Non-halogen-based flame retardant composition for the skin layer of synthetic wood and synthetic wood having a flame-retardant skin layer manufactured therefrom

Abstract

A non-halogen flame-retardant composition for a synthetic wood skin layer and a synthetic wood having a flame-retardant skin layer prepared therefrom are disclosed. A non-halogen flame-retardant composition for a synthetic wood skin layer according to one embodiment of the present invention is intended to be introduced into an auxiliary extruder and bonded in a molten state to the surface of an inner layer of synthetic wood discharged from a main extruder by the auxiliary extruder to form a skin layer of said synthetic wood, and comprises 45 to 76 weight% of either one selected from polyethylene and high-density polyethylene (HDPE) based on the total weight; and 24 to 55 weight% of a non-halogen flame retardant based on the total weight.

Description

Technology Field

[0001] The present invention relates to a non-halogen flame-retardant composition for a synthetic wood surface layer and synthetic wood produced therefrom. More specifically, the invention relates to a non-halogen flame-retardant composition for a synthetic wood surface layer having excellent flame retardancy that does not generate toxic gases, and synthetic wood having a flame-retardant surface layer produced therefrom. Background Technology

[0002] Recently, consumer preference for natural wood has been increasing significantly, particularly in the case of construction materials where demand is high; consumer preference for natural wood is rising sharply across various fields, including furniture and construction.

[0003] These natural woods are widely used for interior and exterior decoration of buildings because they create a soft and cozy atmosphere due to their excellent appearance and texture, as well as the unique properties of the wood. However, in Korea, where forest resources are absolutely scarce and we rely on imports for more than 70% of the wood used, the supply of natural wood is severely lacking, and problems such as forest destruction caused by logging and environmental destruction due to the release of harmful substances in the event of a fire are occurring.

[0004] In particular, natural wood has the problem of being difficult to use as an exterior material for buildings due to the deterioration of its inherent properties such as water resistance, heat resistance, impact strength, bending strength, dimensional stability, flame retardancy, weather resistance, and antibacterial properties. Additionally, the antibacterial properties of the wood material are reduced, shortening its lifespan, and copper, arsenic, and chromium-based preservatives (also known as CCA preservatives) are being mixed in and used to enhance these antibacterial properties.

[0005] Therefore, in the event of a fire, toxic substances are released from the combustion of these copper, arsenic, and chromium-based preservatives, which are harmful to the human body, and the lack of flame-retardant properties leads to the problem of fire spreading.

[0006] To address these issues, there is a growing demand for the development of materials that can replace natural wood. As such an alternative, synthetic wood, which possesses a texture and appearance similar to natural wood, is widely used as an interior and exterior building material.

[0007] Wood plastic composites (WPC) refer to materials formed by mixing wood fibers (wood powder) with thermoplastic polymers (polyethylene, polypropylene, polyvinyl chloride, etc.) and then finally extruding or injection molding the mixture in a state where individual wood fibers are completely encapsulated by the molten polymer.

[0008] Composite wood is a material that compensates for the shortcomings of wood and plastic. Specifically, it has excellent water resistance, moisture resistance, and durability, and exhibits good resistance to expansion, shrinkage, and warping caused by moisture. Furthermore, it is eco-friendly as it emits almost no formaldehyde or volatile organic compounds (VOCs), and it is widely used as an exterior material because it has excellent weather resistance and insect resistance without the need for separate preservative treatment. The produced items are used for flooring, railings, automotive interiors, and exterior finishing materials.

[0009] While these synthetic woods possess various advantages such as color, durability, and eco-friendliness compared to architectural exterior materials including preservative-treated wood, they use hydrophilic wood powder and resins susceptible to sunlight as primary raw materials. Consequently, they may experience issues such as discoloration or warping due to environmental influences like moisture, ultraviolet rays, and temperature changes in outdoor environments, and their flame retardancy is reduced due to the presence of wood powder.

[0010] In particular, there are problems such as the spread of fire due to reduced flame retardancy in the event of a fire, and the release of chlorine gas to the outside, which is harmful to the human body.

[0011] Therefore, if flame retardancy can be added to synthetic wood, its applications could be further expanded. For example, if synthetic wood used for flooring, railings, and exterior walls possesses flame-retardant properties in the event of a fire, it could be used as an evacuation route, fire lines could be installed along the flooring, and its utility could be doubled because flame-retardant synthetic wood used for exterior walls can protect the building from fire.

[0012] Accordingly, there are various conventional technologies to improve the flame retardancy of synthetic wood. For example, Korean Registered Patent Publication No. 10-1314446 includes 1 to 50 parts by weight of expandable graphite per 100 parts by weight of wood powder, thereby improving flame retardancy by allowing the expandable graphite to form char on the surface layer upon ignition. However, when expandable graphite is used, the appearance of the synthetic wood turns black, which causes aesthetic problems and makes actual application difficult.

[0013] Furthermore, most conventional technologies attempt to impart flame retardancy to the entire synthetic wood, which results in poor economic feasibility or inefficiency, making practical application difficult; additionally, some conventional technologies suffer from the problem of generating toxic gases even when flame retardancy is added. Prior art literature

[0014] Korean Patent Publication No. 10-1314446 (October 7, 2013) The problem to be solved

[0015] Therefore, the technical problem to be solved by the present invention is to provide a non-halogenated flame-retardant composition for a synthetic wood skin layer that has excellent flame retardancy without generating toxic gases, is efficient and economical, and is suitable for practical application, and to provide synthetic wood having a flame-retardant skin layer prepared therefrom. means of solving the problem

[0016] According to one aspect of the present invention, a non-halogen flame-retardant composition for a synthetic wood skin layer may be provided, characterized by comprising 45 to 76 weight% of one selected from polyethylene and high-density polyethylene (HDPE) based on the total weight; and 24 to 55 weight% of a non-halogen flame retardant based on the total weight, for forming a skin layer of the synthetic wood by being introduced into an auxiliary extruder and bonded in a molten state to the surface of an inner layer of the synthetic wood discharged from a main extruder by the auxiliary extruder.

[0017] The above-mentioned non-halogen flame retardant may include a phosphorus-nitrogen flame retardant.

[0018] The above phosphorus-nitrogen flame retardant may comprise 40 to 80 weight% of one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant; and 20 to 60 weight% of one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant.

[0019] The above-mentioned non-halogen flame retardant further comprises 2 to 7 weight percent of a flame retardant enhancer relative to the total weight of the above-mentioned phosphorus-nitrogen flame retardant, and the flame retardant enhancer may be one of zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO2), silicon dioxide (SiO2), manganese oxide (MnO), aluminum oxide (Al2O3), iron oxide (Fe2O3), organically modified montmorillonite, or a mixture thereof.

[0020] The flame retardant enhancer is zinc oxide (ZnO), and either one selected from the polyethylene and the high-density polyethylene (HDPE) is 38 to 70 weight percent of the total weight, and the non-halogen flame retardant composition for the synthetic wood skin layer may further include an impact reinforcing agent 1 to 20 weight percent of the total weight; a lubricating / dispersing agent 0.1 to 3 weight percent of the total weight; an antioxidant 0.1 to 0.5 weight percent of the total weight; and a UV stabilizer 0.1 to 0.5 weight percent of the total weight.

[0021] The above impact modifier may include one or more from the group consisting of polyolefin elastomer (POE), ethylene propylene rubber (EPR), ethylene propylene diene terpolymer, and styrene ethylene butadiene styrene (SEBS).

[0022] The above non-halogen flame-retardant composition for the surface layer of synthetic wood may further comprise 0.1 to 5 weight% of a coupling agent based on the total weight; and 0.1 to 5 weight% of a color powder based on the total weight.

[0023] According to another aspect of the present invention, a synthetic wood having a flame-retardant skin layer may be provided, comprising an inner layer discharged from a main extruder containing a composition for an inner layer of synthetic wood, and a skin layer formed by introducing a non-halogen flame-retardant composition for a skin layer of synthetic wood into an auxiliary extruder and bonding it to the surface of the inner layer in a molten state by the auxiliary extruder, wherein the non-halogen flame-retardant composition for a skin layer of synthetic wood comprises 45 to 76 weight% of either polyethylene or high-density polyethylene (HDPE) based on the total weight; and 24 to 55 weight% of a non-halogen flame retardant based on the total weight.

[0024] The above-mentioned non-halogen flame retardant may include a phosphorus-nitrogen flame retardant.

[0025] The above phosphorus-nitrogen flame retardant may comprise 40 to 80 weight% of one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant; and 20 to 60 weight% of one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant.

[0026] The above-mentioned non-halogen flame retardant further comprises 2 to 7 weight percent of a flame retardant enhancer relative to the total weight of the above-mentioned phosphorus-nitrogen flame retardant, and the flame retardant enhancer may be one of zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO2), silicon dioxide (SiO2), manganese oxide (MnO), aluminum oxide (Al2O3), iron oxide (Fe2O3), organically modified montmorillonite, or a mixture thereof.

[0027] The flame retardant enhancer is zinc oxide (ZnO), and either one selected from the polyethylene and the high-density polyethylene (HDPE) is 38 to 70 weight percent of the total weight, and the non-halogen flame retardant composition for the synthetic wood skin layer may further include an impact reinforcing agent 1 to 20 weight percent of the total weight; a lubricating / dispersing agent 0.1 to 3 weight percent of the total weight; an antioxidant 0.1 to 0.5 weight percent of the total weight; and a UV stabilizer 0.1 to 0.5 weight percent of the total weight.

[0028] The above impact modifier may include one or more from the group consisting of polyolefin elastomer (POE), ethylene propylene rubber (EPR), ethylene propylene diene terpolymer, and styrene ethylene butadiene styrene (SEBS).

[0029] The above non-halogen flame-retardant composition for the surface layer of synthetic wood may further comprise 0.1 to 5 weight% of a coupling agent based on the total weight; and 0.1 to 5 weight% of a color powder based on the total weight.

[0030] The composition for the inner layer of the synthetic wood may comprise 20 to 50 weight% of either polyethylene or high-density polyethylene (HDPE) based on the total weight; 35 to 65 weight% of wood powder based on the total weight; 1 to 15 weight% of talc based on the total weight; 0.5 to 5 weight% of a lubricant based on the total weight; 0.5 to 5 weight% of a polyethylene coupling agent based on the total weight; and 0.1 to 1 weight% of an antioxidant based on the total weight. Effects of the invention

[0031] According to the present invention, a non-halogenated flame-retardant composition for a synthetic wood surface layer is provided, which has excellent flame retardancy without generating toxic gases, is efficient and economical, and is suitable for practical application.

[0032] In addition, according to the present invention, a synthetic wood having a flame-retardant skin layer is provided, which has excellent flame retardancy that does not generate toxic gases, is efficient and economical, is suitable for practical application, and is easy to produce. Specific details for implementing the invention

[0033] The present invention is not limited to the embodiments disclosed below but may be implemented in various different forms, and these embodiments are provided merely to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention.

[0034] In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, and actions in addition to the mentioned components, steps, and actions.

[0035] According to an embodiment of the present invention, the synthetic wood having a flame-retardant skin layer comprises an inner layer and a skin layer. Although it is possible to make both the inner layer and the skin layer flame-retardant, as previously mentioned, this is not economical and therefore difficult to apply in practice; thus, considering economic feasibility and efficiency, the skin layer in the embodiments of the present invention is made flame-retardant.

[0036] In addition, the composition for the inner layer of synthetic wood for forming the inner layer and the non-halogen flame-retardant composition for the outer layer of synthetic wood for forming the flame-retardant outer layer can each be fed into a twin-screw extruder to be manufactured into pellets and used in pellet form, but the scope of the present invention is not limited thereto, and the forms may be provided in various ways as needed.

[0037] Meanwhile, the synthetic wood having a flame-retardant skin layer according to the present invention can be prepared by forming a skin layer by bonding a non-halogen flame-retardant composition for the synthetic wood skin layer to the surface of an inner layer, which is discharged from a main extruder containing a composition for the synthetic wood inner layer, in a molten state by means of an auxiliary extruder containing a composition for the synthetic wood inner layer. That is, the synthetic wood having a flame-retardant skin layer according to the present invention can be manufactured by simultaneously performing co-extrusion molding in a co-extrusion system. By doing so, synthetic wood composed of an inner layer and a flame-retardant skin layer can be easily produced.

[0038] Furthermore, the synthetic wood according to the present invention is manufactured such that the surface layer covers one or more sides of the inner layer. That is, it can be manufactured to cover all sides of the inner layer or to cover only one side.

[0039] In addition, the inner layer may be manufactured to have a thickness of 10 mm to 50 mm depending on the purpose or use of the synthetic wood, and the outer layer may have a thickness of 0.1 to 2 mm, but the scope of the present invention is not limited by this.

[0040] Furthermore, although the present embodiment describes the use of a twin-screw extruder for pellet production, the scope of the present invention is not limited thereto, and a single-screw extruder, a dough extruder, etc. may also be used.

[0041] Meanwhile, the method for manufacturing synthetic wood by double extrusion molding using a co-extrusion system follows known equipment and methods, so a detailed description is omitted.

[0042] In this way, the synthetic wood having a flame-retardant skin layer according to the present invention is economical and efficient, making it suitable for actual application and thus significantly increasing the utility of the synthetic wood. Furthermore, since it is manufactured by double extrusion molding, the synthetic wood having a flame-retardant skin layer according to the present invention is easy to produce.

[0043] Meanwhile, in order for the synthetic wood having a flame-retardant skin layer according to the present invention to have excellent flame retardancy, the composition for forming the skin layer must have excellent flame retardancy that does not generate toxic gases, and this is achieved by the non-halogen flame-retardant composition for the skin layer of synthetic wood according to the present invention.

[0044] Hereinafter, the non-halogen flame-retardant composition for the surface layer of synthetic wood and the composition for the inner layer of synthetic wood according to the present invention will be examined in detail as follows.

[0045] A non-halogen flame-retardant composition for a synthetic wood surface layer comprises 45 to 76 weight% of either polyethylene or high-density polyethylene (HDPE) based on the total weight, 24 to 55 weight% of a non-halogen flame retardant based on the total weight, 1 to 20 weight% of an impact modifier based on the total weight, 0.1 to 3 weight% of a lubricant / dispersant based on the total weight, 0.1 to 0.5 weight% of an antioxidant based on the total weight, and 0.1 to 0.5 weight% of a UV stabilizer based on the total weight. Here, the term "based on the total weight" within the composition is used to mean "based on the total weight of the composition."

[0046] In addition, the non-halogen flame-retardant composition for the surface layer of synthetic wood may further include 0.1 to 5 weight% of a coupling agent and 0.1 to 5 weight% of a color powder based on the total weight.

[0047] The olefin resin of the non-halogen flame-retardant composition for the surface layer of synthetic wood may be of the same type as the olefin resin of the inner layer, or a different olefin resin may be applied depending on the function required for the surface layer. The non-halogen flame-retardant composition for the surface layer of synthetic wood according to the present invention may contain 45 to 76 weight% of either polyethylene or high-density polyethylene (HDPE) selected from the total weight, and preferably 38 to 70 weight%.

[0048] In the present invention, polyethylene and high-density polyethylene (HDPE) may include those having a melt index (230℃ / 2.16kg) of 0.1 to 50g / 10min, but the scope of the present invention is not limited thereto.

[0049] And a non-halogen flame retardant is used to impart flame retardancy to the skin layer. The non-halogen flame retardant according to the present invention includes a phosphorus-nitrogen-based flame retardant. The non-halogen flame retardant composition for the skin layer of synthetic wood may contain 24 to 55 weight percent of the non-halogen flame retardant based on the total weight.

[0050] If the content of the non-halogen flame retardant is less than 24 weight%, the flame retardancy is insufficient, and if the content of the non-halogen flame retardant is more than 55%, processing is difficult and physical properties are degraded.

[0051] Meanwhile, in this embodiment, the phosphorus-nitrogen flame retardant of the non-halogen flame retardant comprises 40 to 80 weight% of one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant, and 20 to 60 weight% of one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant.

[0052] In this embodiment, regarding the phosphorus-nitrogen flame retardant, melamine polyphosphate (MPP) and ammonium polyphosphate (APP) can be used as substitutes for dimelamine pyrophosphate; however, if used as such, the total amount of phosphorus-nitrogen flame retardant, including piperazine pyrophosphate, must be increased. Therefore, this is disadvantageous in terms of both cost and processability.

[0053] Therefore, as described above, it is most preferable that the phosphorus-nitrogen flame retardant comprises one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives, and one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives.

[0054] A flame retardant synergist is added to enhance the flame retardant effect. The non-halogenated flame retardant composition for the surface layer of synthetic wood according to the present invention comprises 2 to 7 weight percent of the flame retardant synergist relative to the total weight of the phosphorus-nitrogen flame retardant. If the amount is less than 2 weight percent relative to the total weight of the phosphorus-nitrogen flame retardant, there is almost no flame retardant enhancement effect, and if the amount exceeds 7 weight percent relative to the total weight of the phosphorus-nitrogen flame retardant, there is no further additional flame retardant enhancement effect even if it exceeds the amount, and rather, processability is reduced.

[0055] The flame retardant synergist may be one or a mixture of zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO2), silicon dioxide (SiO2), manganese oxide (MnO), aluminum oxide (Al2O3), iron oxide (Fe2O3), and organically modified montmorillonite; among these, zinc oxide (ZnO) is the most preferred because it exhibits excellent synergistic effects and does not significantly degrade mechanical properties and processability.

[0056] A non-halogenated flame-retardant composition for the surface layer of synthetic wood may contain 1 to 20 weight percent of an impact modifier based on the total weight. The impact modifier is intended to improve impact properties, and may include one or more from the group consisting of polyolefin elastomer (POE), ethylene propylene rubber (EPR), ethylene propylene diene terpolymer, and styrene ethylene butadiene styrene (SEBS).

[0057] One or more of salicylate-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based, benzoate-based, triazine-based, and amine-based UV stabilizers are used. UV stabilizers are used to prevent deterioration caused by ultraviolet (UV) rays and have functions such as absorbing and / or blocking UV rays. A non-halogen flame-retardant composition for the epidermal layer of synthetic wood may contain 0.1 to 0.5 weight percent of UV stabilizers relative to the total weight.

[0058] In addition, the non-halogen flame-retardant composition for the surface layer of synthetic wood may contain 0.1 to 3 weight% of a lubricant / dispersant and 0.1 to 0.5 weight% of an antioxidant based on the total weight.

[0059] Additionally, color powder may be added to the skin layer to create a wood-like texture, and the non-halogen flame-retardant composition for the synthetic wood skin layer may further include 0.1 to 5 weight percent of color powder and 0.1 to 5 weight percent of a coupling agent relative to the total weight.

[0060] Meanwhile, the composition for the inner layer of synthetic wood comprises 20 to 50 weight% of either polyethylene or high-density polyethylene (HDPE) selected from the total weight, 35 to 65 weight% of wood powder based on the total weight, 1 to 15 weight% of talc based on the total weight, 0.5 to 5 weight% of a lubricant based on the total weight, 0.5 to 5 weight% of a polyethylene coupling agent based on the total weight, and 0.1 to 1 weight% of an antioxidant based on the total weight.

[0061] An olefin resin is used in the composition for the inner layer of synthetic wood, and the olefin resin may be polypropylene (PP), polyethylene (PE), copolymers thereof, or mixtures thereof. In this embodiment, a resin selected from polyethylene (PE) and high-density polyethylene (HDPE) may be used. Polyethylene (PE) or high-density polyethylene (HDPE) enables the manufactured synthetic wood to have rigidity, a low coefficient of linear expansion, and weather resistance. The composition for the inner layer of synthetic wood may contain 20 to 50 weight percent of either polyethylene or high-density polyethylene (HDPE) selected from the total weight.

[0062] In addition, the composition for the inner layer of the synthetic wood contains 35 to 65 weight percent of wood powder, which is one of the organic fillers and may be wood flour, wood pellet, wood fiber, or wood powder, and in some cases, two or more may be mixed and used.

[0063] Talc is used as a filler, and a composition for the inner layer of synthetic wood may contain 1 to 15 weight percent of talc relative to the total weight.

[0064] In addition, the composition for the inner layer of synthetic wood may include 0.5 to 5 weight% of a lubricant based on the total weight, 0.5 to 5 weight% of a polyethylene coupling agent based on the total weight, and 0.1 to 1 weight% of an antioxidant based on the total weight.

[0065] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, and that such variations and modifications fall within the scope of the appended claims.

[0066] [Example 1]

[0067] A composition comprising 67.6 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 20 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 1 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 1.

[0068] [Example 2]

[0069] A composition comprising 62.4 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 25 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 1.2 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 2.

[0070] [Example 3]

[0071] A composition comprising 57.1 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 30 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 1.5 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 3.

[0072] [Example 4]

[0073] A composition comprising 51.9 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 25 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 1.7 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 4.

[0074] [Example 5]

[0075] A composition comprising 46.6 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 40 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 2.0 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 5.

[0076] [Example 6]

[0077] A composition comprising 41.4 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 45 wt% non-halogen flame-retardant powder mixed with piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) in a 3:2 ratio, 2.2 wt% zinc oxide, 1 wt% lubricant / dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed into the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the 170-180°C range, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over the inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. The well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting the thickness to 0.1 to 2 mm, and this was designated as Example 6.

[0078] [Comparative Example 1]

[0079] A composition consisting of 58.6 wt% high-density polyethylene (HDPE), 10 wt% polyethylene elastomer, 30 wt% talc, 1 wt% lubricant and dispersant, 0.2 wt% antioxidant, and 0.2 wt% UV stabilizer is mixed in a mixer. The resulting mixture is then fed to the main feeder of a 36 mm twin-screw extruder to produce pellets. The extruder temperature range is maintained within the range of 170-180°C, and the pellets are formed using a strand cutting system. The pellets are then dried at 75°C for 2-3 hours so that the moisture content of the final compound is less than 0.03 wt%. A well-dried compound can be used to form a non-halogen flame retardant layer over an inner layer of synthetic wood using an auxiliary extruder for multilayer manufacturing to produce synthetic wood having a flame-retardant skin layer. A well-dried compound was prepared as a sheet for the skin layer of synthetic wood by adjusting its thickness to 0.1 to 2 mm, and this was designated as Comparative Example 1.

[0080] [Test Example]

[0081] The characteristics of the specimens prepared in Examples 1 to 6 and Comparative Example 1 were measured by the following method, and the results are shown in Table 1 below.

[0082] 1) Tensile strength (MPa): Measured using the ISO 527-1 Standard Test Method with a specimen of 170 x 10 x 4 mm and a Universal Testing Machine from Qmesys.

[0083] 2) Elongation (%): Measured using the ISO 527-1 Standard Test Method with a specimen of size 170 x 10 x 4 mm (length of span between support 100 mm) and a Universal Testing Machine from Qmesys.

[0084] 3) Flexural strength (MPa): Measured using the ISO 178 Standard Test Method with a specimen of size 120 x 10 x 4 mm (length of span between support 100 mm) and a Universal Testing Machine from Qmesys.

[0085] 4) Flexural Modulus: Measured using the ISO 178 Standard Test Method with a specimen of size 120 x 10 x 4 mm (length of span between support 100 mm) and a Universal Testing Machine from Qmesys.

[0086] 5) Charpy Impact Strength (KJ / m2): Measured using the ISO 179 Standard Test Method with a specimen of 80 x 10 x 4 mm size and 1 / 4" notched at 23℃ and a Charpy Impact Strength Test Machine from Qmesys.

[0087] 6) Flame retardancy UL94 V grade @ 1.5 millimeters: Measured using a Qmesys Flammability Tester according to UL V-0 standards.

[0088] 7) Flame Retardancy - UL94 V Total Burn Time(s) @ 1.5mm: Measured using a Qmesys Flammability Tester and stopwatch according to UL V-0 standards.

[0089] Table 1

[0090]

[0091] In Example 1, a non-halogenated flame retardant compound containing 20 wt% piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) is used, and the flame retardancy rating is a failure in the test according to the UL-94V standard (1.5 mm), just like in Comparative Example 1.

[0092] In Example 2, by increasing the amount of a non-halogenated flame retardant compound containing piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) to 25% by weight, a flame retardant rating of V-2 was obtained for the UL-94V standard (1.5 mm thickness).

[0093] Examples 3 to 6 are examples in which the amount of a non-halogenated flame retardant compound containing piperazine pyrophosphate (PIPP) and dimelamine pyrophosphate (DMPY) was gradually increased starting from 30 wt% to 35 wt%, 40 wt%, and 45 wt%, and a flame retardant rating of V-0 was obtained for the UL-94V standard (1.5 mm thickness).

[0094] It was confirmed that increasing the concentration of non-halogen flame retardants improves the flame retardancy grade, but decreases elongation, tensile strength, and Charpy impact strength.

[0095] In addition, it was confirmed that flexural strength and flexural modulus increased by increasing the concentration of non-halogen flame retardants.

[0096] In the above-described embodiments, the composition for the inner layer of synthetic wood comprises 20 to 50 weight% of one selected from polyethylene and high-density polyethylene (HDPE) based on the total weight, 35 to 65 weight% of wood powder based on the total weight, 1 to 15 weight% of talc based on the total weight, 0.5 to 5 weight% of a lubricant based on the total weight, 0.5 to 5 weight% of a polyethylene coupling agent based on the total weight, and 0.1 to 1 weight% of an antioxidant based on the total weight; however, since the present invention has a flame-retardant outer layer of synthetic wood, the composition for the inner layer of synthetic wood can be varied in many ways.

[0097] As such, the present invention is not limited to the described embodiments, and it is obvious to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the invention. Accordingly, such modifications or variations should be deemed to fall within the scope of the claims of the present invention.

Claims

Claim 1 A non-halogen flame-retardant composition for a synthetic wood skin layer, characterized by comprising 45 to 76 weight% of either polyethylene or high-density polyethylene (HDPE) selected by the total weight, and 24 to 55 weight% of a non-halogen flame retardant by the total weight, wherein the composition is introduced into an auxiliary extruder and bonded in a molten state to the surface of an inner layer of synthetic wood discharged from a main extruder by the auxiliary extruder to form a skin layer of said synthetic wood. Claim 2 A non-halogen flame-retardant composition for a synthetic wood surface layer, characterized in that, in claim 1, the non-halogen flame retardant comprises a phosphorus-nitrogen flame retardant. Claim 3 A non-halogenated flame-retardant composition for a synthetic wood skin layer according to claim 2, characterized in that the phosphorus-nitrogen flame retardant comprises 40 to 80 weight% of one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant; and 20 to 60 weight% of one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant. Claim 4 A non-halogen flame-retardant composition for a synthetic wood skin layer according to claim 2, wherein the non-halogen flame retardant further comprises 2 to 7 weight percent of a flame retardant enhancer relative to the total weight of the phosphorus-nitrogen flame retardant, and the flame retardant enhancer is one of zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO2), silicon dioxide (SiO2), manganese oxide (MnO), aluminum oxide (Al2O3), iron oxide (Fe2O3), organically modified montmorillonite, or a mixture thereof. Claim 5 In claim 4, the flame retardant enhancer is zinc oxide (ZnO), and either one selected from polyethylene and high-density polyethylene (HDPE) is 38 to 70 weight% of the total weight, and the non-halogen flame retardant composition for a synthetic wood skin layer further comprises 1 to 20 weight% of an impact reinforcing agent based on the total weight; 0.1 to 3 weight% of a lubricating / dispersing agent based on the total weight; 0.1 to 0.5 weight% of an antioxidant based on the total weight; and 0.1 to 0.5 weight% of a UV stabilizer based on the total weight. Claim 6 A non-halogenated flame-retardant composition for a synthetic wood skin layer according to claim 5, characterized in that the impact modifier comprises one or more of the group consisting of polyolefin elastomer (POE), ethylene propylene rubber (EPR), ethylene propylene diene terpolymer, and styrene ethylene butadiene styrene (SEBS). Claim 7 In claim 4, the non-halogen flame-retardant composition for a synthetic wood skin layer is characterized by further comprising 0.1 to 5 weight% of a coupling agent based on the total weight; and 0.1 to 5 weight% of a color powder based on the total weight. Claim 8 A synthetic wood having a flame-retardant skin layer, comprising an inner layer discharged from a main extruder containing a composition for an inner layer of synthetic wood, and a skin layer formed by introducing a non-halogen flame-retardant composition for a skin layer of synthetic wood into an auxiliary extruder and bonding it to the surface of the inner layer in a molten state by the auxiliary extruder, wherein the non-halogen flame-retardant composition for the skin layer of synthetic wood comprises 45 to 76 weight% of either one selected from polyethylene and high-density polyethylene (HDPE) based on the total weight; and 24 to 55 weight% of a non-halogen flame retardant based on the total weight. Claim 9 Synthetic wood having a flame-retardant skin layer, characterized in that, in claim 8, the above-mentioned non-halogen flame retardant comprises a phosphorus-nitrogen-based flame retardant. Claim 10 Synthetic wood having a flame-retardant skin layer according to claim 9, wherein the phosphorus-nitrogen flame retardant comprises 40 to 80 weight% of one selected from piperazine pyrophosphate and piperazine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant; and 20 to 60 weight% of one selected from dimelamine pyrophosphate and dimelamine pyrophosphate derivatives relative to the total weight of the phosphorus-nitrogen flame retardant. Claim 11 Synthetic wood having a flame-retardant skin layer according to claim 9, wherein the non-halogen flame retardant further comprises 2 to 7 weight percent of a flame retardant enhancer relative to the total weight of the phosphorus-nitrogen flame retardant, and the flame retardant enhancer is one of zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO2), silicon dioxide (SiO2), manganese oxide (MnO), aluminum oxide (Al2O3), iron oxide (Fe2O3), organically modified montmorillonite, or a mixture thereof. Claim 12 Synthetic wood having a flame-retardant skin layer, wherein, in claim 11, the flame-retardant enhancer is zinc oxide (ZnO), and either one selected from polyethylene and high-density polyethylene (HDPE) is 38 to 70 weight% of the total weight, and the non-halogen flame-retardant composition for the synthetic wood skin layer further comprises 1 to 20 weight% of an impact reinforcing agent based on the total weight; 0.1 to 3 weight% of a lubricating / dispersing agent based on the total weight; 0.1 to 0.5 weight% of an antioxidant based on the total weight; and 0.1 to 0.5 weight% of a UV stabilizer based on the total weight. Claim 13 Synthetic wood having a flame-retardant skin layer according to claim 12, wherein the impact reinforcing agent comprises one or more from the group consisting of polyolefin elastomer (POE), ethylene propylene rubber (EPR), ethylene propylene diene terpolymer, and styrene ethylene butadiene styrene (SEBS). Claim 14 Synthetic wood having a flame-retardant skin layer, wherein the non-halogen flame-retardant composition for the skin layer of the synthetic wood described in claim 11 further comprises 0.1 to 5 weight% of a coupling agent based on the total weight; and 0.1 to 5 weight% of a color powder based on the total weight. Claim 15 In claim 8, the composition for the inner layer of the synthetic wood comprises 20 to 50 weight% of either polyethylene or high-density polyethylene (HDPE) based on the total weight; 35 to 65 weight% of wood powder based on the total weight; 1 to 15 weight% of talc based on the total weight; 0.5 to 5 weight% of a lubricant based on the total weight; 0.5 to 5 weight% of a polyethylene coupling agent based on the total weight; and 0.1 to 1 weight% of an antioxidant based on the total weight, thereby having a flame-retardant outer layer of synthetic wood.

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