JPH10109352A - Control of film thickness and surface roughness of extrusion molded film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily regulate film thickness and surface roughness by spraying water droplets regulated in particle size, spray pressure and spray quantity on an extrusion molded resin sheet during a period when the temp. of the sheet from a die is its softening point or higher. SOLUTION: An extruder 10 has an extrusion die 11 and a raw material charging hopper 12 and a pair of chill rolls 14, a plurality of stretching roll groups 16, a film thickness meter 17 and a taking-up roll 18 are provided on the downstream side of the die 11. A plurality of waterdrop nozzles 20 are arranged in the lateral direction of a sheet. Waterdrops are applied to the sheet during a period when the temp. of the sheet is yet the softening point of the sheet immediately after extrusion to regulate film thickness. The particle size of sprayed waterdrops is set to 1-150μm in order to accurately control quenching effect, film thickness and surface roughness. Spray pressure is set to 0.1-10kgf/cm<2> in order to eliminate the deformation of a film and spray quantity (spray density) is set to 0.01-1l/hr/cm<2> so that film thickness and surface roughness can be regulated by quenching effect and water quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the thickness and surface roughness of an extruded resin film, and more particularly, to controlling the thickness and surface roughness of a resin film by spraying water droplets. And a method for effectively controlling the surface roughness.

[0002]

2. Description of the Related Art Extruded films such as unstretched films, biaxially stretched films and microporous films have a film thickness distribution in the width direction as shown in FIG. The part and the thin part are respectively located at the same position in the width direction. The untreated resin film 1 has a front surface 1a and a back surface 1b.
And each surface has finer irregularities 2. In FIG. 5, the irregularities 2 are shown only on the surface 1a. As described above, since the film has a film thickness distribution in the width direction of the film, when the film is stretched and wound as it is, the thick portions and the thin portions overlap each other, and the roll diameter becomes extremely uneven, and the roll winding appearance becomes Inferior. For this reason, the film may be deformed non-uniformly, and the quality is reduced. In order to avoid this problem, a uniform thickness is required for the resin film.

For this reason, the film thickness of these films has been conventionally controlled. However, the conventional control method is a method of adjusting a lip bolt of a sheet extrusion die manually or by a robot, and a heat expansion method utilizing thermal expansion. In this method, the lip bolt is finely adjusted by the expansion and contraction of the bolt, and the lip clearance is automatically adjusted.

In the case of the method described above, the manual operation of the lip bolt depends on the experience and intuition of the operator, and it is difficult to uniformly adjust the film thickness. There is also a problem that it is difficult to cope with a film thickness variation caused by a deviation of the raw material properties (raw material composition, flow characteristics, etc.) during film formation. On the other hand, if a robot is used, the operation will be uniform,
There is a problem that the mechanism becomes complicated.

In the case of the method (1), although the automatic adjustment of the lip clearance can cope with the film thickness fluctuation caused by the deviation of the raw material properties during the film formation, the response time is slow and the adjustment width in the width direction is limited. There are points. In particular, in the case of film formation including a stretching step, there is a problem that it is difficult to control the film thickness only by adjusting the die lip.

[0006] It is necessary to roughen the film surface to prevent blocking as well as to make the film thickness uniform. If the film surface is too flat, blocking tends to occur, which is not preferable. Since the uniformity of the film thickness and the roughening are inconsistent requirements, they cannot be achieved by the above-mentioned conventional method.

Accordingly, it is an object of the present invention to provide a method for adjusting the thickness and surface roughness of an extruded resin film.

[0008]

As a result of intensive studies in view of the above-mentioned object, the present inventors have found that the extruded resin sheet sprays water droplets before reaching the frost line. It has been found that the thickness and the surface roughness of the resin film can be controlled by controlling the thickness, and the present invention has been reached.

That is, in the method of controlling the thickness and surface roughness of an extruded film according to the present invention, a molten resin is extruded from an extrusion die to form a resin sheet, and the resin is formed at a temperature above the softening point. Spray water drops on the sheet,
At this time, the thickness and the surface roughness of the extruded film are controlled by controlling the particle diameter, speed and density of the water droplet.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. FIG. 1 is a schematic diagram showing an apparatus for performing the method of the present invention.
The extruder 10 has an extrusion die 11 and a film material input hopper 12, and a pair of chill rolls 1 is provided downstream of the die 11.
4, a plurality of stretching roll groups 16, a film thickness gauge 17, and a winding roll 18
Are sequentially provided. Although any die can be used as the extrusion die 11, in the present embodiment, a flat die will be described as an example.

[0011] The raw material resin for the film whose film thickness and surface roughness can be controlled by the method of the present invention include polyolefins such as polypropylene, high density polyethylene and ultra high molecular weight polyethylene, polyesters such as polyethylene terephthalate, and 6,6. -Polyamides such as nylon are preferred, and polyolefins are particularly preferred. The melt viscosity of the resin is preferably between 5,000 and 100,000 poise (measured at 230 ° C).

The resin melt-kneaded by the extruder 10 is extruded as a resin sheet S from a flat die 11. The extrusion temperature is preferably the melting point of the resin plus 20 to 150 ° C, and particularly preferably 250 to 280 ° C for polypropylene. The amount of resin discharged is set so as to obtain a desired film thickness. The film thickness of the resin sheet S before stretching suitable for carrying out the method of the present invention is generally 1.0 to 3.0 mm.

Since the resin sheet S is still at a temperature higher than the softening point immediately after extrusion, the resin sheet S is rapidly cooled by contact with the chill roll 14. In the method of the present invention, water droplets are formed while the resin sheet S is at a temperature higher than the softening point. To adjust the thickness of the resin film. For this purpose, water droplets are sprayed on the resin sheet S from a plurality of water droplet nozzles 20 provided upstream of the frost line FL.

FIG. 2 schematically shows a water droplet nozzle 20 as a water droplet spraying device. A plurality of water droplet nozzles 20 are arranged in the width direction of the sheet. The interval between the water droplet nozzles 20 can be set arbitrarily, but is preferably arranged at an interval of 10 to 50 mm.
The distance between the water droplet nozzle 20 and the sheet S is preferably 10 to 100 mm, and particularly preferably about 40 to 70 mm. If the distance from the sheet S is less than 10 mm, the spray pressure on the sheet S is too high, and it is difficult to make the film thickness uniform. On the other hand, if the distance from the sheet S exceeds 100 mm, the effect of spraying water droplets is excessively reduced. Reference numeral 26 denotes a spray area of a water droplet.

In a preferred embodiment, the distance between the flat die 11 and the chill roll 14 is about 100 to 300 mm, and the frost line FL is located at a position substantially equal to or less than about 10 mm downstream of the contact point with the chill roll 14. The spray area 26 of the water droplets may be located on or upstream of the frost line FL, but is practically preferably about 1 to 50 mm upstream of the FL.

The particle size of the sprayed water droplet is controlled in the range of 1 to 150 μm. If the particle size of the water droplets is less than 1 μm, the quenching effect is insufficient, and if it exceeds 150 μm, it does not evaporate instantaneously due to contact with the resin film, and the control of the film thickness and surface roughness becomes inaccurate. Preferred droplet size is 10 to 10
0 μm, especially 10 to 60 μm.

The spray pressure (gauge pressure) is preferably controlled in the range of 0.1 to 10 kgf / cm ² . Quenching effect and by water droplets spray pressure is less than 0.1 kgf / cm ² is insufficient, also 10
If it exceeds kgf / cm ² , the resin film may be deformed due to excessive pressure. The preferable control range of the spray pressure is 0.5 k to
It is 5 gf / cm ² .

The spray amount (spray density) of sprayed water droplets is 0.01
It is controlled in the range of 〜1 liter / hour / cm ² . If the spray amount of the water droplet is less than 0.01 liter / hour / cm ² , the quenching effect by the water droplet is insufficient, and 1 liter / hour / cm 2
^If it exceeds ² , the effect of adjusting the film thickness and the surface roughness cannot be exhibited due to an excessive amount of water. . The preferable spray amount of the water droplet is 0.05 to 0.2 liter / hour / cm ² .

The temperature of the sprayed water droplets is preferably from 5 to 80 ° C, more preferably from 15 to 40 ° C. If the water droplet temperature is less than 5 ° C., the effect of adjusting the film thickness is insufficient, and if it exceeds 80 ° C., it is difficult to make the film thickness uniform.

As shown in FIG. 2A, a plurality of rows of water droplet nozzles 20 are used. The position in the width direction of each water droplet nozzle 20 is a thick portion of the film. The film is quenched by spraying water droplets, and the stretching ratio is reduced, so that the film thickness in the width direction of the stretched film is made uniform. Thereby, the winding appearance of the film roll is improved. Further, by intentionally applying the thickness unevenness periodically in the MD (longitudinal) direction, it is possible to disperse the stress due to the shrinkage of the film, thereby further improving the winding appearance of the film roll.

FIG. 3 shows a cross section of the resin film sprayed with water drops under the above conditions. The difference D between the maximum film thickness A and the minimum film thickness B is a parameter of the film thickness uniformity. The thickness difference D is preferably 0.5 to 15 μm. The thickness difference D is 0.5 μm
If it is less than 15 μm, the surface roughness is insufficient, and if it exceeds 15 μm, the uniformity of the film thickness decreases.

FIG. 4 is a partially enlarged view of the film shown in FIG. The surface roughness of the film is determined by the average pitch P of the surface irregularities 2 and the difference (concavity and convexity) C between the maximum value and the minimum value of the surface irregularities 2. The average pitch P is preferably from 0.1 to 20 mm. If the average pitch P is less than 0.1 mm, the slope of the surface unevenness is too steep, and if it exceeds 20 mm, the surface becomes too smooth and blocking between the films is likely to occur. Further, the unevenness difference C is preferably 0.5 to 10 μm.
If the unevenness C is less than 0.5 μm, blocking between the films is likely to occur, and if it exceeds 10 μm, the uniformity of the film thickness is reduced.

As the film thickness meter 17 before the winding roll 18, it is preferable to use a film thickness meter having a structure capable of measuring the thickness distribution in the width direction of the film F. In this case, the particle diameter, spray pressure, and spray amount of the water droplet ejected from the water droplet nozzle 20 can be adjusted according to the difference (the measured value of the film thickness−the target value of the film thickness) by a normal feedback method.

The sheet S whose thickness has been adjusted passes between a pair of chill rolls 14, is cooled to a temperature sufficiently lower than the softening point, and is stretched by a multi-stage stretching roll group 16. In the embodiment shown in FIG. 1, the film is uniaxially stretched, but may be biaxially stretched if necessary. The stretched film F is finally wound up on a winding roll 18.

[0025]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto.

Examples 1-4 As shown in FIG. 2, melt-kneaded polypropylene (melt viscosity: 15,000 poise (measured at 230 ° C.), density: 0.9 g / cm
³ ) was extruded from an extrusion die (flat die) 11 into a sheet. The film forming conditions are as follows. Molding resin temperature: 280 ° C. Discharge rate: 50kg / hr. Die orifice width: 500 mm. Die orifice lip gap: 1.2 mm. Stretching ratio: 45 times (9 times long x 5 times wide). Average film thickness of the stretched film: 25 μm.

At the position before the frost line FL of the resin sheet, four water droplet nozzles (BIMV8002, Ikeuchi Co., Ltd.)
20) were arranged according to the film thickness distribution. Water droplets were sprayed under the conditions shown in Table 1, and changes in film thickness and surface roughness due to the water droplet spraying conditions were examined. Conditions other than those shown in Table 1 are as follows. Table 2 shows the measurement results. Spray length of water droplet nozzle (treatment length): 10 m. Distance between water drop nozzle and sheet: 50mm. Distance between spray position and frost line FL: 5
mm. Drop temperature: 15 ° C. Spray interval: continuous. Experimental atmosphere temperature: 30 ° C.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that the water droplet spraying treatment was not performed. Table 2 shows the measurement results.

Table 1 Water droplet particle size Spray pressure Spray amount No. (μm) (kgf / cm ² ) (L / hr / cm ² ) Example 1 20 1.0 0.1 Example 2 15 1.5 0.1 Example 3 40 0.7 0.1 Example 4 40 1.0 0.2 Comparative Example 1---

Table 2 Surface roughness average film thickness Film thickness difference Concavo-convex difference C Average pitch P No. (μm) (μm) (μm) (mm) Example 1 23.5 5.0 6.0 5.0 Example 2 23.5 4.0 5.0 4.0 Example 3 23.5 5.0 7.0 7.0 Example 4 23.5 4.0 11.0 12.0 Comparative Example 1 25.0 6.0 4.0 3.0

As is clear from Tables 1 and 2, the uniformity of the film thickness and the surface roughness can be adjusted by adjusting the particle diameter, spray pressure and spray amount of water droplets.

Example 5 Four water droplet nozzles 20 were arranged in the width direction according to the film thickness distribution of the sheet, and under the conditions shown in Table 3, water droplet spraying was performed on the entire surface of the sheet, and the film was wound 4,000 m. Of the roll was observed. Table 3 shows the results.

Comparative Example 2 A film was formed in the same manner as in Example 5 except that the water droplet spraying treatment was not performed. Table 3 shows the measurement results.

Table 3 Water droplet particle size Spray pressure Spray amount No. (μm) (kgf / cm ² ) (L / hr / cm ² ) Appearance of roll Example 5 20 1.0 0.1 Good Comparative Example 2 Wrinkles

As is apparent from Table 3, when the water droplet treatment is performed by the method of the present invention, the roll appearance is improved (Example 5), but when the water droplet treatment is not performed at all, the roll winding is improved. The appearance is inferior (Comparative Example 2).

[0036]

As described in detail above, water droplets are sprayed while the extruded resin sheet is at a temperature equal to or higher than the softening point.
The thickness and surface roughness of the resin film can be easily controlled by adjusting the spraying conditions [particle size of water droplet, spray pressure and spray amount (spray density)]. In particular, since the film thickness unevenness is in the TD (horizontal) direction, the film thickness unevenness can be effectively removed by setting a plurality of spray nozzles arranged in the TD (horizontal) direction to desired spraying conditions. . For this reason, the winding appearance of the film roll is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an apparatus for implementing the present invention.

FIGS. 2A and 2B are schematic views of a water droplet spraying apparatus, wherein FIG. 2A is a front view and FIG. 2B is a side view.

FIG. 3 Width (TD) of resin film sprayed with water droplets
It is sectional drawing which shows the film thickness distribution and surface roughness in a direction.

FIG. 4 Width (TD) of resin film sprayed with water droplets
FIG. 4 is a partially enlarged cross-sectional view illustrating surface roughness in a direction.

FIG. 5 is a schematic cross-sectional view showing a film thickness distribution and a surface roughness in a width (TD) direction of an untreated resin film.

[Explanation of symbols]

 1 Film 1a Front 1b Back 2 Surface unevenness 10 Extruder 11 Extrusion die (flat die) 14 Chill roll 16・ ・ Stretching roll group 17 ・ ・ ・ ・ ・ ・ Film thickness gauge 18 ・ ・ ・ ・ Winding roll 20 ・ ・ ・ ・ Water droplet nozzle F ・ ・ ・ ・ ・ ・ Resin film FL ・ ・ ・ Frost line S ・ ・ ・ ・ Resin sheet

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kotaro Takida 3-1 Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Tonen Chemical Co., Ltd. Technology Development Center (72) Inventor Koichi Kono 3 Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa -1 Tonen Chemical Co., Ltd. Technology Development Center

Claims (5)

[Claims] In a method for controlling the thickness and surface roughness of an extruded film, a molten resin is extruded from an extrusion die to form a resin sheet, and water droplets are formed on the resin sheet while the resin is at a temperature equal to or higher than a softening point. And controlling the thickness and surface roughness of the extruded film by controlling the particle size, velocity and density of the water droplets. 2. The method for controlling the film thickness and surface roughness of an extruded film according to claim 1, wherein a plurality of water droplet nozzles are provided in a width direction of the film, and a particle diameter of the water droplet is 1 to 150 μm. By adjusting the spray pressure in the range of 0.1 to 10 kgf / cm ² and the spray amount in the range of 0.01 to 1 liter / hour / cm ² , the film thickness is 5 to 200 μm.
A method characterized by controlling the average pitch of surface irregularities to be 0.1 to 20 mm in m. 3. The method for controlling the thickness and surface roughness of an extruded film according to claim 1, wherein the water droplets are sprayed on the resin sheet at a position slightly upstream of a frost line of the resin sheet. A method characterized by the following. 4. The method for controlling the film thickness and surface roughness of an extruded film according to claim 1,
Controlling the temperature of the water droplets in the range of 5 to 80C. 5. The method for controlling the film thickness and surface roughness of an extruded film according to claim 1,
A method comprising: arranging the water droplet nozzles at thick portions of the film, and controlling the particle diameter, speed, and density of water droplets ejected from the nozzles according to the thickness of each thick portion.