JP6244286B2 - Polystyrene resin foam sheet and foam container - Google Patents

Description

  The present invention relates to a polystyrene-based resin foam sheet and a foam container.

Conventionally, polystyrene-based resin foam sheets (hereinafter also simply referred to as “foam sheets”) have been widely used as raw materials for foam containers such as tray-type and basket-type food containers.
When producing a foamed container from a foamed sheet, thermoforming such as vacuum forming or pressure forming is performed on the foamed sheet (for example, Patent Documents 1 and 2).

JP-A-5-271456 JP 2009-263512 A

By the way, in the production of the foam sheet, it is desirable to suppress the burden on the environment or improve the productivity.
For example, at the time of thermoforming a foam sheet, if the heating temperature can be performed at a temperature lower than that of the conventional one, energy consumed for heating can be suppressed, and as a result, suppression of environmental load can be expected. In addition, the time (cooling time) required for demolding the foamed container obtained by thermoforming the foamed sheet can be shortened, and an improvement in productivity can be expected.
However, if an attempt is made to produce a foamed container simply by thermoforming the foamed sheet at a lower temperature than in the past, the foamed container may be cracked.
In addition, the container dimensions may change greatly during high-temperature storage.

  In view of the above circumstances, the present invention is a polystyrene-based resin foam sheet that is excellent in moldability in thermoforming at relatively low temperatures, and that suppresses changes in container dimensions during high-temperature storage, and at relatively low temperatures. It is an object of the present invention to provide a foamed container that is easy to manufacture by thermoforming and that suppresses changes in container dimensions during high-temperature storage.

  As a result of intensive research by the present inventors, when a DSC measurement was performed on a polystyrene-based resin foam sheet, the extrapolated glass transition start temperature particularly affects the container dimensions, and the midpoint glass transition temperature is particularly low at low temperatures. It has been found that molding can be affected. Furthermore, by carrying out earnest research and setting the extrapolation glass transition start temperature and the midpoint glass transition temperature within a specific range, it has excellent formability in thermoforming at relatively low temperatures, and at the time of high-temperature storage. The present inventors have found that a foamed sheet in which the change in the container size is suppressed can be obtained, and the present invention has been completed.

That is, the polystyrene resin foam sheet according to the present invention has an extrapolated glass transition start temperature (T _ig ) obtained by DSC measurement of 80 ° C. or higher and lower than 100 ° C., and an intermediate glass transition temperature (T _mg ) of 92 ° C. It is less than 102 degreeC above.

Such a polystyrene-based resin foam sheet has moldability in thermoforming at a relatively low temperature because the extrapolated glass transition start temperature (T _ig ) and the midpoint glass transition temperature (T _mg ) are within the above ranges. It is excellent, and the change in the dimensions of the container during high-temperature storage is suppressed.

Moreover, in the polystyrene-based resin foam sheet having the above configuration,
It is preferable that the absorbance ratio D1728 / D1600, which contains a styrene-acrylic acid ester copolymer resin and is analyzed by infrared spectroscopic analysis by the ATR method, is 0.2 or more and 1.3 or less.

  According to this configuration, when the absorbance ratio is within the above range, both low-temperature moldability and suppression of container dimensional change during high-temperature storage can be achieved at a higher level.

Moreover, in the polystyrene-based resin foam sheet having the above configuration,
A resin composition in which a polystyrene resin and the styrene-acrylic acid ester copolymer resin are melt-kneaded is extruded and foamed,
It is preferable that the content of acrylic acid ester in the styrene-acrylic acid ester copolymer is 1% by mass or more and less than 15% by mass.

  According to such a configuration, the polystyrene-based resin can be obtained by extrusion foaming the resin composition obtained by melt-kneading the polystyrene-based resin and the styrene-acrylic acid ester-based copolymer resin without using an adhesive or the like. And a polystyrene resin foam sheet in which styrene-acrylic acid ester copolymer resin is laminated. Moreover, it becomes easy to set the said extrapolation glass transition temperature and a midpoint glass transition temperature in the said range because content of the said acrylic ester is in the said range.

Moreover, in the polystyrene-based resin foam sheet having the above configuration,
It is preferable that the styrene-acrylic acid ester copolymer resin exhibits strain hardening.

  According to such a configuration, since the styrene-acrylate copolymer resin exhibits strain-hardening properties and is relatively excellent in elongation at a relatively low temperature, it is further improved in thermoforming at a relatively low temperature. Excellent formability. In addition, changes in container dimensions during high-temperature storage are further suppressed.

Moreover, in the polystyrene-based resin foam sheet having the above configuration,
The open cell rate is 15% or less,
The thickness is 0.7 mm or more and 3.0 mm or less,
Apparent density is not more than 0.045 g / cm ³ or more 0.3 g / cm ^3,
The basis weight is preferably 80 g / m ² or more and 250 g / m ² or less.

According to this configuration, when the open cell ratio is within the above range, the polystyrene-based resin foam sheet hardly changes in volume due to heating and has excellent strength.
When the thickness is within the above range, the polystyrene-based resin foam sheet can easily exhibit excellent strength. Moreover, in addition to being more excellent in shape retention of foamed containers and the like molded using polystyrene resin foam sheets, it is excellent in cutting processability, and is lightweight and low in bulk. Become.
When the apparent density is within the above range, the polystyrene-based resin foam sheet is likely to be excellent in strength, and the shape retention property of a foam container formed using the polystyrene-based resin foam sheet is more excellent. obtain. Moreover, a polystyrene-type resin foam sheet becomes lighter and the bulkiness can be suppressed.
When the basis weight is within the above range, the polystyrene-based resin foam sheet can easily exhibit excellent strength, and the shape retaining property of a foam container formed using the polystyrene-based resin foam sheet is more excellent. Can be. Moreover, the polystyrene-based resin foam becomes lighter and the bulkiness can be suppressed.

The foam container according to the present invention is:
The polystyrene resin foam sheet is thermoformed.

  According to such a configuration, the foamed container can be easily manufactured by thermoforming at a relatively low temperature by thermoforming the polystyrene-based resin foamed sheet, and the change in container dimensions during high-temperature storage is suppressed. Will be.

In the foam container of the above configuration,
It is preferable that the heating dimensional change rate when heated at 60 ° C. for 24 hours is less than 1.5%.

  According to this configuration, since the amount of deformation of the container during high-temperature storage is reduced, it is possible to suppress a decrease in hermeticity between the foamed container and the container lid or wrap film.

  According to the present invention, a polystyrene-based resin foam sheet that is excellent in moldability in thermoforming at a relatively low temperature and that suppresses changes in container dimensions during high-temperature storage, and thermoforming at a relatively low temperature. Thus, it is possible to provide a foamed container that is easy to manufacture and that suppresses changes in container dimensions during high-temperature storage.

Graph showing an example of a DSC curve Graph showing an example of a DSC curve Graph showing an example of a uniaxial elongational viscosity curve

  The polystyrene-based resin foam sheet and foam container according to the embodiment of the present invention will be described below.

  The polystyrene-based resin foam sheet of the present embodiment is formed by extrusion-foaming a resin composition containing a polystyrene-based resin, and the resin contains a polystyrene-based resin (hereinafter also referred to as “foamed sheet”). .)

The polystyrene resin foam sheet of this embodiment has an extrapolated glass transition start temperature (T _ig ) obtained by DSC measurement of 80 ° C. or higher and lower than 100 ° C., and an intermediate glass transition temperature (T _mg ) of 92 ° C. or higher and 102 It is less than ℃.

The extrapolated glass transition start temperature (T _ig ) is a differential according to “9.3 Determination of glass transition temperature” of the same standard based on the method described in JIS K7121: 1987 “Method for measuring plastic transition temperature”. It can be measured using a scanning calorimeter (DSC).
More specifically, for example, a model name “DSC6220 type” manufactured by SII Nanotechnology Co., Ltd. is used, and a sample is placed on the DSC sample side so that there is as little gap as possible at the bottom of the aluminum measurement container. Place a 6.5mg filled container, and place an aluminum measuring container with alumina on the reference side, and increase the temperature from 30 ° C to 200 ° C at a rate of temperature increase of 20 ° C / min under a nitrogen gas flow rate of 20ml / min. From the DSC curve obtained when the temperature was raised to 200 ° C. at a rate of temperature increase of 20 ° C./min. The extrapolated glass transition start temperature (T _ig ) can be determined using the attached analysis software (Muse).
As shown in FIG. 1, the extrapolated glass transition start temperature (T _ig ) is a straight line obtained by extending the base line on the low temperature side of the DSC curve obtained by the above measurement to the high temperature side, and the stepwise change portion of the glass transition. It can be determined as the temperature of the intersection with the tangent drawn at the point where the slope of the curve is maximum.
In addition, as shown in FIG. 2, the extrapolated glass transition start temperature (T _ig ) is a straight line obtained by extending the low-temperature base line to the high-temperature side when the resulting DSC curve has two or more steps. And the temperature of the intersection with the tangent drawn at the point where the slope of the step-like change portion at the first stage (low temperature side) of the glass transition becomes maximum.

The intermediate glass transition temperature (T _mg ) can be measured using a differential scanning calorimeter (DSC) based on the method described in JIS K7121: 1987 “Method for Measuring Plastic Transition Temperature”.
More specifically, for example, a DSC curve is obtained in the same manner as the measurement of the extrapolation glass transition start temperature (T _ig ) described above, and the midpoint glass transition temperature (T _mg ) is obtained from the obtained DSC curve. it can.
Specifically, as shown in FIG. 1 and FIG. 2, the midpoint glass transition temperature (T _mg ) is the low temperature side and high temperature side baseline of the DSC curve (see FIG. 1 and FIG. 2) obtained by the above measurement. The temperature at the point where the straight line equidistant from the straight line extending in the direction of the vertical axis and the curve of the step-like change part of the glass transition intersect can be obtained.

  The foam sheet has excellent moldability in thermoforming at a relatively low temperature due to the extrapolated glass transition temperature and the midpoint glass transition temperature being within the above ranges, and changes in container dimensions during high-temperature storage. Is suppressed. Moreover, this makes it easy to obtain a foamed container that is lightweight, excellent in thickness uniformity, and excellent in strength and appearance.

  In addition, the extrapolated glass transition start temperature is 86 ° C. to 97 ° C. in that the moldability is further improved in thermoforming at a relatively low temperature and the change in container dimensions during high temperature storage is further suppressed. The intermediate point glass transition start temperature is preferably 93 ° C to 100 ° C, the extrapolated glass transition start temperature is 90 ° C to 94 ° C, and the midpoint glass transition start temperature is 96 ° C to 99 ° C. More preferably.

The resin contained in the resin composition preferably contains 80% by mass or more of polystyrene-based resin, and more preferably contains 85% by mass or more.
By including 80% by mass or more of the polystyrene resin, the foamed sheet molded using the resin composition (hereinafter also referred to as “polystyrene resin composition”) is excellent due to the polystyrene resin. There is an advantage that the mechanical properties and moldability are more easily exhibited.

The polystyrene resin is a polymer having a styrene monomer as a constituent unit in the molecule, and usually has a styrene monomer as a main constituent unit.
Examples of the polystyrene-based resin include homopolymers of styrene monomers and copolymers of styrene and other monomers.
Examples of such a copolymer include a styrene-acrylic acid ester copolymer, a styrene-vinyl chloride copolymer, a styrene-butadiene copolymer, and a styrene-butadiene-acrylonitrile copolymer.
Examples of the styrene-acrylic acid ester copolymer include a styrene-maleic anhydride copolymer, a styrene-acrylic acid copolymer, a styrene-methyl acrylate copolymer, a styrene-ethyl acrylate copolymer, and a styrene-acrylic copolymer. Examples include butyl acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, and styrene-butyl methacrylate copolymer.
In addition, as such a copolymer, in order to exhibit excellent mechanical properties and moldability derived from a styrene polymer more remarkably in a foamed sheet, the styrene monomer is 60% by mass or more and the other monomer is 40% by mass or less. A copolymer is preferred.

  In the resin, the content of the styrene monomer in terms of monomer is preferably 60% by mass or more in order to make the foamed sheet exhibit excellent mechanical properties and moldability derived from the styrene polymer more remarkably.

  The polystyrene-based resin preferably has a mass average molecular weight of 240,000 or more, and preferably 400,000 or less.

The mass average molecular weight means what is conventionally defined in the field of polymer chemistry, and is determined by the following molecular weight measurement.
Specifically, the mass average molecular weight is determined by gel permeation chromatography (GPC).
More specifically, the polystyrene-based resin has a mass average molecular weight of about 30 mg of a sample dissolved in 10 mL of chloroform, filtered through a non-aqueous 0.45 μm chromatographic disk, and then subjected to polystyrene using Waters HPLC (Detector 484, Pump 510). It can be determined by measuring the converted molecular weight.
Regarding the measurement conditions, two columns “Shodex GPC K-806L (φ8.0 × 300 mm)” (manufactured by Showa Denko) were used, the column temperature was 40 ° C., the mobile phase was chloroform, and the mobile phase flow rate was 1. The injection pump temperature can be room temperature, the detection wavelength can be 254 nm, and the injection volume can be 50 μL.
Standard polystyrene for preparing a calibration curve has a molecular weight of 1,030,000 from Showa Denko KK, and molecular weights of 5,480,000, 3,840,000, 355,000, 102,000, manufactured by Tosoh Corporation. 37,000, 9,100, 2,630, and 495.

  The foamed sheet of this embodiment contains a styrene-acrylate copolymer resin, and an absorbance ratio D1728 / D1600 obtained by analyzing the foamed sheet by infrared spectroscopic analysis using the ATR method is 0.2 or more. It is preferable that it is 1.3 or less.

  When the absorbance ratio is less than 0.2, the low temperature moldability is low and the energy saving property may be poor. When the absorbance ratio is greater than 1.3, the amount of container deformation may increase during high-temperature storage. On the other hand, when the absorbance ratio is 0.2 to 1.3, the low-temperature moldability is excellent, and the low-temperature moldability and the suppression of changes in container dimensions during high-temperature storage can be achieved at a higher level. Considering this point, the preferred absorbance ratio is in the range of 0.3 to 1.0, the more preferred absorbance ratio is in the range of 0.35 to 0.65, and the more preferred absorbance ratio is 0.4 to 0. .6 range.

Absorbance ratio D1728 / D1600 was determined by infrared spectroscopic analysis by ATR method, in the infrared absorption spectrum, means the ratio of the absorbance at 1728 cm ^-1 to the absorbance at 1600 cm ^-1. Here, the absorption at 1728 cm ⁻¹ shows a peak derived from stretching vibration between C═O of the ester group contained in the acrylate ester. The absorption at 1600 cm ⁻¹ indicates the presence of a peak derived from the in-plane vibration of the benzene ring contained in the polystyrene resin.

Here, the infrared spectroscopic analysis in the present invention is an analysis method in which an infrared absorption spectrum is measured by a single reflection type ATR method using total reflection absorption (Attenuated Total Reflectance). This analysis method is a method in which an ATR prism having a high refractive index is brought into close contact with a sample, infrared light is irradiated to the sample through the ATR prism, and light emitted from the ATR prism is spectrally analyzed.
ATR infrared spectroscopic analysis includes organic materials such as polymer materials because of the simplicity of being able to measure the spectrum simply by bringing the sample and the ATR prism into close contact with each other, and the ability to perform surface analysis up to a depth of several μm. It is widely used for surface analysis of various substances.

In the foam sheet of this embodiment, a resin composition obtained by melt-kneading a polystyrene resin that is a homopolymer resin of styrene and a styrene-acrylate copolymer resin is extruded and foamed, and the styrene- The acrylic ester content in the acrylic ester copolymer is preferably 1% by mass or more and less than 15% by mass. When the content of the acrylic ester is less than 1% by mass, excellent low-temperature moldability tends not to be exhibited. When the acrylic ester content is 15% by mass or more, the dispersion state of the polystyrene resin and melt-kneaded styrene-acrylic ester copolymer may be deteriorated, resulting in poor appearance on the surface of the foam sheet. This is not preferable because the thermal stability of the container is lowered. By extruding and foaming a resin composition in which a polystyrene resin and a styrene-acrylic acid ester copolymer resin are melt-kneaded, the above-mentioned midpoint glass transition temperature is more preferably 80 ° C. or more and less than 100 ° C. The outer glass transition temperature can be 92 ° C. or higher and lower than 102 ° C. Moreover, it becomes possible to make the said extrapolation glass transition temperature 80 degreeC or more and less than 100 degreeC more reliably because content of acrylic acid ester exists in the said range.
Moreover, it is more preferable that the content of the acrylate ester is 3% by mass or more and less than 12% by mass in terms of further suppressing changes in container dimensions during high-temperature storage, and 5% by mass or more and less than 8% by mass. Is more preferable.
The content of the acrylic ester in the styrene-acrylic ester copolymer can be determined by the following calibration curve formula from the absorbance ratio determined by the method of measuring the absorbance ratio of styrene-acrylic ester described later.
Y = 5.737X-0.692
Y: Acrylic acid ester content (% by mass)
X: Absorbance ratio of styrene-acrylic acid ester The calibration curve formula here represents the mass ratio of styrene monomer / butyl acrylate monomer to 99/1, 97/3, 95/5, 93/7, 90/10, The styrene-butyl acrylate copolymer resin obtained by adjusting each to 85/15 and 80/20 and suspension polymerization is obtained from the method for measuring the absorbance ratio of styrene-acrylate ester described later. It was prepared from the absorbance ratio.

Moreover, in the polystyrene-type resin foam sheet of this embodiment, it is preferable that the said styrene-acrylic acid ester-type copolymer resin shows distortion sclerosis | hardenability.
The strain hardening property means a characteristic that the uniaxial elongation viscosity is rapidly increased as the strain rate is increased in the measurement of the uniaxial elongation viscosity of the resin. Specifically, the first order of the non-linear region in a logarithmic plot of time (s) -elongation viscosity curve (Pa · s) obtained by measuring uniaxial extensional viscosity at a temperature of 160 ° C. and a constant strain rate of 0.5 / second. It means that the slope (a ₁ ) of the approximate line is larger than the slope (a ₂ ) of the primary approximate line of the linear region in the curve. That is, it means that the ratio (a ₁ / a ₂ ) between the slope (a ₁ ) of the first-order approximation line of the nonlinear region and the slope (a ₂ ) of the first-order approximation line of the linear region is larger than 1 (see FIG. 3). ).

The “nonlinear region” intends a region appearing after the inflection point, and the slope (a ₁ ) of the linear approximation line in the “nonlinear region” is an arbitrary point near the inflection point. It is intended to select the slope of the regression line based on the data observed up to 7 seconds after selection.
In addition, the “linear region” intends a region where linearity is relatively obtained in the data appearing before the inflection point, and the slope (a ₂ ) of the linear approximation line in the “linear region” The slope of the regression line is intended based on the data observed up to 0.1 seconds before the point set at (any point near the inflection point).
Moreover, about uniaxial elongation viscosity, it can measure by the method as described in the Example mentioned later.

The ratio (a ₁ / a ₂ ) between the slope (a ₁ ) of the nonlinear region and the linear region slope (a ₂ ) is greater than 1, that is, the styrene-acrylate copolymer resin has strain hardening properties. As a result, since the elongation at a relatively low temperature is relatively excellent, the moldability is further improved in thermoforming at a relatively low temperature. In addition, changes in container dimensions during high-temperature storage are further suppressed.

  Here, a general styrene-acrylate copolymer resin simply obtained by polymerizing styrene and an acrylate ester has a uniaxial elongation viscosity at a temperature of 160 ° C. and a constant strain rate of 0.5 / sec. When measured, an inflection point is observed in the vicinity of 1 second, but the inclination tends to decrease with the inflection point as a boundary.

  On the other hand, the styrene-acrylate copolymer resin having a plurality of branched structures in the molecule (hereinafter also referred to as “multi-branched styrene-acrylate copolymer resin”) exhibits an inflection point at the same location. In addition, the inclination tends to increase at the inflection point.

  Therefore, considering such a viewpoint, as the styrene-acrylic acid ester copolymer resin exhibiting strain hardening, for example, the above-mentioned multi-branched styrene-acrylic acid ester copolymer resin can be adopted.

  In the foam sheet of the present embodiment, the mass ratio of the polystyrene resin and the styrene-acrylate copolymer resin (polystyrene resin / styrene-acrylate copolymer resin) is 30/70 to 70/30. It is more preferable that it is 60/40 to 30/70 in that it is more excellent in low-temperature moldability and is further excellent in suppression of container dimensionality during high-temperature storage.

  The polystyrene-based resin composition used for forming the foamed sheet of the present embodiment can contain additives such as a foaming agent and a bubble adjusting agent in addition to the polystyrene-based resin as described above.

  Examples of the foaming agent include volatile foaming agents and decomposable foaming agents.

Examples of the volatile blowing agent include hydrocarbons such as propane, butane, pentane, cyclopentadiene, and hexane, ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol, and isopropyl alcohol, dimethyl ether, diethyl ether, and diene. Examples thereof include ether compounds such as propyl ether, methyl ethyl ether and petroleum ether.
Further, as the volatile foaming agent, carbon dioxide, nitrogen, ammonia, water and the like can be employed.
The volatile blowing agent is preferably a hydrocarbon having a boiling point at atmospheric pressure of −45 to 40 ° C., and preferably propane, butane, pentane and the like.
In addition, the said volatile foaming agent may be used individually by 1 type or in combination of 2 or more types.
Among them, the volatile foaming agent is preferably a butane mixture such as normal butane or isobutane, or a butane mixture in which normal butane and isobutane are mixed in an arbitrary ratio.

Examples of the decomposable foaming agent include organic decomposable foaming agents such as azodicarbonamide and dinitrosopentamethylenetetramine, an organic acid such as citric acid or a salt thereof, and a bicarbonate such as sodium bicarbonate. Inorganic decomposable foaming agents and the like.
The decomposable foaming agent can also be used alone or in combination of two or more.

  As the foaming agent, only one of the volatile foaming agent and the decomposable foaming agent may be used, or these may be used in combination.

  The foaming agent is preferably used in an amount of 1 to 10 parts by mass with respect to 100 parts by mass of the resin.

  Examples of the additive include a bubble adjusting agent such as talc, an inorganic filler, an organic pigment, a flame retardant, a flame retardant aid, a lubricant, and a plasticizer.

The foamed sheet is not particularly limited as long as it is in the form of a sheet containing bubbles generated by foaming, and a sheet formed by general extrusion foaming can be employed.
The foam sheet supplies, for example, an additive such as the polystyrene-based resin or a bubble adjusting agent to an extruder equipped with a circular die having an annular discharge port at its tip, and the polystyrene-based resin is fed into the extruder in the extruder. The mixture is heated to a temperature higher than the softening point and melt-kneaded with the additives to form a melt-kneaded product, and a hydrocarbon-based foaming agent is injected from the middle of the extruder and mixed with the melt-kneaded product to obtain The melt-kneaded product containing the foaming agent thus formed can be formed by extrusion from the discharge port of a circular die.

  More specifically, the melt-kneaded material containing the foaming agent is extruded from the discharge port of the circular die to form a cylindrical foam, and the diameter disposed on the downstream side (forward in the extrusion direction) of the circular die is the discharge port. The foam is picked up while the inner surface of the foam is in sliding contact with the outer peripheral surface of the cooling mandrel having a larger diameter, and the foam is expanded by the cooling mandrel and the foam is cooled from the inside. Then, the foam is produced so that it becomes a long strip shape by continuously cutting the foam in the extrusion direction with a cutter provided on the downstream side of the cooling mandrel and developing it into a flat sheet. A sheet can be employed as the foam sheet in the present embodiment.

The foam sheet preferably has an open cell ratio of 15% or less, more preferably 5 to 12%.
When the open cell ratio is 15% or less, the foamed sheet hardly changes in volume due to heating and has excellent strength.
Note that the open cell ratio can be measured by the 1-1 / 2-1 atmospheric pressure method in accordance with ASTM D-2856-87.

The foam sheet preferably has a thickness of 0.7 mm to 3.0 mm, and more preferably 0.9 mm to 2.5 mm.
When the thickness is 0.7 mm or more, excellent strength can be easily exerted on the foamed sheet, and the shape retention of a foamed container or the like formed using the foamed sheet can be further improved.
Moreover, when the thickness is 3.0 mm or less, the foamed sheet can be made excellent in cutting processability, and can be lightweight and low in bulk.

  The thickness of the foamed sheet is measured with a microgauge at intervals of 50 mm in the sheet width direction, and the arithmetic average value is taken as the thickness of the foamed sheet.

The foam sheet preferably has an apparent density of 0.045 to 0.3 g / cm ³ , and more preferably 0.050 to 0.2 g / cm ³ .
When the apparent density is 0.045 g / cm ³ or more, it is easy to make the foamed sheet excellent in strength, and it is possible to improve the retention of foamed containers and the like molded using the foamed sheet.
Moreover, when an apparent density is 0.3 g / cm < ³ > or less, there exists an advantage that a foamed sheet becomes lighter and the bulkiness of a foamed sheet can be suppressed.

  The apparent density of the foamed sheet can be measured by the method described in JIS K7222: 1999 “Foamed Plastics and Rubber—Measurement of Apparent Density”.

The foam sheet preferably has a basis weight of 80~250g / ^{m 2,} and more preferably 100~220g / ^{m 2.}
When the basis weight is 80 g / m ² or more, the foamed sheet can be easily made excellent in strength, and the shape retaining property of a foamed container or the like formed using the foamed sheet can be made more excellent.
Moreover, when a basic weight is 250 g / m < ² > or less, there exists an advantage that it becomes lighter and a bulkiness can be suppressed.

The basis weight of the foam sheet is a portion excluding both ends 20 mm in the width direction of the foam sheet, cut into 10 cm × 10 cm at equal intervals in the width direction, and measure the mass [g] of each section up to 0.01 g unit, The value obtained by converting the average value of the mass [g] of each section into the mass per square meter is defined as the basis weight [g / m ² ] of the foam sheet.

  The foam sheet of the preferred embodiment as described above is the ratio of the outer diameter (D) of the cooling mandrel to the type and amount of foaming agent used in extrusion foaming, the extrusion temperature, the resin pressure, and the outlet diameter (d) of the circular die (D / D), and can be prepared depending on the cooling conditions for the foam after extrusion foaming.

  The foam container of the present embodiment can be obtained by thermoforming the foam sheet of the present embodiment by a general thermoforming method (a method such as vacuum forming, pressure forming, vacuum pressure forming, match mold forming, etc.).

  The foamed container of the present embodiment is easy to manufacture by thermoforming at a relatively low temperature because the foamed sheet is thermoformed, and the container dimensional change during high temperature storage is suppressed. .

  The foam container of this embodiment can be used as a tray-type food container, a bowl-shaped food container, a cup-type container, or the like.

The foam container of this embodiment preferably has a heating dimensional change rate of less than 1.5% when heated at 60 ° C. for 24 hours. When the heating dimensional change rate is 1.5% or more, the amount of deformation increases when the warehouse is stored in the summer or when a high-temperature product of 60 ° C. or higher is placed in the container. The sealing property with the wrap film may be lowered. On the other hand, since the rate of change in heating dimension is less than 1.5, the amount of deformation of the container during high-temperature storage is reduced, so that the deterioration of the sealing property between the foamed container and the container lid or wrap film is suppressed. obtain.
The heating dimensional change rate is the hot air circulation type at 60 ° C., where the dimension between the center of the lip on the long side of the foamed container (on the side in the case of a square in plan view) and the vertical is the dimension before heating. Take out after 24 hours in the dryer, take the dimensions of the same location after standing for 1 hour in a standard state (25 ° C., 1 atm), and determine the heating dimensional change rate by the following formula.
S = | (L ₁ −L ₀ ) | / L ₀ × 100
S: heating dimensional change rate (%), L ₁ : average dimension after heating (mm), L ₀ : average dimension before heating

In addition, the foam sheet and foam container of this invention are not limited to the said illustration.
Moreover, in this invention, it is possible to employ | adopt the various form employ | adopted in a conventionally well-known polystyrene-type resin foam sheet or foam container in the range which the effect of this invention is not impaired remarkably.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to the following.

<Synthesis of styrene-acrylic acid ester copolymer resin>

<Synthesis Example 1>
In a 106 liter autoclave with a stirrer (hereinafter also referred to as a reactor), as a polymerization initiator, 41 g of benzoyl peroxide (purity 75%, manufactured by NOF Corporation, trade name Nyper BW), t-butylperoxy-2- 57 g of ethylhexyl monocarbonate (trade name Perbutyl E, manufactured by NOF Corporation) is dissolved in a mixed solution of 24.4 kg of styrene monomer and 4.0 kg of butyl acrylate monomer, and further 170 g of magnesium pyrophosphate and sodium dodecylbenzenesulfonate. After adding 4.6 g and 56.8 kg of distilled water, the suspension was dissolved and dispersed under stirring at 70 rpm to form a suspension.
Subsequently, the temperature in the autoclave was raised to 90 ° C. and then held at 90 ° C. for 7 hours.
Thereafter, under stirring at 120 rpm, the temperature in the autoclave was further raised to 125 ° C., and then maintained at 125 ° C. for 3 hours, then the temperature in the autoclave was cooled to 40 ° C., and the polymerization slurry was taken out from the autoclave, By dehydrating, washing and drying, a styrene-butyl acrylate copolymer resin (mass average molecular weight: 320,000) containing 14% of a butyl acrylate component was obtained.

<Synthesis Example 2>
A styrene-acrylic acid containing 11% of a butyl acrylate component is operated in the same manner as the above styrene-acrylic acid ester copolymer resin except that 25.3 kg of styrene monomer and 3.1 kg of butyl acrylate monomer are used. A butyl copolymer resin (mass average molecular weight: 330,000) was obtained.

<Synthesis Example 3>
A styrene-acrylic acid containing 7% of a butyl acrylate component is operated in the same manner as the above styrene-acrylate copolymer resin except that 26.4 kg of styrene monomer and 2.0 kg of butyl acrylate monomer are used. A butyl copolymer resin (mass average molecular weight: 320,000) was obtained.

<Production of foam sheet>

<Example 1>
A foam sheet was produced as follows.
As polystyrene resin, 30% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and styrene-butyl acrylate copolymer resin (trade name: “HP-250”, manufactured by DIC) are used. A polystyrene resin containing 70% by mass was used.
100 parts by mass of this polystyrene-based resin, talc-kneaded polystyrene (polystyrene resin: 60% by mass, talc content: 40% by mass) (product name: “DSM1401A”) manufactured by Toyo Styrene Co., Ltd. Six parts by mass were dry blended to obtain a mixture.
Next, using a tandem extruder to which two extruders are connected (the upstream first extruder is a φ115 mm single screw extruder, and the downstream second extruder is a φ150 mm single screw extruder), and The mixture was supplied to the hopper of the first extruder, and the mixture was heated and melt-kneaded in the first extruder so that the maximum temperature setting was 230 ° C.
Further, butane gas (mixed butane gas of isobutane and normal butane) as a blowing agent is press-fitted into the first extruder so that the ratio with respect to 100 parts by mass of the polystyrene resin is 5.0 parts by mass, and melt-kneaded with the mixture. Continued.
Subsequently, the temperature of the melt-kneaded product of the resin composition was lowered to 146 ° C. with a second extruder, and a circular die (caliber: φ160 mm, slit clearance: 0.4 mm) attached to the tip of the second extruder The melt-kneaded material containing the foaming agent is extruded and foamed at a discharge rate of 200 kg / h to form a cylindrical foam, and then the inner side and the outer side of the foam 1. 6N · ^{m 3} / min, in air volume comprising an outer side 1.6 N · ^{m 3} / min blowing cooling air (temperature 30 ° C.), then, Fai675mm, the foam outer peripheral surface of the cooling mandrel length 800mm The foam is slidably contacted with the inner surface to cool the foam from the inside, and the left and right portions of the cylindrical foam are continuously cut along the extrusion direction on the rear side of the cooling mandrel. Divide into two long strip foam sheets Obtained was wound them into a roll, respectively.

<Example 2>
As polystyrene resin, 10% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and styrene-butyl acrylate copolymer resin (manufactured by DIC, trade name: “HP-250”) After using the polystyrene-based resin containing 90% by mass, and after the melt-kneading of the mixture and the foaming agent in the first extruder, the temperature of the melt-kneaded product of the resin composition is increased to 145 ° C. in the second extruder. A foamed sheet was produced in the same manner as in Example 1 except that it was lowered.

<Example 3>
As a polystyrene resin, a polystyrene resin (manufactured by DIC, trade name: “XC-515”) is 60% by mass, and a styrene-butyl acrylate copolymer resin (manufactured by DIC, trade name: “HP-250”). After using the polystyrene-based resin containing 40% by mass, and after the melt-kneading of the mixture and the foaming agent in the first extruder, the temperature of the melt-kneaded product of the resin composition is increased to 148 ° C. in the second extruder. A foamed sheet was produced in the same manner as in Example 1 except that it was lowered.

<Example 4>
As polystyrene resin, 70% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 30% styrene-butyl acrylate copolymer (manufactured by DIC, trade name: “HP-250”) After using a polystyrene-based resin containing mass%, and after melt-kneading the mixture and foaming agent in the first extruder, the temperature of the melt-kneaded product of the resin composition is lowered to 148 ° C. in the second extruder. A foamed sheet was produced in the same manner as in Example 1 except that the above was performed.

<Example 5>
As a polystyrene resin, a polystyrene resin containing 30% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 70% by mass of the styrene-butyl acrylate copolymer synthesized in Synthesis Example 3 is used. A foamed sheet was produced in the same manner as in Example 1 except that it was used.

<Example 6>
As a polystyrene resin, a polystyrene resin containing 55% by mass of a polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 45% by mass of the styrene-butyl acrylate copolymer synthesized in Synthesis Example 2 is used. A foamed sheet was produced in the same manner as in Example 1 except that it was used.

<Example 7>
As a polystyrene resin, a polystyrene resin containing 65% by mass of a polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 35% by mass of the styrene-butyl acrylate copolymer synthesized in Synthesis Example 1 is used. A foamed sheet was produced in the same manner as in Example 1 except that it was used.

<Comparative Example 1>
As polystyrene resin, 71% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 24% styrene-butyl acrylate copolymer resin (trade name “SC-004”, manufactured by PSJ) are used. A foamed sheet was produced in the same manner as in Example 1 except that the polystyrene resin containing by mass% was used.

<Comparative example 2>
As a polystyrene resin, a polystyrene resin containing 30% by mass of a polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 70% by mass of the styrene-butyl acrylate copolymer resin synthesized in Synthesis Example 1 is used. A foamed sheet was produced in the same manner as in Example 1 except that it was used and the temperature of the melt-kneaded product of the resin composition was 142 ° C. in the second extruder.

<Comparative Example 3>
Implementation was performed except that a styrene-butyl acrylate copolymer resin was used as the polystyrene resin of Synthesis Example 3 and that the temperature of the melt-kneaded product of the resin composition was 144 ° C. in the second extruder. A foamed sheet was produced in the same manner as in Example 1.

<Comparative Example 4>
Implementation was performed except that a styrene-butyl acrylate copolymer resin was used as the polystyrene resin of Synthesis Example 2 and that the temperature of the melt-kneaded product of the resin composition was 141 ° C. in the second extruder. A foamed sheet was produced in the same manner as in Example 1.

<Comparative Example 5>
As the polystyrene resin, 95% by mass of polystyrene resin (manufactured by DIC, trade name: “XC-515”) and 5% of styrene-butyl acrylate copolymer resin (trade name “HP-250”, manufactured by DIC) are used. A foamed sheet was produced in the same manner as in Example 1 except that a polystyrene resin containing mass% was used and that the temperature of the melt-kneaded product of the resin composition was 151 ° C. using a second extruder.

<Comparative Example 6>
Polystyrene resin (manufactured by DIC, trade name: “XC-515”) was used as the polystyrene resin (polystyrene resin containing only 100% by mass of polystyrene resin) and melting of the resin composition. A foamed sheet was produced in the same manner as in Example 1 except that the temperature of the kneaded product was changed to 152 ° C. by the second extruder.

  The content of acrylic acid ester in the styrene-acrylic acid ester copolymer resin used in each example and each comparative example was determined by the method described above. In addition, the open cell ratio, thickness, apparent density, basis weight, extrapolated glass transition temperature, and midpoint glass transition temperature of the foamed sheets of each Example and each Comparative Example were determined by the methods described above. The measurement results are shown in Table 1. The foamed sheets of each Example and each Comparative Example were subjected to the following test. The test results are also shown in Table 1. The DSC charts of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively.

<Low temperature formability-1>
The foam sheet was allowed to stand for 24 hours at 27 ± 3 ° C. and a relative humidity of 60 ± 5%.
Next, a flat rectangular test piece of 700 mm length × 1040 mm width was cut out from the foamed sheet.
A single molding machine (trade name “Unic Automatic Molding Machine FM-3A” manufactured by Tosei Sangyo Co., Ltd.) is prepared, the average temperature of the upper heater of this single molding machine is 255 ° C., the average temperature of the lower heater is 210 ° C., The upper ambient temperature was 175 ° C. and the lower ambient temperature was 168 ° C.
Next, the test piece was introduced into a single molding machine and heated for 5 seconds, and then a rectangular parallelepiped foamed container (length 140 mm × width 90 mm × height 17 mm) having an opening at the top was produced by thermoforming.
And the obtained container was visually observed and the moldability was evaluated according to the following criteria.
○: No cracks were observed.
Δ: Slight cracks and wrinkles were observed.
×: Other than ○ and △

<Low temperature formability-2>
The moldability was evaluated in the same manner as in the low temperature moldability-1, except that the test piece was introduced into a single molding machine, heated for 5 seconds and then thermoformed.

<Uniaxial elongation viscosity>
As a measuring device, a viscoelasticity measuring device PHYSICA MCR301 (manufactured by Anton Paar) was used.
A styrene-acrylic acid ester copolymer resin is molded into a plate shape by a hot press, and a test piece having a thickness of 1 mm, a width of 10 mm, and a length of 22 mm is prepared. Using the viscoelasticity measuring apparatus, the temperature is 160 ° C. The uniaxial extensional viscosity was measured at a strain rate of 0.5 sec ^{−1 in a} nitrogen atmosphere.
FIG. 3 shows a uniaxial extensional viscosity chart of a styrene-acrylate copolymer resin (Synthesis Example 3, HP-250) obtained by the above test method. From FIG. 3, it can be seen that the strain-hardening property is expressed in HP-250 while the strain-hardening property is not expressed in the styrene-butyl acrylate 7% copolymer resin of Synthesis Example 3.

<Heating dimensional change rate>
The foam sheet was allowed to stand for 24 hours at 27 ± 3 ° C. and a relative humidity of 60 ± 5%.
Next, a flat rectangular test piece of 700 mm length × 1040 mm width was cut out from the foamed sheet.
Then, after adjusting the heater temperature of the single molding machine so that the thickness of the test piece is about 4.0 mm when the test piece is introduced into the single molding machine and heated for 5 seconds, an opening is formed in the upper part by thermoforming. A rectangular parallelepiped foaming container (length 140 mm × width 90 mm × height 17 mm) was prepared.
It calculated | required by the method mentioned above using the produced foaming container.

<Measurement method of styrene-acrylic ester absorbance ratio>
The absorbance ratio of styrene and acrylate was measured by the following method.
Specifically, an infrared absorption spectrum was obtained only for the surface of the polystyrene-based resin foam sheet cut to 3 cm × 3 cm by the single reflection ATR method using the following measuring apparatus and measurement conditions.
Measurement apparatus: Fourier transform infrared spectrophotometer Nicolet iS10 (manufactured by Thermo SSCIENTIFIC) and single reflection type horizontal ATR Smart-iTR (manufactured by Thermo SSCIENTIFIC)
-ATR crystal: Diamond affixed KRS-5 (angle = 45 °)
・ Measuring method: One-time ATR method ・ Measured wave number region: 4000 cm ^{−1 to} 400 cm ⁻¹
-Wavenumber dependence of measurement depth: No correction-Detector: Deuterated triglycine sulfate (DTGS) detector and KBr beam splitter-Resolution: 4 cm ^-1
・ Number of integration: 16 times (same for background measurement)
The absorbance ratio of styrene and acrylate ester = D1728 / D1600 is determined from the obtained infrared absorption spectrum.
The D1728, based on the straight line connecting the lowest absorption position of wave number 1770 cm ^-1 ± ^{5 cm -1} in the infrared absorption spectrum curve, and a minimum absorption position in wavenumber 1515cm ^-1 ± ^{5cm -1} in the infrared absorption spectrum curve It is the maximum value of the absorbance difference from the baseline (measured absorbance−absorbance at the baseline) in the infrared absorption spectrum curve in the region of wave number 1728 cm ⁻¹ ± 5 cm ⁻¹ as a line, and this is the wave number 1728 cm ⁻ The absorbance at ¹ is D1728.
Further, the D1600, a straight line connecting the lowest absorption position of wave number 1770 cm ^-1 ± ^{5 cm -1} in the infrared absorption spectrum curve, and a minimum absorption position in wavenumber 1515cm ^-1 ± ^{5cm -1} in the infrared absorption spectrum curve Is the maximum value of the difference in absorbance from the baseline in the infrared absorption spectrum curve in the region of wave number 1600 cm ⁻¹ ± 5 cm ⁻¹ with respect to the baseline (measured absorbance−baseline absorbance). The absorbance at 1600 cm ⁻¹ is D1600. In addition, the obtained acrylic ester absorbance ratio is a value only for polystyrene.

As shown in Table 1, when a foamed container was produced using the foamed sheets of Examples 1 to 7 whose extrapolated glass transition start temperature and midpoint glass transition temperature were within the scope of the present invention, at least one of them was Compared with the case where a foamed container was produced using the foamed sheets of Comparative Examples 1 to 6 outside the scope of the present invention, the low-temperature moldability was excellent, and the heating dimensional change rate was small.
Therefore, according to the present invention, the foamed sheet is excellent in formability in thermoforming at a relatively low temperature, and the change in the dimensions of the container during high-temperature storage is suppressed, and thermoforming at a relatively low temperature It was found that a foamed container can be provided that is easy to manufacture and suppresses changes in container dimensions during high-temperature storage.

Claims (7)

A polystyrene-based resin foam sheet having an extrapolated glass transition start temperature (T _ig ) obtained by DSC measurement of 80 ° C. or higher and lower than 100 ° C. and a midpoint glass transition temperature (T _mg ) of 92 ° C. or higher and lower than 102 ° C.   The styrene-acrylic acid ester-based copolymer resin is contained, and the absorbance ratio D1728 / D1600 obtained by analyzing by infrared spectroscopic analysis by the ATR method is 0.2 or more and 1.3 or less. Polystyrene resin foam sheet. A resin composition obtained by melt-kneading a polystyrene resin and the styrene-acrylic acid ester copolymer resin is extruded and foamed,
The polystyrene-based resin foamed sheet according to claim 2, wherein the content of the acrylic ester in the styrene-acrylic ester copolymer resin is 1% by mass or more and less than 15% by mass.   The polystyrene resin foam sheet according to claim 2 or 3, wherein the styrene-acrylic acid ester copolymer resin exhibits strain hardening. The open cell rate is 15% or less,
The thickness is 0.7 mm or more and 3.0 mm or less,
Apparent density is not more than 0.045 g / cm ³ or more 0.3 g / cm ^3,
The polystyrene-based resin foam sheet according to any one of claims 1 to 4, wherein the basis weight is 80 g / m ² or more and 250 g / m ² or less.   A foamed container obtained by thermoforming the polystyrene-based resin foamed sheet according to claim 1.   The foaming container according to claim 6 whose heating dimensional change rate when heated at 60 ° C for 24 hours is less than 1.5%.