JPH0323575B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a styrenic resin film or sheet having excellent bending resistance and impact resistance. [Prior Art] Biaxially stretched polystyrene films and sheets are used in large quantities as packaging films for fruits and vegetables, as films for lamination with HIPS sheets or PSP sheets, and as lightweight containers for food packaging. These can be said to take advantage of the characteristics of polystyrene resin, which is excellent in transparency, gloss, and rigidity, and has a high gas permeability (water vapor, oxygen gas, carbon dioxide gas, etc.). Although these films or sheets are highly oriented in the biaxial stretching process to improve the brittleness of the polystyrene material, they still lack sufficient tear strength and bending strength, and are prone to bending, etc. There is a problem that when stress is applied to the film or sheet, it may tear or crack. Further, if secondary processing involving heating, such as thermal lamination or thermoforming, is performed, the orientation will return, resulting in an extremely low strength. Therefore, in order to improve these, for example, (a) a styrene-butadiene block copolymer is mixed with a styrene polymer as described in JP-A-49-98857, and (b) JP-A-Sho 58. -129038 Publication, JP-A-59-49938
As described in Japanese Patent Publication No. 62-31017, a method has been proposed in which a small amount of impact-resistant polystyrene is further added to a mixed resin of polystyrene and styrene-butadiene block copolymer. There is. [Problems to be solved by the invention] However, the technique (a) above does not contain styrene.
Added a small amount of butadiene block copolymer (15wt
% or less), the improvement in the bending strength and impact resistance of the film or sheet is insufficient; on the other hand, if the copolymer is added in such a large amount that an improvement can be seen, a) Styrenic resin The excellent rigidity of the film or sheet will decrease, resulting in a stiff film or sheet.
Transparency also deteriorates. b) The heat resistance of the styrene resin decreases. Especially in films or sheets such as styrene-maleic anhydride copolymer (SMA) and styrene-methacrylic acid copolymer (SMAA),
Its excellent heat resistance performance cannot be demonstrated. c) When melt-extruded from an extruder for a long time, a gel-like substance is generated due to the styrene-butadiene block copolymer, resulting in a decrease in the quality of the film or sheet (deterioration in appearance). Especially SMA and
When extrusion processing temperatures such as SMAA are high, a large amount of gel-like material is generated in a short period of time, resulting in a significant decrease in not only quality but also productivity. However, simply mixing styrene-butadiene block copolymer has problems in terms of bending strength, impact resistance, other qualities (stiffness, heat resistance, transparency) and production stability (gel-like material). occurrence) could not be balanced. The present invention aims to solve the above-mentioned problems, and aims to solve the above-mentioned problems by utilizing the excellent rigidity, heat resistance, and
The object of the present invention is to provide a manufacturing method that enables stable industrial production of films or sheets that have significantly improved bending strength and impact resistance while maintaining transparency without generating gel-like substances. [Means for solving the problem] As a result of extensive research in order to achieve the above object, the present inventors added a small amount of hydrogenated block copolymer to a styrene resin film or sheet to form molecular orientation. It was discovered that the bending strength and impact resistance were significantly improved, and the present invention was achieved.
That is, the present invention involves melt-extruding a styrenic resin containing 3 to 15% by weight of a hydrogenated block copolymer obtained by hydrogenating a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene, and then stretching the resin. The present invention provides a method for producing a styrenic resin film or sheet with improved bending resistance, which comprises orienting the film or sheet into a film or sheet. Hereinafter, the present invention will be explained in detail using tables and figures. Table 2 shows bending strength, which is an indicator of brittleness improvement, heat resistance, which shows the resistance to thermal deformation, rigidity, which shows the stiffness, and thermal stability, which shows the resistance to gel formation during extrusion processing. In Examples 1 and 2 and Comparative Examples 1 and 2, the ability of each added block copolymer resin to modify the styrene resin was comprehensively evaluated. As shown in Table 2, the hydrogenated block copolymer resins A ₁ and A ₂ used in the present invention significantly improve the brittleness of styrenic resins when added in small amounts of 3 to 5% by weight. I understand. On the other hand, this resin A ₁ ,
5% by weight when using resins B to E instead of A ₂
When a small amount of is added, the bending strength is weak, and no improvement in brittleness has been observed in any of the resins. Moreover, increasing the amount added certainly improves the bending strength, but it also improves thermal stability, heat resistance,
Rigidity and transparency are greatly reduced and it is not possible to find a point of harmony between the two. The above tendency of not being able to balance the performance was observed in Experiments No. 5 to No.
Comparing Experiment No. 16 with Experiment No. 21 to No. 32, Experiment No. 21 to No. 32
The styrene-methacrylic acid copolymer system of
This shows that the balance is even worse. The above facts mean that hydrogenated block copolymers are more useful in modifying styrene-methacrylic acid copolymers. From the results shown in Table 2 above, it can be seen that adding the hydrogenated block copolymer to the styrenic resin is an essential requirement for achieving the effects of the present invention. It should be noted that if the amount of hydrogenated block copolymer added to the styrene resin is less than 3% by weight, the improvement in flexural strength will be insufficient, and if it exceeds 15% by weight, practical transparency will be insufficient. Difficult to maintain. Therefore,
It is best to use it in the range of 3 to 15% by weight, and 5 to 10% by weight.
It is even better if it is within the range of weight %. Next, FIG. 1 shows the effect of stretching orientation on brittleness demonstrated in Example 3 and Comparative Example 3. In the figure, the horizontal axis is the sheet ORS, which is an index of the degree of stretch orientation.
The vertical axis shows the bending strength (logarithmic scale), which is an index of brittleness. Furthermore, the broken line indicates the composition containing simple polystyrene, the one-dot chain line and the two-dot chain line indicate the composition containing the styrene-butadiene block copolymer (Table 2, Experiment No.
5, No. 7), and the solid line shows the composition containing the hydrogenated block copolymer of the present invention (experimental results in the same table).
No. 2) is shown. In FIG. 1, it is noteworthy that the bending strength of the product of the present invention (solid line) reaches about 1000 to 2000 times due to the effect of the stretching orientation of the present invention. In comparison, polystyrene alone (dashed line) has a level of only about 100 times, and a composition containing a small amount (5% by weight) of a conventional styrene-butadiene block copolymer (dotted chain line) has almost no improvement compared to polystyrene. No effect seen. Moreover, even in a composition in which 30% by weight is added (double-dashed line), it is at the level of about 500 times at most. From this, it can be understood that the stretched and oriented product of the present invention is extremely superior. As a sheet ORS, an appropriate range of 1Kg/cm2 or ^more (for example, 15
Kg/cm ² or less) is selected. Bending strength 500~2000
If you require a level of
It is desirable to set it in the range of Kg/cm ² to 10 Kg/cm ² . Moreover, the results shown in FIG. 1 show that in the composition of the present invention, there is a large change in properties between those that are stretched and oriented and those that are not. Therefore,
Using this, low ORS level (1~2Kg/cm ² )
When a sheet is used, mold reproducibility in thermoforming is good, and excellent performance can be exhibited by making lamination easier in heat lamination. Next, Table 3 shows the usefulness of the present invention based on Example 4 and Comparative Example 4. That is, the sheet of the present invention (Experiment No. 4 composition) and the sheet of the resin containing the styrene-butadiene block copolymer (Experiment No. 4).
11, No. 13) A pudding cup molded body with excellent transparency formed from a sheet or a single polystyrene sheet, which can be punched out in layers without causing cracks or cracks in the flange when the mold is punched out with a die blade. This shows the results of comparative evaluation of the numbers. Whereas with polystyrene alone, cracking occurs even when five pieces are punched out, the product of the present invention can be cut out even with 20 pieces, which shows that the brittleness is greatly improved. On the other hand, with sheets containing conventional styrene-butadiene block copolymers, it was impossible to cut out 10 sheets even when the amount added was as high as 30% by weight (Experiment No. 13). From this, it can be understood that the product of the present invention is a suitable sheet for obtaining a molded product with excellent fold-out resistance, and greatly contributes to improving the quality and productivity of the molded product. The hydrogenated block copolymer used in the present invention is a hydrogenated block copolymer obtained by hydrogenating a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene. The content of the block copolymer is preferably in the range of 5 to 60% by weight, preferably 20 to 50% by weight, and the double bond derived from the diene component of the block copolymer is at least 80% by weight.
% or more is preferable. By the way,
It is presumed that the saturated double bonds suppress gel formation during extrusion processing and improve thermal stability. The constituent vinyl aromatic hydrocarbons include, for example, styrene, α-methylstyrene, various alkyl-substituted styrenes, etc., and the conjugated dienes include, for example, butadiene, isoprene, etc. Hydrogen of the styrene-butadiene block copolymer Additives are generally preferred, but from the viewpoint of compatibility with copolymers of styrene and monomers having carboxylic acid groups, such as styrene-maleic anhydride copolymers and styrene-methacrylic acid copolymers, which will be described later. More preferably, a small amount of a known graftable monomer having a carboxylic acid group, such as maleic anhydride, is grafted onto the hydrogenated product. As the styrene resin, a styrene homopolymer or a copolymer of styrene and a monomer copolymerizable with styrene is used. For example, polystyrene, styrene-methacrylic acid copolymer, styrene-methacrylic acid-methyl methacrylate copolymer, styrene-maleic acid copolymer, styrene-
Acrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-α-methylstyrene copolymer, styrene-methacrylic acid-methyl methacrylate-6-membered cyclic acid anhydride copolymer, styrene-methacrylic acid-methacrylate methyl acid-six-membered cyclic acid anhydride-α-methylstyrene copolymer, and the like. Also, a small amount (30% by weight or less) of a high-impact styrenic copolymer (from the Modify range) that can be mixed with these heat-resistant resins may be blended, or the above heat-resistant resins may be blended with Modify as well. You can use the one you made. [Example] Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. In addition, each evaluation item used in Examples and Comparative Examples is based on the following evaluation method and evaluation scale. (1) Flexural strength Based on ASTM D2176, angle 135°, load 1Kg
(Find the average value of n=10) [This is a substitute property for improving the brittleness of sheets and films, and the more times it can withstand bending, the better the toughness] ◎...1000 times or more 〇...300 times or more 1000 Less than 300 times △...50 or more Less than 300 times ×...Less than 50 times (2) Heat resistance In a silicone oil bath with strictly controlled temperature
The sheet is immersed for 10 minutes, the temperature at which it begins to shrink by 2% or more is measured, and the value is compared with that of a single styrene resin sheet. (Average of n = 5) [This is a substitute characteristic for the heat deformability of sheets and films, and the smaller the temperature drop, the better the heat deformation resistance is maintained] ◎...Temperature drop is less than 1℃ 〇...〃 1℃ 2°C or more, less than 5°C ×… 5°C or more (3) Rigidity The tensile modulus of the sheet is measured in accordance with ASTM D882 and compared with the value of a single styrene resin sheet. (Average value of n = 10) [This is a substitute characteristic for the stiffness of sheets and films,
The smaller the decrease in tensile modulus, the better the stiffness can be maintained] ◎... Decrease in tensile modulus less than 5Kg/mm ² 〇... 〃 5Kg/mm ² or more 20Kg/mm ² or less △... 〃 20Kg/mm ² or more 50Kg/mm Less than ² ×... 〃 50Kg/mm ² or more (4) Thermal stability Cut 20 square samples of 20cm x 20cm from the sheet and measure the number of Gel with a size of 0.2mm or more under a polarizing plate. Then, calculate the average value per sample. [This is a substitute property for thermal stability during extrusion, and the smaller the number of gels, the better the thermal stability] ◎...Less than 5 pieces 〇...5 or more but less than 10 pieces △...10 or more but less than 30 pieces ×... 30 or more (5) Transparency Measure HAZE in accordance with ASTM D1003 (average of n = 5) [The smaller the HAZE value, the better the transparency] ◎…Less than 10% 〇…10% or more20 Less than % △...20% or more and less than 40% ×...40% or more Example 1, Comparative Example 1 Resin A ₁ to Resin E shown in Table 1 to polystyrene (weight average molecular weight 320,000) to Table 2 Each of the indicated amounts was added in the prescribed amounts and mixed using a turn blender. Next, using the obtained 16 types of resin and polystyrene alone, each was melt-extruded from a 65 mmφ extruder T-die at a resin temperature of 230 ° C.
Due to the speed difference between the heated rolls, longitudinal stretching is carried out, and immediately after that, transverse stretching is carried out continuously using a tenter. A biaxially oriented sheet with a value of 6 Kg/cm ² was produced. The resulting sheet has bending strength, heat resistance,
The results of each evaluation of rigidity, thermal stability, and transparency are shown in Table 2 (Experiments No. 1 to No. 16, No. 33). As seen in this table, it can be seen that only the present invention in which hydrogenated block copolymers (resins A ₁ and A ₂ ) are added is the method for obtaining sheets that are excellent in all of the above evaluations. Moreover, the amount of resin A ₁ and A ₂ added is only 3
It is surprising that with a small amount of ~5% by weight, it exhibits bending strength comparable to sheets containing 30% by weight of other resins B to E. Example 2, Comparative Example 2 In Example 1 and Comparative Example 1, a styrene-methacrylic acid copolymer (methacrylic acid content: 10% by weight, Vikatsu softening point: 131°C, weight average molecular weight: 260,000) was used instead of polystyrene, and the extruded resin was A biaxially stretched sheet was produced in the same manner except that the temperature was changed to 260°C. The obtained sheet was evaluated in the same manner as in Example 1 and Comparative Example 1, and the results shown in Table 2 were obtained. (experiment
No. 17 to No. 32, No. 34). Looking at this table, it can be confirmed that the product of the present invention is superior. Furthermore, it can be seen that the method of the present invention is particularly effective for styrene resins that need to be melt-extruded at high temperatures, such as styrene-methacrylic acid copolymers, from the viewpoint of thermal stability. Example 3, Comparative Example 3 In the same manner as in Example 1 and Comparative Example 1, using the mixed resin and polystyrene having the compositions of Experiment No. 2, No. 5, and No. 7 of Example 1 and Comparative Example 1, respectively. By extruding and stretching and changing the stretching conditions, various
A biaxially stretched sheet with an ORS and a wall thickness of 0.12 mm was produced. The obtained sheet was evaluated for ORS and bending strength, and the results are shown in Figure 1. This figure shows that the present invention (Experiment No. 2) has a greater stretching orientation effect than polystyrene alone and conventional styrene-butadiene copolymer-added resin sheets (Experiments No. 5, No. 7), and has a slight stretching effect. It can be seen that there is a large change in properties between oriented and non-oriented. Example 4, Comparative Example 4 From Example 1 and Comparative Example 1, mixed resins and simple polystyrene having the compositions of Experiment No. 4, No. 11, and No. 13 with good transparency were selected, and each of them was used as Example 1. , Extrusion stretching was carried out in the same manner as in Comparative Example 1, and the ORS was approximately 2.
A biaxially stretched sheet with a thickness of ~3Kg/cm ² and a thickness of 0.3mm was produced. Next, from this sheet, using a contact heating type air pressure forming machine, the opening diameter is 60mmφ, the bottom diameter is 50mmφ, and the depth is 50mm.
A transparent pudding cup molded article was molded. The obtained molded product was evaluated for overlapping punching performance using an electric single-shot punching machine equipped with a die blade of 70 mmφ. The number of stacks was increased by 5 and the evaluation was continued until cracks or cracks occurred in the flange. The results are shown in Table 3. From this table, it can be seen that the product of the present invention has unprecedented bending resistance and is extremely useful.

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[Table] [Effects of the invention] As explained in detail above, the present invention has the following advantages:
It has the effect of making it possible to create a stable film or sheet with significantly improved brittleness while maintaining the excellent rigidity, heat resistance, and transparency of styrenic resins. Therefore, the present invention can be said to make a particularly large contribution to the food packaging industry, etc., which has strongly desired a solution to the brittleness of styrene resin films or sheets.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the stretching orientation effect of the sheet of the present invention demonstrated in Example 3 and Comparative Example 3.

Claims (1)

[Claims] 1. After melt-extruding a styrenic resin containing 3 to 15% by weight of a hydrogenated block copolymer obtained by hydrogenating a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene, it is stretched and oriented to form a film or A method for producing a styrenic resin film or sheet with improved bending resistance, the method comprising forming a styrenic resin film or sheet into a sheet.