JP2011006626A - Polyethylene open-cell foam and process for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene open-cell foam of high expansion ratio, obtained by extrusion foaming a specific ethylene-based polymer with carbon dioxide which is a clean foaming agent, and to provide a production process therefor.SOLUTION: A polyethylene open-cell foam with 4-30 times expansion ratio and ≥90% open cell ratio, which includes an ethylene-based polymer having a density (d) of 935 kg/mor more, is used.

Description

  The present invention relates to a polyethylene open cell foam. More specifically, the present invention relates to a polyethylene foam having a high expansion ratio obtained by extrusion foaming a specific ethylene polymer with carbon dioxide gas, which is a clean foaming agent, and a production method.

  Polyethylene resin foams are widely used mainly for cushioning materials, cushioning materials, shock absorbing materials and the like. However, since foams obtained from polyethylene resin are generally closed cell foams, they have poor buffering properties compared to open cell foams such as polyurethane foams and soft vinyl chloride resin foams. It was.

  As a method of obtaining a polyethylene-based open cell foam, (1) a method of mechanically deforming a closed-cell foam obtained from a crosslinkable polyethylene-based resin to make the bubbles continuous (for example, see Patent Document 1), (2) A method in which 70 to 97% by weight of a low density polyethylene resin and 3 to 30% by weight of a linear low density polyethylene are mixed and foamed is proposed (for example, see Patent Document 2).

  By the way, conventionally, in order to obtain a foam having a high expansion ratio with a polyethylene-based resin, an organic gas or volatile liquid such as butane, pentane, or dichlorodifluoromethane (Freon R-12) has been used as a foaming agent. . However, when the blowing agent used is a low-boiling organic substance such as butane or pentane, an explosive gas is generated during the production of the foam, which may cause an explosion. In addition, when the blowing agent used is dichlorodifluoromethane (Freon R-12), there is little risk of explosion and it is easy to obtain a foam with a high expansion ratio. Is moving in the direction of total abolition. In order to solve the above problems, (3) a method of extruding a low density polyethylene resin using an inorganic foaming gas such as carbon dioxide or argon as a foaming agent (see, for example, Patent Document 3), (4) low A method in which a high density polyethylene resin is heated in the presence of a radical generator, or carbon dioxide gas is mixed and extruded into a modified low density polyethylene resin obtained by modifying the resin by irradiation (see, for example, Patent Document 4) Etc. have been proposed.

  In addition, the present applicant has previously found that a polyethylene extruded foam can be provided by extrusion foaming an ethylene polymer satisfying the specific requirements (5) and (6).

JP 2001-164020 A JP 2006-131895 A Japanese National Patent Publication No. 10-500151 JP 2002-331666 A JP 2006-096910 A JP 2002-199872 A

  In the method of Patent Documents 1 and 2 proposed for obtaining a polyethylene-based open cell body having a high expansion ratio, an organic gas such as butane, pentane, dichlorodifluoromethane (Freon R-12) or It is necessary to use a volatile liquid, which is not preferable from the viewpoint of safety and environmental load.

  Moreover, in the method of the said patent documents 3-4 which uses inorganic gas as a foaming agent, a foaming magnification rises only to about 5 times, and the obtained foam turns into a closed cell. The reason why a polyethylene foam having a high expansion ratio using an inorganic gas cannot be obtained is as follows. Generally, when polyethylene and foaming agents (physical foaming agents such as organic gas and inorganic gas) are supplied to an extruder and heated and melt-kneaded to form a foamable molten resin mixture, the melt tension decreases due to the plasticizing effect of the foaming agent. A decrease in the crystallization temperature occurs. When the melt tension decreases, the foamable molten resin mixture starts to foam inside the extruder, and a significant reduction in the foaming ratio occurs. For this reason, it is necessary to maintain the melt tension against the foaming force of the foaming agent as a foamable molten resin mixture having a reduced extrusion resin temperature and adjusted to a temperature within an appropriate range. Here, it is well known that carbon dioxide gas is less effective in lowering the crystallization temperature than organic gas such as butane gas. In other words, when carbon dioxide gas is used as the foaming agent, the extrusion resin temperature must be higher than when organic gas is used. Therefore, the melt tension against the foaming force of the foaming agent cannot be maintained, and high It is considered that a polyethylene foam having an expansion ratio could not be obtained.

  Further, in Patent Documents 5 and 6 previously proposed by the present applicant, it is described that a polyethylene extruded foam can be obtained by extrusion foam molding of an ethylene-based polymer that satisfies specific requirements. There is no description or suggestion regarding the use of an inorganic gas as a foaming agent and the improvement of the open cell ratio.

  An object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide a polyethylene open-cell foam having a high expansion ratio by using carbon dioxide gas among clean inorganic gases.

  As a result of diligent research to solve the above problems, the present inventors have found that when an inorganic gas, particularly carbon dioxide gas is used as a foaming agent, an ethylene polymer satisfying specific requirements is excellent in foaming characteristics. The headline and the present invention have been completed.

That is, the present invention comprises an ethylene polymer having a density (d) measured by a density gradient tube method in accordance with JIS K6760 of 935 kg / m ³ or more, and has an expansion ratio of 4 to 30 times and an open cell ratio. 90% or more of polyethylene open cell foam and melt tension of the ethylene polymer measured at 160 ° C. and a draw ratio of 47 using a die having a length / diameter ratio of 8 / 2.095− A gist of the present invention is a polyethylene open-cell body characterized in that A is 30 mN or more and 80 mN or less and satisfies the following formula (1).

1.8 <melt tension−B / melt tension−A <4.2 (1)
(Here, melt tension -B indicates melt tension measured using a die having a length / diameter ratio of 8 / 2.095 and a stretch ratio of 47 at 140 ° C.)
The ethylene-based polymer constituting the polyethylene open cell foam of the present invention has a density measured by a density gradient tube method in accordance with JIS K6760 of 935 kg / m ³ or more, particularly 940 kg / m ³ or more. preferable. Here, since the ethylene polymer having a density of less than 935 kg / m ³ has a low melt tension in the optimum molding temperature region, the carbon dioxide dissolved in the molten resin in the extruder is generated inside the extrusion die. Foaming starts and a significant reduction in the foaming ratio occurs, making it impossible to obtain a foam having a good shape.

  The ethylene polymer constituting the polyethylene open-cell foam of the present invention is a melt tension (hereinafter referred to as “melting tension”) measured at 160 ° C. and a draw ratio of 47 using a die having a length / diameter ratio of 8 / 2.095. , Melt tension-A) is 30 mN or more and 80 mN or less, and particularly preferably 40 mN or more and 70 mN or less. Here, in the case of an ethylene polymer having a melt tension of less than 30 mN, the foam film cannot withstand the expansion pressure of the foaming gas at the stage of bubble growth immediately after being extruded from the die. Occur. On the other hand, an ethylene-based polymer having a melt tension of more than 80 mN is less likely to be continuously bubbled because the bubble film grows without bubble breakage in the process of extruding and foaming from a die connected to an extruder to the atmospheric pressure range. Become.

  The ethylene polymer constituting the polyethylene open-cell foam of the present invention preferably satisfies the above formula (1), and is particularly excellent in moldability and provides an open-cell foam having a high expansion ratio. Therefore, an ethylene polymer that satisfies the following formula (2) is preferable.

2.0 <melt tension-B / melt tension-A <4.0 (2)
Here, when the melt tension-B / melt tension-A of the ethylene-based polymer was 1.8 or less, the melt tension in the optimum molding temperature range was low, so it was dissolved in the molten resin in the extruder. Carbon dioxide gas begins to foam inside the extrusion die, causing a significant reduction in the expansion ratio, and a foam having a good shape cannot be obtained. On the other hand, when the melt tension-B / melt tension-A is 4.2 or more, the fluctuation of the resin pressure in the optimum molding temperature range becomes large and not only stable molding becomes difficult, but also the melt tension increases remarkably. Therefore, foaming is suppressed, and the foaming ratio and the open cell ratio are reduced.

  The ethylene-based polymer may be any ethylene-based polymer as long as the object of the present invention can be achieved. For example, an ethylene homopolymer or a repeating unit derived from ethylene and a C 3-8 α- An ethylene-α-olefin copolymer composed of repeating units derived from olefins may be mentioned. Here, the repeating unit derived from an α-olefin having 3 to 8 carbon atoms is derived from an α-olefin having 3 to 8 carbon atoms, which is a monomer, and is contained in the ethylene-α-olefin copolymer. Examples of the α-olefin having 3 to 8 carbon atoms include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, and 3-methyl-1-butene. . You may use together at least 2 types of these C3-C8 alpha olefins.

  As the method for producing the ethylene polymer constituting the polyethylene open-cell foam of the present invention, any production method can be used as long as it can produce an ethylene polymer that satisfies the above requirements. Examples include a multistage polymerization method in which the catalyst and / or polymerization conditions are changed in multiple stages, a polymerization method using a catalyst in which a plurality of polymerization catalysts are mixed, and a method in which a plurality of ethylene polymers prepared with the same or different polymerization catalysts are blended. Can do.

  The ethylene-based polymer constituting the polyethylene open-cell foam of the present invention can be arbitrarily prepared depending on the production conditions of Examples of the present application described later, or minor fluctuations in the condition factors. Specific examples of condition factor fluctuations include: requirements for catalyst components such as the structure of components (a) and (b) used, the amount of component (b) relative to component (a), the type of promoter component used, and the polymerization temperature It can also be made by controlling polymerization conditions such as ethylene partial pressure, the amount of a molecular weight adjusting agent such as hydrogen to be coexisted, and the amount of comonomer added. Furthermore, the range of physical properties can be expanded by combining with multi-stage polymerization.

  More specifically, for example, melt tension changes the structure of component (a), increases the number of terminal vinyls, changes the structure of component (b), reduces ethylene partial pressure, long-chain branching It is possible to increase the number by increasing the number, increasing the long-chain branch length, changing the amount of component (b) relative to component (a), increasing Mw / Mn, and the like. It is also possible to reduce the number of terminal vinyls by decreasing the ethylene partial pressure, decreasing the comonomer addition amount, changing the structure of component (a), and the like.

  Examples of the polymerization catalyst used for the production of the ethylene-based polymer constituting the polyethylene open-cell foam of the present invention include, for example, JP-A-2004-346304, JP-A-2005-248013, JP-A-2006-321991, Examples thereof include polymerization catalysts described in JP-A Nos. 2007-169341 and 2008-50278. For example, as a metallocene compound, two substituted or unsubstituted cyclopentadienyl groups are cross-linked with a cross-linking group consisting of a chain of two or more atoms, or cross-linked with a cross-linking group consisting of a chain of two or more atoms. Bridged bis (substituted or unsubstituted cyclopentadienyl) zirconium complex [component (a)] and bridged bis (substituted or unsubstituted cyclopentadienyl) zirconium complex having a different structure from component (a) [ In the presence of a metallocene catalyst using component (b)], a method of polymerizing ethylene or a method of copolymerizing ethylene and an α-olefin having 3 to 8 carbon atoms can be used.

  Specific examples of component (a) include dimethylsilylene bis (cyclopentadienyl) zirconium dichloride, dimethylsilylene (cyclopentadienyl) (indenyl) zirconium, dichloride 1,1,3,3-tetramethyldisiloxane-1 , 3-diyl-bis (cyclopentadienyl) zirconium dichloride, 1,1-dimethyl-1-silaethane-1,2-diyl-bis (cyclopentadienyl) zirconium dichloride, propane-1,3-diyl-bis (Cyclopentadienyl) zirconium dichloride, butane-1,4-diyl-bis (cyclopentadienyl) zirconium dichloride, cis-2-butene-1,4-diyl-bis (cyclopentadienyl) zirconium dichloride, 1 , 1,2,2-Tetramethyl Disilane-1,2-diyl - dimethyl body bis (cyclopentadienyl) zirconium dichloride dichloride and the transition metal compound such as chloride, diethyl body, dihydro derivative, diphenyl body, can be exemplified dibenzyl body. Further, compounds in which the hydrogen of the cyclopentadienyl derivative of the above transition metal compound is substituted with a hydrocarbon group, and compounds in which the zirconium atom of the central metal is substituted with a titanium atom or a hafnium atom can also be exemplified.

  Specific examples of component (b) include diphenylmethylene (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride, diphenylmethylene (2-trimethylsilyl-1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride, Diphenylmethylene (1-cyclopentadienyl) (2,7-dimethyl-9-fluorenyl) zirconium dichloride, diphenylmethylene (1-cyclopentadienyl) (2,7-di-t-butyl-9-fluorenyl) zirconium Dichloride, isopropylidene (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride, isopropylidene (1-cyclopentadienyl) (2,7-di-t-butyl-9-fluorenyl) zirconium dichloride, diphenylsila Diyl (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride, dimethylsilanediyl (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride, diphenylmethylene (1-indenyl) (9-fluorenyl) zirconium dichloride Diphenylmethylene (2-phenyl-1-indenyl) (9-fluorenyl) zirconium dichloride, diphenylmethylene (2-phenyl-1-indenyl) (2,7-di-t-butyl-9-fluorenyl) zirconium dichloride, etc. Examples thereof include dimethyl, diethyl, dihydro, diphenyl, and dibenzyl isomers of dichloride and the above transition metal compounds. Further, compounds in which the hydrogen of the cyclopentadienyl derivative of the above transition metal compound is substituted with a hydrocarbon group, and compounds in which the zirconium atom of the central metal is substituted with a titanium atom or a hafnium atom can also be exemplified.

  In the production of the ethylene polymer constituting the polyethylene open-cell foam of the present invention, the amount of the component (b) relative to the component (a) is not particularly limited and is preferably 0.0001 to 100 times mol. Especially preferably, it is 0.001-10 times mole.

  As the metallocene catalyst using the component (a) and the component (b) in the method that can be used for the production of the ethylene polymer constituting the polyethylene open-cell foam of the present invention, the component (a) and the component (b) And a catalyst comprising an organoaluminum compound [component (c)], a catalyst comprising component (a), component (b) and aluminoxane [component (d)], a catalyst comprising component (c), a catalyst comprising at least one salt selected from a), a component (b), a protonic acid salt [component (e)], a Lewis acid salt [component (f)] or a metal salt [component (g)]; A catalyst comprising (c), a catalyst comprising component (a), component (b), component (d) and inorganic oxide [component (h)], component (a), component (b) and component (h) ), Component (e), component (f), component (g) A catalyst comprising at least one salt, a catalyst comprising component (c), a catalyst comprising component (a) and component (b), clay mineral [component (i)] and component (c), component ( Examples of the catalyst include a), a component (b), and a clay mineral [component (j)] treated with an organic compound, preferably from the component (a), the component (b), and the component (j). Can be used.

  The clay mineral that can be used as the component (i) and the component (j) is a fine particle mainly composed of a microcrystalline silicate. Most of the clay minerals have a layered structure as a structural feature, and it can be mentioned that the layer has negative charges of various sizes. In this respect, it is greatly different from a metal oxide having a three-dimensional structure such as silica or alumina. These clay minerals generally have a large layer charge, with pyrophyllite, kaolinite, dickite and talc groups (negative charge per chemical formula is approximately 0), smectite groups (negative charge per chemical formula is from about 0.25). 0.6), vermiculite group (negative charge per chemical formula is approximately 0.6 to 0.9), mica group (negative charge per chemical formula is approximately 1), brittle mica group (negative charge per chemical formula is approximately 2) It is classified. Each group shown here includes various clay minerals, and examples of the clay mineral belonging to the smectite group include montmorillonite, beidellite, saponite, hectorite and the like. Further, a plurality of the above clay minerals can be mixed and used.

  The organic compound treatment in component (j) refers to introducing an organic ion between clay mineral layers to form an ionic complex. Examples of the organic compound used in the organic compound treatment include N, N-dimethyl-n-octadecylamine hydrochloride, N, N-dimethyl-n-eicosylamine hydrochloride, N, N-dimethyl-n-docosylamine hydrochloride, N, N-dimethyloleylamine hydrochloride, N, N-dimethylbehenylamine hydrochloride, N-methyl-bis (n-octadecyl) amine hydrochloride, N-methyl-bis (n-eicosyl) amine hydrochloride, N-methyl -Dioleylamine hydrochloride, N-methyl-dibehenylamine hydrochloride, N, N-dimethylaniline hydrochloride can be exemplified.

  The catalyst comprising component (a), component (b) and component (j) can be obtained by contacting component (a), component (b) and component (j) in an organic solvent. The method of adding component (b) to the contact product of component (j) and component (b), the method of adding component (a) to the contact product of component (b) and component (j), component (a) and component (b) ) And a method of adding the contact product of component (a) and component (b) to component (j).

  As the contact solvent, aliphatic hydrocarbons such as butane, pentane, hexane, heptane, octane, nonane, decane, cyclopentane or cyclohexane, aromatic hydrocarbons such as benzene, toluene or xylene, ethyl ether or n-butyl ether And ethers such as methylene chloride and chloroform, 1,4-dioxane, acetonitrile and tetrahydrofuran.

  About a contact temperature, it is preferable to select between 0-200 degreeC and to process.

  The amount of each component used is 0.0001 to 100 mmol, preferably 0.001 to 10 mmol of component (a) per 1 g of component (j).

  The contact product of component (a), component (b) and component (j) prepared in this way may be used without washing, or may be used after washing. Further, when the component (a) or the component (b) is a dihalogen, it is preferable to further add the component (c). Further, component (c) can be added for the purpose of removing impurities in component (j), polymerization solvent and olefin.

  In the method that can be used for the production of the ethylene-based polymer constituting the polyethylene open-cell foam of the present invention, the polymerization temperature is preferably -100 to 120 ° C, particularly 20 to 120 ° C and further 60 in consideration of productivity. It is preferable to carry out in the range of ~ 120 ° C. The polymerization time is preferably in the range of 10 seconds to 20 hours, and the polymerization pressure is preferably in the range of normal pressure to 300 MPa. As a supply ratio of ethylene and a C3-C8 alpha-olefin, ethylene / C3-C8 alpha-olefin (molar ratio) is 1-200, Preferably it is 3-100, More preferably, it is 5-50. Feed rates can be used. It is also possible to adjust the molecular weight using hydrogen during polymerization. The polymerization can be carried out by any of batch, semi-continuous and continuous methods, and can be carried out in two or more stages by changing the polymerization conditions. In addition, the ethylene copolymer can be obtained by separating and recovering from the polymerization solvent by a conventionally known method after the completion of the polymerization and drying.

  Polymerization can be carried out in a slurry state, a solution state, or a gas phase state. In particular, when the polymerization is performed in a slurry state, an ethylene-based copolymer having a powder particle shape is efficiently and stably produced. Can do. The solvent used for the polymerization may be any organic solvent that is generally used. Specific examples include benzene, toluene, xylene, propane, isobutane, pentane, hexane, heptane, cyclohexane, gasoline, and the like, propylene, Olefin itself such as 1-butene, 1-hexene and 1-octene can also be used as a solvent.

  The ethylene polymer constituting the polyethylene open cell foam of the present invention includes a heat resistance stabilizer, a weather resistance stabilizer, an antistatic agent, an antifogging agent, an antiblocking agent, a slip agent, a lubricant, a nucleating agent, a pigment, and carbon black. Further, known additives such as inorganic fillers or reinforcing agents such as talc, glass powder and glass fiber, organic fillers or reinforcing agents, flame retardants, and neutron shielding agents can be blended.

  As a method for producing the polyethylene open cell foam of the present invention, any method may be used as long as a polyethylene open cell foam is obtained. For example, the ethylene polymer and bubbles such as talc to be added if necessary. Adjusting agent temperature, extrusion die internal pressure, discharge amount, etc. are adjusted after supplying modifier, shrinkage inhibitor, etc. to the extruder, heating and melting, kneading, and further adding foaming agent to make foamable molten resin mixture And the method of extruding to a low pressure area from the die | dye attached to the extruder front-end | tip, and making it foam is mentioned. In particular, in order to obtain a foam having a high open cell ratio, it is preferable to produce the ethylene-based polymer by adding carbon dioxide gas as a foaming agent and performing extrusion foaming.

  Although the mechanism of open cell formation in the polyethylene open cell obtained by the present invention is not clear, it is presumed to be due to the following mechanism.

  That is, in the process of extruding and foaming the ethylene polymer constituting the polyethylene open cell foam of the present invention from a die connected to an extruder to the atmospheric pressure region, the ethylene polymer is immediately after being extruded from the die. Since the film has an appropriate melt tension at the bubble growth stage, the bubble film does not cause remarkable bubble breakage, and the foam has a high expansion ratio while maintaining the internal pressure of the bubbles. In the subsequent bubble growth stage, it is considered that fine pores are generated in the bubble film due to slight bubble breakage, and the pores communicate with each other to form continuous bubbles.

  Furthermore, unlike the prior art, the mechanism of the polyethylene open cell obtained by the present invention that can maintain a high expansion ratio even when carbon dioxide is used as a foaming agent is presumed as follows.

  That is, the ethylene polymer constituting the polyethylene open-cell foam of the present invention is supplied to an extruder together with carbon dioxide gas, and when heated and kneaded to obtain a foamable molten resin mixture, an appropriate range in which extrusion molding is possible. Since the melt tension at the inner temperature is high, foaming does not occur in the extruder, but foaming starts after extrusion from the die, and it is considered that the foam has a good shape and a high foaming ratio.

  Also, extrusion foams of various shapes such as round bar foams, sheet foams, plate foams, etc. are manufactured by selecting a die attached to the extruder tip according to the desired foam shape can do. For example, if a strand die is attached, a round bar-like foam can be obtained; if an annular die is attached, a sheet-like foam can be obtained; and if a slit die is attached, a plate-like foam can be produced. .

  The polyethylene open cell foam of the present invention is prepared by supplying the above-mentioned ethylene polymer, additive, foaming agent and the like to an extruder, heating and kneading to obtain a foamable molten resin mixture, and then the extruded resin temperature is within an appropriate range. It can be formed by adjusting to a low pressure region from the extruder. That is, it is considered that the foamable molten resin mixture whose extrusion resin temperature is adjusted within an appropriate range has a melt tension that resists the foaming force of the foaming agent and foams uniformly.

  The specific extrusion resin temperature is based on the melting point of the ethylene polymer, and the extrusion resin temperature of the foamable molten resin is (melting point of the ethylene polymer−10 ° C.) to (melting point of the ethylene polymer + 10. It is preferable to adjust within the range of (degreeC), and it is more preferable to adjust within the range of (melting point of the said ethylene polymer -5 degreeC)-(melting point of the said ethylene polymer +5 degreeC). When the extrusion resin temperature is lower than (the melting point of the melting point of the ethylene-based polymer −10 ° C.), crystallization occurs at the die part and it becomes difficult to obtain a foam. On the other hand, when the extrusion temperature is higher than (the melting point of the ethylene-based polymer + 5 ° C.), the foam of the obtained foam is broken and the expansion ratio is significantly reduced.

  The melting point of the ethylene-based polymer is a peak apex temperature obtained from a test piece subjected to a constant heat treatment by a heat flux DSC curve based on JIS K7121 (1987). When two or more peaks appear, the vertex temperature of the main peak having the largest peak area is defined as the melting point.

  Examples of the foaming agent in extrusion foam molding include inorganic gas foaming agents such as carbon dioxide, nitrogen, argon, and air. The amount of the foaming agent added is the polyethylene open cell of the present invention. The amount is preferably 1 to 20 parts by weight, more preferably 5 to 15 parts by weight, based on 100 parts by weight of the ethylene polymer constituting the foam.

  The polyethylene open cell foam of the present invention has fine pores uniformly distributed in the cell membrane, has a high expansion ratio, can be recycled, and can be manufactured at low cost. Further, since carbon dioxide gas is used as the foaming agent, there is no risk of explosion due to organic gas such as butane and pentane, and there is no fear of environmental pollution such as ozone layer destruction such as chlorofluorocarbon gas.

  The use of the polyethylene open-cell foam of the present invention is not particularly limited, and is commonly used as an open-cell foam, for example, building materials [insulating members (temperature control materials), etc.], structural materials (lightweight structural materials, etc.), Packaging materials, cushioning materials (or cushioning materials), mat members [for example, mattresses (anti-vibration mattresses, sports mattresses), carpets, etc.], footwear members, filter media, cleaning tools, separators (battery separators, etc.), etc. Available as

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
~ Measurement of melt tension ~
Melt tension is measured by attaching a die with a length of 8mm and a diameter of 2.095mm to a capillary viscometer (Toyo Seiki Seisakusho, trade name: Capillograph) with a barrel diameter of 9.55mm so that the inflow angle is 90 °. did. The temperature was set to 160 ° C., the piston lowering speed was set to 10 mm / min, the stretch ratio was set to 47, and the load (mN) required for take-up was defined as melt tension-A. Further, the load (mN) measured by the same method with the temperature set at 140 ° C. was defined as melt tension −B.

~ Open cell ratio ~
The open cell ratio of polyethylene open cell foam: S (%) is measured using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C described in ASTM D2856-70. The actual volume of the foam (the sum of the volume of the closed cells and the volume of the resin part): a value calculated from the following formula from Vx (L).

S (%) = (Va−Vx) × 100 / (Va−W / ρ)
However, Va, W, and ρ in the above formula are as follows.

Va: Apparent volume (L) calculated from the outer dimensions of the foam specimen used for measurement
W: Weight of test piece (g)
ρ: Density of resin constituting the test piece (g / L)
The density ρ (g / L) of the resin constituting the test piece and the weight W (g) of the test piece are obtained by performing the operation of defoaming the foam test piece with a hot press and then cooling it. It can be obtained from the test piece.

~ Foaming ratio ~
A cylindrical foam having a diameter of 5 cm and a length of 10 cm is cut out from the polyethylene open-cell foam, the weight W2 (g) is measured, and the apparent density is calculated by the following formula according to JIS K6767.

Apparent density (g / cm ³ ) = W2 / (2.5 × 2.5 × π × 10)
The expansion ratio was determined from the apparent density by the following formula.

Foaming ratio = 1 / apparent density-foaming state-
At the time of molding, the foamed state of the molten foamed resin at the extruder die was visually observed.

Example 1
[Preparation of Clay Mineral Treated with Organic Compound [Component (a)]
After aging by adding 1.0 kg of hectorite to 369 g (1.1 mol) of N, N-dimethyl-octadecylamine hydrochloride dissolved in water: ethanol solution (ratio = 50: 50, 6.0 L), washing and drying, By pulverizing, modified hectorite (clay mineral treated with an organic compound [component (1)]) having an average particle diameter of 4.5 μm was obtained.
[Preparation of ethylene polymer production catalyst [component (2)]]
Dimethylsilanediyl (cyclopentadienyl) (2-indenyl) zirconium dichloride [component (a)] 8.81 g (20.0 mmol) was suspended in hexane 2.07 L, and hexane solution of triisobutylaluminum (0.714 M ) 2.93 L was added and reacted. To this reaction solution, 500 g of modified hectorite [component (1)] prepared in [Preparation of clay mineral treated with organic compound [component (1)]] was added and reacted at 60 ° C. for 3 hours. The supernatant liquid containing substances and unreacted substances was removed and washed with a hexane solution (0.03M) of triisobutylaluminum. Further, a hexane solution (0.15 M) of triisobutylaluminum was added to make a total volume of 4 L suspension.

In a separate container, diphenylmethylenemethylene (1-cyclopentadienyl) (9-fluorenyl) zirconium dichloride [component (b)] (0.586 g, 1.05 mmol), triisobutylaluminum (14.6 mmol). It melt | dissolved in the hexane solution containing, added to the suspension prepared above, and stirred at room temperature overnight. The supernatant liquid containing by-products and unreacted substances was removed, and the solid component was washed with a hexane solution (0.03M) of triisobutylaluminum. Further, a hexane solution (0.15M) of triisobutylaluminum was added to make the total amount 5 L, and an ethylene polymer production catalyst [component (2): 100 g / L] was obtained.
[Production of ethylene polymer]
To a 10 L autoclave, hexane (6,000 mL), butene-1 (16.7 g) and 5.0 mL of a hexane solution of triisobutylaluminum (0.714 M) were introduced, and the internal temperature of the autoclave was raised to 85 ° C. To the autoclave, 200 mg (2 ml) of the catalyst [component (2)] was added, and ethylene was introduced until the partial pressure reached 0.9 MPa to initiate polymerization. During the polymerization, an ethylene / hydrogen mixed gas (containing hydrogen: 800 ppm) was continuously introduced so that the total pressure was maintained at 1.1 MPa. The polymerization temperature was controlled at 85 ° C. After 90 minutes from the start of the polymerization, the internal pressure of the autoclave was released, and the contents were suction filtered. After drying, 1,080 g of an ethylene polymer was obtained. The density of the obtained ethylene polymer was 942 kg / m ³ , and the MFR was 3.2 g / 10 minutes.
[Manufacture of polyethylene open cell foam]
A polyethylene resin composition for foam molding containing 0.7 parts by weight of talc (average particle size 8 μm) as a foam nucleating agent was prepared by melt blending with respect to 100 parts by weight of the ethylene polymer. And using a foam molding extrusion equipment of a single screw extruder (screw diameter 50 mmφ, L / D = 36, manufactured by Kyodo Machine) having a barrel hole for injecting a volatile liquid in the middle of the barrel, a polyethylene system for foam molding After the resin composition was supplied at 10 kg / hour and melt-kneaded, the compressed liquid carbon dioxide was injected from the barrel hole at 700 g / hour to disperse the liquid carbon dioxide, and the temperature was set to 130 ° C. A rod-shaped foamed molded product was extruded with a rod die (diameter 13 mmφ). Air was blown to the outside of the rod-like foamed molded article and taken up at 5.0 m / min to obtain a foamed molded article.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

Example 2
[Production of ethylene polymer]
The catalyst obtained in Example 1 was added to a polymerizer having an internal volume of 540 L, hexane at 145 kg / hour, ethylene at 30.0 kg / hour, butene-1 at 0.2 kg / hour, triisobutylaluminum at 5.3 g / hour. [Component (2)] was continuously supplied at 6 g / hr, and the polymerization reaction was continuously carried out while maintaining the total pressure at 3,000 kPa and the polymerization vessel internal temperature at 85 ° C. After continuously removing the slurry from the polymerization vessel and removing unreacted hydrogen, ethylene, and butene-1, ethylene polymer powder was obtained through separation and drying processes. The density of the obtained ethylene polymer was 955 kg / m ³ , and the MFR was 6.7 g / 10 min.
[Manufacture of polyethylene open cell foam]
A polyethylene open cell foam was produced in the same manner as in Example 1 except that the ethylene polymer was used. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

Example 3
[Production of ethylene polymer]
An ethylene polymer powder was obtained by carrying out a polymerization reaction in the same manner as in Example 2 except that the butene-1 supply amount was 4.0 kg / hour and the polymerization temperature was 70 ° C. The density of the obtained ethylene polymer was 936 kg / m ³ , and the MFR was 7.8 g / 10 min.
[Manufacture of polyethylene open cell foam]
A polyethylene open cell foam was produced in the same manner as in Example 1 except that the ethylene polymer was used. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

Example 4
[Production of ethylene polymer]
An ethylene polymer powder was obtained by carrying out a polymerization reaction in the same manner as in Example 2 except that the butene-1 supply amount was 4.0 kg / hr and the polymerization temperature was 65 ° C. The density of the obtained ethylene polymer was 936 kg / m ³ , and the MFR was 2.0 g / 10 min.
[Manufacture of polyethylene open cell foam]
A polyethylene open cell foam was produced in the same manner as in Example 1 except that the ethylene polymer was used. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

Example 5
[Production of ethylene polymer]
A polymerization reaction was carried out in the same manner as in Example 2 except that the butene-1 supply amount was 0.1 kg / hour to obtain an ethylene polymer powder. The density of the obtained ethylene polymer was 954 kg / m ³ , and the MFR was 2.5 g / 10 minutes.
[Manufacture of polyethylene open cell foam]
A polyethylene open cell foam was produced in the same manner as in Example 1 except that the ethylene polymer was used. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

Comparative Example 1
[Preparation of ethylene polymer production catalyst [component (3)]]
500 g of the modified hectorite [component (1)] is suspended in 1.7 liters of hexane, and 6.97 g (20.0 mmol) of dimethylsilanediylbis (cyclopentadienyl) zirconium dichloride and a hexane solution of triisobutylaluminum ( 0.714M) 2.8 liters (2 mol) of a mixed solution was added and stirred at 60 ° C. for 3 hours, and then 15 mol% of diphenyl (1-cyclohexane with respect to dimethylsilanediylbis (cyclopentadienyl) zirconium dichloride. Pentadienyl) (2,7-di-tert-butyl-9-fluorenyl) zirconium dichloride 2.36 g (3.53 mmol) was added and stirred at room temperature for 6 hours. The supernatant was removed by standing, and a hexane solution (0.15 M) of triisobutylaluminum was further added to finally obtain a catalyst slurry of an ethylene polymer production catalyst [component (3): 100 g / L]. .
[Production of ethylene polymer]
Into a polymerization vessel having an internal volume of 540 liters, 300 liters of hexane and 1.3 liters of 1-butene were introduced, and the internal temperature of the autoclave was raised to 80 ° C. To this autoclave, 147 ml of the above-mentioned catalyst [component (3)] was added, and an ethylene / hydrogen mixed gas (hydrogen: 1000 ppm contained) was introduced until the partial pressure became 0.9 MPa to initiate polymerization. During the polymerization, an ethylene / hydrogen mixed gas was continuously introduced so that the partial pressure was maintained at 0.9 MPa. The polymerization temperature was controlled at 80 ° C. After 90 minutes from the start of polymerization, the internal pressure of the polymerization vessel was released, and the contents were filtered and dried to obtain 50 kg of an ethylene polymer powder. The ethylene-based polymer pellets were obtained by melt-kneading and pelletizing the ethylene-based polymer powder using a single screw extruder having a diameter of 50 mm set at 200 ° C.

The density of the obtained ethylene polymer pellets was 950 kg / m ³ , and the MFR was 8 g / 10 minutes.
[Manufacture of polyethylene open cell foam]
A polyethylene open cell foam was produced in the same manner as in Example 1 except that the ethylene polymer was used. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.
[Evaluation of polyethylene open cell foam]
About the polyethylene open-cell foam created by the said manufacturing method, the expansion ratio, the open-cell rate, and the foaming state were evaluated. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

  Since the value of melt tension -A was high, the obtained foam had a low expansion ratio and open cell ratio.

Comparative Example 2
In the same manner as in Example 1 except that a commercially available low density polyethylene (Petrocene 203, manufactured by Tosoh Corporation, MFR = 8.0 g / 10 min, density = 919 kg / m ³ ) was used as the ethylene polymer. Evaluation was performed. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

  Since the value of melt tension-A / melt tension-B was low, the carbon dioxide dissolved in the molten resin in the extruder started to foam inside the extrusion die, and a foam was not obtained.

Comparative Example 3
In the same manner as in Example 1 except that a commercially available high-density polyethylene (Nipolon Hard 2500, manufactured by Tosoh Corporation, MFR = 8.0 g / 10 min, density = 961 kg / m ³ ) was used as the ethylene polymer. Evaluation was performed. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

  Since the value of melt tension-A / melt tension-B was low, the carbon dioxide dissolved in the molten resin in the extruder started to foam inside the extrusion die, and a foam was not obtained.

Comparative Example 4
Example 1 except that a commercially available linear low-density polyethylene (Nipolon Z ZF260, manufactured by Tosoh Corporation, MFR = 2.0 g / 10 min, density = 936 kg / m ³ ) was used as the ethylene polymer. Evaluation was performed in the same manner. The physical properties of the obtained polyethylene and the evaluation results of the foam are shown in the table.

  Since the value of melt tension-A / melt tension-B was low, the carbon dioxide dissolved in the molten resin in the extruder started to foam inside the extrusion die, and a foam was not obtained.

Claims (4)

A polyethylene open cell foam comprising an ethylene polymer having a density measured by a density gradient tube method in accordance with JIS K6760 of 935 kg / m ³ or more and an expansion ratio of 4 to 30 times and an open cell ratio of 90% or more. . An ethylene polymer having a length / diameter ratio of 8 / 2.095 and a melt tension (hereinafter referred to as melt tension-A) measured at 160 ° C. and a draw ratio of 47 is 30 mN or more. The polyethylene open-cell foam according to claim 1, which is 80 mN or less and satisfies the following formula (1).
1.8 <melt tension−B / melt tension−A <4.2 (1)
(Here, melt tension -B indicates melt tension measured using a die having a length / diameter ratio of 8 / 2.095 and a stretch ratio of 47 at 140 ° C.) An ethylene polymer having a density measured by a density gradient tube method in accordance with JIS K6760 of 935 kg / m ³ or more, a melt tension -A of 30 mN or more and 80 mN or less and satisfying the following formula (1) is an extruder. 3. The polyethylene open cell according to claim 1, wherein the mixture is heated and melted and kneaded, and further an inorganic gas blowing agent is supplied to form a foamable molten resin mixture, which is then extruded into a low pressure region and foamed. A method for producing a foam. The method for producing a polyethylene open-cell foam according to claim 3, wherein the inorganic gas blowing agent is carbon dioxide.