Hollow-containing polyester-based film

Abstract

The present invention provides a readily-adhesive hollow-containing polyester film containing hollows of an optimum size, which is not only lightweight but also excellent in hiding power, whiteness, film-forming properties, and thermal dimensional stability, and is excellent in ink adhesion and antistatic properties as an information recording material or a printing material. The present invention relates to a hollow-containing polyester film in which a B layer is laminated on both sides of an A layer, the A layer being a layer containing hollows inside, and the B layer being a layer containing a polyester-based resin containing inorganic particles, the A layer containing a composition containing a polyester-based resin and a polypropylene-based resin, the film having a self-weight deflection of 100 mm or less and 60 mm or more in at least one direction, and at least one side of the hollow-containing polyester film having a readily-adhesive layer having a surface resistivity of 1.0 x 10 13 Ω / sq or less.

Description

Technical Field

[0001] This invention relates to an easily adhesive, porous polyester film containing optimally sized pores. It is not only lightweight, but also has excellent opacity, whiteness, film-forming properties, and thermal dimensional stability. As an information recording material or printing material, it exhibits excellent ink adhesion and antistatic properties. Background Technology

[0002] Synthetic paper, a paper substitute primarily composed of synthetic resins, offers superior water resistance, hygroscopic dimensional stability, and surface stability compared to natural paper, making it widely used in labels, stickers, posters, recording paper, and packaging materials. Polyethylene-based resins, polypropylene-based resins, and polyester-based resins are used as the main raw materials for synthetic paper. In particular, polyester-based resins, represented by polyethylene terephthalate (PET), are widely applied due to their excellent mechanical and thermal properties.

[0003] Methods for obtaining films with functions similar to paper generally include: methods that introduce numerous micropores into the film; and methods that roughen the surface of a flat film through surface treatments such as sandblasting, chemical etching, and matte finishing. Among these, the former method of introducing numerous micropores into the film is widely used due to the following advantages: it not only achieves paper-like opacity and whiteness but also makes the film itself lightweight, thus reducing the cost per unit area; and it provides appropriate softness and cushioning, resulting in excellent image clarity during printing.

[0004] A common method for creating micro-voids within a membrane is as follows: First, an incompatible thermoplastic resin (hereinafter referred to as the incompatible resin) is mixed into a polyester resin, thereby obtaining a melt with an island-shaped structure in which the incompatible resin is dispersed in the polyester resin. Then, an unstretched sheet is formed by extrusion through a die and stretched at least in a uniaxial direction, thereby revealing voids through interfacial peeling between the polyester resin and the incompatible resin. Regarding the type of incompatible resin for the island component, in relation to the polyester resin as the island component, 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 preferred. In particular, among these, polypropylene resins are preferred from the perspective of void manifestation and cost-effectiveness.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 49-134755

[0008] Patent Document 2: Japanese Patent Application Publication No. 2-284929

[0009] Patent Document 3: Japanese Patent Application Publication No. 2-180933

[0010] Patent Document 4: Japanese Patent Publication No. 54-29550

[0011] Patent Document 5: Japanese Patent Application Publication No. 11-116716

[0012] Patent Document 6: Japanese Patent Publication No. 7-17779

[0013] Patent Document 7: Japanese Patent Application Publication No. 8-252857 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] When using existing polyester synthetic paper as a substrate film in various printing fields such as labels, tags, IC cards, magnetic recording materials, packaging materials, electrical insulation materials, photosensitive materials, graphic materials, and photographic materials, insufficient rigidity raises concerns about impaired appearance. For example, when used as a label, the film may wrinkle during delivery and become dented or warped when wound around a product due to unevenness. Conversely, excessive rigidity increases the stress on adhesive surfaces during winding, potentially leading to easy peeling of the adhesive. Therefore, a balance between rigidity and weight-based deflection becomes crucial.

[0016] In addition, during printing and bonding processes for attaching to containers, polyester film has high insulation properties, which often leads to problems such as ink leakage due to dust adsorption caused by static electricity during various processes; poor feed performance due to film adsorption caused by frictional static electricity; and other issues during printing.

[0017] The purpose of this invention is to improve the problems in the prior art mentioned above and provide a porous polyester film containing pores of optimal size. It is not only lightweight, but also has excellent opacity, whiteness, film-forming properties, and thermal dimensional stability. It has easy adhesion and is suitable as an information recording material or printing material with excellent ink adhesion. In addition, it has antistatic properties that are less likely to cause problems in the processing process.

[0018] means for solving problems

[0019] Through repeated and in-depth research, the inventors discovered that by controlling the specific gravity, elastic modulus, and thickness by adjusting the amount of polypropylene resin added and the stretching conditions, the self-weight deflection and bending resistance can be controlled, thereby suppressing the formation of wrinkles and distortions. Furthermore, it was found that this method can produce a porous polyester film that maintains the opacity and whiteness of the film while preventing wrinkles and distortions during label delivery or winding.

[0020] In addition, it was found that by using a functional layer with excellent ink adhesion and antistatic properties, a film that is less likely to cause problems in the processing steps when used for labels and other applications can be obtained.

[0021] That is, the porous polyester membrane of the present invention may include the following composition.

[0022] 1. A porous polyester film, wherein a layer B is laminated on both sides of a layer A, wherein layer A is a layer containing voids, and layer B is a layer containing a polyester resin containing inorganic particles.

[0023] Layer A comprises a composition containing polyester resin and polypropylene resin.

[0024] The membrane's self-weight deflection in at least one direction is less than 100 mm and more than 60 mm.

[0025] The aforementioned porous polyester film has at least one side with a surface resistivity of 1.0 × 10⁻⁶. 13 Easy-to-bond layers with an Ω / sq or less.

[0026] 2. The porous polyester membrane according to claim 1 above, wherein,

[0027] The aforementioned easy-to-adhere layer is formed by curing a composition comprising an ion-conducting antistatic agent, a polyester resin, and a polycarbonate urethane resin.

[0028] 3. The porous polyester film according to 1 or 2 above, wherein,

[0029] Contact the other polyester film with the surface of the above-mentioned easy-to-adhere layer and apply it at 50°C and 1 kg / cm². 2 After being kept under pressure for 3 days, the surface resistivity of the other polyester films that had been in contact with the surface of the aforementioned easily adhesive layer was measured to be 1.0 × 10⁻⁶. 14 Ω / sq or higher.

[0030] 4. The porous polyester film according to any one of the above 1 to 3, in the evaluation of its adhesion to UV ink, has a residual area of ​​the printed layer of more than 90%.

[0031] 5. The porous polyester membrane according to any one of claims 1 to 4 above, wherein,

[0032] Layer A also contains 5-60% by weight of the recycled raw materials of the aforementioned porous polyester membrane.

[0033] 6. The porous polyester membrane according to any one of claims 1 to 5 above, wherein,

[0034] The inorganic particles in layer B are titanium oxide.

[0035] 7. The porous polyester film according to any one of 1 to 6 above has an optical density of 0.55 or more (converted to a thickness of 50 μm) and a hue b value of 4 or less.

[0036] 8. The porous polyester film according to any one of 1 to 7 above has an apparent density in the range of 0.8 to 1.2.

[0037] Invention Effects

[0038] According to the present invention, it is possible to provide a high-rigidity synthetic paper that is not prone to wrinkling or warping and can be used for applications such as labels with excellent opacity, whiteness, and printability. This synthetic paper has easy adhesion suitable for use as an information recording material or printing material with excellent ink adhesion, and antistatic properties that are not prone to causing problems in the processing steps. Detailed Implementation

[0039] (Including porous polyester film)

[0040] In the porous polyester membrane of the present invention, the polyester resin that forms the main components of layer A and layer B is a polymer synthesized from dicarboxylic acid or its ester-forming derivatives and diol or its ester-forming derivatives. Representative examples of such polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene 2,6-naphthalenedicarboxylate. From the viewpoints of mechanical properties, heat resistance, and cost, polyethylene terephthalate is preferred.

[0041] Furthermore, these polyester resins can be copolymerized with other components, provided that this does not impair the purpose of the present invention. Specifically, as copolymer components, examples of dicarboxylic acids include isophthalic acid, naphthalenedicarboxylic acid, 4,4-biphenyldicarboxylic acid, adipic acid, sebacic acid, and their ester-forming derivatives. Examples of diol components include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanediol. Examples of polyoxyalkylene glycols include polyethylene glycol and polypropylene glycol. The copolymerization amount is preferably 10 mol% or less per repeating unit, more preferably 5 mol% or less.

[0042] As a method for manufacturing the polyester resin of the present invention, examples include: first, using the above-mentioned dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as the main starting materials, performing esterification or transesterification reactions according to conventional methods, and then further performing polycondensation reactions under high temperature and reduced pressure, thereby manufacturing the resin.

[0043] The limiting viscosity of the polyester resin particles of the present invention is preferably in the range of 0.50 to 0.9 dl / g, considering factors such as film-forming properties and recyclability. More preferably, it is in the range of 0.55 to 0.85 dl / g.

[0044] Next, the incompatible resins used in this invention will be described. As a thermoplastic resin incompatible with the polyester resin used in this invention, a polypropylene resin is used that is uniformly mixed into the polyester resin in a dispersed state and becomes a source of void formation by peeling at the interface with the base resin during stretching.

[0045] The preferred amount of the aforementioned incompatible resins varies depending on the required amount of void formation and stretching conditions for the final film. It is typically selected from 3% by mass or more and less than 40% by mass, more preferably 5% to 30% by mass, as a percentage of the total resin composition. If it is 3% by mass or more, the amount of voids generated during the stretching process can be sufficiently ensured, resulting in satisfactory lightweight, softness, drawing properties, and writeability. On the other hand, if it is less than 40% by mass, a significant reduction in stretchability can be avoided, exhibiting excellent heat resistance, strength, and stiffness (elasticity).

[0046] Furthermore, without prejudice to the purpose of this invention, these polyester or polypropylene resins may contain small amounts of other polymers, antioxidants, heat stabilizers, matting agents, pigments, ultraviolet absorbers, fluorescent whitening agents, plasticizers, or other additives. In particular, to suppress oxidative degradation of the polypropylene resin, it is preferable to contain antioxidants or heat stabilizers. The types of antioxidants and heat stabilizers are not particularly limited; examples include hindered phenolic, phosphorus-based, and hindered amine-based antioxidants, which can be used alone or in combination. The preferred amount is in the range of 1 to 50,000 ppm.

[0047] In this invention, for porous polyester films, inorganic particles are included in the polyester resin or incompatible 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. From the viewpoint of opacity and whiteness, titanium dioxide, calcium carbonate, and barium sulfate are preferred. Furthermore, these inorganic particles can be used alone or in combination of two or more. These particles can be included in the film by pre-adding them to the polyester resin or incompatible resin.

[0048] In this invention, the method of mixing inorganic particles in polyester resin or incompatible resin is not particularly limited, and examples include: a method of dry mixing polyester resin and incompatible resin and then directly feeding it into a film forming machine; a method of dry mixing polyester resin and incompatible resin and then melt mixing and masterbatching using various general mixing machines, etc.

[0049] The porous polyester film of the present invention has the following laminated structure as a layer: a layer (layer B) containing polyester resin containing inorganic particles is laminated on both sides of a layer (layer A) containing a composition of polyester resin and incompatible resin and containing voids therein. When the incompatible resin-containing layer A is exposed on its surface, there is a concern that some of the exposed incompatible resin particles may cause process contamination such as roller contamination. Furthermore, when recycled materials are present in layer A, covering it with layer B containing inorganic pigments helps prevent a decrease in whiteness.

[0050] From the viewpoint of void exposure and suppression of incompatible resin exposure, the ratio of the sum of the thicknesses of layers B stacked on both sides of layer A is preferably in the range of 1 to 40% relative to the overall film thickness, and more preferably 5 to 30%. When the sum of the thicknesses of layers B is 1% or more, the exposure of incompatible resins can be suppressed, which is therefore preferable. On the other hand, when the sum of the thicknesses of layers B is 40% or less, voids that provide sufficient lightweight and cushioning properties can be formed.

[0051] In this invention, examples of inorganic particles contained in layer B include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, titanium dioxide, and zinc sulfide. From the viewpoint of opacity and whiteness, titanium dioxide, calcium carbonate, and barium sulfate are preferred, with titanium dioxide being particularly preferred. Furthermore, these inorganic particles can be used alone or in combination of two or more. These particles can be included in the film by pre-adding them to a polyester resin.

[0052] From the aspect of printing quality when setting a printing layer or the like in post-processing, the upper limit value of the average particle diameter of the inorganic particles contained in the B layer is preferably 5.0 μm, more preferably 3.0 μm, and particularly preferably 2.5 μm. Further, from the aspects of slidability and shielding property in the film manufacturing process and post-processing process, the lower limit value of the average particle diameter of the inorganic particles is preferably 0.1 μm, and particularly preferably 0.2 μm.

[0053] The addition amount of the inorganic particles in the B layer is preferably 5% by mass or more and 40% by mass or less, and more preferably in the range of 7 to 30% by mass. When the addition amount is 5% by mass or more, the shielding property and whiteness can be improved. On the other hand, when the addition amount is 40% by weight or less, deterioration of film-forming property can be avoided, and deterioration of the mechanical strength of the film can be avoided, and thus it is preferred. The content rate of the inorganic particles in the B layer with respect to the entire film is preferably 1% by mass or more and 30% by mass or less, and more preferably in the range of 2 to 20% by mass. When the addition amount is 1% by mass or more, the shielding property and whiteness can be improved. On the other hand, when the addition amount is 30% by mass or less, deterioration of film-forming property can be avoided, and significant deterioration of the mechanical strength of the film can be avoided.

[0054] The obtained porous polyester-based film can be used in the A layer: a self-regenerating raw material (Japanese: jiko saisei genryo) including ears generated in the film-forming process and broken films generated due to fracture problems or the like. As the addition amount of the self-regenerating raw material, from the viewpoints of reducing raw material costs, whiteness, and film-forming property, it is preferably 5 to 60% by weight with respect to the total amount of each component in the A layer. Further, although the self-regenerating raw material may also be contained in the B layer, from the viewpoints of deterioration of whiteness and exposure of incompatible resins in the self-regenerating raw material, it is preferably not contained.

[0055] (Easy adhesion layer)

[0056] In order to improve the backside mobility of the antistatic agent and the adhesion to the UV ink liquid, an easy adhesion layer formed by curing a composition containing an ion conductive antistatic agent, a polycarbonate urethane resin, and a polyester resin is laminated on at least one surface layer of the easy adhesion polyester film of the present invention. By providing such a layer, the adhesion to the ink liquid is improved, problems such as dust adsorption caused by charging in various use processes can be suppressed, and in addition, the adhesion between the films can be suppressed. Therefore, in addition to the effects brought by the rigidity of the film, the processability is also improved in applications such as labels including printing.

[0057] Although it is believed that the easy-to-adhere layer is formed by curing cationic or anionic antistatic agents, polycarbonate urethane resin, and polyester resin, it is difficult to exhibit the chemical structure of the cured layer itself. Therefore, it is actually formed by curing a composition containing cationic or anionic antistatic agents, polycarbonate urethane resin, and polyester resin. The easy-to-adhere layer can be applied to both sides of the polyester film substrate, or it can be applied to only one side of the polyester film substrate, with a different type of resin coating layer applied to the other side.

[0058] In this invention, it is preferable to have the following antistatic properties, namely, the surface resistivity of the easy-to-adhere layer surface of the easy-to-adhere polyester film is 1.0 × 10⁻⁶. 13 Antistatic properties below Ω / sq. If the surface resistivity of the easily bonded layer is 1.0 × 10⁻⁶. 13 With a resistivity of Ω / sq or less, there is no dust adsorption caused by static electricity generated during friction and peeling, resulting in good print quality and eliminating the toner particle scattering seen in laser printers, making it preferable. Furthermore, it prevents issues such as poor handling and overlapping feeds during transport if the films become electrostatically attracted to each other, which is also preferable. A surface resistivity of 5.0 × 10⁻⁶ is more preferable for the easy-to-adhere layer. 12 Ω / sq or less, more preferably 1.0 × 10 12 Below Ω / sq. On the other hand, if the surface resistivity is 1.0 × 10⁻⁶ 8 With a value of Ω / sq or higher, the polarity will not become excessively high, and it exhibits good adhesion to various inks, making it a preferred choice. A further preferred value is 5.0 × 10⁻⁶. 8 Ω / sq or higher, with a particularly preferred value of 1.0 × 10⁻⁶. 9 Ω / sq or higher.

[0059] The following is a detailed description of the components of the easy-to-adhere layer.

[0060] (Ion-conducting antistatic agent)

[0061] As an antistatic agent, it is preferable to have the ability to suppress migration to other items it comes into contact with or to the back of the film itself. For example, regarding functional groups, examples include: nonionic surfactants such as sorbitan type, ether type, ester type, sorbitol type, and glucose type; cationic surfactants such as quaternary ammonium salt type, quaternary ammonium resin type, and imidazoline type; anionic surfactants such as alkyl sulfate type, alkyl phosphate type, phosphate ester type, and sulfate ester type; and amphoteric surfactants or polymers such as betaine type, amino acid type, and aminosulfate type.

[0062] Among the above antistatic agents, as the counterion of the quaternary ammonium base (Japanese: 4級アンモニウム塩基), as long as it is an anionic compound, there is no particular limitation. Preferably, it can be appropriately selected from halide ions, mono- or polyhaloalkyl ions, nitrate ions, sulfate ions, alkyl sulfate ions, sulfonate ions or alkyl sulfonate ions. From the aspects of the stability of the surface resistivity, the stability of the coating liquid, the ink liquid adhesion, and the suppression of the movement of the antistatic agent to other articles and the back surface, ethyl sulfate is preferred.

[0063] In addition, the following can be cited: polyethyleneimine, polydimethyldiallylammonium salt, polyalkylene polyamine dicyanodiamide ammonium condensate, polyvinylpyridinium halide (Japanese: ポリビニルピリジウムハライド), alkyl quaternary ammonium salt of (meth)acrylic acid, alkyl quaternary ammonium salt of (meth)acrylamide, ω-chloro-poly(oxyethylene-polymethylene-alkyl quaternary ammonium salt), polyvinylbenzyltrimethylammonium salt, polystyrene-based cationic polymer, poly(meth)acrylic acid-based cationic polymer (methyl methacrylate, ethyl acrylate, 2-hydroxyethyl methacrylate, trimethylaminoethyl chloride methacrylate, etc.), polyvinylpyridine-based polymer, cyclic integral type (Japanese: インテグラル型) polymer, linear integral type polymer, a polymer of an aromatic vinyl monomer having two or more quaternary ion groups in a pendant type (Japanese: ペンダント型), a polymer having a pyrrolidinium ring in the main chain, etc. These polymers can be homopolymers or copolymers. For the production of these polymers, known monomers capable of copolymerization can be used. From the aspect of controlling the coating liquid miscibility and the amount of the antistatic agent component present on the surface of the easy-bonding layer, an antistatic agent having a linear alkyl group is preferred, and an antistatic agent having a linear alkyl group and a quaternary ammonium base is more preferred.

[0064] Therefore, in an antistatic agent having a linear alkyl group and a quaternary ammonium base, the number of carbon atoms in the alkyl chain is preferably 10 to 25, more preferably 12 to 19, and particularly preferably 14 to 18. Considering the intermolecular interaction and the suppression of the back surface movement based on the molecular length, it is preferably set within the above range.

[0065] The molecular weight of the quaternary ammonium base having a linear alkyl group is preferably 200 or more and preferably 700 or less. More preferably, it is 400 or more and 600 or less. When the molecular weight becomes 200 or more, the surface resistivity can be exhibited, and the back surface movement can be suppressed with a good balance. If the molecular weight is 700 or less, the surface resistivity can be exhibited, and the occurrence of aggregation caused by the interaction with the resin functional group can be suppressed during the coating liquid formulation.

[0066] In addition, the molecular structure of cationic antistatic agents containing nitrogen may contain at least one amide bond, carbamate bond, etc., between the straight-chain alkyl chain and the quaternary ammonium salt group.

[0067] (Polycarbonate urethane resin)

[0068] The urethane resin with a polycarbonate structure in this invention preferably has at least a urethane bond portion structure derived from the polycarbonate polyol component and the polyisocyanate component, and further includes a chain extender as needed. Furthermore, by ensuring that the terminal functional groups of any of the raw material components constituting the molecular chain as described above are three or more, a branched molecular chain structure can be formed after synthesis and polymerization, thereby appropriately introducing a branched polyisocyanate structure.

[0069] Regarding the polycarbonate urethane resin of the present invention, and the urethane resin having a branched structure, the lower limit of the number of terminal functional groups in the molecular chain is preferably 3, more preferably 4, depending on its branched structure. If there are 3 or more, the anti-blocking property during water adhesion can be improved, and therefore it is preferred. Regarding the urethane resin with a polycarbonate structure of the present invention, the upper limit of the number of terminal functional groups in the molecular chain is preferably 6, depending on its branched structure. If there are 6 or less, the resin can be stably dispersed in an aqueous solution, and therefore it is preferred.

[0070] Preferably, the polycarbonate polyol component used for synthesizing and polymerizing the polycarbonate urethane resin of the present invention contains an aliphatic polycarbonate polyol with excellent heat resistance and hydrolysis resistance. Examples of aliphatic polycarbonate polyols include aliphatic polycarbonate diol and aliphatic polycarbonate triol, with aliphatic polycarbonate diol being preferred. Examples of aliphatic polycarbonate diols used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in this invention include: aliphatic polycarbonate diols obtained by reacting one or more of the following diols, such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,8-nonanediol, neopentanediol, diethylene glycol, and dipropylene glycol, with carbonates such as dimethyl carbonate, ethylene carbonate, and phosgene.

[0071] The number average molecular weight of the polycarbonate polyol used in this invention is preferably 1000 to 3000. More preferably, it is 1200 to 2900, and most preferably, it is 1500 to 2800. If it is 1000 or more, the ink adhesion can be improved, and therefore it is preferred. If it is 3000 or less, the back-side migration of the antistatic agent can be suppressed, and therefore it is preferred.

[0072] Examples of polyisocyanates used in the synthesis and polymerization of polycarbonate urethane resins in this invention include: aromatic aliphatic diisocyanates such as phenyl dimethyl diisocyanate, isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate, alicyclic diisocyanates such as 1,3-bis(isocyanate methyl)cyclohexane, aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, or polyisocyanates obtained by pre-addition of one or more of these compounds with trimethylolpropane, etc. When using the above-mentioned aromatic aliphatic diisocyanates, alicyclic diisocyanates, or aliphatic diisocyanates, there is no problem of yellowing, which is therefore preferred. Furthermore, it does not form an overly hard coating film, resulting in good surface resistivity when using antistatic agents, which is also preferred.

[0073] Examples of chain extenders include: ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol and 1,6-hexanediol, glycerol, trimethylolpropane and pentaerythritol, ethylenediamine, hexamethylenediamine and piperazine, monoethanolamine and diethanolamine, thiodiols such as diethanolamine and diethanolamine, or water.

[0074] To form a branched structure in a urethane resin, a preferred method is to set an appropriate temperature and time to react the aforementioned polycarbonate polyol components, polyisocyanates, and chain extenders, and then add a compound having three or more functional hydroxyl or isocyanate groups to further carry out the reaction.

[0075] Specific examples of compounds having three or more hydroxyl groups include caprolactone triol, glycerol, trimethylolpropane, glycerol, hexanetriol, 1,2,3-hexanetriol, 1,2,3-pentanetriol, 1,3,4-hexanetriol, 1,3,4-pentanetriol, 1,3,5-hexanetriol, 1,3,5-pentanetriol, and polyether triols. As examples of the aforementioned polyether triols, one can be a compound obtained by addition polymerization of one or more monomers such as ethylene oxide, propylene oxide, butane oxide, tetrahydropyran, glycidyl ether, methyl glycidyl ether, tert-butyl glycidyl ether, and phenyl glycidyl ether, using one or more of these compounds having three active hydrogens as initiators.

[0076] Specific examples of compounds having three or more isocyanate groups are any polyisocyanate compounds having at least three isocyanate (NCO) groups in one molecule. In this invention, examples of isocyanate compounds with three or more functions include: biuret compounds, cyanurates, and adducts obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, aromatic aliphatic diisocyanates, and alicyclic diisocyanates having two isocyanate groups.

[0077] Examples of aromatic diisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, and 4,4'-diphenyl ether diisocyanate.

[0078] Examples of aliphatic diisocyanates include: trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylidene diisocyanate, 2,3-butylidene diisocyanate, 1,3-butylidene diisocyanate, dodecamethyl diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0079] Aromatic aliphatic diisocyanates include, for example, phenyl dimethyl diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylphenyl dimethyl diisocyanate, and 1,3-tetramethylphenyl dimethyl diisocyanate.

[0080] Examples of alicyclic diisocyanates include: 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylene bis(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane, etc.

[0081] Biuret compounds are self-condensing compounds with biuret bonds formed by the self-condensation of isocyanate monomers, such as biuret compounds of hexamethylene diisocyanate.

[0082] Cyanurates are trimers of isocyanate monomers, such as trimers of hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate.

[0083] The adduct is a polyfunctional isocyanate compound formed by reacting the above-mentioned isocyanate monomer with a low-molecular-weight active hydrogen compound having three or more functional groups. Examples thereof include: a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with toluene diisocyanate, a compound obtained by reacting trimethylolpropane with phthalic diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and the like.

[0084] As a chain extender having three or more functional groups, alcohols having three or more hydroxyl groups such as trimethylolpropane and pentaerythritol described in the above description of the chain extender are suitable.

[0085] In the present invention, the easy-bonding layer is preferably formed by using an aqueous coating liquid and applying it by the in-line coating method (Japanese: インラインコート法) described later. Therefore, it is desirable that the urethane resin of the present invention has water solubility or water dispersibility. It should be noted that the above-mentioned "water solubility or water dispersibility" means: dispersed in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.

[0086] In order to impart water dispersibility to the urethane resin, a sulfonic acid (salt) group or a carboxylic acid (salt) group can be introduced (copolymerized) into the urethane molecular skeleton. In order to maintain moisture resistance, it is appropriate to introduce a weakly acidic carboxylic acid (salt) group, and it is also possible to suppress the interaction (gelation) with a cationic antistatic agent, and thus it is preferred. A nonionic group such as a polyoxyalkylene group can also be further introduced.

[0087] In order to introduce a carboxylic acid (salt) group into the urethane resin, for example, as a polyol component, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid and dimethylolbutyric acid is introduced as a copolymerization component and neutralized with a salt-forming agent. Specific examples of the salt-forming agent include: trialkylamines such as ammonia, trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine; N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine; N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. They can be used alone or in combination of two or more.

[0088] To impart water dispersibility, when using a polyol compound with a carboxylic acid (salt) group as a copolymer component, and setting the total polyisocyanate content of the urethane resin to 100 mol%, the molar ratio of the polyol compound with a carboxylic acid (salt) group in the urethane resin is preferably 3 to 60 mol%, more preferably 5 to 40 mol%. When the above molar ratio is 3 mol% or more, water dispersibility is obtained, and therefore it is preferred. Furthermore, when the above molar ratio is 60 mol% or less, water resistance is maintained, and resistance to damp heat is obtained, and therefore it is preferred.

[0089] To improve rigidity, the urethane resin in this invention can have a capped isocyanate structure at its end.

[0090] (Cross-linking agent)

[0091] In this invention, a capped isocyanate can be added as a crosslinking agent to the composition for forming the easy-to-adhere layer. More preferably, a capped isocyanate with 3 or more functionalities is used, and particularly preferably, a capped isocyanate with 4 or more functionalities is used. This suppresses the antistatic properties of the easy-to-adhere layer surface and inhibits the back-side migration of the antistatic agent.

[0092] For the capped isocyanate in this invention, in order to impart water solubility or water dispersibility, a hydrophilic group can be introduced into the polyisocyanate used as a precursor. Examples of hydrophilic groups include: (1) quaternary ammonium salts of dialkylamino alcohols, quaternary ammonium salts of dialkylaminoalkylamines, etc., (2) sulfonates, carboxylates, phosphates, etc., and (3) polyethylene glycol, polypropylene glycol, etc., which are capped with alkyl groups at a single end. When a hydrophilic site is introduced, it becomes (1) cationic, (2) anionic, or (3) nonionic. Among these, most other water-soluble resins are anionic, so anionic or nonionic resins that are easily compatible are preferred. In addition, anionic resins have excellent compatibility with other resins, and nonionic resins do not have ionic hydrophilic groups, so they are also preferred in order to improve resistance to damp heat.

[0093] As anionic hydrophilic groups, it is preferable to have: hydroxyl groups for introducing into the polyisocyanate and carboxylic acid groups for imparting hydrophilicity. Examples include: glycolic acid, lactic acid, tartaric acid, citric acid, oxobutyric acid, oxovalerate, hydroxypentanoic acid, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutyric acid, and polycaprolactones having carboxylic acid groups. Organic amine compounds are preferred for neutralizing the carboxylic acid groups. Examples include: ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, ethylenediamine, and other straight-chain or branched primary, secondary, or tertiary amines with 1 to 20 carbon atoms; cyclic amines such as morpholine, N-alkylmorpholine, and pyridine; monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, triethanolamine, and triethanolamine containing hydroxyl groups.

[0094] As a nonionic hydrophilic group, the repeating units of polyethylene glycol, polypropylene glycol ethylene oxide, and / or propylene oxide that are single-terminated with alkyl groups are preferably 3 to 50, more preferably 5 to 30. When the number of repeating units is small, the compatibility with the resin deteriorates, and the haze increases; when the number is large, the adhesion at high temperature and high humidity decreases. Regarding the end-capped isocyanate of the present invention, to improve water dispersibility, nonionic, anionic, cationic, or amphoteric surfactants can be added. Examples include nonionic surfactants such as polyethylene glycol and polyol fatty acid esters, fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, sulfosuccinates, and alkyl phosphates, anionic surfactants such as alkylamine salts and alkyl betaines, cationic surfactants such as carboxylic acid amine salts, sulfonic acid amine salts, and sulfate ester salts.

[0095] In addition to water, it may contain water-soluble organic solvents. For example, the organic solvent used in the reaction may be added, or the organic solvent may be removed and replaced with another organic solvent.

[0096] As a method to improve adhesion, other publicly disclosed compounds can be added. Even other crosslinking agents can further improve adhesion under high temperature and humidity conditions to enhance the adhesion durability of the easily bonded layer. Specific crosslinking agents include urea-based, epoxy-based, melamine-based, oxazoline-based, and carbodiimide-based agents. Furthermore, catalysts can be used as needed to promote the crosslinking reaction.

[0097] (Polyester resin)

[0098] The polyester resin used to form the easy-to-adhere layer in this invention can be linear, and more preferably a polyester resin whose constituent components are dicarboxylic acids and diols with branched structures. Examples of dicarboxylic acids mentioned here include aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. In addition, branched diols refer to diols having branched alkyl groups, such as 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol.

[0099] For polyester resins, it can be said that the branched diol component described above, as a more preferred embodiment, is preferably included in the total diol component at a proportion of 10 mol% or more, and more preferably at a proportion of 20 mol% or more. If it is 10 mol% or more, the crystallinity will not become excessively high, and the adhesion of the easy-to-bond layer will be good, which is therefore preferred. The upper limit of the diol component in the total diol component is preferably 80 mol% or less, more preferably 70 mol% by mass. If it is 80 mol% or less, the concentration of oligomers as byproducts can be suppressed, and the transparency of the easy-to-bond layer is good, which is therefore preferred. Ethylene glycol is most preferably the diol component other than the above-mentioned compounds. If in small quantities, diethylene glycol, propylene glycol, butanediol, hexanediol, or 1,4-cyclohexanediethanol, etc., may also be used.

[0100] The most preferred dicarboxylic acid component of the aforementioned polyester resin is terephthalic acid or isophthalic acid. In addition to the aforementioned dicarboxylic acid, to impart water dispersibility to the copolymer polyester resin, it is preferable to copolymerize 5-sulfonophthalic acid, such as sulfoterephthalic acid, 5-sulfonophthalic acid, and sodium isophthalate-5-sulfonate, in a range of 1 to 10 mol%. Polyester resins containing dicarboxylic acids with a naphthalene backbone can be used; to suppress the decrease in adhesion to UV inks, the proportion of this dicarboxylic acid is preferably 5 mol% or less of the total carboxylic acid component, or it may be omitted.

[0101] As components of the aforementioned polyester resin, triols and tricarboxylic acids may be included to a degree that does not impair the properties of the polyester resin.

[0102] The aforementioned polyester resin may contain polar groups other than carboxyl groups. Examples include sulfonic acid metal salts and phosphate groups, and one or more of these may be present. As a method for introducing sulfonic acid metal salts, examples include using metal salts of 5-sulfoisophthalic acid, 4-sulfonnaphthalene-2,7-dicarboxylic acid, 5-[4-sulfophenoxy]isophthalic acid, or metal salts of 2-sulfo-1,4-butanediol, 2,5-dimethyl-3-sulfo-2,5-hexanediol, etc., containing sulfonic acid metal salts, within a range of 10 mol% or less, preferably 7 mol% or less, and more preferably 5 mol% or less of the total polycarboxylic acid or polyol components. If the percentage exceeds 10 mol%, there is a tendency for a decrease in the hydrolysis resistance of the resin itself and the water resistance of the coating film.

[0103] The resin solids concentration in the coating solution refers to the sum of the solids concentrations of polyester resin, urethane resin with a polycarbonate structure, and crosslinking agent. It is desirable to adjust the resin solids concentration in the coating solution to between 5% and 17%. If the resin solids concentration is 5% or higher, the thickness of the easily bonded layer after drying and curing will not become too thin, and various easily bonded properties, such as those of UV-curable inks, will be good, thus this is preferred. On the other hand, if the resin solids concentration is 17% or lower, sufficient crosslinking properties can be obtained when crosslinking agents are present, which can inhibit the migration of antistatic agents to other items or the back side, and also inhibit adhesion, thus this is preferred.

[0104] When the total solid content in the composition used to form the easy-to-adhere layer is set to 100% by mass, it is desirable to include 1 to 8% by mass of an ion-conducting antistatic agent. If this range is met, antistatic properties can be obtained. Furthermore, this range is preferred because the antistatic component does not migrate to other articles or the back side after heating or moisture-resistant heat treatment.

[0105] When the total mass of the three solid components—polyester resin, urethane resin with a polycarbonate structure, and crosslinking agent—is set at 100% by mass, the content of the urethane resin with a polycarbonate structure is preferably 5-50% by mass. If this range is met, good affinity with various materials and UV inks is achieved, resulting in excellent adhesion, which is therefore preferred. If within the specified range, excellent adhesion is achieved, antistatic properties are provided, and even under humid heat conditions, the migration of the antistatic agent to other articles or the back surface is suppressed, which is also preferred.

[0106] When the total mass of the three solid components—polyester resin, urethane resin with a polycarbonate structure, and crosslinking agent—is set at 100% by mass, the upper limit of the crosslinking agent content is preferably 50% by mass. By satisfying the above range, the crosslinking property of the easy-to-adhere layer becomes higher, the affinity with UV inks becomes better, and the antistatic property is also easily exhibited, which is therefore preferred. In addition, the strength of the easy-to-adhere layer during moisture-resistant treatment can be maintained, and the migration of the antistatic agent to other articles and the back surface can be suppressed, which is also preferred.

[0107] When the total mass of the three solid components—polyester resin, urethane resin with a polycarbonate structure, and crosslinking agent—is set at 100% by mass, the polyester resin content is preferably 10-70% by mass. By satisfying this range, good affinity with various materials and UV inks is achieved, resulting in excellent adhesion. Adhesion to polyester film substrates is particularly improved, making this preferred. Furthermore, the use of cationic antistatic agents suppresses gelation of the coating solution caused by interactions, which is also preferred.

[0108] (additive)

[0109] Within the scope that does not impair the effects of the present invention, known additives may be added to the easily adhesive layer of the present invention, such as surfactants, pH adjusters, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic slip agents, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc.

[0110] The aforementioned surfactants are sometimes used to provide effects such as solubilizers, dispersants, defoamers, and wetting agents. The hydrophilic portion of a surfactant is divided into ionic (cationic, anionic, amphoteric) and nonionic portions. In the manufacture of water-based coatings, they are used because the polyester film used as the substrate has low surface energy and lacks wettability. Therefore, they are frequently used as surface tension adjusters and wetting agents in water-based coatings. While not particularly limited, the surfactants mentioned above are preferably surfactants that can reduce the surface tension of the coating liquid to 50 dyne / cm or less, preferably to 40 dyne / cm or less, and promote wetting of the polyester film. Examples include: alkyl trimethylammonium salts, dialkyl dimethylammonium salts, alkyl benzyl dimethylammonium salts, monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkylbenzene sulfonates, monoalkyl phosphates, alkyl dimethylamine oxides, alkyl carboxybetaine, polyoxyethylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglucosides, fatty acid diethanolamides, alkyl monoglycidyl ethers, etc., with polyether-modified silicones being the most preferred.

[0111] When the total mass of the solid components in the coating liquid is set to 100% by mass, it is preferable to set the amount of surfactant added to be 0.1% by mass or more and 1.0% by mass or less. More preferably, it is in the range of 0.2% by mass to 0.8% by mass. If it is 0.1% by mass or more, wetting effect as a surfactant can be obtained, and therefore it is preferable. In addition, if it is 1.0% by mass or less, easy adhesion can be well maintained, and therefore it is preferable.

[0112] Among the additives mentioned above, pH adjusters are sometimes used. As acids for adjusting the pH, inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid, and organic acids such as oxalic acid, formic acid, citric acid, and acetic acid can be used. For alkali adjustment, examples include sodium carbonate, sodium bicarbonate, and sodium phosphonate. In adjusting water-based coatings, a neutral pH is preferred, preferably in the range of pH 5 to 9, and more preferably in the range of pH 6 to 8.5. If the pH is below 5, there is a concern about corrosion of the coating machine; furthermore, if a capping isocyanate is selected as the crosslinking agent, the detachment-promoting effect of the capping agent is reduced. Additionally, if the pH reaches 9 or above, polyester resins used as resin adhesives will hydrolyze, impairing adhesion and durability, and are therefore not preferred.

[0113] To reduce the gloss of the easy-to-bond layer, inactive particles can be included in the easy-to-bond layer.

[0114] To impart properties such as slip resistance, matte finish, and ink absorption to the surface, lubricant particles can also be included in the easy-to-adhere layer. The particles can be inorganic or organic. Although there are no particular limitations, examples include: (1) inorganic particles such as silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, zirconium oxide, titanium dioxide, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, calcium carbonate, magnesium carbonate, calcium phosphate, magnesium hydroxide, and barium sulfate; (2) organic particles such as acrylic acid or methacrylic acid, vinyl chloride, vinyl acetate, nylon, styrene / acrylic acid, styrene / butadiene, polystyrene / acrylic acid, polystyrene / isoprene, polystyrene / isoprene, methyl methacrylate / butyl methacrylate, melamine, polycarbonate, urea, epoxy, urethane, phenol, diallyl phthalate, and polyester. In order to give the easy-to-adhere layer appropriate sliding properties, silica is particularly preferred.

[0115] The average particle size of the aforementioned inactive particles is preferably 0.1 μm or more and 2.4 μm or less, more preferably 0.3 to 2.0 μm. If the average particle size of the inactive particles is 0.04 μm or more, excessive increase in the gloss of the film surface can be suppressed. On the other hand, if it is 2.4 μm or less, particle detachment from the easy-to-adhere layer can be suppressed, and powder shedding during various processes such as film travel can be avoided.

[0116] It should be noted that the average particle size can be determined based on morphological observations using microscopes such as scanning electron microscopes and transmission electron microscopes. Specifically, in these microscopic observations, the average diameter of 20 arbitrarily selected particles is used. Furthermore, the shape of the particles is not particularly limited as long as it meets the objectives of this invention; spherical particles and irregular non-spherical particles can be used. The particle size of irregular particles can be calculated using the equivalent circle diameter. The equivalent circle diameter is obtained by dividing the area of ​​the observed particle by π, calculating the square root, and multiplying by 2.

[0117] In cases where it is desired to increase the gloss of the easy-to-bond layer, it is preferable that the easy-to-bond layer does not contain particles.

[0118] (Membrane fabrication of porous polyester film)

[0119] Next, the method for forming the porous polyester film of the present invention will be described, but without particular limitation. For example, after drying the mixture containing the above composition by conventional methods, it is melt-extruded in sheet form from a T-shaped tube, and then pressed into a casting drum by electrostatic application or the like, and cooled and solidified to obtain an unstretched film. Next, the unstretched film is stretched and oriented. Hereinafter, the most commonly used successive biaxial stretching method, in particular the method of stretching the unstretched film longitudinally along the length direction and then stretching it laterally along the width direction, will be described as an example. First, in the longitudinal stretching step along the length direction, the film is heated and stretched to 1.0 to 5.0 times between two or more rollers with different circumferential speeds. As the heating method at this time, a heating roller method or a non-contact heating medium method can be used, or a combination of these methods can be used. Preferably, the film temperature is set in the range of (Tg-10°C) to (Tg+50°C). Next, the uniaxially stretched film is fed into a tenter frame and stretched along its width at a temperature below (Tg-10°C) to (Tm-10°C) to a ratio of 1.0 to 6.0 times, thereby obtaining a biaxially stretched film. Here, Tg is the glass transition temperature of the polyester resin, and Tm is the melting point of the polyester. Furthermore, it is preferable to perform heat treatment on the film obtained through the above operation as needed, preferably within the range of (Tm-60°C) to Tm.

[0120] The easy-to-adhesion layer can be applied after the film is manufactured or during the manufacturing process. In particular, from a productivity perspective, it is preferable to form the easy-to-adhesion layer by applying the coating liquid to at least one side of the PET film at any stage of the film manufacturing process, i.e., after it has been unstretched or uniaxially stretched.

[0121] The method for applying the coating liquid to the polyester film can utilize any known method. Examples include reverse roller coating, gravure coating, kiss coating, die coating, roller brush coating, spray coating, air knife coating, wire bar coating, tube doctor blade coating, dip coating, and curtain coating. These methods can be used individually or in combination.

[0122] In this invention, the thickness of the easy-to-adhere layer can be appropriately set within the range of 0.001 to 2.00 μm. To balance processability and adhesion, a range of 0.01 to 1.00 μm is preferred, more preferably 0.02 to 0.80 μm, and even more preferably 0.05 to 0.50 μm. If the thickness of the easy-to-adhere layer is 0.001 μm or more, good adhesion is achieved, and this is therefore preferred. If the thickness of the easy-to-adhere layer is 2.00 μm or less, movement of the antistatic agent onto other parts or the back side can be suppressed, and this is also preferred.

[0123] The optical density (OD value) of the porous polyester film in this invention is preferably 0.55 or higher, more preferably 0.6 or higher. With an OD value of 0.55 or higher, sufficient opacity is achieved, and when used in labels, etc., the clarity of the printed image is well maintained, adding value to the product. The upper limit of the OD value is preferably 1.5. Below 1.5, the whiteness is unsaturated, sufficient whiteness is displayed, and it is also preferable in terms of cost. It should be noted that the OD value is a value calculated based on a thickness of 50 μm obtained by the measurement method described in the evaluation method described later.

[0124] The hue b-value of the porous polyester film in this invention is preferably 4.0 or less, more preferably 3.0 or less. With a b-value of 4.0 or less, good whiteness can be exhibited, and when used in labels or similar products, high clarity can be maintained after printing. Furthermore, it adds value to the product. The lower limit of the hue b-value is preferably -5.0. With a b-value of -5.0 or greater, the film's bluish tint can be avoided, and when used as a printing substrate, a good balance of resolution can be achieved.

[0125] For the porous polyester film of the present invention, by ensuring that the deflection caused by the weight of a 130mm long sample is between 60mm and 100mm, it is possible to achieve the following when using it as a roll label: it can be used as a label that does not wrinkle or warp when the label is fed out or when it is wound around the product. If it is 100mm or less, it can maintain sufficient rigidity and remain upright after the label is affixed to the product, thus giving the label an excellent appearance. For example, it can prevent wrinkling when the label is fed out and is not greatly affected by the unevenness of the product when it is wound around the product, thus avoiding problems such as dents and warping.

[0126] On the other hand, if the self-weight deflection is 60mm or more, excessive rigidity can be avoided, thus preventing increased stress on the bonded areas when winding the product and suppressing easy peeling of the bond. Therefore, maintaining the self-weight deflection within an appropriate range is important. The self-weight deflection can be effectively adjusted by adjusting the specific gravity, thickness, and elastic modulus in the deflection direction.

[0127] The thickness of the porous polyester film of the present invention is arbitrary, preferably 20-300 μm, and more preferably 50-120 μm. The thickness has a significant impact on the self-weight deflection. By increasing the thickness, the film can have bending rigidity, and the self-weight deflection can be suppressed to a small level. If the thickness is kept above a certain level, the self-weight deflection becomes smaller, and the handleability as a label deteriorates.

[0128] While also depending on the film thickness, the elastic modulus in the flexural direction of the porous polyester film of the present invention is preferably 2500 MPa or more, and more preferably 3500 MPa or more. With an elastic modulus of 2500 MPa or more, wrinkles can be suppressed during the transport of roll labels. Even when the film thickness cannot be increased, a film with appropriate self-weight deflection can be adjusted by increasing the elastic modulus. The elastic modulus can be effectively adjusted by the stretch ratio in the length and width directions, as well as the heat treatment conditions.

[0129] The apparent density of the porous polyester film in this invention is preferably 0.8 g / cm³. 3 Above and 1.3g / cm 3 The following is more preferably 0.90 g / cm³. 3 Above and 1.2g / cm 3 The following is an example of a density of 0.8 g / cm³. 3 Under the above conditions, excessive void formation can be suppressed, and the product demonstrates good operability for dimming during post-processing such as printing and general use. At 1.3 g / cm³ 3 Sufficient lightweight and cushioning can be achieved in the following situations.

[0130] In addition, as for the effect on self-weight deflection, at 1.3 g / cm 3 In the following cases, even at the same thickness, an increase in self-weight is prevented, thus avoiding excessive self-weight deflection. It should be noted that the apparent density is a value obtained through the measurement method described in the evaluation methods section below.

[0131] In one approach, the invention can be recycled and used as a recycled polyester raw material; for example, the recycled material can also be used to form a film.

[0132] Example

[0133] The present invention will now be specifically described with reference to specific embodiments. It should be noted that the present invention is not limited to the embodiments described below. It should also be noted that the evaluation items in the embodiments and comparative examples were measured using the following methods.

[0134] (1) Limiting viscosity [η]

[0135] The solution was dissolved in a phenol / tetrachloroethane mixture of 60 / 40 (mass ratio), and the viscosity was measured using an Ostwald viscometer at 30°C. It should be noted that the measurement was performed three times, and the average value was calculated.

[0136] (4) Apparent density

[0137] Cut four 5.0 cm square pieces from the membrane. Overlap the four pieces and use a micrometer to measure the total thickness at 10 points, changing the thickness to four significant figures. Calculate the average thickness of the four overlapping pieces. Divide this average by 4 and round the significant figures to three places to obtain the average thickness (t: μm) of each piece. Use an automatic balance to measure the mass (w: g) of the four identical samples to four significant figures, and calculate the apparent density using the following formula. Note that the apparent density is rounded to three significant figures.

[0138] Apparent density (g / cm³) 3 =w / (5.0×5.0×t×10) -4 ×4)

[0139] (5) Optical density (OD value)

[0140] Measurements were taken using an Ihac-T5 type transmission density meter manufactured by Ihara Electronics Co., Ltd., and the converted film thickness is 50 μm. It should be noted that a higher optical density value indicates greater shielding effectiveness.

[0141] (6) Hue b value

[0142] The b-value of the hue was measured using a colorimeter (ZE6000) manufactured by Nippon Denshoku Co., Ltd., and according to JIS-8722, and converted to a film thickness of 50 μm. The smaller the b-value, the higher the whiteness and the weaker the yellowness.

[0143] (7) Deflection under self-weight

[0144] Prepare a sample (10) with a deflection direction of 150 mm and a width of 20 mm, and fix it with a magnet (13) so that the length of the drooping part from the horizontal plane is 130 mm. The distance between the front end of the drooping part of the membrane and the vertical direction of the membrane fixing part is taken as the self-weight deflection.

[0145] (8) Bending strength

[0146] The bending resistance is calculated using the self-weight deflection obtained through the above method as δ, and then mathematically. The average self-weight deflection of the three pieces is determined as δ.

[0147] Br=WL 4 / 8δ

[0148] Br: Bending strength (mN·cm)

[0149] W: Weight per unit area of ​​the test piece (mN / cm²) 2 )

[0150] L: Length of the test piece (cm)

[0151] δ: Deflection due to self-weight (cm)

[0152] (9) Antistatic surface resistivity

[0153] Three 5.00 cm square pieces were cut from the membrane and used as samples. Surface resistivity was measured using a surface resistivity meter (Nittoseiko Analytech HIRESTA MCP-HT800) under conditions of 500 V voltage, 23 °C, and 65% humidity, according to JIS K6911, and the average value was recorded.

[0154] (10) Adhesion to UV ink

[0155] On the easy-to-adhere layer of an easy-to-adhere polyester film, UV ink [manufactured by T&K TOKA Co., Ltd., trade name "BESTCURE UV161 Blue S"] was used for printing using a printing press [manufactured by Meizoku Co., Ltd., trade name "RI Tester"]. Then, the film coated with the ink layer was irradiated with a high-pressure mercury lamp at 40 mJ / cm². 2The ultraviolet light is used to cure the UV-curable ink. Next, using NICHIBAN celluloid adhesive tape (CT405AP-24), a 24mm wide and 50mm long section is cut out and fully adhered using a portable rubber roller to prevent air from entering the ink layer surface. Then, the celluloid adhesive tape is peeled off vertically, and the area of ​​residual printed layer in the 24mm × 50mm area is observed and judged according to the following criteria.

[0156] ○: If the remaining area of ​​the printed layer is more than 99% of the total area, it is considered qualified.

[0157] △: If the remaining area of ​​the printed layer is more than 90% and less than 99% of the total area, it is considered qualified.

[0158] ×: If the remaining area of ​​the printed layer is less than 90% of the total area, it is considered unqualified.

[0159] The films of the following examples and comparative examples were prepared using the raw materials shown in Table 1 and the granules and coating liquid described below.

[0160] (Cationic antistatic agent)

[0161] An esterification reaction was carried out at 100°C for 10 hours using 116 g of N,N-dimethyl-1,3-propanediamine and 285 g of stearic acid with 17 carbon atoms, under a nitrogen atmosphere. Tetrahydrofuran was added as a quaternization solvent. A specified amount of dimethyl sulfate was added to the target amine, and the reaction was carried out at 70°C for approximately 10 hours. After the reaction, the solvent was removed by distillation under reduced pressure, and isopropanol was added to adjust the concentration of solids to the desired level, yielding an isopropanol solution of a cationic antistatic agent containing quaternary ammonium ethyl sulfate.

[0162] (Polymerization of urethane resins with a polycarbonate structure)

[0163] In a four-necked flask equipped with a stirrer, a Demrod condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 22 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 20 parts by mass of polyethylene glycol monomethyl ether with a number average molecular weight of 700, 53 parts by mass of polyhexamethylene carbonate glycol with a number average molecular weight of 2100, 5 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, 16 parts by mass of a polyisocyanate compound (Asahi Kasei Chemicals, DURANATE TPA, 3-functional) with an isocyanurate structure, using hexamethylene diisocyanate as a raw material, were added. The mixture was stirred at 75°C for 1 hour under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Then, the temperature of the reaction solution was lowered to 50°C, and 7 parts by mass of methyl ethyl ketone oxime were added dropwise. After cooling the reaction solution to 40°C, a polyurethane prepolymer solution was obtained. Next, 450g of water was added to a reaction vessel equipped with a homogenizer capable of high-speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred at a constant speed of 2000 min... -1 The mixture was stirred and mixed while adding a polyurethane prepolymer solution for water dispersion. Then, under reduced pressure, acetone and a portion of the water were removed, thereby preparing a 35% by mass solution of the solids component of the water-dispersible urethane resin.

[0164] (Polymerization of end-capped isocyanate crosslinking agents)

[0165] In a flask equipped with a stirrer, thermometer, and reflux condenser, 100 parts by mass of a polyisocyanate compound (DURANT TPA) with an isocyanurate structure, using hexamethylene diisocyanate as a raw material, 55 parts by mass of propylene glycol monomethyl ether acetate, and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 750) were added. The mixture was kept at 70°C for 4 hours under a nitrogen atmosphere. Then, the temperature of the reaction solution was lowered to 50°C, and 47 parts by mass of methyl ethyl ketone oxime were added dropwise. The infrared spectrum of the reaction solution was measured, confirming the disappearance of absorption of the isocyanate groups. 210 parts by mass of water were added to obtain an aqueous dispersion of the oxime-terminated isocyanate crosslinking agent with a solid content of 40% by mass. This oxime-terminated isocyanate crosslinking agent has 3 functional groups and an NCO equivalent of 170.

[0166] (Polymerization of polyester resin)

[0167] In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux cooler, 194.2 parts by weight of dimethyl terephthalate, 184.5 parts by weight of dimethyl isophthalate, 14.8 parts by weight of sodium dimethyl isophthalate 5-sulfonate, 185 parts by weight of neopentyl glycol, 188 parts by weight of ethylene glycol, and 0.2 parts by weight of tetrabutyl titanate were added. The transesterification reaction was carried out at a temperature of 160°C–220°C for 4 hours. Then, the temperature was raised to 255°C, and the reaction system was slowly subjected to reduced pressure. The reaction was then carried out under reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolyester resin. The obtained copolyester resin was pale yellow and transparent. The reduced viscosity of the copolyester resin was measured and found to be 0.40 dl / g. The glass transition temperature based on DSC was 65℃.

[0168] [Manufacturing of Titanium Oxide Masterbatch Particles (M1)]

[0169] 50% by mass of anatase titanium dioxide with an average particle size of 0.3 μm (electron microscopy) was mixed with 50% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa·s. The resulting mixture was fed into a vented twin-screw extruder for compounding to produce masterbatch pellets (M1) containing titanium dioxide.

[0170] (Example 1)

[0171] The solid components of the coating solution that constitutes the coating layer are as follows.

[0172] [Composition of the coating layer (coating solution A)]

[0173] The total amount of solid components contained in the coating layer is set to 100 by mass.

[0174] • Cationic antistatic agent: 6.2% by mass

[0175] • Urea resin with a polycarbonate structure: 25.5% by mass

[0176] • End-capped isocyanate crosslinking agent: 10.9% by mass

[0177] • Polyester resin: 54.6% by mass

[0178] • Organosilicon surfactant: 0.4% by mass

[0179] • pH adjuster (sodium bicarbonate): 2.4% by mass

[0180] The solid component mass ratio of urethane resin / crosslinking agent / polyester resin is 28 / 12 / 60.

[0181] [Manufacturing of Unstretched Film]

[0182] 74% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa·s, 21% by mass of polypropylene resin with a melt viscosity of 500 Pa·s, and 5% by mass of the above-mentioned masterbatch granules containing titanium oxide (M1) were mixed and vacuum dried to produce a raw material containing a porous polyester A layer. On the other hand, 30% by mass of the above-mentioned masterbatch granules containing titanium oxide (M1) and 70% by mass of polyethylene terephthalate resin with a melt viscosity of 200 Pa·s were mixed and vacuum dried to produce a raw material containing an inorganic polyester B layer. These raw materials were fed to various extruders and melted at 280°C. The porous polyester A layer and the inorganic polyester B layer were stacked in the order B / A / B, and joined by the feed head with a thickness ratio of 10 / 80 / 10. The resulting material was then extruded from a T-die onto a cooling drum adjusted to 30°C to produce two types of three-layer unstretched films.

[0183] [Fabrication of Porous Polyester Membranes]

[0184] The unstretched film a is uniformly heated to 70°C using heating rollers, and then longitudinally stretched to 1.4 times its original size between two pairs of clamping rollers with different circumferential speeds. At this time, as an auxiliary heating device for the film, an infrared heater (rated value 20W / cm) with a gold reflective film in the middle of the clamping rollers is positioned facing both sides of the film and 1cm away from the film surface, and heats it. On one side of the uniaxially stretched film thus obtained, using the above-described coating configuration, a reverse gravure coating method is used to achieve a WET coating amount of 7g / m². 2 After coating in the manner described above, the film is fed into a tenter frame, heated to 140°C and stretched laterally to 4.0 times its original size. The width is then fixed and heat-fixed at 240°C. Further, it is relaxed by 3% in the width direction at 210°C, thereby obtaining a porous polyester film (B / A / B) with a thickness of 50 μm. The evaluation results of Example 1 are recorded in Table 1. As shown in Table 1, the film of Example 1 used raw material resins that satisfy the above elements (1) to (3). Therefore, the dispersed particle size of the polypropylene resin was controlled to an appropriate size of 20 μm. 2 The above-mentioned number of voids is also high, and the apparent density, OD value (occlusion), hue b value, thermal shrinkage rate (MD direction and TD direction), and film-forming properties are all good. Details are shown in the table below.

[0185] (Example 2)

[0186] The amount of polypropylene resin added to the unstretched membrane was set to 30% by mass, and the transverse stretching ratio was set to 3.8 times. Otherwise, the same procedure as in Example 1 was followed to obtain a porous polyester membrane with a thickness of 50 μm.

[0187] (Example 3)

[0188] The longitudinal stretch ratio was set to 3.2 times, and otherwise operated in the same manner as in Example 1, to obtain a porous polyester film with a thickness of 75 μm.

[0189] (Example 4)

[0190] The solid composition of the compound constituting the coating layer was modified as described below, and otherwise operated in the same manner as in Example 3 to obtain a porous polyester film with a thickness of 75 μm.

[0191] [Composition of the coating layer (coating solution B)]

[0192] The total amount of solid components contained in the coating layer is set to 100 by mass.

[0193] • Cationic antistatic agent: 6.2% by mass

[0194] • Urea resin with polycarbonate structure: 36.4% by mass

[0195] • End-capped isocyanate crosslinking agent: 0% by mass

[0196] • Polyester resin: 54.6% by mass

[0197] • Organosilicon surfactant: 0.4% by mass

[0198] • pH adjuster (sodium bicarbonate): 2.4% by mass

[0199] The mass ratio of solid components of urethane resin / crosslinking agent / polyester resin is 40 / 0 / 60.

[0200] (Example 5)

[0201] The amount of polypropylene resin added to the unstretched membrane was set to 15% by mass. Otherwise, the procedure was the same as in Example 3 to obtain a porous polyester membrane with a thickness of 75 μm.

[0202] (Example 6)

[0203] The amount of polypropylene resin added to the unstretched membrane was set to 30% by mass. Otherwise, the procedure was the same as in Example 3 to obtain a porous polyester membrane with a thickness of 75 μm.

[0204] (Example 7)

[0205] The transverse stretch ratio was set to 3.8 times, and otherwise operated in the same manner as in Example 1, to obtain a porous polyester film with a thickness of 75 μm.

[0206] (Example 8)

[0207] The same procedure as in Example 3 was followed to obtain a porous polyester film with a thickness of 100 μm.

[0208] (Example 9)

[0209] The longitudinal stretching ratio was set to 2.5 times, and the transverse stretching ratio was set to 2.5 times. Otherwise, the operation was the same as in Example 1 to obtain a porous polyester film with a thickness of 100 μm.

[0210] (Example 10)

[0211] The amount of polypropylene resin added to the unstretched film was set to 15% by mass, and the longitudinal stretching ratio was set to 3.5 times. Otherwise, the same procedure as in Example 1 was followed to obtain a porous polyester film with a thickness of 100 μm.

[0212] (Example 11)

[0213] The amount of polypropylene resin added to the unstretched membrane was set to 30% by mass. Otherwise, the procedure was the same as in Example 3 to obtain a porous polyester membrane with a thickness of 100 μm.

[0214] (Comparative Example 1)

[0215] The transverse stretch ratio was set to 3.8 times, and otherwise the same procedure was followed as in Example 1 to obtain a porous polyester film with a thickness of 50 μm.

[0216] (Comparative Example 2)

[0217] The longitudinal stretch ratio was set to 3.2 times and the transverse stretch ratio was set to 4.0 times. Otherwise, the operation was the same as in Example 1 to obtain a porous polyester film with a thickness of 50 μm.

[0218] (Comparative Example 3)

[0219] The procedure was repeated in the same manner as in Example 1 to obtain a porous polyester film with a thickness of 75 μm.

[0220] (Comparative Example 4)

[0221] The longitudinal stretching ratio was set to 2.5 times, the transverse stretching ratio was set to 2.5 times, and otherwise the same operation was performed as in Example 1 to obtain a porous polyester film with a thickness of 75 μm.

[0222] (Comparative Example 5)

[0223] The solid composition of the compound constituting the coating layer was modified as described below, and otherwise operated in the same manner as in Example 3 to obtain a porous polyester film with a thickness of 75 μm.

[0224] [Composition of the coating layer (coating solution C)]

[0225] The total amount of solid components contained in the coating layer is set to 100 by mass.

[0226] • Cationic antistatic agent: 0% by mass

[0227] • Urea resin with a polycarbonate structure: 27.2% by mass

[0228] • End-capped isocyanate crosslinking agent: 11.6% by mass

[0229] • Polyester resin: 58.2% by mass

[0230] • Organosilicon surfactant: 0.4% by mass

[0231] • pH adjuster (sodium bicarbonate): 2.6% by mass

[0232] The solid component mass ratio of urethane resin / crosslinking agent / polyester resin is 28 / 12 / 60.

[0233] (Comparative Example 6)

[0234] The solid composition of the compound constituting the coating layer was modified as described below, and otherwise operated in the same manner as in Example 3 to obtain a porous polyester film with a thickness of 75 μm.

[0235] [Composition of the coating layer (coating solution D)]

[0236] The total amount of solid components contained in the coating layer is set to 100 by mass.

[0237] • Cationic antistatic agent: 6.2% by mass

[0238] • Urea resins with a polycarbonate structure: 0% by mass

[0239] • End-capped isocyanate crosslinking agent: 36.4% by mass

[0240] • Polyester resin: 54.6% by mass

[0241] • Organosilicon surfactant: 0.4% by mass

[0242] • pH adjuster (sodium bicarbonate): 2.6% by mass

[0243] The mass ratio of solid components of urethane resin / crosslinking agent / polyester resin is 0 / 40 / 60.

[0244] (Comparative Example 7)

[0245] The solid composition of the compound constituting the coating layer was modified as described below, and otherwise operated in the same manner as in Example 3 to obtain a porous polyester film with a thickness of 75 μm.

[0246] [Composition of the coating layer (coating solution E)]

[0247] The total amount of solid components contained in the coating layer is set to 100 by mass.

[0248] • Cationic antistatic agent: 6.2% by mass

[0249] • Urea resin with polycarbonate structure: 63.7% by mass

[0250] • End-capped isocyanate crosslinking agent: 27.3% by mass

[0251] • Polyester resin: 0% by weight

[0252] • Organosilicon surfactant: 0.4% by mass

[0253] • pH adjuster (sodium bicarbonate): 2.6% by mass

[0254] The mass ratio of solid components of urethane resin / crosslinking agent / polyester resin is 70 / 30 / 0.

[0255] (Comparative Example 8)

[0256] The transverse stretching ratio was set to 3.8 times, and otherwise the same procedure was followed as in Example 1 to obtain a porous polyester film with a thickness of 100 μm.

[0257] (Comparative Example 9)

[0258] The longitudinal stretching ratio was set to 3.5 times, and otherwise operated in the same manner as in Example 1, to obtain a porous polyester film with a thickness of 100 μm.

[0259]

[0260]

[0261] In Comparative Examples 1-4, the deflection amount was outside the scope of the present invention, resulting in wrinkling and adhesion peeling. In Comparative Examples 5-7, the surface resistivity was outside the scope of the present invention, leading to dust adsorption due to static electricity during printing and other processes, resulting in poor print quality. Furthermore, in Comparative Examples 8 and 9, the deflection amount was outside the scope of the present invention, resulting in adhesion peeling.

[0262] Industrial availability

[0263] According to the present invention, even when inexpensive polypropylene resin is used as a void-generating agent, it is possible to provide a void-containing polyester film with good lightweight, excellent cushioning, opacity, whiteness, thermal dimensional stability and film-forming properties.

Claims

1. A porous polyester membrane, wherein a layer B is laminated on both sides of a layer A, wherein layer A is a layer containing voids, and layer B is a layer containing a polyester resin containing inorganic particles. Layer A comprises a composition containing polyester resin and polypropylene resin. The self-weight deflection of the membrane in at least one direction due to the weight of a 130mm long sample is less than 100mm and more than 60mm. The porous polyester membrane has at least one side with a surface resistivity of 1.0 × 10⁻⁶. 8 Ω / sq or higher and 1.0 × 10 13 Easy-to-bond layers with an Ω / sq or lower The flexural modulus of the porous polyester membrane is above 2500 MPa and below 5920 MPa. The apparent density of the porous polyester film is 0.8 g / cm³. 3 Above and 0.99 g / cm 3 the following, The easy-to-bond layer is formed by curing a composition comprising a cationic antistatic agent, a polyester resin, and a polycarbonate urethane resin. When the total solid components in the composition used to form the easy-to-adhere layer are set to 100% by mass, the composition contains 1 to 8% by mass of the cationic antistatic agent.

2. The porous polyester membrane according to claim 1, wherein, In the evaluation of adhesion with UV ink, the residual area of ​​the printed layer reached over 90%.

3. The porous polyester membrane according to claim 1 or 2, wherein, Layer A also contains 5% to 60% by weight of the recycled raw material of the porous polyester membrane.

4. The porous polyester membrane according to claim 1 or 2, wherein, The inorganic particles in layer B are titanium oxide.

5. The porous polyester film according to claim 1 or 2, wherein the optical density is 0.55 or higher based on a thickness of 50 μm, and the hue b value is 4 or lower.

6. The porous polyester film according to claim 1 or 2, having an apparent density of 0.90 g / cm³. 3 ~0.99g / cm 3 Within the range.

Images