Paper making and fiber liberation – Processes and products – Multi-layer waterlaid webs or sheets
Reexamination Certificate
1999-10-27
2002-01-15
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Multi-layer waterlaid webs or sheets
C162S146000, C162S157500
Reexamination Certificate
active
06338772
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyolefin synthetic pulp for use in battery separators, molding fiberboards, heat sealing papers and the like and relates to a heat sealing paper including the polyolefin synthetic pulp.
BACKGROUND OF THE INVENTION
Conventionally, polypropylene (PP) single fibers and polyolefin synthetic pulps are widely used as binders for inorganic powders contained in battery separators, molding fiberboards and the like. They are also widely used in heat sealing papers such as tea bags, sterilizing papers and desiccant bags.
Cost saving through thickness reduction is recently demanded in the field of battery separators, molding fiberboards, heat sealing papers and the like, in which use is made of PP single fibers and polyolefin synthetic pulps. The fibers forming the synthetic pulp must have a large breaking length and a high internal bond strength for enabling reduction of the thickness of battery separators, molding fiberboards, heat sealing papers and the like. However, the conventional PP fibers and polyolefin synthetic pulps do not always have a large fiber breaking length or a satisfactory internal bond strength. Thus, there is room for improvement in this respect.
Therefore, there is a demand for a synthetic pulp which has a larger fiber breaking length and a greater internal bond strength than those of the conventional PP fibers and synthetic pulps, whose heat seal strength is comparable to or greater than that of the conventional PP fibers and synthetic pulps, and which enables a thickness reduction.
With respect to the heat sealing papers for use in tea bags, etc., the conventional mixed type composed of a mixture of pulp fiber and synthetic fiber is being converted to a heat sealing paper of double layer type consisting of a base layer composed mainly of pulp fiber which is laminated with a heat sealing layer composed mainly of synthetic fiber. The reason is to avoid synthetic fiber fusion to a hot plate, which occasionally occurs at a heat seal step in the use of the conventional mixed type to thereby cause a productivity drop.
Interlayer bonding strength with a base layer as fell as heat sealing and hot tack properties can be mentioned as requisite functions of the heat sealing layer of the heat sealing paper of double layer type. Of such requisite functions, stable heat sealing and hot tack properties over a wide sealing temperature range from low to high temperature are especially strongly demanded in accordance with the increase of the operation speed of a bag making machine, etc.
Synthetic fibers having been used in the heat sealing layer are, for example, single fibers prepared from polypropylene (PP) and synthetic pulps prepared from polyethylene (PE). However, the heat sealing papers From PP single fibers, although exhibiting excellent heat sealing and hot tack properties when the temperature is within a high temperature range, are poor in low-temperature-range heat sealing and hot tack properties. On the other hand, the heat sealing papers from PR synthetic pulps, although having low-temperature-range heat sealing and hot tack properties superior to those of the heat sealing papers from PP single fibers, are unsatisfactory in high-temperature-range heat sealing and hot tack properties as compared with those of the heat sealing papers from PP single fibers.
OBJECT OF THE INVENTION
The present invention has been made with a view toward solving the above drawbacks of the prior art. It is an object of the present invention to provide a polyolefin synthetic pulp which has a larger fiber breaking length and a greater internal bond strength than those of the conventional PP single fibers and polyolefin synthetic pulps, whose heat seal strength is comparable to or greater than that of the conventional PP fibers and synthetic pulps, and which enables a thickness reduction.
It is another object of the present invention To provide a polyolefin synthetic pulp which exhibits Stable heat sealing and hot tack properties over a wide temperature range from low to high temperature.
It is a further object of the present invention to provide a heat sealing paper composed of the above synthetic pulps which has excellent heat sealing properties and is suitable to use in a high-speed apparatus such as a high-speed bag making machine.
SUMMARY OF THE INVENTION
The first polyolefin synthetic pulp of the present invention comprises a polyolefin resin graft-modified with an unsaturated carboxylic acid or a derivative thereof.
The second polyolefin synthetic pulp of the present invention comprises a polyolefin resin composition, the polyolefin resin composition comprising 50 to 100% by weight of an ethylene/&agr;,&bgr;-unsaturated carboxylic acid copolymer whose &agr;,&bgr;-unsaturated carboxylic acid content is in the range of 1 to 20% by weight and 0 to 50% by weight of a polyethylene resin.
The third polyolefin synthetic pulp of the present invention comprises the mixture of the graft-modified polyolefin resin described above and the polyolefin resin composition described above.
The heat sealing paper of the present invention comprises a base fiber layer whose at least one surface is laminated and integrated with a layer of the above polyolefin synthetic pulp.
DETAILED DESCRIPTION OF THE INVENTION
First, the polyolefin synthetic pulp of the present invention will be described in detail below
A polyolefin resin graft-modified with an unsaturated carboxylic acid or a derivative thereof, and/or a polyolefin resin composition comprising an ethylene/&agr;,&bgr;-unsaturated carboxylic acid copolymer and a polyethylene resin, is used as the starting material of the polyolefin synthetic pulp of the present invention.
Modified Polyolefin Resin
The modified polyolefin resin as the starting material of the first polyolefin synthetic pulp of the present invention is a polyolefin resin graft-modified with an unsaturated carboxylic acid or a derivative thereof.
Ethylene homopolymer, an ethylene/&agr;-olefin copolymer, propylene homopolymer or a propylene/&agr;-olefin copolymer is preferably used as the polyolefin resin prior to graft modification for forming this modified polyolefin resin.
It is preferred that the ethylene homopolymer for use as the polyolefin resin prior to graft modification exhibit a melt flow rate (MFR), as measured at 190° C. under a load of 2.16 kg in accordance with ASTM D-1238, of 0.01 to 1000 g/10 min, especially 0.1 to 500 g/10min, and still especially 1 to 100 g/10 min. The use of the ethylene homopolymer whose MFR falls within the above ranges enables obtaining a synthetic pulp which is highly branched and exhibits excellent intertwinement.
The ethylene/&agr;-olefin copolymer for use as the polyolefin resin prior to graft modification is a copolymer of ethylene and an &agr;-olefin having 3 to 20 carbon atoms. It is preferred that the copolymer have a density (ASTM D 1505) of 0.850 to 0.950 g/cm
3
, especially 0.870 to 0.945 g/cm
3
, and still especially 0.900 to 0.940 g/cm
3
, and that the copolymer exhibit a melt flow rate (MFR), as measured at 190° C. under a load of 2.16 kg in accordance with ASTM D-1238, of 0.1 to 100 g/10 min, especially 0.5 to 50 g/10 min, and still especially 1 to 20 g/10 min. The use of the ethylene/&agr;-olefin copolymer whose density and MFR fall within the above ranges enables obtaining a synthetic pulp which is highly branched and exhibits excellent intertwinement.
The &agr;-olefin having 3 to 20 carbon atoms for use in the copolymerization with ethylene is, for example, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or 1-eicosene.
It is generally preferred that the above ethylene/&agr;-olefin copolymer have an ethylene content of 50 to less than 100 mol %, especially 80.0 to 99.5 mol %, and still especially 90.0 to 99.0 mol %.
It is preferred that the propylene homopolymer for use as the polyolefin resin prior to graft modification exhibit a melt flow rate (MFR), as measured at 230° C.
Kouno Yukio
Nakagawa Norihiko
Nakamaru Makoto
Senoo Toshikazu
Shoji Masaki
Chin Peter
Mitsui Chemicals INC
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