Stock material or miscellaneous articles – Structurally defined web or sheet – Physical dimension specified
Reexamination Certificate
1998-12-29
2001-04-24
Thibodieau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Physical dimension specified
C428S328000, C428S523000, C428S910000, C106S419000, C423S420200, C524S115000, C524S155000, C524S401000, C524S424000, C524S437000, C524S584000, C524S586000
Reexamination Certificate
active
06221472
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a polyolefin resin composition which is obtained by blending specific hydrotalcite particles with a polyolefin resin to improve the heat deterioration resistance, rust preventing properties, coloration preventing properties, dispersibility and filter permeability of the resin. More specifically, it relates to a polyolefin resin composition which comprises specific hydrotalcite particles and a conventional phosphorus-containing antioxidant agent or/and a sulfur-containing antioxidant and a phenolic antioxidant and, particularly, to the improvement of coloration preventing properties, dispersibility, filter permeability and NO
x
resistance of a polyolefin resin.
The present invention relates to also novel hydrotalcite particles which are contained in a polyolefin resin composition to develop the above advantages.
Since plastics such as polyolefins are oxidized by attack of heat, light and the like to generate a radical and deteriorate acceleratedly, a phenolic antioxidant, phosphorus-containing antioxidant and sulfur-containing antioxidant, and further an ultraviolet absorber and hindered amine-based radical trapping agent have been used alone or in combination of two or more as an antioxidant and a radical trapping agent for these plastics. Meanwhile, while the step of removing a catalyst after polymerization is omitted due to an increase in the activity of a Ziegler-based catalyst, there arises a problem that a polyolefin resin contains several ppm or several hundreds of ppm of the remaining halogen which causes the heat deterioration of the resin or the formation of rust in a molding machine and the like. It is well known as a measure to overcome the above problem that calcium stearate and/or hydrotalcite particles having excellent dispersibility are used as an acid neutralizer or catalyst deactivating agent.
JP-A 55-80447 (the term “JP-A” as used herein means “Unexamined Japanese Patent Application”), for example, teaches that hydrotalcite particles represented by the following formula (to be referred to as “Mg-containing hydrotalcite particles” hereinafter): Mg
1−x
Al
x
(OH)
2
A
n−
x
·mH
2
O (0≦x≦0.5, preferably 0.2≦x≦0.4, A is an anion having a valence of n, and m is a positive number) are more effective than conventionally used calcium stearate or magnesium oxide in preventing the heat deterioration of a halogen-containing polyolefin resin, the formation of rust in a molding machine and coloration.
JP-A 61-113631 proposes that the processing stability and heat resistance of a polyolefin resin are improved effectively by blending a combination of the above Mg-containing hydrotalcite particles, a phenolic antioxidant and organic phosphate.
Although the polyolefin resin compositions having the above hydrotalcite particles have a coloration prevention effect, they are not satisfactory yet and are required to have higher stability.
Hydrotalcite particles which have heat deterioration resistance and rust preventing properties as well as coloration preventing properties, dispersibility and filter permeability which are satisfactory for polyolefin resins could not be obtained so far.
It is therefore an object of the present invention to provide a resin composition which can prevent the coloration such as yellowing or pinking of a polyolefin resin and which has excellent filter permeability, heat deterioration resistance and rust preventing properties.
The inventors of the present invention have conducted intensive studies to attain the above object and have found that the above object can be attained by hydrotalcite particles having specific properties and such chemical composition that the divalent metal of the hydrotalcite particles Is substituted by Zn.
JP-A 52-49258 proposes that Zn-containing hydrotalcite particles represented by the structural formula M
x
Al
y
(OH)
2x+3y−
2z(A)
z
·aH
2
O (M is Mg, Ca or Zn, A is CO
3
or HPO
4
, and x, y, z and a are “0” or a positive number) are mixed with a polyoelfin resin. It describes that a rust prevention effect is obtained with a small amount of the above hydrotalcite particles and even when the hydrotalcite particles are blended with a polyolefin containing a phenolic stabilizer, the yellowing of the polyolefin does not occur. However, the proposal does not mention at all what type of hydrotalcite particles should be used to obtain an excellent effect on preventing rust, deterioration or coloration. Most of the hydrotalcite particles listed in the publication are hydrotalcite particles containing Mg or Ca as M. Only Zn-containing hydrotalcite particles represented by the formula Zn
6
Al
2
(OH)
16
CO
3
·4H
2
O are shown.
Further, JP-A 7-118490 proposes the use of hydrotalcite particles represented by the above formula as a resin composition which is not discolored as a package material even when it is contacted with a vegetable for a long time and has excellent properties of difficultly whitening, heat deterioration resistance and rust resistance. However, the proposal states that synthesized hydrotalcite particles containing Mg as a divalent metal (M) is preferred and hydrotalcite particles containing Zn as M are not used in Examples.
According to studies conducted by the present inventors, it has been found that when hydrotalcite particles represented by Zn
x
Al
2
(OH)
4+2x
CO
3
·mH
2
O are kneaded with a polyolefin resin, many problems such as uncertainty in yellowing resistance and heat stability, poor dispersibility into resins, deterioration in the appearance of a molded product, a reduction in filter permeability and the like arise. Therefore, the present inventors have conducted further intensive studies to find what kind of hydrotalcite particles containing Zn as a divalent metal (to be referred to as “ZnHT particles” hereinafter) should be used and have found that a polyolefin resin composition shown below is effective.
That is, it has been found that a polyolefin resin composition which has excellent coloration preventing properties, dispersibility and filter permeability while retaining rust preventing properties can be obtained by blending hydrotalcite particles represented by the following formula (A), having an average secondary particle size of 2 &mgr;m or less, containing 1 wt % or less of particles having a particle size of 10 &mgr;m or more and having a specific surface area measured by a BET method of 20 m
2
/g or less with a polyolefin containing halogen derived from a polymerization catalyst and/or post-halogenation in an amount of 0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight based on 100 parts by weight of the polyolefin.
Zn
x
Al
2
(OH)
4+2x
CO
3
.m
H
2
O (A)
wherein x and m satisfy 3.5≦x≦4.5 and 0≦m≦4, respectively.
According to studies conducted by the present inventors, when ZnHT particles represented by M
x
Al
y(OH)
2x+3y−2z
(A)
z
.aH
2
O in which M is Zn are kneaded with a polyolefin, many technical problems such as uncertainty in yellowing resistance and heat stability, poor dispersibility into resins, deterioration in the appearance of a molded product, a reduction in filter permeability and the like arise. The reason for this is that ordinary ZnHT particles agglomerate firmly and re-agglomerate even when they are ground because they have a BET specific surface area of 30 m
2
/g or more and a crystal size, measured by an X-ray diffraction method, of about 100 to 300 Å at the <006> face in the C axial direction and are fine crystals with great surface energy. Therefore, it was found that ZnHT particles having good dispersibility could not be obtained.
After the present inventors have conducted further studies, they could form ZnHT particles which have an average secondary particle size of 2 &mgr;m or less, contain 1 wt % or less of particles having a particle size of 10 &mgr;m or more, have a specific surface area measured by a BET method of 20 m
2
/g or less, preferably 4 to 15 m
2
/g and rarely re-agglomerate by synthes
Nosu Tsutomu
Takabatake Harumi
Yoshii Makoto
Kyowa Chemical Industry Co Ltd
Thibodieau Paul
Zacharia Ramsey
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