Resin sheet and food packaging container

Abstract

To provide a resin sheet excellent in heat resistance, rigidity and transparency.SOLUTION: The sheet contains homopolypropylene and a clarifying nucleating agent and has a tensile modulus of elasticity of JISZ1707 or higher as measured according to 1500MPa, a haze of 20% or less as measured according to JISK7136 and converted as a value of thickness 1mm, and a heat resistance temperature of 160 °C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin sheet and a food packaging container. [Background technology]

[0002] Polypropylene is widely used in the packaging field due to its excellent mechanical properties and heat resistance. For example, Patent Document 1 discloses a container molded from a polypropylene sheet as a microwave food container that has sufficient oil resistance and heat resistance to withstand heating in a microwave oven. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-081202 Summary of the Invention [Problem to be solved by the invention]

[0004] Food packaging containers molded from polypropylene are widely used in the food sections of convenience stores, supermarkets, and other locations because the food stored in the container can be reheated in a microwave oven or other device. However, conventional heat-resistant food packaging containers all have insufficient transparency, making it difficult to see the contents. It is believed that food packaging containers that allow the contents to be seen can give consumers a sense of security and increase their purchasing motivation. Therefore, there is a demand for food packaging containers that have excellent heat resistance and mechanical properties as well as high transparency.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a resin sheet and a food packaging container that are excellent in heat resistance, rigidity, and transparency. [Means for solving the problem]

[0006] According to the present invention, it is possible to provide the following resin sheet and food packaging container using the same.

[0007] [1] A resin sheet containing homopolypropylene and a transparent nucleating agent, Tensile modulus measured in accordance with JIS Z 1707 is 1500 MPa or more, Measured in accordance with JIS K 7136, the haze converted to a value of 1 mm thickness is 20% or less. A resin sheet with a heat resistance temperature of 160°C or higher.

[0008] [2] A food packaging container for baking using the resin sheet described in [1]. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a resin sheet and a food packaging container that have sufficient heat resistance and rigidity to withstand baking cooking, while also having enhanced transparency. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described in detail below.

[0011] <Resin sheet> The resin sheet of the present invention is obtained by molding a resin composition containing homopropylene and a transparent nucleating agent into a sheet. The method for producing the resin sheet is not particularly limited, and it can be produced by a general method for producing a sheet material from a resin, such as extrusion molding, coextrusion molding, inflation molding, or in-line lamination. The resin sheet may be a single layer, a laminate obtained by laminating multiple resin sheets, or a sheet obtained by coextruding multiple resins. The resin sheet of the present invention may be in the form of a strip or a roll.

[0012] The resin sheet preferably has a tensile modulus (in the TD or MD direction) measured in accordance with JIS Z 1707 of 1500 MPa or more. Specifically, it is preferable that the tensile modulus in the transverse direction (TD direction) of the resin sheet is 1500 MPa or more and the tensile modulus in the longitudinal direction (MD direction) is 1500 MPa or more. More preferably, the tensile modulus in the transverse direction (TD direction) is 1500 MPa or more and 1700 MPa or less, and the tensile modulus in the longitudinal direction (MD direction) is 1500 MPa or more and 1800 MPa or less.

[0013] The resin sheet is preferably measured in accordance with JIS K 7136 and has a haze of 20% or less when converted to a value of 1 mm in thickness.

[0014] The resin sheet preferably has a heat resistance temperature calculated based on the results of a heat resistance test conducted in accordance with JIS S 2029 of 160 °C or more.

[0015] The thickness of the resin sheet is not particularly limited as long as the tensile modulus, haze, and heat resistance satisfy the above numerical values, but is preferably 0.3 to 1.0 mm.

[0016] <Food packaging container> The present invention is a food packaging container obtained by molding the above resin sheet, and the form is not particularly limited, but is, for example, of a general shape having an opening upward. Further, the present invention is a food packaging container for baking cooking that can perform baking cooking under the following conditions with food accommodated in the container. · Baking temperature (set temperature)… Set at 120 to 260 °C · Temperature in the warehouse (temperature of the container surface)… Set at 90 to 160 °C · Baking time… 30 seconds to 12 minutes The food packaging container of the present invention preferably has a melting point measured by DSC of 165°C or higher. This food packaging container satisfies the heat-resistant temperature of 140°C or higher specified in JIS S 2029 Plastic Tableware for tableware that can be used in a microwave oven, and further preferably has a heat-resistant temperature of 160°C or higher for food packaging containers that can be used for general baking cooking under the above conditions.

[0017] The method for manufacturing the food packaging container is not particularly limited, and it can be manufactured by general methods for manufacturing containers from resin sheets, such as vacuum forming or pressure forming, in which the container is heated and fed into a mold.

[0018] <Homopolypropylene> Homopolypropylene is a highly crystalline homopolypropylene. When the methyl groups in the polypropylene molecular chain are arranged in a three-dimensionally regular manner, the polypropylene becomes highly stereoregular, resulting in a resin sheet with high rigidity and a high melting point. However, if the stereoregularity is too high, the degree of crystallization becomes high, and the difference in refractive index between the amorphous and crystalline phases causes light scattering, resulting in an opaque resin sheet.

[0019] As an index of stereoregularity of polypropylene 13 The mesopentad fraction (mmmm fraction) is measured by C-NMR. If the mesopentad fraction is small, the elastic modulus will be low and heat resistance will be insufficient. The mesopentad fraction of the homopolypropylene used in the resin sheet of the present invention is 96% or more, more preferably 97% or more. There is no particular upper limit to the mesopentad fraction, but from the viewpoints of moldability and transparency, it is preferably 98% or less. When two or more types of homopolypropylene are used, the mesopentad fraction of the homopolypropylene can be the mesopentad fraction of a mixture obtained by melt-kneading the two or more types of homopolypropylene. The regularity of the homopolypropylene can be detected using NMR (nuclear magnetic resonance).

[0020] The high-molecular-weight components in polypropylene are oriented during molding, increasing the crystallinity and rigidity. Therefore, although the impact resistance is high, the fluidity is low, making it difficult to process. On the other hand, the low-molecular-weight components in polypropylene have low impact resistance and high fluidity, making them unsuitable for sheet molding. The low-molecular-weight components are easily crystallized and function as a nucleating agent, maintaining fluidity by acting as a slip agent for the high-molecular-weight components. The homopolypropylene used in the resin sheet of the present invention has a wide molecular weight distribution, from high-molecular-weight components to low-molecular-weight components, resulting in high crystallinity, high rigidity, a high melting point, and ease of molding. Specifically, the molecular weight distribution (Mw / Mn) of the homopolypropylene used in the resin sheet of the present invention is preferably 7 to 15 from the viewpoints of rigidity, heat resistance, and moldability. The molecular weight distribution of the homopolypropylene can be measured by GPC (gel permeation chromatography).

[0021] The homopolypropylene may be used alone or in combination of two or more kinds within a range that does not significantly impair the effects of the present invention.

[0022] <Nucleating agent> The resin composition preferably contains 2.5 wt% or less of a nucleating agent relative to 100 wt% of homopolypropylene. The nucleating agent can promote the crystallization of the resin. By including a nucleating agent in the resin composition, the rigidity and transparency of the resin film can be increased. Known rigid nucleating agents for increasing rigidity and transparent nucleating agents for increasing transparency can be used.

[0023] Common nucleating agents include, for example, acetal-based nucleating agents such as nonitol-based nucleating agents and sorbitol-based nucleating agents; amide-based nucleating agents such as carboxamides, triamides, and bisamides; organic nucleating agents such as metal carboxylate-based nucleating agents and metal phosphate-based nucleating agents; and inorganic nucleating agents such as talc, mica, silica, calcium carbonate, and silicates. A single nucleating agent may be used alone, or two or more may be used in combination. The resin composition used in the resin sheet of the present invention contains at least one transparent nucleating agent, and more preferably contains at least one rigid nucleating agent and one transparent nucleating agent.

[0024] The resin sheet of the present invention preferably contains a nonitol-based nucleating agent or a sorbitol-based nucleating agent as a clarifying nucleating agent, more preferably a nonitol-based nucleating agent. Further, the resin sheet of the present invention preferably contains 1.5 to 2.5 wt% of a clarifying nucleating agent with respect to 100 wt% of homopolypropylene.

[0025] <Optional component> The resin composition used for the resin sheet of the present invention, which is excellent in transparency and heat resistance, contains the above homopolypropylene and clarifying nucleating agent as essential constituent components. However, within a range not significantly impairing the effects of the present invention, if necessary, additional components such as an antioxidant, a stabilizer, a dispersant, a colorant, a lubricant, an antiblocking agent, an antistatic agent, an ultraviolet absorber, a light stabilizer, etc. can be blended into this resin composition.

Examples

[0026] Next, examples of the present invention will be described.

[0027] <Preparation of resin composition> As components constituting the resin composition, the following were used. The method for preparing the resin composition is not particularly limited, but it was prepared by melting homopolypropylene, adding a nucleating agent, and kneading. [[ID=​​​​​​​​​​​​​​​​Comparative Example 2 Homopolypropylene B: mmmm fraction 93%, Mw / Mn 5, melting point 162°C, MFR 2.2 Rigid nucleating agent · Clarifying agent: None

[0028] <Production and evaluation of resin sheets> A resin composition containing homopolypropylene and a nucleating agent was fed into an extruder to obtain a single-layer resin sheet. Resin sheets with thicknesses of 0.45 mm, 0.50 mm, and 0.55 mm were produced, and the resulting resin sheets were evaluated for tensile modulus and transparency. The evaluation results for the resin sheets and the following food packaging containers are shown in Table 1.

[0029] (Measurement of tensile modulus) The tensile modulus was measured in accordance with JIS Z 1707. Resin sheets were cut into test pieces measuring 20 mm wide, 200 mm long, and with a grip spacing of 100 mm. Test pieces were prepared in both the machine direction (MD) and the transverse direction (TD). After conditioning the test pieces at 23°C and 50% RH for 24 hours, tensile tests were performed using a Tensilon tensile tester (A&D, RTG-1210). The tester was operated at a test speed of 5 mm / min, and the stress-strain curve was recorded. The tensile modulus was calculated from the slope of the initial linear portion of the stress-strain curve. Tests were performed on five samples, and the average value was calculated. This was determined for both the MD and TD directions.

[0030] (Transparency Assessment) Haze was measured in accordance with JIS K 7136. The resin sheet was cut to a predetermined size to prepare a test piece. The test piece was conditioned for 24 hours in an environment of 23°C and 50% RH, and then the haze was measured using a haze meter (NDH 2000, manufactured by Nippon Denshoku Industries Co., Ltd.). The test was performed with n=5, and the average value was calculated. Furthermore, the thickness of the resin sheet was used to calculate the haze using the following formula: Haze converted to thickness (% / mm) = Measured haze value (%) / resin sheet thickness (mm) The haze value converted to thickness was determined using a resin sheet having a thickness of 1 mm.

[0031] <Production and evaluation of food packaging containers> The foamed resin sheet was heated and molded into a food packaging container with an opening at the top using a mold. The heat resistance of the molded food packaging container was evaluated, and the melting point was measured using a DSC (DSC 7020, manufactured by SII Technology Inc.).

[0032] (Evaluation of heat resistance) Heat resistance tests were conducted in accordance with JIS S 2029. Based on the test results, the heat resistance temperature was calculated using the following formula in accordance with the Household Products Quality Labeling Act and the Consumer Affairs Agency website. Heat resistance temperature = temperature at which abnormal function or significant deformation occurs - 10°C [Test method] 1. The food packaging container was placed in a constant temperature oven with a blower whose temperature was adjusted to ±2°C and held there for 30 minutes. 2. The door of the thermostatic chamber was opened and the surface temperature of the food packaging container was measured using a non-contact thermometer (infrared thermography). 3. Leave it at room temperature for 30 minutes. 4. After the test, the food packaging containers were visually inspected to see if there were any abnormalities in function or significant deformation. 5. The test was conducted in 5°C increments from a temperature 10°C before the temperature at which deformation began to occur to the temperature at which significant deformation was observed. In Table 1, samples that showed significant changes at the test temperature were marked with a circle, and samples that showed significant deformation were marked with an X.

[0033] [Table 1]

[0034] Comparative Example 2, which used homopolypropylene B, had high transparency but low heat resistance and tensile modulus. Comparative Example 1, which used homopolypropylene A, showed improvements in heat resistance and tensile modulus, but insufficient transparency. Example 1, in which a transparent nucleating agent was added to homopolypropylene A, had high transparency and excellent heat resistance and tensile modulus. Note that, since deformation was observed in Example 1 at a heat resistance test temperature of 170°C, the heat resistance temperature was 160°C according to the above heat resistance temperature calculation formula.

Claims

1. A resin sheet containing homopolypropylene and a transparent nucleating agent, A tensile modulus of elasticity measured in accordance with JIS Z 1707 of 1500 MPa or more; The haze measured in accordance with JIS K 7136 and converted to a value for a thickness of 1 mm is 20% or less. The heat resistance temperature is 160°C or higher. Resin sheet.

2. A food packaging container for baking cooking, which uses the resin sheet according to claim 1.

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