Extruded polystyrene resin foam board and process for producing the same

Abstract

To produce a polystyrene-based resin extruded foam plate in which shrinkage after production is suppressed even when the density is low.SOLUTION: A method for producing an extruded polystyrene foam board having an apparent density of 10kg / m3 or more and 40kg / m3 or less and a volume 20000cm3 or more, the method comprising the step of extruding and foaming a foamable melt obtained by melt-kneading a polystyrene resin-containing base material and a physical blowing agent, and forming the foamable melt into a board shape with a forming tool, wherein the polystyrene resin component has a stress-relaxation time τ of 100 seconds or more as measured by the following tensile stress-relaxation test (I): Tensile stress relaxation test (I) In accordance with JISK7127:1999, when a 20% tensile strain is applied to a 0. 4-mm-thick dumbbell-shaped test piece type 5 made of polystyrene resin at a tensile speed of 50m / min in an atmosphere of 80 °C, and the tensile strain is maintained for 4 minutes from the point in time at which the 20% tensile strain is applied, the initial stress at the point in time at which the 20% tensile strain is applied is set as a reference value, and the time required until the stress reaches one tenth of the reference value is set as a stress relaxation time τ.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an extruded polystyrene resin foam board and a method for producing an extruded polystyrene resin foam board. [Background technology]

[0002] Extruded polystyrene resin foam boards (hereinafter simply referred to as "extruded foam boards") are widely used as building insulation materials and civil engineering materials due to their excellent thermal insulation properties and mechanical strength. Such extruded foam boards are generally produced by heating and melting a base resin containing a polystyrene resin as a main component in an extruder, pressurizing a physical foaming agent into the resulting melt, and further melt-kneading the resulting foamable molten resin mixture, which is extruded into a low-pressure region through a flat die or the like attached to the tip of the extruder, foaming it, and molding it into a board shape using a molding tool.

[0003] In recent years, there has been a demand for further weight reduction in extruded polystyrene resin foam boards by increasing the expansion ratio and lowering the density. For example, Patent Document 1 describes a polystyrene foam board with an apparent density of about 26 kg / m 3 and an extruded polystyrene resin foam board having a relatively high expansion ratio.

[0004] However, when the density of the extruded foam board is further reduced in the technology of Patent Document 1, the resulting extruded foam board may experience significant shrinkage after production. 3 In the production of extruded polystyrene resin foam boards, a technology is disclosed in which shrinkage is suppressed by using a polystyrene resin as a raw material having a weight average molecular weight in the range of 200,000 to 350,000 as determined by the GPC method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-203848 [Patent Document 2] Special Publication No. 62-30218 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even with the technology of Patent Document 2, when an attempt is made to lower the density of the extruded foam board to further reduce its weight, the resulting extruded foam board suffers from significant shrinkage after production. In consideration of the above circumstances, an object of the present invention is to provide an extruded polystyrene resin foam board that has a low density but is suppressed from shrinking after production. [Means for solving the problem]

[0007] [1] A foaming method comprising the steps of extruding and foaming a foamable molten material obtained by melt-kneading a base resin containing a polystyrene-based resin and a physical foaming agent, and molding the foamed material into a plate shape using a molding tool, and an apparent density of 10 kg / m 3 More than 40kg / m 3 Below, volume 20,000 cm 3 The method for producing the above extruded polystyrene resin foam board, wherein the stress relaxation time τ of the polystyrene resin is 100 seconds or more as measured by the following tensile stress relaxation test (I). Tensile stress relaxation test (I) In accordance with JIS K7127:1999, a 20% tensile strain is applied to a 0.4 mm thick dumbbell-shaped test piece of type 5 polystyrene resin in an atmosphere of 80°C at a tensile speed of 50 m / min, and the tensile strain is maintained for 4 minutes from the time when the 20% tensile strain is applied. The initial stress at the time when the 20% tensile strain is applied is defined as a reference value, and the time required for the stress to decrease to one-tenth of the reference value is defined as the stress relaxation time τ.

[0008] [2] The method for producing an extruded polystyrene resin foam board according to [1], wherein the polystyrene resin is a mixed resin containing a polystyrene resin (A) and a polystyrene resin (B), and the weight average molecular weight Mw'A of the polystyrene resin (A) measured by GPC-MALS method is 700,000 or more and 3,000,000 or less, and the weight average molecular weight Mw'B of the polystyrene resin (B) measured by GPC-MALS method is 100,000 or more and less than 700,000.

[0009] [3] The method for producing an extruded polystyrene resin foam board according to [2], wherein the polystyrene resin (A) has an average shrinkage factor of 0.80 or less as determined by a GPC-MALS-VISCO method, and the polystyrene resin (A) has a tetrahydrofuran-insoluble content of 0.1% by mass or less (including 0).

[0010] [4] The method for producing an extruded polystyrene resin foam board according to [2] or [3], wherein the polystyrene resin (A) does not contain components derived from polyfunctional monomers in the molecular chain.

[0011] [5] The method for producing an extruded polystyrene resin foam board according to any one of [2] to [4], wherein the mass proportion of the polystyrene resin (A) is 15 mass% or more and 90 mass% or less based on 100 mass% of the total of the polystyrene resin (A) and the polystyrene resin (B).

[0012] [6] The method for producing an extruded polystyrene resin foam board according to any one of [2] to [5], wherein the weight-average molecular weight Mw'B of the polystyrene resin (B) measured by the GPC-MALS method is 500,000 or more but less than 700,000, and the average shrinkage factor measured by the GPC-MALS method is 0.95 or less.

[0013] [7] The branching degree T per 1000 styrene units of the polystyrene resin (A) m,1000 A is 0.2 or more, and the branching degree T per 1000 styrene units of the polystyrene resin (B) m,1000 Absolute value of the difference with B│(T m,1000 A)-(Tm,1000 B)| is 0.5 or less.

[0014] [8] The method for producing an extruded polystyrene resin foam board according to any one of [1] to [7], wherein the physical blowing agent contains water and / or aliphatic alcohol having 1 to 5 carbon atoms, and the total amount of the water and / or aliphatic alcohol having 1 to 5 carbon atoms added is 0.7 mol or more and 2 mol or less per kg of the base resin.

[0015] [9] Apparent density 10 kg / m 3 More than 40kg / m 3 Below, volume 20,000 cm 3 The above-mentioned extruded polystyrene resin foam board, wherein the average value of the cell deformation ratio of the vertical cross section (TD cross section) perpendicular to the extrusion direction of the extruded polystyrene resin foam board is 0.85 to 1.10 and the coefficient of variation thereof is 3.0% or less, and the average value of the cell deformation ratio of the vertical cross section (MD cross section) perpendicular to the width direction of the extruded polystyrene resin foam board is 1.05 to 1.30 and the coefficient of variation thereof is 3.0% or less.

[0016]

[10] The extruded polystyrene resin foam board according to [9], wherein the average cell diameter in the thickness direction of the extruded polystyrene resin foam board is 250 μm or more and 600 μm or less. [Effects of the Invention]

[0017] According to the production method of the present invention, it is possible to produce an extruded polystyrene resin foam board that is suppressed in shrinkage after production and has excellent dimensional stability, even if the density is low. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram showing the cutting positions of samples from an extruded foam plate for measuring cell diameter and cell deformation rate. [Figure 2] 1 is a graph showing the results of a simulation performed during the production of a polystyrene resin used in an example. [Figure 3] FIG. 2 is a schematic diagram showing how to determine the average dimensions in each direction of an extruded foam board. [Figure 4] FIG. 2 is a schematic diagram showing how to determine the average dimensions in each direction of a shrunk extruded foam board. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Method of manufacturing extruded polystyrene resin foam board> The production method of the present invention includes a step of extruding and foaming a foamable molten material obtained by melt-kneading a base resin containing a polystyrene-based resin (X) and a physical foaming agent, and molding the extrudate into a plate shape using a molding tool (hereinafter referred to as the "molding step"). 3 More than 40kg / m 3 Below, volume 20,000 cm 3 The above is a method for producing an extruded polystyrene foam board (hereinafter simply referred to as "extruded foam board"). The extruded foam board produced by the production method of the present invention has a stress relaxation time τ of 100 seconds or more as measured in a predetermined tensile stress relaxation test (I). The details of the tensile stress relaxation test (I) will be described later.

[0020] In one example of the manufacturing method according to the present invention, a base resin primarily composed of a polystyrene resin (X) and optional additives are first melted and kneaded in an extruder under heating to obtain a molten mixture, which is then further kneaded with a physical foaming agent to obtain a foamable molten resin. Next, in the molding process, the foamable molten resin is adjusted to an appropriate foaming temperature, extruded from the high-pressure extruder through a flat die into a low-pressure region, and foamed. The foam is then passed through a molding tool (e.g., a molding die or molding roll) located at the outlet of the flat die to form a plate-shaped extruded foam board. The molding die is, for example, a guider composed of two plates of polytetrafluoroethylene resin or the like, arranged parallel to each other or so as to gradually expand from the inlet to the outlet.

[0021] [Polystyrene resin (X)] In the manufacturing method of the present invention, a polystyrene-based resin (X) is used as a component contained in the base resin. The polystyrene-based resin (X) is a polymer containing 50 mol% or more of styrene unit components, and refers to a styrene homopolymer or a copolymer of styrene and a vinyl monomer copolymerizable with styrene. Specific examples include polystyrene, and one or more selected from the group consisting of styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-polyphenylene ether copolymer, styrene-acrylonitrile copolymer, styrene-methylstyrene copolymer, styrene-dimethylstyrene copolymer, styrene-ethylstyrene copolymer, and styrene-diethylstyrene copolymer. Among these, polystyrene is preferably used. In addition to the styrene unit components, the polystyrene may also contain unit components derived from a branching agent such as a polyfunctional monomer or a polyfunctional macromonomer. The content of styrene component units in the copolymer is preferably 60 mol % or more, more preferably 80 mol % or more, and even more preferably 90 mol % or more.

[0022] The base resin of the present invention preferably contains a polystyrene resin (X) as a main component. A base resin containing a polystyrene resin (X) as a main component means that 50% by mass or more of the base resin is polystyrene resin (X), preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more of the base resin is polystyrene resin (X).

[0023] (1) Melt viscosity η The melt viscosity η of polystyrene resin (X) is 200°C, shear rate 100 sec -1Under these conditions, the melt viscosity η is preferably 1000 Pa·s or more and 4000 Pa·s or less, more preferably 1200 Pa·s or more and 3500 Pa·s or more, and even more preferably 1500 Pa·s or more and 3000 Pa·s or less. In this specification, the melt viscosity η is a value measured in accordance with JIS K7199:1999. The melt viscosity is measured using a Capilograph 1D manufactured by Toyo Seiki Seisaku-sho, Ltd.

[0024] (2) Melt tension From the viewpoints of improving production stability and improving the appearance of the resulting extruded foam board, the melt tension of the polystyrene resin (X) is preferably 200 mN or more, more preferably 350 mN or more, even more preferably 400 mN or more, and particularly preferably 450 mN or more. The upper limit of the melt tension of the polystyrene resin (X) is not particularly limited, but is, for example, 1000 mN.

[0025] The melt tension of the polystyrene resin (X) is measured in accordance with ASTM D1238 using, for example, a Capilograph 1D (manufactured by Toyo Seiki Seisakusho, Ltd.) using a cylinder with a diameter of 9.55 mm and a length of 350 mm and an orifice with a nozzle diameter of 2.095 mm and a length of 8.0 mm. The cylinder and orifice are set to a temperature of 200°C, the required amount of sample is placed in the cylinder, and after leaving it for 4 minutes, the molten resin is extruded from the orifice in a string shape at a piston speed of 10 mm / min. This string-like material is hung on a tension detection pulley with a diameter of 45 mm. The string-like material is taken up by a take-up roller while the take-up speed is increased at a constant rate so that it reaches 200 m / min from 0 m / min in 4 minutes, and the maximum tension value just before the string-like material breaks is obtained.

[0026] The reason for setting the time required for the take-up speed to reach 200 m / min from 0 m / min to 4 minutes is to suppress thermal degradation of the resin and to improve the reproducibility of the obtained values. The above procedure was repeated 10 times using different samples, and the three largest and three smallest maximum values ​​obtained from the 10 measurements were discarded. The arithmetic mean of the remaining four intermediate maximum values ​​was taken as the melt tension (mN).

[0027] However, when the melt tension is measured by the above-mentioned method and the string-like material does not break even when the take-up speed reaches 200 m / min, the melt tension (mN) obtained by keeping the take-up speed at a constant speed of 200 m / min is used. Specifically, in the same manner as in the above-mentioned measurement, the molten resin is extruded in a string-like form from the orifice, and this string-like material is hung on a tension detection pulley. The take-up roller is rotated while increasing the take-up speed at a constant rate so that it reaches 200 m / min from 0 m / min over 4 minutes, and the system is left waiting until the rotation speed reaches 200 m / min. After the rotation speed reaches 200 m / min, data collection of the melt tension begins, and data collection is completed after 30 seconds. The maximum tension (T) obtained from a tension load curve obtained during these 30 seconds, with the melt tension on the vertical axis and the time on the horizontal axis, is used. max ) and minimum tension (T min ) average value (T ave ) is the melt tension.

[0028] When two or more polystyrene resins are mixed as the polystyrene resin (X), the melt viscosity η and melt tension of the polystyrene resin (X) refer to the melt viscosity η and melt tension of the mixed resin after mixing. In this case, the resin is melt-kneaded at 200°C in a twin-screw extruder (diameter 20 mm, L / D = 500) and extruded to prepare resin pellets made of the mixed resin, which are then subjected to the above measurements. The twin-screw extruder is rotated at 50 rpm and the extrusion rate is 1 kg / h.

[0029] (3) Stress relaxation time τ The polystyrene resin (X) has a stress relaxation time τ of 100 seconds or more, as measured by the following tensile stress relaxation test (I).

[0030] [Tensile stress relaxation test (I)] In accordance with JIS K7127:1999, a 20% tensile strain is applied to a 0.4 mm thick dumbbell-shaped test piece of type 5 polystyrene resin (X) in an atmosphere of 80°C at a tensile speed of 50 m / min, and the tensile strain is maintained for 4 minutes from the time when the 20% tensile strain is applied. The initial stress at the time when the 20% tensile strain is applied is defined as a reference value, and the time required for the stress to decrease to one-tenth of the reference value is defined as the stress relaxation time τ at 80°C.

[0031] Test pieces for the tensile stress relaxation test (I) are prepared as follows. Specifically, a polystyrene resin is fed into a twin-screw extruder (diameter 20 mm, L / D=500), melt-kneaded at a temperature of 200°C, and extruded to prepare resin pellets. The twin-screw extruder is rotated at 50 rpm and has a discharge rate of 1 kg / h during extrusion. When a mixture of two or more polystyrene resins is used as the polystyrene resin (X), each polystyrene resin is fed into the twin-screw extruder.

[0032] The resulting resin pellets were placed in a 150mm x 75mm rectangular mold and heat-pressed at 200°C and 20MPa to obtain a 0.4mm thick unstretched resin sheet. Test pieces were obtained by punching out the resulting 0.4mm thick resin sheet into a Type 5 dumbbell shape as specified in JIS K7127:1999. Five test pieces were prepared in the same manner.

[0033] The obtained test specimen is left to stand for 24 hours in an atmosphere of 23°C and 50% RH. Thereafter, the specimen is conditioned by standing for 5 minutes in an atmosphere of 80°C, the test temperature, and the above-mentioned tensile stress relaxation test (I) is carried out using the conditioned test specimen. The stress relaxation time τ at 80°C is the arithmetic mean value of the stress relaxation times obtained in the measurements for five test specimens.

[0034] By ensuring that the stress relaxation time τ of the polystyrene resin (X) is 100 seconds or longer, shrinkage after production (specifically, shrinkage from immediately after production until one day after production) is suppressed, even if the density is low, and an extruded polystyrene resin foam board with excellent dimensional stability can be obtained. From this perspective, the stress relaxation time τ of the polystyrene resin (X) is preferably 120 seconds or longer, more preferably 150 seconds or longer, and even more preferably 180 seconds or longer. The upper limit of the stress relaxation time τ of the polystyrene resin (X) is not particularly limited, but is, for example, 350 seconds.

[0035] The reason why post-production shrinkage is suppressed when the polystyrene resin (X) has a stress relaxation time τ of 100 seconds or longer, even when the density is low, is not clear, but is thought to be as follows. Typically, in extruded polystyrene resin foam boards, cells begin to form immediately after the board is extruded from a die into a low-pressure region (specifically, atmospheric pressure), and as the cells grow, they are shaped into a board by a molding tool. The extruded foam board is then cooled, maintaining and solidifying the cell structure. One day after extrusion foaming, the extruded foam board cools to room temperature, stabilizing the dimensions of the extruded foam board. If the cells are crushed by atmospheric pressure between the time of foaming and the time of foaming, and are unable to maintain their shape, the cells that make up the extruded foam board will shrink, which is thought to cause the entire extruded foam board to shrink. On the other hand, in the present invention, since the stress relaxation time τ of the polystyrene resin (X) is sufficiently long, at 100 seconds or more, the rate of stress relaxation at high temperatures immediately after foaming is slowed, and residual stress acts sufficiently on the cell membrane, increasing the strength of the cell membrane and maintaining the shape of the cells. As a result, it is thought that an extruded polystyrene resin foam board with reduced shrinkage after production can be obtained, even at a low density.

[0036] (4) Weight average molecular weight Mw' From the viewpoint of further improving moldability and rigidity of the resulting foam, the weight average molecular weight Mw of the polystyrene resin (X) determined by the GPC-MALS method is preferably from 100,000 to 3,000,000, more preferably from 300,000 to 2,500,000, and even more preferably from 400,000 to 2,000,000. Details of the GPC-MALS method will be described later.

[0037] (5) Number average molecular weight Mn' From the viewpoint of further improving moldability and rigidity of the resulting foam, the number average molecular weight Mn' of the polystyrene resin (X) determined by the GPC-MALS method is preferably 80,000 or more and 1,200,000 or less, more preferably 150,000 or more and 1,000,000 or less, and even more preferably 200,000 or more and 850,000 or less.

[0038] (6) Z average molecular weight Mz' From the viewpoint of further improving moldability and rigidity of the resulting foam, the Z-average molecular weight Mz' of the polystyrene resin (X) determined by the GPC-MALS method is preferably 800,000 or more and 8,000,000 or less, more preferably 900,000 or more and 6,000,000 or less, and even more preferably 1,000,000 or more and 5,000,000 or less.

[0039] (7) Mz' / Mn' From the viewpoint of further improving moldability and rigidity of the resulting foam, the ratio Mz' / Mn' of the Z-average molecular weight Mz' determined by GPC-MALS to the number-average molecular weight Mn' determined by GPC-MALS of the polystyrene resin (X) is preferably 3 or more and 15 or less, more preferably 4 or more and 12 or less, and even more preferably 5 or more and 10 or less.

[0040] (8) Average value of contraction factor gw From the viewpoint of further improving moldability and the rigidity of the resulting foam, the average value gw of the shrinkage factor of the polystyrene resin (X) determined by the GPC-MALS-VISCO method is preferably 0.98 or less, more preferably 0.95 or less, and even more preferably 0.93 or less. The lower limit of the average value gw of the shrinkage factor is not particularly limited, but is, for example, 0.60. Details of the GPC-MALS-VISCO method will be described later.

[0041] (9) Branching degree T m,1000 From the viewpoint of further improving moldability and the rigidity of the resulting foam, the degree of branching T per 1000 styrene units of the polystyrene resin (X) is m,1000 is preferably 0.1 or more and 1.5 or less, more preferably 0.2 or more and 1.2 or less, and even more preferably 0.2 or more and 1.0 or less.

[0042] When a mixture of two or more polystyrene resins is used as the polystyrene resin (X), the weight-average molecular weight Mw', the number-average molecular weight Mn', the Z-average molecular weight Mz', and the average value of the shrinkage factor gw are measured using test pieces (resin pellets) prepared in the same manner as the test pieces used in the tensile stress relaxation test (I).

[0043] To make it easier for the polystyrene resin (X) to satisfy the above-mentioned range of the stress relaxation time τ, for example, the following polystyrene resin (A) is used: However, as long as the above-mentioned range of the stress relaxation time τ can be satisfied, the type and number of polystyrene resins used as the polystyrene resin (X) are arbitrary.

[0044] [1] Polystyrene resin (A) The polystyrene resin (X) used in the present invention preferably contains a polystyrene resin (A). The polystyrene resin (A) is preferably a branched polystyrene resin having a branched structure in the molecular chain.

[0045] (1) Weight average molecular weight Mw'A The weight-average molecular weight Mw'A of the polystyrene resin (A) determined by the GPC-MALS method is preferably 700,000 or more and 3,000,000 or less. By using a polystyrene resin (A) with such a large weight-average molecular weight Mw'A, strain hardening is more likely to occur in the cell membrane (i.e., the resin membrane constituting the cells) as the cells grow. As a result, the strength of the thin portions of the cell membrane is increased, the thickness of the cell membrane is made uniform, and the cell strength is improved, thereby further suppressing shrinkage. From the above perspectives, the weight-average molecular weight Mw'A determined by the GPC-MALS method is more preferably 850,000 or more and 2,500,000 or less, and even more preferably 1,000,000 or more and 2,000,000 or less. Details of the GPC-MALS method will be described later.

[0046] (2) Number average molecular weight Mn'A From the viewpoint of maintaining sufficient extrusion foamability of the extruded foam board, the number average molecular weight Mn'A of the polystyrene resin (A) determined by the GPC-MALS method is preferably 300,000 or more and 1,200,000 or less, more preferably 350,000 or more and 1,000,000 or less, and even more preferably 400,000 or more and 800,000 or less.

[0047] (3) Z average molecular weight Mz'A From the viewpoint of broadening the molecular weight distribution and more reliably suppressing shrinkage of the extruded foam board, the Z-average molecular weight Mz'A of the polystyrene resin (A) determined by the GPC-MALS method is preferably 3 million or more and 10 million or less, more preferably 3.5 million or more and 8 million or less, and even more preferably 4 million or more and 6 million or less.

[0048] (4) Mz'A / Mn'A The ratio Mz'A / Mn'A of the Z-average molecular weight Mz'A determined by GPC-MALS to the number-average molecular weight Mn'A of the polystyrene resin (A) determined by GPC-MALS is preferably 4 or more and 20 or less. By using a polystyrene resin (A) with a moderately large ratio Mz'A / Mn'A and a moderately wide molecular weight distribution, strain hardening tends to occur in the cell membrane as the cells grow, thereby further suppressing shrinkage. From the above perspectives, the ratio Mz'A / Mn'A is more preferably 5 or more and 15 or less.

[0049] (5) Average contraction factor gwA The average value gwA of the shrinkage factor of the polystyrene resin (A) determined by the GPC-MALS-VISCO method is preferably 0.80 or less. A polystyrene resin (A) having such an average value gwA of the shrinkage factor has a highly branched structure in the molecular chain, and as the bubbles grow, strain hardening is more likely to occur in the bubble film, thereby further suppressing shrinkage. From the above perspectives, the average value gwA of the shrinkage factor is more preferably 0.75 or less, and even more preferably 0.70 or less. The lower limit of the average value gwA of the shrinkage factor is not particularly limited, but is, for example, 0.40. Details of the GPC-MALS-VISCO method will be described later.

[0050] (6) Branching degree T m,1000 A Degree of branching per 1000 styrene units of polystyrene resin (A) T m,1000 A is preferably 0.2 or more. By using a polystyrene-based resin (A) having such a multi-branched structure, strain hardening is easily exhibited in the cell film when the cells grow, so that shrinkage can be further suppressed. From the above viewpoints, the branching degree T m,1000 A is more preferably 0.3 or more. m,1000 The upper limit of A is not particularly limited, but is, for example, 1.0.

[0051] (7) Melt viscosity ηA From the viewpoint of maintaining sufficient manufacturing stability of the extruded foam board, the melt viscosity ηA of the polystyrene resin (A) is set to 200°C and a shear rate of 100 sec. -1 Under these conditions, the melt viscosity is preferably 1000 Pa·s or more and 4000 Pa·s or less, more preferably 1200 Pa·s or more and 3500 Pa·s or less, and even more preferably 1500 Pa·s or more and 3000 Pa·s or less. The melt viscosity of the polystyrene resin (A) can be determined in the same manner as the melt tension of the polystyrene resin (X).

[0052] (8) Melt tension From the viewpoints of improving production stability and improving appearance, the melt tension of the polystyrene resin (A) is preferably 500 mN or more, more preferably 600 mN or more, and even more preferably 800 mN or more. The upper limit of the melt tension of the polystyrene resin (A) is not particularly limited, but is, for example, 2500 mN. The melt tension of the polystyrene resin (A) can be determined in the same manner as the melt tension of the polystyrene resin (X).

[0053] The polystyrene resin (A) has a tetrahydrofuran-insoluble content of, for example, 0.1% by mass or less (including 0). When the tetrahydrofuran-insoluble content of the polystyrene resin (A) is within the above range, the polystyrene resin (A) has sufficient melt tension while preventing an excessive increase in viscosity, thereby improving expandability and production stability. Furthermore, strain hardening is more likely to occur, further suppressing shrinkage of the resulting extruded foam board. From these perspectives, the polystyrene resin (A) has a tetrahydrofuran-insoluble content of, preferably, 0.05% by mass or less (including 0). Such a polystyrene resin (A) can be achieved, for example, by not including components derived from polyfunctional monomers in the polymer chain of the styrene resin, as described below.

[0054] The method for measuring the content of the tetrahydrofuran insoluble matter in the polystyrene resin (A) will be explained in the Examples.

[0055] Furthermore, it is preferable that the polystyrene resin (A) does not contain components derived from polyfunctional monomers in the molecular chain. That is, it is preferable that the polystyrene resin (A) does not contain components derived from polyfunctional monomers in the polymer chain, despite having a high molecular weight and many long-chain branches. When the polystyrene resin (A) does not contain components derived from polyfunctional monomers, the content of tetrahydrofuran-insoluble matter in the polystyrene resin (A) can be, for example, 0.1 mass % or less (including 0). A method for producing a polystyrene resin (A) having such properties will be described later.

[0056] An example of a method for producing the polystyrene resin (A) having the above-mentioned characteristics will be described in detail below. However, the method is not limited to the following method as long as it is possible to produce the polystyrene resin (A) satisfying the above-mentioned characteristics.

[0057] The method for producing the polystyrene resin (A) includes, for example, a dispersion step, an impregnation step, a polymerization initiation step, and an additional impregnation polymerization step.

[0058] [Dispersion process] In the dispersion step, styrene-based resin core particles are dispersed in an aqueous medium. Hereinafter, styrene-based resin core particles will also be referred to as "core particles." The method for dispersing core particles in an aqueous medium is not particularly limited, and for example, a suspending agent and a surfactant can be added to the aqueous medium together with the core particles and mixed. The dispersion step can be carried out, for example, in a sealed container such as an autoclave.

[0059] (nuclear particle) The core particles contain a styrene-based resin. The styrene-based resin in the core particles usually has a linear polymer chain, but may also contain a branched chain. The core particles may contain a resin other than a styrene-based resin, but the content of the styrene-based resin in the core particles is preferably 70% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, and it is particularly preferred that the substantial resin component is a styrene-based resin.

[0060] The average particle diameter of the core particles is preferably 0.3 to 1.2 mm. When the average particle diameter of the core particles is 0.3 mm or more, the amount of fine particles generated in the hyperbranched styrene-based resin can be reduced. When the average particle diameter of the core particles is 1.2 mm or less, the specific surface area of ​​the core particles increases, improving the impregnation of the core particles with the styrene-based monomer. The average particle diameter of the core particles is more preferably 0.3 to 1.0 mm, and even more preferably 0.3 to 0.5 mm.

[0061] (aqueous medium) As the aqueous medium, water such as deionized water can usually be used. The aqueous medium may contain a water-soluble organic solvent such as alcohol, as long as the core particles are not dissolved therein.

[0062] (surfactant) Examples of surfactants include anionic surfactants, cationic surfactants, zwitterionic surfactants, and nonionic surfactants. Among these, the surfactant preferably includes at least one selected from the group consisting of anionic surfactants, cationic surfactants, and nonionic surfactants. Specific examples include alkyl sulfonates (e.g., sodium dodecyl sulfonate), alkyl benzene sulfonates (e.g., sodium dodecyl benzene sulfonate), polyoxyalkyl ether phosphate esters, alkyl dimethyl ethyl ammonium ethyl sulfates, higher alcohols, glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkyl ethers, and fatty acid salts. One type of surfactant may be used, or two or more types may be used.

[0063] (electrolyte) In the dispersion step, an electrolyte may be added to the aqueous medium together with the surfactant. Examples of the electrolyte include lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium acetate, and sodium succinate.

[0064] (Suspension) Examples of suspending agents include hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, and polyvinylpyrrolidone; and poorly water-soluble inorganic salts such as calcium triphosphate, magnesium nitrate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin, and bentonite. One or more suspending agents may be used. Either one or both of the hydrophilic polymer and the poorly water-soluble inorganic salt may be used. When a poorly water-soluble inorganic salt is used as a suspending agent, it is preferable to use an anionic surfactant such as sodium alkyl sulfonate or sodium alkylbenzene sulfonate in combination.

[0065] The amount of suspending agent used is preferably 0.01 to 5 parts by mass per 100 parts by mass of the total amount of core particles and the styrene-based monomer used in the impregnation step described below. When a suspending agent made of a poorly water-soluble inorganic salt is used in combination with an anionic surfactant, it is preferable to use 0.05 to 3 parts by mass of suspending agent and 0.0001 to 0.5 parts by mass of anionic surfactant per 100 parts by mass of the total amount of core particles and the styrene-based monomer added.

[0066] [Impregnation process] In the impregnation step, a styrene-based monomer and a polymerization initiator are added to the aqueous medium after the dispersion step, and the core particles are impregnated with the styrene-based monomer and the polymerization initiator at a temperature at which the polymerization of the styrene-based monomer does not substantially proceed. By impregnating the core particles with the polymerization initiator together with the styrene-based monomer, the core particles can be sufficiently impregnated with the polymerization initiator. In addition to the core particles, the aqueous medium after the dispersion step contains a suspending agent, a surfactant, and the like, which are added as needed. The polymerization initiator is, for example, an organic peroxide, and preferably contains at least an organic peroxide. The temperature at which the polymerization of the styrene-based monomer does not substantially proceed is a temperature at which the polymerization initiator (specifically, the organic peroxide) does not substantially decompose.

[0067] From the viewpoint of suppressing the decomposition of the polymerization initiator, the temperature of the aqueous medium in the impregnation process is set to (T 1 / 2-15) ° C or less, and (T 1 / 2 It is more preferable to set the temperature at −18°C or lower. 1 / 2 is the 10-hour half-life temperature (unit: °C) of the polymerization initiator. On the other hand, from the viewpoint of preventing a decrease in the impregnation of the styrene-based monomer into the core particles, the temperature of the aqueous medium in the impregnation step is preferably 70°C or higher, and more preferably 75°C or higher. The temperature of the aqueous medium in the impregnation step may be constant or may be changed, for example, by gradually increasing it, but it is preferably within the above range.

[0068] The time for the impregnation step is preferably 0.5 to 2 hours, more preferably 1 to 2 hours, from the viewpoint of sufficiently impregnating the styrene-based monomer and the polymerization initiator into the core particles.

[0069] If the amount of styrene-based monomer added is too small, the core particles may not be sufficiently plasticized, and the core particles may not be sufficiently impregnated with the polymerization initiator. On the other hand, if the amount of styrene-based monomer added is too large, the styrene-based monomer may polymerize outside the core particles, making it easier for fine particles to form. Therefore, the amount of styrene-based monomer added in the impregnation step is preferably 10 to 200 parts by mass per 100 parts by mass of core particles. From the perspective of further improving impregnation, the amount of styrene-based monomer added is more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of core particles. From the perspective of further preventing the formation of fine particles, the amount of styrene-based monomer added is more preferably 100 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of core particles.

[0070] (Polymerization initiator) As the polymerization initiator, at least an organic peroxide is usually used, but a polymerization initiator other than the organic peroxide may be used in combination.

[0071] Examples of organic peroxides include benzoyl peroxide, dilauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-hexylperoxy-2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis-(2-ethylhexanoylperoxy)hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxybenzoate, t-amylperoxyisopropyl carbonate, and t-amylperoxy-2-ethylhexyl carbonate. Examples of organic peroxides include carbonate, t-hexylperoxyisopropyl carbonate, t-butylperoxy-3,5,5-trimethylhexanoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)-2-methylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 2,2-bis(t-butylperoxy)butane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane. These organic peroxides may be used alone or in combination of two or more.

[0072] 10-hour half-life temperature T of the polymerization initiator 1 / 2 The temperature is preferably 85 to 120° C., more preferably 90 to 110° C. When two or more organic peroxides are used as the polymerization initiator, the 10-hour half-life temperature of the organic peroxide having the lowest 10-hour half-life temperature is used as T 1 / 2The organic peroxide preferably has a 10-hour half-life temperature within the above range and a high hydrogen abstraction ability. Examples of such organic peroxides include organic peroxides that generate t-butoxy radicals, such as t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, and t-butyl peroxybenzoate; and organic peroxides that generate cumyloxy radicals, such as dicumyl peroxide.

[0073] The polymerization initiator may contain a polymerization initiator other than an organic peroxide. However, from the viewpoint of facilitating the hydrogen abstraction reaction, the polymerization initiator preferably contains 70% by mass or more of an organic peroxide, preferably 85% by mass or more, and more preferably consists of an organic peroxide.

[0074] The amount of polymerization initiator added is preferably 0.1 to 2.0 parts by mass per 100 parts by mass of the total amount of core particles and styrene-based monomer added. This range facilitates the hydrogen abstraction reaction without excessively reducing productivity. To further enhance this effect, the amount of polymerization initiator added is more preferably 0.2 to 1.5 parts by mass per 100 parts by mass of the total amount of core particles and styrene-based monomer added.

[0075] (Oxygen concentration in aqueous medium) The oxygen concentration of the aqueous medium at a temperature of 30°C is preferably 4 mg / L or more. Oxygen in the aqueous medium functions as a polymerization inhibitor in the aqueous medium and inhibits the generation of fine particles. Therefore, the higher the oxygen concentration in the aqueous medium, the higher the yield of the styrene-based resin. From the viewpoint of further suppressing the generation of fine particles, the oxygen concentration at a temperature of 30°C is more preferably 5 mg / L or more. Furthermore, the generation of fine particles can also be suppressed by adding 30 to 200 ppm by mass of a water-soluble polymerization inhibitor such as sodium nitrite to the aqueous medium.

[0076] [Polymerization initiation step] In the polymerization initiation step, the aqueous medium after the impregnation step is heated to initiate polymerization of the styrene monomer in the styrene resin core particles. Core particles impregnated with a polymerization initiator and a styrene monomer are dispersed in the aqueous medium after the impregnation step. Polymerization of the styrene monomer is initiated by raising the temperature of the aqueous medium in the polymerization initiation step.

[0077] Specifically, it is preferable to raise the temperature to a temperature at which the polymerization initiator (specifically, the organic peroxide) substantially decomposes, thereby initiating the polymerization of the styrene-based monomer. From the viewpoint of productivity, the temperature of the aqueous medium is set to (T 1 / 2 -10) ° C or higher, and (T 1 / 2 It is more preferable to set the temperature at -5°C or higher. The time for raising the temperature to the above temperature (i.e., polymerization initiation temperature) is not particularly limited, but is preferably 3 hours or longer, more preferably 5 hours or longer, from the viewpoint that the polymerization of the styrene-based monomer in the core particles proceeds during the temperature rise and the content of the styrene-based monomer in the core particles can be easily controlled to 10 mass% or less in the additional impregnation polymerization step described below. On the other hand, from the viewpoint of productivity, it is preferably 10 hours or shorter.

[0078] [Additional impregnation polymerization step] In the additional impregnation polymerization step, a styrene-based monomer is additionally added to the aqueous medium after the polymerization initiation step. Then, while the core particles are impregnated with the styrene-based monomer, the styrene-based monomer in the core particles is graft-polymerized onto the polymer chains of the styrene-based resin. That is, in the additional impregnation polymerization step, a styrene-based monomer is additionally added to the aqueous medium containing the core particles in which polymerization of the styrene-based monomer has begun after the polymerization initiation step, and the core particles are impregnated with the styrene-based monomer and polymerized.

[0079] If the amount of styrene-based monomer added in the additional impregnation polymerization step is too small, branched chains may not be sufficiently generated. On the other hand, if the amount is too large, polymerization of styrene-based monomers with each other outside the core particles may occur more easily, resulting in a decrease in the yield of the styrene-based resin. Therefore, the amount of styrene-based monomer added in the additional impregnation polymerization step is preferably 50 to 700 parts by mass per 100 parts by mass of core particles. From the perspective of more sufficient branched chain generation, the amount of styrene-based monomer added per 100 parts by mass of core particles is more preferably 100 parts by mass or more, and even more preferably 200 parts by mass or more. From the perspective of further increasing the yield of the styrene-based resin, the amount of styrene-based monomer added per 100 parts by mass of core particles is more preferably 600 parts by mass or less, and even more preferably 550 parts by mass or less.

[0080] In the additional impregnation polymerization step, it is preferable to maintain the content (specifically, concentration) of the styrene monomer in the core particles at 10% by mass or less. In other words, it is preferable to maintain the polymerization rate at 90% or more. The styrene monomer can be added intermittently or continuously. Through the polymerization initiation step, polymerization of the styrene monomer is initiated within the core particles as a reaction field. In the additional impregnation polymerization step, by maintaining the content of the styrene monomer in the core particles at 10% by mass or less, not only polymerization between styrene monomers but also hydrogen abstraction reactions are likely to occur, which facilitates graft polymerization of the styrene monomer onto the styrene resin (i.e., polymer), and facilitates the formation of branched chains. From the viewpoint of further increasing the degree of long chain branching, the content of the styrene monomer in the core particles in the additional impregnation polymerization step is more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0081] In the additional impregnation polymerization step, it is preferable to maintain the content of the styrene-based monomer in the core particles at 10% by mass or less, as described above. However, the content of the styrene-based monomer in the core particles can exceed 10% by mass within the range in which the above-mentioned styrene-based resin is obtained. The time during which the content of the styrene-based monomer in the core particles exceeds 10% by mass is preferably 20% or less, more preferably 10% or less, of the total time of the additional impregnation polymerization step. It is most preferable to keep the content of the styrene-based monomer in the core particles at 10% by mass or less throughout the entire additional impregnation polymerization step. From the viewpoint of sufficient branched chain growth, the time for the additional impregnation polymerization step is preferably 150 minutes or more, more preferably 180 minutes or more. From the viewpoint of production efficiency, the upper limit of the time for the additional impregnation polymerization step is preferably about 600 minutes.

[0082] The content of the styrene monomer in the core particles in the additional impregnation polymerization step can be calculated based on the chemical properties of the polymerization initiator used in the polymerization, the polymerization rate of styrene calculated from the polymerization temperature, etc., and the content of the styrene monomer in the core particles in the additional impregnation polymerization step can be adjusted by adjusting the timing and addition rate (addition rate) of the additional addition of the styrene monomer so as to obtain a desired content based on the calculated value. The actual content of the styrene monomer in the core particles can be determined by extracting the core particles during polymerization from the reaction system and using the method described below.

[0083] It is believed that the lower the content of styrene-based monomer in the core particles, the more likely it is that not only the polymerization initiation reaction but also the hydrogen abstraction reaction will occur, leading to an improved degree of branching. Furthermore, as mentioned above, by setting the average particle size of the core particles to 1.2 mm or less, the specific surface area will increase, improving the impregnation of the styrene-based monomer and facilitating the generation of branches.

[0084] (chain transfer agent) In the additional impregnation polymerization step, it is preferable to polymerize the styrene monomer in the presence of a chain transfer agent. In this case, the weight average molecular weight Mw'A is 700,000 to 3,000,000, the ratio Mz'A / Mn'A of the Z average molecular weight Mz'A to the number average molecular weight Mn'A is 4 to 20, and the branching degree T per 1,000 styrene units is 0.01. m,1000 A polystyrene resin (A) having a weight average molecular weight Mw'A of 700,000 to 3,000,000, a ratio Mz'A / Mn'A of the Z average molecular weight Mz'A to the number average molecular weight Mn'A of 5 to 15, and a branching degree T per 1,000 styrene units is easily obtained. m,1000 A polystyrene resin (A) having an A of 0.2 or more is more easily obtained. The chain transfer agent is a molecule that induces a chain transfer reaction of radical-reactive molecules such as the growing end radical of the polymer chain, the radical on the polymer chain, the styrene monomer radical, and the initiator radical in the reaction field during polymerization. Examples of chain transfer agents that can be used include α-methylstyrene dimer (hereinafter referred to as "αMSD"), n-octyl mercaptan, t-nonyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, phenylthiol, cyclohexanethiol, 4,4'-thiobisbenzenethiol, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), 4-methylbenzenethiol, isooctyl 3-mercaptopropionate, 1,8-dimercapto-3,6-dioxaoctane, bromotrichloromethane, carbon tetrachloride, 1,4-naphthoquinone, 2,4-diphenyl-4-methyl-1-pentene, and pentaphenylethane. α-Methylstyrene dimer is preferred because it allows the production of a styrene-based resin that has little odor and is not colored.

[0085] When a chain transfer agent is added, the chain transfer agent may be present together with the styrene-based monomer in the additional impregnation polymerization step. i Total amount of chain transfer agent added K t The ratio of (i.e., K t / K iIf K ) is too small, the molecular weight distribution may become narrow. t / K i If K is too large, the weight average molecular weight Mw'A may become small or the degree of branching may become small, which may result in the strain hardening property being difficult to exhibit. t / K i It is preferable to adjust K to 0.1 to 0.9. From the viewpoint of further enhancing the strain hardening property of the styrene-based resin, t / K i is more preferably 0.12 or more, and even more preferably 0.15 or more. t / K i is preferably 0.6 or less, more preferably 0.4 or less.

[0086] Examples of methods for adding the chain transfer agent include the following (I) to (IV). Methods (I) to (IV) may be used alone or in combination. In other words, the chain transfer agent can be added by at least one of methods (I) to (IV). (I) A method in which a chain transfer agent is incorporated into core particles before the dispersion step. (II) A method in which core particles are impregnated with a chain transfer agent in the impregnation step. (III) A method in which core particles are impregnated with a chain transfer agent in the polymerization initiation step. (IV) A method in which core particles are impregnated with a chain transfer agent in an additional impregnation polymerization step.

[0087] In the case of (I), a chain transfer agent can be incorporated into the core particles before adding them to the aqueous medium. Specifically, a styrene-based resin and a chain transfer agent are blended, and the core particles are produced by granulation. This results in styrene-based resin core particles containing the chain transfer agent.

[0088] In the case of (II), the core particles can be impregnated with a chain transfer agent in the impregnation step. The chain transfer agent can be impregnated into the core particles by adding it to the aqueous medium in the impregnation step. The chain transfer agent may be added to the aqueous medium at the same time as the styrene-based monomer and polymerization initiator, or may be added at a different time. The chain transfer agent is preferably added to the aqueous medium together with the styrene-based monomer and polymerization initiator. In this case, the chain transfer agent is sufficiently dispersed in the core particles together with the styrene-based monomer and polymerization initiator in the impregnation step. Therefore, in the polymerization initiation step and the additional impregnation polymerization step, it is possible to suppress side reactions such as polymer chain cleavage reactions while promoting hydrogen abstraction reactions from the polymer chains, thereby sufficiently increasing the degree of long chain branching of the styrene-based resin.

[0089] In the case of (III), the core particles can be impregnated with a chain transfer agent in the polymerization initiation step. The chain transfer agent can be added during or after the temperature increase.

[0090] In the case of (IV), the core particles can be impregnated with a chain transfer agent in the additional impregnation polymerization step. Specifically, after the polymerization initiation step, the core particles can be impregnated with the chain transfer agent while additionally adding a styrene-based monomer to the aqueous medium and adjusting the content of the styrene-based monomer in the core particles to 10% by mass or less. The timing of adding the chain transfer agent can be such that the chain transfer agent is added all at once at the beginning of the additional impregnation polymerization step, or that the chain transfer agent is added at a predetermined addition rate, for example. The addition rate can also be changed, for example, by gradually decreasing it. When the chain transfer agent is added in the additional impregnation polymerization step, it is preferable to add the styrene-based monomer and the chain transfer agent as a mixture, for example.

[0091] When a chain transfer agent is used, it is preferable to impregnate the core particles with the chain transfer agent in the impregnation step, as in (II) among (I) to (IV). In this case, the chain transfer agent can be present near the polymerization initiator in the core particles before the polymerization initiation step, so that some of the highly reactive radicals generated in the polymerization initiation step or the additional impregnation polymerization step can be replaced with appropriately low-reactivity radicals through a chain transfer reaction before side reactions such as polymer chain cleavage occur. As a result, a branched styrene-based resin can be obtained that has a wider molecular weight distribution, a higher degree of branching, and a high level of both melt tension and high fluidity.

[0092] (Temperature conditions) The temperature conditions of the additional impregnation polymerization step are not particularly limited. However, from the viewpoint of facilitating the hydrogen abstraction reaction, the temperature of the aqueous medium in the additional impregnation polymerization step is set to (T 1 / 2 -10)℃~(T 1 / 2 +20) ° C., and (T 1 / 2 -5)℃~(T 1 / 2 +10)° C. The temperature of the aqueous medium in the additional impregnation polymerization step may be constant or may be gradually increased or otherwise changed as long as it is within the above range.

[0093] In addition, the 10-hour half-life temperature T 1 / 2 is 85 to 120°C, and the temperature of the aqueous medium in the impregnation step is 70°C or higher (T 1 / 2 -15) ° C. or less, and the temperature of the aqueous medium in the additional impregnation polymerization step is (T 1 / 2 -10)℃ or more (T 1 / 2 +20°C or lower. In this case, the core particles can be sufficiently impregnated with the styrene-based monomer, initiator, and chain transfer agent in the impregnation step before substantially initiating polymerization, and the polymerization initiation reaction and hydrogen abstraction reaction can occur in the additional impregnation polymerization step.

[0094] In the additional impregnation polymerization step, it is preferable to maintain the concentration of the styrene-based monomer within the core particles, which serve as the polymerization reaction field, within a specific range and polymerize the styrene-based monomer in the presence of a chain transfer agent. i Total amount of chain transfer agent added K t Ratio of (K t / K i ) is preferably adjusted to fall within a predetermined range. This increases the number of branching points of the styrene-based resin, thereby increasing the degree of branching and increasing the molecular weight of the styrene-based resin, and it is believed that gelation can be avoided by widening the distance between branching points and increasing the degree of long chain branching, and further that fluidity can be increased and strain hardening can be more easily exhibited.

[0095] Typically, a polymerization initiator and a large amount of styrene-based monomer are present in the reaction field during polymerization of a styrene-based monomer, and the initiator radicals generated from the polymerization initiator and the growing end radicals of the polymer chain preferentially react with the vinyl groups of the styrene-based monomer, which is thought to facilitate the formation of a linear styrene-based resin. On the other hand, when the concentration of styrene-based monomer in the reaction field is low, as in the above-mentioned additional impregnation polymerization process, the number of polymer chains becomes relatively large, and it is thought that the initiator radicals and the growing end radicals of the polymer chain are more likely to undergo not only polymerization reactions with the styrene-based monomer but also hydrogen abstraction reactions of the polymer chain. As a result, it is thought that radicals are generated on the polymer chain by the hydrogen abstraction reaction, and the styrene-based monomer is graft-polymerized to the radicals on the polymer chain, or the growing end radicals of the polymer chain recombine, resulting in the formation of branched chains in the polymer chain.

[0096] Since the position where a branched chain is generated in the polymer chain is in a sterically crowded state, it is thought that further branched chains are unlikely to be generated near the generated branch point. In other words, it is thought that a hydrogen abstraction reaction occurs again on the polymer chain that is far enough from the branch point that steric hindrance does not occur, and a branched chain is generated. Therefore, since branched chains are generated with the branch points being appropriately spaced apart, it is thought that a styrene-based resin having many branched chains can be obtained without gelation.

[0097] In order to generate many branched chains, it is necessary to increase the radical concentration in the polymerization system during the additional impregnation polymerization step and thereby increase the frequency of hydrogen abstraction reactions on the polymer chain. However, if the concentration of highly reactive initiator radicals is increased by increasing the amount of initiator added or by increasing the temperature in the additional impregnation polymerization step to promote decomposition of the initiator, undesirable side reactions such as polymer chain cleavage reactions are more likely to occur, making it impossible to obtain a styrene-based resin having the desired branched structure.

[0098] On the other hand, in radical polymerization, chain transfer agents are used to adjust the molecular weight of the polymer chain to a low level, and are not usually added to synthesize high molecular weight polymer chains. However, the total amount of polymerization initiators added, K i Total amount of chain transfer agent added K t Ratio of (K t / K i By adjusting the value of Mw'A within a predetermined range, a decrease in molecular weight does not occur, and instead a styrene resin with a high degree of branching and a high molecular weight is produced. The styrene resin thus obtained has a weight average molecular weight Mw'A of 700,000 to 3,000,000, a ratio Mz'A / Mn'A of the Z average molecular weight Mz'A to the number average molecular weight Mn'A of 4 to 20, and a branching degree T per 1,000 styrene units. m,1000 A styrene resin having a weight average molecular weight Mw'A of 700,000 to 3,000,000, a ratio Mz'A / Mn'A of the Z average molecular weight Mz'A to the number average molecular weight Mn'A of 5 to 15, and a branching degree T per 1,000 styrene units. m,1000 This makes it easier to satisfy the condition that A is 0.2 or greater.

[0099] Total amount of polymerization initiator added K i Total amount of chain transfer agent added K t Ratio of (K t / K i) within a specified range, a decrease in molecular weight does not occur, and instead a styrene resin with a high degree of branching and a high molecular weight is produced. This is thought to be because, when the concentration of the styrene monomer in the core particles is within a specific range, some of the highly reactive radicals such as initiator radicals are replaced by radicals with moderately low reactivity through chain transfer reactions, suppressing side reactions such as polymer chain cleavage reactions, and a styrene resin with a high degree of branching and a high molecular weight is produced through a hydrogen abstraction reaction of the polymer chain. i Total amount of chain transfer agent added K t If the total amount of polymerization initiator K is too small, it is thought that side reactions such as polymer chain cleavage reactions cannot be suppressed. i Total amount of chain transfer agent added K t If the amount is too large, it is thought that the hydrogen abstraction reaction will be difficult to occur, and in either case, it will be difficult to obtain a styrene-based resin having a high degree of branching and a high molecular weight.

[0100] Furthermore, since chain transfer agents inherently produce low molecular weight polymers, it is believed that a portion of the chain transfer agent that is not involved in the generation of branched chains also produces a low molecular weight styrene resin. As a result, a high molecular weight styrene resin with a high degree of branching produced by the hydrogen abstraction reaction and a low molecular weight styrene resin produced by the chain transfer reaction are simultaneously produced, which is believed to broaden the molecular weight distribution of the resulting styrene resin. Such styrene resins are believed to have many branched chains and long branched chains. Note that the use of a chain transfer agent can achieve a weight average molecular weight Mw'A of 700,000 to 3,000,000, a ratio Mz'A / Mn'A of the Z average molecular weight Mz'A to the number average molecular weight Mn'A of 4 to 20, and a degree of branching T per 1,000 styrene units. m,1000 Although it becomes easier to obtain a polystyrene-based resin (A) that satisfies the condition that A is 0.2 or more, it is possible to obtain a polystyrene-based resin (A) that satisfies the above condition even without using a chain transfer agent, for example, by maintaining the content (specifically, concentration) of the styrene-based monomer in the core particles to 10 mass% or less in the additional impregnation polymerization step as described above.

[0101] In the method for producing the polystyrene-based resin (A), the polystyrene-based resin (A) can be produced without using a polyfunctional monomer (i.e., a branching agent). That is, even if the amount of the polyfunctional monomer used is reduced to, for example, substantially close to zero, or even if no polyfunctional monomer is used, the polystyrene-based resin (A) can be produced. Reducing the amount of the polyfunctional monomer used or not using a polyfunctional monomer leads to further prevention of gelation and further improvement of fluidity.

[0102] The amount of polyfunctional monomer added in the aqueous medium is preferably 0.2 parts by mass or less, more preferably 0.1 parts by mass or less, and even more preferably 0, relative to 100 parts by mass of core particles. When the polyfunctional monomer is added, it can be added in any step, for example, the impregnation step, the polymerization initiation step, the additional impregnation polymerization step, etc.

[0103] The polyfunctional monomer is, for example, a monomer having two or more radically polymerizable double bonds, and examples of the polyfunctional monomer include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, trimethylolpropane triacrylate, ethylene glycol diacrylate, propylene glycol diacrylate, 1,3-butylene diol diacrylate, hexanediol diacrylate, and cyclohexanediol diacrylate.

[0104] [Residual Monomer Polymerization Step] After the additional impregnation polymerization step, a residual monomer polymerization step can be carried out to polymerize the styrene monomer remaining in the styrene resin. The residual monomer polymerization step is a step that is carried out optionally.

[0105] [Other steps] After the additional impregnation polymerization step or the residual monomer polymerization step, the sealed container is cooled and the styrene-based resin is removed from the sealed container, thereby obtaining, for example, a particulate styrene-based resin. Specifically, the particulate shape is exemplified by shapes such as spheres and ellipsoids, but also includes shapes similar to these in appearance. A washing step can be performed in which suspending agents, surfactants, etc. adhering to the styrene-based resin are washed with water. A coating step can also be performed in which a functional component such as an antistatic agent is coated on the surface of the styrene-based resin. The washing step and the coating step are selectively performed.

[0106] The styrene-based resin produced through the above steps can be used as the polystyrene-based resin (A).

[0107] [2] Polystyrene resin (B) The polystyrene resin (X) used in the present invention may be a mixed resin containing, in addition to the polystyrene resin (A), a polystyrene resin (B) different from the polystyrene resin (A). However, the polystyrene resin (X) used in the present invention does not necessarily have to be a mixed resin, and may, for example, contain the polystyrene resin (A) but not the polystyrene resin (B). When the polystyrene resin (X) contains the polystyrene resin (B), the polystyrene resin (B) is preferably a branched polystyrene resin having a branched structure in the molecular chain.

[0108] (1) Weight average molecular weight Mw'B The weight-average molecular weight Mw'B of the polystyrene resin (B) as determined by the GPC-MALS method is preferably 100,000 or more and less than 700,000. By using a polystyrene resin (B) having such a weight-average molecular weight Mw'B together with the polystyrene resin (A), the foaming temperature range in which an extruded foam board with reduced shrinkage can be produced can be expanded. Furthermore, to further prevent the generation of unmelted material during the production of extruded foam boards, it is desirable that the difference between the weight-average molecular weight Mw'A of the polystyrene resin (B) and that of the polystyrene resin (A) is not too large. Therefore, the weight-average molecular weight Mw'B as determined by the GPC-MALS method is more preferably 300,000 or more and less than 700,000, and even more preferably 500,000 or more and less than 700,000.

[0109] (2) Number average molecular weight Mn'B The number average molecular weight Mn'B of the polystyrene resin (B) determined by the GPC-MALS method is preferably 80,000 or more and 500,000 or less, more preferably 100,000 or more and 400,000 or less, and even more preferably 150,000 or more and 300,000 or less, from the viewpoint of improving the extrusion foamability of the extruded foam board.

[0110] (3) Z average molecular weight Mz'B The Z-average molecular weight Mz'B of the polystyrene resin (B) determined by the GPC-MALS method is preferably 1 million or more and 5 million or less, more preferably 1.5 million or more and 3.5 million or less.

[0111] (4) Mz'B / Mn'B The ratio Mz'B / Mn'B of the Z-average molecular weight Mz'B determined by the GPC-MALS method to the number-average molecular weight Mn'B of the polystyrene resin (B) determined by the GPC-MALS method is preferably 4 or more and 30 or less, and more preferably 5 or more and 25 or less.

[0112] (5) Average contraction factor gwB The average shrinkage factor gwB of the polystyrene resin (B) determined by the GPC-MALS-VISCO method is preferably 0.95 or less. By using a polystyrene resin (B) having such an average shrinkage factor gwB, the generation of unmelted material during the production of an extruded foam board can be suppressed. From the above perspectives, the average shrinkage factor gwB is more preferably 0.92 or less, and even more preferably 0.90 or less. The lower limit of the average shrinkage factor gwB is not particularly limited, but is, for example, 0.70.

[0113] In the present invention, by using a polystyrene resin (B) having a weight-average molecular weight Mw'B of 500,000 or more but less than 700,000 and an average shrinkage factor gwB of 0.95 or less together with the polystyrene resin (A), the occurrence of unmelted material during the production of extruded foam boards can be more reliably suppressed. Note that "unmelted material" primarily refers to high-molecular-weight hyperbranched polystyrene, such as the polystyrene resin (A), extruded in an unmelted state. Unmelted material is observed in the extruded foam board as clumps of unfoamed resin. By suppressing the occurrence of unmelted material, poor appearance of the extruded foam board and a decrease in production stability are suppressed.

[0114] (6) Branching degree T m,1000 B Degree of branching per 1000 styrene units of polystyrene resin (B) T m,1000 From the viewpoint of further reducing unmelted matter, B is preferably 0.1 or more and 1.5 or less, more preferably 0.2 or more and 1.2 or less, and even more preferably 0.3 or more and 1.0 or less.

[0115] In the present invention, the branching degree T m,1000 A and branching degree T m,1000 Since the branching degree T of the polystyrene resin (A) can be more reliably suppressed by the fact that B is in a moderate proximity, m,1000 A is 0.2 or more, and the branching degree T of the polystyrene resin (A) is m,1000 A and the degree of branching of polystyrene resin (B) T m,1000 Absolute value of the difference with B│(T m,1000 A)-(Tm,1000 B)| is preferably 0.5 or less. m,1000 A)-(T m,1000 The lower limit of B)| is not particularly limited, and is, for example, 0.

[0116] (7) Melt viscosity ηB From the viewpoint of improving the manufacturing stability of extruded foam boards, the melt viscosity ηB of polystyrene resin (B) is set to 200°C and a shear rate of 100 sec. -1 Under these conditions, the melt viscosity is preferably 500 Pa·s or more and 3000 Pa·s or less, more preferably 800 Pa·s or more and 2500 Pa·s or less, and even more preferably 1000 Pa·s or more and 2000 Pa·s or less. The melt viscosity of the polystyrene resin (B) can be determined in the same manner as for the polystyrene resin (A).

[0117] (8) Melt tension From the viewpoints of improving production stability and improving appearance, the melt tension of the polystyrene resin (B) is preferably 150 mN or more, more preferably 200 mN or more, and even more preferably 250 mN or more. The upper limit of the melt tension of the polystyrene resin (B) is not particularly limited, but is, for example, 800 mN. The melt tension of the polystyrene resin (B) can be determined in the same manner as for the polystyrene resin (A).

[0118] As the polystyrene resin (B) satisfying the above characteristics, for example, a branched polystyrene sold as a general commercial product can be used. Note that the polystyrene resin (B) may contain, in addition to the styrene unit component, a unit component derived from a branching agent such as a polyfunctional monomer or a polyfunctional macromonomer.

[0119] The mass proportion of polystyrene resin (A) in 100% by mass of the combined total of polystyrene resin (A) and polystyrene resin (B) is preferably 15% by mass or more and 90% by mass or less, since this expands the foaming temperature range at which extruded foam boards with suppressed shrinkage can be produced. From the viewpoint of further expanding the foaming temperature range, the mass proportion of polystyrene resin (A) in 100% by mass of the combined total of polystyrene resin (A) and polystyrene resin (B) is more preferably 20% by mass or more and 80% by mass or less, and even more preferably 30% by mass or more and 70% by mass or less.

[0120] The total mass proportion of the polystyrene resin (A) and the polystyrene resin (B) in the polystyrene resin (X) is, for example, 80 mass% or more, preferably 90 mass% or more, more preferably 95 mass% or more, and is particularly preferably 100 mass%, i.e., the polystyrene resin (X) contains only the polystyrene resin (A) and the polystyrene resin (B) as the polystyrene resins. Note that the polystyrene resin (X) may contain only the polystyrene resin (A) as the polystyrene resin without containing the polystyrene resin (B).

[0121] Furthermore, in the present invention, from the viewpoint of adjusting the stress relaxation time τ within a desired range and from the viewpoint of more reliably suppressing the generation of unmelted material in the foamable resin melt, the amount of linear polystyrene resin in the polystyrene resin (X) is preferably 20 mass% or less (including 0), more preferably 10 mass% or less, even more preferably 5 mass% or less, and particularly preferably 0, i.e., no linear polystyrene resin is contained. In this specification, linear polystyrene resin refers to a polystyrene resin having a branching degree of less than 0.03 per 1000 styrene units.

[0122] [GPC-MALS method] The weight-average molecular weight Mw', number-average molecular weight Mn', and Z-average molecular weight Mz' can be determined using the GPC-MALS method. The weight-average molecular weight Mw', number-average molecular weight Mn', and Z-average molecular weight Mz' determined by the GPC-MALS method are absolute molecular weights.

[0123] The GPC-MALS method is a molecular weight determination method that combines GPC (Gel Permeation Chromatography) and MALS (Multi-Angle Light Scattering). The GPC-MALS method can be performed using a measurement system that combines a gel permeation chromatography device capable of GPC measurement with a multi-angle light scattering detector capable of MALS measurement.

[0124] Specifically, a styrene resin solution is prepared by dissolving polystyrene resin in a solvent such as tetrahydrofuran, and this solution is subjected to GPC measurement to obtain an elution chromatogram. In GPC measurement, polymers with larger molecular sizes elute first, so styrene resins can be separated by molecular size. Subsequently, the styrene resin solution separated by molecular size is subjected to MALS measurement, allowing the absolute molecular weight of the styrene resins separated by molecular size to be calculated.

[0125] The absolute molecular weight M of polystyrene resin in any section i of the elution chromatogram by GPC-MALS method i The concentration of polystyrene resin in section i, c i is determined appropriately using a concentration detector such as a commercially available differential refractometer (RI). The weight-average molecular weight Mw', number-average molecular weight Mn', and Z-average molecular weight Mz' can then be calculated using the following equations (1) to (3).

[0126]

number

[0127]

number

[0128]

number

[0129] The shrinkage factor of polystyrene resins can also be determined by the GPC-MALS-VISCO method. The GPC-MALS-VISCO method can be performed using a measurement system that combines a gel permeation chromatography device capable of GPC measurement, a multi-angle light scattering detector capable of MALS measurement, and a viscosity detector at the downstream stage. Specifically, measurements are performed using a VISCOSTAR III, a four-arm bridge type viscosity detector manufactured by Wyatt Technology. In this viscosity detector, the measurement solution is first uniformly passed through the branched arms, and then a pressure difference is generated because one arm is equipped with a delay column that separates the solvent and the sample. The intrinsic viscosity [η] can be calculated from the specific viscosity calculated from this pressure difference and the concentration information from a differential refractive index detector (RI) that is further combined at the downstream stage. branch Then, the shrinkage factor g of the polystyrene resin and the average value (weight average value) gw of the shrinkage factor g can be calculated using the following equations (4) and (5). Note that [η] in equation (4) linear is the intrinsic viscosity of the standard polymer, linear polystyrene. The shrinkage factor calculated in this way is also called the hydrodynamic shrinkage factor.

[0130]

number

[0131]

number

[0132] Then, using equation (6), the branching degree T mFurthermore, the branching degree T per 1000 styrene units can be calculated using equations (7) and (8). m,1000 The branching degree T m,w is the branching degree per molecule, and T m,i is the degree of branching in section i. The degree of branching is the degree of long chain branching, assuming that the styrene-based resin has a triple-branched structure.

[0133]

number

[0134]

number

[0135]

number

[0136] [Other polymers] The base resin may contain other polymers besides polystyrene-based resins as long as the objects and effects of the present invention are achieved. From the viewpoint of improving the heat insulating properties of the extruded foam board, an example of such other polymers is amorphous polyethylene terephthalate-based copolymers. In this case, the amount of amorphous polyethylene terephthalate-based copolymer blended into the base resin is preferably 5% by mass or more and 30% by mass or less, more preferably 8% by mass or more and 15% by mass or less.

[0137] In the amorphous polyethylene terephthalate copolymer, the heat of fusion accompanying the melting of the resin based on JIS K7122 (1987) is less than 5 J / g. is measured using a heat flux differential scanning calorimeter, employing the method described in JIS K7122 (1987) for "measuring the heat of fusion after a certain heat treatment" (the heating rate and cooling rate for conditioning the test piece are both 10°C / min), and based on the DSC curve obtained by heating the conditioned test piece at a heating rate of 10°C / min.

[0138] Examples of other polymers besides amorphous polyethylene terephthalate copolymers include thermoplastic resins such as polyethylene, polypropylene, polyphenylene ether, and polymethyl methacrylate, and thermoplastic elastomers such as styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, and styrene-ethylene copolymer. The blending amount of these other polymers in the base resin is preferably 20% by mass or less (inclusive of 0), more preferably 10% by mass or less (inclusive of 0), even more preferably 5% by mass or less (inclusive of 0), and particularly preferably 3% by mass or less (inclusive of 0).

[0139] [Physical foaming agent] The physical foaming agent used in the present invention may be one or more selected from organic physical foaming agents and inorganic physical foaming agents.

[0140] Examples of organic physical blowing agents include aliphatic alcohols having 1 to 5 carbon atoms, saturated hydrocarbons having 3 to 5 carbon atoms, dialkyl ethers having an alkyl chain with 1 to 3 carbon atoms, alkyl chlorides, hydrofluoroolefins, and fluorohydrocarbons.

[0141] Examples of inorganic physical foaming agents that can be used include oxygen, nitrogen, carbon dioxide, air, water, etc. Among these, water and carbon dioxide are preferred because they reduce environmental impact and dissipate quickly from the extruded foam plate, allowing the dimensions of the resulting extruded foam plate to be stabilized quickly.

[0142] The physical blowing agent preferably has zero or extremely low ozone depletion potential and low global warming potential. For the purpose of reducing the thermal conductivity of the extruded polystyrene resin foam board, it is preferable to use one or more physical blowing agents selected from the group consisting of saturated hydrocarbons having at least 3 to 5 carbon atoms and hydrofluoroolefins (HFOs).

[0143] Examples of saturated hydrocarbons having 3 to 5 carbon atoms include propane, normal butane, isobutane (2-methylpropane), normal pentane, isopentane (2-methylbutane), cyclobutane, neopentane (2,2-dimethylpropane), and cyclopentane. These blowing agents can be used alone or in combination of two or more. Among these, isobutane is preferably used. The amount of saturated hydrocarbons having 3 to 5 carbon atoms blended is preferably 0.2 mol to 1.2 mol, and more preferably 0.4 mol to 1.0 mol, per 1 kg of base resin.

[0144] Examples of hydrofluoroolefins include 1,3,3,3-tetrafluoropropene (HFO-1234ze), 1-chloro-3,3,3-trifluoropropene (HFO-1233zd), 1-chloro-2,3,3,3-tetrafluoropropene (HFO-1224yd), 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz). These hydrofluoroolefins also include hydrochlorofluoroolefins partially substituted with chloride ions. When using a hydrofluoroolefin as a physical blowing agent, the amount of hydrofluoroolefin blended is preferably 0.1 mol or more and 1.0 mol or less, and more preferably 0.2 mol or more and 0.8 mol or less, per 1 kg of base resin.

[0145] Examples of aliphatic alcohols having 1 to 5 carbon atoms include methyl alcohol (methanol), ethyl alcohol (ethanol), n-propyl alcohol, isopropyl alcohol, butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, aryl alcohol, crotyl alcohol, propargyl alcohol, n-amyl alcohol, sec-amyl alcohol, isoamyl alcohol, tert-amyl alcohol, neopentyl alcohol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, etc. Among these, ethanol is preferably used from the viewpoint of safety for the environment and the human body.

[0146] Aliphatic alcohols having 1 to 5 carbon atoms do not deplete the ozone layer or contribute to global warming, and they quickly dissipate from the extruded foam board, allowing the shape of the extruded foam board to be quickly stabilized.

[0147] Examples of dialkyl ethers having 1 to 3 carbon atoms in the alkyl chain include dimethyl ether, diethyl ether, dipropyl ether, and ethyl methyl ether. Among these, dimethyl ether (DME) is particularly preferred. Using a dialkyl ether as a physical foaming agent can improve the dispersibility of graphite (described below) in the foamable molten resin composition, resulting in more finely dispersed graphite in the extruded foam plate. Therefore, when graphite is contained in the extruded foam plate, the thermal insulation properties can be improved. The amount of dialkyl ether added is preferably 0.1 mol to 0.6 mol, more preferably 0.2 mol to 0.5 mol, per 1 kg of base resin.

[0148] Examples of alkyl chlorides include methyl chloride, ethyl chloride, etc. Alkyl chlorides have a high permeation rate through polystyrene resins and dissipate quickly after production of the extruded foam board, allowing the dimensions of the resulting extruded foam board to stabilize quickly.

[0149] The various physical blowing agents exemplified above can be used in combination with two or more types. In particular, from the viewpoints of increasing the expansion ratio and more easily obtaining an extruded foam board with a low apparent density, of achieving high early dissipation properties and early stabilization of the shape of the extruded foam board, and of improving the surface condition of the extruded foam board, the use of water and / or aliphatic alcohols having 1 to 5 carbon atoms is preferred, and the use of both water and aliphatic alcohols having 1 to 5 carbon atoms is even more preferred. The amount of water and / or aliphatic alcohols having 1 to 5 carbon atoms added is preferably 0.3 mol to 2.0 mol, more preferably 0.5 mol to 2.0 mol, even more preferably 0.7 mol to 2.0 mol, and particularly preferably 0.7 mol to 1.8 mol per kg of base resin. The amount of water and / or aliphatic alcohols having 1 to 5 carbon atoms added refers to the amount of only one of water and alcohol when only one of them is used, and refers to the combined amount when both water and alcohol are used. To ensure the above effects, it is preferable to use both water and alcohol in a total amount within the above range. There is no limitation on the blending ratio of the two, but water:alcohol=90 mol%:10 mol%-50 mol%:50 mol%, and more preferably 80 mol%:20 mol%-60 mol%:40 mol%.

[0150] Here, when the amount of water and / or aliphatic alcohol having 1 to 5 carbon atoms added is large (specifically, when the amount added is 0.7 mol or more and 2.0 mol or less), the extruded foam plate tends to shrink easily. In the present invention, the stress relaxation time of the polystyrene resin is adjusted within a predetermined range, so that shrinkage can be stably suppressed even when the amount of water and / or aliphatic alcohol having 1 to 5 carbon atoms added is large.

[0151] The total amount of physical foaming agent added is adjusted depending on the desired density of the extruded foam board, and is preferably 1.3 mol to 3.0 mol per kg of base resin. If the amount of physical foaming agent added is too small, the apparent density of the resulting extruded foam board will be too high, and it may not be possible to obtain an extruded foam board with the desired low apparent density. On the other hand, if the amount of physical foaming agent added is too large, numerous gas spots may occur, and the appearance of the resulting extruded foam board may be poor. For these reasons, the lower limit of the total amount of physical foaming agent added is preferably 1.5 mol or more, more preferably 2.8 mol or more, per kg of base resin, and the upper limit of the total amount of physical foaming agent added is more preferably 2.5 mol or less per kg of base resin.

[0152] [Additives] In the production method of the present invention, various additives may be added in addition to the polystyrene resin (X) and the physical blowing agent. Examples of additives include cell regulators, flame retardants, flame retardant assistants, inorganic radiation inhibitors, shrinkage inhibitors, antioxidants, heat stabilizers, weathering agents, UV absorbers, inorganic fillers, antibacterial agents, and colorants. The total amount of additives added is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the base resin.

[0153] In the production method of the present invention, the additives (hereinafter also referred to as "various additives") can be blended into the base resin by feeding a predetermined ratio of the additives together with the base resin to a feeder provided upstream of the extruder and kneading them in the extruder. Alternatively, the additives can be fed into a molten polystyrene-based resin from a feeder provided midway through the extruder. Specifically, a dry blend of the additives and the base resin can be fed into the extruder and melt-kneaded; a melt-kneaded mixture of the additives and the base resin kneaded in a kneader or the like can be fed into the extruder; or a masterbatch can be prepared by blending a high concentration of the additives into the polystyrene-based resin, which can then be fed into the extruder and melt-kneaded with the base resin. From the viewpoint of dispersibility in particular, it is preferable to prepare an additive masterbatch and feed it into the extruder.

[0154] In the molding step of the production method of the present invention, as described above, a foamable resin molten composition prepared by melting a polystyrene-based resin (X), a physical foaming agent, and various additives is extruded and foamed under atmospheric pressure, and then shaped into a plate using a molding tool, thereby producing an extruded polystyrene-based resin foam plate.

[0155] <Extruded foam board> Next, the extruded polystyrene resin foam board obtained by the production method of the present invention will be described.

[0156] Dimensions and Volume The extruded foam board according to the present invention has a plate shape with an extrusion direction (MD), a thickness direction (VD), and a width direction (TD) perpendicular to the extrusion direction (MD), and is usually produced by preparing a base plate that is one size larger than the desired size and then cutting the base plate to adjust the width, length, and in some cases the thickness.

[0157] The thickness of the extruded foam board is preferably 10 mm or more and 180 mm or less, more preferably 20 mm or more and 150 mm or less, and even more preferably 30 mm or more and 120 mm or less.

[0158] The width of the extruded foam plate is preferably 100 mm or more, more preferably 300 mm or more, and the upper limit of the width of the extruded foam plate is, for example, 2000 mm.

[0159] The length of the extruded foam plate is preferably 200 mm or more, more preferably 500 mm or more, and the upper limit of the length of the extruded foam plate is, for example, 3000 mm.

[0160] The volume of the extruded foam board is 20,000 cm 3 or more, preferably 50,000 cm 3 More preferably, it is 80,000 cm 3 The volume of the extruded foam board is calculated from the thickness, width, and length. The upper limit of the volume of the extruded foam board is not particularly limited, but for example, it is 300,000 cm 3 In the past, extruded foam boards with such large volumes tended to shrink after production, possibly due to the large variation in cell diameter. However, according to the present invention, the stress relaxation time τ of the polystyrene resin is adjusted within a predetermined range, thereby suppressing shrinkage, and even when producing extruded foam boards with such large volumes, it is possible to obtain extruded foam boards with suppressed shrinkage after production.

[0161] The cross-sectional area of ​​the extruded foam perpendicular to the extrusion direction is 100cm 2 It is preferable that the length is 200cm or more. 2 The upper limit of the cross-sectional area of ​​the extruded foam perpendicular to the extrusion direction is, for example, 3000 cm 2 The cross-sectional area perpendicular to the extrusion direction refers to the area of ​​the cross section (TD cross section) of the extruded foam that is perpendicular to the extrusion direction.

[0162] [Apparent Density] The apparent density of the extruded foam board is 10 kg / m 3 More than 40kg / m 3 or less, preferably 15 kg / m 3 More than 30kg / m 3The apparent density within the above range allows for an extruded foam board with excellent lightness. Conventionally, extruded foam boards with low densities as described above have tended to have thin cell membranes, have difficulty maintaining the cell shape, and are more likely to shrink after production. On the other hand, according to the present invention, the stress relaxation time τ of the polystyrene resin is adjusted within a predetermined range, thereby suppressing shrinkage, and even when producing an extruded foam board with a low density as described above, an extruded foam board with suppressed shrinkage after production can be obtained.

[0163] The apparent density is calculated by dividing the mass of the extruded foam board by its volume. Specifically, the apparent density is measured in accordance with JIS K6767 (1999). Rectangular samples measuring 50 mm long x 50 mm wide x 50 mm thick are cut from each extruded foam board at three locations: the center and both ends in the width direction. The apparent density of each sample is measured, and the arithmetic average of the measurements at the three locations is used as the apparent density.

[0164] [Bubble deformation rate] The average cell deformation ratio of the cells in the vertical cross section (TD cross section) perpendicular to the extrusion direction of the extruded polystyrene resin foam plate is 0.85 to 1.10, and the coefficient of variation is 3.0% or less. The average cell deformation ratio of the cells in the vertical cross section (MD cross section) perpendicular to the width direction of the extruded polystyrene resin foam plate is 1.05 to 1.30, and the coefficient of variation is 3.0% or less.

[0165] When the average value and coefficient of variation of the cell deformation ratio in the transverse cross section (TD cross section) are within the above-mentioned ranges, and when the average value and coefficient of variation of the cell deformation ratio in the transverse cross section (MD cross section) are also within the above-mentioned ranges, it can be said that the cell shape is highly uniform. In the present invention, by using a polystyrene-based resin (X) with a stress relaxation time τ of 100 seconds or more, the rate of stress relaxation at high temperatures immediately after extrusion is slowed, and the strength of the cell film is increased, thereby maintaining the cell shape, and as a result, it is presumed that the cell shape is more uniform. This in turn results in an extruded foam plate with better suppressed shrinkage and superior dimensional stability. In particular, the occurrence of so-called differential shrinkage, in which the dimensions of an extruded foam plate decrease significantly in a specific direction compared to the dimensions in other directions between immediately after production and 24 hours after production, can be suppressed. From these perspectives, the average cell deformation ratio in the transverse cross section is preferably 0.95 to 1.08, and the coefficient of variation is preferably 2.5% or less. The average value of the cell deformation rate in the MD cross section is preferably 1.10 or more and 1.25 or less, and the coefficient of variation is 2.5% or less.

[0166] The average bubble deformation ratios of the TD cross section and the MD cross section are calculated as follows. First, a schematic diagram of an extruded foam plate is shown in Figure 1. As shown in Figure 1, five samples (1) to (5) (20 mm wide x 20 mm long x thickness) are cut out of the extruded foam plate at equal intervals across the width. The illustrated sample thickness is 50 mm. A 10 mm x 10 mm rectangular measurement surface is set at the center of each TD cross section and MD cross section of the cut sample. Then, using image processing software NS2K-pro manufactured by NanoSystems Co., Ltd., the vertical and horizontal Feret diameters of all bubbles present on the measurement surface are calculated, and the ratio (vertical Feret diameter / horizontal Feret diameter) is calculated. The arithmetic mean values ​​of the bubble deformation ratios of the TD cross section and the MD cross section are used. The smaller the bubble deformation ratio, the flatter the bubble. The larger the bubble deformation ratio, the more elongated the bubble. The above operation is further performed at two different points in the extrusion direction, and the bubble deformation ratio is determined at a total of 15 points (5 points x 3 points). The arithmetic mean value of the 15 points in total on the TD cross section is taken as the average bubble deformation ratio of the TD cross section, and the arithmetic mean value of the 15 points in total on the MD cross section is taken as the average bubble deformation ratio of the MD cross section.

[0167] The coefficient of variation of the bubble deformation ratio in the TD cross section and the MD cross section is the percentage of the standard deviation of the bubble deformation ratio divided by the bubble deformation ratio, and is an index that represents the degree of variation from the average value. The standard deviation V of the bubble deformation ratio is as follows. V=(Σ(K i -K ave ) 2 / (n-1)) 1 / 2 K i is the individual bubble deformation rate at 15 locations, and K ave is the average value of the bubble deformation rate, and n is the number of measurements (i.e., 15). The coefficient of variation Cv can be calculated as follows: Cv(%)=(V / K ave ) x 100

[0168] [Average bubble diameter in thickness direction] The average cell diameter in the thickness direction of the extruded foam board is preferably 250 μm to 600 μm, more preferably 300 μm to 500 μm. When the average cell diameter is within the above range, the extruded foam board has high thermal insulation properties and excellent mechanical strength.

[0169] The average bubble diameter through the thickness of an extruded foam board can be determined by taking enlarged photographs of the extruded foam board at three locations: the center and both ends of the TD cross section (cross section perpendicular to the width direction) at a magnification of approximately 50 to 200 times so that the number of cells in the photograph is approximately 200 to 500.The maximum diameter through the thickness of each bubble is measured on each photograph using the image processing software NS2K-pro manufactured by Nano System Co., Ltd., and the arithmetic mean of these values ​​is then calculated. [Example]

[0170] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0171] In the examples and comparative examples, extruded foam boards were produced using the extrusion equipment and raw materials shown below.

[0172] The extrusion equipment used consisted of a first highly mixed extruder with an inner diameter of 115 mm and a second extruder with an inner diameter of 180 mm connected in series, a physical foaming agent injection port near the end of the first extruder, and a flat die equipped with a resin outlet (die lip) with a rectangular cross section measuring 1 mm and a width of 440 mm, connected to the outlet of the second extruder. A forming tool (guider) consisting of a pair of upper and lower polytetrafluoroethylene resin plates placed horizontally at an approximately fixed interval was attached to the resin outlet of the second extruder.

[0173] (1) Base resin The polystyrene resins listed in Table 1 were used as the base resins. No other polymers were used. PS3 is a grade named "HP555" manufactured by DIC Corporation, PS4 is a grade named "HP600ANJ" manufactured by DIC Corporation, and PS5 is a grade named "680" manufactured by PS Japan Co., Ltd.

[0174] PS1 is polystyrene polymerized by the following method.

[0175] [Production of nuclear particles] Equipped with a stirring device, the internal volume is 1m 3 Into the autoclave, 350 kg of deionized water, 2.1 kg of calcium phosphate tribasic (manufactured by Taihei Chemical Industry Co., Ltd., 20.5% slurry) as a suspending agent, 0.158 kg of sodium dodecylbenzenesulfonate (10% aqueous solution) as surfactants, 0.053 kg of disodium dodecyldiphenylethersulfonate (manufactured by Kao Corporation, Pelex SSH 10% aqueous solution) and 0.535 kg of sodium acetate as an electrolyte were charged.

[0176] Next, 0.975 kg of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, Perbutyl O) and 0.284 kg of t-butylperoxy-2-ethylhexyl monocarbonate (manufactured by NOF Corporation, Perbutyl E) as polymerization initiators, and 15.4 g of 4-tert-butylcatechol as a polymerization inhibitor were dissolved in 390 kg of styrene, and the resulting solution was fed into an autoclave while stirring at 110 rpm. After the gas phase in the autoclave was replaced with nitrogen, the temperature was raised to 90°C over 1 hour and 15 minutes.

[0177] After reaching 90°C, the temperature was increased to 100°C over 5 hours. After reaching 100°C, the stirring speed was changed to 90 rpm, and the temperature was increased to 115°C over 1 hour and 30 minutes. The temperature was maintained at 115°C for 2 hours and 40 minutes, and then the temperature was cooled to 40°C over 2 hours. During the temperature increase to 90°C, 1.95 g of potassium persulfate was added to the autoclave as a suspension aid when the temperature reached 60°C.

[0178] After cooling, the contents were removed, and the tribasic calcium phosphate adhering to the surfaces of the styrene-based resin particles was dissolved with nitric acid. The contents were then dehydrated and washed using a centrifuge, and the moisture adhering to the particle surfaces was removed using an airflow dryer to obtain styrene-based resin particles.

[0179] The obtained styrene-based resin particles were sieved to extract particles with a diameter of 0.5 to 1.3 mm (average particle diameter 0.8 mm). These were used as core particles. The average particle diameter d63 of the styrene-based resin particles was measured using a particle size distribution analyzer "Militrack JPA" manufactured by Nikkiso Co., Ltd.

[0180] [Production of styrene-based resin particles] <Dispersion process> Equipped with a stirring device, the internal volume is 1.5m 3 450 kg of deionized water, 2.80 kg of sodium pyrophosphate, and 7.00 kg of magnesium nitrate were fed into an autoclave, and magnesium pyrophosphate was synthesized as a suspension agent within the autoclave by salt exchange. 0.140 kg of sodium alkylsulfonate (Kao Corporation, Latemul PS, 40% aqueous solution) was added as a surfactant, and 70.0 kg of the styrene resin particles (core particles) obtained in the above "Core Particle Production" were added as core particles. The gas phase within the autoclave was then replaced with nitrogen. Specifically, the autoclave was pressurized with nitrogen to 0.3 MPa (G), and the gas within the autoclave was then released until the pressure within the autoclave reached atmospheric pressure.

[0181] <Impregnation process> Next, the temperature was raised to 80 ° C while stirring at 50 rpm. After reaching 80 ° C, the stirring speed was changed to 100 rpm, and a mixture of 100 kg of deionized water, 0.180 kg of sodium alkylsulfonate (Kao Corporation, Latemul PS, 40% aqueous solution), 24.7 kg of styrene (styrene-based monomer), 1.38 kg of t-butylperoxy-2-ethylhexyl monocarbonate (NOF Corporation, Perbutyl E;BE, 10-hour half-life temperature T1 / 299.0 ° C) as a polymerization initiator, and 0.20 kg of α-methylstyrene dimer (NOF Corporation, Nofmer MSD) as a chain transfer agent was prepared into an emulsion using a homogenizer, and the emulsion was fed into an autoclave. The autoclave was then pressurized with nitrogen to 0.1 MPa (G) and maintained at 80 ° C for 15 minutes.

[0182] <Polymerization initiation step> Thereafter, the contents were heated to 105°C over 1 hour while being stirred at 100 rpm.

[0183] <Additional impregnation polymerization process> After the temperature reached 105°C, the contents were maintained for 7 hours and 30 minutes while stirring at 100 rpm. Over a period of 7 hours and 30 minutes, once the temperature inside the autoclave reached 105°C, 316.6 kg of styrene (a styrene-based monomer) was continuously added to the autoclave at a rate of 0.77 kg / min. The styrene addition was simulated based on the styrene polymerization rate calculated from the above-mentioned addition conditions, the chemical properties of the polymerization initiator used in the polymerization, and the polymerization temperature, and additional styrene was added so that the styrene content in the core particles during the styrene addition was 10% by mass or less.

[0184] As a representative example of the simulation results, Figure 2 shows a graph of the simulation results for the production of PS1. The graph plots elapsed time (hr) on the horizontal axis, the styrene monomer content (mass%) in the core particles during the additional impregnation polymerization process on the left vertical axis, and the polymerization temperature (°C) on the right vertical axis. In the graph, the change in styrene content in the core particles versus elapsed time is shown by a solid line, and the change in polymerization temperature versus elapsed time is shown by a dashed line. As illustrated in Figure 2, the relationship between elapsed time, the styrene monomer content in the core particles, and the polymerization temperature can be derived from a simulation based on the polymerization rate calculated from the polymerization conditions. Based on this relationship, the addition of styrene monomer (specifically, styrene) can be adjusted so that the styrene monomer content in the core particles is 10 mass% or less.

[0185] <Residual Monomer Polymerization Process> After the additional impregnation polymerization step, the aqueous medium was heated to 120°C over 2 hours while stirring the contents at 100 rpm, and then maintained at 120°C for 3 hours to polymerize the unreacted styrene monomer.

[0186] <Cooling process> After the residual monomer polymerization step, the aqueous medium was cooled to 35°C over 6 hours while stirring the contents at 100 rpm. After cooling the autoclave, the styrene-based resin particles were removed from the autoclave and washed with dilute nitric acid to dissolve and remove the suspending agent adhering to the resin particle surface. They were then washed with water and dehydrated using a centrifuge. After coating with 0.01 parts by mass of polyoxyethylene lauryl ether (based on 100 parts by mass of styrene-based resin) as an antistatic agent, the moisture on the resin particle surface was removed using an airflow dryer. The styrene-based resin particles thus produced were used as PS1.

[0187] PS2 is polystyrene polymerized by the following method.

[0188] Styrenic resin particles polymerized in the same manner as PS1 were used as PS2, except that the temperature in the polymerization initiation step and the additional impregnation polymerization step was changed from 105°C to 113°C, the amount of styrene added in the impregnation step was changed from 24.7 kg to 37.0 kg, the amount of α-methylstyrene dimer as a chain transfer agent was changed from 0.20 kg to 1.23 kg, and the amount of styrene added in the additional impregnation polymerization step was changed from 316.6 kg to 304.3 kg.

[0189] The number-average molecular weight Mn', weight-average molecular weight Mw', and Z-average molecular weight Mz' listed in Table 1 were determined by GPC-MALS. Specifically, measurements were performed using a Shimadzu Prominence LC-20AD (2HGE) / WS system and a Wyatt Technology DAWN HELE OSII multi-angle light scattering detector under the following conditions: eluent: tetrahydrofuran (THF) at a flow rate of 1.0 ml / min. The concentration detector used was a Wyatt Technology Optilab differential refractometer. One Tosoh TSKgel HHR-H column and two Tosoh TSKgel GMHHR columns were connected in series. Analysis was performed using Wyatt's analysis software ASTRA to determine the number-average molecular weight Mn', weight-average molecular weight Mw', and Z-average molecular weight Mz'. The refractive index concentration increment dn / dc was 0.185 ml / g.

[0190] In addition, the average value of the shrinkage factor g and the branching degree T per 1000 units of styrene m,1000 Specifically, the intrinsic viscosity ([η]) of the polystyrene resin was measured by connecting a viscosity detector VISCOSTARIII manufactured by Wyatt Technology to the MALS. branch ) and the intrinsic viscosity of a standard polymer (linear polystyrene) ([η] linear The ratio of the contraction factor g to the weight average value of the contraction factor g was calculated. The branching degree per molecule T m,w Then, the branching degree T m,1000The polystyrene resin was assumed to have three branched chains, and the branching degree T m The above core particles (linear polystyrene) were used as the standard polymer.

[0191] The number average molecular weight Mn', weight average molecular weight Mw', Z average molecular weight Mz', average value gw of shrinkage factor g, and branching degree T per 1000 units of styrene m,1000 For the measurement, the polystyrene resin to be measured was dissolved in THF, and the solution was left to stand for 5 days or more, and the concentration of the polystyrene resin was 0.3 g / L. The solution was then centrifuged using a membrane filter with a pore size of 0.5 μm to prepare a sample solution.

[0192] The melt viscosity η was measured based on JIS K7199:1999 using a Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. at 200°C and a shear rate of 100 sec -1 The values ​​were measured under the following conditions.

[0193] The melt tension was measured by the above-mentioned method.

[0194] The content of tetrahydrofuran insoluble matter in each polystyrene resin in Table 1 is 0.1% by mass or less.

[0195] [Table 1]

[0196] [Tetrahydrofuran insolubles (THF insolubles)] 1 g of resin pellets made of polystyrene resin was precisely weighed and collected as a sample. 30 ml of tetrahydrofuran was added to this sample, and the sample was immersed at 23°C for 24 hours, then shaken for 5 hours and allowed to stand. The supernatant was then removed by decantation, and 10 ml of tetrahydrofuran was added again, allowed to stand, and the supernatant was removed by decantation. The sample was then dried at 23°C for 24 hours. The weight after drying was determined, and the THF-insoluble content was calculated using the following formula (x). THF insolubles (%) = [weight of insolubles after drying / weight of sample] × 100 (x)

[0197] (2) Physical foaming agent Isobutane (i-Bu) Dimethyl ether (DME) Ethanol (EtOH) Carbon dioxide (CO2) Water (H2O)

[0198] The base resin shown in Table 1 was fed into a first extruder in the formulation shown in Table 2, heated to 200°C, and kneaded. A physical blowing agent was then fed into the first extruder through a physical blowing agent inlet in the amount shown in Table 2, and further kneaded to form a foamable resin melt. Additionally, 0.3 parts by mass of talc (manufactured by Matsumura Sangyo Co., Ltd., product name "High Filler #12," particle size (d50) 7.5 μm) was added as a cell control agent, and 3.75 parts by mass of 134BG (a flame retardant masterbatch (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., GR-134BG) containing a 60% by mass / 40% by mass mixture of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether): Daiichi Kogyo Seiyaku "SR-130" / tetrabromobisphenol A-bis(2,3-dibromopropyl ether): Daiichi Kogyo Seiyaku "SR-720") was added as a flame retardant to the first extruder.

[0199] Next, the obtained foamable resin melt was transferred to a second extruder, where the resin temperature was adjusted, and then the melt was extruded into a guider at a discharge rate of 400 kg / hr. The melt was passed through the guider while foaming and molded (shaped) into a plate to produce a base plate of an extruded foam board with a thickness of 55 mm. Further, the width and length of the base plate were adjusted by cutting, and the molding skins on both sides were evenly cut to produce a rectangular parallelepiped extruded polystyrene resin foam board (width: 910 mm, length: 1820 mm, thickness: 50 mm, volume: 82810 cm) without a molding skin. 3 , Area of ​​cross section perpendicular to the extrusion direction: 455 cm 2 ) was manufactured.

[0200] [Table 2]

[0201] The raw material properties of the polystyrene resins used in the examples and comparative examples (mixtures thereof when two or more types are used) are listed in Table 2, including melt viscosity η, melt tension, stress relaxation time τ, number average molecular weight Mn', weight average molecular weight Mw', Z average molecular weight Mz', average value gw of shrinkage factor g, and branching degree T per 1000 styrene units. m,1000 was measured.

[0202] The stress relaxation time τ was measured by the following tensile stress relaxation test (I).

[0203] [Tensile stress relaxation test (I)] In accordance with JIS K7127:1999, a 20% tensile strain was applied to a 0.4 mm thick dumbbell-shaped test piece of type 5 polystyrene resin in an atmosphere of 80°C at a tensile speed of 50 m / min, and the tensile strain was maintained for 4 minutes from the time when the 20% tensile strain was applied. The initial stress at the time when the 20% tensile strain was applied was defined as a reference value, and the time required for the stress to decrease to one-tenth of the reference value was defined as the stress relaxation time τ at 80°C.

[0204] Test pieces for the tensile stress relaxation test (I) were prepared as follows. Specifically, a polystyrene resin was supplied to a twin-screw extruder (diameter 20 mm, L / D=500), melt-kneaded at a temperature of 200°C, and extruded to prepare resin pellets. The twin-screw extruder was operated at a rotation speed of 50 rpm and had a discharge rate of 1 kg / h during extrusion. When a mixture of two or more polystyrene resins was used as the polystyrene resin (X), each polystyrene resin was supplied to the twin-screw extruder.

[0205] The obtained resin pellets were placed in a 150 mm x 75 mm mold and heat-pressed at a temperature of 200°C and a pressure of 20 MPa to obtain a 0.4 mm thick unstretched resin sheet. Test pieces were obtained by punching out the obtained 0.4 mm thick resin sheet into the shape of a Type 5 dumbbell test piece as described in JIS K7127:1999. Five test pieces were produced by repeating the same method five times.

[0206] The obtained test specimen was left to stand for 24 hours in an atmosphere of 23°C and 50% RH. Thereafter, the specimen was conditioned by standing for 5 minutes in an atmosphere of 80°C, the test temperature, and the above-mentioned tensile stress relaxation test (I) was carried out using the conditioned test specimen. The stress relaxation time τ at 80°C was determined as the arithmetic mean value of the stress relaxation times obtained in the measurements for five test specimens.

[0207] The melt viscosity η, melt tension, number average molecular weight Mn', weight average molecular weight Mw', Z average molecular weight Mz', and average value gw of shrinkage factor g were measured by the same methods as those in Table 1. In these measurements, when a mixture of two or more polystyrene resins was used as the polystyrene resin (X), the measurements were also carried out using test pieces (resin pellets) prepared by the same method as the test pieces used in the tensile stress relaxation test (I).

[0208] The extruded foam boards obtained in the examples and comparative examples were measured as follows.

[0209] [Apparent Density] The apparent density was measured in accordance with JIS K6767 (1999). Rectangular samples measuring 50 mm long, 50 mm wide, and 50 mm thick were cut from each extruded foam plate at three locations: the center and both ends in the width direction. The apparent density of each sample was measured, and the arithmetic mean of the measurements at the three locations was used as the apparent density. The measurements were performed on samples that had been in storage for at least 24 hours after production.

[0210] [Expansion ratio] The expansion ratio is determined by the density of the polystyrene resin used as the base resin for the extruded foam board (i.e., 1050 kg / m 3) to the apparent density (unit: kg / m 3 ) is the value divided by

[0211] [Average bubble diameter in thickness direction] The average bubble diameter in the thickness direction (VD) of the extruded foam board was determined by taking enlarged photographs of the extruded foam board at three locations: the center and both ends of the TD cross section (cross section perpendicular to the width direction) at a magnification of approximately 50 to 200 times so that the number of cells in the photograph was approximately 200 to 500.The maximum diameter of each bubble in the thickness direction was measured on each photograph using the image processing software NS2K-pro manufactured by Nano System Co., Ltd., and the arithmetic mean of these values ​​was then calculated.

[0212] [Bubble deformation rate] The average value and coefficient of variation of the cell deformation ratio of the vertical cross section (TD cross section) perpendicular to the extrusion direction of the extruded foam plate, and the average value and coefficient of variation of the cell deformation ratio of the vertical cross section (MD cross section) perpendicular to the width direction of the extruded foam plate were calculated as follows.

[0213] First, as shown in Figure 1, five samples (20 mm wide x 20 mm long x 50 mm thick) were cut out of the extruded foam board at equal intervals across the width. A 10 mm x 10 mm rectangular measurement area was set at the center of each of the TD and MD cross sections of the cut samples. For example, using image processing software NS2K-pro (Nano System Co., Ltd.), the vertical and horizontal Feret diameters of all bubbles present in the measurement area were calculated, and their ratio (vertical Feret diameter / horizontal Feret diameter) was calculated. The arithmetic mean of each was used as the bubble deformation ratio for the TD and MD cross sections. This procedure was repeated at two different points along the extrusion direction, yielding a total of 15 bubble deformation ratios (5 x 3). The arithmetic mean of the 15 TD cross sections was used as the average bubble deformation ratio for the TD cross section, and the arithmetic mean of the 15 MD cross sections was used as the average bubble deformation ratio for the MD cross section. It is noted that the cell deformation rate was "impossible to measure" because it was difficult to measure the cell deformation rate for extruded foam plates with a volume reduction rate of 6% or more, which will be described later.

[0214] The coefficient of variation of the bubble deformation ratio in the TD cross section and the MD cross section was calculated as a percentage of the value obtained by dividing the standard deviation of the bubble deformation ratio by the deformation ratio of the bubble. The standard deviation V of the bubble deformation ratio is as follows. V=(Σ(K i -K ave ) 2 / (n-1)) 1 / 2 K i is the individual bubble deformation rate at 15 locations, and K ave is the average value of the bubble deformation rate, and n is the number of measurements (i.e., 15). The coefficient of variation Cv was calculated as follows: Cv(%)=(V / K ave ) x 100

[0215] [Volume reduction rate] The volume reduction rate Rv of the extruded foam board produced by the production method of the present invention is calculated by dividing the volume V0 of the original board immediately after production by the volume V of the original board after 24 hours at 23°C. 24 The volume reduction rate Rv was calculated as follows: The volume reduction rate Rv is an index showing how much the volume of the extruded foam board has decreased from immediately after production until 24 hours later, and a large value indicates that the extruded foam board has shrunk after production. Rv = (V0 - V 24 ) / V0×100 The volume was calculated by multiplying the average length in the extrusion direction by the average length in the width direction by the average length in the thickness direction. The average lengths in the extrusion direction, width direction, and thickness direction were calculated as follows. Figure 3 is a schematic diagram showing how to calculate the average dimensions in each direction of an extruded foam board (base board). As shown in Figure 3, the average length of the extruded foam board in the extrusion direction (MD) is measured at the end point (A M ,E M ) and three points that divide the width into four equal parts (B M ~D M ) total of 5 locations (A M ~E M ) are set as measurement points. M~E M ) to the point (A ) opposite to the extrusion direction on the edge of the other side of the extrusion direction of the extruded foam board (the positive side in Figure 3). M '~E M The length from the tip to the tip was measured, and the arithmetic mean value of the five points was taken as the average length in the extrusion direction. M -A M 'line, B M -B M 'line, C M -C M 'line, D M -D M 'Line, E M -E M The lines are parallel to the extrusion direction and are positioned at equal intervals.

[0216] Similarly, the average length in the transverse direction (TD) of the extruded foam plate was measured at a measurement point (A T ~E T ) and set each measurement point (A T ~E T ) to the opposite point (A T '~E T The length from the tip to the tip was measured, and the arithmetic mean value of the five points was taken as the average length in the extrusion direction. T -A T 'line, B T -B T 'line, C T -C T 'line, D T -D T 'Line, E T -E T The lines are parallel to the width direction and are spaced at equal intervals.

[0217] Similarly, the average length in the thickness direction (VD) of the extruded foam board was measured at the edge of one side in the thickness direction (negative side in Figure 3) at the measurement point (A V ~E V ) and set each measurement point (A V ~E V) to the opposite point (A V '~E V The length from the tip to the tip was measured, and the arithmetic mean value of the five points was taken as the average length in the extrusion direction. V -A V 'line, B V -B V 'line, C V -C V 'line, D V -D V 'Line, E V -E V The lines are parallel to the thickness direction and are positioned at equal intervals.

[0218] Figure 4 is a schematic diagram showing how to calculate the average length in the extrusion direction of an extruded foam plate when shrinkage occurs in the extrusion direction. For convenience, Figure 4 shows an extruded foam plate in which shrinkage occurs only on the negative side of the extrusion direction. However, when shrinkage occurs in the extrusion direction, shrinkage occurs in a roughly similar shape on the positive side of the extrusion direction. Shrinkage can also occur in the width and thickness directions. The method for calculating the average dimensions in each direction of an extruded foam plate is basically the same as when no shrinkage occurs.

[0219] The average length of the extruded foam board in the extrusion direction (MD) is measured at the end point (A M ,E M ) and three points that divide the width into four equal parts (B M ~D M ) total of 5 locations (A M ~E M ) is set as the measurement point. Even if shrinkage occurs as shown in Figure 4 and the edge of the extruded foam board on one side in the extrusion direction (the negative side in Figure 4) is curved, the point (A M ~E M ) and point (A M '~E M A line connecting M -A M 'line, B M -B M 'line, C M -CM 'line, D M -D M 'Line, E M -E M The points (A ') are parallel to the extrusion direction and are positioned at equal intervals. M ~E M ) and point (A M '~E M The same applies when shrinkage occurs in the width and thickness directions.

[0220] The volume reduction rate was evaluated as follows: 3.0% or less: "A", 3.0% or more and 4.0% or less: "○", 4.0% or more and 5.0% or less: "△", and over 5.0%: "×".

[0221] [Unmelted material] The surface of the extruded foam plate was observed to check for the presence or absence of unmelted matter. The evaluation was carried out as follows: no unmelted matter was marked "○", slight unmelted matter was marked "△", and significant unmelted matter was marked "×".

[0222] The foaming temperature in Table 2 was the foaming temperature at which the sample with the smallest volume loss was obtained. The foaming temperature range at which a good foam board can be molded refers to the foaming temperature range between 120°C and 140°C at which a passing product with a volume loss of 4% or less (a rating of "Good" or better) can be obtained. The wider this range, the wider the manufacturing range in which extruded foam boards with reduced shrinkage can be produced, which is preferable.

[0223] As can be seen from the volume reduction rates in Table 1, in Examples 1 to 7, the polystyrene resins had a stress relaxation time τ of 100 seconds or longer as measured in the tensile stress relaxation test (I), which enabled the extruded foam boards to be suppressed from shrinking after production (shrinkage one day after production). Furthermore, in all of Examples 1 to 7, the generation of unmelted material was also sufficiently suppressed.

[0224] As can be seen from a comparison of Examples 1 to 5 and 7 with Example 6, the foaming temperature range in which a good foamed board can be molded can be expanded by using a polystyrene resin (A) having a weight-average molecular weight Mw'A of 700,000 or more and 3,000,000 or less in combination with a polystyrene resin (B) having a weight-average molecular weight Mw'B determined by GPC-MALS of 100,000 or more and less than 700,000. Furthermore, a comparison of Examples 1 and 7 confirmed that the formation of unmelted material can be further suppressed when the weight-average molecular weight Mw' of the polystyrene resin (B) used in combination with the polystyrene resin (A) is 500,000 or more and less than 700,000.

[0225] In contrast, in Comparative Examples 1 to 4, the stress relaxation time τ measured in the tensile stress relaxation test (I) was less than 100 seconds, and significant shrinkage occurred after production of the extruded foam boards (shrinkage one day after production). In Comparative Example 4, linear polystyrene with a small molecular weight and a shrinkage factor of 1 was used, which not only caused significant shrinkage but also resulted in significant generation of unmelted material.

[0226] As can be seen from Table 2, the stress relaxation time τ of a polystyrene resin is a value that cannot be directly estimated from data such as the molecular weight of the polystyrene resin. For example, in Example 1 and Comparative Example 2, the molecular weights (Mn', Mw', Mz') of the polystyrene resins are similar, but the stress relaxation times τ are significantly different. In the present invention, it has been discovered that by using a polystyrene resin whose stress relaxation time τ falls within a predetermined range even if the molecular weights and other factors are similar, the foaming temperature range at which a good foam board with reduced volume shrinkage can be molded can be expanded.

Claims

1. The foamable molten material is obtained by melt-kneading a base resin containing a polystyrene-based resin and a physical foaming agent, and the resulting material is extruded and foamed to form a plate using a molding tool. ３ More than 40kg / m ３ Below, volume 20,000 cm ３ The method for producing the above extruded polystyrene resin foam board comprises: The method for producing an extruded polystyrene resin foam board, wherein the polystyrene resin has a stress relaxation time τ of 100 seconds or more as measured by the following tensile stress relaxation test (I). Tensile stress relaxation test (I) In accordance with JIS K7127:1999, a 20% tensile strain is applied to a 0.4 mm thick dumbbell-shaped test piece of type 5 polystyrene resin in an atmosphere of 80°C at a tensile speed of 50 m / min, and the tensile strain is maintained for 4 minutes from the time when the 20% tensile strain is applied. The initial stress at the time when the 20% tensile strain is applied is defined as a reference value, and the time required for the stress to decrease to one-tenth of the reference value is defined as the stress relaxation time τ.

2. 2. The method for producing an extruded polystyrene resin foam board according to claim 1, wherein the polystyrene resin is a mixed resin containing a polystyrene resin (A) and a polystyrene resin (B), and the weight average molecular weight Mw'A of the polystyrene resin (A) measured by GPC-MALS is 700,000 or more and 3,000,000 or less, and the weight average molecular weight Mw'B of the polystyrene resin (B) measured by GPC-MALS is 100,000 or more and less than 700,000.

3. 3. The method for producing an extruded polystyrene resin foam board according to claim 2, wherein the polystyrene resin (A) has an average shrinkage factor of 0.80 or less as determined by a GPC-MALS-VISCO method, and the polystyrene resin (A) has a tetrahydrofuran-insoluble content of 0.1% by mass or less (including 0).

4. 4. The method for producing an extruded polystyrene resin foam board according to claim 2 or 3, wherein the polystyrene resin (A) does not contain a component derived from a polyfunctional monomer in the molecular chain.

5. 4. The method for producing an extruded polystyrene resin foam board according to claim 2, wherein a mass ratio of the polystyrene resin (A) to the total mass of the polystyrene resin (A) and the polystyrene resin (B) is 15 mass% or more and 90 mass% or less.

6. 4. The method for producing an extruded polystyrene resin foam plate according to claim 2, wherein the polystyrene resin (B) has a weight average molecular weight Mw'B of 500,000 or more but less than 700,000 as determined by GPC-MALS, and an average shrinkage factor as determined by GPC-MALS of 0.95 or less.

7. The degree of branching T per 1000 styrene units of the polystyrene resin (A) ｍ,１０００ A is 0.2 or more, and the branching degree T per 1000 styrene units of the polystyrene resin (B) ｍ,１０００ Absolute value of the difference with B | (T ｍ,１０００ A)-(T ｍ,１０００ 4. The method for producing an extruded polystyrene resin foam board according to claim 2, wherein B) | is 0.5 or less.

8. 3. The method for producing an extruded polystyrene resin foam board according to claim 1, wherein the physical blowing agent contains water and / or aliphatic alcohol having 1 to 5 carbon atoms, and the total amount of the water and / or aliphatic alcohol having 1 to 5 carbon atoms added is 0.7 mol or more and 2 mol or less per 1 kg of the base resin.

9. Apparent density 10 kg / m ３ More than 40kg / m ３ Below, volume 20,000 cm ３ The above-mentioned extruded polystyrene resin foam board, the average cell deformation rate of the vertical cross section (TD cross section) perpendicular to the extrusion direction of the extruded polystyrene resin foam board is 0.85 or more and 1.10 or less, and the coefficient of variation thereof is 3.0% or less; The average value of the cell deformation rate of the vertical cross section (MD cross section) perpendicular to the width direction of the extruded polystyrene resin foam board is 1.05 to 1.30, and the coefficient of variation thereof is 3.0% or less.

10. 10. The extruded polystyrene resin foam board according to claim 9, wherein the average cell diameter in the thickness direction of the extruded polystyrene resin foam board is 250 μm or more and 600 μm or less.

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