JP7578743B2 - Stretchable Film - Google Patents

Description

The present invention relates to a stretch film.

Stretch films are used in a wide range of fields, such as hygiene products, sporting goods, and medical products, to improve handling, wearing comfort (fit), etc. For example, they are used in garments such as underwear, waistbands of disposable diapers, side panels, leg gathers, incontinence products, sanitary napkins, bandages, surgical drapes, tightening bands, hats, swimming trunks, sports supports, medical supporters, etc.
As a stretch film, a stretch film has been proposed in which a surface layer such as an olefin layer is provided on the surface of an elastomer layer (Patent Document 1).

JP 2016-112878 A

For example, in the manufacturing process of disposable diapers, a stretch film may be attached to a nonwoven fabric, a backing film, etc. in a stretched state. However, with conventional stretch films such as those described in Patent Document 1, it is difficult to stably perform such attachment.

The objective of the present invention is to provide a stretch film that can be stably attached to nonwoven fabrics, backing films, etc. in a stretched state.

The present invention has the following configuration.
[1] A stretchable film comprising an inorganic filler and a thermoplastic elastomer, in which, in a hysteresis curve obtained by measuring stress at 0 to 100% elongation, when the measurement points at elongation ratios of 30%, 50%, and 70% are designated as A, B, and C, respectively, the slope of a line p connecting points A and B and the slope of a line q connecting points B and C are both 7.0 x ^10-3 or less.
[2] The stretch film described in [1], having an elastomer layer and a surface layer provided on either or both of the first and second sides of the elastomer layer.
[3] The stretch film described in [2], wherein the elastomer layer contains a thermoplastic elastomer and the surface layer contains a polyolefin resin and an inorganic filler.
[4] The stretch film according to [3], wherein the content of the thermoplastic elastomer in the elastomer layer is 80% by mass or more relative to the total mass of the elastomer layer, the content of the polyolefin resin in the surface layer is 40 to 90% by mass relative to the total mass of the surface layer, and the content of the inorganic filler in the surface layer is 10 to 60% by mass relative to the total mass of the surface layer.
[5] The stretch film according to any one of [1] to [4], having a total thickness of 20 to 60 μm.
[6] The stretch film according to any one of [2] to [5], wherein the thickness of the surface layer is 0.5 to 4.0 μm.
[7] The stretch film according to any one of [1] to [6], which has been subjected to a stretching treatment in the width direction.

The present invention provides a stretch film that can be stably attached to nonwoven fabrics, backing films, etc. in a stretched state.

1 is a cross-sectional view showing an example of the stretch film of the present invention. 1 is a cross-sectional view showing an example of the stretch film of the present invention.

The following definitions of terms apply throughout the specification and claims.
The machine direction (MD) is the extrusion direction (longitudinal direction) of the strip-shaped resin film, and the transverse direction (TD) is the direction perpendicular to the machine direction (MD) along the surface of the resin film.

The stretch film of the present invention comprises an inorganic filler and a thermoplastic elastomer.
The inorganic filler is not particularly limited, and examples thereof include calcium carbonate, zeolite, and silica. Among them, calcium carbonate is preferred because it can reduce the stress when the film is stretched and improves the permanent set (stretchability). The inorganic filler contained in the stretch film may be one type or two or more types.

Thermoplastic elastomer refers to a polymer that has rubber elasticity at or above its glass transition temperature. Therefore, thermoplastic elastomers generally have a glass transition temperature below room temperature (23°C). Examples of thermoplastic elastomers include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, and polyester-based elastomers. Among these, olefin-based elastomers are preferred in terms of strength and recovery. Styrene-based elastomers are also preferred in terms of high dimensional stability during film transport. The thermoplastic elastomer contained in the stretch film may be one type or two or more types.

Examples of styrene-based elastomers include styrene-isoprene-styrene copolymers (SIS elastomers), styrene-isoprene block copolymers, styrene-butadiene-styrene block copolymers, styrene-butadiene block copolymers, hydrogenated styrene-isoprene-styrene block copolymers (styrene-ethylene-propylene-styrene block copolymers), and hydrogenated styrene-butadiene-styrene block copolymers (styrene-ethylene-butylene-styrene block copolymers). Among these, SIS elastomers are preferred because of their higher strength and resilience.

The styrene unit content of the SIS elastomer relative to the total units is preferably 14 to 48% by mass. If the styrene unit content of the SIS elastomer is equal to or higher than the lower limit, moldability is improved. If the styrene unit content of the SIS elastomer is equal to or lower than the upper limit, sufficiently high elasticity can be obtained.

As the SIS elastomer, a commercially available product can be used.
Examples of commercially available SIS elastomers include Quintac 3390 (SIS block copolymer, glass transition temperature: -53°C, styrene unit content: 48% by mass, manufactured by Zeon Corporation), Quintac 3620 (SIS block copolymer, glass transition temperature: -50°C, styrene unit content: 14% by mass, manufactured by Zeon Corporation), and the like.

Examples of olefin elastomers include copolymers or homopolymers mainly composed of an olefin having 3 or more carbon atoms, and copolymers mainly composed of ethylene and an olefin having 3 or more carbon atoms. Specific examples include α-olefin homopolymers such as propylene homopolymers and 1-butene homopolymers having low stereoregularity; 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-1-octene copolymers; and ethylene-α-olefin-diene terpolymers such as ethylene-propylene-ethylidenenorbornene copolymers, ethylene-propylene-butadiene copolymers, and ethylene-propylene-isoprene copolymers. Alternatively, the elastomer may be one in which the elastomer is dispersed in a matrix of crystalline polyolefin. The olefin-based elastomer may be used alone or in combination of two or more kinds.

As olefin-based elastomers, from the viewpoints of strength and resilience, propylene-based elastomers (such as propylene-ethylene copolymers, hereinafter also referred to as "PP-based elastomers"), which are copolymers or homopolymers whose main component is propylene, and ethylene-octene elastomers (such as ethylene-octene copolymers), which are copolymers or homopolymers whose main component is ethylene, are preferred. PP-based elastomers are preferred because the difference in physical properties between the TD and MD of the stretch film is small, and the permanent set in TD is improved.

The propylene unit content of the PP elastomer relative to the total units is preferably 70 to 95% by mass, more preferably 80 to 90% by mass. When the propylene content of the PP elastomer is equal to or higher than the lower limit, moldability is improved. When the propylene content of the PP elastomer is equal to or lower than the upper limit, high stretchability is easily obtained.
In this specification, the term "to" indicating a range of values means that the values before and after it are included as the lower and upper limits.

As the olefin-based elastomer, commercially available products can be used.
Examples of commercially available olefin-based elastomers include those under the trade name "VISTAMAXX6102" (propylene-ethylene copolymer, ethylene unit content: 16% by mass, manufactured by ExxonMobil) and those under the trade name "Infuse9007" (ethylene-octene copolymer, manufactured by Dow Chemical).

As the thermoplastic elastomer, from the viewpoints of strength and recovery, one selected from the group consisting of PP-based elastomers and ethylene-octene elastomers is preferred, although two or more types of elastomers may be mixed and used.
As the thermoplastic elastomer, a styrene-based elastomer is preferred because it has high dimensional stability during film transport, although two or more types of styrene-based elastomers may be used in combination.

In the stretch film of the present invention, when the measurement points A, B, and C are A, B, and C, respectively, in a hysteresis curve (stress-strain curve, S-S curve) measuring the stress when stretched from 0 to 100%, the slope of the line p connecting points A and B and the slope of the line q connecting points B and C are both 7.0×10 ⁻³ or less. In this S-S curve, the strain of the stretch film when stretched 100% (stretching ratio is 100%) is taken as 100%.

By making the slope of line p and the slope of line q both 7.0×10 ⁻³ or less, it becomes possible to stretch the stretch film with a small and constant force, and therefore the stretch film in a stretched state can be stably bonded to other members such as nonwoven fabrics and backing films, resulting in excellent process stability.
In the present invention, from the viewpoint of superior process stability, it is preferable that the slope of the line p and the slope of the line q are both 5.0×10 ⁻³ or less.

The stress of the stretch film at 30% elongation is preferably 3.0 N/25 mm or less, more preferably 2.0 N/25 mm or less, and even more preferably 1.7 N/25 mm or less.
The stress of the stretch film at 100% elongation is preferably 3.0 N/25 mm or less, and more preferably 2.0 N/25 mm or less.
If the stress of the stretch film when elongated by 30% and when elongated by 100% is equal to or less than the upper limit value, the stretch film has low rigidity.

The permanent set of the stretch film is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. If the permanent set is equal to or less than the upper limit, the film has excellent stretchability and easily returns to its original state even after being attached to another member such as a nonwoven fabric in a stretched state.

The total thickness of the stretch film is preferably 20 to 60 μm, more preferably 25 to 55 μm, and even more preferably 30 to 50 μm. If the total thickness of the stretch film is equal to or greater than the lower limit of the above range, the stretch film has excellent stretchability. If the total thickness of the stretch film is equal to or less than the upper limit of the above range, the stretch film can be made thinner, has lower rigidity, and has excellent stretchability.

The embodiment of the stretch film of the present invention is not particularly limited, but a preferred embodiment has an elastomer layer and a surface layer provided on either or both of a first surface and a second surface in the thickness direction of the elastomer layer.
For example, the stretch film 1 illustrated in Fig. 1 and the stretch film 2 illustrated in Fig. 2 are exemplified. As shown in Fig. 1, the stretch film 1 includes an elastomer layer 10 and a first surface layer 20 provided on a first surface 10a of the elastomer layer 10. As shown in Fig. 2, the stretch film 2 includes an elastomer layer 10, a first surface layer 20 provided on a first surface 10a of the elastomer layer 10, and a second surface layer 22 provided on a second surface 10b of the elastomer layer 10. The dimensions and the like in Figs. 1 and 2 are merely examples, and the present invention is not necessarily limited thereto, and can be appropriately modified and implemented within the scope that does not change the gist of the present invention.
The stretch film of the present invention may be a film having no surface layer on either the first or second surface of the elastomer layer.

The elastomer layer is a layer that includes a thermoplastic elastomer.
The elastomer layer may contain components other than the thermoplastic elastomer as long as the effects of the present invention are not impaired. Examples of the components include additives such as weather stabilizers, antistatic agents, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, UV absorbers, light stabilizers, antioxidants, discoloration inhibitors, pigments, dyes, and fillers, and resins other than the thermoplastic elastomers, such as polyolefin resins.

The content of the thermoplastic elastomer in the elastomer layer is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the total mass of the elastomer layer. If the content of the thermoplastic elastomer is equal to or more than the lower limit, the elasticity is excellent.

The thickness of the elastomer layer is preferably 20 to 60 μm, more preferably 25 to 55 μm, and even more preferably 30 to 50 μm. When the thickness of the elastomer layer is equal to or greater than the lower limit of the above range, the elastomer layer has excellent elasticity. When the thickness of the elastomer layer is equal to or less than the upper limit of the above range, the elastomer layer has low rigidity.
The elastomer layer may be a single layer or multiple layers. When the elastomer layer is a multiple layer, it is preferable that the total thickness of the elastomer layers is within the above range.

From the viewpoint of excellent blocking resistance, the surface layer preferably contains a polyolefin resin and an inorganic filler.
Examples of polyolefin resins include polypropylene and polyethylene. Polyethylene is preferred because it has excellent elasticity and low rigidity. Polypropylene is preferred because it has excellent heat resistance and is not easily broken even when bonded to nonwoven fabrics or the like with hot melt (110° C. or higher).

Examples of polypropylene include homopolypropylene (H-PP), block polypropylene (B-PP) which is a copolymer with ethylene, random polypropylene (R-PP) which is a copolymer with ethylene, etc. Among them, one or more types selected from the group consisting of B-PP and R-PP are preferred from the viewpoint of excellent flexibility.
Examples of polyethylene include low density polyethylene (LDPE) and high density polyethylene (HDPE).
The surface layer may contain one type of polyolefin resin or two or more types of polyolefin resins.

When a first surface layer and a second surface layer are provided on both sides of the elastomer layer, the polyolefin resin contained in the first surface layer and the polyolefin resin contained in the second surface layer may be the same or different.

The content of polyolefin resin in the surface layer is preferably 40 to 90% by mass, more preferably 50 to 70% by mass, based on the total mass of the surface layer. If the content of polyolefin resin is equal to or greater than the lower limit of the above range, the adhesion to the nonwoven fabric is excellent. If the content of polyolefin resin is equal to or less than the upper limit of the above range, the rigidity is low and the elasticity is excellent.

Examples of inorganic fillers include calcium carbonate, zeolite, silica, talc, and alumina. The surface layer may contain one type of inorganic filler, or two or more types of inorganic fillers.

The content of the inorganic filler in the surface layer is preferably 10 to 60% by mass, more preferably 30 to 50% by mass, based on the total mass of the surface layer. If the content of the inorganic filler is equal to or greater than the lower limit of the range, the film will have excellent blocking resistance, low rigidity, and excellent stretchability. If the content of the inorganic filler is equal to or less than the upper limit of the range, the production of the stretch film will be stable.

The surface layer may contain components other than the polyolefin resin and inorganic filler as long as the effects of the present invention are not impaired. Examples of other components include the additives listed for the elastomer layer.

The thickness of the surface layer is preferably 0.5 to 4.0 μm, more preferably 1.0 to 3.0 μm. If the thickness of the surface layer is equal to or greater than the lower limit of the above range, the production of the stretch film becomes more stable. If the thickness of the surface layer is equal to or less than the upper limit of the above range, the effect of the stiffness of the surface layer on the stretch film becomes small, so that the stiffness of the stretch film becomes low and the stretchability becomes excellent.
When a first surface layer and a second surface layer are provided on both sides of the elastomer layer, it is preferable that the thicknesses of the first surface layer and the second surface layer are each within the above-mentioned ranges.

The method for producing the stretch film is not particularly limited, and examples include the inflation method and the cast film process. Among these, the cast film process is preferred from the viewpoint of productivity.

The stretch film of the present invention may be stretched for the purpose of adjusting the mechanical properties, particularly the shrinkage stress and permanent set. It is preferable that the film is stretched, and more preferably in the transverse direction (TD), because this reduces the stress (rigidity) and makes it easier to obtain a stretch film in which the slope of line p and the slope of line q are 7.0×10 ⁻³ or less.

The stretching method is not particularly limited, and examples thereof include roll stretching, tenter stretching, gear stretching, etc. Among these, gear stretching is preferred from the viewpoint of productivity.
The stretching ratio is not particularly limited and can be, for example, 300 to 400%.

The uses of the stretch film of the present invention are not particularly limited, and it can be used in hygiene products, sports goods, medical products, etc. For example, it can be used in clothing such as underwear, waistbands of disposable diapers, side panels, leg gathers, incontinence products, sanitary napkins, bandages, surgical drapes, tightening bands, hats, swimming trunks, sports supports, medical product supports, etc.

As described above, in the stretch film of the present invention, the slope of line p and the slope of line q are both 7.0 × 10 ^-3 or less. This makes it possible to stretch the stretch film with a small and constant force, and the stretch film in a stretched state can be stably bonded to other members such as nonwoven fabrics and backing films, resulting in excellent process stability.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[Measurement method, evaluation method]
(Thickness of each layer)
The thicknesses of the elastomer layer and the surface layer in the stretch film were determined by observing the cross section with a microscope.

(Permanent deformation of stretch film)
A strip-shaped test piece was cut from the stretch film, 100 mm in the TD of the film and 25 mm in the MD perpendicular to the TD. The test piece was fixed to the gripper of a precision universal testing machine (Shimadzu Corporation, Autograph, Material Test Operation Software: TRAPEZIUM2) so that the distance between the grippers was 25 mm. The test piece was stretched in the longitudinal direction at a speed of 254 mm/min so that the elongation (elongation ratio) calculated by the following formula (I) was 100%, and then the test piece was immediately contracted at the same speed. The permanent set was calculated from the following formula (II). The test was performed at 23°C ± 2°C.
Elongation = (L1 - L0) / L0 x 100 (I)
Permanent set = (L2 - L0) / L0 x 100 (II)
Here, L0 is the distance between the grips (mm) before stretching, L1 is the distance between the grips (mm) after stretching, and L2 is the distance between the grips (mm) when the load (N/25 mm) of the test piece becomes 0 when contracting.

(Hysteresis curve)
Using the same method as used to calculate the permanent set of an elastic film, the test piece is stretched to an elongation ratio of 100%, and then immediately contracted at the same speed. The curve obtained by plotting the elongation ratio (%) on the horizontal axis and the stress (N/25 mm) on the vertical axis is called a hysteresis curve.

(Process Stability)
The process stability was evaluated according to the following evaluation criteria with respect to the slope of a straight line p connecting points A and B and the slope of a straight line q connecting points B and C, where A, B, and C are measurement points on the hysteresis curve where the elongation ratios are 30%, 50%, and 70%, respectively.
⊚ (Excellent): The slope of line p and the slope of line q are both 5.0×10 ⁻³ or less.
◯ (Good): At least one of the slope of line p and the slope of line q exceeds 5.0×10 ⁻³ , but both of the slopes of line p and line q are 7.0×10 ⁻³ or less.
× (bad): At least one of the slope of the line p and the slope of the line q exceeds 7.0×10 ⁻³ .

(Lamination stability)
The stretch film was cut into rectangular test pieces measuring 100 mm in the TD of the film and 25 mm in the MD perpendicular to the TD, and the test pieces were stretched in the longitudinal direction at a speed of 254 mm/min and an elongation ratio of 50% and evaluated for adhesion stability with the nonwoven fabric according to the following evaluation criteria.
◯ (Good): The lamination work was performed stably.
× (bad): The lamination work could not be performed stably.

[Raw materials]
The raw materials used in this example are shown below.
(Thermoplastic elastomer)
Elastomer (A-1): SIS elastomer (Quintac 3390, styrene unit content 48% by mass, manufactured by Zeon Corporation)
Elastomer (A-2): SIS elastomer (Quintac 3620, styrene unit content 14% by mass, manufactured by Zeon Corporation)
Elastomer (A-3): PP-based elastomer (Vistamaxx 6102FL, manufactured by Exxon)
Elastomer (A-4): PP-based elastomer (Vistamaxx 6202, manufactured by Exxon)

(Polyolefin resin)
Resin (B-1): R-PP (F227, melting point 152°C, manufactured by Prime Polymer Co., Ltd.)
Resin (B-2): LDPE (CE3506, melting point 117°C, manufactured by Sumikasen Co., Ltd.)
Resin (B-3): HDPE (Nipolon Hard 1000, manufactured by Tosoh Corporation)

(Inorganic filler)
Filler (C-1): Calcium carbonate (Ryton S, manufactured by Bihoku Powder Industry Co., Ltd.)

[Example 1]
A resin mixture was obtained by mixing the components forming the surface layer in a tumbler mixer in the proportions shown in Table 1. Next, a cast film process was used to produce a stretch film having a three-layer elastomer layer in which a second elastomer layer and a third elastomer layer were provided on both sides of a first elastomer layer, a first surface layer provided on the second elastomer layer side of the elastomer layer, and a second surface layer provided on the third elastomer layer side of the elastomer layer. After molding, the stretch film was stretched 400% in the transverse direction (TD) by gear stretching.

[Examples 2, 3, 5 to 8, Comparative Examples 3 to 7]
A stretch film was produced in the same manner as in Example 1, except that the number of elastomer layers was one and the composition and thickness of each layer, and the presence or absence and conditions of stretching treatment were changed as shown in Tables 1 and 2.
Examples 7 and 8 are reference examples.

[Example 4, Comparative Examples 1 and 2]
Stretch films were produced in the same manner as in Example 1, except that the composition and thickness of each layer, and the presence or absence and conditions of stretching treatment were changed as shown in Tables 1 and 2.

The evaluation results for each example are shown in Tables 1 and 2.

As shown in Tables 1 and 2, the stretch films of Examples 1 to 8 had superior process stability and lamination stability compared to the stretch films of Comparative Examples 1 to 7.

1, 2... stretch film, 10... elastomer layer, 10a... first surface, 10b... second surface, 20... first surface layer, 22... second surface layer.

Claims (5)

Contains an inorganic filler and a thermoplastic elastomer,
A stretch film having an elastomer layer and a surface layer provided on either or both of a first surface and a second surface of the elastomer layer,
The thickness of the elastomer layer is 20 to 60 μm,
the elastomer layer contains a thermoplastic elastomer, and the surface layer contains a polyolefin resin and an inorganic filler,
The content of the inorganic filler in the surface layer is 10 to 60% by mass based on the total mass of the surface layer,
The permanent deformation of the stretch film is 15% or less, and
A stretch film in which, when the measurement points of the elongation ratios of 30%, 50%, and 70% in a hysteresis curve obtained by measuring the stress when elongated from 0 to 100% are designated as A, B, and C, respectively, the slope of the line p connecting points A and B and the slope of the line q connecting points B and C are both 7.0 x ^10-3 or less. The content of the thermoplastic elastomer in the elastomer layer is 80% by mass or more based on the total mass of the elastomer layer,
The stretch film according to claim 1, wherein the content of the polyolefin resin in the surface layer is 40 to 90% by mass relative to the total mass of the surface layer. The stretch film according to claim 1 or 2, having a total thickness of 20 to 60 μm. The stretch film according to any one of claims 1 to 3, wherein the thickness of the surface layer is 0.5 to 4.0 μm. The stretch film according to any one of claims 1 to 4, which has been stretched in the width direction.

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