JP5638843B2 - Method for producing foamed polyethylene terephthalate sheet molded article and foamed polyethylene terephthalate sheet molded article - Google Patents

Description

  The present invention relates to a method for producing a foamed polyethylene terephthalate sheet molded article and a foamed polyethylene terephthalate sheet molded article.

Conventionally, a method of forming a crystalline foamed polyethylene terephthalate sheet by heat is known.
In this molding method, as shown in FIG. 7, the sheet 101 made of crystalline foamed polyethylene terephthalate is conveyed to the oven 102, and is at a temperature required for molding the sheet 101 and not more than a temperature that promotes crystallization of the sheet 101. Preheat with.
Next, using the mold 103 heated to a temperature that promotes crystallization of the sheet 101, the sheet 101 is formed into a desired shape and crystallized.
Finally, the sheet 101 is cooled using the mold 104 maintained at a temperature lower than the temperature necessary for forming the sheet 101.
In this way, the sheet is molded in two stages using the heated mold 103 and the cooled mold 104, thereby increasing the rigidity around the molded product and strengthening the sheet against shrinkage and distortion. (For example, refer to Patent Document 1).

Incidentally, it is known that the crystallinity (%) of the crystalline foamed polyethylene terephthalate sheet affects the heat-resistant temperature. In the above molding, the crystallinity of the molded product depends on the mold temperature and the contact pressure time. Can be changed.
The above sheet is preheated at 140 ° C. to 160 ° C. to soften the sheet, and is molded for about 8 seconds with a mold heated to 180 ° C. and crystallized. Thereby, the sheet having an original crystallinity of 8% to 11% can be increased to a crystallinity of 20% to 25%, and the heat resistance of the molded product is improved.

Japanese Patent No. 2551854

By the way, in the sheet forming method described in Patent Document 1, since the crystallization degree of the sheet used is a low crystallization degree sheet of 8% to 11%, the crystallization is promoted and the molded product is Since the heat resistance can be improved and the elongation of the sheet is large, the molded shape can be sharpened.
However, when a high crystallinity sheet having an original crystallinity of 30% or more is to be molded by the molding method described in Patent Document 1, the molded product of the high crystallinity sheet cannot be sharpened. There was a problem that it was difficult to mold into the shape of the mold.
Furthermore, because the highly crystallized sheet has a small elongation, the sheet becomes non-uniform in elongation due to stretching during molding, uneven thickness occurs, and there is a problem that the dimensional change after standing at high temperature is large due to residual strain at that time. there were.

  The present invention has been made in order to solve the above-described problems. Even when a sheet having a high degree of crystallinity is formed, the follow-up to the forming mold is improved and the shape of the molded product is sharpened. An object of the present invention is to provide a method for producing a foamed polyethylene terephthalate sheet molded product and a foamed polyethylene terephthalate sheet molded product that can suppress uneven thickness and dimensional changes after being left at high temperature.

In order to solve the above problems, the present invention provides:
A preheating step of heating a foamed polyethylene terephthalate sheet having a crystallinity of 30% or more at a temperature at which the surface temperature of the sheet is 200 to 220 ° C. for 6 seconds or more and 10 seconds or less;
A molding step in which a preheated highly crystallized foamed polyethylene terephthalate sheet is molded by a mold heated to a thermal deformation temperature;
It is characterized by having.

Moreover, in the method for producing a foamed polyethylene terephthalate sheet molded article according to the present invention,
In the molding step, molding is performed using a mold heated in a range of 170 to 180 ° C.

Further, the present invention is produced by the method for producing a foamed polyethylene terephthalate sheet molded article according to claim 1 or 2,
In foamed polyethylene terephthalate sheet molded article molded from foamed polyethylene terephthalate sheet that having a a skin layer on the surface of the foamed layer and the foamed layer having air bubbles,
The foam layer directly under the skin layer has 10 or more bubbles having an area of 200 μm ² or more in a region having a cross-sectional area of 0.01 mm ² .

  According to the method for producing a foamed polyethylene terephthalate sheet molded article according to the present invention, when a foamed polyethylene terephthalate sheet having a high crystallinity is heated at a surface temperature of 200 to 220 ° C. for 6 to 10 seconds. Only the surface immediately before the surface of the foamed polyethylene terephthalate sheet melts is burned, and the surface becomes dull. In the state where the surface of this foamed polyethylene terephthalate sheet has been burned, when molding with a mold heated to the heat deformation temperature of polyethylene terephthalate which is the material of the sheet, the shape of the molded product becomes sharp, uneven thickness, The dimensional change after being left at high temperature can be suppressed.

According to the foamed polyethylene terephthalate sheet molded article according to the present invention, the foamed polyethylene terephthalate sheet has 10 or more bubbles having an area of 200 μm ² or more in a region having a cross-sectional area of 0.01 mm ² in the foamed layer. As the sheet follows the mold, the shape of the molded product becomes sharp and the corners are firmly formed. In addition, since the molded product formed sharply is suppressed in uneven thickness, there is little residual strain and dimensional change after being left at high temperature can be suppressed.

The figure which showed the outline | summary of the shaping | molding apparatus. FIG. 2 is a simplified drawing for showing the position and size of each part of the molding apparatus of FIG. 1. The block diagram explaining each structure connected to a control part. The flowchart which shows the manufacturing method of the molded article using a sheet | seat. The SEM photograph of the molded product shape | molded from the sheet | seat. The SEM photograph of the molded article used as a comparative example. The figure which showed the outline | summary of the conventional shaping | molding apparatus.

  Embodiments of a method for producing a foamed polyethylene terephthalate sheet molded article and a foamed polyethylene terephthalate sheet molded article according to the present invention will be described. In the following, the foamed polyethylene terephthalate sheet will be explained first, then the molding apparatus for molding will be explained, and then the production method of the foamed polyethylene terephthalate sheet molded article using the molding apparatus and the foamed polyethylene terephthalate sheet molded article will be explained. explain.

<Polyethylene terephthalate sheet>
As a foamed polyethylene terephthalate sheet (hereinafter referred to as a sheet), for example, an extruded sheet of polyethylene terephthalate is impregnated with carbon dioxide gas under high pressure and then heated and foamed. Can be used (for example, MCPET (registered trademark) manufactured by Furukawa Electric Co., Ltd.). The sheet has a skin layer and a foam layer. Here, the skin layer refers to a surface layer without bubbles.
Specifically, a sheet having a thickness of 1 mm, an expansion ratio of 3 to 4 times, an average cell diameter of 10 μm, and a crystallinity of 37 to 40% (so-called high crystallinity) is preferably used. If this sheet is just manufactured, the inert gas contained in the sheet expands due to the heat of the preheating process and the molding process, so that secondary foaming occurs in the sheet, and after heating There is a problem that the shrinkage and deformation of the sheet and the molded product are large. Therefore, it is preferable to leave the sheet at a normal temperature during which the inert gas remaining on the sheet is released (10 days or more), or as another method, to leave the sheet in an atmosphere at 50 ° C. for 48 hours to remove the inert gas.

<Molding equipment>
FIG. 1 is a diagram showing an outline of the molding apparatus 100, and FIG. 2 is a simplified diagram for showing the position and size of each part of the molding apparatus 100 of FIG. FIG. 3 is a block diagram illustrating each configuration connected to the control unit.
As shown in FIG. 1, the molding apparatus 100 includes a conveyance supply unit 1, a preheating unit 2, a molding unit 3, a cooling unit 4, and a control unit 5. The forming apparatus 100 is arranged in the order of the preliminary heating unit 2, the forming unit 3, and the cooling unit 4 from the upstream side in the conveyance direction of the sheet S conveyed by the conveyance supply unit 1. The forming apparatus 100 heats, forms, and cools different portions of the sheet S by the preheating unit 2, the forming unit 3, and the cooling unit 4 while intermittently conveying the sheet S by the conveyance supply unit 1. Can be performed almost simultaneously.

(Conveying supply unit)
As shown in FIGS. 1 and 2, the conveyance supply unit 1 conveys the sheet S to the preheating unit 2, the forming unit 3, and the cooling unit 4. The conveyance supply unit 1 includes a shaft 11, a spike chain 12, and a cutter 13.
The shaft 11 is mounted with a sheet S winding, and rotatably supports the sheet S winding. Accordingly, the shaft 11 is disposed on the most upstream side in the conveyance direction of the sheet S.
The spike chain 12 feeds the sheet S from the winding and intermittently conveys the sheet S. The spike chain 12 is arranged along the conveying direction of the sheet S, and is arranged above both opposing edges along the conveying direction of the sheet S.
The cutter 13 is for individually cutting the molded products molded by the molding unit 3 and cooled by the cooling unit 4 one by one. Therefore, the cutter 13 is disposed downstream of the cooling unit 4 in the conveyance direction of the sheet S.

(Preheating part)
As shown in FIGS. 1 and 2, the preheating unit 2 is a place where the sheet S fed out from the winding is first guided, and preheats the sheet S before forming. The preheating unit 2 heats the sheet S conveyed by the spike chain 12 from the upper surface side and the lower surface side. The preheating unit 2 includes far infrared heaters 21 and 22 and a radiation thermometer 23.
The far-infrared heaters 21 and 22 are arranged at a certain interval above and below the sheet S conveyed together. The far-infrared heater 21 is disposed so as to face the upper surface of the conveyed sheet S, and heats the sheet S from the upper surface side. The far infrared heater 22 is disposed so as to face the lower surface of the conveyed sheet S, and heats the sheet S from the lower surface side.
As shown in FIG. 2, the far-infrared heaters 21 and 22 are formed in a rectangular shape in plan view, and are sized to cover the area of the sheet S necessary for one molding.
The radiation thermometer 23 is disposed on the surface of the far infrared heater 21 facing the sheet S, and measures the temperature near the surface of the sheet S.

  The far-infrared heaters 21 and 22 are connected to the control unit 5 (see FIG. 3) and controlled by the control unit 5. That is, the control unit 5 controls the amount of current that flows from the power source to the far-infrared heaters 21 and 22 based on the measured temperature value from the radiation thermometer 23. The control unit 5 performs temperature control so that the temperature of the space between the far infrared heaters 21 and 22 is maintained at a temperature at which the surface temperature of the polyethylene terephthalate that is the material of the sheet S is 200 to 220 ° C.

  This temperature is set in advance and stored in a memory in the control unit 5. Here, since the degree of crystallinity of the sheet S is as high as 37% to 40%, if the heating temperature is not lower than the melting point (258 ° C.), the elongation of the sheet S is bad and uneven thickness occurs in the molded product. In a short time of 6 to 10 seconds, preheating is performed so that the surface temperature of the sheet S at the radiation thermometer 23 becomes 200 to 220 ° C.

The heating time is controlled by controlling the conveyance speed of the sheet S and the conveyance timing to the preheating unit 2 by the conveyance supply unit 1 under the control of the control unit 5, so that the sheet S stays in the preheating unit 2. This is done by adjusting the time.
When the sheet S is heated under these conditions, the state immediately before the sheet S melts, that is, only the surface of the sheet S is burned, the skin layer softens and follows the bubbles in the foamed layer, and becomes glossless. . In addition, the bubbles in the foamed layer immediately below the skin layer are expanded. If the preheating is less than 6 seconds, the bubbles in the foam layer immediately below the skin layer do not swell, and if it exceeds 10 seconds, the skin layer that softens and follows the bubbles in the foam layer bursts and is contained in the bubbles. The air that I had escaped. If the surface temperature of the sheet S is less than 200 ° C., the bubbles in the foam layer immediately below the skin layer do not swell, and if it exceeds 220 ° C., the skin layer that softens and follows the bubbles in the foam layer bursts and becomes bubbles. The contained air escapes.

(Molding part)
As shown in FIGS. 1 and 2, the forming unit 3 is arranged on the downstream side in the transport direction of the sheet S in the preheating unit 2. The forming unit 3 is formed by sandwiching the heated sheet S from above and below. Here, the forming method is a known method such as vacuum forming.
The molding unit 3 includes a cavity 31, a core 32, and drive units 33 and 34.

  The cavity 31 is disposed above the conveyance path of the sheet S. That is, the cavity 31 is arranged at a position facing the core 32 with the sheet S interposed therebetween. The cavity 31 is fixed to the base 37. The cavity 31 is formed in a concave shape that is complementary to the core 32. A heater 31 a is embedded in the cavity 31, and is heated to the thermal deformation temperature of polyethylene terephthalate, which is a material of the sheet S, under temperature control by the control unit 5.

  The core 32 is disposed below the conveyance path of the sheet S. That is, the core 32 is disposed at a position facing the cavity 31 with the sheet S interposed therebetween. The core 32 is fixed to the base 38. The core 32 is formed in a convex shape that is complementary to the cavity 31. A heater 32 a is embedded in the core 32, and is heated to the heat deformation temperature of polyethylene terephthalate that is a material of the sheet S under temperature control by the control unit 5.

Here, if the heating temperature of the cavity 31 and the core 32 is too low, the sheet S heated in the preheating process is rapidly cooled to cause distortion, causing deformation and shrinkage. If it is too high, the cavity 31 and the core 32 are heated. Since the peelability of the sheet S from 32 deteriorates and deformation defects and dimensional defects occur, the heat deformation temperature of the material of the sheet S is preferably 170 to 180 ° C.
The heating temperature of the cavity 31 and the core 32 is preferably the same temperature, but the heating temperature may be different depending on the shape of the molded product.

The drive unit 33 moves the cavity 31 along the vertical direction. In other words, the drive unit 33 serves as a drive source that allows the cavity 31 to be brought into and out of contact with the sheet S.
The drive unit 34 moves the core 32 along the vertical direction. In other words, the drive unit 34 serves as a drive source that allows the core 32 to be brought into and out of contact with the sheet S.
The drive units 33 and 34 are connected to the control unit 5, and the drive is controlled by the control unit 5.

(Cooling section)
As shown in FIGS. 1 and 2, the cooling unit 4 is disposed on the downstream side in the conveyance direction of the sheet S in the forming unit 3. The cooling unit 4 cools the sheet S by blowing wind on the formed sheet S from above and below.
The cooling unit 4 includes two air blows 41 and 42.
The air blow 41 is disposed above the conveyance path of the sheet S. That is, the air blow 41 cools the sheet S by blowing air from the upper surface side to the sheet S.
The air blow 42 is disposed below the conveyance path of the sheet S. That is, the air blow 42 cools the sheet S by blowing air from the lower surface side to the sheet S.
The air blows 41 and 42 are connected to the control unit 5, and the drive is controlled by the control unit 5.

(Control part)
As shown in FIG. 3, the control unit 5 controls each drive unit of the molding apparatus 100.
The control unit 5 includes a known CPU, ROM, RAM, and the like.
The control unit 5 includes far infrared heaters 21 and 22, a radiation thermometer 23, a heater 31 a for heating the cavity 31, a heater 32 a for heating the core 32, driving units 33 and 34, and a spike chain driving unit for driving the spike chain 12. 15, a cutter driving unit 16 for driving the cutter 13, and air blows 41 and 42 are connected.

<Method for producing foamed polyethylene terephthalate sheet molding>
FIG. 4 is a flowchart showing a method of manufacturing a molded product using the sheet S.
As shown in FIG. 4, when a molded product is manufactured from the sheet S, the spike chain 12 of the conveyance supply unit 1 is driven under the control of the control unit 5, and the sheet S is unwound and preheated. It conveys toward the part 2 (step S1).

The sheet S conveyed to the preheating unit 2 is subjected to temperature control by the radiation thermometer 23 and the control unit 5, and the sheet at the radiation thermometer 23 is obtained in a short time of 6 to 10 seconds by the far infrared heaters 21 and 22. Heating is performed in an environment where the surface temperature of S is 200 to 220 ° C. (step S2: preheating step). The sheet S heated under these conditions is in a state immediately before melting, that is, only the surface of the sheet S is burned and the skin layer is softened to follow the bubbles in the foam layer and become glossless. In addition, the bubbles in the foamed layer immediately below the skin layer are expanded.
The sheet S heated under the above conditions by the far infrared heaters 21 and 22 is conveyed to the forming unit 3 by the spike chain 12.

In the molding unit 3, the drive unit 33 and 34 are driven by the control unit 5, so that the sheet S is sandwiched between the cavity 31 and the core 32 and molded according to the shape of the cavity 31 and the core 32 (step S <b> 3: molding). Step). At this time, the next sheet S is conveyed and supplied to the preheating unit 2 and preheated.
Here, the cavity 31 and the core 32 are heated to 170 to 180 ° C., which is the heat deformation temperature of the material of the sheet S, and the sheet S is sandwiched between the heated cavity 31 and the core 32 and molded. At this time, since the sheet S is preheated, the bubbles in the foam layer immediately below the skin layer are inflated, and the skin layer is softened to follow the bubbles. Since the follow-up property becomes good, sharp molding becomes possible.
The time from the end of heating of the sheet S by the preheating unit 2 to the start of forming by the cavity 31 and the core 32 is performed within 1 to 2 seconds from the viewpoint of preventing cooling of the preheated sheet S. Is preferred.
The sheet S formed in the forming unit 3 is conveyed to the cooling unit 4 by the spike chain 12.

In the cooling unit 4, the control unit 5 drives the air blows 41 and 42 to cool the sheet S from the upper surface and the lower surface (step S4).
The sheet S cooled in the cooling unit 4 is cut into one molded product by the cutter 13 (step S5).
A molded product is manufactured from the sheet S by the above processing.

<Manufactured foamed polyethylene terephthalate sheet molding>
FIG. 5 is an SEM photograph of a cross section of a molded product formed from the sheet S under the above-described conditions and manufacturing method. This SEM photograph is an image of the foam layer 71 taken at a magnification of 1000 times.
As shown in FIG. 5, the molded article has a foam layer 71 having air bubbles P and a skin layer 72 present on the surface of the foam layer 71.
As can be seen from FIG. 5, 10 or more bubbles P having an area of 200 μm ² or more are formed in a region where the cross-sectional area of the foam layer 71 is 0.01 mm ² .
Thus, by forming a lot of relatively large bubbles, the followability to the cavity 31 and the core 32 is good during molding in the molding process, and a sharp molded product is obtained.

<Action and effect>
As described above, according to the method for producing a foamed polyethylene terephthalate sheet molded article having a high crystallinity (37 to 40%), the surface temperature of the foamed polyethylene terephthalate sheet S having a high crystallinity is the melting point ( When heating is performed until the surface becomes dull in an environment of less than (258 ° C.) (200 to 220 ° C.), only the surface immediately before the surface of the sheet S melts is burned. The state of the surface of the sheet S cannot be realized by a heating method in which preheating is performed slowly over time, and the heat of polyethylene terephthalate, which is the material of the sheet, is in a state where the surface of the sheet S is burnt. When molding is performed with a molding die (cavity 31 and core 32) heated to a deformation temperature (170 to 180 ° C.), the shape of the molded product becomes sharp and suppresses uneven thickness and dimensional changes after being left at high temperature. it can.

According to the molded product from the highly crystallized foamed polyethylene terephthalate sheet thus formed, 10 bubbles P having an area of 200 μm ² or more are present in the area of the foam layer 71 having a cross-sectional area of 0.01 mm ^2. There are more than one, the shape of the molded product is sharp, and the corners are firmly molded. In addition, since the molded product formed sharply is suppressed in uneven thickness, there is little residual strain and dimensional change after being left at high temperature can be suppressed.

<Others>
The present invention is not limited to the above embodiment. In the preheating step, the heating method of the sheet S is arbitrary, but the sheet surface temperature after the preheating is 200 to 220 ° C. Therefore, in the preheating method in which the sheet is sandwiched between the contact type surface heating plates, the surface heating plate is used. Since a sheet sticks to the surface, it is not preferable, and a non-contact heating method such as an infrared heater or hot air heating is preferable.
Further, the cooling method of the sheet S is also a cooling method using the air blows 41 and 42, but may be a method of cooling using a cooling mold (see FIG. 7) as in the prior art. The molding method is not limited to the match mold molding method in which the sheet S is sandwiched between the upper and lower molds of the cavity 31 and the core 32 and pressed, and depending on the shape of the molded product, pressure molding, vacuum molding, plug assist vacuum pressure molding, etc. Other molding methods may be used.

  Next, examples in which the highly crystallized foamed polyethylene terephthalate sheet molded article according to the present invention is specifically implemented based on the above embodiment will be described. In addition, in order to show the superiority of the highly crystallized foamed polyethylene terephthalate sheet molded product according to the present invention, an example of a molded product manufactured under different molding conditions is given as a comparative example, and the quality of the manufactured molded product is Compared.

FIG. 5 is an SEM photograph of the cross section of the molded product when the preheating time of the sheet S by the preheating unit 2 is short (7 seconds), and FIG. 6 shows the preheating of the sheet S by the preheating unit 2. It is a SEM photograph of the section of a molded article when time is long (15 seconds). In the preheating step, preheating was performed so that the surface temperature of the sheet S was the same 200 ° C., and in the forming step, the sheet S was formed with the cavity 31 and the core 32 heated to 170 ° C.
These photographs are 1000 times SEM photographs of the vicinity of the surface of the sheet S. When these photographs are compared, it can be seen that there is a clear difference in the size of the bubbles P in the foam layer 71. Since both of the bubbles are elongated by molding, they are elliptical.

When bubbles are picked up in order of size in the range of 0.01 mm ² and compared with the area of the bubbles, the molded product with a preheating time of 15 seconds has an average area of bubbles of about 165 μm ² and a preheating time of 7 The molded article of seconds had an average bubble area of about 410 μm ² . Looking at the area of each bubble, the molded product with a preheating time of 15 seconds had few bubbles of 200 μm ² or more, and the molded product with a preheating time of 7 seconds had as many as 13 bubbles of 200 μm ² or more. . It was found that there was a clear difference from the average area of the bubbles and the number of bubbles of 200 μm ² or more. Furthermore, there are 10 or more bubbles of 200 μm ² or more when the preheating time is 6 seconds, 8 seconds, 9 seconds or 10 seconds, and 10 bubbles when the preheating time is 5 seconds, 11 seconds, 14 seconds or 15 seconds. It was confirmed that it was less than. The presence of many large bubbles improves the elongation of the sheet S and improves the followability of the sheet S to the mold (cavity 31 and core 32).

Next, when the shapes of the molded products are compared, the molded products having a preheating time of 5 seconds, 11 seconds, 14 seconds, and 15 seconds are not sharp but round, while the preheating time is 6 seconds. The molded products of 7 seconds, 8 seconds, 9 seconds, and 10 seconds had a sharp shape and the corners were firmly formed.
From the above, by performing preheating at a temperature at which the surface temperature of the sheet S becomes 200 to 220 ° C. and in a short time of 6 to 10 seconds, the average area of the bubbles inside the sheet S, You can see that the number increases. This means that when the average area of the bubbles in the sheet S and the number of bubbles increase, the sheet S is also easily stretched and can be molded in a state where it can be easily molded. Thus, it was confirmed that a molded product having good followability to the cavity 31 and the core 32 and having a sharp shape could be manufactured.
Further, even if the preheating time is too short, preferable molding cannot be performed, and it can be confirmed that 6 to 10 seconds is appropriate.

DESCRIPTION OF SYMBOLS 1 Conveying supply part 2 Preheating part 3 Molding part 4 Cooling part 5 Control part 100 Molding apparatus S Sheet (foamed polyethylene terephthalate sheet)

Claims (3)

A preheating step of heating a foamed polyethylene terephthalate sheet having a crystallinity of 30% or more at a temperature at which the surface temperature of the sheet is 200 to 220 ° C. for 6 seconds or more and 10 seconds or less;
A molding step in which a preheated highly crystallized foamed polyethylene terephthalate sheet is molded by a mold heated to a thermal deformation temperature;
A method for producing a foamed polyethylene terephthalate sheet molded article, comprising:   2. The method for producing a foamed polyethylene terephthalate sheet molded article according to claim 1, wherein in the molding step, molding is performed using a mold heated within a range of 170 to 180 ° C. 3. Manufactured by the method for producing a foamed polyethylene terephthalate sheet molded article according to claim 1 or 2,
In foamed polyethylene terephthalate sheet molded article molded from foamed polyethylene terephthalate sheet that having a a skin layer on the surface of the foamed layer and the foamed layer having air bubbles,
A foamed polyethylene terephthalate sheet molded article having 10 or more bubbles having an area of 200 μm ² or more in a region having a cross-sectional area of 0.01 mm ² in the foam layer immediately below the skin layer.