Patent Description:
A typical sandwich panel has structural rigidity similar to that of a metal panel and is effective in reducing weight, and thus, has been 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, etc. to control the physical properties of the panel. For example, for the core layer, a foamed resin material is used to increase a weight reduction effect of the panel, or a general resin, a composite or a 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 that 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 the background art related to the present invention, there is <CIT>, which discloses a sandwich panel and a manufacturing method thereof.

However, in the case of the sandwich panel, physical properties such as high density, high flexural strength and tensile strength, and the like were secured, but in the case of mixing and using a polypropylene fiber serving as a binder in a process of manufacturing non-woven fiber aggregates with a polyester-based fiber, there is a problem in that compatibility with the polyester-based fiber is lowered, and thus, the mechanical properties are deteriorated.

<CIT> discloses a sandwich panel including a core layer which comprises a thermally bonded, thermoformed needlefelt comprising PET fibers and PET bicomponent binder fibers.

<CIT> discloses a sandwich panel comprising a core layer in the form of a nonwoven which can be hot-pressed, comprising a blend of crystalline polymer fibers with fibers comprising a polyethylene-polypropylene block copolymer modified with maleic anhydride.

In order to solve the problems, the present inventors studied a molded body, a sandwich panel using the same, and a method for manufacturing the same, wherein the molded body was manufactured by mixing a polyester-based fiber; and a polypropylene composite fiber including maleic anhydride polyolefin when manufacturing a non-woven fabric (non-woven fiber aggregates) used as a core material of the sandwich panel, and completed the present invention.

Therefore, an object of the present invention is to provide a sandwich panel and a method for manufacturing the same having excellent mechanical properties of flexural rigidity and flexural strength even without adding a separate additional binder, by using a molded body as a core layer, which is manufactured by a polypropylene composite fiber having excellent compatibility with a polyester-based fiber and including maleic anhydride polyolefin used as a binder, when the sandwich panel is manufactured.

According to a first aspect of the present invention, there is provided a molded body having a non-woven fiber aggregate structure comprising two or more non-woven fiber aggregates, including a polyester-based fiber and a polypropylene composite fiber, wherein the polypropylene composite fiber includes polypropylene; and maleic anhydride polyolefin.

The maleic anhydride polyolefin is grafted with polyolefin and maleic anhydride, wherein the polyolefin is polypropylene having a homopolymer structure.

In an exemplary embodiment of the present invention, the non-woven fiber aggregate structure may include <NUM> to <NUM> wt% of the polyester-based fiber and <NUM> to <NUM> wt% of the polypropylene composite fiber with respect to the total weight of the polyester-based fiber and the polypropylene composite fiber.

In an exemplary embodiment of the present invention, the polyester-based fiber may be at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.

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

In an exemplary embodiment of the present invention, the flexural rigidity of the molded body may be <NUM> to <NUM> GPa.

In an exemplary embodiment of the present invention, the flexural strength of the molded body may be <NUM> to <NUM> N.

According to a second aspect of the present invention, there is provided a sandwich panel including a core layer; a skin layer laminated on at least one surface of the core layer; and a bonding layer bonding the core layer and the skin layer, wherein the core layer uses the molded body of claim <NUM>.

In an exemplary embodiment of the present invention, the flexural rigidity of the sandwich panel may be <NUM> to <NUM> GPa.

In an exemplary embodiment of the present invention, the flexural strength of the sandwich panel may be <NUM> to <NUM> N.

In an exemplary 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, electro-galvanized iron (EGI) and galvanized iron (GI).

In an exemplary embodiment of the present invention, the bonding 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 present invention, there is provided a method for manufacturing a sandwich panel according to any of claims <NUM> to <NUM> including steps of: a) preparing non-woven fiber aggregates by mixing a polyester-based fiber and a polypropylene composite fiber; b) preparing a core layer by performing a needle-punching process for the non-woven fiber aggregate at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>; c) forming a bonding layer on at least one surface of the core layer; and d) forming a skin layer on the bonding layer.

According to the present invention, the molded body, the sandwich panel using the same, and the method for manufacturing the same provide an effect of improving mechanical properties such as flexural rigidity, flexural strength, and the like by mixing a polyester-based fiber and a polypropylene composite fiber including maleic anhydride polyolefin when manufacturing a non-woven fabric used as a core material to improve compatibility between fibers. The sandwich panel having the effect is suitable to be used for structural members (a TV back cover, a washing machine board, etc.) for home appliances, 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 members, etc..

Advantages and features of the present invention, and methods for accomplishing the same will be more clearly understood from exemplary embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following exemplary embodiments but may be implemented in various different forms. The exemplary embodiments are provided only to make description of the present invention complete and to fully provide the scope of the present invention to a person having ordinary skill in the art to which the present invention pertains with the category of the invention, and the present invention will be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.

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

As an experiment result of the present inventors, in the case of a core material to be used in a conventional sandwich panel, non-woven fiber aggregates obtained by mixing a polyester-based fiber with a polypropylene fiber serving as a binder were prepared, but there is a problem in that there is a limitation to improve the mechanical properties of the core material due to the deterioration of compatibility between the two fibers, and thus, there is a need for research thereon.

In order to solve the problems, the inventors of the present invention have manufactured a sandwich panel with improved mechanical properties such as flexural strength and flexural rigidity by mixing and using a polypropylene composite fiber including maleic anhydride polyolefin with a polyester-based fiber when manufacturing a non-woven fiber aggregate structure used as a core material to improve compatibility between both the fibers.

The present invention provides a molded body having a non-woven fiber aggregate structure comprising two or more non-woven fiber aggregates. The molded body comprises a polyester-based fiber and a polypropylene composite fiber, wherein the polypropylene composite fiber comprises polypropylene; and maleic anhydride polyolefin.

In the present invention, the 'non-woven fiber aggregate structure' is a structure in which two or more non-woven fiber aggregates are bonded, and the 'non-woven fiber aggregate' means that non-woven fibers on a web or sheet are bonded with an adhesive or using a thermoplastic fiber. Since the molded body according to the present invention has non-woven fiber aggregates in which the fibers are entangled with each other, all or a part of the polyester-based fiber is fused by a binder, and thus, natural pores are included in the molded body, thereby improving air permeability and improving weight reduction. That is, since the molded body has the natural pores formed while the fibers are entangled with each other, unlike a case where pores are artificially formed by an additive such as a foaming agent, the molded body is a non-foaming core to reduce manufacturing costs and the foaming process may be omitted to increase the process efficiency.

The non-woven fiber aggregate structure of the molded body according to the present invention includes a polyester-based fiber. An average length of the polyester-based fiber included in the molded body according to the present invention is preferably <NUM> to <NUM>. When the average length of the fiber is less than <NUM>, it may be difficult to expect an effect of high elongation because the length of the fiber is short. On the contrary, when the average length of the fiber exceeds <NUM>, a space occupied by a gap of the molded body may be reduced because the content of fibers entangled with each other increases. In addition, when the average length of the fiber exceeds <NUM>, the dispersion of the fibers is not made smoothly when manufacturing the molded body, and thus, the physical properties of the molded body may be deteriorated.

The non-woven fiber aggregate structure may include <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt% of the polyester-based fiber with respect to the total weight of the polyester-based fiber and the polypropylene composite fiber. When the polyester-based fiber is included in less than <NUM> wt%, there is a problem that the content of the polyester-based fiber serving as a reinforced fiber is decreased so that the mechanical properties are deteriorated. In addition, when the polyester-based fiber is included in excess of <NUM> wt%, there is a problem that it is difficult to control a lofting phenomenon after thermoforming, so that the formability of the board is deteriorated.

The polyester-based fiber may use at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate.

In addition, the non-woven fiber aggregate structure may further include a sheath-core type bicomponent fiber. The sheath-core type bicomponent fiber may include a core part of the polyester-based fiber; and a sheath part that is a non-hygroscopic copolymer resin surrounding the core part. The sheath-core type bicomponent fiber may be included in the molded body because the resin of the sheath part which has been introduced in the manufacturing step of the molded body remains in a non-melted state.

The core part of the sheath-core type bicomponent fiber may use at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate as the polyester-based fiber.

The sheath part of the sheath-core type bicomponent fiber may use the same non-hygroscopic copolymer resin as a binder which may be included in the molded body.

Specifically, the non-hygroscopic copolymer resin refers to a resin having a property of not absorbing moisture in the air, and specifically, may use a resin having less than <NUM>%, preferably less than <NUM>%, more preferably less than <NUM>% of a weight change rate (i.e., an increase rate of moisture content) of the molded body after left for <NUM> hours at a temperature of <NUM> and a relative humidity of <NUM>% based on the molded body of the present invention manufactured using the resin.

Generally, since the hygroscopic degree of the PET fiber included in the molded body is less than <NUM>%, the fact that the weight change rate of the molded body is more than <NUM>% means that the amount of moisture to be absorbed by the binder which is another configuration in the molded boy is considerable. In this regard, the non-hygroscopic copolymer resin refers to a resin having a low absorption rate of less than <NUM>%, preferably less than <NUM>%, more preferably less than <NUM>% of the weight change rate (that is, the increase rate of the moisture content) of the molded body after left for <NUM> hours at a temperature of <NUM> and a relative humidity of <NUM>% based on the finally manufactured molded body.

Such a non-hygroscopic copolymer resin is prepared by copolymerizing an ester-based resin, a diol-based monomer having strong crystallinity and excellent elasticity, and an acid component capable of imparting flexibility, and may use a resin that satisfies the absorption rate.

Specifically, the ester-based resin may use at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, the diol-based monomer may use at least one selected from the group consisting of neopentyl glycol, diethylene glycol, ethylene glycol, poly(tetramethylene) glycol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-hexanediol, <NUM>,<NUM>-cyclohexanediol, and the like, and the acid component may use at least one selected from the group consisting of isophthalic acid, adipic acid, <NUM>,<NUM>-naphthalenedicarboxylic acid, sebacic acid, succinic acid, and the like.

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

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 the molded body may be manufactured by a dry process to make it easy to prepare a high-density molded layer. In addition, when the non-hygroscopic resin is used as a packaging material for large cargo, it is possible to prevent sagging of the non-woven fabric due to its good physical properties and shape retention even under a high temperature and high humidity atmosphere.

The non-woven fiber aggregate structure of the molded body according to the present invention includes a polypropylene composite fiber.

In addition, the polypropylene composite fiber includes polypropylene; and maleic anhydride polyolefin. The polypropylene composite fiber may comprise <NUM> to <NUM> wt% of polypropylene and <NUM> to <NUM> wt% of maleic anhydride polyolefin based on the total weight of the polypropylene composite fiber.

Referring to <FIG>, the polypropylene composite fiber includes maleic anhydride polyolefin together with polypropylene to serve as a binder, thereby increasing compatibility with the polyethylene terephthalate (PET) fiber and increasing compatibility with a bonding layer when the sandwich panel is manufactured. On the other hand, referring to FIG. <NUM>, when only polypropylene is used instead of the polypropylene composite fiber, it can be confirmed that compatibility with the polyethylene terephthalate (PET) fiber is deteriorated.

The maleic anhydride polyolefin is grafted with polyolefin and maleic anhydride. The maleic anhydride polyolefin may be prepared by grafting polyolefin and maleic anhydride in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>. When the weight ratio is satisfied, there may be effect of improving mechanical properties such as flexural rigidity and flexural strength.

The polyolefin is polypropylene having a homopolymer structure. When preparing maleic anhydride polyolefin included in the polypropylene composite fiber using a homopolymer using a single type of monomer instead of a block copolymer, there is an effect of improving mechanical properties such as flexural strength and the like of the molded body by increasing the tensile strength of the fiber.

It can be confirmed that after physically separating the polypropylene composite fiber from the polyester-based fiber by heat-treating the core material of the sandwich panel at <NUM> to <NUM>, the polymer grafted with maleic anhydride is a homopolymer through gel permeation chromatography (GPC). Specifically, when the homopolymer is used, compared to the case of using the block copolymer, as the analysis result through the GPC, characteristics exhibited in the high range of weight average molecular weight can be confirmed, and mechanical and chemical properties may be better than those of the case of using the block copolymer.

The non-woven fiber aggregate structure may include <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt%, particularly more preferably <NUM> to <NUM> wt% of the polypropylene composite fiber with respect to the total weight of the polyester-based fiber and the polypropylene composite fiber. When polypropylene composite fiber is included in less than <NUM> wt%, there is a problem that the binding area between the fibers is reduced and thus, mechanical properties are lowered. In addition, when polypropylene composite fiber is included in excess of <NUM> wt%, there is a problem that the weight of the polypropylene composite fiber increases, and thus, the numerical stability during thermoforming is lowered.

The non-woven 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, and specifically, may use a resin having less than <NUM>%, preferably less than <NUM>%, more preferably less than <NUM>% of a weight change rate (i.e., an increase rate of moisture content) of the molded body after left for <NUM> hours at a temperature of <NUM> and a relative humidity of <NUM>% based on the molded body of the present invention manufactured using the resin.

All or part of the polyester-based fiber 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 <NUM> or higher. In addition, the molded body having the non-woven fiber aggregate structure according to the present invention has an apparent density of <NUM> to <NUM>/cm<NUM>. Since the density range is satisfied, the molded body may have sufficient mechanical strength to be used for a packaging material for large cargo.

The molded body according to the present invention has the flexural rigidity of <NUM> to <NUM> GPa, preferably <NUM> to <NUM> GPa, more preferably <NUM> to <NUM> GPa, and the flexural strength of <NUM> to <NUM> N, preferably <NUM> to <NUM> N, more preferably <NUM> to <NUM> N, which has excellent mechanical strength. The flexural rigidity and the flexural strength are measured according to ASTM C393.

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

In addition, the molded body 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, additives such as an impact modifier and a heat stabilizer may be further included.

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

The manufacturing method of the molded body according to the present invention includes steps of a) preparing non-woven fiber aggregates by mixing a polyester-based fiber and a polypropylene composite fiber; and b) manufacturing a molded body (core layer) by performing a needle-punching process for the non-woven fiber aggregates at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>.

In step a), (A) a polyester-based fiber and (B) a polypropylene composite fiber are prepared, respectively, and then mixed to prepare non-woven fiber aggregates. At this time, the (A) polyester-based fiber; and the (B) polypropylene composite fiber may be mixed and used in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>, preferably <NUM>:<NUM> to <NUM>:<NUM>, more preferably <NUM>:<NUM> to <NUM>:<NUM>, particularly more preferably <NUM>:<NUM> to <NUM>:<NUM>. When the weight ratio of the (A) polyester-based fiber and the (B) polypropylene composite fiber does not satisfy the range, there is a problem that the compatibility between fibers is lowered due to the lack of a binder, and thus, the flexural rigidity and flexural strength of the molded body and the sandwich panel including the same are lowered.

Before mixing the polyester-based fiber and the polypropylene composite fiber, polypropylene and maleic anhydride polyolefin may be prepared in order to prepare the polypropylene composite fiber.

Specifically, first, maleic anhydride polyolefin (chip) may be prepared by grafting polyolefin which is a homopolymer and maleic anhydride in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>. Thereafter, polypropylene (chip) and the maleic anhydride polyolefin (chip) may be mixed in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM> to spin the polypropylene composite fiber.

The weight average molecular weight (Mw) when the polypropylene (chip) and the maleic anhydride polyolefin (chip) are compounded for bonding may be <NUM>,<NUM> to <NUM>,<NUM>. In the case of less than the weight average molecular weight, it may be difficult to spin the polypropylene composite fiber prepared using the compounded polypropylene (chip) and maleic anhydride polyolefin (chip). In addition, in the case of more than the weight average molecular weight, since a melt index (M. I) is lowered, the graft ratio of polyolefin is lowered, thereby deteriorating compatibility.

The polyester-based fiber may use at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, and the polyolefin may include a monomer selected from the group consisting of ethylene, propylene, and combinations thereof.

Thereafter, in step b), the molded body having the non-woven fiber aggregate structure may be manufactured by performing a needle-punching process of the non-woven fiber aggregate at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>.

The needle-punching process may be performed for the mixed non-woven fiber aggregates at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of the non-woven fiber aggregates of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>. More preferably, the needle-punching process may be performed for the non-woven fiber aggregates at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of the non-woven fiber aggregates of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>.

If the number of times of punching per minute is less than <NUM>, there is a problem that the binding degree between the non-woven fiber aggregates is lowered, and when the number of times of punching per minute is more than <NUM> times, there is a problem that the breakage of the non-woven fiber aggregates occurs. Further, when the movement speed of the non-woven fiber aggregates is slower than <NUM>/min, there is a problem that the production speed is too slow, and when the movement speed is faster than <NUM>/min, there is a problem that it is not easy to control the punching density. If the punching density is less than <NUM> punches/cm<NUM>, there is a problem that the binding degree between the non-woven fiber aggregates is lowered, and when the punching density is more than <NUM> punches/cm<NUM>, there is a problem that the breakage of the non-woven fiber aggregates occurs.

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.

When the needle punching process is performed in the range, the physical bonding force by needle punching is improved, and physical properties such as tensile strength of the molded body used as a core layer are improved, and as a result, the shear rigidity strength and the sagging degree of the finally manufactured sandwich panel may be improved.

Specifically, after mixing the polyester-based fiber and the polypropylene composite fiber, carding is performed using a carding machine, and then the needle punching process is performed under the conditions to prepare non-woven fiber aggregates (non-woven fabric) having a basis weight of <NUM> to <NUM> gsm.

Thereafter, the prepared non-woven fiber aggregates (non-woven fabric) are mounted on a plurality of unwinding devices, and then moved to a hot press. At this time, <NUM> to <NUM> sheets of the prepared non-woven fiber aggregates may be mounted on the plurality of unwinding devices according to the number, and then moved to the hot press for manufacturing the molded body. As such, when the plurality of non-woven fiber aggregates are used by using the plurality of unwinding devices, since the thickness of each non-woven fiber aggregate becomes thin, the length of the non-woven fiber aggregate to be wound on one unwinding device is increased. Accordingly, there is an advantage that the process may be simplified because it is possible to reduce the number of times of use of a joining machine for connecting the non-woven fiber aggregates continuously input during a continuous process.

Thereafter, the plurality of non-woven fiber aggregates (non-woven fabric) moved to the hot press are heated and pressed under a temperature condition of <NUM> to <NUM> and a pressure condition of <NUM> to <NUM> kgf/cm<NUM> to manufacture a molded body having a non-woven fiber aggregate structure.

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

In addition, the manufacturing method of the molded body according to the present invention
may further include preheating for <NUM> to <NUM> minutes at a temperature condition of <NUM> to <NUM> after performing the needle punching process of step b).

Referring to <FIG>, the sandwich panel according to the present invention includes a core layer <NUM>; a skin layer <NUM> laminated on at least one surface of the core layer; and a bonding layer (not illustrated) for bonding 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 constituted by the molded body according to the present invention described above. The thickness of the core layer is preferably <NUM> to <NUM>. When the thickness is less than <NUM>, there is a problem that it is difficult to maintain excellent mechanical strength, and when the thickness exceeds <NUM>, there is a problem 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 preferably, may include at least one selected from the group of aluminum, iron, stainless steel (SUS), magnesium, electro-galvanized iron (EGI) and galvanized iron (GI). For example, in order to have excellent formability and flexural rigidity, a skin layer including EGI may be applied to the sandwich panel. In addition, in order to reduce the weight, a skin layer including aluminum may be applied to the sandwich panel.

The thickness of the skin layer may be <NUM>% or less of the thickness of the entire panel. The skin layer of the conventional sandwich panel had a problem in that since the mechanical strength of the core material is lowered, the thickness of the skin layer needs to be thick, and as a result, the weight of the sandwich panel is increased. In the sandwich panel according to the present invention, as the mechanical strength of the core material is improved, the thickness of the skin layer may be <NUM>% or less of the thickness of the entire panel, and thus, the weight may be reduced.

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

The bonding layer of the sandwich panel according to the present invention is applied between the core layer and the skin layer to bond the core layer and the skin layer. The bonding layer is preferably applied with a uniform thickness in consideration of the viscosity. In the present invention, the sandwich panel may be manufactured by laminating the core layer and the skin layer and then curing the layers, or the sandwich panel may be manufactured by laminating the core layer and the skin layer and then hot-pressing the layers. In this case, as the adhesive penetrates into the core layer during curing or hot-pressing, there is an effect of improving the bonding force 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 is bonded with an upper surface and a lower surface of the core layer through a covalent bond, a hydrogen bond, a van der Waals bond, an ionic bond, and the like.

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

The adhesive constituting the bonding 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 the adhesive is adhesives including a urethane structure (-NH-COO-). 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-based adhesive may include at least one of a bisphenol-A type epoxy adhesive, a bisphenol-F type epoxy adhesive, a novolac epoxy adhesive, linear aliphatic epoxy resins, and cycloaliphatic epoxy resins.

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 thermal-curing method may be used. For example, the sandwich panel may be manufactured by thermal-curing a laminate including the skin layer, the core layer, and the adhesive. The thermal curing may be performed for about <NUM> minutes to <NUM> hours at a curing temperature of the epoxy resin of <NUM> to <NUM>, and the curing may be performed for about <NUM> to <NUM> hours even at room temperature.

The bonding layer may be applied at a thickness of about <NUM> to <NUM>, but is not limited thereto.

As the method of applying the bonding layer to one surface of the skin layer, any one method selected from 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 bonding layer may include a first bonding layer including high-density polyethylene (HDPE) and a second bonding layer including low-density polyethylene (LDPE).

The HDPE may have a density of <NUM> to <NUM>/cm<NUM>, and the LDPE may have a density of <NUM> to <NUM>/cm<NUM>.

The adhesive constituting the bonding layer is not particularly limited as long as the adhesive may form the first bonding layer including HDPE and the second bonding layer including LDPE, but preferably prepared by co-extrusion using a film extruder.

The bonding layer may be applied at a thickness of about <NUM> to <NUM>, and the first bonding layer and the second bonding layer may each have a thickness of <NUM> to <NUM>, but is not limited thereto, and the thicknesses of the first bonding layer and the second bonding layer may be the same as or different from each other.

In order to form the skin layer on the bonding layer, the skin layer is positioned on the bonding layer, and then a laminate including the skin layer, the core layer, and the adhesive is hot-pressed to manufacture the sandwich panel. The hot-pressing may be performed at a pressure of <NUM> to <NUM> MPa at <NUM> to <NUM> for about <NUM> to <NUM> minutes.

At this time, the core layer and the HDPE adhesive are attached to each other, and the skin layer and the LDPE adhesive are attached to each other. As such, the LDPE adhesive is used for the skin layer to be attached easily even with relatively low heat, and for the core layer, the HDPE adhesive is used to prevent an adhesive melted by heat from fully permeating into the core so as not to exhibit the bonding force, thereby improving the bonding force between the respective components.

The sandwich panel to which the non-woven fiber aggregate structure of the molded body is applied may have flexural rigidity of <NUM> to <NUM> GPa and flexural strength of <NUM> to <NUM> N. The flexural rigidity and the flexural strength are measured according to ASTM C393.

The sandwich panel according to the present invention is formed by sequentially laminating the skin layer <NUM>, the core layer <NUM>, and the skin layer <NUM>, and manufactured by applying a bonding layer between the core layer <NUM> and the skin layer <NUM>. After the components are laminated, the curing and pressing steps may be performed, but the present invention is not limited thereto.

Specifically, the method for manufacturing the sandwich panel according to the present invention comprises the steps of:
a) preparing non-woven fiber aggregates by mixing a polyester-based fiber and a polypropylene composite fiber; b) preparing a core layer by performing a needle-punching process for the non-woven fiber aggregates at the number of times of punching per minute of <NUM> to <NUM> times, a movement speed of <NUM> to <NUM>/min, and a punching density of <NUM> to <NUM> punches/cm<NUM>; c) forming a bonding layer on at least one surface of the core layer; and d) forming a skin layer on the bonding layer.

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

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

In addition, the adhesive may include a photocurable adhesive, a hot-melt adhesive, or a thermosetting adhesive, and any one of a photo-curing method and a thermal-curing method may be used. For example, the sandwich panel may be manufactured by thermal-curing a laminate including the skin layer, the core layer, and the adhesive. The thermal curing may be performed for about <NUM> minutes to <NUM> hours at a curing temperature of the epoxy resin of <NUM> to <NUM>, and the curing may be performed for about <NUM> to <NUM> hours even at room temperature.

The bonding layer may be formed at a thickness of about <NUM> to <NUM>, and the first bonding layer and the second bonding layer may each have a thickness of <NUM> to <NUM>, but is not limited thereto, and the thicknesses of the first bonding layer and the second bonding layer may be the same as or different from each other.

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

In order to form the skin layer on the bonding layer, any one of a photo-curing method, a thermal-curing method, and a hot-pressing method may be used. For example, the sandwich panel may be manufactured by thermal-curing or hot-pressing a laminate including the skin layer, the core layer, and the adhesive.

The thermal curing may be performed for about <NUM> minutes to <NUM> hours at a curing temperature of the epoxy resin of <NUM> to <NUM>, and the curing may be performed for about <NUM> to <NUM> hours even at room temperature.

In the hot-pressing, in the case of using the adhesive including the first bonding layer containing the HDPE and the second bonding layer containing the LDPE, the skin layer is positioned on the bonding layer and then the laminate including the skin layer, the core layer, and the adhesive is hot-pressed to manufacture the sandwich panel. The hot-pressing may be performed at a pressure of <NUM> to <NUM> MPa at <NUM> to <NUM> for about <NUM> to <NUM> minutes.

As described above, the sandwich panel according to the present invention has excellent formability as well as mechanical strength by using the core layer which is lightweight and has good mechanical properties. Specifically, the sandwich panel using the core layer (molded body) having the non-woven fiber aggregate structure may have flexural rigidity of <NUM> to <NUM> GPa and flexural strength of <NUM> to <NUM> N.

In addition, problems such as the shear rigidity, the sagging degree, and the bonding force between different fibers of the sandwich panel are improved, so that the sandwich panel is suitable to be used for structural members (a TV back cover, a washing machine board, etc.) for home appliances, interior and exterior boards for construction, interior and exterior materials for automobiles, interior and exterior materials (boards of partitions and the like) for trains/ships/aircraft, various partition boards, elevator structural members, etc..

Hereinafter, preferred Examples will be provided to help in understanding of the present invention. However, the following Examples are just illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and the technical idea of the present invention and it is natural that these variations and modifications are within the scope of the appended claims.

After a polypropylene chip (PolyMirae) and a maleic anhydride polypropylene chip (Hyundai EP) were prepared, the chips were mixed in a weight ratio of <NUM>:<NUM> to spin a polypropylene composite fiber (fineness of <NUM> deniers). The maleic anhydride polypropylene chip was formed by grafting polypropylene, which was a homopolymer, and maleic anhydride.

After spinning, the polypropylene composite fiber was mixed with a polyethylene terephthalate (PET) fiber (Daeyang Industrial, recycled PET Fiber, fineness of <NUM> deniers) in a ratio of <NUM>:<NUM>.

After the mixing of the fibers, carding was performed using a carding machine and then non-woven fiber aggregates (non-woven fabric) were prepared through a needle punching process of the number of times of punching per minute of <NUM> times, a movement speed of the non-woven fiber aggregates of <NUM>/min, and a punching density of <NUM> punches/cm<NUM>.

The non-woven fiber aggregates were mounted on two unwinding devices and then the needle punching process of the number of times of punching per minute of <NUM> times, a movement speed of the non-woven fiber aggregates of <NUM>/min, and a punching density of <NUM> punches/cm<NUM> was repeated to form physical re-bonding between the non-woven fiber aggregates.

The non-woven fiber aggregates bonded by the needle punching were introduced to a preheating chamber having a chamber temperature of <NUM> and then preheated for <NUM> minutes.

Thereafter, the non-woven fiber aggregates were transferred to a heating roll press at a speed of <NUM>/min. At this time, a heating temperature of the heating roll press was <NUM> and a pressure was <NUM> kgf/cm<NUM>, and a core layer (molded body) having the non-woven fiber aggregate structure was prepared by heating/pressing for <NUM> minutes.

A core layer was prepared in the same manner as in Preparation Example <NUM>, except that a polypropylene composite fiber and a polyethylene terephthalate fiber were mixed at different wt% as shown in Table <NUM> below.

A core layer was prepared in the same manner as in Preparation Example <NUM>, except that a polyethylene terephthalate (PET) fiber (Daeyang Industrial, recycled PET Fiber, fineness of <NUM> deniers) and a polypropylene fiber (GH new material, fineness of <NUM> deniers) were prepared and then mixed at wt% in Table <NUM> below.

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

After a polyolefin adhesive (Samsung Gratech) was applied on both sides of the core layer prepared in Preparation Example <NUM> at a thickness of <NUM>, a skin layer formed of galvanized iron (Posco Steel) was formed at a thickness of <NUM>, and then a laminated product was thermal-cured at <NUM> to manufacture a sandwich panel.

Sandwich panels were manufactured in the same manner as in Example <NUM>, except that the core layers prepared in Preparation Examples <NUM> to <NUM> were used according to Table <NUM> below.

With respect to the molded bodies (corresponding to the core layers of the sandwich panels) prepared in Preparation Examples <NUM> to <NUM>, flexural rigidity (GPa) and flexural strength (N) were measured according to ASTM C393, and the results were shown in Table <NUM> below.

Referring to Table <NUM>, it could be seen that Preparation Examples <NUM> to <NUM>, as molded bodies containing <NUM> to <NUM> wt% of polypropylene composite fibers with respect to <NUM>% of the total weight of the molded body, had excellent mechanical properties of flexural rigidity of <NUM> GPa or more and flexural strength of <NUM> N or more. In particular, it could be seen that the molded body of Preparation Example <NUM>, as a molded body containing <NUM> wt% of a polypropylene composite fiber with respect to <NUM>% of the total weight of the molded body, had excellent mechanical properties of flexural rigidity of <NUM> GPa or more and flexural strength of <NUM> N or more.

On the other hand, as a result of comparing measurement values of flexural rigidity and flexural strength in 'Preparation Examples <NUM> and <NUM>', 'Preparation Examples <NUM> and <NUM>', and 'Preparation Examples <NUM> and <NUM>', which were the molded bodies containing the same wt% of a polypropylene composite fiber or a polypropylene fiber with respect to the total weight of the molded body, it could be confirmed that when the polypropylene composite fiber was included, the mechanical properties of the molded bodies were better than those when the polypropylene fiber was included due to high compatibility with the polyethylene terephthalate (PET) fiber.

In addition, in a maleic anhydride polyolefin structure included in the polypropylene composite fiber included in the molded body, it could be seen that Preparation Example <NUM>, in which a polymer grafted with maleic anhydride was a PP homopolymer, had better mechanical properties of flexural rigidity and flexural strength than Preparation Example <NUM> using a PP/PE block copolymer, even if the weight ratio of mixing with the polyethylene terephthalate (PET) fiber was the same. Through this, it could be seen that the flexural rigidity and flexural strength of the molded body were improved as the physical properties of a matrix were increased by copolymerizing polypropylene serving as a binder and a matrix as a homopolymer without additives.

The thicknesses and weights of the sandwich panels manufactured in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were measured, and the results were shown in Table <NUM> below.

After the sandwich panels manufactured in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were prepared as specimens, flexural rigidity and flexural strength were measured according to ASTM C393, and the results were shown in Table <NUM> below.

Referring to Table <NUM>, it could be seen that Examples <NUM> to <NUM>, as sandwich panels containing <NUM> to <NUM> wt% of polypropylene composite fibers with respect to <NUM>% of the total weight of the core material, had excellent mechanical properties of flexural rigidity of <NUM> GPa or more and flexural strength of <NUM>,<NUM> N or more. In particular, Example <NUM> including <NUM> wt% of the polypropylene composite fiber had the best mechanical properties of flexural rigidity of <NUM> GPa or more and flexural strength of <NUM>,<NUM> N or more.

On the other hand, through comparison of results of measuring flexural rigidity and flexural strength in 'Example <NUM> and Comparative Example <NUM>', 'Example <NUM> and Comparative Example <NUM>', and 'Example <NUM> and Comparative Example <NUM>', including the same wt% of the polypropylene composite fiber or the polypropylene fiber with respect to the total weight of the core material, it could be confirmed that when the polypropylene composite fiber was included, the mechanical properties of the sandwich panel were better than those when the polypropylene fiber was included due to high compatibility with the polyethylene terephthalate (PET) fiber. Even through comparison of <FIG> and <NUM> showing SEM images of Example <NUM> and Comparative Example <NUM>, it could be seen that the polypropylene composite fiber had better compatibility with the polyethylene terephthalate fiber than the polypropylene fiber.

In addition, in Example <NUM> of preparing maleic anhydride polyolefin by grafting the 'polypropylene homopolymer' with maleic anhydride, as compared with Comparative Example <NUM> of grafting a 'polypropylene/polyethylene block copolymer' instead of a homopolymer with maleic anhydride, it could be seen that since the molded body prepared by copolymerizing polypropylene serving as a binder and a matrix as a homopolymer without additives was included as a core material, mechanical properties in flexural rigidity and flexural strength of the sandwich panel were excellent.

Claim 1:
A molded body having a non-woven fiber aggregate structure comprising two or more non-woven fiber aggregates, comprising:
a polyester-based fiber and a polypropylene composite fiber,
wherein the polypropylene composite fiber comprises polypropylene; and maleic anhydride polyolefin,
wherein the maleic anhydride polyolefin is grafted with polyolefin and maleic anhydride; and
wherein the polyolefin is polypropylene having a homopolymer structure.