Polyimide composite film

Details Polyimide composite film Polyimide composite film

1999-05-10

2001-11-20

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S215000, C428S458000, C428S473500

Reexamination Certificate

active

06319597

ABSTRACT:

FIELD OF THE INVENTION
This invention relates a polyimide composite film favorably employable for preparing a heat-resistant metal foil/polyimide film composite.
BACKGROUND OF THE INVENTION
An aromatic polyimide film shows a high heat resistance as well as good electric characteristics, and is widely employed as material for electronic devices such as an electronic camera, a personal computer, and a liquid crystal display. For instance, the aromatic polyimide film is bonded to a copper foil via an adhesive such as an epoxy resin to produce a flexible printed circuit (FPC) or a substrate for tape automated bonding (TAB). Although the aromatic polyimide film is highly heat resistant, the conventional adhesive such as an epoxy resin has poor heat resistance. Accordingly, it is a problem that the produced copper foil/adhesive/polyimide film composite does not show satisfactory heat resistance.
In order to produce a copper foil/polyimide film composite having a high heat resistance, a number of improvements have been proposed. For instance, a copper metal is electrolytically plated on a polyimide film having no adhesive layer; a polyamide acid solution is coated on a copper foil, dried and heated to imidize the coated polyamide acid; or a thermoplastic polyimide is bonded to a copper foil by thermocompression.
U.S. Pat. No. 4,543,295 describes a polyimide composite (laminate) which is produced by bonding a polyimide film to a metal foil via a polyimide adhesive.
According to studies of the present inventors, however, the bonding strength of a polyimide composite produced by the above-mentioned process is not high.
Japanese Patent Provisional Publications H4-33847 and H4-33848 describe a method of bonding a multi-layered aromatic polyimide film to a metal foil by thermocompression. This process appears to be disadvantageous in that it requires a considerably high temperature and a high pressure for the thermocompression procedure. In particular, a temperature of higher than 300° C. is required in a continuous process for firmly bonding a multi-layered polyimide film to a metal foil. Such a high temperature is disadvantageous because the continuous process generally employs a rubber roller which is not high in heat resistance.
Therefore, most of these known processes are not appropriately employable for continuously producing a metal foil/polyimide film composite in a long term operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an aromatic polyimide composite film which can be firmly bonded to a metal foil at a relatively low temperature such as a temperature in the range of 230 to 280° C.
It is another object of the invention to provide a metal foil/aromatic polyimide film composite which has both a high heat resistance and a high bonding strength.
It is a further object of the invention to provide a process for preparing an aromatic polyimide composite film which can be firmly bonded to a metal foil at a relatively low temperature.
It is a still further object of the invention to provide a process for preparing a metal foil/aromatic polyimide film composite which has both a high heat resistance and a high bonding strength.
This invention resides in a polyimide composite film which comprises a polyimide substrate showing such a low thermal expansion coefficient of 1×10
−5
to 2×10
−5
cm/cm/° C. in a temperature range of 50 to 200° C. and a polyimide film which is bonded to the polyimide substrate and which comprises a polyimide consisting essentially of 30 to 100 molar % of the following recurring unit (A) and 70 to 0 molar % of the following recurring unit (B):
in which R represents a tetravalent aromatic or aliphatic group and R′ represents a divalent aromatic or aliphatic group.
In the polyimide composite film of the invention, the polyimide substrate preferably comprises a polyimide consisting essentially of the following recurring unit:
wherein Ar is a unit having the formula:
in which n/m is in the range of 0/100 to 30/70.
In the polyimide composite film of the invention, the polyimide film is preferably bonded to the polyimide substrate at a bonding strength of higher than 1.3 kg/cm, which is expressed in terms of 90° peel strength. The bonding strength of higher than 1.5 kg/cm is more preferred. The polyimide substrate preferably has a thickness in the range of 5 to 150 &mgr;m and the polyimide coating film preferably has a thickness in the range of 2 to 20 &mgr;m.
The invention further resides in a metal foil/polyimide film composite which comprises a polyimide substrate showing a thermal expansion coefficient of 1×10
−5
to 2×10
−5
cm/cm/° C. in a temperature range of 50 to 200° C., a polyimide film which is bonded to the polyimide substrate and which comprises a polyimide consisting essentially of 30 to 100 molar % of the aforementioned recurring unit (A) and 70 to 0 molar % of the aforementioned recurring unit (B).
In the metal foil/polyimide film composite of the invention, the polyimide film is preferably bonded to the polyimide substrate at a bonding strength of higher than 1.5 kg/cm in terms of 90° peel strength and the metal foil is preferably bonded to the polyimide film at a bonding strength of higher than 1.0 kg/cm, more preferably 1.3 kg/cm, in terms of 90° peel strength.
The invention further resides in a polyimide film comprising a polyimide consisting essentially of 30 to 100 molar % of the aforementioned recurring unit (A) and 70 to 0 molar % of the aforementioned recurring unit (B).
The invention furthermore resides in a process for preparing a polyimide composite film of the invention, which comprises the steps of:
coating a solution of a polyamide acid which gives a polyimide consisting essentially of 30 to 100 molar % of the aforementioned recurring unit (A) and 70 to 0 molar % of the aforementioned recurring unit (B), on a film of a polyamide acid which gives a polyimide substrate showing a thermal expansion coefficient of 1×10
−5
to 2×10
−5
cm/cm/° C. in a temperature range of 50 to 200° C.; and
heating the polyamide acid film and the coated polyamide acid solution together to give a polyimide composite film.
Furthermore, the invention resides in a process for preparing a metal foil/polyimide film composite of the invention which comprises the steps of:
coating a solution of a polyamide acid which gives a polyimide consisting essentially of 30 to 100 molar % of the aforementioned recurring unit (A) and 70 to 0 molar % of the aforementioned recurring unit (B), on a film of a polyamide acid which gives a polyimide substrate showing a thermal expansion coefficient of 1×10
−5
to 2×10
−5
cm/cm/° C. in a temperature range of 50 to 200 C.;
heating the polyamide acid film and the coated polyamide acid solution together to give a polyimide composite film;
placing a metal foil on the polyimide film prepared from the coated polyamide acid solution; and
bonding the metal foil to the polyimide film by a hot melt method.
DETAILED DESCRIPTION OF THE INVENTION
The polyimide substrate of the polyimide composite film of the invention is made of an aromatic polyimide having a thermal expansion coefficient of 1×10
−5
to 2×10
−5
cm/cm/° C. in a temperature range of 50 to 200° C. Such aromatic polyimide can be an aromatic polyimide prepared from a combination of 3,4,3′,4′-biphenyltetracarboxylic dianhydride (hereinafter referred to as s-BPDA) and p-phenylenediamine (hereinafter referred to as PPD), or an aromatic polyimide prepared from a combination of pyromellitic dianhydride/3,4,3′,4′-biphenyltetracarbonic dianhydride (or/benzophenonetetracarboxylic dianhydride) and p-phenylenediamine or p-phenylenediamine/4,4′-diaminodiphenyl ether (hereinafter referred to as DADE). In the case of using a combination of PPD and DADE, a molar ratio of DADE/PPD preferably is in the range of 0/100 to 85/15. The polyimide of the polyimide substrate can be prepared by random polymerization

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