JP2021167373A - Styrene-methacrylic acid-based copolymer resin composition for film, film, and molded product - Google Patents

Abstract

To provide a resin composition for films that has an improved brittleness without impairing the heat resistance of a styrene-methacrylic acid-based copolymer.SOLUTION: The present disclosure provides a resin composition for films comprising a styrene-methacrylic acid-based copolymer and a conjugated diene-based polymer. The resin composition for films contains a methacrylic acid monomer unit by 2.0 to 8.0 mass% and a conjugated diene monomer unit by 1.0 to 6.0 mass%, and has a Vicat softening temperature of 104°C to 110°C and a weight average molecular weight of 220,000 to 350,000.SELECTED DRAWING: None

Description

The present invention relates to a styrene-methacrylic acid-based copolymer composition having excellent heat resistance and strength, a film comprising the resin composition, and a molded product.

Since styrene-methacrylic acid-based copolymers are superior in heat resistance to general polystyrene, they are used as raw materials for packaging materials for food containers, foam boards for heat insulating materials in houses, light diffusing boards, etc. ing. In the field of packaging materials, foamed sheets obtained by extruding a styrene-methacrylic acid copolymer are excellent in heat resistance and heat insulating properties, and are therefore molded and used in food packaging containers to be heated in a microwave oven or the like. In addition, since the sheet obtained by extrusion-molding a styrene-methacrylic acid-based copolymer and stretched biaxially has excellent heat resistance and strength, it is molded and used as a lid material of a food packaging container to be heated in a microwave oven or the like. There is.

On the other hand, the styrene-methacrylic acid-based copolymer has a drawback that it is more brittle than general polystyrene. For example, in order to improve the brittleness of the styrene-methacrylic acid-based copolymer, MBS resin or styrene -It has been proposed to blend an elastomer component such as the butadiene copolymer SBS.
However, even if only the elastomer component such as MBS resin or styrene-butadiene copolymer is improved, a large amount of addition is required to improve the brittleness when molding into a film, which is inherently possessed by the styrene-methacrylic acid copolymer. Since there is a problem that the heat resistance is lowered, improvement of the styrene-methacrylic acid copolymer is desired.

Japanese Unexamined Patent Publication No. 61-163949 Japanese Unexamined Patent Publication No. 2-558548 Japanese Unexamined Patent Publication No. 3-269040

An object of the present invention is to provide a resin composition for a film having improved brittleness without impairing the heat resistance of the styrene-methacrylic acid-based copolymer.

The present invention is as shown in the following (1) to (5).
(1) A film resin composition containing a styrene-methacrylic acid copolymer and a conjugated diene polymer, wherein the film resin composition contains 2.0 to 8.0 methacrylic acid monomer units. A film containing a mass% and a conjugated diene monomer unit of 1.0 to 6.0% by mass, having a Vicat softening temperature of 104 ° C. to 110 ° C. and a weight average molecular weight of 220,000 to 350,000. Resin composition for.
(2) The film comprising the resin composition according to (1), which has a thickness of 15 to 60 μm and is stretched in at least one axial direction.
(3) A multilayer film having at least one layer made of the resin composition according to (1).
(4) A foamed sheet in which the film according to (2) or (3) is laminated on at least one side.
(5) A food container which is a molded product of the foam sheet according to (4).

Since the styrene-methacrylic acid-based copolymer composition of the present invention has improved brittleness, which is a drawback, it is possible to prevent breakage during film forming and maintain the original characteristics such as heat resistance. ing.

1. 1. Resin Composition The resin composition according to the embodiment of the present invention is a resin composition for a film and includes a styrene-methacrylic acid-based copolymer and a conjugated diene-based polymer.

The styrene-methacrylic acid-based copolymer is a copolymer having a unit structure derived from a styrene-based monomer and a methacrylic acid monomer. The styrene-methacrylic acid-based copolymer can be obtained by copolymerizing a styrene-based monomer and a methacrylic acid monomer. The styrene-based monomer is a single substance or a mixture of styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene and the like, and is preferably styrene.

The styrene-methacrylic acid-based copolymer may have a small amount of other unit structures. Other unit structures are preferably 5% or less. Other unit structures include unit structures derived from vinyl-based monomers copolymerizable with styrene-based monomers and methacrylic acid monomers. Examples of the copolymerizable vinyl-based monomer include acrylonitrile, methacrylic acid ester, and acrylic acid ester.

Examples of the polymerization method of the styrene-methacrylic acid-based copolymer include known polymerization methods such as a massive polymerization method, a solution polymerization method, and a suspension polymerization method, which are industrialized with polystyrene and the like. From the viewpoint of quality and productivity, the bulk polymerization method and the solution polymerization method are preferable, and continuous polymerization is preferable. As the solvent, 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 can be used.

When the styrene-methacrylic acid-based copolymer is polymerized, a polymerization initiator and a chain transfer agent can be used, if necessary. As polymerization initiators, organic peroxides such as benzoyl peroxide, t-butylperoxybenzonate, 1,1-di (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy)- 3,3,5-trimethylcyclohexane, 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane, t-butylperoxyisopropylcarbonate, dicumyl peroxide, t-butylcumyl peroxide, t-Butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, polyethertetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate, t- Butyl peroxyisobutyrate and the like can be mentioned. Examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer and terpinolene.

In the case of continuous polymerization, the polymerization reaction is first controlled by adjusting the polymerization temperature or the like so as to obtain the target molecular weight, molecular weight distribution, and reaction conversion rate by using a completely mixed tank type stirring tank or a column reactor known in the polymerization step. Will be done. The polymerization solution containing the polymer that has left the polymerization step is transferred to the devolatile step, and the unreacted monomer and the polymerization solvent are removed. The devolatilization process consists of a vacuum devolatilization tank with a heater and a devolatilization extruder with a vent. The molten polymer that has left the devolatile step is transferred to the granulation step. In the granulation process, the molten resin is extruded into a strand shape from a porous die and processed into a pellet shape by a cold cut method, an aerial hot cut method, or an underwater hot cut method.

The content of the methacrylic acid monomer unit in the resin composition is 2.0 to 8.0% by mass, preferably 2.5 to 7.8% by mass, and more preferably 3.0 to 7. It is 5% by mass. If the methacrylic acid monomer unit content is less than 2.0% by mass, the heat resistance becomes insufficient. Further, when the content of the methacrylic acid monomer unit exceeds 8.0% by mass, the brittleness is lowered by lowering the viscosity in consideration of productivity. In addition, a large amount of gel may be formed in the copolymer in the copolymer manufacturing process. Specifically, the content of the methacrylic acid monomer unit in the resin composition is, for example, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, It is 5.5, 6.0, 6.5, 7.0, 7.5, 8.0 mass%, and may be within the range between any two of the numerical values exemplified here.

The methacrylic acid monomer unit content can also be adjusted by adjusting the methacrylic acid monomer concentration in the raw material of the styrene-methacrylic acid-based copolymer produced by polymerization or by mixing polystyrene with the styrene-methacrylic acid-based copolymer. can do. When a plurality of reactors are used in the polymerization step, a methacrylic acid-based monomer may be added separately to each reactor.

The methacrylic acid monomer unit content of the styrene-methacrylic acid copolymer was measured at room temperature. Weigh 0.5 g of a styrene-methacrylic acid copolymer, dissolve it in a mixed solution of toluene / ethanol = 8/2 (volume ratio), and then perform neutralization titration with a 0.1 mol / L ethanol solution of potassium hydroxide. , The end point was detected, and the mass-based content of the methacrylic acid-based monomer was calculated from the amount of the potassium hydroxide ethanol solution used. The neutralization titration was measured using AT-510 manufactured by Kyoto Denshi Kogyo Co., Ltd. as an automatic potential difference titrator.

The weight average molecular weight (Mw) of the resin composition is 220,000 to 350,000, preferably 220,000 to 330,000, and more preferably 230,000 to 300,000. If Mw is less than 220,000, brittleness may not be sufficiently improved. On the other hand, when Mw exceeds 350,000, the viscosity at the time of molding is remarkably increased, the molding processability is lowered, and the productivity is deteriorated. Specifically, the weight average molecular weight (Mw) of the resin composition is, for example, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 350,000. It may be within the range between any two of the numerical values exemplified in.

The weight average molecular weight (Mw) of the resin composition is the reaction temperature and residence time of the polymerization step in the styrene-methacrylic acid copolymer, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, and the time of polymerization. The type and amount of the solvent used can be controlled by mixing polystyrene or other copolymers.
The weight average molecular weight (Mw), Z average molecular weight (Mz), and number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) under the following conditions.
GPC model: Showa Denko Corporation Shodex GPC-101
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: Oven 40 ° C, inlet 35 ° C, detector 35 ° C
Detector: Differential refractometer The molecular weight is calculated as the polystyrene-equivalent molecular weight by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.
Further, when measuring the molecular weight of the styrene-methacrylic acid-based copolymer from the resin composition, it can be measured after removing rubber components (SBS, MBS) insoluble in the solvent in the composition by centrifugation. ..

The conjugated diene-based polymer is a butadiene polymer, a styrene-butadiene copolymer, or the like. Styrene-butadiene copolymers are styrene-butadiene block copolymers, styrene-butadiene random copolymers, impact resistant polystyrenes, and hydrogenated products thereof. The butadiene ratio of the styrene-butadiene copolymer is preferably 55% by mass or more. If the butadiene ratio is less than 55% by mass, the content of the styrene-butadiene copolymer that exhibits the expected effect of improving brittleness increases, and the heat resistance and rigidity may decrease.
The ratio of conjugated diene constituting the copolymer is measured by oxidative decomposition with osmium tetroxide as a catalyst and then with methanol added to the decomposition product as a polystyrene component. It was calculated by.

The content of the conjugated diene monomer unit in the resin composition is 1.0 to 6.0% by mass, preferably 1.2 to 3.0%. If the content of the conjugated diene is less than 1.0% by mass, the improvement of brittleness is insufficient, and if it exceeds 6.0% by mass, the transparency is lowered. In addition, heat resistance and rigidity are also reduced. Specifically, the content of the conjugated diene monomer unit in the resin composition is, for example, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, It is 4.5, 5.0, 5.5, 6.0 mass%, and may be within the range between any two of the numerical values exemplified here.

Examples of the method for adding the conjugated diene-based polymer include a method of blending with a styrene-methacrylic acid-based copolymer during molding. Further, a method of melting and blending a styrene-methacrylic acid-based copolymer and a conjugated diene-based polymer with a single-screw or twin-screw extruder can be mentioned. In addition, a method of adding and mixing a conjugated diene polymer in a polymerization step, a devolatilization step, and a granulation step of a styrene-methacrylic acid copolymer can be mentioned, but the method is not particularly limited to these methods.

The Vicat softening temperature of the resin composition is 104 ° C. to 110 ° C., preferably 105 to 109 ° C., and more preferably 106 to 108 ° C. Within such a range, heat resistance and moldability are excellent. Specifically, the Vicat softening temperature of the resin composition is, for example, 104, 105, 106, 107, 108, 109, 110 ° C., even if it is within the range between any two of the numerical values exemplified here. good.

The resin composition may contain a lubricant such as stearic acid, a higher fatty acid metal salt, an ethylene bisstearyl amide, a hindered phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, and a lactone-based antioxidant, if necessary. Even if it contains additives such as agents, UV absorbers, light stabilizers, antistatic agents, mold release agents, plastic agents, colorants, fillers, flame retardants, and high molecular weight processing aids (modifiers). good.

The high molecular weight processing aid (modifier) is a (meth) acrylic acid ester-based copolymer and is produced by a known method such as an emulsion polymerization method. Available processing aids include Mitsubishi Chemical's Metabren P series and Kaneka Corporation's PA series.

Additives can be added by blending during molding, addition during production of styrene-methacrylic acid copolymer, addition during production of styrene-butadiene copolymer, and styrene-methacrylate copolymer. A method of melt-blending the coalescence and the styrene-butadiene copolymer with a single-screw or twin-screw extruder can be mentioned, but the method is not particularly limited to these methods.

In addition to the scraps of the film made of the resin composition, the resin composition and the film according to the embodiment of the present invention include punched debris called a skeleton generated when a foamed sheet or a non-foamed sheet is secondarily molded. The recycled pellets, polystyrene resin, styrene-methacrylic acid copolymer, impact-resistant polystyrene resin, polyethylene resin, and recycled pellets mainly composed of the same can be blended within a range that does not impair the effects of the present invention.

2. Molded product The molded product according to the embodiment of the present invention is a film containing the above resin composition, preferably a film containing the above resin composition as a main component. In one embodiment, the molded product is a film made of the above resin composition.

The film according to one embodiment of the present invention can be obtained by stretching a sheet or film extruded by a known T-die method, tubular method, or the like using the above resin composition in a uniaxial or multiaxial manner. Examples of uniaxial stretching include a method of stretching an extruded sheet or film with a tenter in a direction orthogonal to the extruding direction, a method of stretching an extruded sheet or film in the same direction as the extruding method, and an extruded tubular sheet. Alternatively, a method of stretching the film in the circumferential direction and a method of stretching the extruded tubular sheet or film in the same direction as the extrusion direction can be mentioned. Examples of biaxial stretching include a method of stretching an extruded sheet in the extrusion direction with a roll and then stretching in a direction orthogonal to the extrusion direction with a tenter, a method of simultaneously biaxially stretching the extruded sheet with a tenter, and extruding. Examples thereof include a method of simultaneously or separately stretching the obtained tubular film in the extrusion direction and the circumferential direction.
In order to confirm that the film is stretched at least uniaxially, it can be discriminated from the fact that the size of the test piece changes in the shrinkage direction when the test piece is left in an oven heated to 130 ° C. to 150 ° C. for about 5 minutes. Stretching also includes cooling in film extrusion and applying in the extrusion direction during the take-up process.

The thickness of the film containing the resin composition of the present invention or made of the resin composition is preferably 15 μm to 60 μm, more preferably 17 μm to 45 μm. If it is thinner than 15 μm, it will be difficult to mold. If it exceeds 60 μm, it is not desirable from the viewpoint of weight reduction.

The molded product according to one embodiment of the present invention may be a multilayer film. The multilayer film has at least one layer containing the above resin composition or at least one layer composed of the above resin composition.
Examples of the method for producing the multilayer film include coextrusion, extrusion coating, and dry lamination via an adhesive, which are known methods.

The film made of the composition of the present invention can be printed on at least one side by a known method for the purpose of imparting decorativeness.

The molded product according to the embodiment of the present invention may be a foamed sheet in which the film is laminated on at least one side. The film can be laminated using a thermal roll with respect to a sheet produced by a known extruded foam sheet manufacturing method. In the case of lamination, a styrene-based foam sheet is more preferable in consideration of recycling.

Moreover, you may apply the said resin composition as a resin composition for a foam sheet. A film made of the resin composition of the present invention may be mixed with another main component as a scrap material, or may be used as a main component.

The molded product according to one embodiment of the present invention may be a food container which is a molded product of a foam sheet. The foamed sheet obtained by laminating the film obtained by the above resin composition is obtained by vacuum molding, pressure molding, matched mold molding, reverse draw molding, air slip molding, ridge molding, plug and ridge molding, plug assist molding, plug assist reverse draw molding. Etc., using a known thermoforming method, it can be processed into containers of various shapes and sizes such as trays, lunch containers, bowl containers, cups, and box-shaped containers with lids.

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

(Synthesis of styrene-methacrylic acid copolymers PS-1 to PS-5)
The following first to third reactors were connected in series to form a polymerization step.

1st reactor: Completely mixed reactor with stirring blade of 39 L volume 2nd reactor: Completely mixed reactor with stirring blade of 39 L volume 3rd reactor: Plug flow reactor with static mixer of 16 L volume

The conditions for each reactor were as follows.

First reactor: [Reaction temperature] 124 ° C
Second reactor: [Reaction temperature] 133 ° C.
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 120 to 125 ° C is formed in the flow direction.

The following was used as the raw material liquid.

76.1 parts by weight of styrene, 2.7 parts by weight of methacrylate, 14 parts by weight of ethylbenzene, and 1,1-di (t-butylperoxy) cyclohexane (Perhexa C manufactured by Nippon Oil & Fats Co., Ltd.) as a polymerization initiator in the first reaction. From the inlet of the vessel, the mixture was added and mixed with the raw material solution so as to have an addition concentration of 250 ppm with respect to the monomer.

The raw material liquid was continuously supplied to the first reactor set at 124 ° C. at a supply rate of 12 kg / hr for polymerization, and then continuously charged to the second reactor set at 133 ° C. for polymerization. Further, the polymerization was allowed to proceed in a third reactor adjusted so as to have a temperature gradient of 120 to 125 ° C.
This polymerization solution was introduced into a vacuum devolatilization tank with a preheater composed of two stages in series, and unreacted styrene and ethylbenzene were separated, extruded into strands, cooled, and then cut into pellets. The temperature of the first stage preheater was set to 220 ° C., the pressure of the vacuum devolatilizer tank was set to 600 mmHg, the temperature of the second stage preheater was set to 230 ° C., and the pressure of the vacuum devolatilizer tank was 7. It was set to 0.0 mmHg.
The obtained styrene-methacrylic acid copolymer PS-1 had a weight average molecular weight of 260,000 and a methacrylic acid content of 3.9% by mass.
In the same manner, PS-2 to PS-5 were prepared by changing the mixing ratio of styrene, methacrylic acid, and ethylbenzene, the initiator concentration, the reactor temperature, and the vacuum devolatilization tank temperature conditions while keeping the monomer flow rate the same.

(Examples 1 to 5, Comparative Examples 1 to 6)
Using the styrene-methacrylic acid copolymers PS-1 to PS-5 shown in Table 1, the styrene-butadiene block copolymer SBS-1 (Toughprene 125 manufactured by Asahi Kasei Co., Ltd.) and the modifier A (modifier A) were used as the conjugated diene polymers. Mitsubishi Chemical Co., Ltd. Polymer P531A) was added in the formulation shown in Table 2, and using a twin-screw extruder (Toshiba Machine Co., Ltd. TEM-26SX), the feed amount was 20 kg / h, the screw rotation speed was 250 rpm, and the cylinder temperature. It was melt-extruded and blended at a setting of 180 to 220 ° C. to pelletize it.

Table 2 shows the results of injection molding of the obtained pellets and evaluation of various characteristics.
The measurement of the Vicat softening temperature was performed in accordance with JIS K 7206 at a heating rate of 50 ° C./hr and a test load of 50 N.

The film was produced by the following method.
A film having a lip width of 100 mm, a lip opening of 0.5 mm, a screw diameter of 20 mm, and a temperature setting of 230 ° C. and a screw rotation speed of 30 rpm of 40 μm was produced.

The brittleness of the film was evaluated by the following method.
It was evaluated whether the film was broken when the film cut into a length of 10 mm and a width of 40 mm was folded in half in the longitudinal direction. The film that did not break was marked with 〇, and the film that broke when folded in half was marked with x.

The moldability was evaluated by the following method.
In film molding, an example in which tearing during winding was not observed was evaluated as 〇, and an example in which tearing was frequently observed during winding was evaluated as ×.

The resin composition of the present invention has an excellent balance between heat resistance and brittleness, and is suitable for a lamination film used for food packaging containers and the like.

Claims (5)

A resin composition for a film containing a styrene-methacrylic acid copolymer and a conjugated diene polymer, wherein the resin composition for a film contains 2.0 to 8.0% by mass of a methacrylic acid monomer unit. A resin composition for a film containing 1.0 to 6.0% by mass of a conjugated diene monomer unit, a Vicat softening temperature of 104 ° C. to 110 ° C., and a weight average molecular weight of 220,000 to 350,000. thing. The film comprising the resin composition according to claim 1, which has a thickness of 15 to 60 μm and is stretched in at least one axial direction. A multilayer film having at least one layer made of the resin composition according to claim 1. A foamed sheet in which the film according to claim 2 or 3 is laminated on at least one side. A food container which is a molded product of the foam sheet according to claim 4.