Film manufacturing method and porous film

Abstract

To suppress shrinkage of a film manufactured through a stretching step due to orientational relaxation of high molecular chains.SOLUTION: A method for manufacturing a film has the steps of: extruding a molten resin from a die to form it into a film extending in one direction; stretching the film obtained by the film formation, in a lengthwise direction while conveying it; applying a first heat-treatment to the stretched film while conveying it; and winding the film after the heat-treatment. Immediately before winding the film after the heat-treatment, the film is applied with a second heat-treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a film. Furthermore, this invention relates to a porous film. [Background technology]

[0002] Porous film is often used as the backing sheet for absorbent products such as disposable diapers and sanitary napkins. Absorbent products equipped with a backing sheet made of porous film have the advantage of allowing moisture generated from the wearer's body to be easily released to the outside through the backing sheet while being worn, thus reducing stuffiness while wearing the product.

[0003] In a generally known method for producing porous films, a resin composition containing a thermoplastic resin and an inorganic filler is melted, the molten material is extruded from a die to form a film, the film is stretched to generate numerous micropores within it, and then heat-treated and wound into a roll (see Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-110052 [Patent Document 2] Japanese Patent Publication No. 2000-001557 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the above method, by stretching the film, the polymer chains of the resin constituting the film are stretched and oriented in one direction. The oriented polymer chains are then heat-treated to relax the molecular orientation and stabilize the crystal structure. However, depending on the type of resin, the polymer chain orientation may occur again due to the tension applied in the winding process after the heat treatment, and the film may shrink when the orientation relaxes over a long period of time. When such a film is in a wound state, winding tightness occurs as the film shrinks, and the films may stick together, making it impossible to unwind the film. Also, when such a film is incorporated into an absorbent article, the absorbent article may warp due to the film shrinking over a long period of time, and the absorbent article may not exhibit the desired performance. This phenomenon is显著 observed in flexible films that are easily deformed by small tensions. Therefore, an object of the present invention is to provide a method for producing a film in which the orientation of polymer chains caused by stretching is relaxed, and a porous film.

Means for Solving the Problems

[0006] The present invention extrudes a molten resin from a die to form a film into a film extending in one direction, while conveying the film obtained by film formation, stretches it in the longitudinal direction, while conveying the stretched film, performs a first heat treatment, and winds up the film after the heat treatment. A method for producing a film having the steps, immediately before winding up the film after the heat treatment, performs a second heat treatment on the film, and provides a method for producing a film.

[0007] Further, the present invention contains 50 parts by mass or more and 400 parts by mass or less of an inorganic filler with respect to 100 parts by mass of an olefin resin composition, the olefin resin composition contains a low melting point olefin resin having a melting point of less than 90°C, the degree of flexible deformation in the machine direction is 0.060 N / (mm·(g / m 2 )) or less, This invention provides a porous film having a thermal shrinkage rate of 8% or less in the mechanical direction. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the shrinkage of a film manufactured through a stretching process due to the relaxation of the orientation of polymer chains. [Brief explanation of the drawing]

[0009]

Figure 1

[0010] The present invention will be described below with reference to the drawings, based on preferred embodiments. Figure 1 schematically shows one embodiment of a film manufacturing apparatus used in the method of the present invention. The apparatus 10 shown in the figure has a melt-kneading section 20, a molding section 30, a stretching section 40, a first heat treatment section 50, a cooling section 60, a slitting section 70, a second heat treatment section 80, and a winding section 90 along the conveying direction. Each part of the apparatus 10 will be described below.

[0011] The melting and mixing section 20 has an extruder 22. The extruder 22 is of a conventional structure and has a screw (not shown) inside a cylinder (not shown). The extruder 22 is equipped with a hopper 21 for supplying the resin composition, which is the raw material for the film. Furthermore, the extruder 22 is equipped with a metering pump 23 at its tip for discharging the molten resin composition. The molten material discharged from the metering pump 23 passes through a filter 24 to remove foreign matter before being sent to the molding section 30.

[0012] The forming section 30 includes a die 31. As the die 31, those commonly used in the film manufacturing in the technical field can be used without particular limitation. Typically, a T-die can be used. However, it is not limited to using a T-die, and other dies, for example, a circular die used in the inflation method, can also be used. In the case of a T-die, on the downstream side of the die 31, in order to solidify and shape the film formed by the die 31, there are cases where an air chamber (not shown) and a film-forming roll 32a are installed in pairs, and cases where a pair of film-forming rolls 32a and a nip roll 32b are installed in pairs as shown in FIG. 1. Among these, when using the air chamber and the film-forming roll 32a, the air outlet of the air chamber is arranged parallel to the rotation axis of the film-forming roll 32a. On the other hand, when using the film-forming roll 32a and the nip roll 32b, their rotation axes are arranged parallel and their peripheral surfaces are arranged to contact each other. From the viewpoint that forming defects such as surging are unlikely to occur during the solidification and shaping of the film, it is preferable that the air chamber and the film-forming roll 32a are installed in pairs.

[0013] The stretching section 40 includes a roll stretching machine. The roll stretching machine includes a pair of nip rolls 41a, 41b and another pair of nip rolls 42a, 42b located downstream of the nip rolls. When the peripheral speed of the pair of nip rolls 41a, 41b is V1 and the peripheral speed of the other pair of nip rolls 42a, 42b is V2, V1 and V2 can be set independently. In this embodiment, the peripheral speeds of the respective nip rolls are set so that V1 < V2. Thereby, the formed film is uniaxially stretched along the conveyance direction, that is, the longitudinal direction, between the two pairs of nip rolls. Although not shown, another nip roll rotating at a peripheral speed V1' may be further installed between the nip rolls 41a, 41b and the nip rolls 42a, 42b, and the peripheral speeds of the respective nip rolls may be set so that V1 < V1' < V2, and the stretching may be performed in two stages. Furthermore, instead of using the roll stretching machine described above as the stretching section 40, a tenter stretching machine or a mandrel stretching machine can also be used. Also, stretching is not limited to the uniaxial stretching described above, and biaxial stretching may be performed depending on the type of stretching machine used.

[0014] The first heat treatment unit 50 comprises a first heat roll 51 and a second heat roll 52. The first and second heat rolls 51 and 52 are arranged so that their rotation axes are parallel and their circumferential surfaces are spaced apart. Each heat roll 51 and 52 is equipped with a heating means (not shown) and can be heated to an independent temperature.

[0015] The cooling unit 60 includes a first chill roll 61 and a second chill roll 62. The first and second chill rolls 61 and 62 are arranged so that their rotation axes are parallel and their circumferential surfaces are spaced apart. Each chill roll 61 and 62 is equipped with a cooling means (not shown) that allows them to be cooled to an independent temperature.

[0016] The slit section 70 is equipped with a slitting blade 71. The slitting blade 71 is generally disc-shaped and is positioned so that its surface is parallel to the film transport direction. One or more slitting blades 71 are arranged depending on the number of film sections to be slit.

[0017] The second heat treatment unit 80 is equipped with a heating means 81. The heating means 81 can be a contact-type heating means such as a heat roll, as provided in the first heat treatment unit 50, or a non-contact heating means such as an infrared heater or a hot air blowing device.

[0018] The winding unit 90 is equipped with a winder 91. The film, which has been transported through the second heat treatment unit 80, is wound onto the winder 91 to form a roll.

[0019] A method for manufacturing a film using the apparatus 10 having the above configuration will now be described. First, the compound supplied to the hopper 21 contains a thermoplastic resin. In addition to the thermoplastic resin, the compound may contain other components depending on the specific application of the film. For example, when manufacturing a porous film, the compound that will be the raw material for the porous film may contain an inorganic filler in addition to the thermoplastic resin. The inorganic filler is used to create a large number of pores in the target film. From the viewpoint of successfully creating pores, it is also advantageous for the compound to contain a metal soap along with the inorganic filler. Furthermore, if it is desired to impart water repellency to the target film, the compound may also contain a triglyceride. Details of these components contained in the compound will be described later.

[0020] It is known that adding metal soap to a compound increases the moisture permeability of the target porous film (i.e., it has more micropores and a larger void ratio). As a result, the moisture-permeable film becomes more flexible. Consequently, the porous film becomes more easily stretched during transport, which increases its thermal shrinkage rate and makes it more prone to crumpling. In contrast, the manufacturing method of the present invention yields a porous film in which thermal shrinkage is effectively suppressed, making the present invention particularly effective for producing porous films containing metal soap in the resin composition.

[0021] The compound supplied to the hopper 21 is heated and kneaded in the extruder 22 to become molten resin. The molten resin is quantitatively discharged by the metering pump 23, passes through the filter 24, and is then extruded through the die 31 to form a film 1a that stretches in one direction. In this state, the film 1a is an unstretched film. The unstretched film 1a is then transported to the stretching section 40 after being given the shape of a film by passing between the film-forming roll 32a and the nip roll 32b.

[0022] In the stretching section 40, the unstretched film 1a is stretched while being conveyed. The stretching process is achieved by uniaxially stretching the unstretched film 1a along its conveyance direction (i.e., the longitudinal direction) by making the peripheral speed V2 of the pair of nip rolls 42a and 42b higher than the peripheral speed V1 of the pair of nip rolls 41a and 41b while gripping the unstretched film 1a with the pair of nip rolls 41a and 41b and also gripping the unstretched film 1a with another pair of nip rolls 42a and 42b. As a result, the unstretched film 1a becomes the stretched film 1b. When an inorganic filler is contained in the unstretched film 1a, a large number of micropores are formed in the film by the stretching process. When a pair of nip rolls (not shown) rotating at a peripheral speed V1’ is further installed between the nip rolls 41a and 41b and the nip rolls 42a and 42b, the peripheral speeds of each nip roll can be set so that V1 < V1’ < V2, and stretching can be performed in two stages.

[0023] The stretching ratio of the unstretched film 1a in the stretching process may be appropriately set according to the intended use of the film and the like. For example, when producing a porous film, it is preferable to stretch at a ratio of 1.1 times or more and 5.5 times or less in the uniaxial direction, whether stretching is performed in one stage or two stages, from the viewpoint of successfully generating micropores. The stretching temperature of the unstretched film 1a depends on the type of thermoplastic resin. For example, when the thermoplastic resin contains a low melting point olefin resin described later, setting the stretching temperature preferably at 30°C or higher and 100°C or lower, more preferably at 35°C or higher and 95°C or lower, and even more preferably at 40°C or higher and 90°C or lower is advantageous from the point of view of successfully performing stretching.

[0024] In the stretched film 1b obtained by the stretching process, the polymer chains of the resin constituting it are oriented in the stretching direction (i.e., the transport direction). Since the molecularly oriented state is thermodynamically unstable, it is preferable from the viewpoint of dimensional stability of the stretched film 1b to relax the molecular orientation and make it thermodynamically stable. From this viewpoint, the stretched film 1b obtained by the stretching process is subjected to heat treatment in the first heat treatment unit 50 while being transported. The application of heat relaxes the molecular orientation of the polymer chains of the resin constituting the stretched film 1b, and also causes crystallization of the molecular chains.

[0025] The degree of heating of the stretched film 1b in the first heat treatment unit 50 should be appropriately selected according to the type of resin constituting the stretched film 1b. For example, if the resin constituting the stretched film 1b includes a low-melting-point olefin resin as described later, it is preferable to heat the stretched film 1b to 50°C or higher, from the viewpoint of reliable relaxation of molecular orientation. From this viewpoint, it is even more preferable that the stretched film 1b be heated to 60°C or higher, and even more preferable that it be heated to 70°C or higher. The upper limit of the heating temperature is preferably 130°C or lower, from the viewpoint of preventing the stretched film 1b from melting. From this viewpoint, it is even more preferable that the stretched film 1b be heated to 125°C or lower, and even more preferable that it be heated to 120°C or lower. In summary, if the resin constituting the stretched film 1b includes a low-melting-point olefin resin as described later, the degree of heating of the stretched film 1b is preferably 50°C to 130°C, more preferably 60°C to 125°C, and even more preferably 70°C to 120°C. The heating temperature of the stretched film 1b in the first heat treatment unit 50 refers to the temperature of the circumferential surfaces of the first and second heat rolls 51 and 52. If the circumferential temperatures of the first and second heat rolls 51 and 52 are different, the higher temperature is used.

[0026] The heat treatment performed in the first heat treatment section 50 is preferably carried out at a higher temperature than the stretching treatment performed in the stretching section 40. This ensures that the orientation of the polymer chains in the film 1b is reliably relaxed. The difference between the heating temperature T2 in the first heat treatment unit 50 and the stretching temperature T1 in the stretched unit 40 is preferably 5°C to 70°C, more preferably 10°C to 60°C, and even more preferably 15°C to 50°C, provided that T2 > T1. By performing heat treatment under such a temperature relationship, the orientation of polymer chains in the film 1b can be reliably relaxed.

[0027] The relaxation of the polymer chain orientation in the stretched film 1b due to heating is accompanied by shrinkage of the film 1b in the stretching direction (i.e., the transport direction). Therefore, from the viewpoint of ensuring relaxation of the polymer chain orientation, it is preferable to lower the transport speed of the stretched film 1b in the first heat treatment section 50 than the transport speed of the stretched film 1b in the stretching section 40. By doing so, the force pulling the film in the transport direction in the first heat treatment section 50 is weakened, and the shrinkage of the stretched film 1b by the first heat treatment section 50 is promoted. In other words, the film 1b can be shrunk in the transport direction while heat treatment is being applied. However, if the transport speed of the stretched film 1b in the first heat treatment section is set too low, the film will slacken and wrap around the roll. From this viewpoint, when the transport speed of the stretched film 1b in the stretching section 40 is V2 and the transport speed of the stretched film 1b in the first heat treatment section 50 is V3, V3 / V2 It is advantageous to set the rate relationship to preferably 0.40 or more and 0.95 or less, more preferably 0.45 or more and 0.92 or less, and even more preferably 0.50 or more and 0.90 or less. When heat-treated at this rate relationship, it is preferable to set the shrinkage rate of the stretched film 1b to preferably 5% or more and 60% or less, more preferably 8% or more and 55% or less, and even more preferably 10% or more and 50% or less.

[0028] The stretched film 1b, whose molecular orientation has been relaxed by heating in the first heat treatment unit 50, is then transported to the cooling unit 60 and undergoes a cooling treatment while being transported. The cooling treatment of the stretched film 1b is performed for the purpose of fixing the relaxed molecular orientation. Therefore, the degree of cooling of the stretched film 1b in the cooling unit 60 should be appropriately selected according to the type of resin constituting the stretched film 1b. For example, if the resin constituting the stretched film 1b includes a low-melting-point olefin resin, which will be described later, it is preferable to cool the stretched film 1b to 50°C or below from the viewpoint of ensuring the fixation of the relaxed molecular orientation. From this viewpoint, it is even more preferable that the cooling of the stretched film 1b be 45°C or below, and even more preferable that it be 40°C or below. From the viewpoint of economy, it is preferable that the lower limit of the cooling temperature be 0°C or above. From this viewpoint, it is even more preferable that the cooling of the stretched film 1b be 5°C or above, and even more preferable that it be 10°C or above. In summary, when the resin constituting the stretched film 1b is a low-melting-point olefin resin as described later, the degree of cooling of the stretched film 1b is preferably 0°C to 50°C, more preferably 5°C to 45°C, and even more preferably 10°C to 40°C. The cooling temperature of the stretched film 1b in the cooling section 60 refers to the temperature of the circumferential surfaces of the first and second chill rolls 61 and 62. If the circumferential temperatures of the first and second chill rolls 61 and 62 are different, the lower temperature is used.

[0029] The stretched film 1b, with its molecular orientation relaxed and fixed, is then transported to the slitting section 70, where it is slit into multiple strips while being transported. The slit stretched film 1b is then wound onto the winder 91 in the winding section 90.

[0030] In this embodiment, immediately before winding the heat-treated stretched film 1b, the film 1b is subjected to a second heat treatment in the second heat treatment unit 80. The purpose of performing the second heat treatment is as follows. Before being wound up by the winder 91, the conveyed film 1b is repeatedly subjected to a predetermined tension. In this case, depending on the type of resin that makes up the film, the tension during conveyance may cause the polymer chains to re-orient, and the film 1b, in its molecularly oriented state, is wound up by the winder. Furthermore, tension is also applied to the film 1b during the slitting process, which also easily causes the polymer chains to orient. In particular, if the film 1b contains a low-melting-point olefin resin, as described later, the film 1b is easily deformed even with small tension, and when the film 1b deforms, the polymer chains orient, making this phenomenon more likely to occur. In the case of film 1b, which remains molecularly oriented, the molecular orientation gradually relaxes over time. As a result, the film 1b shrinks along the stretching direction (i.e., the conveyance direction), and its dimensional stability decreases. If the film 1b is in a wound state, the film 1b will tighten. If the film 1b is incorporated into an article, the article will warp. To suppress the occurrence of such shrinkage, in this embodiment, a second heat treatment is performed in the second heat treatment unit 80 to alleviate the orientation of polymer chains caused by the tension during transport. For this purpose, it is advantageous to perform the second heat treatment just before winding the film 1b. In other words, it is advantageous for the second heat treatment unit 80 to be located directly in front of the winding unit 90. This is because if there is a distance between the second heat treatment unit 80 and the winding unit 90, there is a risk that the polymer chains of the film 1b may become re-oriented between them due to the tension during transport. The position immediately before the winding section 90 refers to a position closer to the winding section 90 than half the length of the film transported from the first heat treatment section 50 to the winding section 90 (i.e., the length of the film transport path). From the viewpoint of mitigating the orientation of polymer chains caused by the tension during transport, it is preferable that this position be closer to the winding section 90 than to the slit section 70.

[0031] The first heat treatment performed in the first heat treatment unit 50 and the second heat treatment performed in the second heat treatment unit 80 are distinguished by the presence of one or more other processes besides heat treatment between them. Examples of other processes include the cooling process and slitting process mentioned earlier. Therefore, when heat treatment is performed continuously without any other processes intervening (for example, when the stretched film 1b is continuously brought into contact with multiple heat rolls 51, 52 as shown in Figure 1), the series of heat treatments are considered a single heat treatment.

[0032] The second heat treatment performed in the second heat treatment unit 80 can be carried out using a contact-type heating means with heat rolls 51 and 52, similar to those provided in the first heat treatment unit 50. Alternatively, a non-contact heating means such as an infrared heater or a hot air blowing device can be used. Of these heating means, the use of a non-contact heating means is preferable because even if the film 1b becomes slightly softened and sticky due to the heat applied, it will not interfere with the transport of the film 1b or the winding of the film 1b in the winding unit 90 located immediately after the second heat treatment unit 80.

[0033] The second heat treatment performed in the second heat treatment section 80 is preferably carried out at a higher temperature than the stretching treatment performed in the stretching section 40. This ensures that the re-orientation that has occurred in the polymer chains of the film 1b is reliably alleviated. The degree of heating of the film 1b in the second heat treatment section 80 is preferably higher than the stretching temperature in the stretching section 40. For example, when the resin constituting the film 1b contains a low melting point olefin resin described later, heating the stretched film 1b to preferably 50°C or higher is preferable from the viewpoint of reliably relaxing the molecular orientation. From this viewpoint, the heating of the film 1b is more preferably 60°C or higher, and even more preferably 70°C or higher. The upper limit of the heating temperature is preferably 130°C or lower from the viewpoint of preventing the film 1b from melting. From this viewpoint, the heating of the film 1b is more preferably 125°C or lower, and even more preferably 120°C or lower. Taking all the above into consideration, when the resin constituting the film 1b contains a low melting point olefin resin described later, the degree of heating of the film 1b in the second heat treatment section 80 is preferably 50°C or higher and 130°C or lower, more preferably 60°C or higher and 125°C or lower, and even more preferably 70°C or higher and 120°C or lower.

[0034] The difference between the heating temperature T3 by the second heat treatment section 80 and the stretching temperature T1 in the stretching section 40 is preferably 5°C or higher and 70°C or lower, more preferably 10°C or higher and 60°C or lower, and even more preferably 15°C or higher and 50°C or lower, provided that T3 > T1. By performing the heat treatment with such a temperature relationship, the orientation of the polymer chains in the film 1b can be reliably relaxed. The heating temperature T2 by the first heat treatment section 50 and the heating temperature T3 by the second heat treatment section 80 may be such that T2 > T3, T2 < T3, or T2 = T3. In order to reliably relax the orientation of the polymer chains, it is preferable that T2 < T3.

[0035] Similar to the heating of the stretched film 1b in the first heat treatment section 50, the relaxation of the polymer chain orientation by the second heating of the stretched film 1b in the second heat treatment section 80 also involves shrinkage of the film 1b in the stretching direction (i.e., the transport direction). Therefore, from the viewpoint of ensuring relaxation of the polymer chain orientation, it is preferable to set the winding speed of the stretched film 1b in the winding section 90 lower than the transport speed of the stretched film 1b in the first heat treatment section 50. By doing so, the tension acting on the film between the winding section 90 and the first heat treatment section 50 is reduced, and the shrinkage of the stretched film 1b in the second heat treatment section 80 is promoted. In other words, the film 1b can be shrunk in the transport direction while the second heat treatment is being performed. If the winding speed is set too low, the film will slacken and the winding will become unstable. Unstable winding means that there is a concern that the film may meander during winding, causing winding collapse, or that the film may wrap around the winding shaft. From these perspectives, when the winding speed of the stretched film 1b in the winding section 90 is set to V4 and the transport speed of the stretched film 1b in the first heat treatment section 50 is set to V3, V4 / V3 It is advantageous to set the coefficient to preferably 0.8 to 0.99, more preferably 0.85 to 0.98, and even more preferably 0.90 to 0.97. When heat-treated at this rate relationship, it is preferable to set the shrinkage rate of the stretched film 1b to preferably 1% to 20%, more preferably 2% to 15%, and even more preferably 3% to 10%.

[0036] The film 1b obtained in this way has relaxed polymer chain orientation, making it less prone to shrinkage and resulting in excellent dimensional stability. Specifically, film 1b has high dimensional stability, with a thermal shrinkage rate in the mechanical direction preferably of 8% or less, and more preferably of 6% or less. The method for measuring the thermal shrinkage rate will be explained in the examples described later.

[0037] Next, the compound used in the manufacturing method of the present invention will be described. The compound preferably includes a thermoplastic resin composition, particularly an olefin-based resin composition. In this specification, "thermoplastic resin composition" is a concept consisting solely of various thermoplastic resins and not containing any components other than resin. The term "olefin resin composition" encompasses both cases where it contains only one type of olefin resin and cases where it contains two or more types. Furthermore, "olefin resin composition" is a concept that consists solely of various olefin resins and does not contain other resins or non-resin components. It is not prohibited for a compound to contain thermoplastic resins other than those found in olefin resin compositions.

[0038] The thermoplastic resin included in the compound is selected according to the specific application of the film. For example, olefin resins, polyester resins, acrylic resins, and vinyl chloride resins can be used, but are not limited to these. Examples of olefin resins include polyethylene resin, polypropylene resin, and ethylene-α-olefin copolymer resin. Examples of polyethylene resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), branched low-density polyethylene (LDPE), and high-density polyethylene (HDPE).

[0039] When it is desired to impart flexibility to the target film, it is preferable that the compound contains an olefin-based resin composition, and that the olefin-based resin composition contains a low-melting-point olefin-based resin as the olefin-based resin. The low-melting-point olefin-based resin is preferably a copolymer of ethylene and α-olefin. Examples of α-olefins include propylene, 1-butene, 1-pentene, and 1-hexene.

[0040] From the viewpoint of imparting flexibility to the film, the low-melting-point olefin resin is preferably less than 90°C, more preferably less than 80°C, and even more preferably less than 70°C. Similarly, from the perspective of imparting flexibility to the film, low-melting-point olefin resins have a density of 0.895 g / cm³.3 It is preferably the following, 0.885 g / cm 3 More preferably, it is the following, 0.875 g / cm 3 Even more preferably, it is the following. Also, for the low melting point olefin resin, if its density is preferably 0.840 g / cm 3 or more, blocking is less likely to occur in the target film. From this perspective, the density is 0.850 g / cm 3 or more, which is more preferable, and 0.860 g / cm 3 or more, which is even more preferable. Taking the above into consideration, for the low melting point olefin resin, its density is 0.840 g / cm 3 or more and 0.895 g / cm 3 or less, which is preferable, 0.850 g / cm 3 or more and 0.885 g / cm 3 or less, which is more preferable, 0.860 g / cm 3 or more and 0.875 g / cm 3 or less, which is even more preferable. In addition, each of the above densities is the value at 25°C. In the following description, when referring to "density", it means the value measured at this temperature.

[0041] For the olefin resin composition, it is preferable that the above-mentioned low melting point olefin resin is contained in an amount of 30 parts by mass or more in 100 parts by mass of the olefin resin composition, because it can impart satisfactory flexibility to the target film. From the perspective of making this advantage more prominent, the low melting point olefin resin is more preferably contained in an amount of 33 parts by mass or more, and even more preferably 35 parts by mass or more, in 100 parts by mass of the olefin resin composition. Also, for the olefin resin composition, it is preferable that the above-mentioned low melting point olefin resin is contained in an amount of 95 parts by mass or less in 100 parts by mass of the olefin resin composition, because blocking is less likely to occur in the target film. From the perspective of making this advantage more prominent, the low melting point olefin resin is more preferably contained in an amount of 92 parts by mass or less, and even more preferably 90 parts by mass or less, in 100 parts by mass of the olefin resin composition. In summary, the olefin resin composition preferably contains 30 to 95 parts by mass of the low-melting-point olefin resin described above per 100 parts by mass of the olefin resin composition, more preferably 33 to 92 parts by mass, and even more preferably 35 to 90 parts by mass.

[0042] It is preferable for the olefin resin composition to include a high-melting-point olefin resin in addition to the low-melting-point olefin resin described above, as this allows the high-melting-point olefin resin to crystallize during heat treatment, thereby reducing thermal shrinkage. In particular, from the viewpoint of achieving rapid solidification in a short time for the purpose of high-speed molding of porous films that are melt-molded, the high-melting-point olefin resin is preferably 95°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher.

[0043] From the viewpoint of achieving both flexibility and thermal shrinkage of the film, it is preferable that the high-melting-point olefin resin has a relatively low density, specifically 0.950 g / cm³. 3 Preferably, it is 0.940 g / cm³. 3 It is even more preferable that the following is the case: 0.930 g / cm³ 3 The following is even more preferable: Furthermore, from the viewpoint of reducing the likelihood of blocking, the density of the high-melting-point olefin resin is 0.900 g / cm³. 3 Preferably, it is 0.905 g / cm³ or more. 3 It is even more preferable that the concentration be greater than or equal to 0.910 g / cm³. 3 It is even more preferable that the above conditions are met. In summary, the density of the high-melting-point olefin resin is 0.900 g / cm³. 3 More than 0.950g / cm 3 Preferably, it is 0.905 g / cm³. 3 More than 0.940g / cm 3 It is even more preferable that the following is the case: 0.910 g / cm³ 3 More than 0.930g / cm 3 The following is even more preferable: As the high-melting-point olefin resin having the aforementioned density, it is preferable to use polyethylene such as low-density polyethylene or linear low-density polyethylene, and it is particularly preferable to use linear low-density polyethylene because it promotes crystallization by heat treatment. In particular, linear low-density polyethylene polymerized with a metallocene catalyst is even more preferable because it promotes crystallization by heat treatment.

[0044] A metallocene catalyst is a compound in which a transition metal such as titanium, zirconium, or hafnium is sandwiched between unsaturated cyclic compounds containing a π-electron system cyclopentadienyl group or a substituted cyclopentadienyl group, and a co-catalyst such as an aluminum compound is combined with the metallocene. Examples of metallocenes include titanocene and zirconocene. Examples of aluminum compounds include alkylaluminoxane, alkylaluminum, aluminum halide, and alkylaluminum halide.

[0045] The olefin resin composition preferably contains 5 parts by mass or more of the high-melting-point olefin resin having the density described above per 100 parts by mass of the olefin resin composition, because the high-melting-point olefin resin crystallizes during heat treatment, thereby reducing the thermal shrinkage rate. From the viewpoint of making this advantage even more pronounced, the high-melting-point olefin resin is more preferably contained in 8 parts by mass or more, and even more preferably in 10 parts by mass or more, per 100 parts by mass of the olefin resin composition. Furthermore, in the present invention, it is preferable that the olefin resin composition used contains 70 parts by mass or less of the high-melting-point olefin resin described above per 100 parts by mass of the olefin resin composition, from the viewpoint of achieving compatibility with the flexibility of the porous film. From the viewpoint of making this advantage even more pronounced, the high-melting-point olefin resin is more preferably contained in 65 parts by mass or less, and even more preferably in 60 parts by mass or less, per 100 parts by mass of the olefin resin composition. In summary, the olefin resin composition used in the present invention preferably contains 5 to 70 parts by mass of the high-melting-point olefin resin having the density described above, more preferably 8 to 65 parts by mass, and even more preferably 10 to 60 parts by mass of the olefin resin composition per 100 parts by mass of the olefin resin composition.

[0046] The olefin resin composition used in this invention has a density of 0.900 g / cm³. 3 Preferably less than 0.895 g / cm³ 3 It is even more preferable that the following is the case: 0.885 g / cm³ 3 The following is even more preferable: Furthermore, the olefin resin composition preferably has a density of 0.840 g / cm³. 3 If the above conditions are met, blocking in the film will be less likely to occur. From this perspective, the density of the olefin resin composition should be 0.850 g / cm³. 3 It is even more preferable that the amount be greater than or equal to 0.860 g / cm³. 3 It is even more preferable that the above conditions are met. In summary, the olefin resin composition has a density of 0.840 g / cm³. 3 More than 0.900g / cm 3 Preferably less than 0.850 g / cm³ 3 More than 0.895g / cm 3 It is even more preferable that the following is the case: 0.860 g / cm³ 3 More than 0.885g / cm 3 The following is even more preferable:

[0047] Inorganic fillers contained in compounds are used when manufacturing porous films as the target film. Inorganic fillers are substances that cause delamination at the interface with thermoplastic resins, forming micropores. From this perspective, the average particle size D of inorganic fillers is important. 50 The average particle size D of the inorganic filler is preferably 30 μm or less, more preferably 10 μm or less, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. 50This refers to the cumulative particle size by weight at 50% mass, as measured by laser diffraction scattering particle size distribution analysis.

[0048] Examples of inorganic fillers include calcium carbonate, gypsum, talc, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium phosphate, aluminum hydroxide, zinc oxide, titanium dioxide, alumina, mica, zeolite, and carbon black, as well as mixtures thereof. Calcium carbonate is particularly preferred because it is easy to adjust to the aforementioned particle size.

[0049] The inorganic filler is preferably included in an amount of 50 parts by mass or more per 100 parts by mass of the thermoplastic resin composition, and more preferably 50 parts by mass or more per 100 parts by mass of the olefin-based resin composition, in order to form a sufficient amount of micropores and to sufficiently increase the moisture permeability of the porous film. More preferably, it is 60 parts by mass or more, and even more preferably 80 parts by mass or more. Furthermore, the inorganic filler is preferably included in an amount of 400 parts by mass or less per 100 parts by mass of the thermoplastic resin composition, and particularly 400 parts by mass or less per 100 parts by mass of the olefin-based resin composition, from the viewpoint of sufficiently improving the leak-proof properties of the porous film, more preferably 350 parts by mass or less, and even more preferably 200 parts by mass or less.

[0050] When manufacturing a porous film by incorporating inorganic fillers into a compound, it is preferable to also incorporate metal soaps in addition to the inorganic fillers in order to successfully form micropores. Metal soaps are used to facilitate the stretching of the resin film formed from the compound, which generates micropores. In particular, when using an olefin resin composition containing a low-melting-point olefin resin as the thermoplastic resin composition, flexibility is imparted to the target film, while interfacial delamination between the film and the inorganic filler becomes less likely during film stretching. Therefore, when using an olefin resin composition containing a low-melting-point olefin resin, it is particularly advantageous to use a metal soap to promote interfacial delamination between the olefin resin composition and the inorganic filler.

[0051] As metal soaps, metal salts of fatty acids are preferably used. Examples of fatty acids include caprylic acid, palmitic acid, stearic acid, capric acid, oleic acid, myristic acid, and lauric acid. Examples of metal salts include salts of these fatty acids with calcium, aluminum, magnesium, zinc, etc. Fatty acids themselves are known as substances similar to metal salts of fatty acids and that are incorporated into porous films. Fatty acids are used to improve the dispersibility of inorganic fillers; in other words, fatty acids are dispersants. However, fatty acids do not have the function of promoting interfacial delamination between thermoplastic resin compositions and inorganic fillers. Therefore, in this invention, metal salts of fatty acids and fatty acids are clearly distinguished both materially and functionally.

[0052] It is preferable that the metallic soap be included in an amount of 0.5 parts by mass or more per 100 parts by mass of the inorganic filler, in order to successfully generate fine pores. From the viewpoint of making this advantage even more pronounced, it is even more preferable that the metallic soap be included in an amount of 1.5 parts by mass or more per 100 parts by mass of the inorganic filler, and even more preferable that it be included in an amount of 2.0 parts by mass or more. Furthermore, it is preferable that the metallic soap be included in an amount of 15 parts by mass or less per 100 parts by mass of the inorganic filler, in order to maintain good moldability. From the viewpoint of making this advantage even more pronounced, it is even more preferable that the metallic soap be included in an amount of 10 parts by mass or less per 100 parts by mass of the inorganic filler, and even more preferable that it be included in an amount of 8 parts by mass or less. In summary, the amount of metal soap is preferably 0.5 parts by mass or more and 15 parts by mass or less per 100 parts by mass of inorganic filler, more preferably 1.5 parts by mass or more and 10 parts by mass or less, and even more preferably 2.0 parts by mass or more and 8 parts by mass or less.

[0053] It is preferable that the metal soap be included in an amount of 0.5 parts by mass or more per 100 parts by mass of the thermoplastic resin composition, in order to successfully generate micropores. From the viewpoint of making this advantage even more pronounced, it is even more preferable that the metal soap be included in an amount of 1.0 part by mass or more per 100 parts by mass of the thermoplastic resin composition, and even more preferable that it be included in an amount of 2.0 parts by mass or more. Furthermore, it is preferable that the metal soap be included in an amount of 20 parts by mass or less per 100 parts by mass of the thermoplastic resin composition, in order to maintain good moldability. From the viewpoint of making this advantage even more pronounced, it is even more preferable that the metal soap be included in an amount of 15 parts by mass or less per 100 parts by mass of the thermoplastic resin composition, and even more preferable that it be included in an amount of 10 parts by mass or less. In summary, the metal soap is preferably present in an amount of 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the thermoplastic resin composition, more preferably in an amount of 1.0 part by mass or more and 15 parts by mass or less, and even more preferably in an amount of 2.0 parts by mass or more and 10 parts by mass or less.

[0054] In relation to the aforementioned olefin-based resin composition, it is preferable to use a metal soap whose precipitation temperature is higher than the solidification temperature of the olefin-based resin composition, from the viewpoint of successfully forming micropores and obtaining a moisture-permeable film with high moisture permeability and high water resistance. Specifically, when the precipitation temperature of the metal soap is higher than the solidification temperature of the olefin-based resin composition, the metal soap precipitates faster than the olefin-based resin composition solidifies, allowing the metal soap to smoothly migrate to the surface of the inorganic filler. As a result, the release properties between the inorganic filler and the olefin-based resin composition during stretching are improved, and micropores are smoothly formed. From the viewpoint of making this advantage even more pronounced, when the precipitation temperature of the metal soap is Ts (°C) and the solidification temperature of the olefin-based resin composition is Tp (°C), it is preferable that the value of Ts-Tp is greater than 0°C, more preferably 1°C or higher, and even more preferably 2°C or higher. Furthermore, it is preferable that the value of Ts-Tp is 50°C or lower.

[0055] Provided that the Ts-Tp value is within the aforementioned range, the metal soap deposition temperature Ts is preferably 80°C to 180°C, more preferably 90°C to 170°C, and even more preferably 100°C to 160°C. On the other hand, the solidification temperature Tp of the olefin resin composition is preferably 60°C to 130°C, more preferably 70°C to 120°C, and even more preferably 80°C to 115°C, provided that the value of Ts-Tp is within the aforementioned range.

[0056] The precipitation temperature Ts of metal soap is measured using a hot stirrer and thermocouple in the following manner: Using a hot stirrer, 0.43 g of metal soap is added to 5.0 g of paraffin oil and heated while stirring until the metal soap dissolves. After stopping the stirring of the liquid with the stirrer, the temperature of the paraffin oil is lowered at a rate of 0.2 °C / min, and the temperature of the paraffin oil when the metal soap precipitates is read using a thermocouple, and this temperature is defined as the precipitation temperature of the metal soap. If the metal soap does not dissolve in the paraffin oil even after heating it to 210 °C, the precipitation temperature is defined as 210 °C. On the other hand, the solidification temperature Tp of the olefin resin composition is measured in accordance with JIS K 7121 (Method for determining the end temperature of extrapolation crystallization) by the following method. A sample of approximately 2.0 mg of moisture-permeable film is used, and differential scanning calorimetry (DSC) is performed using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation) under the following conditions: measurement temperature range of 30°C to 260°C, heating rate of 10°C / min, cooling rate of 50°C / min, in an air environment, and data sampling period of 0.5 s. In the cooling process of the obtained DSC curve, an exothermic peak that occurs when the olefin resin composition solidifies (crystallizes) is observed. The solidification temperature of the olefin resin composition is defined as the temperature at the intersection of a straight line drawn from the baseline on the lower side of the peak temperature to the higher side, and an approximate straight line drawn between the two data points where the slope is maximum on the lower side of the peak curve, with respect to the peak with the greatest amount of exothermic heat during the cooling process. If two or more heat-generating peaks overlap, the solidification temperature is determined using the method described above after peak separation, for example, by using the software PeakFit v4.12 (manufactured by Huelinks Co., Ltd.).

[0057] A water-repellent agent can be added to the compound. This makes the target film water-repellent. In particular, if the target film is a porous film, that is, a film that allows vapor to pass through but has difficulty passing water (liquid water) through, adding a water-repellent agent to the compound is preferable because it makes the porous film even more resistant to water permeability.

[0058] It is preferable to use triglycerides as the water repellent. Using triglycerides improves the leak-proof properties of porous films. In particular, it is preferable to use triglycerides that contain a group derived from a fatty acid having 16 to 22 carbon atoms, and that the group is a hydrocarbon group without unsaturated bonds or substituents. Using such triglycerides improves the leak-proof properties of porous films containing the triglycerides compared to conventional methods.

[0059] From the viewpoint of making the above-mentioned advantages even more pronounced, the amount of triglycerides blended into the compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of the thermoplastic resin composition, and particularly per 100 parts by mass of the olefin-based resin composition. Furthermore, from the viewpoint of film moldability, the amount of triglycerides blended is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the thermoplastic resin composition, and particularly per 100 parts by mass of the olefin-based resin composition. In summary, the amount of triglycerides blended is preferably 0.1 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the thermoplastic resin composition, and more preferably 0.5 parts by mass or more and 25 parts by mass or less, and even more preferably 1.0 part by mass or more and 20 parts by mass or less per 100 parts by mass of the olefin-based resin composition.

[0060] Using the compound described above, the film produced by the method of the present invention is preferably a porous, moisture-permeable film, and the film preferably contains 50 to 400 parts by mass of an inorganic filler per 100 parts by mass of the olefin resin composition. In this case, the density of the olefin resin composition is 0.840 g / cm³. 3 More than 0.900g / cm 3 It is preferable that the olefin resin composition contains a low-melting-point olefin resin having a melting point of less than 90°C. Furthermore, the olefin resin composition has a density of 0.840 g / cm³. 3 More than 0.895g / cm 3 From the viewpoint of imparting flexibility to the film, it is preferable to include 30 to 95 parts by mass of the following low-melting-point olefin resin in 100 parts by mass of the olefin resin composition. When the degree of flexibility of a film is expressed in terms of flexibility deformation, the flexibility deformation in the mechanical direction is preferably 0.060 N / (mm·(g / m²). 2It shows a low value of )) or less, and more preferably 0.057 N / (mm·(g / m 2 )) More preferably 0.055 N / (mm·(g / m 2 )) or less. The lower limit of the degree of flexible deformation is 0.005 N / (mm·(g / m) from the viewpoint of maintaining the strength of the film. 2 It is preferable that the values ​​are )) or higher. Furthermore, it is preferable that the thermal shrinkage rate of the film produced by the method of the present invention is 8% or less in the mechanical direction, and particularly 6% or less, as described above.

[0061] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the apparatus 10 shown in Figure 1, a slit section 70 was installed upstream of the second heat treatment section 80, but it is not necessary to install the slit section 70. Instead, if necessary, the wound film may be unwound in a separate process and the unwound film may be slit. Furthermore, in the embodiment 10 shown in Figure 1, a cooling unit 60 was installed between the first heat treatment unit 50 and the second heat treatment unit 80. However, depending on the type of thermoplastic resin used, it may not be necessary to install a cooling unit 60, and the film heated in the first heat treatment unit 50 may be cooled naturally. [Examples]

[0062] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0063] [Examples 1 to 5 and Comparative Example 1] The components shown in Table 1 were weighed to the quantities shown in the table. These were mixed in a Henschel mixer (manufactured by Kawata Co., Ltd.). The resulting mixture was kneaded in a twin-screw extruder (manufactured by Toyo Seiki) at a set temperature of 180°C and a screw rotation speed of 180 rpm to obtain a pelletized compound. The units of composition in Table 1 are parts by mass. A porous film was manufactured using this compound and the apparatus 10 shown in Figure 1. (2) Film formation A 150mm wide T-die (manufactured by Toyo Seiki) was used to form a film from the molten compound. The T-die was set to a temperature of 200°C. (3) Film manufacturing The obtained unstretched film was uniaxially stretched to obtain a porous stretched film. The stretching temperature was set to 60°C and the stretching ratio to 2.5 times. (4) First heat treatment The stretched film was heat-treated using two heat rolls. The circumferential temperature T2 of the heat rolls was set to the values ​​shown in Table 2. In addition, the peripheral speed V2 of the stretching section roll was set to the values ​​shown in Table 2 relative to the peripheral speed V3 of the heat rolls. (5) Cooling process The stretched film was cooled using two chill rolls. The surface temperature of the chill rolls was set to the values ​​shown in Table 2. (6) Slit The stretched film was slit into multiple strips. (7) Second heat treatment The stretched film was heat-treated using an infrared heater. The heat treatment was performed so that the surface temperature T3 of the film reached the values ​​shown in Table 2. The second heat treatment was performed immediately before winding. (8) Winding The winding was performed by setting the ratio of the transport speed of the stretched film in the first heat treatment section (V3) to the winding speed (peripheral speed) (V4) to the values ​​shown in Table 2.

[0064] 〔evaluation〕 The thermal shrinkage rate and degree of flexibility deformation were measured for the films obtained in the examples and comparative examples using the following method. The results are shown in Table 1.

[0065] [Thermal shrinkage rate] Three test pieces were obtained by cutting a porous film to a width of 60 mm and a length of 100 mm. The obtained test pieces were stored in an environment of 50°C for one day. The length L1 of the porous film after storage was measured, and the value of (100-L1) was calculated. The average of these values ​​was taken as the thermal shrinkage rate of the porous film.

[0066] [Degree of flexibility] Three test specimens were obtained by cutting a porous film to a length of 150 mm in the machine direction and 30 mm in the width direction. The obtained test specimens were fixed to a tensile testing machine (product name: AG-1S, manufactured by Shimadzu Corporation) so that the initial length L0 of each test specimen was 100 mm. After fixing, the load read by the tensile testing machine was set to zero, and a cycle test was performed in which the test specimen was stretched to 1.3 times the length of L0 at a deformation speed of 200 mm / min, and then immediately contracted back to L0 at a deformation speed of 200 mm / min. From the obtained data, the load (F) at 1.03 times deformation during the stretching process was determined. 3% Read the value of flexibility (N / (mm·(g / m)) from the following formula and calculate the degree of flexibility (N / (mm·(g / m)) 2 The following was calculated. The average value of the three test pieces was used as the degree of flexibility deformation of the porous film. Flexible deformation degree (N / (mm·(g / m 2 )))=F 3% (N) / (0.03×30(mm)×Basis weight of film (g / m²) 2 ))

[0067] [Table 1]

[0068] [Table 2]

[0069] As is clear from the results shown in Table 2, the porous films obtained in each example had low thermal shrinkage and relaxed polymer chain orientation. In contrast, the porous film obtained in Comparative Example 1 had a higher thermal shrinkage than the examples and showed insufficient relaxation of polymer chain orientation. Furthermore, it can be seen that the porous films obtained in each example are more flexible than the porous film obtained in Comparative Example 1. [Explanation of symbols]

[0070] 10 Manufacturing equipment 20. Melting and mixing section 30 Molding section 40 Stretching section 50 First heat treatment unit 60 Cooling section 70 Slit section 80 Second heat treatment unit 90 Winding section

Claims

1. Molten resin is extruded from the die to form a film that stretches in one direction. The film obtained by film formation is stretched in the longitudinal direction while being transported. The stretched film is transported while undergoing the first heat treatment. A method for manufacturing a film, comprising a step of winding up a heat-treated film, Immediately before winding up the heat-treated film, a second heat treatment is applied to the film. The heating temperature T2 in the first heat treatment and the heating temperature T3 in the second heat treatment are such that T2 < T3. The shrinkage rate of the film due to the first heat treatment is set to be between 10% and 50%, A method for manufacturing a film, wherein the shrinkage rate of the film due to the second heat treatment is set to be 3% or more and 10% or less.

2. The manufacturing method according to claim 1, wherein the film is shrunk in the transport direction while a second heat treatment is applied.

3. The manufacturing method according to claim 1, wherein the second heat treatment is performed at a temperature higher than the stretching temperature.

4. The manufacturing method according to claim 3, wherein the difference between the heating temperature T2 due to the first heat treatment and the stretching temperature T1 is 5°C or more and 70°C or less, provided that T2 > T1.

5. The manufacturing method according to claim 1, wherein the second heat treatment is performed in a non-contact manner.

6. The manufacturing method according to claim 1, wherein the molten resin contains 50 to 400 parts by mass of an inorganic filler per 100 parts by mass of the olefin resin composition.

7. The manufacturing method according to claim 6, wherein the olefin resin composition includes a low-melting-point olefin resin having a melting point of less than 90°C.

8. The manufacturing method according to claim 6 or 7, wherein the molten resin contains 0.5 to 15 parts by mass of metal soap and 0.5 to 5 parts by mass of fatty acid per 100 parts by mass of the inorganic filler.

9. The manufacturing method according to claim 8, wherein when the deposition temperature of the metal soap is Ts (°C) and the solidification temperature of the olefin resin composition is Tp (°C), the value of Ts - Tp is greater than 0°C.

10. The manufacturing method according to claim 6 or 7, wherein the molten resin contains 0.1 parts by mass or more and 30 parts by mass or less of triglyceride per 100 parts by mass of the olefin resin composition.

11. The olefin resin composition has a density of 0.840 g / cm³. ３ 0.900g / cm or more ３ The manufacturing method according to claim 6 or 7, wherein the result is less than [amount missing].

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