Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-04-12
2002-12-03
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S125000, C528S128000, C528S172000, C528S173000, C528S174000, C528S176000, C528S179000, C528S183000, C528S188000, C528S220000, C528S229000, C528S353000
Reexamination Certificate
active
06489431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a novel polyimide and a polyimide precursor (polyamic acid) as a precursor thereof, useful as e.g. protective films and insulating films for liquid crystal display devices and semiconductor devices, and as optical waveguide materials for optical communication, excellent in transparency at not only a visible region but also an ultraviolet region even after baking at a high temperature of from 270° C. to 350° C, and having characteristics such as a low dielectric constant, a low birefringence and a high heat resistance.
2. Background Art
Wholly aromatic polyimide are insoluble in a solvent in general, and by coating a polyimide precursor as a precursor thereof on a substrate by e.g. casting or spin coating, followed by heating at a high temperature, a desired polyimide can be obtained. All such heat resistant aromatic polyimides present deep amber and are colored in general.
Polyimides are widely used as protective materials or insulating materials for liquid crystal display devices and semiconductor devices by virtue of the high mechanical strength, heat resistance, insulating properties and solvent resistance. They are used also as optical waveguide materials for optical communication. However, developments in these fields have been remarkable in recent years, and increasingly high levels of properties have been required for the materials to be used in such fields. Namely, they are expected not only to be excellent in heat resistance, but also to have various performances depending upon application.
In recent years, protective materials and insulating materials for liquid crystal display devices and semiconductor devices are required not only to have a heat resistance but also to maintain transparency at not only a visible region but also an ultraviolet region after baking at a high temperature of from 270° C. to 350° C., or to have a low birefringence and a low dielectric constant when formed into a coating film in some cases.
For example, with respect to a buffer coating material as a protective film for a specific semiconductor device, in order to erase memory errors generated during preparation of the element, through-holes are formed by utilizing lithography technology for electrical erasion, and such makes the process complicated. If the buffer coating material has transparency to ultraviolet light, optical erasion by UV irradiation alone becomes possible without formation of through-holes, and the process can be simplified. In such a case, great absorption of ultraviolet light is fatal. Further, in a field of specific optical waveguide materials, materials having not only a high heat resistance but also a small birefringence and a high transparency at an ultraviolet region are desired.
As one method for realizing transparency at a visible region, it is well known to obtain a polyimide precursor by a polycondensation reaction of an aliphatic tetracarboxylic dianhydride with a diamine, followed by imidizing said precursor to produce a polyimide, whereby a polyimide which is relatively less colored and is excellent in transparency can be obtained (JP-B-2-24294, JP-A-58-208322).
It is certain that when a polyimide is prepared by such a known method using an aromatic diamine as a diamine, a polyimide having excellent transparency at a visible region in the vicinity of 400 nm will be obtained, but a great absorption will usually appear at an ultraviolet region in the vicinity of 300 nm, where electron transition absorption of an aromatic ring is present. Further, many of aliphatic tetracarboxylic dianhydrides have a low reactivity in general, and it is thereby difficult to obtain a polymer having a high degree of polymerization unless structurally suitable one is selected.
Further, as a method to reduce absorption at not only a visible region but also an ultraviolet region and to present a coating film having a low birefringence, a polyimide consisting of a combination of an aliphatic tetracarboxylic dianhydride with a specific aliphatic diamine has been proposed (W. Folksen et al., Reactive & Functional polymer, vol. 30, Page 61, 1996). It is certain that a polyimide consisting of this combination is excellent in transparency at not only a visible region but also an ultraviolet region, but a coating film tends to be yellow by baking at a high temperature in the vicinity of 300° C., and is poor in heat resistance. Further, basicity of an aliphatic diamine is high as compared with that of an aromatic diamine, and accordingly the aliphatic diamine tends to form a salt with a carboxylic acid generated during polymerization, whereby it is difficult to control solubility, and polymerization may not proceed in some cases, and thus it is difficult to say the method is common.
DISCLOSURE OF THE INVENTION
Under these circumstances, the present invention has been made to provide a novel polyimide excellent in transparency at not only a visible region but also ultraviolet region after baking at a high temperature of from 270° C. to 350° C., and having characteristics such as a low dielectric constant, a low birefringence and a high heat resistance.
The present inventors have conducted extensive studies to overcome the above problems and as a result, found that a polyimide obtained by imidizing a polyimide precursor comprising a specific diamine having cyclobutanetetracarboxylic dianhydride and a hexafluoropropylidene group in its molecule can achieve the above object. The present invention has been accomplished on the basis of the above discovery.
Namely, the present invention relates to a polyimide precursor having a repeating unit represented by the following general formula (1):
(wherein R
1
is a bivalent organic group constituting a diamine), wherein R
1
contains a bivalent organic group constituting a diamine having a hexafluoropropylidene group in its molecule represented by the following general formula (2):
(wherein A is a hydrogen atom, a linear alkyl group including a methyl group, or a trifluoromethyl group, and n is the number of a substituent on an aromatic ring and an integer of from 1 to 4), and the reduced viscosity is from 0.05 to 5.0 dl/g (in N-methylpyrrolidone at a temperature of 30° C., concentration: 0.5 g/dl), and further relates to a polyimide having a repeating unit of the general formula (3):
(wherein R
1
is the same as in the above formula (2)) which is obtained by imidizing said precursor.
Now, the present invention will be explained in further detail below.
A tetracarboxylic component to be used to obtain the polyimide precursor represented by the above general formula (1) of the present invention is cyclobutanetetracarboxylic acid, its dianhydride and its dicarboxylic acid diacid halide.
The diamine component may, for example, be 2,2-bis(3-aminophenyl)hexafluoropropane, 2,2-bis(4-methyl-3-aminophenyl)hexafluoropropane, 2,2-bis(4,5-dimethyl-3-aminophenyl)hexafluoropropane, 2,2-bis(4-trifluoromethyl-3-aminophenyl)hexafluoropropane, 2,2-bis(4,5-bistrifluoromethyl-3-aminophenyl)hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(3-methyl-4-aminophenyl)hexafluoropropane, 2,2-bis(2,3-dimethyl-4-aminophenyl)hexafluoropropane, 2,2-bis(3-trifluoromethyl-4-aminophenyl)hexafluoropropane or 2,2-bis(2,3-bistrifluoromethyl-4-aminophenyl)hexafluoropropane. They may be used alone or in combination as a mixture of two or more of them.
In order to achieve the effects of the present invention, preferably from 70 mol % to 100 mol % of a polyimide precursor consisting of the above combination is contained so as to obtain the effects of the present invention remarkably also.
As the other tetracarboxylic dianhydride components, tetracarboxylic dianhydrides and their derivatives, commonly used for synthesis of a polyimide, can be used without any problem.
Specific examples thereof include alicyclic tetracarboxylic acids such as 1,2,3,4-cyclopentanetetracarboxylic acid, 2,3,4,5-tetrahydrofurantetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 3,4-dicarboxy-1-cyclohexyl
Fukuro Hiroyoshi
Ishii Kazuhisa
Nihira Takayasu
Hampton-Hightower P.
Nissan Chemical Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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