JP6170730B2 - Styrene resin composition for foaming, styrene resin foam sheet, method for producing the same, and food packaging container - Google Patents

Description

  The present invention relates to a foaming styrene resin composition, a styrene resin foam sheet, a method for producing the same, and a food packaging container.

  Styrenic resin extruded foam sheets are widely used in food trays, lunch boxes, instant noodle containers, natto containers, cups and the like, taking advantage of buffering properties and heat barrier properties. Such foamed sheets are required to be improved in secondary formability so as to be lighter and to be compatible with various shapes such as deep-drawn molded products.

  However, when the weight of the extruded foam sheet is reduced, the amount of resin constituting the foam sheet decreases, so cracking and tearing during secondary molding are likely to occur, and cracking during sheet winding and lower waist strength of the container are reduced. There is a problem to do. Such a problem is particularly prominent in deep drawing, and a material having a high balance between strength and secondary formability is required.

  As measures for improving this problem, Patent Documents 1 to 3 disclose a method using a polystyrene resin obtained by polymerizing a styrene monomer using a specific organic peroxide as a polymerization initiator. 4 to 5 disclose a method using a styrenic resin having specific fluidity and melt tension.

  Moreover, as a means for improving secondary moldability, for example, as in Patent Documents 6 to 7, a method in which a high molecular weight component is contained in a styrene resin is known.

Japanese Patent Laid-Open No. 11-246624 JP 2003-49033 A JP 2005-281475 A JP 2009-29871 A JP 2011-32362 A JP 2003-292707 A JP 2011-225866 A

However, the prior art described in the above literature has room for improvement in the following points.
First, the techniques of Patent Documents 1 to 5 are insufficient in the secondary formability of the foam sheet in any case.
Secondly, in the techniques of Patent Documents 6 to 7, the addition of a high molecular weight component is not always effective in the strength of the foam sheet, and in some cases the strength may be reduced. It was difficult to achieve both secondary formability.
This invention is made | formed in view of the said situation, and it aims at achieving the subject that it is excellent in the balance of weight reduction and secondary moldability of the styrene resin foam sheet described above.

The inventors of the present invention have made extensive studies to achieve the problem of excellent balance between weight reduction and secondary formability of the styrene resin foam sheet described above. The inventors have found that the object can be achieved by setting the average molecular weight (Mn), the peak molecular weight (Mtop), the Z average molecular weight (Mz), and the degree of branching to specific ranges, and have completed the present invention.
That is, the styrene resin composition for foaming according to the present invention has a melt mass flow rate (MFR) measured at 200 ° C. and a load of 49 N of 0.8 to 3.0 g / 10 minutes, and a number average molecular weight (Mn). 80,000 to 130,000, the peak molecular weight (Mtop) is 200,000 to 350,000, the Z average molecular weight (Mz) is 750,000 or more, and the branching ratio gM at a molecular weight of 1,000,000 to 1,500,000 is 0.85 to 0.40. The foaming styrene resin composition is one embodiment of the present invention, and the styrene resin foam sheet manufacturing method, styrene resin foam sheet, food packaging container, and the like of the present invention have the same configuration. .

  By using the styrenic resin for foaming of the present invention, a foamed sheet having an excellent balance between strength and secondary moldability can be obtained, and the foamed sheet can be reduced in weight and deep drawn. Moreover, even if a recycled material is blended, a good quality foam sheet is obtained with little deterioration in physical properties.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, in order to avoid repetition about the same component, description is abbreviate | omitted suitably. In addition, when describing with AB in this specification, it shall mean A or more and B or less.

<Characteristics of foaming styrenic resin composition>
This embodiment relates to a styrene resin composition for foaming that can be lightened and deep-drawn with a styrene resin foam sheet, and is excellent in strength and secondary moldability, and even when recycled materials are blended. Provided is a styrene resin foam sheet with a low decrease in the styrene resin. The melt mass flow rate (MFR) measured under the conditions of 200 ° C. and 49 N load of the styrene resin composition for foaming of the present embodiment is 0.8 to 3.0 g / 10 minutes, preferably 0.8 to The amount is 2.5 g / 10 minutes, more preferably 1.0 to 2.0 g / 10 minutes. If it exceeds 3.0 g / 10 minutes, the strength and secondary moldability are lowered, and it becomes difficult to reduce the weight of the styrene-based resin foam sheet. In consideration of the productivity of the styrene resin composition, it is preferably 0.8 g / 10 min or more. The melt mass flow rate (MFR) is 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7. 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 It may be within the range of any two values of 0.0 g / 10 min.

  The number average molecular weight (Mn) of the styrene resin composition for foaming of this embodiment is 80 to 130,000. If the Mn is less than 80,000, the foamed sheet becomes brittle, so that cracks may occur during the production or transportation of the foamed sheet. Moreover, when Mn exceeds 130,000, fluidity | liquidity falls, Therefore The productivity of a styrene-type resin composition deteriorates. Mn of the styrene-based resin composition can be adjusted by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, and the type and amount of the solvent used during the polymerization. it can. In the case of continuous polymerization, a devolatilization step is provided to remove unreacted monomers and polymerization solvent after the completion of the polymerization step, and generally a vacuum devolatilization tank with a heater and a devolatilization extruder are provided. At that time, by setting the temperature of the heater as low as possible, generation of low molecular weight components due to polymerization of unreacted monomers can be suppressed, and Mn can be adjusted high. The number average molecular weight (Mn) may be in the range of any two values of 80,000, 90,000, 110,000, 120,000, and 130,000.

  The peak molecular weight (Mtop) of the styrene resin composition for foaming of this embodiment is 200,000 to 350,000, preferably 250,000 to 350,000, and more preferably 280,000 to 350,000. When Mtop is less than 200,000, the waist strength of the foamed sheet and the molded product thereof is lowered, so that it is difficult to reduce the weight. On the other hand, when Mtop exceeds 350,000, the fluidity is lowered, so that the productivity of the styrene resin composition is deteriorated. The Mtop of the styrenic resin composition can be adjusted by the reaction temperature of the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, and the type and amount of the solvent used during the polymerization. it can. The peak molecular weight (Mtop) is 200,000, 210,000, 220,000, 230,000, 240,000, 250,000, 260,000, 270,280, 290,000, 300,000, 310,000, 320,000, 330,000. , 340,000, and 350,000 may be in the range of any two values.

  The Z-average molecular weight (Mz) of the foaming styrenic resin composition of this embodiment is 750,000 or more, preferably 900,000 or more, and more preferably 1,000,000 or more. If Mz is less than 750,000, the secondary formability of the foamed sheet is lowered. Mz of the styrene-based resin composition can be adjusted by the reaction temperature of the polymerization process, the residence time, the type and amount of the polymerization initiator, and the type and amount of the solvent used during the polymerization. In addition to these conditions, Mz can be increased efficiently by adding a solvent-soluble polyfunctional vinyl compound copolymer described later in any of the polymerization steps. The Z average molecular weight (Mz) is 750,000, 800,000, 850,000, 900,000, 950,000, 1 million, 1.05 million, 1.1 million, 1.15 million, 1.2 million, 1.25 million, 1.3 million, 1.35 million, 140 It may be an arbitrary value of 10,000, 145,000, or 1.5 million, or any two of these values.

  The branching ratio gM at a molecular weight of 1,000,000 to 1,500,000 of the foaming styrenic resin composition of this embodiment is 0.85 to 0.40, and preferably 0.80 to 0.50. The branching ratio gM represents the degree of branching of the hyperbranched ultrahigh molecular weight substance contained in the styrene resin composition, and the lower the branching ratio gM, the more branches. If the branching ratio gM exceeds 0.85, branching is insufficient, and the sufficient effect of this embodiment cannot be obtained. Even if the branching ratio gM is less than 0.40 and branching is increased, no further improvement effect can be obtained. In addition, this branching ratio gM is arbitrary among 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, and 0.40. It may be within a range of two values.

  The branching ratio gM is related to the degree of branching and can be adjusted by adding one or both of a polyfunctional polymerization initiator and a polyfunctional vinyl copolymer described later in any of the polymerization steps. However, in order to efficiently produce a hyperbranched ultrahigh molecular weight component, it is preferable to use a polyfunctional vinyl copolymer, and a polyfunctional vinyl copolymer and a polyfunctional polymerization initiator having 4 or more functionalities are used in combination. More preferably, it is used.

  The melt tension value measured at 200 ° C. of the styrene-based resin composition of the present embodiment is preferably 12 to 20 gf, and more preferably 14 to 20 gf. If the melt tension value is less than 12 gf, the foamed sheet is not sufficiently lightened, and if the melt tension value exceeds 20 gf, the secondary formability deteriorates, which is not preferable. The melt tension value may be within a range of two arbitrary values among 12, 13, 14, 15, 16, 17, 18, 19, and 20 gf.

  The methanol-soluble content of the styrene resin composition of the present embodiment is preferably 2.0% by mass or less, and more preferably 1.5% by mass. When the methanol-soluble content exceeds 2.0% by mass, the heat resistance of the container is lowered, which is not preferable. The methanol-soluble component refers to a component soluble in methanol in the resin composition, for example, liquid paraffin in addition to styrene oligomer (styrene dimer, styrene trimer) by-produced in the polymerization process or devolatilization process of styrene resin, Various additives such as silicone oil, low molecular weight components such as residual styrene monomer and polymerization solvent are included. Methanol-soluble matter can be adjusted by the amount of styrene oligomer (styrene dimer, styrene trimer) generated as a by-product in the polymerization process, the amount of various additives such as liquid paraffin, the amount of residual styrene monomer and polymerization solvent. .

<Raw material and production method of styrene resin composition for foaming>
Although the styrene resin composition for foaming of this embodiment uses a styrene monomer as an essential component (essential component) as a raw material, in addition to a homopolymer of styrene, a small amount of a vinyl monomer copolymerizable with styrene is present. It may be included. Examples of vinyl monomers include substituted styrenes such as α-methylstyrene and p-methylstyrene, acrylic monomers such as acrylic acid, methacrylic acid, butyl acrylate, and methyl methacrylate, and vinyl cyanides such as acrylonitrile and methacrylonitrile. Monomer, maleic anhydride, etc. are mentioned.

  Examples of the polymerization method of the foaming styrene resin composition of the present embodiment include known styrene polymerization methods such as bulk polymerization, solution polymerization, and suspension polymerization. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, aliphatic hydrocarbons such as hexane and cyclohexane, and the like can be used. As the type of the reactor, a continuous polymerization system in which a complete mixing type reactor, a plug flow reactor, a loop type reactor and the like are combined is preferably used.

  In the method for polymerizing a styrene resin composition for foaming according to the present embodiment, it is preferable to add a polyfunctional vinyl copolymer (crosslinking agent) having a branched structure to a styrene monomer in an amount of 50 ppm to 1000 ppm, and 100 to 500 ppm. More preferably, it is added. A polyfunctional vinyl copolymer is copolymerized with a styrene monomer to produce a highly branched ultra-high molecular weight product. The polyfunctional vinyl copolymer can be added to the polymerization raw material, but may be mixed with a styrene monomer or a polymerization solvent and supplied from the middle of the polymerization step. When the blending amount of the polyfunctional vinyl copolymer is less than 50 ppm, the production of the hyperbranched ultra high molecular weight is small, and the effect of this embodiment may not be obtained. On the other hand, if it exceeds 1000 ppm, the viscosity of the polymerization solution is remarkably increased in the polymerization step and production may become difficult, and an effect commensurate with the amount added cannot be obtained. The addition amount of the polyfunctional vinyl copolymer (crosslinking agent) is 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850. , 900, 950, and 1000 ppm may be within the range of any two values.

The polyfunctional vinyl copolymer of this embodiment can be obtained according to the methods disclosed in JP-A Nos. 2004-123873, 2005-213443, WO 2009/110453, and the like. Specifically, a raw material containing a divinyl compound and at least one monovinyl compound is copolymerized to obtain a copolymer having a reactive pendant vinyl group represented by the formula (a1). Furthermore, as described in the above-mentioned patent document, those having other terminal groups other than vinyl groups introduced at the terminals can also be used, particularly for compounds having an unsaturated bond in the molecule such as phenoxy methacrylates. In addition to (a1), it is possible to use a terminal-modified one because it can act as a crosslinking point. In this case, since the terminal unsaturated bond-containing structural unit (a2) also has a vinyl group, the total molar fraction (a3) with the structural unit of the formula (a1) indicates the total amount of vinyl groups present. It will be.
(In the formula, R ¹ represents an aromatic hydrocarbon group derived from a divinyl aromatic compound.)

  Examples of divinyl compounds used to obtain polyfunctional vinyl copolymers include divinyl aromatic compounds represented by divinylbenzene and aliphatic and alicyclic (meth) acrylates represented by ethylene glycol di (meth) acrylate. Examples are shown.

  Moreover, as a monovinyl compound used here, the vinyl-type monomers containing monovinyl aromatic compounds, such as styrene as mentioned above, are mentioned.

  As a method for producing a polyfunctional vinyl copolymer, for example, two or more kinds of compounds selected from divinyl aromatic compounds, monovinyl aromatic compounds and other monovinyl compounds are used as promoters selected from Lewis acid catalysts and ester compounds. It can be obtained by cationic copolymerization in the presence. Further, when a (meth) acrylate divinyl or monovinyl compound is used, the reaction does not proceed in cationic polymerization, and therefore, it can be obtained by radical polymerization in the presence of a radical catalyst such as peroxide.

  The amount of divinyl compound and monovinyl compound used is determined so as to give the composition of the polyfunctional vinyl copolymer used in this embodiment, but the divinyl compound is preferably 10 to 50 mol% of the total monomer, More preferably, 30-50 mol% is used. The monovinyl compound is preferably used in an amount of 90 to 50 mol%, more preferably 70 to 50 mol% of the total monomers. Here, in cationic polymerization like 2-phenoxyethyl methacrylate, what acts as a terminal modifier is not calculated as a monomer.

  The Lewis acid catalyst used in the production of the polyfunctional vinyl copolymer is not particularly limited as long as it is a compound composed of a metal ion (acid) and a ligand (base) and can receive an electron pair. Can be used. From the viewpoints of control of molecular weight and molecular weight distribution and polymerization activity, boron trifluoride ether (diethyl ether, dimethyl ether, etc.) complexes are most preferably used. The Lewis acid catalyst is used in the range of 0.001 to 10 mol, more preferably 0.001 to 0.01 mol, per 1 mol of the monomer compound. An excessive amount of the Lewis acid catalyst is not preferable because the polymerization rate becomes too high and it becomes difficult to control the molecular weight distribution.

  Examples of the cocatalyst include one or more selected from ester compounds. Among them, an ester compound having 4 to 30 carbon atoms is preferably used from the viewpoint of controlling the polymerization rate and the molecular weight distribution of the copolymer. From the viewpoint of availability, ethyl acetate, propyl acetate and butyl acetate are preferably used. The cocatalyst is used in the range of 0.001 to 10 mol, more preferably 0.01 to 1 mol, relative to 1 mol of the monomer compound. When the amount of the cocatalyst used is excessive, the polymerization rate decreases and the yield of the copolymer decreases. On the other hand, when the amount of the cocatalyst used is too small, the selectivity of the polymerization reaction is lowered, the molecular weight distribution is increased, the gel is generated, and the polymerization reaction is difficult to control.

  In addition, as a catalyst used for producing a polyfunctional vinyl copolymer by radical polymerization, simple compounds such as azo compounds represented by azobisisobutyronitrile, dibenzoyl peroxide, t-butylperoxybenzoate and the like can be used. Examples of functional peroxides and bifunctional or higher functional peroxides such as 1,1-bis (t-butylperoxy) cyclohexane are exemplified, and they are used alone or in combination of two or more. be able to.

  The polyfunctional vinyl copolymer used in the present embodiment can be obtained by the production method as described above, but it is necessary to leave a part of the vinyl group of the divinyl compound used as a monomer without polymerizing. is there. Then, on average, 2 or more, preferably 3 or more vinyl groups are present in one molecule. This vinyl group exists mainly as a structural unit represented by the above formula (a1). Then, by leaving a part of the vinyl group without being polymerized, the crosslinking reaction can be suppressed and solvent solubility can be imparted. Here, solvent-soluble means that it is soluble in toluene, xylene, THF (tetrahydrofuran), dichloroethane, or chloroform. Specifically, in 100 g of these solvents, 5 g or more is dissolved at 25 ° C., and the gel is dissolved. It does not occur. On the other hand, a part of the divinyl compound needs to be crosslinked or branched by the reaction of two vinyl groups, whereby a copolymer having a branched structure can be obtained. Thus, one of the two vinyl groups is reacted for a part of the divinyl compound, one is left without being polymerized, and the other part is reacted with the two vinyl groups together in the present embodiment. The polyfunctional vinyl copolymer used in (1) can be obtained. The polymerization method for obtaining such a polyfunctional vinyl copolymer is known as described above, and can be produced as described above.

  The weight average molecular weight (Mw) of the polyfunctional vinyl copolymer is preferably 1,000 to 100,000, more preferably 5,000 to 70,000. If it is smaller than 1,000, gelation may proceed in a region where the flow called a boundary film existing on the wall of the polymerization reactor is stopped in continuous polymerization, which is not preferable.

The unit containing a vinyl group derived from a divinyl compound introduced into the polyfunctional vinyl copolymer has a structural unit represented by the above formula (a1), and the molar fraction of the structural unit (a1) is 0.05. ~ 0.50. When the amount is less than 0.05 mol, high molecular weight highly branched polystyrene is difficult to obtain, which is not preferable. On the other hand, when it exceeds 0.50 mol, the molecular weight of the highly branched polystyrene is excessively increased, and gelation tends to occur, which is not preferable. The molar fraction of the structural unit (a1) is 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0. It may be within the range of any two values of .50.
As described above, those having a terminal modification with a compound having an unsaturated bond in the molecule, in addition to the structural unit represented by the formula (a1), the terminal unsaturated bond-containing structural unit (a2) also has a vinyl group. Therefore, the total molar fraction (a3) of both is 0.05 to 0.50.

  The polyfunctional vinyl copolymer has a ratio of the radius of inertia (nm) in the weight average molecular weight to the molar fraction of the structural unit (a1) or the total molar fraction (a3) in the range of 1 to 100. It is preferable that it exists in. In order to adjust the hyperbranched ultra high molecular weight body without gelation, the range of 10 to 80 is more preferable. When the above ratio exceeds 100, gelation does not proceed, but it is not preferable because it is difficult to obtain a high molecular weight highly branched polystyrene. On the other hand, when it is smaller than 1, the molecular weight of the highly branched polystyrene is excessively increased, and gelation tends to occur, which is not preferable. The ratio of the radius of inertia (nm) to the molar fraction of the structural unit (a1) or the molar fraction (a3) is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20 , 30, 40, 50, 60, 70, 80, 90, 100 may be in the range of any two values.

  The ratio of the molar fraction of the structural unit (a1) or the total molar fraction (a3), which is an index representing the content of double bonds and the radius of inertia defined here, constitutes a hyperbranched ultrahigh molecular weight product. In this case, it can be said that this is an index indicating how many reaction points are present in the spread of the polyfunctional vinyl copolymer as a nucleus in the polymerization reaction solution. If this ratio is too small, the reaction point is in the vicinity and gelation is likely to occur, and if this ratio is too large, it is difficult to increase the molecular weight of the branched component.

  When producing the styrene-based resin composition of the present embodiment, from the viewpoint of controlling the polymerization reaction, a polymerization initiator such as a polymerization solvent or an organic peroxide, or a chain transfer agent such as an aliphatic mercaptan, if necessary. Can be used.

  As polymerization initiators, organic oxides such as benzoyl peroxide, t-butylperoxybenzoate, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy)- 3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, 2 , 2-bis (4,4-di-t-butylperoxycyclohexyl) propane, polyether tetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate, t- And butyl peroxyisobutyrate, among others, 2,2-bis (4,4 It is preferred to use di -t- butyl peroxy cyclohexyl) propane, a tetrafunctional initiator polyether tetrakis (t-butyl peroxy carbonate) and the like.

  As the chain transfer agent, for example, aliphatic mercaptan, aromatic mercaptan, pentaphenylethane, α-methylstyrene dimer, terpinolene and the like can be used.

  The styrene resin composition of the present embodiment includes a rubber-reinforced aromatic vinyl resin such as HI-PS resin and MBS resin and an aromatic vinyl thermoplastic elastomer such as SBS as a component containing rubber as necessary. May be contained in the order of several percent. Further, higher fatty acids such as stearic acid, zinc stearate, calcium stearate, magnesium stearate and salts thereof, lubricants such as ethylene bisstearyl amide, plasticizers such as liquid paraffin, and antioxidants may be included.

In addition, the raw material for producing the styrene resin composition of the present embodiment includes 0 to 50% by mass of a recycled raw material composed of at least one of a polystyrene resin foam sheet and a polystyrene resin non-foam sheet. it can. As the polystyrene resin foam sheet, a foam sheet prepared from the styrene resin composition of the present embodiment may be used, or a foam sheet prepared from other polystyrene resin may be used. Moreover, as a polystyrene-type resin non-foamed sheet, a biaxially-stretched polystyrene-type resin sheet etc. can be used. In addition, the content rate of this recycled raw material is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 , 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 , 46, 47, 48, 49, and 50 mass% may be within the range of any two values.
As a form of the recycling raw material, not only the above-mentioned polystyrene-based resin foam sheet and polystyrene-based resin non-foamed sheet, but also these thermoformed products, scraps called skeletons generated when the thermoformed products are punched from the sheet, etc. Is also included. In addition, recycled materials may be used by directly mixing pulverized products such as sheets, thermoformed products, and skeletons with virgin materials. Recycled pellets are made from the pulverized products and introduced into the foam extruder. You may dry-blend and use. Although there is no restriction | limiting in particular about the molecular weight of a recycled raw material, It is preferable that a weight average molecular weight (Mw) is 200,000 or more.

<Styrenic resin foam sheet and method for producing the same>
The foaming styrenic resin composition of the present embodiment is for extrusion foaming and is suitably used as an extruded foam sheet. As a method for producing an extruded foam sheet, a known extruded foam sheet production apparatus can be used. Specifically, two single-screw extruders and two-screw extruders are arranged in series, the foaming agent is melted and kneaded with the foam nucleating agent in the first extruder, and cooled by the second extruder. An example is a method in which the resin temperature is adjusted to 120 ° C. to 180 ° C. and then released into the atmosphere with a circular die and foamed under reduced pressure.

  Examples of blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, 1,1-difluoroethane, Physical foaming agents such as halogenated hydrocarbons such as 1,1-difluoro-chloride and methylene chloride can be used. Also, decomposable foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and citric acid, inorganic gases such as carbon dioxide and nitrogen, and water can be used. These foaming agents can be used by mixing them appropriately, but industrially, butane is often used. From the viewpoint of foaming extrudability, secondary formability of foamed sheets, and foaming agents, a mixture consisting of isobutane and normal butane. It is preferred to use butane. Since butane has a slow permeation rate with respect to the polystyrene-based resin, about 1 to 3% by mass usually remains in the foamed sheet immediately after foam extrusion. Since this remaining amount affects the secondary foam thickness and thermoformability in secondary molding, it is appropriately adjusted by providing a certain aging period.

  Examples of the foam nucleating agent include inorganic powders such as talc, calcium carbonate, and clay, and these can be used alone or as a mixture. Among them, talc is most preferable in that it has a large effect of reducing the bubble diameter and is inexpensive. The method for adding the foam nucleating agent is not particularly limited, and may be added directly to the supply hole of the extruder, or may be added together with the heat resistant resin. A master batch based on a styrene homopolymer, polystyrene or the like may be prepared and supplied using the master batch. The addition amount of the foam nucleating agent is usually 0.1 to 5% by mass. The master batch may contain a higher fatty acid or a metal salt of a higher fatty acid in advance. It may also contain lubricants such as ethylenebisstearylamide, spreading agents such as liquid paraffin and silicone oil, other surfactants, antistatic agents, antioxidants, plasticizers, weathering agents, pigments, etc. good.

  0.5-4.0 mm is preferable and, as for the thickness of the extrusion foaming sheet of this embodiment, 1.0-3.0 mm is more preferable. When the thickness of the extruded foam sheet is less than 0.5 mm, the strength and heat insulation of the container after the secondary molding are lowered. When the thickness of the extruded foam sheet exceeds 4.0 mm, the temperature unevenness of the sheet is likely to occur during secondary molding, and the moldability deteriorates.

The density of the extruded foam sheet of the present embodiment is preferably 80 kg / m ³ or less, and more preferably 70 kg / m ³ or less, from the viewpoint of weight reduction. The density D (kg / m ³ ) can be calculated as D = S / T from the basis weight S (g / m ² ) of the foamed sheet and the sheet thickness T (mm).

  In the extruded foam sheet of this embodiment, the average cell diameter X in the thickness direction of the sheet is preferably 0.10 to 0.40 mm. If the average cell diameter X in the thickness direction of the sheet is less than 0.10 mm, the formability in the secondary molding is lowered. When the average cell diameter X in the thickness direction of the sheet exceeds 0.40 mm, the appearance of the foamed sheet deteriorates and the strength also decreases.

  The ratio of the average bubble diameter Y in the extrusion direction to the average bubble diameter X in the thickness direction (Y / X) and the ratio of the average bubble diameter Z in the width direction to the average bubble diameter X in the thickness direction (Z / X) are respectively It is preferable that it is 1.0-2.5. If Y / X and Z / X are less than 1.0, drawdown during secondary molding is increased, which is not desirable. Moreover, when Y / X and Z / X exceed 2.5, the flatness of the bubbles is large, and the strength of the foamed sheet may be reduced.

The average bubble diameter X in the thickness direction of the sheet, the average bubble diameter Y in the extrusion direction, and the average bubble diameter Z in the width direction are observed using a scanning electron microscope. Based on the average chord length described in ASTM D2842-06, the following formula can be used.
Average chord length = straight line length / number of bubbles Average bubble diameter = average chord length / 0.616

  In addition, the extruded foam sheet of the present embodiment can be provided with a surface layer called a skin layer having a higher density than the central portion in the thickness direction on the front and back surfaces of the sheet. By providing a skin layer, the strength of the sheet can be increased and the appearance is also beautifully finished. The skin layer can be adjusted by air cooling the surface of the foam sheet immediately after leaving the circular die.

  The extruded foam sheet of this embodiment can improve moldability, strength, and rigidity by laminating a thermoplastic resin sheet or film on one or both sides. The thermoplastic resins constituting the sheet and film are polystyrene resins such as polystyrene and high impact polystyrene, polypropylene resins, polyester resins, high density polyethylene, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate. Examples thereof include a copolymer, and a polystyrene resin that can be laminated without using an adhesive layer and has good recyclability is preferable.

  Although there is no restriction | limiting in particular in the thickness of the thermoplastic resin sheet or film laminated | stacked above, 0.01 mm-0.3 mm are preferable. If the thickness of the sheet or film is thin, the effect of improving the physical properties is small, and if it is too thick, it is not desirable from the viewpoint of weight reduction.

The extruded foam sheet of this embodiment can be secondarily formed into containers such as trays, instant noodle containers, natto containers, cups, etc. by thermoforming such as vacuum forming or pressure forming, especially for deep drawing applications. Is suitable.
As mentioned above, although embodiment of this invention was described, these are illustrations of this invention and can also be demonstrated in various forms other than the above.
That is, this embodiment can be expressed in the form shown in the following (1) to (6) from another viewpoint.
(1) Melt mass flow rate (MFR) measured at 200 ° C. and 49 N load is 0.8 to 3.0 g / 10 min, number average molecular weight (Mn) is 80,000 to 130,000, and peak molecular weight (Mtop) is 20 For polydisperse highly branched foams, characterized in that the branching ratio gM at a molecular weight of 1,000,000 to 1,500,000 is from 0.85 to 0.40. Styrenic resin composition.
(2) A solvent-soluble polyfunctional vinyl copolymer having an average of two or more vinyl groups in one molecule and having a branched structure is added to a vinyl monomer essentially containing styrene in an amount of 50 ppm to 1000 ppm on a mass basis. , Including the hyperbranched ultrahigh molecular weight product produced by polymerizing the solvent-soluble polyfunctional vinyl copolymer and the vinyl monomer by supplying the polymer reactor to a continuously arranged polymerization reactor and proceeding the polymerization reaction (1 The polydisperse hyperbranched styrenic resin composition (3) described above is obtained by polymerizing a solvent-soluble polyfunctional vinyl copolymer with a divinyl compound and a monovinyl compound copolymerizable with the following formula (a1). The pendant vinyl group-containing unit derived from the represented divinyl compound is contained in the structural unit in the range of 0.05 to 0.50 as a molar fraction, and the inertia radius (nm) in the weight average molecular weight is Wherein the ratio of the mole fraction, characterized in that in the range of 1 to 100 (2) polydisperse hyperbranched type foaming styrene resin composition.
(In the formula, R ¹ represents a hydrocarbon group derived from a divinyl compound.)
(4) The polydispersed highly branched styrene resin composition for foaming contains 0 to 50% by mass of a recycled material composed of at least one of a polystyrene resin foam sheet and a polystyrene resin non-foam sheet. The polydisperse hyperbranched styrene resin composition for foaming as described in (1) to (3) above.
(5) A method for producing a styrene-based resin foam sheet, which comprises subjecting the polydisperse highly branched styrene resin composition for foaming described in (1) to (4) to foam extrusion.
(6) A styrene resin foam sheet obtained by the production method according to (5).
(7) A food packaging container obtained by molding the styrene resin foam sheet according to (6).

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

<Production of Solvent-Soluble Polyfunctional Vinyl Compound Copolymer A (Crosslinking Agent A)>
3.1 mol (399.4 g) of divinylbenzene, 0.7 mol (95.1 g) of ethylvinylbenzene, 0.3 mol (31.6 g) of styrene, 2.3 mol (463.5 g) of 2-phenoxyethyl methacrylate Then, 974.3 g of toluene was put into a 3.0 L reactor, 42.6 g of boron trifluoride diethyl ether complex was added at 50 ° C., and reacted for 6.5 hours. After stopping the polymerization reaction with a sodium hydrogen carbonate solution, the oil layer was washed three times with pure water, and the reaction mixture was poured into a large amount of methanol at room temperature to precipitate a polymer. The obtained polymer was washed with methanol, filtered, dried and weighed to obtain 372.5 g of a polyfunctional vinyl aromatic copolymer A (crosslinking agent A). The polyfunctional vinyl copolymer A (crosslinking agent A) has a weight average molecular weight Mw of 8000, the molar fraction of the structural unit (a1) containing a vinyl group derived from a divinyl compound is 0.44, and terminal 2-phenoxy. The double bond (a2) derived from ethyl methacrylate was 0.03, and the total molar fraction (a3) of both was 0.47. The inertia radius of the copolymer at a weight average molecular weight of 8000 was 6.3 nm. The ratio of the inertia radius of this copolymer to the molar fraction of double bonds is 13.4, and the polyfunctional vinyl in this synthesis example is compared with the fact that the inertia radius at a linear molecular weight of 8000 is 15 nm. It can be seen that the copolymer has a branched structure.

<Production of Styrenic Resin Compositions PS-1 to PS13>
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor so as to have the addition concentration shown in Table 1 (concentration based on mass relative to the raw styrene), and was uniformly mixed. The polymerization initiators listed in Table 1 were as follows.
Polymerization initiator: 2,2-di (4,4-t-butylperoxycyclohexyl) propane (Pertetra A manufactured by NOF Corporation was used.)
In the third reactor, a temperature gradient was provided along the flow direction, and the temperature in Table 1 was adjusted at the intermediate part and the outlet part.
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, and the preheater was adjusted to the resin temperature shown in Table 1. By adjusting the temperature and adjusting to the pressure shown in Table 1, unreacted styrene and ethylbenzene are separated and then extruded into a strand form from a perforated die, and the strand is cooled and cut by a cold cut method. Pelletized. PS-1 to 9 were used in Examples, and PS-11 to 13 were used in Comparative Examples.
Under the conditions of PS-10, the stirring power load of the reactor increased during the operation, and it was difficult to continue the operation.

In Table 1, the types of cross-linking agents are as follows.
A: Crosslinking agent A
DVB: Divinylbenzene

<Example 1>
Next, a foam sheet was produced with a tandem extruder having a screw diameter of 40 mmφ and 50 mmφ. First, an extruder having a screw diameter of 40 mmφ was prepared by uniformly mixing 2.3 parts by mass of a talc masterbatch composed of 60% by mass of polystyrene and 40% by mass of talc with respect to 100 parts by mass of the styrene resin composition PS-1. Supplied to. Further, 60/40 (mass ratio) mixed butane composed of isobutane and normal butane as a blowing agent was injected from the tip of the extruder at a ratio of 2.5 parts by mass with respect to 100 parts by mass of the resin, and melt mixed. At this time, the cylinder temperature was 160 to 210 ° C, the resin temperature was 190 to 210 ° C, and the pressure was 12 to 18 MPa.
Then, it is transferred to an extruder having a screw diameter of 50 mmφ through a connecting pipe set at 210 ° C., adjusted to a cylinder temperature of 150 to 170 ° C., a resin temperature of 148 to 160 ° C. and 15 to 17 MPa, and a lip opening of 0.6 mm, The foamed sheet was obtained by extruding from a circular die having a diameter of 40 mm at a discharge rate of 10 kg / hr, following a cooled cylinder having a diameter of 152 mm, and incising with a cutter at one lower point of the circumference. Table 2 shows the properties of the foam sheet.

<Examples 2-9, Comparative Examples 1-3>
Except having used the styrenic resin composition of the name shown to Tables 2-3, it carried out like Example 1 and adjusted foaming ratio with the addition amount of the foaming agent, and evaluated in the state with the lowest density.

<Example 10, Comparative Example 4>
The foamed sheet prepared using PS-11 was crushed into small pieces using a crusher, and introduced into a twin screw extruder (Kobe Steel Works, KTX30α) set at a cylinder temperature of 230 ° C. to produce recycled pellets. This was mixed at a ratio of 50 mass% with respect to PS-1 and PS-12 virgin pellets, and a foamed sheet was prepared in the same manner as in Example 1. Table 3 shows the characteristics of the foam sheet.
The recycled pellets had Mn = 60,000, Mw = 310,000, and Mz = 600,000.

  Various physical properties and performance evaluation were performed by the following methods.

The characteristics of the polyfunctional vinyl copolymer were evaluated by the following methods.
(1) Double bond quantification The structural unit (a1), the double bond derived from the terminal modifier (a2), and the total molar fraction of both (a3) were measured using a JNM-LA600 nuclear magnetic resonance spectrometer manufactured by JEOL. The structure was determined by 13C-NMR and 1H-NMR analysis. Chloroform-d1 was used as a solvent, and the tetramethylsilane resonance line was used as an internal standard.
(2) Inertia radius The inertia radius was adjusted to 0.5% THF solution, filtered through a membrane filter, and the filtrate was measured using a GPC multi-angle light scattering method. Further, the sample was adjusted to 0.2% THF solution and allowed to stand for 1 day. Thereafter, it was diluted to a solution having four kinds of concentrations (0.02, 0.05, 0.10, 0.12 wt%) using THF, and dn / dc measurement was performed using these solutions. The radius of inertia of the sample was calculated from the dn / dc value.
The polyfunctional vinyl copolymer is a polymer having a distribution in molecular weight, and naturally, since the inertia radius also has a distribution, the inertia radius in the weight average molecular weight is adopted as the average value of the overall inertia radius. is there.

The characteristics of the styrene resin composition were evaluated by the following methods.
(3) Melt Mass Flow Rate A test piece was prepared using an injection molding machine, and was determined under the conditions of 200 ° C. and 49 N load based on JIS K7210.
(4) Vicat softening temperature A test piece was prepared using an injection molding machine, and obtained under conditions of 50 N load based on JIS K7206.
(5) Charpy impact strength A test piece was prepared using an injection molding machine, and determined according to JIS K7111.
(6) Methanol-soluble component Methanol-soluble component accurately weighs 1 g of resin composition (mass P), 40 mL of methyl ethyl ketone is added and dissolved, and 400 mL of methanol is added rapidly to precipitate methanol-insoluble component (resin component). Precipitated. After leaving still for about 10 minutes, it is gradually filtered through a glass filter to separate methanol-insoluble matter, dried in a vacuum dryer at 120 ° C. under reduced pressure for 2 hours, and then allowed to cool in a desiccator for about 25 minutes. By measuring the mass N of the dried methanol-insoluble matter, it was determined by the following formula.
Methanol-soluble content (mass%) = (P−N) / P × 100
(7) Molecular weight Number average molecular weight (Mn) Weight average molecular weight (Mw), Z average molecular weight (Mz), and peak molecular weight (Mtop) were measured using gel permeation chromatography (GPC) under the following conditions. .
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential Refractometer The molecular weight of the present invention is calculated by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene, and calculating the molecular weight in terms of polystyrene. The peak molecular weight (Mtop) represents the molecular weight in terms of polystyrene corresponding to the peak of the elution curve obtained by the above measurement.
(8) Branching ratio gM
The branching ratio gM is measured with a gel permeation chromatography multi-angle laser light scattering photometer (GPC-MALS method) to measure the molecular weight and the rotation radius, and the rotation radius <r ² > _br of the styrenic resin composition is linear. The branching ratio gM = <r ² > _br / <r ² > _lin was calculated from the rotational radius <r ² > _{lin of} polystyrene, and was calculated as an average value between 1 million and 1.5 million molecular weight. In addition, since a polymer with a large branch has a small radius of rotation, the value of the branching ratio gM is small. GPC-MALS was measured under the following conditions.
GPC model: Shodex DS-4 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: Room temperature Detector: Differential refractometer MALS Model: DAWN DSP-F manufactured by Wyatt Technology
Wavelength: 633 nm (He-Ne)
The branching ratio gM of the present invention is a value calculated when the branching ratio gM of linear polydisperse polystyrene (NBS706) is 1.
(9) Melt tension The melt tension value is “Capillograph 1B type” manufactured by Toyo Seiki, barrel temperature 200 ° C., barrel diameter 9.55 mm, capillary length: L = 10 mm, capillary diameter: D = 1 mm (L / D = 10), the resin is extruded at an extrusion speed of 10 mm / min in the barrel, the load measuring part is set 60 cm downward from the die, and the strand-like resin flowing out from the capillary is set in the winder and wound up. The linear velocity is gradually increased from 4 m / min, and the load until the strand breaks is measured. Since the load is stabilized at a constant value as the winding linear speed is increased, the range in which the load is stable is averaged to obtain a melt tension value.

The characteristics of the foam sheet were evaluated by the following methods.
(10) Thickness Except for 20 mm at both ends of the foamed sheet, positions at intervals of 50 mm in width were used as measurement points. Using the dial thickness gauge Peacock model G (manufactured by Ozaki Mfg. Co., Ltd.) at this measurement point, measuring the thickness to the minimum unit of 0.01 mm while taking care not to deform the test piece, this average value is the thickness of the foam sheet. (Mm).
(11) Density A test piece having a length of 10 cm and a width of 10 cm was carefully cut out from the foamed sheet so that the cell structure of the material was not broken, and was calculated from the weight and thickness of the test piece by the following formula.
Density (kg / m ³ ) = weight of test piece (g) / thickness of test piece (mm) × 100
(12) Average Cell Diameter The average cell diameter X in the thickness direction of the foam sheet, the average cell diameter Y in the extrusion direction, and the average cell diameter Z in the width direction are based on the average chord length measured by the test method of ASTM D2842-06. Calculated.
The average bubble diameter X in the thickness direction is an average chord length determined from a length of the straight line and the number of bubbles intersecting the straight line in a vertical section in the extrusion direction observed with a scanning electron microscope. X1 was determined and calculated from X1 / 0.616.
The average bubble diameter Y in the extrusion direction is obtained by dividing the vertical cross section in the extrusion direction observed with a scanning electron microscope into four equal parts in the thickness direction, and in each of the three line segments in the vicinity of the surface layer, the central part in the thickness direction, and the vicinity of the back surface. The average chord length Y1 is obtained from the length of the straight line and the number of bubbles intersecting the straight line, the average bubble diameter of each line segment is calculated from Y1 / 0.616, and the average bubble in the extrusion direction is calculated using these arithmetic average values. The diameter was Y.
The average bubble diameter Z in the extrusion direction is obtained by dividing the vertical cross section in the width direction observed with a scanning electron microscope into four equal parts in the thickness direction, and in each of the three line segments in the vicinity of the surface layer, the central portion in the thickness direction, and the vicinity of the back surface. The average chord length Z1 is obtained from the length of the straight line and the number of bubbles intersecting the straight line, the average bubble diameter of each line segment is calculated from Z1 / 0.616, and the average bubble in the extrusion direction is calculated using these arithmetic average values. The diameter was Z.
(13) Sheet bending characteristics A test piece cut out from the foamed sheet in the extrusion direction 100 mm and the width direction 30 mm was used as a test piece in the extrusion direction, and a test piece cut out in the width direction 100 mm and the extrusion direction 30 mm was used as a test piece in the width direction. The measurement is based on JIS K7171, using a 3-point bending test jig with punch tip radius R5 x width 34 mm and fulcrum tip radius R2 x width 34 mm, up to a deflection of 10 mm at a fulcrum distance of 30 mm and a descent speed of 100 mm / min. The bending strength was determined from the maximum load when pressed. Moreover, the bending elastic modulus was calculated | required from the maximum inclination between test forces 2-6N.
(14) Sheet impact strength Measurement was performed on the impact spherical surface 10R using a film impact tester (manufactured by Toyo Seiki Co., Ltd.). The measurement was performed 20 times for each of the front and back surfaces of the foam sheet, and the average value of all the sheets was used as the sheet impact strength.
(15) Deep-drawing moldability A deep-drawing bowl-shaped container having a diameter of 100 mm and a depth of 100 mm was thermoformed from a foam sheet using a single-shot molding machine. Regarding the molding conditions, the heating time was kept constant at a heater temperature of 230 ° C., and the crack generation state of the container was observed. Out of 100 molded containers, the case where the number of containers in which cracks are observed is 0, ◎ if less than 5, ○ if 5 or less, and △ if 10 or more, × Deep drawability was evaluated.

The foam sheet of the example has a better balance of bending strength, sheet impact strength and deep drawability than the comparative example, and maintains sufficient strength even when the foam sheet is lighter and deep drawn. can do.
In the above, this invention was demonstrated based on the Example. It is to be understood by those skilled in the art that this embodiment is merely an example, and that various modifications are possible and that such modifications are within the scope of the present invention.

  By using the styrene resin composition for foaming of the present invention, the foamed sheet can be reduced in weight and deep drawn, and can be suitably used as a food packaging container by being processed into various shapes.

Claims (7)

A styrene resin composition for foaming,
Including a high molecular weight derivative derived from a vinyl-based monomer having styrene as an essential component and a solvent-soluble polyfunctional vinyl copolymer having a branched structure;
The melt mass flow rate (MFR) measured at 200 ° C. and a load of 49 N is 0.8 to 3.0 g / 10 minutes,
The number average molecular weight (Mn) is 80,000 to 130,000,
The peak molecular weight (Mtop) is 200,000-350,000,
Z average molecular weight (Mz) is 750,000 or more,
The branching ratio gM at a molecular weight of 1,000,000 to 1,500,000 is 0.85 to 0.40.
A styrene resin composition for foaming. The foaming styrenic resin composition according to claim 1,
50 ppm to 1000 ppm of a solvent-soluble polyfunctional vinyl copolymer having two or more vinyl groups in one molecule and having a branched structure as a number average is added to a vinyl monomer containing styrene as an essential component. Process,
Polymerizing the solvent-soluble polyfunctional vinyl copolymer and the vinyl monomer;
A high molecular weight product obtained by a production method comprising
A styrene resin composition for foaming. The foaming styrenic resin composition according to claim 2,
The solvent-soluble polyfunctional vinyl copolymer is
Obtained by polymerizing a raw material containing a divinyl compound and a monovinyl compound copolymerizable with the divinyl compound,
Furthermore, the pendant vinyl group-containing unit derived from the divinyl compound represented by the following formula (a1) is contained in the structural unit as a molar fraction in the range of 0.05 to 0.50,
The ratio of the radius of inertia (nm) in the weight average molecular weight and the molar fraction is in the range of 1 to 100.
A styrene resin composition for foaming.
(In the formula, R ¹ represents a hydrocarbon group derived from a divinyl compound.) A styrene resin composition for foaming according to any one of claims 1 to 3,
The foaming styrene resin composition is manufactured from a raw material containing 0 to 50% by mass of a recycled raw material consisting of at least one of a polystyrene resin foam sheet and a polystyrene resin non-foamed sheet,
A styrene resin composition for foaming. Including a step of foam-extruding the foaming styrenic resin composition according to claim 1,
A method for producing a styrene resin foam sheet.   A styrene resin foam sheet obtained by the production method according to claim 5.   A food packaging container formed by molding the styrene resin foam sheet according to claim 6.