Recycled resources-derived polyester film and method for producing the same

Abstract

To provide a recycled resources-derived polyester film that is obtained by using a raw material derived from the recycled resources recovered from a polyester film substantially by 100%, and has high strength.SOLUTION: A recycled resources-derived polyester film is formed of a material containing a raw material derived from the recycled resources recovered from a polyester film, the raw material derived from the recycled resources contains two or more polyesters with different inherent viscosities (IV), and at least one of the polyesters has an inherent viscosity (IV) of 0.80 dl / g or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a recycled polyester film obtained from recycled resources recovered from polyester films. [Background technology]

[0002] Polyester films are excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, etc., and for example, release films having a biaxially oriented polyester film as a base material and a release layer containing a silicone resin as a main component are used in many fields.

[0003] Meanwhile, in recent years, in view of resource reuse, environmental issues, and the like, attempts have been made to recover and reuse polyester raw materials after use or generated during the manufacturing process.

[0004] For example, Patent Document 1 discloses a laminated polyester film characterized in that at least one layer uses recycled materials from polyester bottles.

[0005] Patent Document 2 discloses a heat-shrinkable polyester film which contains 25% by weight or more of recycled PET bottle materials, and which, when immersed in 80°C warm water for 10 seconds and then pulled out, has a heat shrinkage rate of 30% or more in the main shrinkage direction and a heat shrinkage rate of 10% or less in the direction perpendicular to the main shrinkage direction, and which is characterized in that, when the film is stored for 28 days in an atmosphere of a temperature of 30°C and a relative humidity of 85%, a tensile test is performed in the direction perpendicular to the main shrinkage direction, and the number of test pieces which break at an elongation of 5% or less is 25% or less of the total number of test pieces.

[0006] However, the polyester films disclosed in Patent Documents 1 and 2 contain 75% or less recycled raw materials.

[0007] In addition, Patent Document 3 describes a biaxially oriented polyethylene terephthalate film made from recycled PET bottle materials, which has a melt resistivity of 1.0 × 10 at a temperature of 285 ° C. 8A biaxially oriented polyester film is disclosed, characterized in that the resistance to deformation is within Ω·cm and the sodium and potassium contents in the film are greater than 0 ppm and less than 150 ppm. The recycled raw material ratio of such polyester films is increased to nearly 95%, but a polyester film obtained from 100% recycled raw materials has not been disclosed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 07-323511 [Patent Document 2] Japanese Patent Application Publication No. 2007-2008 [Patent Document 3] JP 2014-65282 A Summary of the Invention [Problem to be solved by the invention]

[0009] In recycled polyester films, the recycled resource raw materials recovered from polyester films have been subjected to heat history during the manufacturing process, etc., and therefore have a low intrinsic viscosity (IV). Therefore, if a film is manufactured using 100% recycled resource raw materials, there is a problem that a film with high strength cannot be obtained.

[0010] In addition, recycled resource materials recovered from PET bottles vary widely in viscosity, and if a film is made using 100% recycled resource materials, it is not possible to obtain a film with high strength.

[0011] Furthermore, when the ratio of recycled resource-derived raw materials recovered from polyester products is increased, there is a problem that the color turns yellow and cannot be used in products.

[0012] Thus, in order to manufacture film products using recycled resource raw materials, virgin raw materials must still be used, and there is a demand for the development of film products that are substantially made from 100% recycled raw materials.

[0013] Therefore, one of the objects of the present invention is to provide a polyester film derived from recycled resources, which is obtained using substantially 100% raw materials derived from recycled resources recovered from polyester films, and which has high strength. Another object of the present invention is to provide a polyester film derived from recycled resources, which is obtained by using substantially 100% raw materials derived from recycled resources recovered from polyester films and has improved color tone. [Means for solving the problem]

[0014] The present inventors have found that the above problems can be solved by the means described below, and have completed the present invention.

[0015] That is, the present invention has the following configuration.

[0016] [1] The recycled resource-derived polyester film of the present invention is formed from a material containing recycled resource-derived raw materials recovered from polyester film, the recycled resource-derived raw materials containing two or more polyesters having different intrinsic viscosities (IV), at least one of the polyesters having an intrinsic viscosity (IV) of 0.80 dl / g or more.

[0017] [2] The method for producing a polyester film derived from recycled resources of the present invention includes the following steps (1) to (4). (1) A process for preparing raw materials derived from recycled resources recovered from polyester film. (2) A process for producing a recycled resource-derived raw material (a) containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more by solid-phase polymerization of the polyester contained in the recycled resource-derived raw material to make the intrinsic viscosity (IV) of the polyester 0.80 dl / g or more. (3) A process for producing a recycled resource-derived raw material (b) containing polyester recovered from polyester film and having an intrinsic viscosity (IV) of 0.60 dl / g or less. (4) A process of melt-kneading the mixed raw materials of (a) and (b) and then forming them into a film. Effect of the Invention

[0018] The polyester film made from recycled resources of the present invention is formed from raw materials that are substantially 100% made from recycled resources recovered from polyester films, yet has the advantage of having strength equivalent to that of polyester films made from conventional virgin raw materials.

[0019] In addition, the polyester film made from recycled resources of the present invention contains a fluorescent whitening agent, which has the advantage that the color tone is improved compared to conventional recycled products, even though it is made from raw materials made from substantially 100% recycled resources recovered from polyester film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] <Polyester film made from recycled resources> The recycled resource-derived polyester film of the present invention (hereinafter also referred to as "the film") is formed from recycled resource-derived raw materials recovered from polyester films, more specifically, from processes for manufacturing used polyester film products and / or polyester films (hereinafter both of which are referred to collectively or individually as "the film").

[0021] (Composition of this film) The present film may have either a single layer or a laminated structure having two or more layers (laminated film), but it is particularly preferable for the film to have a laminated structure having three or more layers.

[0022] When the present film has a laminate structure having two or more layers, a three-layer structure of A / B / C consisting of a base layer B and surface layers A and C, or A / B / A consisting of a base layer B and surface layer A is preferred.

[0023] (raw materials derived from recycling) "Recycled resource-derived raw materials" refers to raw materials such as polyester that make up this resource film that have been melted at least once after production. In addition, the present resource film is preferably formed from raw materials derived from self-recovered recycled resources generated during the process of manufacturing a polyester film. By using raw materials derived from self-recovered recycled resources, the characteristics of the raw materials derived from recycled resources can be accurately grasped, and a polyester film derived from recycled resources with stable quality can be provided. Furthermore, the term "film" is a concept that includes a sheet, and the term "film" includes a sheet, and the term "sheet" includes a film.

[0024] In addition, it is preferable that the present film is formed from raw materials that are substantially 100% derived from recycled resources, and "substantially" means that virgin polyester raw materials are not intentionally used, and that unavoidable mixing in during the manufacturing process, etc. is acceptable. More specifically, in the present invention, "substantially 100% raw materials derived from renewable resources" means that 99% or more, preferably 99.5% or more, of the raw materials are derived from renewable resources.

[0025] Therefore, the present film does not necessarily need to be made from 100% recycled resource-derived raw materials, but is made from materials that contain 99% or more by mass, preferably 99.5% or more by mass, of recycled resource-derived raw materials.

[0026] As described above, the raw material derived from recycled resources is recovered from the resource film, and the recovered polyester film is reused by being crushed and re-pelletized.

[0027] The recycled resource-derived raw material has a low intrinsic viscosity (IV) and it is difficult to ensure sufficient strength when reused, since the resource film has been subjected to heat history during the manufacturing process. Therefore, it is preferable that the raw material derived from recycled resources contains two or more polyesters having different intrinsic viscosities (IV), and at least one of the polyesters has an intrinsic viscosity (IV) of 0.80 dl / g or more. From this viewpoint, at least one of the polyesters preferably has an intrinsic viscosity (IV) of 0.82 dl / g or more, and most preferably 0.85 dl / g or more. The intrinsic viscosity (IV) is measured at 30° C. using an Uperohde viscometer and a solvent mixture of phenol:tetrachloroethane=1:1.

[0028] In order to obtain a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more from the raw material recovered and recycled from this resource film, it is preferable to subject the recycled polyester raw material to solid-phase polymerization. As the solid-phase polymerization method, a known method can be used, and either a continuous method or a batch method can be used.

[0029] It is also preferred that the recycled resource-derived raw material contains two or more types of polyesters having different intrinsic viscosities (IV), and at least one of the polyesters has an intrinsic viscosity (IV) of 0.60 dl / g or less. By using a raw material derived from recycled resources that contains a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less, it is possible to achieve effects such as maintaining the productivity and cost of the film.

[0030] By using at least two types of polyesters, one with an intrinsic viscosity (IV) of 0.80 dl / g or more and the other with an intrinsic viscosity (IV) of 0.60 dl / g or less, from the raw materials recovered and recycled from this resource film, it is possible to prevent the film from breaking during production due to a decrease in polyester film strength, which is a concern when using recovered and recycled raw materials, and to provide a polyester film with strength equivalent to that obtained using conventional virgin raw materials.

[0031] For these reasons, the present film preferably contains 50% by mass or less of polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more, more preferably 30% by mass or less, and most preferably 25% by mass or less.

[0032] In addition, the film preferably contains 50% by mass or more, more preferably 60% by mass or more, and most preferably 70% by mass or more, of polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less.

[0033] (Other ingredients 1: fluorescent whitening agents) When a film is made from raw materials that are essentially 100% derived from recycled resources, the polymer deteriorates and turns yellow in color, making it difficult to use as a product as is. Therefore, the present film preferably contains a fluorescent whitening agent as a component other than the raw materials derived from recycled resources. The yellowish tint of the film can be improved by adding an optical brightener.

[0034] Furthermore, the fluorescent whitening agent is excited by ultraviolet light and emits blue visible light, so that the fluorescent whitening agent can also serve as a marker for indicating that the film is a recycled product.

[0035] Examples of the fluorescent whitening agent include those having a stilbene-based, coumarin-based, oxazole-based, imidazole-based, and naphthalimide-based structure. Specifically, 4,4'-bis(benzoxazol-2-yl)stilbene, 2,5-bis(5-t-butyl-2-benzoxazolyl)thiophene, 1,2-di(5-methyl-2-benzodiazolyl)ethylene, 1,2-bis(5-methyl-2-benzoxazole)ethylene, 2,2'-(4,4'-diphenolvinyl)dibenzoxazole, 1,1'-biphenyl-4,4'-bis-benzoxazole, 2,5-bis(benzoxazole-2-)thiophene, 4-4'-bis(5- Examples of such an alkyl group include methyl-2-benzoxazole)ethylene, 1,4-bis(benzoxazolyl-2-yl)ethylene, 1,4-bis(benzoxazolyl-2-yl)naphthalene, 4-4'-bis[(4-amino-6-morpholino-1,3,5-triazin-2-yl)amino]stilbene disulfonate, and 2,2'-(1,4-naphthalenediyl)bis-benzoxazole. These may be used alone or in combination of two or more.

[0036] The content of the fluorescent whitening agent in the present film is preferably 0.01 to 1.0% by mass, and more preferably 0.02 to 0.08% by mass. If the content of the fluorescent whitening agent exceeds 1.0% by weight, not only will the color tone improving effect become saturated, but the fluorescent whitening agent will bleed out excessively onto the surface of the film, causing problems such as adverse effects during use.

[0037] (Other component 2: Particles) From the viewpoint of imparting easy slippage and scratch resistance, the present film preferably contains particles as a component other than the raw materials derived from recycled resources.

[0038] Examples of the particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, as well as organic particles such as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, calcium oxalate, and ion exchange resins.

[0039] The content of the particles in the present film is preferably 0.001 to 1.0% by mass, and more preferably 0.01 to 0.08% by mass.

[0040] (Book resource film) The resource film is a film formed by molding polyester or a composition containing polyester, and is composed mainly of polyester. The term "main component" refers to a component that accounts for 50% by mass or more, and preferably 70% by mass or more, of the components that constitute the film.

[0041] (a) Polyester The polyester refers to a polymeric compound having continuous ester bonds in the main chain, and may be a homopolyester or a copolymer polyester. Specific examples of the polyester include polyesters obtained by polycondensation reaction of a dicarboxylic acid component and a diol component.

[0042] In the present invention, it is preferable to use a polyester containing more than 50% of an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid when the dicarboxylic acid component is taken as 100 mol %.

[0043] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfonedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof.

[0044] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0045] When the polyester is a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative examples of polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN). Among these, polyethylene terephthalate (PET) is particularly preferable.

[0046] On the other hand, when the polyester is a copolymer polyester, it is preferable that the polyester is a copolymer containing 30 mol % or less of a third component. Examples of the dicarboxylic acid component of the copolymer polyester include isophthalic acid, terephthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid, and the like, which may be used alone or in combination. Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

[0047] As the polyester, preferred are polyethylene terephthalate in which 80 mol % or more, preferably 90 mol % or more, is an ethylene terephthalate unit, and polyethylene-2,6-naphthalate in which ethylene-2,6-naphthalate unit is, and the like.

[0048] (b) Polyester polycondensation catalyst Examples of the polycondensation catalyst used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, and titanium compounds. In particular, it is preferable to use a polyester obtained using an antimony compound.

[0049] (c) Particles The source film may be formed from a polyester composition containing particles. As the particles, the above-mentioned particles can be appropriately used.

[0050] (d) Fluorescent whitening agents The source film may be formed from a polyester composition that contains an optical brightener. As the fluorescent whitening agent, the above-mentioned agents can be appropriately used.

[0051] (e) Additives The resource film may be formed from a polyester composition containing various additives such as antioxidants, light resistance agents, antigelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants.

[0052] (Form of this film) The film may be a non-stretched film, a uniaxially stretched film, or a biaxially stretched film. Among these, from the viewpoint of film strength, a biaxially stretched film is particularly preferred.

[0053] (Release layer) The present film can also be used in a form having a release layer on at least one surface, that is, in the form of a release film. In this case, it is particularly preferable that the release layer is also made of raw materials derived from recycled resources.

[0054] (Especially preferred embodiment 1) (1) The film has a multilayer structure having at least three layers, A / B / A, the A layer being the outermost layer and formed from a raw material derived from recycled resources recovered from polyester film, the A layer being formed from a raw material derived from recycled resources (A-1) containing a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less, and the B layer being formed from a raw material derived from recycled resources recovered from polyester film, the B layer being formed from a raw material derived from recycled resources (B-1) containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more. (2) In the above (1), the recycled resource-derived raw material (B-1) for forming the B layer contains 30% by mass or less of polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more in the B layer. (3) In the above (1) or (2), the raw material (B-1) derived from recycled resources for forming the B layer further contains a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less. (4) In the above (3), the recycled resource-derived raw material (B-1) for forming the B layer contains 50% by mass or more of polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less in the B layer. (5) In any one of the above (1) to (4), the layer B further contains a fluorescent whitening agent. (6) In any one of (1) to (5) above, the layer A further contains particles. (7) In any one of the above (1) to (6), the film is a biaxially stretched film. (8) In any one of (1) to (7) above, the raw material (B-1) derived from recycled resources for forming the layer B includes a raw material (b-1) derived from recycled resources recovered from a polyester film having a coating layer. (9) In any one of the above (1) to (8), the raw material (A-1) derived from renewable resources for forming the A layer is substantially free of the raw material (b-1) derived from renewable resources. (10) The present film according to any one of (1) to (9) above, wherein at least one surface of the film has a release layer.

[0055] According to the particularly preferred embodiment 1, the recycled resource-derived raw material (B-1) for forming layer B contains a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more, thereby imparting excellent strength to the present film. In particular, since the recycled resource-derived raw material (B-1) for forming layer B further contains a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less, there is an advantage in that the mechanical strength of the film can be maintained while the productivity and cost of the film can be maintained.

[0056] In addition, from the viewpoint of preventing film breakage during production, the recycled resource-derived raw material (B-1) for forming the B layer preferably contains 30% by mass or less, and more preferably 25% by mass or less, of polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more in the B layer.

[0057] From the same viewpoint as above, the recycled resource-derived raw material (B-1) for forming the B layer preferably contains 50% by mass or more, and more preferably 70% by mass or more, of polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less in the B layer.

[0058] Furthermore, by containing the fluorescent brightening agent in layer B, there is an advantage that there is no risk of the fluorescent brightening agent bleeding out to the outermost layer.

[0059] In addition, by including particles in layer A, the film can be made slippery and scratch-resistant.

[0060] From the viewpoint of securing raw materials derived from recycled resources, it is preferable that the raw materials derived from recycled resources (B-1) for forming the B layer contain raw materials derived from recycled resources (b-1) recovered from a polyester film having a coating layer, and from the same viewpoint, it is preferable that the raw materials derived from recycled resources (A-1) for forming the A layer do not substantially contain the raw materials derived from recycled resources (b-1). The term "substantially" means that the raw material (b-1) derived from renewable resources is not intentionally contained, and specifically means that the content of the raw material (b-1) derived from renewable resources in the layer A is less than 5 mass %, and more preferably less than 1 mass %.

[0061] The coating layer has various functions such as easy adhesion, and is obtained by preparing a coating liquid containing a solvent, a binder resin, a crosslinking agent, etc., applying the coating liquid to a film, and then drying the coating liquid.

[0062] Examples of the binder resin used in the coating liquid include acrylic resins, urethane resins, polyester resins, olefin resins, fluorine resins, vinyl resins, chlorine resins, styrene resins, epoxy resins, silicone resins, and mixtures of these resins.

[0063] <Manufacturing method of this film> As an example of the method for producing the present film, a method for producing a biaxially stretched film will be described below. First, using a known method, the above-mentioned recycled resource-derived raw material, for example recycled polyester chips, is supplied to a melt extrusion device, heated to above the melting point of each polymer, and the molten polymer is extruded from a die and cooled and solidified on a rotating cooling drum to a temperature below the glass transition point of the polymer, thereby obtaining an unoriented sheet in a substantially amorphous state.

[0064] Next, the unoriented sheet is stretched in one direction by a roll or tenter type stretching machine. In this case, the stretching temperature is usually 25 to 120° C., preferably 35 to 100° C., and the stretching ratio is usually 2.5 to 7 times, preferably 2.8 to 6 times.

[0065] Next, the film is stretched in a direction perpendicular to the first-stage stretching direction. In this case, the stretching temperature is usually 50 to 140° C., and the stretching ratio is usually 3.0 to 7 times, preferably 4.5 times or more, and more preferably 4.5 to 5.0 times.

[0066] Then, the polyester film is subsequently heat-set at a temperature of 180 to 220° C. under tension or under relaxation of 30% or less, to obtain the present polyester film as a biaxially oriented film. In the above-mentioned stretching, a method in which the stretching in one direction is carried out in two or more stages can also be adopted.

[0067] (Especially preferred embodiment 2) (1) The method for producing the present film includes the following steps A to D. A. A process for preparing raw materials derived from recycled resources recovered from polyester film B. A process for producing a recycled resource-derived raw material (a) containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more by solid-phase polymerization of the polyester contained in the recycled resource-derived raw material, and setting the intrinsic viscosity (IV) of the polyester to 0.80 dl / g or more. C. A process for producing a recycled resource-derived raw material (b) containing polyester recovered from polyester film and having an intrinsic viscosity (IV) of 0.60 dl / g or less. D. A process of melt-kneading the mixed raw materials of (a) and (b) and then forming them into a film. (2) In the above (1), the step D is a molding step of melt-kneading the mixed raw material, melt-extruding the mixture, and cooling the mixture to form a film. (3) In the above (1) or (2), the following step E is included after step D. E. Stretching step of stretching in the longitudinal direction and / or the transverse direction

[0068] As described above, a particularly preferred method for producing the present film uses a raw material (a) derived from renewable resources whose intrinsic viscosity (IV) has been adjusted to 0.80 dl / g or more, and a raw material (b) derived from renewable resources whose intrinsic viscosity (IV) is 0.60 dl / g or less, thereby making it possible to obtain a film that is substantially made from 100% renewable resource raw materials and has excellent strength.

[0069] Furthermore, by incorporating an optical brightener in the film, the color tone of the film can be improved and it becomes possible to identify that the film is obtained from recycled materials.

[0070] In the above-mentioned process A, for example, the recovered polyester film is pulverized using a pulverizer to produce polyester flakes, which are then extruded using an extruder and rapidly cooled and solidified to obtain recycled polyester pellets, i.e., raw materials derived from recycled resources.

[0071] In the above-mentioned step B, the above-mentioned recycled resource-derived raw material is subjected to solid-phase polymerization at 220°C under vacuum to increase the intrinsic viscosity (IV) to 0.80 dl / g or more, thereby obtaining a recycled resource-derived raw material (a) containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more.

[0072] In the above-mentioned step C, for example, the recovered polyester film having an intrinsic viscosity (IV) of 0.60 dl / g or less is pulverized in a pulverizer to produce polyester flakes, which are then extruded in an extruder and rapidly cooled and solidified to obtain recycled polyester pellets, i.e., raw material (b) derived from recycled resources. In addition, the use of raw material (b) derived from recycled resources has the advantage that the mechanical strength of the film can be maintained while the productivity and cost of the film can be maintained.

[0073] In the above-mentioned step D, for example, the raw materials for each layer may be fed into separate extruders and melt-extruded into a sheet from a T-die by a co-extrusion method, or the raw materials may be melted separately in a plurality of extruders and extruded from the die outlets into films that are then laminated together to be molded into a film. In particular, the method of forming into a film by co-extrusion is preferred.

[0074] In the above step E, the unstretched film produced in the above step D is stretched in one direction and / or a direction perpendicular thereto by a roll or tenter type stretching machine to obtain a stretched film.

[0075] More specifically, in the stretching step, the unstretched sheet is stretched in one direction in the longitudinal direction (machine direction (MD)) by a roll or tenter type stretching machine. The stretching temperature in this case is usually 70 to 120° C., preferably 80 to 110° C., and the stretching ratio is usually 2.0 to 7.0 times, preferably 2.5 to 5.0 times.

[0076] Next, the film is stretched in a direction perpendicular to the first-stage stretching direction (transverse direction (TD)). In this case, the stretching temperature is usually 70 to 170° C., and the stretch ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6.0 times. Then, the film is subsequently heat-treated at a temperature of 180 to 270° C. under tension or under relaxation of 30% or less to obtain a biaxially oriented film.

[0077] In the above stretching, a method in which the stretching in one direction is carried out in two or more stages can also be adopted. In this case, it is preferable that the final stretching ratios in both directions are each within the above range.

[0078] (Application) This film can be used for optical filters such as AR film, NIR film, and EMI film; optical films such as diffusion film and prism film; and general industrial materials such as card materials, label materials, electronic materials, packaging materials, graphic materials (photographic materials), plate-making films, magnetic recording media, various types of processing paper, and transparencies. Because it is composed essentially of raw materials derived from 100% recycled resources, it makes a great contribution from an environmental perspective and can help reduce the environmental burden.

[0079] (Explanation of terms, etc.) In the present invention, when it is described as "X to Y" (X and Y are any numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" or "preferably smaller than Y".

[0080] In addition, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. EXAMPLES

[0081] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0082] <Production of raw materials derived from recycled resources> a) Preparation of recycled polyester pellets (1) A self-recoverable polyester film without a coating layer was crushed and processed to obtain recycled polyester pellets (a) with an intrinsic viscosity (IV) of 0.57 dl / g. (2) A self-recoverable polyester film having no coating layer was crushed and processed to obtain recycled polyester pellets (b1) having an intrinsic viscosity (IV) of 0.54 dl / g. (3) A self-recovering polyester film having a coating layer is crushed and processed, and the intrinsic viscosity (I Regenerated polyester pellets (c) having a V of 0.58 dl / g were obtained. (4) Recycled polyester pellets (b1) having an intrinsic viscosity (IV) of 0.54 dl / g were solid-phase polymerized at 220°C under vacuum to obtain recycled polyester pellets (b2) having an intrinsic viscosity (IV) of 0.85 dl / g.

[0083] b) Production of recycled polyester As the raw materials for the front and back layers, recycled polyester pellets (a), recycled polyester pellets (b1), and virgin raw silica particles (x1) with an average particle size of 2.7 μm were mixed so that the contents in the resulting film were 16.48 mass% for (a), 4.08 mass% for (b1), and 0.04 mass% for (x1), respectively. As the raw materials for the intermediate layer, recycled polyester pellets (c), recycled polyester pellets (b2), and recycled polyester pellets (b1) and (c) 52.93% by mass, (b2) 23.41% by mass, (b1) 3.01% by mass, (x2) 0.05% by mass of a virgin fluorescent whitening agent (4,4'-Bis(2-benzoxazolyl)stilbene) were mixed together and fed to two vented twin-screw extruders, melted and kneaded at 280°C, and extruded at a multi-layer T-die where the mixture was joined to give a composition ratio of A / B / A = 3 / 32 / 3. The mixture was rapidly cooled and solidified on a casting drum with a surface temperature set to 28°C to obtain an unstretched film consisting of two types and three layers. Next, the film was stretched 3.40 times in the longitudinal direction (machine direction) at 87°C, then introduced into a tenter and stretched 4.04 times in the width direction (horizontal direction) at 120°C, and then heat-treated at 233°C to relax 4.76% in the transverse direction, resulting in a biaxially stretched film with a thickness of 38 μm. Next, the obtained biaxially stretched film was slit at positions 255 mm from both ends, and the surplus produced during the slitting was recovered as slit edges, which were crushed and treated to obtain recovered polyester (d). The intrinsic viscosity (IV) of the recovered polyester (d) is calculated to be 0.60.

[0084] [Example 1] As the raw materials for the front and back layers, recycled polyester pellets (a), recycled polyester pellets (b1), and virgin silica particles (x1) with an average particle size of 2.7 μm were mixed so that the contents in the resulting film were (a) 13.47% by mass, (b1) 3.33% by mass, and (x1) 0.03% by mass, respectively. As the raw materials for the middle layer, recycled polyester pellets (c), recycled polyester pellets (b2), recycled polyester pellets (b1), and (x2) virgin fluorescent material were mixed. The optical brightener (4,4'-Bis(2-benzoxazolyl)stilbene) and the recovered polyester (d) were mixed so that the contents in the obtained film were (c) 43.24% by mass, (b2) 19.13% by mass, (b1) 2.46% by mass, (x2) 0.04% by mass, and (d) 18.30% by mass, respectively, and fed to two vented twin-screw extruders, melted and kneaded at 280°C, and extruded by joining in a multi-layer T-die so that the composition ratio was A / B / A = 3 / 32 / 3. The mixture was rapidly cooled and solidified on a casting drum with a surface temperature set to 28°C to obtain an unstretched film consisting of two types and three layers. Next, the film was stretched 3.40 times in the longitudinal direction (machine direction) at 87°C, then introduced into a tenter and stretched 4.04 times in the width direction (horizontal direction) at 120°C, after which it was heat-treated at 233°C to relax 4.76% in the horizontal direction, yielding a 38 μm-thick recycled resource-derived polyester film 1. The recycled resource-derived polyester film 1 is formed from materials containing 99.93% by mass of raw materials derived from recycled resources. Furthermore, the recycled resource-derived polyester film 1 had improved color tone. In addition, the content of polyesters in layer A having an intrinsic viscosity (IV) of 0.60 dl / g or less is 99.80 mass%, and the content of polyesters in layer B having an intrinsic viscosity (IV) of 0.60 dl / g or less is 76.96 mass%, and the content of polyesters in layer B having an intrinsic viscosity (IV) of 0.80 dl / g or more is 23.00 mass%.

[0085] [Example 2] A polyester film 2 derived from recycled resources was obtained in the same manner as in Example 1, except that a film having a thickness of 50 μm and a composition ratio of A / B / A=4 / 42 / 4 was used. The recycled resource-derived polyester film 2 is formed from a material containing 99.93 mass % of raw materials derived from recycled resources. Additionally, the recycled resource-derived polyester film 2 had improved color tone. In addition, the content of polyesters in layer A having an intrinsic viscosity (IV) of 0.60 dl / g or less is 99.80 mass%, and the content of polyesters in layer B having an intrinsic viscosity (IV) of 0.60 dl / g or less is 76.96 mass%, and the content of polyesters in layer B having an intrinsic viscosity (IV) of 0.80 dl / g or more is 23.00 mass%.

[0086] Various physical properties of the recycled resource-derived polyester films 1 and 2 produced in Examples 1 and 2 are shown in Table 1.

[0087] [Table 1]

[0088] The tensile strength (MPa) was measured as follows.

[0089] (Tensile strength) Recycled resource-derived polyester films 1 and 2 were cut into rectangles with a width of 15 mm and stretched in a tensile tester at a tension speed of 200 mm / min over a section length of 50 mm to determine the tensile strength, i.e., the stress at break.

[0090] The recycling rate means the usage rate of raw materials derived from recycled resources relative to the total materials constituting the polyester film derived from recycled resources, and is expressed in mass %.

Claims

1. A method for producing a polyester film derived from recycled resources formed from a material containing two or more types of raw materials derived from recycled resources having different intrinsic viscosities (IV), at least one of the raw materials derived from recycled resources having an intrinsic viscosity (IV) of 0.80 dl / g or more, the method comprising the steps of: preparing a recycled resource-derived raw material recovered from a polyester film; A step of producing a raw material derived from recycled resources containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more by adjusting the intrinsic viscosity (IV) of the polyester contained in the raw material derived from recycled resources to 0.80 dl / g or more; Producing a recycled resource-derived feedstock containing polyester recovered from polyester film, the polyester having an intrinsic viscosity (IV) of less than 0.80 dl / g; A process of mixing the raw material derived from recycled resources containing the polyester obtained in the above process and having an intrinsic viscosity (IV) of 0.80 dl / g or more with the raw material derived from recycled resources containing the polyester obtained in the above process and having an intrinsic viscosity (IV) of less than 0.80 dl / g, melt-kneading the mixture, and then molding the mixture into a film.

2. 2. The method for producing a polyester film derived from recycled resources according to claim 1, wherein the polyester having an intrinsic viscosity (IV) of less than 0.80 dl / g has an intrinsic viscosity (IV) of 0.60 dl / g or less.

3. The method for producing a polyester film derived from recycled resources according to claim 1 or 2, wherein the raw material derived from recycled resources is made of self-recovered raw material generated during the production process of a polyester film.

4. The method for producing a polyester film derived from recycled resources according to any one of claims 1 to 3, wherein the material contains a fluorescent whitening agent.

5. The method for producing a polyester film derived from recycled resources according to any one of claims 1 to 4, wherein the polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more is solid-phase polymerized.

6. The method for producing a polyester film derived from recycled resources according to any one of claims 1 to 5, which has a laminated structure of two or more layers.

7. The method for producing a polyester film derived from recycled resources according to claim 6, wherein a fluorescent whitening agent is contained in a layer other than the outermost layer.

8. A method for producing a polyester film derived from recycled resources as described in claim 6 or 7, wherein one of the two or more layers is layer A formed from a raw material (A-1) derived from recycled resources containing polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less, and one of the two or more layers is layer B formed from a raw material (B-1) derived from recycled resources containing polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more.

9. The method for producing a polyester film derived from recycled resources described in claim 8, wherein the raw material (B-1) derived from recycled resources contains 30 mass% or less of polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more.

10. The method for producing a polyester film derived from recycled resources according to claim 8 or 9, wherein the raw material derived from recycled resources (B-1) further contains a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less.

11. A method for producing a polyester film derived from recycled resources described in any one of claims 8 to 10, wherein the raw material derived from recycled resources (B-1) further contains 50 mass% or more of a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less.

12. A method for producing a polyester film derived from recycled resources described in any one of claims 8 to 11, which has a multilayer structure having at least three layers of A / B / A.

13. The method for producing a polyester film derived from recycled resources according to any one of claims 1 to 12, wherein the material contains 99% by mass or more of raw materials derived from recycled resources.

14. A method for producing a recycled resource polyester film described in any one of claims 1 to 13, wherein the two or more types of polyester are all homopolyesters.

15. A method for producing a recycled resource-derived polyester film, comprising the step of providing a release layer on at least one side of the recycled resource-derived polyester film according to any one of claims 1 to 14.

16. The method for producing a recycled resource-derived polyester film according to any one of claims 1 to 15, wherein the step of forming into a film is a step of melt-kneading the mixed raw material, melt-extruding the mixed raw material, and cooling the mixed raw material to form into a film.

17. A method for producing a polyester film derived from recycled resources described in any one of claims 1 to 16, comprising a stretching step of stretching the polyester film in the longitudinal direction and / or width direction after the step of molding the polyester film into a film.

18. A polyester film derived from recycled resources having a laminated structure of two or more layers formed from a material containing raw materials derived from recycled resources recovered from polyester film, one layer of the two or more layers is a layer A formed from a raw material (A-1) derived from recycled resources containing a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less, and one layer of the two or more layers is a layer B formed from a raw material (B-1) derived from recycled resources containing a polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more.

19. The polyester film derived from recycled resources described in claim 18, wherein the raw material (B-1) derived from recycled resources contains 30 mass% or less of polyester having an intrinsic viscosity (IV) of 0.80 dl / g or more.

20. The polyester film derived from recycled resources described in claim 18 or 19, wherein the raw material derived from recycled resources (B-1) further contains a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less.

21. The polyester film derived from recycled resources described in any one of claims 18 to 20, wherein the raw material derived from recycled resources (B-1) further contains 50 mass% or more of a polyester having an intrinsic viscosity (IV) of 0.60 dl / g or less.

22. A polyester film derived from recycled resources described in any one of claims 18 to 21, which has a multilayer structure having at least three layers of A / B / A.