U.S. patent application number 10/182819 was filed with the patent office on 2003-01-30 for heat-seal paper having air permeabillty.
Invention is credited to Kouno, Yukio, Nakagawa, Norihiko, Nakamaru, Makoto.
Application Number | 20030019598 10/182819 |
Document ID | / |
Family ID | 18551767 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030019598 |
Kind Code |
A1 |
Nakagawa, Norihiko ; et
al. |
January 30, 2003 |
Heat-seal paper having air permeabillty
Abstract
A laminate integrated by firmly jointing a heat-seal layer in
web form made from a mixture of synthetic pulp having a branched
configuration and synthetic short fiber to a substrate layer made
from natural fiber. The synthetic pulp is made from a resin
composition comprised of ethylene-.alpha.,.beta.-unsaturated
carboxylic acid copolymer and polyethylene. This laminate has a
high degree of air permeability and exhibits a high heat-seal
strength and good hot tack even at a temperature of 130.degree. C.
On account of said properties it is adequately used as heat-seal
paper suited for filter use, in particular raw material paper for
tea bags.
Inventors: |
Nakagawa, Norihiko;
(Ichihara-shi, JP) ; Kouno, Yukio; (Ichihara-shi,
JP) ; Nakamaru, Makoto; (Ichihara-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18551767 |
Appl. No.: |
10/182819 |
Filed: |
August 2, 2002 |
PCT Filed: |
February 1, 2001 |
PCT NO: |
PCT/JP01/00709 |
Current U.S.
Class: |
162/123 ;
162/141; 162/146; 162/149; 162/157.1; 428/296.7; 428/297.1 |
Current CPC
Class: |
D21H 15/10 20130101;
Y10T 428/249938 20150401; Y10T 428/249939 20150401; D21H 27/30
20130101; D21H 11/12 20130101; D21H 27/10 20130101; D21H 27/08
20130101; B32B 5/22 20130101; D21H 13/14 20130101; D21H 27/38
20130101 |
Class at
Publication: |
162/123 ;
162/141; 162/146; 162/149; 162/157.1; 428/296.7; 428/297.1 |
International
Class: |
D21H 013/02; D21H
011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2000 |
JP |
2000-25980 |
Claims
What we claim is:
1. A heat-seal paper having air permeability, which comprises a
laminated body integrating a heat-seal layer (A) principally
comprised of a synthetic fiber having a branched configuration and
a substrate layer (B) principally comprised of a natural fiber.
2. A heat-seal paper having air permeability according to claim 1,
wherein said synthetic fiber having the branched configuration is a
polyolefin synthetic pulp.
3. A heat-seal paper having air permeability according to claim 2,
wherein said polyolefin synthetic pulp has an average fiber length
of 0.1 to 10 mm and a freeness of 700 cc or less.
4. A heat-seal paper having air permeability according to claim 2
or 3, wherein said polyolefin synthetic pulp is constructed of a
resin composition comprised of 50 to 100% by weight of an
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 0 to 50% by weight of a polyethylene resin.
5. A heat-seal paper having air permeability according to either
one of claims 1 to 4, wherein said heat-seal layer (A) is comprised
of 50 to 100% by weight of the polyolefin synthetic pulp and 0 to
50% by weight of at least one type of fiber selected from the group
consisting of polyethylene fiber, polypropylene fiber, polyester
fiber and conjugate fiber thereof.
6. A heat-seal paper having air permeability according to either
one of claims 1 to 4, wherein said heat-seal layer (A) is comprised
of 50 to 90% by weight of the polyolefin synthetic pulp and 10 to
50% by weight of at least one type selected from the group
consisting of polyethylene fiber, polypropylene fiber, polyester
fiber and conjugate fiber thereof.
7. A heat-seal paper having air permeability, which is a laminated
body integrating a heat-seal layer (A) and a substrate layer (B)
principally containing a natural fiber, wherein said heat-seal
layer (A) is comprised of 1 to 99% by weight of a polyolefin
synthetic pulp having a branched configuration and an average fiber
length of 0.1 to 10 mm and 1 to 99% by weight of a synthetic fiber
having a fineness of 0.1 to 10 deniers and an average fiber length
of 0.1 to 30 mm, and said synthetic pulp is constructed of a resin
composition comprised of 50 to 99% by weight of an
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 1 to 50% by weight of a polyethylene resin.
8. A heat-seal paper having air permeability according to claim 7,
wherein said heat-seal layer (A) is comprised of 50 to 99% by
weight of the polyolefin synthetic pulp and 1 to 50% by weight of
the synthetic fiber.
9. A heat-seal paper having air permeability according to claim 7,
wherein said heat-seal layer (A) is comprised of 50 to 90% by
weight of the polyolefin synthetic pulp and 10 to 50% by weight of
the synthetic fiber.
10. A heat-seal paper having air permeability according to either
one of claims 7 to 9, wherein said synthetic fiber is at least one
type of fiber selected from the group consisting of polyethylene
fiber, polypropylene fiber, polyester fiber and conjugate fiber
thereof.
11. A heat-seal paper having air permeability according to either
one of claims 7 to 10, wherein said
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer is an
ethylene-acrylic acid copolymer or an ethylene-methacrylic acid
copolymer.
12. A heat-seal paper having air permeability according to either
one of claims 7 to 11, wherein said polyethylene resin has a
density of 0.941 to 0.970 (g/cm.sup.3) and a melt flow rate of 0.1
to 100 (g/10 min.).
13. A heat-seal paper having air permeability according to either
one of claims 7 to 12, wherein said polyolefin synthetic pulp has a
freeness of 700 cc or less.
14. A heat-seal paper having air permeability according to either
one of claims 7 to 13, wherein said heat-seal layer (A) has a
thickness corresponding to a grammage of 1 to 10 (g/m.sup.2).
15. A heat-seal paper having air permeability according to either
one of claims 7 to 14, wherein said substrate layer (B) has a
thickness corresponding to a grammage of 10 to 30 (g/m.sup.2)
16. A heat-seal paper having air permeability according to either
one of claims 7 to 15, wherein said substrate layer (B) is
comprised of an abaca pulp.
17. A heat-seal paper having air permeability according to either
one of claims 7 to 16, wherein said laminated body is comprised of
15 to 30% by weight of the heat-seal layer (A) and 70 to 85% by
weight of the substrate layer (B).
18. A heat-seal paper having air permeability according to either
one of claims 7 to 17, wherein said laminated body has a thickness
corresponding to a grammage of 11 to 40 (g/m.sup.2).
19. A heat-seal paper having air permeability according to either
one of claims 7 to 18, wherein said laminated body has a Frazier
air permeability of 100 to 300 (cm.sup.3/cm.sup.2/s)
20. A heat-seal paper having air permeability according to either
one of claims 7 to 19, wherein said laminated body has a heat-seal
strength at a temperature of 130.degree. C. of 100 to 300 (g/15
mm).
21. A heat-seal paper having air permeability according to either
one of claims 7 to 20, wherein said laminated body has a hot tack
as represented by a peel distance at a temperature of 130.degree.
C. is 1 to 100 mm.
22. A heat-seal paper having air permeability according to either
one of claims 7 to 21, wherein said laminated body is a filter bag
paper.
23. A heat-seal paper having air permeability according to either
one of claims 7 to 21, wherein said laminated body is a tea bag
paper.
24. A heat-seal paper having air permeability according to either
one of claims 7 to 23, wherein said heat-seal layer (A) and said
substrate layer (B) constituting the laminated body do not
substantially contain any halogen atom.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a heat-seal paper having
air permeability, and more particularly relates to a heat-seal
paper suitable for the manufacture of tea bags or bags for
packaging sterilized apparatus and tools, desiccators, etc.
BACKGROUND OF THE INVENTION
[0002] The heat-seal paper conventionally used as the raw material
paper for tea bags, etc. used to be made from some type of mixed
pulp composed of natural fiber and synthetic fiber. Such paper
often impaired productivity of automatic packaging machine due to
adhesion of molten synthetic fibers contained in it to the hot
plate when fed to the heat-sealing section of the packaging
machine. Coming into predominant use in the industry these days is
such double layered heat-seal paper constructed of a heat-seal
layer principally composed of synthetic fiber and a substrate layer
principally composed of natural fiber, the former being laminated
on the latter.
[0003] This double layered type heat-seal paper is required to
possess air permeability, to have its heat-seal layer firmly
jointed to the substrate layer, and to have its heat-seal layer
retain good heat-sealability, hot tack, etc.
[0004] Meanwhile, the synthetic fiber used for the conventional
heat-seal layer is polyethylene fiber, polypropylene fiber,
polyester fiber, or conjugate fiber thereof. Heat-seal paper made
from said fibers has good air permeability, but is said to impart
only too low interlayer bond strength between the heat-seal layer
and the substrate layer. What is pointed out as the factor to bring
about low interlayer bond strength is that said fiber makes it
difficult for developing intertwists involving fibers in the
substrate layer because it is in the rod shape and, therefore, is
destitute of ramification.
[0005] As the automatic packaging machines have come to acquire
very high operating speeds recently, the industry is demanding in
particular higher degrees of heat-sealability and hot tack at low
sealing temperatures. Said fibers conventionally put in use for the
heat-seal layer have not necessarily had sufficient
heat-sealability and hot tack at low sealing temperatures, although
they have at high sealing temperatures.
[0006] Japanese Patent Publication No. 1969-16801 (corresponding
foreign patent: German Patent No. 1546330: British Patent No.
1091073) discloses a fiber made from vinyl acetate-vinyl chloride
copolymer (trade name "Vinyon"). There appears a description
therein that said fiber can be used as a raw material for heat-seal
paper to be used in the manufacture of tea bags. Although said
heat-seal paper has good air permeability, heat-sealability, etc.,
it is faced with demands for further improved product qualities so
that it would not give rise to generation of dioxines and other
harmful substances when incinerated as wastes.
DESCRIPTION OF THE INVENTION
[0007] Accordingly it is an object of the present invention to
provide a heat-seal paper which has a heal seal layer and a
substrate layer firmly jointed to each other and retains good air
permeability.
[0008] It is the second object of the present invention to provide
a heat-seal paper which imparts stable and good heat-sealability
and hot tack over a wide range of heat-sealing temperature range
extending from low temperatures to high temperatures.
[0009] It is the third object of the present invention to provide a
heat-seal paper which is few fear of generation of dioxines and
other harmful substances when incinerated as wastes, and thus
contributes to protection of the environments.
[0010] At large, the present invention relates to a heat-seal paper
whose technical details are as enumerated in items 1 to 24 as
follows:
[0011] 1. A heat-seal paper having air permeability, which
comprises a laminated body integrating a heat-seal layer (A)
principally comprised of a synthetic fiber having a branched
configuration and a substrate layer (B) principally comprised of a
natural fiber.
[0012] 2. A heat-seal paper having air permeability according to
item 1, wherein said synthetic fiber having the branched
configuration is a polyolefin synthetic pulp.
[0013] 3. A heat-seal paper having air permeability according to
item 2, wherein said polyolefin synthetic pulp has an average fiber
length of 0.1 to 10 mm and a freeness of 700 cc or less.
[0014] 4. A heat-seal paper having air permeability according to
item 2 or 3, wherein said polyolefin synthetic pulp is constructed
of a resin composition comprised of 50 to 100% by weight of an
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 0 to 50% by weight of a polyethylene resin.
[0015] 5. A heat-seal paper having air permeability according to
either one of items 1 to 4, wherein said heat-seal layer (A) is
comprised of 50 to 100% by weight of the polyolefin synthetic pulp
and 0 to 50% by weight of at least one type of fiber selected from
the group consisting of polyethylene fiber, polypropylene fiber,
polyester fiber and conjugate fiber thereof.
[0016] 6. A heat-seal paper having air permeability according to
either one of items 1 to 4, wherein said heat-seal layer (A) is
comprised of 50 to 90% by weight of the polyolefin synthetic pulp
and 10 to 50% by weight of at least one type selected from the
group consisting of polyethylene fiber, polypropylene fiber,
polyester fiber and conjugate fiber thereof.
[0017] 7. A heat-seal paper having air permeability, which is a
laminated body integrating a heat-seal layer (A) and a substrate
layer (B) principally containing natural fiber wherein said
heat-seal layer (A) is comprised of 1 to 99% by weight of a
polyolefin synthetic pulp having a branched configuration and an
average fiber length of 0.1 to 10 mm and 1 to 99% by weight of a
synthetic fiber having a fineness of 0.1 to 10 deniers and an
average fiber length of 0.1 to 30 mm, and said synthetic pulp is
constructed of a resin composition comprised of 50to 99% by weight
of an ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 1 to 50% by weight of a polyethylene resin.
[0018] 8. A heat-seal paper having air permeability according to
item 7, wherein said heat-seal layer (A) is comprised of 50 to 99%
by weight of the polyolefin synthetic pulp and 1 to 50% by weight
of the synthetic fiber.
[0019] 9. A heat-seal paper having air permeability according to
item 7, wherein said heat-seal layer (A) is comprised of 50 to 90%
by weight of the polyolefin synthetic pulp and 10 to 50% by weight
of the synthetic fiber.
[0020] 10. A heat-seal paper having air permeability according to
either one of items 7 to 9, wherein said synthetic fiber is at
least one type of fiber selected from the group consisting of
polyethylene fiber, polypropylene fiber, polyester fiber and
conjugate fiber thereof.
[0021] 11. A heat-seal paper having air permeability according to
either one of items 7 to 10, wherein said
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer is an
ethylene-acrylic acid copolymer or an ethylene-methacrylic acid
copolymer.
[0022] 12. A heat-seal paper having air permeability according to
either one of items 7 to 11, wherein said polyethylene resin has a
density of 0.941 to 0.970.(g/cm.sup.3) and a melt flow rate of 0.1
to 100 (g/10 min.).
[0023] 13. A heat-seal paper having air permeability according to
either one of items 7 to 12, wherein said polyolefin synthetic pulp
has a freeness of 700 cc or less.
[0024] 14. A heat-seal paper having air permeability according to
either one of items 7 to 13, wherein said heat-seal layer (A) has a
thickness corresponding to a grammage of 1 to 10 (g/m.sup.2).
[0025] 15. A heat-seal paper having air permeability according to
either one of items 7 to 14, wherein said substrate layer (B) has a
thickness corresponding to a grammage of 10 to 30 (g/m.sup.2).
[0026] 16. A heat-seal paper having air permeability according to
either one of items 7 to 15, wherein said substrate layer (B) is
composed of an abaca pulp.
[0027] 17. A heat-seal paper having air permeability according to
either one of items 7 to 16, wherein said laminated body is
comprised of 15 to 30% by weight of the heat-seal layer (A) and 70
to 85% by weight of the substrate layer (B).
[0028] 18. A heat-seal paper having air permeability according to
either one of items 7 to 17, wherein said laminated body has a
thickness corresponding to a grammage of 11 to 40 (g/m.sup.2).
[0029] 19. A heat-seal paper having air permeability according to
either one of items 7 to 18, wherein said laminated body has a
Frazier air permeability of 100 to 300 (cm.sup.3/cm.sup.2/s).
[0030] 20. A heat-seal paper having air permeability according to
either one of items 7 to 19, wherein said laminated body has a
heat-seal strength at a temperature of 130.degree. C. of 100 to 300
(g/15 mm).
[0031] 21. A heat-seal paper having air permeability according to
either one of items 7 to 20, wherein said laminated body has a hot
tack as represented by a peel distance at a temperature of
130.degree. C. is 1 to 100 mm.
[0032] 22. A heat-seal paper having air permeability according to
either one of items 7 to 21, wherein said laminated body is a
filter bag paper.
[0033] 23. A heat-seal paper having air permeability according to
either one of items 7 to 21, wherein said laminated body is a tea
bag paper.
[0034] 24. A heat-seal paper having air permeability according to
either one of items 7 to 23, wherein the heat-seal layer (A) and
the substrate layer (B) constituting said laminated body do not
substantially contain any halogen atom.
[0035] In other words, the present invention relates to a heat-seal
paper having air permeability, which comprises a laminated body
integrating a heat-seal layer (A) principally comprised of a
synthetic fiber having a branched configuration and a substrate
layer (B) principally comprised of a natural fiber.
[0036] It is preferable that said synthetic fiber having the
branched configuration is a polyolefin synthetic pulp. It is
particularly preferable that it is constructed of a resin
composition comprised of 50 to 100% by weight of an
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 0 to 50% by weight of a polyethylene resin.
[0037] It is also preferable that said heat-seal layer (A) is
composed of 50 to 100% by weight, and preferably 50 to 90% by
weight of the polyolefin synthetic pulp and 0 to 50% by weight, and
preferably 10 to 50% by weight of at least one type of fiber
selected from the group consisting of polyethylene fiber,
polypropylene fiber, polyester fiber and conjugate fiber
thereof.
[0038] The present invention relates to a heat-seal paper having
air permeability, which is a laminated body integrating a heat-seal
layer (A) and a substrate layer (B) principally containing a
natural fiber, wherein said heat-seal layer (A) is comprised of 1
to 99% by weight of a polyolefin synthetic pulp having a branched
configuration and an average fiber length of 0.1 to 10 mm and 1 to
99% by weight of a synthetic fiber having a fineness of 0.1 to 10
deniers and an average fiber length of 0.1 to 30 mm, and said
synthetic pulp is comprised of 50 to 99% by weight of an
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
containing 1 to 20% by weight of an .alpha.,.beta.-unsaturated
carboxylic acid and 1 to 50% by weight of a polyethylene resin.
[0039] It is furthermore preferable that said heat-seal layer (A)
is comprised of 50 to 99% by weight, and more preferably 50 to 90%
by weight of the polyolefin synthetic pulp and 1 to 50% by weight,
and more preferably 10 to 50% by weight of the synthetic fiber.
[0040] For said heat-seal paper, it is preferable that said
synthetic fiber is at least one type of fiber selected from the
group consisting of polyethylene fiber, polypropylene fiber,
polyester fiber and conjugate fiber thereof.
[0041] It is preferable that the
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer
constituting polyolefin synthetic pulp is an ethylene-acrylic acid
copolymer or an ethylene-methacrylic acid copolymer, wherein the
polyethylene resin is a high density polyethylene having a density
of 0.941 to 0.970 (g/cm.sup.3) and a melt flow rate of 0.1 to 100
(g/10 min.).
[0042] The weight ratio of each layer constituting the laminated
body is preferably 15 to 30% by weight for the heat-seal layer (A)
and 70 to 85% by weight for the substrate layer.
[0043] It is preferable that the breakdown by thickness of said
laminated body is adjusted to 1 to 10 (g/m.sup.2) for the heat-seal
layer (A), 10 to 30 (g/m.sup.2) for the substrate layer (B) and 11
to 40 (g/m.sup.2) as a whole, respectively, in terms of
grammage.
[0044] The laminated body having said structure is suitable for the
use as a heat-seal paper insofar as its Frazier air permeability is
100 to 300 (cm.sup.3/cm.sup.2/s), its heat-seal strength is 100 to
300 (g/15 mm) at a temperature of 130.degree. C., and its hot tack
at a temperature of 130.degree. C. as expressed by the peel
distance is 1 to 100 mm.
[0045] Since the heat-seal paper of the present invention exhibits
stable and good heat sealability and hot tack over a wide
temperature range extending from low temperatures to high
temperatures, demonstrating high effects particularly at low
temperatures, and at the same time possesses good air permeability
and strong interlayer bond strength between the heat-seal layer and
the substrate layer, it may be utilized as filter bag paper, in
particular as the raw material paper for tea bags.
BRIEF DESCRIPTION OF DRAWINGS
[0046] FIG. 1 is a micrograph depicting a configuration of the
synthetic pulp used in the present invention.
[0047] FIG. 2 is a micrograph depicting a configuration of the
synthetic fiber used in the present invention.
[0048] FIG. 3 is a micrograph depicting a configuration of the
heat-seal layer pertinent to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] A heat-seal paper having air permeability of the present
invention is a laminated body which is comprised of basically a
heat-seal layer and a substrate layer, each of which will be
explained in detail as follows:
Heat-seal Layer (A)
[0050] A heat-seal layer (A) constitutes a unit sheet contained of
a blended fibrous layer comprising a polyolefin synthetic pulp and
a synthetic fiber which as a whole does not readily get separated
due to the presence of branches in the synthetic pulp that are
intertwisted with the synthetic fibers.
[0051] (1) Polyolefin Synthetic Pulp
[0052] The polyolefin synthetic pulp is a pulp-like material formed
from polyolefin resin into short fiber having innumerous branches
which has an average fiber length of 0.1 to 10 mm, and preferably
0.5 to 5 mm. Innumerous branches are located on the surfaces of
such fibers. FIG. 1 is a micrograph depicting a configuration of
the synthetic pulp. The micrograph shows that fine short fibers get
ramified from the surface of a thick short fiber as is normally the
case with a natural pulp.
[0053] While such synthetic pulp can be manufactured from various
types of polyolefin resin or a resin composition, it is preferable
that it be formed from an ethylene-.alpha.,.beta.-unsaturated
carboxylic acid copolymer(a) in consideration of such conditions
that it may be readily formed into a pulp-like material and
possesses good heat-sealability and hot tack, and it is
particularly preferably that it be formed from a resin composition
comprised of (a) and polyethylene resin (b).
[0054] (2) Ethylene-.alpha.,.beta.-Unsaturated Carboxylic Acid
Copolymer
[0055] The Ethylene-.alpha.,.beta.-unsaturated carboxylic acid
copolymer is a copolymer derived by copolymerizing ethylene and an
.alpha.,.beta.-unsaturated carboxylic acid wherein
.alpha.,.beta.-unsaturated carboxylic acid unit is contained by 1
to 20% by weight, preferably 3 to 15% by weight, and more
preferably 5 to 10% by weight. Insofar as the
.alpha.,.beta.-unsaturated carboxylic acid content is within said
ranges, the synthetic pulp containing said copolymer imparts high
levels of heat-sealability and hot tack over a wide temperature
range extending from low temperatures to high temperatures and
possesses sufficient freeness required of a wet process paper.
[0056] As examples of the .alpha.,.beta.-unsaturated carboxylic
acid, the following compounds can be cited. Namely, acrylic acid,
methacrylic acid, maleic acid, maleic anhydride, fumaric acid,
itaconic acid, crotonic acid, himic anhydride, etc. Included in the
category of .alpha.,.beta.-unsaturated carboxylic acid for the
present invention are the following. Namely,
.alpha.,.beta.-unsaturated carboxylic acid esters, which are
derivatives of .alpha.,.beta.-unsaturated carboxylic acid, i.e.,
methyl acrylate, methyl methacrylate, monomethyl maleate, etc.
Particularly preferred among them is acrylic acid or methacrylic
acid, which is a monovalent acid.
[0057] Said ethylene-.alpha.,.beta.-unsaturated carboxylic acid
copolymer may be a random copolymer of ethylene and the
.alpha.,.beta.-unsaturated carboxylic acid, or a graft copolymer
derived by graft copolymerizing the .alpha.,.beta.-unsaturated
carboxylic acid to polyethylene. Particular preferred among them is
the random copolymer manufactured by directly copoly-merizing
ethylene with the .alpha.,.beta.-unsaturated carboxylic acid. This
type is conventionally manufactured according to a high-pressure
radical polymerization process. In executing such copolymerization,
the .alpha.,.beta.-unsaturated carboxylic acids exemplified above
may be used alone or in a combination of two or more types.
[0058] The following copolymers can be cited as examples of the
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer.
Namely, ethylene-acrylic acid copolymer, ethylene-methacrylic acid
copolymer, ethylene-methacrylic acid-methyl methacrylate
terpolymer, and ethylene-acrylic acid-methyl methacrylate
terpolymer.
[0059] The ethylene-.alpha.,.beta.-unsaturated carboxylic acid
copolymer usable for the present invention may be so-called ionomer
resin which is derived by partially neutralizing at least part of
the carboxylic groups contained in the
ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer with
such metal ion as Na.sup.+, K.sup.+, Zn.sup.++, Ca.sup.++,
Mg.sup.++, etc.
[0060] (3) Polyethylene Resin
[0061] Polyethylene resin may be an ethylene homopolymer or an
ethylene-60 -olefin copolymer. It is usable over a wide range
extending from a low density grade to a high density grade.
[0062] It is preferable that the ethylene homopolymer is in the
ranges of 0.900 to 0.970 (g/cm.sup.3) for a density, and preferably
0.920 to 0.970 (g/cm.sup.3); 0.1 to 100 (g/10 min.), and preferably
1 to 20 (g/10 min.) for a melt flow rate (MFR) as determined at a
temperature of 190.degree. C. and under a load of 2.16 kg according
to ASTM D-1238. Insofar as the ethylene homopolymer having the
density and the MFR falling within said ranges is used, a synthetic
pulp of highly branched and well-intertwisted pulp fibers may be
obtained. Among different grades of polyethylene, high density
polyethylene having the density of 0.941 to 0.970 (g/cm.sup.3) is
particularly preferred.
[0063] In the case of the ethylene-.alpha.-olefin copolymer, what
is preferred is a crystalline polymer falling in the ranges of 90
to 99 mol. %, and preferably 95 to 99 mol. % for ethylene content
and 1 to 10 mol. %, and preferably 1 to 5 mol. % for .alpha.-olefin
content. Preferred for such .alpha.-olefin are those olefins having
3 to 20 carbon atoms. Some examples thereof are propylene,
1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene,
1-hexene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene.
[0064] It is preferable that such ethylene-.alpha.-olefin copolymer
has a density of 0.900 to 0.940 (g/cm.sup.3), and preferably 0.920
to 0.940 (g/cm.sup.3) and a melt flow rate (MFR) as determined at a
temperature of 190.degree. C. and under a load of 2.16 kg according
to ASTM D-1238 of 0.1 to 100 (g/10 min.), and preferably 0.5 to 50
(g/10 min.). Insofar as the ethylene-.alpha.-olefin copolymer to be
used has the density and the MFR falling in said ranges, synthetic
pulp obtained from it exhibits highly ramified pulp fiber and
favorable intertwists.
[0065] Particularly preferred among such ethylene-.alpha.-olefin
copolymers are ethylene-1-butene copolymer,
ethylene-4-methyl-1-pentene copolymer and ethylene-1-hexene
copolymer having the density of 0.920 to 0.940 (g/cm.sup.3) and the
MFR of 1 to 10 (g/10 min.).
[0066] These ethylene homopolymer and ethylene-.alpha.-olefin
copolymers can be manufactured by polymerizing ethylene, and
insofar as necessary including .alpha.-olefin monomer in the
reaction system in the presence of Ziegler-Natta catalyst or a
metallocene catalyst according to such conventional polymerization
process as the gas phase process, the bulk process, the slurry
process, and the solution process.
[0067] (4) Manufacture of Synthetic Pulp
[0068] The synthetic pulp usable for the present invention is
formed into pulp-like material from a resin composition preferably
comprising the ethylene-.alpha.,.beta.-unsaturated carboxylic acid
copolymer (a) and the polyethylene resin (b). The blending ratio
(%) of the raw materials (a) and (b) are 50 to 100% by weight,
preferably 50 to 99% by weight, and more preferably 50 to 90% by
weight, and furthermore preferably 60 to 80% by weight for the raw
material (a) and 0 to 50% by weight, preferably 1 to 50% by weight,
more preferably 10 to 50% by weight, and furthermore preferably 20
to 40% by weight for the raw material (b), wherein the sum of the
raw materials (a) and (b) is to be 100% by weight.
[0069] Insofar as the blending ratio (%) of the raw materials (a)
and (b) falls within said ranges, such synthetic pulp may be
obtained that will give excellent freeness when it is made into
paper according to the wet process, and also such synthetic pulp
may be obtained as will impart stable and good heat-sealability and
hot tack over a wide sealing temperature range extending from low
temperatures to high temperatures.
[0070] For manufacturing synthetic pulp from said raw material
resin composition, conventional processes can be employed. Such
processes are explained in detail in Encyclopedia of Chemical
Technology, 3.sup.rded., Vol. 19, p.p. 420 to 425. For instance,
there is introduced a process which comprises cutting melt-spun
fiber into short elements, and then beating the resulting material;
and another process which comprises beating materials obtained by
melt-flash spinning or emulsion-flash spinning. In the pulp
preparation process, various additives, such as antioxidants,
antistatic agents, UV stabilizers, and pigments may be added
insofar as addition of such additives does not go counter to the
object of the present invention.
[0071] It is preferable that the synthetic pulp used in the present
invention has an average fiber length of 0.1 to 10 mm, and
preferably 0.5 to 5 mm, and has a freeness conforming to Canadian
Standard Freeness (CSF) of 700 cc or less. Preferred as the process
for manufacturing such preferable synthetic pulp is the process of
flash spinning a resin solution or an emulsion. Particularly
preferred is the emulsion-flash spinning process in which a
polyvinyl alcohol (PVA) is utilized as the hydrophilic agent, since
this process gives a pulp having such fiber configuration that
promotes formation of intertwists among synthetic fibers in the
heat-seal layer and natural fibers in the substrate layer. The
preferable amount of the PVA to be added is 0.01 to 10% by weight
to the total quantity of the synthetic pulp including the PVA.
[0072] (5) Formation of the Heat-seal Layer (A)
[0073] The heat-seal layer (A) is a fibrous layer comprised of the
polyolefin synthetic pulp and the synthetic fiber.
[0074] The synthetic fiber for this use has a weight fineness of
0.1 to 10 deniers, and preferably 0.5 to 8 deniers and an average
fiber length of 0.1 to 30 mm, and preferably 0.5 to 25 mm, which is
conventionally categorized as short fiber. Such synthetic fiber may
have a round cross-section or oblong cross-section, and furthermore
a polygonal cross-section. It may also have branches on its
surface. FIG. 2 is a micrograph depicting an example of its
configuration. It shows rod-shaped polypropylene short fiber having
a round cross-section and smooth surfaces.
[0075] The usable types of synthetic fiber are fibers having
various qualities such as polyolefin fiber, polyester fiber,
polyamide fiber, etc. Particularly preferred among them are
polyethylene fiber, polypropylene fiber, polyester fiber, or
conjugate fibers thereof. The structure of the conjugate fiber may
be of a sheath & core construction or of a side-by-side
construction. For example, the conjugate fibers of the sheath &
core construction constructed of a polyethylene sheath and a
polypropylene core is usable.
[0076] It is preferable that the blending ratio is 1 to 99% by
weight, and preferably 50 to 99% by weight, and more preferably
50to 90% by weight, of the polyolefin synthetic pulp and 1 to 99%
by weight, preferably 1 to 50% by weight, and more preferably 10 to
50% by weight of the synthetic fiber, so that the total quantity of
the two becomes 100% by weight. A blending ratio falling in said
ranges is advantageous in that the heat-seal layer exhibits high
heat-sealability and hot tack over a wide heat-sealing temperature
range extending from low temperatures to high temperatures, and
thus the bond to the substrate layer is made stronger.
[0077] As for the method of blending the synthetic pulp and the
synthetic fiber, blending can be accomplished without any
difficulty by mechanically mixing the two during the paper making
step. As specific methods, conventional beating/refining machine
such as a pulper and a beater can be utilized. A heat-seal layer
having a sufficient heat-seal strength and hot tack may be formed
by adjusting the thickness of dried web to a grammage, or basis
weight (weight per unit area) of 1 to 20 (g/m.sup.2), and
preferably 1 to 10 (g/m.sup.2), and thus the obtained heat-seal
layer exhibits a sufficient air permeability.
[0078] FIG. 3 is a micrograph depicting an example of the heat-seal
layer. The heat-seal layer shown in the photograph is a fibrous
layer formed by mechanically mixing 70% by weight of the synthetic
pulp and 30% by weight of a polypropylene short fiber. It may be
clearly seen from this micrograph that synthetic pulp having
innumerous branches on its surfaces intertwisted with rod-shaped
polypropylene short fibers which have smooth surfaces.
Heat-seal Paper
[0079] (1) Structure of the Heat-seal Paper
[0080] A laminated body obtained by laminating the heat-seal layer
(A) on a substrate layer (B) so as to integrate them into a united
body may be a double layered laminate of the (A)/(B) construction
or a triple layered laminate of the (A)/(B)/(A) construction. Such
laminate can be utilized as a heat-seal paper. It is typically
utilized extensively in the form of the double layered laminate of
the (A)/(B) construction.
[0081] The substrate layer (B) is a fibrous layer principally
comprised of a natural fiber and may additionally contain small
amounts of synthetic fiber or synthetic pulp or the like. As the
natural fiber for this use, such natural fiber as is utilized for
the conventional tea bags or sterilized paper are usable. A few
examples thereof are abaca pulp, NBKP (needle bleached kraft pulp),
and LBKP (leaf bleached kraft pulp). Particularly preferred among
them is abaca pulp in view of its air permeability and strength.
The thickness of the substrate layer varies with the intended use
of the heat-seal paper. Its suitable grammage is in the range of 10
to 50 (g/m.sup.2), and preferably of 10 to 30 (g/m.sup.2).
[0082] (2) Manufacture of the Heat-seal Paper
[0083] The heat-seal paper can be manufactured according to a
process which comprises laminating the heat-seal layer (A) on at
least one side of the substrate layer (B) and thereupon firmly
integrating the two layers into a united body by heat
treatment.
[0084] A detailed explanation is furnished as follows with
reference to an example. The substrate layer and the heat-seal
layer are individually formed using a sheet machine as separate wet
webs and while the two layers are in the wet state, the heat-seal
layer is stacked onto at least one side of the substrate layer, and
the stack thus prepared is dried at a temperature of 40 to
110.degree. C. using a heating device such as a hot oven or a hot
roll, and thereupon the resulting sheet is subjected to heat
treatment at a temperature of 130 to 200.degree. C. so as to be
made into the heat-seal paper. In the course of said operation, the
heat-seal layer (A) and the substrate layer (B) are bonded to each
other firmly to have a high interlayer bond strength as innumerous
branches of synthetic pulp situated on the surface of the heat-seal
layer are firmly bonded to the fibers constituting the substrate
layer.
[0085] The weight ratio of each layer is 15 to 30% by weight, and
preferably 15 to 25% by weight, of the heat-seal layer (A) and 70
to 85% by weight, and preferably 75 to 85% by weight of the
substrate layer (B). And, the total thickness of the laminated body
is so adjusted that it will correspond to a grammage of 11 to 40
(g/m.sup.2).
[0086] (3) Properties of the Heat-seal Paper
[0087] It is preferable that an air permeability of the heat-seal
paper having aforementioned structure is 100 to 300
(cm.sup.3/cm.sup.2/s), and preferably 100 to 200
(cm.sup.3/cm.sup.2/s) in Frazier air permeability as determined
using Frazier-model air permeability testing apparatus which is
prescribed in JIS L1004. The heat-seal paper having the air
permeability falling in said ranges can be favorably used in
various applications for the filter use.
[0088] A heat-seal strength of said heat-seal paper at a
temperature of 130.degree. C. falls in the range of 100 to 300
(g/15 mm), and preferably 120 to 200 (g/15 mm). Insofar as the
heat-seal strength of the heat-seal paper is within said ranges,
such heat-seal paper exhibits sufficient bond strength and hence it
is applicable to extensive uses.
[0089] The heat-seal strength is determined according to the
following procedure. Namely, two sheets of heat-seal paper are
stacked in such manner that their respective heat-seal layers will
touch face-to-face each other. Thereupon a 10 mm-wide seal bar
controlled to a temperature of 130.degree. C. is pressed from the
substrate layer side under a pressure of 2 kg/cm.sup.2 for 1 sec.
After the heat-sealed area has been cooled to the room temperature,
a specimen of a 15 mm width cut out from it is subjected to such
test that its heat-sealed area is peeled at a crosshead speed of
100 mm/min. so that its peel strength (g/15 mm) is measured. The
measured value is recorded as the heat-seal strength.
[0090] A hot tack of this heat-seal paper at a temperature of
130.degree. C. as expressed in terms of a peel distance is 1 to 100
mm, and preferably 1 to 70 mm. Insofar as the peel distance, which
is an indicator of hot tack, is within said ranges, speedy and
stable packaging operation may be continuously executed when this
heat-seal paper is fed to an automatic filling/packaging machine
designed to accomplish both a bag-making job using the heat-seal
paper and a loading job by itself.
[0091] The peel distance adopted as the indicator of the hot tack
was determined according to the following procedure. Namely, two
sheets of heat-seal paper were stacked in such manner that their
heat-seal layers would touch face-to-face each other, and thereupon
the stacked layers were heat-sealed at a temperature of 130.degree.
C. for 0.5 sec. under a pressure of 1 kg/cm.sup.2, and immediately
afterwards the peel distance of the heat-sealed area was measured
under a load of 45 g.
[0092] As explained in the foregoing, the heat-seal paper of the
present invention retains the high air permeability and the
heat-seal layer and the substrate layer are jointed to each other
to have a high interlayer bond strength. When it is fed to a
heat-seal section in an automatic packaging machine, adhesion
possibly caused in a molten state of the heat-seal paper to a hot
plate in the machine may be prevented while it possesses good hot
tack. For said reason, the heat-seal paper of the present invention
may enhance stable productivity of bags, and bags having high
heat-seal strength may be manufactured on a continuous basis.
EXAMPLES
[0093] Next, the present invention is further described with
reference to examples, but it should be construed that the
invention is in no way limited to those examples.
[0094] The following two types of resin were made available so as
to be used in examples.
[0095] (1) Resin 1: Ethylene-methacrylic acid copolymer
[0096] MFR (at 190.degree. C.) =1.5 (g/10 min.)
[0097] Melting point =99.degree. C.
[0098] Methacrylic acid content=9% by weight
[0099] (2) Resin 2: High density polyethylene
[0100] MFR (at 190.degree. C.)=13 (g/10 min.)
[0101] Melting point=135.degree. C.
[0102] Density=0.965 (g/cm.sup.3)
[0103] Properties of the manufactured synthetic pulp and heat-seal
paper were measured according to the following test procedures.
[0104] (1) Average Fiber Length (Abb.: CFL)
[0105] The average fiber length per unit weight (mm) was determined
using an automatic fiber length testing apparatus FS-200-model
manufactured by Kajaani Co., Finland, and the measured value was
reported as the average fiber length in the unit of millimeter.
[0106] (2) Freeness (Abb.: CSF)
[0107] Canadian Standard Freeness was determined in accordance with
JIS P-8121, and the measured value was reported as the freeness
value in the unit of cubic centimeter (cc).
[0108] (3) Air Permeability
[0109] Frazier air permeability was determined using a
Frazier-model air permeability testing apparatus as prescribed in
JIS L1004, and the measured value was reported as air permeability
in the unit of cm.sup.3/cm.sup.2/s.
[0110] (4) Heat-seal Strength
[0111] Two sheets of double layered hand made sheet were stacked in
such manner that their heat-seal layers will touch face-to-face
each other and were heat-sealed for 1 sec under a pressure of 2
kg/cm.sup.2 at temperatures of 130.degree. C., 150.degree. C.,
170.degree. C. and 190.degree. C., respectively, using a 10 mm-wide
seal bar, and then left to stand until cooled to the room
temperature. Next, 15 mm-wide specimens were cut out from the hand
sheets heat-sealed at said respective temperatures, and the
heat-sealed area of each specimen was peeled at the crosshead speed
of 100 mm/min., and thus was measured its peel strength (g/15 mm).
The measured value was reported as the heat-seal strength.
[0112] (5) Hot Tack
[0113] Two sheets of double-layered hand made sheet were stacked in
such manner that their heat-seal layers will touch face-to-face
each other and were heat-sealed for 0.5 sec under a pressure of 1
kg/cm.sup.2 at temperatures of 130.degree. C., 150.degree. C.,
170.degree. C. and 190.degree. C., respectively, and immediately
afterwards peel distance was measured by peeling the heat-sealed
area under a load of 45 g. The measured peel distance was recorded
as the basis on which to evaluate hot tack of the specimen.
EXAMPLE 1
[0114] Into an 80 liter autoclave equipped with a baffle plate and
an agitator were charged 20 liters of n-hexane (23.degree. C.), 20
liters of water (23.degree. C.), 700 g of ethylene-methacrylic acid
copolymer (resin 1), 300 g of high density polyethylene (resin 2)
and 20 g of polyvinyl alcohol (PVA) (saponification degree 99%;
viscosity of 4% aqueous solution (20.degree. C.) 4.6 to 6.0 cps;
manufactured by Japan Synthetic Chemical Industry Co.; trade name:
Gosenol NL-05). The liquid mixture was heated to a temperature of
145.degree. C. with agitation using the agitator operated at 900
rounds permin. Agitation was continued for 30 min., while the mixed
liquid temperature was maintained at a temperature of 145.degree.
C. to finally obtain a suspension.
[0115] Next, the suspension was flashed into a drum maintained in a
nitrogen atmosphere at a pressure of 400 mm Hg via a pipe connected
to a nozzle of a 3 mm diameter and 20 mm length provided on the
autoclave, and thus was obtained a fiber-like material. The
fiber-like material was then converted into an aqueous slurry of a
10 g/liter concentration in a receptacle, and the slurry was
beaten/refined in a 12 inch-diameter disk-type refiner, and thus
was obtained a pulp-like material.
[0116] Properties of the synthetic pulp thus obtained were an
average fiber length (CFL) of 1.0 mm and a Canadian Standard
Freeness (CSF) of 670 cc.
[0117] As the raw material for the substrate layer, abaca fiber was
made available, and as the raw materials for the heat-seal layer, a
mixture comprised of 70% by weight of said synthetic pulp and 30%
by weight of polypropylene fiber (fineness: 2 deniers; fiber
length: 5 mm; melting point: 165.degree. C.) were made available.
Next, the substrate layer having a grammage of 14 g/m.sup.2 and the
heat-seal layer having a grammage of 4 g/m.sup.2 were formed into
wet webs using a manually operated laboratory-scale square paper
making machine. The two sheets in the form of wet web were stacked
and a double layered paper was produced. Thereupon, the double
layered paper was dried for 5 min. at a temperature of 50.degree.
C. using a hot air drier, and further underwent heat treatment for
1 min. at a temperature of 190.degree. C.
[0118] The obtained double layered paper exhibited firm bond
between the substrate layer and the heat-seal layer. This double
layered paper was referred to tests for measuring its air
permeability, heat-seal strength and hot tack. The test results are
shown in Table 1.
Example 2
[0119] A double layered paper was made available in the same manner
as in Example 1 except that a polypropylene core & polyethylene
sheath conjugate fiber (weight fineness: 2 deniers; fiber length: 5
mm) comprised of polyethylene (PE) (melting point: 130.degree. C.)
for the sheath component and polypropylene (PP) (melting point:
165.degree. C.) for the core was used in place of the polypropylene
fiber which was used in Example 1.
[0120] The obtained double layered paper exhibited firm bond
between the substrate layer and the heat-seal layer. This double
layered paper was referred to tests for measuring its air
permeability, heat-seal strength and hot tack. The test results are
shown alongside in Table 1.
Comparative Example 1
[0121] A double layered paper was prepared in the same manner as in
Example 1 except that polypropylene fiber alone was used as the
fiber to constitute the heat-seal layer in place of the mixed
fibers of synthetic pulp and polypropylene fiber which were used in
Example 1.
[0122] The obtained double layered paper was referred to tests for
measuring its air permeability, heat-seal strength and hot tack.
The test results are shown alongside in Table 1.
Comparative Example 2
[0123] A double layered paper was prepared in the same manner as in
Example 1 except that the polypropylene core & polyethylene
sheath conjugate fiber alone was used as the fiber to constitute
the heat-seal layer in place of the mixed fibers comprised of
synthetic pulp and the polypropylene core & polyethylene sheath
conjugate fiber which was used in Example 2.
[0124] The obtained double layered paper was referred to tests for
measuring its air permeability, heat-seal strength and hot tack.
The test results are shown alongside in Table 1.
1 TABLE 1 Compara. Compara. Ex. 1 Ex. 2 Ex. 1 Ex. 2 Composition of
Heat-Seal Layer wt. % Synthetic pulp 70 70 -- -- Polypropylene
fiber 30 -- 100 -- Polypropylene core & -- 30 -- 100
polyethylene sheath conjugate fiber Frazier 135 129 140 135 air
permeability (cm.sup.3/cm.sup.2/s) Heat-seal strength (g/15 mm)
Sealing 130 132 171 0 0 temp. (.degree. C.) 150 188 202 36 182 170
230 225 210 188 190 224 223 218 180 Hot tack (mm) Sealing 130 65 60
200 200 temp. (.degree. C.) 150 55 55 200 45 170 30 35 30 75 190 35
45 15 150
[0125] As can be clearly seen by comparison of the measured
properties in Examples 1 and 2 and the measured properties in
Comparative Examples 1 and 2, the obtained double layered paper
exhibited good air permeability and at the same time the measured
heat-seal strength was as high as 130 to 190.degree. C. Besides,
the peel distance which is the indicator of hot tack was small,
thus was found that it possesses good hot tack.
Industrial Applicability
[0126] The heat-seal paper of the present invention imparts a high
interlayer bond strength between the heat-seal layer and the
substrate layer, as well as strong bond among fibers, for the
reason that the heat-seal layer comprises the polyolefin synthetic
pulp having the branched configuration and preferably synthetic
fiber, and also retains good air permeability. Since the heat-seal
paper of the present invention possesses such heat-seal layer, it
exhibits the stable and high degree of heat-sealability and hot
tack over the wide temperature range extending from low
temperatures to high temperatures, in particular good
heat-sealability and hot tack at low temperatures.
[0127] This heat-seal paper having good air permeability may be
utilized extensively and suitably as raw material paper for
manufacturing various bags such as filter bags. This heat-seal
paper may be used for tea bags, bags to package sterilized
apparatus and tools with, desiccators bags, etc. In cases where
this heat-seal paper is used on high-speed automatic bag-making
machine, stable operation and high productivity may be secured on
account of its own ability to be heat-sealable over the wide
temperature range, which ability being attributed to freedom from
possible adhesion to the hot plate in the molten state and good hot
tack.
[0128] Furthermore, the heat-seal paper of the present invention
possesses superior physical properties, such as air permeability,
heat-sealability, and hot tack, compared with the heat-seal paper
conventionally in use as the raw material paper for the tea bag
manufacture. Moreover, it is principally comprised of polyolefin
fiber, and hence there is few fear of generation of harmful
substances like dioxines when incinerated as wastes. Hence, it
contributes to protection of the environments.
* * * * *