Polystyrene resin foam and display panel

Abstract

To provide a polystyrene resin foam and an exhibition panel which have excellent flexural strength, little warpage, and excellent surface properties.SOLUTION: A polystyrene resin foam 1 has a plate-like or sheet-like shape and includes a foam layer being an extruded foam containing a polystyrene resin. The polystyrene resin contains a butadiene component. The content of the butadiene component is 0.4-4.0 mass% based on the total mass of the foam layer. The polystyrene resin has a Z-average molecular weight (Mz) of 300,000-650,000.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polystyrene-based resin foam and an exhibition panel. [Background technology]

[0002] Conventionally, plate-shaped polystyrene resin foams have been known as display panels for affixing printed matter such as photographs, posters, advertisements, etc. For display panels, it is required that the printed matter be sufficiently adhered to the polystyrene resin foam and not peel off or lift off.

[0003] As an example of such an exhibition panel, Patent Document 1 proposes a polystyrene resin foam having a surface layer and recesses of a specific size at a specific density on the surface of the surface layer. The invention of Patent Document 1 aims to provide good paper adhesion (paper laminating properties) with glue, making it difficult for the adhered paper to peel off. Patent Document 2 proposes a sheet-like polystyrene resin foam in which the arithmetic mean roughness of the sheet surface is within a specific range and the shape of the air bubbles present within a specific depth range from the surface satisfies a specific relational expression. The invention of Patent Document 2 aims to improve surface smoothness, allowing not only UV-curable inks but also water-based inks to be printed directly on the surface.

[0004] Furthermore, polystyrene-based resin foams are required to not adhere to molds during molding and to have excellent thermal stability. Patent Document 3, for example, proposes an example of such a polystyrene-based resin foam, a styrene-based resin composition for foam molding, which contains a specific amount of a conjugated diene polymer per 100 parts by mass of styrene resin, and in which the total content of styrene dimers and styrene trimers is equal to or less than a specific concentration. The invention of Patent Document 3 aims to achieve excellent thermal stability during molding, extremely low molecular weight reduction, and excellent strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-220639 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-98509 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-315692 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, the surface of polystyrene-based resin foam may develop a surface undulation called "ripples." If rippled polystyrene-based resin foam is used, the ripples on the surface of an exhibition panel to which a printed material is attached become conspicuous, and the aesthetic quality of the surface (surface properties) is impaired. In the techniques of Patent Documents 1 to 3, no consideration is given to reducing ripples.

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a polystyrene-based resin foam and an exhibition panel that have excellent bending strength, little warping, and excellent surface properties. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following aspects. It is in the form of a plate or sheet, The foam layer is an extruded foam containing a polystyrene-based resin, The polystyrene-based resin contains a butadiene component, The content of the butadiene component is 0.4 to 4.0% by mass relative to the total mass of the foamed layer, The polystyrene resin foam has a Z-average molecular weight (Mz) of 300,000 to 650,000. The present invention also has the following aspects. [1] Plate or sheet shape, A foam layer containing a polystyrene-based resin is provided. The polystyrene-based resin contains a butadiene component, The content of the butadiene component is 0.4 to 4.0% by mass relative to the total mass of the foamed layer, The polystyrene resin foam has a Z-average molecular weight (Mz) of 300,000 to 650,000. [2] The polystyrene-based resin contains a styrene-butadiene copolymer, The polystyrene-based resin foam according to [1], wherein the content of the styrene-butadiene copolymer is 10 to 65 mass % based on the total mass of the polystyrene-based resin. [3] The polystyrene-based resin foam according to [1] or [2], wherein the molecular weight distribution (Mz / Mw) obtained by dividing the Z-average molecular weight (Mz) of the polystyrene-based resin by the mass-average molecular weight (Mw) of the polystyrene-based resin is 1.6 to 2.2. [4] The polystyrene-based resin foam according to any one of [1] to [3], wherein the polystyrene-based resin is a polystyrene-based resin derived from recycled products.

[0009] [5] An exhibition panel, comprising the polystyrene resin foam according to any one of [1] to [4], and a surface material provided on either or both surfaces thereof. [Effects of the Invention]

[0010] The polystyrene-based resin foam and display panel of the present invention have excellent bending strength, little warping, and excellent surface properties. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of a polystyrene-based resin foam according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of an apparatus for producing a polystyrene-based resin foam according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing another example of an apparatus for producing a polystyrene-based resin foam according to an embodiment of the present invention. [Figure 4] FIG. 2 is a perspective view illustrating an example of ripples formed on the surface of a polystyrene-based resin foam. [Figure 5] 1 is a photograph of the surface of a polystyrene-based resin foam of Example 5. [Figure 6] 1 is a photograph of the surface of a polystyrene-based resin foam of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, the symbol "to" indicates a range that includes the values ​​at both ends as the lower and upper limits. A preferred embodiment of the present invention will be described below using a plate-shaped polystyrene resin foam as an example. The polystyrene resin foam may be composed of a single foam layer, or may have two or more foam layers. The polystyrene resin foam may have a non-foamed resin layer provided on one side of the polystyrene resin foam, or may have non-foamed resin layers provided on both sides of the polystyrene resin foam. The non-foamed resin layer may be composed of a single non-foamed layer, or may have two or more non-foamed layers.

[0013] [Polystyrene resin foam] The polystyrene resin foam of the present invention (hereinafter also simply referred to as "foam") is a plate- or sheet-like foam having a foam layer containing a polystyrene resin. An embodiment of the foam will be described with reference to the drawings.

[0014] 1 is a foam plate made up of a first foam layer 2a and a second foam layer 2b, which are joined at a joint 3.

[0015] The thickness T1 of the foam 1 can be determined taking into consideration the intended use. For example, the thickness T1 is preferably 3.0 to 15.0 mm, more preferably 4.0 to 12.0 mm, and even more preferably 5.0 to 10.0 mm. When the thickness T1 is equal to or greater than the above lower limit, the bending strength can be further increased and warpage can be suppressed. When the thickness T1 is equal to or less than the above upper limit, the foam 1 can be made lightweight and easy to manufacture. The thickness T1 can be measured, for example, using a microgauge.

[0016] Thickness T of the first foam layer 2a 2a can be determined taking into consideration the application. For example, the thickness T 2a The thickness T is preferably 1.5 to 7.5 mm, more preferably 2.0 to 6.0 mm, and even more preferably 2.5 to 5.0 mm. 2a When the thickness T is equal to or greater than the lower limit, the flexural strength of the foam 1 can be further increased, and warping can be suppressed. 2a When is equal to or less than the upper limit, the foam 1 can be made lightweight and easy to manufacture. Thickness T 2a is determined in the same manner as the thickness T1.

[0017] Thickness T of the second foam layer 2b 2b is the thickness T 2a The thickness T 2b is the thickness T 2a It may be the same as or different from. Thickness T 2b is the thickness T 2a is calculated in the same way.

[0018] <Foam layer> The foam 1 has a first foam layer 2a and a second foam layer 2b. The first foam layer 2a and the second foam layer 2b are joined by fusion at a joint 3. The first foam layer 2a is a layer (foamed resin layer) formed by foaming a foamable resin composition containing a polystyrene-based resin, and air bubbles are formed in the resin. The resin contained in the foamable resin composition is a polystyrene-based resin. The second foam layer 2b is similar to the first foam layer 2a. Hereinafter, the physical properties of the first foamed layer 2a will be described as the foamed layer of the foam 1. The physical properties of the second foamed layer 2b are similar to those of the first foamed layer 2a, and therefore description thereof will be omitted.

[0019] The apparent density of the first foamed layer 2a is, for example, 0.04 to 0.15 g / cm 3 is preferable, and 0.05 to 0.12 g / cm 3 More preferably, 0.06 to 0.10 g / cm 3It is more preferable that the apparent density of the first foamed layer 2a is equal to or greater than the above lower limit, which further increases the bending strength of the foam 1. When the apparent density of the first foamed layer 2a is equal to or less than the above upper limit, the foam 1 can be made lightweight and easy to produce. The apparent density of the first foamed layer 2a can be determined by measuring in accordance with JIS K7222:2005 "Foamed plastics and rubber - Determination of apparent density". Specifically, the mass and apparent volume of a test piece of the first foamed layer 2a cut without changing the original cell structure are measured, and the apparent volume is calculated using the following formula (1). Apparent density (g / cm 3) of the first foam layer 2a 3 ) = mass of test piece (g) / apparent volume of test piece (cm 3 )···(1)

[0020] The basis weight of the first foam layer 2a is, for example, 50 to 600 g / m 2 is preferable, and 90 to 500 g / m 2 More preferably, 150 to 400 g / m 2 It is more preferable that the basis weight of the first foamed layer 2a is equal to or greater than the above lower limit, which further increases the bending strength of the foam 1. When the basis weight of the first foamed layer 2a is equal to or less than the above upper limit, the foam 1 can be made lightweight and easy to manufacture. The basis weight of the first foam layer 2a can be measured by the following method.

[0021] Excluding 20 mm from both ends of the width direction (TD direction) of the first foamed layer 2a, ten pieces of 10 cm x 10 cm are cut out at equal intervals in the width direction, and the mass (g) of each piece is measured to the nearest 0.001 g. The average mass (g) of each piece is calculated as 1 m 2 The value converted into the mass per unit area was used as the basis weight (g / m) of the first foam layer 2a. 2 )

[0022] The expansion ratio of the first foamed layer 2a is, for example, preferably 1.5 to 20 times, more preferably 2 to 15 times, and even more preferably 3 to 10 times. When the expansion ratio of the first foamed layer 2a is equal to or greater than the above lower limit, the impact resistance of the foam 1 can be further improved. When the expansion ratio of the first foamed layer 2a is equal to or less than the above upper limit, the surface properties of the foam 1 can be further improved. The expansion ratio of the first foamed layer 2a is calculated by dividing 1 by the apparent density (g / cm 3 ) is the value divided by

[0023] The average cell diameter of the first foamed layer 2a is, for example, preferably 80 to 450 μm, more preferably 150 to 400 μm, and even more preferably 200 to 350 μm. When the average cell diameter of the first foamed layer 2a is equal to or greater than the above lower limit, the impact resistance of the foam 1 can be further improved. When the average cell diameter of the first foamed layer 2a is equal to or less than the above upper limit, the surface properties of the foam 1 can be further improved. The average cell diameter of the first foamed layer 2a can be measured in accordance with the method described in ASTM D2842-69.

[0024] The closed cell ratio of the first foamed layer 2a is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and may be 100%. The closed cell ratio of the first foamed layer 2a can be measured in accordance with the method described in JIS K7138:2006 "Rigid foamed plastics - Determination of open cell ratio and closed cell ratio."

[0025] <Polystyrene resin> The first foam layer 2a contains a polystyrene resin. Examples of polystyrene resins include homopolymers of styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene, or copolymers thereof; copolymers of styrene-based monomers and vinyl monomers polymerizable therewith, which contain styrene-based monomers as the main component; copolymers of styrene-based monomers and rubber components such as butadiene; so-called high impact polystyrenes, which are mixtures or polymers of homopolymers of styrene-based monomers or copolymers thereof, or copolymers of styrene-based monomers and vinyl monomers with diene-based rubber polymers; and the like.

[0026] Examples of vinyl monomers polymerizable with styrene-based monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and cetyl (meth)acrylate, and bifunctional monomers such as (meth)acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, divinylbenzene, and alkylene glycol dimethacrylate. These vinyl monomers may be used alone or in combination of two or more. Here, "(meth)acrylate" refers to either or both of "acrylate" and "methacrylate", and "(meth)acrylonitrile" refers to either or both of "acrylonitrile" and "methacrylonitrile".

[0027] Examples of diene rubber polymers include polybutadiene, styrene-butadiene copolymers, and ethylene-propylene-non-conjugated diene three-dimensional copolymers. These polystyrene resins may be used alone or in combination of two or more. In this specification, the polystyrene resin refers to a resin containing 50 mol % or more of units derived from a styrene monomer.

[0028] When the polystyrene resin contains a styrene-butadiene copolymer, the content of the styrene-butadiene copolymer is preferably 10 to 65 mass %, more preferably 15 to 55 mass %, and even more preferably 20 to 45 mass %, relative to the total mass of the polystyrene resin. When the content of the styrene-butadiene copolymer is equal to or greater than the above lower limit, the surface properties of the foam 1 can be further improved. When the content of the styrene-butadiene copolymer is equal to or less than the above upper limit, the bending strength of the foam 1 can be further increased, and warpage can be suppressed.

[0029] The polystyrene-based resin may be a polystyrene-based resin not derived from a recycled product, such as general-purpose polystyrene resin (GPPS), a commercially available polystyrene-based resin, or a polystyrene-based resin newly prepared by a method such as suspension polymerization. From the viewpoint of further reducing the environmental load, the polystyrene-based resin is preferably a polystyrene-based resin derived from a recycled product. Examples of polystyrene resins derived from recycled products include those obtained by recovering used polystyrene resin foam molded articles, such as fish boxes, cushioning materials for home appliances, food packaging trays, etc., and regenerating them through a limonene dissolution method or a thermal volume reduction method. Examples of polystyrene resins derived from recycled products include those obtained by crushing scraps generated after punching food packaging trays, etc., from a polystyrene resin foam sheet, melt-kneading them, and re-pelletizing them. Examples of polystyrene-based resins derived from recycled products that can be used include those obtained by recycling molded bodies such as used foam containers, as well as non-foamed polystyrene-based resins separated and recovered from home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.), office equipment (e.g., copiers, facsimiles, printers, etc.), etc.

[0030] The Z-average molecular weight (Mz) of the polystyrene resin is 300,000 to 650,000, preferably 300,000 to 550,000, and more preferably 350,000 to 450,000. When the Mz of the polystyrene resin is at least the above lower limit, the flexural strength of the foam 1 can be further increased. When the Mz of the polystyrene resin is at most the above upper limit, the surface properties of the foam 1 can be further improved. The Mz of the polystyrene resin can be determined by the measurement method described in the Examples.

[0031] The mass average molecular weight (Mw) of the polystyrene resin is preferably 190,000 to 260,000, more preferably 200,000 to 250,000, and even more preferably 210,000 to 250,000. When the Mw of the polystyrene resin is equal to or greater than the above lower limit, the flexural strength of the foam 1 can be further increased. When the Mw of the polystyrene resin is equal to or less than the above upper limit, the surface properties of the foam 1 can be further improved. The Mw of the polystyrene resin can be determined by the same measurement method as that for the Mz of the polystyrene resin.

[0032] The number average molecular weight (Mn) of the polystyrene resin is preferably 75,000 to 110,000, more preferably 85,000 to 110,000, and even more preferably 95,000 to 105,000. When the Mn of the polystyrene resin is equal to or greater than the above lower limit, the flexural strength of the foam 1 can be further increased. When the Mn of the polystyrene resin is equal to or less than the above upper limit, the surface properties of the foam 1 can be further improved. The Mn of the polystyrene resin can be determined by the same measurement method as that for the Mz of the polystyrene resin.

[0033] The molecular weight distribution (Mz / Mw) obtained by dividing the Mz of the polystyrene resin by the Mw of the polystyrene resin is preferably 1.6 to 2.2, more preferably 1.7 to 2.1, and even more preferably 1.8 to 2.0. When the Mz / Mw of the polystyrene resin is at least the above lower limit, the flexural strength of the foam 1 can be further increased. When the Mz / Mw of the polystyrene resin is not more than the above upper limit, the occurrence of die swell (a phenomenon in which a resin composition expands during extrusion molding, causing the cross-sectional area of ​​the extrudate to exceed the cross-sectional area of ​​the die nozzle) can be suppressed, and surface properties can be further improved.

[0034] The value obtained by dividing the Mw of the polystyrene resin by the Mn of the polystyrene resin (Mw / Mn) is preferably 2.2 to 3.0, more preferably 2.3 to 2.8, and even more preferably 2.4 to 2.6. When the Mw / Mn of the polystyrene resin is at least the above lower limit, the flexural strength of the foam 1 can be further increased. When the Mw / Mn of the polystyrene resin is at most the above upper limit, the surface properties can be further improved.

[0035] The melt flow rate (MFR) of the polystyrene resin is preferably 1.0 to 10.0 g / 10 min, more preferably 2.5 to 9.0 g / 10 min, even more preferably 3.5 to 8.5 g / 10 min, and particularly preferably 4.0 to 7.9 g / 10 min. When the MFR of the polystyrene resin is equal to or greater than the above lower limit, the surface properties of the foam 1 can be further improved. When the MFR of the polystyrene resin is equal to or less than the above upper limit, the bending strength can be further improved. In this specification, the MFR of a polystyrene resin refers to a value measured by the following method.

[0036] <Melt flow rate (MFR) measurement method> (Pretreatment) Foam 1 is heat-pressed at 180°C for 5 minutes to defoam it, and the defoamed foam is cut into small pieces to prepare a sample for MFR measurement. (Measurement conditions) MFR is measured using a Yasuda Seiki Seisakusho "Melt Flow Index Tester 120-SAS" in accordance with "b) Measuring the time it takes for the piston to move a specified distance" in Method B of JIS K7210:1999 "Test methods for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastics." Measurement conditions are as follows: sample approximately 3-8 g, preheating time 5 minutes, test temperature 200°C, test load 49.03 N, piston movement distance (interval): 25 mm. Each sample is tested three times, and the average is taken as the MFR (g / 10 min).

[0037] In this specification, the styrene component means a styrene monomer obtained when the foam layer is heated and decomposed. In this specification, the butadiene component refers to butadiene monomer and 4-vinyl-1-cyclohexene monomer obtained by heating and decomposing the foam layer. The butadiene component is derived from a styrene-butadiene copolymer contained in a polystyrene-based resin.

[0038] The content of the butadiene component in the polystyrene resin is 0.4 to 4.0 mass%, preferably 0.6 to 3.5 mass%, more preferably 1.0 to 3.0 mass%, and even more preferably 1.5 to 2.5 mass%, relative to the total mass of the foam layer. When the content of the butadiene component is equal to or greater than the above lower limit, the surface properties of the foam 1 can be further improved. When the content of the butadiene component is equal to or less than the above upper limit, the bending strength of the foam 1 can be further increased, and warpage can be suppressed. The content of the butadiene component in the polystyrene resin can be determined by the following method.

[0039] <Method for measuring butadiene content> A slice of the first foam layer 2a is cut from the foam 1 using a slicer or razor, and approximately 0.1 to 0.5 mg of the sample is precisely weighed. A test specimen is prepared by wrapping the sample in a ferromagnetic metal body "Pyrofoil" manufactured by Japan Analytical Industry Co., Ltd., which has a Curie point of 590°C. The test specimen is prepared so that the ferromagnetic metal body is pressed against the sample, and the test specimen is heated in a Curie point pyrolyzer "JPS-700" manufactured by Japan Analytical Industry Co., Ltd., to decompose the sample.

[0040] The butadiene monomer and 4-vinyl-1-cyclohexene monomer produced by decomposition are measured using an Agilent Technologies GC7820A gas chromatograph (detector: FID), and the combined peak area of ​​butadiene monomer and 4-vinyl-1-cyclohexene monomer is calculated. The combined butadiene monomer and 4-vinyl-1-cyclohexene monomer constitute the butadiene component. The proportion of butadiene contained in the sample is calculated using a calibration curve prepared in advance. The standard sample used to prepare the calibration curve is St / BD=85 / 15 (CAT#07073) resin manufactured by POLYSCIENCES, INC. The gas chromatograph (GC) measurement conditions are as follows:

[0041] (Pyrolysis conditions) Heating: 590°C for 5 seconds. Oven temperature: 300℃ Needle temperature: 300℃ (GC measurement conditions) Apparatus: Agilent Technologies GC7820A gas chromatograph. Column: Agilent Technologies "DB-5" (film thickness 0.25 μm x inner diameter 0.25 mm x length 30 m).

[0042] (GC oven temperature rise conditions) Initial temperature: 50°C (hold for 0.5 minutes). -First stage heating rate: 10℃ / min (up to 200℃, holding time 0 minutes). Second stage heating rate: 20℃ / min (up to 320℃). Final temperature: 320°C (hold for 0.5 minutes). Carrier gas: He gas. ·He flow rate: 63.736mL / min. Inlet pressure: 100kPa. · Column inlet pressure: 100kPa. ·Inlet temperature: 300℃. ·Detector temperature: 300℃. Split ratio: 1 / 50

[0043] The content of the styrene component in the polystyrene resin is preferably 95 to 99.6 mass %, more preferably 94 to 99.6 mass %, and even more preferably 95 to 99 mass %, based on the total mass of the foam layer. When the content of the styrene component is equal to or greater than the above lower limit, the flexural strength of the foam 1 can be further increased, and warping can be suppressed. When the content of the styrene component is equal to or less than the above upper limit, the surface properties of the foam 1 can be further improved. The content of the styrene component in the polystyrene resin is determined by the following method.

[0044] <Method for measuring styrene component content> As in the method for measuring the butadiene content, the sample is precisely weighed to prepare a test specimen, which is then heated to decompose. The styrene monomer produced by decomposition is measured using an Agilent Technologies GC7820A gas chromatograph (detector: FID) to determine the peak area of ​​styrene monomer. The percentage of styrene contained in the sample is calculated using a calibration curve prepared in advance for the styrene monomer peak area. The standard sample used to prepare the calibration curve is suspension-polymerized PS microparticles manufactured by Sekisui Plastics Co., Ltd. The measurement conditions for gas chromatography (GC) are the same as those for the method for measuring the content of butadiene components.

[0045] The foamable resin composition contains a foaming agent. Examples of blowing agents include hydrocarbons such as propane, butane, and pentane; halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane, and difluoroethane; and among these, hydrocarbons are preferred, and butane is preferred. As butane, normal butane or isobutane may be used alone, or normal butane and isobutane may be used in combination in any ratio. These blowing agents may be used alone or in combination of two or more.

[0046] The content of the blowing agent in the expandable resin composition is, for example, preferably 0.1 to 10 parts by mass, more preferably 1 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the polystyrene resin.

[0047] The foamable resin composition may contain components other than the polystyrene resin and the foaming agent (hereinafter also referred to as "optional components"), such as a cell regulator, a stabilizer, an ultraviolet absorber, an antioxidant, a colorant, a deodorizer, a lubricant, a flame retardant, and an antistatic agent. The type of optional component is determined taking into consideration the physical properties required of the foam 1, etc. The optional components may be used alone or in combination of two or more.

[0048] Examples of the cell regulator include mixtures of inorganic powders such as talc and silica, etc. These cell regulators increase the closed cell rate of the foam 1, making it easier to form the foam layer 5. Examples of the stabilizer include calcium zinc-based heat stabilizers, tin-based heat stabilizers, and lead-based heat stabilizers. Examples of the ultraviolet absorber include cesium oxide-based ultraviolet absorbers and titanium oxide-based ultraviolet absorbers. Examples of antioxidants include cerium oxide, cerium oxide / zirconia solid solution, cerium hydroxide, carbon, carbon nanotubes, titanium oxide, and fullerene. Examples of colorants include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine, cobalt blue, calcined pigments, metallic pigments, mica, pearl pigments, zinc oxide, precipitated silica, and cadmium red. Examples of deodorizing agents include silica, zeolite, zirconium phosphate, and calcined hydrotalcite.

[0049] The content of the optional component in the foamable resin composition is, for example, preferably 0.05 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.3 to 5.0 parts by mass, relative to 100 parts by mass of the polystyrene-based resin. When the content of the optional component is equal to or greater than the above-mentioned lower limit, the effects derived from the optional component can be exerted. When the content of the optional component is equal to or less than the above-mentioned upper limit, clogging of the die or the like can be more effectively prevented, and the appearance of the foam 1 can be improved.

[0050] The polystyrene resin foam of the present invention is not limited to the present embodiment shown in FIG. 1, and various changes and modifications are possible. For example, the foam 1 is formed by fusion-bonding a first foam layer 2a and a second foam layer 2b, but the polystyrene-based resin foam may be formed of a single foam layer or three or more foam layers. By using two or more foam layers, the thickness of the polystyrene resin foam increases and the strength of the foam board increases, making it suitable for use as an exhibition panel for pasting posters on it.

[0051] The foam 1 is composed of only a foam layer and does not have a non-foamed resin layer, but a non-foamed resin layer may be provided on one or both sides of the foam layer. The presence of a non-foamed resin layer in the foam further increases the bending strength. The resin constituting the non-foamed resin layer is not particularly limited, and examples thereof include the same resins as those constituting the first foamed layer 2a. The resin constituting the non-foamed resin layer may be the same as or different from the resin constituting the first foamed layer 2a.

[0052] The thickness of the non-foamed resin layer is, for example, preferably 10 to 300 μm, more preferably 20 to 200 μm. When the thickness of the non-foamed resin layer is equal to or greater than the above lower limit, the flexural strength of the foam can be further increased. When the thickness of the non-foamed resin layer is equal to or less than the above upper limit, the weight of the foam can be reduced.

[0053] When the foam has a non-foamed resin layer, the non-foamed resin layer may be laminated directly onto the surface of the foam by heat fusion or the like, or may be laminated via an adhesive. The adhesive may be an oil-based adhesive using an organic solvent as the main solvent, an aqueous adhesive using water as the main solvent, or a heat-fusible adhesive (hot-melt adhesive) using a heat-fusible resin. Examples of aqueous adhesives that can be used include emulsion-based aqueous adhesives such as starch, modified starch, casein, carboxymethyl cellulose, hydroxycellulose, soy protein, polyvinyl acetate, ethylene-vinyl acetate-acrylic copolymer, ethylene-vinyl acetate copolymer, and acrylic-modified vinyl acetate copolymer. Examples of hot-melt adhesives include synthetic rubber-based hot-melt adhesives, polyolefin-based hot-melt adhesives, and polyester-based hot-melt adhesives.

[0054] The foam 1 of this embodiment has a butadiene component content of 0.4 to 4.0 mass% relative to the total mass of the foam layer, and the Mz of the polystyrene resin is 300,000 to 650,000, so it has excellent bending strength, little warping, and an excellent surface.

[0055] [Method of manufacturing polystyrene foam] The method for producing foam 1 includes the steps of melting a polystyrene resin, kneading the molten polystyrene resin with a foaming agent to form a molten mixture, and extruding and foaming the molten mixture to obtain a foam layer. As a suitable method for producing the foam 1, a known method for producing a foam can be adopted, and for example, the following production method can be mentioned. An example of a method for producing the foam 1 will be described below using a foam production apparatus 100 shown in FIG.

[0056] 2 is an apparatus for producing a foam by extrusion molding. The apparatus 100 includes an extruder 10, a blowing agent supply source 18, a circular die 20 attached to the tip of the extruder 10, a guide roller 24 that sends the tubular foam 2 extruded and foamed from the discharge outlet of the circular die 20 to a pinch roll 30, and the pinch roll 30 that presses the tubular foam 2 into a plate shape.

[0057] The extruder 10 is a so-called single-type extruder. The extruder 10 includes a hopper 14. A blowing agent supply source 18 is connected to the extruder 10.

[0058] The extruder 10 of the production apparatus 100 may be an extruder other than a single extruder. For example, the extruder 10 may be a so-called tandem extruder (FIG. 3). The tandem extruder includes a first extrusion section 11 and a second extrusion section 12 connected to the first extrusion section 11 by a pipe 16. The first extrusion section 11 includes a hopper 14. A foaming agent supply source 18 is connected to the first extrusion section 11. A circular die 20 is connected to the second extrusion section 12. Downstream of the circular die 20, a guide roller 24 is provided to send the cylindrical foam 2 extruded and foamed from the discharge outlet of the circular die 20 to a pinch roll 30, and the pinch roll 30 is provided to sandwich and press the cylindrical foam 2 into a plate shape. Furthermore, the extruder 10 of the production apparatus 100 may be a single-screw extruder or a multi-screw extruder such as a twin-screw extruder.

[0059] The raw materials constituting the foam layer are fed from a hopper 14 into the extruder 10. The raw materials fed from the hopper 14 include the resin constituting the foam layer and any optional components that are blended as needed. In the extruder 10, the raw materials are mixed while being heated to a desired temperature to form a resin melt, and a foaming agent is supplied to the extruder 10 from a foaming agent supply source 18, and the foaming agent is mixed with the resin melt to form a foamable resin composition. The heating temperature is appropriately determined in consideration of the type of resin, etc., so long as the resin melts and the optional components are not denatured.

[0060] The heating temperature may be any temperature at which styrene softens, and is, for example, preferably 100 to 180°C, more preferably 110 to 170°C, and even more preferably 120 to 160°C. When the heating temperature is equal to or higher than the lower limit, the cylindrical foam 2 is sufficiently softened, and the first foam layer 2a and the second foam layer 2b can be neatly fusion-bonded. When the heating temperature is equal to or lower than the upper limit, excessive softening of the outer surface of the cylindrical foam 2 can be prevented, and the surface properties can be further improved.

[0061] The foamable resin composition is heated and extruded from the discharge opening of a circular die 20 attached to the tip of the extruder 10, and is simultaneously foamed. At this time, the discharge opening of the circular die 20 is annular, and a tubular foam 2 is formed. The tubular foam 2 is cooled by air 26 sent from an air-ring device (not shown) provided downstream of the circular die 20, and is sent to a pinch roll 30 by a guide roller 24.

[0062] Before the inside of the cylindrical foam 2 cools down completely, the cylindrical foam 2 is pressed from above and below with a pair of pinch rolls 30 to be heat-sealed, thereby forming a foam 1 in which two foam layers are fused together.

[0063] The pressure when the cylindrical foam 2 is squeezed with the pinch rolls 30 is preferably 0.1 to 1.1 MPa, more preferably 0.2 to 1.0 MPa, and even more preferably 0.3 to 0.9 MPa. When the pressure when the cylindrical foam 2 is squeezed with the pinch rolls 30 is equal to or greater than the above-mentioned lower limit, the first foam layer 2a and the second foam layer 2b can be sufficiently bonded together. When the pressure when the cylindrical foam 2 is squeezed with the pinch rolls 30 is equal to or less than the above-mentioned upper limit, the first foam layer 2a and the second foam layer 2b are not excessively crushed, and the surface properties can be further improved.

[0064] The foam 1 may then be cut to a desired size, or its surface may be printed. The foam 1 may also be provided with a non-foamed resin layer.

[0065] Examples of methods for providing a non-foamed resin layer on a foamed body include the following methods (1) to (4). (1) A method in which the resin that will become the non-foamed resin layer is fed into an extruder, and the molten resin for forming the non-foamed resin layer is extruded onto the foam from a T-die attached to the tip of the extruder. (2) A method using a co-extrusion device equipped with two extruders, in which foam extrusion of a foam is carried out by one extruder, and a resin for forming a non-foamed resin layer is co-extruded from the other extruder. (3) A method of laminating a resin film that will become a non-foamed resin layer onto the surface of a foam by heat and pressure bonding. (4) A method in which a resin film that will become a non-foamed resin layer is adhered to the surface of a foam using an adhesive. When a polystyrene resin is used as the non-foamed resin layer, the above methods (1) to (3) are preferred in which the non-foamed resin layer is formed on the surface of the foam without using an adhesive.

[0066] In the foam manufacturing method of this embodiment, by heating both sides of the foam layer and stacking multiple sheets and then applying a pinch pressure, the residual stress in the foam layer can be reduced. As a result, the foam warps less and the surface properties are improved. In addition, because the foam warps less, paper lifting after lamination can be suppressed. In particular, the effect of the present invention is remarkable in that warping and dimensional changes can be suppressed in high temperature environments such as during transportation and storage in summer.

[0067] An example of ripples formed on the surface of a polystyrene-based resin foam will be described with reference to FIG. As shown in FIG. 4, ripples are formed on the surface of the foam 4 over the entire area indicated by A. 4, X indicates the width direction (TD direction) of the resin, and Y indicates the extrusion direction (MD direction) of the resin. The TD direction is a direction perpendicular to the MD direction.

[0068] In the region indicated by A, ripples are formed along the TD direction. Unlike surface irregularities, the ripples are thought to be caused by a phenomenon called die swelling, in which the foamable resin composition expands during extrusion molding, causing the cross-sectional area of ​​the extrudate to become larger than the cross-sectional area of ​​the die nozzle. When die swelling occurs, the shrinkage of the foamable resin composition varies greatly when it cools. This shrinkage variation is thought to be the cause of the ripples. As shown in Figure 4, ripples tend to form along the TD direction. However, ripples can also form along the MD direction. Ripples can also form along directions other than the TD and MD directions, and can also form on part of the surface of a foam.

[0069] In order to suppress the formation of ripples, it is thought that suppressing the occurrence of die swell is effective. The foam of the present invention has a butadiene content of 0.4 to 4.0 mass% based on the total mass of the foam layer, and the polystyrene resin has an Mz of 300,000 to 650,000, which can suppress the occurrence of die swelling, and therefore the foam of the present invention has excellent surface properties.

[0070] [Exhibition panel] The display panel of the present invention is made by cutting the foam 1 of the present invention, manufactured by the above-mentioned manufacturing method, to the desired dimensions as needed to form a panel body, and providing a skin material on both or one side of the panel body. If a skin material is provided on the surface of the foam 1, the bending strength can be further increased, and the surface properties can be further improved. Examples of the skin material include fine paper, glassine paper, parchment paper, kraft paper, synthetic paper, release paper, tack paper, etc. One type of skin material may be used alone, or two or more types may be used in combination.

[0071] The method for providing the surface of the foam 1 with a skin material is not particularly limited. For example, the skin material may be provided using the adhesive described above, or may be provided using a thumbtack or adhesive tape. From the viewpoint of making the appearance of the display panel beautiful, it is preferable that the skin material be provided using the adhesive described above.

[0072] The display panel may further have a printed layer on the surface of the skin material. The method for providing the printed layer is not particularly limited, but inkjet printing is preferably used. Both UV inks and water-based inks can be used for inkjet printing. These inks can be appropriately selected from various commercially available inkjet printing inks. Furthermore, depending on the curing characteristics of the ink used, it is preferable that the inkjet printer be equipped with a UV light source for irradiating ultraviolet light immediately after printing, a heater or dryer for drying, or the like.

[0073] As described above, the display panel of the present invention uses the foam 1, which has little warping and excellent surface properties, as the panel body, and therefore can be used as an display panel on which extremely clear and beautiful printing can be performed. [Example]

[0074] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following descriptions.

[0075] First, the polystyrene resins shown in Table 1 were prepared as the polystyrene resin foams.

[0076] [Table 1]

[0077] The raw materials shown in Table 1 are as follows: HIPS: Product name "E-641N", high impact polystyrene, manufactured by Toyo Styrene Co., Ltd. GPPS: Product name "G0002", general-purpose polystyrene, manufactured by PS Japan Co., Ltd. GPPS: Product name "HRM48N", general-purpose polystyrene, manufactured by Toyo Styrene Co., Ltd. GPPS: Product name "HRM10N", general-purpose polystyrene, manufactured by Toyo Styrene Co., Ltd. HIPS, GPPS mixture: PS1, a mixture of high impact polystyrene and general-purpose polystyrene, a recycled pellet product of the foam scraps obtained in Example 4. HIPS, GPPS mixture: PS2, a mixture of high impact polystyrene and general-purpose polystyrene, a recycled pellet product of the foam scraps obtained in Example 5.

[0078] [Example 1] <Production of polystyrene resin foam> An extruder consisting of a 115 mm inner diameter extruder and a 150 mm inner diameter extruder connected together was prepared. A blended raw material containing 100 parts by mass of polystyrene resin (90 parts by mass of "G0002" manufactured by PS Japan Co., Ltd. and 10 parts by mass of "E-641N" manufactured by Toyo Styrene Co., Ltd.), 0.5 parts by mass of talc (manufactured by Kihara Chemical Co., Ltd.), and 1.2 parts by mass of talc masterbatch (manufactured by Toyo Styrene Co., Ltd. under the trade name "DSM1401A") was added to the extruder. The blended raw material was melted and kneaded at a maximum temperature of 230°C in the extruder. After kneading, 4.0 parts by mass of butane (isobutane / normal butane mass ratio: 68% / 32%) was added as a foaming agent and mixed with the resin to produce a foamable resin composition (molten resin). The molten resin was cooled to a resin temperature (148°C) suitable for foaming. The molten resin was then extruded into the atmosphere through a circular die with a 160mm diameter and a 1.0mm slit clearance, which was attached to the tip of the extruder, and foamed. Cooling air (40°C) was blown onto the outer surface of the extruded cylindrical foam, and the foam was cooled while being pressed from above and below with alligator jaw rolls to fuse the two layers. After cooling, the foam was cut into a thickness of 5mm, length of 935mm, width of 630mm, and basis weight of 320g / m. 2 A board-shaped polystyrene resin foam (foam board) was obtained.

[0079] [Examples 2 to 16, Comparative Examples 1 to 3] A foam board was obtained in the same manner as in Example 1, except that the polystyrene resin was blended as shown in Tables 2 and 3. In the tables, "-" indicates that the component was not blended.

[0080] The butadiene component content and styrene component content of the foam board of each example were measured according to the above <Method for measuring butadiene component content> and <Method for measuring styrene component content>. The thickness, apparent density, molecular weight and MFR of the foamed board of each example were measured by the following methods. The results are shown in Tables 2 and 3.

[0081] <Thickness measurement> The thickness of the resulting foam board was measured using a thickness measuring instrument SM-114 (manufactured by TECLOCK).

[0082] <Measurement of apparent density> The apparent density (g / cm) of the obtained foam board 3 ) is calculated by measuring its mass and apparent volume and dividing the mass (g) by the apparent volume (cm 3 ) was calculated.

[0083] <Molecular weight measurement> The method for measuring the Z-average molecular weight Mz of the polystyrene resin in the foam board obtained in each example is shown below. The mass-average molecular weight Mw and the number-average molecular weight Mn of the polystyrene resin were measured in the same manner as the Z-average molecular weight Mz of the polystyrene resin.

[0084] The foamed board obtained in each example was cut with a slicer or a razor and collected as a sample. The sample was pretreated to obtain a filtrate under the following measurement conditions, and the Z-average molecular weight Mz of the polystyrene resin was measured.

[0085] <Measurement conditions> (Pretreatment) 6 mg of the collected sample was dissolved in 6 mL of tetrahydrofuran (THF) (immersion time: 6±1 hr (complete dissolution)) to obtain a sample solution. The sample solution was filtered using a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu GLC Co., Ltd. to obtain a filtrate.

[0086] The filtrate obtained in the above pretreatment was used to measure the Z-average molecular weight Mz of the polystyrene resin under the following measurement conditions and with the following measurement device. (Measuring equipment) GPC device: Tosoh Corporation, HLC-8320GPC (with built-in RI detector and UV detector). Guard column: TOSOH TSK guard column SuperMP(HZ)-H (4.6mm I.D. x 2cm) x 1 Column (reference): TOSOH TSKgel Super HZ1000 (6.0 mm I.D. x 15 cm) x 1 Column (sample): Two TSKgel SuperMultipore HZ-H (4.6 mm I.D. × 15 cm) in series. (Measurement conditions) Column temperature: 40 °C. Detector temperature: 40 °C. Pump injection part temperature: 40 °C. Solvent: THF. Flow rate (reference): 0.2 mL / min. Flow rate (sample): 0.2 mL / min. Running time: 21 min. Data integration time: 6 - 25 min. Data interval: 200 msec. Injection volume: 20 μL. Detector: RI.

[0087] (Standard polystyrene sample for calibration curve) The standard polystyrene samples for calibration curve were those with weight-average molecular weights Mw of 5,620,000, 3,120,000, 1,250,000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, and 1,320, which were produced by Showa Denko K.K. under the product names "STANDARD SM-105" and "STANDARD SH-75". The above standard polystyrene for calibration curve was grouped into A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (3,120,000, 442,000, 53,500, 7,660, 1,320). After weighing A (2 mg, 3 mg, 4 mg, 4 mg, 4 mg), it was dissolved in 30 mL of THF. After weighing B (3 mg, 4 mg, 4 mg, 4 mg, 4 mg), it was dissolved in 30 mL of THF. The standard polystyrene calibration curve was obtained by creating a calibration curve (linear equation) from the retention times obtained after injecting 20 μL of each of the prepared A and B solutions for measurement. The Z-average molecular weight Mz was calculated using this calibration curve.

[0088] (Measurement of MFR) (Pretreatment) The foamed plate obtained in each example was degassed by hot pressing at 180°C for 5 minutes, and the degassed foamed plate was cut into small pieces to prepare samples for MFR measurement. (Measurement conditions) MFR was measured using a Yasuda Seiki Seisakusho "Melt Flow Index Tester 120-SAS" in accordance with "b) Measuring the time it takes for the piston to move a specified distance" in Method B of JIS K7210:1999 "Test methods for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastics." Measurement conditions were as follows: sample weight approximately 3-8 g, preheating time 5 minutes, test temperature 200°C, test load 49.03 N, piston movement distance (interval): 25 mm. Each sample was tested three times, and the average was used as the MFR (g / 10 min).

[0089] The foamed boards obtained in each example were evaluated for bending strength, warpage, and surface properties according to the following evaluation methods, and an overall evaluation was carried out. The results are shown in Tables 2 and 3.

[0090] <Bending strength evaluation> The bending strength was measured using a Tensilon universal testing machine "RTC-1310A" manufactured by Orientec Co., Ltd. Test specimens were cut to dimensions of 50 mm width x 150 mm length x thickness (thickness for each example) in the extrusion direction (MD) and the direction perpendicular to the extrusion direction (TD). Three test specimens were cut for each direction. The measurement conditions were a test speed of 50 mm / min, a radius of 3.2R at the tip of the pressure wedge and fulcrum, and a distance between the fulcrums of 100 mm. Three-point bending measurements were performed on each test specimen, and the maximum point load was taken as the bending strength (N) of the foam board. Next, the average value (N) of the bending strength (N) in the MD and TD directions was used to evaluate the strength based on the following evaluation criteria. Evaluation Criteria A: The average bending strength is 13N or more... The bending strength is extremely high and excellent. B: The average bending strength is 12N or more and less than 13N. The bending strength is sufficiently high and good. C: The average bending strength is 10N or more but less than 12N... The bending strength is low, but acceptable. D: The average bending strength is less than 10 N. The bending strength is extremely low and poor.

[0091] <Evaluation of the amount of warpage> The foam plate was left to stand for 24 hours in an environment of 23°C and a relative humidity of 50%RH, and the amount of warping was measured by the following measurement method. The two opposing longitudinal sides (long sides) of a rectangular foam board in plan view, measuring 935 mm in length (MD, long side) and 630 mm in width (TD, short side), were placed against a horizontal surface, and the greatest lift distance from the horizontal surface (the distance (mm) from the horizontal surface to the bottom surface of the foam board) was measured, and this measurement was taken as the amount of warpage (mm) in the TD (short side). Next, the two opposing lateral sides (short sides) of the foam board were placed against a horizontal surface, and the greatest lift distance from the horizontal surface (the distance (mm) from the horizontal surface to the bottom surface of the foam board) was measured, and this measurement was taken as the amount of warpage (mm) in the MD (long side). Next, the average value (mm) of the warpage in the TD direction (short side) and the warpage in the MD direction (long side) was used to make a judgment based on the following evaluation criteria. Evaluation Criteria A: The average amount of warping is less than 5 mm... The amount of warping is extremely small and excellent. B: The average amount of warpage is 5 mm or more and less than 7 mm. The amount of warpage is sufficiently small and good. C: The average amount of warping is 7 mm or more and less than 10 mm. The amount of warping is small and acceptable. D: The average amount of warpage is 10 mm or more. The amount of warpage is large and poor.

[0092] <Evaluation of surface properties> The surface of the obtained foam board was visually observed and the surface properties were evaluated based on the following evaluation criteria. Evaluation Criteria A: No ripples are observed. B: Ripples are barely noticeable. C: Ripples slightly mar the appearance, but are acceptable. D: Ripples clearly mar the appearance and it is poor.

[0093] <Overall rating> Based on the results of the above-mentioned <Evaluation of bending strength>, <Evaluation of warpage amount> and <Evaluation of surface properties>, an overall evaluation was made based on the following evaluation criteria. Evaluation Criteria S: All ratings are "A". A: All ratings are either "A" or "B", with one "B" rating. B: There are no "C" or "D" ratings and two or more "B" ratings, or there are no "D" ratings and one "C" rating. C: No "D" grades and two or more "C" grades. D: One or more "D" ratings.

[0094] [Table 2]

[0095] [Table 3]

[0096] As shown in Tables 2 and 3, Examples 1 to 16 to which the present invention was applied received an overall evaluation of "S" to "C." In contrast, Comparative Example 1, in which the butadiene component content was outside the range of the present invention, was evaluated as "D" for surface properties and as "D" for overall evaluation. Comparative Example 2, in which the butadiene component content was outside the range of the present invention, was evaluated as "D" for warpage and as "D" for overall evaluation. Comparative Example 3, which did not contain a butadiene component and in which the butadiene component content was outside the range of the present invention, was evaluated as "D" for surface properties and as "D" for overall evaluation.

[0097] FIG. 5 shows a photograph of the surface of the foam plate of Example 5. As shown in FIG. 5, no ripples were observed on the surface of the foamed plate of Example 5, indicating that the surface was excellent.

[0098] FIG. 6 shows a photograph of the surface of the foam plate of Comparative Example 3. As shown in FIG. 6, ripples were clearly observed on the surface of the foamed board of Comparative Example 3, impairing the appearance.

[0099] These results demonstrate that the polystyrene resin foam of the present invention has excellent bending strength, little warping, and an excellent surface quality. [Explanation of symbols]

[0100] 1. Polystyrene resin foam (foam board) 2a First foam layer 2b Second foam layer 3 Joint

Claims

1. It is in the form of a plate or sheet, The foam layer is an extruded foam containing a polystyrene-based resin, The foam layer has a thickness of 4.0 to 15.0 mm, The polystyrene-based resin contains a butadiene component, the content of the butadiene component is 0.4 to 4.0% by mass relative to the total mass of the foamed layer; The polystyrene-based resin foam has a Z-average molecular weight (Mz) of 300,000 to 650,000.

2. The polystyrene-based resin foam according to claim 1 , wherein the polystyrene-based resin is a polystyrene-based resin derived from recycled products.

3. 3. An exhibition panel, comprising the polystyrene resin foam according to claim 1 or 2, and a surface material provided on either or both surfaces thereof.

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