JP4769205B2 - Impact-resistant polystyrene biaxially stretched sheet, and molded product of this sheet - Google Patents

Description

The present invention relates to a biaxially stretched sheet made of impact-resistant polystyrene and a molded product made of this sheet. More specifically, the impact-resistant polystyrene biaxially stretched sheet and the above-mentioned sheet are reduced in the rate of defective molded products due to poor mold reproducibility and bridge formation in thermoforming (secondary molding), and excellent in high-speed moldability. The present invention relates to molded products such as box-shaped containers, cups, trays, and dishes manufactured by thermoforming.

Conventionally, biaxially stretched sheets of general-purpose polystyrene (hereinafter, sometimes referred to as GPPS) and impact-resistant polystyrene (hereinafter, sometimes referred to as HIPS) made of graft-type rubber-modified polystyrene, It can be manufactured from a resin composition, and its use as a molded product differs as follows depending on the haze value measured in accordance with ASTM D1003. These biaxially stretched sheets made of HIPS are excellent in rigidity and moldability as well as in transparency when the biaxially stretched sheet has a low rubber component content and the haze value of the biaxially stretched sheet is 3% or less. Since the type and appearance of the stored food can be easily confirmed, it is used as a raw material sheet for manufacturing lid bodies such as lunch boxes, container bodies, and containers with lids. If the axially stretched sheet has a haze value of 4% or more, it has excellent rigidity, moldability, and oil resistance, as well as excellent impact resistance, so it can be used to store fresh, dried food, confectionery and other foods. It is used as a raw material sheet for manufacturing a container with a lid, a cup, a container without a lid (a tray, a dish), a lid, etc. (hereinafter collectively referred to as “containers etc.”).

In the food industry, there is a tendency to reduce the thickness and weight of food packaging containers in order to respond to recent environmental problems and regulations under the Containers and Packaging Recycling Law. Development of a raw material sheet that can be molded at high speed and has a low defect occurrence rate of containers and the like is desired. In the case of the above (b), it is desired to make it difficult to break even if it is thinned, but ribs are provided on the side wall surface, bottom wall surface, etc. of the container etc. in order to diversify the design (design) of the container, etc. In many cases, a high-speed molding is made difficult by providing a partition portion and increasing mold reproducibility defects and bridges.

On the other hand, when food is stored in the container or the like and the entire outer side is packaged (soft-wrapped) with a flexible film, (1) an end portion punched with a cutting blade at the time of manufacturing the container or the like ( The edge part) may damage the flexible packaging film, so it is desired to improve the shape of the end part of the container etc., and (2) the container etc. breaks due to external impacts, etc. Therefore, it is desired that the raw material sheet has a suitable strength and is not easily broken.

In JP-A-54-29381 (Patent Document 1), a graft type HIPS having a rubber content of 3% by weight or more and a melt flow index (MFI) of 8 g / 10 min or less is formed into a sheet. A method for producing a container is described in which a biaxially stretched sheet is formed so that the heat shrinkage stress is 4 kg / cm ² or more in both the longitudinal direction and the lateral direction, and the resulting biaxially stretched sheet is formed without substantially returning its orientation. ing. This document states that “when the heat shrinkage stress is 4 kg / cm ² or more, the oil resistance is drastically improved, but when it exceeds 20 kg / cm ² , molding becomes difficult (see the upper left column, page 19, line 2)”. Although described, in the experiments by the present inventors, even if the thermal contraction stress of the sheet is in a preferable range {8 to 15 kg / cm ² (≈0.78 to 1.47 MPa)}, it is biaxial. It has been found that there is a problem in the formability of the stretched sheet, particularly the mold reproducibility.

JP-A-2004-51680 (Patent Document 2) discloses a graft copolymer (HIPS) obtained by graft-polymerizing at least a styrene monomer to a rubber component, and general-purpose polystyrene (GPPS). = 30/70 to 80/20 (weight ratio), and a HIPS sheet obtained by biaxially stretching a blend type HIPS composition having a rubber component of 3 to 10% by weight is described. In the sheet cross section obtained by cutting the sheet in a direction perpendicular to the sheet surface, the product (SI × g) of the swelling degree (SI) of the rubber component in the polymer and the graft ratio (g) is 13 to 80, The major axis of the rubber component is substantially parallel to the sheet surface, the ratio of the rubber component occupying the sheet cross section (area occupancy) is 10 to 25%, and the major axis L and minor axis S of the rubber component Table with ratio Rubber flatness F (F = L / S) is described biaxially oriented sheet of 5 to 18 to. This document also states that “the biaxially stretched styrene resin sheet of the present invention has not only high rigidity and excellent impact resistance even if it is thin and lightweight because the rubber component is dispersed in a specific form. , High secondary formability (see step 0031 part) ".

According to the experiments by the present inventors, in order to exhibit excellent secondary formability in the biaxially stretched sheet made of HIPS, the stretching ratio and heat shrinkage stress during the production of the biaxially stretched sheet are controlled within a predetermined range. I found it necessary to do. However, since Patent Document 2 does not describe any heat shrinkage stress, the biaxially stretched sheet made of HIPS according to Patent Document 2 is not necessarily excellent even if the rubber component is dispersed in a specific form. Does not exhibit secondary formability. In addition, a biaxially stretched sheet made of HIPS having a high GPPS ratio tends to break.

Japanese Patent Laid-Open No. 2005-200572 (Patent Document 3) discloses that at least a styrene monomer is graft-polymerized to a rubber component, and the product of the degree of swelling (SI) and the graft ratio (g) of the rubber component (SI × g) 20 to 80 graft type HIPS and GPPS are blended in the ratio of the former / the latter = 20/80 to 90/10 (weight ratio), the rubber component is 1 to 10% by weight, A HIPS sheet obtained by biaxially stretching a blend type HIPS composition having a volume average particle diameter of 0.1 to 3 μm is described. The HIPS sheet also has an average rubber flatness F (F = L / S) expressed by a ratio of the major axis L to the minor axis S of the rubber component in the cross section of 5 to 18 and a thickness of 0.2. In order for the haze of a 0.25 mm HIPS biaxially stretched sheet to be 15% or less, and for the sheet to exhibit excellent secondary formability (container formability, etc.), a HIPS biaxial It is described that the shrinkage stress of the stretched sheet is in the range of 5 to 15 kg / cm ² .

However, according to the experiments by the present inventors, even if the shrinkage stress of the biaxially stretched sheet made of HIPS is more preferable {6 to 8 kg / cm ² (≈0.59 to 0.78 MPa)}. The secondary moldability (particularly, the container moldability at high speed) was found to be inferior. In addition, in a batch type table stretching machine and a commercial scale stretching machine (for example, a sequential biaxial stretching machine having a longitudinal stretching function by a roll and a transverse stretching function by a tenter), the sheet heating time, the stretching speed (or strain rate), Since the cooling method after biaxial stretching is different, the relationship between the temperature conditions during stretching and the shrinkage stress of the sheet does not match.
JP 54-29381 A JP 2004-51680 A Japanese Patent Laying-Open No. 2005-200572

In view of the above circumstances, the present inventors have completed as a result of intensive studies to provide a biaxially stretched sheet made of impact-resistant polystyrene that has solved the above-mentioned drawbacks, and a molded product made of this sheet. . That is, the object of the present invention is as follows.
1. To provide an impact-resistant polystyrene biaxially stretched sheet that is excellent in impact resistance, tear resistance, folding resistance, and the like, and that is difficult to break even if it is thin and lightweight, and a molded product made from this sheet.
2. To provide an impact-resistant polystyrene biaxially stretched sheet having good mold reproducibility when thermoforming.
3. To provide a biaxially stretched sheet made of impact-resistant polystyrene, which is less likely to cause defective products due to mold reproducibility or bridges even when thermoformed at high speed, and has excellent high-speed moldability.

In the present invention, terms such as mold reproducibility, bridge, and high-speed moldability that are difficult to break have the following meanings.
(1) Hard to break: This means that the biaxially stretched sheet made of impact-resistant polystyrene and the molded product made of this sheet are not easily damaged by external impacts, etc., and it has impact resistance, tear resistance, and folding resistance. When it is excellent in any case, it is difficult to crack.
(2) Mold reproducibility: Molded products obtained by a continuous hot plate heating type air pressure molding machine have the ability to faithfully reproduce (determine the mold) the cavity surface of the mold, and have excellent mold reproducibility. The molded product obtained from the impact polystyrene biaxially stretched sheet has a beautiful appearance.
(3) Bridge: The sheet is not sufficiently drawn into the corners of the convex part and the flat part of the compressed air molding die having a large drawing ratio (maximum depth of the opening part / width of the opening part) and solidifies in the form of a web, It is not fully reproduced on the molded product (the mold is not well defined).
(4) High-speed formability: The heating temperature (hot plate temperature) of the biaxially stretched sheet is made higher than the normal heating temperature by a continuous hot plate heating type pressure forming machine, or the heating time {(upper pressure operating time, lower vacuum Operation time, delay time (time until lower vacuum is activated after lower vacuum operation is completed)} and molding time (lower pressure air operation time, upper vacuum operation time) are shortened, or upper air pressure or lower air pressure is increased Therefore, even if the cycle time per shot is shortened, a mold reproducibility failure or a bridge does not occur, and a molded product having an excellent appearance can be obtained.

In the present invention, in order to solve the above-mentioned problems, in the first invention, the rubber component is made of impact-resistant polystyrene having a content of 4.0 to 12.0% by weight, and the following (1) and (2): An impact-resistant polystyrene biaxially stretched sheet characterized by being simultaneously filled is provided.
(1) The draw ratio is 2.1 to 2.7 times in both the longitudinal direction and the transverse direction. (2) The thermal shrinkage stress in the longitudinal direction is 0.30 to 0.60 MPa, and the transverse heat shrinkage stress is 0.30 to 0.55 MPa

According to a second aspect of the present invention, there is provided a molded product characterized by being produced by a thermoforming method using the impact-resistant polystyrene biaxially stretched sheet according to the first aspect of the present invention as a raw material.

The present invention is as described in detail below, has the following particularly advantageous effects, and its industrial utility value is extremely great.
1. The biaxially stretched sheet made of impact-resistant polystyrene according to the present invention has excellent impact resistance, tear resistance, and folding resistance. Therefore, it is possible to reduce the thickness and weight of a molded product obtained by thermoforming, and unit weight. More molded products can be produced from the raw materials.
2. Since the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention is excellent in high-speed moldability, a molded product such as a food container can be efficiently produced.
3. Since the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention has good mold reproducibility when thermoformed and does not generate bridges, the resulting molded product (food container) has a beautiful appearance. The product value becomes high.
4). The molded product obtained by thermoforming the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention is excellent in impact resistance, tear resistance, folding resistance, etc. It is suitable as a food container because no broken pieces are mixed in and there is no risk of accidental eating.
5. The biaxially stretched sheet made of impact-resistant polystyrene according to the present invention contains an appropriate amount of a rubber component in the rubber-modified styrene resin, and thus has excellent low-temperature impact properties and is refrigerated / frozen for storing fresh foods, frozen foods, etc. It is suitable as a storage container.

Hereinafter, the present invention will be described in detail. The biaxially stretched sheet made of impact-resistant polystyrene in the present invention and a molded product obtained using the same are composed of impact-resistant polystyrene. Specific examples of impact-resistant polystyrene include a graft type HIPS in which at least a styrene monomer is graft-polymerized to a rubber component, or a blend type HIPS in which this graft type HIPS and general-purpose polystyrene (GPPS) are blended. Is mentioned. HIPS exhibits a microstructure in which rubber components are dispersed in a general-purpose polystyrene matrix.

The graft type HIPS can be obtained by polymerizing at least a styrene monomer in the presence of a rubber component. Examples of the rubber component include polybutadiene, polyisoprene, chloroprene rubber, styrene-isoprene copolymer, styrene-isoprene-butadiene copolymer, and random or block polymers of butadiene and other copolymerizable monomers. it can. Monomers copolymerizable with butadiene include vinyl aromatic compounds such as styrene and α-methylstyrene, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and esters thereof, vinyl such as acrylonitrile and methacrylonitrile. A cyan compound can be mentioned.

In addition, these rubber components may be those obtained by hydrogenating unsaturated double bond portions in the molecule, and may be used alone or in combination of two or more. Among the rubber components, a diene rubber is preferable, and polybutadiene, polyisoprene, and a styrene-butadiene copolymer (random or block copolymer) are particularly preferable. The styrene content in the styrene-butadiene block copolymer is 10 to 50% by weight, preferably 10 to 30% by weight. The rubber component is particularly preferably a high cis polybutadiene having a cis 1,4 structure of 90 mol% or more from the viewpoint of thermal stability when HIPS is used and recyclability.

Examples of the styrene monomer to be graft-polymerized include styrene, alkyl styrene (for example, o-, m-, p-methyl styrene, p-ethyl styrene, pt-butyl styrene), and α-alkyl styrene (for example, vinyl aromatic compounds such as α-methylstyrene and ethylstyrene). These styrenic monomers can be used alone or in combination of two or more. Of the styrenic monomers, styrene is preferred.

Examples of GPPS that can be mixed with graft type HIPS include styrene, alkyl styrene (for example, o-, m-, p-methyl styrene, p-ethyl styrene, pt-butyl styrene), α-alkyl styrene (for example, α -Homopolymers of aromatic vinyl compounds such as methyl styrene and ethyl styrene) and copolymers obtained by combining these monomers. These GPPS can be used alone or in combination of two or more. Most preferred GPPS is polystyrene having a weight average molecular weight (hereinafter referred to as Mw) of 180,000 to 350,000.

The impact-resistant polystyrene according to the present invention has a rubber component content in the range of 4.0 to 12.0% by weight. When the rubber component content is less than 4.0% by weight, the high-speed moldability during thermoforming is inferior, and the produced biaxially stretched sheets and molded articles (containers, etc.) have impact resistance and tear resistance. In addition, the folding resistance is inferior and cracking easily occurs. On the other hand, when the content of the rubber component exceeds 12.0% by weight, the rigidity of the produced biaxially stretched sheet and molded product is lowered. The content of the rubber component is preferably 6.0 to 12.0% by weight, and more preferably 8.0 to 12.0% by weight.

The rubber component content is determined by measuring the diene content by potentiometric titration using iodine monochloride, potassium iodide and sodium thiosulfate standard solutions, and calculating the diene content as the rubber component content. Analytical methods include, for example, the Japan Analytical Chemical Society, Polymer Analysis Research Roundtable, “New Edition Polymer Analysis Handbook”, Kinokuniya (1995 version), P.A. 659 (3) rubber content and can be measured by this method.

The average particle size of the rubber component contained in the impact-resistant polystyrene according to the present invention is not limited, but is preferably 0.5 to 10.0 μm. When the average particle diameter is in the above range, the impact-resistant polystyrene biaxially stretched sheet and the molded article made of the sheet according to the present invention have improved impact resistance, tear resistance, and folding resistance. A more preferable average particle size is 1.0 to 8.0 μm, and a more preferable value is 2.0 to 6.0 μm.

The average particle diameter of the rubber component was obtained by taking a magnified photograph of 10,000 times using a transmission electron microscope by an ultrathin section method, measuring the particle diameter of about 1000 photographed graft rubber particles, Rubber average particle diameter [μm] = (ΣniDi ⁴ ) / (ΣniDi ³ ) In this equation, ni represents the number of rubber particles having a particle diameter of Di.

Since the graft rubber particles are not completely circular, the major axis and minor axis are measured, and the average is calculated to calculate the particle diameter. When measuring a biaxially stretched sheet made of impact-resistant polystyrene and a molded product made of this sheet, it is placed in a silicon oil bath having a temperature 40 ° C. higher than the Vicat softening point temperature measured in accordance with JIS K7206 for 10 minutes. Measure using a test specimen immersed and contracted.

The melt flow rate (MFR) of the graft type HIPS is not limited, but is usually 0.5 to 20 g / 10 min at a temperature of 200 ° C. and a load of 5 kg, and a preferable range is 2.0 to 10 g / 10 min. . The melt flow rate of GPPS that can be mixed with graft type HIPS is not limited, but is usually 0.5 to 20 g / 10 min at a temperature of 200 ° C. and a load of 5 kg, and a preferable range is 1.0 to 10 g / 10 min. is there.

In the raw material impact-resistant polystyrene, an internal lubricant, a filler, a heat stabilizer, an ultraviolet absorber, a flame retardant, an antifogging agent, a dispersant, a pigment, a dye, and carbon are used as long as the object of the present invention is not significantly impaired. Various additives such as black, ketjen black, graphite, antioxidant, plasticizer, antistatic agent, antibacterial agent, reinforcing material, fluidity improver, thickener, and other thermoplastic resins it can.

Examples of the internal lubricant include mineral oil, and the blending amount is preferably 2.0% by weight or less. When compounding exceeds 2.0% by weight, a part of the internal lubricant volatilizes during extrusion melting, the internal lubricant volatilized on the biaxial stretching device after extrusion adheres, and then the agglomerated internal lubricant adheres to the sheet. Transfer and ultimately, the appearance of the biaxially stretched sheet is impaired. More preferred is 1.0% by weight or less, and further more preferred is 0.5% by weight or less.

Examples of plasticizers include phthalate esters, fatty acid plasticizers, and phosphoric acid plasticizers. Other thermoplastic resins include olefin resins, vinyl resins, (meth) acrylic resins, and polyvinyl ketone resins. Examples thereof include resins, polyamide resins, polyester resins, polyether resins, polyphenylene oxide resins, thermoplastic polyimides, and epoxy resins. In some cases, a compatibilizing agent can be used in combination in order to improve the mutual solubility of the impact resistant polystyrene and the thermoplastic resin.

The production method of the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention is not limited, and may be performed by a method commonly used in the production of a conventional stretched sheet. One example thereof is a graft type HIPS alone or a mixture thereof with GPPS, and if necessary, a predetermined amount of the above-mentioned various additives and other thermoplastic resins are weighed, and a dry blended product is obtained by a blender or tumbler. The obtained dry blend is melt-kneaded with an extruder, then continuously extruded into a sheet form using a T-die (uses a feed block die or a multi-manifold die in the case of multiple layers), etc., and rapidly cooled with a cooling roll. In this method, a stretched sheet is produced, and this unstretched sheet is continuously and biaxially stretched by a roll stretching method, a tenter method or the like.

The impact-resistant polystyrene-made biaxially stretched sheet according to the present invention can have a multi-layer structure. For example, when the sheet is made of two types and three layers, the composition ratio of GPPS and HIPS may be changed between both surface layers and the core layer, or HIPS having a different rubber content and / or rubber average particle diameter may be used. it can. Furthermore, the impact-resistant polystyrene biaxially stretched sheet pulverized product according to the present invention and / or recycled pellets obtained by remelting and kneading the pulverized product can be mixed with both surface layers and / or the core layer. In any of the above cases, the total content of the rubber component may be 4.0 to 12.0% by weight with respect to the total weight of the impact-resistant polystyrene according to the present invention.

The stretch ratio of the biaxially stretched sheet made of impact-resistant polystyrene in the present invention is described in the longitudinal direction (sheet extrusion direction, hereinafter sometimes referred to as MD), the transverse direction (direction perpendicular to the sheet extrusion direction, hereinafter referred to as TD). Both are required to be 2.1 to 2.7 times. When the draw ratio is less than 2.1 times, the impact resistance and tear resistance are lowered, so that the biaxially stretched sheet and the molded product obtained by thermoforming are easily cracked. On the other hand, if the draw ratio exceeds 2.7 times, the elongation of the sheet is reduced during thermoforming, so that the mold reproducibility is inferior and the appearance of the obtained molded product is deteriorated. Further, if only one of the vertical direction and the horizontal direction is out of the above-mentioned essential range, the anisotropy of the sheet becomes strong, or a bridge is easily generated when a molded product is manufactured. The molded product obtained by thermoforming can be easily broken. A more preferable draw ratio is 2.3 to 2.5 times.

In the present invention, the stretch ratio is the ratio of the length of the straight line written on the test piece of the impact-resistant polystyrene biaxially stretched sheet before and after shrinkage, specifically, the following formula: Stretch ratio = Y / Z, meaning a value calculated by the unit [times]. In this formula, Y represents the length [mm] of a straight line drawn on MD and TD using a ruler and a writing instrument on a test piece of a biaxially stretched sheet made of impact-resistant polystyrene, and Z represents JIS K7206. The length [mm] of the straight line after the test piece is immersed and contracted for 10 minutes in a silicon oil bath having a temperature 40 ° C. higher than the Vicat softening point temperature of the sheet measured in accordance with the above.

The thickness of the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention is not limited, but is preferably selected in the range of 0.06 to 0.45 mm. If the thickness is less than 0.06 mm, the rigidity of the sheet itself and the molded product is insufficient, and it becomes difficult to hold and preserve food stored in the molded product (container or the like). On the other hand, if the thickness exceeds 0.45 mm, it is not preferable from the viewpoint of recycling and cost. From the viewpoint of reducing the thickness and weight, 0.08 to 0.25 mm is more preferable, and 0.10 to 0.18 mm is more preferable.

In the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention, the thermal shrinkage stress of MD is 0.30 to 0.60 MPa, and the thermal shrinkage stress of TD is 0.30 to 0.55 MPa. Required. When the thermal shrinkage stress of MD or TD is less than 0.30 MPa, the sheet itself and a molded product obtained by molding the sheet are easily broken. On the other hand, when the thermal contraction stress of MD is higher than 0.60 MPa and the thermal contraction stress of TD is higher than 0.55 MPa, the defect rate is increased due to defective mold reproducibility and the occurrence of bridges, and high-speed moldability is decreased. More preferable ranges of the heat shrinkage stress are 0.35 to 0.55 MPa for MD and 0.35 to 0.50 MPa for TD. In the present invention, the heat shrinkage stress means the maximum load when the biaxially stretched sheet is heat shrunk using a “DN-type stress tester” manufactured by Niri Kogyo Co., Ltd. in accordance with ASTM D1504. It means a value (unit [MPa]) obtained by dividing the value of the maximum load by the cross-sectional area of the biaxially stretched sheet before heat shrinkage.

Here, the reason why the upper limit value of the heat shrinkage stress is different between MD and TD is based on the results of experiments and examinations by the present inventors. Usually, from the viewpoint of the speed of the molded product punching process performed in conjunction with thermoforming, when the planar shape of the molded product is rectangular, the long side direction is set to MD. In that case, in the TD that is in the short side direction of the molded product, the drawing ratio (maximum depth of the opening / width of the opening) is increased, and it is considered that the bridge is likely to occur. Specifically, it is a container with a rectangular shape and a deep storage part, and a structure in which a partition for separation is provided in the storage part, or a convex or mountain-shaped step is provided in the container storage part. In the structure, the bridge is likely to occur at TD which is the short side direction of the molded product.

The heat shrinkage stress is closely related to the stretching temperature, and is adjusted by changing the roll temperature and / or the tenter temperature so as to achieve the desired heat shrinkage stress depending on the specifications of the stretching device, stretching speed, etc. can do. For example, when the stretching apparatus is a sequential biaxial stretching system, the roll temperature for longitudinal stretching is 100 to 130 ° C, preferably 110 to 125 ° C, and the tenter temperature for transverse stretching is 120 to 150 ° C, preferably 130-145 ° C.

After biaxial stretching, a release agent layer as a coating layer can be formed on at least one surface of the obtained sheet. The method for forming the release agent layer is not particularly limited, and may be a conventionally known method. As an example, a dimethyl silicone emulsion containing a dimethyl silicone oil and an emulsifier having a viscosity at 25 ° C. of 100 to 50,000 mm ² / s (preferably 1,000 to 20,000 mm ² / s), and a solid content concentration of 0. In this method, an aqueous solution having a concentration of about 1 to 5% by weight is applied by a spray coater, an air knife coater, a squeeze roll coater, a gravure roll coater, a knife coater or the like, and dried by a hot air dryer or the like. Here, the film thickness (covering amount) of the release agent layer after drying is 10 to 50 mg / m ² as a solid content.
By applying in an amount of (preferably 20 to 40 mg / m ² ), a sheet with good slipperiness is obtained. Further, in order to obtain a sheet having not only slipperiness but also antistatic property, an antistatic agent can be mixed into the dimethyl silicone emulsion.

Antistatic agents that exhibit excellent antistatic properties and maintain this property include polyglycerin fatty acid esters (for example, hexaglycerin monolaurate), fatty acid alkanolamides {for example, lauric acid diethanolamide (1: 1 Type)}. The ratio to mix is about 30 to 80 weight% with respect to the total amount with a silicone oil (solid content).

  In the release agent, as long as the effect of the present invention is not impaired, an antistatic agent other than the above, an antiblocking agent, a viscosity modifier, an antifoaming agent, an ultraviolet absorber, an anticoloring agent, Various additives such as antibacterial agents, pigments and dyes can be blended.

The impact-resistant polystyrene biaxially stretched sheet according to the present invention can be formed into a molded article such as a container by a thermoforming method. There is no limitation on the thermoforming method, and conventionally known methods such as a vacuum forming method, a pressure forming method, and a differential pressure forming method combining a vacuum forming method and a pressure forming method are exemplified. Since the biaxially stretched sheet made of impact-resistant polystyrene according to the present invention is excellent in thermoformability (particularly high-speed moldability), the sheet is heated by, for example, compressed air pressure from the mold and vacuum pressure from the hot plate side. Hot plate heating type pressure forming method that heats the plate close to or in close contact with the plate, and immediately presses the heated and softened sheet against the die by the pressure from the hot plate and the vacuum from the die. Thus, a molded product can be obtained at high speed.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, unless the summary is exceeded. As the raw material resin, a commercially available resin having the following properties is used, and the measurement items and evaluation items of the impact-resistant polystyrene biaxially stretched sheet and the molded product obtained from this sheet are as follows: It is.

<Raw resin>
[Styrene resin]
1. GPPS: General-purpose polystyrene {manufactured by PS Japan, trade name: HH102, Mw 260,000, MFR (200 ° C., 5 kg) 3.5 g / 10 min}.
[Graft type high impact styrene resin]
2. HIPS-1: high impact polystyrene {manufactured by PS Japan, trade name: HT478, MFR (200 ° C., 5 kg) 3.0 g / 10 min}.
3. HIPS-2: impact-resistant polystyrene {manufactured by PS Japan, trade name: HT516, MFR (200 ° C., 5 kg) 2.5 g / 10 min}.
4). HIPS-3: impact resistant polystyrene {manufactured by PS Japan, trade name: EXG11, MFR (200 ° C., 5 kg) 4.0 g / 10 min}.
5. HIPS-4: high impact polystyrene {manufactured by Toyo Styrene Co., Ltd., trade name: H450, MFR (200 ° C., 5 kg) 5.5 g / 10 min}.

<Measurement item>
(1) Stretch ratio A test piece having a size of 150 mm × 150 mm is punched out with a cutting blade from the biaxially stretched sheet wound in a roll shape obtained in Examples and Comparative Examples so as to be almost uniform in the sheet width direction. 5 sheets were prepared for each sheet. A 100 mm straight line perpendicular to MD and TD was drawn on each cut specimen using a ruler and an oil-based felt pen, and the length [mm] was measured with calipers (this is assumed to be Y). Next, the test piece is immersed in a silicone oil bath having a temperature 40 ° C. higher than the Vicat softening point temperature of the biaxially stretched sheet measured according to JIS K7206 for 10 minutes, and then drawn on MD and TD. The length [mm] of the straight line was measured with a caliper (this is Z). MD and TD draw ratios (Y / Z: unit [times]) were calculated from Y and Z, and the average value of the five test pieces was calculated.

(2) Heat shrinkage stress Five test pieces each having a size of 10 mm × 100 mm and a long side of MD for each sheet from the biaxially stretched sheets wound up in rolls obtained in Examples and Comparative Examples Then, five pieces having TD as the long side were punched out with a cutting blade so as to be almost uniform in the sheet width direction. For these test pieces, the maximum load generated by heat shrinkage was measured at a set temperature of 180 ° C. using a “DN-type stress tester” made by Nichi Kogyo Co., Ltd. in accordance with ASTM D-1504. The value divided by the cross-sectional area was defined as the heat shrinkage stress (unit [MPa]). The average value of the five test pieces was calculated for MD and TD.

<Evaluation items>
(3) Impact resistance A test piece of a predetermined size is punched with a cutting blade from an arbitrary portion of the biaxially stretched sheets obtained in the examples and comparative examples, and five test pieces (in more detail, for each sheet). From a biaxially stretched sheet wound up in a roll shape, a test piece of a predetermined size was punched with a cutting blade so as to be almost uniform in the sheet width direction, and five pieces were prepared for each sheet).
The amount of energy (impact strength [kg · cm]) required to destroy the test piece was measured using a “puncture tester (the tip uses a 12.7 mm round spherical head)” manufactured by Toyo Seiki Co., Ltd. according to P8134. Read from the scale plate. The value obtained by dividing the amount of energy by the sheet thickness [cm] was defined as impact resistance (puncture impact strength, unit [kg · cm / cm]), and the average value of five measured specimens was calculated. If this value is 1000 kg · cm / cm or more, it can be determined that the impact resistance is excellent, and if it is 2000 kg · cm / cm or more, it can be determined that the value is particularly excellent.

(4) Tear resistance test specimens each having a size of 50 mm x 64 mm from any part of the biaxially stretched sheets (biaxially stretched sheets wound up in a roll) obtained in the Examples and Comparative Examples, The five MDs with the long sides and the five TDs with the long sides were punched out with a cutting blade so as to be substantially uniform in the sheet width direction. Insert a notch with a length of 13 mm from the end of the long side (64 mm) direction of these test pieces, and use the “light load tear tester” manufactured by Toyo Seiki Co., Ltd. The value obtained by dividing by the thickness [mm] of the initial test piece was taken as tear resistance (unit [N / mm]). About MD and TD, the average value in five test pieces made into each long side was computed. If this value is 5.0 N / mm or more, it can be determined that the tear resistance is excellent, and if it is 7.0 N / mm or more, it can be determined that the value is particularly excellent.

(5) Folding resistance A predetermined test piece is punched out with a cutting blade from an arbitrary portion of the biaxially stretched sheet (biaxially stretched sheet wound up in a roll) obtained in Examples and Comparative Examples, and 10 per sheet. Each piece (more specifically, five sheets with MD as the long side and five sheets with TD as the long side) was punched with a cutting blade so as to be almost equal in the sheet width direction. For these test pieces, using a “MIT weather resistance tester” manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8115, bending until breaking occurs at a bending angle of ± 90 °, a bending speed of 175 rpm, and a load of 1 kg. The number of times was measured, and this number of times was defined as folding resistance (unit [times]). Each of MD and TD was performed 5 times, and the average value was calculated. If this value is 1000 times or more, it can be determined that the folding resistance is excellent, and if it is 1500 times or more, it can be determined that the value is particularly excellent.

(6) Low temperature impact properties From the biaxially stretched sheet wound up in a roll shape obtained in Examples and Comparative Examples, a test piece of a predetermined size is punched with a cutting blade so as to be substantially uniform in the sheet width direction, Five sheets were prepared per sheet. About these five test pieces, -20 degreeC, striker diameter 12.7mm, mass 6.5kg, fall height 80cm using the "graphic impact tester" by Toyo Seiki Co., Ltd. based on JISK7124-2. The measurement was performed under the condition of an impact speed of about 4.0 m / sec. The amount of energy [J] required to break the specimen is read from a personal computer screen, and the value obtained by dividing this value by the initial specimen thickness [mm] is the total absorbed energy (low temperature impact, unit [J / mm]. And the average value of the measured five test pieces was calculated. If this value is 7.0 J / mm or more, it can be determined that the low-temperature impact property is excellent, and if it is 10.0 J / mm or more, it can be determined that the value is particularly excellent.

(7) Mold reproducibility Test pieces of a predetermined size were prepared from both end portions and the center portion in the sheet width direction of the biaxially stretched sheet wound up in a roll shape obtained in Examples and Comparative Examples. These test pieces were attached to a hot plate heating type pressure forming machine (“PK-450 type” manufactured by Kansai Automatic Molding Machine Co., Ltd.) with the following evaluation type I, hot plate temperature 130 ° C. (normal condition is 120 ° C.), heating time 0 .4 seconds (normal conditions are 2.0 seconds), heating pressure 1.0 kg / cm ² (≈0.10 MPa), molding time 0.7 seconds (normal conditions is 1.0 seconds), molding pressure 4.0 kg / cm Molding was performed under the conditions of cm ² (≈0.39 MPa), and the sheet groove and the appearance of the molded product were visually observed to determine the maximum drawing ratio (unit [none]) with good mold reproducibility. The average value of the above three locations was calculated for each of MD and TD. If this value is 1.0 or more, it can be determined that the mold reproducibility is excellent, and if it is less than 1.0, it can be determined that the value is inferior.
[Evaluation type I] This is a drawing ratio evaluation type having a rectangular shape, a long side (parallel to the MD of the biaxially stretched sheet) 200 mm, and a short side (parallel to the TD of the biaxially stretched sheet) 150 mm. A mold in which a number of grooves with different depths from 0.3 to 1.2 are provided in this rectangular plane with a drawing ratio (maximum depth of opening / width of opening) in increments of 0.1. The groove opening width is 10 mm, the groove length is 50 to 70 mm, and ten grooves are provided in each of the MD and TD directions.

(8) High-speed formability Using the biaxially stretched sheet wound up in a roll shape obtained in Examples and Comparative Examples as it is, a continuous hot plate heating and pressure forming machine (“CK-1200 type” manufactured by Kansai Automatic Molding Machine Co., Ltd.) And a heating plate temperature of 135 ° C. (normal condition is 125 ° C.), a heating time of 0.6 seconds (normal conditions is 2.0 seconds), and a heating pressure of 1.5 kg / cm ² (≈0. 15 MPa), molding time 1.0 seconds (normal conditions are 1.5 seconds), molding pressure 4.0 kg / cm ² (≈0.39 MPa), 5 shots, all molded products molded in 5 shots The ratio of defective products to 135 pieces (defective rate, unit [%]) was calculated. If the defect rate is less than 4.0%, it can be determined that the high-speed moldability is excellent, and if it is 4.0% or more, it can be determined that it is inferior.
[Evaluation Type II] This is a 3 × 9 mold for a donut container (long side 265 mm × short side 85 mm × depth 45 mm, uneven shape with a step on the bottom).

[Production method]
<Example 1>
GPPS and HIPS-2 were weighed in the proportions shown in Table 1 and uniformly mixed with a ribbon blender to obtain a dry blend. The obtained dry blended product is supplied to a tandem 115 mmφ vent type extruder (manufactured by Ikekai Tekko Co., Ltd.), melted under the condition of a cylinder temperature of 220 ° C., and a surface hanger type T- of 850 mm attached to the extruder. The sheet was extruded from a die (manufactured by Pla Giken Co., Ltd.) into a sheet shape and quenched with a cooling roll set at 80 ° C. to obtain an unstretched single layer sheet having a thickness of about 0.8 mm. Subsequently, the obtained unstretched single layer sheet was stretched about 2.5 times in the longitudinal direction and about 2.5 times in the transverse direction by a roll type longitudinal stretching machine and subsequently a tenter transverse stretching machine, and the thickness was 0.13 mm. A biaxially stretched sheet having a width of 980 mm was wound into a roll. After manufacturing the biaxially stretched sheet, the operation of measuring the heat shrinkage stress of the obtained biaxially stretched sheet was repeated to obtain a biaxially stretched sheet in which the heat shrinkage stress of the biaxially stretched sheet falls within a desired range. . Table 1 shows the stretching temperature at which the desired heat shrinkage stress was obtained. From the obtained biaxially stretched sheet, a test piece having a size matching the test method was punched out with a cutting blade or wound into a roll shape, and the measurements (1) to (8) were performed and evaluated. The results obtained are listed in Table 1.

<Example 2 to Example 5>
In the example described in Example 1, a biaxially stretched sheet was produced in the same procedure as in Example 1, except that the raw material resin was changed as described in Table 1. However, in Example 4, the thickness of the unstretched single layer sheet was changed to about 1.5 mm, and when the (7) mold reproducibility was evaluated, the hot plate temperature was changed to 135 ° C., When the (8) high-speed moldability was evaluated, the hot plate temperature was changed to 140 ° C. From the obtained biaxially stretched sheet, a test piece having a size matching the test method was punched out with a cutting blade or wound into a roll shape, and the measurements (1) to (8) were performed and evaluated. The results obtained are listed in Table 1.

<Example 6>
As a raw material resin, HIPS-1 single pellet and the biaxially stretched sheet of Example 2 were pulverized, and a regenerated pellet was produced by a single screw extruder and a strand die set at 220 ° C. Two types of dry blends obtained by uniformly blending -1 single pellet 60% by weight with a ribbon blender and dry blending were prepared. Prepare 115mmφ vent type tandem extruder (Ikegai Iron Works Co., Ltd.) as both surface layer extruders and 65mmφ vent type extruder (Pura Giken Co., Ltd.) as core layer extruders. A layer feed block (manufactured by Plastic Giken Co., Ltd.) was attached, and a surface hanger type T-die (manufactured by Plastic Giken Co., Ltd.) was attached to this feed block. Next, the above HIPS-1 single pellet is supplied to both surface layer extruders at a cylinder temperature of 230 ° C., and the dry blend is supplied to a core layer extruder at a cylinder temperature of 220 ° C. to melt each layer. The extrusion rate of each extruder was adjusted so that the thickness ratio was 10/80/10, and the steps after melt extrusion were the same as in Example 1 to produce a biaxially stretched sheet. From the obtained biaxially stretched sheet, a test piece having a size matching the test method was punched out with a cutting blade or wound into a roll shape, and the measurements (1) to (8) were performed and evaluated. The results obtained are listed in Table 1.

<Comparative Examples 1 to 6>
In the example described in Example 1, a biaxially stretched sheet was produced in the same procedure as in Example 1 except that the raw material resin was changed as described in Table 2. However, in Comparative Example 3, the thickness of the unstretched single layer sheet was changed to about 1.3 mm, and stretched about 3.3 times in the longitudinal direction and about 3.0 times in the lateral direction. From the obtained biaxially stretched sheet, a test piece having a size matching the test method was punched out with a cutting blade or wound into a roll shape, and the measurements (1) to (8) were performed and evaluated. The results obtained are listed in Table 2.

From the above Tables 1 and 2, the following becomes clear.
(1) A biaxially stretched sheet made of impact-resistant polystyrene that satisfies the requirements specified in claim 1 in terms of rubber component content, stretch ratio, and heat shrinkage stress, impact resistance, tear resistance, and folding resistance. , And low temperature impact properties are excellent, and it is difficult to crack at room temperature or low temperature (see Examples 1 to 6).
(2) Further, the above-mentioned impact-resistant polystyrene biaxially stretched sheet that satisfies the requirements defined in claim 1 has good mold reproducibility, a low incidence of defective products, and excellent high-speed moldability. Example 1 to Example 6).
(3) On the other hand, even if the draw ratio and the heat shrinkage stress are within the range of claim 1, the impact-resistant polystyrene biaxially stretched sheet having a rubber component content of less than 4% by weight is impact resistant. Since it is inferior in heat resistance, tear resistance, folding resistance, and low temperature impact resistance, it is easily cracked and inferior in high-speed moldability (see Comparative Examples 1 to 2).
(4) Even if the content of the rubber component and the heat shrinkage stress are within the range of claim 1, the impact-resistant polystyrene biaxially stretched sheet having a stretch ratio exceeding 2.7 times has a mold reproducibility (maximum The drawing ratio is less than 0.8, and the high-speed moldability (defective rate) is 43.7%, which is significantly inferior to Examples 1 to 6 (see Comparative Example 3).
(5) A biaxially stretched sheet made of impact-resistant polystyrene in which the heat shrinkage stress of MD and TD exceeds 0.60 MPa and 0.55 MPa even when the content of the rubber component and the stretch ratio are within the range of claim 1 Is partially reduced in resistance to cracking (impact resistance, tear resistance, folding resistance), and mold reproducibility and high-speed moldability have a maximum drawing ratio of 0.67 to 0.83, defective rate Is significantly inferior to Examples 1 to 6 at 90% or more (see Examples 1 to 6, Comparative Examples 4 to 5).
(6) Even if only the heat shrinkage stress of TD exceeds the scope of claim 1, the biaxially stretched sheet made of impact-resistant polystyrene produced under such conditions has a mold reproducibility (maximum drawing ratio). ) Is 0.93, and the high-speed moldability (failure rate) is 22.2%, which is inferior to those of Examples 1 to 6 (see Examples 1 to 6 and Comparative Example 6).

The biaxially stretched sheet made of impact-resistant polystyrene according to the present invention and the molded product made of this sheet have excellent impact resistance, tear resistance, and folding resistance while maintaining an appropriate rigidity, so that they are hard to break, and confectionery.・ Suitable for food packaging for storage at room temperature such as containers for processed foods such as bread and rice crackers. In addition, since it has excellent low-temperature impact resistance, it is also suitable for low-temperature food packaging applications such as refrigerated storage containers such as meat, vegetables and seafood, and (non) fried foods, frozen storage containers such as ice confectionery, etc. .

Claims (4)

A dry blend comprising an impact-resistant polystyrene having a rubber component content of 4.0 to 12.0% by weight and containing the impact-resistant polystyrene is melt-kneaded by an extruder, and then continuously with a T-die. Extruded into a sheet and rapidly cooled with a cooling roll to produce an unstretched sheet. The unstretched sheet is subjected to a roll stretching method (the roll temperature for longitudinal stretching is 100 to 130 ° C.), the tenter method (the tenter temperature for transverse stretching is An impact-resistant polystyrene biaxially stretched sheet produced by simultaneously biaxially stretching at 130 to 150 ° C. , characterized by satisfying the following (1) and (2) simultaneously.
(1) The stretching ratio is 2.1 to 2.7 times in both the longitudinal direction and the transverse direction. (2) The thermal shrinkage stress in the longitudinal direction is 0.35 to 0.60 MPa, and the thermal shrinkage stress in the transverse direction is 0.35 to 0.55 MPa   The biaxially oriented sheet made of impact-resistant polystyrene according to claim 1, wherein the impact-resistant polystyrene is a graft-type rubber-modified polystyrene alone or a mixture of graft-type rubber-modified polystyrene and general-purpose polystyrene. The impact resistance (puncture impact strength) is 1000 kg · cm / cm or more, the tear resistance is 5.0 N / mm or more, and the folding resistance is 1000 times or more. A biaxially oriented sheet made of impact-resistant polystyrene. A molded article produced by a thermoforming method using the biaxially stretched sheet made of impact-resistant polystyrene according to any one of claims 1 to 3 as a raw material.