JP2023016365A - Method for producing molded article - Google Patents

Abstract

To provide a method capable of producing a molded article having good mechanical strength by suppressing the reduction in strength due to the orientation of a reinforcing fiber.SOLUTION: There is provided a method for producing a molded article 41 which comprises: a step of dispersing a thermosetting resin A and a reinforcing fiber B in a dispersion medium, followed by removing the dispersion medium using a papermaking method to obtain a papermaking article 11; a step of obtaining an elementary article 31 by pressing and molding the papermaking article 11; and a step of pressing, heating and curing the elementary article 31 in the direction orthogonal to the pressurization direction of the elementary article 31 to obtain a moded article 41.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a molded article.

Conventionally, molded articles obtained from paper-made articles can be imparted with desired properties by selecting the types of reinforcing fibers and resins used, and have a high degree of freedom in design, and are therefore used in various articles. In particular, paper-made articles using reinforcing fibers and molded articles obtained therefrom are attracting attention as materials that are light in weight and high in mechanical strength because the mechanical strength of the reinforcing fibers is effectively exhibited.

In Patent Document 1, after dispersing a matrix resin and reinforcing fibers in a viscous dispersion using a special device, the dispersion medium is removed using a papermaking method to obtain a fiber-reinforced plastic molded product. A method of obtaining the substrate is disclosed.

JP 2016-37580 A

However, in the prior art such as Patent Document 1, the paper product obtained by the paper making method is then hardened by heating and pressing from the vertical direction (thickness direction) to be commercialized, so the reinforcing fibers are layered. It was laminated to Therefore, although the reinforcing fibers are arranged two-dimensionally at random in the in-plane direction of the paper product, they are arranged parallel to the out-of-plane direction. Therefore, when the paper product is used as it is, the layers of the reinforcing fibers of the paper product are likely to separate, and the mechanical strength (in the in-plane direction) between the layers is insufficient.

Therefore, the present inventors have been diligent from the viewpoint of obtaining a new molded article using a paper-made article in order to improve the mechanical strength between the layers of the reinforcing fibers of the conventional paper-made article while obtaining high mechanical strength due to the reinforcing fiber. Study was carried out. As a result, after obtaining a papermaking body by a conventional papermaking method, the papermaking body is subjected to pressure molding and preliminary processing, and then pressurized in a direction perpendicular to the pressure direction during preliminary processing to harden. As a result, the orientation of the reinforcing fibers can be reduced, and the reinforcing fibers can be randomly arranged. That is, by applying pressure from a direction perpendicular to the orientation of the reinforcing fibers deposited and layered in the papermaking direction, that is, the direction of gravity, the decrease in strength caused by the orientation of the reinforcing fibers is suppressed. I found that I could do it, and completed the present invention.

According to the invention,
a step of dispersing a thermosetting resin and reinforcing fibers in a dispersion medium and then removing the dispersion medium using a paper making method to obtain a paper product;
a step of obtaining a green body by pressure-molding the papermaking body;
a step of further pressurizing and heating the preform in a direction perpendicular to the pressurizing direction of the preform to obtain a molded body;
A method for manufacturing a molded body is provided, comprising:

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the molded object with favorable mechanical strength which suppresses the fall of strength by orientation of a reinforcing fiber can be provided.

It is a cross-sectional schematic diagram which shows an example of the manufacturing method of the papermaking body which concerns on this embodiment. It is a perspective view which shows an example of the molded object which concerns on this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in all the drawings, the same constituent elements are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

<Method for manufacturing molded body>
FIG. 1 is a schematic cross-sectional view showing an example of the method for producing a papermaking product according to the present embodiment, and FIG. 2 is a schematic cross-sectional view showing an example of the method for producing a molded product according to the present embodiment. Hereinafter, it demonstrates using FIG.1, 2. FIG.

The manufacturing method of the molded body 41 of this embodiment includes the following steps.
[Step 1] After dispersing the thermosetting resin A and the reinforcing fiber B in a dispersion medium, the dispersion medium is removed using a paper making method to obtain a paper product 11 [Step 2] A paper product 11 is added. A step of obtaining the preform 31 by pressing and molding [Step 3] Further pressurizing and heating the preform 31 in a direction orthogonal to the pressing direction of the preform 31 to harden it, thereby obtaining a formed body 41. Steps Steps 1 to 3 are performed in this order. Details of each step will be described below.

[Step 1: Step of obtaining a paper product]
FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing a papermaking body 11 of this embodiment. The manufacturing method of the papermaking body 11 of the present embodiment has, for example, the following steps.
(Step 1a) A step of mixing a thermosetting resin A and a reinforcing fiber B in a dispersion medium to prepare a slurry.
(Step 1b) A step of putting the obtained slurry into a container having a mesh on the bottom to separate the dispersion medium.
(Step 1c) A step of dewatering and pressing the aggregates remaining on the mesh.
(Step 1d) A step of drying.
Each step will be described in detail below.

(Step 1a)
As shown in FIG. 1(a), slurry is prepared by mixing and stirring thermosetting resin A and reinforcing fiber B in a dispersion medium. A known method can be used as a method of mixing in the dispersion medium, and for example, a method of stirring in a vessel equipped with a stirrer can be used.

The dispersion medium is not limited, specifically water; alcohols such as ethanol, 1-propanol, 1-butanol and ethylene glycol; ketones such as acetone, methyl ethyl ketone, 2-heptanone and cyclohexanone; ethyl acetate and acetic acid esters such as butyl, methyl acetoacetate and methyl acetoacetate; and ethers such as tetrahydrofuran, isopropyl ether, dioxane and furfural. As the dispersion medium, one or a combination of two or more of the above specific examples can be used. Among these, it is preferable to use water because it is easily available, has a low environmental impact, and is highly safe.

Various components contained in the slurry are described below.

・Thermosetting resin A
As the thermosetting resin A, one or more selected from phenol resins, epoxy resins, unsaturated polyester resins, melamine resins, and polyurethanes can be used. Among them, from the viewpoint of obtaining high mechanical strength, it preferably contains a phenol resin or an epoxy resin, and more preferably contains a phenol resin.

The content of the thermosetting resin A is preferably 5% by volume or more, more preferably 20% by volume or more, and still more preferably 30% by volume or more with respect to the entire paper product 11 . This makes it easier to improve workability.
On the other hand, the blending amount of the thermosetting resin A is preferably 90% by volume or less, more preferably 70% by volume or less, and still more preferably 60% by volume or less with respect to the entire paper product 11 . As a result, the mechanical strength of the reinforcing fiber B of the paper product 11 can be improved more effectively.

・Reinforcing fiber B
Reinforcing fibers B used in this embodiment include natural fibers such as metal fibers, wood fibers, cotton, hemp, and wool; regenerated fibers such as rayon fibers; semi-synthetic fibers such as cellulose fibers; polyamide fibers, aramid fibers, and polyimide. Synthetic fibers such as fiber, polyvinyl alcohol fiber, polyester fiber, acrylic fiber, polyparaphenylene benzoxazole fiber, polyethylene fiber, polypropylene fiber, polyacrylonitrile fiber, ethylene vinyl alcohol fiber; carbon fiber; inorganic fiber such as glass fiber and ceramic fiber etc., but not limited to these. The reinforcing fibers B may be used singly or in combination of two or more.
Among them, carbon fibers and inorganic fibers are preferable from the viewpoint of obtaining high mechanical strength.

The fiber length of the reinforcing fiber B is desirably selected depending on the required properties, and for example, it is preferably 500 μm or more and 10 mm or less. By setting the fiber length to the above lower limit or more, properties such as mechanical strength and rigidity can be exhibited. On the other hand, by making the fiber length equal to or less than the above upper limit value, it is possible to ensure good moldability.

The diameter of the reinforcing fiber B is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 80 μm or less.
By making the diameter of the reinforcing fiber B equal to or greater than the above lower limit value, the mechanical strength of the molded body 41 can be ensured, and by making it equal to or less than the above upper limit value, it is possible to ensure moldability.

The fiber length and diameter of the reinforcing fibers B can be confirmed, for example, by observing the obtained paper product 11 or molded product 41 with an electron microscope. Furthermore, the average fiber length and average diameter can be obtained by selecting a total of 100 reinforcing fibers B observed from the surface of the obtained papermaking product 11 or molded product 41 and calculating the average value. .

The amount of reinforcing fiber B to be blended is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, relative to the paper product 11 .
The mechanical strength can be improved by setting the blending amount of the reinforcing fiber B to the above lower limit or more. On the other hand, by setting the amount of the reinforcing fiber B to be equal to or less than the above upper limit value, the reinforcing fiber B can be maintained in good and uniform dispersibility, and variations in the mechanical strength of the paper product 11 and the molded product 41 can be suppressed.

- Pulp fiber The paper product 11 and the slurry may contain pulp fiber. Thereby, aggregation of the thermosetting resin A can be caused more effectively.
Pulp fibers refer to fibrillated organic fibers.
Organic fiber is a general term for fibers mainly composed of organic substances among natural fibers and synthetic fibers. Specific examples of pulp fibers include cellulose fibers such as linter pulp and wood pulp; natural fibers such as kenaf, jute, and bamboo; para-type wholly aromatic polyamide fibers and their copolymers; aromatic polyester fibers; Pulp-like fibers obtained by fibrillating synthetic fibers such as sol fibers, meta-aramid fibers and their copolymers, acrylic fibers, acrylonitrile fibers, polyimide fibers, and polyamide fibers can be mentioned. The pulp fibers may be used singly or in combination of two or more.

The content of pulp fibers is preferably 0.5% by volume or more, more preferably 1.5% by volume or more, and even more preferably 3% by volume or more, relative to the entire paper product 11 . As a result, aggregation of the thermosetting resin A can be more effectively generated during the manufacturing process, and more stable manufacturing of the molded body 41 can be realized.
On the other hand, the content of pulp is preferably 15% by volume or less, more preferably 10% by volume or less, and even more preferably 6% by volume or less with respect to the entire papermaking body 11 . As a result, the mechanical properties and thermal properties of the compact 41 can be improved more effectively.

- Flocculant The paper product 11 and the slurry may contain a flocculant. The aggregating agent has a function of aggregating the thermosetting resin A and the reinforcing fibers B into flocks in the method of manufacturing the paper product 11 using the paper making method described later. Therefore, more stable production of the papermaking product 11 and the molded product 41 can be realized.

The flocculant may contain one or more selected from, for example, cationic polymer flocculants, anionic polymer flocculants, nonionic polymer flocculants, and amphoteric polymer flocculants. Examples of such flocculants include cationic polyacrylamide, anionic polyacrylamide, Hoffmann polyacrylamide, Mannic polyacrylamide, amphoteric copolymerized polyacrylamide, cationic starch, amphoteric starch, polyethylene oxide, and the like. . In addition, in the flocculant, the polymer structure, molecular weight, amount of functional groups such as hydroxyl groups and ionic groups, etc. can be adjusted according to the required properties without any particular restrictions.

- Poly(meth)acrylic acid ester emulsion The paper product 11 and the slurry may further contain a poly(meth)acrylic acid ester emulsion. The poly(meth)acrylic acid ester emulsion may be added after mixing the thermosetting resin A, the reinforcing fiber B, and various optional components in a dispersion medium and stirring, or may be mixed at the same time as the above components. You may In order to disperse the various components to a higher degree, the poly(meth)acrylic acid ester emulsion is preferably added after mixing and stirring the above components in the dispersion medium.

・Others In the present embodiment, the paper product 11 and the slurry include, for example, stabilizers such as antioxidants and ultraviolet absorbers for the purpose of improving characteristics, mold release agents, plasticizers, flame retardants, resin curing catalysts and curing agents. Accelerators, pigments, dry strength improvers, wet strength improvers, retention improvers, drainage improvers, sizing agents, antifoaming agents, rosin sizing agents for acidic paper making, neutral Addition of sizing agents such as rosin-based sizing agents for papermaking, alkylketene dimer-based sizing agents, alkenylsuccinic anhydride-based sizing agents, special modified rosin-based sizing agents, and coagulants such as aluminum sulfate, aluminum chloride, and polyaluminum chloride. One or two or more selected from agents can be included for the purpose of adjusting production conditions and expressing required physical properties.

These various components are used by dissolving or dispersing them in the slurry by a known method.

(Step 1b)
In this embodiment, as shown in FIG. 1(b), the dispersion medium is separated by putting the obtained slurry into a container having a mesh 60 on the bottom. As a result, aggregates contained in the slurry remain in the form of a sheet on the mesh 60 as shown in FIG. 1(c).

Here, since the reinforcing fibers B have a certain length, they are deposited on the surface of the mesh 60 so as to overlap each other in layers while being entangled with each other.

The thickness of the sheet-like papermaking body 11 can be adjusted by adjusting the amount of various components in the material slurry, or by repeating the process of preparing slurry again and separating.

Further, by appropriately selecting the shape of the mesh 60, it is possible to adjust the shape of the sheet-like paper product 11 to be obtained later.

(Step 1c)
Then, the aggregate remaining on the mesh 60 is dehydrated and pressed to obtain a sheet-like paper product 11 (Fig. 1(c)). Conditions for the dehydration press can be, for example, a temperature of 20° C. or higher and 30° C. or lower and a pressure of 1 kgf/cm ² or higher and 50 kgf/cm ² or lower.
Here, the dehydration press is preferably performed so that the dehydration rate of the sheet-like paper product 11 is, for example, 20% or less. Note that the dehydration rate according to the present embodiment indicates the mass of the dispersion medium contained in the aggregate after dehydration, assuming that the mass of the dispersion medium contained in the aggregate before dehydration is 100%.

(Step 1d)
In the drying step, as shown in FIG. 2(d), the agglomerate is heat-treated in an oven 70. As shown in FIG. As a result, the dispersion medium is further removed from the sheet-like paper product 11 . The drying method is not limited, and a method other than the oven 70 may be used.

The drying temperature can be above the melting point of the thermosetting resin A and below the reaction temperature. The reaction temperature is the temperature at which the calculated reaction rate first exceeds 0% in the heating process in differential scanning calorimetry (DSC) measurement. Here, the reaction rate is calculated as follows. First, a temperature profile is measured by DSC measurement for a paper product that has not undergone a curing reaction. Let x [mJ/mg] be the amount of heat generated per unit mass at the exothermic peak of the curing reaction, which is calculated from the obtained temperature profile of the curing reaction. Next, for the paper product for which the reaction rate is to be calculated, similarly, the calorific value y [mJ/mg] converted per unit mass of the exothermic peak of the curing reaction is calculated. Using the above x and y, the reaction rate is obtained from the following formula.
(Formula) (reaction rate) = y/x x 100 [%]

Through the above steps, the sheet-like papermaking body 11 in the B-stage state is obtained.

[Step 2: Step of obtaining a preform]
Next, the molded body 31 is obtained by pressurizing and molding the papermaking body 11 . Further, the preformed body 31 is held in the B-stage state.
As shown in FIG. 2(b), for example, the papermaking body 11 is put into a mold, pressure is applied to the papermaking body 11 from above the mold, and preforming is performed to obtain a green body 31. As shown in FIG. Moreover, it is preferable to apply pressure in the direction of gravity.
The pressure is preferably 0.01-1.5 MPa, more preferably 0.05-1 MPa. By setting the pressure to the above lower limit or more, the molded body 31 having appropriate hardness can be obtained. On the other hand, by setting the pressure to the upper limit value or less, it is possible to suppress the reinforcing fibers B from breaking or bending.

[Step 3: Step of obtaining molded product]
After that, the molded body 41 is obtained by further heating and pressurizing the obtained preformed body 31 to completely harden it. The curing conditions are appropriately determined depending on the raw materials used, etc., but it is preferable to heat to a temperature not higher than the melting point of the thermoplastic resin and not less than the curing temperature of the thermosetting resin. For example, when a phenolic resin is used, the temperature is preferably 150 to 200°C, more preferably 160 to 180°C. As for the pressurizing conditions, the pressure is preferably 10 to 80 MPa, more preferably 30 to 60 MPa. Also, the pressurization time is preferably about 1 to 10 minutes.

In addition, the preform 31 is once removed from the mold, the preform 31 is rotated so as to be pressurized in a direction different from the direction of pressure applied in step 3, and then returned to the mold, followed by heating and pressurization. is completely cured to obtain a molded body 41 . In other words, it is preferable to rotate 90° with respect to the direction of gravity. As a result, the reinforcing fibers B once oriented in the pressurizing direction in the preform 31 can be randomized, and a decrease in mechanical strength due to the orientation of the reinforcing fibers B in the compact 41 can be suppressed. From the viewpoint of workability, it is preferable to rotate by 90° with respect to the direction of pressure in step 3, that is, the direction of pressure applied to the preform 31 .

<Molded body>
FIG. 2 is a perspective view showing an example of the molded article according to this embodiment, and FIG. 2(b) is an enlarged side view of FIG. 2(a). As shown in FIG. 2, in the molded body 41 of the present embodiment, the reinforcing fibers B are entangled but randomly arranged, so high mechanical strength can be obtained.
The content of thermosetting resin is preferably 20 to 80% by volume with respect to the total amount of molded body 41 .
Since the molded body 41 of the present embodiment is lightweight and has high mechanical strength, it can be widely used in various applications such as building materials, various transportation machines such as automobiles and aircraft, and sporting goods.

The molded body 41 of this embodiment is excellent in mechanical strength, and has particularly high bending strength. The bending strength can be measured by a known method, for example, using a measuring instrument such as "Tensilon" manufactured by A&D and "Autograph" manufactured by Shimadzu Corporation.

It should be noted that the present invention is not limited to the above-described embodiments, and includes modifications, improvements, etc. within the scope of achieving the object of the present invention.

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

<Example 1>
[Step 1] Preparation of paper product In water as a dispersion medium, 50 parts by weight of a thermosetting resin (resol-type phenolic resin, "Sumilite Resin PR-51723" manufactured by Sumitomo Bakelite Co., Ltd.), reinforcing fibers (recycled carbon, average Fiber length 6 mm) 40 parts by weight and pulp fibers (aramid microfibers, "Tiara KY-400S" manufactured by Daicel Finechem Co., Ltd. average fiber length 500 to 600 μm) 10 parts by weight) are added, stirred for 20 minutes, and the solid content concentration is 0. A slurry of 0.15% by weight was obtained.
To the obtained slurry, a pre-prepared poly(meth)acrylic acid ester emulsion ("Himolo DR-9300" manufactured by Hymo Co., Ltd.) was added so that the solid content in the slurry was 300 ppm. of solids was agglomerated.
Next, the slurry containing the aggregates was filtered through a 30-mesh metal net (screen), and the sheet-like aggregates remaining on the screen were dewatered by pressing at a pressure of 3 MPa. The dehydrated aggregate was dried at 70° C. for 3 hours to obtain a sheet-like paper product (300 mm×300 mm: thickness 5 mm).

[Step 2] Production of Preformed Body The obtained papermaking body was placed in a mold and pressed in the direction of gravity under the following conditions to obtain a substantially rectangular parallelepiped preformed body.
・Conditions Pressure: 0.1 MPa, Time: 1 minute

[Step 3] Production of Molded Body The obtained green body was taken out from the mold, rotated by 90° with respect to the direction of gravity, placed in the mold again, and cured under the following conditions.
・Curing conditions Temperature: 180°C, mold clamping pressure: 30 MPa, time: 10 minutes

<Comparative Example 1>
A molded body was obtained in the same manner as in Example 1, except that in step 3 the molded body was cured as it was without being rotated.

The following measurements and observations were carried out on the obtained compact. Table 1 shows the results.
[measurement]
- Bending strength, bending elastic modulus: Bending stress was applied to the molded body from a direction perpendicular to the thickness direction of the molded body (pressing direction during curing), and converted from the measurement results. A Tensilon manufactured by A&D was used as a testing machine.
Specifically, when the bending moment measured by a Dystat tester using a test piece having a width b [mm] and a thickness h [mm] is M [kg cm], the bending strength is σf [MPa ] was calculated from the relationship σf=9.8×6×10×M/(bh2).
The flexural elasticity was calculated according to Hooke's law (Formula 5.2) from the flexural strength test results.

[observation]
The orientation of the reinforcing fibers was observed by observing the cross section of each compact in the pressurizing direction during curing with an optical microscope.
As a result of observation, in the molded article of Example 1, orientation of the reinforcing fibers was not observed, cracks were dispersed after the bending test, and no progress of the cracks was observed. On the other hand, in the molded article of Comparative Example 1, cracks progressed in the bending test, and cracks almost parallel to the lateral direction were observed.

11 Paper product 31 Preformed product 41 Molded product 60 Mesh 70 Oven A Thermosetting resin B Reinforcing fiber

Claims (5)

a step of dispersing a thermosetting resin and reinforcing fibers in a dispersion medium and then removing the dispersion medium using a paper making method to obtain a paper product;
a step of obtaining a green body by pressure-molding the papermaking body;
a step of further pressurizing and heating the preform in a direction perpendicular to the pressurizing direction of the preform to obtain a molded body;
A method for producing a molded body, comprising: A method for producing a molded article according to claim 1,
A method for producing a molded product, wherein the content of the reinforcing fiber is 30 to 60% by volume relative to the paper product. A method for producing a molded article according to claim 1 or 2,
A method for producing a molded body, wherein the thermosetting resin contains one or more selected from the group consisting of phenol resins, epoxy resins, melamine resins, polyurethanes, and unsaturated polyester resins. A method for producing a molded article according to any one of claims 1 to 3,
The reinforcing fibers include metal fibers, carbon fibers, glass fibers, ceramic fibers, polyamide fibers, aramid fibers, polyimide fibers, polyvinyl alcohol fibers, polyester fibers, acrylic fibers, polyparaphenylene benzoxazole fibers, polyethylene fibers, polypropylene fibers, poly A method for producing a molded article containing one or more selected from acrylonitrile fibers and ethylene vinyl alcohol fibers. A method for producing a molded article according to any one of claims 1 to 4,
A method for producing a molded article, wherein the content of the thermosetting resin is 20 to 80% by volume with respect to the total amount of the molded article.

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