JP3468886B2 - Foamed tubular film, its production method and bag for packaging goods - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam tubular film, a method for producing the same, and a bag for packaging articles. More specifically, the present invention relates to a long-chain branched low-density ethylene polymer, ethylene-vinyl acetate copolymer, linear low-density ethylene-
Foam tubular film formed from a resin composition comprising an α-olefin copolymer and a chemical foaming agent by an air-cooled inflation method, a method for producing the same and an article obtained from the film, for example, high-priced goods, gifts, souvenirs, prizes, In particular, it relates to a bag for packaging ceremonial occasion gifts and the like.

[0002]

2. Description of the Related Art Conventionally, as a bag for packaging various articles, there have been many cases where a non-foamed film formed by an inflation method, a T-die method or the like from an ethylene polymer, a propylene polymer or the like is used as a raw material. Although these packaging bags have high strength, they are not suitable for packaging high-priced items, gifts, souvenirs, prizes, especially ceremonial gifts, etc., because they do not have a good feel and appearance. It was On the other hand, in recent years, a method of forming a foamed film by using an inflation molding machine to supply a resin composition composed of a long-chain branched low-density ethylene polymer by a high-pressure method and a chemical foaming agent to the foamed film has become widespread. I've been Since this foamed film has a clean surface, a soft feel, and a high-grade feeling, it is used as a packaging bag for various items such as ceremonial occasion items. However, when the long-chain branched low-density ethylene polymer by the high pressure method is subjected to the inflation method, the resulting foamed film has insufficient tensile strength, tear strength, elongation, puncture resistance, heat seal strength, etc. When the contents to be packed are heavy or have corners or protrusions, the packaging bag often breaks or has holes, and improvement has been desired.

[0003]

As described above, the conventional foamed film produced by the inflation method using the long-chain branched low-density ethylene polymer produced by the high pressure method as a raw material has a tensile strength, a tear strength, an elongation and a puncture resistance. Since it is inferior in properties, heat seal strength, etc., a new resin composition for improving them and conditions of an inflation method suitable for this are found, and there is flexibility, tensile strength, tear strength, elongation, puncture resistance, Provide a packaging bag with high heat-sealing strength, excellent surface gloss and surface smoothness, good feel to the touch, beautiful appearance and high quality, foam tubular film as its material, and its manufacturing method Is the subject of the present invention.

[0004]

The present inventors have found that although a long-chain branched low-density ethylene polymer produced by a high-pressure method has excellent flexibility and foaming characteristics, it has high tensile strength, tear strength, elongation and resistance to tearing. Focusing on inferior piercing property, heat seal strength, etc., in order to improve these, various ethylene polymers were blended at a specific ratio, a large number of inflation conditions were set, and many experiments were conducted combining these. A resin composition in which two kinds of specific ethylene-based polymers are mixed in a specific ratio with the long-chain branched low-density ethylene-based polymer, and a specific amount of a specific chemical foaming agent is mixed therein under specific inflation conditions. It was found that the above problems can be solved when molded, and further studies were conducted to complete the present invention.

That is, according to the present invention, a long chain branched low density ethylene polymer 100 produced by a high pressure radical polymerization method has a density of 0.917 to 0.925 g / ml and a melt index of 0.1 to 5 g / 10 min. Parts by weight, vinyl acetate content of 5 to 25% by weight produced by high pressure radical polymerization method, density of 0.930 to 0.950 g / ml, melt index of 0.5 to 5 g / 10 min ethylene-vinyl acetate copolymer 40 to 70 parts by weight, density 0.915 to 0.930 g / m
1, a linear low-density ethylene-α-olefin copolymer of 30 to 50 parts by weight and a chemical blowing agent having a decomposition temperature of 130 to 190 ° C.
1 to 2 parts by weight of the resin composition is fed to the extruder,
Melt kneading at 70 to 190 ° C., resin temperature 1 from a die having a circular slit and a die gap width of 0.4 to 0.6 mm.
While extruding at 70 to 190 ° C. and cooling with air blown out from an air ring, air is blown into the film so that the blow ratio is 1.5 to 3.0, and the frost line height relative to the diameter of the die used is 1.5 to 3.0. 3.0 times, take-up speed is 4 ~
It relates to a method for producing a foamed tubular film, which comprises performing inflation molding at 15 m / min.

The long-chain branched low-density ethylene polymer (hereinafter also referred to as HP-LDPE) produced by the high pressure radical polymerization method used in the present invention means ethylene alone or a small amount of propylene and isopropyl in ethylene. In the presence of a catalyst such as oxygen, an organic radical generator, etc., by mixing alcohol, acetone, hydrogen, etc.
It is a polyethylene homopolymer obtained by radical polymerization in a tubular reactor or a tank reactor at 3000 atm and a temperature of 150 to 300 ° C., whereas other polyethylene has only short chain branching, HP- LDPE
Is distinguished from other polyethylenes in that it has both short-chain branches and long-chain branches and has a wide molecular weight distribution.

HP-LDPE used in the present invention
Has a density of 0.917 to 0.925 g / ml,
If it is less than 0.917 g / ml, the tensile strength, tear strength and puncture resistance of the foamed tubular film will be deteriorated, and the film will lose its rigidity. If it exceeds 0.925 g / ml, flexibility and elongation will be deteriorated, which is not desirable. . In addition, the above HP
-The melt index of LDPE is 0.1-5g / 10
If it is less than 0.1 g / 10 minutes, the inflation moldability is deteriorated and the productivity is lowered, and if it exceeds 5 g / 10 minutes, the tensile strength, tear strength and puncture resistance of the foam tubular film are lowered. , Not desirable.

The ethylene-vinyl acetate copolymer (hereinafter also referred to as EVA) produced by the high pressure radical polymerization method used in the present invention means ethylene and vinyl acetate, if desired, propylene, isopropyl alcohol and acetone. Or a copolymer of ethylene and vinyl acetate obtained by radical polymerization in a tubular reactor or a tank reactor in the presence of a catalyst such as oxygen or an organic radical generator together with hydrogen. Due to its presence, the flexibility, rubber elasticity, transparency, low temperature characteristics, etc. are
Superior to DPE.

The EVA used in the present invention has a vinyl acetate content of 5 to 25% by weight, but if it is less than 5% by weight, the tensile strength, tear strength, elongation, flexibility, hand feel and appearance of the foam tubular film are reduced. The heat seal strength is insufficient, and if it exceeds 25% by weight, the melt index exceeds 5 g / 10 minutes and the tensile strength, tear strength, etc. become insufficient, which is not desirable. The density of EVA is 0.9
30 to 0.950 g / ml, 0.930 g / ml
If it is less than 0.95, the tensile strength, tear strength, elongation, flexibility, touch feeling, and appearance of the foamed tubular film are poor, and 0.950.
If it exceeds g / ml, the tensile strength, tear strength, etc. become insufficient, which is not desirable. Further, the EVA has a melt index of 0.5 to 5 g / 10 minutes and a melt index of 0.5 g / 10.
If it is less than 5 minutes, not only the inflation moldability is deteriorated and the productivity is lowered, but also the flexibility and the feeling of touch are deteriorated, resulting in 5 g /
If it exceeds 10 minutes, the tensile strength, tear strength, puncture resistance, heat seal strength, etc. of the foamed tubular film will decrease, which is not desirable.

The linear low-density ethylene-α-olefin copolymer (hereinafter also referred to as LLDPE) used in the present invention is a known method, for example, a transition metal compound (such as titanium or vanadium) as a main catalyst. Compound),
A Ziegler-based catalyst comprising an organometallic compound (eg, organoaluminum) as a co-catalyst, a carrier (eg, an oxide or chloride of silicon, titanium, magnesium, etc.), a chromium oxide-based Phillips-type ion polymerization catalyst, a molybdenum-based catalyst, a metallocene. In the presence of a system catalyst, etc., ethylene and α
-Olefin at high pressure (500 atm or more), medium pressure (80-
(300 atm) or a low pressure (0 to 80 atm), a copolymer obtained by polymerizing under a low pressure (0 to 80 atm), which has many long chain branches and many short chain branches, and is different from the above HP-LDPE. is there. Examples of α-olefins for producing LLDPE include propylene, butene-1, hexene-
1, octene-1, decene-1, 4-methylpentene-
1 etc. are suitable. Further, the polymerization can be carried out by various methods such as a slurry method, a gas phase polymerization method and a high temperature melt polymerization method.

The density of LLDPE used in the present invention is 0.915 to 0.930 g / ml, and the density is 0.91.
If it is less than 5 g / ml, the tensile strength and tear strength of the foamed tubular film will be lowered, and the stiffness will be lost, and if it exceeds 0.930 g / ml, the flexibility and feel will be undesired. The melt index of the LLDPE is 0.3 to 3 g / 10 minutes, and the melt index is 0.3 g.
If it is less than / 10 minutes, the workability of foam inflation is deteriorated and the productivity is inferior, and if it exceeds 3 g / 10 minutes, the tensile strength and tear strength of the foam tubular film decrease, which is not desirable.

In the present invention, HP-LDPE100
40 to 70 parts by weight of EVA is blended with respect to parts by weight.
When the EVA is less than 40 parts by weight, the foamed film has insufficient moldability, and the flexibility, touch feeling, heat seal strength, tensile strength, tear strength, appearance and the like of the foamed film after production are deteriorated. , 70 parts by weight, LLDP
The content of E is relatively decreased, and the characteristics of LLDPE having the highest tensile strength and tear strength among the three resins are not exhibited, which is not desirable.

LLDPE is HP-LDPE100.
Add 30 to 50 parts by weight to parts by weight. If it is less than 30 parts by weight, the tensile strength and tear strength will decrease, and if it exceeds 50 parts by weight, the compounding amount of EVA will relatively decrease, and it will be the most flexible, hand-feeling and appearance among the three resins. E
The characteristics of VA are not expressed, which is not desirable.

In order to obtain a foamed tubular film in the present invention, 0.1 to 2 parts by weight of a chemical foaming agent having a decomposition temperature of 130 to 190 ° C. is added to 100 parts by weight of HP-LDPE. This chemical foaming agent may be added to the resin composition as it is, but it may be added as a masterbatch that is added to the resin component in advance to improve the dispersibility.
If the decomposition temperature of the chemical foaming agent is less than 130 ° C., it is not desirable because it causes foaming during the production of the foamable resin composition or the foamable masterbatch. Absent. If the amount of the chemical foaming agent is less than 0.1 part by weight, the amount of foaming gas generated is small, and a foamed film cannot be obtained. If it exceeds 2 parts by weight, the expansion ratio becomes too large and the tensile strength is increased. , Tear strength, puncture resistance, surface gloss and surface smoothness are reduced, which is not desirable.

Examples of the chemical foaming agent used in the present invention include azodicarbonamide, dinitropentamethylenetetramine, p, p'-oxybisbenzenesulfonylhydrazide, p, p'-oxybisbenzenesulfonylsemicarbazide, N, N'-dimethyl-N, N '
-Dinitrosoterephthalamide and the like.

As foaming aids, talc, silica, titanium oxide, salicylic acid, stearic acid, phthalic acid, zinc stearate, lead stearate, magnesium stearate, calcium stearate, ethylene glycol, glycerin, ethanolamine, urea, urea derivatives. , Melamine, dibasic lead phosphite, tribasic lead sulfate, zinc oxide, etc. in a small amount, for example, 0.0003 to 0.6 parts by weight per 1 part by weight of the chemical blowing agent. Good.

In the present invention, the decomposition temperature is 130 to 190.
An organic peroxide at 0 ° C. may be further added to the resin composition. When an organic peroxide is used together, the melt tension of the molten resin component increases, foaming is performed stably, a higher quality foamed film is obtained, and a cross-linking reaction occurs, resulting in mechanical strength of the foamed film. Is rising and desirable.

The following may be mentioned as examples of organic peroxides (in the parentheses, the decomposition temperature (° C.) is shown): tert-butylperoxyisopropyl carbonate (135), tert-butylperoxylaurate ( 14
0), 2,5-dimethyl-2,5-di (benzoylperoxy) hexane (140), tert-butylperoxyacetate (140), di-tert-butyldiperoxyphthalate (140), tert-butylperoxymaleic acid ( 1
40), cyclohexanone peroxide (145), tert-butyl peroxybenzoate (145), dicumyl peroxide (150), 2,5-dimethyl-2,5-
Di (tert-butylperoxy) hexane (155), tert-butylcumyl peroxide (155), tert-butyl hydroperoxide (158), di-tert-butylperoxide (160), 2,5-dimethyl-2,5- Di (tert-butylperoxy) hexyne-3 (170), diisopropylbenzene hydroperoxide (170), p-menthane hydroperoxide (180).

In the present invention, the foamable resin composition may optionally contain other additives such as an antioxidant, a weather resistance improver, an ultraviolet absorber, an antistatic agent, a slip agent, an antiblocking agent, an antibacterial agent, You may mix | blend a fragrance | flavor, a pigment, a processing aid, a rust preventive, a hygroscopic agent, etc.

In the present invention, the expandable resin composition comprises a resin component, a chemical foaming agent, and optionally other additives, which are mixed or heated and kneaded by a Banbury mixer, a Henschel mixer, a cokneader, a multi-screw extruder, a ribbon blender or the like. Then, it may be pelletized and supplied to the inflation molding machine, or may be supplied to the inflation molding machine by simply mixing the pellets of each resin and the blowing agent-containing master batch pellets.

Next, the conditions of the foam inflation molding in the present invention will be described step by step. First, the foamable resin composition was fed to an inflation extruder,
Melt kneading at 0 to 190 ° C. to decompose the chemical foaming agent and uniformly disperse the foaming gas in the molten resin. If the temperature at this time is less than 170 ° C., the resin composition components do not melt uniformly and the melt tension becomes too large, causing a rough skin phenomenon called shark skin, and causing film breakage and foaming inflation. When the temperature exceeds 190 ° C., the melt tension of the resin composition is excessively lowered, and an over-foaming phenomenon occurs,
Further, the running of the molten tubular film becomes unstable, and a foamed film having a uniform thickness and a folded diameter cannot be obtained, which is not desirable.

In the present invention, a die having a circular slit and a die gap width of 0.4 to 0.6 mm is used. If this is less than 0.4 mm, the molten resin pressure will rise, melt fracture will occur, the stability of the bubbles will be poor, and high discharge extrusion processing will not be possible.
If it exceeds, the discharge will be too high and the cooling with the cooling air from the air ring will not catch up, making it difficult to form bubbles.
Furthermore, the foamed film is oriented only in the longitudinal direction of the film and easily tears only in the longitudinal direction, and the expansion ratio is 1.4.
More than double, which is not desirable.

The blow ratio at the time of foam inflation is in the range of 1.5 to 3.0. If the blow ratio is less than 1.5, the shape of the foam cells will not be uniform, although it depends on the take-up speed. The film is liable to tear in the longitudinal direction, and if it exceeds 3.0, bubbles become unstable, and it becomes difficult to process a stable foamed film, which is not desirable.

In the present invention, the frost line height is in the range of 1.5 to 3.0 times the diameter of the die used. If it is less than 1.5 times, the cooling air for cooling and solidifying the film becomes too strong, the flatness of the film is impaired, and the film appearance and printing process are adversely affected. On the other hand, if it exceeds 3.0 times, the cooling air will become too weak, the bubbles will become unstable, and the foaming cell shape will change due to the increase in the stretching ratio due to the longer distance from the die to the frost line. However, a uniform foamed film cannot be obtained.

Further, the take-up speed in the inflation molding of the present invention is in the range of 4 to 15 m / min. If the take-up speed is less than 4 m / min, orientation in the longitudinal direction of the film does not occur, and productivity is poor, resulting in 15 m / min. If it exceeds the range, film breakage of the film occurs, orientation in the longitudinal direction of the film occurs too much, and the film tends to tear in the longitudinal direction, which is not desirable.

The present invention also relates to a foamed tubular film having a foaming ratio of 1.2 to 1.4 and a thickness of 30 to 300 μm produced by the above method of the present invention. Foaming ratio is 1.2
If it is less than 1.0, the cushioning property is poor, the feeling of touch is poor, and the feeling of high quality of the film is lost, which is not desirable, and if it exceeds 1.4, the film loses its stiffness, and the surface gloss, tensile strength, tear strength, puncture resistance and heat seal strength are poor. Decline, which is undesirable. Further, if the thickness of the foamed film is less than 30 μm, it causes bag breakage when a heavy object is stored in a packaging bag produced from the film, and the film feels poor in touch and appearance, and also deteriorates independence. On the other hand, when it exceeds 300 μm, the expansion ratio exceeds 1.4 times, the surface gloss of the foamed film, the mechanical strength, etc. decrease, and the cost of raw materials used per area of the foamed film increases, resulting in cost increase.
Not desirable.

The foamed tubular film of the present invention has a constant length (eg, 10 mm) substantially perpendicular to the longitudinal direction of the film.
˜100 cm), and as it is or by gusseting both sides of the non-opening, one end of the opening is 3-1
Heat sealed with a width of 0 mm to make a closed bottom, and the other opening as it is or bent to make a double film, heat sealed if desired, and a handle (for example, a string, a molded product, etc.) is attached thereto and a packaging bag. Can be The bottom of the packaging bag may be folded into a box shape and heat-sealed to form a self-supporting bag structure.

The present invention also relates to an article packaging bag produced from the foamed tubular film of the present invention which can be produced in this manner. The bag for packaging articles of the present invention has a beautiful appearance and a high-grade appearance, and is excellent in tensile strength, tear strength, puncture resistance, shock resistance, heat resistance, cold resistance, water resistance, chemical resistance, etc. It is suitable as a packaging bag for expensive and heavy goods, products, articles and gifts. The applicant has conventionally manufactured and sold a ceremonial occasion gift packaging bag, but the article packaging bag of the present invention is particularly suitable as a packaging bag in this field. Compared to those using only density ethylene polymer as the resin component,
As mentioned above, it has excellent properties and has an epoch-making effect. Therefore, the present invention also relates to a ceremonial occasion gift bag made from the foamed tubular film of the present invention.

[0029]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples without departing from the gist of the present invention. Example 1 Production of foamed tubular film Density produced by high pressure radical polymerization method 0.917 g / m
1, 100 parts by weight of a long-chain branched low-density polyethylene polymer (manufactured by Nippon Unicar, trade name: DFDJ-6775) having a melt index of 0.24 g / 10 min, a density of 0.930 g / produced by a high pressure radical polymerization method. ml, melt index 0.5 g / 10 minutes, vinyl acetate content 5% by weight ethylene-vinyl acetate copolymer (manufactured by Nippon Unicar,
Product name: NUC-3050) 40 parts by weight, density 0.92
4 g / ml, 30 parts by weight of a linear low-density ethylene-butene-1 copolymer (manufactured by Nippon Unicar, trade name: NUCG-5172) having a melt index of 0.9 g / 10 min, and a chemical foaming agent (the above long chain) Masterbatch of branched low-density polyethylene-based polymer and azodicarbonamide) 0.
8 parts by weight of pellets each having a diameter of 3 mm and a length of 3 mm are passed through a metering automatic feeder, and the mixed pellets are fed to the hopper of the following inflation molding machine, and the foamed tubular film is fed under the following conditions. Produced: (1) Extrusion device: Φ65 mm inflation film manufacturing device (manufactured by Tommy Machinery) (2) Die: Φ200 mm, die gap width 0.5 m
m, extrusion temperature 175 ° C. (manufactured by Tommy Machinery Co., Ltd.) (3) Cooling device: Single lip straight and with conical color (4) Discharge rate: 50 kg / hour (5) Blow ratio: 2.3 (6) Frost line: 350 mm (7) Collection speed: 5 m / min.

Evaluation of Foamed Tubular Film (1) Film Fold Diameter: 700 mm (2) Film Thickness: 200 μm (3) Foaming Ratio: 1.3 (4) Tensile Strength: Vertical 160 kg / cm ² Horizontal 120 kg / cm ² (measured in accordance with ASTM D882) (5) Tear strength: longitudinal direction 30 kg / cm transverse direction 70 kg / cm (measured in accordance with ASTM D1004) (6) Elongation: longitudinal direction 470% transverse direction 480% ( (Measurement in accordance with ASTM D882) (7) Puncture resistance: 135 g [Measurement in accordance with NUC method (using an Instron type extrusion tester, piercing by pushing with a 1 mm needle, measuring load when broken) (8) Heat seal strength: 2.80 kg / 15 mm (measurement conditions: temperature 160 ° C., seal width 5 mm, seal time 1 second, seal pressure 1.0 g / cm ²⁾ (9) Gloss: 48 when the incident angle 45 °, the better. (10) Surface smoothness: smooth, not roughened. (11) Impact strength: 23 kg · cm (punch-type impact test, using 1/2 inch impact ball) (12) Flexibility (flexural modulus): 83 kgf / mm
² (measured according to JIS K7203)

Production of packaging bag and its evaluation 9 in the longitudinal direction of the foam tubular film produced above.
Cut to a length of 700 mm at an angle of 0 °, gusset-fold both sides of the non-opening portion to a depth of 130 mm, fold the bottom portion into a box shape, and heat-seal the overlapping portion of the bottom film with a width of 7 mm, A bag-shaped material having self-supporting property, the upper part of which is folded by a film width of 50 mm, and the center of the overlapped part of the film (the front surface of the bag-shaped material and the upper center of the facing surface)
Holes with a diameter of 10 mm are made at two locations at intervals of 150 mm, and decorative strings are passed from the outside to the inside, and both ends of the string are ball-knotted so that the strings do not come off and the hand straps are attached, for packaging. Completed the bag. 7k weight
g, a wedding gift with an internal volume of 12000 cm ³ was placed. Appearance is pale yellowish milky white, glossy and gives an elegant and high-class feeling. 2
I carried it, but never broke it.

Example 2 Production of Foamed Tubular Film Density 0.923 g / m Produced by High Pressure Radical Polymerization
l, 100 parts by weight of a long-chain branched low-density polyethylene polymer (manufactured by Nippon Unicar, trade name: DFD-0111) with a melt index of 2.4 g / 10 min, a density of 0.930 g / produced by a high-pressure radical polymerization method ml, melt index 0.5 g / 10 min, vinyl acetate content 18% by weight ethylene-vinyl acetate copolymer (manufactured by Nippon Unicar,
Product name: DQDJ-1868) 60 parts by weight, density 0.9
40 parts by weight of a linear low-density ethylene-hexene-1 copolymer (manufactured by Nippon Unicar, trade name: TUF-2069) having a melt index of 24 g / ml and a melt index of 0.9 g / 10, and a chemical foaming agent (the above long chain). Masterbatch of branched low density polyethylene polymer and azodicarbonamide)
1.5 parts by weight of pellets each having a diameter of 3 mm and a length of 3 mm are passed through a metering automatic feeder, and the pellets are mixed and fed to the hopper of the following inflation molding machine, and the foam tubular under the following conditions. A film was manufactured: (1) Extrusion device: Φ65 mm inflation film manufacturing device (manufactured by Tommy Machinery) (2) Die: Φ200 mm, die gap width 0.6 m
m, extrusion temperature 190 ° C (manufactured by Tommy Machinery Industry) (3) Cooling device: Single lip straight and with conical color (4) Discharge rate: 40 kg / hour (5) Blow ratio: 2.5 (6) Frost line: 400 mm (7) Collection speed: 8 m / min.

Evaluation of Foamed Tubular Film (1) Film Fold Diameter: 700 mm (2) Film Thickness: 100 μm (3) Foaming Ratio: 1.4 (4) Tensile Strength: Longitudinal 193 kg / cm ² Transverse 135 kg / cm ² (measured in accordance with ASTM D882) (5) Tear strength: 38 kg / cm in longitudinal direction, 76 kg / cm in transverse direction (measured in accordance with ASTM D1004) (6) Elongation: 530% in longitudinal direction, 510% in lateral direction ( (Measurement according to ASTM D882) (7) Puncture resistance: 118 g [Measurement according to NUC method (using an Instron type extrusion tester, piercing by pushing with a 1 mm needle, measuring load when ruptured) (8) Heat seal strength: 3.23 kg / 15 mm (measurement conditions: temperature 160 ° C., seal width 5 mm, seal time 1 second, seal pressure 1.0 g / cm ²⁾ (9) Gloss: In case of an incident angle 45 ° 52, the better. (10) Surface smoothness: smooth, not roughened. (11) Impact strength: 28 kg · cm (punch-type impact test, impact ball 1/2 inch used) (12) Flexibility (flexural modulus): 95 kgf / mm
² (measured according to JIS K7203)

Production of packaging bag and evaluation thereof A packaging bag was completed in the same manner as in Example 1 using the foamed tubular film produced above. Weight 10
A wedding gift with a weight of 8,000 cm ^{3 and} a weight of 8,000 cm ³ was put in. Appearance is a pale yellowish milky white, glossy and gives an elegant and high-class feeling. 3
I carried it, but never broke it.

Comparative Example 1 The same experiment as in Example 1 was carried out except that the amount of the ethylene-vinyl acetate copolymer was changed to 30 parts by weight, and a uniform foam tubular film was obtained. No, flexibility, feel, heat seal strength, tensile strength,
Tear strength, appearance, etc. were insufficient.

Comparative Example 2 The same experiment as in Example 1 was carried out except that the amount of the ethylene-vinyl acetate copolymer was changed to 80 parts by weight in Example 1, and the tensile strength of the foamed tubular film was obtained. The strength and tear strength decreased.

Comparative Example 3 In Example 1, linear low density ethylene-butene-1 was used.
The same experiment as in Example 1 was carried out except that the amount of the copolymer was changed to 60 parts by weight. As a result, a uniform foam tubular film was not obtained, and the flexibility, feel of touch, heat seal strength, tensile strength, Tear strength, appearance, etc. were insufficient.

Comparative Example 4 In Example 1, the linear low density ethylene-butene-1 was used.
When the same experiment as in Example 1 was carried out except that the amount of the copolymer was changed to 20 parts by weight, the tensile strength and tear strength of the obtained foamed tubular film were lowered.

Comparative Example 5 The same experiment as in Example 1 was carried out except that the long-chain branched low-density ethylene polymer was not used, and the foaming state was very poor and the expansion ratio was It was as low as 1.05, the appearance of the film was poor, and it could not be used as a product.

Comparative Example 6 The same experiment as in Example 1 was carried out except that the die gap width was 0.3 mm, but the processing speed was lowered and the appearance of the foam tubular film was deteriorated. .

Comparative Example 7 The same experiment as in Example 1 was carried out except that the die gap width was 0.8 mm in Example 1. However, insufficient cooling resulted in difficulty in forming the foam tubular film.

[0042]

Industrial Applicability As described in detail above, the method for producing a foam tubular film of the present invention comprises a specific long-chain branched low-density ethylene polymer, ethylene-vinyl acetate copolymer, and straight-chain type. Flexibility, tensile strength, tear strength, elongation, impact strength, puncture resistance by using low density ethylene-α-olefin copolymer and chemical foaming agent at a specific ratio and performing it under specific foam inflation molding conditions. It is possible to manufacture a foamed tubular film with excellent moldability as well as excellent in surface gloss and surface smoothness. Therefore, the bag for article packaging produced from the foamed tubular film having various excellent properties obtained by the method of the present invention has a beautiful appearance and gives a high-class feeling, and is a high-priced product, It is suitable as a packaging bag for gifts, souvenirs, prizes, especially ceremonial occasion gifts.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-58440 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/06 B29C 55/28

Claims (4)

(57) [Claims] 1. A high-chain branched low-density ethylene polymer having a density of 0.917 to 0.925 g / ml and a melt index of 0.1 to 5 g / 10 min produced by a high-pressure radical polymerization method. Produced by radical polymerization, vinyl acetate content 5 to 25% by weight, density 0.930 to 0.
950 g / ml, melt index 0.5-5 g / 1
0-minute ethylene-vinyl acetate copolymer 40-70 parts by weight, density 0.915-0.930 g / ml, melt index 0.3-3 g / 10 minutes linear low-density ethylene-α-olefin copolymer weight A resin composition consisting of 30 to 50 parts by weight of the coalescence and 0.1 to 2 parts by weight of a chemical foaming agent having a decomposition temperature of 130 to 190 ° C. is supplied to an extruder, and 170 to 190 ° C.
Melted and kneaded with a die having a circular slit and a die gap width of 0.4 to 0.6 mm, and a resin temperature of 170 to 190.
Extruded at ℃, cooled by the air blown out from the air ring, blow air into the film and blow ratio is 1.5.
˜3.0, the frost line height is 1.5 to 3.0 times the diameter of the die used, and the take-up speed is 4 to 15 m / min. 2. A foamed tubular film having a foaming ratio of 1.2 to 1.4 and a thickness of 30 to 300 μm produced by the method according to claim 1. 3. A bag for packaging an article, which is manufactured from the foam tubular film according to claim 2. 4. A bag for ceremonial occasion gifts produced from the foamed tubular film according to claim 2.