COMPOSITION DE RESINE DE RESINE DE POLYPROPYLENE STABLE AUX RAYONNEMENTS

RADIATION-STABLE POLYPROPYLENE RESIN COMPOSITION

Abrégé anglais

- 32 -
Abstract
Disclosed herein is a radiation-stable
polypropylene resin composition having excellent
transparency. It contains a polypropylene resin and
per 100 parts by weight of the polypropylene resin,
0.005 - 8 parts by weight of a specific sorbitol
derivative, 0.01 - 4 parts by weight of a specific
phosphite compound and 0.01 - 4 parts by weight of a
specific polyamine compound. Excellent molding
flowability can be imparted to this resin composition
by subjecting it to thermal degradation at 190°C -
270°C in the presence of an organic peroxide until a
desired melt index is achieved.

Revendications

- 27 -
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as follows:
1. A radiation-stable polypropylene resin
composition having excellent transparency, which
composition comprises:
(a) a polypropylene resin;
(b) a sorbitol derivative represented by the
following formula:
(I)
<IMG>
wherein R means a hydrogen atom or an alkyl group
having 1 - 18 carbon atoms;
(c) a phosphite compound represented by the
following formula:
<IMG> (II)
wherein R1 means a tertiary butyl, 1,1-dimethyl-
propyl, cyclohexyl or phenyl group and R2 denotes a
hydrogen atom or a methyl, tertiary butyl, 1,1-

- 28 -
dimethylpropyl, cyclohexyl or phenyl group; and
(d) a polyamine compound represented by the
following formula:
<IMG>
<IMG> (III)
wherein n stands for an integer of 1 - 40 on average,
the contents of said compounds (b), (c) and (d) being
0.005 - 8 parts by weight, 0.01 - 4 parts by weight
and 0.01 - 4 parts by weight, respectively, all based
on 100 parts by weight of the polypropylene resin (a).
2. A radiation-stable polypropylene resin
composition as claimed in Claim 1, further comprising:
(e) an organic peroxide.
3. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the resin

- 29 -
composition has been thermally degraded at a temper-
ature of 190°C - 270°C in the presence of an organic
peroxide.
4. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the poly-
propylene resin is polypropylene homopolymer, a
propylene-ethylene copolymer having an ethylene
content of 0.1 - 7 wt.% or a propylene-.alpha.-olefin copo-
lymer having an .alpha.-olefin content of 0.1 - 20 wt.%.
5. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the sorbitol
derivative (b) is dibenzylidenesorbitol, 1-3,2-4-di-
(methylbenzylidene)sorbitol or 1-3,2-4-di(hexyl-
benzylidene)sorbitol.
6. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the content
of the sorbitol derivative (b) is 0.05 - 1 part by
weight per 100 parts by weight of the polypropylene
resin.
7. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the phosphite
compound (c) is tris(2,5-di-tert-butylphenyl)phosphite,

- 30 -
tris(2-tert-butylphenyl)phosphite, tris[2-(1,1-
dimethylpropyl)phenyl]phosphite, tris(2-phenylphenyl)-
phosphite, tris(2-cyclohexylphenyl)phosphite, tris(2,4-
di-tert-butylphenyl)phosphite or tris(2-tert-butyl-
4-phenyl)phosphite.
8. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the content
of the phosphite compound (c) is 0.02 - 2 parts by
weight per 100 parts by weight of the polypropylene
resin (a).
9. A radiation-stable polypropylene resin
composition as claimed in Claim 1, wherein the content
of the polyamine compound (d) is 0.02 - 2 parts by
weight per 100 parts by weight of the polypropylene
resin (a).
10. A radiation-stable polypropylene resin
composition as claimed in Claim 2, wherein the organic
peroxide (e) is tert-butyl peroxypivalate, lauroyl
peroxide, benzoyl peroxide, cyclohexanone peroxide, tert-
butyl peroxyisopropylcarbonate, tert-butyl peroxy-
benzoate, methyl ethyl ketone peroxide, dicumyl
peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy)-
hexane, di-tert-butyl peroxide, or 2,5-dimethyl-2,5-

- 31 -
di (tert-butylperoxy) hexyne-3.
11. A radiation-stable polypropylene resin
composition as claimed in Claim 3, wherein the organic
peroxide (e) is tert-butyl peroxpivalate, lauroyl peroxide,
benzoyl peroxide, cyclohexanone peroxide, tert-butyl
peroxyisopropylcarbonate, tert-butyl peroxybenzoate, methyl
ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-
di-(tert-butylperoxy) hexane, di-tert-butyl peroxide, or
2,5-dimethl-2,5-di (tert-butylperoxy) hexyne-3.
12. A food container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 1 to 3.
13. A food container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 4 to 6.
14. A food container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 7 to 9.
15. A food container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 10 and 11.
16. A medical container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 1 to 3.

- 31a -
17. A medical container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 4 to 6.
18. A medical container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 7 to 9.
19. A medical container formed from a
radiation-stable polypropylene resin composition as claimed
in any one of claims 10 and 11.
20. A medical instrument formed from a
radiation-stable polypropylene resin composition as claimed
in any of claims 1 to 3.
21. A medical instrument formed from a
radiation-stable polypropylene resin composition as claimed
in any of claims 4 to 6.
22. A medical instrument formed from a
radiation-stable polypropylene resin composition as claimed
in any of claims 7 to 9.
23. A medical instrument formed from a
radiation-stable polypropylene resin composition as claimed
in either one of claims 10 and 11.

Description

- lZS~339
SPECIFICATION
~adiation-Stable Polypropylene Resin Composition
This invention relates to a polypropylene resin
composition stable to radiation.
Polypropylene resin is hygienically excellent and
its moldings are translucent to such degrees that their
contents can be seen from the outside. They have thus found
wide-spread commercial utility in food containers, medical
containers, medical instruments and the like.
In application flelds such as food containers,
medical containers and the like, it is, however, important
to permit checking whether dust and other foreign matter are
mixed in their contents. It is also desirable to permit
checking of native colors of their contents without being
adversely affected by the containers.
In the above-described application fields,
there is an outstanding demand for improvements to the
~' ~S

-- 2
transparency of containers, instruments and the like
which are made of polypropylene resin.
Furthermore, food containers, medical
containers, medical instruments and the like have to
be subjected to sterilization before their use in view
of their application fields. Their sterilization is
effected generally by steam, ethylene oxide gas having
high sterilizability and hydrogen peroxide, etc.
The radiation sterilization which is effected
by exposing to radiation, has been developed in recent
years and has been finding more and more utility for
the sterilization of food containers or medical containers
and instruments.
Polypropylene resin is stable against steam
sterilization and gas sterilization. It is, however,
accompanied by a drawback that it has poor stability
against radiation sterilization and thus develops
yellowing and undergoes property deterioration.
Pertaining particularly to property
deterioration, the i-mpact resistance of polypropylene
resin is reduced to one half upon exposure to radia-
tion compared with its impact resistance before the
exposure to the radiation. This property deterioration
becomes more remarkable when the polypropylene resin
is heated after exposure to radiation. Thus, the
embrittlement of the polypropylene resin is promoted

- 3
to develop brittle fracture.
Certain specific stabilizers may be added to
polypropylene resin in order to avoid the property
deterioration of the polypropylene resin upon exposure
to radiation. It has been known to use, for example,
a triarylphosphite solely, a triaryl phosphite and
hindered phenolic antioxidant in combination, or a
triaryl phosphite and a hindered amine-type light and
weathering stabilizer in combination (see, Japanese
Patent Publication No. 179,234/1982).
However, a sole addition of a triarylphosphite
such as tris(2,5-di-tert-butylphenyl)phosphite or tris-
(2,4-di-tert-butylphenyl)phosphite is still difficult to
make polypropylene resin moldings resistant sufficient-
ly to irradiation. It is thus desirable to employanother stabilizer in combination. However, a combined
use of such a triarylphosphite with a hindered phenolic
antioxidant such as 2,6-di-tert-butyl-p-methylphenol or
tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-
propionate]methane results in the yellowing problem of
polypropylene resin moldings if they are used in amounts
sufficient to maintain the stability of the moldings
immediately after exposure to radiation and when caused
to go through a heat history subsequent to the exposure.
When such a triarylphosphite is used in
combination with a hindered amine-type light and

543;3'3
-- 4
weathering stabilizer such as bis(2,2,6,6-tetramethyl-
4-piperidyl)sebacate, N,N'-bis(2,2,6,6-tetramethyl-4-
piperidyl)hexamethylenediamine polymer or a conden-
sation product of dimethyl succinate and 2-(4-hydroxy-
2,2,6,6-tetramethyl-1-piperidyl)ethanol, the resulting
polypropylene resin moldings have satisfactory
irradiation stability and are free from the yellowing
problem. However, they involve problems in trans-
parency.
Among various combinations, the combined use
of tris(2,4-di-t-butylphenyl)phosphite and N,N'-bis-
(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine
polymer is good especially in irradiation resistance.
Since these stabilizers are safe, compositions making
a combined use of these stabilizers are excellent for
such application fields as food containers and medical
equipment except for transparency problems.
Although the polypropylene resin moldings
with these stabilizers incorporated therein have good
irradiation resistance as mentioned above, they are
almost opaque. When such moldings are used as containers
adapted to receive materials or chemicals therein, for
example, food containers, medical containers, medical
instruments such as syringes, and the like, they are
accompanied by such serious drawbacks that their
transparency are still insufficient and they do not

~S~339
~ 5 --
permit not only easy checking of minute dust or
foreign matter mixed in the contents but also obser-
vation of the native colors of the contents.
Reflecting the recent requirement for cost
reduction, there are demands toward molded articles
having thinner walls and multiple production in injec-
tion molding. Thus, there is a demand toward a
polypropylene resin composition having high molding
flowability.
In accordance with the present invention, there is
provided a radiation-stable polypropylene resin composition
having excellent transparency, comprising:

1~5~
(a) a polypropylene resin;
(b) a sorbitol derivative represented by the
following formula:
R OCH / HC ~ (I~
HCO R
fHOH
CH2H
wherein R means a hydrogen atom or an alkyl group
having 1 - 18 carbon atoms;
(c) a phosphite compound represented by the
following formula:
~ Rl (II)
wherein Rl means a tertiary butyl, l,l-dimethylpropyl,
cyclohexyl or phenyl group and R2 denotes a hydrogen
atom or a methyl, tertiary butyl, l,l-dimethylpropyl,
cyclohexyl or phenyl group; and
(d) a polyamine compound represented by the
following formula:

i~S ~3;~
H-- N ~CE12) 6 N ---(CH2) 2 -
H3C~< CH3 H3C~ C 3
~H3C H CH3 H3C H 3
n
N ( 2)6 N H
H3C ~ CH3 H3C ~ cH (III)
10 wherein n stands for an integer of 1 - 40 on average,
the contents of said compounds (b), (c) and (d) being
0.005 - 8 parts by weight, 0.01 - 4 parts by weight
and 0.01 - 4 parts by weight, respectively, all based
on 100 parts by weight of the polypropylene resin (a).
Compositions provided in accordance with the
pre~ent invsntion are stable to irradiation and do not
develop yellowing and property deter$oration and have
excellent transparency and molding flowability.
The molding flowability of the above resin
compo~ition may be improved further by subjecting it to
thermal degradation at a temperature of l90~C - 270C in the
presence of (e) an organic peroxide.
The polypropylene resin useful in the practice of
this invention may be propylene homopolymer, a
2S propylene-ethylene copolymer having an ethylene content
of 0.1 - 7 wt.%, a propylene-~r olefin copolymer which
has an ~-olefin content of 0.1 - 20 wt. % and may

liZS'~339
-- 8 --
optionally contain ethylene, or the like. Alternative-
ly, the polypropylene resin may be a blend of these
polymers. The ~-olefin may preferably contaln 4 - 8
carbon atoms with butene-l, hexene-l and 4-methyl-
pentene-l being particularly preferred.
Examples of the sorbitol derivative repre-
sented by the formula (I) which is useful in the
practice of the present invention may include dibenzyl-
idenesorbitol, 1-3,2-4-di(methylbenzylidene)sorbitol,
1-3,2-4-di(ethylbenzylidene)sorbitol, 1-3,2-4-di-
(propylbenzylidene)sorbitol, 1 3,2-4-di(butylbenzyli-
dene)sorbitol, 1-3,2-4-di(hexylbenzylidene)sorbitol,
etc. Each of the above exemplified compounds has
three isomers, i.e., the ortho-isomer, meta-isomer
and para-isomer dependir.g on the position of the
substituent group R in the formula ~I). However,
there is no substantial difference in quality among
the isomers. From the practical viewpoint, their
para-isomers are preferred owing to their ready
availability.
The sorbitol derivative is incorporated in
an amount of 0.005 - 8 parts by weight, preferably
0.01 - 8 parts by weight or most preferably 0.05 - 1
part by weight, all based on 100 parts by weight of
the polypropylene resin. Any amounts less than 0.005
parts by weight are unable to improve the transparency

l~S~
_ 9
to any significant extent. If it is added in any
amounts greater than 8 parts by weight, the bleeding
problem will occur. Therefore, it is not preferred
to incorporate the sorbitol derivative in any amounts
outside the first-mentioned range.
As typical examples of the phosphite compound
represented by the formula (II~ useful in the practice
of this invention, may be mentioned tris(2,5-di-tert-
butylphenyl)phosphite, tris(2-tert-butylphenyl)-
phosphite, tris[2-(1,1-dimethylpropyl)phenyl]phosphite,
tris(2-phenylphenyl)phosphite, tris(2-cyclohexylphenyl)-
phosphite, tris(2,4-di-tert-butylphenyl)phosphite,
tris(2-tert-butyl-4-phenylphenyl)phosphite and the
like.
The phosphite compound is added in an amount
of 0.01 - 4 parts by weight or preferably 0.02 - 2
parts by weight. If it is added in any amounts less
than 0.01 parts by weight, any significant effects for
the stability after exposure to radiation cannot be
exhibited. Even if it is incorporated in any amounts
greater than 4 parts by weight, its effects are not
enhanced to any considerable extent. On the contrary,
such an excess incorporation leads to a higher price.
This is certainly not desirable.
The polyamine compound represented by the
formula (III) useful in the practice of this invention

l;~S~33'3
.
-- 10 --
is added in an amount of 0.001 - 4 parts by weight
or preferably 0.02 - 2 parts by weight. Any amounts
less than 0.01 parts by weight do not bring about any
significant effects for the stability after exposure
to radiation. Even if it is incorporated in any
amounts greater than 4 parts by weight, its effects
are not enhar.ced to any considerable extent~ On the
contrary, s~ch an excess incorporation leads to a
higher pri~e. This is certainly not desirable.
As exemplary organic peroxides, may be
mentioned tert-butyl peroxypivalate~ lauroyl peroxide,
benzoyl per~.xide, cyclohexanone peroxide, tert-butyl
peroxyisopropylcarbonate, tert-butyl peroxybenzGate,
methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-
lS dimethyl-2,i-di(tert-butylperoxy)hexane, di-tert-butyl
peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-
3 and the like. They may be used either singly or
in comblnation. The amount of the organic peroxide
to be incorporated may vary depending on the melt
index of each polypropylene resin and the target melt
index to be obtained after molecular weight adjustment.
It may generally be suitable to add the organic
peroxide in an amount of 0.001 - 0.1 part by weight
per 100 parts by weight of the polypropylene resin.
To the composition of this invention, various
additives which are commonly used in such composition,

li~S~
for example, neutralizer, nucleating agent, antioxidant,
ultraviolet light absorbent, ultraviolet light stabi-
lizer, pigment, dispersant, and the like may be added
as desired.
Illustrative of the antioxidant which may be
incorporated in the composition of this invention
includ~ 2,6-di-tert-butyl-p-methylphenol, n-octadecyl-
3-(~-hydroxy-3,5-di-tert-butylphenyl)propionate,
tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxy-
phenyl)propionate]methane, etc. These antioxidants
however cause yellowing of resins when exposed to
radiztion. Therefore, there is a limitation to the
amount of the antioxidant to be incorporated in the
composition of this invention.
It is also possible to use a sulfur-type
antioxidant such as pentaerythritol tetrakis~-lauryl
thiopropionate), dilauryl dithiopropionate or the
like. Such a sulfur-type antioxidant is however
accompanied by the problem of hemolysis. Therefore,
its use is limited.
As representative ultraviolet light absorbents,
may be mentioned 2-hydroxy-4-n-octoxybenzophenone, 2-
(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzo-
triazole, etc.
As a typical ultraviolet light stabilizer,
may be mentioned bis(2,2,6,6-tetramethyl-4-piperidyl)-

1~5~39
- 12 -
sebacate.
The composition of the present invention may
preferably be prepared in the following manner. Namely,
the polypropylene resin (a), sorbitol derivative (b)
represented by the formula (I), phosphite compound (c)
represented by the formula (II) and polyamine compound
(d) represented by the formula (III), and,if desired,
the organic peroxide (e) as well as additives commonly
used in the art, for example, a neutralizer such as
calcium stearate, nucleating agent, antioxidant,
ultraviolet light absorbent, ultraviolet light
stabilizer and the like are all mixed in a blender
such as Henschel mixer to disperse them uniformly.
The resultant mixture is then molten and pelletized
by an extruder.
If desired, the composition of this invention,
which contains the polypropylene resin, sorbitol
derivative, phosphite compound and polyamine compound,
may then be subjected to thermal degradation at a
temperature of 190C - 270C in the presence of an
organic peroxide. This thermal degradation can be
effected by setting the melt-extrusion temperature in
the above pelletization step within the above range.
Any temperatures lower than 190C will be inconvenient
for the melting and mixing of the composition. On the
other hand, use of any temperatures higher than 270C

l;~S~339
.
- 13
is not preferred as such higher temperatures will lead
to deterioration and coloration of the resin.
The polypropylene resin composition of this
invention has extremely high stability against radia-
tion and also superb transparency. Making use ofthese properties, it can be effectively used for food
packages, medical instruments (syringes, needle bases,
protectors, etc.), medical containers and other
applications. Furthermore, the thermally-degraded
composition has excellent molding flowability.
The present invention will hereinafter be
described more specifically by the following Examples
of this invention and Comparative Examples. It should
however be borne in mind that the following Examples
are merely for the illustration of this invention and
shall thus not be interpreted in limiting sense.
Example 1:
To 100 parts by weight of an ethylene-
propylene random copolymer containing 3.5% by weightof ethylene and having an intrinsic viscosity of 1.62
as measured in tetralin of 135C, were added 0.3 part
by weight of 1 3,2 4-di(ethylbenzylidene)sorbitol,
0.02 part by weight of tris(2,4-di-tert-butylphenyl)-
phosphite, 0.02 part by weight of a polyamine compoundrepresented by the general formula (III) and having

~2S~
- 14 -
an average molecular weight of 1800 - 2200 and 0.07
part by weight of calcium stearate. The sultant
composition was then mixed, followed by its pelleti-
zation at an extrusion temperature of about 240C
through a usual extruder. Using an injecting molding
machine, the thus-prepared pellets were formed at
an injection molding temperature of about 240C into
a plate of 160 mm long, 80 mm wide and 1 mm thick.
After exposing the above-obtained plate to
2.5 Mrad y-rays from a cobalt-60 radiation source, the
plate was allowed to stand for 2 weeks in an atmos-
phere of 80C.
The impact resistance, transparency and
yellowing discoloration of the plate were investigated
both before and after the exposure.
The impact resistance was measured by placing
the plate on a pipe having an internal diameter of 50
mm, mounting an impact core of 1/2" in diameter on
the plate and then dropping a weight from the above.
The impact resistance was expressed in terms of impact
energy corresponding to the height when the plate was
broken.
The transparency was measured using a com-
mercial haze meter (ASTM D-1003 was followed).
The yellowing discoloration was visually
evaluated on the basis of the following standard of

l~S ~339
- 15 -
four levels:
: No yellowing discoloration was observed.
O : Slight yellowing discoloration was
observed.
~ : Yellowing discoloration was observed.
X : Severe yellowing discoloration was
observed.
Results are shown in Table 1.
Example 2:
The procedures of Example 1 were repeated
except that the contents of tris(2,4-di-tert-butylphenyl)-
phosphite and the polyamine compound were increased
to 0.05 part by weight and 0.05 part by weight, res-
pectively.
Results of measurement on the physical
properties of the thus-obtained plate are given in
Table 1.
Example 3:
The procedures of Example 1 were repeated
except that the contents of tris(2,4-di-tert-butylphenyl)-
phosphite and the polyamine compound were increased
to 0.08 part by weight and 0.08 part by weight, res-
pectively.
Results of measurement on the physical

~;~S~
- 16 -
properties of the thus-obtained plate are given in
Table 1.
Comparative Example 1:
The procedures of Example 1 were repeated
except that 0.1 part by weight of tetrakis[methylene-
3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]-
methane was added instead of using tris(2,4-di-tert-
butylphenyl)phosphite and the polyamine compound.
Results of measurement on the physical
properties of the thus-obtained plate are given in
Table 1.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparatlve Example 2:
The procedures of Example 3 were repeated
except that 1 3,2 4-di(ethylbenzylidene)sorbitol was
not used.
Results of measurement on the physical
properties of the thus-obtained plate are given in
Table 1.
Its irradiation resistance was good but its
transparency was low.

1~ 339
Comparative Example 3:
The procedures of Example 3 were repeated
except that the polyamide compound was not used.
Results of measurement on the physical
properties of the thus-obtained plate are given in
Table 1.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparative Example 4:
The procedures of Example 3 were repeated
except that tris(2,4-di-tert-butylphenyl)phosphite
was not used.
Results of measurement on the physical
properties of the thus-obtained plate are given in
Table 1.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparative Example 5:
A plate was prepared in the same manner as
in Example 3 except for the use of 0.1 part by weight
of tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxy-
phenyl)propionate]methane in lieu of the polyamine
compound.
Results of measurement on the physical

- i~S~
- 18 -
properties of the thus-obtained plate are given in
Table 1.
It developed severe yellowing discoloration
right after its exposure to radiation.
Comparative Example 6:
A plate was prepared in the same manner
as in Example 3 except for the use of 0.1 part by
weight of bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate
in lieu of the polyamine compound.
Results of measurement on its physical
properties are given in Table 1.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparative Example 7:
A plate was prepared in the same manner as
in Example 3 except for the use of 0.1 part by weight
of a dimethyl succinate/2-(4-hydroxy-2,2,6,6-tetra-
methyl-l-piperidyl)ethanol condensation product
instead of using 1-3,2-4-di(ethylbenzylidene~sorbitol
and the polyamine compound.
Results of measurement on its physical
properties are given in Table 1.
Its irradiation resistance was good but its
transparency was low.

- 1 9 ~ 5~339
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x x x o x o x a x O ~ c~ ~ O x O x

l~S~;~39
- 20 -
Example 4
To 100 parts by weight of an ethylene-
propylene random copolymer containing 3.5% by weight
of ethylene and having an intrinsic viscosity of 1.62
as measured in tetralin of 135C, were added 0.3 part
by weight of 1-3,2-4-di(ethylbenzylidene)sorbitol,
0.08 part by weight of tris(2,4-di-tert-butylphenyl)~
phosphite, 0.08 part by weight of a polyamine compound
represented by the general formula (III) and having
an average molecular weight of 1800 - 2200 and 0.02
parts by weight of 2,5-dimethyl-2,5-bis(tert-butyl-
peroxy)hexane as well as 0.07 part by weight of
calcium stearate. The resultant composition was then
mixed, followed by its pelletization at an extrusion
temperature of about 240C through a usual extruder.
Using an injecting molding machine, the thus-prepared
pellets were formed at an injection molding temperature
of about 240C into a plate of 160 mm long, 80 mm
wide and 1 mm thick.
On the side, the melt flow index of the
pellets was measured in accordance with ASTM D-1238.
After exposing the above-obtained plate to
2.5 Mrad y-rays from a cobalt-60 radiation source,
the plate was allowed to stand for 2 weeks in an
atmosphere of 80C.
The impact resistance, transparency and

l~S4339
.
- 21 -
yellowing discoloration of the plate were investigated
both before and after the exposure in the manner
described in Example 1.
Results are shown in Table 2.
Example 5:
The procedures of Example 4 were repeated
except that the contents of tri~(2,4-di-tert-butyl-
phenyl)phosphite and the polyamine compound were
10 decreased to 0.05 part by weight and 0.05 part by
weight, respectively.
Test results are given in Table 2.
Example 6:
The procedures of Exan,ple 4 were repeated
except that the contents of tris(2,4-di-tert-butyl-
phenyl)phosphite and the polyamine compound were
changed to 0.02 part by weight and 0.02 part by
weight, respectively.
Test results are given in Table 2.
Comparative Example 8:
The procedures of Example 4 were repeated
except that 0.1 part by weight of tetrakis[methylene-
3-(3,5-di-teri-butyl-4-hydroxyphenyl)propionate]methane
was added instead of using tris(2,4-di-tert-butylphenyl)-

12543~39
.
- 22 -
phosphite and the polyamine compound.
Test results are given in Table 1.
Its irradiation resistance was inferior to
those of compositions accGrding to this invention.
Comparative Example 9:
The procedures of Example 4 were repeated
except that l-3,2-4-di(ethylbenzylidene)sorbitol was
not used.
Test results are given in Table 2.
Its irradiation resistance was good but its
transparency was low.
Comparative Example 10:
The procedures of Example 4 were repeated
except that the polyamine compound was not used.
Test results are given in Table 2.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparative Example 11:
The procedures of Example 4 were repeated
except that tris(2,4-di-tert-butylphenyl)phosphite
was not used.
Test results are given in Table 2.
Its irradiation resistance was inferior to

:~S~;~3~
those of compositions according to this invention.
Comparative Example 12:
The procedures of Example 4 were repeated
except for the use of 0.1 part by weight of tetrakis-
~methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-
propionate]methane iD lieu of the polyamine compound.
Test resu'ts are given in Table 2.
It developed severe yellowing discoloration
right after its expcsure to radiation.
Comparative Example 13:
The procedures of Example 4 were repeated
except for the use of 0.1 part by weight of bis(2,2,6,6-
tetramethyl-4-piper dyl)sebacate in lieu of the poly-
amine compound.
Test results are given in Table 2.
Its irradiation resistance was inferior to
those of compositions according to this invention.
Comparative Example 14:
The procedures of Example 4 were repeated
except for the use of 0.1 part by weight of a dimethyl
succinate/2-(4-hydroxy-2,2,6,6-tetramethyl-1-piperidyl)-
ethanol condensation product instead of using 1-3,2-4-
di(ethylbenzylidene)sorbitol and the polyamine compound.

lZ54339
- 24 -
Test results are given in Table 2.
Its irradiation resistance was good but its
transparency was low.
Example 7:
The procedures of Example 4 were repeated
except that the content of 2,5-dimethyl-2,5-bis(5-
butylperoxy)hexane was changed to 0.04 part by weight.
Test results are given in Table 3.
Example 8:
The procedures of Example 4 were repeated
except that the content of 2,5-dimethyl-2,5-bis(5-
butylperoxy)hexane was changed to 0.06 part by weight.
Tesc results are given in Table 3.
For the sake of comparison, the MI value
and other physical data of the pellets of the compo-
sition of Example 3 are also shown in Table 3.
The irradiation resistance of the composi-
tion of this Example were not different from those ofother compounds of this invention but the molding
flowability of the pellets of the former composition
was somewhat inferior to those of the latter composi-
tions.

- 25 - 12S~33
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