Long fiber-reinforced polyamide resin composition and molded articles therefrom

Long fiber-reinforced normally solid polyamide resin compositions and molded articles formed thereof include a polyamide base resin, between 5 to 80% by weight of reinforcing fibers having a length of at least 3 mm, and between 0.01 to 3% by weight of a processing aid. The processing aid is a lithium salt of a fatty acid or a metal salt of a fatty acid having 22 to 32 carbon atoms. The compositions are preferably in the form of a generally cylindrical pellet having a length of 3 to 50 mm such that the reinforcing fibers are substantially as long as the pellet in which they are incorporated, and are oriented parallel to one another along the longitudinal axis of the pellet.

FIELD OF INVENTION 
The present invention generally relates to fiber-reinforced polyamide resin 
compositions and to molded articles formed therefrom. More specifically, 
the present invention relates to polyamide resins which are reinforced 
with relatively long fibers. The long fiber-reinforced polyamide resin 
compositions of the present invention exhibit excellent moldability 
properties (e.g., improved extruder screw "bite", melt-flow and 
anti-fuming characteristics), as well as exceptional mechanical strength 
properties. 
BACKGROUND AND SUMMARY OF THE INVENTION 
The reinforcement of thermoplastic resins by dispersing fibrous materials, 
such as glass fibers, so as to improve the mechanical strength properties 
of the resulting resin composition is well known. In particular, 
fiber-reinforced polyamide resins are typically produced by mixing a 
polyamide base resin with relatively short fibers, such as chopped fibrous 
strands. The polyamide base resin and short fibers are then mixed and 
extruded to form a fiber-reinforced polyamide resin composition. However, 
conventional processing techniques to obtain fiber-reinforced polyamide 
resin compositions cannot satisfy the need for greater mechanical strength 
properties, since the fiber reinforcement medium will unavoidably break 
into even shorter fiber segments during extrusion thereby decreasing its 
reinforcing effectiveness. 
Investigations have been conducted recently so as to form polyamide resin 
compositions with a relatively long fiber-reinforcement medium in an 
attempt to achieve maximum reinforcement benefit from the presence of the 
long fibers. In this connection, it has been proposed to produce long 
fiber-reinforced polyamide resin compositions by simultaneously drawing 
the reinforcement fibers and impregnating the reinforcement fibers with a 
polyamide resin (for example, an emulsion, solution or melt of polyamide 
resin). 
These prior attempts to achieve a polyamide resin composition which was 
reinforced with a relatively long fiber medium, however, encountered 
several problems. For example, such prior long fiber-reinforced polyamide 
resin compositions experienced molding difficulties, such as incomplete 
filling of the mold cavity due to hopper "breathing" (so-called 
"short-shots"), poor extruder screw "bite", and overall poor fluidity 
characteristics. Adding a conventional slip additive, such as aluminum 
stearate, zinc stearate or calcium stearate, to compositions which contain 
a long fiber reinforcement medium does not solve such problems and, in 
fact, creates further problems in terms of violent fuming (gas generation) 
when the resin is purged during molding. Furthermore, there is a tendency 
for the molded article to become scorched when such a material is molded, 
thereby detracting from its visual appearance. 
The problems noted above are peculiar to polyamide resin which contain 
relatively long fibers as a reinforcing medium. It is presumed that these 
problems are attributable to the incorporation of a large amount of air 
into the resin during plasticization by the screw-extruder and/or by 
virtue of localized heat build-up caused by shear forces. However, no 
detailed mechanisms have been identified as to the precise causes for the 
problems stated above when long fibers are incorporated into a polyamide 
base resin. It is therefore towards providing a solution to the problems 
associated with incorporating a long fiber reinforcement medium into a 
polyamide base resin which the present invention is directed. 
Broadly, the present invention is directed toward polyamide compositions 
which include a processing aid exhibiting selective beneficial effects 
when employed in combination with a relatively long fiber reinforcement 
medium. More specifically, the present invention is directed to polyamide 
resin compositions and to molded articles formed thereof which is composed 
of a blend of a polyamide base resin, a long fiber reinforcement medium, 
and a processing aid which is at least one selected from (i) a lithium 
salt of a fatty acid, or (ii) a metal salt of a fatty acid having between 
22 to 32 carbon atoms. In preferred embodiments, the compositions of this 
invention will include, based on the total composition weight, between 5 
to 80 wt. % of reinforcing fibers having a length of at least 3 mm, and 
between 0.01 to 3 wt. % of the processing aid. 
The polyamide resin compositions according to the present invention are 
most preferably in the form of generally cylindrical pellets having a 
length between 3 to 50 mm. Thus, according to this invention, the fibrous 
reinforcing medium most preferably has a length which is substantially 
coextensive with, and will be oriented in the longitudinal direction of, 
the formed composition pellets. 
Further aspects and advantages of this invention will become more clear 
after careful consideration is given to the following detailed description 
of the preferred exemplary embodiments thereof. 
DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS 
The polyamide base resin that may be used in the present invention includes 
nylon 6, nylon 66, nylon 11, nylon 12, nylon 6.10 and nylon 6.12. However, 
the polyamide base resin is not limited to nylons and thus virtually any 
known thermoplastic polyamide resin may be used. A mixture of two or more 
such polyamide base resins can also be employed, if desired. From the 
viewpoint of composition properties, such as long-term heat-stability, 
heat-resistance and mechanical strength. A polyamide base resin which is 
mainly comprised of nylon 66 is preferred for use in the compositions of 
the present invention. In such a case, the effect of the processing 
aid--i.e., a lithium salt of a fatty acid, or a metal salt of a fatty acid 
having 22 to 32 carbon atoms--is particularly noticeable. 
The types of reinforcing fibers that may be used in the present invention 
are not particularly limited. For example, glass fibers, carbon fibers, 
metal fibers and high-melting (or high-softening) resin fibers are usable. 
According to the present invention, 5 to 80% by weight (based on the entire 
composition weight) of reinforcing fibers having a fiber length of at 
least 3 mm are incorporated into the composition. The length of the fibers 
is determined after the fibers are incorporated into the composition. 
Thus, according to this invention, the length of the reinforcing fibers is 
selected such that, after blending with the polyamide base resin and 
processing aid, the fibers will have a length which is at least 3 mm, and 
most preferably, a length which is substantially coextensive with the 
length of the generally cylindrical composition pellet which is ultimately 
obtained. 
When the amount of the reinforcing fibers is less than 5% by weight, an 
insufficient reinforcement effect of the fibers results. On the other 
hand, when the reinforcing fiber content exceeds 80% by weight, poor 
processability during production of the composition and remolding results, 
improved strength properties cannot be realized. In terms of balancing the 
reinforcing effects of the fibers and the processability of the resin 
composition, the amount of the fibers is preferably between 20 to 70% by 
weight, particularly between 30 to 65% by weight (based on the entire 
composition weight). 
The reinforcing fibers need not be entirely long fibers as discussed above. 
Thus, a minor amount of relatively short fibers (i.e., a length less than 
3 mm) may be incorporated into the compositions of this invention, in 
addition to the above-described long fibers, provided that the total 
amount of the reinforcing fibers that is employed does not exceed 80% by 
weight. 
The present invention is especially characterized by the incorporation of a 
specific processing aid. The processing aid that is used in the 
compositions of this invention is a lithium salt of a fatty acid, or a 
metal salt of a fatty acid having 22 to 32 carbon atoms. When a metal salt 
other than a lithium salt, such as zinc, calcium or aluminum salts of a 
fatty acid having less than 22 carbon atoms or more than 32 carbon atoms, 
e.g. zinc laurate, calcium laurate, aluminum laurate, zinc myristate, 
calcium myristate, aluminum myristate, zinc palmitate, calcium palmitate, 
aluminum palmitate, zinc stearate, calcium stearate, aluminum stearate, 
zinc oleate, calcium oleate or aluminum oleate, is used as the processing 
aid, the thermal stability of the composition is inferior thereby causing 
processing problems, such as fuming or gas generation during molding as 
well as possible scorching of the molded article. On the other hand, use 
of a lithium salt of a fatty acid or a metal salt of a fatty acid having 
22 to 32 carbon atoms according to the present invention serves to prevent 
such problems, thereby exhibiting excellent processing effects and 
improving the composition's moldability. Specific compounds that may be 
used as the processing aid in the compositions of the present invention 
include lithium, zinc, calcium and aluminum salts of behenic, montanic, 
melissic, lacceric and erucic acids. 
The amount of the processing aid (i.e., the lithium salt of a fatty acid or 
a metal salt of a fatty acid having 22 to 32 carbon atoms) that may be 
used in the compositions of the present invention is between 0.01 to 3% by 
weight (based on the entire composition weight). When the amount of the 
processing aid is less than 0.01% by weight, little, if any, beneficial 
effects are realized. When the processing aid is employed in amounts 
exceeding 3% by weight, the composition and/or molded article formed 
therefrom is colored. Furthermore, problems such as mold deposits 
sometimes occur. The amount of the processing aid is most preferably 
between 0.02 to 1% by weight (based on the entire composition weight). 
In the present invention, the processing aid may be incorporated into a 
composition comprised of the polyamide base resin and the reinforcing 
fibers as an internal slip additive. Alternately, the processing aid may 
be applied into the surface of the composition comprised of the polyamide 
base resin and the reinforcing fibers--i.e., so as to function as an 
external slip additive. Of course, the combined use of the lithium salt of 
a fatty acid with the metal salt of a fatty acid having 22 to 32 carbon 
atoms internally and/or externally as described may also be used. 
Although processes for producing the compositions of the present invention 
are not particularly limited, those processes wherein substantially no 
shear forces are applied to the fibers is preferred in order to protect 
the fibers from excessive breakage. In this regard, a pultrusion process 
is particularly preferred. 
The pultrusion process essentially includes impregnating continuous 
reinforcing fibers with a resin while the fibers are being drawn. 
Pultrusion processing includes other known techniques including passing 
fibers through an impregnation bath containing an emulsion, suspension or 
solution of a resin or a molten resin; spraying a resin powder onto 
surfaces of fiber or passing through a tank containing the resin powder so 
that the resin powder is applied to the fibers and thereafter melted so as 
to impregnate the fibers and, passing fibers through a crosshead die while 
feeding a resin into the crosshead die from an extruder or the like to 
thereby impregnate the fibers. The resin composition thus obtained is 
preferably shaped into generally cylindrical pellets having a length of 3 
to 50 mm prior to injection molding. In this case, the reinforcing fibers 
are substantially coextensive with the longitudinal length of the pellet 
and are oriented substantially parallel to one another along the 
longitudinal axis of the pellet. In the case of a resin composition 
wherein the long fibers are arranged in one direction and the fiber length 
is uniform, the presence of a slip additive is often particularly 
necessitated so as to enhance fluidization of the pellet during molding, 
fluidization of the molten resin during plasticization, or to enable 
homogeneous mixing of the fibers. The incorporation of the lithium salt of 
a fatty acid, or the metal salt of a fatty acid having 22 to 32 carbon 
atoms, as a slip additive (processing aid) is particularly effective for 
such purposes. For example, when the resin composition of the present 
invention is subjected to injection molding, the beneficial effects of the 
processing aid is particularly noticeable. 
The resin composition of the present invention can be used in combination 
with one or more other thermoplastic resins provided that the effects 
achieved according to the present invention are not seriously inhibited. 
The resin composition can also contain known additives usually 
incorporated into thermoplastic resins, such as stabilizers, e.g. 
antioxidants, thermal stabilizers and ultraviolet absorbers, antistatic 
agents, flame retardants and flame-retarding assistants, colorants, e.g. 
dyes and pigments, lubricants, plasticizers, crystallization accelerators, 
and nucleators. Furthermore, the compositions can be used in combination 
with a suitable amount of a platy, powdery or granular inorganic compound 
such as glass flakes, mica, glass powder, glass beads, talc, clay, 
alumina, carbon black or wollastonite, or whiskers. 
As will be apparent from the above discussion, the long fiber-reinforced 
polyamide resin compositions of the present invention which are comprised 
of a polyamide base resin reinforced with long reinforcing fibers, and 
further containing a processing aid in the form of a lithium salt of a 
fatty acid or a metal salt of a fatty acid having 22 to 32 carbon atoms, 
has exceptional mechanical properties (such as tensile strength, bending 
strength and impact strength) since it is reinforced with long fibers. 
Furthermore, the "bite" of the resin by the molding machine and the 
fluidity of the resin are improved by the incorporation of the specific 
processing aid described previously (i.e., a lithium salt of a fatty acid 
or the metal salt of a fatty acid having 22 to 32 carbon atoms). In 
addition, such problems as fuming or gas generation during injection 
molding and/or scorching of molded articles are not experienced with the 
compositions of the present invention. Thus, the compositions of the 
present invention exhibit excellent characteristics thereby rendering them 
commercially viable.

EXAMPLES 
The following non-limiting Examples will further illustrate the present 
invention. 
EXAMPLES 1 TO 4 AND COMATIVE EXAMPLES 1 TO 5 
A glass roving was opened and the obtained filaments were drawn and 
simultaneously impregnated with a molten mixture of a polyamide resin 
(nylon 66) and lithium salt of a fatty acid, passed through a shaping die 
and taken off in the form of a strand, which was cut to obtain a 
composition in the form of a pellet having a length of 12 mm and 
comprising components given in Table 1 (Examples 1, 2 and 4). Separately, 
the same glass roving as that described was impregnated with only the 
polyamide resin (nylon 66) and shaped into pellets having a length of 12 
mm, which were blended with lithium salt of a fatty acid (Example 3) in 
the same manner as that described above. 
For comparison, a composition in the form of a pellet impregnated with a 
molten mixture of the polyamide resin (nylon 66) and a slip additive other 
than that of the present invention (Comparative Examples 1, 2 and 4), a 
composition in the form of a pellet impregnated with only the polyamide 
resin (nylon 66) and then blended with a slip additive other than than of 
the present invention (Comparative Example 3) and a composition in the 
form of a pellet impregnated with only the polyamide resin (nylon 66) and 
free from any slip additive (Comparative Example 5) were also produced in 
the same manner as that described above. 
These pellet-shaped compositions were injection-molded and the products 
were evaluated to obtain the results given in Table 1. The evaluation 
methods were as follows: 
Fuming phenomenon: The resin composition was plasticized on an 
injection-molding machine and then left to flow freely. The quantity of 
the fumes generated at the tip of the nozzle was determined by visual 
observation, and evaluated according to the following qualitative scale: 
##STR1## 
Molded article scorching: Scorching (color change) of the molded article 
obtained by the injection molding was determined by visual observation, 
and evaluated according to the following qualitative scale: 
##STR2## 
Bite by molding machine: The resin composition was plasticized on an 
injection-molding machine and the extent of the bite of the pellet to the 
screw during molding step was observed, and evaluated according to the 
following qualitative scale: 
##STR3## 
TABLE 1 
__________________________________________________________________________ 
Comp. Comp. Comp. Comp. Comp. 
Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 
__________________________________________________________________________ 
5 
Composition 
glass fiber 
glass fiber 
glass fiber 
glass fiber 
glass fiber 
glass fiber 
glass fiber 
glass 
glass fiber 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. 
40 wt. % 
LiSt LiPa LiSt LiSt ZnSt AlSt ZnSt ZnSt -- 
0.03 wt. % 
0.03 wt. % 
0.03 wt. % 
0.05 wt. % 
0.03 wt. % 
0.03 wt. % 
0.03 wt. % 
0.05 wt. % 
Slip melt mixing 
melt mixing 
external 
melt mixing 
melt mixing 
melt mixing 
external 
melt mixing 
-- 
additive blending blending 
mixing 
method 
Fuming 1 2 2 2 5 5 5 5 1 
phenomenon 
Scorch of 
1 1 1 1 4 4 4 5 1 
molding 
Bite to 
1 1 1 1 1 1 1 1 5 
molding 
machine 
__________________________________________________________________________ 
Slip additive: 
LiSt: lithium stearate 
LiPa: lithium palmitate 
ZnSt: zinc stearate 
AlSt: aluminum stearate 
EXAMPLES 5 TO 9 AND COMATIVE EXAMPLES 1 AND 3 TO 6 
A glass roving was opened and the obtained filaments were drawn and 
simultaneously impregnated with a molten mixture of a polyamide resin 
(nylon 66) and a metal salt of a fatty acid having 22 to 32 carbon atoms, 
passed through a shaping die and taken off in the form of a strand, which 
was cut to obtain a composition in the form of a pellet having a length of 
12 mm and comprising components given in Table 2 (Examples 5, 6, 7 and 9). 
Separately, the same glass roving as that described above was impregnated 
with only the polyamide resin (nylon 66) and shaped into pellets having a 
length of 12 mm, which were blended with a metal salt of a fatty acid 
having 22 to 32 carbon atoms (Example 8) in the same manner as that 
described above. 
For comparison, a composition in the form of a pellet impregnated with a 
molten mixture of the polyamide resin (nylon 66) and a slip additive other 
than that of the present invention (Comparative Examples 1, 6 and 4), a 
composition in the form of a pellet impregnated with only the polyamide 
resin (nylon 66) and then blended with a slip additive other than that of 
the present invention (Comparative Example 3) and a composition in the 
form of a pellet impregnated with only the polyamide resin (nylon 66) and 
free from any slip additive (Comparative Example 5) were also produced in 
the same manner as that described above. 
These pellet-shaped compositions were injection-molded and the products 
were evaluated to obtain the results given in Table 2. The evaluation 
methods were as described above (See Examples 1 to 4 and Comparative 
Examples 1 to 5). 
TABLE 2 
__________________________________________________________________________ 
Comp. 
Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 1 
__________________________________________________________________________ 
Composition 
glass glass glass glass glass glass 
fiber fiber fiber fiber fiber fiber 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
ZnMon CaMon CaBeh ZnMon ZnMon ZnSt 
0.03 wt. % 
0.03 wt. % 
0.03 wt. % 
0.03 wt. % 
0.5 wt. % 
0.03 wt. % 
Slip additive 
melt melt melt external 
melt melt 
mixing method 
mixing 
mixing 
mixing 
blending 
mixing 
mixing 
Fuming 1 1 1 1 1 5 
phenomenon 
Scorch of 
1 1 1 1 1 4 
molding 
Bite to molding 
1 1 1 1 1 1 
machine 
__________________________________________________________________________ 
Comp. Comp. Comp. Comp. 
Ex. 6 Ex. 3 Ex. 4 Ex. 5 
__________________________________________________________________________ 
Composition 
glass glass glass glass 
fiber fiber fiber fiber 
40 wt. % 
40 wt. % 
40 wt. % 
40 wt. % 
CaLau ZnSt ZnSt -- 
0.03 wt. % 
0.03 wt. % 
0.5 wt. % 
Slip additive 
melt external 
melt -- 
mixing method 
mixing 
blending 
mixing 
Fuming 5 5 5 1 
phenomenon 
Scorch of 
4 4 5 1 
molding 
Bite to molding 
1 1 1 5 
machine 
__________________________________________________________________________ 
Slip additive: 
ZnMon: zinc montanate 
CaMon: calcium montanate 
CaBeh: calcium behenate 
ZnSt: zinc stearate 
CaLau: calcium laurate 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment, it is to be 
understood that the invention is not to be limited to the disclosed 
embodiment, but on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.