JPH03183535A - Honeycomb core of polyimide and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture honeycomb cores industrially by laminating a plurality of aromatic polyimide sheets into a laminate which is laminated and bonded in intermittently bonded regions, and being welded at set intervals in the same cavity layer, and further bonding them to be shifted from each other at set intervals in each adjacent cavity layer. CONSTITUTION:Two polyimide sheets 1a and 1b are put on each other via spacers 3a, 3b..., and heated in the form of being held at a set interval by means of heat sealer 2a, 2a', 2b, 2b'..., and further pressed in the laminating direction so that a laminate is formed by bonding and joining the two sheets. Next, the laminate 4 is superimposed with a sheet 1c via the 3a, 3b and the heat sealers 2a', 2b' are inserted into the welded regions 5a, 5b of the laminated 4 and disposed therebetween at a set interval, and other heat sealers 2a, 2b, which are paired with the heat sealers, are arranged to be opposed to the heat sealers 2a', 2b'.

Description

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

[Conventional technology] Conventionally, honeycomb cores made of metal foil such as aluminum foil
-4062], ), honeycomb core made of general-purpose thermoplastic film such as polyethylene, polypropylene, polyvinyl chloride, polyester, etc. (Special Publication No. 59-3230
6, JP-A-60-190340 and JP-A-6O-24
5547), 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 aromatic polyimide sheets to each other in the honeycomb core manufacturing method using a spreading method using sheets, 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 J] The present invention provides a honeycomb core made of aromatic polyimide, which could not be manufactured industrially in the past, and at the same time, it is possible to produce the honeycomb core made of aromatic polyimide industrially. The present invention provides a method for manufacturing.

[Means for Solving the 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, and developed the present invention. Completed the invention.

That is, according to the present invention, 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 is formed in the same void between the sheets. They are arranged at regular intervals within the 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 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) Represents a tetravalent group selected from the group consisting of aromatic groups and non-fused polycyclic aromatic groups in which male 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. The method for producing a Boimide honeycomb core according to claim 2, wherein the aromatic polyimide is basically an aromatic polyimide represented by a repeating unit of formula (I) (in the formula, R is the same as before).

The present inventors first developed a repeating unit represented by (in the formula, R is the same as above) as a polyimide that has excellent mechanical properties, thermal properties, electrical properties, solvent properties, etc., and has thermoplasticity. We have discovered a polyimide with (Unexamined Japanese Patent Publication No. 63-243
132, Japanese Unexamined Patent Publication No. 1-215825, Patent Application No. 1983-315
086. 63-320581, 63-334655
etc.) The above polyimides, unlike conventionally known polyimides, have good thermoplasticity, can be processed by melt molding methods such as extrusion molding and injection molding, and are polyimides with strong adhesive strength. be.

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 the formation of vinyl poles in the film, and reducing the film thickness. Ta. 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, in JP-A-1-192536, a polyimide that is soluble in phenol, cresol, norogenated phenol, etc. is used. However, since a high boiling point solvent is used, treatment at high temperatures for a long period of time is required to completely volatilize the solvent, resulting in the same problems as when starting from a polyamic acid solution, such as 0 spots, pinholes, and uneven sheet thickness. 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-1-110530 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 manufacture a novel aromatic polyimide honeycomb core that is lightweight, heat resistant, and has excellent radiation resistance, especially when used in outer space, by the spreading method. .

Preferred embodiments of the present invention are as follows.

is a polyimide basically 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 (
The process of heating and pressurizing the part sandwiched between the hot plates to fuse it while sandwiched between the hot plates (heat sealer).

(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 fused portion of the sheet is heated to a temperature 1 to 200°C higher than the glass transition temperature of polyimide, and 1 to 200 kg/
This is carried out by maintaining the pressurized state in 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 spreading 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 (rr), that is, bis[4-(3-(
It is obtained by reaction of 4-aminophenoxy)benzoyl)phenyl]ether 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-mentioned diamine has the formula (III) O○ (in the formula, R is the same as before).

For example, ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, 1゜l-bis(2,3-dicarboxyphenyl)ethane dianhydride. , bis(2,3-
dicarboxyphenyl)methanihydride, bis(3,4
-dicarboxyphenyl)methanihydride, 2,2-bis(3,4-dicarboxyphenyl)propanihydride, 2,2-bis(2,3-dicarboxyphenyl)propanihydride, 2.2-t :'su(3゜A kneet +I Il,→zo 4f S/ -) -j
Ishi) -11133,3,-hexafluoropropanide anhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3,-hexafluoropropanide anhydride substance, pyromellitic dianhydride, 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, bis(2
, 3-dicarboxyphenyl)ether dianhydride, bis3.4-dicarboxyphenyl)sulfone dianhydride, 4
．． 4'-(p-phenylenedioxy)cyphthalic dianhydride, 4.4'-(m-phenylenedioxy)cyphthalic dianhydride, 2.3,6.7-naphthalenetetracarboxylic dianhydride, 1,4゜5.8-naphthalenetetracarboxylic dianhydride, 1.2,5.6-naphthalenetetracarboxylic acid diw7&/mono + ') 2 A-8-
)-+l-) Tetracarboxylic dianhydride, 3,4,9.
10-perylenetetracarboxylic dianhydride, 2.3,6
．． 7-anthracentetracarboxylic dianhydride, 1.2
, 7°8-phenanthrenetetracarboxylic dianhydride, etc., 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 the organic solvent 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, tetrahydrofuran, 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.

0 0 (In the formula, R is the same as above).

This polyamic acid is dehydrated by heating at 100 to 400°C, or chemically imidized using a commonly used imidizing agent, such as triethylamine and acetic anhydride. same).

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

Generally, after producing polyamic acid at low temperature,
Further, this is thermally or chemically imidized. However, it is possible to simultaneously perform the production of polyamic acid and the thermal imidization reaction at a temperature of 60°C to 250°C to obtain polyimide.
-2 = 1 2 ふ ■■ -ノ +19-6 1 After suspending or dissolving the diamine in an organic solvent, a reaction is carried out under heating to simultaneously generate polyamic acid and dehydrate and imidize it. It is also possible to obtain a polyimide having the repeating unit of the above formula (I) as a basic skeleton by carrying out this process.

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. The extrusion temperature is determined as appropriate depending on the melt viscosity, glass transition temperature, and melting temperature of the polymer, but in general, honeycomb cores are manufactured using the aromatic polyimide sheet obtained in this manner. However, 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, 2b', . . . are placed one on top of the other at regular intervals.
The two sheets are heated while being sandwiched between them, and pressure is applied 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 lc is further applied to the laminate 4, followed by a spacer 3a.

3b, ... and heat sealers 2a' and 2b'. ... in the fused region 5a of the laminate 4
, 5b, . . . are inserted into the gaps, arranged at regular intervals, and the other heat sealers 2a, 2b, . Heat sealer 2a' on the opposite side.
, 2b', . . .
The two sheets are sandwiched between the pair of heat sealers and heated, and pressure is applied in the stacking direction to further fuse and join the sheets to the stack.

- By sequentially performing the operation of overlapping sheets on a laminate and fusing/joining them as described in E for each newly overlaid sheet, an even larger number of sheets can be formed into a large number of intermittent fused areas. A laminate is formed by fusing and bonding through the 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.

Preferably, a release agent is applied to prevent staining.

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 range of 50℃ higher, 1~2000kg/c
m", preferably 10 to 500 kg/cm2, more preferably 30 to 50 kg/cm" for 0.1 seconds to 3 hours, preferably 30 seconds to 1 hour.
It is carried out by holding for a period of time, more preferably from 1 minute to 10 minutes.

1. 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.

The above fusing operation for each sheet is performed by arranging the sheets to be fused at regular intervals within the gap between them, and heating and pressurizing the gap between the spacers with a heat sealer, as shown in Figures 1 and 2. or no spacer may 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 for the spacer, it is possible to use 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 Plus Deck material such as polyimide or Teflon. can.

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 in the range of ~1000 IJ, m, 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 the elongated laminate 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, the laminate manufactured as described above is subjected to an appropriate rolling force in the lamination direction (W direction shown in FIG. 4) at a temperature higher than the glass transition temperature of the aromatic polyimide. In addition, it is spread to form a honeycomb structure as shown in FIG. 4 to produce a polyimide honeycomb core.

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

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

[Implementation Example 1] 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 0.50 g of polyimide powder in 1.00 mff of p-chlorophenol/phenol (weight ratio 9/1) mixed solvent, cooling to 35°C and measuring Tg and Tm: DSC (Shimadzu DT-40 series, D
Example 1: 5.92 kg (I0 mol) of bis[4-(3-(4-aminophenoxy)benzoyl)phenyl]ether and 2.07 kg (10 mol) of bilomel nitrate dianhydride (9, Polyimide powder was obtained using 148 g (1 mole) of phthalic anhydride and 148 g (1 mole) of phthalic anhydride as raw materials in accordance with the method disclosed in the above-mentioned patent publication. The glass transition temperature of polyimide is 227°C, and the logarithmic viscosity is 0.55.
dβ/g. This polyimide powder was heated to a thickness of 50 μm1 using a regular extruder at a cylinder temperature of 310 to 330°C.
It 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. A long spacer (iron foil coated with release agent, thickness 50 μm, width 5 mm, length 40 m) was placed on top of this belt-shaped polyimide sheet.
The spacers were arranged at 6 mm intervals so that the longitudinal direction of the spacers was parallel to the width direction of the sheet, and another sheet was laminated thereon. Next, the laminated sheets with spacers sandwiched between them are sandwiched from above and below with a pair of round bar-shaped heat sealers with a diameter of 4 mm at the center of the gap between the spacers, and heated to 300°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 lamination direction at a temperature of 270° 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 ℃ 4.7kg/cm”180℃, -60
The compressive strength at °C is 3.7 kg/cm” and 4, respectively.
．． 0 kg/cm", which was excellent.

Examples 2 to 6 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 spread 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 materials, the glass transition temperature of the polyimide, the extrusion sheeting temperature, the lamination temperature during honeycomb core production, and the spreading temperature.

[Effects of the Invention] According to the present invention, a polyimide honeycomb core having high mechanical strength and excellent heat resistance, and particularly excellent heat and radiation resistance when used in outer space, can be obtained.

Furthermore, according to the present invention, a polyimide honeycomb core can be manufactured industrially 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, 1c... sheet, 2a, 2a 2b, 2b'... heat sealer 3a, 3b
... Spacer, 4... Laminated body, 5a, 5b... Fusion region, A... One side forming 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 spread in the stacking direction,
A polyimide honeycomb core characterized by a honeycomb 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. ▼ (In the formula, 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. The polyimide according to 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. ▼ (in the formula, R is the same as before) Manufacturing method of manufactured honeycomb core.