KR20210068988A - Molded object, sandwich panel using same, and method for manufacturing same - Google Patents

Abstract

The present invention provides a molded article, a sandwich panel using the same as a core layer, and a method for manufacturing the same. The molded article having a nonwoven fiber aggregate structure including two or more nonwoven fiber aggregates includes a polyester-based fiber and a polypropylene composite fiber, and the polypropylene composite fiber includes polypropylene and maleic anhydride polyolefin.

Description

Molded article, sandwich panel using same, and manufacturing method thereof {MOLDED OBJECT, SANDWICH PANEL USING SAME, AND METHOD FOR MANUFACTURING SAME}

The present invention relates to a molded article, a sandwich panel using the same, and a method for manufacturing the same.

A typical sandwich panel has structural rigidity similar to that of a metal panel and is effective in reducing weight, so it is used in various fields such as construction materials.

In such a sandwich panel, a core layer (molded body) is formed between skin layers formed of aluminum, iron, or the like to control the physical properties of the panel. For example, a foamed resin material is used for the core layer to increase the weight reduction effect of the panel, or a general resin, composite material, or balsa wood material is used to increase the mechanical strength of the panel.

However, such a sandwich panel does not have sufficient weight reduction and mechanical strength, and is not excellent in elongation, so there are limitations in product application. In addition, when the panel is formed by applying an adhesive between the skin layer and the core layer, there is a problem in that the formability during processing is poor because the bonding force between the layers is weak.

As a background art related to the present invention, there is Korean Patent Laid-Open No. 10-2017-0140111, which discloses a sandwich panel and a manufacturing method thereof.

However, in the case of the sandwich panel, physical properties such as high density and high flexural strength and tensile strength were secured, but in the case of using a mixture of polypropylene fibers serving as a binder in the process of manufacturing a nonwoven fiber aggregate with polyester fibers, polyester There was a problem in that the compatibility with the fiber-based fibers was lowered and the mechanical properties were deteriorated.

(Patent Document 1) Korean Patent Application Laid-Open No. 10-2017-0140111, Sandwich panel and manufacturing method thereof

In order to solve the above problem, the present inventors have prepared a nonwoven fabric (nonwoven fiber aggregate) used as a core material of a sandwich panel, including polyester-based fibers; and polypropylene composite fiber containing maleic anhydride polyolefin; researched on a molded article prepared by mixing the same, a sandwich panel using the same, and a method for manufacturing the same, and completed the present invention.

Therefore, it is an object of the present invention to use a molded body made of polypropylene composite fiber containing maleic anhydride polyolefin that has excellent compatibility with polyester fibers and is used as a binder as a core layer when manufacturing a sandwich panel. Accordingly, it is an object to provide a sandwich panel having excellent mechanical properties of flexural rigidity to flexural strength without adding an additional binder and a method for manufacturing the same.

According to a first aspect of the invention,

A molded article having a nonwoven fiber aggregate structure including two or more nonwoven fiber aggregates, wherein the molded article includes polyester-based fibers and polypropylene composite fibers, wherein the polypropylene composite fibers include: polypropylene; and maleic anhydride polyolefin; it provides a molded article comprising.

In one embodiment of the present invention, the maleic anhydride polyolefin may be a polyolefin and maleic anhydride grafted.

In one embodiment of the present invention, the polyolefin includes a monomer selected from the group consisting of ethylene, propylene, and combinations thereof, and the polyolefin may have a homopolymer structure.

In one embodiment of the present invention, the polyolefin may be a polypropylene having a homopolymer structure.

In one embodiment of the present invention, the nonwoven fiber aggregate structure comprises 35 to 75% by weight of polyester-based fibers and 25 to 65% by weight of polypropylene composite fibers, based on the total weight of polyester-based fibers and polypropylene composite fibers. may include.

In one embodiment of the present invention, the nonwoven fiber aggregate structure comprises 35 to 65% by weight of polyester-based fibers and 35 to 65% by weight of polypropylene composite fibers, based on the total weight of polyester-based fibers and polypropylene composite fibers. may include.

In one embodiment of the present invention, the polyester fiber may be any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.

In one embodiment of the present invention, the nonwoven fiber aggregate structure is a structure in which two or more nonwoven fiber aggregates are bonded, and the nonwoven fiber aggregate is formed by bonding nonwoven fibers on a web or a sheet with an adhesive or , may be adhered using a thermoplastic fiber.

In one embodiment of the present invention, the flexural rigidity of the molded body may be 0.55 to 1.05 GPa.

In one embodiment of the present invention, the flexural strength of the molded body may be 60 to 135 N.

According to a second aspect of the invention,

core layer; a skin layer laminated on at least one surface of the core layer; and an adhesive layer bonding the core layer and the skin layer to each other, wherein the core layer uses the molded article of claim 1 .

In one embodiment of the present invention, the flexural rigidity of the sandwich panel may be 30 to 50 GPa.

In one embodiment of the present invention, the flexural strength of the sandwich panel may be 1500 to 3000 N.

In one embodiment of the present invention, the skin layer may be at least one selected from the group consisting of aluminum, iron, stainless steel (SUS), magnesium, and electrogalvanized steel (EGI).

In one embodiment of the present invention, the adhesive layer may include at least one of an olefin-based adhesive, a urethane-based adhesive, an acrylic adhesive, and an epoxy-based adhesive.

According to a third aspect of the invention,

a) mixing a polyester-based fiber and a polypropylene composite fiber to prepare a nonwoven fiber aggregate; b) manufacturing a core layer by performing a needle punching process on the nonwoven fiber assembly at a number of punches per minute of 300 to 1000 times, a moving speed of 1 to 8 m/min, and a punching density of 100 to 500 punches/cm ^{2 ;} c) forming an adhesive layer on at least one surface of the core layer; and d) forming a skin layer on the adhesive layer.

A molded article according to the present invention, a sandwich panel using the same, and a method for manufacturing the same can improve compatibility between fibers by mixing a polyester-based fiber and polypropylene composite fiber containing maleic anhydride polyolefin when manufacturing a nonwoven fabric used as a core material. It provides the effect of improving mechanical properties such as flexural rigidity and flexural strength of sandwich panels. Sandwich panel having the above effect is suitable for use in structural materials for home appliances (TV back cover, washing machine board, etc.), interior and exterior boards for construction, interior and exterior materials for automobiles, interior and exterior materials for trains/ships/aircraft, various partition boards, elevator structural materials, etc. Do.

1 is a schematic diagram of a sandwich panel according to the present invention.
2 shows an SEM image of a core layer according to Example 4 of the present invention.
3 shows an SEM image of a core layer according to Comparative Example 2 of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, with reference to the accompanying drawings, a molded article and a sandwich panel according to a preferred embodiment of the present invention will be described in detail as follows.

As a result of the experiments of the present inventors, in the case of the core material used in the conventional sandwich panel, a nonwoven fiber assembly was prepared in which polyester fibers were mixed with polypropylene fibers serving as a binder, but the compatibility between the two fibers was poor, so the mechanical properties of the core material There is a problem that there is a limit to the improvement, and there is a need for research on this.

In order to solve the above problems, the inventors of the present invention mix and use polypropylene composite fibers including maleic anhydride polyolefin with polyester fibers when preparing a nonwoven fiber aggregate structure used as a core material, By improving the compatibility between both fibers, we have produced a sandwich panel with improved mechanical properties such as flexural strength and flexural rigidity.

molded body

The present invention provides a molded article having a nonwoven fiber aggregate structure comprising two or more nonwoven fiber aggregates, wherein the molded article includes a polyester-based fiber and a polypropylene composite fiber, and the polypropylene composite fiber includes: polypropylene; and maleic anhydride polyolefin; it provides a molded article comprising.

In the present invention, the 'nonwoven fiber aggregate structure' is a structure in which two or more nonwoven fiber aggregates are bonded, and the 'nonwoven fiber aggregate' refers to a nonwoven fiber on a web or a sheet by bonding with an adhesive or , refers to a thing bonded using a thermoplastic fiber, and since the molded article according to the present invention has a nonwoven fiber aggregate in which the fibers are entangled with each other, all or part of the polyester-based fibers are fused by a binder, and therefore, in the molded article Natural pores are included, so that air permeability is improved, and weight reduction can be improved. That is, since the fibers have natural pores formed while being entangled with each other, unlike the case where pores are artificially formed by an additive such as a foaming agent, it is a non-foaming core, so manufacturing costs can be reduced and the foaming process can be omitted. Efficiency can also be increased.

The nonwoven fiber aggregate structure of the molded article according to the present invention includes polyester-based fibers. The average length of the polyester fibers included in the molded article according to the present invention is preferably 5 to 100 mm. When the average length of the fiber is less than 5 mm, it may be difficult to expect the effect of high elongation because the length of the fiber is short. Conversely, when it exceeds 100 mm, the space occupied by the gap of the molded body may be reduced because the content of fibers entangled with each other increases. In addition, when it exceeds 100 mm, the dispersion of the fibers is not made smoothly during the manufacture of the molded article, and the physical properties of the molded article may be reduced.

The nonwoven fiber aggregate structure is 35 to 75% by weight, preferably 35 to 65% by weight, preferably 45 to 65% by weight, more preferably 45 to 55% by weight, based on the total weight of the polyester-based fiber and the polypropylene composite fiber. It may include a polyester-based fiber in weight %. When less than 35% by weight of the polyester-based fiber is included, the content of the polyester-based fiber serving as a reinforcing fiber is reduced, and there is a problem in that mechanical properties are lowered. In addition, when the polyester-based fiber in excess of 75% by weight is included, it is difficult to control the lofting phenomenon after thermoforming, and there is a problem in that the formability of the board is reduced.

The polyester fiber may be any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.

In addition, the nonwoven fiber aggregate structure may further include a sheath-core type bicomponent fiber. The sheath-core type bicomponent fiber may include a core part of a polyester fiber; and a non-hygroscopic copolymer resin sheath part surrounding the core part. The sheath-core type bicomponent fiber may be included in the molded article because the resin of the sheath portion remains in a non-melted state, which was introduced in the manufacturing step of the molded article.

In the core part of the sheath-core type bicomponent fiber, any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate may be used as the core part of the polyester fiber. have.

The sheath portion of the sheath-core type bicomponent fiber may use the same non-hygroscopic copolymer resin as the binder included in the molded article.

Specifically, the non-hygroscopic copolymer resin refers to a resin having a property of not absorbing moisture in the air, and specifically, based on the molded article of the present invention prepared using the resin, 100 at 85° C. and 85% relative humidity. A weight change rate (that is, an increase rate of moisture content) of the molded article after standing for a period of time may be less than 0.1%, preferably less than 0.08%, more preferably less than 0.07%.

In general, since the moisture absorption of the PET fibers contained in the molded article is less than 0.05%, if the weight change rate of the molded article exceeds 0.05%, it means that the amount of moisture absorbed by the binder, which is another component in the molded article, is significant. do. In this regard, the non-hygroscopic copolymer resin refers to a weight change rate (that is, an increase in moisture content) of the molded article after being left for 100 hours at 85 ° C. temperature and 85% relative humidity based on the finally manufactured molded article is less than 0.1%, preferably It means having a low absorption rate of less than 0.08%, more preferably less than 0.07%.

As such a non-hygroscopic copolymer resin, an ester-based resin, a diol-based monomer having strong crystallinity and excellent elasticity, and an acid component capable of imparting flexibility are copolymerized together, and one that satisfies the water absorption may be used.

Specifically, as the ester-based resin, any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate may be used, and the diol-based monomer is neopentyl. Selected from the group consisting of glycol, diethylene glycol, ethylene glycol, poly(tetramethylene) glycol, 1,4-butanediol, 1,3-propanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, etc. Any one or more selected from the group consisting of isophthalic acid, adipic acid, 2,6-naphthalenedicarboxylic acid, sebacic acid, succinic acid, and the like may be used as the acid component.

The sheath-core type bicomponent fiber is prepared by melt spinning and drawing using the components of the core and the components of the sheath.

In addition, when the non-hygroscopic resin is used as the sheath component of the sheath-core type bicomponent fiber, flexural strength and tensile strength are improved, and a molded article can be manufactured by a dry process, thereby making it easy to manufacture a high-density molding layer. In addition, when used as a packaging material for large-sized cargo, the nonwoven fabric can be prevented from sagging due to its good physical properties and shape retention even in a high temperature and high humidity atmosphere.

The nonwoven fiber aggregate structure of the molded article according to the present invention comprises polypropylene composite fibers.

In addition, the polypropylene composite fiber is polypropylene; and maleic anhydride polyolefins. The polypropylene composite fiber may comprise 90 to 99 weight percent polypropylene and 1 to 10 weight percent maleic anhydride polyolefin based on the total weight of the polypropylene composite fiber.

Referring to FIG. 2 , the polypropylene composite fiber serves as a binder in that it contains maleic anhydride polyolefin together with polypropylene, thereby increasing compatibility with polyethylene terephthalate (PET) fibers. , it is possible to increase the compatibility with the adhesive layer in the manufacture of sandwich panels. On the other hand, referring to FIG. 3 , it can be seen that when only polypropylene is used instead of polypropylene composite fiber, compatibility with polyethylene terephthalate (PET) fibers is poor.

The maleic anhydride polyolefin may be a polyolefin and maleic anhydride grafted. The maleic anhydride polyolefin may be prepared by grafting polyolefin and maleic anhydride in a weight ratio of 70:30 to 97:3. When the above weight ratio is satisfied, mechanical properties such as flexural rigidity and flexural strength may be improved.

The polyolefin may include a monomer selected from the group consisting of ethylene, propylene, and combinations thereof.

In addition, the polyolefin may have a homopolymer structure, preferably polypropylene having a homopolymer structure. When producing maleic anhydride polyolefin included in the polypropylene composite fiber, when using a homopolymer using a single type of monomer instead of a block copolymer, the tensile strength of the fiber increases It may have an effect of improving mechanical properties such as flexural strength of the molded article.

After the core material of the sandwich panel is heat-treated at 180~220℃ to physically separate the polypropylene composite fiber from the polyester fiber, maleic anhydride and graphene are subjected to gel permeation chromatography (GPC). It can be confirmed that the modified polymer is a homopolymer. Specifically, when a homopolymer is used, in contrast to the case of using a block copolymer, the analysis result through the gel permeation chromatography, it is possible to confirm the characteristics appearing in the high range of the weight average molecular weight, , may have better mechanical and chemical properties than the case of using a block copolymer.

The nonwoven fiber aggregate structure comprises 25 to 65% by weight, preferably 35 to 65% by weight, more preferably 35 to 55% by weight, particularly more preferably 45% by weight, based on the total weight of the polyester-based fiber and the polypropylene composite fiber. to 55% by weight of polypropylene composite fibers. When less than 25% by weight of the polypropylene composite fiber is included, there is a problem in that the binding area between the fibers is reduced and mechanical properties are deteriorated. In addition, when the polypropylene composite fiber in excess of 65% by weight is included, the weight of the polypropylene composite fiber is increased, so there is a problem in that the numerical stability during thermoforming is lowered.

The nonwoven fiber aggregate structure may further include a binder. In addition, the binder may be a non-hygroscopic copolymer resin or a hygroscopic copolymer resin.

In particular, the non-hygroscopic copolymer resin refers to a resin having a property of not absorbing moisture in the air. Specifically, based on the molded article of the present invention prepared using the resin, 100 at 85° C. and 85% relative humidity. A weight change rate (that is, an increase rate of moisture content) of the molded article after standing for a period of time may be less than 0.1%, preferably less than 0.08%, more preferably less than 0.07%.

In general, since the moisture absorption of the PET fibers contained in the molded article is less than 0.05%, if the weight change rate of the molded article exceeds 0.05%, it means that the amount of moisture absorbed by the binder, which is another component in the molded article, is significant. do. In this regard, the non-hygroscopic copolymer resin refers to a weight change rate (that is, an increase in moisture content) of the molded article after being left for 100 hours at 85 ° C. temperature and 85% relative humidity based on the finally manufactured molded article is less than 0.1%, preferably It means having a low absorption rate of less than 0.08%, more preferably less than 0.07%.

As such a non-hygroscopic copolymer resin, an ester-based resin, a diol-based monomer having strong crystallinity and excellent elasticity, and an acid component capable of imparting flexibility are copolymerized together, and one that satisfies the water absorption may be used.

Specifically, as the ester-based resin, any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate may be used, and the diol-based monomer is neopentyl. Selected from the group consisting of glycol, diethylene glycol, ethylene glycol, poly(tetramethylene) glycol, 1,4-butanediol, 1,3-propanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, etc. Any one or more selected from the group consisting of isophthalic acid, adipic acid, 2,6-naphthalenedicarboxylic acid, sebacic acid, succinic acid, and the like may be used as the acid component.

All or part of the polyester-based fibers included in the molded body may be fused by a binder that is a non-hygroscopic resin, and the binder may have a melting point of 160° C. or higher. In addition, the molded article having a nonwoven fiber aggregate structure according to the present invention has an apparent density of 0.2 to 0.8 g/cm ³ . Since it satisfies the above density range, it may have sufficient mechanical strength to be used as a packaging material for large cargo.

The molded article according to the present invention has a flexural stiffness of 0.55 to 1.05 GPa, preferably 0.75 to 1.02 GPa, more preferably 0.85 to 0.97 GPa, and a flexural strength of 60 to 135N, preferably 95 to 133N, more preferably is 120 to 130N and has excellent mechanical strength. The flexural stiffness and flexural strength are measured according to ASTM C393.

Since the molded article according to the present invention satisfies the above mechanical strength, it is included as a core layer in a sandwich panel, and is used as a structural material for home appliances (TV back cover, washing machine board, etc.), interior and exterior boards for construction, interior and exterior materials for automobiles, and trains. It can be used as interior and exterior materials for ships/aircraft (boards such as partitions), boards for various partitions, and elevator structural materials.

In addition, the molded article according to the present invention may further include a filler such as glass fiber, carbon fiber, polymer fiber, and the like. In addition, a flame retardant such as a bromine-based organic flame retardant may be further included. In addition to this, additives such as impact modifiers and heat stabilizers may be further included.

Manufacturing method of molded body

The manufacturing method of the molded article according to the present invention may be manufactured by the following method.

The manufacturing method of the molded article according to the present invention comprises the steps of: a) preparing a nonwoven fiber aggregate by mixing a polyester-based fiber and a polypropylene composite fiber; b) manufacturing a molded body (core layer) by performing a needle punching process on the nonwoven fiber assembly at a number of punches per minute of 300 to 1000 times, a moving speed of 1 to 8 m/min, and a punching density of 100 to 500 punches/cm ^{2 ;} includes

In step a), (A) polyester fibers and (B) polypropylene composite fibers are prepared, respectively, and then mixed to prepare a nonwoven fiber assembly. At this time, (A) polyester fibers; and (B) polypropylene composite fibers; 35:65 to 75:25, preferably 35:65 to 65:35, more preferably 45:55 to 65:35, even more preferably 45:55 to It can be used by mixing in a weight ratio of 55:45. When the weight ratio of the (A) polyester fiber and (B) polypropylene composite fiber does not satisfy the above range, the compatibility between the fibers is lowered due to a lack of a binder, and the flexural rigidity and flexural strength of the molded article and the sandwich panel including the same are lowered there is a problem that

Prior to mixing between the polyester-based fiber and the polypropylene composite fiber, polypropylene and maleic anhydride polyolefin may be prepared to prepare the polypropylene composite fiber.

Specifically, first, a maleic anhydride polyolefin (chip) may be prepared by grafting polyolefin, which is a homopolymer, and maleic anhydride in a weight ratio of 70:30 to 97:3. Thereafter, polypropylene (chips) and the maleic anhydride polyolefin (chips) may be mixed in a weight ratio of 90:10 to 99:1 to spin polypropylene composite fibers.

The weight average molecular weight (Mw) when the polypropylpin (chip) and the maleic anhydride polyolefin (chip) are compounded for bonding may be 190,000 to 230,000. When the weight average molecular weight is less than the above weight average molecular weight, it may be difficult to spin polypropylene composite fibers prepared using the compounded polypropylene (chips) and maleic anhydride polyolefins (chips). In addition, when the weight average molecular weight is exceeded, the M.I (melt index) is lowered, and thus the graft ratio of the polyolefin is lowered, thereby compatibility may be lowered.

As the polyester-based fiber, any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate may be used, and the polyolefin is ethylene, propylene and and a monomer selected from the group consisting of combinations thereof.

Thereafter, in step b), a needle punching process of 300 to 1000 punches per minute, a moving speed of 1 to 8 m/min, and a punching density of 100 to 500 punches/cm ² is performed on the nonwoven fiber assembly to form a nonwoven fiber assembly structure. can be manufactured.

In the needle punching process, the number of punches per minute is 300 to 1000 times per minute, the movement speed of the nonwoven fiber assembly is 1 to 8 m/min, and the punching density is 100 to 500 punches/cm ² , A needle punching process may be performed, and more preferably, the number of punches per minute is 400 to 700 times per minute, the movement speed of the nonwoven fiber assembly is 1.5 to 6 m/min, and the punching density is 200 to 400 punches/cm ² to proceed with the needle punching process.

If the number of punching per minute is less than 300 times, there is a problem in that the degree of binding between the nonwoven fiber aggregates is lowered, and if the number of punchings per minute is more than 1000 times, there is a problem in that the nonwoven fiber assembly is broken. In addition, if the moving speed of the nonwoven fiber aggregate is slower than 1 m/min, there is a problem in that the production speed is too slow, and if it is faster than 8 m/min, there is a problem in that it is not easy to control the punching density. In addition, when the punching density is ^{less than 100 punches/cm 2} , there is a problem in that the degree of binding between the nonwoven fiber aggregates is lowered ^{, and when the punching density is more than 500 punches/cm 2} , there is a problem in that the nonwoven fiber aggregate is broken.

The needle punching process may be performed two or more times. When the needle punching process is performed two or more times, it is possible to increase the binding force of the interlayer fibers, which is effective in preventing delamination.

As the needle punching process in the above range is performed, the physical bonding force by needle punching is improved, and physical properties such as tensile strength of the molded body used as the core layer are improved, and through this, the shear stiffness strength and sag of the finally manufactured sandwich panel degree can be improved.

Specifically, after mixing the polyester-based fiber and the polypropylene composite fiber, carding is performed using a carding machine, and then a needle punching process is performed under the above conditions to achieve a basis weight of 3000 to 4000 gsm of a non-woven fiber aggregate (non-woven fabric). to manufacture

Thereafter, the prepared nonwoven fiber aggregate (nonwoven fabric) is mounted on a plurality of unwinding devices, and then moved to a hot press. At this time, after mounting 1 to 10 manufactured nonwoven fiber aggregates in a plurality of unwinding devices according to the number, it may be moved to a hot press for manufacturing a molded body. When a plurality of nonwoven fiber aggregates are used by using a plurality of unwinding devices in this way, since the thickness of each nonwoven fiber aggregate becomes thin, the length of the nonwoven fiber aggregate wound around one unwinding device becomes longer. Therefore, since it is possible to reduce the number of times of use of the softener for connecting the nonwoven fiber aggregates continuously input during the continuous process, there is an advantage that the process can be simplified.

Thereafter, the plurality of nonwoven fiber aggregates (nonwoven fabrics) moved by the hot press are heated and pressed under a temperature condition of 200 to 210° C. and ^{a pressure condition of 100 to 200 kgf/cm 2} to prepare a molded body having a nonwoven fiber aggregate structure.

The heating press is not particularly limited as long as it is commonly used in the industry, and as a specific example, a double belt press, a heating roll press, and the like may be used.

In addition, the manufacturing method of the molded article according to the present invention,

After performing the needle punching process of step b), preheating for 3 to 10 minutes at a temperature of 190 to 210° C. may be further included.

sandwich panel

1, a sandwich panel according to the present invention includes a core layer 10; a skin layer 20 laminated on at least one surface of the core layer; and an adhesive layer (not shown) for adhering the core layer and the skin layer, wherein the core layer uses the molded body.

The core layer of the sandwich panel according to the present invention is composed of the above-described molded body according to the present invention. The thickness of the core layer is preferably 0.1 to 10 mm. When the thickness is less than 0.1 mm, there is a problem in that it is difficult to maintain excellent mechanical strength, and when the thickness exceeds 10 mm, there is a problem in that the formability is deteriorated during bending or deep drawing molding of the sandwich panel.

The sandwich panel according to the present invention includes a skin layer laminated on at least one surface of the core layer.

The skin layer of the sandwich panel according to the present invention may be formed of a metal material, and is preferably made of aluminum, iron, stainless steel (SUS), magnesium, electro-galvanized steel sheet (EGI) and hot-dip galvanized steel sheet (GI). It may include any one or more selected from the group. For example, in order to have excellent formability and flexural rigidity, a skin layer including an electrogalvanized steel sheet (EGI) may be applied to the sandwich panel. In addition, a skin layer including aluminum may be applied to the sandwich panel in order to reduce the weight.

The thickness of the skin layer may be less than or equal to 6% of the thickness of the entire panel. The skin layer of the conventional sandwich panel had a problem in that the thickness of the skin layer had to be thick due to the low mechanical strength of the core material, which increased the weight of the sandwich panel. However, the sandwich panel according to the present invention has a mechanical strength of the core material. As the strength is improved, the thickness of the skin layer can be set to 6% or less of the total thickness of the panel, and thus the weight can be reduced.

The sandwich panel according to the present invention includes an adhesive layer for bonding the core layer and the skin layer.

The adhesive layer of the sandwich panel according to the present invention is applied between the core layer and the skin layer to adhere the core layer and the skin layer. The adhesive layer is preferably applied with a uniform thickness in consideration of the viscosity. In the present invention, a sandwich panel may be manufactured by laminating the core layer and the skin layer and then curing them, or the core layer and the skin layer may be laminated and then thermocompressed to manufacture a sandwich panel. In this case, as the adhesive penetrates into the core layer during curing or thermocompression bonding, there is an effect of improving the adhesion between the skin layer and the core layer by mechanical bonding as well as chemical bonding with the components constituting the core layer. The chemical bonding means that the adhesive becomes a covalent bond with the upper surface and the lower surface of the core layer, a hydrogen bond, a van der Waals bond, an ionic bond, and the like.

The mechanical bonding refers to a form in which the rings are physically hung as if they are hung with each other as the adhesive permeates into the core layer. This form is also called mechanical interlocking. Due to the natural pores contained in the core layer, the adhesive permeates the upper and lower surfaces of the core layer.

The adhesive constituting the adhesive layer may include at least one of an olefin-based adhesive, a urethane-based adhesive, an acrylic adhesive, and an epoxy-based adhesive. The olefin-based adhesive may be at least one selected from the group consisting of polyethylene, polypropylene, and amorphous polyalphaolefin adhesives. The urethane-based adhesive may be used without limitation as long as it is an adhesive including a urethane structure (-NH-CO-O-). The acrylic adhesive may include at least one of a polymethyl methacrylate adhesive, a hydroxyl group-containing polyacrylate adhesive, and a carboxy group-containing polyacrylate adhesive. The epoxy adhesive is bisphenol-A type epoxy adhesive, bisphenol-F type epoxy adhesive, novolac epoxy adhesive, linear aliphatic epoxy resins, and cycloaliphatic epoxy resins. may include

In addition, the adhesive may include a photocurable adhesive, a hot melt adhesive, or a thermosetting adhesive, and any one of a photocuring method and a thermosetting method may be used. For example, a sandwich panel can be manufactured by thermosetting a laminate including a skin layer, a core layer, and an adhesive. The thermosetting may be performed for about 5 minutes to 2 hours at 50 to 110° C., which is the curing temperature of the epoxy resin, and curing may be performed for about 1 to 10 hours even at room temperature.

The adhesive layer may be applied to a thickness of about 20 to 300 μm, but is not limited thereto.

As a method of applying the adhesive layer to one surface of the skin layer, any one method selected from among a die coating method, a gravure coating method, a knife coating method, and a spray coating method may be used.

Another adhesive used for the adhesive layer may include a first adhesive layer including high-density polyethylene (HDPE) and a second adhesive layer including low-density polyethylene (LDPE).

The high density polyethylene (HDPE) may have a density of 0.940 to 0.965 g/cm ³ , and the low density polyethylene (LDPE) may have a density of 0.910 to 0.925 g/cm ³ .

The adhesive constituting the adhesive layer is not particularly limited as long as it can form a first adhesive layer including high-density polyethylene (HDPE) and a second adhesive layer including low-density polyethylene (LDPE), but it is preferably co-extruded using a film extruder. to manufacture

The adhesive layer may be applied to a thickness of approximately 20 to 300 μm, and the first adhesive layer and the second adhesive layer may each have a thickness of 10 to 150 μm, but is not limited thereto, and the first adhesive layer and the second adhesive layer are not limited thereto. The thickness of the adhesive layer may be the same or different.

In order to form the skin layer on the adhesive layer, the sandwich panel can be manufactured by placing the skin layer on the adhesive layer and then thermocompressing the laminate including the skin layer, the core layer, and the adhesive. The thermocompression bonding may be performed at a pressure of 2 to 10 MPa at 150 to 200° C. for about 3 to 10 minutes.

At this time, the core layer and the high-density polyethylene (HDPE) adhesive are attached, and the skin layer and the low-density polyethylene (LDPE) adhesive are attached to each other. In this way, LDPE adhesive is used for the skin layer so that it can be easily attached even with relatively low heat, and HDPE adhesive is used for the core layer to prevent the adhesive melted by heat from penetrating into the core and failing to exert adhesive force. By doing so, it is possible to improve the adhesion between the respective components.

The flexural rigidity of the sandwich panel to which the nonwoven fiber aggregate structure of the molded body is applied may be 30 to 50 GPa, and the flexural strength may be 1500 to 3000 N. The flexural stiffness and flexural strength are measured according to ASTM C393.

Sandwich panel manufacturing method

The sandwich panel according to the present invention is formed by sequentially stacking the skin layer 20 , the core layer 10 , and the skin layer 20 , and applying an adhesive layer between the core layer 10 and the skin layer 20 . is manufactured by After the above components are laminated, the curing and pressing steps may be performed, but the present invention is not limited thereto.

Specifically, the method for manufacturing a sandwich panel according to the present invention comprises:

a) mixing a polyester-based fiber and a polypropylene composite fiber to prepare a nonwoven fiber aggregate; b) manufacturing a core layer by performing a needle punching process on the nonwoven fiber assembly at a number of punches per minute of 300 to 1000 times, a moving speed of 1 to 8 m/min, and a punching density of 100 to 500 punches/cm ^{2 ;} c) forming an adhesive layer on at least one surface of the core layer; and d) forming a skin layer on the adhesive layer.

The core layer of the sandwich panel according to the present invention is composed of the above-described molded body according to the present invention. Accordingly, steps a) and b) are the same as the above-described method for manufacturing the molded body.

Thereafter, in step c), an adhesive layer may be formed on at least one surface of the core layer.

The adhesive constituting the adhesive layer may include at least one of an olefin-based adhesive, a urethane-based adhesive, an acrylic adhesive, and an epoxy-based adhesive. The olefin-based adhesive may be at least one selected from the group consisting of polyethylene, polypropylene, and amorphous polyalphaolefin adhesives. The urethane-based adhesive may be used without limitation as long as it is an adhesive including a urethane structure (-NH-CO-O-). The acrylic adhesive may include at least one of a polymethyl methacrylate adhesive, a hydroxyl group-containing polyacrylate adhesive, and a carboxy group-containing polyacrylate adhesive. The epoxy adhesive is bisphenol-A type epoxy adhesive, bisphenol-F type epoxy adhesive, novolac epoxy adhesive, linear aliphatic epoxy resins, and cycloaliphatic epoxy resins. may include

In addition, the adhesive may include a photocurable adhesive, a hot melt adhesive, or a thermosetting adhesive, and any one of a photocuring method and a thermosetting method may be used. For example, a sandwich panel can be manufactured by thermosetting a laminate including a skin layer, a core layer, and an adhesive. The thermal curing may be performed for about 5 minutes to 2 hours at 50 to 110° C., which is the curing temperature of the epoxy resin, and curing may be performed for about 1 to 10 hours even at room temperature.

The adhesive layer may be applied to a thickness of about 20 to 300 μm, but is not limited thereto.

As a method of applying the adhesive layer to one surface of the skin layer, any one method selected from among a die coating method, a gravure coating method, a knife coating method, and a spray coating method may be used.

Another adhesive used for the adhesive layer may include a first adhesive layer including high-density polyethylene (HDPE) and a second adhesive layer including low-density polyethylene (LDPE).

The high density polyethylene (HDPE) may have a density of 0.940 to 0.965 g/cm ³ , and the low density polyethylene (LDPE) may have a density of 0.910 to 0.925 g/cm ³ .

The adhesive constituting the adhesive layer is not particularly limited as long as it can form a first adhesive layer including high-density polyethylene (HDPE) and a second adhesive layer including low-density polyethylene (LDPE), but it is preferably co-extruded using a film extruder. to manufacture

The adhesive layer may be formed to a thickness of approximately 20 to 300 μm, and the first adhesive layer and the second adhesive layer may each have a thickness of 10 to 150 μm, but is not limited thereto, and the first adhesive layer and the second adhesive layer are not limited thereto. The thickness of the adhesive layer may be the same or different.

Thereafter, in step d), a skin layer may be formed on the adhesive layer.

The skin layer of the sandwich panel according to the present invention may be formed of a metal material, and is preferably made of aluminum, iron, stainless steel (SUS), magnesium and electro-galvanized steel sheet (EGI) and hot-dip galvanized steel sheet (GI). It may include any one or more selected from the group. For example, in order to have excellent formability and flexural rigidity, a skin layer including an electrogalvanized steel sheet (EGI) may be applied to the sandwich panel. In addition, a skin layer including aluminum may be applied to the sandwich panel in order to reduce the weight.

In order to form the skin layer on the adhesive layer, any one of a photocuring method, a thermosetting method, and a thermocompression bonding method may be used. For example, a sandwich panel may be manufactured by thermosetting or thermocompression bonding a laminate including a skin layer, a core layer, and an adhesive.

The thermosetting may be performed for about 5 minutes to 2 hours at 50 to 110° C., which is the curing temperature of the epoxy resin, and curing may be performed for about 1 to 10 hours even at room temperature.

When the thermocompression bonding is performed using an adhesive including a first adhesive layer containing high-density polyethylene (HDPE) and a second adhesive layer containing low-density polyethylene (LDPE), a skin layer is placed on the adhesive layer, and then a skin layer, A sandwich panel can be manufactured by thermocompression bonding a laminate including a core layer and an adhesive. The thermocompression bonding may be performed at a pressure of 2 to 10 MPa at 150 to 200° C. for about 3 to 10 minutes.

At this time, the core layer and the high-density polyethylene (HDPE) adhesive are attached, and the skin layer and the low-density polyethylene (LDPE) adhesive are attached to each other. In this way, LDPE adhesive is used for the skin layer so that it can be easily attached even with relatively low heat, and HDPE adhesive is used for the core layer to prevent the adhesive melted by heat from penetrating into the core and failing to exert adhesive force. By doing so, it is possible to improve the adhesion between the respective components.

As described above, the sandwich panel according to the present invention is lightweight and has excellent formability as well as mechanical strength by using a core layer having good mechanical properties. Specifically, the flexural rigidity of the sandwich panel using the core layer (molded body) of the nonwoven fiber aggregate structure may be 30 to 50 GPa, and the flexural strength may be 1500 to 3000 N.

In addition, the shear stiffness, deflection degree, and bonding force between different fibers of sandwich panels have been improved, so structural materials for home appliances (TV back cover, washing machine board, etc.), interior and exterior boards for construction, interior and exterior materials for automobiles, interior and exterior materials for trains/ships/aircraft ( It is suitable for use as a partition board), various partition boards, and elevator structure materials.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that changes and modifications fall within the scope of the appended claims.

Example: Preparation of Sandwich Panels

Preparation of core layer (molded body): Preparation Examples 1 to 12

[Production Example 1]

After preparing polypropylene chips (Polymirae) and maleic anhydride polypropylene chips (Hyundai EP), they were blended in a weight ratio of 95:5 and polypropylene composite fibers (fineness of 15 denier) were spun. The maleic anhydride polypropylene chip is formed by grafting polypropylene, which is a homopolymer, and maleic anhydride.

After spinning, the polypropylene composite fiber was mixed with polyethylene terephthalate (PET) fiber (Daeyang Industrial Co., Ltd., recycled PET Fiber, fineness of 25 denier) in a ratio of 10:90.

After mixing with respect to the fibers, after performing carding using a carding machine, the number of punches per minute is 500 times, the movement speed of the nonwoven fiber aggregate is 2 m/min, and the punching density is 200 punches/cm ² Needle punching process A non-woven fiber aggregate (non-woven fabric) was prepared through

After the nonwoven fiber assembly is mounted on two unwinding devices, the number of punches per minute is 500 times, the movement speed of the nonwoven fiber assembly is 2 m/min, and the punching density is 200 punches/cm ^{2 The} needle punching process is repeated. Physical recombination was formed between the nonwoven fiber aggregates.

The nonwoven fiber aggregate bonded by needle punching was preheated for 3 minutes after entering the preheating chamber at a temperature of 200° C. in the chamber.

Thereafter, the nonwoven fiber aggregate was transferred to a heating roll press at a speed of 5 m/min. At this time, the heating temperature of the heating roll press was 200° C., and the pressure was 150 kgf/cm ^{2 ,} and a core layer (molded body) having a nonwoven fiber aggregate structure was prepared by heating/pressing treatment for 2 minutes.

[Preparation Examples 2 to 8]

A core layer was prepared in the same manner as in Preparation Example 1, except that when mixing the polypropylene composite fiber and the polyethylene terephthalate fiber, the weight % was changed as shown in Table 1 below and mixed.

[Preparation Examples 9 to 11]

After preparing polyethylene terephthalate (PET) fibers (Daeyang Industrial, recycled PET Fiber, fineness of 25 denier) and polypropylene fibers (GH new material, fineness of 15 denier), these were mixed at a weight % in Table 1 below, except that , a core layer was prepared in the same manner as in Preparation Example 1.

[Production Example 12]

The same as in Preparation Example 1, except that a copolymer chip formed by grafting a polypropylene/polyethylene block copolymer (PP/PE block copolymer) and maleic anhydride was used instead of the maleic anhydride polypropylene chip. A core layer was prepared by the method.

polypropylene composite fiber polypropylene fiber Polyethylene terephthalate fiber remark Preparation Example 1 10 - 90 Before spinning polypropylene composite fiber,
When producing maleic anhydride polyolefin, polypropylene, which is a homopolymer, is used Preparation 2 20 - 80 Preparation 3 30 - 70 Preparation 4 40 - 60 Preparation 5 50 - 50 Preparation 6 60 - 40 Preparation 7 70 - 30 Preparation 8 80 - 20 Preparation 9 - 30 70 - Preparation 10 - 40 60 - Preparation 11 - 50 50 - Preparation 12 40 - 60 Before spinning polypropylene composite fiber,
When producing maleic anhydride polyolefin, PP/PE block copolymer is used

(Unit: Weight % based on 100% of the total weight of the core (molded body))

Preparation of Sandwich Panels: Examples 1 to 8 and Comparative Examples 1 to 4

[Example 1]

After applying a polyolefin adhesive (Samsung Gratech) to a thickness of 50 μm on both sides of the core layer prepared in Preparation Example 1, a skin layer formed of a hot-dip galvanized steel sheet (Posco Steel) was formed to a thickness of 0.4 mm, followed by lamination The resulting result was heat-cured at 100° C. to prepare a sandwich panel.

[Examples 2 to 8]

A sandwich panel was manufactured in the same manner as in Example 1, except that the core layers prepared in Preparation Examples 2 to 8 were used according to Table 2 below.

[Comparative Examples 1 to 4]

A sandwich panel was manufactured in the same manner as in Example 1, except that the core layers prepared in Preparation Examples 9 to 12 were used according to Table 2 below.

used core layer Example 1 Preparation Example 1 Example 2 Preparation 2 Example 3 Preparation 3 Example 4 Preparation 4 Example 5 Preparation 5 Example 6 Preparation 6 Example 7 Preparation 7 Example 8 Preparation 8 Comparative Example 1 Preparation 9 Comparative Example 2 Preparation 10 Comparative Example 3 Preparation 11 Comparative Example 4 Preparation 12

Experimental Example 1: Measurement of physical properties of a molded body (core layer)

Flexural stiffness (GPa) and flexural strength (N) of the molded articles (corresponding to the core layer of the sandwich panel) prepared in Preparation Examples 1 to 12 were measured in accordance with ASTM C393, and the results are shown in Table 3 below.

Flexural Stiffness (GPa) Flexural strength (N) Preparation Example 1 0.27 31 Preparation 2 0.41 48 Preparation 3 0.70 93 Preparation 4 0.84 111 Preparation 5 0.95 129 Preparation 6 0.83 103 Preparation 7 0.67 85 Preparation 8 0.62 69 Preparation 9 0.65 77 Preparation 10 0.71 102 Preparation 11 0.84 116 Preparation 12 0.73 105

Referring to Table 3, Preparation Examples 4 to 6 are in the case of a molded article containing 40 to 60% by weight of polypropylene composite fibers relative to 100% of the total weight of the molded article, and excellent mechanical properties of flexural rigidity of 0.75 GPa or more and flexural strength of 95 N or more was found to have In particular, it was found that the molded article of Preparation Example 5 was a molded article containing 50% by weight of polypropylene composite fibers relative to 100% of the total weight of the molded article, and had excellent mechanical properties with a flexural rigidity of 0.85 GPa or more and a flexural strength of 120N or more.

On the other hand, 'Preparation Example 3 and Preparation Example 9', 'Preparation Example 4 and Preparation Example 10', 'Preparation Example 5 and a molded body containing polypropylene composite fibers or polypropylene fibers of the same weight % relative to the total weight of the molded article As a result of comparing the measured values of flexural rigidity and flexural strength of Example 11', the case containing the polypropylene composite fiber showed higher compatibility with the polyethylene terephthalate (PET) fiber than the case containing the polypropylene fiber. It was confirmed that the physical properties were more excellent.

In addition, in the structure of the maleic anhydride polyolefin included in the polypropylene composite fiber included in the molded article, Preparation Example 4 in which the polymer to be grafted with maleic anhydride is a PP homopolymer is a PP/PE block copolymer Compared to Preparation Example 12 using (Block copolymer), it was confirmed that the polyethylene terephthalate fiber and mixed weight ratio were the same, but had better mechanical properties of flexural rigidity and flexural strength. Through this, it was found that the flexural rigidity and flexural strength of the molded article were improved as the physical properties of the matrix were increased by copolymerizing polypropylene, which serves as a binder and a matrix at the same time as a homopolymer without additives.

Experimental Example 2: Measurement of physical properties of sandwich panels

The thickness and weight of the sandwich panels prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were measured, and the results are shown in Table 4 below.

Sandwich panel thickness (mm) Sandwich panel weight (kg/m ² ) Example 1 6.42 10.3 Example 2 6.43 10.3 Example 3 6.48 10.3 Example 4 6.41 10.3 Example 5 6.30 10.3 Example 6 6.35 10.3 Example 7 6.37 10.3 Example 8 6.37 10.3 Comparative Example 1 6.40 10.3 Comparative Example 2 6.31 10.3 Comparative Example 3 6.30 10.3 Comparative Example 4 6.32 10.37

After the sandwich panels prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were prepared as specimens, flexural rigidity and flexural strength were measured according to ASTM C393, and the results are shown in Table 5 below.

Flexural Stiffness (GPa) Flexural strength (N) Example 1 15 740 Example 2 21 1010 Example 3 30 1580 Example 4 38 2140 Example 5 43 2600 Example 6 35 1980 Example 7 29 1550 Example 8 27 1450 Comparative Example 1 27 1350 Comparative Example 2 32 1820 Comparative Example 3 35 2320 Comparative Example 4 34 1930

Referring to Table 5, Examples 4 to 6 are sandwich panels containing 40 to 60% by weight of polypropylene composite fibers based on 100% of the total weight of the core material, and have excellent mechanical properties of flexural strength of 35GPa or more and flexural strength of 1900N or more. could see that In particular, Example 5 containing 50% by weight of polypropylene composite fibers exhibited the best mechanical properties by having a flexural rigidity of 40 GPa or more and a flexural strength of 2500 N or more.

On the other hand, 'Example 3 and Comparative Example 1', 'Example 4 and Comparative Example 2', and 'Example 5 and Comparative Example 3 containing polypropylene composite fibers or polypropylene fibers of the same weight% relative to the total weight of the core material Through comparison of the flexural rigidity and flexural strength measurement results of ', the case of including polypropylene composite fiber has higher compatibility with polyethylene terephthalate (PET) fiber than the case of including polypropylene fiber, so the mechanical properties of the sandwich panel I was able to confirm this improvement. Even through the comparison of FIGS. 2 and 3 showing the SEM images of Example 4 and Comparative Example 2, it was confirmed that the polypropylene composite fiber had excellent compatibility with the polyethylene terephthalate fiber compared to the polypropylene fiber.

In Example 4, in which maleic anhydride polyolefin was prepared by grafting 'polypropylene homopolymer' with maleic anhydride, 'polypropylene/polyethylene block copolymer' and maleic anhydride were used instead of homopolymer. In comparison with the grafted Comparative Example 4, since the core material contains a molded article prepared by copolymerizing polypropylene, which serves as a binder and a matrix, as a homopolymer without additives, the sandwich panel has excellent mechanical properties in terms of flexural and flexural strength. could see that

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will become apparent from the appended claims.

10: core layer
20: skin layer

Claims (16)

A molded article having a nonwoven fiber aggregate structure comprising two or more nonwoven fiber aggregates,
The molded body includes a polyester-based fiber and a polypropylene composite fiber,
The polypropylene composite fiber may include polypropylene; and maleic anhydride polyolefin;
The method of claim 1,
Wherein the maleic anhydride polyolefin is a polyolefin and maleic anhydride grafted.
3. The method of claim 2,
The polyolefin comprises a monomer selected from the group consisting of ethylene, propylene, and combinations thereof,
The polyolefin is a homopolymer structure, the molded body.
3. The method of claim 2,
The polyolefin is a polypropylene of a homopolymer structure, a molded article.
The method of claim 1,
The nonwoven fiber aggregate structure is
relative to the total weight of polyester-based fibers and polypropylene composite fibers,
35 to 75% by weight of polyester-based fibers and
A molded body comprising 25 to 65% by weight of polypropylene composite fibers.
The method of claim 1,
The nonwoven fiber aggregate structure is
relative to the total weight of polyester-based fibers and polypropylene composite fibers,
35 to 65% by weight of polyester-based fibers and
35 to 65% by weight of polypropylene composite fibers.
The method of claim 1,
The polyester fiber is any one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, a molded article.
The method of claim 1,
The nonwoven fiber aggregate structure is a structure in which two or more nonwoven fiber aggregates are joined,
The nonwoven fiber assembly is a molded article, wherein the nonwoven fibers on the web or on the sheet are adhered with an adhesive, or adhered using a thermoplastic fiber.
The method of claim 1,
The molded article has a flexural stiffness of 0.55 to 1.05 GPa.
The method of claim 1,
The flexural strength of the molded body is 60 to 135 N, the molded body
core layer;
a skin layer laminated on at least one surface of the core layer; and
Including; an adhesive layer for adhering the core layer and the skin layer;
A sandwich panel, wherein the core layer uses the molded body of claim 1 .
12. The method of claim 11,
The sandwich panel has a flexural stiffness of 30 to 50 GPa.
12. The method of claim 11,
The flexural strength of the sandwich panel is 1500 to 3000 N, the sandwich panel.
12. The method of claim 11,
The skin layer is at least one selected from the group consisting of aluminum, iron, stainless steel (SUS), magnesium, electrogalvanized steel sheet (EGI) and hot-dip galvanized steel sheet (GI), a sandwich panel.
12. The method of claim 11,
The adhesive layer is a sandwich panel comprising at least one of an olefin-based adhesive, a urethane-based adhesive, an acrylic adhesive, and an epoxy-based adhesive.
a) mixing a polyester-based fiber and a polypropylene composite fiber to prepare a nonwoven fiber aggregate;
b) manufacturing a core layer by performing a needle punching process on the nonwoven fiber assembly at a number of punches per minute of 300 to 1000 times, a moving speed of 1 to 8 m/min, and a punching density of 100 to 500 punches/cm ^{2 ;}
c) forming an adhesive layer on at least one surface of the core layer; and
d) forming a skin layer on the adhesive layer;

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