Heat-shrinkable film, resin composition, and resin compound

Abstract

This heat-shrinkable film has a layer containing a biomass filler, wherein the layer contains 25-70 parts by mass of the biomass filler, 20-70 parts by mass of an unmodified polyolefin, and 0.05-4 parts by mass of a dispersant per 100 parts by mass of the entire layer, and the thermal shrinkage of the layer at 100°C is 40% or more.

Description

Heat shrinkable film, resin composition, and resin compound

[0001] This disclosure relates to heat-shrinkable films, resin compositions, and resin compounds.

[0002] In recent years, waste from synthetic resin products has become a serious concern, particularly in the context of marine plastic pollution. Therefore, there is a growing demand for the recycling of synthetic resin products and, for products that are discarded after use, for at least a portion of the raw materials to be replaced with non-synthetic resin materials, thereby reducing the amount of synthetic resin used.

[0003] Patent Document 1 discloses a polyester resin composition containing recycled PET resin and a polyester shrink film derived therefrom. It is stated that this resin composition and shrink film can be suitably applied to various PET bottles, heat-shrinkable labels for various PET bottles, outer covering materials for lunch containers, etc., and can significantly broaden their versatility and environmental characteristics.

[0004] Furthermore, heat-shrinkable films made from polypropylene are also commonly used for labels on PET bottles. For example, Patent Document 2 discloses a stretched film made from a polypropylene resin composition, which has a specific gravity of 0.95 or less and exhibits excellent low-temperature shrinkage and low natural shrinkage, making it a polypropylene-based heat-shrinkable film.

[0005] Japanese Patent Publication No. WO2023 / 188471, Japanese Patent Publication No. 2023-144933

[0006] The technology described in Patent Document 1 contributes to reducing the amount of synthetic resin used by utilizing recycled PET resin. However, if the recycled PET resin itself is derived from petroleum, there is room for improvement in terms of reducing greenhouse gas (GHG) emissions during manufacturing and waste incineration.

[0007] Furthermore, the technology described in Patent Document 2 does not consider reducing the amount of synthetic resin used.

[0008] In this regard, if at least a portion of the raw materials are replaced with non-synthetic resin raw materials such as biomass materials, it may be possible to contribute not only to reducing the amount of synthetic resin used but also to reducing GHG emissions. Biomass materials such as starch materials, cellulose materials, and seashell materials are relatively inexpensive and renewable, and are therefore expected to be used as reinforcing materials for thermoplastic resins and elastomers, which are molding materials for films and the like.

[0009] Therefore, this disclosure aims to provide heat-shrinkable films, resin compositions, and resin compounds that can contribute to further reducing environmental impact by reducing the amount of synthetic resin used and the amount of GHG emissions.

[0010] To achieve the above objective, the heat-shrinkable film of the present disclosure is a heat-shrinkable film having a layer containing a biomass filler, wherein the layer contains 25 to 70 parts by mass of the biomass filler, 20 to 70 parts by mass of unmodified polyolefin, and 0.05 to 4 parts by mass of a dispersant, with the heat shrinkage rate of the layer at 100°C being 40% or more.

[0011] Since the heat-shrinkable film of this disclosure contains biomass filler as part of its raw materials, it can reduce the amount of synthetic resin used and reduce GHG emissions during manufacturing and waste incineration. Therefore, it can contribute to further reducing the environmental burden compared to conventional technologies.

[0012] Cross-sectional SEM images in the TD direction of the raw film roll before stretching in experimental examples 3 and 4.

[0013] The films of this disclosure will be described in detail below. However, the technology of this disclosure is not limited to the embodiments described below and may be modified and applied as appropriate, without altering the gist of this disclosure.

[0014] <<Heat Shrink Film>> The heat shrink film of this disclosure has a layer containing a biomass filler (hereinafter also referred to as the "filler-containing layer").

[0015] The heat-shrinkable film may be a single-layer film consisting of the filler-containing layer. Alternatively, the heat-shrinkable film may be a multi-layer film having other layers, such as a surface layer, on one or both sides of the filler-containing layer, from the viewpoint of improving functionality such as moldability, printability, sealability, and durability. In this specification, when simply referred to as "film," it means a film-like molded product including the filler-containing layer, the heat-shrinkable film, the raw material film and the stretched film described later.

[0016] The filler-containing layer contains a biomass filler, an unmodified polyolefin, a dispersant, an optional olefin-based elastomer, and an optional lubricant. The heat-shrinkable film may further contain other components as needed.

[0017] <Biomass Filler> A biomass filler is a filler made from biomass material. In this specification, the term "biomass" means renewable, biologically derived resources excluding fossil resources. Also, "biomass material" means a material derived from biomass.

[0018] Examples of biomass fillers include starch, cellulose powder such as paper powder, and shell powder from scallops, oysters, etc. The preferred biomass filler is at least one selected from the group consisting of starch, cellulose powder, and shell powder, with starch being the more preferred.

[0019] Starch, though not intended to be limiting, can include, for example, cornstarch, rice starch, wheat starch, potato starch, sweet potato starch, cassava starch (tapioca starch), sago starch, thermoplastic starch, etc., with cornstarch being preferred.

[0020] The average particle size of the biomass filler raw material can be, for example, between 6 μm and 36 μm, although this is not intended to limit it. More specifically, the average particle size of the biomass filler raw material can be, for example, 36 μm or less, but may also be 32 μm or less, or 30 μm or less. If the average particle size exceeds 36 μm, inflation molding may become difficult. If the average particle size is 36 μm or less, there will be no holes due to drawdown during extrusion, resulting in excellent film formability and toughness.

[0021] The average particle size of the biomass filler raw material can be, for example, 6 μm or more, preferably 8 μm or more, and more preferably 10 μm or more, although this is not intended to be limiting. If the average particle size is less than 6 μm, the biomass filler becomes bulky, making it difficult to manufacture the resin composition and film that are the raw materials for the filler-containing layer. In addition, the surface area of ​​the biomass filler increases, so the amount of compatibilizer covering it must be increased, resulting in inferior physical properties of the molded product. If the average particle size is 6 μm or more, the rigidity of the resin composition is excellent, the bulkiness of the biomass filler is reduced, and the manufacture of the resin composition and film becomes easier.

[0022] In this specification, "average particle size" refers to the 50% particle size D50. The particle sizes of biomass fillers (10% particle size D10, 50% particle size D50, and 90% particle size D90) can be measured by volume using a laser diffraction particle size distribution analyzer (Malvern dry particle size distribution analyzer, product name: MASTER SIZER 3000) or the like.

[0023] The biomass filler content, when the entire filler-containing layer is considered to be 100 parts by mass, is 25 to 70 parts by mass, preferably 28 to 65 parts by mass, and more preferably 30 to 60 parts by mass. If the biomass filler content is less than 25 parts by mass, the amount of synthetic resin and CO2 reduction will be affected. ２ The reduction will be limited. If the amount of biomass filler exceeds 70 parts by mass, it may become difficult to manufacture the film, especially the secondary stretching of the raw film roll described later.

[0024] <Unmodified Polyolefins> Examples of unmodified polyolefins include unmodified polyethylene and unmodified polypropylene, and it is preferable to use unmodified polyethylene.

[0025] As unmodified polyethylene, high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-low-density polyethylene (ULDPE), which are homopolymers of ethylene, can be used. One of these may be used alone, or two or more may be used in combination.

[0026] In particular, it is preferable to use one or more of the following types of unmodified polyethylene: low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene, with the use of ultra-low-density polyethylene being more preferable. Low-density unmodified polyethylene has many voids formed between the polymer molecular chains, and biomass fillers can easily enter these voids. Furthermore, the polymer molecular chains can move freely even in the presence of biomass fillers, and it is easily deformed when stress is applied. This is advantageous in improving the moldability of the film.

[0027] Furthermore, as an unmodified polyolefin, low-density polyethylene (density: 0.900-0.935 g / cm³) is used. ３ It is preferable that the low-density polyethylene contains the following. Such low-density polyethylene does not easily lose flexibility when kneaded with biomass filler to produce a resin composition that is the raw material for the filler-containing layer. In addition, since low-density polyethylene is easily compatible with elastomers and other optional components, the manufacturing stability of the resin composition is improved.

[0028] Furthermore, it is preferable to include linear low-density polyethylene (LLDPE) or low-density polyethylene obtained by a metallocene catalyst as the unmodified polyolefin. This improves the stretchability of the resin composition, which is the raw material for the filler-containing layer, and facilitates the production of the film.

[0029] Furthermore, it is preferable to include ultra-low-density polyethylene (ULDPE) as the unmodified polyolefin. Because ultra-low-density polyethylene (ULDPE) has low crystallinity and a low density of about 0.9, it is advantageous not only for improving moldability but also for improving the heat shrinkage rate of the filler-containing layer and the heat-shrinkable film.

[0030] The content of unmodified polyolefin, when the total filler-containing layer is 100 parts by mass, is, for example, 20 to 70 parts by mass, preferably 30 to 68 parts by mass, and more preferably 33 to 66 parts by mass. If the amount of unmodified polyolefin is less than 20 parts by mass, the proportion of biomass filler will increase relatively, which may make it difficult to manufacture the resin composition and film. If the content of unmodified polyolefin is greater than 70 parts by mass, the proportion of biomass filler in the filler-containing layer may decrease.

[0031] <Dispersant> Dispersants primarily act on the interface of biomass fillers to inhibit aggregation between them and promote the dispersion of biomass fillers into the resin component. In addition to improving the dispersibility of biomass fillers, dispersants may also function as compatibilizers to improve the compatibility between biomass fillers and resin components. When the resin composition, which is the raw material for the filler-containing layer, and the filler-containing layer itself contain a dispersant, the biomass fillers become easier to disperse. Furthermore, if the dispersant also functions as a compatibilizer, the affinity between the biomass fillers and resin components in the resin composition and filler-containing layer increases, improving the appearance and physical properties of the heat-shrinkable film. Dispersants may also function as lubricants.

[0032] The dispersant is not particularly limited as long as it can provide sufficient dispersibility of the biomass filler in the resin composition; known dispersants can be used.

[0033] Specific examples of the dispersant include thermoplastic resins such as polyolefins modified with acid anhydrides such as maleic anhydride and succinic anhydride, and polyhydric alcohol fatty acid esters exemplified in the section on lubricants described later. In particular, the dispersant preferably contains at least one of maleic anhydride-modified polyolefin (hereinafter sometimes referred to as "MA-PO") and glycerin fatty acid ester. Examples of the glycerin fatty acid ester include glycerin citrate fatty acid ester. The dispersant may contain both MA-PO and glycerin fatty acid ester.

[0034] Examples of MA-PO include α-olefin-maleic anhydride copolymers, mixtures of α-olefin polymers and maleic anhydride, and mixtures of α-olefin, α-olefin-maleic anhydride copolymer and maleic anhydride. Examples of the α-olefin include ethylene and propylene.

[0035] When the total mass of the filler-containing layer is 100 parts by mass, the content of the dispersant is 0.05 to 4 parts by mass, preferably 0.1 to 3 parts by mass, more preferably 0.5 to 2.5 parts by mass. If the content of the dispersant is less than 0.05 parts by mass, the dispersibility of the biomass filler in the resin component is insufficient, and the biomass filler aggregates, which may reduce moldability. If the content of the dispersant exceeds 4 parts by mass, the strength and solvent resistance of the film may be reduced.

[0036] When the dispersant contains MA-PO, the melt viscosity of MA-PO is preferably 100 to 15000 mPa·s, more preferably 120 to 11000 mPa·s. If the melt viscosity of MA-PO is 100 mPa·s or higher, the resin composition and the film are excellent in moldability and toughness; if it is 15000 mPa·s or lower, the resin composition and the film are more excellent in rigidity.

[0037] The "melt viscosity" refers to the viscosity measured with a capillary rheometer.

[0038] When the dispersant contains MA-PO, the acid value of MA-PO is preferably 2 to 150 mgKOH / g, more preferably 3 to 120 mgKOH / g. If the acid value of MA-PO is 2 mgKOH / g or more, the resin composition and film have excellent moldability, and if it is 150 mgKOH / g or less, the resin composition and film have more excellent appearance.

[0039] The "acid value" refers to a value measured by the potentiometric titration method specified in JIS K 2501, or a value measured in accordance with JIS K 0070.

[0040] When the dispersant contains MA-PO, the weight average molecular weight of MA-PO is not intended to be limited, but may be, for example, 1,000 or more, preferably 2,000 or more. The weight average molecular weight of MA-PO is not intended to be limited, but may be, for example, 100,000 or less, preferably 80,000 or less, more preferably 70,000 or less.

[0041] The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC), as described later.

[0042] <Olefin-based Elastomer> Olefin-based elastomers have better conformability to biomass fillers during molding compared to general thermoplastic resins. Inclusion of the optional olefin-based elastomer is advantageous in improving the moldability of the resin composition.

[0043] Examples of the olefin-based elastomer used in the present disclosure include copolymers or homopolymers containing an olefin having 3 or more carbon atoms as a main component, and copolymers of ethylene as a main component with an olefin having 3 or more carbon atoms.

[0044] More specifically, examples include propylene-ethylene copolymers, ethylene-propylene-diene terpolymers, and the like. One type of olefin-based elastomer may be used alone, or two or more types may be used in combination.

[0045] Furthermore, olefin-based elastomers are generally composed of a hard segment that governs basic physical properties such as mechanical properties, and a soft segment that governs rubber-like properties such as elasticity. Olefin-based elastomers in which the hard segment is made of polypropylene are called propylene-based elastomers, and those in which the hard segment is made of polyethylene are called ethylene-based elastomers. Examples of soft segments of olefin-based elastomers include EPDM, EPM, EBM, IIR, hydrogenated styrene-butadiene rubber (HSBR), NBR, and acrylic rubber (ACM).

[0046] Furthermore, propylene-based elastomers, which are copolymers mainly composed of propylene (for example, the "propylene-ethylene copolymer" mentioned above) or homopolymers of propylene, are preferred because they offer excellent moldability, particularly in low-temperature moldability, as well as excellent toughness.

[0047] In the case of propylene-based elastomers, the propylene unit content relative to the total units is preferably 70% to 95% by mass, and more preferably 80% to 90% by mass. If the propylene unit content of the hard segment is 70% by mass or more, the strength is improved, resulting in excellent moldability. If it is 95% by mass or less, the elasticity of the soft segment provides excellent stretchability.

[0048] The content of olefin-based elastomer, when the total filler-containing layer is 100 parts by mass, can be, for example, 6 parts by mass or less, and may be 0.8 to 6 parts by mass, or 1 to 5 parts by mass. This is advantageous in improving the moldability of the resin composition and film.

[0049] When using a propylene-based elastomer as an olefin-based elastomer, the melt mass flow rate (MFR) of the propylene-based elastomer is preferably 1 to 30 g / 10 min, and more preferably 3 to 16 g / 10 min, although this is not intended to limit it. If the MFR1 of the propylene-based elastomer is 1 g / 10 min or more, the resin composition will have excellent moldability and rigidity, and if it is 30 g / 10 min or less, the resin composition will have excellent moldability and toughness.

[0050] The melt mass flow rate described above was obtained by measurement in accordance with the provisions of JIS K 7210-1:2014, and the measurement conditions for the propylene-based elastomer in this application are those described in the examples.

[0051] Furthermore, MFR can be measured under the conditions of a temperature of 230°C and a load of 2.16 kg for general polypropylene resins, and under the conditions of a temperature of 190°C and a load of 2.16 kg for general polyethylene resins.

[0052] Furthermore, the melting or softening point of the propylene-based elastomer is preferably 50 to 160°C, more preferably 50 to 110°C, and even more preferably 50 to 80°C. If the melting or softening point of the propylene-based elastomer is 50°C or higher, the toughness of the resin composition is superior, and if it is 160°C or lower, the rigidity of the resin composition is superior.

[0053] Note that "melting point" refers to the melting onset temperature on the DSC chart in a differential scanning calorimeter (DSC). Also, "softening point" refers to the Vicat softening temperature measured in accordance with JIS K 7206:2016.

[0054] <Lubricants> Lubricants have the function of improving the sliding properties of a resin composition by forming a film on the material surface and the metal surface of the processing machine during the manufacturing process, thereby reducing the load acting on these surfaces and making processing easier. By adding a lubricant of any component to the resin composition, the granulation properties of the resin composition may be improved. The lubricant is not particularly limited, and general lubricants can be used. Specific examples of lubricants include fatty acids such as stearic acid, fatty acid metal salts such as zinc stearate, barium stearate, and calcium stearate, fatty acid amide compounds such as stearamide and erucamide, and polyhydric alcohol fatty acid esters formed by ester bonding of a polyhydric alcohol and a fatty acid. In particular, it is preferable to use polyhydric alcohol fatty acid esters as lubricants. Polyhydric alcohol fatty acid esters tend to inhibit the function of dispersants, especially when the dispersant contains MA-PO, which is advantageous in ensuring the excellent physical properties of thin films. Note that lubricants may also function as dispersants or compatibilizers.

[0055] The fatty acids contained in the lubricant, particularly those contained in the polyhydric alcohol fatty acid ester, may be either straight-chain or branched-chain fatty acids, and may be either saturated or unsaturated fatty acids. Fatty acids with 6 to 24 carbon atoms are preferred. Examples of such fatty acids include stearic acid, isostearic acid, ricinoleic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, isoarachidic acid, behenic acid, caprylic acid, 2-ethylhexanoic acid, isononanoic acid, capric acid, lauric acid, myristic acid, isomyristateic acid, erucic acid, palmitic acid, isopalmitic acid, and citric acid. From the viewpoint of ensuring sufficient moldability of the resin composition and good physical properties of the molded product, preferred fatty acids include stearic acid, erucic acid, palmitic acid, and citric acid. These fatty acids may be used individually or in combination of two or more.

[0056] The polyhydric alcohol contained in the polyhydric alcohol fatty acid ester is not particularly limited as long as it is an alcohol containing two or more hydroxyl groups in one molecule. Specific examples of polyhydric alcohols include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decandio. Examples include dihydric alcohols such as 1,11-undecanediol and 1,12-dodecanediol; trimethylolethane, trimethylolpropane, trimethylolbutane, ditrimethylolpropane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, polyglycerin (such as 2-20 glycerin products), 1,3,5-pentanetriol, sorbitol, sorbitan, sorbitol-glycerin condensates, adonitol, arabitol, xylitol, mannitol, and other trihydric or higher polyhydric alcohols. Furthermore, examples include sugars that are trihydric or higher polyhydric alcohols such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose, and meridinestose. Preferably, from the viewpoint of availability and ease of reaction with fatty acids, glycerin, polyglycerin; sorbitol, sorbitan; alkylene glycols such as ethylene glycol and propylene glycol and their polymers; pentaerythritol, dipentaerythritol, trimethylolpropane, etc. may be used. These polyhydric alcohols may be used individually or in combination of two or more.

[0057] Furthermore, it is particularly preferable to use a triglyceride consisting of glycerin and a fatty acid and / or a derivative of a fatty acid as the polyhydric alcohol fatty acid ester. Examples of such triglycerides include 12-hydroxystearate triglyceride.

[0058] The lubricant content, when the total filler-containing layer is 100 parts by mass, can be, for example, 5 parts by mass or less, and may be 0.5 to 5 parts by mass, or 1 to 4 parts by mass. This is advantageous for improving the granulation properties of the resin composition. However, if the lubricant content exceeds 5 parts by mass, it may become difficult to ensure good physical properties of the film.

[0059] <Other Components> The filler-containing layer may, if necessary, further contain other components besides the biomass filler, unmodified polyolefin, dispersant, any olefin-based elastomer, and any lubricant mentioned above. Examples of other components include additives such as compatibilizers, thermoplastic resins, eye discharge inhibitors, MFR adjusters, stabilizers, antioxidants, antistatic agents, colorants, and anti-bubble agents.

[0060] Furthermore, the compatibilizer has the function of acting on the interface between the biomass filler and the resin component to improve the compatibility (adhesion) of the interface and promote the dispersion of the biomass filler into the resin component. When the resin composition contains a compatibilizer, the biomass filler becomes easier to disperse in the resin composition and film, the affinity between the biomass filler and the resin increases, and the appearance and physical properties of the film are improved. In addition, the materials added as dispersants and lubricants as described above may also function as compatibilizers. As for the compatibilizer, although this is not intended to limit it, materials that have the function of a compatibilizer among the materials exemplified as dispersants and lubricants described above may be used, or other generally known compatibilizers may be used. Among the materials exemplified as dispersants and lubricants described above, preferred materials that have the function of a compatibilizer are, for example, MA-PO and polyhydric alcohol fatty acid esters.

[0061] Furthermore, although not intended to be limiting, the thermoplastic resin can employ a similar configuration to the unmodified polyolefins mentioned above.

[0062] If the filler-containing layer contains a compatibilizer as another component, the amount of compatibilizer added is, for example, 0.05 to 4 parts by mass, preferably 0.1 to 1 part by mass, when the total filler-containing layer is 100 parts by mass. The content of other components other than the compatibilizer when the total filler-containing layer is 100 parts by mass is preferably less than 3 parts by mass, and more preferably less than 2 parts by mass.

[0063] <Specific Gravity> The specific gravity of at least one of the filler-containing layer and the heat-shrinkable film is preferably 0.95 or less, more preferably 0.93 or less, and even more preferably 0.90 or less. This reduces CO2 emissions during transport of the heat-shrinkable film. ２ This can contribute to reducing the amount of material used and further reducing the environmental burden. The specific gravity of the heat-shrinkable film can be measured in accordance with JIS K 7112 D method (density gradient tube method).

[0064] <Total Light Transmittance> The total light transmittance measured in at least one of the filler-containing layer and the heat-shrinkable film without the presence of colorants is preferably 75% or less, more preferably 20% to 73%, and even more preferably 30% to 70%. This total light transmittance can be measured in accordance with JIS K7361. Note that "total light transmittance measured without the presence of colorants" means the total light transmittance of the film if it does not contain colorants, or the total light transmittance measured for a film made only from components other than the colorants if it contains colorants. The more voids there are in the film, the more light incident on the film is scattered due to the voids, resulting in higher opacity, or in other words, higher whiteness, of the film. A lower total light transmittance of the film means that the film is more opacity and whiter. The more voids there are in the film, the higher the whiteness of the film and the lower the total light transmittance.

[0065] <HAZE> The haze of at least one of the filler-containing layer and the heat-shrinkable film is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more, from the viewpoint of ensuring high opacity (whiteness) of the film. The haze of the film can be measured in accordance with JIS K7136.

[0066] <Tensile Strength> The tensile strength [MPa] of at least one of the filler-containing layer and the heat-shrinkable film is preferably 1 MPa or more, and more preferably 2 MPa or more, in the smaller of the MD direction and the TD direction. The larger of the MD direction and the TD direction is preferably 3 MPa or more, and more preferably 4 MPa or more. The tensile strength can be measured by the method described in the examples.

[0067] <Tensile Elongation Rate> The tensile elongation rate [%] of at least one of the filler-containing layer and the heat-shrinkable film is preferably 100% or more in at least one of the MD direction and the TD direction, and more preferably 200% or more. The tensile elongation rate can be measured by the method described in the examples.

[0068] <Heat Shrinkage Rate> The heat shrinkage rate of at least one of the filler-containing layer and the heat-shrinkable film is 40% or more. This heat shrinkage rate may be in any direction within the plane of the film, for example, it may be in the MD direction or the TD direction. There is no particular upper limit to the heat shrinkage rate, but it may be 80% or less, for example.

[0069] For example, the thermal shrinkage rate in the TD direction at 100°C of at least one of the filler-containing layer and the heat-shrinkable film, as measured by the method described in the examples, is preferably 41% or more, more preferably 50% or more, and even more preferably 55% or more.

[0070] <Natural Shrinkage Rate> The natural shrinkage rate of at least one of the filler-containing layer and the heat-shrinkable film, as measured by the method described in the examples, is not limited, but can be, for example, 5% or less, 3% or less, or 2.5% or less. This natural shrinkage rate may be the natural shrinkage rate in any direction in the in-plane direction of the film, for example, the natural shrinkage rate in the MD direction or the natural shrinkage rate in the TD direction. If the natural shrinkage rate is 5% or less, dimensional changes are less likely to occur when the film is stored, and quality such as printability can be maintained.

[0071] <Applications> The applications of the heat-shrinkable film disclosed herein are not intended to be limited, but specifically include labels for containers such as PET bottles and product packaging, outer bags for packaging products, shopping bags, garbage bags, etc. In particular, the heat-shrinkable film disclosed herein is suitable for labels because it possesses sufficient heat shrinkability, opacity, and breathability.

[0072] ≪Method for Manufacturing Heat Shrinkable Film≫ Next, an example of a method for manufacturing the heat shrinkable film according to this disclosure will be described.

[0073] The heat-shrinkable film relating to this disclosure can be manufactured, for example, by the following procedure, although this is not intended to limit the scope of the invention. For example, a resin composition is produced by pre-kneading and molding the above-mentioned biomass filler, a portion of the unmodified polyolefin, a dispersant, an optional olefin-based elastomer as needed, and an optional lubricant. A resin compound is prepared by mixing the resin composition with the remaining unmodified polyolefin as a diluent resin and various optional additives, and this compound is subjected to various molding processes to produce a filler-containing layer. Other layers are formed on one or both sides of the filler-containing layer as needed by generally known methods such as lamination or hot melt. Alternatively, a multilayer film may be produced by co-extrusion using the above-mentioned resin compound and the raw materials for the other layers. In this specification, the unmodified polyolefin pre-blended in the resin composition may be referred to as unmodified polyolefin (A), and the unmodified polyolefin for dilution may be referred to as unmodified polyolefin (B). In addition, a resin composition may be produced using all the components, and this resin composition may be subjected to various molding processes to produce a filler-containing layer.

[0074] The resin composition is not limited, but it is preferable that it be in the form of a masterbatch, preferably in the form of pellets. This allows for smoother feeding from the hopper to the screw in the extruder process, accommodating films with various biomass filler content and various molding methods, and is easier to handle because it is less likely to scatter compared to powder.

[0075] The resin compound may be obtained, for example, by dry-blending the above-mentioned resin composition and an unmodified polyolefin (B) before putting them into the molding machine, or by putting them into the molding machine in a desired order and kneading them inside the molding machine. In this specification, the term "resin compound" is a concept that includes both the dry-blended state and the state that has been kneaded inside the molding machine.

[0076] The unmodified polyolefin (B) may be the same as or different from the unmodified polyolefin (A). From the viewpoint of obtaining excellent physical properties of the film while ensuring excellent moldability of the resin composition and resin compound, LDPE may be used as the unmodified polyolefin (A) and LLDPE may be used as the unmodified polyolefin (B).

[0077] Furthermore, the ratio of unmodified polyolefin (A) to unmodified polyolefin (B) is not particularly limited and can be appropriately determined as needed to ensure good moldability of the resin composition and resin compound, as well as excellent physical properties of the film.

[0078] <Manufacturing of Resin Composition> First, biomass filler, dispersant, and optional lubricant are mixed in predetermined proportions. Then, the resulting mixture is mixed with unmodified polyolefin (A), optional olefin-based elastomer, and optional other components in predetermined proportions. The mixture is then melt-kneaded in a co-screw extruder equipped with a strand die at a predetermined temperature, for example, 150°C or lower, preferably 140°C to 150°C, and extruded into strands. The extruded mixture is then cut to obtain pellets of the resin composition.

[0079] Regarding mixing methods, dry mixing using a super mixer, Henschel mixer, etc., is one option. In this case, from the viewpoint of improving the mixing efficiency of the biomass filler, dispersant, and lubricant, if the dispersant is in pellet form, for example, it may be crushed beforehand before mixing with the biomass filler and lubricant.

[0080] <Molding of filler-containing layer> A filler-containing layer is obtained by molding pellets of the above-mentioned resin composition, or a resin compound consisting of pellets of the above-mentioned resin composition, unmodified polyolefin (B), and an optional additive, using a generally known molding method.

[0081] For example, when using inflation molding as the molding method, the above resin composition or resin compound is melted and kneaded in a single-screw extruder at a predetermined temperature, preferably 140°C to 200°C, but not limited to, for example, 200°C or less, guided into a circular die and extruded, while simultaneously blowing air into it to expand it and form it into a film, and the film is wound up with a winding roll to obtain a filler-containing layer.

[0082] Furthermore, it is preferable to secondarily stretch the base film obtained by inflation molding using the above-mentioned resin composition or resin compound. In other words, the method for manufacturing a heat-shrinkable film according to the present disclosure preferably comprises the steps of obtaining a base film by inflation molding and secondarily stretching the base film to obtain a stretched film as a filler-containing layer.

[0083] In this specification, the stretching of the resin composition or resin compound in the process of obtaining the raw film may be referred to as "primary stretching," and further stretching of the raw film may be referred to as "secondary stretching" or simply "stretching." The film after secondary stretching may also be referred to as "stretched film."

[0084] By performing secondary stretching on the raw film, voids are formed between at least a portion of the biomass filler and other components in the film, thereby improving the film's air permeability.

[0085] The method of secondary stretching is not particularly limited, and generally known methods can be employed. Specifically, for example, the raw film can be stretched using equipment such as a continuous tenter or batch tenter. The direction of stretching is not particularly limited and may be either the MD direction, which is the flow direction of the resin during raw film manufacturing, or the TD direction, which is perpendicular to the MD direction. Secondary stretching may also be performed in a direction different from both the MD and TD directions. Furthermore, secondary stretching may be performed in both the MD and TD directions. In this case, biaxial stretching may be performed, where secondary stretching in one direction (MD or TD) is performed first, followed by secondary stretching in the other direction.

[0086] The stretching ratio for secondary stretching is preferably 3 times or more, more preferably 3.2 times or more, and particularly preferably 3.5 times or more and 5 times or less, relative to the original film. The strength of the stretched film improves as the stretching ratio increases. On the other hand, in films with a high biomass filler content, increasing the secondary stretching ratio may cause the film to break.

[0087] The thickness of the stretched film is preferably 0.2 to 0.9 times the thickness of the original film, more preferably 0.3 to 0.85 times, and even more preferably 0.4 to 0.8 times.

[0088] The thickness of the raw film roll (also called the "thickness before stretching") is not particularly limited, but from the viewpoint of manufacturing stability, it can be, for example, 60 μm to 250 μm, or 80 μm to 210 μm.

[0089] The thickness of the stretched film (also called the "thickness after stretching") can be 30 μm or more and 140 μm or less, or 50 μm or more and 120 μm or less.

[0090] The film temperature during secondary stretching may be, for example, room temperature (e.g., 25°C), but is preferably 30°C or higher, more preferably 50°C or higher, and particularly preferably 70°C or higher. Setting the temperature during secondary stretching to 30°C or higher improves the film's breathability and improves its suitability for lamination.

[0091] The present disclosure will be described below based on examples. However, the present disclosure is not limited to these examples, and these examples may be modified or altered in accordance with the spirit of the present disclosure, and such modifications do not exclude them from the scope of the present disclosure.

[0092] <Materials> The materials used in this embodiment are shown below. Note that MFR1 is the value under the conditions of temperature: 190°C and load: 2.16 kg in accordance with the provisions of JIS K 7210-1:2014. MFR2 is the value under the conditions of temperature: 230°C and load: 2.16 kg in accordance with the provisions of JIS K 7210-1:2014. MFR3 is the value under the conditions of temperature: 190°C and load: 2.16 kg in accordance with the provisions of JIS K 6922-2:2018. (1) Biomass filler corn starch (average particle size D50: 17.3 μm, 10% particle size D10: 9.95 μm, 90% particle size D90: 30.9 μm, manufactured by Nippon Corn Starch Co., Ltd., product name: Industrial Corn Starch Y-3P) (2) Unmodified polyolefin (A) (2-1) ULDPE-1 (ultra-low density polyethylene, density: 0.900 g / cm³) ３ MFR3: 0.8 g / 10 min, low-temperature melting point: 86.7 °C, high-temperature melting point: 110.6 °C, crystalline fusion enthalpy: 92 mJ / mg, thermal shrinkage rate (100 °C x 10 sec): 64%, manufactured by Tosoh Corporation, product name: LUMITAC (registered trademark) 12-1) (2-2) ULDPE-2 (ultra-low density polyethylene, density: 0.901 g / cm³) ３ (2-3) LLDPE (linear low-density polyethylene, density: 0.913 g / cm³) ３ (2-4) LDPE (Low-density polyethylene, Density: 0.922 g / cm³) ３, MFR1: 2 g / 10 min, manufactured by Lotte Chemical Corporation, trade name: TITANLEN (registered trademark) LDF200YZ) (3) Olefin-based elastomer (3-1) Propylene-based elastomer 1 (propylene-ethylene copolymer, ethylene unit content: 16% by mass, density: 0.862 g / cm ３ , MFR1: 1.4 g / 10 min, MFR2: 3 g / 10 min, softening point: 53.9°C, manufactured by ExxonMobil, trade name: Vistamaxx (registered trademark) 6102FL) (3-2) Propylene-based elastomer 2 (propylene-ethylene copolymer, ethylene unit content: 6% by mass, density: 0.879 g / cm ３ , MFR2: 10,000 g to 100,000 g / 10 min (stated as a converted value based on melt viscosity since actual measurement is not possible), melting point: 97°C, manufactured by ExxonMobil, trade name: Vistamaxx (registered trademark) 8880) Further, MFR1 of a 1:1 mixture (mass ratio) of propylene-based elastomer 1 and propylene-based elastomer 2 was 15.4 g / 10 min (Experimental Examples 1 to 5, 7, 8). (4) Dispersant (4-1) MA-PO (olefin-based wax, α-olefin-maleic anhydride copolymer: 66.8% by mass, α-olefin-based polymer: 32.9% by mass, maleic anhydride: 0.3% by mass, melting point: 70 to 76°C, melt viscosity: 140 to 210 mPa·s, acid value: 95 to 110 mgKOH / g (JIS K 2501), weight average molecular weight Mw: 6.7×10 ３ , manufactured by Mitsubishi Chemical Corporation, trade name: DIACARNA (registered trademark) 30M) (4-2) Glycerin fatty acid ester (citric acid saturated fatty acid monoglyceride, manufactured by Riken Vitamin Co., Ltd., trade name: Poem (registered trademark) K-30P) (5) Lubricant polyhydric alcohol fatty acid ester (triglyceride 12-hydroxystearate, density: 0.888 g / cm ３(Manufactured by Riken Vitamin Co., Ltd., product name: Rikemar (registered trademark) TG-12) (6) Unmodified polyolefin (B) (2-1) ULDPE-1 or (2-3) LLDPE of unmodified polyolefin (A) was used. In addition, LLDPE as a base polymer contained in (7) Anti-foaming agent below was also considered as part of unmodified polyolefin (B). (7) Anti-foaming agent (Calcium oxide, master pellet containing 65% by mass of calcium oxide and 35% by mass of LLDPE as a base polymer, density: 1.73 g / cm³) ３ (Manufactured by Omi Chemical Industry Co., Ltd., product name: BELL-CML EM) [Particle size of biomass filler] The average particle size D50, 10% particle size D10, and 90% particle size D90 of the biomass filler were measured on a volume basis using a laser diffraction particle size distribution analyzer (Malvern dry particle size distribution analyzer, product name: MASTER SIZER 3000).

[0093] [Weight-average molecular weight of MA-PO] The weight-average molecular weight Mw of MA-PO was measured using the following measurement method and conditions.

[0094] GPC system: Manufactured by Tosoh Corporation, product name: HLC-8321GPC / HT (detector: RI) Column: Manufactured by Tosoh Corporation, product name: TSKgel guardcolumnH ＨＲ (39) HT (7.5 mm I.D. x 7.5 cm) x 1 + Tosoh Corporation, Product name: TSKgel GMH ＨＲ -H(20)HT (7.8 mI.D. × 30 cm) × 3 tubes Eluent: 1,2,4-trichlorobenzene (for GPC, manufactured by Fujifilm Wako Pure Chemical Industries) + BHT (0.05%) Flow rate: 1.0 mL / min Detection condition: polarity = (-) Injection volume: 0.3 mL Column temperature: 140°C System temperature: 40°C Sample concentration: 1 mg / mL Calibration curve: Fifth-order approximation curve using standard polystyrene manufactured by Tosoh Corporation Molecular weight: Polystyrene-equivalent molecular weight Pretreatment: The sample was weighed, the eluent was added, and it was dissolved by shaking at 140°C for 1 hour. Then, it was filtered by heating through a sintered filter with a pore size of 0.5 μm. No undissolved material was found by visual inspection.

[0095] <Experimental Examples 1-10> [Preparation of Resin Compositions] The resin compositions of Experimental Examples 1-10 were prepared according to the formulations shown in Table 1 and the following procedure.

[0096]

[0097] First, a mixture was obtained by mixing biomass filler, dispersant, and lubricant in a supermixer. Next, the obtained mixture and the remaining raw materials (unmodified polyolefin (A), propylene-based elastomer) were melt-kneaded in a co-direction twin-screw extruder under conditions of a molding temperature of 150°C and a screw rotation speed of 40 to 120 rpm, extruded into strands with a diameter of 2 to 4 mm, and the extruded kneaded material was cut to obtain resin composition pellets.

[0098] [Film Forming] - Manufacturing of Raw Film Rolls - In Experimental Examples 1 to 6, the obtained resin composition pellets, unmodified polyolefin (B), and anti-bubble agent were dry-blended in the proportions shown in Table 1 to obtain a resin compound. In Experimental Examples 1 to 6, the resin compound was melt-kneaded in a single-screw extruder at a molding temperature of 175°C and a screw rotation speed of 60 rpm. The mixture was then guided into a circular die for inflation molding, cooled and solidified by air cooling, and wound up on a winding machine. The width of the raw film roll (the width when the inflation-molded product is folded; that is, the film is formed into a cylindrical shape with a circumference of 200 mm) was 100 mm. The thickness of the raw film roll was the thickness shown in "Thickness Before Stretching" in Table 1. The screw specifications were full flight, L / D: 25, C / R: 3.08.

[0099] -Secondary Stretching- A 120 mm square film was cut from the raw film roll and placed in the stretching device of a batch tenter equipped with a stretching device and a stretching chamber. The stretching device was then moved to the stretching chamber, which had been pre-set to a predetermined temperature (see "Film Temperature During Stretching" in Table 1), and the temperature was raised for a certain period of time (e.g., 60 sec). After confirming that the sample and stretching device had stabilized at the predetermined temperature, stretching was performed in the MD direction at a predetermined secondary stretching ratio (e.g., 3x, 3.5x, or 4x) and stretching speed (e.g., 40 mm / sec). After stretching was completed, the stretching device was returned to its initial position and switched from heating mode to cooling mode. Air was blown onto the film to cool it until the film temperature reached approximately 65-55°C before the film was removed.

[0100] The "secondary stretching ratio" is expressed as the ratio of the length of the film after secondary stretching to the length of the original film in the MD direction.

[0101] No damage was observed when the raw film rolls from Experimental Examples 1 to 10 were subjected to secondary stretching at the secondary stretching ratios shown in Table 1.

[0102] <Measurement of Film Properties> The stretched films of Experimental Examples 1 to 10 were subjected to the following various measurements. The results are shown in Table 1.

[0103] [Thickness before stretching] The thickness of the film before stretching was measured using a micrometer (Mitutoyo Corporation coolant-proof micrometer). More specifically, the thickness of the film before stretching was measured at three points in the MD direction, and the average value was taken as the thickness of the film before stretching. The measurement points were set at least 50 mm apart from each other.

[0104] [Thickness after stretching] The thickness of the film after stretching was measured using a micrometer (Mitutoyo Corporation coolant-proof micrometer). More specifically, the thickness of the film after stretching was measured at three points in the stretching direction, and the average value was taken as the thickness of the film after stretching. The measurement points were set at least 50 mm apart from each other.

[0105] [Total Light Transmittance] The total light transmittance of the stretched film was measured in accordance with JIS K7361. More specifically, n=3 test pieces were cut from the stretched film. The total light transmittance of each test piece was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the median value was taken as the total light transmittance of the stretched film in question.

[0106] [HAZE] The haze of the stretched film was measured in accordance with JIS K7136. More specifically, n=3 test pieces were cut from the stretched film. The haze of each test piece was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the median value was taken as the haze of the target stretched film.

[0107] [Tensile Strength and Tensile Elongation] A dumbbell-shaped specimen (JIS K 6251 Dumbbell-shaped No. 3, width at both ends: 25 mm, total length: 100 mm, distance between gauge marks: 20 mm, width: 5 mm) was cut from the stretched film obtained in the MD direction and prepared as a test specimen. A tensile test was performed on this test specimen in accordance with JIS K7127, under an atmosphere of 23°C and 50% relative humidity, at a tensile speed of 200 mm / min, and the tensile strength (MPa) and tensile elongation (%) of the stretched film in the MD direction were measured.

[0108] - A dumbbell-shaped piece (JIS K 6251 Dumbbell-shaped No. 3, width at both ends: 25 mm, total length: 100 mm, gauge length: 20 mm, width: 5 mm) was cut from the stretched film obtained in the TD direction and prepared as a test specimen. A tensile test was performed on this test specimen in accordance with JIS K7127, under an atmosphere of 23°C and 50% relative humidity, at a tensile speed of 200 mm / min, and the tensile strength (MPa) and tensile elongation rate (%) of the film in the TD direction were measured. The tensile strength is the value of the force when the test specimen is stretched until it breaks during the tensile test. The tensile elongation rate is a value calculated using the following formula based on the gauge length at the time of breakage of the test specimen, which can be measured simultaneously with the tensile strength. Tensile elongation rate (%) = (Gauge length at fracture of the test specimen (mm) - Gauge length before tensile test (20 mm)) / Gauge length before tensile test (20 mm) × 100

[0109] [Heat Shrinkage Rate (100°C)] The obtained stretched film was cut into a 10 cm x 10 cm square so that one side was parallel to the TD direction, and this was used as a sample for measuring the heat shrinkage rate. This sample was immersed in 100°C ± 0.5°C hot water for 10 seconds. The length in the TD direction of the sample before immersion in hot water was defined as the length before shrinkage, and the length in the TD direction after immersion in hot water was defined as the length after shrinkage. The heat shrinkage rate in the TD direction at 100°C was calculated using the following formula: Heat shrinkage rate (%) = 100 × (length before shrinkage - length after shrinkage) / (length before shrinkage)

[0110] [Natural Shrinkage Rate] The stretched film obtained was cut into 10 cm x 10 cm squares with one side parallel to the TD direction to serve as a sample for measuring the natural shrinkage rate. The sample was placed in a constant temperature bath and left at 40°C for 7 days. The length in the TD direction of the sample before standing was defined as the length before shrinkage, and the length in the TD direction after standing was defined as the length after shrinkage. The natural shrinkage rate in the TD direction was calculated using the following formula: Natural shrinkage rate (%) = 100 × (length before shrinkage - length after shrinkage) / (length before shrinkage)

[0111] <Discussion> As shown in Table 1, secondary stretching of the raw film roll was possible in experimental examples 1 to 10.

[0112] Furthermore, in the stretched films of experimental examples 1 to 10, a tendency was observed for low total light transmittance and high haze. In other words, it was found that the opacity, or whiteness, of the stretched films was relatively high.

[0113] In the stretched films of Experimental Examples 1 to 10, the heat shrinkage rate (at 100°C) was 40% or more, demonstrating that the obtained films function as heat-shrinkable films.

[0114] Furthermore, it was shown that the stretched films in Experimental Examples 1 to 10 had a natural shrinkage rate of 5% or less, demonstrating that their quality could be maintained even during storage.

[0115] <Cross-sectional SEM observation of the film> Cross-sectional SEM observation in the TD direction was performed on the raw film rolls before stretching in Experimental Examples 3 and 4 using a scanning electron microscope (Hitachi High-Tech Science Co., Ltd., product name: Schottky Scanning Electron Microscope SU5000). The results are shown in Figure 1. As shown in Figure 1, it can be seen that the biomass filler is uniformly dispersed within the raw film roll.

[0116] <<Example Configuration>> The technology relating to this disclosure will be further described by the following embodiments.

[0117] [Configuration 1] A heat-shrinkable film having a layer containing a biomass filler, wherein the layer, when the entire layer is 100 parts by mass, contains 25 to 70 parts by mass of the biomass filler, 20 to 70 parts by mass of unmodified polyolefin, and 0.05 to 4 parts by mass of a dispersant, and the heat shrinkage rate of the layer at 100°C is 40% or more.

[0118] [Configuration 2] The heat-shrinkable film according to Configuration 1, wherein the biomass filler is starch.

[0119] [Configuration 3] The heat-shrinkable film according to Configuration 1 or Configuration 2, wherein the unmodified polyolefin is one or more of low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene.

[0120] [Configuration 4] The heat-shrinkable film according to any one of Configurations 1 to 3, wherein the dispersant comprises at least one of a maleic anhydride-modified polyolefin and a glycerin fatty acid ester.

[0121] [Configuration 5] The heat-shrinkable film according to any one of Configurations 1 to 4, wherein the layer further contains 0.5 to 5 parts by mass of a lubricant.

[0122] [Configuration 6] The heat-shrinkable film according to any one of Configurations 1 to 5, wherein the layer further contains 0.8 to 6 parts by mass of an olefin-based elastomer.

[0123] [Configuration 7] The heat shrinkable film according to any one of Configurations 1 to 6, wherein at least one of the heat shrinkable film and the layer is a stretched film with a stretching ratio of 3 times or more.

[0124] [Configuration 8] A resin composition for forming the layer contained in the heat-shrinkable film according to any one of Configurations 1 to 7, wherein, when the total resin composition is 100 parts by mass, it contains 25 to 70 parts by mass of the biomass filler, 20 to 70 parts by mass of the unmodified polyolefin, and 0.05 to 4 parts by mass of the dispersant.

[0125] [Composition 9] A resin compound containing the resin composition described in Composition 8.

[0126] As explained above, the heat-shrinkable film of this disclosure is useful because it can contribute to further reducing environmental impact by reducing the amount of synthetic resin used and the amount of GHG emissions.

Claims

1. A heat-shrinkable film having a layer containing a biomass filler, wherein the layer, when the entire layer is 100 parts by mass, contains 25 to 70 parts by mass of the biomass filler, 20 to 70 parts by mass of unmodified polyolefin, and 0.05 to 4 parts by mass of a dispersant, and the heat shrinkage rate of the layer at 100°C is 40% or more.

2. The heat-shrinkable film according to claim 1, wherein the biomass filler is starch.

3. The heat-shrinkable film according to claim 1, wherein the unmodified polyolefin is one or more of low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene.

4. The heat-shrinkable film according to claim 1, wherein the dispersant comprises at least one of a maleic anhydride-modified polyolefin and a glycerin fatty acid ester.

5. The heat-shrinkable film according to claim 1, wherein the layer further contains 0.5 to 5 parts by mass of a lubricant.

6. The heat-shrinkable film according to claim 1, wherein the layer further contains 0.8 to 6 parts by mass of an olefin-based elastomer.

7. The heat-shrinkable film according to claim 1, wherein at least one of the heat-shrinkable film and the layer is a stretched film with a stretching ratio of 3 times or more.

8. A resin composition for forming the layer contained in the heat-shrinkable film according to any one of claims 1 to 7, wherein the resin composition comprises, when the total resin composition is 100 parts by mass, 25 to 70 parts by mass of the biomass filler, 20 to 70 parts by mass of the unmodified polyolefin, and 0.05 to 4 parts by mass of the dispersant.

9. A resin compound containing the resin composition described in claim 8.

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