Thermoplastic resin composition for biaxial orientation

Thermoplastic resin compositions comprising a thermoplastic resin capable of biaxial orientation and an additive resin, having a molecular weight above 10.sup.6, compatible with said thermoplastic resin and selected from a homopolymer of a vinyl monomer or a copolymer of at least two vinyl monomers.

BACKGROUND OF THE INVENTION 
It is known how to manufacture from thermoplastic resins, such as polyvinyl 
chloride (PVC) and acrylonitrile-butadiene-styrene copolymers (ABS), 
finished articles presenting improved mechanical characteristics by 
orienting the macromolecules. Such is now being practiced in the domain of 
synthetic fibers. Industrial applications of this principle are starting 
to be developed in order to obtain plates, films, tubes or bottles, 
particularly in PVC. Orientation can take place in one direction or in two 
orthogonal directions, and in proportion to the orientation achieved, we 
can observe an important increase in the rigidity and in the impact 
strength (resistance to shock), whereas the gas permeability diminishes. 
This orientation operation carried out in continuous or in discontinuous 
manner comes to be added to the customary stages of the shaping (molding) 
operation of the thermoplastic polymers. The practical conditions for 
obtaining a substantial orientation of the macromolecules, for instance 
the temperature at which the operation must take place, are not customary 
and pose problems with regard to the production of the material. 
In order to orient the macromolecules to the maximum and to preserve a 
sufficient level of orientation in the finished material, a high speed 
traction must be exerted on the material, and this while the polymer is in 
its visco-elastic phase, that is to say at an unusually low temperature, 
near the glass transition temperature; i.e., for example, for PVC in the 
85.degree.-110.degree. C. interval. Then the stretched material must be 
cooled rapidly, as soon as the end of drawing, in order to avoid the 
relaxation phenomenon, if one desires to preserve the maximum benefit of 
the achieved orientation. It has been observed that the closer the 
temperature of the material is, at the moment it is being stretched, to 
the glass transition temperature, the more effective is the final 
orientation or residual orientation or orientation which subsists in the 
material and the better is the rigidity of the final product after 
cooling. 
On the other hand, the closer the vitreous transition temperature is being 
approached, the higher is the stress to be applied onto the material in 
order to stretch it to orient it. Consequently, the means required for the 
orientation of a flat plate, for instance, which comprises fastening 
devices attached to the plate on its edges and one or two traction 
mechanisms, will be all the more voluminous and costly when it is desired 
to stretched the material at low temperature. In the same manner, if one 
desires to orient a tube in both directions, the longitudinal traction and 
the internal pressure to be exerted will be all the greater, thus more 
costly, with lower temperatures being approached. 
A priori it would thus be advantageous to stretch the material at a 
temperature clearly higher than the glass transition temperature, for 
instance in the 130.degree.-150.degree. C. zone, since the necessary 
stress would be lower. Unfortunately, at these higher temperatures, the 
elongation capacity of the material is such smaller and the relaxation 
velocity of the polymer chains is higher, so that only elongations 
insufficient to provide an orientation which appreciably improves the 
final mechanical characteristics can be obtained. Under these conditions, 
only an elongation of the order of 100% can be obtained for the PVC, for 
instance, and such an elongation of the order of 100% is not sufficient 
for bringing on a residual or final orientation. 
These consideration on the behavior on stretching of a thermoplastic resin 
in its elastic phase, as a function of the temperature, are illustrated by 
FIG. 1, a graph, which at (a) gives the elongation at break, at (b) the 
stress at break and at (c) the stress at 200% of elongation as a function 
of the temperature, for non-plasticized PVC stretched at a speed of 666% 
per minute. FIG. 2 is a graph showing the stress at break in traction at 
23.degree. C. and at a speed of 5 mm/minute of non-plasticized PVC 
specimens previously oriented by 200% elongation at a speed of 666%/min; 
then rapidly cooled down, as a function of the temperature at orientation. 
By considering these two graphs simultaneously, it can be seen that if one 
wishes to stretch by 200%, a better final rigidity is obtained by doing it 
at 100% C. rather than at 120.degree. C., but then the stress force to be 
exerted amounts to 3.5 MPa instead of 2.5 MPa. 
SUMMARY OF THE INVENTION 
The present invention provides thermoplastic resin compositions which make 
it possible to obtain biaxially oriented materials with improved 
mechanical properties; which compositions require lower tensile force to 
stretch them during orientation. 
Briefly, the present invention relates to thermoplastic resin compositions 
comprising a thermoplastic resin capable of biaxial orientation and an 
additive resin, having a molecular weight above 10.sub.6, compatible with 
said thermoplastic resin; there being about 0.2 to 5 parts by weight of 
said additive resin for each 100 parts by weight of said thermoplastic 
resin. 
DETAILED DESCRIPTION 
As to the thermoplastic resin capable of biaxial orientation, suitable are 
vinyl chloride homopolymers and copolymers, styrenic homopolymers and 
copolymers, and mixtures of the foregoing with one or more elastomers. 
Specific examples are: 
(A) The homopolymers of vinyl chloride, as is or having undergone, after 
polymerization, a chemical reaction; for instance, a super-chlorination, 
as well as the copolymers of vinyl chloride with one or several other 
copolymerizable monomers such as: vinyl acetate, vinylidene chloride, 
vinyl and vinylidene fluorides, vinyl esters of aliphatic acids, 
alkylvinyl ethers, unsaturated acids (such as acrylic acid, methacrylic 
acid, crotonic acid, maleic acid, fumaric acid, undecanoic acid, metallic 
salts or alkylic esters of such acids, acrylonitrile, or 
methacrylonitrile, olefins such as ethylene, propylene or isobutylene, 
acrylamide and maleimides which are either substituted or not substituted, 
and aromatic vinyl monomers. 
(B) The styrene polymers comprising, in particular, styrene homopolymers, 
copolymers of styrene and/or derivatives of styrene substituted on the 
ring or in the alpha position, such as chloro or dichlorostyrene, 
vinyltoluene, alpha-methylstyrene, with one or several copolymerizable 
monomers, such as acrylonitrile, methacrylonitrile, acrylic and 
methacrylic acids and their alkyl esters, in particular methyl ethyl and 
butyl esters. 
(C) The mixtures of one or several of the products of type A and B above 
with one or several elastomers intended to improve the impact resistance, 
for instance acrylonitrile-styrene copolymer reinforced by a cross-linked 
acrylonitrile-butadiene elastomer prepared in aqueous emulsion, or by a 
grafting product of acrylonitrile and of styrene on a elastomer of 
polybutadiene, PVC or copolymer of vinyl chloride reinforced by an 
acrylonitrile-butadiene elastomer, a chlorinated polyethylene, a grafting 
product of vinyl chloride or of acrylonitrile and of styrene on a 
polybutadiene, or a saturated acrylic elastomer or of polyolefins, or yet 
of the vinyl ethylene-acetate type. 
The additive resin is a polymer obtained by the polymerization of one or 
several copolymerizable vinyl monomers. 
Nonlimiting examples of such additive polymers are the polymers obtained 
from vinylaromatic hydrocarbons like styrene or alpha-methyl-styrene, from 
vinyl cyanide like acrylonitrile or methacrylonitrile, from acrylic and 
methacrylic acids or from their derivatives, principally acrylic and 
methacrylic acid esters. 
The preferred additive polymers are the styrene-acrylonitrile copolymers, 
the polymers of the same type in which the styrene and/or acrylonitrile 
are replaced entirely or in part by the corresponding substituted monomers 
such as the methacrylonitrile-styrene copolymers, or the 
alphamethylstyrene-styrene-acrylonitrile terpolymers, as well as 
polyacrylates or polymethylmethacrylates, the copolymers of acrylate 
and/or methylmethacrylate-ethyl acrylate, the copolymers of methyl 
methacrylate-styrene and/or alpha methylystyrene, the polymers methyl 
methacrylate-styrene-acrylonitrile. 
The molecular weight of the additive polymer, determined by the application 
of the STAUDINGER-MARK-HOUWINK equation: [.eta.]=KM.sup..alpha., in which 
M represents the mean molecular weight, [.eta.] represents the intrinsic 
viscosity in a given solvent, K and .alpha. are specific parameters of the 
solvent polymer couple, must be above 10.sup.6. 
In the compositions of the invention, there can be included, in case of 
need, the classic additives customarily used in thermoplastic polymers 
such as thermal stabilizers, lubricants, fillers, coloring agents, and the 
like in their usual amounts and for their usual purposes. 
The compositions of the invention present the advantage of being able to be 
oriented at a higher temperature, about 15.degree. to 20.degree. C. 
higher, while having the same possibilities of elongation and giving the 
same characteristics for the finished objects as do the thermoplastic 
polymers alone. All this is provided while at the same time requiring 
lower tensile forces of 30% to 50%. The possibility of using less 
voluminous machines in regard to mechanics and less costly machines result 
therefrom. 
In the current practice of the formulation and the transformation of 
polymers, the introduction of polymeric additives to classic polymers aims 
to modify the behavior at the time of fusion of said polymers in order to 
aid with their use by facilitating their mixing on their blending. This 
practice calls upon so-called gelification phenomena which, by modifying 
the interface of the resin grains, favors their flow and their 
interdiffusion and makes it possible to arrive at a better textural 
homogenization of the material used. These additives have a role of 
"processing aids" and their action favors the forming of the base polymer 
in temperature zones in which the material is in a superfused state 
located at about 100.degree. to 140.degree. C. above the glass transition 
temperature, i.e. for example, in the case of non-plasticized PVC, in the 
temperature zone of about 180.degree. to 220.degree. C. 
It must be well understood that the present invention is well founded on 
the rheological properties of mixtures of thermoplastic polymers in the 
temperature zone corresponding to the viscoelastic state. 
More precisely, the invention is based on the effect of additive polymers 
at very high molecular weights being introduced into classic polymers 
whose viscoelastic behavior is profoundly modified in the temperature 
range located just above the vitreous transition zone and over a 
temperature zone of some tens of degrees higher than the transition 
temperature. 
The invention will be described in connection with the following examples 
which are set forth for purposes of illustration only.

EXAMPLE 1 
This example shows modification of the viscoelastic behavior of PVC by the 
addition of a styrene-acrylonitrile having a high molecular weight. 
By emulsion polymerization, a styrene-acrylonitrile (SAN) copolymer is 
prepared in 74/26 proportions, which after flocculation and drying has a 
viscosity in solution at 0.1% in dimethylformamide at 30.degree. C., of 
10.5 dl/g, corresponding to a molecular weight of about 6.times.10.sup.6. 
Tubes are then extruded on a WEBER DS 60 machine to form tubes having an 
external diameter of 63 mm and a thickness of 5 mm starting from two 
compositions, I and II, based on PVC. 
______________________________________ 
I II 
______________________________________ 
PVC (EKAVYL SL 66) 100 kg 100 kg 
Copolymer (SAN with a molecular weight 
-- 5 
of 6 .times. 10.sup.6) 
Calcium stearate 1 1 
Paraffin wax 1 1 
Stearic acid 0.25 0.25 
Calcium carbonate 2.5 2.5 
Titanium dioxide 0.14 0.14 
Carbon black 0.05 0.05 
______________________________________ 
Test specimens of dumbbell form are cut out of these tubes, flattened in 
the hot state, then stretched until rupture at a speed of 666% per minute 
and at temperatures ranging from 95.degree. to 160.degree. C. 
FIG. 3 is a graph representing, for the two compositions, the stress at 
200% elongation as a function of the temperature. 
It can be seen that the elongation force necessary is lower for composition 
II which includes 5% of the additive than it is for composition I without 
additive. 
If it is desired to draw out the product at 200% by having the least force 
to apply, then it must be done at 123.degree. C. for composition I and at 
144.degree. C. for composition II. The necessary stress with composition 
II amounts to 1.3 MPa as against 2.4 MPa with composition I, or 45% less 
for composition II. 
If one draws out the test specimens at 200% at the speed of 666%/min. and 
if they are cooled again rapidly as soon as this elongation has been 
reached, then one obtains test specimens in which the macromolecules have 
been definitely oriented. 
In order to characterize the improvement of rigidity obtained, one carries 
out a tensile test at 23.degree. C. at a speed of 5 mm/min. on these 
oriented test specimens and notes the break point. FIG. 4 illustrates this 
break point as a function of the temperature at which the orientation has 
been carried out. It can be observed that composition II oriented at 
130.degree. C. presents nearly the same final break point as does 
composition I oriented at 115.degree. C. According to the graph of FIG. 3, 
the stress to be exerted for the orientation amounts to 2.8 MPa for 
composition I and 1.9 MPa for composition II. The result of this is that 
the apparatus to be used for carrying out the orientation can be less 
powerful. 
EXAMPLE 2 
Comparative Example 
This example shows the inefficiency of the addition of a 
styrene-acrylonitrile copolymer of low molecular weight in non-plasticized 
PVC. 
By emulsion polymerization a styrene-acrylonitrile copolymer is prepared in 
74/26 proportions, which, after flocculation and drying, exhibits a 
molecular weight of 2.5.times.10.sup.5. 
Subsequently, operating exactly according to Example 1, two compositions 
are prepared based on PVC; one of which contains 5 parts for a hundred of 
PVS of this styrene-acrylonitrile copolymer, and tubes are extruded. 
On the test specimens cut out of these tubes, tensile strength measurements 
between 95.degree. and 135.degree. C. do not show any difference in 
behavior, except for the precision of the measurements, between the two 
compositions. The test speciments are then stretched 200% at the speed of 
666%/minute in a temperature range going from 100.degree. to 130.degree. 
C. and suddenly cooled. On these oriented test specimens, the tensile 
strength at 23.degree. C. and 5 mm/min. does not show any difference 
between the two compositions. 
This styrene-acrylonitrile copolymer having a molecular weight of 
2.5.times.10.sup.5 does not change the viscoelastic behavior of the PVC 
because its molecular weight is not sufficient. 
EXAMPLE 3 
This example shows the modification of the viscoelastic behavior of an ABS 
copolymer by the addition of a styrene-acrylonitrile copolymer of high 
molecular weight. 
To 100 parts by weight of ABS in powder form (UGIKRAL RA) is added 5 parts 
of the same styrene-acrylonitrile copolymer as used in Example 1, having a 
molecular weight of 6.times.10.sup.6 of Example 1, and flat plates with a 
1 mm thickness are extruded. Some test specimens are cut out of these 
plates (I) as well as out of the plates extruded using ABS only with no 
styrene-acrylonitrile added (II). 
FIG. 5 is a graph showing the tensile stress at 200% of elongation at a 
speed of 666%/minute, as a function of the temperature. It can be observed 
that the addition of the additive polymer does not appreciably increase 
the stress and that the difference is annulled as soon as a temperature of 
130.degree. C. is reached. 
FIG. 6 is a graph showing the rupture load in traction at 23.degree. C. and 
5 mm/min. of test specimens having previously been drawn out from 200% to 
666%/minute and suddenly cooled again. It can be observed that in order to 
obtain the same final stress at break when compared with an ABS alone 
oriented at a certain temperature one can use the composition of the 
invention by orienting at about 15.degree. C. higher, which necessitates a 
lower stress by about 50% according to graph 5. 
EXAMPLE 4 
The modification of the viscoelastic behavior of the PVC by the addition of 
a copolymer of methyl methacrylate-ethyl acrylate at high molecular weight 
is illustrated in this example. 
By emulsion polymerization, a copolymer (P-MMA/EA) of methyl 
methacrylate-ethyl acrylate in 95/5 proportions is prepared, which after 
flocculation and drying has a molecular weight of 2.times.10.sup.6. 
As in Example 1, tubes having a 63 mm diameter are extruded with two 
formulas based on unplasticized PVC, one of which contains 5 parts of this 
P-MMA/EA copolymer for each 100 parts by weight of PVC (I), with the PVC 
only tubes serving as a control (II). Test specimens of dumbbell form, cut 
out of the tubes and flattened in the hot state are drawn out at a speed 
of 666%/minute at temperatures ranging from 85.degree. to 130.degree. C. 
FIG. 7 is a graph showing for the two compositions the stress at 200% of 
elongation as a function of the temperature. It can be observed that the 
composition containing the P-MMA/EA additive yields a higher stress, but 
permits drawing by 200% at 132.degree. C., while with pure PVC one cannot 
go beyond 123.degree. C. 
FIG. 8 is a graph showing the stress at break in traction at 23.degree. C. 
and 5 mm/min. of test specimens oriented by elongation of 200%. It can be 
observed that one can obtain the same final resistance by orienting the 
composition containing the additive at higher temperature than for the 
pure composition. The difference varies from 5.degree. to 15.degree. C. 
and the stresses to be exerted on orientation can in the most favorable 
case be lower by 30%. 
EXAMPLE 5 
Comparative Example 
Ineffectiveness of the addition of a copolymer of methyl methacrylate-ethyl 
acrylate of a low molecular weight to unplasticized PVC is shown in the 
example. 
By emulsion polymerization, a copolymer of methyl methacrylate-ethyl 
acrylate is prepared in 95/5 proportions which after flocculation and 
drying shows a molecular weight of 1.5.times.10.sup.5. Operating as in 
Example 4, test samples are made with a composition based on PVC alone 
and, on the other hand, from same composition to which 5 parts by weight, 
for a hundred of PVC, of this copolymer are added. 
The behavior in traction in the hot state and the resistance to traction 
(tensile strength) at 23.degree. C. and 5 mm/min. of test specimens having 
been previously elongated by 200% and cooled down again, show no 
significant difference between the two compositions. The molecular weight 
of the copolymer of methyl methacrylate-ethyl acrylate is too low for the 
viscoelastic behavior of the PVC to be modified in the range of 
temperatures 90.degree.-140.degree. C. 
While the invention has been described in connection with a preferred 
embodiment, it is not intended to limit the scope of the invention to the 
particular form set forth, but, on the contrary, it is intended to cover 
such alternatives, modifications, and equivalents as may be included 
within the spirit and scope of the invention as defined by the appended 
claims.