U.S. patent application number 09/892335 was filed with the patent office on 2002-02-14 for polyamide composition.
This patent application is currently assigned to UBE Industries, Ltd.. Invention is credited to Nakamura, Koji, Yamaguchi, Yutaka.
Application Number | 20020019498 09/892335 |
Document ID | / |
Family ID | 18703081 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019498 |
Kind Code |
A1 |
Nakamura, Koji ; et
al. |
February 14, 2002 |
Polyamide composition
Abstract
A polyamide composition for film formation which deteriorates
little in mechanical properties or transparency even when subjected
to high-temperature retortion and can be satisfactorily formed into
films is described, which comprises (A) 100 parts by weight of a
polyamide mixture comprising two or more polyamides differing in
terminal group concentration and (B) from 0.01 to 1.0 part by
weight of a hydroxyphenylpropionate represented by formula (1),
wherein the polyamide mixture (A) comprising two or more polyamides
differing in terminal group concentration has a terminal amino
group concentration of from 2.0.times.10.sup.5 to
7.0.times.10.sup.-5 eq/g and a terminal carboxyl group
concentration of from 1.5.times.10.sup.-5 to 4.0.times.10.sup.-5
eq/g, the terminal amino group concentration being higher than the
terminal carboxyl group concentration.
Inventors: |
Nakamura, Koji; (Yamaguchi,
JP) ; Yamaguchi, Yutaka; (Yamaguchi, JP) |
Correspondence
Address: |
AKIN, GUMP, STRAUSS, HAUER & FELD, L.L.P.
ONE COMMERCE SQUARE
2005 MARKET STREET, SUITE 2200
PHILADELPHIA
PA
19103
US
|
Assignee: |
UBE Industries, Ltd.
|
Family ID: |
18703081 |
Appl. No.: |
09/892335 |
Filed: |
June 27, 2001 |
Current U.S.
Class: |
525/420 |
Current CPC
Class: |
C08L 77/06 20130101;
C08L 77/00 20130101; C08K 5/134 20130101; C08K 5/134 20130101; C08L
77/02 20130101; C08L 77/06 20130101; C08L 77/00 20130101; C08L
77/02 20130101; C08L 77/00 20130101; C08L 77/00 20130101; C08L
77/00 20130101; C08L 77/00 20130101 |
Class at
Publication: |
525/420 |
International
Class: |
C08L 077/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 2000 |
JP |
P.2000-206098 |
Claims
What is claimed is:
1. A polyamide composition comprising (A) 100 parts by weight of a
polyamide mixture comprising two or more polyamides differing in
terminal group concentration and (B) from 0.01 to 1.0 part by
weight of a hydroxyphenylpropionate represented by formula (1),
wherein the polyamide mixture (A) comprising two or more polyamides
differing in terminal group concentration has a terminal amino
group concentration of from 2.0.times.10.sup.-5 to
7.0.times.10.sup.-5 eq/g and a terminal carboxyl group
concentration of from 1.5.times.10.sup.-5 to 4.0.times.10.sup.-5
eq/g, the terminal amino group concentration being higher than the
terminal carboxyl group concentration, 3wherein R.sup.1 represents
an alkyl group having 1 to 3 carbon atoms.
2. The polyamide composition as claimed in claim 1, wherein the
polyamide mixture (A) comprising two or more polyamides differing
in terminal group concentration has a relative viscosity of from
2.0 to 5.0.
3. The polyamide composition as claimed in claim 1, wherein the
hydroxyphenylpropionate (B) is
3,9-bis[2-[3-(3-t-butyl-4-hydroxy5-methylp-
henyl)propionyloxy]-1,1-dimethyl-ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecan-
e.
4. A polyamide film for food packaging obtained from a polyamide
composition comprising (A) 100 parts by weight of a polyamide
mixture comprising two or more polyamides differing in terminal
group concentration and (B) from 0.01 to 1.0 part by weight of a
hydroxyphenylpropionate represented by formula (1), wherein the
polyamide mixture (A) comprising two or more polyamides differing
in terminal group concentration has a terminal amino group
concentration of from 2.0.times.10.sup.-5 to 7.0.times.10.sup.-5
eq/g and a terminal carboxyl group concentration of from
1.5.times.10.sup.-5 to 4.0.times.10.sup.5 eq/g, the terminal amino
group concentration being higher than the terminal carboxyl group
concentration, 4wherein R.sup.1 represents an alkyl group having 1
to 3 carbon atoms.
5. The polyamide film as claimed in claim 4, wherein the polyamide
mixture (A) comprising two or more polyamides differing in terminal
group concentration has a relative viscosity of from 2.0 to
5.0.
6. The polyamide film as claimed in claim 4, wherein the
hydroxyphenylpropionate (B) is
3,9-bis[2-[3-(3-t-butyl-4-hydroxy5-methylp- henyl)
propionyloxy]-1,1-dimethyl-ethyl]-2,4,8,10-tetraoxaspiro[5.5]undeca-
ne.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a polyamide composition
which comprises a specific amount of a polyamide mixture comprising
two or more polyamides differing in terminal group concentration
and a specific amount of a specific antioxidant. The invention
further relates to a polyamide film for food packaging obtained
from the composition. More particularly, the invention relates to a
polyamide composition suitable for use in producing a film
satisfactory in practical properties, e.g., the property of
deteriorating little in mechanical properties or transparency upon
retortion. This polyamide composition is suitable for use as a
polyamide film for food packaging, especially a packaging film for
retort pouch foods.
BACKGROUND OF THE INVENTION
[0002] Polyamide films are excellent in various properties
including gas barrier properties, toughness, freedom from pinholes,
heat resistance, and oil resistance. Because of this, polyamides
are used as packaging films, in particular, used as a base of
single-layer films or laminate films or as a constituent material
for multilayered films formed by coextrusion with other resins
mainly in the field of food packaging.
[0003] In the step of packaging foods such as uncooked noodles,
cooked foods, and salted vegetables, retortion has come to be
frequently conducted in which the packages are treated for
sterilization at a high temperature and a high humidity for the
purpose of enabling the contents to be stored over long. Recently,
higher temperatures of about 130.degree. C. tend to be used for the
retortion. Films for food packaging are hence required not to
change in mechanical properties or transparency upon treatment with
hot water of steam having a temperature of about 130.degree. C.
[0004] There have been cases where polyamide films, when subjected
to retortion under the conditions of a high temperature of about
130.degree. C. and a high humidity, suffer a considerable decrease
in mechanical properties, in particular tensile strength, or suffer
blushing to have impaired transparency.
[0005] Under these circumstances, investigations are being made in
order to develop a polyamide which deteriorates little in
mechanical properties, transparency, etc. upon high-temperature
high-humidity retortion.
[0006] For example, a technique has been proposed in which a
polyester film is laminated to a surface of a polyamide film so as
to prevent the polyamide film from being directly exposed to a
high-temperature high-humidity atmosphere. However, not only the
properties of the polyamide film itself remain unimproved, but also
this technique has drawbacks in productivity because the production
steps necessitate a prolonged time period or are complicated.
[0007] JP-A-4-28727 (the term "JP-A" as used herein means an
"unexamined published Japanese patent application") discloses a
packaging film for retort pouch foods which comprises a specific
polyamide resin modified with terminal groups. However, even this
polyamide film may be impaired in mechanical properties or
transparency through retortion according to the conditions therefor
and hence are usable in limited applications.
[0008] JP-A-7-268209 discloses a packaging film for retort pouch
foods which comprises a polyamide composition containing a specific
antioxidant. This polyamide film, however, is insufficient in
mechanical properties and transparency after retortion.
[0009] Furthermore, JP-A-59-231089 discloses a polyamide
composition containing a hydroxyphenylpropionate. However, no data
are given therein on properties of this polyamide composition. In
addition, neither a description concerning film uses nor a
suggestion on influences of retortion on practical properties is
given therein.
SUMMARY OF THE INVENTION
[0010] The present inventors made investigations in order to
develop a polyamide for use as a material for a film which
deteriorates little in mechanical properties, transparency, etc.
upon retortion. As a result, it has been found that the object of
the invention is accomplished with a polyamide composition
comprising a polyamide mixture comprising two or more polyamides
differing in terminal group concentration and a specific
antioxidant. The invention has been completed based on this
finding.
[0011] The invention provides, according to the first aspect
thereof, a polyamide composition comprising
[0012] (A) 100 parts by weight of a polyamide mixture comprising
two or more polyamides differing in terminal group concentration
and
[0013] (B) from 0.01 to 1.0 part by weight of a
hydroxyphenylpropionate represented by formula (1),
[0014] wherein the polyamide mixture (A) comprising two or more
polyamides differing in terminal group concentration has a terminal
amino group concentration of from 2.0.times.10.sup.-5 to
7.0.times.10.sup.-5 eq/g and a terminal carboxyl group
concentration of from 1.5.times.10.sup.-5 to 4.0.times.10.sup.-5
eq/g, the terminal amino group concentration being higher than the
terminal carboxyl group concentration, 1
[0015] wherein R.sup.1 represents an alkyl group having 1 to 3
carbon atoms.
[0016] The invention further provides, according to the second
aspect thereof, a polyamide film for food packaging obtained from
the polyamide composition described above.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention will be explained below in detail.
[0018] The polyamides differing in terminal group concentration
which constitute the polyamide mixture (A) used in the invention
are produced by polymerizing or copolymerizing as a starting
material a three-membered or higher lactam, an amino acid, or a
nylon salt formed from a diamine and a dicarboxylic acid. This
(co)polymerization is conducted by a known method such as, e.g.,
melt polymerization, solution polymerization, or solid-state
polymerization in the presence or absence of a specific amount of
an amine or an amine/carboxylic acid mixture. Examples of the
terminal group structures of the polyamides constituting the
polyamide mixture include amino, carboxyl, and hydrocarbon groups
having 1 to 22 carbon atoms.
[0019] Examples of the three-membered or higher lactam include
.epsilon.-caprolactam, .omega.-enantholactam, .omega.-laurolactam,
.alpha.-pyrrolidone, and .alpha.-piperidone. Examples of the amino
acids include 6-aminocaproic acid, 7-aminoheptanoic acid,
9-aminononanoic acid, 11-aminoundecanoic acid, and
12-aminododecanoic acid.
[0020] Examples of the diamine for constituting the nylon salt
include aliphatic amines such as tetramethylenediamine,
hexamethylenediamine, heptamethylenediamine, octamethylenediamine,
nonamethylenediamine, decamethylenedi amine,
undecamethylenediamine, dodecamethylenediamine, and 2,2,4- or
2,4,4-trimethylhexamethylenediamine, alicyclic diamines such as
1,3- or 1,4-bis(aminomethyl)cyclohexane, isophoronediamine,
piperazine, bis(4-aminocyclohexyl)methane, and 2,2-bis
(4'-aminocyclohexyl)propane, and aromatic diamines such as
m-xylylenediamine and p-xylylenediamine.
[0021] Examples of the dicarboxylic acid for constituting the nylon
salt include aliphatic dicarboxylic acids such as malonic acid,
succinic acid, glutaric acid, adipic acid, pimelic acid, suberic
acid, azelaic acid, sebacic acid, and undecanedioic acid and
alicyclic and aromatic dicarboxylic acids such as
1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic
acid, and xylylenedicarboxylic acid.
[0022] In the case where a specific amount of an amine or an
amine/carboxylic acid mixture is used in producing the polyamides
differing in terminal group concentration for use in the invention,
the amine or the amine/carboxylic acid mixture can be added at any
desired stage of the polymerization reaction. It is however
preferred to add the amine or the mixture in the initial state of
the polymerization reaction.
[0023] The amount of the amine or amine/carboxylic acid mixture to
be added is suitably determined in a known manner while taking
account of the terminal amino group concentration, terminal
carboxyl group concentration, and relative viscosity of each
polyamide to be produced. In general, the amine or the
amine/carboxylic acid mixture is added in an amount of from 1 to 25
meq, preferably from 3.5 to 18 meq, per mol of the starting
material for polyamides, such as a three-membered or higher lactam,
an amino acid, or a nylon salt.
[0024] Examples of the amine to be added include aliphatic amines
such as methylamine, ethylamine, propylamine, butylamine,
pentylamine, hexylamine, heptylamine, octylamine,
2-ethylhexylamine, nonylamine, decylamine, and undecylamine,
alicyclic monoamines such as cyclohexylamine and
methylcyclohexylamine, aliphatic monoamines such as benzylamine and
P-phenylmethylamine, sym'etric secondary amines such as
N,N-dimethylamine, N,N-diethylamine, N,N-dipropylamine,
N,N-dibutylamine, N,N-dihexylamine, and N,N-dioctylamine, mixed
secondary amines such as N-methyl-N-ethylamine,
N-methyl-N-butylamine, N-methyl-N-dodecylamine,
N-methyl-N-octadecylamine, N-ethyl-N-hexadecylamine,
N-ethyl-N-octadecylamine, and N-propyl-N-hexadecylamine, aliphatic
diamines such as ethylenediamine, trimethylenediamine,
tetramethylenediamine, pentamethylenediamine, hexamethylenediamine,
heptamethylenediamine, octamethylenediamine, nonamethylenediamine,
decamethylenediamine, undecamethylenediamine,
dodecamethylenediamine, tridecamethylenediamine,
hexadecamethylenediamine, octadecamethylenediamine, and 2,2,4- or
2,4,4-trimethylhexamethylenediami- ne, alicyclic diamines such as
cyclohexanediamine, methylcyclohexanediamin- e, 1,3- or 1,4-bis
(aminomethyl)cyclohexane, isophoronediamine, piperazine,
bis(4,4'-aminocyclohexyl)methane, and 2,2-bis(4'-aminocyclohe-
xyl)propane, and aromatic diamines such as m-xylylenediamine and
p-xylylenediamine.
[0025] Examples of the carboxylic acid include aliphatic
monocarboxylic acids such as acetic acid, propionic acid, butyric
acid, valeric acid, caproic acid, enanthic acid, capric acid,
undecanoic acid, lauric acid, tridecanoic acid, palmitic acid, and
stearic acid, alicyclic monocarboxylic acids such as
cyclohexanecarboxylic acid and methylcyclohexanecarboxylic acid,
aromatic monocarboxylic acids such as benzoic acid, toluic acid,
ethylbenzoic acid, and phenylacetic acid, aliphatic dicarboxylic
acids such as malonic acid, succinic acid, glutaric acid, adipic
acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,
undecanedioic acid, dodecanedioic acid, hexadecanedioic acid,
hexadecenedioic acid, octadecanedioic acid, octadecenedioic acid,
eicosanedioic acid, eicosenedioic acid, docosanedioic acid,
diglycolic acid, and 2,2,4-trimethyladipic acid, alicyclic
dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and
aromatic dicarboxylic acids such as terephthalic acid, isophthalic
acid, phthalic acid, m-xylylenedicarboxylic acid, and
p-xylylenedicarboxylic acid.
[0026] The polyamide mixture (A) has a terminal amino group
concentration of from 2.0.times.10.sup.-5 to 7.0.times.10.sup.-5
eq/g, preferably from 3.0.times.10.sup.-5 to 6.5.times.10.sup.-5
eq/g, and a terminal carboxyl group concentration of from
1.5.times.10.sup.-5 to 4.0.times.10.sup.-5 eq/g, preferably from
2.0.times.10.sup.-5 to 3.5.times.10.sup.-5 eq/g-Furthermore, the
terminal amino group concentration of the polyamide mixture is
higher than the terminal carboxyl group concentration thereof.
Since the polyamide mixture (A) comprises two or more polyamides
differing in terminal group concentration, the terminal amino group
concentration and terminal carboxyl group concentration of the
polyamide mixture (A) are determined by the terminal amino group
concentration and terminal carboxyl group concentration of each
constituent polyamide and by the proportions of these.
[0027] If the polyamide mixture (A) does not satisfy any of the
requirements shown above, for example, if the terminal amino group
concentration or terminal carboxyl group concentration of the
polyamide mixture (A) is outside the range shown above or the
terminal carboxyl group concentration thereof is higher than the
terminal amino group concentration thereof, then there are cases
where the polyamide film suffers a considerable decrease in
mechanical properties or transparency through retortion.
[0028] The polyamide mixture (A) has a relative viscosity as
measured in accordance with JIS K 6810:1977 of generally from 2.0
to 5.0, preferably from 2.5 to 4.0. The relative viscosity of the
polyamide mixture (A) is determined by the relative viscosity of
each of the polyamides constituting the polyamide mixture and by
the proportions of these. If the relative viscosity of the
polyamide mixture is lower than 2.0, the polyamide film obtained
from the composition has impaired mechanical properties. On the
other hand, if the relative viscosity thereof exceeds 5.0, the
composition has too high a melt viscosity, making it difficult to
conduct film formation and to obtain a smooth film.
[0029] In constituting the polyamide mixture, the two or more
polyamides differing in terminal group concentration can be mixed
in any desired proportion as long as the resultant polyamide
mixture satisfies the above-described specific requirements
concerning terminal amino group concentration and terminal carboxyl
group concentration.
[0030] A polyamide mixture comprising polyamides differing in
terminal group concentration at least in some degree is preferred
as the polyamide mixture (A) to a polyamide mixture comprising
polyamides which are alike in terminal group concentration. For
example, such a preferred polyamide mixture is one prepared by
mixing polyamides which differ in terminal amino group
concentration by at least 1.0.times.10.sup.-5 eq/g, preferably by
at least 2.0.times.10.sup.-5 eq/g, more preferably by at least
3.0.times.10.sup.-5 eq/g.
[0031] From the standpoint of accomplishing the object of the
invention, at least one of the polyamides constituting the
polyamide mixture (A) is preferably an amino-rich polyamide in
which the difference between the terminal amino group concentration
and the terminal carboxyl group concentration is 10.times.10.sup.-5
eq/g or larger, preferably 2.0.times.10.sup.-5 eq/g or larger.
[0032] From the standpoint of ease of mixing and ease of film
formation, the polyamides constituting the polyamide mixture are
preferably of the same kind. For example, it is preferred to use
polyamides which each are nylon-6, a nylon-6/nylon-12 copolymer, a
nylon-6/nylon-6,6/nylon-12 copolymer, or the like.
[0033] It is possible to obtain a single polyamide which has
terminal group concentrations and a relative viscosity within the
same respective ranges as the polyamide mixture for use in the
invention. However, there are cases where use of such a single
polyamide results not only in deterioration in mechanical
properties or transparency through retortion but in phenomena
including one in which during continuous film production, many gel
particles come to generate as the film production time is
prolonged, although the reasons for such phenomena are unclear. It
is hence difficult to accomplish the object of the invention with a
single polyamide.
[0034] The hydroxyphenylpropionate (B) represented by formula (1)
(hereinafter referred to simply as hydroxyphenylpropionate) to be
used in the invention can be produced by reacting a
3-(3-alkyl-5-t-butyl-4-hydrox- yphenyl)propionic acid or a reactive
derivative thereof, e.g., the acid chloride or acid anhydride
thereof, with 3,9-bis(1,1-dimethyl-2-hydroxyet- hyl)-2,
4,8,10-tetraoxa-spiro[5.5]undecane or a derivative thereof by a
known method. 2
[0035] In formula (1), R.sup.1 represents an alkyl group having 1
to 3 carbon atoms.
[0036] In the hydroxylphenylpropionate represented by formula (1),
R.sup.1 represents a methyl group, an ethyl group, or a propyl
group but is preferably a methyl group from the standpoint of heat
stability and oxidation resistance. Specific examples of the
hydroxyphenylpropionate include
3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,-
1-dimethylethyl]-2,4,8, 10-tetraoxaspiro[5.5]undecane,
3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-ethylphenyl)propionyloxyl]-1,1
-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, and
3,9-bis[2-[2-(3-t-butyl-4-hydroxy5-isopropylphenyl)-propionyloxy
]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro-[5.5]undecane.
Preferred of these is
3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1-
,1-dimethyl-ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane.
[0037] The polyamide composition of the invention comprises 100
parts by weight of the polyamide mixture and from 0.01 to 1.0 part
by weight, preferably from 0.01 to 0.5 parts by weight, more
preferably from 0.05 to 0.25 parts by weight, of the
hydroxyphenylpropionate. If the amount of the
hydroxyphenylpropionate incorporated is smaller than 0.01 part by
weight, high-temperature retortion may result in a decrease in
mechanical properties and prolongation of the film production time
tends to result in the generation of gel particles. Even when the
hydroxyphenylpropionate is incorporated in an amount exceeding 1.0
part by weight, an improvement in effect corresponding to such a
large ester amount cannot be expected, resulting only in an
economical disadvantage.
[0038] For accomplishing the object of the invention, it is
essential to use a polyamide mixture which comprises two or more
polyamides differing in terminal group concentration and has a
terminal amino group concentration and a terminal carboxyl group
concentration in respective specific ranges and to incorporate a
specific amount of the specific hydroxyphenylpropionate into the
polyamide mixture.
[0039] Various additives may be contained in the polyamide
composition of the invention as long as such additives do not
impair the properties of the composition. Examples thereof include
known phenolic antioxidants other than the hydroxyphenylpropionate
(B), phosphorus compound antioxidants such as
tris(2,4-di-t-butylphenyl) phosphite and
tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene phosphite, sulfur
compound antioxidants, weathering agents including ultraviolet
absorbers, metal soaps such as calcium stearate and magnesium
stearate, bisamide compounds such as methylene bisamides and
ethylene bisamides, antistatic agents such as
poly(oxyethylene)alkylamines, alkyl sulfonates, and quaternary
ammonium sulfates, various fillers such as silica, talc, and
montmorillonites, antiblocking agents, dyes, and pigments.
[0040] The polyamide composition of the invention can be produced
by adding the hydroxyphenylpropionate and various optional
additives to the polyamide mixture and mixing these ingredients
together by a known technique. Examples of usable production
methods include a method which comprises dry-blending the polyamide
mixture with the hydroxyphenylpropionate by means of a known mixing
apparatus, e.g., a tumbler or mixer, to produce the composition, a
method which comprises dissolving the hydroxyphenylpropionate in a
solvent in which the ester is soluble, spraying the resultant
solution over the polyamide mixture, and then evaporating the
solvent to produce the composition, and a method comprising
melt-kneading the polyamide mixture together with the
hydroxyphenylpropionate by means of a known, single- or twin-screw
extruder to produce the composition. The polyamide mixture can be
easily obtained by blending two or more polyamides differing in
terminal group concentration by a known technique such as dry
blending or melt blending.
[0041] For producing a film from the polyamide composition of the
invention, a known process for polyamide film production can be
used. Examples thereof include: a casting process which comprises
melt-kneading the polyamide composition of the invention with an
extruder, extruding the melt in a flat film form with a T-die or
coathanger die, casting the extrudate on a casting roll, and
cooling the extrudate to produce a film; and a tubular process
which comprises extruding a melt of the polyamide composition in a
tubular form with a ring die and cooling the tubular extrudate with
air or water to produce a film. Although usable in the unstretched
state, the film produced is usually used as a stretched film in
most cases. Examples of the stretched film include a uniaxially
stretched film, a biaxially stretched film formed by simultaneous
biaxial stretching, and a biaxially stretched film formed by
successive biaxial stretching. These films are produced by known
stretching techniques such as, for example, uniaxial stretching
with rolls, successive biaxial stretching with a tenter,
simultaneous biaxial stretching with a tenter, and tubular-film
stretching. Such a stretching step may be conducted subsequently to
the production of a polyamide film, or may Age be conducted
separately after the polyamide film formed is temporarily wound
up.
[0042] The stretch ratio of the stretched film varies depending on
the intended use of the film. However, in the case of a uniaxially
stretched film, the stretch ratio thereof is generally from 1.5 to
5, preferably from 1.8 to 3.5. In the case of a film biaxially
stretched with a tenter, the stretch ratio thereof in the film
winding direction (machine direction) is generally from 1.5 to 4
and the stretch ratio thereof in the direction perpendicular to the
winding direction (transverse direction) is generally from 1.5 to
5. In the case of a biaxially stretched film obtained through
tubular-film stretching, the stretch ratios thereof in the machine
and transverse directions each are generally from 1.5 to 4.
[0043] The film obtained from the polyamide composition of the
invention can be used as a laminate with another polymer film,
aluminum foil, etc. Examples of the other laminating polymer film
include films formed from low-density polyethylene, high-density
polyethylene, polypropylene, ethylene/vinyl acetate copolymers, and
ionomer resins.
[0044] For producing a laminate of the polyamide film with other
polymer film(s), a known method can be used. Examples thereof
include: a method in which the polyamide film is bonded with one or
more other polymer films with an adhesive; and a method in which
the polyamide composition and one or more polymers for forming one
or more other polymer films are melted and co-extruded from a
multilayered orifice through an adhesive resin.
[0045] The film obtained from the polyamide composition of the
invention has excellent thermal stability and deteriorates little
in practical properties upon retortion. Consequently, the film is
suitable for use as a material for packaging foods such as uncooked
noodles, processed foods, salted vegetables, and meat. The film is
especially suitable for use as a packaging material for retort
pouch foods.
[0046] The polyamide composition of the invention deteriorates
little in mechanical properties or transparency even when subjected
to high-temperature retortion and can be satisfactorily formed into
films. This polyamide composition is suitable for use as a film for
food packaging, especially a packaging film for retort pouch
foods.
[0047] The invention will be explained below in more detail by
reference to Examples and Comparative Examples. However, the
invention should not be construed as being limited to these
Examples. Methods used for synthesizing the polyamides used in the
Examples and Comparative Examples are shown below together with the
antioxidants used and the methods used for evaluating polyamide
films.
[0048] 1. Syntheses of Polyamide (Nylon)
[0049] (1) Synthesis of A-1 (Nylon-6)
[0050] Into a 70-liter autoclave were introduced 20 kg of
.epsilon.-caprolactam, 1.0 kg of water, and 83 g (6.9 meq per mol
of the caprolactam) of m-xylylenediamine. The atmosphere in the
polymerizer was replaced with nitrogen. Thereafter, the contents
were heated to 100.degree. C. and stirred at this temperature so as
to keep the reaction system homogeneous. The temperature in the
polymerizer was then elevated to 260.degree. C. and the reaction
mixture was polymerized for 2 hours with stirring while regulating
the internal pressure of the reactor to 17.5 kgf/cm.sup.2.
Thereafter, the internal pressure was reduced to ordinary pressure
over about 2 hours and then to 400 mmHg, and polymerization was
conducted at the reduced pressure for further 2 hours.
Subsequently, nitrogen was introduced into the autoclave and the
internal pressure was returned to ordinary pressure. The resultant
reaction mixture was discharged in the form of a strand through a
nozzle disposed in a lower part of the reactor, and the strand was
cut to obtain pellets. The pellets were immersed in hot water to
remove about 10% unreacted monomers by extraction and then
vacuum-dried. The polymer thus obtained had a relative viscosity of
2.6, a terminal amino group concentration of 9.7.times.10.sup.-5
eq/g, and a terminal carboxyl group concentration of
2.3.times.10.sup.5 eq/g.
[0051] (2) Synthesis of A-2 (Nylon-6)
[0052] Into a 70-liter autoclave were introduced 20 kg of
.epsilon.-caprolactam and 1.0 kg of water. The atmosphere in the
polymerizer was replaced with nitrogen. Thereafter, the contents
were heated to 100.degree. C. and stirred at this temperature so as
to keep the reaction system homogeneous. The temperature in the
polymerizer was then elevated to 260.degree. C. and the reaction
mixture was polymerized for 2 hours with stirring while regulating
the internal pressure of the reactor to 17.5 kgf/cm.sup.2.
Thereafter, the internal pressure was reduced to ordinary pressure
over about 2 hours, and polymerization was conducted at ordinary
pressure for further 2 hours in a nitrogen stream while
volatilizing water from the reactor. After completion of the
reaction, the resultant reaction mixture was discharged in the form
of a strand through a nozzle disposed in a lower part of the
reactor, and the strand was cut to obtain pellets. The pellets were
immersed in hot water to remove about 10% unreacted monomers by
extraction and then vacuum-dried. The polymer thus obtained had a
relative viscosity of 3.6, a terminal amino group concentration of
4.1.times.10.sup.-5 eq/g, and a terminal carboxyl group
concentration of 4.2.times.10.sup.-5 eq/g.
[0053] (3) Synthesis of A-3 (Nylon-6)
[0054] Into a 70-liter autoclave were introduced 20 kg of
.epsilon.-caprolactam and 1.0 kg of water. The atmosphere in the
polymerizer was replaced with nitrogen. Thereafter, the contents
were heated to 100.degree. C. and stirred at this temperature so as
to keep the reaction system homogeneous. The temperature in the
polymerizer was then elevated to 260.degree. C. and the reaction
mixture was polymerized for 2 hours with stirring while regulating
the internal pressure of the reactor to 17.5 kgf/cm.sup.2.
Thereafter, the internal pressure was reduced to ordinary pressure
over about 2 hours, and polymerization was conducted at ordinary
pressure for further 3 hours in a nitrogen stream while
volatilizing water from the reactor. After completion of the
reaction, the resultant reaction mixture was discharged in the form
of a strand through a nozzle disposed in a lower part of the
reactor, and the strand was cut to obtain pellets. The pellets were
immersed in hot water to remove about 10% unreacted monomers by
extraction and then vacuum-dried. The polymer thus obtained had a
relative viscosity of 4.4, a terminal amino group concentration of
3.3.times.10.sup.-5 eq/g, and a terminal carboxyl group
concentration of 3.1.times.10.sup.-5 eq/g.
[0055] 2. Antioxidants Used
[0056] B-1:
3,9-Bis[2-[3-(3-t-butyl-4-hydroxy5-methylphenyl)-propionyloxy]-
-1,1-dimethylethyl]-2,4,8, 10-tetraoxaspiro-[5.5]undecane;
antioxidant manufactured by Sumitomo Chemical Co., Ltd.; trade
name, Sumilizer GA-80
[0057] B-2: Pentaerythrityl
tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)pro- pionate];
antioxidant manufactured by Ciba Specialty Chemicals Inc.; trade
name, Irganox 1010
[0058] 3. Measurement of Relative Viscosity of Polyamide
[0059] The relative viscosity .eta..sub.r of a polyamide was
measured in accordance with JIS K 6810:1977 in 98% sulfuric acid
under the conditions of a polyamide concentration of 1% and a
temperature of 25.degree. C.
[0060] 4. Measurement of Terminal Group Concentrations of
Polyamide
[0061] The terminal amino group concentration of a polyamide was
determined by titrating a solution of 1 g of the polyamide in a
phenol/methanol mixed solvent with 0.02 N hydrochloric acid.
[0062] The terminal carboxyl group concentration of a polyamide was
determined by titrating a solution of 1 g of the polyamide in
benzyl alcohol with 0.05 N sodium hydroxide solution.
[0063] 5. Formation of Film to be Evaluated
[0064] One or more polyamides and an antioxidant were fed to a
twin-screw extruder (Type TEX 30, manufactured by The Japan Steel
Works, Ltd.) and melt-kneaded under the conditions of an extruder
barrel temperature of 250.degree. C. and a screw rotational speed
of 100 rpm. The resultant composition was pelletized and dried. The
pellets were fed to a single-screw extruder (Plabor .phi.40 Type
Ex, manufactured by Research Laboratory of Plastics Technology Co.,
Ltd.) equipped with a T-die to produce an unstretched polyamide
film having a thickness of 100 .mu.m under the conditions of an
extruder barrel temperature of 250.degree. C., screw rotational
speed of 40 rpm, and cooling roll temperature of 30.degree. C. A
sample having a length of 90 mm and a width of 90 mm was cut out of
the film and attached to a biaxially stretching machine
manufactured by Iwamoto Seisakusho K. K. The sample was
simultaneously biaxially stretched at a temperature of 70.degree.
C. in a stretch ratio of 2.8 in each direction, and the stretched
state was fixed with heating at 210.degree. C. to produce a
biaxially stretched film. Sample films to be evaluated were cut out
of this biaxially stretched film.
[0065] 6. Retortion
[0066] The unstretched film (150 mm by 150 mm) and stretched film
(150 mm by 150 mm) obtained above were placed in an autoclave for
retort pouch foods (SR-240, manufactured by Tomy Seiko Co., Ltd.)
and treated therewith for 30 minutes under the conditions of a
temperature of 135.degree. C., total pressure of 3.2 kg/cm.sup.2
(gauge pressure), and partial air pressure of 1.0 kg/cm.sup.2.
[0067] 7. Measurement of Retention of Tensile Strength
[0068] Tensile strength was measured in accordance with ASTM
D-882.
[0069] The retention of tensile strength was determined by
calculating the value of [(tensile strength after
retortion)/(tensile strength before retortion)].times.100(%). The
higher the retention of tensile strength, the less the influence of
the retortion.
[0070] 8. Measurement of Haze
[0071] Haze, which is a measure of transparency, was determined in
accordance with ASTM D-1003 using a direct-reading haze computer
(HGM-2DP) manufactured by Suga Test Instruments Co., Ltd. A film
was examined for haze before and after retortion, and the change in
haze through the retortion was calculated. Change in haze=(haze
after retortion)/(haze before retortion)
Examples 1 to 4 and Comparative Examples 1 to 4
[0072] One or more polyamides were mixed with an antioxidant
according to each formulation shown in Table 1. From the resultant
compositions, films to be evaluated were produced by the method
described above. The films obtained were examined for tensile
strength and haze before and after retortion. In Table 1 are shown
tensile strength, haze, and change in haze.
1TABLE 1 Comp. Comp. Comp. Comp. Item Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4
Ex. 1 Ex. 2 Ex.3 Ex.4 Kind of A-1 wt % 36 36 40 30 -- -- -- 36
polyamide A-2 -- -- 60 50 100 -- 100 -- A-3 64 64 -- 20 -- 100 --
64 Terminal carboxyl .times.10.sup.-5 3.3 3.3 3.4 3.5 4.2 3.1 4.2
3.2 group concentration eq/g Terminal amino 5.3 5.4 6.3 5.6 4.0 3.3
4.0 5.5 group concentration Relative viscosity -- 3.57 3.59 2.98
3.29 3.60 4.40 3.60 3.57 Anti- Kind -- B-1 B-1 B-1 B-1 -- -- B-1
B-2 oxidant Amount ppm 1000 3000 1000 1000 -- -- 1000 1000 Tensile
strength* MPa 119/119 123/123 117/115 122/120 120/5 140/20 119/80
125/105 Retention of % 100 100 98 98 4 14 67 84 tensile strength
Haze* % 1.9/2.5 2.3/3.0 2.1/3.0 2.1/2.9 2.5/6.0 2.4/5.9 2.4/5.9
2.3/6.0 Change in haze -- 1.3 1.3 1.4 1.4 2.4 2.4 2.4 2.6 *Found
values of tensile strength or haze before retortion/after
retortion
[0073] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *