JPH0839667A - Production of biaxially stretched resin film - Google Patents

Abstract

PURPOSE:To obtain a biaxially stretched film excellent in heat shrinkability by applying longitudinal stretching to a bubble over a short section by nip rolls in addition to the stretching of the bubble due to air in longitudinal and lateral directions. CONSTITUTION:Air is blown in a thermoplastic resin bubble (e) extruded from an annular molding die (d) in a molten state. The bubble (e) is subjected to inflation molding under such a condition that b/a is 1.5-10 when the diameter of the bubble at the crystallizing temp. of the used thermoplastic resin is set to (a) and the final diameter of the expanded bubble is set to (b) to obtain an oriented film (f) which is, in turn, folded double. This oriented film (f) folded double is longitudinally stretched by 1.2-5 times by utilizing the peripheral speed difference between nip rolls 18,19. The blow ratio of the oriented film obtained by inflation molding is pref. 6-22 times. As the used thermoplastic resin, polyethylene, polypropylene, an ethylene/vinyl acetate copolymer, an ethylene/acrylic acid copolymer and the like are designated.

Description

Detailed Description of the Invention

[0001]

The present invention relates to polyethylene, polypropylene, linear low density polyethylene, ethylene / vinyl acetate copolymer, polybutene-1, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, polystyrene. Biaxially stretched film by blowing air into the thermoplastic resin bubble and biaxially stretching the valve at a temperature lower than the crystallization temperature of the thermoplastic resin and folding it in two, and then changing the take-up speed between the nip rolls. And a biaxially stretched inflation resin film.

The biaxially stretched resin film obtained by the present invention is excellent in heat shrinkage property. For example, the biaxially stretched resin film is once loosely packaged with this and then passed through a heat tunnel to obtain the biaxially stretched resin film. In shrink wrapping in which heat-shrinking is performed to wrap an object to be packaged, the object to be packaged can be tighter than the conventional shrink film, and there is an advantage that a package having a good packaging finish can be provided.

[0003]

2. Description of the Related Art The production of a stretched film of a thermoplastic resin film by an inflation molding method is generally carried out using an inflation film molding machine 1 shown in FIG. 1, for example. In the blown film molding machine 1, the raw material thermoplastic resin c is stored in the supply hopper 2 and supplied.

The extruder 3 incorporates a screw 5 which is driven to rotate by a screw motor 4, and extrudes the thermoplastic resin c supplied from the supply hopper 2 as a molten resin upward from its tip. In the vertical direction of the tip of the extruder 3, a blow head 7 incorporating an annular molding die d is attached via a direct connection pipe 6 to blow air into the extruded molten resin to form a cylindrical bubble e. In addition, an air supply / exhaust pump 10 is connected to the blow head 7 via a bubble pipe 9 having an electromagnetic valve 8.

Above the blow head 7, there is an air cooling ring 1.
1, the cylindrical bubble e is expanded and cooled by the air supplied from the cooling blower 12. The cylindrical bubble e is guided by the guide plates 13 and 13, and is folded into a two-layer sheet by the take-up rolls 14 that are driven to rotate by the take-up motor to form the inflation resin film f.

The inflation resin film f is guided by the guide rolls 17, 20, 20 and nip rolls 18, 18, 19, 19 after the film width is measured by the width sensor 16 of the film width measuring device 15. . The nip rolls 18, 18 and 19, 19 are heated to a temperature lower than the melting point or softening temperature of the thermoplastic resin, and the nip rolls 18, 19 are rotated at a higher speed than the rotational speed of the nip rolls 18, 18 to make the nip rolls 18, 18 shorter. The longitudinal stretching of the section is performed.

This stretched film is inserted into a holding punch j of a film winder w and wound around a paper tube i held. Here, in the case of producing a bag-forming film, the inflation resin film f is wound around the paper tube i in a state of being folded into a two-layer sheet, but in the case of producing a flat film or the like, the inflation resin film f is The film f is divided into a required number of strips in the width direction by a cutter, and then the film f is inserted into a holding punch j of a film winder and wound onto several paper tubes i, i held.

In the production of blown film, the ratio of the inner diameter of the expanded cylindrical bubble to the outer diameter of the annular molding die is called the blow ratio (BUR), and generally 1.
The inflation resin film is molded 2 to 4 times. In the method for producing a stretched film by the inflation method, when the bubble material is a crystalline thermoplastic resin such as polyethylene or polypropylene, the bubble extruded from the annular molding die is generally a cooling blower 1
2 is cooled by the air supplied from the blower 2 and blown out from the air-cooling ring 11. At this time, the bubble e is cooled and solidified (fr).
The film before expansion (frost line: F) is expanded, and further expansion does not occur on the downstream side thereafter. Therefore, the film before the subsequent short-term expansion is not oriented and expanded.

Therefore, this short stretched blown film is not suitable as a shrink wrapping film because the strength in the longitudinal direction and the transverse direction are not balanced and the heat shrinkage rate is small. As a method for producing a biaxially stretched blown film having excellent heat shrinkability, Japanese Patent Publication No. 61-34
No. 372, a tubular unstretched film (valve) made of a thermoplastic resin in a molten state is brought into contact with an outside mandrel that is water-cooled to cool, solidify, and mold the unstretched film to the outside. While holding the stretching tension by sandwiching the mandrel between the mandrel and the outer peripheral portion of the disc-shaped holder provided in the inner holder inside the unstretched film, the unstretched film is heated by a heater. A method for producing a tubular biaxially stretched film, which comprises stretching at a stretching temperature, simultaneously expanding and blowing a pressurized gas from the inside of an unstretched film, and pulling it with a pinch roll to stretch it in the longitudinal and transverse directions. suggest.

However, in this method, the melt-extruded valve is once cooled by the outside mandrel without expanding its diameter, and then the cooling valve is heated by a heater from the outside and a gas is blown into the bubble to blow the valve. Is expanded, so there is much waste in thermal efficiency as compared with the conventional method. In addition, the expansion (stretching) of the valve is 30 atm (3
It is dangerous to handle because it uses high pressure air (water column of 00 m).

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a biaxially stretched blown film excellent in heat shrinkability with good heat efficiency.

[0012]

In the present invention, air is blown into a thermoplastic resin bubble melt-extruded from an annular molding die, and the bubble diameter at the crystallization temperature of the thermoplastic resin using the bubble is calculated as follows: a) and the final diameter of the expanded bubble is (b), the oriented film obtained by inflation molding under the condition that (b) / (a) is 1.5 to 10 is folded in two, This bi-folded oriented film is further stretched in the longitudinal direction by 1.2-
Provided is a method for producing a biaxially stretched resin film, which comprises stretching 5 times.

[0013]

[Function] In addition to stretching the valve vertically and horizontally with air,
By adding short section longitudinal stretching by nip roll,
It is possible to produce a biaxially stretched film having excellent heat shrinkability.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Film Material As a material for the thermoplastic resin film, an ethylene / vinyl acetate copolymer having an vinyl acetate content of 5 to 25% by weight and an MFR of 0.3 to 10 g / 10 min, ethylene 75 .About.99% by weight and an α-olefin having 3 to 8 carbon atoms (propylene,
Butene-1, hexene-1, 4-methylpentene-1,
Octene-1 etc.) 25-1% by weight of linear low density polyethylene, high density polyethylene, low density polyethylene, ethylene / acrylic acid copolymer, ethylene / methyl acrylate copolymer, ethylene / Methacrylic acid copolymer, propylene homopolymer, propylene 60-9
9.5 wt% and ethylene or α-C4 to C8
Copolymer with 40-0.5% by weight of olefin, poly (4
-Olefin resins such as methylpentene-1) and polybutene, and thermoplastic resins such as polystyrene, polycarbonate, polyamide, polyethylene terephthalate, polybutylene terephthalate and polyvinyl chloride are used, and these are used alone or in combination of two or more. Used.

Hydrogenated petroleum resins, hydrogenated styrene / butadiene / styrene copolymer elastomers, ethylene / propylene copolymer elastomers, ethylene-butene-1 copolymer elastomers, 1,2-polybutadiene, ethylene are added to these thermoplastic resins. An impact modifier such as a propylene / ethylidene norbornene copolymer elastomer may be added to such an extent that the transparency of the film is not impaired (0.5 to 20% by weight). Further, a lubricant or a tackifier for improving the slipperiness of the film, a nucleating agent for improving the transparency of the film, an antioxidant, a flame retardant and a UV agent may be added in a proportion of 0.1 to 2% by weight. .

As the above-mentioned lubricant, an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, and 10 to 10 carbon atoms are used.
22, preferably fatty alcohol alcohol fatty acid ester which is a compound with 12-18, specifically, monoglycerin oleate, polyglycerinolate, glycerin triricinoleate, glycerin acetylricinoleate, methylacetylricinoleate , Ethyl acetyl ricinoleate, butyl acetyl ricinoleate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, polyoxyethylene glycerin, polyoxypropylene glycerin, sorbitan oleate, Sorbitan laurate, polyethylene glycol sorbitan oleate, polyethylene glycol sorbitan laurate, etc. Kylene ether polyol, specifically, polyethylene glycol, polypropylene glycol, etc., sugar fatty acid ester, epoxidized soybean oil, polyoxyethylene alkylamine fatty acid ester, polyoxyethylene alkylphenyl ether, maleic acid amide, stearic acid amide, erucic acid Higher fatty acid amides having 12 to 22 carbon atoms such as amide, ethylenebisstearic acid amide, ethylenebisoleic acid amide, polyethylene wax, polypropylene wax, liquid paraffin and the like can be used.

Inorganic substances such as talc and silica can be used as the nucleating agent, and castor oil derivative, low molecular weight porbutene, sorbitan higher fatty acid ester, terpene resin, petroleum resin and the like can be used as the adhesive. The resin film may have a single-layer structure or a laminated structure, and can be appropriately selected depending on the purpose.

For example, if the melting point difference between the resin on the heat-sealing side and the resin on the other side is 10 ° C. or more for the purpose of improving the heat-sealing property as an example of a laminated structure, the heat-sealing temperature range is expanded. It is possible and easy to use. Further, molding of a valve having a high blow ratio of 6 to 25 has an advantage that it can be produced more stably than a single layer product. As an example of such a resin film having a laminated structure, for example, the following laminated structures of (1) to (11) can be considered.

(1) 60 to 95% by weight of ethylene and a monomer selected from vinyl acetate, aliphatic unsaturated carboxylic acid, and aliphatic unsaturated monocarboxylic acid alkyl ester on one or both sides of the low density polyethylene resin layer A resin film in which a copolymer resin layer with 5 to 40% by weight is laminated. (2) 60 to 95% by weight of ethylene on one or both sides of the high-density polyethylene resin layer and 5 to 40 monomers selected from vinyl acetate, aliphatic unsaturated carboxylic acid, and aliphatic unsaturated monocarboxylic acid alkyl ester A resin film in which a copolymer resin layer containing 100% by weight is laminated.

(3) 60 to 95% by weight of ethylene on one or both sides of the linear low-density polyethylene resin layer, and a monoester selected from vinyl acetate, aliphatic unsaturated carboxylic acid, and aliphatic unsaturated monocarboxylic acid alkyl ester. 5 to 40
A resin film in which a copolymer resin layer containing 100% by weight is laminated. (4) Ethylene 6 on one or both sides of the propylene resin layer
A resin film in which a copolymer resin layer of 0 to 95% by weight and 5 to 40% by weight of a monomer selected from vinyl acetate, an aliphatic unsaturated carboxylic acid and an aliphatic unsaturated monocarboxylic acid alkyl ester is laminated.

(5) Polystyrene, polycarbonate,
60 to 95% by weight of ethylene and vinyl acetate ester aliphatic unsaturated carboxylic acid, aliphatic unsaturated monocarboxylic acid alkyl ester selected on one or both sides of the resin substrate layer selected from polyamide, polyethylene terephthalate and polybutylene terephthalate A resin film obtained by laminating a resin layer selected from a copolymer resin with 5 to 40% by weight of the obtained monomer, low density polyethylene, high density polyethylene, linear low density polyethylene, and polypropylene resin.

(6) Ethylene 60 to 90% by weight on one side or both sides of a resin substrate composed of 10 to 90% by weight of an olefinic resin selected from ethylene resin and propylene resin and 90 to 10% by weight of olefinic thermoplastic elastomer. A resin film in which a copolymer resin layer of 95% by weight and 5 to 40% by weight of a monomer selected from vinyl acetate, an aliphatic unsaturated carboxylic acid, and an aliphatic unsaturated monocarboxylic acid alkyl ester is laminated.

(7) Linear low density polyethylene 80-95
20% by weight of a copolymer resin of 60 to 95% by weight of ethylene and 5 to 40% by weight of a monomer selected from vinyl acetate, aliphatic unsaturated carboxylic acid and aliphatic unsaturated monocarboxylic acid alkyl ester. Monomer 5 selected from vinyl acetate, aliphatic unsaturated carboxylic acid, aliphatic unsaturated monocarboxylic acid alkyl ester and 60 to 95% by weight of ethylene on one or both sides of the resin base material layer consisting of 5% by weight.
A resin film in which a copolymer surface layer of about 40% by weight is laminated.

(8) 10 to 90% by weight of butene-1 resin
And ethylene 6 on one or both sides of the resin base material layer consisting of 90 to 10% by weight of an olefin resin (excluding butene-1 resin) or / and an olefin thermoplastic elastomer.
A resin film in which a copolymer surface layer of 0 to 95% by weight and 5 to 40% by weight of a monomer selected from vinyl acetate, aliphatic unsaturated carboxylic acid, and aliphatic unsaturated monocarboxylic acid alkyl ester is laminated. .

(9) A resin film in which a linear low density polyethylene resin layer is laminated on one side or both sides of the low density polyethylene resin layer. (10) A resin film in which a low-density polyethylene, a linear low-density polyethylene, or a propylene-based resin layer is laminated on one side or both sides of a high-density polyethylene resin layer. (11) A resin film in which a linear low-density polyethylene resin layer is laminated on one side or both sides of a propylene-based resin layer.

Crystallization temperature The crystallization temperature is obtained by heating 5 to 8 mg of crystalline thermoplastic resin powder using a differential thermal scanner to melt it once and then lowering it at a temperature lowering rate of 10 ° C./min. It refers to the peak temperature of the thermal scanning curve (DSC curve).

When a block copolymer has a plurality of peaks, a thermoplastic resin is mixed and used, or a laminate is used, the crystallization temperature means the higher peak temperature. In amorphous resin, it is usually called the softening temperature,
Since no clear peak appears, JIS K-7198-
In accordance with 1991, a dynamic viscoelastic temperature-dependent curve of an amorphous resin showing a correlation between temperature and dynamic storage elastic modulus E ′ is drawn, and the absolute value of the differential value of this dynamic viscoelastic temperature-dependent curve is the maximum value. Is taken as the crystallization temperature.

The apparatus used for molding inflation resin film of the device the present invention for use in the film molding, a cooling device 11 shown in FIG. 1, for example 2,
As shown in FIG. 3, the cooling device is replaced with a cooling device including an air cooling ring 21 and a flow straightening cylinder 22 provided in front of the resin discharge port h of the annular molding die d. The air cooling ring 21 has an air outlet 21a, and a downstream side of the air cooling ring 21 has
A plurality of annular rectifying cylinders 22, 22 having different diameters are arranged concentrically with the discharge port 21a at intervals in the radial direction, and an annular air chamber 23 having a downstream opening between adjacent rectifying cylinders. .. are formed, and a plurality of outside air intake ports 24 are radially formed (see FIG. 4) near the air cooling ring on the outermost straightening cylinder wall of these straightening cylinders. Between the lower end and the upper surface of the air cooling ring, outside air intake / exhaust ports that connect the air chambers to each other are formed by holes 25, 25, ...
The heights of the several rectifying cylinders are higher toward the outside, and the shape connecting these downstream ends forms a tapered bubble guide surface that expands to the outside. In FIG. 4, 30 is an air introduction pipe, and 33 is a hose.
In order to further improve the film appearance in the cooling device, as shown in FIG. 5, in addition to the auxiliary outlet 31a on the upstream side of the air cooling ring 30, a plurality of outlets 1 or 2 (3 or more) are provided.
1b, 32), and a cooling device capable of adjusting the amount of air blown from this auxiliary outlet may be used. 26 is the first room, 27
Is a second sub-chamber, 28 is a third sub-chamber, and 29, 29 'are connecting passages. Furthermore, as shown in FIG.
The annular molding die d is erected in a cylindrical shape on the same axis as the axis o of the annular molding die d, and a plurality of air outlets 35a, 35 are provided on the cylindrical peripheral wall.
It is possible to use the cooling device including the inner cooling cylinder 35 provided with b, 35c, and 35d together.

The inner cooling cylinder 35 has a double pipe structure as shown in FIGS. 6 and 7, and the cooling air supplied from the pump 10 passes through the air suction port 36 and is a chamber of the double pipe structure inner pipe. 36a, and the air suction ports 35 are provided at places of the inner pipe and the outer pipe at intervals of 40 to 200 mm, for example.
a, 35a ', 35b, 35b', ... 35d, 35d '
Is provided to cool the bubble e from the inside, and the air cooling ring 11,
In response to the cooling from the inner and outer surfaces of the bubble from 21, the cooling of the inner and outer surfaces of the bubble is made uniform. Further, the air discharged from the inner cooling cylinder 35 is used for cooling the bubble from the inside and expanding the bubble. The upper part of the outer pipe is opened at the center (38), and the chamber 36b formed by the inner pipe and the outer pipe is used as a passage for discharging air, and the air is discharged from the air discharge port 37 to the outside of the bubble.

On the downstream side of the air-cooling ring 21, annular flow straightening cylinders 22 having different diameters are provided.
A plurality of annular air chambers 23 are formed coaxially with the air outlets of the air outlets and are spaced apart in the radial direction, and an annular air chamber 23 having a downstream opening is formed between the adjacent straightening cylinders. A plurality of outside air intakes 24 are radially formed on the peripheral wall near the second air cooling ring 21, and the air chambers are provided between the lower end of the remaining straightening cylinder and the upper surface of the second air cooling ring 21. The outside air intake / exhaust ports 25 that communicate with each other are respectively bored, and the heights of the several rectifying cylinders become higher toward the outside, and the shape connecting these downstream ends is a tapered shape that spreads outward ( This guide surface forms a bubble guide surface having an angle of 45 to 70 degrees with the axis o of the discharge port h.

The generatrix of the guide surface of these tapered bubbles e is not limited to a straight line but may be a quadratic curve depending on the purpose. The flow straightening cylinder 22 is provided on the upper surface of the air cooling ring 21.
The tenon formed at the lower end 22a of 2 and the air-cooled ring-shaped tenon can be detachably attached. The rectifying cylinders 22 having the same diameter should have at least two heights different from each other.
It is advisable to also prepare the seeds so that they can be used for both small and large final bubble diameters. Even when using one with a short height, as a whole, the straightening cylinder group 22
The outer ones are used with a higher height.

When a film having the same take-up speed and the same thickness is formed by utilizing the cooling device having the one-stage and multi-stage air-cooling rings and the straightening tube group forming the tapered bubble guide surface, The larger the bubble diameter, the more cooling holes are added to increase the number of auxiliary cold air outlets, and if necessary, the number of air chambers supporting the bubbles is increased, thereby stabilizing the bubbles regardless of the final bubble diameter. It can be well supported and can form an inflation resin film.

When inflation molding is performed using these cooling devices, the position where the frost line F of the bubble e (which usually appears at the crystallization temperature) appears from the position of the outermost annular flow straightening cylinder which is the downstream side of the circular flow straightening cylinder. Also, the wind speed of the air blown out from the air cooling ring is adjusted so that it is located on the upstream side (1/5 to 4/5 of the height H of the outermost straightening cylinder). Further, the bubbles on the downstream side of the frost line F are forcedly stretched and oriented by reducing the pressure between the bubbles due to the Venturi action and the downstream end of each annular rectifying cylinder, and sucking the bubbles toward the rectifying cylinder side. A biaxially stretched inflation resin film excellent in appearance, heat shrinkage characteristics, etc. can be obtained.

In the oriented film molding method by the inflation molding method of the preceding stage, a plurality of flow straightening tubes are arranged on the downstream surface of the air-cooling ring concentrically with the discharge port with a space therebetween, and between the adjacent flow straightening tubes. An annular air chamber with a side opening is formed, a plurality of outside air intakes are radially formed in the outermost rectifying cylinder peripheral wall, and the air chamber is provided between the remaining rectifying cylinder upstream end and the downstream side surface of the air cooling ring. Since the outside air intake and exhaust ports that communicate with each other are respectively formed, the air flow that is blown from the outlet toward the bubble and has a slightly raised temperature is a venturi action that occurs when flowing between the bubble and the rectifying cylinder downstream end,
Between the bubble and the downstream end of each of the annular rectifying cylinders is in a reduced pressure state
The bubble is sucked toward the rectifying cylinder side and stretched. In addition, an outside airflow can be taken into the annular air chamber through the outside air intake port and the outside air intake / exhaust port, and a part of the air inside the air chamber merges with the air flow from the blowout port and the downstream end The bubbles move along with the bubbles and rapidly cool the bubbles, and due to the plurality of annular air chambers in the depressurized state, a force for attracting the bubbles discharged from the discharge port downward is generated, and the bubbles are taken out from the film take-up machine. A tension is applied between them to allow the film to be oriented and stretched.

In addition, the height of these several rectifying cylinders is made higher toward the outside, and the shape connecting these downstream ends is made a tapered guide surface that expands to the outside, so that the final bubble diameter is large. Also in the film formation, immediately after the film is discharged from the discharge port, the bubble can be expanded-molded at a stretch to a desired diameter without contacting the downstream end of the flow straightening cylinder. Further, the outside air flows between the adjacent air chambers through the outside air intake / exhaust port according to the pressure, and the pressure inside each air chamber is always maintained at a pressure suitable for bubble formation. At this time, the bubble diameter a at the crystallization temperature of the thermoplastic resin bubble is set so that the air volume of the air blown from the air cooling ring is 0. 5 so that it is located 5 to 60 cm upstream from the downstream end of the outermost annular flow straightening cylinder. It is set to 01 to 50 m ³ / min.

The ratio b / a between the bubble diameter a and the final bubble diameter b at the crystallization temperature is 1.5 to 10 times, preferably 2 to 8 times. When the ratio b / a is smaller than 1.5,
The forced stretch orientation is insufficient and the expected resin film has poor physical properties such as film strength and heat shrinkage characteristics. Also, the ratio b /
When a is greater than 10, the amount of air blown out from the air-cooling ring must be increased in order to carry out the forced stretch orientation, and molding must be performed, but the stability of bubbles is reduced by the large amount of air blown out. .

By using the straightening cylinder, an oriented film having a large blow ratio (final diameter b of film / diameter of molding die) of 3 to 25, preferably 6 to 22, can be obtained. Further, at this time, by adjusting the amount of air supplied from the cooling blower, the bubble diameter a at the crystallization temperature is positioned upstream of the position of the outermost annular rectifying cylinder, and the bubble diameter a
On the downstream side, between the bubbles due to the Venturi action and the downstream end of each annular rectifying cylinder is depressurized, and the bubbles are sucked toward the rectifying cylinder to perform forced stretching orientation to produce an oriented inflation resin film f.

The pre-stage biaxially oriented film f thus produced has an excellent mechanical strength balance between the longitudinal and lateral directions and a high heat shrinkage ratio. The oriented film f is folded in two by the rolls 14 and 14, and further, the nip rolls 18 and 18 provided on the downstream side and the nip roll 1 that rotates at a higher speed than the nip rolls 18 and 18.
It is stretched 1.2 to 5 times by 9,19.

Nip roll 1 used for this short section stretching
When the temperature of 8, 18, 19, 19 is a heating roll heated to a temperature 3 to 150 ° C. lower than the crystallization temperature of the thermoplastic resin, the short-section stretching becomes easier. The rotation speed (S ₂ ) of the second nip rolls 19, 19 is 1.2 to 5 of the rotation speed (S ₁ ) of the first nip rolls 18, 18.
Double, preferably 1.5 to 4 times. If it is less than 1.2, the shrink wrapping body wrapped by heat shrinkage does not have a good fit at both ends. If it exceeds 5 times, the strength balance in the machine direction and the transverse direction of the biaxially stretched film is disturbed, the shrink wrapping film is broken, and wrinkles are frequently generated, resulting in poor appearance.

[0040]

【Example】

Example 1 In the molding apparatus 1 shown in FIG. 2, as the rectifying cylinder 22, the rectifying cylinder 22 having an upper end inclination of 60 degrees and the dimensions shown in the following table 1 is used.
An inflation biaxially stretched film having the following three-layer structure was formed.

[0041]

[Table 1] * Height from the upper surface of the die head d.

That is, ethylene 4-methylpentene-1 copolymer resin [density: 0.910 g / cm ³ , MFR at 190 ° C. is 3.6 g / 10 minutes, crystallization temperature in DSC measurement is 100.1 ° C. ] (A) has a diameter of 65 mm, L /
Kneading was carried out at 175 ° C. using an extruder having D of 25, while ethylene / vinyl acetate copolymer resin (vinyl acetate content was 15% by weight, MFR at 190 ° C. was 2.0 g / 10 minutes,
Crystallization temperature in DSC measurement: 75.7 ° C.) 97.1
A resin composition (B) composed of 2.9% by weight of diglycerin oleate (Rikemar O-71-D, manufactured by Riken Vitamin Co.) was used at 160 ° C. using an extruder having a diameter of 50 mm and an L / D of 25. And kneading them with each other, and supplying these to an annular molding die d (diameter 50 mmφ, lip width 1.0 mm) at 175 ° C., both sides of an intermediate layer having a thickness of 11.4 μm made of the resin composition (A) in the die. In addition, each thickness of the composition (B) containing an ethylene / vinyl acetate copolymer resin as a main component, 6.
It was extruded from a die so as to obtain a laminate in which a surface layer of 8 μm was laminated, a cooling air having an air volume of 12 m ³ and a wind speed of 45 m / sec was blown to a valve with a blow ratio of 12.0. Inflation molding with a take-up speed of 20 m / min resulted in a total thickness of 25 μm (6.8 μm).
Oriented laminated film f of (11.4 μm / 6.8 μm) was obtained. At this time, as shown in FIG. 2, the bubble diameter (a) at the crystallization temperature of the bubble is located at a position where the blow ratio is about 3 times [bubble diameter (a) = 150 mm], and on the downstream side, due to the Venturi action. Forced stretching [(b) / (a) = by reducing the pressure between the bubble and each annular flow straightening cylinder]
4].

This is folded in two by rolls 14 and 14, and then the resin film is reheated by the first nip rolls 18 and 18 at a rotation speed (S ₁ ) set to about 60 ° C. and 20 m / min, and further downstream thereof. Rotation speed (S ₂ ) 40 provided on the side
m / min [(S ₂ ) / (S ₁ ) = 2] 30 ° C. second
By passing between nip rolls 19 and 19, further short-section stretching is performed, and the total thickness is 14 μm (3.8 μm).
m / 6.4 μm / 3.8 μm) to produce a three-layer stretched resin film. The strength, appearance, and strength of this three-layer stretched resin film
Table 6 shows film physical properties such as heat shrinkage characteristics and shrink wrapping suitability. Further, the height from the upper surface of the annular molding die to the downstream end of the outermost annular flow straightening cylinder, the bubble diameter, and the bubble surface temperature were as shown in Table 1.

Comparative Example 1 Inflation molding with a blow ratio of 12 times was carried out in the same manner as in Example 1 except that a cooling device except for a plurality of annular flow straightening cylinders 22 provided on the air cooling ring 21 was used. Attempting to do so, the bubble was unstable and it was not possible to produce an inflation film. Comparative Example 2 A resin film having the physical properties shown in Table 6 was obtained in the same manner as in Comparative Example 1 except that the amount of air supplied into the bubble was changed so that an inflation resin film having a blow ratio of 3 times was obtained. (B / a = 1.0).

Example 2 A resin film having the physical properties shown in Table 6 was formed in the same manner as in Example 1 except that the air cooling ring shown in FIG. 5 was used as the air cooling ring and the cooling conditions shown in Table 2 below were used. Obtained.

[0046]

[Table 2] * Height from the upper surface of the die head d.

The tree at the bubble surface temperature at this time
The crystallization temperature of the fat was also set at a position where the blow ratio was about 3 times.
[(B) / (a) = 4]. In addition, the first nip roll and
The rotation speed ratio of the 2 nip roll is (S₂) / (S ₁)But
It was molded to be 2.

Comparative Example 3 In Example 2, the amount of air blown from the air cooling ring was reduced as shown in Table 3 so that the crystallization temperature of the bubble resin appeared at the downstream end of the outermost annular flow straightening cylinder. Was similarly molded to obtain a stretched resin film having the physical properties shown in Table 6 [(b)
/ (A) is 1]. At this time, similarly, (S ₂ ) /
It was molded so that (S ₁ ) was 2.

[0049]

[Table 3] * Height from the upper surface of the die head d.

Comparative Example 4 In Example 2, the temperature of the first nip rolls 18, 18 provided on the downstream side of the rolls 17, 17 was set to 30 ° C., and the rotation speed of the second nip rolls 19, 19 was also changed to the first nip roll 18, 18. Same speed as 18 [(S ₂ ) / (S ₁ ) = 1]
To prevent forcible stretching between the nip rolls, and a take-up speed of 36 m / min so that the total thickness is 14 μm.
m (3.8 μm / 6.4 μm / 3.8 μm) of the physical properties shown in Table 6 were obtained.

Comparative Example 5 In Example 2, the first nip roll was set to about 60 ° C., the rotation speed (S ₁ ) was set to 33 m / min, and the rotation speed (S ₂ ) of the second nip roll was set to 38 m / min, so that the total thickness was 14 μm.
(3.8 μm / 6.4 μm / 3.8 μm) resin films having the physical properties shown in Table 6 were obtained [(S ₂ ) / (S ₁ ) = 1.
15].

Comparative Example 6 In Comparative Example 5, the rotation speed (S ₁ ) of the first nip roll was 5.7 m / min, and the rotation speed (S ₂ ) of the second nip roll was 40 m / min (S ₂ ) / (S _{When 1} ) was tried to be 7, the take-up speed was too slow, the bubbles became unstable, and a stretched film could not be produced.

Example 3 In Example 1, the cooling device with the internal cooling cylinder shown in FIG. 6 was used as the cooling device, the following devices and conditions were used, and the blow ratio was changed to 6.5 times. In the same manner as above, resin films having the physical properties shown in Table 6 were obtained. The crystallization temperature of the bubble resin at this time was set at a position where the blow ratio was about 2.5 times [(b) / (a) = 2.3]. Further, in this case as well, the rotational speed ratio of the first nip roll and the second nip roll was similarly shaped so that (S ₂ ) / (S ₁ ) was 2. Molding die (b) diameter: 120mmφ Lip width: 1.5mm

Air outlet height of the first air-cooling ring: same height as the upper surface of the die head b, air volume 31 m ³ /
Minute, wind speed 21m / sec. Air outlet of the second air cooling ring Auxiliary air outlet: Height 230 mm, air volume 3.5 m ³ / min,
Wind speed 18m / sec Main outlet: Height 250mm, Air volume 35m ³ / min, Wind speed 23m / sec Cylinder wall outer diameter: 380mmφ Cylinder wall height: 210mm Straightening cylinder (taper 60 degree at the upper end): As shown in Table 4 Street

[0055]

[Table 4] * Height from the upper surface of the die head d. Inner cooling cylinder Outer tube diameter: 90 mmφ, inner tube diameter: 60 mmφ, outlet: As shown in Table 5.

[0056]

[Table 5] * Height from the upper surface of the die head d.

Example 4 In Example 2, the take-up speed was 10 m / min and the second nip was
Roll rotation speed (S ₂) Was the same as 40m / min
To obtain a resin film having the physical properties shown in Table 6.
[(S₂) / (S₁) = 4]. The bubble table at this time
The crystallization temperature of the resin at the surface temperature is about 3 times the blow ratio.
It was placed in a place [(b) / (a) = 4]. Example 1
4 and the physical properties of the films obtained in Comparative Examples 1 to 6 are shown.
6 shows. Film evaluation is based on the following method. Tensile breaking strength, tensile breaking elongation: JIS Z-1702 Haze: JIS K-6714 Gloss: JIS Z-8471 (20 degrees)

Thermal shrinkage characteristics: Using the apparatus shown in FIG.
The direction was made clear, and the resin film sampled to 100 mm x 100 mm was immersed in a heat medium (standardized with silicone oil (100 c / s)) adjusted to each measurement temperature for 3 minutes, then taken out, and the shrinkage rate was calculated by the formula below. Calculate by

[0059]

[Number 1] Shrinkage _{(%) = (l V -l} ) / l V × 100 l V: original length of the specimen (100 mm) l: Length after treatment (mm)

Shrink wrapping suitability: An automatic wrapping machine manufactured by Ibaraki Seiki Co., Ltd .: SP601W (trade name) is used, and a wrapping object having a length of 100 mm, a width of 150 mm and a height of 30 mm is used. The film is fusion-sealed and packaged at a position of 20 mm. Then, this package 1
The film was shrunk by passing through a shrink tunnel set at 20 ° C. for 0.5 seconds, and the tightness of the film to the article to be packaged was evaluated according to the criteria of three stages shown in FIG. 9.

Good: Good, the heat-shrinkable film was in close contact with the article to be packed, and the appearance was good. △
Indicates that the appearance is good, but there is some air pocket. In the case of x, the heat shrinkage is not sufficient and a part of the tail remains on the film, and the appearance is poor.

[0062]

[Table 6]

[0063]

INDUSTRIAL APPLICABILITY A biaxially stretched film having excellent heat shrinkability can be efficiently produced by an inflation molding method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a stretched film molding apparatus according to a conventional inflation method.

FIG. 2 is a cross-sectional view of an inflation film molding device used for carrying out the present invention.

FIG. 3 is a cross-sectional view of a cooling device.

FIG. 4 is a partial cross-sectional view of a state in which a film is being manufactured.

FIG. 5 is a cross-sectional view of a cooling device used to carry out the present invention.

FIG. 6 is a cross-sectional view of another cooling device used to carry out the present invention.

FIG. 7 is a cross-sectional view of an inner cooling cylinder.

FIG. 8 is a perspective view of an apparatus used to measure the heat shrinkage rate of a film.

FIG. 9 shows three levels in shrink packaging suitability evaluation.

[Explanation of symbols]

 a Bubble diameter at crystallization temperature of bubble b Final bubble diameter d Molding die e Bubble f Bi-folding film 1 Inflation molding machine 11, 12 Air cooling ring 14 Take-up roll 15 Film width control device 18 Nip roll 19 Nip roll 22 Straightening cylinder 23, 23 ′ Air chamber 24 Outside air intake 25 Outside air intake / exhaust port 31 Upstream air outlet 32 Downstream air outlet 34 Circumferential wall 35 Inner cold cylinder

Front page continuation (72) Inventor Noriyuki Kobayashi 1 Toho-cho, Yokkaichi-shi, Mie Prefecture Yokkaichi Research Institute, Mitsubishi Petrochemical Co., Ltd. (72) Inventor Haruka Akaike 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Co., Ltd. Company Yokkaichi Research Institute

Claims (2)

[Claims] 1. An expanded bubble, wherein air is blown into a thermoplastic resin bubble melt-extruded from an annular molding die, and the bubble diameter at the crystallization temperature of the thermoplastic resin using the bubble is defined as (a). When the final diameter of is (b),
The oriented film obtained by inflation molding under the condition that (b) / (a) is 1.5 to 10 is folded in two, and the oriented film folded in two is further utilized by utilizing the peripheral speed difference of the nip roll group. A method for producing a biaxially stretched resin film, which comprises stretching 1.2 to 5 times in the machine direction. 2. The production method according to claim 1, wherein the blown ratio of the oriented film obtained by inflation molding is 6 to 22 times.