KR20180115913A - Method of manufacturing molded foam - Google Patents

Abstract

Provided is a method of manufacturing molded foam, which comprises the following steps of: providing a mixture of base resin containing an ethylene single polymer or an ethylene copolymer and a foaming agent; inputting the mixture into an extruder to extrude the mixture in a cylinder of the extruder to foam; obtaining a foaming pellet by cutting the foaming extruded object obtained through extruding; inputting the foaming pellet into a mold to be molded; and removing a molded object from the mold.

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing molded foam,

TECHNICAL FIELD [0002] The present invention relates to a method for manufacturing a molded foam, and more particularly, to a method for manufacturing a new shaped foam having a simple process and excellent cost competitiveness.

Generally, plastic foams made of plastic are made by the following methods.

First, there is a method of injecting a plastic raw material containing a foaming agent into a hopper of a plastic injection machine and injecting the plastic raw material by simply injecting the plastic raw material into a cooled mold or by widening a cavity of the mold at a constant speed.

Second, there is a method to inject the plastic material in the plastic injection molding machine to a portion of a cylinder is installed a gas injection hole hopper and the injection, while injection to the cooled mold were injected into the gas injection hole supercritical carbon dioxide (supercritical CO ₂ gas) .

Third, there is a method in which a liquid resin such as a polyurethane foam is mixed with a foaming agent in a high-speed mixer to form a foam, injected into a mold, and cured at a temperature or room temperature.

Fourth, a method for making a bead foam by using a bead foam material as in the case of expanded polystyrene (EPS), expanded polypropylene (EPP), and expanded polyethylene (EPE) ), Put it in a high-pressure tank filled with a certain amount of inert gas, pressurize the inert gas into the mini pellet of the resin by applying a high pressure, and then transfer the inert gas from the machine equipped with the steam chest mold When the pellet is injected and the steam and the air pressure are simultaneously applied, the surface of the mini pellet is simultaneously heated and the inert gas expands and the mini pellet is foamed to fill the mold cavity. After that, steam and air are taken out and cooling air is injected to cool the product and demold it.

The first method has not been used in recent years because it can not breathe much and can only bubble at 10-20%, the internal cell structure is irregular, and the physical properties are not constant.

In the second method, the cell structure of the foamed material is uniform and the appearance is good, but it is difficult to make a product having a density of less than 0.5 g / cc because there is a limit to increase the expansion ratio.

The third method is to produce a product which is easy to produce and has homogeneous physical properties, but its weatherability is so weak that it can not be used outdoors, and hydrolysis is severe, so the physical properties are rapidly deteriorated in the presence of water, It is difficult to make high hardness products because of low strength.

The fourth method, ie, the bead foam, is low cost and easy to manufacture, and is used for various purposes such as packaging. However, since the material is easily broken, it is shattered during handling and causes pollution. Especially, when used for oyster cultivation, And waves, which severely pollute the sea and the surrounding coasts. EPP is used as a shock absorbing material for automobile bumpers, motorcycle helmets, etc. It is hard to mold, expensive, hardened, and soft and elastic. Since EPE has a low hardness of polyethylene and inert gas is trapped in the resin and is not stored for a long time, it is difficult to obtain a product having a high expansion ratio and it is difficult to maintain the uniformity of the product according to the state of gas storage. EPE of LLDPE or HDPE, which has higher hardness than LDPE, is actually produced. This bead foam has many risk factors such as handling of high-pressure gas, so that the supply of beads is supplied in large quantities in large-scale factories, and it is difficult to make products of various materials and various properties because it can not use materials directly from small businesses.

According to an aspect of the present invention, there is provided a method for producing a foamed article, comprising the steps of: providing a mixture of a foaming agent and a base resin containing an ethylene homopolymer or an ethylene copolymer; Introducing the mixture into an extruder, extruding and foaming the mixture in a cylinder of the extruder; Cutting the foamed extrudate obtained through the extrusion processing to obtain a foamed pellet; Molding the foamed pellets into a mold to form the foamed pellets; And a step of demolding the molded product from the mold.

According to another aspect of the present invention, there is provided a molded foam produced by the above manufacturing method.

According to another aspect of the present invention, there is provided a pellet for the production of a shaped foam produced by extruding and foaming a mixture containing a base resin containing an ethylene homopolymer or an ethylene copolymer and a blowing agent, wherein the pellet has a diameter of from 1.0 to 20 mm and a specific gravity of 0.25 or less.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow diagram of a method of manufacturing a shaped foam according to an embodiment of the present invention. FIG.
FIG. 2 is a view showing a process for manufacturing a culture port using a foam pellet.
3 is a view showing a process of manufacturing a foam for a car seat.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which: Fig.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow diagram of a method of manufacturing a shaped foam according to an embodiment of the present invention. FIG. Referring to Figure 1, in step S1, a mixture of a base resin containing an ethylene homopolymer or an ethylene copolymer and a blowing agent is provided.

The ethylene homopolymer may be, for example, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE) and the like.

Wherein said ethylene copolymer is selected from the group consisting of i) ethylene, and ii) a C3 to C10 alpha olefin, a C1 to C12 alkyl ester of an unsaturated C3 to C20 monocarboxylic acid, an unsaturated C3 to C20 mono or dicarboxylic acid, an anhydride of an unsaturated C4 to C8 dicarboxylic acid, A vinyl ester of a C2-C18 carboxylic acid, or an ionomer of the copolymer.

In the ethylene copolymer, ethylene preferably accounts for a major mole fraction of the whole polymer, and ethylene generally accounts for at least about 50 mole% of the total polymer. More preferably, ethylene accounts for at least about 60 mole percent, at least about 70 mole percent, or at least about 80 mole percent.

Preferably, in view of the high elasticity, the ethylene copolymer is a copolymer of ethylene and an alpha olefin. Wherein the alpha olefin is an olefin having 3 or more carbon atoms and having a double bond at the terminal. The substantial remainder, excluding ethylene, in the total ethylene alpha olefin copolymer preferably comprises one or more other comonomers which are alpha olefins having three or more carbon atoms. In particular, the alpha olefin is preferably butene, hexene or octene in view of commercialization and availability. For example, in the case of ethylene octene copolymers, preferred compositions comprise an ethylene content of at least about 80 mole percent of the total polymer, and an octene content of from about 10 to about 15 mole percent, preferably from about 15 to about 20 mole percent, of the total polymer .

The ethylene and alpha olefin copolymers may be random copolymers or block copolymers. Commercial products include Engage and Infuse of Dow Chemical, Tafmer of Mitsui, Exact Mobile of Exxon Mobile, and LG-POE of LG Chemical. In particular, a random copolymer of ethylene and alpha olefin is preferable for the low-cost process of the present invention Do. In the case of the ethylene random copolymer, the ethylene content may be from about 60 mol% to about 99.5 mol%, in some embodiments from about 80 mol% to about 99 mol%, and in some embodiments from about 85 mol% to about 98 mol% have. Likewise, the alpha-olefin content may range from about 0.5 mol% to about 40 mol%, in some embodiments from about 1 mol% to about 20 mol%, and in some embodiments from about 2 mol% to about 15 mol%. The distribution of the -olefin comonomers is typically random and uniform over different molecular weight fractions forming the ethylene copolymer.

Specific examples of the ethylene copolymer include ethylene vinyl acetate, EVA copolymer, ethylene butyl acrylate (EBA) copolymer, ethylene methyl acrylate (EMA) copolymer, ethylene ethyl acrylate Ethylene Ethyl Acrylate (EEA) copolymer, Ethylene Methylmethacrylate (EMMA) copolymer, Ethylene Butene Copolymer (EB-Co) and Ethylene Octene Copolymer (EO -Co), and the like.

The ethylene homopolymer or the ethylene copolymer as the base resin may be appropriately selected according to the use of the molding foam. For example, when the molding foam is a culture bag, a suitable base resin may be a low-density polyethylene in terms of price. For example, if the shaped foam is a foam for a car seat, the base resin may be a blend of a low density polyethylene and an ethylene octene copolymer for resilience and shock absorption. Also, for example, if the shaped foam is a swimming aid for swimming, the base resin may be linear low density polyethylene in terms of price and buoyancy. Also, for example, if the molded foam is a bicycle helmet, it may be a blend of EVA and ethylene octene copolymers for shock absorption and softness.

In addition, the base resin may be blended with two or more different ethylene homopolymers or ethylene copolymers, if necessary, and may be blended with each other. Depending on the melt index (MI) of each component, the content ratio of the components and the polarity of each component, Can affect the physical properties of the polymer.

For example, if a resin having an excessively high melt index is contained as the base resin, the mixture may be too tacky immediately after passing through the extrusion die, resulting in poor cutting of the extrudate, resulting in poor workability of the pellets. When an ethylene-octene copolymer, which is a non-polar polyethylene elastomer, is blended with polar ethylene vinyl acetate as a base resin, the adhesive strength with other materials can be controlled depending on the content thereof.

In addition, the raw material composition for making the various shaped foam products also includes any known foaming agent (also known as bubbling agent or swelling agent), including gaseous materials that are broken down into gases and other by-products, volatile liquids and chemical agents . The foaming agent is added to the base resin in order to produce a foam with a cell by generating gas under a certain temperature and pressure time. By forming such a foam, light weight of the foam, cushioning property, and cost reduction can be achieved .

The blowing agent may include a physical blowing agent or a chemical blowing agent alone or in combination. The physical blowing agent (PBA) forms cells by phase change such as liquid volatilization or decomposition of gas, and has the advantages of non-toxic, odorless, thermal stability, low cost and solid residue remained but disadvantages .

Examples of useful physical blowing agents include inorganic blowing agents and organic blowing agents. Suitable physical blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen and helium. Organic foaming agents include C _1-9 aliphatic hydrocarbons, C _1-3 aliphatic alcohols, and C _1-4 halogenated aliphatic hydrocarbons. The aliphatic hydrocarbon includes methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane and the like. The aliphatic alcohols include methanol, ethanol, n-propanol and isopropanol. The halogenated aliphatic hydrocarbon includes fluorocarbon, chlorocarbon, and chlorofluorocarbon. Specific examples of the fluorocarbon include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC- 1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoromethane (HFC-134), pentafluoroethane, difluoromethane, perfluoroethane, 2 , 2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, and perfluorocyclobutane. Specific examples of halogenated aliphatic hydrocarbons include partially halogenated aliphatic hydrocarbons such as methyl chloride, methylene chloride, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1-fluoroethane (HCFC- 141b), 1-chloro-1,1-difluoroethane (HCFC-142b), chlorodifluoromethane (HCFC-22), 1,1-dichloro-2,2,2-trifluoroethane -123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Specific examples of fully halogenated aliphatic hydrocarbons in halogenated aliphatic hydrocarbons include trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113) , 1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane and dichlorohexafluoropropane.

Chemical blowing agents (CBA) generate gases by chemical reactions such as pyrolysis or component reactions to form cells. These gases are usually N ₂ and CO ₂ and they behave like physical blowing agents but carry residues from the decomposition process. Chemical foaming agents are classified as exothermic CBA and endothermic CBA. Pyrogenic CBA generates heat during decomposition and the main decomposition gas is N ₂ . On the other hand, endothermic CBA absorbs heat during the decomposition process and the main decomposition gas is CO ₂ .

It is important to select the appropriate chemical blowing agent in plastic foaming. The first problem to consider for this is the first decomposition temperature. If the decomposition temperature is too high, the low molecular weight melt strength at the foaming temperature is lowered, so that it is not strong enough to maintain the bubble structure or to prevent cell aggregation. If the decomposition temperature is too low, the polymer melt becomes rigid and the foam expansion is suppressed. Another problem is that CBA decomposition residues and gases are compatible with polymers and processing systems.

The chemical blowing agent may be selected from the group consisting of azodicarbonamide (ADCA), azadiisobutyronitrile, benzene sulfone hydrazide, 4,4-oxybenzenesulfonyl semicarbazide, p-toluenesulfonyl semi- (DPT), p, p'-oxybisbenzenesulfonylhydrazide (OBSH), and N, N'-dimethyl-N, N'- dinitrosoterephthalamide, Azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluenesulfonyl semicarbazide, barium azodicarboxylate, and trihydrazinotriazine But are not limited thereto. Preferably, the foaming agent may be an azo-based compound having a decomposition temperature of 130 to 210 ° C. In general, when ADCA is pyrolyzed, the gas is generated at a high rate and the amount of gas generated is large. Since self-extinguishing and non-toxic, to be. Considering the specific gravity of the foamed pellets and the pellet processing step for preparing the molded foam, the decomposition temperature of the suitable foaming agent may be 130 to 170 ° C. If necessary, a kicker may be used to activate the foaming agent by lowering the foaming temperature of the chemical foaming agent. Examples of the kicker include polyols, urea, amines, salts, and metal compounds such as lead, zinc and cadmium And pigments and fillers usually play this role.

When the foaming agent is a physical foaming agent, the foaming agent is preferably used in an amount of 0.1 to 5 grams based on 1 kg of the base resin. When the foaming agent is a chemical foaming agent, the foaming agent is preferably used in an amount of 0.1 to 6 parts by weight based on 100 parts by weight of the base resin. If the amount is less than the above range, the specific gravity can be greatly increased and the hardness can be excessively high. If the amount is over the above range, the specific gravity is lowered and the strength of the product may be lowered. If the decomposition temperature is less than 150 ° C, early foaming occurs during compound production. If it exceeds 210 ° C, it is difficult to decompose in the extruder. If the temperature of the extruder cylinder is increased to increase the decomposition temperature, It may be difficult to form the foam.

According to one embodiment, the base resin used for forming foams may further comprise a synthetic rubber. Meanwhile, the synthetic rubber may be added to improve the elasticity and strength of the final product, and may be included in an amount of 5 to 30 parts by weight based on 100 parts by weight of the base resin.

The synthetic rubber may be at least one selected from the group consisting of styrene butadiene rubber (SBR), modified styrene butadiene rubber, butadiene rubber (BR), modified butadiene rubber, chlorosulfonated polyethylene rubber, epichlorohydrin rubber, fluorine rubber, silicone rubber, (NBR), modified nitrile butadiene rubber, chlorinated polyethylene rubber, styrene butadiene styrene rubber (SBS), styrene ethylene butylene styrene (SEBS) rubber, styrene isoprene styrene rubber (SIS), ethylene propylene rubber, ethylene propylene (EPDM) rubber, hyaluron rubber, chloroprene rubber, ethylene vinyl acetate rubber, acrylic rubber, hydrin rubber, vinyl benzyl chloride styrene butadiene rubber, bromomethyl styrene butyl rubber, maleic styrene butadiene rubber, carboxylic styrene butadiene rubber , Epoxy isoprene rubber, maleic acid Ethylene propylene rubber, carboxylic acid nitrile-butadiene rubber, brominated polyisobutyl isoprene-co-consisting of para-methylstyrene (brominated polyisobutyl isoprene-co-paramethyl styrene, BIMS), and combinations thereof may be any one selected from the group.

In some embodiments, the composition for making the shaped foam may include a silane coupling agent. The silane coupling agent may be used for reinforcing tensile strength and adhesion strength. The silane coupling agent is present in the composition and is subjected to a grafting reaction with the ethylene copolymer by a radical initiator contained in the composition to allow the crosslinking reaction to proceed in the presence of water. Due to the silane coupling agent present in a mixed state in the composition, the raw material in which the composition is subsequently pelletized can be crosslinked by heating in water. Also, if the composition is pelletized and then left as it is, it is possible to cause moisture in the atmosphere to cause natural crosslinking with passage of time.

The silane coupling agent is chemically bonded to the base resin to form a silane graft copolymer and functions as a functional group for crosslinking the pelletized extrudate. The silane coupling agent may have the form of an alkoxysilane compound. Examples of the alkoxysilane compound include vinyltrimethoxysilane, vinyltriethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, methyltriethoxysilane, methyltrimethoxysilane, methyltri (2-methoxy 3-methacryloyloxypropyl-trimethoxysilane, 3-mercaptopropyl-trimethoxysilane, 3-aminopropyl-triethoxysilane, 3-aminopropyl-trimethoxysilane, 3-glycidyloxypropyl-trimethoxysilane and the like can be used. These silane coupling agents may be used alone or in combination of two or more. The degree of crosslinking can be controlled by the amount of the silane coupling agent in the composition.

In the composition for use in the method for producing a shaped foam of the present invention, the content of the silane coupling agent is 0.5 to 5 parts by weight, preferably 0.8 to 3 parts by weight, more preferably 1 To 2 parts by weight. If the content of the silane coupling agent is less than the above range, the effect of crosslinking may be small. If the content is above the range, the crosslinking density may not rise to some extent and the cost may be increased.

A radical polymerization initiator may be contained in the composition to constitute the silane graft copolymer. The radical polymerization initiator chemically grafts the base resin and the silane coupling agent, wherein the radical polymerization initiator is at least one selected from the group consisting of t-butyl cumyl peroxide, benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, t -Butyl peroxybenzoate, t-butyl peroxy isopropyl carbonate, t-butyl peroxylaurate, t-butyl peroxyacetate, di-t-butyl peroxyphthalate, t- , T-butyl hydroperoxide, t-butyl hydroperoxide, 1,3-bis (t-butylperoxyisopropyl) benzene, methyl ethyl ketone peroxide, 2,5- 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butyl peroxide, 2,5- Butylperoxy) -3-hexane, n-butyl-4,4-bis (t-butylperoxy) valerate, Benzene or a mixture thereof may be used. The radical polymerization initiator may be contained in the base resin in an amount of 0.02 to 4 parts by weight based on 100 parts by weight of the base resin.

If desired, a catalyst may be further added to the composition to shorten the number of times in the grafting step. Examples of the catalyst used herein include dibutyl tin dilaurate, dibutyl tin dimaleate, dibutyl tin diacetate, dibutyl tin dilaurate, dioctyl tin maleate, dibutyl tin diacetate, dibutyl tin dioctoate, tetrabutyl Titanate, hexylamine, dibutylamine acetic acid, ferric tin, ferric tin octoate, lead naphthenate, zinc caprylate, cobalt naphthenate, and the like.

The catalyst may be contained in an amount of 0.05 to 1 part by weight, preferably 0.1 to 0.7 part by weight based on 100 parts by weight of the base resin. When the content of the catalyst is less than the above range, the crosslinking rate is low and a lot of energy and time are required. When the amount of the catalyst is less than the above range, the crosslinking rate may not be further accelerated.

The composition according to an embodiment of the present invention may further include a crosslinking agent. The crosslinking agent may be used in an amount of 0.01 to 0.5 parts by weight, preferably 0.02 to 0.25 parts by weight, based on 100 parts by weight of the base resin, of an organic peroxide crosslinking agent capable of sufficiently collecting decomposed gas generated in the foaming agent and imparting high temperature viscoelasticity to the resin . As the amount of the cross-linking agent increases, high temperature viscoelasticity is exhibited and extrusion foaming is facilitated. However, when the amount exceeds the above range, foaming can not occur due to cross-linking and the foam pellets may become heavy pellets.

Examples of such crosslinking agents include organic peroxide crosslinking agents which are frequently used in rubber compounding, such as t-butyl peroxyisopropyl carbonate, t-butyl peroxylylate, t-butyl peroxyacetate, di-t-butyl peroxyphthalate butyl dicumyl peroxide, dicumyl peroxide, 1,3-bis (t-butylperoxy) propyl peroxide, t-butyl dicumyl peroxide, t-butyl dicumyl peroxide, Dimethyl-2,5-di (t-butylperoxy) hexane, di (2,5-dimethylbenzyloxy) (t-butylperoxy) valerate, a, t-butylperoxide, 2,5-dimethyl- bis (t-butylperoxy) diisopropylbenzene, and the like.

The composition may further contain one or more selected from the group consisting of metal oxides, stearic acid, antioxidants, zinc stearate, titanium dioxide, a crosslinking assistant, and a filler, which are commonly used in the production of foams for improving the properties of the foam, Other additives may be further included.

The additive may be added in an amount of 4 to 15 parts by weight based on 100 parts by weight of the base resin. As the metal oxide, zinc oxide, titanium oxide, cadmium oxide, magnesium oxide, silver oxide, tin oxide, lead oxide, calcium oxide, etc. may be used for improving the physical properties of the foam, and 1 to 4 wt. Can be used.

Stearic acid and Zinc stearate may be used in a fine and uniform manner to form a foamed cell and facilitate demolding during foaming and may be generally used in an amount of 1 to 4 parts by weight based on 100 parts by weight of the base resin. Sonnoc, butylated hydroxy toluene (BHT), octadecyl 3,5-di-tert-butyl-hydroxyhydrocinnamate and the like are used as the antioxidant. Usually 0.25 to 2 parts by weight based on 100 parts by weight of the resin. Titanium dioxide is used as a white pigment and has the same function as the above-mentioned metal oxide, and usually 2 to 5 parts by weight can be used.

Fillers that may be included in the composition serve to lower the cost of the composition. Examples of the filler include silica (SiO ₂ ), MgCO ₃ , CaCO ₃ , talc, Al (OH) ₃ and Mg (OH) ₂ , Can be used.

The base resin and the foaming agent are essentially included as raw materials to be used for the production of the molded foam and, if necessary, include components such as synthetic rubber, silane coupling agent, and crosslinking agent. Each component is formed using a kneading machine such as an open roll or kneader mixer. Using the kneader, the components are kneaded at a temperature of, for example, 130 to 160 ° C and discharged at a temperature of 140 to 170 ° C.

The mixture has a melt index (MI) of 0.01 to 6.8 g / 10 min, preferably 0.1 to 6.0 g / 10 min, more preferably 0.5 to 5.0 g / 10 min as measured by ASTM D1238 (190 캜, 2.16 kg) 10 minutes is good. When the MI (190 DEG C, 2.16 kg) of the final mixed composition is less than the above range, too high a pressure is applied to the extruder and the risk of breakage of the machine is high and the extrusion amount is too small, If the MI (190 DEG C, 2.16 kg) is in the above range, the viscosity of the mixture exiting the die of the extruder is low, so that the viscosity of the mixture may become too high after passing through the extrusion die. In this case, the pelletizing operation may be difficult because the extrudate is not easily cut. Further, if the viscosity of the melt passing through the extrusion die is too low, the force for collecting the foamed gas is weak, so that the pellets are shrunk, so that the foaming may not be achieved for the desired purpose.

Referring back to FIG. 1, in step S2, a mixture containing the base resin and the foaming agent is put into an extruder, and the mixture is extruded and foamed in a cylinder of the extruder.

The extrusion process can be performed using various extruders including a Buss kneader, a single screw extruder, or a twin screw extruder. Various products can be produced by changing the process conditions such as the screw configuration of the extruder, the set temperature, the screw rotation speed, and the extrusion amount.

The mixture injected through the hopper of the extruder is conveyed by the screw and melted and mixed in the cylinder of the extruder.

It is preferable that the temperature of the cylinder is controlled at a temperature above the decomposition temperature of the foaming agent, because the mixture can be melted to have appropriate flowability. However, if the temperature of the cylinder is too high, the viscosity of the mixture may be lowered and the gas in the mixture may be released, making it difficult to cut the extrudate at a later time. As a result, the specific gravity of the pellets may increase, or the pellet processability may deteriorate.

 The temperature of the cylinder may be in the range of 150 to 180 ° C. The screw rotation speed and the extrusion amount can be suitably controlled in accordance with the specific gravity and shape of the foam pellets produced by foaming. .

During the extrusion process, gas is generated by decomposition or volatilization of the foaming agent contained in the mixture to form a foamed body with cells, and the foamed extrudate is conveyed through screw rotation to the die of the extruder It comes out. The size and shape of the cross section of the extrudate may be determined according to the size and shape of the die hole, and is not particularly limited, but typically has a size of 1.0 to 10 mm and may be circular or elliptical.

In step S3, the foamed extrudate obtained through the extrusion processing is cut to obtain foamed pellets. The extrudate can be cut with a face cutter, and can be cut with a cutter, such as a face cutter, preferably with a cooling device, to easily cut into a cooled state. As a result, pellets having a diameter of 1.0 to 20 mm and a thickness of 1.0 to 20 mm can be produced.

The cells distributed in the foamed pellets generally have a relatively small average cell size, typically an average cell size of about 2.0 mm or less. The average cell size can be measured, for example, according to ASTM D3576-77. In one embodiment, the foamed pellets may have an average cell size of from about 0.01 to about 1.5 mm. When the cell size is within the above range, the molded product produced by molding the pellets in a mold may have rebound resilience suitable for a conventional molded foam product.

The foamed pellets may also generally have a large amount of closed cells and a small amount of open cells. The relative amount of closed cells can be measured, for example, according to ASTM D2856-A. In one embodiment, about 80% or more of the foamed cells of the foamed pellets may be composed of closed cells. In another embodiment, at least about 85% of the foamed cells of the foamed pellet are comprised of closed cells. In a preferred embodiment, at least about 90% of the foamed cells of the foamed pellets are closed cells. In a more preferred embodiment, at least about 95% of the cells of the foamed pellet are closed cells. If the closed cells of the foamed cells in the foamed pellets are 80% or more, they may have a repulsive elasticity suitable for the molded foam product.

On the other hand, the specific gravity of the foamed pellets is preferably controlled to 0.25 or less, preferably 0.20 or less, more preferably 0.15 or less. The lower limit of the specific gravity of the foamed pellets may be 0.05 or more. If the specific gravity of the foamed pellets is too high, the molded foam product becomes heavy and the product value may be lowered. If the specific gravity of the foamed pellet is too low, the molded product may not meet the required physical properties. The specific gravity of the foamed pellets may depend on the decomposition temperature of the foaming agent of the mixture (polymer compound). For example, when a foaming agent having a decomposition temperature too high is used, the polymer compound is not sufficiently foamed during processing, Can be increased.

In step S4, the foamed pellets are put into a mold to be molded.

The manufacturing method according to one embodiment of the present invention is performed by injecting foamed pellets into a mold, and molding of the foamed pellets can be performed in such a manner that the foamed pellets are pressed in the mold at elevated temperatures and cooling conditions.

The process of processing in the mold can be carried out in various ways, and the foamed pellets can be molded by a method of putting them in a heated mold and pressing them, or the foamed pellets are put into a cooled mold, . Heating and pressurization in one product molding process can be performed several times under different temperature conditions. In one embodiment, the foamed pellets are first warmed and pressed at elevated temperatures to facilitate transfer of heat to the interior of the expanded pellets so that they are fully plasticized to facilitate deformation, plasticized, and pressed to form a deformed mixture The product can be obtained by demolding after cooling to the softening point or lower of the mixture. Specifically, molding using a mold can be carried out, for example, in the following manner. First, the amount of the foamed pellets is 1.5 to 2 times as large as the volume of the mold, and the pellets are heated at 150 to 170 DEG C for 10 to 20 minutes and pressurized. Next, after warming to 15 to 30 ° C, pressurize the product for 10 to 20 minutes to mold the product.

Then, the molded article is demolded from the mold in step S5. After the previous pressurizing process, the mold is transferred to a cooling press to cool the product, cooled for 10 to 20 minutes, the mold is opened, and the molded product is taken out to obtain a finished molded foam product.

Depending on the type of the shaped foam product, the specific gravity of a suitable shaped foam product that is normally required is from 0.1 to 0.5, preferably from 0.1 to 0.3. The hardness (Asker C) of a suitable molded foam may also be about 30 to 70, preferably about 50 to 60. [

According to the above-described method for producing a molded foam, a molded foam is produced by using a foamed pellet obtained by extruding a polymer compound in which a base resin essentially containing an ethylene homopolymer or an ethylene copolymer is mixed with a foaming agent .

Molded foam products made by this manufacturing method can easily produce products with a density of less than 0.5 g / cc, and generally have a closed cell (closed cell) structure, making it easy to produce high-hardness products with high compressive strength. Also, the material loss is small, and the appearance of the product is good. In addition, the pellets are excellent in dimensional stability and surface condition as compared with a method of directly foaming pellets in a mold. In the case of the present production method, it is possible to manufacture a molded foam having a very high surface strength according to the degree of heating and pressing in a heating and pressing process as a new method which is not existing at all. In addition, since the pellets are continuously produced by the extrusion method, the process is simple and the cost is considerably low, and the mixture of the various compositions can be easily tried in the extrusion pellet process, which is suitable for small quantity production of various kinds.

Hereinafter, the techniques disclosed in this specification will be described in detail with reference to various embodiments, but the technical idea of the technology disclosed in this specification is not limited by the following embodiments.

<Examples>

1) Preparation of pellets using a chemical blowing agent: A mixture prepared by mixing the composition of the examples and comparative examples containing the following chemical blowing agent in a Henshel mixer into a hopper of a co-rotational twin screw extruder of L / D 36 , Extruded at a cylinder temperature of 180 ° C and cut with a face cutter equipped with a cooling device to obtain a foam pellet having a diameter of 3 mm.

2) Production method of pellet using physical foaming agent: A single screw extruder hopper equipped with L / D 55 and gas injected from the high-pressure pump for gas injection into the cylinder of the extruder is compared with the embodiment including the following physical foaming agent A mixture obtained by mixing the exemplified composition in a Henshel mixer was charged and extruded at a cylinder temperature of 180 캜 while injecting a physical foaming agent and then cut into a face cutter equipped with a cooling device to obtain a foam pellet having a diameter of 3 mm.

3) Preparation of uncrosslinked foam: 200 g of the pellet obtained by using the chemical foaming agent or the physical foaming agent was poured into a lower plate of a mold having a volume of 2.5 cm x 20 cm x 20 cm. Next, the upper plate of the mold having the compression part of the piston shape was covered on the lower plate, and the plate was put in a press and heated and pressed at 150 DEG C for 20 minutes. The mold was then transferred to a cooling press at 20 ° C and cooled for 15 minutes. The mold was opened and a 2.5 cm x 20 cm x 20 cm volume forming foam was taken out.

4) Preparation of Crosslinked Molded Foam: 200 g of the pellet obtained by using the above chemical blowing agent, physical foaming agent, silane coupling agent, peroxide polymerization initiator and DBTDL (Dibutyltin dilaurate) was placed on a lower plate of a mold having a volume of 2.5 cm x 20 cm x 20 cm Poured. Next, the upper plate of the mold having the compression part of the piston shape was covered on the lower plate, and the plate was put in a press and heated and pressed at 150 DEG C for 20 minutes. The mold was then transferred to a cooling press at 20 ° C and cooled for 15 minutes. The mold was opened and a 2.5 cm x 20 cm x 20 cm volume forming foam was taken out. Next, the crosslinking molding foam was obtained by proceeding watering for 24 hours in a heat room at a temperature of 60 캜 and a humidity of 90%.

5) Molded foam raw material

PE-1: LDPE 5310 (specific gravity 0.923, MI 0.8): Hanhwa products

PE-2: LDPE 724 (specific gravity 0.915, MI 45): Hanwha products

POE-1: Engage 8003 (Ethylene-Octene-Copolymer, specific gravity 0.885 MI 1.0)

POE-2: Engage 8401 (Ethylene-Octene-Copolymer, specific gravity 0.885 MI 30): Dow chemical product

CFA-1: DX74M (Modified ADCA, decomposition temperature: 140 캜, gas volume: 155 cc / g)

CFA-2: DX74HP (Modified ADCA, decomposition temperature 175 캜, gas amount 172 cc / g)

PFA-1: Isobutane: GS Caltex Products

Silane-1: A-171 (Vinyltrimethoxysilane): Momentive product

The foamed pellets made from the above raw materials were used to produce molded foams, and evaluated as applied foams. The results are shown in Tables 1 and 2.

Example 1 Comparative Example 1 Comparative Example 2 Example 2 Comparative Example 3 Example 3 Comparative Example 4 PE-1 100 100 100 PE-2 100 100 POE-1 100 POE-2 100 Zincification 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Stearic acid 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Silane-1 DCP DBTDL CFA-1 3.0 3.0 3.0 3.0 CFA-2 2.5 PFA-1 #One #One MI (compound) 0.8 0.8 40 1.0 28 0.8 40 Pellet workability Good Good Bad Good Bad Good Bad Pellet shrinkage Good Good Extreme Good Extreme Good Extreme Pellet Specific Gravity g / cc 0.07 0.90 0.70 0.06 0.80 0.07 0.60 Molded foam specific gravity g / cc 0.14 0.13 0.14 Molding hardness Asker C 55 53 55 Molding Tensile Strength Kg / cm2 21 23 21 Compression Permanent String Ratio% 70 60 70 Molded foam application part possible Impossible Impossible possible Impossible possible Impossible

Example 4 Comparative Example 5 Example 5 Comparative Example 6 Example 6 Example 7 Example 8 PE-1 50 50 80 80 90 80 80 PE-2 POE-1 50 20 20 20 POE-2 50 20 10 Zincification 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Stearic acid 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Silane-1 3.0 DCP 0.1 DBTDL 0.03 CFA-1 3.0 3.0 3.0 3.0 3.0 3.0 CFA-2 PFA-1 #One Water bridge MI (compound) 0.9 13 0.9 7 3.2 0.9 1.3 Pellet workability Good Bad Good Bad Good Good Good Pellet shrinkage Good Extreme Good Severe Good Good Good Pellet Specific Gravity g / cc 0.07 0.50 0.07 0.40 0.08 0.07 0.07 Molded foam specific gravity g / cc 0.14 0.14 0.14 0.14 0.14 Molding hardness Asker C 54 55 55 55 56 Molding Tensile Strength Kg / cm2 22 21 21 21 30 Compression Permanent String Ratio% 65 67 69 67 20 Molded foam application part possible Impossible possible Impossible possible possible possible

# 1: 0.5 g-moles per kg of polymer

- Pellet workability: When pellet is extruded while cutting with a face cutter, it is good when it is cut well, and when the pellet is clipped, if it can not be cut, it is marked as bad.

- Pellet shrinkage: If the size of the foamed particles is maintained even after the pellet is cut off, it is good. When the pellets are cooled, they are shrunk and marked as severe and extreme depending on the size.

Molding Foam Tensile Strength: The molded foam was measured according to ASTM D-412 after skiving to a thickness of 3.0 mm. When the tensile strength was 20 kg / cm ² or more, it was judged to be suitable for the molding foam.

Compression Permanent Ribbon Tone: Tested according to ASTM D3575, and judged as acceptable if less than 70%.

<Manufacture of various yarn products>

1) Production of yarn product of uncrosslinked molded foam Example 3: A foamed pellet having a diameter of 3 mm was obtained from the composition of Example 1, and a piston having a compression section of 50 cm Φ × 25 cm in the upper portion and having a cavity volume of 50 cm Φ × 100 cm 13 kg of foamed pellets were poured into the lower plate of the mold for aquaculture. After covering the upper plate on the lower plate, it was put in a press and heated and pressed at 180 ° C for 30 minutes. The mold was transferred to a cooling press at 20 ° C and cooled for 20 minutes. The mold was opened and a buoy of 50 cm Φ × 100 cm was taken out. FIG. 2 is a view showing a process for manufacturing a culture port using a foam pellet.

2) Production Example of Synthetic Products of Crosslinked Molded Foam A foamed pellet having a diameter of 3 mm was obtained from the composition of Example 8, and a mold having a compression portion having a volume of 1/2 of the cavity volume was formed on the cavity of the foamed mold for automobile chair And the foam pellets were poured into the lower plate. The mold was covered with a top plate on the bottom plate and then put in a press. The mold was heated and pressed at 180 ° C for 20 minutes. The mold was transferred to a cooling press at 20 ° C and cooled for 15 minutes. The mold was opened to obtain a sheet for automobile seat. A 24-hour water flow was conducted in the heat room to obtain a foam for a water-feeding car seat. 3 is a view showing a process of manufacturing a foam for a car seat.

Claims (11)

Providing a mixture of a blowing agent and a base resin containing an ethylene homopolymer or an ethylene copolymer;
Introducing the mixture into an extruder, extruding and foaming the mixture in a cylinder of the extruder;
Cutting the foamed extrudate obtained through the extrusion processing to obtain a foamed pellet;
Molding the foamed pellets into a mold to form the foamed pellets; And
And releasing the molded product from the mold. The method according to claim 1,
Wherein the mixture further comprises a silane coupling agent. The method according to claim 1,
Wherein the foaming agent comprises a physical foaming agent or a chemical foaming agent singly or in combination. The method according to claim 1,
Wherein the mixture has a melt index (MI, 190 占 폚, 2.16 kg) of 0.01 to 6.8 g / 10 min as measured according to ASTM D1238. The method according to claim 1,
Wherein the foaming agent is a chemical foaming agent, and the extrusion processing is performed at a decomposition temperature or higher of the chemical foaming agent. The method according to claim 1,
Wherein the average cell size distributed in the foamed pellets is 2.0 mm or less. The method according to claim 1,
Wherein the foamed pellets have a specific gravity of 0.25 or less. The method according to claim 1,
Wherein the molding of the foamed pellets is carried out in such a manner that the mold is pressurized under the temperature elevating and cooling conditions in the mold. The method according to claim 1,
Wherein the molded foam has a specific gravity of 0.1 to 0.3 and a hardness (Asker C) of 30 to 70. [ A molded foam produced by the method according to any one of claims 1 to 9. A pellet for the production of a molded foam, which is produced by extruding and foaming a mixture containing a base resin containing an ethylene homopolymer or an ethylene copolymer and a blowing agent,
Wherein the foamed pellets have a diameter of 1.0 to 20 mm and a specific gravity of 0.25 or less.

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