U.S. patent application number 10/192697 was filed with the patent office on 2003-03-27 for method of producing heat-sealable composite films.
Invention is credited to Kimura, Junichi, Sakaguchi, Takatoshi, Yoshida, Teruaki.
Application Number | 20030059593 10/192697 |
Document ID | / |
Family ID | 16493397 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030059593 |
Kind Code |
A1 |
Sakaguchi, Takatoshi ; et
al. |
March 27, 2003 |
Method of producing heat-sealable composite films
Abstract
A composite film is provided by providing a polypropylene or
other base resin layer, laminating a first covering layer of a
resin composition (1) comprising the following components (A), (B),
(C) and (D) to one side of the base resin layer and a second
covering layer of a resin composition (2) comprising the components
(A) and (D) to the other side of the base resin layer, which
composite film is optionally stretched. The resin composition (2)
may contain component (C). (A) a heat-sealable olefinic polymer
(e.g. a propylene series copolymer such as propylene-ethylene
copolymer, propylene-butene-1 copolymer or
propylene-ethylene-butene-1 copolymer) (B) a diorganopolysiloxane
(e.g. dimetylpolysiloxane) (C) a fine-powdered heat-resistant resin
(e.g. microspheres of a thermosetting resin) (D) a higher fatty
acid amide This composite film is excellent in slidability,
antistaticity, releasability and clarity and compatible with a
high-speed automatic overwrap packaging machine.
Inventors: |
Sakaguchi, Takatoshi;
(Amagasaki-shi, JP) ; Kimura, Junichi;
(Toyonaka-shi, JP) ; Yoshida, Teruaki; (Sano-shi,
JP) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Family ID: |
16493397 |
Appl. No.: |
10/192697 |
Filed: |
July 11, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10192697 |
Jul 11, 2002 |
|
|
|
08726745 |
Oct 7, 1996 |
|
|
|
08726745 |
Oct 7, 1996 |
|
|
|
08280835 |
Jul 26, 1994 |
|
|
|
Current U.S.
Class: |
428/216 ;
264/173.12; 264/173.14; 264/173.15; 264/290.2; 264/469; 264/80;
428/327; 428/447; 428/475.8; 428/476.3; 428/516; 428/518; 428/520;
428/910 |
Current CPC
Class: |
Y10T 428/24975 20150115;
Y10T 428/3192 20150401; Y10T 428/31743 20150401; B32B 2323/10
20130101; Y10T 428/31924 20150401; Y10T 428/265 20150115; B32B
27/18 20130101; Y10T 428/3175 20150401; B32B 2307/31 20130101; Y10S
428/91 20130101; Y10T 428/254 20150115; B32B 27/08 20130101; Y10T
428/31928 20150401; Y10T 428/31663 20150401; Y10T 428/31913
20150401; B32B 2307/306 20130101; B32B 27/32 20130101; Y10T
428/24967 20150115; B32B 2307/21 20130101 |
Class at
Publication: |
428/216 ;
428/447; 428/516; 428/327; 428/518; 428/520; 428/475.8; 428/476.3;
428/910; 264/469; 264/80; 264/173.12; 264/173.14; 264/173.15;
264/290.2 |
International
Class: |
B32B 007/02; B32B
027/08; B32B 027/30; B29C 047/06; B29C 055/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 1993 |
JP |
204614/1993 |
Claims
What is claimed is:
1. A composite film comprising a base resin layer, a first covering
layer of a resin composition (1) comprising the following
components (A), (B), (C) and (D) as laminated to one side of said
base resin layer and a second covering layer of a resin composition
(2) comprising the following components (A) and (D) as laminated to
the other side of said base resin layer: (A) a heat-sealable
olefinic polymer (B) a diorganopolysiloxane (C) a fine-powdered
heat-resistant resin (D) a higher fatty acid amide
2. A composite film as claimed in claim 1, wherein said resin
composition (2) further contains said fine-powdered heat-resistant
resin (C).
3. A composite film as claimed in claim 1, wherein said base resin
layer is formed with a resin composition containing 0.01 to 5 parts
by weight of an antistatic agent per 100 parts by weight of a
polypropylene with an isotactic index of not less than 92%.
4. A composite film as claimed in claim 1, wherein said
heat-sealable olefinic polymer (A) is at least one propylene series
copolymer selected from the group consisting of propylene-ethylene
copolymer, propylene-butene-1 copolymer,
propylene-ethylene-butene-1 copolymer, ethylene-butene-1 copolymer,
ethylene-3-methylpentene-1 copolymer,
ethylene-propylene-3-methylpentene-1 copolymer,
ethylene-4-methylpentene-- 1 copolymer,
ethylene-propylene-4-methylpentene-1 copolymer and
ethylene-butene-1-3-methylpentene-1 copolymer.
5. A composite film as claimed in claim 1, wherein said
heat-sealable olefinic polymer is at least one propylene series
copolymer selected from the group consisting of propylene-ethylene
copolymer, propylene-butene-1 copolymer and
propylene-ethylene-butene-1 copolymer.
6. A composite film as claimed in claim 1, wherein said
diorganopolysiloxane (B) is dimethylpolysiloxane having an average
molecular weight of 1.times.10.sup.4 to 18.times.10.sup.4 and is
contained in said resin composition (1) in a proportion of 0.5 to 3
parts by weight relative to 100 parts by weight of said
heat-sealable olefinic polymer (A).
7. A composite film as claimed in claim 1, wherein said
fine-powdered heat-resistant resin (C) is microspheres having a
mean particle diameter of 1 to 6 .mu.m and is contained in said
resin composition (1) in a proportion of 0.1 to 1 part by weight
relative to 100 parts by weight of said heat-sealable olefinic
polymer (A).
8. A composite film as claimed in claim 2, wherein said
fine-powdered heat-resistant resin (C) is microspheres having a
mean particle diameter of 1 to 6 .mu.m and is contained in said
resin composition (2) in a proportion of 0.1 to 1 part by weight
relative to 100 parts by weight of said heat-sealable olefinic
polymer (A).
9. A composite film as claimed in claim 1, wherein said
fine-powdered heat-resistant resin (C) is microspheres of a
thermosetting resin or thermoplastic resin having a thermal
deformation temperature higher than the film forming
temperature.
10. A composite film as claimed in claim 1, wherein said higher
fatty acid amide (D) is a C.sub.16-24 monocarboxylic acid amide and
is contained in said resin composition (1) and resin composition
(2) in a proportion of 0.01 to 1.0 part by weight relative to 100
parts by weight of said heat-sealable olefinic polymer (A).
11. A composite film as claimed in claim 1, wherein the thickness
of said first covering layer is not greater than 1 .mu.m.
12. A composite film as claimed in claim 1, wherein said second
covering layer has a surface tension of not less than 38
dyne/cm.
13. A composite film as claimed in claim 1, which is a oriented
film stretched in at least one direction at a stretching ratio of
not less than 2.
14. A composite film comprising a base resin layer of a
polypropylene having an isotactic index of not less than 94%, a
first covering layer of a resin composition (1) comprising the
following components (A), (B), (C) and (D) as laminated to one
surface of said base resin layer and a second covering layer formed
from a resin composition (2) comprising the following components
(A), (C) and (D) as laminated to the other surface of said base
resin layer, wherein said composite film is a biaxially oriented
film: (A) a heat-sealable polymer having a propylene content of 68
to 99% by weight (B) dimethylpolysiloxane (C) microspheres of a
heat-resistant resin having a mean diameter of 1.5 to 5 .mu.m (D) a
C.sub.16-24 monocarboxamide
15. A composite film as claimed in claim 12, which comprises a base
resin layer, a first covering layer formed of a resin composition
comprising the following components (A), (B), (C) and (D) as
laminated to one side of said base resin layer and a second
covering layer of a resin composition (2) comprising the following
components (A), (C) and (D) as laminated to the other side of said
base resin layer: (A) a propylene series copolymer having a
propylene content of 70 to 96.5% by weight as selected from the
group consisting of propylene-ethylene copolymer,
propylene-butene-1 copolymer and propylene-ethylene-butene-1
copolymer (B) dimethylpolysiloxane in a proportion of 0.7 to 1.2
parts by weight based on 100 parts by weight of the propylene
series copolymer (A) (C) microspheres of a thermosetting resin in a
proportion of 0.2 to 0.7 part by weight based on 100 parts by
weight of propylene series copolymer (A) (D) a monocarboxamide in a
proportion of 0.1 to 0.8 part by weight based on 100 parts by
weight of propylene series copolymer (A)
16. A composite film as claimed in claim 14, wherein said base
resin layer is formed with a resin composition containing 1 to 30
parts by weight of a hydrocarbon series polymer relative to 100
parts by weight of a polypropylene having an isotactic index of not
less than 94%.
17. A composite film as claimed in claim 14, wherein said base
resin layer is formed with a resin composition containing 0.1 to
2.5 parts by weight of an antistatic agent and 5 to 15 parts by
weight of a hydrocarbon series polymer relative to 100 parts by
weight of a polypropylene having an isotactic index of not less
than 94%.
18. A composite film as claimed in claim 14, wherein said first
covering layer has a thickness of 0.1 to 0.7 .mu.m and said second
covering layer has a surface tension of not less than 38 dyne/cm
and a thickness of 0.1 to 5 .mu.m.
19. A method of producing a composite film which comprises
laminating a first covering layer of a resin composition (1)
comprising the following components (A), (B), (C) and (D) to one
side of a base resin layer and a second covering layer of a resin
composition (2) comprising the following components (A) and (D) to
the other side of said base resin layer; (A) a heat-sealable
olefinic polymer (B) a diorganopolysiloxane (C) a fine-powdered
heat-resistant resin (D) a higher fatty acid amide
20. A method of producing a composite film as claimed in claim 19,
wherein said second covering layer is formed from said resin
composition (2) which further contains said fine-powdered
heat-resistant resin (C).
21. A method of producing a composite film as claimed in claim 19,
which comprises co-extruding a resin composition for the base resin
layer, the first resin composition (1) and the second resin
composition (2), stretching the extrusion-molded composite film
with a stretching ratio of 5 to 10 in the machine direction and the
transverse direction and surface-treating the second covering layer
of the oriented film.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a composite film suited for
overwrap packaging and a method for producing the film.
BACKGROUND OF THE INVENTION
[0002] As packaging materials, a variety of types of film,
particularly polypropylene film and polyethylene terephthalate
film, both of which are particularly satisfactory in clarity,
rigidity and other characteristics, are in use today. Furthermore,
a film coated with a vinylidene chloride copolymer which has a heat
sealing property as well as a gas barrier property with respect to
oxygen and water vapor is in use for the overwrap packaging of
various commercial items such as food products, tobacco products,
cassette tapes and so on.
[0003] Meanwhile, a stretched film such as biaxially oriented
polypropylene film is poor in heat sealability. Therefore,
development work is in progress on a stretched laminated film
comprising a base polymer layer composed of polypropylene or the
like and a heat-sealable surface polymer layer of an olefinic
polymer. However, the laminate film having an olefinic polymer ply
is unsatisfactory in mechanical properties so that it is hardly
compatible with an automatic overwrapping machine which is operated
at a high speed of, for example, not less than 300 units of
packaging load per minute. Thus, if such a laminated film is fed to
an automatic overwrapping machine, where it is exposed to both heat
and pressure, the slidability and releasability of the film with
respect to the machine hardware such as the metal guide plate are
markedly decreased. Therefore, overwrap packaging cannot be carried
out at a high speed so that the packaging efficiency is remarkably
sacrificed.
[0004] To improve the slidability of film, it is practiced to add
an antiblocking agent, e.g. microfine particles of an inorganic
substance such as silica, alumina, synthetic zeolite, etc., those
of an organic substance such as polyethylene, or a mineral or
petroleum wax to the olefinic polymer [cf. Japanese Patent
application No. 71830/1991 (JP-A-3-71830)].
[0005] However, even when such an additive is incorporated, the
releasability of film with respect to the metal guide plate is
unsatisfactory in the sealing stage where the film is subjected to
both heat and pressure. Therefore, packaging at a speed over 300
units of packaging load/minute is not feasible.
[0006] Also known is a film comprising a polypropylene base layer
and an ethylene homopolymer or copolymer covering layer containing
a fatty acid amide as a slidability improver or lubricant. However,
even with the formation of such a fatty acid amide-containing
covering layer, the releasability of film with respect to the metal
guide plate in the heat-sealing stage is poor and, therefore,
high-speed packaging can not be realized.
[0007] To overcome the above disadvantages, Japanese Patent
Publication No. 56864/1988 (JP-B-63-56864) proposes a multi-layer
film comprising a polypropylene layer and a laminatable layer made
of ethylene homopolymer or copolymer, the laminatable layer
containing a higher fatty amine, a dispersed thermoplastic resin
incompatible with ethylene homopolymer or copolymer and a
dialkylpolysiloxane. This film is suited for wrapping cigaret
cartons.
[0008] Japanese Patent application Laid-open No. 133050/1984
(JP-A-59-133050) discloses an oriented or a stretched multi-layer
polypropylene film comprising a polypropylene base layer containing
a C.sub.8-.sub.24 monocarboxylic acid amide and a polyolefin
surface or skin layer containing a finely divided powder of silica
and silicone oil.
[0009] Furthermore, Japanese Patent application Laid-open No.
60745/1990 (JP-A-2-60745) discloses a biaxially oriented film
comprising a polypropylene-containing base layer and, as laminated
to at least one side thereof, a surface layer made from a random
copolymer containing ethylene and propylene as constituent units
and a diorganopolysiloxane gum. Japanese Patent application
Laid-open No. 205440/1991 (JP-A-3-205440) discloses a biaxially
oriented film comprising the same base layer as above and, as
laminated thereto, a surface layer containing the same copolymer as
above, finely divided insoluble silicone rubber and a
diorganopolysiloxane gum.
[0010] These films are generally well slidable and compatible with
high-speed packaging. However, when any of these films is fed to an
automatic overwrapping machine for packaging the load at a speed of
300 units of load/minute, the following troubles are encountered.
Thus, because of its low-temperature slidability or insufficient
antistatic property, the film tends to be electrostatically stuck
to a member such as the metal guide plate of the automatic
overwrapping machine and cannot be cut to the required size and,
hence, cause a jam in the machine, thus preventing high-speed
continuous packaging. If an attempt is made to improve the
slidability of film by increasing the amount of the incompatible
thermoplastic resin or silica powder to the copolymer containing
ethylene and propylene as constituent units, the clarity of the
film is sacrificed. On the other hand, an organopolysiloxane of
high degree of polymerization can hardly be dispersed uniformly in
the copolymer so that the film quality as a whole cannot be
critically controlled.
SUMMARY OF THE INVENTION
[0011] Therefore, it is an object of this invention to provide a
composite film with which products can be packaged at high
speed.
[0012] It is a further object of this invention to provide a
composite film which is remarkably improved in clarity,
slidability, releasability and antistaticity and with which
products can be packaged on an automatic overwrapping machine at
high speed.
[0013] It is still another object of this invention to provide a
method for producing a composite film having the above-mentioned
desirable characteristics.
[0014] The inventors of this invention found after a great deal of
research done to accomplish the above objects that when a first
covering layer on one side and a second covering layer on the other
side of a base resin layer of a laminate film are respectively
formed from resin compositions comprising herein-defined
components, there is obtained a composite film which is improved
markedly in slidability, releasability, clarity and antistaticity
and compatible with high-speed packaging.
[0015] Thus, the composite film of the present invention comprises
a base resin layer, a first covering layer of a resin composition
(1) comprising the following components (A), (B), (C) and (D) as
laminated to one side of the base resin layer and a second covering
layer of a resin composition (2) comprising the following
components (A) and (D) as laminated to the other side of the base
resin layer.
[0016] (A) a heat-sealable olefinic polymer
[0017] (B) a diorganopolysiloxane
[0018] (C) a fine-powdered heat-resistant resin
[0019] (D) a higher fatty acid amide
[0020] The method for producing a composite film according to the
present invention comprises laminating a first covering layer of a
resin composition (1) comprising the following components (A), (B),
(C) and (D) to one side of a base resin layer and a second covering
layer of a resin composition (2) comprising the following
components (A) and (D) to the other side of the base resin
layer.
[0021] (A) a heat-sealable olefinic polymer
[0022] (B) a diorganopolysiloxane
[0023] (C) a fine-powdered heat-resistant resin
[0024] (D) a higher fatty acid amide
DETAILED DESCRIPTION OF THE INVENTION
[0025] The resin which constitutes the above-mentioned base resin
layer includes, for example, polyolefin resins such as
polyethylene, polypropylene, ethylene-propylene copolymer, etc.;
vinyl alcohol series polymers such as polyvinyl alcohol,
ethylene-vinyl alcohol copolymer, etc.; polyvinyl chloride;
vinylidene chloride series polymers; styrenic polymers such as
polystyrene, styrene-acrylonitrile copolymer,
styrene-acrylonitrile-butadiene copolymer, etc.; polyesters such as
polyethylene terephthalate, polybutylene terephthalate, etc.;
nylons or polyamides such as nylon 6, nylon 11, nylon 12, nylon 66,
nylon 6/66, nylon 66/610, nylon 6/11, etc.; polyacrylonitrile; and
polycarbonates.
[0026] The base resin layer is preferably made of polyolefin resin
(particularly a polypropylene series resin) or polyester resin
(particularly polyethylene terephthalate). The preferred base resin
layer is formed from a polypropylene series resin which is
generally satisfactory in clarity, rigidity and packaging machine
compatibility.
[0027] The polypropylene series resin is preferably a crystalline
polypropylene series resin. The polypropylene series resin may be a
copolymer predominantly composed of propylene, such as copolymers
of propylene with a-olefins such as ethylene, butene-1,
3-methylpentene-1, 4-methylpentene-1, etc.; although propylene
homopolymer is preferred.
[0028] The isotactic index (II) of polypropylene series resin
should be not less than 92%, preferably not less than 94%, and more
preferably not less than 96%. The film produced from a
polypropylene series resin having such an isotactic index (II)
value does not curl in the course of travel but travels
rectilinearly so that it is well adapted to automatic machine
packaging.
[0029] The intrinsic viscosity [.eta.] of polypropylene series
resin is generally about 0.8 to 4 dl/g and preferably about 1 to
2.5 dl/g.
[0030] The base resin layer may be a single-layer film or a
laminate film composed of two or more resin layers. The thickness
of the base resin layer is not restricted but may for example be
about 1 to 250 .mu.m and preferably about 5 to 100 .mu.m.
[0031] Unless the compatibility of film with a high-speed packaging
machine is adversely affected, the base resin layer may contain a
variety of additives, for example, various stabilizers such as
antioxidants, ultraviolet absorbers, heat stabilizers, etc.;
antistatic agents such as cationic antistatic agents (e.g.
polyoxyethylene-alkylamines, quaternary ammonium salts, hydantoin
derivatives, etc.), anionic antistatic agents (e.g. sulfuric acid
derivatives, alkyl sulfonates, phosphoric acid derivatives, etc.),
nonionic antistatic agents (e.g. fatty acid esters of polyhydric
alcohols, such as diols, glycerin, sorbitol, etc., adducts of fatty
acid esters to alkylene oxides such as ethylene oxide, etc.,
polyoxyethylene alkyl phenols, etc.), amphoteric anti-static agents
(e.g. alkyl betaines); nucleating agents; hydrocarbon polymers such
as styrenic resins, terpene resin, petroleum resin,
dicyclopentadiene resin, chroman resins such as chroman-indene
resin, phenolic resin, rosin and its derivatives and the
corresponding hydrogenated resins; plasticizers; fillers; higher
fatty acids and their salts, higher fatty acid esters, waxes such
as natural waxes of the mineral or plant origin, and synthetic
waxes such as polyethylene; finely divided powdery substances such
as powdered silica; etc.
[0032] For preventing static adherence of the film to the packaging
machine hardware during packaging and further improving its
high-speed packaging compatibility, the base resin layer, in
particular, preferably contains an antistatic agent. The amount of
such antistatic agent may for example be about 0.01 to 5 parts by
weight, preferably about 0.1 to 2.5 parts by weight based on 100
parts by weight of the base resin.
[0033] For increasing the rigidity or stiffness of film, the base
resin layer preferably contains any of the hydrocarbon polymers
such as hydrogenated terpene resin, hydrogenated petroleum resin,
dicyclopentadiene resin and so on. The amount of the hydrocarbon
polymer may for example be generally about 1 to 30 weight % and
preferably about 5 to 15 weight %.
[0034] The base resin layer may further contain a wax. The amount
of the wax is about 0.01 to 5 parts by weight, preferably about 0.1
to 2.5 parts by weight, based on 100 parts by weight of the base
resin.
[0035] When the first covering layer of resin composition (1) is
formed on either side (i.e. both surfaces) of the base resin layer,
the tendency of the film towards static charge build-up is
increased, possibly due to bleeding of the diorganopolysiloxane (B)
out onto the surface of the covering layer so that automatic
packaging at high speed will be hindered. Therefore, the other side
or surface of the base resin layer is preferably covered with a
second covering layer formed from the resin composition (2) which
may contain diorganopolysiloxane (B) in an amount less than 0.5
part by weight based on 100 parts by weight of the heat-sealable or
-bondable olefinic polymer or particularly the resin composition
(2) which does not contain diorganopolysiloxane (B).
[0036] The heat-sealable olefinic polymer (A) which can be
incorporated in the resin compositions (1) and (2) includes, for
example, homopolymers of olefins such as ethylene, propylene,
butene-1, 3-methylpentene-1, 4-methylpentene-1, etc. and copolymers
containing any of such olefins as a constituent unit.
[0037] The preferred olefinic polymer (A) includes heat-sealable
polymers, for example, olefinic copolymers such as
propylene-ethylene copolymer, propylene-butene-1 copolymer,
propylene-ethylene-butene-1 copolymer, ethylene-butene-1 copolymer,
ethylene-3-methylpentene-1 copolymer,
ethylene-propylene-3-methylpentene-1 copolymer,
ethylene-4-methylpentene-- 1 copolymer,
ethylene-propylene-4-methylpentene-1 copolymer,
ethylene-butene-1-3-methylpentene-1 copolymer, and so on. The
olefinic copolymer may be random copolymers or block copolymers,
although random copolymers are more practically employed.
[0038] Among particularly preferred species of olefinic polymer (A)
are propylene series copolymers such as propylene-ethylene
copolymer, propylene-butene-1 copolymer and
propylene-ethylene-butene-1 copolymer. Among them,
propylene-ethylene-butene-1 copolymer is practically
recommendable.
[0039] The propylene content of such propylene series copolymers
may for example be generally about 68 to 99 weight % and preferably
about 70 to 96.5 weight %. The ethylene content of
propylene-ethylene-butene-1 copolymer may for example be generally
about 0.3 to 8 weight % and preferably about 0.5 to 5.0 weight %,
while the butene-1 content of this copolymer is about 1 to 30
weight % and preferably about 3 to 25 weight %.
[0040] The olefinic polymer (A) is possessed of heat-sealability,
particularly low-temperature sealability, which is required in the
heat sealing stage of high-speed overwrap packaging. Thus, the
olefinic polymer (A) is useful for forming a sealant layer.
However, if both sides of the resin base layer are covered with
surface plies composed exclusively of olefinic polymer (A), the
slidability of the film against the metal guide plate of a
high-speed overwrapping machine, where both heat and pressure are
affect on the film, is unsatisfactory.
[0041] In contrast, when one side of the base resin layer is
covered with a first covering layer of resin composition (1)
comprising the heat-sealable (or heat-bondable) olefinic polymer
(A), diorganopolysiloxane (B), fine-powdered (or finely divided)
heat-resistant resin (C) and higher fatty acid amide (D) and the
other side of the same base resin layer is covered with a second
covering layer formed from the resin composition (2) comprising the
heat-sealable olefinic polymer (A) and higher fatty acid amide (D)
or, preferably, the resin composition (2) which contains the
components (A) and (D) and does not contain diorganopolysiloxane
(B), there is obtained a composite film having excellent
slidability and releasability with respect to the metal guide plate
and other hardware in the heat-sealing stage of a high-speed
overwrapping machine as well as a high degree of clarity. This
composite film is capable of overlap-packaging at least 300 units
of packaging load/minute without trouble.
[0042] The diorganopolysiloxane (B) mentioned above includes, among
others, polysiloxanes having aliphatic hydrocarbon groups such as
dimethylpolysiloxane, diethylpolysiloxane, methylethylpolysiloxane,
etc.; polysiloxane having aromatic hydrocarbon groups such as
diphenylpolysiloxane etc.; and polysiloxanes having both an
aliphatic and an aromatic hydrocarbon group, such as
methylphenylpolysiloxane. These polysiloxanes can be used alone or
in combination. Among the above-mentioned polysiloxanes,
dimethylpolysiloxane is practically preferred.
[0043] The average molecular weight of diorganopolysiloxane (B) is
about 1.times.10.sup.4 to 18.times.10.sup.4. If the average
molecular weight is less than 1.times.10.sup.4, no remarkable
enhancement of slidability can be expected, and when it exceeds
18.times.10.sup.4, such a diorganopolysiloxane cannot be uniformly
compounded with the heat-sealable olefinic polymer (A), for
instance. The viscosity of diorganopolysiloxane (B) at 25.degree.
C. is generally about 1.times.10.sup.4 to 2.times.10.sup.6
centistokes and preferably about 1.times.10.sup.5 to
1.times.10.sup.6 centistokes.
[0044] The diorganopolysiloxane (B) may be used in combination with
modified silicones such as carboxyl-modified silicone,
polyether-modified silicone, etc.
[0045] The proportion of diorganopolysiloxane (B) in resin
composition (1) is about 0.5 to 3 parts by weight, preferably about
0.7 to 1.2 parts by weight, based on 100 parts by weight of
heat-sealable olefinic polymer (A). If the diorganopolysiloxane
content is less than 0.5 part by weight, the slidability and
releasability of the film will not be adequate, and when it exceeds
3 parts by weight, both clarity and heat sealability tend to be
sacrificed.
[0046] As mentioned above, the resin composition (2) may contain
not more than 0.5 part by weight of diorganopolysiloxane (B) based
on 100 parts by weight of heat-sealable olefinic polymer (A) but
preferably does not contain the component (B).
[0047] The fine-powdered or powdery heat-resistant resin (C)
mentioned above functions as an antiblocking agent as well as a
lubricant. Powders of inorganic substances such as silica have only
low affinities for the polymer and if such inorganic powders are
added to the covering layer, the clarity of the film is decreased
due probably to gaps between the fine inorganic particles. In
contrast, the fine-powdered heat-resistant resin (C) has a high
affinity for the polymer and, therefore, no gaps are formed between
the particles so that the clarity of the film is not sacrificed and
is improved in comparison with a film used a powdery inorganic
substance. Moreover, compared with microfine powders of random
configuration, spherical particles are conducive to high
slidability at a low level of addition and contribute more to film
clarity.
[0048] It is sufficient that fine-powdered heat-resistant resin (C)
be contained at least in the first covering layer but it is
preferably incorporated in both the first and second covering
layers. When the powdery heat-resistant resin (C) is contained in
both the first and the second covering layers, both high clarity
and high slidability are insured.
[0049] The heat-resistant resin that can be used includes a variety
of resins whose thermal deformation temperatures are higher than
the film forming temperature, for example, thermosetting resins
such as crosslinked acrylic resin, amino resins (e.g. crosslinked
melamineformaldehyde resin, benzoguanamine resin, urea resin and
the like), furan resin, epoxy resin, phenolic resin, unsaturated
polyester resin, vinyl ester resin, diallyl phthalate resin,
polyimide resin, etc., and thermoplastic resins such as
polyethersulfone, polyetherimide, polyphenylene sulfide,
polyetheretherketone, polyamideimide and so on. The thermosetting
resin may have been hardened. These powdery heat-resistant resins
may be used alone or in combination.
[0050] The powder morphology of the fine-powdered heat-resistant
resin (C) is preferably spherical and, for still better results,
true round (closed to sphere) in profile. When microspheres are
used, the desired degree of slidability develops at a low level of
addition without sacrificing the clarity of film. The mean particle
diameter of powdery heat-resistant resin (C) may be within the
range not adversely affecting the slidability and clarity of film
and may for example be about 1 to 6 .mu.m and preferably about 1.5
to 5 .mu.m.
[0051] The proportion of powdery or fine-powdered heat-resistant
resin (C) is, for example, about 0.1 to 1 part by weight and
preferably about 0.2 to 0.7 part by weight based on 100 parts by
weight of heat-sealable olefinic polymer (A). If the proportion of
heat-resistant resin (C) is less than 0.1 part by weight,
slidability will not be appreciably improved, and when the amount
of the heat-resistant resin (C) exceeds 1 part by weight, it may
happen that clarity is decreased.
[0052] As the higher fatty acid amide (D) mentioned above, there
may be mentioned saturated higher fatty acid amides such as
lauroamide (lauric acid amide), myristamide (myristic acid amide),
palmitamide (palmitic acid amide), stearamide (stearic acid amide),
behenamide (behenic acid amide), etc.; unsaturated higher fatty
acid amides such as oleamide (oleic acid amide), erucamide (erucic
acid amide) etc.; and alkylenebisstearamides such as
methylenebisstearamide, ethylenebisstearamide, etc., among others.
These higher fatty acid amides (D) can be used singly or in
combination.
[0053] The higher fatty acid amide (D) is preferably a higher fatty
acid amide of 16-24 carbon atoms and, for still better results, a
monocarboxamide (monocarboxylic acid amide).
[0054] The proportion of higher fatty acid amide (D) is generally
about 0.01 to 1.0 part by weight and preferably about 0.1 to 0.8
part by weight based on 100 parts by weight of the heat-sealable
olefinic polymer (A). If the amount of higher fatty acid amide (D)
is less than 0.01 part by weight, the low-temperature slidability
with respect to the packaging load is poor so that smooth packaging
may not be achieved. On the other hand, if the proportion exceeds 1
part by weight, film clarity tends to be sacrificed. Incidentally,
higher fatty acid amide (D) contributes greatly to low-temperature
slidability, for example at temperatures up to 100.degree. C.
[0055] The first covering layer and/or the second covering layer
may contain a variety of additives, for example, stabilizers such
as antioxidants, ultraviolet absorbers, heat stabilizers, etc.;
antistatic additives; plasticizers; inorganic fillers such as
silica, talc, etc.; and waxes, among others.
[0056] The thickness of the first covering layer may for example be
not greater than about 1 .mu.m, preferably about 0.1 to 0.7 .mu.m
and more preferably about 0.3 to 0.7 .mu.m. If the thickness of the
first covering layer exceeds 1 .mu.m, tackiness may be increased to
sacrifice releasability from the metal guide plate, with the result
that high-speed packaging may not be feasible.
[0057] The thickness of the second covering layer can be liberally
selected within the range not adversely affecting the
heat-sealability and other characteristics of the film and may for
example be about 0.1 to 5 .mu.m and preferably about 0.5 to 2.5
.mu.m.
[0058] The composite film comprising the base resin layer, first
covering layer and second covering layer may be an non-oriented
film but is preferably an oriented film. The oriented film may be a
uniaxially oriented film but is preferably a biaxially oriented
film, particularly a biaxially oriented composite film having a
biaxially oriented polypropylene series polymer layer(s). If
necessary, the oriented film may have been heat-treated.
[0059] The surface of the composite film may be subjected to the
conventional surface treatment such as corona discharge treatment,
flame treatment, plasma treatment or the like. The preferred
composite film has a surface-treated second covering layer
(particularly, a diorganopolysiloxane (B)-free second covering
layer surface-treated) to present a surface tension of not less
than about 38 dyne/cm, preferably about 40 to 42 dyne/cm.
[0060] The composite film of the present invention can be
manufactured by a method which comprises laminating a first
covering layer of a resin composition (1) comprising the
heat-sealable olefinic polymer (A), diorganopolysiloxane (B), the
fine-powdered heat-resistant resin (C) and higher fatty acid amide
(D) to one side or surface of a base resin layer and a second
covering layer of a resin composition (2) comprising the
heat-sealable olefinic polymer (A) and higher fatty acid amide (D)
to the other side or surface of the same base resin layer. As
pointed out above, resin composition (2) preferably does not
contain the diorganopolysiloxane (B) but contains the fine-powdered
heat-resistant resin (C).
[0061] The composite film can be manufactured by the dry laminating
technique which comprises laminating the covering layers to the
base resin layer with the aid of an anchor coating agent, e.g. a
titanium type, polyethyleneimine type or urethane type anchor
coating composition, but is preferably manufactured by the
coextrusion molding technique.
[0062] By the coextrusion molding technique, the composite film can
be produced by co-extruding a resin composition for the base resin
layer, the first resin composition (1) and the second resin
composition (2). Preferably, the extrusion-molded composite film
may be subjected to orientation.
[0063] For coextrusion molding, a molding machine equipped with a
T-die, ring die or the like can be employed. When the
base-layer-forming resin composition, the first layer-forming resin
composition (1) and the second layer-forming resin composition (2)
are independently fed to such a molding machine and melt-extruded
concurrently into the die, these three resin compositions converge
or meet in the passageway within the die to lie upon one another.
As the multi-layer film emerging from the die is cooled, the
desired composite film is obtained.
[0064] The stretching of the composite film can be performed after
the composite film extruded from the die has cooled in the case of
the T-die process, while it can be done simultaneously with
melt-extrusion from the die in the inflation process.
[0065] The technology for stretching or orientation includes, for
example, the conventional techniques such as roll stretching,
tenter stretching, tube stretching and combinations of these
stretchings. The stretching or draft ratio can be appropriately set
according to the desired characteristics of composite film. The
draft ratio at least in one direction should be generally not less
than about 2 and preferably about 5 to 10. The second covering
layer of the oriented film may usually be surface-treated to
enhance a surface tension.
[0066] Despite the formation of a surfacing layer containing a
higher fatty acid amide which is generally believed to be
incompatible with high-speed packaging, the composite film of this
invention is capable of high-speed overwrap packaging. Thus, the
composite film is suited to the packaging of various articles,
especially for automatic packaging of tobacco cartons and the like
at a high speed of 300 units/minute. This specification further
discloses an overwrapping method for packaging articles with the
above-described composite film at a high speed of not less than 300
units per minute.
[0067] Since the surface layers of the composite film of the
present invention are formed with-compositions comprising defined
component materials in defined proportions, the film is able to
package articles at high speed. Moreover, this composite film is
remarkably high in clarity, slidability, releasability and
antistaticity. Therefore, articles can be packaged with this film
at high speed using an overwrap packaging machine where both heat
and pressure are involved.
[0068] In accordance with the method of this invention, the
composite film having the very desirable characteristics described
above can be easily manufactured.
EXAMPLES
[0069] The following examples are intended to describe this
invention in further detail and should by no means be construed as
defining the scope of the invention.
Example 1
[0070] The following compositions (X), (Y.sub.1) and (Z.sub.1) were
provided for the base resin layer, first covering layer and second
covering layer, respectively.
[0071] Base resin layer composition (X): a mixture of 90 parts by
weight of isotactic polypropylene (melt index 2.0 g/10 min.,
isotactic index 94%), 10 parts by weight of petroleum resin
(Arakawa Chemical Industries, Ltd., Japan; trade name Arkon P-125)
and 0.5 parts by weight of a mixture of an alkylamine-ethylene
oxide adduct and glyceryl monostearate.
[0072] First covering layer composition (Y1): a compounded mixture
of 100 parts by weight of propylene-ethylene-butene-1 random
copolymer (ethylene content 3.9% by weight, butene-1 content 4.4%
by weight; melt index 9.0 g/10 min.), 1.1 parts by weight of
dimethylpolysiloxane (average molecular weight 16.times.10.sup.4),
0.4 part by weight of crosslinked acrylic resin microspheres having
a mean particle diameter of 4 .mu.m (Soken Chemical &
Engineering Co., Ltd., Japan; trade name MR-7G) and 0.1 part by
weight of stearamide.
[0073] Second covering layer composition (Z1): a compounded mixture
of the components of the first covering layer composition (Y1)
exclusive of dimethylpolysiloxane.
[0074] The above compositions (X), (Y1) and (Z1) are respectively
fed to an extrusion molding machine equipped with a T-die and
coextruded at a temperature of 220 to 230.degree. C. to provide a
3-layered sheet of Y1/X/Z1 structure. This sheet was stretched at a
stretching ratio of 6 in the machine direction using rolls at 115
to 125.degree. C. and, then, at a stretching ratio of 10 laterally
(i.e. in the transverse direction) at a temperature of 160.degree.
C. The film was then heat-treated at 160.degree. C. for 10 seconds,
after which the surface of the Z1 layer of the film was subjected
to corona discharge treatment to provide a ternary 3-layer
composite film. The surface tension of the corona discharge-treated
surface was 41 dyne/cm and the thickness of the composite film was
22 .mu.m (the thicknesses of X layer=20 .mu.m, and the thickness of
Y1 and Z1 layers=0.5 .mu.m and 1.5 .mu.m, respectively).
Example 2
[0075] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that the following composition (Y2)
and composition (Z2) were used in lieu of the compositions (Y1) and
(Z1) for the first covering layer and second covering layer,
respectively.
[0076] First covering layer composition (Y2): a compounded mixture
of 100 parts by weight of propylene-ethylene copolymer (ethylene
content 5.8% by weight, melt index 5.5 g/10 min.), 0.5 part by
weight of benzoguanamine-melamine-formaldehyde condensation
copolymer microspheres having a mean particle diameter of 2 .mu.m
(Nippon Shokubai Co., Ltd., Japan; trade name Epostar MS), 0.7 part
by weight of dimethylpolysiloxane (average molecular weight
16.times.10.sup.4) and 0.3 part by weight of erucamide.
[0077] Second covering layer composition (Z2): a compounded mixture
of 100 parts by weight of propylene-ethylene copolymer, 0.5 part by
weight of benzoguanamine-melamine-formaldehyde condensation
copolymer microspheres with a mean diameter of 2 .mu.m and 0.3 part
by weight of erucamide.
Example 3
[0078] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that the following compositions
(Y3) and (Z3) were used in lieu of the compositions (Y1) and (Z1)
for the first covering layer and second covering layer,
respectively.
[0079] First covering layer composition (Y3): a com pounded mixture
of 100 parts by weight of propylene-butene-1 copolymer (butene-1
content 23.2% by weight, melt index 5.0 g/10 min.), 0.6 part by
weight of cross-linked acrylic resin microspheres having a mean
particle diameter of 2 .mu.m (Nippon Shokubai Co., Ltd., Japan;
trade name Epostar MA1004), 1.0 part by weight of
dimethylpolysiloxane (average molecular weight 10.times.10.sup.4)
and 0.3 part by weight of erucamide.
[0080] Second covering layer composition (Z3): a compounded mixture
of the components of the first covering layer composition (Y3)
exclusive of dimethylpolysiloxane.
Comparative Example 1
[0081] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that the finely divided crosslinked
acrylic resin was omitted from the first covering layer composition
(Y1).
Comparative Example 2
[0082] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that stearamide was omitted from
the first covering layer composition (Y1).
Comparative Example 3
[0083] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that dimethylpolysiloxane was
omitted from the first covering layer composition (Y1).
Comparative Example 4
[0084] A ternary 3-layer composite film of Y1/A/Y1 structure was
manufactured in the same manner as Example 1 except that the first
covering layer composition (Y1) of Example 1 was used in lieu of
the second covering layer composition (Z1).
Comparative Example 5
[0085] A ternary 3-layer composite film was manufactured in the
same manner as Example 1 except that 0.4 part by weight of
fine-powdered silica having a mean particle diameter of 4 .mu.m was
used in lieu of 0.4 part by weight of fine-powdered crosslinked
resin in the first covering layer composition (Y1) and second
covering layer composition (Z1).
Comparative Example 6
[0086] Both sides of a biaxially oriented film (thickness 20 .mu.m)
of isotactic polypropylene (melt index 2.0 g/10 min., isotactic
index 94%) were coated with a chlorinated polypropylene-containing
anchor coating composition. Then, a coating composition containing
0.3 part by weight of fine-powdered silica lubricant and 0.3 part
by weight of antistatic agent per 100 parts by weight of vinylidene
chloride copolymer was coated on the anchor coating layer to
provide a coated film.
[0087] The high-speed overwrap packaging machine compatibility,
antistaticity, heat sealability and clarity of the composite films
manufactured in the Examples and Comparative Examples were
evaluated by the following methods.
[0088] High-speed Overwrap Packaging Machine Compatibility:
[0089] Using an automatic overwrap packaging machine (Tokyo
Automatic Machinery Works, Ltd., Japan; W323), cartons each
containing 20 cigarettes were packaged with the respective films.
Packaging was carried out under conditions of 20.degree. C., 55% RH
and 300 cartons/min. for 2 minutes and the packaging compatibility
of each film was evaluated according to the following criteria.
[0090] (1) Adhesion of film to the metal guide plate
[0091] Good: not adhered
[0092] Poor: adhered
[0093] (2) Jamming of film in the machine; the number of cartons
which can be packaged until the machine has stopped.
[0094] (3) Seal quality of packaged cartons
[0095] Good: sealed
[0096] Poor: not sealed
[0097] Antistaticity:
[0098] Using a static honestmeter (manufactured by Shishido
Seidenki Co., Ltd., Japan), the antistaticity of film was evaluated
at 20.degree. C. and 55% RH. The test film specimen (37 mm.times.50
mm) being fixed in position, a voltage of 6 kV was applied for 20
seconds to measure the static potential (mV) and, then, the
attenuation half-time t (seconds) of the potential after suspension
of voltage application was measured. The result was expressed in
V/t=mV/second.
[0099] Heat Sealability:
[0100] Using a gradient heat sealer (Toyo Seiki Co., Ltd., Japan),
the corona discharge-treated side and non-treated side of the film
were heat-sealed under a pressure of 1 kg/cm.sup.2 for 1 second.
Using a tensile tester (Toyo Baldwin Co., Ltd., Japan; Tensilon),
the peeling strength over a width of 15 mm was measured at the
pulling speed of 300 mm/min.
[0101] Clarity:
[0102] In accordance with Japanese Industrial Standards (JIS)
K-6714, the haze value of 4 laps of the film was measured with a
haze meter (Toyo Seiki Seisakusho Co., Ltd., Japan)
[0103] The results are shown in Tables 1 and 2.
1 TABLE 1 Comp. Comp. Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple
3 ple 1 ple 2 High-speed overwrap packaging machine compatibility
(1) Adhesion of film to Good Good Good Poor Good the metal guide
plate (2) Number of cartons No No No which can be packaged Jam-
Jam- Jam- 50 continuously ming ming ming (3) Seal quality Good Good
Good Good Antistaticity (mV/sec.) 30/40 30/30 30/30 25/30 30/50
Clarity 10.0 10.8 11.0 8.0 10.0 (Haze value, 4 laps) Heat-seal
strength (g/15 mm) 120.degree. C. 300 280 270 290 300 130.degree.
C. 320 300 300 300 310
[0104]
2 TABLE 2 Comp. Comp. Comp. Comp. Example 3 Example 4 Example 5
Example 6 High-speed overwrap packaging machine compatibility (1)
Adhesion of film to Good Poor Good Good the metal guide plate (2)
Number of cartons 20 No No which can be packaged Jamming Jamming
continuously (3) Seal quality Good Good Good Antistaticity
(mV/sec.) 30/20 35/300 30/30 30/30 Clarity 8.4 18.0 17.0 17.0 (Haze
value, 4 laps) Heat-seal strength (g/15 mm) 120.degree. C. 320 200
300 110 130.degree. C. 350 350 320 110
[0105] It is apparent from Tables 1 and 2 that the composite films
obtained in Examples 1-3 are highly compatible with packaging even
at a high speed of 300 units/minute, without trouble, and can be
smoothly heat-sealed. Moreover, the films were very satisfactory in
antistaticity and heat sealability and, compared with the film of
Comparative Example 6 which is generally used for overwrap
packaging, were superior in clarity and in heat-seal strength.
[0106] In contrast, the composite film of Comparative Example 1 was
poorly slidable and adhered to the metal guide plate, thus failing
to permit continuous automatic packaging. Moreover, the composite
films of Comparative Examples 2 and 3 were poor in slidability and
high-speed packaging compatibility and the machine stopped when 50
cartons had been packaged in the case of the composite film
according to Comparative Example 2 and when 20 cartons had been
packaged in the case of the composite film according to Comparative
Example 3. Furthermore, the composite film according to Comparative
Example 4 were poor in clarity and antistaticity and adhered to the
metal guide plate, thus failing to permit continuous automatic
packaging.
* * * * *