JPS645813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel honeycomb core. More specifically, the present invention relates to a lightweight and highly strong honeycomb core made of heat-resistant fibers, such as aromatic polyamide fibers, and heat-resistant resin.

Prior Art Conventionally, honeycomb cores have been useful as lightweight and highly strong structures, and materials such as aluminum foil and craft paper have been used.

For example, honeycomb cores made of aluminum foil have a high level of strength and are used in aircraft components. However, there has been a demand for a higher degree of weight reduction and strength and reliability in components for such aircraft, etc., and there has been a demand for the development of even lighter and stronger honeycomb cores.

On the other hand, although honeycomb cores based on kraft paper are also lightweight and inexpensive, they have drawbacks such as insufficient mechanical strength and large shrinkage due to temperature and humidity.

In recent years, synthetic paper made of wholly aromatic polyamide has attracted attention as a lightweight and thermally stable base material for honeycomb cores. This paper is based on a sheet of synthetic paper made by mixing polymethaphenylene isophthalamide fibers and synthetic pulp (fibrids) made from polymetaphenylene isophthalamide. Since the pulp of metaphenylene isophthalamide is amorphous, it functions as a binder, but the result shows a weakness in mechanical strength.

As a honeycomb core free from such drawbacks, a honeycomb core based on a nonwoven fabric consisting essentially of aromatic polyamide fibers was proposed (Japanese Patent Application Laid-open No.
57-144746).

Products based on this aromatic polyamide fiber nonwoven fabric are much superior in strength after being impregnated with resin compared to those based on synthetic paper, and the nonwoven fabric itself is highly impregnated with resin, but the actual honeycomb core It was found that there were various problems in the manufacturing process.

That is, in the production of honeycomb cores, paste (adhesive) is generally coated in stripes on a sheet-like material made of aromatic polyamide fiber or the like so that a predetermined cell size is obtained. Publication No. 7640, Japanese Patent Publication No. 17910, Japanese Patent Publication No. 1791-
134075, etc.), the coated sheet,
After stacking them with a half-pitch shift, heat press is performed to obtain an unexpanded material, which is then cut to a predetermined core thickness and expanded (for example, in Japanese Patent Application Laid-Open No.
(Refer to Publication No. 129267), when the honeycomb shape is obtained, a method is adopted in which a fixed honeycomb core is obtained by coating or impregnating with a thermosetting resin and applying a heat treatment. The most difficult part is applying the glue and impregnating with the resin. In particular, it is extremely difficult to uniformly impregnate the finished honeycomb with resin, and it is necessary to repeat the process of dipping it in a dilute resin solution, pulling it up, blowing off the resin remaining on the surface with air, and dipping it again. .

In addition, with conventional non-woven fabrics, when applying glue, there is a lot of see-through in areas other than the coated area, and the applied glue easily passes through the non-woven fabric, allowing it to seep through to the surface. This means that parts that should not be glued will be glued to the surface.

Purpose of the Invention The purpose of the present invention is to eliminate the above-mentioned drawbacks of conventional aromatic polyamide synthetic paper or aromatic polyamide fiber nonwoven fabric, and to provide a paper that has appropriate resin impregnation properties and adhesive coating properties. The object of the present invention is to provide a honeycomb core that is easy to manufacture, has excellent mechanical properties (particularly shear properties), and is useful as a component of lightweight, high-performance structural materials.

Composition of the Invention As a result of intensive research to achieve the above-mentioned object, the present inventors have discovered that even if there is a honeycomb core based on a non-woven fabric made of heat-resistant fibers such as aromatic polyamide fiber, conventional non-woven fabric as the base material We have discovered that only when a special non-woven fabric with a denser structure than that used in honeycomb cores is used, the drawbacks of conventional honeycomb cores can be overcome and products with extremely high usefulness can be obtained, and have thus arrived at the present invention.

That is, the present invention provides a honeycomb core constructed by impregnating a heat-resistant resin into a non-woven fabric made of heat-resistant fibers, wherein the mode of the pore size distribution of the non-woven fabric when measured with a mercury porosimeter is 1 to 1.
It is a honeycomb core characterized by having a diameter of 15 μm and a porosity (void press-fitting ratio) of 0.05 to 0.4.

The heat-resistant fiber in the present invention is a general term for fibers with a softening point of 200°C or higher (preferably 250°C or higher), and in the present invention, aromatic polyamide fibers and aromatic polyamide-imide fibers, which have particularly excellent heat resistance, are Fibers, polyarylate fibers, etc. are suitable. However, depending on the use of the honeycomb core, polyethylene
2,6-naphthalate fiber, polyethylene terephthalate fiber, etc. can also be used.

Among these, aromatic polyamide fibers are most preferred, and examples of the aromatic polyamide fibers include metaphenylene isophthalamide, paraphenylene terephthalamide, metaphenylene terephthalamide, paraphenylene isophthalamide, 4,
Examples include aromatic polyamide fibers whose main repeating structural unit is one or more selected from the group consisting of 4'-oxydiphenylene terephthalamide, 3,4'-oxydiphenylene terephthalamide, etc. .

As mentioned above, the aromatic polyamide suitably used in the present invention has a terephthalic acid unit or an isophthalic acid unit as an acid component, and a paraphenylenediamine unit, a metaphenylenediamine unit, or a diamino diphenyl ether unit as an amine component. , a diaminodiphenylmethane unit or a diaminodiphenylesulfone unit as a main structural unit, and is a polymer having particularly good heat resistance. These aromatic polyamides are prepared by dissolving them in an inorganic solvent such as sulfuric acid or an organic solvent such as N-methylpyrrolidone, spinning them in a wet, dry or semi-dry and semi-wet process, and subjecting them to stretching heat treatment as necessary. As a result, fibers with good heat resistance can be obtained.

In the present invention, it is preferable that 70% by weight or more (particularly 85% by weight or more) of the nonwoven fabric consists of polymetaphenylene isophthalamide fibers. On the other hand, synthetic paper made by mixing cut fibers made of polymetaphenylene isophthalamide-based fibers and fibrids obtained from polymethphenylene isophthalamide has a strength that is thought to be due to the amorphous nature of the fibrids (for example, compressive strength ) deficiency results in unsuitability for use as a honeycomb core.

In order to more effectively exhibit the characteristics of the honeycomb core of the present invention, the aromatic polyamide fibers include (A) drawn and heat-treated fibers, (B) undrawn fibers, drawn and unheated fibers, and/or easily soluble fibers. It is preferable to use a skin core fiber having a skin layer and a poorly soluble or insoluble core layer in combination.

The undrawn fibers and the drawn and unheated fibers of aromatic polyamide (B) are produced by a well-known spinning method, for example, by passing a solution of the aromatic polyamide in a polar organic solvent through small holes into a coagulating solution. It can be obtained through a spinning and washing process.

That is, undrawn fibers can be obtained by drying the fibers after the above-mentioned washing,
The drawn and unheated fibers are obtained by drawing the above-mentioned undrawn fibers in hot water.

Furthermore, in the present invention, a skin-core type aromatic polyamide fiber having an easily soluble skin layer and a slightly soluble or insoluble core layer may be used as the fiber (B). The fibers can be obtained by, for example, changing the coagulation conditions in the step of obtaining the drawn and heat-treated fibers described above (for details, see European Patent Application Publication No. 0040833).

On the other hand, the drawn and heat-treated fiber (A) can be obtained by further heat-treating the drawn and unheated aromatic polyamide fiber described below by passing it through an atmosphere at a high temperature, for example, 200 to 600° C., or on a plate under tension.

As described above, it is a preferred embodiment of the present invention to use (A) drawn and heat-treated fibers together with (B) undrawn fibers and/or drawn and unheated fibers or skin/core fibers. The ratio can be arbitrarily changed depending on the intended use of the honeycomb core.

That is, the mixing ratio of the (A) drawn heat-treated fibers and the (B) fibers may be such that the (B) fibers are 5% by weight or more, preferably 95 to 5% by weight, and more preferably 95% to 5% by weight.
80-20% by weight. If the amount of drawn heat-treated fibers exceeds about 95% by weight, the intertwining between the fibers becomes weaker and the strength of the sheet-like structure becomes weaker, which is not preferable.

In other words, when forming a nonwoven fabric, a mixture of fibers that are substantially deformed and fused together under heating and pressurized conditions (temperature, pressure, addition of plasticizer, etc.) and fibers that maintain their fiber shape even if deformed. Because there are fibers that deform and fuse, the mode of the pore size distribution is 1 to 15 μm, and because there are no fine fibrils, pores with a diameter of 1 μm or less are unlikely to occur. Note that fibrids here are those shown in, for example, Japanese Patent Publications No. 35-11851 and No. 37-5732, etc., and the specific surface area of ordinary fibers is 10 ^-1 ~
10 ¹ m ² /g, whereas it is about 10 ² to ^{10 4} m ² /g.

In addition, in the present invention, webs having different blending ratios of the (A) fibers and (B) fibers or webs made of fibers with different finenesses may be laminated to form a nonwoven fabric whose density changes in the thickness direction. For example, by laminating a web of fibers (B) as an intermediate layer and webs of fibers (A) as both surface layers, it is possible to obtain a nonwoven fabric with particularly high density of the intermediate layer.

In a preferred embodiment of the present invention, in addition to aromatic polyamide fibers, various fibers may be used in combination as necessary. Examples of such fibers include:
Polypropylene fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, aliphatic polyamide fibers such as nylon-6 and nylon 66, organic fibers such as polyarylate fibers and polyacrylonitrile fibers, glass fibers, asbestos, metal fibers, potassium titanate fibers, etc. Inorganic fibers, carbon fibers, alumina fibers, etc. can be mentioned.

Among such fibers, it is possible to use fibers with a low softening point within a range that does not impair the heat resistance as a honeycomb core base material, but it is usually possible to use 30% by weight or less, preferably 15% by weight or less. .

One practical method is to combine polyethylene terephthalate fibers with drawn and heat-treated aromatic polyamide fibers. However, from the point of view of heat resistance, it is easier to handle fibers made only of aromatic polyamide fibers.

In the present invention, the method of obtaining a nonwoven fabric from the fibers includes a method of opening long fibers, a method of mixing short fibers and spreading them into a planar shape, a method of performing these steps in a wet manner such as in water, a method of performing a dry method. Various methods can be adopted, such as the method.

For example, in the case of using polymetaphenylene isophthalamide fibers as heat-resistant fibers, the stretched heat-treated polymetaphenylene isophthalamide fibers and the unstretched fibers are each cut into a length of 51 mm, and the weight After mixing the fibers at a ratio of 40:60, a web-like material is obtained by continuously spreading the fibers into a homogeneous surface to a predetermined weight (g/m ² ). Furthermore, a desired sheet-like material can be obtained by impregnating the web-like material with a plasticizer and then pressurizing and heating it at high temperature and pressure using a means such as a hot roll.

Any plasticizer may be used as long as it has the effect of plasticizing the fibers that make up the web, but in the case of polymetaphenylene isophthalamide fibers, N-methyl-2-pyrrolidone, dimethylacetamide, dimethyl Amide polar solvents such as formamide and/or water are suitable.

Heat and pressure treatment uses higher temperature and pressure conditions than conventional heat pressing of nonwoven fabrics, and generally
Conditions of ~400°C and linear pressure of 50 to 600 Kg/cm are suitable.

Such nonwoven fabrics have extremely high density compared to conventional nonwoven fabrics. The distribution state and size of the voids inside the nonwoven fabric are determined by the mode of the pore size distribution measured by a mercury porosimeter.
15μ, preferably within the range of 1 to 13μ, and
It is characterized by a porosity (injection cavity ratio) within the range of 0.05 to 0.4. When the distribution and size of the voids in the nonwoven fabric are within this range, the nonwoven fabric exhibits appropriate resin impregnating properties and good paste coating properties, and forms a honeycomb core of excellent quality.

The equipment used for measurement here is American
60000psi manufactured by Instrument Company
“POROSIMETER” and pressure (pore diameter R (μ)
After determining the relationship between the mercury penetration amount V (ml/g) and the mercury penetration amount V (ml/g), the pore diameter R (μ) and △V/△R (ml/g/
A graph obtained by calculating μ) is shown in FIG.

The curve [] in the figure shows an example of the nonwoven fabric specified in the present invention, and corresponds to Example 1, which will be described later. The curve [ ] is an example of a commercially available general aromatic polyamide nonwoven fabric (registered trademark "FIBREX" 1113),
[ ] indicates an example of commercially available aromatic polyamide synthetic paper (registered trademark "Nomex" 410, 412).
As is clear from the figure, many of the conventional commercially available nonwoven fabrics have a pore size distribution peak of 15 μ or more and a porosity (press-in void ratio) of 0.5 or more. In addition, synthetic paper has a maximum peak in pore size distribution where the pore size is very small. On the other hand, the maximum peak of the pore size distribution of the nonwoven fabric used as the base material in the present invention is within the range of 1 to 15 μm.

If the mode of the pore size distribution exceeds 15 μm, the penetration is too large when applying the adhesive, and it is difficult to increase the strength of the fiber-resin composite material when impregnated with resin, and the mode of the pore size distribution is less than 1 μm. In some cases, it is difficult to impregnate every corner with the resin.

The honeycomb core of the present invention is made by impregnating such a special heat-resistant nonwoven fabric with a heat-resistant resin, but the adhesive used in manufacturing the honeycomb core is epoxy resin, phenol, etc. It is possible to use various heat-resistant adhesives such as resin-based, polyimide-based, and polyamideimide-based adhesives.

Further, examples of the impregnating resin used for fixing the honeycomb core include epoxy resin, phenol resin, polyimide resin, polyamide-imide resin, and various other heat-resistant resins.

The method for producing honeycomb cores is to coat the surface of a nonwoven fabric with glue in stripes to form a predetermined cell size, stack the sheets with a half-pitch shift, and then heat press the sheets to make them unexpanded. Obtain the material, then cut it to the specified core thickness,
A fixed honeycomb core can be obtained by spreading the core, coating or impregnating it with a thermosetting resin when it reaches a honeycomb shape, and subjecting it to heat treatment.

In the case of the non-woven fabric, the non-woven fabric is first impregnated with resin and cured, and then a paste (adhesive) is applied in stripes to a predetermined cell size, and the coated sheet is , stacked on top of each other by shifting half a pitch at a time, heated while pressing to obtain an unexpanded material, cut to obtain a predetermined core thickness, expanded to obtain a honeycomb-like material, and fixed to form a honeycomb core. It is also possible to adopt the method of

Effects of the invention Due to its structure, the above-mentioned nonwoven fabric has
It has appropriate resin impregnating properties and adhesive coating properties, making it possible to impregnate resin or resin solution in the production of honeycombs in an extremely quick and efficient manner, and to apply the desired amount of adhesive. Coating is also easy.

The obtained honeycomb core has extremely excellent mechanical properties (especially shear properties) and is extremely useful as a component of lightweight, high-performance structural materials.

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

In the examples, "parts" simply means "parts by weight."

Example 1 (a) Preparation of sheet material Cut fiber (fineness 1.5 denier, fiber length 51 mm) of drawn heat-treated polymetaphenylene isophthalamide fiber (registered trademark "Conex") 40
60 parts of cut fibers (fineness: 1.5 denier, fiber length: 51 mm), which are so-called drawn and unheated fibers drawn in hot water after coagulating and washing with water in the spinning process of the polymetaphenylene isophthalamide, were mixed to form a flat card. Carding was performed using a machine to obtain a web-like material.

Next, after spraying 100 parts of a 3% aqueous solution of N-methyl-2-pyrrolidone onto this web-like material,
Linear pressure of 200 with a pair of press rolls set at 280℃
By hot-pressing at a speed of 8 m/min at Kg/cm, a sheet-like product with a weight of 54 g/m ² and a thickness of 0.049 mm was obtained. The porosity of this sheet-like material is 0.21,
The maximum peak of the pore size distribution was 12μ, and there was another small peak at 0.2μ.

(b) Coating and lamination of adhesive Apply an epoxy resin adhesive (Epicoat 828: Epikot
871: Epicure Z (all Ciel Chemical products) =
50 parts: 50 parts: 20 parts mixture) in a 28 mm pitch.
After coating in stripes with a width of mm, layers were stacked while shifting the coated surfaces by half a pitch.

Next, this laminate was heat-bonded using a press heated to 140° C. at a pressure of 30 kg/cm ² for 20 minutes to obtain an unexpanded honeycomb core.

(c) Expanding, resin impregnation, and curing The unexpanded honeycomb core obtained in (b) above was cut perpendicularly to the stripes of the adhesive to a width of 7 mm (corresponding to the thickness of the honeycomb core).

The amount of adhesive applied was 70% by weight on average based on the sheet material as the base material.

The cut unexpanded honeycomb core was expanded into a honeycomb shape, fixed as it was, and impregnated in a previously prepared epoxy resin solution (Epicoat 828: Epicure Z: acetone = 100 parts: 20 parts: 180 parts).

Then, after removing the acetone by air drying,
It was further heated at 140°C for 4 hours to harden it.

(d) Performance measurement of resin-impregnated honeycomb core The resin-impregnated honeycomb core obtained in (c) above has an apparent specific gravity of 0.026 g/cm ³ and a compressive strength (cell size 7 mm, core thickness 7 mm) of 10.5 Kg. / ^cm2 .

For comparison, a commercially available synthetic paper (registered trademark "Nomex" 410, (2 mil): weight 38 g/m ² ) consisting of polymetaphenylene isophthalamide fibrils and polymetaphenylene isophthalamide fibers was used. A resin-impregnated honeycomb core (apparent specific gravity 0.025 g/cm ³ ) was obtained in the same manner as in Example 1 (b) and (c).

The compressive strength of this honeycomb core was only 2.8 Kg/cm ² .

The maximum peak of the pore size distribution of this synthetic paper is
It was 0.04μ.

Example 2 An unexpanded honeycomb core obtained in the same manner as the prototype in Example 1 was expanded into a honeycomb shape,
It was fixed as it was and impregnated into a phenol resin solution (Cemedine #100: methyl methyl ketone = 20 parts: 80 parts) prepared in advance.

Then, after air drying, the process was repeated two more times. It was heated in a steam dryer (95°C) for 30 minutes and then heated at 120°C for 2 hours to harden it.

The resin-impregnated honeycomb core thus obtained had an apparent specific gravity of 0.07 g/cm ³ and a compressive strength (cell size 7 mm, core thickness 7 mm) of 35 Kg/cm ² .

In addition, the shear strength is 20Kg/cm ² and 10Kg/cm ²
(The direction of the honeycomb is the sheet direction for the former, and the direction perpendicular to the sheet for the latter), and the shear modulus is 7Kg/mm ² and 4
It was Kg/ ^mm2 .

Comparative Example 1 (a) Manufacture of a sheet-like product Cut fiber (fineness 1.5 denier, fiber length 51 mm) of drawn heat-treated polymetaphenylene isophthalamide fiber (registered trademark "Konex") 40
A so-called undrawn cut fiber (fineness 4.7 denier,
Fiber length: 51 mm) 60 parts were mixed and carded using a flat card machine to obtain a web-like material.

Next, the web-like material was pressed at 8 m/min under a linear pressure of 100 Kg/cm using a roll press set at 300°C to obtain a sheet-like material having a weight of 64.0 g/m ² and a thickness of 0.082 mm. The porosity of this sheet-like material is
0.45, and the maximum peak of the pore size distribution was 27μ.

(b) Coating and lamination of adhesive Apply an epoxy resin adhesive (Epicoat 828: Epikot
871: Epicure Z (all Ciel Chemical products) =
50 parts: 50 parts: 20 parts mixture) in a 28 mm pitch.
The coating was applied in mm-wide stripes and laminated while shifting the coated surfaces by half a pitch.

Next, this laminate was colored by heating at a pressure of 30 kg/cm ² for 20 minutes using a press pressurized at 140° C. to obtain an unexpanded honeycomb core.

(c) Expansion The unexpanded honeycomb core obtained in the above (b) was cut perpendicularly to the stripes of the adhesive to a width of 7 mm (corresponding to the thickness of the honeycomb core).

The amount of adhesive applied was 70% by weight on average based on the sheet material as the base material.

An attempt was made to expand the cut, unexpanded honeycomb core, but the adhesive passed through the nonwoven fabric sheet and adhered to unnecessary areas, making it difficult to expand successfully.

Example 3 (a) Preparation of sheet material 100 parts of cut fiber (fineness 0.5 denier, fiber length 6 mm) of drawn heat-treated polyethylene terephthalate fiber (registered trademark "Tetron") was mixed with 50,000 parts of water to form 400 meshes. Spread on wire mesh,
A sheet material having a basis weight of 75 g/m ² was obtained. This is 160
℃, treated with a press roll at 200Kg/cm,
A sheet-like product having a weight of 70 g/m ² and a thickness of 0.07 mm was obtained.

The porosity obtained with a mercury porosimeter is 0.25, and the maximum peak of the pore size distribution is 11μ, and other
There was a small peak at the position of 0.1μ.

(b) Coating and lamination of adhesive The sheet-like material obtained in (b) above was
An adhesive was applied by the method shown in (b), followed by lamination and pressing to obtain an unexpanded honeycomb core.

(c) Expanding, resin impregnation and curing The unexpanded honeycomb core obtained in (b) above was used in Example 1 (c).
Similar to the method described above, a honeycomb shape was formed, fixed as it was, and a pre-prepared epoxy resin solution (Epicoat 828: Epiquure Z: Acetone = 100
parts: 20 parts: 180 parts).

Then, after removing the acetone by air drying,
It was further heated at 140° C. for 4 hours to harden it.

(c) Performance measurement of resin-impregnated honeycomb core The resin-impregnated honeycomb core obtained in (c) above has an apparent specific gravity of 0.026 g/cm ³ and a compressive strength (cell size 7 mm, core thickness 7 mm) of 10 kg. / ^cm2 .

Example 4 (a) Preparation of sheet material Cut fiber (fineness 1.5 denier, fiber length 51 mm) of drawn heat-treated polymetaphenylene isophthalamide fiber (registered trademark "Cornetx") 40
60 parts of cut fibers (fineness: 4 denier, fiber length: 51 mm), which are so-called drawn and unheated fibers that were drawn in hot water after coagulation and washing in the spinning process of the polymetaphenylene isophthalamide, were mixed to form a flat card. Carding was performed using a machine to obtain a web-like material.

Then, the web-like material was hot-pressed for 2 minutes under a pressure of 400 kg/cm ² in a press set at 280° C., to obtain a sheet-like material having a weight of 64.0 g/m ² and a thickness of 0.065 mm. The porosity of this sheet-like material is 0.12,
The maximum peak of the pore size distribution was 12μ, and there was an even smaller peak at 0.3μ.

(b) Resin impregnation and curing Pre-prepared phenolic resin solution (registered trademark "Cemedine"#100: Methyl ethyl ketone = 20
part: 180 parts). Then, after removing the acetone by air drying, impregnation was performed again. 30 at 95℃
The phenolic resin was cured by heating at 120° C. for 2 hours, and the amount of phenol resin deposited was 50%.

(c) Coating and lamination of adhesive On the resin-impregnated sheet obtained in the above (b), apply an epoxy resin adhesive (Epikoat 828: Epikoat 871: Ebiquiure Z (all manufactured by Ciel Chemical) = A mixed system of 50 parts: 50 parts: 20 parts) was applied in stripes of 7 mm width with a pitch of 28 mm, and then the coated surfaces were laminated while shifting the coated surfaces by half a pitch.

This laminate was then heated and bonded for 20 minutes at a pressure of 30 kg/cm ² using a press pressurized at 140° C. to obtain an unexpanded honeycomb core.

(d) Measurement of physical properties of honeycomb core The unexpanded honeycomb core obtained in (c) above was expanded and fixed, and the apparent specific gravity was 0.026 g/cm ³ and the compressive strength (cell size 7 mm, core thickness 7
mm) was 10.5Kg/ ^cm2 .

The shear strength was 35Kg/cm ² and 18Kg/cm ² .
The shear modulus was 3.5Kg/mm ² and 2Kg/mm ² .

Example 5 In Example 4, the number of repetitions of resin impregnation in (b) above was increased, and the amount of phenolic resin impregnated was 150%.
A honeycomb core was obtained in the same manner as in Example 4. The apparent specific gravity of this honeycomb core is
The compressive strength was 0.05g/cm ² and the compressive strength was 20Kg/cm ² .

Comparative Example 2 A honeycomb core as in Example 5 was prepared using commercially available polymetaphenylene isophthalamide synthetic paper (registered trademark "Nomex" 410). When an attempt was made to expand the obtained unexpanded honeycomb core after resin impregnation and curing, adhesive coating, and lamination, a part of the phenolic resin peeled off and the process failed. When this synthetic paper was measured with a mercury porosimeter, the pore size distribution had a peak at 12μ, but the maximum peak was 0.04μ.

Example 6 A honeycomb core was obtained in the same manner as in Example 4 using the polyethylene terephthalate sheet in Example 3.

The compressive strength was 9Kg/cm ² , and the shear strength was 30Kg/cm ² and 20Kg/cm ² .

[Brief explanation of drawings]

Figure 1 shows the measurements of the nonwoven fabric constituting the honeycomb core of the present invention, a conventional commercially available nonwoven fabric (“FIBREX 1113” manufactured by Karl Freudenberg), and a conventional commercially available synthetic paper (“Nomex 410” manufactured by Dupont) using a mercury porosimeter. This is a graph showing the state of pore size distribution when the vertical axis is △V/△R (ml/
g/μ) and the horizontal axis is the pore diameter (μ). In the figure, the curve [] indicates an example of the nonwoven fabric specified in the present invention, [] indicates an example of the commercially available nonwoven fabric, and [] indicates an example of the commercially available synthetic paper. [ ] has a pore size distribution that is biased toward the larger side for honeycomb core materials.
[ ] indicates that there is a problem with resin impregnation composite and adhesion, as the pore size distribution is biased toward the smaller side, making it difficult for resin to enter.

Claims (1)

[Scope of Claims] 1. A honeycomb core constructed by impregnating a heat-resistant resin into a non-woven fabric made of heat-resistant fibers, wherein the mode of the pore size distribution of the non-woven fabric when measured with a mercury porosimeter is 1 to 15 μm; A honeycomb core characterized by a porosity (press-fit void ratio) of 0.05 to 0.4. 2. The honeycomb core according to claim 1, wherein the nonwoven fabric made of heat-resistant fibers contains 70% by weight or more of aromatic polyamide fibers. 3. A nonwoven fabric made of heat-resistant fibers includes (A) stretched heat-treated fibers, (B) stretched unheat-treated fibers, unstretched fibers, and/or
Alternatively, the honeycomb core according to claim 1 or 2, wherein the surface layer is composed of skin/core fibers that are easily soluble in solvents and the core fibers that are insoluble or poorly soluble in solvents.