Aromatic polycarbonate containing N,N-dialkyl amide mold release agent

A composition comprising an aromatic carbonate polymer in admixture with a mold release effective amount of a compound of the formula ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and are alkyl of one to twenty-five carbon atoms, inclusive with the proviso that the amide is not excessively volatizable under polymer processing conditions.

BACKGROUND OF THE INVENTION 
Injection molding provides a convenient way for preparing various articles 
from thermoplastic resins, particularly objects of a relatively intricate 
nature. In order to injection mold articles in an economic manner, it is 
important to minimize the adhesion of the molded part to the mold surface 
through the use of a release agent. It is additionally advantageous that 
the release agent be incorporated in the material to be demolded. However, 
such an internal agent must be compatible with the resin as measured by 
the usual characteristics of the resin under normal conditions and heat 
treatments. 
Of the thermoplastic resins which find a mold release agent useful from 
time to time one of the most sensitive to chemical attack or degradation 
is polycarbonate. The carbonate bond is susceptible to bond cleavage, for 
example, hydrolysis from the usual sources. Acids and various acid 
derivatives have been used as mold release agents for polycarbonate. 
Examples of carboxylic acids employed as mold release agents for 
polycarbonate include U.S. Pat. Nos. 4,409,351 and 4,408,000. Examples of 
carboxylic acid esters useful as mold release agents for polycarbonate 
include U.S. Pat. Nos. 3,836,499; 4,097,435; 3,784,595; 4,065,436; 
4,131,575; 4,444,935; and 4,446,268. Amides in general are also known as 
additives useful in improving the processing of polycarbonates, U.S. Pat. 
No. 4,119,603. Certain carboxylic acid amides have been employed as mold 
release agents in polycarbonate but have met with limited utility. 
Specifically, the Mitsubishi Gas Chemical Japanese application No. 72 
41092 describes three different amides--lauryl amide, stearyl amide and 
ethylene bis stearamide-- as mold release agents for polycarbonate at 0.5 
wt. percent levels and found that an ester exchange reaction with the 
polycarbonate had occured. It has also been found that amides lead to 
unacceptable drops in melt viscosity. 
It is thus perceived that amides would not be thought to be useful 
additives for polycarbonate. It has now been surprisingly found that a 
limited class of amides are effective mold release agents for 
polycarbonate without seriously compromising the properties of the resin 
under normal molding conditions. 
DESCRIPTION OF THE INVENTION 
In accordance with the invention, there is a composition comprising an 
aromatic carbonate polymer in admixture with a mold release effective 
amount of an amide of the formula 
##STR2## 
wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and are 
alkyl of one to about 25 carbon atoms, inclusive, with the proviso that 
the amide is not excessively volatizable under polymer processing 
conditions. 
The aromatic carbonate polymers are prepared by well known techniques 
available in the art, see for example U.S. Pat. No. 4,444,935, column 2, 
line 26 to column 3, line 61. The amides can be prepared by the well known 
reaction of an alkyl acid chloride with the desired amine. 
The amides of this invention are also suitable as mold release agents for 
blends of polycarbonates or copolyestercarbonates with various other 
polymers, for example polyalkylene terephthalates. Other polymer systems 
include blends of polycarbonate or copolyestercarbonate with aromatic 
polyesters of cyclohexane dimethanol. The polyesters have units derived 
from the above diol and terephthalic acid or ester precursor or mixtures 
of terephthalic acid and isophthalic acid or their ester precursors. An 
example of the latter is known as Kodar A150.RTM. and is available from 
Eastman. Also present in the series of polyesters can be alkylene units of 
two to four carbon atoms derived from glycols such as ethylene glycol and 
butylene 1,4 glycol. The molar units of alkylene glycol residues to 
cyclohexane dimethanol residue in the polymer can vary from about 1:4 to 
4:1. 
The amides useful in this invention are those of Figure I. Any amide of 
Figure I which is insufficiently volatile at processing conditions so as 
to maintain most of its presence in the composition can be used. The alkyl 
groups can be normal or branched. Examples of the alkyl groups include 
methyl, ethyl, isopropyl, butyl, 2,2-dimethylbutyl, 2,2,4-trimethylpentyl, 
isodecyl, butyldecyl, octadecyl, eicosyl and the like. Illustrative 
compounds of Figure I include compounds wherein R.sub.1 is tridecyl, 
R.sub.2 is methyl and R.sub.3 is methyl; R.sub.1 is ethyl, R.sub.2 is 
methyl and R.sub.3 is lauryl; R.sub.1 is methyl and R.sub.2 and R.sub.3 
are octyl. 
An effective mold releasing amount of the compound of Figure I is employed 
in the thermoplastic composition. Any amount of material which reduces the 
amount of pressure needed to eject the article from the injection mold and 
obtain an substantially unblemished article in comparison to the pressure 
needed to eject the thermoplastic composition control is an effective mold 
releasing amount. In general, effective amounts of the compound of Formula 
I are from about 0.01 to about 1.0 weight percent, based on the quantity 
of thermoplastic resin present, preferably from about 0.05 to about 0.5 
weight percent. The material can be added to the resin in the normal 
manner that the other additives are added, for example, in the dry or 
liquid stage and coextruded. Depending upon the volatility of the compound 
at common processing and extrusion temperatures, an excess may be 
initially employed in the composition. 
Other common additives for thermoplastic resins may also be employed. For 
example with respect to aromatic polycarbonate, additives which are 
commonly known to stabilize the resin thermally such as a phosphite can be 
employed. Hydrolytic stabilizers such as epoxides may also be employed as 
well as agents which are flame retardants, drip inhibitors, ductility 
enhancers, antioxidants, solvent resistance enhancers, ultraviolet light 
stabilizers and various inert fillers. Impact modifiers may also be 
present in the composition. Active fillers and pigments can be used with 
passivating agents and treatments.

Below are specific examples of the invention. The examples are intended to 
illustrate but not narrow the inventive concept. All percentages of the 
additives are in weight percent of the thermoplastic resin. 
In all the ensuing examples the aromatic polycarbonate is LEXAN.RTM. 140, a 
polymer produced by reacting bisphenol-A and phosgene. The mold release 
agent was dry formulated into the polycarbonate at levels of 0.3 weight 
percent unless otherwise stated. Also present in the composition was 0.03 
weight percent of a phosphite stabilizer. 
Mold release effectiveness was determined in an injection molding machine 
with a 4 ounce shot capacity. The part molded was a 3".times.3" box with a 
11/2" wall height. It had ejector pins at four corners with two of the 
pins being attached to strain gauge transducers for measuring the part 
ejection pressure. The mold was designed with very little draft so that 
the part would tend to stick to the core unless mold release is used. To 
vary the amount of shrinkage on the core, the temperature of the 
stationary and moving mold halves could be varied. The ejector pin 
pressure, measured in pounds per square inch, reflects the difficulty of 
ejecting the part under mold conditions. Results are reported below in 
Table I. 
The Yellowness Index (Y.I.) was measured in accordance with ASTM D1825 on 
2".times.3".times.1/8" chips molded at 580.degree. and 650.degree. F. The 
magnitude of the yellowness index and the difference in the Y.I. at two 
molding temperatures are both indications of the detrimental effect of an 
additive on the optical properties of polycarbonate. These measurements 
are also reported in Table I. 
The Kasha Index (KI) was measured to determine the effect of the amide 
release agents on the melt stability of the resin. The KI of a resin is a 
measurement of its melt viscosity and is obtained in the following manner: 
7 grams of resin, dried a minimum of 90 minutes at 125.degree. C., are 
added to a modified Tinius-Olsen model T3 melt indexer; the temperature in 
the indexer is maintained at 300.degree. C. and the resin is heated at 
this temperature for 6 or 12 minutes; after 6 or 12 minutes the resin is 
forced through a 0.04125 inch radius orifice using a plunger of radius 
0.1865 inch and an applied force of 17.7 lbs.; the time required for the 
plunger to travel two inches is measured in centiseconds; that is reported 
as the KI. For a given resin compounded with a series of different 
additives, the most melt stable additive (i.e. the additive which reduces 
the melt viscosity of the resin the least) will display the highest KI. 
Additionally, the smaller the KI drop between 6 and 12 minutes residence 
times or the smaller the KI drop between pellet and part KI, the more melt 
stable the resin additive. Six and twelve minutes as well as part KI data 
are presented in Table I. 
TABLE I 
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650.degree. F. T 
EJECTION PELLET KI (cs) 
KI (6 MIN) 
YI YI DELTA 
ADDITIVE 
PRESSURE (psi) 
6 MIN 
12 MIN 
CENTISECONDS 
580.degree. F. 
650.degree. F. 
YI 
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Pentaeryth- 
5005 2820 
2840 2770 1.7 1.7 0.0 
ritol tetra- 
stearate 
N,N dimethyl 
4220 2610 
2390 2280 2.6 2.8 0.2 
stearamide 
N--methyl, N- 
5300 2320 
2210 1960 2.1 2.5 0.4 
(C.sub.13, C.sub.15 alkyl 
acetamide)* 
N--methyl 
3800 2170 
1730 1410 5.7 18.6 
12.9 
stearamide 
Stearamide 
3350 1740 
1610 1480 2.0 2.5 0.5 
__________________________________________________________________________ 
*This dialkyl acetamide was prepared by the reaction of acetyl chloride 
with a synthetic fatty amine sold under the tradename of Synprolam 35M by 
ICI where R is a mixture of approximately 70% C.sub.13 and 30% C.sub.15. 
The ejection pressure data shows that amides of the invention exhibit mold 
release behavior that is equivalent to or better than the behavior of a 
known mold release agent, pentaerythritol tetrastearate. However, amides 
which are not N,N"-dialkylated (i.e. N-methyl stearamide and stearamide) 
provided much lower resin melt viscosity as measured by 6 and 12 min. KI. 
In addition, the mono N-alkylated amides gave rise to large increases in 
the yellowness, especially when molded at high temperature.