JP2010174194A - Resin expanded sheet of non-crosslinked polyethylene and method for producing the same, and floating buoyant material and life vest - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a resin expanded sheet of non-crosslinked polyethylene having a buoyancy property and physical strength (tensile strength). <P>SOLUTION: The resin expanded sheet of non-crosslinked polyethylene has a thickness in a range of 2.0 to 6.0 mm, a density in a range of 0.015 to 0.030 g/cm<SP>3</SP>, a tensile strength of 250 kPa or higher in both of the TD and MD directions, and a strength degradation of 25% or less after an exposure test for leaving it in a light oil for 70 hours. Preferably, the melt index of a polyethylene resin used as the raw material of the expanded sheet is 0.28 g/10 min or smaller, and the melt index of a resin obtained by degassing the expanded sheet is 0.4 g/min or smaller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-crosslinked polyethylene resin foam sheet that is suitably used as a buoyancy material such as an inner packaging material for a life jacket.

In general, a polyethylene resin foam sheet is made into a cylindrical shape from the outlet of a circular die connected to the tip of the extruder after the polyethylene resin is placed in an extruder together with a foaming agent, a bubble regulator, etc., and kneaded under high temperature and high pressure conditions. Manufactured by an extrusion foaming method in which it is extruded, foamed and cooled. The melt-softened resin extruded from the die reaches the cooling mandrel while being air-cooled in the atmosphere to suppress foaming. The foam sheet cooled here is cut by a cutter, wound around a paper tube or the like as a single sheet of a flat body, and manufactured as a foam sheet.
These foam sheets have a foam expansion ratio of 30 times or more, are lightweight and flexible, are not only used as cushioning materials, but also can be obtained with light weight and high buoyancy. It is also used as a material.

On the other hand, life jackets have not only buoyancy but also a particularly high tensile strength due to the characteristics of the product, so it is necessary to maintain the performance of the product itself without being destroyed in water or light oil for a long time. is there.
Until now, it was sufficient if the life jacket itself had physical strength, but there is a social need to increase safety, and it has sufficient physical strength even for buoyancy materials used as packaging materials. In addition, its durability has been demanded.
Until now, both foamability and physical strength could be easily obtained with crosslinked polyethylene resin foam sheets, but it is difficult to adapt to environmental conditions such as recyclability because crosslinked polyethylene is difficult to adapt to the current social situation. It has become. Therefore, in the future, it will be necessary to use a non-crosslinked polyethylene resin foam sheet as a buoyancy material.

Conventionally, for example, techniques disclosed in Patent Documents 1 to 3 have been proposed as techniques focusing on the strength of a polyethylene resin foam sheet.
Patent Document 1 discloses that the maximum take-up speed during melting measured at a resin temperature of 130 ° C. and a melting rate of 20 mm / min while increasing the tensile speed at a rate of 20 m / min is 5 to 30 m / min. It is formed of a crosslinked polyethylene resin, has a density of 0.01 to 0.1 g / cm ³ , a thickness of 0.5 to 20 mm, an average cell diameter of 0.2 to 5.0 mm, and a closed cell ratio of 50 to 50. An uncrosslinked polyethylene resin foam characterized by 95% is disclosed.

  Patent Document 2 discloses a polyolefin resin laminated foam sheet in which a stretched film is laminated on at least one surface of a polyolefin resin foam sheet, and the MD is the longitudinal direction of the polyolefin resin laminate foam sheet in a long winding state. A polyolefin-based resin laminated foam sheet is disclosed in which the tear strength in the direction is smaller than the tear strength in the TD direction perpendicular thereto.

  In Patent Document 3, a low density polyolefin-based resin having a blocking property obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst is added to a shrinkage inhibitor and foamed at a high magnification to form a sheet. A non-crosslinked polyolefin-based non-slip foamed resin sheet characterized by being configured is disclosed. Moreover, in the Example of this reference 3, a foamed sheet is produced using polyethylene resins of MFR 7.5 g / 10 min and 4.0 g / 10 min, and the tensile strength, elongation, tear strength, friction coefficient of the foamed sheet are produced. The result of measuring is described.

JP 2002-36338 A JP 2005-131952 A Japanese Patent Laid-Open No. 11-60781

However, the above-described conventional technique has the following problems.
The non-crosslinked polyethylene meter resin foam disclosed in Patent Document 1 is a polyethylene-based resin foam sheet for thermoforming, and the melt tension when the resin is softened by applying temperature is taken into consideration. The strength at normal temperature before softening is not considered. Also, the density range is wide and buoyancy is not considered.

  Patent Document 2 discloses a polyethylene-based foam sheet in which a tearing direction different from the tearing direction of the foamed sheet is maintained by laminating films. In this prior art, lamination of films is indispensable. As a result, the overall density becomes heavy and buoyancy is lowered, which is not suitable as a buoyancy material. Moreover, since it is an easily tearable sheet, it cannot maintain a practically sufficient tear strength as a buoyancy material.

  The non-crosslinked polyolefin-based non-slip foamed resin sheet disclosed in Patent Document 3 is left to stand in light oil for 70 hours, which is an important required performance as a buoyancy material, although the measurement results are described for the physical strength of the sheet itself. It does not take into account the strength reduction after the exposure test, and it is unclear whether it can be suitably used as a buoyancy material. Furthermore, as demonstrated in [Comparative Example 5] in the examples to be described later, when a polyethylene resin having a high MI (MFR) is used, the strength decrease after the exposure test becomes large, and the buoyancy material Since it turned out that it was not preferable, the sheet | seat using the polyethylene resin whose MFR used in the Example of patent document 3 is 7.5 g / 10min and 4.0 g / 10min has a big strength fall after an exposure test. Therefore, it is presumed that it is not preferable as a buoyancy material.

  The present invention has been made in view of the above circumstances, and an object thereof is to obtain a non-crosslinked polyethylene resin foam sheet having both buoyancy and physical strength (tensile strength).

To achieve the above object, the present invention has a thickness in the range of 2.0Mm～6.0Mm, density is in the range of ^{0.015g / cm 3 ~0.030g / cm 3} , tensile strength Provided is a non-crosslinked polyethylene-based resin foam sheet characterized in that it is 250 kPa or more in both the TD direction and MD direction, and the strength decrease after an exposure test that is left in light oil for 70 hours is 25% or less.

  In the non-crosslinked polyethylene resin foam sheet of the present invention, the raw material polyethylene resin preferably has a melt index of 0.28 g / 10 min or less.

  In the non-crosslinked polyethylene resin foam sheet of the present invention, the melt index of the resin obtained by degassing the non-crosslinked polyethylene resin foam sheet is preferably 0.4 g / min or less.

  In the non-crosslinked polyethylene resin foam sheet of the present invention, the fatty acid ester is preferably contained in an amount of 1.0 part by mass or more with respect to 100 parts by mass of the raw material polyethylene resin.

  In the non-crosslinked polyethylene resin foam sheet of the present invention, the tear strength is preferably 13 N / cm or more in both the TD direction and the MD direction.

  Further, in the present invention, 100 parts by mass of a polyethylene resin having a melt index of 0.28 or less and 13 to 20 parts by mass of a foaming agent are supplied to an extruder, and after melt-kneading in the extruder, 105 to 115 ° C. An uncrosslinked polyethylene-based resin foamed sheet according to any one of claims 1 to 5, wherein the uncrosslinked polyethylene resin foamed sheet according to any one of claims 1 to 5 is obtained by cooling the resin to a resin temperature of A method for producing a resin-based resin foam sheet is provided.

  The present invention also provides a buoyancy material comprising the non-crosslinked polyethylene resin foam sheet according to the present invention.

  Moreover, this invention provides the life jacket characterized by including the said non-crosslinked polyethylene-type resin foam sheet which concerns on this invention as a buoyancy material.

Uncrosslinked polyethylene resin foam sheet of the present invention has a density in the range of ^{0.015g / cm 3 ~0.030g / cm 3} , while maintaining sufficient buoyant buoyancy material, TD direction and MD direction Since both have a tensile strength of 250 kPa or more, the buoyancy and strength are maintained at the same time, and the decrease in strength after an exposure test that is left in light oil for 70 hours is as small as 25% or less. This is suitable as a buoyancy material.
Since the non-crosslinked polyethylene resin foam sheet of the present invention is made of an uncrosslinked polyethylene resin, it is excellent in recyclability of the resin after use as compared with a sheet using the crosslinked polyethylene resin.
Moreover, the melt index of the raw material polyethylene resin is 0.28 g / 10 min or less, and the melt index of the resin obtained by degassing the non-crosslinked polyethylene resin foam sheet is 0.4 g / min or less. By using the flow resin, the strength of the obtained foamed sheet can be improved.
Furthermore, by containing 1.0 part by mass or more of the fatty acid ester with respect to 100 parts by mass of the raw material polyethylene-based resin, heat generation during extrusion can be suppressed when a foam sheet is produced using a low-flow resin. By obtaining a foam sheet at a low temperature, the strength of the foam sheet can be further improved. In addition, when a life jacket is produced by stitching with an external member as a buoyancy material, for example, an inner material for a life jacket, the addition of a fatty acid ester makes it difficult for the foamed sheet to slip and facilitates the sewing operation.
In addition, the non-crosslinked polyethylene resin foam sheet of the present invention can maintain the strength against cracks and the like because the tensile strength and the tear strength can be improved to 13 N / cm or more in both the TD direction and the MD direction. Thus, an uncrosslinked polyethylene resin foam sheet having more excellent physical strength can be obtained.

The life jacket which concerns on this invention is illustrated, (a) is a perspective view of a life jacket, (b) is a side view.

Embodiments of the present invention will be described below.
The non-crosslinked polyethylene resin foam sheet (hereinafter abbreviated as a foam sheet) of the present invention has a thickness in the range of 2.0 mm to 6.0 mm and a density of 0.015 g / cm ^{3 to} 0.030 g / cm. ³ , the tensile strength is 250 kPa or more in both the TD direction and the MD direction, and the strength decrease after an exposure test that is left in light oil for 70 hours is 25% or less.
The MD direction refers to the longitudinal direction (machine direction) of a long foam sheet that is continuously extruded, foamed and wound up when producing the foam sheet, and is orthogonal to the MD direction. The direction is referred to as the TD direction (also referred to as the width direction).

  If the thickness of the foam sheet is within a range of 2.0 mm to 6.0 mm, preferably 2.0 mm to 4.5 mm, a foam sheet having a uniform cell diameter and density is produced by an extrusion foam molding method. Therefore, there is an advantage that a high-quality foam sheet can be provided at low cost. A foamed sheet having a thickness outside the above range may have insufficient mechanical strength such as tensile strength.

The density of foam ^{sheet, 0.015g / cm 3 ~0.030g / cm} 3, if preferably is in the range of ^{0.018g / cm 3 ~0.025g / cm 3} , sufficient buoyant buoyancy material As a result, a tensile strength of 250 kPa or more is obtained in both the TD direction and the MD direction. When the density of the foamed sheet is less than 0.015 g / cm ³ , it becomes difficult to obtain sufficient mechanical strength. When the density of the foamed sheet exceeds 0.030 g / cm ³ , sufficient buoyancy as a buoyancy material is obtained. It becomes difficult to be.

  The tensile strength of the foamed sheet is measured according to the method described in JIS K6767 “Foamed Plastic-Polyethylene Test Method”. In this foam sheet, if the tensile strength is 250 kPa or more in both the TD direction and the MD direction, preferably 280 kPa or more, sufficient strength can be obtained when this foam sheet is used as a buoyancy material such as an inner material for a life jacket. . When the tensile strength is less than 250 kPa, it is difficult to obtain sufficient strength when the foamed sheet is used as a buoyancy material such as an inner material for a life jacket.

For the foam sheet exposure test, light oil No. 2 specified in JIS K2204: 2007 was used. The foam sheet piece was immersed in a light oil tank at 23 ° C. to a depth of 40 mm and foamed with a lid-shaped member from the top so as not to float. The sheet was submerged in light oil and left for 70 hours. The strength reduction rate was measured by the same method as that for measuring the tensile strength after wiping the surface of the foam sheet after the exposure test with a filter paper.
The strength reduction rate was 1- (tensile strength after exposure test / tensile strength before exposure test) × 100 (%). If the strength decrease after the exposure test that is left in light oil for 70 hours is 25% or less, preferably 20% or less, sufficient mechanical strength can be obtained when this foamed sheet is used as a buoyancy material such as an inner material for a life jacket. Durability can be obtained. If this strength drop exceeds 25%, the durability when used as a buoyancy material will be poor.

  The foamed sheet of the present invention preferably has a tear strength measured in accordance with the method described in JIS K6767 “Foamed plastic-polyethylene test method” of 13 N / cm or more in both the TD direction and the MD direction. If the tear strength is 13 N / cm or more, preferably 14 N / cm or more, the strength against cracks can be maintained, and when this foam sheet is used as a buoyancy material such as an inner material for a life jacket, Safety can be increased.

  The foamed sheet of the present invention preferably contains 1.0 part by mass or more of fatty acid ester with respect to 100 parts by mass of the raw material polyethylene resin. By containing the fatty acid ester in an amount of 1.0 part by mass or more, the temperature rise due to the friction of the resin when the foamed sheet is produced by the extrusion foaming method can be alleviated, and the obtained foamed sheet surface is prevented from slipping, It is possible to improve the handleability when stacking a large number of sheets and sewing them together with the outer jacket material of the life jacket. The fatty acid ester is not particularly limited, and examples thereof include glycerin monostearate and glycerin monopalmitate.

  Examples of the polyethylene resin that is the resin material of the foam sheet of the present invention include ethylene homopolymers, and copolymers of ethylene and other monomers alone or in combination of two or more. Can be used. Examples of the ethylene homopolymer include low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene. Examples of other monomers that form a copolymer with ethylene include vinyl acetate, propylene, α-olefin (1-butene, etc.), styrene, acrylic ester, acrylonitrile, vinyl chloride, and the like. As the copolymer, those having a ratio of the other monomer component of 30% by mass or less are preferably used. In addition, other resins may be mixed with the polyethylene resin as long as the effects of the present invention are not impaired. Examples of the other resin include polystyrene, polyvinyl chloride, polyacrylonitrile, α-olefin copolymer polyethylene, and acrylate. The other resin is preferably mixed at a ratio of 30% by mass or less in the total amount of the resin.

In the foamed sheet of the present invention, the melt index of the polyethylene resin as the resin material is 0.28 g / 10 min or less, and the melt index of the resin obtained by degassing the non-crosslinked polyethylene resin foamed sheet is 0.00. It is preferable to use a low flow resin that is 4 g / min or less.
In the present invention, the melt index of the polyethylene resin is determined according to the test method of JIS K7210 after preparing pellets of polyethylene resin as a resin material or resin pellets obtained by defoaming a non-crosslinked polyethylene resin foam sheet. It was measured by the method described in Method B. That is, a sample of 3 to 8 g is filled in a cylinder of a measuring apparatus (a semi-auto melt indexer manufactured by Toyo Seiki Seisakusho), and the material is compressed using a filling rod. The test temperature was 190 ° C., and the test load was measured at a specified load (21.18 N).
When the melt index of the polyethylene resin that is the resin material exceeds 0.28 g / 10 min, or when the melt index of the resin obtained by defoaming the non-crosslinked polyethylene resin foam sheet exceeds 0.4 g / min, The resulting foamed sheet cannot be sufficiently obtained in tensile strength and tear strength, and the strength reduction after an exposure test that is left in light oil for 70 hours exceeds 25%, making it unsuitable as a buoyancy material.

  This resin material, polyethylene-based resin, has foaming aids, lubricants, anti-shrinkage agents, antioxidants, antistatic agents as necessary, as long as it does not affect foamability and mechanical strength of the resulting foamed sheet. Various additives such as a light stabilizer such as a flame retardant, an ultraviolet absorber, a hindered amine compound, a colorant, an inorganic cell nucleating agent, and an inorganic filler may be added.

  The foamed sheet of the present invention is prepared by supplying 100 parts by mass of a polyethylene-based resin having a melt index of 0.28 g / 10 min or less and 13 to 20 parts by mass of a foaming agent to the extruder, and melt-kneading in the extruder. It can be obtained by an extrusion foaming method in which it is cooled to a resin temperature of ˜115 ° C. and extruded through a die at the tip of the extruder.

  As the extruder used in the production method of the present invention, a single screw extruder, a twin screw extruder, or an extruder in which a plurality of these extruders are connected can be used. In any of the extruders, it is desirable to provide a foaming agent pressure inlet in the middle of the barrel, and when using a volatile foaming agent, this is pressure-injected from the pressure inlet and kneaded with the non-crosslinked polyethylene resin. As the die attached to the tip of the extruder, either a circular die or a T die can be used. However, considering the thickness uniformity in the width direction, it is preferable to employ a process using a circular die.

  In the production method of the present invention, first, a polyolefin-based resin and a foaming agent are supplied to an extruder, melted and kneaded, and then extruded into a cylindrical shape through the circular die to cause foaming. Next, this cylindrical foam is taken along the outer periphery of the annular mandrel and cooled. The production method of the present invention is characterized in that a resin material is melt-kneaded in an extruder, cooled to a resin temperature of 105 to 115 ° C., and then extruded and foamed through a die at the tip of the extruder. Thus, by cooling the resin material to be extruded and foamed to a resin temperature of 105 to 115 ° C., even when a polyethylene resin having a low melt index is used as described above, the appearance is good and the mechanical strength is improved. An excellent foam sheet can be produced. When the resin temperature is less than 105 ° C., extrusion foaming is not performed smoothly, cracks are likely to occur in the sheet, and it becomes impossible to produce a foam sheet having good appearance and excellent mechanical strength. On the other hand, when the resin temperature exceeds 115 ° C., it is difficult to obtain a sufficient thickness for the foamed sheet, and the appearance is likely to be wrinkled.

As a foaming agent for foaming the polyolefin resin, either a volatile foaming agent or a decomposable foaming agent may be used. Examples of volatile blowing agents include a wide variety of inert gases, aliphatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, ethers, ketones, etc. Among these, examples of inert gases include carbon dioxide gas, nitrogen, and the like. Is mentioned. Examples of aliphatic hydrocarbons include propane, butane (normal butane, isobutane), pentane (normal pentane, isopentane, etc.), and examples of alicyclic hydrocarbons include cyclopentane, cyclohexane, and the like. It is done. Examples of the halogenated hydrocarbon include one or more of halogenated hydrocarbons such as trichlorofluoromethane, trichlorotrifluoroethane, tetrafluoroethane, chlorodifluoroethane, difluoroethane, and the like. Furthermore, examples of the ether include dimethyl ether and diethyl ether, and examples of the ketone include acetone and methyl ethyl ketone.
Examples of decomposable foaming agents include inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium nitrite, azide compounds, sodium borohydride, azodicarbonamide, barium azodicarboxylate, and dinitrosopentamethylene. Organic foaming agents such as tetramine are listed.
The said foaming agent may be used independently and may mix and use 2 or more types.

The material resin by extrusion foaming under the conditions as described above, the thickness is in the range of 2.0Mm～6.0Mm, density in the range of 0.015g ^/ cm ³ ~0.030g ^/ cm 3 Yes, it is possible to efficiently produce the foamed sheet of the present invention in which the tensile strength is 250 kPa or more in both the TD direction and the MD direction, and the strength reduction after the exposure test is left for 70 hours in light oil is 25% or less. .

  The foamed sheet of the present invention has sufficient buoyancy as a buoyancy material such as an inner material of a life jacket, has high tensile strength and tear strength, and is further exposed to light oil for 70 hours. Since it has excellent physical performance with a subsequent strength reduction of 25% or less, the strength of the buoyancy material can be improved when used as a buoyancy material such as an inner material for a life jacket. Can be improved.

FIG. 1 is a view showing an example in which the foam sheet of the present invention is applied as a life jacket inner material, (a) is a perspective view of the life jacket, and (b) is a side view.
The life jacket 1 has a structure in which an inner packaging material (not shown) in which a large number of foam sheets of the present invention are stacked is wrapped with an outer skin material 2 and these are stitched together. The thickness of the inner packaging material is appropriately set depending on the size of the life jacket and each part.

  Since the life jacket 1 uses the above-described foam sheet of the present invention as the inner packaging material, it is possible to improve the strength and durability of the life jacket by improving the mechanical strength of the life jacket inner material. Can improve safety.

[Example 1]
As a non-crosslinked polyethylene resin which is a resin material of the foam sheet, low density polyethylene (DFDJ6766 manufactured by Nihon Unicar Co., Ltd. (melt index (hereinafter referred to as MI) = 0.22, density 0.922 g / cm ³ )) is used. A raw material obtained by mixing 0.05 part of Selmark C-2 manufactured by Sankyo Kasei Co., Ltd. as a foam nucleating agent into 100 parts by mass of the resin (hereinafter, “parts by mass” is simply referred to as “parts”), has a diameter of 90φ and 180φ. Put into a connected single screw extruder and heat melt knead in the extruder so that the maximum temperature setting is 210 ° C., 1.5 parts of glycerin monostearate and volatile blowing agent (isobutane / normal butane = 50) / 50) After press-fitting 16 parts, the resin temperature is cooled to 112 ° C., from a circular die with a die diameter of 125φ and a die slit clearance of 0.36 mm After leaving the foam, then cooled at a cooling mandrel 440Mmfai, was flat foam sheet leading the cylindrical sheet obtained by cooling.
After passing through the cooling mandrel, the shrinkage was small, and the film was wound into a roll at a winding speed of 53.0 m / min of the winding device. After a aging period of about 2 weeks, a foam sheet was obtained.
The following test was done about the obtained foam sheet. The results are shown in Table 1.

<Thickness of foam sheet>
The thickness of the foamed sheet was defined as the average value (unit: mm) measured at 10 cm intervals with a weight of 100 g applied to PG-12 manufactured by Teclock Corporation.

<Density of foam sheet>
As for the density of the foam sheet, a 10 cm × 100 cm foam sheet section is prepared, the mass is measured, the volume is obtained from the thickness measured as described above, and the density (unit: g / cm ³ ) is calculated from the mass and the volume. did.

<Tensile strength / Tear strength>
The tensile strength of the foamed sheet was measured according to the method described in JIS K6767: 1999 “Foamed Plastics-Polyethylene Test Method”. That is, after being left in a standard temperature and humidity environment (temperature 23 ° C. ± 2 ° C., humidity 50 ± 5%) for 16 hours or more, a tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.) It was set to 100 mm and measured at a pulling speed of 500 mm / min. For the punched sample, a punching die defined in the dumbbell shape No. 1 is used.
The tensile strength is calculated by the following formula.
T = F / W t T: Tensile strength (MPa)
F: Maximum load until cutting (N)
W: Specimen width (mm)
t: thickness of test piece (mm)
The tear strength of the foamed sheet was measured according to JIS K6767: 1999 “Foamed plastic-polyethylene test method” using a Tensilon universal testing machine UCT-10T manufactured by Orientec Co., Ltd. The test speed was 500 mm / min and the chuck interval was 50 mm. For the punched sample, a punching die defined in the test piece shape shown in FIG. 2 of JIS K6767: 1999 is used.
The tear strength was calculated by the following formula.
Tear strength (N / cm) = Maximum load (N) / Test piece thickness (cm)

<Strength reduction rate after exposure test>
In the exposure test, light oil No. 2 specified in JIS K2204: 2007 is used. The foam sheet is immersed in a light oil tank at 23 ° C. to a depth of 40 mm, and the foam sheet is light oiled with a lid-shaped member from the top so as not to float. It was submerged and left for 70 hours.
The strength reduction rate was measured by wiping the foam sheet surface after the exposure test with a filter paper by the same method as that for measuring the tensile strength.
The decrease rate was calculated by 1− (tensile strength after exposure test / tensile strength before exposure test) × 100 (%).

<Melt index>
The melt index of the polyethylene resin is described in the test method B method of JIS K7210 after preparing a pellet of a polyethylene resin as a resin material or a resin pellet obtained by defoaming a non-crosslinked polyethylene resin foam sheet. Measured by the method. That is, a sample of 3 to 8 g is filled in a cylinder of a measuring apparatus (a semi-auto melt indexer manufactured by Toyo Seiki Seisakusho), and the material is compressed using a filling rod. The test temperature was 190 ° C., and the test load was measured at a specified load (21.18 N).

[Example 2]
A foam sheet was produced in the same manner as in Example 1 except that the slit clearance of the die attached to the tip of the extruder was 0.55 mm and the winding speed was changed to 29.0 m / min. The same test as in Example 1 was performed. The results are shown in Table 1.

[Example 3]
About the obtained foamed sheet, the foamed sheet was prepared in the same manner as in Example 2 except that the addition part of the volatile foaming agent was changed from 16 parts to 12 parts and the winding speed was changed to 21 m / min. The same test as in Example 1 was performed. The results are shown in Table 1.

[Example 4]
A foamed sheet was prepared in the same manner as in Example 1 except that glycerin monostearate was not added and the amount of volatile foaming agent was 15.5 parts. The same test as in Example 1 was performed. The results are shown in Table 1.

[Comparative Example 1]
Except having used low density polyethylene (LB-280 (MI = 0.5, density 0.926 g / cm < ³ >) by Nippon Polyethylene Co., Ltd.) from which MI differs as polyethylene resin, it is the same as that of Example 1. A foam sheet was prepared, and the same test as in Example 1 was performed on the obtained foam sheet. The results are shown in Table 1.

[Comparative Example 2]
A foamed sheet was produced in the same manner as in Example 2 except that the same low density polyethylene as in Comparative Example 1 was used, and the same test as in Example 1 was performed on the obtained foamed sheet. The results are shown in Table 1.

[Comparative Example 3]
The resin temperature before extrusion was lowered to 100 ° C., and the production of the foamed sheet was tried in the same manner as in Example 2 except that. However, cracks occurred on the surface of the foam sheet, and a foam sheet having a good appearance could not be obtained.

[Comparative Example 4]
The resin temperature before extrusion was raised to 125 ° C., and the production of the foamed sheet was tried in the same manner as in Example 2 except that. However, only a foam sheet having a thickness of 4 mm or less could be obtained, and the resulting foam sheet was wrinkled in appearance, and a good foam sheet could not be obtained.

[Comparative Example 5]
Low density polyethylene having a high MI as the polyethylene resin (foamed sheet in the same manner as in Example 1 except that LC-561 (MI = 3.0, density 0.929 g / cm ³ ) manufactured by Nippon Polyethylene Co., Ltd. was used. The foam sheet thus obtained was tested in the same manner as in Example 1. The results are shown in Table 1.

As noted in Table 1, foamed sheets of Examples 1 to 4 according to the present invention, the thickness ranging 2.0Mm～6.0Mm, density of 0.015g ^/ cm ³ ~0.030g ^/ cm 3 The tensile strength is 250 kPa or more in both the TD direction and MD direction, and the decrease in strength after an exposure test that is left in light oil for 70 hours is as small as 25% or less, so that it has excellent performance as a buoyancy material. is doing.

  On the other hand, the foamed sheets of Comparative Examples 1 and 2 using a polyethylene resin having a higher MI than the polyethylene resins used in Examples 1 to 4 have lower tensile strength / tear strength than the foamed sheets of Examples 1 to 4. It was. Moreover, the rate of strength reduction after the exposure test exceeded 25%, and the foamed sheets of Comparative Examples 1 and 2 were unsuitable as buoyancy materials.

Moreover, although the comparative example 3 uses the same polyethylene resin as what was used in Examples 1-4, the resin cooling temperature at the time of extrusion is 100 degreeC and lower than the case (112 degreeC) of Examples 1-4. As a result, a foam sheet having a good appearance could not be obtained.
On the other hand, Comparative Example 4 uses the same polyethylene resin as used in Examples 1 to 4, but the resin cooling temperature at the time of extrusion was higher than 125 ° C. and Examples 1 to 4 (112 ° C.). As a result, good products could not be produced.

  Further, the foamed sheet of Comparative Example 5 using a polyethylene resin having a high MI = 3.0 and MI was lower in tensile strength / tear strength than those of Examples 1-4. Moreover, the rate of strength reduction after the exposure test exceeded 25%, and the foamed sheet of Comparative Example 5 was unsuitable as a buoyancy material.

  The non-crosslinked polyethylene resin foam sheet of the present invention has a high tensile strength and tear strength, and has a small strength decrease of 25% or less after an exposure test that is left in light oil for 70 hours. In addition to the use of conventional foam sheets such as, and the like, it is suitable as a buoyancy material such as an inner material for a life jacket that requires high mechanical strength and durability.

  1. Life jacket, 2. Skin material.

Claims (8)

The thickness is in the range of 2.0Mm～6.0Mm, density is in the range of ^{0.015g / cm 3 ~0.030g / cm 3} , a tensile strength of at least 250kPa in both the TD direction and the MD direction A non-crosslinked polyethylene resin foam sheet, characterized in that a decrease in strength after an exposure test that is allowed to stand in light oil for 70 hours is 25% or less.   2. The non-crosslinked polyethylene resin foam sheet according to claim 1, wherein the raw material polyethylene resin has a melt index of 0.28 g / 10 min or less.   The non-crosslinked polyethylene resin foam sheet according to claim 1 or 2, wherein a melt index of a resin obtained by defoaming the uncrosslinked polyethylene resin foam sheet is 0.4 g / min or less.   The non-crosslinked polyethylene-based resin foamed sheet according to any one of claims 1 to 3, further comprising 1.0 part by mass or more of a fatty acid ester with respect to 100 parts by mass of the raw material polyethylene-based resin.   The uncrosslinked polyethylene resin foam sheet according to any one of claims 1 to 4, wherein the tear strength is 13 N / cm or more in both the TD direction and the MD direction.   100 parts by mass of a polyethylene resin having a melt index of 0.28 or less and 13 to 20 parts by mass of a foaming agent are supplied to an extruder, melted and kneaded in the extruder, and then cooled to a resin temperature of 105 to 115 ° C. Then, the non-crosslinked polyethylene resin foam sheet according to any one of claims 1 to 5 is obtained by extruding and foaming through a die at the tip of the extruder. Production method.   A buoyancy material comprising the uncrosslinked polyethylene resin foam sheet according to any one of claims 1 to 5.   A life jacket including the non-crosslinked polyethylene resin foam sheet according to any one of claims 1 to 5 as a buoyancy material.

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