Cavity-containing polyester film and method for manufacturing the same

Abstract

This invention enables the application of thermoplastic resins recycled from injection-molded products to film products, and further provides a void-containing polyester film with excellent void formation, opacity, and whiteness. [Solution] A cavity-containing polyester film comprising a layer (layer A) containing a cavity inside, wherein layer A comprises at least a polyester resin and a thermoplastic resin recycled from injection-molded products.

Description

[Technical Field]

[0001] This invention relates to a cavity-containing polyester film using a thermoplastic resin recycled from injection-molded products as a non-compatible resin used as a cavity-inducing agent. [Background technology]

[0002] Synthetic paper, a paper substitute primarily composed of synthetic resins, offers superior water resistance, moisture absorption, dimensional stability, and surface stability compared to natural paper. It is widely used in labels, stickers, posters, recording paper, and packaging materials. While polyethylene, polypropylene, and polyester resins are commonly used as raw materials for synthetic paper, polyester resins, particularly polyethylene terephthalate, are widely used due to their excellent mechanical and thermal properties.

[0003] Methods for obtaining films with functions similar to paper generally include incorporating a large number of microscopic cavities into the film, or roughening a flat film by performing surface treatments such as sandblasting, chemical etching, or matting. Among these, the former method of incorporating a large number of microscopic cavities into the film is widely adopted because it not only provides paper-like opacity and whiteness, but also reduces the cost per unit area by making the film itself lighter, and provides appropriate flexibility and cushioning, resulting in superior image clarity during printing.

[0004] A common method for creating fine cavities within a film involves mixing an incompatible thermoplastic resin (hereinafter referred to as the incompatible resin) with a polyester resin to obtain a sheet in which the incompatible resin is dispersed in the polyester resin, and then stretching the sheet in at least one axial direction to create cavities through interfacial delamination between the polyester resin and the incompatible resin. For the incompatible resin used to create cavities in the polyester resin, polyolefin resins such as polyethylene resins, polypropylene resins, and polymethylpentene resins (see, for example, Patent Documents 1-3) and polystyrene resins (see, for example, Patent Documents 4 and 5) are preferably used. Among these, polypropylene resins are particularly preferred in terms of cavity creation properties and cost-effectiveness.

[0005] With the enforcement of the Plastic Resource Recycling Promotion Act in 2022, the use of recyclable materials and biomass materials has been increasingly demanded in recent years. Recycled materials are being developed for injection-molded products (e.g., CD cases, DVD cases), which are the most common products using thermoplastic resins. One known method of utilization is to add them to injection-molded products, as shown in Patent Documents 6 and 7. Furthermore, as shown in Patent Documents 8 and 9, injection-molded products with improved physical properties of recycled materials have been developed by using additives. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Unexamined Patent Publication No. 49-134755 [Patent Document 2] Japanese Patent Application Publication No. 2-284929 [Patent Document 3] Japanese Patent Application Publication No. 2-180933 [Patent Document 4] Special Publication No. 54-29550 [Patent Document 5] Japanese Patent Application Publication No. 11-116716 [Patent Document 6] Japanese Patent Publication No. 2024-159325 [Patent Document 7] Japanese Patent Publication No. 2024-144954 [Patent Document 8] Japanese Patent Publication No. 2018-87294 [Patent Document 9] Japanese Patent Publication No. 2024-137917 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the recycled products described in Patent Documents 6-9 are limited to injection-molded products only, which is insufficient for the widespread use of recycled materials. A problem with recycled materials for injection-molded products made of thermoplastic resins is that their viscosity is low due to degradation and their molecular weight distribution is broad, which limits the products in which they can be used.

[0008] This invention has been made in view of the above circumstances, and its purpose is to enable the application of thermoplastic resin recycled from injection molded products to film products, and furthermore, to provide a void-containing polyester film that has excellent void formation properties, as well as excellent opacity and whiteness. [Means for solving the problem]

[0009] The inventors have discovered that a thermoplastic resin recycled from injection-molded products can be used as a cavity-forming agent in a cavity-containing polyester film, and have further discovered that a cavity-containing polyester film with excellent cavity-forming properties, as well as excellent opacity and whiteness, can be obtained. In addition, we discovered that cavity formation and opacity can be controlled by adjusting the molecular weight of the polypropylene resin used in the blend.

[0010] In other words, the cavity-containing polyester film of the present invention has the following configuration. [Section 1] A cavity-containing polyester film containing a layer (layer A) containing cavities inside, wherein the layer A contains at least a polyester resin and a thermoplastic resin recycled from an injection molded product. [Item 2] The cavity-containing polyester film according to Item 1, wherein a layer (layer B) made of a polyester resin containing inorganic particles is laminated on at least one surface of the layer (layer A) containing cavities inside. [Item 3] The cavity-containing polyester film according to Item 1, wherein the thermoplastic resin recycled from the injection molded product is an olefin resin. [Item 4] The cavity-containing polyester film according to Item 3, wherein the olefin resin recycled from the injection molded product satisfies the following (1) and (2). (1) The weight average molecular weight Mw measured by gel permeation chromatography is in the range of 100,000 to 500,000, and the molecular weight distribution represented by the weight average molecular weight Mw / number average molecular weight Mn is 4 to 8. (2) The melt viscosity measured by a capillary graph is 50 to 100 Pa·s. [Item 5] The cavity-containing polyester film according to Item 1, wherein the injection molded product includes at least a CD case or a DVD case. [Item 6] The apparent density is 0.7 to 1.3 g / cm 3 The cavity-containing polyester film according to Item 1. [Item 7] The cavity-containing polyester film according to Item 1, wherein the inorganic particles in the layer B are titanium oxide. [Item 8] The cavity-containing polyester film according to Item 1, having a total light transmittance of less than 70% and an optical density of 0.10 or more. [Item 9] A method for manufacturing a cavity-containing polyester film, including the following steps. (Step a) A step of preparing a polyester resin and an olefin resin recycled from an injection molded product. (Step b) A step of obtaining a polyester resin composition by melt-mixing the polyester resin and an olefin resin recycled from injection-molded products. (Step c) Step of extruding the polyester resin composition into a sheet to obtain a sheet-like material. (Step d) Step of stretching the sheet-like material in at least one direction. [Effects of the Invention]

[0011] The present inventors have found that by using a thermoplastic resin recycled from injection-molded products as a cavity-forming agent in a cavity-containing polyester film, it is possible to provide a cavity-containing polyester film with excellent environmental friendliness, and furthermore, a cavity-containing polyester film with excellent cavity-forming properties, as well as excellent opacity and whiteness, can be obtained. In addition, the tendency for void formation and opacity can be controlled by the molecular weight of the polypropylene resins being blended, and this can be controlled by dry blending polypropylene resins with different molecular weights. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below. First, in this specification, the notation "○○~△△" (where ○○ and △△ are numbers) indicates that it is greater than or equal to ○○ and less than or equal to △△. Furthermore, ○○ and △△ are not necessarily fixed combinations; they are independent as greater than or equal to ○○ and less than or equal to △△, and can be arbitrarily combined with the numerical value of "~" in the same item, representing greater than or equal to and less than or equal to. In addition, "greater than or equal to ○○" means that it is the same as ○○ or greater than ○○, and "less than or equal to △△" means that it is the same as △△ or less than or equal to △△. The cavity-containing polyester film of the present invention has at least one layer (layer A) containing a cavity inside, and layer A is composed of a composition containing at least a polyester resin and a thermoplastic resin recycled from injection-molded products.

[0013] Furthermore, a layer (layer B) made of a polyester resin containing inorganic particles may be laminated on at least one side of the layer A. Laminating layer B can further improve opacity.

[0014] In the cavity-containing polyester film of the present invention, the polyester resin that forms the main component of layers A and B is a polymer synthesized from a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative. Typical examples of such polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, with polyethylene terephthalate being preferred from the viewpoint of mechanical properties, heat resistance, and cost.

[0015] Furthermore, these polyester resins may be copolymerized with other components, as long as the objectives of the present invention are not impaired. Specifically, examples of copolymerized components include isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid and its ester-forming derivatives as dicarboxylic acid components. Examples of diol components include ethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Polyoxyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol are also examples. The copolymerization amount is preferably 10 mol% or less per constituting repeating unit, and more preferably 5 mol% or less. Alternatively, homopolyesters such as polyethylene terephthalate may be blended with copolymerized polyesters. In this case, the amount of copolymerized component in the blended polyester resin composition is the same as described above.

[0016] One method for producing polyester resins involves first using the aforementioned dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as the main starting materials, carrying out esterification or transesterification reactions according to conventional methods, and then further carrying out polycondensation reactions under high temperature and reduced pressure.

[0017] The intrinsic viscosity of the polyester resin is preferably in the range of 0.50 to 0.9 dl / g, and more preferably in the range of 0.55 to 0.85 dl / g, from the viewpoint of film-forming properties.

[0018] Next, the thermoplastic resin recycled from injection-molded products in this invention can be used as a cavity-forming agent. Examples of injection-molded products include industrial products such as housings for electrical appliances and smartphone covers, as well as daily necessities such as cups and plates, and CD and DVD cases. Preferred thermoplastic resins include olefin resins, polyester resins, polyamide resins, polyvinyl chloride, polystyrene, and ABS resin. Olefin resins are particularly suitable and provide sufficient effectiveness as cavity-forming agents. The cavity-containing polyester film of this invention, which uses an olefin resin recycled from injection-molded products as a cavity-forming agent, maintains cavity-forming properties even when using recycled raw materials, thus providing sufficient lightness and excellent opacity and whiteness. The injection-molded product described above may be crushed, washed, dried, and then further finely ground if necessary. The resulting pulverized product may be used directly in the manufacture of film, or it may be melted and processed into pellets.

[0019] As thermoplastic resins recycled from injection molded products, styrene-based resins and olefin-based resins are preferred, with olefin-based resins being more preferred. Examples of olefin-based resins include polymethylpentene (TPX), polypropylene (PP), and polyethylene (PE). Among these, PP is particularly preferred from the viewpoint of being cheaper and more versatile for industrial use.

[0020] The following explanation will use olefin resins, which are preferred thermoplastic resins, as an example. Note that the numerical values ​​for olefin resins in the following explanation are examples for polypropylene, but they can also be applied to other olefin resins. The olefin resin recycled from injection-molded products used in this invention is originally used in injection-molded products, so its weight-average molecular weight (Mw) is preferably 100,000 to 500,000, and more preferably 200,000 to 400,000. When the weight-average molecular weight (Mw) of the olefin resin recycled from injection-molded products is within the above range, the recycled olefin resin can be used for film applications and can also be used as a cavity-forming agent to create cavities. Because injection-molded products have a relatively low molecular weight, it may not be possible to create sufficient cavities. Therefore, in order to form sufficient cavities, a high-molecular-weight olefin resin can be blended with the above olefin resin. The weight-average molecular weight (Mw) of the high-molecular-weight olefin resin used in the blend is preferably 500,000 to 700,000. When the weight-average molecular weight (Mw) is 700,000 or less, the dispersibility of the olefin-based dispersed particles is good, fine cavities are formed, and sufficient opacity is obtained, which is preferable. By blending the above resin with olefin-based resin recycled from injection-molded products, the opacity can be further improved and the specific gravity reduced.

[0021] Furthermore, the olefin resin recycled from injection-molded products used in this invention preferably has a molecular weight distribution (Mw / Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), of 4 to 8, and more preferably 5 to 7. Mw / Mn is an indicator that represents the breadth of the molecular weight distribution; the larger this value, the wider the molecular weight distribution. An Mw / Mn of 8 or less is preferable because it suppresses low molecular weight components and improves cavity formation. Also, an Mw / Mn of 4 or more is suitable for industrial production from a cost standpoint. Note that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are values ​​measured by gel permeation chromatography (GPC).

[0022] The olefin resin recycled from injection-molded products used in this invention is originally used in injection-molded products, so a melt viscosity of 50 to 100 Pa·s is preferred. When the melt viscosity of the olefin resin recycled from injection-molded products is within the above range, the recycled olefin resin can be used for film applications and can also create cavities as a cavity-forming agent. Because injection-molded products have a low melt viscosity, it may not be possible to create sufficient cavities. Therefore, in order to form sufficient cavities, a high-melt-viscosity olefin resin can be blended with the above-mentioned olefin resin. The melt viscosity of the high-melt-viscosity olefin resin used in the blend is preferably 200 to 700 Pa·s, more preferably 300 to 600 Pa·s, and even more preferably 400 to 500 Pa·s. When the melt viscosity is 700 Pa·s or less, the dispersibility of the olefin-based dispersed particles is good, fine cavities are formed, and sufficient opacity is obtained, which is preferable. Note that the melt viscosity is a value measured by a capillograph.

[0023] When blending recycled olefin resin from injection-molded products with high molecular weight olefin resin (or high melt viscosity olefin resin), the proportion of recycled olefin resin from injection-molded products is preferably 1 to 99% by mass, more preferably 5 to 95% by mass, and even more preferably 10 to 90% by mass, of the total olefin resin, in order to balance the environmental benefits of using recycled resin with the benefits of using high molecular weight olefin resin (or high melt viscosity olefin resin). The higher the proportion of high molecular weight olefin resin (or high melt viscosity olefin resin) (the lower the proportion of recycled olefin resin from injection-molded products), the higher the void formation, the lower the apparent density, and the higher the opacity and whiteness. Considering environmental benefits and the characteristics of the resulting film, it is possible to decide whether or not to add high molecular weight olefin resin (or high melt viscosity olefin resin), and if so, what is the appropriate range of addition.

[0024] For example, from an environmental perspective, the proportion of olefin resin recycled from injection molded products is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 40% by mass or more, and most preferably 50% by mass or more. From the perspective of improving cavity formation, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

[0025] In the cavity-containing polyester film of the present invention, the content of the olefin resin is preferably 3 to 35% by weight, and more preferably 5 to 30% by weight, relative to the total amount of each component in layer A, from the viewpoint of cavity formation and film-forming properties. By setting the olefin resin content to 3% by weight or more, cavities can be formed to obtain sufficient lightness and cushioning properties. On the other hand, by setting the olefin resin content to 35% by weight or less, good film-forming properties can be obtained.

[0026] When a large proportion of polyolefin resin is recycled from injection-molded products, a higher content of olefin resin in the cavity-containing polyester film tends to make it more prone to breakage during film formation. Therefore, when a large proportion of polyolefin resin is recycled from injection-molded products, it is preferable to reduce the content of olefin resin in layer A. For example, if the recycled olefin resin from injection-molded products accounts for 50% by mass or more of the total olefin resin, the content of olefin resin in layer A is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 22% by mass or less. Furthermore, if the recycled olefin resin from molded injection products accounts for 70% by mass or more of the total olefin resin, or if the film contains only recycled olefin resin from injection-molded products, the content of olefin resin in layer A is preferably 25% by mass or less, more preferably 22% by mass or less, and even more preferably 20% by mass or less.

[0027] Furthermore, if the olefin resin recycled from injection-molded products is 25% by mass or less, the olefin resin content in layer A may be 15% by mass or more, 20% by mass or more, or 25% by mass or more.

[0028] Furthermore, other miscible resins besides olefin resins may be included as long as they do not impair the objectives of the present invention. However, it is preferable that the olefin resin is present in an amount of 90% by weight or more, more preferably 95% by weight or more, and most preferably 100% by weight, relative to the total amount of miscible resins in layer A. In addition, it is preferable that dispersants such as polyethylene glycol and surfactants are not included from the viewpoint of whiteness and cavity formation.

[0029] Furthermore, to the extent that the objectives of the present invention are not impaired, these polyester resins or olefin resins may contain small amounts of other polymers, antioxidants, heat stabilizers, matting agents, pigments, UV absorbers, fluorescent whitening agents, plasticizers, or other additives. In particular, it is preferable to include antioxidants or heat stabilizers to suppress oxidative degradation of the olefin resin. The types of antioxidants and heat stabilizers are not particularly limited, but examples include hindered phenols, phosphorus, and hindered amines, which may be used individually or in combination. The amount added is preferably in the range of 1 to 50,000 ppm relative to the entire film. In this invention, excellent whiteness can be ensured even without adding a fluorescent whitening agent to the film.

[0030] In the present invention, the cavity-containing polyester film may contain inorganic particles in the polyester resin or olefin resin as needed to improve opacity and whiteness. Examples of such inorganic particles include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, titanium dioxide, and zinc sulfide, but titanium dioxide, calcium carbonate, and barium sulfate are preferred from the viewpoint of opacity and whiteness. These inorganic particles may be used individually or in combination of two or more types. These particles can be incorporated into the film by adding them to the polyester resin or olefin resin in advance.

[0031] In the present invention, the method of mixing inorganic particles with a polyester resin or an olefin resin is not particularly limited, and examples include a method of dry blending the polyester resin and the olefin resin and then directly feeding them into a film-making machine, or a method of dry blending the polyester resin and the olefin resin and then melt-kneading them using various general kneaders to form a masterbatch.

[0032] The cavity-containing polyester film of the present invention has a layer structure consisting of a composition containing a polyester resin and an olefin resin, and has a layer (layer A) containing a cavity inside, and a layer (layer B) made of polyester resin containing inorganic particles may be laminated on at least one side of layer A. If layer A containing the olefin resin is exposed to the surface, some of the exposed olefin dispersion particles may cause process contamination such as roll staining. Furthermore, covering layer A containing recycled olefin resin from injection molded products with layer B containing inorganic pigment has the effect of preventing a decrease in whiteness.

[0033] The thickness of layer B (the sum of the thicknesses of both outermost layers) is preferably in the range of 1 to 40% of the total film thickness, and more preferably in the range of 5 to 30%, from the viewpoint of cavity formation and suppression of olefin resin exposure. When the thickness of layer B is 1% or more, it is preferable because it can suppress the exposure of the olefin resin. On the other hand, when the thickness of layer B is greater than 40%, it tends to be difficult to form cavities necessary to obtain sufficient lightness and cushioning.

[0034] In the present invention, examples of inorganic particles to be contained in layer B include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, titanium dioxide, and zinc sulfide. However, from the viewpoint of opacity and whiteness, titanium dioxide, calcium carbonate, and barium sulfate are preferred, and titanium dioxide is particularly preferred. Furthermore, these inorganic particles may be used individually or in combination of two or more types. These particles can be incorporated into the film by adding them to a polyester resin in advance.

[0035] The amount of inorganic particles added to layer B is not particularly limited, but is preferably 1 to 35% by weight of the entire layer B, and more preferably 2 to 30% by weight. When the amount added is 1% by weight or more, the opacity and whiteness can be improved, and when the amount added is 35% by weight or less, the film-forming properties and the mechanical strength of the film are good, which is preferable.

[0036] Furthermore, the cavity-containing polyester film of the present invention may have a coating layer on at least one side in order to improve the wettability and adhesion to printing inks, coatings, and the like. A polyester resin is preferred as the compound constituting the coating layer, but other compounds known as means of improving the adhesion of ordinary polyester films, such as polyurethane resins, polyester urethane resins, and acrylic resins, can also be applied.

[0037] Commonly used methods for applying the coating layer include gravure coating, kiss coating, dip coating, spray coating, curtain coating, air knife coating, plate coating, and reverse roll coating. The coating process can be carried out before film stretching, after longitudinal stretching, or on the film surface after stretching.

[0038] An example of a method for producing a cavity-containing polyester film according to the present invention will be described. First, polyester resin and olefin resin, including recycled olefin resin from injection-molded products, are fed into an extruder and melted and mixed. Subsequently, this molten mixture is extruded in a sheet-like manner from a T-shaped die onto a casting drum or the like to obtain a sheet-like material. The layer consisting of this composition containing polyester resin and olefin resin is layer A. If layer B is to be provided, polyester resin and inorganic particles are fed into a separate extruder and melted and mixed. Layer A and layer B are then laminated together in the die and extruded to obtain a laminated sheet-like material. When obtaining a sheet-like material, it is preferable to bring it into close contact with the casting drum using methods such as electrostatic application. Next, the unstretched film is stretched and oriented. Below, the most commonly used sequential biaxial stretching method, particularly the method of stretching the unstretched film longitudinally and then transversely in the width direction, will be explained as an example. First, in the longitudinal stretching step, the film is heated and stretched 2.5 to 5.0 times between two or more rolls with different peripheral speeds. The heating method at this time may be a method using heated rolls or a method using a non-contact heating medium, or a combination of both, but it is preferable to keep the film temperature in the range of (Tg-10℃) to (Tg+50℃). Next, the uniaxially oriented film is introduced into a tenter and stretched 2.5 to 5 times in the width direction at a temperature of (Tg-10℃) to (Tm-10℃ or lower) to obtain a biaxially oriented film. Hereinafter, Tg is the glass transition temperature of the polyester resin, and Tm is the melting point of the polyester resin. Furthermore, it is preferable to subject the film obtained from the above to heat treatment as needed, and the treatment temperature is preferably in the range of (Tm - 60°C) to Tm.

[0039] In the longitudinal stretching process, the lower limit of the stretching temperature is preferably 65°C, and more preferably 75°C. A stretching temperature of 65°C or higher provides sufficient opacity. The upper limit of the stretching temperature is preferably 125°C, more preferably 115°C, even more preferably 105°C, and particularly preferably 95°C. A stretching temperature of 125°C or lower can suppress deformation of the dispersed particles, and performing the process at a lower temperature tends to result in a lower apparent density.

[0040] The cavity-containing polyester film in this invention has an apparent density of 0.7 to 1.3 g / cm³ from the viewpoint of cushioning and lightness. 3 It is preferable that this is the case. When only recycled PP is used, or when a large proportion of olefin resin is recycled from injection-molded products (for example, when the recycled olefin resin from injection-molded products accounts for 50% or more by mass of the total olefin resin, and even more specifically, 70% or more by mass), the apparent density is 1.0 to 1.3 g / cm³. 3It is preferably 1.1 to 1.3 g / cm 3 More preferably, it is. To make it the above, it is preferable to add high molecular weight pp. In that case, 0.7 to 1.3 g / cm 3 It is preferably, and from the viewpoints of recyclability and strength, 0.8 g / cm 3 It may be above, and may be above 0.9 g / cm 3 By making the apparent density 0.7 g / cm 3 or more, it is possible to suppress the excessive generation of cavities and improve the handling property during post-processing such as printing or during use. By making it 1.3 g / cm 3 or less, sufficient light weight and cushioning properties can be imparted. The apparent density is a value obtained by the measurement method described in the evaluation method described later

[0041] In the case of only the A layer in the cavity-containing polyester film of the present invention, the optical density (OD value) is preferably 0.10 or more, and more preferably 0.20 or more. By making the OD value 0.10 or more, sufficient concealability can be obtained, which is suitable for printing applications such as labels. Also, by providing the B layer as a skin layer on both sides of the A layer, the concealability can be improved. In this case, the OD value is preferably 0.30 or more, and more preferably 0.35 or more. When the OD value is 0.30 or more, sufficient concealability is easily obtained. When used for labels or the like, the image sharpness during printing is excellent and the commercial value is high.

[0042] In the case of only the A layer in the cavity-containing polyester film of the present invention, the total light transmittance is preferably 70% or less, and more preferably 66% or less. By making the OD value 70% or less, sufficient concealability is easily obtained, which is suitable for printing applications such as labels. Also, by providing the B layer as a skin layer on both sides of the A layer, the concealability can be improved. In this case, the total light transmittance is preferably 40% or less, and more preferably 35% or less. When the total light transmittance is 40% or less, sufficient concealability is easily obtained. When used for labels or the like, the image sharpness during printing is excellent and the commercial value can be increased.

[0043] The thickness of the cavity-containing polyester film of the present invention is arbitrary, but is preferably 20 to 300 μm.

[0044] The resulting cavity-containing polyester film is lightweight, has good opacity and whiteness, and is suitable for use as a base material for labels, cards, packaging materials, and the like. [Examples]

[0045] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below. The evaluation items in the examples and comparative examples were measured by the following methods.

[0046] (1) Intrinsic viscosity [η] The viscosity was measured at 30°C using an Ostwald viscometer after dissolving in a phenol / tetrachloroethane mixed bath medium of 60 / 40 (weight ratio).

[0047] (2) Weight-average molecular weight Mw and molecular weight distribution (Mw / Mn) The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined using Gerber emission chromatography (GPC) and converted to polystyrene equivalents. The measurement conditions for GPC are as follows: Equipment: HLC-8321GPC / HT (manufactured by Tosoh) Measurement temperature: 140℃ Columns: Styragel HT6E, HT4, HT3 (Waters brand, 4.6mm x 300mm, 3 strips) (Fractional range: 500-10,000,000) Solvent: Orthodichlorobenzene (ODCB) with dibutylhydroxytoluene (BHT) Added (BHT concentration: 0.5g / L). Sample concentration: 1 mg / 1 ml Flow rate: 0.3mL / min Injection volume: 200μl Detection: RI (Polarity (-))

[0048] (3) Melt viscosity Using a Capillograph 1DPMD-C manufactured by Toyo Seiki Seisakusho, the extrusion speed was 10 mm / min and the shear speed was 1.216 × 10⁻⁶. 2 sec -1 The melt viscosity was measured at a temperature of 280°C using a φ1 × 10 mm capillary tube.

[0049] (4) Apparent density The film was cut into 10.0 cm squares, and the total thickness was measured at 9 points using a micrometer, with 4 significant figures, at different locations. The average thickness was calculated and taken as the average thickness per sheet (t: μm). The weight (w: g) was measured with 4 significant figures using an automatic top-loading balance, and the apparent density was calculated using the following formula. Apparent density (g / cm³) 3 ) = w / (10.0 × 10.0 × t × 10 -4 )

[0050] (5) Total light transmittance (TT) Measurements were taken using a NDH-7000II haze meter manufactured by Nippon Denshoku Industries. Note that a lower total light transmittance value indicates greater opacity.

[0051] (6) Optical density (OD value) Measurements were taken using the "IhAc-T5" transmission density meter manufactured by Ihara Electronics Industry Co., Ltd. Note that a higher optical density value indicates greater opacity.

[0052] (7) Film forming properties The following evaluation was performed based on the number of fractures when the film was manufactured with a deposition time of 2 minutes. ○: No breakage ×: Frequent breakage, film formation impossible.

[0053] The following resins were used in the examples. [Olefin resin] The pellets shown in Table 1 were used as olefin resins. Polyolefin resin a was recycled (crushed, melted, washed, and then pelletized) from polypropylene DVD cases collected from the market, while polyolefin resins b1 and b2 were unused polypropylene that had been polymerized and then pelletized. [Polyester resin] Polyethylene terephthalate (PET) pellets with an intrinsic viscosity of 0.62 were used. [Titanium Oxide Master Pellets] A mixture of 50% by weight of PET resin and 50% by weight of anatase-type titanium dioxide with an average particle size of 0.3 m (by electron microscopy) was supplied to a vented twin-screw extruder and kneaded to produce a master pellet (M1).

[0054] [Table 1]

[0055] (Example 1) [Manufacturing of unstretched film] 79.8% by weight of PET resin, 18.7% by weight of polyolefin resin a, and 1.5% by weight of master pellet (M1) were dry-blended and vacuum-dried to produce the raw material for the cavity-containing polyester A layer. Meanwhile, 30% by weight of master pellet (M1) and 70% by weight of PET resin were dry-blended and vacuum-dried to produce the raw material for the inorganic particle-containing polyester B layer. These raw materials were supplied to separate extruders and melted at 280°C. The cavity-containing polyester A layer and the inorganic particle-containing polyester B layer were laminated in the order B / A / B, joined with a feed block to achieve a thickness ratio of 10 / 80 / 10, and extruded from a T-die onto a cooling drum adjusted to 20°C to produce an unstretched film with a 2-type, 3-layer structure.

[0056] [Fabrication of cavity-containing polyester films] The obtained unstretched film was uniformly heated to 105°C using a heated roll and longitudinally stretched 3.2 times between two pairs of nip rolls with different peripheral speeds. The uniaxially oriented film thus obtained was guided to a tenter, heated to 110°C and transversely stretched 3.8 times, the width was fixed, and heat treatment was performed at 240°C to relax it by 3% in the width direction, thereby obtaining a cavity-containing polyester film with a thickness of 50 μm. The results for apparent density, total light transmittance, and film-forming properties are shown in Table 2. The cavity-containing polyester film of Example 1 contains sufficient cavities and is a film with excellent opacity and whiteness, and can also contribute to reducing environmental impact.

[0057] (Example 2) In the preparation of the cavity-containing polyester film in Example 1, the cavity-containing polyester film was obtained in the same manner as in Example 1, except that the heating roll was uniformly heated to 95°C and the film was longitudinally stretched 3.2 times between two pairs of nip rolls with different peripheral speeds. The results are shown in Table 2. The cavity-containing polyester film of Example 2 contains more voids because it is MD-stretched at a low temperature, and is a film with excellent opacity and whiteness, which can also contribute to reducing environmental impact.

[0058] (Example 3) In the preparation of the cavity-containing polyester film in Example 1, the cavity-containing polyester film was obtained in the same manner as in Example 1, except that the heating roll was uniformly heated to 115°C and the film was longitudinally stretched 3.2 times between two pairs of nip rolls with different peripheral speeds. The results are shown in Table 2. The cavity-containing polyester film of Example 3 has good film-forming properties because it was MD-stretched at high temperature, and although its apparent density is relatively high, it contains voids that make it practical as a cavity-containing film, and it is a film with excellent opacity and whiteness, which can also contribute to reducing environmental impact.

[0059] (Example 4) In the production of the unstretched film of Example 1 described above, a cavity-containing polyester film was obtained in the same manner as in Example 1, except that a dry blend of polypropylene resin a and polypropylene resin b1 in a ratio of 1:9 was used as the olefin resin for layer A. The results are shown in Table 2. The cavity-containing polyester film of Example 4 contains sufficient cavities and is a film with excellent opacity and whiteness, and can also contribute to reducing environmental impact.

[0060] (Example 5) In the production of the unstretched film of Example 1 described above, a cavity-containing polyester film was obtained in the same manner as in Example 1, except that 18.7% of the polypropylene resin for layer A was a dry blend of polypropylene resin b1 with Mw=290000 recycled from injection molded products in a 3:7 ratio. The results are shown in Table 2. The cavity-containing polyester film of Example 5 contains sufficient cavities by dry blending 70% high molecular weight material with 18.7% total polypropylene resin, and is a film with excellent opacity and whiteness. Furthermore, since 5.6% of the raw material is recycled from injection molded products, it can also contribute to reducing environmental impact.

[0061] (Example 6) In the production of the unstretched film of Example 1 described above, a cavity-containing polyester film was obtained in the same manner as in Example 1, except that 28.1% of the polypropylene resin of layer A was a dry blend of polypropylene resin a and polypropylene resin b1 in a ratio of 1:9. The results are shown in Table 2. The cavity-containing polyester film of Example 6 contains sufficient cavities by dry blending 90% high molecular weight material with 28.1% total polypropylene resin, and is a film with excellent opacity and whiteness. Furthermore, since it uses recycled raw materials from injection-molded products, it can also contribute to reducing environmental impact.

[0062] (Example 7) In the production of the unstretched film of Example 1 described above, a cavity-containing polyester film was obtained in the same manner as in Example 1, except that a dry blend of polypropylene resin a and polypropylene resin b2 in a ratio of 1:9 was used as the polypropylene resin for layer A. The results are shown in Table 2. The cavity-containing polyester film of Example 7 contains sufficient cavities by using a polypropylene resin with a higher molecular weight, and is a film with excellent opacity and whiteness. Furthermore, since 1.9% of the raw material is recycled from injection-molded products, it can also contribute to reducing the environmental impact.

[0063] (Example 8) In the production of the unstretched film of Example 1 described above, a cavity-containing polyester film was obtained in the same manner as in Example 1, except that a dry blend of polypropylene resin a and polypropylene resin b2 in a ratio of 3:7 was used as the polypropylene resin for layer A. The results are shown in Table 2. The cavity-containing polyester film of Example 8 contains sufficient cavities by using a polypropylene resin with a high molecular weight, and is a film with excellent opacity and whiteness, and can also contribute to reducing environmental impact.

[0064] (Reference example 1) Reference Example 1 is an example of a conventional, known cavity-containing polyester film that does not use recycled resin. In the production of the unstretched film of Example 1, a cavity-containing polyester film was obtained using the same method as in Example 1, except that only polypropylene resin b1 was used as the polypropylene resin for layer A. The results are shown in Table 2.

[0065] (Reference example 2) Reference Example 2 is a conventional recycling method in which the gripping portion (ear portion) of the clip used when stretching the film horizontally with a tenter is recovered and used as part of the raw material. A cavity-containing polyester film was manufactured in the same manner as in Example 1, except that 85.0% by weight of PET resin, 10.0% by weight of polypropylene resin a, and 5.0% by mass of master pellet (M1) were dry-blended and vacuum-dried to be used as the raw material for the cavity-containing polyester A layer. The edges of the film generated during this manufacturing process were recovered, crushed, and melt-extruded to produce recovered raw material pellets. This recovered material was added to layer A at a rate of 25% by weight. Furthermore, 63.3% by weight of PET resin, 8.0% by weight of polypropylene resin b1, and 3.7% by weight of master pellet (M1) were mixed and vacuum-dried to obtain the raw material for the cavity-containing polyester layer A. Otherwise, a cavity-containing polyester film with a thickness of 50 μm was obtained using the recovered material in the same manner as in Example 1. At this time, the MD stretching temperature was set to 70°C to be favorable for cavity formation. The results are shown in Table 2.

[0066] [Table 2] [Industrial applicability]

[0067] According to the present invention, even when using a low molecular weight, low melt viscosity olefin resin recycled from injection molded products, it is possible to provide a void-containing polyester film with excellent lightness and opacity without impairing the film's properties.

Claims

1. A cavity-containing polyester film comprising a layer (layer A) containing internal cavities, wherein layer A comprises at least a polyester resin and a thermoplastic resin recycled from injection-molded products.

2. The cavity-containing polyester film according to claim 1, wherein a layer (layer B) made of a polyester resin containing inorganic particles is laminated on at least one side of the layer (layer A) which contains a cavity inside.

3. The cavity-containing polyester film according to claim 1, wherein the thermoplastic resin recycled from the injection-molded product is an olefin-based resin.

4. The cavity-containing polyester film according to claim 3, wherein the olefin resin recycled from the injection-molded product satisfies the following (1) and (2). (1) The weight-average molecular weight Mw measured by gel permeation chromatography is in the range of 100,000 to 500,000, and the molecular weight distribution expressed as weight-average molecular weight Mw / number-average molecular weight Mn is 4 to 8. (2) The melt viscosity measured by capillary graph is 50 to 100 PA·s.

5. The cavity-containing polyester film according to claim 1, wherein the injection-molded product includes at least a CD case or a DVD case.

6. Apparent density is 0.7–1.3 g / cm³ ３ The cavity-containing polyester film according to claim 1.

7. The cavity-containing polyester film according to claim 1, wherein the inorganic particles in the B layer are titanium dioxide.

8. A cavity-containing polyester film according to claim 1, wherein the total light transmittance is less than 70% and the optical density is 0.10 or higher.

9. A method for producing a cavity-containing polyester film, comprising the following steps. (Step a) Step of preparing polyester resin and olefin resin recycled from injection molded products, (Step b) A step of obtaining a polyester resin composition by melt-mixing the polyester resin and an olefin resin recycled from injection-molded products. (Step c) Step of extruding the polyester resin composition into a sheet to obtain a sheet-like material. (Step d) Step of stretching the sheet-like material in at least one direction.

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