JPS6264846A - Method for producing polyethylene stretched molded body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a stretched polyethylene article,
In particular, it relates to the production of polyethylene stretched molded bodies with low stretching ratios.

[Prior Art] High-pressure polyethylene has particularly good processability, is chemically stable, and has excellent physical properties such as transparency and flexibility, so it can be used for various purposes, such as films, blow molding, It has been widely used in injection molding, tubes, laminates, wire coatings, steel pipe coatings, etc. However, in recent years, there has been a demand for bottles for general food packaging to use materials with high mechanical strength such as rigidity and creep properties to reduce the weight of the product. In addition, for medical drug bottles such as infusion bottles, conventional glass bottles are being replaced with plastic bottles in order to reduce weight and reduce the chance of breakage during transportation. However, there are problems such as deformation and fusion of bottles during sterilization, and there is a need in this field for materials that can withstand sterilization and various chemicals.

The recently developed low-density ethylene/α-olefin copolymer has a density similar to that of high-pressure polyethylene, but
It has high rigidity and a high melting point, and has good environmental stress cracking resistance and creep resistance, so it is a material that is suitable to meet the demands of each of the above uses. However, this ethylene/α-olefin copolymer has a higher degree of crystallinity than high-pressure polyethylene produced by radical polymerization, and has a larger crystal size, so it has a high internal haze and cannot be said to be transparent. Furthermore, since the molecular weight distribution is narrow,
Shark skin tends to occur during extrusion molding, resulting in high external haze, resulting in a product that is opaque as a whole.

Conventionally, as a method to improve these drawbacks, internal Ha
Regarding ze, there is knowledge that (a) quenching, (b) addition of a nucleating agent, and (c) lowering the density of the ethylene/α-olefin copolymer. On the other hand, methods for improving external haze include (d) widening the grip width and lowering the extrusion shear rate, and (e) using high-pressure polyethylene with good processability in 6 oz.
(f) Mix 5 to 75 weight 2 of high-pressure polyethylene with a higher MFH than the ethylene fiber α-olefin copolymer (U.S. Pat. No. 3,178,152), (f) raise the resin temperature during molding. It is known that

However, there are few cooling methods that are effective for the rapid cooling in (a) when manufacturing hollow products with a wall pressure of 0.2 m+* or more, and only a method of cooling with carbon dioxide gas is known in the literature. Recently, when the contents to be filled into a hollow product are liquid, a method has been developed in which the contents are cooled and shaped while being blown with the liquid. However, it also has the disadvantage that it cannot be applied to viscous liquids such as ketchup. (b) Improvement of internal haze by adding a nucleating agent is avoided in products used for medical purposes due to concerns about bleed-out.

The effect (c) on internal haze due to density reduction can only be realized when the density is set to 0.850 to 0.880 g/c3, but this is not preferable because it causes a decrease in heat resistance. Changing the grip lip in (d) to improve external haze naturally requires a new grip, and in blow molding, the lip width is automatically changed (for example, from 10 to 80 points) to improve the extrusion parison. Since the wall pressure is controlled, depending on the wall thickness of the product, the lip width may become narrower, resulting in shark skin. (E) or (F) high-pressure polyethylene blends are unsatisfactory in terms of mechanical strength and environmental stress cracking resistance, and (G) cannot be used because raising the resin temperature causes drawdown.

Other known methods for improving internal haze include biaxial stretching in the case of polypropylene, and short-section-axial stretching in the case of high-density polyethylene. Application of this stretching method to ethylene/α-olefin copolymer is as follows:
As stated in Japanese Patent Publication No. 52-794,
When the density is less than 0.940 g/ell', crystal orientation is difficult to occur, and when the stretching ratio is 4 times or more, stretching breakage occurs;
In addition, our studies have revealed that stretching unevenness occurs even at a stretching ratio of 4 times or less, and in either case, these stretching methods have the disadvantage of being practically unusable.

[Problem to be solved by the invention 1 This stretching method increases mechanical strength such as tensile strength and flexural modulus, significantly improves transparency, and separates the stretching temperature conditions from the original fabric manufacturing time. Therefore, in some cases, low-temperature molding is possible.5For example, we emphasize that this is a useful molding method for preventing oxidative deterioration during molding without adding antioxidants, and we have decided to change the stretching method to ethylene/α-olefin. We have made extensive efforts to reduce stretching unevenness, which is a problem when applied to copolymers.

[Means for solving the problem] As a result, at a low stretching ratio of 50 (H) or less, a composition in which high-pressure polyethylene having an MFR equivalent to or lower than that of an ethylene/α-olefin copolymer was added could be stretched evenly. In addition, it is possible to
It has been found that by controlling the temperature to 120 to 200°C, deterioration phenomena such as blistering, gelling, and smearing can be suppressed even when molding is performed for a long time without substantially adding an antioxidant.

That is, the present invention is an ethylene/α-olefin copolymer having an MFR of 0.1 to 20 g/10 min, a density of 0.900 to 0.940 g/amx, and a flow ratio of 5 to 18.
0% by weight and III of the ethylene/α-olefin copolymer
This is a method for producing a stretched molded article, which is characterized in that a polyethylene composition consisting of 5 to 40 parts by weight of high-pressure polyethylene having an MFR equivalent to or lower than FR is heated from a solid state and stretched to 10 to 50 oz.

The ethylene/α-olefin copolymer used in the present invention is produced by a gas phase method using a Ziegler catalyst that combines a transition metal such as titanium or vanadium with an organoaluminum compound.
It is a copolymer of ethylene and α-olefin that can be obtained by various polymerization methods such as a solution method, a slurry method, and a high-pressure method.

α-olefins include propylene, butene-1, pentene-1, hexene-1,4-methyl-pentene-1,
It is selected from 1-olefins having 3 to 10 carbon atoms, such as octene-1. The more preferred α-olefin is butene-
1, hexene-1,4-methyl-pentene-1, or octene-1. The content of these α-olefins in the copolymer is 3 to 25 weight units, preferably 4 to 18 weight units.
It is.

The density of the copolymer is 0.800-0.940 g/c+w
', preferably 0.1315 to 0.930 g/
cm'. If the density is less than 0.900 g/cmM, the heat resistance will be poor, and there is a risk that the bottles will fuse together during high-temperature sterilization. If the density is greater than 0.840 g/am', the tear strength of products such as tapes and sheets after stretching is undesirable.

The NFR of the copolymer is 0.1-20 g/10 min, preferably 0.5-10 g/10 min. MFR is 0.1
If it is less than g/10 minutes, surface roughness will occur at the extrusion speed during production of the original fabric on an industrial scale, resulting in a wavy appearance with large cycles even after stretching, reducing the commercial value.

If the MFR is greater than 20 g/10 minutes, the mechanical strength, particularly the environmental stress cracking resistance, which is the object of the present invention, decreases. Also,
Jl! Using an MFR device compliant with lli K8780,
load! The flow ratio expressed as the high load MFR (MFR+.) extruded at 2.18 kg divided by the normal MFR at 2.18 kg load is between 5 and 18, preferably between 7 and 9. When the flow ratio is less than 5, shark skin and melt fracture occur during extrusion of the raw material when the MFR is less than the lower limit of 0.1 g/10 minutes, which is not preferable. Furthermore, if the flow ratio is greater than 18, melt fracture will not occur, but there is a risk that residual residue will occur during stretching.

The high-pressure polyethylene blended into the copolymer in the present invention is radically polymerized in an autoclave or tube at a pressure of 1000 to 3000 atm and a temperature of 200 to 250°C using, for example, oxygen or peroxide. It is a polyethylene obtained by
Polyethylene has more long chain branches than olefin copolymers. It is necessary that the MFR of this high-pressure polyethylene is equal to or lower than the MFR of the above-mentioned ethylene fist α-olefin copolymer. If high-pressure polyethylene having an NFR larger than this is mixed, it is not preferable because it may cause residual residue during stretching.

The density of high pressure polyethylene is o, sto ~ 0.938g
/c+s'' is preferred. If the density OJ is less than 10 g/cm', the heat resistance of the composition will be relatively reduced;
, 113Bg/amx, the high pressure process substantially increases the cost and has low industrial value.

The mixing ratio of high-pressure polyethylene to the ethylene/α-olefin copolymer is 5 to 40% by weight2, preferably 10 to 40% by weight.
Weight%. If the weight is less than 5%, the effect of improving unevenness during stretching will be small, and if the weight exceeds 40%, ethylene/α
B5OR, creep properties of olefin copolymer,
Decreases the excellent properties of mechanical strength.

For mixing the ethylene/α-olefin copolymer and high-pressure polyethylene, generally known melt mixing methods such as a single screw extruder, twin screw extruder, Banbury, and roll can be used. It is also possible to tri-blend pellets together just before molding! However, since the present invention uses high-pressure polyethylene with a low NFR, goui lines may occur depending on the type of raw material extruder, gouey structure, and goui shape, so it is necessary to melt and mix it once to form a pellet. is preferred.

A neutralizing agent, an antioxidant, a pigment, an antistatic agent, an antifogging agent, an antiblocking agent, a slip agent, a weather resistance improver, etc. can be added to this composition within a range that does not impair the physical properties.

These compositions were heated to a resin temperature of 120 from a T-die and a cylindrical die.
A film, sheet, or pipe is extruded at a temperature of ~200°C, and then cooled by contact with a cooling roll or by passing through a water cooling bath to form a stretched original fabric. If the extrusion temperature of the raw material is lower than 120°C, shark skin will occur during extrusion, and if the temperature is higher than 200°C, a small amount of deterioration products will be generated, in the case of medical containers.

Depending on the contents, fine particles of 2 to 30 IL may float in the drug, which is not preferable.

Next, stretching is performed uniaxially or biaxially in a roll or oven temperature atmosphere at a temperature of 90 to 130°C. Biaxial stretching may be simultaneous stretching or sequential stretching.

The stretching temperature is selected to be 80 to 130°C, but if the stretching temperature is less than 90°C, for example, in the case of an infusion bottle, if the bottle is heat sterilized with a low liquid filling rate, the bottle will begin to shrink and its dimensions will become unstable. It is not preferable because the stretching temperature is 1.
When the temperature is higher than 30°C, the effect of improving internal haze by stretching is small.

A stretching ratio of 10 to 50 oz is applied. Stretching ratio is 1
If it is less than 0%, the improvement in internal haze is small. When stretching is performed at higher than 50 oz, it is possible to stretch the ethylene/α-olefin copolymer alone without leaving any residue, and there is no need to use the composition of the present invention.

The density after stretching is 0. l]10-0.944 g/cta
S is preferred, but the density is 0. ! If it is less than 310g/cm', heat sterilization temperature (e.g. 105°C) may be required depending on the application.
0. l]44g/am5
If the height is higher, the product becomes more rigid and may lack flexibility.

[Example] Example 1 Polymerized with Ziegler catalyst MFR2.0g/10 minutes, density 0.922g/cya', 70-sio7
．． 5. Ethylene-butene-1 copolymer with butene-1 content 8.5 weight 2, MFR 0.1 g/10 min, density 0.918 g/cts' 20 weight high-pressure polyethylene with no antioxidant added Mix 2 and use a 40mm granulator (
Screw/mouth = 24), both cylinder and die are 1
The temperature was set at 80°C for granulation. The MFR of this composition is 1.
2 g/10 min, density Q, 1121 g/cmM. The pellets were put into a 65 mm 1φ T die extruder made by Mitsubishi Heavy Industries, and the hopper temperature was 180°C and the cylinder (CI) 1
70℃, cylinder (C2) temperature 17Q℃, adapter temperature 170℃, die temperature 180℃, screw rotation speed 89rp-, plasticize the sheet, lip width 2cm, width 3cm.
0-1, extruded from a manifold type die with a chrome-plated surface. Next, this sheet is cooled while being brought into close contact with a roll at 20° C. using an air knife to form a stretched original fabric. At this time, no phenomena related to deterioration such as smear, strange odor, or discoloration were observed.

This stretched raw sheet was brought into contact with a 105° C. preheating roll to be heated, then stretched at a stretching ratio of 20 oz between rolls having different rotational speeds, and then taken off. Average fabric thickness is 0.85mm
, original fabric density 0.91? Og/cm' and the average stretched sheet thickness O,? 2+s cabinet, density 0.9204g/cs+
A stretched sheet of S was obtained. The center part of this stretched sheet in the width direction is 2? When the thickness was measured over 0mm, the thickness unevenness was (maximum film thickness / minimum film thickness) / average film thickness = 0.25
Compared to Comparative Example 1, which will be described later, in which high-pressure polyethylene was not added, the film of this example was stretched with less uneven thickness. In addition, in accordance with ASTM 01003, Ha
When the haze was measured, the haze of the stretched sheet was 17.7% compared to 35.13% for the original sheet, and the transparency was improved by stretching.

Example 2 A stretched sheet was prepared in Example 1 except that the stretching ratio was 50 oz. The thickness of this original sheet is the same as in Example 1, but the average stretched sheet thickness is 9.25 m, and the density after stretching is 0.
．． l]22Bg/cm1. The thickness unevenness measured over 27 hm at the center in the width direction of this sheet was 0.
08, and it was stretched with very little unevenness. Further, the stretched sheet has a haze of 2.5z, and has excellent transparency considering its thickness.

Example 3 MFR 0.7 g/10 min polymerized with Phillips catalyst,
Density 0. ! 1130g/cya'', 70-resi No. 16.5, buty 7-1 content of 5.5wt ethylene-butene-1 copolymer 80wt2 and MFRo, 5g/10
40 weight pellets of high-pressure polyethylene having a density of 0.832 g/am' were granulated under the same conditions as in Example 1 and subjected to molding. The stretching ratio was set to 300. The thickness of the original sheet in this case is the same as in Example 1, but the average stretched sheet thickness is 0.44.
+u+. The thickness unevenness of this sheet over 270 mm in the widthwise center part was 0.21, and compared to Comparative Example 2, the sheet was stretched with less unevenness. Further, the stretched sheet has a haze of 8.3z, and has excellent transparency considering its thickness.

Comparative Example 1 Ethylene-butene-1 copolymer of Example 1 (MFR2,
0g/10min, density 0.922g/c■3. Only the sample with a flow ratio of 7.5 and a butene-1 content of 8.5 weight 2) was subjected to molding. The original film thickness and average stretched sheet thickness are the same as in Example 1 when the stretching ratio is 200%. The thickness unevenness of this sheet over the center 270 cm in the width direction is 0.3
5, and the unevenness is larger than that in Example 1. The haze of the stretched sheet is 38.8, and the haze of the original sheet is 79.8%.
Although the transparency was improved by stretching compared to Example 1, it was significantly inferior to Example 1.

Comparative Example 2 When an experiment was conducted using only the ethylene-butene-1 copolymer used in Example 3, the thickness unevenness was 0.28, which was compared to Example 3.
The unevenness is large compared to . Haze of stretched sheet is 20
．． Although the transparency was improved by stretching when compared to the Haze of the original fabric of 0% and 35.5%, it was inferior when compared to Example 3.

Comparative Example 3 When the stretching temperature was set to 135°C in Example 1, the thickness unevenness was 0.06, and although the unevenness was smaller than in Example 1, the Haze of the stretched sheet was 44.7%, which was the same as in Example 1. Compared to No. 1, the effect of improving transparency is small.

[Operation and Effect] The polyethylene composition of the present invention can be used to form molded products with a low draw ratio by blending an ethylene/α-olefin copolymer with specific physical properties with high-pressure polyethylene having an MFR equivalent to or lower than the ethylene/α-olefin copolymer. It has excellent molding properties for general use, and can be manufactured at temperatures of 120 to 200℃.
By adopting an extrusion temperature of Obtainable.

Therefore, by the method of the present invention, hollow bottles and films for food and medical use with excellent transparency, heat resistance and chemical resistance, sheets with excellent flexibility and transparency, and longitudinal tear resistance can be obtained. Tapes, ribbons, etc. with less uneven thickness can be obtained.

Claims (4)

[Claims] (1) MFR is 0.1-20g/10min, density is 0.9
00~0.940g/cm^3 and flow ratio is 5~1
8 ethylene/α-olefin copolymer 95-80% by weight
and a high-pressure polyethylene 5 to 5 having an MFR equal to or lower than the MFR of the ethylene/α-olefin copolymer.
A method for producing a polyethylene stretched molded article, which comprises heating a polyethylene composition consisting of 40% by weight from a solid state and stretching it by 10 to 500%. (2) The method according to claim 1, wherein the original fabric is produced under extrusion conditions at a temperature of 120 to 200°C. (3) The method according to claim 1 or 2, wherein the heating for stretching is 90 to 130°C. (4) The density of the stretched product is 0.910 to 0.944
g/cm^3, claims 1 to 3
The method described in any of the paragraphs.