Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-10-24
2001-12-04
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...
C521S059000, C521S134000
Reexamination Certificate
active
06326409
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an in-mold foaming article of a polypropylene resin composition which is foamed in mold, and used for insulation materials, cushioning packing materials, delivery boxes; automobile parts such as a bumper core material, pillar, platform, and side projection material; pallet materials, tool boxes and the like. More particularly, the present invention relates to an in-mold foaming article of a polypropylene resin composition which is foamed in mold having high density and excellent in both mechanical strength properties of compressive strength and tensile strength.
A foamed article of a polypropylene resin is excellent in chemical resistance, heat resistance, strain recovering property after compression and the like compared to polystyrene resin foamed article, and widely used for cushioning packing materials, delivery boxes; automobile parts such as a bumper core material, pillar, platform, and side projection material; pallet materials, tool boxes and the like.
Conventionally, for production of a polypropylene resin pre-foamed particle giving the a polypropylene resin foamed article, there have been used volatile foaming agents typically including hydrocarbon foaming agents such as CFC-12, HCFC-22, HCFC-142b, and HFC-134a; hydrocarbon foaming agents such as propane, butane, and pentane. However, since any of these agents cause global environmental problems such as decomposition of the ozone layer and globe temperature rising, and safety problems inevitably occurring due to inflammability thereof, there have been recently used inorganic gas foaming agents such as a nitrogen gas, air, carbon dioxide gas for necessity of countermeasures against such problems (for example, Japanese Unexamined Patent Publication Nos. 6-192462/1994, 7-173321/1995, 8-259724/1996 and the like). Among them, particularly when a carbon dioxide gas is used as a foaming agent, this gas has excellent compatibility with a polypropylene resin and production of a pre-foamed particle having desired physical properties and of an internal foamed article comprising the particle is relatively easy. Therefore, there are widely known arts regarding a polypropylene resin pre-foamed particle obtained by using a carbon dioxide gas as a foaming agent and a foamed article comprising the particle.
By the way, it is also well known that a carbon dioxide gas is a cause of global temperature rising, and in arts using an inorganic gas foaming agent, the above-mentioned global environmental problems are not yet solved to date.
In view of such current conditions, investigations regarding selection of foaming agents for also solving global environmental problems have been conducted. And development of a polypropylene resin pre-foamed particle obtained by using, as a forming agent, water which had not been admitted as a foaming agent at all, and development of a foamed article comprising the particle have become successful and a lot of applications have been filed until now (for example, Japanese Unexamined Patent Publication Nos. 10-245437/ 1998, 11-21368/ 1999, 11-100458/1999 and the like).
Any of these arts is an epoch-making art giving a polypropylene resin pre-foamed particle unharmful to global environment and an internal foamed article comprising this particle, which can completely solve the above-mentioned problems.
Among other, an art described in Japanese Unexamined Patent Publication No. 11-100458/1999, for example, has an excellent feature which reverses conventional common knowledge in foamed articles using a polypropylene resin as a base material resin. Under this feature, tensile strength can be kept high even if fusion ratio of a foamed article is at most 70% which can not conventionally be imagined. And resultantly, improvement in productivity in internal molding and stability of quality can be attained simultaneously while maintaining the quality of the foamed article at the same level or more.
SUMMARY OF THE INVENTION
Then, the present inventors have intensively continued studying to further improve degree of completion of an art for preparing a foamed article having such an excellent feature, and resultantly found that not only tensile strength but also compressive strength can be improved when open cell ratio of a foamed article is at most 12%. Further, the present inventors have found that this effect is remarkable in high density range of at least 90 g/L to complete the present invention.
Namely, the present invention relates to an in-mold foaming article of propylene resin composition having a density of 90 to 300 g/L and an open cell ratio of at most 12% obtained by using a pre-foamed particle, wherein the pre-foamed particle comprises a resin composition containing (A) 100 parts by weight of a polypropylene resin and (B) 0.01 to 20 parts by weight of a hydrophilic polymer as a base material resin, and water as a foaming agent, and the pre-foamed particle has at least two endothermic peaks in a DSC curve obtained in differential scanning calorimetry.
In the above-mentioned in-mold foaming article, a fusion ratio is preferably 10 to 70%.
In the above-mentioned in-mold foaming article, a tensile strength is 0.6 to 3.0 MPa, and a density x and a compressive strength y satisfy the following formula (1):
y−
0.013
x+
0.645≧0 (1)
DETAILED DESCRIPTION
The in-mold foaming article of the present invention uses, as a raw material, a pre-foamed particle comprising a resin composition having (A) 100 parts by weight of a polypropylene resin and (B) 0.01 to 20 parts by weight of a hydrophilic polymer as a base material resin, and water as a foaming agent, wherein the pre-foamed particle has at least two endothermic peaks in a DSC curve obtained in differential scanning calorimetry.
The above-mentioned polypropylene resin is a component used for obtaining a pre-foamed particle having excellent balance in foamability, moldability, and mechanical strength, heat-resistance and flexibility of the resulting in-mold foaming article. Further, the above-mentioned hydrophilic polymer is a component used for preparing a pre-foamed particle having desired physical properties by using water as a foaming agent.
The above-mentioned polypropylene resin is preferably a resin comprising 92 to 100% by weight, particularly 92 to 99.95% by weight of a propylene monomer unit, and 0 to 8% by weight, particularly 0.05 to 8% by weight of a monomer unit copolymerizable therewith. When the propylene monomer unit is contained in an amount of at least 92% by weight, a foamed article is obtained having excellent mechanical strength, processability, electric insulation property, water-resistance and chemical-resistance. The monomer unit copolymerizable with the propylene monomer unit is a component used for improving foamability, moldability, fusion property, flexibility, adhesion property, transparency, impact-resistance, gas barrier property and the like. For obtaining the effect of use thereof, it is preferable to use the monomer unit in an amount of at least 0.05% by weight, particularly at least 0.1% by weight.
Examples of the above-mentioned monomer copolymerizable with the propylene monomer unit are &agr;-olefin monomers having 2 to 8 carbon atoms such as ethylene, butene, pentene, hexene, heptene and octene; cyclic olefins such as norbornene monomers; vinyl alcohol esters such as vinyl acetate; alkyl (meth)acrylates having 1 to 6 carbon atoms in an alkyl group such as methyl methacrylate, ethyl acrylate and hexyl acrylate; vinyl alcohol; methacrylic acid; vinyl chloride and the like. Among them, ethylene is preferable from the viewpoint of excellent balance in foamability, moldability, fusion property, mechanical strength, heat-resistance and flexibility of the resulting in-mold foaming article. These may be used solely or in a combination use of two or more thereof.
A melt index (MI) of the above-mentioned polypropylene resin is, for example in case of an ethylene-propylene random copolymer, preferably 0.2 to 50 g/10 minutes, more preferably 1 to 30 g/10 mi
Goda Takayuki
Mihayashi Tsuyoshi
Yanagihara Yutaka
Armstrong Westerman Hattori McLeland & Naughton LLP
Foelak Morton
Kaneka Corporation
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