JP2803012B2 - Method for producing thick foamed synthetic resin sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thick foamed synthetic resin sheet, and more particularly, to extruding a foamed synthetic resin sheet into a tubular shape from a circular die, and pressing the tubular sheet with a pinch roll to form two sheets. An improved method for fusing and thereby producing a thick foam synthetic resin sheet.

[0002]

2. Description of the Related Art When a synthetic resin containing a foaming agent is extruded into a tubular shape from a circular die to form a tubular foam sheet, the cross section of the tubular foam sheet is formed by three-dimensional foaming.
A so-called chrysanthemum pattern is exhibited as shown in FIG. It is well known that it is necessary to control the resin temperature within a certain range in order to prevent the generation of the chrysanthemum pattern or to prevent the generation of the chrysanthemum pattern from causing a problem in molding.

When a chrysanthemum pattern is generated in a tubular foamed sheet when a tubular foamed sheet is pressed and fused to produce a thick foamed synthetic resin sheet, the tubular foamed sheet is pressed and fused as shown in FIG. In this case, unevenness in fusion and uneven patterns on the surface occur, which makes it impossible to obtain a sheet that is not only unfavorable in appearance but also excellent in physical properties. In order to suppress the generation of chrysanthemum patterns to such an extent that molding is not hindered, the extrusion temperature of the resin may be lowered. However, at low temperatures, the sheet cannot be fused by pinching with a pinch roll. Various methods have been proposed to solve this.

[0004] As one of effective methods for this purpose, as shown in FIG. 3, a circular die 2 attached to the tip of the extruder 1 on the discharge side as shown in FIG. At a temperature equal to or higher than the temperature at which the resin is generated, a synthetic resin containing a foaming agent is extruded into a tubular shape. Immediately after the extrusion, air is blown from the air ring 3 onto the outer surface of the tubular sheet 4 to cool the outer surface of the sheet. The escape of the volatile components and the foaming gas from the surface is prevented, and the tubular foam sheet 4 is guided to the pinch roll 6 by the guide plate 5 and sandwiched by the pinch roll 6 to fuse the inner surfaces of the tubular foam sheet 4 together. After cutting, the take-off machine 7 cuts it with the take-off / cutting machine 8 so that no chrysanthemum pattern is generated.
In addition, a method has been developed and proposed for obtaining a thick foam sheet in which two sheets are firmly combined (Japanese Patent Publication No. 56-21590).

[0005] According to the above method, since the outer surface of the sheet is cooled by air immediately after the foamed sheet is extruded from the circular die into a tubular shape, volatile components such as a foaming agent and a cell regulator and foaming gas are reduced. Escaping from the outer surface is suppressed and accumulates inside the tubular sheet. When this is pressed with a pinch roll, the inner surface of the tubular foamed sheet is fused to obtain a two-piece thick foamed sheet. The obtained thick foam sheet does not have a chrysanthemum pattern and is strongly fused 2
A laminated sheet having high strength, particularly high bending strength, is obtained. Further, since the outer surface of the foamed sheet is covered with unfoamed or finely foamed, a visually attractive sheet is obtained.

[0006]

The applicant of the present invention has continuously manufactured a thick foamed synthetic resin sheet by the above-mentioned method, and in the process, a product having a thickness of about 3 mm or more will be obtained. Then, it was perceived that wrinkles were easily generated on both sides of the foamed sheet which was melted and fixed at the time of pinching. The generation of wrinkles sometimes impaired the appearance and caused unevenness in strength. In addition, when wrinkles occurred, both sides had to be cut, resulting in a large loss.

An object of the present invention is to solve the above-mentioned disadvantages of the conventional method for producing a thick foamed synthetic resin sheet. More specifically, the thickness of the product is 3 mm to 15 mm.
It is an object of the present invention to provide an improved production method capable of producing a thick foamed synthetic resin sheet without causing wrinkles on both sides even if it is of a small degree.

[0008]

Means for Solving the Problems In order to solve the above problems and achieve the object, the present applicant extrudes a foamed synthetic resin sheet into a tubular shape from a circular die and presses the tubular sheet with a pinch roll. By continuing analysis and experiments on a method of manufacturing a thick foamed synthetic resin sheet by fusing two sheets up and down, the synthetic resin containing a foaming agent is extruded from a circular die as a tubular sheet, and then extruded. It has been perceived that maintaining the shape of the tubular sheet in a particular shape eliminates the above disadvantages.

That is, in the present invention, the object is to extrude a synthetic resin containing a foaming agent as a tubular sheet from a circular die at a temperature lower than a temperature at which bubbles are broken and higher than a temperature at which a chrysanthemum pattern is generated, Immediately after the extrusion, the outer surface is cooled with a gas to suppress the volatile components and the escape of the foaming gas from the outer surface of the sheet. The tubular sheet is pressed with a pinch roll to fuse the inner surfaces to form two sheets. In a method for producing a thick foamed synthetic resin sheet, wherein a laminated foamed synthetic resin sheet is obtained, the cross-sectional shape of the extruded tubular sheet at a point near the end of foaming has a major axis / minor axis = 1.1 to The problem is solved by pinching with a pinch roll while controlling to have an elliptical shape of 3.0.

[0010] In the present invention, "at the end of foaming" refers to the time when the volume of the tubular sheet after being extruded from the circular die becomes maximum. Further, the tubular sheet may be extruded from the circular die in a single-layer state, or may be extruded in layers in the circular die by co-extrusion. When extruding in a layered form, it is a preferable embodiment to make the expansion ratio of the outer layer lower than that of the inner layer, thereby obtaining a thick foam synthetic resin sheet having a beautiful appearance and improved printability. Can be.

In the method according to the present invention, as the synthetic resin as a raw material, a styrene polymer, a copolymer with a monomer such as butadiene, acrylonitrile, methyl methacrylate or the like, which is mainly composed of styrene and can be copolymerized with styrene, is preferably used. Is done. In particular, in the case of a polystyrene resin, those having a weight average molecular weight of 150,000 to 550,000 can be suitably used, and a product having a better appearance can be obtained as the molecular weight is smaller.

The resin temperature in extrusion of a synthetic resin varies depending on the thickness of the synthetic resin tubular foam sheet, the content of volatile components such as a foaming agent and a cell regulator, and the like. The temperature is adjusted to be lower than the temperature and higher than the temperature at which the chrysanthemum pattern is generated. The outer surface of the tubular synthetic resin foam sheet extruded from the circular die is cooled by blowing air immediately after extrusion. Although not uniform depending on the conditions, it is usually preferred that this cooling be performed within 3 seconds after extrusion.

The relationship between the amount of gas for cooling and the pressure is preferably within the following range. 3 × 10 ⁻⁴ ≦ P × M ≦ 2.48 × 10 ⁻¹ , P ≦ 4, M ≦ 0.5 (where P is the gas pressure (kg / cm ² ), M is the gas amount (m ³ / m ² )) The distance between the circular die and the pinch roll also varies depending on the amount of the total volatile components, the extrusion temperature of the foam sheet, the expansion ratio of the foam sheet, and the like. It has been experimentally confirmed that it is desirable to be within the range.

In the present invention, in particular, the extruded tubular sheet is controlled so as to have an elliptical cross section at a point near the end of the foaming in which the major axis / minor axis is 1.1 to 3.0. In this case, the cross-sectional shape is such that the major axis / minor axis = 1.1 to 3.
The point at which the ellipsoidal shape of 0 is reached does not need to be strictly at the end of foaming of the tubular sheet, and the object can be achieved within a time range of about 2 seconds before and after the end of foaming. The control method is optional, but the control method is most effective from the relationship between the distance between the circular die and the pinch roll and the angle of the guide plate for guiding the tubular foam sheet to the pinch roll.
Not limited to this, adjusting the shape of the inner guide plate arranged near the extrusion outlet of the circular die to an elliptical shape,
And the like, or a combination of them as appropriate. In the method for measuring the major axis and the minor axis in the present invention, when the guide plate is installed vertically, the major axis is the direction seen from directly above the tubular sheet, and the minor axis is the direction seen from the side. Therefore, a photograph is taken from both directions, or both directions are measured mechanically (using a ruler or the like).

[0015]

[Example 1]

A polystyrene raw material (Idemitsu HH-31) was made to contain a foaming agent (isobutane 6.5 wt%), and an extruder (barrel diameter 1) was used.
Melted at 50 mm, cylinder tip zone temperature 86 ° C), circular die, diameter 180 mm, thickness 1.7 m
extruded through the slit of m. Air was blown to the outer surface of the tubular foam sheet immediately after extrusion at a rate of 0.15 m ³ / m ² from an air ring. The distance between the die and the pinch roll is related to the fusing ability, and varies depending on the resin temperature and the expansion ratio. In this case, the distance is 1.2 m, and the opening of the guide plate expanding from the pinch roll side is 50 degrees. And As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape after extrusion while gradually expanding its cross-sectional shape, and when the foaming was completed, the ratio of long diameter / short shape was 1.28.

Thereafter, the cross-sectional shape is gradually flattened by being guided by a guide plate, and the pinching pressure {(thickness immediately before fusion-thickness after fusion) / (thickness immediately before fusion)} is about 15% with a pinch roll. Crushed to become. Thereafter, the sheet was cut by a take-off cutter using a take-off cutter to obtain a rectangular foamed resin sheet having a density ρ = 0.053 g / cc, a maximum thickness of 5.3 mm, and a minimum thickness of 5.0 mm. The bubble shape was 0.966: 1.275: 0.812 in the ratio of MD (near the center of the cut surface in the flow direction): TD (near the center of the cut surface in the width direction): VD (thickness direction) (hereinafter, referred to as The same measurement is performed for the bubble shape).
The residual gas measured by loss on heating 24 hours after extrusion was 4.
9 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. The maximum thickness after about one month was 5.4 mm, and the minimum thickness was 5.1 mm, and there was no significant change. Next, the surface hardness was measured using Kyoto Polymer Instruments S, S, HARDNE.
It is 7 when measured with SS TESTERTYPE CS
It was 0. In addition, the measuring method of the bubble shape ratio in the above was based on ASTM-2842-69. That is, the bubbles in the flow direction (MD) and the width direction (TD) of the foamed resin sheet are photographed at a magnification of 20 times, and the thickness from the center of the thickness from the surface to the fused portion to 1 / of the thickness from the surface to the fused portion The length L was measured 2/3 in total, the average chord length (t) was measured from the number of bubbles between them, and the average diameter (d) of the bubbles was calculated by the following equation. MD and TD were calculated for the same length. Thereafter, MD: TD: VD was calculated from this numerical value. t = L / bubble number, d = t / 0.616

Example 2 A polystyrene raw material (Asahi Kasei QG254) containing a blowing agent (normal butane 3.8 wt%) was extruded (barrel diameter 150 mm, cylinder tip zone temperature 1).
06 ° C.), inserted into a circular die, and
It was extruded through a slit having a thickness of 00 mm and a thickness of 2.0 mm.
Air was blown from an air ring at a rate of 0.09 m ³ / m ² to the outer surface of the tubular foam sheet immediately after extrusion. The distance between the die and the pinch roll was 1.3 m, and the opening of the guide plate expanding from the pinch roll side was 55 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape after extrusion while gradually expanding its cross-sectional shape, and when the foaming was completed, the ratio of long diameter / short shape was 1.11.

Thereafter, the cross-sectional shape was gradually flattened by being guided by a guide plate, and crushed with a pinch roll so that the pressure was about 7%. Then, it is cut by a take-off cutter with a take-off machine, and has a density ρ = 0.131 g / cc and a maximum thickness of 5.
A rectangular foamed resin sheet having a thickness of 5 mm and a minimum thickness of 5.3 mm was obtained. The residual gas measured by loss on heating 24 hours after extrusion was 2.3 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. Also, the maximum thickness after about one month is 5.9mm,
The minimum thickness is 5.5mm, 0.2mm ~ 0.4mm
It became thick. The surface hardness was 81.

Example 3 A polystyrene raw material (Idemitsu HH-31) containing a foaming agent (normal butane 7, isobutane 3, 5.7 wt%) was extruded (barrel diameter 150 mm, cylinder tip zone temperature). (91 ° C.), inserted into a circular die, and extruded through a slit having a diameter of 180 mm and a thickness of 2.5 mm. Air was blown from an air ring at a rate of 0.05 m ³ / m ² to the outer surface of the tubular foam sheet immediately after extrusion. The distance between the die and the pinch roll is 1.2 m, and the opening of the guide plate expanding from the pinch roll side is 35 mm.
Degree. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while being gradually expanded in cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short shape was 2.5.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinching roll reduces the pressure by about 12%.
Crushed to become. Then, it is cut by a take-off cutter with a take-off machine and has a density ρ = 0.075 g / cc and a maximum thickness of 1
A rectangular foamed resin sheet having a thickness of 0.2 mm and a minimum thickness of 9.9 mm was obtained. The bubble shape ratio is MD: TD: VD = 1.67.
8: 1.066: 0.559. The residual gas measured by loss on heating 24 hours after extrusion was 3.8 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. Also,
After about one month, the maximum thickness is 11.0mm and the minimum thickness is 1
0.4 mm, and 0.5 mm to 0.8 mm thicker. The surface hardness was 72.

Example 4 An extruder (barrel diameter) containing 4.9 wt% of a blowing agent (normal butane 7: isobutane 3) in a polystyrene raw material (QG254 manufactured by Asahi Kasei: Tufprene manufactured by Asahi Kasei 9: 1) was added. 150 mm, cylinder tip zone temperature 89
° C) and inserted into a circular die, with a diameter of 180
extruded from a slit having a thickness of 1.0 mm and a thickness of 1.0 mm. Air was blown onto the outer surface of the tubular foam sheet immediately after extrusion at a rate of 0.11 m ³ / m ² from an air ring. The distance between the die and the pinch roll was 0.9 m, and the opening of the guide plate expanding from the pinch roll side was 50 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while being gradually expanded in cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short form was 1.35.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinch roll reduces the pressure by about 10%.
Crushed to become. Thereafter, the sheet was cut by a take-off cutter to obtain a rectangular foamed resin sheet having a density ρ = 0.105 g / cc, a maximum thickness of 3.7 mm, and a minimum thickness of 3.6 mm. The bubble shape ratio is MD: TD: VD = 1.25.
2: 1.516: 0.527. The residual gas measured by loss on heating 24 hours after extrusion was 3.1 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. Also,
The maximum thickness after about one month is 3.9mm, the minimum thickness is 3.8
mm and 0.2 mm thicker. The surface hardness was 78.

Example 5 A heat-resistant polystyrene resin raw material (DAIRAK # 232)
A foaming agent (Normal butane 5.1)
extruder (barrel diameter 150 m)
m, the temperature at the tip zone of the cylinder is 105 ° C)
1. Insert into a circular die, diameter 200mm, thickness 2.
It was extruded through a 0 mm slit. 0.10 m ³ / m ² from the air ring on the outer surface of the tubular foam sheet immediately after extrusion
Air was blown at the rate of The distance between the die and the pinch roll was 1.3 m, and the opening of the guide plate expanding from the pinch roll side was 45 degrees. As a result, the tubular foamed sheet is deformed from a circular shape to an elliptical shape while gradually expanding its cross-sectional shape after extrusion, and at the time of completion of foaming, the long diameter / short form = 1.
23.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinch roll reduces the pressure by about 13%.
Crushed to become. Thereafter, the sheet was cut by a take-off cutter to obtain a rectangular foamed resin sheet having a density ρ = 0.087 g / cc, a maximum thickness of 6.2 mm, and a minimum thickness of 6.0 mm. The residual gas measured by loss on heating 24 hours after extrusion was 3.6 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. The maximum thickness after one month is 6.8m
m, the minimum thickness is 6.3 mm, and 0.3 mm to 0.6
mm thicker. The surface hardness was 75.

Example 6 A polystyrene raw material (Idemitsu HH-31) containing a foaming agent (9.5 wt% of isobutane) was extruded (barrel diameter: 150 mm, tip zone temperature of cylinder: 79 ° C.).
Melted and inserted into a circular die, 200m in diameter
m, extruded through a 2.2 mm thick slit. The outer surface of the tubular foam sheet immediately after extrusion is placed on the outer surface by an air ring.
Air was blown at a rate of 20 m ³ / m ² . The distance between the die and the pinch roll was 1.4 m, and the opening of the guide plate expanding from the pinch roll side was 40 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while gradually expanding its cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short form was 2.80.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinch roll reduces the pressure by about 28%.
Crushed to become. Then, it was cut by a take-off cutter with a take-off machine to obtain a square foamed resin sheet having a density ρ = 0.045 g / cc, a maximum thickness of 7.5 mm, and a minimum thickness of 7.1 mm. The residual gas measured by loss on heating 24 hours after extrusion was 7.8 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. The maximum thickness after one month is 7.8m
m, the minimum thickness is 7.2 mm, and 0.1 mm to 0.3
mm thicker. The surface hardness was 67.

Example 7 A polystyrene raw material (Idemitsu HH-31) containing a foaming agent (isobutane 10 wt%) was melted by an extruder (barrel diameter 150 mm, cylinder tip zone temperature 74 ° C.), and then circular. Insert into the die, 180mm in diameter,
It was extruded through a slit having a thickness of 2.2 mm. 0.31 from the air ring on the outer surface of the tubular foam sheet immediately after extrusion
Air was blown at a rate of m ³ / m ² . The distance between the die and the pinch roll was 1.3 m, and the opening of the guide plate expanding from the pinch roll side was 45 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while being gradually expanded in cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short shape was 1.32.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinching roll reduces the pressure by about 30%.
Crushed to become. Then, it was cut by a take-off cutter with a take-off cutter to obtain a square foamed resin sheet having a density ρ = 0.044 g / cc, a maximum thickness of 7.6 mm, and a minimum thickness of 7.2 mm. The residual gas measured by loss on heating 24 hours after extrusion was 8.2% by weight. The resulting square foamed resin sheet had some roughness in appearance, but no wrinkles were observed near the sides. Curling of the surface of the resin sheet was observed after 3 days. In addition, the maximum thickness after about one month is 7.9 mm, the minimum thickness is 7.5 mm,
It became 0.3 mm thick. The surface hardness was 67.

Example 8 A polystyrene raw material (Asahi Kasei QG254) containing a foaming agent (normal butane 5.0 wt%) was extruded (barrel diameter 150 mm, cylinder tip zone temperature 9).
0 ° C) and inserted into a circular die, with a diameter of 20
It was extruded through a slit having a thickness of 0 mm and a thickness of 2.2 mm. Air was blown from an air ring at a rate of 0.05 m ³ / m ² to the outer surface of the tubular foam sheet immediately after extrusion. The distance between the die and the pinch roll was 1.1 m, and the opening of the guide plate expanding from the pinch roll side was 38 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while being gradually expanded in cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short shape was 2.3.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinching roll reduces the pressure by about 39%.
Crushed to become. Thereafter, the sheet was cut by a take-off cutter to obtain a rectangular foamed resin sheet having a density ρ = 0.111 g / cc, a maximum thickness of 6.3 mm, and a minimum thickness of 6.0 mm. The residual gas measured by loss on heating 24 hours after extrusion was 2.1 wt%. Although the obtained square foamed resin sheet was somewhat soft, the appearance was beautiful and no wrinkles were observed near the sides. The maximum thickness after about one month was 6.9 mm, the minimum thickness was 6.5 mm, and the thickness was 0.5 mm to 0.6 mm. Surface hardness is 7
It was 7.

Example 9 A tubular sheet was extruded by laminating two layers in a circular die by a co-extrusion method. The inner layer (high-magnification layer) is made of a polystyrene raw material (Asahi Kasei QG254) in which 1.2 parts of talc and a foaming agent (4.7 wt% of isobutane) are injected, and the outer layer (low-magnification layer) is a styrene resin (Asahi Kasei SC)
001) to a blowing agent (isobutane / carbon dioxide = 8/2,
(1.2 wt%) was used. The extruder has a barrel diameter of 150 mm for polystyrene raw material, a cylinder tip zone temperature of 85 ° C, and a barrel diameter of 6 for styrene resin.
Using a 5 mm cylinder with a cylinder tip zone temperature of 82 ° C., after melting, insert into a confluent circular die,
It was extruded through a slit having a thickness of 80 mm and a thickness of 2.0 mm.
The discharge amount was 160 kg / H of polystyrene raw material and 45 kg / H of styrene resin.

Air was blown to the outer surface of the tubular foam sheet immediately after extrusion from the air ring at a rate of 0.09 m ³ / m ² . The distance between the die and the pinch roll is 1.2 m,
The opening of the guide plate expanding from the pinch roll side was set to 50 degrees. As a result, the laminar tubular foamed sheet was deformed from circular to elliptical while being gradually expanded in cross-sectional shape after extrusion, and the ratio of major axis / short form was 1.15 when foaming was completed.

Thereafter, the cross-sectional shape was gradually flattened by being guided by a guide plate, and crushed by a pinch roll so that the clamping pressure was about 7%. Then, it was cut by a take-off cutter with a take-off machine, and the overall density ρ = 0.142 g / cc (polystyrene layer density 0.077 g / cc, maximum thickness 5.5 mm,
A rectangular foamed resin sheet having a minimum thickness of 5.3 mm was obtained. The bubble shape ratio is MD: TD: VD = 1.003: 1.090:
0.915. The residual gas measured by loss on heating 24 hours after extrusion was 2.4 wt%. The resulting square foamed resin sheet had a beautiful appearance and no wrinkles were observed near the sides. The printability was also good. The maximum thickness after about one month was 5.6 mm, and the minimum thickness was 5.4 mm, which was 0.1 mm thick. The surface hardness was 98.

Comparative Example 1 Extrusion and cooling with air were performed under the same conditions as in Example 1. However, the distance between the die and the pinch roll was 1.2 m, and the opening of the guide plate was 30 degrees. As a result, the tubular foamed sheet was deformed from a circular shape to an elliptical shape while being gradually expanded in cross-sectional shape after extrusion, and when the foaming was completed, the ratio of long diameter / short form was 3.30.

Thereafter, the cross section is gradually flattened by being guided by a guide plate, and the pinching roll reduces the pressure by about 15%.
Crushed to become. Then, it was cut by a take-off cutter. As a result, the density ρ = 0.055 g / c
c, A rectangular foamed resin sheet having a maximum thickness of 5.2 mm and a minimum thickness of 4.7 mm was obtained. The residual gas measured by loss on heating 24 hours after extrusion was 4.7% by weight. The resulting square foamed resin sheet had a beautiful appearance, but wrinkles were observed in the vicinity of the side, and thickness variation (maximum thickness−
(Minimum thickness) was also large. In addition, the balloon meandered.

Comparative Example 2 Extrusion and cooling by air were performed under the same conditions as in Example 4. However, the distance between the die and the pinch roll was 1.0 m, and the opening of the guide plate was 60 degrees. As a result, the cross-sectional shape of the tubular foamed sheet was maintained substantially circular after extrusion, and when the foaming was completed, the ratio of long diameter / short form was 1.05.

Thereafter, the cross-sectional shape is gradually flattened by being guided by a guide plate, and the pinch roll reduces the pressure by about 10%.
Crushed to become. Then, it was cut by a take-off cutter. As a result, the density ρ = 0.112 g / c
c, a rectangular foamed resin sheet having a maximum thickness of 3.6 mm and a minimum thickness of 3.4 mm was obtained. The residual gas measured by loss on heating 24 hours after extrusion was 2.9% by weight. The resulting square foamed resin sheet had a beautiful appearance, but wrinkles were observed near the sides.

[Discussion] As can be seen from the description of the above examples and comparative examples, when the cross-sectional shape of the tubular tubular sheet at the time of completion of foaming is almost circular (the ratio of long diameter / short form <1.1). For wrinkles, wrinkles were observed near the side of the sheet during pinching, and the ratio of long diameter / short form was> 3.0.
If the thickness exceeds, the balloon shape changes, and wrinkles are generated, and the thickness accuracy is deteriorated. The cross-sectional shape is major axis / minor axis = 1.1-
By pinching with a pinch roll while controlling to have an elliptical shape of 3.0, a thick foam synthetic resin sheet having no wrinkles near the side and high thickness accuracy can be obtained.

As shown in Example 7, the extrusion 24
When the residual gas measured by loss on heating after time exceeded 8 wt%, curl occurred in the sheet over time and a change in thickness was observed. Therefore, it is a very preferable embodiment to set the residual gas value to 8 wt% or less when implementing the present invention. Further, as shown in Example 8, when the "clamping pressure" value exceeded about 35%, the material became somewhat soft.
This is probably due to the increase in open cells. Therefore, it is a very preferable embodiment that the pinching pressure value is 35% or less when the present invention is carried out.

[0040]

According to the present invention, a thick foamed synthetic resin sheet having a large thickness can be obtained without wrinkles occurring on the side portions.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a balloon.

FIG. 2 is a diagram showing a cross section of a thick foamed synthetic resin sheet as a defective product.

FIG. 3 is a diagram illustrating an apparatus for implementing the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Extruder, 2 ... Circular die, 3 ... Air ring, 4 ... Balloon, 5 ... Guide plate, 6 ... Pinch roll,
7 ... Retractor

Claims (3)

(57) [Claims] 1. A synthetic resin containing a foaming agent is extruded as a tubular sheet from a circular die at a temperature lower than a temperature at which bubbles are destroyed and higher than a temperature at which a chrysanthemum pattern is generated. A thickness for obtaining a two-piece foamed synthetic resin sheet by pressing the tubular sheet with a pinch roll and fusing the inner surface of the tubular sheet in a state where the volatile components and the escape of the foaming gas from the sheet outer surface are suppressed by cooling. A method of manufacturing a foamed synthetic resin sheet, wherein the extruded tubular sheet is controlled such that its cross-sectional shape becomes an elliptical shape in which a major axis / a minor axis is 1.1 to 3.0 at a point near the end of foaming. A method for producing a thick foamed synthetic resin sheet, wherein the sheet is pinched with a pinch roll. 2. The method for producing a thick foamed synthetic resin sheet according to claim 1, wherein the tubular sheet is extruded in layers in a circular die by co-extrusion. 3. The method according to claim 1, wherein the point near the end of the foaming is a point within a time range of about 2 seconds before and after the end of the foaming. [0001]