GB2156360A

GB2156360A - Radiation-stable polypropylene resin composition

Info

Publication number: GB2156360A
Application number: GB08505499A
Authority: GB
Inventors: Yoichi Kawai; Masami Maki; Katsumi Sekiguchi; Sachio Yokote; Akio Yoshihara; Masaru Abe
Original assignee: Mitsui Toatsu Chemicals Inc
Current assignee: Mitsui Toatsu Chemicals Inc
Priority date: 1984-03-13
Filing date: 1985-03-04
Publication date: 1985-10-09
Also published as: AU3957185A; NL8500696A; GB8505499D0; IT1184148B; FR2561247B1; AU552479B2; PT80096A; PT80096B; GB2156360B; KR870002104B1; DE3508983A1; IT8519844A0; FR2561247A1; KR850006433A; CA1254339A

Abstract

A radiation-stable polypropylene resin composition having excellent transparency, and comprising 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 DEG C-270 DEG C in the presence of an organic peroxide until a desired melt index is achieved.

Description

Radiation-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 a degree 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 fields 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 natural colors of their contents without being hindered by the containers.

In the above-described application fields, there is an outstanding demand for improvements to the 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.

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 deveiops yellowing and undergoes property deterioration.

Pertaining particularly to property deterioration, the impact resistance of polypropylene resin is reduced to one half upon exposure to radiation 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 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, sole addition of a triarylphosphite such as tris(2,5-di-tert-butylphenyl)phosphite or tris- (2,4di-tert-butylphenyl)phosphite is still difficult to make polypropylene resin moldings restant sufficiently to irradiation. It is thus desirable to employ another stabilizer in combination. However, combined use of such a triarylphosphite with a hindered phenolic antioxidant such as 2,6-di-tert-butyl-p-methylphenol or tetrakis [methyl ene-3-(3,5-d i-te rt-butyl-4-hyd roxyphenyl)- 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 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 condensation product of dimethyl succinate and 2-(4-hydroxy 2,2,6,6-tetramethyl-i-piperidyl)ethanol, the resulting polypropylene resin moldings have satisfactory irradiation stability and are free from the yellowing problem. However, they involve problems in transparency.

Among various combinations, the combined use of tris (2,4-di-t-butyphenyl)phosphite and N,N'-bis (2,2,6,6- tetramethyl-4-piperidyl)nexamethylenediamine 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 pesistance as mentioned above, they are almost opaque. When such moldings are used as containers adapted to receive materials or chemicals therein, for example, containers for food, medicines, medical instruments such as syringes, and the like, they are accompanied by such serious drawbacks that their transparency is still insufficient and they do not permit easy checking of minute dust or foreign matter mixed in the contents or observation of the natural colors of the contents.

Reflecting the recent requirement for cost reduction, there are demands for molded articles having thinner walls and multiple production in injection molding. Thus, there is a demand for a polypropylene resin composition having high molding flowability.

It is therefore desirable to provide a polypropylene resin composition which is stable to irradiation and does not develop yellowing and property deterioration and has excellent transparency, and preferably also has excellent transparency and molding flowability.

The present invention provides the following polypropylene resain composition: A transparent, radiation-stable polypropylene resin composition, comprising: (a) a polypropylene resin; (b) a sorbitol derivative represented by the following formula:

wherein R means a hydrogen atom or an alkyl group having 1 - 18 carbon atoms; (c) a phosphite compound represented by the following formula:

wherein R1 means a tertiary butyl, 1,1-dimethylpropyi, cyclohexyl or phenyl group and R2 denotes a hydrogen atom or a methyl, tertiary butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl group; and (d) a polyamine compound represented by the following formula:

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).

The molding flowability of the above resin composition may be improved further by subjecting it to thermal degradation at a temperature of 190"C - 270 C in the presence of (e) an organic peroxide.

The polypropylene resin useful in the practice of this invention may be propylene homopolymer, a propylene-ethylene copolymer having an ethylene content of 0.1 - 7 wt.%, a propylene-a-olefin copolymer which has an a-olefin content of 0.1 - 20 wt.% and may optionally contain ethylene, or the like. Alternatively, the polypropylene resin may be a blend of these polymers. The a-olefin may preferably contain 4 8 carbon atoms with butene-1, hexene-1 and 4-methyl-pentene-1 being particularly preferred.

Examples of the sorbitol derivative represented by the formula (I) which is useful in the practice of the present invention may include dibenzylidenesorbitol, 1,3,2,4-di(methybenzylindene)sorbitol, 1.3,2.4-di (ethylbenzylidene)sorbitol, 1.3,2.4-di-(propylbenzylidene)sorbitol, 1,3,2,4-di(butylbenzylidene)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 depending on the position of the sbustituent 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 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 is added in an amount of 0.01 - 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 enhanced to any considerable extent. On the contrary, such an excess incorporation leads to a higher price. This is certainly not desirable.

As exemplary organic peroxides, may be mentioned tert- butyl peroxypivalate, 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, 2,5-dimethyl-2, 5-di(tert- butylperoxy)hexyne-3 and the like. They may be used either singly or in combination. 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, for example, neutralizer, nucleating agent, antioxidant, ultraviolet light absorbent, ultraviolet light stabilizer, pigment, dispersant, and the like may be added as desired.

Illustrative of the antioxidant which may be incorporated in the composition of this invention include 2,6-di- tert-butyl-p-methyl phenol, n-octadecyl-3-(4-hydroxy- 3,5-di-tert-butylphenyl)propionate, tetrakis[methylene- 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionatejmethane, etc. These antioxidants however cause yellowing of resins when exposed to radiation. 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(ss-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)-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 (3) 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 1900C - 270"C 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 1900C will be inconvenient for the melting and mixing of the composition.

On the other hand, use of any temperatures higher than 270"C is not preferrred 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 radiation and also superb transparency. Making use of these properties, it can be effectively used for food packages, medical instruments (syringes, needle bases, protectors, etc.), medial 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 container 3.5% by weight of ethylene and having an intrinsic viscosity of 1.62 as measured in tetralin of 135"C, 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 compound represented by the general formula (III) and having 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 pelletization at an extrusion temperature of about 240"C through a usual extruder.Using an injecting molding machine, the thus-prepared pellets were formed at an injection molding temperature of about 240"C into a plate of 160 mm long, 80 mm wide and 1 mm thick.

After exposing the above-obtained plate to 2.5 Mrad trays from a cobalt-60 radiation source, the plate was allowed to stand for 2 weeks in an atmosphere of 80"C.

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 commercial haze meter (ASTM D-1003 was followed).

The yellowing discoloration was visually evaluated on the basis of the following standard of four levels: !: No yellowing discoloration was observed.

O: Slight yellowing discoloration was observed.

A: 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, respectively.

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, respectively.

Comparative Example 1 The procedures of Example 1 were repeated except that 0.1 part by weight of tetrakis[methylene-3-(3,5di- tert-butyl-4-hydroxyphenyl)propionate]-methane was added instead of using tris(2,4-di-tert-butyiphenyl) phosphite and the polyamine compound.

Its irradiation resistance was inferior to those of compositions according to this invention.

Comparative Example 2 The procedures of Example 3 were repeated except that 1 .3,2.4-di(ethylbenzylidene)sorbitol was not used.

Its irradiation resistance was good but its transparency was low.

Comparative Example 3 The procedures of Example 3 were repeated except that the polyamide compound was not used.

Comparative Example 4 The procedures of Example 3 were repeated except that tris(2,4-di-tert-butylphenyl)phosphite was not used.

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-phenol) propionate]methane in lieu of the polyamine compound.

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.

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-1-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.

Table 1

> (parts by o a- 3 I a x at 80'C bG Before exposure Right after exposure after expos're Resin Impact > Impact i(sze Impact haze A N C D E F G r( resistance O o > O O O O (kg.cm) (%) (kg.cm) (kg.cm) 3u a, 3 w O cl u C Ê O O O O O O O Ex. u 100 0.02 0.02 0.3 0.07 U Q N ttl n 30 10 0 - > 15 - 20 10 0 Eq q u . < H < Ex. 2 100 < 0.05 0.3 0.07 50 I I 1. V I V I II Vll HV 7 0 0 0 0' v < Ex. 3 100 0.08 0.08 0.3 0.07 50-60 10 30 - 40 10 25.30 10 Comp. z z X O O O X O &commat; o , eJ O Comp. 100 > 0.08 Q.07 50 - 60 80 30 - 40 80 20 - 30 80 Ex. 2 O N O O O O O O O O O O Comp. R 0.08 H H < 50 m 60 10 15 H 25 10 ' < c0 o Q Ev v Cl 3 e umo m u u h( hl C? 0 zr Comp. 100 0.08 0.3 0.07 50 o 60 10 20 X 30 10 o run ç c ax Ex. v h( C1 m r( h( I h( m IIJ 0.08 0.3 0.1 0.07 50 O 60 10 20 O 30 10 10 O 20 10 mM r ci r( r( m r( ri oo O Ex. 6 I I I I I I I I I I Comp. 100 0.08 0.1 0.07 50 E 60 80 30 o s o o o Ex. 7 N N N S N N N b l b CD O O O O O O O O O O O O O O O O O O O o oo W H D &num; O Q vu e:z o' oi X X n n re to < : c7 i o' o oi oi o oi: cO 9 H O O O o o u 1t1 'O O O oi o' o oEc , < o o o o o o o o U O o O O O o o o C O o o o O o o o O O 5} o s o o o o o o o o Cd H H H H H < H H H H H cs O b . E E E c X O X o X o X * A: Tris(2,4-di-tert-butylphenyl)phosphite B: Polyamine compound (average molecular weight: 1800 - 2200) C: 1.3,2.4-Di(ethylbenzylidene)sorbitol D: Tetrakis methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate methane E: Bis(2.2,6.6-tetramethyl-4-piperidyl)sebacate F: Dimethyl succinate/2-(4-hydroxy-2,2,6,6-tetramethyl-1-piperidyl)ethanol condensation product C:Calcium stearate 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 tetraline of 135"C, were added 0.3 part by weight of 1.3,2.4-di(ethylebenzylidene)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 (Ill) and having an average molecular weight of 1800 - 2200 and 0.02 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)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 240"C through a usual extruder.

Using an injecting molding machine, the thus-prepared pellets were formed at an injection molding temperature of about 240"C 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 "-rays from a cobalt-60 radiation source, the plate was allowed to stand for 2 weeks in an atmosphere of 80"C.

The impact resistance, transparency and 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 tris(2,4-di-tert-butylphenyl)phosphite and the polyamine compound were 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 Example 4 were repeated except that the contents of tris(2,4-di-tert-butylphenyl)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-(3,5di- tert-butyl-4-hydroxyphenyl)propionate]methane was added instead of using tris(2,4-di-tert-butylphenyl)- phosphite and the polyamine compound.

Test results are given in Table 1.

Comparative Example 9 The procedures of Example 4 were repeated except that 1.3,2.4-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.

Comparative Example ii 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.

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 in lieu of the polyamine compound.

Test results are given in Table 2.

Comparative Example 13 The procedures of Example 4 were repeated except for the use of 0.1 part by weight of bis(2,2,6,6tetramethyl- 4-piperidyl)sebacate in lieu of the polamine compound.

Test results are given in Table 2.

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.

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.

Test results are given in Table 3.

For the sake of comparison, the Ml value and other physical data of the pellets of the composition of Example 3 are also shown in Table 3.

The irradiation resistance of the composition of this Example were not different from those of other compounds of this invention but the molding flowability of the pellets of the former composition was somewhat inferior to those of the latter compositions.

Table 2

Composition (parts a o Physical properties * Two weeks at 800C CJX 3 of Before z Ri8ht after exposure after O Resin pellets (gilO mim.) Impact ia::e Impact Naze Impact Naze A B C D E F C (kg-cm) stance Yellowing resistance o Yellowing (II Q mN rl rl r( rl O (kg.cm) (kg.cm) 3LI B 3 so Ex. e4 e, C 8 rtl r, n 18 50 - 60 10 30 o 40 10 Qo 25 o 30 10 Ex. 5 100 0.05 0.05 0.3 6ss < 4 I I 1 V I V I Qo 25 I vl Ex. 6 100 0.02 0.02 0.3 0.0718 50 n 60 10 20 n 30 10 O o O O ao rn 11 Ex. 8 Comp. 100 0.08 0.08 0.07 n 50 H O Ex. 9 r4 X rD ~ Nh O 0 0 0 0 0 0 0 0 0 Comp. 14 sxJ 0.3 < 18 50 H 60 10 15 H 25 10 H < 10 10 )( H X Ex. 10 U Comp. 100 0.08 0.3 0.07 é 50 o o o 20-30 o o 10 o o o o Sc a 11 ffi n to E n O O O O o rn O O O O Comp. rrl 0.08 0.3 0.1 0.07 18 50 o 60 10 20 n 30 10 H 10 - r.

Ex. 12 Comp. 100 0.08 0.3 0.1 0.07 N 50 O 60 O O O O O 0 < 10 O A- 0 Ex. 13 1 TV Comp. 100 0.08 = 0.1 0.07 18 ç o 60 80 O O O O O O 30 80 UCE Ex. o.

re4 H f o o o o o o o o O o ffi rn n rn n n n rn rn rn rn n e o X rx H H o , x AH Y r cn o o o o o o o o o o i o o o o o o o o o o 3 o > W A3 .

CI &num; Q ~ O s4 > H ra U O O c U < çU . O O O O O O O O ç rvo n rs rs) m o o o o o 0o O o o O o O rna n rN X e e O o O O O O O O < o O rD O O O O O o o rn O O O O O O O O O O aJ d Ck O H rs r, > < ,n rm . i &commat; E e E * E ^ E * E o E * X X X o X O X o X O X U * A: Tris(2,4-di-tert-butylphenyl)phosphite B: Polyamine compound (average molecular weight: 1800 - 2200) C: 1.3,2.4-Di(ethylbenzylidene)sorbitol D: Tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane E: Bis(2.2,6.6-tetramethyl-4-piperidyl)sebacate F: Dimethyl Succinate/2-(4-hydroxy-2,2,6,6-tetramethyl-1-piperidyl)ethanol condensation product G:Calcium stearate Table 3

U o0 PI m D rU R X N O 0 0 0 m gN r( rl > 3 a U rn rn rn n Zrr a tu Oh el es r. > rw "c ;o I I I I E-Y UV t: O lowing &commat; 4 &commat; co X a U X U 4 0.02 O O O O ~s Fr r4 R H H H H Ex. 7 0.04 25 45 - 55 10 30 - 40 10 25 - 30 10 2 o o 4 o uso u u m Ex. 8 0.06 I 40 - da 10 25 l 35 10 20 l 30 10 o o o Ex. 3 .. - 15 c?mhio al < 1 N ~ O O O O 14 a R H H H 1 n Xv Ço ~ u u a E o ín O O o r; U , so rn rn v0 aO É v ,, H rn-~ o rn O O 1 rD rn < < re H C D E O. rn o rn O H rn ~ aE: a&num;u S rD D 3 "^4 < o Ç O O O U D O O O C n t za o aZ ^;r N X rn X * Parts by weight used per 100 parts by weight of resin.

Claims

1. A transparent, radiation-stable polypropylene resin composition, which compsition comprises: (a) a polypropylene resin; (b) a sorbitol derivative represented by the following formula:

wherein R1 means a tertiary butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl group and R2 deontes a hydrogen atom or a methyl, tertiary butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl group; and (d) a polyamine compound represented by the following formula:

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 polypropylene resin composition as claimed in claim 1, further comprising: (e) an organic peroxide.

3. A polypropylene resin composition as claimed in claim 1, wherein the resin composition has been thermally degraded at a temperature of 1900C - 270"C in the presence of an organic peroxide.

4. A polypropylene resin composition of claim 2 or claim 3, wherein the organic peroxide (e) is tertbutyl peroxypivalate, lay royal 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-dimethyl-2,5- di-(tertbutylperoxy)hexyne-3.

5. A polypropylene resin composition of any one of the preceding claims, wherein the polypropylene resin is polypropylene homopolymer, a propylene-ethylene copolymer having an ethylene content of 0.1 - 7 wt.% or a propylene-n-olefin copolymer having an a-olefin content of 0.1 - 20 wt.%.

6. A polypropylene resin composition of any one of the preceding claims, wherein the sorbitol derivative (b) is dibenzylidenesorbitol, 1.3,2.4-di(methylbenzylidene)- sorbitol, or 1.3,2.4di(hexylbenzylidene)sorbitol.

7. A polypropylene resin composition of any one of the preceding claims, wherein the content of the sorbitol derivative (b) is 0.05 - 1 part by weight per 100 parts by weight of the polypropylene resin.

8. A polypropylene resin composition of any one of the preceding claims, wherein the phosphite compound (c) is tris(2,5-di-tert-butylphenyl)phosphite, tris(2- tert-butylphenyl)phosphite, tris[2-(1,1-dime- thylpropyl) phenyl]-phosphite, tris(2-phenylphenyl)phosphite, tris(2-cyclohexylphenyl)phosphite, tris(2,4di-tert- butylphenyl)phosphite or tris(2-tert-butyl-4-phenyl) phosphite.

9. A polypropylene resin composition of any one of the preceding claims, 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).

10. A polypropylene resin composition of any one of the preceding claims, wherein the content of the polyamine compound (d) is 0.02 - 2 parts by weight per 100 parts by weight of the polyropylene resin (a).

11. A food container incorporating a radiation-stable polypropylene resin composition of any one of the preceding claims.

12. A medical container incorporating a radiation- stable polypropylene resin composition of any one of the preceding claims.

13. A container for medical instruments incorporating a radiation-stable polypropylene resin composition of any one of the preceding claims.

14. A polypropylene resin composition substantially as described herein.