JPH03182334A - Honeycomb core of polyimide and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture heat-resistant honeycomb core to be suitably used for an aerospace structure or the like by using thermoplastic polyimide sheets of specified structure. CONSTITUTION:Aromatic polyimide sheets are composed of polyimide formed with the repeated unit of the Formula 1, and respective fused areas of a laminate are in the state of being disposed at the constant interval in the same space layer between the sheets and being disposed at the constant inverval slipping off by the half of the interval in the adjacent space layers, and the sheets are pinched between hot plates, heated, pressurized and fused to manufacture a honeycomb core.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a honeycomb core with high heat resistance 1. More specifically, the present invention comprises a sandwich structure,
A heat-resistant honeycomb that can be suitably used in structures such as aircraft, railway vehicles, automobiles, hovercraft, and buildings, as well as space structures such as artificial satellites, such as deployable solar panels for artificial satellites. Regarding the core.

[Conventional technology]

Conventionally, honeycomb cores made of metal foil such as aluminum foil
-40621), honeycomb core made of general-purpose thermoplastic film such as polyethylene, polypropylene, polyvinyl chloride, polyester, etc. (Special Publication No. 5Q-32306
, JP-A-60-190340 and JP-A-6O-245
547), paper honeycombs, etc. are known.

However, the honeycomb cores known so far have not been fully satisfactory in terms of both lightness and heat resistance.

On the other hand, although aromatic polyimide is a material that is both lightweight and heat resistant, conventionally known aromatic polyimide sheets do not easily exhibit bending deformability even when heated to high temperatures. It also has no thermoplastic properties. For this reason, it is difficult to fuse the aromatic polyimide sheets to each other in the honeycomb core manufacturing method using the sheet expansion method, and conventionally, honeycomb cores made of aromatic polyimide have not been manufactured industrially. Therefore, it is not in general use.

[Problem to be solved by the invention]

The present invention provides a honeycomb core made of aromatic polyimide, which has conventionally been impossible to produce industrially, and at the same time provides a method for producing the honeycomb core made of aromatic polyimide industrially. be.

[Means for Solving the Three Problems] As a result of intensive research to solve the above problems, the present inventors discovered that a thermoplastic polyimide sheet having a specific structure is effective for this purpose, The invention has been completed.

That is, according to the present invention, 1. It is a laminate in which a plurality of aromatic polyimide sheets are laminated and joined by intermittent fused regions, and each fused region of the laminate has the same area between the sheets. They are arranged at regular intervals within the void layer, and in each adjacent void layer, they are arranged at regular intervals and shifted from each other, and furthermore, the stack is spread in the stacking direction,
A polyimide honeycomb core characterized by a honeycomb structure.

2. A large number of aromatic polyimide sheets are stacked together, and the fused areas between the sheets are arranged at regular intervals within the same void layer between the sheets, and are shifted from each other at regular intervals in each adjacent void layer. The sheets are fused together by applying pressure in the stacking direction while heating to form a laminate that is fused and joined through a number of intermittent fused areas, and then A method for manufacturing a polyimide honeycomb core, comprising expanding the laminate described in . . . in the lamination direction at a temperature equal to or higher than the glass transition temperature of polyimide to form a honeycomb structure.

3. As an aromatic polyimide, basically repeating units of the formula (I> 0 111) 1 1 0 (1) (wherein R is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group,
Represents a tetravalent group selected from the group consisting of a monocyclic aromatic group, a fused polycyclic aromatic group, and a non-fused polycyclic aromatic group in which aromatic groups are interconnected directly or through a bridge member. . ) The honeycomb core made of polyimide according to item 1 above, which is an aromatic polyimide represented by:

4. The polyimide honeycomb according to item 2 above, wherein the aromatic polyimide is basically an aromatic voimite represented by (I) with 0 repeating units (1) (wherein X and R are the same as above) core.

The present inventors first developed polyimide (1) (in the formula, R is the same as before) as a polyimide that has excellent mechanical properties, thermal properties, electrical properties, solvent resistance, etc., and has thermoplasticity. We have discovered a polyimide having the repeating unit shown in JP-A-64-9226.
64-9227. JP-A-1-221428, etc.). The above-mentioned polyimide differs from conventionally known polyimides in that it has good thermoplasticity, can be processed by melt molding methods such as extrusion molding and injection molding, and has strong adhesive strength.

Conventionally known polyimides other than those mentioned above, once imidized, have a melting temperature close to the decomposition temperature, so it has been difficult to mold them by heating and melting them. Therefore, for example, in the manufacturing method of polyimide sheets, polyamic acid, which is a precursor of polyimide, is usually dissolved in a solvent, applied to a substrate by a casting method, and then heat treated at high temperature to remove the solvent and imidize it. A method is used. In this case, if the heat treatment is insufficient, a portion of the amic acid will remain in the imide film, causing a decline in physical properties. For this reason, the heating time is inevitably long, and the polyimide forming process is extremely complicated, such as gradually raising the temperature and heating in stages to prevent pinholes from forming in the film, and thinning the film. there were. In addition, since a dehydration cyclization reaction occurs during heating, there are problems such as non-uniformity of the film or adhered layer and generation of voids.Furthermore, polyamic acid is unstable and the solution gradually gels even at room temperature. Alternatively, they needed to be stored frozen to cause hydrolysis.

For the above reasons, a method using a solvent-soluble polyimide has been provided. For example, JP-A-1-192536 discloses a method for manufacturing a honeycomb core using a polyimide that is soluble in phenol, cresol, halogenated phenol, etc. However, since a high boiling point solvent is used, treatment at high temperatures for a long time is required to completely volatilize the solvent, resulting in pinholes and uneven sheet thickness, just like when starting from a polyamic acid solution. The problem of compatibility remains.

On the other hand, since the aromatic polyimide used in the present invention is thermoplastic, for example, powdered polyimide that has been completely imidized by the method disclosed in JP-A-1-221428 is used, and a desired thickness can be obtained by melt extrusion. A uniform polyimide sheet can be obtained. The polyimide sheet thus obtained can be easily processed by a method such as heat fusion, if necessary.

In this way, it has become possible to industrially produce a novel aromatic polyimide honeycomb core that is lightweight, heat resistant, and has excellent radiation resistance, especially when used in outer space, by a spreading method.

Preferred embodiments of the present invention are as follows.

(1) In the present invention, the aromatic polyimide sheet is basically a polyimide consisting of repeating units of the formula (I).

(2) In the honeycomb core of the present invention, the fused regions of the laminate are arranged at regular intervals within the same void layer between the sheets, and are spaced at regular intervals in each adjacent void layer and from each other. They are arranged so that they are shifted by half of the above distance.

(3) In the honeycomb core manufacturing method of the present invention, the stacked sheets are heated at regular intervals by a pair of hot plates (
heat sealer), heat and pressurize the part sandwiched between the hot plates to fuse.

(4) In the method for manufacturing a honeycomb core of the present invention, the fusing operation described in item 3 above is performed sequentially for each sheet to form a laminate.

(5) In the method for manufacturing a honeycomb core of the present invention, the sheets are fused by heating the fused portion to a temperature 1 to 200°C higher than the glass transition temperature of the polyimide, and applying 1 to 200 kg/
This is carried out by maintaining the pressurized state within the range of Cm2 for 0.1 seconds to 3 hours.

(6) In the method for manufacturing a honeycomb core of the present invention, the development of the laminate is 1 to 5 times higher than the glass transition temperature of polyimide.
Perform at a temperature 0°C higher.

In the present invention, the term "sheet" refers to a sheet material in a broad sense, including anything from a substantially film-like material to a plate-like material.

The aromatic polyimide used in the present invention is basically a polyimide consisting of repeating units of the above formula (I), and the manufacturing method thereof is described in detail in the above-mentioned JP-A-Sho.
Aromatic diamine represented by formula (H) υ, i.e. bis[4-(4
-(4-Aminophenoxy>phenoxy)phenyl 1-sulfone obtained by reaction with one or more tetracarboxylic dianhydrides.

Note that, as long as the good physical properties of the aromatic polyimide used in the method of the present invention are not impaired, there is no problem in substituting a part of the above-mentioned diamine with a diamine used in other known polyimides.

Moreover, the tetracarboxylic dianhydride to be reacted with the above diamine has the general formula (III) 0 111 (in the formula, R is the same as before).

For example, ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, 1゜1-bis(2,3-dicarboxyphenyl)ethane dianhydride, Bis(2,3-
dicarboxyphenyl)methanihydride, bis(3,4
-Dicarboxyphenyl> Methanihydride, 2,2-bis(3,4-dicarboxyphenyl)propanidanhydride, 2,2-bis(2,3-dicarboxyphenyl)propanidanhydride, 2.2-bis (3゜4-Levoxyphenyl)-1,1,1,3゜3.3. -hexafluoropropani dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3,-hexafluoropropani dianhydride, pyromellitic dianhydride thing, 3
．． 3°,4,4°-benzophenonetetracarboxylic dianhydride, 2,2°,3.3'-benzophenonetetracarboxylic dianhydride, 3,3°4.4'-biphenyltetracarboxylic dianhydride , 2.2″, 3,3°-biphenyltetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(3 ,4
-dicarboxyphenyl)sulfone-anhydride, 4.4'
-(p-phenylenedioxy)cyphthalic dianhydride, 4
, 4°-(m-phenylenedioxy)cyphthalic dianhydride, 2,3°6.7-naphthalenetetracarboxylic dianhydride, 1.4,5.8-naphthalenetetracarboxylic anhydride, 1. 2,5.6-naphthalenetetracarboxylic dianhydride, 1,2,3.4-benzenetetracarboxylic dianhydride, 3,4,9.10-perylenetetracarboxylic dianhydride, 2,3, These include 6°7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and the like, and these tetracarboxylic dianhydrides may be used alone or in combination of two or more.

As the method for reacting the diamine and tetracarboxylic dianhydride, conventionally known methods can be used without limitation, but it is preferable to carry out the reaction in an organic solvent, for example. Examples of organic solvents used in this reaction include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, N-methyl-2-pyrrolidone, 1, 3-dimethyl-2-imidazolidinone, N-methylcaprolactam, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)
Ethane, bis(2-(2-methoxyethoxy)ethyl)
ether, tetravitrofuran, 1,3-dioxane,
Examples include 1.4-dioxane, pyridine, picoline, dimethylsulfoxide, dimethylsulfone, tetramethylurea, hexamethylphosphoramide, phenol, m-cresol, p-cresol, p-chlorophenol, anisole, and the like. Further, these organic solvents may be used alone or in combination of two or more.

The reaction temperature is 0°C to 250°C. Usually 6
It is carried out at a temperature below 0°C. The reaction pressure is not particularly limited, and normal pressure can be sufficient. The reaction time varies depending on the type of tetracarboxylic dianhydride, diamine, solvent, and reaction temperature used, but 30 minutes to 24 hours is usually sufficient.

Through such a reaction, a polyamic acid having a repeating unit of the following formula (IV) as a basic skeleton is produced.

(TV) (In the formula, R is the same as above).

By heating and dehydrating this polyamic acid at 100 to 400°C or chemically imidizing it using a commonly used imidizing agent, such as triethylamine and acetic anhydride, the following formula (1) () (where R is Same as above).

A polyimide having the repeating unit of as a basic skeleton is obtained.

After the polyamic acid has been produced at a numerically low temperature, it is further imidized thermally or chemically. However, polyimide can also be obtained by simultaneously performing the production of polyamic acid and the thermal imidization reaction at a temperature of 60°C to 250°C. That is, the tetracarboxylic dianhydride and the diamine are suspended or dissolved in an organic solvent and then reacted under heating to simultaneously generate polyamic acid and dehydrate imidization, thereby repeating the above formula (I). It is also possible to obtain a polyimide having the unit as a basic skeleton.

In addition to tetracarboxylic dianhydride and diamine, aromatic monoamines, aliphatic monoamines, cycloaliphatic group monoamines,
It is a particularly preferred method to add one or more compounds selected from aromatic dicarboxylic acid monoanhydrides, aliphatic dicarboxylic acid monoanhydrides, and cycloaliphatic dicarboxylic acid monoanhydrides during the reaction.

The obtained polyimide powder is dried to volatilize the organic solvent, and then melt-extruded to form a sheet-like molded product. Although the extrusion temperature is appropriately determined depending on the melt viscosity, glass transition temperature, and melting temperature of the polymer, extrusion molding is generally performed at a temperature higher than the glass transition temperature and/or melting temperature.

A honeycomb core is manufactured using the aromatic polyimide sheet obtained in this manner, and the method for manufacturing a honeycomb core of the present invention will be described in detail below with reference to the attached drawings as necessary.

FIGS. 1 and 2 are cross-sectional views showing one embodiment of the step of laminating polyimide sheets in the method for manufacturing a honeycomb core of the present invention.

First, as shown in FIG. 1, two polyimide sheets 1a and 1b are placed on spacers 3a and 3b.

A pair of rod-shaped heat sealers 2a, 2a'', 2b are placed one on top of the other at regular intervals.

2b', . . . are heated and pressed in the stacking direction to fuse and join the two sheets to form a laminate.

The spacer and heat sealer are removed from the laminate, and then, as shown in FIG. 2, a sheet 1c is further attached to the laminate 4, and a spacer 3a is placed on the laminate 4.

3b, . . . and heat sealers 2a', 2b', . . . are inserted into the gaps of the fused areas 5a, 5b, . , the other heat sealer 2a, 2b, .
a', 2b', . Fusion/joining.

By sequentially performing the above-mentioned operation of stacking sheets on a laminate and fusing and joining each new stack, a larger number of sheets can be bonded through a large number of intermittent fused areas. are fused and joined to form a laminate.

In the above-mentioned operation, it is preferable to arrange a pair of heat sealers in the fused regions in adjacent void layers, for example in the center of the gap between the fused regions 5a and 5b. By arranging the paired heat sealers in this way and performing the fusion operation of the sheet materials, each fusion area is arranged at regular intervals within the same void layer between the sheets, and is adjacent to each other. A laminate is obtained in which each void layer is arranged at regular intervals and shifted by half the interval from each other.

FIG. 3 is a perspective view showing a laminate obtained by the above method.

FIG. 4 is a plan view showing one embodiment of the honeycomb core of the present invention. In FIG. 4, the intervals at which the fused regions are arranged are as follows:
The length may be appropriately selected to form one side A of the polygonal honeycomb structure, and for example, the length may be about 5 to 20 mm.

As the heating means used in the method of the present invention, a conventionally known heat sealer for plastic welding can be used, as long as it can heat and pressurize the sheets while sandwiching the sheets in pairs. The shape is not particularly limited; for example, the tip may have an edge, or it may simply be a round bar with a circular cross section.

The heat sealer is preferably coated with a release agent to prevent the sheet from fusing to the heat sealer.

The above-mentioned heating and pressure treatment for fusion bonding between the sheets heats the portion of the stacked sheets sandwiched between the pair of heat sealers to the glass transition temperature of the aromatic polyimide and/or
or 1 to 200°C above the melting temperature, preferably 20 to 1°C
Heating to a temperature 50℃ higher, 1 to 2000kg/C
m2, preferably 10-500 kg/cm
2 More preferably, in a pressurized state at a pressure in the range of 30 to 50 kg/cm2, for 0.1 seconds to 3 hours, preferably 3 hours.
This is carried out by holding for 0 seconds to 1 hour, more preferably 1 minute to 10 minutes.

The length of the fused region between the sheets formed by heating and pressing between the heat sealers is about 0.1 to 20 mm, preferably about 0.5 to 10 mm.

As shown in Figures 1 and 2, the fusing operation for each sheet described in L is performed by arranging spacers that do not fuse with the sheets at regular intervals in the gaps between the sheets to be welded. , the gap between the spacers may be heated and pressurized with a heat sealer, or the spacer may not be used. The spacers are preferably arranged at regular intervals within the void layer between the newly stacked sheet and the adjacent sheet, and as shown in FIG. It is more preferable to arrange the positions so that they coincide with each other. Preferably, the spacer is placed and removed sequentially after each sheet is fused. As the material of the spacer, a glass plate, a silicon plate, a metal plate such as copper or iron coated with a release agent, an inorganic material such as iron foil, or a sheet-like heat-resistant plastic material such as polyimide or Teflon can be used. . As for the size of the spacer, the thickness and width may be appropriately selected to form one side A of the polygonal honeycomb structure and the fused region 5 as shown in FIG. ~
It may be within a range of about 1000 μm/width 5 to 50 mm.

When the laminate is a long laminate, it is then cut in the width direction to obtain a laminate having a predetermined shape. If necessary, the laminate obtained by cutting the laminate or elongated laminate in the width direction is further cut in the direction perpendicular to the fused portion (
A laminate having a predetermined shape may be obtained by cutting in the longitudinal direction of the elongated laminate. The cutting can be performed using a conventionally known cutting device such as a band saw.

In the manufacturing method of the present invention, an appropriate developing force is applied to the laminate manufactured as described above in the lamination direction (W direction shown in FIG. 4) at a temperature higher than the glass transition temperature of the aromatic polyimide. The polyimide honeycomb core is manufactured by expanding the polyimide core to form a honeycomb structure as shown in FIG.

In the manufacturing method of the present invention, as described above, the laminate is developed at a temperature within the above-mentioned range to form a honeycomb structure, and then cooled to room temperature while maintaining the honeycomb structure. Preferably, a polyimide honeycomb core is obtained.

In the manufacturing method of the present invention, the cooling conditions are not particularly limited, and known methods, conditions, etc. can be employed.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

In addition, the physical properties in Examples were measured by the following methods.

Logarithmic viscosity: After heating and dissolving 50 g of polyimide powder in 100 mJ2 of p-chlorophenol/phenol (9/1 weight ratio) mixed solvent, cooling to 35°C and measuring Tg, Tm: DSC (odorous DT-40 series) ,D
Measurement Example 1 Bis[4-(4(4-aminophenoxy)phenoxy)
Using 6.17 kg (10 mol) of pyromellitic dianhydride, 2.07 kg (9.5 mol) of pyromellitic dianhydride, and 148 g (1 mol) of phthalic anhydride as raw materials, polyimide powder was obtained according to the above-mentioned Japanese Patent Application Publication No. Ta. The glass transition temperature of polyimide is 285°C, the melting point is 420°C, and the logarithmic viscosity is 0.
It was 55 dl/g. This polyimide powder is processed into a thickness of 50μ using a regular extruder at a cylinder temperature of 420-430℃.
, and was continuously melt-extruded into a sheet with a width of 36 cm.

Twenty sheets of the polyimide sheet were cut into strips each having a width of 2 cm and a length of 32 cm. Long spacers (iron foil coated with release agent, thickness 50 μm, width 5 mm, length 40 mm) are placed on top of this strip-shaped polyimide sheet at 6 mm intervals so that the longitudinal direction of the spacers is parallel to the width direction of the sheet. and then layered another sheet on top of it. Next, the laminated sheets with spacers sandwiched between them are sandwiched from below L using a pair of heat sealers in the shape of round rods with a diameter of 4 mm at the center of the gap between the spacers, and heated to 425°C.
and held under a pressure of 50 kg/cm2 for 5 minutes to fuse the part sandwiched between the heat sealers.
A laminate was formed which was fused and bonded through intermittent fused areas of mm.

Next, after removing the heat sealer and spacer from the laminate, another spacer was placed on top of the laminate, and another sheet was further laminated thereon. The newly placed spacers were placed so that the center line of each spacer coincided with the center line of each fused region in the adjacent void layer and at the same spacing as above. Then, the stacked sheets with spacers sandwiched therebetween were fused and joined in the same manner as described above. This fusing operation was performed sequentially on 17 more sheets to form a laminate consisting of 20 polyimide sheets.

Next, the laminate was expanded in the stacking direction at a temperature of 330° C. to form a honeycomb structure, and finally cooled to room temperature to produce a polyimide honeycomb core.

The polyimide honeycomb core obtained in this example was 25
Compressive strength at °C is 5.0 kg/cm2200 °C, -60
The compressive strength at °C is 4.3 kg/cm24.5, respectively.
kg/cm2, which was excellent.

Examples 2 to 5 Various polyimides were synthesized in the same manner as in Example 1, except that the type and amount of diamine and tetracarboxylic dianhydride, and the amount of phthalic anhydride were changed. Then, melt extrusion was performed in the same manner as in Example 1 to obtain a polyimide sheet.

Then, in the same manner as in Example 1, it was cut into strips, laminated, and expanded to obtain a polyimide honeycomb core. The compressive strength of the obtained honeycomb core was measured at 25°C, 200°C and -60°C, and the results shown in Table 1 were obtained.

Table 1 also lists the polyimide synthetic raw material, the glass transition temperature of polyimide, the extrusion sheeting temperature, the lamination temperature during honeycomb core production, and the development temperature.

(Effects of the Invention) According to the present invention, it is possible to provide a polyimide honeycomb core that has high mechanical strength and excellent heat resistance, and particularly has excellent heat and radiation resistance when used in outer space.

Furthermore, the present invention can provide a method for industrially manufacturing a polyimide honeycomb core by using specific aromatic polyimide sheets and fusing the sheets alternately.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing an embodiment of the step of laminating polyimide sheets in the method for manufacturing a polyimide honeycomb core of the present invention, and FIG. FIG. 4 is a perspective view showing one embodiment of the sheet laminate, and FIG. 4 is a plan view showing one embodiment of the honeycomb core. la, lb, lc---sheet, 2a, 2a', 2b, 2b'...-heat sealer 3a, 3b...1 spacer, 4...laminate, 5a, 5
b...Fusion area. A... Edges that form a honeycomb structure.

Claims (1)

[Scope of Claims] 1. A laminate in which a plurality of aromatic polyimide sheets are laminated and joined by intermittent fused regions, and each fused region of the laminate has the same area between the sheets. They are arranged at regular intervals within the void layer, and in each adjacent void layer they are arranged at regular intervals and shifted from each other, and furthermore, the stack is expanded in the stacking direction, forming a honeycomb. A polyimide honeycomb core characterized by a structured structure. 2. A state in which a large number of aromatic polyimide sheets are stacked, and the fused areas between the sheets are arranged at regular intervals within the same void layer between the sheets, and are shifted from each other at regular intervals in each adjacent void layer. The sheets are fused together by applying pressure in the stacking direction while heating to form a laminate that is fused and joined through a large number of intermittent fused areas, and then, A method for manufacturing a polyimide honeycomb core, comprising expanding the laminate in the lamination direction at a temperature equal to or higher than the glass transition temperature of polyimide to form a honeycomb structure. 3. Aromatic polyimide is basically a repeating unit of formula (I) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (I) (wherein, R is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group,
Represents a tetravalent group selected from the group consisting of a monocyclic aromatic group, a fused polycyclic aromatic group, and a non-fused polycyclic aromatic group in which aromatic groups are interconnected directly or through a bridge member. . ) The polyimide honeycomb core according to claim 1, which is an aromatic polyimide represented by: 4. Claim 2, wherein the aromatic polyimide is basically an aromatic polyimide represented by the repeating unit of formula (I) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (I) (in the formula, R is the same as before) The method for manufacturing the polyimide honeycomb core described above.