JP3520223B2 - Method for manufacturing honeycomb panel structure - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a panel having cells of regular shape (usually hexagonal), ie a panel known as a honeycomb panel.

[0002]

2. Description of the Related Art Honeycomb panels can be manufactured from various sheet materials. Previously, the sheet material was previously formed into a corrugated shape, and the corrugated sheet was adhered along the flat portion. However, this method requires good cell registration and is currently used only for high modulus materials such as metal sheets.

For paper or similar fibrous sheet materials, the conventional method is to print or apply parallel lines of adhesive known as node lines. The printed sheet material is cut into individual sheets, and the sheets are laminated so that the node lines of adjacent sheets are located at positions separated from each other by ½ pitch (distance between lines). The resulting laminated sheet material consists of hundreds to thousands of sheets, this number depending on the size of the final honeycomb block required.

An adhesive is set by a method according to the property of the adhering means to join the sheets, and the resulting block is expanded at right angles to the direction of the node line by the pressure applied to the side surface thereof, and the sheet is formed at each cell point. Are expanded, that is, divided to form a cellular structure. The obtained block is cut at a right angle to the node line to cut out a panel, and a core for a composite panel is prepared. A composite sheet is made by applying a face sheet across the surface of the open cells to one or both sides of the core.

These cores have a wide range of applications in many industries, such as packaging, furniture, display panels, and, in all of these applications, the need for strong yet lightweight components. There is.

Originally, these cores were made of kraft paper, the paper walls of the cells being bonded with a simple adhesive, in some cases after which the entire surface of the core material was coated with a polymeric resin. .

However, paper honeycomb materials have many drawbacks, for example, low strength, especially in compressive strength. When a resin is combined with such a paper core material, there is an effect of considerably improving the compressive strength, but the obtained core material is extremely brittle and lacks elasticity.

A further major drawback of cellulose-based paper honeycombs is their lack of fire resistance. Techniques for imparting fire resistance include coating a polymer (eg, in the form of a latex) containing a powdered flame retardant on a core made of relatively porous paper, eg, kraft paper, impregnated with an aqueous phenolic resin. There is a way to do it. This method is described in British Patent GB-A-1444346.
The coating of the first resin enhances the moisture resistance of the core paper, but since it is kraft paper, the core is extremely brittle. Also, the core tends to be very heavy and has poor mechanical properties because it is made from kraft paper. Papers containing flame retardants were also tried, but they were difficult to print with node adhesives and were stiffer and difficult to spread.

Japanese Patents JP06272190, A294
0927 (Nettetsu Kogyo Co., Ltd.) describes a sheet consisting of 65 to 80% of fire resistant powder, 3477 flame retardant resin powder and 15 to 25 of cellulose fiber, which is essentially a paper made of cellulose fiber. Not an inorganic sheet. Other patents of the same company (JP08103979, A296
0423), a core made of this sheet formed into a honeycomb is impregnated with a flame retardant such as guanidine phosphate.

Recognizing this drawback, in the composite manufacturing industry, honeycomb core materials based on other paper-like materials, in particular aramid paper, ie materials made from fibers of highly aromatic polyamide resin, are used. Was developed. The best known example is Nomex ™ poly (m-phenylene isophthalamide) (a product of Deupon). These aramid papers consist of one or more fibers in the form of fibers, so-called chemical fibres, such as Nomex or Kevlar® and are formed into non-penetrable sheets.

The development of such a core meets today's increasing demands, and requires, for example, floor materials for aircraft and ships, members for skis and snowboards, and lightweight, strong and strong structural materials. It has been adopted for other purposes. However, aramid paper is more expensive than paper, and this cost prevents the use of aramid cores in many applications.

Other factors are the weight and poor nature of the conventional paper used (kraft paper). It is desired to improve the weight (density) of the core and the strength of the cellular structure.

In the manufacture of aramid paper honeycombs, sheet laminates or blocks are placed in a heated press to cure the node line adhesive and then expanded to form hexagonal cells. Prior to spreading, the aramid paper block is sprayed with water to facilitate spreading, but this method is not applicable to cellulosic paper such as kraft paper. The reason is that the paper breaks due to wetting, so wet paper cannot be spread.

The aramid paper-expanded block is set in this shape by heating it to a temperature above the glass transition temperature (Tg) of the aramid resin in the expanded state and cooling it.
Cellulose-based papers cannot be "heat-set" in this way because cellulose thermally degrades at temperatures well below its Tg.

However, it is desirable to set the shape of the paper honeycomb, otherwise the honeycomb will collapse once it is expanded. It is also desirable to remove the spread paper honeycomb from its spreading frame prior to resin coating. It is not impossible to coat the expanded honeycomb with a resin when the expanded honeycomb is attached to the expansion frame, but it is usually not convenient. The reason is that there is a problem that the cured resin is removed from the frame after the curing process.

Heat setting on the spreading frame was effective with kraft paper. This method is possible because of the wet contact inherent in kraft paper. However, in many cases it is not necessary to stabilize the kraft paper core as the kraft paper is continuously spread and fed to its final position.

[0017]

SUMMARY OF THE INVENTION The present invention provides a low cost, light weight, strong and tough paper honeycomb panel and a method for manufacturing the same.

[0018]

SUMMARY OF THE INVENTION The present invention provides a method of making a cellular material in which expanded cellular structures are formed from dense, non-porous cellulose paper, said paper comprising 30
It has a breathability of not more than ml / min, and after applying the aqueous composition to the cellular structure, it is sufficiently heated to stabilize the structure, and the resulting cellular structure is coated with a thermosetting resin, Cure the resin.

In another aspect, the invention provides a cellular structural core for a composite cellular material having three cell walls.
Has a breathability of 0 ml / min or less (before forming into cells),
Formed from shape-set, dense, low porosity cellulose-based paper. Shape set means that the sheets forming the cell walls maintain the cell shape without any external force.

Preferably, the aqueous liquid is a solution of flame retardant material. This method produces a lightweight honeycomb using paper as a material, which is extremely comparable to the outstanding performance obtained with aramid paper, yet significantly reduces the cost, and the aqueous solution contains a flame retardant. Therefore, it is comparable to the excellent flame retardancy of the aramid cellular structure.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the cell-shaped structure is formed by stacking sheets having adhesive node lines, curing the adhesive under heat and pressure, and arranging the cured laminate in a honeycomb expansion frame. Spreading the cellular structure, spraying the expanded structure with water or other aqueous liquid, heating for a sufficient time to set the shape of the cellular structure, removing the set structure from the spreading frame, It consists of applying a thermosetting resin to cure the resin.

The set cellular structure can be easily taken out of the spreading frame after the setting step and before the resin is dipped. Since the aqueous liquid contains the flame retardant, it is not necessary to mix the flame retardant in the initial paper manufacturing process. Aqueous liquids can be applied by spraying or other techniques, such as dipping or Curtain coating.

The aqueous liquid used to set the cellular structure is simple water or an insecticide containing a bactericide, a surfactant, and, preferably, a water penetration and flame retardant penetration aid. It contains an organic liquid.

The amount of aqueous liquid applied to the cellular structure is
It can be easily determined by a simple test of mixing an effective aqueous liquid so as to obtain a setting effect when heated. The amount of liquid is just that which wets the surface of the paper across the block. Addition of excess water such that the block becomes saturated with liquid and drops off should be avoided as it causes the block to collapse. In particular, if the liquid contains a flame retardant, the amount of solution or dispersion and the concentration of the solution or dispersion are such that a suitable amount of flame retardant can be accumulated in the paper structure. The desired setting is to provide the structure with sufficient rigidity for industrial use. After applying the aqueous liquid, the amount of the aqueous liquid remaining in the cellular structure is preferably 4 to 20% by weight based on the weight of the cellular structure block. It should be noted that the amount of liquid applied should not appear to soften the cellular structure excessively.

The paper used in the present invention is a dense paper having a breathability of 30 ml / min or less, which is represented by a type of paper known as glassine paper. In the manufacture of this paper, paper pulp is highly beaten or refined to obtain or loosen the fibers of the paper. In addition, the obtained sheet is subjected to advanced calendering. The resulting paper is dense and translucent. Encyclopedia of Polymer Science and Technology, 19
1968, Vol. 9, p. 719, chapter of John Willie's paper.

The low porosity of this paper is evidenced by the wicking force (detailed below) obtained by measuring the pick-up of liquids, which is different from breathability.

The paper used in the present invention has never been used to make a honeycomb cell structure. It is believed that this is because the paper is difficult to mold. Therefore, the method of the present invention is surprising in that it enables molding of a cellular structure using such paper.

The paper used in the method of the present invention is a very dense paper, has a smooth surface, high strength and a low porosity of less than 30 ml / min breathability. Paper weight is 30 ~ 15
It is 0 g / m ² . However, the surface must be sufficiently porous to allow the resin material used to form the cellular structure to adhere to the surface. For this reason, glassine papers that have been calendered and subsequently surface treated with a material that creates a water repellent surface, such as a silicone treated surface or a surface treated with a fluorinated composition, are usually unsuitable for the present invention, and Paper tends to interfere with the adhesion of resinous materials. Also, this paper has a low wicking power, ie it tends to absorb organic solutions.

The resin used to make the node lines is the resin conventionally used, for example, thermosetting epoxy adhesives, when making cellular structures from paper materials. A typical adhesive is sodium silicate,
Starch, polyvinyl acetate, phenol resin, resorcin
Formaldehyde resin, urea-formaldehyde resin and epoxy resin. One third is bondable at room temperature, the rest often requires heating.

In a particularly preferred embodiment of the invention, the aqueous solution is a solution or dispersion containing a flame retardant. Suitable flame retardant materials are nitrogen-containing phosphates, especially polyphosphates, and nitrogen-containing phosphates, especially amines, ammonium or melamine and optimally ammonium polyphosphate. Other types of flame retardants that can be used are ammonium orthophosphate, ethylenediamine phosphate, and other amine phosphates such as melamine phosphate. Instead of these,
Or other compounds that can be used in addition to these include brominated compounds such as brominated phenols, brominated imides and cycloaliphatic compounds, chlorinated compounds such as paraffin chloride, alumina trihydrate, magnesium hydroxide, There are zinc borates and aromatic phosphates and phosphonates. The amount of flame retardant in the aqueous liquid depends on the amount of aqueous liquid left on the core after application. Usually, 0.1-40
A wt% phosphate solution is used.

The amount of flame retardant added is such that it gives a dry flame retardant weight of 0.5 to 20% by weight, in particular 5 to 10% by weight, based on the total dry core weight. The flame retardant may be applied to the walls of the cellular structure as an aqueous system and subsequently dried to leave a coating of the flame retardant, or by dipping to penetrate the flame retardant into the body of the structure.

The heating conditions and time for heat setting the block depend to some extent on the block size, paper thickness and cell size factor. This method is 100-190
It is carried out under conditions of 1 ° C. to 1 hour, preferably 10 to 40 minutes. A typical combination is 20 minutes at 40 ° C. or time until the weight of the block no longer decreases.

The amount of water added, the heating time and the temperature are empirically determined, but when a cell structure having set stability is prepared and the structure is released from an external force, the structure changes its cell shape. It may be determined by simple testing that it can be maintained. Often, the paper sheets can be folded, moistened, and slightly heated to determine the initial approximation of the combination conditions depending on whether the sheets can remain folded when external force is released.

The resin used for coating the core of the present invention can be selected from phenol, epoxy, cyanate ester, bis-maleimide, polyimide, benzobisoxazine, unsaturated polyester, and other resins well known in the art. The resin is preferably EP 0,8
20,858, containing particles of a thermosetting polymer or a thermoplastic polymer. The resin is
Flame retardants, such as the phosphate ester type, or especially ammonium polyphosphate or other finely divided materials may be included, but this is usually unsatisfactory because of the excellent fire resistance obtained by the above application methods. is necessary.

A conventional sandwich structure is prepared using the obtained honeycomb. An adhesive layer may be present in the assembly between the core and the skin. However, the presence of a separate adhesive layer is not necessary. If you use glue,
The adhesive can be of any type known in the industry, namely phenol, epoxy, contact (contac).
t) or thermoplastics can be used.

One or more skins may be formed on one or both sides of the core, which skin is made of metal, especially aluminum; wood; prepregs such as glass, carbon, polyethylene or Kevlar reinforced prepregs. The matrix material can be any material well known in the art, such as cyanate esters, epoxies, phenols, polyesters, and the reinforcement can be unidirectional or multidirectional and can be used in the form of woven or matte. Or composed of discontinuous fibers; or a precure laminating resin such as phenol, melamine / formaldehyde or urea / formaldehyde laminating resin; or a combination of said skins, eg a metal skin on one side and a glass prepreg on the other. But it's okay.

In some cases, the honeycomb cells may be filled with polymer foam prior to applying the skin. This is effective for applications that require a high degree of sound absorption and heat insulation. Also, for the same reason, the cells may be filled with different types of powders.

The invention will be described with reference to the accompanying examples.
This is done to explain the invention.

[0039]

【Example】Example 1 65 g / m²And 94 g / m²Bleached glassine paper and unbleached paper
Rusin paper, 40g / m ²Machine glossy paper, 41g / m²A
Ramide paper, 89g / m²Kraft paper, and 80g / m²of
Honeycomb core sample using bleached neutral size processed paper
Created.

The air permeability of this paper was measured using the Bendtsen test, BS 6538: 2 and the results are recorded in Table 1. The table shows the tendency to absorb an organic solvent as a measured value of the wicking force. It is measured using a recordable microbalance (Model Kahn Instrument DCA315) and represents the force exerted when dipping a paper sample of constant size in a solvent, in this case hexadecane. The force acting downward due to surface tension is measured with a microbalance on which a paper sample is attached.

[0041]

[Table 1]

A pattern of node lines is printed on the paper using a solvent-based thermosetting epoxy adhesive and dried to remove the solvent, so that the node lines of adjacent sheets are ½
The sheets were laminated so as to cover each other by the pitch, and a block of the adhesive sheet was created. The laminate was cured under a pressure of 25 bar at 140 ° C for 100 minutes. The cured block was expanded into a uniform hexagonal cell shape using a general-purpose expansion frame, and the cell width was 5 mm or 6.5 mm.

The spread paper block was sprayed with a fine mist of water (except Nomex ™) to set the shape and then placed in an oven at 140 ° C for 40 minutes. In the preferred case, the water mist contained dissolved ammonium polyphosphate.

The obtained block was resol type phenol resin (the molar ratio of phenol and formaldehyde was 0.6.
It was immersed in a 1: 1) acetone solution. Air purge was used to remove excess solvent. The core was placed in an oven and treated with a cure cycle of 140 ° C for 1 hour. Each cured block was cut at a right angle to the node line to make a slice with a thickness of 12.7 mm.

[0045]

[Table 2]

Air permeability value of 100 ml / min or more and 110
Brittle honeycomb core samples were obtained from papers with a wicking power of mg or more, that is, when the cells were compressed,
The paper is completely destroyed. 5ml / min breathability value and about 10
A paper having a wicking power of 4 m is not brittle when a phenol resin is applied, and a honeycomb having excellent mechanical properties is obtained, that is, when the cell is compressed, the resin cracks but the lower paper is originally Maintained its shape.

The compression characteristics of the core and the short b
eam) Shear properties were tested as follows. The honeycombs were placed between sheets of woven glass reinforced phenolic prepreg (57% glass content) for short beam shear test specimen preparation. The test piece was heated at a rate of 5 ° C./minute so as to be cured at 135 ° C. for 90 minutes. The test piece was cut into 150 × 75 × 12.7 mm. The compression test sample was cut into a rectangular core 75 × 75 × 12.7 mm. Compressive strength measurements were made with an Instron 4483 tester at a crosshead speed of 0.5 mm / min. The short beam shear test was performed using a Twick 2010 tester at a speed of 2 mm / min. The results are shown in the table below as an average value of 3 samples.

[0048]

[Table 3]

Example 2 A series of core samples were prepared by spraying an aqueous solution onto a spread paper core, applying ammonium polyphosphate and then heat setting. In Experiment 2.3, a solution of ammonium polyphosphate (APP) dissolved in 100 parts of water was prepared. After spraying this solution on a spread paper core, the core was placed in an oven and kept at 140 ° C for 40 minutes to set the core and dry the polyphosphate coating. Similarly to Example 1, the dried core was dipped and applied in an acetone solution of a resol-type phenol resin.

In Experiment 2.4, in addition to ammonium polyphosphate added in the spreading step, finely particulate water-insoluble (8 μ) ammonium polyphosphate (NH 4 PO 3) n, n> 1
000 was dispersed at a level of 20 parts by weight of ammonium polyphosphate with respect to 100 parts by weight of the solid phenol resin in the phenol resin used for the paper honeycomb coating.

For comparison, a cellular structure to which no flame retardant was applied was prepared by using aramid paper (2.1) and glassine paper (2.
2) was used. The flammability properties of the materials were tested as follows. The core material sample was vertically clamped, and a Bunsen burner flame at a temperature of 820 ° C. was placed below the sample. 60
After seconds, the test piece was removed from the flame and the charred area was recorded. The flame retardant properties are shown in the table below.

[0052]

[Table 4] The results show that honeycomb core materials with excellent mechanical properties and fire resistance can be produced from the method of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Graham Kemp, UK Cambs, Lynton, Backlord 135 (72) Inventor Tarens Charles Web England, Essex, Saffron Walden, Akersden, Wickenlord, Wickenbrook ( 56) References JP-A-5-57825 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (8)

(57) [Claims] 1. A method for producing a cellular material, which is expanded from a dense, non-porous cellulose paper to form a cellular structure, said paper having a breathability of 30 ml / min or less, Characterized in that after applying the aqueous composition to the cellular structure to sufficiently heat the structure to stabilize the structure, a thermosetting resin is applied to the obtained cellular structure to cure the resin. Production method. ^2. The method according to claim 1, wherein the paper has a weight of 30 to 150 g / m ² . 3. The method according to claim 1, wherein the paper is glassine paper. 4. The method according to claim 1, wherein heating is performed at 100 to 190 ° C. for 1 to 60 minutes. 5. The method according to claim 1, wherein the aqueous composition contains the flame retardant as a solution or dispersed in the solution. 6. The amount of flame retardant is from 0.5 to dry core.
The method according to claim 5, which is 20% by dry weight. 7. The method according to claim 1, wherein the thermosetting resin contains a flame retardant. 8. The method according to claim 1, wherein the cellular structure is cut into thin pieces, and a protective layer is applied to the surface including the cell openings.