JPH04236240A - High-strength biaxially orientated styrenic resin sheet - Google Patents

Abstract

PURPOSE:To obtain the title sheet having a shortened molding cycle in vacuum molding and pressure forming by molding a styrenic resin comprising a specific styrenic monomer, an acrylic ester monomer and methyl methacrylate into a sheetlike state. CONSTITUTION:A styrenic resin comprising (A) 40-89 wt.% constituent unit shown by formula I (R1 is H or methyl; R2 is H or 1-5C alkyl), (B) 0.5-20wt.% constituent unit shown by formula II (R3 is H or methyl; R4 is 2-8C alkyl) and (C) 10-55wt.% constituent unit shown by formula III is made into a sheetlike state by an extruder, etc., and orientated by a drawing device, etc., to give the objective high-strength orientated styrenic resin sheet not causing draw cracks during trimming. The sheet has preferably 1-15kg/cm<2> orientation relaxing stress.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a biaxially oriented styrene system with excellent transparency that shortens the molding cycle during vacuum forming and pressure forming, increases toughness, and prevents punching and cracking during trimming of molded products. Regarding resin sheets.

0002

BACKGROUND OF THE INVENTION Conventional biaxially oriented polystyrene resin sheets are widely used in lightweight containers for storing food products because of their excellent stiffness, transparency, and moldability. Biaxially oriented polystyrene resin sheets are thermoformed into various lightweight containers using vacuum forming and pressure forming machines. Shortening the molding cycle during thermoforming improves productivity, so biaxially oriented styrene can shorten the molding cycle. There is a demand for resin sheets based on this type of resin.

In order to shorten the molding cycle, attempts have been made to create biaxially oriented polystyrene resin sheets that have less molecular orientation due to stretching and lower orientation relaxation stress, and biaxially oriented polystyrene resin sheets that have lower molecular weight. but,
There was a problem in that the molded products would break when they were overlapped and trimmed. Furthermore, in order to shorten the molding cycle, attempts have been made to use biaxially oriented polystyrene resin sheets to which internal plasticizers have been added, but no significant improvement effect has been observed. In addition, attempts have been made to use biaxially oriented styrenic resin sheets blended with rubber-like elastic materials, such as styrene-butadiene block copolymers, to increase strength. No improvement effect was observed. Moreover, transparency also deteriorates. Also, sheets,
If the remaining portion of the molded product is reused, there is a problem in that the rubber-like elastic body gels, deteriorating the appearance of the sheet surface.

[0004] With conventional styrene-based resins, due to the high heat resistance of polystyrene, little improvement has been made in shortening the molding cycle, and the market demands a balance between strength, transparency, and molding cycle. The situation is that the level has not been reached. Rigid vinyl chloride sheets (PVC sheets) are often used as food storage containers and packaging materials. PV
C sheet is a resin sheet with an excellent balance of moldability, strength, transparency, and cost, but due to recent environmental issues, P sheet
There is a demand for a resin sheet that can replace VC resin sheets. Currently, polypropylene resin sheets, amorphous polyester resin sheets, and styrene-butadiene copolymer sheets are being considered as alternatives to PVC resin sheets, but none of them satisfy the balance of moldability, strength, transparency, and cost. is the current situation.

[0005]

[Means for Solving the Problems] In view of the current situation, the present inventors have developed a styrene resin consisting of a styrene monomer, an acrylic acid ester (methacrylic acid ester) monomer, and methyl methacrylate. We have conducted intensive studies to develop a biaxially oriented styrenic resin sheet with excellent transparency that shortens the molding cycle during molding, has increased toughness, and finally arrived at the present invention.

That is, the present invention provides the following general formula (A),

[0007]

[C4]

[0008] The following general formula (B),

[0009]

[C5]

[0010] The following general formula (C),

[0011]

[C6]

It consists of the structural unit shown as
The ratio of A), (B), and (C) is (A): 40 to 89% by weight (B): 0.5 to 20% by weight (C): 10 to 55% by weight (However, (A) + ( The present invention provides a biaxially oriented styrenic resin sheet with excellent strength, characterized in that it is formed of a styrene resin consisting of (B) + (C) = 100% by weight). Furthermore, the present invention provides a biaxially oriented styrenic resin sheet according to claim 1, characterized in that the orientation relaxation stress of the biaxially oriented styrenic resin sheet is 1 to 15 kg/cm<2>.

The present invention will be explained in detail below. Constituent unit (
The amount of B) is between 0.5 and 20% by weight. More preferably, it is in the range of 2 to 15% by weight. When the amount is less than 0.5% by weight, the heat resistance decreases so much that molding at low temperatures becomes difficult. If it exceeds 20% by weight, it is not preferable because the heat resistance will be greatly reduced and the practical temperature of the product molded from the sheet will be low, greatly restricting the range of use. The amount of structural unit (C) is 10-55% by weight. More preferably 20-4
It is 5% by weight. If it is less than 10% by weight, the strength improvement of the biaxially stretched resin sheet will be small, and if it exceeds 55% by weight, the rate of strength improvement will be small. Moreover, this is not preferable because it increases the cost of the styrene resin.

The degree of polymerization of the styrenic polymer of the present invention is not particularly limited, but the viscosity of a 10% by weight toluene solution at 25° C. is 20 centipoise to 20 centipoise, taking into account the shape of the molded product, the purpose of use, etc. In the region of 80 centipoise,
More preferably, it is set in the range of 25 centipoise to 70 centipoise. The viscosity of a 10% by weight toluene solution is 2
If the viscosity is less than 0 centipoise, it will be difficult to obtain a biaxially oriented styrenic resin sheet with excellent strength, and if the viscosity exceeds 80 centipoise, the extrusion processability of the styrenic resin will be extremely degraded, making it impractical. isn't it.

In the present invention, the structural unit (A) includes, for example, those having the following structure.

[0016]

[C7]

Examples of the structural unit (B) include those having the following structure.

[0018]

[Chemical formula 8]

To produce the styrenic resin for obtaining the biaxially oriented styrenic resin foam of the present invention, methods known for producing styrenic resins, such as bulk polymerization and solution polymerization, are used. Moreover, at this time, it is also possible to use a polymerization initiator commonly used in the production of styrene resins. In addition, it is possible to polymerize styrenic resins with a uniform composition using a complete mixing reactor, which is often used in the copolymer manufacturing method, or a tubular reactor, or a combination of a complete mixing reactor and a tubular reactor. A styrenic resin having a non-uniform composition may be produced using a device. However, styrenic resins that are opaque, which greatly restricts the range of use, or have non-uniform compositions that cause phase separation during extrusion, molding, etc., are not preferred. In this case, it is possible to maintain usable transparency by adding additional raw materials, which is commonly used in the production of styrenic resins, and to control the composition to a level that does not cause phase separation. is necessary.

Styrene is preferably used as the styrenic monomer used to obtain the styrenic resin which is the base material of the present invention. As the acrylic ester (methacrylic ester) monomer, butyl acrylate, butyl methacrylate, etc. can be used. These monomers can be used alone or in combination. In order to create the biaxially oriented styrenic resin sheet according to the present invention, after extruding the styrene resin into a sheet using an extruder, the sheet is stretched using a generally known tenter method, inflation method, etc., and the stretching ratio is It is preferable to increase the amount by 2 to 5 times. The biaxially oriented styrenic resin sheet according to the present invention is AS
Orientation relaxation stress measured in accordance with TM D-1504 is 1 to 15 Kg/cm2, more preferably 2 to 10 K
It is preferable that the film be biaxially stretched so as to have a molecular weight within the range of g/cm2. If the orientation relaxation stress exceeds the above range, molding cannot be performed using a general molding machine, and only molded products with poor mold reproducibility can be obtained. Moreover, if it is less than the above range, the strength of the sheet will be weak and a phenomenon during trimming will occur, which is not preferable.

The biaxially oriented styrenic resin sheet according to the present invention has good moldability, and can be vacuum formed by a straight method or drave method, or hot plate pressure forming (contact heating pressure forming).
Alternatively, the molding cycle can be shortened when molding lightweight containers, lids, etc. by indirect heating and pressure molding using the straight method, drape method, or plug assist method. The biaxially oriented styrenic resin sheet according to the present invention has high sheet strength, and no punching cracks occur in the molded product during trimming. Furthermore, by increasing the amount of the structural unit (B), the glass transition temperature of the biaxially oriented styrenic resin sheet is lowered, so that it is also possible to mold it under the same molding conditions as for a hard PVC sheet.

[0022] In obtaining the biaxially oriented styrenic resin sheet, plasticizers, lubricants, antistatic agents, pigments, flame retardants, etc. may be used in combination. Further, an antistatic agent, silicone, antibacterial agent, etc. may be applied to the surface of the obtained biaxially oriented styrenic resin sheet or sheet molded product. It is also possible to mix and use the specific styrenic resin used in the present invention with other styrenic resins within a range that does not impair the function of the biaxially oriented styrenic resin sheet intended in the present invention. In addition, in the present invention, the viscosity of a 10% by weight toluene solution, which is a measure of the degree of polymerization, is determined using the Ostwald-Cannon-Fenske viscosity tube 5.
0 in a constant temperature bath at 25°C.

The proportions of structural units (A), (B), and (C) are determined by the following method. After dissolving the biaxially stretched styrene resin sheet in methyl ethyl ketone, methanol is added to precipitate the styrenic resin. Using the styrene resin pretreated in this way, JASCO Corporation JNM-GX27
0 FT-NMR is used to measure 1H under the conditions described below.

(1H measurement) Pulse width = 8.4 μs Data points = 16384 Repetition time = 7.559 seconds AD converter = 16 bits Number of integration = 1,000 Sample concentration = 10 wt% Solvent = 1, 1, 2, 2 -tetrachloroethane-(d2)
Sample tube = 5 mm Measurement temperature = 120°C A peak derived from the hydrogen of the phenyl group of the structural unit (A) appears at 6.2 to 7.4 ppm. A peak derived from hydrogen in the structural unit (B) appears at 3.4 to 3.8 ppm. Moreover, a peak derived from the methyl groups of the structural units (B) and (C) appears at 0.2 to 1.1 ppm. A peak separation operation is performed to determine the weight percent of the structural unit (A), structural unit (B), and structural unit (C) from the peak area ratio.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

[0026]

[Example] The physical property test method in the example is described below. Melt flow rate (MFR): ISO R1133
According to. Vicat Softening Point (VICAT): ASTM D152
According to 5. Single-hit impact strength: Using Toyo Seiki Seisakusho's "Drop Weight Graphic Impact Tester," a missile with a mass of 6.5 kg is allowed to fall naturally from a height of 20 cm, and the maximum severity of destruction is determined.

Transparency: Measured according to ASTM D1003. (Styrenic polymer-1) 1 part by weight of butyl acrylate, 66 parts by weight of styrene, 33 parts by weight of methyl methacrylate, 2.98 parts by weight of ethylbenzene, 1,1-bis(t
A raw material solution consisting of 0.02 parts by weight of -butylperoxy)cyclohexane was continuously supplied to a 5 L complete mixing reactor and polymerized at a polymerization temperature of 120°C. The average residence time in the reactor is 5 hours. The polymerization solution exiting the reactor is led to an extruder, where unreacted monomers and polymerization solvent are recovered from a vent.
Pelletize. (Styrenic Polymer-2) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that 2 parts by weight of butyl acrylate, 64 parts by weight of styrene, and 34 parts by weight of methyl methacrylate are used. (Styrenic polymer-3) 4.5 parts by weight of butyl acrylate, 62 parts by weight of styrene, 33 parts by weight of methyl methacrylate
．． A styrenic polymer is obtained by the same operation as for styrenic polymer-1 except that the amount is 5 parts by weight. (Styrenic polymer-4) 9.5 parts by weight of butyl acrylate, 57 parts by weight of styrene, 33 parts by weight of methyl methacrylate
．． A styrenic polymer is obtained by the same operation as for styrenic polymer-1 except that the amount is 5 parts by weight. (Styrenic Polymer-5) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that 13 parts by weight of butyl acrylate, 53 parts by weight of styrene, and 34 parts by weight of methyl methacrylate are used. (Styrenic polymer-6) Butyl acrylate 15.5
A styrenic polymer is obtained in the same manner as in styrenic polymer-1 except that the parts by weight are 50.5 parts by weight of styrene and 34 parts by weight of methyl methacrylate. (Styrenic polymer-7) 8 parts by weight of butyl acrylate, 73.5 parts by weight of styrene, 18 parts by weight of methyl methacrylate
．． A styrenic polymer is obtained by the same operation as for styrenic polymer-1 except that the amount is 5 parts by weight. (Styrenic polymer-8) 9.5 parts by weight of butyl acrylate, 51 parts by weight of styrene, 39 parts by weight of methyl methacrylate
．． A styrenic polymer is obtained by the same operation as for styrenic polymer-1 except that the amount is 5 parts by weight. (Styrenic Polymer-9) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that styrene is used in an amount of 100 parts by weight. (Styrenic polymer-10) Butyl acrylate 7.5
A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that the parts by weight are 85.5 parts by weight of styrene and 7 parts by weight of methyl methacrylate. (Styrenic Polymer-11) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that 67 parts by weight of styrene and 33 parts by weight of methyl methacrylate are used.

Table 1 shows the results of measuring the physical properties of the styrene polymer.

[0029]

[Examples 1 to 8, Comparative Examples 1 to 3] Styrenic resin was extruded using a 50 mmφ extruder to prepare sheets with a thickness of 0.75 mm. 10 cm long and 10 cm wide using a biaxial stretching device
AS of 3 times the sheet cut into cm in both the vertical and horizontal directions
120°C to 130°C so that the orientation relaxation stress measured in accordance with TM D-1504 is 8 to 9Kg/cm2.
A biaxially stretched styrene resin sheet having a thickness of 150 μm was obtained by stretching at a temperature of °C.

The obtained styrene resin sheet was thermoformed using a hot plate air pressure molding machine. Heating pressure 1.0Kg/
cm2 and molding pressure 2.5Kg/cm.
2. Molding was performed under the conditions of a molding time of 2.0 seconds and a mold temperature of 60°C, and a heating time that could be reproduced as the hinge 3R mold of the mold (food pack) was determined at a hot plate temperature of 115°C and 130°C. In addition, the transparency (HAZE) of all biaxially stretched sheets is 4.
It was 0 to 4.2%. The single impact impact strength of this sheet was also determined. The results are shown in Table 2.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

Effects of the Invention The biaxially oriented styrenic resin sheet of the present invention can be molded at a lower temperature than conventional biaxially oriented styrenic resin sheets. Furthermore, the strength of the biaxially oriented styrene resin sheet has been significantly improved. The biaxially oriented styrenic resin sheet of the present invention has significantly better formability and strength balance than conventional biaxially oriented styrenic resin sheets, and has excellent transparency that conventional biaxially oriented styrenic resin sheets had. Maintained.

Claims (2)

[Claims] [Claim 1] Consisting of a structural unit represented by the following general formula (A), [Chemical formula 1] the following general formula (B), [Chemical formula 2] the following general formula (C), [Chemical formula 3], the structural unit (A ), (B)
, (C) is (A): 40-89% by weight (B): 0.5-20% by weight (C): 10-55% by weight (However, (A) + (B) + (C) A biaxially oriented styrenic resin sheet with excellent strength, characterized in that it is formed of a styrene resin consisting of 100% by weight). 2. The biaxially oriented styrenic resin sheet according to claim 1, wherein the orientation relaxation stress of the biaxially oriented styrenic resin sheet is 1 to 15 kg/cm 2 .