Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-01-18
2002-08-13
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S035400, C428S036600, C428S036700, C428S500000, C428S520000, C524S399000, C524S400000
Reexamination Certificate
active
06432552
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a saponified ethylene-vinyl acetate copolymer (hereinafter briefly referred to as EVOH) and a laminate comprising a layer which comprises said EVOH. More particularly, it relates to an EVOH species excellent in long-run moldability, nonretainability in extruders and heat stability, among others, and to a laminate which comprises a layer comprising said EVOH species and is excellent in appearance and in heat stability during regrinding.
BACKGROUND OF THE INVENTION
Generally, EVOH copolymers are excellent in transparency, gas barrier and aroma-retaining properties, solvent resistance and oil resistance, among others, and are used, for making the best use of such characteristic features, in the form of moldings such as films, sheets, or bottles or like containers, for packaging foodstuffs, drugs, industrial chemicals, agrochemicals and so forth. However, EVOHs are susceptible to thermal degradation, hence to rapid changes in melt viscosity and, at the same time, may undergo discoloration. Therefore, in the step of molding (melt molding) of such products, special care should be taken. Furthermore, EVOHs are frequently used in laminates together with another or other thermoplastic resins and therefore required to have good appearance characteristics.
Accordingly, various attempts have so far been made, for example sufficient washing of EVOHs with water or incorporation of a certain metal salt. As far as long-run continuous molding is concerned, however, there is still room for improvement.
For achieving such improvement, JP Kokai S64-64843 or U.S. Pat. No. 5,360,670 and JP Kokai S64-66262 or U.S. Pat. No. 5,118,743 propose an EVOH species which exhibits such flow characteristics that, in the relationship between the heating time and the extrusion rate at least one temperature in a range of from 10 to 80° C. higher than the melting point of said EVOH measured with a Koka flow tester, the extrusion rate does not substantially increase for the initial 15 minutes, thereafter the extrusion rate at any heating time after 15 minutes until 2 hours is in a range of from 1/10 to 50 times that after the initial 15 minutes, and the extrusion rate at any heating time after 2 hours until 10 hours is at least once in a range from 2 to 50 times that after the initial 15 minutes.
However, intensive investigations made by the present inventors concerning such flow characteristics of EVOHs revealed that EVOHs with the flow characteristics such that the extrusion rate at any heating time after 2 hours until 10 hours is at least once in a range from 2 to 50 times that after the initial 15 minutes still have a heat stability problem. In particular, in the step of processing at high temperatures or processing during which EVOHs tend to undergo a shearing action, decomposition gases generate in considerable amounts and thus the heat stability decreases. Improvements in this respect are thus required.
In the case of laminates in which an EVOH is used, recycling, regrinding or like processing for reuse results in a decrease in processability, hence it is difficult to obtain good recycled laminates. Improvements in this respect are also required.
The present invention has been accomplished as a result of intensive investigations concerning the flow characteristics of EVOHs and has for its object to provide an EVOH species excellent in long-run moldability, nonretainability in extruders and heat stability as well as an EVOH laminate excellent in appearance and in heat stability in the step of regrinding.
SUMMARY OF THE INVENTION
The saponified ethylene-vinyl acetate copolymer (EVOH) of the present invention is characterized in that, in the relationship between the heating time and the extrusion rate as measured with a Koka flow tester at at least one temperature higher by 10 to 80° C. than the melting point thereof as measured by differential scanning calorimetry (DSC), it shows an extrusion rate at any time within the period of 15 minutes to 2 hours of heating which is 0.1 to 50 times the extrusion rate at 15 minutes of heating and an extrusion rate at any time within the period of 2 to 10 hours of heating which is less than 2 times the extrusion rate at 15 minutes of heating and that, in the relationship between the heating time and the torque as measured with a torque detecting rheometer at at least one temperature higher by 30 to 60° C. than the melting point thereof as measured by DSC, it shows, at any time within the range of 1 to 2 hours of heating, a toruque value within the range of ⅙ to ⅚ of the maximum torque value found within the initial 20 minutes of heating. The laminate of the present invention is characterized in that it comprises at least one layer comprising said EVOH.
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention is described in detail.
The melting point as so referred to herein means the value of the main endothermic peak temperature in DSC (differential scanning calorimetry; programmed hating rate: 10° C./min). The extrusion or discharge rate is measured on a Koka flow tester (capillary rheometer) using a nozzle having a diameter of 1 mm and a length of 10 mm under a load of 10 kg/cm
2
and the measurement time includes 5 minutes of preheating.
The relationship between time and torque is determined using a torque-detecting rheometer using a mixer and roller blade for measurement with a chamber capacity of 60 cc. The sample (55 g) (90 to 100% by volume filling) is charged, under air, through the feed opening and, after tight sealing under a load of 7 kg applied to the lid, preheated for 5 minutes and then kneaded by increasing the rate of revolutions to 50 rpm within 30 seconds, and the torque value after 60 minutes of kneading is detected and recorded.
As specific examples of such torque-detecting rheometer, there may be mentioned Brabender “Plasti-Corder” and Toyo Seiki Seisakusho “Labo-Plastomil”, among others.
Usable as the roller blade are “Roller Mixer W50” for “Plasti-Corder” and “Roller Blade R60B” for “Labo-Plastomil”.
As mentioned above, the EVOH according to the present invention has specific flow characteristics such that, in the relationship between the heating time and the extrusion rate as measured with a Koka flow tester at at least one temperature higher by 10 to 80° C. than the melting point thereof as measured by DSC, the extrusion rate at any time within the period of 15 minutes to 2 hours of heating is 0.1 to 50 times the extrusion rate at 15 minutes of heating and the extrusion rate at any time within the period of 2 to 10 hours of heating is less than 2 times the extrusion rate at 15 minutes of heating and that, in the relationship between the heating time and the torque as measured with a torque-detecting rheometer at at least one temperature higher by 30 to 60° C. than the melting point thereof as measured by DSC, the toruque value at any time within the range of 1 to 2 hours of heating is within the range of ⅙ to ⅚ (preferably ⅓ to ⅔) of the maximum torque value found within the initial 20 minutes of heating. Said EVOH is not particularly restricted but may be any one satisfying the above necessary conditions. For obtaining such an EVOH species, it is generally necessary to subject an ordinary EVOH species to a specific treatment.
Said specific treatment will be described later herein. The EVOH species to be treated is not particularly restricted but may be one with an ethylene content of 20 to 60 mole percent (preferably 25 to 55 mole percent) and a saponification degree of not less than 90 mole percent (preferably not less than 95 mole percent). When said ethylene content is less than 20 mole percent, the gas barrier properties under high humidity conditions and the melt moldability will be low. When, conversely, it exceeds 60 mole percent, sufficient gas barrier properties may not be obtained. A saponification degree less than 90 mole percent is unfavorable since it gives only low gas barrier properties, heat stability and moisture resist
Armstrong Westerman & Hattori, LLP
Nakarani D. S.
Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha
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