JP5036122B2 - Heat-resistant styrene resin stretched sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-resistant styrene resin stretched sheet which is excellent in heat resistance, folding endurance and oil resistance, has good secondary processability and permits reuse of waste originating therefrom as a polystyrene stretched sheet without causing deterioration in various properties. <P>SOLUTION: The styrene resin stretched sheet, stretched at least in one direction, comprises a resin mainly composed of a styrene copolymer having a monomer composition of (A), (B) and (C) below (provided that the total amount of (A), (B) and (C) is 100 wt%) manufactured by a bulk polymerization method or a solution polymerization method using an organic peroxide having in the molecule at least three -O-O- bonds as a polymerization initiator: (A) 60-99 wt% of a styrene monomer; (B) 1-40 wt% of an &alpha;-methylstyrene monomer; and (C) 0-6 wt% of at least one monomer selected from among an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride and a maleimide compound. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to an improvement of a styrene resin stretched sheet. More specifically, the present invention relates to a stretched sheet having improved secondary formability and excellent heat resistance, oil resistance, and folding strength, which is improved in recoverability of sheet trimming waste and skeleton after molding and sheet productivity.

  Polystyrene biaxially stretched sheets are superior in rigidity (sheet stiffness) and optical properties (transparency), so they are thermoformed by vacuum molding, compressed air molding, and other methods for food packaging as lightweight packaging containers. It is often used as the beginning. However, since these sheets and containers are inferior in heat resistance, they are difficult to use for applications in direct contact with boiling water, microwave heating applications, and the like.

  For this reason, styrene-α-methylstyrene copolymer (SAMS), styrene-acrylic acid copolymer (SAA), styrene-methacrylic resin as styrene resins that maintain the transparency and rigidity of polystyrene and have improved heat resistance. Heat-resistant styrene copolymers such as acid copolymers (SMAA) and styrene-maleic anhydride copolymers (SMA) are generally known. As a method for improving the heat resistance of the styrenic biaxially stretched sheet, an attempt to use SAA, SMAA, and SMA has been made. For example, Patent Document 1 and Patent Document 2 describe biaxially stretched styrene with improved heat resistance. System sheets have been proposed. However, in the former method using SAMS, the secondary formability and folding strength of the sheet are insufficient, and the effects of improving heat resistance and oil resistance are not sufficient. In addition, the latter method using SAA, SMAA, and SMA gives a sheet having an excellent balance of formability, bending strength, heat resistance, oil resistance, etc., but the sheet trimming waste and the skeleton after the secondary molding of the sheet are used. When mixed with general polystyrene, it tends to become cloudy.

For this reason, it is necessary to separate and collect from polystyrene at the production site and molding site of the sheet. This is one reason why heat-resistant styrene resin sheets are not widely used in the market at present.
Further, regarding the heat-resistant styrene copolymer, the problems other than the cloudiness will be described in detail. In order to increase the heat resistance of the styrene-based resin sheet, a copolymer component such as methacrylic acid or acrylic acid is added in an amount of 6-8. In this case, SMAA and SAA are likely to undergo a dehydration cross-linking reaction between molecules during melt extrusion of the resin, and are easily gelled, resulting in poor sheet productivity. In addition, SMA tends to lower stretchability, and has a drawback that it is difficult to obtain a sheet having a narrow stretchable condition range and a uniform thickness. On the other hand, SAMS has the great advantage that it does not become cloudy even when mixed with general polystyrene, but due to the low polymerization reactivity of α-methylstyrene, it is difficult to increase the molecular weight, and secondary sheet molding Properties and bending strength were insufficient, and were not put into practical use.

Japanese Patent Laid-Open No. 55-071530 JP 62-025031 A

  As described above, stretched sheets using heat-resistant styrene copolymers are difficult to effectively recycle waste generated during film formation and secondary molding, and also have drawbacks in sheet productivity. there were. The present invention provides a stretched sheet having excellent secondary formability, which is excellent in heat resistance, oil resistance, bending strength, and environmental suitability, which is improved in the above-mentioned drawbacks, that is, recyclability of waste generated from the sheet and sheet productivity. And providing a stretched sheet that uses waste generated from the sheet and is excellent in economy and resource saving.

In order to improve the low polymerization reactivity of α-methylstyrene and to obtain a copolymer having a sufficient molecular weight capable of maintaining bending strength, the present invention has a molecular weight of —O—O as a polymerization initiator. -An organic peroxide containing three or more bonds is used. Further, a styrene copolymer comprising the following monomers (A), (B) and (C) (however, the total amount of (A) to (C) is 100% by weight) produced by the above method is mainly used. It is a styrene resin sheet made of resin and stretched in at least one direction.
(A) Styrene monomer: 60 to 99% by weight
(B) α-methylstyrene monomer: 1 to 40% by weight
(C) 0 to 6% by weight of at least one monomer selected from unsaturated carboxylic acid, unsaturated carboxylic acid anhydride, and maleimide compound

  The stretched sheet produced by the production method according to the present invention is a sheet with good secondary workability that is excellent in heat resistance, folding strength, and oil resistance, and the physical properties generated from the waste generated from the sheet again as a polystyrene stretched sheet. It can be used without deterioration, and is excellent in economy, resource saving, and environmental characteristics, and is particularly suitable for forming a packaging container.

The present invention will be described in detail below.
The stretched styrenic resin sheet of the present invention has a specific copolymer comprising the above-mentioned monomers (A), (B), (C) (however, the total amount of (A) to (C) is 100% by weight) ( Hereinafter, it may be simply referred to as a styrene copolymer). The content of the monomer (A) constituting the styrene copolymer is preferably 60 to 90% by weight, more preferably 60 to 80% by weight.
Further, (B), that is, α-methylstyrene monomer is preferably in the range of 1 to 40% by weight. Below this lower limit, the improvement in heat resistance of the sheet is insufficient. On the other hand, when the upper limit is exceeded, the fluidity of the resin is lowered, film formation and secondary molding become difficult, and the productivity further decreases. In order to achieve a high balance between film formability, secondary moldability, heat resistance, and productivity, the preferred content of (B) α-methylstyrene monomer is 10 to 35% by weight, more preferably 15 to 30%. % By weight. (C) The content of at least one monomer selected from unsaturated carboxylic acid, unsaturated carboxylic acid anhydride, and maleimide compound is preferably 0 to 6% by weight. If the upper limit is exceeded, the recyclability decreases and the environmental suitability is impaired.

A method for producing a styrene copolymer comprising the above monomers (A), (B), and (C) (however, the total amount of (A) to (C) is 100% by weight) is an intramolecular O-O as a polymerization initiator. An organic peroxide containing three or more —O— bonds is used. Organic peroxides which contain -O-O- bond three or more in its molecule 2,2-bi scan (4,4-di - (t-butylperoxy) cyclohexyl) propane, 2,2 bi scan (4,4-di - (t-amyl peroxy) cyclohexyl) propane, 2,2-bi scan (4,4-- (Kumirupaokishi) cyclohexyl) propane, 2,2-bi scan (4,4 Contains four —O—O— bonds in the molecule such as di- (t-butylperoxy) cyclohexyl) butane and 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone Organic peroxides, tris (t-butylperoxy) triazine, tris (t-amylperoxy) triazine, tris (t-butylperoxycyclohexyl) triazine, tris (dicumylperoxycyclohexyl) In a molecule such as lyazine, 1,2,4-tri (t-butyl) trimellitate, 1,2,3-tri (t-butyl) trimellitate, 1,3,5-tri (t-butyl) trimellitate, etc. An organic peroxide containing three —O— bonds may be mentioned.

The polymerization method is a bulk polymerization method or a solution polymerization method. You may carry out either a continuous type or a batch type.
The molecular weight of the copolymer resin composed of the monomer is preferably 150,000 to 500,000 in terms of styrene-converted weight average molecular weight measured by GPC method. When the weight average molecular weight is less than 150,000, it is difficult to obtain a sufficient stretch orientation effect, and when it exceeds 500,000, the tendency of the stretch processability and secondary processability to decrease is developed. Further, the Vicat softening point (based on ISO 304, hereinafter referred to as VSP) of the resin is preferably 110 ° C. or higher, more preferably 115 ° C. or higher when used as a heat-resistant sheet. The upper limit is not particularly limited, but is preferably 135 ° C. or less, more preferably 130 ° C. or less, and still more preferably 125 ° C. or less in view of stretched film formability of the sheet, secondary formability, and use of recycled resin.
The stretched styrenic resin sheet of the present invention is mainly composed of a copolymer comprising the above-described monomers (A), (B), (C) (however, the total amount of (A) to (C) is 100% by weight). It is a single layer sheet made of a resin or a multilayer sheet containing this copolymer sheet. One type of copolymer may be used, or two or more types may be combined. As the multilayer sheet, a sheet described below having the above-described styrene copolymer as a main component and a surface layer is preferable.

  In the present invention, the resin mainly composed of a styrene copolymer is a resin containing 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more of the above-mentioned styrene copolymer. As the ratio of the above-mentioned styrene copolymer decreases, the balance of transparency, heat resistance, oil resistance, and moldability of the sheet becomes worse. Other resins used in combination include polystyrene, high-impact polystyrene, styrene-conjugated diene block copolymers (including those obtained by hydrogenating part or all of the conjugated diene blocks, and acid-grafted modified products), styrene- Hydrogenated conjugated diene block copolymer, styrene-acrylonitrile copolymer, styrene- (meth) acrylic acid ester copolymer, ABS (rubber graft styrene-acrylonitrile copolymer, MBS (rubber graft styrene-methyl methacrylate) Copolymers), rubber-grafted styrene- (meth) acrylic acid ester copolymers, styrene resins, copolymerized polyesters, polycarbonates, polyphenylene ethers, petroleum resins, etc. Of these, transparent when polystyrene is used in combination. Growth without deteriorating Preferable because sex good sheet is obtained.

  Moreover, you may add a well-known additive, for example, a plasticizer, a heat stabilizer, an antistatic agent, a mold release agent, an antifogging agent, a ultraviolet absorber, etc. to the styrene resin of this invention. The stretched styrenic resin sheet of the present invention is a uniaxially or biaxially stretched sheet, and its production method is not particularly limited, and can be carried out by a generally known method. For example, a method in which a molten resin is extruded from a T-die or a circular die and then stretched by a tenter method or a bubble method can be employed. Of these, particularly preferred are a sequential biaxial method in which a sheet extruded from a T-die is stretched in one direction according to the speed ratio of the roll group and then stretched in the vertical direction with a tenter, or a method of simultaneous biaxial stretching with a tenter. The draw ratio. The ratio is preferably 1.5 to 8 times, more preferably 2 to 7 times in at least one direction. The stretching temperature is preferably VSP to (VSP + 60 ° C.) of the entire resin constituting the sheet, more preferably (VSP + 15 ° C.) to (VSP + 50 ° C.). More preferably, the film is stretched under the conditions of high strain rate and high temperature-high magnification stretching disclosed in JP-A-62-25031, and the sheet ORS retention rate described later is set to 0.7 to 1.0.

  The above-mentioned trims generated during the film formation of the stretched sheet of the present invention made of a resin mainly composed of the above-mentioned styrenic copolymer, the skeleton generated after forming the sheet, the waste after use of the container, etc. A resin derived from a styrene resin stretched sheet mainly composed of styrene copolymer (hereinafter referred to as a recycled polymer) can be mixed with polystyrene and reused as a general polystyrene stretch sheet that is widely used. . It can also be used as a packaging container, household goods, etc. by mixing with polystyrene and injection molding. Preferably, it is a case where it is used as a polystyrene stretched sheet, and a sheet having almost no deterioration in transparency, other physical properties, and moldability is obtained. Moreover, the same sheet can be obtained also when a resin mainly composed of the above-mentioned unused styrene-based copolymer and polystyrene are mixed.

  The ratio of mixing the recycled polymer with polystyrene is not particularly limited, but for use as a general polystyrene stretched sheet, the stretched film formation condition and the viewpoint of secondary molding of the sheet, the polystyrene content is 50% by weight or more. It is preferable that the amount is 70% by weight or more. The upper limit of polystyrene is not particularly defined, but is preferably 97% or less, more preferably 95% by weight or less, from the viewpoint of resin recovery efficiency. When the recycled polymer is used as a heat-resistant stretched sheet, the polystyrene content is preferably less than 50% by weight and more preferably 30% or less in order to maintain the heat resistance of the sheet. Polystyrene to be mixed with the recycled polymer is a polymer having a weight average molecular weight of about 200,000 to 400,000, which is generally made of a styrene monomer used in a stretched polystyrene sheet, and the amount of 3% by weight or less in the mixed polystyrene. It may also contain impact-resistant polystyrene, inorganic substances such as calcium carbonate and silicon dioxide, and 30% by weight or less of a styrene-conjugated diene block copolymer. Moreover, a part or all of the polystyrene to be mixed may be a recycled product of a polystyrene stretched sheet or other polystyrene resin products, and if necessary, an arbitrary amount of the above-mentioned styrene copolymer other than the recycled polymer may be used. It is also possible to mix them separately.

  If necessary, in addition to recycled polymer and polystyrene, other resins include impact-resistant polystyrene, styrene-conjugated diene block copolymer, hydrogenated styrene-conjugated diene block copolymer, styrene-acrylonitrile copolymer, Styrene resins such as styrene- (meth) acrylic acid ester copolymer, ABS (rubber graft styrene-acrylonitrile copolymer, MBS (rubber graft styrene-methyl methacrylate copolymer)), copolymer polyester, polycarbonate, Polyphenylene ether, petroleum resin, etc. may be contained in the total resin in an amount of 30% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less. , Heat stabilizer, antistatic agent, mold release agent, anti-proof Agents, ultraviolet absorbers may be added. These other resins, additives may be used singly or in combination of two or more kinds.

The recycled polymer is preferably pulverized, melt-extruded and used in the form of pellets, but can also be used in a pulverized state. The production of a stretched sheet from a composition comprising a recycled polymer and polystyrene can be carried out by a known method in the same manner as the above-described stretched sheet mainly composed of a styrene copolymer. Also, the maximum heat shrinkage stress (ORS) in the stretching direction is preferably in the above range.
Furthermore, as a preferred embodiment of the stretched sheet containing a recycled polymer, a resin layer mainly composed of the above-mentioned unused styrene-based copolymer is formed on both surfaces of the sheet made of the above-mentioned resin composition composed of the recycled polymer and polystyrene. Is a stretched sheet having three or more layers laminated together. In this case, the deterioration of the physical properties of the resin due to the thermal history of the recycled polymer, the adverse effects of dirt, flow unevenness, etc. can be compensated by the resin coating on the surface layer, and a sheet without deterioration of stretchability, transparency, etc. can be formed, and secondary formability Is also preferable. When using the container shape | molded from a sheet | seat especially for food packaging, it is preferable on hygiene to set it as a stretched sheet | seat of 3 or more layers.

The present invention includes a multilayer sheet made of an unused resin in addition to the multilayer sheet using the above recycled polymer. The resin constituting the inner layer is selected from the above-described styrene copolymers, polystyrene, and mixtures thereof. Moreover, as resin which comprises a surface layer, it selects from the resin which has the above-mentioned styrene-type copolymer as a main component. When the transparency and gloss of the sheet are particularly important, the surface layer is preferably the styrene copolymer alone. The mixing ratio in the case of using a resin mixture in each layer is not particularly limited, and can be mixed at an arbitrary ratio as long as the characteristics of the present invention are not impaired.
In order to obtain a multilayer sheet having good heat resistance and excellent moldability, the VSP of the resin or resin composition constituting both surface layers should be 2 ° C. or higher than the VSP of the resin or resin composition constituting the inner layer. preferable. In particular, it is more preferable to control the difference in VSP to be 5 ° C. or more in order to control the moldability and heat resistance in a well-balanced manner, for example, to perform spraying molding. The upper limit is not particularly defined, but when a multilayer sheet is obtained by co-stretching, the VSP difference is preferably 50 ° C. or less, more preferably 40 ° C., in order to give stability and effective stretching orientation to each layer during stretching. Hereinafter, it is 30 degrees C or less more preferably.

The above-mentioned other resins and additives may be added in an amount of 30% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less in 100% by weight of the resin constituting the inner layer. The total thickness of the surface layer made of the resin mainly composed of the above-mentioned styrene-based copolymer is not particularly limited, but is preferably 6% or more, more preferably 10 to 60%, and still more preferably 16 to 40% of the total thickness of the sheet. %. The lower limit is a region where the effect of improving heat resistance due to the effect of the surface layer appears, and the upper limit is a region where the improvement of the effect is weakened.
In addition to the surface layer and the inner layer, an adhesive resin layer may be provided in order to improve the bonding force between the layers, or a layer made of styrene resin or other resin may be provided as an additional inner layer. The multilayer sheet can be formed by a generally known method. For example, in the case of producing a three-layer sheet, it is obtained by using a two-layer extruder and a three-layer die to melt-extrude each resin and then stretching in the same manner as a single layer sheet. Moreover, after preparing separately the extending | stretching sheet | seat of resin which comprises each layer, each sheet is obtained by laminating by a well-known method. Furthermore, it can also be obtained by preparing an unstretched sheet of each layer and then bonding and stretching.

All of the styrene-based resin stretched sheets included in the present invention are stretched in at least one direction, preferably in two directions, and the maximum heat shrinkage stress (hereinafter referred to as ORS) in the stretch direction is preferably 2-18 kg / cm ^2, more preferably 3~15kg / cm ^2, more preferably from 3.5~10kg / cm ^2. Since the stretching effect of the sheet becomes insufficient as the ORS becomes lower, the sheet becomes brittle and easily broken, and the secondary molded product tends to have insufficient strength particularly at the flange portion. As the ORS increases, the resistance of the sheet increases during the secondary molding, and the mold definition of the molded product tends to deteriorate. In some cases, the sheet may be excessively oriented, resulting in a decrease in strength. In the case of a biaxially stretched sheet, the ORS difference in the two directions is preferably within a range of ± 1.5 kg / cm ² in performing secondary molding. More preferably, it is ± 1.0 kg / cm ² . Moreover, it is preferable that the ORS retention represented by (value of heat shrinkage stress after 5 seconds of maximum heat shrinkage stress) / (value of maximum heat shrinkage stress) is 0.7 to 1.0 (constituting the sheet). Measured in VSP + 25 ° C. silicone oil of all resin compositions). When the ORS retention is 0.7 or more, a very advantageous sheet and molded product having particularly good moldability and excellent oil resistance can be obtained.
From the viewpoint of maintaining transparency, the stretched sheet of the present invention preferably has a HAZE value measured in accordance with JIS K7105 of 10% or less, more preferably 5% or less, and even more preferably 3% or less. The thickness of the sheet of the present invention is sometimes not limited, but is usually 0.01 to 1 mm, and is preferably 0.1 to 0.7 mm, more preferably 0.12 to 0.5 mm for use in molding. is there.

All the above-mentioned styrene biaxially stretched sheets of the present invention are secondarily molded by a known method such as a pressure forming method, a vacuum forming method, a plug assist forming method, a hot plate contact pressure forming method, and used as various containers. I can do it. If necessary, one or both surfaces of the sheet may be surface-treated by a known method. Examples of the surface treatment prescription include an antifogging treatment, a mold release treatment, an antistatic treatment, a printing treatment, and a corona treatment. These may be used in combination.
Further, a stretched or unstretched polystyrene film, a polyester film, a polyolefin film, and other plastic films may be laminated on both surfaces of the sheet of the present invention or one arbitrary surface by a known method. On the contrary, the sheet of the present invention can be used by laminating on both surfaces or any one surface such as high impact polystyrene (HIPS) sheet, polystyrene foam sheet (PSP), polyolefin sheet, other plastic sheet, paper, etc. It is. In particular, when laminated to a HIPS sheet or PSP, gloss and heat resistance are often improved, which is preferable.
Hereinafter, the present invention will be described in detail by way of examples, but is not limited thereto.

The obtained copolymer and sheet were evaluated by the following methods. Unless otherwise specified, the mixing ratio of the resin is a weight ratio and weight%.
(1) Measurement sample preparation of weight average molecular weight (Mw): Dissolve about 1000 ppm of resin composition in tetrahydrofuran Measurement equipment: Showa Denko Shodex21
(Gel permeation chromatography)
Column: sample; two KF-806L
Reference; KF-800RL 2 temperature: 40 ° C
Carrier: THF 1 ml / min
Detector: RI, UV (254 nm)
Calibration curve: Tosoh monodispersed PS data processing: Sic-480

(2) Measurement of melt tension After the sample is heated to a predetermined temperature and melted, it flows into the cylinder of a capillary rheometer (Rosand Advanced Capilary Extrusion Rheometer) and then a capillary (diameter 2 mm) connected to this cylinder The length of 20 mm) was extruded in a string shape while maintaining a constant extrusion speed of 20 mm / min. Next, after passing the string-like material through a tension detection pulley disposed below the nozzle, the winding speed is varied from 5 m / min to 100 m / min using a winding roll, and the maximum tension is obtained. Was used as melt tension.
(3) Vicat softening temperature (VSP): measured in accordance with ISO 306 (4) Folding strength: in accordance with JIS P8115, bending strength is measured from the center to the left and right under a condition of 135 ° load 1 kg. did.
(5) Transparency: HAZE was measured according to JIS K7105.

(6) ORS: Peak stress value measured at VSP + 25 ° C. of the resin or resin composition constituting the sheet in silicon oil in accordance with ASTM-D1504.
(7) ORS retention: Measured according to the above ORS measurement method. It calculated from ratio (ORS2 / ORS1) of the peak stress value (ORS1) and the stress value (ORS2) 5 seconds after the peak expression.
(8) Heat resistance of the sheet: The shrinkage rate of the sheet when the test sheet was immersed in boiling water for 5 minutes was evaluated according to the following criteria. The shrinkage rate is preferably less than 2%, but depending on the use, even if it is less than 5%, there is no practical problem.
A: Shrinkage is less than 2%. ○: Shrinkage is 2% or more and less than 5%. Δ: Shrinkage is 5% or more and less than 10%. X: Shrinkage is 10% or more.
(9) Heat-resistant temperature: measured from the temperature at which 3% or more of shrinkage starts when the sheet is immersed in silicon oil for 1 minute. The heat resistant sheet is preferably 100 ° C. or higher.

(10) Oil resistance: Measure the HAZE of the sheet after immersing the sheet in VSP-15 ° C salad oil of the resin or resin composition constituting the sheet for 10 minutes according to JIS K7105. Compared with the HAZE of the sheet before immersion, the oil resistance was evaluated according to the following criteria.
A: Change in HAZE is less than 3%. ○: The change of HAZE is 3% or more and less than 7%. X: The change of HAZE is 7% or more.
(11) Thermal stability: A sheet was cut into a 25 mm square, the number of gels having a size of 0.2 mm or more was measured, and evaluated according to the following criteria (average of 20 samples, substitution characteristics of thermal stability during extrusion) Become).
A: Less than 5 gels. ○: 5 or more and less than 10 gels. Δ: 10 or more and less than 20 gels. X: 20 or more gels.

(12) Formability: A sheet was formed with a hot plate pressure forming machine by changing the hot plate temperature of a cylindrical cup having an opening diameter of 120 mm and a depth of 35 mm under the conditions of a heating time of 2.5 seconds and a forming pressure of 3 kg / cm ² . Formability was evaluated according to the following criteria from the difference between the temperature at which raindrops began to occur in the molded product and the temperature at which defective mold reproducibility began to occur. The larger the temperature difference, the wider the molding is possible and the better the moldability.
A: Temperature difference is 15 ° C. or more. ○: Temperature difference is less than 15 and 10 ° C. or more. X: Temperature difference is less than 10 ° C.
(13) Recyclability: After pulverizing the sheets formed in Examples 1 to 4, Comparative Examples 1 to 3 and Reference Example 1, pelletized with a 30 mm extruder and polystyrene having a weight average molecular weight of 260,000 (PS Japan) 685) is mixed at a ratio of 50:50 (weight ratio) and pelletized with a 30 mm extruder, and the above-mentioned composition adjusted in the same manner as HAZE of a 50 mm × 50 mm, 2 mm thick plate prepared by injection molding. Evaluated from the difference between the HAZE and the plate of the resin alone (◎: the difference in HAZE is less than 3%. ○: the difference in HAZE is 3% or more and less than 5%. Δ: the difference in HAZE is 5% or more and less than 10%. X: The difference of HAZE is 10% or more).

Example 1
74 parts by weight of styrene, 25 parts by weight of α-methylstyrene, 1 part by weight of methacrylic acid and 0.005 part by weight of a polymerization initiator 2,2-di (4,4-di- (t-butylperoxy) cyclohexyl) propane Dissolved and continuously fed to a fully mixed polymerization apparatus having a capacity of 4.3 liters at a rate of 0.55 kg / hour. The reaction mixture discharged from the polymerization apparatus was supplied to a single screw extruder to remove volatile components under reduced pressure and pelletize. The polymerization reaction conditions in the polymerization process are a polymerization temperature of 120 ° C. The polymerization rate at the outlet of the reactor is 45%. The single screw extruder in the devolatilization process was set to a temperature of 230 to 240 ° C. and a vacuum degree of 14 torr.
The composition (% by weight) and physical properties of the obtained pellets are shown in Table 1.
The obtained pellets were fed to a 50 mm extruder having a screw with a L / D of 24. It is melt extruded from a T die, continuously stretched 3.7 times at VSP + 35 to 41 ° C. of each resin in the flow direction (hereinafter referred to as MD direction) according to the speed ratio of the roll, and then perpendicular to the flow (hereinafter referred to as TD) with a tenter. The resin was stretched 4.3 times at VSP + 34 to 39 ° C. of each resin to obtain a biaxially stretched sheet having a thickness of 0.20 to 0.22 mm. Table 2 shows the physical properties of the sheet.

(Example 2)
Pelletization was performed in the same manner as in Example 1 except that 70 parts by weight of styrene and 30 parts by weight of α-methylstyrene were used. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet having a thickness of 0.20 to 0.22 mm was obtained in the same manner as in Example 1. Table 2 shows the physical properties of the sheet.
(Example 3)
Pelletization was performed in the same manner as in Example 1 except that 0.005 parts by weight of the polymerization initiator 3,3,4,4-tetra (t-butylperoxycarbonyl) benzophenone was used in Example 1. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet having a thickness of 0.20 to 0.22 mm was obtained in the same manner as in Example 1. Table 2 shows the physical properties of the sheet.
Example 4
Pelletization was performed in the same manner as in Example 1 except that 74 parts by weight of styrene, 25 parts by weight of α-methylstyrene, and 1 part by weight of maleic anhydride were used. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet having a thickness of 0.20 to 0.22 mm was obtained in the same manner as in Example 1. Table 2 shows the physical properties of the sheet.

(Comparative Example 1)
Pelletization was performed in the same manner as in Example 1 except that 60 parts by weight of styrene, 30 parts by weight of α-methylstyrene, and 10 parts by weight of methacrylic acid were used. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet having a thickness of 0.20 to 0.22 mm was obtained in the same manner as in Example 1. Table 2 shows the physical properties of the sheet.
(Comparative Example 2)
Pelletization was performed in the same manner as in Example 1 except that 0.01 parts by weight of the polymerization initiator 1,1-di (t-butylperoxy) cyclohexane was used. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet having a thickness of 0.20 to 0.22 mm was obtained in the same manner as in Example 1. Table 2 shows the physical properties of the sheet.

(Comparative Example 3)
Pelletization was performed in the same manner as in Example 2 except that 0.02 part by weight of the polymerization initiator t-butylperoxy-3,5,5-trimethylhexanoate was used in Example 2. The composition and physical properties of the obtained pellets are shown in Table 1.
A biaxially stretched sheet was attempted by the same method as in Example 1, but only a sheet with large thickness unevenness was obtained. The physical properties are shown in Table 2.
As a result of Table 2, the sheet of the present invention has good transparency and bending strength, heat resistance and oil resistance are superior to the stretched polystyrene sheet of Reference Example 1, has good moldability, and is mixed with polystyrene. It can be seen that it can be recycled without deterioration of transparency. On the other hand, Comparative Example 1 is an example in which methacrylic acid exceeds the scope of the present invention and is inferior in recyclability with polystyrene.
In Comparative Example 2, the polymerization initiator is monofunctional only and is inferior in film formability and thermal stability. In Comparative Example 3, the polymerization initiator is similarly monofunctional and has a low weight average molecular weight. Therefore, it was difficult to make a stretched sheet. The stretched sheet excellent in all of the transparency, strength, moldability, film forming stability, and recyclability of the sheet is only the stretched sheet of the present invention.

(Examples 5-8, Comparative Examples 4-6, Reference Example 2)
The sheets obtained in Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1 and the skeleton after the molding test (hereinafter referred to as recycled resin) were pulverized by a pulverizer and pelletized through an extruder, and the weight. After mixing polystyrene having an average molecular weight of 260,000 (PS Japan 685) in the ratio shown in Table 3, a sheet was formed in the same manner as in Example 1. The TD direction was stretched 3.4 times at 133 ° C. to 140 ° C. to obtain a biaxially stretched sheet having a thickness of 0.17 to 0.19 mm and an ORS of 5.8 to 7.0 (Example 5). 8). Similarly, a mixed resin sheet of the pulverized sheet obtained in Comparative Examples 1 to 3 and polystyrene having a weight average molecular weight of 260,000 (PS Japan 685) was obtained (Comparative Examples 4 to 6). Table 3 shows the physical properties of the sheet.
In Table 3, Reference Example 2 is an example of a polystyrene stretched sheet obtained by mixing a polystyrene stretched sheet scrap and polystyrene. The transparency and folding strength of Examples 5 to 8, which were prepared by mixing the stretched sheet scraps of Examples 1 to 4 and polystyrene, were close to those of the polystyrene stretched sheet of Reference Example 2 and good. Further, the thermal stability and moldability are also in a good range. Thus, the scrap of the stretched sheet of the present invention can be mixed with polystyrene and used again as a stretched sheet, and the scrap can be used effectively and is economically advantageous.
Moreover, it turns out that it is excellent also in co-productivity with a polystyrene stretched sheet.
On the other hand, all of Comparative Examples 4 to 6 are inferior in transparency, thermal stability, and moldability, and further have low folding strength. The scrap resin of Comparative Examples 1 to 3 is mixed with polystyrene and stretched again. It turns out to be difficult to use as.
This indicates that when it is produced in parallel with a polystyrene stretched sheet, scrap cannot be used and a large amount of scrap loss occurs.

(Examples 9 to 12, Comparative Examples 7 and 8)
The surface layer resin shown in Table 4 was supplied to a 40 mm extruder and the inner layer resin was supplied to a 50 mm extruder, and a three-layer sheet was stretched and formed from a three-layer T die under the same conditions as in Examples 5-8.
The thickness of the surface layer and the surface layer were adjusted to be equal, and VSP when determining the stretching temperature was based on the resin or resin composition of the surface layer. The obtained sheet had a thickness of 0.24 mm to 0.26 mm, an ORS of 4.3 to 5.6, and an ORS retention of 83 to 94%. Note that the sheet of Comparative Example 8 was inferior in stretchability, and had to be stretched by the method of Comparative Example 2 to obtain a uniform sheet. Table 4 shows the physical properties of these sheets.
In Table 4, it can be seen that the example is a sheet having an excellent balance of various properties as with the single layer sheet. On the other hand, Comparative Example 8 is particularly inferior in moldability and has little improvement in heat resistance.

  The stretched heat-resistant styrene-based resin sheet of the present invention is thermoformed by a method such as vacuum molding or pressure molding, and is provided as various packaging containers including food packaging applications.

Claims (2)

2,2-bis (4,4-di- (t-butylperoxy) cyclohexyl) propane, 2,2-bis (4,4-di- (t-amylperoxy) cyclohexyl) propane, 2,2- Bis (4,4-di- (cumylperoxy) cyclohexyl) propane, 2,2-bis (4,4-di- (t-butylperoxy) cyclohexyl) butane, 3,3 ′, 4,4′-tetra ( From t-butylperoxycarbonyl) benzophenone, tris (t-butylperoxy) triazine, tris (t-amylperoxy) triazine, tris (t-butylperoxycyclohexyl) triazine or tris (dicumylperoxycyclohexyl) triazine Bulk polymerization method using an organic peroxide containing 3 or more —O—O— bonds in the selected molecule as a polymerization initiator Is a resin mainly composed of a styrene-based copolymer having the following monomer composition (A) (B) (provided that the total amount of (A) to (B) is 100% by weight) produced using a solution polymerization method: A styrene resin stretched sheet stretched in at least one direction.
(A) Styrene monomer: 60 to 80% by weight
(B) α-methylstyrene monomer: 20 to 40% by weight A multilayer sheet comprising at least three layers,
The inner layer is 2,2-bis (4,4-di- (t-butylperoxy) cyclohexyl) propane, 2,2-bis (4,4-di- (t-amylperoxy) cyclohexyl) propane, 2 , 2-bis (4,4-di- (cumylperoxy) cyclohexyl) propane, 2,2-bis (4,4-di- (t-butylperoxy) cyclohexyl) butane, 3,3 ′, 4,4 ′ -Tetra (t-butylperoxycarbonyl) benzophenone, tris (t-butylperoxy) triazine, tris (t-amylperoxy) triazine, tris (t-butylperoxycyclohexyl) triazine or tris (dicumylperoxycyclohexyl) ) Using an organic peroxide containing 3 or more —O—O— bonds in the molecule selected from triazine as a polymerization initiator, Styrene-based copolymer comprising the following monomer composition (A) (B) (provided that the total amount of (A) to (B) is 100% by weight) produced using a polymerization method or a solution polymerization method (A) Styrene Monomer: 60-80% by weight
(B) α-methylstyrene monomer: 20 to 40% by weight
And a resin layer mainly composed of at least one of polystyrene,
Both surface layers are layers made of a resin mainly composed of the styrene copolymer,
A styrenic resin stretched multilayer sheet stretched in at least one direction, wherein the Vicat softening point of the resin constituting the surface layer is 2 ° C. or more higher than the Vicat softening point of the resin constituting the inner layer.