JP2015115212A - Method for manufacturing flexible heater and flexible heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible heater with a thin and fine shape, and also to provide a large-area flexible heater.SOLUTION: A method for manufacturing a flexible heater includes the steps of: printing a circuit pattern on a surface of a polyimide-based film by an alkali-containing ink (pattern printing step); adsorbing a metal ion serving as a catalyst to an expressed carboxyl group (catalyst imparting step); reducing the metal ion (catalyst reducing step); and forming a metal layer by electroless plating treatment (metal layer forming step).

Description

  The present invention relates to a method for manufacturing a flexible heater. In detail, it is related with the manufacturing method of the flexible heater which forms a heat generating body in the surface of a polyimide-type film base material by a full additive method. The present invention also relates to a flexible heater manufactured by this method.

  Conventionally, a planar heating element is known in which a metal heating element is sandwiched between insulating resin films and the like. In particular, flexible heaters that can be deformed using a highly flexible resin film are used in various fields.

  The heating element portion has a redundant circuit shape made of metal, and nickel, nickel alloy, stainless steel or the like is mainly used as the metal. For example, in Patent Document 1, a metal resistance wire such as a nichrome wire is sandwiched and fixed by an insulating resin through an adhesive layer. Since the metal resistance wires are directly arranged in a circuit shape, the pattern has a high degree of freedom. Patent Documents 2 and 3 disclose a method of obtaining a heating element by bonding a resin film and a metal foil such as stainless steel or nickel alloy and forming a pattern by photolithography etching. Patent Document 4 describes a method of obtaining a laminate in which a metal film is deposited on the surface of an insulating film by plating, vacuum deposition or sputtering, and punching the laminate into a heater shape to form a heating element. ing. This method has a feature that a complicated process such as etching is not required.

JP 2003-257597 A JP 2008-123869 A JP2012-134132A JP 2001-257060 A

  The above prior art has the following problems. In the methods of Patent Document 1 and Patent Document 4, it is difficult to form a fine circuit or to manufacture a thin flexible heater. The methods of Patent Documents 2 and 3 require equipment for photolithography etching, and the manufacturing process becomes complicated. For this reason, it is unsuitable for manufacturing a large area flexible heater. Furthermore, the metal removed by etching is wasted.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a flexible heater having a thin and fine circuit shape can be manufactured by a simple process and completed the present invention.

  That is, the present invention includes a pattern printing step of printing a circuit pattern with an alkali-containing ink on the surface of a polyimide film, a catalyst applying step of adsorbing metal ions serving as a catalyst to a carboxyl group expressed by the action of the alkali-containing ink, It is a manufacturing method of a flexible heater including a catalytic reduction process for reducing metal ions and a metal layer forming process for forming a metal layer on the circuit pattern portion by performing an electroless plating process.

  An imide ring cleavage step can be provided between the pattern printing step and the catalyst application step. The metal layer is preferably made of nickel and / or a nickel alloy.

  The flexible heater of this invention is manufactured by the manufacturing method of the said flexible heater.

  According to the present invention, a flexible heater having a thin and fine shape can be manufactured. Furthermore, it can respond to the manufacture of a flexible heater with a large area.

It is a flowchart which shows the manufacturing method of the flexible heater of this invention. It is a schematic diagram of the flexible heater of this invention. It is a cross-sectional schematic diagram of the flexible heater of this invention.

  The method of this invention consists of a pattern printing process, a catalyst provision process, a catalyst reduction process, and a metal layer formation process. FIG. 1 shows a preferable example of the steps included in the method of manufacturing the flexible heater of the present invention and its order. The example of FIG. 1 also includes an imide ring cleavage step.

(Pattern printing process, S1 in FIG. 1)
The polyimide film used in the present invention has sufficient heat resistance and chemical resistance for use as an electronic material, and the imide ring of the main chain is cleaved by an alkali hydrolysis reaction to generate a carboxyl group. . Examples of the polyimide film include polyimide, polyetherimide, and polyamideimide. Among these, polyimide is preferred because it is widely used as a general electronic material and is relatively easy to obtain in film form. As industrial products, for example, “Kapton (registered trademark)” manufactured by DuPont, “Upilex (registered trademark)” manufactured by Ube Industries, Ltd., “Apical (registered trademark)” manufactured by Kaneka Corporation, and the like are known.

  The alkali-containing ink includes an alkali agent and a solvent. The alkaline agent may be either an organic compound or an inorganic compound. Examples of organic compounds include quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). Can be mentioned. On the other hand, examples of the inorganic compound include sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, and ammonium hydroxide.

  Of these, tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH) are preferable as the organic compound, and sodium hydroxide and potassium hydroxide are preferable as the inorganic compound because of the solubility in the solvent described later.

  The alkali concentration (concentration of the alkali agent) in the alkali-containing ink is preferably 0.05 to 50% by mass, more preferably 3 to 30% by mass. If the alkali concentration is 0.05% by mass or more, the imide ring on the surface of the polyimide film is sufficiently cleaved and the formation of the metal layer becomes good. If the alkali concentration is 50% by mass or less, excessive imide ring cleavage on the surface of the polyimide film can be suppressed, and a decrease in pattern accuracy can be prevented.

The solvent is other than water and preferably does not contain water. If the solvent is water or contains water, the printing apparatus may be damaged. However, this is not the case when using an alkali-resistant printing apparatus, and an alkali-containing ink containing water can be used. When an alkali-containing ink containing water is used, cleavage of the imide ring proceeds simultaneously with printing, so that there is an advantage that the imide ring cleavage step described later can be omitted or simplified.

Furthermore, it is preferable to use an organic solvent having a boiling point of 120 ° C. or higher from the viewpoint of handleability in the pattern printing process. When an organic solvent having a boiling point of 120 ° C. or higher is used, it is possible to suppress a decrease in fluidity of the alkali-containing ink in the printing process. As a result, the print quality can be kept high and a precise pattern can be formed. The organic solvent is required to have an electrical polarity capable of stably dissolving the alkaline agent, and therefore preferably has a hydroxyl group in the molecule. Furthermore, the organic solvent must be capable of dissolving or dispersing the alkaline agent.

Examples of the organic solvent that satisfies the above conditions include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and 1,3-butylene glycol as diol-based solvents; O. Diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether; O. Examples of the system include propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Of these, diethylene glycol, diethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether are preferred because they have a relatively high boiling point and are suitable for printing. Two or more of these organic solvents may be mixed and blended.

  The alkali-containing ink used in the present invention may further contain a water-soluble polymer compound. The water-soluble polymer compound is soluble in the organic solvent and soluble in water. By containing the water-soluble polymer compound, a wide range of viscosity can be adjusted. As a result, it is possible to adjust the viscosity optimized for various printing methods, and it is possible to prevent printing leakage and blurring, thereby greatly improving printing accuracy. Further, by contacting with water after printing, the water-soluble polymer compound takes in water and causes dissociation of the alkaline agent, thereby specifically promoting the cleavage of the imide ring in the printed portion. When removing the alkali-containing ink, the water-soluble polymer compound dissolves in water and can be easily removed.

  Examples of water-soluble polymer compounds used in the present invention include polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene oxide, sodium polyacrylate, polyacrylamide, polyethyleneimine, polyethylene oxide, and other synthetic polymer compounds, and Examples include natural polymer compounds such as corn starch, mannan, pectin, chitosan, agar, sodium alginate, hyaluronic acid, sericin, various gums, dextran, and gelatin. Among them, polyvinylpyrrolidone is preferable because of its excellent alkali resistance. .

The viscosity of the alkali-containing ink in the present invention is not particularly limited. For example, when a cone plate viscometer is used and the rotor rotation speed is 0.5 rpm at 25 ° C., the viscosity is preferably 50 to 500 Pa · s, more preferably in the range of 100 to 400 Pa · s. When the alkali-containing ink is within this viscosity range, a fine pattern can be printed with high accuracy.

  In addition to the above essential components, the alkali-containing ink of the present invention may optionally contain components suitable for the printing method. For example, when used for screen printing, it is possible to impart properties suitable for screen printing by adding thickening polymers, inorganic fine particles (fillers), rheology control agents, dispersion stabilizers, and the like. In addition, when used for inkjet printing, printing properties such as viscosity, surface tension, and ejection properties can be added by blending thickeners, pigments and inorganic fine particles (fillers), leveling agents, dispersion stabilizers, and antifoaming agents. Can be controlled.

  As a printing method using an alkali-containing ink, known printing methods such as screen printing, intaglio printing, relief printing, and ink jet printing can be employed. In particular, according to inkjet printing, a free circuit pattern can be formed. According to intaglio printing, especially gravure printing, it is possible to print a fine pattern with high production efficiency.

(Imide ring cleavage step, S2 in FIG. 1)
In order to cause cleavage of the imide ring on the surface of the polyimide film, the alkali agent needs to be dissociated by water. When the alkali-containing ink contains water as a solvent, the imide ring is cleaved from the time when it is applied to the surface of the polyimide film. However, when water is not included as a solvent, an imide ring cleavage step may be provided in order to contact with water separately. The contact method with water may immerse the polyimide-based film in water while the alkali-containing ink is applied in a pattern, or spray water with a spray or the like. Or the method of leaving still in the atmosphere containing much water vapor | steam may be used. Prior to contact with water, a drying step for removing the solvent in the alkali-containing ink may be introduced. According to this, it is possible to suppress swelling of the alkali-containing ink in contact with water, and to prevent a decrease in accuracy due to wetting and spreading.

  The degree of imide ring cleavage on the polyimide film surface can be adjusted by adjusting the temperature and time when contacting with water. For example, when the immersion method is used, the cleavage of the imide ring is sufficiently promoted by immersing in water at 10 ° C. or higher for 5 seconds or longer, preferably 20 ° C. or higher for 90 seconds or longer. By immersing in pure water at 21 ° C. for 90 seconds, the ratio of cleaving the imide ring is dramatically improved by 3 times or more compared with the case of not immersing. Moreover, since the same effect is acquired even if the aqueous solution which some solute melt | dissolved, you may use arbitrary aqueous solutions. In order not to cause chemical changes on the polyimide film surface, it is preferable to use pure water having a pH of 9 or less, preferably without the influence of ions.

  It is preferable to wash and remove the alkali-containing ink after contact with water or simultaneously with contact with water. For the cleaning and removal, a known cleaning method can be applied. For example, ultrasonic cleaning, spray cleaning, shower cleaning, brush cleaning, immersion cleaning, two-fluid cleaning and the like can be used as appropriate, and there is no particular limitation.

(Catalyst application step, S3 in FIG. 1)
Subsequently, in the catalyst application step, an electroless plating catalyst is applied to the site where the alkali-containing ink is printed in the pattern printing step. Specifically, a metal ion-containing solution that becomes an electroless plating catalyst is brought into contact by reduction to generate a metal salt with a carboxyl group generated by cleavage of the imide ring. That is, the metal ion-containing solution is brought into contact with the polyimide film surface whose imide ring has been cleaved by the alkali-containing ink.

  Examples of the metal ion include one or more selected from palladium ions, copper ions, and nickel ions. The metal ions are coordinated to the carboxyl group generated on the polyimide film in the pattern printing step, and a metal salt (complex) is formed.

  The metal ion concentration in the metal ion-containing solution is preferably 0.0001% by mass to 1% by mass, more preferably 0.001% by mass to 0.4% by mass, and still more preferably 0.001% by mass to It is 0.2 mass%, Most preferably, it is 0.002 mass%-0.02 mass%. As will be described later, in the present invention, when an acidic treatment liquid containing a reducing agent is used in the metal salt reduction step, metal ions are not dropped off in the subsequent step. Therefore, it can be processed with a low concentration of metal ions, and is highly practical.

  The solvent used in the metal ion-containing solution is not particularly limited, but is preferably water. Examples of the method of bringing the polyimide film into contact with the metal ion-containing solution include a method of immersing the polyimide film in the metal ion-containing solution and a method of spraying the metal ion-containing solution in a spray form on the polyimide film. It is done.

  The reaction temperature when the polyimide film is brought into contact with the metal ion-containing solution is 10 ° C to 80 ° C, preferably 30 ° C to 50 ° C. The contact time of the metal ion-containing solution is preferably 10 seconds to 800 seconds, more preferably 60 seconds to 500 seconds.

  After contacting with the metal ion-containing solution, the polyimide film is washed with water to remove non-specifically attached metal ions. At this time, if ultrasonic cleaning or the like is performed, cleaning can be performed efficiently.

(Catalyst reduction step, S4 in FIG. 1)
In the catalyst reduction step, the polyimide film is brought into contact with a treatment liquid containing a reducing agent, and the metal ions adsorbed on the polyimide film surface in the catalyst application step are reduced. At this time, it is preferable that the treatment liquid containing the reducing agent is an acidic treatment liquid because dropping of metal ions can be suppressed. Examples of the reducing agent used in the treatment liquid containing the reducing agent include dimethylamine borane, sodium hypophosphite, hydrazine, methanol, diethylmethylamine, and ascorbic acid. Among these, dimethylamine borane is particularly preferable because it can be used in an acidic region.

  Moreover, 0.005 mass%-0.5 mass% are preferable, and, as for the reducing agent density | concentration of the process liquid containing a reducing agent, More preferably, they are 0.05 mass%-0.15 mass%. The solvent used in the treatment liquid containing the reducing agent of the present invention is not particularly limited, but water is preferable.

  The pH of the treatment liquid containing the reducing agent of the present invention is preferably 6 or less, more preferably 2 to 6, and further preferably 3 to 5.9. If pH is this range, it can reduce | restore, suppressing the omission of the metal ion which adsorb | sucked to the polyimide-type film surface at the catalyst provision process.

  The treatment liquid containing the reducing agent of the present invention can be prepared by appropriately dissolving the reducing agent in a buffering agent in order to maintain an appropriate pH range. Known acidic buffering agents can be used, and examples include 0.1 M citrate buffer and acetate buffer. The acidic treatment liquid containing the reducing agent of the present invention neutralizes the alkaline agent applied to the polyimide film, prevents re-modification of the polyimide film, and suppresses dropping of metal ions adsorbed on the polyimide film. effective. Therefore, as described above, a low-concentration metal ion-containing liquid can be used, and the metal salt can be efficiently reduced.

  The time for which the polyimide film is brought into contact with the acidic treatment liquid containing a reducing agent is 60 seconds to 600 seconds, preferably 180 seconds to 300 seconds. The contact temperature is 10 ° C to 80 ° C, preferably 30 ° C to 50 ° C. After making it contact with the acidic processing liquid containing a reducing agent, a polyimide-type film is washed with water and the reducing agent solution adhering non-specifically is removed.

(Metal layer forming step, S5 in FIG. 1)
After reducing the metal ions, electroless plating is performed to form a metal layer. For electroless plating, an existing method can be used, and the aforementioned polyimide film may be immersed in a plating bath. The reaction time and temperature of the plating can be appropriately adjusted according to the thickness of the metal layer.

  The thickness of the metal layer in the present invention is 0.5 μm to 20 μm, more preferably 1 μm to 10 μm. After forming the metal layer by electroless plating, the polyimide film is washed with water to remove the non-specifically deposited plating solution.

Examples of the metal forming the metal layer include those having electrical resistance, such as nickel, copper, and alloys thereof, and capable of forming a metal layer by electroless plating. Among them, those having a specific electric resistance of 1 × 10 ⁻⁷ Ωm or more are preferable. Specifically, nickel and its alloys are preferable.

The polyimide film on which the metal layer is formed through the above steps is connected to an electrode to which a voltage is applied and can be used as a flexible heater. On the surface on which the metal layer is formed,
Further, a polyimide film can be laminated and used.

(Example 1)
As the polyimide film, a polyimide film having a thickness of 25 μm (trade name “Kapton H”; manufactured by Toray DuPont, 10 cm × 10 cm) was used. Next, an alkali-containing ink was pattern printed on the material using an inkjet printer. The alkali-containing ink used here was an ink containing 2.5% by mass of dipropylene glycol monomethyl ether as a solvent and potassium hydroxide (KOH) as an alkali agent. As a result, a printed pattern intended for a heating element circuit having a line width of 3 mm and a total length of 61.6 cm was formed on the polyimide film. Subsequently, the polyimide film on which the alkali-containing ink was pattern-printed was heated at 120 ° C. for 20 minutes, and then washed with spray water to make contact with water. The alkali-containing ink was removed by spray water washing while proceeding with the cleavage reaction of the imide ring.

  Next, the polyimide film was immersed in a 0.015 mass% palladium chloride aqueous solution at 40 ° C. for 300 seconds, and palladium ions were adsorbed to the carboxyl groups formed by the alkali agent. Thereafter, the polyimide film was taken out and washed with water to remove palladium ions adhering non-specifically. Subsequently, the polyimide film was immersed in a treatment solution containing a reducing agent (pH 6, 0.1M citrate buffer solution containing 0.1% by mass of dimethylamine borane) at 40 ° C. for 180 seconds, and then on the polyimide film. Of palladium ions was reduced. Next, the polyimide-type film was taken out from the acidic treatment liquid containing the reducing agent, washed with water, removed the non-specifically attached reducing agent, and then dried.

Next, the polyimide film was subjected to an immersion treatment at 80 ° C. for 40 minutes using an electroless nickel plating bath (Melplate NI-869: manufactured by Meltex Co., Ltd.), and a nickel-phosphorus alloy plating film (specific resistivity 1). 0.000 × 10 ⁻⁶ Ωm). By the above process, a flexible heater having a heating element circuit pattern having a line width of 3 mm, a total length of 61.6 cm, a metal film thickness of 8 μm, and an inter-terminal resistance of 25Ω was obtained.

(Example 2)
A flexible heater was obtained in the same manner as in Example 1 except that the pattern printing process was gravure printing. The alkali-containing ink used here contained 15% by mass of potassium hydroxide (KOH) as an alkali agent, and was adjusted by appropriately adding carboxymethylcellulose and a thixotropic agent for viscosity adjustment. The viscosity of the alkali-containing ink was measured at 25 ° C. using a cone plate viscometer at a rotor rotational speed of 0.5 rpm, and found to be 370 Pa · s. As a result, a flexible heater having a heating element circuit pattern having a line width of 1 mm, a total length of 190 cm, a metal film thickness of 8 μm, and an inter-terminal resistance of 250Ω was obtained.

(Example 3)
A flexible heater was obtained in the same manner as in Example 1 except that a nickel-copper alloy was used as the metal for forming the metal layer. After the catalyst reduction step, immersion treatment was performed at 80 ° C. for 60 minutes using an electroless nickel-copper alloy plating bath to form a nickel-copper alloy plating film (specific resistivity 0.80 × 10 ⁻⁶ Ωm). For the electroless nickel-copper alloy plating, nickel sulfate 26.0 g / l, copper sulfate 2.5 g / l, sodium hypophosphite 21.0 g / l, citric acid 25.0 g / l, acetic acid 12.5 g / L, Rochelle salt 16 g / l, and thiourea 15.0 g / l. By the above process, a flexible heater having a heating element circuit pattern having a line width of 3 mm, a total length of 61.6 cm, a metal film thickness of 8 μm, and an inter-terminal resistance of 20Ω was obtained.

1 Polyimide film 2 Metal layer

Claims (4)

A pattern printing step for printing a circuit pattern with an alkali-containing ink on the surface of the polyimide film, a catalyst applying step for adsorbing metal ions serving as a catalyst to carboxyl groups expressed by the action of the alkali-containing ink, and metal ions serving as the catalyst A method for producing a flexible heater, comprising: a catalytic reduction step of reducing, and a metal layer forming step of forming a metal layer on the circuit pattern portion by performing an electroless plating treatment   The method for producing a flexible heater according to claim 1, further comprising an imide ring cleavage step between the pattern printing step and the catalyst application step.   The method for manufacturing a flexible heater according to claim 1, wherein the metal layer is made of nickel and / or a nickel alloy. The flexible heater manufactured by the manufacturing method of the flexible heater of Claim 1

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