JP2010059341A - Polystyrene-based resin foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polystyrene-based resin foamed sheet which reduces cut deviation in the cross section, cut by a hot wire, of a hot-molded article and alleviates sticking of foreign substances on the hot wire, in a polystyrene-based resin foamed sheet used in such an application where the foamed sheet is secondarily foamed, hot-molded, and cut into individual vessels by the hot wire to obtain products. <P>SOLUTION: The polystyrene-based resin foamed sheet is obtained by using, as a base resin, a polystyrene-based resin having a melt mass flow rate of 2.0-4.0 g/10 min when measured under such conditions that the resin temperature is 200°C and the load is 49 N. In the cross section perpendicular to the longitudinal direction of a secondarily foamed sheet obtained by heating the polystyrene-based resin foamed sheet, the cell diameter in the thickness or width direction is characterized in that the content of cells each having a small diameter of ≤1/2 times of the average cell diameter in the thickness direction is ≤20%, in a core part except the upper and lower surface layer parts each having a thickness of 20% of the whole thickness. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polystyrene resin foam sheet.

  A plurality of molded articles are connected by thermoforming a polystyrene resin foamed sheet (hereinafter sometimes referred to as “primary foamed sheet”) (heating and secondary foaming followed by molding with a mold). A method of stacking a plurality of sheet-like molded bodies and separating them into individual shapes using a heat ray (for example, nichrome wire) is widely used in the production of natto containers and the like, for example.

  In the hot wire cutting process, there may be a case where a cut of the melted section occurs. The cut shift is a state in which the end surfaces of the molded product that are stacked when a plurality of sheets are fused with a heat ray are not in a straight line, and some of the end surfaces are uneven and uneven. When cut misalignment occurs, the dimensional accuracy of the molded product will be low, especially in natto containers where the main body and lid are integrated and precise dimensional accuracy is required. The beauty is impaired. On the other hand, as a method for eliminating the cut-off, there is a method for increasing the temperature of the hot wire. However, this method causes a problem that the frequency of heat rays is increased and productivity is lowered.

  On the other hand, in the heat ray cutting step, the polystyrene resin melted by fusing with heat rays adheres to the heat rays and becomes brown or black foreign matter (hereinafter referred to as “foreign matter”) due to thermal oxidative degradation. From the above viewpoint, the work must be interrupted each time to clean the hot wire, which causes a problem of greatly reducing production efficiency.

On the other hand, as a method for preventing foreign matter from adhering to the heat ray, a method is known in which the ash content in the foamed sheet is 0.35% by weight or less (Patent Document 1).
However, Patent Document 1 describes that it is effective to reduce talc, which is a bubble regulator, as a means for reducing ash. The cell regulator is the core of the foam sheet manufacturing process when generating the cells (bubbles) that make up the foam. If the cell modifier is reduced, the number of cells decreases, and the foam sheet and thermoforming Since the cell in the product becomes large, the texture of the surface becomes rough and the appearance becomes inferior, and there is a problem of lowering the commercial value. In addition, when the amount of the air conditioning agent is reduced, the adhesion of the foreign matter to the heat ray should be reduced while maintaining the quality such as strength and flexibility of the molded product obtained by thermoforming (secondary foaming) the foamed sheet. It becomes difficult.

Therefore, there is a demand for a polystyrene-based resin foam sheet that does not cause cutout or adhesion of foreign matter to the heat rays during hot wire cutting.
JP 2004-35712 A

    The present invention has been studied in view of the above situation, while maintaining the quality such as good appearance, strength of the molded body, flexibility, etc. without reducing the amount of the air-conditioning agent at the time of foam sheet production. The present invention provides a polystyrene-based resin foam sheet capable of preventing cutout of a molded product and reducing foreign matter adhesion to heat rays.

As a result of intensive investigations on means for solving the problem of cuts in the hot wire melt cross section and foreign matters, while maintaining the quality of the container appearance, strength, etc., the present invention is a base resin of a polystyrene resin foam sheet (primary foam sheet). Melt mass flow rate (hereinafter referred to as “MFR”) is greatly affected by the cell structure in the secondary foamed sheet obtained by heating the primary foamed sheet, and the thickness and basis weight of the secondary foamed sheet. As a result, they have reached the present invention.
That is, it is effective to reduce the contact resistance between the heat ray and the secondary foam sheet in order to suppress the cut-off of the heat ray cut surface and the generation of foreign matter, and as a means thereof, a base resin having a low melt viscosity is used, and By making the cell structure in the secondary foam sheet specific, the contact resistance can be reduced. Furthermore, it is more preferable that the secondary foamed sheet is difficult to bend when the hot wire is cut. In order to make it difficult to bend, it has been found that it is effective to reduce the content of small-diameter cells in the thickness direction, particularly in the cell structure.

That is, the present invention
[1] A polystyrene-based resin foam sheet using a polystyrene-based resin having a melt mass flow rate of 2.0 to 4.0 g / 10 min as a base resin, measured at a resin temperature of 200 ° C. and a load of 49 N. The cell diameter in the thickness direction and the width direction in the core portion excluding the surface layer portion corresponding to 20% of the total thickness in the longitudinal section perpendicular to the longitudinal direction of the secondary foam sheet obtained by heating the foam sheet However, the polystyrene-based resin foam sheet, and the [2] polystyrene-based resin foam sheet are heated, wherein the small cell content rate is 1/2% or less of the average cell diameter in the thickness direction. and the thickness of the secondary foamed sheet obtained is 2.0～3.5Mm, a basis weight of 80 to 150 g / ^{m 2,} and, in the thickness direction of the polystyrene-based resin foam sheet 2. The polystyrene-based resin foam sheet according to claim 1, wherein the number of cells is in the range of 9-12.

  Since the polystyrene-based resin secondary foam sheet of the present invention has few cut deviations in the melted section when fusing the stacked sheet-like molded product in which a plurality of molded bodies are connected by thermoforming using heat rays, Highly dimensional accuracy when the container body and the lid are fitted together, and an aesthetically molded product can be obtained. Moreover, since the polystyrene-type resin secondary foam sheet of this invention can reduce the adhesion amount of the foreign material to a heat ray, the frequency | count of hot wire cleaning in a shaping | molding process reduces, and a molded product with high production efficiency is obtained.

  The polystyrene-based resin foam sheet of the present invention can be produced by a widely used method. That is, for example, by adding an air conditioner to a polystyrene resin, using a tandem extruder, after melting and mixing the polystyrene resin and the like in the first stage extruder, the foaming agent is press-fitted into the second stage extruder. After cooling to a suitable foaming temperature, extrusion foaming is performed from a circular die. Furthermore, by blowing cooling air to the foam sheet immediately after extrusion, appropriately adjusting the density of the sheet surface, cooling the foam sheet along the cooling cylinder, and then opening the cylindrical foam sheet, A method of winding in a roll with a winder is generally used.

  Examples of the base resin used for the polystyrene-based resin foam sheet (primary foam sheet) of the present invention include polystyrene, styrene homopolymers such as poly-p-methylstyrene, styrene-maleic anhydride copolymer, Styrene copolymer such as styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-acrylonitrile-butadiene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, or polystyrene and polyphenylene The mixture with an oxide etc. are mentioned.

  The base resin in the present invention has a melt mass flow rate (MFR) of 2.0 to 4.0 g / 10 min measured under the conditions of a resin temperature of 200 ° C. and a load of 49 N according to JIS K7210. Preferably, the thing of 2.2-3.2 g / 10min is more preferable. When the MFR of the base resin is less than 2.0 g / 10 min, the melt viscosity of the resin is high, so that the contact resistance between the foamed sheet and the heat ray increases, and cut deviation may occur. At the same time, when the cut-off occurs, the contact time / contact amount between the heat ray and the sheet increases, and the amount of foreign matter adhering to the heat ray tends to increase. On the other hand, when the MFR exceeds 4.0 g / 10 min, since the melt viscosity of the resin is low, the contact resistance of the heat ray is reduced, and a good molded body with little cut-off is obtained, but the foamed sheet was molded and heated (2 In the case of subsequent foaming), the cell may be easily broken and a good molded product may not be obtained.

  Examples of the air conditioner used in the polystyrene resin foam sheet (primary foam sheet) of the present invention include porous inorganic powders such as calcium carbonate, barium sulfate, silica, titanium oxide, clay, aluminum oxide, bentonite, and diatomaceous earth. , Talc, etc. can be used. Further, if necessary, in order to improve the dispersion of the air conditioner in the resin, a fatty acid metal salt such as ethylene bisstearylamide and magnesium stearate, a lubricant such as a fatty acid ester, and the like may be added.

  Additives may be added to the polystyrene resin foam sheet (primary foam sheet) in the present invention as long as the effects of the present invention are not impaired. Examples of the additive include pigments, stabilizers, ultraviolet absorbers, antistatic agents and the like.

  Examples of the foaming agent used in the polystyrene-based resin foam sheet (primary foam sheet) of the present invention include physical foaming agents such as propane, butane, pentane, and carbon dioxide, or chemical foaming agents such as sodium bicarbonate-citric acid. can give. Industrially, butane is widely used. However, since the sheet has a high thermoformability / foaming agent gas retention property and a long molding life, the isobutane is 65 to 100% by weight and the normal butane is 0 to 35. It is preferable to use mixed butane consisting of% by weight.

  Next, a method for forming the polystyrene foam sheet (primary foam sheet) of the present invention into a container by thermoforming will be described. For example, a general-purpose sheet molding machine is used as the molding machine, and the primary foamed sheet wound in a roll shape is unwound and heated using an infrared heater or the like. The foam sheet in this state is referred to as a secondary foam sheet. In this case, it is preferable to heat the heater so that the thickness becomes about 80 to 90% of the maximum secondary thickness obtained when the heating amount is increased. By molding the obtained secondary foamed sheet using a molding die, a continuous sheet-like molded product in which a plurality of molded bodies are connected is obtained. Subsequently, the obtained continuous sheet-shaped molded product is cut with a cutter or the like at regular intervals to obtain a sheet-shaped sheet molded product in which a plurality of molded products are connected. The sheet molded product is separated into individual shapes by a hot wire cutting device.

  In the hot wire cutting step, generally, it is preferable to use a nichrome wire having a nichrome wire diameter of 0.5 mm and a surface temperature of 350 ° C. and performing fusing under a feed rate of 6.0 mm / sec.

  Specific examples of thermoforming in the above are plug molding, match molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding, reverse draw molding. , Free drawing molding, plug-and-ridge molding, ridge molding, and the like, and match mold molding is preferred from the standpoint of container shape and surface properties.

  In the polystyrene-based resin foam sheet of the present invention, in the core part excluding the surface layer part corresponding to 20% above and below the entire thickness in the longitudinal section perpendicular to the longitudinal direction of the secondary foam sheet obtained by heating the foam sheet, The content of small-diameter cells whose cell diameter in the thickness direction is ½ or less of the average cell diameter in the thickness direction is preferably 20% or less, and more preferably 15% or less. When the content ratio of the small-diameter cell exceeds 20%, the number of cell films increases, so that the contact resistance between the foamed sheet and the heat ray increases, and cutout tends to occur. Further, when the cut-off occurs, the contact time / contact amount between the heat ray and the sheet increases, and the amount of foreign matter attached to the heat ray tends to increase.

Here, a method for measuring the cell diameter will be described.
As shown in FIG. 1, the secondary foamed sheet is cut along a plane perpendicular to the sheet longitudinal direction, and a photograph of the longitudinal section is taken. Regarding the photograph of the obtained sheet cross section, in the core part excluding the surface layer part corresponding to 20% of the total thickness, the thickness of the core part and the number of cells in the thickness direction were measured, and the thickness of the core part was measured in the thickness direction. The value divided by the number was taken as the average cell diameter.
Next, the total number of cells existing between 5 mm in the sheet width direction in the core portion was counted. About each cell, the cell diameter of the thickness direction and the width direction was measured using calipers.
Finally, cells whose cell diameters in the width direction and the thickness direction were 1/2 or less of the average cell diameter were defined as small-diameter cells, and the number thereof was counted. Then, the ratio of the number of small-diameter cells to the total number of cells existing in the width direction of 5 mm in the core portion was determined, and was defined as “small-diameter cell content”. In the measurement in the 5 mm region in the width direction, 10 points were measured at equal intervals in the sheet width direction, and the arithmetic average value was obtained.

  In the present invention, as a method for reducing the content of small-diameter cells, a method of reducing baffle plates, rectifying plates, etc. existing in the resin flow path of the circular die used when producing the primary foamed sheet can be mentioned. . The circular die structure is a mold having an annular slit, and is composed of die slips outside (outer cylinder) and inside (inner cylinder) of the annular slit. Therefore, a support (baffle plate or current plate) for fixing the inner cylinder is necessary. When there are many supports (baffle plates and baffle plates), the resin flow in the thickness direction is disturbed and the resin pressure distribution tends to be non-uniform, resulting in uneven foaming, non-uniform cell diameter, and small diameter. Cell content tends to increase. On the other hand, as a method for reducing the number, a circular die having a two-pointed two-end structure that supports the inner cylinder support portion only at two places can be cited. On the other hand, a circular die having a large number of support portions includes a circular die having a porous plate structure with a large number of resin flow paths.

  FIG. 2 shows an example of a circular die having the above two-end structure and a circular die having a perforated plate structure. FIG. 2 is a cross-sectional view of the support portion of these dies. In FIG. 2, 1 is an inner cylinder, 2 is an outer cylinder, 3 is a support portion, and 4 is a resin flow path.

The thickness of the secondary foamed sheet obtained by heating the polystyrene resin foamed sheet in the present invention is preferably 2.0 to 3.5 mm, and more preferably 2.5 to 3.0 mm. If the thickness of the secondary foamed sheet is less than 2.0 mm, the sheet is likely to be bent at the time of hot-wire fusing, so cuts are likely to occur, the strength of the molded body tends to be low, and an acceptable product tends to be difficult to obtain. is there. On the other hand, when the thickness of the secondary foamed sheet exceeds 3.5 mm, the cut deviation is small, but the bulkiness when the molded bodies are stacked tends to increase, and the transportation cost tends to increase.
The thickness of the secondary foam sheet can be adjusted by the amount of foaming agent injected during the production of the primary foam sheet, the amount of heat applied during heating, and the like.

The basis weight of the secondary foamed sheet obtained by heating polystyrene-based resin foam sheet of the present invention is preferably from 80 to 150 g / ^{m 2,} more preferably 90~120g / ^{m 2.} When the basis weight of the secondary foamed sheet is less than 80 g / m ² , it is good with little cut deviation, but the strength of the molded body is low, and an acceptable product tends to be difficult to obtain. On the other hand, when the basis weight exceeds 150 g / m ² , since the amount of resin melted by the heat ray at the time of fusing is large, the contact resistance between the foamed sheet and the heat ray is increased, and cut slip tends to occur. In addition, when the cut-off occurs, the contact time and amount of contact between the heat ray and the sheet increase, and the amount of foreign matter adhering to the heat ray tends to increase.
In addition, the basic weight of a secondary foam sheet can be adjusted with the taking-up speed at the time of manufacture of a primary foam sheet.

The number of cells of the polystyrene resin foam sheet (primary foam sheet) in the present invention is preferably 9 to 12, more preferably 10 to 11. When the number of cells in the primary foamed sheet is less than 9, there are few cuts and it is good, but the cells (bubbles) in the foamed sheet and container become large, so the surface texture becomes rough and the appearance may be inferior. is there. On the other hand, when the number of cells exceeds 12, the number of cell membranes increases, so the contact resistance between the foamed sheet and the heat ray increases, resulting in cut displacement, and when cut displacement occurs, the contact time and amount of contact between the heat ray and the sheet. May increase and the amount of foreign matter adhering to the heat rays may increase.
In addition, the number of cells of the polystyrene-based resin foam sheet (primary foam sheet) can be adjusted by the amount of the air conditioner at the time of manufacture.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to an Example.

  The evaluation methods implemented in the examples and comparative examples are as follows.

(Thickness measurement)
Five measurement points were set at equal intervals in the sheet width direction, and the thickness of each measurement point was measured using a dial gauge (manufactured by PEACOCK, DIAL TICHKNESS GAUGE) to obtain an arithmetic mean value.

(Number of cells)
Regarding the number of cells, the vertical longitudinal section of the foam sheet in the width direction perpendicular to the extrusion direction was projected with a microscope in the thickness direction. It calculated | required by counting the number of cells laminated | stacked in the thickness direction measured using this projection figure visually.

(Secondary foaming ratio)
A value obtained by dividing the thickness of the secondary foamed sheet of the polystyrene-based resin foamed sheet by the thickness of the primary foamed sheet was defined as the secondary foaming ratio.

(Evaluation of cut displacement due to nichrome wire cutting)
50 sheet-shaped molded products in which a plurality of molded articles are joined by thermoforming a polystyrene resin foam sheet are stacked, and a nichrome wire (nichrome wire diameter 0.5 mm, surface temperature 350 ° C.) is used in the thickness direction. Was moved from top to bottom (feeding speed: 6.0 mm / sec), melted and separated into individual molded bodies. The unevenness of the cut surface in the width direction perpendicular to the extrusion direction of the 50-layer sheet-like molded product was observed.
In addition, the evaluation criteria of cut deviation are as follows.
◯: The maximum / minimum difference between the 50-layer overlapping irregularities is 1.0 mm or less.
(Triangle | delta): The difference of the maximum / minimum of 50 unevenness | corrugations is larger than 1.0 mm and is 2.0 mm or less.
X: The maximum / minimum difference between the 50-layer overlapping irregularities is larger than 2.0 mm.

(Evaluation of adhesion of foreign matter to nichrome wire by melting nichrome wire)
A cycle (about 1 min) in which 50 sheets of sheet-molded articles in which a polystyrene resin foam sheet was thermoformed and a plurality of molded bodies were connected and fusing with nichrome wire was repeated. At that time, the state of foreign matter adhesion to the nichrome wire and the state of foreign matter adhesion to the molding container were observed, and the time until the foreign matter began to adhere to the molded body was measured. A sample having a time of 2 hours or more until the start of adhesion of foreign matter was regarded as acceptable.

(Comprehensive evaluation by nichrome wire fusing)
Comprehensive evaluation regarding nichrome wire fusing was performed according to the following criteria.
(Double-circle): Cut shift evaluation is (circle) and foreign material adhesion evaluation is a pass.
○: The cut-off evaluation is ○, and the foreign matter adhesion evaluation is unacceptable. Alternatively, the cut deviation evaluation is Δ and the foreign matter adhesion evaluation is acceptable.
(Triangle | delta): Cut shift evaluation is (triangle | delta) and foreign material adhesion evaluation is unacceptable.
X: Cut shift evaluation is x, and foreign matter adhesion evaluation is unacceptable.

Example 1
HH102 (manufactured by PS Japan Co., Ltd., MFR = 3.0 g / 10 min) was used as the polystyrene resin, and talc (manufactured by Hayashi Kasei Co., Ltd., Talcan powder PK) and magnesium stearate (堺) A mixture of SM-1000 manufactured by Chemical Industry Co., Ltd. at a weight ratio of 88:12 was mixed with 0.16 parts by weight with respect to 100 parts by weight of polystyrene resin.
The obtained mixture was supplied to a 115-150 mmφ tandem extruder and melted in the first stage extruder, and then a mixed gas having a composition ratio of isobutane and normal butane of 85:15 (% by weight) as a blowing agent. Was 3.0 parts by weight. Then, after cooling to the proper foaming temperature in the second stage extruder, it is discharged under a atmospheric pressure from a circular die having a two-end structure at both ends, and is taken out at a take-up speed of 16 m / min while being molded in a cooling cylinder. The sheet was wound up while being cut into two sheets, to obtain a polystyrene-based resin foam sheet. Table 1 shows the evaluation results of the obtained polystyrene resin foam sheet.

(Example 2)
HRM13N (manufactured by Toyo Styrene Co., Ltd., MFR = 2.2 g / 10 min) is used as the polystyrene-based resin, and talc (manufactured by Matsumura Sangyo Co., Ltd., high filler KA-1) is used as the polystyrene regulator 100 as the foam regulator. A polystyrene-based resin foam sheet was obtained in the same manner as in Example 1 except that a mixture obtained by mixing 0.30 parts by weight with respect to parts by weight was used. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

(Example 3)
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 2 except that the pressure of the foaming agent was changed to 2.2 parts by weight. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

Example 4
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 2 except that the take-up speed was changed to 10.5 m / min. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

(Comparative Example 1)
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 2 except that the circular die structure was changed from the two-end structure to the perforated plate structure. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

(Comparative Example 2)
Polystyrene resin foam sheet in the same manner as in Example 2 except that the amount of talc (manufactured by Matsumura Sangyo Co., Ltd., high filler KA-1) was changed to 0.50 parts by weight with respect to 100 parts by weight of polystyrene resin. Got. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

(Comparative Example 3)
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 2 except that HRM26 (manufactured by Toyo Styrene Co., Ltd., MFR = 1.6 g / 10 min) was used as the polystyrene resin. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

(Comparative Example 4)
HRM26 (manufactured by Toyo Styrene Co., Ltd., MFR = 1.6 g / 10 min) is used as the polystyrene resin, and the amount of talc (manufactured by Matsumura Sangyo Co., Ltd., High Filler KA-1) is 100 parts by weight of polystyrene resin. Thus, a polystyrene-based resin foam sheet was obtained in the same manner as in Example 2 except that the circular die structure was changed from a two-end two-point structure to a perforated plate structure. The evaluation results of the obtained polystyrene resin foam sheet are shown in Table 1.

  From the results in Table 1, by using a polystyrene-based resin having a melt mass flow rate (MFR) in the range of 2.0 to 4.0 g / 10 min as the base resin, the content of small-diameter cells is 20% or less. It has been found that a polystyrene-based resin foam sheet is obtained in which the amount of foreign matter adhering to the heat ray is reduced with little cut-off.

FIG. 1 is a schematic diagram of a longitudinal section perpendicular to the longitudinal direction in a foam sheet. FIG. 2 is a schematic diagram showing the structure of a circular die.

Explanation of symbols

D Vertical section s in foamed sheet s Surface layer part c Core part 1 Inner cylinder 2 Outer cylinder 3 Support part 4 Resin flow path

Claims (2)

A polystyrene resin foam sheet using a polystyrene resin having a melt mass flow rate of 2.0 to 4.0 g / 10 min as a base resin, measured under conditions of a resin temperature of 200 ° C. and a load of 49 N,
In the core portion excluding the surface layer portion corresponding to 20% of the total thickness in the longitudinal section perpendicular to the longitudinal direction of the secondary foam sheet obtained by heating the foam sheet, the cell diameters in the thickness direction and the width direction are A polystyrene-based resin foam sheet, characterized in that the content of the number of small-diameter cells that is 1/2 or less of the average cell diameter in the thickness direction is 20% or less. The thickness of the secondary foamed sheet obtained by heating polystyrene resin foam sheet 2.0～3.5Mm, a basis weight of 80 to 150 g / ^{m 2,} and, in the thickness direction of the polystyrene-based resin foam sheet The polystyrene-based resin foam sheet according to claim 1, wherein the number of cells is in the range of 9 to 12.