JPH0327366B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a lightweight fiberboard that has a closed cell structure, is lightweight, has excellent heat insulation properties, has low water absorption and hygroscopicity, and has improved mechanical strength and dimensional stability, and a method for manufacturing the same. Traditionally, lightweight fiberboard has a specific gravity of 0.4.
Semi-rigid fiberboards with a specific gravity of less than 0.8 and soft fiberboards with a specific gravity of less than 0.4 have been made lighter by lowering their specific gravity, but in the dry fiberboard manufacturing method, fibers are bonded to each other using an additive adhesive. In order to lower the specific gravity, it is necessary to reduce the clamping pressure during hot-press molding, which reduces the contact area between the fibers, that is, the bonding area, and creates voids between the fibers. increase As a result, as the specific gravity decreases, mechanical strength and water resistance decrease, and the fiberboard's internal bonding strength, water absorption, and dimensional stability due to moisture absorption decrease significantly. As a countermeasure to prevent this, it is possible to manufacture fiberboard by increasing the amount of adhesive added, but the specific gravity increases depending on the amount added, making it possible to produce lightweight fiberboard with improved mechanical strength and water resistance. Can't get the board. In addition, the use of a large amount of adhesive increases manufacturing costs, and as the amount of adhesive used increases, moisture inevitably increases, so there is a risk of punctures due to evaporation of the moisture during hot-press molding. In order to prevent the occurrence of punctures, it is necessary to perform hot pressing at low temperatures for a long period of time, which has many problems such as decreased productivity and decreased yield due to thickness deviation, which is not practical. The present invention solves the above-mentioned problems with conventional fiberboards, and aims to provide a lightweight fiberboard with improved mechanical strength and dimensional stability, which is lightweight, highly insulating, absorbs little water and moisture, and has improved mechanical strength and dimensional stability. purpose. The details will be explained below regarding the case of, for example, wood fiber among vegetable fibers. Wood chips such as hardwoods and softwoods are steamed to loosen the bonds between fibers, and then defibrated by a refiner (defibration device) to obtain wood fibers. In addition to wood fibers, vegetable fibers such as bamboo, bamboo, rice leaves, bakasu, and knot lees, which are abundantly produced as by-products from pulp mills, can be used. Refineers include those that defibrate wood chips taken out from a steaming device using high-temperature, high-pressure steam (10 to 12 kg/cm ² ), and those that defibrate wood chips that are directly connected to a steaming device and are under high temperature and high pressure. etc. are used. Since the wood fiber discharged from the refiner contains a large amount of water, it is put into a hot air duct from the refiner and dried while being blown. Wind speed is 10-30m/
sec, the air blowing atmosphere temperature is around 30 to 120°C, but it can be adjusted over a wide range depending on the specific gravity of the wood fiber, the amount of feed, the processing capacity of the previous and subsequent steps, etc. This hot air blowing dries the wood fiber to a moisture content of about 5 to 10%. The dried wood fibers are put into a blender (mixing device). A heat-curable adhesive to which a foaming agent, which is made of a thermoplastic synthetic resin capsule containing a volatile liquid, is mixed is mixed in a blender, and the adhesive is applied to the wood fiber. Alternatively, without using a blender, it is also possible to add a thermosetting adhesive or a foaming agent at the same time as defibration, or to spray it into an air duct and apply it to the floating wood fibers. In the blowing agent made of a thermoplastic synthetic resin capsule containing a volatile liquid used in the present invention, the volatile liquid is n-butane, n-pentane, neopentane,
n-hexane, neohexane, cyclohexane,
Chain or cyclic saturated hydrocarbons such as n-octane, iso-octane, chain or cyclic unsaturated hydrocarbons such as n-pentene, n-hexene, cyclohexene, n-octene, benzene, toluene,
Aromatic hydrocarbons such as xylene, ethyl ether,
Generally organic solvents such as ethers such as ethyl-propyl ether, ketones such as acetone and methyl ethyl ketone, acetate esters such as methyl acetate and ethyl acetate, cellosolves such as cellosolve acetate and butyl cellosolve, and alcohols such as methanol and ethanol. It mainly contains organic compounds called fluorine-based compounds or fluorine-based compounds. The thermoplastic synthetic resin constituting the capsule shell is selected to be insoluble in the volatile liquid contained therein, and to have an appropriate softening point depending on the foaming temperature. Examples of such thermoplastic synthetic resins include polyethylene, polypropylene, acrylic resin, methacrylic resin, styrene resin, vinyl chloride resin, vinylidene chloride resin, acrylonitrile resin, vinylbenzyl chloride resin, and the like. The capsule-type foaming agent is, for example, disclosed in Japanese Patent Publication No. 1973-
Details are given in Publication No. 26524. The thermosetting adhesive used in the present invention is a urea resin,
Melamine resin, urea-melamine cocondensation resin, phenolic resin, alkylphenol resin, resorcin resin, alkyl resorcin resin (including resin made of an alkyl resorcin mixture called siel oil resorcin obtained from oil mother rock etc.),
Various thermosetting synthetic resins or thermoplastic synthetic resins such as epoxy resins, urethane resins, alkyd resins, and thermosetting acrylic resins are included, and paraffin, wax, etc. may be mixed with the synthetic resins. Compositions other than the above, such as fillers such as calcium carbonate, titanium white, bentonite, talc, wood flour, wheat flour, acid or alkali curing catalysts, condensation regulators such as ε-caprolactam, urea, resorcinol, or formalin catchers, aging Inhibitors, ultraviolet absorbers, preservatives, insect repellents, waterproofing agents, flame retardants, water repellents, dyes, pigments, etc. may be mixed. The amount of heat-curable adhesive added is usually 30% or less by weight based on the wood fiber, and the resin percentage is 20 to 60%, and in general, the lower the resin percentage, the more uniform the mixing with the wood fiber. It can be done. The foaming agent is used by adding and mixing it to the adhesive in an amount of about 0.1 to 200%. First, add and mix the adhesive into a blender into which the wood fibers are placed, and then add and mix the capsule-type foaming agent, or vice versa. It may be added to and mixed with. The capsule-type foaming agent is easily mixed uniformly, and the wood fiber coated with the heat-curable adhesive mixed with the capsule-type foaming agent uniformly in this way is blown again and conveyed to the felter to form a mat-like material. None Continuous conveyance. The pine-like wood fiber is cut into a regular size and then inserted into a hot press and molded under hot pressure. The continuously conveyed pine-like wood fibers may be inserted into a continuous press such as a heated roller press, subjected to continuous hot-press molding, and then cut into regular sizes. The heat and pressure conditions (heat and pressure, temperature, time, etc.) are adjusted over a wide range depending on the foaming temperature, expansion ratio, amount of foaming agent added, adhesive curing temperature, amount of adhesive added, etc. Generally 100 to 160 if the heat-curing adhesive is urea resin
℃, 5Kg/cm ² to 40 at a temperature of 160 to 200℃ for phenolic resin and 100 to 150℃ for resorcinol resin.
Hot pressure molding takes about 1 to 20 minutes at a pressure of about Kg/ ^cm2 . When trying to obtain a lightweight fiberboard, especially one with a specific gravity of 0.8 or less, hot-press molding may be performed by adjusting the spacing between hot plates using a distance bar during hot-press molding. The foaming agent in the adhesive is foamed by heating during hot-press molding, and the adhesive is heated and cured. A blowing agent consisting of a thermoplastic synthetic resin capsule containing a volatile liquid that evaporates when heated is softened by heating because the outer shell of the blowing agent is made of thermoplastic synthetic resin, and the volatile liquid contained therein evaporates. Due to the accompanying volumetric expansion, the adhesive is expanded and expanded to form closed cells, and the adhesive is cured. The internal pressure within the compressed wood fiber mat increases due to the volume expansion accompanying the foaming of the capsule-type foaming agent, and together with the pressure from the hot plate, the wood fibers come into close contact with each other, and the contact area between the wood fibers decreases. The bonding area is increased, and since the wood fibers are connected to each other by the adhesive and thermoplastic resin, the bonding area is substantially increased, the adhesive force is improved, and the mechanical strength and internal bonding force are significantly improved. Furthermore, closed synthetic resin cells derived from the capsule-type foaming agent are uniformly formed in the gaps between the wood fibers, and the gaps between the fibers are reduced, thereby improving heat insulation and moisture barrier properties. In this way, a lightweight fiberboard in which a closed foam structure is formed between the wood fibers in the fiberboard due to the foaming of the foaming agent can be easily and efficiently obtained. The present invention is a lightweight fiberboard having the above-mentioned structure, and even if it is difficult to obtain a uniform internal structure in a fiberboard, if the capsule-type foaming agent is mixed uniformly, synthetic resin bubbles can be formed in the gaps between the wood fibers. Because it has a uniform closed-cell structure consisting of
Moisture barrier properties are improved, expansion and contraction due to water absorption and moisture absorption are strongly suppressed, dimensional stability is improved, and internal destruction does not occur due to freezing of built-in water in low-temperature environments. In addition, the adhesive strength of adhesives, the adhesive strength of thermoplastic synthetic resins, mechanical cross-linked adhesion between wooden fibers due to the resin coating caused by foaming, and the contact area between wooden fibers due to internal pressure caused by foaming of foaming agents ( A high adhesion effect can be obtained by increasing the adhesion area). Example 1 Coniferous wood chips were steamed and defibrated with a single-disc stiffener, and at the same time, 1% of molten wax was added, then the air blowing speed was 15 m/sec, and the air blowing atmosphere temperature was
Dry by blowing air at 60-100℃ to a moisture content of about 5-10%. The dried wood fibers are placed in a blender. In a blender, a phenolic resin adhesive with a resin content of 30% and a foaming agent added is mixed with the wood fiber at a weight ratio of 10%. As the blowing agent, polyvinyl chloride benzyl polymer capsules (particle size 10μ) containing neoheptane are used, and 100 parts by weight of the blowing agent is added to 100 parts by weight of the adhesive. The resulting mixture is formed into a pine shape using a felting device, then temporarily pressed and cut into a specified length, and the pine-like wood fiber of the specified length is then formed using a hot press equipped with a 10 mm thick distance bar.
Heat pressed for 10 minutes at 180℃ and 30Kg/ ^cm2 , resulting in a plate thickness of 10
A lightweight fiberboard A with a specific gravity of 0.5 mm and a specific gravity of 0.5 is obtained. Example 2 Hardwood chips were steamed and defibrated with a double-disc stiffener, and at the same time 3% of molten wax was added, then the air blowing speed was 10 m/sec and the air blowing atmosphere temperature was 60°C.
Dry by blowing air at ~80℃ to a moisture content of about 5 to 10%. The dried wood fibers are placed in a blender. In a blender, a urea resin adhesive with a resin content of 50% and a foaming agent added is mixed with the wood fiber at a weight ratio of 15%. As the blowing agent, methyl methacrylate-styrene copolymer capsules (particle size 15 μm) containing neohexane are used, and 150 parts by weight of the blowing agent is added to 100 parts by weight of the adhesive. Further, 1% by weight of ammonium chloride is added to the adhesive as a hardening agent. The resulting mixture was formed into a pine shape using a felting device, then temporarily pressed and cut into a specified length, and the pine-like wood fibers of the specified length were formed using a hot press equipped with a 15 mm thick distance bar. Heat pressing was carried out at 150°C and a pressure of 30 kg/cm ² for 15 minutes to obtain lightweight fiberboard B with a thickness of 15 mm and a specific gravity of 0.4. Comparative Example 1 A lightweight fiberboard with a thickness of 15 mm and a specific gravity of 0.4 was obtained using a urea resin adhesive to which no foaming agent was added as the adhesive of Example 2. Table 1 shows the physical properties of the lightweight fiberboards A and B and the soft fiberboards obtained in the above Examples and Comparative Examples.

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Claims (1)

[Claims] 1. Vegetable fibers are intertwined with each other and the fibers are bonded with an adhesive, and a thermoplastic synthetic resin capsule containing a volatile liquid maintains an independent foam structure between the fibers. Lightweight fiberboard filled with solid wood. 2. After applying a foaming agent made of a thermoplastic synthetic resin capsule containing a volatile liquid and a thermosetting adhesive to vegetable fibers, the fibers are made into a mat shape,
If necessary, by hot-pressing molding using a hot press with a distance bar, the foaming agent is heated to foam and the heat-curable adhesive is heated to harden, forming a closed foam structure in the fiber gaps and increasing the adhesive pressure at the intersections between the fibers. A method for manufacturing lightweight fiberboard that increases the