JP7788892B2 - Stretchable Film - Google Patents

Description

The present invention relates to a stretch film.

Stretch films are used in a wide range of fields, including hygiene products, sports equipment, and medical products, to improve handling and comfort (fit). For example, they are used in garments such as underwear, disposable diaper waistbands, side panels, leg gathers, incontinence products, sanitary napkins, bandages, surgical drapes, tightening bands, hats, swimming trunks, sports supporters, medical supporters, and adhesive bandages.

For example, one proposed stretch film is one that contains a polymer component containing a propylene-based elastomer and a filler, and is manufactured by stretching an unstretched film. It is described that this type of structure can provide a stretch film with excellent stretchability and breathability (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2016-204625

However, in the stretch film described in Patent Document 1, the stretching process is carried out at a temperature higher than the actual use temperature (e.g., 60°C) in order to ensure breathability. This prevents the elastomer from returning to its original state, maintaining the open pores and resulting in poor stretchability.

Furthermore, the stretching process in Patent Document 1 involves stretching the stretch film in the machine axis (longitudinal) direction (hereinafter also referred to as "MD"), so when raw film obtained by extrusion molding is used, the film is oriented in the MD to some extent and cannot be stretched until sufficient breathability is achieved. Therefore, transverse stretching in the direction perpendicular to the machine axis (hereinafter also referred to as "TD") is necessary, but transverse stretching using commonly used methods such as tentering or inflation molding requires large equipment, posing a problem of increased manufacturing costs, particularly for disposable products such as disposable diapers.

The present invention was conceived in consideration of the above problems, and aims to provide a stretch film that can reduce manufacturing costs while also achieving excellent stretchability and breathability.

To achieve the above objective, the stretch film of the present invention is a stretch film containing a thermoplastic elastomer, a polyethylene resin, and an inorganic filler, and has an air permeability of 500 s/100 cc or more and 10,000 s/100 cc or less as measured using an Oken air permeability tester, a permanent set in at least one direction of 30% or less, and has alternating band-shaped first regions with surface destruction extending along the mechanical axis of the stretch film and band-shaped second regions adjacent to the first regions and extending along the mechanical axis which are less stretchable than the first regions, and is characterized in that the average elongation ratio of the first regions is 1.8 times or more and 3.0 times or less, and the average elongation ratio of the second regions is 1.0 times or more and 1.8 times or less.

(Permanent deformation of stretch film)
A strip-shaped test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to the one direction was cut from the stretch film, and this test piece was fixed to the gripping tools of the testing machine so that the distance between the gripping tools was 25 mm. The test piece was stretched in the longitudinal direction of the test piece at a speed of 254 mm/min so that the elongation (elongation ratio) calculated by the following formula (1) was 100%, and then the test piece was immediately contracted at the same speed, and the permanent set [%] was calculated using the following formula (2).

Elongation [%] = (L1 - L0) / L0 x 100 (1)

Permanent set [%] = (L2 - L0) / L0 x 100 (2)

where L0 is the distance between the grips (mm) before extension, L1 is the distance between the grips (mm) after extension, and L2 is the distance between the grips (mm) when the load on the test piece (N/25 mm) becomes 0 when contracted.

(Average extension ratio)
A strip-shaped test piece measuring 50 mm in the mechanical axis direction of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction is cut from the stretch film. The test piece is fixed to the grips of the testing device so that the distance between the grips is 30 mm. The test piece is stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a speed of 100 mm/min so that the elongation calculated by the following formula (3) is 100%. The elongation ratio (times) is calculated using the following formula (4). The elongation ratios are calculated at five randomly selected locations in both the first and second regions, and the average is calculated.

Elongation [%] = (L1 - L0) / L0 x 100 (3)

Stretch ratio [times] = R1/R0 (4)

where L0 is the distance between the grippers (mm) before stretching, L1 is the distance between the grippers (mm) after stretching, R0 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction before stretching, and R1 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction after stretching (however, R0 and R1 are measured at the same location in the same region).

Another stretch film of the present invention is a stretch film comprising an elastomer layer containing a thermoplastic elastomer, a polyethylene resin, and an inorganic filler, and a surface layer laminated on at least one side of the elastomer layer, characterized in that the film has an air permeability of 500 s/100 cc or more and 10,000 s/100 cc or less as measured using an Oken air permeability tester, a permanent set in at least one direction of 30% or less, and alternates between first band-shaped regions with surface destruction extending along the mechanical axis of the stretch film and second band-shaped regions adjacent to the first regions and extending along the mechanical axis that are less stretchable than the first regions, the first regions having an average elongation ratio of 1.8 times or more and 3.0 times or less, and the second regions having an average elongation ratio of 1.0 times or more and 1.8 times or less.

(Permanent deformation of stretch film)
A strip-shaped test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to the one direction was cut from the stretch film, and this test piece was fixed to the gripping tools of the testing machine so that the distance between the gripping tools was 25 mm. The test piece was stretched in the longitudinal direction of the test piece at a speed of 254 mm/min so that the elongation (elongation ratio) calculated by the following formula (1) was 100%, and then the test piece was immediately contracted at the same speed, and the permanent set [%] was calculated using the following formula (2).

Elongation [%] = (L1 - L0) / L0 x 100 (1)

Permanent set [%] = (L2 - L0) / L0 x 100 (2)

where L0 is the distance between the grips (mm) before extension, L1 is the distance between the grips (mm) after extension, and L2 is the distance between the grips (mm) when the load on the test piece (N/25 mm) becomes 0 when contracted.

(Average extension ratio)
A strip-shaped test piece measuring 50 mm in the mechanical axis direction of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction is cut from the stretch film. The test piece is fixed to the grips of the testing device so that the distance between the grips is 30 mm. The test piece is stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a speed of 100 mm/min so that the elongation calculated by the following formula (3) is 100%. The elongation ratio (times) is calculated using the following formula (4). The elongation ratios are calculated at five randomly selected locations in both the first and second regions, and the average is calculated.

Elongation [%] = (L1 - L0) / L0 x 100 (3)

Stretch ratio [times] = R1/R0 (4)

where L0 is the distance between the grippers (mm) before stretching, L1 is the distance between the grippers (mm) after stretching, R0 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction before stretching, and R1 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction after stretching (however, R0 and R1 are measured at the same location in the same region).

The present invention makes it possible to provide a stretch film that can reduce manufacturing costs while also achieving excellent stretchability and breathability.

1 is a plan view illustrating a stretch film according to a first embodiment of the present invention. FIG. FIG. 2 is an enlarged view showing an example of a pair of shaping rolls. FIG. 4 is a cross-sectional view illustrating a stretch film according to a second embodiment of the present invention. FIG. 10 is a plan view illustrating a stretch film according to a second embodiment of the present invention.

The stretch film of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and can be modified and applied as appropriate within the scope of the present invention.

(First embodiment)
The stretch film of this embodiment is a film-like molded article containing a thermoplastic elastomer, low-density polyethylene, and an inorganic filler, and has alternating strip-shaped first regions extending along the mechanical axis (longitudinal direction) of the stretch film (i.e., MD) and strip-shaped second regions extending along the MD adjacent to the first regions and less stretchable than the first regions, and has a plurality of through holes formed therein.

<Thermoplastic elastomer>
"Thermoplastic elastomer" means a polymer or polymer blend that has properties similar to those of vulcanized rubber at use temperatures, loses these properties at processing temperatures, is easily processed, and regains its original properties when returned to use temperatures.

Examples of thermoplastic elastomers include olefin-based elastomers, styrene-based elastomers, urethane-based elastomers, and polyester-based elastomers.

For example, the olefin-based elastomer used in the present invention may be a copolymer or homopolymer whose main component is an olefin having 3 or more carbon atoms, or a copolymer whose main component is ethylene and an olefin having 3 or more carbon atoms.

More specifically, examples include: (1) α-olefin homopolymers such as propylene homopolymers and 1-butene homopolymers with low stereoregularity; (2) α-olefin copolymers such as propylene-ethylene copolymers, propylene-ethylene-1-butene copolymers, 1-butene-ethylene copolymers, 1-butene-propylene copolymers, 4-methylpentene-1-propylene copolymers, 4-methylpentene-1-1-butene copolymers, 4-methylpentene-1-propylene-1-butene copolymers, propylene-1-butene copolymers, ethylene-propylene copolymers, ethylene-hexene copolymers, and ethylene-octene copolymers; and (3) ethylene-α-olefin-diene terpolymers such as ethylene-propylene-ethylidenenorbornene copolymers, ethylene-propylene-butadiene copolymers, and ethylene-propylene-isoprene copolymers. Elastomers in which the above-mentioned elastomers are dispersed in a crystalline polyolefin matrix may also be used. The olefin-based elastomers may be used alone or in combination of two or more.

Thermoplastic elastomers are generally composed of hard segments that govern basic physical properties such as mechanical properties, and soft segments that govern elasticity, a rubber-like property. Olefin-based elastomers whose hard segments consist of polypropylene are called propylene-based elastomers, while those whose hard segments consist of polyethylene are called ethylene-based elastomers. Examples of soft segments in olefin-based elastomers include EPDM, EPM, EBM, IIR, hydrogenated styrene-butadiene rubber (HSBR), NBR, and acrylic rubber (ACM). Examples of hard segments in styrene-based elastomers include polystyrene, and examples of soft segments in styrene-based elastomers include polybutadiene, polyisoprene, polyethylene, or hydrogenated versions of these.

In the case of propylene-based elastomers, the propylene unit content relative to all units is preferably 70% to 95% by mass, and more preferably 80% to 90% by mass. If the propylene unit content of the hard segment is 70% by mass or more, strength is improved, resulting in excellent moldability, while if it is 95% by mass or less, the elasticity of the soft segment results in excellent stretchability.

Furthermore, from the viewpoint of achieving excellent stretchability, the content of thermoplastic elastomer in the entire stretch film is preferably 20% by mass or more and 50% by mass or less, and more preferably 35% by mass or more and 45% by mass or less, out of 100% by mass of the stretch film. If the content of thermoplastic elastomer is within the above range, excellent stretchability can be achieved due to the elasticity of the soft segments contained in the elastomer.

<Polyethylene Resin>
The polyethylene resin is preferably one that is compatible with the thermoplastic elastomer, and examples of the polyethylene resin that can be used include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-low-density polyethylene (ULDPE). One type of polyethylene resin may be used alone, or two or more types may be used in combination.

Furthermore, from the perspective of improving breathability by contributing to the fixation of pores, the content of polyethylene resin in the entire stretch film is preferably 10% by mass or less out of 100% by mass of the stretch film. This is because if the content is greater than 10% by mass, the stretchability of the film may be significantly reduced, as ordinary polyethylene itself is not stretchable.

In order to improve air permeability, it is preferable to use low-density polyethylene as the polyethylene-based resin, and to have the low-density polyethylene content of the entire stretch film be 10% by mass or less.

<Inorganic filler>
The inorganic filler is a component that forms through-holes by making the film porous. By performing a stretching process while the film contains this inorganic filler, the stretchable film of this embodiment can exhibit excellent breathability.

Examples of inorganic fillers include calcium carbonate, zeolite, silica, titanium oxide, calcium oxide, magnesium oxide, zinc oxide, clay, mica, barium sulfate, and magnesium hydroxide. One type of inorganic filler may be used alone, or two or more types may be used in combination.

The inorganic filler content of the entire stretch film is preferably 50% by mass or more and 70% by mass or less, and more preferably 50% by mass or more and 60% by mass or less, based on 100% by mass of the stretch film. If the inorganic filler content is within the above range, the stretching process will promote porosity.

The average particle size of the inorganic filler is preferably 0.8 to 15 μm. If the average particle size of the inorganic filler is 0.8 μm or more, secondary aggregation of the inorganic filler is suppressed, resulting in good dispersibility in the resin. If the average particle size is 15 μm or less, there is no risk of holes due to drawdown during extrusion, resulting in excellent moldability.

Note that "average particle size" here refers to the particle size at 50% of the particle size distribution measured using a particle size distribution analyzer.

<Other ingredients>
The stretch film may contain components other than the thermoplastic elastomers described above, as long as the stretchability of the stretch film is not impaired.

Other ingredients include amide antiblocking agents (such as stearic acid amide), plasticizers, UV absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, lubricants, etc. These other ingredients may also be added to the stretch film material as a masterbatch.

<First Region and Second Region>
Fig. 1 is a plan view showing a stretchable film of the present embodiment. As shown in Fig. 1, the stretchable film 1 of the present embodiment has a first region 2, which is a portion of the surface that is stretch-broken when the film before gear stretching is stretched into stripes by gear stretching, as described below, and a second region 3, which is a portion of the surface that is not stretch-broken when the film before gear stretching is stretched into stripes by gear stretching, as described below.

The surface of the first region 2 is stretch-ruptured, while the surface of the second region 3 is not stretch-ruptured. This makes the second region 3 less likely to stretch than the first region 2, and the first region 2 more likely to stretch than the second region 3.

Note that "the second region is less stretchable than the first region (or the first region is more stretchable than the second region)" means that when the stretch film is stretched in a direction perpendicular to the mechanical axis direction of the first and second regions (i.e., TD), the elongation (%) of the second region is smaller than the elongation (%) of the first region (or the elongation (%) of the first region is greater than the elongation (%) of the second region).

Furthermore, the width of the first region 2 and the width and length of the second region 3 are not particularly limited and may be determined appropriately depending on the intended use of the stretchable film 1. For example, the width _W1 of the first region 2 may be set to 1.5 to 2.5 mm, and the width _W2 of the second region 3 may be set to 0.2 to 0.4 mm.

<Through hole>
1, the stretchable film 1 of this embodiment has a plurality of through holes 4 formed therein. As will be described later, the through holes 4 are formed by performing a stretching process on the raw film before it is made porous.

The stretchable film 1 of this embodiment is configured to be porous by performing a stretching process on the raw film while it contains the inorganic filler 5 described above.

In Figure 1, the through-holes 4 are formed in the first region 2, but they may also be formed in the second region 3. Whether the through-holes 4 are formed in the first region 2 or the second region 3, breakage originating from the through-holes 4 is less likely to occur when the stretch film 1 is stretched.

Furthermore, because the surface of the first region 2 is destroyed, it stretches with low stress. This reduces the stress around the through-hole 4, making it less likely to break when stretched. On the other hand, because the surface of the second region 3 is not destroyed, it is highly rigid and less likely to deform when stretched, making it less likely to break.

When the stretch film 1 is manufactured using the manufacturing method of the present invention described below, most of the through holes 4 will be formed in the first region 2.

The diameter of the through-holes 4 is preferably between 1 μm and 100 μm. If the diameter is 1 μm or more, the holes will not clog even in stretchy materials such as elastomers, providing excellent breathability, while if the diameter is 100 μm or less, waterproofing will be achieved. Note that the diameter of the through-holes 4 is the average value of the opening diameters of 50 randomly selected through-holes 4.

<Method of manufacturing stretch film>
Next, an example of a method for producing the stretch film of this embodiment will be described in detail.

When manufacturing the stretch film of this embodiment, a raw material containing the above-mentioned thermoplastic elastomer, polyethylene resin, and inorganic filler is first formed into a film using an extruder to produce a raw film before it is porous.

More specifically, first, a thermoplastic elastomer, a polyethylene resin, an inorganic filler, and, if necessary, the other components described above are mixed in a predetermined mixing ratio, and the mixture is extruded into strands using a co-rotating twin-screw extruder equipped with a strand die, and then cut to obtain pellets.

Next, the pellets are melt-extruded in a single-screw extruder equipped with a T-die to form a film, and the film is wound up on a take-up roll to obtain the raw film before it is made porous.

Then, the raw film is subjected to uniaxial stretching (gear stretching in the TD), stretching the raw film into stripes and making it porous, resulting in the production of a stretchable film 1 having alternating first regions 2 and second regions 3 and multiple through-holes 4, as shown in Figure 1.

In order to improve breathability, a biaxial stretching process may be performed in both the MD and TD directions. For example, the raw film described above may be roll-stretched in the MD, and then the MD-stretched film may be gear-stretched in the TD.

Gear stretching is performed using a first shaping roll having multiple ridges extending circumferentially or axially, and a second shaping roll having multiple ridges extending in the same direction as the ridges on the first shaping roll, arranged opposite each other so that the ridges on one shaping roll intermesh with the grooves between the ridges on the other shaping roll.

Figure 2 is an enlarged view showing an example of a pair of shaping rolls. A first shaping roll 20 has multiple ridges 24 extending circumferentially on the peripheral surface of a cylindrical roll body 22, and a second shaping roll 30 has multiple ridges 34 extending circumferentially on the peripheral surface of a cylindrical roll body 32. The first shaping roll 20 and the second shaping roll 30 are arranged opposite each other with a predetermined clearance so that the ridges 24 of the first shaping roll 20 intermesh with the grooves 36 between the ridges 34 of the second shaping roll 30, and so that the grooves 26 between the ridges 24 of the first shaping roll 20 intermesh with the ridges 34 of the second shaping roll 30.

Then, while the first shaping roll 20 and the second shaping roll 30 are rotating, the film before the above-mentioned gear stretching (i.e., the original film in the case of uniaxial stretching, or the film after MD stretching in the case of biaxial stretching) is passed between the first shaping roll 20 and the second shaping roll 30, thereby forming a stretched first region 2 and an unstretched second region 3 between the ridges 24 of the first shaping roll 20 and the ridges 34 of the second shaping roll 30.

In addition, with the pair of shaping rolls shown in Figure 2, the film passing between them before gear stretching is pushed downward by the ridges 24 of the first shaping roll 20 and upward by the ridges 34 of the second shaping roll 30. As a result, the film before gear stretching is partially stretched diagonally up and down by the adjacent ridges 24 of the first shaping roll 20 and ridges 34 of the second shaping roll 30, forming the first region 2. At this time, cracks can be generated at the interface between the inorganic filler 5 and the resin in the stretched area, resulting in sufficient breathability.

On the other hand, in the film before gear stretching, the portions that contact the tops of the ridges 24 of the first shaping roll 20 or the tops of the ridges 34 of the second shaping roll 30 are not stretched and therefore become the second region 3.

Because the direction in which the film before gear stretching is partially stretched by the pair of shaping rolls in Figure 2 is TD, gear stretching using the pair of shaping rolls in Figure 2 is also called TD gear stretching. With TD gear stretching, as shown in Figure 1, strip-shaped first regions 2 extending in the MD and strip-shaped second regions 3 extending in the MD are formed alternately in the TD.

Gear stretching is usually performed at room temperature, but not limited to gear stretching. By stretching at room temperature, residual strain that remains during molding can be removed, which has the effect of reducing permanent strain. Furthermore, when performing biaxial stretching, which involves stretching in both the MD and TD directions as described above, the stretching temperature in the MD stretching process is between 20°C and 70°C.

In gear stretching, the stretching ratio can be adjusted by adjusting the width W of the apex of the ridges on the shaping roll, the height H of the ridges, the spacing P between the apexes of adjacent ridges, and the depth D of engagement between the ridges 24 of the first shaping roll 20 and the ridges 34 of the second shaping roll 30.

Furthermore, when uniaxial stretching (gear stretching in the TD) is performed on raw film, the stretching ratio is 4 to 9 times. This is because a stretching ratio of 4 times or more promotes porosity through the stretching process, further improving the moisture permeability of the stretchable film 1, but if it is greater than 9 times, the film may break when stretched. Note that "stretching ratio" here refers to the multiple, in the stretching direction, of the length of the film after stretching relative to the length of the film before stretching.

Furthermore, when performing biaxial stretching in both the MD and TD directions, the stretch ratio for gear stretching in TD can be adjusted to correspond to the stretch ratio in MD, from the perspective of preventing film breakage during gear stretching in TD.

For example, if the MD stretch ratio is 2x, the TD gear stretch ratio can be adjusted to 3-7x, and if the MD stretch ratio is 3-4x, the TD gear stretch ratio can be adjusted to 2-6x.

Furthermore, the stretch ratio in gear stretching can be easily calculated using Pythagoras' theorem based on the principles of stretching. For example, if the distance between the top of the ridge 24 of the first shaping roll 20 and the top of the ridge 34 of the second shaping roll 30 (the width of the stretched portion of the film before gear stretching) is 1 mm and the meshing depth is √3 mm, the width of the stretched portion of the film will be 2 mm, and the stretch ratio will be 2 times. If the permanent set of this film is 30%, the width of the stretched portion will change from 1 mm before stretching to 1.3 mm.

In this way, in this embodiment, the raw film is gear-stretched in the TD using a pair of shaping rolls as shown in Figure 2. This, unlike the conventional technology described above, makes it possible to avoid increasing the size of the equipment and reduce manufacturing costs.

Furthermore, the stretch film of this embodiment manufactured by the above-described method has an air permeability of 500 s/100 cc or more and 10,000 s/100 cc or less as measured using an Oken air permeability tester, making it possible to achieve excellent breathability. The air permeability is preferably 7,500 s/100 cc or less, more preferably 5,000 s/100 cc or less, and even more preferably 2,000 s/100 cc or less.

In addition, the stretch film of this embodiment has a permanent strain of 30% or less in at least one of the MD and TD directions, making it possible to achieve excellent stretchability.

Note that "permanent strain" here refers to the value calculated using the following method.

A rectangular test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to that direction was cut from the stretch film, and this test piece was fixed to the grips of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) with a distance between the grips of 25 mm. The test piece was then stretched in the longitudinal direction at a speed of 254 mm/min until the elongation (elongation ratio) calculated using the following formula (1) reached 100%, and then the test piece was immediately retracted at the same speed. The permanent set [%] was then calculated using the following formula (2).

Elongation [%] = (L1 - L0) / L0 x 100 (1)

Permanent set [%] = (L2 - L0) / L0 x 100 (2)

where L0 is the distance between the grips (mm) before extension, L1 is the distance between the grips (mm) after extension, and L2 is the distance between the grips (mm) when the load on the test piece (N/25 mm) becomes 0 when contracted.

In order to improve stretchability, the permanent strain in the TD where gear stretching is performed is preferably 15% or less, and more preferably 10% or less.

Furthermore, from the perspective of stretching the stretch film with a weak force, it is preferable that the test force (test force at 100% elongation) used when stretching the film in the TD so that the elongation (elongation ratio) calculated by the above formula (1) is 100% is 2 N or less. This test force is more preferably 1.2 N or less, even more preferably 1 N or less, and particularly preferably 0.5 N or less.

Furthermore, in the stretch film 1 of this embodiment produced by the above-mentioned gear stretching, the average elongation ratio of the first region 2 is 1.8 times or more and 3.0 times or less, and the average elongation ratio of the second region 3 is 1.0 times or more and 1.8 times or less, making it possible to obtain excellent stretchability.

Note that the "average elongation ratio" referred to here is calculated using the following method.

A strip-shaped test piece measuring 50 mm in the mechanical axis direction (i.e., MD) of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction (i.e., TD) is cut from the stretch film. The test piece is fixed to the grips of the testing device so that the distance between the grips is 30 mm. The test piece is stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a rate of 100 mm/min so that the elongation calculated using equation (3) below is 100%. The elongation ratio (times) is calculated using equation (4) below. The elongation ratio is calculated at five randomly selected locations in both the first and second regions, and the average is calculated.

Elongation [%] = (L1 - L0) / L0 x 100 (3)

Stretch ratio [times] = R1/R0 (4)

where L0 is the distance between the grippers (mm) before stretching, L1 is the distance between the grippers (mm) after stretching, R0 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction before stretching, and R1 is the length (μm) of the first or second region in the direction perpendicular to the mechanical axis direction after stretching (however, R0 and R1 are measured at the same location in the same region).

If the average elongation ratio of the first region 2 is 1.8 times or more, the first region 2 will elongate preferentially when the stretch film 1 is stretched. This will result in good stretchability for the entire stretch film 1. Furthermore, if the average elongation ratio of the first region 2 is 3.0 times or less, appropriate stretchability will be obtained.

Furthermore, if the average elongation ratio of the second region 3 is 1.0 or more and 1.8 or less, the permanent set will be small, resulting in good stretchability of the entire stretch film.

Furthermore, if the average elongation ratio of the second region 3 is 1.0 to 1.8 times, and the average elongation ratio of the first region 2 is 1.8 times or more, the first region 2, whose surface is damaged, will elongate preferentially when the stretch film 1 is stretched. This reduces the stress around the through-holes, making breakage less likely to occur during stretching. Furthermore, the second region 3, whose surface is not damaged, has high rigidity and undergoes little deformation when the stretch film 1 is stretched, making breakage less likely to occur.

The width of the first region 2 and the width of the second region 3 before stretching are not particularly limited and may be determined appropriately depending on the stretchability, breathability, flexibility, etc. required of the stretch film 1.

The thickness of the raw film before stretching is preferably 10 to 80 μm, and more preferably 20 to 60 μm. If the thickness of the raw film is 10 μm or more, handling properties such as wrinkles during winding and ease of trimming during slitting can be ensured. Furthermore, if the thickness of the raw film is 80 μm or less, the stretch film after stretching can have sufficient breathability.

Furthermore, the thickness of the stretched film after stretching is 40-60% of the original film if stretched at heat, and 85-95% of the original film if stretched at room temperature. In the case of gear stretching, the unstretched portion is the same thickness as the original film, and the stretched portion is 85-95% of the original film.

By using the above method, in this embodiment, it is possible to reduce manufacturing costs and obtain a stretch film that combines excellent stretchability and breathability.

The stretch film may be a single layer, or may be a multi-layer film consisting of two or more layers. If the stretch film is a multi-layer film, the composition and thickness of each layer may be the same or different. When the stretch film is a multi-layer film, the thickness refers to the total thickness of the multi-layer film.

Second Embodiment
Next, a second embodiment of the present invention will be described. Note that components similar to those in the first embodiment are given the same reference numerals and descriptions thereof will be omitted.

Figure 3 is a cross-sectional view showing a stretch film according to a second embodiment of the present invention. As shown in Figure 3, the stretch film 10 of this embodiment comprises an elastomer layer 6 made of a stretch film containing a thermoplastic elastomer, low-density polyethylene, and an inorganic filler, as described in the first embodiment above, and surface layers 7 and 8 laminated on the surface of the elastomer layer 6.

The elastomer layer 6 may also contain other components described in the first embodiment above, as long as the components do not impair the stretchability of the stretch film 10.

<Surface layer>
The surface layers 7 and 8 are layers for suppressing the occurrence of blocking in the stretch film 10. As shown in Figure 3, the surface layers 7 and 8 are provided on either or both of the first and second surfaces of the elastomer layer 6, but from the viewpoint of sufficiently suppressing the occurrence of blocking in the stretch film 10, it is preferable that the surface layers 7 and 8 be provided on both the first and second surfaces of the elastomer layer 6. Note that the surface layers 7 and 8 may be the same type of surface layer or different types of surface layers.

The surface layers 7 and 8 contain a thermoplastic resin (excluding a thermoplastic elastomer) and preferably further contain an inorganic filler. Furthermore, the surface layers 7 and 8 may contain other components as needed, as long as the effects of the present invention are not impaired.

<Thermoplastic resin>
The thermoplastic resin is preferably one that is compatible with the thermoplastic elastomer in the elastomer layer 6, and is, for example, a polyethylene-based resin or a polypropylene-based resin. In addition, from the viewpoint of excellent hot melt properties, a polyethylene-based resin is preferred, and from the viewpoint of excellent heat resistance, a polypropylene-based resin is preferred.

Examples of polyethylene-based resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). Examples of polypropylene-based resins include homopolypropylene (H-PP) obtained by polymerizing propylene alone, random polypropylene (R-PP) obtained by copolymerizing ethylene and propylene, and block polypropylene (B-PP) obtained by polymerizing homopolypropylene and then copolymerizing ethylene and propylene in the presence of the homopolypropylene. Note that one type of thermoplastic resin may be used alone, or two or more types may be used in combination.

In addition, from the viewpoint of achieving excellent stretchability, the content of the thermoplastic resin in the entire surface layer is preferably 30% by mass or more and 60% by mass or less, and more preferably 40% by mass or more and 50% by mass or less, of 100% by mass of the surface layer.

<Inorganic filler>
The inorganic filler is a component that imparts slipperiness to the surfaces of the surface layers 6 and 7, thereby further suppressing the occurrence of blocking in the stretchable film 10. It is also a component that forms the through holes 4 by making the film porous, and by performing a stretching process in a state containing this inorganic filler, the stretchable film of the present embodiment can exhibit excellent breathability.

Examples of inorganic fillers include calcium carbonate, zeolite, silica, titanium oxide, calcium oxide, magnesium oxide, zinc oxide, clay, mica, barium sulfate, and magnesium hydroxide. One type of inorganic filler may be used alone, or two or more types may be used in combination.

The content of inorganic filler in the entire surface layer is preferably 40% by mass or more and 70% by mass or less, and more preferably 50% by mass or more and 60% by mass or less, of the 100% by mass of the surface layer. If the content of inorganic filler is within the above range, porosity is promoted by performing a stretching treatment.

The average particle size of the inorganic filler is preferably 0.8 to 10 μm. If the average particle size of the inorganic filler is 0.8 μm or more, secondary aggregation of the inorganic filler is suppressed, improving dispersibility in the resin, while if it is 10 μm or less, it will feel good to the touch.

<Other ingredients>
Other components include amide antiblocking agents (such as stearic acid amide), plasticizers, ultraviolet absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, lubricants, etc. The other components may be made into a masterbatch and added to the material for the stretch film.

<First and second areas>
Fig. 4 is a plan view showing the stretchable film of this embodiment. As shown in Fig. 4, the stretchable film 10 of this embodiment has first regions 20, which are portions of the surface layers 7, 8 that were stretch-broken when the pre-gear-stretched film was stretched into stripes by the above-mentioned gear stretching, and second regions 30, which are portions of the surface layers 7, 8 that were not stretch-broken when the pre-gear-stretched film was stretched into stripes by the above-mentioned gear stretching.

In the first region 20, although the surface layers 7 and 8 remain, the surface layers 7 and 8 have been stretched and destroyed, so the stretchability is closer to that of the elastomer layer alone.

Furthermore, in the second region 30, the surface layers 7 and 8 are not stretched to failure, meaning that the non-stretchable surface layers 7 and 8 remain on the surface of the elastomer layer, and therefore the stretchability is somewhat insufficient.

Furthermore, the width of the first region 20 and the width and length of the second region 30 are not particularly limited and may be determined appropriately depending on the intended use of the stretch film 10. For example, the width _W3 of the first region 20 may be set to 1.5 to 2.5 mm, and the width _W4 of the second region 30 may be set to 0.2 to 0.4 mm.

<Through hole>
As shown in Figure 4, the stretchable film 10 of this embodiment has a plurality of through holes 4 formed therein. As will be described later, these through holes 4 are formed by stretching the raw film before it is made porous. The stretchable film 10 of this embodiment is configured so that the raw film is made porous by stretching it while it contains the inorganic filler 5 described above.

In Figure 4, the through-holes 4 are formed in the first region 20, but they may also be formed in the second region 30. Whether the through-holes 4 are formed in the first region 20 or the second region 30, breakage originating from the through-holes 4 is less likely to occur when the stretch film 10 is stretched.

Furthermore, since the surface layers 7 and 8 of the first region 20 are destroyed, it stretches with low stress. This reduces the stress around the through-hole 4, making it less likely to break when stretched. On the other hand, since the surface layers 7 and 8 of the second region 30 are not destroyed, it has high rigidity and is less likely to deform when stretched, making it less likely to break.

When the stretchable film 10 is manufactured using the manufacturing method of the present invention described below, most of the through holes 4 will be formed in the first region 20.

Furthermore, as mentioned above, by including an inorganic filler in the surface layers 7 and 8, it is possible to promote porosity during the stretching process. Furthermore, as in the first embodiment described above, the diameter of the through holes 4 is preferably 1 μm to 100 μm.

<Method of manufacturing stretch film>
Next, an example of a method for producing the stretch film of this embodiment will be described in detail.

In the stretch film of this embodiment, similar to the first embodiment described above, a thermoplastic elastomer, a polyethylene resin, an inorganic filler, and, if necessary, the other components described above are first mixed in a predetermined blending ratio, and the mixture is extruded into strands using a co-rotating twin-screw extruder equipped with a strand die or the like and cut to obtain pellets for forming the elastomer layer. Similarly, a thermoplastic resin, and, if necessary, an inorganic filler, and other components are mixed in a predetermined blending ratio, and the mixture is extruded into strands using a co-rotating twin-screw extruder equipped with a strand die or the like and cut to obtain pellets for forming the surface layer.

Next, using an extruder equipped with a T-die, the pellets for forming the elastomer layer and the pellets for forming the surface layer are extruded at a predetermined temperature, and a cast film process is used to obtain a raw film before being porous, which has an elastomer layer, a first surface layer formed on the first side of the elastomer layer, and a second surface layer formed on the second side of the elastomer layer.

Then, the raw film is subjected to uniaxial stretching (gear stretching in the TD) using a pair of shaping rolls as shown in Figure 2 at the same stretching temperature and stretch ratio as in the first embodiment described above, stretching the raw film into stripes and making it porous, resulting in the production of a stretchable film 10 as shown in Figure 4, which has alternating first regions 20 and second regions 30 and has multiple through-holes 4 formed therein.

As with the first embodiment described above, biaxial stretching, in which stretching is performed in both the MD and TD directions, may be performed to improve breathability. For example, the raw film described above may be roll-stretched in the MD, and then the MD-stretched film may be gear-stretched in the TD.

Furthermore, in the stretch film 10 of this embodiment manufactured by the above-described method, as in the first embodiment described above, the air permeability measured using an Oken air permeability tester is 500 s/100 cc or more and 10,000 s/100 cc or less, and the permanent strain in at least one direction is 30% or less, making it possible to obtain a stretch film that combines excellent stretchability and breathability.

Furthermore, in the stretch film 10 of this embodiment manufactured by the gear stretching described above, as in the first embodiment described above, the average elongation ratio of the first region 20 is 1.8 times or more and 3.0 times or less, and the average elongation ratio of the second region 30 is 1.0 times or more and 1.8 times or less, thereby achieving excellent stretchability.

The thickness of the elastomer layer 6 in the raw film is preferably 10 to 80 μm, and more preferably 20 to 60 μm. If the thickness of the elastomer layer 6 is 10 μm or more, the stretchable film 10 after stretching can ensure sufficient MD test force, and can prevent wrinkles and dimensional changes, ensuring ease of handling. If the thickness of the elastomer layer 5 is 80 μm or less, the stretchable film 10 after stretching can achieve sufficient breathability.

The thickness of the surface layers 7, 8 in the raw film is preferably 1 to 6 μm, and more preferably 2 to 4 μm. If the thickness of the surface layers 7, 8 is 1 μm or more, the occurrence of blocking in the stretchable film 10 after stretching can be sufficiently suppressed and the breathability of the stretchable film 10 can be improved. If the thickness of the surface layers 7, 8 is 6 μm or less, the stretchability of the stretchable film 10 can be sufficiently obtained. Note that the surface layers 7, 8 may have the same thickness or different thicknesses.

Furthermore, the thickness of the stretchable film 10 after stretching is 40-60% of the original film when stretched at room temperature, and 85-95% of the original film when stretched at room temperature. In the case of gear stretching, the unstretched portion has the same thickness as the original film, and the stretched portion is 85-95% of the original film.

Furthermore, from the perspective of improving breathability, even in stretch films 10 in which the thickness ratio of the surface layers 7, 8 to the entire stretch film is small, the thickness ratio of the surface layer 7 (or surface layer 8) to the elastomer layer 5 of the raw film and stretch film 10 is preferably surface layer:elastomer layer = 1:10 to 1:30, and more preferably surface layer:elastomer layer = 1:15 to 1:20.

In this embodiment, as with the first embodiment described above, the above-described method reduces manufacturing costs and produces a stretch film that combines excellent stretchability and breathability.

The stretch film may be a single layer, or may be a multi-layer film consisting of two or more layers. If the stretch film is a multi-layer film, the composition and thickness of each layer may be the same or different. When the stretch film is a multi-layer film, the thickness refers to the total thickness of the multi-layer film.

The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples may be modified or altered based on the spirit of the present invention, and such modifications are not excluded from the scope of the present invention.

The materials used to prepare the stretch film are listed below.
(1) Inorganic filler: calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., product name: PO-150B-10)
(2) HDPE: High-density polyethylene, density: 0.951 g/cm ³ , MFR: 9.1 g/10 min (manufactured by Asahi Kasei Corporation, product name: Hizex 2110JH)
(3) R-PP: Random polypropylene, density: 0.90 g/cm ³ , MFR: 6.7 g/10 min (manufactured by Prime Polymer Co., Ltd., trade name: F227)
(4) Propylene-based elastomer (Vistamaxx (registered trademark) 6102FL (manufactured by ExxonMobil, propylene-ethylene copolymer, ethylene unit content: 16% by mass)
(5) LDPE: low-density polyethylene, density: 0.922 g/cm ³ , MFR: 0.3 g/10 min (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumikathene, F101-1)

Example 1
<Preparation of stretchable film>
First, the materials shown in Table 1 were mixed to prepare a material for Example 1 having the composition (parts by mass) shown in Table 1. Next, this material was extruded into a strand shape at 200°C using a co-rotating twin-screw extruder (manufactured by JSW Corporation, product name: TEX28V-42CW-4V) equipped with a strand die, and cut to obtain pellets.

Next, these pellets were melt-extruded (extrusion temperature: 200°C) into a film using a single-screw extruder (manufactured by Nagata Seisakusho Co., Ltd.) equipped with a T-die, and the film was wound up on a take-up roll to obtain the raw film before being made porous.

Then, this raw film was gear-stretched in the TD using a pair of shaping rolls as shown in Figure 2 under the stretching temperature and stretch ratio conditions shown in Table 1, stretching the raw film into a striped pattern to make it porous, producing a stretchable film with multiple through-holes.

<Measurement of air permeability>
Next, the air permeability of the produced stretched film was measured using an Oken type air permeability meter (s/100cc) (manufactured by Asahi Seiko Co., Ltd., product name: EG01-6-1MR). Films that did not exhibit air permeability in this measurement were expressed as 99999 (s/100cc). The results are shown in Table 1.

<Measurement of permanent set>
From the prepared stretch film, strip-shaped test pieces measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to that direction were cut, and these test pieces were fixed to the grippers of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) with a distance between the grippers of 25 mm. The test pieces were then stretched in the longitudinal direction at a rate of 254 mm/min until the elongation (elongation ratio) calculated by the above formula (1) was 100%, and then immediately shrunk at the same rate. The permanent set [%] in the MD and TD was calculated from the above formula (2). The test was conducted at room temperature (23°C ± 2°C). The results are shown in Table 1. Table 1 also shows the test force [N] at 100% elongation in the MD and TD obtained during the measurement of permanent set.

<Measurement of average elongation ratio>
From the prepared stretch film, strip-shaped test pieces measuring 50 mm in the mechanical axis direction of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction were cut, and the test pieces were fixed to the grippers of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) so that the distance between the grippers was 30 mm. The test pieces were then stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a speed of 100 mm/min so that the elongation (elongation ratio) calculated by the above formula (3) was 100%. The elongation ratio (times) was then calculated using the above formula (4). The elongation ratios were calculated at five randomly selected locations in both the first and second regions, and the average values were calculated. The results are shown in Table 1.

<Waterproofness evaluation>
An A4 size test piece was cut out from the prepared stretch film, and the end of this test piece was fixed, and 50 ml of water was dropped onto the test piece from above. At this time, the presence or absence of moisture such as water droplets on the back surface of the test piece was visually confirmed, and the test piece was evaluated according to the following evaluation criteria.

No water droplets or other moisture were observed on the back of the test piece: ◯ Water droplets or other moisture were observed on the back of the test piece: ×

Example 2
Except for changing the conditions of the stretching ratio in the stretching process to the conditions shown in Table 1, the raw film having the thickness shown in Table 1 was stretched in the same manner as in Example 1 described above to produce a stretchable film.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

Example 3
First, a raw film before being porous was obtained in the same manner as in Example 1. Next, this raw film was roll-stretched in the MD under the conditions of the stretching temperature and stretch ratio shown in Table 1, and then gear-stretched in the TD using a pair of shaping rolls shown in Figure 2. The raw film was stretched into stripes to make it porous, and a stretchable film having a plurality of through-holes was produced.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

Example 4
Except for changing the conditions of the stretching ratio in the stretching process to the conditions shown in Table 1, the raw film having the thickness shown in Table 1 was stretched in the same manner as in Example 1 described above to produce a stretchable film.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

(Examples 5 to 7)
Except for changing the conditions of the stretching ratio in the stretching process to the conditions shown in Table 1, the raw film having the thickness shown in Table 1 was stretched in the same manner as in Example 3 described above to produce a stretchable film.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

(Example 8)
Except for changing the composition (mass parts) of the stretch film to the conditions shown in Table 1, a raw film having the thickness shown in Table 1 was stretched in the same manner as in Example 1 described above to produce a stretch film.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

Example 9
<Preparation of stretchable film>
First, the materials shown in Table 1 were mixed to prepare a material for forming an elastomer layer and a material for forming a surface layer of Example 9 having the composition (parts by mass) shown in Table 1. Next, these materials were extruded into strands at 200°C using a co-rotating twin-screw extruder (manufactured by JSW Corporation, product name: TEX28V-42CW-4V) equipped with a strand die, and then cut to obtain pellets for forming an elastomer layer and pellets for forming a surface layer.

Next, the pellets for forming the elastomer layer and the pellets for forming the surface layer were extruded at 200°C using an extruder equipped with a T-die (manufactured by Sumitomo Heavy Industries Modern Co., Ltd.), and a film having an elastomer layer, a first surface layer formed on a first side of the elastomer layer, and a second surface layer formed on a second side of the elastomer layer was formed using a cast film process. The film was then wound up on a take-up roll to obtain the raw film before being made porous.

Then, this raw film was gear-stretched in the TD using a pair of shaping rolls as shown in Figure 2 under the stretching temperature and stretch ratio conditions shown in Table 1, stretching the raw film into a striped pattern to make it porous, producing a stretchable film with multiple through-holes.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

Example 10
Except for changing the composition (parts by mass) of the surface layer to the conditions shown in Table 1, a raw film having the thickness shown in Table 1 was stretched in the same manner as in Example 9 above to produce a stretchable film.

Then, in the same manner as in Example 1 above, measurements of air permeability, permanent set, and average elongation ratio were carried out, and waterproofness was evaluated. The results are shown in Table 1.

(Comparative Example 1)
Except for changing the conditions of the stretching ratio in the stretching process to the conditions shown in Table 2, an attempt was made to stretch the raw film having the thickness shown in Table 2 in the same manner as in Example 1 described above, to produce the stretch film of Comparative Example 1. However, in Comparative Example 1, because the stretching ratio in the TD gear stretching was very high, the film broke during stretching, and it was not possible to produce a stretch film.

Therefore, in Comparative Example 1, it was not possible to measure air permeability, permanent set, average elongation ratio, or evaluate waterproofness.

(Comparative Examples 2 to 5)
Except for changing the conditions for the stretching ratio in the stretching process to those shown in Table 2, the raw film having the thickness shown in Table 2 was stretched in the same manner as in Example 3 described above to attempt to produce a stretchable film. However, in Comparative Examples 2 to 5, the stretching ratio in the gear stretching in the TD was higher than the stretching ratio in the MD, so the film broke during stretching and it was not possible to produce a stretchable film.

Therefore, in Comparative Examples 2 to 5, it was not possible to measure air permeability, permanent set, average elongation ratio, or evaluate waterproofness.

(Comparative Example 6)
Raw films having the thicknesses shown in Table 2 were prepared in the same manner as in Example 1 above, except that no stretching treatment was carried out.

Then, air permeability, permanent deformation, and waterproofness were evaluated in the same manner as in Example 1 above. The results are shown in Table 2.

(Comparative Examples 7 to 8)
Except for changing the composition (parts by mass) of the stretch film to the conditions shown in Table 2, a raw film having the thickness shown in Table 2 was stretched in the same manner as in Example 1 described above to produce a stretch film.

Then, air permeability, permanent deformation, and waterproofness were evaluated in the same manner as in Example 1 above. The results are shown in Table 2.

(Comparative Example 9)
First, a raw film before being porous was obtained in the same manner as in Example 1. Next, this raw film was stretched in the MD by roll stretching under the conditions of the stretching temperature and stretch ratio shown in Table 2, thereby stretching the raw film to make it porous, and a stretchable film having a plurality of through holes was produced.

Then, air permeability, permanent deformation, and waterproofness were evaluated in the same manner as in Example 1 above. The results are shown in Table 1.

(Comparative Example 10)
Except for changing the conditions of the stretching ratio in the stretching process to those shown in Table 2, the raw film having the thickness shown in Table 2 was stretched in the same manner as in Comparative Example 9 described above to produce an elastic film.

Then, air permeability, permanent deformation, and waterproofness were evaluated in the same manner as in Example 1 above. The results are shown in Table 1.

As shown in Table 1, the stretch films of Examples 1 to 10 have an air permeability of 500 s/100 cc or more and 10,000 s/100 cc or less, measured using an Oken air permeability tester, a permanent set in at least one of the MD and TD directions of 30% or less, an average elongation ratio in the first region of 1.8 times or more and 3.0 times or less, and an average elongation ratio in the second region of 1.0 times or more and 1.8 times or less, demonstrating that they are capable of achieving both excellent stretchability and breathability.

On the other hand, as shown in Table 2, in Comparative Example 6, no stretching treatment was performed, so no through holes were formed due to porosity, and the fabric exhibited no breathability at all (air permeability was displayed as 99,999 s/100 ml).

Furthermore, in Comparative Example 7, since no inorganic filler was added, no through holes were formed due to porosity, and the material exhibited no breathability at all (the air permeability was displayed as 99,999 s/100 ml).

Furthermore, in Comparative Example 8, because LDPE is not blended, separation between the resin and inorganic filler is unlikely to occur, and it shows no breathability at all (air permeability is displayed as 99,999 s/100 ml).

In addition, in Comparative Example 9, only MD stretching (room temperature) was performed, and gear stretching in TD was not performed, so it was found to have poor breathability (air permeability greater than 10,000 s/100 ml).

In addition, in Comparative Example 10, only MD stretching (room temperature) was performed, and gear stretching in TD was not performed, so it was found to have poor breathability (air permeability greater than 10,000 s/100 ml) and poor stretchability (TD permanent set greater than 15%).

As described above, the present invention is suitable for stretch films and their manufacturing methods used in, for example, garments such as underwear, disposable diaper waistbands, side panels, leg gathers, incontinence products, sanitary napkins, bandages, surgical drapes, tightening bands, hats, swimming trunks, sports supports, medical supports, adhesive bandages, etc.

REFERENCE SIGNS LIST 1 Stretchable film 2 First region 3 Second region 4 Through-hole 5 Inorganic filler 6 Elastomer layer 7, 8 Surface layer 10 Stretchable film 20 First region 30 Second region

Claims (8)

A stretch film containing a thermoplastic elastomer, a polyethylene resin, and an inorganic filler,
The air permeability measured by an Oken type air permeability tester is 500 s/100 cc or more and 10,000 s/100 cc or less,
The following permanent strain in at least one direction is 30% or less,
the permanent strain in a direction perpendicular to the mechanical axis direction is 10% or less,
The stretch film has alternating band-shaped first regions having a broken surface extending along the mechanical axis direction of the stretch film and band-shaped second regions adjacent to the first regions and extending along the mechanical axis direction, which are less stretchable than the first regions;
The first region has an average elongation ratio of 1.8 times or more and 3.0 times or less,
The stretchable film characterized in that the average elongation ratio of the second region is 1.0 times or more and 1.8 times or less.
(Permanent deformation of stretch film)
A strip-shaped test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to the one direction was cut from the stretch film, and this test piece was fixed to the gripping tools of the testing machine so that the distance between the gripping tools was 25 mm. The test piece was stretched in the longitudinal direction of the test piece at a speed of 254 mm/min so that the elongation (elongation ratio) calculated by the following formula (1) was 100%, and then the test piece was immediately contracted at the same speed, and the permanent set [%] was calculated using the following formula (2).
Elongation [%] = (L1 - L0) / L0 × 100 (1)
Permanent set [%] = (L2 - L0) / L0 × 100 (2)
where L0 is the distance (mm) between the grippers before stretching, L1 is the distance (mm) between the grippers after stretching, and L2 is the distance (mm) between the grippers when the load (N/25 mm) on the test piece becomes 0 when contracting.
(Average extension ratio)
A strip-shaped test piece measuring 50 mm in the mechanical axis direction of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction is cut from the stretch film. The test piece is fixed to the grips of the testing device so that the distance between the grips is 30 mm. The test piece is stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a speed of 100 mm/min so that the elongation calculated by the following formula (3) is 100%. The elongation ratio (times) is calculated using the following formula (4). The elongation ratios are calculated at five randomly selected locations in both the first and second regions, and the average is calculated.
Elongation [%] = (L1 - L0) / L0 × 100 (3)
Elongation ratio [times] = R1/R0 (4)
where L0 is the distance between the grippers (mm) before stretching, L1 is the distance between the grippers (mm) after stretching, R0 is the length (μm) of the first region or the second region in the direction perpendicular to the mechanical axis direction before stretching, and R1 is the length (μm) of the first region or the second region in the direction perpendicular to the mechanical axis direction after stretching (where R0 and R1 are measured at the same location in the same region). The stretch film of claim 1, characterized in that the thermoplastic elastomer content of the entire stretch film is 20% by mass or more and 50% by mass or less, the inorganic filler content of the entire stretch film is 50% by mass or more and 70% by mass or less, and the polyethylene resin content of the entire stretch film is 10% by mass or less. The stretch film according to claim 1 or 2, characterized in that it has an air permeability of 7500 s/100 cc or less. A method for producing the stretch film according to any one of claims 1 to 3 ,
preparing a raw film containing the thermoplastic elastomer , the polyethylene resin, and the inorganic filler;
and a step of gear-stretching the raw film in a direction perpendicular to the machine axis direction. A stretch film comprising an elastomer layer containing a thermoplastic elastomer, a polyethylene resin, and an inorganic filler, and a surface layer laminated on at least one surface of the elastomer layer,
The air permeability measured by an Oken type air permeability tester is 500 s/100 cc or more and 10,000 s/100 cc or less,
The following permanent strain in at least one direction is 30% or less,
the permanent strain in a direction perpendicular to the mechanical axis direction is 10% or less,
The stretch film has alternating band-shaped first regions having a broken surface extending along the mechanical axis direction of the stretch film and band-shaped second regions adjacent to the first regions and extending along the mechanical axis direction, which are less stretchable than the first regions;
The first region has an average elongation ratio of 1.8 times or more and 3.0 times or less,
The stretchable film characterized in that the average elongation ratio of the second region is 1.0 times or more and 1.8 times or less.
(Permanent deformation of stretch film)
A strip-shaped test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to the one direction was cut from the stretch film, and this test piece was fixed to the gripping tools of the testing machine so that the distance between the gripping tools was 25 mm. The test piece was stretched in the longitudinal direction of the test piece at a speed of 254 mm/min so that the elongation (elongation ratio) calculated by the following formula (1) was 100%, and then the test piece was immediately contracted at the same speed, and the permanent set [%] was calculated using the following formula (2).
Elongation [%] = (L1 - L0) / L0 × 100 (1)
Permanent set [%] = (L2 - L0) / L0 × 100 (2)
where L0 is the distance (mm) between the grippers before stretching, L1 is the distance (mm) between the grippers after stretching, and L2 is the distance (mm) between the grippers when the load (N/25 mm) on the test piece becomes 0 when contracting.
(Average extension ratio)
A strip-shaped test piece measuring 50 mm in the mechanical axis direction of the first and second regions and 100 mm in the direction perpendicular to the mechanical axis direction is cut from the stretch film. The test piece is fixed to the grips of the testing device so that the distance between the grips is 30 mm. The test piece is stretched in the direction perpendicular to the mechanical axis direction of the first and second regions at a speed of 100 mm/min so that the elongation calculated by the following formula (3) is 100%. The elongation ratio (times) is calculated using the following formula (4). The elongation ratios are calculated at five randomly selected locations in both the first and second regions, and the average is calculated.
Elongation [%] = (L1 - L0) / L0 × 100 (3)
Elongation ratio [times] = R1/R0 (4)
where L0 is the distance between the grippers (mm) before stretching, L1 is the distance between the grippers (mm) after stretching, R0 is the length (μm) of the first region or the second region in the direction perpendicular to the mechanical axis direction before stretching, and R1 is the length (μm) of the first region or the second region in the direction perpendicular to the mechanical axis direction after stretching (where R0 and R1 are measured at the same location in the same region). The stretch film described in claim 5, characterized in that the content of the thermoplastic elastomer relative to the entire elastomer layer is 20% by mass or more and 50% by mass or less, the content of the inorganic filler relative to the entire elastomer layer is 50% by mass or more and 70% by mass or less, and the content of the polyethylene-based resin relative to the entire elastomer layer is 10 % by mass or less. 7. The stretchable film according to claim 5 , wherein the air permeability is 7500 s/100 cc or less. A method for producing the stretch film according to any one of claims 5 to 7 ,
preparing a raw film having an elastomer layer containing the thermoplastic elastomer , the polyethylene resin, and the inorganic filler, and a surface layer provided on at least one surface of the elastomer layer;
and a step of gear-stretching the raw film in a direction perpendicular to the machine axis direction.