JPH0367016B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in the manufacturing method of styrenic resin sheets with excellent transparency, and more specifically, the present invention relates to improvements in the manufacturing method of styrenic resin sheets with excellent transparency. This invention relates to a styrene resin sheet. Conventionally, polystyrene resin sheets have been widely used because of their excellent transparency and are mainly molded into containers whose contents can be viewed from the outside. However, since polystyrene resin sheets are extremely fragile, they are not supplied in an unstretched state, and even when they are used for molding, they are usually stretched to a heat shrinkage stress value of 5 kg/cm ² or more. hand,
Moreover, the current molding method is generally a contact heating type pressure forming method (hereinafter abbreviated as the pressure forming method). In short, this pressure forming method is a method in which the sheet is heated while being held in contact with a heated hot plate, and then the sheet is formed by being spread out in the mold using compressed air. There are many problems such as sticking, raindrops, and low molding efficiency, so it is not considered to be an excellent molding method.
Polystyrene resin sheet (heat shrinkage stress: 5Kg/cm ²
Even for stretched products with the above values, this method is used as a forming method to compensate for the inherent fragility. Therefore, for example, in order to eliminate hot plate patterns and raindrops in molded products and to increase molding efficiency, a radiation heating method is used in which the sheet is radiantly heated in a heating furnace and then vacuumed into a mold for molding. The sheet is heated for the vacuum (straight) molding method [hereinafter abbreviated as vacuum straight molding method] or for the purpose of obtaining a deep-drawn molded product, a molded product with good mold reproducibility and excellent appearance quality. Radiant heating vacuum (plug assist type) molding method in which radiant heating is performed in a furnace, and then a plug is inserted from the opposite direction while being sucked into the mold using vacuum pressure and molded along with the inside of the mold [hereinafter referred to as vacuum plug molding method] In other words, if you try to apply each of them, the problem arises that you cannot industrially apply them to a molding machine before you can obtain the desired molded product. Therefore, at present, when meeting the conditions of the vacuum straight molding method and vacuum plug molding method, so-called HI polystyrene mixed with a large amount of rubber substance,
There is no choice but to use a resin sheet or an improved styrene resin sheet called MI polystyrene resin sheet. However, these molded products have the disadvantage of being opaque white or milky white, which is far from making the most of the clear transparency inherent in polystyrene resin. As a result, it becomes necessary to mold the molded product thicker, which further promotes clouding of the molded product. On the other hand, one of the ways to improve polystyrene resins is to reduce the amount of butadiene rubber added to take advantage of the transparency of the resin, and to compensate for the lack of toughness by increasing the stretching orientation of the sheet. However, although the sheet obtained can be slightly improved by the same pressure forming method as polystyrene sheets, it has not been improved to the extent that it can be applied to the vacuum straight forming method, vacuum plug forming method, etc. mentioned above. . The reason for this is that the improvement of the resin by adding a rubber substance and the improvement of the properties that increase molecular orientation are different in nature, and the range in which the two can complement each other is narrow, and the range of the amount of rubber added that can take advantage of clear transparency. This will not improve the toughness to withstand the conditions of vacuum straight molding and vacuum assisted molding, and increasing molecular orientation to compensate for this will lead to defects such as increased uneven thickness of the molded product. It is. The present invention has been made in view of the current situation, and has been completed based on a unique phenomenon that occurs in the stretching orientation of low thermal shrinkage stress, which has not been seen before by anyone. The first object of the present invention is to develop a transparent styrene resin sheet that can be applied to vacuum straight molding and vacuum assisted molding, which were previously thought to be inapplicable, and which can yield high-quality molded products. The second purpose is to provide better appearance quality such as deep drawability, raindrops, hot plate pattern, clear transparency, mold reproducibility, etc. compared to conventional products even when applied to conventional pressure forming methods. The third purpose is to provide a styrenic resin sheet with improved moldability, and the third purpose is to make it possible to make a generally transparent styrenic resin sheet into a high-quality molded product using various molding methods, Until now, we had been unable to enter the market for molded products due to the drawbacks of the air-pressure forming method, but we have developed a plan to utilize the characteristics of transparent styrene resin sheets to meet market demands and expand sheet sales. The purpose of the present invention is to provide an innovative sheet manufacturing method. The above three objects are achieved by the production method of the present invention, that is, the styrene resin has an average particle size of about
Styrene-butadiene copolymer rubber of 0.03 μ or less,
When extruding a styrene resin dispersed with a butadiene concentration of 5 to 12% by weight from an extruder to obtain a flat sheet, ASTM
Heat shrinkage stress according to D1504, approximately 2-4Kg/cm ²
By using a method for producing a transparent styrenic resin sheet with improved moldability, which is characterized by carrying out stretching orientation with a value of , and a difference between two axes of about 1 kg/cm ² or less. can be easily achieved. Hereinafter, the content of the present invention will be explained in detail using drawings and the like. In FIGS. 1A and B, the manufacturing method of the present invention is explained in detail. Styrene-butadiene block copolymer particles containing 35 to 80% by weight of styrene component and 65 to 20% by weight of butadiene component, and polystyrene resin The mixed particles are supplied from the hopper 1 into the extruder 2, and are melt-kneaded in the extruder. The kneaded mixed resin is extruded into a flat plate from a temperature-controlled T-die 3 onto a temperature-controlled cooling roll 4. At this time, the styrene-butadiene rubber is adjusted so that the butadiene concentration is in the range of 5 to 12% by weight and the weight component ratio is uniform when the mixed particles are supplied. Furthermore, the average particle size of the styrene-butadiene rubber in the extruded mixed resin is adjusted to a value of about 0.03μ.
This adjustment of the rubber particle size can be achieved by carefully selecting and using commercially available styrene-butadiene block copolymer particles. Next, the flat styrene resin extruded onto the cooling roll 4 is transferred to the following roll groups 5, 6, 7, 7', 8,
The temperature is controlled between 8', 9, and 10, and first-axis stretching is performed in the extrusion direction by the difference in circumferential speed between the roll groups, followed by tenter steps 12, 13, 14, 15,
Then, it is expanded and stretched in the heating furnace 13 along the stretching guide 11 in a direction perpendicular to the first-axis stretching, resulting in a smooth sheet that has been biaxially stretched, and passed through guide roll groups 16, 16', and 17. Winding shaft 1 of winding machine
8, it is rolled up as a transparent styrene resin sheet. In the method of the present invention, in this biaxial stretching process, the sheet has a heat shrinkage stress of about 2 to 4 Kg/cm ² in two axial directions, measured in accordance with ASTM D1504, and a difference between the two axial directions. It is necessary to stretch the film to a value of about 1 Kg/cm ² or less. In this case, it is desirable to select conditions for the sheet stretching ratio of 1.4 to 1.9 times, but the specific conditions include the extrusion resin temperature, the temperature and gradient of the stretching roll group, and the peripheral speed of the roll group. It is difficult to express this numerically because it changes depending on the combination of heating furnace temperature, furnace length, expansion stretching ratio, expansion gradient, residence time in the furnace after stretching, etc. That's funny. For this reason, also in the present invention, the content of biaxial stretching is expressed by a target structural index (thermal shrinkage stress). In this case, it is important to keep in mind that even when using the same tenter-type biaxial stretching process, processes that emphasize productivity or their testing machines, etc.
The problem is that the conditions cannot be set unless the basic design is changed. The reason for this is that these facilities are generally designed to increase the productivity per unit by increasing the elongation in the 1st and 2nd axial directions, and the heat shrinkage stress is 5Kg/ ^cm3. This is because it is designed to be easy to set to the above value. In addition, since sequential two-stage stretching is adopted for productivity reasons, conditions must be set in consideration of stress relaxation of the heat shrinkage stress of the drawn product that occurs after the second stage of stretching. Like a target indicator 2~
At a low value of 4 Kg/cm ² , the rate of stress relaxation becomes a significant contributor. What should also be noted is the phenomenon of resin sagging (resin viscosity, adhesiveness) and tension stress relaxation that occurs during stretching. If such a phenomenon occurs, for example, during uniaxial stretching, it will cause small variations in the heat shrinkage stress in the length direction of the sheet, and if it occurs during second axial stretching, it will cause variations in the width direction of the sheet. become. Such variations in heat shrinkage stress cannot be completely eliminated even under the experiments of the present inventors.
Maximum 0.5Kg/ when considering fluctuations caused by measurement method
cm ² will be generated. In the present invention, about 2 to 4 kg/
That is why the expression cm ² is used. The manufacturing method of the present invention is based on the above-mentioned method, but if this is analyzed and explained based on the main requirements of the structure of the invention, the manufacturing method of the present invention is based on the method in which styrene-butadiene rubber is contained in polystyrene resin with an average particle size. The styrene-butadiene rubber concentration is 5 to 12% by weight.
The heat shrinkage stress value of this product is approximately 2 to 4 kg/cm ³ in the two axes, and the difference between the two axes is approximately 1.
It can be analytically expressed as a combination of the above and , which performs stretching orientation with a value of Kg/cm ² or less. The necessity for this will be discussed below.The first necessity is shown in Figure 2. Figure 2 shows the average particle diameter (μ) of styrene-butadiene rubber and the transparency [HAZE] of the resulting sheet.
(%). Rubber concentration 6% by weight, rubber concentration 6% by weight,
It is an experimental diagram when the sheet thickness is 200μ. According to the results in Figure 2, the transparency of the sheet is reduced to 1%.
Considering the need to maintain the HAZE value below, it is clear that particles with an average particle size of at least about 0.03μ or less should be selected. The sheet with less than 1% HAZE proves that it does not impair the properties of polystyrene resin, namely its clear transparency, and means that even when the sheet is stacked in layers, it does not give a yellowish appearance. As for the small-diameter homogeneous dispersion of styrene-butadiene rubber, if it is carefully selected from those of styrene-butadiene block copolymers, it is currently possible to obtain a particle size of about 0.01 μm. The next requirement is that if the amount of rubber is less than 5% by weight, the sheet will lack toughness and deformability, and will not continue to improve the moldability described above. on the other hand,
This is because if it exceeds 12% by weight, it will be difficult to satisfy the following requirements. Although the analysis of this phenomenon is still insufficient, according to the observations of the present inventors, increasing the amount of rubber seems to act in the direction of reducing the viscosity and increasing the stickiness of the extruded resin, and further increasing the relaxation of tension stress. %, there is a remarkable phenomenon in which the unsolidified sheet stretched over the rolls adheres tightly to the rolls and loosens in small increments in the uniaxially stretched roll group.
It was observed that the variation in the heat shrinkage force of the obtained sheets also increased accordingly. This phenomenon could not be controlled by adjusting the resin temperature. FIG. 3 is an experimental diagram showing the relationship between the folding strength of the sheet and the compression resistance of the molded article with respect to the butadiene concentration. According to Figure 3, the butadiene concentration is 5-12% by weight.
In this range, the sheet has a bending strength that can be put to practical use, and when it is made into a molded product, the negative effect on compression resistance is unexpectedly small, and a molded product with sufficient stiffness can be obtained. It allows you to predict what will happen. The following requirement is not only an orientation index indicating a combination of orientation conditions in the production method of the present invention, but also an important requirement that influences the moldability of the obtained sheet. Table 1 is a results table showing the relationship between the orientation index of the obtained sheet and the overall moldability index. According to the results in Table 1, the orientation index of sheets that can be molded using any of the three different molding methods is approximately 2 to 4 Kg/cm ² in biaxial heat shrinkage stress, and This indicates the need for extremely narrow stretching conditions in which the difference in direction is less than about 1 Kg/cm ² .

[Table] The existence of an appropriate range of this orientation state and its effectiveness were something that no one could have predicted in the past.
Moreover, this is a peculiar phenomenon observed in an extremely small range of stretching conditions that could not be confirmed. Furthermore, Table 2 shows the results of evaluating the sheets produced by the method of the present invention by air pressure forming in comparison with commercially available sheets. According to the results in Table 2, the sheet produced by the method of the present invention has been modified to have better overall molding performance in air pressure molding than any commercially available styrenic resin sheet. Moreover, in terms of transparency, it has the significance of being a clear and transparent molded product with a HAZE of 1% or less, no different from that of polystyrene resin. That is, the combination of Tables 1 and 2 shows that the sheet obtained by the method of the present invention has a significantly high molding performance that cannot be obtained with conventional styrene resin sheets. Therefore, the sheet obtained by the method of the present invention can be used in a conventionally undeveloped field, that is, the dual limitations of the conventionally applicable molding method and the quality of the obtained molded product.

[Table] Application fields where transparent styrene resin sheets could not be utilized due to the limitations of the table, specifically, for example, transparent molded cups, sealed cup containers whose lids and containers are both transparent.
When applied to fields such as tablet packaging, which is called PTP, it is possible to develop demand in the same way as if a completely new suitable sheet was developed, and it is possible to continue to expand sales of the sheet by meeting market demands. This has the extremely revolutionary effect of increasing the amount of energy. The molding methods used in Examples and Comparative Examples are as follows. Contact heating pressure air forming method (molding method A) Machine used: Contact heating air forming machine manufactured by Fujita Iron Works Co., Ltd. (GF-1000 automatic forming machine) Process: See Figure 4 Molding process: In Figure 4, The sheet unwound from a rolled sheet 1 placed on a winder is sent onto a hot plate 3 after passing through guide rolls, dicer rolls, etc. Next, the mold 5 descends and presses the sheet, and the heated and softened sheet is pressed against the mold surface and spread by extrusion of pressurized air blown out from the mold vents and vacuum suction from the mold vents. and mold it. When the molding is completed, the mold is moved upward away from the hot plate, and pressurized air is again blown out from the vents of the mold to push the molded product out of the mold. Next, the formed sheet is sandwiched between the pinch guides 7 and the pinch guides are moved to the position 7'.
This allows simultaneous transfer of the unformed sheet to the hot plate. The transferred molded sheet is punched out into a molded product by a die cutting blade 8, and the trim sheet is wound up by a winder 9. Operating conditions: Molding is performed under two types of conditions shown in the table below.

[Table] Mold used: A mold is selected from the following four types for each evaluation criterion. (Mold a) Opening 100mm x 100mm, bottom 90mm x 90mm, depth
A female mold that can produce 64 20mm square tray-shaped container-shaped products per shot, with 8 rows in the sheet width direction and 8 rows in the sheet travel direction. (Mold b) There are 8 molded products in the shape of a shallow tray container with an opening of 100 mm x 100 mm, a bottom surface of 95 mm x 95 mm, and a depth of 5 mm, arranged in 8 rows in the sheet width direction and in the sheet traveling direction, 64 molded products per shot. A female mold that can take pieces. (Mold c) A female mold in which round cup-shaped recesses with an opening diameter of 100 mmφ are arranged in 8 rows in the sheet traveling direction and in 8 rows in the width direction (64 in total). is a round cup deep drawability evaluation mold in which the angle of inclination is constant at 80° and the depth is sequentially varied from 7.5 mm to 60 mm at 7.5 mm intervals. (Mold d) Opening diameter is 80mmφ, bottom diameter is 75mmφ, depth is 20mm
A female mold that can produce 64 round cup container-shaped molded products per shot, with 8 rows in the sheet width direction and 8 rows in the sheet travel direction. Radiant heating vacuum (straight method) molding method (molding method B) Machine used: Sanwa Kogyo Co., Ltd., radiant heating straight vacuum forming machine Process: See Figure 5 Molding process: In Figure 5, the unwinder The sheet unwound from the rolled sheet 1 placed on the roller passes through guide rolls, etc., and then is placed on a pin tenter 2.
It is fixed to the pins by inserting pins near both ends of the sheet in the width direction. Next, the pin is moved to transfer the sheet into the oven 4, where the sheet is radiantly heated by an infrared heater. The heated sheet is further molded into mold 5 using a pin tenter.
The sheet is transferred to the bottom of the mold, and the sheet is drawn into the mold and stretched by vacuum suction through the air holes of the mold, thereby forming the sheet. When the molding is completed, the molded sheet is released from the mold by blowing out pressurized air from the mold vents, and is transported using a pin tenter. Next, the molded product is punched out with a die cutting blade 8, and the trim sheet after punching out the molded product is wound up with a winder 9. Operating conditions: Molding is performed under two types of conditions shown in the table below.

[Table] Mold used: (Mold e) Opening diameter 100mmφ, bottom diameter 90mmφ, depth 30mm
A female mold that can produce 64 round cup-shaped container-shaped products per shot, with 8 rows in the sheet width direction and 8 rows in the sheet travel direction. Radiant heating vacuum (plug assist method) Molding method (molding method C) Machine used: Sanwa Kogyo Co., Ltd., radiant heating plug assist vacuum forming machine Process: See Figure 6 Molding process: Figure 6 In this case, the feeding and transport of the sheet to the oven 4 and the heating process of the sheet in the oven are the same as in the case of forming method B. The heated sheet is transferred to the bottom of the mold 5 using a pin tenter. Next, the mold is lowered and at the same time the plug 6 is raised, and at the same time, the sheet is molded in such a way that it is brought into close contact with the mold and stretched by vacuum suction through the air holes of the mold. When the molding is completed, the plug is lowered, and then the mold is raised while the molded sheet is released from the mold by blowing out pressurized air from the vents of the mold. The formed sheet is further conveyed to below the die-cutting blade 8 using a pin tenter. Next, the molded product is punched out using a die-cutting blade, and the trim sheet after punching out the molded product is wound up using Wonder 9. Operating conditions: Molding is performed under two types of conditions shown in the table below.

【table】

[Table] Mold used: (Mold f) There are 8 molded products in the shape of a deep cup-shaped container with an opening diameter of 70 mmφ, a bottom diameter of 60 mmφ, and a depth of 70 mm in the sheet width direction and 8 rows in the sheet traveling direction. A female mold that can produce 64 pieces per shot. The evaluation criteria for each evaluation item in Examples, Comparative Examples, and Experimental Examples are as follows. (1) Heat shrinkage stress In accordance with ASTM D1504, the value is measured at a bath temperature of 125℃, and is the average of 20 measurements each in both the extrusion direction (MD) and width direction (TD) of the sheet. Determine the value and use it as the respective heat shrinkage stress (Kg/cm ² ). (2) Moldability index The moldability index was determined using the following formula, where M is the number of molded products that met all of the respective molding standards. Molding suitability index = M / number of molded pieces (target 3200) x 100 (3) Molded product transparency 20 pieces were randomly selected from the molded items molded by mold b, and the bottom part of the molded items was The HAZE was measured according to ASTM D1003, and the average value H [%] was determined. Evaluation criteria

[Table] (4) Raindrop resistance Randomly select 20 of the molded products molded using mold b, count the number of raindrops observed in the molded product, and calculate the average raindrop per molded product. The number of occurrences (X) was calculated. Note that raindrops are uneven patterns D on the sheet surface that occur when the sheet is heated in contact with a hot plate, as shown in Figure 7, and when viewed from above, they look like raindrops and have a diameter of 3 to 20 mm. It is of a certain degree. Evaluation criteria

[Table] (5) Deep drawing formability For the molded products formed by mold C, 8 types of molded products each with a drawing depth of 10 mm to 80 mm, 10 of each, were randomly selected, and for the molded products,
For each drawing depth, we counted the number of molds that had no mold breakage, mold whitening (stress cracks), and had mold reproducibility in accordance with the molding standards, and determined the maximum drawing depth h [mm] at which the number was 9 or more. . Evaluation criteria

[Table] (6) Stiffness of molded products Five molded products molded using mold d were randomly selected and were manufactured by Toyo Baldwin.
Using TENSILON UTM--1000, the compression resistance force [Kg] when compressed by 5 mm at a compression speed of 4 mm/min was measured, and the average value P [Kg] was determined. Evaluation criteria

[Table] Example, Comparative Example 1 Asahi Kasei Kogyo Co., Ltd., GP polystyrene [Product name:
Styron 685] 85 parts by weight and 77.5 parts by weight and 15 parts by weight and 22.5 parts by weight of trial product styrene-butadiene block copolymer rubber (butadiene content 40%) manufactured by Asahi Kasei Corporation, a total of 100 parts by weight. (butadiene concentration is 6% for the former and 9% for the latter), and after melt-kneading with a 50mmφ extruder,
It was extruded into a sheet form from a T-die, and sequentially biaxially stretched under the eight conditions shown in Table 3 in the process shown in FIG. 1 to obtain a rolled sheet with a thickness of 0.2 mm and a width of 1200 mm. As a result of determining the heat shrinkage stress of this sheet, the values shown in the column of heat shrinkage stress in Table 3 were obtained. Furthermore, the particle size of the rubber in this sheet is approximately 0.03μ.
It was dispersed in Cut off the edges of the seven types of sheets manufactured so that each has a width of 1020 mm, roll and form the sheets uniformly.
According to conditions 1 to 6 for the three methods ABC, and the mold used is a for molding method A, e for molding method B, and f for molding method C.
, each target number of shots is 50 (target number of molded products)
3200) and evaluated the moldability index. The results are shown in Table 1. From Table 1, the following is clear. 1 From Experiment Nos. 1 to 4, the heat shrinkage stress of the sheet is in the range of approximately 2 to 4 Kg/cm ² and the difference between the two axes of heat shrinkage stress (between MD and TD) is 1 Kg/cm ² or less. In this case, its moldability is very good. 2 From Experiment No. 5, the heat shrinkage stress of the sheet was approximately 2
If it is smaller than Kg/cm ² , it cannot be molded using any molding method. 3 From Experiments No. 6, 7, and 8, even if the heat shrinkage stress of the sheet is in the range of about 2 to 4 Kg/cm ² , there are cases where the difference between the two axes is larger than about 1 Kg/cm ² , and each If the heat shrinkage stress in the axial direction is greater than about 4 kg/cm ² , molding cannot be performed using the vacuum forming method. The above results demonstrate that the sheet obtained by the method of the present invention can be formed by any of the following forming methods: pressure forming, vacuum straight forming, and vacuum plug forming.

[Table] Example, Comparative Example 2 The five types of commercially available styrene resin sheets shown in Table 2 and the sheet from Experiment No. 2 in Example were each 1020 mm wide.
After trimming, the target number of shots is 50 each using three types of molds b, c, and d under condition 1 of molding method A.
(Target number of molded products: 3200) After molding, mold b
The molded product in mold C was evaluated for molded product transparency and raindrop resistance, the molded product in mold C was evaluated for deep drawing formability, and the molded product in mold d was evaluated for molded product stiffness. The results are shown in Table 2. According to the results in Table 2, the sheet obtained by the method of the present invention also showed better molding performance than any commercially available sheet even in the air forming method, and was able to provide high-quality molded products with high transparency. I can see that it has been improved. Experimental example 1 HIPS containing commercially available styrene and butadiene rubber
and three types of elastomers [HIPS manufactured by Company X: butadiene concentration 7.5% by weight, HIPS manufactured by Company Y: butadiene concentration
11.7% by weight, Z company elastomer: butadiene concentration 60%] and the trial product styrene-butadiene copolymer rubber used in Example 1 (butadiene concentration 40%).
weight%) respectively manufactured by Asahi Kasei Industries, Ltd. [Product name:
Styron 685] was mixed with a butadiene concentration of 6% by weight, and after melt-kneading with an extruder, T
It was extruded into a sheet form from a die, and sequentially biaxially stretched under the same conditions as Experiment No. 2 in Table 3 in the steps shown in FIG. 1 to obtain a wound layered sheet with a thickness of 0.2 mm and a width of 1200 mm. The HAZE of the sheet was measured according to ASTM D1003, and the average particle diameter of the rubber dispersed in the sheet was measured, and the relationships between these measurements are plotted in FIG. 2. According to the results shown in FIG. 2, it is clear that in order to obtain a clear transparent sheet (HAZE of 1.0% or less), the particle size of the rubber must be dispersed to at least about 0.03 μm or less. Experimental Example 2 The mixing ratio of GP polystyrene and styrene-butadiene block copolymer rubber used in Example 1 was changed to give butadiene concentrations of 0, 3, 5,
After mixing to give 9 and 12% by weight, the mixture was extruded and stretched into a sheet under conditions such that the MD and TD heat shrinkage stresses were both approximately 2 kg/cm ² in the process shown in Figure 1. A rolled sheet with a thickness of 0.2 mm and a width of 1200 mm was obtained.
The folding strength [times] of these sheets was determined using ASTM D2176, and five molded products each with an opening diameter of 80 mmφ and a depth of 20 mm were molded using a discontinuous manual molding tester (manufactured by Erich). Then, the compressive restraint force [Kg] at the time of 5 mm compression at a compression speed of 4 mm/min was measured using TENSILON UTM--1000 manufactured by Toyo Baldwin Co., Ltd., and the average value thereof was determined. The relationship between the folding strength and compression resistance with respect to the butadiene concentration is illustrated in FIG. As is clear from Figure 3, the strength of the sheet increases greatly when the butadiene concentration is around 5% by weight, and when the butadiene concentration is lower than 5% by weight, the strength of the sheet is insufficient and it is easy to break. . On the other hand, the effect of butadiene concentration on the compression resistance of the molded product was unexpectedly small;
It can be seen that within a range of up to 12% by weight, there is no adverse effect on the properties of the molded product, that is, the stiffness of the molded product.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a convenient process example for the manufacturing method of the present invention, A is a side view, B is a plan layout diagram, and Figure 2 is a diagram showing rubber particle diameter [μ] and transparency (HAZE) [%]. Figure 3 is an experimental diagram showing the relationship between butadiene concentration (wt%), folding strength, and compression resistance of the molded body [Kg]
Fig. 4 is a process diagram of the pressure forming method, Fig. 5 is a process diagram of the vacuum (straight) forming method, and Fig. 6 is a process diagram of the vacuum (plug) forming method. FIG. 7 is a schematic diagram of a raindrop that occurs in a molded product.

Claims (1)

[Claims] 1. In obtaining a flat sheet by extruding a styrene-based resin in which a styrene-butadiene copolymer rubber having an average particle diameter of about 0.03μ or less and a butadiene concentration of 5 to 12% by weight is dispersed in a styrene resin from an extruder,
It is recommended that stretching orienting be carried out in two perpendicular axes directions of the sheet with a heat shrinkage stress of approximately 2 to 4 Kg/cm ² in accordance with ASTM D1504, and a difference between the two axes of approximately 1 Kg/cm ² or less. A method for producing a transparent styrenic resin sheet with improved moldability.