JP2992074B2 - 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). In any direction, it has a flat shape in longitudinal section and has a shape like a go stone as a whole, whereas the styrene resin foam sheet showing good cutting workability has a compressive strength and flexural modulus within a specified range. It is preferable that the bubbles have a flattened shape like an ellipse in the extrusion direction for the cutting process in the extrusion direction of the foam sheet, and the bubbles are formed in the groove direction in the width direction. It has been found that it is preferable that the circular shape is longer in the thickness direction and that the diameter of each cell in the thickness direction is substantially uniform over the entire thickness direction of the sheet, and the present invention has been completed.

That is, the extruded styrene-based resin foam sheet having excellent machinability according to the present invention is formed by pressing the inner surface of a tubular foam extruded from an extruder into a sheet to form a sheet having a density: ρ of 0.05 to 0.1.
A 2 g / cm ³ extruded styrene resin foam sheet, wherein the corrected compressive stress: X and the corrected flexural modulus: Y of the expanded sheet are as follows: X = x (0.07 / ρ) ^1.42 > 0.7... Y = y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ … [x: 5% compressive stress of foam sheet (kgf / cm ² ) y: flexural modulus of foam sheet in extrusion direction (kgf / 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 axial section perpendicular to the extrusion direction are represented by the following formula: 1.4 ≦ a / b <3.8... 0.7 ≦ c / b <2.0 ... (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) Average bubble diameter b
The average cell diameter in both front and back surface layer portions corresponding to a thickness range of 5% of the total thickness from both surfaces of the sheet: b ₁ and the average cell diameter in the inner layer portion corresponding to the thickness range other than both surface layer portions: b
₂ satisfies the relationship of b ₂ / b ₁ <2.0.

Further, in the production method of the present invention, the molten styrene-based resin containing a foaming agent is extruded into a low pressure region in a tubular shape from an extruder to form a tubular foam, and then passed between rolls to form an inner surface of the tubular foam. The extruded foam sheet is formed by pressing, and thereafter, the extruded foam sheet whose surface temperature has become equal to or lower than the deformation temperature is reheated to secondary foam and stretched in the extrusion direction. is there. Furthermore, the method of the present invention performs secondary foaming so that the secondary foaming ratio (density of the foamed sheet before heating / density of the foamed sheet after heating and stretching) is in the range of 1.01 to 1.4, and also stretches in the extrusion direction (drawing). Stretching is performed so that the ratio of the speed of the take-up roll / the speed of the feed roll) is in the range of 1.05 to 1.5.

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

The extruded foam sheet of the present invention is formed by pressing the inner surface of a tubular foam extruded into a tubular shape from an extruder into a sheet, and has a density: ρ of 0.05 to 0.2 g / cm ^3. The corrected compressive stress of foamed sheet: X and the corrected bending elastic modulus: Y satisfy the formula and X = x (0.07 / ρ) ^1.42 > 0.7… Y = y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ … is there. In the formula, x is the 5% compressive stress (kgf / cm ² ) of the foam sheet, and y is the flexural modulus (kgf / cm ² ) of the foam sheet in the extrusion direction. Here, when X ≦ 0.7, the compressive strength is insufficient, so that the groove is easily cut off on both sides of the groove during the sculpture processing, and sometimes the chip is broken. Y ≦ 1.
In the case of 2 × 10 ³ , the bending strength in the extrusion direction is not sufficient.

Further, in the present invention, as shown in FIG. 1, the sheet has an average bubble diameter in a longitudinal section in the extrusion direction (the arrow α direction in the figure),
1.4, that is, ≦ a / b <3.8 (where a represents the average cell diameter in the sheet extrusion direction and b represents the average cell diameter in the sheet thickness direction). 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
In the case of, the bending strength in the extrusion direction is adversely affected, and troubles such as being caught by the cutting machine easily occur, and a / b ≧
In the case of 3.8, the stretching in the extrusion direction is too large and 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 the arrow β in FIG. 1) orthogonal to the extrusion direction, that is, 0.7 ≦ c / b <2.0. 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 the production itself becomes difficult. When c / b ≧ 2.0, the bubbles in the vertical cross section in the width direction have a flat shape. In addition, it is easy to cause burrs in the groove processing in the width direction.

Furthermore, the sheet of the present invention has a total thickness of 5 from both surfaces of the sheet.
% Of both front and back surface layers (1p in Fig. 1)
Average cell diameter in: average cell diameter b ₁ and the inner layer portion corresponding to the thickness range other than the both surface layer portions in the (1q in FIG): b ₂
Satisfy the relationship of b ₂ / b ₁ <2.0. This b ₂
/ b ₁ is preferably _{0.5 <b 2 / b 1 <} 1.5. This means that the air bubbles in both surface layers on the front and back of the sheet and the air bubbles in the inner layer have substantially uniform cell diameters in the thickness direction. In other words, each cell of the foam sheet has a state in which the cell diameter in the thickness direction is substantially uniform over the entire thickness direction of the sheet. b ₂
When / b ₁ ≧ 2.0, it causes burrs in the groove processing in the width direction.

Therefore, the extruded foamed sheet 1 of the present invention has a cell structure that simultaneously satisfies the conditions represented by the above formulas to secure excellent cutting workability in the extrusion direction and excellent groove processing in the width direction. Is done. 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.

Accordingly, in the method of the present invention, as shown in FIG. 4, the extruded foamed sheet 2 is transported while being sandwiched between the feed rolls 3 when the surface temperature becomes lower than the above-mentioned thermal deformation temperature, and is heated again by the heating device 4 to perform secondary foaming. At the same time, it is stretched in the extrusion direction by the cooling / take-off roll 5. Thereby, the extruded styrene-based 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 ² ) of the foam sheet before heating (the sheet at point I in the figure) / the density (g / cm ² ) of the foam sheet after heating and stretching (the sheet at 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 the speed of the take-up roll (m / min) /
The stretch ratio expressed by the speed of the feed roll (m / min) is 1.05 to 1.
5, preferably in the range of 1.1 to 1.4. 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 perfect circular shape or a slightly longer circular shape in the thickness direction, and the skin portion of the sheet And the size (bubble diameter in the thickness direction) of the bubble inside the sheet and the bubble inside the sheet cannot be made uniform. vice versa
If it exceeds 1.4, 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 it becomes impossible to satisfy the above expression. Conversely, if it exceeds 1.5, the cell shape in the extrusion direction is extremely long in the extrusion direction. 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 extruding a molten polystyrene resin material containing a foaming agent from a circular die into a tubular shape, and passing the tubular foam between rolls. Internal pressure bonding (adhesion)
This is a sheet (by a laminating method) obtained by the above 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 and a stretching device are connected to an extruder or the like and installed so as to perform a series of processes following the extrusion foaming process.

The extruded foamed sheet 1 obtained by the present invention can be used as a constituent material of an assembling type container (particularly, a lunch container).
It can be used for applications such as architectural model materials, lightweight display materials, and concrete formwork.

〔Example〕

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

Examples 1 to 4 and Comparative Examples 1 to 4 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 having a MFR of 4 g / 10 min was discharged at a rate of 65 kg / hr. 200 kg / cm ² in the extruder
After melt-kneading with G, the molten composition at 163 ° C. is extruded into the air from a circular die attached to the tip of the extruder into a cylinder, and it is passed between rolls so that the inner surfaces of the foam are compressed and extruded. The sheet was obtained, and subsequently, when the surface temperature of the foamed sheet reached 60 ° C. below the heat distortion temperature, the sheet was transferred by a feed roll and a take-off roll as shown in FIG. By reheating with an infrared heater, secondary foaming and stretching in the extrusion direction are performed so as to have the secondary foaming ratio and stretching ratio shown in the following table. (Comparative Example 4 performs the reheating and stretching. No), and a polystyrene resin extruded foam sheet having a thickness of 3.4 to 3.7 mm was obtained.

For each of the extruded foam sheets thus obtained, 7
Days after the density, thickness and each average bubble diameter (a, b, c, b ₁ ,
b ₂₎ and the correction compressive strength and with measuring the correct flexural modulus, Mizoho by rotation saw blade cutting resistance and the width direction of the razor blade of the sheet extrusion direction (groove width: 2 mm, depth: 2 mm)
Workability was investigated. The results are shown in the table below.

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

：: No swelling Δ: Partly swelling X: Hooked by a cutting machine, unable to cut * 2: Expanding workability was evaluated according to the following criteria by observing groove recesses due to processing.

○: no swelling △: some swelling ×: skipping due to defects [Effect of the Invention] As described above, the styrene resin extruded foam sheet of the present invention is a tubular foam extruded from an extruder into a tubular shape. It has a specific compressive stress and flexural modulus, and the cell structure in the vertical section in the extrusion direction and the cell structure in the vertical section in the width direction have a specific cell shape. It is intended to provide, and because it is stipulated for the cell diameter in the thickness direction of each cell in the surface layer portion and the inner layer portion of the sheet, excellent cutting processability in the extrusion direction and excellent groove forming processability are obtained, At the same time, appropriate compressive strength and bending strength can be obtained. Further, according to the production method of the present invention, the extruded foamed sheet having excellent cutting workability as described above is formed by so-called lamination type extrusion foaming, and the extruded foamed sheet having a surface temperature equal to or lower than the heat deformation temperature is re-formed. By heating and secondary foaming and stretching in the extrusion direction, it can be simply and efficiently produced.

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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // B29K 25:00 105: 04 B29L 7:00 C08L 25:00 (56) References JP-A-4-91920 (JP, A JP-A-63-122515 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00 C08J 9/00-9/42 B29C 67/20-67 / 22 B29C 47/00-47/96 B29C 55/00-55/30

Claims (3)

(57) [Claims] An inner surface of a tubular foam extruded from an extruder into a tubular shape is pressed to form a sheet having a density: ρ of 0.05 to 0.2 g.
/ cm ³ , wherein the corrected compressive stress: X and the corrected flexural modulus: Y of the expanded sheet are represented by the following formula: X = x (0.07 / ρ) ^1.42 > 0.7... Y = y (0.07 / ρ) ^1.76 > 1.2 × 10 ³ … [x: 5% compressive stress of foam sheet (kgf / cm ² ) y: flexural modulus of foam sheet in extrusion direction (kgf / 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 axial direction perpendicular to the extrusion direction are as follows: 1.4 ≦ a / b <3.8... 0.7 ≦ c / b <2.0. (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), and the average of the foam sheet in the thickness direction. Bubble diameter b
The average cell diameter in both front and back surface layer portions corresponding to a thickness range of 5% of the total thickness from both surfaces of the sheet: b ₁ and the average cell diameter in the inner layer portion corresponding to the thickness range other than both surface layer portions: b
_{2. An} extruded styrene resin sheet having excellent machinability, wherein ₂ satisfies the relationship of b ₂ / b ₁ <2.0. 2. A method in which a molten styrene resin containing a foaming agent is extruded from an extruder into a low-pressure region in a tubular shape to form a tubular foam, and then passed between rolls to press the inner surface of the tubular foam. The extruded foamed sheet is formed by the above method, and thereafter, the extruded foamed sheet having a surface temperature equal to or lower than the deformation temperature is reheated to form a secondary foam and stretched in the extrusion direction. A method for producing an extruded styrene resin foam sheet. 3. The secondary foaming ratio (density of foam sheet before heating /
Secondary foaming is performed so that 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.
3. The method for producing an extruded styrene resin sheet according to claim 2, wherein the sheet is stretched so as to fall within the range of 5.