Polyamide composition and method of producing goods

Certain polyamide resin compositions make it possible to shorten the injection molding processing cycle for polyamide resins. The polyamide resin compositions are obtained by adding an external lubricant to polyamide resin granules composed of from 55 to 85% by weight of polyamide resin, 10 to 40% by weight of filler, and 0.3 to 2.0% by weight of at least one type of higher fatty acid ester type internal lubricant selected from among esters of higher alcohols and higher fatty acids and higher fatty acid partial esters of polyhydric alcohol compounds.

BACKGROUND OF THE INVENTION 
The molding process of synthetic resin consists of, first, a step whereby 
resin supplied from the material supply port (hopper) of the molding 
machine is melted by heating (plasticization step); second, a step whereby 
the plasticized resin is made to completely fill the screw groove or mold 
while kneading by applying shear force (injection/filling step); third, a 
step whereby the resin placed in the mold is solidified by cooling 
(cooling step); followed by a step whereby the molded product is 
discharged from the mold (mold release step). 
In a continuous process, the plasticization step and the cooling step are 
generally conducted simultaneously in these processes. In other words, 
plasticization of the resin of a molding processing cycle is carried out 
while the resin placed in the mold in the immediately prior cycle is being 
cooled in the aforementioned molding processing cycle. Nonetheless, the 
time necessary for plasticization and cooling is longer than the time 
necessary for the injection and discharge steps. 
Conducting molding at high molding efficiency and maintaining high quality 
of the molded goods are demanded when producing molded goods by injection 
molding processes. When using resins that solidify rapidly such as nylon 
and polystyrene and when molding thin-shaped molded goods, problems, such 
as short shots, arise because the injection speed slows during molding. 
Another problem is that injection cannot be continued by melting the resin 
inside the cylinder of the molding machine in the prescribed cycle time 
when the plasticization capacity of the resin is low during high cycle 
operation. 
Prior to now, shortening of the plasticization time, which generally 
accounts for approximately 50% of the molding cycle time, was concluded to 
be the major factor contributing to shortening the molding processing 
cycle time to obtain higher productivity while avoiding the aforementioned 
problems. However, since the cooling time may be shorter than the 
plasticization time when the heat conductivity of the resin is large, the 
ability to shorten the plasticization time in some way should be the key 
to shortening the molding processing cycle. In other words, the molding 
cycle time, especially the duration of the plasticization step, controls 
the molding performance and quality of the molded goods. Therefore, 
attempts were made in the past to accelerate plasticization by raising the 
screw rotation while lowering the screw backpressure. 
A molding method that resolves poor molding and molding defects directly 
associated with the molding process (such as valleys and short shots) 
while continually maintaining the necessary molding cycle time while 
operating the injection molding machine on a high cycle, and elucidation 
of an improved polyamide resin composition to be used in this method were 
demanded because of the situation described above. Shortening of the 
plasticization time while maintaining a high quality of the molded goods 
was demanded to attain the goal of shortening the molding cycle time. 
In the plasticization step of the injection molding process, the resin 
material, granules, or pellets that have fallen into the heating cylinder 
for injection under their own weight from the hopper are placed in a 
molten condition by elevation of the temperature from inside (through the 
heat of friction generated by the kneading action) together with heat from 
the outer circumference of the heating cylinder while being mixed and 
kneaded by the rotations of the screw and carried to the tip of the 
cylinder through the groove. Molten resin is simultaneously stored in the 
tip of the heating cylinder. The reaction force (backpressure) of this 
material pushes the screw backward. The measurement step that determines 
the mount injected is subsequently carried out by controlling the mount of 
retraction by a limit switch and stopping the rotation of the screw at a 
set position. 
SUMMARY OF THE INVENTION 
In the present invention, it has been discovered that the combined use of 
an internal lubricant and external lubricant with polyamide resin has the 
greatest shortening effect on the plasticization time when molding 
polyamide resin. Nonetheless, it is evident that the cooling step acts in 
a rate determining manner and the injection molding cycle time will not be 
shortened by shortening the plasticization time in cases wherein the 
cooling step vastly exceeds the duration of the plasticization step 
(because the plasticization step and cooling step are carried out 
simultaneously, as was mentioned above). Therefore, the polyamide resin 
composition used in the present invention is a resin composition that 
contains a filler, and it is a requisite condition that the content of 
filler be from 10 to 40% by weight in a polyamide resin such that the 
cooling step does not act in a rate determining manner. The polyamide 
resin composition also contains 0.3 to 2.0% by weight of a higher fatty 
acid ester internal lubricant as well as an external lubricant. 
The polyamide resin composition of the present invention is excellent for 
molding with lowered frictional resistance between the polyamide resin 
granules or pellets and the barrel and screw of the injection molding 
machine. Furthermore, the polyamide resin composition makes it possible to 
shorten the plasticization in the injection molding process and to thereby 
attain high molding performance. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention makes it possible to shorten the plasticization time 
while maintaining the quality of the molded goods in an injection molding 
process by using an internal and external lubricant in combination with a 
filler-containing polyamide resin composition. This makes it possible to 
shorten the molding processing cycle time and to thereby greatly improve 
productivity. 
The present invention concerns a polyamide resin composition obtained by 
adding an external lubricant to polyamide resin granules or pellets, said 
polyamide resin granules or pellets comprising from 55 to 85% by weight of 
polyamide resin, 10 to 40% by weight of filler, and 0.3 to 2.0% by weight 
of at least one type of higher fatty acid ester internal lubricant 
selected from esters of higher alcohols and higher fatty acids or higher 
fatty acid partial esters of polyhydric alcohol compounds. 
Moreover, the present invention also concerns a method of producing 
Injection molded polyamide resin goods using a polyamide resin composition 
obtained by adding an external lubricant to polyamide resin granules or 
pellets, said polyamide resin granules or pellets comprising from 55 to 
85% by weight of polyamide resin, 10 to 40% by weight of filler, and 0.3 
to 2.0% by weight of at least one type of higher fatty acid ester internal 
lubricant selected from esters of higher alcohols and higher fatty acids 
or higher fatty acid partial esters of polyhydric alcohol compounds. 
The polyamide resin used in the present invention is a resin well known in 
the art. It is a high molecular weight substance wherein hydrocarbon 
groups or hydrocarbon groups broken by oxygen or sulfur are joined by 
amide bonds. This includes those that are generally called nylon and have 
a molecular weight of at least 5,000. 
This polyamide resin can be one produced by condensing a linear diamine 
represented by the formula H.sub.2 N--(CH.sub.2).sub.x --NH.sub.2 (wherein 
x is an integer of from 6 to 12) and a linear dicarboxylic acid 
represented by the formula HO.sub.2 C(CH.sub.2).sub.y --CO.sub.2 H 
(wherein y is an integer of from 2 to 8). These polyamides can also be 
produced from amide-forming derivatives of said amine and acid, e.g., 
esters, acid chlorides, and amine salts. Examples of a dicarboxylic acid 
used in the production of this polyamide include butyric acid, adipic 
acid, pimelic acid, suberic acid, sebacic acid, and dodecane dioate. 
Examples of diamines include hexamethylenediamine and 
octamethylenediamine. 
Another type of polyamide resin is produced by condensation of 
.omega.-aminocarboxylic acid represented by the formula H.sub.2 
N--(CH.sub.2).sub.x --CO.sub.2 H (wherein x is an integer of from 3 to 12) 
or an intramolecular amide thereof. 
The polyamides may also include polyamides wherein part of the diamine 
component is bis(3-aminopropyl)ether, bis(aminomethyl)cyclohexane, 
m-phenylenediamine, m-xylylenediamine, or 4,4'-diaminodiphenyl ether and 
pan of the dicarboxylic acid component is isophthalic acid, terephthalic 
acid, etc. Examples of the polyamides include polyhexamethylene adipamide 
(nylon 66), polyhexamethylene azelamide (nylon 69), polyhexamethylene 
sebacamide (nylon 610), polyhexamethylene dodecanoamide (nylon 612), 
polycaprolactam (nylon 6), polylauryl lactam, poly-11-amino-undecanoamide, 
and polybis-(p-aminocyclohexyl)methanedodecanoamide. The aforementioned 
polyamides also include copolymers and multicomponent polymers obtained by 
combining a number of the aforementioned monomers. 
The polyamide resin composition of the present invention contains a filler 
made from inorganic compounds to improve the thermal and mechanical 
properties and obtain reinforcement. Examples of these fillers include 
glass fibers, especially crushed (milled) glass fibers with an aspect 
ratio of no more than 30, glass flakes, carbon fibers, wollastonite, talc, 
kaolin, calcium carbonate, diatomaceous earth, mica, and potassium 
titanate whiskers. One type or a combination of types of these fillers may 
be used. These fillers are added in an mount of from 10 to 40% by weight 
of the polyamide resin composition. When a smaller amount is used, the 
cooling step becomes rate determining and the object of the present 
invention, which is to shorten the injection molding cycle is not met. The 
internal lubricant contained in the polyamide resin composition of the 
present invention refers to a lubricant combined with the composition in 
such a way that it is present in a state integrally mixed with the 
composition. This is distinguished from the external lubricant which is 
used on the surface of the granules or pellets of the polyamide resin 
composition in the composition of the present invention. 
The internal lubricant used in the present invention is selected from 
esters of higher alcohols and higher fatty acids and higher fatty acid 
partial esters of polyhydric alcohol compounds. These internal lubricants 
may be used individually or in combinations of two or more. 
Esters of higher alcohols and higher fatty acids refers to esters of 
aliphatic alcohols having at least 12 carbon atoms and fatty acids having 
at least 16 carbon atoms. Included are esters of aliphatic alcohols having 
at least 12 carbon atoms such as lauryl alcohol, myristyl alcohol, 
palmityl alcohol, stearyl alcohol, eicosyl alcohol biphenyl alcohol, 
tetracosyl alcohol, serotinyl alcohol, and melissinyl alcohol and fatty 
acids such as lauric acid, myristic acid, palmitic acid, stearic acid, 
alginic acid, behenic acid, lignoceric acid, serotinic acid, and melissic 
acid. Examples include lauryl laurate, lauryl myristate, lauryl palmitate, 
lauryl stearate, lauryl behenate, lauryl lignocerate, lauryl melissate, 
myristyl laurate, myristyl myristate, myristyl stearate myristyl behenate, 
myristyl lignocerate, myristyl melissate, palmityl laurate, palmityl 
myristate, palmityl stearate, palmityl behenate, palmityl lignocerate, 
palmityl melissate, stearyl laurare, stearyl myristate, stearyl palmitate, 
stearyl stearate, stearyl behenate, stearyl alginate, stearyl lignocerate, 
stearyl melissate, eicosyl laurate, eicosyl palmitate, eicosyl stearate, 
eicosyl behenate, eicosyl lignocerate, eicosyl melissate, biphenyl 
laurate, biphenyl melissate, biphenyl palmitate, biphenyl stearate, 
biphenyl behenate, biphenyl alginate, biphenyl melissate, tetracosanyl 
laurate, tetracosanylpalmitate, tetracosanylstearate, 
tetracosanylbehenate, tetracosanyl lignocerate, tetracosanyl serotate 
serotinyl stearate serotinyl behenate, serotinyl serotinate, melissyl 
laurate, melissyl stearate, melissyl behenate, and melissyl melissate. 
Partial esters of polyhydridic alcohols and higher fatty acids refers to 
mono-, di-, or triesters of polyhydric alcohols such as glycerin, 
1,2,3-butanetriol, 1,2,3-pentanetriol, erythritol, pentaerythritol, 
trimethylopropane, mannitol, and sorbitol and higher fatty acids such as 
lauric acid, myristic acid, palmitic acid, stearic acid, eicosanoic acid, 
behenic acid, lignoceric acid, serotinic acid and melissic acid. Examples 
include higher fatty acid monoglycerides such as glycerin monolaurate, 
glycerin monomyristate, glycerin monostearate, glycerin monobehenate, 
glycerin monolignocerate, and glycerin monomelissate, mono- or di- higher 
fatty acid esters of pentaerythritol such as pentaerythritol mono- or 
dilaurate, pentaerythritol mono- or dimyristate, pentaerythritol mono- or 
dipalmitate, pentaerythritol mono- or distearate, pentaerythritol mono-, 
or dibehenate, pentaerythritol mono- or dilignocerate, and pentaerythritol 
mono- or dimelissate, mono- or di higher fatty acid esters of 
trimethylopropane such as trimethylopropane mono- or dilaurate, 
trimethylopropane mono- or dimyristate, trimethylopropane mono- or 
dipalmitate, trimethylopropane mono- or distearate, trimethylopropane 
mono-or dibehenate, trimethylopropane mono- or dilignocerate, and 
trimethylolpropane mono- or dimelissate, sorbitan mono-, di-, or tri- 
higher fatty acid esters such as sorbitan mono- di- or trilaurate, 
sorbitan mono-, di- or trimyristate, sorbitan mono- di- or tristearate 
sorbitan mono-, or di, or tribehenate, sorbitan mono-, di-, or 
trilignocerate, sorbitan mono-, di-, or trimelissate and mannitan mono-, 
di, or tri higher fatty acid esters such as mannitan mono-, di-, or 
trilaurate, mannitan mono-, di-, or trimyristate, mannitan mono-, di-, or 
tripalmitate, mannitan mono-, di-, or tristearate, mannitan mono-, di-, or 
tribehenate, mannitan mono-, di-, or trilignocerate, and mannitan mono-, 
di-, or trimelissate. 
The aforementioned polyamide resin, filler, and internal lubricant are 
first mixed in the prescribed proportions and blended homogeneously using 
a kneader. The kneader used may be a uniaxial extruder, biaxial extruder, 
or other compounder. A polyamide bulk material in the form of pellets or 
particles is produced in this way. 
The external lubricant is next added to the polyamide bulk material 
obtained in this way. The external lubricant is satisfactory as long as it 
acts to decrease the friction between the polyamide resin and the 
injection molding machine barrel and screw. Commonly known lubricants such 
as hydrocarbon oil, higher aliphatic alcohols, higher fatty acids, fatty 
acid metal salts, fatty acid esters, and fatty acid amide derivatives may 
be used. These external lubricants are applied to the polyamide granules 
or pellets by a method such as stirring in a dosed container using a 
blender such as a cone blender or a rotating pan or by applying molten 
lubricant. These external lubricants are applied in a quantity of from 
about 0.3 to 3% by weight in relation to the polyamide resin composition. 
Additives commonly added to polyamide resin, e.g., stabilizers and 
inhibitors of deterioration by oxidation, heating, and ultraviolet rays, 
mold release agents, coloring agents (including dyes and pigments), 
plasticizers, nucleating agents, etc., can also be combined with the 
composition of the present invention.

EXAMPLES 
The present invention is further illustrated in the examples that follow. 
The present invention is not limited to the examples. 
Examples 1 to 3 
For Examples 1 to 3, glass fibers (33% by weight) with a mean fiber 
diameter of 13 microns and 0.5, 0.75 and 1.0% by weight of behenic 
monoglyceride were respectively added to 66.5, 66.25 and 66% by weight of 
additive-free, dried nylon 66 pellets and mixed in a blender. The mixture 
obtained was molten mixed at a temperature of 280.degree. C. and screw 
rotational count of 280 rpm while producing a vacuum using a biaxial screw 
extruder (9-barrel) (ASK-40 made by W&P). Pellets for molding were 
obtained by quenching the molten strands extruded from the die in a water 
bath and pelletizing with the pelletizer of a cantilevered cutter. The 
pellet surface was then coated with external lubricant using 0.1 part by 
weight of aluminum distearate per 100 parts by weight of these pellets. 
The pellets that contained these internal and external lubricants were 
continuously injection molded at a cylinder temperature of 270.degree. C., 
injection pressure of 700 kg/cm.sup.2, mold temperature of approximately 
70.degree. C., and cooling time of 12 seconds with an injection molding 
machine SYCAP H111 165/75 made by Sumitomo Necktaryl) with a screw 
diameter of 28 mm, nozzle diameter of 15 mm, and nozzle hole diameter of 5 
mm. Table 1 shows the results obtained by examining and testing the screw 
retraction time and total cycle time in each of the injection molding 
processes, the mechanical strength of the injection molded goods obtained, 
and the existence of poor molding/molding defects. 
TABLE 1 
______________________________________ 
Example 1 
Example 2 Example 3 
______________________________________ 
Internal lubricant 
Behenic Behenic Behenic 
monoglyceride 
monoglyceride 
monoglyceride 
0.5 0.75 1.0 
External lubricant 
Aluminum Aluminum Aluminum 
distearate distearate distearate 
Screw retraction 
10.2 8.4 7.1 
time 
Total cycle time 
18.7 18.8 18.6 
Tensile strength 
1877 1902 1813 
(kg/cm.sup.2) 
Tensile elongation 
2.96 3.01 2.83 
on rupture (%) 
Flexural modulus 
90,936 90,610 90,026 
of elasticity 
(kg/cm.sup.2) 
Flexural strength 
2697 2625 2612 
(kg/cm.sup.2) 
Notched Izod 
11.64 11.15 10.88 
impact strength 
(kg-cm/cm) 
______________________________________ 
Example 4 and Comparative Examples 1 to 4 
For Comparative Examples 1 to 4, pellets for molding were produced by 
mixing in the same way as in Example 1 a composition with no internal 
lubricant added to 66.5 parts by weight of dried nylon 66 pellets and 33 
parts by weight of glass fibers with a mean fiber diameter of 13 microns. 
This composition served as Comparative Example 1. Furthermore, 
compositions with 0.3 part by weight of aluminum distearate (Comparative 
Example 2), 0.5 part by weight of calcium behenate (Comparative Example 
3), 0.5 pan by weight of polyethylene glycol distearate (Comparative 
Example 4), and 0.5 part by weight of behenyl behenate added as an 
internal lubricant (Example 4) were prepared. The pellet surface for each 
comparative example, and Example 4, was coated with 0.1 pan by weight of 
aluminum distearate per 100 parts by weight of these pellets as an 
external lubricant. The pellets obtained in this way were injection molded 
into Izod test pieces in the same way as in practical Example 1. The screw 
retraction time and total cycle time in the injection molding process, the 
mechanical strength of the injection molded goods obtained, and the 
existence of poor molding/molding defects were tested and observed. The 
results are shown in Table2. 
TABLE 2 
______________________________________ 
Compa- Compa- Compa- Compa- 
rative rative rative rative 
Example 1 Example 2 
Example 3 
Example 4 
Example 4 
______________________________________ 
Internal 
None Alumi- Calcium 
Polyethy- 
Behenyl 
lubricant num behenate 
lene behenate 
distearate 
0.5 glycol 0.5 
0.3 distearate 
0.5 
External 
Alumi- Alumi- Alumi- Alumi- Alumi- 
lubricant 
num num num num num 
distearate 
distearate 
distearate 
distearate 
distearate 
Screw 11.3 11.7 12.2 12.2 8.7 
retraction 
time 
Total 18.7 18.7 19.0 19.1 18.6 
cycle 
time 
Tensile 2016 1843 1856 1816 1931 
strength 
(kg/cm.sup.2) 
Tensile 3.03 2.92 2.94 3.22 2.71 
elonga- 
tion on 
rupture 
Flexural 
94,412 93,881 90,981 91,186 86,060 
modulus 
of 
elasticity 
(kg/cm.sup.s) 
Flexural 
2968 2682 2680 2707 2847 
strength 
(kg/cm.sup.2) 
Notched 11.97 11.40 11.13 11.20 12.62 
Izod 
impact 
strength 
(kg- 
cm/cm) 
______________________________________ 
As is evident from Tables 1 and 2, shortening of the plasticization time is 
found by adding from 0.3 to 2.0% by weight of the total quantity of these 
internal lubricants melted and mixed by extruder when using ester type 
lubricants in combination as external lubricants and internal lubricants. 
The mechanical strength properties of the molded goods were in no way 
changed in comparison to molded goods obtained from pellets that did not 
contain internal lubricants. Poor molding and molding defects such as 
valleys and short shots also did not arise.