JP2023065202A - Cushioning material for glass substrates - Google Patents

Abstract

To provide a cushioning material for glass substrates that comprises a polyethylene resin foam with reduced shrinkage after its production, the cushioning material also allowing for reduced contamination of the glass substrate.SOLUTION: The present invention provides a cushioning material for glass substrates comprising a polyethylene resin foam, formed by extrusion-foaming a composition comprising a polyethylene resin and a specific amount of a shrinkage inhibitor with a foamer comprising isobutane of 60 mol% or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cushioning material for glass substrates.

2. Description of the Related Art As electronic devices such as flat panel displays have become more sophisticated, careful handling and storage of glass substrates used in the manufacture of electronic devices is required. Problems that occur during transport and storage of glass substrates include physical damage, dust adhesion, organic matter contamination, and static electricity. These problems cause yield in the manufacture of electronic devices.

Conventionally, a method of transporting and storing a plurality of glass substrates by stacking a plurality of glass substrates with interleaving paper between the glass substrates has been adopted. As the interleaving paper, for example, a polyethylene-based resin foam sheet is used.

For example, in Patent Document 1, a polyethylene resin (A), a polymeric antistatic agent (B), and a masterbatch (C) containing an anionic surfactant and a base resin are melt-mixed, A method for producing a polyethylene-based resin foam sheet is disclosed in which a molten mixture is extruded and foamed. In the production method of Patent Document 1, the melt mass flow rate of the base resin and the melt mass flow rate of the polyethylene resin satisfy a specific relational expression, and the melt mass flow rate of the polyethylene resin is within a specific range.

On the other hand, the polyethylene-based resin extruded foam has good cushioning performance and can be suitably used as a cushioning material for glass substrates.

In recent years, shrinkage inhibitors (anti-shrinkage agents) are generally used in the production of extruded polyethylene resin foams.

For example, in Patent Document 2, a low-density polyethylene resin having a specific melt index is placed in an extruder together with a foaming agent and an anti-shrinking agent consisting of isobutane alone or a mixture with another foaming agent containing 60 mol% or more of isobutane. A method for producing a low-density polyethylene-based resin foam is disclosed, which includes a step of melt-kneading at to form a foamable melt-kneaded product.

Patent Document 3 describes a method of obtaining a foam by extruding a molten gel obtained by supplying a polyolefin resin, a foaming agent, a cell nucleus controlling agent, etc. into an extruder, heating and kneading, into a low pressure region, A method for producing a polyolefin resin foam is disclosed, which is characterized by feeding both of two specific fatty acid esters into an extruder.

Patent Document 4 discloses a polyolefin resin foam characterized by heating and mixing a non-crosslinked polyolefin resin containing a complete ester represented by a specific general formula and a volatile organic foaming agent, followed by extrusion foaming. A method of manufacture is disclosed.

JP 2013-124269 A JP-A-2-303815 JP-A-7-48469 Japanese Patent Publication No. 58-025339

However, the above-described conventional techniques are not sufficient from the viewpoint of achieving both suppression of shrinkage of the polyethylene resin foam and reduction of contamination of the glass substrate by the cushioning material containing the polyethylene resin foam. There was room for further improvement.

One embodiment of the present invention has been made in view of the above problems, and an object thereof is to provide a cushioning material for a glass substrate containing a polyethylene-based resin foam that shrinks little after production, and that does not contaminate the glass substrate. It is to provide a novel small cushioning material for a glass substrate.

As a result of intensive studies aimed at solving the above problems, the present inventors have found that the above problems can be solved by using a specific shrinkage inhibitor in a specific amount, and have completed the present invention.

That is, one embodiment of the present invention includes the following configurations:
[1] A cushioning material for a glass substrate containing a polyethylene-based resin foam, wherein the polyethylene-based resin foam comprises a composition containing a polyethylene-based resin and a shrinkage inhibitor having a melting point of 85°C or higher, and isobutane. The composition is formed by extrusion foam molding using a foaming agent containing 60 mol% or more of the above, and the composition contains 0.05 to 0.50 parts by weight of the shrinkage inhibitor with respect to 100 parts by weight of the polyethylene resin. A cushioning material for glass substrates.
[2] The polyethylene resin includes an uncrosslinked polyethylene resin A and a slightly crosslinked polyethylene resin B, and the uncrosslinked polyethylene resin A is uncrosslinked branched low-density polyethylene 55 to 100 parts by weight. It contains 0 to 45 parts by weight of an uncrosslinked ethylene/α-olefin copolymer, and the slightly crosslinked polyethylene resin B contains 55 to 100 parts by weight of slightly crosslinked branched low-density polyethylene and slightly crosslinked. 0 parts by weight to 45 parts by weight of an ethylene/α-olefin copolymer, and the polyethylene resin contains, with respect to a total of 100% by weight of the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B, The cushioning material for a glass substrate according to [1], containing 5% by weight to 45% by weight of the slightly crosslinked polyethylene resin B.
[3] The cushioning material for a glass substrate according to [1] or [2], wherein the polyethylene-based resin foam is plate-shaped.
[4] The cushioning material for a glass substrate according to any one of [1] to [3], wherein the polyethylene-based resin foam has a thickness of 20 mm to 200 mm.
[5] The cushioning material for a glass substrate according to any one of [1] to [4], wherein the polyethylene-based resin foam has an expansion ratio of 4 to 35 times.
[6] The cushioning material for a glass substrate according to any one of [1] to [5], wherein the shrinkage inhibitor is 12-hydroxystearic acid triglyceride.

According to one embodiment of the present invention, it is possible to provide a cushioning material for a glass substrate that contains a polyethylene-based resin foam that undergoes little shrinkage after production and that causes little contamination of the glass substrate. Effective.

An example of a differential molecular weight distribution curve of raw material polyethylene resin and a differential molecular weight distribution curve of slightly crosslinked polyethylene resin is shown.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. Further, embodiments or examples obtained by combining technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. In addition, all the scientific literatures and patent documents described in this specification are used as references in this specification. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

In addition, unless otherwise specified in this specification, the structural units include a structural unit derived from the ^X1 monomer, a structural unit derived from the ^X2 monomer, ... and an ^Xn monomer (n is An integer of 2 or more) is also referred to as "X ¹ /X ² /.../X ⁿ copolymer". The X ¹ /X ² /.../X ⁿ copolymer is not particularly limited in its polymerization mode unless otherwise specified, and may be a random copolymer or a block copolymer. may be a graft copolymer.

Further, in this specification, a structural unit derived from a Y monomer is referred to as a "Y unit".

[I. Technical idea according to one embodiment of the present invention]
As described above, a polyethylene-based resin foam sheet is conventionally used as interleaving paper for transporting and storing a plurality of glass substrates. On the other hand, a polyethylene-based resin extruded foam can also be suitably used as a cushioning material for glass substrates.

Freon-based blowing agents have been used in the production of polyethylene-based resin extruded foams. However, in recent years, environmental problems such as global warming have become apparent, and it has become difficult to use flon-based blowing agents with low environmental compatibility, which may lead to the depletion of the ozone layer. Therefore, in recent years, the use of non-Freon-based foaming agents (for example, aliphatic hydrocarbons such as butane) as foaming agents in the production of extruded polyethylene resin foams by the extrusion foaming method has been investigated. Butane has a faster gas permeation rate than Freon. Therefore, when butane is used as a foaming agent, the foaming agent (butane) rapidly diffuses from the resulting foam after extrusion foaming, which may reduce the pressure in the cells, resulting in significant shrinkage of the foam. There is If the foam shrinks significantly after extrusion foaming, even if air flows into the cells of the foam, it will not recover to the desired expansion ratio.

Therefore, when using butane as a blowing agent, the use of a shrinkage inhibitor has been proposed to suppress the shrinkage of the foam after extrusion foaming.

The present inventors have extensively studied the production of polyethylene-based resin foams using butane as a foaming agent. In the course of intensive studies, the present inventor independently obtained the following findings: (1) When a large amount of shrinkage inhibitor is used to suppress the shrinkage of the foam, the foaming agent diffuses from the foam. Too slow, and the blowing agent will remain in the foam in large amounts for a long period of time. As a result, there is a risk that the foam will undergo dimensional changes after processing due to changes in the residual amount of the foaming agent in the foam and changes in the internal pressure of the cells due to the inflow of atmospheric air into the cells. In order to reduce such dimensional changes, it is necessary to take a long curing period in order to sufficiently diffuse the blowing agent from the foam; and (2) to suppress shrinkage of the foam, a large amount of shrinkage inhibitor is used. If so, the shrinkage inhibitor bleeds out of the foam. As a result, when the foam is used as a cushioning material for a glass substrate, the shrinkage inhibitor that bleeds out may cause cloudiness on the surface of the glass and contaminate the glass substrate.

That is, when a polyethylene resin foam using butane as a foaming agent is applied to a glass substrate, from the viewpoint of achieving both shrinkage suppression of the polyethylene resin foam and reduction of contamination of the glass substrate, further developments have been made in the prior art. There was room for

As a result of intensive studies aimed at solving the above problems, the present inventors have found that the addition of a specific shrinkage inhibitor in a specific amount reduces the gas permeability of isobutane, a foaming agent, to a polyethylene resin. . Therefore, by adding a specific amount of a specific shrinkage inhibitor and using a foaming agent whose main component is isobutane, the shrinkage rate is very small, and it is possible to suppress stains such as white cloudiness on the glass substrate. The inventors have found that a foam can be obtained, and have completed the present invention.

[II. Cushioning material for glass substrate]
A cushioning material for a glass substrate according to an embodiment of the present invention is a cushioning material for a glass substrate containing a polyethylene-based resin foam, and the polyethylene-based resin foam has a polyethylene-based resin and a melting point of 85°C or higher. A composition containing a shrinkage inhibitor is subjected to extrusion foam molding using a foaming agent containing 60 mol% or more of isobutane, and the composition contains the shrinkage inhibitor with respect to 100 parts by weight of the polyethylene resin. Contains 0.05 to 0.50 parts by weight.

Since the cushioning material for a glass substrate according to one embodiment of the present invention has the structure described above, it has the advantage that the glass substrate is less contaminated. Moreover, since the cushioning material for a glass substrate according to one embodiment of the present invention has the above-described structure, it has the advantage of including a polyethylene-based resin foam that shrinks little after production.

The composition according to one embodiment of the present invention can be made into a polyethylene-based resin foam by subjecting the composition to extrusion foam molding using a foaming agent. Further, the polyethylene-based resin foam can be used as a cushioning material for glass substrates. In this specification, the "composition according to one embodiment of the present invention" may be referred to as "the present composition". Further, in this specification, "polyethylene resin foam" may be referred to as "foam", and "polyethylene resin foam according to one embodiment of the present invention" may be referred to as "this foam". be.

(1. Polyethylene resin foam)
(1-1. Composition)
A composition according to one embodiment of the present invention contains a polyethylene resin and a shrinkage inhibitor having a melting point of 85° C. or higher.

(1-1-1. Polyethylene resin)
Examples of polyethylene-based resins include (co)polymers having, as structural units, 50 mol % or more of ethylene units in 100 mol % of all structural units. As the polyethylene-based resin, from the viewpoint of the type of structural unit, (a) a polyethylene homopolymer composed only of ethylene units, and (b) an ethylene unit and a monomer other than ethylene that can be copolymerized with ethylene. Examples thereof include polyethylene-based copolymers composed of structural units derived from the polyether.

Examples of monomers other than ethylene copolymerizable with ethylene include (a) α-olefins such as propylene, 1-butene and 1-hexene, and (b) vinyl monomers such as vinyl acetate. . Examples of polyethylene copolymers include (a) ethylene/propylene copolymers, ethylene/propylene/1-butene copolymers, ethylene/1-butene copolymers, ethylene/1-hexene copolymers, ethylene/4 - ethylene/α-olefin copolymers such as methyl-1-pentene copolymers and ethylene/1-octene copolymers, and (b) ethylene/vinyl unit copolymers such as ethylene/vinyl acetate copolymers , and so on. In the present specification, a copolymer having ethylene units and α-olefin units other than ethylene refers to ethylene/α- It is called an olefin copolymer. In other words, the ethylene/α-olefin copolymer may contain structural units derived from monomers other than the α-olefin. In a polyethylene-based copolymer, the content ratio of ethylene units is the highest among various structural units constituting the polyethylene-based copolymer.

Examples of polyethylene-based resins include high-density polyethylene (HDPE or PE-HD), medium-density polyethylene (MDPE or PE-MD), low-density polyethylene (LDPE or PE-LD), and the like, from the viewpoint of differences in density. . Regarding HDPE, MDPE and LDPE, according to JIS K 6760, each density range is HDPE: 942 kg/m ³ or more, MDPE: 930 kg/m ³ or more and less than 942 kg/m ³ , LPDE: 910 kg/m ³ or more and 930 kg/m ³ stipulated as less than

Low-density polyethylene (LPDE) further includes (a) low-density polyethylene produced by a high-pressure method and having long-chain branches in addition to short-chain branches such as ethyl groups (hereinafter also referred to as branched low-density polyethylene); and (b) low-density polyethylene (hereinafter also referred to as linear low-density polyethylene (LLDPE or PE-LLD)) that is produced using a transition metal catalyst at a medium or low pressure and has short-chain branches. obtain. Branched low density polyethylene is a homopolymer of polyethylene. Linear low-density polyethylene is a copolymer obtained by linearly polymerizing ethylene and an α-olefin such as 1-butene, 1-hexene and/or 4-methyl-1-pentene, It has short chain branches derived from the side chains of α-olefins. Therefore, linear low-density polyethylene can also be called an ethylene/α-olefin copolymer.

As polyethylene resins, styrene-modified polyethylene resins and chlorinated polyethylene can also be used.

As the polyethylene-based resin, one selected from the group consisting of the above-described polyethylene homopolymer, polyethylene-based copolymer and various resins may be used alone, or two or more may be used in combination. good.

The polyethylene-based resin preferably contains branched low-density polyethylene because the melt of the composition has excellent foamability in the process of producing the foam. The polyethylene-based resin preferably contains branched low-density polyethylene in an amount of 50% by weight or more, more preferably 55% by weight or more, more preferably 60% by weight or more, based on 100% by weight of the polyethylene-based resin. It is more preferably contained in an amount of 80% by weight or more, and particularly preferably 85% by weight or more. The upper limit of the branched low-density polyethylene in the polyethylene-based resin is not particularly limited, but may be 100% by weight in 100% by weight of the polyethylene-based resin, that is, the polyethylene-based resin is composed only of branched low-density polyethylene. may The upper limit of the branched low-density polyethylene in the polyethylene resin may be 95% by weight or less, 90% by weight or less, or 85% by weight or less with respect to 100% by weight of the polyethylene resin. may

As the branched low-density polyethylene, one type of branched low-density polyethylene may be used alone, or two or more types of branched low-density polyethylene may be used in combination. For example, two or more branched low density polyethylenes with different densities may be used in combination, and two or more branched low density polyethylenes with different MFRs may be used in combination.

Since the resulting foam has excellent wear resistance, the polyethylene resin preferably contains an ethylene/α-olefin copolymer. It is more preferable to contain more than 0% by weight and 45% by weight or less, more preferably 5% to 45% by weight, more preferably 10% to 40% by weight, and 15% to 35% by weight. It is even more preferable, and it is particularly preferable to contain 15% by weight to 30% by weight.

As the ethylene/α-olefin copolymer, one ethylene/α-olefin copolymer may be used alone, or two or more ethylene/α-olefin copolymers may be used in combination. good. For example, two or more ethylene/α-olefin copolymers having different densities may be used in combination, and two or more ethylene/α-olefin copolymers having different MFRs may be used in combination. may

The polyethylene-based resin preferably contains branched low-density polyethylene and an ethylene/α-olefin copolymer. -More preferably, it contains 0 to 45 parts by weight of an olefin copolymer, and contains 55 to 95 parts by weight of a branched low-density polyethylene and 5 to 45 parts by weight of an ethylene/α-olefin copolymer. It is more preferable to contain 60 parts by weight to 90 parts by weight of branched low density polyethylene and 10 parts by weight to 45 parts by weight of ethylene / α-olefin copolymer, and 70 parts by weight of branched low density polyethylene 85 parts by weight and 15 to 30 parts by weight of the ethylene/α-olefin copolymer are particularly preferred. This configuration has the advantage that the melt of the composition has better foamability during the production process of the foam, and the resulting foam has better heat resistance and wear resistance.

The melt of the composition has better foamability, and the resulting foam has better heat resistance and wear resistance. The total of branched low-density polyethylene and ethylene/α-olefin copolymer is more preferably 60% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and 80% by weight to 100% by weight. % is more preferable.

In one embodiment of the present invention, the polyethylene-based resin may have no crosslinked structure or may have a crosslinked structure. In this specification, the polyethylene-based resin having no crosslinked structure may be referred to as "uncrosslinked polyethylene-based resin", "uncrosslinked polyethylene-based resin", or "uncrosslinked polyethylene-based resin A" for convenience. When the polyethylene-based resin has a crosslinked structure, it may be a polyethylene-based resin that is crosslinked to a relatively small degree or a polyethylene-based resin that is crosslinked to a relatively large degree. In this specification, the polyethylene resin crosslinked to a relatively small degree may be referred to as "slightly crosslinked polyethylene resin", "slightly crosslinked polyethylene resin", or "slightly crosslinked polyethylene resin B" for convenience. . The slightly crosslinked polyethylene resin can also be referred to as "a slightly crosslinked polyethylene resin" or "a polyethylene resin having a slightly crosslinked structure". In this specification, a polyethylene resin that is crosslinked to a relatively large degree may be referred to as a "highly crosslinked polyethylene resin", a "highly crosslinked polyethylene resin", or a "highly crosslinked polyethylene resin B". The highly crosslinked polyethylene resin can also be referred to as "highly crosslinked polyethylene resin" or "polyethylene resin having a highly crosslinked structure".

In this specification, the polyethylene-based resin before cross-linking treatment (slight cross-linking treatment or high cross-linking treatment) is also referred to as "raw material polyethylene-based resin".

The method for cross-linking the raw material polyethylene-based resin is not particularly limited, and a known cross-linking method can be appropriately employed. Methods for crosslinking the raw material polyethylene resin include (a) electron beam irradiation treatment of the raw material polyethylene resin, (b) chemical crosslinking treatment with an organic peroxide, (c) water crosslinking of the silane-grafted resin, and (d) ) is exemplified by a heat treatment that imparts a heat history. For example, the heat treatment for imparting a heat history to the raw material polyethylene resin includes a method of melt extruding the raw material polyethylene resin using an extruder for plastics. The extruder may be a single-screw extruder, a twin-screw extruder, an extruder with three or more screws, or a tandem extruder in which two or more extruders are connected. The temperature during extrusion is preferably 180° C. or higher, more preferably 190° C. or higher, and even more preferably 200° C. or higher. The upper limit of the temperature is up to 300° C. At a high temperature exceeding 300° C., the reduction in the molecular weight of the raw material polyethylene resin becomes more pronounced due to the main chain in the raw material polyethylene resin being cut rather than the cross-linking of the raw material polyethylene resin, resulting in cross-linking. These conditions are unsuitable for the formation of The operation of imparting a crosslinked structure to the raw material polyethylene-based resin may be performed once, or may be performed twice or more. Further, when obtaining a crosslinked resin, other additives such as a crosslinking agent and an antioxidant for suppressing oxidative deterioration and excessive crosslinking may be used as necessary. By adjusting the amounts of the cross-linking agent and antioxidant used, the degree of cross-linking to be introduced into the starting material polyethylene-based resin can be adjusted. Slightly cross-linked polyethylene resin or highly cross-linked polyethylene resin is not limited to those prepared by intentionally cross-linking raw material polyethylene resin, but also use waste materials and waste generated during molding of other polyethylene resins. It is possible.

In one embodiment of the present invention, as the branched low-density polyethylene described above, uncrosslinked branched low-density polyethylene, slightly cross-linked branched low-density polyethylene, and highly cross-linked branched low-density polyethylene are used alone. may be used, or two or more of these may be used in combination. In one embodiment of the present invention, the above-described ethylene/α-olefin copolymer includes an uncrosslinked ethylene/α-olefin copolymer, a slightly crosslinked ethylene/α-olefin copolymer, and a highly crosslinked ethylene/α-olefin copolymer. Each α-olefin copolymer may be used alone, or two or more thereof may be used in combination.

The polyethylene-based resin that is crosslinked to a relatively small extent, that is, the slightly crosslinked polyethylene-based resin, as used herein, will be described below. The gel fraction of the slightly crosslinked polyethylene resin is substantially 0%. In the present specification, a gel fraction of substantially 0% means that the gel fraction calculated as follows is less than 0.5% by weight.

In this specification, the gel fraction of the polyethylene resin is a value obtained by performing the following (1) to (5) in order: (1) About 1 g of the polyethylene resin is weighed and placed in a 100-mesh wire mesh. (2) Boil a wire mesh containing a polyethylene resin in 100 g of xylene for 8 hours; (3) Remove the wire mesh from the xylene and recover the xylene-insoluble matter remaining in the wire mesh; (4) Remove the xylene-insoluble matter. After drying at 20°C for 24 hours, the weight of the xylene-insoluble matter is weighed; (5) the gel fraction is calculated based on the following formula;
Gel fraction (%) = 100 x (weight of xylene-insoluble matter/weight of polyethylene resin weighed in (1) above (polyethylene resin before boiling in xylene)).

A graph showing the molecular weight distribution of the polyethylene resin can be obtained by measuring the molecular weight distribution of the polyethylene resin using gel permeation chromatography (GPC). FIG. 1 shows a differential molecular weight distribution curve of a slightly crosslinked polyethylene resin obtained by molecular weight distribution measurement using GPC, and a differential molecular weight distribution curve of a raw material polyethylene resin that is a raw material of the slightly crosslinked polyethylene resin. An example is shown. In the present specification, the slightly crosslinked polyethylene-based resin is compared with the molecular weight distribution of the raw material polyethylene-based resin, which is the raw material, in the molecular weight distribution obtained by measuring the molecular weight distribution using GPC, as shown in FIG. , it can be confirmed that the peak is slightly larger in the high molecular weight region near 3.0E+5 to 3.0E+7 in terms of standard polystyrene molecular weight. An increase in such peaks indicates the formation of a slightly crosslinked structure. In FIG. 1, the horizontal axis indicates the logarithm of the weight average molecular weight (MW), and the vertical axis indicates the value obtained by differentiating the concentration fraction with the logarithm of the molecular weight. In addition, M on the vertical axis means molecular weight, and W means weight.

That is, in the present specification, the slightly crosslinked polyethylene resin has a gel fraction of less than 0.5% by weight as measured by the method described above, and is obtained by molecular weight distribution measurement using GPC. In the obtained molecular weight distribution, it is intended to be a resin in which a peak larger than that of the raw material polyethylene resin is detected in a high molecular weight region in the vicinity of 3.0E+5 to 3.0E+7 in terms of standard polystyrene.

<Uncrosslinked polyethylene resin A>
The polyethylene-based resin preferably contains uncrosslinked polyethylene-based resin A. As long as the uncrosslinked polyethylene-based resin A is an uncrosslinked resin, it may contain one selected from the group consisting of the above-mentioned polyethylene homopolymers, polyethylene copolymers and various resins, Any two or more types may be included.

The uncrosslinked polyethylene-based resin A preferably contains uncrosslinked branched low-density polyethylene because the melt of the composition has excellent foamability in the process of producing a foam.

The density of the uncrosslinked branched low-density polyethylene contained in the uncrosslinked polyethylene-based resin A is not particularly limited. The density of the uncrosslinked branched low-density polyethylene is preferably 910 kg/m ³ to 935 kg/m ³ , more preferably 912 kg/m ³ to 930 kg/m ³ , and more preferably 913 kg/m ³ to 927 kg/m 3 . /m ³ , particularly preferably 914 kg/m ³ to 924 kg/m ³ . According to this configuration, there is an advantage that the foamability of the molten composition in the production process of the foam and the heat resistance of the obtained foam are well balanced.

The fluidity (for example, melt mass flow rate (MFR)) of the uncrosslinked branched low-density polyethylene contained in the uncrosslinked polyethylene-based resin A is not particularly limited. The MFR of the uncrosslinked branched low-density polyethylene is preferably 0.2 g/10 minutes to 10.0 g/10 minutes, more preferably 0.3 g/10 minutes to 8.0 g/10 minutes, and 0.5 g/ 10 min to 6.0 g/10 min is more preferred, 0.8 g/10 min to 5.0 g/10 min is even more preferred, and 1.0 g/10 min to 4.0 g/10 min is particularly preferred. According to this configuration, the melt of the composition has a high melt tension in the process of manufacturing the foam, and excessive shear heating in the extruder can be prevented. That is, according to this configuration, there is an advantage that there is a tendency to easily set conditions suitable for extrusion foaming in the production of the present foam.

In this specification, the MFR of the branched low-density polyethylene is obtained by measuring at 190 ° C. and a load of 2.16 kg according to JISK-7210, regardless of the crosslinked state of the branched low-density polyethylene. is the value

Since the melt of the composition has excellent foamability in the manufacturing process of the foam, the uncrosslinked polyethylene resin A is 50% by weight of uncrosslinked branched low-density polyethylene in 100% by weight of the uncrosslinked polyethylene resin A. % or more, more preferably 55 wt% or more, more preferably 60 wt% or more, more preferably 70 wt% or more, even more preferably 80 wt% or more, 85 wt% % or more is particularly preferable. The upper limit of the uncrosslinked branched low-density polyethylene in the uncrosslinked polyethylene resin A is not particularly limited. It may be 100% by weight based on 100% by weight of the uncrosslinked polyethylene resin A, that is, the uncrosslinked polyethylene resin A may be composed only of uncrosslinked branched low-density polyethylene. The upper limit of the uncrosslinked branched low-density polyethylene in the uncrosslinked polyethylene resin A may be 95% by weight or less, or 90% by weight or less, relative to 100% by weight of the uncrosslinked polyethylene resin A. It may be 85% by weight or less.

As the uncrosslinked branched low-density polyethylene contained in the uncrosslinked polyethylene-based resin A, one type of uncrosslinked branched low-density polyethylene may be used alone, or two or more types of uncrosslinked branched low-density polyethylene may be used. A combination of low density polyethylenes may also be used. For example, two or more uncrosslinked branched low-density polyethylenes having different densities may be used in combination, and two or more uncrosslinked branched low-density polyethylenes having different MFRs may be used in combination. may

The uncrosslinked polyethylene-based resin A preferably contains an uncrosslinked ethylene/α-olefin copolymer because the resulting foam has excellent abrasion resistance.

The density of the uncrosslinked ethylene/α-olefin copolymer contained in the uncrosslinked polyethylene resin A is not particularly limited. The density of the uncrosslinked ethylene/α-olefin copolymer is preferably 870 kg/m ³ to 920 kg/m 3 , more preferably 875 kg/m ³ to 918 kg/m ³ , and more preferably 880 kg/m ³ to 918 kg/m 3 . ³ to 916 kg/m ³ , more preferably 885 kg/m ³ to 914 kg/m ³ , still more preferably 888 kg/m ³ to 912 kg/m ³ , 890 kg/m ³ to 910 kg/m ³ is particularly preferred. According to this configuration, there is an advantage that the foamability of the molten composition in the production process of the foam and the heat resistance of the obtained foam are well balanced.

The MFR of the uncrosslinked ethylene/α-olefin copolymer contained in the uncrosslinked polyethylene resin A is not particularly limited. The MFR of the uncrosslinked ethylene/α-olefin copolymer is preferably 0.3 g/10 min to 20.0 g/10 min, more preferably 0.5 g/10 min to 15.0 g/10 min. 0 g/10 min to 10.0 g/10 min is more preferred, 1.5 g/10 min to 8.0 g/10 min is even more preferred, and 2.0 g/10 min to 6.0 g/10 min is particularly preferred. According to this configuration, the melt of the composition in the process of manufacturing the foam has a high melt tension, and excessive shear heating can be prevented in the extruder. That is, according to this configuration, there is an advantage that there is a tendency to easily set conditions suitable for extrusion foaming in the production of the present foam. In the present specification, the MFR of the ethylene/α-olefin copolymer is a value obtained by the same measurement method as for branched low-density polyethylene, regardless of the crosslinked state of the ethylene/α-olefin copolymer.

Since the obtained foam has excellent wear resistance, the uncrosslinked polyethylene resin A contains more than 0% by weight of the uncrosslinked ethylene/α-olefin copolymer in 100% by weight of the uncrosslinked polyethylene resin A. More preferably 45% by weight or less, more preferably 5% to 45% by weight, even more preferably 10% to 40% by weight, even more preferably 15% to 35% by weight, A content of 15% to 30% by weight is particularly preferred.

As the uncrosslinked ethylene/α-olefin copolymer contained in the uncrosslinked polyethylene-based resin A, one type of uncrosslinked copolymer having the same structural unit composition may be used alone. Two or more uncrosslinked copolymers having different compositions of structural units may be used in combination. As the uncrosslinked ethylene/α-olefin copolymer, one uncrosslinked ethylene/α-olefin copolymer may be used alone, or two or more uncrosslinked ethylene/α-olefin copolymers may be used. Combinations of copolymers may also be used. For example, two or more uncrosslinked ethylene/α-olefin copolymers having different densities may be used in combination, and two or more uncrosslinked ethylene/α-olefin copolymers having different MFRs. A combination of coalescences may be used, and a combination of two or more uncrosslinked ethylene/α-olefin copolymers composed of different comonomers may be used.

The uncrosslinked polyethylene resin A preferably contains uncrosslinked branched low-density polyethylene and an uncrosslinked ethylene/α-olefin copolymer. More preferably, it contains 55 to 100 parts by weight of density polyethylene and 0 to 45 parts by weight of uncrosslinked ethylene/α-olefin copolymer, and 55 to 95 parts by weight of uncrosslinked branched low-density polyethylene. It is more preferable to contain 5 parts by weight to 45 parts by weight of uncrosslinked ethylene/α-olefin copolymer, and 60 parts by weight to 90 parts by weight of uncrosslinked branched low density polyethylene and uncrosslinked ethylene. It is more preferable to contain 10 parts by weight to 40 parts by weight of /α-olefin copolymer, and 70 parts by weight to 85 parts by weight of uncrosslinked branched low density polyethylene and uncrosslinked ethylene/α-olefin copolymer It is particularly preferred to contain 15 to 30 parts by weight. According to this configuration, there is an advantage that the melt of the composition has excellent foamability in the process of producing the foam, and the obtained foam has excellent abrasion resistance.

The uncrosslinked polyethylene resin A contains 60% to 100% by weight in total of the uncrosslinked branched low-density polyethylene and the uncrosslinked ethylene/α-olefin copolymer in 100% by weight of the uncrosslinked polyethylene resin A. more preferably 70% to 100% by weight, even more preferably 80% to 100% by weight. According to this configuration, there is an advantage that the melt of the composition has better foamability in the process of producing the foam, and the obtained foam has better abrasion resistance.

The uncrosslinked polyethylene-based resin A may contain an uncrosslinked polyethylene-based resin other than the uncrosslinked branched low-density polyethylene and the uncrosslinked ethylene/α-olefin copolymer.

<Slightly crosslinked polyethylene resin B>
The polyethylene-based resin preferably contains a slightly crosslinked polyethylene-based resin B. Slightly crosslinked polyethylene resin B, as long as it is a slightly crosslinked resin, may contain one selected from the group consisting of the above-described polyethylene homopolymer, polyethylene copolymer, various resins, and the like. Any two or more kinds may be included. The slightly crosslinked polyethylene resin B has a more complicated molecular structure than the uncrosslinked polyethylene resin A due to the slightly crosslinked structure. Therefore, when the polyethylene-based resin contains the slightly crosslinked polyethylene-based resin B, the crystallinity of the polyethylene-based resin becomes low. It has the advantage of being able to reduce the generation of porosity (cavities) due to cooling. In addition, when polyethylene-type resin contains the slightly crosslinked polyethylene-type resin B, the foam obtained turns into a slightly crosslinked foam.

The slightly crosslinked polyethylene-based resin B preferably contains a slightly crosslinked branched low-density polyethylene because the melt of the composition has excellent foamability in the process of producing the foam. A slightly crosslinked branched low-density polyethylene can be obtained by subjecting a raw material polyethylene-based resin containing branched low-density polyethylene to a slightly cross-linking treatment. As the branched low-density polyethylene contained in the raw material polyethylene-based resin, the same resin as the uncrosslinked branched low-density polyethylene contained in the uncrosslinked polyethylene-based resin A can be preferably applied. As the branched low-density polyethylene contained in the raw material polyethylene-based resin, one type of branched low-density polyethylene may be used alone, or two or more types of branched low-density polyethylene may be used in combination. . For example, two or more branched low density polyethylenes with different densities may be used in combination, and two or more branched low density polyethylenes with different MFRs may be used in combination. Moreover, the branched low-density polyethylene contained in the raw material polyethylene-based resin may be the same as or different from the uncrosslinked branched low-density polyethylene contained in the uncrosslinked polyethylene-based resin A.

The density of the slightly crosslinked branched low-density polyethylene contained in the slightly crosslinked polyethylene resin B is not particularly limited. The density of the slightly crosslinked branched low-density polyethylene is preferably 910 kg/m ³ to 925 kg/m ³ , more preferably 911 kg/m ³ to 924 kg/m ³ , and more preferably 912 kg/m ³ to 923 kg/m 3 . /m ³ , particularly preferably 913 kg/m ³ to 922 kg/m ³ . According to this configuration, there is an advantage that the foamability of the molten composition in the production process of the foam and the heat resistance of the obtained foam are well balanced.

The MFR of the slightly crosslinked branched low-density polyethylene contained in the slightly crosslinked polyethylene resin B is not particularly limited. The MFR of the slightly crosslinked branched low-density polyethylene is preferably 0.3 g/10 minutes to 10.0 g/10 minutes, more preferably 0.4 g/10 minutes to 8.0 g/10 minutes, and 0.5 g/ 10 min to 6.0 g/10 min is more preferred, 0.8 g/10 min to 5.0 g/10 min is even more preferred, and 1.0 g/10 min to 4.0 g/10 min is particularly preferred. According to this configuration, the melt of the composition has a high melt tension in the process of manufacturing the foam, and excessive shear heating can be prevented in the extruder. That is, according to this configuration, there is an advantage that there is a tendency to easily set conditions suitable for extrusion foaming in the production of the present foam.

Since the melt of the composition has excellent foamability in the production process of the foam, the slightly crosslinked polyethylene resin B contains 50% by weight of slightly crosslinked branched low-density polyethylene in 100% by weight of the slightly crosslinked polyethylene resin B. % or more, more preferably 55 wt% or more, more preferably 60 wt% or more, more preferably 70 wt% or more, even more preferably 80 wt% or more, 85 wt% % or more is particularly preferable. The upper limit of the slightly crosslinked branched low-density polyethylene in the slightly crosslinked polyethylene resin B is not particularly limited, but may be 100% by weight in 100% by weight of the slightly crosslinked polyethylene resin B, that is, the slightly crosslinked polyethylene resin B may be composed only of slightly crosslinked branched low-density polyethylene. The upper limit of the slightly crosslinked branched low-density polyethylene in the slightly crosslinked polyethylene resin B may be 95% by weight or less, or 90% by weight or less, relative to 100% by weight of the slightly crosslinked polyethylene resin B. It may be 85% by weight or less.

The slightly crosslinked polyethylene-based resin B preferably contains a slightly crosslinked ethylene/α-olefin copolymer because the resulting foam has excellent abrasion resistance and a high closed cell content. A slightly crosslinked ethylene/α-olefin copolymer can be obtained by subjecting a raw material polyethylene resin containing an ethylene/α-olefin copolymer to a slightly cross-linking treatment. As the ethylene/α-olefin copolymer contained in the raw material polyethylene resin, the same copolymer as the uncrosslinked ethylene/α-olefin copolymer contained in the uncrosslinked polyethylene resin A can be preferably applied. As the ethylene/α-olefin copolymer contained in the raw material polyethylene resin, one type of polymer having the same composition of structural units may be used alone, or two or more types of polymers having different compositions of structural units may be used. Combinations of polymers may also be used. As the ethylene/α-olefin copolymer contained in the raw material polyethylene resin, one kind of ethylene/α-olefin copolymer may be used alone, or two or more kinds of ethylene/α-olefin copolymers may be used. Combinations of coalescing may also be used. For example, two or more ethylene/α-olefin copolymers having different densities may be used in combination, and two or more ethylene/α-olefin copolymers having different MFRs may be used in combination. Also, two or more ethylene/α-olefin copolymers composed of different comonomers may be used in combination. Further, the ethylene/α-olefin copolymer contained in the raw material polyethylene resin may be the same as the uncrosslinked ethylene/α-olefin copolymer contained in the uncrosslinked polyethylene resin A, can be different.

The density of the slightly crosslinked ethylene/α-olefin copolymer contained in the slightly crosslinked polyethylene resin B is not particularly limited. The density of the slightly crosslinked ethylene/α-olefin copolymer is preferably 875 kg/m ³ to 918 kg/m 3 , more preferably 880 kg/m ³ to 916 kg/m ³ , more preferably 885 kg/m ³ to 916 kg/m 3 . It is more preferably ³ to 914 kg/m ³ , still more preferably 888 kg/m ³ to 912 kg/m ³ , particularly preferably 890 kg/m ³ to 910 kg/m ³ . According to this configuration, there is an advantage that the foamability of the molten composition in the production process of the foam and the heat resistance of the obtained foam are well balanced.

The MFR of the slightly crosslinked ethylene/α-olefin copolymer contained in the slightly crosslinked polyethylene resin B is not particularly limited. The MFR of the slightly crosslinked ethylene/α-olefin copolymer is preferably 0.3 g/10 min to 20.0 g/10 min, more preferably 0.5 g/10 min to 15.0 g/10 min. 0 g/10 min to 10.0 g/10 min is more preferred, 1.5 g/10 min to 8.0 g/10 min is even more preferred, and 2.0 g/10 min to 6.0 g/10 min is particularly preferred. According to this configuration, the melt of the composition in the process of manufacturing the foam has a high melt tension, and excessive shear heating can be prevented in the extruder. That is, according to this configuration, there is an advantage that there is a tendency to easily set conditions suitable for extrusion foaming in the production of the present foam.

Since the resulting foam has excellent abrasion resistance and a high closed cell ratio, the slightly crosslinked polyethylene resin B is a slightly crosslinked ethylene/α-olefin copolymer in 100% by weight of the slightly crosslinked polyethylene resin B. It is more preferable to contain more than 0% by weight and 45% by weight or less, more preferably 5% to 45% by weight, more preferably 10% to 40% by weight, and 15% to 35% by weight. It is even more preferable, and it is particularly preferable to contain 15% by weight to 30% by weight.

The slightly crosslinked polyethylene resin B preferably contains a slightly crosslinked branched low-density polyethylene and a slightly crosslinked ethylene/α-olefin copolymer. Slightly cross-linked branched low-density polyethylene, slightly cross-linked ethylene/α-olefin copolymer, And a mixture (slightly crosslinked polyethylene-based resin B) containing branched low-density polyethylene and a resin in which an ethylene/α-olefin copolymer is slightly crosslinked can be obtained. In addition, separately prepared slightly crosslinked branched low density polyethylene and slightly crosslinked ethylene/α-olefin copolymer are mixed to obtain a slightly crosslinked branched low density polyethylene and slightly crosslinked ethylene/α-olefin copolymer. A slightly crosslinked polyethylene resin B containing a polymer may be prepared.

In addition, when obtaining a mixture containing a plurality of types of slightly crosslinked polyethylene resins in desired proportions, a mixture containing a plurality of types of polyethylene resins in desired proportions may be used as the raw material polyethylene resin. That is, when a raw material polyethylene resin containing ¹ part by weight of polyethylene resin ^E1 and ² parts by weight of ^e2 is subjected to a slight cross-linking treatment, the polyethylene resin ^E1 is slightly cross-linked. A mixture containing ¹ part by weight of the slightly crosslinked polyethylene resin E1 and ^{2 parts} by ^weight of the slightly crosslinked polyethylene resin E2 obtained by slightly crosslinking the polyethylene resin ^E2 is obtained.

Slightly crosslinked polyethylene resin B comprises 55 to 100 parts by weight of slightly crosslinked branched low-density polyethylene and 0 to 45 parts by weight of slightly crosslinked ethylene/α-olefin copolymer in 100 parts by weight of slightly crosslinked polyethylene resin B. It is more preferable to contain 55 to 95 parts by weight of a slightly crosslinked branched low density polyethylene and 5 to 45 parts by weight of a slightly crosslinked ethylene/α-olefin copolymer. More preferably, it contains 60 parts by weight to 90 parts by weight of a slightly crosslinked branched low density polyethylene and 10 parts by weight to 40 parts by weight of a slightly crosslinked ethylene/α-olefin copolymer. It is particularly preferable to contain 70 to 85 parts by weight of branched low density polyethylene and 15 to 30 parts by weight of slightly crosslinked ethylene/α-olefin copolymer. According to this configuration, the melt of the composition has excellent foamability in the production process of the foam, and the obtained polyethylene resin foam has excellent abrasion resistance and a high closed cell content. have advantages.

Slightly crosslinked polyethylene resin B contains 60% to 100% by weight of the total of slightly crosslinked branched low-density polyethylene and slightly crosslinked ethylene/α-olefin copolymer in 100% by weight of slightly crosslinked polyethylene resin B. more preferably 70% to 100% by weight, even more preferably 80% to 100% by weight. According to this configuration, the melt of the composition has superior foamability in the foam manufacturing process, and the resulting foam has superior abrasion resistance and a high closed cell content. .

The slightly crosslinked polyethylene resin B may contain a slightly crosslinked polyethylene resin other than the slightly crosslinked branched low density polyethylene and the slightly crosslinked ethylene/α-olefin copolymer.

The polyethylene-based resin preferably contains an uncrosslinked polyethylene-based resin A and a slightly crosslinked polyethylene-based resin B. According to this configuration, the resulting foam has the advantage of having a small average cell diameter and a high closed cell ratio. In addition, by using the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B together as the polyethylene resin, compared to the case of using the polyethylene resin A alone, the dispersion of each resin during extrusion kneading Since the properties are further improved, a more uniform melt-kneaded product is obtained, and the foamability of the composition is further improved.

The polyethylene resin contains 55% to 95% by weight of the polyethylene resin A and 5% to 45% by weight of the polyethylene resin B in the total amount of 100% by weight of the polyethylene resin A and the slightly crosslinked polyethylene resin B. More preferably, it contains 60% to 93% by weight of polyethylene resin A and 7% to 40% by weight of polyethylene resin B, and 63% to 88% by weight of polyethylene resin A and It is more preferable to contain 12% to 37% by weight of the slightly crosslinked polyethylene resin B, and 65% to 85% by weight of the polyethylene resin A and 15% to 35% by weight of the slightly crosslinked polyethylene resin B. is particularly preferred. According to this configuration, (a) the melt of the composition has superior foamability in the foam production process, and (b) the obtained foam has a small average cell diameter and a high number of closed cells. It has the advantage of having a rate.

When the uncrosslinked polyethylene-based resin A contains uncrosslinked branched low-density polyethylene and an uncrosslinked ethylene/α-olefin copolymer, the slightly crosslinked polyethylene-based resin B also contains a slightly crosslinked branched low-density It preferably contains polyethylene and a slightly crosslinked ethylene/α-olefin copolymer. Ethylene/α-olefin copolymers tend to have a higher shear viscosity during extrusion than branched low-density polyethylene, and are difficult to disperse uniformly. However, when the slightly crosslinked polyethylene resin B has a slightly crosslinked branched low density polyethylene and a slightly crosslinked ethylene/α-olefin copolymer, the uncrosslinked branched low density contained in the uncrosslinked polyethylene resin A It is possible to improve the dispersibility of the polyethylene and the uncrosslinked ethylene/α-olefin copolymer, making it easier to obtain a foam having a high closed cell ratio.

Therefore, the polyethylene-based resin includes uncrosslinked branched low-density polyethylene and uncrosslinked polyethylene-based resin A containing an uncrosslinked ethylene/α-olefin copolymer, and slightly crosslinked branched low-density polyethylene and slightly crosslinked and a slightly crosslinked polyethylene resin B containing an ethylene/α-olefin copolymer. The polyethylene resin is (1) an uncrosslinked polyethylene resin containing 55 to 100 parts by weight of uncrosslinked branched low-density polyethylene and 0 to 45 parts by weight of an uncrosslinked ethylene/α-olefin copolymer. A, and (2) a slightly crosslinked polyethylene resin B containing 55 to 100 parts by weight of a slightly crosslinked branched low density polyethylene and 0 to 45 parts by weight of a slightly crosslinked ethylene/α-olefin copolymer. (3) 55% to 95% by weight of the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B with respect to the total 100% by weight of the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B is more preferably contained in an amount of 5% to 45% by weight. According to this configuration, (i) the melt of the composition has excellent foamability in the foam manufacturing process, and (ii) the obtained foam has excellent abrasion resistance, small average cell diameter, and high isolation. It has the advantages of having a high porosity and having few porosity (cavities).

(1-1-2. Other resins)
The composition according to one embodiment of the present invention may contain resins other than polyethylene-based resins (other resins). Other resins include (a) polyolefin-based resins other than polyethylene-based resins and (b) synthetic resins other than polyolefin-based resins. In this specification, the polyethylene-based resin and other resins contained in the composition may be collectively referred to as "raw material resin".

Examples of polyolefin-based resins other than polyethylene-based resins include polypropylene-based resins.

Examples of polypropylene-based resins include polypropylene homopolymers, polypropylene copolymers, long-chain branched polypropylenes having high melt tension, isoprene-modified polypropylenes, and polypropylenes containing ultra-high molecular weight components. Examples of polypropylene copolymers include propylene/α-olefin copolymers, propylene/chlorinated vinyl copolymers, propylene/maleic anhydride copolymers, and the like. Propylene/α-olefin copolymers include propylene/ethylene block copolymers, propylene/ethylene random copolymers, propylene/1-butene copolymers, propylene/ethylene/1-butene copolymers, and the like. be done. In the polypropylene copolymer, the content ratio of the propylene unit is the largest among the various structural units constituting the polypropylene copolymer.

Examples of synthetic resins other than polyolefin resins include (a) thermoplastic resins such as vinyl acetate resins, polyester resins, acrylic resins, acrylate ester resins, styrene resins, polyamide resins, polycarbonate resins, and polyvinyl chloride resins. , (b) polyamide-based elastomers such as polyamide/polyol copolymers, and (c) thermoplastic elastomers such as polyvinyl chloride-based elastomers, polybutadiene-based elastomers, ethylene/propylene rubbers, and ethylene/propylene/butadiene rubbers. be done.

The raw material resin contained in the composition preferably contains 50% by weight or more in total of the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B in 100% by weight of the raw material resin, and more preferably contains 60% by weight or more. Preferably, it contains 70% by weight or more, more preferably 75% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more. According to this configuration, (a) the melt of the composition has excellent foamability in the foam production process, and (b) the obtained foam has excellent abrasion resistance, small average cell diameter and high independent It has the advantages of having a high porosity and having few porosity (cavities).

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

(1-1-3. Shrinkage inhibitor)
The melting point of the shrinkage inhibitor according to one embodiment of the present invention is 85° C. or higher. In the process of intensive investigation, the present inventors independently obtained the finding that, surprisingly, a shrinkage inhibitor having a melting point of 85°C or higher causes no or very little bleeding out from the foam. rice field. Therefore, by using a shrinkage inhibitor having a melting point of 85° C. or higher as the shrinkage inhibitor, it is possible to obtain a polyethylene-based resin foam that undergoes less shrinkage after production and less contamination to the glass substrate.

The shrinkage inhibitor is not particularly limited as long as it has a melting point of 85°C or higher. Examples of shrinkage inhibitors include (a) fatty acid esters of fatty acids having 8 to 30 carbon atoms and polyhydric alcohols having 3 to 7 hydroxyl groups, (b) fatty amines and (c) fatty acid amides, etc., can be used.

Examples of fatty acids having 8 to 30 carbon atoms include lauric acid, oleic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, heptakoic acid, montanic acid, melissic acid and laxeric acid. Among these, higher fatty acids having 14 or more carbon atoms are preferred. Suitable examples include saturated fatty acids such as stearic acid and hydroxystearic acid.

Examples of polyhydric alcohols having 3 to 7 hydroxyl groups include glycerin, diglycerin, triglycerin, erythritol arabit, xylimaat, mannitol, sorbitol and sorbitan.

Aliphatic amines include dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, eicosylamine, docosylamine, N-methyloctadecylamine, N-ethyloctadecylamine, hexadecylpropylenediamine, octadecylpropylenediamine, and the like. .

Fatty acid amides include stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide, lauric acid bisamide, and the like.

One of these shrinkage inhibitors may be used alone, or two or more thereof may be used in combination.

Among these shrinkage inhibitors, fatty acid esters are preferred because they have little effect on the foamability and physical properties of the foam and have a large shrinkage inhibitory effect. Among fatty acid esters, partially esterified fatty acid esters are preferable to fully esterified fatty acid esters.

Among the fatty acid ester compounds, a monoesterified fatty acid ester is preferable as the shrinkage inhibitor in order to obtain a remarkable shrinkage inhibitory effect. A tri-esterified fatty acid ester compound is preferable in order to exhibit the effect. A tri-esterified fatty acid ester compound has a higher molecular weight and a higher melting point than a mono-esterified fatty acid ester compound. The shrinkage inhibitor is an ester of 12-hydroxystearic acid and glycerin as a polyhydric alcohol fatty acid ester, and 12-hydroxystearic acid triglyceride having a melting point of 87° C. is particularly preferred.

The content of the shrinkage inhibitor in the composition is 0.05 to 0.50 parts by weight, preferably 0.10 to 0.50 parts by weight, per 100 parts by weight of the polyethylene resin. , It is more preferably 0.10 to 0.45 parts by weight, more preferably 0.10 to 0.40 parts by weight, and 0.15 to 0.35 parts by weight is particularly preferred. According to this configuration, it is possible to obtain a foam with less post-production shrinkage and less contamination on the glass substrate.

In addition to the shrinkage inhibitor having a melting point of 85° C. or higher, the shrinkage inhibitor having a melting point of less than 85° C. (i.e., the shrinkage inhibitor according to one embodiment of the present invention) inhibitor) may be used in combination. In addition to the shrinkage inhibitor having a melting point of 85°C or higher, when a shrinkage inhibitor having a melting point of less than 85°C is used in combination, the content of the shrinkage inhibitor having a melting point of less than 85°C is 100 parts by weight of the polyethylene resin. 0.10 parts by weight or less is preferable.

(1-1-4. Other additives)
The composition according to one embodiment of the present invention may optionally contain a cell nucleating agent, a cell nucleating aid, a weathering agent, an antioxidant, a crystal nucleating agent, a heat stabilizer, an antistatic agent, and a conductive agent. Other additives such as imparting agents, functional additives such as flame retardants, lubricants, inorganic fillers, colorants (eg, pigments) may be further included.

(Bubble nucleating agent)
Cell nucleating agents include pyrolytic blowing agents, organic acids (salts) and inorganics (such as talc). As used herein, "organic acid (salt)" means "organic acid and/or organic acid salt". The cell nucleating agent preferably comprises a pyrolytic blowing agent and/or an organic acid (salt). When the cell nucleating agent contains a pyrolytic blowing agent and/or an organic acid (salt), the cell nucleating agent does not contain a pyrolytic blowing agent and/or an organic acid (salt) and only an inorganic substance (such as talc). The cell diameter of the obtained foam can be more easily reduced compared to the case of containing. More preferably, the cell nucleating agent comprises a thermally decomposable blowing agent and an organic acid (salt), and more preferably consists of a mixture of a thermally decomposing blowing agent and an organic acid (salt).

Thermal decomposition type foaming agents include, for example, ADCA (azodicarbonamide), DPT (N,N'-dinitropentamethylenetetramine), OBSH (4,4'-oxybisbenzenesulfonyl hydrazide), hydrogencarbonate, and carbonate. etc. Preferred pyrolytic blowing agents are bicarbonates, carbonates, or mixtures of bicarbonates and carbonates. Hydrogen carbonates include, for example, sodium hydrogen carbonate.

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

As the bubble nucleating agent, a mixture of hydrogen carbonate and citric acid (salt), a mixture of carbonate and citric acid (salt), and One or more mixtures selected from the group consisting of mixtures of hydrogen carbonates, carbonates and citric acid (salts) are preferred, mixtures of hydrogen carbonates and citrates are more preferred, sodium hydrogen carbonate and citric acid Mixtures with monosodium are particularly preferred.

The content ratio of the thermal decomposition foaming agent and the organic acid (salt) in the cell nucleating agent is 10% for the thermal decomposition foaming agent when the total amount of the thermal decomposition foaming agent and the organic acid (salt) is 100% by weight. % to 90% by weight and 90% to 10% by weight of the organic acid (salt), preferably 20% to 85% by weight of the thermal decomposition blowing agent and 80% by weight to More preferably 15% by weight, more preferably 30% to 80% by weight of the thermally decomposable blowing agent and 70% to 20% by weight of the organic acid (salt). This configuration has an advantage that a small amount of the bubble nucleating agent can easily obtain an efficient nucleation effect.

In the production of the present foam, the larger the amount of cell nucleating agent used, the smaller the cell diameter of the resulting foam tends to be. However, in the production of the foam, as the amount of the cell nucleating agent used increases, the manufacturing cost rises, and the risk of foreign matter generation due to decomposition products of the cell nucleating agent may increase. Therefore, the amount of the cell nucleating agent used in the production of the present foam (in other words, the content of the cell nucleating agent in the composition) is 0.03 parts by weight to 1 part by weight with respect to 100 parts by weight of the polyethylene resin. 0.50 parts by weight is preferred, 0.08 to 1.20 parts by weight is more preferred, and 0.10 to 1.00 parts by weight is even more preferred.

In the production of the present foam, as the cell nucleating agent, a powdery cell nucleating agent may be directly used. May be used. As the masterbatch of the cell nucleating agent, a commercially available product can be used.

(crosslinking agent)
In making the foam, the composition may be crosslinked during extrusion.

The method for cross-linking the composition is not particularly limited as long as it is a known cross-linking method. Examples include heat treatment and cross-linking treatment with a cross-linking agent such as an organic peroxide. From the viewpoint of easy control of the degree of cross-linking, a method of cross-linking the composition with a cross-linking agent is preferable. That is, the composition may contain a cross-linking agent such as an organic peroxide.

Examples of the cross-linking agent include, but are not particularly limited to, radical polymerization initiators such as peroxides and azo compounds. As the cross-linking agent, a substance capable of abstracting hydrogen from the polyethylene resin is preferable. Substances capable of abstracting hydrogen from polyethylene resins generally include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters. is mentioned. Among these, organic peroxides having particularly high hydrogen abstraction ability are preferable. Examples of organic peroxides having particularly high hydrogen abstraction ability include 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n -butyl 4,4-bis(t-butylperoxy)valerate, peroxyketals such as 2,2-bis(t-butylperoxy)butane, dicumyl peroxide, 2,5-dimethyl-2,5- Di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5-dimethyl- Dialkyl peroxides such as 2,5-di(t-butylperoxy)-3-hexyne, diacyl peroxides such as benzoyl peroxide, t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t- Butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxy isopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t- Peroxy esters such as butyl peroxyacetate, t-butyl peroxybenzoate, di-t-butyl peroxy isophthalate and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.

The degree of cross-linking (gel fraction) of the present foam is not particularly limited, but is preferably as small as possible. For example, it is preferably 5% by weight or less, more preferably 4% by weight or less, and 3% by weight or less. It is more preferably 2% by weight or less, still more 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 0.5% by weight or less, that is, it is particularly preferred that the present foam is slightly 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. The smaller the degree of cross-linking (gel fraction) of the present foam, the better the heat-sealing property and the better the workability. Moreover, according to the said structure, it becomes possible to return the obtained foam to the original resin, and to reuse it, As a result, it also has the advantage that recycling is easy. The degree of cross-linking (gel fraction) of the foam can be measured by the same method as for the gel fraction of the polyethylene-based resin, except that the foam is used instead of the polyethylene-based resin.

(1-2. Manufacturing method of polyethylene resin foam)
A method for producing a polyethylene-based resin foam according to one embodiment of the present invention is not particularly limited. As a method for producing a polyethylene-based resin foam according to one embodiment of the present invention, for example, a composition containing a polyethylene-based resin and a shrinkage inhibitor having a melting point of 85° C. or higher contains 60 mol % or more of isobutane. A polyethylene-based composition having a step of extrusion foam molding using a foaming agent, wherein the composition contains 0.05 to 0.50 parts by weight of the shrinkage inhibitor with respect to 100 parts by weight of the polyethylene-based resin. and a method for producing a resin foam.

The method for producing the present foam is not particularly limited, and a known extrusion molding method can be employed. A tandem extruder device in which a twin-screw extruder and a single-screw extruder are connected may be used in the present foam manufacturing method. A specific example of the method for producing the present foam includes a method in which the following operations (1) to (6) are performed in order: (1) raw material resin such as polyolefin resin, shrinkage inhibitor, and necessary Depending on the above, a predetermined amount of other additives such as a bubble nucleating agent and a heat stabilizer are prepared, and all the prepared raw materials (composition) are transferred to the first extruder (first stage extruder, twin screw). (2) Melt-knead the supplied raw material at a temperature suitable for kneading; (3) Inject a foaming agent into the obtained melt-kneaded product from the middle of the first extruder (4) The resin melt obtained is adjusted to a desired discharge rate and discharged from the first extruder to a connected second extruder (second stage extruder, single screw); (5) Then, in the second extruder, the temperature of the extruded resin melt is adjusted (for example, cooled) to a temperature suitable for foaming; (6) the resin melt adjusted to a temperature suitable for foaming is 2. The resin melt is foamed by extruding from a die attached to the tip of the extruder into a region of lower pressure than in the extruder.

(foaming agent)
As the foaming agent, as long as it contains 60 mol % or more of isobutane, there are no particular restrictions on other constitutions, and any foaming agent commonly used in extrusion foaming can be used. Examples of foaming agents commonly used in extrusion foaming include (a) (a-1) aliphatic hydrocarbons such as propane, normal butane, isobutane, 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) air , nitrogen, and inorganic gases such as carbon dioxide; and (a-6) physical foaming agents such as water, and (b) thermal decomposition foaming agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine. and chemical foaming agents containing. As the foaming agent, among these, a physical foaming agent is preferable because a desired expansion ratio, a desired closed cell ratio, and a desired average cell diameter can be easily obtained, and aliphatic hydrocarbons are more preferable, and particularly Normal butane and/or isobutane are preferred. The foaming agents described above may be used alone or in combination of two or more.

In one embodiment of the present invention, the foaming agent contains 60 mol% or more of isobutane, preferably 65 mol% or more, more preferably 70 mol% or more, more preferably 75 mol% or more, and 80 More preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more. The blowing agent may contain 100 mol % of isobutane, ie, the blowing agent may consist of isobutane only.

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

Here, the operation of supplying all the prepared raw materials to the first extruder in the operation (1) will be specifically described. All of the prepared raw materials may be supplied to the first extruder from separate feeders, or may be supplied to the first extruder together with some or all of the raw materials. When each prepared raw material is supplied to the first extruder from separate feeders, each raw material may be supplied to the first extruder at the same time or at any time. When some or all of the prepared raw materials are supplied together to the first extruder, some 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 is a temperature at which the raw material resin is reliably melted and kneading of the melted raw material resin, additives added as necessary, and a foaming agent is preferably performed. There is no particular limitation. In one embodiment of the present invention, the temperature suitable for kneading is preferably a temperature equal to or higher than the melting point of the raw material resin (for example, polyethylene resin). When using a bubble nucleating agent in one embodiment of the present invention, the temperature suitable for kneading is preferably a temperature at which the effect of the bubble nucleating agent to be used is efficiently exhibited. When the cell nucleating agent contains a decomposable foaming agent, the temperature at which the effect of the cell nucleating agent is efficiently exhibited is the temperature at which decomposition of the decomposable foaming agent proceeds sufficiently to obtain the desired nucleating action. is. For example, when using a mixture of sodium bicarbonate and monosodium citrate as the bubble nucleating agent, the temperature suitable for kneading is the temperature at which the effect of the bubble nucleating agent is efficiently exhibited. °C to 240°C is preferred.

The temperature suitable for foaming is not particularly limited. The temperature suitable for foaming is generally preferably in the range of -10°C to +20°C with respect to the melting point of the polyethylene-based resin, which is the temperature of the resin melt extruded from the die. In the operation (5), it is also possible to adjust (for example, cool) the temperature to be suitable for foaming using a cooling mixer.

By selecting the die attached to the tip of the second-stage extruder according to the desired shape of the foam, it is possible to manufacture various shapes of extruded foam such as plate-shaped foam and round bar-shaped foam. can. The extrusion conditions for the resin melt, the conditions for taking the extruded foam, the cooling conditions for the extruded foam, and the like may be appropriately set.

Said region of lower pressure than in the extruder is preferably a region under atmospheric pressure. In other words, the pressure inside the extruder is preferably higher than the atmospheric pressure.

(1-3. Physical properties of foam)
(shape)
The shape of the present foam includes a plate shape, a round bar shape, and the like. Since the present foam is used as a cushioning material (for example, interleaving paper) for glass substrates, it is preferably in the form of a plate, in other words, it is preferably a polyethylene-based resin foam plate.

The present foam is preferably a plate-like foam having a thickness of 10 mm or more. This configuration has the advantage that it can be easily applied to various cushioning materials by processing such as cutting and punching.

(thickness)
The thickness of the present foam is not particularly limited. The thickness of the present foam is preferably 10 mm or more, more preferably 10 mm to 200 mm, more preferably 20 mm to 200 mm, more preferably 20 mm to 160 mm, more preferably 20 mm to 130 mm, further preferably 30 mm to 100 mm. , 40 mm to 70 mm are particularly preferred. According to this configuration, (a) the foam can be processed into various cushioning shapes, and a single piece (that is, one foam) can be used as a cushioning material instead of a laminate of sheets. , has the advantage that it is easy to obtain a homogeneous cushioning material. The thickness of the resulting foam can be adjusted by appropriately adjusting the thickness of the die opening, the size of the molding die, the size of the foam sandwiched in the molding machine, the take-up speed of the foam, and the like.

(Closed cell rate)
The closed cell ratio of the present foam is not particularly limited, but is preferably greater than 66%, more preferably 70% or more, more preferably 75% or more, more preferably 80% or more, more preferably 83% or more, 85% or more is more preferred, 88% or more is particularly preferred, and 90% or more is most preferred. According to this configuration, the resulting foam has the advantage of being excellent in cushioning performance as a cushioning material for glass substrates, repeated use performance, and dimensional recovery during punching. In the present specification, the expansion ratio of a foam is a value obtained by the measuring method described in Examples below.

(Expansion ratio)
The expansion ratio of the present foam is not particularly limited, and can be appropriately selected depending on the weight and/or required physical properties of the product. The expansion ratio of the present foam is preferably 4 to 35 times, more preferably 5 to 33 times, still more preferably 5.5 to 30 times, and particularly preferably 6 to 28 times. According to this configuration, the resulting foam has the advantage of having an excellent balance of lightness, product grip and cushioning properties, and the like. Moreover, according to the said structure, the processability of the foam for making a cushioning material becomes favorable. As a result, it becomes possible to process the resulting foam into a cushioning material and use it as a cushioning material for a wide range of goods to be conveyed, from lightweight parts to heavy parts. In the present specification, the expansion ratio of a foam is a value obtained by the measuring method described in Examples below.

(Average bubble diameter)
The average cell diameter of the present foam is not particularly limited, but is preferably 100 μm to 600 μm, more preferably 150 μm to 500 μm, still more preferably 180 μm to 500 μm, and particularly preferably 200 μm to 400 μm. According to this configuration, (a) the obtained foam can be easily adjusted to a desired closed cell rate and expansion ratio, and (b) the obtained foam can be used as a cushioning material for a glass substrate, and can protect the glass substrate. It has the advantage of being superior to In the present specification, the average cell diameter of the foam is a value obtained by the measuring method described in Examples below.

(Shrinkage factor)
The shrinkage rate of the present foam is not particularly limited, but is preferably 5.0% or less, more preferably 4.5% or less, and more preferably 4.0% or less. It is more preferably 5% or less, more preferably 3.0% or less, even more preferably 2.5% or less, and particularly preferably 2.0% or less. This configuration has the advantages of low shrinkage after production, small changes in dimensions over time, and excellent dimensional stability. In the present specification, the shrinkage rate of the foam is a value obtained by the measurement method described in Examples below.

(1-4. Other uses of polyethylene resin foam)
The polyethylene-based resin foam according to one embodiment of the present invention can be used not only as a cushioning material for glass substrates, but also as a substrate for precision devices (for example, substrates of silicon, plastic, etc. used in the manufacture of electronic equipment), and precision equipment. It can also be particularly suitably used when transporting and storing device members (for example, ceramic and metal materials used for device members).

(2. Other configurations)
The cushioning material for a glass substrate according to one embodiment of the present invention may contain a substance other than the polyethylene resin foam, or may be composed only of the polyethylene resin foam. In other words, the polyethylene-based resin foam according to one embodiment of the present invention described above itself may be used as a cushioning material for a glass substrate.

[III. Manufacturing method of cushioning material for glass substrate]
The method for manufacturing the cushioning material for a glass substrate according to one embodiment of the present invention is not particularly limited. For example, a method for manufacturing a cushioning material for a glass substrate according to an embodiment of the present invention may include a method for manufacturing a polyethylene-based resin foam according to an embodiment of the present invention. Therefore, a method for producing a cushioning material for a glass substrate according to an embodiment of the present invention is a method for producing a cushioning material for a glass substrate containing a polyethylene-based resin foam, wherein the polyethylene-based resin and the melting point of 85°C or higher are used. A composition containing a shrinkage inhibitor and a foaming agent containing 60 mol% or more of isobutane is subjected to extrusion foam molding, and the composition is added to 100 parts by weight of the polyethylene resin, the above and a method for producing a cushioning material for a glass substrate containing 0.05 to 0.50 parts by weight of a shrinkage inhibitor.

An embodiment of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Test method)
The test methods used for measuring and evaluating various physical properties in Examples and Comparative Examples are as follows.

<Melt mass flow rate (MFR)>
The MFR of the resin was measured according to JIS K7210-1 (2014). Specifically, using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), the amount (g) of resin extruded from the die per unit time was measured at 190° C. under a constant load (2.16 kg). A value was calculated by converting the obtained resin amount (g) into the resin amount (g) extruded in 10 minutes.

The unit time is 120 seconds when the melt mass flow rate is more than 0.5 g/10 minutes and 1.0 g/10 minutes or less, and when it is more than 1.0 g/10 minutes and 3.5 g/10 minutes or less. is 60 seconds, 30 seconds if over 3.5 g/10 minutes and 10 g/10 minutes or less, 10 seconds if over 10 g/10 minutes and 25 g/10 minutes or less, and 100 g/10 over 25 g/10 minutes 5 seconds when less than 10 minutes, and 3 seconds when more than 100 g/10 minutes.

One resin unit was defined as the amount of resin extruded from the die per unit time. In the measurement of MFR, 3 units of resin were sampled, the value converted to the amount (g) of resin extruded in 10 minutes was calculated for each unit, and the average value was taken as the MFR of each resin. If 3 units of resin could not be sampled in one measurement, the measurement was continued until 3 units were sampled.
If the melt mass flow rate 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 mass flow rate.

<Molecular weight distribution>
The molecular weight distribution of the resin was measured using a Viscotek Triple Detector HT-GPCModel-SG system manufactured by Malvern. By gel permeation chromatography using ortho-dichlorobenzene as the solvent and using Styragel HT6E, HT4, HT3 (4.6 mm × 300 mm, triplicate, fractionation range 500-10,000,000) manufactured by Waters as the column. I made a measurement. The temperature was 140°C. An RI was used as a detector, and commercially available monodisperse polystyrene was used as a standard substance to create a calibration curve. The obtained results are shown in terms of polystyrene.

<Closed cell rate>
Three test pieces each having a length of 30 mm, a width of 20 mm, and a thickness of 20 mm were cut out from each of the foams obtained in Examples and Comparative Examples. Using one of the test pieces, the volume Vc (cm ³ ) of the test piece is measured using an air pycnometer (comparative air specific gravity meter model 1000 manufactured by Tokyo Science Co., Ltd.) in accordance with the method described in ASTM D2856. bottom. Next, the same test piece after measurement was submerged in ethanol in a graduated cylinder containing ethanol. Apparent volume Va (cm ³ ) was obtained from the rise in the liquid level (ethanol level) of the graduated cylinder. Such an apparent volume measurement method is sometimes called a submersion method. The closed cell ratio (%) was obtained according to the following formula.
Closed cell rate (%) = (Vc/Va) x 100
In addition, the measurement was implemented for three test pieces per one foam, and the average value was made into the closed-cell rate of the foam.

<Expansion ratio>
The resin density of the raw material resin used in Examples and Comparative Examples was measured according to JIS K7112. The foam density was obtained by the following formula using the weight W (Kg) of the test piece used in the measurement of the closed cell ratio and the volume Va (m ³ ) obtained by the submersion method.
Foam density (Kg/m ³ ) = W/Va
In addition, the measurement was implemented for three test pieces per one foam, and the average value was made into the density of the foam.
Using the foam density (Kg/m ³ ) and the resin density (Kg/m ³ ), the expansion ratio was determined by the following formula.
Foaming ratio (times)=resin density/foam density.

<Foam size>
For the foams obtained in Examples and Comparative Examples, the surface perpendicular to the thickness direction was defined as surface a, the surface perpendicular to the extrusion direction was defined as surface b, and the surface perpendicular to the width direction was defined as surface c. Here, the thickness direction of the foam can be said to be the transverse 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 plane b to prepare three samples A each having a length of 20 mm in the extrusion direction. 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 points, 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 3 samples A was taken as the length (thickness dimension) of the foam in the thickness direction. A specific description will be given of the length in the width direction. 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) of the foam in the width direction. Moreover, the product of the obtained thickness dimension and width dimension was calculated, and the product was defined as the cross-sectional area.

<Average bubble diameter>
From each of the three samples A prepared for measuring the foam size, a cube (sample B) with each side of 5 to 10 mm was cut out for each measurement point (five points) shown below. Using a double-edged razor [feather, high stainless steel double-edged blade], sample B was cut along a plane parallel to each of the above-described planes a, b, and c, and careful not to break the bubble membrane (cell membrane). and disconnected. The resulting cut surfaces (three surfaces) were observed using a microscope [VHX-900 manufactured by Keyence Corporation] to obtain images of each cut surface. In each obtained image, a line segment with a length of 4000 μm was drawn, the number of bubbles n passed by the line segment was measured, and the bubble diameter was calculated by the following formula.
Bubble diameter (μm) = 4000/n
The arithmetic mean value of the cell diameters obtained from the images of the three cross-sections of the sample B (15 pieces) obtained for each measurement point (5 points) of the three samples A is defined as the average cell diameter (μm). bottom. That is, the arithmetic average value of the bubble diameters of 45 surfaces (3 surfaces×5 locations×3 sample A) was defined as the average bubble diameter (μm).
The measurement points are described for sample A. Five measurements were made for one sample A, as shown below:
(a) the 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) on the surface b of sample A, the central portion in the thickness direction, the central portion between the measurement point A and the widthwise end (two points at both widthwise ends);
(c) Central portions between the measuring point A and the ends in the thickness direction (two points at both ends in the thickness direction) in the center portion in the width direction on the surface b of the sample A.

<Shrinkage rate>
The obtained foam was cut into a size of about 100 mm x 100 mm immediately after extrusion (within about 6 hours), and the length and width thereof were measured with a steel rule immediately after extrusion (within about 6 hours). In addition, the thickness immediately after extrusion (within about 6 hours) was measured with a dial gauge. The volume immediately after extrusion was calculated from the dimensions measured immediately after extrusion.

Then, the foam was left for 7 days under an environment of 23° C. temperature and 50 RH % humidity. The dimensions (length, width and thickness) of the foam after standing for 7 days were measured by the same method as immediately after extrusion. The volume after standing for 7 days was calculated from the dimensions measured after standing for 7 days. The shrinkage ratio was obtained by the following formula. The shrinkage rate can also be said to be "the shrinkage rate after being left for 7 days".
Shrinkage (%)=(1-(foam volume after standing for 7 days)/(foam volume immediately after extrusion))×100.

<Contamination degree evaluation of glass surface>
The obtained foam was cut into a size of 100 mm×100 mm×50 mm (one side skin layer) to obtain a test piece. Next, the test piece is placed on a flat plate so that the skin layer of the test piece faces up, and a piece of glass (thickness 5 mm) having the same length and width as the test piece is placed on the test piece. A weight of 1 kg was placed on the A test body composed of the weight, glass, test piece and flat plate thus obtained was left in an atmosphere of 40° C. temperature and 80 RH % humidity for 3 days. After 3 days, the surface of the glass that was in contact with the test piece was observed, and the degree of contamination (degree of contamination) of the glass was evaluated according to the following criteria.
0: no stains were observed, transparent 1: fine stains were detected, but transparent 2: cloudy stains were detected, the opacity measurement sample number n = 3,
◎ (excellent): less than 0.5 ○ (good): 0.5 or more and less than 1.0 △ (acceptable): 1.0 or more and less than 1.5 × (improper): 1.5 or more.

<Scratch resistance evaluation of glass surface>
As a glass substrate, a glass plate for a display panel (0.7 mm thick, 60 mm long and 60 mm wide) was used. Also, the obtained foam was cut into the same size as the glass substrate, and used as a cushioning material for the glass substrate. Three glass substrates and three cushioning materials for glass substrates were alternately laminated on the cushioning material for glass substrates placed horizontally to obtain a laminate (three glass substrates and four cushioning materials for glass substrates). The uppermost and lowermost layers were cushioning materials for glass substrates).

A weight of 210 Kg/m ² was applied from the upper surface of the laminate using a pressure weight. The weight and the cushioning material were tied and fixed with a string made of PP (polypropylene) to prepare a test piece of the weight and the laminate. The test specimen was placed in a shaking device (trade name “Bioshaker V BR-36”, manufactured by Taitec Co., Ltd.), and under the conditions of a temperature of 23 ° C. and a shaking speed of 200 r / min, 6 gave time vibration.

After that, the PP string of the specimen was untied to dismantle the laminate, and the glass substrate was recovered. Next, light was applied from the side surface of the glass substrate, and scratches on the surface of the glass substrate were confirmed using a microscope. Evaluation criteria for the occurrence of scratches were as follows.
⊚ (excellent): Scratches cannot be observed on all three glass substrates.
○ (good): less than 3 scratches occurred in one glass plate in all three glass substrates × (improper): scratches occurred in any one of the three glass substrates is 3 or more.

<Comprehensive evaluation>
The criteria for comprehensive evaluation are as follows.
◯ (Good): Excellent (⊚) in the scratch resistance evaluation of the glass surface and good (◯) or better in the contamination degree evaluation of the glass surface.
Δ (acceptable): Evaluation of good (◯) or better in the scratch resistance evaluation of the glass surface and acceptable (Δ) in the evaluation of the degree of contamination of the glass surface.
x (improper): evaluation of acceptable (Δ) or lower in the evaluation of the scratch resistance of the glass surface, or evaluation of unacceptable (x) in the evaluation of the degree of contamination of the glass surface.

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

<Polyethylene resin>
As the polyethylene-based resin, a mixture obtained by mixing the polyethylene-based resin A and the polyethylene-based resin B in the amounts shown in Table 1 was used. Methods for preparing polyethylene resin A and polyethylene resin B are as follows.

(Polyethylene resin A)
A polyethylene resin A was obtained by blending the uncrosslinked branched low-density polyethylene and the uncrosslinked ethylene/α-olefin copolymer shown below in the amounts shown in Table 1.
● Uncrosslinked branched low-density polyethylene: Ube Maruzen Polyethylene, "C470", MFR: 2.0 g/10 minutes, density: 918 kg/m ³
● Uncrosslinked ethylene/α-olefin copolymer: “0540F” manufactured by Ube Maruzen Polyethylene, MFR: 4.0 g/10 minutes, density: 904 kg/m ³ . 0540F is linear low-density polyethylene.

(Slightly crosslinked polyethylene resin B)
By blending the uncrosslinked branched low-density polyethylene and the uncrosslinked ethylene/α-olefin copolymer in the blending amounts shown in Table 1, a starting polyethylene resin was obtained. The obtained raw material polyethylene resin was supplied to a twin-screw extruder with a diameter of 40 mm. Next, the raw material polyethylene resin was melt-kneaded by the extruder set at a cylinder temperature of 210° C. and extruded at a discharge rate of 50 kg/hr. A strand of the melt-kneaded material discharged from a die attached to the tip of the extruder was cooled with water and cut to obtain a pellet-shaped slightly crosslinked polyethylene resin B. As shown in FIG. 1, when the molecular weight distribution of the obtained slightly crosslinked polyethylene resin B was measured using gel permeation chromatography (referred to as GPC), the molecular weight in terms of standard polystyrene was 3.0E+5 to 3.0E+5. It was confirmed that in the high molecular weight region around 0E+7, the peak was slightly larger than that of the starting material polyethylene resin. As a result, it was confirmed that the slightly crosslinked polyethylene resin B had a slightly crosslinked structure. That is, the slightly crosslinked polyethylene-based resin B includes slightly crosslinked branched low-density polyethylene, slightly crosslinked ethylene/α-olefin copolymer, and slightly branched low-density polyethylene and ethylene/α-olefin copolymer. including crosslinked resins.

The density of the slightly crosslinked branched low density polyethylene contained in the slightly crosslinked polyethylene resin B was 918 kg/m ³ and the MFR was 2.5 g/10 minutes. The density of the slightly crosslinked ethylene/α-olefin copolymer contained in the slightly crosslinked polyethylene resin B was 900 kg/m ³ and the MFR was 4.0 g/10 minutes.

The slightly crosslinked branched low-density polyethylene and the slightly crosslinked ethylene/α-olefin copolymer contained in the slightly crosslinked polyethylene resin B were separated by the following method: (1) Slightly crosslinked polyethylene resin B was separated. (2) Then, the obtained sample was injected into the TREF column by the temperature rising elution fractionation method (TREF method); components were crystallized. At this time, the highly crystalline, slightly crosslinked ethylene/α-olefin copolymer component with few branches is crystallized first, and then, as the temperature drops, the slightly crystalline, slightly crosslinked, branched low-density polyethylene component is formed. (4) After that, the temperature was increased at a constant rate. At this time, the slightly crosslinked branched low-density polyethylene of the low crystalline component was eluted first, and then the slightly crosslinked ethylene/α-olefin copolymer was eluted.

<Bubble nucleating agent>
Cell nucleating agent: "EE275F" manufactured by Eiwa Kasei Co., Ltd. (masterbatch of sodium bicarbonate citric acid-based chemical blowing agent; carrier resin: polyethylene-based resin, blowing agent concentration: 27% by weight).

<Shrinkage inhibitor>
● 12-hydroxy stearic acid triglyceride: manufactured by Riken Vitamin Co., Ltd., "Rikemal TG-12", melting point: 87 ° C.
- Stearate monoglyceride: manufactured by Riken Vitamin Co., Ltd., "Rikemar S-100", melting point: 65°C
● Behenic acid monoglyceride: “Rikemal B-100” manufactured by Riken Vitamin Co., melting point: 80°C.
Note that only a is a shrinkage inhibitor in one embodiment of the present invention, and b and c are shrinkage inhibitors outside the scope of one embodiment of the present invention.

(Example 1)
Prepared were 100 parts by weight of a polyethylene resin, 2 parts by weight of a bubble nucleating agent and 0.30 parts by weight of 12-hydroxystearic acid triglyceride as a shrinkage inhibitor with respect to 100 parts by weight of the polyethylene resin. A first extruder consisting of a twin screw extruder with a diameter of 40 mm and a second extruder consisting of a single screw extruder with a diameter of 90 mm is supplied to the first extruder of a tandem extruder connected to the prepared raw material, and the composition was prepared. The cylinder temperature of the first extruder was set to 210°C, and the composition supplied to the first extruder was melt-kneaded at 210°C. Here, 2.2 parts by weight of isobutane as a foaming agent was injected into the obtained melt-kneaded material from the middle of the first extruder to prepare a resin melt.

Subsequently, after discharging the obtained resin melt from the first extruder to the second extruder, the resin melt is extruded and foamed by adjusting the barrel temperature and the screw rotation speed in the second extruder. cooled to a suitable temperature. Thereafter, the molten resin was extruded and foamed by extruding from a die attached to the tip of the second extruder under atmospheric pressure at a discharge rate of 40 kg/hour. Here, the die had a rectangular shape and the die opening had dimensions of 5.0 mm×50 mm.

Subsequently, a size-free foam and a plate-like foam were obtained. Specifically, a size-free foam was obtained by foaming the foam extruded from the die without using a molding die. On the other hand, for the plate-shaped foam, the foam discharged from the die is rectangularized by a molding die, and the size of the foam is adjusted by a molding machine while controlling the take-up speed. A plate-like foam molded into a plate-like shape was obtained. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Example 2)
A plate-like foam was obtained in the same manner as in Example 1, except that the shrinkage inhibitor (12-hydroxystearic acid triglyceride) was changed to 0.15 parts by weight. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Example 3)
A plate-like foam was obtained in the same manner as in Example 1, except that the shrinkage inhibitor (12-hydroxystearic acid triglyceride) was changed to 0.50 parts by weight. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Example 4)
A foam plate was obtained in the same manner as in Example 1, except that the take-up speed of the molding machine was controlled and the foam size was molded into a plate having a width of 145 mm and a thickness of 74 mm. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Comparative example 1)
A plate-like foam was obtained in the same manner as in Example 1, except that 0.30 parts by weight of monoglyceride stearate was used as the shrinkage inhibitor instead of triglyceride 12-hydroxystearate. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Comparative example 2)
A plate-like foam was obtained in the same manner as in Example 1, except that 0.30 parts by weight of behenic acid monoglyceride was used as the shrinkage inhibitor instead of 12-hydroxystearic acid triglyceride. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Comparative Example 3)
A plate-like foam was obtained in the same manner as in Example 1, except that 0.50 parts by weight of monoglyceride stearate was used as the shrinkage inhibitor instead of triglyceride 12-hydroxystearate. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Comparative Example 4)
A plate-like foam was obtained in the same manner as in Example 1, except that the shrinkage inhibitor (12-hydroxystearic acid triglyceride) was changed to 3.00 parts by weight. Table 2 shows the results of measuring and evaluating various physical properties of the resulting foam.

ADVANTAGE OF THE INVENTION According to one embodiment of the present invention, it is possible to provide a polyethylene-based resin foam that has a small shrinkage rate and that can prevent stains such as clouding of the glass substrate. Therefore, the polyethylene-based resin foam according to one embodiment of the present invention can be particularly suitably used when transporting and storing substrates for precision devices and members for precision devices.

Claims (6)

A cushioning material for a glass substrate containing a polyethylene-based resin foam,
The polyethylene-based resin foam is obtained by extruding and foam-molding a composition containing a polyethylene-based resin and a shrinkage inhibitor having a melting point of 85° C. or higher using a foaming agent containing 60 mol % or more of isobutane,
The composition is a cushioning material for a glass substrate, containing 0.05 to 0.50 parts by weight of the shrinkage inhibitor with respect to 100 parts by weight of the polyethylene resin. The polyethylene resin includes an uncrosslinked polyethylene resin A and a slightly crosslinked polyethylene resin B,
The uncrosslinked polyethylene resin A contains 55 to 100 parts by weight of uncrosslinked branched low-density polyethylene and 0 to 45 parts by weight of an uncrosslinked ethylene/α-olefin copolymer,
The slightly crosslinked polyethylene resin B contains 55 to 100 parts by weight of a slightly crosslinked branched low-density polyethylene and 0 to 45 parts by weight of a slightly crosslinked ethylene/α-olefin copolymer,
The polyethylene resin contains 5% to 45% by weight of the slightly crosslinked polyethylene resin B with respect to the total 100% by weight of the uncrosslinked polyethylene resin A and the slightly crosslinked polyethylene resin B. The cushioning material for a glass substrate described above. The cushioning material for a glass substrate according to claim 1 or 2, wherein the polyethylene-based resin foam is plate-shaped. The cushioning material for a glass substrate according to any one of claims 1 to 3, wherein the polyethylene-based resin foam has a thickness of 20 mm to 200 mm. The cushioning material for a glass substrate according to any one of claims 1 to 4, wherein the polyethylene-based resin foam has an expansion ratio of 4 to 35 times. The cushioning material for a glass substrate according to any one of claims 1 to 5, wherein the shrinkage inhibitor is 12-hydroxystearic acid triglyceride.

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