JPS6128538A - Low-density polyethylene resin composition - Google Patents

Abstract

PURPOSE:The titled resin composition which has excellent high-speed processing characteristics and excellent heat-sealing strength, etc. and is suitable for use as a food packaging material, etc., obtained by mixing an ethylene/alpha-olefin copolymer and a high-pressure low-density polyethylene. CONSTITUTION:90-50wt% ethylene/alpha-olefin copolymer (e.g. an ethylene-propylene copolymer or an ethylene/1-butene copolymer) having a density of 0.9- 0.94g/ cm<3> and a melt index of 1-25g/10min, and 10-50wt% high-pressure low- density polyethylene having a ratio of the weight-average molecular weight to the number-average molecular weight of 4-15, a weight-average molecular weight of 50,000-300,000, and a fraction of a molecular weight of 50,000 or higher of 5-24wt% are kneaded sufficiently using a Banbury mixer, an extruder, etc. by multi-melt-compounding, simple melt-compounding, etc. to give an objective low-density polyethylene resin composition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-density polyethylene resin composition, and more particularly to a low-density polyethylene resin composition that has excellent high-speed processability and excellent heat-sealing strength.

In general, linear low-density polyethylene film has good heat sealing strength, impurity sealing strength, and hot tack property4, but on the other hand, it is difficult to process at high speed due to its narrow molecular weight distribution and linearity of the molecular structure. It has the disadvantage of being inferior to In particular, this drawback of poor high-speed processability becomes noticeable when the film is subjected to extrusion lamination processing, and the width and thickness of the resin film fluctuates, a so-called draw resonance phenomenon, which significantly reduces the commercial value. Lose.

As a means to eliminate such drawbacks, it has been proposed to blend high-pressure low-density polyethylene into the polyethylene.
qe Kaisho 58-194935 No. 1% Kaisho 58-1228
26 etc.]. However, even with these measures, the above-mentioned drawbacks are not sufficiently improved.

In view of these circumstances, the inventors of the present invention have conducted repeated studies to develop a polyethylene resin composition that eliminates the above-mentioned drawbacks. It has been discovered that a film obtained from a resin composition containing a predetermined amount of the following is excellent in high-speed processability and has good heat-sealing strength, etc., and based on this knowledge, the present invention has been completed.

That is, the present invention has a density of 0.900 to 0.9409/c
IIL" + 90-50% by weight of ethylene-α-olefin copolymer with melt index 1-25#/10 minutes
, weight average molecular weight (M, ) and number average molecular weight (Mn)
The ratio My/MH is 4 to 15, and the weight average molecular weight is 5.
The present invention provides a low density polyethylene resin composition comprising 10 to 50% by weight of high-pressure low density polyethylene having a molecular weight of 5 to 24% by weight.

The α-olefin in the ethylene-α-olefin copolymer used in the present invention is 08 to CI. α-olefins, preferably 04 to C8, specifically propylene, 1-butene, 1-pentene, 4-methyl-
Examples include pentene-1,1-hexene, 1-octene, and l-decene. This ethylene-α-olefin copolymer has a density of 9.900 to 0.94011/lx", preferably 0.915 to 0.9351/crX, and a melt index (MI) of 1 to 25 g/10 min, preferably Use one with 3 to 1011710 minutes.Here, the density (
(based on JI8 K6760) is 0.9001/cat”
If it is less than 0.940g/aILa, the heat sealing strength of the resulting film will be reduced, and if it exceeds 0.940g/aILa, the hot tackiness of the film will be reduced.

This is not preferable because it results in poor transparency. MI(JISK)
6760) for less than 19710 minutes will result in poor fluidity and low critical processing speed force, resulting in poor productivity; if it exceeds 25 F/10 minutes, the heat sealing strength of the film will be insufficient. do.

Next, as mentioned above, the high-pressure low-density polyethylene
&/Mn is from 4 to 15, preferably from 8 to 12. Here, the molecular weight distribution ('\'h/'□) was measured using Waters Co., Ltd. 1500 (column: MuD80M).
x 2, Mu D807 x 2, solvent: orthodichlorobenzene, temperature: 135°C, flow rate: l d/min)
If this ratio is less than 4, the effect of blending into the ethylene-α-olefin copolymer will be small, and the increase in critical processing speed will be small, resulting in insufficient improvement in productivity. . On the other hand, when the ratio exceeds 15,
Drawdown properties (high-speed take-up properties) deteriorate, making it impossible to produce a film.

Further, this polyethylene has a Mw, that is, a weight average molecular weight of 50,000 to 300,000, preferably 100,000 to 200,000, and a fraction of molecular weight of 50,000 or more is 5 to 24% by weight, preferably 9 to 18% by weight. Use the one. If - is less than 50,000, the effect of incorporation into the ethylene-α-olefin copolymer is small and the increase in critical processing speed is small, resulting in insufficient improvement in productivity. Also, MY is 30
If it exceeds 10,000, the drawdown properties will not improve, making it impossible to manufacture the film. The fraction with a molecular weight of 50,000 or more is 5
If the weight is less than 5, the increase in critical machining speed due to blending will be small and productivity will not improve.

On the other hand, if it exceeds 24% by weight, the drawdown properties will deteriorate, making it impossible to produce a film.

In the resin composition of the present invention, the blending ratio of the ethylene-α-olefin copolymer and high-pressure low density polyethylene is 90 to 50% by weight, preferably 85 to 70% by weight of the former, and 10 to 50% by weight of the latter. Preferably it should be between 15 and 30% by weight. If the blending ratio of the ethylene-α-olefin copolymer exceeds 90% by weight, the critical processing speed will decrease, productivity will not improve, and extrusion lamination processability will not be improved. On the other hand, if the blending ratio of the copolymer is less than 50% by weight, the mechanical strength and heat sealability of the extrusion-coated laminated film will not be sufficiently improved, and it will not be suitable for use as a large packaging material such as packaging for water products. becomes unsuitable for this purpose. .

The resin composition of the present invention contains various additives such as ultraviolet absorbers, heat stabilizers, antistatic agents, antioxidants, light stabilizers, and nucleating agents, taking into consideration the properties of the above components and the purpose of use. Can be added as appropriate.

The resin composition of the present invention can be obtained by blending the above-mentioned components in predetermined amounts and thoroughly kneading the mixture by, for example, a dry-wet/melt-mixing method, a multistage melt-mixing method, a simple melt-mixing method, or the like. In addition, the crosstalk is Banbury mixer, co-kneader,
This can be carried out using an extruder, a twin-screw kneader, or the like.

The thus obtained resin composition of the present invention improves the critical processing speed, which has been considered a drawback of linear low-density polyethylene films, and not only significantly improves productivity, but also It has excellent heat seal strength, fiber seal strength, and hot tack properties. Therefore, it is extremely useful for extrusion lamination processing and packaging materials (particularly food packaging materials).

Next, examples of the present invention will be shown.

Examples 1 to 7 The ethylene-α-olefin copolymer and high-pressure low-density polyethylene shown in the table were mixed in a V-blender, and then extruded from a T-die while being melt-kneaded in a single-screw extruder to form a film. Note that the T-die has a lip opening length of 470wn. A straight manifold type with a slit width of 0.7 mm was used.

Next, a 15 μm thick stretched nylon extruded and coated with 20 μm thick low density polyethylene was used as a base material, and a film made of the above composition was extruded and laminated thereon, and the critical processing speed was measured. Further, a laminate film was obtained by extrusion coating at a processing speed such that the thickness of the film was 30 μm. The heat seal strength, impurity seal strength, and hot tack property of the obtained laminate film were measured. The results are shown in the table.

Comparative Examples 1 to 3 Single films of high-pressure low-density polyethylene shown in the table were subjected to extrusion lamination using the same equipment and conditions as in Examples. The results are shown in the table.

Comparative Example 4.5 A single film of the ethylene-α-olefin copolymer shown in Table 2 was extrusion laminated using the same equipment and conditions as in Example. However, the processing is unstable and the critical processing speed is slow, and when the critical processing speed is exceeded, the coating width and coating thickness fluctuate greatly, and only extrusion laminate products with no commercial value can be obtained.

Comparative Examples 6 and 7 The same procedure as in Example was carried out except that the blending ratio of the ethylene-α-olefin copolymer and the high-pressure low-density polyethylene was changed. In this case, although the critical processing speed increases to some extent, it is not sufficient and only extrusion laminate products with no commercial value can be obtained.

Comparative Examples 8 to 11 Films of the compositions of the ethylene-α-olefin copolymer and high-pressure low-density polyethylene shown in the table were extrusion laminated using the same equipment and conditions as in the examples. In this case as well, although the critical processing speed was increased to some extent, it was not sufficient and only extrusion laminate products with no commercial value were obtained.

*1 Ethylene-α-olefin coj1 body A: Ethylene-
Octene-1 copolymer (density 0.920 g/arr"
, XI 4.09/x o min) B: Ethylene-butene-1 copolymer (density 0.92311/value s, MI
+, Og/l, o min) *2 High pressure low density polyethylene a: 10.5 200,000 17 0.910
8.0k): 7.0 150,000 15
0.915 7.5C: 5.2 140,000
13 0.923 6.3 (i: 3.5
90,000 5 0.918 25. Oe:
16.0 180,000 15 0.920 2.
0f: 6.0 40,000 6 0.917
4.7g: 5.5 110,000 4 0
．． 919 4.5*3 Critical machining speed Refers to the machining speed at which draw resonance occurs, and a machining speed of 1507 FL/min or higher is required for actual production machines. Draw resonance is a phenomenon in which the width and thickness of the film fluctuate and unevenness occurs when the processing speed exceeds a certain level.

*4 Heat seal strength 2 Sealed with Toyo Seiki's heat-gradient heat sealer °-
The heat seal strength of the laminated film is shown. In addition, the heat sealing pressure 2 is 9/α21 hours 1. After heat sealing for θ seconds, measurements were taken at a width of 25 m and a take-up speed of 200 IIV' minutes.

*5 Contaminant sealing strength This is a method to evaluate heat sealability when the front of the heat sealing surface is contaminated with contents, such as mayonnaise, edible oil, powder, etc. Specifically, the film surface contaminated with salad oil is on the inside. After heat-sealing them under the same conditions as the heat-sealing strength test, the strength was determined.

*6 Hot-tack property Fix one end of the two laminated films to the upper grip of the heat sealer, attach a 31g weight to the other end, heat seal the films together, and as soon as the seal bar separates, attach the weight to the sealing part. The peeling force was applied to the film, and the peeling length of the sealed portion was measured (width 15B of the film sample).

Claims (1)

[Claims] 90 to 50% by weight of an ethylene-α-olefin copolymer with a density of 0.900 to 0.940 g/cm^3, a melt index of 1 to 25 g/10 minutes, and a weight average molecular weight (@M
@w) and number average molecular weight (@M@n) ratio @M@w/@M
A low-density polyethylene resin consisting of 10-50% by weight of high-pressure low-density polyethylene in which @n is 4 to 15, the weight average molecular weight is 50,000 to 300,000, and the fraction of molecular weight of 50,000 or more is 5 to 24% by weight. Composition.