JP2016193539A - Multilayer sheet for heat molding and method for producing the same, and container for heating - Google Patents

Abstract

[Problem] To provide a multilayer sheet for thermoforming that is more excellent in adhesion. A foamed layer 10 of a thermoplastic resin containing a polystyrene resin and a non-foamed layer 20 of a polyolefin resin provided on one surface of the foamed layer, the foamed layer 10 having a glass transition The non-foamed layer 20 has a melting point of 150 to 165 ° C, a melt viscosity of 2500 to 4000 Pa · s at a strain rate of 20s-1 at 180 ° C, and a strain rate of 1000s-. The multilayer sheet 1 for thermoforming whose melt viscosity in 1 is 200-350 Pa.s. [Selection] Figure 1

Description

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

Conventionally, a multilayer sheet for thermoforming comprising a foamed layer of polystyrene-based resin and a non-foamed layer of polyolefin-based resin is known. Such a multilayer sheet for thermoforming is excellent in heat resistance, heat insulation, light weight and the like, and is used as a raw material for food containers and the like.
For example, Patent Document 1 discloses a multilayer sheet for thermoforming in which a foam sheet using a styrene- (meth) acrylic acid copolymer as a base resin and a polyolefin resin film are laminated. According to Patent Document 1, the multilayer sheet is excellent in heat resistance, heat insulation, and oil resistance, and can suppress the occurrence of blisters that partially exfoliate and expand when the resin film is heated in a microwave oven. . 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 excellent in heat insulation, heat resistance, rigidity, and lightness.

JP 2014-79985 A JP 2013-221128 A

  However, the multilayer sheet for thermoforming comprising a foamed layer of polystyrene resin and a non-foamed layer of polyolefin resin loses adhesion due to, for example, air bubbles entering between the foamed layer and the non-foamed layer during production. It was sometimes. When a container is thermoformed from such a sheet with insufficient adhesion, the molded container is likely to be deformed, and the strength of the molded container is likely to decrease. Furthermore, blisters are likely to occur when the container is heated in a microwave oven or the like.

  This invention is made | formed in view of the said situation, and aims at the multilayer sheet | seat for thermoforming which is more excellent in adhesiveness.

As a result of intensive studies, the present inventors have found that the following multilayer sheet for thermoforming can solve the above problems.
[1] A foamed layer of a thermoplastic resin containing a polystyrene resin and a non-foamed layer of a polyolefin resin provided on one surface of the foamed layer, and the foamed layer has a glass transition temperature of 110 ° C. The non-foamed layer has a melting point at 150 to 165 ° C., a melt viscosity at a strain rate of 20 s ⁻¹ at 180 ° C. of 2500 to 4000 Pa · s, and a melt viscosity at a strain rate of 1000 s ⁻¹ . A multilayer sheet for thermoforming, which is 200 to 350 Pa · s.
[2] The foam layer has a melt viscosity of 6500 to 10,000 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 . Multi-layer sheet for thermoforming.
[3] The multilayer sheet for thermoforming according to [1] or [2], wherein the polystyrene-based resin includes a styrene- (meth) acrylic acid copolymer.
[4] The non-foamed layer according to any one of [1] to [3], wherein the calorific value obtained by differential scanning calorimetry at a heating rate of 10 ° C./min is 60 J / g or more and less than 100 J / g. Multi-layer sheet for thermoforming.
[5] A heating container formed from the multilayer sheet for thermoforming according to any one of [1] to [4].
[6] The method for producing a multilayer sheet for thermoforming according to any one of [1] to [4], comprising a step of laminating the foam layer and the non-foam layer. Manufacturing method.
[7] The method for producing a multilayer sheet for thermoforming according to [6], wherein the foamed layer and the non-foamed layer are laminated by a coextrusion method.

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

It is sectional drawing which shows one Embodiment of the multilayer sheet for thermoforming which concerns on this invention.

(Multi-layer sheet for thermoforming)
As shown in FIG. 1, a multilayer sheet for thermoforming (hereinafter also simply referred to as “multilayer sheet”) 1 of the present invention includes a foamed layer 10 of a thermoplastic resin containing a polystyrene resin and a non-foamed polyolefin resin. Layer 20 is provided.
Although the thickness T of the multilayer sheet 1 is not specifically limited, For example, 0.6-3.5 mm is preferable and 1.2-3.0 mm is more preferable. In addition, the thickness in this invention is an arithmetic mean value of the thickness which measured the measuring object with the thickness gauge at intervals of 50 mm in the width direction (TD direction).

<Foaming layer 10>
The foam layer 10 is formed of a thermoplastic resin containing a polystyrene resin.
The thickness T ₁ of the foamed layer 10 is appropriately adjusted according to the use of the multilayer sheet 1, but is preferably 0.5 to 3.5 mm, and more preferably 1.0 to 3.0 mm.
Although the basic weight of the foamed layer 10 is not specifically limited, For example, 50-500 g / m < ² > is preferable and 100-400 g / m < ² > is more preferable.

The glass transition temperature of the foam layer 10 is 110 ° C. or higher, preferably 115 ° C. or higher.
The glass transition temperature (Tg) of the present invention is a value measured according to JIS K7121: 1987 “Method for Measuring Plastic Transition Temperature”, and specifically, is measured by the following procedure.
[Measurement method of glass transition temperature (Tg)]
It was measured by the method described in JIS K7121: 1987 “Method for measuring plastic transition temperature”. However, the sampling method and temperature conditions were as follows. About 6 mg of sample (foamed layer 10) is filled in the bottom of the aluminum measuring container using a differential scanning calorimeter DSC6220 (made by SII Nano Technology Co., Ltd.), and the nitrogen gas flow rate is 20 mL / min. The temperature was raised from 30 ° C. to 200 ° C. at a rate of 20 ° C./min, quickly removed after holding for 10 minutes, allowed to cool in an environment of 25 ± 10 ° C., and then 30 ° C. at a rate of 20 ° C./min. From the DSC curve obtained when the temperature was raised from 200 ° C. to 200 ° C., the value obtained by calculating the midpoint glass transition temperature using the analysis software attached to the apparatus is taken as the glass transition temperature (Tg) of the foamed layer 10. Alumina was used as the reference material. The midpoint glass transition temperature was determined from the standard (9.3 “How to determine the glass transition temperature”).
The Tg of the foam layer 10 is easily adjusted by adjusting the composition of the thermoplastic resin that forms the foam layer 10.

The foamed layer 10 has a melt viscosity (η _A1 ) at a strain rate of 20 s ⁻¹ at 200 ° C. of preferably 6500 to 10,000 Pa · s, more preferably 6500 to 9000 Pa · s, and even more preferably 6500 to 8000 Pa · s. The foam layer 10 has a melt viscosity (η _A2 ) at a strain rate of 1000 s ⁻¹ at 200 ° C. of preferably 700 to 1500 Pa · s, more preferably 700 to 1200 Pa · s, and still more preferably 700 to 1000 Pa · s. 700 to 800 Pa · s is particularly preferable.
When η _A1 and η _A2 of the foamed layer 10 are in the above preferred ranges, the adhesion is more likely to be enhanced. Furthermore, the moldability and the heat resistance of the molded product are easily improved.
In the present invention, η _A1 and η _A2 are measured as follows.

[Measuring method of melt viscosity (η _A1 ) at a strain rate of 20 s ⁻¹ at 200 ° C.]
Η _A1 of the present invention is measured by the following procedure.
First, the object to be measured (foamed layer 10) is cut out, heated for 3 minutes in a 200 ° C. hot press molding machine, and then pressed for 2 minutes to produce a plate that does not contain air bubbles, and this plate is cut and measured. A sample.
A twin-bore capillary rheometer Rheological 5000T (manufactured by Chiast Corp.) was used as a measuring device, a capillary die (die diameter 1.0 mm, die length 10 mm, inflow angle 90 °) was attached, and a barrel (barrel diameter) heated to 200 ° C. 15 mm), the sample is filled and preheated for 5 minutes, and then the apparent viscosity is maintained while the piston descending speed is held at 0.01111 mm / s (strain rate 20 s ⁻¹ ) from the capillary die of the measuring device and extruded into a string shape. Is measured and this is taken as the melt viscosity (η _A1 ). The measurement point is where the test pressure has reached a constant value for a predetermined time.

[Measuring method of melt viscosity (η _A2 ) at a strain rate of 1000 s ⁻¹ at 200 ° C.]
Η _A2 of the present invention is measured in the same manner as the measurement method of η _A1 except that the piston lowering speed is adjusted so that the strain speed becomes 1000 s ⁻¹ .
In addition, η _A1 and η _A2 of the foam layer 10 are easily adjusted by adjusting the composition of the raw material forming the foam layer.

  As the thermoplastic resin containing a polystyrene resin that forms the foam layer 10, a thermoplastic resin containing a polystyrene resin as a main component is preferable. The said main component means the range from which the content mass of a polystyrene-type resin will be 50 mass% or more with respect to all the thermoplastic resin components (100 mass%) which form the foaming layer 10. FIG. 70 mass% or more is preferable, as for the content mass of the said polystyrene-type resin, 80 mass% or more is more preferable, and 100 mass% may be sufficient.

Examples of the polystyrene resins include homopolymers or copolymers of styrene monomers, copolymers of styrene monomers and other vinyl monomers, or mixtures thereof.
The polystyrene resin preferably contains 50% by mass or more, more preferably 70% by mass or more of the structural unit based on the styrene monomer, based on the total structural unit of the polystyrene resin. What is contained by mass% or more is more preferable.

As a homopolymer or copolymer of a styrene monomer, for example, a styrene monomer such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, etc. Homopolymers or copolymers of the body. Among these, what has 50 mass% or more of structural units based on styrene with respect to all the structural units is preferable, and polystyrene is more preferable.
Moreover, high impact polystyrene containing a rubber component may be used as the polystyrene resin.

Examples of the copolymer of styrene monomer and other vinyl monomer include styrene-maleic anhydride copolymer, styrene- (meth) acrylic acid copolymer, styrene-methacrylic acid-methacrylic acid. Examples include a methyl copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene-acrylonitrile copolymer, and a styrene-butadiene copolymer.
As the copolymer of the styrene monomer and the other vinyl 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.

  The copolymer of the styrene monomer and the other vinyl monomer includes a constituent unit based on the styrene monomer in an amount of 50% by mass or more based on the total constituent 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 suspension polymerization, polystyrene resins that are not recycled materials (virgin polystyrene) can be used, used polystyrene foam plates, polystyrene resins Recycled raw materials obtained by reclaiming resin foam moldings (such as food packaging trays) can be used. Examples of the recycled material include recycled materials obtained by collecting used polystyrene foam plates and polystyrene resin foam moldings and regenerating them by a limonene dissolution method or a heat volume reduction method.

  The polystyrene resin preferably contains a styrene- (meth) acrylic acid copolymer and a styrene-methacrylic acid-methyl methacrylate copolymer. The content mass 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 mass%) forming the foamed layer 10. It is preferably at least 70% by mass, more preferably at least 70% by mass, even more preferably at least 80% by mass, and may be 100% by mass.

Resins other than the above-mentioned polystyrene resins 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-nonconjugated diene three-dimensional copolymer resins, acrylic resins, polyphenylene ether resins, and the like. Of these, polyphenylene ether resins are preferred. Examples of the polyphenylene ether resin include poly (2,6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether), poly (2.6-dichlorophenylene-1, 4-ether) and the like.

  The thermoplastic resin of the present invention preferably contains a homopolymer or copolymer of a styrene 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 monomer homopolymer or copolymer and the polyphenylene ether resin is preferably 50% by mass or more, and 70% by mass with respect to the total thermoplastic resin component (100% by mass). % Or more is more preferable, 80 mass% or more is further more preferable, and 100 mass% may be sufficient. The mass ratio of the homopolymer or copolymer of the styrene monomer and the polyphenylene ether resin [polyphenylene ether resin / styrene polymer homopolymer or copolymer] 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 addition to the thermoplastic resin, the foamed layer 10 includes a foaming agent, a bubble regulator, a crosslinking agent, a filler, a flame retardant, a flame retardant aid, a lubricant (hydrocarbon, fatty acid, fatty acid amide, ester, alcohol System, metal soap, silicone oil, wax such as low molecular weight polyethylene, etc.), spreading agents (liquid paraffin, polyethylene glycol, polybutene, etc.), and additives such as colorants may be included. Among these, it is preferable that a foaming agent and a cell regulator are included.

Examples of the foaming agent include known foaming agents, for example, hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, hexane, 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 and water.
Further, as the foaming agent, a decomposable foaming agent such as an organic acid such as azodicarbonamide, dinitrosopentamethylenetetramine, sodium hydrogen carbonate, citric acid or a mixture thereof and sodium hydrogen carbonate may be used. .
Any one of these foaming agents may be used alone, or two or more thereof may be used in combination.
The foaming agent is preferably a hydrocarbon. Among the 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 air conditioner include talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay, citric acid and the like. Of these, talc is preferable.
Any one of the bubble regulators may be used alone, or two or more may be used in combination.
As for content of a bubble regulator, 0.01-5 mass parts is preferable with respect to 100 mass parts of thermoplastic resins.

<Non-foamed layer 20>
The non-foamed layer 20 is formed of a polyolefin resin. Here, the polyolefin resin means a resin composition containing a polyolefin resin as a main component. The said main component means the range from which the content mass of polyolefin resin will be 50 mass% or more with respect to all the resin components (100 mass%) which form the non-foamed layer 20. FIG. 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 basic weight of the non-foaming layer 20 is not specifically limited, For example, 20-300 g / m < ² > is preferable and 30-200 g / m < ² > is more preferable.

The non-foamed layer 20 has a melting point at 150 to 165 ° C, preferably has a melting point at 155 to 165 ° C, and more preferably has a melting point at 160 to 165 ° C.
The melting point of the non-foamed layer 20 is determined by, for example, 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. The non-foamed layer 20 has a melt viscosity (η _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.
When η _B1 and η _B2 of the non-foamed layer 20 are in the above range, the adhesion of the non-foamed layer 20 is enhanced. Furthermore, moldability and heat resistance of the molded product are improved.

In the present invention, η _B1 and η _B2 are measured as follows.
[Measuring method of 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 η _A1 measuring method except that the measurement object is the non-foamed layer 20 and the barrel heating temperature is 180 ° C.

[Measuring method of melt viscosity (η _B2 ) at a strain rate of 1000 s ⁻¹ at 180 ° C.]
Η _B2 of the non-foamed layer 20 of the present invention is measured in the same manner as the measurement method of η _B1 except that the piston lowering speed is adjusted so that the strain rate is 1000 s ⁻¹ .
In addition, melting | fusing point, (eta) _B1 , (eta) _B2 of the non-foaming layer 20 is easily adjusted by adjusting the composition of the polyolefin-type resin which forms the non-foaming layer 20.

The non-foamed layer 20 preferably has a calorific value (ΔH) determined by differential scanning calorimetry at a temperature rising rate of 10 ° C./min, of 60 J / g or more and less than 100 J / g, preferably 70 J / g or more and less than 100 J / g. It is more preferable that
In the present invention, ΔH is measured as follows.
[Measurement method of calorific value ΔH]
Measured by the method described in JIS K7122: 1987 “Method for measuring the transition heat of plastic”. However, the sampling method and temperature conditions were as follows. About 6 mg of the sample (non-foamed layer 20) is filled with a differential scanning calorimeter DSC6220 type (made by SII Nano Technology Co., Ltd.) so that there is no gap at the bottom of the aluminum measurement container, and the nitrogen gas flow rate is 20 mL / min. Then, the temperature was lowered from 30 ° C. to −40 ° C. and then held for 10 minutes, and the temperature was raised from −40 ° C. to 220 ° C. (1st Heating). After holding for 10 minutes, the temperature was lowered from 220 ° C. to −40 ° C. (Cooling), 10 A DSC curve was obtained when the temperature was raised from −40 ° C. to 220 ° C. (2nd Heating) after holding for minutes. All the temperature increases / decreases were performed at a rate of 10 ° C./min, and alumina was used as a reference material. In the present invention, the calorific value ΔH is the amount of crystallization heat (J / g) determined from the area of the crystallization peak observed in the cooling process. For the calorific value ΔH, using the analysis software attached to the device, the DSC curve is surrounded by a straight line connecting the point at which the crystallization peak (exothermic peak) moves away from the high temperature side baseline and the point at which the exothermic peak returns to the low temperature side baseline. It is calculated from the area of the portion to be processed.
Note that ΔH is easily adjusted by adjusting the composition of the polyolefin resin forming the non-foamed layer 20.

Examples of polyolefin resins include polypropylene resins, polyethylene resins, and cyclic polyolefin resins.
As the polypropylene resin, for example, propylene homopolymer (homo PP), ethylene and propylene are copolymerized so that the content of the constituent unit based on ethylene is more than 0 and 5% by mass or less in the copolymer. And a random copolymer (random PP), a block copolymer (block PP) in which a homopolymer of polypropylene is produced and then ethylene is copolymerized with the homopolymer.
When the non-foamed layer 20 is formed of a polypropylene resin, the polypropylene resin may be a stretched film (OPP) or a non-stretched film (CPP).

Examples of the polyethylene resin include low density polyethylene resin (LDPE) in which ethylene is polymerized under high pressure to form long chain branches in the molecule, and ethylene is polymerized under medium and low pressure using a Ziegler-Natta catalyst or a metallocene catalyst. A 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 in the HDPE polymerization process is added to the molecule. Examples thereof include a linear low density polyethylene resin (LLDPE) having a short chain branching density of less than 0.942 g / cm ³ .

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

As the polyolefin-based resin, a polypropylene-based resin is preferable from the viewpoint of excellent heat resistance and oil resistance. It is preferable that 80 mass% or more of the polypropylene resin is contained in the polyolefin resin.
Moreover, as polyolefin resin, it is preferable that random PP and HDPE are 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, or 100% by mass in the polyolefin resin. Further, the content ratio of random PP to HDPE (random PP / HDPE) is preferably 80/20 to 95/5.

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

  From the point which the adhesiveness of the multilayer sheet 1 is improved, the said foaming layer 10 is thermoplasticity containing 80 mass% or more of a styrene- (meth) acrylic acid copolymer and / or a styrene-methacrylic acid-methyl methacrylate copolymer. It is preferable that the non-foamed layer 20 is formed of a resin and is formed of an olefin resin containing 80% by mass or more of homo PP. For the same reason, the foamed layer 10 is formed of a thermoplastic resin containing a styrene monomer homopolymer or copolymer and polyphenylene ether resin in a total amount of 80% by mass or more. The foam layer 20 is preferably formed of an olefin-based resin containing 80% by mass or more of homo PP.

The peel strength at 23 ° C. of the foamed layer 10 and the non-foamed layer 20 is preferably 1.0 to 6.0N, more preferably 2.0 to 5.9N, and even more preferably 2.5 to 5.8N. The peel strength at 110 ° C. between the foamed layer 10 and the non-foamed layer 20 is preferably 0.1 to 1.5N.
The peel strength of the present invention is a value measured as follows.
[Measurement method of peel strength]
The peel strength of the present invention is measured as follows.
The multilayer sheet 1 is cut into a width of 25 mm and a length of 150 mm to obtain a measurement sample. As a measuring device, Tensilon universal testing machine (Orientec Co., UCT-10T) and universal testing machine data processing software UTPS-458P (Soft Brain Co., Ltd.) were used, and the measurement sample was a symbol “23 / of JIS K7100: 1999”. 50 ”(temperature 23 ° C., relative humidity 50%), condition adjustment over 16 hours or more in a second grade standard atmosphere, and chuck spacing on a tensile test jig attached to the testing machine under the same standard atmosphere Attach so that is 20 mm. Thereafter, the measurement sample is first peeled off by 25 mm from the end, set in the test machine so that the peeling direction of the non-foamed layer is 180 ° with respect to the foamed layer, and the 180 ° peel test is performed at a tensile speed of 300 mm / min. . The intensity is averaged until the measurement sample is peeled off by 60 mm (measurement jig moving distance: 120 mm). The said measurement is performed 5 times and let the average value be peeling strength (N / 25mm width) in 23 degreeC.
Moreover, the thermostat TCLF-U4-HW (manufactured by TSE Co., Ltd.) attached to the test machine was set to 110 ° C. atmosphere, and the measurement sample conditioned in the same manner as described above was set to the 110 ° C. atmosphere. The peel strength was measured in the same manner as above except that the test was started after being set in the tensile test jig in the thermostat within 5 seconds (from opening the thermostat door to closing) and held for 2.5 minutes. A thing is made into the peeling strength (N / 25mm width) in 110 degreeC.

  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 improved.

<Adhesive layer>
It does not specifically limit as an adhesive layer, The adhesive layer formed from well-known resin is used.
When the adhesive layer is used, the thickness is not particularly limited, but is preferably 2 to 50 μm, for example.
Although the basic weight of an contact bonding layer is not specifically limited, For example, 1-60 g / m < ² > is preferable, 3-50 g / m < ² > is more preferable, 5-30 g / m < ² > is further more preferable.

The adhesive layer has a complex viscosity (η _C ) at a frequency of 1 Hz at 130 ° C. of preferably 15000 to 45000 Pa · s, more preferably 20000 to 40000 Pa · s, and further preferably 25000 to 38000 Pa · s. When η _C is within the above preferred range, adhesion to both the foamed layer 10 and the non-foamed layer 20 is likely to be enhanced. Furthermore, it becomes easy to suppress deformation when the multilayer sheet 1 is heated.
Further, the complex viscosity of the adhesive layer is preferably set 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 foamed layer 10, when the foamed layer 10 and / or the non-foamed layer 20 and the adhesive layer are laminated by coextrusion, resin breakage of the adhesive layer is suppressed. It becomes easy.
Η _C of the adhesive layer of the present invention is a value measured as follows.

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

The adhesive layer is preferably formed of a mixed resin containing an ethylene-vinyl acetate copolymer and a styrene thermoplastic elastomer. When the adhesive layer is formed of the mixed resin, adhesion to both the foamed layer 10 and the non-foamed layer 20 is likely to be improved. Furthermore, it becomes easy to adjust the complex viscosity of the adhesive layer to the above preferred range.
The mixing ratio of the ethylene-vinyl acetate copolymer and the styrene thermoplastic elastomer in the mixed resin is not particularly limited, but the styrene thermoplastic elastomer is 10 to 300 per 100 parts by mass of the ethylene-vinyl acetate copolymer. It is preferable to mix by the ratio of a mass part, and it is more preferable to mix by the ratio of 30-250 mass parts. Adhesiveness with respect to both the foamed layer 10 and the non-foamed layer 20 becomes easy to be in the said mixing ratio.

  The ethylene-vinyl acetate copolymer preferably has a constitutional unit content based on vinyl acetate in the copolymer of more than 0% by mass to 30% by mass and more than 0% by mass to 10% by mass. More preferred is 3 to 10% by mass. Further, the melting point of the copolymer is preferably 70 to 110 ° C. from the viewpoint of achieving both moldability and heat resistance.

Examples of the styrene thermoplastic elastomer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-butylene-styrene block copolymer (SBBS), and 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. Modified products modified with acid are mentioned.
Among these, SBS, SBBS, and SEBS are preferable because superior adhesiveness can be obtained.
For the same reason, the styrene-based thermoplastic elastomer preferably has a styrene-based constituent unit content of 30 to 40% by mass in the styrene-based thermoplastic elastomer.
Additives such as resins and colorants other than the ethylene-vinyl acetate copolymer and styrene-based thermoplastic elastomer may be added to the adhesive layer.

(Manufacturing method of multilayer sheet 1)
Although it does not specifically limit as a manufacturing method of the multilayer sheet 1, A thermal lamination method, a coextrusion method, etc. are mentioned.
As the thermal laminating method, the foamed layer 10 and the non-foamed layer 20 are prepared separately, laminated and passed between heating rollers, and heated and pressed from above and below to form the foamed layer 10 and the non-foamed layer. The method of integrating the layer 20 is mentioned. In the said method, the said contact bonding layer may be arrange | positioned between the said foaming layer 10 and the non-foaming layer 20, and it may be set as the laminated sheet of 3 layers.
In this case, the heating temperature is preferably 140 to 210 ° C, more preferably 160 to 200 ° C.

  The coextrusion method includes a step of melt-kneading a thermoplastic resin, an additive and a foaming agent to form a foamed layer to obtain a foamed layer molten resin, and a melt-kneading of an olefinic resin and an additive to form a non-foamed layer A step of obtaining a non-foamed layer molten resin and a step of supplying the foamed layer molten resin and the non-foamed layer molten resin to a confluence mold and extruding from one die to form and laminate the foamed layer and the non-foamed layer. (Hereinafter also referred to as “coextrusion method 1”).

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 thermoplastic resin. . The glass transition temperature of the thermoplastic resin is preferably 110 ° C. or higher, and more preferably 115 ° C. or higher.
Η _{A1 of the} thermoplastic resin is preferably 6500 to 10000 Pa · s, more preferably 6500 to 9000 Pa · s, and further preferably 6500 to 8000 Pa · s. Further, η _{A2 of the} thermoplastic resin is preferably 700 to 1500 Pa · s, more preferably 700 to 1200 Pa · s, further preferably 700 to 1000 Pa · s, and particularly preferably 700 to 800 Pa · s.
In the said coextrusion method 1, 160-190 degreeC is preferable and, as for the resin temperature of the foamed layer molten resin immediately before supplying to the said confluence | merging metal mold | die, 165-190 degreeC is preferable.

The non-foamed layer molten resin in the coextrusion method 1 preferably contains 0 to 30 parts by mass of the additive with respect to 100 parts by mass of the olefin resin. The olefin resin preferably has a melting point at 150 to 165 ° C, more preferably has a melting point at 155 to 165 ° C, and still more preferably has a melting point at 160 to 165 ° C.
The olefin resin η _B1 is preferably 2500 to 4000 Pa · s, and more preferably 2800 to 3500 Pa · s. The polyolefin resin has η _B2 of preferably 200 to 350 Pa · s, more preferably 200 to 340 Pa · s, and still more preferably 210 to 330 Pa · s.
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 confluence mold is preferably 170 to 200 ° C, and more preferably 175 to 190 ° C.

  The coextrusion method when the adhesive layer is included in the multilayer sheet includes a step of obtaining a foamed layer molten resin by melting and kneading a thermoplastic resin, an additive and a foaming agent that form the foamed layer, and a resin that forms the adhesive layer And a step of melt-kneading the additive to obtain an adhesive layer molten resin, a step of melt-kneading the olefin-based resin forming the non-foamed layer and the additive to obtain a non-foamed layer molten resin, the foamed layer molten resin, A method comprising the steps of supplying an adhesive layer and a non-foamed layer molten resin to a converging mold and extruding from a single die to form and laminate the foam layer, the adhesive layer and the non-foamed layer (hereinafter, “coextrusion method 2”) Also called).

  The foamed layer molten resin in the coextrusion method 2 is preferably the same as in the coextrusion method 1. Further, the resin temperature immediately before being supplied to the confluence mold of the foamed layer molten resin in the coextrusion method 2 is preferably the same temperature as in the coextrusion method 1.

It is preferable that 0-30 mass% of additives are contained in the adhesive layer molten resin in the coextrusion method 2 with respect to 100 parts by mass of the resin forming the above-described adhesive layer. Moreover, 15000-45000 Pa.s is preferable, as for (eta) _C of the said resin, 20000-40000 Pa.s is more preferable, and 25000-38000 Pa.s is further more preferable.
In the coextrusion method 2, the resin temperature of the adhesive layer molten resin immediately before being supplied to the merging mold is preferably 160 to 190 ° C, and more preferably 165 to 180 ° C.

  The non-foamed layer molten resin in the coextrusion method 2 is preferably the same as in the coextrusion method 1. Further, the temperature immediately before being supplied to the confluence mold of the non-foamed layer molten resin in the coextrusion method 2 is preferably the same temperature as in the coextrusion method 1.

  Conventionally, when a multilayer sheet comprising a foamed layer of polystyrene resin and a non-foamed layer of olefin resin is produced, sufficient adhesion may not be obtained. The multilayer sheet of the present invention has improved adhesion by setting the glass transition temperature of the foamed layer to a specific range and the melting point and melt viscosity of the non-foamed layer to a specific range. In particular, when the multilayer sheet of the present invention is produced by a coextrusion method, the adhesion is further improved. Furthermore, in the coextrusion method, each layer can be formed and laminated simultaneously, and the productivity is excellent. Therefore, the multilayer sheet of the present invention is preferably produced by a coextrusion method.

(Other embodiments)
The multilayer sheet of the present invention is not limited to the above-described embodiment.
For example, in the above-described embodiment, the non-foamed layer is provided only on one surface of the foamed layer, but the present invention is not limited to this. A non-foamed layer may also be provided on the other surface of the foamed layer.
In the above-described embodiment, the two-layer sheet of the foamed layer and the non-foamed layer, the three-layer sheet of the foamed layer, the adhesive layer, and the non-foamed layer is used, but the present invention is not limited thereto. For example, a resin layer other than the above, such as a resin layer formed from stretched polystyrene, may be provided on one or both surfaces of the foam layer, so that four or more sheets may be formed.
Moreover, it is also arbitrary to give decorations, such as printing, to the surface of a foam layer and / or a non-foam layer. The decoration may be performed by laminating paper or a resin film on the surface of the foam layer and / or the non-foam layer.

(Heating container)
Since the multilayer sheet 1 of the present invention is excellent in adhesion, moldability, molded product strength, heat resistance, light weight, etc., it is suitably used as a raw material for food containers. Examples of the food container include a tray-type container, a bowl-type container, and a cup-type container. Moreover, since the multilayer sheet 1 of this invention is excellent in the suppression property of the blister produced when it heats, it is used suitably as a raw material of the container for range up heated with the microwave oven in the state in which the foodstuff was accommodated.
Examples of the method for producing a food container include a normal thermoforming method, for example, a method in which the multilayer sheet 1 is sandwiched between a female mold and a male mold and thermoformed.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. In this example, “%” indicates “% by mass” unless otherwise specified.
The composition of the multilayer sheet of each example is shown in Table 1. In Table 1, the content of the air conditioner in the foamed layer represents a part by mass with respect to 100 parts by mass of the total resin components in the foamed layer.
The raw materials used in this example are as follows.

(Foam layer)
ML195: Styrene-methacrylic acid copolymer, manufactured by PS Japan Corporation.
-AMM11: Blend product of styrene-methacrylic acid copolymer and MBS resin (trans-type butadiene block-containing product), manufactured by PS Japan Corporation.
H8117: cis-type styrene-butadiene block copolymer resin, manufactured by PS Japan Corporation.
-DSM1401: Bubble regulator, talc content, manufactured by Toyo Styrene Co., Ltd.
(Non-foamed layer)
-PL400A: Homo PP, manufactured by Sun Allomer.
FY4: Homo PP, manufactured by Nippon Polypro Co., Ltd.
E111G: Homo PP copolymer, manufactured by Prime Polymer Co., Ltd.
-Wintech WFW4F: Random PP, manufactured by Nippon Polypro Co., Ltd.
(Adhesive layer)
LV-244A1: ethylene-vinyl acetate copolymer, manufactured by Nippon Polyethylene Corporation.
Tuftec H1041: Styrene-ethylene-butylene-styrene block copolymer (content of 30% by mass of structural unit based on styrene), manufactured by Asahi Kasei Corporation.
PC540R: Random PP, manufactured by Sun Allomer 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 the coextrusion method as follows.
As a manufacturing apparatus by the co-extrusion method, the following first extruder, second extruder and third extruder, a merging mold for joining the molten resins supplied from these extruders, and a circular die are provided. Was used.
As the first extruder, a first-stage single-screw extruder having a diameter of 115 mm, a second-stage single-screw extruder having a diameter of 150 mm connected to the first-stage single-screw extruder, and A tandem extruder consisting of As the second extruder, a single screw extruder having a diameter of 90 mm was used. As the third extruder, a single screw extruder having a diameter of 50 mm was used.

  ML195, AMM11, H8117 and DSM1401 were supplied to the first-stage single-screw extruder of the first extruder at the blending ratio shown in Table 1 and 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) as a blowing agent was injected from the inlet and melt-kneaded to obtain a melt-kneaded product. This melt-kneaded product was supplied to a second stage single-screw extruder and melt-kneaded to obtain 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 blending ratio shown in Table 1, and melt-kneaded to obtain a melt-kneaded product. This 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 the 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 foamed layer molten resin, the adhesive layer molten resin, and the non-foamed layer molten resin are supplied to a confluence mold, and these molten resins are merged to form a foamed layer, an adhesive layer, and a non-foamed material from the inside to the outside. Cylindrical foams laminated in the order of the layers were formed by coextrusion from a circular die.
The cylindrical foam is air-cooled, and then the cylindrical foam is continuously cut and opened in the extrusion direction, and the foam layer, the adhesive layer, and the non-foam layer are laminated and integrated. A multilayer sheet was produced. The thickness of the multilayer sheet of Example 1 was 2 mm, the basis weight of the foam layer was 200 g / m ² , the basis weight of the non-foam layer was 65 g / m ² , and the basis weight of the adhesive layer was 15 g / m ² .

(Examples 2-6, Comparative Examples 1-2)
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.
Further, a multilayer sheet of Example 5 was produced in the same manner as in Example 1 except that the amount of foaming agent injected was 2.5 parts by mass and the basis weight of the foamed layer was 260 g / m ² .

About the obtained multilayer sheet of each example, Tg of the foam layer, η _A1 , η _A2 , melting point of the non-foam layer, η _B1 , η _B2 , ΔH, η _{C of} the adhesive layer, and the foam layer and the non-foam layer The peel strength was measured by the measurement method described above. The measurement results are shown in Table 2. For the multilayer sheet of Comparative Example 1, the peel strength was not measured because the adhesion was clearly poor.

The adhesion, moldability, and heat resistance of the molded product of each example multilayer sheet were evaluated as follows. The evaluation results are shown in Table 2. The multilayer sheet of Comparative Example 1 was not evaluated for heat resistance because the moldability was clearly poor.
≪Evaluation of adhesion≫
About the multilayer sheet of each example, the contact | adherence state of the non-foamed layer was observed visually and tactilely, and adhesiveness was evaluated based on the following criteria. ○ and △ were regarded as acceptable.
[Judgment criteria for adhesion]
○: No swelling is observed in the non-foamed layer. And when a non-foamed layer and a foamed layer are made to peel, material destruction is observed in either a foamed layer or a non-foamed layer. (That is, the foamed layer and the non-foamed layer do not peel between the layers, and one of the two layers is destroyed when peeled.)
Δ: No swelling is observed in the non-foamed layer. Moreover, when the non-foamed layer and the foamed layer are peeled off, no material destruction is observed in the foamed layer and the non-foamed layer. (That is, the foamed layer and the non-foamed layer are separated from each other.)
X: Obvious 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 was prepared by preheating the multilayer sheet of each example for 21 seconds in a heating chamber set to an atmospheric temperature of 165 ° C., and then forming a tray container (outer dimensions of container opening: 205 mm × 105 mm, outer dimensions of bottom: 75 mm × 175 mm, container It was manufactured by mold-molding a non-foamed layer of the multilayer sheet with a mold having a depth outside dimension: 20 m) so that the non-foamed layer of the multilayer sheet becomes the inner surface of the container. The obtained container was observed visually and by touch, and the moldability was evaluated based on the following criteria. ○ and △ were regarded as acceptable.
[Judgment criteria for moldability]
○: No swelling is observed on the surface of the container, and the surface is smooth.
Δ: A part of the surface of the container slightly swells. Or a slight unevenness | corrugation is felt in a part of surface of a container.
X: Obvious swelling is observed in the container. Or the unevenness | corrugation of the surface of a container is clearly felt.

≪Evaluation of heat resistance≫
160 g of vegetable oil heated to 150 ° C. was put into the food container produced as described above, and held for 30 seconds, and then the vegetable oil was discharged from the food container. The food containers after the vegetable oil was discharged were observed visually and by touch, and the heat resistance was evaluated based on the following criteria. ○ and △ were regarded as acceptable.
[Criteria for heat resistance]
○: Melted on the surface of the container, no swelling was observed, and the surface was smooth.
(Triangle | delta): Although melting is not observed on the surface of a container, there exists a part which is slightly swollen in a part of surface.
X: Obvious swelling and melting are observed in the container.

From the results shown in Table 2, it was confirmed that the multilayer sheets of Examples 1 to 6 to which the present invention was applied were more excellent in adhesion. Moreover, it has confirmed that the multilayer sheet of Examples 1-6 was excellent in thermoformability, and the container formed from this multilayer sheet was excellent in heat resistance.
On the other hand, the 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 of the non-foamed layer does not satisfy the scope of the present invention is sufficient adhesion and molding. Sex was not obtained. The multilayer sheet in which the melting point of the non-foamed layer does not satisfy the range of the present invention (Comparative Example 2) could not obtain sufficient heat resistance.

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

Claims (7)

A thermoplastic resin foam layer containing a polystyrene resin, and a polyolefin resin non-foam layer provided on one surface of the foam layer,
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 · s at a strain rate of 1000 s ⁻¹ . s, a multilayer sheet for thermoforming. 2. The thermoforming molding according to claim 1, wherein the foam layer has a melt viscosity of 6500 to 10,000 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 . Multi-layer sheet.   The multilayer sheet for thermoforming according to claim 1 or 2, wherein the polystyrene-based resin contains a styrene- (meth) acrylic acid copolymer.   The said non-foamed layer is the thermoforming as described in any one of Claims 1-3 whose calorific value calculated | required by differential scanning calorimetry in the temperature increase rate of 10 degree-C / min is 60 J / g or more and less than 100 J / g. Multilayer sheet.   A heating container formed from the thermoforming multilayer sheet according to any one of claims 1 to 4. It is a manufacturing method of the multilayer sheet for thermoforming according to any one of claims 1 to 4,
The manufacturing method of the multilayer sheet for thermoforming which has the process of laminating | stacking the said foaming layer and the said non-foaming layer.   The method for producing a multilayer sheet for thermoforming according to claim 6, wherein the foamed layer and the non-foamed layer are laminated by a coextrusion method.

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