JPH10151662A - Roll for molding extruded sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance uniform emboss shaping properties and the smoothness and non-flaw properties of a mirror surface by constituting a roll for molding a smooth surface of a rubber layer for covering a shaft core part and a metal layer for covering the rubber layer, and forming the surface of the metal layer into a mirror surface. SOLUTION: A shaft core part 1 is made of a steel material and a passage for circulating heating medium oil is provided in the shaft core part. Next, the shaft core part 1 is covered with liquid silicone rubber containing an SiO2 powder as a filler and, after the rubber is cured, the thickness of a rubber layer 2 is adjusted by polishing. Next, a nickel tube is formed by an electric casting method and the surface thereof has good mirror surface properties. A silicone adhesive is applied to the surface of the rubber layer 2 covering the shaft core layer 1 and the shaft core part is inserted into the nickel tube and the adhesive is cured to obtain a mirror surface roll. By this constitution, a lens sheet excellent in optical accuracy can be inexpensively provided with good mass-productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror roll for forming a smooth surface in an extruded sheet forming apparatus for extruding a plastic sheet having a smooth surface from a thermoplastic resin as a raw material. A plastic sheet having at least one smooth surface, for example, a Fresnel lens sheet, a lenticular lens sheet, a prism lens sheet, and the like is used for optical applications, and a surface having a high degree of smoothness is required on a surface opposite to a surface having a lens shape. The roll according to the present invention is suitably used for forming such a smooth surface.

[0002]

2. Description of the Related Art A lens function sheet typified by a Fresnel lens sheet, a lenticular lens sheet, a prism lens sheet and the like is provided with a shape exhibiting the above-mentioned lens function on one surface, and a surface having a high smoothness on the opposite surface. It is required that the mirror surface has (specularity). Generally, in order to manufacture the above-mentioned lens functional sheet by an extrusion continuous molding method which is excellent in mass productivity, it is necessary to form a molten resin film between an embossing roll for shaping a lens-shaped surface and a mirror-surface roll for mirror-surface molding opposed thereto. By passing through and clamping
A method of transferring a fine uneven shape exhibiting an optical function to one surface and forming a smooth mirror surface on the other surface has been performed.

As the mirror roll, i) a metal mirror roll whose surface is polished or plated; ii) a core having a mirror-finished inner surface formed by casting and curing silicone rubber or the like on the surface of the shaft core. Mirror surface rubber roll or a mirror surface rubber roll provided with a rubber layer on the surface of the shaft core by casting method, iii) After coating the shaft core with a heat-shrinkable tube made of fluororesin, A mirror-surface fluororesin roll mirror-finished by polishing is used.

[0004]

The thickness accuracy of an extruded sheet using a T-die mold has been dramatically improved due to the recent development of mold design and processing techniques. No epoch-making improvement measures have been found for a thickness unevenness, that is, a thickness unevenness between two adjacent points. Such thickness unevenness appears as a non-uniform shape of the lens function sheet, resulting in a decrease in quality, that is, a partial deterioration in optical performance.

The embossing roll is basically a metal roll engraved with a desired lens shape. A lens functional sheet is formed by combining a variety of mirror-like rolls and passing a molten resin between them to form a film and sandwiching them. Molding has been performed.

On the other hand, the mirror roll has the following problems. First, the metal mirror roll i) is excellent in mirror precision and defect-freeness, but has no ability to absorb thickness unevenness of the resin due to its own deformation due to lack of flexibility. Therefore, when the molten resin is passed through a film using a metal mirror roll and pressed, the pressure concentrates on the thick part due to uneven thickness of the resin and the pressure on the thin part becomes insufficient. Insufficient shape.

[0007] The mirror rubber roll ii) is capable of absorbing the resin thickness unevenness due to its own flexibility, so that the molten resin can pass through the film in the form of a film with a uniform pressure and can be pressed. Inevitably, micro defects caused by gas generated when the rubber layer is formed are unavoidable, and the rubber is deteriorated by being exposed to a high-temperature resin, so that the rubber layer cannot be used in a short time. Therefore, with this roll, it was difficult to finish one surface of the sheet into a mirror surface or a thin mat having a surface roughness Ra of about 0.01 to 0.25 μm.

Further, although the mirror-surface fluororesin roll iii) is excellent in heat deterioration resistance, it is inferior in flexibility to a mirror-surface rubber roll, and inferior in mirror-like and defect-free properties to a metal mirror-surface roll.

As described above, the conventional mirror rolls used in the extrusion of the lens function sheet each have disadvantages, which lowers the production yield of the lens function sheet and limits its optical performance. An object of the present invention is to provide an extruded sheet forming roll that overcomes the above problems.

[0010]

Means for Solving the Problems In order to obtain a good optical function by performing uniform shaping, the present inventors have to absorb unevenness in the thickness of the resin, press the sheet with a uniform pressure, and apply a high degree of pressure to the sheet. As a result of studying to find a mirror-finished roll capable of imparting a mirror surface or a thin mat, a roll for forming a sheet according to the present invention was provided.

[0011] A sheet forming roll according to the present invention is a roll for forming a smooth surface in an extruded sheet forming apparatus for extruding a plastic sheet having at least one surface having a smooth surface. A rubber layer covering the portion and a metal layer further covering the rubber layer, and the surface of the metal layer is mirror-finished.

The thickness of the metal layer is preferably 0.03 to 1 m
m, and more preferably 0.03 to 0.5 mm. The surface roughness of the roll is preferably Ra = 0.01 to 3 µm. The thickness of the rubber layer is preferably from 0.3 to 3 mm. The metal layer is preferably a seamless tube. Such a seamless tube is obtained, for example, by an electroforming method. Hereinafter, the present invention will be described in more detail.

The core of the roll for forming a sheet according to the present invention may be the same as that of a conventionally used mirror roll, and is not particularly limited. During molding, the surface of the roll is transferred to the sheet by passing the molten resin between the two pairs of rolls in a film form and applying a narrow pressure, so the rolls have a robust structure made of a material that can withstand pressure. Is required. Therefore, a metal core such as steel, stainless steel or aluminum is suitably used as the shaft core of the mirror roll. The mandrel may also have accessories for driving the roll.

In general, the roll temperature greatly affects the transferability in embossing, so that a shaft core having a structure capable of adjusting the roll to an appropriate temperature is preferable. As the temperature adjusting means preferably used, an electric heating system in which a sheath heater is incorporated in the shaft core to heat the roll, an induction heating system in which the roll is heated by electromagnetic induction by an induction heating coil, and provided in the shaft core And a heating medium circulation heating system in which a roll is indirectly heated by circulating a heating medium for temperature control through the flow path. Particularly preferred is a heating medium circulation heating method, and this heating medium may be a gas, but water,
Liquids such as oil are preferred. Preferred examples of the heat medium flow path include those having a structure such as a double spiral or a four spiral inside.

The material of the rubber layer may be any material having a rubber elasticity at room temperature or higher. For example, neoprene rubber, NBR
Rubber, silicone rubber and the like are exemplified. In particular, JIS
A material having a rubber hardness of 60 to 90 [deg.] Specified in K7215 is preferable, and silicone rubber is preferable in consideration of life at a high temperature. The rubber layer may contain various fillers such as SiO ₂ powder for the purpose of adjusting rubber hardness.

The thickness of the rubber layer is such that the elastic force can be maintained.
For example, it may be about 0.3 mm or more, and the upper limit is not particularly defined. However, when emphasis is placed on the transferability of the unevenness to the resin sheet, the thinner is advantageous, and the upper limit is preferably about 3 mm. That is, when the thickness of the rubber layer is 0.3 mm or less, the elastic deformation of the rubber layer is insufficient, and there is a possibility that the thickness unevenness of the resin may not be absorbed. In addition, the pressure applied to the resin sheet sandwiched between the embossing roll and the embossing roll is dissipated, and the unevenness transferability is reduced.

The surface condition of the rubber layer is not particularly limited as long as it can adhere and fix the metal layer to be covered with the rubber layer. However, it is preferable to appropriately roughen the adhesion surface of the rubber layer according to the adhesiveness of the rubber.

The above-mentioned metal layer may be formed by any method as long as it can be formed to a predetermined thickness. For example, a strip-shaped metal piece may be rolled into a tube and joined, or the surface of a metal tube may be formed. It can be manufactured by a method of cutting to a predetermined thickness or the like. If a strip-shaped metal piece is wound into a tube, a seam is formed at the joint, and the thickness of about 0.3 mm is the limit of the thickness in the method of shaving the surface of the metal pipe.

A particularly preferred metal layer is a seamless tube. For example, a strip-shaped copper piece wound into a tube and welded and plated, a thick steel pipe thinned by lathing and polished, and a nickel tube manufactured by an electroforming method may be used. A seamless tube manufactured by the electroforming method is most suitable because it has excellent mirror-like properties and defect-free properties and excellent wall thickness accuracy.

The thickness of the metal layer is preferably 0.03 to 1
mm, more preferably 0.03 to 0.5 mm. If the thickness is less than 0.03 mm, the sheet is easily broken at the time of clamping, and the setting of the pressure may be limited. When the thickness exceeds 1 mm, the obtained sheet lacks flexibility and may not be able to absorb the thickness unevenness of the resin.

The rubber layer and the metal layer may be fixed by using an adhesive, or the rubber layer may be fixed by cooling and shrinking, inserting the rubber layer into the tube-shaped metal layer, and increasing the frictional force. . Position the shaft core and the tubular metal layer first,
In the meantime, the mirror roll of the present invention can be produced by injecting liquid rubber.

After the mirror surface roll according to the present invention is thus obtained, the mirror surface and the defect-free property may be improved by polishing the roll surface. Also, if you want a thin mat,
Perform sandblasting on the roll surface. In this case, the surface roughness can be appropriately adjusted depending on the size of the particles that collide with the roll.

The surface roughness of the roll is Ra = 0.
μm, and more preferably Ra = 0.01 to 1 μm. There is no difference in performance even when Ra is less than 0.01 μm, and when Ra exceeds 3 μm, the mat state of the molding surface of the obtained sheet is too dark. Furthermore,
When the sheet is actually handled, the sheet may come into close contact with another smooth surface. In such a case, if Ra is too small, a problem occurs in that the sheet is intimately adhered and difficult to peel off.
The lower limit of a is 0.02 μm, more preferably 0.03 μm
If so, it is extremely preferable that both optical smoothness and adhesion prevention can be achieved. In addition, Ra is JIS B 06
The center line average roughness specified in No. 01 is shown.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to examples.

Example 1 i) The shaft core was made of S45C steel material, and a flow path for circulating the heat medium oil was provided inside the shaft core. The flow path had a four-row spiral structure.

Ii) Next, the shaft core is covered with a liquid silicone rubber containing SiO ₂ powder as a filler,
After the rubber was cured, the thickness of the rubber layer was adjusted to 2 mm by polishing. The rubber hardness after curing was 75 °.

Iii) Next, a thickness of 0.1
mm nickel tube was prepared. The surface of the nickel tube had good specularity. A silicone-based adhesive was applied to the surface of the rubber layer covering the shaft core, inserted into a nickel tube, and then cured to obtain a mirror-finished roll according to the present invention.

FIG. 1 shows the structure of the obtained extruded sheet forming roll. In FIG. 1, 1 is a shaft core, 2 is a rubber layer covering the shaft core, 3 is a metal layer covering the rubber layer, and 4 is an extruded sheet forming roll of the present invention composed of these.

Example 2 A mirror roll was obtained in the same manner as in Example 1 except that the thickness of the rubber layer was adjusted to 3.0 mm in step ii) of Example 1.

Comparative Example 1 The surface of the same S45C steel shaft core used in Example 1 was chrome-plated to obtain a mirror-finished roll.

Comparative Example 2 A mold having a mirror-finished inner surface was prepared, and silicone rubber was poured between the inner surface of the mold and the surface of the same shaft core made of S45C steel used in Example 1. And cured to obtain a mirror-finished rubber roll having a 4.5 mm-thick rubber layer covering the shaft core.

Comparative Example 3 The same S45C steel shaft core as used in Example 1 was covered with a 2.0 μm-thick fluororesin heat-shrinkable tube, and the surface was mirror-polished by polishing. A resin roll was obtained.

Example 3 Except that step iii) of Example 1 was replaced by the following steps:
The same operation as in Example 1 was performed.

That is, a strip-shaped stainless steel piece having a thickness of 0.15 mm was prepared by forging. The surface of the strip-shaped stainless steel piece had a good mirror surface. A strip of stainless steel was wound into a tube and joined by welding to produce a stainless tube. A silicone adhesive was applied to the surface of the rubber layer covering the mandrel obtained in steps i) and ii), and the rubber layer was coated with a metal layer made of a stainless tube by inserting it into a stainless tube. . After curing the adhesive,
The surface of the roll is subjected to a surface roughness Ra =
Finished to 0.15 μm. Thus, a mirror roll according to the present invention was obtained.

Example 4 The same operation as in Example 1 was carried out except that the thickness of the rubber layer was adjusted to 3.5 mm in Step ii) of Example 1 and Step iii) was changed to the following step. Was.

That is, a strip-shaped stainless steel piece having a thickness of 0.1 mm was prepared by forging, and this was wound into a tube and joined by welding to form a stainless steel tube. The layer was provided to form a stainless-chrome tube. The tube surface had a good mirror surface. Thereafter, a silicone-based adhesive is applied to the surface of the rubber layer covering the mandrel obtained in steps i) and ii) and inserted into a stainless-chrome tube to form a metal layer made of a stainless-chrome tube. To cover the rubber layer. After the adhesive is cured, the roll surface is
Sand blasting was performed by a dry method using mesh glass beads to finish the surface roughness Ra = 0.05 μm. Thus, a mirror roll according to the present invention was obtained.

COMPARATIVE EXAMPLE 4 The same S45C steel shaft core as used in Example 1 was chromium-plated on its surface, and then the surface of the roll was subjected to a surface roughness Ra =
Finished to 0.15 μm to obtain a metal roll.

Comparative Example 5 The same shaft core made of S45C steel as used in Example 1 was covered with the same heat-shrinkable tube made of fluororesin as used in Comparative Example 2, and the surface was thinned by polishing. It was matted to obtain a mirror surface fluororesin roll.

Performance Evaluation Each of the mirror rolls and the embossing rolls for forming the prism sheet obtained in the examples and comparative examples were respectively set in a take-up machine, and a polycarbonate molten resin extruded from a T-die was formed into a film between these rolls. And embossing was performed by narrowing the pressure. The temperature of the resin immediately after extrusion from the T-die was 270 ° C., the temperature of the heat medium flowing in the embossing roll was controlled at 130 ° C., and the temperature of the heat medium flowing in the mirror roll according to the present invention was controlled at 30 ° C. The resulting molded sheet was well peeled from the embossing roll and had a thickness of 200
μm.

The prepared sheet was observed, and the transfer uniformity and transfer rate of the embossed shape, the smoothness of the mirror surface (Examples 1 and 2 and Comparative Examples 1 to 3), and the surface roughness of the thin mat (Examples 3 and 4) , Comparative Examples 4 and 5), adhesion, mirror-free defect, and roll life were evaluated by the following measurements. The evaluation results are shown in Tables 1 and 2.・ Transfer uniformity: visually determine gloss unevenness of reflected light over the entire width of the sheet ・ Transfer rate: ratio of transfer sheet unevenness depth to emboss roll unevenness depth ・ Smoothness Ra: measured according to JIS B 0601 ・ Surface roughness Degree: Measured according to JIS B 0601 ・ Adhesion: Judge the presence or absence of adhesion to a commercially available smooth acrylic plate ・ Defectiveness of mirror surface: Visual observation of the number of defects per 1 m of 55 cm wide molded sheet ・ Roll life: Perform molding under the above molding conditions and measure the time until the rubber layer or metal layer peels off, or the time until the surface of the rubber layer or metal layer is scratched

[0041]

[Table 1]

[0042]

[Table 2]

In Tables 1 and 2, .largecircle.
Δ means that the uniformity is not sufficient, and X means that the uniformity is not good.

As is clear from Tables 1 and 2, the mirror rolls of the examples obtained good evaluations in all items.

[0045]

According to the present invention, a mirror roll capable of absorbing unevenness in the thickness of the resin, holding the sheet with a uniform pressure, and imparting a high degree of specularity to the sheet is realized. Thus, it became possible to form an extruded sheet with dramatically improved mirror smoothness and defect-free properties. Therefore, according to the present invention, it has become possible to provide a lens sheet having excellent optical precision with good mass productivity and at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an extruded sheet forming roll according to the present invention.

[Explanation of symbols]

 1: Shaft core 2: Rubber layer 3: Metal layer 4: Extruded sheet forming roll of the present invention

Claims (6)

[Claims] 1. A roll for forming a smooth surface in an extruded sheet forming apparatus for extruding a plastic sheet having at least one surface having a smooth surface, comprising: a shaft core;
An extruded sheet forming roll comprising a rubber layer covering the shaft core and a metal layer further covering the rubber layer, wherein the surface of the metal layer is mirror-finished. 2. The extruded sheet forming roll according to claim 1, wherein the thickness of the metal layer is 0.03 to 1 mm. 3. The surface roughness of the roll is Ra = 0.
3. The roll for forming an extruded sheet according to claim 1, which has a thickness of μm. 4. The extruded sheet forming roll according to claim 1, wherein the thickness of the rubber layer is 0.3 to 3 mm. 5. The roll for forming an extruded sheet according to claim 1, wherein the metal layer is a seamless tube. 6. The roll for forming an extruded sheet according to claim 5, wherein the seamless tubular material is obtained by an electroforming method.