JPS6268852A - Improved polyimide film - Google Patents

Abstract

PURPOSE:To obtain a polyimide film having improved runnability and adhesivity and suitable for flexible printed circuit sheet, etc., by adding a specific amount of a specific inorganic powder to a polyimide film resin, thereby generating controlled protrusions on the surface without lowering the original physical properties. CONSTITUTION:A polyimide film resin is compounded with 0.1-0.5wt% (based on the resin) inorganic powder consisting of the group IIa alkaline earth metal orthophosphate [preferably anhydrous dibasic calcium phosphate (CaHPO4) or calcium pyrophosphate (Ca2P2O7)] and composed mainly of particles having diameter of 1-5mum.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a heat-resistant polyimide film, and more specifically, the present invention relates to a heat-resistant polyimide film, and more specifically, the present invention relates to a heat-resistant polyimide film, and more specifically, by adding inorganic fine powder, fine protrusions are generated on the surface and the surface condition is changed. The present invention relates to a polyimide film that has improved running properties and adhesion properties.

(Prior art and problems) Polyimide films are known to have excellent properties such as heat resistance, cold resistance, chemical resistance, electrical insulation properties, and mechanical strength. Widely used as a base film for flexible printed wiring boards. One of the important practical properties of polyimide films used in these applications is runnability (slipability). In various film processing processes, by ensuring the ease of slipping between the film support (for example, a roll) and the film, as well as the slipperiness between the films, it improves operability and handling in each process, and furthermore film 1
The occurrence of defective areas such as wrinkles can be avoided. On the other hand, in flexible printed wiring board applications, which are the main uses of polyimide films, they are usually bonded to copper foil through various adhesives. ) Adhesion to copper foil is often insufficient due to stability, and currently adhesives are applied to polyimide films by surface treatment (alkaline treatment, corona treatment, sandbranut treatment, etc.).

As a result of intensive research into these market demands, the inventor of the present invention has found that
We have discovered an improved polyimide film that simultaneously improves runnability (slidability) and adhesion, and have arrived at the present invention.

With conventional polyester film slipping technology,
Inert inorganic compounds (e.g. silica, clay, titania, etc.) and organic compounds (e.g. calcium terephthalate,
A method of forming protrusions on the film surface by adding a high melting point polyester) and/or using catalyst residue has been adopted. Furthermore, a polyester film to which an inert inorganic compound has been added is stretched uniaxially or biaxially while heating to increase the number of protrusions formed on the surface and to adjust the height of the protrusions. . These methods actively generate protrusions on the surface to reduce the coefficient of friction on the film surface, thereby obtaining an easier-to-slide effect. It is effective to generate many protrusions. In this case, the more inorganic or organic fine particles or catalyst residue particles are added to the resin, the more the number of protrusions on the surface increases, but on the other hand, this leads to a decrease in the mechanical strength of the film. There is a problem of increasing non-uniformity in quality.

(Means for Solving the Problems) The present invention provides a method in which the particle size is strictly controlled and the particle size is 1 to . 5 μm
The content is a polyimide film made by uniformly dispersing 0.1 to 0.5% by weight of inorganic powder based on the weight of the resin in the film resin, without deteriorating its mechanical properties and other physical properties. By reducing the coefficient of friction on the film surface while maintaining the physical properties of polyimide film, which requires a high degree of reliability as a material for electronic components, we have discovered that controlled protrusions can be generated on the surface of polyimide. This improves the slipperiness of the polyimide film, enables fine control of surface roughness, and improves the adhesive strength when bonding the polyimide film to the copper foil via an adhesive. The present invention will be explained in detail below.

As mentioned above, in conventional techniques for improving runnability in polyester films, inert inorganic compounds (e.g., silica, clay, titania, etc.) or organic compounds (e.g., calcium terephthalate, high melting point polyester) are added, or ( (and) catalyst residue is used to form protrusions on the film surface, whereas the present invention focuses on controlling the fine protrusions on the surface or the surface roughness, and uses inorganic powder with an extremely controlled particle size distribution. By using a film, protrusions are formed on the film surface, the surface roughness is adjusted, and the film runnability and the adhesive strength with the copper foil via the adhesive are simultaneously improved.

In the formation of protrusions on the surface of a polyester film, the protrusions are increased and adjusted by stretching under heat in the -axis or biaxial direction, whereas in the present invention, protrusions on the surface of an unstretched polyimide film can be controlled. It is possible. In addition, for polyimide films, which have a problem of low tear resistance (pulling strength) due to their physical properties, adding inorganic powder will essentially form tear initiation points, which will significantly affect the film's physical properties. Although there is a concern about a wide decline, the present invention has solved this problem by finding a particle size range for the additive powder that does not affect the physical properties of the film and is effective in forming protrusions on the surface.

The polyimide film to which the present invention is applicable refers to a chemical substance containing aromatic tetracarboxylic dianhydride, aromatic diamine, or both as main components, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl Using a varnish-like polyamic acid solution that is addition-polymerized in a polar solvent such as nulphoxide or n-methylpyrrolidone,
After mixing the varnish-like polyamic acid solution and a dehydration cyclization reagent containing acetic anhydride as a main component, casting the mixture onto a support and special holiday;
This film is obtained by a chemical conversion method in which solvent removal and imide ring closure are simultaneously performed by preliminary drying on a support and heating at high temperature under restraint. Further, the varnish-like polyamic acid solution is reacted with the dehydration cyclization reagent to completely or partially close the imide ring while maintaining the varnish state, and then the varnish-like polyimide solution is cast onto a support. Also included in the polyimide film to which the present invention can be applied is a film formed by preliminary drying on a support and heating at high temperature under restraint to perform solvent removal and imide ring closure.

The inorganic fine powder added to the resin to form protrusions on the film surface of the present invention needs to be inert to all chemicals that come into contact with it in the polyimide film manufacturing process, It also needs to be insoluble. As a result of extensive studies, the present inventor found that group IIa alkaline earth metals (Be, Mg, Ca).

It has been found that the orthophosphate compound of SrJ and Ra ) is chemically and physically stable in the varnish composition and the polyimide film, and does not affect the physical properties of the polyimide film. More preferably, dibasic calcium phosphate anhydride (CaHPO4) or (and) calcium pyrophosphate (Ca2P2O7) is used as the orthophosphate compound powder of an alkaline earth metal of the Ra group.
Uniform dispersibility in the varnish solution and the polyimide film is good. That is, in the present invention, it is chemically and physically stable in the varnish solution and the polyimide film, has good dispersibility and is dispersed extremely uniformly, and is chemically stable throughout the polyimide film manufacturing process. It is essential to use a physically stable inorganic powder in order to form fine protrusions on the surface of the polyimide film without affecting or changing the physical properties of the polyimide film.

In the present invention, the particle size of the inorganic powder added to form protrusions on the surface of the polyimide film is mainly 1 to 5 μm. When it is in the range of 1 μm or more and 5 μm or less, the amount of inorganic powder added can be adjusted arbitrarily without causing a decrease in the mechanical properties of the polyimide film, and the formation of protrusions on the film surface (film surface fine control of roughness) is possible. That is, usually 7.
Adding inorganic particles with a large particle size exceeding 5 μm to a polyimide film used in the thickness range of 5 μm to 125 μm is effective for forming protrusions on the film surface, but This is equivalent to physically damaging the film, reducing its mechanical strength. In addition, the addition of inorganic particles with a particle size of less than 1 μm has little effect on the mechanical properties of the film, but it forms protrusions on the surface of a size that is effective for improving runnability (slipability) and adhesion. Therefore, if an inorganic powder containing a large amount of particles with a particle size of less than 1 μm is used, the amount added will increase unnecessarily.

According to the present invention, when the inorganic powder is added to the polyimide film, the amount added is 0.000000000000000 000000 per the weight of the film resin.
When added in a range of 1 to 0.5% by weight, it is effective in improving running properties (slip properties) and adhesive properties. That is, when the amount of inorganic powder added is in the range of 0.1 to 0.5% by weight based on the weight of the film resin, the properties of the polyimide film are not changed and the uniformity of the film is maintained. , a polyimide film with excellent running properties (slip properties) and adhesive properties can be obtained. When the amount of inorganic powder added is less than 0.1% by weight based on the weight of the film resin, the number of protrusions formed on the film surface is small, and the effect of improving runnability (slipability) and adhesion is low. low. In addition, if it exceeds 0.5% by weight,
Although it has the effect of improving runnability (slidability) and adhesiveness, it becomes difficult to uniformly disperse the inorganic powder in the film resin, and the homogeneity of various physical properties of the polyimide film is impaired.

In the present invention, sufficient runnability (slipability) is obtained as a practical characteristic.
This is a case where the coefficient of dynamic friction is 0.50 or less as measured based on .

In the present invention, by adding the above-mentioned inorganic powder, desired protrusions are formed on the film surface, and the adhesive strength when bonded to copper foil via an adhesive is improved. Focusing on the surface roughness of the film surface.

When expressed as line average roughness, Ra>, the surface roughness of the film when no inorganic powder is added is Ra-0,006
-0.012 μm, whereas the effect of improving adhesion is expressed when the surface roughness of the film is Ra≧≧ by adding inorganic powder and forming protrusions on the film surface. 0.018, and a practically sufficient adhesive strength is obtained when Ra≧0.025 μm. Further, as the Ra value increases, the adhesiveness also improves, but when the Ra value exceeds 0.055 μm, it becomes difficult to further improve the adhesiveness. The surface roughness of the film can be arbitrarily controlled by adjusting the amount of inorganic powder added. That is, the surface of the film can be roughened by adding inorganic powder, and the same effect as the conventional method of improving adhesive force by roughening the adhesive surface by sandblanut treatment or the like can be obtained. Furthermore, in order to uniformly roughen the film surface, it is necessary to use inorganic powder with extremely controlled particle size distribution.

The method for measuring physical properties in the present invention is as follows.

(a) Measurement of film surface roughness Measured using a stylus type surface roughness measuring device based on JIS B-0601r surface roughness. The cut-off value in the case of measuring the Ra (center line average roughness) value is 0.25 mm.

(b) Film mechanical strength (tensile strength, elongation rate) AST
Measured with an autograph device according to MD-882-80.

(c) Friction coefficient (Uk: dynamic friction coefficient) ASTM
D-1894-68, measured in the machine direction of the film.

(d) Adhesive strength JIS C-6481 (1976) Printed circuit copper clad laminate test method Section 5.7 Based on peel test, polyimide film and copper foil were bonded with epoxy/nylon adhesive and heated at 160°C. After curing for 12 hours, the film surface was fixed on a hard plate and measured.

(e) Particle size distribution of inorganic powder Powder dispersed in an electrolyte solution (eg, isotone) was measured using a Coulter Counter TAi type with an aperture diameter of 23 μm.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

Comparative Example I Approximately equal moles of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether were reacted in N,N-dimethylformamide to obtain a varnish-like polyamic acid solution.

Thereafter, the polyamic acid solution was converted into polyimide using a continuous film forming apparatus and simultaneously dried and solidified to obtain a polyimide film having a nominal thickness of 25 μm.

Examples 1 to 2 A varnish-like polyamic acid solution obtained using the same raw materials and the same method as in Comparative Example 1 was added with an anhydrous second solution having an average particle size of 2.5 μm from which particles less than 1 μm and 5 μm or more were removed. Calcium phosphate (CaHPO4) or calcium hapyrophosphate (Ca2P2Oy) was added in an amount of 0.1% by weight based on the weight of the film resin, and after thorough stirring and dispersion, the same method as in Comparative Example 1 was used to form a film with a nominal thickness of 25 μm. A polyimide film was obtained.

Examples 3 to 6 Using the same raw materials as in Comparative Example 1 and the same inorganic powder as in Example 1, the amount of inorganic powder added to the varnish-like polyamic acid solution was 0.0. 2% by weight and 0.5% by weight, respectively, using the same method as Comparative Example 1.
A polyimide film with a nominal thickness of 5 μm was obtained.

Comparative Examples 2 to 3 Anhydrous dibasic calcium phosphate having a particle size distribution of 0.1 to 25 μm and an average particle size of 11.3 to 12.0 μm was added to a varnish-like polyamic acid solution obtained using the same raw materials and the same method as Comparative Example 1. (CaHPO4) or calcium pyrophosphate (Ca2P2O7) per weight of film resin, 0
．． After adding 2% by weight and sufficiently stirring and dispersing, a polyimide film having a nominal thickness of 25 μm was obtained in the same manner as in Comparative Example 1.

Comparative Examples 4 to 5 Using the same raw materials as Comparative Example 1 and the same inorganic powder as Example 1, the amount of powder added to the varnish-like polyamic acid solution was 0.7 per film weight. % by weight, and polyimide films with a nominal thickness of 25 μm were obtained in the same manner as in Comparative Example 1.

Table 1 shows the mechanical properties, running properties, and adhesive evaluation results of the polyimide films obtained in Examples 1 to 6 and Comparative Examples 1 to 5.

(Effect) As is clear from Table 1, inorganic powder mainly having a particle size of 1 to 5 μm was added by 0.1 to 0.5 weight i per film resin weight.
%, the polyimide film of the present invention retains the physical properties inherent to polyimide, and also makes the surface slippery, thereby significantly improving adhesiveness. Therefore, it can be suitably used in a wide range of fields such as flexible printed wiring board applications.

(Margin below) Q

Claims (4)

[Claims] (1) A polyimide film containing 0.1 to 0.5% by weight of inorganic powder mainly having a particle size of 1 to 5 μm, based on the weight of the film resin. (2) The polyimide film according to claim 1, wherein the inorganic powder is an orthophosphate of a group IIa alkaline earth metal. (3) The polyimide film according to claim 2, wherein the group IIa alkaline earth metal orthophosphate is dicalcium phosphate anhydride (CaHPO_4). (4) The polyimide film according to claim 2, wherein the orthophosphate of the group IIa alkaline earth metal is calcium pyrophosphate (Ca_2P_2O_7).