JP2023102266A - Polyester film for dry film resist - Google Patents

Abstract

To provide a polyester film containing a little coarse foreign matter and having a good film-forming property.SOLUTION: Provided is a polyester film for dry film resist, having a laminate structure including at least two or more layers, where at least one layer contains an organic salt containing a sulfur element and a phosphorus element, a content of the sulfur element relative to a weight of the polyester film is 2-20 wt. ppm, a content of the phosphorus element is 1-25 wt. ppm, and a total of contents of a calcium element and a magnesium element is 20 wt. ppm or less.SELECTED DRAWING: None

Description

The present invention relates to a polyester film for dry film resist.

Dry film resist (hereinafter sometimes referred to as DFR) is used to form circuits such as printed wiring boards, semiconductor packages, and flexible boards. A DFR has a structure in which a photosensitive layer (photoresist layer) is laminated on a polyester film as a support, and then sandwiched between protective films (cover films) made of polyethylene film, polypropylene film, polyester film, or the like. In order to create a conductor circuit using this DFR, the following steps are generally performed.
1) A step of peeling off the protective film from the DFR and laminating it with the substrate/conductive substrate layer so that the surface of the exposed resist layer and the surface of the conductive substrate layer such as copper foil on the substrate are in close contact.
2) Next, a step of placing the photomask with the conductive circuit pattern printed on it on a support made of a polyester film, and irradiating the resist layer mainly composed of a photosensitive resin thereon with ultraviolet rays to expose it.
3) Then, after removing the photomask and the polyester film, a step of dissolving and removing the unreacted portion in the resist layer with a solvent.
4) Next, a step of etching with an acid or the like to dissolve and remove the exposed portion of the conductive substrate layer.

After step 4), the photoreacted portions in the resist layer and the portions of the conductive substrate layer corresponding to the photoreacted portions remain as they are. After that, the remaining resist layer is removed to form a conductive circuit on the substrate. Therefore, the polyester film used as the support is required to efficiently transmit ultraviolet rays. Thereby, the conductive circuit pattern is accurately reflected on the resist layer. In particular, in recent years, with the miniaturization and weight reduction of IT equipment, etc., printed wiring boards have become finer and denser, and a fine pattern with a wiring width and wiring spacing of about 5 μm is formed, and a polyester film for a dry film resist support that can achieve high resolution is required.

Further, when a polyester resin is made into a film, an electrostatic application casting method is often employed in which a high voltage is applied to the upper surface of an unsolidified sheet-like material to bring the sheet-like material into close contact with a rotating cooling drum. Patent Documents 1 and 2 propose a method of adding a large amount of an alkali metal compound, an alkaline earth metal compound, or a phosphorus compound to a polyester as a method for improving electrostatic applicability. However, although this method can improve the electrostatic applicability to some extent, the use of a large amount of magnesium acetate causes the generation of metallic foreign matter, which causes exposure inhibition during ultraviolet irradiation during the exposure process. Patent Document 3 proposes a method of adding a quaternary phosphonium sulfonate as a method of improving electrostatic applicability, but since a large amount of alkali metal or alkaline earth metal is contained, it was insufficient to suppress metallic foreign matter.

Patent Document 4 proposes a method for producing a polyester film in which a sulfonic acid compound is added and no metal element other than a polymerization catalyst is added.

Japanese Patent Application Laid-Open No. 2006-249213 Japanese Unexamined Patent Application Publication No. 2008-201822 JP-A-2000-44703 JP-A-10-36495

With the above-mentioned conventional technology, it is difficult to satisfy the demand for high resolution, and defects such as distortion, voids, and poor condition of the resist pattern wall surface in the patterning of the resist after development cannot be sufficiently resolved, and quality improvement for high resolution is still required. In particular, in recent years, fine patterns with wiring widths and spacings of about 5 μm are required, so it is believed that coarse patterns of about 1 μm lead to resist defects. An object of the present invention is to provide a polyester film which contains less metal-derived foreign matter, has good film-forming properties, has less resist defects, and is excellent in handleability when producing a resist film.

As a result of intensive studies to solve the above problems, the present invention has the following configurations. It has a laminated structure of at least two layers, contains an organic salt having a sulfur element (atom) and an organic salt having a phosphorus element (atom) for at least one layer, and has a sulfur element (atom) content relative to the weight of the polyester film of 2 to 20 weight ppm, a phosphorus element (atom) content of 1 to 25 weight ppm, and a calcium element (atom) and magnesium element (atom) content of 20 weight ppm or less. Polyester film suitably used as a dry film resist application.

An object of the present invention is to provide a polyester film that contains less foreign matter, has good film-forming properties, has less defects in the resist, and is excellent in handleability when producing a resist film.

The polyester film of the present invention has a laminate structure of two or more layers. A laminate of a polyester resin layer containing particles and a polyester resin layer not containing particles may be used, or a laminate of a plurality of particle-containing resin layers having different particle concentrations may be used. The film of the present invention is preferably a laminate of three or more layers from the viewpoint of increasing the slipperiness of the film and also improving the high permeability.

In the polyester film of the present invention, having a polyester resin as a main component means that at least 70 mol% or more of the polyester is a polyester obtained by polymerization from monomers or low polymers containing dicarboxylic acids, diols, and ester-forming derivatives thereof as main constituents. In the present invention, it is preferable to use an aromatic dicarboxylic acid as the dicarboxylic acid.

The dicarboxylic acid component of the present invention includes terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenyl 4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, malonic acid, dimer acid and the like. A more preferred embodiment of the dicarboxylic acid of the present invention is terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, or alkyl esters thereof, since it has a high melting point and can be easily processed into a film. These acid components may be used singly or in combination of two or more. Other aromatic dicarboxylic acids such as isophthalic acid or fatty acids may be partially copolymerized.

The diol component of the present invention includes aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol and neopentyl glycol, and saturated alicyclic primary diols such as cyclohexanedimethanol, cyclohexanediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecanediethanol, decalindimethanol and decalindiethanol as alicyclic diols. Saturated heterocyclic primary diols including cyclic ethers such as diols and isosorbide, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, and adamantanediol Alicyclic diols and aromatic cyclic diols such as paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, and 9,9'-bis(4-hydroxyphenyl)fluorene can be exemplified. In addition to diols, polyfunctional alcohols such as trimethylolpropane and pentaerythritol can also be used as long as they do not impair the effects of the present invention. Among these, diols having a boiling point of 230° C. or less are preferable because they are easily distilled out of the reaction system, and aliphatic diols are more preferable because they are low in cost and have high reactivity. Furthermore, ethylene glycol is particularly preferred from the viewpoint of the mechanical properties of the resulting polyester film. These diol components may be used alone or in combination of two or more.

Although the polyester film in the present invention is not particularly limited, it preferably has at least one structural unit selected from ethylene terephthalate, ethylene-2,6-naphthalate, propylene terephthalate, butylene terephthalate, hexamethylene terephthalate, cyclohexanedimethylene terephthalate, propylene-2,6-naphthalate, butylene-2,6-naphthalate, hexamethylene-2,6-naphthalate, cyclohexanedimethylene-2,6-naphthalate unit as a main constituent. Among them, polyester having ethylene terephthalate as a main structural unit is particularly preferable because of its excellent moldability. Moreover, two or more polyesters may be mixed, or a copolymerized polyester may be used.

The polyester film of the present invention contains sulfur element (atom) and phosphorus element (atom), the content of sulfur element (atom) is 2 to 20 ppm by weight, the phosphorus element (atom) content is 1 to 25 ppm by weight, and the total content of calcium element (atom) and magnesium element (atom) is 20 weight ppm or less.

In the present invention, an element may be used in the sense of an atom.

The polyester film of the present invention preferably has a sulfur element content of 2 to 20 ppm by weight, more preferably 9 to 17 ppm by weight, relative to the weight of the polyester film. As the content of elemental sulfur increases, good electrostatic applicability during film formation can be obtained. When the content of the sulfur element is 2 ppm by weight or more, the volume resistivity when the polyester film is melted is reduced, and the electrostatic castability during film molding is improved.

Organic salts containing elemental sulfur are exemplified by sulfide compounds, thiophene compounds, thiol compounds, sulfonic acid compounds and the like, and the organic sulfur salts to be contained in the polyester film of the present invention are not particularly limited. However, a sulfonic acid compound is preferable from the viewpoint of obtaining good electrostatic applicability when forming a film using a polyester film. Examples of the sulfonic acid compound include sulfonium anions such as methanesulfonic acid, butylsulfonic acid, trifluoromethanesulfonic acid, tetrafluoroethanesulfonic acid, nonafluorobutanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, styrenesulfonic acid, perfluorooctane sulfonic acid, and heptadecafluorooctane sulfonic acid, and cations paired with these include known ones such as alkali metal cations, quaternary phosphonium cations, and quaternary ammonium cations. Also, the sulfonic acid compound may be copolymerized in the polyester molecular chain. Sulfonium anions having two or more ester-forming functional groups, such as 3,5-dicarboxybenzenesulfonic acid, are exemplified as the sulfonic acid compound copolymerized in the polyester molecular chain.

The method for adding elemental sulfur to the polyester film of the present invention is not particularly limited. One or more compounds containing elemental sulfur may be added to the polyester film during the polycondensation reaction, or may be kneaded with the polyester film after the polycondensation reaction using a twin-screw kneading extruder or the like.
The polyester film of the present invention preferably has a phosphorus element content of 1 to 25 ppm by weight, more preferably 5 to 17 ppm by weight, relative to the weight of the polyester film. When the elemental phosphorus content is 1 ppm by weight or more, the polyester film has good foreign matter count and heat resistance.

The method for adding the phosphorus element to the polyester film of the present invention is not particularly limited. One or more known organic salts containing a phosphorus element, such as ionic compounds such as phosphoric acid, trimethyl phosphate, ethyldiethylphosphonoacetate, phosphorous acid, alkali metal phosphate, and quaternary phosphonium cations, can be used. These phosphorus compounds can be incorporated into the polyester film by a known method such as a method of adding during the polycondensation reaction of the polyester film or a method of kneading with the polyester film after the polycondensation reaction using a twin-screw kneading extruder or the like.

In the polyester film of the present invention, the total content of elemental calcium and elemental magnesium must be 20 ppm by weight or less relative to the entire polyester film. When the total content of elemental calcium and elemental magnesium is 20 ppm by weight or less, a polyester film having good color tone and solution haze and less foreign matter can be obtained. In particular, when an organic sulfonic acid salt is used to contain elemental sulfur in the polyester film of the present invention, the sulfonic acid and calcium ions and magnesium ions tend to form foreign matter. Therefore, the polyester film of the present invention preferably does not contain calcium element or magnesium element from the viewpoint of reducing foreign matter.

The inventors of the present invention have made further efforts to observe coarse foreign matter in more detail, and as a result, have found that it is possible to detect finer foreign matter and improve detection accuracy by using a laser microscope. When the polyester film of the present invention has a laminated structure of three or more layers, the number of coarse particles having a major diameter of 1.0 μm or more present in the C layer is preferably 5 pieces/mm ^or less when the layer having no surface is C layer. The coarse matter in the present invention refers to a solid matter that exists without being dissolved in the polyester film or a void having the solid matter as a central core, and even if it is composed of a single particle or an aggregate of a plurality of particles, it is regarded as a coarse matter. In addition, the major diameter of the coarse matter as used in the present invention refers to the longest measured length of the coarse matter detected by the measuring method described later.

The method for controlling the number of coarse foreign matter within the above range is not particularly limited, and examples thereof include a method of controlling the mesh size of a foreign matter collection filter used during melt film formation.

The method for adding elemental calcium and elemental magnesium to the polyester film of the present invention is not particularly limited, but it is preferable to add the calcium compound and magnesium compound during the polycondensation reaction of the polyester film, and the form at the time of addition may be any of powder, slurry, and solution, and it is preferable to add as a solution from the viewpoint of dispersibility. The solvent at this time is preferably the same as the diol component of the polyester composition. Examples of calcium compounds include calcium acetate, calcium propionate, calcium chloride, calcium bromide, calcium iodide, and calcium hydroxide. Examples of magnesium compounds include magnesium acetate, magnesium propionate, magnesium chloride, magnesium bromide, magnesium iodide, and magnesium hydroxide.

The method for producing the polyester film of the present invention is specifically described below.
For example, when the polyester film in the present invention is polyethylene terephthalate, it is usually produced by using terephthalic acid or dimethyl terephthalate and ethylene glycol as raw materials, obtaining a low polymer represented by bishydroxyethyl terephthalate (hereinafter referred to as BHT) by reactions such as esterification reaction and transesterification reaction, and then obtaining high molecular weight PET by polycondensation reaction.

The reaction to obtain the low-polymer BHT is not particularly limited, and can be carried out by a known reaction. However, the esterification reaction is preferable because the reaction proceeds sufficiently due to the self-catalytic action of the carboxylic acid even without a catalyst, and there is no need to add a reaction catalyst such as a calcium compound or a magnesium compound. By carrying out the esterification reaction without a catalyst, it is possible to suppress thermal decomposition and generation of foreign matter during the polycondensation reaction stage.
A known polymerization catalyst can be used for the catalyst used in the polycondensation reaction of the polyester film of the present invention. Examples include compounds such as antimony, titanium, aluminum, tin and germanium. Antimony compounds include antimony oxides, antimony carboxylates, antimony alkoxides, and the like. Titanium compounds include titanium chelate complexes, titanium alkoxides, and titanium oxides obtained by hydrolysis of titanium alkoxides. Aluminum compounds include aluminum carboxylates, aluminum alkoxides, aluminum chelate compounds, basic aluminum compounds, and the like. Examples of tin compounds include tin compounds having an alkyl group and tin compounds having a hydroxyl group. Germanium compounds include germanium oxides and germanium alkoxides. Also, these metal compounds may be hydrates. From the viewpoint of polymerization time and economy, it is preferable to use an antimony compound as a polymerization catalyst. The polymerization catalyst may be added in any form of powder, slurry, or solution, and is preferably added as a solution from the viewpoint of dispersibility. The solvent at this time is preferably the same as the diol component of the polyester composition.
The obtained polyester film is preferably pre-crystallized before the drying step. For pre-crystallization, a method of subjecting the polyester film to shearing treatment by giving mechanical impact, a method of subjecting the polyester film to heat treatment in a stream of hot air, or the like can be employed.

The polyester composition of the present invention may be subjected to solid state polymerization in order to obtain a high molecular weight polyester film.

When processing the polyester film of the present invention into a film, one or more additives such as various additives such as colorants including pigments and dyes, lubricants, antistatic agents, flame retardants, ultraviolet absorbers, antibacterial agents, nucleating agents, plasticizers, and release agents can be added within a range that does not impair the effects of the present invention.
The lower limit of the intrinsic viscosity of the polyester is preferably 0.5 dl/g or more, and the upper limit is preferably 0.8 dl/g or less. More preferably, the lower limit is 0.55 dl/g and the upper limit is 0.70 dl/g.

The polyester film of the present invention may be an unstretched film obtained by melt extrusion, or a stretched film obtained by uniaxially or biaxially stretching. Sequential stretching and simultaneous stretching can be adopted for the stretching. For example, in the sequential biaxial stretching, the step of stretching in the longitudinal direction (longitudinal) and the width direction (horizontal) can be performed once in the vertical-horizontal direction, or twice in the vertical-horizontal-longitudinal-horizontal direction. When lubricant particles are added, biaxial stretching is particularly preferred because they can be uniformly dispersed on the film surface.

The polyester film of the present invention preferably has a total thickness of 10 μm or more and less than 50 μm. Particularly preferably, it is 12 μm or more and less than 40 μm. If the total thickness is less than 10 μm, it may be difficult to handle in the processing step due to insufficient strength.

In the polyester film of the present invention, it is preferable that the dimensional change rate is within the following range, since the occurrence of distortion and wrinkles due to heat shrinkage in the DFR process can be suppressed. The dimensional change rate can be achieved by appropriately adjusting conditions such as relaxation and heat treatment in film forming conditions by a known method. The dimensional change rate at 150° C. is preferably 3.0% or less in the longitudinal direction and 2.5% or less in the width direction, more preferably 0.5% or more and 2.0% or less in the width direction, and more preferably 1.0% or more and 2.0% or less in the width direction. Moreover, the dimensional change rate at 100° C. is preferably 1.0% or less in both the longitudinal direction and the width direction, and more preferably in the range of 0.2% or more and 0.8% or less. If the dimensional change rate is below the lower limit of the above range, poor planarity may occur due to slack when the resist layer is applied. In either case, unevenness may occur in the coating thickness of the resist layer.

Further, the strength when the film is stretched by 5% in the longitudinal direction (hereinafter referred to as F-5 value) is preferably 70 MPa or more and less than 150 MPa. If the F-5 value in the longitudinal direction is less than 70 MPa, the lack of strength may result in the occurrence of flaws and the like, resulting in poor workability. On the other hand, if the F-5 value in the longitudinal direction is 150 MPa or more, it may be difficult to achieve compatibility with the F-5 value in the width direction. The F-5 value in the longitudinal direction is preferably 80 MPa or more and less than 140 MPa, more preferably 90 MPa or more and less than 130 MPa.

Furthermore, the F-5 value in the width direction is preferably 80 MPa or more and less than 160 MPa. If the F-5 value in the width direction is less than 80 MPa, the workability may deteriorate due to the occurrence of scratches due to insufficient strength, and if it is 160 MPa or more, it may be difficult to achieve both the F-5 value in the longitudinal direction. It is preferably 90 MPa or more and less than 150 MPa, more preferably 100 MPa or more and less than 140 MPa.

The longitudinal breaking strength is preferably 200 MPa or more and less than 360 MPa, more preferably 220 MPa or more and less than 340 MPa. The breaking strength in the width direction is preferably 260 MPa or more and less than 420 MPa, particularly preferably 280 MPa or more and less than 400 MPa. The above F-5 value and breaking strength can be achieved by appropriately adjusting the stretching temperature and stretching ratio in the longitudinal and transverse directions.

Furthermore, the polyester film of the present invention preferably has a film haze of less than 1.0%. If the film haze is 1.0% or more, the polyester film, which is the support for the resist layer, will scatter more ultraviolet rays when the resist layer is laminated on the polyester film and then irradiated with ultraviolet rays for exposure.

The polyester film of the present invention has few foreign substances, good color tone, excellent transparency (haze), heat resistance, and good electrostatic application properties, so it can be suitably used for high-quality films such as dry resist films.

The polyester film of the present invention may contain particles. As the particles, organic and inorganic particles can be used. Examples of organic particles include polyimide resins, olefin or modified olefin resins, crosslinked polystyrene resins, and silicone resins. Examples of inorganic particles include spherical silica, silicon oxide, calcium carbonate, aggregated alumina, aluminum silicate, mica, clay, talc, and barium sulfate. In adopting these particles, in order to suppress increases in light transmittance and haze value, a method of surface-modifying the particle surface with a surfactant or the like to improve affinity with polyester can be preferably employed from the viewpoint of suppressing the generation of voids around the added particles. In addition, when the particle shape is close to spherical and the difference in refractive index from polyester is small, scattered light can be suppressed when ultraviolet rays pass through the film layer. In particular, colloidal silica and organic particles are preferred, and silicone particles and crosslinked polystyrene particles are preferred. Among them, crosslinked polystyrene particles made of a styrene-divinylbenzene copolymer prepared by emulsion polymerization are preferable because they have a particle shape close to a true sphere and a uniform particle size distribution, so that uniform protrusions can be formed. Crosslinked polystyrene particles made of colloidal silica or styrene-divinylbenzene copolymer are preferably contained in the polyester resin composition constituting the surface layer (A layer, B layer), and the content thereof is preferably 0.01% by weight or more and less than 0.1% by weight with respect to the entire polyester resin composition constituting the surface layer (A layer, B layer). If the content is less than 0.01% by weight, the handling property may deteriorate in the resist coating process, the coating may become unstable, and coating spots may occur. If the content is 0.1% by weight or more, the crosslinked polystyrene particles tend to agglomerate with each other, and the effect of reflection and scattering of light due to non-uniform incident angles of light in the exposure process may cause the resist pattern to come off, which is not preferable.

It is also one of desirable forms to use agglomerated alumina together with the above-described particles for both the A layer and the B layer. Here, aggregated alumina refers to aggregated particles having an average primary particle size of 5 nm or more and less than 30 nm, from several to several hundreds. More preferably, the average primary particle size of the aggregated alumina is 8 nm or more and less than 15 nm. The agglomerated alumina can be produced by flame hydrolysis using anhydrous aluminum chloride as a raw material, or hydrolysis of alkoxide alumina. Agglomerated alumina is known as a crystal type such as δ-type, θ-type, and γ-type, and δ-type alumina is particularly suitable for use. These aggregated aluminas can be used by being added during polyester polymerization, but for example, as a slurry of ethylene glycol, which is a part of the raw material during polyester polymerization, pulverization and dispersion are performed using a sand grinder or the like, and precision filtration is performed. Thus, aggregated alumina having an average secondary particle size of 10 nm or more and less than 200 nm can be obtained. When the agglomerated alumina obtained in this way is added to a film, since it is arranged in the plane direction by biaxial stretching, it does not substantially form protrusions, has little effect on surface roughness, and has good transparency, so deterioration of light transmittance and haze value can be suppressed. By containing agglomerated alumina, the effect of reinforcing the surface texture of the film is greatly obtained, the abrasion resistance is improved, and the effect of suppressing the dent defect that occurs when the film comes into contact with rolls during stretching is obtained. Agglomerated alumina is preferably contained in the polyester resin composition forming the surface layers (layers A and B), and the content thereof is preferably 0.1% by weight or more and less than 5.0% by weight with respect to the entire polyester resin composition. If the content is less than 0.1% by weight, the handling property in the resist coating process will be deteriorated, the coating will be unstable, and coating spots will occur. If the content is 5.0% by weight or more, the aggregated alumina tends to aggregate more easily, and the resist pattern may come off due to the influence of light reflection and scattering due to the uneven incidence angle of light in the exposure process, which is not preferable.

As a method for incorporating inert particles into polyester in melt film formation by coextrusion, for example, the inert particles are dispersed in ethylene glycol, which is a diol component, in the form of a slurry at a predetermined ratio. For example, after performing high-precision filtration capable of collecting 95% or more of coarse particles of 2 μm or more or 5 μm or more, this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. Here, when adding the particles, for example, it is preferable to add the water sol or alcohol sol obtained during the synthesis of the particles without drying them once, because the dispersibility of the particles is good and the occurrence of coarse protrusions can be suppressed. A method in which an aqueous slurry of particles is directly mixed with predetermined polyester pellets, supplied to a vent-type twin-screw kneading extruder, and kneaded into polyester is also effective for the effects of the present invention. As a method for adjusting the particle content, it is effective to prepare a master pellet of particles with a high concentration by the above method, and to adjust the particle content by diluting it with PET that does not substantially contain particles at the time of film formation. At this time, the density of the particle-containing voids can be controlled by adjusting the intrinsic viscosity of the particle-free PET to be higher than that of the particle-containing pellets. In addition, when the intrinsic viscosity of the particle-containing pellet is higher than or equal to the intrinsic viscosity of the PET containing no particles, the dispersibility of the particles decreases and the distance between the particles decreases, resulting in a tendency for the density of the particle-containing voids to increase.

In this way, the particle-containing master pellets prepared for each layer and the pellets substantially free of particles and the like are mixed in a predetermined ratio, dried, and then supplied to a known melt lamination extruder under a nitrogen stream or under reduced pressure so as not to lower the intrinsic viscosity. A single-screw or twin-screw extruder can be used as the extruder for producing the biaxially oriented polyester film of the present invention. In order to omit the pellet drying process, a vent type extruder provided with a vacuum drawing line can also be used. In addition, when an intermediate layer is provided, the extrusion rate is the largest, so a so-called tandem extruder that shares the function of melting the pellets and the function of keeping the melted pellets at a constant temperature in each extruder can be used. It is preferable to use a twin-screw vent type extruder for extruding the layer that constitutes the surface of the polyester film of the present invention, since it is possible to maintain good particle dispersibility and suppress particle agglomeration.

The polymer melted and extruded by the extruder is filtered through a filter. If even a very small foreign matter enters the film, it becomes a coarse protrusion defect. Therefore, it is effective to use a high-precision filter that can collect 95% or more of foreign matter having a size of 2 μm or more or 5 μm or more. Subsequently, it is extruded into a sheet through a slit-shaped slit die and cooled and solidified on a casting roll to form an unstretched film. That is, the sheets are laminated using a plurality of extruders, a multi-layered manifold or a confluence block (eg, a confluence block having a rectangular confluence), the sheet is extruded through a spinneret, and cooled on a casting roll to form an unstretched film. In this case, it is effective to install a static mixer or a gear pump in the polymer flow path from the viewpoint of stabilizing the back pressure and suppressing the thickness variation.

The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. In the case of sequential stretching, the stretching temperature in the longitudinal direction is preferably 90°C or higher and lower than 130°C, more preferably 110°C or higher and lower than 120°C. When the stretching temperature is less than 90°C, the film tends to break, and when the stretching temperature is 130°C or higher, the film surface tends to be thermally damaged, which is not preferable. In addition, from the viewpoint of preventing stretching unevenness and scratches, it is effective to provide a preheating zone before stretching and heat in stages, and the preheating temperature in the longitudinal direction is preferably 65 ° C. to 135 ° C., more preferably 70 ° C. to 130 ° C.. The draw ratio in the longitudinal direction is preferably 3 times or more and less than 4.5 times, more preferably 3.5 times or more and less than 4.3 times.

The obtained uniaxially stretched film is Once cooled. The cooling temperature is preferably 18°C or higher and 40°C or lower, more preferably 21°C or higher and 35°C or lower. By cooling, the width dimension stability is stabilized, and even if the film surface of the present invention is smooth, it is possible to prevent scratches and suppress wrinkles on film transport rolls.

Subsequently, the film is stretched in the width direction by a known stenter oven to form a biaxially stretched film. The film is held by clips running on rails in the stenter oven, heated again to a temperature above the glass transition temperature of the resin in the oven, and stretched in the width direction as the rails on which the clips run expand. At this time, the draw ratio in the width direction is preferably 3.2 times or more and less than 5 times, more preferably 4.0 times or more and less than 4.6 times.

Here, it is important to heat the film step by step in order to control the surface roughness and protrusion distribution of the film. By heating the uniaxially stretched film at 90 ° C. or higher and 110 ° C. or lower before stretching in the width direction, and stretching the film sufficiently heated to the glass transition temperature or higher at 110 ° C. or higher and 120 ° C. or lower in the width direction, the film can be easily stretched, and slight stretching unevenness due to particles forming the film surface can be suppressed.

Heat treatment of the resulting biaxially stretched film can then be carried out. The heat treatment may be performed in the same stenter oven following the stretching in the width direction, or may be performed in an oven separate from the stenter oven in which the stretching in the width direction was performed. The heat treatment temperature is preferably 170° C. or higher and 250° C. or lower. Heat treatment is preferable because it improves the dimensional stability when exposed to high temperatures in subsequent processing steps or when used as a final product. It is also preferable to relax the film in the width direction under conditions of more than 0% and 8% or less during the heat treatment to further improve the dimensional stability.

The biaxially stretched film is preferably cooled as it exits the oven. The cooling temperature is preferably 100°C or higher and 130°C or lower, more preferably 110°C or higher and 125°C or lower. By cooling, the width dimension is stabilized, and even if the film surface of the present invention is smooth, it is possible to prevent scratches and wrinkles on film transport rolls.

The intermediate product is then obtained after cutting the edges and winding. In this conveying process, the thickness of the film is measured, and the data is fed back and used to adjust the film thickness by adjusting the die thickness and the like, and foreign matter is detected by the defect detector.

The biaxially oriented polyester film of the present invention thus obtained has good permeability and slipperiness, and therefore can be suitably used as a dry film resist support.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention should not be construed as being limited thereto. The physical properties were measured and the effects were evaluated by the following methods.

(1) Element (atom) content in polyester film (unit: weight ppm)
The content of elemental phosphorus (atoms), elemental magnesium (atoms), and elemental calcium (atoms) was calculated from a calibration curve prepared in advance by molding a polyester film into a cylindrical shape with a melt press, and using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Denki Co., Ltd. to determine the fluorescent X-ray intensity.

Regarding the content of elemental sulfur (atoms), the polyester film was burned using an automatic sample combustion device (model number: AQF-2100) manufactured by Mitsubishi Chemical Analytic Tech, and after absorbing the generated gas into the solution, a part of the absorption liquid was analyzed by ion chromatography (model number: ICS1600) manufactured by DIONEX. Samples were weighed and measured at n=2, and the average value of the measured values was taken as the elemental sulfur content.

(2) Number of Coarse Foreign Matters A biaxially oriented polyester film was cut into a size of 5 cm×5 cm, and an image of 1 mm 2 was taken with a laser microscope (VK-X250 manufactured by Keyence) using a 50× objective lens. The captured image was binarized, and a particle analysis module (VKH1XG manufactured by Keyence Corporation) was used to count the number of large particles with a major diameter of 1.0 μm or more present within a certain depth range from the film surface. In the present invention, the major diameter of the coarse foreign matter refers to the longest measured length of the foreign matter detected by the laser microscope.

(3) Film formability of polyester film When biaxially stretched films were formed in Examples and Comparative Examples, the film formability was judged according to the following criteria.
⊚: A film could be produced without any problem.
◯: A decrease in adhesion to the cast drum was observed, but there was no problem in film production.
x: Adhesion to the cast drum was poor, making film production difficult.

(4) Evaluation of Resist Defects A method for evaluating resist defects in the polyester film of the present invention was performed according to the following procedures.
(i) A 6-inch Si wafer mirror-polished on one side was coated with a negative resist "PMER N-HC600" manufactured by Tokyo Ohka Co., Ltd., and spun with a large spinner to form a resist layer with a thickness of 7 μm. Then, preheat treatment was performed for about 20 minutes at a temperature of 70° C. using a ventilated oven with nitrogen circulation.
(ii) The A-layer side surface of the polyester film was placed in contact with the resist layer, and the polyester film was laminated on the resist layer using a rubber roller. L/S (μm) (Line and Space) was set to 5/5.
(iii) After peeling off the polyester film from the resist layer, the resist layer was placed in a container containing developer N-A5 and developed for about 1 minute. After that, it was taken out from the developing solution and washed with water for about 1 minute.
(iv) The state of the resist pattern formed after development was observed using a scanning electron microscope SEM at 1000 magnifications for 50 fields of view. Evaluation of resist defects was based on the following criteria. In addition, the evaluation of △ or more is a practical level.
A: No distortion or holes were observed in the resist pattern.
◯: Distortion of less than 1 μm was observed in the resist pattern, but it was practically possible.
Δ: Distortion and holes of 1 μm or more were observed in the resist pattern, which was inferior to the above but practically acceptable.
x: A large number of holes of 1 µm or more and distortion were observed in the resist pattern, and it was impractical.
(5) Handleability of resist film (slipperiness evaluation)
Using the biaxially oriented polyester film of the present invention as a support, a resist layer made of a negative photosensitive resin was formed on the layer A side by coating to prepare a resist film. Evaluation of slipperiness as handleability at the time of resist film production was performed according to the following criteria. In addition, the evaluation of △ or more is a practical level.
◯: Appropriate slidability and good handleability.
Δ: Poor slidability and poor handleability.
×: Difficult to handle due to lack of proper slipperiness (not applicable to production)
(material)
(Preparation of Polyester A)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.0175 parts by weight of tetrabutylphosphonium p-toluenesulfonate and 0.0084 parts by weight of antimony trioxide were added as an ethylene glycol solution, followed by heating to 279° C. under vacuum to carry out a polycondensation reaction to obtain polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester A).

(Creation of polyester B)
In producing polyester in the same manner as described above, after the esterification reaction was completed, instead of adding tetrabutylphosphonium p-toluenesulfonate, tetrabutylphosphonium 3,5-dicarboxybenzenesulfonate, which is a copolymer component, was added to obtain polyester pellets. (Polyester B).

(Preparation of Polyester C)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.02 parts by weight of trimethyl phosphate, 0.06 parts by weight of magnesium acetate, 0.01 parts by weight of lithium acetate, and 0.0085 parts by weight of antimony trioxide were added, followed by heating to 290° C. under vacuum to carry out polycondensation reaction to obtain polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester C).

(Preparation of polyesters D and E)
The water slurry of the average particle diameter of 0.15 μm, a volume -shaped coefficient F = 0.51, which is obtained by the method of adsorbing a monomer is contained in a homopoliester pellet that does not contain particles, using a vent type two -axis mixture using a vent -type two -axis mixture. The average volume particle diameter of 0.3 μm, 0.45 μm of dibinylbenzene / styrene co -polymerized bridge particles, each with a master pellet containing 0.2 % or 1 % percent of polyester (polyester D, E).

(Creation of polyester F)
Further, a 10% ethylene glycol slurry of delta-alumina was used as agglomerated alumina, pulverized and dispersed using a sand grinder, and filtered using a 3 μm filter with a collection efficiency of 95%. 1.9 mol of ethylene glycol and 0.05% of magnesium acetate tetrahydrate and 0.015% of phosphoric acid were added to dimethyl terephthalate to perform heat transesterification, the slurry containing the aggregated alumina described above was added after transesterification, and then 0.025% of antimony trioxide was added, the temperature was raised, and a polycondensation reaction was performed under vacuum to obtain master pellets containing 1.5% by weight of aggregated alumina and having an intrinsic viscosity of 0.62 dl / g (Polyester F).

(Preparation of Polyester G)
In producing polyester in the same manner as described above, after transesterification, spherical silica having a volume average particle diameter of 0.2 μm, a volume shape factor f = 0.51, and a Mohs hardness of 7 was added, and a polycondensation reaction was performed to obtain silica-containing master pellets containing 2% by weight of particles relative to the polyester (polyester C). The spherical silica to be used was prepared by adding a mixed solution of ethanol, pure water, and ammonia water as a basic catalyst to the mixed solution of ethanol and ethyl silicate while the mixed solution was being stirred, and the obtained reaction solution was stirred to carry out the hydrolysis reaction of ethyl silicate and the polycondensation reaction of the hydrolysis product, followed by stirring after the reaction to obtain monodisperse silica particles.

(Preparation of polyester H)
In producing a polyester in the same manner as polyester C, after the esterification reaction was completed, 0.02 parts by weight of trimethyl phosphate, 0.06 parts by weight of magnesium acetate, 0.01 parts by weight of lithium acetate, 0.0079 parts by weight of sodium p-toluenesulfonate, and 0.0085 parts by weight of antimony trioxide were added, followed by heating to 290° C. under vacuum to conduct a polycondensation reaction, thereby obtaining polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester H).

(Preparation of polyester I)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.0175 parts by weight of tetrabutylphosphonium p-toluenesulfonate, 0.0079 parts by weight of sodium p-toluenesulfonate, and 0.0084 parts by weight of antimony trioxide were added as an ethylene glycol solution, followed by heating to 279° C. under vacuum for polycondensation reaction to obtain polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester I).

(Preparation of Polyester J)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.06 parts by weight of magnesium acetate, 0.01 parts by weight of lithium acetate, and 0.0085 parts by weight of antimony trioxide were added, followed by heating to 290° C. under vacuum to conduct a polycondensation reaction to obtain polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester J).

(Preparation of polyester K)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.02 parts by weight of trimethyl phosphate, 0.01 parts by weight of lithium acetate, and 0.0085 parts by weight of antimony trioxide were added, followed by heating to 290° C. under vacuum to conduct a polycondensation reaction to obtain polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester K).

(Creation of polyester L)
86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol are subjected to an esterification reaction at 255° C. while distilling off water. After completion of the esterification reaction, 0.01 parts by weight of lithium acetate and 0.0085 parts by weight of antimony trioxide were added, followed by heating to 290° C. under vacuum to carry out polycondensation reaction, thereby obtaining polyester pellets having an intrinsic viscosity of 0.63 dl/g. (Polyester L)
(Example 1)
After stirring a mixture of raw materials prepared according to the formulation shown in Table 1 for each layer in a blender, the raw materials for the A layer and B layer are the raw materials after stirring, and the vented twin screw extruder for the A layer and the B layer. Subsequently, it was melt extruded at 275 ° C., filtered with a high-precision filter that collects 95% or more of foreign substances of 2 μm or more in both layers A and B, and then merged and laminated with a rectangular three-layer confluence block to form a three-layer laminate consisting of A layer, B layer, and C layer. After that, the film was wound on a casting drum having a surface temperature of 23° C. using an electrostatic casting method on a chill roll through a slit die kept at 285° C., and solidified by cooling to obtain an unstretched laminated film. Winding speed is 60m/min. was carried out.

After preheating this unstretched film with a heating roll at 70 to 130° C., it was stretched 4 times in the longitudinal direction at 110 to 120° C. using a stretching roll having a surface roughness Ra of 0.2 μm, and then the stretching temperature was lowered by 80 to 100° C. to cool the film after uniaxial stretching. Further, the film was subsequently stretched 4.5 times in the width direction under hot air of 110 to 115°C with a stenter, heat treated at 220°C for 4 seconds under constant tension, and then subjected to relaxation treatment of 0.1% in the longitudinal direction and 3.2% in the width direction to obtain an intermediate product of a biaxially oriented polyester film having a thickness of 16 µm. The thickness of the A layer and the B layer was 0.6 μm, and the thickness of the C layer was 14.8 μm. This intermediate product was slit by a slitter to obtain a roll of biaxially oriented polyester film having a thickness of 16 μm. Table 2 shows the evaluation results of the obtained film. As described above, the polyester film of the present invention was excellent in the number of coarse foreign matter, film formability, and resist defects.

(Examples 2-9)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the compositions of the layers A, B and C were changed as shown in Table 1. Table 2 shows the evaluation results of the obtained film. As described above, the biaxially oriented polyester film of the present invention was excellent in the number of coarse foreign matters and in film formability, as in Example 1.

(Comparative Examples 1 to 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the compositions of the A layer, B layer, and C layer were changed as shown in Table 1. Table 2 shows the evaluation results of the obtained film.

Since the polyester film of the present invention has a good number of coarse foreign matter, good film formability, and few resist defects, it can be suitably used as a dry film resist support.

Claims (2)

A polyester film for a dry film resist, which has a laminated structure of at least two layers, contains an organic salt having a sulfur element and an organic salt having a phosphorus element in at least one layer, has a sulfur element (atom) content of 2 to 20 ppm by weight relative to the weight of the polyester film, a phosphorus element (atom) content of 1 to 25 ppm by weight, and a total content of calcium element (atom) and magnesium element (atom) content of 20 ppm by weight or less. 2. The polyester film for dry film resist according to claim 1, wherein the number of coarse foreign matter having a major axis of 1.0 μm or more is 5 particles/mm ² or less.