Polyoxymethylene/thermoplastic polyurethane compositions having 5-40 weight percent polyurethane are modified by incorporating therein 0.2-1.0 weight percent ethylene bis-stearamide to improve mold release and mold deposit.

TECHNICAL FIELD 
This invention relates to certain polyoxymethylene compositions which are 
characterized by improved mold release and reduced mold deposit 
characteristics. Polyoxymethylene compositions are generally understood to 
include compositions based on homopolymers of formaldehyde or of cyclic 
oligomers of formaldehyde, for example trioxane, the terminal groups of 
which are end-capped by esterification or etherification, as well as 
copolymers of formaldehyde or of cyclic oligomers of formaldehyde, with 
oxyalkylene groups with at least two adjacent carbon atoms in the main 
chain, the terminal groups of which copolymers can be hydroxyl terminated 
or can be end-capped by esterification or etherification. The proportion 
of the comonomers can be up to 20 weight percent. Compositions based on 
polyoxymethylene of relatively high molecular weight, i.e. 20,000 to 
100,000 are useful in preparing semi-finished and finished articles by any 
of the techniques commonly used with thermoplastic materials, e.g. 
compression molding, injection molding, extrusion, blow molding, 
rotational molding, melt spinning, stamping and thermoforming. Finished 
products made from such compositions possess extremely desirable physical 
properties, including high stiffness, strength and solvent resistance. 
Polyoxymethylene compositions have been recently developed containing 5-40 
weight percent of certain thermoplastic polyurethanes and having 
extraordinary toughness and/or impact resistance. However it has been 
discovered that such polyoxymethylene/polyurethane compositions exhibit 
mold sticking and/or mold deposit under certain conditions. This invention 
relates to improved polyoxymethylene/polyurethane compositions in which 
the mold sticking and mold release problems have been significantly 
reduced or eliminated. 
BACKGROUND ART 
U.S. patent application Ser. No. 464,412, filed Feb. 7, 1983 by E. A. 
Flexman, now abandoned, and its copending continuation-in-part U.S. patent 
application Ser. No. 570,036, filed Jan. 16, 1984, discloses 
polyoxymethylene compositions having extraordinary impact resistance i.e. 
a Gardner impact value (measured according to ASTM D-3029, Method G, 
Geometry D using a 3.6 kg (8 pound) weight and injection molded 
7.62.times.12.7.times.0.16 cm (3.times.5.times.1/16 inch) plaques of 
greater than 9 J (80 in-lb), which compositions consist essentially of 
(a) 5-15 weight percent of at least one thermoplastic polyurethane, which 
polyurethane has a glass transition temperature of lower than 0.degree. 
C., and 
(b) 85-95 weight percent of at least one polyoxymethylene polymer, which 
polyoxymethylene polymer has a molecular weight of from 20,000 to 100,000, 
the above-stated percentages being based on the total amount of components 
(a) and (b) only, the thermoplastic polyurethane being dispersed 
throughout the polyoxymethylene polymer as discrete particles, and the 
composition having a Gardner impact value of greater than 9 J. 
U.S. patent application Ser. No. 464,411, filed Feb. 7, 1983 by E. A. 
Flexman, now abandoned, and its copending continuation-in-part U.S. patent 
application Ser. No. 570,037, filed Jan. 16, 1984, discloses 
polyoxymethylene compositions having extraordinary toughness i.e. a 
notched Izod value (measured according to ASTM D-256, Method A) of greater 
than 375 J/m (7.0 ft-lb/in), which compositions consist essentially of 
(a) greater than 15 weight percent and not more than 40 weight percent of 
at least one thermoplastic polyurethane, which polyurethane has a glass 
transition temperature of lower than -15.degree. C., and 
(b) at least 60 weight percent and less than 85 weight percent of at least 
one polyoxymethylene polymer, which polyoxymethylene polymer has a 
molecular weight of from 20,000 to 100,000, 
the above-stated percentages being based on the total amount of components 
(a) and (b) only, the thermoplastic polyurethane being dispersed 
throughout the polyoxymethylene polymer as a separate phase having an 
average cross-sectional size in the minimum dimension of not greater than 
0.9 microns, and the composition having an Izod value of greater than 375 
J/m. 
The polyoxymethylene compositions disclosed in these two copending 
applications are compositions which can be improved by the present 
invention to give polyoxymethylene compositions characterized by improved 
mold release and reduced mold deposit characteristics. 
U.S. Pat. No. 3,236,929, granted Feb. 22, 1966 to Jupa et al., discloses 
various compounds that are generally added to polyoxymethylene 
compositions to improve mold release characteristics of such compositions. 
Among the compounds disclosed as suitable for this purpose are long-chain 
aliphatic amides, e.g. ethylene bis-stearamide. However the 
polyoxymethylene compositions disclosed in this patent do not contain any 
thermoplastic polyurethane, and one can not extrapolate from 
polyoxymethylene compositions not containing any polyurethane to those 
containing 5-40 weight percent polyurethane with respect to additives for 
improving mold release and reducing mold sticking. This is evidenced by 
the fact that many of the mold release agents disclosed in the reference 
for use in polyoxymethylene compositions not containing any polyurethane 
are not suitable for use in polyoxymethylene compositions containing 5-40 
weight percent polyurethane. 
DISCLOSURE OF THE INVENTION 
This invention relates to certain polyoxymethylene compositions which are 
characterized by improved mold release and reduced mold deposit 
characteristics. The term "polyoxymethylene" as used herein includes 
homopolymers of formaldehyde or of cyclic oligomers of formaldehyde, the 
terminal groups of which are end-capped by esterification or 
etherification, and copolymers of formaldehyde or of cyclic oligomers of 
formaldehyde with oxyalkylene groups with at least two adjacent carbon 
atoms in the main chain, the terminal groups of which copolymers can be 
hydroxyl terminated or can be end-capped by esterification or 
etherification. 
It has been found that toughened and/or impact resistance polyoxymethylene 
compositions consisting essentially of 
(a) 5-40 weight percent of at least one thermoplastic polyurethane, which 
polyurethane has a glass transition temperature of lower than 0.degree. 
C., and 
(b) 60-95 weight percent of at least one polyoxymethylene polymer, which 
polyoxymethylene polymer has a molecular weight of from 20,000 to 100,000. 
the above-stated percentages being based on the total amount of components 
(a) and (b) only, will exhibit mold sticking and/or mold deposit under 
certain conditions. 
It has been further been found that the mold sticking and mold deposit 
characteristic of such polyoxymethylene/polyurethane compositions can be 
significantly reduced or eliminated by incorporating into such 
polyoxymethylene/polyurethane compositions a small quantity of ethylene 
bis-stearamide. More specifically, it has been found that the mold 
sticking and mold deposit characteristic of such 
polyoxymethylene/polyurethane compositions can be significantly reduced or 
eliminated by blending with such polyoxymethylene/polyurethane 
compositions 0.2-1.0 weight percent of ethylene bis-stearamide. 
It has further been found that this small quantity of ethylene 
bis-stearamide will be effective in reducing mold sticking and mold 
deposit characteristic of such polyoxymethylene/polyurethane compositions, 
if it is incorporated into such polyoxymethylene/polyurethane compositions 
at any time prior to molding of such compositions. That is, the ethylene 
bis-stearamide can be blended with the polyoxymethylene, followed by 
blending the polyurethane with the polyoxymethylene/ethylene 
bis-stearamide mixture. Alternatively, the ethylene bis-stearamide can be 
blended with the polyurethane, followed by blending the polyoxymethylene 
with the polyurethane/ethylene bis-stearamide mixture. Alternatively, the 
polyoxymethylene can be blended with polyurethane, followed by blending 
the ethylene bis-stearamide with the polyoxymethylene/polyurethane 
mixture. Alternatively, all three of these ingredients may be blended 
simultaneously. All that is required is that the ethylene bis-stearamide 
be reasonably evenly distributed throughout the 
polyoxymethylene/polyurethane composition. 
It has further been found that of the many and varied compounds that are 
known to be useful for reducing mold sticking and mold deposit of 
polyoxymethylene compositions containing no polyurethane, only ethylene 
bis-stearamide will significantly reduce or eliminate mold sticking and 
mold deposit of the polyoxymethylene/polyurethane compositions described 
above. 
It has further been found that the amount of mold sticking and/or mold 
deposit in such polyoxymethylene/polyurethane compositions increases as 
the quantity of polyurethane in such compositions increases, and 
accordingly, the quantity of ethylene bis-stearamide necessary to 
significantly reduce or eliminate mold sticking and mold deposit in such 
compositions will also increase as the quantity of polyurethane in such 
compositions increases. In any event, amounts of ethylene bis-stearamide 
greater than about 1.0 weight percent seem to offer little additional 
benefit. Similarly, amounts of ethylene bis-stearamide less than about 0.2 
weight percent do not seem to offer significant improvement in the mold 
sticking and mold deposit characteristic of the 
polyoxymethylene/polyurethane compositions described above. 
It has further been found that the small quantity of ethylene 
bis-stearamide used in the compositions of the present invention has the 
additional benefit of increasing the toughness of these compositions as 
measured by elongation and Izod standard tests. 
Accordingly, compositions of the present invention will consist essentially 
of 
(a) 5-40 weight percent of at least one thermoplastic polyurethane, which 
polyurethane has a glass transition temperature of lower than 0.degree. 
C., 
(b) 0.2-1.0 weight percent of ethylene bis-stearamide, and 
(c) a complemental amount of at least one polyoxymethylene polymer, which 
polyoxymethylene polymer has a weight average molecular weight of from 
20,000 to 100,000. 
Various other ingredients, modifiers and/or additives can be included in 
the compositions of the present invention without significantly altering 
the essential features of the present invention as described herein.

For compositions containing 5-15 weight percent polyurethane, such as 
described in copending U.S. Ser. No. 464,412, perferably the Gardner 
impact value will be greater than 9 J (80 in-lb), more preferably greater 
than 17 J (150 in-lb), and most preferably greater than 25 J (225 in-lb). 
For compositions containing 15-40 weight percent polyurethane, such as 
described in copending U.S. Ser. No. 464,411, preferably the Izod value 
will be greater than 375 J/m (7.0 ft-lb/in), more preferably greater than 
500 J/m (9.4 ft-lb/in), and most preferably greater than 650 J/m (12.2 
ft-lb/in). 
For compositions containing 5-15 weight percent polyurethane, such as 
described in copending U.S. Ser. No. 464,412; it is preferred to 
incorporate therein 0.2-0.4 weight percent ethylene bis-stearamide. More 
preferably 0.2 to 0.3 weight percent for the more preferred compositions 
containing 8-12 weight percent polyurethane, and most preferably about 
0.25 weight percent ethylene bis-stearamide for the most preferred 
compositions containing about 10 weight percent polyurethane. For 
compositions containing 15-40 weight percent polyurethane, such as 
described in copending U.S. Ser. No. 464,411, it is preferred to 
incorporate therein 0.3-1.0 weight percent ethylene bis-stearamide, more 
preferably 0.7-0.9 weight percent for the more preferred compositions 
containing 20-35 weight percent polyurethane, and most preferably about 
0.8 weight percent for the most preferred compositions containing 25-32 
weight percent polyurethane. The preferences stated in this paragraph are 
based on both technological and economic consideration. 
It has further been found that incorporation of 0.2-1.0 weight percent 
ethylene bis-stearamide into the polyoxymethylene/polyurethane 
compositions described above does not adversely affect the other important 
physical properties of such polyoxymethylene/polyurethane compositions, 
including extraordinary toughness and/or impact resistance and high 
stiffness, strength, chemical stability and solvent resistance. 
It should be noted that, with respect to compositions containing 5-15 
weight percent polyurethane, for compositions having extraordinary impact 
resistance the polyoxymethylene polymer can be branched or linear and must 
have a weight average molecular weight in the range of 20,000 to 100,000, 
preferably 25,000 to 90,000, more preferably 30,000 to 70,000, and most 
preferably 35,000 to 40,000. 
As an alternative to characterizing the polyoxymethylene by its molecular 
weight, it can be characterized by its melt flow rate. Polyoxymethylenes 
which are preferred for compositions having extraordinary impact 
resistance will have a melt flow rate (measured according to ASTM D-1238, 
Procedure A, Condition G with a 1.0 mm (0.0413 inch) diameter orifice) of 
0.1-30 grams/10 minutes. Preferably, the melt flow rate of the 
polyoxymethylene will be from 0.5-10 grams/10 minutes, most preferably 
about 5 grams/10 minutes for homopolymer and about 9 grams/10 minutes for 
copolymer. 
As indicated above, the polyoxymethylene can be either a homopolymer, a 
copolymer or a mixture thereof. Copolymers can contain one or more 
comonomers generally used in preparing polyoxymethylene compositions. 
Comonomers more commonly used include alkylene oxides of 2-12 carbon 
atoms. If copolymer is selected, the quantity of comonomer will be not 
more than 20 weight percent, preferably not more than 15 weight percent, 
and most preferably about 2 weight percent. The most preferred comonomer 
is ethylene oxide, and preferred polyoxymethylene copolymers are 
dipolymers of formaldehyde and ethylene oxide where the quantity of 
ethylene oxide is about 2 weight percent. Generally, polyoxymethylene 
homopolymer is preferred over copolymer. The most preferred homopolymers 
for use in compositions having extraordinary impact resistance are those 
with a molecular weight of about 38,000 and those with terminal hydroxyl 
groups which have been end-capped by a chemical reaction to form ester or 
ether groups, preferably acetate or methoxy groups, respectively. 
Thermoplastic polyurethanes preferred for use in compositions having 
extraordinary impact resistance can be selected from those commercially 
available or can be made by processes known in the art. (See, for example, 
Rubber Technology, 2nd edition, edited by Maurice Morton (1973), Chapter 
17, Urethane Elastomers, D. A. Meyer, especially pp. 453-6). Polyurethanes 
are derived from the reaction of polyester or polyether polyols with 
diisocyanates and optionally also from the further reaction of such 
components with chain-extending agents such as low molecular weight 
polyols, preferably diols. Polyurethane elastomers are generally composed 
of soft segments, for example polyether or polyester polyols, and hard 
segments, derived from the reaction of the low molecular weight diols and 
diisocyanates. While a polyurethane elastomer with no hard segments can be 
used, those most useful will contain both soft and hard segments. 
In the preparation of the thermoplastic polyurethanes, preferred for use in 
compositions having extraordinary impact resistance, a polymeric soft 
segment material having at least two hydroxyl groups per molecule and 
having a molecular weight of at least about 500 and preferably from about 
550 to about 5,000 and most preferably from about 1,000 to about 2,500, 
such as a dihydric polyester or a polyalkylene ether diol, is reacted with 
an organic diisocyanate in a ratio such that a substantially linear 
polyurethane polymer results, although some branching can be present. A 
diol chain extender having a molecular weight less than about 250 may also 
be incorporated. The mole ratio of isocyanate to hydroxyl in the polymer 
is preferably from about 0.95 to 1.08, more preferably 0.95 to 1.05, and 
most preferably, 0.95 to ?1.00. 
Suitable polyester polyols include the polyesterification products of one 
or more dihydric alcohols with one or more dicarboxylic acids. Suitable 
dicarboxylic acids include adipic acid, succinic acid, sebacic acid, 
suberic acid, methyladipic acid, glutaric acid, pimelic acid, azelaic 
acid, thiodipropionic acid and citraconic acid and mixtures thereof. 
Suitable dihydric alcohols include ethylene glycol, propylene glycol, 
1,4-butanediol, 1,3-butanediol, 2-methyl pentane diol-1,5, diethylene 
glycol, pentanediol, hexanediol and mixtures thereof. 
Further, hydroxycarboxylic acids, lactones, and cyclic carbonates, such as 
caprolactone and hydroxybutyric acid can be used in the preparation of the 
polyester. 
Preferred polyesters include poly(ethylene adipate), poly(1,4-butylene 
adipate), mixtures of these adipates and polycaprolactone. 
Suitable polyether polyols include the condensation products of one or more 
alkylene oxides with a small amount of one or more compounds having active 
hydrogen containing groups, such as water, ethylene glycol, 1,2- or 
1,3-propylene glycol, 1,4-butanediol and 1,5-pentanediol, and mixtures 
thereof. Suitable alkylene oxide condensates include those of ethylene 
oxide, 1,2-propylene oxide and butylene oxide and mixtures thereof. 
Suitable polyalkylene ether glycols may also be prepared from 
tetrahydrofuran. In addition, suitable polyether polyols can contain 
comonomers, especially as random or block comonomers, ether glycols drived 
from ethylene oxide, propylene oxide, and/or tetrahydrofuran (THF). 
Alternatively, a THF polyether copolymer with minor amounts of 3-methyl 
THF can also be used. 
Preferred polyethers include polytetramethylene ether glycol (PTMEG), 
polypropylene oxide, copolymers of propylene oxide and ethylene oxide, and 
copolymers of tetrahydrofuran and ethylene oxide. 
Suitable organic diisocyanates include 1,4-butylene diisocyanate, 
1,6-hexamethylene diisocyanate, cyclopentylene-1,3-diisocyanate, 
4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 
cyclohexylene-1,4-diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene 
diisocyanate, isomeric mixtures of 2,4- and 2,6-tolylene diisocyanate, 
4,4'-methylene bis(phenylisocyanate), 
2,2-diphenylpropane-4,4'-diisocyanate, p-phenylene diisocyanate, 
m-phenylene diisocyanate, xylylene diisocyanate, 1,4-naphthylene 
diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diphenyl diisocyanate, 
azobenzene-4,4'-diisocyanate, m- or p-tetramethylxylene diisocyanate and 
1-chlorobenzene-2,4-diisocyanate. 4,4'-Methylene bis(phenylisocyanate), 
1,6-hexamethylene diisocyante, 4,4'-dicyclohexylmethane diisocyanate and 
2,4-tolylene diisocyanate are preferred. 
Secondary amide linkages including those derived from adipyl chloride and 
piperazine, and secondary urethane linkages, including those derived from 
the bis-chloroformates of PTMEG and/or butanediol, can also be present in 
the polyurethanes. 
Dihydric alcohols suitable for use as chain extending agents in the 
preparation of the thermoplastic polyurethanes include those containing 
carbon chains which are either uninterrupted or which are interrupted by 
oxygen or sulfur linkages, including 1,2-ethanediol, 1,2-propanediol, 
isopropyl-a-glyceryl ether, 1,3-propanediol, 1,3-butanediol, 
2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 
2-ethyl-2-butyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 
2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-butanediol, 
2,5-hexanediol, 1,5-pentanediol, dihydroxycyclopentane, 1,6-hexanediol, 
1,4-cyclohexanediol, 4,4'-cyclohexanedimethylol, thiodiglycol, diethylene 
glycol, dipropylene glycol, 2-methyl-1,3-propanediol, 
2-methyl-2-ethyl-1,3-propanediol, dihydroxyethyl ether of hydroquinone, 
hydrogenated bisphenol A, dihydroxyethyl terephthalate and dihydroxymethyl 
benzene and mixtures thereof. 1,4-butane diol, 1,2-ethane diol and 
1,6-hexane diol are preferred. 
In the preparation of the thermoplastic polyurethanes the ratio of 
isocyanate to hydroxyl should be close to unity, and the reaction can be a 
one step or a two step reaction. Catalyst can be used, and the reaction 
can be run neat or in a solvent. 
Apart from what is described above concerning selection of the 
polyurethane, the most important characteristic of the thermoplastic 
polyurethane with respect to obtaining compositions having extraordinary 
impact resistance is its glass transition temperature (Tg). Wherever a 
glass transition temperature is reported herein, it is as determined using 
a Du Pont Model 981 Dynamic Mechanical Analysis Cell attached to a Model 
990 Thermal Analyzer. The cell is modified to use liquid nitrogen as the 
coolant and to allow the use of a 3.2 cm (1.25 inch) gap holding the 
specimen. The oscillation amplitude is set at 0.2 mm. A heating rate of 
2.5.degree. C./min is used from -170.degree. C. to 0.degree. to 40.degree. 
C. depending on the signal amplitude. Readings are taken every 1.degree. 
C. increment. The storage and loss moduli are plotted and the major loss 
modulus peak is defined as the soft segment glass transition temperature. 
Compositions having extraordinary impact resistance can best be made when 
the soft segment glass transition temperature of the thermoplastic 
polyurethane is less than 0.degree. C. Preferably, the soft segment glass 
transition temperature of the polyurethane should be less than -10.degree. 
C., more preferably below -15 C., and most preferably below -30.degree. C. 
Combinations or mixtures of thermoplastic polyurethanes can also be used. 
For compositions having extraordinary impact resistance the molecular 
weight of the soft segment of the thermoplastic polyurethane should 
average between about 500 and about 5000, preferably about 850-3000, more 
preferably about 1000-2500, with the most preferred polyurethanes having 
soft segments with an average molecular weight of about 2000. 
Similarly, for compositions having extraordinary impact resistance, the 
moisture content of the composition, and of the polyurethane, should be 
less than 0.2 percent by weight of water, preferably less than 0.1 
percent, especially when there is no opportunity for the water to escape, 
for example during injection molding. 
For compositions having extraordinary impact resistance the polyurethane 
must be intimately mixed and dispersed as discrete particles in the 
polyoxymethylene, and it must be maintained in that state during the 
formation of the finished products. 
Any intensive mixing device capable of developing high shear at 
temperatures above the melting points of the ingredients can be used to 
disperse the polyurethane in the polyoxymethylene and to incorporate the 
ethylene bis-stearamide into the polyoxymethylene/polyurethane 
compositions. Examples of such devices include rubber mills, internal 
mixers such as "Banbury" and "Brabender" mixers, single or multiblade 
internal mixers with a cavity heated externally or by friction, 
"Ko-kneaders", multibarrel mixers such as "Farrel Continuous Mixers", 
injection molding machines, and extruders, both single screw and twin 
screw, both co-rotating and counter rotating. These devices can be used 
alone or in combination with static mixers, mixing torpedos and/or various 
devices to increase internal pressure and/or the intensity of mixing such 
as valves, gates or screws designed for this purpose. Continuous devices 
are preferred. Twin screw extruders are especially preferred, particularly 
those incorporating high intensity mixing sections such as reverse pitch 
elements and kneading elements. The mixing device used in all of the 
examples of the present application unless noted otherwise was a 28 mm 
co-rotating Werner and Pfleiderer twin screw extruder, using a screw 
design containing two working sections with a total of five kneading 
elements, two reverse elements, and a vacuum port at about 70% of the 
distance from the feed throat to the die. All zones were set at 
190.degree. C. Temperature of the melt coming out of the die was about 
220.degree.-260.degree. C. A low flow of cooling water was used to reduce 
temperatures in some cases. The extruder was operated at 200-250 rpm with 
6.8-13.6 kg (15-30 pounds) per hour throughput. A nitrogen blanket was 
maintained over the feed throat to exclude oxygen and preserve dryness of 
the ingredients, and the strand exiting the die was quenched in water and 
cut into pellets. One can deviate from those conditions. For example melt 
temperatures below 190.degree. C. or higher than 260.degree. C. are 
possible if throughput is adjusted to compensate. However, 
170.degree.-260.degree. C. is considered preferred, with 
185.degree.-240.degree. C. preferred, and 200.degree.-230.degree. C. most 
preferred for melt compounding. 
For compositions having extraordinary impact resistance it is important to 
maintain the conditions created in the melt compounded material, such as 
distribution of the thermoplastic polyurethane as discrete particles in 
the polyoxymethylene, dryness of the composition, etc. Shaped articles 
made from the compositions of the present invention can be made by any of 
several common methods, including compression molding, injection molding, 
extrusion blow molding, rotational molding, thermoforming and stamping. 
Such shaped articles can be post treated by orientation, stretching, 
coating, annealing, painting, laminating and plating. Unused shaped 
articles, rejected shaped articles or waste composition of the present 
invention can be ground and remolded. 
Generally, the conditions used in the preparation of shaped articles will 
be similar to those described above for melt compounding. More 
specifically, melt temperatures and residence times can be used up to the 
points at which significant degradation of the composition occurs. 
Preferably, the melt temperature will be about 170.degree.-250.degree. C., 
more preferably about 185.degree.-240.degree. C., and most preferably 
about 200.degree.-230.degree. C. When injection molding the compositions 
of the present invention, it is preferable that the mold be as cold as 
possible consistent with the intricacy of the shape being produced. 
However, colder molds are harder to fill, particularly where the passages 
may be narrow or the shape is intricate. Generally, the mold temperature 
will be 10.degree.-120.degree. C., preferably 10.degree.-100.degree. C., 
and most preferably the mold temperature will be about 
50.degree.-90.degree. C. Similarly, the cycle time, which determines the 
total hold-up time in the melt, can be adjusted to fit the particular 
conditions being encountered. For example, if the total hold-up time in 
the melt is too long, the composition can degrade. If the cycle time is 
too short, the shaped article may not totally solidify while the mold is 
still under pressure. Generally, total hold-up time in the melt will be 
about 3-15 minutes, with the shorter times being preferred, consistent 
with giving a high quality shaped article. 
The preferences stated above with respect to the preparation of 
compositions containing 5-15 weight percent polyurethane and having 
extraordinary impact resistance will hold for the preparation of 
compositions containing &gt;15-40 weight percent polyurethane and having 
extraordinary toughness except as specified below. Certain additional 
preferences stated below will apply to the preparation of compositions 
containing &gt;15-40 weight percent polyurethane and having extraordinary 
toughness. 
For compositions having extraordinary toughness the polyoxymethylene 
polymer will preferably have a weight average molecular weight in the 
range of 20,000 to 100,000, preferably 25,000 to 90,000, more preferably 
30,000 to 70,000, and most preferably 60,000-70,000. 
As an alternative to characterizing the polyoxymethylene by its weight 
average molecular weight, it can be characterized by its melt flow rate. 
Polyoxymethylenes which are preferred for compositions having 
extraordinary toughness will have a melt flow rate (measured according to 
ASTM D-1238, Procedure A, Condition G with a 1.0 mm (0.0413 inch) diameter 
orifice) of 0.1-30 grams/10 minutes. Preferably, the melt flow rate of the 
polyoxymethylene used in the compositions of the present invention will be 
from 0.5-10 grams/10 minutes. The most preferred polyoxymethylenes are 
linear polyoxymethylenes with a melt flow rate of about 1 gram/10 minutes 
or branched polyoxymethylenes with a melt flow rate of less than 1 gram/10 
minutes polyoxymethylene homopolymer is preferred. The most preferred 
homopolymers for use in compositions having extraordinary toughness are 
those with a molecular weight of about 65,000 and those with terminal 
hydroxyl groups which have been end-capped by a chemical reaction to form 
ester or ether groups, preferably acetate or methoxy groups, respectively. 
For compositions having extraordinary toughness the polyoxymethylene 
polymer will comprise the continuous phase of such compositions and the 
thermoplastic polyurethane will be dispersed throughout the continuous 
phase polyoxymethylene. The thermoplastic polyurethane can comprise 
discrete particles dispersed throughout the polyoxymethylene continuous 
phase, and this configuration is most commonly found when the proportion 
of polyurethane in the composition is relatively low. These particles of 
polyurethane can be approximately spherical in shape (i.e. the particles 
will have an aspect ratio approximately equal to 1.0) or elongated (i.e. 
the particles will have an aspect ratio substantially greater than 1.0), 
and their size distribution can be Gaussian, bi- or polymodal, or other. 
If elongated, they can be only slightly elongated and approximately oval 
in shape, or they can be greatly elongated and resemble strands of 
thermoplastic polyurethane running through the polyoxymethylene continuous 
phase. In fact it is possible for such strands to run continously the full 
length of an article made from such compositions. Alternatively, such 
strands can be interconnected so as to form a network of thermoplastic 
polyurethane particles throughout the polyoxymethylene continuous phase, 
and this configuration is most commonly found when the proportion of 
polyurethane in the composition is relatively high. 
It has been observed that when the polyurethane phase is elongated, the 
direction of elongation is generally the same for all the phase and is 
generally in the direction of the shear applied during the final stage of 
the preparation of the composition while still in its molten state. For 
example, in the preparation of such compositions in a rod shape by melt 
compounding in a twin-screw extruder, followed by passage through a round 
die and quenching in water, the elongation, if any, of the thermoplastic 
polyurethane will generally run parallel to the axis of the rod. It has 
been found most useful for the purpose of characterizing such compositions 
to measure average cross-sectional size of the polyurethane phase in a 
plane perpendicular to the direction of elongation of the thermoplastic 
polyurethane particles and in the center of the formed article. 
Average cross-sectional size is measured by the following technique. A 
"Sorvall" MT-2B ultra-microtome equipped with a diamond knife and a 
"Sorvall-Christensen" FTS-LTC-2 sectioner, operating at -90.degree. C., is 
used to cut sections 200 nanometers thick from the center area of a molded 
0.32.times.1.27.times.12.7 cm (1/8.times.1/2.times.5 in) bar perpendicular 
to the bar axis. Ethanol is used as a knife lubricant and a number of 
slices are collected and then placed a petri dish containing distilled 
water. The mixing action of the ethanol and water spreads the microtomed 
slices apart and allows them to float on the top of the water. The 
microtomed slices are placed on a 200 mesh copper microscope grid. 
Electron photomicrographs of typical areas are photographed at 2500X using 
a Zeiss EM10A electron microscope at 80 KV equipped with a 70 mm roll film 
camera and Eastman 5302 film. Darkroom enlargements of the microscope 
negatives results in final 20.3.times.25.4 cm (8.times.10 in) 
photomicrographs at 11,800X. 
Two 10.2.times.12.7 cm (4.times.5 in) pieces are cut from each 
20.3.times.25.4 cm (8.times.10 in) photomicrograph with the 12.7 cm (5 in) 
edge of each piece parallel to the preferential direction, if any, in 
which most of the polyurethane was oriented. Most photomicrographs have 
such a direction. Each photomicrograph is scanned across the short 
dimension one row at a time by a flying spot scanner 200 microns square. 
This photomicrograph line of spots appears as a pattern of light and dark 
areas with varying levels of grey between them. The average density of 
this line is calculated. All images darker (more dense) than this average 
value are considered to be the thermoplastic polyurethane phase. 
Conversely all images lighter than this line are considered to be the 
polyoxymethylene matrix. The mean length of the up pulses (dark areas or 
thermoplastic polyurethane phase) is calculated. This measure is referred 
to hereinafter as the average cross-sectional size in the minimum 
dimension. 
Compositions having extraordinary toughness can be made when the average 
cross-sectional size of the thermoplastic polyurethane is not greater than 
0.9 microns. Preferably the average cross-sectional size of the 
thermoplastic polyurethane will be less than 0.7 microns, most preferably 
less than 0.5 microns. As a practical matter, the polyurethane phase 
should also have an average cross-sectional size of at least 0.01 microns. 
Apart from what is described above concerning selection of the 
polyurethane, the most important characteristic of the thermoplastic 
polyurethane with respect to obtaining compositions having extraordinary 
toughness is its soft segment glass transition temperature (Tg). 
Compositions having extraordinary toughness can best be made when the soft 
segment glass transition temperature of the thermoplastic polyurethane is 
less than -15.degree. C. Preferably, the soft segment glass transition 
temperature of the polyurethane should be less than -20.degree. C. and 
most preferably below -30.degree. C. Combinations or mixtures of 
thermoplastic polyurethanes can also be used. For compositions having 
extraordinary toughness one should generally use a thermoplastic 
polyurethane with an inherent viscosity of 0.7 or above (as measured by 
ASTM D-2857 with a "Schott" automatic viscometer at 0.1% polyurethane in 
dimethyl formamide at 30.degree. C.). Thermoplastic polyurethanes having 
inherent viscosities up to 2.7 have been used successfully in such 
compositions, but those having inherent viscosities of 0.75-2.5 are 
generally preferred, with those having inherent viscosities of 1.0-1.7 
being most preferred. Alternatively, it is possible to start with a 
polyurethane having a very low inherent viscosity, and then modify it 
during the blending operation, e.g. by further polymerization or 
cross-linking, thus increasing the effective viscosity of the polyurethane 
to a desirable level, even though the inherent viscosity of the starting 
material polyurethane was quite low. Alternatively, one could begin with a 
polyurethane having a higher inherent viscosity and degrade or hydrolyze 
it during compounding to obtain the desired effective viscosity. 
In the following examples, there are shown specific embodiments of the 
present invention and certain side-by comparisons with embodiments of 
control experiments with compositions containing a compound generally used 
to reduce mold sticking and mold deposit of polyoxymethylene compositions 
not containing any polyurethane, said compound being other than ethylene 
bis-stearamide. It will be seen that the compositions of the present 
invention are characterized by significantly reduced or eliminated mold 
sticking and mold deposit, while the control compositions are not. All 
parts and percentages are by weight, and all temperatures are in degrees 
Celsius unless otherwise specified. Measurements not originally in SI 
units have been so converted and rounded where appropriate. 
In each of the following examples, molding of the blends to determine mold 
sticking and mold deposit was conducted with a 125 ton Spartan injection 
molding machine manufactured by HPM, Inc. This unit was equipped with a 
screw injection unit having a 4.5 cm (1.75 inch) diameter screw. Plaques 
0.32 cm (1/8 inch) thick were molded at cylinder temperatures of 
176.degree.-197.degree. C., cycles (injection/hold) of 15/15 seconds, 
20/15 seconds and 30/15 seconds. The procedure throughout was to purge the 
machine with each example, to clean the mold of all deposit with a slurry 
of alumina in water, and then to mold 30 shots on cycle unless the parts 
stuck so severly that the machine had to be stopped to remove the parts, 
in which case no further molding of that example was attempted. 
All of Examples 1-25 were based on blends of 30 weight percent of a 
thermoplastic polyurethane having an inherent viscosity of 1.33, a glass 
transition temperature of -35.degree. C., and a chemical composition of 37 
weight percent adipic acid, 39 weight percent butane diol, and 24 weight 
percent methylene bisphenyl isocyanate, 0.75 weight percent of a polyamide 
stabilizer (terpolymer of approximately 38% polycaprolactam/35% 
polyhexamethylene adipamide/27% polyhexamethylene sebacamide), 0.11 weight 
percent of 2,2'-methylene bis(6-t-butyl-4-methyl phenol)antioxidant, 
lubricant and polycarbodiimide as specified in Table I, and a complemental 
amount of acetate end-capped polyoxymethylene homopolymer (prepared 
according to U.S. Pat. No. 2,998,409) having a weight average molecular 
weight of about 63,000. In addition to varying the quantity and type of 
lubricant as indicated in Table I, certain compositions (as indicated in 
Table I) contained 0.1 weight percent (except for control Example Number 2 
which had 0.3 weight percent) of a polycarbodiimide (or a mixture of 
polycarbodiimides) having a molecular weight of about 1000 and containing 
units of the formula 
##STR1## 
where n has an average value of about 3. 
In Table I, all data is reported for a 0.32 cm (1/2 inch) plaque mold, with 
100.degree. C. mold surface temperature. The term "delamination" refers to 
a surface defect produced when parts which are stuck to the mold surface 
are mechanically forced from the mold by ejector pins, thus forming a 
partially detached thin layer. 
It should be noted that the polyurethane used in all of the following 
examples was a commercial product that contained 0.6 weight percent 
ethylene bis-stearamide. Accordingly, compositions containing 30 weight 
percent polyurethane will contain about 0.18 weight percent ethylene 
bis-stearamide plus whatever quantity and type of lubricant is indicated 
in the Table. Thus, the values listed in the Table under "% Added 
Lubricant" do not include the 0.18% ethylene bis-stearamide that enters 
the compositions tested via the polyurethane. Similarly, in Example 26, 
which contains 10 weight percent polyurethane, 0.06% ethylene 
bis-stearamide is added via the polyurethane. Example 26 recites only the 
added lubricant. However, at all other places in this application, 
including in the claims, the amount of ethylene bis-stearamide recited is 
the total amount, including any amount that may be incorporated via the 
polyurethane. 
TABLE 1 
__________________________________________________________________________ 
% Added 
Polycarbo- 
Molding Performance 
Example 
Lubricant 
Lubricant 
imide (%) 
Sticking 
Delamination 
Deposit 
__________________________________________________________________________ 
1 None -- 0 Yes Yes Yes, after 
30 shots 
2 None -- 0.3 Yes, totally 
No yes 
stuck on shot 
#16 
3 ethylene-bis- 
0.5 0 No No slight 
stearamide 
4 pentaeryth- 
0.5 0 Yes Yes severe 
ritol tetra- 
stearate 
5 polyethylene 
1.5 0 No Yes moderate 
glycol 
6 silicone oil 
1.0 0 Decomposed/ 
-- -- 
stuck 
7 polyethylene 
1.0 0 Totally stuck 
-- -- 
wax on shot #5 
8 stearyl eruca- 
0.3 0.1 No Yes moderate 
mide 
9 stearyl eruca- 
0.6 0.1 No severe moderate 
mide 
10 polyethylene 
2.0 0.1 No severe -- 
wax 
11 alkyl phthalate 
1.0 0.1 No severe severe 
12 benzyl phthalate 
1.0 0.1 No severe slight 
13 benzene sulfon- 
1.0 0.1 No severe moderate 
amide 
14 neopentyl 
1.0 0.1 No severe heavy 
glycol 
dibenzoate 
15 N,N'erucyl 
1.0 0.1 No Yes slight 
adipamide 
16 polyethylene 
1.0 0.1 Yes very 
glycol bis-2- slight 
ethylhexanoate 
17 ethylene bis- 
0.3 0.1 No No moderate 
stearamide 
18 ethylene bis- 
0.4 0.1 No No slight 
stearamide 
19 ethylene bis- 
0.5 0.1 No No slight 
stearamide 
20 ethylene bis- 
0.6 0.1 No No slight 
stearamide (haze on 
mold) 
21 ethylene bis- 
0.8 0.1 No No slight 
stearamide (haze on 
mold) 
22 ethylene bis- 
1.0 0.1 No No slight 
stearamide (haze on 
mold) 
23 ethylene bis- 
1.25 0.1 No No slight 
stearamide (haze on 
mold) 
24 ethylene glycol 
0.6 0.1 No severe heavy 
distearate 
25 ethylene bis- 
0.6 0.1 No Yes heavy 
oleamide 
__________________________________________________________________________ 
EXAMPLE 26 
A sample was prepared for evaluation containing 10 weight percent of the 
same thermoplastic polyurethane used in Examples 1-25, 0.75 weight percent 
of the same polyamide stabilizer, 0.11 weight percent of the same 
antioxidant, 0.1 weight percent of the same polycarbodiimide, 0.2 weight 
percent added ethylene bis-stearamide and a complemental amount of acetate 
end-capped polyoxymethylene homopolymer having a weight average molecular 
weight of about 38,000. It was evaluated for mold sticking and deposit 
against a compositions as described above, but with no added ethylene 
bis-stearamide. Neither resin showed mold deposit. The sample with added 
ethylene bis-stearamide showed little mold sticking, while the sample with 
no added ethylene bis-stearamide showed considerable sticking in hot 
molds. 
EXAMPLES 27-41 
A series of experiments was conducted to evaluate the effect of ethylene 
bis-stearamide on the elongation and Izod values of the compositions of 
the present invention. Compositions were prepared substantially as 
described for Examples 1-25 except as noted in the following table. 
Tensile strength was measured in accord with ASTM-D-638; elongation was 
measured in accord with ASTM-D-638; and Izod was measured in accord with 
ASTM-D-256. Antioxidant A was 4,4'-butylidene 
bis(6-t-butyl-3-methylphenol) and antioxidant B as 1,6-hexamethylene 
bis(3,5-di-tert-butyl-4-hydroxyhydro cinnamate). All compositions 
contained 0.1% antioxidant. 
TABLE I 
______________________________________ 
Ethylene Anti- Elon- 
Ex- bis-stear- Oxi- Tensile 
gation Izod 
ample amide (%) dant (MPa) (%) J/m 
______________________________________ 
27 0 A 42.0 200 1015 
28 0.3 A 42.0 230 961 
29 0.6 A 42.0 205 1175 
30 0 A 42.7 135 908 
31 0.2 A 42.7 140 1015 
32 0.4 A 42.0 205 1121 
33 0.6 A 40.7 185 1282 
34 0 B 44.1 110 534 
35 0.6 B 40.7 245 854 
36 0 B 42.7 175 908 
37 0.6 B 42.0 205 1015 
38 0 B 42.0 280 961 
39 0.6 B 41.4 260 961 
40 0 B 42.7 135 934 
41 0.6 B 41.4 190 1041 
______________________________________ 
INDUSTRIAL APPLICABILITY 
The polyoxymethylene compositions of the present invention are useful in 
the manufacture of finished articles such as sports helmets, safety 
helmets, shoe cleats, safety steering column components, specialty 
zippers, railroad tie insulators, ski bindings, mechanical conveyors and 
small engine components. The extraordinary impact resistance and/or 
toughness and exceptional wear resistance of articles made from these 
compositions combined with other outstanding properties normally found in 
polyoxymethylene compositions make them particularly well suited for 
applications such as gears, moving parts and fuel tanks. 
BEST MODE 
Although the best mode of the present invention, i.e. the single best 
polyoxymethylene composition of the present invention, will depend upon 
the particular desired end use and the specific requisite combination of 
properties for that use, the single composition and molding conditions of 
the present invention that result in a product most preferred for its 
overall balance of properties is described in detail in Example 20 for 
compositions containing 30 weight percent polyurethane and in Example 26 
for compositions containing 10 weight percent polyurethane. While it is 
not a part of the present invention, it is preferred to incorporate in the 
compositions of the present invention about 0.1 weight percent of a 
polycarbodiimide (or a mixture of polycarbodiimides) having a molecular 
weight of about 1000 and containing units of the formula 
##STR2## 
where n has an average value of about 3.