Method for producing thermoplastic resin film

Abstract

The present invention addresses the problem of providing a method which is for producing a thermoplastic resin film and which can suppress the contamination of a cast roll used for molding in the production of the thermoplastic resin film by means of a melt extrusion method. The problem is solved by a method for producing a thermoplastic resin film, the method including a conveyance step in which a molten resin composition (2) extruded from a die (1) is conveyed by a cast roll (3). In the conveyance step, air (5) having a specific flow rate and temperature is sprayed onto the film-like resin composition (2).

Description

Method for producing thermoplastic resin film

[0001] The present invention relates to a method for producing a thermoplastic resin film.

[0002] In recent years, the separate collection and composting of food waste has been promoted, particularly in Europe, and there is a demand for biodegradable plastic products that can be composted together with food waste. As an example of such a biodegradable plastic product, Patent Document 1 discloses a processed product obtained by thermoforming a sheet made of a polylactic acid-based polymer.

[0003] Regarding plastics, environmental problems caused by discarded plastics have also been highlighted, and it has become clear that large amounts of plastics, particularly those dumped in the ocean or that have entered the ocean via rivers, are drifting in the oceans on a global scale. Because such plastics retain their shape for long periods of time, they can trap and capture marine organisms, a phenomenon known as ghost fishing, and when ingested by marine organisms, can remain in their digestive tracts, causing feeding disorders, and other problems that have been pointed out as having an impact on the ecosystem.

[0004] Furthermore, it has been pointed out that microplastics, which are plastics that have broken down and become tiny particles due to ultraviolet rays and other factors, absorb harmful compounds in seawater, and when marine organisms ingest these, the harmful substances are absorbed into the food chain.

[0005] The use of biodegradable plastics is expected to solve the problem of marine pollution caused by plastics. However, a report compiled by the United Nations Environment Programme in 2015 pointed out that conventional biodegradable plastics such as polylactic acid cannot be expected to decompose in a short period of time in the cold ocean, and therefore cannot be used to combat marine pollution.

[0006] In this situation, polyhydroxyalkanoate resins, which are thermoplastic resins that can be used as plastics and can be rapidly biodegraded even in seawater, have attracted attention as materials that can solve the above problems.

[0007] Patent Document 2 describes a polyester resin composition containing two types of polyhydroxyalkanoates, and describes that examples of molded articles thereof include films and sheets.

[0008] Japanese Patent Publication No. 2002-248677 International Publication No. 2015 / 146194

[0009] As a method for producing a film made of a crystalline thermoplastic resin (thermoplastic resin film), a method (melt extrusion method) in which a molten crystalline thermoplastic resin is brought into contact with a casting roll to form the thermoplastic resin is known. In studying a method for producing a thermoplastic resin film using the melt extrusion method, the present inventors found that this method has a problem in that the casting roll used for forming the thermoplastic resin is contaminated.

[0010] One embodiment of the present invention has been made in consideration of the above-described current situation, and its object is to provide a method for producing a thermoplastic resin film that can suppress contamination of a casting roll used in molding when producing a thermoplastic resin film by a melt extrusion method.

[0011] In order to solve the above problems, one aspect of the present invention is a method for producing a thermoplastic resin film, comprising a conveying step of extruding a resin composition containing a molten crystalline thermoplastic resin from a die into a film, bringing the resulting film-like resin composition into contact with a casting roll, and conveying the film-like resin composition by rotating the casting roll, wherein the conveying step includes an air blowing step of blowing air into a portion where the film-like resin composition and the casting roll first come into contact, or in the vicinity thereof, to bring the film-like resin composition into close contact with the casting roll, wherein the air flow rate in the air blowing step is 50 L / min to 1,000 L / min, and the air temperature is Tc-95°C to Tc°C, where Tc is the crystallization temperature of the resin composition.

[0012] According to one embodiment of the present invention, it is possible to provide a method for producing a thermoplastic resin film that can suppress contamination of a casting roll used in molding when producing a thermoplastic resin film by melt extrusion.

[0013] Fig. 1 is a schematic view showing an example of a production line that performs the transfer step according to the present manufacturing method; Fig. 2 is a schematic view showing another example of a production line that performs the transfer step according to the present manufacturing method; Fig. 3 is a schematic view showing another example of a production line that performs the transfer step according to the present manufacturing method; and Fig. 4 is a schematic view showing another example of a production line that performs the transfer step according to the present manufacturing method.

[0014] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0015] A method for producing a thermoplastic resin film according to one embodiment of the present invention includes a conveying step of extruding a resin composition containing a molten crystalline thermoplastic resin through a die into a film, contacting the resulting film-like resin composition with a casting roll, and conveying the film-like resin composition by rotating the casting roll. The conveying step includes an air blowing step of blowing air into the area where the film-like resin composition first contacts the casting roll or its vicinity to form the film-like resin composition by adhering it to the casting roll. In the air blowing step, the air flow rate is 50 L / min to 1,000 L / min, and the air temperature is Tc-95°C to Tc°C, where Tc is the crystallization temperature of the resin composition. In this specification, the "method for producing a thermoplastic resin film according to one embodiment of the present invention" may also be referred to as the "present production method."

[0016] While studying a method for producing a thermoplastic resin film using a melt extrusion method, the present inventors discovered that in this method, contamination occurs on the casting roll used to mold the thermoplastic resin and accumulates over time. This contamination is particularly pronounced when the extruded resin composition contains a crystal nucleating agent. Furthermore, when a thermoplastic resin film is produced using a contaminated casting roll, the contamination is transferred to the resulting thermoplastic resin film, resulting in a film with poor appearance.

[0017] In light of the above-described circumstances, the present inventors have conducted extensive research into methods for suppressing contamination of the casting roll used in molding in the production of thermoplastic resin films by melt extrusion. As a result, they have discovered that the generation and accumulation of contamination on the casting roll can be suppressed by blowing air at a specific flow rate and temperature onto the extruded resin composition, which led to the completion of the present invention.

[0018] That is, the present production method can provide a method for producing a thermoplastic resin film that can suppress contamination of a casting roll used in molding when producing a thermoplastic resin film by melt extrusion. Furthermore, in conventional methods for producing a thermoplastic resin film by melt extrusion, contamination accumulates on the casting roll, which requires periodic removal, making it impossible to produce a thermoplastic resin film with good appearance continuously for a long period of time. However, the present production method does not cause contamination to accumulate on the casting roll, and does not require removal of the contamination, making it possible to stably produce a thermoplastic resin film with good appearance continuously for a long period of time.

[0019] First, each material used in this manufacturing method will be described in detail.

[0020] <Resin Composition> In the present production method, a resin composition containing a crystalline thermoplastic resin is used as a raw material for the thermoplastic resin film. The resin composition used in the present production method may consist of only the crystalline thermoplastic resin, or may contain other components described below in addition to the crystalline thermoplastic resin.

[0021] (Crystalline Thermoplastic Resin) The crystalline thermoplastic resin contained in the resin composition according to the present production method is not particularly limited, and examples thereof include polyethylene-based resins, polypropylene-based resins, polyamide-based resins, polyacetal-based resins, polyethylene terephthalate-based resins, polybutylene terephthalate-based resins, polymethylpentene-based resins, polyphenylene sulfide-based resins, polyether ether ketone-based resins, liquid crystal polymers, polytetrafluoroethylene-based resins, polyhydroxyalkanoate-based resins, etc. Furthermore, the resin composition according to the present production method may contain, as a thermoplastic resin component, an aliphatic polyester-based resin other than polyhydroxyalkanoate-based resins, such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, or polylactic acid, or an aliphatic aromatic polyester-based resin such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, or polybutylene azelate terephthalate. Among these thermoplastic resins, polyhydroxyalkanoate resins, aliphatic polyester resins other than polyhydroxyalkanoate resins, or aliphatic aromatic polyester resins are preferred as the crystalline thermoplastic resin contained in the resin composition according to the present manufacturing method, as they have excellent biodegradability. Polyhydroxyalkanoate resins are more preferred, as they biodegrade rapidly even in seawater, thereby further reducing the environmental burden.

[0022] (Polyhydroxyalkanoate Resin) Polyhydroxyalkanoate resin (hereinafter sometimes referred to as "PHA") is a general term for polymers containing hydroxyalkanoate (hydroxy)alkanoic acid as a monomer unit (monomer repeating unit, sometimes simply referred to as monomer unit), and is biodegradable. In particular, in this specification, "PHA" refers to a polymer containing hydroxyalkanoate repeating units, which contains 50 mol% or more of hydroxyalkanoate repeating units out of all monomer repeating units (100 mol%). The PHA contained in the resin composition according to this production method is preferably a PHA containing 60 mol% or more of hydroxyalkanoate repeating units out of all monomer repeating units (100 mol%), more preferably a PHA containing 70 mol% or more.

[0023] When the resin composition according to the present manufacturing method contains a PHA as a thermoplastic resin component, the content of the PHA in 100% by weight of the thermoplastic resin component is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and even more preferably 80% by weight or more. The upper limit of the PHA content is not particularly limited and may be 100% by weight. That is, the resin composition according to the present manufacturing method may contain only PHA as a thermoplastic resin component (in other words, the thermoplastic resin is PHA).

[0024] The PHA that may be contained in the resin composition according to the present production method is not particularly limited, and examples thereof include poly(3-hydroxyalkanoate)-based resins (hereinafter sometimes referred to as "P3HA") and poly(4-hydroxyalkanoate)-based resins. The resin composition according to the present production method may contain only one type of PHA as the crystalline thermoplastic resin component, or may contain two or more types of PHA. P3HA is particularly preferred as the PHA contained in the resin composition according to the present production method, as it has excellent biodegradability and can be produced using renewable biomass resources as raw materials, making it effective in reducing the environmental burden.

[0025] P3HA has the formula: [-CHR-CH ２-CO-O-] (wherein R is C ｎ H ２ｎ＋１ where n is an integer of 1 to 15.) as an essential repeating unit. In this specification, "P3HA" refers to a polymer containing 3-hydroxyalkanoate repeating units in an amount of 50 mol % or more of all monomer repeating units (100 mol %).

[0026] Among P3HAs, poly(3-hydroxybutyrate) resins are preferred as the P3HA contained in the resin composition according to the present production method, because they can be produced by microorganisms and have a low environmental impact during production. The poly(3-hydroxybutyrate) resin is not particularly limited as long as it is a polymer containing a 3-hydroxybutyrate unit, and may be, for example, a homopolymer of 3-hydroxybutyrate, or a copolymer of 3-hydroxybutyrate and a 3-hydroxyalkanoate other than 3-hydroxybutyrate, such as 3-hydroxypropionate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynanoate, 3-hydroxydecanoate, 3-hydroxydodecanoate, 3-hydroxydodecenoate, 3-hydroxytetradecanoate, 3-hydroxyhexadecanoate, and 3-hydroxyoctadecanoate. The resin composition according to the present production method may contain, as the poly(3-hydroxybutyrate)-based resin, a mixture of a homopolymer of 3-hydroxybutyrate and a copolymer of one or more types of 3-hydroxybutyrate with a 3-hydroxyalkanoate other than 3-hydroxybutyrate, or a mixture of a copolymer of two or more types of 3-hydroxybutyrate with a 3-hydroxyalkanoate other than 3-hydroxybutyrate.

[0027] When the poly(3-hydroxybutyrate) resin is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxybutyrate) resin is preferably 3-hydroxybutyrate units / other hydroxyalkanoates = 99 / 1 to 80 / 20 (mol % / mol %), more preferably 97 / 3 to 85 / 15 (mol % / mol %), from the viewpoint of achieving both strength and productivity of the resulting thermoplastic resin film.

[0028] The average content ratio of each monomer unit in all monomer units constituting a poly(3-hydroxybutyrate)-based resin can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139. Here, the average content ratio of a monomer in a resin (copolymer) refers to the molar ratio of each monomer unit in all monomer units constituting the copolymer (e.g., a poly(3-hydroxybutyrate)-based resin). Note that when the target resin is a mixture of two or more copolymers, the average content ratio of a monomer in the resin refers to the molar ratio of each monomer unit contained in the entire mixture.

[0029] Specific examples of poly(3-hydroxybutyrate)-based resins include poly(3-hydroxybutyrate) (hereinafter, sometimes referred to as "P3HB"), which is a homopolymer of 3HB, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter, sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate). The resin composition according to the present production method may contain only one of these resins as the poly(3-hydroxybutyrate)-based resin, or may contain two or more of them.

[0030] P3HA can be produced by microorganisms. Such microbially produced P3HA is typically composed solely of D-form (R-form) 3-hydroxyalkanoic acid repeating units. Among microbially produced P3HAs, P3HB and P3HB3HH are preferred, with P3HB3HH being more preferred, due to ease of industrial production.

[0031] Microorganisms that produce P3HA are known. For example, the first bacterium to produce a P3HB homopolymer was Bacillus megaterium, discovered in 1925. Other examples include naturally occurring microorganisms such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. In these microorganisms, P3HB accumulates intracellularly. Examples of bacteria that produce copolymers of 3HB and other hydroxyalkanoates include Aeromonas caviae, a P3HB3HH-producing bacterium, and Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bacteriol., 179, pp. 4821-4830 (1997)), into which genes encoding P3HA synthases have been introduced to increase P3HB3HH productivity. In addition to the above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may also be used, depending on the P3HA to be produced. Furthermore, when culturing these microorganisms, the culture conditions, including the type of substrate, may be optimized.

[0032] The weight-average molecular weight of the PHA is not particularly limited, but from the viewpoint of achieving both strength and productivity of the resulting thermoplastic resin film, the weight-average molecular weight of the PHA is preferably 50,000 to 3,000,000, preferably 100,000 to 2,000,000, and more preferably 150,000 to 1,500,000. Note that, when the resin composition according to this production method is a mixture containing two or more PHAs, the weight-average molecular weight of the PHA refers to the weight-average molecular weight of the mixture. The weight-average molecular weight of the PHA is... From the viewpoint of achieving both film strength and productivity, the weight-average molecular weight can be measured using gel permeation chromatography (GPC) (Shimadzu Corporation's "High-Performance Liquid Chromatograph 20A System"), a polystyrene gel column (Showa Denko K.K.'s "K-G 4A" or "K-806M", etc.), and chloroform as the mobile phase. The weight average molecular weight can be determined as a molecular weight converted into polystyrene using a calibration curve obtained by measuring polystyrenes with known molecular weights using the same measurement method.

[0033] (Additives) The resin composition according to the present production method may contain usable additives to the extent that the effects of the present invention are not impaired. Examples of such additives include colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, fillers, plasticizers, organic peroxides, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding properties improvers. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use.

[0034] The crystal nucleating agent, lubricant, organic peroxide, filler, and plasticizer will be described in more detail below.

[0035] (Crystal Nucleating Agent) The resin composition according to the present production method may contain a crystal nucleating agent. By including a crystal nucleating agent in the resin composition according to the present production method, crystallization of the thermoplastic resin can be promoted, thereby improving the strength of the resulting thermoplastic resin film. Examples of crystal nucleating agents that may be included in the resin composition according to the present production method include polyhydric alcohols such as pentaerythritol, galactitol, and mannitol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, pentaerythritol is preferred because of its particularly excellent effect in promoting the crystallization of thermoplastic resins. The resin composition according to the present production method may contain only one of these crystal nucleating agents, or two or more of them. The content ratio can also be appropriately adjusted depending on the purpose.

[0036] The content (mixed amount) of the crystal nucleating agent in the resin composition according to the present production method is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, relative to 100 parts by weight of the total amount of the thermoplastic resin contained in the resin composition.

[0037] (Lubricant) The resin composition according to the present production method may contain a lubricant. The inclusion of a lubricant in the resin composition according to the present production method has advantages such as promoting crystallization of the thermoplastic resin and improving the releasability of the resulting thermoplastic resin film from a casting roll. Examples of lubricants that may be contained in the resin composition according to the present production method include behenic acid amide, oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, N-stearylbehenic acid amide, N-stearylerucic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, ethylene bislauric acid amide, ethylene biscapric acid amide, p-phenylene bisstearic acid amide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenic acid amide and erucic acid amide are preferred because of their particularly excellent lubricating effect on thermoplastic resins (especially PHA). The resin composition according to the present production method may contain only one of these lubricants, or two or more of them. The content ratio can also be adjusted appropriately depending on the purpose.

[0038] The content (mixed amount) of the lubricant in the resin composition according to the present production method is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, relative to 100 parts by weight of the total amount of the thermoplastic resin contained in the resin composition.

[0039] (Organic Peroxide) The resin composition according to the present production method may contain an organic peroxide. By containing an organic peroxide in the resin composition according to the present production method, it is possible to modify the thermoplastic resin component, which has the advantage of enabling stable film processing. Examples of organic peroxides that may be contained in the resin composition according to the present production method include diisobutyl peroxide, cumyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, bis(4-t-butylcyclohexyl)peroxydicarbonate, bis(2-ethylhexyl)peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl)peroxide, dilauroyl peroxide, 1,1,3,3-tetramethylbutyl Examples of peroxyalkylene compounds include t-butylperoxy-2-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butylperoxy-2-ethylhexyl carbonate, t-butylperoxyisopropyl carbonate, 1,6-bis(t-butylperoxycarbonyloxy)hexane, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyacetate, t-butylperoxybenzoate, t-amylperoxy-3,5,5-trimethylhexanoate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, and 2,2-di-t-butylperoxybutane. Among these, t-butylperoxy 2-ethylhexyl carbonate or t-butylperoxy isopropyl carbonate is preferred because it has the advantage of being uniformly dispersed and the modification reaction is easily controlled.The resin composition according to the present production method may contain only one of these organic peroxides or may contain two or more of them, and the content ratio can be appropriately adjusted depending on the purpose.

[0040] The content (mixed amount) of the organic peroxide in the resin composition according to the present production method is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.03 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, relative to 100 parts by weight of the total amount of the thermoplastic resins contained in the resin composition.

[0041] (Filler) The resin composition according to the present manufacturing method may contain a filler. By including a filler in the resin composition according to the present manufacturing method, it is possible to provide a thermoplastic resin film with higher strength. The filler that may be included in the resin composition according to the present manufacturing method may be either an inorganic filler or an organic filler, or a combination of both. The inorganic filler is not particularly limited, but examples include silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, carbon black, etc. The resin composition according to the present manufacturing method may contain only one of these fillers, or two or more of them. Furthermore, the content ratio can be appropriately adjusted depending on the purpose. Only one type of inorganic filler may be used, or two or more types may be used in combination.

[0042] The content (mixed amount) of the filler in the resin composition according to the present manufacturing method is not particularly limited, but is preferably 1 to 100 parts by weight, more preferably 3 to 80 parts by weight, even more preferably 5 to 70 parts by weight, and even more preferably 10 to 60 parts by weight, relative to 100 parts by weight of the total amount of the thermoplastic resin contained in the resin composition.

[0043] (Plasticizer) The resin composition according to the present manufacturing method may contain a plasticizer. By including a plasticizer in the resin composition according to the present manufacturing method, a thermoplastic resin film with excellent flexibility can be provided. The plasticizer that may be included in the resin composition according to the present manufacturing method is not particularly limited, and examples thereof include glycerin ester compounds, citrate ester compounds, sebacic acid ester compounds, adipate ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among these, glycerin ester compounds, citrate ester compounds, sebacic acid ester compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on thermoplastic resins (especially PHA). Specific examples of glycerin ester compounds include glycerin diacetomonolaurate. Specific examples of citrate ester compounds include acetyl tributyl citrate. Specific examples of sebacic acid ester compounds include dibutyl sebacate. Specific examples of dibasic acid ester compounds include benzyl methyl diethylene glycol adipate. The resin composition according to the present production method may contain only one of these plasticizers, or may contain two or more of them. Furthermore, the content ratio can be appropriately adjusted depending on the purpose.

[0044] The content (mixed amount) of the plasticizer in the resin composition according to the present production method is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, relative to 100 parts by weight of the total amount of the thermoplastic resin contained in the resin composition.

[0045] (Crystallization Temperature (Tc)) The crystallization temperature (Tc) of the resin composition according to the present production method is not particularly limited, and may be, for example, 50°C to 150°C, or 100°C to 150°C.

[0046] In this specification, the crystallization temperature of a resin composition is a value measured by the following method: using a differential scanning calorimeter (for example, a differential scanning calorimeter "DSC-60" manufactured by Shimadzu Corporation), the target resin composition is heated from room temperature to 200°C at a heating rate of 10°C / min, held at 200°C for 1 minute, and then cooled to room temperature at a cooling rate of 10°C / min. The exothermic peak temperature that occurs in this process is taken as the crystallization temperature of the resin composition.

[0047] Next, each step included in this manufacturing method will be described in detail.

[0048] <Conveying step> The present production method includes a conveying step of extruding a resin composition containing a molten crystalline thermoplastic resin through a die into a film, bringing the obtained film-like resin composition into contact with a casting roll, and conveying the film-like resin composition by the rotation of the casting roll.

[0049] A specific embodiment of the conveying step will be described in more detail below with reference to Fig. 1. Fig. 1 is a schematic diagram showing a part of a production line in which the conveying step according to the present production method is carried out. Note that the description of the "resin composition containing a crystalline thermoplastic resin (resin composition)" will be omitted in this section, and the description in the above <Resin composition> section will be used as appropriate.

[0050] As shown in Figure 1, in the conveying step, first, a molten resin composition 2 is continuously extruded downward from a die 1 in the form of a film. The die 1 is connected to an extruder (not shown) and has the function of extruding the molten resin composition 2 melt-kneaded in the extruder while processing it into a film-like shape. The shape of the die 1 is not particularly limited, and may be, for example, a T-type (T-die). The extruder connected to the die 1 is also not particularly limited as long as it can melt-knead the resin composition before melting, and may be a screw extruder, a twin-screw extruder, a tandem extruder, or the like.

[0051] In the conveying process, the thickness of the film-like resin composition 2 extruded from the die 1 can be adjusted by adjusting the take-up speed of the resin composition 2 at the die 1 and the discharge amount of the resin composition 2 from the extruder connected to the die 1.

[0052] The film-like resin composition 2 extruded from the die 1 comes into contact with a casting roll 3 arranged below the die 1, and is transported downstream in the transport direction with one side of the composition in contact with the casting roll 3. The casting roll 3 is a cylindrical member configured so that its surface temperature can be set as desired. Immediately after being extruded from the die 1, the film-like resin composition 2 has some thermoplastic resin in a molten state (uncrystallized state). However, upon contact with the casting roll 3, the crystallization of this uncrystallized thermoplastic resin progresses, and the composition is molded into a thermoplastic resin film. The molded thermoplastic resin film is transported downstream in the transport direction by the rotation of the casting roll 3.

[0053] The temperature (surface temperature) of the casting roll 3 in the conveying step is not particularly limited, but is preferably 10°C to Tc-5°C, more preferably 12°C to Tc-10°C, and even more preferably 15°C to Tc-15°C. Here, "Tc" is the crystallization temperature of the thermoplastic resin contained in the resin composition 2. By controlling the temperature (surface temperature) of the casting roll 3 in the conveying step to 10°C to Tc-5°C, crystallization of the thermoplastic resin contained in the resin composition 2 can be sufficiently promoted and adhesion (sticking) of the thermoplastic resin film to the casting roll 2 can be suppressed.

[0054] (Air Blowing Step) The conveying step includes an air blowing step in which air 5 is blown onto the portion where the film-like resin composition 2 is in contact with the casting roll 3 or the vicinity thereof, thereby adhering the film-like resin composition 2 to the casting roll 3. By carrying out the air blowing step, the film-like resin composition 2 extruded from the die 1 can be adhered to the casting roll 3, thereby making it possible to suppress contamination of the casting roll 3. In particular, when the resin composition 2 contains a nucleating agent, sublimation of the nucleating agent can be suppressed, and it is also possible to suppress contamination of the casting roll 3 due to adhesion of the sublimated nucleating agent.

[0055] In the air blowing step, the flow rate of the air 5 is 50 L / min to 1,000 L / min. By controlling the flow rate of the air 5 to 50 L / min to 1,000 L / min, contamination of the casting roll 3 can be suppressed. The flow rate of the air 5 is more preferably 100 L / min to 900 L / min, more preferably 200 L / min to 800 L / min, and even more preferably 300 L / min to 700 L / min.

[0056] In the air blowing step, the temperature of the air 5 is Tc-95°C to Tc°C. Controlling the temperature of the air 5 to Tc-95°C to Tc°C has advantages such as suppressing contamination of the casting roll 3 and improving the appearance of the resulting thermoplastic resin film. The temperature of the air 5 is more preferably Tc-95°C to Tc-5°C, more preferably Tc-85°C to Tc-15°C, and even more preferably Tc-80°C to Tc-25°C.

[0057] In the air blowing step, the means for blowing the air 5 is not particularly limited, and a method using an air knife, a method using an air chamber, a method using an air nozzle, etc. can be employed, but it is preferable to use an air knife to blow the air 5 because it is easy to control the flow rate and temperature of the blown air. Note that, although Fig. 1 illustrates a method using an air knife as an example of a means for blowing air, the means for blowing air in this production method is not limited to this.

[0058] In the air blowing step, it is preferable to blow air 5 in the width direction (i.e., the direction perpendicular to the conveying direction) of the film-shaped resin composition 2, and in this case, it is particularly preferable to blow air 5 over an area equal to or greater than the entire width of the film-shaped resin composition 2. By blowing air 5 over an area equal to or greater than the entire width of the film-shaped resin composition 2, it is possible to produce a uniformly molded thermoplastic resin film with a good appearance. In this specification, the term "full width" refers to the length in the width direction of the film-shaped resin composition 2, and "blowing air 5 over an area equal to or greater than the entire width of the film-shaped resin composition 2" refers to an operation of blowing air 5 so that the air 5 is blown over at least the entire width direction of the film-shaped resin composition 2.

[0059] In the air blowing process, air 5 is blown onto the area where the film-like resin composition 2 is in contact with the casting roll 3, preferably onto the area where the film-like resin composition 2 first comes into contact with the casting roll 3 (hereinafter also referred to as the "landing point"), or the vicinity thereof.

[0060] In the air blowing step, the position of the equipment or the like that blows the air (in other words, the position where the air is generated) is not particularly limited, as long as the air 5 can be blown onto the portion where the film-like resin composition 2 and the casting roll 3 are in contact, preferably onto the landing point or its vicinity.

[0061] For example, as shown in Fig. 1, in one embodiment of the present production method, the device for blowing air (air knife 4 in Fig. 1) may be installed adjacent to the casting roll 3. In another embodiment of the present production method, as shown in Fig. 2, the device for blowing air (air knife 4a in Fig. 2) may be installed at a horizontal distance from the casting roll 3a.

[0062] Specifically, the distance between the equipment blowing air in the air blowing step and the casting roll 3 can be, for example, 1 mm to 50 mm, preferably 2 to 20 mm, and more preferably 3 to 10 mm. In particular, by setting the distance between the equipment blowing air in the air blowing step and the casting roll 3 to the range of 3 to 10 mm, it is possible to suppress the occurrence of poor appearance such as wind patterns, peeling patterns, and vertical streaks in the obtained thermoplastic resin film.

[0063] In the air blowing step, the air 5 may be blown onto the landing point, or onto a region in the vicinity of the landing point.

[0064] For example, in one embodiment of the present production method, the position where air 5 is blown (indicated by the arrow representing air 5 in FIG. 1) may be the landing point. Also, in another embodiment of the present production method, as shown in FIG. 3, the position where air is blown (indicated by the arrow representing air 5b in FIG. 3) may be a region on the casting roll 3b located above the landing point in the longitudinal direction (i.e., the conveying direction) and near the landing point. In another embodiment of the present production method, as shown in FIG. 4, the position where air is blown (indicated by the arrow representing air 5c in FIG. 4) may be a region on the casting roll 3c located below the landing point in the longitudinal direction and near the landing point.

[0065] Specifically, the "region near the landing point" in the air blowing step refers to a region on the film-like resin composition 2, and refers to a region up to 30 mm above and below (front and back) the landing point in the longitudinal direction. In the air blowing step, among the regions near the landing point, it is preferable to blow air 5 into a region up to 20 mm above and below the landing point in the longitudinal direction, and it is more preferable to blow air 5 into a region up to 10 mm above and below the landing point in the longitudinal direction. Since this can suppress the occurrence of appearance defects such as wind patterns, peeling patterns, and vertical streaks in the obtained thermoplastic resin film, it is preferable to blow air 5 into a region up to 10 mm above and below the landing point in the longitudinal direction, and it is particularly preferable to blow air 5 at the landing point in the air blowing step.

[0066] In this production method, contamination of the casting roll 3 is suppressed by a non-contact method (with the resin composition 2), namely, air blowing. Therefore, there are advantages in that contamination can be suppressed continuously for a long period of time and periodic cleaning is not required.

[0067] In this production method, the conveying speed of the film-like resin composition 2 and the thermoplastic resin film is not particularly limited, but is preferably 1 m / min or more from the viewpoint of film productivity, and is preferably 50 m / min or less from the viewpoint of production stability.

[0068] <Thermoplastic Resin Film> The thickness of the thermoplastic resin film produced by the present production method is not particularly limited and can be appropriately set depending on the application. From the viewpoints of uniform thickness, appearance, strength, lightness, etc., the thickness is preferably 20 to 600 μm, more preferably 30 to 500 μm, and even more preferably 40 to 400 μm.

[0069] The thermoplastic resin film produced by this production method may be laminated with other layers. Examples of such other layers include a resin layer, an inorganic layer, a metal layer, a metal oxide layer, and a printed layer. These other layers may be laminate layers, coating layers, or vapor-deposited layers. Furthermore, this production method may include a lamination step in which another layer is laminated on the produced thermoplastic resin film.

[0070] The thermoplastic resin film produced by this production method can be suitably used as a packaging film, a heat-sealable film, a twist film, etc.

[0071] <Others> One aspect of the present invention may include the following configuration.

[0072] [1] A method for producing a thermoplastic resin film, comprising a conveying step of extruding a resin composition containing a molten crystalline thermoplastic resin through a die into a film, bringing the resulting film-like resin composition into contact with a casting roll, and conveying the film-like resin composition by rotating the casting roll, wherein the conveying step includes an air blowing step of blowing air onto a portion where the film-like resin composition and the casting roll first come into contact, or the vicinity thereof, to bring the film-like resin composition into close contact with the casting roll, wherein the flow rate of the air in the air blowing step is 50 L / min to 1,000 L / min, and the temperature of the air is Tc-95°C to Tc°C, where Tc is the crystallization temperature of the resin composition.

[0073] [2] The method for producing a thermoplastic resin film according to [1], wherein the thickness of the thermoplastic resin film is 20 to 600 μm.

[0074] [3] The method for producing a thermoplastic resin film according to [1] or [2], wherein the air is blown using an air knife in the air blowing step.

[0075] [4] A method for producing a thermoplastic resin film according to any one of [1] to [3], wherein in the air blowing step, the air is blown over an area equal to or greater than the entire width of the film-like resin composition.

[0076] [5] The method for producing a thermoplastic resin film according to any one of [1] to [4], wherein the resin composition contains a polyhydroxyalkanoate resin as the thermoplastic resin.

[0077] [6] The method for producing a thermoplastic resin film according to any one of [5], wherein the resin composition contains a poly(3-hydroxybutyrate)-based resin as the thermoplastic resin.

[0078] [7] The method for producing a thermoplastic resin film according to any one of [1] to [6], wherein the temperature of the casting roll is 10 ° C. to Tc - 5 ° C.

[0079] [8] The method for producing a thermoplastic resin film according to any one of [1] to [7], wherein the resin composition contains a crystal nucleating agent.

[0080] [9] The method for producing a thermoplastic resin film according to [8], wherein the nucleating agent is pentaerythritol.

[0081]

[10] In the air blowing step, air is blown onto an area on the film-like resin composition, the area being up to 30 mm above and below the area where the film-like resin composition first comes into contact with the casting roll, in the longitudinal direction.

[11] The method for producing a thermoplastic resin film according to any one of [1] to [9].

[0082] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0083] [Materials] The following raw materials were used in the examples and comparative examples.

[0084] (Thermoplastic resin) A-1: ​​P3HB3HH (average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%)) A-1 was produced in accordance with the method described in Example 2 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 660,000 g / mol by treatment with an aqueous sodium hydroxide solution. A-2: P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%)) A-2 was produced in accordance with the method described in Example 9 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 660,000 g / mol by treatment with an aqueous sodium hydroxide solution. A-3: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%)) A-3 was produced in accordance with the method described in Example 1 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 600,000 g / mol by treatment with an aqueous sodium hydroxide solution. A-4: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%)) A-4 was produced in accordance with the method described in Example 1 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 400,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0085] (Nucleating agent) B-1: Pentaerythritol (Neuraizer P, manufactured by Mitsubishi Chemical Corporation) (Lubricant) C-1: Behenic acid amide (BNT-22H, manufactured by Nippon Fine Chemical Co., Ltd.).

[0086] [Measurement Methods] Measurement and evaluation of each physical property in the examples and comparative examples were carried out by the following methods.

[0087] (Crystallization Temperature) The crystallization temperature (Tc) of the resin composition was measured by the following method: Using a differential scanning calorimeter "DSC-60" manufactured by Shimadzu Corporation, the target resin composition was heated from room temperature to 200°C at a heating rate of 10°C / min, held at 200°C for 1 minute, and then cooled to room temperature at a cooling rate of 10°C / min. The exothermic peak temperature that occurred during this process was taken as the crystallization temperature of the resin composition.

[0088] (Casting Roll Contamination) The casting roll contamination in the examples and comparative examples was evaluated as follows. After continuous film production for 30 minutes, the surface condition of the casting roll was visually observed. If contamination of the casting roll was observed, the casting roll contamination was evaluated as "present," and if no contamination of the casting roll was observed, the casting roll contamination was evaluated as "absent."

[0089] (Film Appearance) The appearance of the thermoplastic resin films obtained in the Examples and Comparative Examples was visually inspected and evaluated according to the following criteria: A (Good): No wind ripples, peel marks, or vertical streaks were observed on the film. B (Acceptable): Any one of wind ripples, peel marks, or vertical streaks was observed on the film. C (Poor): Any two or more of wind ripples, peel marks, and vertical streaks were observed on the film.

[0090] [Production Example 1: Production of Resin Composition] As the thermoplastic resin, a mixture of 30 parts by weight of A-1, 30 parts by weight of A-2, 10 parts by weight of A-3, and 30 parts by weight of A-4 (total 100 parts by weight) was used. This thermoplastic resin mixture was dry-blended with 1.0 parts by weight of B-1 as a nucleating agent and 0.5 parts by weight of C-1 as a lubricant. The resulting dry blend was placed in a φ26 mm co-rotating twin-screw extruder hopper with the cylinder temperature and die temperature set to 150 ° C, melt-kneaded, extruded into strands from the die, passed through a water bath filled with hot water at 45 ° C to solidify the strands, and then cut with a pelletizer to obtain a pellet-shaped resin composition, resin pellets P-1. The crystallization temperature (Tc) of the resulting resin composition (resin pellets P-1) was 105 ° C.

[0091] Example 1 A single-screw extruder having a diameter of 40 mm and connected to a T-die having a width of 350 mm was prepared, and the cylinder temperature and die temperature were both set to 165°C.

[0092] The resin composition (resin pellets P-1) prepared in Production Example 1 was charged into this single-screw extruder and melted. The molten resin composition at a temperature of 165°C was extruded into a film using a T-die. The discharge rate and take-up speed were adjusted so that the thickness of the resulting film-like resin composition would be 100 μm. This film-like resin composition was brought into contact with a casting roll set at 60°C and molded. At this time, air was blown at a flow rate and temperature shown in Table 1 using an air knife installed at a position shown in Table 1 in the width direction of the film-like resin composition (relative to the entire width of the film-like resin composition) toward the contact point between the film-like resin composition and the casting roll. By continuously performing this operation, thermoplastic resin films were continuously obtained. The physical properties of the resulting thermoplastic resin films were evaluated. The results are shown in Table 1.

[0093] [Examples 2 to 8, Comparative Examples 1 to 4] Thermoplastic resin films were obtained in the same manner as in the Examples, except that the installation position of the air knife and the air flow rate and temperature were changed to the conditions shown in Table 1 (air blowing was not performed in Comparative Example 1). The physical properties of each obtained thermoplastic resin film were evaluated. The results are shown in Table 1. In Comparative Examples 3 and 4, the molded thermoplastic resin film remained attached to the casting roll and was not peeled off, making it impossible to obtain a thermoplastic resin film at all.

[0094] According to one embodiment of the present invention, there is provided a method for producing a thermoplastic resin film by melt extrusion, which can suppress contamination of a casting roll used in molding. The thermoplastic resin film obtained by this production method can be suitably used for applications such as packaging film, heat-sealable film, and twist film.

[0095] REFERENCE SIGNS LIST 1 Die 2 Resin composition 3 Cast roll 4 Air knife 5 Air

Claims

1. A method for producing a thermoplastic resin film, comprising a conveying step of extruding a resin composition containing a crystalline thermoplastic resin in a molten state from a die into a film shape, bringing the resulting film-like resin composition into contact with a casting roll, and conveying the film-like resin composition by rotating the casting roll, wherein the conveying step includes an air blowing step of blowing air onto a portion where the film-like resin composition first comes into contact with the casting roll, or the vicinity thereof, to bring the film-like resin composition into close contact with the casting roll, wherein the air flow rate in the air blowing step is 50 L / min to 1,000 L / min, and the air temperature is Tc-95°C to Tc°C, where Tc is the crystallization temperature of the resin composition.

2. The method for producing a thermoplastic resin film according to claim 1, wherein the thickness of the thermoplastic resin film is 20 to 600 μm.

3. The method for producing a thermoplastic resin film according to claim 1, wherein the air is blown using an air knife in the air blowing step.

4. The method for producing a thermoplastic resin film according to claim 1, wherein in the air blowing step, the air is blown over an area equal to or greater than the entire width of the film-like resin composition.

5. The method for producing a thermoplastic resin film according to claim 1, wherein the resin composition contains a polyhydroxyalkanoate resin as the thermoplastic resin.

6. The method for producing a thermoplastic resin film according to claim 5, wherein the resin composition contains a poly(3-hydroxybutyrate)-based resin as the thermoplastic resin.

7. The method for producing a thermoplastic resin film according to claim 1, wherein the temperature of the casting roll is 10°C to Tc - 5°C.

8. The method for producing a thermoplastic resin film according to claim 1, wherein the resin composition contains a crystal nucleating agent.

9. The method for producing a thermoplastic resin film according to claim 8, wherein the crystal nucleating agent is pentaerythritol.

10. A method for producing a thermoplastic resin film as described in claim 1, wherein in the air blowing process, air is blown onto an area on the film-like resin composition that is up to 30 mm above and below the point where the film-like resin composition first comes into contact with the casting roll in the longitudinal direction.

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