melt blending
polyamide resins with low tensile modulus copolymers that have adherent sites
to
obtain a highly toughened polyamide material. However, addition of tougheners
also increases the viscosity of the resin. This fact has inevitably led to
compromises in property selection.
Preparation of tough, high melt flow polyamides has also been addressed
somewhat in the literature. For example, US 5,274,033 discloses blending of
low
molecular weight polyamide into the toughened polyamide blend as a route to
production of a high flow toughened polyamide. While quite suitable, this has
the
disadvantage of adding expensive process steps such as preparation of the low
molecular weight polyamide. Meeting the objective of producing high melt flow
toughened polyamides in an easily commercial step had previously eluded the
trade.
It is an object of the present invention to provide toughened nylon
compositions exhibiting improved flow as compared to conventional resins
during injection molding operations. It is a further object of the invention
to
provide rubber or ionomer-toughened nylon compositions that exhibit such
desirable flow characteristics while not detracting from their toughness. A
feature
of the present invention is its applicability across a wide range of process
conditions. An advantage of the invention is the incorporation of organic
acids
into the polyamide-functionalized rubber or ionomer system to enhance flow but
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
without sacrificing toughness properties. These and other objects, features
and
advantages will become better appreciated upon having reference to the
following
description of the invention herein.
SUMMARYOFTHE INVENTION
Toughened polyamide compositions are provided, comprising:
(a) 40-94 percent by weight polyamide;
(b) 6-60 percent by weight toughener selected from the group consisting of
rubber and ionic copolymer; and
(c) up to 10 percent by weight organic acid.
Useful polyamides in conjunction with the compositions of the invention
include those listed throughout the description, together with blends and
copolymers thereof. The toughener is preferably used in amounts of from about
8 to about 40 percent by weight, and most preferably from about 10 to about 30
percent by weight.
In a preferred embodiment of the invention, the polyamide compositions
comprise 50-94 weight percent polyamide, 6-~0 weight percent of the toughener,
and up to 10 weight percent of organic acid.
Any number of organic acids may be selected. Organic acids are organic
compounds of C, H, and O containing one or more carboxylic acid
functionalities.
Examples of suitable organic acids include adipic acid, pimelic acid, suberic
acid,
azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid (all
dicarboxylic acids); and, valeric acid, trimethylacetic acid, caproic acid,
and
caprylic acid (all monocarboxylic acids). Dodecanedioic acid ("DDDA") is of
particular interest.
There is also disclosed and claimed herein processes for the preparation of
toughened polyamide compositions exhibiting high flow and toughness,
3
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
comprising melt-mixing in a conventional extruder 40-94 p~rcenl by weight
polyamide, 6-60 percent by weight toughcner selected from the group consisting
of rubber and ionic copolymer, and up to I(> percent by wei<;ht organic acid.
There are many process variations contemplated herein. For example, the
polyamide, toughener and organic acid may be melt-mixed as one step; a blend
of
polyamide and toughener may be melt-mixed with the acid; or polyamide and
toughener may be blended and subsequently melt-mixed with the acid. Further,
melt-mixing may be effected by extrusion or molding alone or in combination.
1o
DETAILED DESCRIPTION OF THE INVENTION
A process is herein provided for the manufacture of rubber-toughened
nylon compositions with improved flow during injection molding. It has been
discovered that a rubber-toughened nylon composition can be produced by the
15 addition of organic acids added during the melt compounding step.
Rubber-toughened polyamide compositions have been commercially
available for more than twenty years. The technology involves incorporating an
olefinic rubber in the polyamide. This is often done in the melt phase. The
rubber dispersion must be fairly stable, i. e., the rubber phase must not
coalesce
2o substantially during subsequent melt processing such as injection molding.
Since
olefinic rubbers are incompatible with polyamides, it is necessary to modify
the
rubber with functional groups that are capable of reacting with the acid or
amine
ends in the polyamide polymer. The reaction of an anhydride with amine is very
fast, therefore, an anhydride is often the functionality of choice. When an
?5 incompatible olefinic rubber with an anhydride functionality is mixed with
a
polyamide, the anhydride functionality of the rubber reacts with the amine
ends of
the polyamide resulting in the rubber becoming grafted on the polyamide
molecule. This molecular bonding minimizes coalescence of the robber phase.
The use of ionic copolymers to produce toughened nylon blends is well
,o known in the art. See for example US 3,845,163 which discloses blends of
nylon
and ionic copolymers. Further, US x,688,868 discloses the preparation of such
a
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
toughened blends wherein the ionic copolymer is prepared in-situ with very
high
levels of neutralization. USP 5,091,478 discloses flexible thermoplastic
blends
wherein the nylon component may be between ?~-50 volume % with the
polyamide comprising at least one continuous phase of the composition.
Finally,
US 5,866,68 covers ionomer i polyamide blends in the range 40-60 weight
percent ionomer and 60-40 weight percent polyamide. The present invention may
be applied to the types and ranges of ionic copolymers as disclosed therein.
The reaction between the functionality of the toughener and the end
to groups of the polyamide is necessary for the grafting to occur., For
example, with
the anhydride-amine end, reaction is necessary in order for the rubber
toughening
to occur. Any significant interference with this reaction will impact
negatively on
the toughening. It is also important that the melt viscosities of the rabber
and the
polyamides are close to each other to accomplish good dispersion. The
discovery
15 herein involves a process for the preparation of a rubber-toughened
polyamide
wherein excess organic acid is incorporated in the polyamide-functionalized
rubber system without negative impact on the toughness of the system. Without
intending to be limited to any particular theory, it is thought that the added
organic acids react with the polyamide decreasing the polyamide molecular
2o weight and its melt viscosity without apparent interference with the
toughening
chemistry. This is very surprising because the expected interference of the
organic acids on the anhydride-amine end reaction and the negative effect of
lowered melt viscosity did not have an impact on toughness.
Those skilled in the art will appreciate that the above described benefits are
25 suitable for a wide range of polyamide compositions. Without intending to
limit
the generality of the foregoing, the following are of particular interest:
~ Polyamides selected from the group consisting of nylon-4,6, nylon-6,6,
nylon-6,10, nylon-6,9, nylon-6,12, nylon-6, nylon-1 I , nylon-12, 6T
3o through 12T, 6I through 12I, polyamides formed from 2-
methylpentamethylene diamine with one or more acids selected from the
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
group consisting of isophthalic acid and terephthalic acid, and blends and
copolymers of all of the above.
~ Notched Izod toughnesses of at least 3.0 ft-lb (however, compositions
featuring lower Notched Izod values are observed as the rubber or ionomer
content is decreased).
The polyamides disclosed herein are also used in blends with other
polymers to produce engineering resins. The blends of this invention may also
contain certain additional polymers that could partially replace the polyamide
component. Examples of such additional polymers are melamine formaldehyde,
phenol formaldehyde (novolac), polyphenylene oxide (see for example EP 0 936
237 A2), polyphenylene sulfide, polysulfone and the like. These polymers can
be
added during the mixing step. It will be obvious to those skilled in the art
that the
present invention relates to modification of the polyamide component and that
additional polymers could be added appropriately without departing form the
spirit of this present invention.
Representative tougheners useful in the practice of this invention include
many branched and straight chain polymers and block copolymers and mixtures
?o thereof. These are represented by the formula:
Ar~~-BrerCr~~-Drn~-Ere-F~-Gr~-Hr~~,
derived in any order, e.g., random, from monomers A to H where
A is ethylene;
B is CO;
C is an unsaturated monomer taken from the class consisting of a ~3-
ethylenically unsaturated carboxylic acids having form 3 to 8 carbon atoms,
and
derivatives thereof taken from the class consisting of monoesters of alcohols
of 1
:o to 29 carbon atoms and the dicarboxylic acids and anhydrides of the
dicarboxylic
acids and the metal salts of the monocarboxylic, dicarboxylic acids and the
monoester of the dicarboxylic acid having from 0 to 100 percent of the
carboxylic
acid groups ionised by neutralization with metal ions and dicarboxylic acids
and
6
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
monoesters of the dicarboxylic acid neutralized by amine-ended caprolactain
oligomers having a DP to 6 to 24;
D is an unsaturated epoxide of 4 to 1 1 carbon atoms;
E is the residue derived by the loss of nitrogen from an aromatic sulfonyl
azide substituted by carboxylic acids taken from the class consisting of
monocarboxylic and dicarboxylic acids having from 7 to 12 carbon atoms and
derivatives thereof taken from the class consisting of monoesters of alcohols
of 1
to 29 carbon atoms and the dicarboxylic acids and anhydrides of the
dicarboxylic
acids and the metal salts of the monocarboxylic, dicarboxylic acids and the
monoester of the dicarboxylic acid having form 0 to 100 percent of the
carboxylic
acid groups ionized by neutralization with metal ions;
F is an unsaturated monomer taken form the class consisting of acrylates
esters having form 4 to 22 carbons atoms, vinyl esters of acids having form 1
to
carbon atoms (substantially no residual acid), vinyl ethers of 3 to 20 carbon
15 atoms, and the vinyl and vinylidene halides, and nitrites having from 3 to
6
carbon atoms;
G is an unsaturated monomer having pendant hydrocarbon chains of 1 to
12 carbon atoms capable of being grafted with monomers having at least one
reactive group of the type defined in C, D and E, and pendant aromatic groups
2o which my have 1 to 6 substituent groups having a total of 14 carbon atoms;
and
H is an unsaturated monomer taken from the class consisting of branched,
straight chain and cyclic compounds having from 4 to 14 carbon atoms and at
least one additional nonconjugated unsaturated carbon-carbon bond capable of
being grafted with a monomer having at least one reactive group of the type
?5 defined in C, D and E.
The aforementioned monomers may be present in the polymer in the
following mole fraction:
(a) 0 to 0.95;
(b) 0 to 0.3;
(c) 0 to 0.~;
(d) 0 to 0.~;
(e) 0 to O.J;
7
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
( t~ 0 to 0.99;
(g) 0 to 0.99; and
(h) 0 to 0.99
so that the total of all components is a mole fraction of 1Ø
Preferably (a) to (h) are present in the following mole fraction:
(a) 0 to 0.9;
(b) 0 to 0.2, most preferably 0.1
to 0.2
1o (c) 0.0002 to 0.2 most preferably
0.002 to 0.05;
(d) 0.005 to 0.2, most preferably
0.01 to 0.1;
(e) 0.0002 to 0.1, most preferably
0.002 to 0.01;
(f) 0 to 0.98;
(g) 0 to 0.98; and
t s (h) 0 to 0.98
The blends of this invention may also contain one or more conventional
additives such as stabilizers and inhibitors of oxidative, thermal, and
ultraviolet
light degradation, lubricants and mold release agents, colorants including
dyes
2o and pigments, flame-retardants, plasticizers, and the like. These additives
are
commonly added during the mixing step. They may be added in effective
amounts as is readily appreciated by those having skill in the art.
Representative oxidative and thermal stabilizers which may be present in
blends of the present invention include halide salts, e.g:, sodium, potassium,
25 lithium with copper salts, e.g., chloride, bromide, iodide; hindered
phenols,
hydroquinones, and varieties of substituted members of those groups and
combinations thereof.
Representative ultraviolet light stabilizers, include various substituted
resorcinols, salicylates, benzotriazoles, benzophenones, and the like.
3o Representative lubricants and mold release agents include stearic acid,
stearyl alcohol, and stearamides. Representative organic dyes include
nigrosine,
8
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
while representative pigments, include titanium dioxide, cadmium sulfide,
cadmium selenide, phthalocyanines, ultramarine bloc, carbon black, and the
like.
Representative flame-retardants include organic halogenated compounds
such as decabromodiphenyl ether and the like.
The toughener can be used in neat or diluted form. In the latter case,
either EPDM, EPR, or polyethylene can be used as the diluent.
EYAMPLES
The invention is illustrated by the following Examples and Comparative
1o Examples herein. Melt Viscosity data were obtained at 280 C using a
commecial
rheometer such at the Kayeness Rheometer, Model 8052. Notched Izod
toughness were determined in accordance with ASTM D256 at room temperature
on a 5" x %z" x 1/8"specimens, or with ISO 527-2C at room temperature an a
4mm thick x 80mm in length specimen.
Comparative Example 1
A pellet blend of 141.8 1b of nylon 66 under the tradename ZYTEL~ 101
(available from E.I. duPont de Nemours and Co., Wilmington, DE) and 33.2 1b of
anhydride functionalized rubber under the tradename FUSABOND~ N MF521D
(available from E.I. duPont de Nemours and Co.) was introduced into the first
2o barrel of a ten-barrel 53 mm Werner & Pfleiderer twin-screw extruder at a
rate of
300 lb/hr, extruder RPM of 250 with a high shear screw, and vacuum of 14" -
15"
applied on barrel 9. The melt temperature during the extrusion process was 329
C. The polymer strands coming from the extender were quenched in water and
fed to a cutter. The hot pellets were collected in a vessel that was
continuously
2, swept with nitrogen gas to avoid moisture absorption from the air.
Example 1
Example 1 was prepared in the manner described for Comparative
Example 1 above from a pellet blend of 140.9 Ib of ZYTEL ~~ 101, 33.2 1b of
FUSABOND~~ N MF521 D, and 397.2 g of dodecanedioic acid. Using the same
9
CA 02380223 2002-O1-22
WO 01/21712 PCT/L1S00/26125
extruder conditions as in the Comparative Example and a rate of 300 Ibi'hr,
the
melt temperature during extension was 314 C. The polymer strands coming from
the extruder were quenched in water and fed into a cutter. The hot pellets
were
collected in a vessel that was continuously swept with nitrogen gas.
Example 2
A pellet blend of 135.1 Ib of ZYTEL ~J 101 and 39.9 1b of FUSABOND~~
N MF521 D was introduced into the first barrel of a ten-barrel 53 mm Werner &
Pfleiderer twin-screw extruder at 250 lb/hr using same conditions as
Comparative
Example 1. At the same time a blend of 169.8 1b ZYTEL~ 101 and ~.2 1b of
to dodecanedioic acid was introduced into barrel #7 at a rate of 5'0 lb/hr.
This
composition is equivalent to Example 1. The melt temperature during extrusion
was 312 C. The polymer strands coming from the extruder were quenched in
water and fed into a cutter. The hot pellets were collected in a vessel that
was
continuously swept with nitrogen gas.
A comparison of the results of this work is provided in Table 1 below.
Table 1
Sample Notched Melt Viscosity
Izod (Pa-S) @
Various
Shear Rates
(ft-lb/in) 1001/sec 10001/sec 29991/sec
Comparative 19.99 920 165 78
Example 1
Example 1 19.00 494 96 48
Example 2 19.2 481 111 47
The results above show that in the presence of the dodecanedioic acid
2o there was a dramatic decrease in melt viscosity. The change in melt
viscosity also
is essentially unaffected by the location of the where the dodecanedioic acid
is
introduced. The results also show that there is essentially no change in the
Notched Izod toughness in the presence of the diacid.
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
Comparative Examples 2-3 and Example 3
In the following series of experiments the ingredients were melt blended
with each other under high shear. The various ingredients may first be dry
blended with each other by tumbling in a drum or they may be combined with one
another via simultaneous or separate metering of one or more of the
components.
Preferably the melt blending will be done in a twin screw extruder
manufactured
by Werner & Pfleiderer or Berstorff, although numerous other high shear melt
blending devices, apparent and well known to those skilled in the art, may be
used.
Table 2 shows re-extrusion of a polyamide blend together with the
dodecanedioic acid. The polyamide blend and dodecanedioic acid feeds were
controlled by dry blending and feeding with a single metering device. The
ingredients were blended by tumbling 74.5 pounds. ZYTEL~ ST801HS NCO10
(a rubber-toughened 6,6-nylon available commercially from E. I. DuPont de
Nemours & Co.) and 221.3 grams dodecanedioic acid (available commercially
from E. I. DuPont de Nemours & Co.) in a drum. The blended ingredients were
fed into the extruder by a K-Tron loss-in-weight screw feeder running at 180
lb/hr. In this case the melt blending occurred in a 40 mm Werner & Pfleiderer
twin screw extruder operating 300 rpm screw speed with a high shear screw. The
ingredients were fed into barrel 1 with a screw feeder. A vacuum was applied
at
barrel 8. After exiting through a 4-hole die, the strands were quenched in an
ambient water trough with circulating water. The strands were subsequently
pelletized and allowed to cool under nitrogen sparge.
Table
Ingredient (weight Example 3 Comp Ex Comp Ex
"/u) 2 3
ZYTST801 HS NC010 99.35 % 100.00 % 100.00 o
Dodecanedioic Acid 0.65%
Notched Izod, DAM, 63.37 69.7 59.28
23C, kJ/ m'-
Melt viscosity, 96 198 182
Pa-S
a;
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
This series of examples demonstrates that the benefits and attributes of the
invention herein are recognized even with the addition of the acid as a
separate
step. The commercial grade of nylon selected as above is already rubber-
toughened, and the subsequent introduction of the acid still imparted the
desirable
enhancement in melt viscosity without compromising the toughness. This is
illustrative of the range of applicability of the process and compositions of
the
invention, and for example is well suited for injection-molding applications.
Comparative Example 4 and Examples 4-6
This series of examples shows the applicability of dodecanedioic acid in
1o reducing the viscosity of nylon/ionic polymer blends without degrading
physical
properties.
Table 3 shows compositions containing nylon 66 as the thermoplastic
polyamide and an ionic polymer as the toughening material together with the
dodecanedioic acid sufficient to produce an appropriate degree of viscosity
reduction. In these examples, the nylon and toughener feeds were controlled by
separate metering. The ionic polymer feed stream was SURLYN ~ 9520W acid
(available commercially from E. I. DuPont deNemours & Co.). It was fed by a
K-Tron loss-in-weight screw feeder running at 31.6 lb/hr. The nylon feed
stream
was comprised of a 66-nylon polymer having an RV of approximately 50 and
about 40 amine ends), copper-based heat stabilizer, Ampacet Black Concentrate
19238 ("Amp Bk 19238") (available commercially from Ampacet Corp.,
Tarrytown, NY), and optionally, dodecanedioic acid (available commercially
from E. I. DuPont deNemours & Co.). The nylon feed stream ingredients were
blended by tumbling in a drum. This feed stream was fed into the extruder by a
K-Tron loss-in-weight screw feeder running at 148.=I lb/hr. In this case the
melt
blending occurred in a ~l0 mm Warner & Pfleiderer twin screw extruder
operating
300 rpm screw speed with a high shear screw. The ingredients were fed into
barrel 1 with a screw feeder. A vacuum was applied at barrel 8. After exiting
through a 4-hole die, the strands were quenched in an ambient water trough
with
3o circulating water. The strands were subsequently palletized and allowed to
cool
under nitrogen spurge.
12
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
Table 3
Ingredient Comp Example Example Example
(weight "/o) Ex 4 4 5 6
HS711 0.003 0.003 0.003 0.003
66-nylon 0.777 0.7745 0.772 0.7705
polymer
SURLYN~ 0.1755 0.1755 0.1755 0.1755
9520W
Amp Bk 19238 0.0445 0.0445 0.0445 0.0445
DDDA 0 0.0025 0.005 0.0065
Notched Izod,18.5 17.02 16.76 17.04
DAM, 23C,
ft-lb/ in
Melt Viscosity,146 110 91 87
Pa-S
NOTE: HS711 is a physical blend of cuprous iodide / potassium iodide /
aluminum distearate in the ratio of 7/1/l.
Comparative Examples ~-6 and Examples 7-12
to A series of experiments was conducted to illustrate the
effect of high amounts of DDDA (up to 1.0 weight percent) on
properties of nylon 66 compositions including 7.0 weight % and
19.0 weight % FUSABOND~ N MF521 D toughener. These
compositions were prepared in the manner detailed in Comparative
t, Example 1 and Example 1. The results are shown in Table 4.
Surprisingly, even at 1.0'% DDDA there was only about a 14%
13
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
decrease in the blotched Izod toughness at both low and high levels
of toughener. There are enough acid equivalents at I .0 °/o DDDA
to react completely with the amine ends of the nylon
These results indicate that the composition of the invention
is fairly robust across various levels of DDDA, and with this
information one of ordinary skill in the art will readily appreciate
that existing manufacturing equipment and procedures are capable
of producing these types of products.
14
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
U
47
H
N
_
O ~ ~ O
N N N ~ CO M ~ N
L O
R N
O
t
N v
d
N N
7 r
O
O
~ O I~ ~ Cp ~ M t~ O O
O CO CD ~ e- O CO N
N r-
N
e0
a
.r
~N
V U
M ~ O ~ ~ ~ ~ N
O N
O
O
'O
O
N
d C
J
0
O w, CO O O lf) N N
Z ~ r- r- T
r-
a
0 ~ O ~
O CD O CO O
a O O O r- O O O
Z
0
Z 0
N O O O p O O O O
O O O m
N
O O O O O O O O
ca _
N N N N N N N N
O O O O O O O O
Z O O O O O O O O
O O t1~O O O tn O
J O ~ M O O ~ M O
Z O O O O 00 a0 O 00
L _
p x 'n ~
,~ m a~ r
Q
o-E Q n a a a a
a E ~ E a E E E
V E c c E c c c
v v o a a
x o x x x o x x x
w U t~ ttluI U tm u w
CA 02380223 2002-O1-22
WO 01/21712 PCT/US00/26125
It is to be further appreciated that these compositions are adaptable to suit
any number of processing techniques. For example, molders of toughened
polyamide parts may find very different means of using these products to
improve
their existing injection molding processes. A molder using a multi-cavity mold
to
produce small parts may have difficulty completely filling the mold due to the
limits of temperature, maximum machine pressure, and resin viscosity. A higher
melt flow resin would allow use of even higher numbers of mold cavities
without
exceeding the machine's maximum injection pressures. In other cases, a
manufacturer may have difficulties arising from high melt temperatures, such
as
part surface blemish defects commonly referred to as "ghosting." While
reductions of melt temperatures frequently alleviate such defects, certain
manufacturers may be unable to operate successfully at lower melt temperatures
due to the viscosity of the resin in use. A higher melt flow resin would allow
molders to use lower melt temperatures and thereby eliminate part appearance
defects.
6
