Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-08-12
2001-10-30
Wu, David W. (Department: 1609)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S117000, C526S172000, C525S240000, C502S155000
Reexamination Certificate
active
06310167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ethylene homopolymer and its molded article. More precisely, the invention relates to an ethylene homopolymer having a high melting point relative to its density, and having good low-temperature heat-sealability and moldability, and also to its molded article.
2. Description of the Related Art
As a rule, polyethylenes from ethylene through polymerization are grouped into low-density polyethylene (LDPE) to be from ethylene through high-pressure radical polymerization and high-density polyethylene (HDPE) also to be from it but through polymerization in the presence of a Ziegler-Natta catalyst, depending on the methods of producing them. Polyethylenes of those types have different characteristics, and are used for different applications depending on their characteristics.
Specifically, low-density polyethylene (LDPE) to be produced through high-pressure radical polymerization of ethylene has a combined structure of long-chain branches and short-chain branches, of which the melt tension is high and the activation energy for melt fluidity is large. Therefore, it is suitable to high-speed molding and is favorable to applications for films and blow molded containers. However, as having a low melting point relative to its density, LDPE is defective in that its heat resistance is poor. In addition, since its molecular weight distribution is broad and since it contains a low-molecular-weight, low-melting-point component (low polymer), LDPE is still defective in that its environmental stress crack resistance (ESCR) is poor and its mechanical strength including, for example, impact strength, tensile strength and tear strength is low.
On the other hand, high-density polyethylene (HDPE) to be produced through polymerization of ethylene in the presence of a Ziegler-Natta catalyst has good heat resistance and high mechanical strength, as its structure has few branches. However, since its melt tension is low and its activation energy for melt fluidity is small, HDPE is defective in that its high-speed moldability is poor. In addition, HDPE is further defective in that its heat-sealing temperature is high. In that situation, improving such LDPE and HDPE is desired.
Heretofore, nobody has obtained ethylene homopolymer having well-balanced properties of good heat resistance, high mechanical strength, good low-temperature heat-sealability and good moldability.
At present, linear low-density polyethylene (LLDPE) to be produced through copolymerization of ethylene and &agr;-olefins in the presence of a Ziegler-Natta catalyst are used in place of ethylene homopolymer. However, since the ability of the Ziegler-Nata catalyst to catalyze the copolymerization is poor, the compositional distribution in the resulting linear low-density polyethylene (LLDPE) is broad. Therefore, LLDPE is problematic in that its molded articles such as films and others are often sticky. Another problem with it is that LLDPE shall contain a larger amount of a low-molecular-weight, low-melting-point component (low polymer) with its density being lowered, and its molded articles could not have high mechanical strength.
In addition, linear low-density polyethylene (LLDPE) is often limited in its production, as it must be produced at high temperatures or must be produced through multi-stage polymerization.
Apart from the above, blending various polyolefin resins such as HDPE, LDPE, LLDPE and others is tried for improving the properties of the resins. However, this is still defective, as requiring some additional equipment for blending them, and taking a lot of time for obtaining the intended resins having high mechanical strength and good moldability.
Given that situation, if an ethylene homopolymer having well balanced properties of good heat resistance, high mechanical strength, good low-temperature heat-sealability and good moldability could be obtained, it could solve all the problems noted above.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the problems as above, and its object is to provide an ethylene homopolymer having well-balanced properties of good heat resistance, good heat-sealability and good moldability, and also to provide molded articles of the ethylene homopolymer.
We, the present inventors have assiduously studied, and, as a result, have found that an ethylene homopolymer having a specific branched structure, a specific compositional distribution and a specific molecular weight distribution has a high melting point relative to is density, and has good low-temperature heat-sealability and good moldability. On the basis of these findings, we have completed the present invention. Specifically, the invention provides an ethylene homopolymer mentioned below, and its molded article.
1. An ethylene homopolymer, which is characterized in that the number of butyl branches per 100 methyl branches therein falls between i and 20, as measured through
13
C-NMR, that its density, d (kg/m
3
), falls between 880 and 980, and that the density, d, and its melting point, Tm (° C.) as measured through differential scanning calorimetry, satisfy the conditions defined by the following formulae (1) to (3):
Tm≧
1.2×
d−
982(980≧
d≧
925) (1),
Tm≧
0.6×
d−
430(925>
d≧
915) (2),
Tm≧
0.16×
d−
28.4(915>
d≧
880) (3).
2. The ethylene homopolymer of 1, of which the weight-average molecular weight, Mw
i30
and Mw
f70
, of the initial 30 wt. % eluate and the final 70 wt. % eluate, respectively, as fractionated in temperature rising elution fractionation and measured through gel permeation chromatography, satisfy the condition defined by the following formula (4):
Mw
i30
/Mw
f70
≧1.0 (4).
3. The ethylene homopolymer of 1 or 2, of which the weight-average molecular weight, Mw
60L
and Mw
60U
, of the eluate at an elution temperature of not higher than 60° C. and that at an elution temperature of higher than 60° C., respectively, as fractionated in temperature rising elution fractionation and measured through gel permeation chromatography, satisfy the condition of the following formula (5):
Mw
60L
/Mw
60U
≧1.0 (5).
4. The ethylene homopolymer of any one of 1 to 3, of which the ratio, Mw/Mn, of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) as measured through gel permeation chromatography, and the ratio, MI
21.6
/MI
2.16
, of the melt index (MI
21.6
) at a temperature of 190° C. and under a load of 21.6 kg to the melt index (MI
2.16
) at a temperature of 190° C. and under a load of 2.16 kg, as measured according to the method in JIS K7210, satisfy the condition of the following formula (6):
MI
21.6
/MI
2.16
≧6.9×(
Mw/Mn
)+4.5 (6)
5. The ethylene homopolymer of any one of 1 to 4, of which the ratio, Mw/Mn, of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), as measured through gel permeation chromatography, is at least 5.
6. The ethylene homopolymer of any one of 1 to 5, of which the melting point, Tm (°C), as measured through differential scanning calorimetry, is not higher than 132° C.
7. A molded article prepared from the ethylene homopolymer of any one of 1 to 6.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described in detail hereinunder.
1. Ethylene Homopolymer
The ethylene homopolymer of the invention is characterized in that the number of butyl branches per 100 methyl branches therein falls between 1 and 20, but preferably between 1 and 15, more preferably between 1 and 10, as measured through
13
C-NMR.
If the number of butyl branches per 100 methyl branches therein is smaller than 1, the ethylene homopolymer could not exhibit high melt fluidity (non-Newtonian fluidity); but if larger than 20, it could not also exhibit high melt fluidity (non-Newtonian fluidity) like that where the number of branches is smaller than 1. Therefore, the ethylene homopolymer where the number of
Housaki Tatsuya
Kanzawa Mitsugu
Okuda Fumio
Tatsumi Tomio
Harlan R.
Idemitsu Petrochemical Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
LandOfFree
Ethylene homopolymer and its molded article does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ethylene homopolymer and its molded article, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ethylene homopolymer and its molded article will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2605106