JP7196427B2 - Laminated film and square bottom bag - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminated film and a square-bottom bag using a plant-derived resin.

In recent years, with the aim of reducing the environmental impact, studies have been made to replace some of the materials that make up the resin film used for packaging materials from fossil fuel-derived resins such as petroleum with plant-derived resins (for example, patent References 1 and 2).
Although plant-derived resins are highly environmentally friendly, they often exhibit different properties from fossil fuel-derived resins. Therefore, if some of the materials constituting the resin film are simply replaced with a plant-derived resin, the intended properties of the resin film may not be obtained.

JP 2012-167172 A JP 2013-151623 A

In particular, in the resin film (laminated film) used for making square-bottom bags, the V-seal strength at the V-seal portion becomes too high while maintaining a high weld-cut seal strength at the side portion (i.e., the V-seal portion too low releasability) must be avoided.

The problem to be solved by the present invention is to achieve the desired characteristics while using a plant-derived resin, and to maintain high weld-cut seal strength at the side portions even when square-bottomed bags are made. Another object of the present invention is to provide a laminate film that can prevent the V-seal portion from becoming too high in V-seal strength, and to provide a square-bottom bag using (bag-making) such a laminate film.

The present invention provides a laminated film used for making a square-bottom bag, comprising a laminated surface layer (A), an intermediate layer (B) and a seal layer (C), wherein the surface layer ( A) contains plant-derived low-density polyethylene, and the intermediate layer (B) and the seal layer (C) each contain a propylene-based resin to solve the above problems.

Although the laminated film of the present invention uses a plant-derived resin, it has the desired properties, and therefore can be an environmentally friendly film. In particular, the laminated film of the present invention can prevent the V-sealing strength of the V-sealing portion from becoming too high while maintaining high fusion-cut sealing strength of the side portions even when the bag is made into a square-bottomed bag. , bread, etc., can be suitably used for packaging.

Hereinafter, the laminated film and square bottom bag of the present invention will be described in detail based on preferred embodiments.
The laminated film of the present invention is a film used for making square bottom bags. This laminated film has at least a surface layer (A), an intermediate layer (B) and a seal layer (C), one surface layer being the surface layer (A) and the other surface layer being the seal layer (C). .
In the present invention, the surface layer (A) contains plant-derived low-density polyethylene (hereinafter referred to as "bio-low-density polyethylene"), and the intermediate layer (B) and the seal layer (C) each contain propylene. Contains system resin.

Here, the square-bottom bag is a bag (V-cut bag) manufactured in the following manner. First, after folding the laminated film in half with the seal layer (C) on the inside, the inside of the fold is folded back to form a double-folded bottom. Next, both isosceles right-angled triangles having the inner fold as the vertex and the outer fold as the base of the double-folded bottom are fused and bonded together. After that, it is fused and adhered perpendicular to the flow direction through the vertices of the isosceles right triangle. Hereinafter, the fusion bond formed along both isosceles is also referred to as a "V-seal portion", and the fusion bond formed perpendicular to the flow direction is also referred to as a "side portion".

When making a square bottom bag, the surface layers (A) are arranged to face each other in the portion from the outer fold to the inner fold of the double-fold bottom, and the seal layers (C) are arranged to face each other in the other portions, In this state, a V-seal portion and side portions are formed. At this time, the adhesive strength between the seal layers (C) (hereinafter referred to as "fusion seal strength") must be sufficiently high, while the square-bottom bag can be converted from a folded form into a bag form. In the V-seal portion, the adhesive strength between the surface layers (A) or between the surface layer (A) and the intermediate layer (B) (hereinafter referred to as "V-seal strength") must be kept sufficiently low. .

In the present invention, the surface layer (A) contains bio-low-density polyethylene, and the intermediate layer (B) and the seal layer (C) each contain a propylene-based resin, thereby increasing the weld-cut seal strength and V-seal. Intensity can be kept low. This is because the affinity (compatibility) between ethylene-based resin (bio-low-density polyethylene) and propylene-based resin is low, and the affinity (compatibility) between propylene-based resins is high. Therefore, bio-low-density polyethylene can be used at a high usage ratio with respect to the surface layer (A). As a result, it contributes to the reduction of carbon dioxide emissions and can be an environmentally friendly laminated film.

In the laminated film of the present invention, each layer (A) to (C) is designed so as to satisfy the above characteristics.
The structure of each layer (A) to (C) will be described below in order.
[Surface layer (A)]
The surface layer (A) is a layer that constitutes a surface layer when the laminated film is formed into a square-bottom bag (packaging bag), and functions as a printing layer or the like on which printing is applied.
This surface layer (A) contains plant-derived low-density polyethylene (bio-low-density polyethylene).

Bio-low-density polyethylene can be produced by producing a monomer (ethylene) from plants such as sugarcane, corn, and beets, and using a monomer derived from fossil fuels such as petroleum, in the same manner as low-density polyethylene is produced. . The production method is not particularly limited, but a known method (eg, radical polymerization reaction) can be used.
Commercially available products of bio-low density polyethylene include SPB681, SBC818 and STN7006 manufactured by Braskem.

By containing the bio-low-density polyethylene in the surface layer (A), it is possible to prevent or suppress an excessive increase in adhesive strength with the intermediate layer (B) containing a propylene-based resin. As a result, when the laminated film is formed into a square-bottomed bag, the peelability of the V-seal portion can be sufficiently secured.
In particular, the use of bio-low-density polyethylene for the surface layer (A) contributes to the reduction of carbon dioxide emissions, making it possible to provide an eco-friendly laminated film.

The density of the bio-low density polyethylene is preferably 0.93 g/cm ³ or less, more preferably 0.925 g/cm ³ or less. By using bio-low-density polyethylene having such a density, it is possible to obtain a laminated film exhibiting suitable V-sealing properties.

The melt flow rate (MFR) of bio-low-density polyethylene is preferably about 0.1 to 20 g/10 minutes, more preferably about 0.3 to 15 g/10 minutes, and more preferably about 0.5 to 10 g/10 minutes. More preferably, it is about 10 minutes. By using such MFR bio-low-density polyethylene, the fluidity of the materials forming the surface layer (A) and the intermediate layer (B) in a molten state can be brought close to each other, and the film formability and moldability of the laminated film can be improved. Decrease can be suppressed. Therefore, the transparency of the resulting laminated film is less likely to be lowered. Further, by setting the MFR to 3 g/10 min or more, particularly high transparency can be easily obtained, and by setting the MFR to 5 g/10 min or less, a particularly suitable V seal strength can be easily obtained. preferable.
In this specification, the MFR is measured in accordance with JIS K 7210:1999 under the conditions of a temperature of 230° C. and a load of 21.18 N.

The content of bio-low-density polyethylene in the resin component contained in the surface layer (A) is preferably as large as possible from the viewpoint of improving environmental friendliness. Specifically, the content of bio-low-density polyethylene is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and substantially 100% by mass. % by mass.
Bio-low density polyethylene may be used in combination with other ethylene-based resins derived from fossil fuels. From the viewpoint of imparting the above-described properties to the laminated film, it is preferable that the other ethylene-based resin is also low-density polyethylene. The density and MFR of this fossil fuel-derived low-density polyethylene are also preferably similar to those described above.

The surface layer (A) may be composed only of a resin containing bio-low-density polyethylene, or may contain various additives within a range that does not impair the effects of the present invention. Examples of such additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, and pigments.

The coefficient of friction of the surface of the surface layer (A) as defined in ASTM D 1894-95 is preferably about 0.05 to 0.7, more preferably about 0.07 to 0.6, More preferably, it is about 0.1 to 0.5. By setting the coefficient of friction within the above range, it becomes easy to improve film feedability during packaging, alignment after bag making, packing workability, and the like. In addition, it becomes easy to favorably suppress film breakage during bundling with a closure. The coefficient of friction can be adjusted by appropriately adding additives such as lubricants and anti-blocking agents depending on the resin component used in the surface layer (A).

[Intermediate layer (B)]
The intermediate layer (B) is a layer having a function of imparting properties required for making square-bottom bags and properties required for square-bottom bags to the laminated film.
This intermediate layer (B) contains a propylene-based resin. By containing the propylene-based resin, it is possible to provide the laminated film with good heat-sealing properties, suitable fusion-cut sealing properties in a wide temperature range, as well as suitable impact resistance and bag breakage resistance. .

The content of the propylene-based resin in the resin component contained in the intermediate layer (B) is preferably 60% by mass or more because it facilitates imparting suitable fusion-cut sealability and bag-making suitability to the laminated film. It is preferably 70% by mass or more, more preferably 80% by mass or more. The upper limit is not particularly limited, but when other resins are used in combination, the content is preferably 92% by mass or less, more preferably 90% by mass or less.
In addition, when other resins are not used in combination, the content of the propylene-based resin may be substantially 100% by mass.

When the laminated film is used as a transparent film, the propylene-based resin preferably contains at least one of a propylene homopolymer and a propylene-α-olefin random copolymer.

The MFR of the propylene homopolymer is not particularly limited as long as a laminated film can be formed, and is preferably 0.5 g/10 minutes or more, more preferably 2 g/10 minutes or more, More preferably, it is 10 minutes or longer. In order to obtain good moldability of the laminated film, the MFR is preferably 20 g/10 minutes or less, more preferably 15 g/10 minutes or less, and 10 g/10 minutes or less. More preferred.

The density of the propylene homopolymer is preferably about 0.88-0.92 g/cm ³ , more preferably about 0.885-0.915 g/cm ³ .
The melting point of the propylene homopolymer is preferably 145° C. or higher, more preferably 150° C. or higher, from the viewpoint of sufficiently maintaining processability of the laminated film such as bag making.

The content of the propylene homopolymer in the resin component contained in the intermediate layer (B) is preferably 55% by mass or more because it easily imparts suitable rigidity and transparency to the laminated film. It is more preferably 60% by mass or more, and even more preferably 65% by mass or more. In addition, since it is easy to impart suitable impact resistance to the laminated film, the content is preferably 85% by mass or less, more preferably 80% by mass or less, and further preferably 75% by mass or less. preferable.

The MFR of the propylene-α-olefin random copolymer is not particularly limited as long as the laminated film can be formed. More preferably, it is 5 g/10 minutes or more. In order to obtain good moldability of the laminated film, the MFR is preferably 20 g/10 minutes or less, more preferably 15 g/10 minutes or less, and even more preferably 12 g/10 minutes or less. .

The density of the propylene-α-olefin random copolymer is preferably about 0.88-0.905 g/cm ^{3 , more preferably about 0.89-0.9 g/cm 3 .}
The melting point of the propylene-α-olefin random copolymer is preferably 110° C. or higher, more preferably 115° C. or higher, from the viewpoint of preventing adhesion to the fusion seal blade during bag making. In addition, the melting point is preferably 150° C. or less, because sufficient fusion ball formation is necessary in order to develop a suitable fusion sealability for the laminated film during fusion sealing during bag making. °C or less is more preferable.

The α-olefin content in the propylene-α-olefin random copolymer is not particularly limited, but is preferably about 1 to 20% by mass, more preferably about 1.5 to 15% by mass.

Such propylene-α-olefin random copolymers include, for example, propylene-ethylene random copolymers, propylene-1-butene random copolymers, propylene-ethylene-1-butene random copolymers, and the like. These may be used individually by 1 type, or may use multiple types together. Among them, it is preferable to use a propylene-ethylene random copolymer as the propylene-α-olefin random copolymer because it is easy to impart suitable transparency to the laminated film.

The content of the propylene-α-olefin random copolymer in the resin component contained in the intermediate layer (B) tends to impart suitable bag-making aptitude and bag-breakage resistance to the laminated film. It is preferably 10% by mass or more, more preferably 15% by mass or more. Also, the content thereof is preferably 30% by mass or less, more preferably 25% by mass or less.

On the other hand, when the laminated film is a matte film, the propylene-based resin preferably contains a propylene-α-olefin block copolymer. The propylene-α-olefin block copolymer may be used alone or in combination of multiple types.
The MFR of the propylene-α-olefin block copolymer is preferably 0.5 g/10 minutes or more because the laminate film has good moldability and is easy to impart suitable impact resistance and matte feeling. It is preferably 1 g/10 minutes or more, and more preferably. Also, the MFR is preferably 20 g/10 minutes or less, more preferably 10 g/10 minutes or less.

The melting point of the propylene-α-olefin block copolymer is preferably 155° C. or higher, more preferably 165° C. or lower, since it facilitates imparting suitable bag-making properties to the laminated film.
In addition, since it is easy to impart matte feeling, fusion sealability and bag-making suitability to the laminated film with an excellent balance, commercial products of propylene-α-olefin block copolymers include, for example, BC8 and BC7 (either Also available from Japan Polypropylene), E150GK, F704V (all from Prime Polymer), PC480A, PC684S, PC380A, VB370A (all from SunAllomer) and the like can be preferably used.

Such an intermediate layer (B) may further contain a plant-derived polyethylene (b1). By including the polyethylene (b1) in the intermediate layer (B), it is possible to increase the usage ratio of the plant-derived resin (hereinafter also referred to as "biological content") in the laminated film. As a result, the environmental friendliness of the laminated film can be further improved.
Examples of polyethylene (b1) include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), linear medium density polyethylene (LMDPE), high density polyethylene (HDPE), Linear high density polyethylene (LHDPE) and the like are included. These may be used individually by 1 type, or may use multiple types together. Among them, low-density polyethylene is preferable as the polyethylene (b1).

The low-density polyethylene used for the surface layer (A) can be preferably used as the low-density polyethylene as the polyethylene (b1). The preferred ranges of MFR, density, melting point, etc. are also the same as those of bio-low-density polyethylene.
If bio-low-density polyethylene is used as the polyethylene (b1), the surface layer (A) also contains bio-low-density polyethylene. Obtainable. As a result, it is possible to prevent the surface layer (A) from unintentionally peeling off from the intermediate layer (B).

The content of polyethylene (b1) in the resin component contained in the intermediate layer (B) is preferably 3% by mass or more, more preferably 5% by mass or more. By containing the polyethylene (b1) in such a range, it becomes easier to contribute to the improvement of the biometrics of the laminated film. In addition, although the upper limit is not particularly limited, it is preferably 30% by mass or less because it is easy to prevent or suppress an extreme decrease in properties such as fusion sealability, impact resistance, and bag breakage resistance of the laminated film. It is preferably 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less.
In particular, it is possible to prevent a large deviation in the fluidity of the materials forming the surface layer (A) and the intermediate layer (B) in a molten state, and to prevent deterioration of the transparency of the resulting laminated film.

The intermediate layer (B) may further contain polyethylene (b2) derived from fossil fuels. Since the propylene-based resin used for the intermediate layer (B) is also a fossil fuel-derived resin, the polyethylene (b2) has a high affinity (compatibility) with the propylene-based resin. Therefore, when the polyethylene (b1) is used together, the presence of the polyethylene (b2) facilitates uniform mixing of the polyethylene (b1) and the propylene-based resin. As a result, the properties of the intermediate layer (B) can be made uniform.

Examples of polyethylene (b2) include ethylene-based homopolymers, ethylene-based copolymers, ionomers of ethylene-(meth)acrylic acid copolymers, and the like. These may be used individually by 1 type, or may use multiple types together.
Ethylene-based homopolymers include, for example, linear low-density polyethylene (LLDPE), linear medium-density polyethylene (LMDPE), linear high-density polyethylene (LHDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high density polyethylene (HDPE).

Examples of ethylene copolymers include ethylene-butene-rubber copolymer (EBR), ethylene-propylene-rubber copolymer (EPR), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate. copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene- acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), and the like.

Among them, the polyethylene (b2) is preferably linear low-density polyethylene. By using linear low-density polyethylene as the polyethylene (b2), the impact resistance of the laminated film can be further improved.
The MFR of linear low-density polyethylene is preferably 10 g/10 minutes or less, more preferably about 1 to 5 g/10 minutes. By using such a linear low-density polyethylene with MFR, the film-forming properties of the laminated film can be easily improved, and the polyethylene (b2) has good dispersibility in the intermediate layer (B). On the other hand, it becomes easier to impart uniform characteristics.

The density of the linear low-density polyethylene is preferably 0.915 g/cm ³ or less, more preferably 0.91 g/cm ^{3 or less, even more preferably 0.906 g/cm 3 or} less. . By using a linear low-density polyethylene having such a density, it becomes easier to impart suitable fusion-cut sealability, high impact resistance, and high bag-breakage resistance to the laminated film.
The content of polyethylene (b2) in the resin component contained in the intermediate layer (B) is preferably about 5-20% by mass, more preferably about 5-15% by mass. By containing the polyethylene (b2) in such a range, it is possible to impart suitable bag-making aptitude, fusion-cut sealability, and excellent bag breakage resistance to the laminated film.

The intermediate layer (B) may be composed only of a resin containing a propylene-based resin, or may contain various additives as long as the effects of the present invention are not impaired. Examples of such additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, and pigments.

[Seal layer (C)]
The sealing layer (C) is a layer that is adhered when the laminated film is made into a square bottom bag.
This seal layer (C) contains a propylene-based resin. By containing the propylene-based resin, high adhesion between the sealing layer (C) and the intermediate layer (B) can be obtained.

The content of the propylene-based resin in the resin component contained in the seal layer (C) is preferably 50% by mass or more because it facilitates imparting suitable fusion-cut sealability and bag-making aptitude to the laminated film. It is preferably 70% by mass or more, more preferably 90% by mass or more, and may be substantially 100% by mass.

The laminated film is formed into a square-bottomed bag by sealing (adhering) the sealing layers (C) to each other. For this reason, the propylene-based resin preferably contains a propylene-α-olefin random copolymer from the viewpoint of imparting an appropriate fusion-cut sealing property to the laminated film.
Propylene-α-olefin random copolymers include, for example, propylene-ethylene random copolymers and propylene-1-butene random copolymers. These may be used individually by 1 type, or may use multiple types together.
The propylene-ethylene random copolymer is the same as the propylene-ethylene random copolymer described for the intermediate layer (B).

The 1-butene content in the propylene-1-butene random copolymer is preferably about 60 to 95 mol% because it facilitates imparting suitable fusion-cut sealability and blocking resistance to the laminated film. , about 65 to 95 mol %, more preferably about 70 to 90 mol %. Further, the propylene content in the copolymer is preferably about 2 to 10 mol%, more preferably about 3 to 9 mol%, because it is easy to impart suitable low-temperature sealing properties to the sealing layer (C). and more preferably about 4 to 8 mol %.

The content of the propylene-1-butene random copolymer in the resin component contained in the sealing layer (C) is preferably 50% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass. More preferably: Moreover, the content thereof is preferably 10% by mass or more, more preferably 15% by mass or more. If the content of the propylene-1-butene random copolymer is set within the above range, it is easy to impart suitable low-temperature sealability, fusion-cut sealability and tear resistance to the laminated film, and also to reduce costs. Advantageous.

The sealing layer (C) may also contain a plant-derived polyolefin (for example, a plant-derived low-density polyethylene as described above). From the viewpoint of improving the bio-efficiency, the content of the plant-derived polyolefin in the resin component contained in the seal layer (C) is preferably 10% by mass or more, more preferably about 20 to 50% by mass. preferable.
On the other hand, when the characteristics of the laminated film such as fusion-cut sealability and impact resistance are emphasized, the content of the plant-derived polyolefin is preferably less than 10% by mass, more preferably less than 5% by mass. , is more preferably substantially 0% by mass.

The seal layer (C) may be composed only of a resin containing a propylene-based resin, or may contain various additives within a range that does not impair the effects of the present invention. Examples of such additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, and pigments.

The coefficient of friction of the surface of the seal layer (C) as defined in ASTM D 1894-95 is preferably about 0.01 to 0.4, more preferably about 0.02 to 0.35. More preferably, it is about 0.05 to 0.3. By setting the coefficient of friction within the above range, it becomes easier to improve the film feedability during packaging and the workability of packaging work by suppressing wrinkles and swelling after bag making.

In addition, even if the inner surface of the laminated film (the surface of the seal layer (C)) rubs against the inner surface of the laminated film when the contents such as bread are filled, the occurrence of scratches can be suppressed. Furthermore, it is easy to impart wear resistance and tear resistance to the laminated film, and it is possible to suitably suppress film tearing. The coefficient of friction can be adjusted by appropriately adding additives such as lubricants and anti-blocking agents depending on the resin component used in the sealing layer (C).

[Laminated film]
The laminated film of the present invention is a laminated film used for making square-bottomed bags, comprising a surface layer (A) containing bio-low-density polyethylene, an intermediate layer (B) containing a propylene-based resin, and propylene Contains system resin. The laminated film having this configuration can realize good opening properties of the V-seal portion while maintaining high weld-cut seal strength in the side portion when a square-bottom bag is manufactured, while using a plant-derived resin. In addition, according to the laminated film having such a configuration, it is easy to achieve good weld-cut seal strength, unsealability, and the like even when the use ratio of bio-low-density polyethylene is increased.

The average thickness of the laminated film may be appropriately adjusted according to the application and mode of the square-bottomed bag to be manufactured. About 50 μm is preferable, and about 30 to 45 μm is more preferable.
The proportion of each layer in the thickness of the laminated film and the specific thickness of each layer are not particularly limited, but can be set as follows.

The proportion of the surface layer (A) is preferably about 1 to 10%, more preferably about 3 to 7%.
The proportion of the intermediate layer (B) is preferably about 70 to 94%, more preferably about 73 to 87%.
The proportion of the sealing layer (C) is preferably about 5 to 20%, more preferably about 10 to 20%.

A specific average thickness of the surface layer (A) is preferably about 0.5 to 5 μm, more preferably about 1 to 4 μm.
A specific average thickness of the intermediate layer (B) is preferably about 5 to 35 μm, more preferably about 10 to 25 μm.
A specific average thickness of the sealing layer (C) is preferably about 1 to 20 μm, more preferably about 5 to 10 μm.

In addition, the content of bio-low-density polyethylene in the resin component contained in the entire laminated film is preferably 20% by mass or more, more preferably 25% by mass or more, from the viewpoint of improving environmental responsiveness. , more preferably 30% by mass or more.

The haze of the laminated film is preferably 10% or less, more preferably 6% or less, and further preferably 4.5% or less because the contents to be packaged are easy to see. preferable. Even when the laminated film has such high transparency, it is difficult for the bag to break due to friction or rubbing between the contents and the film, although the laminated film has suitable packaging properties.

In order to improve the transparency of the laminated film, it is preferable not to use a resin such as a block copolymer that causes an increase in haze, or to minimize the amount of resin used in each layer. In this case, the content of the block copolymer in the resin component contained in the entire laminate film is preferably 10% by mass or less, more preferably 5% by mass or less.

The laminated film of the present invention may have any resin layer other than the surface layer (A), intermediate layer (B) and sealing layer (C). However, the thickness of the other resin layers is preferably 20% or less of the total thickness (total thickness) of the laminated film. In particular, it is preferable that the laminated film consist of only the surface layer (A), the intermediate layer (B) and the sealing layer (C) as described above. Furthermore, in such a structure, the intermediate layer (B) may be composed of a laminated body in which a plurality of layers are laminated.

As an example of a specific layer structure, an intermediate layer (B) is provided between the surface layer (A) and the seal layer (C): surface layer (A)/intermediate layer (B)/seal layer (C) or a four-layer structure of surface layer (A)/intermediate layer (B1)/intermediate layer (B2)/seal layer (C) in which the intermediate layer (B) is a laminate. Among them, a three-layer structure consisting of surface layer (A)/intermediate layer (B)/seal layer (C) is preferable because it facilitates adjustment of the properties of the laminated film and production of the laminated film.

A method for producing the laminated film is not particularly limited, but for example, a coextrusion method can be used. In the co-extrusion method, the resins or resin mixtures used for each layer are heated and melted in separate extruders, and laminated in a molten state by a method such as a co-extrusion multilayer die method or a feed block method. - Obtain a laminated film by molding into a film by a chill roll method or the like.
According to the co-extrusion method, it is possible to relatively freely adjust the thickness ratio of each layer, and it is possible to obtain a laminated film excellent in sanitation and cost performance.
In addition, since the laminated film obtained by the above manufacturing method is obtained as a substantially non-stretched multilayer film, secondary forming such as deep drawing forming by vacuum forming is also possible.

It is also preferable to subject the surface of the surface layer (A) to a surface treatment in order to improve adhesion (adhesiveness) of the printing ink. Such surface treatments include, for example, corona discharge treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, surface oxidation treatment such as ozone/ultraviolet treatment, and surface roughening treatment such as sandblasting. can be done. These treatments may be used singly or in combination of multiple kinds. Among them, corona discharge treatment is preferable as the surface treatment.

The surface energy of the surface layer (A) after surface treatment is preferably 35 mN/m or more, more preferably 40 mN/m or more, and may be about 42 to 44 mN/m. On the surface of the surface layer (A) having such surface energy, even an ink containing a plant-derived component with poor adhesion to the resin surface (so-called botanical ink) is adhered (printed) with high adhesion. )be able to.
On the other hand, when the surface layers (A) having surfaces with high surface energy are adhered to each other, the adhesion strength tends to decrease. For this reason, such a laminated film is not suitable for making gusset bags that require high adhesive strength (fusion-cut seal strength) between the surface layers (A), but peeling at the interface between the surface layers (A) It is preferable for making square-bottomed bags that allow
The surface energy can be measured by the wet tension test method specified in JIS K 6768.

The square-bottom bag made of the laminated film of the present invention can be used for packaging (storing) foods, medicines, industrial parts, miscellaneous goods, magazines, and the like.
In the case of a packaging bag for loaf of bread, a rectangular bottom bag having a V-seal portion can be obtained by folding and sealing the printed surface. Specifically, a square-bottomed bag is made with a bag-making machine (for example, "HK-40V" manufactured by Totani Giken Kogyo Co., Ltd.) so that the seal layer (C) of the laminated film of the present invention is on the inside of the bag. processed into

The laminated film of the present invention can be used particularly preferably for making square-bottomed bags because it exhibits suitable fusion-cut sealability and suitability for making bags.
The weld-cut seal strength of the side portion is preferably 13 N/15 mm or more, more preferably 14 N/15 mm or more, still more preferably 14.5 N/15 mm or more, and 16 N/15 mm or more. Especially preferred. Although the upper limit is not particularly limited, it is preferably 30 N/15 mm or less. On the other hand, the V seal strength of the V seal portion is preferably 3 N/15 mm or less, more preferably 2.5 N/15 mm or less, and even more preferably 2 N/15 mm or less. The fusion seal strength and the V-seal strength can be set by adjusting the fusion seal temperature and the bag-making speed during bag making.

Since the laminated film of the present invention can easily obtain suitable scratch resistance and bag breakage resistance, its rigidity (MD) is preferably 450 MPa or more, more preferably 550 MPa or more, and 600 MPa or more. is more preferred. The stiffness is measured by measuring the 1% tangential modulus of the obtained laminated film at 23° C. based on ASTM D 882-12 using a Tensilon tensile tester (manufactured by A&D Co., Ltd.).

Since the laminated film of the present invention can easily suppress bag breakage and leakage of contents when used as a packaging material, the impact strength is preferably 0.10 J or more, more preferably 0.15 J or more. is more preferable, and 0.20 J or more is even more preferable. The impact strength is measured by the film impact method using a spherical metal impact head with a diameter of 1.5 inches after holding the laminated film in a thermostatic chamber set at 0° C. for 6 hours.

The obtained square bottom bag is supplied to an automatic loaf bread filling machine, and after filling with loaf bread, it is heat-sealed so as to be easy to open. The heat seal strength at this time is preferably about 0.1 to 5 N/15 mm, more preferably about 0.2 to 4 N/15 mm.
After that, if necessary, the top of the bag may be tied using a tie such as a plastic plate, tape, string, or the like.

When the laminated film of the present invention is applied to bread packaging such as loaves of bread and sweet buns in which a closure having a sharp tip or hook is used, the bag is less likely to break during binding and can be transported. Pinholes and tears are less likely to occur even when contact with a binding tool or a transport container occurs. In addition, pinholes and tears are less likely to occur due to rubbing between food, which is the content, and the inner surface (seal surface) of the film, friction with a mixed plastic tray, piercing, and the like. Furthermore, the laminated film of the present invention can ensure a suitable weld-cut seal strength even when the V-seal portion and the side portion are formed, so it is preferably applied to square-bottom bags used for bread packaging.

Although the laminated film and square-bottom bag of the present invention have been described above, the present invention is not limited to the above-described embodiments.
For example, the laminated film and the square-bottom bag of the present invention may be partially replaced with other structures exhibiting similar functions, or may be added with arbitrary structures.

EXAMPLES Next, the present invention will be described in more detail with reference to examples and comparative examples. Hereinafter, "parts" and "%" are based on mass unless otherwise specified.
1. Preparation of laminated film (Example 1)
First, materials for forming the surface layer, the intermediate layer, and the seal layer were prepared using the following resins.

Next, these resin mixtures were supplied to each of three extruders and co-extruded to form a laminated film having a three-layer structure of surface layer/intermediate layer/seal layer. The average thickness of the surface layer was 1.5 μm, the average thickness of the intermediate layer was 23.5 μm, and the average thickness of the seal layer was 5 μm. Therefore, the average thickness of the laminated film as a whole is 30 μm.
After that, the surface of the obtained laminated film (surface layer) was subjected to corona discharge treatment so that the surface energy was 36 mN/m.

[Material for forming surface layer]
・ Low-density polyethylene derived from sugar cane (bio LDPE (1)): 100 parts Product name: “SPB681” manufactured by Braskem
Density: 0.922g/ ^cm3
MFR: 3.8 g/10 minutes

[Material for Intermediate Layer]
・Propylene homopolymer (HOPP): 70 parts Density: 0.90 g/cm ³
MFR: 7.5 g/10 minutes Propylene-ethylene random copolymer (COPP (1)): 20 parts Ethylene content: 5.2%
Density: 0.90g/ ^cm3
MFR: 5.4 g/10 minutes Linear low-density polyethylene (LLDPE): 10 parts Density: 0.905 g/cm ³
MFR: 4.0 g/10 minutes

[Material for Forming Sealing Layer]
・COPP (1): 70 parts ・Propylene-1-butene random copolymer (COPP (2)): 30 parts Density: 0.995 g/cm ³
MFR: 4 g/10 minutes

(Example 2)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 67 parts, COPP (1): 20 parts, LLDPE: 10 parts, Bio LDPE (1): 3 parts

(Example 3)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 65 parts, COPP (1): 20 parts, LLDPE: 10 parts, Bio LDPE (1): 5 parts

(Example 4)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 65 parts, COPP (1): 17 parts, LLDPE: 10 parts, Bio LDPE (1): 8 parts

(Example 5)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 65 parts, COPP (1): 15 parts, LLDPE: 8 parts, Bio LDPE (1): 12 parts

(Example 6)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 62 parts, COPP (1): 12 parts, LLDPE: 6 parts, Bio LDPE (1): 20 parts

(Example 7)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the intermediate layer was changed as follows.
HOPP: 55 parts, COPP (1): 10 parts, LLDPE: 10 parts, Bio LDPE (1): 25 parts

(Example 8)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the surface layer was changed as follows.
- Sugarcane-derived low-density polyethylene (bio LDPE (2)): 100 parts Product name: "STN7006" manufactured by Braskem
Density: 0.924g/ ^cm3
MFR: 0.6 g/10 minutes

(Example 9)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the surface layer was changed as follows.
- Sugarcane-derived low-density polyethylene (bio LDPE (3)): 100 parts Product name: "SBC818" manufactured by Braskem
Density: 0.922g/ ^cm3
MFR: 8.1 g/10 minutes

(Reference example 1)
A laminated film was obtained in the same manner as in Example 1, except that the composition of the material for forming the surface layer was changed as follows.
・Fossil fuel-derived low-density polyethylene (LDPE): 100 parts Density: 0.920 g/cm ³
MFR: 5.0 g/10 minutes

2. Measurement and Evaluation Using the laminated films obtained in Examples and Reference Examples, the following measurements and evaluations were performed.

[Measurement of stiffness]
The 1% tangential modulus at 23° C. of the laminated films obtained in Examples and Reference Examples was measured according to ASTM D 882-12 using a Tensilon tensile tester (manufactured by A&D Co., Ltd.).
The measurement was carried out in the extrusion direction (hereinafter referred to as "MD direction") during film production.

[Transparency measurement]
The haze of the laminated films obtained in Examples and Reference Examples was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd.) based on JIS K 7105:1981.

[Evaluation of bag-making aptitude]
After folding the laminated film in half with the sealing layer of the laminated film obtained in Examples and Reference Examples facing inside, a gusset was put in the bottom, and the V-sealing temperature was 320°C and the sealing part temperature (bag making temperature) was 298°C. to form a bag (bag-making machine: "HK-40V" manufactured by Totani Giken Factory Co., Ltd., bag-making speed: 120 sheets/min). Thus, a square bottom bag (length: 345 mm (side portion: 245 mm, gusset portion: 60 mm), width: 235 mm) was produced, and bag-making aptitude was evaluated. Also, 300 sheets were taken as one set, and the sheets were aligned and bundled together to evaluate the alignment property.

<Evaluation Criteria>
◯: Even at a bag-making speed of 120 shots, the laminated film follows, and there is no problem in evenness.
Δ: Even at a bag-making speed of 120 shots, the laminated film follows, but there is a problem in the uniformity of partial sticking.
x: Some of the laminated films cannot keep up with the bag-making speed of 120 shots, and the evenness is poor.

[Measurement of V seal strength and fusion seal strength]
After folding the laminated film in half with the seal layer of the laminated film obtained in Examples and Reference Examples facing inside, a gusset was put in the bottom, and the V-sealing temperature was 320°C and the fusion sealing temperature (bag making temperature) was 298°C. to form a bag (bag-making machine: "HK-40V" manufactured by Totani Giken Factory Co., Ltd., bag-making speed: 120 sheets/min). Thus, a square bottom bag (length: 345 mm (side portion: 245 mm, gusset portion: 60 mm), width: 235 mm) was produced.
From the center of the V-seal portion of the obtained five square-bottom bags (V-cut bags) and the center of the upper side portion of the V-seal portion, one test piece with a width of 15 mm was obtained (2 per bag). sheet), and a total of 10 sheets were cut out so that the seal part was in the central part in the length direction. Then, each test piece was peeled off with a Tensilon tensile tester (manufactured by A&D Co., Ltd.) under conditions of 23° C. and a tensile speed of 300 mm/min. The maximum load measured at this time was taken as the V-seal strength and the fusion seal strength.

<Evaluation Criteria for Fusion Seal Strength>
⊚: The weld-cutting seal strength of the side portion is 16 N/15 mm or more in all cases.
◯: The fusion cut seal strength of the side portion is 14.5 N/15 mm or more and less than 16 N/15 mm.
Δ: The fusion-cut seal strength of the side portion is 13 N/15 mm or more and less than 14.5 N/15 mm.
x: The weld-cutting seal strength of the side portion is less than 13 N/15 mm.

<Evaluation Criteria for V Seal Strength>
A: The peel strength of the V-seal portion is 2.0 N/15 mm or less in all cases.
○: The peel strength of the V-seal portion is more than 2.0 N/15 mm and 2.5 N/15 mm or less.
Δ: The peel strength of the V-seal portion is more than 2.5 N/15 mm and 3.0 N/15 mm or less.
x: The peel strength of the V-seal portion is all over 3.0 N/15 mm.

[Measurement of heat seal strength]
Using the laminated films obtained in Examples and Reference Examples, square-bottom bags were produced in the same manner as in the evaluation of bag-making aptitude described above. A heat sealer (manufactured by Tester Sangyo Co., Ltd., pressure: 0.2 MPa, time: 1 second, sealing temperature: upper seal bar 95 °C, lower seal bar 50 °C, seal bar shape: 300m x 10mm plane).
Two test pieces each having a length of 70 mm and a width of 15 mm were prepared from the heat-sealed portions of the obtained five square-bottomed bags (two pieces per bag) so that the heat-sealed portion was the central portion in the width direction. , a total of 10 sheets were cut out. Then, each test piece was peeled off with a Tensilon tensile tester (manufactured by A&D Co., Ltd.) under conditions of 23° C. and a tensile speed of 300 mm/min. The maximum load measured at this time was taken as the heat seal strength.

<Evaluation Criteria>
◯: The heat seal strength was less than 5 N/15 mm for all films, and the film was not torn when peeled off.
x: The heat seal strength was 5 N/15 mm or more, or the film was torn when it was peeled off.

[Measurement of impact strength]
The laminated films obtained in Examples and Reference Examples were kept in a thermostatic chamber set at 0° C. for 6 hours, and then impact strength was measured by the film impact method using a spherical metal impact head with a diameter of 1.5 inches. was measured.
These measurement results and evaluation results are shown in Table 1 below.

As is clear from Table 1, the laminated films of the present invention obtained in the examples exhibited suitable V-seal strength while maintaining high weld-cut seal strength in the side portions even when square-bottomed bags were made. It had.

Claims (15)

A laminated film used for making square bottom bags,
Having a laminated surface layer (A), an intermediate layer (B) and a sealing layer (C),
The surface layer (A) contains plant-derived low-density polyethylene,
The intermediate layer (B) and the sealing layer (C) each contain a propylene-based resin,
A laminated film, wherein the intermediate layer (B) further contains a plant-derived polyethylene (b1) in an amount of 3 to 20% by mass based on the resin component contained in the intermediate layer (B). 2. The laminated film according to claim 1, wherein the content of the propylene-α-olefin random copolymer in the resin component contained in the intermediate layer (B) is 10% by mass or more and 30% by mass or less. The laminated film according to claim 1 or 2, wherein the content of the low-density polyethylene in the resin component contained in the surface layer (A) is 50% by mass or more. The laminated film according to any one of claims 1 to 3, wherein said polyethylene (b1) is low-density polyethylene. Claims 1 to 4, wherein the melt flow rate of the low-density polyethylene measured in accordance with JIS K 7210:1999 is 1 to 7 g/10 minutes under measurement conditions of a temperature of 230°C and a load of 21.18N. The laminated film according to any one of 1. 6. The intermediate layer (B) according to any one of claims 1 to 5, wherein the intermediate layer (B) further contains 5 to 20% by mass of the resin component contained in the intermediate layer (B), containing polyethylene (b2) derived from a fossil fuel. laminated film. 7. The laminated film according to claim 6, wherein said polyethylene (b2) is linear low-density polyethylene. The laminated film according to any one of claims 1 to 7, wherein the content of the propylene-based resin in the resin component contained in the intermediate layer (B) is 60 to 92 mass%. The laminated film according to any one of claims 1 to 8, wherein the propylene-based resin of the intermediate layer (B) contains at least one of a propylene homopolymer and a propylene-α-olefin random copolymer. The laminated film according to any one of claims 1 to 9, wherein the content of the propylene-based resin in the resin component contained in the seal layer (C) is 50% by mass or more. The laminated film according to any one of claims 1 to 10, wherein the propylene-based resin of the seal layer (C) contains a propylene-α-olefin random copolymer. In the thickness of the laminated film, the surface layer (A) accounts for 1 to 20%, the intermediate layer (B) accounts for 60 to 94%, and the seal layer (C) accounts for 5 to 5%. The laminated film according to any one of claims 1 to 11, which is 20%. The laminated film according to any one of claims 1 to 12, wherein the laminated film has an average thickness of 25 to 50 µm. A square-bottom bag using the laminated film according to any one of claims 1 to 13. The square-bottomed bag according to claim 14, which is used for packaging bread.