JPS592456B2 - Resin composition for extrusion lamination - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin composition for extrusion laminates consisting of a mixture of low-density polyethylene mainly composed of polypropylene and polypropylene.

Traditionally, extrusion lamination has been used to create superior packaging materials by imparting properties such as moisture resistance, oil resistance, abrasion resistance, gas barrier properties, and heat sealability to base materials such as cellophane, paper, aluminum foil, cloth, and plastic films. It has been widely used as a method of providing However, extrusion lamination is used because molten resin is discharged from an extruder onto a moving base material, crimped between nip rolls, stretched to a high magnification in the narrow space between the die tip and the nip roll, and taken off at high speed. The resin is low-density polyethylene with excellent drawdown properties.
It was limited to resins such as ethylene-vinyl acetate copolymer and ionomer. On the other hand, polypropylene has the advantage of being superior to polyethylene in heat resistance, oil resistance, moisture resistance, gas barrier properties, transparency, etc., and is also strong and easy to process.

Therefore, by laminating this polypropylene onto a transparent film base material such as biaxially oriented polypropylene or cellophane, a laminated product with strong heat seal strength can be obtained without impairing the transparency of the base material. Polypropylene is attracting attention as a material for extrusion laminates. However, polypropylene has poor drawdown properties, and when extruded and laminated at high speeds of 30 m/mm or higher, surge fern occurs, making it impossible to laminate a uniform thin film. If polypropylene with a sufficiently large melt index is used, it is possible to extrude laminate at a speed high enough for industrial use, but it is still not practical due to the new drawback that the resulting laminate does not have sufficient mechanical strength. has not been standardized. Furthermore, if polypropylene with a small melt indentation is used, a laminate product with excellent mechanical strength, heat sealability, transparency, etc. can be obtained, but it has the disadvantage of poor high-speed processability. In this way, polypropylene alone has high-speed processability, mechanical strength,
It has not been possible to obtain a laminate product that satisfies both heat sealability and transparency. As a method for improving the lamination processability of polypropylene as described above, a method of adding low-density polyethylene to polypropylene has been proposed, for example, in Japanese Patent Publication No. 45-33298 and Japanese Patent Publication No. 47-47-
This method has been proposed in Publication No. 30614 and the like.

These methods provide laminate products that have excellent high-speed processability, good mechanical strength, heat sealability, transparency, etc. However, even in this case, if polypropylene with a low melt index of 0.5 to 30 y/10 min is used, satisfactory high-speed processability cannot be obtained.
As a result of extensive research into compositions that can be economically laminated at a sufficiently high speed even when polypropylene with a low melt index is used, the inventors of the present invention have surprisingly found that they can be laminated simply by melt-kneading in the presence of air. The present inventors have discovered that a composition modified by oxidative decomposition in a laminate has significantly improved drawdown properties, and that even when polypropylene with a low melt index is used, a laminating composition with excellent high-speed processability can be obtained. I was able to complete it.

That is, in the present invention, a mixture of polypropylene and low density polyethylene added in an amount of 5 to 15% by weight is melt-kneaded in the presence of an oxygen-containing gas, and the melt flow index ratio of the kneaded product is 9.0 to 12.5. This is a resin composition for extrusion lamination, which is mainly composed of polypropylene, which is characterized by being modified as described above. The melt flow index ratio described in the uninvention is expressed as the ratio of the melt index at 2160 load at 260° C. to the melt index at the same 325 t load. Generally, in processes such as kneading and granulation of polypropylene, contact with air is avoided and processing is carried out under an inert gas atmosphere in order to prevent oxidative decomposition of the polypropylene and to prevent quality loss.

However, in the present invention, melt-kneading the mixture of polypropylene and low-density polyethylene in the presence of an oxygen-containing gas such as air to oxidize and decompose it is extremely effective in significantly improving the high-speed processability of extrusion laminate. is important.
Although the mechanism by which the resin composition according to the present invention improves high-speed processability when used for extrusion lamination is not clear, a remarkable change in the flow behavior of the composition is observed, and the dependence of viscosity on shear stress is small.

For example, when expressed as a melt flow index ratio, this value becomes smaller due to oxidative decomposition. The melt flow index ratio of commercially available polypropylene is usually in the range of 13 to 15, and even if low density polyethylene is added thereto within the range of the present invention, the melt flow index ratio will not fall below the above range. However, when a polypropylene/low-density polyethylene mixture is oxidatively decomposed to lower its molecular weight, the melt flow index ratio decreases, and by controlling the decomposition, it is possible to obtain a composition with an arbitrary melt flow index ratio of 8 to 13. I can do it. High speed processability when laminating polypropylene-based compositions improves as the melt flow index ratio decreases. Therefore, even if polypropylene with a low melt index is used, by oxidatively decomposing it and adjusting the melt flow index ratio within an appropriate range, it is possible to easily obtain high-speed processability that was previously unattainable. . In the present invention, the melt flow index ratio of the composition is 9.0 to 12.5, preferably 10 to 12.
It is necessary to oxidize and decompose and denature so that it becomes within the range of
If the melt flow index ratio is 12.5 or more, economically sufficient high-speed processability cannot be obtained, and in order to obtain a composition with a melt flow index ratio of 9.0 or less, it is necessary to carry out quite severe oxidative decomposition, and it is necessary to control the oxidative decomposition. is difficult. In the present invention, a mixture of polypropylene and low-density polyethylene is kneaded in the presence of an oxygen-containing gas to cause oxidative decomposition. Specifically, an extruder or kneader is used to blow air into the material input port or vent. Therefore, it is easily done.

Oxidative decomposition can be easily controlled by adjusting the operating conditions of the extruder, such as the air concentration, resin temperature, and residence time. For example, to adjust the air amount concentration, it is preferable to blow air together with nitrogen gas into a portion of the hopper of the extruder to a desired concentration because it is simple. Methods for decomposing a mixture of polypropylene and polyethylene include, in addition to oxidative decomposition using air, adding decomposition aids such as organic peroxides, thermal decomposition, and mechanical molecular cutting. This method not only makes it difficult to control decomposition, but also has the drawback that the resulting composition undergoes abnormally accelerated decomposition during lamination, making it impossible to obtain a good laminate.

Further, in the method of thermal decomposition, the required degree of decomposition cannot be obtained unless the temperature is higher than the usual kneading temperature, and furthermore, in the method of mechanically cutting the molecules, the necessary degree of decomposition cannot be obtained with ordinary kneading equipment. By kneading and oxidizing decomposition in the presence of air as in the present invention, the desired composition can be obtained very easily. The polypropylene used in the present invention is not limited in any way and commercially available polypropylene can be used.
It is meaningful to use as much as possible.

In the present invention, polypropylene is a general term that includes not only propylene homopolymers but also random copolymers or block copolymers with other olefin monomers such as ethylene and butene. The low density polyethylene used in the present invention generally has a density of 0.930 or less and a melt index of 2 to 157/10. However, in order to reduce the melt flow index ratio of the composition of the present invention, it is preferable to use a low density polyethylene having a melt flow index ratio of 8 to 13. If the density of polyethylene is 0.930 or more, high-speed processability necessary for extrusion lamination cannot be obtained. In addition, if the melt index of polyethylene is 2 or less, the effect of improving the high-speed processability of polypropylene is small, and if the melt index is 15 or more, small pinholes will occur in the laminate product during high-speed processing, making it impossible to obtain a good product, so it is preferable. do not have. The amount of low density polyethylene added to polypropylene in the composition of the present invention is 5 to 15% by weight.
, preferably 7 to 12% by weight; if the amount added is less than the above range, practically satisfactory high-speed processability cannot be obtained, and if it is more than the above range, the transparency, heat sealability, and mechanical properties that are characteristic of polypropylene may be impaired. This is not preferable because the target strength decreases. In the present invention, in addition to the two components of polypropylene and low density polyethylene, an ethylene-α-olefin copolymer can be further added. The addition of the ethylene-α-olefin copolymer improves the compatibility between polypropylene and low-density polyethylene, resulting in a laminate with good transparency when laminated on a transparent substrate such as biaxially oriented polypropylene or cellophane. can get.
The ethylene-α-olefin copolymer used in the present invention is a general term for copolymers of ethylene and α-olefin, such as ethylene-propylene copolymers containing 50 to 90% by weight of ethylene, and ethylene-butene-1 copolymers. In general, the melt index is 2 to 30y/10 min, and if the amount added is less than 1% by weight, the effect is not significant, and if the amount added is 10% by weight or more, even if the amount added is increased, the effect is not significant. It is not preferred for economic reasons because it is not effective. In the present invention, a mixture consisting of polypropylene and low-density polyethylene, or a mixture in which an ethylene-α-olefin copolymer is added, is further added with an antioxidant, a lubricant, an antiblocking agent, an antistatic agent, a crystal nucleating agent, and an ultraviolet ray. Absorbents and the like can be mixed within the range that does not impede the purpose of the heather invention.

Also, the properties of the composition, such as transparency, heat sealability,
Terpene resins, petroleum resins such as rosin, etc. can also be added for the purpose of improving the appearance of the film. In the present invention, a resin composition for extrusion lamination mainly composed of polypropylene, which has excellent high-speed processability, is obtained, and a composite film laminated with this composition has good transparency, mechanical properties,
Since it has excellent heat sealability, it can be applied not only to light packaging but also to heavy packaging.

In addition, in this specification, the melt index is based on ASTM
230' for polypropylene according to D-1238
C, low density polyethylene and ethylene-α-olefin copolymer were measured at 190°C.

The present invention will be described below with reference to Examples, but the present invention is not limited thereto.

In the examples, M is the melt index and MFI
R is an abbreviation for melt flow index ratio.

Further, the haze was measured using a haze meter (manufactured by Toyo Sokki Co., Ltd.) in accordance with JlSK67l4. Example
1 Low density polyethylene (density 0.9247/CT!T) in crystalline ethylene-propylene random copolymer (ethylene content 2.0 weight percent, Ml2O.Oy/10 min)
．． ．． A mixture to which 12% by weight of Ml3.27/10 min) was added was completely replaced with nitrogen gas in a portion of the hopper of the extruder, and a mixture of nitrogen gas and air was further blown in so that the oxygen concentration was 5%. Ml
A composition of 24.6 and MFIRl of 2.3 was obtained.

The composition was applied onto a biaxially stretched polypropylene film substrate using a laminator with a die temperature of 270°C.
When laminated with a thickness of 0μ, it is 150m/Mi! l
We were able to perform laminate molding at the above speed. Comparative Example 1 The same polypropylene/low-density polyethylene mixture as in Example 1 was supplied to the hopper of an extruder while completely purging a portion of the hopper with nitrogen and blowing nitrogen gas, and was heated in a twin-screw extruder set at 240°C. When melt-kneaded in the same manner as in Example 1, a composition with MIl 9.7 and MFIRl 3.5 was obtained.

As a result of laminating the composition in the same manner as in Example 1,
At a lamination speed of 50 m/Mm or more, surging occurred and a uneven laminated film could not be obtained. Comparative Example 2 Crystalline ethylene-propylene random copolymer:
1. '． --; Intimidation゜Yugogami 1.・Nobuy/C77i, M3.
When a mixture containing 12% by weight of 29/10 min) was kneaded in the same manner as in Comparative Example 1, the Ml was 25. ly/10
A composition of MFIR13,3 was obtained.

As a result of laminating the composition in the same manner as in Example 1,
At a lamination speed of 60 m/- or more, surging occurred and a good laminated film could not be obtained. Example 2 Low density polyethylene (density 0,9247/CTil) was added to crystalline ethylene-propylene random copolymer (ethylene content 2.0 weight percent MI8.
, MI3.2y/10 minutes) was added in a twin-screw extruder set at 260°C while blowing a mixed gas of nitrogen gas and air into a part of the extruder hopper so that the oxygen concentration was 10%. When melted and kneaded with
10 minutes, MFIRll. 4 compositions were obtained.

As a result of laminating the composition in the same manner as in Example 1,
Laminate molding was possible at a speed of 150 m/m. Example 3 Crystalline polypropylene (MIO.6'I7/1
0 minutes) to low density polyethylene (density 0.924V/~,
A mixture containing 12% by weight of MI3.2y/10min) was added to the extruder hopper for 2 hours while blowing air into a portion of the extruder hopper.
When kneaded at 260°C with a screw extruder, Mll3.3, M
FIRIO. A composition of No. 5 was obtained.

As a result of laminating the composition in the same manner as in Example 1,
Laminate molding was possible at a speed of 150 m/- or more. Examples 4, 5, 6 Crystalline ethylene-propylene copolymer (ethylene content 2.0 weight percent, Ml 8.O 7/10 min) in Table 1
12 weight percent of the low density polyethylene described in Example 2 was added and kneaded under the same conditions as in Example 2, and the resulting composition was laminated.

In all cases, lamination molding was possible at a speed of 150 m/m or more. Examples 7 and 8 Low density polyethylene (density 0.9247/Cril, Ml3
．． 2y/10 min) were added to 8% by weight and 15% by weight and kneaded under the same conditions as in Example 2, and Ml2
l. O7/10 minutes, MFIRIO. 7 composition and M
l8. O7/10 minutes, MFIRll. A composition No. 8 was obtained.

Each of the obtained compositions was laminated and molded. As a result, it was possible to perform lamination molding at a speed of 150 m/Mm or more in all cases. Comparative Examples 3, 4 Low density polyethylene (density 0.9247/CTit, M3.
2y/10 minutes) were added in an amount of 4% by weight and 20% by weight and kneaded under the same conditions as in Example 2 to obtain Mll9.
．． 87/10 minutes, MFlRlO. Composition of 5 and MI
l7.27/10 minutes, MFIRl2. A composition of 1 was obtained.

Each of the obtained compositions was laminated and molded. As a result, when the amount of low density polyethylene added was 4% by weight, surging occurred at a lamination speed of 40 m/m or higher, and a good laminated film could not be obtained. Further, when the amount of low density polyethylene added was 20% by weight, cracks appeared in the longitudinal direction near the center of the laminate layer at a lamination speed of 150 m/Mm, and a good laminate film could not be obtained. Example 9 Low density polyethylene (density 0.9247/~, M3.27/10 minutes) was added to crystalline ethylene-propylene copolymer (ethylene content 2.0 weight percent, Ml 8.0y/10 min).
10 minutes) to 9 weight percent ethylene-propylene random copolymer (ethylene content 75 weight percent, M
l4. A composition obtained by adding 3% by weight of O) and kneading under the same conditions as in Example 2 (Mll7.Oy/1
0 minutes, MFIRll. 7) was laminated and molded.

As a result, molding was possible at a lamination speed of 150 m/Mm or more. 100 on the base material of biaxially stretched polypropylene film
m/Mi! The haze of the laminate film formed by lamination at a speed of 8.3% was 8.3%.

When the ethylene-propylene random copolymer was not added, it was 9.1%. Example 10 Low density polyethylene (density 0.924y/CTII, MI3
．． 27/10 minutes) and 3 percent by weight of ethylene-butene-1 random copolymer (ethylene content 75 weight percent, MI2O7/10 minutes) were added and kneaded under the same conditions as in Example 2. Composition (
Mll8.37/10 minutes, MFIRll. 5) was laminated and molded.

Molding was possible at a lamination speed of 150 m/Ttil or higher.

The haze of the laminate film formed by lamination at a speed of 100 m/Mm was 7.9%.

Comparative Example 5 Crystalline ethylene-propylene random copolymer (ethylene content 2.0 weight percent, Ml8.O
f7/10 min) and low density polyethylene (density 0.924
A mixture of 30.05 weight percent of 2.5-dimethyl, 2.5-di(tertiarybutylperoxy)hexyne and 12 weight percent of 2.5-dimethyl, 2.5-di(tertiarybutylperoxy)hexyne (Y/~, Ml3, 27/10 min) was added to one part of the hopper of the extruder. Flow nitrogen gas into the
After completely purging the air and supplying it to the hopper of an extruder while blowing nitrogen gas, it was kneaded in a twin-screw extruder set at 210°C to give a MIL of 9.9MFIRll. A composition No. 6 was obtained.

The composition could be laminated at speeds of 150 m/m or more. However, the Ml of the composition after molding is 50
．． It rose to 8. On the other hand, the M after molding of the compositions obtained in Example 1 and Example 2 was 28.57/10 min and 2, respectively.
The molding time was 2.3 y/10 min, and the increase in MI due to molding was slight.

Claims (1)

[Claims] 1. A mixture of polypropylene and low density polyethylene added in an amount of 5 to 15% by weight is melt-kneaded in the presence of an oxygen-containing gas, and the melt flow index ratio of the kneaded product is 9.0.
A resin composition for extrusion laminates, the main component of which is polypropylene, characterized in that it has been modified so that the polypropylene has a molecular weight of 12.5. 2 Polypropylene with 5 to 15% by weight of low density polyethylene and 1 to 1% of ethylene-α-olefin copolymer
The mixture containing 0% by weight was melt-kneaded in the presence of oxygen-containing gas, and the melt flow index ratio of the kneaded product was 9.
．． 1. A resin composition for extrusion lamination, the main component of which is polypropylene, characterized in that it has been modified to have a molecular weight of 0 to 12.5. 3 Melt index of polypropylene is 0.5 to 3
The composition according to claim 1 or 2, which has a rate of 0 g/10 minutes. 4. The composition according to claim 1 or 2, wherein the oxygen-containing gas is air.