JPH05318580A - Biaxially stretched synthetic resin sheet - Google Patents

Abstract

PURPOSE:To obtain a biaxially stretched styrene series resin film having excellent oil resistance. CONSTITUTION:The biaxially stretched synthetic resin sheet is obtained by biaxially stretching a two-type two-layer laminate obtained by so eutectically extruding styrene-methacrylate copolymer (containing 3wt.% of methacrylate) and polystyrene by a T die as to become 5/95 of a layer ratio (%), and the copolymer layer side is used as a surface in contact with oil. Thus, the resin having excellent white keeping oil resistance and coconut oil resistance as compared with those of a polystyrene single-layer biaxially stretched film is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched synthetic resin sheet, and more specifically, a light weight container for food packaging such as a lid of a lunch box, which is required to have oil resistance without impairing the excellent characteristics of the OPS sheet, Also, the present invention relates to a sheet requiring oil resistance and a biaxially stretched styrene resin sheet having excellent oil resistance used in various containers.

[0002]

2. Description of the Related Art Biaxially oriented polystyrene sheet (hereinafter referred to as O
PS sheet) is often used for packaging lightweight food packaging containers and other products because it does not contain substances that are harmful to the human body and has excellent waist strength, transparency, and moldability. It is used.

However, OPS sheets generally have poor oil resistance. For example, when the sheet is used as a lid material for a lunch box, the lunch box container may be cracked when the lunch boxes are packed in a container and then stacked and stocked. This is generally OPS
It is believed that the sheet is susceptible to white keep oil, which is often used as a luster of cooked rice and a release agent after molding of cooked rice that is molded and packaged in a container.

As described above, although a styrene-based resin sheet having oil resistance has been desired as a differentiated product of the OPS sheet, it has not been practically available.

[0005]

Under the circumstances, the present inventors can collect the scrap sheet while maintaining the rigidity, transparency, formability, etc., which are the characteristics of the OPS sheet. In addition, the present invention is intended to provide a laminated biaxially stretched synthetic resin sheet that is more oil resistant than conventional OPS sheets.

[0006]

[Means for Solving the Problems] The inventors of the present invention have studied to solve the oil resistance among the above problems, and found that the aromatic vinyl-based resin is not biaxially stretched but the aromatic vinyl-based resin. It was found that a biaxially stretched sheet having a surface excellent in oil resistance can be obtained by laminating an oil-resistant aromatic vinyl-based resin on and then biaxially stretching this.

Moreover, the oil-resistant aromatic vinyl-based resin is a copolymer obtained by polymerizing aromatic vinyl and ethylenically unsaturated carboxylic acid as essential components, and the ethylenically unsaturated carboxylic acid polymer units are When 1% by weight or more and less than 4% by weight of the total weight of the copolymer is used, a sheet having not only oil resistance but also good transparency can be obtained, and further, at the time of sheet production or when the sheet is molded and punched It was also found that the generated scrap can be collected and reused in the same sheet and is economical, and the present invention has been completed.

The present invention will be described in detail below. The sheet of the present invention comprises two layers of an oil resistant aromatic vinyl resin and an aromatic vinyl resin.

The oil-resistant aromatic vinyl resin is, for example, a copolymer resin obtained by polymerizing ethylenically unsaturated carboxylic acid and aromatic vinyl as essential components. Examples of the ethylenically unsaturated carboxylic acid include acrylic resins. Acid, methacrylic acid, maleic anhydride, itaconic acid and the like, and examples of the aromatic vinyl include vinyl monomers having an aromatic ring such as styrene and α-methylstyrene. In addition, aromatic vinyl or ethylenically unsaturated carboxylic acid may be added to, for example, methyl (meth) acrylate or stearyl (meth) as necessary.
You may use together (meth) acrylic acid alkyl ester, such as an acrylate.

The oil-resistant aromatic vinyl resin preferably contains 1% by weight or more of an ethylenically unsaturated carboxylic acid polymerized unit in terms of good oil resistance of the obtained sheet. When the polymerized unit is used in an amount of 1% by weight or more and less than 4% by weight, oil resistance in tempura oil, rapeseed oil, almond oil, etc. is superior to that of the OPS sheet, and at the time of recovery of the sheet, an oil resistant aromatic vinyl type The difference in the refractive index between the resin component and the conventional aromatic vinyl-based resin having no oil resistance is remarkably small, and the sheet obtained is not clouded even when reused, which is particularly preferable.

The aromatic vinyl resin in the present invention means
Any resin that does not have oil resistance, such as the oil-resistant aromatic vinyl-based resin described above, may be used, and examples thereof include polystyrene.

The aromatic vinyl resin preferably has a weight average molecular weight of about Mw = 25 × 10 ⁴ for the aromatic vinyl resin and about Mw = 24 × 10 ^{4 for} the oil-resistant aromatic vinyl resin. .

The laminated biaxially stretched synthetic resin sheet of the present invention comprises
An oil-resistant aromatic vinyl-based resin is laminated on one surface of the aromatic vinyl-based resin, and the laminate may be biaxially stretched as a whole, and the manufacturing method thereof is not particularly limited. .

As a method for laminating the oil-resistant aromatic vinyl-based resin on one side of the aromatic vinyl-based resin, there is a method of adhering them with an adhesive, but a method of hot melt extrusion is generally used.

In the extrusion at this time, each resin is usually 200 to 250 ° C. which is the condition of polystyrene sheet.
It is carried out by melt-extruding with a T-die and laminating at the resin temperature of.

The layer ratio of the aromatic vinyl-based resin and the oil-resistant aromatic vinyl-based resin in this laminate is not particularly limited, but when the total thickness (total thickness) is 100%, the oil-resistant aromatic vinyl-based resin is used. The layer thickness of 3 to 20% is preferable because it is excellent in both oil resistance and cost balance.

For biaxial stretching of the laminate as described above, various biaxial stretching methods such as sequential biaxial stretching and simultaneous biaxial stretching can be adopted. Specific conditions include, for example, a draw ratio of 1.
5 to 4 times, a stretching temperature of 120 to 150 ° C., a sheet thickness of 0.05 to 1.0 mm, and an OS value as an orientation relaxation stress of 1.5 to 13 are preferably performed. It is preferable that the stretching temperature is within the above range because the sheet will not be stretched and the expected OS value is easily exhibited. When the OS value is in the range of 1.5 to 13, not only the resulting sheet has good folding crackability, but also the sheet has very good moldability itself. However, when the molecular weight of the aromatic vinyl resin becomes larger, it becomes 1.5 to 13
Even if it deviates from the range, the sheet tends to have a better fold cracking property and the sheet has a better moldability.

The laminated biaxially stretched sheet of the present invention has a general O content.
A slip material, an antistatic agent, a release agent, an antifogging agent, etc. which are commonly used for PS sheets are contained in the aromatic vinyl resin layer or oil-resistant aromatic vinyl resin layer of the sheet, if necessary. You can also do it.

In the biaxially stretched sheet of the present invention thus obtained, the oil resistant aromatic vinyl resin layer may be used as the surface requiring oil resistance. The biaxially stretched sheet of the present invention,
The desired container, lid material and the like can be easily obtained by thermocompression molding with a die having a predetermined shape under the same conditions as in the conventional biaxially oriented polystyrene sheet.

[0020]

EXAMPLES Next, the present invention will be described in detail with reference to Examples, but it goes without saying that the biaxially stretched sheet of the present invention is not limited to these Examples. Example 1 In the layer constitution of the sheet, 5 oil-resistant aromatic vinyl resin layers were used.
A 0 mm diameter, aromatic vinyl resin layer was melted at a resin temperature of 230 ° C. using a coextrusion machine having a diameter of 65 mm, and 2 types 2
After passing through the layer distributor, extruded from the T-die, thickness 1.0
A mm laminated sheet was prepared. The oil-resistant aromatic vinyl-based resin (B) and aromatic vinyl-based resin (A) are listed in Table 1.
Those shown in were used respectively.

[0021]

[Table 1] Using a biaxial stretching device, a sheet cut into a length of 10 cm and a width of 10 cm is stretched 2.2 times in both longitudinal and transverse directions according to ASTMD.
0.21 mm in thickness by stretching at a temperature of 130 ° C. so that the orientation relaxation stress measured according to −1504 is 6.0.
Got a sheet of. This sheet consisted of two layers, an oil resistant aromatic vinyl resin layer 5% and an aromatic vinyl resin layer 95%.

Tensile properties (JIS
K-7127), tear strength (JISP-8116), and moldability (in-house method using a compressed air molding machine) were respectively measured, and all had equivalent performance to the OPS sheet of Comparative Example 1 described later. .

Further, the white-keeping oil resistance and the coconut oil resistance of this sheet were measured. The results are shown in Tables 2 and 3. The oil resistance was measured by the following method. [Oil resistance] Heating pressure 1.0 Kg / cm ² , molding pressure 3.
0 kg / cm ² , molding time 1.5 seconds, mold temperature 40 ° C.,
Under the condition of the hot plate temperature of 130 ° C., the lid of the bento was molded by the pressure molding method so that the oil resistant aromatic vinyl resin layer was on the inside. Apply oil to the inner surface of the lid of this lunch box, and in a specified atmosphere,
The oil resistance was compared.

Judgment Criteria Sheet Surface: Good;
Δ: Cloudy, ×: White Comparative Example 1 The oil-resistant aromatic vinyl-based resin layer (B) in a 50 mm diameter extruder was replaced with the same aromatic vinyl-based resin (A) in a 65 mm diameter extruder. Except for the above, a sheet of aromatic vinyl resin (A) single layer was obtained in the same manner as in Example 1, and the sheet was stretched at the same magnification, orientation relaxation stress and temperature as in Example 1 to give a thickness of 0.21 mm. Got the sheet. The white-keeping oil resistance and the coconut oil resistance of this sheet were measured in the same manner as in Example 1. The results are shown in Tables 2 and 3.

[0025]

[Table 2]

[0026]

[Table 3] In addition, when the sheet of Example 1 is used as a lid material for a lunch box,
The bento containers did not crack even if they were stacked and stocked after they were packed.

[0027]

The biaxially stretched sheet according to claim 1 of the present invention is a biaxially stretched sheet of a two-layer laminate of aromatic vinyl resin / oil resistant aromatic vinyl resin, so that the oil resistant surface is oil resistant. If the molding is carried out so that the aromatic vinyl resin layer comes, a molded article which is remarkably excellent in oil resistance can be obtained as compared with the molded article of the biaxially stretched sheet of the aromatic vinyl resin single layer.

Since the sheet according to claim 2 uses an oil-resistant aromatic vinyl resin containing a specific amount of an acid component, the sheet itself is excellent not only in oil resistance but also in transparency. Further, even if it is used as a mixture with an aromatic vinyl-based resin, the risk of clouding is extremely small.

Since the sheet according to claim 3 uses the oil-resistant aromatic vinyl-based resin layer in a specific layer ratio, it can be regarded as an aromatic vinyl-based resin single-layer sheet and can be recovered, that is, scrap can be recovered. Yes, it is extremely economical.

Further, not only the sheet of the present invention but also the molded container obtained therefrom is recovered and reused (recycled) as an aromatic vinyl resin single layer sheet.
Therefore, the effect of the invention is very large from the viewpoint of protecting the global environment.

Claims (3)

[Claims] 1. An oil-resistant laminated biaxially stretched synthetic resin sheet obtained by biaxially stretching a bilayer laminate in which an oil-resistant aromatic vinyl-based resin and an aromatic vinyl-based resin are laminated. 2. An oil-resistant aromatic vinyl-based resin is a copolymer obtained by polymerizing aromatic vinyl and an ethylenically unsaturated carboxylic acid as essential components, and the ethylenically unsaturated carboxylic acid polymer units are those units. 1% by weight or more in the total weight of
The sheet according to claim 1, which is less than 4% by weight of a copolymer. 3. The sheet according to claim 1, wherein the oil-resistant aromatic vinyl resin layer is 3 to 20% when the total thickness is 100%.