JP5474457B2 - Mandrel for manufacturing foam sheet, thermoplastic resin foam sheet manufacturing apparatus, and thermoplastic resin foam sheet manufacturing method - Google Patents

Description

  The present invention relates to a mandrel for a foamed sheet manufacturing apparatus (hereinafter abbreviated as a mandrel), a thermoplastic resin foamed sheet manufacturing apparatus, and a thermoplastic resin foamed sheet such as a polyethylene resin foamed sheet and a polypropylene resin foamed sheet. The present invention relates to a method for producing a thermoplastic resin foam sheet, and more particularly, to a technique in which the width of the foam sheet can be easily changed, and the production efficiency and the loss of resin used can be improved due to the sheet width change.

  Thermoplastic resin foam sheets, such as polyethylene resin foam sheets and polypropylene resin foam sheets, are lightweight, flexible, buffer-rich, inexpensive, more hydrophobic, hygienic, It has various advantages such as excellent heat insulation and heat insulation properties, and is widely used, for example, as a cushioning packing material.

  As one of the methods for producing these thermoplastic resin foam sheets, an extrusion foam molding method is applied. The extrusion foam molding method will be briefly described. In this method, a thermoplastic resin is melted and mixed with a foaming agent in an extruder, and the molten mixture is attached to a tip portion of the extruder and is a die composed of an outer ring and a core. The outer peripheral surface of a cooled cylindrical mandrel (also called a plug, a cooling plug, etc.) is extruded through an annular gap formed by the outer ring and the core into an external low-pressure region. The foamed intermediate is passed along, and the foamed intermediate is stretched to form a cylindrical foam, and the foam is cut open with a cutter to obtain a foamed sheet.

The thermoplastic resin foam sheet thus obtained is cut in the width and length directions and used as a single packing material sheet for cushioning.
The cut width and length are arbitrarily set according to the dimensions of the package, but the foam sheet roll has several types of product rolls, and the product with the smallest sheet width among them. A roll is used.

For example, Patent Documents 1 and 2 have been proposed as conventional techniques of the extrusion foam molding method and mandrels used therein.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-36337) discloses a sheet-like foam formed of a non-crosslinked polyethylene resin, and the maximum wave height of the sheet is 1 to 10 mm and the wave number. 10/200 mm or less, the center line average roughness Ra of the foam surface is 9.0 μm or more, the average cell diameter is 0.2 to 2.5 mm, the density is 0.015 to 0.05 g / cm ³ , and A non-crosslinked polyethylene resin foam characterized by a thickness of 0.7 to 20 mm; a non-crosslinked polyethylene resin and a foaming agent are supplied to an extruder, melt-kneaded, and then cylindrical through a circular die A method of producing a non-crosslinked polyethylene resin foam by extruding and foaming, and taking this cylindrical foam along the outer periphery of an annular mandrel, and having a diameter Cφ (mm) of a circular die The ratio Mφ / Cφ to the outer diameter Mφ (mm) of the mandrel is in the range of 2.5 to 3.5, the resin extrusion rate Ex (kg / hour) per unit time, and the diameter Cφ (mm) of the circular die. The ratio Ex / Cφ in the range of 0.7 to 2.1, and the shear rate of extrusion in the die portion of the circular die is set to 500 to 5000 / sec. A manufacturing method is disclosed.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-246849) discloses an extruder that melts and mixes a thermoplastic resin and a foaming agent to extrude a molten mixture, a die attached to a discharge port of the extruder, and a die. A sheet contact surface in a plug used in a thermoplastic foam sheet manufacturing apparatus comprising a plug (mandrel) that cools an extruded foam intermediate body along an outer peripheral surface to produce a thermoplastic resin foam sheet A plug characterized in that a fluororesin coating layer is provided on the outer surface of the plug, and the arithmetic average roughness Ra of the fluororesin coating layer is in the range of 0.5 μm to 4 μm; heat melted and mixed in the extruder A molten mixture of the plastic resin and the foaming agent is extruded from a die attached to the extruder into a low pressure region and foamed, and the foamed intermediate obtained by the foaming is removed from the plug. In a method for producing a thermoplastic resin foam sheet, which is cooled while proceeding according to an aspect to produce a thermoplastic resin foam sheet, a production method using the plug is disclosed.

JP 2002-36337 A JP 2005-246849 A

In the above-described prior art, the foam sheet is moved along the outer peripheral surface of the mandrel, and the mandrel outer peripheral surface and the foam sheet are brought into contact with each other for cooling. The sheet width of the obtained thermoplastic resin foam sheet is equal to the diameter of the mandrel. Determined by size. For this reason, when changing the sheet width, it is necessary to change the sheet width by replacing with another mandrel having an outer diameter corresponding to the target sheet width.
When changing the mandrel, it is necessary to stop the extruder or replace the mandrel with another mandrel while removing the extruded resin. Therefore, mandrels having different outer diameters depending on the type of sheet width are required, and there is a problem that production efficiency deteriorates due to time loss, loss of resin used, etc. when changing the sheet width.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a mandrel capable of easily changing the sheet width without replacing the entire mandrel, and a thermoplastic resin foam sheet manufacturing apparatus and manufacturing method using the mandrel.

In order to achieve the above object, the present invention is obtained by foaming a molten mixture of a resin and a foaming agent melt-mixed in an extruder through a die attached to the extruder into a low-pressure region and foaming. In the mandrel for producing the thermoplastic resin foam sheet by stretching the foam intermediate along the outer surface of the mandrel,
Provided is a mandrel characterized in that a plurality of movable pieces that move forward and backward along the radial direction of the mandrel by a driving means are provided with an outer diameter varying portion that is provided continuously along the circumferential direction of the mandrel. To do.

  In the mandrel of the present invention, the mandrel is provided with at least front, middle and rear regions in order from the upstream side to the downstream side in the flow direction of the foam sheet, and the middle part has an inner surface side of the foam intermediate. Preferably, gas supply means for blowing gas is provided, and the outer diameter varying portion is provided in one or both of the front portion and the rear portion.

  In the mandrel of the present invention, the outer diameter varying portion is provided with a flexible sheet that expands so as to fill a gap between adjacent movable pieces when the movable piece moves outward along the radial direction. It is preferable.

  In the mandrel of the present invention, the movable piece may have a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction.

Further, the present invention is obtained by the above-mentioned foaming, an extruder that melt-mixes the melt-mixed resin and the foaming agent, a die that is attached to the extruder and extrudes the molten mixture in the extruder into a low-pressure region and foams. In the thermoplastic resin foam sheet manufacturing apparatus having a mandrel that cools the foamed intermediate while being stretched and cools to produce a thermoplastic resin foam sheet,
A thermoplastic resin foam sheet manufacturing apparatus characterized by using the mandrel according to the present invention as a mandrel is provided.

Further, the present invention provides a foamed intermediate product obtained by foaming by extruding a molten mixture of a resin and a foaming agent melt-mixed in an extruder through a die attached to the extruder into a low-pressure region. In the thermoplastic resin foam sheet manufacturing method of manufacturing a thermoplastic resin foam sheet by stretching along the outer surface of
Provided is a method for producing a thermoplastic resin foam sheet, wherein the mandrel according to the present invention is used as a mandrel.

  In the thermoplastic resin foam sheet manufacturing method of the present invention, when changing the sheet width of the thermoplastic resin foam sheet, each movable piece is moved along the radial direction by the driving means of the outer diameter varying portion, and the outer surface of each movable piece It is preferable to produce a thermoplastic foam sheet having a changed sheet width by changing the maximum outer diameter of the mandrel formed by connecting the two.

  In the method for producing a thermoplastic resin foam sheet according to the present invention, the thermoplastic resin foam sheet to be produced is preferably a polyethylene resin foam sheet or a polypropylene resin foam sheet.

In the method for producing a thermoplastic resin foam sheet of the present invention, the density of the thermoplastic resin foam sheet to be produced is preferably in the range of 0.015 to 0.060 g / cm ³ .

  In the method for producing a thermoplastic resin foam sheet of the present invention, it is preferable to produce a thermoplastic resin foam sheet by stretching a foamed intermediate body along the outer surface of the mandrel while jetting gas from the middle gas supply means.

The mandrel of the present invention has a configuration in which a plurality of movable pieces that move forward and backward along the radial direction of the mandrel by a driving means are provided with an outer diameter varying portion that is continuously provided along the circumferential direction of the mandrel. Therefore, when producing a thermoplastic resin foam sheet using this mandrel, when trying to change the sheet width of the foam sheet, the driving means is driven to increase the maximum outer diameter of the outer diameter variation portion, By changing according to the sheet width of the foam sheet to be manufactured, a foam sheet having a target sheet width can be continuously manufactured. Therefore, according to the mandrel of the present invention, when changing the sheet width, the sheet width can be changed without exchanging the mandrel, thereby preventing a decrease in manufacturing efficiency due to continuous production stoppage and replacement work associated with mandrel replacement. In addition, it is possible to eliminate the loss of the resin extruded at the time of replacement, and it is possible to improve the manufacturing efficiency and the resin yield.
Further, at least front, middle and rear regions are sequentially provided from the upstream side to the downstream side in the foam sheet flow direction, gas supply means for blowing gas on the inner surface side of the foam intermediate is provided in the middle portion, and With the configuration in which the outer diameter varying portion is provided in one or both of the front part and the rear part, the foam intermediate is stretched along the outer surface of the mandrel while jetting gas from the gas supply means in the middle part of the mandrel. In the production of a flexible thermoplastic resin foam sheet, the contact between the sheet and the mandrel can be reduced, and a flexible thermoplastic resin foam sheet can be stably and continuously produced without breaking. .
Further, the outer diameter varying portion is provided with a flexible sheet that swells so as to fill a gap between adjacent movable pieces when the movable piece moves outward along the radial direction. Thus, in the diameter-expanded state in which each movable piece is moved outward along the radial direction, the gap between the movable pieces is filled with the flexible sheet, and the outer surface of the outer diameter varying portion is uneven. Thus, it is possible to prevent the occurrence of problems such as the foamed intermediate body being caught by the unevenness and rupturing, or the frictional resistance being increased and being stopped.
In addition, if the movable piece is provided with a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction, the foam intermediate is expanded in the process of extending the foam intermediate to the maximum diameter. Since the diameter gradually increases while contacting the movable piece, continuous production can be performed more stably without breaking the foamed sheet.

Since the thermoplastic resin foam sheet manufacturing apparatus of the present invention has the mandrel according to the present invention described above, the sheet width can be changed without replacing the mandrel when the sheet width is changed. It is possible to prevent a decrease in manufacturing efficiency due to continuous production stop and replacement work, etc., and it is possible to eliminate a loss of resin pushed out at the time of replacement, thereby improving manufacturing efficiency and resin yield.
Further, at least front, middle and rear regions are sequentially provided from the upstream side to the downstream side in the foam sheet flow direction, and a gas supply means for blowing gas to the inner surface side of the foam intermediate is provided in the middle portion. When using the mandrel provided with the outer diameter variation part in one or both of the rear part and the rear part, the foam intermediate is stretched along the outer surface of the mandrel while jetting gas from the gas supply means in the middle part of the mandrel In the production of a flexible thermoplastic resin foam sheet, the contact between the sheet and the mandrel can be reduced, and the flexible thermoplastic resin foam sheet can be stably and continuously produced without breaking.
Further, a mandrel provided with a flexible sheet that swells so as to fill a gap between adjacent movable pieces when the movable piece moves outward along the radial direction is used in the outer diameter varying portion. In this case, in the expanded diameter state in which each movable piece is moved outward along the radial direction, the gap between the movable pieces is filled with the flexible sheet, and the outer surface of the outer diameter varying portion is uneven. Thus, it is possible to prevent the occurrence of problems such as the foamed intermediate body being caught by the concavities and convexities and being broken, or the frictional resistance increasing and stopping.
Further, in the case where a mandrel provided with a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction is used as the movable piece, in the process of extending the foam intermediate to the maximum diameter, Since the diameter of the foamed intermediate body is gradually increased while contacting the movable piece, continuous production can be performed more stably without breaking the foamed sheet.
Further, since it is not necessary to change the mandrel accompanying the change in the sheet width, the equipment cost can be reduced compared to the case where a plurality of mandrels are prepared.

The thermoplastic resin foam sheet manufacturing method of the present invention uses the mandrel according to the present invention described above, and when changing the sheet width of the thermoplastic resin foam sheet, each movable piece is moved in the radial direction by the driving means of the outer diameter varying portion. The maximum outer diameter of the mandrel formed by connecting the outer surfaces of each movable piece is changed to produce a thermoplastic foam sheet with a changed sheet width, so when changing the sheet width, the mandrel The width of the sheet can be changed without exchanging the sheet, the production efficiency can be prevented from being reduced due to the continuous production stoppage and exchange work associated with the mandrel exchange, and the loss of the resin extruded during the exchange can be eliminated. Manufacturing efficiency and resin yield can be improved.
Further, at least front, middle and rear regions are sequentially provided from the upstream side to the downstream side in the foam sheet flow direction, and a gas supply means for blowing gas to the inner surface side of the foam intermediate is provided in the middle portion. When using the mandrel provided with the outer diameter variation part in one or both of the rear part and the rear part, the foam intermediate is stretched along the outer surface of the mandrel while jetting gas from the gas supply means in the middle part of the mandrel In the production of a flexible thermoplastic resin foam sheet, the contact between the sheet and the mandrel can be reduced, and the flexible thermoplastic resin foam sheet can be stably and continuously produced without breaking.
Further, a mandrel provided with a flexible sheet that swells so as to fill a gap between adjacent movable pieces when the movable piece moves outward along the radial direction is used in the outer diameter varying portion. In this case, in the expanded diameter state in which each movable piece is moved outward along the radial direction, the gap between the movable pieces is filled with the flexible sheet, and the outer surface of the outer diameter varying portion is uneven. Thus, it is possible to prevent the occurrence of problems such as the foamed intermediate body being caught by the concavities and convexities and being broken, or the frictional resistance increasing and stopping.
Further, in the case where a mandrel provided with a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction is used as the movable piece, in the process of extending the foam intermediate to the maximum diameter, Since the diameter of the foamed intermediate body is gradually increased while contacting the movable piece, continuous production can be performed more stably without breaking the foamed sheet.

It is a block diagram which shows an example of the thermoplastic resin foam sheet manufacturing apparatus of this invention. It is a side view which shows an example of the mandrel used for the thermoplastic resin foam sheet manufacturing apparatus of this invention. It is sectional drawing of the B-B 'part in FIG. FIGS. 4A and 4B show a moving direction of the movable piece in FIG. 3, and FIG. 4A is an enlarged side view, and FIG. 4B is a main part side view showing a reduced diameter state. It is a principal part side view which shows the modification of the mandrel of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an example of a thermoplastic resin foam sheet manufacturing apparatus of the present invention. The thermoplastic resin foam sheet manufacturing apparatus of this example is an extruder for melt-mixing a melt-mixed resin and a foaming agent. 1, a die 2 which is attached to the extruder 1 and extrudes the molten mixture in the extruder 1 into a low pressure region and foams, and foams the foamed intermediate obtained by the foaming and is cooled while being stretched to foam a thermoplastic resin. And a mandrel 6 for manufacturing the sheet 7. Further, this manufacturing apparatus is provided with another extruder 3 connected to the resin supply section 4 of the extruder 1 and also provided with a foaming agent press-fitting pump 5 for press-fitting a foaming agent into the extruder 1. It has been.

  In the manufacturing apparatus of this example, a circular die having an annular hole is attached to the tip of the extruder 1, a cylindrical foam intermediate is extruded from the die, and cooled while being stretched by a mandrel 6. The case of manufacturing a single thermoplastic resin foam sheet 7 by cutting it with a cutter (not shown) is illustrated, but the structure of the die 2 and the shape of the sheet obtained are It is not limited to examples only. The thermoplastic resin foam sheet 7 obtained as described above is wound around a paper tube or the like through a guide roll 8 to obtain a product 7a.

2 to 4 show an example of a mandrel used in the thermoplastic resin foam sheet manufacturing apparatus of the present invention, FIG. 2 is a side view of the mandrel 6, and FIG. 3 is a BB ′ line portion in FIG. 2. Sectional drawing and FIG. 4 are principal part side views of FIG.
The mandrel 6 is provided with at least the front part 12, the middle part 13 and the rear part 14 in this order from the upstream side to the downstream side in the foam sheet flow direction A. The middle part 13 includes an inner surface of the thermoplastic resin foam sheet 7. A plurality of air supply ports 15 (gas supply means) for blowing air to the side are provided, and an outer diameter varying portion 11 is provided at the rear portion 14.
In addition, although this example shows the case where the outer diameter fluctuation | variation part 11 is provided in the rear part 14, the installation position of the outer diameter fluctuation | variation part 11 is not limited to this illustration, One or both of the front part 12 and the rear part 14 It can be.
Moreover, the length of the front part 12, the middle part 13, and the rear part 14 is not specifically limited. Further, the arrangement of the air supply ports 15 in the middle portion 13 can be changed as appropriate.

The material of the mandrel 6 and the presence or absence of surface treatment are not particularly limited, but at least the material of the outer surface portion of the mandrel 6 that comes into contact with the foamed intermediate is a metal having high thermal conductivity such as aluminum, aluminum alloy, copper, or copper alloy. Materials are preferably used. As for the surface treatment, for example, a surface treatment for friction reduction such as a fluororesin coat layer or a ceramic welding layer or a knurling process for providing irregularities on the surface so as to reduce the contact resistance between the foam intermediate and the outer surface of the mandrel 6. Etc. are preferably applied.
Moreover, it is preferable to chamfer a corner | angular part with radius R5-20mm.

  Although not shown, the mandrel 6 is provided with a plurality of passages for a cooling medium such as cooling water. By passing a cooling medium such as water through these passages, a foamed intermediate that contacts the outer surface of the mandrel 6 is provided. Can be cooled.

  In this example, the middle part 13 of the mandrel 6 has an outer diameter smaller than the outer diameters of the front part 12 and the rear part 14, and a large number of air supply ports 15 are provided substantially uniformly over the entire peripheral surface. ing. High pressure air is supplied from an air supply means such as a compressor provided inside or outside the mandrel 6 to an air supply line (not shown) connected to these air supply ports 15, and the high pressure air is supplied to each air supply port. It is comprised so that it may eject from 15.

  As shown in FIG. 1, the middle portion 13 of the mandrel 6 guides the foamed intermediate body extruded from the die 2 to the mandrel 6 and supplies a large number of air supplies when passing from the upstream side to the downstream side in the sheet flow direction A. By blowing high-pressure air from the mouth 15, the foamed intermediate body is floated and allowed to pass through the foamed intermediate body in a non-contact state with the outer surface of the middle portion 13. Thus, a flexible thermoplastic resin foam sheet is manufactured by extending the foamed intermediate body along the outer surface of the mandrel 6 while jetting high-pressure air from the air supply port 15 of the middle part 13 of the mandrel body 6a. Even in this case, the contact between the foam intermediate and the mandrel can be reduced, and a flexible thermoplastic resin foam sheet can be stably and continuously produced without breaking. In addition, the amount of high-pressure air jetted from the air supply port 15, the pressure, and the like are not limited, and are preferably adjusted as appropriate according to the material, strength, and the like of the thermoplastic resin foam sheet to be manufactured.

  As shown in FIG. 3, the outer diameter varying portion 11 includes a plurality of movable pieces 16 that move along the radial direction of the mandrel 6 by an air cylinder 17 that is driving means, along the circumferential direction of the mandrel 6. It has a structure that is connected continuously. In this example, the fixed side of a plurality (six in FIG. 3) of air cylinders 17 is fixed along the outer peripheral surface of the central base material 19, and the movable arm 18 of each air cylinder 17 has a circular arc cross section. The movable piece 16 is fixed. Further, in this example, a mandrel body 20 is extended on the radially inner side of the movable piece 16.

  As shown in FIG. 4, each movable piece 16 of the outer diameter varying portion 11 configured as described above advances and retreats along the radial direction of the mandrel 6 in accordance with the driving of the air cylinder 17. 4A shows an enlarged state in which the movable piece 16 has moved outward in the radial direction, and FIG. 4B shows a reduced diameter state in which the movable piece 16 has moved inward in the radial direction from the enlarged state in FIG. Indicates. The displacement amount (stroke) between the expanded diameter state (a) and the reduced diameter state (b) can be adjusted according to the sheet width of the thermoplastic resin foam sheet 7 to be manufactured, and controls the driving state of the air cylinder 17. It is also possible to change automatically.

In this example, the air cylinder 17 is used as the driving means. However, the driving means is not limited to this, and other driving means such as a hydraulic cylinder, a moving mechanism driven by a servo motor, and a moving mechanism using a piezoelectric actuator are adopted. You can also.
In this example, the movable piece 16 is directly moved by moving the movable arm 18 of the air cylinder 17 up and down. However, the movable piece 16 is moved by moving the movable piece 16 in the longitudinal direction or the circumferential direction of the mandrel 6. It is good also as a structure which is displaced to the predetermined position of radial direction.

In a preferred embodiment of the present invention, when the movable piece 16 moves outward along the radial direction in the outer diameter varying portion 11, a flexible sheet that swells so as to fill a gap between adjacent movable pieces 16 ( (Not shown) can also be provided. As the flexible sheet used here, a rubber sheet is preferable, and as a method of expanding and contracting the rubber sheet so as to fill a gap between the adjacent movable pieces 16, the rubber sheet is made to have a sealed structure and the outer diameter varying portion 11. It is preferable to employ a method such as arranging in an appropriate place and expanding and contracting by taking air in and out of the air.
In the case of using the mandrel 6 provided with the flexible sheet, the gap between the movable pieces 16 is the flexible sheet in the expanded diameter state in which each movable piece 16 is moved outward along the radial direction. The outer surface of the outer diameter variable portion 11 is not filled with irregularities, and the foamed intermediate body is caught by the irregularities and broken, or the frictional resistance rises and stops. Can be prevented.

FIG. 5 is a side view of an essential part showing a modification of the mandrel of the present invention.
In the present example, a plurality of movable pieces 20 that move forward and backward along the radial direction of the mandrel 6 by the air cylinder 17 are arranged in a row along the circumferential direction of the mandrel 6. Is characterized in that a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction A is provided.

  Since the mandrel of this example is provided with the movable piece 20 provided with the tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction A, in the process of extending the foam intermediate to the maximum diameter. Since the foamed intermediate body is gradually expanded in diameter while being in contact with the tapered surface of the movable piece 20, the resistance of the foamed intermediate body when passing through the mandrel can be reduced, and even a flexible thermoplastic resin foam sheet is broken. More stable and continuous production.

  The inclination angle θ of the movable piece 20 is preferably in the range of 0 to 20 degrees, and more preferably in the range of 5 to 15 degrees. If the inclination angle θ is less than the above range, there is no significant difference in the resistance when the foamed intermediate body passes through the mandrel with the movable piece 16 that does not have a tapered surface, and if the inclination angle θ exceeds the above range, The resistance will increase.

Next, an example of the thermoplastic resin foam sheet manufacturing method according to the present invention will be described.
The production method of the present invention is characterized in that the thermoplastic resin foam sheet 7 is produced using the thermoplastic resin foam sheet production apparatus having the mandrel 6 having the outer diameter varying portion 11 described above.

  In the production method of the present invention, examples of the thermoplastic resin used include polyolefins such as polyethylene, polypropylene, and polybutene, copolymers of olefin monomers and other copolymerizable monomers, blend polymers of polyolefin and other resins, Use as appropriate by selecting from polystyrene, copolymers of styrene monomers and other copolymerizable monomers, blend polymers of polystyrene and other resins, thermoplastic polyester resins such as polyethylene terephthalate resins, etc. Among these, polyethylene resins and polypropylene resins are preferable.

Moreover, in the thermoplastic resin foam sheet manufacturing method of this invention, it is preferable that the density of the thermoplastic resin foam sheet to manufacture is the range of 0.015-0.060 g / cm < ³ >. More preferably, it is the range of 0.018-0.045 g / cm < ³ >. When the density is less than 0.015 g / cm ³ , the strength of the foamed sheet becomes insufficient, and breakage and tearing are likely to occur during production, which makes production difficult. When the density exceeds 0.060 g / cm ³ , a foamed sheet having sufficient flexibility, impact resistance, and heat insulating properties cannot be obtained in a polyethylene resin or polypropylene resin.

  In order to produce a thermoplastic resin foam sheet using the production apparatus, a raw material thermoplastic resin is supplied into the extruder 1 from the hopper 4 together with an additive added as necessary. Additives include, for example, bubble regulators, antioxidants, metal deactivators, flame retardants, UV absorbers, crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, charging Examples include inhibitors.

  The resin and additive supplied into the extruder 1 are melted and mixed in the extruder 1 to form a resin melt, and a foaming agent is injected into the resin melt via a foaming agent press-fitting pump 5 to obtain a resin melt. Mixed with. Examples of the blowing agent used include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, hexane, and heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane, and chlorodifluoro. Examples thereof include one or more of halogenated hydrocarbons such as methane, chloroethane, dichlorotrifluoroethane, and inorganic gases such as nitrogen, carbon dioxide, and air.

  Next, the mixture is transferred to the discharge side while being kneaded, cooled to a temperature suitable for foaming, and then guided to the resin flow path of the die 2 attached to the discharge port of the extruder 1. The molten mixture introduced into the resin flow path of the die 2 is extruded into the atmosphere in an arbitrary amount from the outlet of the die 2 (the outlet of the resin flow path) into the atmosphere, and foamed simultaneously with the extrusion. .

  The cylindrical foaming intermediate obtained by this foaming is cooled by a cooling mandrel 6, and then a predetermined portion is cut by a cutter and developed into a flat shape to form a thermoplastic resin foam sheet 7 having a predetermined width. . This thermoplastic resin foam sheet 7 is pulled by a guide roll 8 and wound up in a roll shape to become a product 7a.

  In this thermoplastic resin foam sheet manufacturing method, when the sheet width of the thermoplastic resin foam sheet 7 to be manufactured is to be changed, in the conventional technique, the entire mandrel has to be replaced. It must be stopped or the extruded resin must be wasted, and the replacement work, such as switching the flow path of the cooling water provided in the mandrel, requires a lot of time for replacement. There were many problems.

  On the other hand, in the manufacturing method of the present invention, the sheet width of the thermoplastic resin sheet 7 obtained by driving the air cylinder 17 and expanding or reducing the outer diameter of the outer diameter varying portion 11 without removing the mandrel 6. Can be changed. The outer diameter of the outer diameter varying portion 11 can be changed even during the continuous production of foamed sheets, and the sheet width can be changed without stopping the manufacturing equipment such as an extruder.

Thus, when the sheet width of the thermoplastic resin foam sheet 7 is changed using the mandrel 6 described above, each movable piece 16 is moved along the radial direction by the air cylinder 17 of the outer diameter varying portion 11, and each movable piece is moved. By changing the maximum outer diameter of the mandrel 7 formed by connecting the outer surfaces of the 16 and manufacturing the thermoplastic resin foam sheet 7 having a changed sheet width, the mandrel 6 is not replaced when the sheet width is changed. The sheet width can be changed, the production efficiency can be prevented from being lowered due to the suspension of continuous production and replacement work due to the mandrel replacement, and the loss of the resin extruded during the replacement can be eliminated. Yield can be improved.
In addition, each region of the front part 12, the middle part 13 and the rear part 14 is provided in order from the upstream side to the downstream side in the foam sheet flow direction A, and an air supply port 15 for blowing air to the inner side of the foam intermediate in the middle part 13 is provided. When the mandrel 6 provided with the outer diameter variation part 11 is provided at one or both of the front part 12 and the rear part 14, the foamed intermediate is made to flow out of the mandrel while blowing out gas from the gas supply means of the middle part 13. In the production of a flexible thermoplastic resin foam sheet that can be stretched along the outer surface, the contact between the sheet and the mandrel 6 can be reduced, and the flexible thermoplastic resin foam sheet 7 can be formed without breaking. Stable and continuous production is possible.
Further, the mandrel 6 provided with a flexible sheet that swells so as to fill a gap between the adjacent movable pieces 16 when the movable piece 16 moves outward along the radial direction is provided on the outer diameter varying portion 11. When used, in the diameter-expanded state in which each movable piece 16 is moved outward along the radial direction, the gap between the movable pieces 16 is filled with the flexible sheet, and the outer surface of the outer diameter varying portion 11 is As a result, it is possible to prevent the occurrence of defects such as the foamed intermediate body being caught by the unevenness and being broken, or the frictional resistance being increased and being stopped.
Further, when the mandrel 6 provided with a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction A is used as the movable piece 16, the process of extending the foam intermediate to the maximum diameter Thus, since the diameter of the foamed intermediate body is gradually expanded while contacting the movable piece, continuous production can be performed more stably without breaking the foamed sheet.

Hereinafter, the effects of the present invention will be demonstrated by examples.
The following examples are merely examples of the present invention, and the present invention is not limited to the description of the following examples.
Moreover, the thickness and density of the obtained foamed sheet were measured as follows.
(Method for measuring thickness of foam sheet)
From the obtained foam sheet, a rectangular section sheet having a flow direction (MD direction) of 10 cm and a width direction (TD direction) of 100 cm is cut out. The thickness when a load of 100 g was applied to 15.2 cm ² (a disk having a diameter of 4.4 cm) using a constant-pressure thickness measuring instrument (Model PG-12 manufactured by Teclock) was determined in the width direction (TD direction) of the section sheet. ) At an interval of 10 cm, and the average value was taken as the thickness (mm) of the foamed sheet.
(Method for measuring density of foam sheet)
The weight and volume of the section sheet used for measuring the thickness were measured, and the density (g / cm ³ ) of the foamed sheet was calculated. In addition, the thickness at the time of calculating the volume of a section sheet used the thickness of the foam sheet | seat calculated | required previously.

[Example]
A thermoplastic resin foam sheet was manufactured using the manufacturing apparatus shown in FIG. 1 having the mandrel 6 having the structure shown in FIGS.
As the thermoplastic resin, a polyethylene resin (manufactured by Nippon Unicar Co., Ltd., low density polyethylene, trade name “DFDJ6776” (MI = 0.22, density 0.922 g / cm ³ )) was used.

  With respect to 100 parts by mass of this resin, 0.05 part by mass of a foam nucleating agent (manufactured by Sankyo Kasei Co., Ltd., trade name “Celmarc C-2”) was mixed to obtain a raw material. This raw material is put into a tandem extruder in which a first extruder with an inner diameter of 90 mm and a second extruder with an inner diameter of 180 mm are connected, heated and melt-kneaded in the extruder so that the maximum temperature setting is 210 ° C., and charged in the middle As an inhibitor, 1.5 parts by mass of glycerin monostearate and 16 parts by mass of a blowing agent (isobutane / normal butane = 50/50) were press-fitted, and then the resin temperature was cooled to 112 ° C. and attached to the discharge port of the extruder. After extruding from a circular die having a die diameter of 120 mm and a slit clearance of 0.2 mm and foaming, the resulting cylindrical foamed intermediate is guided to a cylindrical mandrel having an outer diameter of 440 mmφ and allowed to pass through the outer peripheral surface for cooling. One portion was cut open to obtain a foam sheet.

As shown in FIG. 2, the mandrel 6 used here is provided with regions of the front portion 12, the middle portion 13, and the rear portion 14 in order from the upstream side to the downstream side in the foam sheet flow direction A, and the front portion 12 is water-cooled. The middle portion 13 is configured to allow high-pressure air to blow out and float inside the foamed intermediate body, thereby allowing the foamed intermediate body to pass through in a non-contact state. Twenty-four round hole-shaped air supply ports having a diameter of 2 mmφ were formed on the outer peripheral surface of the middle portion 13, and high-pressure air was ejected from each air supply port at a pressure of 2.5 kgf / cm ² . As shown in FIG. 3, the fixed side of the six air cylinders 17 is fixed to the rear portion 14 of the mandrel 6 along the circumferential direction of the central base material 19, and the movable arm 18 of the air cylinder 17 is attached to the mandrel body. The outer diameter varying portion 11 was configured by protruding from the portion 20 and fixing the movable piece 16 having a circular arc shape at the tip thereof. In the production of the foam sheet, the maximum outer diameter of the outer diameter varying portion 11 was set to 440 mmφ as with the outer diameter of the front portion 12.

As a result of manufacturing the foam sheet using the mandrel, the foam sheet was obtained with the same outer diameter of the mandrel 6 as 440 mmφ before the incision.
The polyethylene resin foam sheet having a thickness of 1.25 mm, a width of 1280 mm, and a density of 0.0186 g / cm ³ could be continuously produced by incising and winding the paper tube.

Next, each air cylinder 17 was driven, and the maximum outer diameter of the outer diameter varying portion 11 was increased to 480 mmφ. The time required for expanding the diameter was about 1 second.
In this outer diameter change, without stopping the continuous production of foam sheets, there is no breakage due to frictional resistance at the time of diameter change, and after the outer diameter change, foam sheets with changed sheet width are continuously produced. I was able to.
As a result of manufacturing a foam sheet using a mandrel having an enlarged maximum outer diameter of the outer diameter varying portion, a foamed sheet having a diameter of 480 mmφ which was the same as the maximum outer diameter of the outer diameter varying portion was obtained before cutting.
The polyethylene resin foam sheet having a thickness of 1.26 mm, a width of 1380 mm, and a density of 0.0185 g / cm ³ could be continuously produced by incising and winding the paper tube.

  In this example, a cylindrical mandrel having an outer diameter of 440 mmφ was used, and the continuous production of the foam sheet was stopped in order to switch from the state of continuously producing the foam sheet having a width of 1280 mm to the production of the foam sheet having a width of 1380 mm. Without changing the diameter of the outer diameter varying portion 11, the sheet width can be easily changed. In this example, the time required for changing the sheet width was about 1 second, and no resin loss was caused by the change.

[Comparative example]
In the comparative example, a cylindrical shape with an outer diameter of 440 mmφ is the same as that of a conventional mandrel that does not distinguish between the front part, the middle part, and the rear part and does not have an air supply port, and the outer diameter is 480 mmφ. A replacement mandrel was prepared, and a foamed sheet was produced in the same manner as in the example except for the mandrel.
First, a mandrel having an outer diameter of 440 mmφ was used, and a foamed sheet was produced in the same manner as in the examples. Thus, a polyethylene resin foam sheet having a thickness of 1.25 mm, a width of 1280 mm, and a density of 0.0186 g / cm ³ could be continuously produced.
Next, in order to replace the mandrel, the foamed sheet was once broken, the mandrel having an outer diameter of 440 mmφ was removed while removing the resin extruded from the die, and a replacement mandrel having an outer diameter of 480 mmφ was attached. . In the mandrel replacement, many replacement operations including a change of cooling water piping were required.
After the replacement with the replacement mandrel, the production of the foam sheet was started again. Thereby, a polyethylene resin foam sheet having a thickness of 1.26 mm, a width of 1380 mm, and a density of 0.0185 g / cm ³ could be continuously produced.
However, in this comparative example, the time required for exchanging the mandrels was as long as about 10 minutes, and the amount of excess resin extruded during that time was considerable.

According to the present invention, in the production of a thermoplastic resin foam sheet, a mandrel capable of easily changing the sheet width without exchanging the entire mandrel, and a thermoplastic resin foam sheet production apparatus and production method using the mandrel are produced. be able to.
The thermoplastic resin foam sheet produced according to the present invention is used, for example, as a cushioning packing material.

  DESCRIPTION OF SYMBOLS 1,3 ... Extruder, 2 ... Die, 4 ... Hopper, 5 ... Foaming agent press injection pump, 6 ... Mandrel, 6a ... Mandrel body, 7 ... Thermoplastic foam sheet, 7a ... Product, 8 ... Guide roll, 11 ... Outer diameter variation part, 12 ... front part, 13 ... middle part, 14 ... rear part, 15 ... air supply port (gas supply means), 16, 21 ... movable piece, 17 ... air cylinder (drive means), 18 ... movable arm, 19 ... base material, 20 ... mandrel body, A ... foam sheet flow direction.

Claims (9)

A molten mixture of the resin and the foaming agent melt-mixed in the extruder is extruded through a die attached to the extruder into a low-pressure region and foamed, and the foamed intermediate obtained by the foaming is placed along the outer surface of the mandrel. In the mandrel for producing a foam sheet for producing a thermoplastic resin foam sheet by stretching
A plurality of movable pieces that move forward and backward along the radial direction of the mandrel by a driving means are provided with an outer diameter varying portion that is continuously provided along the circumferential direction of the mandrel ,
Foam, wherein the outer diameter variation portion is provided with a flexible sheet that expands so as to fill a gap between adjacent movable pieces when the movable piece moves outward along the radial direction. Mandrel for sheet manufacturing.   The mandrel is provided with at least front, middle and rear regions in order from the upstream side to the downstream side in the foam sheet flow direction, and a gas supply means for blowing gas onto the inner surface side of the thermoplastic resin foam sheet in the middle portion The mandrel for manufacturing a foam sheet according to claim 1, wherein the outer diameter varying portion is provided in one or both of the front portion and the rear portion. The mandrel for manufacturing a foam sheet according to claim 1 or 2, wherein the movable piece is provided with a tapered surface that gradually increases in height from the upstream side to the downstream side in the foam sheet flow direction. An extruder that melt-mixes the melt-mixed resin and the foaming agent, a die that is attached to the extruder and that foams the molten mixture in the extruder by extrusion into a low-pressure region, and a foaming intermediate obtained by the foaming. In a thermoplastic resin foam sheet production apparatus having a mandrel for producing a thermoplastic resin foam sheet by cooling while stretching,
A thermoplastic resin foam sheet manufacturing apparatus using the foam sheet manufacturing mandrel according to any one of claims 1 to 3 as a mandrel. A molten mixture of the resin and the foaming agent melt-mixed in the extruder is extruded through a die attached to the extruder into a low-pressure region and foamed, and the foamed intermediate obtained by the foaming is placed along the outer surface of the mandrel. In the thermoplastic resin foam sheet manufacturing method of manufacturing a thermoplastic resin foam sheet by stretching
A method for producing a thermoplastic resin foam sheet, wherein the mandrel for foam sheet production according to any one of claims 1 to 3 is used as a mandrel. When the sheet width of the thermoplastic resin foam sheet is changed, the maximum outer diameter of the mandrel formed by connecting the outer surface of each movable piece by moving each movable piece along the radial direction by the driving means of the outer diameter varying portion. 6. The method for producing a thermoplastic resin foam sheet according to claim 5 , wherein a thermoplastic resin foam sheet having a changed sheet width is produced. The method for producing a thermoplastic resin foam sheet according to claim 5 or 6 , wherein the thermoplastic resin foam sheet to be produced is a polyethylene resin foam sheet or a polypropylene resin foam sheet. The density of the thermoplastic resin foam sheet to manufacture is the range of 0.015-0.060 g / cm < ³ >, The thermoplastic resin foam sheet manufacturing method of Claim 7 characterized by the above-mentioned. A mandrel according to claim 2 is used as a mandrel, and a thermoplastic resin foam sheet is produced by stretching a foamed intermediate body along the outer surface of the mandrel while jetting gas from a middle gas supply means. The thermoplastic resin foam sheet manufacturing method according to any one of claims 5 to 8 .

Images