JP2005153400A - Plug and method and apparatus for manufacturing thermoplastic resin foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plug constituted so as to reduce friction resistance or the take-over resistance due to the shrinkage of a foamed sheet to perform the production of a polypropylene resin foamed sheet having a low expansion ratio and a low weight basis, a thermoplastic resin foamed sheet manufacturing apparatus using it and a manufacturing method using it. <P>SOLUTION: In this thermoplastic resin foamed sheet manufacturing apparatus equipped with an extruder for melting and mixing a thermoplastic resin and a foaming agent to extrude a molten mixture, the die attached to the discharge port of the extruder and the plug for cooling the foamed intermediate body extruded from the die while advancing the same along an outer peripheral surface to manufacture the thermoplastic resin foamed sheet, an Alumite treatment layer or a hard Alumite treatment layer is provided to the outer surface of the plug 7 and a fluoroplastic resin coating layer is provided to the outer surface of the treatment layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plug used in a thermoplastic resin foam sheet manufacturing apparatus, a thermoplastic resin foam sheet manufacturing apparatus using the plug, and a method of manufacturing a thermoplastic resin foam sheet.

    One of the methods often used as a method for producing a resin foam sheet is a so-called extrusion foam molding method. This extrusion foam molding method is also applied to thermoplastic resins such as polystyrene resins, polyester resins, polypropylene resins, and polyethylene resins.

  The extrusion foam molding method will be briefly described. This is a method in which a thermoplastic resin is melted and mixed with a foaming agent in an extruder, and this molten mixture (hereinafter referred to as “resin melt”) is used as a tip portion of the extruder. The die formed of the outer ring and the core attached to the outer ring is extruded from an annular gap formed by the outer ring and the core (hereinafter referred to as “resin flow path”) to an external low pressure region. By extending the intermediate body along the axial direction of the plug along the outer peripheral surface of the cooled cylindrical plug, the foamed intermediate body is stretched to form an annular foam body, and this foam body is cut open by a cutter. This is a method for obtaining a foam sheet. By the way, this plug is also called a mandrel or sizing drum.

  An example of the overall configuration of an apparatus provided with this plug is shown in the schematic diagram of FIG. In FIG. 1, reference numeral 1 is a first extruder, 2 is a second extruder, 3 is a die (circular die), 4 is a raw material blending device, 5 is a hopper, 6 is a blowing agent press-fitting pump, 7 is a plug, A cutter, 9 is a foam sheet, 10 is a take-up roll, and 11 is a foam sheet roll. Briefly describing the operation of this apparatus, the resin and additive charged from the hopper 5 into the first extruder 1 of the tandem extruder are melted and mixed in the first extruder 1 to form a resin melt. A foaming agent is pressed into the resin melt through a foaming agent press-fitting pump 6 and mixed with the resin melt. This mixture is supplied to the second extruder 2, further kneaded, cooled to an appropriate temperature, and then guided to the resin flow path of the die 3 attached to the discharge port of the second extruder 2. The molten mixture guided to the resin flow path of the die 3 is extruded into the atmosphere in a cylindrical shape with an arbitrary extrusion amount at the outlet of the die 3 (the outlet of the resin flow path), and simultaneously with the extrusion. Foam. The cylindrical resin foam sheet obtained by this foaming is cooled by a cooling plug 7, then a predetermined portion is cut by a cutter 8, developed in a plane, and pulled by a take-up roll 10, and rolled. To form a foam sheet roll 11.

And as a plug used for manufacture of the resin foam sheet by such an extrusion foaming method, a metal material such as aluminum having good flatness and thermal conductivity is larger than the diameter of the resin flow path of the die. What was formed in the cylindrical shape which has a diameter is used (for example, refer patent documents 1-5).
Japanese Examined Patent Publication No. 6-22889 JP 2001-191391 A Japanese Examined Patent Publication No. 6-28889 JP 2001-328155 A JP 2000-254955 A

  Among the above-described conventional techniques, the conventional plugs described in Patent Documents 1 to 4 are suitable for the production of polystyrene resin foam sheets, but other than this, for example, a low-magnification foam of polyethylene terephthalate resin When it was going to be used for manufacturing, the frictional resistance on the plug surface of the foamed sheet was large, which caused a quality problem in the sheet.

  In other words, when a foam sheet made of polyethylene terephthalate resin extruded from a resin flow path of a die is pulled by a take-up roll, the frictional resistance due to surface friction generated between the plug and the foam sheet is large, and the surface is Since the foam sheet does not slide smoothly, a horizontal stripe is generated in the foam sheet. This horizontal stripe occurs as follows. If the foamed sheet is pulled with a certain force, the foamed sheet is caught on the plug surface due to surface friction generated between the foamed sheet and the plug at a certain point of time and cannot be taken up. Therefore, even if temporarily, an extra force is applied to try to take off the foam sheet. In order to make the surface of the foam sheet smooth, the thickness of the foam sheet needs to be constant, and in order to make the thickness constant, the foam sheet has to be taken up with a constant force, like this The force applied to the foam sheet fluctuates, so the force applied to the foam sheet is not constant, so the thickness of the foam sheet is partially reduced. As a result, the thinned part becomes a horizontal stripe. It ends up.

  Also, when the foam sheet is pulled, the resistance generated between the plug and the plug cannot be pulled straight, and the product may meander. Furthermore, repeated use of the plug may cause aluminum wear on the plug surface, which may cause black streaks on the foam sheet.

  In addition, in the technique described in Patent Document 5, alumite treatment is applied to the plug surface using conventional aluminum so that a low-magnification foamed sheet of polyethylene terephthalate resin can be manufactured, and the surface is plated with hard anodized. The plug is used. As a result, the frictional resistance on the plug surface of the foamed sheet was reduced, and problems such as lateral stripes, thickness fluctuations, and meandering of the product were improved to some extent when producing a low-magnification foamed sheet of polyethylene terephthalate resin.

However, even when the improved plug described in Patent Document 5 is used, problems still remain in the production of a polypropylene resin foam sheet.
That is, in the extrusion molding of a polypropylene resin foam sheet which is a crystalline resin, the melt tension of the resin at the foamed resin temperature is low, and the tensile strength of the foam resin immediately after being extruded from the mold is low. When the take-up resistance of the foamed sheet is large, the foam may be cut, and there is a problem that a foam with a low foaming ratio and a low basis weight (basis weight = basis weight) cannot be produced.
Also, if the bubble diameter of the foam sheet is made finer in an attempt to improve the appearance of the foam sheet, a phenomenon that the take-up resistance further increases is observed, so that the appearance cannot be improved by making the bubbles finer. There were also challenges.
Further, in Patent Document 5, shot blasting on the plug surface, which has a resistance reducing effect in the production of a low-magnification foamed sheet of polyethylene terephthalate resin, is said to generate concave streaks on the foamed sheet surface in the production of a polypropylene resin foamed sheet. A problem occurred.

  The present invention has been made in view of the above circumstances, and reduces the resistance to friction due to friction and shrinkage of the foamed sheet, thereby making it possible to produce a polypropylene resin foamed sheet having a low foaming ratio and a low basis weight. It aims at providing the plug used for a manufacturing apparatus, the thermoplastic resin foam sheet manufacturing apparatus using the same, and the manufacturing method of a thermoplastic resin foam sheet.

To achieve the above object, the present invention provides an extruder for extruding a molten mixture by melt-mixing a thermoplastic resin and a foaming agent, a die attached to a discharge port of the extruder, and a foam extruded from the die. In a plug used for a thermoplastic resin foam sheet manufacturing apparatus comprising a plug for manufacturing a thermoplastic resin foam sheet by cooling the intermediate body along the outer peripheral surface, an alumite treatment layer or a hard alumite treatment is provided on the outer surface of the plug. A plug is provided in which a layer is provided and a fluororesin coating layer is provided on an outer surface thereof.
In the plug of the present invention, a configuration can be provided in which an outer periphery gradually decreasing portion is provided in which the outer periphery of the plug is gradually decreased from the die side toward the downstream side in the sheet take-up direction.
The outer periphery gradually decreasing portion can be provided from the die side of the plug to the end in the sheet take-up direction.
Further, the outer periphery gradually decreasing portion is provided between the die side of the plug and a predetermined position on the downstream side in the sheet take-up direction, and on the downstream side in the sheet take-up direction, the outer periphery of the plug may be a straight portion having a constant length. Good.
Further, a plurality of the outer periphery gradually decreasing portions may be provided, and the outer periphery gradually decreasing portions may be formed so as to have different outer periphery reduction rates.

  The present invention also includes an extruder for extruding a molten mixture by melt-mixing a thermoplastic resin and a foaming agent, a die attached to a discharge port of the extruder, and a foaming intermediate extruded from the die on the outer peripheral surface. A thermoplastic resin foam sheet manufacturing apparatus comprising a plug for producing a thermoplastic resin foam sheet by cooling while proceeding along the thermoplastic resin foam, wherein the plug according to the present invention is provided as the plug. A foam sheet manufacturing apparatus is provided.

  The present invention also provides a foamed intermediate obtained by foaming a molten mixture of a thermoplastic resin and a foaming agent melt-mixed in an extruder by extruding from a die attached to the extruder into a low pressure region and foaming. In the thermoplastic resin foam sheet manufacturing method in which the thermoplastic resin foam sheet is manufactured by cooling along the outer peripheral surface of the plug to produce the thermoplastic resin foam sheet, and the plug according to the present invention is used as the plug. Provided is a method for producing a plastic resin foam sheet.

According to the present invention, particularly in the production of a foam sheet by extrusion foam molding of a crystalline thermoplastic resin, in particular, a polypropylene resin, an increase in take-up resistance of the foam sheet at the plug portion due to shrinkage on the plug of the foam sheet. This makes it possible to produce a polypropylene resin foam sheet having a low magnification and a low basis weight.
Moreover, it becomes possible to produce a thermoplastic resin foam sheet having a small cell diameter and excellent in appearance.
Moreover, the productivity fall resulting from the take-up resistance of the thermoplastic resin foam sheet can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The thermoplastic resin foam sheet manufacturing apparatus according to the present invention is a thermoplastic resin foam sheet manufacturing apparatus configured as shown in FIG. 1 and is cooled while a foamed intermediate body extruded from the die 3 is advanced along the outer peripheral surface. As the plug 7 for forming the thermoplastic resin foam sheet 9, a plug 7 having an alumite treatment layer or a hard alumite treatment layer on the outer surface and a fluororesin coating layer on the outer surface is used. It is a feature.

In order to provide the anodized layer on the outer surface of the plug 7, it can be obtained by subjecting the surface of the plug base made of aluminum to an anodized treatment or a hard anodized treatment. Further, the hard anodized layer can be provided by subjecting the surface of the plug 7 to an anodizing process and plating the surface with the hard anodized. This alumite treatment is a treatment for forming an oxide film on the surface by so-called anodizing treatment, but in this embodiment, the plug surface is treated so as to become so-called hardened alumite with high hardness.
The alumite layer formed by the alumite treatment has a hardness (Hv) of about 100 to 400 and a film thickness of about 5 to 30 μm.
The hard anodized layer has a hardness (Hv) of about 400 to 550 and a film thickness of about 30 to 100 μm.

  In the plug 7 according to the present invention, a fluororesin coating is further provided on the outer surface of the anodized layer or the hard anodized layer. By providing the fluororesin coating, the take-up resistance of the foam sheet taken along the surface can be further reduced. The fluororesin used for this is polytetrafluoroethylene (PTFE), perfluoroalkoxy / fluororesin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene tetrafluoride ethylene co Polymer (ETFE), polychlorotrifluoride ethylene (PCTFE), vinylidene fluoride (PVDF), vinyl fluoride (PFV), etc. Among them, polytetrafluoroethylene excellent in heat resistance, wear resistance, etc. Resins are preferred. The thickness of the fluororesin coating is not limited and can be formed by various methods known in the art in the field of fluororesin coating.

  In the thermoplastic resin foam sheet manufacturing apparatus, each component other than the plug 7 can be used by appropriately combining each component of a conventionally known thermoplastic resin foam sheet manufacturing apparatus, and the thermoplastic resin foam illustrated in FIG. 1 is used. In the sheet manufacturing apparatus, a first extruder 1 and a second extruder 2 constituting a tandem type extruder, a die 3 (circular die) attached to a discharge port of the second extruder 2, A raw material blending device 4 for feeding a thermoplastic resin and an additive to one extruder 1, a hopper 5 for feeding the raw material from the raw material blending device 4, and a plug 7 provided adjacent to the outlet of the die 3; A tubular sheet cutting cutter 8 provided on the downstream side of the plug 7 in the sheet take-up direction, and a take-off roll for applying a take-up force to the two foamed sheets 9 obtained by cutting with the cutter 8. And Le 10, is configured to include a winder for the foamed sheet 9 winding foam sheet roll 11 taken off.

  In a preferred embodiment of the present invention, the plug 7 of the present invention has an outer peripheral gradually decreasing portion whose outer periphery is gradually decreased from the die 3 side toward the downstream side in the sheet take-up direction. FIG. 3 is a front view illustrating the plug 7 used in the thermoplastic resin foam sheet manufacturing apparatus. The plug 7 has a structure in which a metal material such as aluminum is formed in a substantially cylindrical shape having a diameter larger than the diameter of the resin flow path of the die 3. A temperature sensor or the like is provided. Note that the vertical cross-sectional shape of the plug 7 is not limited to a circular shape, and may be an elliptical shape, an oval shape, a quadrangular shape with rounded corners, or the like.

In FIG. 3, the left side of the plug 7 is closer to the die 3, and the right side of the plug 7 is on the downstream side in the sheet take-up direction. The plug 7 is provided with an outer peripheral gradually decreasing portion in which the outer periphery of the plug 7 is gradually decreased from the die 3 side toward the downstream side in the sheet take-up direction. The outer peripheral gradually decreasing portion can be formed by the following patterns (A) to (C).
(A) The outer periphery gradually decreases from the die 3 side of the plug 7 to the end of the sheet take-up direction with a constant outer periphery reduction rate.
(B) An outer periphery gradually decreasing portion having a constant outer periphery reduction ratio is provided between the die 7 side of the plug 7 and a predetermined position on the downstream side in the sheet take-up direction. Is a constant straight part.
(C) A plurality of outer periphery gradually decreasing portions are provided, and the outer periphery gradually decreasing portions are formed so as to have different outer periphery reduction rates.
Here, the “peripheral decrease rate” is a value calculated by (minimum outer periphery of the outer periphery gradually decreasing portion / maximum outer periphery of the outer periphery gradually decreasing portion) × 100 (unit:%).
In the following description, “decreasing angle” means the inclination angle of the plug when the diameter of the plug 7 is gradually reduced from D1 to D2 (D1> D2) with a length L1 in FIG.
(D1-D2) / 2L1 = tanB
And the angle B is set as a decrease angle.

  In the plug 7, when the outer peripheral gradually decreasing portion is provided in the pattern (A), the preferable decreasing angle of the outer peripheral gradually decreasing portion is in the range of 0.2 to 0.8 degrees (when the plug 7 is cylindrical). Moreover, the preferable outer periphery decreasing rate of an outer periphery gradually decreasing part is the range of 99.4 to 97.7% (when the plug 7 is cylindrical or not cylindrical).

In the case of providing the first-stage outer periphery gradually decreasing portion in the pattern (B) or in the case of providing the second-stage outer periphery gradually decreasing portion in the pattern (C), the preferable decreasing angle of the first-stage outer periphery gradually decreasing portion is 0.8 to. The range is 2.5 degrees (when the plug 7 is cylindrical). Moreover, the preferable outer periphery decreasing rate of the outer periphery gradually decreasing part of the 1st step is the range of 99.1 to 97.3% (when the plug 7 is cylindrical or not cylindrical). A preferable reduction angle of the outer peripheral gradually decreasing portion in the second stage is in a range of 0.1 to 0.6 degrees (when the plug 7 is cylindrical). Moreover, the preferable outer periphery decreasing rate of the outer periphery gradually decreasing part of the 2nd step is 99.8 to 98.9% (when the plug 7 is cylindrical or not cylindrical).
A more preferable reduction angle of the first-stage outer periphery gradually decreasing portion is in a range of 1.0 to 2.0 degrees (when the plug 7 is cylindrical). Moreover, the preferable outer periphery decreasing rate of the outer periphery gradually decreasing part of the 1st step is the range of 98.9 to 97.9% (when the plug 7 is cylindrical or not cylindrical).

  The gradually decreasing shape of the outer periphery gradually decreasing portion is a taper or a quadratic curve shape. The outer periphery gradually decreasing portion may be one stage, but in the production of a crystalline thermoplastic resin foam sheet having a large change in shrinkage rate on the plug 7, a multi-stage outer periphery gradually decreasing portion should be formed in accordance with the shrinkage rate of the foam sheet. Is preferred. By forming the multi-stage outer periphery gradually decreasing portion in accordance with the shrinkage rate of the foam sheet, it is possible to achieve appropriate adhesion over the entire length of the plug 7. In this case, it is preferable that the outer periphery gradually decreasing portion closer to the die 3 is steeper than the outer periphery gradually decreasing portion on the downstream side (the outer periphery decreasing rate is smaller). As a result, it is possible to reduce the take-up resistance at the portion where the shrinkage rate of the foamed sheet is large, and it is possible to achieve appropriate adhesion over the entire length.

Next, the manufacturing method of the thermoplastic resin foam sheet concerning this invention is demonstrated.
As described above, the method of the present invention includes the plug 7 provided with the alumite treatment layer or the hard alumite treatment layer on the outer surface of the plug 7, the fluororesin coating layer on the outer surface thereof, and further having the outer peripheral gradually decreasing portion. It is suitably implemented using the thermoplastic resin foam sheet manufacturing apparatus shown in FIG.
In the method of the present invention, various thermoplastic resins such as polystyrene resin, polyethylene resin, polypropylene resin, and polyethylene terephthalate resin can be used as the raw material thermoplastic resin. In particular, in the method of the present invention, it is possible to produce a polypropylene resin foam sheet having a low magnification and a low basis weight by using a crystalline thermoplastic resin, particularly a polypropylene resin, which is difficult to produce by the conventional method.

  A thermoplastic resin such as a polypropylene resin as a raw material is blended together with an additive by the raw material blending apparatus 4 and supplied from the hopper 5 to the extruder. 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 charged into the first extruder 1 of the tandem type extruder from the hopper 5 are melted and mixed in the first extruder 1 to form a resin melt, and a foaming agent press-fitting pump 6 is added to the resin melt. The foaming agent is pressed through and mixed with the resin melt. 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, this mixture is supplied to the second extruder 2, further kneaded, cooled to an appropriate temperature, and then guided to the resin flow path of the die 3 attached to the discharge port of the second extruder 2. The molten mixture guided to the resin flow path of the die 3 is extruded into the atmosphere in a cylindrical shape with an arbitrary extrusion amount at the outlet of the die 3 (the outlet of the resin flow path), and simultaneously with the extrusion. Foam.

  The cylindrical foamed sheet obtained by this foaming is cooled by a cooling plug 7, and then a predetermined portion is cut by a cutter 8 and developed into a flat shape to form two foamed sheets 9. Each of these foam sheets 9 is pulled by a take-up roll 10 and wound into a roll shape to form a foam sheet roll 11.

In the method of the present invention, an alumite treatment layer or a hard alumite treatment layer is provided on the outer surface of the plug 7 and a plug 7 having a fluororesin coating layer on the outer surface thereof is used. In the production of foamed sheets by extrusion foaming of polypropylene resin, the increase in the take-up resistance of the foamed sheet at the plug portion due to the shrinkage of the foamed sheet on the plug 7 can be alleviated, and low basis weight with low magnification foaming. This makes it possible to produce a polypropylene resin foam sheet.
Moreover, it becomes possible to produce a thermoplastic resin foam sheet having a small cell diameter and excellent in appearance.
Moreover, the productivity fall resulting from the take-up resistance of the thermoplastic resin foam sheet can be improved.

<Slip evaluation of surface treatment materials>
For aluminum test pieces,
(1) alumite treatment,
(2) Hard anodized treatment,
(3) Using each surface treatment material coated with hard alumite treatment + polytetrafluoroethylene resin (PTFE), each surface treatment with reference to the measurement method of static friction coefficient and the slope method specified in JIS P 8147 The sliding property of the material was measured and evaluated. The method of this experiment is shown in FIG. In FIG. 2, reference numeral 13 denotes a test piece subjected to the surface treatment of any one of (1) to (3), 14 denotes a polypropylene resin foam sheet, and 15 denotes a stainless steel plate that can displace the inclination angle θ.
A polypropylene resin foam sheet 14 (100 mm × 100 mm) is fixed with a double-sided tape on a stainless steel plate (SUS304, surface roughness Ry = 0.1 μm or less) on a flat plate with a smooth surface. The test piece 13 subjected to the surface treatment of (1) to (3) was placed almost at the center. Each test piece 13 produced a columnar aluminum casting having a diameter of 50 mm and a height of 50 mm, and was subjected to any one of the surface treatments (1) to (3) above. Each test piece 13 has a weight of 230 g / piece. Next, the angle θ is increased by inclining the stainless steel plate 13 once per second. Then, the inclination angle θ when the test piece 13 starts to slide is read. This was measured five times, and the average value was defined as the inclination angle θ. The results are shown in Table 1.

  In Table 1, “durability” is actually a resin foam sheet manufacturing apparatus, when the surface-treated plugs (1) to (3) are used on the surface. It can be used for a certain period of time, and the better the durability, the better.

  From the results in Table 1, it was found that particularly excellent slipperiness was obtained with respect to the polypropylene resin foam sheet in the test piece subjected to the surface treatment of hard alumite + PTFE.

<Example of foam sheet production using a surface treatment plug>
A plug (A, B) subjected to surface treatment according to the present invention and a plug (C) subjected only to an alumite treatment according to the prior art are produced, and these are applied to a thermoplastic resin foam sheet production apparatus having the configuration shown in FIG. The polypropylene resin foam sheet was manufactured by incorporating it.

Plug A: In FIG. 3, D1 = 684 mm, D2 = 676 mm, D3 = 673, L1 = 210 mm, L2 = 350 mm, a substantially cylindrical, two-stage outer periphery gradually decreasing portion (first stage: reduction angle B = 1. The aluminum plug base material having the pattern of (C) having an outer peripheral reduction rate of 9 ° and a second stage: a reduction angle B = 0.25 ° and an outer peripheral reduction rate of 99.6%). It was prepared and the surface was subjected to hard anodized treatment + PTFE treatment. This surface treatment was performed by Tefrohard made by Hoshi Giken.

Plug B: In FIG. 3, D1 = 682 mm, D2 = 673 mm, D3 = 673, L1 = 210 mm, L2 = 350 mm, and is a substantially cylindrical shape with a gradually decreasing outer periphery (reduction angle B = 1.23) at the front (L1). The outer peripheral reduction rate was 98.7%), and the plug part made of aluminum having the pattern (B) having a straight rear part (L2) was prepared, and the surface thereof was subjected to hard anodized treatment + PTFE treatment. did. This surface treatment was performed by Tefrohard made by Hoshi Giken.

Plug C: An aluminum plug base material having the same dimensions as the plug B was prepared, and only the hard anodized treatment was applied to the surface. This surface treatment was performed by Hoshi Giken Co., Ltd.

[Example 1]
The plug A was incorporated in the manufacturing apparatus shown in FIG.
As a polypropylene resin, PM600A (75% by mass) manufactured by Sun Allomer Co., Ltd. and SD632 (25% by mass) manufactured by Basell are mixed, and 100 parts by mass of the mixed resin is manufactured by Clariant Co. HK-70 of 0.2 parts by mass was dry blended. This mixed raw material is supplied to a hopper of a first extruder of a tandem extruder composed of a first extruder and a second extruder having a diameter of 90 mm to 115 mm, heated and melted, and then butane (isobutane / normal butane = 35/65) was press-fitted into 1.0 part by mass with respect to 100 parts by mass of the resin melt and kneaded. This mixture is subsequently transferred to the second extruder and cooled to a suitable foaming temperature, and is extruded and foamed at an extrusion rate of 140 kg / hour from a circular die having a cylindrical extrusion port with a diameter of 190 mm attached to the tip of the second extruder. I let you. The obtained cylindrical foam is cooled along the plug A, the inside of which is cooled with cooling water at 25 ° C., and the outer surface thereof is air-cooled by an air cooling device having an outlet larger than the diameter of the plug A. Were blown and cooled, and cut by a cutter attached downstream of the plug and wound on a roll as two continuous sheets.
As a result, a polypropylene resin foam sheet having a basis weight of 270 g / m ² and a thickness of 0.82 mm could be stably produced. The take-up resistance was evaluated by the motor load of the take-up machine. The take-up resistance is desirably expressed in units of force such as tension, but since this force can be substituted as the drive torque of the take-up machine, it can be compared as the load of the take-up machine motor. In Example 1, the motor load was 15.0 A. The results are shown in Table 2.

[Example 2]
A foam sheet was produced in the same manner as in Example 1 except that the extrusion rate from the die was 155 kg / hour.
As a result, a polypropylene resin foam sheet having a basis weight of 270 g / m ² and a thickness of 0.82 mm could be stably produced. The motor load was 15.5A. The results are shown in Table 2.

[Example 3]
A foam sheet was produced in the same manner as in Example 1 except that the plug B was used in place of the plug A and the foaming agent was increased to 1.1 parts by mass with respect to 100 parts by mass of the resin melt.
As a result, a polypropylene resin foam sheet having a basis weight of 300 g / m ² and a thickness of 0.90 mm could be stably produced. The motor load was 15.5A. The results are shown in Table 2. Furthermore, the take-up speed was increased and the take-up speed was set so that the basis weight was 270 g / m ^2. However, the take-up resistance increased, and the foamed sheet was cut, and stable production could not be performed.

[Example 4]
A foam sheet was produced in the same manner as in Example 1 except that the plug B was used instead of the plug A.
As a result, a polypropylene resin foam sheet having a basis weight of 300 g / m ² and a thickness of 0.82 mm could be stably produced. The motor load was 16.0A. The results are shown in Table 2. Furthermore, the take-up speed was increased and the take-up speed was set so that the basis weight was 270 g / m ^2. However, the take-up resistance increased, and the foamed sheet was cut, and stable production could not be performed.

[Comparative Example 1]
A foam sheet was produced in the same manner as in Example 1 except that the plug C was used in place of the plug A and the extrusion rate from the die was 155 kg / hour.
The take-up speed was set so that the basis weight was 300 g / m ² , but the take-up resistance increased, the foamed sheet was cut, and stable production was not possible. The basis weight capable of stable production was 330 g / m ² and the thickness was 0.90 mm, and the motor load at this time was 17.0 A. The results are shown in Table 2.

[Comparative Example 2]
A foam sheet was produced in the same manner as in Example 1 except that the plug C was used instead of the plug A.
The take-up speed was set so that the basis weight was 300 g / m ² , but the take-up resistance increased, the foamed sheet was cut, and stable production was not possible. The basis weight capable of stable production was 330 g / m ² and the thickness was 0.90 mm, and the motor load at this time was 16.0 A. The results are shown in Table 2.

From the results of Table 2, in Examples 1 to 4 using the plugs A and B according to the present invention, the take-up resistance of the foamed sheet passing through the plug is reduced, so that the basis weight is 300 g / m ² or less. An amount of the polypropylene resin foam sheet could be stably produced.
On the other hand, in Comparative Examples 1 and 2 using the plug C subjected only to the alumite treatment, a low basis weight polypropylene-based resin foam sheet having a basis weight of 300 g / m ² or less could not be stably produced.

It is a block diagram which shows an example of the thermoplastic resin foam sheet manufacturing apparatus of this invention. It is a block diagram of the experimental apparatus used for the slipperiness evaluation of the Example of this invention. It is a front view which shows an example of the plug of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st extruder, 2 ... 2nd extruder, 3 ... Die, 4 ... Raw material compounding apparatus, 5 ... Hopper, 6 ... Foaming agent press injection pump, 7 ... Plug, 8 ... Cutter, 9 ... Foam sheet, 10 ... Take-up roll, 11 ... foam sheet roll, 13 ... test piece, 14 ... polypropylene resin foam sheet, 15 ... stainless steel plate.

Claims (7)

An extruder for extruding the molten mixture by melting and mixing the thermoplastic resin and the foaming agent, a die attached to the discharge port of the extruder, and a foaming intermediate extruded from the die are allowed to travel along the outer peripheral surface. In the plug used for the thermoplastic resin foam sheet manufacturing apparatus provided with a plug for producing a thermoplastic resin foam sheet by cooling while
A plug characterized in that an alumite treatment layer or a hard alumite treatment layer is provided on the outer surface of the plug, and a fluororesin coating layer is provided on the outer surface thereof.   2. The plug according to claim 1, further comprising an outer periphery gradually decreasing portion that gradually decreases the outer periphery of the plug from the die side toward the downstream side in the sheet take-up direction.   The plug according to claim 2, wherein the outer circumferential gradually decreasing portion is provided from a die side of the plug to a terminal end in a sheet take-up direction.   The said outer periphery gradually decreasing part is provided between the die | dye side of a plug and the predetermined position downstream of a sheet | seat taking-off direction, and the outer periphery of a plug is made into the straight part with a fixed outer periphery from the sheet | seat taking-out direction downstream from it The plug described.   The plug according to claim 2, wherein a plurality of the outer periphery gradually decreasing portions are provided, and the outer periphery gradually decreasing portions have different outer periphery reduction rates. An extruder for extruding the molten mixture by melting and mixing the thermoplastic resin and the foaming agent, a die attached to the discharge port of the extruder, and a foaming intermediate extruded from the die are allowed to travel along the outer peripheral surface. In a thermoplastic resin foam sheet manufacturing apparatus comprising a plug for cooling and manufacturing a thermoplastic resin foam sheet while
A thermoplastic resin foam sheet manufacturing apparatus comprising the plug according to any one of claims 1 to 5 as a plug. The molten mixture of the thermoplastic resin and the foaming agent melt-mixed in the extruder 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 expanded to the outer periphery of the plug. In the method for producing a thermoplastic resin foam sheet, which is cooled while proceeding along the surface to produce a thermoplastic resin foam sheet,
A method for producing a thermoplastic resin foam sheet, wherein the plug according to claim 1 is used as the plug.

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