KR19980034355A - Manufacturing method of low density fiberboard - Google Patents

Abstract

The present invention relates to a method for producing a low density fiberboard, and more particularly, to multi-stage pressure for spraying MDI (diphenyl methane diisocyante) on wood fiber and appropriately adjusting hot pressure temperature, hot pressure time, hot pressure rate, sea pressure and number of repetition times of hot pressure. The present invention relates to a method for manufacturing low density fiberboard useful as a raw material for general furniture, office furniture, electronic products, kitchen furniture, etc. by reinforcing water resistance, bending strength, adhesive strength, etc. by applying a thermoforming method.

Description

Manufacturing method of low density fiberboard

The present invention relates to a method for producing a low density fiberboard, and more particularly, to multi-stage pressure for spraying MDI (diphenyl methane diisocyante) on wood fiber and appropriately adjusting hot pressure temperature, hot pressure time, hot pressure rate, sea pressure and number of repetition times of hot pressure. The present invention relates to a method for manufacturing low density fiberboard useful as a raw material for general furniture, office furniture, electronic products, kitchen furniture, etc. by reinforcing water resistance, bending strength, adhesive strength, etc. by applying a thermoforming method.

Fibreboards are made of low density, medium density, high density fiberboards by the content of wood fibers and adhesives or by thermoforming. In order to manufacture high-density fiber boards, a relatively large amount of wood fibers and adhesives are consumed, which leads to an increase in manufacturing costs and a deterioration of workability and workability. Also, since urea resins contained as adhesive components are easily hydrolyzed by water, moisture There is a problem that the adhesive strength is lowered when exposed to a long time. Therefore, the high-density fiberboard is mainly limited to interior materials and furniture materials for its use.

On the other hand, low-density fiberboard has a relatively low use of wood fibers and excellent workability compared to high-density fiberboard.

Fibreboard has received the spotlight as a new wood board material that replaces plywood and particle board because it has the advantage of using waste materials and excellent workability. However, since the fiber board is bulk unlike other wood plate materials, the density of the surface layer is relatively high when compared to the density of the middle layer during hot press molding. Because of this falling problem, the side workability and screw holding power is poor, and change occurs in the middle layer, it has to be commonly used as a low-cost plate material.

In the manufacture of low-density fiberboard, most of the fiberboard manufacturers adopt the same method as the existing medium-density manufacturing method and adjust only the density. However, the decrease of the density causes a deepening of the material deviation of the wood plate material. Was done. Therefore, the low density fiber board made by the conventional manufacturing method is significantly lowered in various physical properties compared to the medium density fiber board, and a lot of change occurs during the luther processing.

Therefore, various studies have been conducted to enhance the physical properties by reducing the density difference between the surface layer and the middle layer.

For example, German Patent Publication No. 42,229,396 (1994) uses polymeric MDI (polymeric diphenyl methane diisocyanate, hereinafter referred to as PMDI) as an adhesive in the manufacture of fiberboard, and uses amine as a catalyst in suspension or emulsion. The present invention discloses a method of forming a fiber board by thermoforming while applying a constant pressure to a press. This method is a technique of shortening the thermal pressure time and reducing the amount of adhesive used, and is merely an example of applying a PMDI adhesive to a fiber board.

In Korean Patent Publication No. 8192 (1989), a method of immersing a fibrous material in a matrix composed of a mixture of polyethylene glycol or polyamines in the presence of a catalyst in the presence of a catalyst is used as a crude product and fiber material of MDI (diphenyl methane diisocyanate). A method of making a reinforced thermoset material is disclosed.

In addition, Australian Patent Publication No. 8,434,219 (1985) has a polystyrene sheet having a density of 25 to 30 kg / m 3 in a middle layer, and adheres a high density fiberboard having a density of 600 to 800 kg / m 3 to both sides of the middle layer to form a low density high strength plate-like material. Techniques for making are disclosed. This is a technique of lowering the density of products by placing a relatively low density sheet between low density surface layers, which is completely different from the technique of adjusting the density gradient suitable for low density fiber boards by the thermoforming method.

In the present invention, an effort has been made to develop a new low density fiberboard manufacturing method that reduces the density difference between the surface layer and the middle layer to the maximum. As a result, instead of the conventional urea formaldehyde resin, wood fiber is replaced with a relatively inexpensive MDI to improve the water resistance and durability, and to reduce the amount of adhesive input. The present invention was completed by further increasing the durability of the middle layer by increasing the relative density of the middle layer with respect to the surface layer by selecting another multi-stage pressure-thermoforming method.

Accordingly, the present invention realizes the competitiveness of the raw material reduction effect and cost reduction through weight reduction of the fiber board and improves the workability according to the weight reduction, and reinforces the physical properties such as water resistance, bending strength, adhesive strength, general furniture, office furniture, electronic products, It is an object of the present invention to provide a method for producing low density fiberboard useful as a raw material for kitchen furniture.

1 is a density gradient diagram of a fiber board manufactured by applying a general thermoforming method.

Figure 2 is a density gradient diagram of the fiber plate produced by applying the multi-stage pressure-thermoforming method of the present invention.

The present invention is a method for producing a low density fiberboard by thermal pressure molding method by the main component of wood fiber and spraying an adhesive thereto, wherein the adhesive component EMEM (emulsified MDI), PMDI (polymeric MDI) or a mixture thereof It is characterized by a method of producing a low density fiber board using the multi-stage pressure-thermoforming method.

In addition, the present invention includes a method for producing a low density fiber board using urea formaldehyde (urea formaldehyde), polyethylene glycol (PEG) or a mixture thereof in the adhesive content in a certain content range.

Referring to the present invention in more detail as follows.

The present invention is a new hot pressing method that contains MDI as an adhesive to reinforce adhesion, bending strength and water resistance, and lowers the difference in density gradient between the surface layer and the middle layer in order to improve internal adhesion and side workability. The present invention relates to a method for producing a low density fiber board which reduces the density difference between the surface layer and the middle layer.

The urea-formaldehyde resin, which has been mainly used as an adhesive in the manufacture of fiber boards, is easy to dissipate formaldehyde and hydrolyze in water, and thus there are many problems in applying to the production of low density fiber boards, thereby reducing formaldehyde dissipation amount. Although a low molar ratio adhesive having a small content was used, this caused a decrease in the physical properties of the fiberboard. However, MDI (diphenyl methane diisocyante) used as an adhesive component in the present invention exerts an adhesive force by forming a polyurea bond by reacting with water as a thermosetting resin. In addition, since MDI does not contain formaldehyde, it does not cause problems due to dissipation, has a short hot press time and a low hot press temperature, and can be applied even in a high mat content range, thereby saving drying costs of raw materials. In addition, there is almost no premature curing on the surface of the plate-like material, and even with a small amount of adhesive, it has the advantage of improving strength and dimensional stability.

As such an adhesive component, PMDI alone, EMDI alone, or a combination thereof may be used, and these are preferably sprayed within a range of 3 to 6 parts by weight based on 100 parts by weight of wood fiber. If the injection amount of the adhesive component is less than 3 parts by weight, the physical properties including the adhesive force are lowered, and it is economically disadvantageous to use the excess in excess of 6 parts by weight.

The PMDI used in the present invention is prepared by condensing MDI with aniline and formaldehyde and reacting with COCl ₂ , which is mainly used in construction and furniture. It is preferable to use a molecular weight in the range of 350 ~ 400, it is used by melting with a solvent such as acetone, xylene (xylene) or by melting with heat.

EMDI is an emulsified resin for improving compatibility with water, and is particularly excellent in coating property during resin spraying.

In addition, the present invention also includes a conventional urea-formaldehyde resin as an adhesive component in a certain content range. It is preferable to contain the urea-formaldehyde resin within a range of less than 12 parts by weight with respect to 100 parts by weight of wood fibers, and when the content is added in excess of 12 parts by weight, the effect of addition according to the dosage is reduced.

In addition, MDI used as an adhesive component in the present invention has a high molecular weight compared to the conventional urea formaldehyde resin (urea formaldehyde) resin may have excellent adhesive strength or other physical properties, but MDI fiber board because it is inferior in dispersibility or permeability When spraying as an adhesive, the treatment for viscosity adjustment is important. And since MDI has the property of adhering to the hot plate, the release agent should be applied on the hot plate before the thermoforming process. In the present invention, polyethylene glycol is contained less than 2.5 parts by weight based on 100 parts by weight of wood fiber. In this case, the polyethylene glycol used serves to further strengthen the strength by forming a crosslink with PMDI during the thermoforming process by maintaining the molecular weight range of 1000 ~ 1450.

In the fiber board manufacturing method according to the present invention, the most important step is a hot press molding process. When the formed mat is pressurized under a certain temperature, a bonding force is generated between the adhesive and the wood fibers to form a plate-like material after the hot pressing process. Each layer of the mat becomes resistant when a certain press pressure is applied and begins to deform and deform as time passes. The higher the temperature and the more moisture, the less the resistance of each layer of the mat and the greater the deformation. Therefore, the condition setting that makes the resistance to press pressure equal between the surface layer and the middle layer is the most important requirement to reduce the density difference between the surface layer and the middle layer. In addition, since the deformation of the pressure proceeds from the beginning of the thermoforming process to the time when the middle layer reaches the curing temperature, in the present invention, the pressure-repressurization treatment is performed until the time of reaching the middle curing temperature.

Referring to the multi-stage pressure-thermoforming method according to the present invention in more detail.

The press used in the present invention is an intermittent press, in which the re-pressurization speed is accelerated after the depressurization in the initial-medium stage during the repetition of the depressurization-repressurization, thereby preventing the density sinking around the surface layer and slowing down the middle-end stage. Raise. It is possible to increase the middle layer density by slowing down the hot plate descending rate before the depressurization-repressurization step. Therefore, in order to reduce the surface polishing amount, the hot plate lowering speed should be increased. Preferably, the re-pressurization speed is 0.3-0.5 mm / sec in the early-middle stage at the time of re-pressurization after depressurization, and 0.1-0.2 mm / sec in the middle-end stage. In the early and middle stages, the density of the mat is controlled to 400 ~ 450 ㎏ / m ³ after dissolution, and repeatedly carried out until the middle layer reaches the curing temperature, and in the middle and end stages, the fiber board density is 550 ~ 600 ㎏ / ㎥ Repeat the pressurization and depressurization process. It should be noted that the pressure-repressurization schedule should be adjusted so that premature curing of the used adhesive (resin) occurs and the bond between fibers and adhesive is lost. In addition, since the thermal pressure temperature is suitably 170 to 190 ° C, the thermal pressure time can be shortened at a temperature higher than 190 ° C, but carbonization of the surface layer, premature curing of the adhesive, and discoloration occur. The pressure is 25 ~ 30 ㎏ / ㎠ to vary depending on the species or thermal pressure conditions. And the thermal pressure time is preferably extended until the middle layer temperature reaches the curing time and the internal saturated steam pressure is sufficiently low.

Attached Figure 1 is a density gradient when making a fibrous plate by applying a general thermoforming method, Figure 2 is a density gradient when making a fibrous plate by applying the multi-stage pressure-thermoforming method of the present invention. 2 shows that the surface density is lower than that of FIG. 1 while the middle layer density is improved. The density gradient distribution shown in FIG. 2 is preferable for reinforcing the middle layer of the low density fiber board aimed at by the present invention. 2, the ratio of minimum density / average density is improved by 88 to 90%. In the general pressurization method, the mat of the fiberboard is pressed to the target thickness and maintained for a certain time while depressurizing when the middle layer reaches the curing temperature and saturated steam occurs. The ratio of the minimum density / average density obtained by this pressurization method is shown in FIG. As shown in the figure, the density difference between the surface layer and the middle layer is about 80%, and many voids are formed in the middle layer, which weakens the side workability, the screw holding force, and the adhesive force. The ratio of minimum density / average density is one of the items for evaluating the density gradient distribution of the plate material. The minimum density is the density of the middle layer, and the higher the minimum density / average density ratio shows the gentle density gradient from the surface layer to the middle layer.

As described above, in the method for manufacturing a low density fiber board according to the present invention, MDI is sprayed onto wood fibers as an adhesive component to compensate for adhesive strength, bending strength, durability, and the like. Processability was improved.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 8 and Comparative Example 1

After dissociating the wood fiber after dissociation, the wood fiber was mixed by dry method of spraying the adhesive component with compressed air and adjusted to a constant mat thickness through cold pressure. Then, a low density fiber board having a thickness of 15 mm and a target density of 600 kg / cm 3 was prepared by applying a multi-stage pressure-thermoforming method under the conditions shown in Table 1 below, and the minimum / average density value of the manufactured fiber board was measured.

At this time, the used press is an intermittent press that re-pressurizes the pressure to 0.40 ㎜ / sec after depressurization in the initial and middle stages during repeated pressurization and re-pressurization to prevent density depressions around the surface layer and 0.15 ㎜ in the middle and end stages. It was slowed down to / sec to increase the middle layer density. In the initial-middle stage, the density of the mat was adjusted to 450 kg / m ³ after depressurization, and the low density fiberboard was manufactured by repeating until the middle layer reached the curing temperature.

Comparative Example 2

The wood fiber after dissociation is moisturized, and then 12% by weight of urea resin is mixed by a dry method of spraying with compressed air and adjusted to a constant mat thickness through cold pressure. In addition, a low density fiber board having a thickness of 15 mm and a target density of 600 kg / cm 3 was manufactured by applying a general thermoforming method under a hot pressure temperature of 185 ° C., a hot pressure time of 5 minutes, and a pressure of 30 kg / cm 2. The ratio of density was measured.

Experimental Example

For each of the low-density fibreboards prepared in Examples 1 to 8 and Comparative Examples 1 to 2, the flexural strength, the adhesive force, and the absorption thickness expansion rate were measured by KS F 3104, and the results are shown in Table 1 below.

division Raw material substance (part by weight) Target density (kg / ㎥) % Of minimum density / average density Flexural strength (kg / ㎠) Adhesive force (kg / ㎠) Thickness expansion rate (%) Example 1 Wood fiber 100EMDI 3 603 85.4 362 3.9 8.9 Example 2 Wood fiber 100EMDI 6 601 84.8 400 9.3 5.8 Example 3 Wood fiber 100EMDI 1.2 Urea resin 10.8 599 89.3 307 4.1 10.2 Example 4 Wood fiber 100EMDI 3.6 Urea resin 8.4 604 87.5 364 5.4 8.5 Example 5 Wood fiber 100PMDI 3PEG1.5 602 85.1 275 3.4 9.1 Example 6 Wood fiber 100PMDI 6PEG1.5 603 85.0 376 6.6 7.3 Example 7 Wood fiber 100PMDI 3 602 84.6 263 3.2 9.3 Example 8 Wood fiber 100PMDI 6 600 84.2 381 6.7 7.2 Comparative Example 1 Wood fiber 100 Urea resin 12 602 88.2 236 3.1 9.8 Comparative Example 2 Wood fiber 100 Urea resin 12 601 80.6 255 2.2 9.5

a) PMDI: Hanwha BASF M20S

b) EMDI: ICI Polyurethanes 3054

c) Urea resin: Hansol Chemical DR-101

The multi-stage pressure-thermoforming method according to the present invention is mainly aimed at improving the durability of the low density fiberboard middle layer. According to Table 1, the multi-stage pressure-thermoforming method (Examples 1 to 8) of the present invention has a ratio of the minimum density / average density of the plate material from 80% to 88 as compared with the conventional thermoforming method (Comparative Example 2). Increasing the percentage, the adhesive strength also improved by at least 1.4 times. Therefore, the thermoforming method attempted in the present invention contributed to the improvement of the density of the middle layer and produced a density gradient suitable for the low density fiberboard. In comparison with Comparative Example 1 in which urea resin was used as the adhesive component, the flexural strength was increased by 1.7 times, the thickness expansion ratio was 1.7 times, and the adhesive strength was improved by 4.2 times.

The fiber board manufactured in the present invention has an effect of reducing the amount of raw materials by about 15 to 20% compared to the conventional medium density fiber board having a density of 700 kg / m ³ by adjusting the density down to 600 kg / m ³ or less. Therefore, the present invention has various advantages such as the reduction of raw materials through cost reduction and cost reduction, and the improvement of the workability and weight reduction of the tool due to the weight reduction of the fiber board, thereby securing market share through product diversification. Has the effect of

Claims (7)

In the method for producing a low density fiberboard by thermo-pressure molding method by using wood fibers as a main component and spraying an adhesive thereto, Emulsified MDI (EMDI), polymeric MDI (PMDI) or a mixture thereof as the adhesive component, and the multi-stage pressure-thermoforming molding method for producing a low density fiber board. The method of claim 1, wherein the adhesive component is sprayed 3 to 6 parts by weight based on 100 parts by weight of wood fiber. The method of manufacturing a low density fiber board according to claim 1, wherein the adhesive component is sprayed by containing urea formaldehyde resin together. 4. The method of claim 3, wherein the urea-formaldehyde resin is contained in an amount of less than 12 parts by weight based on 100 parts by weight of wood fiber. The method for producing a low density fiber board according to claim 1, wherein the adhesive component is sprayed together with polyethylene glycol. The method of claim 5, wherein the polyethylene glycol is contained in less than 2.5 parts by weight with respect to 100 parts by weight of wood fibers. According to claim 1, wherein the multi-stage pressure-thermoforming is a re-pressurization rate 0.3 ~ 0.5 ㎜ / sec in the initial-middle period under the heat pressure temperature 170 ~ 190 ℃, pressure 25 ~ 30 kg / ㎠, fiber board density 400 ~ 450 kg during depressurization Pressurizing and depressurizing process is repeated until the middle hardening temperature is reached, and m / m ³ , and pressurizing and depressurizing process is carried out so that re-pressurization speed is 0.1 ~ 0.2 ㎜ / sec and target fiber board density is 550 ~ 600 ㎏ / ㎥ Method for producing a low density fiberboard, characterized in that for repeating.