JPH0289619A - Manufacture of film - Google Patents

Abstract

PURPOSE:To obtain film, the longitudinal and lateral strengths of which balance well and which has uniform thickness by a method wherein annular starting film having thick wall portions is formed from thermoplastic composition by inflation technique and, after that, bixially stretched by mandrel technique. CONSTITUTION:In an extrusion equipment 1 of lay-flat film, annular starting film 12 is produced by extruding filler-containing thermoplastic resin under molten state from an inflation die 11. At that time, thick wall portions 12A and 12A are formed at two positions on the annular starting film 12 by partially widening the lip clearance of the die 11. Next, on the downstream side of the extrusion equipment 1 of lay-flat film, a biaxially stretching device 2 employing mandrel technique is provided so as to restore lay-flat starting film 12 to an annular shape by pouring air flow in the interior of the film 12 in order to biaxially stretch by fittingly inserting onto a self-standing type mandrel 22. The stretched film 12 is cut in two, developed and trimmed at both side edges. Finally, the residual stress at stretching in the film is relieved by being passed through heat-treating rolls 27 and 27 and cooling rolls 28 and 28.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a film, particularly a method for producing a film with a thin film thickness.
The present invention relates to a method for producing a stretched film that is uniform and has well-balanced longitudinal and lateral strengths.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Stretching by the mandrel method begins with the use of a stable guide in the tubular method stretching, and is then used to obtain strong films (hereinafter simply referred to as ``films'') such as Sudex film for heavy duty packaging bags made by Mitsubishi Yuka. as,
Techniques have been developed to forcibly stretch the film by passing it along the oblique angle of the mandrel, that is, along the outermost circumferential surface of the mandrel. The method for manufacturing Sudenox film is to stretch the film while maintaining a balance of longitudinal and lateral strength by using the film pulling force in the longitudinal direction as stress for transverse stretching, and this method requires the original film to have a certain degree of strength. In addition, it is technically excellent in that it reduces the surface resistance of the mandrel. A method for manufacturing porous films using this mandrel method was published in 1986.
Although it is proposed in Publication No. 026009, in order to form micropores in a film by the method described in the publication, it is difficult to form a porous film by the tubular method because air escape occurs, so it is difficult to form a porous film by the inflation method. The annular or tubular original fabric is produced as a low-cost, uniform film by stretching by a mandrel method or the like. However, according to this method, the film is stretched in the transverse direction against the resistance of the gradually expanding mandrel, so the film is likely to break due to the stretching force against the resistance, especially in films containing fillers. Naturally, only low-magnification lateral stretching can be expected. Moreover, the only force that can be applied from the outside as a stretching force is the component force based on the pulling stress of the film, and in order to increase the horizontal stretching, the longitudinal stretching must also be increased, and in this way, it is necessary to increase the stretching in the longitudinal direction. The resulting film had a problem in that the strength in the longitudinal direction was considerably higher than the strength in the transverse direction, lacking a balance between the longitudinal and lateral strengths, and was particularly susceptible to tearing in the longitudinal direction.

In addition, biaxial stretching using the mandrel method requires technical proficiency, and if the raw material of the film is changed, there will be problems such as countermeasures for the resistance between the changed raw material and the mandrel surface. Furthermore, there are problems such as the need for the film to have enough transverse strength to prevent it from breaking in the longitudinal direction with biaxial stretching using only a pulling force in the longitudinal direction, so a biaxial stretching method using the mandrel method It can be said that this is a stretching method that is limited to films such as heavy-duty packaging bags that are inherently strong, such as thick films such as the above-mentioned Sudefukus film.

In addition, as mentioned above, stretching using the 7-drel method is suitable for producing porous films used in disposable diapers and other products because it is inexpensive and can produce films that maintain flexibility. On the other hand, if the above-mentioned mandrel method is applied directly to the production of porous films, there are problems such as unevenness in the film. Therefore, as a pre-stretching process using a mandrel, l-axis preliminary stretching is performed in the longitudinal direction, and this operation reduces the stretching stress in the lateral direction due to the mandrel, thereby performing biaxial stretching (Japanese Patent Publication No. 60-26009). However, the manufacturing process is complicated when performing uniaxial pre-stretching, and the increased strength in the machine direction due to the pre-stretching remains in the film, resulting in a film that has a longitudinal strength that is much stronger than its transverse strength. As a result, the vertical and horizontal strength becomes unbalanced,
When such a film is used for supplies such as the above-mentioned disposable diapers, there is a problem in that the film is torn in the longitudinal direction at the adhesive portion of the tape. Additionally, in film production, the raw film must have film strength that can withstand pulling force, so the mandrel method is suitable for thick films but not for thin films. .

Therefore, an object of the present invention is to propose a method of manufacturing a film that can produce a film having a well-balanced '#1 transverse strength, a uniform film thickness, and at a low cost.

[Means to solve the problem]

The method for producing a film of the present invention includes forming a composition for forming a thermoplastic film into an annular raw film having at least a partially thick portion by an inflation method,
The above object has been achieved by providing a method for producing a film, which is characterized in that the film is then biaxially stretched by a mandrel method.

In the method of the present invention, a thermoplastic composition is first formed into an annular raw film that is intentionally formed in a thick portion by an inflation method.

In other words, at least a portion of the annular original film (for example,
By forming a thick inner part in two places), the strength of that part is increased, and the breaking strength against the pulling force of the film is increased by the thick part, and the stretching of the part other than the thick part is increased. By forming the thin part of the film in the desired part of the film, it is possible to obtain a strong film, including bags for heavy duty packaging, etc.

Furthermore, in the method of the present invention, the annular original film obtained by the inflation method is processed by the mandrel method.
In the method of the present invention, it is possible to obtain a uniform film without unevenness as described above by providing a thick portion in a part of the annular raw film. This also makes it possible to mold films in the same way. That is, since the raw film is provided with, for example, two thick parts, the inner part is difficult to stretch, and the other thin parts are easily stretched. In other words, the strength of the thick portion suppresses the elongation of the raw film in the longitudinal direction, and the component force of the pulling force acts effectively as the stress of the horizontal stretching of the raw film, making the horizontal stretching ratio lower than that of the conventional raw film. It can be made larger than the anti-film, and as a result, it is possible to obtain a film that is uniform and has well-balanced longitudinal and lateral strength. According to the method of the present invention, when obtaining a porous film, it can also be formed as a porous film with a good balance of longitudinal and lateral strength and a uniform thickness.

Next, a case in which a porous film is manufactured based on the method of the present invention shown in FIGS. 1 to 5 will be specifically described.

As shown in FIG. 1, the inflation molding apparatus + extrudes a thermoplastic resin containing a filler in a molten state from an inflation die 11 to form an annular filler-containing raw film (hereinafter referred to as "raw film"). 12 is formed, passed through a guide plate 13, and then passed through a pair of nip rolls 14.
．． It is configured to be pulled out by 14.

A biaxial stretching device 2 using a mandrel method is disposed downstream of the inflation forming device 1, and a pair of nip rolls 212 are located at the upstream end of the biaxial stretching device 2.
1 is configured to take over the original film 12 from the inflation molding apparatus 1.

The biaxial stretching device 2 passes the flat film 12 through the nip rolls 21 and 21 onto a self-supporting mandrel 22.
The structure is such that when it is guided, it is returned to an annular shape by the air flow injected into the inside thereof, and is inserted into the self-supporting mandrel 22 for biaxial stretching. That is, freestanding mandrel 2
2 is a mandrel upper part 22A formed to have a small diameter and a mandrel lower part 22B having a connecting portion gradually enlarged in diameter, which are integrally formed. Furthermore, an external heater 23 is arranged around the mandrel upper part 22A.
3 heats and softens the annular raw film 12 to facilitate stretching, and the mandrel lower part 22B serves as a cooling section to prevent the stretched raw film 12 (hereinafter referred to as "stretched film" for convenience) from being stretched any further. That's what I do.

Further, at the downstream end of the self-supporting mandrel 22, a cutter 24 is disposed that passes through the center of the lower part 22A of the mandrel, and the cutter 24 cuts the stretched stretched film I2 flowing down into two pieces and unfolds it. Then, the two spread sheets of stretched film 12 are separated into two directions on the downstream side, each of the separated stretched films 12.12 is taken up by a nip roll 25.25, and both side edges are cut by a cutter 26.26. Each stretched film 12.12 with both sides aligned is passed through a heat treatment roll 27.27 and a cooling roll 2.
8.28, during which stretching residual stress is removed, and then wound up by a winding device 29.29.

The optimum temperature for the process from preheating by the external heater 23 to the heat treatment roll 27 differs depending on the resin raw material forming the base of the stretched film 12, and in terms of -C, the raw film 12 forms this. 20℃ above the melting point of raw materials
If the temperature is lower than that, it is used again as a raw material in the inflation molding device 1 or the like.

The above-mentioned inflation molding apparatus 1 applied to the method of the present invention is constructed as shown in FIG.
It is configured to be molded as a film having thick portions 12A, 12A at two locations. That is, the lip clearance in the inflation die 11 may be partially widened, the cooling process after exiting the die 11 may be controlled so that the resin partially solidifies, or coextrusion may be performed. Thick wall portion 12A.

12A can be obtained.

In particular, according to the first two methods, the thick portions 12A, 12A can be formed easily and inexpensively. In addition, in order to stably obtain the annular raw film 12 having the thick portions 12A, 12A, the blow ratio in the inflation method cannot be increased too much, and the blow ratio is preferably 3.5 or less, more preferably is 2.5 or less.

By forming the thick portions 12A, 12A at two opposite locations of the annular raw film 12 in this manner, the pulling force in the longitudinal direction, that is, in the flow direction of the raw film 12 during the stretching process using the self-supporting mandrel 22 can be reduced. Thick part 12A,
12A, thereby increasing the component force in the lateral direction and making it possible to further increase the lateral stretching. Further, the thick portion 12A has an average thickness of at least 1 part of the average thickness of the film portion 12B having a normal thickness.
The film portion 12 has a thickness of 20% or more, preferably 125 to 350%, and has a normal thickness from the thick portion 12A.
It is preferable that the boundary portion transitioning to B is formed gently within a range that does not impede productivity. Incidentally, it is sufficient that the thick portion 12A provided in the annular raw film 12 is provided in at least one place, but if it is provided in two places,
It is easy to cut and remove the thick portion 12A when preparing the film, which is preferable in terms of manufacturing. Of course, the method of the present invention can also be applied to an annular original film which has been subjected to preliminary l-axis stretching treatment as in Japanese Patent Publication No. 60-26009.

Further, the self-supporting mandrel 22 of the biaxial stretching apparatus 2 applied to the method of the present invention has a diameter of Dl for the mandrel L portion 22A, and a diameter of D2 for the lower part 22B of the mandrel, as shown in FIG. 3(al). The annular original film 12 is inserted into the mandrel upper part 22A as shown in FIG.
5. When pulled off by 25, the annular original film 1
2 reaches the lower part 22B of the mandrel having the maximum diameter D2 while being gradually stretched via a portion whose diameter gradually increases, and the third
After being stretched to the final stretching ratio D2/Di as shown in Figure (C), it is divided into two parts by a cutter 24.

The stretching action described above works as follows. That is, the original film 12 is transferred from the mandrel upper part 22A to the mandrel lower part 2.
Direction of film movement in the process of reaching 2B (/A downward direction)
If the tangential direction to the circumference between XL and XL is x2, and the direction perpendicular to xt is x3, the stress that can be applied to the annular raw film 12 from the outside is the pulling force on the annular raw film 12 acting in the X1 direction. Only. Moreover, the stress of the lateral stretching on this annular raw film 12 is X2
This is the component force of the pulling force that acts in the direction. Therefore, the force acting in the X1 direction is applied to the film by the thick portions 12A, 12A.
By suppressing elongation in the direction and effectively working as a lateral stretching force in the X2 direction, a film with good longitudinal and lateral balance can be obtained. In the method of the present invention, the annular raw film 12 having two thick parts 12A, 12A is formed by the above-mentioned inflation molding apparatus l, so that the film strength in the longitudinal direction is
2A and 12A, the stretching of the annular raw film 2 in the X1 direction is minimized, and the force acting as the lateral stretching stress in the X2 direction in the other film portion 12B of average film thickness is efficiently reduced. The annular original film 12 can be horizontally stretched uniformly. Of course, it can also be stretched in the X1 direction at a large magnification, and as a result,
The area stretching ratio of the annular raw film 12 can also be further increased by increasing the stretching ratio in two directions.

``1. In the drawing process, the shape of the mandrel, especially D2/DI, which is the transverse drawing ratio, and the mandrel angle θ1, which is involved in the action of stress in the deformation process, are important factors, but in the method of the present invention, such control is conditions can be reduced as much as possible, and the lateral stretching force can be applied effectively.

In addition, in the method of the present invention, the areal stretching ratio is basically 1.5 to 1.5.
By using a low stretching ratio of 10.0 times, a uniform film can be obtained and flexibility can be maintained even if the film is porous.

Next, the operation of the method of the present invention using the apparatus having the above configuration will be explained.

First, when molten resin is extruded from the inflation die 11 of the inflation molding device 1, an annular raw fabric fillet 12 having two thick portions 12A, 12A is formed and passed through the guide plate 13 to a nip roll. 1
4.14. The drawn out annular raw film 12 becomes a belt shape with the thick portions 12A and 12A located at both ends, and is passed through the nip rolls 21 of the biaxial stretching device 2.
．． 21 and flows down to a self-supporting mandrel 22. In the self-supporting mandrel 22, the injected air flow returns to the annular original film 12, and the mandrel 22 is heated by the external heater 23 and smoothly biaxially stretched in the process from the mandrel upper part 22A to the mandrel lower part 22B. Ru. During biaxial stretching, since the annular raw film 12 has two thick portions 12A, 12A, stretching in the longitudinal direction is slightly suppressed, while stretching in the lateral direction is promoted, resulting in a well-balanced longitudinal and lateral direction. Biaxial stretching is performed. After that, the stretched film 12 is cut into two parts by the cutter 24.
The cutter 26 between the nip roll 25.25 and the heat treatment roll 27.27 is separated and taken up by the two tube rolls 25.25 on the downstream side and reaches the heat treatment roll 27.27.
The thick parts 12A and 1 at both ends of the stretched film 12 are
2A is cut and removed to adjust the middle dimension. The heat-treated stretched film 12.12 is further passed through a cooling roll 28.
．． After being cooled by 28, it is wound up as a final product film by a winding device 29.29.

Next, a case where a tenter method is applied as the biaxial stretching device 2 will be described with reference to FIGS. 4 and 5. The apparatus used in the method of the present invention is an apparatus that uses mandrel stretching by applying a tenter method in place of the self-supporting mandrel 22 used in the above-described method of the present invention. Therefore, thick portion 1
Since the inflation molding apparatus 1 for producing the annular original film 12 having 2A and 12A is the same as the apparatus described above, only the biaxial stretching apparatus 3 will be described.

The method of the present invention is carried out using an apparatus that performs horizontal stretching after longitudinal stretching by uniaxial roll stretching, similar to the sequential biaxial stretching method used onboard ships. A stretching method characterized by gripping a folded film with a belt, a clip, etc. so that the thick portions 12A and +2A are positioned as both ends in the middle direction, and guiding the film 31 in this state to a mandrel 3 serving as a resistor. The steps will be explained below in order.

A pair of low-speed nip rolls 32 and 32 are used to longitudinally stretch an annular raw film 12 made up of two flat sheets.
Then, the film is guided between a pair of high speed nip rolls 33.33, and uniaxial longitudinal stretching is performed by the speed difference between the speed 3 of the low speed nip roll 32.32 and the speed V4 of the high speed nip roll 33.33. Therefore, the longitudinal stretching ratio in this case is (V4)/
The ratio is (v3).

Next, both ends of the annular original film 12 in the width direction are held by belts or clips, and in this state, it is guided to the preheating mandrel part 34 (the arc portion between the dotted line a and the dotted line 2 in FIG. 4), After heating the raw film 12 to a temperature that allows stretching in the preheating mandrel section 34, the stretching mandrel section 35 (upper point VAb and dotted line C in FIG. 4) heats the film 12 to an appropriate stretching temperature below its melting point. (the arc between the two). As shown in FIG.
The film gripping interval at the exit portion of is set to L2, and therefore, the ratio of 1 and L2 mentioned above, that is, (1
-2)/(Ll) is the lateral stretching ratio. The heating of the preheating mandrel section 34 and the stretching mandrel section 35 is performed by
Although a heating method such as external far-infrared heating 36 (in the figure, a rectangular portion surrounded by a two-dot chain line indicates an area in which a heating means is provided) may be used, the annular raw film 12 may be heated using a mandrel 3. The method of direct heating is more advantageous in controlling the stretching temperature of the annular raw film 12, and the method of using the above two heating methods in combination is more effective. In addition, the annular original film 12 extends from the preheating mandrel part 34 to the exit part of the stretching mandrel part 35.
There are two passages 37° 37 of healds or crimps gripping the ends of the direction, the two passages 37.
The intersection of the extension lines of 37, that is, θ2 in FIG. 5 is 90
° or less is a condition for suitable stretching. However, if θ2 is too small, it will be necessary to enlarge the stretching mandrel part in order to obtain a predetermined stretching ratio, so θ2=
It is appropriate to set it at 60 to 90@. The mandrel 3 also includes a cooling mandrel part 38 (the arc portion between the dotted line C and the dotted line d in FIG. 4) that is integrally provided at the rear of the drawing mandrel part 35. The film 12 is cooled by the cooling mandrel section 38 to remove residual stress during stretching. In addition, this cooling mandrel part 3
The width of 8 (see Fig. 5) is approximately equal to 2 as described above, and the cooling method for this cooling mandrel portion 38 may be an external air cooling method, an internal circulation water cooling method, or a combination thereof. However, water cooling is effective. Stretched film 12 sufficiently cooled after stretching in this way
The cutter 40 installed at the rear end of the cooling mandrel section 3 removes slits from both end portions 43 of the cooling mandrel.
It is separated into sheets and guided to a winding process.

In this case, if the film has such properties that the residual stress at the mandrel 3 portion is insufficiently removed, a reheating roll 41 and a recooling roll 42 are provided in the winding process.
It is also possible to perform heat treatment again on the film 12 from which the slits have been removed.

Incidentally, a flat plate having an arcuate cross section (a cross section along the film passing direction) is arranged in the film passage section (between the passages 37 and 37) in the preheating mandrel section 34, the stretching mandrel section 35, and the cooling mandrel section 38. It is.

Note that the method of the present invention is not limited to the above-described method; for example, the thick portion of the film may be removed immediately before the winding device 29, or the winding device 29 may be It is also possible to wind up two sheets stacked on a stand. In addition, a hanging mandrel may be used instead of the free-standing mandrel 22 (in that case, the film 12 is taken out in a folded state without being opened into two films, and the film 12 is heat-treated in the two-layered state). After cooling, the thick portion may be removed.

As described above, the method of the present invention is a method for producing films such as porous films by the mandrel stretching method, and in order to compensate for the drawback of films produced by the conventional mandrel method, in which the longitudinal strength is much larger than the transverse strength. , in order to suppress longitudinal elongation, the thick part is formed into the original film, and as a result,
The present invention is intended to produce films such as porous films with improved longitudinal tear strength.

The composition for forming the plastic film used in the method of the present invention includes polyolefin resins, which mainly contain monoolefin polymers and copolymers such as ethylene, propylene, butene, etc. For example, high density polyethylene, linear low density polyethylene, polypropylene, ethylene-propylene copolymer,
Examples include polybutene, ethylene-vinyl acetate copolymer, and mixtures thereof. In particular, when linear low-density polyethylene is used to produce a porous film, a flexible and tough porous film can be obtained.

Furthermore, when producing a porous film, a filler is added and a third component that imparts functions such as flexibility to the film is also added.

Preferred fillers include inorganic and organic fillers, and inorganic fillers include calcium carbonate, barium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, gypsum, talc, sauce, kaolin, silica, diatomaceous earth, oxidized Zinc, titanium oxide, alumina, mica, zeolite, carbon black, etc. are used, and organic fillers include wood flour, pulp powder, and resin powders with a higher melting point than the above-mentioned polyrefin resin raw materials used as the base, such as When linear low-density polyethylene is used as the base resin, polyethylene terephthalate powder or the like is used. These may be used alone or in combination.

The average particle size of the filler is preferably 30μ or less, more preferably 10μ or less, and most preferably 0.5 to 5.0μ.

Surface treatment of fillers is important for uniform dispersion in resin.
As the surface treatment agent, those capable of making the surface hydrophobic, such as fatty acids or metal salts thereof, are preferred. For this surface treatment, a filler that has already been surface-treated may be used, or it is also possible to carry out an in-line treatment by kneading with the above-mentioned surface treatment agent in the step of uniformly dispersing the raw materials. Also,
When trying to obtain a porous film by containing a filler, the blending ratio of the thermoplastic resin and the filler is 30 to 500 parts by weight of the filler to 100 parts by weight of the thermoplastic.
It is preferably 100 to 300 parts by weight based on 100 parts by weight of the thermoplastic resin. The reason for this is that a membrane structure can be easily created by stretching, and the strength of the film can be maintained during production and as a product, and the upper limit is closely related to the strength and the lower limit to the creation of the membrane structure.

Further, preferred third components for imparting functions such as flexibility and prevention of rustling sounds to the porous film include hydrogenated polybutadiene and isoprene described in Japanese Patent Publication No. 57-47334, and JP-A-62 Compounds such as polyesters obtained from polybasic acids and polyhydric alcohols as described in JP-A No. 280233, compounds and rubber-like resins and other components as described in JP-A-62-280234 and JP-A-62-280235. can be added as necessary, and each component can be appropriately selected and used depending on the intended use of the film. The amount of the third component to be added also depends on the purpose, and it is usually preferable to use the third component in an amount of 50 parts by weight or less per 100 parts by weight of the thermoplastic.

As described above, the method of the present invention makes full use of the original characteristics of mandrel method stretching to obtain a stretched film with well-balanced longitudinal and lateral strength, and is particularly suitable for manufacturing porous films that are difficult to manufacture using the tubular method. is suitable. In particular, the porous film produced in this way is much cheaper than a film made by stretching a flat film such as T-die using the tenter method, so it can be used for backsheets such as disposable diapers, cream room supplies, and clothing.・A low-cost film can be obtained as a disposable item for medical purposes. Of course, it is not limited to the above-mentioned disposable items.

In addition, since the original film forming process using inflation silane molding has been modified without changing the conventional combination of inflation molding and mandrel stretching, the cost of equipment improvements etc. has been improved. Despite almost no need for film, the performance of the film is significantly improved compared to conventional methods, and even porous films can be produced with uniform thickness and at low cost. can.

〔Example〕

Next, the present invention will be explained based on the following examples.

However, the present invention is not limited to the following examples.

In addition, the polyolefin resin, filler, and third component shown in Table 1 above were used in the following Examples and Comparative Examples.

In addition, Table 3 shows the blending ratios of the compositions used in the present examples and comparative examples from the raw materials shown in Table 1.

Table 3: Blend composition Note that supplementary information regarding the third component is shown in Table 2.

Example 1 The composition No. 1 shown in Table 3 above was melt-molded by the inflation method, and the average thickness of the normal thickness part was 7.
A film with a thickness of 0μ and a thick portion of 110μ is obtained. This film was biaxially stretched by the mandrel method shown in FIGS. 1 and 3, (tal, (bl, (C1) under the following stretching conditions.

Inside the film (after stretching) 600 x 2 sheets Preheating temperature
95°C Stretching temperature 95°C Stretching ratio 2.3x length x 2.3x width Winding speed 15m/min However, in this case, the lateral stretching ratio is almost the same as the normal width in the lateral direction excluding the thick portion that remains unstretched. It shows the stretching ratio of the thick part. Table 4 shows the performance of the obtained film.

Example 2 After uniformly kneading the above blended composition NO12, a film was obtained in the same manner as in Example 1. However, the stretching ratio in this case is 1.8 times in the vertical direction and 2.0 times in the horizontal direction, and the obtained film is a porous film, and the performance of the porous film is shown in Table 4.
It was shown to.

Example 3 The same procedure was carried out except that the above blended composition No. 2 was changed to blended composition No. 013, the stretching ratio was 1.6 times in the vertical direction and 1.8 times in the horizontal direction, and the preheating temperature was 80° C. and the stretching temperature was 70° C. A porous film was obtained in exactly the same manner as in Example 2, and the performance of the obtained porous film is shown in Table 4.

Example 4 The above blended composition No. 3 was replaced with blended composition No. 4
A porous film was obtained in the same manner as in Example 3, except that the stretching ratio was changed to 1.6 times in length and 2.0 times in width.
Table 4 shows the performance of the obtained porous film.

Example 5 A porous film was produced in the same manner as in Example 3, except that the above blended composition No. 3 was changed to blended composition No. 095, and the stretching ratio was 1.5 times in the vertical direction and 1.8 times in the horizontal direction. Obtained. Table 4 shows the performance of the obtained porous film.

Example 6 The above blended composition No. 3 was replaced with blended composition No. 5
A porous film was obtained in the same manner as in Example 3, except that the stretching ratio was changed to 1.5 times in length and 2.0 times in width.
Table 4 shows the performance of the obtained porous film.

Comparative Example 1 An attempt was made to obtain a stretched film in exactly the same manner as in Example 1, except that a normal blown film having an average thickness of 70 μm was used without providing a thick portion.

Comparative Example 2 A stretched film was obtained in the same manner as Comparative Example 1, except that the stretching ratio was 1.8 times in the vertical direction and 1.8 times in the horizontal direction, and the performance of the obtained film is shown in Table 4.

Comparative Example 3 An attempt was made to obtain a porous film in exactly the same manner as in Example 2, except that a normal blown film having an average thickness of 70 μm was used without providing a thick portion.

Comparative Example 4 A porous film was obtained in the same manner as Comparative Example 3, except that the stretching ratio was 1.5 times in the vertical direction and 1.5 times in the horizontal direction, and the performance of the obtained porous film is shown in Table 4.

Comparative Example 5 An attempt was made to obtain a porous film in exactly the same manner as in Example 3, except that a normal blown film having an average thickness of 70 μm was used without providing a thick portion.

Comparative Example 6 A porous film was obtained in the same manner as Comparative Example 5, except that the stretching ratio was 1.5 times in the vertical direction and 1.5 times in the horizontal direction, and the performance of the obtained porous film is shown in Table 4.

Table 4: Comparison of physical properties In Table 4, transparent 7? The test methods for strength, flexibility, and stretching unevenness were conducted under the following conditions.

However, since Example 1 and Comparative Examples 1 and 2 did not contain a filler, porous films could not be obtained, and moisture permeability was not measured.

Moisture permeability + Measured according to JIS Z-0208.

Unit: g/100-hr Vertical crack strength: Measured according to JIS P-8116.

Converted to g'11 degrees when the film thickness is 50 μm Flexibility: Sensory evaluation A - Extremely soft, B - Soft C - Hard stretching unevenness: Appearance evaluation A = Even - B - Fine unevenness C = Significant unevenness The results shown in Table 4 reveal the following. Comparing Example 1, which does not result in a porous film, and Comparative Example 1.2, it is clear that Example 1 has the effect of increasing the stretching ratio; Even if this were done, the film would have many unevenness, resulting in a product that could not be used in actual use.

The same thing can be said about porous films; in porous films, stretching unevenness is more noticeable due to the inclusion of fillers, and the film is more likely to break under unreasonable stretching conditions. This becomes clear as shown in . Specifically, as shown in Comparative Examples 3 to 6, when an attempt is made to increase the transverse stretching ratio of a filler-containing raw film with a uniform thickness, the film breaks or the film collapses due to resistance on the mandrel. As a result of the stagnation, breakage occurs in the take-off direction, making it impossible to obtain a porous film. Therefore, it is only possible to obtain a porous film with a reduced transverse stretching ratio. As a result, as shown in Table 4, compared to other Examples 2 to 6, the water vapor permeability and longitudinal tear strength were unbalanced, and uneven stretching remained, resulting in poor flexibility.

From these results, it is clear that there is a correlation with the area stretching ratio, and in particular, it can be seen that there is a deep correlation with the lateral stretching ratio with respect to stretching unevenness. From the above results, it is clear that the effect of providing a thick portion in this example is that the physical properties are improved by about twice as compared to the conventional method, that is, a porous film without a thick portion. It turns out that you are getting it.

In addition, X3 moisture leakage proof sheet used for sanitary products such as disposable diapers 1. U? measured according to JIS Z-0208? ``If the X degree is 1.Og/100-・hr or more,
Since the porous film is recognized to have an effect of preventing stuffiness when used, it is found that the film is fully satisfactory for use in such sanitary products.

〔Effect of the invention〕

According to the film manufacturing method of the present invention, a film with well-balanced longitudinal and lateral strength can be produced with a uniform film thickness and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a manufacturing apparatus suitable for implementing the film manufacturing method of the present invention, FIG. 2 is a sectional view showing a raw film obtained by inflation molding 'AH,
Figure 3 ta+, [bl, tel are views showing the state in which the original film is stretched by the mandrel, the same figure (a) is a side view thereof, the same figure (bl is a cross-sectional view along the BB line of the same figure tal) , FIG. 4(c) is a sectional view taken along line C-C of fat in the same figure, and FIGS. 4 and 5 are a configuration diagram showing a side view and a plan view of other stretching devices, respectively. 1: Inflation device 2.3i Biaxial stretching device Fig. 2 12B Fig. 5

Claims (1)

[Claims] 1. A method for producing a film, which comprises forming a composition for forming a thermoplastic film into an annular raw film having at least a partially thickened portion by an inflation method, and then biaxially stretching the film by a mandrel method.