JP2626944B2 - Method and apparatus for forming blown film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention has a low melt tension.
In the blown film forming method, it has been difficult to form the bubble shape into a so-called long neck type (which means a bubble shape in which the bubble expands at a position far away from the die). Ethylene copolymers such as LLDPE), low density polyethylene (hereinafter LDPE) or high density polyethylene (hereinafter HDPE), ethylene-vinyl acetate copolymer, ethylene-acrylate monomer copolymer, Polypropylene, polyamide,
Even if it is a synthetic resin such as polyester, high-speed molding is possible, and a long neck type that can obtain a film with high strength is obtained. By using an inflation film molding method, heat having excellent transparency (haze, gloss, clarity) and excellent strength can be obtained. The present invention relates to a film forming method and a forming apparatus for manufacturing a plastic resin film with high productivity.

[0002]

2. Description of the Related Art There are many proposals for a method of producing an inflation film by an air cooling method, and the shape of a resin bubble for forming a film is roughly divided into four or five types according to those proposals (FIG. 1). ~ Fig.2, Fig.4
~ FIG. 5).

Factors that determine the shape of the molten resin bubble include cooling capacity, film take-up speed, molten resin temperature, and the like. Linear polyethylene such as ultra-high molecular weight high-density polyethylene (hereinafter, referred to as HMWHDPE) is used. In the case of polyethylene having a high melt tension, film forming using a so-called long neck type bubble shown in FIG. 1 or 2 is often employed, and a large amount of a high strength balance film is supplied to the field of shopping bags and the like.

However, in this method, a transparent film cannot be obtained because the molten bubble is gradually cooled.

On the other hand, currently marketed LLDPE is:
The melt tension is extremely small, the flow characteristics are significantly different from HMWHDPE, the stability of the bubble is poor, and it is difficult to form the bubble into a shape like a long neck type,
Usually, a bubble shape (referred to as a low frost line type) of the type shown in FIG.
Molded by die method. The same applies to other thermoplastic resins having a low melt tension.

In the production of blown film using this low frost line type, the molten bubble is rapidly cooled,
Although a transparent film can be obtained, the biggest problem with this method is that the stability of the bubble is poor at high speed production, the thickness and the film width are easily varied due to the sway of the bubble, and the film is produced at a high speed. Sometimes the orientation in the take-off direction becomes stronger and the strength in the vertical direction (machine direction) increases, while the strength in the direction perpendicular to this (horizontal direction) tends to be remarkably easily lost. Therefore, it is difficult to increase the take-up speed, and the productivity is limited.

In order to form a film of a synthetic resin having a low melt tension by the inflation method,
The only option is to adopt a low frost line type bubble shape that enables stable production even at low speeds, or to employ production by the T-die method.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin having a low melt tension by the air-cooled inflation method. The aim was to eliminate the instability of resin bubbles, stabilize bubbles, and establish a high productivity molding method for films with excellent transparency (haze and clarity).

[0009]

According to the present invention, there is provided a method for forming a blown film of a thermoplastic resin, wherein cooling air is blown from a first air ring provided close to a die outlet to a molten resin bubble. Then, the bubble is brought into contact with the inner surface of a stabilizer provided on the die surface while being taken off, and further a second air ring having a plurality of annular slits provided at positions where the molten resin bubble is rapidly expanded. The above object has been achieved by developing a method for forming an inflation film, wherein the temperature of the bubble at the inlet is adjusted to the melting point of the thermoplastic resin and the temperature in a range of 110 ° C. higher than the melting point. .

In addition, the extruder contacts the inner surface of the molten resin bubble.
Circular die for inflation provided with bubble stabilizer for taking out while touching, first for cooling molten resin bubble
In an apparatus for forming a blown film of a thermoplastic resin comprising an air ring and a second air ring, the second air ring has a plurality of annular slits and a second air ring.
By developing a blown film forming apparatus characterized by having a temperature measuring means for measuring the temperature of the mouth, it was confirmed that the above-mentioned blown film forming could be performed by a lieutenant.

The thermoplastic resin to be used in the present invention is L
Polyethylene such as LDPE, HDPE and LDPE; ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer and other copolymers of ethylene and radical polymerizable monomers; polypropylene, vinyl chloride, Even a thermoplastic resin having a low melt tension such as polyamide, polyester or a mixture thereof can be used. However, a high molecular weight material having as high a melt tension as possible has better bubble stability.

[0012] Even LLDPE can be taken up at high speed because of good bubble stability during molding, and the film molded by the method of the present invention is excellent in transparency and strength.
Its transparency is comparable to that of cast polypropylene film, and it can be used as an inexpensive film that can be used at low temperatures.

The following description is based on the assumption that LLDP is used as the thermoplastic resin.
With E as a representative, the molding method and apparatus of the present invention will be described with reference to the drawings.

[0014] Inflation molding methods that can be used in the present invention include upward blow (FIG. 2) and downward blow (FIG. 2).
Any of 1 ) may be used.

The extrusion temperature of the resin supplied from the extruder is:
Although it varies slightly depending on the type of the resin, the temperature is usually within a range of 40 ° C. higher than the melting point and 120 ° C. higher than the melting point.
For example, in the case of LLDPE, it is preferable to mold in a temperature range of 170 to 250 ° C.

If the temperature is lower than 170 ° C., melt fracture is likely to occur, and if the temperature is higher than 250 ° C., the melt tension is reduced, and the stability of the bubble is easily impaired.

In particular, since LLDPE or a resin composition containing the same has a property of easily causing melt fracture, the lip gap of the die is set to 2.0 to 10.0 mm.
(Preferably 2.5 to 5.5 mm) and larger than in the case of HDPE, or the surface of the molten resin bubble 3 is placed between the first air ring 2 and the second air ring 5 (on the die side from the expansion point). Taking measures such as providing a bubble heater (not shown in the drawings) for heating can prevent surface roughening. As the lip gap becomes larger than 7.0 mm, the uniformity of the film thickness is lost. Therefore, even if the melt fracture can be reduced, it should not be larger than 10.0 mm. Is preferred.

The molten resin bubble 3 extruded at a relatively low temperature is cooled by cooling air from the first air ring 2 near the die outlet.

The cooling air blowing direction of the first air ring 2 is as follows.
Although it may be blown obliquely to the take-off direction like a normal air ring, it is preferable to make it substantially horizontal.

In particular, in the case of an air ring which blows out obliquely with respect to the take-off direction, as shown in FIG.
In order to prevent the depressurized atmosphere caused by the blowing of the main cooling air from having an adverse effect on the molten resin bubble 3, a secondary outlet 22 for supplying a small amount of secondary cooling air only to compensate for the depressurized atmosphere is provided. One air ring may be used. The sub-outlet may be air from the same supply source as the main outlet, or the amount of blow-out may be adjustable independently, but the range that does not affect is relatively large, so fine adjustment is not required. Both effects are fully exhibited.

It is also a good method to provide an outlet internal stabilizer B substantially the same as or slightly thicker than the slit diameter of the die 1 at the portion where the cooling air is blown by the first air ring 2. The outlet stabilizer B may be formed of a plate, mesh, spring, or the like in order to minimize the contact resistance. With this, even if the blowing pressure of the first air ring 2 is strong, the bubble shape is maintained by the outlet stabilizer B, and this portion is effective because this portion is stabilized.

The molten resin bubble is cooled by the first air ring, is taken up while increasing the melt tension, and expands rapidly after contacting the stabilizer.

It is preferable that the stabilizer generally has an outlet stabilizer on the die side, and further coaxially supports an internal stabilizer or the like generally used for HDPE thereafter. in this case,
The molten resin bubble away from the outlet stabilizer has a long neck type shape, and has a tendency to shrink as the outlet stabilizer diameter increases, so that it stabilizes contact with the internal stabilizer.
The diameter of the internal stabilizer is not particularly limited, and may be larger than the die diameter, but preferably smaller than the outlet stabilizer,
Usually, it is preferably 0.7 to 1.0 with respect to the diameter of the die. This means that even when films of the same size are manufactured using dies of the same size, the substantial expansion ratio (ratio of bubble diameter after expansion / bubble diameter before rapid expansion) can be increased.

Conversely, this shows that there is an advantage that a film having the same expansion ratio can be produced from a film of the same size by using a die having a larger diameter.

Increasing the substantial expansion ratio has effects such as increasing the strength in the lateral direction (in the direction perpendicular to the film take-off direction) and increasing the impact strength. The substantial expansion ratio is usually 1.3. To 6.0, preferably 1.5 to 4.5.

The film obtained when the substantial expansion ratio is smaller than this value is liable to cause vertical tearing and has a low impact strength. On the other hand, when the substantial expansion ratio is 6.0 or more,
It should be avoided since the film is likely to be broken due to excessively strong lateral orientation, and it is easy to cause cutting of bubbles during production.

The internal stabilizer can be used even if it is a stabilizer for HDPE-balance film. However, it is preferable to use an internal stabilizer having a low contact resistance, for example, a ball bearing or a barrel-shaped roller is embedded at a contact position of a bubble. It is preferable to use a stabilizer using a spring, a stabilizer using a spring, a stabilizer provided with a belt that rotates in synchronization with the film running direction on the surface of the internal stabilizer, a Teflon stabilizer having a small frictional resistance, or the like.

If the contact resistance between the internal stabilizer 4 and the molten resin bubble 3 is large, even if the melt tension is increased, the bubble is easily cut due to a low dimension, so that the internal stabilizer 4 having a small contact resistance is employed. Should.

One of the important requirements in the present invention is the molten resin bubble temperature. The molten resin bubble 3 extruded from the die 1 is cooled by cooling air from the first air ring 2 or the like, and the second air bubble having a plurality of annular slits.
At the entrance of the ring (extended bottom of the die side of the second air ring)
The contact between the long line and the bubble entering the second air ring
Point part) manufactured by Chino Corporation, type IR-AP thermometer
It is necessary that the bubble temperature measured by any temperature measuring means is in the melting point of the resin used and in a temperature range higher by 110 ° C. than the melting point, and is preferably a melting point + 30 ° C. to a melting point + 80.
° C, more preferably the temperature range of melting point + 40 ° C to melting point + 80 ° C. When the temperature is lower than the melting point, not only does the molten bubble gradually cool and the transparency is reduced, but also the expansion becomes impossible or incomplete, and the dispersion becomes large. Film cannot be obtained. If the temperature is higher than this temperature, the expansion of the molten resin bubble 3 becomes uneven or the stability of the bubble is impaired, so that it is difficult to produce a uniform film.

For example, in the case of linear low-density polyethylene, the resin temperature at the inlet of the second air ring is 125 to 22.
It must be in the range of 0 ° C. The molten resin bubble expands sufficiently in the second air ring 5 or expands immediately after leaving the second air ring 5 to form a film having a predetermined thickness and size. When necessary, the film thickness is preferably 50 μm or less, more preferably 40 μm or less. According film thickness becomes thicker, which inevitably opacifying for the slow cooling. As a countermeasure, this problem can be solved to a considerable extent by using a bubble heater.

The outlets (52, 53, 54) of the plurality of annular slits of the second air ring 5 having an outlet having concentric annular slits for blowing two or more cooling air are provided.
Although air may be blown out of the bubble diameter, air is preferably blown almost parallel to the bubble take-off direction as shown in FIG.

The reduced pressure atmosphere created by blowing the cooling air from the annular slit of the air ring in the bubble take-off direction affects the molten resin bubble, and the bubble starts to expand rapidly at this position.

In FIG. 3, the outlets (52, 53, 54) of the second air ring are shown as triple annular slits. Each outlet 52, 5
Means such as making the upper end wall surfaces of the 3, 54 air outlets oblique to increase the degree of pressure reduction may be adopted. Further, a cover 55 may be attached to the tip of the air ring, which also serves to shut off the flow of the external air and the reduced-pressure atmosphere from the outside.

Therefore, the position of the frost line 8 which affects the properties of the obtained film can be freely changed by moving the position of the second air ring 5. The position of the second air ring 5 usually needs to be at least 50 mm away from the die surface, preferably at least 100 mm, more preferably at least 200 mm. If they are too close, the cooling effect is reduced and high-speed pick-up becomes difficult.

When the molten resin bubble 3 expands rapidly, the resin film becomes thinner and rapidly cooled because it becomes thin. After solidification, the air is squeezed by nip rolls as in ordinary inflation, and is taken up by a winder to form a film.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an ordinary HMWHD for a balance film.
This is an effective manufacturing method for thermoplastic resins with high melt tension, such as PE, as well as thermoplastic resins, which have low melt tension and are difficult to blow long-neck type inflation with conventional inflation molding equipment. is there.

The reason that the resin obtained by the method of the present invention has high transparency is considered as follows.

In general, it is well known that a molten resin bubble extruded from a die swells at an outlet by a swell effect, and the outer diameter of the molten resin bubble becomes larger by several% to several tens% than the diameter of the die.

When the bubble expands, the surface of the bubble shows a state of large irregularities. When the film is formed in a low frost line type bubble shape shown in FIG. 4 or FIG. 5, since the film is rapidly expanded from that state, the film surface is strongly affected by the swell effect.

However, in the case of the long neck type, the molten resin bubbles move slowly to the expansion point, and the unevenness of the surface generated by the swell is greatly alleviated. Can be greatly reduced, which is presumed to contribute to obtaining a film having a smoother surface.

For example, haze is one index of the transparency of a film. It is known that most of the haze of the film is external haze (opacity due to light impermeability caused by unevenness on the surface of the film). ing.

It is considered that the high transparency of the film in the present invention was obtained by using a long neck type which partially reduces the swell effect.

When the neck point (point immediately before rapid expansion) is lowered to the crystallization temperature, the crystal grows and the haze deteriorates. In the present invention, the temperature at the inlet of the second air ring is regulated. This problem is also avoided, and this is also considered to be one of the causes of obtaining a highly transparent film.

In the molding method of the present invention, the temperature of the molten resin bubble at the inlet of the second air ring 5 is regulated by cooling by the first air ring 2, and a plurality of annular slits (52, 53, 54) of the second air ring. Inflation molding without any problem, not only for resin with high melt tension, but also for low melt tension, by adopting a method of rapidly expanding the molten resin bubble by the reduced pressure atmosphere accompanying the blowing of cooling air from It is estimated.

In particular, the molten resin bubbles are stabilized by being brought into contact with and supported by the stabilizing body, and the high-speed take-off is possible due to the improvement of the cooling capacity due to the use of the two-stage air ring. It is considered that the transparency such as haze and image clarity was significantly improved due to a synergistic effect such as quenching.

[0046]

EXAMPLES (Example 1) Density 0.923 g / cm ³ , melting point 122 ° C, JIS K
-7210, melt flow under conditions 4 (hereinafter MF)
Called R. ) Using 1.0 g / 10 min linear polyethylene, a downward blown film forming apparatus equipped with a die having a lip gap of 3 mm and a diameter of 100 mm,
Extruded at a resin temperature of 200 ° C.

The stabilizer has a diameter of 1 whose surface is coated with Teflon.
Using a cylinder of 00mmφ, folded width 314mm, thickness 30μ
m film was formed at a take-off speed of 50 m / min. The molten resin bubble is cooled by cooling air from the first air ring or the like, and the second bubble is formed of a double annular slit.
167 ° C at the inlet of the air ring and 131 ° C at the outlet
Met. The frost line is 650 mm from the die surface,
The frost line temperature is 111 ° C. The evaluation of the obtained film is shown in Table 1.

The temperature at the inlet of the second air ring was measured using a model IR-AP thermometer manufactured by Chino Corporation at a distance of 15 mm.
The portion closest to the air ring with a diameter of 45 mm and a measurement area of 0 cm was measured. Haze, gross, and clarity were measured by the method specified in JIS K-7105.

(Examples 2 to 5) Density 0.923 g / cm
³ , MLD 1.0 g / 10 min LLDPE 80% by weight, density 0.925 g / cm ³ , MFR 0.8 g / 1
Using a resin composition consisting of 20% by weight of LDPE for 0 minutes,
Using the same apparatus as in Example 1, the film was formed under different conditions. The evaluation of the obtained film is shown in Table 1.

Example 6 Density 0.953 g / cm ³ ,
HDPE 60% by weight with MFR 0.5 g / 10 min, density 0.925 g / cm ³ , MFR 0.8 g / 10 min L
Example 1 using a resin composition comprising 40% by weight of DPE
Using the same apparatus as above, a film was formed at a resin temperature of 200 ° C. under the conditions shown in Table 1. The evaluation of the obtained film is shown in Table 1.

(Embodiment 7) In the film forming of the embodiment 4, 3.0 is provided between the first air ring and the second air ring.
A kw infrared heater (bubble heater) was provided to improve the transparency. The evaluation of the obtained film is shown in Table 1. The transparency (haze, gloss, clarity) indicates a significant improvement.

Comparative Example 1 A film was formed using the same resin and equipment as in Example 2 under the conditions shown in Table 1.
The transparency (haze, gloss, clarity) of the resulting film was significantly reduced.

(Comparative Examples 2 to 4) Inflation film molding of a low frost line type (bubble shape as shown in FIG. 4 or FIG. 5) in which a molten resin bubble expands immediately from a die outlet is made of the same resin as in Example 2. went. The evaluation of the obtained film is shown in Table 1.

Although the transparency was slightly reduced in Comparative Examples 2 and 3, even when the frost line was almost the same as in Example 1 as in Comparative Example 3, the mechanical properties of the film were significantly reduced. . In addition, the pickup speed was set to the value in the first embodiment.
When the speed was set to 50 m / min as in the cases of ２ to 2, 4 to 7, the molten resin bubbles became unstable, and cutting occurred frequently, and molding was impossible.

[0055]

[Table 1]

[0056]

According to the present invention, when a thermoplastic resin is formed into a film by an inflation method, a molten resin bubble is cooled by a first air ring provided close to a die outlet, and then brought into contact with a stabilizer. A long neck type in which the temperature of the inlet of the second air ring having a plurality of annular slits provided at the position for supporting and abruptly expanding is adjusted to a melting point of the thermoplastic resin and a temperature range higher by 100 ° C. than the melting point. It has been found that, when a film is formed by using, for example, a thermoplastic resin having a low melt tension such as LLD, the molten resin bubble is stable and a film excellent in transparency (haze and clarity) can be produced at high speed.

The molding apparatus used for this purpose can be suitably used for the above-mentioned blown film molding method.

Further, it has been found that haze and clarity can be greatly improved by providing a bubble heater between the first air ring and the second air ring to produce even a thermoplastic synthetic resin in which melt fracture easily occurs. Was.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a blown film forming method according to the present invention.

FIG. 2 is a conceptual diagram showing another example of the blown film forming method according to the present invention (an example in which the diameter of a stable body is larger than the diameter of a die).

FIG. 3 is a sectional view showing an example of a second air ring.

FIG. 4 is a conceptual diagram of an example of a conventional method of forming a blown film by a low frost line type.

FIG. 5 is a conceptual diagram of another example of a blown film forming method using a low frost line according to a conventional method.

[Explanation of symbols]

 Reference Signs List 1 die 2 first air ring 21 main outlet 22 auxiliary outlet 3 molten resin bubble 4 stabilizer 5 second air ring 51 air passage 52 outlet 53 outlet 54 outlet 55 cover 8 frost line B outlet stabilizer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Onoda 3-2 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko KK Kawasaki Resin Research Laboratories (72) Tomoaki Kobayashi 3- Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa 2 Showa Denko KK Kawasaki Resin Laboratory (56) References JP-A-63-51124 (JP, A)

Claims (6)

(57) [Claims] In a method for forming a blown film of a thermoplastic resin, cooling air is blown against a molten resin bubble from a first air ring provided near an exit of a die to cool the bubble. The inner surface of the bubble is brought into contact with the stabilizer provided on the die surface while the bubble resin temperature at the inlet of the second air ring having a plurality of annular slits provided at a position where the molten resin bubble is rapidly expanded. A method for forming an inflation film, comprising adjusting the melting point of the plastic resin to a temperature in a range of 110 ° C. higher than the melting point. 2. The thermoplastic resin having low melt tension according to claim 1, wherein the temperature of the extruded resin is adjusted to a range of 40 ° C. higher than the melting point of the thermoplastic resin and 120 ° C. higher than the melting point. Method of forming blown film. 3. The diameter of the stabilizer in contact with the molten resin bubble /
The die diameter ratio is 0.7 to 1.0, and the actual expansion ratio is 1.
3. The method for forming a blown film according to claim 1, wherein the distance from the die surface to the frost line is 3 to 6.0 mm. 4. The thermoplastic resin is a linear low density polyethylene having a lip gap of 2.5 to 5.5 mm, an extruded resin temperature of 170 to 250 ° C., and a resin temperature of 125 to 250 ° C. at the inlet of the second air ring. The method for forming a blown film according to claim 1, wherein the temperature is 220C and the thickness of the produced film is 10 to 80 m. 5. An extruder, which contacts an inner surface of a molten resin bubble.
In a blown film forming apparatus made of thermoplastic resin comprising a circular die for inflation provided with a bubble stabilizer for pulling while taking, a first air ring and a second air ring for cooling a molten resin bubble, the second air ring has a plurality of Annular slit and second air ring inlet
An inflation film forming apparatus comprising a temperature measuring means for measuring the temperature of the blown film. 6. The blown film forming apparatus according to claim 5, wherein means for heating the surface of the molten resin bubble is provided between the first air ring and the second air ring.