JP2008100459A - Polystyrene-based resin laminated foam sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polystyrene-based resin laminated foam sheet which exhibits an excellent thermal moldability and can be thermally molded into moldings with outstanding appearance as a secondary product featuring its printability to a curved surface right after thermal molding. <P>SOLUTION: This laminated foam sheet has a degree of thermal shrinkage at 135°C or below showing not more than 15% in the extrusion direction and not more than 30% in the width direction. In addition, the sheet is composed of a polystyrene-based resin foamed layer and an impact-resistant polystyrene-based resin layer overlying one surface of the foamed layer. Further, in the TMA curve obtained by thermomechanical analysis of a 200 μm thick part from the surface of a non-laminated layer of the foamed layer, at 10°C/min heat-up speed, the ratio (thickness/number of air bubbles in the thickness direction) of the thickness (μm) of the foamed layer to the number of air bubbles (piece), in the thickness direction, of a perpendicular section of the foamed layer, falls within the range of 100 to 180 μm/piece. Besides, the ratio (σ/X) of a standard deviation (σ) of the air bubble diameter, in the horizontal direction, of the air bubble which is present in an optional straight line, in the thickness direction, of a perpendicular section of the foamed layer, for the average air bubble diameter (X), in the horizontal direction, of the air bubble which is present in the described optional straight line, is not more than 0.40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polystyrene-based resin laminated foam sheet, and more particularly to a polystyrene-based resin laminated foam sheet suitable for deep-drawing thermoforming such as wrinkles.

  Conventionally, polystyrene-based resin laminated foam sheets have been widely used as molding sheets for obtaining molded articles by thermoforming. This polystyrene-based resin-laminated foam sheet (hereinafter also simply referred to as “laminated foam sheet”) is used as a polystyrene-based resin foam layer (hereinafter also simply referred to as “foam layer” or “foam sheet”). A sheet in which a resin layer (hereinafter, also simply referred to as “HIPS layer”) is laminated. The laminated foam sheet is made into a foamable melt-mixed resin by melt-kneading a polystyrene resin, various additives such as a bubble regulator and a foaming agent using an extruder, After forming a foam sheet by extruding from the inside of the die under atmospheric pressure, an impact-resistant polystyrene resin layer is laminated by an extrusion lamination method, or a melt of a foamable melt-mixed resin and an impact-resistant polystyrene resin It is manufactured by coextrusion.

  A foamed sheet molded body (hereinafter also simply referred to as a “molded body”) obtained by heat-molding the laminated foamed sheet thus obtained is excellent in heat insulation, and is lightweight and inexpensive. Widely used.

  Such a laminated foam sheet is usually thermoformed with the HIPS layer facing outward, and in order to increase the commercial value, curved printing such as symbols and characters is applied to the outer HIPS layer. In this case, the outer surface of the molded body is required to be smooth and beautiful. If it is not beautiful, the product value will be low, and if it is not smooth, printing defects such as fading will tend to occur during curved surface printing, and the defective product will lose its product value.

  As a method for improving the appearance and printability of the laminated foam sheet, a method for making the appearance beautiful by reducing the bubble diameter of the foam sheet is generally used. However, since the moldability deteriorates when the bubble diameter is reduced, it is difficult to obtain a good molded product. That is, in order to reduce the bubble diameter, a method is generally used in which a large amount of a bubble adjusting agent is added to generate a large amount of bubbles, and quenching is performed immediately after extrusion to suppress bubble growth. However, excessive residual strain remains on the surface of the sheet due to rapid cooling during foaming, which hinders the elongation of the sheet during thermoforming and makes it impossible to perform good molding.

  Therefore, the present applicant has proposed the invention described in Patent Document 1 as a method for improving a decrease in thermoformability due to excessive residual strain remaining on the sheet surface due to rapid cooling in the process of manufacturing a polystyrene resin foam sheet. . That is, in Patent Document 1, a laminated foamed sheet in which an impact-resistant polystyrene-based resin layer is laminated on one side of a polystyrene-based resin foamed sheet, and the rate of temperature increase is 10 ° C. for a portion having a thickness of 200 μm from the surface of the non-laminated surface. In the TMA curve obtained by thermomechanical analysis at / min, the peak value at 135 ° C. or less of the heat shrinkage rate in the extrusion direction is 0 to 15%, and the peak at 135 ° C. or less of the heat shrinkage rate in the width direction A laminated foam sheet having a value of 0 to 30% was proposed. This laminated foam sheet has excellent thermoformability and is excellent for curved surface printing. However, the curved surface printability immediately after thermoforming was insufficient.

  The curved surface printability refers to the surface of the impact-resistant polystyrene resin layer outside the container such as cup noodles, which is thermoformed with the impact-resistant polystyrene resin layer facing outward, by a curved surface printing machine. This refers to printing of a pattern or the like, and a curved surface printed container is colorful and excellent in design. Problems with curved surface printing include spots on the solid print portion, concavity and convexity, and blurring and blurring of characters and patterns. As one method for solving these problems, there is a method of extremely slowing the curved surface printing speed. That is, if the height of container printing per minute is reduced, the printability can be improved. However, productivity is extremely reduced by such a method. As another method for improving the printability, characters, patterns, and the like are transferred by increasing the printing pressure between the container and the printing roll. However, the container includes a foamed layer, and the thickness accuracy of the foamed layer itself is not so high, and the thickness is further changed when heated and subjected to secondary foaming during thermoforming, so the thickness accuracy of the resulting container is not so high. For this reason, when the printing pressure is increased to improve printing, a new problem arises that the container is wrinkled.

  Furthermore, it is desired that the curved surface printing is excellent in printability immediately after printing, even immediately after thermoforming. Immediately printability means that curved surface printing is possible even immediately after thermoforming. In general, the curved surface printability of a molded product varies depending on the lapse of time after molding, and is worst immediately after molding, and improves as the aging time becomes longer, and tends to be constant in about 5 days. For this reason, if the time is increased after forming the container, the curved surface printing characteristic is improved. However, for this purpose, the container before printing must be stored for several days, and the productivity is deteriorated. Therefore, in order to improve productivity, it is desired to develop a laminated foamed sheet capable of thermoforming a molded article having excellent printability.

  The laminated foam sheet described in the cited document 1 is excellent in curved surface printability, but inferior in printability immediately after thermoforming. This is because the surface of the foam layer is sufficiently cooled in the die, so that many small bubbles exist and the residual strain is small, but the effect of cooling is not sufficient inside, and the growth of the bubbles proceeds. This is due to the occurrence of a difference in the bubble diameter in the thickness direction.

  The inside / outside difference of the bubble diameter correlates with the inside / outside difference of the density of the foam layer, and the smaller the outside bubble diameter and the larger the inside, the smaller the apparent density inside the foam layer. As a result, the compression strength of the molded body is reduced, and if the curved surface printing is performed immediately after molding, the side surface of the molded body cannot withstand the printing pressure, and spots of the solid print portion, unevenness, bleeding of characters and patterns, , Fading will occur. This problem can be solved by reducing the expansion ratio of the foam layer or / and increasing the thickness of the impact-resistant polystyrene resin layer. However, this method is not an effective solution because it leads to a decrease in the heat insulating property of the obtained molded body and an increase in weight.

  On the other hand, in Patent Document 2 and Patent Document 3, a laminated foamed sheet in which an impact-resistant polystyrene resin is laminated on one side of a polystyrene-based resin foam layer is used, and the impact-resistant polystyrene-based resin layer is placed outside to form a bowl shape. It is disclosed that a molded body capable of printing a curved surface on the outside of the container within 30 minutes after molding is obtained by thermoforming the container.

However, the laminated foam sheet actually manufactured in the example of Patent Document 2 has a foaming ratio of the foamed layer of 4 times (apparent density is 0.26 g / cm ³ ). In addition to the high compressive strength, the thickness of the impact-resistant polystyrene resin is too thick for the low expansion ratio of the foam layer (133 μm). Lowering the expansion ratio of the foamed layer necessitates a decrease in the heat insulating property of the foamed layer, and in order to impart high heat insulating properties, the thickness of the foamed layer is inevitably increased, leading to an increase in weight, which is not an effective solution. Moreover, the laminated foam sheet actually manufactured in the Example of Patent Document 3 has an expansion ratio of the foam layer of 9.3 to 9.6 times (apparent density is 0.109 to 0.113 g / cm ³ ). Although it has a high expansion ratio, the impact-resistant polystyrene resin has a large thickness (140 μm), and by increasing the thickness of the resin layer in this way, the printability is improved immediately. It is not an effective solution because it leads to an increase in weight.

JP 2005-349593 A JP 2002-210891 A Japanese Patent Laid-Open No. 2003-12843

  An object of the present invention is to provide a polystyrene-based resin-laminated foam sheet that is excellent in thermoformability and further excellent in the appearance of the resulting molded body, and is capable of thermoforming a molded body capable of curved printing immediately after thermoforming. To do.

  As a result of intensive studies to solve the above problems, the present inventors have found that in the conventional laminated foam sheet, although there are many small bubbles near the foam layer surface, the inside is not sufficiently cooled. For this reason, the growth of bubbles progresses, and as a result, the inside / outside difference of the bubble diameter size in the thickness direction occurs, and along with this, the larger the inside / outside difference of the bubble diameter size, the smaller the apparent density inside the foam layer, As a result, it was found that the compression strength of the molded body was lowered. Based on this knowledge, by reducing the bubble diameter and reducing the difference between the inside and outside of the bubble diameter, it is possible to improve the printability immediately while improving both the appearance and the compression strength. Thus, the present invention has been completed.

  Specifically, when extrusion foaming, by cooling the foamable molten resin mixture corresponding to the surface of the foam sheet that is the inside of the molded body inside the die, the amount of strain in the cooling and stretching process is reduced, In other words, in the TMA curve obtained by thermomechanical analysis, by reducing the heat shrinkage rate in the extrusion direction and the heat shrinkage rate in the width direction, the laminated foam sheet in which the resin layer is laminated on the foam sheet has a reduced cell diameter By combining the conventional knowledge that moldability is sufficiently excellent with the design of the resin flow path inside the die, it is possible to reduce variations in the cell diameter in the thickness direction of the resulting foam sheet. As a result, it has been found that the strength of the molded body can be sufficiently maintained even immediately after thermoforming, and the present invention has been completed.

That is, according to the present invention, the following polystyrene-based resin laminated foam sheet is provided.
[1] A polystyrene-based resin foam layer and an impact-resistant polystyrene-based resin layer laminated on one surface of the foam layer, and a temperature increase rate of 10 ° C./200 μm from the surface of the non-laminated surface of the foam layer. In the TMA curve obtained by thermomechanical analysis at min, the peak value at 135 ° C. or less of the heat shrinkage rate in the extrusion direction is 0 to 15%, and the peak value at 135 ° C. or less of the heat shrinkage rate in the width direction is In a laminated foam sheet having an apex value of 0 to 30%, the ratio (thickness / number of bubbles in the thickness direction) of the thickness (μm) of the foam layer to the number of bubbles in the thickness direction (units) in the vertical section of the foam layer is 100 to 180 μm. Horizontal bubbles of the bubbles existing on the straight line with respect to the horizontal average bubble diameter (X) of the bubbles in the vertical range of the foamed layer and existing on an arbitrary straight line in the thickness direction Polystyrene-based resin laminate foam sheet, wherein the ratio of the standard deviation (σ) (σ / X) is 0.40 or less.
[2] The polystyrene-based resin laminated foam sheet according to [1], wherein the impact-resistant polystyrene-based resin layer has a thickness of 110 to 130 μm.

  According to the present invention, since excessive residual strain does not remain on the surface of the foam layer, the moldability is excellent, and the bubble diameter is sufficiently small so that the appearance is excellent, and the variation in the thickness direction of the bubble diameter is small, and the appearance is small. Since the variation in density is small, there is provided a polystyrene-based resin-laminated foam sheet that is excellent in compressive strength immediately after molding while maintaining light weight and heat insulation, and capable of printing immediately after.

Hereinafter, the polystyrene resin laminated foam sheet of the present invention will be described in detail.
The polystyrene-based resin laminated foam sheet of the present invention comprises a polystyrene-based resin foam layer and an impact-resistant polystyrene-based resin layer laminated on one side of the foam layer.
The thickness of the foam layer is preferably 1.8 to 3.0 mm, more preferably 2.0 to 2.9 mm, and still more preferably 2.1 to 2.8 mm. If the thickness is 1.8 mm or more, deep drawing with a large drawing ratio is possible, and even if hot water is added to the obtained molded body, there is no risk of deformation. On the other hand, if the thickness is 3.0 mm or less, molding defects such as cracking due to excessive thickness are unlikely to occur.

The apparent density of the foam layer is preferably 0.085~0.210g / cm ^3, more preferably 0.090~0.200g / cm ^3, more preferably 0.090~0.190g / cm ^3. If the apparent density is 0.085 g / cm ³ or more, the mechanical strength such as the compression strength of the laminated foamed sheet and the compression strength of the top and bottom that compresses with the opening of the obtained molded body facing up will be sufficient. On the other hand, if the apparent density is 0.210 g / cm ³ or less, the heat insulating property is ensured and there is no possibility of increasing the cost.

  A HIPS layer is laminated on one side of the laminated foam sheet of the present invention. The thickness of the HIPS layer is preferably 100 to 135 μm, more preferably 105 to 130 μm, and still more preferably 110 to 125 μm. If the thickness is 100 μm or more, the HIPS layer will not be too thin, the mechanical strength of the molded body will be excellent, and sufficient printability will be obtained when printing is performed on the outside of the obtained molded body. be able to. On the other hand, if the thickness is 135 μm or less, the quality will not be excessive and there is no risk of increased costs.

The basis weight of the laminated foam entire sheet of the present invention is preferably 300~550g / ^{m 2,} more preferably ^{320~450g / m 2, 340~390g / m} 2 is more preferable.
When the basis weight is 300 g / m ² or more, since the resin amount is sufficient, the mechanical strength such as the compression strength of the laminated foamed sheet and the top-and-bottom compression strength of the molded article obtained is excellent. On the other hand, when the basis weight is 550 g / m ² or less, there is no possibility that a drawdown due to the weight of the laminated foam sheet occurs during thermoforming.

  In this specification, the thickness of the laminated foam sheet, the thickness of the foam layer, the thickness of the HIPS layer, the basis weight of the laminated foam sheet, the basis weight of the HIPS layer, the basis weight of the foam layer, and the apparent density of the foam layer are measured according to the following methods. Is done.

  First, at a randomly selected point from the laminated foamed sheet of the present invention, the direction coincides with the direction of extrusion of the laminated foamed sheet (hereinafter also simply referred to as “MD”), and is orthogonal to the MD of the laminated foamed sheet. A 50 cm square sample is cut out in a direction that coincides with the width direction (hereinafter also simply referred to as “TD”). At this time, the central part of the TD and the central part of the sample are made to coincide.

Next, in any one of the cut surfaces of the sample TD, a total of nine points excluding both ends of the TD up to the other end at intervals of 5 cm on the basis of one end of the laminated foam sheet The thickness and the thickness of the foam layer are photographed with a microscope and obtained from the photograph.
In the calculation described later, numerical values up to the second decimal place obtained by the above measurement are used.

  The thickness of the laminated foam sheet in this specification means the arithmetic average value “F” (mm) of the measured values of the nine points. In addition, the thickness “H” (μm) of the HIPS layer is calculated from the arithmetic average value “T” (mm) of the measured values of the nine points of the thickness of the laminated foamed sheet to the arithmetic average value “F” ( mm) is obtained by converting the value obtained by subtracting the unit (μm).

Next, the weight of the sample is measured to the unit of g, and the measured value is converted into the weight of the laminated foamed sheet per 1 m ² , and this is defined as the basis weight “t” (g / m ² ) of the laminated foamed sheet. The basis weight of the HIPS layer is the weight per 1 m ² of the HIPS layer "h" (g / ^{m 2)} of, fixed for convenience 1.05 g / ^{m 3} density of HIPS layer, the HIPS layer said seal degree It is obtained by multiplying the thickness “H” (μm). The basis weight “f” (g / m ² ) of the foam layer, which is the weight per 1 m ² of the foam layer, is calculated from the basis weight “t” (g / m ² ) of the laminated foam sheet, h ”(g / m ² ) is subtracted.

Also, the apparent density of the foam layer is 1000 in order to divide the basis weight “f” (g / m ² ) of the foam layer by the thickness “F” (mm) of the foam layer to give a unit of g / cm ^3. It is calculated by dividing. The density of the foam layer in this specification means this calculated value.

  In the laminated foam sheet of the present invention, examples of the polystyrene resin constituting the foam layer include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-methyl methacrylate copolymer, and styrene-acrylic. Examples include acid copolymers, styrene-maleic anhydride copolymers, polymethylstyrene, and a mixture of polystyrene and polyphenylene ether.

  Among the above, the polystyrene resin constituting the foamed layer preferably has a total content of styrene dimer and styrene trimer of 2000 ppm or less, more preferably 1500 ppm or less, and still more preferably 1000 ppm or less. When the total content exceeds 2000 ppm, the surface is partially melted or cracked during thermoforming, which is not preferable.

  Further, among polystyrene resins having a total content of styrene dimer and styrene trimer of 2000 ppm or less, a polystyrene resin having a number average molecular weight (Mn) of 80000 or more and a molecular weight distribution (Mw / Mn) of less than 2.9 is preferable. A resin having a molecular weight distribution (Mw / Mn) of less than 2.9 is usually produced by a continuous polymerization method and is preferable because it can be produced at a low cost. In addition, since the polystyrene-based resin having a number average molecular weight (Mn) of 80000 or more has excellent mechanical strength, the resulting molded article has excellent mechanical strength such as compression strength and tensile strength.

In the present invention, Mw and Mn are values obtained by gel permeation chromatography (GPC method). Specifically, the foamed layer of the laminated foamed sheet is dissolved in 20 mL of tetrahydrofuran (THF) (if there is an insoluble matter in THF, it is removed by filtration), and the following analysis is performed using the equipment shown below. Measured by GPC method under the conditions, horizontal (parallel to the horizontal axis) on the basis of the peak start position by the styrenic resin of the chart (in the present invention, the molecular weight of 5.4 × 10 ⁶ position is adopted for convenience) A baseline is drawn and each molecular weight is calculated by a standard calibration curve generated using standard polystyrene.

Equipment used: GPC high performance liquid chromatograph manufactured by GL Sciences Inc.
Column: Showa Denko Co., Ltd. column, trade name Shodex GPC KF-806, KF-805, KF-803 are connected in series in this order.
Column temperature: 40 ° C.
Solvent: THF.
Flow rate: 1.0 mL / min.
Concentration: 0.15 W / V%.
Injection volume: 0.2 ml.
Detector: UV-visible detector manufactured by GL Sciences Inc., trade name: UV702 type (measurement wavelength: 254 nm).
The molecular weight range of the calibration curve used for the calculation of the molecular weight distribution: 1.9 × 10 ^{7 to} 5.4 × 10 ³ .

The base resin of the impact-resistant polystyrene resin layer constituting the laminated foam sheet of the present invention comprises a styrene component and a rubber component, and when the total of both is 100% by weight, the styrene component is 65 to 98% by weight, Styrenic resin composed of 35 to 2% by weight of a rubber component. Specific examples include the following.
(1) A random copolymer resin comprising a styrene component and a rubber component, a block copolymer resin, a graft copolymer resin, or a mixture of two or more of these copolymer resins.
(2) A mixture of the resin of (1) above and a styrene homopolymer.
(3) A mixture of styrene homopolymer and rubber (including thermoplastic elastomer).
(4) A mixture of the resin (1) or the resin (2) and rubber (including a thermoplastic elastomer).
However, as the resin constituting the resin layer, from the viewpoint of imparting impact resistance and strength to the laminated foam sheet and its thermoformed body, the Charpy impact strength JIS K7111 (1996) is classified into ISO 179 / It is preferable to use 1eA having a value of 3 to 20 kJ / m ² , preferably 6 to 16 kJ / m ² .

  In the present invention, the ratio of the thickness (μm) of the foam layer to the number of bubbles in the thickness direction (number) in the vertical section of the foam layer (thickness / number of cells in the thickness direction) is in the range of 100 to 180 μm / month. Is preferably in the range of 105 to 160 μm / month, and more preferably in the range of 110 to 140 μm / month. If the ratio (thickness / number of bubbles in the thickness direction) is less than 100 μm / month, the film thickness of the bubbles becomes too small, and there is a risk of forming defects (naki) in which the bubbles break when forming a deep-drawn container. . On the other hand, when the ratio (thickness / the number of bubbles in the thickness direction) exceeds 180 μm / month, the smoothness of the container printing surface is poor, and a phenomenon called printing blanking, in which a portion where ink has fallen off during printing, tends to occur. There is a fear.

  Further, in the foamed layer of the present invention, the horizontal bubble diameter of the bubbles present on the straight line relative to the horizontal average bubble diameter (X) of the bubbles present on an arbitrary straight line in the thickness direction in the vertical cross section of the foamed layer is determined. The ratio (σ / X) of the standard deviation (σ) needs to be 0.40 or less, preferably 0.35 or less, more preferably 0.30 or less. The lower limit of the ratio (σ / X) is preferably 0.0, which means that there is no variation in bubble diameter, but technically it is difficult to make it smaller than 0.2.

When the ratio (σ / X) is more than 0.40, the variation in the horizontal bubble diameter arranged in the thickness direction, and consequently the variation in the bubble diameter arranged in the thickness direction, is too large. The apparent density inside the foam layer is too small relative to the apparent density. As a result, the compressive strength immediately after molding inside the foam layer becomes too low, and if printing is performed immediately after that, there is a possibility that spots of solid print portions, unevenness, bleeding of characters or patterns, or blurring may occur.
In the present invention, “immediate printing” means printing on the outer surface of the molded body within 30 minutes after thermoforming of the laminated foam sheet.

  In the present specification, the ratio of the foam layer in the laminated foam sheet (thickness / number of bubbles in the thickness direction), the standard deviation (σ) of the horizontal bubble diameter, and the average average bubble diameter (X) are measured and calculated according to the following methods. The

  First, the sheet is cut in a direction that coincides with the extrusion direction (MD) of the laminated foamed sheet and in a vertical direction (thickness direction) at random points selected from the laminated foamed sheet of the present invention. The cut surface is photographed using a microscope, and at a randomly selected point on the photograph, a straight line that coincides with the sheet thickness direction and runs through the thickness of the foamed layer is drawn, and the number of bubbles located on the straight line ( Request). Further, the thickness (μm) of the foamed layer portion on the straight line is obtained by calculation in consideration of the magnification, and [thickness / number of bubbles in the thickness direction] is obtained by calculation. Further, the maximum horizontal length of the bubbles is measured for all the bubbles located on the straight line, the arithmetic average value of these maximum lengths is calculated, and this is defined as the horizontal average bubble diameter (X). Further, the standard deviation is calculated for the maximum horizontal length of all the bubbles that are the basis for the calculation of the average bubble diameter in the horizontal direction, and this is set as the standard deviation (σ) of the horizontal bubble diameter. The standard deviation of the diameter / the average bubble diameter in the horizontal direction] is calculated. These measurements are performed at five different locations so that the bubbles to be measured do not overlap. For each of [Thickness / Number of bubbles in the thickness direction] and [Standard deviation of horizontal bubble diameter / Horizontal average bubble diameter] obtained respectively. Further, an arithmetic average value is calculated to obtain a ratio (thickness / number of bubbles in a cross section) and a ratio (σ / X).

  When measuring the bubble diameter, it is very convenient to use an accurate trace of the bubble shape from a micrograph of the cut surface of the laminated foam sheet. In addition, FIG. 1 is what traced the bubble shape correctly from the microscope picture of the cut surface of the lamination foam sheet obtained in Example 1 mentioned later, and FIG. 2 is the lamination | stacking obtained in Comparative Example 2 mentioned later The cell shape is accurately traced from a micrograph of the cut surface of the foam sheet.

  Ratio (thickness / number of bubbles in the thickness direction), ratio (σ / X) is a cut surface obtained by cutting the sheet in a direction that coincides with the extrusion direction (MD) of the laminated foamed sheet and in the vertical direction (thickness direction) of the laminated foamed sheet The same evaluation can be made when observed and measured in FIG. However, when the sheet is cut in the direction that coincides with the width direction (TD) and in the vertical direction (thickness direction) of the laminated foam sheet, the visibility of the bubbles is excellent, and more accurate measurement is possible. The measurement result of the cross section obtained by cutting the sheet in the direction that coincides with the TD is represented. It is also possible to evaluate the variation in the bubble diameter with the maximum length of the bubble in the vertical direction. However, since the foam layer is stretched in the horizontal direction, Since the error is smaller when the evaluation is performed with larger bubbles, the evaluation is performed based on the maximum length of the bubbles in the horizontal direction.

In the foamed layer of the present invention, the density (hereinafter also referred to as “surface layer density”) having a thickness of 200 μm from the surface of the non-laminated surface is preferably 0.15 to 0.35 g / cm ³ , and 0.17 to 0. more preferably ^{.30g / cm 3, 0.19~0.28g / cm} 3 is more preferred. Said surface layer density higher is is excellent in moldability such as hard out squeaking rich in stretchability, since the distortion due to cooling when stretched during extrusion exceeds 0.35 g / cm ³ remains largely The elongation at the time of molding is poor, and there is a risk of cracking. On the other hand, when the density is low, there is a risk that the inner surface of the molded product obtained by the foam layer of the foamed layer of the laminated foam sheet becoming too thin may be easily scratched or cracked.
In addition, in this specification, the surface of a non-laminate surface means the surface of the polystyrene-type resin foam layer of the side by which the impact-resistant polystyrene-type resin layer is not laminated | stacked.

The density of 200 μm is measured from the surface of the non-laminated surface as follows.
A 200 μm portion is sliced from the surface of the non-laminated surface and cut into test pieces having a width of 5 mm and a length of 20 mm, and the weight and thickness of the test piece are measured. Divide the weight of the test piece by the volume of the test piece (width × length × thickness), and convert the unit to obtain the density.
In addition, the length direction of a test piece shall be made to correspond with MD direction of a foam layer.

  The laminated foam sheet of the present invention is excellent in deep drawability because the residual strain of the 200 μm thick portion (hereinafter also referred to as “surface layer part”) from the surface of the non-laminated surface of the foamed layer is small. . The magnitude of this residual strain can be evaluated by TMA. Specifically, in the TMA curve obtained by measuring TMA at a heating rate of 10 ° C./min for the surface layer portion, the peak apex value at 135 ° C. or less of the MD heat shrinkage is 0 to 15%, The value of the peak apex at 135 ° C. or less of the heat shrinkage rate of TD is 0 to 30% (hereinafter, the value of the peak apex of the heat shrinkage rate of 135 ° C. or less by TMA at a heating rate of 10 ° C./min is used. Also referred to as “TMA maximum shrinkage”).

  When the TMA maximum shrinkage of MD is more than 15%, there is a possibility that cracks may occur on the peripheral wall in the vicinity of the mouth edge of the molded body during thermoforming. That is, there is a possibility that bubbles on the surface of the laminated foam sheet break without being able to withstand the elongation and cause a phenomenon that cracks occur along the TD. From the standpoint of further preventing the occurrence of cracks, it is preferably 13% or less, more preferably 11% or less. When the TD TMA maximum shrinkage ratio is more than 30%, there is a possibility that cracks may occur on the peripheral wall in the vicinity of the edge of the molded body during thermoforming. From the standpoint of further preventing the occurrence of cracks, it is preferably 28% or less, more preferably 26% or less.

On the other hand, the lower limit of the TMA maximum shrinkage of MD and TD is usually 0%, but if it is too close to 0%, large irregularities are formed on the exposed surface of the foam sheet during heating during thermoforming. Since it becomes easy, the lower limit of the TMA maximum shrinkage of MD is preferably 2% or more, and more preferably 4% or more. Further, the lower limit value of the TD TMA maximum shrinkage is preferably 3% or more, and more preferably 5% or more.
The TMA maximum shrinkage of 0% means that there is no peak of heat shrinkage at 135 ° C. or lower.

The reason for evaluating the magnitude of residual strain using the value of the peak of the heat shrinkage rate at 135 ° C. or lower is as follows.
Two peaks are usually observed in the TMA curve of displacement and temperature (however, the second peak may be difficult to observe depending on the size of the first peak from the low temperature side). Of these two peaks, the peak on the low temperature side is due to strain generated in the process of cooling and stretching the foam sheet extruded from the annular die, and the peak on the high temperature side is due to strain generated in the die. . The distortion that hinders molding when the laminated foam sheet is molded in the thermoforming process of the molded body is predominantly related to the peak on the low temperature side of these two peaks. Therefore, if the value of the peak of the heat shrinkage rate at 135 ° C. or lower is used, the moldability can be accurately evaluated.

The measurement of TMA in this specification is performed as follows.
A surface layer portion from the surface of the non-laminated surface of the foamed layer in the laminated foam sheet to a thickness of 200 μm is sliced to produce a test piece having a length of 20 mm, a width of 5 mm, and a thickness of 200 μm. In this case, when measuring the TMA maximum shrinkage of the MD, the length direction of the test piece is matched with the MD of the foam layer. On the other hand, when measuring the TMA maximum shrinkage in the width direction of the surface layer portion, the length direction of the test piece is matched with the width direction (TD) of the foam layer. Next, as shown in FIG. 3, the sample holder supporting the test piece with a displacement of 0 and a chuck distance (A) of 10 mm and an initial load of 1.0 g by a support tube and a detection rod is set to 25 to 180 ° C. in an electric furnace. While heating at a temperature rising rate of 10 ° C./min until, the detection unit detects a dimensional change caused by the contraction, and graphs the horizontal axis as temperature and the vertical axis as displacement of the dimensional change.
The number (N) of test pieces is 2 for both MD and TD, and the average value is adopted.

TMA measurement conditions Shimadzu Corporation Thermomechanical analyzer TMA-50 use Specimen: 5mm x 15mm Chuck spacing: 10mm Chuck offset: 3.0g
Initial load: 1.0 g Temperature increase rate: 10 ° C./min

  From the obtained TMA curve, the TMA maximum shrinkage ratio is a percentage of the amount of displacement at the apex of the heat shrinkage peak at 135 ° C. or less with respect to the initial distance between chucks of 10 mm. This will be described in more detail with reference to FIGS. FIG. 4 is a TMA curve of MD on the surface of the non-laminated surface of the foam layer of each laminated sheet of Example 1 and Comparative Example 3 to be described later, and FIG. 5 is each laminated layer of Example 1 and Comparative Example 3 to be described later. It is a TMA curve of TD in the surface of the non-lamination surface of the foam layer of a sheet | seat. The apex of the heat shrinkage peak at 135 ° C. or lower is the position shown in each figure. In the case of Example 1 in FIG. 4, the amount of displacement at the apex of the heat shrinkage peak at 135 ° C. or lower is minus 540 μm (minus means shrinkage, plus means expansion), and the maximum TMA shrinkage rate is 0.54. × 100 ÷ 10 = 5.4% is calculated. Moreover, in the case of the comparative example 3 of FIG. 4, the displacement amount of the peak of the heat shrinkage peak at 135 ° C. or less is minus 1640 μm, and the TMA maximum shrinkage is calculated as 1.64 × 100 ÷ 10 = 16.4%. Is done. In the case of Example 1 in FIG. 5, the amount of displacement at the apex of the heat shrinkage peak at 135 ° C. or lower is minus 1880 μm, and the TMA maximum shrinkage is calculated as 1.88 × 100 ÷ 10 = 18.8%. Is done. In the case of Comparative Example 3 in FIG. 5, the displacement amount at the apex of the heat shrinkage peak at 135 ° C. or lower is minus 3200 μm, and the TMA maximum shrinkage is calculated as 3.20 × 100 ÷ 10 = 32.0%. Is done.

  In addition, when the peak of the heat shrinkage peak cannot be clearly determined, the downward curve of the low temperature side peak is affected by the rising curve of the high temperature side peak as in the TMA curve shown in FIG. 6, for example. If not, the tangent A of the rising curve of the peak on the low temperature side and the portion assumed to be a descending curve if not affected by the peak on the high temperature side (the portion that is substantially horizontal in the case of FIG. 6) ) Is adopted as the apex of the heat shrinkage peak.

Next, the manufacturing method of the laminated foam sheet of this invention is demonstrated.
First, various additives such as polystyrene resin and bubble regulator are supplied to the extruder, heated, melted and kneaded, and the foaming agent is press-fitted and further kneaded to obtain a foamable molten resin mixture, The foamable molten resin mixture is adjusted to a foaming suitable temperature and extruded into the atmosphere through an annular die attached to the outlet of the extruder to be foamed into a cylindrical shape. Next, the obtained cylindrical foam is cooled while being taken along a cylindrical cooling device (hereinafter also simply referred to as “mandrel”), and is cut open to form a sheet-like foam layer.

  The resin layer may be laminated by an extrusion lamination method using another extruder immediately after extrusion, or a coextrusion die is used to laminate the foamable molten resin mixture and the molten resin mixture for the resin layer and then extrude. You may form by an extrusion method. Alternatively, a film may be laminated if it may be laminated by an extrusion lamination method using an extruder several days after the foam layer is formed.

  As the foaming agent to be press-fitted into the extruder, for example, a volatile foaming agent, an inorganic gas-based foaming agent, a decomposable foaming agent, or the like may be used alone or in combination of two or more. Examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane, and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, Examples thereof include halogenated hydrocarbons such as methyl chloride, ethyl chloride, and ethylene chloride. As the inorganic gas-based foaming agent, an inert gas such as carbon dioxide, nitrogen or air is used. Examples of the decomposable foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate, and the like. However, from the viewpoint of improving secondary foamability during heating prior to thermoforming of the laminated foamed sheet, it is desirable to use a volatile foaming agent as the main foaming agent. The amount of foaming agent added depends on the type of foaming agent, the base resin, the target foaming ratio, etc., so add the foaming agent so that the desired foaming ratio is obtained according to the type of foaming agent and base resin. Select the amount.

  Examples of the air conditioner supplied to the extruder together with the polystyrene resin include inorganic powders such as talc and silica, acidic salts of polyvalent carboxylic acids, reaction mixtures of polyvalent carboxylic acids with sodium carbonate or sodium bicarbonate, etc. Is mentioned. The amount of the bubble regulator added is usually at most about 5 parts by weight per 100 parts by weight of the resin.

As a method for adjusting the TMA maximum shrinkage ratio for the 200 μm thick part from the surface of the non-laminated surface in the foam layer, at least the foam layer is non-laminated inside and outside the flow path of the foamable molten resin mixture in the die. There is a method of adjusting the temperature of the side corresponding to the surface side. Examples of the method of adjusting the temperature of the die include a method of adjusting the temperature of the die shaft (core metal) positioned on the outer periphery of the die or inside the die to a temperature lower than the die temperature by a cooling medium lower than the die temperature. In this case, examples of the cooling medium include oil and water. In this case, it is preferable to set the temperature of the wall of the die shaft (mandrel) located inside the die to be 10 to 40 ° C. lower than the temperature of the foamable molten resin mixture. Moreover, when temperature-controlling the outer periphery of die | dye, it is preferable to set the temperature of the outer wall of the flow path in die | dye of a foamable molten resin mixture 3-20 degreeC lower than the temperature of a foamable molten resin mixture. The reason why the temperature of the outer wall of the flow path in the die is lower than the temperature of the wall of the mandrel is that the outer side of the cylindrical foam immediately after extrusion is more easily cooled than the inner side.
In addition, as described above, in the process of drawing the cylindrical foam extruded from the die to the mandrel, the TMA maximum shrinkage is adjusted and the air temperature is lowered by blowing air on the surface of the foam layer and cooling it. Alternatively, the TMA maximum contraction rate can be increased by increasing the air volume.

  Adjusting the ratio (thickness / number of bubbles in the thickness direction) to fall within the range of 100 to 180 μm / month and adjusting the ratio (σ / X) to be 0.40 or less is the flow in the die. In addition to the method of adjusting the temperature of the outside or / and inside of the path, it can be achieved by the resin flow path design inside the die. This method has been found by the present inventors as a method capable of reducing the variation in the cell diameter in the thickness direction of the obtained foamed sheet as a result of pursuing the problems of the conventional method for producing a laminated foamed sheet.

  In this method, a value obtained by multiplying the resin shear rate of the molten resin flow path in the die and the time during which the resin moves inside the die (hereinafter referred to as “residence time”) is the shear amount received by the resin, Adjust the thickness variation. The amount of shear is calculated as the sum of each part by calculating (shear rate × dwell time) for each part of the die based on the shape inside the die. However, for the part including the support part that supports the core of the die and the side closer to the extruder, and the part where the residence time near the die outlet including the die outlet is less than 1 second, the calculation is complicated, but the bubble diameter Since this is not a part that greatly affects the variation of the shear, it is omitted from the accumulation of the shear amount.

  Next, a method for calculating the shear amount will be described with reference to FIG. FIG. 7 is a vertical cross-sectional view of the die from the portion (left side in the figure) to the die outlet part (right side in the figure) beyond the core support part of the die used in Example 1, and the hatched portion is foamed. 1 shows a flow path of a soluble molten resin. Moreover, the unit of the numerical value in FIG. 7 is all mm.

In Example 1, the extrusion rate per hour is 100 kg, and in this case, the extrusion rate per second is calculated as 27.8 g / second (100,000 g ÷ 3600 seconds). In addition, since most of the extrudate is polystyrene resin, the extrudate is regarded as polystyrene resin, and for the sake of convenience, the density of polystyrene resin at the time of melting shall be 1.05 g / cm ³ at room temperature. For Example 1, the volume flow rate per second is calculated to be 26.46 cm ³ / second (27.8 g / second ÷ 1.05 g / cm ³ ).

In the case of Example 1, the shearing amount is obtained by adding the shearing amounts in the respective flow paths (a), (b), and (c) in FIG. In addition, since the residence time is less than 1 second, the part of the flow path of the foamable molten resin indicated by (D) is excluded from the calculation of the shear amount.
First, the amount of shear in the part (a) is obtained. The volume of the resin flow path in part (a) is calculated to be 457.8 cm ³ by subtracting the volume of a cylinder having a length of 138 mm and a diameter of 76 mm from the volume of a cylinder having a length of 138 mm and a diameter of 100 mm. The residence time of the foamable molten resin passing through the flow path (A) is calculated as 17.3 seconds by dividing the volume of the flow path (A) by the volume flow rate (457.8 cm ³ ÷ 26. 46 cm ³ / sec).

The shear rate for determining the amount of shear is expressed by the following equation (1), assuming that the molten resin is a Newtonian fluid in a portion where the channel cross section is an annulus.
6Q / π ((R _o + R _i ) (R _o −R _i ) ² ) (1)
Where Q is the volume flow rate (cm ³ / sec), R _o is the outer radius (cm) of the ring, and R _i is the inner radius (cm) of the ring.

From the equation (1), the shear rate of the channel (A) is calculated to be 3.99 sec- ¹ . Further, the amount of shear in the part of the channel (A) is calculated as 69.0 because it is the product of the shear rate of the part of the channel (A) and the residence time of the part of the channel (A) (3 .99 seconds- ¹ x 17.3 seconds).

Next, the amount of shear in the portion of the flow path (A) is obtained. In the portion (A) where the inner diameter and the outer diameter of the flow path continuously change, it is regarded as a parallel double pipe having the outer diameter and the inner diameter of the middle point portion of the flow path (A), and the shear rate is calculated. Further, the volume of the channel (A) can be obtained by subtracting the volume of the inner truncated cone from the volume of the outer truncated cone. The volume (V) of the truncated cone is calculated by the following equation (2).
V = (A + B + (AB) ^1/2 ) × H / 3 (2)
However, A is the area of the upper surface of a truncated cone, B is the area of the lower surface of a truncated cone, and H is the height of a truncated cone.

In this case, the volume of the portion of the flow path (A) is calculated as 68.3 cm ³ . The residence time of the foamable molten resin passing through the flow path (A) is calculated as 2.58 seconds by dividing the volume of the flow path (A) by the volume flow rate (68.3 cm ³ ÷ 26. 46 cm ³ / sec). Further, the outer diameter of the midpoint portion of the flow path (A) is 86.5 mm, and the inner diameter is calculated as 68 mm. Therefore, the shear rate obtained by substituting this value into the equation (1) is 7.64. in seconds ^-1 shear amount of part of the flow path (b) is the product of the residence time of the portion of the channel shear rate and the flow path of the portion of (b) (i), 19.7 and calculation (7.64 sec- ¹ x 2.58 sec).

Next, the amount of shear at the portion of the flow path (c) is obtained. The amount of shear in the portion of the channel (c) can be obtained in the same manner as the amount of shear in the portion of the channel (a). Similarly, the residence time is calculated as 3.08 seconds, the shear rate is calculated as 17.98 seconds ^−1, and the shear amount of the flow path (c) portion is calculated as 55.4.
When the shearing amounts of the flow path (A), the flow path (A), and the flow path (C) are added up, the result is 144.1 (69.0 + 19.7 + 55.4), and the shearing quantity 144 is obtained.

  As a result of repeating the experiment, the present inventors have found that the optimum shear amount for making the bubble diameter uniform is generally 100 to 210, preferably 110 to 200, and more preferably 120 to 190. I found out. If the amount of shear is too large, the heat generated inside the die will be excessive, so there is a risk that the internal and external differences will occur in the resin temperature and the bubble diameter will vary widely. Conversely, if the amount of shear is too small, Since foaming starts inside the die, the state of the generated bubbles deteriorates, and conversely, there is a possibility that the variation in the bubble diameter becomes large.

  The laminated foam sheet of the present invention can be formed by a conventionally known forming method, and is particularly excellent in deep drawability. Forming methods include vacuum forming, pressure forming, and applications such as free drawing, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, Plug-assist molding, plug-assist reverse load molding, or a combination of these is employed.

  The drawing ratio of the molded article formed using the laminated foamed sheet of the present invention is preferably 0.25 or more, more preferably 0.4 or more, and further preferably 0.5 or more from the viewpoint of being suitable for deep drawing. On the other hand, the upper limit is preferably 1.1 or less, more preferably 1.0 or less, and even more preferably 0.9 or less because there is a possibility that a thin portion may be partially generated. The laminated foam sheet of the present invention is suitable for a deep-drawn molded product, but can be molded even with a molded product having a shallow depth such as a tray. In addition, the said drawing ratio means the value which remove | divided the diameter of the circle of the same area as the area of the opening part of a molded object by the height of the molded object.

  As a molded object shape | molded using the laminated foam sheet of this invention, a tray, a bowl, a lunch box, a cup etc. are mentioned, for example. In particular, deep-drawn bottles and cups are excellent.

  Hereinafter, the laminated foam sheet of the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.

Example 1
As the foam sheet production apparatus, a tandem type extruder comprising a first extruder having a barrel inner diameter of 115 mm and a second extruder having a barrel inner diameter of 180 mm connected to the first extruder is used, and the outlet of the second extruder is used. A tubular die having the shearing amount of 235 was attached to. Moreover, the 3rd extruder by which T-die was attached to the exit was used as an apparatus for the lamination of a HIPS layer.

As a polystyrene resin, G0302 (number average molecular weight (Mn) 11.8 × 10 ⁴ , molecular weight distribution (Mw / Mn) 2.5, total content of styrene dimer and styrene trimer, 1320 ppm) manufactured by PS Japan Co., Ltd. is used. A raw material in which 1.2 parts by weight of talc is blended with 100 parts by weight of the polystyrene-based resin is put into the first extruder and heated to melt and knead to obtain a molten resin, and the molten resin contains 65% by weight of isobutane. A mixed butane foaming agent of 35% by weight of normal butane was press-fitted and kneaded to obtain a foamable molten mixed resin. The amount of the foaming agent added was 3.3 parts by weight with respect to 100 parts by weight of the polystyrene resin.

Next, the foamable melt-mixed resin is sent to the second extruder, and the measurement temperature of the foamable melt-mixed resin is 156 ° C. at the breaker part (the breaker is installed at the joint between the second extruder and the tubular die). The foamable melt-mixed resin is gradually cooled through an annular die having an outlet gap of 0.65 mm at an extrusion rate of 1100 kg / hr, and immediately after that, cooling air (air volume) at a temperature of 25 ° C. is sent from the inside. , 1.8 m ³ / min) and at the same time cooling air (air volume, 1.5 m ³ / min) at a temperature of 25 ° C. is blown from the outside to form a cylindrical foam, and the inner surface of the foam has a diameter After cooling while passing on the side of a 668 mm cylindrical cooling device (mandrel), two foam sheets with a width of about 1000 mm are obtained by incising two places in the extrusion direction. It was. The blow-up ratio obtained by dividing the mandrel diameter by the die exit diameter was 4.0. In addition, the die | dye used was a shape whose shape after a mandrel support part was shown by FIG.

  In Example 1, a flow path through which oil circulates was provided in a die shaft (mandrel) portion located inside the die, oil set at 120 ° C. was put into the flow path inlet, and the flow returned to the flow path outlet again. The heat was continuously removed by adjusting the temperature of the oil to a temperature of 120 ° C. On the other hand, the outer wall of the die was adjusted to 145 ° C. with a heater covering the outer wall.

  Next, after the obtained roll-shaped foam sheet was cured at room temperature and normal pressure for 3 weeks, an impact-resistant polystyrene resin was extrusion laminated on one side of the foam sheet. That is, as an impact-resistant polystyrene resin, PS4 XL4 is supplied to the third extruder, heated, melted and kneaded, and then the impact-resistant polystyrene resin melt extruded through a T-die is used. The laminated foam sheet was formed by extrusion laminating on the surface opposite to the mandrel side of the foam sheet (the outer surface of the cylindrical foam).

  The obtained laminated foam sheet was excellent in appearance, and both the moldability and the printability immediately after the molded body were good.

Example 2
Example except that the amount of talc added was 1.0 part by weight with respect to 100 parts by weight of the polystyrene-based resin, and the amount of foaming agent added was 3.4 parts by weight with respect to 100 parts by weight of the polystyrene-based resin. A laminated foam sheet was formed in the same manner as in 1.
The obtained laminated foam sheet was excellent in appearance and sufficiently satisfied both moldability and printability immediately after the molded body.

Example 3
A laminated foam sheet was formed in the same manner as in Example 1 except that the die was calculated so that the shear amount after the mandrel support portion was calculated as 182. In FIG. 7, the shear amount was set to 182 by changing the inner diameter of the end flow path on the (c) side and the inner diameter of (c) to 65 mm.
The obtained laminated foam sheet was excellent in appearance and sufficiently satisfied both moldability and printability immediately after the molded body.

Comparative Example 1
Implementation was performed except that the amount of talc added was 0.6 parts by weight with respect to 100 parts by weight of polystyrene resin and the amount of foaming agent was changed to 3.6 parts by weight with respect to 100 parts by weight of polystyrene resin. A laminated foam sheet was formed in the same manner as in Example 1.
As a result of reducing the amount of talc of the cell regulator, the resulting laminated foam sheet was inferior in appearance due to the large cell diameter and satisfactory in formability, but inferior in printability immediately after the molded article. .

Comparative Example 2
A laminated foamed sheet was formed in the same manner as in Example 1 except that the amount of butane added was 3.2 parts by weight and the die was changed so that the shear amount after the mandrel support part was calculated as 239. In FIG. 7, the shear amount was set to 239 by changing the inner diameter of the flow path at the end on the (c) side and the inner diameter of (c) to 68 mm.
As a result of the excessive amount of shear, the obtained laminated foam sheet had a large σ / X of the foam layer, and the moldability was satisfactory, but the printability immediately after the molded body was poor. .

Comparative Example 3
A laminated foam sheet was formed in the same manner as in Example 1 except that the oil was not circulated through the die shaft (core) in the die. As a result of insufficient cooling in the die on the non-laminated surface side of the foam layer, the resulting laminated foam sheet has a TMA maximum shrinkage ratio on the surface of the non-laminate surface of the foam layer that is too large for both MD and TD. The moldability was inferior.

Comparative Example 4
Implementation was performed except that the amount of talc added was 1.7 parts by weight with respect to 100 parts by weight of polystyrene resin, and the amount of foaming agent was changed to 3.1 parts by weight with respect to 100 parts by weight of polystyrene resin. A laminated foam sheet was formed in the same manner as in Example 1.
As a result of increasing the amount of the talc of the cell regulator, the resulting laminated foam sheet had a too small cell diameter, and was inferior in moldability and immediately printability.

  Examples, shear amount when obtaining foam sheets of comparative examples, apparent density of foam layers obtained in examples, comparative examples, thickness of foam layers, surface layer density of non-laminated surfaces of foam layers, thickness of HIPS layers, Total basis weight, horizontal average bubble diameter (X), variation in horizontal bubble diameter (σ), ratio (σ / X), maximum shrinkage (%) of TMA, formability, immediately printability and comprehensive evaluation Table 1 shows. Moreover, the TMA curve measured with respect to each of MD and TD about the surface by the side of the non-lamination surface of the foaming layer of the laminated foam sheet obtained in each example of Example 1 and Comparative Example 3 is shown in FIG. 5 (TD).

Evaluation of moldability About the laminated foamed sheets obtained in Examples and Comparative Examples, the heater temperature on the HIPS layer side was set to 325 ° C. using a molding machine manufactured by Asano Laboratory, product number FKS-0631-10, and the non-foamed layer The heater temperature on the laminated surface side was set to 275 ° C., and the laminated sheet was heated for 14 seconds, and then the surface on which the HIPS layer was laminated was thermoformed so as to be positioned on the outer surface side by a plug assist method, and the opening portion had a diameter of 141 mm. A round shaped molded body having a depth of 73 mm and a drawing ratio of 0.52 was molded, and the occurrence of cracks on the peripheral wall near the mouth edge of the molded body was observed. The results are shown in Table 1.

  The case where no pricking occurred was marked with ◯, and the case where pricking occurred was marked with x. The problems that occurred were listed together with the evaluation.

Evaluation of printability In order to determine the printability of a container, curved surface printing was performed immediately after thermoforming (30 minutes after completion of molding), and the presence or absence of printing defects was evaluated. The case where the strength of the container is sufficient, the printing pressure is not lost due to the printing pressure, and there is no printing, no printing fading, and clear printing is marked as ○, and any one of wrinkling, printing, and fading However, the case where it was was made into x. Among the evaluations of ◯, those having a smooth surface and excellent appearance were rated as ◎. The problems that occurred were listed together with the evaluation.

Comprehensive evaluation It evaluated as follows based on evaluation of a moldability, immediately printability, and a molded object strength.
○ ・ ・ ・ All ○
There is × ・ ・ ・ ×

FIG. 1 is a drawing obtained by accurately tracing a bubble shape from a micrograph of a vertical cut surface in a direction corresponding to TD of the laminated foamed sheet obtained in Example 1. FIG. 2 is a drawing in which the bubble shape is accurately traced from a micrograph of a vertical cut surface in a direction corresponding to the TD of the laminated foamed sheet obtained in Comparative Example 2. FIG. 3 is a schematic explanatory diagram of a thermomechanical analysis (TMA) measuring device. FIG. 4 is a TMA curve in MD of the surface of the non-laminated surface of the laminated foamed sheet obtained in Example 1 and Comparative Example 3. FIG. 5 is a TMA curve in TD of the surface of the non-laminated surface of the laminated foamed sheet obtained in Example 1 and Comparative Example 3. FIG. 6 is an example of a TMA curve in which the peak of the heat shrinkage peak is difficult to understand. FIG. 7 is an explanatory diagram for explaining a method for obtaining a shearing amount from the molten resin flow path in the die after the mandrel.

Claims (2)

  It consists of a polystyrene-based resin foam layer and an impact-resistant polystyrene-based resin layer laminated on one side of the foam layer, and a temperature increase rate of 10 ° C./min for a portion having a thickness of 200 μm from the surface of the non-laminated surface of the foam layer. In the TMA curve obtained by thermomechanical analysis, the value of the peak apex at 135 ° C. or less of the heat shrinkage rate in the extrusion direction is 0 to 15%, and the value of the peak apex at 135 ° C. or less of the heat shrinkage rate in the width direction. In a laminated foam sheet having a thickness of 0 to 30%, the ratio of the thickness (μm) of the foam layer to the number of cells in the thickness direction of the vertical section of the foam layer (μm) (thickness / number of cells in the thickness direction) is 100 to 180 μm / The horizontal bubble diameter of the bubbles existing on the straight line with respect to the average bubble diameter in the horizontal direction (X) of the bubbles existing on the straight line in the thickness direction in the vertical cross section of the foam layer Polystyrene-based resin laminate foam sheet, wherein the ratio of the standard deviation (σ) (σ / X) is 0.40 or less.   2. The polystyrene-based resin laminated foam sheet according to claim 1, wherein the impact-resistant polystyrene-based resin layer has a thickness of 110 to 130 μm.

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