JPS6216164B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for forming fiberboard for improving the physical properties of the fiberboard, such as bending strength, tensile strength, and water absorption. In general, in the case of molds for fiberboards that have unevenness, it is difficult for the fibers to move and deform at the bends, making it difficult to arrange them in an orderly manner. Cracks often occur on the inside. Therefore, in order to improve this problem, conventional methods such as stacking fiberboard of the same quality on the folded part have been used, but although this method has some effect in the case of loose folds, Once the condition is reached, it is practically difficult to mold.
This cannot necessarily be said to be sufficient. In addition, fiberboard is usually manufactured using an internal addition method in which a sizing agent is added after the fibers are defibrated.
There is also a method of improving the bending state by improving the strength and water resistance to some extent in advance by impregnating a fiberboard with no adhesive added with a sizing agent or by applying a resin solution to the surface. Although attempts have been made, the water absorption rate is around 20% after 24 hours, making it almost impossible to use in applications that require water resistance. The present invention is in immediate response to the above-mentioned existing situation, and aims to solve these technical problems.The present invention aims to solve the technical problems described above, and is capable of reinforcing flat parts and bent parts in molding fiberboard, improving the appearance, and further improving water resistance. The purpose is to Therefore, the feature of the present invention that achieves the above object is that after impregnating a fiberboard with a specific gravity of 0.4 to 0.7 with a thermosetting resin solution having a solid content concentration of 20 to 30% dissolved in a solvent, Dry for 3 to 6 minutes at ~120°C to form a semi-dry flat mat, then heat the mat at 130°C to 200°C using a desired shaping mold.
℃, a pressure of 30 to 50 Kg/cm ² , and a pressing time of 1 to 3 minutes to obtain a semi-hardened rough molded product, and then further flatten the surface of the rough molded product to a thickness of 0.1 to 1.0 mm. Covered with thermoplastic resin film of mm, and molded again with the above mold.
100~240℃, pressure 30~50Kg/ ^cm2 , clamping time 5~10
It is heated and compressed in minutes. Hereinafter, the details of the method of the present invention will be explained step by step. The fiberboard used in the present invention is made of vegetable fiber as the main raw material, which is made into pulp and is made into a pulp without the addition of adhesive. It is called a plate that is artificially formed by means, and has a specific gravity of 0.4 to 0.7.
It is easy to impregnate. The first step of the present invention is to first impregnate this fiberboard with a thermosetting resin solution by coating or dipping, and then dry it to form a semi-dry mat. It is effective that the amount of the curable resin solution deposited is 40 to 50% of the weight of the fiberboard. If it is less than 40%, it will be difficult to mold the bent part with a mold, and if it is more than 50%, the thermosetting resin will be squeezed out along with the solvent during subsequent molding, reducing the amount of resin attached to the fiberboard. This is because it causes a decrease in strength. Examples of the thermosetting resin used in the present invention include phenol resins, resorcinol resins, urea resins, melamine resins, epoxy resins, and isocyanates. Therefore, impregnation of the above-mentioned thermosetting resin into the fiberboard is carried out by a normal coating or impregnation method, and the adhering solid content is suitably 5 to 15 parts by weight, but not more than 5 parts by weight, based on 100 parts by weight of the fiberboard. If the amount is more than 15 parts by weight, the strength of the molded product will decrease, and if it is more than 15 parts by weight, the adhesion to the thermoplastic resin film will be poor and the cost will be high, which is not desirable. Next, in the second step of the present invention, the semi-dry pine is heat-pressed using a desired mold to produce a semi-hardened rough molded product. Appropriate thermal compression conditions must be selected depending on the type of thermosetting resin used for bonding. For example, if this condition is urea or melamine resin, the mold temperature is 100 to 147℃, or if phenol or resorcinol resin is used, the mold temperature is 130 to 160℃.
℃ is appropriate, and the pressure condition is 40℃ in both cases.
~50Kg/cm ² and a short time of 1 to 2.5 minutes is sufficient. If the thermosetting resin impregnated into the fiberboard is completely cured at this stage, the adhesion of the thermoplastic resin film, especially the anchoring effect, will deteriorate, so it is hot pressed for a short time and removed from the mold in a semi-cured state. is preferable. After that, the surface of the rough molded product taken out from the mold is coated with a thermoplastic resin film, which greatly improves its water resistance and is suitable for outdoor use where water resistance is required. At the same time, the details of the folded portion, that is, the portions where the fiber material has not flowed, are completely replenished, resulting in a remarkable reinforcing effect. The thermoplastic resin film used here is
High-pressure, medium-pressure, and low-pressure polyethylene, polypropylene, vinyl chloride, polymethyl methacrylate, etc., having a softening point of 90 to 180°C and a thickness of about 0.1 to 1.0 mm, are appropriately selected and used. The molded product material whose surface has been coated with a thermoplastic resin film is placed again in the above-mentioned shaping mold, heated and compressed to form the final molded product, and then A molded product is obtained by cooling. The temperature and pressure conditions at this time may be approximately the same as those for producing the crude molded product, including a temperature of 100 to 180°C,
It is selected at any time within the range of 40 to 50 Kg/cm ² , but the time does not necessarily have to be the same, and may be more than 2.5 minutes, or about 5 to 10 minutes or more depending on the material of the product. It may also be heated and compressed. Further, cooling after heating and compression may be performed by natural cooling or forced cooling, but it is effective from the viewpoint of solidifying the molded product to allow it to cool naturally until it reaches a predetermined temperature or lower, for example, 90° C. or lower. Next, the fiberboard molding method of the present invention will be described in more detail with reference to Examples and Comparative Examples, but of course the present invention is not limited to the following examples.
Needless to say, modifications may be made as appropriate without departing from the purpose. (Example 1) Width (W) 100 mm, depth (h) 50 as shown in Figure 1
mm, length (l) 240 mm, thickness (t) 3 mm, in manufacturing channel-shaped molded product 1, approximately 100 parts by weight of fiberboard with a specific gravity of 0.5 is calculated as
A resol-type phenolic resin dissolved in ethyl alcohol with a solid content of 25% was uniformly applied and impregnated to approximately 10 parts by weight, and the mat was dried at 100° C. for 5 minutes to obtain a semi-dry mat. Then, this semi-dry pine is heat pressed using molding molds 2 and 2' shown in Fig. 2 at a temperature of 150°C, a pressure of 40 kg/cm ² , and a time of 2 minutes to semi-cure it. A rough molded product 3 was obtained. Next, the surface of the rough molded product was
Covered with ^a low-pressure polyethylene film with a thickness of I got the item. When the adhesion between the modified fiberboard and the polyethylene film of the obtained molded article was observed, it was found to be extremely good, with the bent portions being neatly aligned and having a good appearance. Table 1 shows the physical properties of the flat part 4 of the molded product, and Table 2 shows the fracture measurement results of the bent part 5. (Comparative Example 1) After immersing fiberboard with a specific gravity of 0.5 in water (moisture content approximately 50%) in the same manner as in Example 1, using the mold shown in Example 1, the temperature was 220°C and the pressure was 40 kg/kg.
cm ² for 7 minutes under high temperature and pressure to obtain a molded product. The folded parts of the obtained molded product were irregular and had a poor appearance. Table 1 shows the physical properties of the flat part of the molded product, and Table 2 shows the fracture measurement results of the bent part. (Comparative Example 2) This was the same as the crude molded product of Example 1, and was created using fiberboard and impregnating the fiberboard with resin. Table 1 shows the physical properties of the flat part of the rough molded product of Example 1 and the same comparative molded product, and Table 2 shows the fracture measurement results of the bent part. The bending strength of the molded product is measured by cutting a sample piece from the bottom of the width (W) according to JIS K6911, and the water absorption rate is {(weight after water absorption - weight before water absorption)/weight before water absorption} x I found it in 100. In addition, for destructive measurements, a roof-shaped sample with an isosceles triangular cross section (side length 30 mm) and a length of 80 mm was placed on an autograph support stand with the top of the bent portion facing upward, at a crosshead speed of 50 mm/min. The point at which the compressive force suddenly drops was used as a guideline for the destructive force.

【table】

[Table] As described above, according to the molding method of the present invention, after treating the fiberboard with a thermosetting resin, a rough molded product is once molded using a mold, and then a rough molded product is formed using a thermoplastic resin film. It is clear that by covering the surface of the molded product, the appearance, bending strength, breaking force, water absorption rate, etc. of the molded product can be significantly improved compared to other cases, and it is sufficient for outdoor use where water resistance is required. It has a remarkable effect that it is possible to form a usable fiberboard.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a molded product obtained by the method of the present invention, and FIG. 2 is a sectional view of the same molding die.

Claims (1)

[Scope of Claims] 1. A fiberboard with a specific gravity of 0.4 to 0.7 is impregnated with a thermosetting resin solution with a solid content concentration of 20 to 30% dissolved in a solvent, and this is made into a semi-dry mat. The mat is hot-pressed using a desired shaping mold to form a semi-hardened rough molded product, then the surface of the rough molded product is covered with a thermoplastic film, and the mat is heated and compressed again using the mold. How to form fiberboard. 2. The method for forming a fiberboard according to claim 1, wherein the means for impregnating the fiberboard with the thermosetting resin solution is coating and/or dipping. 3. The fiberboard according to claim 1 or 2, wherein the thermosetting resin is one or two selected from phenolic resins, resorcinol resins, melamine resins, urea resins, epoxy resins, and isocyanates. Molding method. 4 The coating thermoplastic resin film has a thickness of 0.1~
2. The method for molding fiberboard according to claim 1, wherein the fiberboard is a 1.0 mm resin film selected from high, medium and low pressure polyethylene, polypropylene, and vinyl chloride.