JPH043417B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-resistant and transparent biaxially stretched thermoplastic resin sheet, and more specifically, a biaxially stretched thermoplastic resin sheet that is transparent, has high heat resistance, oil resistance, and has excellent secondary processability such as thermoforming. It is related to. Biaxially stretched styrene resin sheets are widely used in various food packaging containers due to their transparency and excellent secondary processability such as thermoforming, but their heat resistance is around 80°C, so they are not suitable for heated foods. It could not be used for food packaging, containers that require sterilization at high temperatures of around 100°C, such as steam heating, or food packaging containers with high oil content, such as tempura. In order to solve this technical problem, a patent application was filed in 1983 as a resin with excellent transparency, heat resistance, oil resistance, and secondary processability.
95832 and the like, thermoplastic resins containing specific six-membered ring compounds have been proposed. That is, (A) general formula (R ₁ and R ₂ in the formula are 5 to 85% by weight, preferably 20 to 60% by weight of six-membered cyclic acid anhydride units represented by a hydrogen atom or a methyl group, and (B) 1 to 80% by weight of methyl methacrylate units. % by weight, preferably 20-50% by weight, (C) aromatic vinyl compound unit 1-65% by weight,
Preferably 5 to 40% by weight and (D) methacrylic acid or acrylic acid units 0.5 to 10
It is a copolymer having a composition of % by weight. However, in order to biaxially stretch the present quaternary copolymer, there were more problems than in stretching a thermoplastic resin having high heat resistance. That is, the quaternary copolymer is produced by a condensation cyclization reaction between (B) component methyl methacrylate, (D) component methacrylic acid or acrylic acid, and (D) component (A).
The component 6-membered cyclic acid anhydride is produced,
In order to perform biaxial stretching, it is necessary to plasticize and mix the resin well using an extruder with good kneading properties in order to uniformly thermoplasticize the resin. Due to the long thermal history due to the overheating and soaking process, the pressurized molten resin is released from the extrusion die under atmospheric pressure, making it easy to foam. Even if a bubble source occurs, the bubbles expand due to biaxial stretching, and in any case, appearance defects like volatile pit marks tend to appear, which is a very difficult problem in terms of practical appearance and strength. It is. As a result of intensive studies from this point of view, we found that the quaternary copolymer resin of the present application has a value obtained by dividing the weight% of component (A) by the weight% of component (D) at 3 or more, preferably at least 10, and more preferably at least 15. The present invention was completed by making a biaxially stretched sheet using the following. That is, although it depends on the manufacturing equipment and manufacturing conditions of the biaxially stretched sheet, if the value obtained by dividing the weight percent of component (A) by the weight percent of component (D) is 3 or less, many air bubbles will occur and the surface will not be smooth. It is not possible to obtain a large and transparent sheet. In addition, the molecular weight of the quaternary copolymer also affects the biaxial stretchability, and the copolymer concentration of 10% by weight methyl
The viscosity of ethyl ketone solution at 25℃ is 7
~20 centipoise is important. If it is less than 7 centipoise, the melt viscosity is low, making it difficult to stretch uniformly, and it is brittle.If it is more than 20 centipoise, the strength is strong, but the uniform extrudability is poor and the biaxial drawing property is poor. The heat-resistant and transparent biaxially stretched sheet according to the present invention is obtained by stretching the above-mentioned copolymer in the biaxial direction within a range of 1.5 times to 5.0 times. To biaxially stretch the above-mentioned copolymer, a generally known tenter method, inflation method, or the like may be employed. If the stretching ratio is less than 1.5 times, the toughness of the sheet will not improve, which is undesirable.
If the thickness is more than twice that, it is not preferable because when a container is manufactured by so-called thermoforming such as a vacuum forming method and/or a pressure forming method, uneven thickness of the sheet tends to occur when the sheet is heated. Stretching is 2.0 in biaxial direction
Particularly preferred is one that has been stretched almost evenly within the range of ~3.0 times. Further, the identification of the biaxially stretched sheet and the magnification of the biaxially stretched sheet are quantified by measuring the heating expansion/contraction rate of the sheet. The heating expansion/contraction rate measurement method is based on JIS K6872, and the heating temperature is 130±2℃ for polystyrene, but since the sheet of this application has high heat resistance, the heating temperature is 150±2℃ for sheets with a thermal deformation onset temperature of 110℃ or lower. Heat at 2℃,
170 for those with a thermal deformation onset temperature of 110℃ or higher.
Heating and measuring at ±2℃ Also, the heating time is JIS
It is the same 30 minutes as K6872. The heating expansion/contraction rate S as defined in JIS K6872 is expressed by the following formula. S=l ₂ −l ₁ /l ₁ ×100 l ₁ : Distance between marked lines before heating l ₂ : Distance between marked lines after heating By the way, the stretching ratio A in this application is A=S=l ₁ /l Represented by ₂ . That is, S = -60% Heat shrinkage rate -60%, that is, a sheet that has been heat-shrinked by 60% means a sheet with a stretching ratio A of 2.5 times. A well-balanced stretching ratio in both vertical and horizontal directions, with approximately the same stretching ratio, is useful for practical use. For example, if a sheet with a vertical and horizontal stretching ratio of 3 x 2.5 times, the mold reproducibility when thermoforming is 2.5 x
Not better than a 2.5x sheet. Heat-resistant and transparent 2 of the present invention obtained in this way
The axially stretched thermoplastic resin sheet has the following characteristics. (1) The moldability of conventional biaxially oriented polystyrene sheets is not impaired, and they are transparent and smooth, and depending on the composition, they have better transparency and clearness than polystyrene. (2) Practical heat resistance has been improved by 10 to 30°C over biaxially oriented polystyrene sheets, and it has heat resistance that does not cause dimensional or appearance changes even when used for boiling food containers and packaging or pressurized steam cooking food containers and packaging. have (3) Superior oil resistance than biaxially oriented polystyrene sheets. (4) The heat-resistant and transparent biaxially stretched styrenic resin sheet according to the present invention has been properly stretched, so it has high impact resistance and does not cause uneven sheet thickness due to heating during container manufacturing. Never. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless the gist of the present invention is exceeded. The basic idea is to use JIS, etc., as much as possible for the physical properties in each example, but just in case, an overview of the evaluation method will be explained. (a) Heat resistance Form a cup-shaped jam packaging container with a diameter of 75 mm and a depth of 30 mm. The jam container has circular ribs on the bottom surface, and during thermal backwashing, it is possible to accurately determine whether thermal deformation has occurred, such as when the circular ribs become shallower, before the external dimensions are clearly deformed. The container is exposed to a hot air circulating type constant temperature bath for 30 minutes to determine the presence or absence of thermal deformation. The heat resistance of the axially stretched sheet was determined based on the thermal deformation onset temperature. (b) Oil resistance Pour salad oil, a representative type of edible oil, into the cup-shaped jam packaging container mentioned above and hold it at 60℃ for 30 minutes. Check whether cracks occur in the cup. If cracks occur, mark the container with an x. Cases where there is no change such as deformation or discoloration are indicated by a circle. (c) Impact resistance A falling weight impact test was conducted using 50 biaxially stretched sheets with a thickness of 0.2 mm, and the impact strength at which 50% of the sheets were destroyed was expressed as the amount of energy based on the weight and height of the falling weight. (d) Sheet appearance The appearance of the sheet is judged with the naked eye. A sheet with a smooth, colorless and transparent sheet surface without air bubbles or volatile pit marks is marked with an ○, and sheets with clearly visible appearance defects such as air bubbles are marked with an x. In addition, the appearance defects that are visible when you strain your eyes and look closely are indicated by a △ mark. Examples 1 to 5 Styrene, methyl methacrylate, and methacrylic acid or acrylic acid as aromatic vinyl compounds were dissolved in methyl ethyl ketone, and 1,1-bis(tert-butylperoxy)-3, as a polymerization initiator.
35-Trimethylsiloxane was added and polymerized at a temperature of about 125°C to a reaction rate of about 50%. The composition of the reaction mixture immediately after polymerization is shown in the table below.

[Table] Next, this reaction compound is held at 260°C for about 20 to 40 minutes under a reduced pressure of 1 to 10 mmHg to remove the solvent and unreacted monomers, and the molecules of methyl methacrylate and methacrylic acid or acrylic acid are removed. Cyclization is caused by internal condensation or intramolecular condensation of methacrylic acid or acrylic acid to form a six-membered cyclic acid anhydride unit of component (A). The composition of the copolymer containing the six-membered cyclic acid anhydride is
As shown in the table. When methyl methacrylate and methacrylic acid are intramolecularly condensed When methacrylic acids are intramolecularly condensed with each other [A] R ₁ and R ₂ in the general formula become methyl groups and when methyl methacrylate and acrylic acid are intramolecularly condensed R ₁ is a methyl group, R ₂ is a hydrogen atom, and when acrylic acids are intramolecularly condensed, R ₁ and R ₂ are hydrogen atoms. A copolymer having the composition shown in Table 1 was extruded through a T-die, and the sheet was stretched with a tenter in both longitudinal and transverse directions with 2.5 medium to form a 0.2 mm thick sheet. Table 1 shows the results of evaluating the sheet in the evaluation directions described above. The sheet has the same or slightly better transparency as a biaxially oriented polystyrene sheet, and is also rigid.
Improved heat resistance: Although it is necessary to raise the thermoforming temperature by 10 to 30°C, other conditions are almost the same, and the moldability is very good and thermoforming is possible, and as shown in Table 1, it has even better heat resistance, oil resistance, and impact resistance. It can be seen that it is an excellent sheet. Comparative Examples 1 to 7 Copolymers having the compositions shown in Table 1 were prepared in Example 1.
A biaxially stretched sheet was prepared in the same manner as in Steps 5 to 5. Only Comparative Example 3 is the unstretched sheet of Example 1. The evaluation method was also the same as in Examples 1-5. It can be seen that in both cases, the heat resistance, oil resistance, and impact resistance, which are the objectives of the present application, are not simultaneously satisfied at a high level. Comparing Comparative Examples 1 and 2, the weight percent of (A) component is (D)
Example 1: The values divided by the weight percent of the ingredients are 1.8 and 5.6, respectively.
-5 are all 10 or more, but it can be seen that there is a clear difference in sheet appearance depending on the value. As explained above, the heat-resistant and
Transparent thermoplastic resin biaxially oriented sheets have the same moldability as conventional biaxially oriented polystyrene, but also have higher heat resistance, oil resistance, and better properties than biaxially oriented polystyrene.
It has excellent impact resistance and practical heat resistance, so when used as a food container packaging material, it can be heated in a microwave oven, etc. with the food container intact.
Moreover, since it has better oil resistance than conventional biaxial polystyrene, even oily foods can be packaged, and its benefits are immeasurable.

【table】

【table】

Claims (1)

[Claims] 1 (A) General formula 5 to 85 six-membered cyclic acid anhydride units represented by (R ₁ and R ₂ in the formula are hydrogen atoms or methyl groups)
(B) 1 to 80% by weight of methyl methacrylate units, (C) 1 to 65% by weight of aromatic vinyl compound units, and (D) 0.5 to 10 methacrylic acid or acrylic acid units.
1.5 to 5.0 times in each biaxial direction for a copolymer sheet in which the value obtained by dividing the weight % of component (A) by the weight % of component (D) is 3 or more in a copolymer having a composition of % by weight. A heat-resistant, transparent biaxially stretched thermoplastic resin sheet characterized by being stretched in the range of .