Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-07-07
2001-07-17
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S081000, C521S134000, C521S140000
Reexamination Certificate
active
06262138
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a foamed extrusion board of the mixed resin comprising a polypropylene resin and a styrene resin. More specifically, it relates to a foamed extrusion board of the mixed resin comprising a polypropylene resin and a styrene resin, which can be suitably used for, for example, structural materials and heat insulating materials such as walls and floor partitions of buildings.
BACKGROUND ART
Since the foamed article comprising a thermoplastic resin has generally lightweight, good heat insulating property and cushioning property against outside stress, it is widely used for many fields such as heat-insulating material, cushioning material, core material and food containers.
In the foamed article comprising a polyolefin resin used as a base resin, low-density polyethylene is mainly utilized. But the polyethylene resin has a defect of insufficient heat resistance. On the other hand, a polypropylene resin has high elasticity and is excellent in chemical resistance, heat resistance, hinge characteristics and the like. Consequently, when the foamed article is prepared with the polypropylene resin, an extremely wide range of applications can be expected. But it is extremely difficult to prepare the foamed article having a large wall thickness as in case of a polypropylene resin, since viscosity and tension at melting is low, and strength of the cell wall at foaming is not sufficiently kept.
As an attempt to overcome these difficulties, foaming methods using polypropylene with a high melt tension are disclosed in Japanese Unexamined Patent Publication No. 43766/1978, Japanese Unexamined Patent Publication No. 197132/1982, Japanese Unexamined Patent Publication No. 363227/1992, and the like. However, even if these methods are used, satisfactory foamed boards have not yet been obtained.
In recent years, a method for producing sheet-like foamed article by using polypropylene with a long chain branching structure has been reported as in Japanese Unexamined Patent Publication No. 506875/1993. However, in the above-mentioned method, only the foamed article with wall thickness less than 10 mm can be prepared, and the foamed article having excellent impact resistance and cushioning property can not be obtained due to corrugates or voids generation.
Japanese unexamined Patent Publication No. 504471/1996 discloses a foamed article of propylene having an expansion factor F (density of foamed article×average cell particle size×tan &dgr;
0.75
) of less than 1.8. However, because of a special method of a convergent foam by a porous die, the method has a defect that thick foamed article can be obtained only by the foamed article with defects in quality.
Japanese Unexamined Patent Publication No. 252318/1995 discloses a polypropylene resin for foamed extrusion article having thick wall, of which biaxial elongation viscosity is specified. However, the resin is a special linear polypropylene resin containing a super high molecular weight component, which has Mz of more than 8×10
6
and Mz/Mw of more than 10, and the disclosed preparing method is a special method of the two-step polymerization.
On the other hand, as the foamed article of a mixed resin comprising polyolefin and polystyrene, a foamed article of a mixture using a block copolymer of hydrogenated styrene and butadiene as a compatibilizer is disclosed in Japanese Unexamined Patent Publication No. 32263/1975. However, in this publication, only polyethylene is described as polyolefin and polypropylene is not described.
In addition, Japanese Unexamined Patent Publication No. 174237/1987 discloses a foamed article of mixed resin comprising polyolefin and polystyrene by using a special hydrogenated block copolymer of styrene and butadiene block copolymer, in which an amount of 1, 2-binding butadiene and styrene are specified. And in this publication, an example using polypropylene as polyolefin is also disclosed. But according to this method, only the foamed article having several mm thickness is obtained.
As described above, a method for preparing the foamed article having a low density, large thickness, a high closed cell ratio and a small average cell diameter according to extrusion foaming has not yet been found by improving foamability of a polypropylene resin.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a foamed extrusion board of a polypropylene resin having a low density, large thickness, high closed cell ratio, and small average cell diameter.
Namely, the present invention relates to
a foamed extrusion article having a density of 50 to 10 kg/m
3
and
a closed cell ratio of at least 40%, which is obtained by mixing a mixed resin comprising (a) 50 to 95 parts by weight of a polypropylene resin having a melt tension at 230° C. of at least 0.05 N, (b) 50 to 5 parts by weight of a polystyrene resin, and (c) 0.5 to 15.0 parts by weight of a hydrogenated block copolymer of styrene, isoprene and styrene (hereinafter referred to as “SEPS”) based on 100 parts by weight of the polypropylene resin (a) and the polystyrene resin (b) with a foaming agent in an extruder, and then releasing into a low-pressure zone (claim
1
),
the foamed extrusion article of claim
1
, wherein the polypropylene resin is the modified polypropylene resin which is modified with a monomer selected from the group consisting of isoprene, styrene and 1,3-butadiene, and a radical polymerization initiator (claim
2
),
a foamed extrusion article having a density of 50 to 10 kg/m
3
and a closed cell ratio of at least 40%, which is obtained by mixing a mixed resin comprising (a) 50 to 95 parts by weight of a polypropylene resin having a melt tension at 230° C. of at least 0.05 N, (b) 50 to 5 parts by weight of a polystyrene resin, and (c) 0.5 to 15.0 parts by weight of a hydrogenated block copolymer of styrene and butadiene (hereinafter referred to as “SEBS”) based on 100 parts by weight of the polypropylene resin (a) and the polystyrene resin (b) with a foaming agent in an extruder, and then releasing into a low-pressure zone (claim
3
), and
the foamed extrusion article of claim
3
, wherein the polypropylene resin is the modified polypropylene resin, which is modified with a monomer selected from the group consisting of isoprene, styrene and 1,3-butadiene, and a radical polymerization initiator (claim
4
).
DETAILED DESCRIPTION OF THE INVENTION
In order to obtain a foamed extrusion board of a polypropylene resin having a low density, a large thickness, a high closed cell ratio, and a small average cell diameter from a polypropylene resin, it is important to lower temperature dependency of melt viscosity as well as to suppress foaming inside a die. Namely, it is necessary for the polypropylene resin to have the melt viscosity sufficient for increasing the die pressure at foaming to the pressure suppressing foaming inside the die.
The present invention has made it possible to prepare a foamed extrusion board of a polypropylene resin by using a mixed resin comprising a polypropylene resin having a melt tension of at least 0.05 N (a), a polystyrene resin (b), and SEPS (a hydrogenated block copolymer of styrene, isoprene and styrene) (c), or using a modified polypropylene resin (a) obtained by reacting a polypropylene resin with a monomer selected from the group consisting of isoprene, styrene and 1,3-butadiene, and a radical polymerization initiator. Using the mixed resin comprising the modified polypropylene resin (a), a polystyrene resin (b), and SEBS (hydrogenated block copolymer of styrene and butadiene) (c) has made it possible to prepare an excellent foamed extrusion board to complete the present invention.
Examples of the polypropylene resin (a) having melt tension at 230° C. of at least 0.05 N are polypropylene with a long-chain branch generated by electron beam radiation, linear polypropylene containing super high molecular weight component, modified polypropylene obtained by reacting the monomer selected from the group consisting of isoprene, styrene, and 1,3-butadiene, and a radica
Miyama Osamu
Tomita Haruo
Armstrong Westerman Hattori McLeland & Naughton LLP
Foelak Morton
Kaneka Corporation
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