JPH0775862B2 - Method for producing polystyrene-based resin foam sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin foam sheet, and more particularly to a method for producing a polystyrene resin foam sheet having excellent moldability.

[0002]

2. Description of the Related Art A so-called extrusion foam molding method, in which a resin foam sheet is manufactured by melt-kneading a resin together with a foaming agent in an extruder and then extruding it into the atmosphere, has a simple manufacturing process and a stable resin foam sheet quality. It has been widely used from the past because of its characteristics such as being present.

In a method for producing a resin foam sheet using an extrusion foam molding method, a resin composition melt-kneaded with a foaming agent is extruded into the atmosphere from an annular die lip made of metal to form a tube. It is manufactured by bringing a cooling drum into contact with the inner surface of the resin composition molded in (1) to cool the foamed resin composition, and then axially cutting one end of the tube open.

In the process of manufacturing such a resin foam sheet, in order to increase the strength of a molded product (hereinafter simply referred to as a molded product) when the obtained resin foam sheet is molded into a container or the like, a tubular shape immediately after extrusion is used. The surface of a resin composition is rapidly cooled (hereinafter referred to as surface cooling) to form a high-density layer (hereinafter referred to as a skin layer) on the surface of a resin foam sheet.

In this case, while the mechanical strength of the molded article is improved by the skin layer, the expansion rate of the skin layer (the rate at which the resin expands in response to the volume expansion due to foaming) because foaming in the skin layer is suppressed. Becomes smaller and the ratio to the take-up speed of the resin foam sheet (hereinafter simply referred to as speed ratio) becomes larger, so that the stress inside the skin layer (heat shrinkage stress) becomes larger. Therefore, there is a defect that molding failure occurs (moldability deterioration) when a container or the like is molded using the obtained resin foam sheet, and this defect is particularly caused when polystyrene resin is used as the resin. Remarkable.

In order to improve such drawbacks, a method of decreasing the speed ratio by decreasing the opening of the die lip and increasing the extrusion speed, or a resin sheet extruded from the die lip and formed into a tubular shape is heated. Method to relieve stress by passing through
No. 29) is proposed.

[0007]

However, when the die lip opening is reduced and the extrusion speed is increased, the die head pressure increases, making it difficult to maintain a constant extrusion flow rate of the resin composition. It had the drawback of poor stability. Further, in the case of the method of passing the heating ring, there is a drawback that the cost of the apparatus is increased because the special heating ring is required and the energy consumption by heating is increased.

Therefore, the inventors of the present invention have conducted extensive studies to solve the above-mentioned drawbacks, and as a result, by using zirconia ceramic for the resin flow path surface of the die lip, a polystyrene resin foam sheet having excellent moldability is obtained. The inventors have found that they can be achieved and reached the present invention. Therefore, an object of the present invention is to provide a method for producing a polystyrene-based resin foam sheet having excellent moldability.

[0009]

The above objects of the present invention are as follows.
After melt-kneading a polystyrene-based resin in an extruder with a foaming agent, the melt-kneaded polystyrene-based resin composition is extruded into the atmosphere from an annular die lip in a method for producing a polystyrene-based resin foam sheet, wherein the annular die lip is formed. This has been achieved by a method for producing a polystyrene-based resin foam sheet, wherein at least the resin flow path surface of the inner lip and / or the outer lip is formed of zirconia ceramic.

Examples of polystyrene resins usable in the present invention include general-purpose polystyrene resins, high-impact polystyrene resins, styrene-methylmethacrylate copolymer resins, styrene-acrylic acid copolymer resins, styrene-maleic anhydride. It is possible to appropriately select and use from among known polystyrene-based resins such as a copolymer resin or a mixture of these resins.

Such polystyrene-based resins include inorganic substances such as talc and calcium carbonate depending on desired physical properties,
It is also possible to add a plasticizer or a stabilizer. The foaming agent that can be used in the present invention can be appropriately selected and used from among the foaming agents known as physical foaming agents or chemical foaming agents for polystyrene resins.

Specific examples of the physical foaming agent include, for example,
Hydrocarbon compounds such as propane, butane, hexane, heptane, Freon-11, Freon-12, Freon-1
13, Fluorochloro substitution products of hydrocarbons such as Freon-114 (Freon is a trade name manufactured by DuPont Co., Ltd.),
Examples thereof include halogenated hydrocarbon compounds such as methyl chloride and methylene chloride.

Examples of the chemical foaming agent include organic pyrolytic foaming agents such as azodicarbonamide, bicarbonates, and combinations of bicarbonates with organic acids such as citric acid.

In the present invention, the polystyrene resin composition melt-kneaded with the foaming agent may be cooled to a temperature within the range of the heat distortion temperature of the polystyrene resin to the temperature + 50 ° C. and then extruded into the atmosphere from the annular die lip. Particularly preferred.

If the resin is cooled below the heat deformation temperature, the viscosity of the resin becomes high and the resin die cannot be extruded uniformly from the annular die lip into the atmosphere, and a resin foam sheet of constant quality cannot be manufactured. In addition, the extrusion temperature is the heating deformation temperature of the resin +5
When the temperature is 0 ° C. or higher, the viscosity of the polystyrene resin composition is lowered, but since the zirconia ceramic is also used, the extrusion resistance in the resin flow path inside the die lip is reduced and the die head pressure is reduced. Deteriorates, which makes it difficult to control foaming and causes a defect in appearance called scratch on the surface of the resin foam sheet.

In the present invention, at least the resin flow path surface of the inner lip and / or the outer lip constituting the annular die lip used is made of zirconia ceramic. The entire die may be made of zirconia ceramic, but the zirconia ceramic may be used only in the portion of the resin flow path surface and the other portion may be made of metal. In this case, the zirconia ceramic member can be easily supported on the metal member by a method such as shrink fitting, adhesion, or caulking. It is sufficient that the thickness of the ceramic portion is 0.1 mm to 5 mm.

In the present invention, the resin passage surface of the inner lip or the outer lip may be made of metal. The metal used for the die lip is mainly steel, but the surface of the die lip can be plated if necessary.

The zirconia ceramic used in the present invention is a ceramic containing zirconia as a main component, but yttria, alumina,
Magnesia or the like may be appropriately contained in the ceramic.

Zirconia ceramics are fine powders of zirconia having a primary particle size of 200 to 400 angstroms obtained by a wet method, and high-purity alumina, spinel, mullite powder obtained by a wet method or a coprecipitation method. As a raw material,
It can be easily produced by molding it into a predetermined shape by a rubber pressing method or the like and firing it by a normal pressure firing method, a hot isostatic pressure firing method or the like.

The method for producing the polystyrene resin foam sheet of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an apparatus used for carrying out the manufacturing method of the present invention. In FIG. 1, a portion 1-2 of the inner lip 1 facing the resin flow passage and a portion 2 of the outer lip 2 facing the resin flow passage 2-
Zirconia ceramic is used for each of the two.

The polystyrene resin composition containing a foaming agent is melted and kneaded by an extruder (not shown), and is cooled to a temperature within a range from the heat distortion temperature of the polystyrene resin to the heat distortion temperature + 50 ° C. Guided by 3. The polystyrene-based resin composition containing the foaming agent guided to the resin flow path 3 is extruded from the die lip 4 into the air into a tube shape and simultaneously foamed by the foaming agent (resin foam tube 8).
Next, the air is blown up from the inner cooling air ring 5 and the outer cooling air ring 6, and is cooled at a constant cooling rate.

Further, a cooling drum 7 is brought into contact with the inside of the resin foam tube 8 to sufficiently cool it, and a take-up machine (not shown).
The resin foam tube 8
One end is cut open in the axial direction to produce a polystyrene resin foam sheet.

It is not clear why the polystyrene resin foam sheet having excellent moldability can be obtained by the production method of the present invention, but in the present invention,
Since the resin flow path surface of the die lip uses a zirconia ceramic that is incompatible with the polystyrene resin, the extrusion resistance in the resin flow path inside the die lip becomes small, and the extrusion speed of the polystyrene resin composition can be increased. Therefore, it is presumed that the ratio of the extension speed of the resin foam sheet and the take-up speed of the resin foam sheet can be reduced, and therefore the stress inside the skin layer can be reduced.

Further, in the present invention, the melt-kneaded polystyrene resin composition is cooled to a temperature within the range of the heat distortion temperature of the polystyrene resin to the temperature + 50 ° C. and then extruded into the atmosphere from the annular die lip. Even when an annular die lip whose road surface is zirconia ceramic is used, foaming can be easily controlled, the quality of the polystyrene-based resin foamed sheet becomes uniform, and the appearance can be made good.

[0025]

According to the manufacturing method of the present invention, since the stress remaining in the skin layer can be reduced, it is possible to manufacture a polystyrene resin foam sheet having excellent moldability. Further, the quality of the obtained resin foam sheet is uniform and the appearance is also good.

[0026]

EXAMPLES The present invention will be described in more detail with reference to Examples below.
The present invention is not limited to this.

Example 1. Using the apparatus shown in FIG. 1, 100 parts by weight of polystyrene resin (heating deformation temperature according to JIS-6871 86 ° C.) was mixed with 0.5 parts by weight of talc,
The obtained mixture was charged into a 40 mmΦ extruder heated to 200 ° C. and melt-kneaded.

Then, 5 parts by weight of butane was pressed into the mixture through the injection port provided in the middle of the extruder to mix with the above mixture, and the obtained mixture (polystyrene resin composition) was cooled by an oil circulation type cooling mechanism. It was cooled, guided to the resin flow path 3 of the die, and extruded into the atmosphere from the annular die lip 4 of 150 mmΦ to obtain a resin foam tube 8. In this case, the cooling mechanism was adjusted so that the surface temperature of the resin foam tube obtained was 130 ° C.

The surface temperature of the resin foam tube is JTG.
-3210 type thermoviewer (a thermography device manufactured by JEOL Ltd., which is a trade name of a device that captures infrared rays emitted from an object and quantitatively measures the temperature distribution on the surface).

Next, the inner and outer surfaces of the resin foam tube 8 are covered by the inner cooling air ring 5 and the outer cooling air ring 6 in which air of 20 ° C. is being blown while the resin foam tube 8 is being drawn at a drawing speed of 3 m / min. The resin foam tube 8 is blown up while being cooled, brought into contact with a cooling drum 7 having a diameter of 400 mm to be further cooled, and one end of the resin foam tube 8 is cut open in the axial direction to give a thickness of 2 mm, a weight of 200 g / m ² , and a density of A polystyrene-based resin foam sheet of 0.1 g / ml was prepared.

The obtained resin foam sheet was processed into a bowl having a diameter of 145 mm and a depth of 70 mm by using a continuous pressure molding machine, and the skin layer was not cracked at the mouth of the bowl and had gloss. Also, the appearance was excellent.

Comparative Example 1. Inner lip 1-2 and outer lip 2
The same resin foam sheet was produced in exactly the same manner as in Example 1 except that the zirconia ceramic portion of -2 was replaced with a die lip made of carbon steel material JIS standard S45C for machine structure. Example 1 using the obtained resin foam sheet
When a bowl was processed in exactly the same manner as above, cracks in the skin layer were found at the mouth of the bowl, and the appearance was remarkably inferior. The above results demonstrate that the polystyrene resin foam sheet obtained by the production method of the present invention has excellent moldability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an apparatus used in the manufacturing method of the present invention.

[Explanation of symbols]

 1-1 Inner lip support 1-2 Inner lip 2-1 Outer lip support 2-2 Outer lip 3 Resin flow path 4 Die lip 5 Inner cooling air ring 6 Outer cooling air ring 7 Cooling drum 8 Resin tube 9 Air exhaust pipe 10 cavities

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B29K 105: 04 B29L 7:00 C08L 25:00 (56) Reference JP-A-49-110761 (JP , A) JP-A-56-69132 (JP, A) JP-A-62-286721 (JP, A) Actual development Sho-59-194911 (JP, U)

Claims (2)

[Claims] 1. A method for producing a polystyrene-based resin foam sheet, comprising the steps of: melt-kneading a polystyrene-based resin together with a foaming agent in an extruder, and then extruding the melt-kneaded polystyrene-based resin composition into the atmosphere through an annular die lip. A method for producing a polystyrene-based resin foam sheet, wherein at least the resin flow path surface of the inner lip and / or the outer lip constituting the die lip is formed of zirconia ceramic. 2. A polystyrene-based resin composition obtained by melt-kneading, wherein the polystyrene-based resin has a heating deformation temperature to the temperature +5.
The method for producing a polystyrene-based resin foam sheet according to claim 1, wherein the foamed sheet is extruded into the atmosphere from an annular die lip after being cooled to a range of 0 ° C.