JPS6052929B2 - Method for manufacturing expanded polystyrene sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing expanded polystyrene sheets.

Expanded polystyrene sheets are generally thermoformed and widely used in various food packaging containers, such as trays, ramen cups, and lunch boxes.

In order to improve the appearance of these containers and improve their strength, polystyrene foam is melt-extruded through an annular slit in order to provide a thick resin layer with significantly suppressed foaming (hereinafter referred to as an unfoamed layer) on the surface of the sheet. A method for producing expanded polystyrene sheets by cooling polystyrene containing low-boiling organic compounds has already been developed. However, foamed polystyrene sheets with a thick unfoamed layer produced by conventional techniques retain strong orientation, so when heated and continuously vacuum-formed into trays, ramen cups, and lunch boxes, the sheets Due to the strong shrinkage force of the sheet, the sheet comes off from the molding machine's sheet clamp and a molded product cannot be obtained.Also, due to the repeated strong contraction of the sheet in the molding machine,
This causes wear and damage to the clamp part, and improvements are required.

The purpose of the present invention is to produce an improved foamed polystyrene sheet that has a thick unfoamed layer, relaxes the orientation of the sheet during the process of being extruded through an annular slit and is taken off, and has less shrinkage force during hot molding. That is.

In order to achieve these objects of the present invention, it was discovered that the use of a cooling ring and further heating of the surface of a foamed polystyrene sheet with a heating ring was effective, and the present invention was completed.

That is, the present inventor has developed a method for obtaining a foamed polystyrene sheet by melt-kneading polystyrene with a low-boiling organic compound, extruding it into a cylindrical body through an annular slit, expanding the diameter of the cylindrical body, and then cutting it open. The surface of the cylindrical body was brought into contact with a cooling ring maintained at -10 to 90'C, which was installed immediately behind the annular slit (that is, on the front side in the direction of resin progression), and the heating deformation temperature of polystyrene was adjusted to ±10°C. It is characterized in that it is cooled to a temperature within a range of 100° C. and then brought into contact with a heating ring that is placed immediately behind the cooling ring and maintained at a heating deformation temperature of ±10° C. or higher.

Hereinafter, the content of the present invention will be explained in more detail. The polystyrene used in the present invention is a thermoplastic synthetic resin whose main component is styrene, and it can be used in combination with general-purpose polystyrene, other impact-resistant polystyrene, copolymerized polystyrene with bromustyrene and α-methylstyrene, and copolymerized polystyrene with maleic anhydride. Includes polymerized polystyrene, etc. Further, the polystyrene used in the present invention may contain a small amount of an inorganic substance such as talc, silica gel, calcium carbonate, etc. in order to adjust the size of bubbles. The low-boiling organic compounds used in the present invention are those commonly used as blowing agents for polystyrene, such as hydrocarbon compounds such as propane, butane, pentane, hexane, Freon-11, Freon-12, Freon-113s Freon-11ton Chloroform, methyl chloride, methylene chloride, and other halogenated hydrocarbon compounds, petroleum ether, etc. are typical examples.
The low boiling point organic compound is usually added in an amount of 0.02 to 0.07 mol per 100y of polystyrene.

In addition, small amounts of inorganic chemical blowing agents such as ammonium carbonate and sodium bicarbonate, and organic chemical blowing agents such as azodicarbonamide, azobisformamide, N-N''-dinitrosopentamethylenetetramine, and P-toluenesulfonyl hydrazide are used. There is no problem in using them together.

The cooling ring in the present invention is installed on the outside or inside of a resin cylinder extruded through an annular slit to cool the surface of the cylinder, and the contact surface with the cylinder is It has a shape that matches the expansion of the outer diameter or inner diameter of the cylindrical body, and expands in a tapered manner in the direction of movement of the cylindrical body.

Examples of the cooling ring include a cooling ring with a smooth contact surface having a circulation path for passing a cooling medium therein, and a cooling ring having a porous structure from which the cooling medium seeps from the contact surface with the cylindrical body. be.

The temperature of the cooling ring is one of the factors that determines the thickness of the unfoamed layer to be applied, and is determined by the contact area with the cylindrical body and the take-up speed.

In order to provide an unfoamed layer with a sufficient thickness of 20μ or more, it is necessary to cool the surface of the cylindrical body to the heating deformation temperature ±10℃, and for this purpose, the temperature of the cooling ring is usually -10~10℃.
It is kept at 90℃.

If the temperature is less than -10°C, no matter how small the contact area with the cylindrical body of the cooling ring, it is impossible to obtain a foamed polystyrene sheet uniformly provided with an unfoamed layer. On the other hand, at temperatures above 90° C., no matter how large the contact area is, it is not possible to form an unfoamed layer of 20 μm or more. Here, the heating deformation temperature is 127×(12.7±0.2
)×(6.4±0.2)TgL using a test piece,
It is measured according to the test method of JISK-6871-1961. In addition, the porous structure in the case of the above example includes a glass filter, sintered metal, nonwoven fabric, etc., and there is no particular restriction on the roughness of the cooling ring, but the cooling medium is uniform from the entire circumference. In order to seep out and finely disperse the cooling medium, a material with a mesh size of 100 mesh or more is usually used. As the cooling medium, water is usually used, and a substance such as alcohol that adjusts surface tension and heat of vaporization, as well as an antistatic agent and a coloring agent, may be used. The heating ring referred to in the present invention is a cylindrical body that is placed in contact with the cooling ring during the process of expanding its diameter and continues to be in contact with the cooling ring, and has a heating medium circulation path inside the heating ring. However, there are those that are heated with a heating medium and those that are heated with an electric heater.

The temperature of the heating ring is determined by the extent to which the orientation of the foamed polystyrene sheet is relaxed, and is further determined by the contact area with the cylindrical body and the take-up speed, but must be at least 10° C. above the heating deformation temperature of the polystyrene.

If the heating deformation temperature is lower than +10° C., the orientation of the expanded polystyrene sheet will not be relaxed. Moreover, the upper limit temperature of the heating ring is a temperature at which the surface of the expanded polystyrene sheet being pulled does not fuse. It should be noted that, when manufacturing a foamed polystyrene sheet by installing a heating ring following the cooling ring of the present invention, it is within the scope of the present invention to use an air ring in combination for the purpose of adjusting the thickness of the sheet or expanding the cylindrical body. It is included in.

Next, the present invention will be explained with reference to the drawings. FIG. 1 shows one embodiment of the present invention, in which a cooling ring and a heating ring are installed outside a cylindrical body.

Polystyrene and a low-boiling organic compound are melt-kneaded by an extruder (not shown) and extruded through an annular slit 2 of a die 1. Die 1 is attached to the tip of the extruder and has a diameter of 100 to 1
It is heated to 70°C. Extruded cylindrical body (resin) 3
starts contacting the cooling ring 4, and the surface of the cylindrical body 3 is
It is cooled to a temperature in the range of ±10° C., the heat deformation temperature of polystyrene, and a sufficient unfoamed layer with a thickness of 20 μm or more is provided on the surface. The cooling ring 4 is installed immediately behind the annular slit 2 with a gap large enough to prevent it from coming into contact with the die 1.
It has a circulation path 5 for passing a cooling medium therein, and is maintained at an appropriate temperature in the range of -10 to 90 DEG C. by the cooling medium being circulated by a cooling medium circulation device (not shown). After contacting the cooling ring 4, the tubular body 7 contacts the heating ring 6. The heating ring 6 has a circulation path 7 through which a heating medium passes inside, and is maintained at an appropriate temperature above the heating deformation temperature +10°C by the heating medium being circulated by a heating medium circulation device (not shown). It's dripping. Next, the cylindrical body 3 has 10
It is cooled and solidified by a cooling drum 8 through which cooling water of ~30°C is passed, and then cut open by a slitter (not shown).
It is rolled up on a winding roll. On the other hand, die 1 and cooling drum 8
Air is discharged from an air blowing pipe 10 into the cavity 9 formed by the cylindrical body 3 to increase the air pressure inside the cavity 9. The air pressure causes the cylindrical body 3 to expand its inner diameter while being pressed against the inner wall surfaces of the cooling ring 4 and the heating ring 6, and reaches the cooling drum 8, where it is completely cooled and solidified. In this way, the cylindrical body 3 becomes a foamed polystyrene sheet having an unfoamed layer on the outer surface and having a reduced heat-shrinking force. In Figure 1, the heating ring is installed separately from the cooling ring, but in order to keep the cylindrical body with the unfoamed layer in contact with the heating ring for a long time, the heating ring is cooled through a heat insulating material. There is no problem in installing it connected to the ring. Next, FIG. 2 shows another embodiment in which a cooling ring and a heating ring are installed inside a cylindrical body, and an example of an air ring 11 is also used.

The cylindrical body 3 is extruded from the annular slit 2 and starts foaming, and at the same time contacts the cooling ring 4 and then the heating ring 6, expands its diameter, and is cooled and solidified by the cooling drum 8. , and then cut open to obtain expanded polystyrene sheets.

The foamed polystyrene sheet obtained in the present invention has an unfoamed layer of 30μ or more, and at the same time, the orientation created by cooling immediately after extrusion is relaxed by the heating ring, and the heating shrinkage force is reduced without using the heating ring. This was a decrease of 115 to 112 compared to the sheet obtained by the method, and was generated during secondary processing.

The problem of the seat clamp coming off when heated has been resolved.
Also, due to the reduction in shrinkage force, wear and damage to the clamp part was significantly reduced. Furthermore, the present invention eliminates the drawback of the prior art in which the unfoamed layer does not fully expand and cracks occur during the expansion process of the cylindrical body extruded from the annular slit after contacting the cooling ring, and the unfoamed layer further expands. Can be applied thickly. In addition, since the present invention uses a heating ring, the surface smoothness of the expanded polystyrene sheet is improved.
The effect of increasing photo selectivity and improving printability was also obtained. As described above, the present invention is of high value in producing a foamed polystyrene sheet having a thick unfoamed layer.

Note that heat shrinkage refers to a specified size, for example, 500×
When expanded polystyrene + made to a length of 100 m is left in a dryer heated to 1000 C or more, the residual stress existing within the sheet is a force that tries to tighten the sheet itself.

The value of the heat shrinkage force used in the explanation of the present invention is 500
The maximum value is shown when a test piece of ×100Tfn is left in a dryer at 150°C. Next, the present invention will be specifically explained with reference to Examples.

Example 1 Polystyrene 1 (4
) part and 0.5 part of talc were mixed and melted and kneaded in a 90Tnφ extruder, and then 0.05 parts of butane was added to 100y of polystyrene through an injection port provided in the middle of the extruder.
The mixture was press-mixed in a molar ratio and extruded as a cylindrical body into the atmosphere through an annular slit with a diameter of 60 in the order provided in an extrusion port set at 135°C.

Contact area 150 kept at 30°C immediately after the annular slit
A cooling ring of cIt was placed in contact with the outer surface of the cylindrical body, and then a contact area of 100 cI was maintained at 130°C.
A heating ring t was placed in contact with the outer surface of the cylindrical body, and after forming an unfoamed layer on the outer surface of the cylindrical body, the cylindrical body was expanded while relaxing its orientation, and then the diameter was 207 W$.
5n1/Min.L cooling drum maintained at 200C. It was taken at a speed of The sheet with a basis weight of 200y/7n obtained in this way has a width of 650Tf1m1
Thickness is 1.2TIr! An unfoamed layer of 70 μm was formed on one side. This sheet has a heating shrinkage force of 210V, so there is no problem of it coming off from the sheet clamp of the molding machine during continuous vacuum forming, and the sheet surface has a glossy appearance with no cracks in the unfoamed layer. It was hot.

Comparative Example 1 In the equipment of Example 1, the heating ring was removed and the temperature of the cooling ring was set to 30°C to produce a foamed polystyrene sheet.

The thickness of the obtained sheet was almost the same as that of the sheet produced by attaching a heating ring kept at a temperature of 110°C, and the thickness of the unfoamed layer, but the heating shrinkage force was 380y, which was obtained by contacting with the heating ring. It was about 80% more expensive than a sheet, and when heated in a tray molding machine, it came off from the sheet clamp.

[Brief explanation of the drawing]

1 and 2 are schematic cross-sectional views for explaining examples of embodiments of the present invention. 1...Die, 2...Annular slit, 3
......Cylindrical body, 4...Cooling ring, 5.
... Cooling medium circulation path, 6 ... Heating ring, 7 ... Heating medium circulation path, 8 ... Cooling drum, 9 ... Cavity , 10... Air blowing pipe, 11... Air ring.

Claims (1)

[Claims] 1. A method for obtaining a foamed polystyrene sheet by melt-kneading polystyrene with a low-boiling organic compound, extruding it into a cylindrical body through an annular slit, expanding the diameter of the cylindrical body, and then cutting it open. Then, the surface of the cylindrical body was brought into contact with a cooling ring maintained at -10 to 90°C installed immediately behind the annular slit, and the heating deformation temperature of polystyrene was ±10°C.
A method for manufacturing a foamed polystyrene sheet, which comprises cooling the sheet to a temperature within the range of 10°C, and then bringing it into contact with a heating ring placed immediately behind the cooling ring and maintained at a heating deformation temperature +10°C or higher. 2. The manufacturing method according to claim 1, wherein the polystyrene is general-purpose polystyrene, impact-resistant polystyrene, copolymerized polystyrene with bromustyrene or α-methylstyrene, or copolymerized polystyrene with maleic anhydride. 3. The manufacturing method according to claim 1, wherein the heating ring is installed adjacent to the cooling ring via a heat insulating material.