JP6502727B2 - Multi-layer sheet for thermoforming, method for producing the same, and container for heating - Google Patents

Description

  The present invention relates to a multilayer sheet for thermoforming, a method for producing the same, and a container for heating.

Conventionally, a multilayer sheet for thermoforming comprising a foamed layer of polystyrene resin and a non-foamed layer of polyolefin resin is known. Such a multilayer sheet for thermoforming is used as a raw material for containers for food and the like because it is excellent in heat resistance, heat insulation, lightness, and the like.
For example, Patent Document 1 discloses a multi-layer sheet for thermoforming, in which a foam sheet having a styrene- (meth) acrylic acid copolymer as a base resin, and a polyolefin resin film are laminated. According to Patent Document 1, it is considered that the multilayer sheet is excellent in heat resistance, heat insulation and oil resistance, and can suppress the occurrence of blisters in which the resin film partially peels and swells when heated in a microwave oven . Further, Patent Document 2 discloses a styrene resin heat-resistant foam sheet in which a styrene resin foam sheet using a specific styrene-methacrylic acid copolymer as a raw material resin and a polyolefin resin film are laminated. According to Patent Document 2, the heat-resistant foam sheet is considered to be excellent in heat insulation, heat resistance, rigidity, and lightness.

JP, 2014-79985, A JP, 2013-221128, A

  However, in the case of a multilayer sheet for thermoforming comprising a foamed layer of a polystyrene resin and a non-foamed layer of a polyolefin resin, adhesion is impaired due to, for example, air bubbles entering between the foamed layer and the non-foamed layer during production. I had a problem. When the container is thermoformed from such a sheet with insufficient adhesion, the container after molding is likely to be deformed, and the strength of the container after molding is also likely to be reduced. Furthermore, when the container is heated by a microwave oven or the like, blistering is likely to occur.

  The present invention has been made in view of the above-described circumstances, and an object thereof is a multilayer sheet for thermoforming which is more excellent in adhesion.

As a result of intensive studies, the present inventors have found that the following multilayer sheet for thermoforming can solve the above-mentioned problems.
[1] A foamed layer of a thermoplastic resin containing a polystyrene based resin and a non-foamed layer of a polyolefin based resin provided on one surface of the foamed layer are provided, and the foamed layer has a glass transition temperature of 110 ° C. The non-foamed layer has a melting point of 150 to 165 ° C., and has a melt viscosity of 2500 to 4000 Pa · s at a strain rate of 20 s ⁻¹ at 180 ° C. and a melt viscosity at a strain rate of 1000 s ⁻¹ The multilayer sheet for thermoforming which is 200-350 Pa.s.
[2] The foam layer according to [1], wherein the melt viscosity at a strain rate of 20 s ⁻¹ at 200 ° C. is 650 to 10000 Pa · s, and the melt viscosity at a strain rate of 1000 s ⁻¹ is 700 to 1500 Pa · s. Multilayer sheet for thermoforming.
[3] The multilayer sheet for thermoforming according to [1] or [2], wherein the polystyrene resin contains a styrene- (meth) acrylic acid copolymer.
[4] The non-foamed layer according to any one of [1] to [3], wherein the calorific value determined by differential scanning calorimetry at a heating rate of 10 ° C./min is 60 J / g or more and less than 100 J / g. Multilayer sheet for thermoforming.
The heating container formed from the multilayer sheet for thermoforming in any one of [5] [1]-[4].
[6] A method for producing a multilayer sheet for thermoforming according to any one of [1] to [4], which comprises the step of laminating the foam layer and the non-foam layer. Manufacturing method.
[7] The method for producing a heat-forming multilayer sheet according to [6], wherein the foam layer and the non-foam layer are laminated by a coextrusion method.

  The multilayer sheet for thermoforming of the present invention is more excellent in adhesion.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows one Embodiment of the multilayer sheet for thermoforming which concerns on this invention.

(Multilayer sheet for thermoforming)
As shown in FIG. 1, the multilayer sheet for thermoforming of the present invention (hereinafter, also simply referred to as "multilayer sheet") 1 is a foamed layer 10 of a thermoplastic resin containing a polystyrene resin and a non-foamed polyolefin resin. The layer 20 is provided.
Although thickness T of multilayer sheet 1 is not particularly limited, for example, 0.6 to 3.5 mm is preferable, and 1.2 to 3.0 mm is more preferable. The thickness in the present invention is an arithmetic mean value of the thickness measured with a thickness gauge at intervals of 50 mm in the width direction (TD direction) of the object to be measured.

<Foamed layer 10>
The foam layer 10 is formed of a thermoplastic resin containing a polystyrene resin.
Although thickness T ₁ of foaming layer 10 is suitably adjusted according to the use etc. of multilayer sheet 1, 0.5-3.5 mm is preferred, for example, and 1.0-3.0 mm is more preferred.
Although the basis weight of the foam layer 10 is not particularly limited, for example, 50 to 500 g / m ² is preferable, and 100 to 400 g / m ² is more preferable.

The glass transition temperature of the foam layer 10 is 110 ° C. or more, preferably 115 ° C. or more.
The glass transition temperature (Tg) of the present invention is a value measured in accordance with JIS K 7121: 1987 "Method for measuring transition temperature of plastic", and specifically measured according to the following procedure.
[Method of measuring glass transition temperature (Tg)]
It measured by the method described in JISK7121: 1987 "transition temperature measurement method of plastics". However, the sampling method and temperature conditions were as follows. About 6 mg of a sample (foam layer 10) is filled using a differential scanning calorimeter DSC2220 type (manufactured by SII Nano Technology Co., Ltd.) so that the bottom of the aluminum measurement container is not separated, and the nitrogen gas flow rate is 20 mL / min. The temperature is raised from 30 ° C to 200 ° C at a rate of 20 ° C / min, held immediately for 10 minutes, taken out immediately, allowed to cool under an environment of 25 ± 10 ° C, and then 30 ° C at a rate of 20 ° C / min. The value obtained by calculating the midpoint glass transition temperature from the DSC curve obtained when the temperature is raised from 200 ° C. to 200 ° C. is used as the glass transition temperature (Tg) of the foam layer 10. Alumina was used as a reference material. The midpoint glass transition temperature was determined from the standard (9.3 “How to Determine Glass Transition Temperature”).
The Tg of the foam layer 10 is easily adjusted by adjusting the composition of the thermoplastic resin forming the foam layer 10.

The melt viscosity (η _A1 ) at a strain rate of 20 s ⁻¹ at 200 ° C. is preferably 650 to 10000 Pa · s, more preferably 6500 to 9000 Pa · s, and still more preferably 6500 to 8000 Pa · s. The melt viscosity (発 泡_A2 ) at a strain rate of 1000 s ⁻¹ at 200 ° C. is preferably 700 to 1500 Pa · s, more preferably 700 to 1200 Pa · s, and still more preferably 700 to 1000 Pa · s. And 700 to 800 Pa · s are particularly preferred.
When the や_すく_A1 and η _A2 of the foam layer 10 are within the above-described preferred range, the adhesion is more likely to be enhanced. Furthermore, the moldability and the heat resistance of the molded article are likely to be enhanced.
In the present invention, η _A1 and η _A2 are measured as follows.

[Method of measuring melt viscosity (η _A1 ) at a strain rate of 20 s ⁻¹ at 200 ° C.]
The η _A1 of the present invention is measured by the following procedure.
First, an object to be measured (foamed layer 10) is cut out, heated for 3 minutes with a hot press molding machine at 200 ° C., and pressed for 2 minutes to produce a plate containing no air bubbles, and this plate is cut and measured. It will be a sample.
As a measuring device, using a twin-bore capillary rheometer Rheologic 5000T (manufactured by Thiast), a capillary die (die diameter 1.0 mm, die length 10 mm, inflow angle 90 °) is attached and a barrel heated to 200 ° C. (barrel diameter After filling the measurement sample in 15 mm) and preheating for 5 minutes, the apparent viscosity is obtained while extruding in a string shape while holding the piston lowering speed at 0.01111 mm / s (strain speed 20 s ⁻¹ ) from the capillary die of the measuring device. Of the melt viscosity (溶 融_A1 ). The measurement point is a point where the test pressure has become constant for a predetermined time.

[Method of measuring melt viscosity (粘度_A2 ) at a strain rate of 1000 s ⁻¹ at 200 ° C.]
The η _A2 of the present invention is measured in the same manner as the above A _A1 measurement method except that the lowering speed of the piston is adjusted so that the strain rate is 1000 s ⁻¹ .
Note that η _A1 and η _A2 of the foam layer 10 can be easily adjusted by adjusting the composition of the raw material forming the foam layer.

  As a thermoplastic resin containing polystyrene resin which forms the foaming layer 10, the thermoplastic resin which contains a polystyrene resin as a main component is preferable. The main component means a range in which the mass of the polystyrene resin is 50% by mass or more with respect to the total thermoplastic resin component (100% by mass) forming the foam layer 10. 70 mass% or more is preferable, as for content mass of the said polystyrene resin, 80 mass% or more is more preferable, and 100 mass% may be sufficient.

As said polystyrene resin, the homopolymer or copolymer of a styrene-type monomer, the copolymer of a styrene-type monomer and another vinyl-type monomer, or these mixtures etc. are mentioned.
The polystyrene resin preferably contains 50% by mass or more, and more preferably 70% by mass or more, of structural units based on a styrene-based monomer, based on the total structural units of the polystyrene resin. It is more preferable that the material is contained by mass% or more.

Examples of homopolymers or copolymers of styrene-based monomers include styrene-based units such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene and bromostyrene The homopolymer or copolymer of the body is mentioned. Among these, those having a structural unit based on styrene in an amount of 50% by mass or more based on all the structural units are preferable, and polystyrene is more preferable.
Further, high impact polystyrene containing a rubber component may be used as the polystyrene resin.

As a copolymer of a styrene-based monomer and another vinyl-based monomer, for example, styrene-maleic anhydride copolymer, styrene- (meth) acrylic acid copolymer, styrene-methacrylic acid-methacrylic acid Methyl copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-butadiene copolymer and the like can be mentioned.
As a copolymer of the said styrene-type monomer and another vinyl-type monomer, a styrene- (meth) acrylic acid copolymer and a styrene- methacrylic acid-methyl methacrylate copolymer are preferable.
In the present specification, (meth) acrylic acid means acrylic acid or methacrylic acid.

  As a copolymer of a styrene-based monomer and another vinyl-based monomer, one containing a constitutional unit based on a styrene-based monomer in an amount of 50% by mass or more based on the total constitutional units of the copolymer Preferably, those containing 70% by mass or more are more preferable, and those containing 80% by mass or more are more preferable.

  As polystyrene resins, commercially available polystyrene resins, polystyrene resins synthesized by a suspension polymerization method, etc., polystyrene resins (virgin polystyrene) which are not recycled materials can be used, and polystyrene foam plates already used, polystyrene resins The recycled raw material obtained by reprocessing resin foam molded articles (trays for food packaging etc.) etc. can be used. Examples of the recycled raw materials include recycled raw materials obtained by recovering used polystyrene foam plates and polystyrene resin foam molded bodies and regenerating them by a limonene dissolution method or a heating volume reduction method.

  The polystyrene resin preferably contains a styrene- (meth) acrylic acid copolymer and a styrene-methacrylic acid-methyl methacrylate copolymer. The content of the styrene- (meth) acrylic acid copolymer and / or the styrene-methacrylic acid-methyl methacrylate copolymer is 50 with respect to the total thermoplastic resin component (100% by mass) forming the foam layer 10. The mass% or more is preferable, 70 mass% or more is more preferable, 80 mass% or more is more preferable, and 100 mass% may be sufficient.

A resin other than the above-mentioned polystyrene-based resin may be added to the thermoplastic resin of the present invention.
Examples of resins other than polystyrene resins include polyethylene resins, polypropylene resins, polybutadiene resins, ethylene-propylene non-conjugated diene three-dimensional copolymer resins, acrylic resins, polyphenylene ether resins and the like. Among them, polyphenylene ether resins are preferable. Examples of polyphenylene ether resins include poly (2,6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether), poly (2.6-dichlorophenylene-1, 4-ether) etc. are mentioned.

  The thermoplastic resin of the present invention preferably contains a homopolymer or copolymer of a styrenic monomer and a polyphenylene ether resin, and more preferably contains polystyrene and a polyphenylene ether resin. In this case, the total content of the styrene-based homopolymer or copolymer and the polyphenylene ether resin is preferably 50% by mass or more, based on 100% by mass of the total thermoplastic resin component, and 70% by mass. % Or more is more preferable, 80 mass% or more is more preferable, and 100 mass% may be sufficient. In addition, the content ratio by mass of the homopolymer or copolymer of a styrenic monomer to the polyphenylene ether resin [polyphenylene ether resin / homopolymer or copolymer of styrenic monomer] is 1/99 to 50/50 is preferable, 5/95 to 45/55 is preferable, and 10/90 to 40/60 is more preferable.

  In the foam layer 10, in addition to the above-mentioned thermoplastic resin, a foaming agent, a cell regulator, a crosslinking agent, a filler, a flame retardant, a flame retardant auxiliary, a lubricant (hydrocarbon, fatty acid type, fatty acid amide type, ester type, alcohol) Additives such as a system, metal soap, silicone oil, wax such as low molecular weight polyethylene, spreading agent (liquid paraffin, polyethylene glycol, polybutene etc.), coloring agent, etc. may be included. Among these, a foaming agent and a cell regulator are preferably contained.

Examples of the blowing agent include known blowing agents, and examples thereof include hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, hexane and the like, ketones such as acetone and methyl ethyl ketone, Examples thereof include alcohols such as methanol, ethanol and isopropyl alcohol, ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether and petroleum ether, carbon dioxide, nitrogen, ammonia, water and the like.
In addition, as the foaming agent, a degradable foaming agent such as a mixture of sodium hydrogencarbonate or an organic acid such as azodicarbonamide, dinitrosopentamethylenetetramine, sodium hydrogencarbonate, citric acid or a salt thereof may be used. .
One of these foaming agents may be used alone, or two or more thereof may be used in combination.
The blowing agent is preferably a hydrocarbon. Among hydrocarbons, normal butane, isobutane, normal pentane, isopentane or a mixture thereof is preferable.
Although content of the said foaming agent is not specifically limited, 0.1-10 mass parts is preferable with respect to 100 mass parts of thermoplastic resins.

Examples of the cell regulator include talc, sodium hydrogencarbonate, ammonium hydrogencarbonate, calcium carbonate, clay, citric acid and the like. Among them, talc is preferred.
Any one type of cell regulator may be used alone, or two or more types may be used in combination.
The content of the cell regulator is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the thermoplastic resin.

<Non-foamed layer 20>
The non-foamed layer 20 is formed of a polyolefin resin. Here, the polyolefin-based resin means a resin composition containing a polyolefin-based resin as a main component. The main component means a range in which the content mass of the polyolefin resin is 50% by mass or more with respect to the entire resin component (100% by mass) forming the non-foamed layer 20. 70 mass% or more is preferable, as for the content mass of the said polyolefin resin, 80 mass% or more is more preferable, and 100 mass% may be sufficient.
The thickness _{T 2} of the non-foamed layer 20 is moisture-proof multilayer sheet may be appropriately adjusted in consideration of the thermoforming and the like, for example 20~300μm preferably, 30 to 200 [mu] m is more preferable.
Although the basis weight of the non-foamed layer 20 is not particularly limited, for example, 20 to 300 g / m ² is preferable, and 30 to 200 g / m ² is more preferable.

The non-foamed layer 20 has a melting point of 150 to 165 ° C., preferably a melting point of 155 to 165 ° C., and more preferably a melting point of 160 to 165 ° C.
The melting point of the non-foamed layer 20 is determined, for example, by differential scanning calorimetry (DSC).

The non-foamed layer 20 has a melt viscosity (η _B1 ) at a strain rate of 20 s ⁻¹ at 180 ° C. of 2500 to 4000 Pa · s, and preferably 2800 to 3500 Pa · s. Further, the non-foamed layer 20 has a melt viscosity ( _{2 B2} ) at a strain rate of 1000 s ⁻¹ at 180 ° C. of 200 to 350 Pa · s, preferably 200 to 340 Pa · s, and more preferably 210 to 330 Pa · s. preferable.
The adhesion of the non-foamed layer 20 is enhanced when the η _B1 and η _B2 of the non-foamed layer 20 are in the above range. Furthermore, the moldability and the heat resistance of the molded product are enhanced.

In the present invention, _{B B1} and η _B2 are measured as follows.
[Method of measuring melt viscosity (η _B1 ) at a strain rate of 20 s ⁻¹ at 180 ° C.]
The η _B1 of the non-foamed layer 20 of the present invention is measured in the same manner as the above η _A1 except that the object to be measured is the non-foamed layer 20 and the heating temperature of the barrel is 180 ° C.

[Method of measuring melt viscosity (η _B2 ) at a strain rate of 1000 s ⁻¹ at 180 ° C.]
The _{B B2} of the non-foamed layer 20 of the present invention is measured in the same manner as the above η _B1 measuring method except that the lowering speed of the piston is adjusted so that the strain rate is 1000 s ^-1 .
The melting point, _{B B1} and η _B2 of the non-foamed layer 20 can be easily adjusted by adjusting the composition of the polyolefin resin forming the non-foamed layer 20.

The non-foamed layer 20 preferably has a calorific value (ΔH) of at least 60 J / g and less than 100 J / g, preferably at least 70 J / g and less than 100 J / g, as determined by differential scanning calorimetry at a heating rate of 10 ° C./min. It is more preferable that
In the present invention, ΔH is measured as follows.
[Method of measuring calorific value ΔH]
It was measured by the method described in JIS K 7122: 1987 "Method of measuring transition heat of plastic". However, the sampling method and temperature conditions were as follows. About 6 mg of a sample (non-foamed layer 20) is filled using a differential scanning calorimeter DSC2220 (manufactured by SII Nano Technology Co., Ltd.) so that the bottom of the measurement container made of aluminum has no gaps, and the nitrogen gas flow rate is 20 mL / min The temperature is lowered from 30 ° C to -40 ° C and then held for 10 minutes, the temperature is raised from -40 ° C to 220 ° C (1st Heating), and after held for 10 minutes, the temperature is lowered from 220 ° C to -40 ° C (Cooling), 10 After holding for a minute, a DSC curve was obtained when the temperature was raised (−2nd heating) from −40 ° C. to 220 ° C. In addition, all temperature rising / falling was performed at a rate of 10 ° C./min, and alumina was used as a reference substance. In the present invention, the calorific value ΔH is the heat of crystallization (J / g) determined from the area of the crystallization peak observed in the cooling process. The calorific value ΔH is surrounded by a DSC curve, which is a straight line connecting the point where the crystallization peak (exothermic peak) leaves the baseline on the high temperature side and the point where the exothermic peak returns to the baseline on the low temperature side using analysis software attached to the device. Calculated from the area of the
Note that ΔH is easily adjusted by adjusting the composition of the polyolefin resin forming the non-foamed layer 20 or the like.

Examples of polyolefin resins include polypropylene resins, polyethylene resins, cyclic polyolefin resins and the like.
As the polypropylene-based resin, for example, ethylene and propylene are copolymerized so that the homopolymer contained in propylene (homoPP) and the content mass of the structural unit based on ethylene are greater than 0 and not more than 5% by mass in the copolymer. The random copolymer (random PP), a block copolymer (block PP) obtained by copolymerizing ethylene with the homopolymer after producing a homopolymer of polypropylene, and the like can be mentioned.
When the non-foamed layer 20 is formed of a polypropylene-based resin, the polypropylene-based resin may be a stretched film (OPP) or a non-stretched film (CPP).

As the polyethylene resin, for example, low density polyethylene resin (LDPE) in which ethylene is polymerized under high pressure to form long chain branches in the molecule, ethylene is polymerized under medium and low pressure using Ziegler Natta catalyst or metallocene catalyst High density polyethylene resin (HDPE) having a density of 0.942 g / cm ³ or more, and a small amount of α-olefin such as 1-butene, 1-hexene, 1-octene or the like added in the polymerization process of the HDPE Examples thereof include linear low density polyethylene resin (LLDPE) having a density of less than 0.942 g / cm ^{3 in} which short chain branches are formed.

  Examples of the cyclic polyolefin resin include a copolymer (COC) of ethylene and norbornene, and a polymer (COP) obtained by polymerizing cyclopentanediol by a metathesis reaction.

As a polyolefin resin, a polypropylene resin is preferable from the point which is excellent in heat resistance and oil resistance. It is preferable that the said polypropylene resin is contained 80 mass% or more in polyolefin resin.
Moreover, as a polyolefin resin, it is preferable that random PP and HDPE be used together from the point which is excellent in heat resistance and oil resistance. In this case, the total content of random PP and HDPE is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass, and 100% by mass in the polyolefin resin. Moreover, the content mass ratio (random PP / HDPE) of random PP and HDPE is preferably 80/20 to 95/5.

The non-foamed layer 20 of the present invention may contain additives in addition to the above-mentioned polyolefin resin. Examples of the additive include mineral particles, flame retardants, flame retardant aids, lubricants, spreading agents, coloring agents and the like.
Examples of mineral particles include plate-like mineral particles such as talc, kaolin, calcined kaolin, bentonite, mica group minerals (sericite, muscovite, phlogopite, biotite) and the like. Among these, talc is preferred. Moreover, as for the median diameter (D50) in the particle size distribution by the laser diffraction method of the said mineral particle, 1-15 micrometers is preferable.
When the additive is contained in the non-foamed layer 20, the content is preferably more than 0 parts by mass and 30 parts by mass or less with respect to 100 parts by mass of the polyolefin resin.

  A thermoplastic resin containing 80% by mass or more of the styrene- (meth) acrylic acid copolymer and / or the styrene-methacrylic acid-methyl methacrylate copolymer from the viewpoint that the adhesion of the multilayer sheet 1 is enhanced. It is preferable that it is formed with resin and the said non-foaming layer 20 is formed with the olefin resin which contains 80 mass% or more of homo PP. For the same reason, the foamed layer 10 is formed of a thermoplastic resin containing 80% by mass or more of a styrene-based monomer homopolymer or copolymer and a polyphenylene ether resin as a total amount of both. The foam layer 20 is preferably formed of an olefin resin containing 80% by mass or more of homoPP.

1.0-6.0N is preferable, as for the peeling strength at 23 degrees C of the foaming layer 10 and the non-foaming layer 20, 2.0-5.9 N are more preferable, and 2.5-5.8 N are more preferable. Moreover, as for the peeling strength in 110 degreeC of the foaming layer 10 and the non-foaming layer 20, 0.1-1.5 N is preferable.
The peel strength of the present invention is a value measured as follows.
[Method of measuring peel strength]
The peel strength of the present invention is measured as follows.
The multilayer sheet 1 is cut out into a width 25 mm × length 150 mm to be a measurement sample. As a measuring device, using a Tensilon universal tester (manufactured by ORIENTEC Co., Ltd., UCT-10T) and a universal tester data processing software UTPS-458P (manufactured by Softbrain Co., Ltd.) 50 "(temperature 23 ° C, relative humidity 50%), after conditioning for 16 hours or more in a standard atmosphere of a second grade, then the chuck distance between the tensile test jigs attached to the tester under the same standard atmosphere Attach so that it becomes 20mm. Thereafter, the measurement sample is peeled off from the end by 25 mm at first, and the foamed layer is set in the above testing machine so that the peeling direction of the non-foamed layer is 180 °, and the 180 ° peel test is performed at a tensile speed of 300 mm / min. . The strength until the time when the measurement sample is separated by 60 mm (measurement jig moving distance 120 mm) is integrated and averaged. The said measurement is performed 5 times and let the average value be the peeling strength (N / 25 mm width) in 23 degreeC.
In addition, a constant temperature bath TCLF-U4-HW (manufactured by T.S.E., Ltd.) attached to the above-mentioned testing machine was set to 110 ° C. atmosphere, and the measurement sample adjusted in the same manner as above was set to 110 ° C. atmosphere. The peel strength was measured in the same manner as above except that the tensile test jig in the thermostat was set within 5 seconds (from opening the thermostat door to closing) and held for 2.5 minutes and then the test was started. Let the thing be 110 degreeC peel strength (N / 25 mm width).

  The multilayer sheet 1 may be provided with an adhesive layer between the foam layer 10 and the non-foam layer 20. By providing the adhesive layer, the adhesion of the non-foamed layer 20 is further enhanced. Furthermore, the integrity of the multilayer sheet 1 is further enhanced.

<Adhesive layer>
The adhesive layer is not particularly limited, and an adhesive layer formed of a known resin is used.
When the adhesive layer is used, its thickness is not particularly limited, but preferably 2 to 50 μm, for example.
The basis weight of the adhesive layer is not particularly limited, for example, preferably 1~60g / ^{m 2,} more preferably 3 to 50 g / ^{m 2,} more preferably 5 to 30 g / ^{m 2.}

The adhesive layer preferably has a complex viscosity (η _C ) of 15000 to 45000 Pa · s at a frequency of 1 Hz at 130 ° C., more preferably 20000 to 40000 Pa · s, and still more preferably 25000 to 38000 Pa · s. When η _C is within the above-mentioned preferred range, the adhesion to both the foam layer 10 and the non-foam layer 20 tends to be enhanced. Furthermore, deformation when the multilayer sheet 1 is heated can be easily suppressed.
Further, the complex viscosity of the adhesive layer is preferably lower than the complex viscosity of the foam layer 10. When the complex viscosity of the adhesive layer is lower than the complex viscosity of the foam layer 10, resin breakage of the adhesive layer is suppressed when laminating the adhesive layer with the foam layer 10 and / or the non-foam layer 20 by coextrusion. It will be easier.
The η _C of the adhesive layer of the present invention is a value measured as follows.

[Method of measuring complex viscosity (η _C ) at a frequency of 1 Hz at 130 ° C.]
The η _C of the adhesive layer of the present invention is measured as follows.
As a measuring apparatus, what combined the viscoelasticity measuring apparatus "PHYSICA MCR301" made from Anton Paar and temperature control system "CTD450" is used.
First, a resin composition constituting an object to be measured (adhesive layer) is melt-kneaded with an extruder at 200 ° C., discharged in a strand shape, cooled, and cut into a pellet shape. The resulting pellet-like resin composition is preheated for 3 minutes in a heat press molding machine at 200 ° C., and press molded for 2 minutes to obtain a disk-shaped measurement sample of Φ25 mm. The measurement sample is set on a plate of a viscoelasticity measuring device heated to a measurement start temperature of 230 ° C., and left for 5 minutes under a nitrogen atmosphere for melting. Thereafter, the space is crushed to 2.0 mm with a parallel plate of 25 mm in diameter, and the sample protruding from the plate is removed. The measurement sample is heated again to 230 ° C and left for 5 minutes, and then the dynamic viscoelasticity measurement is performed up to 130 ° C under conditions of strain 5%, frequency 1 Hz, temperature decrease rate 2 ° C / minute, measurement interval 30 seconds, normal force ON. Measure η _C (Pa · s).

The adhesive layer is preferably formed of a mixed resin containing an ethylene-vinyl acetate copolymer and a styrenic thermoplastic elastomer. When the adhesive layer is formed of the mixed resin, the adhesiveness to both the foam layer 10 and the non-foam layer 20 tends to be enhanced. Furthermore, the complex viscosity of the adhesive layer can be easily adjusted to the above-mentioned preferable range.
The mixing ratio of the ethylene-vinyl acetate copolymer and the styrene thermoplastic elastomer in the mixed resin is not particularly limited, but 10 to 300 of the styrene thermoplastic elastomer is based on 100 parts by mass of the ethylene-vinyl acetate copolymer. It is preferable to mix by the ratio of mass part, and it is more preferable to mix by the ratio of 30-250 mass parts. With the mixing ratio, adhesion to both the foam layer 10 and the non-foam layer 20 tends to be enhanced.

  As the ethylene-vinyl acetate copolymer, one having a content weight of a constituent unit based on vinyl acetate in the copolymer of more than 0% by mass and 30% by mass or less is preferable, and one having more than 0% by mass and 10% by mass or less More preferably, 3 to 10% by mass is more preferable. Moreover, as for the melting | fusing point of the said copolymer, 70-110 degreeC is preferable from a point with which moldability and heat resistance are made compatible.

As a styrene-based thermoplastic elastomer, styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene -Ethylene-butylene-styrene block copolymer (SEBS), styrene-isoprene-propylene-styrene block copolymer (SIPS), styrene-ethylene-propylene-styrene block copolymer (SEPS) or these are maleic anhydride etc. Acid-modified products, and the like.
Among these, SBS, SBBS, and SEBS are preferable in terms of obtaining better adhesion.
Moreover, as the styrene-based thermoplastic elastomer, for the same reason, the content of the structural unit based on styrene is preferably 30 to 40% by mass in the styrene-based thermoplastic elastomer.
In the adhesive layer, additives such as resins other than the ethylene-vinyl acetate copolymer and the styrene-based thermoplastic elastomer and a colorant may be added.

(Manufacturing method of multilayer sheet 1)
Although it does not specifically limit as a manufacturing method of the multilayer sheet 1, A heat lamination method, a co-extrusion method, etc. are mentioned.
As the thermal laminating method, the foamed layer 10 and the non-foamed layer 20 are separately prepared, they are laminated, passed between heating rollers, and heated and pressed from above and below to form the foamed layer 10 and the non-foamed. A method in which the layer 20 is integrated may be mentioned. In the method, the adhesive layer may be disposed between the foam layer 10 and the non-foam layer 20 to form a three-layer laminated sheet.
140-210 degreeC is preferable and, as for the heating temperature in this case, 160-200 degreeC is more preferable.

  As a co-extrusion method, a step of melt-kneading a thermoplastic resin for forming a foamed layer, an additive and a foaming agent to obtain a foamed layer molten resin, an olefin-based resin for forming a non-foamed layer and an additive are melt-kneaded A step of obtaining the non-foamed layer molten resin, and a step of supplying the foamed layer molten resin and the non-foamed layer molten resin to the joining mold and extruding from one die to form and laminate the foamed layer and the non-foamed layer The method which it has (Hereinafter, it is also called "the co-extrusion method 1.") is mentioned.

The foamed layer molten resin in the coextrusion method 1 preferably contains 1 to 10 parts by mass of a foaming agent and 0.01 to 5 parts by mass of a cell regulator with respect to 100 parts by mass of the above-mentioned thermoplastic resin. . Moreover, 110 degreeC or more is preferable and, as for the glass transition temperature of the said thermoplastic resin, 115 degreeC or more is more preferable.
As for (eta) _A1 of the said thermoplastic resin, 6500-10000 Pa.s are preferable, 6500-9000 Pa.s are more preferable, and 650-8000 Pa.s are more preferable. The thermoplastic resin 0〜150 _A2 is preferably 700 to 1,500 Pa · s, more preferably 700 to 1,200 Pa · s, still more preferably 700 to 1,000 Pa · s, and particularly preferably 700 to 800 Pa · s.
In the coextrusion method 1, the resin temperature of the foamed layer molten resin immediately before being supplied to the joining mold is preferably 160 to 190 ° C, and more preferably 165 to 190 ° C.

The non-foamed layer molten resin in the coextrusion method 1 preferably contains 0 to 30 parts by mass of an additive based on 100 parts by mass of the above-mentioned olefin resin. The olefin resin preferably has a melting point of 150 to 165 ° C, more preferably a melting point of 155 to 165 ° C, and still more preferably a melting point of 160 to 165 ° C.
Eta _B1 olefinic resin is preferably 2500~4000Pa · s, 2800~3500Pa · s is more preferable. Eta _B2 of the polyolefin resin is preferably 200~350Pa · s, more preferably from 200~340Pa · s, more preferably 210~330Pa · s.
The ΔH of the olefin resin is preferably 60 J / g or more and less than 100 J / g, and more preferably 70 J / g or more and less than 100 J / g.
In the coextrusion method 1, the resin temperature of the non-foamed layer molten resin immediately before being supplied to the joining mold is preferably 170 to 200 ° C., and more preferably 175 to 190 ° C.

  The coextrusion method in which the adhesive layer is contained in the multilayer sheet includes a step of melt-kneading the thermoplastic resin forming the foamed layer, the additive and the foaming agent to obtain the foamed layer molten resin, and the resin forming the adhesive layer And melt-kneading an additive to obtain an adhesive layer molten resin, melt-kneading an olefin resin and an additive to form a non-foamed layer to obtain a non-foamed layer molten resin, the foamed layer molten resin, A method including the steps of supplying the adhesive layer and the non-foamed layer molten resin to the joining mold and extruding from one die to form and laminate the foamed layer, the adhesive layer and the non-foamed layer (hereinafter referred to as "co-extrusion method 2" Also referred to as

  As the foamed layer molten resin in co-extrusion method 2, the same one as in co-extrusion method 1 is preferable. The resin temperature immediately before being supplied to the merging die of the foamed layer molten resin in the co-extrusion method 2 is preferably the same temperature as the co-extrusion method 1.

The adhesive layer molten resin in the co-extrusion method 2 preferably contains 0 to 30% by mass of an additive based on 100 parts by mass of the resin forming the above-mentioned adhesive layer. Moreover, 150000-45000 Pa.s is preferable, as for (eta) _C of the said resin, 20000-40000 Pa.s is more preferable, and 2500-38000 Pa.s is further more preferable.
In the co-extrusion method 2, the resin temperature of the adhesive layer molten resin immediately before being supplied to the joining mold is preferably 160 to 190 ° C, and more preferably 165 to 180 ° C.

  As the non-foamed layer molten resin in co-extrusion method 2, the same one as in co-extrusion method 1 is preferable. Further, the temperature just before being supplied to the merging die of the non-foamed layer molten resin in the co-extrusion method 2 is preferably the same temperature as the co-extrusion method 1.

  Heretofore, in the case of producing a multilayer sheet comprising a foamed layer of polystyrene resin and a non-foamed layer of olefin resin, sufficient adhesion may not be obtained. In the multilayer sheet of the present invention, adhesion is enhanced by setting the glass transition temperature of the foam layer to a specific range and setting the melting point and melt viscosity of the non-foam layer to a specific range. In particular, the multilayer sheet of the present invention has higher adhesion when produced by a coextrusion method. Furthermore, in the co-extrusion method, formation of each layer and lamination can be performed simultaneously, which is excellent in productivity. Therefore, the multilayer sheet of the present invention is preferably produced by coextrusion.

(Other embodiments)
The multilayer sheet of the present invention is not limited to the embodiment described above.
For example, in the above-mentioned embodiment, although the non-foaming layer was provided only in one side of a foaming layer, it is not limited to this. A non-foamed layer may also be provided on the other side of the foam layer.
In the above-mentioned embodiment, although it was set as the bilayer | two_layer sheet of a foaming layer and a non-foaming layer, a foaming layer, an adhesive layer, and a non-foaming layer, it is not limited to this. For example, resin layers other than the above, such as a resin layer formed of stretched polystyrene, may be provided on one or both surfaces of the foam layer, and may be a sheet of four or more layers.
In addition, it is optional to provide a decoration such as printing on the surface of the foam layer and / or the non-foam layer. The decoration may be performed by laminating a paper or a resin film on the surface of the foam layer and / or the non-foam layer.

(Container for heating)
The multilayer sheet 1 of the present invention is suitably used as a raw material for food containers because it is excellent in adhesion, moldability, molded article strength, heat resistance, lightness and the like. Examples of food containers include tray-type containers, bowl-type containers, and cup-type containers. Moreover, since the multilayer sheet 1 of this invention is excellent in the suppression property of the blister produced when it is heated, it is used suitably as a raw material of the container for range ups heated with a microwave in the state in which the foodstuff was accommodated.
As a manufacturing method of the container for foodstuffs, the usual thermoforming method is mentioned, for example, the method of sandwiching the multilayer sheet 1 by a female type | mold and a male type, and thermoforming it is mentioned.

EXAMPLES The present invention will be described in more detail using the following examples, but the present invention is not limited to these examples. In the present example, “%” indicates “% by mass” unless otherwise noted.
The composition of the multilayer sheet of each example is shown in Table 1. In Table 1, the content of the cell regulator in the foam layer indicates a part by mass with respect to 100 parts by mass of the entire resin component of the foam layer.
The raw materials used in this example are as follows.

(Foam layer)
ML 195: Styrene-methacrylic acid copolymer, manufactured by PS Japan Co., Ltd.
AMM 11: A blended product of a styrene-methacrylic acid copolymer and an MBS resin (trans butadiene block-containing product), manufactured by PS Japan Co., Ltd.
H8117: cis-styrene-butadiene block copolymer resin, manufactured by PS Japan Co., Ltd.
-DSM 1401: Bubble regulator, containing talc, manufactured by Toyo Styrene Co., Ltd.
(Non-foamed layer)
PL400A: HomoPP, manufactured by Sun Aroma.
FY4: HomoPP, manufactured by Japan Polypropylene Corporation.
E111G: homoPP copolymer, manufactured by Prime Polymer Co., Ltd.
Wintech WFW4F: Random PP, manufactured by Japan Polypropylene Corporation.
(Adhesive layer)
LV-244A1: ethylene-vinyl acetate copolymer, manufactured by Japan Polyethylene Corporation.
Tuftec H1041: styrene-ethylene-butylene-styrene block copolymer (containing 30% by mass of a structural unit based on styrene) manufactured by Asahi Kasei Corporation.
PC 540R: Random PP, manufactured by Sun Aroma Co., Ltd.
-Tufprene 125: styrene-butadiene-styrene copolymer, manufactured by Asahi Kasei Corporation.

The multilayer sheet of Examples 1-6 and Comparative Examples 1-2 was manufactured as follows.
Example 1
The multilayer sheet of Example 1 was produced by coextrusion as follows.
As a manufacturing apparatus by the co-extrusion method, the following first extruder, second extruder and third extruder, a joining die for joining molten resins supplied from these extruders, and a circular die Was used.
As the first extruder, a first-stage single-screw extruder having a diameter of 115 mm, and a second-stage single-screw extruder having a diameter of 150 mm connected to the first-stage single-screw extruder Using a tandem extruder. As a second extruder, a single screw extruder having a diameter of 90 mm was used. As a third extruder, a single-screw extruder having a bore of 50 mm was used.

  ML195, AMM11, H8117, and DSM 1401 were supplied at the mixing ratio shown in Table 1 to the first-stage single-screw extruder of the first extruder, melt-kneaded, and then provided in the middle of the first-stage 3.0 parts by mass of butane (normal butane: 35% by mass, isobutane: 65% by mass) was injected as a foaming agent from the inlet, and melt-kneaded to obtain a melt-kneaded product. The melt-kneaded product was supplied to the single-stage extruder at the second stage and melt-kneaded while obtaining a melt-kneaded product having a resin temperature of 172.5 ° C. (foamed layer molten resin).

  LV-244A1 and Tuftec H1041 were supplied to the second extruder at the mixing ratio shown in Table 1, and melt-kneaded to obtain a melt-kneaded product. The melt-kneaded product was cooled to obtain a melt-kneaded product having a resin temperature of 175 ° C. (adhesive layer molten resin).

  PL400A was supplied to the third extruder at a blending ratio shown in Table 1 and melt-kneaded to obtain a melt-kneaded product. The melt-kneaded product was cooled to obtain a melt-kneaded product having a resin temperature of 175 ° C. (non-foamed layer molten resin).

Next, the above-mentioned foamed layer molten resin, adhesive layer molten resin and non-foamed layer molten resin are supplied to the joining mold, these molten resins are joined together, and the foamed layer, adhesive layer, non-foaming from the inside to the outside A cylindrical foam, laminated in order of layers, was formed by coextrusion from a circular die.
The cylindrical foam is air cooled, and then the cylindrical foam is continuously cut and cut in the extrusion direction, and the foam layer, the adhesive layer, and the non-foam layer are integrally laminated. A multilayer sheet was produced. The multilayer sheet of Example 1 had a thickness of 2 mm, a basis weight of the foamed layer of 200 g / m ² , a basis weight of the non-foamed layer of 65 g / m ² , and a basis weight of the adhesive layer of 15 g / m ² .

(Examples 2 to 6, Comparative Examples 1 to 2)
Multilayer sheets of Examples 2 to 4 and 6 and Comparative Examples 1 to 2 were produced in the same manner as in Example 1 except that the composition of the non-foamed layer or the adhesive layer was changed to that shown in Table 1.
A multilayer sheet of Example 5 was produced in the same manner as Example 1, except that the amount of pressing of the foaming agent was 2.5 parts by mass and the basis weight of the foam layer was 260 g / m ² .

With respect to the multilayer sheet of each example obtained, Tg of the foamed layer, _{1 A1} , η _A2 , melting point of the non-foamed layer, η _B1 , 、 _B2 , ΔH, 接着_{C of} the adhesive layer, and between the foamed layer and the non-foamed layer Peeling strength was measured by the above-mentioned measuring method. The measurement results are shown in Table 2. In the case of the multilayer sheet of Comparative Example 1, the peel strength was not measured because the adhesion was apparently poor.

The adhesiveness, the moldability, and the heat resistance of the molded article of each multilayer sheet were evaluated as follows. The evaluation results are shown in Table 2. The heat resistance of the multilayer sheet of Comparative Example 1 was not evaluated because the formability was apparently poor.
«Evaluation of adhesion»
About the multilayer sheet of each case, the adhesion state of the non-foamed layer was observed visually and tactilely, and the adhesion was evaluated based on the following judgment criteria. ○ and を were accepted.
[Criteria for determining adhesion]
:: No swelling was observed in the non-foamed layer. And, when the non-foamed layer and the foamed layer are peeled off, material failure is observed in either the foamed layer or the non-foamed layer. (That is, the foamed layer and the non-foamed layer do not peel off between the layers, and when peeling off, either of the layers is broken.)
Fair: no swelling was observed in the non-foamed layer. And, when the non-foamed layer and the foamed layer are peeled off, no material breakage is observed in the foamed layer and the non-foamed layer. (Ie, the foam layer and the non-foam layer delaminate between the layers).
X: A clear swelling is observed in the non-foamed layer.

«Evaluation of moldability»
The multilayer sheet of each example was thermoformed to produce a tray-type food container. The container preheats the multilayer sheet of each example for 21 seconds in a heating chamber set at an ambient temperature of 165 ° C., and then the tray container shape (container opening external dimensions: 205 mm × 105 mm, bottom external dimensions: 75 mm × 175 mm, container It manufactured by match molding molding so that the non-foamed layer of the said multilayer sheet might become an inner surface of a container with the metal mold | die which has a depth external dimension: 20 m. The obtained container was observed visually and tactilely, and the moldability was evaluated based on the following judgment criteria. ○ and を were accepted.
[Judgment criteria of moldability]
:: No swelling was observed on the surface of the container, and the surface was smooth.
Δ: A portion of the surface of the container is slightly swollen. Alternatively, slight unevenness may be felt on part of the surface of the container.
X: A clear bulge is observed in the container. Or, the unevenness of the surface of the container is clearly felt.

«Evaluation of heat resistance»
After 160 g of vegetable oil heated to 150 ° C. was charged into the food container manufactured as described above and held for 30 seconds, the vegetable oil was discharged from the food container. The container for food after discharging the vegetable oil was observed visually and tactilely, and the heat resistance was evaluated based on the following judgment criteria. ○ and を were accepted.
[Judgment criteria of heat resistance]
○: Melted on the surface of the container, no swelling was observed, and the surface was smooth.
Δ: No melting is observed on the surface of the container, but a part of the surface is slightly swollen.
X: Clear swelling and melting observed in the container.

From the results shown in Table 2, it can be confirmed that the multilayer sheets of Examples 1 to 6 to which the present invention is applied are more excellent in adhesion. Moreover, the multilayer sheet of Examples 1-6 was excellent in thermoforming property, and it has confirmed that the container formed from this multilayer sheet was excellent in heat resistance.
On the other hand, a multilayer sheet (comparative example 1) in which the melt viscosity at a strain rate of 20 s ^-1 at 180 ° C. and the melt viscosity at a strain rate of 1000 s ^-1 do not satisfy the range of the present invention I did not get sex. The multilayer sheet (Comparative Example 2) in which the melting point of the non-foamed layer does not satisfy the range of the present invention did not have sufficient heat resistance.

1 Multi-layer sheet for thermoforming 10 Foamed layer 20 Non-foamed layer

Claims (7)

A foamed layer of a thermoplastic resin containing a polystyrene-based resin, a non-foamed layer of a polyolefin-based resin provided on one surface of the foamed layer, and an adhesive layer for bonding the foamed layer and the non-foamed layer Equipped
The foam layer has a glass transition temperature of 110 ° C. or higher,
The non-foamed layer has a melting point of 150 to 165 ° C., and has a melt viscosity of 2500 to 4000 Pa · s at a strain rate of 20 s ⁻¹ at 180 ° C. and a melt viscosity of 200 to 350 Pa · at a strain rate of 1000 s ⁻¹ . s der is,
The adhesive layer contains 25 to 75% by mass of a styrenic thermoplastic elastomer based on the total mass of the adhesive layer,
The adhesive layer is a multilayer sheet for thermoforming, having a complex viscosity of 25200 to 42300 Pa · s at a frequency of 1 Hz at 130 ° C. 2. The thermoforming according to claim 1, wherein the foamed layer has a melt viscosity of 650 to 10000 Pa · s at a strain rate of 20 s ⁻¹ at 200 ° C. and a melt viscosity of 700 to 1500 Pa · s at a strain rate of 1000 s ⁻¹ . Multilayer sheet.   The multilayer sheet for thermoforming of Claim 1 or 2 in which the said polystyrene resin contains a styrene- (meth) acrylic acid copolymer.   The heat molding according to any one of claims 1 to 3, wherein the non-foamed layer has a calorific value of 60 J / g or more and less than 100 J / g as determined by differential scanning calorimetry at a temperature rising rate of 10 ° C / min. For multilayer sheet.   The heating container formed from the multilayer sheet for thermoforming as described in any one of Claims 1-4. It is a manufacturing method of the multilayer sheet for thermoforming as described in any one of Claims 1-4, Comprising:
The manufacturing method of the multilayer sheet for thermoforming which has the process of laminating | stacking the said foam layer and the said non-foam layer through the said contact bonding layer . The manufacturing method of the multilayer sheet for thermoforming of Claim 6 which laminates | stacks the said foaming layer, the said non-foaming layer, and the said contact bonding layer by the co-extrusion method.

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