CA1314517C - Polyimide film having improved adhesive properties - Google Patents
Polyimide film having improved adhesive propertiesInfo
- Publication number
- CA1314517C CA1314517C CA000527950A CA527950A CA1314517C CA 1314517 C CA1314517 C CA 1314517C CA 000527950 A CA000527950 A CA 000527950A CA 527950 A CA527950 A CA 527950A CA 1314517 C CA1314517 C CA 1314517C
- Authority
- CA
- Canada
- Prior art keywords
- film
- polyimide film
- corona discharge
- polyimide
- discharge treatment
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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- Treatments Of Macromolecular Shaped Articles (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
- Facsimile Scanning Arrangements (AREA)
- Light Guides In General And Applications Therefor (AREA)
- Optical Elements Other Than Lenses (AREA)
- Light Sources And Details Of Projection-Printing Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed herein is a polyimide film produced by forming a film from a raw material having incorporated therein a finely divided inorganic powder that forms minute projections on the film surface and subsequently subjecting the film to corona discharge treatment.
According to this invention, it is possible to obtain a heat-resistant polyimide film having improved adhesive properties and uniform bond strength. The film does not cause blocking when wound into a roll.
Polyimide film finds general use as electrical insulation film, heat insulation film and base film for flexible printed circuit boards.
Disclosed herein is a polyimide film produced by forming a film from a raw material having incorporated therein a finely divided inorganic powder that forms minute projections on the film surface and subsequently subjecting the film to corona discharge treatment.
According to this invention, it is possible to obtain a heat-resistant polyimide film having improved adhesive properties and uniform bond strength. The film does not cause blocking when wound into a roll.
Polyimide film finds general use as electrical insulation film, heat insulation film and base film for flexible printed circuit boards.
Description
13~4~17 POLYIMIDE FILM I~AVING IMPROVED AD~IESIVE PROPERTIES
BACKGROUND OF THE I~VENTION
1. Field of the Invention:
The present invention relates to a heat-resistant polyimide film, and more particularly, it relates to a polyimide film having improved adhesive properties which i5 produced by forming a film from a raw material having incorporated therein a finely divided inorganic powder that forms minute projections on the film surface and subsequently sub~ecting the film to corona discharge treatment.
BACKGROUND OF THE I~VENTION
1. Field of the Invention:
The present invention relates to a heat-resistant polyimide film, and more particularly, it relates to a polyimide film having improved adhesive properties which i5 produced by forming a film from a raw material having incorporated therein a finely divided inorganic powder that forms minute projections on the film surface and subsequently sub~ecting the film to corona discharge treatment.
2. DescriPtion of the Prior Art:
It is known that polyimide film has good heat resistance, low temperature resistance, chemical resistance, electrical insulation properties, and mechanical strength, and other good properties. It finds general use as electrical insulation film, heat insulation film, and base film for flexible printed circuit boards. A polyimide film as the base film for a flexible printed circuit board is bonded to a copper foil with an adhesive. Often the bonding is poor on account of the chemical structure and high chemical (solvent) resistance of polyimde film. At present, this drawback is mitigated by subjecting polyimide film to surface treatment such as alkali treatment, corona discharge treatment and sandblasting.
The conventional alkali treatment or sandblasting encounters some problems because it has to be performed separately after the film-making step and requires the additional steps of washing and drying. All this reduces productivity, increases production cost, and impairs stable production. In contrast, corona discharge treatment has an advantage over the above-mentioned two methods of treatment. It has long been used to improve the printability of paper and plastics moldings, and it can be easily performed in-line on the film-making machine because it requires only a simple apparatus.
The present inventors investigated corona discharge treatment as a means of improving the adhesive properties of polyimide film. As a ~..
13145~7 r~sult, it w<l~ f`o~lnd tilat corona discharee treatment has a slight effect in the c.lse of polyimide film with a s-nooth surface produced by casting from a raw material contaillillg no inorganic fine particles. However, the adhes;ve strength which is slightly improved by corona discharge treatment is however generally low and uneven on the film surface. It was also found that the corona-treated film causes blocking when it is wound into a roll and that the blocking is accompanied by organic decomposition products which presumably result from the corona discharge treatment. All this indicates that the corona discharge treatment is not completely practical.
SUMM RY OF THE INVENTION
The present invention provides a heat-resistant polyimide film having improved adhesive properties.
The present invention also provides a heat-resistant polyimide film having improved adhesive properties, said film having uniform adhesive strength on the film surface and not being subject to blocking when it is wound into a roll.
Other and further features and advantages of the invention will appear more fully from the following description.
In order to achieve the above-mentioned object, the present inventors carried out research which led to the finding that a polyimide film having practically improved adhesive properties can be obtained by producing a polyimi~e film from a raw material having incorporated therein a finely divided inorganic powder which forms minute projections on the film surface and subseqùently subjecting the film to corona discharge ereatment. The present invention was completed on the basis of this finding.
DETAILED DESCRIPTION OF THE INVFNTION
According to this invention, the polyimide film is produced from a raw material having incorporated therein a finely divided inorganic powder which forms minute projections on the film surface and the film is subjected to corona discharge treatment.
~ 3 ~
The polyimide film of this invention is one which is obtained from a raw material composed solely or mainly of aromatic tetracarboxylic acid dianhydride and aromatic diamine.
It is one feature of this invention to use a polyimide film having minute projections on the film surface. Such projections can be formed by incorporating in the polyimide film a finely divided inorganic powder. The inorganic powder must be stable chemically and physically throughout the entire process of producing the polyimide film. In addition, it should not adversely affect the physical properties of the polyamide film and the characteristic properties required for the application in which the polylmide film is used. With this in mind, a proper selection should be made with respect to the kind, particle size, and amount to be added. Examples of chemical compounds as the inorganic powder include SiO2, TiO2, CAHP04, and Ca2P207. The inorganic powher should be selected from electrically insulating materials meeting the above-mentioned requirements.
The particle size of the inorganic powder should not be larger than 100 ~m in particle diameter, preferably not smaller than 1 ~m and not larger than 5 ~m. An inorganic powder having large particle size (in excess of 5 ~m) is not desirable for polyimide film which usually has a thickness of 7.5 to 125 ~m, because it forms such large projections on the film surface that it decreases the mechanical strength of the resulting film. On the other hand, an excessively fine inorganic powder having a particle diameter smaller than 1 ~m does not form projections of adequate size required for the improvement of adhesive properties by corona discharge treatment (mentioned later), although it has little effect on the mechanical properties of the polyimide film. The amount of the inorganic powder to be added varies depending on the type of chemical _--compound. In the case of CAHP04, for example, it is about 0.05 to 0.5 wt% based on the weight of the film. Too small an amount of the inorganic powder does not form projections sufficient for the improvement of adhesive properties. An excessive amount of the inorganic powder does not uniformly disperse in the polyimide resin and consequently causes the properties of the polyimide film to fluctuate. The inorganic powder should be added in the process of polyimide film production while the 13145~7 polyimide resin or a precursor thereof is still fluid, in such a rnanner that a uniform dispersion is ensured.
The polyimide film of this invention has improved runnability because the minute projections formed on the film surface reduce the film-to-film or film-to-object contact area and consequently reduce the coefficient of friction of the film surface. According to the conventional technology, the improvement in runnability was achieved by using an inert inorganic or organic compound or catalyst residues that form projections on the film surface.
The polyimide film having projections on the surface thereof formed by the addition of inorganic powder is subjected to corona discharge treatment for improvement of adhesive properties. The electric power for corona discharge treatment may be properly selected. It is preferably not lower than 20 W min/m2 and more preferably not lower than 50 W min/m2. Corona discharge treatment with an electric power lower than 20 W min/m2 is not enough to impart sufficient adhesive strength to polyimide film as the base film for flexible printed circuit boards.
Rlectric power in excess of 500 W min/m2 decomposes the resin on the film surface and adversely affects the film properties. The treatment with such high electric power can only be carried out at a sacrifice of production speed. Therefore, it is not practical from the view point of productivity and production cost.
The polyimide film of this invention having surface projections is more uniform and stable in adhesive properties than the smooth polyimide film without surface projections. This is because it has good runnability as mentioned above. In other words, the polyimide film having good runnability can receive uniform corona discharge treatment because it runs smoothly without wrinkles. Conventional polyimide film, which is poor in runnability, does not undergo uniform corona discharge treatment because it runs unsmoothly and wrinkles upon contact with the film guide rolls and corona discharge roll.
According to this invention, the polyimide film with surface projections is superior in adhesive properties to a polyimide film with a smooth surface. The reason for this is presumed as follows: It is generally believed that the outermost resin layer taking part in adhesion 131~17 has a weak boundary layer (abbreviated as WBI. hereinafter) which inhibits adhesion. This is true of polyimide film. The W~L is closely related to the lower resin layer, and it is thin on the layer formed on the projections. On the other hand, not only does the corona discharge treatment modify the surface through the introduction of oxygen-containing groups, but it also substantially removes the WBL.
Therefore, the WBL formed on the surface projections is effectively removed by corona discharge treatment and the interface effective for adhesion is exposed. Thus, the film as a whole has good adhesive properties.
Polyimide film having a smooth surface causes blocking, and organic decomposition products are deposited on the blocked surface, when wound into a roll after corona discharge treatment; whereas the polyimide film of this invention with surface proJections does not cause blocking.
Presumably, this is because the projections greatly reduce the film-to-film contact area, permitting the diffusion of organic decomposition products resulting from the corona discharge treatment.
According to the present invention, it is possible to improve the adhesion of polyimide film to copper foil, which has been a problem when polyimide film is applied to its major application, flexible printed circuit boards. The polyimide film of this invention is also improved in runnability. Thus, the present invention is of great industrial value for the production and use of polyimide film.
The invention is now described in more detail with reference to the Z5 following examples, which are not intended to limit the scope of this invention.
The physical properties in the examples were measured according to the following methods. ~--(a) Kinetic coefficient of friction (Uk) of film: Measured in the machine direction according to ASTM D-1894-63, as an index of film runnability.
(b) Adhesion strength: Measured according to JIS C-6481 (1976), Section 5.7 (method of testing the copper-clad laminate for printed circuit board). A specimen of polyimide film is bonded to a copper foil with an epoxy~nylon adhesive.
S
~31~
After curing at 1600C for 12 hollrs, the peel test was conducted, with the film fixed onto a hard board.
A polyimide film having a nominal thickness of 25 ym was prepared from a polyimide of the following formula produced from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether.
0, 0 Il 11 -O ~ N ~ N ~
O O (n = 5 to 500) COMPARATIVE EX~MPLE 2 0.15 wt% (based on resin) of anhydrous calcium secondary phosphate (CaHP04) having a particle size distribution of 1 to 5 ~m, with an average particle diameter of 2.0 ~m was incorporated in a polyiMide of the same formula as in Comparative Example 1. The resu].ting polyimide was made lnto a polyimide film with surface projections and having a nominal thickness of 25 ~
The same polyimide film as in Comparative Example 1 was subjected to corona discharge treatment at 100 W :nintm2 to give a treated polyimide film.
EXA~PLES 1 to 6, COMPARATIVE EXA~PLE 4 The same polyimide film as in Comparative Example 2 was subjected to corona discharge treatment at 5 to 400 W min/m2 to give treated polyi.~.ide films.
~. .
131~517 The polyimicle films obtained in Comparative l~xampl.es 1 to 4 and Examples 1 to 6 were exami.ned for bond strength and kinetic coefficient of fri.ction They were also examined for the presence or absence of organic decomposition products deposited on the film surface. The results are sho~n in Table 1.
It is apparently noted from Table 1 that the polyimide films having incorporated therein an inorganic powder and subjected to corona discharge treatment are remarkably improved in adhesive properties as compared with the polyimide film which does not include an inorganic powder and is not subjected to corona discharge treatment. The polyimide films in the examples are suitable for flexible printed circuit boards and many other applications.
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~,
It is known that polyimide film has good heat resistance, low temperature resistance, chemical resistance, electrical insulation properties, and mechanical strength, and other good properties. It finds general use as electrical insulation film, heat insulation film, and base film for flexible printed circuit boards. A polyimide film as the base film for a flexible printed circuit board is bonded to a copper foil with an adhesive. Often the bonding is poor on account of the chemical structure and high chemical (solvent) resistance of polyimde film. At present, this drawback is mitigated by subjecting polyimide film to surface treatment such as alkali treatment, corona discharge treatment and sandblasting.
The conventional alkali treatment or sandblasting encounters some problems because it has to be performed separately after the film-making step and requires the additional steps of washing and drying. All this reduces productivity, increases production cost, and impairs stable production. In contrast, corona discharge treatment has an advantage over the above-mentioned two methods of treatment. It has long been used to improve the printability of paper and plastics moldings, and it can be easily performed in-line on the film-making machine because it requires only a simple apparatus.
The present inventors investigated corona discharge treatment as a means of improving the adhesive properties of polyimide film. As a ~..
13145~7 r~sult, it w<l~ f`o~lnd tilat corona discharee treatment has a slight effect in the c.lse of polyimide film with a s-nooth surface produced by casting from a raw material contaillillg no inorganic fine particles. However, the adhes;ve strength which is slightly improved by corona discharge treatment is however generally low and uneven on the film surface. It was also found that the corona-treated film causes blocking when it is wound into a roll and that the blocking is accompanied by organic decomposition products which presumably result from the corona discharge treatment. All this indicates that the corona discharge treatment is not completely practical.
SUMM RY OF THE INVENTION
The present invention provides a heat-resistant polyimide film having improved adhesive properties.
The present invention also provides a heat-resistant polyimide film having improved adhesive properties, said film having uniform adhesive strength on the film surface and not being subject to blocking when it is wound into a roll.
Other and further features and advantages of the invention will appear more fully from the following description.
In order to achieve the above-mentioned object, the present inventors carried out research which led to the finding that a polyimide film having practically improved adhesive properties can be obtained by producing a polyimi~e film from a raw material having incorporated therein a finely divided inorganic powder which forms minute projections on the film surface and subseqùently subjecting the film to corona discharge ereatment. The present invention was completed on the basis of this finding.
DETAILED DESCRIPTION OF THE INVFNTION
According to this invention, the polyimide film is produced from a raw material having incorporated therein a finely divided inorganic powder which forms minute projections on the film surface and the film is subjected to corona discharge treatment.
~ 3 ~
The polyimide film of this invention is one which is obtained from a raw material composed solely or mainly of aromatic tetracarboxylic acid dianhydride and aromatic diamine.
It is one feature of this invention to use a polyimide film having minute projections on the film surface. Such projections can be formed by incorporating in the polyimide film a finely divided inorganic powder. The inorganic powder must be stable chemically and physically throughout the entire process of producing the polyimide film. In addition, it should not adversely affect the physical properties of the polyamide film and the characteristic properties required for the application in which the polylmide film is used. With this in mind, a proper selection should be made with respect to the kind, particle size, and amount to be added. Examples of chemical compounds as the inorganic powder include SiO2, TiO2, CAHP04, and Ca2P207. The inorganic powher should be selected from electrically insulating materials meeting the above-mentioned requirements.
The particle size of the inorganic powder should not be larger than 100 ~m in particle diameter, preferably not smaller than 1 ~m and not larger than 5 ~m. An inorganic powder having large particle size (in excess of 5 ~m) is not desirable for polyimide film which usually has a thickness of 7.5 to 125 ~m, because it forms such large projections on the film surface that it decreases the mechanical strength of the resulting film. On the other hand, an excessively fine inorganic powder having a particle diameter smaller than 1 ~m does not form projections of adequate size required for the improvement of adhesive properties by corona discharge treatment (mentioned later), although it has little effect on the mechanical properties of the polyimide film. The amount of the inorganic powder to be added varies depending on the type of chemical _--compound. In the case of CAHP04, for example, it is about 0.05 to 0.5 wt% based on the weight of the film. Too small an amount of the inorganic powder does not form projections sufficient for the improvement of adhesive properties. An excessive amount of the inorganic powder does not uniformly disperse in the polyimide resin and consequently causes the properties of the polyimide film to fluctuate. The inorganic powder should be added in the process of polyimide film production while the 13145~7 polyimide resin or a precursor thereof is still fluid, in such a rnanner that a uniform dispersion is ensured.
The polyimide film of this invention has improved runnability because the minute projections formed on the film surface reduce the film-to-film or film-to-object contact area and consequently reduce the coefficient of friction of the film surface. According to the conventional technology, the improvement in runnability was achieved by using an inert inorganic or organic compound or catalyst residues that form projections on the film surface.
The polyimide film having projections on the surface thereof formed by the addition of inorganic powder is subjected to corona discharge treatment for improvement of adhesive properties. The electric power for corona discharge treatment may be properly selected. It is preferably not lower than 20 W min/m2 and more preferably not lower than 50 W min/m2. Corona discharge treatment with an electric power lower than 20 W min/m2 is not enough to impart sufficient adhesive strength to polyimide film as the base film for flexible printed circuit boards.
Rlectric power in excess of 500 W min/m2 decomposes the resin on the film surface and adversely affects the film properties. The treatment with such high electric power can only be carried out at a sacrifice of production speed. Therefore, it is not practical from the view point of productivity and production cost.
The polyimide film of this invention having surface projections is more uniform and stable in adhesive properties than the smooth polyimide film without surface projections. This is because it has good runnability as mentioned above. In other words, the polyimide film having good runnability can receive uniform corona discharge treatment because it runs smoothly without wrinkles. Conventional polyimide film, which is poor in runnability, does not undergo uniform corona discharge treatment because it runs unsmoothly and wrinkles upon contact with the film guide rolls and corona discharge roll.
According to this invention, the polyimide film with surface projections is superior in adhesive properties to a polyimide film with a smooth surface. The reason for this is presumed as follows: It is generally believed that the outermost resin layer taking part in adhesion 131~17 has a weak boundary layer (abbreviated as WBI. hereinafter) which inhibits adhesion. This is true of polyimide film. The W~L is closely related to the lower resin layer, and it is thin on the layer formed on the projections. On the other hand, not only does the corona discharge treatment modify the surface through the introduction of oxygen-containing groups, but it also substantially removes the WBL.
Therefore, the WBL formed on the surface projections is effectively removed by corona discharge treatment and the interface effective for adhesion is exposed. Thus, the film as a whole has good adhesive properties.
Polyimide film having a smooth surface causes blocking, and organic decomposition products are deposited on the blocked surface, when wound into a roll after corona discharge treatment; whereas the polyimide film of this invention with surface proJections does not cause blocking.
Presumably, this is because the projections greatly reduce the film-to-film contact area, permitting the diffusion of organic decomposition products resulting from the corona discharge treatment.
According to the present invention, it is possible to improve the adhesion of polyimide film to copper foil, which has been a problem when polyimide film is applied to its major application, flexible printed circuit boards. The polyimide film of this invention is also improved in runnability. Thus, the present invention is of great industrial value for the production and use of polyimide film.
The invention is now described in more detail with reference to the Z5 following examples, which are not intended to limit the scope of this invention.
The physical properties in the examples were measured according to the following methods. ~--(a) Kinetic coefficient of friction (Uk) of film: Measured in the machine direction according to ASTM D-1894-63, as an index of film runnability.
(b) Adhesion strength: Measured according to JIS C-6481 (1976), Section 5.7 (method of testing the copper-clad laminate for printed circuit board). A specimen of polyimide film is bonded to a copper foil with an epoxy~nylon adhesive.
S
~31~
After curing at 1600C for 12 hollrs, the peel test was conducted, with the film fixed onto a hard board.
A polyimide film having a nominal thickness of 25 ym was prepared from a polyimide of the following formula produced from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether.
0, 0 Il 11 -O ~ N ~ N ~
O O (n = 5 to 500) COMPARATIVE EX~MPLE 2 0.15 wt% (based on resin) of anhydrous calcium secondary phosphate (CaHP04) having a particle size distribution of 1 to 5 ~m, with an average particle diameter of 2.0 ~m was incorporated in a polyiMide of the same formula as in Comparative Example 1. The resu].ting polyimide was made lnto a polyimide film with surface projections and having a nominal thickness of 25 ~
The same polyimide film as in Comparative Example 1 was subjected to corona discharge treatment at 100 W :nintm2 to give a treated polyimide film.
EXA~PLES 1 to 6, COMPARATIVE EXA~PLE 4 The same polyimide film as in Comparative Example 2 was subjected to corona discharge treatment at 5 to 400 W min/m2 to give treated polyi.~.ide films.
~. .
131~517 The polyimicle films obtained in Comparative l~xampl.es 1 to 4 and Examples 1 to 6 were exami.ned for bond strength and kinetic coefficient of fri.ction They were also examined for the presence or absence of organic decomposition products deposited on the film surface. The results are sho~n in Table 1.
It is apparently noted from Table 1 that the polyimide films having incorporated therein an inorganic powder and subjected to corona discharge treatment are remarkably improved in adhesive properties as compared with the polyimide film which does not include an inorganic powder and is not subjected to corona discharge treatment. The polyimide films in the examples are suitable for flexible printed circuit boards and many other applications.
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Claims
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A polyimide film produced by forming a polyimide film having a thickness of 7.5 to 125 µm from a raw material composed solely or mainly of aromatic tetracarboxylic acid dianhydrides and aromatic diamines, incorporating a finely divided inorganic powder selected from the group consisting of SiO2, TiO2, CaHPO4 and Ca2P2O7, having a particle size of 1 to 5 pm that forms minute projections on the surface of the film, and subsequently subjecting the film to a corona discharge treatment at 20 to 500 W.min/m2.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12683/1986 | 1986-01-23 | ||
| JP61012686A JPS62171268A (en) | 1986-01-23 | 1986-01-23 | Picture input device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1314517C true CA1314517C (en) | 1993-03-16 |
Family
ID=11812259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000527950A Expired - Fee Related CA1314517C (en) | 1986-01-23 | 1987-01-22 | Polyimide film having improved adhesive properties |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS62171268A (en) |
| CA (1) | CA1314517C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2521824B2 (en) * | 1989-12-22 | 1996-08-07 | 株式会社エンプラス | Lighting equipment |
| JP3890128B2 (en) * | 1997-10-28 | 2007-03-07 | 沖電気工業株式会社 | Reflective prism |
| US8755005B2 (en) * | 2008-09-24 | 2014-06-17 | Koninklijke Philips N.V. | Thin edge backlight with LEDS optically coupled to the back surface |
-
1986
- 1986-01-23 JP JP61012686A patent/JPS62171268A/en active Pending
-
1987
- 1987-01-22 CA CA000527950A patent/CA1314517C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62171268A (en) | 1987-07-28 |
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