JP7208799B2 - Composition, foamed sheet and molded article - Google Patents

Description

The present invention relates to compositions, foam sheets and molded articles.

Foamed sheets using polystyrene resins are used as materials for food containers, packaging containers, and the like. On the other hand, food containers made only of polystyrene resin may not have sufficient properties such as heat resistance. Various proposals have been made for the composition of For example, Patent Document 1 discloses a resin foam sheet containing predetermined amounts of a styrene-methacrylic acid copolymer, polyphenylene ether, and polystyrene.

JP 2014-205761 A

In order to obtain a molded product of excellent quality, a foamed sheet with less unevenness, excellent appearance, and excellent impact resistance is required. Furthermore, since the food container may be heated in a microwave oven, it is also required to have excellent heat resistance.

An object of the present invention is to provide a composition from which a foamed sheet having excellent appearance, impact resistance, and heat resistance can be obtained, and a foamed sheet and molded article obtained by using the composition.

The present invention provides the composition, foamed sheet and molded article shown below.
(1) A composition containing two or more polymers, wherein monomer units constituting the two or more polymers include (meth)acrylic acid, (meth)acrylic acid alkyl esters, styrene, and conjugated The content of (meth)acrylic acid is 2 to 15% by mass, and the content of (meth)acrylic acid alkyl ester is 3 to 15, based on the total amount of monomer units that contain a diene and constitute two or more polymers. Composition, in % by weight.
(2) The composition according to (1), wherein the styrene content is 68 to 95% by mass based on the total amount of monomer units constituting the two or more polymers.
(3) The composition according to (1) or (2), wherein the content of the conjugated diene is 0.01 to 4% by mass based on the total amount of monomer units constituting the two or more polymers.
(4) Polymer (A) containing styrene and (meth)acrylic acid as monomer units, and methyl (meth)acrylate and (meth)acrylic acid other than methyl (meth)acrylate as (meth)acrylic acid alkyl esters Any one of (1) to (3) containing a polymer (B) containing an acid alkyl ester as a monomer unit and a polymer (C) obtained by polymerizing a rubber component containing a conjugated diene as a monomer unit with styrene. The described composition.
(5) Based on the total amount of monomer units contained in the polymer (A), the content of styrene is 85 to 97% by mass and the content of (meth)acrylic acid is 3 to 15% by mass. (4) The composition according to .
(6) Based on the total amount of monomer units contained in the polymer (B), the content of methyl (meth)acrylate is 65 to 90% by mass, and the (meth)acrylic acid alkyl ester other than methyl (meth)acrylate The composition according to (4) or (5), wherein the content of is 10 to 35% by mass.
(7) The composition according to any one of (4) to (6), wherein the particles formed by the polymer (C) have an average rubber particle size of 1.2 to 12.0 μm.
(8) A foam sheet made of the composition according to any one of (1) to (7).
(9) The foam sheet according to (8), which has an expansion ratio of 1.1 to 20 times.
(10) The foam sheet according to (8) or (9), wherein the flatness of cells is 1.1 to 9.0.
(11) A molded product obtained by molding the foamed sheet according to any one of (8) to (10).
(12) The molded article according to (11), which is a food container.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a composition from which a foamed sheet having excellent appearance, impact resistance, and heat resistance can be obtained, and a foamed sheet and molded article obtained using the composition.

1 is a perspective view of a molded body according to one embodiment; FIG.

Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments.

As used herein, "(meth)acrylic acid" means acrylic acid and methacrylic acid corresponding thereto. The same applies to similar expressions such as "(meth)acrylic acid alkyl ester".

The weight average molecular weight (Mw) in this specification is calculated from the molecular weight distribution measured under the following conditions by gel permeation chromatography (GPC). The molecular weight was calculated as a polystyrene-equivalent molecular weight based on the molecular weight calculated at each elution time from the elution curve of monodisperse polystyrene.
Model: Shodex GPC-101 (manufactured by Showa Denko K.K.)
Column: PLgel 10 μm MIXED-A manufactured by Polymer Laboratories
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: oven 40°C, inlet 35°C, detector 35°C
Detector: Differential Refractometer

A foam sheet according to one embodiment is composed of the following composition. The foamed sheet does not necessarily have to have the same composition as the composition described below, and depending on the manufacturing conditions and the like, some of the components contained in the composition may be lost due to volatilization or the like during the sheet-forming process. That is, the foam sheet according to one embodiment is formed using the following composition.

A composition according to one embodiment contains two or more polymers. Monomer units that constitute two or more polymers include (meth)acrylic acid, (meth)acrylic acid alkyl esters, styrene, and conjugated dienes.

The two or more polymers contain 2 to 15% by mass of (meth)acrylic acid based on the total amount of monomer units constituting the two or more polymers. This makes it possible to obtain a foamed sheet that is particularly excellent in appearance and heat resistance. The content of (meth)acrylic acid contained as a monomer unit in the two or more polymers is based on the total amount of the monomer units constituting the two or more polymers, from the viewpoint of making it easier to obtain a foamed sheet with excellent heat resistance. It is preferably 2.3% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more. It is more preferably 12% by mass or less, still more preferably 10% by mass or less. The content of (meth)acrylic acid contained as a monomer unit in the two or more polymers is, based on the total amount of the monomer units constituting the two or more polymers, 2 to 15% by mass, 2 to 14.5% by mass, 2 ~12% by mass, 2-10% by mass, 2.3-15% by mass, 2.3-14.5% by mass, 2.3-12% by mass, 2.3-10% by mass, 3-15% by mass , 3 to 14.5% by mass, 3 to 12% by mass, 3 to 10% by mass, 5 to 15% by mass, 5 to 14.5% by mass, 5 to 12% by mass, or 5 to 10% by mass good too.

The two or more polymers contain 3 to 15% by mass of (meth)acrylic acid alkyl ester based on the total amount of monomer units constituting the two or more polymers. This makes it possible to obtain a foamed sheet with excellent appearance, impact resistance and heat resistance.

The (meth)acrylic acid alkyl ester may be a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate (n-butyl (meth)acrylate, (meth) isobutyl acrylate, t-butyl (meth)acrylate) and the like.

The content of the (meth)acrylic acid alkyl ester contained as a monomer unit in the two or more polymers is based on the total amount of the monomer units constituting the two or more polymers, from the viewpoint of making it easier to obtain a foamed sheet with even better heat resistance. , preferably 4% by mass or more, more preferably 4.5% by mass or more, and still more preferably 5% by mass or more. The content of the (meth)acrylic acid alkyl ester contained as a monomer unit in the two or more polymers is adjusted from the viewpoint of making it easier to obtain a foamed sheet having further excellent appearance and impact resistance. It is preferably 13% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, and particularly preferably 7% by mass or less, based on the total unit amount. The content of the (meth)acrylic acid alkyl ester contained as a monomer unit in the two or more polymers is 3 to 15% by mass, 3 to 13% by mass, 3 to 13% by mass, based on the total amount of the monomer units constituting the two or more polymers. ~12% by mass, 3-10% by mass, 4-15% by mass, 4-13% by mass, 4-12% by mass, 4-10% by mass, 4.5-15% by mass, 4.5-13% by mass , 4.5-12% by weight, 4.5-10% by weight, 5-15% by weight, 5-13% by weight, 5-12% by weight, or 5-10% by weight.

Two or more polymers may contain alkyl (meth)acrylates other than methyl (meth)acrylate and methyl (meth)acrylate as alkyl (meth)acrylates. In this case, the number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester other than methyl (meth)acrylate may be, for example, 2-8 or 3-7. (Meth)acrylic acid alkyl esters other than methyl (meth)acrylate are preferably butyl (meth)acrylate (n-butyl (meth)acrylate, (meth)acrylic acid isobutyl, t-butyl (meth)acrylate).

When two or more polymers contain methyl (meth)acrylate and a (meth)acrylic acid alkyl ester other than methyl (meth)acrylate, the content of methyl (meth)acrylate is more excellent in heat resistance. From the viewpoint of facilitating the production of a foamed sheet, it is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more based on the total amount of monomer units constituting two or more polymers. The content of methyl (meth)acrylate constitutes two or more polymers from the viewpoint of making it easier to obtain a foam sheet with a more excellent appearance by generating uniform cells (also called foam cells or cells). It is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 6% by mass or less based on the total amount of monomer units.

When two or more polymers contain methyl (meth)acrylate and a (meth)acrylic acid alkyl ester other than methyl (meth)acrylate, the content of the (meth)acrylic acid alkyl ester is (meth)acrylic acid From the viewpoint of suppressing the discoloration of the foamed sheet due to the decomposition of methyl and making it easier to obtain a foamed sheet with an excellent appearance and from the viewpoint of making it easier to obtain a foamed sheet with excellent impact resistance, monomers constituting two or more polymers. It is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and still more preferably 0.6% by mass or more, based on the unit total amount. The content of the (meth)acrylic acid alkyl ester is preferably 6 mass from the viewpoint of suppressing a decrease in the glass transition point of the composition and making it easier to obtain a foamed sheet having excellent heat resistance and strength. % or less, more preferably 4 mass % or less, and still more preferably 2 mass % or less.

The content of styrene contained as a monomer unit in the two or more polymers is preferably 68% by mass, based on the total amount of monomer units constituting the two or more polymers, from the viewpoint of making it easier to obtain a foamed sheet with a more excellent appearance. Above, more preferably 70% by mass or more, still more preferably 75% by mass or more. The content of styrene is preferably 95% by mass or less, more preferably 90% by mass or less, based on the total amount of monomer units constituting two or more polymers, from the viewpoint of making it easier to obtain a foamed sheet with further excellent heat resistance. More preferably, it is 87% by mass or less. The content of styrene contained as a monomer unit in the two or more polymers is 68 to 95% by mass, 68 to 90% by mass, 68 to 87% by mass, 70% by mass, based on the total amount of monomer units constituting the two or more polymers. ~95 wt%, 70-90 wt%, 70-87 wt%, 75-95 wt%, 75-90 wt%, or 75-87 wt%.

Conjugated dienes contained as monomer units in two or more polymers include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 1-chloro-1,3-butadiene, 2-chloro- 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene (piperylene), 1,3-hexadiene. The conjugated diene is preferably 1,3-butadiene.

The content of the conjugated diene is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass, from the viewpoint of making it easier to obtain a foamed sheet with further excellent impact resistance. That's it. The content of the conjugated diene is preferably 4% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0.5% by mass, from the viewpoint of easily obtaining a foam sheet having excellent strength. % or less. 0.01 to 4 mass%, 0.01 to 2 mass%, 0.01 to 1 mass%, 0.03 to 4 mass%, 0.03 to 2 mass%, 0.03 to 1 mass%, 0.03 to 4 mass% 05-4% by weight, 0.05-2% by weight, or 0.05-1% by weight.

Each of the monomer units described above may be contained in a separate polymer to constitute four or more polymers, or two or more monomer units may be contained in one polymer to constitute a copolymer. good too. The composition may contain two or more copolymers and may contain homopolymers and copolymers.

As a combination of two or more polymers containing the above monomer units, in one embodiment, a polymer containing styrene and (meth)acrylic acid as monomer units, and one or more (meth)acrylic acid alkyl esters as monomer units. and polymers containing styrene and conjugated dienes as monomer units.

The polymer containing one or more (meth)acrylic acid alkyl esters as monomer units is a polymer containing (meth)acrylic acid alkyl esters other than methyl (meth)acrylate and methyl (meth)acrylate as monomer units. good. The polymer containing styrene and a conjugated diene as monomer units may be a polymer obtained by polymerizing a rubber component containing a conjugated diene as a monomer unit with styrene. That is, the composition according to one embodiment includes a polymer (A) containing styrene and (meth)acrylic acid as monomer units, methyl (meth)acrylate, and an alkyl (meth)acrylate other than methyl (meth)acrylate It contains a polymer (B) containing an ester as a monomer unit and a polymer (C) obtained by polymerizing a rubber component containing a conjugated diene as a monomer unit with styrene.

In the polymer (A), the content of styrene, based on the total amount of monomer units contained in the polymer (A), may be 80% by mass or more, 85% by mass or more, 87% by mass or more, 97% by mass or less, and 95% by mass. % or less, or 93% or less by mass. The content of styrene is 80 to 97% by mass, 80 to 95% by mass, 80 to 93% by mass, 85 to 97% by mass, 85 to 95% by mass, 85% by mass, based on the total amount of monomer units contained in the polymer (A). ˜93 wt %, 87-97 wt %, 87-95 wt %, or 87-93 wt %.

In the polymer (A), the content of (meth)acrylic acid may be 3% by mass or more, 5% by mass or more, or 7% by mass or more based on the total amount of monomer units contained in the polymer (A). % by mass or less, 15% by mass or less, or 13% by mass or less. The content of (meth)acrylic acid is 3 to 20% by mass, 3 to 15% by mass, 3 to 13% by mass, 5 to 20% by mass, 5 to 15% by mass, based on the total amount of monomer units contained in the polymer (A). % by weight, 5-13% by weight, 7-20% by weight, 7-15% by weight, or 7-13% by weight.

The polymer (A) may contain only styrene and (meth)acrylic acid as monomer units, or may contain monomer units other than styrene and (meth)acrylic acid. Other monomer units include (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms, maleic anhydride, and the like. The (meth)acrylic acid alkyl ester in this case may be methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, or the like.

The content of other monomer units may be 1% by mass or more and 17% by mass or less based on the total amount of monomer units contained in the polymer (A).

The weight-average molecular weight (Mw) of the polymer (A) is preferably 120,000 or more, more preferably 150,000 or more, and still more preferably 180,000 or more, from the viewpoint of improving film-forming properties when producing a foamed sheet. Also, it is preferably 250,000 or less, more preferably 220,000 or less, and still more preferably 200,000 or less.

The content of the polymer (A) contained in the composition, based on the total amount of the composition, may be 65% by mass or more, 70% by mass or more, or 75% by mass or more, 99% by mass or less, 98% by mass or less, Or it may be 97% by mass or less.

Polymerization methods for the polymer (A) include known polymerization methods such as bulk polymerization, solution polymerization and suspension polymerization, which are industrialized for polystyrene and the like. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization of these is preferred. Solvents used in the polymerization may be, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

When polymerizing the polymer (A), a polymerization initiator and a chain transfer agent can be used as necessary. An organic peroxide can be used as the polymerization initiator. Specific examples of organic peroxides include benzoyl peroxide, t-butylperoxybenzoate, 1,1-di(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3 , 3,5-trimethylcyclohexane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t -butyl peroxyacetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis(t-butylperoxycarbonate), ethyl-3,3-di(t-butylperoxy)butyrate, t-butyl and peroxyisobutyrate. Specific examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene and the like.

In the polymer (B), the content of methyl (meth)acrylate is preferably 50% by mass, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with even better heat resistance. Above, more preferably 60% by mass or more, still more preferably 65% by mass or more. The content of methyl (meth)acrylate is preferably 98% by mass or less, more It is preferably 93% by mass or less, more preferably 90% by mass or less. The content of methyl (meth)acrylate is 50 to 98% by mass, 50 to 93% by mass, 50 to 90% by mass, 60 to 98% by mass, 60 to 98% by mass, based on the total amount of monomer units contained in the polymer (B). It may be 93% by weight, 60-90% by weight, 65-98% by weight, 65-93% by weight, or 65-90% by weight.

The (meth)acrylic acid alkyl ester other than methyl (meth)acrylate that can be contained in the polymer (B) is the same as the (meth)acrylic acid alkyl ester other than methyl (meth)acrylate described above. good.

The content of the (meth)acrylic acid alkyl ester is preferably 2% by mass or more, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with further excellent appearance and impact resistance. More preferably 7 mass % or more, still more preferably 10 mass % or more. The content of the (meth)acrylic acid alkyl ester is preferably 50% by mass or less, more preferably 40% by mass, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of obtaining a foamed sheet with even better heat resistance. % or less, more preferably 35 mass % or less. The content of the (meth)acrylic acid alkyl ester is 2 to 50% by mass, 2 to 40% by mass, 2 to 35% by mass, 7 to 50% by mass, based on the total amount of monomer units contained in the polymer (B). ~40 wt%, 7 to 35 wt%, 10 to 50 wt%, 10 to 40 wt%, or 10 to 35 wt%.

Polymer (B) may contain only methyl (meth)acrylate and the above alkyl (meth)acrylate as monomer units, and in addition to methyl (meth)acrylate and alkyl (meth)acrylate, It may contain other monomeric units. Other monomer units may be aromatic vinyl compounds such as styrene.

The content of other monomer units may be 1% by mass or more and 40% by mass or less based on the total amount of monomer units contained in the polymer (B).

The weight-average molecular weight (Mw) of the polymer (B) is preferably 1,000,000 or more, more preferably 2,000,000 or more, and still more preferably 3,000,000 or more, from the viewpoint of obtaining a foamed sheet having excellent moldability when molding a container. is preferably 10 million or less, more preferably 8 million or less, and even more preferably 6 million or less, from the viewpoint of easily obtaining a foamed sheet having a further excellent appearance.

The content of the polymer (B) contained in the composition, based on the total amount of the composition, may be 0.5% by mass or more, 1% by mass or more, or 3% by mass or more, and 30% by mass or less and 20% by mass. or less, or 15% by mass or less.

The method of polymerizing the polymer (B) is not particularly limited, and may be an emulsion polymerization method, a soap-free polymerization method, a suspension polymerization method, a fine suspension polymerization method, a dispersion polymerization method, or the like. The polymerization method of the polymer (B) is preferably an emulsion polymerization method or a soap-free polymerization method. According to these polymerization methods, it is easy to control the structure of the particles such as the core-shell structure. A mixture of these is added and polymerized to produce core-shell type polymer microparticles. Methods for recovering polymer fine particles (polymer (B)) from a latex containing polymer fine particles obtained by the above polymerization methods, particularly emulsion polymerization methods include spray drying (spray drying), freeze drying, dehydration after salting out and coagulation. Various methods such as drying may be used, but spray drying is preferred.

When the polymer (B) is recovered as fine polymer particles, the properties and structure of the fine polymer particles as a dry powder do not matter. For example, a large number of primary particles obtained by polymerization may aggregate to form aggregated particles (secondary particles), or may have a higher order structure. However, in the case of such an aggregated structure, it is preferable that the primary particles are loosely aggregated without being strongly bonded to each other so that the primary particles are finely and uniformly dispersed in the composition.

The polymer (C) may be, for example, a graft copolymer obtained by graft-polymerizing styrene to a rubber component containing a conjugated diene as a monomer unit. Such a polymer (C) is also called a rubber-modified styrenic resin, high impact polystyrene (HIPS), or the like. The polymer (C), which is a graft copolymer, can be obtained, for example, by graft polymerizing styrene in the presence of a rubber-like polymer as a rubber component. The polymerization method may be a known method such as a bulk polymerization method, a bulk/suspension two-stage polymerization method, and a solution polymerization method.

The rubber component may be a polymer or copolymer containing the conjugated dienes described above as monomer units. The rubber component may be a polymer or copolymer containing only one or more of the conjugated dienes described above as monomer units, or may be a copolymer containing conjugated dienes and monomer units other than conjugated dienes. Copolymers containing other monomeric units include, for example, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, butadiene-styrene-acrylonitrile copolymers, isobutylene-acrylate copolymers, ethylene-propylene-terpolymers (EPDM), and the like. The rubber component is preferably polybutadiene (a polymer of 1,3-butadiene).

The content of the rubber component contained in the polymer (C), based on the total amount of the polymer (C), may be 1% by mass or more, 1.5% by mass or more, or 2% by mass or more, and may be 50% by mass or less, 45% by mass, or less. % by mass or less, or 40% by mass or less.

The content of styrene contained in the polymer (C) may be 50% by mass or more, 55% by mass or more, or 60% by mass or more, and 99% by mass or less, or 98% by mass, based on the total amount of the polymer (C). may be:

The polymer (C) forms particles (rubber-like dispersed particles) in the composition and is dispersed in the composition. The average rubber particle diameter (Ro) of the particles formed by the polymer (C) is preferably 0.5 µm or more, more preferably 1.2 µm or more, and still more preferably It is 1.5 μm or more, particularly preferably 1.7 μm or more, and from the viewpoint of obtaining a foamed sheet with excellent strength, it is preferably 50.0 μm or less, more preferably 30.0 μm or less, still more preferably 12.0 μm or less, especially It is preferably 5.0 μm or less. The average rubber particle diameter is 0.5 to 50.0 μm, 0.5 to 30.0 μm, 0.5 to 12.0 μm, 0.5 to 5.0 μm, 1.2 to 50.0 μm, 1.2 to 30.0 μm, 1.2-12.0 μm, 1.2-5.0 μm, 1.5-50.0 μm, 1.5-30.0 μm, 1.5-12.0 μm, 1.5-5. It may be 0 μm, 1.7-50.0 μm, 1.7-30.0 μm, 1.7-12.0 μm, or 1.7-5.0 μm.

（式中、ｎは測定個数、Ｄｉは測定したゴム状分散粒子の粒子径を示す。） For the average rubber particle size (Ro), the rubber component of the composition is dyed with osmium tetroxide (OsO ₄ ), and then the particle size of 100 rubber-like dispersed particles is measured with a transmission microscope. 1) can be calculated.

(In the formula, n represents the number of particles measured, and Di represents the particle diameter of the rubber-like dispersed particles measured.)

The weight average molecular weight (Mw) of the polymer (C) may be 100,000 or more, 130,000 or more, or 150,000 or more, and may be 500,000 or less, 300,000 or less, or 200,000 or less.

The content of the polymer (C) contained in the composition may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, and 20% by mass or less based on the total amount of the composition. , 15 mass % or less, or 10 mass % or less.

When the composition contains polymer (A), polymer (B), and polymer (C), it may contain other components in addition to these polymers. Other ingredients may be, for example, polymeric processing aids. A polymer processing aid is a compound that exerts an effect on thickness accuracy, film-forming stability, and reduction of fish eyes when the composition is formed into a sheet. Polymeric processing aids are typically polymer particles having a particle size of 0.05 to 0.5 μm, which can be produced by emulsion polymerization methods. The polymeric processing aid may consist of a resin different from the polymer (A), polymer (B) and polymer (C) described above, for example polymer (A), polymer (B) and polymer (C) may contain an acrylic resin different from The polymer processing aid may be a monolayer particle composed of a polymer having a single composition ratio and a single intrinsic viscosity, or a multilayer particle composed of two or more polymers having different composition ratios or intrinsic viscosities. good.

A foam sheet can be obtained using the composition described above. The method for producing the foamed sheet is not particularly limited, and for example, it can be produced by a method of mounting a die (especially a T-die) at the tip of the extruder to perform extrusion foaming, a method of obtaining a foamed molded article by injection molding, or the like. As a manufacturing method, it is preferable to manufacture by extrusion foaming from the viewpoint of suppressing costs.

A foaming agent may be added to the composition during the production of the foamed sheet. Examples of foaming agents include volatile foaming agents and chemical foaming agents. Volatile blowing agents include gases such as carbon dioxide, nitrogen and air; volatile hydrocarbons such as propane, butane and pentane; halogenated hydrocarbons such as methyl chloride; Chemical foaming agents include sodium bicarbonate, anhydrous monosodium citrate, ammonium carbonate, azodicarbonamide, 4,4'-oxybisbenzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, N,N'-dinitrosopentamethylenetetramine. , trihydrazinotriazine, benzenesulfonyl semicarbazide and the like. A foaming agent may be used individually by 1 type or in combination of 2 or more types.

The expansion ratio of the foam sheet is preferably 1.1 times or more, more preferably 1.5 times or more, and still more preferably 2 times or more, from the viewpoint of excellent heat insulating properties of the foam sheet. The expansion ratio is preferably 25 times or less, more preferably 20 times or less, and even more preferably 15 times or less, from the viewpoint of further improving the appearance and impact resistance of the foamed sheet. The expansion ratio is 1.1 to 25 times, 1.1 to 20 times, 1.1 to 15 times, 1.5 to 25 times, 1.5 to 20 times, 1.5 to 15 times, and 2 to 25 times. , 2-20 times, or 2-15 times. The expansion ratio is a value obtained by dividing the specific gravity of the composition before foaming by the specific gravity of the foamed sheet measured according to the water substitution method (JIS K 7112).

In the foam sheet, the flatness of the cells is preferably 1.1 or more, more preferably 1.2 or more, and still more preferably 1.5 or more, from the viewpoint of excellent heat insulating properties of the foam sheet. The flatness of the cells is preferably 9.0 or less, more preferably 5.0 or less, and still more preferably 3.0 or less, from the viewpoint of excellent bending strength of the foamed sheet. The cell flatness is 1.1 to 9.0, 1.1 to 5.0, 1.1 to 3.0, 1.2 to 9.0, 1.2 to 5.0, 1.2 to It may be 3.0, 1.5-9.0, 1.5-5.0, or 1.5-3.0. The flatness of the cells is a value expressed by the volume average of the ratio of the major axis to the minor axis of the cell diameter, and the observation surface is perpendicular to the main surface of the foam sheet and parallel to the flow direction of the foam sheet. The long-axis direction cell diameter D _L and the short-axis direction cell diameter D _S of ni cells having an elliptical cross section which are cut and observed with a microscope can be measured and calculated by the following formula (2).

A foam sheet can be processed into a molded body having a desired shape, for example, by thermoforming. That is, the foam sheet can be used, for example, as a thermoforming foam sheet. Since the molded foam sheet is excellent in appearance, impact resistance, and heat resistance, it can be suitably used as a food container or packaging container, particularly as a food container. The molded foam sheet may be a container that is used by being heated in a microwave oven (container for microwave heating).

The shape and size of the molded foam sheet are not particularly limited. The planar shape of the molded body can be various shapes such as quadrilateral, circle, ellipse, and polygon. The three-dimensional shape of the molded body can be various shapes such as a box shape (especially a lunch box shape), a tray shape and a bowl shape. The molded body is part or all of a container separately provided with a lid and a container body, or part or all of a lidded container in which the lid and container body are connected via a part of the side wall serving as a hinge. may

FIG. 1 is a perspective view showing a molded foam sheet according to one embodiment. A molded body 10 shown in FIG. 1 is composed of a foamed sheet 1 . As shown in FIG. 1, the molded body 10 is molded in the shape of a hollow box with one side open, and can contain items such as foodstuffs therein. The molded body 10 can be suitably used as a container body in a container separately provided with a container body and a lid.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

<Production Example 1: Production of polymer (A) (styrene-methacrylic acid copolymer (A-1))>
100 kg of pure water and 100 g of polyvinyl alcohol were added to a 200 L jacketed autoclave equipped with a stirrer and stirred at 130 rpm. Subsequently, 72.0 kg of styrene, 4.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, and the temperature was raised to 110° C. for 5 hours of polymerization (Step 1). Further, 4.0 kg of methacrylic acid was added evenly over 2 hours after the polymerization temperature reached 110° C. (Step 2). Further, the temperature was maintained at 140° C. for 3 hours to complete the polymerization (Step 3). The obtained beads were washed, dehydrated, dried, and extruded to obtain a styrene-methacrylic acid copolymer (A-1) in the form of pellets. As a result of analyzing this copolymer using pyrolysis gas chromatography, the mass composition ratio of styrene monomer units/methacrylic acid monomer units was 92/8. Also, the weight average molecular weight (Mw) determined by GPC measurement was 190,000.

<Production Example 2: Production of polymer (A) (styrene-methacrylic acid copolymers (A-2) to (A-5))>
Styrene-methacrylic acid copolymers (A-2) to (A-5) were obtained in the same manner as in Production Example 1, except that the amounts of styrene and methacrylic acid charged were changed so that the mass ratios shown in Table 1 were obtained. . All weight average molecular weights (Mw) obtained by GPC measurement were 190,000.

<Production Example 3: Production of polymer (B) (methyl methacrylate-butyl acrylate copolymer (B-1))>
In a separable flask (capacity 5 L) equipped with a thermometer, a nitrogen inlet tube, a cooling tube and a stirring device, 300 parts by mass (3000 g) of ion-exchanged water as a dispersion medium, 1.1 parts by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.01 parts by mass of n-octyl mercaptan as a chain transfer agent, 80 parts by mass of methyl methacrylate and 20 parts by mass of butyl acrylate as monomers were added. The atmosphere in the flask was replaced with nitrogen by passing a nitrogen stream through the separable flask. Next, the internal temperature was raised to 60° C., and 0.15 parts by mass of potassium persulfate and 5 parts by mass of deionized water were added. After that, heating and stirring was continued for 2 hours to complete the polymerization, and an acrylic resin latex was obtained.
After cooling the obtained acrylic resin latex to 25° C., it was dropped into 500 parts by mass of hot water at 70° C. containing 5 parts by mass of calcium acetate, and then heated to 90° C. for coagulation. After separating and washing the obtained coagulate, it was dried at 60° C. for 12 hours to obtain a methyl methacrylate-butyl acrylate copolymer (B-1) as the polymer (B). The glass transition temperature of the methyl methacrylate-butyl acrylate copolymer (B-1) was measured by differential scanning calorimetry (DSC) according to JIS K 7121:2012, a method for measuring the transition temperature of plastics, and was 60°C. rice field. Also, the weight average molecular weight (Mw) obtained by GPC measurement was 4,000,000.

<Production Example 4: Production of polymer (B) (methyl methacrylate-butyl acrylate copolymer (B-2) to (B-5))>
Methyl methacrylate-butyl acrylate copolymers (B-2) to (B-5) were obtained in the same manner as in Production Example 3, except that the charged amounts of methyl methacrylate and butyl acrylate were changed as shown in Table 2. . The weight average molecular weight (Mw) determined by GPC measurement was 4,000,000.

<Production Example 6: Production of polymer (C) (graft copolymer (C-1))>
Low-cis polybutadiene rubber (manufactured by Asahi Kasei Co., Ltd., trade name "Diene 55AS") is used as the rubber-like polymer, and 3.4% by mass of this rubber-like polymer and 91.6% by mass of styrene are dissolved in 5% by mass as a solvent. It was dissolved in ethylbenzene of 0% by mass to obtain a polymerization raw material. Further, 0.1 part by mass of a rubber antioxidant (Ciba-Geigy, trade name “Irganox 1076”) was added. This polymerization raw material was supplied at 12.5 kg/hr to a 14-liter jacketed reactor (R-01) equipped with an anchor-shaped stirring blade with a blade diameter of 0.285 m. Polymerization was carried out by stirring at a reaction temperature of 140° C. and a rotational speed of 2.17 sec ⁻¹ to obtain a polymer liquid. The polymer ratio of the obtained polymer liquid was 25%. The resulting polymer liquid was introduced into two 21-liter jacketed plug-flow reactors arranged in series. In the first plug flow type reactor (R-02), the jacket temperature was adjusted so that the reaction temperature was 120 to 140° C. in the flow direction of the polymer liquid. In the second plug flow type reactor (R-03), the jacket temperature was adjusted so that the reaction temperature had a gradient of 130 to 160° C. in the flow direction of the polymer liquid. The polymer rate at the R-02 outlet was 50%, and the polymer rate at the R-03 outlet was 70%. Here, the polymer ratio is calculated by the following formula.
Polymer rate (%) = 100 x (amount of polymer produced)/{(amount of monomer charged) + (amount of solvent)}
After the obtained polymer liquid was heated to 230° C., it was sent to a devolatilization tank with a degree of vacuum of 5 torr to separate and recover unreacted monomers and solvent. Then, it was extracted from the devolatilization tank with a gear pump, passed through a die plate to form a strand, passed through a water tank, pelletized, and recovered as a polymer (C-1) (graft copolymer (C-1)). The rubber component content of the resulting polymer (C-1) was 10.0% by mass. Also, the weight average molecular weight (Mw) determined by GPC measurement was 190,000.

<Production Example 7: Production of polymer (C) (graft copolymers (C-2) to (C-3))>
Graft copolymers (C-2) to (C-3) were obtained in the same manner as in Production Example 6, except that the charged amounts of styrene and butadiene were changed so that the mass ratios shown in Table 3 were obtained. The weight average molecular weight (Mw) determined by GPC measurement was 190,000.

<Production Example 8: Production of polymer (C) (graft copolymers (C-4) to (C-5))>
In Production Example 6, graft copolymers (C-4) to (C-5) having different average rubber particle sizes, which will be described later, were obtained by changing the stirring strength and the polymerization temperature during polymerization.

[Preparation of composition]
<Examples 1 to 74, Comparative Examples 1 to 5>
Based on the compositions shown in Tables 4 to 14 described later, the polymers obtained in Production Examples 1 to 8 were processed by a single screw extruder (VS40-36 (φ40 mm, L / D = 36, compression ratio 2.7), Tanabe Plastic (manufactured by Sukai Co., Ltd.), and melted and kneaded to a maximum temperature of 230°C to obtain a composition. The average rubber particle size of the composition was measured by the method described above, and the results are shown in Tables 4-14.

[Preparation of foam sheet]
5.3 parts by mass of butane gas (isobutane/n-butane = 68/32 (mass ratio)) as a foaming agent per 100 parts by mass of the composition is pressurized into the composition in a molten state, so that the butane gas is injected into the composition. evenly distributed in the The composition is applied to a 600 mm wide T die (coat hanger type A sheet-like foam was obtained by extruding and foaming from a horizontal discharge type) with a clearance of 0.5 mm. Subsequently, this sheet-like foam was supplied to cast rolls, sandwiched between nip rolls, and cooled. At this time, the foaming ratio was adjusted as shown in Tables 4 to 14 by adjusting the addition amount of the foaming agent. When confirming the expansion ratio, the specific gravity of the foamed sheet was measured using an electronic balance (MDS-300, manufactured by Alpha Mirage).
After cooling, the ends of the sheet-like foam were continuously cut in the extrusion direction to obtain a foam sheet (thickness: 4 mm, width: 500 mm) cut into a predetermined sheet width.
Moreover, the flatness of the obtained foam sheet was calculated. The results are shown in Tables 4-14.

[Evaluation of foam sheet]
(exterior)
The appearance (surface condition) of the foamed sheet was visually observed and evaluated based on the following criteria. If the evaluation result is A or B, it can be said that the appearance is excellent. The results are shown in Tables 4-14.
A: The unevenness on the surface is minute, and no cell breakage is observed.
B: Little unevenness on the surface, or slight breakage of the cells.
C: Appearance is impaired due to significant surface unevenness or cell breakage.

(shock resistance)
Using a foam sheet, a lunch container (length: 20 cm, width: 13 cm, Container depth: 3 cm) was molded. A 500-g weight was put in, and a lidded bento container was dropped from a height of 1 m. The test was performed 10 times, and the number of times the container was damaged was evaluated. The evaluation criteria were as follows. If the evaluation result is A or B, it can be said that the impact resistance is excellent. The results are shown in Tables 4-14.
A: 2 or less damaged containers B: 3-4 damaged containers C: 5 or more damaged containers

(Heat-resistant)
After the lunch container was placed in a hot air dryer set at 110° C. for 60 minutes, the length of the long side of the bottom of the container was compared with the length before heating and evaluated according to the following criteria. If the evaluation result is A or B, it can be said that the heat resistance is excellent. The results are shown in Tables 4-14.
A: No deformation B: Less than 5% outer dimension change C: 5% or more outer dimension change

Furthermore, the following evaluations were performed on the foamed sheet or lunch box container of each example. Evaluation results are shown in Tables 15-19.

(bending strength)
Regarding the flexural strength of the foam sheet, the bending endurance in the sheet extrusion direction (longitudinal direction) and in the direction perpendicular thereto (transverse direction) was measured according to ASTM D2176, the minimum value was determined, and the evaluation was made based on the following criteria. If the evaluation result is A or B, it can be said that the bending strength is excellent.
A: 5 times or more B: 2 times or more and less than 5 times C: Less than 2 times

(Container formability)
After forming the lunch container, the appearance of the lunch container was evaluated based on the following criteria. The evaluation criteria were as follows. If the evaluation result is A or B, it can be said that the container moldability is excellent.
A: The surface roughness (Rz) is less than 40 µm at any of the four corners.
B: Some of the four corners have a surface roughness (Rz) exceeding 40 µm.
C: All of the four corners have a surface roughness (Rz) exceeding 40 μm.
The surface roughness (Rz) was calculated by measuring the surface shape of an arbitrary portion of the corner at a length of 12.5 mm using a laser microscope (OLS4000) manufactured by Olympus.

(Thermal insulation properties)
The thermal conductivity of the foam sheet was measured using a quick thermal conductivity meter (QTM-710, manufactured by Kyoto Electronics Industry Co., Ltd.), and the sheet thickness at the measurement location (measured using a micrometer) Thermal conductivity The value obtained by dividing by was taken as the thermal resistance value. Thermal resistance was evaluated based on the following criteria from the thermal resistance value. If the evaluation result is A or B, it can be said that the heat insulating property is excellent.
A: Thermal resistance value is 5×10 ⁻³ (m ²・K/W) or more B: Thermal resistance value is 4×10 ⁻³ (m ²・K/W) or more 5×10 ⁻³ (m ²・K /W) C: Thermal resistance value is less than 4×10 ⁻³ (m ²・K/W)

(Strength)
A weight of 500 g was placed in the lunch box described above, and the lunch boxes covered with lids were piled up in five layers. After standing still for 24 hours, the state of deformation of the lowest container was confirmed, and the strength of the container was evaluated based on the following criteria. If the evaluation result is A or B, it can be said that the strength is excellent.
A: No shape change B: Deformed C: Cracked

1... Foamed sheet, 10... Molded body.

Claims (8)

A foam sheet made of a composition containing two or more polymers,
The two or more polymers are
a polymer (A) containing styrene and (meth)acrylic acid as monomer units;
a polymer (B) containing, as monomer units, methyl (meth)acrylate and an alkyl (meth)acrylate other than the methyl (meth)acrylate, the alkyl group having 3 to 7 carbon atoms;
Consisting only of a polymer (C) obtained by polymerizing styrene to a rubber component containing a conjugated diene as a monomer unit,
Based on the total amount of monomer units contained in the polymer (A), the content of the styrene is 85 to 97% by mass, the content of the (meth)acrylic acid is 3 to 15% by mass,
Based on the total amount of monomer units contained in the polymer (B), the content of the methyl (meth)acrylate is 65 to 90% by mass, and the (meth)acrylic acid alkyl ester other than the methyl (meth)acrylate The content is 10 to 35% by mass,
Based on the total amount of monomer units contained in the polymer (C), the content of the rubber component is 2 to 40% by mass, and the content of the styrene is 60 to 98% by mass,
The content of the (meth)acrylic acid is 2 to 15% by mass, and the content of the (meth)acrylic acid alkyl ester is 3 to 15% by mass, based on the total amount of monomer units constituting the two or more polymers. A foam sheet. The foam sheet according to claim 1, wherein the styrene content is 68 to 95% by mass based on the total amount of monomer units constituting the two or more polymers. 3. The foamed sheet according to claim 1, wherein the content of said conjugated diene is 0.01 to 4% by mass based on the total amount of monomer units constituting said two or more polymers. The foamed sheet according to any one of claims 1 to 3 , wherein the average rubber particle diameter of particles formed by the polymer (C) is 1.2 to 12.0 µm. The foamed sheet according to any one of claims 1 to 4, which has an expansion ratio of 1.1 to 20 times. The foam sheet according to any one of claims 1 to 5 , wherein the flatness of cells is 1.1 to 9.0. A molded article obtained by molding the foamed sheet according to any one of claims 1 to 6 . The molded article according to claim 7 , which is a food container.

Images