JP2970876B2 - Extruded styrene-based resin foam sheet excellent in cutting workability and method for producing the same - Google Patents

Description

The present invention relates to an extruded styrene-based resin foam sheet having excellent machinability and a method for producing the same.

[Conventional technology]

In recent years, using a styrene-based resin foam sheet with a thickness of 2 to 5 mm and a density of 0.05 to 0.2 g / cm ³ , the foam sheet can be cut, grooved, fused, etc. as appropriate, and used for a lunch box or the like. It is widely used to assemble and use various container shapes such as box type and barrel type. The styrene-based resin foam sheet used for such an application is mainly formed by extruding a molten styrene-based resin containing a foaming agent into a cylindrical shape from a circular die to form a cylindrical foam (balloon). A method of manufacturing a sheet by passing between the rolls and pressing the inner surface of the balloon or cutting the balloon in the extrusion direction has been adopted.

[Problems to be solved by the invention]

However, when the above-mentioned styrene resin foam sheet 10 is cut by a cutting blade in the sheet extrusion direction (the direction of arrow α in the figure) as shown in FIG. When a plurality of grooves are formed by a rotary saw or the like in the width direction of the sheet (the direction of the arrow β in the drawing), both sides of the groove concave portion 12 can be easily cut off or sometimes broken. As a result, the appearance of the container to be assembled is impaired, or dusts due to scabs or the like fall and adhere to articles to be packaged such as food, which is undesirable. As described above, the conventional styrene-based resin foam sheet has not yet been satisfactory in terms of cutting workability such as cutting and grooving.

[Means for solving the problem]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned drawbacks of the prior art, and as a result, have found that the cutting workability of the extruded styrene resin foam sheet is greatly affected by the foam shape, compressive strength and flexural modulus of the foam. Further research was conducted based on the findings.

As a result, in the conventional foam sheet having insufficient cutting workability, the foam 13 is biaxially stretched at the time of forming the balloon after extrusion, so that the bubble 13 is extruded in the extrusion direction and width as shown in FIG. 5 (b). The styrene resin foam sheet that has a flat cross-section in any direction and has a shape like a go stone as a whole and exhibits good cutting workability has a compressive strength and flexural modulus in a specific range. Within
For cutting in the extrusion direction of the foam sheet, it is preferable that the air bubbles have a flattened shape like an ellipse in the extrusion direction, and for the groove processing in the width direction, the air bubbles are in the thickness direction. The present inventors have found that it is preferable to form a long circular shape, and have completed the present invention.

That is, the extruded styrene-based resin foam sheet of the present invention having excellent machinability is formed by cutting a tubular foam extruded from an extruder into a tubular shape in the extrusion direction and forming a sheet having a density: ρ of 0.05.
A styrene resin extruded foam sheet of ~0.2g / cm ^3,
The corrected compressive stress of the foamed sheet: X and the corrected flexural modulus: Y are represented by the following formula: X = x (0.07 / ρ) ^1.42 > 1.0 Y = y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ ... [x: foaming 5% compressive stress of the sheet (kg f / cm ² ) y: Flexural modulus of the foamed sheet in the extrusion direction (kg f / cm ² )] and the average cell diameter in the longitudinal section of the foamed sheet in the extrusion direction And the average cell diameter in the longitudinal section in the width direction orthogonal to the extrusion direction is as follows: 1.4 ≦ a / b <3.1… 0.7 ≦ c / b <1.5… (a: average cell diameter in the extrusion direction of the foamed sheet, b : Average cell diameter in the thickness direction of the foamed sheet, and c: average cell diameter in the width direction of the foamed sheet).

Further, the method of the present invention for producing an extruded styrene-based resin foamed sheet comprises, after extruding a molten styrene-based resin containing a foaming agent from an extruder into a low-pressure region into a tubular foam,
The foamed sheet is formed by cutting the tubular foamed body in the extrusion direction, and thereafter, the extruded foamed sheet whose surface temperature has become equal to or lower than the heat deformation temperature is reheated to obtain a secondary foaming rate (before heating). The secondary foaming is performed so that the density of the foamed sheet / the density of the foamed sheet after the heat stretching is in the range of 1.01 to 1.4, and the stretching ratio in the extrusion direction (the speed of the take-up roll / the speed of the feed roll) is 1.05 to 1.05. It is characterized in that it is stretched to be in the range of 2.0.

 Hereinafter, the present invention will be described with reference to the drawings.

The extruded foam sheet of the present invention is formed by cutting a tubular foam extruded from an extruder into a tubular shape in the extrusion direction to form a sheet, and has a density ρ of 0.05 to 0.2 g / cm ^3. The corrected compressive stress: X and the corrected flexural modulus: Y of the foamed sheet satisfy the following expression and X = x (0.07 / ρ) ^1.42 > 1.0... Y = y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ . Things. In the formula, x is the 5% compressive stress (kg f / cm ² ) of the foam sheet, and y is the flexural modulus (kg f / cm ² ) of the foam sheet in the extrusion direction. Here, when X ≦ 1.0, the compressive strength is insufficient, so that both sides of the groove concave portion are easily crushed during groove engraving, and sometimes the chip is broken. Y ≦
In the case of 1.2 × 10 ³ , the bending strength in the extrusion direction is not sufficient.

Further, as shown in FIG. 1, the sheet of the present invention has an average cell diameter in the longitudinal section in the extrusion direction (the direction of the arrow α in the figure) that satisfies the formula, that is, 1.4 ≦ a / b (where a is the sheet. Of the sheet in the extrusion direction, and b indicates the average cell diameter in the thickness direction of the sheet).
In other words, as shown in FIG. 2, this means that the shape of each cell forming the cell structure in the cross section in the extrusion direction of the foam sheet is an elliptical shape that is long in the extrusion direction. a / b <
1.4 has an adverse effect on the bending strength in the extrusion direction,
Troubles such as getting stuck in the cutting machine are easy to occur.
When b ≧ 3.1, the stretching in the extrusion direction is too large, which adversely affects the compressive strength.

Further, the sheet 1 of the present invention has an average cell diameter in a longitudinal section in the width direction (the direction of arrow β in FIG. 1) orthogonal to the extrusion direction, that is, 0.7 ≦ c / b <1.5. The middle c indicates the average bubble diameter in the width direction of the sheet). In other words, in other words, as shown in FIG. 3, the shape of each cell forming the cell structure in the cross section in the width direction of the foamed sheet is substantially a perfect circle or a circle slightly longer in the thickness direction. I do. When c / b <0.7, it is good for grooving in the width direction, but it is difficult to manufacture itself. When c / b ≧ 1.5, bubbles in the widthwise vertical cross section have a flat shape. None, it is easy to cause burrs in groove processing in the width direction.

Therefore, the extruded foamed sheet 1 of the present invention has a cell structure that simultaneously satisfies the above formulas (1) to (4), thereby ensuring excellent cutting workability in the extrusion direction and excellent groove machining in the width direction. At the same time, appropriate compression strength and bending strength can be obtained.

The styrene resin usable in the present invention is a polymer mainly composed of styrene, a styrene homopolymer and a copolymer with another vinyl monomer copolymerizable with styrene, and furthermore generally has an impact resistance. A copolymer or mixture with a rubber polymer mainly composed of polystyrene called a polystyrene resin, or a copolymer with a diene monomer, a copolymer of styrene and maleic anhydride, and a copolymer of styrene Copolymers of methacrylic acid, copolymers of styrene and methyl methacrylate, and the like are included. In addition, the melt flow rate (MFR: JIS K72)
10 Condition 8) is preferably 0.3 to 10 (g / 10 min).

The production method of the present invention is a method of extruding a molten styrene-based resin containing a foaming agent from an extruder into a low-pressure region (usually in the air) by a normal extrusion foaming technique, and the surface temperature of the styrene-based resin is reduced to a heat deformation temperature or lower. It is applied to an extruded foam sheet. The above-mentioned heat deformation temperature conforms to the deflection temperature under load according to JIS K7207, and a method such as air cooling or water cooling is used to keep the sheet below this heat deformation temperature. When the surface temperature of the sheet 2 becomes equal to or lower than the heat distortion temperature, it means that the sheet surface is at least solidified.

Therefore, in the method of the present invention, as shown in FIG. 4, the extruded foamed sheet 2 whose surface temperature has become equal to or lower than the above-mentioned thermal deformation temperature is transported while being sandwiched between the feed rolls 3, and is again heated by the heating device 4. While being foamed, it is stretched in the extrusion direction by the cooling / take-off roll 5. Thereby, the extruded styrene resin sheet 1 having the specific cell structure described above is obtained. In the figure, reference numeral 6 denotes a cutting blade for cutting the obtained sheet. As the heating device 4, a device using infrared heating, hot air heating, steam heating, or the like is used.

The secondary foaming of the sheet 2 is determined by the density (g / cm ³ ) of the foam sheet before heating (the sheet at the point I in the figure) / the density (g / cm ³ ) of the foam sheet after heating and stretching (the sheet at the point II in the figure). The secondary foaming ratio expressed in cm ³ ) is in the range of 1.01 to 1.4, preferably 1.05 to 1.3. The stretching in the extrusion direction is performed by appropriately changing the rotation speeds of the feed roll 3 and the take-up roll 5, and is represented by the speed of the take-up roll (m / min) / the speed of the feed roll (m / min). Stretching ratio is 1.05 to 2.
0, preferably in the range of 1.3 to 1.6. When the secondary foaming ratio is less than 1.01, heating is insufficient, so that the shape of the bubbles in the cross section in the sheet width direction cannot be made into a substantially circular shape or a slightly longer circular shape in the thickness direction. 1.4
If it exceeds, the sheet surface becomes rough due to overheating. If the stretching ratio is less than 1.05, the cell shape in the extruded foam sheet 2 hardly changes, and the above formula cannot be satisfied. When a groove is formed by a rotary saw blade in the sheet width direction, it is easy to flank both sides of the groove recess. In the present invention, the secondary foaming and the stretching in the extrusion direction are usually performed simultaneously.

As the foaming agent contained in the styrene resin, an aliphatic hydrocarbon, a halogenated hydrocarbon or Freon gas is used alone or in combination. Specific examples of the aliphatic hydrocarbon include, for example, propane, butane, isobutane, pentane, isopentane, and the like. Examples of the halogenated hydrocarbon include a chlorine- or bromine-substituted aliphatic hydrocarbon. In addition, chlorodifluoromethane, trifluoromethane, 1,2,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-
Difluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, trichlorofluoromethane, 1,1-dichloro-2,2,2-tetrafluoromethane and the like are used. The addition amount of these foaming agents is usually 1.0 to 5.0 parts by weight based on 100 parts by weight of the styrene resin. In addition to such a foaming agent, a bubble regulator, a pigment, an antistatic agent, a flame retardant, and the like can be appropriately added as needed.

The extruded foam sheet 2 applied to the method of the present invention is formed by cutting a cylindrical foam obtained by extruding a molten polystyrene-based resin material containing a foaming agent from a circular die into a cylindrical shape and then passing through a mandrel (incision). (According to the method). In the method of the present invention, it is preferable from the viewpoint of production efficiency that an in-line system in which a heating device or a stretching device is connected to an extruder or the like and a series of processes are performed following the extrusion foaming process.

The extruded foamed sheet 1 obtained by the present invention can be used as a constituent material of a prefabricated container, and can also be used for applications such as architectural model materials, lightweight display materials, concrete forms and the like.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Examples 1 to 4, Comparative Examples 1 to 4 and Reference Example A resin composition obtained by adding 2.5 parts by weight of butane and 1 part by weight of talc to 100 parts by weight of a styrene-based resin of MFR 4 g / 10 min was discharged. 200 kg / cm ² pressure in a 65 kg / hr extruder
After melt-kneading at G, the molten composition at 163 ° C. was extruded into the atmosphere from a circular die attached to the extruder tip, passed through a mandrel and cut open to obtain an extruded foamed sheet, and subsequently the foamed sheet was extruded. At the stage when the surface temperature became 60 ° C. below the thermal deformation temperature, as shown in FIG. 4, it was transferred by a feed roll and a take-up roll, and reheated by an infrared heater installed between the two rolls. The secondary foaming and stretching in the extrusion direction were carried out so as to have the secondary foaming ratio and stretching ratio shown in Table 2 to obtain a 3.5 to 3.8 mm thick extruded polystyrene resin sheet.

For each of the extruded foam sheets thus obtained, 7
Density after day, thickness and each average bubble diameter (a, b, c),
The corrected compressive strength and the corrected flexural modulus were measured, and the cutting workability by a razor blade in the sheet extrusion direction and the groove engraving (groove width: 2 mm, depth: 2 mm) by a rotating saw blade in the width direction were examined. The results are shown in the table below. As a reference example, a styrene equivalent to a conventional product obtained by a laminating method in which a balloon-shaped cylindrical foam is extruded into a balloon shape and the inner surface of the foam is pressure-bonded by passing the balloon-shaped tubular foam between rolls. Extruded resin-based foam sheets were mentioned.

* 1: Cutting workability was evaluated according to the following criteria by observing the cut processing surface.

：: no swelling △: some swelling ×: caught by the cutting machine and impossible to cut * 2: Grooving workability was evaluated according to the following criteria by observing groove recesses due to processing.

○: no swelling △: some swelling ×: skipping due to deficiency [Effect of the Invention] As described above, the extruded styrene resin foam sheet of the present invention has a specific compressive stress and flexural modulus, and
Since the cell structure in the cross section in the extrusion direction and the cell structure in the cross section in the width direction have a specific shape, excellent cutting workability in the extrusion direction and excellent groove processing are obtained, and at the same time, moderate compressive strength and bending Strength is also obtained. According to the production method of the present invention, the pressed foamed sheet having excellent cutting workability as described above is formed by extruding foaming of a cutting method, and the extruded foamed sheet having a surface temperature equal to or lower than a heat deformation temperature is reheated. By performing secondary foaming and stretching in the extrusion direction, a simple and efficient production can be achieved.

Therefore, if the extruded foamed sheet of the present invention is used, cutting and grooving can be performed beautifully and accurately without occurrence of swelling or the like.For example, when the foamed sheet is used as a constituent material of a prefabricated container In addition, it is possible to provide a high-quality assembling type container that can be accurately assembled, has a beautiful appearance, and has no fear of falling off of shavings and the like.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of an extruded styrene resin foam sheet of the present invention, FIG. 2 is an enlarged model diagram of bubbles in a cut longitudinal section in the extrusion direction (α) of FIG. 1, and FIG. Fig. 1 is an enlarged model view of bubbles in a cut longitudinal section in the width direction (β), Fig. 4 is an explanatory view of a production process showing one embodiment of the production method of the present invention, and Fig. 5 (a) is a conventional extrusion foaming. FIG. 2B is a perspective view showing a sheet, and FIG. 2B is a schematic perspective view for explaining a bubble structure in a conventional product sheet. 1. Extruded styrene resin foam sheet 2. Extruded foam sheet whose surface temperature is lower than the heat distortion temperature 3. Feed roll 4, Heating device 5. Take-up roll

Claims (2)

(57) [Claims] (1) A sheet obtained by cutting a tubular foam extruded from an extruder into a sheet in the extrusion direction and having a density ρ of 0.05 to
Extruded styrene resin foam sheet of 0.2 g / cm ³ , wherein the corrected compressive stress: X and the corrected bending elastic modulus: Y of the expanded sheet are represented by the following formula, and X = x (0.07 / ρ) ^1.42 > 1.0 ... Y = Y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ ... [x: 5% compressive stress of foam sheet (kg f / cm ² ) y: Flexural modulus of foam sheet in extrusion direction (kg f / cm ² )] And the average cell diameter in the longitudinal section in the extrusion direction of the foam sheet and the average cell diameter in the longitudinal section in the width direction orthogonal to the extrusion direction are represented by the following formula: 1.4 ≦ a / b <3.1 ... 0.7 ≦ c / b <1.5 ... (a: average cell diameter in the extrusion direction of the foam sheet, b: average cell diameter in the thickness direction of the foam sheet, c: average cell diameter in the width direction of the foam sheet) Extruded styrene resin foam sheet with excellent processability. 2. A foamed sheet obtained by extruding a molten styrene-based resin containing a foaming agent from an extruder into a low-pressure region in a tubular shape to form a tubular foam, and cutting the tubular foam in the extrusion direction. After that, the extruded foamed sheet whose surface temperature has become equal to or lower than the heat distortion temperature is reheated, and the secondary foaming ratio (the density of the foamed sheet before heating / the density of the foamed sheet after heating and stretching) is 1.01. Cutting process characterized by secondary foaming in the range of ~ 1.4 and stretching in the extrusion direction (drawing roll speed / feeding roll speed) in the range of 1.05 to 2.0. Method for producing extruded styrene resin foam sheet with excellent properties.