JP2003039462A - Manufacturing method for molded article using vegetable fibers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding method for molding a molded article having uneven parts using vegetable fibers partially containing reinforcing fibers without generating thickness irregularity and the lowering of a physical property value. SOLUTION: At least one kind of a low temperature curing formaldehyde resin or a low temperature solidifying resin and a high temperature curing formaldehyde resin are used to mold a preform to prevent the thickness irregularity and the lowering of the physical property value generated in a conventional molding method. By this molding method, the reinforcing fibers can be uniformly arranged in a product and the physical property value of the product can be stably enhanced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a technique for producing a molded product having a concavo-convex portion by using a rigid and difficult-to-form vegetable filament.

[0002]

2. Description of the Related Art Typical examples of rigid and difficult-to-form vegetable fibers include palm fibers and hemp fibers produced in a wide range of Southeast Asia. It is known that these vegetable fibers are long fibers and are excellent fibers having high tensile strength. However, these vegetable fibers are judged to be unsuitable as a molding raw material due to their rigidity and are not suitable as a molding raw material, and in particular, molding of a molded article that requires an uneven portion is extremely difficult in terms of molding technology. It has been. Therefore, for example, in the case of coconut fiber, it is customary to dispose of it as waste or incineration because its use is limited. Further, in the case of hemp fiber, it is almost always used as a string-like material or a bag material for conventional applications, and no other applications have been considered. further,
Examples of rigid and difficult-to-form vegetable fibers are bamboo fibers,
Sugarcane fibers and the like can be mentioned as an example, but these fibers also had the same problem. The most important reason why plant long fibers with strong rigidity are not often used as a raw material for producing molded products with deep drawing or unevenness is that the fibers themselves are rigid and long fibers, and flat plate-shaped products However, there is a problem in that during the molding process of the concave-convex portion, a large internal stress is generated during the molding due to the shape of the concave-convex portion, and the fiber is cut or the partial thickness is insufficient.
Furthermore, when these plant fibers are preformed according to the present invention (hereinafter referred to as preforms), that is, immediately formed without undergoing the shape forming step before the main formation, the raw material of the plant fibers has rigidity. It became a thick mat, and it was extremely difficult to insert it into the mold even in flat plate molding. As a solution to this, it was necessary to reduce the thickness by using a preform or the like. The following is a description of the molding method proposed so far with the use of palm fiber. After mechanically disintegrating the coconut fibers, the long fibers are made into a mat and used as it is as a molding material, or a material that promotes the entanglement of fibers in the mat by needle punching is used as a molding material to spread or bond an adhesive. A general method is to pass the agent through the agent tank to impregnate and carry the binder, and then hot-press and mold in a molding die. However, with this method, it is not possible to mold uneven parts, and there is no method other than molding by cutting long fibers into short fibers in order to cope with uneven part molding.In that case, the strength of the molded product Was known to drop extremely. It has been desired to provide a molding method suitable for efficient molding of uneven portions without lowering the partial strength of the molded product. Further, conventionally, in the molding of uneven portions, it has been extremely difficult to simultaneously integrate organic fibers or inorganic fibers into a molded product to exhibit high strength.
In the conventional method, due to the accumulation of internal stress during fiber cutting or press molding, product bending occurs after the product is removed from the product, and only a product with low accuracy can be manufactured. It became possible for the first time by combining the resins of the present invention with a preform.
Also, if the preform process by pre-molding is not used, the workability of inserting into the molding die in the main molding is poor,
It was desired to reduce the thickness to obtain this molded material.

[0003]

[PROBLEMS TO BE SOLVED] To provide a method that is rigid and that enables molding of an uneven portion without shortening a long fibrous plant fiber and a method of manufacturing a molded product. Further, it provides a method for imparting high strength performance to the molded product.

[Means for Solving the Problems]

The present inventor, as a result of thorough studies in view of the above problems, has found that a molded product having an uneven portion can be efficiently processed if the conditions for pre-curing by a preform are overcome. The present inventor pays attention to the fact that various formaldehyde-based resins have different curing temperatures due to their raw material compositions, and that a mixture of a plurality of these resins can be used. It has been found that it is possible to mix a thermoplastic polymer resin or a resin emulsion thereof as an alternative to the resin. Based on this finding, it was found that effective preform can be precured, and a means capable of efficiently forming uneven parts without shortening the long fibrous plant fibers can be provided, and its means And Furthermore, based on the knowledge of this pre-curing and preform molding, it has become possible to manufacture a high-strength product by preform molding in which organic fibers or inorganic fibers are incorporated, or simultaneous molding by high temperature molding.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention employs a two-step molding method of preform and main molding (curing) when manufacturing a molded article having an uneven portion as described above. This is the stress that pulls the fiber in the length direction of the fiber due to the internal stress caused by narrowing down when molding the convex and concave parts of highly rigid vegetable fiber when performing one-shot molding by conventional molding (curing) as in the past. In many cases, the fibers in the uneven portion were pulled, and problems such as fiber cutting, uneven product thickness, and cracking occurred. The present inventor has found that the preform method is the most suitable method for preventing and solving these problems. further,
As a result of earnest studies, the present inventor has found that the curing temperatures of various formaldehyde-based resins are different, and that two or more raw materials, for example, urea resin and phenol resin, which are independently produced, are not reacted by mixing urea and phenol with formaldehyde. It was found that the mixture can be used as a one-liquid type. Furthermore, it was confirmed that a part of the thermoplastic polymer resin or its resin emulsion could be replaced and used. The above is suitable as a binder for long-fiber plant fibers, and is suitable as a new method suitable for preform molding. Was confirmed. Further, by this preform molding method, it becomes possible to perform molding by inserting or covering various tough fibers inside or outside as a strength auxiliary material.

Next, a preform molding method and a main molding when using various formaldehyde resins provided by the present inventor will be described. Formaldehyde resin is a resin produced by reaction using one or more raw materials such as urea resin, melamine resin, phenol resin, resorcinol resin, etc. and formalin (formaldehyde aqueous solution), which is in liquid or powder form. Although any of them can be used, a liquid form is preferable for use. As examples of the use of the liquid, those which are frequently used as adhesives such as plywood, particle board, and laminated wood are similar, and in particular, concentration, viscosity, etc. do not cause any problems in use. In addition, various formaldehyde-based resins differ in performance derived from their raw material compositions, and more preferably, they are capable of mixing multiple resins and are highly compatible, and the reaction temperature and reaction rate of each resin. The fact that the curing rate differs depending on the heating temperature was a means to complete the purpose. In addition, as an example of use in powder form, it is generally used as a molding material, and it is possible to use a mixture of powder forms. The present inventor has found that a resin or a resin liquid obtained by reacting urea, thiourea, melamine, or a mixture thereof with formaldehyde can be cured at a temperature of 120 ° C. or less, and therefore, it is a binder for preform molding, a low temperature curing type binder. Classified as formaldehyde resin.
In addition, since the resin or resin solution obtained by the reaction of phenol, resorcinol, etc. with formaldehyde is difficult to cure at low temperature and can be cured at 150 ° C. or higher, it was classified as the main molding high temperature curable formaldehyde resin. When a low-temperature curable formaldehyde resin and a high-temperature curable formaldehyde resin with different curing temperatures are mixed and mixed into one liquid, first, the fact that the low-temperature curable formaldehyde resin is cured by low-temperature molding is applied. A molding method was invented, in which the shape of a reformed molded product is adjusted by curing a low-temperature curable formaldehyde-based resin, and then the high-temperature curable formaldehyde-based resin is cured by main molding to adjust the shape of the final product. That is, the present invention is a novel method for carrying out preform molding and main molding with a one-pack resin.

Next, a detailed description will be given of the process of forming the uneven portion molded product of the rigid plant fiber through the preform molding and the main molding using the above resin. The vegetable fiber may be a matte fiber, but it is preferable that the fiber is entwined with a needle punch so as not to become messy in the subsequent step of supporting the resin liquid. On the other hand, the resin liquid is prepared by mixing at least one low temperature curable formaldehyde resin and at least one high temperature curable formaldehyde resin. That is, at least one low-temperature curable formaldehyde resin is required as a preform molding condition. As for the mixing method, it is permissible to thoroughly mix the liquid or powder. The mixing ratio of the low temperature curable formaldehyde resin and the high temperature curable formaldehyde resin is as follows:
0%) 100 parts by weight, low temperature curable formaldehyde resin solution (solid content 45%) 5-40 parts by weight, preferably 10-20 parts by weight and sufficiently mixed resin solution is prepared. This resin mixture (hereinafter referred to as "resin mixture A") is supported on plant fibers by the method described below.
It is common to fill the inside of the resin liquid tank with vegetable fiber through it, and then remove the excess resin with a roll or the like, but examples of methods such as the flow coater method and the spray method are also given. To be Next, in the preform molding step, the plant fiber supporting the resin mixture A was placed inside the preform molding die similar to the main molding die, and 1
It is cured at a temperature of 20 ° C or lower. The mold for preform molding is preferably a mold or a similar male / female mold that can be lightly clamped, and more preferably a heating type in which electric heat or steam piping is circulated. The clamping pressure is preferably 5 kg / cm ² or less. Mold temperature of 130 ℃ or less when the low temperature curing type formaldehyde resin is urea resin alone, and 1 when it is co-condensation of urea and melamine resin.
Mold temperatures below 40 ° C. are preferred. At this time, it is important to set the temperature according to the curing temperature of the selected low temperature curable formaldehyde resin solution, and the curing time is
It is necessary to perform it within a range that does not affect the main molding. That is, at this temperature setting, the low temperature curable formaldehyde resin solution in the resin mixture A first cures, and the contained high temperature curable formaldehyde resin solution hardly cures. Since the preform molded product produced by such a process contains an uncured high temperature curable formaldehyde resin in the inside thereof, the preform molded product is stored in the high temperature curable mold and kept at 150 ° C. or higher. When main molding is performed at temperature,
The uncured high temperature curable formaldehyde resin is completely cured. At that time, since the preform molding die and the main molding die are similar to each other, the shape of the preform molded article is similar to the product shape, and the stress in the uneven portion molding portion in the main molding is almost the same. The original purpose could be achieved without any occurrence.

Next, when the main molding is carried out through the preform molding using the resin mixture A, the water resistance of the final product may be considered important. The ratio of the low temperature curable formaldehyde resin in the resin mixture A can be used within the range of 5 to 100 parts of the low temperature curable formaldehyde resin with respect to 100 parts of the high temperature curable formaldehyde resin. Is most preferably 5 to 10 parts. The ratio of low temperature curing type formaldehyde resin increased,
If it is more than 30 parts, the preform molding becomes hard,
Stretchability of the fibers is hindered by compression in the main molding, and defects such as cutting of the fibers are likely to occur. Further, it is well known that the low temperature curable formaldehyde-based resin is inferior in water resistance to the high temperature curable formaldehyde-based resin, and the higher the ratio in the resin mixture A, the lower the water resistance. Therefore, it is necessary to determine the composition depending on the purpose of the product.

Next, it is also possible to use a resin emulsion in place of a part or the whole of the low temperature curable formaldehyde resin in the resin mixture A. The resin emulsion is an acrylic resin emulsion, a vinyl acetate resin emulsion, a petroleum resin emulsion, a synthetic rubber emulsion or the like, which can be dispersed in a formaldehyde resin liquid. These emulsion groups can mix low-temperature and high-temperature curable formaldehyde-based resins (hereinafter referred to as resin mixture B), have the effect of exhibiting adhesiveness in preform molding and converging fibers. Since it is possible to impart softness (elasticity), it is easy to mold and demold the preform molded product, and it is also easy to handle in the main molding. The preform molding method using the resin mixture B is
The resinous mixture B is added to the rigid vegetable fiber by a method such as spray coating, roll coater coating, flow coater coating, and impregnation. For example, in addition to the above curing method, a heat curing furnace,
It is also possible to adjust the shape by a method such as infrared drying or hot air drying. The temperature at that time is preferably 120 ° C. or lower.

The use of the powder low temperature curable formaldehyde resin and the powder high temperature curable formaldehyde resin mixture (hereinafter referred to as the resin mixture C) is effective in increasing the resin content of the molded product. In this case, the compounding ratio of the resin mixture C to the vegetable fiber is 1 by weight.
It is possible to set it in the range of 0 or more, but the range of 40 to 60 parts by weight is the most preferable in view of the uniformity and aesthetics of the molded product. The resin mixture C may be attached to the vegetable fibers by dispersing the resin mixture C between the vegetable fibers and performing preform molding or main molding. As a method for dispersing the resin mixture C in the vegetable fiber at that time, a method in which the resin mixture C is dispersed in water and at least one selected from the above emulsion group and used to produce a product having the most uniform production Is the way to do it. This method produces less free formaldehyde and is effective as a molding method related to pollution and sick house measures.

[0011] When a high-strength molded product is manufactured using the above-mentioned plant fiber, it is possible to easily use other fibers simultaneously in the molding process of the product. That is, for example, carbon fibers that exhibit high strength, aramid fibers, organic fibers such as nylon fibers, or inorganic fibers such as steel fibers and glass fibers and their processed products are combined with plant fibers before preform molding. It is possible to use a method of forming a mat-like material, arranging it between mat layers, or placing it on the surface and simultaneously performing preform molding. The organic fibers or inorganic fibers used in this case may be long fibers, tapes, woven fabrics, or non-woven fabrics, and can be integrally molded. In addition, after preform molding, the surface of the preform molded product is formed of long fibers of organic or inorganic fibers, tape, woven cloth,
It is also possible to place a non-woven fabric on the front surface or the back surface and simultaneously perform high temperature molding. At this time, these organic fibers or inorganic fibers are preferably impregnated with a resin mixture or a high temperature curable formaldehyde resin. It is possible to manufacture a molded product having high strength adhered to the surface of the molded product or a high strength molded product internally provided.

[0012]

EXAMPLES The present invention will be described below with reference to examples, but the invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 As an example of the molding method invented by the present inventor, coconut fiber was used as a rigid plant fiber, and preform molding and main molding were performed using a resin mixture A which was a mixture of a urea resin and a phenol resin. An example in which a molded product is completed will be described.
The coconut fiber is originally in a converged state, and if it is not sufficiently defibered, there is a problem in the adhesion of the resin before the preform, and since molding is difficult, unevenness of the molded product is likely to occur. . In addition, it is important that the fiber is cut so that the fiber is not cut. The same thing could be observed for other plant fibers. The vegetable fiber has a matte shape before being impregnated with the resin, and the fiber is in a state of being easily moved as it is. In this state, when the resin mixture A is impregnated into the fibers, a non-uniform thickness occurs, and a non-uniform dispersion phenomenon of the fibers occurs in the stage of deep drawing preform molding. As a countermeasure against this, in the present embodiment, a mat having internal entanglement by a needle punch was used. The vegetable fiber mat entwined with a needle punch has a thickness of 10 cm, has very many voids, and contains a large amount of air. Next, the resin mixture A is a liquid urea resin (manufactured by Mitsui Chemicals, Inc .: solid content 45%) produced by reacting urea and formaldehyde as a low temperature curable formaldehyde resin and phenol and formaldehyde as a high temperature curable formaldehyde resin. The liquid urea resin (Mitsui Chemicals, Inc .: solid content 50%) obtained by reacting the
The resin mixture A was prepared and used as a mixture with the addition of 100%.
The resin mixture A was filled in a resin tank, the matt vegetable fiber was dipped in the resin tank for 15 minutes to sufficiently impregnate it, and the excess resin liquid was removed by a roll, and then 130 ° C.
Insert and place in the preform mold set to the mold temperature of
It was compressed to a thickness of 2 cm by applying a pressure of 3 kg / cm ² and then heat-cured for 2 minutes. After demolding, it was confirmed that the preform molding retained its state without the thickness being restored. Next, the preform molding is inserted and placed in a main molding die set at a die temperature of 200 ° C.,
A pressing pressure of 12 kg / cm ² was applied and pressure molding was performed for 10 minutes. As a result, a molded product (molded product 1) having an average thickness of 0.5 cm was obtained. For comparison, the resin-immersed product of the mat-shaped plant fiber before preform was directly inserted into the main molding die without preform molding, and a pressing pressure of 12 kg / cm ² was applied to the resin dip. Molding was carried out for 1 minute to obtain a molded product (molded product 2). Ten products each of the above-mentioned molded products 1 and 2 were manufactured. Table 1 shows the measured thickness values of the respective parts (FIG. 1) of the molded article by both molding methods, and Table 2 shows the physical property values of the respective parts (FIG. 2). As a result, it was confirmed that the molded product 1 had extremely small thickness unevenness at each site, and was excellent in physical properties as compared to the molded product 2 and had very few variations.

EXAMPLE 2 The present inventor uses a cloth made of hemp fiber as the plant fiber, and performs preform molding and main molding with a resin mixture C which is a mixture of a vinyl acetate emulsion and a phenol resin. An example of manufacturing the product will be described. It is known that a vinyl acetate emulsion is well dispersed in a liquid phenol resin solution (aqueous solution). Although it may be left at room temperature, it is also known that the emulsion particles are combined with each other in a short time due to mutual evaporation and water vaporization due to efficient heat and pressure to form a lump or a film-like substance to converge the fibers. In this example, hemp fibers are used, and heat molding is performed in a region where the phenol resin is difficult to cure in low temperature heating preform molding, and moisture in the resin mixture C is diffused and removed to bond and solidify the vinyl acetate emulsion. The method of forming a preform molded product in which the fibers are bundled is adopted. Further, the preform molded product was molded by heating at a high temperature to mold a completely cured molded product. The vinyl acetate emulsion (manufactured by Sunstar) used had a solid content of 45%, and the high temperature curable formaldehyde resin resin was a liquid phenol resin (manufactured by Mitsui Chemicals, Inc .: solid content 50).
%)It was used. The hemp fiber cloth is a cloth made from Bangladesh, which has been sufficiently defibrated and then woven into a cloth. The weight of the cloth was 320 g / m ² in an absolutely dry state. The compounding ratio in the production of the resin mixture C was tested as vinyl acetate emulsion: liquid phenol resin = 10: 100 (volume ratio). After thoroughly mixing and stirring in the same manner as in Example 1, the resin mixture C was filled in a resin tank, the cloth-like hemp fibers were dipped in the resin tank, and excess resin liquid was removed by a roll, and then 130 ° C. Inserted and placed in the preform mold set to the mold temperature of ² cm, and pressurizing it to 3 cm / cm ² for 2 cm.
After being compressed to a thickness of 5 mm, it was heat-cured for 5 minutes. It was confirmed that water was scattered out of the mold at the same time as the heating, and it was confirmed that the preform molded product after demolding can be easily inserted and set in the main molding mold. Next, the preform-molded product was inserted and placed in a main-molding mold set at a mold temperature of 200 ° C., and a pressing pressure of 12 kg / cm ² was applied to perform pressure molding for 10 minutes. As a result, a molded product (molded product 3) having an average thickness of 1.2 cm was obtained. For comparison, the resin-impregnated product of the mat-shaped plant fiber before preform molding was directly inserted into the main molding die without preform molding, and placed.
A pressing pressure of kg / cm ² was applied and pressure molding was performed for 12 minutes to obtain a molded product (molded product 4). Ten of each of the above-mentioned molded products 3 and 4 were manufactured. Table 1 shows the measured thickness values of the respective parts (FIG. 1) of the molded article by both molding methods, and Table 2 shows the physical property values of the respective parts (FIG. 2). As a result, it was confirmed that the molded product 3 had extremely small thickness unevenness at each site, and was excellent in physical properties as compared with the molded product 4 and had very few variations.

Example 3 As a rigid plant fiber, coconut fibers which were sufficiently defibered were prepared, three mats were internally entangled with a needle punch, and three carbon fibers were inserted into the gaps. An example will be described in which a preform molded product having an uneven portion is manufactured by low temperature molding, and then the molded product is manufactured via main molding by high temperature molding. The above needle punched mat has a thickness of 3 cm and is 120 g /
Three sheets of m ² were prepared and used. Next, carbon fibers (manufactured by Toray) are vertically and horizontally arranged between the three sheets at intervals of 5 cm as shown in FIG. 5, and preform molding having an uneven portion using the resin mixture A of Example 1 is performed. After obtaining a preform molded product by the same process as that of the product, the preform molded product is inserted and placed in a main molding mold set at a mold temperature of 200 ° C., and a pressing pressure of 12 kg / cm ² is applied to the preform molded product for 10 minutes. It was pressure molded for a minute. As a result, a molded product (molded product 5) having an average thickness of 0.5 cm was obtained. Separately, on the surface of the preform molded product obtained in Example 1, a glass fiber cloth-like material (usually FRP
Glass cloth (200 g / m ² product) used in, and inserted and placed in the mold for main molding set at the mold temperature of 200 ° C., and a pressing pressure of 12 kg / cm ² is applied for 10 minutes. A molded product (molded product 6) was obtained by pressure molding. Ten molded products 5 and 6 were manufactured. Table 1 shows the measured thickness values of the respective parts (FIG. 1) of the molded article by both molding methods, and Table 2 shows the physical property values of the respective parts (FIG. 2). As a result, it was confirmed that the molded product 5 had extremely small thickness unevenness at each site, and was excellent in physical properties as compared to the molded product 6 and had very few variations.

[0015]

[Table 1] <Reference> Molded article 1: preform molding (low temperature molding) + high temperature molding. Use of coconut fiber Resin composition is liquid urea resin + liquid phenol resin, molding 2: high temperature molding only. Use of coconut fiber Resin composition is liquid urea resin + liquid phenol resin Molded product 3: preform molding (low temperature molding) + high temperature molding. Use hemp fiber Resin composition is vinyl acetate emulsion + liquid phenol resin Molded product 4: High temperature molding only. Use hemp fiber Resin composition is vinyl acetate emulsion + liquid phenol resin Molded product 5: preform molding (low temperature molding) + high temperature molding. Palm + carbon fiber Resin composition is liquid urea resin + liquid phenol resin Molded product 6: preform molding (low temperature molding) + high temperature molding. Palm + glass fiber Resin composition is liquid urea resin + liquid phenol resin

[0016]

[Table 2] <Reference> * 1, 5, 9 in the table are measurement sample sampling points. * Molded items 1-6 are

Follow <Reference> in [Table 1]. * Surface hardness is measured using a Barcol hardness tester (G / 2J
934-1 type). After molding, leave at room temperature for 24 hours. * Bending strength is measured according to JIS-6911. * Measurement of physical properties of molded product 6 was performed with the glass fiber facing downward.

[0017]

The preform molding method using the low temperature curable formaldehyde resin and the high temperature curable formaldehyde resin according to the present invention and the main molding procedure using the preform molding method, regardless of the presence of irregularities. , Table 1 and Table 2
As shown in, it is possible to provide a stable product by preventing uneven thickness of the product.

[0018]

[Brief description of drawings]

FIG. 1 Perspective view of a gantry product with uneven parts

[Fig. 2] Top view of a gantry product with uneven parts

FIG. 3 is a perspective view (AA ′) cross-sectional view of a gantry product having an uneven portion.

[Fig. 4] Partial cross-sectional view of a product containing reinforcing fibers

[0019]

[Explanation of symbols]

1 convex part-a flat part 2 convex part-a R part (R: 3.0 mm) 3 Recessed part rising part-1 4 Recessed bottom R part-1 (R: 3.0 mm) 5 Recessed bottom flat surface 6 Recessed bottom R part-2 (R: 3.0 mm) 7 Recessed rising part-2 8 Convex part-b R part (R: 3.0 mm) 9 Convex part-b Flat part 10 Convex part-a Reinforcing part 11 Convex part-b Reinforcing part 12 A-A'Cross section of pedestal with uneven parts

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Claims (4)

[Claims] 1. A method for producing a molded article having a concavo-convex portion using a vegetable fiber by a production method comprising preforming and main forming. 2. A method for producing a plant fiber preform according to claim 1, which comprises using a thermosetting resin. 3. A process for producing a plant fiber preform, which comprises using the thermoplastic polymer resin or a resin emulsion thereof according to claim 1. 4. A method of manufacturing a molded article according to claim 1, 2 or 3, wherein the high strength fibers are simultaneously molded.