Polyethylene porous stretched film

Abstract

To provide a polyethylene-based porous stretched film having uniform moisture vapor permeability while having high moisture vapor permeability, even when two or more polyethylene having different density are used in combination.SOLUTION: A porous stretched film comprising 100 pts.mass of a resin component containing two or more types of polyethylene having different densities and 80 to 130 pts.mass of an inorganic filler, wherein the polyethylene has a melt index (MI) of 1.5 to 5.0 g / 10 min, allows a difference of a maximum value and a minimum value of MI of 1.5 g / 10 min at the maximum, and has a moisture permeability of 3500 g / m2 24hr or more measured at a temperature of 40°C and a relative humidity of 90%, a difference of the maximum value and the minimum value of the moisture permeability in a film width direction of 500 g / m2 24hr or less, and a water pressure resistance of 150 kPa or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a novel polyethylene-based porous stretched film. More specifically, it provides a polyethylene-based porous stretched film that has high moisture permeability and uniform moisture permeability even when two or more types of polyethylene with different densities are used in combination. [Background technology]

[0002] Conventionally, porous films, formed by stretching a sheet of a resin composition containing fillers added to polyethylene, are known to possess both moisture permeability and liquid impermeability. These properties have led to their use in various applications, including sanitary materials such as backsheets for disposable diapers and sanitary napkins, and packaging materials for desiccants and dehumidifiers.

[0003] In the above applications, porous stretched films are required to have high moisture permeability and liquid impermeability, as well as physical properties such as flexibility, tensile strength, and tear strength.

[0004] Conventionally, it has been known that two or more types of polyethylene porous stretched films are used in combination to improve the physical properties such as molding stability, tensile strength, tear strength, and moisture permeability, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). For example, in the example of Patent Document 1, by using a combination of LLDPE and HDPE, it was possible to achieve good molding stability while maintaining high strength and high moisture permeability.

[0005] However, as described above, when using polyethylenes of different densities, it has been found that, depending on the combination, the uniformity of the resin composition decreases, and the performance of the polyethylene-based porous stretched film obtained using this composition deteriorates. In other words, when two or more types of polyethylene with different densities are used in combination, not only is sufficient moisture permeability not achieved, but a phenomenon in which the moisture permeability of the film varies greatly may occur. In particular, in recent years, plant-derived polyethylene, which is increasingly being used from the perspective of carbon neutrality, is increasingly being used in combination with petroleum-derived polyethylene, but there is a lack of diverse products, and the above problem is likely to occur when combined with petroleum-derived polyethylene. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 1-4338 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the object of the present invention is to provide a polyethylene-based porous stretched film that has high moisture permeability while maintaining uniform moisture permeability, even when two or more types of polyethylene with different densities are used in combination. [Means for solving the problem]

[0008] The inventors of this invention conducted intensive research to solve the above problems and found that when two or more types of polyethylene with different densities are used in combination, if there is polyethylene with a low MI or if there is a large difference in the MI of each polyethylene, the uniformity of the composition decreases, leading to the aforementioned problems. Based on the above findings, further research revealed that by using polyethylenes with MIs within a specific range, it is possible to ensure uniformity of composition even if the MIs of each polyethylene are slightly different, and we succeeded in obtaining a polyethylene-based porous stretched film with high moisture permeability and uniform moisture permeability, leading to the proposal of the present invention.

[0009] In other words, the present invention provides a porous stretched film made of 100 parts by mass of a resin component containing two or more polyethylenes with different densities and 80 to 130 parts by mass of an inorganic filler, characterized in that the melt index (MI) of the polyethylenes is 1.5 to 5.0 g / 10 min, and the difference between the highest and lowest MI values ​​is limited to a maximum of 1.5 g / 10 min.

[0010] The polyethylene porous stretched film is particularly effective when at least one of the two or more types of polyethylene is plant-derived polyethylene.

[0011] Furthermore, in the polyethylene porous stretched film, it is preferable that the difference between the highest and lowest MI values ​​of two or more types of polyethylene is 0.5 g / 10 min or less.

[0012] Furthermore, the polyethylene porous stretched film contains two or more types of polyethylene with a density of 0.930 g / cm³. 3 The above polyethylene has a density of 0.930 g / cm³. 3 Preferably, it contains less than [amount] polyethylene.

[0013] Furthermore, it is preferable that the polyethylene porous stretched film is substantially free of plasticizers.

[0014] According to the polyethylene-based porous stretched film of the present invention, the following characteristics can be exhibited.

[0015] (1) The water vapor permeability measured at a temperature of 40 ° C and a relative humidity of 90% is 3500 g / m 2 ·24 hr or more (2) The difference between the maximum value and the minimum value of the water vapor permeability in the width direction of the film is 500 g / m 2 ·24 hr or less (3) The water pressure resistance is 150 kPa or more The polyethylene-based porous stretched film of the present invention contains two or more types of polyethylene, the MI of the above polyethylene is 1.5 to 5.0 g / 10 min, and the difference between the maximum value and the minimum value of MI is at most 1.5 g / 10 min. After forming a resin composition composed of 100 parts by mass of the resin component and 80 to 130 parts by mass of the inorganic filler into a sheet shape, it can be produced by stretching 150 to 200% in the machine direction (MD) and 110 to 160% in the vertical direction (TD), respectively.

[0016] In the present invention, the MI of polyethylene is a value measured by the A method at a measurement temperature of 190 ° C and a load of 2.16 kg in accordance with JIS K 7210. Further, the density of polyethylene in the present invention is measured by the JIS K 7112 method. Furthermore, the water vapor permeability is a value measured by the calcium chloride method under the conditions of 40 ° C, a relative humidity of 90%, and a measurement time of 24 hours in accordance with JIS Z 0208. Still further, the water pressure resistance is a value measured by a water pressure resistance measuring instrument in accordance with JIS L 1092. [Effects of the Invention]

[0017] According to the present invention, in a polyethylene-based porous stretched film using two or more types of polyethylene having different densities, a polyethylene-based porous stretched film having high moisture permeability and uniform water vapor permeability can be obtained. [Embodiments for Carrying Out the Invention]

[0018] [Polyethylene-based Porous Stretched Film] The polyethylene porous stretched film of the present invention comprises a resin composition consisting of 100 parts by mass of a resin component containing two or more polyethylenes with different densities and 80 to 130 parts by mass of an inorganic filler.

[0019] In the present invention, any known polyethylene can be used without particular limitations, but linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE) are particularly preferred. Examples of LLDPE include copolymers of ethylene with butene-1, hexene-1, and 4-methylpentene-1.

[0020] Regarding the polyethylene mentioned above, the origin of the ethylene used as a raw material is not particularly limited. Petroleum-derived polyethylene polymerized from petroleum-derived ethylene and plant-derived polyethylene polymerized from plant-derived ethylene can both be used. However, it is preferable to use plant-derived polyethylene as part or all of the polyethylene because it is superior in terms of addressing environmental issues such as petroleum depletion and global warming. If the polymerization process after obtaining ethylene is exactly the same, the properties of the polyethylene will not change in any way between plant-derived polyethylene and petroleum-derived polyethylene, and they can be blended in any ratio considering costs and other factors.

[0021] In the present invention, the combination of two or more polyethylenes with different densities is not particularly limited, but a density of 0.930 g / cm³ is used. 3 The above polyethylene has a density of 0.930 g / cm³. 3 It is preferable to include less than a certain amount of polyethylene, as this allows for the acquisition of a polyethylene-based porous stretched film with excellent flexibility and rigidity.

[0022] In the present invention, it is important that the MI of the two or more polyethylenes with different densities is all within the range of 1.5 to 5.0 g / 10 min. That is, by using polyethylenes with an MI within the above range as the polyethylene constituting the polyethylene-based porous stretched film, sufficient moisture permeability can be ensured even if there is a difference in MI between the polyethylenes, and moreover, the phenomenon of variations in moisture permeability can be effectively prevented.

[0023] The difference between the highest and lowest MI values ​​of the two or more polyethylenes mentioned above is permissible up to a maximum of 1.5 g / 10 min, but is preferably 1.0 g / 10 min or less, and in particular, by setting it to 0.5 g / 10 min or less, the resins are mixed more uniformly, exhibiting high moisture permeability and ensuring uniform moisture permeability.

[0024] On the other hand, while a lower limit of 0 is most preferable for the difference between the highest and lowest values, in light of the objectives of the present invention, it is particularly effective when the difference is 0.2 or more. That is, as mentioned above, when it is desired to use plant-derived polyethylene with a relatively small number of grades in combination with other polyethylenes of different densities, the greatest advantage of the present invention is that it can be used without problems even if there is a slight difference in density.

[0025] In the present invention, the inorganic filler can be any inorganic filler that has been conventionally known in the manufacture of porous films, without any particular limitations. Calcium carbonate is the most commonly used inorganic filler and is most preferably used in the present invention.

[0026] The particle size of the inorganic filler is not particularly limited, but considering the balance of performance of the resulting polyethylene-based porous stretched film, an average particle size of 1 to 10 μm, preferably 1 to 5 μm, is preferred. When the average particle size is within the above range, the formation of interconnected pores is facilitated during stretching, and breakage during film molding can be suppressed.

[0027] The above inorganic filler is blended at a ratio of 80 to 130 parts by mass, preferably 90 to 120 parts by mass, based on 100 parts by mass of the mixed resin. When the ratio of the above inorganic filler is less than 80 parts by mass, sufficient porosity cannot be imparted to the polyethylene-based porous stretched film, and sufficient moisture permeability cannot be ensured. Also, when it exceeds 130 parts by mass, it becomes difficult to impart sufficient strength to the polyethylene-based porous stretched film.

[0028] In the resin composition of the present invention, additives used in ordinary resin compositions may be included. Examples of the additives include antioxidants, heat stabilizers, light stabilizers, neutralizing agents, antiblocking agents, slip agents, antistatic agents, lubricants, and the like.

[0029] Incidentally, it is preferable not to blend a plasticizer as an additive in the resin composition of the present invention. The plasticizer in the present invention is a general term for compounds that improve the plasticity of the resin and impart flexibility to the film. When a plasticizer is added, the MI of the resin composition tends to become excessively large, and the moisture permeability and the uniformity of the moisture permeation rate tend to decrease.

[0030] The polyethylene-based porous stretched film of the present invention is composed of the composition of the above resin component and inorganic filler, and has a moisture permeation rate of 3500 g / m 2 ·24 h or more, particularly 4000 g / m 2 ·24 h or more and has high moisture permeability.

[0031] Also, in the polyethylene-based porous stretched film of the present invention, the difference between the maximum value and the minimum value of the moisture permeation rate measured at five points at equal intervals with respect to the width of the film is 500 g / m 2 ·24 h or less, particularly 400 g / m 2 ·24 h or less, indicating that it is also excellent in the uniformity of the moisture permeation rate.

[0032] The uniformity of moisture permeability described above is measured in the width direction of the film. If the film is wound in a roll, this corresponds to the width direction of the roll. For cut film, the longitudinal direction of the film should be determined from the stretched state, and the measurement should be taken in a direction perpendicular to it. Furthermore, for film immediately after manufacturing, the measurement is taken excluding 20% ​​of the total width of the film from both ends. In addition, it is preferable to perform the above measurement on film with a width of 1 m or more, and the sampling at each measurement point is generally done in a size that allows for measurement of moisture permeability, specifically about 100 mm x 100 mm. Furthermore, the water pressure resistance should be a value of 150 kPa or higher.

[0033] Other properties of the polyethylene-based porous stretched film of the present invention are not particularly limited. For example, the basis weight of the film may be 10 to 200 g / m². 2 In particular, 30-100g / m 2 That is the general rule. Furthermore, in the polyethylene porous stretched film of the present invention, the tear strength in the mechanical direction (MD) of the film is preferably 0.4 N or higher, and more preferably 0.6 N or higher. The tear strength is the value obtained by measuring the tearing force required for the tear to reach the end of the long axis of the test piece, in accordance with JIS K 7128-1 (Trouser tearing method).

[0034] [Method for manufacturing polyethylene porous stretched film] The method for producing the polyethylene-based porous stretched film of the present invention is not particularly limited, but a typical production method is to produce the film by forming a resin composition consisting of 100 parts by mass of a resin component and 80 to 130 parts by mass of an inorganic filler, which contains two or more of the above-mentioned polyethylenes, each of which has an MI of 1.5 to 5.0 g / 10 min, and the maximum and minimum MI values ​​are a maximum of 1.5 g / 10 min, into a sheet, and then stretching it by 150 to 200% in the mechanical direction (MD) and 110 to 160% in the vertical direction (TD).

[0035] In the above manufacturing method, the polyethylene and inorganic filler described above are used. Furthermore, in the above manufacturing method, the method of forming the resin composition into a film is not particularly limited, but extrusion from a T-die or annular die is common. The resin composition extruded into a film is then stretched by a known stretching method according to the respective shape. For example, a film extruded from a T-die is stretched longitudinally by a roll and transversely by a tenter. A film extruded from an annular die is stretched longitudinally by a roll and then transversely via a mandrel. The stretching temperature of the film is preferably 40 to 120°C. Furthermore, the stretched film may be heat-set if necessary. The treatment temperature in the heat-set treatment is a temperature above the softening point and below the melting point of the resin, preferably 80 to 120°C. [Examples]

[0036] The present invention will be described in more detail below, but the present invention is not limited to these examples. The various physical properties in the examples and comparative examples were measured by the following methods. (1) Basis weight (g / m 2 ) A 100mm x 100mm test piece was taken from the sample film, and its mass was measured using a balance. The basis weight was calculated from the area and mass of this sample.

[0037] (2) Moisture permeability (g / m 2 (24 hours) A 100mm x 100mm test piece was taken from the sample film and measured according to JIS Z 0208 at 40°C, 90% relative humidity, and for 24 hours using the calcium chloride method.

[0038] (3) Uniformity of moisture permeability [maximum value - minimum value] (g / m 2 (24 hours) Five 100mm x 100mm test pieces were taken at equal intervals within the range excluding 20% ​​of the total width of the sample film from both ends. These were measured according to JIS Z 0208 using the calcium chloride method at 40°C, 90% relative humidity, and for 24 hours, and the difference between the maximum and minimum measured values ​​was calculated.

[0039] (4) Water pressure resistance (kPa) A 150mm x 150mm test piece was taken from the sample film, and in accordance with JIS L 1092 Method A (low water pressure method), polyolefin nonwoven fabric (manufactured by ENEOS Techno Material Co., Ltd., product name: Warif) was placed on the front side as a reinforcing material, and the test piece was mounted on a water pressure resistance testing apparatus. Water pressure was applied to the front side of the test piece, and the water pressure was read when water came out from three locations on the back side of the test piece.

[0040] (5) Tear strength (N) A test specimen measuring 40 mm in width and 150 mm in length was taken from the sample film, and a test specimen with a 75 mm long slit was added to its center. The slit was then pulled at a chuck distance of 50 mm and a tensile speed of 200 mm / min in accordance with JIS K 7128-1 (Trouser tearing method), and the tearing force required for the tear to reach the end of the long axis of the test specimen was measured.

[0041] The following raw materials were used in the examples and comparative examples.

[0042] A: Linear low-density polyethylene [manufactured by Dow Chemical Ltd., product name: CEFOR1221P, density: 0.918 g / cm³] 3 , MI:2.0g / 10min] B: Linear low-density polyethylene [SABIC Corporation, product name: 318BJ, density: 0.918 g / cm³] 3 , MI:2.8g / 10min] C: High-density polyethylene [(Manufactured by Prime Polymer Co., Ltd., Product name: Hyzex 5000SF, Density: 0.956 g / cm³)] 3 , MI:0.7g / 10min] D: Branched low-density polyethylene [(Manufactured by ENEOS NUC Corporation, Product name: NUC8008, Density: 0.918 g / cm³)]3 , MI:4.7g / 10min] E: Plant-derived linear low-density polyethylene [Braskem, product name: SLL118, density: 0.918 g / cm³] 3 , MI:1.0g / 10min] F: Plant-derived linear low-density polyethylene [Braskem, product name: SLH218, density: 0.916 g / cm³] 3 , MI:2.3g / 10min] G: Plant-derived high-density polyethylene [Braskem Corporation, product name: SGE7252NS, density: 0.953 g / cm³] 3 , MI:2.0g / 10min] H: Calcium carbonate [(Manufactured by Calfine Co., Ltd., Product name: LAC-2000)] I: Plasticizer (hydrogenated castor oil) [Manufactured by KF Trading Co., Ltd., Product name: HCO-P3] J: Additives [Hindered phenolic heat stabilizer (manufactured by BASF Japan Ltd., product name: IRGANOX3114) 15 parts by mass, phosphorus-based heat stabilizer (manufactured by BASF Japan Ltd., product name: IRGAFOS168) 85 parts by mass].

[0043] Example 1 A resin composition containing 100 parts by mass of a mixed resin consisting of 44 parts by mass of linear low-density polyethylene A, 33 parts by mass of linear low-density polyethylene B, and 23 parts by mass of plant-derived high-density polyethylene G, as shown in Table 1, was mixed with 122 parts by mass of calcium carbonate H and 0.6 parts by mass of additive J, and processed into pellets using a twin-screw extruder at 190°C. Next, the pellets were supplied to an extruder at 190°C and a film was obtained by inflation molding using an annular die. The film was further uniaxially stretched longitudinally (stretching ratio: 180%) between the film and a stretching roll heated to 45°C, and then biaxially stretched transversely (stretching ratio: 120%) via a mandrel heated to 85°C to obtain a biaxially oriented film. Subsequently, a heat-setting treatment was performed using a heat-set roll heated to 90°C, and the film was wound into a film shape using a winding machine to obtain a polyethylene porous stretched film.

[0044] Table 2 shows the results of evaluating the basis weight, moisture permeability, uniformity of moisture permeability, water pressure resistance, and tear strength in the mechanical direction (MD) of the obtained polyethylene porous stretched film.

[0045] Examples 2-6 A polyethylene porous film was manufactured and evaluated in the same manner as in Example 1, except that the composition was changed as shown in Table 1. The results are shown in Table 2. All porous stretched films had good moisture permeability, and the difference between the maximum and minimum moisture permeability was 500 g / m². 2 • The results were uniform over 24 hours and showed excellent water resistance.

[0046] Comparative Examples 1-5 A polyethylene porous stretched film was manufactured and evaluated in the same manner as in Example 1, except that the composition was changed as shown in Table 1. The results are shown together in Table 2.

[0047] [Table 1]

[0048] [Table 2]

Claims

1. A porous stretched film comprising 100 parts by mass of a resin component containing two or more polyethylenes of different densities and 80 to 130 parts by mass of an inorganic filler, wherein the melt index (MI) of each polyethylene is 1.5 to 5.0 g / 10 min, and the difference between the highest and lowest MI values ​​is limited to a maximum of 1.5 g / 10 min, and the film has the following characteristics. (1) A moisture permeability of 3500 g / m² measured at a temperature of 40°C and a relative humidity of 90%. ２ ・24 hours or more (2) The difference between the maximum and minimum values ​​of the moisture permeability in the width direction of the film is 500 g / m ２ ・24 hours or less (3) Water pressure resistance of 150 kPa or more

2. The polyethylene porous stretched film according to claim 1, wherein at least one of the two or more types of polyethylene is plant-derived polyethylene.

3. The polyethylene porous stretched film according to claim 1 or 2, wherein the difference between the highest and lowest MI values ​​of the two or more polyethylenes is 0.5 g / 10 min or less.

4. The two or more types of polyethylene mentioned above have a density of 0.930 g / cm³. ３ The above polyethylene has a density of 0.930 g / cm³. ３ A polyethylene-based porous stretched film according to any one of claims 1 to 3, comprising less than [amount] polyethylene.

5. A polyethylene porous stretched film according to any one of claims 1 to 4, which is substantially free of plasticizers.

6. A method for producing a polyethylene porous stretched film according to any one of claims 1 to 5, characterized in that a resin composition comprising 100 parts by mass of a resin component and 80 to 130 parts by mass of an inorganic filler, each containing two or more types of polyethylene, wherein the MI of each polyethylene is 1.5 to 5.0 g / 10 min and the difference between the highest and lowest MI values ​​is a maximum of 1.5 g / 10 min, is formed into a sheet, and then stretched by 150 to 200% in the mechanical direction (MD) and 110 to 160% in the vertical direction (TD).

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