KR20080058969A - Process for preparation of wood plastic composite of microcellular foam - Google Patents

Abstract

A method for preparing microcellular foam of wood plastic composite is provided to increase the thickness of a skin layer of an extrusion mold structure and prohibit the excessive growth of a microcellular foam cell so that the strength of the microcellular foam cell is improved. An extrusion die includes a pressure dropping section(100), a cooling section(300), and a temperature change section(200). The pressure dropping section includes a nozzle(400). A heating unit(500) is mounted at a termination point according to the forwarding direction of an extrusion mold structure. The cooling section includes a cooling unit(600) mounted on a starting point. The temperature change between the pressure dropping section and the cooling section occurs in the temperature change section.

Description

Process for Preparation of Wood Plastic Composite of Microcellular Foam

1 is an enlarged cross-sectional view of an extrusion die including a general pressure drop section and a cooling section;

2 is an enlarged cross-sectional view of an extrusion die used in a manufacturing method according to one embodiment of the present invention;

3 is an electron micrograph (SEM) of the fracture surface of the synthetic wood micro-foam sheet prepared according to Example 1 of the present invention;

Figure 4 is an electron micrograph (SEM) of the fracture surface of the synthetic wood micro-foam sheet prepared according to Comparative Example 1 of the present invention.

The present invention relates to a method for producing a synthetic wood fine foam, and more particularly, a) mixing a plasticized synthetic wood mixture and a blowing agent using an extruder; b) passing the plasticized mixture through a pressure drop zone of the extrusion die to form voids; And c) passing the molten mixture having the fine pores through the cooling section of the extrusion die and cooling, wherein the end point temperature of the pressure drop section and the starting point temperature of the cooling section exhibit a temperature difference of 30 to 200 ° C. The present invention relates to a method for producing a synthetic wood micro-foam that greatly suppresses the growth of foam cells to greatly improve the mechanical strength and surface properties of the foam.

Wood Plastic Composite is a composite material formed by mixing natural materials such as wood powder or wood fiber and thermoplastic resin, and it has excellent durability compared with natural wood and has excellent natural texture and processability not obtained from plastic. As a substitute for internal and external materials, the market is growing more than 20% annually in North America and Japan, and the market is growing in Korea.

Such synthetic wood is mainly used as exterior materials such as decks, fences and siding, but it is difficult to be applied to interior and exterior materials because it is weak to impact and has a specific gravity of 1.1 to 1.3, which is relatively higher than natural wood. Therefore, in order to overcome this disadvantage, various methods have been studied such as molding a product into a shape having a hollow structure in order to reduce the weight of synthetic wood. However, by adding a reinforcing material in order to compensate for the reduction in physical properties that occur when forming a hollow structure, the cost of the product was increased.

Accordingly, efforts have been made to produce synthetic wood foams by using conventional methods for foaming thermoplastic resins.

As a specific example, a method of foaming synthetic wood by adding a chemical foaming agent, which is a typical foaming method, has been attempted, but it is difficult to mix the foaming agent evenly, and in order to decompose the foaming agent to generate gas, a certain temperature level must be maintained. In the case of 50% or more high-filling synthetic wood, it is difficult to meet these conditions, there is a problem that the physical properties of the final product after foaming is seriously degraded because residue remains after decomposition.

On the other hand, when using a physical blowing agent such as carbon dioxide, nitrogen or hydrofluorocarbons, it is known that there is no residue at all to obtain a better foam (see US Patent No. 6225365), the pore density is large, the pore size Ultrafine foaming methods are known for producing small plastic foams (see US Pat. No. 4473665).

In addition, as a foaming method of the thermoplastic resin, a method of continuously forming the micro-foam by continuously dropping the pressure of the single-phase solution of the foam and the polymer to form a nucleus of the void, and maintaining the nucleation rate sufficiently high (US Patent No. 5866053), a supercritical gas is introduced into the fiber-forming polymer, and a method for producing microporous fibers having high cell density, uniformity, light weight and excellent touch (see Korean Patent Application Publication No. 2004-34974) is known. have.

In addition, U.S. Patent No. 3555986 discloses a gas dissolving process for forming a completely compatible state of a thermoplastic resin and an inert gas by a first extruder, a cooling process by a second extruder, a nucleation process due to a sudden pressure drop, and a foaming control process. A method for producing a thermoplastic resin foam is disclosed. In Japanese Patent Application Laid-Open No. 2004-322341, a melt mixed with an inert fluid is brought to a temperature higher than the solidification temperature, extruded so as not to foam or become low-foamed at the moment of extrusion, and foamed by applying an external force to the extruded molding material. Disclosed is a method for extrusion molding microfoams.

Based on the above research results, a manufacturing process for foaming synthetic wood by using a physical blowing agent has been developed. Representatively, US Pat. No. 6,936,200 continuously introduces the physical blowing agent into the extruder in a supercritical state. Disclosed is a process in which a material called synthetic wood is grafted to a general microfoam manufacturing method of foaming.

On the other hand, US Patent Application Publication No. 2005-0067729 is a method for producing a low-density foam wood-plastic composite containing wood flour and high density polyethylene (HDPE), a process of mixing the fine wood flour with a polymer, sufficient pressure A step of inserting a blowing agent into the plasticized mixture under a step, and a step of reducing the pressure before discharging the mixture from the extruder, and mixing the ground wood powder and the polymer resin to promote foaming, thereby increasing the porosity and decreasing the density of the foamed wood-plastic A method for producing a composite is disclosed.

However, when producing synthetic wood foams by the method disclosed in the above patents, the mechanical strength is significantly lower than that of the unfoamed body due to the decrease in density. In particular, synthetic wood is a composite material filled with wood powder and natural materials of several hundreds to hundreds of microns in size, and since these fillers induce bubble nucleation, the level of physical property reduction is more severe.

More specifically, the residual moisture and volatile gases are discharged from the wood powder during the extrusion process, and this gas serves as an additional blowing agent to promote the foaming process. On the other hand, since the viscosity of the extrudate is increased by the addition of wood powder, the process can proceed at a high melt pressure, making it difficult to disperse the blowing agent and further increase the porosity. Thus, the problem of lowering mechanical properties in the production of synthetic wood foam becomes more serious.

Since the synthetic wood foam is mainly produced by extrusion method, an enlarged cross-sectional view of an extrusion die including a pressure drop section and a cooling section that have been used in a conventional extrusion process is schematically illustrated.

Referring to FIG. 1, the extrusion die includes a pressure drop section 10 in which a nozzle 40 is formed inside and an external heating means 50, and a cooling section in which an internal cooling means 60 is mounted ( 30 and a temperature change section 20 in which a temperature change occurs between the pressure drop section 10 and the cooling section 30.

Accordingly, the extrudate plasticized by an extruder (not shown) is foamed while passing through the pressure drop section 10 along the nozzle 40 inside the extrusion die, and extruded through the temperature change section 20. It passes through the cooling section 30 to cool the profile of the shape and solidify the shape.

However, in the extrusion die, since a moderate temperature change rate is formed in the temperature change section due to the heat conduction from the high pressure drop section 10 to the low temperature cooling section 30, over-foaming proceeds, and the size of the voids is increased. As it grows, the density of the foam decreases and the mechanical properties significantly decrease. In addition, since no uniform foaming occurs, serious problems such as uneven physical properties occur.

In this regard, Korean Patent Application Publication No. 2006-037386 is a technique for improving the mechanical properties of synthetic wood by including a polymer resin having a high affinity with wood components, a predetermined proportion of wood and a predetermined ratio of crosslinked melamine A method of making a composite material is disclosed including a crosslinked plastic that is a mixture of resin ethers or thermoplastics and crosslinked melamine resin ethers.

However, the above technique must include a radical initiator or the like to induce crosslinking of the polymer resin, crosslinking polymerization is performed at a high temperature, and two extruders must be used, resulting in an increase in manufacturing cost, and crosslinking of the polymer resin. Due to the bonding, it is difficult to form a foam having a uniform porosity and thus has many problems such as greatly deteriorating the physical properties of the foam.

On the other hand, Japanese Patent Application Laid-Open No. 2005-238554 is a technique related to the extrusion foam molding method of a composite material containing wood powder, which solves the problem of deteriorating the physical properties when the gas generated by the action of the blowing agent is trapped inside the molded article. For this purpose, there is disclosed a technique for discharging excess foam gas inside the foam by pressurizing the synthetic wood micro-foam foam extruded from the die by using a compression roller outside the cooling section and an internal roller penetrating from the molding die.

However, in the process of pressurizing the foam with the compression roller, there is a difference in physical properties between the contacting portion of the roller and the other portion, and the temperature change between the forming die and the cooling portion is gentle, so that the mechanical properties of the foam are deteriorated. I still have

In addition, Japanese Patent Application Laid-Open No. 2004-314371 discloses that an internal core layer is foamed with a chemical foaming agent by extruding the wood resin composition by using an extrusion die having a center body penetrating therein, thereby causing a high specific gravity with a low specific inner core layer. Disclosed is a method for producing a microfoam of an extruded molded article having an outline.

However, the technique uses expensive chemical blowing agents, which increases the manufacturing cost and, when using chemical blowing agents, must maintain a constant temperature level as described above, which makes it difficult to meet these conditions and residues after decomposition. Because of this, there is a problem that the physical properties of the final product after foaming is seriously lowered.

Therefore, there is a high need for a technology for producing a synthetic wood micro-foam excellent mechanical properties.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application use an extruder to mix a plasticized synthetic wood mixture and a blowing agent, and pass the plasticized mixture through a pressure drop section of the extrusion die to form voids. In the process of cooling the molten mixture in which the fine pores are formed while passing through the cooling section of the extrusion die, when the end point temperature of the pressure drop section and the starting point temperature of the cooling section have a predetermined temperature difference, the skin layer thickness of the foam is increased. Increasing and suppressing the growth of excessive foam cells, the reduction of the mechanical properties of the synthetic wood micro-foam was found to be minimal and excellent surface properties, and came to complete the present invention.

Therefore, the method for producing a synthetic wood micro-foam according to the present invention comprises the steps of: a) mixing the plasticized synthetic wood mixture and the blowing agent using an extruder; b) passing the plasticized mixture through a pressure drop zone of the extrusion die to form voids; And c) passing the molten mixture having the fine pores through the cooling section of the extrusion die and cooling the composition, wherein the end point temperature of the pressure drop section and the starting point temperature of the cooling section have a temperature difference of 30 to 200 ° C. It consists of doing.

Therefore, the plasticized synthetic wood mixture and the foam is rapidly solidified by the compression sizing effect caused by the rapid temperature difference during the passage of the cooling section of the extrusion die, thereby preventing the phenomenon of excessively large micropore size due to the excessive generation of bubbles. It is possible to produce foams having pores of fine size. In particular, since the density of the skin layer is more dense than the density of the core layer due to the rapid solidification in the cooling section, even when there are relatively large voids or unsolidified portions of the core layer to block over-foaming. No deformation of the extrudate occurs and foams with good surface properties and very good mechanical properties can be produced.

The end point temperature of the pressure drop section and the start point temperature of the cooling section according to the present invention, as defined above, are configured to exhibit a temperature difference of 30 to 200 ° C. Due to such a sharp temperature difference, the skin part of the extrudate is stable in a dense state. By solidifying to, even when an unsolidified portion is present in a part of the center portion of the extrudate, deformation of the extrudate does not occur, and mechanical strength is very excellent.

If the temperature difference is less than 30 ° C, sufficient solidification is not achieved, and thus the micropores continue to grow, so that a skin layer having a sufficient thickness is difficult to be formed in the foam, and the density is lowered, so that the desired mechanical properties cannot be obtained. On the contrary, when the temperature difference exceeds 200 ° C., the manufacturing process may be difficult to proceed due to the decrease in fluidity due to the rapid solidification of the extrudate, and expensive equipment may be required for setting such conditions, which is not preferable.

A section showing a sudden temperature difference between the pressure drop section and the cooling section is also referred to as a "temperature change section" below.

In one preferred example, including a temperature change section between the pressure drop section and the cooling section, the temperature change rate according to the progress direction in the temperature change section may be 2 to 40 ℃ / mm in the calculation of Equation 1 below. have.

T _L = (T _H -T _C ) / L (1)

In the above formula, T _L is the temperature change rate, T _H is the end point temperature of the pressure drop section, T _C is the start point temperature of the cooling section, and L is the length of the temperature change section.

If the temperature change rate is less than 2 ℃ / mm it is difficult to form a skin layer of sufficient thickness in the foam and it is difficult to expect the improvement of the desired mechanical properties, on the contrary, if the temperature change rate exceeds 40 ℃ / mm It may be undesirable in terms of processability due to reduced fluidity during extrusion and increased frictional force. However, in general, as the temperature change rate in the temperature change section is higher, the density of the extrudate applied to the foamed extrudate can be solidified in a denser state, and thus, the foamed extrudate having excellent mechanical properties can be manufactured.

The length of the temperature change section may be preferably 1 to 150 mm. The shorter the temperature change section is, the more preferable it is. If it exceeds 150 mm, even if the temperature difference between the pressure drop section and the cooling section is set large, the rate of change of temperature is small, and the problems described above may occur.

As a result, the temperature change section defined as above serves to prevent heat exchange between the temperature change section and the cooling section so that a sharp temperature difference can be maintained between the pressure drop section and the cooling section.

The pressure drop section and the cooling section may be integrally included in one extrusion die or separately included in each block-type extrusion die separated by sections, and when included integrally, it may be effective in controlling micropores and forming a skin layer of the microfoam. Can be. In the latter case, it is preferable to fasten so that the pressure at the end point of the pressure drop section is maintained in the cooling section.

The extrusion die may preferably comprise heating means for preventing temperature drop near the end point of the pressure drop section. The heating means may be formed inside the extrusion die, or may be formed together inside and outside the extrusion die. It does not specifically limit as said heating means, For example, a normal electric heating element etc. can be used.

In addition, the extrusion die may preferably include cooling means for preventing the temperature rise near the time point of the cooling section. Like the heating means, the cooling means may be formed only inside the extrusion die, or may be formed together inside and outside the extrusion die. The cooling means is not particularly limited, and for example, a cooling device such as a pipeline through which a refrigerant flows can be used.

The heating means and the cooling means can be added and used in an appropriate number as necessary.

The end point temperature of the pressure drop section may be appropriately adjusted according to the type of extrusion raw material to be extruded, preferably, may be 150 to 250 ℃. If the end point temperature of the pressure drop section is less than 150 ℃ it is difficult to form a sufficient micro-pore, if it exceeds 250 ℃ it is not preferable because there is a risk of deterioration and over-exposure of the thermoplastic resin.

The time point of the cooling section may be appropriately adjusted according to the type of synthetic wood mixture to be extruded, it is preferable to maintain at a level slightly higher than the melting point or softening point of the thermoplastic resin constituting the synthetic wood mixture, more preferably , 40 to 150 ° C. When the temperature of the cooling section is less than 40 ℃, due to the rapid solidification of the synthetic wood mixture is not smoothly flowing out of the manufacturing process is difficult to proceed, on the contrary, if it exceeds 150 ℃ fine formed in the pressure drop section This is because the voids continue to grow even in the cooling section, making it difficult to form a skin layer having a sufficient thickness in the foam.

The temperature change in the pressure drop section and the cooling section is preferably 5 ° C, more preferably maintained within ± 2 ° C. This is because when the temperature change exceeds ± 5 ° C., the outflow rate of the synthetic wood mixture becomes non-uniform, so that an extrudate having uniform physical properties cannot be obtained, and thus the mechanical properties of the synthetic wood mixture are lowered.

The feed rate of the molten mixture in which the fine pores are formed is not particularly limited, and may be preferably 0.5 to 20 m / min in terms of production efficiency.

The synthetic wood mixture comprises a wood fiber component and an extrudable polymer resin such as a thermoplastic polymer resin. In the synthetic wood microfoam produced through extrusion, the matrix component may be a wood fiber component or a polymer resin. In the former case, a structure in which a polymer resin is impregnated with a wood fiber component is mentioned, for example, and in the latter case, a structure in which a wood fiber component is added as a filler to a polymer resin is mentioned. Preferably, the synthetic wood micro-foam has a structure in which the wood fiber component is added as a filler to the polymer resin as the matrix component.

The wood fiber component is not particularly limited as long as it is a fibrous material having a cellulose molecular structure. For example, wood powder or other natural fibers (eg, Hemp, Flex, Jute, Kenaf, Cellulose, etc.). When the polymer resin is a matrix component in the synthetic wood micro-foam, the size of the wood powder is preferably 10 to 200 mesh, more preferably 30 to 150 mesh. Although it may vary depending on the application, when the size of the wood flour is too large, the content of the polymer resin decreases, so that the bonding strength between the wood flour decreases and the surface of the composite material is very rough. On the contrary, the size of the wood flour If too small, there is a disadvantage that the dispersion is not easy, it may not be preferable. Such wood flour includes coniferous wood flour and hardwood wood flour, and the like, and is preferably coniferous wood flour such as pine or maple.

The thermoplastic polymer resin is not particularly limited as long as it is an extrudable thermoplastic resin such as polyethylene, acrylic resin, vinyl chloride resin, vinyl acetate resin, vinylacetyl resin, polyamide resin, celluloid resin, and preferably acrylonitrile-butadiene-styrene. One or two selected from the group consisting of (ABS) copolymers, polycarbonate (PC), polyvinylchloride (PVC), polystyrene (PS), polymethylmethacrylate (PMMA), polyester, polypropylene, and nylon It may be a polymer or more.

The synthetic wood mixture may further include various additives such as a crosslinking agent, a lubricant, a suitable agent, and an accelerator.

The blowing agent is not particularly limited, and for example, an inert gas can be used, and preferably carbon dioxide, nitrogen, or a mixed gas thereof can be used. In addition, the blowing agent is preferably mixed at 3 to 0.1% by weight relative to 97 to 99.9% by weight of the thermoplastic resin. When the content of the blowing agent is less than 0.1% by weight, it is not preferable because sufficient foaming does not occur in the pressure drop section, so that the micropores cannot be formed, and when the content of the blowing agent exceeds 3% by weight, the blowing agent is no longer melted in the thermoplastic resin.

It is particularly preferable that the blowing agent is mixed in a supercritical state, and the foaming agent in the supercritical state increases the compatibility with the polymer resin, thereby making it possible to form uniform pores in the resin, reducing the size of the pores, and increasing the pore density. Because it can increase. In this case, a foaming agent which is already in a supercritical state may be used, or the foaming agent may be converted into a supercritical state after the blowing agent is introduced into the extruder.

For example, for carbon dioxide, the critical pressure is 75.3 kgf / cm ² , the critical temperature is 31.35 ° C., and for nitrogen, the critical pressure is 34.6 kgf / cm ² and the critical temperature is -147 ° C. In general, the conditions for converting the gas into the supercritical state in the extruder are preferably at a pressure of 70 to 400 kgf / cm ² and a temperature of 100 to 400 ° C. In addition, the conditions for converting nitrogen into the supercritical state are not particularly limited and may be adjusted according to the kind of blowing agent used, for example.

The present invention also includes a skin layer having a porosity of less than 5% and a core layer having a porosity of 5% or more, and the thickness of the skin layer is 5 to 50% of the total thickness, which is defined by Equation 2 below. do. In addition, the skin layer preferably has a thickness of 50 to 500 ㎛.

Porosity (%) = (ρN-ρF) / ρN × 100 (2)

Where ρN is the density of foam-free and ρF is the density of foam.

When the porosity of the skin layer is less than 5% or the thickness of the skin layer is less than 50 μm, mechanical properties such as elongation may be lowered. In contrast, the porosity of the skin layer exceeds 50% or the thickness of the skin layer. When it exceeds 500 micrometers, since the effect of the desired specific gravity reduction effect is hard to be obtained, it is unpreferable.

Therefore, the composite wood micro-foaming foam according to the present invention is composed of a thick and dense skin layer and a core layer formed with micropores compared to the conventional synthetic wood foam, the voids due to the skin layer of dense density having a porosity of less than 5% It has excellent mechanical strength by preventing the growth and at the same time having a predetermined thickness, and has excellent physical properties due to the core layer in which pores of fine size are formed.

The core layer is preferably formed with pores having an average diameter of 0.1 to 50 ㎛, the smaller the size of the pores, the better the effect of improving the physical properties of the synthetic wood micro-foam, but in actual process the average diameter of less than 0.1 ㎛ It is difficult to form micropores having an average diameter of more than 50 μm, which is not preferable because mechanical properties are greatly reduced.

It is preferable that the total porosity of the synthetic wood microfoam is 5 to 80%. If the total porosity of the synthetic wood microfoam is less than 5% on average, the physical properties of the foam may not be exhibited. The voids are not preferred because the mechanical properties of the synthetic wood microfoam may be lowered.

In one preferred embodiment, the synthetic wood micro-foam has a total porosity of 15 to 30%, the impact absorption energy by the rheological drop test measured according to the ASTM D4226 method, and according to the ASTM D638 method The elongation measured, and the tensile strength measured according to the ASTM D638 method may be 70% or more with respect to the impact absorption energy, elongation and tensile strength of the non-foaming body prepared under the same conditions, respectively, more preferably 90 to 150% Can be.

The higher the shock absorption energy, elongation and tensile strength are all better, but it is difficult to obtain a value of more than 150% compared to the non-foaming, less than 70% compared to the non-foaming is not preferable because the physical properties are difficult to be applied to the product.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

2 is an enlarged cross-sectional view schematically showing an extrusion die used in the manufacturing method according to one embodiment of the present invention.

Referring to FIG. 2, the extrusion die is internally cooled at a pressure drop section 100 having a nozzle 400 formed therein and a heating means 500 mounted at an end point in a traveling direction of the extrudate. It consists of a cooling section 300 is equipped with a means 600, and a temperature change section 200 in which a sudden temperature change occurs between the pressure drop inlet section 100 and the cooling section 300.

The plasticized extrudate is foamed by mixing the plasticized synthetic wood mixture and the blowing agent by an extruder (not shown) and passing through the pressure drop section 100 along the nozzle 400 inside the extrusion die 100. In order to cool the profile of the extruded shape and to solidify the shape, it passes through the cooling section 300 through the temperature change section 200 having a sharp temperature difference of 30 to 200 ° C. At this time, the temperature change rate is formed at 2 to 40 ℃ / mm in the temperature change section.

Thus, for various technical reasons as described above, it is possible to prevent over-foaming, to produce a foam having a fine pore size, and to form a skin layer having a dense density and a sufficient thickness, thereby greatly improving mechanical properties. Can be.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

As shown in FIG. 2, the pressure drop section, the temperature change section, and the cooling section, which are capable of temperature control, are integrally formed, and heating means is provided at an end point inside the pressure drop section, and at a time point inside the cooling section. An extrusion die and an adapter equipped with cooling means were mounted on a twin screw extruder to prepare an extrusion apparatus for producing a fine foam. At this time, the length of the pressure drop section was 125 mm, the length of the cooling section was 40 mm, and the length of the temperature change section between the hot die and the cold die was 27 mm.

After 65% by weight and 33% by weight of the polypropylene resin mixture was completely plasticized, 2 parts by weight of nitrogen was injected into the twin screw extruder using a high pressure pump, and the single phase mixture was foamed and molded to have a thickness of 3.5 mm. , 100 mm wide synthetic wood microfoam sheet was prepared.

The conditions of the extruder were such that the sequential temperature of the barrels were 190 ° C-180 ° C-175 ° C and the temperature of the adapter was maintained at 130 ° C. In addition, the start point and the end point of the pressure drop section were respectively 165 ° C., the start point temperature of the temperature change section was 150 ° C., the end point was 80 ° C., the start point temperature of the cooling section was 80 ° C., and the end point was 30 ° C. Each was set.

Comparative Example 1

Except for using a conventional extrusion die provided with a heating means on the outside of the pressure drop section, and a cooling means inside the cooling section, the synthetic wood micro-foam sheet in the same manner as in Example 1 Prepared.

However, although the time point temperature of the cooling section was set to 150 ° C, the actual temperature measurement result showed that the temperature could not be maintained at 150 ° C and about 130 ° C.

Experimental Example 1

The composite wood microfoam sheet prepared in Example 1 and Comparative Example 1 was prepared according to the ASTM D638 method and the tensile strength was measured.

As a result, the tensile strength of the composite wood micro-foam sheet of Comparative Example 1 is 76 kgf / cm ² , whereas the synthetic wood micro-foam sheet of Example 1 shows a tensile strength of 100 kgf / cm ² , the mechanical properties are very It was confirmed that greatly improved.

Experimental Example 2

In order to measure the porosity, the pore size, and the thickness of the skin layer of the synthetic wood micro-foamed sheet prepared in Example 1 and Comparative Example 1, the fracture surface was formed on the sheet, and an electron microscope (SEM) photograph was taken. SEM photographs of the fracture surfaces of the synthetic wood microfoam sheets according to Example 1 and Comparative Example 1 are shown in FIGS. 3 and 4, respectively.

As shown in these photos, it can be seen that the fracture surface of the synthetic wood micro-foam sheet according to Example 1 shows a smooth and uniform shape compared to the fracture surface of the synthetic wood micro-foam sheet according to Comparative Example 1.

While the above has been described above with reference to embodiments according to the present invention, those of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention. will be.

As described above, the method for producing a synthetic wood micro-foam according to the present invention is passed through the cooling section of the extrusion die and the plasticized synthetic wood mixture and the melt mixture of blowing agent, the end temperature of the pressure drop section and the cooling section By configuring the time point of the temperature to exhibit a predetermined temperature difference, it is possible to produce a synthetic wood micro-foamed body having excellent mechanical strength and improved surface properties.

Claims (14)

a) mixing the plasticized synthetic wood mixture and the blowing agent using an extruder; b) passing the plasticized mixture through a pressure drop zone of the extrusion die to form voids; And c) passing the molten mixture having the fine pores through the cooling section of the extrusion die and cooling the composition, wherein the end point temperature of the pressure drop section and the starting point temperature of the cooling section have a temperature difference of 30 to 200 ° C. Method for producing a synthetic wood micro-foam, characterized in that. The method of claim 1, wherein the extrusion die comprises a heating means for preventing the temperature decrease near the end point of the pressure drop section. The method of claim 1, wherein the extrusion die comprises a cooling means for preventing the temperature rise near the time point of the cooling section. The method of claim 1, wherein the end point temperature of the pressure drop section is 150 to 250 ℃. The method of claim 1, wherein the cooling zone time point temperature is 40 to 150 ℃. The method of claim 1, wherein the temperature change in the pressure drop section and the cooling section is maintained within ± 5 ℃. The method of claim 1, wherein the feed rate of the composite wood mixture is 0.5 to 20 m / min. The method according to claim 1, wherein the temperature change interval is included between the pressure drop section and the cooling section, and the temperature change rate according to the traveling direction in the temperature change section represented by the following Equation 1 is 2 to 40 ° C / mm. Method for producing a synthetic wood micro-foam characterized by: T _L = (T _h -T _c ) / L (1) In the above formula, T _L is the temperature change rate, T _h is the end point temperature of the pressure drop section, T _c is the start point temperature of the cooling section, L is the length of the temperature change section. 10. The method of claim 8, wherein the temperature change section has a length of 1 to 150 mm. A synthetic wood microfoam comprising a skin layer having a porosity of less than 5% and a core layer having a porosity of 5% or more, wherein the thickness of the skin layer is 5 to 50% of the total thickness as defined by Equation 2 below: Porosity (%) = (ρN-ρF) / ρN × 100 (2) Where ρN is the density of foamless foam and ρF is the density of foam. 11. The method of claim 10 wherein the skin layer is a synthetic wood micro-foam, characterized in that having an average thickness of 50 to 500 ㎛. 11. The method of claim 10 wherein the core layer is a synthetic wood micro-foam, characterized in that the voids are formed having an average diameter of 0.1 to 50 ㎛. 11. The synthetic wood microfoam of claim 10, wherein the total porosity of the microfoam is 5 to 80%. The method of claim 10, wherein the micro-foam has a total porosity of 15 to 30%, the impact absorption energy by the rheological drop test (Rheometric Drop Test) measured according to the ASTM D4226 method, measured according to the ASTM D638 method Elongation, and the tensile strength measured according to the ASTM D638 method, the composite wood micro-foamed body, characterized in that more than 70% with respect to the shock absorption energy, elongation and tensile strength of the non-foaming body prepared under the same conditions.

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