JP6684086B2 - Heating device and heating method - Google Patents

Description

  The present invention relates to a heating device and a heating method for a material having a property that the apparent volume expands while generating voids inside by heating, and a high-frequency heating device and a high-frequency heating device for heating a non-heating object by high frequency. It is also related to the method.

  Heretofore, carbon fibers and carbon fiber composite materials have been mainly used in fields such as aerospace and sports / leisure due to their characteristics such as light weight, high strength and high elastic modulus. It can be said that this field can be used even if the material cost and the production cost are a little high because the performance and function are prioritized. From the viewpoints of weight reduction and energy saving, application of carbon fibers and carbon fiber composite materials to the fields of automobiles, energy-related products and general industrial machinery is currently expected, and carbon fiber composite materials that can be mass-produced at lower cost. And the manufacturing and molding methods thereof are required. In low cost and mass production of carbon fiber composite parts, it is essential to improve the production speed and molding speed, and one of the solutions is expected to be the adoption of thermoplastic resin.

  The conventional carbon fiber composite material is mainly in a form in which carbon fibers are encapsulated in a thermosetting resin as a matrix resin typified by epoxy or the like, which is excellent in mechanical strength and elastic modulus, In manufacturing parts using it, it is necessary for humans to perform mainstream molding process, heating process for several hours in a firing furnace called autoclave, etc. , Its production cost and productivity were not always sufficient.

  On the other hand, a carbon fiber composite material made of a thermoplastic resin is slightly inferior in mechanical strength and elastic modulus, but is particularly excellent in moldability and molding speed because it is thermoplastic, and further, existing molding methods such as injection, extrusion, and press. It also has the feature that the device can be used as it is or with minor changes.

  Especially in automobiles and automobile parts applications where mass production is required, the existing injection molding method, equipment, press molding method, equipment can be diverted, etc., and the merit is large, and application of thermoplastic carbon fiber composite material for members with moderate strength Consideration is in progress.

  One form of thermoplastic carbon fiber composite material is expected to be a sheet-like or plate-like carbon fiber composite material such as stampable sheet, LFTP (Long Fiber Thermoplastic), thermoplastic SMC (Sheet Molding Compound), etc. It is an intermediate material (collectively referred to as stampable sheet below). These are carbon fibers or carbon fiber bundles cut into a state (0.1 to 10 cm, preferably 1 to 7 cm, more preferably 2 to 5 cm) closer to the long fibers than the carbon fiber composite material for injection molding. Is randomly distributed in a thermoplastic resin, which is a matrix resin, and is dispersed and included. It is often provided as a sheet-shaped or flat-shaped intermediate material having a thickness of about 1 mm to 10 mm.

  A molded product having a desired shape can be manufactured by pressing the stampable sheet in a softened state by heating (called preheating) above the softening start temperature of the thermoplastic resin. It may be considered that the sheet metal material in the sheet metal press working is replaced with the stampable sheet.

  By the way, the sheet metal material in the sheet metal stamping is basically a metal which is an isotropic material, and therefore the sheet metal material which is flat before molding can be plastically deformed into a three-dimensional shape without wrinkles or tears. That is, in order to replace the sheet metal material in the sheet metal press working with the carbon fiber composite material, it is essential to impart an isotropic property to the carbon fiber composite material. However, it is not easy to impart an isotropic property to the carbon fiber composite material without sacrificing strength and rigidity.

  Generally, as a method for producing a planar carbon fiber composite material, a single yarn or a fiber bundle of carbon fibers having a considerable length is arranged, woven, or knitted into a planar so-called carbon fiber cloth, and the cloth is heated. It is customary to manufacture by impregnating a hardened or thermoplastic resin. Therefore, an anisotropic material having different physical properties such as elasticity and rigidity is usually used in the direction in which the carbon fibers (bundles) are arranged and in the other directions.

  When such an anisotropic material is pressed in the same manner as a sheet metal press, the deformation of the material is affected by the anisotropy, and easily deformable parts, non-deformable parts, and non-deformable parts are generated. In most cases, the molded shape of 1 cannot be obtained. This is easily inferred from the fact that when the cloth is forcibly molded into a three-dimensional shape, the cloth is excessively wrinkled, and the cloth is insufficient to cause tension and breakage.

  On the other hand, it is also possible to mold the carbon fiber composite material by injection molding, and in this case, it is customary to use carbon fibers or fiber bundles whose length is cut to about 1 mm or less. Each carbon fiber or fiber bundle is randomly distributed and dispersed mainly by kneading and stirring before injection molding, so that a pseudo isotropic property is realized as a carbon fiber composite material. Therefore, a carbon fiber composite material made of such short fibers may be easily pressed, but the strength and rigidity of the composite material are poor due to the relatively short carbon fiber or fiber bundle length. This is often difficult to do.

  That is, the stampable sheet is to optimize the length and distribution state of the carbon fiber or fiber bundle while ensuring the isotropic properties necessary for press working and realizing the necessary and sufficient strength and rigidity. It can be said that it was realized by.

  A stampable sheet is often manufactured by the following steps. First, the appropriately opened carbon fiber bundle is cut into a desired length. These are stacked by randomly dropping them on a plane, vibrating, stirring, etc. while randomly arranging them. At this time, the thermoplastic resin in the form of powder or granules may be supplied at the same time to form a layer in which the carbon fiber bundles and the thermoplastic resin in the form of powder or granules are uniformly mixed. Alternatively, the film-shaped thermoplastic resin and the carbon fiber bundle layer may be alternately laminated. Regardless of the method, the carbon fiber bundle layer may be said to be cotton-like, and its apparent thickness is much thicker than the thickness after molding. Next, the resin is impregnated into the carbon fiber bundles while being heated and melted while being compressed, or the already existing thermoplastic resin in the form of powder or granules is melted and impregnated into the carbon fiber bundles. Then, it is cooled to obtain a stampable sheet having a desired thickness. The volume content of carbon fiber, so-called Vf, is usually about 30%.

  Due to the above-described manufacturing method, the stacked carbon fiber bundles are in a compressed state within the stampable sheet. Therefore, when the stampable sheet is preheated and its thermoplastic resin is softened, the compression of the laminated carbon fiber bundle is released, and the thickness of the stampable sheet is increased while creating voids in the stampable sheet (between the carbon fiber bundles). It usually expands apparently in the direction. In press molding, a stampable sheet that has been apparently expanded by preheating is placed between molds for press molding, and the molds are clamped for molding, whereby the voids are eliminated and desired molding is performed.

  In addition, the property that the apparent volume expands while generating voids is not limited to the stampable sheet using carbon fiber, and the fiber bundle layer may be in a compressed state in the stampable sheet. For example, regardless of glass fiber, metal fiber, organic fiber typified by polyimide, and the like, the properties are the same.

Ishikawa Prefectural Industrial Technology Research Institute 2012 Research direction vol.24 Electro Heat Handbook Japan Electro Heat Center Edition 1st edition 1st volume 2015.9.25 The Chemical Society of Japan Autumn Program Sponsored by the Chemical Society of Japan The 4th CSJ Chemistry Festa 2014 Proceedings Lecture number H2-08

  In the press molding of the stampable sheet, at least the softening start temperature of the thermoplastic resin is preheated and then the press molding is performed, as described above. This preheating has an optimum temperature range, and it is not preferable that the preheating temperature is higher or lower.

  There is a temperature range in which the thermoplastic resin exhibits appropriate fluidity for press molding, and it is necessary to preheat within this appropriate range. If the temperature is lower than this, the flowability of the thermoplastic resin will be insufficient and molding failure will occur.On the contrary, if it is too high, the resin will flow too much, and the resin itself will be decomposed, oxidized, and deteriorated (deteriorated) such as vaporization of low molecular weight components ) Is significant. This may lead to problems such as insufficient strength of the molded product after molding and promotion of deterioration over time.

  In the prior art, atmospheric heating or infrared heating is often used for preheating. That is, the stampable sheet is heated by standing in a furnace having a known heat source such as electric heating to heat the atmosphere or radiating infrared rays from a far-to-near (in some cases, visible range) infrared lamp. Use the method.

Such a conventional technique has the following problems.
First, atmospheric heating and infrared heating are heating from the surface of the object to be heated, and in many cases a temperature difference is created between the surface of the stampable sheet and the inside thereof (Reference 1). The stampable sheet contains a thermoplastic resin as a main component and has a lower thermal conductivity than metal or the like. Therefore, even if the surface reaches the optimum temperature range, the inside may not reach the optimum temperature lower limit. On the contrary, when the inside reaches the optimum temperature range, the surface may exceed the upper limit of the optimum temperature range.

  To alleviate this problem, it is basically preferable to reduce the output of the heating source and slowly heat it over time to minimize the temperature difference between the surface and the inside. It is necessary to reduce the output of the heat source at the ambient temperature and the output of the infrared lamp at the time of infrared heating to heat for a long time, which causes a problem that the heating time becomes long.

  It is also possible to appropriately adjust the output of the heating source while monitoring the temperature of the stampable sheet that is the object to be heated, but the heating device becomes complicated and expensive, and its operation and control are complicated. There is also the problem of becoming.

  Further, the time required for preheating may be longer than the time required for press molding of a stampable sheet (usually possible in about 1 minute). In this case, in order to maintain the process throughput from preheating to press molding, a plurality of preheating devices are required for one press machine, which leads to problems such as increase in equipment cost and installation place. .

  Furthermore, as described above, the stampable sheet apparently expands while generating voids inside by heating. The softening start temperature is usually lower than the above-mentioned optimum temperature range, and therefore the stampable sheet starts apparent expansion while generating voids before reaching the optimum temperature range and reaches the optimum temperature. In the meantime, the heating is continued with the formation of voids.

  When voids start to be generated, it is expected that the voids are thermally close to the insulator and the macroscopic heat transfer coefficient is also lowered. It is considered that this further promotes the temperature difference between the inside and the surface.

Further, even if the thermoplastic resin is within the above-mentioned optimum temperature range or lower, if it is heated for a long time, the above-mentioned decomposition, oxidation, and vaporization of low molecular weight components may occur (deterioration). In particular, it is remarkable on the surface, and when voids are generated, the substantial surface is also increased by the voids, and there is a problem that deterioration (deterioration) such as decomposition, oxidation, vaporization of low molecular weight components is promoted. In order to avoid these problems associated with the technique, there has been a demand for a heating technique for preheating a stampable sheet in which a temperature difference between the surface and the inside is unlikely to occur, a void is not generated in a short time.

In order to solve the above-mentioned problems, according to the present invention, a heating device for a flat object to be heated, which is made of a material in which at least a part of the matrix resin contains reinforcing fibers which are carbon fibers ,
Heating the object to be heated while suppressing expansion of the object to be heated at least until the object to be heated reaches a temperature at which expansion starts (expansion start temperature), a pair of opposing heating surfaces,
An electromagnetic wave generation source for applying an electromagnetic wave having a frequency of 10 MHz or more and 100 MHz or less is provided between the pair of heating surfaces,
For the object to be heated, heating by heat conduction from the heating surface,
There is provided a heating device capable of simultaneously performing dielectric heating of the matrix resin due to application of the electromagnetic wave and heating from the inside by induction heating of the carbon fiber .

According to a preferred aspect of the present invention, the pair of heating surfaces is brought into contact with the object to be heated to heat the object to be heated, and at least a part of the object to be heated reaches the expansion start temperature or higher, A heating device is provided which releases contact between at least one of the pair of heating surfaces and the object to be heated.

According to a preferred embodiment of the present invention, the pair of heating surfaces of the heating means, characterized in that as it has conductivity is provided.

  According to a further preferred aspect of the present invention, there is provided a heating device characterized in that an insulating material layer is present between the object to be heated and at least one of the pair of heating surfaces.

  According to a further preferred aspect of the present invention, there is provided a heating device characterized in that the matrix resin contains a thermoplastic resin.

    From the viewpoint of shortening the heating time, the purpose of the present invention is to bring a stampable sheet into contact with a heating surface to utilize the effect of rapid heating by contact heat transfer, and further to reduce the temperature difference between the surface and the inside. By applying a high frequency from the surface, the effect of internal heating by so-called high frequency heating is exhibited.

  Further, the surface also exerts an effect of suppressing the apparent volume expansion of the stampable sheet.

  As can be seen from the publication of various handbook-like books (Non-Patent Document 2), heating technology using electromagnetic waves such as high-frequency waves and microwaves is used uniformly for the purpose of heating, melting, heat treatment, bonding, thawing, etc. It is a heating technique used.

  In the high frequency region, the frequencies used for heating and the like in various industrial fields are substantially approved to be used in three frequency bands of 13.56 MHz, 27.12 MHz and 40.68 MHz in Japan. (So-called ISM band frequency). It should be noted that even if high frequencies of frequencies other than these three frequency bands are taken so that the leakage electromagnetic field strength is equal to or less than the specified value, it can be used for industrial purposes.

  The heating by electromagnetic waves such as high frequency waves and microwaves is due to the interaction between the electromagnetic waves and the substance represented by the formula (1).

_{P = πfε 0 ε r "|} E | 2 + πfμ 0 μ r" | H | 2 + (1/2) σ | E | 2
.. (1)
here,
P: Energy loss per unit volume (= calorific value) [W / m ³ ]
π: Circularity f: Electromagnetic wave frequency [s ⁻¹ ]
ε ₀ : Dielectric constant in vacuum [F / m]
ε _r ”: Dielectric loss of material [F / m]
E: Electric field of electromagnetic waves [V / m]
μ ₀ : Permeability of vacuum [H / m]
μ _r ”: Magnetic loss of material [H / m]
H: Magnetic field of electromagnetic waves [A / m]
σ: electric conductivity of the substance [S / m]
Is.

In the formula (1), the first term described as πfε ₀ ε _r ″ | E | ² is also called a dielectric term, and indicates heat generation due to dielectric loss caused by an electric field of an applied electromagnetic wave.
The second term, which is written as πf μ ₀ μ _r ″ | H | ² , is also called a magnetic term, and Joule heat generation of an eddy current that is mostly generated in an object to be heated that is an electric conductor due to an alternating magnetic field of an applied electromagnetic wave. This is a term showing induction heat generation by.
Further, the third term described as (1/2) σ | E | ² is called a current term and represents Joule heat generation due to an electrostatic induction current generated by an electric field of an applied electromagnetic wave.

  The case where the first term is dominant may be called dielectric heating, and the case where the second term is dominant may be called induction heating.

Dielectric heating is often used when an object to be heated is an insulator (dielectric), and is often used for the purpose of heating and drying plastic, wood, paper, adhesive, and the like. A typical example is dielectric heating of water molecules by a microwave of 2.45 GHz in a so-called microwave oven.
As a form of a dielectric heating device using high frequency, as shown schematically in FIG. 1, an object to be heated is placed between a pair of electrodes facing each other, and a high frequency is applied between both electrodes to generate a high frequency dielectric Many of them are heated. Although the electrode shape is a substantially flat plate shape in FIG. 1, it is also possible to change the electrode shape according to the shape of the object to be heated, such as by forming the electrode surface with a curved surface or the like.

  On the other hand, the induction heating is often an object to be heated which is a conductor, and is typically performed by heat treatment such as quenching of a steel material, melting of the material in powder metallurgy, or heating. It can be said that this is also applied to a heating cooker using an alternating magnetic field, which is called a so-called IH cooker.

  In addition, there are few application examples in which the third term (current term) is dominant in the heating method using electromagnetic waves.

The following three points can be considered as features of heating by electromagnetic waves such as microwaves and high frequencies.
Feature 1: Rapid heating In a general heating method, heat energy from a heating source is generally propagated slowly by conduction and convection, except for radiant heating. On the other hand, heating by electromagnetic waves can be expressed as energy required for heating being transmitted in the form of electromagnetic waves through the space at the speed of light, and one of its characteristics is that heating can be performed rapidly.
Feature 2: Internal heating electromagnetic waves are absorbed by the object to be heated while penetrating and penetrating into the inside, and are converted into thermal energy, though it depends on the physical properties of the object to be heated. Therefore, heating can be performed not only from the surface of the object to be heated but also from the inside.
Feature 3: Selective heating There is wavelength (frequency) selectivity of the electromagnetic wave absorbed depending on the physical properties of the heated object. Therefore, even if it is a mixture of a plurality of substances, it is possible to selectively heat only a specific substance by selecting the wavelength of the electromagnetic wave.

  It can be said that the present invention solves the problem that the second effect is positively utilized, a temperature difference between the surface and the inside is less likely to occur, and heating is performed in a short time.

  According to the present invention, it is possible to realize an apparatus that hardly causes a temperature difference between the surface and the inside and can preheat a stampable sheet in a short time without generating voids as much as possible.

1 is a schematic view showing a preheating device according to the present invention. It is a figure showing expansion of a stampable sheet by heating. It is a figure which shows typically the cross section of the stampable sheet expanded by heating. It is a figure which shows the effect of the heating of the stampable sheet by the preheating apparatus by this invention. It is a figure which shows the effect of the heating of the stampable sheet by different high frequency. It is a figure which shows the effect of the high frequency heating of a carbon fiber, a carbon fiber composite material, and a resin material.

  In the following description of this specification, an electromagnetic wave in the range of 10 MHz to 100 MHz will be referred to as a high frequency unless otherwise specified.

The schematic diagram of the preheating device 1 according to the present invention is shown in FIG.
An object to be heated 11 is arranged between a pair of opposing heating electrodes 10 (the opposing surfaces are the heating surfaces according to the present invention, and the heating electrodes also serve as expansion suppressing members). The heating electrode 10 is made of a conductive material, and one (lower side in the figure) heating electrode (lower electrode 2) is electrically insulated from the housing 12 of the heating device 1 and grounded. The other electrode (referred to as the upper electrode 3) is also electrically insulated from the housing 12 and the like of the preheating device 1 and connected to the high frequency power source 6 (electromagnetic wave generation source) via the matching device 5. An aluminum alloy, stainless steel, or the like can be used as the conductive material of the heating electrode 10. Stainless steel is preferably non-magnetic.

  The lower electrode 2 is fixed to the housing 12 of the preheating device 1 via the insulating member 4, and the upper electrode 3 can be moved up and down relative to the lower electrode 2 by the electrode elevating device 9 as indicated by arrow A in the figure. Has become.

  Both the upper electrode 2 and the lower electrode 3 have a heater and a temperature measuring element (not shown) therein, and the entire electrode (that is, the heating surface) is heated to a desired temperature by a temperature control device (not shown). The heating temperature of the electrode is preferably equal to or higher than the softening start temperature of the thermoplastic resin in the article to be heated 11 and equal to or lower than the upper limit of the optimum heating range. Within this temperature range, the temperature of the article to be heated 11 does not exceed the upper limit of the optimum heating range regardless of how long the article to be heated 11 contacts the upper electrode 2 or the lower electrode 3, which is preferable.

  The object to be heated 11 is placed on the lower electrode 2. Next, the upper electrode 3 is lowered by the electrode elevating device 9 and is brought into close contact with the object to be heated 11 with a predetermined pressure. At the same time, a high frequency is oscillated from the high frequency power supply 6. The object to be heated 11 is heated both by heating from the surface by heat conduction from the heating electrode 10 in contact with it and by heating from the inside by the applied high frequency.

  Even if the temperature of the object to be heated 11 becomes equal to or higher than the softening start temperature, the object to be heated 11 is sandwiched by the upper and lower electrodes 2 and 3 which are expansion suppressing members, and the apparent volume thereof does not expand while forming voids inside. Absent. Of course, the predetermined pressure of the upper electrode 3 must be higher than the pressure generated by the expansion of the object to be heated 11.

  After the elapse of a predetermined heating time, or when the object to be heated 11 reaches a predetermined temperature within the optimum temperature range based on the measurement result of a temperature measuring device (not shown) for the object to be heated 11 provided separately, the upper electrode 3 Are separated upwards. From this moment, the object to be heated 11 starts expanding.

  The high frequency may stop the oscillation when the upper electrode 3 starts to separate, or may be applied for a predetermined time after the upper electrode 3 starts to separate or until the upper electrode 3 reaches a predetermined height. You may continue.

  When the upper electrode 3 reaches a predetermined height, the article 11 to be heated is taken out from between the heating electrodes 10 and conveyed to the pressing step.

  In the above aspect, even after the object 11 to be heated reaches the softening start temperature at which it starts to expand, the expansion is suppressed by the upper and lower heating electrodes 10 that are expansion suppressing members until the temperature reaches the optimum heating temperature. Therefore, the time when the object to be heated 11 is in the expanded state is shortened, and the time when the void is generated can be shortened as much as possible.

Furthermore, the heating time is shortened and the temperature difference between the surface and the inside of the object to be heated 11 is shortened by using the heating from the surface of the object to be heated 11 by the heat conduction from the heating electrode 10 and the heating from the inside by the high frequency. The effect of reduction can be exhibited.
(Example)
Examples of the present invention will be described below.
As a preheating device, a device obtained by modifying a compact type high frequency welder YRP-400T-RC manufactured by Yamamoto Vinita Co., Ltd. was used. The high frequency oscillation frequency of the device is 40.68 MHz and the maximum output is 400W.

  The heating electrode is made of aluminum and has a size of 85 mm in width × 55 mm in length × 15 mm in thickness. A sheathed heater (200 W) and a temperature sensor are built in the heating electrode, and the heating surface temperature can be maintained at a maximum of 300 ° C. The upper electrode is directly connected to the ROBO Cylinder (registered trademark), and can be vertically moved by arbitrarily setting a start position, a stop position, and timings, moving speeds, and the like.

  The stampable sheet that is the object to be heated has a thickness of 3 mm, a nylon 6 thermoplastic resin with a volume content Vf of 30%, and a carbon fiber bundle (length 3 to 5 cm) randomly distributed and dispersed. . The optimum heating temperature range of the stampable sheet is a lower limit of 250 ° C and an upper limit of 290 ° C.

  FIG. 2 shows the relationship between temperature and expansion when the stampable sheet was allowed to stand in a constant temperature bath and slowly heated. The stampable sheet starts to expand at around 190 ° C. and apparently expands to about 15 mm which is about 5 times the original thickness (3 mm). FIG. 3 shows a schematic sectional view of the expanded stampable sheet. The carbon fibers inside are laminated in layers, and voids are formed so that the layers are separated.

  FIG. 4 shows an example of a temperature profile when a sample obtained by cutting this stampable sheet into 80 mm × 50 mm is heated by the preheating device.

  The high frequency oscillation output at this time is 200 W and the electrode heating temperature is 250 ° C. At 10 seconds on the horizontal axis, the upper electrode descends and comes into contact with the stampable sheet, and high frequency oscillation starts at the same time. High frequency oscillates for 60 seconds, and at 70 seconds on the horizontal axis, the upper electrode separates and at the same time the high frequency oscillation stops. To do.

Note that the high-frequency oscillation may be stopped at the same time as the separation of the upper electrode is started as described above, or may be continued for a predetermined time during the separation operation of the upper electrode or after the separation is completed.
As can be seen from FIG. 4, even if the stampable sheet reaches the expansion start temperature of 190 ° C., its expansion is suppressed by the heating electrode, that is, the expansion suppressing member, and after reaching the optimum heating range of 260 ° C., the upper electrode The expansion starts only after they are separated from each other.

In addition, the heating device also incorporates an automatic matching follow-up circuit and a reflected wave measurement circuit, and the reflected wave energy during high frequency oscillation is 2 W or less (that is, matching efficiency is 99% or more). In the following discussion, The matching efficiency may be 100%.
For temperature measurement, a fluorescence type optical fiber thermometer FL-2000 manufactured by Anritsu Keiki Co., Ltd. and a fluorescence type optical fiber thermometer probe FS-1M were combined, and a diameter of 1.8 mm was formed on the end face of the stampable sheet as shown in the right side of FIG. The measurement is carried out by inserting the probe into a small hole having a depth of 15 mm.

  In the figure, the broken line is a temperature profile when high frequency oscillation is not performed, that is, when heating is performed only by heat transfer from the heating electrode. It can be said that the difference in temperature between the two (about 70 ° C. in the vicinity of 70 s) is the effect of high frequency heating.

  In the figure, the white circles (without high-frequency oscillation) and black circles (with high-frequency oscillation) are the temperatures of the upper surface of the stampable sheet immediately after the upper electrode was separated at 70 s, measured with a radiation thermometer (TASCO, THI-500). Is. It is considered that the one to which the high frequency is applied has a small temperature difference from the temperature measured by the temperature probe and the temperature difference between the inside and the surface is small, that is, the effect of the internal heating by the high frequency is exhibited.

FIG. 5 shows the heating results at different frequencies. The measurement was performed by replacing the high frequency power source, the matching circuit, etc. of the preheating device of the example. The electrodes were not heated. Only at 27.12 MHz, the temperature rise is slightly small, but it can be seen that heating is performed at any frequency.
Equivalent temperature when heating stampable sheets of the same size with conventional atmosphere heating (Yamato Scientific Co., Ltd., vacuum drying furnace DP-21 set at 260 ° C. and normal pressure, built-in heater 680 W) It took 4 to 5 minutes to reach the expanded state.

  From the above results, in the preheating device according to the present invention, as compared with the heating device according to the prior art, it is less likely to cause a temperature difference between the surface and the inside, and the stampable sheet is preliminarily prepared in the shortest time without generating voids. It is possible to heat.

  When heating a sample of carbon fiber itself or a carbon fiber composite material such as a stampable sheet in this preheating device, a local leak or spark may occur between the electrode and the sample depending on the composition of the sample. is there. In such a case, it is preferable to provide an insulating layer between the heating electrode and the sample because leakage and sparks can be suppressed. As a material for the insulating layer, a material having excellent heat resistance, being less likely to be heated by a high frequency, and having a small dielectric loss is preferable. Specifically, fluorine-based resins such as PTFE (Teflon (registered trademark)), polyamide-based resins (trade name Kapton, etc.), PPS resins, inorganic materials such as ceramics are preferable. The sheet or film material made of these may be sandwiched between the sample and the electrode, or the electrode itself may be coated with a fluororesin, ceramic or the like.

  According to the observation of the inventor of the present invention, as compared with the upper electrode, a leak and a spark are relatively often generated between the lower electrode grounded to the ground and the sample, and the insulating layer may be provided only between the lower electrode and the sample. It is suitable.

Now, according to the present invention, the stampable sheet which is a carbon fiber composite material is heated using a high frequency of 10 MHz-100 MHz. At this time, it is an interesting question which one of the constituent elements of the stampable sheet, carbon fiber or nylon 6 type resin, is predominantly heated.
FIG. 6 shows the results of heating the carbon fibers, the carbon fiber composite material, and the resin from room temperature under the conditions of 40.68 MHz, 200 W, and 30 seconds using the preheating device of the example. The surface of the sample after heating was measured by the above-mentioned radiation thermometer. The size, shape, mass, and physical properties (carbon fiber content, specific heat, thermal conductivity, etc.) of each sample are different, and of course no quantitative comparison is made, but it is certain that all materials are heated. That is, when the carbon fiber composite material is heated by high frequency, it is considered that both the carbon fiber and the resin are heated by high frequency to some extent.

Regarding the mechanism of heating the carbon fiber itself by high frequency, the effect of induction heating in the above-mentioned equation (2) or the effect of heating by the third term (current term) can be considered.
As a heating method using electromagnetic waves, there is microwave heating using a microwave band having a higher frequency. In microwave heating, 2.45 GHz, which is one of ISM bands, is often used. It is known that the carbon fiber can be easily heated even by this microwave, and conversely, it is overheated. Therefore, in the carbon fiber composite material, the problem of excessive temperature rise of the resin at the interface between the carbon fiber and the resin is described. Is also known. The present inventors have also confirmed a phenomenon in which a carbon fiber bundle is heated in a microwave oven set to 200 W and ignites in about 20 seconds.

  On the other hand, in the high frequency range used in the present invention, as shown in FIG. 6, carbon fibers alone do not ignite, and relatively gentle heating is possible. It is considered that the high frequency band is more suitable than the microwave band.

1 Preheating Device 2 Lower Electrode 3 Upper Electrode 4 Insulating Member 5 Matching Circuit 6 High Frequency Power Supply 7 Upper Electrode Base 8 Connecting Member 9 Electrode Elevating Device 10 Heating Electrode 11 Heated Object 12 Housing

Claims (6)

A heating device for a plate-shaped object to be heated, which is made of a material in which at least a part of a matrix resin is a reinforcing fiber which is a carbon fiber ,
Heating the object to be heated while suppressing expansion of the object to be heated at least until the object to be heated reaches a temperature at which expansion starts (expansion start temperature), a pair of opposing heating surfaces,
An electromagnetic wave generation source for applying an electromagnetic wave having a frequency of 10 MHz or more and 100 MHz or less is provided between the pair of heating surfaces,
For the object to be heated, heating by heat conduction from the heating surface,
A heating device capable of simultaneously performing dielectric heating of the matrix resin due to application of the electromagnetic waves and heating from the inside by induction heating of the carbon fibers . Heating the object to be heated by bringing the pair of heating surfaces into contact with the object to be heated;
The heating according to claim 1, wherein the contact between at least one of the pair of heating surfaces and the object to be heated is released after at least a part of the object to be heated reaches or exceeds the expansion start temperature. apparatus. The heating device according to claim 1, wherein the pair of heating surfaces are electrically conductive. The heating device according to claim 3, wherein an insulating material layer is present between the object to be heated and at least one of the pair of heating surfaces. Heating apparatus according to claim 1 to 4, wherein the matrix resin is one that contains a thermoplastic resin. A heating method for heating a flat object to be heated, which is composed of a material in which at least a part of carbon fibers is contained in a matrix resin,
At least until the heated object reaches a higher temperature to start expansion (expansion starting temperature), the same time is heated heat transfer while suppressing the expansion of the heated object, frequency by applying the following electromagnetic 10MHz or 100MHz A heating method, wherein the object to be heated is heated from the inside by dielectric heating of the matrix resin and induction heating of the carbon fiber .

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