JP2005154498A - Polyester film for masking tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a polyester film for a masking tape, which has excellent via-hole processability by an UV laser method, or the like, without incorporating a low-molecular ultraviolet light absorber into the film and coating a film surface with the ultraviolet light absorber. <P>SOLUTION: The polyester film for the masking tape is a substrate for a masking tape, which comprises a polyester composed of a naphthalenedicarboxylic acid as a carboxylic acid component and has preferably ≤30% light transmittance at 365 nm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polyester film suitable as a masking tape for via hole processing by a UV (ultraviolet) laser method.

In recent years, with the miniaturization of semiconductors, printed wiring boards and packages on which semiconductors are mounted have been miniaturized, and via holes provided in substrates and packages have also been reduced in diameter. Conventionally, as a method for processing a via hole on a printed circuit board, a photo via method has been generally used. However, a via hole processing method using a CO ₂ laser or a UV laser has recently become common as the diameter of the via hole is reduced. After processing the via hole in the printed circuit board, the conductive paste is filled into the via hole to conduct interlayer conduction of the printed wiring board, the package, etc., but the conductive paste does not prevent adhesion when filling the conductive paste. A masking tape is generally used to mask and protect the parts that should not be covered. A polyester film is suitable as the base material layer of the masking tape because the strength of the film is strong and the dimensional stability at the time of adhesive processing is excellent.

  The masking tape has a structure in which an adhesive is provided on the base material layer, and the via hole processing is performed in a state where the masking tape is attached to the covering portion with the adhesive layer, so that the masking tape itself has an optimum hole when processing the via hole. It must be empty. In the case of a method using a UV laser, since a normal base material layer transmits UV (ultraviolet light), there arises a problem that via hole processing to the masking tape itself is difficult. There have been proposed a method of blending a substrate with an ultraviolet absorber and a method of coating the substrate surface with an ultraviolet absorber (Patent Document 1). However, with this method, there is a risk of contamination of the system with the UV absorber during base material production or masking tape processing, and contamination of the substrate due to the UV absorber during via hole processing. It has been.

JP 2002-322438 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that, without blending a low molecular weight UV absorber into the film or applying a coating treatment to the film surface, the UV laser method, etc. An object of the present invention is to provide a polyester film for a masking tape which is excellent in suitability for via hole processing.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention resides in a masking tape substrate comprising a polyester film containing a polyester having naphthalenedicarboxylic acid as a carboxylic acid component.

Hereinafter, the present invention will be described in detail.
In the present invention, the polyester having naphthalenedicarboxylic acid as a carboxylic acid component is selected from 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 1,4-naphthalenedicarboxylic acid. It is a polyester having at least one naphthalenedicarboxylic acid as an acid component. As an acid component of this polyester, in addition to naphthalenedicarboxylic acid, 1 of dicarboxylic acid such as terephthalic acid, isophthalic acid, adipic acid, sebacic acid, 4,4′-diphenyldicarboxylic acid, 1,4-cyclohexyldicarboxylic acid It does not matter if it contains more than seeds.

  In the present invention, examples of the glycol used for the polyester include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like.

  Polyesters composed of these acid components and glycol components can be produced by arbitrarily using a commonly used method. For example, a transesterification reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or a direct esterification of an aromatic dicarboxylic acid and a glycol, to form a substantially bisglycol of an aromatic dicarboxylic acid A method is employed in which an ester or a low polymer thereof is formed and then polycondensed by heating under reduced pressure. Depending on the purpose, an aliphatic carboxylic acid may be copolymerized.

  In the present invention, a polyester containing naphthalenedicarboxylic acid as a carboxylic acid component may be used alone to form a film, or may be blended with other polyesters to form a film. Other polyesters can be obtained by the same method as described above.

  Examples of the polyester using the naphthalenedicarboxylic acid of the present invention as a carboxylic acid component include polyethylene-2,6-naphthalate. Examples of the polyester film of the present invention include a film of polyethylene-2,6-naphthalate itself, a film in which polyethylene-2,6-naphthalate and polyethylene terephthalate are mixed, polyethylene-2,6-naphthalate and polyethylene terephthalate. Can be mentioned. In addition, the polyester which copolymerized said acid component and glycol component may be sufficient, and the polyethylene terephthalate film containing the polyester compound which uses naphthalene dicarboxylic acid as a component may be sufficient. You may contain the other component and additive as needed.

  These polyesters include inorganic particles such as calcium carbonate, kaolin, silica, aluminum oxide, titanium oxide, alumina, and barium sulfate, organic particles such as acrylic resin and guanamine resin, and catalysts for the purpose of improving film runnability. Precipitated particles obtained by granulating the residual can be contained. Moreover, you may color with carbon black, a pigment, and dye. In order to erase the gloss of the surface, a large amount of particles may be blended, and the particle size and amount of these particles can be appropriately determined according to the purpose. In addition, various stabilizers, lubricants, antistatic agents and the like can be added as appropriate.

  The film of the present invention usually has a pressure-sensitive adhesive layer on one side and is bonded to a substrate or a package. For the purpose of improving adhesiveness, the film of the present invention is subjected to corona treatment or primer treatment. You may give it. Further, an antistatic coating layer may be provided on the surface opposite to the adhesive layer.

  The via hole processing suitability of the polyester film depends on the UV laser intensity, the film thickness, and the light transmittance of the masking tape with the adhesive, but the 365 nm light transmittance of the above polyester film is designed to be 30% or less. It is preferable to keep it.

  The method for forming the polyester film of the present invention is not particularly limited and may be a generally known method. For example, first, it is stretched 2 to 6 times at 60 to 150 ° C. by a roll stretching method to obtain a uniaxially stretched polyester film, and then at 80 to 150 ° C. in the direction perpendicular to the previous stretching direction in the tenter. A film forming method may be used in which the film is stretched by 6 times and further subjected to heat treatment at 150 to 250 ° C. for 1 to 600 seconds.

  As a method for providing the primer coat layer and the antistatic layer, the biaxially stretched film may be coated by a conventional technique, or may be coated by a conventional technique in the process of producing a polyester film. For example, in the sequential biaxial stretching method, there are a method of coating a film after longitudinal uniaxial stretching and then stretching laterally, or a method of coating and drying after a biaxially stretched film. Although the method is not limited, the method of coating a uniaxially stretched film, then laterally stretching, and heat-treating is preferable because it has a feature that the coat layer can be uniformly thinned.

  As a method for coating the polyester film, for example, a coating technique as shown in “Coating system” published by Yuji Harasaki, Tsuji Shoten, published in 1979 can be used. Specifically, air doctor coater, blade coater, rod coater, knife coater, squeeze coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, kiss roll coater, cast coater, spray coater, curtain coater, calendar coater And techniques such as an extrusion coater and a bar coater.

  The polyester film of the present invention preferably has a thickness of 6 to 50 μm. If the film is thin, the workability tends to deteriorate, and if it is thick, the via hole processing suitability by the UV laser method tends to deteriorate.

  Since the polyester film of the present invention itself is excellent in via hole processing suitability by the UV laser method, by using this film as a base material, a masking tape having good via hole suitability can be produced. Is expensive.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In addition, the evaluation method and the processing method of a sample in an Example and a comparative example are as follows. Further, “parts” in Examples and Comparative Examples represents “parts by weight”.

(1) Method for Measuring Intrinsic Viscosity [η] (dl / g) of Polymer 1 g of polymer is dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and 30 ° C. using an Ubbelohde viscometer. Measured with

(2) Measuring method of 365 nm light transmittance Using a spectrophotometer UV3100 manufactured by Shimadzu Corporation, the light transmittance is measured continuously at a scanning speed of 2 nm, a sampling pitch of 2 nm, and a wavelength range of 300 to 700 nm. The light transmittance of was detected.

(3) Method for measuring the thickness of the laminated polyester layer The film piece was fixed with an epoxy resin and then cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed in parallel with the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the laminated thickness.

(4) Evaluation method of via hole processing suitability (4.1) Preparation of masking tape A curing agent for 100 parts by weight of acrylic resin adhesive (trade name “BPS5125”, manufactured by Toyo Ink Co., Ltd.) on one side of a polyester film. (Product name “BXX5134”, manufactured by Toyo Ink Manufacturing Co., Ltd.) A coating liquid containing 0.2 part by weight was applied and dried at 120 ° C. for 3 minutes to obtain a masking tape having a pressure-sensitive adhesive layer thickness of 5 μm. This was stored at 23 ° C. for 1 week and then used for evaluation.
(4.2) Suitability of via hole processing by UV laser method A masking tape was attached to the glass epoxy plate side of the copper clad laminate, and via holes were processed by UV laser (wavelength 355 nm). The evaluation criteria for workability were as follows.
○: Via hole processing of masking tape is good ×: Via hole processing of masking tape is difficult

The polyester raw materials used in the following examples and comparative examples were produced by the following method.
<Manufacture of polyethylene naphthalate>
100 parts of dimethyl naphthalene-2,6-dicarboxylate, 60 parts of ethylene glycol and 0.1 part of magnesium acetate tetrahydrate are charged in a reactor, and the temperature is increased from 180 ° C. to 230 ° C. over 4 hours. The transesterification reaction was terminated. To this, 0.2 part of amorphous silica having an average particle diameter of 2.5 μm was added as a slurry of ethylene glycol, and then 0.04 part of phosphoric acid and 0.04 part of antimony trioxide were added. Then, a polycondensation reaction was performed by a conventional method. In this way, polyethylene naphthalate having an intrinsic viscosity of 0.58 was obtained. This was chipped and subjected to solid phase polymerization under reduced pressure at 235 ° C. to obtain polyethylene naphthalate having an intrinsic viscosity of 0.68.

<Manufacture of polyethylene terephthalate>
By the same melt polymerization method as described above, polyethylene terephthalate having a melt viscosity of 0.66 containing 0.2 part of amorphous silica having an average particle diameter of 2.5 μm was obtained.

  The polyethylene naphthalate raw material obtained above was dried, extruded into a sheet form from an extruder at 300 ° C., and rapidly cooled to obtain an amorphous sheet. This was stretched 3.0 times in the machine direction, then 3.5 times in the transverse direction, and heat-set at 240 ° C. to obtain a biaxially stretched polyethylene-2,6-naphthalate film having a thickness of 16 μm. . The 365 nm transmittance of this film was 0%. The evaluation result of via hole processing suitability was ○.

  15 parts of polyethylene naphthalate was blended with 85 parts of polyethylene terephthalate obtained above, extruded from a extruder at 295 ° C. into a sheet, and rapidly cooled to obtain an amorphous sheet. This was stretched 3.0 times in the longitudinal direction, then stretched 3.5 times in the transverse direction, and heat-set at 230 ° C. to obtain a biaxially stretched polyester film having a thickness of 16 μm. The transmittance at 365 nm was 18%, and the evaluation result of via hole processing suitability was ◯.

  Each of the polyethylene naphthalate and polyethylene terephthalate obtained above is dried and led to a multi-layer die from two different extruders to form three layers so that the core layer is polyethylene terephthalate and both surface layers are polyethylene naphthalate. Extruded and quenched to obtain an amorphous sheet. This was stretched 3.5 times in the longitudinal direction, then stretched 3.5 times in the transverse direction, and heat-set at 230 ° C. to obtain a biaxially stretched polyester film having a core layer of 12 μm and a total thickness of 16 μm. The 365 nm light transmittance of this film was 5%. The evaluation result of via hole processing suitability was ○.

(Comparative Example 1)
Using only the polyethylene terephthalate obtained above, the film was stretched 3.5 times in the longitudinal direction, then stretched 3.5 times in the transverse direction, and heat-set at 230 ° C. to obtain a biaxially stretched polyethylene terephthalate film having a thickness of 16 μm. Obtained. The 365 nm light transmittance of this film was 78%. The evaluation result of via hole processing suitability was x.

  The film of the present invention can be suitably used as a masking tape during via hole processing by a UV (ultraviolet) laser method.

Claims (1)

A masking tape substrate comprising a polyester film containing a polyester having naphthalenedicarboxylic acid as a carboxylic acid component.