Stretched porous film and method for manufacturing the same

Abstract

The present invention provides a stretched porous film which has excellent air permeability, texture and printability. This stretched porous film has a thermal shrinkage in the longitudinal direction of 1.2% or less and a water vapor transmission rate of 2,000 g / m2∙24 h or more, while being formed of a resin composition which contains: 100 parts by mass of a polyethylene resin that contains 20% by mass to 70% by mass of a linear low density polyethylene having a density of 0.931 to 0.940 g / cm3, 8% by mass to 20% by mass of a branched low density polyethylene having a density of 0.901 to 0.940 g / cm3, and other resins, while containing 0.5% by mass or less of a resin having a density of 0.900 g / cm3 or less; and 80 to 200 parts by mass of an inorganic filler.

Description

[Technical Field]

[0001] The present invention relates to a stretched porous film and a method for producing the same. [Background technology]

[0002] Traditionally, personal care products such as diapers are required to allow air and vapor to pass through but not liquids to prevent stuffiness and other issues. Therefore, breathability and water resistance are required for personal care products such as diapers. To meet these requirements, stretched porous films are used, which are made by molding water-repellent resins such as polyethylene resins into a film and forming fine pores. Such stretched porous films allow air to pass through but do not allow liquids to pass through. Due to this property, stretched porous polyolefin films are widely used in sanitary materials such as disposable diapers and sanitary napkins, functional packaging materials such as desiccants and disposable hand warmers, simple clothing such as disposable gloves and raincoats, waterproof building materials such as house wraps, agricultural applications such as mulching sheets, and waste treatment applications such as compost covering sheets.

[0003] Such stretched porous polyolefin films are required to have a variety of physical properties. For example, when used as a backsheet for disposable diapers, moisture permeability and flexibility are important properties during use, and printability is also important from the perspective of handling during the manufacturing process.

[0004] When a porous film is used for the backsheet of a disposable diaper, for the purpose of enhancing the brand and added value of the product and further improving the purchasing desire of consumers, printing with high design and aesthetic quality with characters or figures arranged is performed. When printing is performed on a porous film, if the variation in the printing pitch (interval) is large, it causes deterioration in the yield of the diaper during productization, and thus stability of the printing pitch is required. However, when the printed film is wound and stored as a roll, during storage, the winding shape of the roll changes so that the central part of the roll tightens and the beginning and ending parts of the winding loosen, and it has been known that thereby the variation in the printing pitch occurs subsequently. The variation in the printing pitch is likely to occur when the line tension applied in the longitudinal direction (film flow direction) during printing is large, and a film with little elongation is required. It is known that the printability of a film is improved by heat-fixing the film after stretching to suppress the heat shrinkage rate of the film.

[0005] Conventionally, studies focusing on the above physical properties have been conducted. For example, in Patent Document 1, a polyolefin stretched porous film having high moisture permeability, excellent texture, and excellent printability is disclosed. In this document, by using a resin composition with a special formulation in which the amount of polypropylene is relatively small and adopting a large draw ratio for production, a polyolefin stretched porous film having high moisture permeability, excellent texture, a small heat shrinkage rate, and excellent printability is obtained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Although the polyolefin stretched porous film of Patent Document 1 is excellent in printability, in order to further improve the printability and enhance the productivity, it was desired to lower the thermal shrinkage rate even more. However, when the inventors conducted investigations, even if the manufacturing conditions of the polyolefin stretched porous film of Patent Document 1 were adjusted, the thermal shrinkage rate could not be drastically suppressed, and a significant improvement in printability could not be achieved.

[0008] Therefore, an object of the present invention is to provide a stretched porous film excellent in air permeability, texture, and printability.

Means for Solving the Problems

[0009] As a result of intensive studies by the inventors to solve the above problems, by using a polyethylene-based resin having a specific composition and heat-fixing it under specific conditions, a stretched porous film with a low thermal shrinkage rate can be obtained without deteriorating the air permeability and texture, and it has been found that the above problems can be achieved. That is, the present invention includes the following configurations. [1] 20 to 70% by mass of linear low-density polyethylene having a density of 0.931 to 0.940 g / cm 3 , 3 , 3 , , 2 , , 3 , 3 , ,

[0009] , , , , , 8 to 20% by mass of branched low-density polyethylene having a density of 0.901 to 0.940 g / cm 3 , and other resins, and a resin composition containing 100 parts by mass of a polyethylene-based resin in which resins having a density of 0.900 g / cm 3 or less are 0.5% by mass or less, 80 to 200 parts by mass of an inorganic filler, and having a longitudinal thermal shrinkage rate of 1.2% or less and a moisture permeability of 2000 g / m 2 ·24 h or more, a stretched porous film characterized by the above. [2] The above stretched porous film, wherein the polyethylene-based resin contains 22 to 67% by mass of linear low-density polyethylene having a density of 0.901 to 0.930 g / cm 3 as the other resin. [3] The above stretched porous film, wherein the polyethylene-based resin contains 22 to 67% by mass of high-density polyethylene having a density of 0.941 to 0.975 g / cm 3 as the other resin. 〔4〕The above-mentioned stretched porous film, wherein the inorganic filler is calcium carbonate. 〔5〕A resin composition comprising 20 to 70% by mass of linear low-density polyethylene having a density of 0.931 to 0.940 g / cm 3 3, 8 to 20% by mass of branched low-density polyethylene having a density of 0.901 to 0.940 g / cm 3 3, and other resins, and a resin having a density of 0.900 g / cm 3 or less is 0.5% by mass or less. A film formed from 100 parts by mass of a polyethylene-based resin and 80 to 200 parts by mass of an inorganic filler is stretched 1.8 to 3.5 times in the longitudinal direction, and then heat-fixed at a temperature exceeding 95°C and not exceeding 120°C for at least 0.2 seconds while maintaining the shrinkage rate in the longitudinal direction at 3 to 20%. A method for producing the above-mentioned stretched porous film, characterized by this.

Advantages of the Invention

[0010] [ According to one embodiment of the present invention, a stretched porous film excellent in air permeability, texture, and printability can be obtained.

Mode for Carrying Out the Invention

[0011] One embodiment of the present invention will be described below, but the present invention is not limited thereto. [

[0012] [ <00​​​​​​​​​​​​

[0013] The stretched porous film may consist of a resin composition containing a polyethylene resin and an inorganic filler, or, for example, a sheet of another material may be laminated in addition to the resin composition.

[0014] <1-1. Polyethylene resins> The polyethylene resin used in this invention has a density of 0.931 to 0.940 g / cm³. 3 Linear low-density polyethylene 20-70% by mass, density 0.901-0.940 g / cm³ 3 It can be used without particular limitations as long as it contains 8-20% by mass of branched low-density polyethylene and other resins.

[0015] The aforementioned density is 0.931 to 0.940 g / cm³. 3 The linear low-density polyethylene (hereinafter sometimes referred to as first LLDPE) is a copolymer of ethylene and a small amount of α-olefin, and has a linear polyethylene main chain and short-chain branches with about 2 to 6 carbon atoms. The first LLDPE has a density of 0.931 g / cm³ 3 More than 0.940g / cm 3 The following, and more preferably 0.932 g / cm³ 3 More than 0.938g / cm 3 The following is the case. It is presumed that by having a density within the above range, the crystallinity of the polyethylene resin is increased and molecular movement is suppressed, making it possible to suppress the thermal shrinkage rate of the stretched porous film. In addition, it becomes easier to obtain a stretched porous film with excellent breathability and liquid leakage resistance. The melt index (MI) of the first LLDPE is preferably 1.0 to 5.0 g / 10 min, and particularly preferably 1.5 to 5.0 g / 10 min. By having a melt index within the above range, it becomes easy to obtain a stretched porous film with low thermal shrinkage rate and excellent breathability and liquid leakage resistance.

[0016] The content of the first LLDPE is 20 to 70% by mass relative to the polyethylene resin, and more preferably 28 to 65% by mass. By setting the content of the first LLDPE to 20% by mass or more, it is possible to suppress the thermal shrinkage rate and increase the rigidity and flexibility of the stretched porous film, thereby suppressing elongation during film processing and improving handling. If the content of the first LLDPE exceeds 70% by mass, the texture may deteriorate.

[0017] The aforementioned density is 0.901 to 0.940 g / cm³. 3 Branched low-density polyethylene (hereinafter sometimes referred to as LDPE) is generally also called high-pressure low-density polyethylene (HP-LDPE) and has a main chain of polyethylene with long-chain branching. LDPE can usually be synthesized by polymerizing ethylene under high pressure in the presence of a radical polymerization catalyst. The density of the LDPE is preferably 0.910 to 0.940 g / cm³. 3 , more preferably 0.915~0.930 g / cm³ 3 The density being within the above range makes it easier to obtain good extrusion characteristics and moldability of the film, and to provide the mechanical strength required for a stretched porous film. The LDPE preferably has a melt index of 1.0 to 5.0 g / 10 min, and in particular, 2.0 to 4.5 g / 10 min. The melt index being within the above range makes it easier to obtain good extrusion characteristics, moldability, and mechanical strength.

[0018] The LDPE content is 8 to 20% by mass relative to the polyethylene resin, and preferably 10 to 19% by mass. The LDPE content affects the uniformity of the thickness of the resulting stretched porous film. If the LDPE content is higher than the above range, the frequency of pinholes in the film tends to increase, while if it is low, the uniformity of the film's thickness deteriorates, and draw resonance tends to occur more easily in the film.

[0019] The polyethylene resin used in the resin composition of the present invention may contain other resins besides the first LLDPE and the LDPE, to the extent that they do not impair the effects of the present invention. The other resin may be other polyethylenes, for example, with a density of 0.901 to 0.930 g / cm³. 3 Linear low-density polyethylene (hereinafter sometimes referred to as second LLDPE) is an example. Including second LLDPE makes it easier to improve the tear strength of the film. The amount of second LLDPE added is preferably 22 to 67% by mass, and more preferably 28 to 60% by mass, relative to the polyethylene resin.

[0020] In addition, other resins have a density of 0.941 to 0.975 g / cm³. 3 High-density polyethylene (HDPE) can also be mentioned. The HDPE content is preferably 22 to 67% by mass relative to the polyethylene resin, and more preferably 23 to 55% by mass. By blending HDPE within the above range, it becomes easier to suppress changes in the film's dimensions.

[0021] Furthermore, with respect to the first LLDPE, second LLDPE, LDPE, and HDPE 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 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 the global environment, 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 petroleum-derived polyethylene and plant-derived polyethylene, and they can be blended in any ratio considering costs and other factors.

[0022] Furthermore, the polyethylene used in the present invention may be a resin produced using a multi-site catalyst such as a Ziegler catalyst, or a resin produced using a single-site catalyst such as a metallocene catalyst.

[0023] The polyethylene resin used in the resin composition of the present invention may contain resins other than the first LLDPE, second LLDPE, LDPE, and HDPE (for example, ultra-low density polyethylene, polypropylene, ethylene-butene copolymer, etc.) as long as they do not impair the effects of the present invention, but the density must be 0.900 g / cm³. 3 The following resins have low crystallinity, and incorporating them tends to increase the thermal shrinkage rate of the film. Furthermore, performing thermal fixation under specific conditions described later to suppress thermal shrinkage can easily have adverse effects on the film. Therefore, a density of 0.900 g / cm³ is used. 3 The blending ratio of the following resins must be controlled to 0.5% by mass or less relative to the polyethylene resin, and it is preferable that they are not blended at all.

[0024] The density of the resin in this invention was measured according to the JIS K 7112 method. Furthermore, the melt index of the resin in this invention was measured at 190°C using Method A in accordance with JIS K 7210.

[0025] <1-2. Inorganic Fillers> Inorganic fillers are added to make the film porous. By stretching a resin composition containing inorganic fillers, the film can be made porous, thereby increasing its moisture permeability.

[0026] Any known inorganic fillers can be used without limit, including, for example, inorganic salts such as calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, and aluminum hydroxide; inorganic oxides such as zinc oxide, magnesium oxide, and silica; silicates such as mica, vermiculite, and talc; and organometallic salts. Of the inorganic fillers, calcium carbonate is preferred from the viewpoint of cost performance and dissociability with polyethylene resins.

[0027] In the resin composition, the blending ratio of the inorganic filler is preferably 80 parts by mass or more and 200 parts by mass or less, and more preferably 85 parts by mass or more and 160 parts by mass or less, per 100 parts by mass of the total polyethylene resin. If the blending ratio of the inorganic filler is 80 parts by mass or more, the frequency of void generation per unit area, which is formed by the separation of the polyethylene resin and the inorganic filler, can be increased. As a result, adjacent voids are more likely to communicate with each other, and the air permeability is improved. If the blending ratio of the inorganic filler is 200 parts by mass or less, the elongation during film stretching is good and stretching is easy.

[0028] The average particle size of the inorganic filler, as measured by laser diffraction scattering, is preferably 10 μm or less, more preferably 0.5 to 5.0 μm, and even more preferably 0.7 to 3.0 μm. When the average particle size is within the above range, it exhibits excellent dispersibility, facilitates the formation of interconnected pores during stretching, and reduces the likelihood of film tearing during molding, enabling the efficient production of stretched porous films. If the average particle size of the inorganic filler is larger than the above range, it is likely to cause pinholes, and if it is smaller, it is likely to cause draw resonance during film formation.

[0029] The inorganic filler described above is preferably one that has been surface-treated to improve its dispersibility in polyethylene resins. The surface treatment agent is preferably one that can hydrophobicize the surface of the inorganic filler by coating it, and examples include fatty acids, higher fatty acids, or metal salts thereof, as well as waxes. The amount of the surface treatment agent is not particularly limited, but is preferably about 0.5 to 2.0% by mass relative to the inorganic filler, more preferably 1.5% by mass or less, and particularly preferably 1.0% by mass or less.

[0030] <1-3. Other ingredients> The resin composition of the present invention may further contain additives commonly used in resin compositions. Examples of such additives include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizing agents, lubricants, antifogging agents, antiblocking agents, antistatic agents, slip agents, colorants, and plasticizers.

[0031] The plasticizer incorporated into the resin composition of the present invention is preferably less than 2 parts by mass, and more preferably less than 1 part by mass, per 100 parts by mass of polyethylene resin. In the present invention, "plasticizer" is a general term for compounds that improve the plasticity of a film and give the film flexibility. If the plasticizer content is high, the melt index of the resin composition will increase, making it difficult to obtain a low thermal shrinkage rate and high moisture permeability. The type of plasticizer is not particularly limited, but examples include fatty acids, higher fatty acids, low molecular weight polyethylene, epoxidized soybean oil, polyethylene glycol, fatty acid esters, etc.

[0032] <1-4. Physical properties of stretched porous films> The melt index of the resin composition of the present invention is preferably 1.0 g / 10 min or higher, more preferably 1.5 g / 10 min or higher and 5.0 g / 10 min or lower, and even more preferably 1.5 g / 10 min or higher and 4.0 g / 10 min or lower. If the melt index is within the above range, more stable film formation is possible. If the melt index is 1.0 g / 10 min or higher, the resin pressure of the extruder during film formation can be suppressed, preventing adverse effects on film formation. Furthermore, if the melt index is 5.0 g / 10 min or lower, neck-in during film formation with a T-die can be further suppressed. Therefore, the required product width can be easily obtained. Note that the smaller the melt index, the greater the 5% tensile strength tends to be. The melt index of the resin composition is measured by Method A at 190°C in accordance with JIS K 7210.

[0033] The stretched porous film of the present invention has a moisture permeability of 2000 g / m². 2 • 24 hours or more, 2200g / m² 2It is preferable that the moisture permeability is 24 hours or more. Having the moisture permeability within the above range results in excellent breathability and moisture permeability. For example, when a stretched porous film is used as the backsheet of a disposable diaper, it can prevent stuffiness during wear. While there is no particular upper limit to the moisture permeability, from the viewpoint of mechanical properties, water resistance, and leakage resistance, 10,000 g / m² is preferable. 2 Preferably 24 hours or less, and 5000 g / m² 2 It is more preferable that it be 24 hours or less.

[0034] The moisture permeability is measured according to ASTM E96, under the conditions of 40°C, 60% relative humidity, a measurement time of 24 hours, and the pure water method. In this specification, the moisture permeability is the average value of 10 10cm × 10cm samples taken from the stretched porous film.

[0035] The air permeability of the stretched porous film of the present invention is preferably 200 seconds / 100mL or more and 2000 seconds / 100mL or less, more preferably 300 seconds / 100mL or more and 1600 seconds / mL or less, and even more preferably 300 seconds / 100mL or more and 1100 seconds / mL or less. A smaller value for air permeability indicates that gas passes through more easily. If the air permeability is within the above range, when the stretched porous film is used as a backsheet for disposable diapers, stuffiness during wear can be prevented. The air permeability is measured using the Ogane testing machine method in accordance with JIS P 8117.

[0036] It is important that the stretched porous film of the present invention has a longitudinal thermal shrinkage rate of 1.2% or less. By setting the longitudinal thermal shrinkage rate to 1.2% or less, shrinkage (tightening) of the film during printing is less likely to occur, sufficient stability of the print pitch can be obtained, and printability is improved. It is more preferable that the longitudinal thermal shrinkage rate of the stretched porous film of the present invention is 1.0% or less.

[0037] The longitudinal thermal shrinkage rate is measured by the following method: A 15cm x 15cm sample is taken from the stretched porous film. Mark the sample so that the distance between the markings is 10cm in the longitudinal direction. Leave the sample at 50°C for 24 hours, then cool it to room temperature and measure the length between the markings. The longitudinal thermal shrinkage rate can be calculated using the following formula I. Equation I: Thermal shrinkage rate in the vertical direction (%) = {(10cm - length between markings after cooling (cm)) / 10cm} × 100

[0038] The basis weight (weight per unit area) of the stretched porous film of the present invention is 10 g / m². 2 More than 25g / m 2 Preferably, it is 11 g / m 2 More than 22g / m 2 More preferably, the following is true: 12 g / m 2 More than 20g / m 2 The following is even more preferable: A basis weight within the above range makes it easier to obtain a stretched porous film with excellent breathability, moisture permeability, and mechanical strength. A basis weight of 10 g / m² is preferable. 2 If the above is achieved, it becomes easier to increase the mechanical strength of the film. Also, if the basis weight is 25g / m² 2 The following conditions make it easy to achieve high breathability.

[0039] [2. Method for manufacturing stretched porous film] The stretched porous film of the present invention is not limited by its manufacturing method, but has a density of 0.931 to 0.940 g / cm³. 3 Linear low-density polyethylene 20-70% by mass, density 0.901-0.940 g / cm³ 3 It contains 8-20% by mass of branched low-density polyethylene and other resins, with a density of 0.900 g / cm³. 3The stretched porous film can be easily manufactured by a method for producing stretched porous films, characterized by molding a film from a resin composition containing 100 parts by mass of polyethylene resin and 80 to 200 parts by mass of an inorganic filler, wherein the resin composition contains 0.5% by mass or less of the following resin, stretching the film 1.8 to 3.5 times in the longitudinal direction, and then heat-setting it for at least 0.2 seconds in a temperature range of 95°C to 120°C while maintaining a longitudinal shrinkage rate of 3 to 20%. The manufacturing method will be described in detail below.

[0040] The aforementioned resin composition can be obtained by mixing a polyethylene resin, an inorganic filler, and other additives in predetermined proportions. The mixing method is not particularly limited, and known methods can be used. For example, it is preferable to mix for about 5 minutes to 1 hour using a mixer such as a Henschel mixer, a super mixer, or a tumbler mixer. In this case, multiple resins will be mixed as the polyethylene resin, but by making the melt index of each resin approximately the same, stable pelletization will be made easier.

[0041] The resulting mixture can generally be kneaded and pelletized using a kneader such as a high-kneading twin-screw extruder or a tandem-type kneader by methods such as strand cutting, hot cutting, or underwater cutting. Pre-mixing and kneading before pelletizing is preferable because it promotes uniform dispersion of the resin composition. Depending on the formulation of the resin composition, it may also be possible to directly feed the mixture into the kneader without performing the above mixing operation and then form a film.

[0042] The pellets obtained as described above are formed into a film using an extruder. It is preferable to form the film using a circular die or T-die attached to the tip of the extruder.

[0043] The film obtained by the molding process can be made porous by stretching it at least in the longitudinal direction. By stretching the film obtained by the molding process, the interface between the polyethylene resin and the inorganic filler is separated. This creates minute voids at the separated interface, and these voids form interconnected holes that penetrate in the thickness direction of the film, resulting in a stretched porous film. Stretching can be carried out by known methods such as roll stretching or tenter stretching.

[0044] The longitudinal stretching ratio is 1.8 times or more, preferably 2.0 times or more. If the stretching ratio is too high, the tear strength will be low and it will be impractical. The upper limit is 3.5 times, preferably 3.3 times. Furthermore, the stretching may be uniaxial stretching or biaxial stretching. The stretching may be single-stage stretching or multi-stage stretching.

[0045] The stretching temperature is preferably in the range of room temperature or higher, but below the softening point of the resin composition. If the stretching temperature is above room temperature, uneven stretching is less likely to occur, making it easier to achieve a uniform thickness. Also, if the stretching temperature is below the softening point, it is possible to prevent the film from melting. Therefore, it is possible to prevent the pores of the film from collapsing and the air permeability and moisture permeability from decreasing. The stretching temperature can be appropriately adjusted depending on the physical properties of the resin composition used and the stretching ratio.

[0046] The most distinctive feature of this manufacturing method is that the film obtained by stretching the resin composition is heat-set under specific conditions. Heat-setting is a heat treatment performed on the stretched film while maintaining the tension caused by stretching, in an environment that does not change its dimensions. By heat-setting the resin composition under specific conditions, specifically by heat-setting at a higher temperature than conventional methods, it is possible to achieve lower thermal shrinkage than was previously possible. Furthermore, heat-setting can suppress elastic recovery and coiling during storage.

[0047] The heat-setting temperature is preferably between 95°C and 120°C, and more preferably between 100°C and 115°C. A heat-setting temperature above 95°C ensures sufficient heat-setting and reduces thermal shrinkage of the stretched porous film. A heat-setting temperature of 120°C or lower prevents the pores of the stretched porous film from collapsing due to heat, thereby achieving high breathability and moisture permeability.

[0048] The heat setting time is 0.2 seconds or longer, more preferably 0.5 seconds or longer, and even more preferably 1.0 second or longer. By setting the heat setting time to 0.2 seconds or longer, sufficient heat setting is achieved, making it possible to reduce the thermal shrinkage of the stretched porous film. Furthermore, there is no particular upper limit to the heat setting time, but it is preferably 20 seconds or less, and more preferably 15 seconds or less. By setting the heat setting time to 20 seconds or less, it is possible to prevent the pores from collapsing due to the melting of the stretched porous film, making it easy to obtain high breathability and moisture permeability.

[0049] When using the roll stretching method, one heat-setting method is to heat the stretched film with a heated roll (annealing roll). When using the tenter stretching method, one heat-setting method is to heat the stretched film near the tenter exit.

[0050] The heat-setting time is the time during which the stretched porous film is held at the heat-setting temperature. For example, when using the roll stretching method, it refers to the time the film is in contact with the annealing roll. There is no particular limit to the number of annealing rolls, but if there are two or more, the heat-setting time is the sum of the time the stretched porous film is in contact with each annealing roll. When using the tenter stretching method, the heat-setting time indicates the time the film is heated and maintained at the heat-setting temperature at the tenter exit. If the heat-setting is divided into multiple heating stages, it is the sum of the heating times for each stage.

[0051] The longitudinal shrinkage rate during heat setting is 3-20%, preferably 5-18%, and more preferably 10-15%. The shrinkage rate during heat setting refers to the percentage decrease in the speed of the nip roll at the heat setting location compared to the speed of the nip roll immediately preceding it. For example, a shrinkage rate of 10% during heat setting means that the speed of the nip roll at the heat setting location is 10% slower than the speed of the nip roll immediately preceding it (i.e., 90% of the speed of the nip roll immediately preceding it).

[0052] [3. Applications of stretched porous films] The applications of the stretched porous film of the present invention are not particularly limited and can be used for sanitary materials such as disposable diapers and sanitary napkins, functional packaging materials such as desiccants and disposable hand warmers, simple clothing such as disposable gloves and raincoats, waterproof building materials such as house wrap, agricultural applications such as mulching sheets, and waste treatment applications such as compost covering sheets. However, due to its excellent breathability, texture, and printability, it is preferably used as a sanitary material, especially as a back sheet for disposable diapers and sanitary napkins. [Examples]

[0053] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0054] [Evaluation Method] Each physical property was measured using the method described below.

[0055] (1) Melt Index The resin melt index was measured according to JIS K 7210, using Method A with a measurement temperature of 190°C and a load of 2.16 kg.

[0056] (2) Inspection A 10cm x 10cm sample was cut from a stretched porous film, and its mass was measured using a balance. The basis weight was determined from the area and mass of this sample.

[0057] (3) Moisture permeability Ten 10cm x 10cm samples were taken from a stretched porous film. The water vapor permeability of these samples was measured according to ASTM E96, under conditions of 40°C, 60% relative humidity, 24 hours of measurement, and the pure water method. The average value was then calculated.

[0058] (4) Air permeability Air permeability was measured using the Wang-Gan testing machine method in accordance with JIS P 8117.

[0059] (5) Thermal contraction ratio in the vertical direction A 15cm x 15cm sample was taken from a stretched porous film. Marks were made on the sample so that the distance between the markings was 10cm in the longitudinal direction. The sample was left at 50°C for 24 hours, then cooled to room temperature and the distance between the markings was measured. The longitudinal thermal shrinkage coefficient was calculated using the following formula (Equation I). Equation I: Thermal shrinkage rate in the vertical direction (%) = {(10cm - length between markings after cooling (cm)) / 10cm} × 100

[0060] [Ingredients used] A: Petroleum-derived linear low-density polyethylene [manufactured by Dow Chemical Co., Ltd., product name: Dowlex 2036P, density: 0.935 g / cm³] 3 MI: 2.5g / 10 minutes] B: Petroleum-derived linear low-density polyethylene [manufactured by Dow Chemical Co., Ltd., product name: CEFOR] TM 1221P, density: 0.918g / cm 3 , MI:2.0g / 10min] C: Plant-derived linear low-density polyethylene [Manufactured by Braschem, product name: SLL118, density: 0.918 g / cm³] 3 , MI:1.0g / 10min] D: Plant-derived linear low-density polyethylene [Blaschem Corporation, product name: SLH218, density: 0.916 g / cm³] 3 , MI:2.3g / 10min] E: Plant-derived high-density polyethylene [Manufactured by Braschem, product name: SGE7252, density: 0.953 g / cm³] 3 , MI:2.0g / 10min] F: Branched low-density polyethylene [Manufactured by Mitsui DuPont Polychemical Co., Ltd., Product name: Mirason 16P, Density: 0.917 g / cm³] 3 , MI:3.7g / 10min] G: Polypropylene [(Manufactured by Prime Polymer Co., Ltd., Product name F-704NP, Density: 0.900 g / cm³)] 3 , MI:2.8g / 10min] H: Ethylene-1-butene copolymer [Manufactured by Mitsui Chemicals, Inc., Product name: Toughmer A-4085S, Density: 0.885 g / cm³] 3 MI: 3.6g / 10 minutes] I: Calcium carbonate [(Manufactured by Calfine Co., Ltd., Product name: LAC-2000)] J: Barium sulfate [Manufactured by Sakai Chemical Co., Ltd., Product name: Variace B-54] K: Additive [A mixture of 40% by mass of hindered phenol-based heat stabilizer (manufactured by BASF Japan Ltd., product name: IRGANOX3114) and 60% by mass of phosphorus-based heat stabilizer (manufactured by BASF Japan Ltd., product name: IRGAFOS168)]

[0061] [Example 1] 54 parts by mass of polyethylene A, 30 parts by mass of polyethylene C, 16 parts by mass of polyethylene F, 147 parts by mass of inorganic filler I, and 2 parts by mass of additive K were mixed and granulated. Granulation (pellet production) was carried out as follows: Using a 30mm diameter twin-screw extruder with a vent, the resin composition was extruded in strand form at a cylinder temperature of 180°C and cooled in a water bath. After that, the extruded resin composition was cut into pieces of approximately 5 mm and dried to produce pellets. Next, the pellets were used to form a film using an inflation film deposition machine (φ150mm die). Film formation was performed under the following conditions: lip clearance = 1.1 mm, die temperature = 170°C, blow-up ratio = 2.1, and take-up speed = 12 m / min. Furthermore, the film was stretched 3.0 times in the longitudinal direction using a roll stretching machine set to 60°C. Then, it was heat-set using a heat-setting roll set to 110°C (heat-setting temperature 110°C, heat-setting time 2.5 seconds). The longitudinal shrinkage rate during heat-setting was 12%.

[0062] [Examples 2-13 and Comparative Examples 1-8] In Examples 2-13 and Comparative Examples 1-8, films were formed in the same manner as in Example 1, except that the mixing ratio of each component or the stretching conditions (stretching ratio or heat-fixing temperature) were changed as shown in Table 1.

[0063] [Table 1]

[0064] In Table 1, "Polyethylene Resin: Blending Ratio (mass%)" represents the blending ratio of each resin relative to 100% by mass of polyethylene resin in the resin composition. The blending ratios of calcium carbonate or barium sulfate and additives are listed as the blending ratio relative to 100 parts by mass of polyethylene resin.

[0065] Furthermore, in Table 1, stretching condition *1 represents a stretching ratio of 3.0 and a heat-fixing temperature of 110°C. Stretching condition *2 represents a stretching ratio of 2.0 and a heat-fixing temperature of 110°C. Stretching condition *3 represents a stretching ratio of 3.0 and a heat-fixing temperature of 100°C. Stretching condition *4 represents a stretching ratio of 3.0 and a heat-fixing temperature of 55°C.

[0066] 〔result〕 The basis weight, moisture permeability, air permeability, and thermal shrinkage rate of the stretched porous films obtained in Examples 1-13 and Comparative Examples 1-8 were measured and are shown in Table 2.

[0067] [Table 2]

[0068] The stretched porous films in Examples 1-13 all had a density of 2000 g / m². 2 The films exhibited excellent moisture permeability for over 24 hours and possessed a good texture. Furthermore, the stretched porous films of Examples 1 to 13 maintained low thermal shrinkage rates, and none of them resulted in printing defects caused by variations in print pitch.

[0069] In Comparative Examples 1 and 6, the densities were 0.931 to 0.940 g / cm³. 3 Linear low-density polyethylene was not used. As a result, the thermal shrinkage rate was high, resulting in a stretched porous film with poor print pitch accuracy, and printing defects caused by fluctuations in the print pitch occurred.

[0070] In comparative examples 2 and 8, the densities were 0.901 to 0.940 g / cm³. 3 Because branched low-density polyethylene was not used, the uniformity of the thickness deteriorated, the appearance of the film was impaired, and the stretched porous film became impractical. In addition, the density was 0.931~0.940 g / cm³. 3 Comparative Example 8, which incorporated more than 70% by mass of linear low-density polyethylene, had a poor texture and was therefore impractical in this respect as well.

[0071] In comparative examples 3 and 4, the density was 0.900 g / cm³. 3 The following polypropylenes were blended into polyethylene resin at a concentration exceeding 0.5% by mass. As a result, the thermal shrinkage rate increased, resulting in a stretched porous film with poor print pitch accuracy, and printing defects caused by fluctuations in the print pitch occurred.

[0072] In Comparative Example 5, the density was 0.900 g / cm³. 3 The following ethylene-1-butene copolymer was blended into a polyethylene resin in an amount exceeding 0.5% by mass. As a result, it was not possible to set the heat-fixing temperature above 95°C, resulting in a stretched porous film with a very high thermal shrinkage rate and poor print pitch accuracy, leading to printing defects caused by fluctuations in the print pitch.

[0073] In Comparative Example 7, the same resin composition as in Example 10 was used, and a film was manufactured under the condition that the heat-fixing temperature was 55°C. As a result, a stretched porous film with a very large thermal shrinkage rate and poor print pitch accuracy was obtained, resulting in printing defects caused by fluctuations in the print pitch.

Claims

1. Density 0.931-0.940g / cm ３ Linear low-density polyethylene 20-70% by mass, density 0.901-0.940 g / cm³ ３ It contains 8 to 20% by mass of branched low-density polyethylene and other resins, wherein the other resins are linear low-density polyethylene with a density of 0.901 to 0.930 g / cm³ or high-density polyethylene with a density of 0.941 to 0.975 g / cm³, and the density is 0.900 g / cm³. ３ The resin composition comprises 100 parts by mass of polyethylene resin, in which the following resin is present in an amount of 0.5% by mass or less, and 80 to 200 parts by mass of inorganic filler, with a longitudinal thermal shrinkage rate of 1.2% or less and a moisture permeability of 2000 g / m². ２ A stretched porous film characterized by having a hardness of 24 hours or more.

2. The polyethylene resin is the other resin with a density of 0.901 to 0.930 g / cm³. ３ The stretched porous film according to claim 1, comprising 22 to 67% by mass of linear low-density polyethylene.

3. The polyethylene resin is, as the other resin, with a density of 0.941 to 0.975 g / cm³. ３ The stretched porous film according to claim 1, comprising 22 to 67% by mass of high-density polyethylene.

4. The stretched porous film according to any one of claims 1 to 3, wherein the inorganic filler is calcium carbonate.

5. A linear low-density polyethylene having a density of 0.931 to 0.940 g / cm ３ in an amount of 20 to 70% by mass, a branched low-density polyethylene having a density of 0.901 to 0.940 g / cm ３ in an amount of 8 to 20% by mass, and other resins, wherein the other resins are a linear low-density polyethylene having a density of 0.901 to 0.930 g / cm³ or a high-density polyethylene having a density of 0.941 to 0.975 g / cm³, and resins having a density of 0.900 g / cm ３ or less are 0.5% by mass or less, a film formed from 100 parts by mass of a polyethylene-based resin and 80 to 200 parts by mass of an inorganic filler is stretched 1.8 to 3.5 times in the longitudinal direction, and then heat-fixed at a temperature range exceeding 95°C and not exceeding 120°C for at least 0.2 seconds while maintaining the shrinkage rate in the longitudinal direction at 3 to 20%, The method for producing a stretched porous film according to any one of claims 1 to 4, characterized in that

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