JPH11192661A - Manufacture of inflation film and film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a inflation film and its manufacturing method excellent in low odor characteristics, low taste migration, heat stability, and mechanical properties. SOLUTION: An inflation film is manufactured by an ion polymerization method. A density is 0.89-0.96 g/cm<3> , and a melting viscosity η* [170] is from 0.001×10<4> to 3.5×10<4> poise at 170 deg.C and at a shear rate of 100 rad/sec. An ethylenic polymer or a resin composition containing the ethylenic polymer having a weight ratio (a) (wt.%) of a soluble matter of a cold xylene satisfying an expression: a <4.8×10<4> ×(0.95-d)<3> -+10<6> ×(0.95-d)<4> +0.5, where (a) represents the weight ratio (wt.%) of the cold xylene-soluble portion, and (d) represents a density (g/cm<2> ) of the ethylenic polymer, is processed in a die gap at a melting temperature of 170 deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an inflation film by processing a specific ethylene polymer or a resin composition containing the ethylene polymer at a low temperature, an inflation film and a multilayer inflation film.

[0002]

2. Description of the Related Art Ethylene polymers are widely used in packaging materials. Such an ethylene polymer is required to have mechanical properties such as rigidity and impact strength. As a method for improving the strength of a packaging film by an inflation method, for example, a technique of processing at a temperature lower than a normal inflation processing temperature using a specific die gap is disclosed (Japanese Patent Publication No. 6-9863, Japanese Patent Publication No. Fairness 6-9
864).

[0003] However, this technique is not preferable because processing at a low melting temperature involves an increase in the viscosity of the resin, resulting in an increase in the load on the processing machine and an increase in power consumption. In order to reduce the melt viscosity of the resin and obtain good processability, it is disclosed that the molecular weight of the resin is reduced to improve the flowability. In the case of high-density polyethylene, the strength of the resulting film is significantly reduced due to the decrease in molecular weight, and it cannot be said that the mechanical strength has reached a practically satisfactory level.

In recent years, an ethylene polymer having a small proportion by weight of a cold xylene-soluble portion, for example, a catalyst containing a transition metal compound having a group having a cyclopentadiene-type anion skeleton, that is, ethylene produced by a metallocene polymerization catalyst It is known that a system polymer exhibits excellent mechanical properties. However, ethylene polymers produced with such metallocene-based polymerization catalysts generally have high torque during processing and are susceptible to shearing heat, and therefore have problems such as generation of fish eyes during film forming processing due to poor thermal stability. Have a point.

On the other hand, food packaging materials in which ethylene polymers are often used are required to have high quality such as low odor and low taste.

However, it is difficult to say that a film obtained by molding an existing ethylene polymer by a conventional processing method has a sufficient level of odor and taste. In general, the odor of packaging films manufactured using ethylene polymers and the taste of foods that migrate to foods are often caused by the fact that when ethylene is formed by inflation molding, the molten ethylene polymers are air-oxidized and thermally decomposed. It is thought that this will occur. Further, as one of the causes of the deterioration of odor and taste, additives to the ethylene-based polymer such as an antioxidant and a lubricant are also mentioned. These additives are added for the purpose of preventing fish eyes generated in the film at the time of processing and blocking of the film and the like, and in the conventional technology, the addition was essential.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inflation film excellent in low odor, low taste transferability, heat stability and mechanical properties, and a method for producing the same.

[0008]

Means for Solving the Problems The present inventors have made intensive studies on a method for producing an inflation film by processing an ethylene-based polymer or a resin composition containing the ethylene-based polymer. The present inventors have found that a method for processing a specific ethylene polymer or a resin composition containing the ethylene polymer at a melting temperature of 170 ° C. or less at a die gap and a film thereof achieve the object of the present invention, It was completed.

That is, the present invention is produced by an ionic polymerization method and has a density of 0.89 to 0.96 g / cm ³ , 170
° C, melt viscosity η at a shear rate of 100 rad / sec
* [170] is 0.001 × 10 ^{4 to} 3.5 × 10 ⁴ poi
and an ethylene polymer or a resin composition containing the ethylene polymer having a weight ratio a (% by weight) of the cold xylene-soluble portion satisfying the following formula (1) is 170 ° C. or less at a die gap. A method for producing an inflation film, characterized by processing at a melting temperature of a <4.8 × 10 ⁴ × (0.95-d) ³ +10 ⁶ × (0.95-d) ⁴ +0.5 Formula (1) (In the above formula (1), a is the ethylene polymer cold xylene. The weight ratio of the soluble part (% by weight) and d is the density of the ethylene polymer (g / cm ³ ).) The present invention relates to a blown film obtained by the above-mentioned production method. is there. Furthermore, a multilayer blown film comprising at least one layer of the blown film obtained by the above-mentioned production method. Hereinafter, the present invention will be described in detail.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ethylene polymer used in the present invention is produced by an ionic polymerization method and has a density of 0.89.
０．９0.96 g / cm ³ , 170 ° C., shear rate 100 rad /
Melt viscosity η * [170] in sec is 0.001 × 1
0 ⁴ a to 3.5 × 10 ⁴ poise, and the weight ratio a (% by weight) of cold xylene-soluble portion is an ethylene-based polymer satisfying the following formula (1). a <4.8 × 10 ⁴ × (0.95-d) ³ +10 ⁶ × (0.95-d) ⁴ +0.5 Formula (1) (In the above formula (1), a is the ethylene polymer cold xylene. The weight ratio of the soluble part (% by weight) and d is the density (g / cm ³ ) of the ethylene polymer.)

The ethylene polymer used in the present invention is:
Ethylene homopolymer produced by an ionic polymerization method,
It is a copolymer of ethylene and at least one α-olefin having 3 to 20 carbon atoms or a diolefin having 4 to 20 carbon atoms. Other than the ethylene homopolymer, for example, an ethylene-α-olefin copolymer, an ethylene-diolefin copolymer, and an ethylene-α-olefin-diolefin copolymer can be mentioned. Examples of the copolymer component used in the present invention include propylene, butene-
1, pentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, hexadecene
1, eicosene-1,4-methyl-pentene-1,4-
Methyl-hexene-1, vinylcyclohexane, vinylcyclohexene, styrene, norbornene, butadiene, 1,5-hexadiene, isoprene and the like. The content of the copolymer component is usually 0.05 to 50% by weight.
It is.

The ionic polymerization method in the present invention is a polymerization method including so-called coordination polymerization, anionic polymerization or cationic polymerization, and excludes radical polymerization. Therefore, the ethylene polymer referred to in the present invention is a low-density polyethylene (high-pressure LDP) produced by a high-pressure radical polymerization method.
E) and ethylene-vinyl acetate copolymer are excluded. The high-pressure LDPE produced by the high-pressure radical polymerization method is not preferable because the strength is low even when the production method of the present invention is applied. Coordination polymerization is preferred as the ionic polymerization method.
As the metal component contained in the catalyst used for coordination polymerization, for example, titanium, zirconium, hafnium, vanadium,
Chromium, nickel, palladium or lanthanide series transition metals are mentioned.

The ethylene polymer used in the present invention is:
A catalyst produced in the presence of a catalyst containing the transition metal, particularly a catalyst containing a transition metal compound having a group having a cyclopentadiene-type anion skeleton is preferable. The transition metal compound is a so-called metallocene-based compound and usually has a general formula MLaXn-a (where M is a transition metal atom belonging to Group 4 of the periodic table of elements or a lanthanide series. L is a cyclopentadiene-type anion) A group having a skeleton or a group containing a hetero atom, at least one of which is a group having a cyclopentadiene-type anion skeleton, a plurality of Ls may be cross-linked to each other, and X is a halogen atom, hydrogen or carbon number. A hydrocarbon group of 1 to 20. n represents the valence of a transition metal atom, a represents an integer satisfying 0 <a ≦ n.) And may be used alone or in combination of two or more.
Further, the catalyst may include an organoaluminum compound containing an alumoxane compound and / or an ionic compound such as trityl borate and anilinium borate, and / or an inorganic carrier such as SiO ₂ and Al ₂ O ₃ , Alternatively, a particulate carrier containing an organic polymer carrier such as an olefin polymer such as styrene may be used in combination.

The ethylene polymer used in the present invention is:
A density of 0.89 to 0.96 g / cm ³ , preferably 0.89
5 to 0.935 g / cm ³ , more preferably 0.895 to
0.930 g / cm ³ . If the density is less than 0.89 g / cm ³ , the bubble stability during molding of the blown film is not preferable because it is poor. If it is more than 0.96 g / cm ³ , the impact strength of the inflation film is undesirably reduced. The density in the present invention is defined by JIS
K6760-1981, measured by the method specified in K6760-1981.

The ethylene polymer used in the present invention has a melt viscosity η * [170] at 170 ° C. and a shear rate of 100 rad / sec of 0.001 × 10 ^{4 to} 3.5.
× 10 ⁴ poise, preferably 0.05 × 10 ⁴ to 2.
5 × 10 ⁴ poise, more preferably 0.1 × 10 ⁴
~ 2.0 × 10 ⁴ poise, most preferably 0.5 ×
It is 10 ^{4 to} 2.0 × 10 ⁴ poise. If the melt viscosity is larger than 3.5 × 10 ⁴ , the load on the processing machine increases, which is not preferable. If the melt viscosity is smaller than 0.001 × 10 ⁴ , the bubble stability at the time of forming the blown film is poor. Is not preferred because the impact strength is lowered.

In the present invention, 170 ° C., shear rate 100 r
The melt viscosity η * [170] in ad / sec refers to a value obtained by measuring under the following conditions. (1) Apparatus: Reometrics manufactured by Reometrics
ics Mechanical Spectromet
er RMS-800 (2) Geometry: parallel plate, diameter 25m
m, plate interval: 1.5 to 2 mm (3) Strain: 5% (4) Frequency: 100 rad / sec (5) Temperature: 170 ° C

Further, the ethylene-based polymer used in the present invention may be one wherein the weight ratio a (% by weight) of the cold xylene-soluble portion satisfies the formula (1), preferably satisfies the formula (2). Preferably, the formula (3) is satisfied. When the weight ratio a (% by weight) of the cold xylene-soluble portion does not satisfy the formula (1), the mechanical strength of the blown film is reduced, and the effect of reducing odor is not preferable. a <4.8 × 10 ⁴ × (0.95-d) ³ +10 ⁶ × (0.95-d) ⁴ +0.5 Equation (1) a <4.8 × 10 ⁴ × (0.95-d) ³ +10 ⁶ × (0.95-d) ⁴ +0.3 Equation (2) a <4.8 × 10 ⁴ × (0.95-d) ³ Equation (3) (In the above equation (1), a is the weight ratio (weight) of the cold xylene-soluble portion of the ethylene polymer. %) And d are the density (g / cm ³ ) of the ethylene-based polymer.) The cold xylene-soluble portion referred to in the present invention is the US code of fede
ral regulations, Food and Drugs Administration§
It is measured by the method specified in 175.1520.

The ethylene polymer used in the present invention may be a resin composition containing the ethylene polymer and various other resins as required. As other resins, for example, olefin resins such as high-pressure low-density polyethylene for the purpose of improving melt tension and transparency, high-density polyethylene for improving rigidity, and low-density elastomer for improving impact strength, and the like. These components can be used alone or in combination of two or more. The mixing ratio is at least 50% by weight, more preferably at least 70% by weight of the ethylene-based polymer.

The ethylene polymer or the resin composition containing the ethylene polymer used in the present invention is obtained by extruding a melt from an annular die, blowing a fixed volume of air into the inside, expanding the melt, and further expanding the melt from the outside. While cooling with air using a blower, take up the take-up winder at a constant take-up speed.
The film is formed by a so-called inflation processing method.

In the present invention, the ethylene polymer or the resin composition containing the ethylene polymer is not more than 170 ° C., preferably not more than 150 ° C., more preferably not more than 135 ° C., most preferably not more than 125 ° C. at a die gap. It is characterized by processing at the following melting temperature. If the melting temperature exceeds 170 ° C., the bubble stability during the formation of the blown film is poor, and the odor and taste of the blown film are undesirably deteriorated. The melting temperature at the die gap referred to in the present invention refers to the temperature of at least one point of the molten resin from a portion immediately before the entrance of the die to immediately after the exit of the die when the resin is extruded from the extruder. The lower limit of the melting temperature at the die gap is preferably higher than the solidification temperature of the ethylene polymer or the resin composition containing the ethylene polymer. The solidification temperature here means
A temperature at which a part of the melted ethylene polymer crystallizes, which depends on cooling conditions, shearing conditions, and the like. As an indicator of the solidification temperature, there is a maximum crystallization temperature. The maximum crystallization temperature is the differential scanning calorimeter DS manufactured by PerkinElmer.
Using a C-7 type apparatus, 10 mg of a sample is packed in an aluminum pan, kept at 150 ° C. for 2 minutes, and then cooled at a rate of 5 ° C./min to 40 ° C., which means the highest crystallization peak temperature. . The solidification temperature during the melt extrusion process is generally several degrees to several tens of degrees lower than the maximum crystallization temperature.

The ethylene polymer or the resin composition containing the ethylene polymer used in the present invention does not need to contain an antioxidant because of its low processing temperature. One or more antioxidants may be included. In the present invention, when an antioxidant is contained,
The content can be reduced with respect to the conventional content.
The odor and taste after processing the film are better as the content of the antioxidant is smaller, and the content of the antioxidant is preferably 0.5% by weight or less, more preferably 0.1% by weight or less, and still more preferably. Is 0.05% by weight or less. The antioxidant is preferably used in combination with a primary antioxidant having a phenol skeleton and a secondary antioxidant containing a phosphorus compound or the like.

The blown film produced in the present invention may be a single-layer blown film or a multilayer blown film including at least one layer obtained by a method for producing a blown film. When the production method of the present invention is applied to a multilayer blown film, it may be applied to the production of all layers or to the production of at least one layer in a multilayer film. When the production method of the present invention is applied to at least one layer in a multilayer film, it can be easily processed using a stack die or the like. When the production method of the present invention is applied to at least one of the multilayer films, it is preferably applied to the inner surface or outer surface layer, but may be applied to a layer inside the surface. Further, the single-layer or multilayer film thus produced may be used as a raw laminate for dry lamination on a substrate such as another polymer film.

[0023]

As described above, according to the present invention, it is possible to provide an inflation film excellent in low odor, low taste transferability, heat resistance and specifically excellent mechanical properties, and a method for producing the film. Further, since the present invention is processed at a low temperature, it is possible to provide a blown film and a method for producing the same, which use less or no antioxidant than conventionally used. Furthermore, the blown film of the present invention
Since it has the above excellent properties, it is suitable for packaging materials, especially food packaging materials.

[0024]

Next, the present invention will be described based on examples, but the present invention is not limited to these examples.

The evaluation method was as follows. (1) Melting Temperature at Die Gap The temperature of the molten resin at the exit of the die was measured with a thermocouple while extruding the ethylene-based polymer at the set processing temperature. (2) Odor A sample film (30 μm, 700 cm ² ) was placed in a 1-liter wide-mouthed glass bottle, heated in an oven at 80 ° C. for 1 hour, then cooled, and the odor was compared by a sensory test. With Comparative Example 6 as a blank, x was given when the odor was stronger than the blank, Δ was given when the odor was equivalent, Δ was given when the odor was weak, and 〇 was given when the odor was extremely weak. (3) Taste Sample film (30 μm, 1200 cm ² )
immersed in a 1 liter wide-mouthed glass bottle containing
For 1 hour in an oven and then cooled, and the taste was compared by sensory test. When Comparative Example 6 was used as a blank, the sample having a stronger taste than the blank was evaluated as ×, the equivalent sample as Δ, and the sample with weak taste as Δ. (4) Drop weight impact strength According to the method specified in ASTM D1709. (5) Current value The current value of the extruder required for extruding the molten resin was measured. A high value means that the extrusion load is high, and in the extruders used in Examples 1 to 3 and Comparative Examples 1 to 6,
Usually, it is preferably 50 A or less, and in the extruder used in Example 4 and Comparative Example 7, it is usually preferably 6 A or less. (6) Fish Eyes The number of fish eyes that can be visually confirmed was more than 5 per 200 cm ^{2, and the} number of fish eyes that were 5 or less was evaluated as ○ (Example 4, Comparative Example 7).

The metallocene catalyst of the ethylene polymer
Bei metallocene PE1: Nippon EVOLUE Co. vapor phase metallocene-based ethylene - SUMIKATHENE E FV402 hexene-1 copolymer (density = 0.915g / cm ^3, MI =
4 g / 10 min). Metallocene PE2: Sumikacene E FV403, a vapor-phase metallocene ethylene-hexene-1 copolymer manufactured by Evolu Japan (density = 0.919 g / cm ³ , MI =
4 g / 10 min). Metallocene PE3: Sumikacene E FV404 (density = 0.928 g / cm ³ , MI =) which is a vapor phase metallocene ethylene-hexene-1 copolymer manufactured by Evolue Japan
4 g / 10 min). Metallocene PE4: Methylalumoxane PMAO was allowed to act on toluene in silica particles calcined at 700 ° C., followed by bis (normal butylcyclopentadienyl) zirconium dichloride to obtain a solid catalyst component. Preliminary polymerization was performed by reacting ethylene with the solid catalyst component and triisobutylaluminum in butane to obtain a prepolymerized catalyst. This prepolymerization catalyst and triisobutylaluminum were allowed to act on a mixed gas of ethylene, butene-1 and hydrogen in a continuous fluidized bed gas phase polymerization apparatus to obtain an ethylene-butene-1 copolymer powder.

Ethylenic polymer of Ziegler-Natta catalyst
Preparation of Zigguranatta PE1: Neozex 3510 manufactured by Mitsui Petrochemical was used. Ziegler-Natta PE2: Porous styrene-divinylbenzene copolymer particles were treated with tetrabutoxytitanium and tetraethoxysilane in toluene, followed by butylmagnesium chloride to obtain a solid component. Furthermore, butyl ether and titanium tetrachloride were further allowed to act on the solid component obtained by allowing diisobutyl phthalate to act on the solid component in toluene to obtain a solid catalyst component. Preliminary polymerization was carried out by reacting ethylene with the solid catalyst component and triethylaluminum in butane to obtain a prepolymerized catalyst. This prepolymerization catalyst and triethylaluminum were allowed to act on a mixed gas of ethylene and hexene-1 in a continuous fluidized-bed gas-phase polymerization apparatus to obtain an ethylene-hexene-1 copolymer. The density of the ethylene-hexene-1 copolymer is adjusted by the concentration ratio of ethylene and hexene-1, and the molecular weight is adjusted by the concentration of hydrogen to be introduced.
Ethylene polymers of the Ziegler-Natta catalyst shown in Table 1 were obtained. The polymer thus obtained was applied to Irganox 1076 6 manufactured by Ciba Specialty Chemicals Co., Ltd.
20ppm, Ciba Specialty Chemicals Co., Ltd.
1000 ppm of Irgafos 168 and 1000 ppm of calcium stearate were added, melt-extruded, pelletized by water cooling and cutting. High pressure method Sumikasen L716H manufactured by Sumitomo Chemical Co., Ltd. manufactured by LDPE high pressure radical polymerization method was used.

Examples 1 to 3 and Comparative Examples 1 to 6 Inflation films were produced using the ethylene polymers shown in Table 1 and under the processing conditions shown in Table 1 and below. (1) Equipment: K-40R inflation machine manufactured by Placo (2) Set temperature: Table 1 shows the extrusion cylinder and die
Were set to the temperatures shown in the column of processing temperature. (3) Die: 125 mmφ, gap: 2 mm (4) Extrusion amount: 23 kg / hr (5) Film thickness: 30 μm (6) Blow-up ratio: 1.8 The results of evaluation of the obtained film are shown in Table 1. Show.

Example 4, Comparative Example 7 Using the ethylene polymer shown in Table 2, a blown film was produced under the processing conditions shown in Table 2 and below. (1) Apparatus: VS2 manufactured by Tanabe Plastics Machine Co., Ltd.
0 Inflation machine (2) Set temperature: Extrusion cylinder and die are shown in Table 2.
The temperature was set to the temperature shown in the column of set temperature. (3) Die: 30 mmφ, gap: 2 mm (4) Extrusion amount: 360 g / hr (5) Film thickness: 20 μm (6) Blow-up ratio: 1.8 The results of evaluating the obtained film are shown in Table 2. Show.

The following was found from the results of the examples and comparative examples. Melt viscosity η * [170] is 1.6 × 10 ⁴ poise, density 0.91
5 and the weight ratio of the cold xylene-soluble portion at 0.919 g / cm ³ 1.0
wt%, the weight percentage of the cold xylene-soluble portion at a density 0.928 g / cm ³ is
When a 0.8 wt% ethylene polymer is processed into a film at a processing temperature of 120 ° C. and 130 ° C. (Examples 1 to 3), there is no problem in the extrusion torque during the processing of the film, and the odor and taste are low and A film having an extremely high impact strength was obtained. On the other hand, when the same resin is processed at a temperature at which the melting temperature in the die gap exceeds 170 ° C. (Comparative Example 1,
2) The level of odor and taste deteriorated.

When a film is processed at a melting temperature of a die gap of 170 ° C. or more using an ethylene polymer polymerized with a Ziegler-Natta catalyst that does not satisfy the formula (1) (Comparative Example 3), odor and taste are poor. Thus, a film having low impact strength was obtained. When a film was processed at a melting temperature at a die gap of 170 ° C. or more using an ethylene-based polymer polymerized with a Ziegler-Natta catalyst in which the weight ratio of the cold xylene-soluble portion exceeded 8 wt% (Comparative Example 4), In addition, a film with poor taste and low impact strength was obtained. By increasing the molecular weight, some improvement in impact strength can be expected, but in this case, the load on the processing machine is further increased due to an increase in melt viscosity during processing, which is not preferable. High pressure LDPE that does not satisfy equation (1) is 170
When the film was processed at a melting temperature at a die gap of not less than ° C (Comparative Example 5), a film having poor odor and taste and low impact strength was obtained. When high-pressure LDPE was processed into a film at a processing temperature of 120 ° C. (Comparative Example 6), the odor and taste were partially improved, but the impact strength of the film was lower than that of Ziegler-Natta catalyst or metallocene-catalyzed polyethylene. Obtained.

Melt viscosity η * [170] is 2.5 × 10 ⁴ poise, density
An ethylene polymer having a weight ratio of 0.919 g / cm ³ and a cold xylene-soluble portion of 0.5 wt% was added to 200% without adding any antioxidant.
When the film was processed at a processing temperature of ° C (Comparative Example 7), many fish eyes were generated, and the levels of odor and taste were extremely poor. On the other hand, the same resin
When a film is processed at a processing temperature of 0 ° C. (Example 4),
No fish eyes were generated, and the odor and taste were good.

[0033]

[Table 1]

[0034]

[Table 2]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 9:00

Claims (5)

[Claims] (1) It is produced by an ionic polymerization method and has a density of 0.5.
89 to 0.96 g / cm ³ , 170 ° C., shear rate 100 ra
The melt viscosity η * [170] at d / sec is 0.001
× 10 ⁴ to 3.5 × a 10 ⁴ poise, and the resin weight proportion a of cold xylene-soluble portion (% by weight) contains an ethylene-based polymer or the ethylene polymer satisfying the following formula (1) A method for producing an inflation film, comprising processing the composition at a melting temperature of 170 ° C. or lower at a die gap. a <4.8 × 10 ⁴ × (0.95-d) ³ +10 ⁶ × (0.95-d) ⁴ +0.5 Formula (1) (In the above formula (1), a is the ethylene polymer cold xylene. The weight ratio of the soluble part (% by weight) and d is the density (g / cm ³ ) of the ethylene polymer.) 2. The method for producing a blown film according to claim 1, wherein the ethylene polymer or the resin composition containing the ethylene polymer does not contain an antioxidant. 3. The process for producing a blown film according to claim 1, wherein the ethylene polymer is produced in the presence of a catalyst containing a transition metal compound having a group having a cyclopentadiene-type anion skeleton. 4. A blown film obtained by the production method according to claim 1. 5. A multilayer blown film comprising at least one layer of the blown film obtained by the production method according to claim 1.