JP2007070377A - Method for producing resin foam, resin foam, heat insulating material and circuit board material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a resin foam securing heat insulating properties, with which a compression process is omitted and productivity is improved and to obtain a resin foam, a heat insulating material and a circuit board material. <P>SOLUTION: The resin foam is formed by impregnating inert gas into a molding made of a polyimide-based resin having a remaining incomplete part of imidization reaction under pressure, abruptly releasing pressure acting on the polyimide-based resin of the molding and heating the molding to expand the polyimide-based resin. Then imidization reaction is selectively advanced by heating and the produced resin foam is used as an heat insulating material for building and a circuit board material for electronic and electric equipment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a resin foam, a resin foam, a heat insulating material, and a circuit board material used in fields such as electric and electronic fields, particularly high frequency applications.

About the manufacturing method of the foam of an imide-type resin, conventionally, the manufacturing method of the foam of polyetherimide is disclosed by patent document 1, 2, for example. However, polyetherimide has a glass transition point (Tg) as low as 217 ° C, so that it has insufficient heat resistance when used in electrical and electronic applications that are exposed to high temperatures such as around the engine and solder reflow. I can't.
Patent Document 3 discloses a method for producing a foamed polyimide having a glass transition point (Tg) of 300 ° C. or higher.
JP 62-39225 A Japanese Patent Laid-Open No. 7-138402 Japanese Patent Laid-Open No. 2003-82100

  However, in the case of the manufacturing method of Patent Document 3, since the expansion ratio is 20 times or more, compression processing is necessary to obtain an appropriate expansion ratio, and it is impossible to improve productivity. is there. Moreover, since the foam manufactured with the manufacturing method which concerns has gas permeability (open bubble), there is not a possibility that it lacks heat insulation.

  The present invention has been made in view of the above, and a method for producing a resin foam, a resin foam, and a heat insulating material that can improve productivity by omitting compression processing and can ensure heat insulation. An object of the present invention is to provide a circuit board material.

  In the present invention, in order to solve the above-mentioned problems, an inert gas is impregnated under pressure into a polyimide resin that has left an incomplete imidation reaction, the pressure acting on the polyimide resin is released, and then heated. Then, a resin foam is formed by foaming a polyimide resin.

In addition, a polyimide resin can be formed into a substantially sheet shape by a solution casting method, and the formed polyimide resin can be impregnated with an inert gas under pressure.
In addition, the imidization reaction can proceed after the resin foam is formed.

Moreover, in order to solve the said subject in this invention, the resin foam was manufactured by the manufacturing method of the resin foam in any one of Claim 1 thru | or 4. It is characterized by the above-mentioned.
Moreover, in order to solve the said subject in this invention, the resin foam manufactured by the manufacturing method of the resin foam in any one of Claim 1 thru | or 4 was used for the heat insulation material.

  Furthermore, in order to solve the above-mentioned problems, the present invention is characterized in that a resin foam produced by the method for producing a resin foam according to any one of claims 1 to 4 is used as a circuit board material.

  Furthermore, the polyimide resin that has left the unfinished imidation reaction is impregnated with a supercritical fluid in a supercritical state, the pressure acting on the polyimide resin is released, and then heated to foam the polyimide resin. It is good also as forming the resin foam by making it.

  Here, the polyimide resin in the claims includes at least a polyimide, a polyamideimide, a polyetherimide, or the like in which a portion where the imidization reaction has not been completed is left. This polyimide resin includes a modified product obtained by modifying each of the above resins and a mixture obtained by mixing other resins. Furthermore, the resin foam, the heat insulating material, and the circuit board material can be widely used in fields such as electricity, electronics, communication, architecture, and automobiles.

According to the present invention, the productivity can be improved by omitting the compression work, and the heat insulation can be maintained and improved.
Moreover, if the imidation reaction is advanced by heating after forming the resin foam, the heat resistance can be improved.

  Hereinafter, a preferred embodiment of the present invention will be described. A method for producing a resin foam in the present embodiment is that an inert gas is pressurized to a molded body made of a polyimide resin in which an imidation reaction is left unfinished. The pressure acting on the polyimide resin of this molded product is suddenly released, and the resin foam is formed by heating and foaming the polyimide resin, and then the imidization reaction is selectively performed by heating. The produced resin foam is appropriately used as a heat insulating material for buildings and a circuit board material for electric and electronic equipment.

  The polyimide resin is made of, for example, polyimide, polyamide imide, polyether imide, etc., and generally has a structure represented by chemical formulas 1 and 2 and a portion in which an imidation reaction such as chemical formulas 3 and 4 has not been completed. And formed into molded bodies of various shapes.

  Polyimide and polyamideimide preferably have a glass transition point (Tg) of 300 ° C. or higher and 260 ° C. or higher, respectively, from the viewpoint of heat resistance. It is preferable that a polyimide has a polyamic acid in the molecule | numerator obtained from aromatic tetracarboxylic dianhydride and aromatic diamine. The polyamideimide preferably has an amic acid in the molecule obtained by the PMDA method, the acid chloride method, or the dephenol method.

  The reason why the imidation reaction is not completed is that the foaming state can be controlled by adjusting the progress of imidization. That is, polyimide and polyamideimide having completed imidization have a high storage elastic modulus at the foaming temperature, and cannot sufficiently expand by suppressing gas expansion. In addition, the region where the storage elastic modulus is low is very high at 300 ° C. or higher, and in this region, the foaming of bubbles and coalescence of bubbles are caused by the rapid expansion of the inert gas, thereby obtaining a uniform resin foam. It is because it is not possible.

On the other hand, a sufficient and uniform resin foam can be easily obtained by leaving a portion of the polyimide resin in which the imidization reaction has not been completed. The progress of imidization can be adjusted by the time of standing in the imidization temperature. Further, the storage elastic modulus of the polyimide resin is preferably 10 ⁵ Pa to 10 ⁸ Pa from the viewpoint of obtaining good foaming.

  A molded body of polyimide resin can be formed by a molding method such as casting molding, extrusion molding, calender molding, or compression molding. In melt molding such as extrusion molding, calender molding, and compression molding, an imide is formed during molding. Casting molding that allows easy control of imidization is preferred because of the progress of the imidization reaction and the difficulty of controlling imidization.

  In the case of producing a molded body by this casting, first, a polyimide resin is dissolved in a polar solvent, and then the solution is made into a thin film with a die, made of metal, a resin endless belt or a biaxially stretched polyethylene terephthalate film, A coated body of a film or a sheet can be produced by coating on a support such as a biaxially stretched polypropylene film, drying and peeling. Examples of the polar solvent include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone.

  In the case of producing a molded body by extrusion molding, if a polyimide resin is melt-kneaded and extruded in a molding facility in which a T-die or a round die is attached to a single-screw extruder or a twin-screw extruder, and then taken out by a take-up roll, A molded body of a film or sheet can be produced.

  When manufacturing a molded body by calender molding, calendar devices such as inverted L type, L type, upright three type, upright two type, inclined two type, Z type and inclined Z type can be used. By rolling a polyimide resin with a calender roll, a film, sheet, or plate-shaped molded body can be produced.

  When a molded body is produced by compression molding, a plate-shaped molded body can be produced by filling a polyimide resin in a mold heated to a temperature equal to or higher than the melting point and heating and compressing. Moreover, if a polyimide resin is once melt-kneaded with a mixing roll and the melt-kneaded material is filled in a mold heated to a melting point or higher, a plate-shaped molded body can be obtained.

  The molded body made of polyimide resin obtained by the above method can be used after being heat-treated and imidized within a range where foam molding can be performed. The heat treatment for imidization is desirably performed by limiting the shrinkage of the molded body made of polyimide resin. This is because, when dried by free shrinkage, partial shrinkage occurs, which may result in thickness unevenness and further damage the flatness of the molded body. In order to perform the heat treatment while restricting the shrinkage, for example, the heat treatment may be performed with a tenter dryer or a metal frame.

  In the molded body, an inorganic filler, an organic filler, an electromagnetic wave absorber, a heat conductive particle, an ultraviolet absorber, a heat stabilizer, an antioxidant, a stretching aid, a lubricant, etc., as long as the characteristics of the present invention are not impaired. Additives can be added. Moreover, the thickness of a molded object is although it does not specifically limit, 5-5000 micrometers or less are preferable.

  Examples of the inert gas include nitrogen, carbon dioxide, helium, and argon. Carbon dioxide is preferable from the viewpoint of increasing the amount of impregnation into the polyimide resin or making the impregnation speed easy. The conditions for impregnation of the inert gas may be normal temperature or higher, but normal temperature from the viewpoint of impregnation speed, amount of impregnation, number of foam nuclei formed by releasing pressure, bubble diameter, and uniformity of bubble diameter. As described above, 5 MPa or more, more preferably 31 ° C. or more and 7.4 MPa or more where carbon dioxide is in a supercritical state. Further, in order not to proceed with imidization at this stage, 200 MPa or less and 30 MPa or less are preferable in view of safety in handling high-pressure gas.

  The supercritical state refers to a state where a supercritical fluid is generated when the temperature and pressure (critical point) determined by the type of gas are exceeded, in other words, the state of a substance above the critical point. For example, in the case of carbon dioxide, the critical temperature is 31.0 ° C. and the critical pressure is 7.4 MPa, and in the case of nitrogen, the critical temperature is −147.0 ° C. and the critical pressure is 3.4 MPa. A supercritical fluid is a fluid having properties intermediate between a gas and a liquid, and having both a high density similar to a liquid and a diffusivity (solubility in a molten resin) similar to a gas. For this reason, if a supercritical fluid is used, the impregnation rate into the polyimide resin is faster than that of gas in a gaseous state, which is actually preferable.

  The impregnation time of the inert gas is not particularly limited, and the foaming ratio and the foaming state can be controlled by appropriately changing the impregnation time. That is, if the impregnation time is shortened, the thermal conductivity and dielectric constant of the resin foam can be adjusted. In addition, the foaming ratio can be adjusted by arbitrarily selecting the impregnation time between the amount of gas impregnation and 0 to the saturated state, whereby a resin foam in which only the surface layer is foamed can be produced.

  The pressure acting on the polyimide resin is suddenly released at a rate of 1 MPa / second or more, but foaming nuclei are formed by the induction of thermodynamic instability accompanying the sudden release of this pressure, and the polyimide resin does not react. A mixture of active gases is obtained. The reason why a speed of 1 MPa / second or more is required is that when it is less than 1 MPa / second, the number of foam nuclei is reduced, and the bubbles are greatly non-uniform. The faster the pressure release speed, the better.

When a mixture of the polyimide resin and the inert gas is obtained, if this is heated, the gas expands with the foaming nucleus as a starting point, and the bubbles grow to produce a resin foam. The heating temperature may be selected depending on the required expansion ratio and cell diameter, but the temperature in the region where the storage elastic modulus of the resin is 10 ⁵ Pa to 10 ⁸ Pa is preferable. This is because, at a high temperature of less than 10 ⁵ Pa, bubble breakage and bubble coalescence occur due to rapid expansion of the gas, and a uniform resin foam cannot be obtained. Further, if it exceeds 10 ⁸ Pa, gas expansion is hindered, resulting in insufficient foaming.

  When heat resistance is required for the resin foam, the imidization reaction may be advanced by heating after foaming to complete the resin foam.

  According to the above method, a compression operation for obtaining an appropriate foaming ratio is not necessary, and productivity can be improved. Moreover, the heat insulation excellent in the resin foam can also be provided. Furthermore, it is possible to produce a resin foam having heat-resistant uniform fine closed cells, a heat insulating material that requires heat resistance exceeding 280 ° C., and a circuit board material that requires low dielectric constant and solder reflow heat resistance. Provision is possible.

Examples of the method for producing a resin foam, the resin foam, the heat insulating material, and the circuit board material according to the present invention will be described below together with comparative examples.
The resin foams of Examples 1, 2, and 3 and Comparative Examples 1 and 2 were produced, respectively, and their storage elastic modulus, expansion ratio, bubble generation state, surface property, imidization rate, thermal conductivity, dielectric constant, etc. And the results are summarized in Table 1.

Storage elastic modulus (E ')
Using a test piece having a width of 7 mm and a length of 32 mm and a viscoelasticity analyzer [RSA-11 manufactured by Rheometric Co., Ltd.], the measurement was performed under the conditions of a vibration frequency of 1 Hz, a heating rate of 5 ° C./min, and a load of 100 g.
Foaming ratio The density (ρ _f ) of the resin foam was measured by an underwater substitution method, and was calculated as a ratio ρ / ρ _f with the density (ρ) of the molded body before foaming.

Formation state of bubbles The cross section of the resin foam was photographed with a scanning electron microscope [JSM-5300LV, manufactured by JEOL Ltd.] and visually evaluated according to the evaluation criteria of A, B, and C.
A: Uniform (bubble diameter was about 30 μm)
B: Non-uniform (Bubble diameter was several μm to several tens of μm, the number of bubbles was small, and the generation of bubbles was sparse.)
C: Heterogeneous (a large number of bubbles with a bubble diameter of several millimeters were generated by the combination of broken bubbles and bubbles, the number of bubbles was very small, and the generation of bubbles was sparse)

Surface property The surface of the resin foam was visually evaluated according to the evaluation criteria of ○ and ×.
○: The surface of the resin foam did not swell and had a surface equivalent to that of the unfoamed body. ×: A huge swell of several hundred μm to several mm was observed on the surface of the resin foam.

Imidization rate Polyamideimide resin before film formation, and infrared absorption spectrum of the polyamideimide resin film [Infrared spectroscopic analyzer Micro ATR manufactured by Sensor Technologies, Ltd.] are measured by total reflection absorption measurement method, and symmetric stretching vibration of imidecarbonyl group Evaluation was made at an absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of a band (1780 cm ⁻¹ , parallel dichroism) and an inter-benzene skeleton stretching vibration body (1500 cm ⁻¹ , parallel dichroism) as an internal standard. The imidization was completed when the absorbance ratio became constant.

The imidization rate was calculated | required by the following formula | equation.
Imidation ratio = XY / ZY × 100
X: Absorbance ratio of polyamideimide resin film A ₁₇₈₀ / A ₁₅₀₀
Y: Absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of polyamideimide resin before film _formation
Y = 0.08
Z: Absorbance ratio A ₁₇₈₀ / A _{1500 of} the polyamideimide resin film that has been imidized completely
Z = 0.23

Thermal conductivity Using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Industry Co., Ltd.), the thermal conductivity was determined by comparison with a reference material. There are three types of reference materials: expanded polyethylene (thermal conductivity: 0.0357 W / mK), silicone rubber (thermal conductivity: 0.238 W / mK), and quartz glass (thermal conductivity: 1.409 W / mK). used.
Dielectric constant Measured using an RF impedance material analyzer (Hewlett Packard, HP4291A).

Example 1
First, a polyamide-imide resin solution is prepared by dissolving 100 parts by mass of polyamide-imide resin in N-methyl-2-pyrrolidone so that the solid content concentration is 30% by mass. The film was coated on a biaxially stretched polyethylene terephthalate film having a thickness of 100 μm by a bar coating method so as to have a thickness of 100 μm, and left to dry in a hot air oven heated to 150 ° C. for 1.5 hours.

After drying in a hot air oven, it was cooled to room temperature and peeled off from the biaxially stretched polyethylene terephthalate film to obtain a polyamideimide resin film that was a molded article having an average thickness of 96 μm. When a polyamideimide resin film was obtained, its absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ and storage elastic modulus were measured, and the storage elastic modulus is shown in FIG. The absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of the polyamideimide resin film was 0.13, and the imidization ratio was 33%.

Incidentally, the absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of a film before the polyamide-imide resin is 0.08, absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ polyamide-imide resin film imidization is complete was 0.23 .

  Next, the polyamideimide resin film is cut into 20 cm × 20 cm, and the mass is measured. The polyamideimide resin film is sealed in a pressure vessel, and left in supercritical carbon dioxide at a temperature of 40 ° C. and a pressure of 8 MPa for 1 hour. Impregnated. Immediately after impregnation with carbon dioxide, the mass of the polyamide-imide resin film was measured, the amount of carbon dioxide impregnation was measured, and the results are summarized in Table 1.

Next, the polyamideimide resin film impregnated with carbon dioxide was immersed in an oil bath heated to a temperature of 160 ° C. for 1 minute and foamed to produce a resin foam, and the foaming ratio was measured. Summarized in The density of the obtained foam was 0.39 g / cm ³ .
The density of the polyamideimide resin was 1.29 g / cm ³ . Further, a cross-section of the resin foam was photographed with a scanning electron microscope to obtain FIG.

Example 2
The polyamideimide resin film obtained in Example 1 was fixed to a metal frame and left in a hot air oven at a temperature of 260 ° C. for 30 minutes. The absorbance ratio A ₁₇₈₀ / A _{1500 of} the obtained polyamideimide resin film and storage were obtained. Each elastic modulus was measured, and the storage elastic modulus is shown in FIG. The absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of the polyamideimide resin film was 0.15, and the imidization ratio was 47%.

  Next, the obtained polyamideimide film resin film was cut out to 20 cm × 20 cm, and its mass was measured, sealed in a pressure vessel, and left in a supercritical carbon dioxide at a temperature of 60 ° C. and a pressure of 10 MPa for 30 minutes. Impregnated with carbon dioxide. When carbon dioxide was impregnated in this way, the mass of the polyamide-imide resin film was immediately measured, the amount of carbon dioxide impregnation was measured, and the results are summarized in Table 1.

Next, a polyamide-imide resin film impregnated with carbon dioxide was placed in a metal mold for 1 minute in a gap of 0.2 mm heated to a temperature of 200 ° C. and foamed to produce a resin foam, and the expansion ratio was measured. The results are summarized in Table 1. The density of the obtained foam was 0.47 g / cm ³ . The density of the polyamideimide resin was 1.32 g / cm ³ .

Example 3
The polyamideimide resin film obtained in Example 2 was fixed to a metal frame and left in a hot air oven at a temperature of 315 ° C. for 10 minutes, and the absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ and the storage elastic modulus of the polyamideimide resin film were determined. Each was measured, and the storage elastic modulus is shown in FIG. The absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of the polyamideimide resin film was 0.20, and the imidization ratio was 80%.

  Next, the polyamideimide film resin film is cut into 20 cm × 20 cm, the mass thereof is measured, sealed in a pressure vessel, and left in supercritical carbon dioxide at a temperature of 25 ° C. and a pressure of 6 MPa for 3 hours. Impregnated. Immediately after the impregnation, the mass of the polyamide-imide resin film was measured, the amount of carbon dioxide impregnation was measured, and the results are summarized in Table 1.

Next, a polyamide-imide resin film impregnated with carbon dioxide was placed in a metal mold for 1 minute in a gap of 0.2 mm heated to a temperature of 300 ° C. and foamed to produce a resin foam, and the foaming ratio was measured. The results are summarized in Table 1. The density of the obtained resin foam was 0.55 g / cm ³ . The density of the polyamideimide resin was 1.34 g / cm ³ .

Comparative Example 1
The polyamideimide resin film obtained in Example 2 was fixed to a metal frame and left in a hot air oven at a temperature of 315 ° C. for 1 hour to completely imidize it. The absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ and the storage elastic modulus of the obtained polyamideimide resin film were measured, and the measurement results of the storage elastic modulus are shown in FIG. The absorbance ratio A ₁₇₈₀ / A ₁₅₀₀ of the polyamideimide resin film was 0.23, and the imidization ratio was 100%.

  A polyamide-imide resin film is cut into a 20 cm × 20 cm, its mass is measured, sealed in a pressure vessel, and left in supercritical carbon dioxide at a temperature of 40 ° C. and a pressure of 8 MPa for 1 hour, impregnated with carbon dioxide. I let you. Immediately after the impregnation, the mass of the polyamide-imide resin film was measured, the amount of carbon dioxide impregnation was measured, and the results are summarized in Table 1. Further, a cross-section of the resin foam was photographed with a scanning electron microscope to obtain FIG.

Comparative Example 2
First, a polyamide-imide resin was melt-kneaded with a mixing roll at a temperature of 340 ° C. for 5 minutes, and the polyamide-imide resin was peeled off from the mixing roll to prepare a polyamide-imide resin kneaded product. After preparing the polyamideimide resin kneaded material in this way, the polyamideimide resin kneaded material is cooled and placed in a metal mold, preheated at 350 ° C., and then compression molded for 5 minutes by applying a pressure of 350 ° C. and 20 MPa, A plate-shaped molded product having a thickness of 530 μm was prepared by cooling at room temperature with a pressure of 20 MPa applied. The storage elastic modulus of the plate-like molded product of polyamideimide resin is shown in FIG.

  Next, the obtained plate-like molded product of polyamideimide film resin was cut into 20 cm × 20 cm, and its mass was measured. The mass was sealed in a pressure-resistant container and allowed to stand in carbon dioxide at a temperature of 25 ° C. and a pressure of 6 MPa for 3 days. Impregnated with carbon dioxide. Immediately after impregnation, the mass of the polyamide-imide resin plate-like molded product was measured, the amount of carbon dioxide impregnation was measured, and the results are summarized in Table 1.

  The polyamideimide resin film impregnated with carbon dioxide was placed in a metal mold heated to a temperature of 300 ° C. for 1 minute and foamed, and the results are summarized in Table 1.

It is a graph which shows the storage elastic modulus in Example 1 of the manufacturing method of the resin foam which concerns on this invention. It is a photograph which shows the cross section of the resin foam in Example 1 of the manufacturing method of the resin foam which concerns on this invention. It is a graph which shows the storage elastic modulus in Example 2 of the manufacturing method of the resin foam which concerns on this invention. It is a graph which shows the storage elastic modulus in Example 3 of the manufacturing method of the resin foam which concerns on this invention. It is a graph which shows the storage elastic modulus in the comparative example 1 of the manufacturing method of the resin foam which concerns on this invention. It is a photograph which shows the cross section of the resin foam in the comparative example 1 of the manufacturing method of the resin foam which concerns on this invention. It is a graph which shows the storage elastic modulus in the comparative example 2 of the manufacturing method of the resin foam which concerns on this invention.

Claims (6)

  Resin by impregnating an inert gas under pressure to a polyimide resin that has left unfinished imidation reaction, releasing the pressure acting on the polyimide resin, and then heating to foam the polyimide resin A method for producing a resin foam, comprising forming a foam.   The method for producing a resin foam according to claim 1, wherein a polyimide resin is formed into a substantially sheet shape by a solution casting method, and the formed polyimide resin is impregnated with an inert gas under pressure.   The method for producing a resin foam according to claim 1 or 2, wherein the imidization reaction is advanced after the resin foam is formed.   A resin foam produced by the method for producing a resin foam according to claim 1.   A heat insulating material using a resin foam produced by the method for producing a resin foam according to any one of claims 1 to 3. A circuit board material using a resin foam produced by the method for producing a resin foam according to any one of claims 1 to 3.

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