JPH0977894A - Flame-retardant polyethylene-based resin composition for foaming and foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition capable of providing a uniform and beautiful foam having self-extinguishing properties, excellent in flexibility by using a polyethylene-based resin polymerized by a specific catalyst without using a halogen-containing compound as a flame-retardant. SOLUTION: This flame-retardant polyethylene-based resin composition comprises (A) 100 pts.wt. of a polyethylene-based resin polymerized by using a tetravalent transition metal-containing metallocene compound as a catalyst, (B) 1-50 pts.wt. of a thermally expandable graphite (preferably >=60wt.% particles not passing through 80 mesh) and (C) 1-20 pts.wt. of a phosphorus compound (e.g. red phosphorus). Preferably the component A has 0.86-0.95g/cm<3> density, <=30 deg.C difference in temperature between a temperature to elute 10% of the component A and a temperature to elute 100% of the component A by a cross fractionation method and 1.5-3.5 value of the weight-average molecular weight/number-average molecular weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant polyolefin resin composition for foaming and a foam, and more specifically, a polyethylene resin polymerized by a specific catalyst is combined with a specific flame retardant system. The present invention relates to a foaming resin composition having excellent foaming properties, and a flame-retardant polyethylene-based resin foam obtained by foaming the resin composition. The foam of the present invention is an environment-friendly non-halogen flame-retardant polyethylene resin foam that does not contain a halogen-containing compound as a flame retardant.

[0002]

2. Description of the Related Art Polyethylene-based resin foams are excellent in flexibility and heat insulation and have been conventionally used for various purposes as cushioning materials and heat insulating materials. The type of polyethylene resin used is selected according to the purpose. For example, when more flexibility is required, low-density polyethylene is used, and when toughness is particularly required, ethylene and α
-A linear low-density polyethylene that is a copolymer with an olefin is used, and in order to obtain a balance of physical properties,
These resins are used in combination (Japanese Patent Publication No. 61-57334).

However, when a polyethylene-based resin having an increased amount of a copolymerization component is used to increase flexibility, such a resin is copolymerized with a component having a low molecular weight because the copolymerization component is introduced into the molecular chain. Since the components are almost not introduced into the molecular chain and are separated into the components having a high molecular weight, the melt viscosity in the resin largely varies, and the foamability decreases. Specifically, even if the expansion ratio does not increase, even if a foam with a satisfactory expansion ratio is obtained, problems such as unevenness in appearance occur, or very large bubbles or small bubbles are mixed, However, there was a problem that the non-uniform foamed portion was broken during the secondary processing.

Further, in the field of application where the foam is required to have flame retardancy, it is necessary to make the polyethylene resin which is a flammable resin flame-retardant, and a method of adding a halogen-based flame retardant is general. . Halogen-based flame retardants certainly give a high degree of flame retardancy, but they generate halogenated gas during processing and combustion, which poses problems of corrosiveness to equipment and toxicity to humans. Therefore, in recent years, from the viewpoint of safety, non-halogen flame retardation, that is, flame retardation of a resin that does not use a halogen-based flame retardant has been strongly demanded.

As a flame retarding method which does not use a halogen-based flame retardant, for example, flame retardation of a resin by adding a hydrated metal compound such as aluminum hydroxide, magnesium hydroxide and basic magnesium carbonate has been actively studied. It became so.
Using these hydrated metal compounds as flame retardants,
Does not generate toxic gas when burned. However, using only these hydrated metal compounds, it is necessary to add a large amount in order to impart sufficient flame retardancy to the polyolefin resin that is easily flammable, and as a result, the mechanical strength decreases. Remarkably, there is a problem that only polyethylene resin compositions and foams that cannot be used practically can be obtained.

Recently, there has been proposed a flame-retardant polyolefin-based resin composition obtained by adding red phosphorus and heat-expandable graphite having 80 mesh-on of 80% or more to a polyolefin-based resin (JP-A-6- 25476 publication). When a thermally expansive graphite having such a large particle size is added to a polyolefin resin, a highly flame-retardant resin composition can be obtained, but when a foam is produced using the resin composition, when foaming occurs, There are problems such as gas escape from the heat-expandable graphite part, heat-expandable graphite becoming nuclei of giant cells, insufficient expansion ratio, and unevenness on the surface of the foam. I couldn't get a body.

[0007]

The object of the present invention is to obtain a non-halogen flame-retardant polyolefin resin foam having good foamability, remarkable flame retardancy and good appearance. It is to provide a polyolefin resin composition. Another object of the present invention is to provide a flame-retardant polyolefin resin composition foam obtained by foaming the flame-retardant polyolefin resin composition for foaming.

As a result of intensive studies, the present inventors have found that the above object can be achieved by using a polyethylene resin polymerized by a specific catalyst as the polyethylene resin and combining this with a specific flame retardant system. It was In particular, when a polyethylene resin having specific crystallinity and thermal properties is selected and used according to the purpose, more remarkable effects can be obtained. The present invention has been completed based on these findings.

[0009]

According to the present invention, (A)
100 parts by weight of polyethylene-based resin polymerized using a metallocene compound containing a tetravalent transition metal as a catalyst, (B) 1 to 50 parts by weight of thermally expandable graphite, and (C) phosphorus compounds 1 to 2
Provided is a flame-retardant polyethylene resin composition for foaming, which contains 0 part by weight. Further, according to the present invention, there is provided a flame-retardant polyethylene resin foam obtained by foaming the above resin composition.

Further, according to the present invention, the following preferred embodiments are provided. 1. The flame-retardant polyethylene composition for foaming, wherein the thermally expansive graphite has a particle size of 60% by weight of 80 mesh on. 2. Polyethylene resin has a density of 0.860 to 0.95
0 / cm ³ , the temperature range from the temperature at which 10 wt% was eluted by the cross fractionation method to the temperature at which 100 wt% was completed was 30 ° C or less, and the weight average molecular weight / number average molecular weight value was 1.5 to The above flame-retardant polyethylene-based composition for foaming having a composition of 3.5. 3. Polyethylene resin is a differential scanning calorimeter (DSC)
Has one crystal melting peak measured by using, and
The flame-retardant polyethylene composition for foaming, wherein the temperature range from the melting peak temperature to the end of melting of all crystals is within 20 ° C.

The present invention will be described in detail below. (A) Polyethylene Resin The polyethylene resin used in the present invention is a polymer of ethylene alone or a copolymer of ethylene and α-olefin. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene,
-Methyl-1-pentene, 1-heptene, 1-octene and the like. The polyethylene resin used in the present invention is polymerized by using a metallocene compound containing a tetravalent transition metal as a catalyst. The metallocene compound is generally a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and a bis (cyclopentadienyl) metal complex is typical. Examples of the metallocene compound used in the present invention include tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum, and one or more cyclopentadienyl rings and their analogs as ligands (ligands). ).

Specific examples of the ligand include a cyclopentadienyl ring, a hydrocarbon group, a substituted hydrocarbon group or a cyclopentadienyl ring substituted with a hydrocarbon-substituted metalloid group, a cyclopentadienyl oligomer ring, an indenyl ring. And an indenyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon-substituted metalloid group. Examples of ligands other than these include monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, arylphosphides and the like. It Typical of the above hydrocarbon groups are methyl, ethyl, propyl, butyl, amyl, isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl,
2-ethylhexyl and phenyl.

The metallocene compounds coordinated with these ligands include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethylsilyl tetra Methylcyclopentadienyl-tert-butylamide zirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamide hafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamide zirconium chloride, methylphenyl Silyltetramethylcyclopentadienyl-tert-butylamide hafnium dichloride, indenyl titanium tris (dimethylamide), indenyl Titanium tris (diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

Polymerization of the polyethylene resin is usually carried out in a catalyst system in which methylaluminoxane (MAO) as a cocatalyst, a boron compound and the like are added to these metallocene compounds. The ratio of the cocatalyst used to the metallocene compound is 10 to 100 with respect to 1 mol of the metallocene compound.
It is 0000 mol, usually 50 to 5000 mol. The polymerization conditions are not particularly limited, and a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, or a gas phase polymerization method can also be used. The polymerization temperature is generally -100 ° C to 300 ° C, and the polymerization pressure is generally atmospheric pressure to 100 kg / cm ² .

The polyethylene resin polymerized using these metallocene compounds has a narrow molecular weight distribution, and in the case of a copolymer, the copolymer component is introduced in almost equal proportion to any molecular weight component. Such polyethylene resins are commercially available as CGCT manufactured by Dow Chemical Company, EXACT manufactured by Exxon Chemical Company, and the like. The polyolefin resin used in the present invention has (1) a density of 0.8
60 to 0.950 / cm ³ , 1 by cross fractionation method
The range of the temperature from 0% by weight elution to 100% by weight elution is 30 ° C or less, and the weight average molecular weight / number average molecular weight value is 1.5 to 3.5, or (2 ) It is preferable that the number of crystal melting peaks measured by using a differential scanning calorimeter (DSC) is one and the temperature range from the melting peak temperature to the end of melting of all crystals is within 20 ° C.

(Cross fractionation method) The "cross fractionation method" used in the present invention is as follows. First, a polyethylene resin is dissolved in o-dichlorobenzene at 140 ° C. or a temperature at which the polyethylene resin is completely melted, and then cooled at a constant rate to form a thin polymer layer on the surface of an inert carrier prepared in advance to form a crystalline polymer. It is generated in the descending order of high molecular weight and high molecular weight. Next, the temperature is raised continuously or stepwise, the temperature of the eluted components is detected sequentially, and the composition distribution (crystallinity distribution) is measured <temperature rising elution fractionation>, and the eluted components are analyzed by high temperature GPC. Analyze to determine molecular weight and molecular weight distribution. In the present invention, the temperature rising elution fractionation (TREF = Temperature Ri described above
sing Elution Fractionatio
n) part and high temperature GPC (SEC = Size Excel)
The above-mentioned data was measured by using a cross fractionation chromatograph apparatus <CFC-T150A type: manufactured by Mitsubishi Petrochemical Co., Ltd.> which is provided with a system including a "Usion Chromatograph" part.

(Differential scanning calorimetric analysis) Differential scanning calorimetric distribution in the present invention was carried out by the following method. About 10 mg of polyethylene resin sample was put in a platinum van and measured with a differential scanning calorimeter (DSC) <SSC5200 type: manufactured by Seiko Instruments Inc.>. The measurement conditions were such that the sample was once melted, cooled to −50 ° C. at a rate of 5 ° C./min, and then heated at a rate of 5 ° C./min for measurement.

The polyethylene resin used in the present invention preferably has a density of 0.860 to 0.950 g / cm ³ , and more preferably 0.860 to 0.945 g / cm ³ . If the density is less than 0.860 g / cm ³ , the crystallinity of the resin will be lowered, and the heat resistance of the foam will be problematic. 0.9
When it exceeds 50 g / cm ³ , problems occur in flexibility and elongation of the foam.

The polyethylene resin used in the present invention has a temperature range from the temperature at the time of elution of 10% by weight to the temperature at the end of 100% by weight elution by the cross fractionation method described above.
It is preferably 0 ° C. or lower, more preferably 28 ° C. or lower. If the temperature range exceeds 30 ° C., a highly crystalline component and a low crystalline component are present in the polyethylene resin at the same time, and the viscosity of the molten resin during foaming is uneven,
It is not possible to obtain a uniform foam. The polyethylene resin used in the present invention has a weight average molecular weight / number average molecular weight of 1.5 measured by the above-mentioned cross fractionation method.
What is in the range of -3.5 is preferable, More preferably, it is 1.7-3.0. If this value is less than 1.5, the strength of the resin foam will be improved, but the resin will not flow easily during melting, and molding will be difficult. On the other hand, if this value exceeds 3.5, the abundance ratio of low molecular weight molecules and high molecular weight molecules becomes high, and the viscosity of the molten resin during foaming becomes uneven,
It is not possible to obtain a uniform foam.

The polyethylene resin used in the present invention has one crystal melting peak in the differential scanning calorimetric distribution, and has a temperature range within 20 ° C. from the melting peak temperature until all the crystals are melted. preferable. The presence of a plurality of crystal melting peaks means that a plurality of components having different crystallinity are present, in which case the viscosity of the molten resin during foaming becomes uneven, and a uniform foam cannot be obtained. In addition, even if there is only one melting peak, if the temperature range from the melting peak temperature to the end of melting of all crystals exceeds 20 ° C, the crystallinity between high and low crystallinity between polyethylene molecules is high. And the viscosity of the molten resin becomes uneven at the time of foaming, and a uniform foam cannot be obtained.

In the present invention, in addition to the above polyethylene resin, other thermoplastic resins such as low density polyethylene, linear low density polyethylene, medium density polyethylene,
High density polyethylene, polypropylene, ethylene-propylene rubber, ethylene-vinyl acetate copolymer, polyvinyl acetate, polybutene, etc. may be added to form a foam. The blending ratio of these other thermoplastic resins is usually 5
It is 0% by weight or less.

(B) Thermally Expandable Graphite The thermally expandable graphite used in the present invention is a conventionally known substance, and powders of natural scaly graphite, pyrolytic graphite, quiche graphite and the like are mixed with concentrated sulfuric acid, nitric acid and selenic acid. A graphite intercalation compound is produced by treating it with a strong oxidizer such as concentrated nitric acid, perchloric acid, perchlorate, permanganate, dichromate, hydrogen peroxide, etc. It is a crystalline compound that maintains the layered structure of carbon. In the present invention, the thermally expansive graphite thus obtained by the acid treatment is used after being neutralized with ammonia, an aliphatic lower amine, an alkali metal compound, an alkaline earth metal compound or the like.

Examples of the aliphatic lower amine include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine and butylamine. Examples of the alkali metal and alkaline earth metal compounds include hydroxides, oxides, carbonates, sulfates, organic acid salts and the like of potassium, sodium, calcium, parium, magnesium and the like. The particle size of the thermally expandable graphite is preferably in the range of 60 to 80% by weight when 80 mesh is on. 8
If 0 mesh-on is less than 60% by weight, it becomes difficult to obtain a foam having sufficient flame retardancy. The addition amount is 1 to 50 parts by weight, preferably 1.3 to 40 parts by weight. If the amount added is too small, the flame retardancy will be insufficient. Conversely, if it is too large, the flame retardance will be slightly improved, and the mechanical strength of the composition will be significantly deteriorated, which is not preferable.

(C) Phosphorus Compound Examples of the phosphorus compound in the present invention include phosphoric acid esters such as triphenyl phosphate, octyl diphenyl phosphate, octyl diphenyl phosphate, trioctyl phosphate, tricresyl phosphate, trixylyl phosphate; methylphosphonic acid, Ethylphosphonic acid, isopropylphosphonic acid, n-butylphosphonic acid,
Various phosphonic acids such as t-butylphosphonic acid and phenylphosphonic acid; metal salts of phosphoric acid such as sodium phosphate, potassium phosphate, magnesium phosphate, zinc phosphate, aluminum phosphate, and hydrates of these metal salts And ammonium phosphate, ammonium polyphosphate, ethylenediamine phosphate, linidine phosphate, phosphine and phosphine oxide, melamine-modified ammonium polyphosphate, red phosphorus and the like. These may be used alone or in combination of two or more. The addition amount of these phosphorus compounds is 1 to 100 parts by weight of the polyethylene resin.
It is 20 parts by weight, preferably 3 to 15 parts by weight. If the addition amount of the phosphorus compound is too small, the flame retardancy becomes insufficient, and conversely, if the addition amount is too large, the flame retardancy is slightly improved, and the mechanical properties of the composition are significantly deteriorated, which is not preferable.

Other additives, etc. In the present invention, in addition to the above flame retardant, a hydrated metal compound or the like may be added, if necessary, to enhance the flame retardancy. As the hydrated metal compound, known compounds may be used, and examples thereof include aluminum hydroxide, magnesium hydroxide, magnesium carbonate and dawsonite. Flame-retardant polyolefin-based resin compositions include phenol-based, phosphorus-based, amine-based, sulfur-based, etc. antioxidants, metal damage inhibitors, fillers, antistatic agents, stabilizers within the range that does not impair foamability. , Pigments and the like may be added.

Foam molding and foam The flame-retardant polyethylene resin composition for foaming of the present invention is preferably crosslinked depending on the foaming method and the heat resistance and physical properties of the foam product finally obtained. . As a general cross-linking method, a method of thermally decomposing a radical generator such as a peroxide blended in a resin to perform cross-linking, cross-linking by irradiation with ionizing radiation, in the presence of a polyfunctional monomer as a cross-linking aid, Examples include crosslinking by irradiation with peroxide or ionizing radiation, silane crosslinking, and the like.

As a method for producing a foam from the flame-retardant polyethylene resin composition for foaming of the present invention, for example, a substance that generates a gas by heating is mixed, and the substance is heated or degassed by gasification or decomposition. And the like, a method of generating bubbles in the polymer molded body can be mentioned. As a substance which becomes a gas generating source, (1) a substance which is itself a gas at room temperature and atmospheric pressure, but is in a state of being dispersed or dissolved in a resin, for example, carbon dioxide gas, difluorodichloromethane,
Monochlorodifluoroethane and the like (2) those that gasify when heated, such as methanol and water, and (3) compounds that generate a decomposition gas by heating, such as azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluene Examples thereof include sulfonyl hydrazide and 4,4-oxybis (benzenesulfonyl hydrazide). Carbon dioxide gas, ethanol, water and the like are called physical type blowing agents, and azodicarbonamide and the like which generate decomposition gas upon heating are called thermal decomposition type blowing agents.

The following production method is exemplified as a typical method for producing a foam using the flame-retardant polyolefin resin composition of the present invention. Crosslinking and foaming using a thermal decomposition type foaming agent The above-mentioned polyethylene resin, flame retardant type, thermal decomposition type foaming agent such as azodicarbonamide, and a predetermined amount of a polyfunctional monomer as a crosslinking aid are mixed in a single screw extruder, a twin screw extruder. Using a general-purpose kneading device such as a machine, a Banbury mixer, a kneader mixer, and a roll, the mixture is melt-kneaded at a temperature lower than the decomposition temperature of the heat-decomposable foaming agent to form a sheet. The flame-retardant polyethylene-based resin composition sheet thus obtained is irradiated with a predetermined amount of ionizing radiation to be crosslinked, thereby forming a crosslinked resin sheet. Thereafter, the crosslinked foamed product can be obtained by heating the sheet to a temperature above the decomposition temperature of the foaming agent for foaming. Examples of the ionizing radiation include α rays, β rays, γ rays, and electron beams. The thermal decomposition type foaming agent is usually added in an amount of 1 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the polyethylene resin.

Foaming in a pressure vessel A flame retardant system is blended with the polyethylene resin and molded into a desired shape such as a sheet or block with a press or an extruder. The molded body is put into a pressure vessel, the physical type foaming agent is sufficiently melted in the resin, and then the pressure is reduced to produce a foamed body. Further, a pressure vessel containing the molded body is filled with a physical foaming agent at room temperature and pressurized, and after depressurization,
It is also possible to take it out and heat it in an oil bath or an oven to foam it.

Extrusion Foaming When a polyethylene resin and a flame retardant system are put in a hopper of an extruder and extruded at a temperature near the melting point of the resin, a physical type foaming agent is press-fitted through a press-fitting hole provided in the middle of the extruder. hand,
A foam can be continuously obtained by extruding from a die having a predetermined shape.

The flame-retardant polyethylene-based resin foam obtained by using the polyethylene-based resin in the present invention is a uniform and beautiful foam and is excellent in flexibility, toughness and moldability. The reason why such an excellent effect is obtained is not always clear, but at the present stage, it is estimated as follows.

The metallocene-catalyzed polymerization reaction is characterized in that the reaction active points are uniform, so that polymers having the same molecular weight and the same degree of branching are produced by the reaction. This phenomenon is most prominent in the copolymerization of ethylene and α-olefin, as compared with the case of the usual Ziegler-Natta catalyst polymerization. In the polymerization using an ordinary catalyst, a large amount of α-olefin which is a copolymerization component is introduced into a component having a low molecular weight, and hardly introduced into a component having a high molecular weight. As a result, a very hard component,
A component having high crystallinity, a soft component and a component having low crystallinity are mixed in the resin. The process of foaming can be divided into the process of growing bubbles in the molten resin and the process of fixing the bubble cells due to crystallization and solidification of the resin. If there is a difference in the rate of formation, the process of fixing the bubble cells is affected, resulting in defective foaming due to outgassing and defective appearance due to variations in bubble diameter. It is clear that if a flame retardant is added to the resin causing the above problems, the foamability will be adversely affected.

On the other hand, in the polymerization of a polyethylene resin with a metallocene compound (metallocene catalyst), a resin having uniform molecular weight and crystallinity can be obtained. Therefore, the density, the elution temperature by the cross fractionation method and the molecular weight in the present invention can be obtained. It is considered that the resin having the specified distribution does not cause the above-mentioned problems during foaming even if the flame retardant is added.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The methods for measuring physical properties are as follows. <Appearance> The foam was visually observed and judged according to the following criteria. ○: When blurring, blistering, dents, surface roughness, etc. were not observed ×: When blurring, blistering, dents, surface roughness, etc. were observed even at one location <Cell shape> Cross-section of foam made by Hitachi Electron microscope S-2300 was used to take a 50 times electron micrograph, and it was confirmed whether or not extremely small bubbles having a diameter of 20 μm or less and maximum bubbles having a diameter of 3 mm or more were present. <Combustibility classification> The flame retardancy evaluation method is JIS D120.
Based on the combustion test No. 1, the flammability classification was determined. Self-extinguishing: 1) Extinguishing by A marked line (38 mm), or 2) Extinguishing within 50 mm and extinguishing within 60 seconds Flame retardant: Burning speed of 100 mm / min or less Flammability: Burning rate exceeding 100 mm / min <Particle size distribution of thermally expandable graphite> Using a 80 mesh sieve, the thermally expandable graphite is sieved for 10 minutes to obtain a ratio of 80 mesh or more (on) and below (pass). It was measured.

Example 1 Polyethylene resin polymerized using a metallocene compound as a polymerization catalyst (EXACT3027 manufactured by Exxon Chemical Co .; density 0.900 g).
/ Cm ³ , molecular weight distribution = 2.0, measurement result of cross distribution method and measurement result of DSC are shown in Table 1) 100 parts by weight of heat-expandable graphite (manufactured by Nippon Kasei) as a flame retardant Parts by weight, 5 parts by weight of red phosphorus (manufactured by Rin Chemical Industry Co., Ltd.),
5 parts by weight of ammonium polyphosphate (Sumitomo Chemical Co., Ltd.), 0.8 parts by weight of divinylbenzene as a crosslinking aid, 11 parts by weight of azodicarbonamide as a foaming agent, and 2,6-di-t-butyl as an antioxidant. 0.3 parts by weight of p-cresol and 0.3 of dilauryl thiodipropionate
2 parts by weight of a mixture containing 0.5 parts by weight of methylbenzotriazole as a metal damage inhibitor,
Melt kneading at 150 ° C, hot pressing, thickness 1
mm sheet was obtained. 70 sheets of ionizing radiation
Crosslinking was carried out by irradiating 2.0 Mrad with an acceleration voltage of 0 kV.
The crosslinked sheet was hung in an oven at 250 ° C to foam. The obtained foam had a uniform expansion with a foaming ratio of 20 times. The results are shown in Table 1.

[Example 2] A polyethylene resin polymerized using a metallocene compound as a polymerization catalyst (EXACT4011 manufactured by Exxon Chemical Co .; density 0 = 0.855).
g / cm ³ , molecular weight distribution = 2.1, the result of measurement by the cross distribution method and the result of measurement by DSC are shown in Table 1) 50 parts by weight and low density polyethylene (YK-40 manufactured by Mitsubishi Petrochemical Co., Ltd .; density 0. 922 g / cm ³ ) 50 parts by weight (total 100 parts by weight), 36 parts by weight of thermally expansive graphite (manufactured by Chuo Kasei Co., Ltd.) as a flame retardant, 3 parts by weight of ammonium polyphosphate (manufactured by Rin Kagaku Kogyo Co., Ltd.), a foaming agent. As azodicarbonamide (7.5 parts by weight), and as an antioxidant, 2,6-di-t
-Butyl-p-cresol (0.3 parts by weight), dilaurylthiodipropionate (0.3 parts by weight), and methylbenzotriazole (0.5 parts by weight) as a metal damage inhibitor were added in an amount of 150 parts using a two-roll mill. The mixture was melt-kneaded at 0 ° C. and further hot pressed to obtain a sheet having a thickness of 1 mm. The sheet was hung in an oven at 250 ° C to foam. The obtained foam had a uniform expansion with a foaming ratio of 9 times. The results are shown in Table 1.

[Example 3] Polyethylene resin polymerized using a metallocene compound as a polymerization catalyst (EXACT3001 manufactured by Exxon Chemical Co .; density = 0.910)
g / cm ³ , molecular weight distribution = 2.0, measurement result of cross distribution method and measurement result of DSC are shown in Table 1.) 100 parts by weight of thermal expansion graphite (Chuo Kasei) 3 as a flame retardant
Parts by weight, red phosphorus (manufactured by Rin Kagaku Kogyo Co., Ltd.) 15 parts by weight, and talc 0.6 parts by weight were added and pressed at 160 ° C. for 5 minutes to obtain a 2 mm thick sheet. This sheet and monochlorodifluoroethane as a physical foaming agent were put into a pressure vessel, and the pressure in the vessel was 25 kg /
It was held in a state of cm ³ . From this state, the pressure was released all at once to cause foaming. The obtained foam had a uniform expansion with a foaming ratio of 4 times. The results are shown in Table 1.

Example 4 Polyethylene resin polymerized by using a metallocene compound as a polymerization catalyst (EXACT2009 manufactured by Exxon Chemical Co .; density = 0.922)
g / cm ³ , molecular weight distribution = 2.2, measurement result of cross distribution method and measurement result of DSC are shown in Table 1.) 100 parts by weight of thermally expansive graphite (manufactured by Nippon Kasei) as a flame retardant 15 parts by weight, 8 parts by weight of red phosphorus (manufactured by Rin Chemical Industry Co., Ltd.),
2 parts by weight of ammonium polyphosphate (manufactured by Hoechst) and 0.6 parts by weight of talc were added at 160 ° C. for 5
After pressing for 1 minute, a 2 mm thick sheet was obtained. Charge this sheet and carbon dioxide gas as a physical type foaming agent into a pressure vessel, and
It was kept at 10 ° C. for 2 hours under the condition of the internal pressure of the container of 50 kg / cm ³ . From this state, the pressure was released all at once to cause foaming. The obtained foam had a uniform expansion with an expansion ratio of 18 times. The results are shown in Table 1.

Example 5 A foam was obtained in the same manner as in Example 1 except that the number of added parts of the thermally expandable graphite and the particle size distribution were changed as shown in Table 1. The results are shown in Table 1.

[0040]

[Table 1] (* 1) Mw: weight average molecular weight, Mn: number average molecular weight (* 2) T1: 10% by weight of total resin eluted by cross fractionation analysis (* 3) T2: end temperature of all resin elution by cross fractionation analysis ( * 4) T3: melting peak temperature by DSC analysis (* 5) T4: melting end temperature by DSC analysis

[Comparative Example 1] The polyethylene-based resin in Example 1 was replaced by a conventional linear low-density polyethylene having a density of 0.925 g / cm ³ and a molecular weight distribution of 4.0 (1044D manufactured by Idemitsu Kasei Co .; The measurement results and the DSC measurement results are shown in Table 2), and a foam was produced in the same manner as in Example 1 except that the flame retardant was not added. As a result, a foam having an expansion ratio of 18 was obtained, but there were irregularities on the surface, and thin portions of the resin, which were considered to be caused by large bubbles, were observed in some places when it was held over the light. Table 2 shows the results.

[Comparative Example 2] The polyethylene-based resin in Example 1 was replaced by a normal linear low-density polyethylene having a density of 0.925 g / cm ³ and a molecular weight distribution of 4.0 (1044D manufactured by Idemitsu Petrochemical Co., Ltd .; The measurement results and the DSC measurement results were the same as in Example 1 except that the foam was produced in the same manner as described in Table 2. As a result, the expansion ratio is 13
Although twice as many foams were obtained, there were irregularities on the surface, and thin portions of the resin, which were thought to be due to large bubbles when spotted over the light, were observed in some places. Table 2 shows the results.

[Comparative Example 3] The polyethylene-based resin used in Example 3 was replaced by an ordinary linear ultra-low density polyethylene having a density of 0.905 g / cm ³ and a molecular weight distribution of 4.0 (Tosoh Corporation 43-1; A foam was produced in the same manner as in Example 1 except that the measurement result of the cross fractionation method and the DSC measurement result were changed to those described in Table 2. The foamed product thus obtained had a foaming ratio of only 1.1 times and was out of gas. Table 2 shows the results.

[Comparative Example 4] A foamed product was obtained in the same manner as in Example 1 except that the number of parts added and the particle size distribution of the thermally expandable graphite were changed as shown in Table 2. Table 2 shows the results.

Comparative Example 5 A foam was obtained in the same manner as in Example 2 except that the number of parts added and the particle size distribution of the thermally expandable graphite were changed as shown in Table 2. Table 2 shows the results.

[0046]

[Table 2] (* 1) Mw: weight average molecular weight, Mn: number average molecular weight (* 2) T1: 10% by weight of total resin eluted by cross fractionation analysis (* 3) T2: end temperature of all resin elution by cross fractionation analysis ( * 4) T3: melting peak temperature by DSC analysis (* 5) T4: melting end temperature by DSC analysis

[0047]

EFFECTS OF THE INVENTION According to the present invention, a flame-retardant polyethylene for foaming, which does not contain a halogen-containing compound as a flame retardant, has self-extinguishing properties, and is capable of forming a beautiful foam having excellent flexibility. A resin composition and a foam obtained by foaming the resin composition can be provided. INDUSTRIAL APPLICABILITY The foam of the present invention is suitable for use as a polyolefin resin foam that requires flame retardancy.

Claims (5)

[Claims] 1. A polyethylene resin 10 polymerized using (A) a metallocene compound containing a tetravalent transition metal as a catalyst.
A flame-retardant polyethylene resin composition for foaming, comprising 0 part by weight, (B) 1 to 50 parts by weight of thermally expandable graphite, and (C) 1 to 20 parts by weight of a phosphorus compound. 2. Thermally expansive graphite is 80 mesh on 6
The flame-retardant polyethylene-based composition for foaming according to claim 1, which has a particle size of 0% by weight or more. 3. The polyethylene resin has a density of 0.860.
~ 0.950 / cm ^Three, 10 weight by cross separation method
When 100% by weight elution was completed from the temperature at which
The temperature range of mushrooms is 30 ° C or less, and the weight average molecular weight / number
The average molecular weight value is from 1.5 to 3.5.
Alternatively, the flame-retardant polyethylene composition for foaming according to 2. 4. The polyethylene resin has one crystal melting peak measured using a differential scanning calorimeter (DSC), and the temperature range from the melting peak temperature to the end of melting of all crystals is 20 ° C. Claims 1 to 3 which are within
A flame-retardant polyethylene-based composition for foaming according to any one of 1. 5. A flame-retardant polyethylene-based resin foam obtained by foaming the flame-retardant polyethylene-based resin foaming composition according to any one of claims 1 to 4.