Ethylene-based resin foamed sheet, formed product and method for producing the ethylene-based resin foamed sheet

The present invention relates to an ethylene resin foam sheet, a molded product, and a method for producing an ethylene resin foam sheet.

High-density polyethylene is used for various purposes because it has excellent heat resistance, cold resistance, mechanical strength, and chemical resistance, and is foamed to impart heat insulation, flexibility, and cushioning properties. Some of them have been put into practical use.

Here, since the ethylene resin is a crystalline polymer, its physical properties change remarkably at the melting point. Specifically, when the ethylene resin is heated from a temperature below the melting point, the melt viscosity of the ethylene resin drops sharply at a temperature higher than the melting point, and it is difficult to obtain the melt viscosity required for foaming. When the ethylene-based resin is cooled from a temperature above the melting point, it rapidly crystallizes at a temperature below the melting point and does not flow. Therefore, in order to make the ethylene-based resin a melt viscosity suitable for foaming, The temperature of the ethylene resin must be adjusted in a narrow temperature range near the melting point of the ethylene resin.

Among the ethylene-based resins having such characteristics, low-density polyethylene has a long-chain branch of an appropriate length in its molecular chain, so that the melt viscosity at the time of melting is compared by the entanglement of the molecular chains. In addition to being highly targeted, the change in crystallinity near the melting point is also gradual compared to other ethylene-based resins, and although it is necessary to adjust a narrow temperature range near the melting point as described above, other ethylene-based resins It can be foamed relatively easily as compared with.

On the other hand, high-density polyethylene has a very low melt viscosity at the time of melting because its molecular chain has few branches, and has high crystallinity and a high crystallization rate, so that it is suitable for foaming. In order to obtain the viscosity, it is necessary to adjust a narrower temperature range, and therefore, it is very difficult to foam high-density polyethylene to produce a foam having a high closed cell ratio.

Further, although it is conceivable to increase the molecular weight of the high-density polyethylene in order to improve the melt viscosity of the high-density polyethylene, increasing the molecular weight of the high-density polyethylene imposes a heavy burden on the motor of the extruder and extrudes. There is a problem that the resin temperature in the extruder must be raised significantly.

Then, Patent Document 1 proposes a high-density polyethylene foam having an apparent specific gravity of 0.012 to 0.10 and a high foaming ratio. However, since such a high-density polyethylene foam having a high foaming ratio uses a large amount of foaming agent in its production, it is possible to utilize the cooling effect of the molten resin by the latent heat of evaporation of the foaming agent at the time of foaming. Although it is easier to manufacture than a high-density polyethylene foam having an apparent specific gravity of more than 0.10, a high-density polyethylene foam having a high foaming ratio has a problem that it is inferior in mechanical strength and cannot be thermoformed.

<patcit num="1"><text>Japanese Patent Application Laid-Open No. 58-208328</text></patcit>

<p> As described above, the present inventor has set the melt mass flow rate, melt tension, and elongation at break as the melt resin characteristics of the ethylene resin under the situation where it is difficult to manufacture the ethylene resin foam sheet having a predetermined apparent density. , We proceeded with the research using the resin density as an index as the crystal characteristics of ethylene resin.</p><p> However, the index of the ethylene resin has a low relationship with the foamability of the ethylene resin and the moldability of the foamed sheet, and even if the index is adjusted, a good foamed sheet cannot be stably obtained. The resulting foamed sheet was inferior in surface smoothness and thermoformability.</p><p> Therefore, the present inventors focused on the melt elastic property among the molten resin properties, and as a result of diligent research focusing on the die-sell, which is one of the indexes of the melt elastic property, set this die-sell to a specific value or more. As a result, it has been found that the obtained ethylene-based resin foam sheet has uniform and fine closed cells and is excellent in appearance and thermoformability.</p><p> The present invention provides an ethylene-based resin foam sheet having uniform and fine closed cells and excellent in appearance and thermoforming property, and a method for producing the same.</p>

<p> The ethylene-based resin foam sheet of the present invention is an ethylene-based resin composed only of high-density polyethylene having a die-sell of 1.50 or more at 190 ° C, or a die-sell containing 60 to 95% by weight of high-density polyethylene at 190 ° C. It is made of ethylene resin with an apparent density of 0.11 to 0.80 g / cm.³It is characterized by having a thickness of 0.5 to 5.0 mm and an open cell ratio of 50% or less.</p><p> The ethylene-based resin constituting the ethylene-based resin foam sheet of the present invention consists only of high-density polyethylene having a die-sell of 1.50 or more at 190 ° C, or contains 60 to 95% by weight of high-density polyethylene and 190 ° C. It consists of an ethylene-based resin with a die-sell of 1.55 or more in C.</p><p> In the present invention, the ethylene resin is a homopolymer of ethylene, a copolymer of ethylene and a 1-olefin monomer, and a non-olefin monomer having only carbon, oxygen and hydrogen atoms as functional groups with ethylene. It refers to a copolymer of and may be used alone or in combination of two or more.</p><p> Here, examples of the 1-olefin include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like, and non-olefins having only carbon, oxygen and hydrogen atoms as functional groups. Examples of the olefin monomer include vinyl acetate, vinyl alcohol, acrylic acid, methacrylic acid, methyl acrylate, and methyl methacrylate. The ethylene content of the copolymer of ethylene and 1-olefin monomer and the copolymer of ethylene and non-olefin monomer having only carbon, oxygen and hydrogen atoms as functional groups is 70 mol. % Or more is preferable, and 80 to 97 mol% is more preferable.</p><p> In the present invention, high-density polyethylene has a density of 0.942 g / cm among the above ethylene-based resins.³The above. The density of ethylene-based resin is measured using Method A (underwater substitution method) specified in JIS K7112: 1999 "Plastic-Non-foamed plastic density and specific gravity measurement method".</p><p> First, a case where the ethylene-based resin foam sheet of the present invention is composed of only high-density polyethylene having a die-sell of 1.50 or more at 190 ° C. will be described. If the density of the high-density polyethylene is low, the mechanical strength and heat resistance of the ethylene-based resin foamed sheet may decrease. For example, when the ethylene-based resin foamed sheet is heat-molded into a food container and used. Since it is necessary to increase the apparent density of the ethylene resin foam sheet, the lightness of the ethylene resin foam sheet may decrease, or the ethylene resin foam sheet may be deformed when heated in a microwave oven. So 0.945g / cm³The above is preferable, 0.950 g / cm³However, if it is large, the foamability of the high-density polyethylene and the thermoformability of the ethylene-based resin foam sheet are lowered, or fine lumps are likely to be generated due to the crystallization of the high-density polyethylene. cm³The following is preferred, 0.965 g / cm³Is more preferable.</p><p> The die-sell of high-density polyethylene at 190 ° C is limited to 1.50 or more, preferably 1.55 or more, and more preferably 1.60 or more. This is because if the die wheel of high-density polyethylene at 190 ° C is small, the bubble stability during extrusion foaming will decrease and foam breakage will occur, and the closed cell ratio of the ethylene-based resin foam sheet will decrease, or ethylene-based This is because the surface of the resin foam sheet becomes uneven and the surface smoothness is lowered. Furthermore, when the ethylene resin foam sheet is manufactured, the foam sheet hangs down or is cut between the circular die and the mandrel. This is because it becomes easy and it becomes difficult to handle a wide foam sheet. In addition, the temperature range of the obtained ethylene-based resin foam sheet during thermoforming becomes narrow, and a good molded product cannot be obtained due to poor elongation or the like.</p><p> However, if the die-sell of high-density polyethylene at 190 ° C is too large, the shrinkage of the ethylene-based resin foamed foam sheet during thermoforming becomes large and the elongation becomes low, so that the thermoforming into a desired shape is stable and accurate. 1.90 or less is preferable, and 1.80 or less is more preferable.</p><p> Next, a case where the ethylene-based resin foam sheet of the present invention is made of an ethylene-based resin containing 60 to 95% by weight of high-density polyethylene and having a die wheel at 190 ° C. of 1.55 or more will be described.</p><p> If the content of high-density polyethylene in the ethylene-based resin is low, the mechanical strength and heat resistance of the ethylene-based resin foam sheet will decrease, while if it is high, ethylene-based resin other than high-density polyethylene will be contained and ethylene will be contained. Since the effect of improving the extrudability of the foamed resin foam sheet and the thermoformability of the foamed ethylene resin sheet during production is not exhibited, the content is limited to 60 to 95% by weight, preferably 70 to 85% by weight.</p><p> If the density of the high-density polyethylene is low, the mechanical strength and heat resistance of the ethylene-based resin foamed sheet may decrease. For example, when the ethylene-based resin foamed sheet is heat-molded into a food container and used. Is that the lightness of the ethylene resin foam sheet is reduced because it is necessary to increase the apparent density of the ethylene resin foam sheet, or the ethylene resin foam sheet is deformed when heated in a microwave oven. Because there is 0.945g / cm³The above is preferable, 0.950 g / cm³However, if it is large, the foamability of the ethylene resin and the thermoformability of the obtained ethylene resin foam sheet may decrease, so 0.970 g / cm.³The following is preferred, 0.965 g / cm³The following is more preferable.</p><p> As ethylene resin, high density polyethylene is 60 to 95% by weight and the density is 0.915 to 0.930 g / cm.³It is preferably composed of 5 to 40% by weight of ethylene resin, 0.950 g / cm.³High density polyethylene 70 ~ 85% by weight and 0.915 ~ 0.925g / cm³It is preferably composed of 15 to 30% by weight of the ethylene resin.</p><p> This is because high-density polyethylene is excellent in mechanical strength and heat resistance, but inferior in foamability, while ethylene-based resin, which has a low density, is excellent in extrusion foamability and thermoformability, but mechanical strength. In addition, since it is inferior in heat resistance, by using high-density polyethylene and a low-density ethylene resin having a density within a predetermined range in combination, the characteristics of both can be effectively exhibited while complementing each other's shortcomings. Because it can be done.</p><p> The die sell of the ethylene resin containing 60 to 95% by weight of high-density polyethylene at 190 ° C. is limited to 1.55 or more, preferably 1.65 or more, and more preferably 1.70 or more. This is because if the die wheel of the ethylene resin at 190 ° C is small, the bubble stability during extrusion foaming will decrease and foam breakage will occur, and the closed cell ratio of the ethylene resin foam sheet will decrease, or the ethylene type This is because the surface smoothness of the resin foam sheet is lowered, and further, when the ethylene-based resin foam sheet is manufactured, the foam sheet hangs down or is easily cut between the circular die and the mandrel, resulting in wide foaming. This is because it becomes difficult to handle the seat. In addition, the temperature range of the obtained ethylene-based resin foam sheet during thermoforming becomes narrow, and a good molded product cannot be obtained due to poor elongation or the like.</p><p> However, if the die sell of the ethylene resin at 190 ° C is too large, the shrinkage of the ethylene resin foam foam sheet during thermoforming becomes large and the elongation becomes low, so that the thermoforming into a desired shape is stable and accurate. 1.90 or less is preferable, and 1.80 or less is more preferable.</p><p> The die sell of ethylene resin at 190 ° C means the one measured by the method described in JIS K 7199: 1999 "Plastic-Plastic flow characteristic test method by capillary rheometer and slit rheometer". The die sell of the ethylene resin at 190 ° C can be measured using a capillograph sold by Toyo Seiki Seisakusho Co., Ltd. under the trade name "PMD-C". Specifically, an ethylene-based resin as a measurement sample is supplied into the cylinder of the capillograph and heated and melted at 190 ° C. The heat-melted ethylene-based resin is used as a capillary die (inner diameter: 2.095 mm, length: 8 mm). , Inflow angle: 90 °) and extrude into a string at a constant piston descent speed of 10 mm / min. Then, the diameter of the string-like material is measured at 190 ° C, and the die sell of the ethylene resin at 190 ° C is calculated based on the following formula. Diesel of ethylene resin at 190 ° C = diameter of string (mm) / inner diameter of capillary die (mm)</p><p> If the apparent density of the ethylene resin foam sheet is small, the mechanical strength of the ethylene resin foam sheet is lowered, while if it is large, the heat insulating property, light weight and flexibility of the ethylene resin foam sheet are lowered. , 0.11 ~ 0.80g / cm³Limited to 0.15 ~ 0.60g / cm³Is preferable, 0.20 to 0.50 g / cm³Is more preferable, 0.20 to 0.45 g / cm³Is particularly preferable.</p><p> The apparent density of the ethylene-based resin foamed sheet is such that a planar square-shaped test piece having a side of 100 mm is obtained by cutting the foamed sheet from an arbitrary portion of the ethylene-based resin foamed sheet over the entire length in the thickness direction. Measure the volume and weight of each test piece. Then, the density of each test piece is calculated by dividing the weight of each test piece by the volume, and the arithmetic mean value of the density of each test piece is taken as the apparent density of the ethylene resin foam sheet.</p><p> Further, if the thickness of the ethylene resin foam sheet is thin, the mechanical strength and heat insulating property of the ethylene resin foam sheet are lowered, while if it is thick, the moldability of the ethylene resin foam sheet is lowered, so that it is 0.5 to 5.0. It is limited to mm, preferably 0.6 to 3.0 mm.</p><p> Further, the open cell ratio of the ethylene resin foam sheet is limited to 50% or less, preferably 30% or less, and more preferably 20% or less. This is because when the open cell ratio of the ethylene resin foam sheet is high, the mechanical strength and surface smoothness of the ethylene resin foam sheet are lowered, and when the ethylene resin foam sheet is thermally molded, the ethylene resin foam sheet is formed. This is because there is a possibility that irregularities may be generated on the surface of the ethylene resin foam sheet to reduce the surface smoothness, and the elongation of the ethylene resin foam sheet may be reduced to cause tearing.</p><p> The open cell ratio of the ethylene resin foam sheet is measured by the 1-1 / 2-1 atmospheric pressure method in accordance with ASTM D-2856-87. Specifically, an ethylene-based resin foam sheet is cut into a planar square shape having a side of 25 mm, and a plurality of the cut pieces are stacked in the thickness direction to prepare a test piece having a thickness of about 25 mm. Five test pieces are prepared in this way, and the open cell ratio of each test piece is measured by the 1-1 / 2-1 atmospheric pressure method using an air comparison hydrometer (trade name "1000 type" manufactured by Tokyo Science Co., Ltd.). The arithmetic mean value is taken as the open cell ratio of the ethylene resin foamed sheet.</p><p> Further, if the center line surface roughness (Ra) of the ethylene resin foam sheet is large, the appearance of the ethylene resin foam sheet deteriorates, and after the ethylene resin foam sheet is heat-molded and used as a food container, this When the food container is reused, dirt may enter the recesses formed on the surface of the ethylene resin foam sheet, making cleaning difficult. Therefore, 8 μm or less is preferable, and 5 μm or less is more preferable.</p><p> Here, the center line surface roughness (Ra) of the ethylene resin foam sheet is measured as follows. That is, the surface roughness of the front and back surfaces of the ethylene resin foam sheet was measured using a surface roughness measuring instrument under the conditions of a cutoff value of 2.5 μm and a measurement length of 12.5 mm, and ethylene was measured from these measured values. The center line surface roughness (Ra) of the front and back surfaces of the resin foam sheet was calculated. Then, of the center line surface roughness (Ra) of the front and back surfaces of the ethylene resin foam sheet, the larger center line surface roughness (Ra) is defined as the center line surface roughness (Ra) of the ethylene resin foam sheet. .. The center line surface roughness (Ra) of the ethylene resin foam sheet can be measured, for example, by using a measuring device commercially available from Tokyo Seimitsu Co., Ltd. under the trade name "Handy Surf E-30A".</p><p> Further, the surface smoothness of the ethylene resin foam sheet may be improved by laminating and integrating the thermoplastic resin film on at least one surface of the ethylene resin foam sheet.</p><p> Examples of such a thermoplastic resin film include olefins such as the above-mentioned film made of an ethylene resin, a homopolymer of propylene, and a film made of a propylene resin such as a copolymer of propylene and a 1-olefin monomer. Examples thereof include an ethylene resin film, and an ethylene resin film is preferable. Examples of the 1-olefin monomer include ethylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like.</p><p> Subsequently, a method for producing the ethylene-based resin foam sheet will be described. As a method for producing this ethylene-based resin foam sheet, 1) an ethylene-based resin composed only of high-density polyethylene having a die-sell within a predetermined range, or a die-sell containing 60 to 95% by weight of high-density polyethylene and within a predetermined range. The ethylene resin having the above is supplied to an extruder, melt-kneaded in the presence of a foaming agent, and extruded from a circular die attached to the extruder to produce a cylindrical foamed molded product. A method of producing an ethylene resin foam sheet by continuously cutting and expanding the foamed molded product in the extrusion direction after supplying it to the mandrel while expanding the diameter in the radial direction and cooling it. In the presence of a foaming agent, an ethylene resin consisting only of high-density polyethylene having a high-density polyethylene or an ethylene-based resin containing 60 to 95% by weight of high-density polyethylene and having a die-sell within a predetermined range is supplied to an extruder. Examples thereof include a method of melt-kneading and extruding and foaming a T-die attached to an extruder into a sheet to produce an ethylene resin foam sheet.</p><p> In any of the above methods 1) and 2), the ethylene resin immediately after being discharged from the extruder foams and the resin itself expands, so that the circumferential direction of the cylindrical foam molded body or the width of the sheet A wavy phenomenon called corrugation is observed in the direction, and if this corrugation remains on the ethylene resin foam sheet, the quality of the ethylene resin foam sheet becomes uneven or the use of the ethylene resin foam sheet is used. It is preferable to remove the corrugation from the ethylene-based resin foamed sheet, because there is a possibility that the amount of corrugation may be limited.</p><p> In the manufacturing method of 1) above, since the cylindrical foam molded product is expanded in the radial direction and stretched in the circumferential direction of the foamed molded product, it is easy to remove the corrugation generated in the foamed molded product. Therefore, the manufacturing method of 1) above is suitable for manufacturing an ethylene resin foamed sheet having a high foaming ratio, which easily causes corrugation. Specifically, the apparent density is 0.11 to 0.50 g / cm.³Suitable for manufacturing ethylene resin foam sheets, with an apparent density of 0.11 to 0.35 g / cm.³It is more suitable for producing ethylene-based resin foam sheets.</p><p> Further, if the ratio of the outer diameter of the inner die in the lip portion of the circular die attached to the extruder to the outer diameter of the tip on the extruder side of the mandrel is small, the corrugation generated in the cylindrical foam molded body is removed. On the other hand, if it is too large, the foamed molded product may break, so 2.00 or more is preferable, 2.25 or more is more preferable, 2.50 or more is particularly preferable, and if it is too large, the cylindrical foamed molded product may tear. Alternatively, it may be torn off, so 4.0 or less is preferable, and 3.5 or less is more preferable.</p><p> Then, in the production method of 1) above, it is preferable to adjust the average cell diameter of the obtained ethylene resin foam sheet to be 0.20 to 1.00 mm, and more preferably to adjust it to 0.25 to 0.80 mm. , 0.25 to 0.60 mm is particularly preferable. The average cell diameter of the ethylene-based resin foam sheet can be determined by using a physical foaming agent described later and a thermally decomposable foaming agent described below which also acts as a bubble nucleating agent, or by adding a bubble nucleating agent. It can be controlled, and specifically, it is preferable to add 0.5 to 3.0 parts by weight of the bubble nucleating agent with respect to 100 parts by weight of the ethylene resin during the production of the ethylene resin foamed sheet. Examples of such a bubble nucleating agent include talc and mica.</p><p> This is because when the average cell diameter of the ethylene resin foam sheet is small, the bubble film becomes thin and bubble breakage occurs when the diameter of the cylindrical foam molded product is expanded in the radial direction. This is because the surface smoothness may be lowered, but if it is large, the surface smoothness of the ethylene resin foam sheet may be lowered.</p><p> Further, in the above-described method for manufacturing 1), push in the ethylene-based resin foam sheet and average cell diameter of the outgoing direction (MD), the ratio of the average cell diameter (average cell diameter / average cell diameter in MD) is a 0.70 to 1.60 It is preferable to adjust so as to be.</p><p> On the other hand, in the manufacturing method of 1) above, the ratio of the average cell diameter in the direction (TD) along the surface of the foamed sheet and orthogonal to the extrusion direction of the ethylene resin foamed sheet to the average cell diameter (average cell diameter of TD / It is preferable to adjust the average cell diameter) to be 1.10 to 2.00.</p><p> This is because when the ratio of the average cell diameter of MD or TD to the average cell diameter (average cell diameter of MD or TD / average cell diameter) in the ethylene resin foam sheet is small, the cylindrical foam molded product is stretched. May not be sufficient to remove the corrugation generated in the foamed molded product, but if it is large, bubbles will break during the production of the ethylene resin foam sheet and the open cell ratio of the ethylene resin foam sheet will be large. Because it can be. The ratio of the average cell diameter of MD or TD to the average cell diameter (average cell diameter of MD or TD / average cell diameter) in the ethylene resin foam sheet is the outer diameter of the inner die in the lip portion of the circular die. , It can be controlled by adjusting the ratio of the mandrel to the outer diameter of the tip on the extruder side and the slit clearance of the circular die.</p><p> The average cell diameter of the ethylene resin foam sheet is measured as follows. That is, the average cell diameter of the ethylene resin foam sheet is calculated based on the average chord length measured according to the test method of ASTM D2842-69. Specifically, an ethylene-based resin foam sheet is cut along a surface along the direction in which the average cell diameter is to be measured, and the central portion of the cut surface excluding the outer peripheral portion is arbitrarily set at four locations, a scanning electron microscope. Magnify and take an electron micrograph using.</p><p> Next, draw a straight line with a length of 60 mm on each photograph in the direction in which you want to measure the average cell diameter, and calculate the average chord length t of the bubbles from the number of bubbles on this straight line based on the following formula 1. To do. Six straight lines are drawn for each photo, the average chord length t is calculated for each straight line, the arithmetic mean of the average chord length t is calculated for each photo, and this arithmetic mean value is used as the average chord length of the bubbles. Let t. If you cannot draw a straight line with a length of 60 mm on the straight line, draw a straight line with a length of 20 mm or 30 mm on the photo, measure the number of bubbles on this straight line, and measure the number of bubbles on the straight line. Convert proportionally to a number. Average string length t = 60 / (number of bubbles x magnification of photo) Equation 1</p><p> Then, the bubble diameter D is calculated by the following formula 2, and the arithmetic mean of the bubble diameter D in each photograph is taken as the average cell diameter in the desired direction of the ethylene resin foam sheet. Bubble diameter D = average chord length t / 0.616 Equation 2</p><p> For the average cell diameter of the ethylene resin foam sheet, the average cell diameter of MD, the average cell diameter of TD, and the average cell diameter in the directions orthogonal to MD and TD (VD) were measured as described above. , MD, TD and VD can be calculated by arithmetically averaging the average cell diameters.</p><p> The foaming agent used in the above 1) production method is not particularly limited as long as it is conventionally used for producing a foam sheet, but if only a pyrolysis type foaming agent is used as the foaming agent, It is difficult to foam to a low apparent density, and since the pyrolysis-type foaming agent also acts as a bubble nucleating agent, the bubbles of the obtained ethylene-based resin foam sheet are easily made finer, and the bubbles are made finer to make the bubble film thinner. In this case, the surface smoothness of the ethylene-based resin foamed sheet may be deteriorated due to the occurrence of bubble breakage when the diameter of the cylindrical foamed molded product is expanded in the radial direction or the poor elongation of the resin. Therefore, as the foaming agent used in the production method of 1) above, a physical foaming agent is preferable, and it is more preferable to use a physical foaming agent and a thermal decomposition foaming agent in combination.</p><p> Examples of such a physical foaming agent include hydrocarbons such as butane and pentane, halides thereof, ethers such as dimethyl ether, and inorganic gases such as alcohol, ketone, nitrogen, and carbon dioxide. The amount of the physical foaming agent added is preferably 0.05 to 3.0 parts by weight with respect to 100 parts by weight of the ethylene resin.</p><p> Examples of the heat-decomposable foaming agent include azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, 4,4-oxybis (benzenesulfonylhydrazide), and a mixture of baking soda and citric acid. Azodicarbonamide, a mixture of baking soda and citric acid, is preferred. The amount of the thermal decomposition foaming agent added is preferably 0.05 to 2 parts by weight with respect to 100 parts by weight of the ethylene resin.</p><p> On the other hand, in the manufacturing method of 2) above, since the foamed sheet is extruded and foamed from the T die attached to the extruder, the foamed sheet discharged from the T die cannot be greatly stretched in the width direction, so that the foamed sheet is corrugated. It is suitable for the production of ethylene resin foam sheet with low foaming ratio so as not to generate, specifically, the apparent density is 0.30 to 0.80 g / cm.³Suitable for manufacturing ethylene resin foam sheets, with an apparent density of 0.40 to 0.80 g / cm.³It is more suitable for producing ethylene-based resin foam sheets.</p><p> In the manufacturing method of 2) above, the degree of stretching of the foamed sheet discharged from the extruder is lower than that of the manufacturing method of 1) above, so that the surface smoothness caused by the foaming of the obtained ethylene resin foamed sheet is smooth. It is possible to reduce the average cell diameter of the ethylene-based resin foam sheet without causing problems such as deterioration of properties.</p><p> Specifically, it is preferable to adjust the average cell diameter of the obtained ethylene resin foam sheet to be 0.10 to 0.50 mm, and more preferably to adjust it to 0.15 to 0.40 mm. The average cell diameter of the ethylene resin foam sheet can be controlled by adjusting the type of foaming agent used or the like.</p><p> This is because if the average cell diameter of the ethylene-based resin foamed sheet is small, open cells are likely to be formed during the production of the ethylene-based resin foamed sheet, while if it is large, the surface smoothness of the ethylene-based resin foamed sheet may decrease. Is.</p><p> Further, in the manufacturing method of 2) above, the ratio of the average cell diameter in the extrusion direction (MD) to the average cell diameter (MD average cell diameter / average cell diameter) of the ethylene resin foamed sheet is 1.10 to 2.00. It is preferable to adjust so as to.</p><p> On the other hand, in the manufacturing method of 2) above, the ratio of the average cell diameter in the direction (TD) along the surface of the foamed sheet and orthogonal to the extrusion direction of the ethylene resin foamed sheet to the average cell diameter (average cell diameter of TD / It is preferable to adjust the average cell diameter) to be 0.70 to 1.10.</p><p> This is because the ratio of the average cell diameter of MD or TD to the average cell diameter (average cell diameter / average cell diameter of MD or TD) in the ethylene resin foam sheet is an ethylene resin foam sheet having a high closed cell ratio. It is a guideline for obtaining, and if (MD or TD average cell diameter / average cell diameter) is small, corrugation may occur, while if it is large, the open cell ratio of the ethylene resin foam sheet is large. Because it can be.</p><p> Since the method for measuring the average cell diameter of the ethylene resin foam sheet and the average cell diameter in the desired direction is the same as the above-mentioned procedure, the description thereof will be omitted.</p><p> The foaming agent used in the production method of 2) above is not particularly limited as long as it has been conventionally used in the production of foam sheets, but it also acts as a bubble nucleating agent and is obtained as an ethylene resin. The above-mentioned thermal decomposition type foaming agent is preferable because the bubbles in the foam sheet become fine. The amount of the thermal decomposition foaming agent added is preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the ethylene resin.</p><p> Further, as a method of laminating and integrating a thermoplastic resin film on one surface of an ethylene resin foam sheet, a general-purpose method is used, and examples thereof include a coextrusion method, a heat laminating method, and a method using an adhesive. The coextrusion method is preferable because of its high efficiency.</p><p> Specifically, in the above coextrusion method, a foaming agent-containing ethylene-based resin constituting a foam sheet is extruded from one extruder, and a thermoplastic resin constituting a thermoplastic resin film is extruded from another extruder. , These resins are supplied to the merging die to form a laminated resin in which a thermoplastic resin film is laminated on the front and back surfaces or the inner and outer surfaces of the foaming agent-containing ethylene resin, and then this laminated resin is used as a merging die or a merging die. This is a method of extrusion foaming from a connected die.</p><p> In the above coextrusion method, in order to stabilize the resin flow in the merging die, it is necessary to make the melt viscosities of the foaming agent-containing ethylene resin and the thermoplastic resin as close as possible. Then, the foaming agent-containing ethylene-based resin is cooled to a temperature suitable for foaming in the extruder and then supplied to the merging die. However, since the melt viscosity of the thermoplastic resin is too high at this foaming appropriate temperature, the thermoplastic resin is thermoplastic. It is necessary to set the temperature of the resin high so that the melt viscosities of the foaming agent-containing ethylene resin and the thermoplastic resin are close to each other.</p><p> By doing so, the conventional ethylene-based resin has a problem that the temperature at the interface with the thermoplastic resin becomes too high and induces foam breakage. In the conventional ethylene-based resin, one surface of the ethylene-based resin foam sheet is generated. It has been considered difficult to laminate and integrate thermoplastic resin films by the coextrusion method.</p><p> Therefore, in the present invention, as described above, an ethylene-based resin composed only of high-density polyethylene having a die-sell of a predetermined value or more, or an ethylene-based resin containing a predetermined amount of high-density polyethylene and having a die-sell of a predetermined value or more is used. By using it, the stability of air bubbles in the foaming process is improved, and as described above, even if the temperature of the thermoplastic resin is set high, the ethylene resin containing a predetermined amount of high-density polyethylene or high-density polyethylene. It is possible to effectively suppress the occurrence of foam breakage during foaming and maintain good foamability, and while making the bubbles of the obtained ethylene-based resin foamed sheet uniform and fine, this ethylene-based resin foamed sheet The thermoplastic resin film can be efficiently laminated and integrated on one surface.</p><p> The ethylene-based resin foam sheet obtained as described above is thermoformed by using a general-purpose thermoforming method such as a vacuum forming method, a vacuum forming method, or a vacuum / pressing air forming method to obtain a molded product. It is preferably thermoformed by a molding method.</p><p> The molded product obtained by thermoforming an ethylene-based resin foam sheet can be used for a wide variety of purposes. For example, various containers such as food containers and containers for industrial parts, and partitions for partitioning the inside of these containers. It can be used as a material.</p>

<p> The ethylene-based resin foam sheet of the present invention is an ethylene-based resin composed only of high-density polyethylene having a die-sell of 1.50 or more at 190 ° C, or a die-sell containing 60 to 95% by weight of high-density polyethylene at 190 ° C. It is made of ethylene resin with an apparent density of 0.11 to 0.80 g / cm.³Since the thickness is 0.5 to 5.0 mm and the open cell ratio is 50% or less, it has uniform and fine closed cells and is excellent in thermoformability.</p><p> That is, by limiting the die of the ethylene-based resin, which is one of the indexes of the characteristics of melt elasticity, to a predetermined value or more, the elastic properties of the ethylene-based resin at the time of melting are improved, and by the improvement of the elastic properties, the elastic properties are improved. The local elongation of the ethylene resin in the foaming process of the ethylene resin is alleviated to suppress the foam rupture. As a result, the resulting ethylene resin foam sheet has uniform bubbles and a fine closed cell ratio. It has a high level of ethylene and has excellent surface smoothness.</p><p> Further, even during thermoforming of the ethylene-based resin foam sheet, since the elastic properties at the time of melting the ethylene-based resin are high as described above, compressive stress and stretching stress applied to the ethylene-based resin foam sheet during thermoforming, etc. The stress of the above can be effectively dispersed and relaxed, and according to the ethylene-based resin foam sheet of the present invention, it is prevented from breaking or breaking during thermoforming, and the appearance is excellent and complicated. It is possible to accurately thermoform a molded product having a different shape.</p><p> The ethylene resin is 60 to 95% by weight of high density polyethylene and the density is 0.915 to 0.930 g / cm.³When the ethylene resin is 5 to 40% by weight, the high density polyethylene has excellent mechanical strength and heat resistance, and the density is 0.915 to 0.930 g / cm.³The extrusion stability of the ethylene resin can be synergistically exhibited, and the ethylene resin foam sheet has more uniform and fine closed cells and is more excellent in appearance and thermoformability. There is.</p><p> Further, when the thermoplastic resin film is laminated and integrated on one surface of the ethylene resin foam sheet, the ethylene resin foam sheet is further excellent in surface smoothness and mechanical strength.</p><p> Further, an ethylene-based resin consisting only of high-density polyethylene having a die-sell of 1.50 or more at 190 ° C, or an ethylene-based resin containing 60 to 95% by weight of high-density polyethylene and having a die-sell of 1.55 or more at 190 ° C. It is supplied to an extruder, melt-kneaded in the presence of a physical foaming agent, extruded and foamed from the extruder to produce a cylindrical foam molded product, and the foam molded product is expanded in the radial direction and then the foamed product is manufactured. When the foamed molded product is developed into a sheet to produce an ethylene-based resin foamed sheet, ethylene-based resin is used because the die-sell has a predetermined value or more and has high elastic properties at the time of melting. Foaming can be suppressed by relaxing the local elongation of the ethylene resin in the foaming step of the resin.</p><p> Moreover, a physical foaming agent is used as the foaming agent to prevent the bubble diameter generated in the foamed molded product from becoming too fine, and to control so that foam breakage does not occur in the subsequent diameter expansion step of the foamed molded product. Therefore, it is possible to produce an ethylene-based resin foamed sheet having uniform bubbles, fine particles, a high closed cell ratio, and excellent surface smoothness and thermomoldability.</p><p> Further, an ethylene-based resin consisting only of high-density polyethylene having a die-sell of 1.50 or more at 190 ° C, or an ethylene-based resin containing 60 to 95% by weight of high-density polyethylene and having a die-sell of 1.55 or more at 190 ° C. When an ethylene resin foam sheet is produced by supplying it to an extruder, melt-kneading it in the presence of a heat-decomposable foaming agent, and extruding and foaming it into a sheet from the extruder, the die sell has a predetermined value or more. Since an ethylene resin having high elastic properties at the time of melting is used, local elongation of the ethylene resin in the foaming process of the ethylene resin can be alleviated and foam rupture can be suppressed, and moreover, foaming can be suppressed. Using a heat-decomposable foaming agent as an agent, the bubbles in the foam extruded from the extruder are made fine, and the bubbles are made uniform and fine, with a high closed cell ratio, and surface smoothness and thermoformability. It is possible to produce an excellent ethylene-based resin foam sheet.</p>

(Example 1) As an ethylene resin, the density is 0.949 g / cm.³High-density polyethylene with a die-sell of 1.58 at 190 ° C (trade name "KM458A" manufactured by Nippon polyolefin Co., Ltd., melt mass flow rate (hereinafter referred to as "MFR"): 2.1 g / 10 minutes, melting point: 131 ° C) 100 By weight, as a heat-decomposable foaming agent, a master batch of a mixture of baking soda and citric acid (Clariant product name "Hydrocelol CF40E", mixture of baking soda and citric acid: 40% by weight, ethylene resin: 60% by weight) 0.3 parts by weight is supplied to the first extruder for melt kneading, and 1.2 parts by weight of butane gas is press-fitted into the first extruder as a physical foaming agent for melt kneading. After continuously supplying molten resin to the second extruder connected to the tip and adjusting the resin temperature to 145 ° C, the circular die attached to the tip of the second extruder (temperature: 145 ° C). ) Was extruded into a cylindrical shape at an extrusion rate of 25 kg / hour. The outer diameter of the inner die of the circular die was 80 mm, and the slit clearance was 0.68 mm.

Then, after gradually expanding the diameter of the cylindrical foam molded product, the cylindrical foam molded product is supplied to the cooling mandrel and the inner peripheral surface of the cylindrical foam molded product is slidably contacted with the outer peripheral surface of the mandrel to cool the cylindrical foam molded product. Then, this cylindrical foam was continuously cut and expanded between the inner and outer surfaces in the extrusion direction to obtain an ethylene resin foam sheet. The cooling mandrel was formed in a cylindrical shape having an outer diameter of 206 mm and a length of 200 mm.

(Example 2) Density is 0.963 g / cm³High-density polyethylene (trade name "KM490K" manufactured by Japan Polyolefins Co., Ltd., MFR: 4.0 g / 10 minutes, melting point: 135 ° C) 75 parts by weight and density 0.922 g / cm³Ethylene resin (trade name "JF120N" manufactured by Japan Polyolefins Co., Ltd., MFR: 0.3g / 10 minutes, melting point: 111 ° C) 25 parts by weight is supplied to the extruder and melt-kneaded at 200 ° C to increase the diameter. Ethylene resin pellets were prepared by extruding into 5 mm strands, cooling with water, and then cutting at predetermined lengths. This ethylene resin pellet has a die-sell of 1.74 and a density of 0.953 g / cm.³, MFR was 2.1 g / 10 min, melting point: 134 ° C.

Except for using the above ethylene resin pellets instead of high-density polyethylene and extruding and foaming from a circular die held at 144 ° C after adjusting the resin temperature to 144 ° C with a second extruder. An ethylene resin foam sheet was obtained in the same manner as in Example 1.

(Example 3) Density is 0.963 g / cm³High-density polyethylene (trade name "KM490K" manufactured by Japan Polyolefins Co., Ltd., MFR: 4.0 g / 10 minutes, melting point: 135 ° C) 75 parts by weight and density 0.922 g / cm³Ethylene resin (trade name "JK401N" manufactured by Japan Polyolefins Co., Ltd., MFR: 2.0 g / 10 minutes, melting point: 110 ° C) 25 parts by weight is supplied to the extruder and melt-kneaded at 200 ° C to increase the diameter. Ethylene resin pellets were prepared by extruding into 5 mm strands, cooling with water, and then cutting at predetermined lengths. This ethylene resin pellet has a die sill of 1.72 and a density of 0.952 g / cm.³, MFR was 3.4 g / 10 min, melting point: 133 ° C.

Except for using the above ethylene resin pellets instead of high-density polyethylene and extruding and foaming from a circular die held at 142 ° C after adjusting the resin temperature to 142 ° C with a second extruder. An ethylene resin foam sheet was obtained in the same manner as in Example 1.

(Example 4) As an ethylene resin, the density is 0.949 g / cm.³As a heat-decomposable foaming agent, 100 parts by weight of high-density polyethylene (trade name "KM458A" manufactured by Nippon polyolefin Co., Ltd., MFR: 2.1 g / 10 minutes, melting point: 131 ° C) with a die of 1.58 at 190 ° C. , Master batch of mixture of baking soda and citric acid (trade name "Hydrocerol CF40E" manufactured by Clariant, mixture of baking soda and citric acid: 40% by weight, ethylene resin: 60% by weight) 1.5 parts by weight is the first After supplying to the extruder and melt-kneading, the molten resin is continuously supplied to the second extruder connected to the tip of the first extruder to adjust the resin temperature to 145 ° C. An ethylene resin foam sheet was obtained by extrusion foaming from a T die (slit width: 720 mm, slit clearance: 1.00 mm) attached to the tip of the second extruder.

(Example 5) As an ethylene resin, the density is 0.949 g / cm.³100 parts by weight of high-density polyethylene for foamed sheets (trade name "KM458A" manufactured by Nippon polyolefin Co., Ltd., MFR: 2.1 g / 10 minutes, melting point: 131 ° C) with a die-sell of 1.58 at 190 ° C. As a mold foaming agent, a master batch of a mixture of baking soda and citric acid (trade name "Hydrocerol CF40E" manufactured by Clariant, a mixture of baking soda and citric acid: 40% by weight, ethylene resin: 60% by weight) 0.3 weight Parts are supplied to the first extruder and melt-kneaded, and 1.2 parts by weight of butane gas is press-fitted into the first extruder as a physical foaming agent for melt-kneading, and then connected to the tip of the first extruder. While continuously supplying molten resin to the extruder and adjusting the resin temperature to 145 ° C, high-density polyethylene for film (manufactured by Nippon Polymediate Co., Ltd.) Product name "HF562", MFR: 7.5g / 10 minutes, melting point: 134 ° C) was supplied to the third extruder, melt-kneaded at 170 ° C, and extruded from the second extruder. The high-density polyethylene extruded from the three extruders is supplied to the feed block type confluence die, and the high-density polyethylene for the film is laminated on the inner and outer surfaces of the high-density polyethylene for the foam sheet, and then the circular die (temperature). Extruded from: 145 ° C) into a cylindrical shape with an extrusion rate of 35 kg / hour. The outer diameter of the inner die of the circular die was 80 mm.

Then, the diameter of the cylindrical foamed molded product is gradually expanded and then supplied to the cooling mandrel to cool the cylindrical foamed molded product by sliding the inner peripheral surface of the cylindrical foamed molded product against the outer peripheral surface of the mandrel. Then, the cylindrical foam was continuously cut and developed between the inner and outer surfaces in the extrusion direction to obtain an ethylene resin foam sheet in which a high-density polyethylene film was laminated and integrated on both sides. The cooling mandrel was formed in a cylindrical shape having an outer diameter of 206 mm and a length of 200 mm.

(Example 6) As an ethylene resin, the density is 0.949 g / cm.³High-density polyethylene for foamed sheets with a die-sell of 1.58 at 190 ° C (trade name "KM458A" manufactured by Nippon polyolefin Co., Ltd., MFR: 2.1 g / 10 minutes, melting point: 131 ° C) 100 parts by weight and heat-decomposable type As a foaming agent, a masterbatch of a mixture of baking soda and citric acid (trade name "Hydrocerol CF40E" manufactured by Clariant, a mixture of baking soda and citric acid: 40% by weight, ethylene resin: 60% by weight) 1.5 parts by weight Is continuously supplied to the first extruder and melt-kneaded, and then the molten resin is continuously supplied to the second extruder connected to the tip of the first extruder to adjust the resin temperature to 145 ° C. On the other hand, high-density polyethylene for film (manufactured by Nippon polyolefin Co., Ltd.) Product name "HF562", MFR: 7.5g / 10 minutes, melting point: 134 ° C) was supplied to the third extruder, melt-kneaded at 170 ° C, and extruded from the second extruder. The high-density polyethylene extruded from the three extruders is supplied to the feed block type confluence die, and the high-density polyethylene for the foam sheet is laminated on the front and back surfaces of the high-density polyethylene for the foam sheet, and then the T-die (slit). Width: 720 mm, slit clearance: 1.00 mm) was extruded to obtain an ethylene-based resin foam sheet in which high-density polyethylene films were laminated and integrated on both sides.

(Comparative example 1) As high-density polyethylene, the density is 0.963 g / cm³Same as Example 1 except that high-density polyethylene (trade name "KM490K" manufactured by Japan Polyolefins Co., Ltd., MFR: 4.0 g / 10 minutes, melting point: 135 ° C) was used at 190 ° C. To obtain an ethylene-based resin foam sheet.

(Comparative example 2) As high-density polyethylene, the density is 0.946 g / cm.³Using high-density polyethylene (trade name "KB145N" manufactured by Japan Polyolefins Co., Ltd., MFR: 0.25 g / 10 minutes, melting point: 130 ° C) with a die-sell of 1.46 at 190 ° C, a pyrolysis foaming agent An ethylene resin foamed sheet was obtained in the same manner as in Example 1 except that 1.0 part by weight was used instead of 0.3 part by weight.

The apparent density, thickness, open cell ratio, centerline surface roughness (Ra), average cell diameter, MD average cell diameter, TD average cell diameter, and VD average cell diameter of the obtained ethylene resin foam sheet are described above. In addition, the MFR of the ethylene resin that composes the ethylene resin foam sheet, the melt tension and elongation at break, the thermoformability of the ethylene resin foam sheet, and the ethylene resin. The appearance of the molded product obtained by molding the foam sheet was measured as follows, and the results are shown in Table 1.

(MFR) The MFR of the ethylene resin that composes the ethylene resin foam sheet is JIS K7210: 1999 "Test method of melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic plastic". The measurement was performed based on the method described in Method B.

Specifically, the cylinder of the measuring device (trade name "Semi-auto melt indexer" manufactured by Toyo Seiki Seisakusho Co., Ltd.) is filled with 3 to 8 g of the measurement sample, and this measurement sample is filled with a filling rod at a test temperature of 190 ° C. The MFR was measured under the conditions of a test load of 21.18 N and a preheating time of 4 minutes. Three measurement samples were prepared, and the arithmetic mean value of the MFR of each measurement sample was taken as the MFR of the ethylene resin.

(Melting tension at break and melt elongation at break) The melt tension and melt elongation at break of the ethylene resin constituting the ethylene resin foam sheet were measured as follows. That is, after heating the measurement sample to 190 ° C, it is filled in the cylinder of Capillograph (trade name "PMD-C" manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the piston is lowered at a constant descent speed of 10 mm / min. The measurement sample in the cylinder was extruded vertically downward in a string shape from the nozzle of the cylinder (diameter: 2.095 mm, length: 8 mm, inflow angle: 90 °).

Then, the string-like material extruded from the nozzle of the cylinder is passed through a pulley for tension detection arranged at a position 35 mm vertically downward from the lower end of the nozzle of the cylinder, and then the winding speed is reduced to the winding roll. 66m / min²The tension at the time when the string-like material was cut was defined as the melt tension at the time of breaking, and the winding speed at the time when the string-like material was cut was defined as the melt-break elongation. When the string-like material did not break at the winding speed of 150 m / min, the tension of the string-like material at the winding speed of 150 m / min was defined as the melt tension at the time of fracture.

(Thermoforming property and appearance) A planar square test piece having a side of 300 mm was cut out from an ethylene resin foam sheet. This test piece was molded into a dish-shaped molded product having a bottom surface of 180 mm in length × 100 mm in width in a flat rectangular shape and a depth of 28 mm by using a press molding method. The press molding was performed by heating at each temperature of 125 ° C, 130 ° C, and 135 ° C for 18 seconds. Then, the thermoformability is visually determined based on the following criteria, and as an index of appearance, visually observe whether or not irregularities due to foam rupture or poor elongation of the resin are formed on the surface of the molded product. Judged by. In Table 1, the case where there is unevenness is described as "yes", and the case where there is no unevenness is described as "none".

[Thermoformability] : The corners of the molded product were accurately molded, and no breakage was observed. × ... The corners of the molded product were not accurately molded, and breakage was also observed.

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