JP2014213934A - Container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer container excellent in low temperature impact resistance and rigidity with excellent transparency.SOLUTION: A multi-layer plastic container 1 comprises: internal and external layers (an external layer 2 and an internal layer 6); polypropylene; polyethylene based elastomer; and a mixture of straight-chain polyethylene and low density polyethylene.

Description

  The present invention relates to a plastic container, and more particularly to a food bottle. More specifically, the present invention relates to a material using polypropylene that has low temperature impact resistance, high heat resistance rigidity, and suitable for heat filling.

  Patent Documents 1 to 4 are cited as documents describing techniques related to the present invention. Patent Document 1 is a precedent example of a plastic container, and describes that a low temperature impact resistance is improved from that of a single polypropylene by a resin composition obtained by blending a linear polyethylene with a polypropylene resin. The low temperature impact resistance is an index of container physical properties using an evaluation method for preventing breakage at a low temperature of less than 5 degrees Celsius assuming the temperature in the refrigerator. Containers with higher resistance to low temperature impact have less damage at low temperatures.

  Patent Documents 2 and 3 describe that low-temperature impact resistance is improved from that of polypropylene alone by using a composition of polypropylene, linear polyethylene, and low-density polyethylene.

  Patent Document 4 discloses that by adding a hydrogenated polymer of a styrene-butadiene random copolymer to polypropylene, the low-temperature impact resistance and transparency are improved as compared with polypropylene alone, and the resin thus obtained There is a description about using the composition for the main layer (thickest layer) (see paragraph 0017 of Patent Document 4).

Japanese Patent No. 2691494 JP 2012-148810 A JP 2012-148811 A JP 2003-226323 A

  In conventional techniques to improve low-temperature impact strength by blending linear polyethylene or low-density polyethylene with polypropylene, a large amount of linear polyethylene or low-density polyethylene must be carried to obtain sufficient modified strength. However, there is a problem in that the transparency and heat-resistant rigidity of the main polypropylene are impaired. In addition, when a hydrogenated polymer of a styrene-butadiene random copolymer is contained in polypropylene, although low temperature impact resistance and transparency can be improved from polypropylene alone, there is a problem in that the heat resistance rigidity is lowered.

  The heat-resistant rigidity is an index related to the rigidity of the container at a high temperature of about 80 ° C. When filling a high-viscosity seasoning among seasonings, it may be filled at a temperature around 80 ° C. for the purpose of adjusting the viscosity. It is necessary to prevent the rigidity of the container from being lowered and difficult to handle in the filling line due to the heat of filling at that time. Therefore, the tensile elastic modulus at 80 ° C. is measured and evaluated.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the highly transparent container excellent in low temperature impact resistance and heat-resistant rigidity.

  As a result of repeated studies to achieve the above problems, the present inventors have found that the above object can be achieved with the following configuration, and have completed the present invention.

  A plastic container having a mixed layer in which polypropylene, linear polyethylene, low-density polyethylene, and a polyethylene-based elastomer are arranged is used in at least one layer of the container.

  According to the present invention, it is possible to provide a highly transparent container excellent in low-temperature impact resistance and heat-resistant rigidity.

It is a figure which shows the longitudinal cross-section of the multilayer plastic container of embodiment of this invention. It is a schematic cross section which shows one suitable example of the layer structure of the A section of the plastic container of FIG.

  The multilayer plastic container of the present embodiment is a container filled with the contents at a high temperature, and at least one layer has a layer made of a mixture of polypropylene, polyethylene elastomer, linear polyethylene and low density polyethylene. It is characterized by that. Here, the polyethylene elastomer refers to an elastomer having polyethylene as a hard segment and a predetermined rubber component as a soft segment. For example, C-4 polyethylene elastomer containing butene as a comonomer with respect to ethylene, C-6 polyethylene elastomer containing hexene, C-8 polyethylene elastomer containing octene, and the like.

  Examples of the multilayer plastic container of this embodiment include containers of various shapes including hollow bottles as seen in FIG. 1, and these plastic containers can be produced by a method such as rotary blow molding or shuttle blow molding. Can be manufactured.

  The multilayer plastic container of this embodiment is useful as a food bottle such as ketchup, mayonnaise, sauce, and the like. In particular, a fluid having a characteristic of high viscosity at normal temperature but low viscosity at high temperature such as ketchup and sauce needs to be filled at high temperature. As a result, the production efficiency is improved as compared with a propylene simple substance multilayer container.

  FIG. 2 shows a preferred example of the layer configuration of part A of the plastic container of FIG. In the layer configuration shown in FIG. 2, the outer layer 2 (mixed layer), the adhesive layer 3, the gas barrier layer 4, the adhesive layer 3, the intermediate layer 5, and the inner layer 6 (mixed layer) are stacked in this order. is there. The outer layer 2 and the inner layer 6 use a mixture of polypropylene excellent in low-temperature impact resistance and heat-resistant rigidity, linear polyethylene, low-density polyethylene and polyethylene-based elastomer. Specifically, a ratio of polypropylene / linear polyethylene / low density polyethylene / polyethylene elastomer = 84.6 / 9.4 / 1/5 is preferable. As the adhesive layer 3, an adhesive resin such as maleic anhydride grafted polypropylene is used. As the gas barrier layer 4, a gas barrier layer made of an ethylene vinyl acetate copolymer (EVOH) is used. As the intermediate layer 5, scrap resin such as burrs generated at the time of molding a plastic container or a mixed resin obtained by blending scrap resin and unused polypropylene can be used.

  A gas barrier layer uses a resin that has a lower gas permeability compared to polyolefin, which is a main material such as ethylene-vinyl acetate copolymer (EVOH) and polyamide, and blocks gas that lowers the flavor of food typified by oxygen. It is a layer.

  The optimum film ratio to be disposed in the container having the layer configuration shown in FIG. 2 is 20% or more of the total thickness of the container including the outer layer 2 (mixed layer) and the inner layer 6 (mixed layer). By that. A multilayer container excellent in low temperature impact resistance and heat resistance rigidity can be produced. Here, the thickness of the entire container is obtained by measuring the thickness for every 10 mm in the container height direction and for every 10 mm in the container circumferential direction over the entire area of the container and averaging it. Further, the thicknesses of the outer layer 2 and the inner layer 6 are the average values of numerical values obtained by measuring the slices cut in the circumferential direction 12 at a half height position of the total height of the container and cutting with a microtome using an optical microscope. can get. In the present embodiment, the total thickness of the container is 0.6 mm, and the total thickness of the outer layer 2 and the inner layer 6 is 120 μm or more.

  For example, in the case of a container having a thickness of 0.6 mm as shown above, the outer layer 2 (mixed layer) is 141 μm, the adhesive layer 3 (outer layer side) 7.5 μm, the gas barrier layer 4 is 24 μm, and the adhesive layer 3 (inner layer side) 7 5 μm, the intermediate layer 5 is preferably 240 μm, and the inner layer 6 (mixed layer) is preferably 180 μm.

  The polypropylene as the main component of the resin composition is preferably an ethylene-propylene / random copolymer (r-PP) from the viewpoint of transparency.

  Further, as shown in the following examples, the total amount of polypropylene is preferably 70% by weight or more from the viewpoint of transparency and heat-resistant rigidity. Further, the preferable range is 80% or more from the viewpoint of obtaining a high level of heat resistance rigidity, and less than 90% from the viewpoint of low temperature impact resistance.

[Example]
Hereinafter, examples and comparative examples of material configurations used as the inner and outer layer materials of the present invention (both outer layer 2 and inner layer 6 are mixed layers) will be described. Since the multilayer container is a multilayer structure of each layer, each layer has a function. Basically, because the inner and outer layer materials have the functions of low temperature shock resistance, heat resistance rigidity, and transparency, the low temperature shock resistance and heat resistance rigidity of the multilayer container are evaluated by evaluating the physical properties of the inner and outer layer materials. , Leading to transparency evaluation. In the following examples, a sheet having a thickness of 1.5 mm and a width of 25 mm was formed and evaluated.

[Material composition]
Experiments were made with various combinations of polypropylene (PP), polyethylene elastomer (PE elastomer), linear low density polyethylene (LLDPE), and low density polyethylene (LDPE), and compared with Example 1 below. Examples 1 to 5 were obtained.

[Example 1]
84.6% by weight of random polypropylene (r-PP density: 0.890 g / cm ³ , MFR (230 ° C., 2.16 kg): 1.20 g / 10 min, melting point: 135 ° C.) is used as the total mixture of 100% by weight. 9.4% by weight of linear low density polyethylene (LLDPE density: 0.898 g / cm ³ , MFR (190 ° C., 2.16 kg): 2.00 g / 10 min, melting point: 94 ° C.) (LDPE density: 0.923 g / cm ³ , MFR (190 ° C., 2.16 kg): 0.60 g / 10 min, melting point: 112 ° C.) 1% by weight, polyethylene elastomer (PE elastomer 1 (comonomer is 1 -Butene) Density 0.860 g / cm ³ , MFR (190 ° C., 2.16 kg): 0.50 g / 10 min, melting point 50 ° C.) 5 wt% were blended and kneaded to obtain The resin composition was evaluated for transparency at 23 ° C., heat-resistant rigidity at 80 ° C., and low-temperature impact resistance at −5 ° C. The density of physical properties and MFR were measured based on JIS K 7112, and the melting point was judged from the peak of DSC. Moreover, it is as follows when the mixing | blending of Example 1 is shown in a specific ratio. r-PP / LLDPE / LDPE / PE elastomer 1 = 84.6 / 9.4 / 1/5

[Example 2]
In the formulation of Example 1, PE-based elastomer 1 is a PE-based elastomer 2 having a large density and MFR (comonomer is 1-butene density 0.880 g / cm ³ , MFR (190 ° C., 2.16 kg): 1.20 g / 10 min, The melting point was 66 ° C., and a resin composition was prepared and evaluated under the same conditions as in Example 1 except for the ratio. The formulation of Example 2 is shown as a specific ratio as follows.
r-PP / LLDPE / LDPE / PE elastomer 2 = 84.6 / 9.4 / 1/5

[Example 3]
PE-based elastomer 3 having an increased number of unsaturated hydrocarbons using PE-based elastomer 1 as a comonomer in the formulation of Example 1 (comonomer is 1-octene density 0.863 g / cm ³ , MFR (190 ° C., 2. 16 kg): 0.50 g / 10 min, melting point 47 ° C.), and a resin composition was prepared and evaluated under the same conditions as in Example 1 except for the ratio. The formulation of Example 3 is shown as a specific ratio as follows.
r-PP / LLDPE / LDPE / PE elastomer 3 = 84.6 / 9.4 / 1/5

[Comparative Example 1]
A resin composition was prepared and evaluated under the same conditions except that LDPE was excluded from the formulation of Example 1. The composition of Comparative Example 1 is shown in a specific ratio as follows.
r-PP / LLDPE / PE elastomer 1 = 85.5 / 9.5 / 5

[Comparative Example 2]
A resin composition was prepared and evaluated under the same conditions except that LDPE was excluded from the formulation of Example 2. The composition of Comparative Example 2 is shown in a specific ratio as follows.
r-PP / LLDPE / PE elastomer 1 = 85.5 / 9.5 / 5

[Comparative Example 3]
A resin composition was prepared and evaluated under the same conditions except that LDPE was excluded from the formulation of Example 3. The composition of Comparative Example 3 is shown in a specific ratio as follows.
r-PP / LLDPE / PE elastomer 1 = 85.5 / 9.5 / 5

[Comparative Example 4]
A resin composition was prepared and evaluated under the same conditions except that LLDPE and LDPE were excluded from the formulation of Example 1. The composition of Comparative Example 4 is shown in a specific ratio as follows.
r-PP / PE elastomer 1 = 85/15

[Comparative Example 5]
A resin composition was prepared and evaluated under the same conditions except that the PE elastomer 1 and LDPE were removed from the formulation of Example 1. The composition of Comparative Example 5 is shown in a specific ratio as follows.
r-PP / LLDPE = 85/15

  There is an Izod impact strength as a method for estimating the low temperature impact resistance of a container from the mechanical properties of a material without performing an actual drop test. The Izod impact strength was measured at −5 ° C. based on JIS K 7110, and the results are shown in Table 1.

  In order to estimate the heat-resistant rigidity of the container, the tensile modulus of the test piece at 80 ° C. was measured based on JIS K 7161, and the results are shown in Table 1.

  Table 1 shows the results of measuring the light transmittance at a wavelength of 450 nm, which increases the numerical value when the transparency of visible light is high, with UV-2400PC, Shimadzu Corporation.

  In Example 1 and Comparative Example 1 described above, Comparative Example 1 is that in which LDPE is blended in a mixture of polypropylene, linear polyethylene, and a polyethylene-based elastomer, but not blended in Example 1. It can be seen that Example 1 has improved tensile modulus of Izod impact strength as compared with Comparative Example 1.

  This is presumably because LDPE improved the compatibility of polypropylene, linear polyethylene and polyethylene elastomer, and further improved the crystallization rate. The crystallization rate is a ratio of crystals contained in the resin, and the crystalline resin is divided into a crystal part having excellent heat resistance rigidity and an amorphous part having no heat resistance rigidity. The improvement in the compatibility of the mixed resin leads to the dispersion of the rubber component that absorbs impact or stress in the order of submicrometers where the most effective effect is achieved, and the low temperature impact property is improved. Furthermore, the crystallization rate increases because the dispersion is improved and the resin is arranged in an orderly manner and is easily crystallized. Many crystal components having excellent heat resistance rigidity are present in the mixed resin, and the heat resistance rigidity is improved.

  This can be explained in the same way in Example 2 and Comparative Example 2, and in Example 3 and Comparative Example 3.

When Examples 1 to 3 were compared, there was a difference in the improvement tendency of the izod impact strength of −5 ° C. and the tensile elastic modulus of 80 ° C. depending on the PE elastomer. The most effective PE-based elastomer is the PE-based elastomer of Example 1 having an Izod impact strength increased from 4.67 kJ / cm ² to 11.01 kJ / cm ² and a tensile elastic modulus increased from 126 MPa to 147 MPa. That is, it was found that a PE-based elastomer having a density of 0.860 g / cm ³ and 1-butene as the comonomer has the highest improvement effect.

  Moreover, in the case of blending polypropylene and polyethylene elastomers having different refractive indexes, the transparency tends to decrease. In particular, as in Comparative Example 4, when the relative amount of polyethylene-based elastomer is large with respect to polypropylene, polypropylene aggregates with polypropylene and elastomer aggregates with elastomer, resulting in poor dispersion and extremely low transparency.

  Furthermore, since the ratio of the elastomer of Comparative Example 4 is larger than that of Examples 1 to 3, the low temperature impact resistance is improved, but the heat resistant rigidity is rapidly deteriorated.

  In Comparative Example 5, it can be seen that the Izod impact strength is low as compared with Examples 1 to 3, and the improvement effect is small even when a large amount of linear polyethylene is added.

  As described above, the material composition blended with polypropylene, linear low density polyethylene, low density polyethylene, and polyethylene elastomer is compared with the material composition blended with polypropylene, polyethylene elastomer, and linear low density polyethylene. It can be seen that the Izod impact value at 5 ° C. and the rigidity at 80 ° C. are improved. This can provide a highly transparent container excellent in low-temperature impact resistance and heat-resistant rigidity.

  The optimum material composition is 70% to 89% polypropylene, 3% to 10% polyethylene elastomer, 7% to 15% linear low density polyethylene, and 1% to 5% low density polyethylene. It is a configuration.

1 Multilayer plastic container 2 Outer layer (mixed layer)
3 Adhesive layer 4 Gas barrier layer 5 Intermediate layer 6 Inner layer (mixed layer)

Claims (4)

  A plastic container having a mixed layer in which polypropylene, linear polyethylene, low-density polyethylene and polyethylene-based elastomer are arranged in at least one layer of the container.   2. The plastic container according to claim 1, wherein in the mixed layer, the total of the linear polyethylene, the low density polyethylene, and the polyethylene elastomer is 30% by weight or less. The plastic container according to claim 1 or 2, wherein the polyethylene elastomer has a density of less than 0.880 g / cm ³ and the comonomer to be introduced is 1-butene.   The multilayer container according to claim 1, 2 or 3, further comprising a gas barrier layer as an intermediate layer.

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