JPS6268853A - Improved heat-resistant 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 dispersing a specific amount of porous silicon dioxide powder having a specific particle diameter, thereby generating controlled protrusions on the surface without lowering the original physical properties. CONSTITUTION:A polyimide film resin is compounded with 0.005-0.5wt%, preferably 0.005-0.2wt% (based on the resin) porous silicon dioxide powder composed mainly of particles having diameter of 1-5mum (preferably a porous silica gel having a pore volume of 0.4-1.7ml/g and a specific surface area of 250-350m<2>/g).

Description

[Detailed explanation of inventions] (Use of industrial use) In the present invention, a fine protrusion on the surface is generated by adding a specific porous silicon dioxide microider for further details on heat -resistant polyimide film. The present invention relates to a heat-resistant polyimide film that has improved runnability and adhesion by controlling the surface condition and improving the running properties and adhesion of the film.

(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. It is widely used as a base film for flexible printed wiring boards. One of the most 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 (e.g. roll) and the film, as well as the ease of slipping between the films, it improves operability and handling in each process, and furthermore The occurrence of defective spots such as wrinkles on the film 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 using various adhesives, but polyimide films are unique because of their chemical structure and high chemical (solvent) resistance In many cases, the adhesion to copper foil is insufficient due to the nature of the film, so at present, polyimide films are surface-treated (alkaline treatment, corona treatment, sandbranut treatment, etc.) and then bonded.

In response to these market demands, the present inventors have discovered an improved polyimide film that simultaneously achieves improvements in runnability (easiness of slipping) and adhesiveness, 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 a large number of 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. There is a problem of increasing non-uniformity.

(Another Means to Solve the Problems) In the present invention, porous silicon dioxide powder whose particle size is strictly controlled and whose main particle size is 1 to 5 μm is added to a film resin in an amount of 0.5 μm per resin weight. It has been discovered that controlled protrusions can be generated on the surface of a polyimide film containing a large amount of 0.005 to 0.5 W dispersed therein without deteriorating its mechanical properties and other physical properties. While maintaining the physical properties of polyimide film, which requires a high level of reliability as a material, by reducing the coefficient of friction on the film surface, the film's runnability (slipability) is improved, and even fine surface roughness is improved. This makes it possible to improve the adhesive strength when a polyimide film is bonded to 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) In contrast to forming protrusions on the film surface using catalyst residue, the present invention focuses on controlling fine protrusions on the surface or surface roughness, and forms a porous structure with extremely controlled particle size distribution. The use of silicon dioxide powder has the advantage of forming protrusions on the film surface, adjusting the surface roughness, and simultaneously improving the running properties of the film and the adhesive strength with the copper foil via the adhesive.

In the formation of protrusions on the surface of a polyester film, the protrusions are increased and adjusted by heating and stretching in the -axis or biaxial direction, whereas the present invention is capable of controlling the protrusions on the surface of an unstretched polyimide film. 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 discovering an additive powder and its particle size range 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 can be applied is a chemical substance containing aromatic tetracarboxylic dianhydride, aromatic diamine, or both as main components.

Using a solution of alligator-like polyamic acid subjected to addition polymerization in a polar solvent such as N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, or n-methylpyrrolidone, the main components are the alligator-like polyamic acid solution and acetic anhydride. After mixing with a dehydration cyclization reagent, the mixture is cast onto a support, pre-dried on the support, and then heated at high temperature under restraint. This is a chemical method that allows simultaneous desolvation and imide ring closure. This is a film obtained by a conversion method.

Further, the alligator-like polyamic acid solution is reacted with the dehydration cyclization reagent to completely or partially close the imide ring while maintaining the face state, and then the alligator-like polyimide solution is cast onto a support. However, the polyimide film to which the present invention can be applied also includes a film formed by preliminary drying on a support and heating under restraint at high temperature 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 the use of porous silicon dioxide (silica gel, 5i02) is chemically and physically stable in the varnish-like solution and polyimide film, and has no effect on the physical properties of the polyimide film. I found out that there are many things that can be done. More preferably, a porous silica gel in which the silicon dioxide powder has a pore volume of 0.4 to 1.70 tttl/g and a specific surface area of 250 to 850 nf/g as measured by the BET method is used. Uniform dispersibility in the solution and the polyimide film is good. That is, in the present invention, the polyimide film is chemically and physically stable in the varnish solution and the polyimide film, has good dispersibility and is dispersed extremely uniformly, and furthermore, the polyimide film It is essential to use an inorganic powder that is physically and physically stable 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 porous silicon dioxide powder added to form protrusions on the surface of the polyimide film is mainly 1 μm or more and 5 μm or less. When the porous silica gel has a distribution in which the particle size is mainly 1 μm or more and 5 μm or less, the amount of porous silicon dioxide powder added can be arbitrarily adjusted without causing a decrease in the mechanical properties of the polyimide film. This makes it possible to finely control the formation of protrusions on the film surface (film surface roughness). That is, for a polyimide film that is normally used in a thickness range of 7.5μ to 125μ, the particle size is 5μ.
Adding inorganic particles with a large particle size exceeding μm
Although it is effective in forming protrusions on the film surface, it is essentially equivalent to physically damaging the film, reducing the mechanical strength of the film. In addition, the addition of fine particles with a particle size of less than 1 μm has little effect on the mechanical properties of the film, but it improves runnability (slipability) on the surface.
Moreover, when an inorganic powder containing a large amount of particles with a particle size of less than 1 μm is used, it is impossible to form protrusions of a size effective for improving adhesion, and the amount of addition increases unnecessarily. Therefore, in the present invention, it is essential to use porous silicon dioxide powder having an extremely sharp particle size distribution in the range of 1 to 5 μm from the viewpoint of chemical stability and improved physical properties.

According to the present invention, when the porous silicon dioxide powder is added to the polyimide film in an amount of 0.005 wt% or more and 0.5 wt% or less based on the weight of the film resin, It is effective in improving slipperiness and adhesion. More preferably, the amount of the powder added is 0.005 wt % or more, 0.2 wt % or more, based on the weight of the film resin.
When the amount is within the range of wt% or less, a polyimide film with excellent runnability (slipability) and adhesiveness can be obtained without changing the physical properties of the polyimide film and maintaining the uniformity of the film. That is, if the amount of the powder added is less than 0.005wt1 per weight of film resin, the number of protrusions formed on the film surface is small, and the effect of improving runnability (slipability) and adhesion is low. . In addition, if the amount of the powder added exceeds 0.5 wtq6 per weight of the film resin, there is an effect of improving runnability (slipability) and adhesion, but the amount of the powder in the film resin is Uniform dispersion becomes difficult, and the homogeneity of various physical properties of the polyimide film is impaired.

In the present invention, sufficient running properties (sliding properties) can be obtained as a practical property when the coefficient of dynamic friction is 0.50 or less as measured based on ASTM D-1894-63.

In the present invention, by adding the above-mentioned porous silicon dioxide powder, desired protrusions are formed on the film surface, and the adhesive strength when bonded to copper foil via an adhesive is improved. When the surface roughness of the film surface is expressed as the center line average roughness (Ra), the surface roughness of the film when the powder is not added is Ra = 0.006 to 0.012 pm (
In contrast, the effect of improving adhesion is expressed when the surface roughness of the film is Ra≧0.018 by adding the powder and forming protrusions on the film surface.
In this case, practically sufficient adhesive strength can be obtained when Ra≧0.025 μm. Also, Ra
As the Ra value increases, the adhesiveness also improves, but when the Ra value exceeds 0.055 μm, the adhesiveness improvement effect does not improve any further. The surface roughness of the film can be arbitrarily controlled by adjusting the amount of the powder added. That is,
By adding the powder, the surface of the film can be roughened, and the same effect as the conventional method of roughening the adhesive surface by sandblasting or the like to improve adhesive strength can be obtained.

Furthermore, in order to uniformly roughen the film surface, it is necessary to use the powder with extremely controlled particle size distribution.

The method for measuring physical properties in this specification 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 for the measurement of Ra (center line average roughness) values 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.

(a) 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 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 (for example, Inton) 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.

Example 1 A varnish-like polyamic acid solution obtained using the same raw materials and the same method as in Comparative Example 1 had a particle size distribution of particle size in volume ratio of 5μ or more 1.6% 5μm to 4μm 10.1% 2μfr1 to 4μfn56 .1q6 1pfn~2pm 21.2% Less than 1μ After adding 0.005wt% of porous silica gel with an average particle size of 2.6μm, which is 11.0cm, based on the weight of the film resin, and thoroughly stirring and dispersing it. , 25μ by the same method as Comparative Example 1
A polyimide film of m nominal thickness was obtained.

Examples 2 to 5 Using the same raw materials as in Comparative Example 1 and the same porous silica gel powder as in Example 1, the amount of the powder added to the varnish-like polyamic acid solution was determined based on the weight of the film resin. 0.
05wt%, 0.10wtchi, 0.2wt% and 0.5
wt%, and 25 μm each in the same manner as Comparative Example 1.
A polyimide film of nominal thickness was obtained.

Comparative Example 2 Porous silica gel with a wide particle size distribution of 0.1 to 30 μm and an average particle size of 12.5 μm was added to a varnish-like polyamic acid solution obtained using the same raw materials and the same method as Comparative Example 1. After adding 0.05 wt% based on the weight of the film resin and thoroughly stirring and dispersing it, 25% was added in the same manner as in Comparative Example 1.
A polyimide film with a nominal thickness of μm was obtained.

Comparative Example 3 The same porous silica gel used in Example 1 was added at 0.7 wt% based on the weight of the film resin to a solution of polyamide acid having the same raw materials and the same method as in Comparative Example 1.
After addition and dispersion, 25% was added in the same manner as in Comparative Example 1.
A polyimide film with a nominal thickness of μm was obtained.

In Examples 1 to 5 and Comparative Examples 1 to 3, the evaluation results of the mechanical properties, running properties, and adhesive properties of the obtained polyimide films are shown in Table 1.

(Effects) As is clear from Table 1, the polyimide film of the present invention contains 0.005 to 0.5 wt% of porous silicon dioxide powder mainly having a particle size of 1 to 5 μm, based on the weight of the film resin. maintains the properties unique to polyimide, and also makes the surface slippery, resulting in markedly improved adhesion. Therefore, it can be suitably used in a wide range of fields such as flexible printed wiring board applications.

(To)

Claims (1)

[Claims] (1) Porous silicon dioxide powder with a particle size of 1 μm or more and 5 μm or less is added to the film at a rate of 0.0
A heat-resistant polyimide film comprising 0.05 wt% or more and 0.5 wt% or less.