JP2021113252A - Polyethylene resin foam and method for producing the same - Google Patents

Abstract

To provide a novel polyethylene resin foam that has a small average cell diameter, a high closed-cell ratio, and few nests.SOLUTION: A polyethylene resin foam has a polyethylene resin comprising an ethylenic polymer A of a specific structure and an ethylenic polymer B of a specific structure, the polyethylene resin having a weighted average resin density of more than 902 kg/m3.SELECTED DRAWING: None

Description

The present invention relates to a polyethylene-based resin foam and a method for producing the same.

The polyethylene-based resin foam is widely used as a cushioning material (for example, a cushioning material for packaging) because it is relatively excellent in flexibility and abrasion resistance. Polyethylene-based resin foams include bead foams, crosslinked batch foams, extruded foams, and the like, depending on the manufacturing method.

Some bead foams have excellent wear resistance. However, the bead foam has a concern that the foamed beads may fall off. Foamed beads that fall off cause contamination. Therefore, the use of the beaded foam may be restricted from the viewpoint of preventing contamination.

Since the crosslinked batch foam has excellent properties such as abrasion resistance and heat resistance, it is widely used not only as a cushioning material but also as a vehicle interior material, industrial heat insulating material, sports equipment, etc. ing. However, the polyethylene-based resin crosslinked batch foam has a drawback that the processability is poor because the heat-sealing property is inferior to that of the polyethylene-based resin extruded foam.

On the other hand, the polyethylene-based resin extruded foam produced by the extrusion method has many merits such as no possibility of the foamed beads falling off and good heat-sealing property. In recent years, polyethylene-based resin extruded foam having a fine bubble diameter has been preferred because it has a soft feel.

Various manufacturing methods have been developed for foams of polyethylene-based resins. For example, Patent Document 1 describes foaming a low-density polyethylene resin having a density of 0.922 to 0.926 g / cm ³ , a weight average molecular weight of 90,000 or more, and a crystallization rate index A of 10 or less. A low-density polyethylene-based resin foam is disclosed. Further, Patent Document 2 contains two types of polyolefin-based resins having different densities, and foamed a polyolefin-based resin composition having ^{a weighted average resin density of 0.900 g / cm 3 or less of these two types of polyolefin resins.} , Polyolefin-based resin foam sheets are disclosed.

Japanese Unexamined Patent Publication No. 3-103449 International Publication WO2016 / 052557

However, the above-mentioned prior art is not sufficient from the viewpoint of providing a polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, and few nests, and there is room for further improvement. was there.

One embodiment of the present invention has been made in view of the above problems, and an object of the present invention is to provide a novel polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, and few nests. That is.

As a result of diligent studies to solve the above problems, the present inventors have made that the average cell diameter is small, the closed cell ratio is high, and the nest is formed by containing at least two kinds of polyethylene-based polymers having a specific constitution. We have found that we can provide a small number of novel polyethylene-based resin foams, and have completed the present invention.

That is, one embodiment of the present invention includes the following configurations.
[1] A polyethylene-based resin composed of an ethylene-based polymer A and an ethylene-based polymer B is contained, and the polyethylene-based resin has a weighted average resin density of ^{more than 902 kg / m 3} , and the ethylene-based polymer A has a density. There was ^{910kg / m 3 ~935kg / m 3} , the ethylene polymer B is, (a) a density of ^{870kg / m 3 ~900kg / m 3} , and (b) a melting point of 55 ° C. to 100 ° C. There is a polyethylene-based resin foam.
[2] The polyethylene-based resin contains 60% by weight to 95% by weight of the ethylene-based polymer A and 5% by weight to 40% by weight of the ethylene-based polymer B in 100% by weight of the polyethylene-based resin. The polyethylene-based resin foam according to [1].
[3] The polyethylene-based resin foam according to [1] or [2], wherein the ethylene-based polymer A contains branched low-density polyethylene.
[4] The polyethylene-based resin foam according to any one of [1] to [3], wherein the ethylene-based polymer B contains an ethylene / α-olefin copolymer.
[5] The polyethylene-based resin foam according to any one of [1] to [4], wherein the polyethylene-based resin foam is a plate-shaped foam having a thickness of 10 mm or more.
[6] The polyethylene-based resin comprises a step A of preparing a resin melt containing a polyethylene-based resin and a step B of discharging the resin melt obtained in the step A through a die and extruding and foaming the resin melt. consists ethylene polymer a and the ethylene-based polymer B, and the weighted average resin density of 902kg / ^{m 3} greater than the ethylene polymer a has a density at 910kg ^{/ m 3} ~935kg ^/ m 3 There, the ethylene-based polymer B has a density of ^{870kg / m 3 ~900kg / m 3} , and a melting point of 55 ° C. to 100 ° C., a manufacturing method of a polyethylene resin foam.

According to one embodiment of the present invention, it is possible to provide a polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, and few nests.

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims. The technical scope of the present invention also includes embodiments or examples obtained by appropriately combining the technical means disclosed in the different embodiments or examples. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. In addition, all the academic documents and patent documents described in the present specification are incorporated as references in the present specification.

Unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more (including A and larger than A) and B or less (including B and smaller than B)".

Unless otherwise specified in the present specification, the structural units include _{a structural unit derived from an X 1} monomer, a structural unit derived from an X ₂ monomer, ..., And an X _n monomer (n is 2 or more). A copolymer containing a structural unit derived from (an integer of) is also referred to _{as an X 1} / X ₂ / ... / X _{n copolymer.} Unless otherwise specified, the X ₁ / X ₂ / ... / X _n copolymer is not particularly limited in the polymerization mode, and may be a random copolymer or a block copolymer. It may be a graft copolymer or a graft copolymer. Further, the structural unit derived from the X monomer may be referred to as "X unit".

[1. Technical Thought of One Embodiment of the Present Invention]
As a result of diligent studies by the present inventor, it has been found that the techniques described in Patent Documents 1 and 2 described above have room for improvement or problems as shown below.

In the conventional polyethylene-based resin extrusion foaming, when the temperature of the resin melt is lowered to the limit of the temperature at which the resin crystallizes in the extruder, a part of the resin in the resin melt crystallizes to obtain a foam. There was a problem that huge bubbles (nests) were generated around the crystallized part as a nucleus. In Patent Document 1, in order to solve this problem, a low-density polyethylene-based resin having a specific density, molecular weight, and crystallization rate index is obtained by blending two or more types of low-density polyethylene having different crystallization temperatures. There is. In the technique described in Patent Document 1, the low-density polyethylene to be blended has a density of 0.920 to 0.930 g / cm ³ at normal temperature and pressure. The present inventor is a low-density polyethylene obtained by blending two or more types of low-density polyethylene having a density of 0.920 to 0.930 g / cm ^{3 at normal temperature and pressure and different crystallization temperatures (hereinafter, Bren).} When using dead low-density polyethylene), we have independently found that there are the following problems. That is, when blended low-density polyethylene is used, the resin temperature tends to be difficult to drop when the resin is cooled during extrusion. Therefore, the resin temperature cannot be sufficiently lowered when the discharge amount is high and / or when the cooling capacity of the extruder is poor. As a result, the foam obtained by using the blended low-density polyethylene has a low closed cell ratio. In particular, cooling of the resin temperature is strictly required for the production of a plate-shaped foam having a small average cell diameter, a high closed cell ratio, few nests, and a large thickness. Therefore, with the technique described in Patent Document 1, it is not possible to obtain a plate-shaped polyolefin resin extruded foam having a small average cell diameter, a high closed cell ratio, few nests, and a thickness. ..

The technique described in Patent Document 2 is a technique for foaming a polyolefin-based resin composition containing two types of polyolefin-based resins having different densities and a weighted average density of 0.900 g / cm ^{3 or less.} According to the present inventor, a foam using a resin having a weighted average density of 0.900 g / cm ³ or less tends to reduce the compressive strength of the foam, and is used as a cushioning material, which is one of the main uses of the foam. We have independently found that the performance is insufficient when used.

By including at least two kinds of polyethylene-based polymers having a specific constitution, the present inventors have a small average cell diameter and a small number of nests in addition to the high closed cell ratio, which is a problem in Patent Documents 1 and 2. We have independently found that we can provide a novel polyethylene-based resin foam that can achieve the above, and have completed the present invention.

[2. Polyethylene resin foam]
Polyethylene foam according to an embodiment of the present invention comprises an ethylene-based polymer A and the ethylene-based polyethylene resin comprising a polymer B, wherein the polyethylene resin is a weighted average resin density of 902kg / m ³ than in There, the ethylene-based polymer a has a density of ^{910kg / m 3 ~935kg / m 3} , the ethylene polymer B is (a) a density of ^{870kg / m 3 ~900kg / m 3} , and (B) The melting point is 55 ° C to 100 ° C.

The "polyethylene resin foam" may be referred to as a "foam". The "polyethylene resin foam according to one embodiment of the present invention" may be referred to as the "present foam".

Since this foam has the above-mentioned structure, the average cell diameter is small, the closed cell ratio is high, and the number of nests is small. Further, the present foam has an effect that the processability is good because it is excellent in heat-sealing property.

(Polyethylene resin)
(Ethylene polymer A)
The ethylene polymer A, as a structural unit, in all the structural units 100 mol%, has a constitutional unit derived from ethylene 50 mol% or more, and as long as density of ^{910kg / m 3 ~935kg / m 3} , Other configurations are not particularly limited. The ethylene-based polymer A may have a structural unit derived from another monomer copolymerizable with ethylene. The ethylene-based polymer A may be a homopolymer of ethylene or a copolymer of ethylene and a monomer other than ethylene.

The density of ethylene polymer A ^is preferably ^{911kg / m 3 ~933kg / m 3} , more preferably from ^{913kg / m 3 ~930kg / m 3} , with 915kg / ^{m 3} ~928kg / m 3 It is more preferably 916 kg / m ^{3 to} 925 kg / m ³ . According to this configuration, there is an advantage that the balance between the foamability of the resin melt in the manufacturing process and the heat resistance of the obtained foam is excellent.

The MFR of the ethylene polymer A is not particularly limited. The MFR of the ethylene polymer A is preferably 0.1 g / 10 minutes to 10.0 g / 10 minutes, more preferably 0.3 g / 10 minutes to 7.0 g / 10 minutes, and 0.5 g / 10 minutes to 5 minutes. .0 g / 10 minutes is more preferable, 0.8 g / 10 minutes to 4.0 g / 10 minutes is further preferable, and 1.0 g / 10 minutes to 3.0 g / 10 minutes is particularly preferable. According to this configuration, the resin melt in the manufacturing process has a high melt tension and can prevent excessive shear heat generation in the extruder. As a result, in the production of the present foam, it tends to be easy to set conditions suitable for extrusion foaming.

In this specification, the MFR of the ethylene-based polymer A is a value obtained by measuring at 190 ° C. and a load of 2.16 kg according to JIS K-7210.

The melting point of the ethylene polymer A is not particularly limited. The melting point of the ethylene polymer A is larger than 100 ° C., preferably 130 ° C. or lower, more preferably 102 ° C. to 125 ° C., more preferably 103 ° C. to 120 ° C., and preferably 104 ° C. to 104 ° C. It is more preferably 118 ° C., and particularly preferably 105 ° C. to 115 ° C.

In this specification, the melting point of the ethylene polymer A is measured by a differential scanning calorimetry method (hereinafter referred to as “DSC method”). The specific operation procedure is as follows: (1) After heating 5 to 6 mg of the ethylene-based polymer A from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min and melting it; (2) ) After lowering the temperature from 220 ° C. to 40 ° C. at a temperature lowering rate of 10 ° C./min for crystallization; (3) Further raising the temperature from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min. The temperature of the peak (melting peak) of the DSC curve obtained at the time of the second temperature rise of the ethylene-based polymer A (that is, at the time of (3)) can be determined as the melting point of the ethylene-based polymer A.

Since the resin melt in the production process is excellent in foamability, the ethylene-based polymer A preferably contains branched low-density polyethylene. The ethylene-based polymer A preferably contains 50% by weight or more of branched low-density polyethylene, more preferably 60% by weight or more, and more preferably 70% by weight or more in 100% by weight of the ethylene-based polymer A. , 80% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, and particularly preferably 100% by weight. That is, the ethylene-based polymer A is particularly preferably branched low-density polyethylene. The branched low density polyethylene is sometimes referred to as "LDPE".

As the ethylene-based polymer A, one kind of polymer having the same composition of the constituent units may be used alone, or two or more kinds of polymers having different constituent units may be used in combination. .. As the ethylene-based polymer A, two or more kinds of polymers having different densities may be used in combination, and for example, two or more kinds of branched low-density polyethylenes having different densities may be used in combination. ..

(Ethylene polymer B)
The ethylene-based polymer B has (a) 50 mol% or more of ethylene-derived structural units out of 100 mol% of all structural units, and (b) a density of 870 kg / m ^{3 to} 900 kg / m. ^{As long as} it is 3 and (c) the melting point is 55 ° C. to 100 ° C., other configurations are not particularly limited. The ethylene-based polymer B may have a structural unit derived from another monomer copolymerizable with ethylene. The ethylene-based polymer B may be a homopolymer of ethylene or a copolymer of ethylene and a monomer other than ethylene.

The density of the ethylene-based polymer B ^is preferably ^{875kg / m 3 ~899kg / m 3} , more preferably from ^{880kg / m 3 ~898kg / m 3} , with 885kg / ^{m 3} ~897kg / m 3 more preferably ^in, more preferably from ^{888kg / m 3 ~896kg / m 3} , particularly preferably ^{890kg / m 3 ~895kg / m 3} . According to this configuration, there is an advantage that the balance between the foamability of the resin melt in the manufacturing process and the heat resistance of the obtained foam is excellent.

The MFR of the ethylene polymer B is not particularly limited. The MFR of the ethylene polymer B is preferably 0.1 g / 10 minutes to 20.0 g / 10 minutes, more preferably 0.5 g / 10 minutes to 15.0 g / 10 minutes, and 1.0 g / 10 minutes to 10 minutes. .0 g / 10 minutes is more preferable, 1.5 g / 10 minutes to 8.0 g / 10 minutes is further preferable, and 2.0 g / 10 minutes to 5.0 g / 10 minutes is particularly preferable. According to this configuration, the resin melt in the manufacturing process has a high melt tension and can prevent excessive shear heat generation in the extruder. As a result, in the production of the present foam, it tends to be easy to set conditions suitable for extrusion foaming. In the present specification, the MFR of the ethylene-based polymer B is a value obtained by the same method as that of the ethylene-based polymer A.

The melting point of the ethylene polymer B is preferably 60 ° C. to 97 ° C., more preferably 65 ° C. to 95 ° C., more preferably 68 ° C. to 93 ° C., and 70 ° C. to 90 ° C. It is more preferably 75 ° C to 88 ° C, and particularly preferably 80 ° C to 85 ° C. According to this configuration, there is an advantage that the heat resistance of the foam is not impaired while suppressing the generation of nests in the obtained foam. In the present specification, the melting point of the ethylene-based polymer B is a value obtained by the same method as the melting point of the ethylene-based polymer A.

Surprisingly, the present inventor has independently found that the use of the ethylene-based polymer B tends to facilitate the cooling of the resin melt made of the polyethylene-based resin. The reason for this is unclear. The present inventor has further independently found that the use of the ethylene-based polymer B has the following advantages: it is possible to reduce the rotation speed of the extruder and further cool the resin melt. thing. The reason for this is not clear, but it is presumed that one of the reasons is that the propulsive force of the resin melt in the extruder increases. The present invention is not limited to such speculation.

The ethylene-based polymer B preferably contains an ethylene / α-olefin copolymer because it is easy to adjust the molded product to a desired closed cell ratio and average cell diameter. The ethylene-based polymer B preferably contains 50% by weight or more of the ethylene / α-olefin copolymer, more preferably 60% by weight or more, and 70% by weight or more, based on 100% by weight of the ethylene-based polymer B. Is more preferable, 80% by weight or more is more preferably contained, 90% by weight or more is further preferably contained, 95% by weight or more is further preferably contained, and 100% by weight or more is particularly preferably contained. That is, the ethylene-based polymer B is particularly preferably an ethylene / α-olefin copolymer.

As the ethylene-based polymer B, one kind of polymer having the same composition of the constituent units may be used alone, or two or more kinds of polymers having different constituent units may be used in combination. .. As the ethylene-based polymer B, two or more kinds of polymers having different densities may be used in combination. As the ethylene-based polymer B, two or more kinds of polymers having different melting points may be used in combination.

The polyethylene-based resin is composed of an ethylene-based polymer A and an ethylene-based polymer B. The polyethylene-based resin contains 60% by weight to 95% by weight of the ethylene-based polymer A and an ethylene-based polymer in 100% by weight of the polyethylene-based resin (that is, 100% by weight of the total amount of the ethylene-based polymer A and the ethylene-based polymer B). It preferably contains 5% to 40% by weight of B, more preferably 65% to 95% by weight of the ethylene-based polymer A and 5% to 35% by weight of the ethylene-based polymer B, and more preferably contains 5% to 35% by weight of the ethylene-based polymer. It is more preferable to contain 70% by weight to 95% by weight of the coalescence A and 5% to 30% by weight of the ethylene-based polymer B, and 75% by weight to 95% by weight of the ethylene-based polymer A and the ethylene-based polymer B. It is more preferable to contain 5% by weight to 25% by weight, and even more preferably to contain 73% by weight to 95% by weight of the ethylene-based polymer A and 5% by weight to 27% by weight of the ethylene-based polymer B. It is particularly preferable that A is contained in an amount of 80% by weight to 95% by weight and the ethylene-based polymer B is contained in an amount of 5% to 20% by weight. According to this configuration, the resulting foam has the advantages of smaller average cell diameter, higher closed cell ratio, and / or fewer nests.

Polyethylene resin, a weighted average resin density is preferably at 903kg / ^{m 3} or more, more preferably 905 kg / ^{m 3} or more, more preferably 908 kg / ^{m 3} or more, 910 kg / ^{m 3} The above is more preferable, and 912 kg / m ³ or more is particularly preferable. According to this configuration, the obtained foam has an advantage that it tends to have excellent mechanical properties such as compressive strength.

The upper limit of the weighted average resin density of the polyethylene resin is not particularly limited. The weighted average resin density of the polyethylene resin is preferably at 935 kg / ^{m 3} or less, more preferably 930 kg / ^{m 3} or less, more preferably 928 kg / ^{m 3} or less, 925 kg / ^{m 3} or less It is more preferably 923 kg / m ³ or less, and particularly preferably less than 922 kg / m ^3.

(Other resins)
The present foam may contain other resins in addition to the polyethylene-based resin described above. Examples of other resins include (a) polyolefin resins other than the above-mentioned polyethylene resins, and (b) synthetic resins other than polyolefin resins. In the present specification, the polyethylene-based resin described above and other resins may be collectively referred to as a "raw material resin".

Examples of the polyolefin-based resin other than the above-mentioned polyethylene-based resin include polypropylene-based resins and polyethylene-based resins other than the above-mentioned polyethylene-based resin.

Examples of polypropylene-based resins include polypropylene homopolymers, polypropylene / ethylene block copolymers, polypropylene / ethylene random copolymers, propylene / α-olefin copolymers, propylene / 1-butene copolymers, and ethylene / 1-butene. Examples thereof include / propylene copolymer, propylene / vinyl chlorinated copolymer, propylene / maleic anhydride copolymer, long-chain branched polypropylene having high melt tension, isoprene-modified polypropylene, and polypropylene containing an ultra-high molecular weight component.

Examples of the polyethylene-based resin other than the above-mentioned polyethylene-based resin include high-density polyethylene, linear low-density polyethylene (LLDPE), ethylene / vinyl acetate copolymer, ethylene / propylene copolymer, and ethylene / propylene / 1-butene. Polymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, ethylene / 4-methyl-1-pentene copolymers, ethylene / 1-octene copolymers, styrene-modified polyethylene-based resins, etc. Can be mentioned.

Examples of synthetic resins other than polyolefin resins include (a) thermoplastic resins such as vinyl acetate resin, polyester resin, acrylic resin, acrylic acid ester resin, styrene resin, polyamide resin, polycarbonate resin, and polyvinyl chloride resin. , (B) Polyamide-based elastomers such as polyamide / polyol copolymers, and (c) Polyvinyl chloride-based elastomers, polybutadiene-based elastomers, ethylene / propylene rubbers, thermoplastic elastomers such as ethylene / propylene / butadiene rubbers, and the like. Be done.

The raw material resin preferably contains 50% by weight or more of the above-mentioned polyethylene-based resin, more preferably 60% by weight or more, more preferably 70% by weight or more, and 75% by weight or more, based on 100% by weight of the raw material resin. It is more preferably contained, more preferably 80% by weight or more, and further preferably 85% by weight or more. According to this configuration, (a) the resin melt is excellent in foamability, and (b) the obtained foam is a foam having a small average cell diameter, a high closed cell ratio, and few nests. Has advantages.

When the raw material resin contains a plurality of types of resins, it may be possible to specify the type and content ratio of the resin contained in the raw material resin by analyzing the foam.

(Other additives)
This foam can be used as a bubble nucleating agent, a bubble nucleating auxiliary agent, a weather resistant agent, an antioxidant, an antioxidant, a crystal nucleating agent, a heat stabilizer, an antistatic agent, a conductivity-imparting agent, and the like. It may further contain functional additives such as flame retardants, lubricants, inorganic fillers, and other additives such as colorants (eg pigments).

(Bubble nucleating agent)
Examples of the bubble nucleating agent include a pyrolytic foaming agent, an organic acid (salt) and an inorganic substance (for example, talc). As used herein, the term "organic acid (salt)" means "organic acid and / or organic acid salt". The bubble nucleating agent preferably contains a pyrolytic foaming agent and / or an organic acid (salt). If the bubble nucleating agent contains a pyrolysis foaming agent and / or an organic acid (salt), the bubble nucleating agent does not contain a pyrolysis foaming agent and / or an organic acid (salt) and is only an inorganic substance (eg, talc). The bubble diameter of the obtained foam can be made smaller more easily than in the case of containing. The bubble nucleating agent more preferably contains a pyrolysis-type foaming agent and an organic acid (salt), and further preferably consists of a mixture of a pyrolysis-type foaming agent and an organic acid (salt).

Examples of the pyrolytic foaming agent include ADCA (azodicarbonamide), DPT (N, N'-dinitropentamethylenetetramine), OBSH (4,4'-oxybisbenzenesulfonyl hydrazide), bicarbonate, and carbonate. And so on. As the pyrolytic foaming agent, a hydrogen carbonate, a carbonate, or a mixture of a hydrogen carbonate and a carbonate is preferable. Examples of the hydrogen carbonate include sodium hydrogen carbonate.

Examples of the organic acid (salt) include oxalic acid (salt), lactic acid (salt), succinic acid (salt), malic acid (salt), citric acid (salt) and the like. Citric acid (salt) is preferable as the organic acid (salt) because the effect of refining the bubble diameter is high. Examples of citric acid (salt) include citric acid, monosodium citrate, trisodium citrate, sodium hydrogen citrate, potassium citrate and the like.

As a bubble nucleating agent, since it is easy to handle and has a high effect of forming bubble nuclei, a mixture of bicarbonate and citric acid (salt), a mixture of carbonate and citric acid (salt), and One or more mixtures selected from the group consisting of bicarbonate and a mixture of carbonate and citric acid (salt) are preferred, a mixture of bicarbonate and citrate is more preferred, sodium hydrogen carbonate and citric acid. A mixture with monosodium is particularly preferred.

The content ratio of the pyrolysis foaming agent and the organic acid (salt) in the bubble nucleating agent is 10% by weight, assuming that the total amount of the pyrolysis foaming agent and the organic acid (salt) is 100% by weight. % To 90% by weight and organic acid (salt) are preferably 90% to 10% by weight, pyrolytic foaming agent is 20% to 85% by weight, and organic acid (salt) is 80% to 15% by weight. More preferably, the pyrolysis type foaming agent is 30% by weight to 80% by weight, and the organic acid (salt) is 70% by weight to 20% by weight. According to this configuration, there is an advantage that a nucleation effect can be easily obtained efficiently with a small amount of bubble nucleating agent.

In the production of the present foam, the larger the amount of the bubble nucleating agent used, the smaller the bubble diameter of the obtained foam tends to be. However, in the production of the foam, the larger the amount of the bubble nucleating agent used, the higher the production cost, and the risk of foreign matter generation due to the decomposition product of the bubble nucleating agent may increase. Therefore, the amount of the bubble nucleating agent used in the production of the present foam is preferably 0.03 parts by weight to 1.50 parts by weight, and 0.08 parts by weight to 1.20 parts by weight, based on 100 parts by weight of the polyethylene resin. The parts by weight are more preferable, and 0.10 parts by weight to 1.00 parts by weight are further preferable.

In the production of the present foam, as the bubble nucleating agent, a powdery bubble nucleating agent may be directly used, or a master batch of the bubble nucleating agent in consideration of mixing with the raw material resin is used. Is also good. As the masterbatch of the bubble nucleation agent, a commercially available product can also be used, and examples thereof include Policelen EE275F manufactured by Eiwa Kasei Kogyo and Finecell Master SSC PO217K manufactured by Dainichiseika Kogyo.

In the production of the present foam, it is possible to use a bubble nucleation aid for the purpose of promoting the effect of the bubble nucleating agent. Examples of the bubble nucleation aid include talc, silica, calcium carbonate, zeolite, zinc oxide, and lithium compounds. Examples of the lithium compound include lithium acetate, lithium oxalate, lithium citrate, lithium carbonate, lithium borate, lithium stearate and the like. The bubble nucleation aid preferably contains a lithium compound, and more preferably lithium carbonate, because it has a high effect of reducing the bubble diameter when used in combination with the bubble nucleation agent. In the production of this foam, a powdery bubble nucleation aid may be directly used as the bubble nucleation aid, and a master batch of the bubble nucleation aid in consideration of mixing with the raw material resin is used. You may use it.

(Weather resistant)
As the weathering agent, a weathering agent usually used for polyethylene-based resin foam can be used. Examples of the weather resistant agent include a hindered amine-based light stabilizer (sometimes referred to as "HALS"), an ultraviolet absorber (sometimes referred to as "UVA"), an ultraviolet shielding agent such as carbon black, and an organic nickel compound. Quenching agents such as, etc.

As HALS, as commercially available products available, (a) BASF's Tinuvin622SF, TinuvinPA123, TinuvinPA144, Tinuvin770DF, Uvinul4050FF, Chimassorb944FDL, Chimassorb2020FDL, Chimassorb's 2020FD, and (b) ADEKA. And so on.

Examples of UVA include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers.

The melting point of UVA is preferably 160 ° C. or lower, more preferably 150 ° C. or lower, and even more preferably 145 ° C. or lower, because uniform bubbles are formed. When the melting point of UVA is 160 ° C. or lower, the resin melt is difficult to solidify even when the resin temperature at the time of extrusion is lowered, and the generation of agglomerates in the resin melt can be suppressed. As a result, it is easy to obtain a foam having a uniform bubble diameter.

Weatherproofing agents such as HALS and UVA can be used in the form of liquids, powders, granules, pellets and the like. The weathering agent can also be used as a composition (so-called masterbatch) in which the weathering agent is previously mixed in a high concentration with components such as a resin and a resin additive.

The amount of the weathering agent used in the production of the foam, in other words, the content of the weathering agent in the foam is not particularly limited, but is 0.005 parts by weight with respect to 100 parts by weight of the polyethylene resin. ~ 3.000 parts by weight is preferable, 0.010 parts by weight to 0.600 parts by weight is more preferable, and 0.030 parts by weight to 0.200 parts by weight is further preferable. When the amount (content) of the weathering agent used is 0.005 parts by weight or more with respect to 100 parts by weight of the polyethylene resin, the weather resistance of the obtained foam is good. When the amount (content) of the weathering agent used is 3.000 parts by weight or less with respect to 100 parts by weight of the polyethylene resin, the bleeding of the weathering agent on the surface of the obtained foam over time is suppressed. Can be done. As a result, the transfer of the weather resistant agent to the buffered material can be suppressed.

(Antioxidant)
In the production of the present foam, it is preferable to use a weather resistant agent and an antioxidant in combination. In other words, the foam preferably contains a weathering agent and an antioxidant. According to this configuration, there is an advantage that the processing thermal stability of the weather resistant agent is excellent. Examples of the antioxidant include a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant. These antioxidants may be used alone or in combination of two or more.

Examples of the phenolic antioxidant include 2,6-di-t-butyl-4-methylphenol and tetrakis [methylene-3 (3', 5'-di-t-butyl-4-hydroxyphenyl) propionate]. Methan, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 3,9-bis [2- {3- (3-t-butyl-4-hydroxy-5-methylphenyl) ) Propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, 1,3,5-tris2 [3 (3,5-di-t-) Butyl-4-hydroxyphenyl) propionyloxy] ethyl isocyanate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris (3, 5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, pentaerythritol tetrakis [3- (3,5-Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-N-bis-3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate, 1,6 -Hexandiolbis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,2-thiobis-diethylenebis [3- (3,5-di-t-butyl-4-) Hydroxyphenyl) propionate], 2,2'-methylene-bis- (4-methyl-6-t-butylphenol), 2,2'-methylene-bis- (4-ethyl-6-t-butylphenol), 2, 2'-Methyl-bis- (4,6-di-t-butylphenol), 2,2'-ethylidene-bis- (4,6-di-t-butylphenol), 2,2'-butylidene-bis- (4,6-di-t-butylphenol) 4-Methyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol), 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-) Methylbenzyl) -4-methylphenyl acrylate, 2,4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate, tocopherols, etc. Can be mentioned. As the 2,2'-ethylidene-bis- (4,6-di-t-butylphenol), a commercially available product such as "Cheminox 1129" manufactured by Chemipro Kasei Co., Ltd. can also be used.

Examples of phosphorus-based antioxidants include tris (nonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, distearylpentaerythritol diphosphite, and bis (2,4-di-). t-Butylphenyl) pentaerythritol diphosphite, bis (2,4-di-t-butyl-6-methylphenyl) pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) ) Pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, tetrakis (2,4-di-t-butylphenyl) -4,4'-diphenylenediphosphonite, 2, 2'-Methylenebis (4,6-di-t-butylphenyl) 2-ethylhexyl phosphite, 2,2'-ethylidenebis (4,6-di-t-butylphenyl) fluorophosphite, bis (2,4) -Di-t-butyl-6-methylphenyl) ethylphosphite, 2- (2,4,6-tri-t-butylphenyl) -5-ethyl-5-butyl-1,3,2-oxaphosphorinane , 2,2', 2''-Nitrilo [triethyl-tris (3,3'5,5'-tetra-t-butyl-1,1'-biphenyl-2,2'-diyl) phosphite, 2, 4,8,10-Tetra-t-butyl-6- [3- (3-methyl-4-hydroxy-5-t-butylphenyl) propoxy] dibenzo [d, f] [1,3,2] dioxa Hosfepine and the like can be mentioned.

Examples of the sulfur-based antioxidant include dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide, di-n-butyl disulfide, di-sec-butyl disulfide, di-t-butyl disulfide, and di-t-amyl disulfide. , Dicyclohexyl disulfide, di-t-octyl disulfide, di-n-dodecyl disulfide, di-t-dodecyl disulfide and the like.

As the shrinkage inhibitor, conventionally known agents such as fatty acid esters, aliphatic amines, and fatty acid amides can be used. As the fatty acid ester, an ester of a fatty acid having 8 to 30 carbon atoms and a polyhydric alcohol having 3 to 7 hydroxyl groups is preferable. Examples of fatty acids having 8 to 30 carbon atoms include lauric acid, oleic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, heptacoic acid, montanic acid, melissic acid, and laxelic acid. Examples of the polyhydric alcohol having 3 to 7 hydroxyl groups include glycerin, diglycerin, triglycerin, erythrit arabit, xylimaat, mannitol, sorbit, and sorbitan.

Examples of the aliphatic amine include dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, eicosylamine, docosylamine, N-methyloctadecylamine, N-ethyloctadecylamine, hexadecylpropylenediamine, octadecylpropylenediamine and the like. ..

Examples of the fatty acid amide include stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, ethylene bisstearic acid amide, and lauric acid bisamide. These shrinkage inhibitors may be used alone or in combination of two or more.

Among these shrinkage inhibitors, fatty acid esters are preferable from the viewpoint of having a small effect on the foamability and physical characteristics of the foam and having a large shrinkage prevention effect. Among the fatty acid ester compounds, a partial esterified product, particularly a mono esterified product, is preferable to a complete esterified product because a more remarkable shrinkage-preventing effect can be obtained. Among the fatty acid esters, stearic acid monoglyceride, behenic acid monoglyceride, or a mixture of stearic acid monoglyceride and behenic acid monoglyceride is more preferable, and stearic acid monoglyceride (glycerin monostearate) is particularly preferable.

There are no particular restrictions on the use of colorants (pigments) in the production of this foam. In the production of the present foam, a natural color foam may be obtained without using a colorant, or a foam of a desired color may be obtained by using a colorant such as blue, red, or black. Examples of the colorant include perylene-based organic pigments, azo-based organic pigments, quinacridone-based organic pigments, phthalocyanine-based organic pigments, slene-based organic pigments, dioxazine-based organic pigments, isoindoline-based organic pigments, carbon black and the like.

The present foam may be crosslinked or non-crosslinked. The degree of cross-linking (gel fraction) of the present foam is preferably as small as possible, for example, preferably 5% by weight or less, more preferably 4% by weight or less, and even more preferably 3% by weight or less. It is more preferably 2% by weight or less, further preferably less than 2% by weight, and even more preferably 1% by weight or less. The degree of cross-linking (gel fraction) of the present foam is particularly preferably 0% by weight, that is, the present foam is particularly preferably non-cross-linked. According to this configuration, in the production of the foam, there is an advantage that the raw material and time for cross-linking can be reduced and the production cost is excellent. Further, according to the structure, the obtained foam can be returned to the original resin composition and reused, and as a result, there is an advantage that recycling is easy.

The foaming ratio of the present foam is not particularly limited and may be appropriately selected depending on the weight of the product and / or the required physical characteristics. The foaming ratio of the present foam is preferably 3 to 35 times, more preferably 4 to 33 times, further preferably 5 to 30 times, and particularly preferably 6 to 28 times. According to this configuration, the obtained foam has an advantage that it has an excellent balance of lightness, grip of the product, cushioning property and the like. Further, according to the structure, the processability of the foam for making it into a cushioning material, which is one of the main uses of the foam, is improved. As a result, the obtained foam can be processed into a cushioning material, which can be used as a cushioning material for a wide range of transported products from lightweight parts to heavy parts. In the present specification, the foaming ratio of the foam is a value obtained by the measuring method described in Examples described later.

This foam can achieve both a fine average cell diameter and a high closed cell ratio. The average cell diameter of the foam is preferably 100 μm to 600 μm, more preferably 150 μm to 500 μm, further preferably 180 μm to 500 μm, and particularly preferably 200 μm to 400 μm. According to this configuration, (a) the resulting foam can be easily adjusted to the desired closed cell ratio and foaming ratio, and (b) the obtained foam is used as a cushioning material, which is the main application of the foam. It has the advantage of excellent product protection. In the present specification, the average cell diameter of the foam is a value obtained by the measuring method described in Examples described later.

The closed cell ratio of the foam is preferably larger than 60%, more preferably 65% or more, more preferably 70% or more, more preferably 73% or more, more preferably 75% or more, and more preferably 78% or more. Preferably, 80% or more is more preferable, 83% or more is more preferable, 85% or more is more preferable, 88% or more is more preferable, and 90% or more is more preferable. According to this configuration, the obtained foam has the advantages of good cushioning performance as a cushioning material, repetitive use performance, and dimensional recovery during punching.

The thickness of the foam is not particularly limited. The thickness of the foam is preferably 10 mm or more, more preferably 10 mm to 160 mm, more preferably 20 mm to 160 mm, more preferably 20 mm to 130 mm, further preferably 30 mm to 100 mm, and particularly preferably 40 mm to 70 mm. .. According to this configuration, (a) the advantage of being able to process the foam into various cushioning material shapes, and the fact that it can be used as a cushioning material in a single piece (that is, in one foam) instead of a laminated sheet. Therefore, it has an advantage that a homogeneous material can be easily obtained as a cushioning material. The thickness of the obtained foam can be adjusted by appropriately adjusting the thickness of the opening of the die, the size of the molding die, the size of sandwiching the foam in the molding machine, the pick-up speed of the foam, and the like.

The polyethylene-based resin foam according to the embodiment of the present invention is preferably produced by extrusion foaming, and is preferably a polyethylene-based resin extrusion foam. According to this configuration, there is also an advantage that a foam having excellent heat-sealing properties and good processability can be continuously obtained.

The shape of the foam is not particularly limited, and examples thereof include a flat plate shape and a round bar shape. The present foam is preferably a polyethylene-based resin flat foam, in other words, a polyethylene-based resin foam plate. The present foam is preferably a plate-shaped foam having a thickness of 10 mm or more. According to this configuration, there is an advantage that it can be easily applied to various cushioning materials by processing such as cutting and punching.

[3. Manufacturing method of polyethylene resin foam]
In the method for producing a polyethylene-based foam according to an embodiment of the present invention, a step A for preparing a resin melt containing a polyethylene-based resin and the resin melt obtained in the step A are discharged through a die. The polyethylene-based resin is composed of an ethylene-based polymer A and an ethylene-based polymer B, and has a weighted average resin density of more than ^{902 kg / m 3, including the step B of extrusion foaming.} is a density of ^{910kg / m 3 ~935kg / m 3} , the ethylene polymer B is a density of ^{870kg / m 3 ~900kg / m 3} , and a melting point of 55 ° C. to 100 ° C..

The "method for producing a polyethylene-based resin foam according to an embodiment of the present invention" may be referred to as "the present production method".

Since this production method has the above-mentioned structure, it is possible to provide a polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, and few nests. In particular, this production method has an advantage that a polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, few nests, and a large thickness can be easily obtained.

Hereinafter, each step related to this production method will be described, but except for the matters described in detail below, [2. Polyethylene resin foam] section is incorporated.

(Step A)
Step A is a step of preparing a resin melt by melt-kneading a resin composition containing a polyethylene-based resin. Step A can also be said to be a step of preparing a resin melt to be discharged through a die in step B. The resin melt may include a polyethylene-based resin, a foaming agent, and optionally other resins and / or other additives.

The specific aspect of the step A is not particularly limited. In step A, a tandem extruder in which a twin-screw extruder and a single-screw extruder are connected, or a tandem extruder in which a single-screw extruder and a single-screw extruder are connected may be used. Further, in step A, a static mixer may be used in addition to the extruder. Specific embodiments of step A include a method of sequentially performing the following operations (A1) to (A5): (A1) (a) polyethylene-based resin and, if necessary, (b) (b). -1) Other resins and (b-2) Other additives such as weather resistant agent, bubble nucleating agent and shrinkage inhibitor are prepared in predetermined amounts, and all the prepared raw materials are used in the first extruder (first stage). Supply to an extruder (biaxial); (A2) melt-knead the supplied raw materials at a temperature suitable for kneading; (A3) a first extruder for the obtained mixture (melt-kneaded product). A foaming agent is press-fitted in the middle of the process to prepare a resin melt; (A4) The obtained resin melt is adjusted to a desired discharge amount, and the first extruder is connected to the first extruder. Discharge to a two extruder (second stage extruder, single shaft); (A5) In the second extruder, the resin melt is cooled to a desired temperature. In the present specification, other resins used as necessary are also referred to as "arbitrary resins", other additives used as necessary are also referred to as "optional additives", and optional resins and optional additives are collectively referred to as "optional additives". Also referred to as "arbitrary component".

In the above (A1), the operation of supplying all the prepared raw materials to the first extruder will be specifically described. For all the prepared raw materials, each raw material may be supplied to the first extruder from a separate feeder, or a part or all of the raw materials may be supplied to the first extruder together. When each of the prepared raw materials is supplied to the first extruder from a separate feeder, each raw material may be supplied to the first extruder at the same time, or may be supplied at any time. When a part or all of the prepared raw materials are supplied to the first extruder together, a part or all of the prepared raw materials may be mixed in advance to form a mixture, and the mixture may be supplied to the first extruder.

The temperature suitable for kneading in (A2) is that the polyethylene-based resin and the optional resin are surely melted, and the melted polyethylene-based resin and the optional resin, the foaming agent, and the optional additive are preferably kneaded. Any temperature is acceptable, and the temperature is not particularly limited. In one embodiment of the present invention, the temperature suitable for the kneading is preferably a temperature equal to or higher than the melting point of the polyethylene resin. When the bubble nucleating agent is used in one embodiment of the present invention, the temperature suitable for the kneading is preferably a temperature at which the effect of the bubble nucleating agent used is efficiently exhibited. When the bubble nucleating agent contains a thermally decomposable foaming agent, the temperature at which the effect of the bubble nucleating agent is efficiently exhibited is the temperature at which the decomposition of the pyrolytic foaming agent proceeds sufficiently and the desired nucleation action is obtained. It is the temperature to be. For example, when a mixture of sodium hydrogen carbonate and citric acid is used as the bubble nucleating agent, the temperature suitable for the kneading is 180 ° C. to which the effect of the bubble nucleating agent is efficiently exhibited. 230 ° C is preferable.

In this production method, a composition composed of a polyethylene-based resin, a foaming agent and an optional component is also referred to as a resin composition. The resin melt obtained in (A3) above is intended as a melt-kneaded product of the resin composition.

In the above (A5), the resin melt cooled to a desired temperature is discharged through a die in the subsequent step B. Therefore, the desired temperature in (A5) is also referred to as a resin temperature.

(Resin temperature)
The step A preferably further includes a step of cooling the temperature of the resin melt to a desired resin temperature. The resin temperature is preferably Tm-27 ° C. or higher, more preferably Tm-18 ° C. or higher, and more preferably Tm-10 ° C. or higher with respect to the melting point (° C.) (hereinafter referred to as Tm) of the ethylene polymer A. , Tm-6 ° C. or higher is more preferable, and Tm-5 ° C. or higher is particularly preferable. The resin temperature is preferably Tm + 12 ° C. or lower, more preferably Tm + 8 ° C. or lower, more preferably Tm + 5 ° C. or lower, further preferably Tm + 2 ° C. or lower, and particularly preferably Tm-1 ° C. or lower. According to this configuration, a foam having a high closed cell ratio and few nests can be obtained.

(Foaming agent)
In this production method, a foaming agent may be used, and the foam may contain a foaming agent. The foaming agent that can be used in this production method is not particularly limited as long as it is a commonly used foaming agent used in extrusion foaming, and for example, (a) (a-1) propane, normal butane, isobutane, and the like. Aliper hydrocarbons such as normal pentane, isopentane and hexane; (a-2) alicyclic hydrocarbons such as cyclopentane and cyclobutane; (a-3) ethers such as dimethyl ether, diethyl ether and methyl ethyl ether; (A-4) Alcohols such as methanol and ethanol; (a-5) Inorganic gases such as air, nitrogen and carbon dioxide; and (a-6) Water and other physical foaming agents, and (b) Hydrocarbons. Examples thereof include chemical foaming agents containing thermally decomposable foaming agents such as sodium carbonate, azodicarboxylic amide, and dinitrosopentamethylenetetramine. Among these, as the foaming agent, a physical foaming agent is preferable, and aliphatic hydrocarbons are more preferable, and particularly, because a desired foaming ratio, a desired closed cell ratio, and a desired average cell diameter can be easily obtained. Normal butane and / or isobutane are preferred.

The above-mentioned foaming agent may be used alone or in combination of two or more.

The amount of the foaming agent used is not particularly limited. The amount of the foaming agent used may be appropriately adjusted according to the type of the foaming agent and the target foaming ratio of the foam. The total amount of the foaming agent used in this production method is preferably 0.5 parts by weight to 20.0 parts by weight, preferably 1.0 parts by weight to 15.0 parts by weight, based on 100 parts by weight of the polyethylene resin. Is more preferable.

(Step B)
The step B is a step of obtaining a polyethylene-based resin foam by discharging (that is, extruding) the resin melt obtained in the step A through a die and extruding and foaming the resin melt.

In step B, foams having various shapes such as a flat plate-shaped foam and a round bar-shaped foam can be produced by appropriately selecting the shape of the die according to the shape of the target foam. This manufacturing method is suitable for a method for manufacturing a flat foam, in other words, a polyethylene-based resin foam plate.

In step B, the conditions for picking up the discharged foam, the cooling conditions for the discharged foam, the size of the molding die used for molding the foam, the dimensions for sandwiching the foam in the molding machine, and the like are appropriately determined. You can set it.

Hereinafter, an embodiment of the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

The test methods and criteria used for the various evaluation methods in the examples and comparative examples are as follows.

<Melt flow rate (MFR)>
The MFR of the ethylene-based polymer A, B or C was measured in accordance with the provisions of Method A described in JIS K 7210 (1999). Specifically, a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the amount of resin (g) extruded from the die in a unit time under a constant load (2.16 kg) at 190 ° C. A value obtained by converting the obtained resin amount (g) into the resin amount (g) extruded in 10 minutes was calculated.

The unit time is 120 seconds when the melt flow rate is more than 0.5 g / 10 minutes and 1.0 g / 10 minutes or less, and is when the melt flow rate is more than 1.0 g / 10 minutes and 3.5 g / 10 minutes or less. Is 60 seconds, more than 3.5 g / 10 minutes and less than 10 g / 10 minutes for 30 seconds, more than 10 g / 10 minutes and more than 25 g / 10 minutes for 10 seconds, more than 25 g / 10 minutes and more than 100 g / 10 When it was less than a minute, it was set to 5 seconds, and when it exceeded 100 g / 10 minutes, it was set to 3 seconds.

The amount of resin extruded from the die per unit time was defined as one resin unit. In the measurement of MFR, 3 units of resin are collected, a value converted into the amount of resin (g) extruded in 10 minutes is calculated for each unit, and the average value is the ethylene polymer A, B or C. MFR. If it was not possible to collect 3 units of resin in one measurement, the measurement was continued until 3 units could be collected. If the melt flow rate when measured in a certain unit time was not within the corresponding range, the measurement was performed again in a unit time corresponding to the melt flow rate.

<Weighted average density>
For each resin component (ethylene-based polymer A and ethylene-based polymer B) to be blended as a polyethylene-based resin, the resin density (kg / m ³ ) and the blending amount (when the total amount of the resin components is 100% by weight), ^{The weighted average density (kg / m 3} ) of the polyethylene-based resin was obtained by multiplying (% by weight of the components to be blended) and adding the values obtained for each resin component to be blended.

<Closed cell ratio>
From each of the foams obtained in Examples and Comparative Examples, three test pieces having a length of 30 mm, a width of 20 mm, and a thickness of 20 mm were cut out. ^{Using the test piece, the volume Vc (cm 3} ) of the test piece was measured using an air pycnometer (air comparative hydrometer model 1000 manufactured by Tokyo Science Co., Ltd.) in accordance with the method described in ASTM D2856. Next, the same test piece after the measurement was submerged in ethanol in a measuring cylinder containing ethanol. ^{The apparent volume Va (cm 3} ) was determined from the amount of increase in the liquid level (ethanol level) of the graduated cylinder. Such a method of measuring the apparent volume may be referred to as a submersion method. The closed cell ratio (%) was calculated according to the following formula:
Closed cell ratio (%) = (Vc / Va) × 100.

The measurement was carried out for three test pieces per foam, and the average value was taken as the closed cell ratio of the foam.

<Foam density>
Using the weight W (kg) of the test piece used in the measurement of the closed cell ratio and the volume Va (m ³ ) determined by the submersion method, the foam density was determined by the following formula:
Foam density (kg / m ³ ) = W / Va.

The measurement was carried out for three test pieces per foam, and the average value was taken as the density of the foam.

<Effervescence magnification>
The resin density of the raw material resin (a blend of the ethylene-based polymer A, the ethylene-based polymer B, and the ethylene-based polymer C used) used in Examples and Comparative Examples was measured according to JIS K 7112. Using the foam density (kg / m ³ ) and the resin density (kg / m ³ ), the foaming ratio was calculated by the following formula:
Foaming magnification (times) = resin density / foam density.

<Foam size>
For the foams obtained in Examples and Comparative Examples, the surface perpendicular to the thickness direction was designated as the surface a, the surface perpendicular to the extrusion direction was designated as the surface b, and the surface perpendicular to the width direction was designated as the surface c. Here, the thickness direction of the foam can be said to be the short direction in the cross section perpendicular to the extrusion direction of the foam, and the width direction of the foam can be said to be the longitudinal direction in the cross section perpendicular to the extrusion direction of the foam. .. The foams obtained in Examples and Comparative Examples were cut along the surface b to prepare three samples A having a length in the extrusion direction of 20 mm. For sample A, the length in the thickness direction and the length in the width direction were measured. The length in the thickness direction will be specifically described. For each sample A, the length in the thickness direction was measured at a total of three locations, the center in the width direction and 30 mm inside from both ends in the width direction. The average value of a total of 9 values at 3 locations for each of the 3 samples A was defined as the length (thickness dimension) in the thickness direction of the foam. The length in the width direction will be specifically described. For each sample A, the length in the width direction was measured. The average value of the values of the three samples A was taken as the length (width dimension) in the width direction of the foam. Further, the product of the obtained thickness dimension and width dimension was calculated, and the product was used as the cross-sectional area.

<Average cell diameter>
From each of the three samples A prepared by measuring the foam size, a cube (referred to as sample B) having a side of 5 to 10 mm was cut out at each measurement point (5 points) shown below. Use a double-edged razor [Feather, high stainless double-edged] along the plane parallel to each of the above-mentioned surfaces a, b, and c, and take sufficient care not to destroy the bubble film (cell film). And disconnected. The obtained cut surfaces (three surfaces) were observed using a microscope [VHX-900, manufactured by KEYENCE CORPORATION], and images of each cut surface were obtained. In each of the obtained images, a line segment having a length of 4000 μm was drawn, the number of bubbles n through which the line segment passed was measured, and the bubble diameter was calculated by the following formula:
Bubble diameter (μm) = 4000 / n.

The arithmetic mean value of the bubble diameters obtained from the images of the three cut surfaces of the sample B (15 pieces) obtained for each measurement point (5 points) of the three samples A is defined as the average bubble diameter (μm). did. That is, the arithmetic mean value of the bubble diameters of 45 faces (3 faces x 5 locations x 3 samples A) was defined as the average bubble diameter (μm).

The measurement points will be described for Sample A. As shown below, 5 points were measured for one sample A:
(A) Central portion in the width direction and the thickness direction on the surface b of the sample A (one point, referred to as "measurement point A");
(B) The central portion of the surface b of the sample A in the thickness direction, the central portion between the measurement point A and the end portion in the width direction (two locations at both ends in the width direction);
(C) The central portion of the surface b of the sample A in the width direction, the central portion between the measurement point A and the end portion in the thickness direction (two locations at both ends in the thickness direction).

<Evaluation of nest (cavity)>
The foams obtained in Examples and Comparative Examples were cut along the surface b to prepare three samples C having a length in the extrusion direction of 120 mm. Sample C was cut along the surface b with a pan-cut slicer to prepare Sample D having a length of 15 mm in the extrusion direction. Seven sample Ds were prepared for each sample C, and a total of 21 sample Ds were prepared. Of the 21 samples D, 20 samples D arbitrarily selected were cut with a pan-cut slicer and the cut surface obtained was observed to examine the presence or absence of cavities. The major axis and the minor axis were measured for each of the discovered cavities, and the average value of the major axis and the minor axis was taken as the average diameter of the cavity. Using the obtained average diameter, points were given according to the following criteria. The number of cavities is the total value of the cross sections of 20 samples D.

5 points: No cavities with an average diameter of 1 mm or more 4 points: There are cavities with an average diameter of 1 mm or more and less than 2 mm, and there are no cavities with an average diameter of 2 mm or more and less than 5 mm 3 points: Average diameter of 2 mm or more and less than 5 mm There are 1 or more and 3 or less cavities, and there are no cavities with an average diameter of 5 mm or more.・ A series of evaluations from sampling of sample C with cavities with an average diameter of 5 mm or more to scoring were performed for any three locations with different foams, and the total score of the three locations was 10 points or more (5 points x). 3 places = 15 points out of 100).

The raw materials used in the following examples and comparative examples are as follows.

<Polyethylene resin>
The ethylene-based polymer A and the ethylene-based polymer B shown below were mixed in the blending amounts shown in Tables 1 and 2 to obtain a polyethylene-based resin.
(Ethylene polymer A)
A-1: Branched low density polyethylene "C470" (made of Ube Maruzen polyethylene, MFR 2.0 g / 10 minutes, density 918 kg / m ³ , melting point Tm 109 ° C)
A-2: Branched low-density polyethylene "450E" (manufactured by Dow Chemical, MFR 2.0 g / 10 minutes, density 923 kg / m ³ , melting point Tm 113 ° C)
A-3: Branched low-density polyethylene "G201" (manufactured by Sumitomo Chemical, MFR 2.0 g / 10 minutes, density 919 kg / m ³ , melting point Tm 107 ° C)
(Ethylene polymer B)
B-1: Ethylene / α-olefin copolymer "A-20090S" (manufactured by Mitsui Chemicals, Inc., density 893 kg / m3, MFR 18 g / 10 minutes, melting point Tm 82 ° C.)
B-2: Ethylene / α-olefin copolymer "DF940" (manufactured by Mitsui Chemicals, Inc., density 893 kg / m3, MFR 3.6 g / 10 minutes, melting point Tm 82 ° C.)
B-3: Ethylene / α-olefin copolymer "DF840" (manufactured by Mitsui Chemicals, Inc., density 885 kg / m3, MFR 3.6 g / 10 minutes, melting point Tm70 ° C.).

<Ethylene polymer C>
The following ethylene-based polymer C was used as a resin other than the polyethylene-based resin.
C-1: Ethylene / α-olefin copolymer "KF370" (manufactured by Japan Polyethylene Corporation, density 905 kg / m3, MFR 3.5 g / 10 minutes, melting point Tm 98 ° C)
C-2: Linear low-density polyethylene "0540F" (made of Ube-Maruzen polyethylene, MFR 4.0 g / 10 minutes, density 904 kg / m ³ , melting point Tm 112 ° C)
<Bubble nucleating agent>
As the bubble nucleating agent, "EE275F" manufactured by Eiwa Kasei Co., Ltd., which is a mixture of a pyrolytic foaming agent and an organic acid (salt), was used. EE275F is a masterbatch containing a mixture of sodium bicarbonate and citric acid.

<Anti-shrinkage agent>
Monoglyceride stearate was used as the shrinkage inhibitor.

(Example 1)
Each of the ethylene-based polymer A, the ethylene-based polymer B, the ethylene-based polymer C, the bubble nucleating agent, and the shrinkage inhibitor was prepared in the blending amounts shown in Table 1. The prepared raw material was supplied to the first extruder of the tandem extruder apparatus. Here, as the tandem extruder device, a tandem extruder device in which a twin-screw extruder having a diameter of 40 mm is connected as the first extruder and a single-screw extruder having a diameter of 90 mm is connected as the second extruder is used. The first extruder was set at 220 ° C., that is, the mixture supplied to the first extruder was melt-kneaded at 220 ° C. Here, 2.0 parts by weight of isobutane as a foaming agent was press-fitted into the obtained mixture from the middle of the first extruder. By such an operation, a resin melt was prepared.

Subsequently, the obtained resin melt was discharged from the first extruder to the second extruder (diameter 90 mm). Then, in the second extruder, the resin melt was cooled so that the resin temperature became the temperature shown in Table 1 by adjusting the barrel temperature and the screw rotation speed. Subsequently, the resin melt was discharged from the die attached to the tip of the second extruder at a discharge rate Q of 35 kg / hour under atmospheric pressure to extrude and foam. Here, the die had a rectangular shape, and the size of the opening of the die was 50 mm × 50 mm.

Subsequently, the foam extruded from the die is rectangularized with a molding die, and the foam is adjusted in size while adjusting the take-up speed with a molding machine to be molded into a plate shape having a width of 140 mm and a thickness of 55 mm. A plate-shaped foam was obtained. The obtained plate-shaped foam had no nests and had a high closed cell ratio. Table 1 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Examples 2 to 7)
A plate-shaped foam was obtained by the same method as in Example 1 except that each formulation and resin temperature were changed as shown in Table 1. Table 1 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Comparative Example 1)
A plate-shaped foam was obtained in the same manner as in Example 1 except that the blending amount of the ethylene-based polymer A used was changed to the amount shown in Table 2 and the ethylene-based polymer B was not used. rice field. Table 2 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Comparative Example 2)
A plate-shaped foam was obtained in the same manner as in Example 3 except that the blending amount of the ethylene-based polymer A used was changed to the amount shown in Table 2 and the ethylene-based polymer B was not used. rice field. Table 2 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Comparative Example 3)
The plate was prepared in the same manner as in Example 1 except that the ethylene-based polymer B was not used and the ethylene-based polymer A and the ethylene-based polymer C C-1 were used in the amounts shown in Table 2. A foam was obtained. Table 2 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Comparative Example 4)
The ethylene-based polymer A used was changed to A-2 and A-3, the blending amounts of A-2 and A-3 were set to the amounts shown in Table 2, and the ethylene-based polymer B was not used and the ethylene-based polymer B was not used. A plate-shaped foam was obtained in the same manner as in Example 7 except that the rotation speed of the second extruder was adjusted in order to adjust the pressure balance between the first extruder and the second extruder. Table 2 shows the results of measuring and evaluating various physical properties of the obtained foam.

(Comparative Example 5)
A plate-shaped foam was obtained in the same manner as in Example 6 except that the blending amounts of the ethylene-based polymer A and the ethylene-based polymer B used were changed to the amounts shown in Table 2. Table 2 shows the results of measuring and evaluating various physical properties of the obtained foam.

As shown in Table 1, Examples 1 to 7 had a small average cell diameter, a high closed cell ratio, and no nest.

As shown in Table 2, in Comparative Examples 1 to 3, the obtained foams had a low "nest" evaluation score.

In Comparative Example 4, the pressure at the tip of the first extruder tended to increase as compared with Example 7. On the other hand, the screw rotation speed of the second extruder was increased. As a result, in Comparative Example 4, the resin temperature was high, and the obtained foam had a low closed cell ratio.

As shown in Table 2, in Comparative Example 5, the obtained foam had a low closed cell ratio.

According to one embodiment of the present invention, it is possible to provide a polyethylene-based resin foam having a small average cell diameter, a high closed cell ratio, and few nests. Therefore, one embodiment of the present invention can be suitably used for various cushioning materials, packaging materials, heat insulating materials, and the like.

Claims (6)

Contains a polyethylene-based resin composed of an ethylene-based polymer A and an ethylene-based polymer B.
The polyethylene-based resin has a weighted average resin density of more than ^{902 kg / m 3.}
The ethylene polymer A is a density of ^{910kg / m 3 ~935kg / m 3} ,
The ethylene polymer B is, (a) a density of ^{870kg / m 3 ~900kg / m 3} , and (b) a melting point of 55 ° C. to 100 ° C., a polyethylene resin foam. Claim 1 that the polyethylene-based resin contains 60% by weight to 95% by weight of the ethylene-based polymer A and 5% by weight to 40% by weight of the ethylene-based polymer B in 100% by weight of the polyethylene-based resin. The polyethylene-based resin foam according to. The polyethylene-based resin foam according to claim 1 or 2, wherein the ethylene-based polymer A contains branched low-density polyethylene. The polyethylene-based resin foam according to any one of claims 1 to 3, wherein the ethylene-based polymer B contains an ethylene / α-olefin copolymer. The polyethylene-based resin foam according to any one of claims 1 to 4, wherein the polyethylene-based resin foam is a plate-shaped foam having a thickness of 10 mm or more. Step A to prepare a resin melt containing a polyethylene-based resin,
Including the step B in which the resin melt obtained in the step A is discharged through a die and extruded and foamed.
The polyethylene-based resin is composed of an ethylene-based polymer A and an ethylene-based polymer B, and has a weighted average resin density of more than ^{902 kg / m 3.}
The ethylene polymer A is a density of ^{910kg / m 3 ~935kg / m 3} ,
The ethylene polymer B is a density of ^{870kg / m 3 ~900kg / m 3} , and a melting point of 55 ° C. to 100 ° C., a manufacturing method of a polyethylene resin foam.