JP3207213B2 - Ethylene copolymer for lamination with improved adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ethylene copolymer for laminating, and more specifically to aluminum foil, biaxially oriented polypropylene film (OPP), paper, polyethylene terephthalate (PET) and ethylene-vinyl acetate copolymer. The present invention relates to an ethylene copolymer which is extruded and lamination-molded onto a substrate such as a combined saponified product (EVOH) film and imparts heat sealability to the substrate. The present invention enables efficient lamination molding by providing a copolymer of ethylene and propylene having a specific composition obtained by a high-pressure radical polymerization method.

[0002]

2. Description of the Related Art Aluminum foil, paper, OPP, PET and EVOH
Despite having many useful properties such as gas barrier properties, transparency, heat resistance and mechanical properties, they usually do not have heat sealing properties themselves, so they can be used alone as food packaging materials, beverage packaging materials, etc. Is difficult to use. For this reason, a packaging material obtained by laminating an ethylene polymer having heat sealing properties by a molding method such as extrusion lamination has been used as such a packaging material.

[0003] However, since ethylene polymers generally do not contain a polar functional group, they have low affinity with the above-mentioned base material and show little adhesion to them. Therefore, in order to enhance the adhesion between the ethylene polymer and the base material, the molding temperature during extrusion lamination molding is maintained at 320 ° C. or higher to oxidatively modify the surface of the ethylene polymer,
It is common practice to introduce polar groups such as carbonyl groups, aldehyde groups and / or carboxyl groups into ethylene-based polymer molecules. That is, by increasing the extrusion temperature, or increasing the distance from the die to the cooling roll (air gap) or increasing the passage time of the air gap, the polar group content in the ethylene-based polymer is increased, Adhesion between the ethylene polymer and the substrate can be improved.

However, in extrusion lamination molding, the higher the molding temperature is, the more smoke and bad odors are generated, and the heat sealing strength is lowered. On the other hand, if the air gap is made longer, the neck-in becomes larger, and if the passage time of the air gap is made longer, the molding speed is lowered, which is not preferable in industrial production.

[0005]

As described above, in particular,
Prior art extrusion lamination molding at high temperatures has room for improvement because of the generation of smoke and odors, and reduced strength (eg, heat seal strength and adhesive strength over time). In view of these circumstances, an object of the present invention is to provide an ethylene-based polymer having sufficient adhesiveness to a substrate, capable of performing lamination molding at a high speed without the above-described disadvantages during extrusion lamination molding. To provide.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on the above problems, and as a result, obtained by a high-pressure radical polymerization method, the number of methyl branches is determined by the number of carbon atoms in a polymer chain.
A copolymer of ethylene and propylene having 3.5 or more per 1,000 pieces can be mixed with the substrate at a molding temperature 10 to 20 ° C lower than the extrusion temperature (usually 320 ° C or more) conventionally used in extrusion lamination molding. The present inventors have found that they have sufficient adhesiveness and can solve the above-mentioned problems, and have completed the present invention.

That is, the present invention relates to a copolymer of ethylene and propylene obtained by a high-pressure radical polymerization method,
The number of methyl branches is 3.000 per 1000 carbon atoms in the polymer chain.
5 or more, melt flow rate (MFR) 1-20g
/ 10 min and the long chain branching index is 0.3-0.3.
By providing an ethylene-based copolymer for extrusion lamination characterized by being within the range of 9, the disadvantages associated with the prior art can be improved.

Hereinafter, the present invention will be described specifically. The present invention provides a copolymer of ethylene and propylene obtained by a high-pressure radical polymerization method. Such polymerization methods are known per se in the art, and various copolymers are commercially available, but since propylene, which is usually used as a comonomer, has a large chain transfer effect, methyl branch is introduced into the polymer chain by copolymerization. It is not intended to do so, but rather to adjust the molecular weight to achieve a given MFR or density. On the other hand, the present invention is characterized in that a certain amount or more of methyl branch is positively supported in the polymer chain.

Accordingly, the ethylene / propylene copolymer of the present invention is a copolymer obtained by a high-pressure radical polymerization method and having 3.5 or more methyl branches per 1,000 carbon atoms in the polymer chain. is there. As used herein, the “number of carbon atoms in the polymer chain” refers to the number of carbon atoms in the polymer main chain and long-chain branched chain. The number of methyl branches per carbon atom is a value measured by ¹³ C-NMR.
In general, when the number of methyl branches is less than 3.5, the adhesion to the substrate surface is insufficient, whereas when it is introduced in excess of 10, it is substantially difficult to produce the same under general production conditions. Therefore, from 3.5 to 10 per 1000 carbon atoms,
Preferably, the number is 4 to 8.

The melt flow rate (MFR) of the copolymer of the present invention is a value measured according to a method (JIS K6760) standardized as a flow test of a general thermoplastic resin, and is 1 to 20 g. Within the range of / 10 minutes. Usually, MFR is 1
If the extrusion lamination temperature is less than 320 ° C
In the following, there is a problem in the moldability. On the other hand, when the MFR exceeds 20, both the neck-in property and the heat-sealing property are reduced, so that the usefulness is substantially reduced. In order to satisfy both of these characteristics, the MFR value is 3 to 15 g /
Those within the range of 10 minutes are preferred.

The density is not particularly limited as long as it can be obtained by a high-pressure radical polymerization method.
In consideration of drawdown properties and adhesiveness, it is preferable to select a copolymer within the range of 0.915 to 0.930. The long-chain branching index of the copolymer of the present invention is the intrinsic viscosity of the copolymer (η) b
And the intrinsic viscosity [η] 1 of a linear polyethylene having the same weight average molecular weight as the copolymer obtained by the light scattering method, expressed as g ′ = ([η] b / [η] 1). Value,
It is in the range of 0.3 to 0.9 (each intrinsic viscosity is a value measured at 130 ° C. using tetralin as a solvent).
If g 'is less than 0.3, the high-speed moldability is inferior, and if it exceeds 0.9, the neck-in tends to increase, so that g' is preferably in the range of 0.35 to 0.85.

Such a copolymer has the advantages of the present invention, that is, at an extrusion temperature of 295 to 320 ° C. for lamination molding, it does not cause generation of smoke and lowers the heat seal strength and has a relatively high speed. It can be inferred that tertiary hydrogen of methyl branching is easily dissociated at the above temperature in an atmosphere where oxygen is present, and thus a polar group such as a carbonyl group is easily formed at the above temperature in an atmosphere where oxygen is present. . High pressure radical polymers of ethylene include ethyl, butyl, amyl branches and long chain branches.
However, since the dissociation energy of hydrogen bonded to tertiary carbon to which a branch other than methyl is bonded is large, the temperature at which a polar group is formed by oxidation needs to be higher than that of a methyl group, and the effects of the present invention can be obtained. Can not.

[0013] Such copolymers, from commercially available starting materials ethylene and propylene, in per se known radical polymerization method
In, for example, the blending amount of propylene, the polymerization temperature,
That-out <br/> in it is prepared by appropriately adjusting the production conditions. The specific manufacturing conditions are obvious to those skilled in the art,
It may be appropriately optimized, for example, in the presence of a radical generator such as peroxide under a high pressure of 1000 to 3500 atmospheres, the amount of Puropuren ethylene and propylene of about 0.
It can be obtained by copolymerizing as 3 to 1.0% by volume .

The high-pressure-process polyethylene thus produced generally has a considerable proportion of short-chain branches such as the above-mentioned ethyl group, butyl group and amyl group in addition to the methyl group, and thus has a low melting point and low-temperature heat sealability. Excellent. In addition, since it has long-chain branching, it also has a characteristic of small neck-in, which is an important characteristic in extrusion lamination molding. Further, since it has excellent heat stability, it can be widely used in the field of packaging of foods, beverages and the like.

The copolymer of ethylene and propylene of the present invention is particularly suitable for a processing method in which the molten resin is extruded from a T-die and laminated on a substrate, that is, a so-called extrusion lamination molding method.

[0016]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the scope of the present invention is not limited thereto.

Method for Evaluating Polymer The method for evaluating the copolymer or molded article described in the present specification is as follows. (Smoke index) When a polymer is extruded from a T-die at a screw rotation speed of 50 rpm with a laminating extruder (T-die width: 750 mm) having a diameter of 90 mm (L / D = 29), the generated smoke is guided to a digital dust meter. ,
The amount of dust was measured. The dust meter reading at this time was taken as the smoke index. (Degree of Surface Oxidation) The infrared absorption spectrum of the sample was measured on the laminated surface of the extruded laminate molded product by a multiple reflection surface infrared method using a Fourier transform infrared spectrophotometer. Measurement is KRS
The measurement was performed at a reflection angle of 45 ° using a -5 crystal plate. In this way, the ratio A ₁₇₂₀ / A ₁₃₇₀ in absorbance absorbance and 1370 cm ^-1 in the infrared spectrum obtained in the 1720 cm ^-1 was surface oxidation degree. (Adhesive strength) The extruded laminate molded product was cut out to a width of 15 mm, and the peeling force between the substrate and the lami film was defined as the adhesive strength. The measurement was carried out with a universal tensile tester manufactured by Orientec Co., Ltd. at a pulling speed of 300 mm / min and 180-degree peeling. (Neck-in) During extrusion lamination, the amount of decrease in lami film width expressed as the sum of both sides under the conditions of a T-die width of 750 mm, a screw rotation speed of 80 rpm, and a molding speed of 130 m / min was defined as a neck-in. Example 1 Using a 2 L autoclave with a stirrer, at 1900 atm and an average polymerization temperature of 225 ° C., a radical polymerization initiator and ethylene monomer and propylene were fed in a propylene feed.
By feeding continuously at 65 vol%, a copolymer of ethylene and propylene was obtained. The MFR of the obtained copolymer is 8.2,
The density was 0.923 (JIS K6760). ^The number of methyl branches determined by ¹³ C-NMR was calculated per 1000 carbon atoms in the polymer chain.
6.3 and g 'was 0.55. This copolymer was obtained using a Sumitomo Heavy Industries laminating machine model 90 model 310
Air gap 120mm on aluminum foil at ℃, forming speed
Molded at 150 m / min. The smoke index at this time is 1460 c /
Minutes. The surface oxidation degree of the film is 0.28,
The adhesive strength was 210 g / 15 mm after 180-degree peeling.
The results are summarized in Table 1.

Comparative Example 1 The average polymerization temperature was 200 ° C., and only ethylene was fed.
Polymerization was carried out in the same manner as in Example 1 to obtain a polyethylene containing no methyl branch . The results of molding this polyethylene under the same conditions as in Example 1 are shown in Table 1 below.

Example 2 Using the same autoclave as in Example 1, at 2,000 atm, a radical polymerization initiator, ethylene and propylene were converted to propylene.
The feed was continuously fed at a feed rate of 0.70 vol%, and polymerized at 200 ° C. to obtain an ethylene-propylene copolymer. The MFR of the obtained copolymer was 3.5 and the density was 0.924. ¹³ C-
The number of methyl branches determined by NMR was 7.0 per 1000 carbon atoms in the polymer chain. G 'of this is 0.71
Met.

The copolymer was extrusion-laminated on paper at 300 ° C. using the same laminator as in Example 1. The molding at this time is air gap: 120mm, molding speed: 2
It was performed at 00 m / min. The thickness of the laminate was 20μ.
The neck-in was 50mm. This film had a surface oxidation degree of 0.21 and an adhesive strength of 180 g / 15 mm or more after peeling at 180 degrees, breaking the paper layer. The results are summarized in Table 1 below.

Example 3 By repeating the same polymerization method as in Example 2, a copolymer having the physical properties shown in Table 1 below was obtained. Example 2 was repeated under the conditions shown in Table 1 below. The results are shown in Table 1 together with the above conditions.

Comparative Examples 2 to 4 Polyethylene containing no methyl branch was prepared according to Example 2.
It was molded under the conditions shown in Table 1. The results are summarized in Table 1 below.

[0023]

[Table 1]

[0024]

Industrial Applicability The present invention provides a copolymer of ethylene and propylene which enables molding at a relatively high speed without producing smoke and offensive odor during extrusion lamination molding and has improved adhesive strength. provide. Such properties can be achieved by incorporating a certain amount or more of methyl branches into the polymer.

Continuation of the front page (72) Inventor Hiroshi Kasahara 3-2 Chidori-cho, Kawasaki-ku, Kawasaki-city, Kanagawa Prefecture Inside the Kawasaki Resin Research Laboratory (72) Inventor Shuichi Tanaka 3-2 Akira Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Takaya Tabira, Inventor Takaya Tabira 3-2 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Electric Power Company Kawasaki-resin Research Institute (56) References JP 50-5027987 (JP, A JP-A-59-219350 (JP, A) JP-A-59-219351 (JP, A) JP-A-60-36548 (JP, A) JP-A-60-36549 (JP, A) JP-A 60-36549 123544 (JP, A) JP 60-51486 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 210/00-210/18

Claims (1)

(57) [Claims] 1. A copolymer of ethylene and propylene obtained by a high-pressure radical polymerization method, wherein the number of methyl branches is 3.5 or more per 1000 carbon atoms in a polymer chain, and the melt flow rate is An ethylene copolymer for extrusion lamination, characterized in that (MFR) is in the range of 1 to 20 g / 10 minutes and the long-chain branching index is in the range of 0.3 to 0.9.