JP7219001B2 - cushioning material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cushioning material made of an extruded polyolefin resin foam and used for transporting various articles.

Conventionally, when transporting products that are vulnerable to external shocks, such as electrical and electronic parts, or relatively heavy items, such as automobile parts, it is necessary to reduce the impact during transportation and damage the product. Various cushioning materials are used to protect against Among them, foamed plastic is one of the most widely used cushioning materials because it has excellent properties of absorbing impact and mitigating the impact applied to the product. The level of cushioning properties of foamed plastic varies depending on the type of plastic that makes up the foam. The foam made of polystyrene, which is the most widely used material, has the disadvantage that repeated impacts cause the foam to break and the cushioning performance to rapidly decrease due to the lack of flexibility of polystyrene. On the other hand, a cushioning material made of foamed polyethylene resin does not deteriorate in cushioning properties against repeated impacts as described above because polyethylene resin is highly flexible, and is preferably used in applications where it is used repeatedly.

For example, in Patent Document 1, a crosslinkable composition containing a polyethylene resin and an ethylene-vinyl acetate copolymer is heated and foamed as a material suitable as a simple packaging material for preventing electrostatic breakdown of ICs and the like. The resulting crosslinked polyethylene-based foam is disclosed. In general, ethylene-vinyl acetate copolymers are inferior in foamability, but when crosslinked, foams having a high closed cell ratio can be obtained, and thick molded articles can be molded. However, since the foam is highly crosslinked, it is difficult to recycle, and the cushioning material using the foam must be disposed of by landfilling or burning after use, which poses a problem in that it places a burden on the environment.

Patent Document 2 discloses anti-slip properties obtained by foaming an ethylene-vinyl acetate copolymer or a mixture of an ethylene-vinyl acetate copolymer and a polyethylene-based resin having a specific vinyl acetate component content. A non-crosslinked polyethylene resin foam sheet having Such non-crosslinking extruded foam sheets are widely used in the field of cushioning materials as easily recyclable and environmentally friendly foams. However, copolymers with a high vinyl acetate content tend to have poor foamability, and it is difficult to stably obtain a foam with a high closed cell content. In particular, it is difficult to achieve desired physical properties in a thick foam that is difficult to refine cells and maintain a high closed cell content, and it is difficult to obtain a thick cushioning material with good anti-slip properties.

Moreover, as a cushioning material made of a recyclable non-crosslinked foam, a non-crosslinked foam using low-density polyethylene with good foamability is generally used. In general, low-density polyethylene with a branched structure has high melt hearing ability and excellent foaming properties, so although it achieves a high closed cell ratio, it is mainly used with coarse cell diameters, and it is effective in preventing product slippage. It is difficult to apply to cushioning materials that require excellent properties, that is, high gripping power.

Japanese Patent Application Laid-Open No. 2003-253033 Japanese Patent Application Laid-Open No. 2004-359709

SUMMARY OF THE INVENTION An object of the present invention is to obtain a cushioning material which is low-cost, recyclable, excellent in product gripping properties, and suitable for transporting large parts such as automobile parts and heavy goods.

As a result of intensive research in view of the above problems, the present inventors have found that a thick non-crosslinked polyethylene resin foam in which the expansion ratio, average cell diameter and closed cell rate are controlled within a specific range can be used when a product is placed. The present inventors have found that a cushioning material can be obtained that has both excellent adhesiveness during transportation and strength that can withstand momentary overloads during the transportation of heavy products, and has completed the present invention.

That is, the present invention relates to a cushioning material using a non-crosslinked polyolefin resin extruded foam that satisfies the following a) to d).

a) The expansion ratio is 5 times or more and 30 times or less b) The average cell diameter is 100 μm or more and 600 μm or less c) The closed cell ratio is 70% or more d) The thickness is 20 mm or more In addition, the present invention satisfies the following e) to h) The present invention relates to a cushioning material using a non-crosslinked polyolefin resin extruded foam.

e) Foaming ratio of 5 times or more and 30 times or less
f) Average cell diameter that satisfies the relationship of the following formula (1) - (33.3 x foaming ratio) ≤ 350 - formula (1)
g) Closed cell ratio of 70% or more h) Thickness of 20 mm or more In the present invention, the non-crosslinked polyolefin resin extruded foam preferably has a dynamic friction coefficient of 0.310 or more.

In the present invention, the non-crosslinked polyolefin resin extruded foam preferably satisfies the relationship of the following formula (2).

Compressive stress ratio ≥ 0.4 × Ln (expansion ratio) -0.4 - formula (2)
Compressive stress ratio = S2550/S04
S04: difference in compressive stress at strain 0% and 4% (MPa)
S2550: difference in compressive stress at 25% and 50% strain (MPa)
In the present invention, the polyolefin-based resin preferably contains a polyethylene-based resin.

In the present invention, it is preferable that 60% by weight or more of low-density polyethylene is contained in 100% by weight of the polyolefin resin.

In the present invention, the density of the low density polyethylene is preferably 900-930 kg/m ³ .

The cushioning material of the present invention is suitable for transporting heavy goods.

The present invention comprises a step of melt-kneading a polyolefin resin and a foaming agent containing an aliphatic hydrocarbon, and cooling the molten resin composition containing the foaming agent obtained by the melt-kneading, followed by It relates to a method for producing a non-crosslinked polyolefin resin extruded foam that satisfies the following requirements a) to d), including the step of extruding and molding the foam.
a) Expansion ratio of 5 to 30 times b) Average cell diameter of 100 μm to 600 μm c) Closed cell ratio of 70% or more d) Thickness of 20 mm or more The present invention provides a polyolefin resin and an aliphatic hydrocarbon. and a step of cooling the molten resin composition containing the foaming agent obtained in the melt-kneading step and extruding under reduced pressure to form a foamed product. , to a method for producing a non-crosslinked polyolefin resin extruded foam that satisfies the following requirements e) to h).

e) Foaming ratio of 5 times or more and 30 times or less
f) satisfying the relationship of the following formula (1)
Average bubble diameter - (33.3 x foaming ratio) ≤ 350 - formula (1)
g) closed cell ratio of 70% or more h) thickness of 20 mm or more In the present invention, the resin composition preferably contains a chemical foaming agent as a cell nucleating agent.

In the present invention, the chemical blowing agent is preferably a mixture of sodium bicarbonate and citrate.

In the present invention, the resin composition preferably contains an anti-shrinkage agent.

According to the present invention, it is possible to obtain a cushioning material which is excellent in gripping force for transported products and which is suitable for automobile parts and various industrial products, particularly large and heavy products that tend to be out of balance.

The first cushioning material of the present invention has an expansion ratio of 5 times or more and 30 times or less, an average cell diameter of 100 μm or more and 600 μm or less, a closed cell ratio of 70% or more, and a thickness of 20 mm or more. It is characterized by comprising a non-crosslinked polyolefin resin extruded foam. Expansion ratio, closed cell ratio, and thickness are properties required for plate-shaped foams conventionally used as cushioning materials. By using a non-crosslinked polyolefin resin extruded foam that satisfies the above requirements, it is possible to obtain a cushioning material that has both excellent product grip and strength enough to withstand the transportation of heavy objects. Furthermore, since the cushioning material of the present invention is made of non-crosslinked polyolefin resin extruded foam, it also has recyclability.

The average cell diameter of the non-crosslinked polyolefin resin extruded foam is preferably 120 μm or more, more preferably 140 μm or more, and even more preferably 150 μm or more, from the viewpoint of facilitating adjustment to a desired closed cell ratio and expansion ratio. In addition, it is preferably 500 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less, because the coefficient of friction that affects the grip performance of the product increases. Here, the average bubble diameter is measured by the measuring method described in Examples described later.

The expansion ratio of the non-crosslinked polyolefin resin extruded foam is in the range of 5 to 30 times, so it has good workability as a cushioning material, and can be used as a cushioning material for lightweight parts to heavy parts such as automobile engines. becomes possible. The expansion ratio is appropriately selected depending on the weight of the product, but the lower limit is preferably 6 times, more preferably 7 times, from the viewpoint of easily obtaining a balance between grip and cushioning properties. On the other hand, the upper limit is preferably 25 times, more preferably 20 times.

When the non-crosslinked polyolefin resin extruded foam has a closed cell ratio of 70% or more, the cushioning performance as a cushioning material, the repeated use performance, and the dimensional recovery property during punching are improved. It is preferably 75% or more, more preferably 80% or more.

The thickness of the non-crosslinked polyolefin resin extruded foam should be uniform from the standpoint that it can be processed into a variety of cushioning material shapes, and when used as a single piece instead of a laminated sheet, it will be uniform as a cushioning material. is preferably 30 mm or more, and more preferably 40 mm or more, from the viewpoint that is easy to obtain. The upper limit of the thickness is not particularly limited, but it is usually 150 mm or less, more preferably 100 mm or less, and particularly preferably 70 mm or less, due to the difficulty of ensuring the thickness by extrusion foaming.

The second cushioning material of the present invention has an expansion ratio of 5 times or more and 30 times or less, a closed cell ratio of 70% or more, satisfies the following formula (1), and has a thickness of 20 mm or more. It is characterized by using an extruded resin foam.

Average bubble diameter - (33.3 x foaming ratio) ≤ 350 - formula (1)
In the process of examining the present invention, it has been found that the coefficient of friction of the foam is affected by the expansion ratio and the average cell diameter. That is, at a high expansion ratio, the coefficient of friction becomes high, so a somewhat large average cell diameter is acceptable, but at a low expansion ratio, a smaller average cell diameter is required. Specifically, by satisfying formula (1), a foam with a high coefficient of friction tends to be obtained. Ral. The coefficient of friction here means the coefficient of dynamic friction.
The value of the right-hand side of formula (1) is preferably 200, more preferably 100, especially -50.

The expansion ratio and thickness of the non-crosslinked polyolefin resin extruded foam in the second cushioning material are similarly suitable for the expansion ratio and thickness of the non-crosslinked polyolefin resin extruded foam in the first cushioning material. As for the average cell diameter, the average cell diameter of the non-crosslinked polyolefin resin extruded foam in the first cushioning material is also suitable.

The non-crosslinked polyolefin resin extruded foam used in the cushioning material of the present invention preferably has a dynamic friction coefficient of 0.310 or more, more preferably 0.340 or more, from the viewpoint of product grip. It is preferably 0.360 or more, and more preferably 0.360 or more.

Furthermore, the non-crosslinked polyolefin resin extruded foam preferably satisfies the following formula (2).

Compressive stress ratio ≥ 0.4 × Ln (expansion ratio) -0.4 - formula (2)
Compressive stress ratio = S2550/S04
・ S04: difference in compressive stress between 0% and 4% strain (MPa)
・ S2550: difference in compressive stress between 25% and 50% strain (MPa)
The above S04 is the stress at the initial stage of compression of the foam, and is a factor that affects softness and adhesion when a product is placed on the foam when used as a cushioning material. If this value is large, sufficient adhesion between the product and the cushioning material cannot be obtained, and localized loads are likely to occur, and depending on the conditions during transportation, the surface of the highly designed product may be damaged. On the other hand, S2550 represents the rate of improvement of compressive stress with respect to strain when a large compressive strain occurs. A foam with a large value of S2550 has the property that stress tends to increase when a large compressive strain occurs, and it can withstand momentary overloads that occur during product transportation. It is a measure to prevent crushing and receiving external impact directly). A foam with a high compressive stress ratio tends to provide a cushioning material that has both a soft feel and a good bottoming property, but the values differ depending on the expansion ratio. Specifically, by satisfying formula (2), it is easy to obtain a cushioning material that has both a soft feeling and bottoming property according to the expansion ratio, and the right side of formula (2) is preferably "0.4 × Ln (expansion ratio) −0.3”, more preferably “0.4×Ln (expansion ratio)−0.2”. In addition, the compressive stress ratio may satisfy formula (2), but from the viewpoint of facilitating both softness and bottoming, it is preferably 0.55 or more, more preferably 0.60 or more. , particularly preferably 0.65 or more.

The non-crosslinked polyolefin resin extruded foam used for the cushioning material of the present invention is obtained by melt-kneading a raw material resin component containing a polyolefin resin, a foaming agent, and, if necessary, various additives described later using an extruder. A foamable resin melt containing a foaming agent is extruded from a die attached to the extruder to a low pressure region and foamed. It can be manufactured by molding. It is also possible to use a molding die attached to a die.

As the polyolefin-based resin, any resin can be used without any particular restrictions as long as it is foamable and has excellent cushioning performance when foamed. The polyolefin-based resin may be any resin having an olefin component unit of 50 mol % or more, and examples thereof include polyethylene-based resins and polypropylene-based resins.

Examples of polyethylene-based resins include resins having ethylene component units of 50 mol% or more, such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-propylene copolymer. coalescence, ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer A coalescence etc. are illustrated.

Examples of polypropylene-based resins include propylene homopolymers and copolymers of propylene with other copolymerizable components such as olefins. Other olefins copolymerizable with propylene include, for example, ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1 C4-C10 α-olefins such as -heptene and 3-methyl-1-hexene are exemplified. The above copolymer may be a random copolymer, a block copolymer, or the like, and may be a terpolymer as well as a binary copolymer. Among these polyolefin-based resins, polyethylene-based resins are preferable from the viewpoint of excellent flexibility and protection of non-cushioning objects. Among them, polyethylene-based resins having a density of 935 kg/m ³ or less as a main component are preferable. . Specifically, it is preferable to use low-density polyethylene, linear low-density polyethylene, or the like, and it is more preferable to use low-density polyethylene with good foamability. The term "main component" consisting of a polyethylene-based resin having a density of 935 kg/m ³ or less means that the content of the polyethylene-based resin is 60% by weight or more based on 100% by weight of the polyolefin-based resin. Moreover, the lower limit of the density of polyethylene resin is approximately 890 kg/m ³ . The preferred range of density of the polyethylene resin is from 900 kg/m3 to 930 kg/ ^{m3 ,} more preferably from 910 kg/ ^m3 to 925 kg/m3 ^, particularly from 913 kg/ ^m3 to 923 kg/ ^m3 . is preferred.

These polyolefin-based resins may be used alone or as a mixture of two or more, and two or more of the same resin species but different densities may be used in combination. Examples of mixtures of two or more polyolefin resins include mixtures of low density polyethylene and linear low density polyethylene.

The MFR of the polyolefin resin is preferably 0.05 to 15 g from the viewpoint that it has a melt tension and can prevent excessive shear heat generation in the extruder and tends to facilitate the setting of conditions suitable for extrusion foaming. /10 min, more preferably 0.5 to 10 g/10 min, still more preferably 0.8 to 5.0 g/10 min, particularly preferably 1.0 to 3.0 g/10 min.

As a method for adjusting the average cell diameter of the non-crosslinked polyolefin resin extruded foam used in the present invention, the amount of cell nucleating agent added, the temperature conditions during extrusion foaming, the shear rate during extrusion foaming, and the shape of the die opening. For example, conventionally known adjustments are effective.

As the cell nucleating agent, it is possible to use inorganic substances, chemical foaming agents, and the like that are commonly used in the production of foams. Examples of inorganic substances include talc, silica, calcium carbonate, zeolite, lithium carbonate, and zinc oxide. Chemical foaming agents are classified into organic chemical foaming agents and inorganic chemical foaming agents. Organic chemical foaming agents include ADCA (azodicarbonamide), DPT (N,N'-dinitropentamethylenetetramine), OBSH (4,4'-oxybisbenzenesulfonyl hydrazide) and the like are often used. Examples of inorganic chemical foaming agents include hydrogen carbonates, carbonates, mixtures of hydrogen carbonates and organic acid salts, and the like. These bubble nucleating agents can be used alone or in combination of two or more. The cell nucleating agent may be directly added in the form of powder, or may be used as a masterbatch in consideration of mixability with the main material (raw material resin component). In particular, when the shrinkage preventing agent described below is used, the air bubbles tend to be coarsened, and an agent having a high nucleation effect capable of achieving a desired air bubble diameter with a small addition amount is preferred. Inorganic chemical foaming agents are preferable among the above from the viewpoint that a nucleation effect can be easily obtained with a small amount, and among them, a mixture of a hydrogen carbonate and an organic acid salt is preferable, and a mixture of sodium hydrogen carbonate and a citrate is particularly preferable. is preferred. In order to enhance the bubble nucleation effect, it is preferable to use a mixture of sodium hydrogencarbonate and citrate in combination with the above inorganic substance, and talc and lithium carbonate are preferable as the inorganic substance. The chemical foaming agent is preferably used as a masterbatch with a concentration of about 15% to 50% by weight. "EE275F" (manufactured by Eiwa Kasei Co., Ltd.) and the like can be mentioned as a chemical blowing agent masterbatch having such a high bubble nucleation effect. If the amount of these cell nucleating agents used is increased, the resulting foam tends to have a smaller cell diameter, but exceeding the appropriate amount leads to a decrease in closed cell ratio. Therefore, the amount used is preferably 0.1 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, even more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the starting resin component.

In addition, the closed cell ratio and expansion ratio can be adjusted by conventionally known methods. Specifically, the closed cell ratio includes adjustment of the extrusion temperature of the molten resin during extrusion foaming, and the expansion ratio includes adjustment of the amount of foaming agent and the extrusion temperature of the molten resin during extrusion foaming. .

Examples of foaming agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; aliphatic cyclic hydrogens such as cyclopentane and cyclobutane; dimethyl ether, diethyl ether, methyl ethyl ether, and the like. alcohols such as methanol and ethanol; inorganic gases such as air, nitrogen and carbon dioxide; and water. These foaming agents may be used alone or in combination of two or more. Among these, aliphatic hydrocarbons are preferable, and normal butane and isobutane are particularly preferable, from the viewpoint that desired expansion ratio, closed cell ratio and average cell diameter can be easily obtained. The amount of the foaming agent to be added may vary depending on the type of the foaming agent and the expansion ratio of the target foam, so it may be adjusted as appropriate. is preferred, and it is more preferably 1 part by weight or more and 15 parts by weight or less.

It is preferable to use a so-called shrinkage inhibitor for the purpose of preventing shrinkage after foaming, if necessary, in the foam used in the present invention. In particular, it is preferable to add an anti-shrinkage agent when using the above-mentioned foaming agent in place of the flon-based foaming agent conventionally used as the foaming agent.

Conventionally well-known agents such as fatty acid esters, fatty amines and fatty acid amides can be used as the shrinkage inhibitor.

As the fatty acid ester, an ester of a fatty acid having 8 to 30 carbon atoms and a polyhydric alcohol having 3 to 7 hydroxyl groups is preferable. Examples of fatty acids having 8 or more carbon atoms include lauric acid, oleic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, heptakoic acid, montanic acid, melissic acid and laxeric acid. Examples of polyhydric alcohols having 3 to 7 hydroxyl groups include glycerin, diglycerin, triglycerin, erythritol arabit, xylimaat, mannitol, sorbitol and sorbitan. Among these ester compounds, partial esters, particularly monoesters, are preferable to full esters because they provide a more pronounced anti-shrinkage effect. Mixtures of monoglycerides are more preferred.

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

Examples of the fatty acid amide include stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide, and lauric acid bisamide.

The amount of the shrinkage inhibitor to be blended is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, and still more preferably 0.7 parts by weight or more based on 100 parts by weight of the raw material resin component. If the amount is too small, the anti-shrinkage effect may be insufficient. On the other hand, if the blending amount is too large, the shrinkage prevention effect reaches a peak, and not only is there no merit in terms of cost, but also strength physical properties such as compressive stress of the obtained foam may be lowered. Therefore, the upper limit of the content is preferably approximately 3 parts by weight, more preferably 2 parts by weight.

In addition, other synthetic resins than polyolefin resins may be added as long as the effects of the present invention are not impaired. Synthetic resins other than polyolefin resins include polystyrene, styrene-maleic anhydride copolymer, styrene-ethylene copolymer, styrene-isobutylene-styrene copolymer, styrene-isobutylene copolymer, styrene-butadiene. Styrene-based resins such as -styrene copolymers, styrene-isoprene-styrene copolymers, and hydrogenated products thereof, polyamide-based resins, thermoplastic polyurethanes, and the like are exemplified.

In the present invention, stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metallic soaps, antacid adsorbents, etc. Alternatively, additives such as cross-linking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants and antistatic agents may be added.

In the present invention, the addition of a coloring agent is not limited, and a natural color can be obtained without adding a coloring agent, or a desired color can be obtained by adding a coloring agent such as blue, red, or black. . Examples of coloring agents include perylene organic pigments, azo organic pigments, quinacridone organic pigments, phthalocyanine organic pigments, threne organic pigments, dioxazine organic pigments, isoindoline organic pigments, and carbon black.

The resulting non-crosslinked polyolefin resin extruded foam is processed into a desired shape by cutting, punching, or the like, and used as a cushioning material.

Since the cushioning material of the present invention uses the non-crosslinked polyolefin resin extruded foam, it has excellent gripping power for heavy items and large items that tend to lose balance, and compressive stress that prevents these items from bottoming out during transportation. Also excellent. Therefore, it is most suitable as a cushioning material for transportation of heavy industrial products such as automobile parts, metal industrial parts, and large plastic products. Moreover, since the cushioning material of the present invention is recyclable, it is environmentally friendly.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited by these examples.

Test methods and criteria used for various evaluation methods in Examples and Comparative Examples are as follows.

<Melt flow rate (MFR)>
MFR conforms to the provisions of A method described in JIS K 7210 (1999), using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), 190 ° C., from the die under a constant load (2.16 kg) for a certain time. The value was obtained by converting the amount of resin extruded in 10 minutes into the amount extruded in 10 minutes.

The fixed time is 120 seconds when the melt flow rate is more than 0.5 g/10 minutes and 1.0 g/10 minutes or less, and 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.

Three cut pieces cut out in the above-mentioned fixed period of time were collected, and the average value was calculated. If three pieces could not be collected in one measurement, the measurement was continued until three pieces could be collected. If the melt flow rate measured for a certain number of seconds was not within the corresponding range, the measurement was repeated for the number of seconds corresponding to the melt flow rate.

<Closed cell rate>
A test piece having a width of 20 mm, a thickness of 20 mm, and a length of 30 mm was prepared from each foam obtained in Examples and Comparative Examples, and measured in accordance with the method described in ASTM D2856 with an air pycnometer (air comparison manufactured by Tokyo Science Co., Ltd.). Using a hydrometer model 1000), the volume Vc (cm ³ ) of the test piece was measured. Next, the same test piece after measurement is submerged in a graduated cylinder containing ethanol, and the apparent volume Va (cm ³ ) is obtained from the amount of liquid level rise in the graduated cylinder (submersion method), and the closed cell ratio ( %) was obtained.
Closed cell rate (%) = (Vc/Va) x 100
In addition, the measurement was implemented about three test pieces, and the average value was made into the closed-cell rate of the foam.

<Foam density>
It was obtained by the following formula from the weight W (g) of the test piece used in the measurement of the closed cell ratio and the volume Va (cm ³ ) obtained by the above water immersion method.
Foam density (g/cm ³ ) = W/Va

<Expansion ratio>
It was obtained from the foam density (g/cm ³ ) and the resin density (g/cm ³ ) according to the following formula.
Foaming ratio (times) = resin density / foam density

<Average bubble diameter>
The foams obtained in Examples and Comparative Examples were cut into 20 mm lengths in the direction of extrusion at three arbitrary cross-sections perpendicular to the direction of extrusion to prepare samples A. Furthermore, a cubic sample B with each side of 5 to 10 mm was cut out from the sample A at the following measurement points. Each observation surface (thickness direction, width direction, extrusion direction) of sample B was cut with a double-edged razor [feather made, high stainless steel double-edged blade], being careful not to destroy the bubble membrane (cell membrane), The cut surface was observed with a microscope [VHX-900 manufactured by Keyence Corporation]. In the 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
This measurement was carried out for each measurement point in the thickness direction, width direction, and extrusion direction, and the arithmetic mean value of these was taken as the average cell diameter (μm).
*) Measurement points: The average cell diameter at the following five points was measured at each of three arbitrary cross-section points perpendicular to the extrusion direction of the foam.

・Central part (measurement point 1)
・Middle part between the central part and both ends in the width direction (measurement points 2 and 3)
・Intermediate part between the central part and the upper and lower ends in the thickness direction (measurement points 4 and 5)

<Void evaluation>
The cross section perpendicular to the extrusion direction of the foam was observed in the same manner as the measurement of the average cell diameter, and the presence or absence of voids was evaluated as voids generated by communicating cells that were 3.246 times or more the average cell diameter. .

<Evaluation of physical properties as a cushioning material>
A cushioning material sample having a width of 50 mm, a thickness of 25 mm, and a length of 200 mm was cut out from the foam and subjected to the following evaluations.

1) Appearance
The cut surface of the cushioning material sample was visually evaluated according to the following criteria.
A: Air bubbles are uniform and fine, giving an impression that the surface is smooth.
B: between A and C;
C: Bubbles are coarse and each one is distinct, and surface unevenness due to bubbles can be easily visually confirmed.

2) Dynamic Friction Coefficient Measured according to ASTM D1894 using a surface property tester (HEIDON TRIBOGEAR Type 14, manufactured by Shinto Kagaku Co., Ltd.). A test piece having a width of 50 mm, a thickness of 9 mm, and a length of 200 mm was cut from the cushioning material sample. Friction was produced by horizontal movement of an ASTM flat indenter attached to the surface tester over the specimen. The measurement was performed at a load of 1150 g (flat indenter: 150 g, weight: 1000 g), a test speed of 150 mm/min, and a distance of 70 mm. The dynamic friction coefficient was calculated from the average value of the dynamic friction force from 1.5 seconds to 5 seconds after the start of measurement and the test load. The same measurement was carried out three times, and the average value of these was taken as the dynamic friction coefficient of the foam, and evaluated according to the following criteria.
A: 0.360 or more B: 0.340 or more and less than 0.360 C: 0.310 or more and less than 0.340 D: less than 0.310

3) Compressive stress ratio A test piece of width 50 mm x length 50 mm x thickness 25 mm is cut out from the above buffer material sample, and an autograph (manufactured by Shimadzu Autograph AG-X/R, load capacity 20 kN) is used, and according to JIS K6767. The compressive stress was measured according to the test speed (test speed 10 mm/min, elongation origin (measurement start point) set at 0.3% (60 N) of test force full scale (20 kN)). From the obtained compressive stress data, the ratio of the difference S04 (MPa) in compressive stress between 0% and 4% strain and the difference S2550 (MPa) in compressive stress between 25% and 50% strain was obtained by the following formula. .
Compressive stress ratio = S2550/S04

(Example 1)
To 100 parts by weight of low-density polyethylene ("C470" manufactured by Ube Maruzen Polyethylene, MFR 2.0 g/10 min, density 918 kg/m ³ ), a chemical foaming agent (EE275F manufactured by Eiwa Kasei, sodium bicarbonate-citric acid heat 3.0 parts by weight of decomposable foaming agent masterbatch) and 1.0 parts by weight of stearic acid monoglyceride as an anti-shrinkage agent were added to a Φ40 twin-Φ90 mm single-screw tandem extruder. After melting in the first extruder (φ40 twin screw) set at 230°C, 3.5 parts by weight of isobutane as a foaming agent is injected and mixed, and then in the second extruder (φ90 mm) set at 97°C. After cooling, it was extruded at a discharge rate of 50 kg/hour under atmospheric pressure from a rectangular die (opening 50 mm×4 mm) connected to the tip of the extruder. A plate-like foam was obtained by a forming die while the foam extruded from the die was taken by a take-up machine. The resulting foam was free of voids and had a high closed cell content. Table 1 shows the results of measuring and evaluating various physical properties of the resulting foam.

(Examples 2-3)
A foam was obtained in the same manner as in Example 1 except that the formulation was adjusted as shown in Table 1. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Example 4)
A foam was obtained in the same manner as in Example 1, except that the amount of isobutane added was changed to 2.0 parts. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Examples 5-6)
A foam was obtained in the same manner as in Example 1 except that the formulation was adjusted as shown in Table 1. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Comparative example 1)
A foam having a large average cell diameter was obtained in the same manner as in Example 1, except that the amount of cell nucleating agent added was changed to 0.33 parts. The cushioning material sample produced from the foam having a large average cell diameter had a poor appearance due to conspicuous surface irregularities due to the cells, a low dynamic friction coefficient, and a low compressive stress ratio. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Comparative example 2)
A foam with a low closed cell content was obtained in the same manner as in Example 1, except that the extrusion conditions and molding conditions were adjusted. When the presence or absence of voids was evaluated for the resulting foam, the foam was free of voids. This void-free cushioning material sample made from a foam with a low closed cell content had a low compressive stress ratio. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Comparative Example 3)
A foam having a large average cell diameter was obtained in the same manner as in Example 4, except that the amount of cell nucleating agent added was changed to 1.0 part. The cushioning material sample produced from the foam having a large average cell diameter had a poor appearance due to conspicuous surface irregularities due to the cells, a low dynamic friction coefficient, and a low compressive stress ratio. Table 1 shows the results of similarly measuring and evaluating various physical properties of the resulting foam.

(Reference example 1)
Table 1 shows the results of similarly measuring and evaluating various physical properties of commercially available non-crosslinked polyethylene foam (Suntech Foam "Q15" manufactured by Asahi Kasei Corporation). Similar to Comparative Example 1, since the average cell diameter was large, the appearance was poor and the coefficient of dynamic friction was low.

Claims (16)

A cushioning material using a non-crosslinked polyolefin resin extruded foam that satisfies the following a) to d),
The non-crosslinked polyolefin resin extruded foam includes high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and ethylene-propylene-butene-1 copolymer. one selected from the group consisting of coalescence, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer and ethylene-octene-1 copolymer Including the above polyethylene resin ,
100% by weight of the polyolefin resin in the extruded non-crosslinked polyolefin resin foam contains 60% by weight or more of the polyethylene resin having a density of 935 kg/m ³ or less among the polyethylene resins.
a) Foaming ratio of 5 times or more and 30 times or less b) Average cell diameter of 100 μm or more and 600 μm or less c) Closed cell ratio of 70% or more d) Thickness of 20 mm or more A cushioning material using a non-crosslinked polyolefin resin extruded foam satisfying the following e) to h),
The non-crosslinked polyolefin resin extruded foam includes high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and ethylene-propylene-butene-1 copolymer. one selected from the group consisting of coalescence, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer and ethylene-octene-1 copolymer Including the above polyethylene resin ,
100% by weight of the polyolefin resin in the extruded non-crosslinked polyolefin resin foam contains 60% by weight or more of the polyethylene resin having a density of 935 kg/m ³ or less among the polyethylene resins.
e) The expansion ratio is 5 times or more and 30 times or less f) The average cell diameter that satisfies the relationship of the following formula (1) - (33.3 x expansion ratio) ≤ 207 - formula (1)
g) Closed cell ratio of 70% or more h) Thickness of 20 mm or more A cushioning material using a non-crosslinked polyolefin resin extruded foam that satisfies the following a) to d),
The non-crosslinked polyolefin resin extruded foam contains a polyolefin resin,
A cushioning material containing 60% by weight or more of low-density polyethylene and/or linear low-density polyethylene in 100% by weight of the polyolefin resin.
a) Foaming ratio of 5 times or more and 30 times or less b) Average cell diameter of 100 μm or more and 600 μm or less c) Closed cell ratio of 70% or more d) Thickness of 20 mm or more A cushioning material using a non-crosslinked polyolefin resin extruded foam satisfying the following e) to h),
The non-crosslinked polyolefin resin extruded foam contains a polyolefin resin,
A cushioning material containing 60% by weight or more of low-density polyethylene and/or linear low-density polyethylene in 100% by weight of the polyolefin resin.
e) The expansion ratio is 5 times or more and 30 times or less f) The average cell diameter that satisfies the relationship of the following formula (1) - (33.3 x expansion ratio) ≤ 207 - formula (1)
g) Closed cell ratio of 70% or more h) Thickness of 20 mm or more The cushioning material according to claim 3 or 4, wherein the density of said low density polyethylene is 900-930 kg/m ³ . The cushioning material according to any one of claims 1 to 5, wherein the polyolefin resin has an MFR of 1.0 to 3.0 g/10 minutes . The cushioning material according to any one of claims 1 to 6 , wherein the non-crosslinked polyolefin resin extruded foam has a dynamic friction coefficient of 0.310 or more. The cushioning material according to any one of claims 1 to 7 , wherein the non-crosslinked polyolefin resin extruded foam satisfies the relationship of the following formula (2).
Compressive stress ratio ≥ 0.4 × Ln (expansion ratio) -0.4 - formula (2)
Compressive stress ratio = S2550/S04
S04: difference in compressive stress at strain 0% and 4% (MPa)
S2550: difference in compressive stress at 25% and 50% strain (MPa) The cushioning material according to any one of claims 1, 2, 6 , 7 and 8 , wherein 60% by weight or more of low density polyethylene and/or linear low density polyethylene is contained in 100% by weight of said polyolefin resin. The cushioning material according to any one of claims 1 to 9, wherein 60% by weight or more of low-density polyethylene is contained in 100% by weight of the polyolefin resin. The cushioning material according to claim 10 , wherein the density of said low density polyethylene is 900-930 kg/m ³ . The cushioning material is for transporting heavy goods,
The cushioning material according to any one of claims 1 to 11 , wherein the heavy goods are one or more selected from the group consisting of automobile parts, metal industrial parts, and large plastic products. A step of melt-kneading a polyolefin resin and a foaming agent containing an aliphatic hydrocarbon, and extruding under reduced pressure after cooling the molten resin composition containing the foaming agent obtained in the melt-kneading step. including the step of foaming and molding the foam,
Satisfy the following requirements a) to d),
The resin composition contains a chemical foaming agent as a cell nucleating agent,
the chemical blowing agent is a mixture of sodium bicarbonate and citrate;
The polyolefin resins include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene. -1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer and ethylene-octene-1 copolymer, at least one polyethylene resin selected from the group consisting of including
100% by weight of the polyolefin-based resin includes 60% by weight or more of the polyethylene-based resin having a density of 935 kg/m ³ or less among the polyethylene-based resins.
a) Foaming ratio of 5 times or more and 30 times or less b) Average cell diameter of 100 μm or more and 600 μm or less c) Independent cell ratio of 70% or more d) Thickness of 20 mm or more A step of melt-kneading a polyolefin resin and a foaming agent containing an aliphatic hydrocarbon, and extruding under reduced pressure after cooling the molten resin composition containing the foaming agent obtained in the melt-kneading step. including the step of foaming and molding the foam,
Satisfy the following requirements e) to h),
The resin composition contains a chemical foaming agent as a cell nucleating agent,
the chemical blowing agent is a mixture of sodium bicarbonate and citrate;
The polyolefin resins include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene. -1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer and ethylene-octene-1 copolymer, at least one polyethylene resin selected from the group consisting of including
100% by weight of the polyolefin-based resin includes 60% by weight or more of the polyethylene-based resin having a density of 935 kg/m ³ or less among the polyethylene-based resins.
e) Foaming ratio of 5 times or more and 30 times or less
f) satisfying the relationship of the following formula (1)
Average bubble diameter - (33.3 x foaming ratio) ≤ 207 - formula (1)
g) Closed cell ratio of 70% or more h) Thickness of 20 mm or more A step of melt-kneading a polyolefin resin and a foaming agent containing an aliphatic hydrocarbon, and extruding under reduced pressure after cooling the molten resin composition containing the foaming agent obtained in the melt-kneading step. including the step of foaming and molding the foam,
meet the following requirements a) to d) and f) ,
The resin composition contains a chemical foaming agent as a cell nucleating agent,
the chemical blowing agent is a mixture of sodium bicarbonate and citrate ;
A method for producing a non-crosslinked polyolefin resin extruded foam, wherein 100% by weight of the polyolefin resin contains 60% by weight or more of low density polyethylene and/or linear low density polyethylene .
a) Foaming ratio of 5 times or more and 30 times or less b) Average cell diameter of 100 μm or more and 600 μm or less c) Closed cell ratio of 70% or more d) Thickness of 20 mm or more
f) satisfying the relationship of the following formula (1)
Average bubble diameter - (33.3 x foaming ratio) ≤ 207 - formula (1) The method for producing a non-crosslinked polyolefin resin extruded foam according to any one of claims 13 to 15 , wherein the resin composition contains a shrinkage inhibitor.