JPH0790588B2 - Polystyrene foam sheet and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polystyrene resin foam sheet, which is particularly suitable for incinerating and discarding containers and the like.
The present invention relates to a polystyrene-based resin foam sheet having a low density and excellent mechanical strength, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, it has been widely practiced to produce a resin foam sheet by extrusion foam molding. Generally, a polystyrene-based resin foam sheet for molding is produced by extruding a molten polystyrene-based resin composition into a tube shape from an annular die orifice, and then slitting it vertically. In the manufacturing process of such a polystyrene resin foam sheet (hereinafter simply referred to as a resin foam sheet), in order to maintain the mechanical strength when the resin foam sheet is molded into a container, a tubular resin composition immediately after extrusion is used. It is practiced to rapidly cool an object to form a dense skin layer on the surface of the foam.

When a resin foam sheet having a skin layer formed by such surface quenching is molded into a container, the mechanical strength of the container is improved, but the density of the central portion of the resin foam sheet is lowered. However, if the density of the skin layer is too high, the stress (heat shrinkage stress) of the skin layer at the time of molding the container increases, so that the thermoformability of the container deteriorates.

Therefore, even if it is attempted to increase the mechanical strength, the density of the skin layer cannot be made too high, and the density of the central portion cannot be made too low, so that the weight of the secondary molded product such as a container is heavy. In addition, there is a drawback that the combustion heat at the time of incineration processing after discarding the container or the like cannot be reduced.

As a means for solving the above-mentioned drawbacks, a low-density resin foam sheet is manufactured in advance, and a non-foamed resin film is attached to the resin foam sheet on one side or both sides of the resin foam sheet. Methods for increasing mechanical strength have also been proposed. However, such a method has drawbacks in that the production efficiency is poor due to the large number of manufacturing steps, the amount of the upper raw material is high, and a laminator for attaching the non-foamed sheet is required.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied the polystyrene-based resin foam sheet and a method for producing the same, and as a result, by providing a ring in the die of an extruder, the density of the resin foam sheet in the thickness direction can be improved. It is found that the resin foam sheet obtained in this manner is excellent in moldability of a container and the like while having a low density, and even when it is molded by itself, it is sufficiently excellent in mechanical strength. The invention was reached.

Accordingly, a first object of the present invention is to provide excellent mechanical strength is excellent in formability, low density polystyrene resin foam sheet which can be unitary molded. A second object of the present invention is to provide a method for producing a low-density polystyrene- based resin foam sheet that can be unitarily molded and has excellent moldability and mechanical strength.

The above first object of the present invention is in an extruder.
Polystyrene resin composition melt-kneaded with foaming agent
By a ring with a cooling mechanism installed in the die
Inside the die after splitting into two layers and cooling the split surface
Immediately from the die orifice
B ): The thickness is 1.0 to 3.0 m.
A polystyrene-based resin foam sheet having a density distribution that is symmetric with respect to the thickness center plane at m, and b): ⅕ to 1 to 1 of the total thickness of the sheet from the front and back directions. The average density of a layer having a thickness of / 10 is a, c): a layer including the center line in the total thickness of the sheet and having a thickness of 1/5 to 1/10 of the total thickness. When the average density of layers other than b), d): b) and c) is represented by c, c <b ≦ a and the density of the entire sheet is 0.03 to 0.1. (G / ml), which is achieved by a polystyrene resin foam sheet.

The second object of the present invention is to provide a method for producing a polystyrene-based resin foam sheet by melt-kneading a polystyrene-based resin together with a foaming agent in an extruder and discharging it into the atmosphere from an annular die orifice. The polystyrene-based resin composition melt-kneaded with the foaming agent in the extruder is once divided into two annular layers by a ring having a cooling mechanism provided in the die and the divided surface is immediately cooled to form one layer in the die, Then, it was achieved by a method for producing a polystyrene-based resin foam sheet, which is characterized in discharging from the die orifice into the atmosphere. still,
The cooling by the ring may be substantially cooled.
Included and limited to active cooling only
Absent.

The styrenic resin which can be used in the present invention is not particularly limited. For example, general-purpose polystyrene resin, impact-resistant polystyrene resin, styrene-acrylonitrile copolymer resin, styrene-methylmethacrylate copolymer resin, styrene- Acrylic acid copolymer resin,
The styrene-maleic anhydride copolymer resin and a mixture thereof can be appropriately selected and used. Talc These polystyrene resins, inorganic substances such as calcium carbonate, plasticizers, and stabilizers, etc., can be added according to the desired physical properties.

The foaming agent that can be used in the present invention can be appropriately selected and used from among physical foaming agents and chemical foaming agents known as foaming agents for polystyrene resins. Examples of the physical foaming agent include hydrocarbon compounds such as propane, butane, hexane, heptane, Freon-11, Freon-12, Freon113, Freon-1.
14 (Freon is a trade name of Dyupon Co., Ltd.), halogenated hydrocarbon compounds such as methyl chloride and methylene chloride. Examples of the chemical foaming agent include organic pyrolyzable foaming agents such as azodicarbonamide, bicarbonates, and combinations of bicarbonates with organic acids such as citric acid.

The polystyrene resin foam sheet of the present invention has layers having different densities in the thickness direction, and
Density in the thickness direction is symmetrical with respect to the thickness center line, and within the total thickness, 1/5 to 1/1 of the total thickness from the front surface and the back surface direction.
The average density of a layer having a thickness of 0 is a, and ⅕ to 1 of the total thickness
If the average density of a layer having a thickness of / 10 and including the thickness center line is b and the average density of the other layers is c, then c <b ≦ a
It is represented by.

Therefore, the foamed sheet of the present invention is illustrated in FIG. When the density is uniform as c = b = a, the average density of the resin foam sheet is 0.1 to 0.03 g.
/ Ml significantly lowers the mechanical strength, and in the conventional case of c = b <a, lowering the resin foaming density lowers the compressive strength in the thickness direction, while increasing the density improves the mechanical strength. However, the moldability is poor. Further, when the average density of the resin foam sheet is 0.1 g / ml or more, the combustion heat at the time of discarding the sheet-made container or the like and then incineration cannot be reduced, and when it is 0.03 g / ml or less, the mechanical strength is low. Inferior strength. Therefore, the average density of the entire foamed sheet of the present invention is 0.03 g.
~ 0.1 g / ml is required.

Next, a method for manufacturing the resin foam sheet of the present invention will be described with reference to the drawings. FIG. 2 is a cross-sectional view of a die and its peripheral devices used in the manufacturing method of the present invention. In the figure,
Ring 2 is a spacer which is provided a polystyrene resin composition which passes through the resin flow path 5 in the die 1 to the resin flow path 5 in order to divide into two layers in the annular, for cooling the split surface It has a cooling medium circulation path 3.

Therefore, a polystyrene resin containing a foaming agent
The composition is melt-kneaded by an extruder (not shown) and introduced into a die 1 attached to the tip of the extruder,
The mandrel 4 in the die 1 unfolds it in a ring shape, and then the ring 2 provided in the resin flow path 5 divides it into two layers in a ring shape. In this case, since the divided surface is cooled at the same time, the resin viscosity near the divided surface is higher than the resin viscosity in other portions. Therefore, the resin tube 7 which has passed through the ring 2 and merged again to be discharged from the annular die orifice 6 into the atmosphere has a high resin viscosity at the center portion in the thickness direction. Foaming in the central part is suppressed and a dense layer is formed. Furthermore, resin tube 7
Is rapidly cooled by the air blown from the outer cooling air ring 8 and the inner cooling air ring 9, so that a high density layer in which foaming is suppressed is formed on the front and back layers of the resin tube 7 and then transferred to the cooling drum 10. Be taken over.

[0016]

The resin foam sheet of the present invention has a five-layer structure in which the density of the front and back layers and the central layer of the sheet is high, and the density of the other intermediate layers is low, so that the density of the entire sheet is high. Since the mechanical strength is excellent even if the value is small, it is suitable for producing a container having a small unit weight. Moreover, there is no need to form a high skin layer overly density, on which excellent moldability when molded into a container or the like, raw Sanko ratio is good can be manufactured in a single step. Further, since the combustion heat at the time of discarding the container or the like formed by the resin foam sheet according to the present invention after discarding it can extend the life of the incinerator.

[0017]

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 Polystyrene resin (heat distortion temperature 86 ° C. according to JIS-6871) was measured by the apparatus shown in FIG.
After mixing 0 part by weight and 0.5 part by weight of talc, 200
The mixture was put into an extruder having a diameter of 40 mm and heated at 0 ° C., and melt-kneaded. Then, 5 parts by weight of butane was press-fitted and mixed from an injection port provided in the middle of the extruder, and then introduced into a resin flow path 5 in a die 1 attached to the tip of the extruder and provided in the resin flow path 5. After passing through a ring 2 in which hot water at a certain temperature of 50 ° C circulates, it is ejected in a tube shape from the annular orifice of 150 mmΦ into the atmosphere, and air at a temperature of 20 ° C is blown out to form an outer cooling air ring 8 and an inner cooling air ring 9 I let it blow up while passing between. Then, the diameter 40 kept at 30 ℃
While contacting the 0 mm cooling drum 10, the tube 7 was collected at a speed of 3 m / min to be cooled and solidified, and then cut open.
A resin sheet according to the present invention having a sheet thickness of 2 mm, a weight of 134 g / m ² , and a density of 0.067 g / ml was prepared.

The resin sheet thus obtained is vertically
It was formed into a tray having a size of 80 mm, a width of 130 mm, and a depth of 20 mm. The lateral strength of the obtained tray was 270 g. The combustion heat of the obtained sheet is 670,000 kcal.
/ M ³ (measured with a bomb calorimeter and converted into heat quantity per cubic meter).

[0019]

[Comparative Example 1] Except for removing the ring 2 in the die 1, the same apparatus as in Example 1 was used, and the thickness of the sheet was 2 mm, the weight was 134 g / m ² , and the density was 0.067 g / ml. A resin foam sheet was prepared so that Using the obtained sheet, the same length 280 mm and width 130 m as in Example 1
When a tray with m and a depth of 20 mm was formed, the transverse strength of the obtained tray was 220 g. The heat of combustion of the obtained sheet was 670,000 kcal / m ³ (measured with a bomb calorimeter and converted into heat quantity per cubic meter).

[0020]

[Comparative Example 2] The same apparatus as in Comparative Example 1 was used. The thickness of the sheet was 2 mm, the weight was 200 g / m ² , and the density was 0.1 g / m ² .
A resin foam sheet was prepared so as to be ml. Using the obtained resin sheet, the same vertical length of 280 m as in Example 1
When formed into a tray having m, width 130 mm, and depth 20 mm, the obtained tray had a transverse strength of 270 g. The combustion heat of the obtained sheet is 1,000,000 kca.
It was 1 / m ³ (measured with a bomb calorimeter and converted into heat quantity per 1 cubic meter).

From the results of the above Examples and Comparative Examples, the lateral strength of the sheet of the present invention is higher when the density is the same as that of the conventional one, while the present invention is obtained when the lateral strength is the same. It has been proved that the density of the sheet is smaller than that of the conventional one, and hence the heat of combustion can be made smaller than that of the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a resin sheet of the present invention.

FIG. 2 is a schematic view of an apparatus used in the manufacturing method of the present invention.

FIG. 3 is a schematic cross-sectional view taken along the line A-A ′ in FIG.

[Explanation of symbols]

 Symbol a ... Resin sheet layer a Symbol b ... Resin sheet layer b Symbol c ... Resin sheet layer c Symbol 1 ... Die symbol 2 ... Ring symbol 3 ... Cooling medium circulation channel symbol 4・ ・ ・ Mandrel code 5 ・ ・ ・ Resin flow path code 6 ・ ・ ・ Die orifice code 7 ・ ・ ・ Resin tube code 8 ・ ・ ・ Outer cooling air ring code 9 ・ ・ ・ Internal cooling air ring code 10 ・ ・ ・ Cooling Drum code 11 ... Air exhaust pipe code 12 ... Cavity

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C08L 25:00 (56) References Japanese Patent Publication No. 39-22368 (JP, B1) Japanese Patent Publication No. 1- 24619 (JP, B2)

Claims (2)

[Claims] 1.Melt kneaded with foaming agent in extruder
Cooling mechanism with polystyrene resin composition in die
With a ring having
Immediately after cooling the split surface, make one layer in the die, then
It is discharged from the die orifice into the atmosphere.
B): The thickness is 1.0 to 3.0 mm, with respect to the thickness center plane.
Polystyrene resin foam sheet with symmetrical symmetrical density distribution
B): Of the extra thickness of the sheet, the entire thickness from the front and back sides
The average density of a layer having a thickness of 1/5 to 1/10 of the thickness is represented by a, c): a layer including a center line in the total thickness of the sheet.
The average density of a layer with a thickness of 1/5 to 1/10 of the total thickness
b, d): When the average density of layers other than b) and c) is represented as c
In this case, c <b ≦ a and the density of the entire sheet is 0.0
3 to 0.1 (g / ml), characterized by
Len resin foam sheet. 2. A method for producing a polystyrene-based resin foam sheet by melt-kneading a polystyrene-based resin together with a foaming agent in an extruder and discharging it into the atmosphere from an annular die orifice. The prepared polystyrene resin composition was cooled in a die.
Once divided into two layers of an annular by a ring having a retirement mechanism
A method for producing a polystyrene-based resin foam sheet, characterized in that the divided surface is cooled together with it and then immediately formed into a single layer in the die, and then discharged from the die orifice into the atmosphere.