JPH0463843A - Polyester film for wiring board - Google Patents

Abstract

PURPOSE:To obtain the title film improved in adhesion to ink, humidity-resistant adhesion, durability and blocking resistance by forming a surface modifying layer based on an aqueous self-emulsifiable heat-reactive urethane on a polyester film. CONSTITUTION:An unstretched sheet of a polyester (e.g. polyethylene terephthalate) of an intrinsic viscosity of 0.5 or above is stretched at 70-120 deg.C at a stretch ratio of 2.0-5.0 to obtain a film of a centerline average roughness of 0.02-0.5mum. A coating material based on an aqueous self-emulsifiable heat- reactive urethane of a degree of swelling by solvent of 50% or below and a degree of swelling by water of 80% or below is applied to at least either surface of this film in a thickness of 0.001-3.0mum and dried to form a surface-modifying layer thereon. This film is simultaneously or consecutively stretched at 70-150 deg.C at a stretch ratio in the machine direction of 2.0-5.0 and a stretch ratio in the transverse direction of 2.0-5.0. This stretched film is further heat-treated at 150-240 deg.C for 1-60sec while a relaxation of 0.10% is optionally given thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyester film for wiring boards. Specifically, the present invention relates to a polyester film for wiring boards that has excellent adhesion to conductive layers, resistor layers, insulating layers, and printing ink layers.

[Prior Art] Biaxially stretched polyester films have been used as flexible wiring boards and membrane switches because of their excellent mechanical properties, dimensional stability, heat resistance, electrical insulation properties, etc. Particularly in recent years, as a method for forming a conductive circuit on the polyester film base layer, in addition to the method of laminating and etching copper foil, conductive paste, conductive ink, resistor ink, insulator ink, and marking ink have been used. A method of printing etc. is used.

Furthermore, these inks are not only solvent-containing types, but also ultraviolet curing types and electron beam curing types have recently been used for the purpose of simplifying processes and reducing production costs. Along with this, polyester films have been subjected to various surface modifications to improve their ink receptivity.For example, polyester films coated with polyester copolymer resin have been used as polyester films for wiring boards that have excellent adhesion with various inks. film (for example, Japanese Patent Application Laid-Open No. 62162540)
JP-A-62-59636) or a polyester film coated with a urethane resin (for example, JP-A-62-59636).

[Problems to be Solved by the Invention] However, the above-mentioned conventional polyester films for wiring boards not only still have insufficient adhesion of the ink layer, but also have a marked decrease in adhesion, especially under high temperature and high humidity atmospheres. It lacked reliability as a wiring base.

An object of the present invention is to provide a polyester film for wiring boards that has excellent adhesion to inks and polymer pastes for conductors, resistors, and insulators, particularly moisture-resistant adhesion.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes the following configuration. That is, at least one side of a biaxially oriented polyester film having a center line average roughness of 0.02 to 0.5 μm is coated with an aqueous self-emulsifier having a solvent swelling rate of 50% or less and a water swelling rate of 80% or less. The gist of this invention is a polyester film for wiring boards, which is characterized by being coated with a surface-modified layer containing heat-reactive urethane as a main component.

In the present invention, polyester refers to well-known polyesters,
Specifically, for example, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, bis-α,β(2-chlorophenoxy)ethane-4,4′-dicarboxylic acid, adipic acid,
At least one difunctional carboxylic acid such as sebacic acid,
Examples include polyesters obtained by polycondensation with at least one glycol such as ethylene glycol, triethylene glycol, tetramethylene glycol, hexamethylene glycol, and decamethylene glycol. In addition, the polyester may be blended or copolymerized with other polymers within a range that does not impede the purpose of the present invention, and may contain antioxidants, heat stabilizers, lubricants, pigments, ultraviolet absorbers, etc. It may be The intrinsic viscosity of polyester (measured in orthochlorophenol at 25°C) is 0.4
to 2°0, preferably 0.5 to 1.0.

In the present invention, it is preferable to use polyethylene terephthalate or polyethylene-2,6-naphthalate as the polyester because particularly excellent effects can be obtained.

The surface-modified layer as used in the present invention is a layer made of a composition whose main component is a water-based self-emulsifying heat-reactive urethane (hereinafter simply referred to as reactive urethane). The main component refers to a component that accounts for 50% or more, preferably 65% or more in the modified layer, and may contain an appropriate amount of substance. The resin to be added is not particularly limited, but examples include various resins such as epoxy resins, polyolefin resins, polyamide resins, and fluorine group-containing resins. In the present invention, such a surface-modified layer is provided on at least one side of the polyester film, but if it is provided on both sides, the following description of the surface-modified layer applies to at least one side. be.

The reactive urethane referred to in the present invention refers to Japanese Patent Publication No. 52-439
No. 53, Special Publication No. 53-29198, Special Publication No. 53-34
No. 220, Special Publication No. 53-17642, Special Publication No. 53-2
No. 9175, Special Publication No. 559424, Special Publication No. 61514
This is publicly known in various publications such as No. 74. That is, a molecular weight of 200 to 20,000 having two or more active hydrogen atoms.
Specifically, one or more compounds containing two or more hydroxyl groups, carboxyl groups, amino groups, or mercapto groups at the terminal or in the molecular chain, and an excess amount of polyisocyanate are combined with a chain extender having an active hydrogen atom. make use of,
A urethane prepolymer containing free isocyanate groups is prepared and stabilized in an aqueous system by reacting the urethane prepolymer with bisulfites to block the active isocyanate groups. By applying the aqueous solution and subjecting it to an appropriate heat treatment, the blocking agent of the urethane prepolymer is dissociated, and high reactivity is obtained by regenerating the active isocyanate groups. Incidentally, compounds containing active hydrogen atoms, chain extenders containing active hydrogen, polyisocyanates, blocking agents, etc. constituting the reactive urethane are all disclosed in the above-mentioned publications.

In the present invention, the solvent swelling rate of reactive urethane, that is,
After forming a reactive urethane into a solution film and drying it at 50°C for 5 hours,
After heat-treating at 160°C for 10 minutes and forming into a film, the film was immersed in a mixed solvent of ethyl acetate/toluene (1/1) at 25°C for 24 hours, and the solvent swelling rate determined from the area change was 50. % or less, preferably 40% or less, more preferably 30% or less. If the solvent swelling rate exceeds 50%, when printing a conductive circuit using an ink containing an organic solvent on the surface modified layer, the solvent resistance may be insufficient, and depending on the solvent, the surface modified layer may swell or become partially damaged. It may cause dissolution and clouding of the film.

Furthermore, in the present invention, the water swelling rate of the reactive urethane, that is, the water swelling rate determined from the area change after immersing the film formed under the above-mentioned conditions in water at 25° C. for 24 hours, is preferably 80% or less. is 70% or less, more preferably 5
It needs to be 0% or less. If the water swelling rate exceeds 80%, the adhesion of printed circuits is significantly reduced in a high humidity environment, and various adverse effects associated with deterioration of moisture resistance due to surface modification are likely to increase. Therefore, the reactive urethane of the present invention is
As the compound having an active hydrogen atom that most dominates its properties, compounds containing hydroxyl groups are preferred, and polyesters and polyether esters having two or more hydroxyl groups are particularly preferred.

The polyester film constituting the film of the present invention is at least biaxially oriented by a conventional method, and the film thickness is not particularly limited, but is 5 to 600 μm.
m is preferable, and a range of 25 to 3.0 μm is more preferable, and is excellent in practical handling as a base material. The biaxially stretched polyester film of the present invention has a center line average roughness of 0.02 to 0.5 μm, preferably o, 05 to
0.15 μm1, more preferably 0.08-0. 13μ
It is necessary to be within the range of m. If it is smaller than the range of the present invention, it is not preferable because the films will easily stick to each other when the films are stacked and heat treated to impart dimensional stability to the substrate base. If it is larger than the range of the present invention, it is not preferable because the uniformity of coating various inks and polymer pastes is likely to deteriorate and electrical insulation properties are likely to be deteriorated.

The laminated thickness of the surface modified layer constituting the film of the present invention is not particularly limited, but is preferably 0.001 to 3.0 μm, and 0.01 to 1.0 μm. A thickness in the range of 0 μm is desirable in terms of uniform formation and adhesion of the surface-modified layer. In addition, the modified layer contains known crosslinking catalysts to improve the adhesion, water resistance, solvent resistance, and mechanical strength of reactive urethane, specifically salts, inorganic substances, organic substances, acid substances, and alkali substances. A reactive compound such as an epoxy compound, an aziridine compound, a blocked polyisocyanate, or a vinyl compound may be contained as a crosslinking agent or a known adhesion promoter.

Furthermore, if necessary, known additives such as antifoaming agents, coating properties improvers, thickeners, antistatic agents, dyes, pigments, lubricants, etc. may be included in amounts that do not impair the effects of the present invention. .

Next, a method for producing the film of the present invention will be explained. First, polyester pellets polymerized by a conventional method are thoroughly dried, and then a known extruder is used, preferably at a compression ratio of 3.
The pellets are fed into a melt extruder of 8 or more, and melt-extruded into a sheet through a slit-shaped die at a temperature above the melting temperature of the pellets and below the temperature at which the polymer decomposes, and then cooled and solidified to produce an unstretched sheet. At this time, the intrinsic viscosity of the unstretched sheet is 0. It is desirable that it is 5 or more.

Next, the unstretched sheet or the unstretched sheet is heated to 70 to 12
2.0 to 5 at 0°C. When using an unstretched film, apply a coating material prepared by adjusting the above composition to a predetermined amount onto a 0 times stretched film, dry the coating film to form a predetermined coating layer, and then heat at 70 to 150°C. , vertical direction D2. 0-5. 0
2.0 to 5.0 times circumferential stretching or sequential stretching in the transverse direction, or 2.0 times when using an axially stretched film. 0-5.
Stretch horizontally by 0 times.

Furthermore, the biaxially oriented film may be heated at 150°C to 24°C if necessary.
Heat treatment is performed at 0° C. for 1 to 60 seconds while giving 0 to 10% relaxation.

The method of applying the surface modification layer is not particularly limited, and an extrusion lamination method or a melt coating method may be used. It is preferable to apply a known method such as a gravure coating method, a reverse coating method, a kitsu coating method, a die coating method, or a metal ring bar code method. At this time, if necessary, the film may be subjected to a known surface treatment such as corona discharge treatment in the air or in various other atmospheres before coating, which not only improves the coating properties but also improves the surface. A stronger layer can be formed on the film surface. Although the coating agent concentration and coating drying conditions are not particularly limited, it is desirable that the coating film drying conditions be within a range that does not adversely affect the properties of the polyester film.

This method of stretching the surface-modified layer in at least one direction is particularly effective because it allows the surface-modified layer to be formed uniformly and uniformly, and the thermal reaction of the reactive urethane can proceed quickly. preferable.

[Evaluation method code] The characteristic values of the present invention are based on the following measurement method and evaluation criteria.

(1) Blocking resistance (adhesiveness) Thickness of 100 μm with specified surface modification layers on both sides of the film
50 sheets of A4 size film were stacked and left at an ambient temperature of 170° C. for 60 minutes. Next, the samples are slowly cooled at room temperature and then peeled off one by one. At that time, those that can be peeled off in the same way as before the heat treatment without adhesion to each other are judged as "○", and the others are judged as "x".

(2) 1 biaxially stretched polyester film provided with a surface modified layer using room temperature adhesion method
After heat treatment at 40°C for 4 hours, an ultraviolet curable ink Electrodag450ss/ML2 was applied on the surface modified layer.
5089 (50150) (manufactured by Acheson Japan) 22
Print with a 5Mδ screen, and cure by irradiating with an ultraviolet lamp with an output of 80 W/cm at a speed of 4 m/min (distance: 140 mm).

Next, a cellophane tape (CT-24 manufactured by Chiban ■) was applied on the ink layer and adhered using a hand roller, and then cut to a width of 5M, and the 180° peeling force between the ink layer and the base material was measured using a Schopper type. The ink adhesion was determined using a tensile tester.

(3) Moisture resistant adhesion The ink printed product of (2) above was printed at 60°C with 195% RI-(
After being left in the atmosphere for 600 hours, the adhesion was determined using the same method as in (2) above.

(4) Dielectric breakdown characteristics Electrodag 450SS from Acheson Japan was applied to a thickness of 25 μm, and an ultraviolet lamp of 120 W/cm x 2
After curing by irradiating with a lamp at 6 m/min (distance 150 mm), the dielectric breakdown voltage was 20 based on ASTM-D-149A.
00V-AC/port is measured with n50, and if the variation excluding the maximum and minimum exceeds 40% of the average breakdown voltage, "
×”, and if smaller than that, “○”.

(5) Center line average roughness In accordance with J I 5-B-, 0601, using a stylus type surface roughness meter 5D-3 manufactured by Kosaka Institute Co., Ltd., with a cutoff of 0.25 mm and a measurement length of 1 mm. Average roughness Ra (μm)
was measured.

[Effects of the Invention] In the present invention, a surface-modified layer containing a specific reactive urethane as a main component is formed on a biaxially stretched polyester film having a specific centerline average roughness. I was able to get the desired effect.

(1) Polyester films for wiring boards have excellent adhesion to various inks and polymer pastes.

(2) Polyester films for wiring boards have excellent moisture-resistant adhesion with various inks and polymer pastes, and therefore maintain sufficient durability even in high-humidity environments.

(3) Polyester films for wiring boards have excellent blocking resistance and are therefore easy to handle during processing.

[Examples] The present invention will be explained using the following Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1.2, Comparative Example 1.2 Polyethylene terephthalate (
Intrinsic viscosity: 0.62, melting point: 259°C) and average particle size of 0.
0.018% by weight of 15 μm silicon oxide (Example 1.
), 0.06% by weight (Example 2), 0.008% by weight (
Comparative Example 1), 0.14% by weight (Comparative Example 2) was added, and the resin was melt-extruded at 280°C and cooled and solidified on a cooling drum with a surface temperature of 20°C using an electrostatic application method to form an unstretched film. The obtained film was stretched 3.3 times in the longitudinal direction by roll stretching at 90°C, and the coated surface was subjected to corona discharge treatment, and then a reactive urethane with a solvent swelling rate of 30% and a water swelling rate of 45% was prepared. A water-based coating material containing 0.8 parts of silica sol with an average particle size of 1.5 μm per resin solid content added to “Elastron” E-37 (manufactured by Daiichi Kogyo Seiyaku ■) at a concentration of 3.0% by weight was applied to the above-mentioned -axially stretched film. After coating both sides of the metal ring using one method, the coated layer was dried and laterally heated at 100°C for 3 times.
Stretched 5 times and stretched at 220℃ for 20 minutes with 2% relaxation in the transverse direction.
A biaxially stretched film with a thickness of 100 μm on which a surface modified layer of 0.09 μm was laminated was obtained by heat treatment for seconds. The properties of the film thus obtained are shown in Table 1. As shown in the table, it can be seen that good characteristics can be obtained only when the base material is within the range of the present invention.

Example 3.4, Comparative Examples 3 to 5 Based on Example 1, reactive urethane (“Elastron” manufactured by Daiichi Kogyo Seiyaku ■) was prepared using raw materials to which 0.035% by weight of silicon oxide with an average particle size of 0.15 μm was added. Biaxially stretched polyester films provided with a surface-modified layer were obtained using the same method except that coating materials with various solvent swelling rates and water swelling rates were used. The characteristics for wiring boards are shown in Table 1.
Only when the reactive urethane was within the range of the present invention, excellent properties were exhibited, and when the reactive urethane was outside the range of the present invention, the properties were insufficient.

Claims (2)

[Claims] (1) At least one side of a biaxially oriented polyester film with a center line average roughness of 0.02 to 0.5 μm is coated with an aqueous polymer having a solvent swelling rate of 50% or less and a water swelling rate of 80% or less. A polyester film for wiring boards characterized by having a surface-modified layer coated with emulsified heat-reactive urethane as the main component. (2) The polyester film for a wiring board according to claim (1), wherein the surface modified layer is stretched in at least one direction.