JP7497801B2 - Heat-sealable laminated film - Google Patents

Description

The present invention relates to a polyolefin-based laminated film, and more specifically, to a laminated film that is suitable for use as a lid material, has excellent impact resistance, particularly when combined with plastic containers, and reduces the environmental impact by using plant-derived resins.

Packaging in which a plastic container in the form of a bottle, cup, or tray is sealed with a lid made of a plastic laminated film is widely used as packaging for various foods such as aseptic cooked rice. Such packaging is required to have mechanical strength to withstand distribution channels, seal strength to maintain hygiene, and ease of opening when used.
As a plastic laminate film to be used as a lid material, a laminate film having a heat-sealing layer containing petroleum-derived low-density polyethylene or the like has been proposed (see, for example, Patent Document 1), but it is known that such a laminate film is excellent in peel strength, etc., but does not necessarily have high impact resistance. Lid materials for plastic containers may be subjected to impacts during handling in the distribution process, and in consideration of use as a lid material, there has been a demand for such laminate films to have a further improved impact resistance.

JP 2007-176056 A

In view of the above technical background, the object of the present invention is to provide a laminated film having a heat-sealing layer containing petroleum-derived low-density polyethylene and the like, which has high impact resistance suitable for use as a lid material for plastic containers while maintaining excellent properties such as heat-sealing properties.

Means for Solving the Problems The inventors of the present invention have, after extensive investigation, found that in a laminate film having a heat-sealing layer, an intermediate layer, and a laminate layer, the impact resistance of the film is significantly improved by adding a predetermined amount of biomass-derived low-density polyethylene and/or biomass-derived linear low-density polyethylene to the heat-sealing layer, thereby achieving the above-mentioned object, and have thus completed the present invention.
That is, the present invention provides:
[1]
A laminated film having (A) a heat-sealing layer, (B) an intermediate layer, and (C) a laminate layer, wherein the (A) heat-sealing layer contains 2 to 6% by mass of (a) a low-density polyethylene derived from biomass;
Regarding.

Below, [2] to [6] are each a preferred aspect or embodiment of the present invention.
[2]
2. The laminated film according to claim 1, wherein the heat of fusion ΔH at 100° C. to 170° C. calculated from a melting curve obtained by DSC measurement is 50 to 87.5 J/g.
[3]
(a) The laminate film according to [1] or [2], wherein the molecular weight distribution Mw/Mn of the biomass-derived low-density polyethylene is 3.5 or more.
[4]
The laminate film according to any one of [1] to [3], wherein the heat-sealing layer (A) further contains a petroleum-derived ethylene polymer.
[5]
The laminate film according to any one of [1] to [4], further comprising a base layer (D) on the side of the laminate layer (C).
[6]
A packaging container comprising a cover material made of the laminated film according to any one of [1] to [5] and a body containing at least one of polypropylene, polyethylene terephthalate, and polybutylene terephthalate.

The laminate film of the present invention maintains the excellent properties of conventional polyolefin-based laminate films, while significantly improving impact resistance, particularly when combined with plastic containers, and reducing the environmental impact of its production, etc. It combines these highly valuable properties at a high level that goes beyond the limits of conventional technology, and can be suitably used in a variety of applications, including as a lid material for plastic containers.

The present invention is a laminated film having (A) a heat-sealing layer, (B) an intermediate layer, and (C) a laminate layer, wherein the (A) heat-sealing layer contains 2 to 6 mass % of (a) a biomass-derived low-density polyethylene.
That is, the laminated film of the present invention contains (a) biomass-derived low-density polyethylene in its (A) heat-sealable layer. The content of (a) biomass-derived low-density polyethylene in the (A) heat-sealable layer is 2 to 6 mass %.

(a) Biomass-derived low-density polyethylene (a) Biomass-derived low-density polyethylene used in the present invention includes both low-density polyethylene obtained by polymerizing ethylene produced using a biomass-derived raw material and linear low-density polyethylene. Either one of the low-density polyethylene and the linear low-density polyethylene may be used, or a mixture of the two may be used.
Here, "low density polyethylene" refers to an ethylene polymer or ethylene copolymer having a density of 910 to 930 kg/ ^m3 .
(a) The biomass-derived low-density polyethylene may be a linear low-density polyethylene or another low-density polyethylene. In the case of a linear low-density polyethylene, it is preferable that the linear low-density polyethylene has 10 to 30 SCBs (side chains having 1 to 5 carbon atoms, also called "short chain branches") per 1,000 carbon atoms.

The density of the (a) biomass-derived low-density polyethylene is preferably 910 to 930 kg/m ³ , more preferably 915 to 925 kg/m ³ .
(a) The MFR of the biomass-derived low-density polyethylene is not particularly limited, but from the viewpoint of moldability, etc., it is preferably 0.5 to 20 g/10 min, more preferably 1.0 to 15.0 g/10 min, and even more preferably 1.5 to 10.0 g/10 min.

(a) There are no particular limitations on the molecular weight distribution of the biomass-derived low-density polyethylene, but from the standpoint of flexibility, moldability, etc., the molecular weight distribution (expressed as the ratio of weight average molecular weight: Mw to number average molecular weight: Mn: Mw/Mn) is preferably 3.5 or more, more preferably 3.7 to 10.0, and even more preferably in the range of 3.8 to 9.0. This Mw/Mn can be measured by gel permeation chromatography (GPC), and more specifically, for example, can be measured by the method described in the examples of this application.

(a) Biomass-derived low-density polyethylene has one or more sharp peaks as determined from an endothermic curve measured with a differential scanning calorimeter (DSC) at a heating rate of 10°C/min, and the maximum temperature of the peak, i.e., the melting point, is preferably in the range of 90 to 140°C, and more preferably in the range of 100 to 130°C.

(a) The biomass-derived low-density polyethylene may be a commercially available product, for example, a product manufactured and sold by Braskem Co., Ltd. A specific example of a suitable brand is SPB681.
The (a) biomass-derived low-density polyethylene used in the present invention is obtained by polymerizing a monomer containing biomass-derived ethylene. The biomass-derived ethylene is preferably obtained by the following production method, but is not limited thereto. Since biomass-derived ethylene is used as the raw material monomer, the polymerized low-density polyethylene is derived from biomass. Note that the raw material monomer for polyethylene does not have to contain 100% by mass of biomass-derived ethylene, and may contain ethylene that is not biomass-derived or raw material monomers other than ethylene.

(a) The method for producing biomass ethylene, which is the raw material for biomass-derived low-density polyethylene, is not particularly limited, and can be obtained by a conventionally known method. An example of a method for producing biomass ethylene is described below.

Biomass ethylene can be produced using biomass-derived ethanol as a raw material. In particular, it is preferable to use biomass-derived fermented ethanol obtained from plant raw materials. There are no particular limitations on the plant raw material, and any conventionally known plant can be used. Examples include corn, sugarcane, beet, and manioc.

In the present invention, the fermented ethanol derived from biomass refers to ethanol produced by contacting a culture solution containing a carbon source obtained from a plant raw material with an ethanol-producing microorganism or a product derived from its crushed material, and then purifying the ethanol. Conventionally known methods such as distillation, membrane separation, and extraction can be applied to purify ethanol from the culture solution. For example, a method of adding benzene, cyclohexane, etc., and removing water by azeotropy or membrane separation can be used.
In order to obtain biomass ethylene, further advanced purification may be carried out at this stage, for example, to reduce the total amount of impurities in the ethanol to 1 ppm or less.

A catalyst is usually used when obtaining ethylene by the dehydration reaction of ethanol, but the catalyst is not particularly limited and any conventionally known catalyst can be used. From the viewpoint of the process, a fixed bed flow reaction is advantageous because it is easy to separate the catalyst from the product, and for example, γ-alumina is preferable.
Since this dehydration reaction is an endothermic reaction, it is usually carried out under heating conditions. As long as the reaction proceeds at a commercially useful reaction rate, the heating temperature is not limited, but is preferably 100° C. or higher, more preferably 250° C. or higher, and even more preferably 300° C. or higher. There is no particular upper limit, but from the viewpoint of energy balance and equipment, it is preferably 500° C. or lower, more preferably 400° C. or lower.
The reaction pressure is not particularly limited, but is preferably equal to or higher than atmospheric pressure in order to facilitate the subsequent gas-liquid separation. From an industrial perspective, a fixed bed flow reaction is preferred because it is easy to separate the catalyst, but a liquid phase suspension bed, a fluidized bed, etc. may also be used.

In the dehydration reaction of ethanol, the yield of the reaction depends on the amount of water contained in the ethanol supplied as a raw material. In general, when performing a dehydration reaction, it is preferable to have no water, considering the efficiency of removing water. However, in the case of the dehydration reaction of ethanol using a solid catalyst, it has been found that the amount of other olefins, especially butene, produced tends to increase if water is not present. This is probably because the presence of a small amount of water makes it difficult to suppress ethylene dimerization after dehydration. The lower limit of the allowable water content is 0.1 mass% or more, preferably 0.5 mass% or more. There is no particular limit to the upper limit, but from the viewpoint of material balance and heat balance, it is preferably 50 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less.

By carrying out the dehydration reaction of ethanol in this manner, a mixture of ethylene, water and a small amount of unreacted ethanol is obtained, but since ethylene is in a gaseous state at room temperature below about 5 MPa, water and ethanol can be removed from this mixture by gas-liquid separation to obtain ethylene. This method may be performed by any known method.
The ethylene obtained by the gas-liquid separation is further distilled. The distillation method, operation temperature, residence time, etc. are not particularly limited, except that the operation pressure at this time is normal pressure or higher.

When the raw material is fermented ethanol derived from biomass, the resulting ethylene contains trace amounts of carbonyl compounds such as ketones, aldehydes, and esters, which are impurities mixed in during the ethanol fermentation process, as well as carbon dioxide, which is their decomposition product, and nitrogen-containing compounds such as amines and amino acids, which are enzyme decomposition products and impurities, as well as ammonia, which is their decomposition product. These trace amounts of impurities may be problematic in the production and use of polyethylene, so they may be removed by purification. The purification method is not particularly limited, and can be performed by a conventionally known method. An example of a suitable purification operation is an adsorption purification method. The adsorbent used is not particularly limited, and conventionally known adsorbents can be used. For example, a material with a high surface area is preferable, and the type of adsorbent is selected depending on the type and amount of impurities in the ethylene obtained by the dehydration reaction of fermented ethanol derived from biomass.

Caustic water treatment may also be used in combination as a method for purifying impurities in ethylene. If caustic water treatment is used, it is preferable to carry it out before adsorption purification. In that case, it is necessary to carry out a moisture removal treatment after the caustic treatment and before adsorption purification.

The monomers that are the raw materials for biomass-derived polyethylene may further contain ethylene and/or α-olefins derived from fossil fuels, or may further contain α-olefins derived from biomass.

The above biomass-derived α-olefins are not particularly limited in the number of carbon atoms, but those with 3 to 20 carbon atoms can usually be used, and butylene, hexene, or octene is preferable. This is because butylene, hexene, or octene can be produced by polymerizing ethylene, which is a raw material derived from biomass. In addition, by including such biomass-derived α-olefins, the polymerized polyolefin has alkyl groups as a branched structure, making it more flexible than a simple linear one.

(a) It is preferable that the biomass-derived low-density polyethylene is an ethylene homopolymer. This is because, by using ethylene, which is a raw material derived from biomass, it is theoretically possible to produce it from components that are 100% derived from biomass.

(a) The biomass-derived ethylene concentration in biomass-derived low-density polyethylene (hereinafter sometimes referred to as "biomass degree") is a value obtained by measuring the content of biomass-derived carbon by radioactive carbon ( ^14C ) measurement. Carbon dioxide in the atmosphere contains a certain proportion of ^14C (105.5 pMC), and it is known that ^{the 14C} content in plants that grow by absorbing carbon dioxide from the atmosphere, such as corn, is also about 105.5 pMC. It is also known that fossil fuels contain almost no ^14C . Therefore, the proportion of biomass-derived carbon can be calculated by measuring the proportion of ^14C contained in the total carbon atoms in the polyethylene. In the present invention, when the content of ^14C in the polyethylene is _P14C , the content of biomass-derived carbon _Pbio can be calculated as follows.
_Pbio (%) = _P14C / 105.5 x 100

In the (a) biomass-derived low-density polyethylene that can be used in the present invention, theoretically, if all biomass-derived ethylene is used as the raw material for the polyethylene, the concentration of biomass-derived ethylene is 100%, and the biomass degree of the biomass-derived polyethylene is 100%. Note that the concentration of biomass-derived ethylene in fossil fuel-derived polyethylene produced only from raw materials derived from fossil fuels is 0%, and the biomass degree of the fossil fuel-derived polyethylene is 0%.

In the present invention, (a) the biomass-derived low-density polyethylene does not need to have a biomass content of 100%. This is because if even a part of (a) the biomass-derived low-density polyethylene is made from biomass-derived raw materials, the amount of fossil fuel used can be reduced compared to conventional methods.

In the (a) biomass-derived low-density polyethylene that can be used in the present invention, the polymerization method of the monomer containing biomass-derived ethylene is not particularly limited, and can be carried out by a conventionally known method. The polymerization temperature and polymerization pressure are preferably adjusted appropriately depending on the polymerization method and polymerization apparatus. The polymerization apparatus is also not particularly limited, and a conventionally known apparatus can be used, but it is preferable to use a high-pressure polymerization apparatus because a molecular structure with a high branching degree can be obtained.
It is preferable to use, as the polymerization catalyst, a multi-site catalyst such as a Ziegler catalyst or a Phillips catalyst, or a single-site catalyst such as a metallocene catalyst, and to carry out the polymerization in one stage or in two or more stages by any of gas phase polymerization, slurry polymerization, solution polymerization, and high pressure ion polymerization.

From the viewpoint of obtaining biomass polyethylene having a broad molecular weight distribution and excellent flexibility and moldability, it is preferable to use a multi-site catalyst such as a Ziegler catalyst or a Phillips catalyst.
Preferred Ziegler catalysts may be those generally known as Ziegler catalysts used in the coordination polymerization of ethylene and α-olefins, and examples thereof include catalysts containing a titanium compound and an organoaluminum compound, such as catalysts consisting of a titanium halide compound and an organoaluminum compound, and catalysts consisting of a solid catalyst component consisting of titanium, magnesium, chlorine, etc., and an organoaluminum compound. More specifically, examples of such catalysts include a catalyst comprising a catalyst component (a) obtained by reacting a reaction product of an alcohol pretreatment product of anhydrous magnesium dihalide and an organometallic compound with a titanium compound, and an organometallic compound (b); a catalyst comprising a catalyst component (A) obtained by reacting magnesium metal with an organic hydroxide compound or an oxygen-containing organic compound such as magnesium, an oxygen-containing organic compound of a transition metal, and an aluminum halide, and an organometallic compound catalyst component (B); and a catalyst comprising a solid catalyst component (A) obtained by reacting (i) metallic magnesium with at least one member selected from an organic hydroxide compound, an oxygen-containing organic compound of magnesium, and a halogen-containing compound, (ii) at least one member selected from an oxygen-containing organic compound of a transition metal and a halogen-containing compound, or (iii) a silicon compound, with (iv) an aluminum halide compound, and an organometallic compound catalyst component (B).

The Phillips catalyst may be any of those generally known as Phillips catalysts used in the coordination polymerization of ethylene and α-olefins, such as a catalyst system containing a chromium compound such as chromium oxide. Specific examples include catalysts in which a chromium compound such as chromium trioxide or chromate ester is supported on a solid oxide such as silica, alumina, silica-alumina, or silica-titania.

(a) When the biomass-derived low-density polyethylene is linear low-density polyethylene, the linear low-density polyethylene is usually a copolymer of ethylene and an α-olefin, but it can also be produced using only ethylene as a raw material by allowing ethylene to polymerize during polymerization.

As the α-olefin, a compound having 3 to 20 carbon atoms can be used, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, 4-methyl-1-hexene, etc., or a mixture of these may be used. The α-olefin is preferably a compound having 4, 6, or 8 carbon atoms or a mixture of these, such as 1-butene, 1-hexene, 1-octene, or a mixture of these.

The biomass-derived linear low-density polyethylene may be a commercially available product, for example, a product manufactured and sold by Braskem Co., Ltd. A specific example of a suitable brand is SLH218.
Good too.

The linear low density polyethylene can be produced by a conventionally known production method using a conventionally known catalyst including a multi-site catalyst such as a Ziegler catalyst, or a single-site catalyst such as a metallocene catalyst.
The linear low density polyethylene can be preferably produced using a single-site catalyst. However, from the viewpoint of obtaining linear low density polyethylene having a broad molecular weight distribution (Mw/Mn), for example, 3.5 or more, it is preferable to use a multi-site catalyst.

(a) The biomass-derived low-density polyethylene may be used alone or in a mixture of two or more types. It may also be used together with other polymers, including other ethylene-based polymers.

(a) The biomass-derived low-density polyethylene may be blended with various known additives that are typically added to olefin polymers, such as antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, slip agents, etc., as necessary, to the extent that the objective of the present invention is not impaired.

Propylene polymer: It is preferable that some or all of the layers of the laminated film of the present invention contain a propylene polymer. Since the propylene polymer is lightweight, highly heat resistant, and relatively low cost, the laminated film of the present invention can be lightweight, highly heat resistant, and relatively low cost.
The propylene polymer used in this embodiment is a resin generally manufactured and sold under the name of polypropylene, and is usually a propylene homopolymer having a density of about 890 to 930 kg/ ^m3 , or a propylene copolymer, that is, a copolymer derived from propylene and at least one comonomer selected from a small amount of other α-olefins. In the case of a copolymer, it may be a random copolymer or a block copolymer, but a block copolymer is particularly preferred. In the case of a propylene copolymer, examples of the other α-olefin include ethylene and an α-olefin having about 4 to 20 carbon atoms, such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, and 4-methyl-1-pentene. Such other α-olefins may be copolymerized alone or in combination with two or more α-olefins.

Among propylene polymers, propylene polymers having a melting point measured by a differential scanning calorimeter (DSC) in the range of 110 to 170°C, particularly 115 to 165°C, are preferably used in view of the balance between the heat resistance of the resulting laminated film and the wearability with the heat-sealing layer (A).

The propylene polymer used in this embodiment, either alone or in a blend with other resins such as ethylene polymers, ethylene-α-olefin random copolymers, and tackifier resins, is not particularly limited in melt flow rate (MFR) (ASTM D1238, 230°C, 2160 g load) as long as it has film-forming ability, but from the viewpoint of extrusion processability, etc., it is usually in the range of 0.01 to 100 g/10 min, preferably 0.1 to 70 g/10 min.

In this embodiment, two or more types of propylene polymers can be used in combination.

The propylene polymer used in this embodiment can be produced by various known production methods, specifically, for example, using an olefin polymerization catalyst such as a Ziegler-Natta catalyst or a single-site catalyst. In particular, it can be produced using a single-site catalyst. A single-site catalyst is a catalyst with a uniform (single-site) active site, such as a metallocene catalyst (so-called Kaminsky catalyst) or a Brookhart catalyst. The metallocene catalyst is a catalyst consisting of a metallocene transition metal compound and at least one compound selected from the group consisting of an organoaluminum compound and a compound that reacts with the metallocene transition metal compound to form an ion pair, and may be supported on an inorganic material.

Various additives such as inorganic fillers such as silica and talc, antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, slip agents, and pigments can be blended into the propylene polymer, provided such blending does not conflict with the objectives of the present invention.

The laminated film of the present invention has (A) a heat-sealing layer, (B) an intermediate layer, and (C) a laminate layer, as described below.

(A) Heat-sealing layer When the laminated film of the present invention is used to form a packaging film, a packaging bag, or the like, the (A) heat-sealing layer constituting the laminated film of the present invention is often the innermost layer and is fused to other films. For this reason, it is preferable to use a resin having a low melting point so as to obtain high seal strength. Preferable examples of the low-melting point resin include relatively low-density ethylene-based polymers such as high-pressure low-density polyethylene and ethylene-α-olefin random copolymers; aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, aromatic hydrocarbon resins, polyterpene resins, rosins, styrene resins, and tackifying resins such as coumarone-indene resins. From the viewpoints of cost and availability, the ethylene-based polymer is preferably a petroleum-derived ethylene-based polymer.
The content of the low melting point resin in the heat-sealing layer (A) is preferably 20 to 50 mass %, more preferably 25 to 35 mass %, and even more preferably 26.5 to 30 mass %.
The content of the petroleum-derived ethylene polymer in the heat-sealing layer (A) is preferably 5 to 25 mass %, more preferably 8 to 20 mass %, and even more preferably 10 to 15 mass %.

On the other hand, when the (B) intermediate layer contains a propylene polymer from the viewpoint of heat resistance and light weight, it is preferable that the (A) heat seal layer also contains a propylene polymer from the viewpoint of lamination strength with the (B) intermediate layer, etc. In this case, the propylene polymer is not particularly limited, but it is preferable to use a propylene polymer of the same or similar type and physical properties as the propylene polymer used in the (B) intermediate layer.
The content of the propylene polymer (a) in the heat-sealing layer (A) is preferably 56 to 59% by mass or more.

The (A) heat-sealing layer contains (a) 2 to 6 mass % of biomass-derived low-density polyethylene.
By containing the above amount of the low-density polyethylene derived from biomass (a) in the heat-sealing layer (A), a remarkable technical effect of improving impact resistance beyond the limits of the prior art is realized. In addition, the amount of petroleum-derived raw materials used can be reduced, thereby reducing the environmental load.
The content of the biomass-derived low-density polyethylene (a) in the heat-sealing layer (A) is preferably 2.5 to 5.5 mass %, particularly preferably 2.2 to 5.2 mass %.

The content of (a) biomass-derived low-density polyethylene can be appropriately increased or decreased, for example, by adjusting the blending of the resin composition when producing (A) the heat-sealable layer.
The content of (a) biomass-derived low-density polyethylene and/or (b) biomass-derived linear low-density polyethylene in the (A) heat-sealable layer after production can be calculated, for example, by measuring the content of biomass-derived carbon in the film by radiocarbon ( ¹⁴ C) measurement and from this measurement result and the content of biomass-derived carbon in the (a) biomass-derived low-density polyethylene and/or (b) biomass-derived linear low-density polyethylene.

There are no particular limitations on the thickness of the heat-sealing layer (A). From the viewpoint of ease of opening, the thickness is preferably 0.2 μm or more, more preferably 0.5 μm or more, and particularly preferably 0.8 μm or more.
On the other hand, from the viewpoint of stringiness and the like, the thickness is preferably 20.0 μm or less, more preferably 15.0 μm or less, and particularly preferably 10.0 μm or less.

(B) Intermediate Layer The components of the (B) intermediate layer constituting the laminated film of the present invention are not particularly limited, but it is preferable that the intermediate layer contains a propylene polymer from the viewpoints of the strength, heat resistance, light weight, etc. of the laminated film. Also, from the viewpoints of further improving the impact resistance and improving the lamination strength with the (A) heat-sealing layer, it is preferable that the intermediate layer contains (a) a biomass-derived low-density polyethylene.

Propylene polymers are highly heat resistant, lightweight, and low cost, and therefore by including them, the intermediate layer (B) can be made highly heat resistant, lightweight, and low cost.
Furthermore, from the viewpoint of interlayer affinity, when a propylene polymer is used in the (B) intermediate layer, it becomes easier to use a propylene polymer in the (A) heat-sealing layer and the (C) laminate layer as well, making the entire laminate film highly heat-resistant, lightweight, and low-cost.
The content of the propylene polymer (B) is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

Among the layers constituting the laminated film of the present invention, the (A) heat-sealing layer is preferably designed so as to obtain an appropriate seal strength, and the (C) laminate layer is preferably designed in consideration of the lamination strength between the (D) base layer, etc., whereas the (B) intermediate layer is relatively less restricted in this respect, and can be designed with priority given to imparting the desired physical properties and performance, such as mechanical properties, to the entire laminated film of the present invention. In this case, the thickness of the (B) intermediate layer is preferably made larger than the thicknesses of the (A) heat-sealing layer and the (C) laminate layer, and is particularly preferably made larger than the sum of the thicknesses of the (A) heat-sealing layer and the (C) laminate layer.
The thickness of the intermediate layer (B) is preferably in the range of 10 to 85 μm, and more preferably in the range of 15 to 80 μm.

For the purpose of improving impact resistance, etc., the (B) intermediate layer preferably contains (a) biomass-derived low-density polyethylene, for example, in an amount of 1% by mass or more, and particularly preferably 3% by mass or more.

(C) Laminate Layer The (C) laminate layer constituting the laminate film of the present invention can be laminated with other layers including the (D) substrate layer described below, as necessary or desired.
Therefore, it is preferable to design the laminate layer (C) taking into consideration the lamination strength between the laminate layer and other layers including the base layer (D).
For example, it is preferable to use the same type of material as the other layers including the (D) base layer, and therefore it is preferable to use a polypropylene material or a polyester-based material, which is preferably used for the (D) base layer.
In order to further improve the laminate strength between other layers, (C) the surface of the laminate layer ((B) the surface opposite to the surface to be laminated with the intermediate layer) may be subjected to a corona treatment, a roughening treatment, or the like.

When the (B) intermediate layer contains a propylene polymer, it is preferred that the (C) laminate layer also contains a propylene polymer from the viewpoint of lamination strength with the (B) intermediate layer.
More specifically, the content of the propylene polymer (a) in the laminate layer (C) is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

The (C) laminate layer may contain (a) biomass-derived low-density polyethylene.
By containing the (C) laminate layer containing the (a) biomass-derived low-density polyethylene, the impact resistance can be further improved. In addition, the lamination strength between the (C) laminate layer and the (B) intermediate layer can be further improved in some cases.
The total content of (a) biomass-derived low-density polyethylene in (C) laminate layer is preferably 0.5% by mass or more, more preferably 1 to 20% by mass, and particularly preferably 2 to 15% by mass.

From the viewpoint of preventing blocking during storage of the laminated film of the present invention, the laminate layer (C) may contain an anti-blocking agent.
As the blocking inhibitor, powdered silica, preferably synthetic silica, etc., can be suitably used. From the viewpoint of uniformly dispersing the powdered silica in the (C) laminate layer, the powdered silica may be dispersed in a resin having excellent miscibility with the petroleum-derived linear low-density polyethylene constituting the (C) laminate layer, for example, in low-density polyethylene, to form a master batch, and then the master batch may be added to the petroleum-derived linear low-density polyethylene.

(C) There are no particular limitations on the thickness of the laminate layer, but it is preferably 1 to 20 μm, and more preferably in the range of 3 to 15 μm.

In any of the (A) heat-sealing layer, (B) intermediate layer, and (C) laminate layer, various additives and fillers other than (a) biomass-derived low-density polyethylene (may be linear low-density polyethylene), petroleum-derived ethylene polymer, and propylene polymer, such as heat stabilizers, antioxidants, light stabilizers, antistatic agents, antiblocking agents, lubricants, nucleating agents, flame retardants, pigments, dyes, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, antibacterial agents, and antifogging agents, may be added, so long as they do not violate the object of the present invention. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins, etc. may also be added, so long as they do not violate the object of the present invention.

The laminated film of the present invention has the heat-sealing layer (A), the intermediate layer (B), and the laminate layer (C) as described above. In the laminated film of the present invention, the laminate layer (C) and the heat-sealing layer (A) are preferably laminated via the intermediate layer (B), but other layers may also be present.

The laminated film of the present invention can be produced by various known film forming methods, such as a method of forming films to be the (C) laminate layer, the (B) intermediate layer, and the (A) heat-sealing layer in advance, and then laminating the films together to produce a laminated film, a method of using a multilayer die to obtain a multilayer film consisting of the (B) intermediate layer and the (A) heat-sealing layer, and then extruding the (C) laminate layer onto the (B) intermediate layer surface to produce a laminated film, a method of using a multilayer die to obtain a multilayer film consisting of the (C) laminate layer and the (B) intermediate layer, and then extruding the (A) heat-sealing layer onto the (B) intermediate layer surface to produce a laminated film, or a method of using a multilayer die to obtain a laminated film consisting of the (C) laminate layer, the (B) intermediate layer, and the (A) heat-sealing layer.

As the film forming method, various known film forming methods, specifically, a T-die cast film forming method and an inflation film forming method can be adopted.
The laminated film of the present invention and each of the layers constituting the laminated film may be a non-stretched film (unstretched film) or a stretched film.

The thickness of the laminated film of the present invention is not particularly limited, but from the viewpoint of ensuring practical strength, it is 5 μm or more, preferably 10 μm or more, and more preferably 15 μm or more. On the other hand, from the viewpoint of having practical flexibility even after being laminated with the (D) base layer, for example, it is usually 100 μm or less, preferably 90 μm or less, and more preferably 80 μm or less.

The laminate film of the present invention contains (a) biomass-derived low-density polyethylene and/or (b) biomass-derived linear low-density polyethylene in (A) the heat-sealing layer, and preferably in (B) the intermediate layer, and/or (C) the laminate layer, thereby making it possible to reduce the amount of fossil fuel used in the production and to reduce the environmental load.
The biomass degree of a laminated film can be calculated by averaging the biomass degree of each layer weighted by the weight of each layer.
The biomass degree of the laminated film can be appropriately increased or decreased by adjusting the biomass degree of each layer, and the biomass degree of each layer can be appropriately increased or decreased by adjusting the biomass degree of the resin used in each layer and the amount used.
The biomass degree of the laminated film of the present invention is preferably 0.01 to 0.58 mass%, more preferably 0.03 to 0.50 mass%, even more preferably 0.05 to 0.45 mass%, and still more preferably 0.07 to 0.40 mass%.

The heat of fusion ΔH of the laminated film of the present invention at 100° C. to 170° C., calculated from a melting curve obtained by DSC measurement, is preferably 50 to 87.5 J/g.
When the heat of fusion ΔH at 100° C. to 170° C. is within the above range, the impact resistance can be improved more effectively.
The measurement of the melting curve by DSC and the calculation of the heat of fusion ΔH from 100° C. to 170° C. from the melting curve can be carried out by a conventionally known method, and more specifically, for example, can be carried out by the method described in the Examples of the present application.
The heat of fusion ΔH at 100° C. to 170° C. is more preferably 60 to 87.5 J/g, more preferably 70 to 87.5 J/g, even more preferably 80 to 87.5 J/g, and particularly preferably 83 to 87.5 J/g.
The heat of fusion ΔH at 100° C. to 170° C. can be reduced by (a) lowering the crystallinity of the film by adding biomass-derived low-density polyethylene, petroleum-derived polyethylene, or the like.

The laminated film of the present invention may be a stretched film or a non-stretched film.
From the viewpoint of improving mechanical properties, a stretched film is preferable, and a biaxially stretched film is particularly preferable.
As the biaxial stretching, a method such as sequential biaxial stretching, simultaneous biaxial stretching, or multi-stage stretching is appropriately adopted.
The conditions for biaxial stretching may be those for producing a known biaxially stretched film. For example, in the case of a sequential biaxial stretching method, the longitudinal stretching temperature is set to 100° C. to 145° C., the stretching ratio is set to a range of 4 to 7 times, the transverse stretching temperature is set to 150° C. to 190° C., and the stretching ratio is set to a range of 8 to 11 times.

(D) Substrate Layer If desired, the laminate film of the present invention can be laminated with a (D) substrate layer at its (C) lamination layer.

There are no particular limitations on the base layer (D), and for example, a film that is normally used for plastic packaging can be suitably used.
Preferred materials for the (D) base layer include plastic films composed of thermoplastic resins such as polyolefins, such as crystalline polypropylene, crystalline propylene-ethylene copolymer, crystalline polybutene-1, crystalline poly-4-methylpentene-1, low-, medium-, or high-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), and ionically crosslinked olefin copolymer (ionomer); aromatic vinyl copolymers, such as polystyrene and styrene-butadiene copolymer; halogenated vinyl polymers, such as polyvinyl chloride and vinylidene chloride resin; nitrile polymers, such as acrylonitrile-styrene copolymer and acrylonitrile-styrene-butadiene copolymer; polyamides, such as nylon 6, nylon 66, and para- or meta-xylylene adipamide; polyesters, such as polyethylene terephthalate (PET) and polytetramethylene terephthalate; various polycarbonates; and polyacetals, such as polyoxymethylene. In addition, when the contents to be packaged are sensitive to oxygen, the above film may be provided with a film vapor-deposited with a metal oxide or the like, a film coated with an organic compound, or a layer made of ethylene vinyl alcohol copolymer (EVOH) resin.
Plastic films made of these materials may be used in an unstretched, uniaxially stretched, or biaxially stretched state.

As the (D) base layer, these plastic films can be used as a single layer or as a laminate of two or more types. Also, one or more types of these plastic films can be laminated with a metal foil such as aluminum, paper, cellophane, etc.
Examples of preferred (D) substrate layers include single-layer films made of stretched nylon film or stretched polyester film, two-layer films made of a polyolefin film such as low-density polyethylene or polypropylene and PET, and three-layer films made of PET/nylon/polyethylene. When producing these laminated films, an adhesive or anchoring agent can be interposed between the layers as necessary. An ink layer expressing a design can also be provided.

There is no particular restriction on the method for laminating the (D) base material layer on the (C) laminate layer, but for example, the (D) base material layer can be directly laminated on the (C) laminate layer by extrusion lamination, etc. Also, the (D) base material layer may be laminated on the (C) laminate layer via an adhesive by dry lamination, etc. As the adhesive, a normal adhesive such as a urethane adhesive, an acid-modified polyolefin adhesive, a polyester adhesive, a polyether adhesive, or a polyamide adhesive can be used.
The thickness of the base layer (D) can be set arbitrarily, but is usually selected from the range of 5 to 1000 μm, preferably 9 to 100 μm.

The laminate film of the present invention and the laminate film obtained by laminating the (D) base layer to the (C) laminate layer of the laminate film of the present invention are preferably used in various applications, and are particularly suitable for use as packaging materials.

A preferred example of such a packaging material is a lid material, which can be used as a lid material for a container in which the heat-sealing layer (A) is used as the innermost layer on the container side, and the laminate film of the present invention and the laminate film in which the laminate layer (C) of the laminate film of the present invention is laminated with the base layer (D).
When used as a container lid material, the laminated film of the present invention may be used as a lid material as it is, or may be printed before use. It may be further laminated with a printed or unprinted (D) base layer to form a lid material. Depending on the application, it may be cut in advance to fit the shape of the container to form a lid material. When used as a container lid material, it is preferable to laminate it with a (D) base layer.

The laminated film of the present invention can form a heat seal layer by heat sealing to various adherends in the heat seal layer (A). Examples of such adherends include propylene polymers, polystyrene, polyester, polycarbonate, polyvinyl chloride, etc. These adherends can be in various shapes such as films, sheets, trays, cups, bottles, etc. Among these, it is particularly preferable to use propylene polymers as the adherend, since the heat seal layer is excellent in sealing property, easy opening property, heat resistance, oil resistance, etc.
Such a propylene polymer is in the same category as the above-mentioned propylene polymer preferably used in the laminate of the present invention, but the individual physical properties may be the same or different. For example, in the case of an adherend made of a propylene polymer, a propylene polymer formed into various shapes such as a film, sheet, tray, cup, bottle, etc. by a known method according to the packaging material can be used. In the case of a film or sheet, it can be produced by the same method as the laminated film of the present invention. In the case of a tray or cup, it can be produced by first producing a sheet by the above-mentioned method, and then forming it into a container such as a tray or cup by thermoforming such as vacuum forming or pressure forming. In addition, in the case of a cup or bottle, it can be formed into a container by injection molding, injection blow molding, blow molding, etc.

When the laminated film of the present invention is used as a packaging material, the laminated film itself may be, for example, folded and sealed on three sides, or two sheets of the laminated film may be sealed on all four sides to form a package. Alternatively, the laminated film or a lid material formed by bonding the laminated film to a base layer (D) may be bonded to the above-mentioned various adherends to form a heat seal layer to form a package.
A suitable example of such a package is a packaging container comprising the above-mentioned lid material and a container body containing at least one of polypropylene, polyethylene terephthalate, and polybutylene terephthalate.
There are no particular limitations on the items to be stored in the packaging container, but the packaging container can be preferably used for packaging foods, medicines, medical instruments, daily necessities, miscellaneous goods, etc. Taking advantage of the high impact resistance of the laminated film of the present invention, the packaging container can be particularly preferably used as a packaging container for aseptic cooked rice, which is often subjected to impacts during distribution.

The present invention will be specifically described below with reference to examples and comparative examples. Note that the present invention is not limited in any way by the following examples.

The physical properties and characteristics in the examples and comparative examples were evaluated by the following methods.
(1) Molecular weight distribution (Mw/Mn)
After pretreatment of a polymer sample under the following conditions, the molecular weight was measured by GPC, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was taken as the molecular weight distribution.
i) Pretreatment A sample (30 mg) was added with 20 mL of mobile phase for GPC measurement (o-dichlorobenzene) and dissolved by shaking at 145° C. The resulting solution was hot-filtered through a sintered filter having a pore size of 1.0 μm and used for GPC measurement.
ii) GPC
Apparatus: Tosoh Corporation, gel permeation chromatograph HLC-8321
Column: Tosoh Corporation, inner diameter 7.5 mm x 30 cm, 4 columns (TSKgel GMH6-HT: 2 columns, and TSKgel GMH6-HTL: 2 columns)
Column temperature: 140 ° C.
Detector: differential refractometer Flow rate: 1 mL/min
Sampling interval: 0.5 seconds (2) Heat of fusion Using a TA Instruments Q100 differential scanning calorimeter (DSC), about 5 mg of a sample was precisely weighed out, and a thermal melting curve was measured in accordance with JIS K7121 under conditions of a nitrogen gas inflow rate of 50 ml/min from -50°C to 250°C at a heating rate of 10°C/min, and the crystalline heat of fusion ΔH of the sample from 100 to 170°C on the obtained thermal melting curve was calculated.

(3) Dart Impact Test A laminate film was prepared by laminating a 12 μm-thick biaxially oriented polyethylene terephthalate film (PET) and a 15 μm-thick biaxially oriented nylon film (NY) in that order to produce a laminate film, and laminating the (C) laminate layer of the laminated film of the Examples/Comparative Examples to the NY side of the laminate film. A cup sealer was then used to heat-seal the (A) heat-sealing layer of the film to a sterile rice container (material: polypropylene) under conditions of 185° C., 1 second, and 1500 N to produce a package.
A 750 g weight was dropped from a height of 80 cm onto the prepared package, and the number of times it was dropped until it broke was counted. Measurements were performed on three packages, and the average value was taken as the evaluation result.

Details of each of the constituent components such as resins used in the examples and comparative examples are as follows.
- Propylene-ethylene block copolymer (b-PP)
MFR (2.16 kg, 230 ° C): 7.0 g / 10 min Density: 900 kg / m ³
Melting point: 163°C
Propylene-ethylene-1-butene random copolymer (r-PP)
Ethylene content: 3.6 mol% (2.4 wt%)
1-Butene content: 1.9 mol% (2.5 wt%)
Density: 910 kg/ ^m3
Melt flow rate (MFR) (2.16 kg, 230°C): 7.2 g/10 min Melting point: 143°C
Propylene homopolymer (h-PP)
MFR (2.16 kg, 30 ° C): 7 g / 10 min Density: 910 kg / m ³
Melting point: 161°C
・High density polyethylene (HDPE)
Density: 954 kg/ ^m3
MFR (2.16 kg, 190°C): 1.1 g/10 min Melting point: 132°C
・Ethylene-1-butene random copolymer (EBR)
Ethylene content: 89.1 mol%
Crystallinity: 10%
Density: 886 kg/m ³ ,
MFR (2.16 kg, 190° C.): 4.0 g/10 min. Ethylene-propylene copolymer (EPR)
Ethylene content: 82.6 mol%
Density: 870 kg/ ^m3
MFR (2.16 kg, 190°C): 2.9 g/10 min. Tackifier resin: Hydrogenated aromatic hydrocarbon resin Ring and ball softening point: 115°C.
・Biomass-derived linear low-density polyethylene (B-LLDPE)
MFR (2.16 kg, 190 ° C.): 2.3 g / 10 min
Density: 916 kg/ ^m3
Molecular weight distribution (Mw / Mn): 4.12
・Biomass-derived low-density polyethylene (B-LDPE)
MFR (2.16 kg, 190 ° C.): 3.8 g / 10 min
Density: 922 kg / ^m3
Molecular weight distribution (Mw / Mn): 5.88

(Comparative Example 1)
The components constituting each layer were fed to separate extruders in the formulations shown in Table 1, and a 50 μm-thick laminated film was formed by the T-die method, which was a three-layer coextruded film consisting of (A) heat-sealing layer/(B) intermediate layer/(C) laminate layer, and the laminate layer was subjected to a corona treatment to obtain an easy-to-open laminated film. The thickness ratio of each layer was (A) heat-sealing layer:(B) intermediate layer:(C) laminate layer=7:75:18.
The heat of fusion of the obtained laminated film alone was measured according to the method described in (1) above.
Next, a package was prepared according to the method (2) above, and a dart impact test was carried out.
The results are shown in Table 1.

(Examples 1 to 2, and Comparative Example 2)
A laminated film and then a package were produced in the same manner as in Comparative Example 1, except that the composition of the heat-sealing layer (A) was changed as shown in Table 1, such as by adding biomass-derived linear low-density polyethylene (B-LLDPE) to the heat-sealing layer (A), and then the package was produced and evaluated.
The results are shown in Table 1.

(Examples 3 to 4 and Comparative Example 3)
A laminated film and then a package were produced in the same manner as in Comparative Example 1, except that the composition of the heat-sealing layer (A) was changed as shown in Table 1, such as by adding biomass-derived low-density polyethylene (B-LDPE) to the heat-sealing layer (A), and then the package was produced and evaluated.
The results are shown in Table 1.

The laminated film of the present invention maintains the excellent properties inherent to conventional polyolefin-based resins, while at the same time significantly improving impact resistance, particularly when combined with plastic containers, and reducing the environmental impact of its production, etc., thereby combining at a high level properties that are of great practical value. The film is suitable for use in packaging applications such as lid materials for plastic containers, particularly for packaging foods such as sterile cooked rice, and has high applicability in various industrial fields such as agriculture, food processing, distribution, and restaurant serving.

Claims (6)

A laminated film having (A) a heat-sealing layer, (B) an intermediate layer, and (C) a laminate layer, wherein (A) the heat-sealing layer contains 2 to 6 mass% of (a) a low-density polyethylene derived from biomass, and (B) the intermediate layer contains a propylene polymer. The laminated film according to claim 1, in which the heat of fusion ΔH at 100°C to 170°C calculated from the melting curve obtained by DSC measurement is 50 to 87.5 J/g. The laminated film according to claim 1 or 2, wherein (a) the molecular weight distribution Mw/Mn of the biomass-derived low-density polyethylene is 3.5 or more. The laminated film according to any one of claims 1 to 3, wherein (A) the heat-sealing layer further contains a petroleum-derived ethylene polymer. The laminate film according to any one of claims 1 to 4, further comprising a substrate layer (D) on the side of the laminate layer (C). A packaging container comprising a cover material made of the laminated film according to any one of claims 1 to 5 and a body portion containing at least one of polypropylene, polyethylene terephthalate, and polybutylene terephthalate.