JPS6411054B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides transparency obtained by biaxially stretching a styrenic resin sheet, particularly a copolymer obtained by grafting styrene onto styrene-butadiene rubber, a styrenic resin composition containing a styrene polymer and methylphenyl polysiloxane, This invention relates to a biaxially oriented styrenic resin sheet with excellent printability and mold release properties. Conventionally, biaxially oriented polystyrene sheets have been widely used for food packaging because they have excellent transparency and stiffness, and do not contain harmful substances. However, when forming a large number of containers from these sheets, then stacking a large number of sheets, punching them, and then filling them with articles, the peelability between the molded products is poor, the work efficiency is low, and the peeling is forced. This caused problems such as inducing tearing of the molded product. In order to solve this problem, attempts have been made to improve this by adding various additives such as wax, oil, plasticizers, etc., but they are not satisfactory even in small amounts, and if they are used in large amounts, they cause cloudiness. There was a problem that it caused When using a commercially available biaxially oriented polystyrene sheet, a silicone emulsion is applied to it for the purpose of imparting a mold release effect. However, according to this method, countless adhesion spots of silicone oil emulsion occur on the sheet surface, which significantly reduces the commercial value of the sheet and molded product, and furthermore, during subsequent processing such as printing, heat sealing, etc. There was a problem. The present invention solves such drawbacks and is a graft copolymer (hereinafter referred to as rubber-modified polystyrene) with a rubber concentration of 5 to 9% by weight, which is obtained by grafting styrene to styrene-butadiene rubber containing 20 to 40% by weight of styrene. By biaxially stretching a styrenic resin composition that is a uniform mixture of a transparent styrene polymer and methylphenyl polysiloxane, it has excellent transparency and sheet release properties, and also has printability and thermal properties that have been difficult to achieve in the past. The present invention aims to provide a biaxially oriented styrenic resin sheet that has excellent sealing effects. That is, the present invention involves biaxially stretching a styrenic resin composition having a rubber concentration of 0.2 to 0.5% by weight, in which 0.1 to 0.5% by weight of methylphenyl polysiloxane is added to a mixture of rubber-modified polystyrene and a styrene polymer. It is characterized by The present invention will be further explained in detail below. The styrenic resin composition according to the present invention is a mixture of rubber-modified polystyrene, a styrene polymer, and methylphenyl polysiloxane (hereinafter abbreviated as MFPS), and the rubber-modified polystyrene has a styrene content of 20 to 40% by weight. Styrene-butadiene rubber grafted with styrene at a rubber concentration of 5 to 9% by weight
It is a graft copolymer of
0.5% by weight is mixed to give a rubber concentration of 0.2 to 0.5% by weight. The styrene-butadiene rubber used in the present invention has a weight ratio of styrene and butadiene of 40/60 to
It must be in the 20/80 range. When the proportion of styrene exceeds 40% by weight, the effect of roughening the surface becomes weaker, and the proportion of styrene exceeds 20% by weight.
If it is less than that, it is difficult to maintain transparency. In addition, the average particle diameter of the rubber is preferably 2 to 6μ, and if it is less than 2μ, it will be transparent but the physical properties will deteriorate.
If it exceeds 6μ, transparency decreases. Next, the rubber concentration of rubber-modified polystyrene is 5-
A range of 9% by weight is preferred, with a rubber concentration of 5% by weight.
If it is less than that, the amount added when forming into a sheet will increase,
This is not preferable because the production cost of the sheet increases. Moreover, if it exceeds 9% by weight, the viscosity of the polymer solution during polymerization of rubber-modified polystyrene becomes high, making it difficult to produce a graft copolymer, and the addition amount when forming into a sheet is small, which affects the physical properties of the sheet. This causes variation. Generally, a styrene polymer blended with a small amount of synthetic rubber is extruded from a die into a sheet to form fine irregularities on its surface, and then biaxially stretched to form synthetic rubber particles. When stretched flat, the transparency is almost the same as that of a biaxially stretched polystyrene sheet that does not contain synthetic rubber, and the surface of the sheet is uneven to the extent that it does not impair gloss. It is known that this surface unevenness improves the printability and mold release properties of the sheet, but this effect also varies depending on the concentration and particle size of the synthetic rubber.
It is thought that the effect mainly improves as the concentration of rubber increases. However, when increasing the rubber concentration,
The transparency of the sheet after stretching decreases. In order to add more rubber with a normal particle size than before and create unevenness on the surface, which is expected to be effective, and maintain transparency, it is necessary to use a synthetic rubber whose refractive index is as close as possible to that of the base polystyrene. is necessary. The reason why the rubber concentration of the styrene-based resin used in the present invention was specified as 0.2 to 0.5% by weight is because the sheet has a degree of cloudiness that does not impair the transparency of conventional polystyrene biaxially stretched sheets, and more specifically,
ASTM D- for 0.02cm gauge thick sheets
In order to obtain a biaxially oriented sheet with a haze degree of 1% or less that complies with the 1003 method, the rubber concentration of the styrene resin must be adjusted.
Must be 0.5% or less. In addition, in order to enhance the mold release effect, as mentioned above, the surface of the sheet needs to have a certain level of unevenness, and in order to create this surface roughness, the rubber This is because it is necessary to add a graft copolymer of styrene and styrene-butadiene rubber in a concentration of 0.2% by weight or more. Additives that further improve the mold release effect include:
Use MFPS. This is because the refractive index is close to that of styrene polymer, so even if the amount added increases, the clouding phenomenon hardly occurs. In order to improve the mold release effect, the amount added must be 0.1% by weight or more, and if it is less than 0.1% by weight, no effect will be observed. There is no upper limit to the amount added, but
If it exceeds 0.5% by weight, no increase in effect can be expected even if the amount added is increased. Biaxial stretching as used in the present invention refers to biaxial stretching performed by the generally known tenter biaxial stretching method, inflation biaxial stretching method, and the like. The normal stretching method is the tenter method.
In both the vertical and horizontal directions, the size is 2.5 times to 5 times, and in the case of the inflation method, the size can be obtained in the range of 2 to 30 times both in the vertical direction and the horizontal direction, and is appropriately selected depending on the purpose. The principle of the present invention is effective regardless of the stretching method. Using the biaxially stretched sheet obtained by the above method, a large number of containers were formed using a hot plate forming machine, stacked, and punched using a die press.The containers were then peeled off by hand. Regarding releasability, there is no difference at all from that of a sheet with silicone oil emulsion applied to the surface of the sheet.
Furthermore, when this sheet was subjected to printing, the adhesion of the printing ink was good and no printing unevenness occurred at all. In this way, completely contradictory effects of mold releasability and printability were produced. The present invention will be further explained below with reference to Examples. Examples 1 to 16 Rubber modified with styrene butadiene rubber containing 30% by weight of styrene and grafted with polybutadiene rubber having an average particle size of 2μ or 6μ. Rubber-modified polystyrene consisting of a graft copolymer containing 6% by weight of polybutadiene rubber Polystyrene manufactured by Denki Kagaku Kogyo Co., Ltd. under the trade name “Denka Styrol HRM-”
6", add 0.1 and 0.3% by weight of methylphenylpolysiloxane to increase the rubber concentration to 0.2~
The content was adjusted to 0.5% by weight. This resin was extruded into a sheet using an extruder manufactured by Toshiba Machine Co., Ltd. under the trade name "SE-65", and stretched 3 times vertically and horizontally using a tenter method to form a sheet with a gauge thickness of 0.02 cm. The transparency of the sheets was measured in accordance with the ASTM-D-1003 method, and as a result, the degree of haze was 1% or less, which was good. The sheet is then processed using a hot plate pressure air forming machine (Kansai Jidoki Machinery Co., Ltd.).
Co., Ltd., product name "PK-400"), and then stacked 20 sheets each and punched them using a die press.
A packaging test was carried out using "No. 22", and the results showed that the packaging was carried out completely smoothly, and there were no problems with the peelability between the molded products. Further, the sheet was printed using a gravure printing machine manufactured by Higashiya Tekko Co., Ltd. using Toyo Ink Co., Ltd.'s trade name "Styrene B." As a result, there is no blurring in the version,
The print finish was good. Furthermore, the adhesion of the ink was examined using a commercially available adhesive tape, and the results showed that it was good. The results are shown in Table 1.

[Table] Comparative Examples 1 to 10 The type of rubber in the graft copolymer of Example was changed to polybutadiene, and the average rubber particle size was 2μ and
A resin mixed with 0.1 to 0.6% by weight so that it is 6μ,
A stretched sheet was prepared, and then silicone oil emulsion (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KM-787") was applied to it, and the test was carried out under the same conditions as in the examples. Although the results were shown, nothing satisfying transparency, mold releasability, and printability could be obtained.

[Table] The physical properties shown in Tables 1 and 2 of Examples and Comparative Examples were determined by the following method. (1) Transparency Cloudiness (%) according to ASTM D-1003 law
showed that. (2) Mold releasability Evaluated by the number of troubles in the automatic packaging machine. ◎ 0 times for 200 trays 〇 〃 1 to 3 times △ 〃 3 to 10 times × 〃 10 times or more (3) Printability The ink adhesion was evaluated on a five-grade scale by cellophane tape peeling. Note that evaluations 4 and 5 pose no practical problem. 5... No peeling at all 4... Light transfer to cellophane tape 3... Partial peeling 2... Approximately 1/2 peeling 1... Almost entire peeling

Claims (1)

[Claims] 1 0.1 to 0.5% of methylphenyl polysiloxane is added to a mixture of a graft copolymer and a styrene polymer with a rubber concentration of 5 to 9% by weight, which is obtained by grafting styrene onto styrene-butadiene rubber containing 20 to 40% by weight of styrene. Weight% added rubber concentration 0.2~
A biaxially stretched styrene resin sheet characterized by biaxially stretching a 0.5% by weight styrene resin composition.