JP2008120009A - Polystyrene-based resin laminate foam sheet and its molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminate foam sheet which has excellent deep drawing properties in thermal molding of a light laminate foam sheet and an improved drawing rate in thermal molding and gives container moldings having not-thin side walls and high strength. <P>SOLUTION: A polystyrene-based resin laminate foam sheet 1 has an impact-resistant polystyrene-based resin layer laminated on one side of a polystyrene-based resin foam layer of a content of the styrene dimer and trimer of ≤2,000 ppm. The tensile elastic modulus of the unfoamed resin obtained by defoaming the polystyrene-based resin foam layer of the laminated foam sheet, measured in a tensile test at 120°C, is 110-170 MPa. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polystyrene-based resin laminated foam sheet and a molded product thereof. Particularly, when thermoforming a deep-drawn shaped molded article such as a flaw from a relatively lightweight laminated foam sheet, the present invention has excellent formability and excellent strength. The present invention relates to a polystyrene-based resin laminated foam sheet from which a molded product can be obtained and a molded product thereof.

  Conventionally, polystyrene-based resin laminated foam sheets have been widely used as molding sheets for obtaining molded articles by thermoforming. This polystyrene-based resin laminated foam sheet (hereinafter also simply referred to as “laminated foam sheet”) has an impact-resistant polystyrene resin layer (hereinafter also simply referred to as “resin layer”) laminated on the polystyrene resin foam sheet. A foamable melt-mixed resin by melt-kneading a polystyrene resin, various additives such as a bubble regulator and a foaming agent using an extruder, and the foamable melt-mixed resin After forming a foam sheet by releasing it from the inside of the die under atmospheric pressure, an impact-resistant polystyrene resin sheet is laminated, or a melt of a foamable melt-mixed resin and an impact-resistant polystyrene resin is coextruded. It is manufactured by doing.

  The laminated foamed sheet thus obtained is a material excellent in thermoformability, and a molded body obtained by thermoforming the sheet (hereinafter also simply referred to as “molded body”) is lightweight and heat insulating. In addition, it has been widely used as a thermoforming material for food containers such as lunch boxes, trays, bowls, and cups.

  Such food containers are always required to be lightweight and must be strong enough to withstand use as food packaging containers, especially in the case of deep-drawn containers such as bags and cups. Compressive strength in the horizontal direction (hereinafter also referred to as “lip strength”) at the portion is required as an important characteristic.

  For example, Patent Document 1, Patent Document 2, and Patent Document 3 disclose techniques for obtaining a deep-drawn shaped molded article such as a cup or cup having excellent strength.

  Patent Document 1 discloses a technique for controlling a tensile load of a laminated foam sheet to be obtained within a specific range by using a polystyrene resin having specific viscoelasticity for a foam layer.

  In Patent Document 2, when a foamed sheet is produced, the foamed sheet is stretched by controlling the blow-up ratio of the foamed sheet (a value obtained by dividing the plug diameter by the mold slit diameter) and the take-off speed. A technique for controlling the shrinkage ratio (length change before and after heating) of a laminated foam sheet during molding to a specific range is disclosed.

  In Patent Document 3, the shrinkage rate during thermoforming is thermoformed by utilizing the stretch of the foam sheet when producing the foam sheet and the stretch of the resin layer when laminating the resin layer on the foam sheet. A technique for controlling to a value suitable for the above is disclosed.

  On the other hand, the polystyrene resin foam sheet contains oligomers such as styrene monomer, styrene dimer, styrene trimer, and there is a problem that these may be eluted in a very small amount in the container.

  In "SPEED '98" created by the Environment Agency in 1998, various compounds suspected as environmental hormones were listed, and as a result, the safety of expanded polystyrene containers containing styrene dimers and trimers was questioned. . However, the safety of oligomers such as styrene dimers and trimers has been proved by reports (Yoichi Nobuhara et al., Journal of Food Hygiene, vol. 40, No. 1, 1999, February). On March 31, it was decided to exclude styrene dimers and trimers from the environmental hormone list.

  As described above, the suspicion of styrene dimer and styrene trimer (hereinafter also referred to as styrene oligomers) as environmental hormones is clear, and the safety of the expanded polystyrene container has not been proved. Is a so-called impurity generated during the synthesis of polystyrene, and it is desired to reduce the amount of such impurities eluted into the container.

  Containers with reduced elution amount of styrene oligomer into the container are demanded by the food industry, and it is recommended to use polystyrene resins with low styrene dimer and trimer content. Since there are few low molecular weight components, such as a styrene oligomer, thermoformability fell, and there existed a problem that the surface of a foaming layer tends to crack in the peripheral wall near the lip | edge part of a molded article at the time of deep drawing (hereinafter, this is called The phenomenon that cracks occur on the surface of the foam layer is also called “Naki”).

  Therefore, Patent Document 4 discloses that a specific amount of liquid paraffin is added to a polystyrene-based resin having a low content of styrene dimer or trimer, thereby adjusting the resin to a specific melt property, thereby foaming during thermoforming. Techniques for improving sheet elongation are disclosed.

JP 2001-293822 A Japanese Patent Laid-Open No. 10-324759 JP 2003-251762 A Japanese Patent Laid-Open No. 2003-118047

  In recent years, strength that can withstand use as a food packaging container has been demanded, and from the viewpoint of cost reduction and resource saving, the weight of laminated foam sheets has been further reduced, and the number of containers to be thermoformed Development of a laminated foam sheet corresponding to the reduction of the pitch interval between containers accompanying the increase in the number of containers is required.

  In the case of conventional laminated foam sheets, particularly in the case of deep-drawn containers such as baskets, if a large number is taken, the laminated foam sheets from the laminated foam sheet portions (hereinafter also referred to as skeleton parts) between the containers are sufficiently drawn. In other words, the thickness of the side wall of the resulting container is reduced, and the required strength, particularly the lip strength, cannot be satisfied. When the basis weight of the laminated foam sheet is increased in order to obtain sufficient strength, the lightness is reduced. Therefore, in order to achieve weight reduction of the laminated foam sheet while satisfying the strength of the container, it is necessary to improve the pulling rate during thermoforming and increase the pulling amount from the skeleton portion.

  In the laminated foam sheet of Patent Document 1, the tensile stress of the foam sheet at normal temperature is specified, but the tensile stress at the time of heating has not been studied, and the heating tensile stress at the time of thermoforming was not sufficient. When thermoforming is performed using a lightweight laminated foam sheet, the strength of the resulting molded product is still insufficient if the pitch interval of the container is narrowed during thermoforming.

  In the laminated foam sheet of Patent Documents 2 and 3, by controlling the heat shrinkage rate of the laminated foam sheet within a specific range, it effectively prevents the laminated foam sheet from being drawn down during thermoforming. No consideration has been given to the tensile properties at the time of heating of the laminated foam sheet, and when thermoforming is performed using a lightweight laminated foam sheet, if the pitch interval of the container is narrowed during thermoforming, The strength was insufficient.

  In the laminated foam sheet of Patent Document 4 described above, when a compound such as liquid paraffin is added, the elongation during thermoforming of the laminated foam sheet is improved, but the pull-in rate from the skeleton part is reduced. When the pitch interval is narrowed, the strength of the resulting molded product is lowered, and there is a problem that the basis weight of the laminated foamed sheet must be increased in order to obtain a high-strength molded product.

  The present invention provides a high-strength, low-thickness, thin-walled container-formed product that is excellent in deep drawability and improves the pull-in rate during thermoforming when lightweight laminated foam sheets are thermoformed. It aims at providing the laminated foam sheet from which a molded article is obtained.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when the tensile properties at 120 ° C. of the polystyrene resin forming the foam layer of the polystyrene resin laminated foam sheet are within a specific range, The inventors have found that the pulling rate during thermoforming is improved despite the relatively large elongation during molding, and have reached the present invention.

That is, the present invention
[1] In a polystyrene resin laminated foam sheet in which an impact-resistant polystyrene resin layer is laminated on one side of a polystyrene resin foam layer having a styrene dimer and styrene trimer content of 2000 ppm or less, the laminated foam sheet is formed. The polystyrene-based resin laminated foam sheet is characterized in that the non-foamed resin obtained by defoaming the polystyrene-based resin foam layer has a tensile elastic modulus of 110 to 170 MPa in a tensile test at 120 ° C.

Furthermore, the present invention provides
[2] The polystyrene-based resin constituting the polystyrene-based resin foamed layer in the polystyrene-based resin laminated foamed sheet has a Z-average molecular weight of 5.8 × 10 ⁵ or more and a low molecular weight saturated hydrocarbon content. The polystyrene-based resin laminated foam sheet according to [1], wherein the content is 0.1% by weight or less (including 0),
[3] The apparent density of the polystyrene-based resin foam layer is 0.08 to 0.35 g / cm ³ , the thickness is 1.8 to ³ mm, the open cell ratio is 0 to 25%, and the cell shape is (1 ) To (3), the polystyrene-based resin laminated foam sheet according to [1] or [2],
(Equation 2)
0.3 <Z / X <0.8 (1)
0.3 <Z / Y <0.8 (2)
0.08 <Z <0.2 (3)
(However, in the formula, each of X, Y, and Z is an average cell diameter in the extrusion direction (MD), width direction (TD), and thickness direction of the foamed layer, and the unit is mm.)
And

The present invention also provides
[4] A gist is a molded product obtained by thermoforming the styrene resin laminated foam sheet according to any one of [1] to [3].

According to the invention relating to claim 1 of the present invention, since the pulling rate at the time of thermoforming is excellent, even if a lightweight laminated foam sheet is used, the weight per molded product increases, and molding with sufficient strength It becomes possible to obtain goods.
Moreover, according to the invention concerning Claim 2 and 3 of this invention, the laminated foam sheet which has the further outstanding moldability is provided.

Hereinafter, the polystyrene resin laminated foam sheet of the present invention (hereinafter simply referred to as a laminated foam sheet) will be described in detail.
The laminated foam sheet of the present invention comprises a polystyrene resin foam layer (hereinafter also simply referred to as a foam layer) and an impact-resistant polystyrene resin layer (hereinafter also simply referred to as a resin layer) laminated on one side of the foam layer. Become.

The polystyrene-type resin as used in the field of this invention means what corresponds to either of the following (a)-(e).
(A) A homopolymer whose structural unit derived from a styrene monomer represented by the following general formula (1) is 100% by weight.
(B) A copolymer having 100% by weight of structural units derived from two or more styrene monomers represented by the following general formula (1).
(C) a copolymerizable monomer having at least 60% by weight, preferably at least 80% by weight of structural units derived from one or more styrenic monomers represented by the following general formula (1), the remainder being different from that A copolymer composed of derived structural units.
(D) A mixture of two or more selected from the group of (a) to (c) above.
(E) A mixture of any one of the above (a) to (d) and a component selected from the group of synthetic resins and elastomers different from any of the above (a) to (d), wherein in the mixture, The structural unit derived from the styrenic monomer represented by the following general formula (1) is at least 60% by weight, preferably at least 80% by weight.

  In the general formula (1), R represents a hydrogen atom or a methyl group, Z represents a halogen atom or a methyl group, and p is 0 or an integer of 1 to 3.

  Examples of the polystyrene resins represented by (a) to (e) include polystyrene, rubber-modified polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, and styrene. -Methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-maleic anhydride copolymer Examples thereof include a blend, a polystyrene-polyphenylene ether copolymer, and a mixture of polystyrene and polyphenylene ether.

  The impact-resistant polystyrene resin that forms the resin layer of the laminated foam sheet of the present invention is one that is modified by rubber such as synthetic rubber among the above-mentioned polystyrene resins, and has improved impact resistance. is there. The modification by rubber in the present invention means that a rubber component is contained in a polystyrene resin as a copolymer component or / and a rubber component as a mixed component. Among the impact-resistant polystyrene resins, impact-resistant polystyrene (hereinafter also referred to as HIPS), a blend of HIPS and polystyrene (hereinafter also referred to as GPPS), or GPPS and styrene-butadiene-styrene copolymer. A blend (SBS) or a blend thereof with a hydrogenated product (SEBS) is included.

  The rubber content in the impact-resistant polystyrene resin of the resin layer is preferably in the range of 0.5 to 15% by weight. Particularly preferred is 2 to 12% by weight.

The impact-resistant polystyrene resin of the present invention preferably has a flexural modulus (measured according to JIS K 7171 (1994)) of 1800 to 2800 MPa, more preferably 2000 to 2600 MPa.
The impact-resistant polystyrene-based resin of the present invention has a Charpy impact strength (measurement method conforms to JIS K 7111 (1996). However, ISO 179 / 1eA is used as the method classification) is 3 to 30 kJ /. It is preferable to use m ² , preferably 5 to 20 kJ / m ² . If it is an impact-resistant polystyrene resin within these ranges, the laminated foam sheet of the present invention can maintain high strength even if it is thin.
In addition, the resin layer in the present invention is preferably non-stretched because it is excellent in deep drawability.

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

  The resin layer may be laminated to the foamed sheet by extrusion lamination using another extruder immediately after forming the foamed sheet by extrusion foaming, or laminated to the foamed sheet by extrusion lamination several days after forming the foamed sheet by extrusion foaming. May be. Moreover, you may form a resin layer by laminating | stacking a foamable molten resin mixture and the molten resin mixture for resin layers using a coextrusion die, and then extruding. Furthermore, you may laminate | stack a film on the outer surface of a resin layer as needed. Moreover, you may laminate | stack a film on the foaming layer surface on the opposite side to the surface where the resin layer is laminated | stacked in the range which does not inhibit the objective and effect of this invention.

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

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

  The total content of styrene dimer and styrene trimer in the polystyrene-based resin foam layer in the present invention is 2000 ppm or less, more preferably 1600 ppm or less, and still more preferably 1400 ppm or less.

  The content of styrene dimer and styrene trimer in the polystyrene-based resin foam layer in the present specification is a value determined as follows.

A. Preparation and measurement method of sample 1) About 0.2 g of a measurement sample cut out from the foamed layer is accurately weighed to 0.0001 g and dissolved in about 10 ml of tetrahydrofuran in a beaker.
2) After confirming that the sample for measurement was completely dissolved in tetrahydrofuran, the total amount of about 10 ml of the sample tetrahydrofuran solution was dropped into about 250 ml of normal heptane at 23 ° C. to precipitate the resin. Furthermore, about 10 ml of tetrahydrofuran is put into a beaker, the inside of the beaker is washed, and the whole amount of about 10 ml of tetrahydrofuran used for washing is further dropped into the normal heptane twice.
3) The resin precipitated in normal heptane is separated by filtration into an eggplant flask using No. 5B quantitative filter paper. In the filtration, suction filtration is not performed and natural filtration is performed.
4) Connect the eggplant flask containing the filtrate to a rotary evaporator, evaporate the normal heptane in a 40 ° C. water bath, and concentrate the filtrate to about 5-10 ml. The concentrated filtrate is taken in a beaker, and about 20 ml of normal heptane is put into a further flask to wash the flask. Add the normal heptane used for washing to the filtrate in the beaker.
5) Add about 10 ml of acetonitrile to the filtrate and concentrate the filtrate to about 6-9 ml over about 1 hour while blowing compressor air over the filtrate.
6) The filtrate concentrated to about 6-9 ml was diluted with acetonitrile so that the total volume became 10 ml, and then filtered through a polytetrafluoroethylene filter (Fluorinert membrane filter manufactured by Yamato Scientific Co., Ltd.) with a pore size of 0.5 μm. Is a measurement sample.
7) The measurement sample is injected into the high performance liquid chromatograph and measured.

B. Measuring device (high performance liquid chromatograph)
Liquid feed pump LC-6A (2 units), automatic sample injection device SIL-6A, ultraviolet spectrophotometer detector SPD-6A, column oven CTO-6A, system controller SCL-6A, data processing device C-R3A (any (Manufactured by Shimadzu Corporation).

C. Measurement condition column: ULTRON VX-ODS (filler ODS silica, particle size 5 μm, column inner diameter 4.6 mm, column length 250 mm) (manufactured by Shinwa Kako Co., Ltd.).
Column temperature: 50 ° C
Mobile phase: Acetonitrile: water (volume ratio 6: 4) was used as the initial concentration, and acetonitrile was used alone for 13 minutes from the immediately after injection of the measurement sample, followed by further elution for 22 minutes.
Flow rate: 1.5 ml / min.
Detection wavelength: 225 nm
Injection volume: Adjust appropriately within the range of 5-100 μl.
Calibration curve: A standard sample of styrene dimer and styrene trimer (manufactured by Kanto Chemical Co., Ltd.) is used and quantified by the absolute calibration curve method.

  The polystyrene resin laminated foam sheet of the present invention has a tensile elastic modulus of 110 to 170 MPa in a tensile test at 120 ° C. of a non-foamed resin obtained by defoaming the polystyrene resin foam layer of the laminated foam sheet. Preferably it has 120-160 MPa.

  When the said tensile elasticity modulus is too small, the drawing rate at the time of thermoforming will worsen, and the intensity | strength of the molded product obtained will become weak. On the other hand, when the tensile elastic modulus is too large, the pulling rate at the time of thermoforming is sufficient, but the moldability is deteriorated, for example, the elongation is deteriorated and cracks are generated.

  Further, the polystyrene resin laminated foam sheet of the present invention has a tensile yield strength of 5 MPa or more in a tensile test at 120 ° C. of a non-foamed resin obtained by defoaming the polystyrene resin foam layer of the laminated foam sheet. It is preferably 6 MPa or more, more preferably 7 MPa or more. When the tensile yield strength is within the above range, it is possible to obtain a laminated foam sheet having a higher pulling rate during thermoforming. The upper limit of the tensile yield strength under the above measurement conditions is approximately 20 MPa.

  The polystyrene resin laminated foam sheet of the present invention has a tensile elongation at break of 200% or more in a tensile test at 120 ° C. of a non-foamed resin obtained by defoaming the polystyrene resin foam layer of the laminated foam sheet. Preferably, it is 250% or more, more preferably 300% or more. If the tensile elongation at break is too small, the elongation at the time of thermoforming deteriorates, and there is a possibility that the moldability deteriorates, such as the occurrence of cracks. That is, when the tensile elongation at break is within the above range, a laminated foam sheet having more excellent deep drawability can be obtained. The upper limit of the tensile fracture elongation under the above measurement conditions is approximately 1000%.

  The tensile test at 120 ° C. described in this specification is based on JIS K 7113 (1995) and is measured as follows. As the measuring device, a Tensilon universal testing machine such as Tencilon universal testing machine RTC-1250A manufactured by Orientec Co., Ltd. can be used.

  First, a foam layer and a resin layer are separated from a polystyrene-based resin laminated foam sheet, and the foam layer is left in a vacuum oven at 200 ° C. for 4 hours to remove the foaming agent and air in the foam layer. Next, the foaming layer from which the foaming agent and air have been removed is superposed on the number of samples necessary for sample preparation, and is pressurized to 5 MPa at 230 ° C. to give a 1.5 mm thick non-foamed resin sample (hereinafter also referred to as a solid sample). Is made. From this solid sample, a portion not containing bubbles is cut out and cut into a shape of No. 2 type test piece described in JIS K 7113 (total length 115 mm, parallel portion width 6 mm, distance between marked lines 33 mm). Measure the width and thickness of the parallel part of this specimen up to 0.01 mm at one central part between the marked lines and one place 5 mm inside each marked line, and calculate the average and minimum sectional areas. calculate.

  Next, the temperature chamber set in the Tensilon universal testing machine is preheated to 120 ° C., the prepared test piece is placed in the gripping tool, and after 40 seconds, the tensile test is performed under the condition of a tensile speed of 500 mm / min. I do. In addition, the temperature in a thermostat is measured using a thermocouple in the position shifted 20 mm in the horizontal direction from the center part between grips.

  Using the stress-strain curve obtained by the measurement, the tensile yield strength is calculated from the equation (4), the tensile elastic modulus is calculated from the equation (5), and the tensile fracture elongation is calculated from the equation (6).

(Equation 3)
Tensile yield strength σ (MPa) = F / A (4)
In the above equation (4), F is the load at the yield point, and A is the original minimum cross-sectional area of the test piece.

(Equation 4)
Tensile modulus E (MPa) = Δσ / Δε (5)
However, in the above equation (5), Δσ is the difference in stress due to the original average cross-sectional area between two points on the first straight line of the stress-strain curve, and Δε is the difference in strain between the same two points.

(Equation 5)
Tensile elongation at break (%) = {(L−L ₀ ) / L ₀ } × 100 (6)
However, in the above equation (6), L is the distance between marked lines at the time of fracture, and L ₀ is the original distance between marked lines.

The surface temperature of the laminated foam sheet when thermoforming the laminated foam sheet is about 120 ° C. Therefore, in evaluating thermoformability, mechanical properties when the laminated foam sheet is heated to 120 ° C. are important. However, since the laminated foam sheet has excellent heat insulation properties, Since the temperature in the vicinity of the central portion in the thickness direction is lower than that of the surface portion, it has been difficult to specify resin characteristics having excellent thermoformability until now.
In addition, since the molecular weight of polystyrene resins decreases due to shearing and heat applied during extrusion, the mechanical properties of polystyrene resins after extrusion are more important than those before extrusion in evaluating thermoformability. . Furthermore, when the resin layer is separated from the laminated foam sheet, the bubbles in the foam layer are destroyed, so that it is impossible to accurately evaluate the mechanical properties of the foam layer.

  Therefore, when the inventors heated a test piece having a thickness of 1.5 mm in which the foamed layer was defoamed to a non-foamed state in a 120 ° C. atmosphere for 40 seconds, the temperature distribution of the test piece was It was found that there was a correlation between the tensile physical properties during heating and the thermoformability of the laminated foam sheet, especially the pull-in ratio, by evaluating the tensile physical properties at that time. It was.

In order to achieve the heat tensile properties, the Z-average molecular weight of the polystyrene resin constituting the polystyrene resin foam layer is preferably 5.8 × 10 ⁵ or more, and 6.0 × 10 ⁵ to 1. It is more preferable that it is .6 × 10 ⁶ , and 7.0 × 10 ^{5 to} 1.1 × 10 ⁶ is even more preferable. When the Z average molecular weight is within the above range, the high molecular weight component in the polystyrene resin increases, so the pulling rate during thermoforming increases, and the resulting molded product has excellent strength and thermoforming. Since it is excellent in elongation of the laminated foam sheet at the time, the thermoformability of the sheet is excellent.

  In order to achieve the above Z average molecular weight, the following (A) or (I) is usually selected as the raw material polystyrene resin used in the present invention, but it can be carried out inexpensively and efficiently. (I) is preferred because it is easy to adjust the molecular weight of the polystyrene-based resin to a molecular weight suitable for thermoforming.

(A) High molecular weight polystyrene resin (hereinafter referred to as “a”) in which the content of the styrene oligomer contained in the polystyrene resin is 2000 ppm or less and the Z average molecular weight after extrusion is 5.8 × 10 ⁵ or more. "HMW-PS").

Usually, when a polystyrene resin is extruded, the molecular weight, particularly the Z average molecular weight, of the polystyrene resin is lowered by shear and heat received during extrusion. In order to set the Z average molecular weight of the resin after extrusion to 5.8 × 10 ⁵ or more, it is necessary to use a polystyrene resin having a Z average molecular weight higher than 5.8 × 10 ⁵ . In particular, when extruding under high shear and high temperature, the Z average molecular weight is greatly reduced, so it is necessary to use a polystyrene resin having a higher Z average molecular weight.
However, high-molecular-weight polystyrene resins with a low content of styrene oligomers are generally not on the market and are suitable for thermoformability in the present invention, particularly for the pull-in rate during thermoforming. It is extremely difficult to obtain a resin having a hot tensile property from the market.

Accordingly, the polystyrene resin having a heat tensile property suitable for thermoformability having a Z average molecular weight of 5.8 × 10 ⁵ or more is (i) a content of styrene oligomer contained in the polystyrene resin is 2000 ppm or less. A polystyrene resin (hereinafter referred to as “NMW-PS”) having a general molecular weight of 1 and a polystyrene resin (hereinafter referred to as “UHMW-PS”) having a very large molecular weight as compared with NMW-PS is used in combination. The Z average molecular weight after extrusion can be adjusted to 5.8 × 10 ⁵ or more.

  In this case, the amount of UHMW-PS used is preferably 3 to 50 parts by weight, more preferably 5 to 40 parts by weight, based on 100 parts by weight of NMW-PS, although it depends on the molecular weight of the UHMW-PS used. More preferred is ˜30 parts by weight. If the amount of UHMW-PS used is too small, it will be difficult to maintain the molecular weight of the polystyrene resin constituting the resulting foamed layer within the above range. On the other hand, when there is too much usage-amount of UHMW-PS, cost will increase. In order to maintain the molecular weight of the polystyrene resin constituting the extruded foam within the above range, the larger the Mz of the UHMW-PS used, the smaller the amount used, and the Mz of the UHMW-PS used is smaller. There is a tendency that the smaller the amount is, the larger the amount used.

The NMW-PS has a weight average molecular weight (Mw) of 2.0 × 10 ⁵ or more and less than 3.5 × 10 ⁵ and a Z average molecular weight (Mz) of 4.0 × 10 ⁵ or more and 5.8 ×. It is less than 10 ⁵ .

On the other hand, UHMW-PS refers to those having a weight average molecular weight (Mw) of 4.0 × 10 ⁵ or more and a Z average molecular weight (Mz) of 1.0 × 10 ⁶ or more. The UHMW-PS Mw is ^{4.0 × 10 5 ~1.0 × 10 6} , preferably has Mz is ^{1.0 × 10 6 ~3.0 × 10 6} , Mw is 4.5 × 10 ⁵ to 6.0 is × 10 ^5, is more preferable Mz is ^{1.0 × 10 6 ~2.0 × 10 6} . If Mw and Mz of UHMW-PS are small, it may be difficult to achieve the object of the present invention, and if Mw and Mz of UHMW-PS are large, melt kneading with NMW-PS may be difficult. There is. That is, when the molecular weight of UHMW-PS is within the above range, the UHMW-PS is mixed with NMS-PS having a general molecular weight, so that the molecular weight of the mixture can be drawn from the skeleton during thermoforming. And can be adjusted to a molecular weight suitable for deep drawing.

  UHMW-PS can be produced, for example, by employing a continuous polymerization method, adding an appropriate amount of organic peroxide divided into a plurality of times, and polymerizing a styrene monomer within a range where no gel is generated. As another method, it can also be produced by employing a suspension polymerization, seed polymerization or emulsion polymerization method. Among the above polymerization methods, the content of styrene oligomers in UHMW-PS obtained by suspension polymerization, seed polymerization or emulsion polymerization tends to decrease, which is preferable.

  If a polymerization initiator (usually an organic peroxide) remains in the obtained UHMW-PS, the molecular weight will be greatly reduced during subsequent thermal processing, depending on the amount remaining. The polymerization initiator is preferably completely or substantially completely deactivated.

In the present invention, Mw and Mz are values determined by gel permeation chromatography (GPC method). Specifically, the foamed layer of the laminated foamed sheet is dissolved in 20 ml of tetrahydrofuran (THF) (after being removed by filtration if insoluble matter in THF is present), and the following analysis is performed using the equipment shown below. Measured by GPC method under the conditions, horizontal (parallel to the horizontal axis) on the basis of the peak start position by the styrenic resin of the chart (in the present invention, the molecular weight of 5.4 × 10 ⁶ position is adopted for convenience) Draw a baseline and calculate each molecular weight with a standard calibration curve created using standard polystyrene.

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

  The average molecular weight of polystyrene resin raw materials such as HMW-PS, NMW-PS and UHMW-PS is the same as the above measurement method by using a polystyrene resin raw material instead of the foamed layer as a measurement sample. Can be measured by the method.

  In the present invention, the content of the low molecular weight saturated hydrocarbon in the foamed layer is preferably 0.1% by weight or less (including 0). Normally, low molecular weight saturated hydrocarbons are added to improve the flowability of polystyrene resins and improve extrudability, but the addition of low molecular weight saturated hydrocarbons increases the mechanical properties during heating, especially tensile stress and tensile strength. There is a possibility that the elastic modulus is lowered. Therefore, if the content of the low molecular weight saturated hydrocarbon is within the above range, the resulting molded product is excellent in strength without reducing the pulling rate during thermoforming.

  Examples of the low molecular weight saturated hydrocarbon in the present invention include paraffinic compounds such as liquid paraffin, natural paraffin, paraffin wax, polyolefin paraffin, and partial oxides thereof.

  The content of the low molecular weight saturated hydrocarbon in the polystyrene-based resin foam layer in the present specification is a value determined by the following method.

  First, the resin layer is completely removed from the laminated foam sheet to obtain only the foam layer. About 10 g of sample is taken from this foamed layer, weighed to 0.0001 g, and the sample is dissolved using about 20 ml of tetrahydrofuran (THF) in a beaker. After confirming that the sample was completely dissolved in THF, a total amount of about 20 ml of the sample THF solution was dropped into about 200 ml of normal heptane to reprecipitate the polystyrene resin. The polystyrene resin precipitated in this normal heptane was No. It is removed by natural filtration using a quantitative filter paper of 5B, and filtered into a flask forming a normal heptane phase. The eggplant flask containing the filtrate is connected to a rotary evaporator and concentrated to about 50 ml by evaporating normal heptane in a 40 ° C. water bath. The concentrated filtrate is taken in a beaker, about 200 ml of acetonitrile is added to remove higher fatty acids and low molecular weight styrene components by solvent extraction into acetonitrile, and separated into a normal heptane phase and an acetonitrile phase using a separatory funnel. . The normal heptane phase is dried at 120 ° C., and the weight WA of the low molecular weight saturated hydrocarbon obtained as a residue is measured.

Next, the following operation is performed in order to separate from the acetonitrile phase a trace amount of low molecular weight saturated hydrocarbon that may have migrated to the acetonitrile phase during solvent extraction. It is put in the flask which makes the acetonitrile phase remaining by the above operation, and the flask containing the filtrate is connected to a rotary evaporator and concentrated to about 50 ml by heating in a 40 ° C. water bath. This concentrated acetonitrile phase is transferred to a beaker and about 200 ml normal heptane is added to extract the low molecular weight saturated hydrocarbons by solvent. Then, it is separated into an acetonitrile phase and a normal heptane phase using a separatory funnel, and the operation of concentration, solvent extraction, separation, and drying is performed using the normal heptane phase under the same conditions as those for obtaining the WA. By performing, the weight WB of the low molecular weight saturated hydrocarbon is obtained.
The value obtained by multiplying the value obtained by dividing the sum of WA and WB obtained by the above operation by the weight WF of the original test piece by 100 is the content of low molecular weight saturated hydrocarbons in the polystyrene resin foam layer in the present invention ( % By weight).

Apparent density of the laminated foamed sheet of the foamed layer of the present invention is preferably 0.08~0.35g / cm ^3, more preferably ^{0.09~0.2g / cm 3, 0.1~0.19g / cm} 3 Is more preferable. If the apparent density is too low, the shape-retaining property of the obtained molded product and the mechanical strength such as lip strength may be lowered. On the other hand, when the apparent density is too large, there is a risk that the lightness and heat insulation may be insufficient, and the cost may be increased.

  The thickness of the foamed layer of the laminated foam sheet of the present invention is preferably 1.8 to 3.0 mm, more preferably 1.9 to 2.9 mm, and further preferably 2.0 to 2.8 mm. If the thickness is too thin, deep drawing with a large drawing ratio may not be possible, and deformation may occur when hot water is added to the resulting molded product. On the other hand, when the thickness is too thick, there is a possibility that a molding failure of the naki occurs.

The apparent density and thickness of the foamed layer in this specification are measured according to the following method.
First, from the laminated foam sheet of the present invention, a square sample of 50 cm is cut out in a direction coinciding with the extrusion direction of the laminated foam sheet and 50 cm in a direction coinciding with the width direction of the laminated foam sheet. At this time, the central portion in the width direction is made to coincide with the central portion of the sample.

  Next, in any one of the vertical cross sections in the width direction of the sample, a total of nine measurement points excluding both end portions in the width direction from the one end portion to the other end portion at intervals of 5 cm are laminated and foamed. The thickness of the sheet and the thickness of the foam layer are measured based on a photograph taken with a microscope.

  The thickness (mm) of the laminated foam sheet and the thickness (mm) of the foamed layer are obtained by arithmetically averaging the measured values at the nine measurement points. The value obtained by subtracting the thickness (mm) of the foamed layer from the thickness of the laminated foamed sheet is taken as the thickness (mm) of the resin layer.

Moreover, the weight (g) of the said sample is measured, The measured value is converted into the weight of the laminated foam sheet per 1 m < ² >, and it is set as the basic weight (g / m < ² >) of a laminated foam sheet. The basis weight of the resin layer is the weight of 1 m ² per resin layer (g) (g / m 2 ) , the density of the resin layer, i.e. multiplied the thickness unit of the density of the base resin of the resin layer resin layer Is obtained by converting to The basis weight of the weight of 1 m ² per foam layer foamed layer (g / ^{m 2)} of basis weight of the laminated foam sheet basis weight of (g / ^{m 2)} from the resin layer (g / ^{m 2)} It is obtained by subtraction.

The apparent density of the foam layer is determined by dividing the basis weight (g / m ² ) of the foam layer by the thickness of the foam layer and converting it to g / cm ³ units.

  The open cell ratio of the foam layer in the laminated foam sheet of the present invention is preferably 0 to 25%, more preferably 0 to 20%, still more preferably 0 to 15%, and particularly preferably 0 to 10%. When the open cell ratio is in the above range, the secondary foaming property at the time of thermoforming is excellent, and the strength and thickness uniformity of the obtained molded product are particularly good.

In the present specification, the open cell ratio (%) of the foamed layer is based on ASTM D-2856-70 (Procedure C), and the actual volume of the laminated foamed sheet test piece (measured using an air comparison hydrometer) ( The sum of the volume of closed cells and the volume of the resin portion): Vx (cm ³ ) can be obtained and calculated by the following equation (7).

(Equation 6)
Open cell ratio (%) = {(Va−Vx) / (Va−W / 1.05)} × 100 (7)
However, Va and W in the above formula (7) are as follows.
Va: Apparent volume Va (cm ³ ) calculated from the outer dimensions of the laminated foam sheet test piece used for the measurement
W: Weight of laminated foam sheet test piece (g)

The test piece is recommended to be 25 cm ³ in size, but the object to be tested is a thin object of about 2 mm and must be stored in an uncompressed state in the sample cup attached to the air comparison hydrometer. . Therefore, from the laminated foamed sheet, cut samples with a length of 25 mm, a width of 40 mm, and a thickness as it is, and a total sum of thicknesses closest to 25 mm (but not exceeding 25 mm) are stored in a sample cup at the same time. This is a test piece for measuring the open cell ratio.

  In the laminated foam sheet of the present invention, the average cell diameter (mm) in the thickness direction of the foam layer: Z, the average cell diameter (mm) in the extrusion direction (MD) of the foam layer: X, the width direction (TD) of the foam layer Average bubble diameter (mm): between Y and 0.3 <Z / X <0.8, 0.3 <Z / Y <0.8, 0.08 <Z <0.2 The relationship is preferably satisfied, and more preferably, 0.4 <Z / X <0.6, 0.5 <Z / Y <0.7, and 0.1 <Z <0.18.

  The laminated foam sheet having air bubbles in such a shape that the values of Z / X and Z / Y satisfy the above ranges have improved thermoformability, particularly deep drawability, and the mechanical strength of the resulting molded product. It will be excellent. However, when at least one of Z / X and Z / Y is less than or equal to the above range, air bubbles are too flat, and the mechanical strength of a molded product obtained by thermoforming the laminated foam sheet may be reduced. On the other hand, a laminated foam sheet in which at least one of Z / X and Z / Y is in the above range or more tends to have a large drawdown at the time of thermoforming, which may deteriorate the thermoformability. If Z is too small, the thermoformability and mechanical strength may be deteriorated. On the other hand, if Z is too large, the appearance may be poor, and the flexibility may be insufficient, and bubbles tend to buckle when subjected to external force. Therefore, when a laminated foam sheet having a bubble shape that satisfies the above range is used, the thermoformability is excellent, and the mechanical strength of the molded product obtained by thermoforming is also excellent.

In addition, the said bubble diameter and bubble shape are measured about the center part of a foamed layer. Here, the center portion includes the center in the thickness direction and does not include the range from the surface S1 on the side where the resin layer is not laminated and the interface S2 between the resin layer and the foamed layer to 10% of the total thickness of the foamed layer. Meaning of the part. That is, as shown in FIG. 1, it is the center part of the thickness direction of the foam layer which occupies 80% of the total thickness of the foam layer.
The bubbles existing in the vicinity of the surface S1 are finer than the bubbles in the center due to the effect of air cooling at the time of sheeting, are greatly deformed by stretching, and may contain fine bubbles of about several tens of μm. . On the other hand, when laminating the resin layer on the foam layer, the bubbles existing near the interface S2 are expanded by the heat from the resin layer, or the number of fine bubbles of about several tens of μm is present in the foam layer near the interface S2. Or increase. Therefore, the bubbles existing in the above range are excluded from the measurement of the average bubble diameter, and the bubble diameter and the bubble diameter ratio are obtained only for the bubbles existing in the central portion of the foam layer.

  FIG. 1 shows a schematic diagram of a cross section of a laminated foam sheet for explaining a method for measuring the cell diameter of the laminated foam sheet. FIG. 1A shows a vertical sectional view in the extrusion direction, and FIG. 1B shows a vertical sectional view in the width direction. FIG.1 (c) shows the elements on larger scale explaining the bubble diameters X, Y, and Z of a foam layer. In FIG. 1, 1 is a laminated foam sheet, 2 and 2a are bubbles, S1 is the surface of the foam on which the resin layer is not laminated, and S2 is the interface between the resin layer and the foam layer. T represents the thickness of the foam layer.

In this specification, the average cell diameters X, Y, and Z are measured as follows.
Average cell diameter (mm) in the extrusion direction (MD) at the center of the foam layer: X, average cell diameter (mm) in the width direction (TD): Y, average cell diameter (mm) in the thickness direction: Z The vertical cut surface in the extruding direction of the layer and the vertical cut surface in the width direction are magnified with a microscope and measured based on the obtained micrograph, and the average cell diameter X and average cell size obtained by the measurement are measured. Z / X and Z / Y are determined from Y and average bubble diameter Z.

More specifically, the surface S1 on the side where the foam resin layer is not laminated and the resin layer are obtained by obtaining a microscopic enlarged photograph of the cross section in the thickness direction in the MD direction of the foam layer. A line is drawn from the interface S2 between the foam and the foam layer to a position corresponding to a position of 0.1 × (total thickness of the foam layer: T), and is divided into bubbles at the center and other than the center. As shown in FIG. 1 (a), the maximum bubble diameter in the MD and thickness direction for all the bubbles present is measured with a caliper to obtain the x and z values of each bubble 2 for each bubble, and the thus obtained x ₁ , x ₂ , x ₃ ... X _n , and z ₁ , z ₂ , z ₃ ... Z _n are obtained as arithmetic mean values X and Z, respectively, and from these X and Z values, Z / Get the value of X. As a matter of course, the values of X and Z are converted based on the enlargement ratios of the above photographs to obtain the true average bubble diameter.

The value of Y is obtained by obtaining a microscopic enlarged photograph of the thickness direction cross section in the direction along TD of the foam layer, and 0.1 × from the surface S1 and the interface S2 based on the obtained photograph (total foam layer thickness: A line is drawn at a position corresponding to the position of T), divided into bubbles at the center and other than the center, and the maximum bubble diameter of TD is shown in FIG. in as measured by calipers obtain the value of y of the bubble 2 for each bubble, give Y is an arithmetic mean value from the thus obtained values of the y _1, y _2, y ₃ · · · y _n as, The Z / Y value is obtained from the Y value and the previously obtained Z value. As a matter of course, the value of Y is converted based on the magnification of the above photograph to obtain the true average bubble diameter. Further, in the measurement of Z, X, and Y, the bubble 2a on the line of 0.1 × (foamed layer total thickness: T) from the surface S1 and the interface S2 is excluded from measurement.

The bubble diameter ratio and the bubble diameter can be adjusted as follows.
As a method for adjusting the bubble diameters X, Y, Z, 0.1 to 3 parts by weight of an inorganic or organic bubble regulator such as talc or sodium bicarbonate is added to 100 parts by weight of the base resin, or extrusion. It can be adjusted by adjusting the pressure of the die during foaming. That is, within a range where a foam sheet having a good appearance, a desired apparent density and thickness can be obtained, the bubble diameter can be reduced by increasing the amount of the bubble regulator, and the bubble diameter can be increased by increasing the die pressure. Can be reduced.
The bubble diameter ratio Z / X can be adjusted by adjusting the take-up speed of the foam sheet after extrusion foaming, and the bubble diameter ratio Z / Y is adjusted for the expansion ratio (blow-up ratio) of the foam sheet after extrusion foaming. ) Can be adjusted.

  The laminated foam sheet of the present invention can be molded by a conventionally known molding method, and in particular, a drawing ratio (molded body depth / diameter when the molded body upper surface opening area is converted into a circle) is 0.5 or more deep. Excellent drawability. Forming methods include vacuum forming, compressed air forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming. Plug assisted reverse load molding or the like, or a combination of these methods is employed. Among the above molding methods, matched mold molding or the like that improves the mold adhesion of the laminated foamed sheet is preferably employed.

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

[Production of polystyrene]
Production Example 1
350 kg of ion exchange water, 1.4 kg of tricalcium phosphate, and 17.5 g of sodium dodecylbenzenesulfonate are added to a reactor equipped with a stirrer having an internal volume of 1.2 m ³ . Next, a styrene solution in which a polymerization initiator was dissolved in advance was added, and the inside of the system was purged with nitrogen. Then, heating was started and suspension polymerization was performed to produce true spherical polystyrene beads. Specific polymerization (heating) conditions at that time were as follows. The reactor contents were heated from 25 ° C. to 90 ° C. over 1 hour and held at 90 ° C. for 10 hours. Subsequently, the temperature was raised from 90 ° C. to 120 ° C. over 1.5 hours, held at 120 ° C. for 5 hours, then cooled to room temperature, and the resulting spherical polystyrene beads were taken out from the reactor.
The styrene solution was prepared by previously dissolving 610 g of t-butylperoxy-2-ethylhexanoate as a polymerization initiator and 203 g of t-butylperoxy-2-ethylhexyl monocarbonate in 350 kg of styrene monomer. It is.
Subsequently, the true spherical polystyrene beads were washed and dried. The obtained spherical polystyrene beads had Mn: 1.4 × 10 ⁵ , Mw: 5.1 × 10 ⁵ , Mz: 1.3 × 10 ⁶ , and the total of styrene dimer and styrene trimer in the styrene beads The content is 370 ppm. Hereinafter, the polystyrene beads obtained in Production Example 1 are referred to as polystyrene A.
In addition, the total content of styrene dimer and styrene trimer in the polystyrene resin raw material is determined by using the polystyrene resin raw material instead of the foam layer as a measurement sample, and the method for measuring the styrene oligomer content in the foam layer described above. It is a value measured by the same method.

Production Example 2
350 kg of ion exchange water, 1.4 kg of tricalcium phosphate, and 17.5 g of sodium dodecylbenzenesulfonate are added to a reactor equipped with a stirrer having an internal volume of 1.2 m ³ . Next, a styrene solution in which a polymerization initiator and the like were dissolved in advance was added and the system was purged with nitrogen. Then, heating was started and suspension polymerization was performed to produce true spherical polystyrene beads. Specific polymerization (heating) conditions at that time were as follows. The reactor contents were heated from 25 ° C. to 90 ° C. over 1 hour. Subsequently, the temperature was raised from 90 ° C. to 100 ° C. over 15 hours. Subsequently, the temperature was raised from 100 ° C. to 120 ° C. over 1.5 hours, held at 120 ° C. for 5 hours, then cooled to room temperature, and the resulting spherical polystyrene beads were taken out from the reactor.
The styrene solution was composed of 350 kg of styrene monomer, 175 g of t-butylperoxy-2-ethylhexanoate, 245 g of t-butylperoxy-2-ethylhexyl monocarbonate, divinylbenzene (Kida Chemical) 81 g of a product of a purity of about 55% manufactured by Co., Ltd.) is previously dissolved.
Subsequently, the true spherical polystyrene beads were washed and dried. The obtained spherical polystyrene beads were Mn: 2.1 × 10 ⁵ , Mw: 1.3 × 10 ⁶ , Mz: 3.8 × 10 ⁶ , and the total of styrene dimer and styrene trimer in the styrene beads The content is 570 ppm. Hereinafter, the polystyrene beads obtained in Production Example 2 are referred to as polystyrene B.

Production Example 3
350 kg of ion exchange water, 1.4 kg of tricalcium phosphate, and 17.5 g of sodium dodecylbenzenesulfonate are added to a reactor equipped with a stirrer having an internal volume of 1.2 m ³ . Next, a styrene solution in which a polymerization initiator and the like were dissolved in advance was added and the system was purged with nitrogen. Then, heating was started and suspension polymerization was performed to produce true spherical polystyrene beads. Specific polymerization (heating) conditions at that time were as follows. The reactor contents were heated from 25 ° C. to 90 ° C. over 1 hour and held at 90 ° C. for 10 hours. Subsequently, the temperature was raised from 90 ° C. to 120 ° C. over 1.5 hours, held at 120 ° C. for 5 hours, then cooled to room temperature, and the resulting spherical polystyrene beads were taken out from the reactor.
The styrene solution was prepared by adding 350 kg of styrene monomer, 1220 g of t-butylperoxy-2-ethylhexanoate, 203 g of t-butylperoxy-2-ethylhexyl monocarbonate, divinylbenzene (purity of about (55% product) 81 g previously dissolved.
Subsequently, the true spherical polystyrene beads were washed and dried. The obtained spherical polystyrene beads were Mn: 1.1 × 10 ⁵ , Mw: 5.6 × 10 ⁵ , Mz: 1.9 × 10 ⁶ , and the total of styrene dimer and styrene trimer in the styrene beads The content is 350 ppm. Hereinafter, the polystyrene beads obtained in Production Example 3 are referred to as polystyrene C.

Production Example 4
350 kg of ion exchange water, 1.4 kg of tricalcium phosphate, and 17.5 g of sodium dodecylbenzenesulfonate are added to a reactor equipped with a stirrer having an internal volume of 1.2 m ³ . Next, a styrene solution in which a polymerization initiator was dissolved in advance was added, and the inside of the system was purged with nitrogen. Then, heating was started and suspension polymerization was performed to produce true spherical polystyrene beads. Specific polymerization (heating) conditions at that time were as follows. The reactor contents were heated from 25 ° C. to 90 ° C. over 1 hour and held at 90 ° C. for 10 hours. Subsequently, the temperature was raised from 90 ° C. to 120 ° C. over 1.5 hours, held at 120 ° C. for 5 hours, then cooled to room temperature, and the resulting spherical polystyrene beads were taken out from the reactor.
The styrene solution is prepared by previously dissolving 910 g of t-butylperoxy-2-ethylhexanoate and 350 g of t-butylperoxy-2-ethylhexyl monocarbonate in 350 kg of styrene monomer.
Subsequently, the true spherical polystyrene beads were washed and dried. The obtained spherical polystyrene beads were Mn: 1.1 × 10 ⁵ , Mw: 3.7 × 10 ⁵ , Mz: 1.0 × 10 ⁶ , and the total of styrene dimer and styrene trimer in the styrene beads The content is 300 ppm. Hereinafter, the polystyrene beads obtained in Production Example 4 are referred to as polystyrene D.

Production Example 5
350 kg of ion exchange water, 1.4 kg of tricalcium phosphate, and 17.5 g of sodium dodecylbenzenesulfonate are added to a reactor equipped with a stirrer having an internal volume of 1.2 m ³ . Next, a styrene solution in which a polymerization initiator was dissolved in advance was added, and the inside of the system was purged with nitrogen. Then, heating was started and suspension polymerization was performed to produce true spherical polystyrene beads. Specific polymerization (heating) conditions at that time were as follows. The reactor contents were heated from 25 ° C. to 90 ° C. over 1 hour. Subsequently, the temperature was raised from 90 ° C. to 100 ° C. over 4 hours. Subsequently, the temperature was raised from 100 ° C. to 120 ° C. over 1.5 hours, held at 120 ° C. for 5 hours, then cooled to room temperature, and the resulting spherical polystyrene beads were taken out from the reactor.
The styrene solution was prepared by previously dissolving 2440 g of t-butylperoxy-2-ethylhexanoate and 203 g of t-butylperoxy-2-ethylhexyl monocarbonate in 350 kg of styrene monomer.
Subsequently, the true spherical polystyrene beads were washed and dried. The obtained spherical polystyrene beads were Mn: 6.7 × 10 ⁴ , Mw: 2.3 × 10 ⁵ , Mz: 7.6 × 10 ⁵ , and the total of styrene dimer and styrene trimer in the styrene beads The content is 270 ppm. Hereinafter, the polystyrene beads obtained in Production Example 5 are referred to as polystyrene E.

Example 1
As a polystyrene-based resin, G0002 (continuous polymerization method: total content of styrene dimer and styrene trimer: 1210 ppm, Mn: 1.1 × 10 ⁵ , Mw: 3.0 × 10 ⁵ , Mz: 5.7) × 10 ⁵ , liquid paraffin content 0 wt% (hereinafter also simply referred to as G0002) 85 parts by weight and polystyrene A 15 parts by weight obtained in Production Example 1 are mixed with 100 parts by weight of polystyrene resin. A raw material blended with 0.9 parts by weight of talc is put into an extruder with an inner diameter of 90 mm, heated and melt-kneaded to make a molten resin, and mixed butane foamed with 65% by weight of isobutane and 35% by weight of normal butane. The agent was injected and kneaded to obtain a foamable molten resin mixture. The amount of the foaming agent added was 3.2 parts by weight with respect to 100 parts by weight of the polystyrene resin.
Subsequently, the foamable molten resin mixture is cooled by an extruder having an inner diameter of 120 mm connected to the downstream side of the 90 mm extruder so that the measurement temperature of the breaker portion is 156 ° C. The mixture was extruded and foamed through an annular die having an outlet slit gap of 0.67 mm at a discharge rate of 100 kg / hr. Immediately after that, cooling air at a temperature of 25 ° C. was blown from the inside at an air volume of 1.8 m ³ / min, and at the same time a temperature of 25 While blowing cooling air at 1.5 ° C. at 1.5 m ³ / min, a cylindrical foam is formed, and the inner surface of the foam is along the column side of a columnar cooling device (mandrel) having a diameter of 270 mm, and the speed is 7.8 m / min. After cooling while passing through, a foamed sheet having a width of about 850 mm was obtained by opening in the extrusion direction. The blow-up ratio obtained by dividing the diameter of the mandrel by the diameter of the die outlet (slit gap) was 3.7.

After curing the foamed sheet obtained by the above method for 3 weeks, a resin layer was formed on one side of the foamed sheet by the following extrusion lamination method.
That is, Toyo Styrene Co., Ltd. product name: XL-4 was charged as impact-resistant polystyrene in another extruder, and melted and kneaded under heating in the extruder to obtain a melted product through a T-die. A 240 ° C. molten resin was extruded on the outer surface side (on the side opposite to the cooling surface of the columnar cooling device), and an unstretched resin layer was laminated and bonded so as to be 125 g per 1 m ² to obtain a laminated foamed sheet.

Example 2
A laminated foamed sheet was obtained in the same manner as in Example 1 except that a polystyrene resin obtained by mixing 70 parts by weight of G0002 and 30 parts by weight of polystyrene A obtained in Production Example 1 was used as the polystyrene resin.

Example 3
A laminated foamed sheet was obtained in the same manner as in Example 1 except that a polystyrene resin obtained by mixing 85 parts by weight of G0002 and 15 parts by weight of polystyrene C obtained in Production Example 3 was used as the polystyrene resin.

Example 4
A laminated foam sheet was obtained in the same manner as in Example 1 except that 100 parts by weight of polystyrene D obtained in Production Example 4 was used as the polystyrene resin.

Example 5
A laminated foam sheet was obtained in the same manner as in Example 1 except that the amount of the foaming agent added was 3.3 parts by weight with respect to 100 parts by weight of the polystyrene resin, and the take-up speed of the foam was 8.3 m / min. .

Comparative Example 1
As polystyrene resin, PS Japan Co., Ltd. G0302 (continuous polymerization method: total content of styrene dimer and styrene trimer 1210 ppm, Mn: 1.2 × 10 ⁵ , Mw: 3.0 × 10 ⁵ , Mz: 5.7 A laminated foam sheet was obtained in the same manner as in Example 1 except that 100 parts by weight of (× 10 ⁵ , liquid paraffin content 0.6 wt%) was used.

Comparative Example 2
A laminated foamed sheet was obtained in the same manner as in Example 1 except that 50 parts by weight of G0002 and 50 parts by weight of polystyrene E obtained in Production Example 5 were used as the polystyrene resin.

Comparative Example 3
A laminated foam sheet was obtained in the same manner as in Example 1 except that 75 parts by weight of G0002 and 25 parts by weight of polystyrene B obtained in Production Example 2 were used as the polystyrene resin.

Comparative Example 4
A laminated foam sheet was obtained in the same manner as in Comparative Example 1 except that the amount of the foaming agent added was 3.3 parts by weight with respect to 100 parts by weight of the polystyrene resin, and the take-up speed of the foam was 8.3 m / min. .

  Example, tensile physical properties during heating of test pieces prepared by removing the foamed layer of the laminated foamed sheet obtained in Comparative Example, molecular weight of resin constituting the foamed layer, low molecular weight saturated hydrocarbon in the foamed layer Tables 1 and 2 show the results of measuring the content, the apparent density of the foam layer, the thickness, the basis weight, the open cell ratio, the cell diameter, the cell shape, the styrene oligomer content, the resin layer basis weight, and the basis weight of the laminated foam sheet. Show.

About the laminated foam sheets obtained in Examples and Comparative Examples, the surface on which the resin layer is laminated by the matched mold method is positioned on the outer surface side of the container using a molding machine manufactured by Asano Laboratories, product number FKS-0631-10. Thermoforming was performed as follows. The molding machine includes a heating zone for heating the laminated foam sheet and a molding zone for molding, and heaters are provided in the heating zone at positions above and below the laminated sheet. The laminated foam sheet is fixed to a frame having a 600 mm square opening so that the resin layer is on the upper side, the upper heater is adjusted to 325 ° C., the lower heater is adjusted to 275 ° C., and the laminated foam sheet is heated by 13. 6 seconds. Thereafter, the heated laminated foam sheet was sent to the molding zone, and a round container having a diameter of 141 mm in diameter, a depth of 73 mm, and a drawing ratio of 0.52 was molded. The number of containers per shot in this molding was 9 in total, 3 in the length direction and 3 in the width direction of the laminated foam sheet, and the pitch interval in the length direction and the width direction was 156 mm, respectively. .
Tables 1 and 2 show the moldability, the pull-in rate, and the lip strength of the obtained molded product.

[Formability evaluation]
Formability was evaluated according to the following criteria.
○: A molded product was obtained without any cracking during molding.
X: Naki occurred during molding, and a good molded product could not be obtained.

[Retraction rate]
The value obtained by dividing the weight per molded product by the weight of the laminated foam sheet per upper opening area of the molded product was taken as the pulling rate. In addition, the measurement of the pulling rate is performed for all nine containers obtained by molding for one shot, and the minimum value among the pulling rates obtained for each of the nine containers is set as the pulling rate for that shot. . This measurement was performed for 10 shots, and the pull-in rate was obtained by averaging the pull-in rate for each shot.

[Molded product lip strength]
The measurement of the lip strength of the molded product was performed using an orientec Co., Ltd. Tensilon universal testing machine RTC-1250A, with an upper mounting jig provided with a rectangular groove and a groove on an arc. Measurement was performed using the lower mounting jig. Specifically, the upper and lower portions of the flange portion formed on the periphery of the molded product are inserted into the rectangular groove of the upper mounting jig, and the lower portion of the flange portion is inserted into the groove on the arc of the lower mounting jig. The maximum load (N) up to the yield point is measured by inserting and holding the molded product between the upper and lower mounting jigs and compressing the molded product at a speed of 50 mm / min. The measurement was performed 10 times using 10 molded products in each of the extrusion direction and the width direction, and the average value was defined as the lip strength.

  From Tables 1 and 2, the laminated foam sheet of the present invention has no problem in moldability and the strength of the molded product obtained by molding, whereas the laminated foam sheet of the comparative example has a low pull-in ratio, and therefore has a lip strength. It turns out that it is small.

It is a mimetic diagram of a lamination foam sheet cut section for explaining a measuring method of a bubble diameter of a lamination foam sheet.

Explanation of symbols

1 Laminated foam sheet 2 Air bubbles

Claims (4)

  In a polystyrene resin laminated foam sheet in which an impact-resistant polystyrene resin layer is laminated on one side of a polystyrene resin foam layer having a content of styrene dimer and styrene trimer of 2000 ppm or less, the polystyrene series that forms the laminated foam sheet A polystyrene-based resin-laminated foam sheet, wherein a non-foamed resin obtained by defoaming a resin foam layer has a tensile elastic modulus of 110 to 170 MPa in a tensile test at 120 ° C. The polystyrene-based resin constituting the polystyrene-based resin foamed layer in the polystyrene-based resin laminated foamed sheet has a Z-average molecular weight of 5.8 × 10 ⁵ or more and a low-molecular-weight saturated hydrocarbon content of 0.1. The polystyrene-based resin laminated foam sheet according to claim 1, wherein the content is not more than% by weight (including 0). The apparent density of the polystyrene-based resin foam layer is 0.08 to 0.35 g / cm ³ , the thickness is 1.8 to ³ mm, the open cell rate is 0 to 25%, and the cell shape is the following (1) to ( The polystyrene-based resin laminated foam sheet according to claim 1 or 2, wherein the formula (3) is satisfied.
(Equation 1)
0.3 <Z / X <0.8 (1)
0.3 <Z / Y <0.8 (2)
0.08 <Z <0.2 (3)
(However, in the formula, each of X, Y, and Z is an average cell diameter in the extrusion direction (MD), width direction (TD), and thickness direction of the foamed layer, and the unit is mm.)   The molded product formed by thermoforming the styrene resin laminated foam sheet in any one of Claims 1-3.

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