JP2023151066A - Method for producing foam sheet and foam sheet - Google Patents

Abstract

To provide a method for producing a foam sheet which can obtain a foam sheet having good moldability while reducing a content of inorganic powder, and can obtain a foam sheet which suppresses occurrence of yellow discoloration, even if it produces a foam sheet using a polystyrene-based resin containing a recycled raw material derived from the produced foam sheet, and a foam sheet.SOLUTION: A method for producing a foam sheet by extruding and foaming a foamable resin molten material obtained by kneading a polystyrene-based resin and a physical foaming agent, wherein the physical foaming agent contains hydrocarbon having 3 to 5 carbon atoms and/or dialkyl ether whose alkyl group has 1 to 3 carbon atoms, and nitrogen, the total of the addition amount of the hydrocarbon and/or the dialkyl ether and the addition amount of the nitrogen is 0.2 mol% or more and 1.2 mol or less per 1 kg of the foamable resin molten material, the addition amount of the nitrogen is 0.01 mol% or more and 0.20 mol% or less per 1 kg of the foamable resin molten material, and a ratio of the addition amount of the nitrogen to the addition amount of the hydrocarbon and/or the dialkyl ether is 0.03 or more and 0.4 or less.SELECTED DRAWING: None

Description

The present invention relates to a foam sheet manufacturing method and a foam sheet.

Resin foam sheets are used as foam sheets for thermoforming because they are lightweight and have excellent moldability. For example, molded objects (molded products) obtained by thermoforming a foamed sheet using polystyrene resin as the base resin (sometimes referred to as a polystyrene resin foamed sheet) can be used for lunch boxes, bowls, cups, etc. Used in a wide range of applications such as various containers.

As a method for manufacturing a polystyrene resin foam sheet, for example, a polystyrene resin and a physical foaming agent are supplied to an extruder to form a foamable resin melt, and the foamable resin melt is extruded and foamed to form a foam sheet. A manufacturing method is known (for example, Patent Document 1). When carrying out such a method for manufacturing a foamed sheet, inorganic powder is usually added in order to obtain a foamed sheet having a desired cell structure. The inorganic powder functions as a foam regulator.

Japanese Patent Application Publication No. 2015-145486

In the production of polystyrene resin foam sheets, from the perspective of reducing environmental impact, foam sheets derived from foam sheets, which are formed from foam sheet scraps generated during the manufacture of foam sheets and scraps generated during thermoforming of foam sheets, are used. Recycled raw materials may be reused as polystyrene resin to form foam sheets.

In the foamed sheet manufactured by the method shown in Patent Document 1, the above-mentioned inorganic powder and a dispersant added to disperse the inorganic powder well in the resin are usually added to the foamed sheet. remain in the If a recycled raw material is formed from a foam sheet with residual inorganic powder, etc. and reused in the manufacture of foam sheets, depending on the amount of recycled raw materials used, etc., the foam sheet containing the recycled raw materials may turn yellow. There was a risk that the quality of the foam sheet would deteriorate. Regarding this point, it is possible to reduce the amount of inorganic powder and dispersant contained in the foam sheet, which is a recycled raw material, but it is generally possible to reduce the amount of inorganic powder and dispersant added to the foam sheet. In such cases, it may become impossible to obtain the desired foam sheet.

An object of the present invention is to be able to obtain a good foam sheet while reducing the blended amount of inorganic powder, and to use a polystyrene resin containing recycled raw materials derived from manufactured foam sheets (recycled foam sheets). To provide a method for producing a foamed sheet, which can obtain a foamed sheet containing recycled raw materials in which the occurrence of yellowing is suppressed even when manufacturing a foamed sheet containing recycled materials (sometimes referred to as a foamed sheet containing raw materials), and a foamed sheet. It is in.

The gist of the present invention is the inventions shown in the following (1) to (8).

(1) A method for manufacturing a foam sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, the method comprising:
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The total amount of the hydrocarbon and/or dialkyl ether added and the amount of nitrogen added is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamable resin melt,
The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per kg of the foamable resin melt, and
characterized in that the ratio of the added amount of nitrogen to the added amount of the hydrocarbon and/or the dialkyl ether is 0.03 or more and 0.4 or less,
Method for manufacturing foam sheets.
(2) The foamable resin melt does not contain inorganic powder, or the foamable resin melt contains the inorganic powder, and the amount of the inorganic powder is 100 parts by mass of the polystyrene resin. 0.2 parts by mass or less,
The method for manufacturing a foam sheet according to (1) above.
(3) The foamable resin melt does not contain the fatty acid metal salt, or the foamable resin melt contains the fatty acid metal salt, and the amount of the dispersant is 100 parts by mass of the polystyrene resin. 0.02 parts by mass or less,
The method for producing a foam sheet according to (1) or (2) above.
(4) The method for producing a foamed sheet according to any one of (1) to (3) above, wherein the foamed sheet has an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less.
(5) The foam sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less;
The method for producing a foam sheet according to any one of (1) to (4) above.
(6) A physical foaming agent is kneaded with a polystyrene resin containing recycled raw materials derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of (1) to (5) above. A method of manufacturing a foam sheet by extruding and foaming a foamable resin melt.
(7) A foamed sheet made by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, and having an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less,
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The average cell diameter of the foam sheet is 0.08 mm or more and 0.5 mm or less,
The combustion residue when the foam sheet is burned is 0.2% by mass or less (including 0),
foam sheet.
(8) does not contain a fatty acid metal salt, or contains the fatty acid metal salt, and the blending amount of the fatty acid metal salt is 0.02% by mass or less;
The foam sheet described in (7) above.

According to the present invention, it is possible to obtain a good foam sheet while reducing the amount of inorganic powder blended, and the foam sheet is manufactured using a polystyrene resin containing recycled raw materials derived from the manufactured foam sheet. It is possible to provide a method for manufacturing a foamed sheet and a foamed sheet that can obtain a recycled material-containing foamed sheet in which the occurrence of yellowing is suppressed even in cases where yellowing is suppressed.

Regarding the embodiment of the present invention, 1. Method for manufacturing foam sheet, 2. Foam sheet, 3. A method for manufacturing a foam sheet using recycled raw materials derived from foam sheets will be explained below in order.

Note that the present invention is not limited to the embodiments described below.

[1 Method for manufacturing foam sheet]
[1-1 Configuration]
The method for producing a foamed sheet according to the present invention is to produce a polystyrene resin foamed sheet (hereinafter referred to as a foamed sheet) by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent. This is a manufacturing method (so-called extrusion foaming method). In the description of the configuration of the method for manufacturing a foamed sheet, the description will be continued using an example in which the foamable resin melt does not contain an inorganic powder and a dispersant. However, as will be described later, this does not exclude the presence of residual components such as inorganic powder in the foam sheet. Further, the case where the foamable resin melt contains an inorganic powder and a dispersant within a predetermined range is not excluded. Note that the polystyrene resin foam sheet is referred to as a foam sheet and the method for manufacturing the foam sheet according to the present invention is an extrusion foaming method. The same applies to any method of manufacturing a foamed sheet using a polystyrene resin containing.

The extrusion foaming method can be used to manufacture a general extrusion foam sheet using manufacturing equipment. Examples of the manufacturing apparatus include an apparatus having extruders connected in series (a first extruder on the upstream side and a second extruder on the downstream side) and a die provided on the downstream side of the second extruder. can. Note that it is preferable that an annular die is used as the die. In the following explanation, the explanation will be continued using, as an example, a manufacturing apparatus that is equipped with an annular die on the downstream side of the second extruder. The manufacturing equipment is equipped with a cooling cylinder (mandrel) for cooling the cylindrical foam sheet downstream of the annular die, and a cutter for cutting the extruded and cooled cylindrical foam sheet. suitable. Moreover, it is preferable that the manufacturing apparatus is provided with a winder that takes up the foam sheet into a roll. Note that the upstream side and the downstream side are defined based on the direction of transport of the polystyrene resin that is the base resin of the foam sheet. Further, the manufacturing apparatus shown here is an example, and the present invention is not limited thereto.

(Formation of foamable resin melt)
In the method for manufacturing a foamed sheet, a polystyrene resin and a physical foaming agent are kneaded. At this time, a foamable resin melt is formed. In the manufacturing apparatus described above, polystyrene resin is supplied to the first extruder on the upstream side, and a physical foaming agent is further press-fitted therein. Then, the polystyrene resin and the physical foaming agent are kneaded inside the first extruder or the second extruder to form a foamable resin melt.

(Extruded foam)
The foamable resin melt is transferred from the first extruder on the upstream side to the second extruder on the downstream side, and the temperature of the foamable resin melt is adjusted by the second extruder. Then, the foamable resin melt is extruded into atmospheric pressure from an annular die provided in the second extruder, and a cylindrical foam is formed. The cylindrical foam is drawn along a mandrel and cooled. Thereafter, the cylindrical foam is cut open along the extrusion direction with a cutter, developed into a sheet, and then wound up into a roll using a winder. In this way, a foamed sheet is manufactured by extruding and foaming the foamable resin melt.

The obtained foamed sheet may be used as it is, or may be further used as a molded product using the foamed sheet. The molded product refers to a molded product obtained by shaping a foamed sheet into a predetermined shape, and specifically includes a container and the like.

(Polystyrene resin)
The polystyrene resin used in the foam sheet manufacturing method is not particularly limited as long as it can be used for polystyrene resin foam applications. In this specification, polystyrene resin refers to a resin containing 50% by mass or more of styrene monomer component units. Examples of polystyrene resins include polystyrene, rubber-modified polystyrene (impact-resistant polystyrene), styrene-α-methylstyrene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene-maleic anhydride. Polymers such as copolymers, styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, styrene-acrylonitrile copolymers, etc. , a mixture of polystyrene and polyphenylene ether, and the like. Among these, it is preferable to use polystyrene as the polystyrene resin. Note that the concept of polystyrene resin includes cases in which one of the various polymers and mixtures described above is used (singlely), and cases in which two or more of the various polymers and mixtures described above are used in combination.

(foaming agent)
As the foaming agent used in the foam sheet manufacturing method, a physical foaming agent is suitably employed. Preferably, the physical blowing agent comprises a hydrocarbon and/or a dialkyl ether. Regarding hydrocarbons, from the viewpoints of solubility in resin and volatility from foamed sheets, ease of manufacturing desired foamed sheets by extrusion foaming, and ease of obtaining foamed sheets with excellent thermoformability, Preferably, hydrocarbons having 3 to 5 carbon atoms are used. Specifically, examples of the hydrocarbon having 3 to 5 carbon atoms include propane, normal butane, isobutane, normal pentane, and isopentane. Among these, it is preferable to use normal butane and/or isobutane as the hydrocarbon. Note that hydrocarbons having 3 to 5 carbon atoms used as physical blowing agents are sometimes simply referred to as hydrocarbons.

As the dialkyl ether, from the same point of view as in the case of hydrocarbons, and from the viewpoint that it is easy to obtain a molded product that is difficult to expand (tertiary foaming) when a molded product containing food etc. is heated in a microwave oven, etc., an alkyl group is used. It is preferable to use a dialkyl ether having 1 to 3 carbon atoms. Specifically, examples of the dialkyl ether having an alkyl group having 1 to 3 carbon atoms include diethyl ether, dimethyl ether, and ethyl methyl ether. Among these, dimethyl ether is preferably used as the dialkyl ether. Note that dialkyl ethers in which the alkyl group has 1 to 3 carbon atoms and are used as physical blowing agents are sometimes simply referred to as dialkyl ethers.

It is preferable to use a hydrocarbon as the physical foaming agent from the viewpoint of easily producing a desired foamed sheet by extrusion foaming and from the viewpoint of easily obtaining a foamed sheet with excellent thermoformability. Further, from the viewpoint of easily suppressing tertiary foaming of the molded product while enhancing extrusion foamability and thermoformability, it is preferable to use a hydrocarbon and a dialkyl ether together as the physical foaming agent.

(nitrogen)
The physical blowing agent contains nitrogen. Nitrogen is considered to function as a foaming agent in that it separates from the molten polystyrene resin and forms a cell structure within the polystyrene resin during extrusion and foaming. In addition, as described below, although the detailed mechanism of its function is not clear, nitrogen effectively functions as a blowing agent with the above-mentioned hydrocarbons and/or dialkyl ethers used as physical blowing agents. It is thought that it can also function as a so-called bubble regulator. As will be described later, the cell control agent refers to an additive that has a cell control effect by forming cell nucleus points, controls the foaming of the resin by the physical foaming agent, and adjusts the state of the cell structure. Therefore, in the method for producing a foamed sheet of the present invention, nitrogen is considered to have a function as a foaming agent and a function of exerting a bubble regulating effect, and by adding nitrogen as a physical foaming agent, It is thought that this may affect the foam adjustment effect and extrusion foaming properties during extrusion foaming.

Note that the timing of nitrogen addition is not particularly limited as long as the intended purpose of the present invention can be achieved. For example, nitrogen may be added together with the hydrocarbon and/or dialkyl ether, or nitrogen may be added at a different timing than the hydrocarbon and/or dialkyl ether.

Physical blowing agents other than the above-mentioned hydrocarbons, the above-mentioned dialkyl ethers, and nitrogen may be used in combination within the range in which the intended purpose of the present invention can be achieved. Further, nitrogen may be added singly or in a mixed state. An example of adding nitrogen in a mixed state is adding air.

(Additional amount of physical foaming agent)
In the foam sheet manufacturing method, the total amount of the added amount of hydrocarbon and/or dialkyl ether and the added amount of nitrogen (referred to as the total added amount of the physical blowing agent) is 0.2 mol per 1 kg of the foamable resin melt. The amount is 1.2 mol or less. If the total amount of physical foaming agents added is too small, foaming by extrusion foaming may be insufficient, and it may be difficult to obtain a foamed sheet having a desired foaming ratio. From the viewpoint of stably producing a foamed sheet with low apparent density, the total amount of physical blowing agents added is preferably 0.3 mol or more, and 0.4 mol or more per 1 kg of foamable resin melt. is more preferable, and even more preferably 0.5 mol or more.

If the total amount of physical foaming agents added is too large, it will be difficult to control the expansion ratio and cell structure, which may make it difficult to obtain the desired foamed sheet, and the thermoformability of the resulting foamed sheet will decrease. There is a possibility that From the viewpoint of stably producing a foamed sheet with excellent appearance and thermoformability, the total amount of physical blowing agents added is preferably 1.1 mol or less, and 1.0 mol or less per 1 kg of foamable resin melt. It is more preferable.

In addition, when the physical foaming agent contains hydrocarbons and dialkyl ethers, it is possible to stably produce the desired foamed sheet by extrusion foaming, and when the molded product containing food etc. is heated in a microwave oven etc., it expands. From the viewpoint of easily producing a molded article that is difficult to cause (tertiary foaming) more stably, the ratio of the amount of the hydrocarbon added to the amount of the dialkyl ether added (hydrocarbon:dialkyl ether) is 6:4 to 6:4. The ratio is preferably 9:1, more preferably 7:3 to 8:2. Note that the ratio of the above hydrocarbon to dialkyl ether is a molar ratio.

(Addition ratio of nitrogen in foamable resin melt)
In the method for producing a foamed sheet according to the present invention, the proportion of nitrogen added to the foamable resin melt (referred to as nitrogen addition amount) is 0.01 mol or more and 0.20 mol or less per 1 kg of the foamable resin melt. If the amount of nitrogen added is too small, foaming does not occur, probably because the effect of forming cell nucleus points by nitrogen during extrusion foaming is insufficient, making it difficult to obtain a desired foamed sheet.

On the other hand, if the amount of nitrogen added is too large, the bubbles in the foam sheet tend to become finer, probably because the effect of forming bubble nucleus points due to nitrogen tends to be too strong. As a result, corrugation tends to occur in the foam sheet during extrusion foaming, and the foam sheet also tends to break when the foam sheet is taken off, which may make it difficult to obtain a good foam sheet.

From the viewpoint of being able to stably produce a foam sheet having a desired expansion ratio and a good cell structure, the amount of nitrogen added should be 0.02 mol or more per 1 kg of the foamable resin melt. is preferable, more preferably 0.05 mol or more, and still more preferably 0.08 mol or more. From the same viewpoint, the amount of nitrogen added is preferably 0.18 mol or less, more preferably 0.15 mol or less, and even more preferably 0.12 mol or less per 1 kg of the foamable resin melt. In addition, as will be described later, when the foamable resin melt contains inorganic powder, from the viewpoint of being able to further improve the controllability of the cell structure of the foam sheet, the amount of nitrogen added per kg of the foamable resin melt is It is preferably 0.15 mol or less, more preferably 0.12 mol or less, even more preferably 0.10 mol or less.

(Ratio (relative ratio) of nitrogen in physical blowing agent)
In the physical blowing agent, the ratio (FA2/FA1) of the amount of nitrogen added (FA2) to the amount of hydrocarbon and/or dialkyl ether added (FA1) is set to be 0.03 or more and 0.4 or less. In this specification, FA2/FA1 may be referred to as the relative ratio of nitrogen.

If the relative ratio of nitrogen is excessively high, the bubbles in the foam sheet tend to become finer, probably because the effect of forming bubble nucleus points due to nitrogen becomes excessively strong. As a result, corrugation tends to occur in the foam sheet during extrusion foaming, and it may be difficult to obtain a good foam sheet. Furthermore, if the relative ratio of nitrogen is excessively low, foaming due to extrusion foaming becomes difficult to occur, probably because the effect of forming bubble nucleus points is insufficient. Therefore, it may be difficult to obtain a desired foamed sheet with a low apparent density.

From the viewpoint of making it easier to obtain a foamed sheet in which cells with relatively large cell diameters are formed and to stably produce a foamed sheet with excellent thermoformability, the upper limit of the relative ratio of nitrogen (FA2/FA1) is set to 0. It is preferably 35, more preferably 0.32, and even more preferably 0.30. Further, the lower limit of the relative ratio of nitrogen (FA2/FA1) is preferably 0.05, preferably 0.08, and more preferably 0.1. In addition, as will be described later, when the foamable resin melt contains inorganic powder, the upper limit of the relative ratio of nitrogen (FA2/FA1) is It is preferably 0.30, more preferably 0.25, and even more preferably 0.20.

In the method for manufacturing a foamed sheet according to the present invention, a foamed sheet having the following basis weight and apparent density can be obtained.

(Basic weight of foam sheet)
Regarding the foam sheet that can be obtained by the foam sheet manufacturing method according to the present invention, the basis weight of the foam sheet is preferably 80 g/m ² or more and 400 g/m ² or less. With the above basis weight, a molded article that is lightweight, has good thermoformability, and has appropriate rigidity can be stably obtained. From the viewpoint of increasing the rigidity of a foam sheet or a molded product obtained by thermoforming a foam sheet, the basis weight of the foam sheet is preferably 100 g/m ² or more, more preferably 120 g/m ² or more. preferable. Moreover, from the viewpoint of increasing the lightweight property of the foam sheet, the weight is preferably 300 g/m ² or less, more preferably 250 g/m ² or less, and even more preferably 200 g/m ² or less.

(Method of measuring basis weight of foam sheet)
The basis weight of the foam sheet is measured as follows. First, in the foamed sheet obtained by the manufacturing method of the present invention, 10 locations are selected at equal intervals along the width direction of the foamed sheet (direction perpendicular to the extrusion direction of the foamed sheet and the thickness direction of the foamed sheet). Next, test pieces measuring 25 mm in length x 25 mm in width (the thickness is the thickness of the foam sheet) are cut out at each of the 10 positions. The mass of each of the obtained test pieces is measured. Then, the basis weight (mass/area) of each test piece is calculated based on the measured mass and the area of the test piece, and the obtained values are arithmetic averaged. This arithmetic average value is determined as the basis weight (g/m ² ) of the foam sheet.

(apparent density of foam sheet)
Regarding the foam sheet that can be obtained by the foam sheet manufacturing method according to the present invention, it is preferable that the foam sheet has an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less. By having the above apparent density, it is possible to stably obtain a molded article that is lightweight, has good thermoformability, and has appropriate rigidity. The apparent density of the foam sheet is preferably 50 kg/m ³ or more, more preferably 60 kg/m ³ or more. Further, from the viewpoint of increasing the strength of a molded product obtained by thermoforming a foam sheet, the apparent density of the foam sheet is preferably 180 kg/m ³ or less, more preferably 170 kg/m ³ or less, More preferably, it is 160 kg/m ³ or less.

(Method for measuring apparent density of foam sheet)
The apparent density of the foam sheet is measured as follows. Test pieces for each of the 10 positions are prepared using the same method and conditions as the method for measuring the basis weight of the foam sheet described above, and the basis weight is calculated for each test piece. In addition, the thickness of the test piece (thickness of the foam sheet) is measured, and the measured basis weight is divided by the thickness of the test piece (thickness of the foam sheet). As a result, the density of each test piece is calculated, and the obtained values are arithmetic averaged. This arithmetic average value is determined as the apparent density (kg/m ³ ) of the foam sheet.

(Width of foam sheet)
Regarding the foam sheet that can be obtained by the foam sheet manufacturing method according to the present invention, the width of the foam sheet is not particularly limited, but in the foam sheet manufacturing method according to the present invention, the foam sheet is The length in the direction perpendicular to the extrusion direction and the thickness direction of the foamed sheet (sometimes referred to as sheet width) is preferably 500 mm or more. When the sheet width is 500 mm or more, when manufacturing molded products using foam sheets, foam sheets can improve productivity because many molded products can be molded at once using multi-cavity thermoforming. It will be excellent. From this point of view, the width of the foam sheet is more preferably 600 mm or more. Note that the upper limit of the foam sheet is approximately 2000 mm, although it is not particularly limited.

(Thickness of foam sheet)
Regarding the foam sheet that can be obtained by the foam sheet manufacturing method according to the present invention, the thickness of the foam sheet is preferably approximately 0.5 mm or more and 4 mm or less, and more preferably 1 mm or more and 3 mm or less. In this case, it becomes easy to obtain a molded article that is lightweight, has good thermoformability, and has appropriate rigidity. The thickness of the foam sheet is measured as follows. First, ten locations are selected at equal intervals along the width direction of the foam sheet. Next, the thickness of the foam sheet is measured at each of the 10 positions, and the arithmetic mean value of the measured thicknesses is calculated. This measurement is performed at three randomly selected positions along the extrusion direction, and the arithmetic mean value of these measurements is taken as the thickness of the foam sheet.

(Average cell diameter of foam sheet)
The average cell diameter (mm) of the foamed sheet obtained by the manufacturing method of the present invention is 0.08 mm or more and 0.5 mm or less from the viewpoint of improving the moldability (thermoformability) of the foamed sheet and the appearance of the foamed sheet. It is preferable that In addition, from the viewpoint that it is easy to stably obtain a foamed sheet with excellent thermoformability, the average cell diameter of the foamed sheet is preferably 0.10 mm or more, more preferably 0.12 mm or more, and 0.15 mm or more. It is more preferable that it is above. In addition, from the viewpoint of easily forming a smooth surface, increasing gloss, and stably obtaining a molded product with a good appearance in a molded product obtained by thermoforming a foamed sheet, foamed sheets are The average cell diameter is preferably 0.4 mm or less, more preferably 0.35 mm or less, even more preferably 0.30 mm or less, and particularly preferably 0.26 mm or less. The average cell diameter of the foam sheet is the average cell diameter along the width direction (TD) of the foam sheet, the average cell diameter along the extrusion direction (MD) of the foam sheet, and the average cell diameter along the thickness direction (VD) of the foam sheet. Indicates the average value of the average bubble diameter along the line.

(Method for measuring average cell diameter of foam sheet)
The average cell diameter (mm) of the foam sheet is measured as follows. In the foam sheet, a test piece is cut out from approximately the center (near the center) along the width direction of the foam sheet. At this time, the size of the test piece is 10 cm in length along the width direction, 10 cm in length along the extrusion direction, and the length in the thickness direction of the test piece is the thickness of the foam sheet. . In addition, test pieces similar to the above-mentioned test pieces were cut out from around the center of the foam sheet from both approximately one end and approximately the other end (near the ends of both ends) along the width direction of the foam sheet. A specimen of the same size is cut out.

For each cut out test piece, an enlarged photograph (MD direction enlarged photograph) of a vertical cross section of the foam sheet along the extrusion direction (MD) is taken. An optical microscope can be used to take enlarged photographs. A specific example of the optical microscope includes a digital microscope ("VHX-7000") manufactured by Keyence Corporation. Note that when taking a photograph of an enlarged cross section, the magnification of the cross section can be set to, for example, 100 times. Furthermore, an enlarged photograph of a vertical cross section along the width direction (TD) of the foam sheet (TD direction enlarged photograph) is taken using the same method as for taking an enlarged photograph in the MD direction.

On each of the enlarged photographs in the MD direction and the enlarged TD direction, line segments are drawn at equal intervals along the thickness direction of the foam sheet. In each of the MD direction enlarged photograph and the TD direction enlarged photograph, based on the image of the bubble that intersects the line segment, the bubbles along the MD direction, TD direction, and VD direction are calculated for each bubble, taking into account the enlargement magnification of the enlarged photograph. Measure the maximum diameter. Note that, as the bubbles that intersect with the line segment, all bubbles that are recognized to intersect with the line segment when visually observed by the measurer are selected. Then, by arithmetic averaging the bubble diameters along the MD direction, TD direction, and VD direction measured for each bubble, the average bubble diameters in the MD direction, TD direction, and VD direction are calculated. For example, by calculating the arithmetic mean value of the bubble diameters along the TD direction measured for a plurality of bubbles, the average bubble diameter in the TD direction in the test piece is calculated.

Then, by calculating the arithmetic mean value of the average cell diameters in the MD direction, TD direction, and VD direction calculated for each test piece, the average cell diameter of the foam sheet in the MD direction, TD direction, and VD direction is calculated. be done. For example, the average cell diameter in the TD direction in the foam sheet is calculated by calculating the arithmetic mean value of the average cell diameter in the TD direction measured for a plurality of test pieces.

Furthermore, the arithmetic mean value of the average cell diameter in the TD direction, the average cell diameter in the MD direction, and the average cell diameter in the VD direction in the foam sheet is calculated. This calculated value is determined as the average cell diameter (mm) of the foam sheet.

(Closed cell ratio of foam sheet)
The closed cell ratio of the foam sheet is preferably 70% or more. When the closed cell ratio of the foamed sheet is within the above range, the secondary foamability of the foamed sheet can be improved when thermoforming a molded article using the foamed sheet. Moreover, the strength etc. of the molded product obtained by thermoforming the foam sheet can be ensured. From this viewpoint, the closed cell ratio of the foam sheet is more preferably 80% or more, and even more preferably 90% or more.

(Method for measuring closed cell ratio of foam sheet)
A test piece is prepared by cutting the foam sheet into a size of 25 mm x 25 mm x sheet thickness (thickness of the extruded foam sheet) from approximately the center. A plurality of test pieces are stacked so that the total sheet thickness is closest to 20 mm to form a test piece. Next, in accordance with Procedure C of ASTM-D2856-70, the true volume Vx of the test piece was measured using an air comparison hydrometer model 930 manufactured by Toshiba Beckman Corporation, and the true volume Vx was calculated using the following formula (Equation (1)). Calculate the closed cell ratio S (%). The above measurement is performed using five test pieces, and the arithmetic mean value thereof is taken as the closed cell ratio of the foam sheet.

however,
Vx: The true volume (cm ³ ) of the test piece measured by the above method, which corresponds to the sum of the volume of the resin constituting the foam sheet and the total volume of the cells in the closed cell portion within the test piece.
Va: apparent volume of the test piece (cm ³ ) calculated from the outer dimensions of the test piece used for measurement,
W: total mass (g) of the test piece used in the measurement, and ρ: density (g/cm ³ ) of the resin constituting the foam sheet.
It is.

[1-2 Action and effect]
In the method for manufacturing a foamed sheet according to the present invention, nitrogen is used in addition to hydrocarbons and/or dialkyl ethers as a physical foaming agent. It is thought that nitrogen functions both as a foaming agent and as a foam control agent. Although the reason for this is not certain, the following may be considered. During extrusion foaming, nitrogen contained in the foamable resin melt separates from the molten polystyrene resin earlier than hydrocarbons and/or dialkyl ethers, leading to the formation of bubbles in the extruded resin. It is considered that a bubble nucleus is formed as a starting point. Furthermore, as the foaming of the foamable resin melt progresses, the separation of hydrocarbons and/or dialkyl ethers from the resin progresses, and the formation of bubbles starting from the bubble nucleus (or its vicinity) formed by nitrogen. It is thought that growth will progress.

Therefore, in the method for manufacturing a foamed sheet according to the present invention, nitrogen can function as a cell regulator, thereby suppressing the amount of inorganic powder that has been conventionally added as a cell regulator. Alternatively, even if a foamed sheet is manufactured without adding inorganic powder, it is possible to obtain a foamed sheet that has a desired expansion ratio and cell structure and has good thermoformability.

Furthermore, as described above, in the production of foam sheets, recycled raw materials derived from foam sheets are sometimes reused as polystyrene resin for forming the foam sheets. In conventional foam sheets in which inorganic powder is added as a cell control agent, the inorganic powder and the dispersant added to disperse the inorganic powder well in the resin usually remain in the foam sheet. . Therefore, if recycled raw materials are manufactured from conventional foam sheets with residual inorganic powder, etc. and reused as raw materials for foam sheets, yellowing etc. may occur in the foam sheets depending on the amount of recycled raw materials used. , there was a risk that the quality of the foam sheet would deteriorate.

In the method for producing a foamed sheet according to the present invention, since the amount of inorganic powder that is generally added as a cell regulator can be suppressed, recycled raw materials derived from the foamed sheet obtained according to the present invention can be suppressed. Even if a foamed sheet is manufactured using the above method, it is possible to obtain a foamed sheet (foamed sheet containing recycled raw materials) in which the occurrence of yellowing is suppressed.

Furthermore, in conventional foam sheets, a large amount of inorganic powder and a dispersant added to disperse the inorganic powder in the resin remain in the foam sheet. In addition to this, the amount of inorganic powder and dispersant added to the foam sheet often varies depending on the use of the foam sheet and manufacturing conditions. For this reason, when recycled raw materials derived from conventional foam sheets are reused as polystyrene resin for forming foam sheets, the foam sheet has a desired magnification and cell structure (cell size, cell distribution, etc.). There is a possibility that it may be difficult to adjust the temperature within this range, and there is a possibility that the productivity of the foam sheet may decrease.

In the method for producing a foamed sheet according to the present invention, since the amount of inorganic powder that is generally added as a cell regulator can be suppressed, recycled raw materials derived from the foamed sheet obtained according to the present invention can be suppressed. Even when using polystyrene resin as a raw material for foam sheets, it is easy to obtain foam sheets with the desired cell structure (i.e., stabilizing the quality of foam sheets using polystyrene resin containing recycled raw materials). .

Furthermore, when a conventional foam sheet is used as a recycled raw material, the recycled raw material-containing foam sheet contains inorganic powder. Conventional foam sheets and foam sheets containing recycled raw materials are processed into molded products such as containers by, for example, thermoforming. At this time, the foam sheet is sometimes formed with a large number of containers connected together by multi-cavity thermoforming, but in order to separate these containers into individual containers, there is a gap between adjacent containers. The joint is cut (fused) with a heating wire (nichrome wire, etc.). At this time, it has been pointed out that the inorganic powder contained in the foam sheet may adhere to the heating wire, contaminating the heating wire, and causing a decrease in the cutting function of the heating wire.

In this regard, according to the present invention, since nitrogen can also function as a conventional inorganic powder (functioning as a bubble regulator), the foam sheet can be formed in a state in which no dispersant or inorganic powder is contained; Alternatively, even if a dispersant or inorganic powder is contained, the content of the dispersant or inorganic powder can be reduced compared to conventional foam sheets. Therefore, according to the present invention, it is possible to obtain a foam sheet that can suppress deterioration in the cutting function of heating wires.

[1-3 Regarding residual components and combustion residue]
As described above, in the method for producing a foamed sheet of the present invention, the obtained foamed sheet does not need to contain residual components such as inorganic powder derived from the cell regulator; , may contain residual components within a predetermined range. When the residual component contains inorganic powder, nitrogen and inorganic powder are used together in the foamable resin melt.

(Residual component)
In the foamed sheet of the present invention, residual components derived from the inorganic powder and the dispersant may be present. The term "residual component" refers to the raw materials used in manufacturing the foam sheet, excluding the resin component and the foaming agent, and indicates what remains in the foam sheet. As the residual component, various additives such as a cell regulator and a dispersant can be mentioned, and specifically, an inorganic powder having the function of a cell regulator as described later can be exemplified. Specific examples of the inorganic powder include talc, calcium carbonate, barium sulfate, silica, titanium oxide, clay, and aluminum oxide. Among these, talc can be preferably used as the inorganic powder added as a bubble regulator. When using an inorganic powder containing talc, the average particle diameter of talc is preferably 0.1 μm or more and 15 μm or less, more preferably 0.5 μm or more and 10 μm or less, from the viewpoint of enhancing the bubble regulating effect. . In addition, from the viewpoint of being able to disperse talc well without adding a large amount of dispersant, the average particle diameter of talc is preferably 2 μm or more, more preferably 3 μm or more, and 5 μm or more. It is more preferable that

The above average particle diameter can be measured by a laser diffraction scattering method. Specifically, the average particle diameter means a particle diameter (D ₅₀ ) corresponding to 50% of the cumulative volume in a volume-based particle size distribution measured by a laser diffraction scattering method. Note that the above-mentioned average particle diameter means the diameter of a virtual sphere having the same volume as the volume of particles corresponding to 50% of the above-mentioned cumulative volume.

(Amount of inorganic powder)
When blending inorganic powder into the foamable resin melt, the amount of the inorganic powder blended is preferably 0.2 parts by mass or less based on 100 parts by mass of the polystyrene resin. If the amount of inorganic powder is too large, there is a risk of contamination of heating wires during the production of molded products and a risk of impairing the stability of the quality of foam sheets made using the foam sheets as recycled raw materials.

When blending inorganic powder into a foamable resin melt, it is important to improve the stabilizing effect on the quality of foamed sheets that are used as recycled raw materials, and to further suppress heating wire contamination during the production of molded products. The blending amount of the inorganic powder is preferably 0.15 parts by mass or less, more preferably 0.12 parts by mass or less, and 0.10 parts by mass based on 100 parts by mass of the polystyrene resin. It is more preferable that the amount is less than 1 part.

In addition, when blending inorganic powder into a foamable resin melt, from the perspective of increasing the effect of the inorganic powder (facilitating the control of the foaming ratio (facilitating the control of the cell diameter)), which will be described later, The blending amount of the inorganic powder is preferably 0.02 parts by mass or more, preferably 0.03 parts by mass or more, and 0.05 parts by mass or more with respect to 100 parts by mass of the polystyrene resin. It is even more preferable that there be. Note that the amount of inorganic powder contained in the foam sheet usually corresponds to the amount of inorganic powder added at the time of manufacturing the foam sheet.

(Combustion residue of foam sheet)
From the perspective of increasing the stabilizing effect on the quality of foam sheets using foam sheets as recycled raw materials, the proportion of combustion residue when the foam sheets are combusted must be 0.2% by mass or less (including 0). is preferred. Note that the combustion residue is a component mainly derived from inorganic powder. From the viewpoint of further enhancing this effect, the proportion of combustion residue when the foam sheet is burned is preferably 0.15% by mass or less, more preferably 0.12% by mass or less, and 0.15% by mass or less, more preferably 0.12% by mass or less. More preferably, it is 10% by mass or less.

The proportion of combustion residue can be determined from the mass of combustion residue of the foam sheet measured as follows. A crucible containing a predetermined amount (for example, 5 g) of the foam sheet is heated for 1 hour in an electric furnace with an ambient temperature of 600°C. After heating, the mass of the residue (combustion residue) remaining in the crucible is measured. By dividing the mass of the measured combustion residue by the mass of the foam sheet used in the measurement and expressing it as a percentage, the proportion of combustion residue when the foam sheet is combusted can be determined. In addition, in the measurement, a test piece may be prepared by cutting the foam sheet so that a predetermined amount of the foam sheet enters the crucible, and the measurement may be performed using this test piece.

(Effect when using nitrogen and inorganic powder together in foamable resin melt)
When manufacturing a foamed sheet having a desired expansion ratio and cell diameter, it is preferable to strictly control the amount of nitrogen added in order to exhibit the function of a cell regulator using only nitrogen. In this regard, if the foamable resin melt contains inorganic powder to an extent that does not significantly impair the effects of the present invention, a state in which nitrogen and inorganic powder are used together as components that perform the function of a cell regulator. Therefore, it is possible to improve the controllability of the amount of nitrogen added in order to obtain a desired foamed sheet. The reason for this is that the expansion ratio increases more slowly with an increase in the amount of inorganic powder blended than the expansion ratio with an increase in the amount of nitrogen added. . Therefore, it is easier to produce a foamed sheet by controlling the expansion ratio by adjusting the amount of inorganic powder added than by controlling the expansion ratio by adjusting the amount of nitrogen added. For example, when obtaining a foam sheet with an expansion ratio of about 12 times, nitrogen is added at the time of production so that the foam sheet can be produced with an expansion ratio of 11 to 12 times, and the amount of inorganic powder blended is By adjusting the foaming ratio to be about 12 times, it is possible to stably obtain a foam sheet having a foaming ratio of about 12 times. Therefore, when the foamable resin melt contains inorganic powder within a predetermined range, the expansion ratio and cell diameter of the foam sheet can be controlled while suppressing the possibility that the inorganic powder will significantly impair the effects of the present invention. This allows for easier adjustment.

[1-4 About dispersant]
In the production method of the present invention, the foamable resin melt does not need to contain a dispersant, but may contain a dispersant within a predetermined amount. As mentioned above, the dispersant is usually included together with the inorganic powder when the foamable resin melt contains the inorganic powder.

(dispersant)
The dispersant has a function of increasing the dispersibility of the inorganic powder when the polystyrene resin and the inorganic powder are kneaded to form a state in which the inorganic powder is dispersed in the resin. Dispersants include fatty acid metal salts. Examples of fatty acid metal salts include salts of fatty acids (higher fatty acids) having 12 to 30 carbon atoms and metals, and more specifically, metal stearates, metal laurates, metal palmitates. Examples include: Furthermore, examples of metals constituting the fatty acid metal salt include zinc, magnesium, calcium, barium, and aluminum. When the dispersant contains a fatty acid metal salt, the proportion of the fatty acid metal salt in the dispersant is preferably 50% by mass or more, preferably 60% by mass or more, and more preferably 80% by mass or more. , 90% by mass or more is particularly preferred.

(Amount of dispersant)
The amount of the dispersant (fatty acid metal salt) contained in the foamable resin melt is preferably 0.02 parts by mass or less (including 0) per 100 parts by mass of the polystyrene resin. By setting the blending amount of the dispersant within the above range, it is possible to manufacture a foamed sheet having a desired expansion ratio and cell diameter, and when manufacturing a foamed sheet using recycled raw materials derived from the foamed sheet, It is possible to more stably suppress yellowing of the foam sheet. From this point of view, when the foamable resin melt contains a dispersant, the amount of the dispersant blended is preferably 0.015 parts by mass or less, and 0.012 parts by mass, based on 100 parts by mass of the polystyrene resin. It is preferably at most 0.010 parts by mass, even more preferably at most 0.008 parts by mass. In addition, from the viewpoint of further suppressing yellowing of the resulting foamed sheet, it is particularly preferable that the foamable resin melt does not contain a dispersant (that is, the amount of dispersant blended is 0). In addition, from the same viewpoint as above, the foamed sheet obtained also does not contain a dispersant (fatty acid metal salt), or contains the dispersant (fatty acid metal salt) and has a combination of the dispersant. It is preferred that the amount is 0.02% by mass or less. Further, when the foam sheet contains the dispersant, the amount of the dispersant is preferably 0.015% by mass or less, preferably 0.012% by mass or less, and 0.010% by mass or less. It is more preferable that the amount is 0.008% by mass or less, and even more preferably 0.008% by mass or less. Note that the amount of dispersant contained in the foam sheet roughly corresponds to the amount of dispersant added at the time of manufacturing the foam sheet.

[2 Foam sheet]
The foamed sheet according to the present invention is obtained by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, and has an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less. The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether whose alkyl group has 1 to 3 carbon atoms, and nitrogen. This foam sheet preferably has an average cell diameter of 0.08 mm or more and 0.5 mm or less. The foam sheet according to the present invention is a polystyrene resin foam sheet manufactured using the method described in [1. Method for manufacturing foam sheet] above. Therefore, regarding the foamed sheet according to the present invention, the respective components such as the polystyrene resin and the physical foaming agent are the same as those described in [1. Method for manufacturing a foamed sheet] above, so explanations thereof will be omitted.

As mentioned above, the foam sheet may not contain any residual components, but it may also contain some residual components. Further, in the foamed sheet according to the present invention, the proportion of combustion residue when the foamed sheet is burned is preferably 0.2% by mass or less (including 0). In the foamed sheet according to the present invention, when the foamed sheet contains a fatty acid metal salt as a dispersant, the amount of fatty acid metal salt blended in the foamed sheet is preferably 0.02% by mass or less.

According to the foam sheet according to the present invention, it is possible to suppress the possibility that yellowing occurs in a foam sheet using the foam sheet according to the present invention as a recycled raw material. According to the foam sheet according to the present invention, it is possible to stabilize the quality of the foam sheet using the foam sheet as a recycled raw material. Moreover, according to the foamed sheet according to the present invention, it is possible to suppress a decrease in the cutting function of the heating wire used in the process of manufacturing a molded product using the foamed sheet according to the present invention.

[3 Method for manufacturing foam sheets using recycled raw materials derived from foam sheets]
Next, a method for manufacturing a foam sheet using recycled materials derived from foam sheets (hereinafter sometimes referred to as a method for manufacturing a foam sheet containing recycled materials) will be described.

The method for producing a foamed sheet containing recycled raw materials is a method of producing a foamed sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin containing recycled raw materials and a physical foaming agent. The extrusion foaming method as explained in [Manufacturing method] can be suitably employed.

The method for producing a foam sheet containing recycled raw materials is the same as that shown in [1 Method for producing a foam sheet], except that the polystyrene resin contains recycled raw materials and the foam sheet to be manufactured is a foam sheet containing recycled raw materials. Since physical blowing agents (hydrocarbons, diethyl ether, nitrogen), etc. may be used, descriptions of physical blowing agents (hydrocarbons, diethyl ether, nitrogen), etc. will be omitted. In addition, each step of extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent is the same as that described in [1. Method for manufacturing a foamed sheet], so the explanation will be omitted. .

(Polystyrene resin)
Polystyrene resin contains recycled raw materials. The polystyrene resin may be a mixture of recycled raw materials and non-recycled raw materials (non-recycled raw materials), or may be composed entirely of recycled raw materials. From the viewpoint of enabling efficient recycling through the use of recycled raw materials, the proportion of recycled raw materials in the polystyrene resin is preferably 5% or more, more preferably 10% or more, and 20% or more. It is more preferable that it is, and even more preferable that it is 30% or more. In addition, from the viewpoint of increasing the production stability of foam sheets, the proportion of recycled raw materials in the polystyrene resin is preferably 80% or less, more preferably 70% or less, and 60% or less. is more preferable, and even more preferably 50% or less. The non-recycled raw material is the same as the polystyrene resin explained in [1. Method for manufacturing foamed sheet], so the explanation will be omitted.

(Recycled raw materials)
Recycled raw materials are raw materials derived from foam sheets. Specifically, recycled raw materials include foamed sheets produced by the foamed sheet production method of the present invention, offcuts generated during the production of these foamed sheets, offcuts generated during thermoforming of these foamed sheets, etc. Indicates raw materials manufactured from these materials.

(Production method of recycled raw materials)
For recycled raw materials, for example, materials such as scraps of foam sheets are supplied to an extruder, the materials are melted and kneaded inside the extruder to form a resin melt, and then the resin melt is extruded from the extruder to form a predetermined amount. Manufactured by pelletizing into shapes. However, this is an example of a method for producing recycled raw materials, and the method for producing recycled raw materials is not limited to this method.

(Foam sheet containing recycled materials)
According to the method for producing a foamed sheet containing recycled raw materials, a foamed sheet having an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less can be obtained as a polystyrene resin foamed sheet. Descriptions regarding various physical properties such as the apparent density of the polystyrene resin foam sheet obtained by the method for producing a foam sheet containing recycled raw materials are the same as those for the foam sheet obtained by [1. Method for producing a foam sheet], so the explanation will be omitted.

(action and effect)
According to the method for producing a foam sheet containing recycled raw materials, the foam sheet is produced using recycled raw materials derived from the foam sheet obtained by the method for producing a foam sheet according to the present invention. As explained in [Method], it is possible to obtain a foam sheet in which the occurrence of yellowing is suppressed, and the quality of the foam sheet using recycled raw materials can be easily stabilized.

Next, the explanation will be continued using examples.

(Polystyrene resin and physical foaming agent)
General polystyrene (trade name GX154) manufactured by PS Japan Co., Ltd. (density 1050 kg/m ³ , MFR 1.6 g/10 minutes, glass transition temperature 122° C.) was prepared as a polystyrene resin. Isobutane, dimethyl ether, and nitrogen were prepared as physical blowing agents.

(Bubble regulator)
A masterbatch containing an inorganic powder and a dispersant was prepared as a foam regulator (in Table 1, for convenience, it was written as a foam regulator). This masterbatch uses polystyrene resin as a base resin, and contains 40% by mass of inorganic powder and 2.5% by mass of a dispersant. Further, the inorganic powder is talc (particle size (D ₅₀ ) 7.5 μm), and the dispersant is magnesium stearate. The particle size of talc is determined by measuring the volume-based particle size distribution by laser analysis diffraction scattering method using a laser diffraction particle size distribution measuring device SALD-2100 manufactured by Shimadzu Corporation, and is equivalent to 50% of the cumulative volume. It was calculated by determining the particle diameter (D ₅₀ ).

Among the Examples and Comparative Examples described later, in the Examples (Examples 3, 4, 6, and 8, Comparative Example 5) in which the foamable resin melt contains an inorganic powder and a dispersant, foaming was performed using the above masterbatch. A state was formed in which the inorganic powder and the dispersant were added to the resin melt.

(Manufacturing equipment)
A manufacturing device for manufacturing foam sheets was prepared. The manufacturing equipment consists of two extruders: a first extruder (65 mm in diameter) and a second extruder (90 mm in diameter) (however, the upstream extruder is called the first extruder, and the downstream extruder is called the second extruder. A tandem extruder (referred to as an extruder) is connected in series, an annular die (outlet diameter 60 mm) installed on the discharge port side of the second extruder, and a cooling device installed downstream of the annular die. It was equipped with a mandrel (diameter 212 mm), a cutter for cutting open the cylindrical foam cooled by the mandrel, and a winder for winding up the foam sheet cut open by the cutter.

Examples 1, 2, 5, 7 and 9
For each of Examples 1, 2, 5, 7, and 9, the polystyrene resin was supplied to the first extruder and heated and kneaded at about 220°C. Furthermore, for each of Examples 1, 2, 5, 7, and 9, a physical blowing agent was injected into the molten resin of the first extruder in the amount shown in Table 1. Regarding the timing of injecting the physical blowing agent, nitrogen (nitrogen gas) was injected at the same time as the physical blowing agent other than nitrogen (isobutane and/or dimethyl ether). In Table 1, the amount of physical foaming agent added (mol/kg) indicates the amount (mol) of the physical foaming agent added per 1 kg of the foamable resin melt. In addition, in Table 1, physical foaming agents other than nitrogen (isobutane and/or dimethyl ether) among the physical foaming agents are designated as A, nitrogen is designated as B, and the total amount of the addition amount of A and the addition amount of B is entered in the total amount column. The ratio of the amount of B added when the amount of A added is 1 is shown in the B/A column.

The molten resin containing the physical blowing agent formed by the first extruder was transferred from the first extruder to a second extruder connected downstream of the first extruder. Then, the temperature of the molten resin was adjusted to about 159° C. using the second extruder. A foamable resin melt was thus formed.

The foamable resin melt from the second extruder was extruded under atmospheric pressure from the annular die of the second extruder under conditions such that the discharge amount per hour was 50 kg (50 kg/h). This formed a cylindrical foam. Furthermore, while the extruded cylindrical foam is placed along the outer surface of the mandrel, the blowing ratio is set to 3.5, and the take-up speed (for example, the winding speed with a winding machine) is adjusted so that the basis weight is approximately as shown in Table 2. I took it while adjusting it. A foam sheet with a sheet width of about 670 mm was manufactured by cutting the cylindrical foam with a cutter along the extrusion direction as the cylindrical foam moved as it was taken off. Note that the foamed sheet was wound up into a roll using a winding machine.

The thickness, basis weight, apparent density, and closed cell ratio of the obtained foamed sheet were measured. In addition, the proportion of combustion residue when the foam sheet was burned was measured. The methods described above were used for each measurement. The results are shown in Table 2.

In addition, the measurement of combustion residue was specifically performed as follows. As the electric furnace, Muffle Furnace MF28 manufactured by Yamato Kagaku was used. Further, as a test piece for measurement, about 5 g worth of foamed sheet was taken, its mass was measured, and it was cut to fit into the crucible.
The cut foam sheet was placed in a ceramic crucible, and the crucible containing the foam sheet was heated for 1 hour in an electric furnace with an ambient temperature of 600°C. After heating, the mass of the crucible containing the residue (combustion residue) was measured, and the mass of the combustion residue was measured by subtracting the mass of the crucible from this mass. The mass of the measured combustion residue was divided by the mass of the foam sheet used for measurement, and the result was expressed as a percentage to determine the proportion of combustion residue when the foam sheet was burned.

In addition, for the foam sheet, the average cell diameter in the extrusion direction (MD) of the foam sheet, the average cell diameter in the width direction (TD) of the foam sheet, and the average cell diameter in the thickness direction (VD) of the foam sheet were measured. The average cell diameter of the foam sheet was calculated based on the average cell diameter of MD, the average cell diameter of TD, and the average cell diameter of VD. The results are shown in Table 2. In Table 2, the average cell diameter of MD, the average cell diameter of TD, the average cell diameter of VD, and the average cell diameter of the foamed sheet are respectively listed in the MD column, TD column, VD column, and average column in the average cell diameter column. ing.

Further, using the obtained foamed sheet, a yellowing degree test and a heating wire contamination degree test were conducted. The results are shown in Table 2.

(yellowing test)
The yellowing degree test is a test for evaluating the degree of yellowing of the recycled raw material when the obtained foamed sheet is used to produce the recycled raw material.

The yellowing test was conducted as follows. A recycled raw material was produced by melting the foamed sheet obtained in the example using an extruder for producing recycled raw materials and repelletizing it. In re-pelletizing a foam sheet, first, the obtained foam sheet is crushed into a size that can be fed to an extruder, and the crushed material is fed to a single screw extruder with an inner diameter of 65 mm, and is heated at a maximum temperature of 230 ° C. A molten resin was formed by melt-kneading. Next, the molten resin was extruded into a strand from an extruder at a discharge rate of 20 kg/hr, and the extruded resin was cut into pellets to produce a recycled raw material. Next, the recycled raw material was hot pressed to produce a test piece (solid sheet) with a thickness of 1 mm.

Regarding the prepared test piece, L ^* a ^* b ^* (color space) was determined using a spectrocolor difference meter (Nippon Denshoku: Spectro Color Meter SE2000).

(Evaluation of yellowing inhibition)
The ability to suppress yellowing was evaluated based on the b ^* value obtained in the yellowing test. Note that the value of b ^* means the color in the yellow direction, and the larger the value of b ^* , the more yellowing has occurred. Furthermore, if the recycled raw material is prone to yellowing, the foam sheet obtained using the recycled raw material is also likely to yellow.

From the viewpoint of the obtained foam sheet becoming a recycled raw material that can further suppress yellowing, the value of b ^* is preferably 3.6 or less, more preferably 3.4 or less, and 3. More preferably, it is .0 or less. Each Example (Examples 1 to 9) had a smaller b ^* value than Comparative Example 5, and all satisfied 3.6 or less.

(Heating wire contamination level test)
The heating wire contamination level test was conducted as follows. A laminate was formed by stacking 50 of the obtained foam sheets, and the laminate was subjected to cutting treatment over the entire width of the foam sheet. The cutting process was carried out by cutting the laminate in the thickness direction using a heating wire (nichrome wire) that generated heat through electricity.

(Evaluation of suppression of heating wire pollution)
The ability to suppress heating wire contamination was evaluated by observing whether inorganic powder was observed to adhere to the heating wire after cutting. The heating wire contamination degree was evaluated as follows.

〇 (Good): No inorganic powder adhesion was observed on the heating wire.
× (Poor): Adhesion of inorganic powder was observed on the heating wire.

Comparative examples 1 to 4
For each of Comparative Examples 1 to 4, the same method as Example 1 was carried out. However, the physical blowing agent was press-fitted into the first extruder in an amount shown in each column of Comparative Examples 1 to 4 in Table 1.

Regarding Comparative Examples 1 and 2, a cell structure was not formed in the polyethylene resin (no foamed state was formed) when extruded from the manufacturing equipment, and a foamed sheet could not be obtained. Therefore, the thickness, basis weight, apparent density, closed cell ratio, and average cell diameter of the foam sheet were not measured. In addition, a yellowing test and a heating wire contamination test were not conducted.

Regarding Comparative Examples 3 and 4, the bubbles formed in the polyethylene resin became too fine when extruded from the manufacturing equipment, making it impossible to take off the foam sheet, and as a result, it was not possible to obtain a foam sheet. . Therefore, the thickness, basis weight, apparent density, closed cell ratio, and average cell diameter of the foam sheet were not measured. In addition, a yellowing test and a heating wire contamination test were not conducted.

Examples 3, 4, 6 and 8, Comparative Example 5
For each of Examples 3, 4, 6, and 8, and Comparative Example 5, instead of supplying polystyrene resin to the first extruder, a master containing polystyrene resin, inorganic powder, and a dispersant was used. A foamed sheet was obtained using the same method as in Example 1, except that the batch was fed to the first extruder. In Table 1, the amounts of the inorganic powder and the dispersant correspond to the amounts (parts by mass) of the inorganic powder and the dispersant mixed per 100 parts by mass of the polystyrene resin.

The thickness, basis weight, apparent density, and closed cell ratio of the obtained foamed sheet were measured using the same method as in Example 1. Further, in the same manner as in Example 1, the proportion of combustion residue when the foam sheet was burned was measured. Regarding the foam sheet, the average cell diameter in the extrusion direction (MD) of the foam sheet, the average cell diameter in the width direction (TD) of the foam sheet, and the average cell diameter in the thickness direction (VD) of the foam sheet were determined using the same method as in Example 1. The average cell diameter was measured and the average cell diameter of the foamed sheet was calculated. The results are shown in Table 2.

Further, using the obtained foamed sheet, a yellowing degree test and a heating wire contamination degree test were conducted using the same method and evaluation criteria as in Example 1. The results are shown in Table 2.

The manufacturing method and examples of the present invention described above are merely examples, and the present invention is not limited thereto.

Although the present invention has been described, the present invention can have the following configuration.
(A1)
A method for manufacturing a foam sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, the method comprising:
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The total amount of the hydrocarbon and/or dialkyl ether added and the amount of nitrogen added is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamable resin melt,
The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per kg of the foamable resin melt, and
characterized in that the ratio of the added amount of nitrogen to the added amount of the hydrocarbon and/or the dialkyl ether is 0.03 or more and 0.4 or less,
Method for manufacturing foam sheets.
(A2)
The foamable resin melt does not contain the inorganic powder, or the foamable resin melt contains the inorganic powder, and the amount of the inorganic powder is 0 based on 100 parts by mass of the polystyrene resin. .2 parts by mass or less;
The method for producing a foam sheet according to (A1) above.
(A3)
The foamable resin melt does not contain a fatty acid metal salt, or the foamable resin melt contains the fatty acid metal salt, and the amount of the fatty acid metal salt is 0.00 parts by mass based on 100 parts by mass of the polystyrene resin. 02 parts by mass or less,
The method for producing a foam sheet according to (A1) or (A2) above.
(A4)
The method for producing a foamed sheet according to any one of (A1) to (A3) above, wherein the foamed sheet has an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less.
(A5)
The foam sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less,
The method for producing a foam sheet according to any one of (A1) to (A4) above.
(A6)
A foamable resin obtained by kneading a polystyrene resin containing recycled raw materials derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of (A1) to (A5) above and a physical foaming agent. A method of manufacturing foam sheets by extruding and foaming a molten material.
(A7)
A foamed sheet made by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, and having an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less,
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The foam sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less,
The proportion of combustion residue when the foam sheet is combusted is 0.2% by mass or less (including 0);
foam sheet.
(A8)
Does not contain a fatty acid metal salt, or contains the fatty acid metal salt, and the amount of the fatty acid metal salt is 0.02% by mass or less,
The foam sheet described in (A7) above.
(A9)
The thickness of the foam sheet is 1 mm or more and 3 mm or less,
The foam sheet described in (A7) or (A8) above.
(A10)
The basis weight of the foam sheet is 80 g/m ² or more and 400 g/m ² or less,
The foam sheet according to any one of (A7) to (A9) above.

Claims (8)

A method for manufacturing a foam sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, the method comprising:
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The total amount of the hydrocarbon and/or dialkyl ether added and the amount of nitrogen added is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamable resin melt,
The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per kg of the foamable resin melt, and
characterized in that the ratio of the added amount of nitrogen to the added amount of the hydrocarbon and/or the dialkyl ether is 0.03 or more and 0.4 or less,
Method for manufacturing foam sheets. The foamable resin melt does not contain the inorganic powder, or the foamable resin melt contains the inorganic powder, and the amount of the inorganic powder is based on 100 parts by mass of the polystyrene resin. It is 0.2 part by mass or less,
The method for manufacturing a foam sheet according to claim 1. The foamable resin melt does not contain the fatty acid metal salt, or the foamable resin melt contains the fatty acid metal salt, and the amount of the fatty acid metal salt is based on 100 parts by mass of the polystyrene resin. It is 0.02 part by mass or less,
The method for manufacturing a foam sheet according to claim 1 or 2. The method for producing a foamed sheet according to any one of claims 1 to 3, wherein the foamed sheet has an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less. The foam sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less,
The method for manufacturing a foam sheet according to any one of claims 1 to 4. A foamable resin melt obtained by kneading a polystyrene resin containing recycled raw materials derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of claims 1 to 5 and a physical foaming agent. A method of manufacturing foam sheets by extrusion foaming. A foamed sheet made by extruding and foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, and having an apparent density of 40 kg/m ³ or more and 200 kg/m ³ or less,
The physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and/or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen,
The foam sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less,
The proportion of combustion residue when the foam sheet is combusted is 0.2% by mass or less (including 0);
foam sheet. Does not contain a fatty acid metal salt, or contains the fatty acid metal salt, and the amount of the fatty acid metal salt is 0.02% by mass or less,
The foam sheet according to claim 7.