Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-03-06
2004-02-17
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S143000
Reexamination Certificate
active
06693140
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a container comprising a foamed olefin resin, and a process for producing same.
BACKGROUND OF THE INVENTION
Although a container comprising a foamed olefin resin is extensively used for articles such as detergents, medicines, drinks and foods, it is desired to develop a container comprising a foamed olefin resin, which container is light in its weight per content volume.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a container comprising a foamed olefin resin, which container is light in its weight per content volume, and has enough rigidity to use practically.
It is another object of the present invention to provide a process for producing such a container.
The present invention provides a container comprising a foamed olefin resin, wherein weight W (g) and content volume V (ml) of the container satisfy the following expression (1):
W(g)/V(ml)≦0.055 (1).
The present invention also provides a process for producing a container comprising a foamed olefin resin, which comprises the steps of:
(1) extruding a composition comprising an olefin resin and an expanding agent with an extruder to form a parison comprising a foamed olefin resin,
(2) setting the parison in a mold having a shape of the container, which mold is installed in a blow molding machine,
(3) blowing a gas having a pressure of from 0.01 to 3 kg/cm
2
to both the outside surface of the parison and the inside surface thereof to cool the surfaces of the parison,
(4) blowing a gas having a pressure of from 2 to 10 kg/cm
2
to the inside of the parison to expand and cool the parison, until the outer wall of the parison reaches the inner wall of the mold, and
(5) taking out the resulting container comprising a foamed olefin resin from the mold.
DETAILED DESCRIPTION OF THE INVENTION
The weight (W) and content volume (V) of the container in accordance with the present invention satisfy the above-defined expression (1), preferably satisfy the following expression (2), and more preferably satisfy the following expression (3).
0.012 ≦W(g)/V (ml)≦0.050 (2)
0.017 ≦W(g)/V (ml)≦0.045 (2)
A thickness of the body of the container in accordance with the present invention is preferably from 0.2 to 3 mm, and more preferably from 0.4 to 2 mm from a viewpoint of accomplishing more effectively the objects of the present invention.
An expansion ratio of the container in accordance with the present invention is preferably from 1.1 to 5 times, and more preferably from 1.2 to 4.5 times.
While rigidity of a container, namely toughness thereof, generally depends greatly upon a thickness of the body of the container, a container in accordance with the present invention has a higher rigidity than a non-foamed container having the same weight and volume as the container in accordance with the present invention, because the body of the container in accordance with the present invention is greater in its thickness.
The “olefin resin” used in the present invention means a thermoplastic resin containing not less than 50% by mol of a structure unit derived from an olefin (hereinafter referred to as “olefin unit”) and less than 50% by mol of a structure unit derived from a comonomer other than the olefin, which comonomer is copolymerizable with the olefin. Examples of the olefin resin are olefin homopolymers, copolymers containing at least two olefin units only, and copolymers containing at least one olefin unit and a structure unit derived from a comonomer other than the olefin, which comonomer is copolymerizable with the olefin.
Preferred examples of the olefin are ethylene; an &agr;-olefin having 3 to 12 carbon atoms such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and 1-decene; and a vinylcycloalkane such as vinylcyclohexane and vinylcyclopentane.
Examples of the comonomer other than the olefin are a conjugated diene such as butadiene and isoprene; a non-conjugated diene such as 1,4-pentadiene; acrylic acid; an acrylic acid ester such as methyl acrylate and ethyl acrylate; methacrylic acid; a methacrylic acid ester such as methyl methacrylate and ethyl methacrylate; and vinyl acetate.
Preferred olefin resins are those having a propylene unit. Of these, a propylene homopolymer and a block copolymer of propylene and ethylene are preferred.
A particularly preferred propylene homopolymer is that (hereinafter referred to as “propylene resin (A)”, cf. JP-A 11-228629) obtained by a process comprising the steps of:
(1) homopolymerizing propylene to obtain a crystalline polymer (a) having an intrinsic viscosity of not less than 5.0 dl/g, and
(2) homopolymerizing propylene in the presence of the polymer (a) obtained in the above step (1) to further produce a crystalline polymer (b) having an intrinsic viscosity of less than 3.0 dl/g, thereby obtaining the propylene resin (A).
Here, it is important to satisfy the following conditions (i) to (iii) at the same time:
(i) an amount of the polymer (a) contained in the propylene resin (A) is from 0.05 to 25% by weight, provided that an amount of the propylene resin (A) is assigned to be 100% by weight,
(ii) an intrinsic viscosity of the propylene resin (A) is less than 3.0 dl/g, and
(iii) a molecular weight distribution of the propylene resin (A) is less than 10.
The above-mentioned “block copolymer of propylene and ethylene” means a copolymer obtained by a process comprising the steps of:
(1) polymerizing propylene or a mixture of propylene and ethylene to obtain a propylene homopolymer or propylene/ethylene copolymer containing an ethylene unit of from 0 to 2% by weight, wherein an amount of the propylene homopolymer or propylene/ethylene copolymer is from 70 to 90% by weight, provided that an amount of the desired block copolymer of propylene and ethylene is assigned to be 100% by weight, and
(2) copolymerizing propylene and ethylene in the presence of the homopolymer or copolymer obtained in the above step (1) to further produce a propylene/ethylene copolymer containing an ethylene unit of from 10 to 50% by weight, thereby obtaining the block copolymer of propylene and ethylene.
A preferred combination of the olefin resin used in the present invention is (i) a combination of from 1 to 100% by weight of the above-mentioned propylene resin (A) with from 99 to 0% by weight of the above-mentioned block copolymer of propylene and ethylene containing an ethylene unit of from 1 to 10% by weight, and (ii) a combination of from 1 to 100% by weight of the above-mentioned propylene resin (A) with from 99 to 0% by weight of the propylene homopolymer, provided that the sum of two components in each combination is 100% by weight.
A container in accordance with the present invention can be produced by a process comprising the steps of:
(1) extruding a composition comprising an olefin resin and an expanding agent with an extruder to form a parison comprising a foamed olefin resin,
(2) setting the parison in a mold having a shape of the container, which mold is installed in a blow molding machine,
(3) blowing a gas having a pressure of from 0.01 to 3 kg/cm
2
to both the outside surface of the parison and the inside surface thereof to cool the surfaces of the parison,
(4) blowing a gas having a pressure of from 2 to 10 kg/cm
2
to the inside of the parison to expand and cool the parison, until the outer wall of the parison reaches the inner wall of the mold, and
(5) taking out the resulting container comprising a foamed olefin resin from the mold.
The formation of the parison in the above step (1) is carried out at a temperature higher than a higher temperature between a melting point of the olefin resin and a decomposition temperature of the foaming agent. When said temperature is too high, a melt viscosity of the olefin resin and a viscosity of the parison obtained decrease, respectively, and as a result, the resulting cells in the parison are crushed by pressure of the gas in the succeeding step (4), and therefore it is not recommendable. In the step (1), i
Sakamoto Akinobu
Shiromoto Seiji
Suzuki Haruyuki
Cooney Jr. John M.
Sumitomo Chemical Company Limited
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