JPH0834053A - Production of stretched resin film - Google Patents

Abstract

PURPOSE:To produce a stretched resin film excellent in longitudinal and lateral strength balance and increased in its heat shrinkage area ratio by specifying the ratio of the diameter of a bubble and the final diameter of an expanded bubble at temp. making the absolute value of the differential value of a dynamic viscoelasticity temp. dependence curve max. CONSTITUTION:A cooling device consists of the air cooling ring 21 provided so as to face to the resin emitting orifice (h) of an annular molding die (d) and distribution cylinders 22. When inflation molding is performed by using the cooling device, the velocity of the air blown out of the air cooling ring 21 is adjusted so that a position where the temp. Tmax showing the max. of the differential value of the dynamic viscoelasticity temp. dependence curve of a bubble (e) appears is set on the upstream side of the position of the outermost annular distribution cylinder being the downstream side of the other annular distribution cylinders 5. The ratio b/a of the diameter (a) of the bubble at temp. Tmax and the final diameter (b) of the bubble is set to 1.5-10 times, pref., 2-8 times.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a stretched film of an amorphous thermoplastic resin such as polystyrene, polyvinyl chloride, polycarbonate, polymethylmethacrylate, and amorphous polyester.

[0002]

2. Description of the Related Art A blown film of a thermoplastic resin film is generally manufactured by using a blown 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 has a built-in screw 5 that is driven to rotate by a screw motor 4, and extrudes the thermoplastic resin a supplied from the supply hopper 2 as a molten resin upward from the 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 measured by the width sensor 16 of the film width measuring device 15 and then guided by the guide rolls 17, 18 and 18 and inserted into the holding punch 20 of the film winder 19. It is wound around the held paper tube g. Here, in the case of producing a bag forming film, the inflation resin film d is wound around the paper tube g 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 d 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 the holding punch 20 of the film winder and wound on several paper tubes g, g, g, g 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), which is generally 1.
The inflation resin film is molded 2 to 4 times. In the method for forming an inflation film, when the material of the bubble is a crystalline thermoplastic resin such as polyethylene or polypropylene, the bubble extruded from the annular forming die is generally supplied from the cooling blower 12 and the air cooling ring 11 Although it is cooled by the air blown out more, at this time, the bubble e is cooled and solidified (freezin).
g) It expands in the area up to (frost line: F), and on the downstream side thereafter, since it does not expand further, it is not oriented and stretched, and an inflation resin film is formed with a constant diameter.

Therefore, in the conventional blown film molding method using a crystalline thermoplastic resin, the stretch orientation is imparted to the bubbles only by the melt stretch orientation in the melting region, so that sufficient stretch orientation is not imparted to the film strength. ,
Physical properties such as appearance and heat shrinkage properties were not sufficient, and it was practically limited depending on the application (especially heat shrinkable packaging). A method of producing a stretched film by an inflation film molding method has been proposed for an amorphous thermoplastic resin which is polystyrene.

JP-A-59-49938 discloses a resin composition having a polystyrene content of 10 to 90% by weight and a styrene-butadiene block copolymer content of 90 to 10% by weight, based on 100 parts by weight of a resin composition. When a resin composition containing 8 to 70 parts by weight of high impact polystyrene is formed by an inflation method, the tubular resin composition (bubble) extruded from the die is expanded in the extrusion direction without expanding. After that, the cooling air adjusted to 45 to 110 ° C is blown onto the bubbles extruded from the die by an air ring provided near the exit of the die to cool them appropriately and the expansion start point of the bubbles is determined by the die lip. When the bubble is expanded in the extrusion direction at the same time as being expanded in the direction orthogonal to the extrusion direction by fixing the distance from 370 to 450 mm. Tighten if possible, and yet the draft ratio of the film 12 to 100, a blow ratio of 1.5 to 10.
It is described that a biaxially oriented blown polystyrene film was obtained by forming a film having a total deformation ratio of 0 to 18 to 1,000.

[0009]

Since the stretched polystyrene film produced by the above inflation molding method has a low degree of stretch orientation and a small heat shrinkage area ratio, it is a shrink film for heat shrink wrapping an article using a heating tunnel. When used as, the packaging of the corner portion of the article becomes unsatisfactory, and a contracted film tail is formed as shown in FIG. 9, resulting in a poor product appearance.

The present invention is excellent in longitudinal and lateral strength balance,
An object is to provide a method for producing an inflation stretched film of an amorphous thermoplastic resin having a large heat shrinkage area ratio.

[0011]

The present invention is a method for producing an oriented inflation resin film by blowing air into a bubble made of an amorphous thermoplastic resin to produce an oriented inflation resin film. Thermoplastic Resin Temperature-
The temperature T _{max at} which the absolute value of the differential value (rate of change) of the dynamic viscoelasticity temperature-dependent curve showing the correlation of the dynamic storage elastic modulus shows the maximum value.
Of the stretched resin film, wherein b / a is 1.5 to 10 times, and b is the final diameter of the expanded bubble. A manufacturing method is provided.

According to a second aspect of the present invention, in the above-mentioned method, an air-cooling ring having an annular blowing port is provided at the annular molten resin ejection port of the annular molding die for ejecting bubbles. On the downstream side of the air-cooling ring, a plurality of annular rectifying cylinders having different diameters are concentrically arranged with the discharge port at radial intervals, and an annular air rectifying tube having a downstream opening is provided between adjacent rectifying cylinders. A chamber is formed, and a plurality of outside air intakes are radially formed near the air-cooling ring on the outermost flow-straightening cylinder wall of these straightening cylinders, and between the lower end of the remaining straightening cylinder and the upper surface of the air-cooling ring. The outside air intake and exhaust ports that connect the air chambers to each other are bored in each of the air chambers, and the height of these several rectifying cylinders becomes higher toward the outside, and the shape connecting these downstream ends is Form a tapered bubble guide surface that expands outward Using're cooling device, a method of manufacturing a blown stretch film characterized in that the position of the bubble diameter a at the temperature T _max of the amorphous resin bubble is produced so that in the middle of the flow-guide cylinder.

According to a third aspect of the present invention, in the method according to the second aspect, air is blown from the outer periphery of the molten bubble to the bubble with an air-cooling ring which is provided in front of the annular molten resin discharge port. In addition to cooling, it is composed of a double tube that stands up from the inside of the bubble in a cylindrical shape on the same axis as the axis of the annular forming die, and multiple air blows on each cylindrical peripheral wall of the double tube. Manufacture by providing an outlet, introducing air from the inner pipe, and cooling the air from the passage between the outer pipe and the inner pipe by the air blown out from the inner cooling cylinder that can be discharged to the outside. And a method for producing an inflation stretched film.

According to a fourth aspect of the present invention, in the method described in the third aspect, the bubble extruded from the annular forming die, the outer peripheral surface of which is first provided with a first air-cooling ring immediately after the annular forming die. After being pre-cooled by the first air cooling ring, the second air cooling ring is provided downstream from the first air cooling ring and is connected to the first air cooling ring by a circumferential wall surrounding the bubble. The present invention relates to a method for producing an inflation stretched film, which is characterized in that the inside of the bubble is cooled and the inside of the bubble is cooled by an inner cooling tube.

[0015]

[Effect] According to the method of the present invention, in blown film molding, the molten amorphous thermoplastic resin bubbles extruded from the annular molding die are stored longitudinally by the air supplied from the cooling ring. After being cooled to the temperature T _max at which the rate of change of the rate becomes maximum, a plurality of annular shapes are also arranged in the downstream area thereafter, concentrically with the discharge port of the annular forming die, and located higher on the outside. By installing a straightening cylinder, by the Venturi effect,
By depressurizing the space between the bubble and the downstream end of each annular rectifying cylinder and sucking the bubble toward the rectifying cylinder, the bubble is given a further forced stretching orientation (b / a is 1.5 to 10 times) film strength, It is possible to obtain an inflation resin film having excellent appearance and heat shrinkage characteristics.

According to the present invention, the airflow blown from the air-cooling ring flows along the outer peripheral surface of the bubble, and the velocity of the airflow increases as it passes through the bubble and the upper edge of the flow straightening cylinder, and the bubble acts due to the venturi action. And a pressure-reduced state is created between the downstream ends of the respective annular rectification cylinders, and the outside air is sucked into the air chambers through the outside-air intake port and the outside-air intake / exhaust port due to the reduced pressure, and the air flow from the wind-cooling ring causes the bubble outer peripheral surface As the air flows in the air chamber, part of the air in the air chamber also moves to the outside, flows along the outer peripheral surface of the bubble, effectively cools the bubble, and the annular molding is performed by the dynamic pressure in the plurality of air chambers. A bubble in a molten state immediately after being extruded from the discharge port of the die can be stably supported from its peripheral surface, and an inflation resin film can be molded with a desired blow ratio.

When a resin film having the same take-up speed and the same thickness is formed by using this air-cooling ring and a cooling device provided with a straightening tube group having a constant tapered bubble guide surface at the downstream end of each annular straightening tube. Inflation stretched film while maintaining stable bubbles regardless of the final bubble diameter by increasing the number of air outlets for cooling air as the final bubble diameter increases and increasing the number of air chambers supporting the bubbles as necessary. Can be molded.

[0018]

[Detailed Description of the Invention] Film material The material of the thermoplastic resin film is polystyrene,
Amorphous thermoplastic resins such as polyvinyl chloride, polycarbonate, polymethylmethacrylate, and amorphous polyester are used, and these may be used alone or in admixture of two or more.

Hydrogenated petroleum resin in addition to the amorphous thermoplastic resin,
Impact improvement of hydrogenated styrene / butadiene / styrene copolymer elastomer, ethylene / propylene copolymer elastomer, ethylene / butene-1 copolymer elastomer, 1,2-polybutadiene, ethylene / propylene / ethylidene norbornene copolymer elastomer The agent 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 polybutene, 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.

Dynamic Viscoelastic Temperature Dependent Curve The dynamic viscoelastic temperature dependent curve of the amorphous resin is JIS K-
7198-991, temperature and dynamic storage modulus E '
It shows the correlation of. The temperature T at which the absolute value of the differential value (rate of change) of this dynamic viscoelastic temperature-dependent curve shows the maximum value.
_max is the temperature at which the slope (differential value) of the dispersion curve (FIG. 8) becomes _maximum . This slope is the slope of a straight line connecting two points on the dependence curve,

[0023]

## EQU1 ## Δi = (E ′ _Tn −E ′ _{Tn + 1} ) / (E ′ _{Tn + 1} −
E ′ _{Tn + 2} ) × 100 (where Δi is the gradient (differential value), and E ′ _Tn , E ′
_{Tn + 1} and E ′ _{Tn + 2} have respective temperatures T _n , T _{n + 1} ,
It is a dynamic storage elastic modulus at T _{n + 2} . ), And the temperature at which the absolute value of this gradient becomes _maximum is T _max .

When two or more kinds of the above-mentioned amorphous thermoplastic resins different from each other are used as a laminated structure or when they are used as a mixture, they are measured by the storage elastic modulus on the dynamic viscoelastic temperature dependence curve of the resins. There are a plurality of temperatures at which the rate of change of the slope of the straight line connecting the two continuous points is maximized, and the temperature on the higher temperature side is taken as T _max .

Apparatus Used for Film Forming The cooling apparatus used for forming the inflation resin film of the present invention is, for example, as shown in FIG.
The air-cooling ring 21 and the rectifying cylinder 22 are provided so as to be present in the resin discharge port h. The air-cooling ring 21 has an air outlet 21a, and on the downstream side of the air-cooling ring, a plurality of annular flow straightening cylinders 22, 22, ... It is arranged at intervals in the direction,
An annular air chamber 2 having a downstream opening between adjacent straightening cylinders
.. are formed, and a plurality of outside air intake ports 24 are provided near the air cooling ring on the outermost straightening cylinder wall of these straightening cylinders.
Are radially formed (see FIG. 3), and outside air intake / exhaust ports connecting the air chambers are formed between the lower end of the flow straightening cylinder and the upper surface of the air cooling ring. However, the heights of these several straightening cylinders become higher as they are located on the outside, and the shape connecting these downstream ends forms a tapered bubble guide surface that expands to the outside. In FIG. 3, 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. 4, in addition to the auxiliary outlet 31a on the upstream side of the air-cooling ring 30, a plurality of outlets 1 or 2 (31 or more) are provided.
b, 32), and a cooling device capable of adjusting the amount of air blown from this auxiliary outlet may be used. 26 is a first part chamber, 27 is a second part chamber, 28 is a third part chamber, and 29 and 29 'are connecting passages. Further, as shown in FIG. 5, the inside of the bubble e is also the axial center of the annular forming die d. Stand up in a cylindrical shape on the same axis as o.
A plurality of air outlets 35a, 35b, 3 are provided on the cylindrical peripheral wall.
A cooling device using the inner cooling cylinder 35 provided with 5c and 35d can be used together.

The inner cooling cylinder 35 has a double pipe structure as shown in FIGS. 5 and 6, and the cooling air supplied from the pump 10 passes through the air suction port 36 and the chamber of the inner pipe having the double pipe structure. 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 wall thickness is formed by using 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 carried out using these cooling devices, the position where the temperature T _{max at} which the differential value of the dynamic viscoelastic temperature-dependent curve of the bubble e appears is the outermost position which is the downstream side of the annular flow straightening cylinder. The wind speed of the air blown out from the air cooling ring is adjusted so that it is located upstream of the position of the annular flow straightening cylinder (1/5 to 4/5 of the height H of the outermost flow straightening cylinder).

Further, the bubbles on the downstream side of the temperature T _max are forcibly 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 having excellent film strength, appearance, heat shrinkage characteristics and the like can be obtained. In the blown film molding method of the present invention, a plurality of flow straightening cylinders are arranged on the downstream surface of the air-cooling ring in a space concentric with the discharge port, and an annular air chamber having a downstream opening between adjacent straightening air cylinders. Is formed, and a plurality of outside air intakes are radially formed in the outermost rectifying cylinder peripheral wall, and the outside air intake and exhaust for communicating the air chambers are provided between the remaining rectifying cylinder upstream end and the downstream side surface of the air cooling ring. Since each of the mouths is formed, the air flow blown toward the bubble from the air outlet and slightly heated is caused by the venturi action that occurs when flowing between the bubble and the downstream end of the straightening cylinder. A pressure is reduced between the downstream ends, and the bubbles are 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 flow straightening cylinders is made higher toward the outside, and the shape connecting the 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 temperature T _{max at} which the differential value of the dynamic viscoelastic temperature-dependent curve of the amorphous thermoplastic resin bubble is maximum is located 5 to 60 cm upstream from the downstream end of the outermost annular flow straightening cylinder. As described above, the air volume of the air blown from the air cooling ring is set to 0.
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 temperature of T _max is 1.5 to 10 times, preferably 2 to 8 times. When the ratio b / a is less than 1.5, the forced stretch orientation is insufficient and the expected physical properties such as film strength and heat shrinkage properties of the resin film are deteriorated. On the other hand, if the ratio b / a is greater than 10, the amount of air blown from the air-cooling ring must be increased in order to carry out the forced stretching orientation, and molding must be performed, but the large amount of air blows off bubbles. Stability decreases.

Further, at this time, by adjusting the amount of air supplied from the cooling blower, the bubble diameter a at the temperature T _max is located upstream of the position of the outermost annular rectifying cylinder, and is larger than the bubble diameter a. On the downstream side, the pressure between the bubble due to the Venturi action and the downstream end of each annular flow straightening cylinder is reduced,
A bubble is sucked toward the rectifying cylinder to perform forced stretching and orientation to produce an oriented inflation resin film.

The biaxially stretched film produced in this manner has an excellent balance of mechanical strength in the longitudinal and transverse directions and a high heat shrinkage ratio.

[0036]

【Example】

Example 1 (1) Measurement of T _max Specific gravity is 1.01, melt flow rate is 5 g / 10 minutes,
Polystyrene (measured at 200 ° C. and a load of 5 kgf)
Compression molded at 180 ° C, length 200mm, width 200mm,
A sheet having a thickness of 1 mm was obtained. This is 25 mm long and 2 m wide
The sample was cut into a sample having a thickness of m and a thickness of 1 mm.

Non-resonant forced extension vibration type device "RHEO VIBRON" DDV-II / III manufactured by Orientec Co., Ltd.
-Using EA (trade name), with a driving frequency of 3.5 Hz, a temperature rising rate of 2 ° C / min, and the conditions of the measurement driving unit DDV-II are vibration displacement (single amplitude) 16 µm, static tension 5 g, DDV-
Dynamic viscoelasticity was measured under the condition of III as a vibration displacement of 25 μm and a static tension of 100 g, and a dynamic viscoelasticity temperature dispersion (dependence) curve shown in FIG. 7 was obtained. The temperature T _max showing the maximum value of the differential value of this dispersion curve by the computer was 117 ° C.

(2) The cooling device shown in FIG. 4, that is, Table 1 below.
Air-cooled ring 30 having a blowout port

[0039]

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

On the top, the inclination of the upper end is 60 degrees, and the annular molding die d (diameter 50 mmφ, lip width 1.0 mm)
The height from the upper surface of the to the downstream end of the outermost annular flow straightening cylinder is shown in Table 2.
A cooling device having a rectifying cylinder 22 of the size shown in FIG. 2 was used instead of the air cooling ring 11 of the inflation molding machine shown in FIG. 1, and polystyrene having T _max of 117 ° C. and a diameter of 50 m was used.
k, using an extruder with m and L / D of 25 at 195 ° C.,
It is supplied to the annular forming die so that the thickness becomes 35 μm, the annular forming die temperature: 195 ° C., the final bubble diameter b: 4
A resin film was produced by inflation molding at 00 mm and a take-up speed of 12 m / min.

At that time, the line of temperature T _{max of} 117 ° C. of the bubble is located at a distance of 215 mm from the surface of the annular forming die, and the bubble diameter a on this line is about 210.5 m.
m (the bubble diameter and temperature in each rectifying cylinder portion are shown in Table 2), and on the downstream side, the pressure between the bubble due to the Venturi action and each annular rectifying cylinder is reduced so that the forced stretching orientation is achieved. It carried out (b / a = 1.9).

[0042]

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

Table 7 shows the physical properties of the obtained stretched film such as mechanical strength, appearance and heat shrinkage property. Comparative Example 1 In the same manner as in Example 1, except that a cooling device excluding a plurality of annular rectifying cylinders provided on the air cooling ring was used, an inflation molding with a final bubble diameter b of 400 mm was performed in the same manner. The bubble was unstable and the blown film could not be produced.

Comparative Example 2 A resin having the physical properties shown in Table 7 was prepared 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 final bubble diameter of 250 mm was obtained. A film was obtained (b / a = 1.0). Comparative Example 3 In Example 1, the bubble diameter a at the temperature T _{max of} 117 ° C. was the downstream end of the outermost annular rectifying cylinder (bubble diameter a = 40).
0 mm), the same amount of air was blown out from the air-cooling ring as shown in Table 3, and the same molding was performed to obtain an inflation resin film having the final bubble diameter b of 400 mm shown in Table 7 ( b / a = 1.0).

[0045]

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

Example 2 Inflation molding machine shown in FIG. 1 in which polystyrene having T _max of 117 ° C. was used, and a cooling device having an internal cooling cylinder shown in FIG. 5 as a cooling device was used instead of the air cooling ring 11. Melted with an extruder and the die diameter is 120 mm
It is supplied to an annular molding die d having a diameter of φ and a lip width of 1.5 mm at 195 ° C., a film is formed under the following conditions at a take-up speed of 12 m / min, and a final bubble diameter b is 840 mm and a wall thickness is 3
An inflation film having a physical property of 5 μm and shown in Table 7 was obtained.

The position of the bubble at T _{max of} 117 ° C. was 360 mm from the surface of the annular molding die, and b / a had a value of 2.3. Air outlet height of the first air-cooling ring 11: same height as the upper surface of the die head b, air volume 33 m ³ /
Minute, wind speed 22 m / sec Air outlet of the second air-cooling ring 21 Auxiliary air outlet: Height 230 mm, air volume 38 m ³ / min, wind speed 20 m / sec Main air outlet: Height 250 mm, air volume 39 m ³ / min, wind speed 26 m / Sec. Outer diameter of cylindrical wall: 380 mmφ Height of cylindrical wall: 210 mm Rectifying cylinder (upper end taper 60 °): As shown in Table 4

[0048]

[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

[0050]

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

Comparative Example 4 Using the inflation molding machine shown in FIG. 1, T _max 11
Polystyrene at 7 ° C was kneaded at 195 ° C using an extruder having a diameter of 50 mm and an L / D of 25, and a circular molding die (diameter 5
0mmφ, lip width 1.2mm), thickness 35
μm so that the temperature of the annular forming die is 195 ° C.,
The hot air temperature blown out from the air cooling ring 11 was 98 ° C., the blow ratio was 3.0, the take-up speed was 15 m / min (draft ratio 25), the final bubble diameter was d150 mm, and the bubble position at the temperature of T _max was 180 mm above the molding die. Inflation film molding was performed (b / a = 1).

At this time, Table 6 shows the height from the upper surface of the annular molding die to the bubble expansion end position, the bubble diameter, and the bubble surface temperature.

[0053]

[Table 6] * Height from the upper surface of the die head d.

Table 7 shows the physical properties of the films obtained in Examples 1 and 2 and Comparative Examples 2 to 4. Film evaluation is based on the following method. Tensile Fracture Strength, Tensile Fracture Elongation: JIS Z-1702 Haze Degree: JIS K-6714 Gloss: JIS Z-8471 (20 degree) Heat Shrinkage Property: The direction is clarified by using the device shown in FIG. After immersing the resin film sampled to 100 mm × 100 mm in a heat medium (silicon oil (100 c / s) is standard) adjusted to each measurement temperature for 3 minutes,
Take out and calculate the shrinkage rate by the following formula.

[0055]

[Number 2] Shrinkage _{(%) = (l V -1} ) / 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 is good, the heat-shrinkable film is in close contact with the article to be packed, and the appearance is 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.

[0058]

[Table 7]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a conventional blown film molding apparatus.

FIG. 2 is a cross-sectional view of a cooling device.

FIG. 3 is a partial cross-sectional view of a state in which a film is being manufactured.

FIG. 4 is a cross-sectional view of a cooling device used to carry out the present invention.

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

FIG. 6 is a cross-sectional view of an inner cooling cylinder.

FIG. 7 shows a dynamic viscoelastic temperature dependence curve.

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 temperature T _max of bubble b final bubble diameter d molding die e bubble f resin film 1 inflation molding machine 11, 21 air cooling ring 14 take-up roll 15 film width control device 19 winder 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Kobayashi 1 Toho-cho, Yokkaichi-shi, Mie Prefecture Yokkaichi Research Institute, Mitsubishi Petrochemical Co., Ltd. (72) Inventor Osamu Akaike 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Oil Chemical Company Yokkaichi Research Institute

Claims (4)

[Claims] 1. A method for producing an oriented inflation resin film by blowing air into a bubble made of an amorphous thermoplastic resin to expand the bubble, wherein the temperature-dynamics of the amorphous thermoplastic resin as a bubble raw material is changed. The bubble diameter at the temperature T _{max at} which the absolute value of the differential value (rate of change) of the dynamic viscoelasticity temperature dependence curve showing the correlation of the dynamic storage elastic modulus is the maximum is a, and the final diameter of the expanded bubble is b. In the above, a blown resin film is produced under the condition that b / a is 1.5 to 10 times. 2. The method according to claim 1, wherein an annular molten resin discharge port of an annular molding die that discharges a bubble,
An air-cooled ring having an annular outlet is provided so as to exist,
On the downstream side of the air-cooling ring, a plurality of annular flow straightening cylinders having different diameters are arranged concentrically with the discharge port at radial intervals, and an annular ring having a downstream opening is formed between adjacent straightening flow cylinders. An air chamber is formed, and a plurality of outside air intakes are radially formed near the wind cooling ring on the outermost flow straightening cylinder wall of these straightening cylinders, and the remaining bottom of the straightening cylinder and the upper surface of the air cooling ring. Outside air intake / exhaust ports that connect the air chambers to each other are formed between the air chambers, and the heights of the several straightening cylinders become higher toward the outside, and the shape connecting the downstream ends thereof is formed. Is manufactured by using a cooling device that forms a tapered bubble guide surface that spreads outward so that the position of the bubble diameter a at the temperature T _max of the amorphous resin of the bubble is in the middle of the rectifying cylinder. The manufacturing method according to claim 1, which is characterized in that. 3. The method according to claim 2, wherein
The air-cooling ring provided in front of the annular molten resin discharge port blows air from the outer periphery of the molten bubble to cool the bubble, and also from the inside of the bubble, the cylinder is on the same axis as the axis of the annular molding die. It is composed of a double pipe standing upright in the shape of a tube, and a plurality of air outlets are provided on the cylindrical peripheral wall of each of the double pipes, air is introduced from the inner pipe, and the outer pipe and the inner pipe 3. The manufacturing method according to claim 2, wherein the manufacturing is performed by cooling the air from the passage between them with the air blown out from the inner cooling cylinder that can be discharged to the outside. 4. The method according to claim 3, wherein
The outer peripheral surface of the bubble extruded from the annular forming die is first pre-cooled by the first air cooling ring provided immediately after the annular forming die, and then provided on the downstream side of the first air cooling ring, and 1 Air-cooling ring means that the second air-cooling ring, which is connected by the circumferential wall that surrounds the bubble, cools the bubble in earnest, while the inside of the bubble is also cooled by the inner cooling tube. The manufacturing method according to claim 3, characterized in that