JP4293443B2 - Method for forming foamed polyethylene terephthalate sheet - Google Patents

Description

  The present invention relates to a method for forming a foamed polyethylene terephthalate sheet, and more particularly, to a method for forming a foamed polyethylene terephthalate sheet that can obtain a molded article that is not likely to be drawn during molding with a mold.

  It is known to form a foamed polyethylene terephthalate (PET) sheet into a highly heat-resistant container using a mold. For example, in Patent Document 1 (Japanese Patent No. 2551854), a foamed polyethylene terephthalate sheet is heated to a temperature not higher than a temperature for promoting crystallization of the sheet and a temperature required for molding (130 ° C. or higher and lower than 150 ° C.). By holding by a pair of surface heating plates, the sheet is preheated up to the inside of the sheet without promoting crystallization of the sheet surface, and then the sheet is heated to a temperature higher than the temperature that promotes crystallization of the sheet. Molded into a predetermined shape by a pair of molds heated to (160 ° C. to 190 ° C.), and then cooled by a pair of molds maintained at or below the temperature required for molding (40 ° C. to 50 ° C.). Thus, a method for forming a molded article having excellent heat resistance is described.

  Patent Document 2 (Patent No. 3021262) also describes a method for forming a similar foamed polyethylene terephthalate sheet, where the preheated foamed polyethylene terephthalate sheet is lower than the temperature of the heated sheet, A pair of forming dies that are sandwiched between a pair of forming dies maintained at a temperature that does not stop the forming ability of the sheet, formed into a predetermined shape, and then maintained at a temperature equal to or higher than the temperature at which crystallization of the sheet is promoted. In order to increase the crystallization, the sheet having the increased crystallization is cooled to a temperature at which crystallization does not proceed.

Japanese Patent No. 2551854 Japanese Patent No. 3021262

  By adopting the molding method described in the above-mentioned patent document, it becomes possible to produce a molded product having good heat resistance with high productivity and low cost by using a foamed polyethylene terephthalate sheet. The present inventors have produced many foamed polyethylene terephthalate sheet molded products using this method. When molding a product having a shape having a protrusion with a small R (curvature radius) at the tip, We have experienced that the wrinkle at the time of molding sometimes appears in the vicinity of the tip. Even if such drawing wrinkles occur, the function of the molded product itself is not affected. For example, a disk such as a CD (Compact Disk) or a DVD (Digital Video Disc or Digital Versatile Disk) (hereinafter referred to as a CD). It is desirable that such wrinkles do not occur when molding a product that is also required to have a beautiful appearance, such as a tray for storing the like.

  The present invention has been made in view of the circumstances as described above, and when molding a product using a foamed polyethylene terephthalate sheet, even if the molding conditions are severe, the wrinkle is not formed on the surface. It is an object of the present invention to provide a method for forming a foamed polyethylene terephthalate sheet that can provide a molded product with a beautiful appearance.

  The method for forming a foamed polyethylene terephthalate sheet according to the present invention includes a step of surface-treating the foamed polyethylene terephthalate sheet at a temperature that promotes crystallization of the surface layer, and crystallization of the surface-treated foamed polyethylene terephthalate sheet is not promoted A step of heating to a temperature at which molding can be performed, and a step of sandwiching the heated foamed polyethylene terephthalate sheet with a pair of molds maintained at a temperature lower than the temperature of the heated sheet and molding the sheet into a predetermined shape It is characterized by including.

In the present invention, the foamed polyethylene terephthalate sheet serving as the base material may be the same as the foamed polyethylene terephthalate sheet used in a conventionally known molding method as described in Patent Documents 1 and 2 described above. There is no particular limitation on the thickness, basis weight, etc., and it may be appropriately selected according to the characteristics of the product to be molded. However, in consideration of moldability, the thickness is between 0.3 mm and 4.0 mm, and the basis weight is 250 g / It is practical to use a foamed polyethylene terephthalate sheet of a degree between m ^{2 and} 900 g / m ² .

  The step of surface-treating the foamed polyethylene terephthalate sheet at a temperature that promotes crystallization of the surface layer is performed by heating the foamed polyethylene terephthalate sheet with a heating roll or a surface heating means. The temperature at which the crystallization of the expanded polyethylene terephthalate sheet is promoted is about 160 ° C. to 190 ° C. Therefore, the heating temperature at the surface treatment is higher than that temperature, for example, 170 ° C. or higher. If the heating time is increased, crystallization proceeds to the inside and the moldability in the subsequent process is deteriorated, which is not preferable. The heating conditions are set so that only the surface layer is crystallized.

  Moreover, since it will become difficult to control so that crystallization of only a surface layer is accelerated | stimulated when heating temperature is too high, Preferably surface treatment temperature is the range of 170 to 180 degreeC. When surface treatment is performed using a heating roll, the temperature of the roll and the rotation speed of the roll are adjusted. When the surface heating means is used, the temperature of the surface heating means and the sheet feeding speed are adjusted. Thus, a foamed polyethylene terephthalate sheet in which crystallization of the surface layer is promoted as desired is obtained.

  The above surface treatment may be performed only on one side of the sheet or on both sides. If the product to be molded is such that only one side of the product is mainly in contact with the eyes of the purchaser, the surface treatment can be performed only on the sheet side that is in contact with the eye. The purpose of the period can be achieved.

  After the surface-treated foamed polyethylene terephthalate sheet is cooled to about room temperature, a process of heating to a temperature at which the crystallization is not promoted but the sheet can be formed is performed. After the foamed polyethylene terephthalate sheet surface-treated at a temperature that promotes crystallization of the surface layer is cooled to about room temperature by natural heat dissipation, for example, the heating is performed by passing through a heating furnace of a conventionally known molding machine. be able to. The sheet temperature is preferably 76 ° C to 150 ° C, more preferably 100 ° C to 130 ° C. Below 76 ° C., heat is insufficient, and molding with a molding die in the next process is somewhat difficult. Moreover, when it heats exceeding 150 degreeC, crystallization inside a sheet | seat accelerates | stimulates, a moldability will worsen, a brittleness will come out and it will become easy to be broken in shaping | molding by the shaping | molding die in the following process. Although the heating time varies depending on the thickness of the sheet and the like, the inside of the sheet is sufficiently heated.

  The foamed polyethylene terephthalate sheet after heating is sandwiched between a pair of molding dies that are lower than the temperature of the heated sheet and maintained at a temperature that does not stop the molding ability of the sheet, and is molded into a predetermined shape. By this step, the foamed polyethylene terephthalate sheet is molded according to the cavity shape of the mold. A vacuum forming method, a match mold forming method, or the like can be adopted as the forming method. The temperature of the mold is desirably a temperature that does not cause deformation of the molded product when the mold is opened and the molded sheet is taken out, preferably about 90 ° C. or less, more preferably 50 ° C. or less. is there.

  In the experiments of the present inventors, the R (curvature radius) of the tip portion is formed on the surface of the molded product molded as described above, that is, on the surface subjected to the surface treatment at a temperature that promotes crystallization of the surface layer. However, no wrinkle at the time of molding appeared in the vicinity of the portion having a small protrusion, and the entire surface was a beautiful molding surface. In the method according to the present invention, before passing the foamed polyethylene terephthalate sheet through the molding machine, the surface treatment is performed at a temperature that promotes crystallization of the surface layer. It is thought that wrinkles were prevented from occurring.

  The above lead-in wrinkles are particularly likely to occur when the protruding portion is to be molded to the same thickness as other regions including its side surfaces, but in that case by adopting the molding method according to the present invention. No wrinkles occurred.

  According to the present invention, when a product having a protruding portion with a small R (curvature radius) at the tip is formed from a foamed polyethylene terephthalate sheet, it is possible to eliminate the wrinkle that has conventionally occurred around the tip. A molded product with a beautiful surface can be obtained. Since the crystallization of the molded product has not progressed to the inside of the sheet, the heat resistance is somewhat lower than that of the conventional molded product, but the crystallization of the surface layer has been promoted and is mainly used at room temperature. The molded product does not cause any trouble. In addition, unlike the conventional molding method, the last cooling step is not required, so the number of steps can be simplified.

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings. FIG. 1 shows a tray for storing the above-described CD and the like as an example of a product molded by the method for molding a foamed polyethylene terephthalate sheet according to the present invention, and FIG. 2 shows a method for molding a foamed polyethylene terephthalate sheet according to the present invention. It is a schematic sectional drawing which shows an example of the shaping | molding apparatus for implementing this.

  A tray 10 for storing a CD or the like has a cylindrical projection 11 for positioning the CD or the like at the center and a circumferential wall 12 shaped along the outer peripheral edge of the CD or the like to be stored. The height of the peripheral wall 12 is slightly higher than the thickness of the CD or the like to be stored. In the case of a product produced by a conventional method for forming a foamed polyethylene terephthalate sheet, it is in the vicinity of a protruding portion (region indicated by A in FIG. 1) having a small R (curvature radius) at the tip of the circumferential wall 11 or a cylindrical shape having a small diameter. It was difficult to avoid the occurrence of minute wrinkles (drawing wrinkles) at the rising portion of the protrusion 11 from the base portion 13 (the region indicated by B in FIG. 1). In particular, when a molding method is employed in which the rising wall portion has substantially the same thickness as the base portion 13 in order to give the cylindrical protrusion 11 and the circumferential wall 12 the required strength, the generation of the wrinkle is remarkable. Met. By adopting the molding method according to the present invention, it is possible to perform a desired molding without causing such drawing wrinkles.

  The molding apparatus 1 includes a surface heating unit 2 and a molding die 3, and the molding die 3 includes a female die 3 a and a male die 3 b, and moves in a direction of approaching and separating from each other by hydraulic means (not shown). Except for the temperature condition, the surface heating unit 2 and the mold 3 may be the same as the surface heating unit and the mold in the conventional foamed polyethylene terephthalate sheet molding apparatus.

The foamed polyethylene terephthalate sheet 4 is positioned on the upstream side (left side in the figure) as the roll-shaped raw fabric 5, and the foamed polyethylene terephthalate sheet 4 unwound from the raw fabric 5 is rotationally driven. After passing between a pair of rolls 6 a and 6 b equipped with a device (not shown) and being heated, the surface heating unit 2 and the mold 3 are passed. As mentioned above, as this foamed polyethylene terephthalate sheet 4 used in the invention, the thickness 0.3Mm～4.0Mm, those of about basis weight of 250g ^{/ m 2} ~900g ^/ m 2 are suitably used.

In this example, of the pair of rolls 6a and 6b, the upper roll 6a is heated to a temperature of 170 ° C. to 180 ° C. by an appropriate heating unit, and the lower roll 6b does not include a heating unit. When the foamed polyethylene terephthalate sheet 4 passes between a pair of rotationally driven rolls 6a and 6b, the surface on the side in contact with the heated roll 6a (upper surface side) is exposed to a temperature that promotes crystallization. It is processed. In addition, since the acceleration | stimulation degree of crystallization changes with the feed rate (rotation speed) of the rolls 6a and 6b, it adjusts so that it may become an optimal feed rate (usually thickness 0.3mm-4.0mm, basic weight 250g / In the case of a sheet of m ^{2 to} 900 g / m ² , 2 m / min to 3 m / min).

  The foamed polyethylene terephthalate sheet 4 that has been surface-treated at a temperature that promotes crystallization of the surface layer is cooled to about room temperature by natural heat dissipation, and then passes through the surface heating unit 2. The surface heating unit 2 is configured to be able to heat both surfaces of the sheet. By passing through the surface heating unit 2, both surfaces of the sheet are heated to 100 ° C. to 130 ° C. Since this temperature is lower than the temperature at which the crystallization of the expanded polyethylene terephthalate sheet 4 is promoted, only the softening of the sheet proceeds without promoting the crystallization. It is preferable to set the heating region length of the surface heating unit 2 so that the center of the sheet is heated to 100 ° C. to 130 ° C.

  The heated polyethylene foam terephthalate sheet 4 then enters the mold 3 where the required molding is performed between the female mold 3a and the male mold 3b. The mold 3 is maintained at a temperature lower than the temperature of the heated sheet 4, preferably lower than 50 ° C., but the foamed polyethylene terephthalate sheet 4 heated to 100 ° C. to 130 ° C. Is not hindered, and molding proceeds along the cavity surface of the mold. The foamed polyethylene terephthalate sheet 4 is molded as desired and cooled by leaving it between the cavities for a predetermined time. The mold 3 is opened, and the molded polyethylene terephthalate sheet 4 is sent downstream. Since the molded sheet 4 has already been cooled, the molded product is not deformed there. If a predetermined cutter is used to cut the product, a molded product is completed. Note that in the case of multi-piece molding, trimming may be performed after molding.

  As described above, in the method of the present invention, the foamed polyethylene terephthalate sheet 4 is surface-treated at a temperature at which crystallization of the surface layer proceeds, and the elongation of the portion is deteriorated. No wrinkle is generated. Therefore, the molded product finally obtained is a cylindrical shape having a small diameter in the vicinity of the protruding portion having a small R (curvature radius) at the distal end portion of the circumferential wall 12 (the region indicated by A in FIG. 1). A rising portion (a region indicated by B in FIG. 1) of the protrusion 11 from the base portion 13 is also a flat surface without wrinkles, and is a molded product having a beautiful surface property.

  Hereinafter, the present invention will be described with reference to specific examples and comparative examples.

[Example 1]
A foamed polyethylene terephthalate sheet (trade name: Selpet CLF-DG070EA-17B, manufactured by Sekisui Plastics Co., Ltd.) (thickness 0.8 mm, basis weight 350 g / m ² ) 4 unwound from the original fabric 5 is shown in FIG. It was allowed to pass between a pair of rolls 6a, 6b of the molding apparatus 1 shown. The upper roll 6a was a heated roll made of iron (surface: fluorine processing) having a diameter of 150 mm and maintained at 170 ° C., and the lower roll 6b was a non-heated roll made of silicon rubber having a diameter of 150 mm. The two rolls were driven to rotate, and the sheet 4 was sent out at 2.5 m / min.

  The foamed polyethylene terephthalate sheet 4 that passed through the pair of rolls 6a and 6b was passed through the surface heating unit 2 in which the internal environment was maintained at 150 ° C. The sheet moving speed was 2.5 m / min, and the length of the heating area was 2.4 m. When the temperature of the foamed polyethylene terephthalate sheet 4 coming out of the surface heating unit 2 was measured, the temperature of the front and back surfaces was 120 ° C., and the temperature of the center portion was 115 ° C.

  The heated polyethylene terephthalate sheet 4 after heating was fed into the male and female molds 3 to form a tray 10 containing the CD or the like having the shape shown in FIG. During molding, the temperature of the mold 3 was maintained at 50 ° C. After the molding, the mold was opened, the molded foamed polyethylene terephthalate sheet 4 was sent out, and the tray 10 storing the CD and the like was cut out with a cutter. No deformation of the molded product was observed between mold removal and cutting with a cutter. About the cut-out molded article 10, when the area | region part of A and the B area | region part were observed visually in FIG. 1, there was no wrinkle generation | occurrence | production and it became a flat surface.

The perspective view which shows the tray which accommodates CD etc. as an example of the product shape | molded with the shaping | molding method by this invention. The schematic sectional drawing which shows an example of the shaping | molding apparatus for enforcing the shaping | molding method by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Molding apparatus, 2 ... Surface heating part, 3 ... Mold, 4 ... Foamed polyethylene terephthalate sheet, 6 ... A pair of rolls, 10 ... Molded article (tray which accommodates CD etc.), 11 ... Cylindrical protrusion, 12 ... Circumferential wall, 13 ... Base part, A, B ... A region where minute wrinkles (retraction lines) are likely to occur

Claims (3)

  A step of surface-treating the foamed polyethylene terephthalate sheet at a temperature that promotes crystallization of the surface layer; a step of heating the surface-treated foamed polyethylene terephthalate sheet to a temperature that does not promote crystallization but allows the sheet to be molded; A foamed polyethylene terephthalate sheet comprising a step of sandwiching the heated foamed polyethylene terephthalate sheet between a pair of molds maintained at a temperature lower than the temperature of the heated sheet, and molding the sheet into a predetermined shape. Molding method. Thickness 0.3Mm～4.0Mm, a foamed polyethylene terephthalate sheet having a basis weight of ^{250g / m 2 ~900g / m 2} , and heated to a temperature of 160 ° C. to 190 ° C. to promote crystallization of the surface layer of the sheet, the following Next, the foamed polyethylene terephthalate sheet whose crystallization of the surface layer has been promoted is heated to a temperature of 100 ° C. to 130 ° C. to be moldable, and then sandwiched between a pair of molds maintained at a temperature of 90 ° C. or less. And forming the foamed polyethylene terephthalate sheet into a predetermined shape.   The method for molding a foamed polyethylene terephthalate sheet according to claim 2, wherein the foamed polyethylene terephthalate sheet is molded in a state where the mold is maintained at a temperature of 50 ° C or lower.

Images