Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-07-14
2002-09-10
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S352000, C526S348500, C526S348600, C524S115000, C524S147000, C524S151000
Reexamination Certificate
active
06448357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polyolefin resin composition. More particularly, the present invention relates to a polyolefin resin composition which has excellent heat resistance, moisture resistance and discoloration resistance, and also when used as a packaging material, does not impair the taste of contents to be packaged, such as flavor or odor, and therefore does not impair the taste of the contents.
2. Description of the Related Art
Polyolefins or resin compositions mainly comprising polyolefin have excellent properties of transparency, strength, chemical resistance, moldability and the like, and hence are used in various applications as various molded products. Further, in recent years, in view of the facts that polyolefins do not contain halogen atoms such as chlorine and therefore do not generate chlorine harmful substances such as dioxin during incineration, the polyolefins are strongly noted as a material having small environmental load.
However, when polyclefins were heated at high temperature in mold processing, there were the cases that the polyolefins cause disadvantages such as deterioration of mechanical strength due to deterioration by crosslinking or drop of MFR, poor appearance of a molded product due to formation of gelled product, deterioration of printability, and the like. Further, there was the case that the resin deteriorated under a wet atmosphere containing an acid, an alkali or the like and therefore the resin did not have excellent moisture resistance.
Further, polyolefins may discolor due to the influence of pollution substances in air, such as NO
x
or SO
2
.
Furthermore, when foods, drinks or the like are packed in a packaging material comprising a sheet or film of polyolefins, components such as additives elute during keeping or storage over a long period of time, such an elution adds offensive smell, taste or odor to the contents, and as a result, taste, odor, flavor or the like of the contents themselves may be impaired.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a polyolefin resin composition which has excellent heat resistance, moisture resistance and discoloration resistance, and also when used as a packaging material, does not impair the taste of contents to be packaged, such as flavor or odor, and therefore does not impair the taste of the contents.
To achieve the above object, the present invention provides a polyolefin resin composition comprising (A) an ethylene-based polyolefin having a density of 0.865 to 0.980 g/cm
3
and MFR of 0.01 to 50 g/10 min, (B) a phosphorus compound, and (C) at least one heat stabilizer selected from the group consisting of a phenol-based heat stabilizer and a tocopherol-based heat stabilizer.
Preferably, the phosphorus compound (B) is a compound represented by the following formula (b-1):
wherein R
1
represents a branched or linear alkyl group having 1 to 4 carbon atoms, and R
2
, R
3
and R
4
which may be the same or different each represent hydrogen atom or a branched or linear alkyl group having 1 to 4 carbon atoms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The polyolefin resin composition of the present invention (hereinafter referred to as a “composition of the present invention” for brevity) is explained in detail below.
The composition of the present invention comprises (A) an ethylene-based polyolefin and (B) a phosphorus compound as essential components, and further comprises (c) at least one heat stabilizer selected from the group consisting of a phenol-based heat stabilizer and a tocopherol-based heat stabilizer.
The ethylene-based polyolefin (A) which is the essential component in the composition of the present invention is a homopolymer of ethylene or a copolymer comprising ethylene and other monomer. The copolymer may be a random copolymer or a block copolymer. Examples of the other monomer include &agr;-olefins having 3 to 20 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or 1-eicocene. Examples of the copolymer of ethylene and other monomer include copolymers of ethylene and &agr;-olefins such as 4-methyl-1-pentene or 1-hexene.
The composition of the present invention may contain, as the ethylene-based polyolefin (A), only one kind selected from homopolymers of ethylene and copolymers of ethylene and other monomers, or a combination of two kinds or more. In particular, the preferred ethylene-based polyolefin is a copolymer of ethylene and at least one kind selected from &agr;-olefins having 4 to 8 carbon atoms.
The ethylene-based polyolefin (A) has a density of 0.865 to 0.980 g/cm
3
, preferably 0.885 to 0.965 g/cm
3
and more preferably 0.895 to 0.960 g/cm
3
. In the present invention, the density is a value obtained by heat-treating a strand which is obtained in measuring a melt flow rate (MFR) under a load of 2.16 kg at 190° C., at 120° C. for 1 hour, gradually cooling the heat-treated strand to room temperature over 1 hour, and measuring its density with a density gradient tube.
Melt flow rate (MFR) of the ethylene-based polyolefin is 0.01 to 50 g/10 min, preferably 0.05 to 40 g/10 min and more preferably 0.1 to 35 g/10 min. The MFR used in the present invention is a value measured under the conditions of 190° C. and 2.16 kg load according to ASTM D1238.
The ethylene-based polyolefin is obtained by polymerizing ethylene alone or ethylene and other monomer such as &agr;-olefin by, for example, a polymerization using a Ziegler catalyst or a polymerization using a metallocene catalyst.
The metallocene catalyst is prepared by contacting (1) a transition metal compound such as bis(n-propylcyclopentadienyl)zirconium dichloride, (2) a benzene-soluble aluminooxane or a benzene-insoluble organoaluminumoxy compound (as disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 2-276807), (3) fine particulate carrier having a particle diameter of 10 to 300 &mgr;m comprising SiO
2
, Al
2
O
3
or the like, and if necessary, (4) an organoaluminum compound such as ET
2
AlOAlET
2
.
Examples of the ethylene-based polyolefin obtained by polymerization using the metallocene catalyst include ethylene-&agr;-olefin copolymers as disclosed in Japanese Patent Application Laid-Open No. Hei 9-183816.
The phosphorus compound (B) which is the essential component in the composition of the present invention is trivalent phosphorus compound(phosphite derivative). The preferred phosphorus compound (B) is a phosphorus compound represented by the above formula (b-1) . In the formula (b-1), R
1
represents a branched or linear alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group for R
1
include methyl group, ethyl group, butyl group and t-butyl group. R
2
, R
3
and R
4
which may be the same or different each represent hydrogen or a branched or linear alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group for R
2
, R
3
and R
4
include methyl group, ethyl group, butyl group and t-butyl group.
Examples of the phosphorus compound (B) represented by the formula (b-1) include bis(2,4-t-butyl-6-methyl)methylphosphite, bis(2,4-t-butyl-6-methyl)ethylphosphite, bis(2,4-t-butyl-6-methyl)t-butylphosphite and bis(2,4-t-butyl-6-methyl) butylphosphite. Of those, bis(2,4-t-butyl-6-methyl)ethylphosphite is preferable from the point that such is chemically stable.
The phosphorus compound also includes commercially available product: Irgafos 38, trade name, a product of Ciba Specialty Chemical.
In the composition of the present invention, the blending proportion of the phosphorus compound (B) is preferably 0.005 to 0.3 part by weight and more preferably 0.01 to 0.2 part by weight, per 100 parts by weight of the ethylene-based polyolefin. If the proportion of the phosphorus compound (B) is too large, the phosphorus compound separates on a surface of a molded product, resulting in poor appearance. On the other hand, if it is too small, the effect of preventing heat degradat
Hamada Naoshi
Hirakawa Sadamu
Yamamoto Akihiko
Birch & Stewart Kolasch & Birch, LLP
Cheung William K
Mitsui Chemicals Inc.
Wu David W.
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