Polyolefin-based longitudinally oriented film

Abstract

To provide a polyolefin-based antifogging-added uniaxial vertically-stretched film which comprises practical heat sealability even if a corona discharge treatment making express an antifogging property is applied to a heat-sealing surface.SOLUTION: A polyolefin-based uniaxial vertically-stretched film comprises at least two layers in which a heat seal layer 30 is laminated on one face side of a substrate layer 20 including polypropylene resin as a main body, and either one of the substrate layer 20 or heat seal layer 30 includes an antifogging agent. The film is drawn in a lengthwise direction by drawing between rolls. A corona treatment is applied to the heat seal layer 30. The heat seal layer 30 comprises a linear low-density polyethylene in which a surface wet tension of the heat seal layer 30 is 32 mN / m or more; a melt flow rate measured at 190°C under load of 2.16 kg is in a range of 1 to 10 g / 10 min; and a density is in the range of 0.860 to 0.935 g / cm3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyolefin film, and more particularly to a longitudinally uniaxially stretched polyolefin film in which a heat seal layer has been subjected to a corona treatment for anti-fogging properties. [Background technology]

[0002] In the packaging of various items such as food, films and items are simultaneously fed into an automatic packaging machine, and filling, packaging, and sealing are performed continuously. Stretched films are sometimes used as the films used for packaging these types of items, and various properties are required for suitable use as packaging bags, such as strength sufficient to withstand processing and distribution, heat sealing properties, and easy cutting properties.

[0003] Furthermore, when the film is used as a food packaging bag, moisture emitted from the food can cause droplets to adhere to the inside of the bag, so an anti-fog agent is sometimes added to the film. In this case, in order to impart anti-fog properties to the heat-sealed surface of the film, corona treatment is performed to promote bleeding of the anti-fog agent. However, when the heat-sealed surface is subjected to corona treatment, the heat-sealed surface cannot be heat-sealed at the same temperature as before the corona treatment, and a problem arises in that heat-sealing must be performed at a higher temperature.

[0004] As a technique for solving the above problems, for example, a laminated film is known which is composed of a heat seal layer and a base layer, in which the heat seal layer is composed of two or more copolymers selected from the group consisting of a propylene polymer and a propylene-1-butene copolymer, a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and a copolymer of 1-butene and an α-olefin having 3 or 5 to 20 carbon atoms (see Patent Document 1).

[0005] Also known is a multilayer film having two or more layers, at least one surface layer of which is made of a propylene-based copolymer containing a propylene-based copolymer component having a content of 1 to 5% by weight of monomer units derived from an α-olefin and a propylene-based copolymer component having a content of 20 to 40% by weight of monomer units derived from an α-olefin, and a propylene-ethylene copolymer having a content of 6 to 20% by weight of monomer units derived from ethylene (see Patent Document 2).

[0006] The films described in Patent Documents 1 and 2 are both biaxially stretched films. Biaxially stretched films are formed by longitudinal stretching through inter-roll stretching, which involves stretching using a speed difference between rolls, followed by transverse stretching and heat setting in a tenter oven. In this type of film, the heat-sealing initiation temperature can be lowered by simply increasing the heat-setting temperature. However, in the case of biaxially stretched films, a sufficient amount of heat can be applied in a tenter oven, allowing the heat-sealing initiation temperature to be appropriately lowered. Therefore, a low heat-sealing initiation temperature can be maintained even when the heat-sealing surface is subjected to a corona treatment.

[0007] Incidentally, from the viewpoint of easy opening, uniaxially stretched films, which have excellent easy-to-tear properties, are preferably used for packaging bags. Uniaxially stretched films include longitudinally uniaxially stretched films that are stretched only longitudinally and transversely uniaxially stretched films that are stretched only transversely. Longitudinal uniaxially stretched films are formed by longitudinal stretching through inter-roll stretching and then heat setting with a heating roll. In order to lower the heat-seal initiation temperature of a longitudinally uniaxially stretched film, it is necessary to increase the heat-setting temperature with the heating roll. However, when heating with a heating roll, the film comes into contact with the high-temperature heating roll, causing the film to melt and stick to the heating roll, resulting in peeling marks and a poor appearance.

[0008] To avoid the appearance defects of films due to heat setting, it is necessary to heat set the film at a temperature range where the film does not melt, but this does not allow for sufficient heat to be applied to the film. Therefore, the heat sealing temperature of longitudinally uniaxially stretched films is unavoidably higher than that of biaxially stretched films. Another problem is that if the heat-sealed surface of a longitudinally uniaxially stretched film is subjected to corona treatment, the heat sealing temperature becomes even higher. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] WO2016 / 027885 publication [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-205909 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed in view of the above circumstances, and provides a longitudinally uniaxially stretched polyolefin film containing an anti-fogging agent, which has practical heat sealability even when subjected to a corona treatment to impart anti-fogging properties to the heat seal surface. [Means for solving the problem]

[0012] Claim 1The invention relates to a polyolefin-based longitudinal uniaxially stretched film which comprises at least two layers, a base layer mainly made of a polypropylene-based resin and a heat-seal layer laminated on one side thereof, the base layer or the heat-seal layer containing an anti-fogging agent, the film being stretched in the longitudinal direction by roll-to-roll stretching, the heat-seal layer being subjected to a corona treatment, and the heat-seal layer having a surface with a wet tension of 32 mN / m or more, the heat-seal layer containing at least 50% by weight of a linear low-density polyethylene (A) and a polypropylene-based resin (B), the linear low-density polyethylene (A) having a melt flow rate of 1 to 10 g / 10 min and a density of 0.860 to 0.935 g / cm, as measured at 190°C under a load of 2.16 kg. 3 The polypropylene-based resin (B) is selected from at least one of a propylene-ethylene random copolymer and a propylene-ethylene-butene random copolymer, each having a melting point of less than 135°C, or a propylene-ethylene block copolymer, and the heat-sealing initiation temperature between the heat-sealable layers is 155°C or lower.

[0014] Claim 2 The invention of claim 1 further comprises a surface layer laminated on the other side of the base layer. 1 to The present invention relates to a polyolefin-based longitudinal uniaxially stretched film. [Effects of the Invention]

[0016] Claim 1According to the invention, the polyolefin-based longitudinal uniaxially stretched film comprises at least two layers, a base layer mainly made of a polypropylene-based resin and a heat-seal layer laminated on one side thereof, the base layer or the heat-seal layer containing an anti-fogging agent, the polyolefin-based longitudinal uniaxially stretched film being longitudinally stretched by roll-to-roll stretching, and the heat-seal layer being subjected to a corona treatment so that the wet tension of the heat-seal layer surface is 32 mN / m or more, the heat-seal layer containing at least 50% by weight or more of a linear low-density polyethylene (A) and a polypropylene-based resin (B), the linear low-density polyethylene (A) having a melt flow rate of 1 to 10 g / 10 min and a density of 0.860 to 0.935 g / cm, as measured at 190°C under a load of 2.16 kg. 3 The polypropylene-based resin (B) is selected from at least one of a propylene-ethylene random copolymer or a propylene-ethylene-butene random copolymer, each having a melting point of less than 135°C, or a propylene-ethylene block copolymer. The heat-sealing initiation temperature between the heat-sealing layers is 155°C or lower. Therefore, even if the heat-sealing surface is subjected to a corona treatment, the heat-sealing initiation temperature can be appropriately prevented from increasing, preventing poor appearance due to peeling marks. Furthermore, good anti-fogging properties can be achieved, resulting in a polyolefin-based longitudinally uniaxially stretched film with practical heat-sealing properties. Furthermore, interlayer delamination between the base layer and the heat-sealing layer can be effectively prevented. Furthermore, because the heat-sealing initiation temperature between the heat-sealing layers is 155°C or lower, heat-sealing is easy and the film is highly practical.

[0018] Claim 2 According to the invention of the polyolefin-based longitudinal uniaxially stretched film, 1 of In the present invention, since a surface layer is laminated on the other side of the base material layer, the practicality of the product as a packaging bag or the like can be improved. [Brief explanation of the drawings]

[0019] [Figure 1]FIG. 1 is a schematic cross-sectional view of a polyolefin-based longitudinal uniaxially stretched film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a roll-to-roll drawing process. DETAILED DESCRIPTION OF THE INVENTION

[0020] FIG. 1 shows a polyolefin-based longitudinal uniaxially stretched film 10 according to one embodiment of the present invention, which is composed of at least two layers, with a heat seal layer 30 laminated on one side of a base layer 20 mainly made of a polypropylene-based resin. The illustrated longitudinal uniaxially stretched film 10 is composed of three layers, with a surface layer 40 laminated on the other side of the base layer 20. The longitudinal uniaxially stretched film 10 is not limited to two or three layers, and can be any suitable multi-layer film. This longitudinal uniaxially stretched film 10 is suitable for use as a packaging material for various items, such as food, daily necessities, and parts.

[0021] The longitudinally uniaxially stretched film 10 of the present invention contains an anti-fog agent in either the base layer 20 or the heat-sealable layer 30, and is stretched in the longitudinal direction by inter-roll stretching. In inter-roll stretching, the film is stretched in the uniaxial direction by the speed difference between the rolls. The stretching ratio in inter-roll stretching is preferably 2 to 15 times, more preferably 3 to 10 times, and even more preferably 3 to 6 times. If the stretching ratio is too low, uneven stretching is likely to occur, and if the stretching ratio is too high, breakage may occur during the stretching process.

[0022] In an embodiment, as shown in Fig. 2, a film F co-extruded from a film forming machine 50 such as a T-die is taken up around multiple rolls R, passes through a preheating section 51 that preheats the film F, and is then uniaxially stretched longitudinally in the take-up direction (MD) in a stretching section 52 consisting of a slow-rotating roll R1 and a fast-rotating roll R2 due to the difference in speed between them, and the stretched film F1 is then heated to a predetermined temperature in a heat-setting section 53. In Fig. 2, the symbol Fr denotes a film roll around which the film F has been taken up.

[0023] Furthermore, in this longitudinally uniaxially stretched film 10, the heat seal layer 30 is subjected to a corona treatment so that the surface wet tension of the heat seal layer 30 is 32 mN / m or more. The corona treatment of the heat seal layer 30 is a treatment for promoting bleeding of the anti-fog agent contained in the base layer 20 or the heat seal layer 30, thereby imparting anti-fog properties to the heat-sealed surface. If the surface wet tension of the heat seal layer 30 is less than 32 mN / m, the corona treatment may be insufficient, resulting in insufficient bleeding of the anti-fog agent, which is undesirable.

[0024] The wet tension of the surface of the heat seal layer 30 increases in proportion to the input power of the corona treatment, or increases up to a saturation point. Therefore, the discharge amount (W·min / m 2 ) is used. The discharge amount is the input power per unit time and unit area, and is calculated based on the following formula (i). In the discharge amount calculation formula, P (W) is the discharge power, L (m) is the discharge electrode length, and v (m / min) is the film speed.

[0025]

number

[0026] The base layer 20 is mainly composed of a polypropylene-based resin, and is formed to be relatively thicker than the other layers in the longitudinally uniaxially stretched film 10, thereby imparting stiffness (rigidity) to the film and making it suitable for bag formation. Examples of polypropylene-based resins that constitute the base layer 20 include propylene homopolymers, propylene-ethylene random copolymers, and propylene-ethylene block copolymers.

[0027] The heat seal layer 30 is the layer that becomes the inner surface when the longitudinally uniaxially stretched film 10 is made into a packaging bag, and is heat-sealed between the heat seal layers. In the heat seal layer 30, the heat seal initiation temperature between the heat seal layers is preferably 155°C or lower. If the heat seal initiation temperature is higher than 155°C, heat sealing must be performed at a high temperature during bag production, which is not practical.

[0028] In the longitudinally uniaxially stretched film 10 of the first embodiment, the heat seal layer 30 has a melt flow rate (MFR) of 1 to 10 g / 10 min measured at 190°C under a load of 2.16 kg, and a density of 0.860 to 0.935 g / cm 3 It is made of linear low-density polyethylene. If the MFR of the linear low-density polyethylene is too low, it may lead to poor appearance and poor moldability, while if it is too high, it may lead to an increase in the heat-seal initiation temperature after corona treatment, blocking, and poor moldability. If the density of the linear low-density polyethylene is too low, it may be more prone to blocking due to a lower melting point, while if it is too high, it may lead to an increase in the melting point, leading to an increase in the heat-seal initiation temperature after corona treatment and poor anti-fogging properties.

[0029] In the longitudinally uniaxially stretched film 10 of the second embodiment, the heat seal layer 30 is configured to contain at least 50% by weight or more of linear low-density polyethylene (A) and a polypropylene-based resin (B).

[0030] The linear low-density polyethylene (A) has a melt flow rate of 1 to 10 g / 10 min measured at 190°C under a load of 2.16 kg and a density of 0.860 to 0.935 g / cm 3 On the other hand, the polypropylene-based resin (B) is selected from at least one of a propylene-ethylene random copolymer or a propylene-ethylene-butene random copolymer, each having a melting point of less than 135°C, or a propylene-ethylene block copolymer. By adding the polypropylene-based resin (B) to the linear low-density polyethylene (A), it is possible to prevent the heat-sealing initiation temperature from decreasing too much. Therefore, it is possible to adjust the heat-sealing initiation temperature by adjusting the blending ratio of the polypropylene-based resin (B). Furthermore, since the polypropylene-based resin (B) is the same type of resin composition as the base layer 20, which is mainly composed of a polypropylene-based resin, it is possible to more effectively prevent delamination from occurring.

[0031] The surface layer 40 is laminated on the other side of the base layer 20, i.e., the side opposite to the side on which the heat seal layer 30 is laminated, and is primarily composed of a polypropylene-based resin. The surface layer 40 is the outer surface when the longitudinally uniaxially stretched film 10 is manufactured into a packaging bag. The surface layer 40 can be appropriately printed to function as a printed layer, thereby improving the practicality of products such as packaging bags. The surface of this surface layer 40 may be subjected to a surface treatment such as corona treatment, as necessary, to improve the printability of the film surface. The polypropylene-based resin constituting the surface layer 40 is selected from propylene-based polymers such as propylene homopolymers and copolymers of propylene with other olefins such as ethylene or butene.

[0032] In order to make the longitudinally uniaxially stretched film 10 of the present invention an environmentally friendly product, one or more of the substrate layer 20, heat seal layer 30, and surface layer 40 may contain recycled materials, such as those obtained through material recycling or chemical recycling, or biomass-derived polyolefin resin. Examples of biomass-derived polyolefin resins include polyethylene-based resins obtained by processing plant materials. Specifically, they are linear low-density polyethylene-based resins produced by subjecting sugar syrup extracted from plant materials such as sugarcane to alcoholic fermentation using yeast to produce ethanol, which is then ethyleneized, and then subjected to a known resinification process. The higher the weight proportion of biomass-derived polyolefin resin, the greater the contribution to reducing environmental impact. [Example]

[0033] [Preparation of polyolefin-based longitudinally uniaxially stretched film] The materials described below were blended, melted, and kneaded, and then co-extruded into two layers (base layer and heat-sealing layer) or three layers (surface layer, base layer, and heat-sealing layer) using the T-die method with a co-extrusion T-die film molding machine to produce a sheet.The sheet was then uniaxially stretched longitudinally in the take-up direction (MD) using a roll-to-roll stretching machine, and the heat-sealing layer was subjected to corona treatment to obtain polyolefin-based longitudinal uniaxially stretched films of prototype examples 1 to 30.

[0034] In each of the prototypes 1 to 30, the resin blending ratio was 100% by weight for each layer. The prototypes 1 to 8 and 11 to 30 were made with a sheet thickness of 250 μm and a longitudinal uniaxial stretching ratio of 5 times, the prototype 9 was made with a sheet thickness of 150 μm and a longitudinal uniaxial stretching ratio of 3 times, and the prototype 10 was made with a sheet thickness of 300 μm and a longitudinal uniaxial stretching ratio of 6 times, resulting in a film thickness of 50 μm for each of the prototypes 1 to 30. The discharge amount for the corona treatment was 5 W·min / m for the prototype 20. 2 , Prototype 21 is 40W·min / m 2 The other prototypes 1 to 19, 22 to 30 were 20 W·min / m 2 The thickness of each film was measured based on the film thickness measurement method in accordance with JIS K 7130 (1999).

[0035] [Materials used] The following resins were used as the resin compositions for the surface layer, base layer, and heat seal layer. Regarding the properties of each resin, the melt flow rate (MFR) was measured at 230°C and a 2.16 kg load in accordance with JIS K 7210 (2014) or at 190°C and a 2.16 kg load, and the density was measured in accordance with JIS K 7112 (1999). The anti-fogging agent used was "Anstex SA-300F" manufactured by Toho Chemical Industry Co., Ltd.

[0036] Resin A1: Linear low-density polyethylene (Prime Polymer Co., Ltd.: "SP2040"), MFR (190°C, 2.16 kg load): 3.8 g / 10 min, density 0.918 g / cm 3 , melting point 116℃ Resin A2: Linear low-density polyethylene (manufactured by Japan Polyethylene Co., Ltd.: "KS340T", MFR (190°C, 2.16 kg load): 3.5 g / 10 min, density 0.88 g / cm 3 , melting point 60℃ Resin A3: Linear low-density polyethylene (Prime Polymer Co., Ltd.: "SP2540"), MFR (190°C, 2.16 kg load): 3.8 g / 10 min, density 0.924 g / cm 3 , melting point 120℃ Resin A4: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "3540F"), MFR (190°C, 2.16 kg load): 4.0 g / 10 min, density 0.931 g / cm 3 , melting point 123℃ Resin A5: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "4040F"), MFR (190°C, 2.16 kg load): 4.0 g / 10 min, density 0.938 g / cm 3 , melting point 126℃ Resin A6: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "4540F"), MFR (190°C, 2.16 kg load): 4.0 g / 10 min, density 0.944 g / cm 3 , melting point 128℃ Resin A7: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "1520F"), MFR (190°C, 2.16 kg load): 2.0 g / 10 min, density 0.913 g / cm 3 , melting point 114℃ Resin A8: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "715FT", MFR (190°C, 2.16 kg load): 4.0 g / 10 min, density 0.913 g / cm 3 , melting point 113℃ Resin A9: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "022GS", MFR (190°C, 2.16 kg load): 8.0 g / 10 min, density 0.904 g / cm 3 , melting point 102℃ Resin A10: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "015AN", MFR (190°C, 2.16 kg load): 14.0 g / 10 min, density 0.911 g / cm 3 , melting point 103℃

[0037] Resin B1: Low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.: "F222"), MFR (190°C, 2.16 kg load): 2.0 g / 10 min, density 0.922 g / cm 3 , melting point 110℃

[0038] Resin C1: High-density polyethylene (Keiyo Polyethylene Co., Ltd.: "M8500"), MFR (190°C, 2.16 kg load): 5.0 g / 10 min, density 0.962 g / cm 3 , melting point 135℃

[0039] Resin D1: Propylene-ethylene random copolymer (Japan Polypropylene Corporation: "WFW4M", MFR (230°C, 2.16 kg load): 7.0 g / 10 min, melting point 135°C) Resin D2: Propylene-ethylene random copolymer (Japan Polypropylene Corporation: "WFX4M", MFR (230°C, 2.16 kg load): 7.0 g / 10 min, melting point 125°C)

[0040] Resin E1: Propylene-ethylene-butene random copolymer (manufactured by Japan Polypropylene Corporation: "FW4BT", MFR (230°C, 2.16 kg load): 7.0 g / 10 min, melting point 139°C) Resin E2: Propylene-ethylene-butene random copolymer (Japan Polypropylene Corporation: "FX4G"), MFR (230°C, 2.16 kg load): 5.0 g / 10 min, melting point 126°C Resin E3: Propylene-ethylene-butene random copolymer (Japan Polypropylene Corporation: "FX4E"), MFR (230°C, 2.16 kg load): 5.0 g / 10 min, melting point 132°C

[0041] Resin F1: Propylene homopolymer (Japan Polypropylene Corporation: "FL203D"), MFR (230°C, 2.16 kg load): 3.0 g / 10 min, density 0.90 g / cm 3 Resin F2: Propylene homopolymer (Japan Polypropylene Corporation: "FY6", MFR (230°C, 2.16 kg load): 2.4 g / 10 min, melting point 160°C)

[0042] Resin G1: Propylene-ethylene block copolymer (Japan Polypropylene Corporation: "BC6DRF"), MFR (230°C, 2.16 kg load): 2.5 g / 10 min, melting point 165°C

[0043] [Prototype 1] The film of prototype 1 consisted of two layers: a base layer and a heat seal layer with a layer thickness ratio of 7:1. The base layer was composed of 99.5 wt% resin F1 and 0.5 wt% anti-fogging agent, and the heat seal layer was composed of 70 wt% resin A1 and 30 wt% resin D2.

[0044] [Prototype 2] The film of prototype 2 consisted of three layers: a surface layer, a base layer, and a heat-seal layer, with a layer thickness ratio of 1:6:1. The surface layer was composed of 100% resin F1 by weight, the base layer was composed of 99.5% resin F1 by weight and 0.5% anti-fogging agent by weight, and the heat-seal layer was composed of 100% resin A1 by weight.

[0045] [Prototype 3] The film of Prototype 3 was the same as the film of Prototype 2, except that the heat seal layer contained 85% by weight of Resin A1 and 15% by weight of Resin D2.

[0046] [Prototype 4] The film of Prototype 4 was the same as the film of Prototype 2, except that the heat seal layer contained 70% by weight of Resin A1 and 30% by weight of Resin D2.

[0047] [Prototype 5] The film of Prototype 5 was the same as the film of Prototype 2, except that the heat seal layer contained 50% by weight of Resin A1 and 50% by weight of Resin D2.

[0048] [Prototype 6] The film of Prototype 6 was the same as the film of Prototype 2, except that the heat seal layer contained 30 wt % of Resin A1 and 70 wt % of Resin D2.

[0049] [Prototype 7] The film of Prototype 7 was the same as the film of Prototype 2, except that the heat seal layer contained 15 wt % of Resin A1 and 85 wt % of Resin D2.

[0050] [Prototype 8] The film of Prototype Example 8 was the same as the film of Prototype Example 2, except that the heat seal layer contained 100% by weight of Resin D2.

[0051] [Prototype 9] The film of Prototype Example 9 was identical to the film of Prototype Example 4 except that the longitudinal uniaxial stretching ratio was 3 times.

[0052] [Prototype 10] The film of Prototype 10 was the same as the film of Prototype 4 except that the longitudinal uniaxial stretching ratio was 6 times.

[0053] [Prototype 11] The film of Prototype 11 was the same as the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A2 and 30% by weight of Resin D2.

[0054] [Prototype 12] The film of Prototype 12 was the same as the film of Prototype 4, except that the heat seal layer contained 60% by weight of Resin A3 and 40% by weight of Resin D2.

[0055] [Prototype 13] The film of Prototype 13 was the same as the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A4 and 30% by weight of Resin D2.

[0056] [Prototype 14] The film of Prototype 14 was the same as the film of Prototype 4, except that the heat seal layer contained 85% by weight of Resin A5 and 15% by weight of Resin D2.

[0057] [Prototype 15] The film of Prototype 15 was the same as the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A6 and 30% by weight of Resin D2.

[0058] [Prototype 16] The film of Prototype 16 was identical to the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A7 and 30% by weight of Resin D2.

[0059] [Prototype 17] The film of Prototype 17 was identical to the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A8 and 30% by weight of Resin D2.

[0060] [Prototype 18] The film of Prototype 18 was identical to the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A9 and 30% by weight of Resin D2.

[0061] [Prototype 19] The film of Prototype 19 was identical to the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin A10 and 30% by weight of Resin D2.

[0062] [Prototype 20] The film of prototype 20 was treated with a corona discharge of 5 W·min / m 2 The rest of the film was the same as that of Prototype 16.

[0063] [Prototype 21] The film of prototype 21 was treated with a corona discharge of 40 W·min / m 2 The rest of the film was the same as that of Prototype 16.

[0064] [Prototype 22] The film of Prototype 22 was the same as the film of Prototype 4, except that the heat seal layer contained 70% by weight of Resin B1 and 30% by weight of Resin D2.

[0065] [Prototype 23] The film of Prototype 23 was the same as the film of Prototype 4, except that the heat seal layer contained 70% by weight of resin C1 and 30% by weight of resin D2.

[0066] [Prototype 24] The film of Prototype 24 was the same as the film of Prototype 4, except that the resin D2 in the heat seal layer was replaced with 30 wt % of resin D1.

[0067] [Prototype 25] The film of Prototype 25 was the same as the film of Prototype 4, except that the resin E1 was used in place of the resin D2 in the heat seal layer at 30 wt %.

[0068] [Prototype 26] The film of Prototype 26 was the same as the film of Prototype 4, except that Resin E2 was used in place of Resin D2 in the heat seal layer at 30 wt %.

[0069] [Prototype 27] The film of Prototype 27 was the same as the film of Prototype 4, except that the resin E3 was used in place of the resin D2 in the heat seal layer at 30 wt %.

[0070] [Prototype 28] The film of Prototype 28 was the same as the film of Prototype 4, except that the heat seal layer contained 15 wt % of Resin D2 and 15 wt % of Resin E2 instead of Resin D2.

[0071] [Prototype 29] The film of Prototype 29 was the same as the film of Prototype 4, except that the resin F2 was used in place of the resin D2 in the heat seal layer at 30 wt %.

[0072] [Prototype 30] The film of prototype 30 was the same as the film of prototype 4, except that resin G1 was used at 30 wt % in place of resin D2 in the heat seal layer.

[0073] For the longitudinally uniaxially stretched films of Samples 1 to 30, the resin composition of each layer, sheet thickness, stretch ratio, film thickness, layer thickness ratio (layer ratio), and discharge amount in corona treatment are shown in Tables 1 to 5.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] [Table 4]

[0078] [Table 5]

[0079] To evaluate the performance of the longitudinally uniaxially stretched films of Prototype Examples 1 to 30, the wet tension and heat seal initiation temperature were measured, and the anti-fogging property was evaluated.

[0080] [Wetting tension measurement] The wet tension (mN / m) was measured using a wet tension test method in accordance with JIS K 6768 (1999).

[0081] [Measurement of heat seal initiation temperature] The heat seal initiation temperature (°C) was measured using a heat seal initiation temperature test conforming to JIS Z 1713 (2009), and the heat seal initiation temperatures after corona treatment were measured for the longitudinally uniaxially stretched films of Prototype Examples 1 to 30. First, a test piece 50 mm wide x 250 mm long was cut from the film of each of Prototype Examples 1 to 30, and the heat seal layers of two test pieces were placed together and heat sealed using a heat seal tester (Toyo Seiki Seisakusho Co., Ltd.; thermal gradient tester) under conditions of a heat seal pressure of 0.34 MPa, a heat seal time of 1.0 sec, and a temperature gradient (increase) of 5°C each. After heat sealing, test pieces were cut to a width of 15 mm, and the heat-sealed test piece was opened 180°. The unsealed portion was clamped in the chuck of a tensile tester (Shimadzu Corporation; EZ-SX), and the sealed portion was peeled off at a tensile speed of 200 mm / min. The temperature at which the heat seal strength reached 3 N was determined as the heat seal initiation temperature. Measurement results of 155°C or less were rated as "good (◯)," and those exceeding 155°C were rated as "unacceptable (×)."

[0082] [Anti-fogging evaluation] To evaluate anti-fogging properties, 50 ml of room temperature distilled water was first poured into a 100 ml beaker, and a test piece cut to 100 mm x 100 mm was placed over the beaker and stored in a 5°C atmosphere for 60 minutes. After storage, the beaker was placed on a piece of paper with printed letters, and the degree of fogging inside the film covering the beaker was evaluated based on how visible the letters were. In evaluating anti-fogging properties, if there were no water droplets on the film and the letters were clearly visible, the rating was "Excellent (◎)," if there were water droplets on the film but the letters were still visible, the rating was "Good (〇)," and if there were water droplets on the film and the letters were not visible, the rating was "Poor (×)."

[0083] The measurement results of the longitudinally uniaxially stretched films of prototypes 1 to 30 are shown in Tables 6 to 10. In Tables 6 to 10, the overall evaluation was given as "good (◯)" when all the judgments of each measurement were good (◯) or better, and as "bad (×)" when even one judgment was bad (×).

[0084] [Table 6]

[0085] [Table 7]

[0086] [Table 8]

[0087] [Table 9]

[0088] [Table 10]

[0089] [Results and Discussion] As shown in Tables 6 to 10, the wet tension was good at 32 mN / m or more for all of Samples 1 to 30. In addition, in the overall evaluation, Samples 1 to 5, 9 to 13, 16 to 18, 20, 21, 26 to 28, and 30 were rated "Good (◯)," while Samples 6 to 8, 14, 15, 19, 22 to 25, and 29 were rated "Poor (×)."

[0090] First, the three-layer longitudinally uniaxially stretched films of Samples 2 to 8 are examples in which the blending ratio of linear low-density polyethylene (Resin A1) in the heat-sealable layer was changed from 100% by weight to 0% by weight. Sample 2, in which the blending ratio of Resin A1 was 100% by weight, exhibited extremely good heat-seal initiation temperature and anti-fogging properties. On the other hand, in Samples 3 to 8, in which propylene-ethylene random copolymer (Resin D2) was added to the heat-sealable layer, the heat-seal initiation temperature was adequately suppressed when the blending ratio of Resin A1 was 50% by weight or more (Samples 3, 4, and 5), but was not sufficiently suppressed when the blending ratio of Resin A1 was less than 50% by weight (Samples 6, 7, and 8).

[0091] The longitudinally uniaxially stretched films of Prototypes 9 and 10 are examples in which the stretching ratio was changed relative to the good Prototype 4. In both cases where the stretching ratio was smaller (Prototype 9) and larger (Prototype 10) than that of Prototype 4, the heat seal initiation temperature and anti-fogging properties were good.

[0092] The longitudinally uniaxially stretched films of Samples 11 to 19 are examples in which Resins A2 to A10 were used in place of Resin A1 in the heat seal layer of Sample 4, which was a good product. Sample 14, which used Resin A5, and Sample 15, which used Resin A6, did not achieve sufficient anti-fogging properties. Furthermore, Sample 19, which used Resin A10, was unable to sufficiently suppress the increase in the heat seal initiation temperature.

[0093] Comparing Prototype Examples 4, 11 to 13, 16 to 18, which had good heat seal initiation temperatures and anti-fog properties, with Prototype Examples 14 and 15, resins A5 and A6 used in Prototype Examples 14 and 15 had higher densities than resins A1 to A4 and A7 to A9 used in Prototype Examples 4, 11 to 13, 16 to 18. Furthermore, comparing Prototype Examples 4, 11 to 13, 16 to 18 with Prototype Example 19, resin A10 used in Prototype Example 19 had a higher MFR than resins A1 to A4 and A7 to A9 used in Prototype Examples 4, 11 to 13, 16 to 18.

[0094] The longitudinally uniaxially stretched films of Prototypes 20 and 21 are examples in which the discharge amount of the corona treatment was changed compared to the good Prototype 16. In both cases where the discharge amount of the corona treatment was lower (Prototype 20) and higher (Prototype 21) than in Prototype 16, the heat seal initiation temperature and anti-fogging properties were good.

[0095] The longitudinally uniaxially stretched films of Samples 22 and 23 are examples in which Resin B1 (low-density polyethylene) or Resin C1 (high-density polyethylene) was used in place of Resin A1 (linear low-density polyethylene) in the heat-seal layer of Sample 4, which was a good product. In Sample 22, the heat-seal strength did not reach 3N when measuring the heat-seal initiation temperature, making it impossible to measure. In Sample 23, the heat-seal initiation temperature could not be prevented from increasing, and the anti-fogging properties were also insufficient.

[0096] The longitudinally uniaxially stretched film of Prototype Example 24 is an example in which resin D1 (a propylene-ethylene random copolymer different from resin D2) was used in place of resin D2 (propylene-ethylene random copolymer) in the heat seal layer of the good Prototype Example 4. In Prototype Example 24, which used resin D1, it was not possible to sufficiently suppress the heat seal initiation temperature from increasing. Comparing Prototype Examples 4 and 24, resin D1 used in Prototype Example 24 was a propylene-ethylene random copolymer with a higher melting point than resin D2 used in Prototype Example 4.

[0097] The longitudinally uniaxially stretched films of Samples 25, 26, and 27 are examples in which Resin E1, Resin E2, or Resin E3 (propylene-ethylene-butene random copolymer) was used in place of Resin D2 (propylene-ethylene random copolymer) in the heat seal layer of Sample 4, which was a good product. Sample 25, which used Resin E1, did not achieve sufficient anti-fogging properties, but Samples 26 and 27 had good heat seal initiation temperatures and anti-fogging properties. Comparing Samples 26 and 27 with Sample 25, Resin E1 used in Sample 25 was a propylene-ethylene-butene random copolymer with a higher melting point than Resins E2 and E3 used in Samples 26 and 27.

[0098] The longitudinally uniaxially stretched film of Sample 28 is an example in which Resin D2 and Resin E2 were used in place of Resin D2 (propylene-ethylene random copolymer) in the heat seal layer of Sample 4, which was a good product. Sample 28 had good heat seal initiation temperature and anti-fogging properties.

[0099] The longitudinally uniaxially stretched films of Samples 29 and 30 are examples in which either Resin F2 (propylene homopolymer) or Resin G1 (propylene-ethylene block copolymer) was used in place of Resin D2 (propylene-ethylene random copolymer) in the heat seal layer of Sample 4, which was a good product. Sample 29, which used Resin F2, was unable to prevent the heat seal initiation temperature from increasing, and the anti-fogging properties were also insufficient. Sample 30, which used Resin G1, was good in both heat seal initiation temperature and anti-fogging properties.

[0100] As can be seen from Examples 2 to 10, 22, and 23, the preferred blend ratio of the resin in the heat-seal layer is at least 50% by weight of linear low-density polyethylene, including 100% by weight of linear low-density polyethylene. Furthermore, as can be seen from Examples 24 to 30, when the heat-seal layer is not 100% by weight of linear low-density polyethylene, the other resin constituting the heat-seal layer is preferably selected from at least one of a propylene-ethylene random copolymer or a propylene-ethylene-butene random copolymer, each having a melting point of less than 135°C, or a propylene-ethylene block copolymer.

[0101] As can be seen from Examples 11 to 21, the preferred conditions for the linear low-density polyethylene used in the heat-sealing layer are a melt flow rate (MFR) of 1 to 10 g / 10 min, measured at 190°C under a load of 2.16 kg, and a density of 0.860 to 0.935 g / cm. 3 It is thought that this is the case.

[0102] The longitudinally uniaxially stretched film of Prototype Example 1 consists of two layers, a base layer and a heat seal layer, and does not have a surface layer, but is otherwise constructed in the same manner as Prototype Example 4. Since the heat seal initiation temperature and anti-fogging performance of Prototype Example 1 are the same as those of Prototype Example 4, it is thought that if the base layer and heat seal layer have similar configurations, the heat seal initiation temperature and anti-fogging performance of the two-layer film and the three-layer film will be the same.

[0103] As explained above, the longitudinally uniaxially stretched film of the present invention can appropriately suppress an increase in the heat-seal initiation temperature even when subjected to a corona treatment for anti-fogging on the heat-sealed surface, and therefore, even when heat-setting is performed using a heated roll, the film can be prevented from melting and sticking to the heated roll, thereby suppressing the occurrence of poor appearance due to peel marks. Furthermore, the longitudinally uniaxially stretched film of the present invention can obtain good anti-fogging properties. Therefore, even when subjected to a corona treatment for imparting anti-fogging properties on the heat-sealed surface, a polyolefin-based longitudinally uniaxially stretched film having practical heat-sealing properties can be obtained. [Industrial Applicability]

[0104] As described above, the polyolefin-based longitudinal uniaxially stretched film of the present invention appropriately suppresses the heat-sealing initiation temperature from increasing too high and has good anti-fogging properties, making it highly practical and promising as a replacement for conventional polyolefin-based longitudinal uniaxially stretched films. [Explanation of symbols]

[0105] 10 Polyolefin-based longitudinal uniaxially stretched film 20 Base material layer 30 Heat seal layer 40 Surface layer 50 Film forming machine 51 Preheating section 52 Stretching section 53 Heat setting section F,F1 film Fr film roll R, R1, R2 roll

Claims

1. It consists of at least two layers, with a base layer mainly made of polypropylene resin and a heat seal layer laminated on one side of the base layer, An anti-fogging agent is contained in either the base layer or the heat seal layer, stretched in the machine direction by roll-to-roll stretching, A polyolefin-based longitudinal uniaxially stretched film in which the heat seal layer has been subjected to a corona treatment and the wet tension of the surface of the heat seal layer is 32 mN / m or more, the heat seal layer contains at least 50% by weight of a linear low-density polyethylene (A) and a polypropylene-based resin (B), The linear low-density polyethylene (A) has a melt flow rate of 1 to 10 g / 10 min measured at 190° C. under a load of 2.16 kg, and a density of 0.860 to 0.935 g / cm 3 and The polypropylene-based resin (B) is selected from at least one of a propylene-ethylene random copolymer and a propylene-ethylene-butene random copolymer, each having a melting point of less than 135°C, and a propylene-ethylene block copolymer; The heat seal initiation temperature between the heat seal layers is 155°C or less. A polyolefin-based longitudinal uniaxially stretched film characterized by:

2. The polyolefin-based longitudinal uniaxially stretched film according to claim 1, wherein a surface layer is laminated on the other side of the base layer.

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