JPH06200218A - Heat-resistant adhesive sheet - Google Patents

Abstract

PURPOSE:To obtain the subject sheet which can be applied to an adherend at low temperature within a short time by forming the adhesive layer from a specified thermoplastic polyimide terminated with a dicarboxylic acid anhydride. CONSTITUTION:A thermoplastic polyimide comprising repeating units of formula II [wherein Y is a group of formula III (wherein X is a direct bond or CO or O] and terminated with a dicarboxylic acid anhydride of formula I (wherein Z is a bivalent group selected from among a monocyclic aromatic group, a fused polycyclic aromatic group and a nonfused polycyclic aromatic group consisting of aromatic groups bonded with each other directly or through bridging members) is used to form an adhesive layer on at least one side of a polyimide support to form the objective adhesive sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant adhesive sheet for flexible wiring boards and ICs, which has a high adhesive strength and is extremely excellent in heat resistance.

[0002]

2. Description of the Related Art Conventionally, with respect to a flexible wiring board on which a circuit has already been formed, 1) the role of a solder resist in a soldering portion, 2) folding resistance in a bent portion, 3) ensuring electrical insulation and protecting the surface. For the purpose, a method of laminating a cover lay film having an adhesive layer on one side by applying heat and pressure to a flexible wiring board is generally performed. When manufacturing a multilayer flexible wiring board or a rigid-flexible wiring board, a laminated ply is manufactured by applying heat and pressure with a bond ply having adhesive layers on both sides thereof being sandwiched therebetween. In addition, relatively recently, a part of the lead frame fixing tape (single-sided adhesive layer) and the lead-on-chip adhesive tape (double-sided adhesive layer) have begun to be used in IC-related.

[0003]

The adhesive sheet of the present invention is
The above-mentioned four types are included, but the conventional adhesive sheet has a semi-cured (B-stage) adhesive layer of epoxy or acrylic, and is a thermosetting type that adheres to FPC by applying heat and pressure. Therefore, 1) lack of heat resistance due to the material, 2) deterioration of electrical insulation during humidification, 3) short life due to B-stage, 4) curing of the adhesive layer of B-stage during pressing However, there is a drawback in that it requires a long time because it needs to be performed.

[0004]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above-mentioned drawbacks, the present inventors found that the glass transition temperature was 20.
The present invention has been completed, paying attention to the fact that the above-mentioned drawbacks can be solved by using an adhesive sheet having an adhesive layer of thermoplastic polyimide which is excellent in flowability at 0 ° C. or lower and at high temperature. That is, in the present invention, the polymer molecule terminal is represented by the formula (1), [Chemical Formula 4]

[0005]

[Chemical 4] (In the formula, Z is selected from the group consisting of a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which aromatic groups are connected to each other directly or by a bridging member. A dicarboxylic acid anhydride represented by the formula (2), [Formula 5]

[0006]

[Chemical 5] (In the formula, Y represents formula (3) or [Chemical Formula 6], and X represents a direct bond, -CO- or -O-).

[0007]

[Chemical 6] Is a heat-resistant adhesive sheet formed by forming a thermoplastic polyimide adhesive layer made of a polymer having a repeating unit represented on one side or both sides of a polyimide supporting substrate, preferably represented by the formula (1). Dicarboxylic acid anhydride
A heat-resistant adhesive sheet that is phthalic anhydride, and also
A heat-resistant adhesive sheet having a glass transition temperature of 200 ° C. or less as an adhesive layer, which can be adhered by fusing to an adherend during hot pressing at 230 ° C., and 230 ° C. In the hot press lamination, the adhesive strength with the glossy surface of the copper foil is 0.7 kg / c
The heat-resistant adhesive sheet according to claim 1, wherein the elastic modulus at 230 ° C is 10 ³ dynes / cm.
A heat-resistant adhesive sheet having a polyimide of ² or less as an adhesive layer, and the thickness of the polyimide supporting substrate is 5 to 2
A heat-resistant adhesive sheet having a thickness of 00 microns and an adhesive layer having a thickness of 1 to 50 microns.

The present invention also provides a polyimide, which is a polymer in which the polymer molecule ends are blocked with a dicarboxylic acid anhydride.
After taking out as a polyimide powder, a polyimide varnish obtained by dissolving and containing it in a solvent that dissolves it, is a method for producing the above heat-resistant adhesive sheet, in which a polyimide supporting substrate is cast and dried to form an adhesive layer. Preferably, a varnish consisting of a reaction mixture obtained by subjecting a polyamic acid to end-capping and subsequent thermal imidization is directly cast on a polyimide supporting substrate, followed by drying to form a heat-resistant adhesive sheet for forming an adhesive layer. In addition, the reaction mixture in which imidization is not completed and polyamic acid remains in the range of 0.1 to 10% is directly cast on a polyimide supporting substrate and then dried to form an adhesive layer. A method for manufacturing a heat-resistant adhesive sheet,
And a method for producing a heat-resistant double-sided adhesive sheet in which a varnish is cast on both sides of a polyimide supporting substrate and then dried to form an adhesive layer, and the first surface side is coated with a coater dryer. A method for producing a heat-resistant double-sided adhesive sheet, in which the second side is cast-coated and the initial drying is performed in the same manner, and then the final drying is performed on both sides simultaneously with this dryer. In addition, in order to prevent the adhesive layer on the first surface from tacking on the roll in the coater dryer during the initial casting by casting on the second surface, (1) Dry the first surface at high temperature. After sufficiently reducing the residual solvent over a long period of time, the second surface side is cast and the initial drying is performed.
And a method for producing a heat-resistant double-sided adhesive sheet, which comprises drying the second surface side at a relatively low temperature in a short time, or (2) casting and coating the second surface side and continuously drying both surfaces in a non-contact manner. And a method for producing a heat-resistant double-sided adhesive sheet by a method of continuously drying both sides in a non-contact manner when performing final drying on both sides simultaneously with the present dryer.

The present invention will be described in detail below. The polyimide forming the adhesive layer of the heat-resistant adhesive sheet of the present invention basically uses 1,3-bis (3-aminophenoxy) benzene (hereinafter abbreviated as APB) as a diamine,
On the other hand, as tetracarboxylic dianhydride 3,3 ', 4,4
′ -Diphenyl ether tetracarboxylic dianhydride (hereinafter abbreviated as ODPA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (hereinafter BTDA)
Abbreviated) and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter abbreviated as BPDA)
Is a polyimide obtained by polycondensation with at least one tetracarboxylic acid dianhydride selected from the group consisting of, and the polymer molecule end has a thermoplastic polyimide sealed with a dicarboxylic acid anhydride as an adhesive layer heat resistance Adhesive sheet, which solves the above-mentioned problems of conventional adhesive sheets.

The following polyimides are already known as polyimides using APB as a diamine component. For example, (1) a polyimide oligomer having a terminal acetylene group produced from APB, BTDA and 3-aminophenylacetylene (N, Biow et al., USP 3,8).
45,018 and USP 3,879,349),
(2) Polycondensation type polyimide consisting of APB and pyromellitic dianhydride (TP Gannett et al., USP 4,48
5,140), (3) APB and various tetracarboxylic dianhydrides, which are heat-resistant polyimides (JP-A-61-143).
477 and JP-A-61-291670).

However, these polyimide (1)
Is an addition-type thermosetting polyimide in which the oligomer terminus is sealed with 3-aminophenylacetylene, but these terminal acetylene groups undergo a crosslinking reaction by heat treatment, and the condensation-type thermoplastic polyimide in the present invention. The heat-resistant polyimide consisting of belongs to a completely different category. Further, (2) is a condensation-type polyimide using APB as a raw material monomer, which is characterized by using pyromellitic dianhydride as a tetracarboxylic dianhydride component, and the heat-resistant polyimide in the present application has no structure. It is different. Also, (3) is APB
Although it is a heat-resistant polyimide consisting of various tetracarboxylic acid dianhydrides, the reactive end group of the polymer molecule terminal remains, and high-temperature, high-pressure bonding conditions are required as compared with the heat-resistant polyimide in the present application. It is what is done.

The polyimide according to the present invention contains the above-mentioned aromatic diamine component and aromatic tetracarboxylic dianhydride as the main components, but the formula is within the range that does not impair the characteristics of the heat-resistant adhesive sheet according to the present invention. (4), [Chemical formula 7]

[0013]

[Chemical 7] (In the formula, R is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group,
A tetravalent group selected from the group consisting of a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which the aromatic groups are connected to each other directly or by a crosslinking member. There is no problem even if the tetracarboxylic acid dianhydride represented by the formula (4) is contained in the range of 0 to 30% as a substitute for the aromatic tetracarboxylic acid dianhydride.

That is, examples of the tetracarboxylic acid dianhydride which can be partially substituted include, for example, ethylene tetracarboxylic acid dianhydride, cyclopentanecarboxylic acid dianhydride, pyromellitic acid dianhydride, and 2,2 '. , 3,3'-Benzophenonetetracarboxylic dianhydride, 2,2 ', 3,3'
-Biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride,
2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone Dianhydride, 1,1-bis (2,3
-Dicarboxyphenyl) ethane dianhydride, bis (2,2
3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride,
2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1, 2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2, 7,8-phenanthrene tetracarboxylic acid dianhydride and the like can be mentioned.

Further, the polyimide according to the present invention does not cause any problem even if it contains other aromatic diamine in the range of 0 to 30% as long as the characteristics of the heat resistant adhesive sheet are not impaired.
Examples of diamines that can be partially substituted include, for example, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, bis (3-aminophenyl) sulfide, and (3- Aminophenyl) (4-aminophenyl) sulfide, bis (4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, (3-aminophenyl) (4-aminophenyl) sulfoxide, bis (3-aminophenyl) Sulfone, (3-aminophenyl) (4-aminophenyl) sulfone, bis (4-aminophenyl) sulfone, 3,3′-diaminobenzophenone, 3,4′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3 , 3'-diaminodiphenylmethane, 3, 4 '
-Diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,3'-
Diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] methane, 1,1-bis [4- (3- Aminophenoxy) phenyl] ethane, 1,1-bis [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4 −
(4-aminophenoxy) phenyl] ethane, 2,2-bis [4- (3-aminophenoxy) phenylpropane,
2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,2-bis [3- (3-aminophenoxy) Phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoro Propane, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4'-bis (3- Aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy)
Biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy)
Phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfoxide, bis [4- (aminophenoxy) phenyl] sulfoxide, bis [4-
(3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone,
Bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3- Bis [4- (3-aminophenoxy) benzoyl] benzene, 4,4-bis [3- (4-aminophenoxy) benzoyl] diphenyl ether, 4,
4-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-
α, α-Dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, bis [4
-{4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4 -Aminophenoxy) -α, α-dimethylbenzyl] benzene and the like.

Further, in the present invention, in order to obtain a polyimide forming a heat resistant adhesive sheet capable of bonding at low temperature / low pressure, the following formula (1) is used for the purpose of sealing the end of the reactive polymer. , [Chemical 8]

[0017]

[Chemical 8] (In the formula, Z is a monocyclic aromatic group, a condensed polycyclic aromatic group,
A dicarboxylic acid anhydride represented by a divalent group selected from the group consisting of non-condensed polycyclic aromatic groups in which aromatic groups are connected to each other directly or by a crosslinking member) is used.

Examples of the dicarboxylic acid anhydride used as the terminal blocking agent include phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride and 2,3-dicarboxyphenylphenyl. Ether anhydride, 3,4-dicarboxyphenylphenyl ether anhydride, 2,3-biphenyldicarboxylic acid anhydride, 3,4-biphenyldicarboxylic acid anhydride, 2,3
-Dicarboxyphenyl phenyl sulfone anhydride, 3,4
-Dicarboxyphenyl phenyl sulfone anhydride, 2,3
-Dicarboxyphenyl phenyl sulfide anhydride,
1,2-naphthalenedicarboxylic acid anhydride, 1,8-naphthalenedicarboxylic acid anhydride, 1,2-anthracene dicarboxylic acid anhydride, 2,3-anthracene dicarboxylic acid anhydride, and 1,9-anthracene dicarboxylic acid anhydride Can be mentioned. These dicarboxylic acid anhydrides may be substituted with a group having no reactivity with amines or dicarboxylic acid anhydrides.

The reaction for forming the polyimide (or polyimide varnish) according to the present invention is usually carried out in an organic solvent. Examples of the organic solvent used in this reaction include N-
Methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, N, N-diethylacetamide, N, N-dimethylmethoxyacetamide, dimethylsulfoxide , Pyridine, dimethyl sulfone, hexamethylphosphoramide, tetramethylurea, N-methylcaprolactam, ptyloractam, tetrahydrofuran, m-dioxane, p-dioxane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether,
1,2-bis (2-methoxyethoxy) ethane, bis2
-(2-methoxyethoxy) ethyl ether, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane,
Pyridine, picoline, dimethyl sulfoxide, dimethyl sulfone, O-cresol, m-cresol, p-cresol, cresylic acid, p-chlorophenol, anisole and the like can be mentioned.

The heat-resistant adhesive sheet of the present invention can be obtained by synthesizing a polyimide varnish by the following method, then coating and drying on one side or both sides of the polyimide supporting substrate. The coating polyimide varnish is manufactured as follows. (1) After synthesizing a polyamic acid, a polymer molecule end is sealed with a dicarboxylic acid anhydride and chemically imidized with an imidizing agent. The resulting reaction mixture is discharged into a poor solvent such as methanol under strong stirring, and the precipitate is dried. Method of Dissolving This Polyimide in a Solvent for Dissolving This to Form a Polyimide Varnish for Coating (2) After synthesizing a polyamic acid, the polymer molecule ends are sealed with a dicarboxylic acid anhydride, and thermal imidization is performed by heating. The resulting reaction mixture is discharged into a poor solvent such as methanol under strong stirring, and the precipitate is dried. Method of Dissolving This Polyimide in a Solvent for Dissolving it to Form a Polyimide Varnish for Coating (3) After synthesizing a polyamic acid, the terminal of the polymer molecule is sealed with a dicarboxylic acid anhydride, and thermal imidization is performed by heating. Method in which the obtained reaction mixture is directly used as a polyimide varnish for coating Further, the above method (3) can be performed by the following method. (A) After synthesizing a polyamic acid, the polymer molecule end is sealed with a dicarboxylic acid anhydride, a ring-closing catalyst is added, and thermal imidization is performed, and water produced by imidization is N-methyl-2-pyrrolidone generated by a nitrogen stream. And the solvent are distilled off together with the reaction solvent. (B) After synthesizing the polyamic acid, the ends of the polymer molecules are sealed with a dicarboxylic acid anhydride, a ring-closing catalyst and an azeotropic solvent such as xylene are added, and then heated and heated to carry out thermal imidization. Water produced by imidization is distilled off by azeotropic distillation with xylene or the like and nitrogen stream. (C) Diamine and tetracarboxylic acid dianhydride are added all at once and stirred for a short time, then dicarboxylic acid anhydride, ring-closing catalyst,
Add an azeotropic solvent and start heating. Thermal imidization is performed while simultaneously progressing the synthesis of the polyamic acid, the blocking of the polymer molecule ends, and the azeotropic distillation of the generated water.

The amount of the aromatic tetracarboxylic dianhydride used is 0.8 to 0.999 mol per mol of APB, and the amount of the aromatic dicarboxylic anhydride used is the molar amount of APB and tetracarboxylic dianhydride. When the number difference is a, it is preferable to use a mole number of 2a or more and 8a or less.

If the number of moles of the aromatic tetracarboxylic dianhydride used is less than 0.8 moles per mole of APB, the degree of polymerization of the polymer is not sufficient and heat resistance is impaired. If it exceeds, it will be difficult to seal the polymer end, and adhesion at low temperature / low pressure will be impossible. Further, when the amount of the aromatic dicarboxylic acid anhydride used is less than 2 amol, the polymer is not sufficiently blocked at the end, and the adhesion becomes difficult at low temperature / low pressure, and when it exceeds 8 amol, the heat resistance is impaired. .

Particularly preferably, the amount of the aromatic tetracarboxylic dianhydride to be used is 0.9 to 1 mol of APB.
The amount of the aromatic dicarboxylic acid anhydride used is 3a to 6a mol, where a is the difference in the number of used mols of APB and aromatic tetracarboxylic dianhydride.
In addition, the concentration during polyamic acid synthesis is usually 15 to 35%.
In the range of. It is particularly preferably 20 to 30%.

When the synthesis of the polyamic acid is completed and then the amidation is carried out in the reactor, the reaction temperature for producing the polyamic acid is usually 60 ° C. or lower, preferably 30 ° C. or higher and 50 or higher. It is below ℃. Further, the reaction pressure is not particularly limited, and it can be sufficiently carried out at normal pressure. The reaction time varies depending on the type of tetracarboxylic dianhydride used, the type of solvent, the reaction temperature, etc., and usually the reaction is performed for a time sufficient to complete the production of polyamic acid. Usually, the reaction is performed for 2 to 24 hours. Thus, the logarithmic viscosity (measurement is N-methyl-2
-0.5% concentration in pyrrolidone, 35 ° C) is 0.3-
1.5 dl / g of polyamic acid is obtained.

When the obtained polyamic acid is chemically imidized, an acid anhydride such as acetic anhydride, propionic anhydride, or benzoic anhydride is used as a chemical imidizing agent. In the imidization reaction in this case, if necessary, pyridine,
There is no problem even if a tertiary amine such as γ-picoline, imidazole or triethylamine is added as a base catalyst. When chemically imidizing, the reaction temperature is usually from room temperature to 2
The temperature is 00 ° C or lower, preferably 100 ° C or lower than room temperature, and the reaction time of 0.5 to 24 hours is sufficient.

On the other hand, in the case of subjecting the obtained polyamic acid to thermal imidization, a tertiary amine such as pyridine, γ-picoline, imidazole or triethylamine is usually added as a ring-closing catalyst as an essential component. The water produced by this thermal imidization is removed by azeotropic removal from the system by adding an azeotropic solvent such as toluene or xylene to the reaction system.
It does not matter which method is used to remove the reaction solvent such as methyl-2-pyrrolidone or the like out of the system by a nitrogen stream.
The reaction temperature in this case can be from 80 ° C. to the reflux temperature of the solvent used at that time, but preferably 100 ° C. to 200 ° C. A particularly preferred reaction temperature is 150 ° C to 195 ° C. The reaction time may be in the range of 1 hour to 24 hours. Particularly preferably 3 hours to 10
It's time.

The above is a method on the premise that the polyamic acid is synthesized and then transferred to imidization. As described in (c) above, diamine and tetracarboxylic dianhydride are added in a reaction solvent. After being suspended or dissolved in, the dicarboxylic acid anhydride, the ring-closing catalyst and the azeotropic solvent were all added at the stage where the synthesis of the polyamic acid did not proceed sufficiently,
There is no problem even if the method of starting the heating and heating is adopted. The reaction temperature and reaction time in this case are 150 to 195 as above.
C., 3 to 10 hours are preferable. In the case of this method, the synthesis of polyamic acid, the blocking of the polymer molecule ends, and the azeotropic distillation of the produced water proceed simultaneously.

When chemical imidization or thermal imidization is carried out in the reactor, a method may be employed in which the imidization is not completed and the polyamic acid is left in the range of 0.1 to 10%. This is because the remaining polyamic acid changes into stable polyimide in the drying step after coating on the polyimide supporting substrate. By leaving a small amount of polyamic acid, it is possible to increase the adhesion to the copper foil and the storage stability (precipitation resistance) of the polyimide varnish. Further, as a method for increasing the precipitation resistance, it is effective to adopt a copolymerization method by using two kinds or several kinds of tetracarboxylic acid dianhydride.

The polyimide varnish thus obtained is coated on one or both sides of a polyimide supporting substrate and dried to produce a heat resistant adhesive sheet. When the adhesive layer is a single-sided adhesive sheet on one side, it can be used for coverlay film and lead frame fixing tape,
On the other hand, when the adhesive layer is a double-sided adhesive sheet having both sides, it can be used for a multilayer flexible substrate, a bond ply for rigid flex, and an adhesive tape for lead-on-chip. As the polyimide support substrate, any of commercially available products such as Kapton (Toray-Dupont), Apical (Kanebuchi Kagaku), and Upilex (Ube Industries) may be used. The thickness of the polyimide support substrate is usually 5 to 20.
Use a 0 micron object. If the thickness is less than 5 μm, the film tends to be broken, which makes it difficult to handle. On the other hand, a film exceeding 200 μm is not suitable for a coverlay film application requiring folding resistance. Particularly preferably, it is 10 to 50 microns. Further, in order to increase the adhesiveness with the adhesive layer after drying, physical treatment such as matting treatment or electrical treatment such as plasma or corona treatment may be applied to the polyimide supporting substrate.

The coating and drying of the polyimide varnish are carried out by combining the coating and initial drying by a usual coater dryer and the subsequent drying by the main dryer. As the coater dryer, any of a commonly used comma coater, die coater, triple reverse, and wire bar may be used. Depending on the coating method, the final thickness of the adhesive layer should be 1-5
In order to adjust the thickness to 0 micron, a coater drier coats a polyimide varnish with a resin content of 15 to 30% to a thickness of 10 to 400 microns, and gradually raises the drying temperature in the temperature range of 90 to 180 ° C to 3 to 15 The initial drying is performed for a period of time of some minutes, the residual solvent in the adhesive layer is adjusted to 25% or less, and the adhesive layer is wound while being dried until tack-free. .

Next, the temperature is raised stepwise by the dryer and finally dried at a temperature not lower than the glass transition temperature of the polyimide forming the adhesive layer, and the residual solvent of the adhesive layer is 1.
It is 0% or less. Since the glass transition temperature of the polyimide forming the adhesive layer of the adhesive sheet of the present application is 175 to 200 ° C., a final drying temperature of about 240 ° C. can be adopted, but the final temperature is usually set to increase the drying efficiency. Two
Dry to 50 to 400 ° C. In this case, there is no problem in performance even if a far infrared heater is used supplementarily.

When a double-sided adhesive sheet is produced, the first side is coated with a coater dryer and the initial drying is performed, then the second side is coated with the same method, and the initial drying is performed. Final dry on both sides simultaneously. When the initial drying is performed after coating the second surface side, the adhesive layer on the first surface side, which has a property of easily tacking with 10% to 30% of the solvent remaining, is inevitably formed on the roll in the coater dryer. Since they come into contact with each other, they tend to stick to the roll. In particular, the present inventors have found that this problem is likely to occur when the adhesive layer on the first surface side has a large amount of residual solvent and the second surface side is dried at a high temperature for a long time. As measures against this, 1) sufficiently dry after the first side coating, and 2) dry after the second side coating at a relatively low temperature and a short time within a range where the residual solvent is 25% or less. To do. As another measure against the trouble caused by this tack, a method of continuously drying both surfaces after coating on the second surface without contacting the roll can be adopted. That is, one method is to coat the second surface side, balance the air volumes from above and below with a floating dryer, and convey the coated polyimide support substrate in a floating state to 90-1.
It is a method of continuously drying in a temperature range of 80 ° C, and the other is to install an unwinding / winding device at intervals of 3 to 5 m and prepare a drying device in which a drying furnace is installed during this period, This is a method in which after coating the second surface side with an attached coater part, the film is continuously wound while applying tension so that the film does not sag, and continuously dried in a temperature range of 90 to 180 ° C.

With regard to the dryer, in the production of a single-sided adhesive layer type product, an ordinary drying oven in which the polyimide supporting base material side is brought into contact with the roll and conveyed can be used, and a temperature of 250 to 400 ° C. Dry in the range. On the other hand, when manufacturing a double-sided adhesive layer type product, it is preferable to dry in a temperature range of 250 to 400 ° C. using the two-type double-sided non-contact drying furnace in view of the above tack problem.

In the present invention, a polyimide varnish whose polymer molecular ends are sealed and which has already been imidized is used as a coating varnish. Conventionally, a polyamic acid varnish is generally coated on a polyimide supporting substrate and dried. It is a method of imidizing at times. The major differences in performance between the final products of these two methods are described below.

When the polyamic acid varnish is used as a coating varnish, after coating, imidization and removal of the solvent are carried out while drying on the polyimide supporting substrate. We have found that the flowability of the adhesive layer when the product is hot pressed onto a flexible wiring board becomes insufficient, resulting in insufficient adhesive strength. In addition, when imidization is carried out on the polyimide supporting substrate, water generated by imidization tends to cause foaming and surface defects. As a result, they have found that the solder heat resistance after lamination tends to be insufficient.

On the other hand, when the polyimide varnish of the present invention in which the polymer molecule ends are sealed and which has already been imidized is used as the coating varnish, it is a simple step of simply removing the solvent, and the above-mentioned polyamic acid varnish is used. Since there is no problem of cross-linking or surface defects seen in the case of 1, the adhesive strength to the flexible wiring board and the solder heat resistance after lamination are extremely good.

The heat-resistant adhesive sheet according to the present invention can be laminated with a flexible wiring board using an ordinary electrothermal press to obtain an adhesive strength of 0.7 kg / cm or more as the adhesive strength with the glossy surface of the copper foil. This value of 0.7 kg / cm itself is a value that was difficult to obtain by the conventional method, but according to the present invention, 0.7 kg / cm
Instead of easily obtaining cm, as shown in the examples below, 0.9 kg / cm, and in some cases 1.1 kg / c
It is possible to obtain a surprisingly high adhesive strength of m.

A pressing temperature of 210 to 230 ° C. is sufficient because the glass transition temperature of the thermoplastic polyimide forming the adhesive layer is as low as 175 to 200 ° C. Note that 23
The product after lamination has no problem in performance even at 0 ° C or higher, but since it has excellent performance, the maximum temperature of repeated use of the silicone cushion material that is often used when laminating a coverlay film on a flexible wiring board is 230 ° C.
Therefore, the maximum pressing temperature is 230 ° C (2
If the press is performed at a temperature over 30 ° C, the life of the press will be extremely reduced). The heat-resistant adhesive sheet according to the present invention is excellent in that it can be laminated in the temperature range in which this general-purpose silicone cushion material can be repeatedly used.

The pressing pressure is usually in the range of ^{20 to} 75 kg / cm ² . If it is less than 20 kg / cm ² , the development of the adhesive force will be delayed and the embedding property will be deteriorated. On the other hand, 75k
When the pressure exceeds g / cm ² , the life of the silicone cushion material is shortened. The pressing is performed for 2 to 60 minutes after reaching a predetermined temperature of 210 to 230 ° C. Usually, a sufficient adhesive force can be obtained in 5 to 20 minutes. In the case of a commercially available thermosetting type cover lay film, a relatively long time (one hour or more) is required because the B-stage adhesive layer needs to be cured during pressing, but the thermoplastic adhesive layer according to the present invention is used. In the case of an adhesive sheet containing a cover lay film having the above, essentially only the time sufficient for fusion bonding is required.
It excels in productivity because it requires only a short press for about a minute. In addition, the polyimide constituting the adhesive layer in the present invention is 23
The elastic modulus at 0 ° C. is sufficiently small, for example, 10 ³ dynes / cm ² or less. Therefore, when the copper foil is hot-pressed and laminated at 230 ° C., it sufficiently flows so that sufficient adhesive strength can be obtained.

When the cover lay film is laminated on the flexible wiring board, a set construction includes a stainless steel plate, a silicon cushion material, a polyimide release film,
The method of laying up the cover lay film, the flexible wiring board, the polyimide release film, the silicon cushion material, and the stainless steel plate in this order is excellent in terms of adhesive strength and dimensional change of the flexible wiring board due to lamination.

Polyimide generally tends to absorb moisture, and the same applies to the adhesive layer of the adhesive sheet of the present invention. According to the examination results by the present inventors, high adhesive strength to the copper foil is exhibited by predrying the adhesive sheet to reduce the water content of the adhesive layer. Therefore, the coverlay film should be 100-150 in advance.
It is preferable to carry out preliminary drying for 0.5 to 5 hours in the temperature range of [deg.] C. before transferring to the laminate. Usually 120-130
Drying at 0.5 ° C. for about 0.5 hours is sufficient.

[0042]

EXAMPLES The present invention will now be described in more detail with reference to examples. Example 1 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1802.9g were charged, and it stirred and melt | dissolved in nitrogen atmosphere at room temperature. 308.5 g of ODPA with stirring
(0.995 mol) was added in portions and the temperature was raised to 50 ° C.
Stir for hours. After that, 4.434 g of phthalic anhydride
(0.03 mol) was added and stirring was continued at 50 ° C. for another 2 hours. The polyamic acid thus obtained had an inherent viscosity of 0.69 dl / g (measured with N-methyl-2-
0.5% concentration in pyrrolidone at 35 ° C.).

40 parts of acetic anhydride was added to the above polyamic acid solution.
8 g (4.0 mol) and γ-picoline 186.2 g (2.
(0 mol) was added dropwise and stirring was continued at room temperature for 10 hours. The obtained reaction mixture was discharged into 10 kg of methanol under strong stirring, and the precipitate was separated by furnace. The obtained powdery precipitate was further washed with methanol and then dried at 150 ° C. for 12 hours to obtain 556.4 g of polyimide powder (yield 9
8.5%). The glass transition temperature of the obtained polyimide powder was 177 ° C. (measured by DSC). 500 g of the polyimide powder thus obtained was dissolved in 1500 g of N-methyl-2-pyrrolidone (concentration 25%) to obtain a polyimide varnish for coating.

As a polyimide supporting base material, a 25-micron-thick apical (manufactured by Kanebuchi Kagaku Co., Ltd.) having a matte surface on one side was used, and the above-mentioned polyimide varnish was continuously coated with a thickness of about 100 micron by an ordinary coater dryer. The drying was performed while gradually increasing the temperature. 90
As a result of drying at ˜140 ° C. for a residence time of about 5 minutes, the residual solvent in the adhesive layer was about 20%. When this was further dried with this dryer at about 300 ° C,
The residual solvent was 0.3% and the thickness of the adhesive layer was 25 microns.

The coverlay film thus obtained is
After drying at 130 ° C for 30 minutes, BHY-13-T, 1 Oz
It was laminated on a glossy surface of copper foil (made by Nikko Kouseki). For the lamination, an ordinary electric heat press is used. After being set in the press at room temperature, a pressure of 50 kg / cm ² is applied, the temperature starts to rise at a set temperature of 230 ° C., and after reaching the predetermined temperature, 20
Press for minutes. When this laminated product was evaluated, the adhesive strength to the copper foil glossy surface was 0.9 kg / cm (3 m
m width, 90 degree peel) was extremely high. Also, it passed the solder float test at 288 ° C. for 10 seconds (the test method is IPC-TM-650, 2.4.13).

Example 2 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1802.9g were charged, and it stirred and melt | dissolved in nitrogen atmosphere at room temperature. 308.5 g of ODPA with stirring
(0.995 mol) was added in portions and the temperature was raised to 50 ° C.
Stir for hours. After that, 4.434 g of phthalic anhydride
(0.03 mol) was added and stirring was continued at 50 ° C. for another 2 hours. Γ was added to the polyamic acid solution thus obtained.
93.1 g (0.1 mol) of picoline was charged, and the temperature was increased by heating while stirring under a nitrogen stream. The water generated by the imidization reaction was removed to the outside of the system while the temperature was rising. After the temperature was raised to 180 ° C., thermal imidization was carried out for 5 hours, and during that time, the produced water and the reaction solvent carried by the nitrogen stream were partially removed outside the system. After carrying out the thermal imidization for 5 hours, the heating was stopped, the mixture was cooled to room temperature with stirring for about 2 hours, and then the stirring was continued for 10 hours.

The viscosity of the obtained polyimide varnish is 100.
It was a poise (E type viscometer, 25 ° C). Logarithmic viscosity was 0.55 dl / g (measurement was carried out by diluting a part of polyimide varnish with N-methyl-2-pyrrolidone,
% Concentration, 35 ° C. ). The glass transition temperature by DSC was 175 ° C. Using the polyimide varnish of the reaction mixture obtained in this example as a varnish for direct coating, a coverlay film was produced in the same manner as in Example 1, and laminated with a copper foil glossy surface at 230 ° C. with an electric heating press. . When evaluated in the same manner as in Example 1, the adhesive strength was 1.1 kg / cm, and the solder float test was also passed.

Example 3 A polyamic acid varnish with a polymer terminal blocked was synthesized in the same manner as in Example 2, and γ-picoline was added to 93.1.
g (0.1 mol) and 601 g of xylene were charged, and the mixture was heated and heated with stirring under a nitrogen stream. While the temperature was rising, water generated by the imidization reaction was removed out of the system as an azeotrope with xylene. After the temperature was raised to 180 ° C., thermal imidization was carried out for 5 hours, and water produced during the heating, xylene and N-methyl-2.
-The azeotrope of pyrrolidone was removed out of the system.

The polyimide varnish of the reaction mixture obtained in this example was used as a varnish for direct coating in Example 1.
A coverlay film was produced by the same method as in (1) and laminated with a copper foil glossy surface at 230 ° C. with an electric heat press.
When evaluated in the same manner as in Example 1, the adhesive strength was 1.0 kg / cm and the solder float test passed.

Example 4 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1802.9g were charged, and it stirred and melt | dissolved in nitrogen atmosphere at room temperature. 308.5 g of ODPA with stirring
(0.995 mol) was charged all at once and then stirred for 30 minutes. 4.434 g of phthalic anhydride in the obtained suspension
(0.03 mol), 93.1 g (0.1 mol) of γ-picoline and 601 g of xylene were all charged, and the mixture was heated and heated while stirring under a nitrogen stream. While the temperature was rising, water generated by the imidization reaction was removed from the system while azeotroping with xylene. After the temperature was raised to 180 ° C., thermal imidization was performed for 5 hours, and during that time, part of the generated water, xylene, and the reaction solvent carried by the nitrogen stream were removed to the outside of the system. After carrying out the thermal imidization for 5 hours, the heating was stopped, the mixture was cooled to room temperature with stirring for about 2 hours, and then the stirring was continued for 10 hours.

The polyimide varnish of the reaction mixture obtained in this example was used as a varnish for direct coating in Example 1.
A coverlay film was produced by the same method as in (1) and laminated with a copper foil glossy surface at 230 ° C. with an electric heat press.
When evaluated in the same manner as in Example 1, the adhesive strength was 0.9 kg / cm, and the solder float test was also passed.

Comparative Example 1 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1802.9g were charged, and it stirred and melt | dissolved in nitrogen atmosphere at room temperature. 308.5 g of ODPA with stirring
(0.995 mol) was added in portions and the temperature was raised to 50 ° C.
Stir for hours. After that, 4.434 g of phthalic anhydride
(0.03 mol) was added and stirring was continued at 50 ° C. for another 4 hours. The polyamic acid thus obtained had an inherent viscosity of 0.69 dl / g (measured with N-methyl-2-
0.5% concentration in pyrrolidone at 35 ° C.). In this way, a varnish not imidized, that is, using the obtained polyamic acid as a coating varnish, a coverlay film was produced in the same manner as in Example 1, and a copper foil glossy surface and Laminated at ° C.
When evaluated in the same manner as in Example 1, it passed the solder float test, but had an adhesive strength of 0.6 kg /
It was only cm.

Comparative Example 2 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1802.9g were charged, and it stirred and melt | dissolved in nitrogen atmosphere at room temperature. 308.5 g of ODPA with stirring
(0.995 mol) was added in portions and the temperature was raised to 50 ° C and 4
Stir for hours. The polyamic acid thus obtained had an inherent viscosity of 0.68 dl / g (measured with N-methyl-2-
0.5% concentration in pyrrolidone at 35 ° C.).

Varnish not imidized in this way,
That is, a coverlay film was produced in the same manner as in Example 1 using the obtained polyamic acid as a coating varnish. After drying, surface defects due to foaming were found on the surface of the adhesive layer. 230 with copper foil glossy surface with electric heat press
Laminated at ° C. When evaluated in the same manner as in Example 1, the adhesive strength was as low as 0.45 kg / cm, and swelling occurred in the solder float test.

Example 5 A was placed in a vessel equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1838.4g were charged, and the mixture was stirred at room temperature under a nitrogen atmosphere and dissolved. While stirring, BTDA320.59
g (0.995 mol) was added in portions, the temperature was raised to 50 ° C., and the mixture was stirred for 1 hour. After that, 4.434 g of phthalic anhydride
(0.03 mol) was added and stirring was continued at 50 ° C. for another 2 hours. 93.1 g (0.1 mol) of γ-picoline was charged into the thus obtained polyamic acid solution, and the mixture was heated and heated with stirring under a nitrogen stream. The water generated by the imidization reaction was removed to the outside of the system while the temperature was rising. After the temperature was raised to 180 ° C., thermal imidization was carried out for 5 hours, and during that time, the produced water and the reaction solvent carried by the nitrogen stream were partially removed outside the system. After carrying out the thermal imidization for 5 hours, the heating was stopped, the mixture was cooled to room temperature with stirring for about 2 hours, and then the stirring was continued for 10 hours. The viscosity of the obtained polyimide varnish was 60 poise (E type viscometer, 25 ° C.). Logarithmic viscosity was 0.55 dl / g (measurement was carried out by using a part of the polyimide varnish as N-methyl-2-
Diluted with pyrrolidone and performed at 35% at 0.5% concentration. ). The glass transition temperature by DSC was 190 ° C.

The polyimide varnish of the reaction mixture obtained in this example was used as a varnish for direct coating in Example 1.
A coverlay film was produced by the same method as in (1) and laminated with a copper foil glossy surface at 230 ° C. with an electric heat press.
When evaluated in the same manner as in Example 1, the adhesive strength was 1.0 kg / cm and the solder float test passed.

Comparative Example 3 A was placed in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube.
PB292.2g (1.0 mol) and N-methyl-2-pyrrolidone 1838.4g were charged, and the mixture was stirred at room temperature under a nitrogen atmosphere and dissolved. While stirring, BTDA320.59
g (0.995 mol) was added in portions, the temperature was raised to 50 ° C., and the mixture was stirred for 4 hours. Using the obtained polyamic acid as a coating varnish, a coverlay film was produced in the same manner as in Example 1, and a copper foil glossy surface and
Laminated at 0 ° C. When evaluated in the same manner as in Example 1, the solder float test passed,
The adhesive strength was only 0.4 kg / cm.

Example 6 A polyimide varnish was synthesized in the same manner as in Example 2,
Using the reaction mixture as a varnish for direct coating, the following double-sided adhesive tape (bond ply) was produced. That is, using a 25-micron apical (manufactured by Kanegafuchi Chemical Co., Ltd.) that has been subjected to a matte treatment on both sides, a first coat side is usually coated with a thickness of about 100 microns by a coater dryer, and the temperature is increased stepwise to 90-130. About 1 in the temperature range of ℃
After drying for a residence time of 5 minutes, the second surface side is also coated with a thickness of about 100 microns to 60-1.
It was dried in the temperature range of 20 ° C. so that the residence time was about 6 minutes. Further, it was dried in a floating dryer in a temperature range of 160 to 270 ° C. under a non-contact condition on both sides so that the residence time was about 20 minutes.

The residual solvent in the adhesive layer of the obtained bond ply was 0.5% on average. The thickness of each adhesive layer was 25 μm. The bond ply thus obtained is dried at 130 ° C. for 30 minutes, and then BHY-13-T, 1 Oz copper foil (manufactured by Nikko Kouseki Co., Ltd.) is set on the top and bottom of the bond ply and laminated on the glossy surface of the copper foil. did. For lamination, an ordinary electric heat press machine was used. After being set in the press machine at room temperature, a pressure of 50 kg / cm ² was applied, the temperature started to rise at a set temperature of 230 ° C., and pressing was performed for 20 minutes after reaching the predetermined temperature. . When this laminated product was evaluated, the adhesive strength to the glossy surface of the copper foil was 1.0 kg / cm on the first surface side and 0.9 kg / cm on the second surface side.

Example 7 A double-sided adhesive tape (bond ply) was produced in the same manner as in Example 6 by synthesizing a polyimide varnish in the same manner as in Example 5 and using the reaction mixture as a direct coating varnish. The residual solvent in the adhesive layer of the obtained bond ply was 0.6% on average. The thickness of each adhesive layer was 24 μm. When the bond ply thus obtained was pressed and evaluated in the same manner as in Example 6, the adhesive strength to the glossy surface of the copper foil was 0.9 kg / cm for both the first surface side and the second surface side. .

[0061]

The heat-resistant adhesive sheet of the present invention is an all-polyimide heat-resistant adhesive sheet comprising a thermoplastic polyimide adhesive layer and a polyimide supporting substrate, and the glass transition temperature of the adhesive layer is 200 ° C. or lower and the temperature is high. Since it has a particularly excellent flowability at the time, it can be adhered to an adherend at a low temperature in a short time. Moreover, unlike the thermosetting type, there is no problem of life due to B-stage, and it is easy to handle.

The heat-resistant adhesive sheet according to the present invention is used for a coverlay film and a lead frame fixing tape when the adhesive layer is on one side, and a multilayer flexible substrate or a bond ply for rigid flex when the adhesive layer is on both sides. It is also extremely useful as an adhesive tape for lead-on-chip.

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Claims (13)

[Claims] 1. A polymer molecule terminal is represented by the following formula (1): [Chemical Formula 1] (In the formula, Z is selected from the group consisting of a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which aromatic groups are connected to each other directly or by a bridging member. A dicarboxylic acid anhydride represented by the formula (2) (In the formula, Y is the formula (3) or [Chemical Formula 3], and X is a direct bond, -CO- or -O-). A heat-resistant adhesive sheet formed by forming a thermoplastic polyimide adhesive layer made of a polymer having a repeating unit represented by on one side or both sides of a polyimide supporting substrate. 2. The heat-resistant adhesive sheet according to claim 1, wherein the dicarboxylic acid anhydride represented by the formula (1) is phthalic anhydride. 3. The heat resistance according to claim 1, wherein a polyimide having a glass transition temperature of 200 ° C. or lower is used as an adhesive layer and can be adhered by fusing to an adherend during hot pressing at 230 ° C. Adhesive sheet. 4. The heat-resistant adhesive sheet according to claim 1, which has a bond strength of 0.7 kg / cm or more with a glossy surface of a copper foil when laminated by hot pressing at 230 ° C. 5. The heat resistant adhesive sheet according to claim 1, wherein the adhesive layer is a polyimide having an elastic modulus at 230 ° C. of 10 ³ dyne / cm ² or less. 6. The polyimide supporting substrate has a thickness of 5 to 200.
The heat-resistant adhesive sheet according to claim 1, wherein the adhesive layer has a thickness of 1 to 50 microns. 7. A polyimide varnish obtained by taking out polyimide, which is a polymer having a polymer molecule terminal blocked with a dicarboxylic acid anhydride, as a polyimide powder, and dissolving and containing it in a solvent that dissolves the polyimide powder. The method for producing a heat-resistant adhesive sheet according to claim 1, wherein the adhesive layer is formed by casting and coating on the sheet and drying. 8. A varnish comprising a reaction mixture obtained by end-capping a polyamic acid and subsequent thermal imidization is directly cast on a polyimide supporting substrate and then dried to form an adhesive layer. A method for producing the heat-resistant adhesive sheet described. 9. The adhesive layer is formed by directly casting a reaction mixture, which does not complete imidization and leaves polyamic acid in a range of 0.1 to 10%, directly on a polyimide supporting substrate and then drying. Of the heat-resistant adhesive sheet of. 10. The method for producing a heat-resistant double-sided adhesive sheet according to claim 7, wherein the varnish is cast on both surfaces of the polyimide supporting substrate and then dried to form an adhesive layer. 11. A coater dryer is used to cast and coat the first side with the initial drying, and then, a similar method is cast to the second side to carry out the initial drying, and then the final drying is performed on both sides simultaneously with the main dryer. The method for producing a heat-resistant double-sided adhesive sheet according to claim 10, wherein 12. In order to prevent the adhesive layer on the first surface side from tacking on the roll in the coater dryer during the initial casting by casting on the second surface side, (1) drying on the first surface side is performed. After the residual solvent is sufficiently reduced at a high temperature for a long time, the second surface side is subjected to casting coating and initial drying, and the second surface side is dried at a relatively low temperature and a short time, or (2 The method for producing a heat-resistant double-sided adhesive sheet according to claim 11, wherein after the casting and coating on the second surface side, the both surfaces are continuously dried without contact. 13. The method for producing a heat-resistant double-sided adhesive sheet according to claim 11, wherein when the final drying is performed on both sides simultaneously with the present dryer, the both sides are continuously dried without contact.