Method for manufacturing thermoplastic sheets bearing embossed patterns thereon and an apparatus therefor

Abstract

Provided is a method for manufacturing a thermoplastic resin sheet bearing an embossed pattern, which employs a manufacturing apparatus having a first roll having an elastic material coated surface, a mirror-faced metal, endless belt, which is wound around the first roll and a second roll, and a third roll so provided that the metal, endless belt is wrapped partially around the third roll, which contacts the first roll via the metal, endless belt and which has an embossed pattern formed on one surface. According to this method, the thermoplastic resin sheet, partially melted, is fed between the metal, endless belt, which contacts the first roll, and the third roll. The elastic member is elastically deformed by application of a pressing force between the first and the third roll, while face pressure welding the thermoplastic sheet by using the first and the third rolls to transfer the embossed pattern and to cool the thermoplastic resin sheet. A surface temperature for the third roll of from 0°C C. to (resin's Tg +20)°CC. is maintained when the thermoplastic resin sheet is formed of an amorphous resin, and a surface temperature for the third roll of 0°C C. to (resin's m.p. -30)°CC. is maintained when the thermoplastic resin sheet is formed of a crystalline resin. Subsequently, face pressure welding of the thermoplastic resin sheet is performed by using the metal, endless belt relative to the third roll.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

First Embodiment

A method and an apparatus according to a first embodiment of the present invention for manufacturing a thermo-plastic resin sheet 11 having an embossed pattern will now be described while referring to FIGS. 1 through 5.

The structure of the apparatus in the embodiment for manufacturing the thermo-plastic resin sheet 11 having an embossed pattern will be described.

The apparatus comprises a T die 12 of an extruder, a metal, endless belt that is wound around a first roll 13 and a second roll 14; a third roll 33, for an embossed pattern formation, that contacts the first roll 13 via the metal, endless belt 15; and a fourth roll 17, provided in the vicinity of the second roll 14, and two pressing rolls (back rolls) 34 for pressing the thermo-plastic resin sheet 11.

The first roll 13 is coated with an elastic material 18, such as a silicone rubber. The elastic material 18 has a hardness (conforming to JIS K6301A) of 95 degrees or less, and a thickness of 1 mm to 50 mm.

The metal, endless belt 15 is formed of stainless steel, and has a mirror finish face whose surface roughness is equal to or less than 0.5 S.

At least one of the rotary shafts 19 of the first and the second rolls 13 and 14 is coupled to rotating driving means (not shown).

As is shown in FIGS. 2 and 3, a mold 35 is formed on the outer, peripheral surface of the third roll 33 to transfer an embossed pattern 36 (see FIGS. 4 and 5) to the thermo-plastic resin sheet 11. The mold 35 has a raised and recessed profile that corresponds to a triangular pyramid diamond cut pattern for a sheet having a reflective capability.

The third roll 33 is located at the position where the endless belt 15 extending between the first and the second rolls 13 and 14 is recessed inward, as if one part of the outer periphery of the third roll 33 were wrapped in the endless belt 15. More specifically, during the manufacturing process for the thermo-plastic resin sheet 11 having an embossed pattern, the endless belt 15 and the sheet 11 drifts while being wrapped around one part of the outer periphery of the third roll 33. The two pressing rolls 34 are so located that they press the thermo-plastic resin sheet 11 against the embossed pattern formation roll 33 from the rear face of the endless belt 15.

The fourth roll 17 is used to guide the thermo-plastic resin sheet, so that the endless belt 15 performs face pressure welding of the sheet 11 at one part of the outer periphery of the second roll 14.

A water cooled temperature adjustment means (not shown) for regulating the surface temperatures is provided for the rolls 13, 14, 32 and 33.

As is indicated by a chain line in FIG. 1, another roll 32 may be provided before the first roll 13 along the metal, endless belt 15 in order to increase the cooling efficiency of the endless belt 15 that goes to the first roll 13.

An explanation will now be given for the method employed in this embodiment, which uses the above described apparatus, to manufacture a thermo-plastic resin sheet 11 having an embossed pattern in this embodiment.

First, the temperature of the third roll 33 is controlled to maintain a surface temperature of 0°C C. to (resin's Tg +20)°CC. when the thermoplastic resin sheet 11 is formed of an amorphous resin, and a surface temperature of 0°C C. to (resin's m.p -30)°CC. when the thermoplastic resin sheet 11 is formed of crystalline resin.

After the thermo-plastic resin sheet 11 is melted and extruded by the T die 12 of the extruder, the sheet 11 is fed between the first roll 13 and the embossed pattern formation roll 33, the sheet 11 contacting the endless belt 15, which is in contact with the first roll 13, and the third roll 33 at substantially the same time. The sheet 11 is then welded under pressure applied by the rolls 13 and 33 and cooled. At this time, the elastic material 18 is compressed and elastically deformed by a pressing force exerted between the first roll 13 and the third roll 33 and is elastically deformed. In the surface area described by angles θ₁ originating at the centers of the rolls 13 and 33, where the elastic material 18 is elastically deformed, face pressure welding is performed on the sheet 11 by the rolls 13 and 33, and the embossed pattern of the mold 35 on the roll 33 is transferred to the sheet 11. The face pressure applied to the sheet 11 is 0.1 MPa to 20.0 MPa.

Sequentially, the thermo-plastic resin sheet 11 is pressed against the third roll 33 by the endless belt 15 and cooled. The sheet 11, which is pressed against the roll 33 by the pressing rolls 34 via the endless belt 15, is wrapped around the roll 33 the distance described by an angle θ₂ originating at the center of the roll 33, and face pressure welding of the sheet 11 is performed by the endless belt 15 and the roll 33 or in the surface area described by the angle θ₂, while the face pressure relative to the sheet 11 at this time is 0.01 MPa to 0.5 MPa.

Then, the thermo-plastic resin sheet 11 is moved to the second roll 14 by the travel of the endless belt 15. The sheet 11 on which the embossed pattern is formed is pressed against the second roll 14 under pressure applied via the endless belt 15, and cooled. Within the surface area described by an angle θ₃ originating at the center of the roll 14, face pressure welding of the sheet 11, which is guided by the second roll 17 and is wrapped around the second roll 14, is performed. The face pressure at this time is 0.01 MPa to 0.5 MPa.

According to this embodiment, within the surface areas of the first roll 13 and the embossed pattern formation roll 33 that are described by the angles θ₁, while the elastic material 18 is elastically deformed, face pressure welding and cooling of the sheet 11 are performed by the rolls 13 and 33, via the endless belt 15, to transfer the embossed pattern 36 to the sheet 11. Thus, the embossed pattern 36 can be formed at a high speed on the thermo-plastic resin sheet 11 that has been melted and extruded. The resultant sheet 11 bearing the embossed pattern 36 has satisfactory transparency.

Following the face pressure welding and the cooling, within the surface area described by the angle θ₂ of the embossed pattern formation roll 33, face pressure welding and cooling are performed on the sheet 11 by the endless belt 15 and the roll 33, and at the surface area of the second roll 14 described by the angle θ₃, face pressure welding and the cooling are performed on the sheet 11 by the endless belt 15 and the second roll 14. As a result, the transparency of the thermo-plastic resin sheet 11 can be further improved.

Second Embodiment

A method and an apparatus according to a second embodiment of the present invention for manufacturing a thermo-plastic resin sheet 11 having an embossed pattern will now be described while referring to FIG. 6.

The apparatus in the embodiment differs from the apparatus of the first embodiment in the following ways.

In the apparatus in this embodiment, while the fourth roll 17 of the first embodiment is not provided, a first roll 13 coated with an elastic material 18, a second roll 14, a metal, endless belt 15 and a third roll 16 are provided in the same manner.

The manufacturing method for the thermo-plastic resin sheet 11, which is employed by the above apparatus, differs from the method used in the first embodiment in that the face pressure welding and cooling are not performed on a sheet 11 that is guided by a fourth roll 17 while using the endless belt 15.

The partially melted thermo-plastic resin sheet 11, which is extruded by a T die 12 in an extruder, is fed between the first and the third rolls 13 and 16. Face pressure welding is performed for the sheet 11 by the first and the third rolls 13 and 16, and the sheet 11 is then cooled. Following this, face pressure welding of the resultant thermo-plastic resin sheet 11 is performed relative to the third roll 16 along the mirror-faced endless belt 15, and the sheet 11 is then cooled.

According to the present invention, at the surface areas described by the angles θ₁ on the first and the third rolls 13 and 16, while the elastic material 18 is elastically deformed, face pressure welding and cooling are performed on the sheet 11 by the rolls 13 and 16, as it is carried along the endless belt 15, to transfer an embossed pattern 36 to the sheet 11. Therefore, the embossed pattern 36 can be transferred at a high speed to the thermo-plastic resin sheet 11 that has been melted and extruded. In addition, the resultant sheet 11 bearing the embossed pattern 36 has superior transparency.

In addition to the above face pressure welding and cooling, face pressure welding and cooling are also performed on the sheet 11 by the endless belt 15 and the embossed pattern formation roll 16 at the surface area of the roll 16 described by the angle θ₂. Thus, the transparency of the thermo-plastic resin sheet 11 can be further enhanced.

Embodiment 1

In Embodiment 1, the conditions for the manufacturing apparatus and method were specifically determined as follows.

Diameter of the screw of a single screw extruder: 65 mm

Width of T die: 600 mm

Thermoplastic resin:

poly(vinyl chloride) 50 weight %

(polymerization degree: 1000, Tg: 60°C C.)

Resin additive:

plasticizer 45 weight % of DOP(di-2-ethylhexylphthalate)

stabilizer 0.1 weight % of stearic zinc propylene 0.1 weight % of stearic barium

Thickness of thermoplastic resin sheet: 0.3 mm

Elastic material:

silicone rubber having a thickness of 10 mm and a hardness of 50 degrees

Line speed: 3 m/min

Surface temperature of third roll: 50°C C.

Embodiment 2

Only the material for the sheet and the surface temperature of the third roll were changed in the method in Embodiment 1.

Thermal plastic resin: polypropylene (m.p.: 160°C C.)

Surface temperature of third roll: 70°C C.

Embodiment 3

Only the material for the sheet and the surface temperature of the third roll were changed in the method in Embodiment 1.

Thermal plastic resin: polycarbonate (Tg: 145°C C.)

Surface temperature of third roll: 140°C C.

Comparison Example 1

Only the surface temperature of the third roll was changed in the method in Embodiment 1.

Surface temperature of third roll: 85°C C.

Comparison Example 2

Only the surface temperature of the third roll was changed in the method in Embodiment 1.

Surface temperature of third roll: 140°C C.

Comparison Example 3

Only the surface temperature of the third roll was changed in the method in Embodiment 1.

Surface temperature of third roll: 170°C C.

For Embodiments 1 through 3 and Comparison Examples 1 through 3, the obtained thermo-plastic resin sheets were evaluated. The results are shown in Table 1 below.

The evaluation references in Table 1 are as follows.

⊚ . . . sufficient reflective capability

x . . . no reflective capability

	TABLE 1
		Third roll
		temperature
	Sheet resin	(°C C.)	Performance
Embodiment 1	poly(vinyl chloride)	50	⊚
Embodiment 2	polypropylene	70	⊚
Embodiment 3	polycarbonate	140	⊚
Comparison	poly(vinyl chloride)	70	x
example 1
Comparison	polypropylene	140	x
example 2
Comparison	polycarbonate	160	x
example 3

As is apparent from Table 1, the thermo-plastic resin sheets 11 bearing the embossed pattern in Embodiments 1 through 3 were obtained by the apparatus described in the above embodiments. These sheets 11 were manufactured with a surface temperature for the third roll 33 of zero to (resin's Tg+20)°CC. when the resin for the sheet 11 was an amorphous resin, and with a surface temperature for the third roll 33 of zero to (resin's m.p. -30)°CC. when the resin for the sheet 11 was a crystal resin. It is obvious that the embossed pattern of the mold 35 was satisfactorily transferred to the sheet 11, and that the sheet 11 had a sufficient reflective capability.

In Comparison Example 1, although the thermo-plastic resin sheet bearing an embossed pattern was obtained by the apparatus described in the embodiments, the surface temperature of the third roll 33 was higher than 80°C C., which is (resin's Tg +20)°CC., so that the mold transfer was defective due to the mold breaking when the embossed pattern was peeled from the mold, and no reflective capability was confirmed.

In Comparison Example 2, although the thermo-plastic resin sheet bearing an embossed pattern was obtained by the apparatus described in the embodiments, the surface temperature of the third roll 33 was higher than 130°C C., which is (resins' m.p -30)°CC., so that the mold transfer was defective due to the mold breaking when the embossed pattern was peeled from the mold, and no reflective capability was confirmed.

In Comparison Example 3, although the thermo-plastic resin sheet bearing an embossed pattern was obtained by the apparatus described in the embodiments, the surface temperature of the third roll 33 was higher than 165°C C., which is (resins' Tg +20)°CC., so that no reflective capability was confirmed as in the preceding comparison examples.

Claims

1. A method of manufacturing an amorphous thermoplastic resin sheet having an embossed pattern comprising the steps of:

providing a manufacturing apparatus comprising a first roll having an outer surface coated with an elastic material, a second roll, a third roll having an embossed pattern provided on an outer surface thereof and a metal endless belt having a mirror-finished surface wound around said first and second rolls and in contact with said third roll;

feeding the amorphous thermoplastic resin sheet, in a partially molten state, between the metal endless belt and the third roll;

maintaining the outer surface temperature of the third roll of from 0°C C. to the amorphous thermoplastic resin's Tg;

elastically deforming the elastic material by applying a pressing force between said first and third rolls to conduct face pressure welding of said amorphous thermoplastic resin sheet and cool and transfer the embossed pattern to the amorphous thermoplastic resin sheet; and

performing face pressure welding of the amorphous thermoplastic resin sheet having the embossed pattern thereon between the metal endless belt and the third roll.

2. A method of manufacturing a crystalline thermoplastic resin sheet having an embossed pattern comprising the steps of:

providing a manufacturing apparatus comprising a first roll having an outer surface coated with an elastic material, a second roll, a third roll having an embossed pattern provided on an outer surface thereof and a metal endless belt having a mirror-finished surface wound around said first and second rolls and in contact with said third roll;

feeding the crystalline thermoplastic resin sheet, in a partially molten state, between the metal endless belt and the third roll;

maintaining the outer surface temperature of the third roll of from 0°C C. to the crystalline thermoplastic resin's m.p. -30°C C.;

elastically deforming the elastic material by applying a pressing force of from 0.1-20 MPa between said first and third rolls to conduct face pressure welding of said crystalline thermoplastic resin sheet and cool and transfer the embossed pattern to the crystalline thermoplastic resin sheet; and

performing face pressure welding of the crystalline thermoplastic resin sheet having the embossed pattern thereon between the metal endless belt and the third roll at a pressure of from 0.1 0.01-0.5 MPa.

3. A method for manufacturing a crystalline thermoplastic resin sheet bearing an embossed pattern according to claim 2, wherein, said surface temperature of said third roll is between zero and the resin's m.p. -50°C C.

4. A method for manufacturing an amorphous thermoplastic resin sheet bearing an embossed pattern according to claim 1, wherein the pressure during said face pressure welding of said thermoplastic resin sheet is 0.1 MPa to 20.0 MPa, and wherein said pressure during said face pressure welding of said thermoplastic resin sheet having the embossed pattern thereon is from 0.1 0.01 to 0.5 MPa.

5. A method for manufacturing an amorphous thermoplastic resin sheet bearing an embossed pattern according to claim 1, wherein the surface roughness of the mirror-finished surface of said metal endless belt is 3 S or lower.

6. A method for manufacturing a crystalline thermoplastic resin sheet bearing an embossed pattern according to claim 2, wherein the surface roughness of the mirror-finished surface of said metal endless belt is 3 S or lower.