JPH0333840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing molded fiberboard.

(Prior Art) A conventional molded fiberboard is manufactured as follows.

Using a fiberboard with a specific gravity of 0.6 or more obtained by a normal wet method, water or water to which a penetrant has been added is applied directly or permeated to the surface of the fiberboard to form a primary fiberboard. This is then hot-press molded using a mold press to form a molded fiberboard.

The primary fiberboard in this case has the following properties. That is, by adding moisture to the fibers, the fibers become more flexible and easier to mold, and in the mold press, the fibers are adhesively molded by the adhesive action of cellulose, lignin, etc. in the fibers.

However, the method of manufacturing a molded fiberboard using such a primary fiberboard still has the following problems.

If the specific gravity is less than 0.6, the fiberboard becomes brittle, making it difficult to handle up to the mold press and causing more defects due to damage to the fiberboard itself.

Since it has a specific gravity of 0.6 or more, it must be heated at high temperature and pressure, and the resulting molded fiberboard has a high specific gravity.

In order to add moisture, molding must be done under low temperature and long-term heat pressure (if heat pressure is performed at high temperatures, punctures will occur due to the evaporation pressure of the water). Therefore, the adhesive action of cellulose, lignin, etc. in the fibers However, spring punctures occur after hot pressing, and clean molding is not possible.
Furthermore, the strength of the molded fiberboard itself is low.

Since fibers with high specific gravity are molded, mechanical destruction of the fibers is likely to occur during molding, making deep molding impossible.

The present invention aims to solve the problems of the conventional molded fiberboard manufacturing method as described above. That is, in the method of the present invention, an aqueous slurry is prepared by mixing plant fibers with thermoplastic synthetic resin capsules containing an expandable substance, and then the slurry is made into a mat shape, and the plant fibers are heated and compressed using a hot press. It uses a primary fiberboard that is molded to form a foamed structure between the internal fibers.

The present invention aims to obtain a molded fiberboard having the above-described configuration, which is easy to handle, has a low specific gravity, has high strength, and has high molding performance.

Examples of the method of the present invention will be described below.

(Description of Examples) The present invention is a method for manufacturing molded fiberboard, in which a foaming agent is mixed in advance into an adhesive, the foaming agent is foamed during hot-pressure pre-molding, and a foamed structure is formed between the fibers. The main idea is to mold the foam while maintaining the foamed structure in some areas between the fibers.

The details will be explained below.

Plant fiber raw materials include hardwoods, softwoods, bamboo, bamboo, bamboo, rice leaves, bagasse, and knot lees, which are produced in large quantities from pulp mills.These raw materials are made into chips and further processed by steaming or soaking at room temperature. After softening, the plant fibers are defibrated into fibers. A thermoplastic synthetic resin capsule containing a foamable substance, a sizing agent, water, etc. are added to the thus obtained plant fibers to form an aqueous slurry.

The following thermoplastic synthetic resin capsules containing an expandable substance are used.

Thermoplastic synthetic resins such as polyethylene, polypropylene, acrylic resins, methacrylic resins, styrene resins, vinyl chloride resins, vinylidene chloride resins, acrylonitrile resins, vinyl chloride benzol resins, etc. are used as capsules, and 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-octyne, benzene, toluene, xylene, etc. Aromatic hydrocarbons, ethers such as ethyl ether, ethyl, and propyl ether; ketones such as acetone and methyl ethyl ketone; acetate esters such as methyl acetate and ethyl acetate; and alcohols such as cellolube, acetate, and butyl cellosolve. Generally called organic solvents. It consists of a thermoplastic synthetic resin capsule containing a volatile substance that evaporates when heated, which mainly contains organic compounds, as a foaming substance. The thermoplastic synthetic resin capsule containing these foamable substances is softened by heating and foams due to the volume expansion caused by the volatilization of the contained volatile substance.

This foaming agent is described in detail in Japanese Patent Publication No. 42-26524.

Ammonium carbonate, sodium bicarbonate, azobisisobutyronitrile, diazoaminebenzene,
Toluenesulfonylhydrazide, azodihexahydrobenzonitrile, oxobisbenzene, sulfohydrazide (OBSH), dinitropentamethylenetetramine (DPT), azodicarbonamide (ADLA), azodicarboxylic acid diethyl ester, etc. Decomposes when heated. It consists of a thermoplastic synthetic resin capsule containing a foaming agent that emits gas and foams.

These thermoplastic synthetic resin capsules containing foamable materials are softened by heating, and the built-in foaming agent is decomposed by heating, causing foaming due to the foaming of the foaming agent that emits gas. do.

A sublimable substance that sublimates when heated may be used as the foamable substance contained in the thermoplastic synthetic resin capsule described above.

The thermoplastic synthetic resin constituting the capsule shell may be selected depending on the volatile substance or foaming agent contained therein, or depending on the foaming temperature, curing temperature of the adhesive, etc.

For example, polyethylene, polypropylene, acrylic resin, styrene resin, vinyl chloride resin, methacrylic resin, vinylidene chloride resin, acrylonitrile resin, vinylbenzyl chloride resin, etc. are used as the thermoplastic synthetic resin for the capsule shell.

Sizing agents include natural resins such as casein, starch, and rosin, urea resins, melamine resins, urea-melamine cocondensation resins, phenolic resins, alkylphenol resins, resorcinol resins, and alkylresorcinol resins (shell oil resorcinol obtained from oil matrix shale, etc.). various thermosetting synthetic resins such as epoxy resins, urethane resins, alkyd resins, acrylic resins, vinyl acetate resins, styrene resins, etc.
A thermoplastic synthetic resin, paraffin, wax, or a mixture thereof is used.

Compositions other than those mentioned 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 carriers. agent, anti-aging agent,
Ultraviolet absorbers, preservatives, insect repellents, waterproofing agents, flame retardants, water repellents, dyes, pigments, etc. may be mixed.

If there is a risk that the foaming agent may flow out together with the water discharged from the pine during temporary compaction or heat compaction, the particle size of the capsules should be increased and the capsules should be entangled between plant fibers and fixed, or aggregated. The foaming agent may be adsorbed onto the fibers by adding a foaming agent or by ionizing the foaming agent.

The above composition ratio is usually 100 parts by weight of fiber for thermoplastic synthetic resin capsules containing a foamable substance.
The amount is 0.03 to 60 parts by weight, and the sizing agent is 0.1 to 10 parts by weight.

Water is added to the above mixture to form a slurry having a concentration of about 0.01 to 5% by weight, and the slurry is poured out using a paper machine, flow coater, spray, etc. made of a porous carrier such as a wire mesh, felt, or nonwoven fabric to form a mat.

The manufactured pine is cut into appropriate dimensions as required, and then subjected to cold or hot pressing to be temporarily formed.

When hot pressing, a distance bar is installed as necessary, and a roll press, plate press, ^etc. is usually used. Temperature is 50~250℃
shall be.

In the case of cold pressing, the mat is heated and preformed under the above hot pressing conditions after the required period of time has elapsed.

In this way, the intertwining of the fibers or the bonding of the fibers by the sizing agent is strengthened, and at the same time the foamable substance within the mat is foamed. A thermoplastic synthetic resin capsule containing a foamable substance is plasticized by heat as the foamable substance inside decomposes and the gas released and the volatile substance volatilizes when heated. It expands and bubbles form.

The internal pressure inside the fiber mat increases due to the volumetric expansion associated with the foaming of the foamable material, which, together with the external pressure from the heating plate, causes the fibers to adhere to each other, increasing the contact area between the fibers, that is, the bonding area. Alternatively, the fibers are connected to each other by the sizing agent and the thermoplastic resin, and the bonding area is substantially increased, the bonding force is improved, and the mechanical strength and internal bonding force are significantly improved.

Furthermore, synthetic resin bubbles are formed between the fibers, and the voids between the fibers are reduced, resulting in improved water resistance.

In this way, a primary fiberboard with a low specific gravity is obtained in which a foamed structure is formed due to the foaming of a thermoplastic synthetic resin capsule containing a foamable substance between the fibers in the fiberboard.

Although the primary fiberboard has a low specific gravity, its adhesive strength and mechanical strength are improved, so it can be handled satisfactorily.

Next, the primary fiberboard is inserted into a mold press and hot-pressed.

Primary fiberboard has a foamed structure formed between its internal fibers and has a low specific gravity, so it can be easily molded using a mold press.

In addition, during the heat-pressing process, since the capsules that make up the foam structure are made of thermoplastic synthetic resin, they are easily plasticized at low temperatures, and a portion of the foam structure is destroyed by the pressure, and the adhesive strength of the resin Molding can be carried out without reducing adhesive strength or mechanical strength.

In this way, the fibers are intertwined with each other and bonded together using a sizing agent and a thermoplastic synthetic resin, and a foaming substance that foams when heated is filled between the fibers while maintaining the foamed state. Fiberboard is easily obtained. Further, there is no problem in molding using a die press so as to completely destroy the foamed structure formed between the fibers, and the molded fiberboard obtained in this case is finished with a high specific gravity.

(Actions and Effects of the Present Invention) The present invention has the above configuration, and its effects are summarized as follows.

The primary fiber has a foamed structure in which the foaming agent is held in a foamed state between the internal fibers, and the fibers are entangled, the adhesive force of the thermoplastic synthetic resin, and the crosslinked adhesion between the fibers of the resin coating due to foaming. Due to the increase in the contact area (adhesion area) between the fibers due to the internal pressure caused by the foaming of the foaming agent, the fibers and thermoplastic synthetic resin are firmly integrated, and the product has a low specific gravity and strong mechanical strength, making it easy to handle. . By molding the first fiberboard with a mold press at a low molding pressure in this manner, a molded fiberboard in which a portion of the foamed structure is retained without being destroyed can be obtained.

The molded fiberboard thus obtained is lightweight because a portion of the foam structure remains, and
It inherits the mechanical strength of the primary fiberboard and is also strong enough. Furthermore, it is possible to obtain a molded body that accurately matches the mold of the mold press. If a portion of the foamed structure is not destroyed, a shape matching the mold cannot be obtained due to the restoring force of the foamed structure.

Claims (1)

[Scope of Claims] 1. Thermoplastic synthetic resin capsules containing a foamable substance in vegetable fibers, an aqueous slurry mixed with a sizing agent, made into a mat shape, and then preformed under heat and pressure using a hot press to form a foamed structure. A method for producing a molded fiberboard comprising: forming a primary fiberboard having the following properties, and hot pressing the primary fiberboard in a die press to obtain a molded fiberboard while retaining a portion of the foamed structure between the fibers. Method.