JP2706822B2 - Method and apparatus for producing elastomer film - Google Patents

Description

The present invention relates to a method and an apparatus for producing a blown film made of a thermoplastic elastomer composition sufficiently stretched not only in the MD direction but also in the TD direction.

[Conventional technology]

BACKGROUND ART A film of a thermoplastic elastomer composition comprising an elastomer and a thermoplastic resin has elasticity and stretchability not found in a thermoplastic resin film, and is expected to be used in many fields.

As a film composed of such a thermoplastic elastomer composition, an ethylene-vinyl acetate copolymer (EV
A) Components containing components are formed by inflation, but most of them are formed by casting or extrusion. However, in film formation by casting or extrusion, stretching in the MD (longitudinal direction of the apparatus) is relatively easy, but stretching in the TD (transverse) is difficult. There's a problem. In addition, it is necessary to wrap a release paper to prevent blocking between films, which is economically problematic.

[Problems to be solved by the invention]

On the other hand, film formation by the inflation method does not have the above-mentioned problems, but it is difficult to stabilize bubbles due to the low melt tension of the thermoplastic elastomer composition during film formation. In particular, thin films (30 μm or less) are used. There was a problem that a uniform film could not be obtained because the bubbles were not stable during molding.

An object of the present invention is to provide a method and an apparatus for producing a thin and uniform air-cooled blown film made of a thermoplastic elastomer composition in view of the above problems.

[Means for solving the problem]

In view of the above problems, as a result of intensive research, the present inventors have found that when producing a film of a thermoplastic elastomer composition by an air-cooled inflation method, the film is sufficiently stretched not only in the MD direction but also in the TD direction from the neck portion to the frost line. In order to provide a cooling means that can adjust the melt tension of the thermoplastic elastomer composition to an optimal level,
By lowering the temperature of the stretching region by lengthening the neck sufficiently to allow sufficient stretching in the TD direction, the bubbles are stabilized, and it has been discovered that a uniform and thin biaxially stretched elastomer film can be obtained. The present invention has been made.

That is, the method for producing an elastomer film of the present invention comprises the steps of: (a) setting the temperature of the thermoplastic elastomer composition extruded from an annular die to 170 ° C. or lower; In order to be 1.0 to 4.0 times the diameter of the annular die,
(C) reducing the temperature of the neck portion of the bubble of the elastomer film to 120 ° C. or less by cooling air ejected from a first cooling ring provided near the annular die; While the temperature of the frost line of the bubble is 45 ° C. or less, stretching is performed in both the MD direction and the TD direction at the expansion portion of the bubble between the neck portion and the frost line. The temperature of the bubble is reduced to 35 ° C. or less by the cooling air ejected from the second cooling ring provided slightly above, and (f) the third cooling ring provided slightly above the second cooling ring The method is characterized in that the bubble is cooled to a temperature of 30 ° C. or less, and thereafter, the film is not stretched.

Further, an apparatus for producing an elastomer film comprising the thermoplastic elastomer composition of the present invention includes: (a) an annular die for extruding the thermoplastic elastomer composition at a temperature of 170 ° C. or lower; and (b) an annular die provided near the annular die. A first cooling ring for cooling the neck portion of the formed bubble to a temperature of 120 ° C. or less; and (c) provided slightly above the frost line of the bubble for cooling the bubble to a temperature of 35 ° C. or less. A second cooling ring, (d) a third cooling ring provided slightly above the second cooling ring and cooling the bubble to a temperature of 30 ° C. or lower, and (e) a bubble take-up device. In addition, the bubble take-up speed by the take-up device is such that the length of the neck portion is 1.0 to 4.0 times the diameter of the annular die.

 The present invention will be described in detail below.

In the present invention, examples of the thermoplastic elastomer composition to be formed into an elastomer film include a composition containing an ethylene-α-olefin copolymer rubber and an ethylene-vinyl acetate copolymer.

The ethylene-α-olefin copolymer rubber used in the present invention is a copolymer rubber containing ethylene and α-olefin, for example, propylene, butene-1, hexene-1, octene-1, and the like. Ternary copolymer rubber (hereinafter referred to as EPDM) obtained by copolymerizing a non-conjugated diene such as ethylidene norbornene, dicyclopentadiene, 1,4-hexadiene or the like as a third component in a combined rubber (EPR) or an ethylene-propylene system. ). Of these, EPDM is preferred.

The ethylene-propylene-diene copolymer (EPDM) used in the present invention has a content of repeating units derived from ethylene of 60 to 70 mol% and a content of repeating units derived from propylene of 30 to 40 mol. % And the content of the repeating unit derived from the diene compound is preferably 1 to 10 mol%. More preferred ranges are from 62 to 66 mol% of ethylene repeating units, from 33 to 37 mol% of propylene repeating units, and from 3 to 37 mol% of diene compound repeating units.
6 mol%.

The number average molecular weight of the ethylene-propylene-diene copolymer is preferably 400,000 to 600,000, and the density is preferably 0.87 g / cm ³ or less.

Further, the melt index (190 ° C., 2.16 kg load) of the ethylene-propylene-diene copolymer is 0.1
~ 5.0 g / 10 min is preferred, more preferably 0.30
~ 1.0g / 10min.

The ethylene-propylene-diene copolymer (EPDM) used in the present invention is basically composed of the above-mentioned repeating units, but within a range not impairing the properties of the copolymer, for example, butene-1 Alternatively, it may contain another repeating unit such as a repeating unit derived from an α-olefin such as 4-methylpentene-1.

Ethylene-vinyl acetate copolymer (EV used in the present invention)
A) is a copolymer having a vinyl acetate repeating unit content of 5 to 30% by weight and a melt index (190 ° C., 2.16 kg load) of 0.2 to 25 g / 10 minutes. When the content of vinyl acetate is less than 5% by weight, rubber elasticity is inferior. On the other hand, when the content is more than 30% by weight, the film is blocked and film formation becomes difficult. Preferred vinyl acetate content is 15-30
% By weight. The melt index is 0.
If it is less than 2 g / 10 minutes, the film forming processability is poor, and if it exceeds 25 g / 10 minutes, it becomes difficult to form a film by the air-cooled inflation method. The preferred melt index is between 0.5 and 25 g / 10 minutes.

The mixing ratio of the ethylene-propylene-diene copolymer (EPDM) in the thermoplastic elastomer composition is 30 to 70% by weight based on the resin component (100% by weight).
Preferably, it is in the range of 0 to 60% by weight. The mixing ratio of the ethylene-propylene-diene copolymer (EPDM) is
If the amount is less than 30% by weight, the stretch ratio of the obtained elastomer film is reduced, and when a composite film is formed, microporization due to heat shrinkage is insufficient. On the other hand, when it is higher than 70% by weight, the moldability of the obtained elastomer film is reduced.

On the other hand, the ethylene-vinyl acetate copolymer (EV
The compounding ratio of A) is based on the resin component (100% by weight).
It is preferably from 70 to 30% by weight, particularly preferably from 50 to 40% by weight. The above ethylene-vinyl acetate copolymer (EV
The reason for limiting the blending ratio of A) is exactly the same as the reason for limiting the ethylene-propylene-diene copolymer described above.
If the amount is less than 70% by weight, the moldability decreases. If the amount is more than 70% by weight, the elongation of the elastomer film becomes insufficient.

The rigidity and moldability of the thermoplastic elastomer composition of the present invention can be improved by adding a thermoplastic polyolefin. Examples of the thermoplastic polyolefin include homopolymers of α-olefins such as ethylene, propylene, butene-1, pentene-1, hexene-1, and 4-methylpentene-1; and ethylene and propylene or other α-olefins. And copolymers of two or more of these α-olefins.
Among these, polyethylene and polypropylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene are preferable. Polypropylene is not limited to homopolymer,
Random or block copolymers with other α-olefins containing at least mol%, preferably at least 80 mol%, can also be used. Comonomers copolymerized with propylene include ethylene and other α-olefins, with ethylene being particularly preferred. Thus, the term "polypropylene" as used herein is to be understood as not being limited to homopolymers of propylene but also including copolymers.

The addition amount of the thermoplastic polyolefin is the above-mentioned EPDM
The amount is preferably 1 to 30 parts by weight based on the weight of + EVA (100 parts by weight). If the amount is less than 1 part by weight, there is no effect on the improvement of rigidity and moldability, and if it exceeds 30 parts by weight, the elastomeric properties of the obtained composition are reduced.

By adding a powdery inorganic filler, the thermoplastic elastomer composition can also improve blocking resistance and heat resistance, and can facilitate microporosity in a composite film. it can. As the inorganic filler, talc, calcium carbonate, gypsum,
Carbon black, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, calcium phosphate, aluminum hydroxide, zinc oxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide,
Alumina, mica, shirasu balloon, zeolite, silicate clay, cement, silica fume, mica powder and the like can be used, but talc, titanium oxide, calcium carbonate, silica and the like are particularly preferable. The average particle size of the inorganic filler is 5 μm or less, preferably 1 to 3 μm.

These powdery inorganic fillers can be used alone or in combination. The total amount of the powdered inorganic filler added is preferably 2 to 15 parts by weight based on the weight of EPDM + EVA (100 parts by weight). If the amount is less than 2 parts by weight, the effect of adding the powdery inorganic filler may not be remarkably exhibited, and if the amount exceeds 15 parts by weight, the strength of the obtained composition may be rather reduced. However, since the film forming property and stretch processability of the composition obtained by adding the inorganic filler are reduced, the amount of the inorganic filler is
It is preferable to appropriately select within the above range according to the use of the elastomer film.

In the present invention, in addition to the above additives, a heat stabilizer, an ultraviolet absorber, an antistatic agent, an antioxidant, a coloring agent, and the like can be appropriately compounded.

To produce an elastomer film from the thermoplastic elastomer composition, first, kneading the ethylene-propylene-diene copolymer (EPDM), ethylene-vinyl acetate copolymer (EVA) and desired additives, It is necessary to perform at a resin temperature of 170 ° C. or less. In particular, in the present invention, kneading is preferably performed at a resin temperature in the range of 145 to 165 ° C. If the kneading temperature is higher than 170 ° C., the thermal deterioration of the resin proceeds, generating an unusual odor or exhibiting tackiness. Therefore, when kneading is performed in an extruder such as a twin-screw extruder, one having a screw structure that does not generate heat, or one having an appropriate cooling device is used. When the lower limit of the kneading temperature is lower than 145 ° C., the extrusion amount becomes unstable, which is not preferable.

The resin temperature immediately after being extruded from the inflation annular die also needs to be 170 ° C. or less. If the temperature of the bubble immediately after the annular die extrusion exceeds 170 ° C., the bubble cannot be cooled to 45 ° C. or less by the first cooling ring. Particularly preferably, the temperature of the bubble immediately after the extrusion of the annular die is 145 to 165 ° C.

The bubble extruded from the annular die is stretched not only in the MD direction but also in the TD direction while being cooled by the air-cooled inflation method by the apparatus of the present invention. This is shown schematically in FIG.

In FIG. 1, the air-cooled inflation device includes an annular die 1, a first cooling ring 2 provided near the annular die 1, a second cooling ring 3 provided above the first cooling ring 2, And a third cooling ring 4 provided slightly above the two cooling rings.

In the apparatus having the above configuration, the arrangement of each cooling ring is determined by controlling the temperature of the bubble formed by the air-cooled inflation method. First, the shape and temperature distribution of the bubble will be described.

The molten thermoplastic elastomer composition is extruded from the annular orifice 11 of the die 1 to form a bubble 5.
The bubble 5 immediately after being extruded has a small diameter due to a low melt tension, and forms a so-called neck portion 51. Neck
At 51, the bubble 5 is stretched mainly in the MD direction.
Next, the bubble 5 expands rapidly and reaches a predetermined bubble diameter. In the expanding portion 52, the bubble 5 is extended not only in the MD direction but also in the TD direction. A frost line 54 is provided near the upper end of the expanded portion 52, where the thermoplastic elastomer composition is cooled and solidified. The bubbles are further cooled by the second cooling ring 3 and the third cooling ring 4 provided in the bubble region 53 above the frost line 54.

In order to obtain a biaxially stretched elastomer film by the air-cooled inflation method, it is necessary to control the temperature of each part of the bubble 5 as follows.

(A) The temperature immediately after extrusion from the annular die 1 is 170 ° C. or less.

(B) The neck 51 is cooled down to 120 ° C. or less.

(C) In the frost line 54, cool down to 45 ° C or less.

(D) Cooling to 35 ° C. or less by the second cooling ring 3.

(E) Cool down to 30 ° C. or less by the third cooling ring 4.

The above condition (a) is as described above. However, in the condition (b), unless the neck portion 51 is cooled down to 120 ° C. or less, the TD direction stretching is sufficiently achieved in the next expanded portion 52. Can not do. That is, if the temperature is not cooled to 120 ° C. or lower in the neck portion 51, the expansion portion 52 does not have a sufficient melt tension, and stretching in the MD direction is mainly performed. On the other hand, if the neck portion 51 is excessively cooled, it is difficult to form the expansion portion 52 (that is, the bubble 5 extends in the TD direction).
The lower limit of the bubble temperature in 51 needs to be about 90 ° C. Cooling at the neck 51 is preferably performed at 90 to 110 ° C.

In order to satisfy such a temperature condition, it is necessary to make the neck 51 relatively long. The length of the neck portion 51 depends on the bubble diameter, wall thickness, temperature, the flow rate of the cooling air from the first cooling ring 2, and the like. The diameter of the annular die is equal to the diameter of the die or 5 to 15% smaller than the diameter of the annular die.
The take-off speed may be 0 to 4.0 times as long. Further, the blow-up ratio is preferably 1.5 to 5.0, particularly 3.0
~ 4.5 is desirable.

With respect to the condition (c), the cold stretching of the bubble 5 can be achieved by lowering the bubble temperature in the frost line 54 to 45 ° C. or less. When the thermoplastic elastomer composition is stretched at about 35 to 50 ° C., the ethylene-propylene-diene copolymer component partially elongates and crystallizes. For this reason, if the bubble temperature in the frost line 54 is higher than 45 ° C., the expansion of the bubble 5 in the MD direction and the TD direction in the expansion section 52 is insufficient.

Regarding the condition (d), the formation of a uniform thin bubble can be stabilized by cooling the bubble 5 to 35 ° C. or lower above the frost line 54. Without providing the second cooling ring 3, the temperature of the bubble above the frost line 54 is reduced.
If the temperature is kept higher than 35 ° C., non-uniform stretching may occur, so that the entire bubble becomes unstable. It is preferable to cool the temperature of the region 53 of the bubble 5 to 25 to 30 ° C. by the second cooling ring 3.

Regarding the condition (e), if the bubble 5 is completely cooled only by the second cooling ring 3, uneven cooling may occur. Therefore, it is necessary to further cool using the third cooling ring 4. . The cooling of the bubble 5 by the third cooling ring 4 is not more than 30 ° C., particularly preferably 20 to 25 ° C. Due to the second cooling ring 3 and the third cooling ring 4, stretching does not occur in bubbles above it.

In order to control the temperature of the bubble 5 as described above, the arrangement of the first cooling ring 2, the second cooling ring 3, and the third cooling ring 4, and the take-up speed of the take-up device must be as follows. is there.

(A) The first cooling ring 2 is provided in the immediate vicinity of the annular die 1 and the temperature of the neck 51 is
Inject cooling air so that the temperature drops to 0 ° C or less.
Thus, the temperature of the bubble 5 in the frost line 54 after the expansion section 52 becomes 45 ° C. or less.

(B) The second cooling ring 3 The annular die 1 has a distance H ₂ of 5 to 10 times the diameter of the annular die 1.
And air is blown out so that the temperature of the bubble 5 becomes 35 ° C. or less.

(C) disposed from the third cooling ring 4 an annular die by a distance H ₃ of 0.5 to 5.0 times the first diameter second cooling ring 3 above the position, the temperature of the bubble 5 30
Cooling air is blown out to below ℃.

(D) the length H ₁ of the take-up speed neck portion 51 of the take-up device is set to be 1.0 to 4.0 times the diameter of the annular die 1. Thus, the temperature of the neck portion 51 can be reduced to 120 ° C. or less by the first cooling ring 2.

In the above method, it is preferable to use humidified air as the cooling air injected from the first to third cooling rings 2 to 4 into the bubble 5 from the viewpoint of cooling efficiency. The humidified air is air humidified and cooled with cold water, contains almost saturated water, and has a cooling effect of about 5 ° C. greater than that of mere cooling air.
If a stable cooling effect cannot be obtained, the bubble 5 becomes unstable, so it is necessary to control the temperature and humidity of the cooling air so as not to change as much as possible.

The obtained elastomer film is preferably annealed to suppress heat shrinkage and prevent blocking. For this, the elastomer film is heat-treated at 50-60 ° C. and then cooled.

The elastomer film thus obtained is MD
Since it is stretched not only in the direction but also in the TD direction, there is no anisotropy with respect to heat shrinkage. Specifically, the draw ratio represented by the heat shrinkage at 50 ° C. is 5 to 35% in the MD direction, particularly 15%.
3535%, 5-25% in the TD direction, especially 10-25%. In the case of unstretched, the heat shrinkage is 0. in this way,
Since both the MD direction and the TD direction have a sufficiently large heat shrinkage, a good microporous film can be obtained when combined with a woven or nonwoven fabric.

Here, for the case of EPDM / EVA = 60/40 (weight ratio), an example of the film forming conditions for producing an elastomer film by the air-cooled inflation method of the present invention is shown below with typical film forming conditions by a water-cooled inflation method. The comparison is shown in Table 1 below.

As described above, in the air-cooled inflation method, both the melt-kneading temperature of the resin in the extruder and the temperature at the exit of the annular die are set to 170 ° C. or less, and the inflation is performed so that a thin film is formed at a high take-off speed. You can see that.

In the case of the air-cooled inflation method, the effect of the resin temperature at the outlet of the annular die on the melt tension and film-forming properties of the bubble is described by taking EPDM / EVA = 60/40 (weight ratio) as an example.
It is shown in Table 2 below.

Thus, in the air-cooled inflation method, if the resin temperature at the outlet of the annular die is not higher than 170 ° C., the melt tension is not sufficient, and stable bubbles are not formed. On the other hand, when the temperature is lower than 140 ° C., the melt tension becomes too large, and the bubbles become rather unstable.

(Operation)

The thermoplastic elastomer composition is rich in stretchability in a relatively low temperature range of 40 to 60 ° C. Accordingly, whether or not bubbles can be formed in the stretched region determines the film forming property, thinning, and physical properties of the film. In order to perform stretching by the air-cooled inflation method in a low temperature region of 40 to 60 ° C., first, a neck portion is formed in a temperature region showing a melt tension capable of forming a stable film, and then a neck portion is formed from a frost line. The material is cooled and solidified while being axially stretched. In this way, uniform thin bubbles can be stably formed.

〔Example〕

 The present invention is described in more detail by the following examples.

Example 1, Comparative Examples 1-2 Ethylene-propylene-diene copolymer (Vistalone
3708, manufactured by Exxon Chemical Co., Ltd.) and a composition comprising 40% by weight of an ethylene-vinyl acetate copolymer (vinyl acetate content: 28% by weight, melt index: 20 g / 10 minutes) was mixed with a twin-screw kneader. The mixture was melt-kneaded and formed into an elastomer film by an air-cooled inflation method (Example 1, Comparative Example 1) and a water-cooled inflation method (Comparative Example 2). Table 3 shows film forming conditions and properties of the obtained elastomer film. FIG. 2 shows the film forming conditions of Example 1.

[Effects of the Invention] As described in detail above, the elastomer film manufactured by the method of the present invention is stretched not only in the MD direction but also in the TD direction, so that it shows substantially uniform heat shrinkage in the biaxial directions. . Further, in the method for producing an elastomer film by the air-cooled inflation method of the present invention, the temperature of each part of the bubble of the elastomer film (immediately after extrusion, the neck portion, the expanded portion, the frost line) is controlled to an optimum range, so that the uniform thickness can be obtained. The obtained biaxially stretched elastomer film can be obtained stably.

Since the elastomer film obtained by the present invention is itself biaxially stretched, it is possible to form a microporous composite film by directly forming a composite with a woven or nonwoven fabric without heat-shrinking without a stretching step. it can.

Such a microporous film can be used for various kinds of clothing by utilizing waterproofness and moisture permeability, in particular, it can be used not only for disposable rain gear, gloves, sheets, diapers, etc., but also for deodorants and fragrances. It can also be widely used for packaging materials such as sustained release agents.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a manufacturing apparatus of the present invention, and FIG. 2 is a schematic diagram showing film forming conditions of Example 1. 1 ... annular die 2 ... first cooling ring 3 ... second cooling ring 4 ... third cooling ring 5 ... bubble 51 ... neck 52 ... expansion section 54 ... frost line

Claims (9)

(57) [Claims] 1. A method for producing an elastomer film from a thermoplastic elastomer composition by an air-cooled inflation method, comprising: (a) setting the temperature of the thermoplastic elastomer composition extruded from an annular die to 170 ° C. or lower; As the length of the neck portion of the bubble of the elastomer film is 1.0 to 4.0 times the diameter of the annular die,
(C) the temperature of the neck portion is reduced by cooling air ejected from a first cooling ring provided near the annular die.
120 ° C. or less; (d) While the temperature of the frost line of the bubble is 45 ° C. or less, the expansion portion of the bubble between the neck portion and the frost line extends in both the MD direction and the TD direction. (E) the temperature of the bubble is reduced to 35 ° C. or less by cooling air ejected from a second cooling ring provided slightly above the frost line, and (f) provided slightly above the second cooling ring. Cooling the bubble to a temperature of 30 ° C. or less by the third cooling ring provided, and thereafter, does not perform stretching of the film. 2. The method for producing an elastomer film according to claim 1, wherein humidified air is used as said cooling air. 3. The method for producing an elastomer film according to claim 1, wherein the bubble is drawn at a stretching ratio of 50 ° C.
In the MD direction) is 5 to 35%,
A method characterized by being 5 to 25% in the TD direction. 4. An apparatus for producing an elastomer film made of a thermoplastic elastomer composition by an air-cooled inflation method, comprising: (a) an annular die for extruding the thermoplastic elastomer composition at a temperature of 170 ° C. or less; A first cooling ring provided near the annular die and cooling the neck of the formed bubble to a temperature of 120 ° C. or less; and (c) provided slightly above the frost line of the bubble, and cooling the bubble to 35 ° C. or less. (D) a third cooling ring provided slightly above the second cooling ring and cooling the bubble to a temperature of 30 ° C. or less; and (e) pulling the bubble. A take-up device, wherein the take-up speed of the bubble by the take-up device is such that the length of the neck portion is 1.0 to 4.0 times the diameter of the annular die. Characteristic device. 5. The apparatus according to claim 4, wherein said second cooling ring is located at a distance of 5 to 10 times the diameter of said annular die. 6. The apparatus according to claim 4, wherein the third cooling ring is located at a distance of 0.5 to 5.0 times the diameter of the annular die from the second cooling ring. And equipment. 7. The apparatus according to claim 4, wherein the diameter of the neck portion immediately after extrusion is 0 to 15% smaller than the diameter of the annular die. 8. The apparatus according to claim 4, wherein humidified air at 5 to 28 ° C. is used as cooling air. 9. Apparatus according to claim 4, wherein said annular die is provided with stabilizing means positioned to be surrounded by said neck.