JPH10158582A - Protection coating and application of the liquid for ink cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition for flexible printed circuit board, containing an epoxy group reacted with other polymer, etc., and capable of supplying a protecting coating in liquid state to a flexible printed circuit for transmitting control signals to an ink-jet printer head. SOLUTION: This liquid polymer coating composition for a flexible printed circuit is applicable in liquid state and contains an epoxy group reacted with other polymer or monomer in the presence of an initiator. The flexible circuit has a signal transmission channel for the pattern control of an ink-jet printing ink containing a solvent and a surfactant and is curable by the exposure to an energy source selected from heat and ultraviolet rays. The circuit is sealed with a protection layer to prevent the intrusion of ink-jet printing ink. The coating has a durable minimum radius of 0.5mm when subjected to the corrosion test and protects the substrate after immersing in a gold-plating solution at 60 deg.C for 24hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to liquid compositions useful for providing protective coatings in flexible circuits used to transmit control signals to ink jet printheads. In addition, the present invention addresses the signal-frequency requirements of modern inkjet printers operating at higher print speeds, which require high protection from insulating coatings.

[0002]

2. Description of the Related Art A thermal transfer ink jet printer is a quick and quiet apparatus for producing high-quality printed matter by ejecting ink onto paper, and a print head moves laterally on an ink recording medium such as paper. So the paper
It is not hit by elements other than ink.

[0003] A thermal transfer ink jet print cartridge is used for producing ink dots on a recording medium.
It operates by ejecting the evaporated ink through one or more orifices. The ink evaporates during ejection by rapidly heating a small amount of the ink. The orifices are aligned on the nozzle plate. As the printhead moves across the recording media,
A continuous jet of ink occurs at the desired image printing location.
Typically, after each pass of the printhead, the recording medium is moved to allow the next printhead pass to deposit ink in adjacent areas until all desired areas have been printed. I do.

A typical ink jet print cartridge includes a printhead, an ink reservoir containing liquid ink delivered to the printhead, and a flexible circuit for transmitting signals to the printhead. The printhead may be of various conventional constructions, including those with nickel nozzle plates and the like, or may be formed using Tape Automated Bonding (TAB).

[0005] Damage to the printhead cartridge can be
It can occur in several ways. A common problem is erosion by the inkjet ink composition on the surfaces of the inkjet printhead chambers and nozzles. Erosion on the surface due to erosion occurs before and during ink droplet ejection. Droplet ejection process is about 300 ° C
Occurs at temperatures of Such high temperatures can promote the wear that occurs in the printhead. Protective hard coatings can extend printhead life by reducing erosion rates.

[0006] The use of organic coatings to protect flexible circuits from environmental agents such as dust and humidity is well known. Useful coatings can typically be screen printed for ease of application and low cost,
Provides good or sufficient barrier properties. Organic polymer hard coatings are known, but they typically decompose at temperatures on the order of 300 ° C. Therefore, a solution to the problem of printhead chambers and nozzles must be found using organic mineral protective layers.

[0007] Although unsuitable for avoiding printhead erosion, organic polymers can be introduced into the interior of the printed circuit from environmental sources such as dust and humidity, especially from inkjet ink sprays, near the inkjet printhead. Useful for protecting structures like connections. The ink spray present during the operation of an ink jet printer can be deposited as ink droplets on copper interconnects (including conductive traces that carry electrical signals). The ink droplet contains an ionic compound. The gap between the independent circuit traces is such that ionic conductive ink droplets can span the gap between adjacent traces that cause an electrical short. In the presence of an electrical short, the inkjet printer may not work properly. Obviously, electrical shorts are well suited to deployment if the circuit traces are exposed without a protective electrical insulating coating. With such a protective coating, deposition of ink droplets in the conductive circuit trace area can eventually cause an electrical short between the traces. This is possible because inkjet inks contain solvents as well as ionic compounds. Solvents in the ink gradually dissolve some insulating coatings, exposing underlying circuit traces. Solvent erosion can be easily facilitated by surfactants also included in the inkjet ink. Information on the inkjet ink composition is described in, for example, Japanese Patent No. 309.
No. 7771, U.S. Pat.No. 4,853,037,
Nos. 4,791,165, 4,786,327, EP 259001, U.S. Pat.
No. 694,302, No. 5,286,286,
Nos. 5,169,438, 5,223,026, 5,429,860, and 5,439,5
No. 17, No. 5,421,871 and No. 5,3
Nos. 70,730, 5,165,968, 5,000,786, and 4,990,18.
It can be obtained by referring to Jpn.

[0008] Problems with the deterioration of the ink jet chamber and nozzles affect the useful supply life of the ink jet cartridge. The problem of electrical shorts between circuit traces of interconnecting flexible circuits has the more pronounced problem of premature failure of the printhead if the signal control circuit becomes dirty. It is the latter problem that provides the subject matter in the present invention.

The prior art includes the disclosure of protective coatings for flexible circuits used to transmit control signals to an ink jet printhead. These publications make no statement about environmental protection or protection from chemical erosion. Unfortunately, such statements fail to provide details of the limitations of protection.
This deficiency of the generic disclosure confounds the selection of a suitable electrically insulating protective coating to prevent premature inkjet printhead failure. The inventors of the above publication have found that a number of coatings claimed to provide protection from environmental and chemical erosion do not meet expectations. Even commercially available products that claim to be "protected" acknowledged that there were no apparent limitations in effective performance. Many of these have proven insufficient for current printer requirements. For example, advances in printer technology require higher printing speeds. This increases the likelihood of a lack of coating by increasing the control signal frequency and the associated ink drop deposition rate, if any, for the control circuit protection coating.

[0010] Accordingly, the present invention enhances the performance of modern high speed ink jet printers by focusing on the desirable properties of a coating for insulating gaps between conductive circuit traces. This includes a reference to the polymer species most suitable for producing a durable protective coating. The key to polymer type lies in the mere difference between thermoplastic and thermoset polymers. Such differences can also be said for uncrosslinked and crosslinked polymer layers.

US Pat. No. 5,380,806 (assigned to Chisso Corporation) discloses an uncured coating for flexible printed circuit substrates. Although mentioning high storage stability, printing performance, electrical properties, chemical resistance, flexibility and heat resistance, the above disclosure does not provide performance limitations. Such a lack of specificity offers good performance under selected conditions. Uncured coatings are typically more susceptible to solvent erosion than cured coatings,
There will be conditions under which the coating of US Pat. No. 5,380,806 is predisposed to premature failure. Similar discussions relate, for example, to Japanese Patent Nos. 5,256,631 and 5,815,070.

Another requirement for useful coatings is that
High flexibility. Conventional methods of increasing impermeability can reduce flexibility by increasing the crosslink density which increases diffusion time. However, typical flexible circuits used in ink jet print cartridges must withstand a bending radius of about 0.5 mm to wrap around the pen body.

US Pat. No. 5,442,386 discloses that
A tape for use in encapsulating a conductor on a flexible circuit is disclosed. The tape is composed of three layers [polyethylene terephthalate (PET) core coated on each side with an adhesive layer]. The coating is stamped into a shape adapted to the area of the tape to be coated and then laminated thereon. PET is taught to have two functions: to provide structural strength for punching operation and to ensure that the coating has no holes to allow ink to flow through the conductor. The three-layer construction is taught to provide the material with easier handling, adhesion to the desired substrate and ink sealability. The one-layer structure
It states that a single layer may be used if it can provide the desired structural properties.

US Pat. No. 5,144,742 discloses a liquid precursor for use as an essential protective layer on a subassembly of a rigid flexible printed circuit board. Useful precursors include UV curable acrylics, epoxies, and the like.

US Pat. No. 4,88,269 discloses an epoxy vinyl ester resin obtained by reacting a specific photopolymerizable polyfunctional vinyl monomer with a phenol novolak epoxy resin and / or a cresol novolak epoxy resin. Are disclosed.

US Pat. No. 5,032,467 discloses that
A method is disclosed for electroplating an electroactive polymer substrate at a potential sufficient to cause reduction of the substrate. It is useful to plate the polyimide substrate with gold.
Articles made using this method exhibit high polymer-metal adhesion at elevated temperatures.

[0017]

SUMMARY OF THE INVENTION The present inventors have discovered a protective insulating coating containing a liquid polymer, at least one epoxy compound and at least one other polymer. The coating can be deposited as a liquid, preferably in the form of an image, for example by screen printing, to provide the desired protection from environmental agents (eg, dust, etc.) and to prevent ink penetration and Protect conductors from attendant electrical shorts. In addition, the liquid protective coating also cures films that have good flexibility sufficient to have a minimum bend radius resistance of about 0.5 mm, preferably about 0.3 mm.

The coating of the present invention can be applied directly to copper traces and performs the function of a mask for gold plating without the need for expensive gold overcoating on all surfaces. According to this aspect of the invention, the chosen gold plating method is also suggested.

[0019]

SUMMARY OF THE INVENTION The present invention provides a liquid polymer composition useful as an insulating protective coating for copper flexible circuits used to transmit control signals to an ink jet cartridge. ,
The coating can be provided as a liquid and has excellent adhesion to copper. After application, the liquid can be cured to provide a crosslinked coating that provides a barrier to erosion by materials (eg, conductive contaminants) that can come into contact with the coating. The coating can be applied in whole or in an imagewise manner using suitable screening methods or photopolymer imaging techniques.

Further, the present invention includes a liquid polymer coating composition for a flexible printed circuit, the composition comprising at least one epoxy group reacted with at least one other polymer or monomer, said flexible circuit coating comprising: Has a signaling pathway useful for controlling the pattern of an ink-jet ink, wherein the coating composition is cured upon exposure to heat and / or ultraviolet light and comprises an ionic compound, a solvent and a surfactant. Providing a suitable protective layer on the track to seal the track from erosion by the ink, said layer comprising the components over a temperature range of about 20 to about 70 ° C.
Providing protection from solvents and surfactants, the coating, once cured, has a minimum radius of about 0.5 mm, preferably about 0.3 mm, and a coating thickness of about 20 mm.
It is flexible enough to withstand bending of about 75 μm.

Surprisingly, such a coating protects copper circuit traces from corrosion without the need for gold plating and does not need to be plated by withstanding the gold plating bath without leaching into it. A method is provided for selectively plating gold by masking regions.

In particular, the present invention provides a cured epoxy-containing protective coating for a tape comprising a flexible circuit on at least one surface, wherein the circuit includes a signaling pathway. The track is substantially encapsulated by a cured coating that can be applied in a liquid state prior to curing.

[0023] Preferably, the protective coating of the present invention comprises a phenol novolak type epoxy resin derived from epichlorohydrin or methyl epichlorohydrin and phenol and formaldehyde.

The present invention is directed to a tape having a surface opposite a tape surface having a signal transmission path formed on a surface of a flexible circuit and a plurality of opposite ends, wherein the signal transmission path is connected to the end by the end. Terminating in an adjacently arranged connecting conductor, the track is substantially encapsulated by a protective coating, the cured coating can be applied in an uncured liquid, and the coating comprises at least one epoxy compound. Also provided is a flexible connector from the signal source to the ink cartridge comprising a connecting conductor extending from the protective coating.

Typically, the signaling tracks and connecting leads are comprised of copper traces that occupy 60-80% of the total circuit area.

Surprisingly, the coating of the invention can be applied directly on copper. Alternatively, if desired for component manufacturing for additional reliability, the copper traces can be gold plated using methods known to those skilled in the art before applying a protective coating.

Accordingly, the present invention comprises: a) applying a coating to a preselected area of an article where gold plating is not desired; and b) subjecting the article to a gold plating bath, wherein the gold is applied to a gold plating bath. There is also provided a method of plating gold on an area of an article, the method comprising substantially not depositing on the area of the article.

The present invention satisfies the requirements of recent high speed ink jet printers in view of the high potential for spray depositing ink droplets on a flexible circuit. In addition, the cured coatings of the present invention overcome the disadvantages of many prior art coatings by providing protection at the temperatures associated with current ink jet printheads. During operation of the printhead, the flexible circuit is at a temperature in the range of 20-70C.

Here, the following terms have the following meanings. 1. The “form of the image mode” means that the deposition of the coating is
Rather than in a blanket form, it is meant to be deposited to form a pre-selected pattern of coated and uncoated areas. 2. The “non-connection region” means a region other than a region where an electrical connection can be formed or a junction can occur. 3. "Bend radius resistance" means that the coating will withstand at least the indicated value of the bend radius. The sample bends with the coating inside the radius. 4. "Overcoat" and "Protective coating"
Is a synonym and means a layer of a suitable polymer that covers the electrical signal carrying conductor structure and avoids erosion due to environmental pollution.

[0030] All percentages, parts and ratios are by weight unless otherwise specified.

[0031]

DETAILED DESCRIPTION OF THE INVENTION The coating of the present invention must contain at least one epoxy compound. Epoxy compounds contain one or more free epoxide groups per molecule because they are reactive. It may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, of the monomer or polymer, and may include other substituents such as hydroxyl, ether, halogen atoms and the like. The epoxy group may be a terminal or internal 1,2-epoxy group and may be linked to an oxygen atom (ie, a glycidyl ether group or a glycidyl ester group).

The composition of the present invention has an epoxide equivalent of about 90.
To about 950, preferably about 170 to about 450. The average epoxy equivalent is the average molecular weight of the resin, 1
It is a numerical value divided by the number of epoxy groups per molecule.

Epoxy compounds having a low epoxide equivalent weight in the range of about 90 to about 250 are typically preferred for their low viscosity, but higher equivalent weights, including those up to about 950 and melting points up to about 75 ° C. Provides the advantage that viscosity is not a factor. Liquid epoxy compounds with an equivalent weight of 170 to about 220 are most preferred.

Suitable examples include polyphenols and epihalohydrins, polyalcohols and epihalohydrins, polycarboxylic acids and epihalohydrins, amines and epihalohydrins, sulfur-containing compounds and epihalohydrins, mixtures of the above compounds and epihalohydrins, polyhalides. Epoxy compounds from the reaction of isocyanates with 2,3-epoxy-1-propanol and from the epoxidation of blends of olefinically unsaturated compounds with such compounds.

Preferred epoxies include phenolic resins such as the reaction product of epihalohydrin with an aromatic polyphenolic compound (including the glycidyl ether of bisphenol A) or the reaction product of a phenol-formaldehyde resin. Can be A preferred type of the resin is a bisphenol A type epoxy resin having an average epoxy equivalent of about 170 to about 220, and an average epoxy equivalent of about 3
100 to about 800 brominated bisphenol A type epoxy resin.

Suitable examples include polyglycidyl ethers of polyhydric phenols such as bis (4-hydroxyphenyl) methane, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, Tris (4-hydroxyphenyl) methane and 2,
2-bis (4-hydroxyphenyl) -1,1,1,3,3,3
-Hexafluoropropane, etc.], and the reaction products of aldehydes (especially formaldehyde) with phenols of one or more valences (commonly referred to as novolak resins). Commercially available resins from bisphenol A and epihalohydrin include Shell Chemical Co.
Company (Shell Chemical Company) Epon (Epon,
Registered trademark) 826. A typical novolak resin is Dow Chemical Company
y) "DER431".

Other suitable polyepoxides include N,
Glycidyl ethers of aromatic amines such as N, N ', N'-tetraglycidylmethylenediamine; polyvalent aromatic acids,
Glycidyl esters of fatty acids and cyclic fatty acids (eg, diglycidyl phthalate and diglycidyl hexahydrophthalate); glycidyl ethers of polyhydric alcohols (eg, diglycidyl ether of hydrogenated bisphenol A); Epoxidized products of saturated compounds; Epoxidized polymers (eg, epoxidized butadiene-acrylonitrile copolymer); Epoxides of alicyclic esters of dicarboxylic acids (eg, bis (3,4-epoxycyclohexylmethyl) -adipate); Epoxides of cyclic esters (eg, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, etc.); hydantoin epoxy resins; and glycidyl ethers of polypropylene ether glycol ( Example, Dow Chemical Company, Ltd., "DER736"), but may be mentioned, but are not limited to these.

A number of other suitable polyepoxide materials are:
It is commercially available or easily prepared using well-known techniques and will be obvious to those skilled in the art.

A preferred coating comprises a cresol novolak type epoxy derived from epichlorohydrin or methyl epichlorohydrin and phenol and formaldehyde. Cresol novolak type epoxy resin refers to a resin obtained by reacting epichlorohydrin with cresol novolak.

Epoxy resins can react with small amounts of other compounds, especially vinyl esters. Useful monomers / polymers include acrylates (eg, acrylic acid, methacrylic acid, itaconic acid, 2-ethylhexyl acrylate, butyl acrylate, isopropyl acrylate,
Crotonic acid, acrylamide, monomethylmalate, etc.); N-vinylpyrrolidone, N-vinylcaprolactam, polyoxyalkylene glycol poly (meth) acrylate, adducts of glycerol, and the like.

[0041] The coatings of the present invention preferably contain one or more polymerization initiators and / or catalysts and can act thermally or by other mechanisms (eg, photoinitiators). Catalysts useful for the esterification reaction include tertiary amines (eg, triethylamine, diethylamine hydrochloride, etc.). Useful initiators include carbonyl compounds such as benzoin isobutyl ether, azo compounds, amines, sulfur compounds and the like. The initiator is used in an amount of about 0.1 to about 1 per 100 parts by weight of the epoxy resin.
It is contained in an amount of 0 parts by weight.

[0042] The protective coating of the present invention may also include other auxiliaries (eg, antistatic agents, fillers, etc.). When an auxiliary is included, it typically contains a small amount of the formulation (eg, about 0.01-10%) so as not to interfere with the desired flexibility, adhesion, and ink resistance.

The protective coating has a thickness of about 10 to about 200 μm, preferably about 10 to about 75 μm, on the conductor.
Thus, the conductor can be sealed.

[0044] Useful coatings of the present invention can be used for at least 15 days, at least about 12 days, and most preferably at least 28 days when tested under current while penetrating into an electrolyte (eg, ink solution). It must be sufficiently moisture resistant to prevent leakage.

As mentioned above, the coating of the present invention surprisingly protects copper circuit traces from erosion without the need for gold plating on unconnected areas of the circuit. Thus, selective gold plating can be performed. Typically, copper circuit traces on a polymer / adhesive substrate are plated (e.g., gold tin or palladium) on all exposed copper surfaces by complete metal engineering after circuit assembly. The cover coat is applied over the entire area of the flexible circuit except for the above-mentioned portion connected to the printer body. Functional areas, i.e., areas where bonding must occur or electrical connections must be made, typically occupy a very small portion of the total exposed circuit area. Only those areas require gold to make a good and easy connection.
This is significantly different from the typical process of placing gold over all copper circuit features, even in unconnected areas. In a typical process, a cover coat is applied after the completion of circuit assembly, including a gold plating step. In the case of the protective coating of the present invention, the cover coat may be placed on a copper flexible circuit prior to the gold plating step so that the copper traces under the cover coat are not gold plated. Obviously, in a typical circuit, this eliminates about 80% or more of the required gold and is substantially cost saving. Copper plating may be performed using commercially available copper electroplating processes (eg, Shipley Co., Inc., Newt, known to those skilled in the art).
on) and Mass).

Where bonding is not desired in theory, conventional protective coatings may not be able to meet the stringent requirements for protecting copper circuit traces. Gold, a noble metal, provides some corrosion protection to copper. Without such plating, the absorption of water through the protective coating can cause a corrosion reaction at the copper / protective coating interface. If enough copper ions are generated from the traces by corrosion, the ions can migrate from the positively charged or anode traces, resulting in metal migration that is negatively biased or deposited on the cathode traces. is there. Then the metal dendrite grows,
This can result in electrical shorts between adjacent traces, resulting in circuit loss. That is, the protective coating must not absorb moisture and / or
Alternatively, copper must be inactivated to avoid metal migration.

The epoxy-containing protective coating of the present invention is 1000 ° C. at 85 ° C./85% relative humidity and 20V.
Tests up to hours show little or no copper corrosion. In addition, the coatings of the present invention do not exhibit a wicking effect (phenomenon of the gold plating salt penetrating the cover coat during the electroplating process). Gold penetrates the small gap between the protective coating and the polyimide / copper trace interface. The protective coatings of the present invention show good fit and show little penetration of gold salts. Gold plating itself,
Known gold plating baths and process equipment therefor (e.g.,
Using an ammonium gold cyanide electroplating solution substantially free of arsenic) by conventional means. The solution may contain a buffer and other additives, and typically has a gold concentration of about 5 to about 20 g / L, preferably about 1 to about 20 g / L.
2 to about 15 g / L. The solution operates at a temperature in the range of about 50 to about 60 ° C, and a pH of about 4.5 to about 6. The electroplating potential of the solution is typically in the range of 20-110 mV relative to a silver / silver chloride reference electrode. Useful current density is in the range from 2 to about 12A / m ^2, typical residence times, gold thickness of about 0.25 to about 1.25 .mu.m (about 10
50 μ inch), preferably from about 0.25 to about 0.75 μm
Range from 2 to about 10 minutes to obtain Alkali metal-containing gold cyanide plating solutions are available from Englehard Corporation and American Chemical and Refining Company.
(American Chemical & Refining Company). The alkali metal replaces the ammonium ion in a known manner. Complexes that do not contain alkali metals (eg, chloride, bromide, and thiosulfate complexes) can also be used in the methods of the invention. For example, U.S. Pat. No. 4,775,5
Nos. 56 and 5,032,467, the contents of which are all inserted here.

[0048]

The following examples are for illustrative purposes and do not limit the scope of the invention as defined herein. Test method 1. Corrosion Test The corrosion test determines the decomposition of a selected coating immersed in a liquid ink contained in a heated reservoir. The determination of the decomposition depends on an electric circuit consisting of a power supply with a potential of 19.5 V, voltage change measuring means and a sample cell. The sample cell contains an ink bath of sufficient capacity to accommodate 500 mls of ink of the type used for inkjet printers. With the ink volume temperature controlled at 70 ° C., the pre-prepared test circuit (immersed in the heated ink) was applied to a coating applied over parallel copper traces carried on a suitable insulating substrate. Provide means for sensing change. Often, the substrate carrying the series of parallel copper traces is a flexible film such as Kapton®. However, many substrates, whether rigid or flexible, may be equally suitable for testing purposes. A pair of adjacent traces provides the basic sensor elements for determining coating degradation and consequent degradation. Given several trace pairs, the test can be repeated for accurate results.

The connection between the sensor and the electrical circuit requires that a conductor be connected to each adjacent trace. The conductor extends from a bath that is in electrical communication with the rest of the electrical circuit. Since the traces are not in contact, the immersed sensor initially represents an open circuit with infinite resistance. This condition should be maintained if the protective coating applied on the parallel traces remains completely. As the coating degrades, bath fluid penetrates the coating because it is immersed in the ink. When fluid penetration reaches the surface of the parallel traces that are conductors, conductive paths can occur through the ink between the traces. This is due to the use of ionic conductive materials in the ink. When this occurs, a voltage change occurs and is recorded by a voltmeter that is part of the electrical circuit. The change in voltage indicates the start of deterioration of the coating. If there is no such voltage change, the test ends after 28 days, or after other selected times as shown in Tables 3 and 3.

[0050] 2. Bend Radius Resistance The "Bend Radius Resistance" test uses a specific fixture consisting of two metal parts integrated with a spring connector. Each metal part has a well-fitting contour during the halving. In one aspect, the fixture comprises a square block and an L-shaped metal block, with the top and bottom surfaces of the square block being flat while the sides are vertical and rounded with a set radius. It is designed to represent an angle.
Similarly, the interior corners of the L-shaped block represent structures with supplemental rounded angles that exactly match the rounded corners of the square block. The separation of the blocks creates a groove between the side surface of the square block and the inner surface of the L-shaped block. The springs that are placed sideways and placed at each end of the groove,
Blocks are provided to suppress contact with each other and with the adjacent grooves. Attempts to separate the blocks to open the grooves require an excess of force over the combined force of the connecting springs. The samples are tested at radii of 0.7 mm, 0.5 mm and 0.3 mm.

The sample to be tested requires the length of the coated flexible circuit to be inserted into the groove formed by applying a force to separate the blocks. The stretching requirement is that the protective coating applied to the flexible circuit be placed in contact with the side surface of the square block. After relaxing the force by inserting the length of the circuit into the groove, the fixture is closed and the circuit is bent into a defined shape with the surfaces of the square block and the L-shaped block together. The retaining spring applies enough force to overcome the residual tension in the flexible circuit material. After a short dwell time at the bending position, the fixture block is separated and the flexible circuit is moved to another position in the groove, distorting another part of the circuit. After repeating this process several times, it is examined at 5x magnification to determine the formation of cracks or delamination traces of the protective coat from the circuit. The circuit sample passes if there is no crack or delamination after the test.

Examples 1-4 The coating of Example 1 is a thermosetting phenol novolak epoxy derived from epichlorohydrin and phenol and formaldehyde. The coating of Example 2 is a thermosetting epoxy acrylate.
The coating of Example 3 is an epoxy acrylate. The coating of Example 4 is a two-part epoxy resin.

[0053]

[Table 1]

The compositions disclosed in Table 1 were subjected to a corrosion test. The results for the duplicate samples from this experiment in Table 2 show the remaining time of the coating in days and the voltage recorded after extended immersion of the coated circuit subject to high temperature and high humidity. The numbers in parentheses represent the thickness of the protective coating measured from the surface of the support substrate for the circuit.

[0055]

[Table 2]

* Values in parentheses indicate the thickness (μm) on the surface of the polyimide substrate. The thickness of the conductive trace is
It was 25.0 μm.

After exposing the composition of Example 1 to high temperatures, it was bent before conducting the ink immersion test. Table 3 shows the corrosion test life. Control samples were not heated. Pretreatment combining heat and bending degrades more often than heating alone, which is itself considered severe. This pretreatment is used to simulate processes such as solder reflow or material curing that a protective coating would experience during flexible circuit fabrication.

[0058]

[Table 3]

Comparative Examples C5 to C11

The compositions of the present invention were compared to commercially available coatings that were described as being useful for coating and protective printed circuits. A general description of each composition used for comparison is shown below.

The coating of Comparative Example C5 was coated with Coats (Co
ates) epoxy acrylate AS for liquid photo imaging
I / Aquaflex CKXN0025. It is described as a waterborne cover layer for flexible circuits.

Comparative Example C6 is a 100% solids compatible Emcast 1904 UV curable epoxy from TC Services Inc. Its properties include chemical resistance, water resistance, and impact resistance on PC board components and substrates.

Comparative Example C7 is an epoxy film "confo" for photoimaging made by Morton Electronic Materials.
r) Mask ". It claims to be the latest advance in highly compatible soldermask technology that provides environmental protection to printed substrates.

Comparative Example C8 is a thiol / ene formulation that cures under the influence of UV radiation. It's about
Earl Grace and Company (WRGrace &
Co.) 123WE7 cover coat. The material is described as a screen-printable photopolymer and is designed to form a durable continuous covercoat on copper.

The coating of Comparative Example C9 is a thermosetting epoxy material CCR-2200FX from Asahi Chemical Company. This is a two-part screen printable system that supplies a flexible solder mask.

The coating of Comparative Example C10 is a commercially available material and is available from Asahi Chemical Company as Asahi Chemical Super Resist CCR-232GF No. 6 (see Example 1).

The coating of Comparative Example C11 was obtained from Nippon Polytechnic C
Orporation) NPR-5.

[0068]

[Table 4]

* Pre-bake is used to simulate processes that a protective coating will experience during flexible circuit fabrication, such as solder re-free or material curing.

Example 12 The sample of Example 1 was cut into a 2.5 cm square test piece. Next, the test piece was placed in a newly prepared gold (Au) bath 50 m.
And heated to 60 ° C. with stirring. Thereafter, the test piece was placed in the solution and immersed at 60 ° C. for 24 hours. Twenty-four hours later, the specimens were removed for signs of erosion, such as fading under the protective coating, and for reduced adhesion or gaps of the coating to the substrate. No evidence of solvent erosion was found under the coating.

[0071]

The present invention can be applied directly on a conductor of a flexible printed circuit. Furthermore, since the function of the mask for gold plating is exhibited, it is not necessary to coat the entire surface of the conductor with expensive gold overcoating.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Nathan Philip Klutter, 3M Center, St. Paul, Minnesota, USA 55144-1000 (72) James Randall White, Inventor St. Paul, Minnesota, 55144-1000 Paul, 3M Center

Claims (8)

[Claims] 1. A flexible printed circuit wherein the coating can be applied in liquid form in the form of an image and the coating composition comprises at least one epoxy group which has been reacted with at least one further polymer or monomer in the presence of an initiator. A liquid polymer coating composition for use in a printing apparatus, wherein the flexible circuit has a signal transfer path useful for controlling the pattern of an inkjet ink including a solvent and a surfactant, wherein the coating composition is selected from heat and ultraviolet light. Subjected to curing by exposure to an applied energy source, the coating can provide a conformable protective layer on the track to seal the track from erosion by the inkjet ink, wherein the layer has about 2
It provides protection from solvents and surfactants over a temperature range from 0 to about 70 ° C.
The substrate has a minimum durable radius when subjected to a corrosion test of 60 m and is substantially free of solvent leaching under the protective layer after immersion in a gold plating solution at 60 ° C. for 24 hours. A liquid polymer coating composition for flexible printed circuits that protects liquids. 2. The epoxy is a phenol novolak type epoxy derived from epichlorohydrin or methyl epichlorohydrin and phenol and formaldehyde, wherein said another polymer is selected from the group consisting of acrylates and vinyl lactams. The protective coating according to claim 1. 3. The protective coating of claim 1 having a minimum durable radius of about 0.3 mm. 4. A flexible polymer tape comprising, on at least one surface, a flexible circuit having a conductor formed thereon. 5. The flexible polymer tape of claim 4, wherein the tape exhibits essentially no leaching under the protective coating after immersion in the gold plating solution at 60 ° C. for 24 hours. 6. The flexible polymer tape of claim 5, wherein the coating is applied over the copper traces to form a mask to prevent gold plating on the traces. 7. A tape having on its surface a conductor substantially encapsulated with a protective coating according to claim 1, wherein said conductor has an end extending from the protective coating; b) a conductor And c) an ink cartridge comprising an ink reservoir fluidly coupled to the printhead substrate. 8. A step of: a) providing the coating of claim 1 to a preselected area of the article where gold plating is not desired; and b) providing a gold plating bath that does not substantially deposit gold on said area of the article. A method of plating gold on a preselected area of an article, comprising applying the article.