JP3639768B2 - Thin low-magnification foam sheet molding method and molding sizing block - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for compactly and inexpensively molding a foamed sheet of thermoplastic resin material such as plastic having a skin layer with a flat surface and a thickness of 2 mm or less and an expansion ratio of 1.4 to 3.0 times. And its sizing block.
[0002]
[Prior art]
Conventionally, the T-die method has been widely used in extrusion molding of sheets and films of thermoplastics and the like. However, it has been difficult to extrude a foam sheet such as a plastic having a foam gas by the T-die method. This is because a material such as plastic is held in a substantially unfoamed state by the internal pressure while it is present in the T-die system from the extruder, but once it is extruded from the T-die outlet into the atmosphere, The sheet material suddenly expands in three dimensions, and the sheet material is difficult to absorb the expansion of the sheet material, particularly in the direction perpendicular to the flow, and the so-called corrugated undulation phenomenon occurs. As a result, it was difficult to obtain a smooth surface, a uniform thickness and a uniform foamed state.
[0003]
Further, in the case of a thin sheet, the air gap section immediately after extrusion from the T-die is likely to sag due to insufficient strength and sheet breakage, which makes the molding more difficult. This phenomenon also occurs when a sheet having a low expansion ratio is extruded. Therefore, the extrusion molding by the T-die method of the foam sheet having a small thickness and a low expansion ratio further increases the difficulty.
[0004]
In addition, the foaming gas mixed and distributed in the thermoplastic resin material such as molten plastic plays a role of a lubricant in the T-die system from the extruder, and apparently lowers the melt viscosity of the material. . The greater the amount of foaming gas, that is, the higher the foaming ratio, the more pronounced the effect. In the extrusion molding of a sheet having a high expansion ratio, the amount of foaming gas is large, so the apparent viscosity reduction effect is high, and even if the molding temperature is lowered, the increase in power load on the extruder can be kept low, and low-temperature molding can be performed. It becomes possible.
The lower the temperature of the melted material, the higher the foam cell trapping rate of the material, and the more uniformly dispersed within the material. In the foamed sheet, the foamed cells are uniformly and homogenized and pushed out of the T-die. In addition to increasing the sheet strength after that, not only the subsequent cooling and solidification process is facilitated, but also a smoother sheet is provided.
[0005]
However, in the sheet of the melted material having a low expansion ratio, the effect of lowering the viscosity is low, and the molding temperature range that can be lowered due to restrictions on the power load of the extruder is narrow. As a result, the molding temperature must be higher than the desired level. Did not get. High molding temperatures have negative effects on foam cell uniformity, homogenous dispersion, sheet strength and smoothness and cooling rate, making extrusion difficult, and for thin foam sheets, as described above Extrusion molding was made more difficult due to the tendency of sagging and sheet breakage.
[0006]
Sheets with extremely low expansion ratios have a small distribution ratio of foam cells, so the sheet strength does not decrease much, the sheet does not easily sag or break, and the expansion rate after extrusion of the T-die is low. Is relatively easy to implement.
[0007]
The T-die extrusion method is particularly difficult when the expansion ratio is 1.4 to 3.0 times and the sheet thickness is 2 mm or less. In sheet molding having this condition, after T-die extrusion, the so-called corrugation phenomenon is likely to occur, and the sheet having insufficient melt tension has a difficult problem that a smooth skin layer must be applied. is there.
In order to solve these problems, a foam sheet forming method has been proposed in which a sheet surface extruded from a T-die is cooled and solidified using a roll or a metal belt.
[0008]
[Problems to be solved by the invention]
However, the roll method has a problem that although the air gap can be narrowed when the roll diameter is reduced, the strength of the roll itself is insufficient and it is easy to bend. Conversely, when the roll diameter is increased, the roll strength deficiency is resolved, but the air gap widens, the sheet strength deficiency becomes obvious, the sheet is liable to sag and break, and the sheet surface is cooled and solidified. The foam cell grows due to gas pressure until the roll touch occurs, so that not only the so-called corrugated undulation phenomenon occurs, but the foam cell continues to progress or the grown foam cell is There is a problem that it easily reaches a hole-drilling phenomenon and surface roughness.
[0009]
Moreover, in the single-sided roll contact method, not only the cooling of the non-contact surface of the foam sheet is insufficient, but also a pressing force in the sheet thickness direction cannot be expected. In the two-roll crimping method, the crimping time and the crimping area are limited, and it has not been possible to sufficiently apply uniform cooling and pressing force to the sheet continuously.
[0010]
In addition, the metal belt method can apply uniform cooling and pressing force to the sheet, but the belt drive roll is large and the air gap cannot be narrowed, so that the sheet is likely to sag and the sheet breaks. There are problems such as easy overgrowth of foam cells due to cooling delay, and difficulty in maintaining a constant gap between the upper and lower belts between rolls. Smooth skin layer and uniform foaming. There were many problems in producing a thin sheet having cells and a low expansion ratio. Furthermore, this metal belt system has a problem that the apparatus itself becomes large and complicated, which not only increases the equipment cost but also increases the maintenance cost.
[0011]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a plastic having a skin layer having excellent flatness and a foam cell having good uniformity. Another object of the present invention is to provide a method for forming a foamed sheet having a foaming ratio of 1.4 to 3.0 times with a thickness of 2 mm or less of a thermoplastic resin material such as a sizing block.
[0012]
[Means for Solving the Problems]
For this purpose, the invention according to claim 1 is an invention in which a thermoplastic resin material such as plastic containing foaming gas is extruded from a T-die into a sheet shape, the thickness is 2 mm or less, and the foaming ratio is 1.4-3. A method of forming a 0 times foam sheet,
First and second sizing blocks arranged at positions slightly spaced downstream of the T-die and facing each other with both sides of the sheet-like material extruded from the T-die sandwiched from both sides Immediately after both sides of the sheet-like material passing between the bodies are pushed out from the T-die, each suction vertical hole and each narrow hole of the first and second sizing block bodies connected to an external suction pressure reducing mechanism are provided. A cooling medium that circulates in each cooling medium flow path of the first and second sizing block bodies by bringing them into suction contact with the surfaces of the first and second sizing block bodies through grooves and increasing the degree of adhesion between both interfaces. The cooling rate of the sheet-like material is increased, the smoothness of both sides of the sheet-like material is also increased, the substantial growth of the foamed cells is prevented, and a smooth skin layer is formed to have the thickness and the foaming ratio. It is characterized in molding the sheet.
[0013]
The invention according to claim 2 is a foamed sheet having a thickness of 2 mm or less and a foaming ratio of 1.4 to 3.0 times by extruding a thermoplastic resin material such as plastic containing foaming gas from a T-die in a sheet shape. A sizing block for forming the sheet-like material so as to be in a position slightly separated on the downstream side of the T-die and so as to contact both sides of the sheet-like material extruded from the T-die from both sides. The first and second sizing block bodies arranged opposite to each other, and an adjusting mechanism for adjusting the gap between the first and second sizing block bodies over the entire width thereof. A plurality of narrow grooves are provided at appropriate intervals in a direction orthogonal to the flow direction of the sheet-like material, leaving both end portions on the surface side in contact with the sheet-like material, and A cooling medium that is provided with a plurality of suction vertical holes that communicate with the narrow groove and that communicates with an external suction pressure reducing mechanism, and further cools the surfaces of both sizing block bodies over the entire width at a portion that does not interfere with each suction vertical hole. A plurality of cooling medium flow paths are provided, and both sides of the sheet-like material passing between the first and second sizing block bodies are immediately connected to the suction pressure reducing mechanism after being pushed out from the T-die. Cooling by the cooling medium circulating in each cooling medium flow path by making suction contact with the surfaces of the first and second sizing block bodies through each suction vertical hole and each narrow groove and increasing the adhesion degree of both interfaces The foamed sheet having the above-mentioned thickness and expansion ratio is formed by increasing the speed and also improving the smoothness of both sides of the sheet-like material, preventing the substantial growth of the foamed cells and forming a smooth skin layer. It is characterized by a configuration to form.
[0014]
According to a third aspect of the present invention, each of the narrow grooves in the first and second sizing block bodies is formed in a three-chamber type having independent both ends and a central part, and each of the narrow grooves is respectively It can be adjusted to an independent decompression state.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic front view of an example of a sizing block according to the present invention, FIG. 2 is a schematic plan view, showing a piping system of each cooling medium flow path, and FIG. 3 is a schematic side sectional view of both sizing block bodies. . In these figures, a thermoplastic resin material such as plastic containing foaming gas is heated in an extruder (not shown), plasticized and melted, and homogeneously kneaded and mixed with the T-die connected to the tip of the extruder. 1 and then formed into a sheet shape in the T-die 1, and then extruded from the T-die 1, and the extruded sheet-like material 2 passes through the sizing block to form a smooth skin. The thickness of the layer formed is 2 mm or less, and the foaming sheet 3 has an expansion ratio of 1.4 to 3.0 times.
[0016]
The sizing block includes a pair of metal first and second sizing block bodies and an adjusting mechanism for adjusting the gap between the first and second sizing block bodies over the entire width.
[0017]
The first sizing block body 4a and the second sizing block body 4b are equivalent and have a square shape in plan view, and these first and second sizing block bodies 4a and 4b are located downstream of the T-die 1. In addition, the sheet-like material 2 pushed out from the T-die 1 is disposed so as to be in contact with the both sides of the sheet-like material 2 pushed out from both sides at a position very slightly away from the outlet of the T-die 1.
[0018]
The first and second sizing block bodies 4a and 4b are arranged at positions very slightly away from the T-die exit, because a skin layer having a smooth surface is generated without causing a so-called corrugated wavy phenomenon. In order to obtain, after being extruded from the T-die 1, both sides of the foamed sheet are brought into contact with the sizing block bodies 4a and 4b set to a desired temperature within a short time, and the cooling and solidification proceed quickly. This is because the temperature field of the sizing block bodies 4 a and 4 b is independent from that of the T-die 1.
[0019]
In the illustrated embodiment, the T-die 1 and the two sizing block bodies 4a and 4b are arranged horizontally. However, the present invention is not limited to this and may be arranged vertically.
[0020]
As shown in FIGS. 2 and 3, in the vicinity of the side surface of the sizing block bodies 4a and 4b on the sheet-like material 2 side, one cooling medium flow path 5a and 5b having a slightly small diameter over the entire width, Four cooling medium flow paths 6a and 6b having an appropriate interval and having a slightly larger diameter are provided. Inside these cooling medium flow paths 5a, 5b, 6a and 6b, a pipe which will be described later shown in FIG. A cooling medium such as water or oil whose temperature is controlled by the system flows, and the temperature of the sizing block bodies 4a and 4b is maintained at a predetermined level.
[0021]
Leave both ends of the sizing block bodies 4a, 4b on the wall surface on the sheet material 2 side and over the full width in the direction perpendicular to the flow of the sheet-like material 2 between the cooling medium flow paths 5a, 5b, 6a, 6b. The narrow narrow grooves 7a and 7b are provided in the width direction in the three-chamber direction, and suction vertical holes 8a and 8b communicating with the narrow grooves 7a and 7b are formed at the bottoms of the narrow grooves 7a and 7b. A plurality of (four in total, twelve in three rows) are provided in the direction, and a pressure regulating valve and a vacuum suction mechanism, which will be described later, are connected to the suction vertical holes 8a and 8b.
[0022]
Note that slightly larger R-surface portions 9a and 9b are formed on the outflow side of the lower end of the suction vertical holes 8a and 8b, which comes into contact with the sheet-like material 2, so that the sheet-like material 2 is not caught during suction contact.
[0023]
The cooling medium flow paths in both sizing block bodies 4a and 4b are connected by the piping system shown in FIG. In addition, since the piping system of the 1st sizing block body 4a and the 2nd sizing block body 4b is the same, it demonstrates about the 1st sizing block body 4a and the description about the 2nd sizing block body 4b is abbreviate | omitted.
[0024]
In FIG. 2, the coolant flow path 5 a on the inflow side of the sheet-like material 2 is measured by a temperature sensor 10 attached to the sizing block body 4 a, and a predetermined temperature is detected by a temperature controller 12 in the temperature adjustment unit 11. The cooling medium adjusted and held in the refrigerant circulates through pipes 13 and 14 provided with valves and a medium thermometer, and in each cooling medium flow path 6a, a temperature sensor 15 attached to the sizing block body 4a. The cooling medium that has been temperature-detected by the temperature controller 17 and adjusted and held at a predetermined temperature by the temperature controller 17 in the temperature control unit 16 is a pipe 18 with a valve and a medium thermometer, a manifold 19, each branch pipe 20, 21, and a manifold. 22, and circulates through the pipe 23.
[0025]
And since the cooling medium temperature of the cooling medium flow paths 5a and 5b on the side into which the sheet-like material 2 flows in causes the non-foamed skin layer to be generated earlier in the sheet-like material 2, The coolant temperature is set lower than the coolant temperature of the coolant flow paths 6a and 6b.
[0026]
Each cooling medium flow path is not particularly shown, but instead of the through hole, a cooling pipe is provided in a groove formed on the surface of both sizing block bodies, and the surface of the cooling pipe is formed into a sheet-like material. It is also possible to make it contact directly with the surface of 2, and in this case, a larger amount of heat transfer occurs, the cooling temperature of the sheet-like material 2 is further increased, and the generation of the skin layer is also accelerated. In this engraved groove of the cooling pipe, a slight gap may be provided on the downstream side of the sheet-like material 2 of the cooling pipe with respect to the cooling pipe, and the gap may be used as a reduced pressure narrow groove.
[0027]
As shown in FIG. 5, at the tip of each suction vertical hole 8a, 8b, the sheet-like material 2 is sucked through the narrow grooves 7a, 7b and brought into contact with the surfaces of the sizing block bodies 4a, 4b. Therefore, a vacuum suction mechanism is connected.
[0028]
The vacuum suction mechanism is composed of a vacuum pump 24, an intermediate tank 25, a pipe 26 provided with a valve and a pressure gauge, and branch pipes 27 and 28. In FIG. 5, the piping system of the first sizing block body 4a is schematically shown. Since the second sizing block body 4b is the same, only the suction vertical hole 8b is schematically shown, and the piping system thereof is not shown.
[0029]
In this way, the narrow grooves 7a and 7b are held at a predetermined decompression level by the decompression suction mechanism. However, the narrow grooves 7a and 7b have different levels at the center and both ends, and are located near the center. Tend to be held stronger. Therefore, in this embodiment, the narrow groove is provided in a three-room type in the width direction of both sizing block bodies 4a and 4b, and each room can be adjusted to an independent decompression level. Thereby, the sheet-like material 2 can obtain substantially the same adhesion degree with respect to both sizing block bodies 4a and 4b over the width direction.
[0030]
Further, the three-room type narrow grooves 7a and 7b can set the pressure reduction level in the entrance-side narrow groove where the surface cooling solidified layer of the sheet-like material 2 is thin to a low level.
[0031]
The gap adjusting mechanism for adjusting the distance between the first sizing block body 4a and the second sizing block body 4b over the entire width thereof has four support legs as schematically shown in FIGS. A lifting screw rod 30 that is rotatably arranged on both left and right ends of a base frame 29 (not shown) and that has a screw direction opposite to the upper and lower sides of the center portion, and a first sizing block Block-shaped lift housing 31 fixed to the left and right end central portions of the upper surface of the body 4a and the left and right end center portions of the lower surface of the second sizing block body 4b. The nut member 32 that is screwed with the motor, the motor driving portion 33 that rotates the lifting screw rod 30 forward and backward, and the rotational force of the driving portion 33 is received to rotate the lifting screw rod 30. When the thickness of the sheet-like material 2 and the foaming ratio are different, both the lifting and lowering are performed through the driving of both driving conducting portions 34 and 34 by the rotation of the motor driving portion 33. The screw rod 30 rotates forward (reverse), the first sizing block body 4a rises (falls) and the second sizing block body 4b descends (rises), so that the gap between the sizing block bodies 4a, 4b is appropriately set. It can be adjusted to.
[0032]
Next, the operation will be described. When a thermoplastic resin material such as a plastic containing a foaming gas is extruded from the T-die 1 into a sheet shape, the thermoplastic resin material is released under atmospheric pressure and starts to expand three-dimensionally. Since the first and second sizing block bodies 4a and 4b are arranged at positions slightly away from the T-die 1, the air gap is extremely short, and the sheet material 2 extruded from the T-die 1 has a predetermined length. Immediately flows between the first sizing block body 4a and the second sizing block body 4b set in the gap.
[0033]
The sheet material 2 that also expands in the thickness direction and flows between the sizing block bodies 4a and 4b is set to a predetermined temperature level by the cooling medium circulating through the cooling medium flow paths 5a, 5b, 6a, and 6b on both sides. Then, the surfaces of both the sizing block bodies 4a and 4b that are held are brought into contact with each other immediately, and cooling and solidification are started. Since the temperature drops in a very short time after being extruded from the T-die 1 in this way, both surfaces of the sheet-like material 2 are rapidly cooled and solidified, and the growth of the foam cells is hindered. An unfoamed skin layer is formed on both sides. During this cooling, the sheet-like material 2 is sucked under reduced pressure by an external vacuum suction mechanism through the narrow grooves 7a, 7b and the suction vertical holes 8a, 8b of both sizing block bodies 4a, 4b, and both sizing block bodies 4a. The degree of adhesion with the surface of 4b is increased.
[0034]
Since the vacuum suction from the narrow grooves 7a and 7b is performed in a state where the double-sided thin layers of the sheet-like material 2 are substantially cooled and solidified, both sizing block bodies 4a are conversely damaged without damaging both sides of the sheet-like material 2. In order to increase the degree of adhesion to the surface of 4b and to increase the smoothness of both surfaces and the amount of heat for cooling removal, the finish of the skin layer can be achieved more quickly.
[0035]
Thus, the early generation of the skin layer having excellent smoothness suppresses the expansion deformation in the width direction due to the ongoing foaming in the sheet material 2 and prevents the occurrence of the so-called corrugated wavy phenomenon. In addition, the uniformity of the thickness of the sheet material 2 is enhanced, and a more uniform foaming state is brought about inside the sheet material 2.
[0036]
The sheet material 2 on which the smooth ski layer is formed in this way passes through the auxiliary cooling roll 35 and has a thickness of 2 mm or less as a foamed sheet 3 having a foaming ratio of 1.4 to 3.0 times to a take-up device (not shown). Proceed with
[0037]
【The invention's effect】
Thus, according to the present invention, both surfaces of the sheet-like material extruded from the T-die can be quickly cooled, and at the same time, the degree of adhesion of the sheet material to both sizing block bodies is increased through the reduced pressure narrow groove. By increasing the cooling rate and generating the skin layer at an early stage, it suppresses expansion deformation in the width direction of the sheet material, and has excellent smoothness of the surface skin layer, uniformity of thickness, and uniformity of the foam cell, A foam sheet having a thickness of 2 mm or less and an expansion ratio of 1.4 to 3.0 times can be formed.
[0038]
In addition, since the present invention has a simple structure and is compact, both the manufacturing cost and the maintenance cost are low, and a sizing block excellent in cost performance can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic front view of an example of a sizing block according to the present invention.
FIG. 2 is a schematic plan view showing a piping system of each cooling medium flow path.
FIG. 3 is a schematic sectional side view of both sizing block bodies.
FIG. 4 is a partially enlarged cross-sectional view of a narrow groove.
FIG. 5 is an explanatory view of piping in a vacuum suction mechanism showing a cross section of both sizing block bodies.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 T-die 2 Sheet-like material 3 Foam sheet | seat 4a, 4b Sizing block body 5a, 5b, 6a, 6b Suction vertical hole 7a, 7b Fine narrow groove | channel 11, 16 Temperature control unit 13,14,18,23 Piping 19,22 Manifold 20, 21 Branch pipe 24 Depressurization pump 26 Pipe 27, 28 Branch pipe 29 Base frame 30 Lifting screw rod 31 Lifting housing 32 Nut member 33 Motor drive section 34 Drive conduction section

Claims (3)

A method of forming a foamed sheet having a thickness of 2 mm or less and a foaming ratio of 1.4 to 3.0 times by extruding a thermoplastic resin material such as plastic containing foaming gas from a T-die,
First and second sizing blocks arranged at positions slightly spaced downstream of the T-die and facing each other with both sides of the sheet-like material extruded from the T-die sandwiched from both sides Immediately after both sides of the sheet-like material passing between the bodies are pushed out from the T-die, each suction vertical hole and each narrow hole of the first and second sizing block bodies connected to an external suction pressure reducing mechanism are provided. A cooling medium that circulates in each cooling medium flow path of the first and second sizing block bodies by bringing them into suction contact with the surfaces of the first and second sizing block bodies through grooves and increasing the degree of adhesion between both interfaces. The cooling rate of the sheet-like material is increased, the smoothness of both sides of the sheet-like material is also increased, the substantial growth of the foamed cells is prevented, and a smooth skin layer is formed to have the thickness and the foaming ratio. Molding a thin low-magnification foam sheet, which comprises forming a sheet. A sizing block for extruding a thermoplastic resin material such as plastic containing foaming gas from a T-die into a sheet to form a foamed sheet with a thickness of 2 mm or less and an expansion ratio of 1.4 to 3.0. There,
First and second sizing blocks that are arranged to face each other with both sides of the sheet-like material extruded from the T-die being sandwiched from both sides at a slightly separated position on the downstream side of the T-die. Body,
An adjustment mechanism for adjusting the gap between the first and second sizing block bodies over the entire width,
A plurality of the first and second sizing block bodies are provided with appropriate intervals in a direction perpendicular to the flow direction of the sheet-like material, leaving both ends on the surface side in contact with the sheet-like material. Are provided with a plurality of suction vertical holes that communicate with these narrow grooves and communicate with an external suction pressure reducing mechanism. Further, the portions that do not interfere with the respective suction vertical holes extend over the entire width thereof. A plurality of cooling medium flow paths through which a cooling medium for cooling the surfaces of both sizing block bodies flows are provided,
After both sides of the sheet-like material passing between the first and second sizing block bodies are pushed out from the T-die, they are promptly passed through the suction vertical holes and the fine narrow grooves connected to the suction pressure reducing mechanism. The surfaces of the first and second sizing block bodies are brought into suction contact, and the degree of adhesion of both interfaces is increased to increase the cooling rate by the cooling medium circulating in each cooling medium flow path, and the both sides of the sheet-like material are A thin low-magnification foam sheet characterized in that the foaming sheet having the above-mentioned thickness and foaming ratio is formed by increasing the smoothness and preventing the substantial growth of the foaming cell to form a smooth skin layer. Sizing block for molding. Each of the narrow grooves in the first and second sizing block bodies is formed in a three-chamber type having both independent end portions and a central portion, and each of the narrow grooves can be adjusted to an independent reduced pressure state. The sizing block for molding a thin low-magnification foamed sheet according to claim 2, wherein

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