JPH10180846A - Method for forming embossed sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To score accurately efficiently embossment of an embossed sheet by heating a sheet surface to a secondary shaping side when shaping by rolling is carried out with an embossed roll after melt extrusion of thermoplastic resin from a T-die. SOLUTION: An embossed roll is arranged to an under roll 4 or an intermediate roll 5 and an upper roll. That is, primary shaping is carried out with the under roll 4 or the intermediate roll and secondary shaping is carried out with the upper roll. However, since enough contact time with the roll can be taken, the embossed roll is preferably arranged at the intermediate roll and the upper roll. When a sheet is secondarily shaped, a far-infrared radiation heater 9 is installed as a heating means for a sheet surface. At that time, in order to heat effectively the sheet surface to be secondarily shaped, a recessed surface is so arranged to be constituted along the intermediate roll 5, and it is preferably arranged to be further near to the intermediate roller 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing technique for engraving a precise emboss on a surface of a thermoplastic resin sheet.

[0002]

2. Description of the Related Art Conventionally, embossing has been performed on the surface of a thermoplastic resin sheet. As an embossing sheet forming apparatus, a sheet extrusion equipment having a basic equipment organization as shown in FIG. 1 is used. Used. In FIG. 1, 1 is an extruder, 2 is a T-die, 3 is a cooling roll unit, 4 is a lower roll, 5 is a middle roll, 6 is an upper roll, 7 is a guide roll, and 8 is a take-up roll unit.

Conventionally, in forming a double-sided embossed sheet, an embossed roll is composed of a lower roll 4 and a middle roll 5.
The lower roll 4 is used to shape the lower surface and the middle roll 5 is used to shape the upper surface. However, since the contact time between the molten resin and the lower roll 4 is short, the embossing of the surface to be formed on the lower surface is accurate. There was a problem that it could not be engraved.

On the other hand, the embossed roll is placed on the middle roll 5 and the upper roll 6, and the primary (upper) shaping is performed by the middle roll 5, and the secondary (lower) shaping is performed by the upper roll 6.
Both the primary shaping and the secondary shaping can have a sufficient contact time with the roll, but since the surface to be secondary shaped requires a long time to reach the upper roll 6, the temperature of the surface tends to decrease. However, there is a problem that the emboss on the surface cannot be accurately cut.

Therefore, in order to cut an accurate emboss, it has been widely practiced to limit molding conditions such as the temperature of a melt-extruded resin and the temperature of a roll for shaping.

Japanese Patent Application Laid-Open No. Hei 4-299329 discloses that the embossing accuracy is improved by arranging a low-viscosity resin on the surface layer of a molten resin by coextrusion.

[0007]

However, the conventional techniques have disadvantages such as low operating conditions and lack of stability as industrial techniques, and a complicated facility configuration resulting in poor economic efficiency.

An object of the present invention is to provide a method for efficiently and accurately engraving an emboss in forming an embossed sheet.

[0009]

In order to solve the above-mentioned problems, the present inventors analyzed the stress of the portion of the embossing roll to be rolled and formed, and analyzed the macro rolling stress to spread the entire sheet thinly. And found that the forming mechanism is established by dividing into micro forming stresses for press-fitting the thermoplastic resin into the emboss. That is, the macro rolling stress should be as large as possible, and the micro shaping stress should be as small as possible.

[0010] In order to incorporate such contradictory states into the molding mechanism of the molten resin as a single body, the sheet surface on the side of the secondary shaping is heated so as to facilitate the embossing. .

Specifically, after completing the primary forming, a device for heating the sheet surface of the secondary forming surface is arranged until just before the secondary forming roll is engaged, and the temperature of the sheet surface is rolled. Maintaining a temperature sufficient for shaping reduces the stress required for shaping.

As a result, the melting temperature of the molten resin discharged from the T-die can be lowered, the rolling stress can be set high, and the sheet temperature of the rolled portion by the secondary roll can be raised. The penetration of resin into the body is promoted.

That is, according to the present invention, when a thermoplastic resin is melt-extruded from a T-die and then roll-formed by a roll engraved with an emboss, the sheet surface on the side of the secondary shaping is heated to form the emboss. The method for forming an embossed sheet is characterized in that

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as shown in FIG. 1, a sheet extrusion equipment which is usually used for extrusion molding of an acrylic resin sheet or a polycarbonate resin sheet can be used.

The embossed roll is arranged on the lower roll 4 or the middle roll 5 and the upper roll 6, that is, the lower roll 4 or the middle roll 5 performs primary shaping, and the upper roll 6 performs secondary shaping. It is preferable to arrange embossed rolls on the middle roll 5 and the upper roll 6 in order to allow sufficient contact time with the rolls.

FIG. 2 is an enlarged view of an example of the secondary shaping portion of the sheet according to the present invention. Reference numeral 9 denotes a far-infrared heater as heating means for heating the sheet surface. The heating means is not particularly limited. In addition to the far-infrared heater, for example, a hot air heater, a gas burner and the like can be mentioned.
A far-infrared heater is preferred because 4 μm far-infrared rays are excellent in absorption into the resin and can efficiently heat the sheet surface.

The method of installing the far-infrared heater 9 is not particularly limited. However, in order to effectively heat the sheet surface to be subjected to secondary shaping, a concave surface is formed along the middle roll 5 as shown in FIG. It is preferable to arrange them and further arrange them close to the middle roll 5.

Further, in the present invention, the temperature of the tip of the T-die lip is set to be higher than the resin temperature at the time of melt extrusion, and the temperature of the surface layer portion of the thermoplastic resin is selectively raised to thereby increase the primary temperature. The shaping is also preferable because it can be cut more accurately. It depends on the type of resin, sheet thickness, emboss shape to be shaped, etc.
By raising the average resin temperature of 0 to 500 μm by 5 to 20 ° C. higher than the average resin temperature of the entire cross section, the melt viscosity of the resin surface layer can be substantially reduced by 1000 to 3000 poise, and from the lip tip surface Since the heating is performed by the heat conduction, the higher the temperature is, the closer to the surface layer portion.

FIG. 3 is a cross-sectional view showing an example of the lip portion of the T-die used in the present invention.
In order to heat the surface layer of the molten resin effectively, it is preferable to cut the groove 12 between the base and the tip of the lip to form a heat insulating structure.

Further, a hole 13 is formed at the tip of the lip for the entire length of the lip. For example, an induction coil using a pipe material is inserted into the hole 13 so as to allow a heat medium to flow through and cool the coil itself, thereby performing high-frequency induction heating. The temperature of the tip of the T-die lip is set to be higher than the resin temperature at the time of melt extrusion by inserting a rod-shaped heater adjusted so that the temperature can be made uniform in the longitudinal direction.

At this time, at least one of the upper lip 10 and the lower lip 11 may be heated, that is, one of the upper lip 10 and the lower lip 11 may be heated. Both may be heated, in which case the heating means for the upper lip 10 and the lower lip 11 may be the same or different.

The thermoplastic resin used in the present invention is not particularly limited, but is preferably a transparent resin, and specific examples include an acrylic resin, a polycarbonate resin, and a polystyrene resin.

[0023]

The present invention will be specifically described below with reference to examples and comparative examples.

As an extruder, SE-9 having the structure shown in FIG. 1 was used.
An extruder with a 0 DVB type vent (manufactured by Toshiba Machine Co., Ltd.) was used. The lower roll 4 has a diameter of 250φ and a roll surface length of 130.
A mirror roll having a thickness of 0 mm and the outer surface of which was plated with hard chrome was used. The roll of the middle roll 5 and the upper roll 6 has a diameter of 2
50φ, roll surface length 1300mm, # 7 on the outer surface
An embossing roll engraved with 404 patterns (made by Asahi Roll Co., Ltd.) was used.

Further, as shown in FIG.
(Jard Co., Ltd. Planar far infrared heater CL100 ×
400-700 W (3 columns × 3 rows) was placed close to the middle roll 5.

The molding conditions are as follows. Resin: acrylic resin (70H) Discharge amount: 200 kg / h Discharge resin temperature: 265 ° C. Die temperature: 265 ° C. Roll speed: 1.1 m / h Thickness: 2.0 mm

The evaluation of the embossed sheet was performed by a weight coefficient. The weight coefficient is a measure for evaluating the quality of the emboss represented by the following formula, and is 1.0 if no emboss is formed.

Weight coefficient = weight per square meter of a molded embossed plate / weight per square meter of a flat plate having a thickness equal to that of a molded embossed plate. "
Means the distance between two parallel lines circumscribing the cross-sectional shape of the formed embossed plate.

(Examples 1 to 3) Under the conditions shown in Table 1, a heater was heated to form an embossed sheet. The molding operation could be performed stably. Table 1 shows the results.

Example 4 Using a T-die having a lip tip shown in FIG. 3, the lip temperature was set at 285 ° C., and the heater was heated under the conditions shown in Table 1 to form an embossed sheet.

As a means for heating the tip of the lip, a heat medium (Barrel Thermo 400 manufactured by Matsumura Petroleum Institute) is allowed to flow through the hole 12 at the tip of the lip.
One 350 / 42AA heat medium circulation unit (manufactured by Matsui Seisakusho) was used for each of the upper lip 9 and the lower lip 10.

The molding operation could be performed stably. Table 1 shows the results.

(Comparative Examples 1 to 3) Under the conditions shown in Table 1, an embossed sheet was formed without heating with a heater. The secondary imprint surface was not sufficiently imprinted. Table 1 shows the results.

[0034]

[Table 1]

[0035]

As described above, the melting temperature of the molten resin can be lowered, the rolling stress can be set high, and the onset of the cooling effect by the roll is delayed, so that the resin bites into the roll embossed surface is promoted. Accurate embossing can be engraved on the surface of the thermoplastic resin sheet. In addition, the average resin temperature of the molten resin and the roll temperature for rolling can be selected in a wide range of combinations, and efficient operation can be stably performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic equipment organization of a sheet extrusion equipment.

FIG. 2 is an enlarged view of an example of a secondary shaping portion of a sheet according to the present invention.

FIG. 3 is a sectional view showing an example of a lip portion of a T-die used in the present invention.

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Claims (2)

[Claims] 1. After melt-extrusion of a thermoplastic resin from a T-die, when rolling and shaping with a roll engraved with an emboss, the sheet surface on the side of the secondary shaping is heated to facilitate shaping of the emboss. A method for forming an embossed sheet, comprising: 2. The method according to claim 1, wherein the temperature of the tip of the T-die lip is set to be higher than the resin temperature during melt extrusion, and the surface layer of the thermoplastic resin is selectively heated. A method for forming the embossed sheet according to the above.