Resin materials and films made therefrom

Details Resin materials and films made therefrom Resin materials and films made therefrom

1999-11-05

2003-03-18

Wilson, D. R. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S386000, C524S387000, C524S388000, C524S247000

Reexamination Certificate

active

06534580

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a resin material having gas barrier properties and a film comprising the same.
DESCRIPTION OF BACKGROUND ART
Shrink packaging using a stretched film (a heat-shrinkable film) is widely used in industrial packaging such as packaging of foods, medicines, industrial parts, and the like. For example, a content is packaged by inserting the content in the bag of a stretched film, optionally evacuating an air from the bag, sealing the opening of the bag, and then heating the bag to shrink the stretched film.
A film used in such shrink packaging is desired to shrink sufficiently by heating. Furthermore, it is desired to lower a temperature at which a film can be thermally shrunk from the viewpoint of the reduction of packaging process cycles.
A stretched film should be heated to a temperature higher than a stretching temperature encountered in the production of the stretched film to thermally shrink the stretched films. Thus, it is assumed that the thermally shrinking temperature of the stretched film may depend on a stretching temperature encountered in the production of the stretched film.
Saponified ethylene-vinyl ester copolymers have better transparency and gas barrier properties, in particular, against oxygen gas, than other resins. Therefore, the films of such saponified copolymers are widely used in industrial packaging.
However, the saponified ethylene-vinyl ester copolymers, in particular, saponified ethylene-vinyl acetate copolymers, have high stiffness and thus less stretchability, in particular, at a low temperature, they should be stretched at a relatively high temperature. If they are stretched at a low temperature, they are split, unevenly stretched or whitened, and thus stretched films having insufficient properties are obtained. Accordingly, it is desired to improve the stretchability of saponified ethylene-vinyl ester copolymers.
For example, JP-A-53-88067 and JP-A-59-20345 describe the improvement of the stretchability of saponified ethylene-vinyl ester copolymers by the addition of various plasticizers. However, the improvement of the stretchability of saponified ethylene-vinyl ester copolymers by such conventional methods are still unsatisfactory.
Hitherto, Nylon, polyvinylidene chloride, polyvinyl alcohol, liquid crystal polymers and the like are used as gas barrier materials. However, it is known that Nylon and polyvinyl chloride have inferior gas barrier properties to saponified ethylene-vinyl ester copolymers, while polyvinyl alcohol and liquid crystal polymers have inferior stretchability to saponified ethylene-vinyl ester copolymers. Thus, those polymers having gas barrier properties do not have good balance of gas barrier properties and stretchability.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a material having gas barrier properties which are comparable with those of saponified ethylene-vinyl ester copolymers, and better stretchability than saponified ethylene-vinyl ester copolymers.
According to one aspect of the present invention, there is provided a resin material comprising a resin, which satisfies at least one relationship selected from the group consisting of the following relationships [I] and [II]:
ln(
OTR
/22.5)+4.78 ln(
Fy/Fy
′)<−0.13, and
T
2
−T
1
<20  [I]
in which
Fy′ is a yield strength of a standard saponified ethylene-vinyl acetate copolymer at 60° C.;
Fy is a yield strength of said resin material at 60° C.; OTR is an oxygen gas permeability (cc/m
2
·day·atm) of said resin material per a unit thickness of 1 &mgr;m at 23° C. and a relative humidity of 0%;
T
1
is a haze (%) of a film of said resin material having a thickness of 30 &mgr;m after being maintained at 23° C. and a relative humidity of 48% for 48 hours; and
T
2
is a haze (%) of a film of said resin material having a thickness of 30 &mgr;m after being maintained at 40° C. and a relative humidity of 90% for 24 hour, and
ln(
OTR
/22.5)+0.0698(
T
im
−157)<−0.06  [II]
in which
OTR is an oxygen gas permeability (cc/m
2
·day·atm) of said resin material per a unit thickness of 1 &mgr;m at 23° C. and a relative humidity of 0%; and
T
im
is a melting point of said resin material.
This and other embodiments of the present invention will be explained in detail.
PREFERABLE EMBODIMENTS OF THE INVENTION
One embodiment of the resin material according to the present invention comprises a resin as a main component, and satisfies the following inequalities (1) and (2):
ln(
OTR
/22.5)+4.78 ln(
Fy/Fy
′)<−0.13  (1)
and
T
2
−T
1
≦20  (2)
In the inequality (1), ln(OTR/22.5) is the natural logarithm of (OTR/22.5), and ln(Fy/Fy′) is the natural logarithm of (Fy/Fy′).
OTR is an oxygen gas permeability (cc/m
2
·day·atm) of the resin material of the present invention per a unit thickness of 1 &mgr;m at 23° C. and a relative humidity of 0%. OTR is preferably less than 22.5, more preferably 18 or less, in particular 11 or less.
Fy is a yield strength of the resin material of the present invention at 60° C., and expressed by the yield strength of a test specimen (No. 1 dumbbell defined by JIS K 6301) at 60° C., which is cut out from a pressed sheet having a thickness of 300 &mgr;m obtained by heat pressing the resin material of the present invention at 200° C. for 3 minutes and cold pressing it at 30° C. for 5 minutes. A yield strength is read from a tensile stress-strain curve (namely S—S curve), which is drawn based on the results of a tensile test carried out using a tensile tester in which the temperature of a test specimen can be controlled (for example, AGS 500D manufactured by Shimadzu Corporation) at a specimen temperature of 60° C. at a pulling rate of 1,000 mm/min.
Fy′ is a yield strength of a standard saponified ethylene-vinyl acetate copolymer at 60° C., and can be obtained in the same way as Fy except that the standard saponified ethylene-vinyl acetate copolymer is used in place of the resin material of the present invention.
When the inequality (1) is not satisfied, the oxygen gas permeability of the resin material is too high, that is, the gas barrier properties are insufficient, the stretchability of the resin material at a low temperature is low, and thus, a high stretching temperature is required to sufficiently stretch the resin material. When the inequality (1) is satisfied, but the inequality (2) is not satisfied, the stretchability and/or gas barrier properties of the resin material are not satisfactory. To achieve both good gas barrier properties and stretchability, ln(OTR/22.5)+4.78ln(Fy/Fy′) is preferably less than −0.4, more preferably less than −0.7.
Herein, a “standard saponified ethylene-vinyl acetate copolymer” means a saponified ethylene-vinyl acetate copolymer having an ethylene unit content of 44%, a saponification value of at least 98%, a melt index (MI) of 5.5 g/10 min., which is measured at 190° C. under a load of 2.16 kg after preheating a sample at 190° C. for 6 minutes, an oxygen gas permeability of 22.5 cc/m
2
·day·atm per a unit thickness of 1 &mgr;m at 23° C. and a relative humidity of 0%, and a melting point of 157° C.
An ethylene unit content is a ratio of the number of ethylene units to the number of whole polymerized monomer units of a saponified ethylene-vinyl acetate copolymer. The content of ethylene units and the saponification value can be measured by an infrared absorption method.
A standard saponified ethylene-vinyl acetate copolymer may be obtained by copolymerizing ethylene and vinyl acetate and saponifying the copolymer so that the copolymer satisfies the above ethylene unit content, saponification degree and MI. One example of a commercially available standard saponified ethylene-vinyl acetate copolymer is EP-E105B which is produced by KURARAY CO., LTD. Saponified ethylene-vinyl acetate copolymers, which are substantially the same as EP-E105B may be used as standard

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