Laminate with polypropylene layer

Abstract

To provide a laminate having all of low-temperature drop impact resistance, blocking resistance, slipperiness, and flavor properties.SOLUTION: A laminate comprises a polypropylene layer comprising an ethylene / propylene block copolymer as a surface layer. The polypropylene layer has a phase dispersion structure in which a resin comprising polypropylene as a main component constitutes a matrix and a spindle-shaped polypropylene-based elastomer constitute domains. The polypropylene layer has a surface roughness of 0.15 μm to 1.0 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate having a polypropylene layer as a surface layer, and more specifically to a laminate that has drop impact resistance, blocking resistance, slip properties, and flavor properties and is suitable for use in food packaging. [Background technology]

[0002] Laminates having a surface layer made of a propylene-based polymer are widely used as packaging materials for various foods because they can exhibit heat-sealing properties and are also excellent in heat resistance, hygiene, and flavor. In recent years, packaging containers have become thinner in order to reduce weight and save money, and drop impact resistance (impact resistance) at low temperatures is also required for use in cold regions, etc., and higher drop impact resistance is therefore required. As a polypropylene having such high drop impact resistance, propylene block copolymers, also known as impact polypropylenes, are also being used in packaging materials.

[0003] Another performance requirement for packaging materials is blocking resistance, i.e., it is necessary that blocking does not easily occur when films are laminated together, but the laminate having a surface layer made of the above-mentioned propylene block copolymer has poor blocking resistance because it contains a soft rubber component, and further improvement of this property is desired. In order to improve properties such as drop impact resistance and blocking resistance, for example, Patent Document 1 listed below proposes a propylene-based resin composition obtained by blending a propylene block copolymer with an ethylene-α-olefin copolymer.

[0004] Furthermore, Patent Document 2 listed below proposes a multilayer film using a polypropylene block copolymer and having a surface layer in which substantially spherical elastomer particles are dispersed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-161033 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-198977 Summary of the Invention [Problem to be solved by the invention]

[0006] For containers such as trays and cups, the processes of container formation, filling and sealing of the contents, and packaging are carried out continuously while the container is being transported on a conveyor line, so they are required to have good transportability, i.e., slipperiness, so that the container does not clog on the line, and polypropylene-based packaging materials also need to have excellent slipperiness. Furthermore, for food applications, it is particularly important that the flavor of the contents is not affected. However, it was difficult for the packaging materials using the propylene block copolymers described in Patent Documents 1 and 2 to fully satisfy all of the drop impact resistance, blocking resistance, and slipperiness under low-temperature conditions. Moreover, it was difficult to provide a laminate having a polypropylene surface layer that not only had these properties but also had appearance properties and flavor properties.

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laminate having a surface layer of polypropylene that has all of the following properties: drop impact resistance under low temperature conditions, blocking resistance, slip properties, and flavor properties. [Means for solving the problem]

[0008] According to the present invention, in a laminate having a polypropylene layer made of an ethylene-propylene block copolymer as a surface layer, , the polypropylene layer The resin mainly composed of polypropylene is a matrix, and the spindle-shaped polypropylene elastomer has a phase dispersion structure as a domain, and the surface roughness (Sa) of the polypropylene layer is 0.15 μm to 1.0 μm. The polypropylene layer contains 1 to 30 parts by mass of homopolypropylene relative to 100 parts by mass of the ethylene-propylene block copolymer, and the polypropylene elastomer has a weight average molecular weight (Mw) of 500,000 to 1,000,000 and a number average molecular weight (Mn) of 10,000 to 300,000. A laminate is provided, characterized in that

[0009] In the laminate of the present invention, 1. The minor axis of the domain is in the range of 0.2 to 4.0 μm, and the major axis is in the range of 0.5 to 5.0 μm; 2. The polypropylene layer contains 1 to 30 parts by mass of the polypropylene-based elastomer per 100 parts by mass of the resin containing polypropylene as a main component; 3 .before The weight average molecular weight (Mw) of the resin mainly composed of polypropylene is 300,000 to 800,000, and the number average molecular weight (Mn) is 10,000 to 300,000. 4 The polypropylene layer is provided as an inner and outer layer, and an oxygen absorbing layer and a gas barrier layer are provided as an intermediate layer. 5 .having the shape of a tray or cup, is preferred.

[0010] According to the present invention, there is also provided a method for producing a laminate having a polypropylene layer made of an ethylene-propylene block copolymer as a surface layer, the method comprising the steps of: 100 parts by mass to In contrast , homopolypropylene is used as a viscosity modifier 1~30 parts by mass By blending and melt-kneading the components, the viscosity is adjusted to a range of MFR (230°C, 2.16 kg load) of 0.1 to 10 g / 10 min, and the viscosity-adjusted molten resin is extruded. The polypropylene-based resin has a phase dispersion structure in which the matrix is ​​a resin containing polypropylene as a main component and the spindle-shaped polypropylene-based elastomer is a domain, and the weight-average molecular weight (Mw) of the polypropylene-based elastomer is 500,000 to 1,000,000 and the number-average molecular weight (Mn) is 10,000 to 300,000, A method for producing a laminate is provided, characterized in that a surface layer having a surface roughness (Sa) of 0.15 μm to 1.0 μm is formed.

[0011] In the method for producing a laminate of the present invention, 1 .before The polypropylene-based elastomer is contained in an amount of 1 to 30 parts by mass relative to 100 parts by mass of the resin mainly composed of polypropylene. 、 2 The weight average molecular weight (Mw) of the resin mainly composed of polypropylene is 300,000 to 800,000, and the number average molecular weight (Mn) is 10,000 to 300,000. is preferred. [Effects of the Invention]

[0012] In the laminate of the present invention, the surface layer is a polypropylene layer having a dispersion structure in which spindle-shaped polypropylene elastomer domains are dispersed in a resin mainly composed of polypropylene, and the surface roughness (Sa) of the surface layer is 0.15 to 1.0 μm, thereby enabling excellent drop impact resistance, slip properties, and blocking resistance to be simultaneously achieved. Furthermore, since the laminate of the present invention uses a propylene-based polymer having a molecular weight within the above range, it also has excellent flavor properties. Furthermore, in the method for producing the laminate of the present invention, by blending homopolypropylene, it is possible to adjust the viscosity of the ethylene-propylene block copolymer to a viscosity suitable for molding, thereby improving the moldability (workability) without impairing the drop impact resistance of the laminate. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram illustrating the domain shape in the packaging material of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Laminate) As described above, the laminate of the present invention has a first important feature in that the polypropylene layer constituting the surface layer has a phase dispersion structure in which a resin whose main component is polypropylene is used as the matrix and spindle-shaped polypropylene-based elastomer domains are used as the domains, and a second important feature in that the surface layer has a surface roughness (Sa) of 0.15 to 1.0 μm. Note that surface roughness (Sa) is a parameter obtained by extending the arithmetic mean height (Ra) of a line to a surface, and is the average of the absolute values ​​of the height differences at each point relative to the average plane of the surface as specified in ISO 25178. The surface layer of the laminate has a dispersed structure in which spindle-shaped domains made of a polypropylene-based elastomer are dispersed in a matrix made of a resin whose main component is polypropylene, thereby further improving drop impact resistance and enabling the laminate to exhibit excellent drop impact resistance even at low temperatures.In addition, since the surface roughness is within the above range, it is possible to exhibit excellent sliding properties and blocking resistance.

[0015] That is, in order to achieve excellent drop impact resistance even at low temperatures in a laminate having a surface layer made of a propylene block copolymer, it is preferable that the polypropylene layer constituting the surface layer has a high content of rubber component (polypropylene-based elastomer), and that domains (dispersed particles) made of this rubber component are finely dispersed, not only in terms of drop impact resistance but also in terms of appearance characteristics. On the other hand, in order to improve blocking resistance and slip properties, it is preferable that the content of the rubber component is low, and that the dispersed particles made of this rubber component are large enough to form unevenness on the surface. From this perspective, the present invention has discovered that the polypropylene surface layer has a dispersed structure in which spindle-shaped domains made of a polypropylene-based elastomer are formed in a matrix made of a resin whose main component is polypropylene, and that by having a surface roughness (Sa) within the above range, it is possible to achieve both excellent drop impact resistance, blocking resistance, and slip properties.

[0016] In the present invention, in order to achieve excellent drop impact resistance through the domains made of polypropylene-based elastomer, it is preferable that the domains have a minor axis of 0.2 to 4.0 μm, particularly 0.2 to 2.0 μm, and a major axis of 0.5 to 5.0 μm, particularly 0.5 to 3.0 μm. The method for measuring the minor and major axes of the domains will be described later. It is also preferable that the aspect ratio of the spindle-shaped domains is in the range of 1.2 to 9.0, 1.2 to 8.0, 1.9 to 8.0, particularly 1.9 to 5.0. The domain size equivalent to a circle is preferably in the range of 0.5 μm to 5.0 μm, particularly 0.5 μm to 1.0 μm. If the domain size is too small, no surface irregularities are formed, resulting in poor slip properties, whereas if the domain size is too large, irregularities are formed, resulting in good slip properties but poor drop impact resistance. The control of the domain shape and size is determined by the molecular weight and composition of the matrix resin containing polypropylene as the main component and the polypropylene-based elastomer, as well as the resin production method such as kneading. In the laminate of the present invention, the polypropylene elastomer is preferably contained in an amount of 1 to 30 parts by mass, particularly 5.0 to 25 parts by mass, per 100 parts by mass of the resin mainly composed of polypropylene. If the amount of polypropylene elastomer is less than the above range, the drop impact resistance may not be sufficiently improved compared to when it is within the above range, while if the amount of polypropylene elastomer is more than the above range, not only will the blocking resistance and slipperiness be reduced, but the flavor will also be reduced and the surface irregularities will increase, resulting in poor appearance properties.

[0017] [Polypropylene-based resin] In the laminate of the present invention, the resin containing polypropylene as a main component, which serves as the matrix, is a homo- or random polypropylene obtained by polymerizing a monomer mainly containing propylene. The resin containing polypropylene as the main component preferably has a weight-average molecular weight (Mw) in the range of 300,000 to 800,000, particularly 300,000 to 600,000, and a number-average molecular weight (Mn) in the range of 10,000 to 300,000, particularly 50,000 to 200,000. If the molecular weight of the resin containing polypropylene as the main component is smaller than the above range, there is a risk that drop impact resistance will be reduced and hygiene will be impaired compared to when it is within the above range. On the other hand, if it is larger than the above range, there is a risk that moldability will be reduced due to abnormal resin pressure compared to when it is within the above range. Furthermore, it is preferable that the resin containing polypropylene as the main component has a mesopentad fraction ([mmmm]), which is an index of stereoregularity, in the range of 95 to 99 from the viewpoint of heat resistance and moldability.

[0018] [Polypropylene elastomer] In the laminate of the present invention, examples of the polypropylene-based elastomer constituting the spindle-shaped domains include propylene-ethylene-based elastomers. The propylene-ethylene-based elastomer is preferably a random copolymer of propylene and ethylene, with a mass ratio of ethylene units to propylene units ranging from 15:85 to 50:50. If necessary, an elastomer copolymerized with an α-olefin or the like may be used to improve compatibility and drop impact resistance. The polypropylene elastomer preferably has a weight-average molecular weight (Mw) of 500,000 to 1,000,000, preferably 650,000 to 1,000,000, more preferably 700,000 to 1,000,000, and particularly preferably 700,000 to 900,000, and a number-average molecular weight (Mn) of 10,000 to 300,000, preferably 20,000 to 200,000, and particularly preferably 100,000 to 200,000. If the molecular weight is lower than the above range, the domain shape will be streaky, the particle size will be small, and the particles will be finely dispersed, resulting in a smooth container surface. This may result in unsatisfactory blocking resistance and slipperiness. On the other hand, if the molecular weight is higher than the above range, the domain shape will be roughly spherical, the particle size will be large, and the particles will be loosely dispersed, resulting in poor drop impact resistance. Furthermore, flavor retention tends to be reduced. Therefore, by controlling the mass ratio of ethylene units to propylene units and the molecular weight of the polypropylene-based elastomer and the molecular weight of the resin mainly composed of polypropylene, it is possible to elongate the domains of the polypropylene-based elastomer into a spindle shape, improve the compatibility between the two, and finely disperse the domains of the polypropylene-based elastomer to the above-mentioned size, thereby achieving both drop impact resistance and blocking resistance and slip properties.

[0019] The reason why the polypropylene-based elastomer of the present invention takes on a spindle shape is presumed to be as follows. In the formed film or sheet, or in the processed containers such as cups and trays, the resin is stretched in the extrusion (molding) direction. Therefore, the domain shape in the resin follows suit, tapering off toward the extrusion direction and forming a spindle shape as shown in Figure 1. However, it is thought that the domain shape varies depending on the molecular weight between the matrix and the domain, the molecular weight of the domain itself, and the compatibility between the matrix and the domain. For example, if the molecular weight of the domain is low and compatibility with the matrix is ​​high, the domain will be streaky, with low surface roughness and smoothness, resulting in poor slip resistance. On the other hand, if the molecular weight of the domain is high and compatibility with the matrix is ​​low, the domain will be roughly spherical, resulting in poor drop impact resistance. Compatibility is affected by the composition of the polypropylene-based elastomer and the addition of an ethylene-α-olefin copolymer, etc.

[0020] [Ethylene-propylene block copolymer] From the viewpoint of molding, it is preferable that the MFR (230°C, 2.16 kg load) of an ethylene-propylene block copolymer having a phase-dispersed structure in which a resin mainly composed of polypropylene is the matrix and spindle-shaped polypropylene-based elastomer domains is in the range of 0.1 to 10 g / 10 min, particularly 0.2 to 5 g / 10 min. Furthermore, the raw materials or part of the raw materials for polypropylene-based resins and polypropylene-based elastomers may not only be derived from petroleum, but may also be chemically recycled materials from waste plastics using monomerization techniques such as gasification or liquefaction, or ethylene-propylene block copolymers produced from biomass materials such as plant-based materials. The biomass content can be measured by measuring radioactive carbon concentration, etc. Furthermore, when producing polypropylene-based resins and polypropylene-based elastomers, SVHC substances (listed under the European Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations) such as phthalate ester compounds may be used in the polymerization stage from raw materials in order to reduce the environmental impact. S ubstance of Very H igh C It is desirable to produce it using a catalyst system that does not use an oxidizer.

[0021] [Other ingredients] The polypropylene surface layer in the laminate of the present invention preferably contains homopolypropylene as a viscosity modifier in addition to the ethylene-propylene block copolymer. In other words, resin compositions consisting of a resin primarily composed of polypropylene and a polypropylene-based elastomer tend to have a high molecular weight of the polypropylene-based elastomer in order to achieve both drop impact resistance and slip properties, which can result in high viscosity and poor moldability.However, by blending in homopolypropylene, the viscosity can be adjusted and the extrudability of the molten resin can be improved, thereby improving moldability (workability) without compromising the drop impact resistance of the laminate. The MFR (230° C., 2.16 kg load) of the homopolypropylene is preferably in the range of 0.5 to 20 g / 10 min from the viewpoint of viscosity adjustment. The homopolypropylene is preferably added in an amount of 1 to 40 parts by mass, particularly 1 to 30 parts by mass, per 100 parts by mass of the ethylene-propylene block copolymer.

[0022] To further improve drop impact resistance, rubber components such as ethylene-α-olefin copolymers (e.g., high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene), elastomers, and plastomers may be added. Furthermore, to improve slip properties, lubricants (e.g., calcium stearate) and antiblocking agents (e.g., silica particles) may be added or used in combination with the rubber components described above. Small amounts of known additives, such as antioxidants, may also be added as needed. As part of the move away from plastics due to growing environmental concerns in recent years, it is also important to incorporate chemically recycled materials from waste plastics using monomerization technologies such as gasification and oilification, or biomass materials derived from plants.

[0023] [Multilayer structure] In the laminate of the present invention, it is important that the polypropylene layer is a surface layer (outermost layer or innermost layer), and it is preferable that it is at least the outermost layer, and preferably both the outermost and innermost layers. As long as the surface layer is made of a polypropylene layer, various multilayer structures can be used, but it is preferable that other conventionally known layers such as a gas barrier layer, an oxygen absorbing layer, an adhesive layer, a regrind layer, an adsorbent-containing layer, etc. are included as intermediate layers. The laminate of the present invention can have the following layer configurations, but is not limited to these. Examples include polypropylene layer (outermost layer) / adhesive layer / gas barrier layer / adhesive layer / polypropylene surface layer (innermost layer), polypropylene layer (outermost layer) / adhesive layer / gas barrier layer / adhesive layer / oxygen absorbing layer / polypropylene layer (innermost layer), polypropylene layer (outermost layer) / adhesive layer / gas barrier layer / adhesive layer / oxygen absorbing layer / adhesive layer / gas barrier layer / adhesive layer / polypropylene layer (innermost layer), polypropylene layer (outermost layer) / regrind layer / adhesive layer / gas barrier layer / adhesive layer / oxygen absorbing layer / polypropylene layer (innermost layer), polypropylene layer (outermost layer) / regrind layer / adhesive layer / gas barrier layer / adhesive layer / polypropylene surface layer (innermost layer), polypropylene layer (outermost layer) / regrind layer / adhesive layer / gas barrier layer / oxygen absorbing layer with gas barrier resin as matrix resin / gas barrier layer / adhesive layer / adsorbent-containing layer / polypropylene layer (innermost layer), etc. The innermost layer may be a layer made of an easily peelable resin instead of or in addition to the polypropylene layer.

[0024] In the laminate of the present invention, the thickness of each layer varies depending on the laminate's configuration and manufacturing method, and cannot be generally defined. However, in the case of a film or sheet, the thickness of the polypropylene surface layer (outermost layer) is preferably in the range of 5 to 800 μm, particularly 5 to 500 μm, and the thickness of the polypropylene surface layer (innermost layer) is preferably in the range of 5 to 800 μm, particularly 5 to 500 μm. Regarding the thicknesses of the other layers, when the outermost and innermost layers are within the above thickness ranges, the gas barrier layer (total thickness when multiple layers are formed) is preferably in the range of 5 to 500 μm, particularly 5 to 200 μm, and the oxygen absorbing layer is preferably in the range of 5 to 500 μm, particularly 5 to 200 μm. Furthermore, if a regrind layer is provided, it is preferably formed to a thickness of 50 to 1000 μm, particularly 50 to 800 μm. Furthermore, if an adsorbent-containing layer is provided, it is preferably formed to a thickness of 5 to 500 μm, particularly 5 to 300 μm.

[0025] Furthermore, when the laminate of the present invention is a multilayer container (cup, tray, etc.) formed by thermoforming such as pressure forming, the thickness of the polypropylene surface layer (outermost layer) in the body, which is the thinnest-walled portion of the multilayer container, is preferably in the range of 1 to 160 μm, particularly 1 to 100 μm, and the thickness of the polypropylene surface layer (innermost layer) is preferably in the range of 1 to 160 μm, particularly 1 to 100 μm. Furthermore, when the thicknesses of the other layers are within the above-mentioned thickness ranges, the gas barrier layer (total thickness when multiple layers are formed) is preferably in the range of 1 to 100 μm, particularly 1 to 40 μm, and the oxygen absorbing layer is preferably in the range of 1 to 100 μm, particularly 1 to 40 μm. Furthermore, when a regrind layer is provided, it is preferably formed to a thickness of 10 to 200 μm, particularly 10 to 160 μm. Furthermore, when an adsorbent-containing layer is provided, it is preferably formed to a thickness of 1 to 100 μm, particularly 1 to 60 μm. This allows the effects of each layer, such as gas barrier properties, oxygen absorption properties, flavor properties, etc., to be fully exhibited without impairing drop impact resistance or moldability.

[0026] [Gas barrier layer] The gas barrier layer of the laminate of the present invention can be made of any conventionally known barrier resin, but is preferably made of an ethylene-vinyl alcohol copolymer. For example, a saponified copolymer obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol%, particularly 25 to 50 mol%, to a degree of saponification of 96% or higher, particularly 99 mol% or higher, is suitable from the viewpoint of gas barrier properties. In the present invention, however, it is particularly preferred to use a blend of an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 35 mol% and an ethylene-vinyl alcohol copolymer having an ethylene content of 36 to 50 mol%, in a blending ratio (mass ratio) of 90:10 to 50:50, particularly 80:20 to 60:40. This improves the moldability of the gas barrier layer while maintaining excellent gas barrier properties, making it possible to mold a laminate with a uniform appearance. The ethylene-vinyl alcohol copolymer should have a molecular weight sufficient to enable film formation, and generally has an intrinsic viscosity of 0.01 dL / g or more, particularly 0.05 dL / g or more, measured at 30°C in a mixed solvent of phenol / water in a mass ratio of 85 / 15.

[0027] Examples of gas barrier resins other than ethylene-vinyl alcohol copolymers include polyamides such as nylon 6, nylon 6·6, nylon 6 / 6·6 copolymer, metaxylylenediadipamide (MXD6), nylon 6·10, nylon 11, nylon 12, and nylon 13. Among these polyamides, those having 5 to 50 amide groups per 100 carbon atoms, and particularly 6 to 20 amide groups per 100 carbon atoms, are preferred. These polyamides should also have a molecular weight sufficient to form a film, and for example, it is desirable for the relative viscosity measured in concentrated sulfuric acid (concentration 1.0 g / dL) at 30°C to be 1.1 or higher, and particularly 1.5 or higher. The polyamide may be blended with an ethylene-vinyl alcohol copolymer, and the compounding ratio (mass ratio) of the ethylene-vinyl alcohol copolymer to the polyamide is preferably 50:50 to 99:1. In addition, as will be described later, when polyamide is used as the matrix resin of the oxygen absorbing resin composition, the terminal amino group concentration is 40 eq / 10 6 Polyamide resins with a molecular weight of 1000 or more are preferred because they do not deteriorate due to oxidation when absorbing oxygen.

[0028] [Oxygen absorbing layer] In the laminate of the present invention, the oxygen-absorbing layer can be made of a resin composition obtained by using the propylene-based polymer constituting the polypropylene layer described above, a known propylene-based polymer (hereinafter, these may be collectively referred to simply as "propylene-based polymer"), a gas barrier resin, a regrind resin, or the like as a matrix resin, and incorporating into the matrix resin an inorganic oxygen absorber or an organic oxygen absorber comprising (i) an oxidizing organic component and (ii) a transition metal catalyst (oxidation catalyst).

[0029] (inorganic oxygen absorber) Examples of inorganic oxygen absorbers include iron powder, titanium oxide, cerium oxide, ferrous salts, dithionites, sulfites, metal halides, and zeolites. Iron powder and metal halides are particularly desirable. Known iron powders, such as reduced iron powder, atomized iron powder, electrolytic iron powder, and carbonyl iron powder, can be used as the iron powder. Among these, reduced iron powder, particularly rotary reduced iron powder, which is porous and has a relatively large specific surface area, is preferred. Rotary reduced iron powder has high purity and a large specific surface area, resulting in excellent oxygen absorption performance. These iron powders may be used alone or in combination. The content of iron powder in the oxygen absorber is preferably 3 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the oxygen absorber.

[0030] Examples of the metal halides include halides of alkali metals, alkaline earth metals, copper, zinc, iron, etc. Specific examples include sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, calcium chloride, magnesium chloride, barium chloride, etc. Among these, sodium chloride is preferred. These metal halides may be used alone or in combination of two or more.

[0031] The metal halide is preferably blended in an amount of 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of iron powder, which is the main component of the oxygen absorber. By blending 0.1 part by mass or more of the metal halide per 100 parts by mass of iron powder, sufficient oxygen absorption performance can be obtained. Furthermore, by blending 10 parts by mass or less of the metal halide per 100 parts by mass of iron powder, it is possible to prevent a decrease in oxygen absorption performance due to a decrease in the iron powder content, and also to prevent poor appearance and adhesion to the contents due to bleeding of the metal halide.

[0032] The oxygen absorber according to the present invention may further contain an alkaline substance in addition to iron powder and metal halide. By including an alkaline substance, the amount of hydrogen generated by the reaction between iron and water can be reduced. Examples of the alkaline substance include magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate. Among these, calcium hydroxide and calcium oxide, which is a dehydrated product of calcium hydroxide, are preferred. These alkaline substances may be used alone or in combination.

[0033] (organic oxygen absorber) (i) Oxidizable organic components The oxidizable organic component may be an ethylenically unsaturated group-containing polymer, which has a carbon-carbon double bond, and the double bond, and in particular the α-methylene adjacent to the double bond, are easily oxidized by oxygen, thereby capturing oxygen. Such an ethylenically unsaturated group-containing polymer can be, for example, a homopolymer of a polyene derived from a polyene as a monomer, or a random copolymer or block copolymer obtained by combining two or more of the above polyenes or by combining them with other monomers, as the oxidizable polymer. Among the polymers derived from polyenes, polybutadiene (BR), polyisoprene (IR), natural rubber, nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), chloroprene rubber, ethylene-propylene-diene rubber (EPDM), and the like are preferred, but of course, are not limited to these.

[0034] In addition to the above-mentioned ethylenically unsaturated group-containing polymers, polymers that are themselves easily oxidized, such as polypropylene, ethylene-propylene copolymers, or polymetaxylylenediadipamide with a terminal amino group concentration of less than 40 eq / 106 g, can also be used as the oxidizable organic component. From the standpoint of moldability, it is preferable that the viscosity of the above-mentioned oxidizable polymer or its copolymer at 40° C. is in the range of 1 to 200 Pa·s. These polyene polymers are preferably acid-modified polyene polymers into which a carboxylic acid group, a carboxylic anhydride group, or a hydroxyl group has been introduced. The oxidizable organic component consisting of these oxidizable polymers or copolymers thereof is preferably contained in the oxygen absorbing resin at a ratio of 0.01 to 10% by mass.

[0035] (ii) Transition metal catalyst As the transition metal catalyst, metals of Group VIII of the periodic table such as iron, cobalt, nickel, etc. are preferred, but other metals may also be used, such as Group I metals such as copper and silver, Group IV metals such as tin, titanium, and zirconium, Group V metals such as vanadium, Group VI metals such as chromium, and Group VII metals such as manganese. Transition metal catalysts are generally used in the form of low-valent inorganic salts, organic salts, or complex salts of the transition metals. Examples of inorganic salts include halides such as chlorides, sulfur oxysalts such as sulfates, nitrogen oxysalts such as nitrates, phosphorus oxysalts such as phosphates, and silicates. Examples of organic salts include carboxylates, sulfonates, and phosphonates. Examples of transition metal complexes include complexes with β-diketones or β-keto acid esters. The transition metal catalyst preferably has a transition metal atom concentration (based on mass concentration) in the oxygen absorbing resin in the range of 100 to 3000 ppm.

[0036] [Adhesive layer] In the laminate of the present invention, an adhesive layer can be formed between each layer as needed. In particular, when the gas barrier layer is made of an ethylene-vinyl alcohol copolymer, it is preferable to interpose an adhesive layer therebetween, since the adhesive strength between the gas barrier layer and the polypropylene layers that form the inner and outer layers is poor. Examples of adhesive resins used in the adhesive layer include thermoplastic resins containing carbonyl (-CO-) groups based on carboxylic acid, carboxylic anhydride, carboxylic acid salt, carboxylic acid amide, carboxylic acid ester, etc. in the main chain or side chain at a concentration of 1 to 700 milliequivalent (meq) / 100g resin, particularly 10 to 500 (meq) / 100g resin.

[0037] Suitable examples of adhesive resins include ethylene-acrylic acid copolymers, ionically crosslinked olefin copolymers, maleic anhydride grafted polyethylene, maleic anhydride modified polypropylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefins, ethylene-vinyl acetate copolymers, and blends of ethylene-vinyl alcohol copolymers with maleic anhydride modified olefin resins, with maleic anhydride modified polypropylene and maleic anhydride grafted polypropylene being particularly preferred. The adhesive resins can be used alone or in combination of two or more, or can be blended with a polyolefin resin.

[0038] [Adsorbent-containing layer] In the laminate of the present invention, the adsorbent-containing layer, which is formed as needed, is preferably located closer to the inner layer than the oxygen-absorbing layer, thereby suppressing the migration of by-products generated by the oxygen absorption reaction into the container and improving the flavor of the contents. The adsorbent is preferably blended with the above-mentioned propylene polymer or regrind resin. As the adsorbent, any conventionally known adsorbent can be used, but porous inorganic materials whose main component is silicate, such as zeolite and activated clay powder obtained by acid-treating smectite clay minerals such as montmorillonite, are preferred, and high-silica zeolite (with a silica / alumina ratio of 100 or more), which is Na-type ZSM5 zeolite, is particularly preferred because it has an excellent function of capturing the odor specific to plastics and the above-mentioned oxidative decomposition products. In general, it is preferable to blend such an adsorbent in the adsorbent-containing layer in an amount of 0.5 to 10% by mass.

[0039] [Easily peelable layer] In the laminate of the present invention, for example, when the laminate of the present invention is a tray or cup with a flange obtained by thermoforming a multilayer sheet, it is preferable that the innermost layer of the laminate is an easy-open layer. That is, in such a tray or cup, the easy-open layer is on the upper surface of the flange to which the lid material is joined, thereby significantly improving the ease of opening the lid. As such an easy-open layer, for example, it is preferable to form an easy-open layer from a blend of a propylene-based polymer and an ethylene-based polymer for a lid material in which at least the joining surface with the flange portion is made of a propylene-based polymer or an ethylene-based polymer. Examples of the propylene-based polymer include homopolypropylene and random copolymers of propylene with ethylene or other α-olefins, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Examples of the ethylene-based polymer include ethylene homopolymers such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and medium- to high-density polyethylenes (MDPE and HDPE), copolymers of ethylene with other α-olefins, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene, and copolymers of ethylene with vinyl monomers, such as (meth)acrylic acid, ethyl (meth)acrylate, methyl (meth)acrylate, vinyl acetate, and styrene, and ionomers.

[0040] (Method of manufacturing laminate) In the method for producing a laminate of the present invention, the ethylene-propylene block copolymer is blended with homopolypropylene as a viscosity modifier and melt-kneaded to adjust the viscosity to a range of 0.2 to 5 g / 10 min in MFR (230°C, 2.16 kg load), and the molten resin is extruded to form a laminate having a surface roughness (Sa) of 0.15 to 1.0 μm, particularly 0.15 to 0.80 μm. As mentioned above, by blending the homopolypropylene in an amount of 1 to 40 parts by mass, particularly 1 to 30 parts by mass, per 100 parts by mass of the ethylene-propylene block copolymer, the viscosity of the resin composition can be adjusted to the above range without impairing the excellent properties of the laminate of the present invention, such as drop impact resistance, blocking resistance, and slippage. This improves moldability (workability) and allows the surface roughness (Sa) of the polypropylene layer to be adjusted to the above range. That is, if the MFR of the resin composition is lower than the above range, the desired laminate cannot be obtained due to abnormal resin pressure, making film formation impossible, or waviness due to unstable flow may occur, making it difficult to adjust the surface roughness (Sa) to the above range. Furthermore, if the MFR is higher than the above range, the surface layer tends to be smoother, making it difficult to adjust the surface roughness (Sa) to the above range.

[0041] The ethylene-propylene block copolymer and homopolypropylene can be melt-kneaded by known methods, such as dry-blending pellets of these in a mixer or the like and then melt-extruding the mixture, or melt-kneading the pellets in a kneader. In the present invention, it is necessary to melt-knead the polypropylene-based elastomer so that the domains of the polypropylene-based elastomer are dispersed in a spindle shape having the above-mentioned size, and it is necessary to adjust the kneading conditions appropriately depending on the viscosity of the resin used, etc. The temperature conditions for melt-kneading are not particularly limited, but it is preferable to perform the melt-kneading in the range of 170 to 270° C. At temperatures lower than the above range, efficient kneading may not be possible, and at temperatures higher than the above range, the resin may be deteriorated.

[0042] The laminate of the present invention can be produced by a conventionally known method except for using a molten resin (blend) with an adjusted MFR as described above, including, but not limited to, lamination with other layers by coextrusion, coinjection, or extrusion lamination, or by forming a single-layer film or sheet from the blend by extrusion molding in advance and laminating it with other layers by dry lamination, thereby forming it into a multilayer film, multilayer sheet, multilayer tube, etc. Furthermore, the multilayer sheet can be formed into a cup, tray, etc. by thermoforming.

[0043] In the method for producing the laminate of the present invention, it is desirable to use various resins or resin compositions constituting the intermediate layer of the laminate, which have a thermal shrinkage rate similar to that of the resin composition (blend) constituting the polypropylene layer. For example, by using the resin composition (blend) constituting the polypropylene layer as the matrix of the oxygen-absorbing resin layer, it is possible to suppress winding slippage caused by differences in the shrinkage rates of the molded laminate sheet, and to suppress the occurrence of molding defects. Furthermore, according to the manufacturing method of the present invention, a laminate having a polypropylene surface layer with a surface roughness (Sa) in the range of 0.15 to 1.0 μm can be molded, which improves slipperiness. Even when the molding process, filling / sealing process, packaging process, etc. are carried out continuously on a conveying line, no clogging of containers occurs, and excellent productivity can be achieved. [Example]

[0044] The present invention will be further explained by way of experimental examples, but the present invention is not limited thereto. (Experimental Examples 1 to 5) Using a 6-type, 7-layer multilayer sheet molding machine, each resin was melt-kneaded in a single-screw extruder, extruded into a sheet from a T-die at a T-die temperature of 230°C, solidified by contact with a cooling roll, and wound up to form a 500μm-thick multilayer sheet. The layer structure from outside was: outermost PP layer / regrind layer / adhesive layer / barrier layer / adhesive layer / oxygen scavenger layer / inner PP layer / easy-adhesion layer. The outermost and inner PP layers were made using pellets of ethylene-propylene block copolymers composed of polypropylene-based resins and polypropylene-based elastomers with the compositions and molecular weights shown in Table 1, as well as white coloring resin. The regrind layer was made by blending 44 parts by weight of the ethylene-propylene block copolymer shown in Table 1 with 100 parts by weight of scraps (shredded portions of the multilayer sheet, trim, and sheet skeleton generated during this test) and adding a compatibilizer and white coloring resin. The adhesive layer was made using maleic anhydride-modified polypropylene, and the oxygen scavenger layer was made using a resin composition consisting of 29 parts by weight of an iron-based oxygen absorber (a mixture of 100 parts by weight of reduced iron powder, 2 parts by weight of sodium chloride, and 1 part by weight of calcium hydroxide) kneaded with 71 parts by weight of random polypropylene with a MFR of 0.6 g / 10 min. The adhesive layer was made using a dry-blended resin of polypropylene and polyethylene. The resulting multilayer sheet was heated to 145°C and plug-assisted vacuum-pressure formed into flanged multilayer trays. The container dimensions were flange outer diameter (long axis: 155 mm x short axis: 120 mm), opening diameter (long axis: 135 mm x short axis: 100 mm), bottom outer diameter (long axis: 115 mm x short axis: 90 mm), and height 35 mm.

[0045] (Experimental Example 6) A multilayer tray was molded in the same manner as in Experimental Example 1, except that a resin was used in which 17.7 parts by mass of homopolypropylene with an MFR of 2.0 g / 10 min (230°C, 2.16 kg load) was dry-blended with 100 parts by mass of resin for the outermost PP layer and the inner PP layer.

[0046] The various measurement methods are as follows: <Structural analysis of ethylene-propylene block copolymer> In the ethylene-propylene block copolymers used in Experimental Examples 1 to 5, the compounding ratio and molecular weight of the resin (PP component) mainly composed of polypropylene and the polypropylene-based elastomer (rubber component) were 13The content was determined by C-NMR measurement (manufactured by JEOL) and GPC measurement (manufactured by Agilent). As a pretreatment for the measurement sample, the resin was refluxed and dissolved in xylene, allowed to cool, and then separated into solid and liquid forms. The xylene-soluble portion was reprecipitated with methanol, and the precipitate was filtered and dried, after which the mass was measured and used as the amount of rubber component. The xylene-insoluble portion was redissolved and reprecipitated with methanol, and the filtered and dried resin was used as the PP component. In Experimental Example 6, a homopolypropylene was dry-blended, so the value was calculated.

[0047] (1) Dispersion state (domain shape and size) The cross section of the bottom of the obtained multilayer tray, cut parallel to the pulling direction during sheet production, was observed using a transmission electron microscope (TEM) (Hitachi, Ltd.) As a pretreatment, a sample cut from the multilayer tray was attached to a cryo-supporting table, and the surface was polished using an ultramicrotome (Leica) equipped with a diamond knife using a cryo-system (Leica). Then, vapor staining with metal oxide was performed to prepare ultrathin sections. From the obtained TEM photograph (20 μm × 20 μm square), all domains of the polypropylene-based elastomer in the outermost PP layer of the multilayer tray were measured using image analysis particle size distribution software (Mac-View manufactured by Mountec Co., Ltd.), and the minor and major axes of each were measured, and the aspect ratio and circle-equivalent domain size were calculated. The average value was calculated from the measurement results of the total number of domains.

[0048] (2) Surface roughness Sa (unit: μm) A 10mm x 10mm sample piece was cut from the bottom of the resulting multi-layer tray. The shape of the container's outer surface was measured using a non-contact surface profiler (Zygo). MetroPro (Ver. 9.1.4 64-bit) was used for measurements and image analysis. An area of ​​282µm x 212µm was measured, and wavelengths of 1.326µm or less were cut from the resulting raw data to remove noise. The average value was calculated using an N number of 5.

[0049] (3) Slipperiness (unit: N) The sliding properties of the resulting multilayer tray were evaluated using a friction tester (manufactured by Toyo Seiki Seisakusho) to determine the drag resistance value, with the load applied to the load cell during measurement being taken as the dynamic friction force. Measurements were carried out at a speed of 100 mm / min in an environment of 23°C and 50% RH, with the multilayer tray placed on a SUS plate and a 600 g weight applied. The average value was calculated from an N count of 5. The evaluation criteria are as follows: ○: Less than 2.5N △: 2.5N or more and less than 3.0N ×: 3.0N or more

[0050] (4) Drop impact resistance The resulting multi-layer tray was filled with 200 g of distilled water, heat-sealed with a lid, sterilized by boiling at 95°C for 30 minutes, and then stored at 5°C for 24 hours. After storage, the tray was dropped from a height of 150 cm in a 5°C environment to determine its drop resistance. N=20. Evaluation criteria were as follows: ○: There were 3 or fewer cracks △: Less than 10 cracks ×: 10 or more broken pieces

[0051] (5) Flavor The resulting multi-layer tray was filled with 200 g of distilled water, heat-sealed with a lid, sterilized by boiling at 95°C for 30 minutes, and then stored at room temperature for 24 hours. After storage, a sensory evaluation was conducted by 10 panelists using a 4-point scale, and the average score was calculated. The evaluation criteria were as follows: 0 is tasteless, and 4 is a level where the taste can be detected very strongly. ○: Less than 2.5 △: 2.5 or more and less than 3.5 ×: 3.5 or more

[0052] The results showed that Experimental Examples 1 and 6 had a spindle-shaped polypropylene elastomer that achieved both smoothness and drop impact resistance, resulting in favorable results. Experimental Example 6 in particular had low resin viscosity and excellent film-forming properties. Experimental Example 2 had slightly low drop impact resistance, which is thought to be due to the small amount of polypropylene elastomer used. Experimental Examples 3 and 5 had slightly low drop impact resistance, which is thought to be due to the shape or particle size of the polypropylene elastomer. Furthermore, the flavor properties were poor, which is presumably due to the molecular weight of the polypropylene elastomer. Experimental Example 4 had good drop impact resistance but poor slip resistance. This is thought to be because the polypropylene elastomer had a striated shape and a high aspect ratio, which smoothed out the surface irregularities and created a large contact area.

[0053] [Table 1] [Industrial Applicability]

[0054] The laminate of the present invention has excellent drop impact resistance, blocking resistance, and flavor properties, and also has excellent slip properties, making it easy to transport on a production line. Therefore, it can be suitably used as a packaging material for mass-produced foods, particularly for containers for storing cooked rice and other foods for which flavor is important. Furthermore, since it is made of a propylene-based polymer with excellent heat resistance, it can also be suitably used as a packaging material for pouches and other products that are subjected to retort sterilization, etc.

Claims

1. A laminate having a polypropylene layer made of an ethylene-propylene block copolymer as a surface layer, the polypropylene layer has a phase-dispersed structure in which a resin containing polypropylene as a main component is a matrix and a spindle-shaped polypropylene-based elastomer is a domain; The surface roughness (Sa) of the polypropylene layer is 0.15 μm to 1.0 μm, the polypropylene layer contains 1 to 30 parts by mass of homopolypropylene per 100 parts by mass of the ethylene-propylene block copolymer, The polypropylene elastomer has a weight average molecular weight (Mw) of 500,000 to 1,000,000 and a number average molecular weight (Mn) of 10,000 to 300,000.

2. 2. The laminate according to claim 1, wherein the domains have a minor axis in the range of 0.2 to 4.0 μm and a major axis in the range of 0.5 to 5.0 μm.

3. 3. The laminate according to claim 1, wherein the polypropylene layer contains 1 to 30 parts by mass of the polypropylene-based elastomer per 100 parts by mass of the resin containing polypropylene as a main component.

4. The laminate according to any one of claims 1 to 3, wherein the resin containing polypropylene as a main component has a weight average molecular weight (Mw) of 300,000 to 800,000 and a number average molecular weight (Mn) of 10,000 to 300,000.

5. 5. The laminate according to claim 1, comprising at least the polypropylene layers as inner and outer layers, an oxygen absorbing layer, and a gas barrier layer as an intermediate layer.

6. 6. The laminate according to claim 1, which has the shape of a tray or a cup.

7. A method for producing a laminate having a polypropylene layer made of an ethylene-propylene block copolymer as a surface layer, comprising: A method for producing a laminate, characterized in that 100 parts by mass of the ethylene-propylene block copolymer are blended with 1 to 30 parts by mass of homopolypropylene as a viscosity modifier, and the mixture is melt-kneaded to adjust the viscosity to a range of 0.1 to 10 g / 10 min in MFR (230°C, 2.16 kg load), and the viscosity-adjusted molten resin is extruded to form a surface layer having a phase dispersion structure in which a resin containing polypropylene as a main component is a matrix and a spindle-shaped polypropylene-based elastomer is a domain, the polypropylene-based elastomer having a weight-average molecular weight (Mw) of 500,000 to 1,000,000, a number-average molecular weight (Mn) of 10,000 to 300,000, and a surface roughness (Sa) of 0.15 μm to 1.0 μm.

8. 8. The method for producing a laminate according to claim 7, wherein the polypropylene elastomer is contained in an amount of 1 to 30 parts by mass per 100 parts by mass of the ethylene-propylene block copolymer.

9. The method for producing a laminate according to any one of claims 7 to 8, wherein the resin containing polypropylene as a main component has a weight average molecular weight (Mw) of 300,000 to 800,000 and a number average molecular weight (Mn) of 10,000 to 300,000.

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