JP7420528B2 - Polypropylene resin laminated foam sheets and molded products - Google Patents

Description

An object of the present invention is to provide a polypropylene resin laminated foam sheet that is lightweight and has excellent interlayer adhesion, and a molded product obtained by molding the laminated foam sheet.

Foamed sheets of polypropylene (hereinafter referred to as "PP")-based resins have excellent physical properties and are therefore widely used as various molded products, such as containers for food and beverages. Furthermore, in order to exhibit various functions, a laminated foam sheet is used in which other layers are laminated on a PP resin foam sheet as a base material.

Patent Document 1 discloses that a foamed sheet or a filler sheet mainly composed of an unstretched PP film and PP is thermally laminated via an intermediate layer containing an acid-modified PP resin having a specific acid value and weight average molecular weight. A method for producing a PP laminate is described in which the intermediate layer is formed by dissolving the acid-modified PP resin in an organic solvent. In addition, Patent Document 2 discloses that a PP resin film printed on a PP resin foam sheet is laminated with the printed surface facing inside (foam sheet side), and the printed layer and PP resin film are bonded to the PP resin foam sheet side. A method for manufacturing a PP-based laminated foam sheet is described in which PP-based resin is laminated by extrusion lamination so that the peel strength between the sheet and the resin film becomes a specific value.

Patent No. 4987200 Japanese Patent Application Publication No. 2008-68529

Laminated foam sheets are required to have excellent adhesive strength between each layer. In particular, in recent years, there has been an increase in demand for food and drink containers made of PP resin laminated foam sheets due to the increasing demand for bento boxes and the like that can be heated and eaten in a microwave oven. The PP resin laminated foam sheet used for such uses is required to have excellent adhesive strength between each layer after heating. Further, in order to use it as a molded product such as a container for food and drink, it is desirable that the PP resin laminated foam sheet be lightweight.

One method for molding a laminated foam sheet is extrusion lamination, in which molten resin is poured between a PP resin foam sheet as a base material and a film. By using the extrusion laminate, an adhesive layer is formed between the PP resin foam sheet and the film, making it possible to form a laminated foam sheet with excellent adhesive properties. Depending on the temperature and material of the resin extruded by extrusion lamination, the adhesion between the foam sheet and the film laminated to the extrusion lamination sheet may be insufficient, and containers obtained by thermoforming from laminated foam sheets may not be suitable for food products. When packaged and heated in a microwave oven, large or small peeling may occur between the foam sheet and the film, resulting in blisters.

In addition, when laminating a non-foamed PP resin and a PP resin printed film onto a PP resin foam sheet by extrusion lamination, the thinner the non-foamed PP resin layer constituting the adhesive layer, the more the PP resin foam sheet The peel strength between the layer and the PP resin printed film layer becomes low, and the non-foamed PP resin layer easily peels off. Furthermore, even when a molded product obtained by thermoforming a PP resin laminated foam sheet with a thinner non-foamed PP resin layer constituting the adhesive layer is heated in a microwave oven, the foam sheet and film are In between, large peeling may occur, or small peeling may occur and appear as blisters. On the other hand, if the non-foamed PP resin layer is made thicker in order to obtain sufficient adhesive strength, there is a problem in that the weight of the resulting laminate increases.

In the method for manufacturing a PP laminate described in Patent Document 1, an intermediate layer is formed between a film and a PP foam sheet by thermal lamination. However, in this method, it is necessary to dissolve the acid-modified PP resin in an organic solvent, and the production requires many steps. Further, in the PP laminated foam sheet obtained by the method described in Patent Document 2, the sheet peels off in a container using polyurethane as an ink resin. Further, Patent Document 2 does not mention at all the adhesive strength of each layer of the obtained container after heating.

An object of the present invention is to provide a PP resin laminated foam sheet that is lightweight and has excellent interlayer adhesion, and a molded product obtained by molding the laminated foam sheet.

In the PP resin laminated foam sheet for molding of the present invention, a polypropylene resin printed film is laminated on a polypropylene resin foam sheet via a non-foamed polypropylene resin layer by extrusion lamination, and the polypropylene resin printed film is made of polypropylene resin. the printing layer is disposed on the side of the non-foamed polypropylene resin layer, the non-foamed polypropylene resin layer has a thickness of 30 to 100 μm, and has a thickness of at least 30 μm to 100 μm, It is characterized by a two or more layered structure in which a modified polypropylene resin layer is disposed on the printed layer side of the polypropylene resin printed film, and a homopolypropylene resin layer is disposed on the polypropylene foamed resin sheet side.

A polypropylene resin printed film is obtained by thermoforming a polypropylene resin laminated foam sheet laminated to a polypropylene resin foam sheet via a non-foamed polypropylene resin layer by extrusion lamination, and the polypropylene resin printed film is , comprising a polypropylene resin film and a printed layer, the printed layer is disposed on the side of the non-foamed polypropylene resin layer, and the non-foamed polypropylene resin layer has a thickness of 30 to 100 μm, and has at least The polypropylene resin printed film is characterized by having a two or more layer structure in which a modified polypropylene resin layer is disposed on the printing layer side and a homopolypropylene resin layer is disposed on the polypropylene resin foam sheet side.

The PP resin laminated foam sheet and molded article of the present invention are excellent in light weight and have excellent interlayer adhesion, especially adhesion when heated. Therefore, the PP resin laminated foam sheet and molded article of the present invention can be suitably used as packaging containers for food and drink products, particularly packaging containers heated by microwave ovens and the like, and materials thereof.

FIG. 1 is a diagram schematically showing a PP resin laminated foam sheet of the present embodiment. It is a figure showing the outline of extrusion laminate of an example.

Embodiments of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

(1) PP resin laminated foam sheet for molding An example of a PP resin laminated foam sheet for molding according to the present embodiment (hereinafter referred to as "this laminated foam sheet") is shown in FIG. The laminated foam sheet 1 includes a PP resin foam sheet layer 11 and a PP resin printed film layer 13. The PP resin printed film layer 13 has a printed layer 131 and a film layer 132.

The PP resin foam sheet layer 11 and the PP resin printed film layer 13 are bonded and laminated with the non-foamed PP resin layer 12 in between. The non-foamed PP resin layer 12 has a two-layer structure consisting of a homo-PP resin layer 121 and a modified PP resin layer 122. The modified PP resin layer 122 is disposed on the printed layer 131 side of the PP resin printed film 13 and is adhered to the printed layer 131. Further, the homo-PP resin layer 121 is disposed on the PP resin foam sheet 11 side and is adhered to the PP resin foam sheet 11.

The PP resin foam sheet constituting the PP resin foam sheet layer is not limited in its specific structure as long as it is a foam sheet containing PP resin as a main component. The PP resin may be a homopolymer of propylene, or a copolymer of propylene and other monomers. Examples of the copolymer include block copolymers, random copolymers, and graft copolymers. Further, the polypropylene resin may be a linear polypropylene resin in which long chain branches are introduced by a method such as irradiation with an electron beam. The PP resin foam sheet can be obtained by a known method, for example, by melt-kneading the main component polypropylene resin and a foaming component, followed by extrusion foaming. The conditions for melt-kneading and foaming are not particularly limited and can be appropriately set as necessary.

The non-foamed PP resin layer functions as an adhesive layer that adheres the PP resin foam sheet layer and the PP resin printed film layer. The non-foamed PP resin layer is composed of two or more layers, at least a modified PP resin layer is arranged on the printed layer side of the PP resin printed film, and a homo PP resin layer is arranged on the PP resin foam sheet side. It has a layered structure. With this configuration, sufficient adhesion of the layer can be achieved while making the non-foamed PP resin layer thinner by extrusion lamination. In particular, it is possible to improve adhesion when heated, and to achieve excellent adhesion regardless of the type of resin used in the film ink.

The modified PP resin constituting the modified PP resin layer is PP modified by introducing a polar group using graft polymerization, and has a polar group in the non-polar polypropylene skeleton, so it is effective for adhesion between different materials with different polarities. Good sex. There is no particular limitation on the specific structure of the modified PP resin. A specific example of the modified PP resin is an acid-modified PP resin. In order to acid-modify the PP resin, unsaturated carboxylic acids (eg, acrylic acid and methacrylic acid, unsaturated dicarboxylic acids such as maleic acid) and derivatives thereof (eg, acid anhydrides) can be used. Specific examples of the acid-modified PP resin include (meth)acrylic acid-modified PP resin, maleic acid-modified PP resin, and maleic anhydride-modified PP resin, with maleic anhydride-modified PP resin being preferred.

The non-foamed PP resin layer may be composed of two layers, the homo PP resin layer and the modified PP resin layer, or a three layer structure having another layer between the homo PP resin layer and the modified PP resin layer. The above layered structure may be used.

The thickness of the non-foamed PP resin layer is 20 to 150 μm, preferably 20 to 100 μm, and more preferably 30 to 100 μm. It is preferable that the thickness of the non-foamed PP resin layer is within the above range, since it is possible to achieve sufficient layer adhesion while reducing the weight of the laminated foam sheet.

Further, the thicknesses of the homo-PP resin layer and the modified PP resin layer in the non-foamed PP resin layer can be appropriately determined as necessary. The thickness of the homo-PP resin layer and the modified PP resin layer may be the same or different. From the viewpoint of cost, it is preferable that the homo-PP resin layer is thicker than the modified PP resin layer. The thickness of the homo-PP resin layer can be, for example, 20 to 100 μm. The thickness of the modified PP resin layer can be 1 to 20 μm, preferably 3 to 15 μm. Further, the thickness ratio between the homo-PP resin layer and the modified PP resin layer in the non-foamed PP-based resin layer is not particularly limited, and can be appropriately determined as necessary. The ratio can be, for example, (20-1):1, preferably (20-3):1. The above thicknesses and ratios can be combined as appropriate.

The PP resin printed film layer has a printed layer and a film layer. There is no restriction on the method of forming the printing layer as long as it can impart design to the laminated foam sheet. The film layer is not limited in its specific structure as long as it contains polypropylene resin as a main component. The polypropylene resin may be a propylene homopolymer or a copolymer of propylene and other monomers. Examples of the copolymer include block copolymers, random copolymers, and graft copolymers. Further, the film layer may be a non-stretched film or a stretched film such as a biaxially stretched film. The film layer is preferably a non-stretched film (CPP).

There is no particular limitation on the type of resin constituting the ink applied to the PP resin printed film layer. Specific examples of the resin include halogenated PP resins (chlorinated PP resins, etc.), polyester resins, urethane resins, epoxy resins, melamine resins, alkyd resins, phenolic resins, and acrylic resins.

In this laminated foam sheet, the peel strength between the PP resin film and the printed layer is determined by (a) measuring a test piece with a width of 15 mm at a peeling speed of 300 mm/min and a peeling angle of 180° in accordance with JIS Z 0238. or (b) 2.6 N/1 when measured on a 25 mm wide test piece at a peeling rate of 200 mm/min and a peeling angle of 90° in accordance with JIS Z 0237. It is preferable that it is 25 mm or more. When the peel strength is within the above range, sufficient layer adhesion can be achieved.

The thicknesses of the present laminated foam sheet, the PP resin foam sheet layer, and the PP resin printed film layer are not particularly limited, and can be appropriately determined as necessary. The thickness of the laminated foam sheet can be, for example, more than 0.8 mm and less than 2 mm, preferably more than 0.8 mm and less than 1.8 mm. The thickness of the PP resin foam sheet can be, for example, 0.8 to 2.0 mm. The thickness of the PP resin printed film layer can be, for example, 10 to 100 μm, preferably 20 to 70 μm.

The present laminated foam sheet may be composed only of the PP resin foam sheet layer, the non-foamed PP resin layer, and the PP resin printed film layer, and the lightness of the present laminated foam sheet and the adhesiveness of each layer can be improved. If necessary, other layers may be included as long as they do not cause significant damage.

Each layer constituting the present laminated foam sheet may contain other components as necessary, as long as the lightness of the present laminated foam sheet and the adhesion of each layer are not significantly impaired. Specifically, the other components include, for example, additives used in known resin sheets, such as flame retardants, ultraviolet absorbers, optical brighteners, antistatic agents, antifogging agents, lubricants, and antiblocking agents. agents, flow improvers, plasticizers, dispersants, and antimicrobial agents.

There are no particular limitations on the shape, dimensions, and specific uses of this laminated foam sheet. As described below, this laminated foam sheet can be used to obtain various molded products by molding. Specific examples of the molded product include containers such as packaging containers, for example containers for packaging food and beverages. Therefore, the present laminated foam sheet can be preferably used for thermoforming or producing molded products, and more preferably for producing packaging containers. Note that the above-mentioned "container" includes not only the entire container but also a part of the container. For example, the "container" includes not only the main body of the container but also the lid of the container.

This laminated foam sheet is manufactured by laminating a PP resin printed film on a PP resin foam sheet via a non-foamed PP resin by extrusion lamination. An example is shown in FIG. A homo PP resin and a modified PP resin, which are molten non-foamed PP resins 5, are merged in a die 2 and extruded into a film form from two extruders (not shown), and then a non-foamed PP resin is extruded by a roll 3. By press-bonding the PP foam resin sheet 4 and the PP resin print film 6 via the PP resin 5, the laminated foam sheet can be obtained.

In the extrusion laminate, the resin temperature of the non-foamed PP resin immediately after being extruded from the die can be 280°C to 290°C. When the resin temperature is within the above range, each layer constituting the laminated foam sheet has excellent adhesion, and even if the molded product obtained by thermoforming is heated in a microwave oven, none of the layers will peel off. Therefore, it is preferable.

If the resin temperature of the non-foamed PP resin immediately after being extruded from the die is high, it will dissolve the ink contained in the printing layer of the PP resin printed film, and the adhesiveness between the PP resin printed film and the PP resin foam sheet will deteriorate. It is thought that this will increase. Additionally, if the resin temperature of the non-foamed PP resin immediately after being extruded from the die is high, a portion of the non-foamed PP resin will easily enter the porous structure of the foamed PP resin sheet, resulting in a poor anchoring effect. It is believed that this increases the adhesion between the foam sheet and the non-foamed PP resin layer (the above explanation is the inventor's opinion and is not intended to define or limit the present invention in any way).

As a specific method for measuring the resin temperature, for example, the temperature of the non-foamed PP resin layer extruded from the T-die is measured using a contact temperature sensor (such as a portable thermometer DP-350 manufactured by Rikagaku Kogyo Co., Ltd.). can be measured and taken as the resin temperature of the PP resin.

In the extrusion laminate, the temperature of the cooling roll can be 30 to 70°C, preferably 40 to 70°C, more preferably 40 to 60°C.

Other specific conditions for the extrusion lamination can be appropriately set as necessary. For example, the line speed can be 10 to 40 m/min, preferably 10 to 35 m/min, and more preferably 12 to 31 m/min. By setting the line speed within the above range, the productivity of the laminated foam sheet can be increased. In particular, it is preferable to increase the resin temperature of the non-foamed PP resin because the line speed can be increased, and as a result, the productivity of the laminated foam sheet can be further improved.

(2) Molded product The molded product according to this embodiment (hereinafter referred to as "this molded product") is obtained by molding the present laminated foam sheet. There are no particular limitations on the shape, dimensions, and specific uses of this molded article. Applications of the molded article include containers such as packaging containers, for example containers for packaging food and beverages. As will be described later, this molded product has excellent peel strength against heating by a microwave oven or the like, and therefore, this molded product can be suitably used as a heating container. Note that the above-mentioned "container" includes not only the entire container but also a part of the container. For example, the "container" includes not only the main body of the container but also the lid of the container.

There is no particular limitation on the specific method of the molding. The molding usually includes thermoforming. The specific method of thermoforming is not particularly limited, and known thermoforming methods such as hot plate forming, vacuum forming, pressure forming, or vacuum pressure forming can be used. Furthermore, there are no particular limitations on the conditions for thermoforming. Molding conditions can be appropriately determined as necessary.

As mentioned above, this laminated foam sheet has excellent adhesion between each layer. Therefore, the molded product of the present invention also has excellent adhesion between each layer. Specifically, even if the molded product is heated in a microwave oven (conditions: 500 to 1600W, 60 to 100 seconds), it will cause damage between any of the layers of the PP resin laminated foam sheet constituting the molded product, for example. , Peeling does not occur between the printed layer and the film layer of the PP resin printed film layer or between the printed layer of the PP resin printed film layer and the non-foamed PP resin layer. As a method for producing a molded product that does not peel off due to heating, for example, when manufacturing this laminated foam sheet by extrusion lamination, the resin temperature of the non-foamed PP resin immediately after extrusion from the die or the temperature of the cooling roll can be adjusted. One example is how to control the Specifically, for example, the resin temperature of the non-foamed PP resin immediately after extrusion from the die is 280°C to 290°C, and the cooling roll temperature is 30 to 90°C, preferably 40 to 70°C, more preferably This can be achieved by setting the temperature to 40 to 60°C. The method for measuring the resin temperature is as described above.

Hereinafter, the present invention will be specifically explained with reference to Examples. Note that the present invention is not limited to the embodiments shown in the examples. The embodiments of the present invention can be variously modified within the scope of the present invention depending on the purpose, use, etc.

(1) Manufacture of PP resin laminated foam sheet PP resin foam sheet is made into a sheet by melting PP resin in an extruder, press-feeding a foaming agent, cooling to the appropriate foaming temperature, and extruding it through a die to foam. (thickness 1.5 mm). As the PP resin printing films, CPP films "KT" (thickness 25 μm, ink: chlorinated PP) and "KL" (thickness 25 μm, ink: urethane) manufactured by Suntox were used. Among the non-foamed PP resins, Novatec PP "FL03H" manufactured by Nippon Horipro Co., Ltd. was used as the homo-PP resin, and Modic AP "P555" (maleic anhydride modified PP manufactured by Mitsubishi Chemical Corporation) was used as the modified PP resin. )It was used.

A schematic diagram of extrusion laminate is shown in FIG. By supplying molten homo-PP and modified PP from the die 2 and passing the PP-based foamed resin sheet 4 and the PP-based resin printed film 6 through the roll 3, a non-foamed PP-based resin consisting of homo-PP resin and modified PP resin is produced. A PP resin printed film was laminated on a PP resin foam sheet via a layer to obtain PP resin laminated foam sheets of Examples 1 to 4 . A schematic diagram of the laminated foam sheet is shown in FIG. Table 1 shows the extrusion resin temperature, roll temperature, and line speed. The thicknesses of the homo-PP resin layer and modified PP resin layer of the obtained PP-based resin laminated foam sheet and the PP-based resin printed film are also listed in Table 1. The temperature of the extruded resin was measured using a contact temperature sensor (portable thermometer DP-350, manufactured by Rikagaku Kogyo Co., Ltd.).

The PP resin laminated foam sheets obtained by the above method were thermoformed by vacuum pressure forming to produce containers of Examples 1 to 4 (container size: length 152 mm, width 215 mm, height 30 mm).

PP resin laminated foam sheets and containers of Comparative Examples 1 to 6 were produced in the same manner as above, except that only the homo-PP resin was used as the non-foamed PP resin.

(2) Peel strength test of PP resin laminated foam sheets The PP resin laminated foam sheets of Examples 1 to 4 and Comparative Examples 1 to 6 obtained by the above method were tested for peel strength in the 90° direction and peel strength in the 180° direction. Peel strength was measured. Table 1 shows the results of the above peel strength test.

The peel strength in the 90° direction was measured in accordance with JIS Z 0237. Specifically, a strip-shaped test piece with a width of 25 mm was cut out from a PP resin laminated foam sheet (n=3). Approximately 20 mm of the edge of the film constituting the PP resin laminated foam sheet is peeled off, the film and the edge of the base sheet from which the film has been peeled are grabbed with a jig, and the film and sheet are pulled in a 90° direction at a speed of 200 mm/min. The test force at the time of film peeling was measured.

The peel strength in the 180° direction was measured in accordance with JIS Z 0238. in particular,
A strip-shaped test piece with a width of 15 mm was cut out from the PP resin laminated foam sheet (n=3). Approximately 20 mm of the edge of the film constituting the PP resin laminated foam sheet is peeled off, the film and the edge of the base sheet from which the film has been peeled are grabbed with a jig, and the film and sheet are pulled in a 180° direction at a speed of 300 mm/min. The test force at the time of film peeling was measured.

(3) Heating test Fill the container obtained by the above method with stewed beef tendon (180 g) as an ingredient, heat it in a microwave (test conditions: 500 W, 1 minute 40 seconds), and then construct the container. The presence or absence of peeling of the layers of the PP resin laminated foam sheet was visually confirmed. The results are shown in Table 1. In Table 1, "◎" indicates that there is no delamination (delamination; peeling that occurs at the interface between the printed layer and the non-foamed PP resin layer), and "○" indicates that there is almost no delamination (a level that cannot be noticed unless you look carefully). ), "△" indicates that several independent delaminations are observed, and "x" indicates that continuous delamination is conspicuous.

1; PP resin laminated foam sheet, 11; PP resin foam sheet layer, 12; non-foamed PP resin layer, 121; homopolypropylene resin layer, 122; modified polypropylene resin layer, 13; PP resin printed film layer, 131; Print layer, 132; Film layer, 2; Die, 3; Roll, 4; PP foam resin sheet, 5; Non-foamed PP resin, 6; PP resin print film.

Claims (4)

A molded product obtained by thermoforming a polypropylene resin laminated foam sheet in which a polypropylene resin printed film is laminated on a polypropylene resin foam sheet via a non-foamed polypropylene resin layer by extrusion lamination,
The polypropylene resin printing film has a polypropylene resin film and a printing layer, the printing layer is arranged on the non-foamed polypropylene resin layer side,
The non-foamed polypropylene resin layer has a thickness of 30 to 100 μm, and includes at least a modified polypropylene resin layer on the printing layer side of the polypropylene resin printing film and a homopolypropylene resin layer on the polypropylene resin foam sheet side. It is a layered structure of two or more layers in which each is arranged,
A molded article, characterized in that the thickness ratio of the homopolypropylene resin layer to the modified polypropylene resin layer is (9 to 1):1 . The molded article according to claim 1, characterized in that the peel strength between the polypropylene resin film and the printing layer of the polypropylene resin laminated foam sheet satisfies the following (a) or (b):
(a) In accordance with JIS Z 0238, the peel strength measured using a test piece with a width of 15 mm at a peel rate of 300 mm/min and a peel angle of 180° is 1.8 N/15 mm or more;
(b) In accordance with JIS Z 0237, a peel strength of 2.6 N/25 mm or more is measured using a 25 mm wide test piece at a peel rate of 200 mm/min and a peel angle of 90°. A polypropylene resin printing film is laminated to a polypropylene resin foam sheet via a non-foamed polypropylene resin layer by extrusion lamination,
The polypropylene resin printing film has a polypropylene resin film and a printing layer, the printing layer is arranged on the non-foamed polypropylene resin layer side,
The non-foamed polypropylene resin layer has a thickness of 30 to 100 μm, and includes at least a modified polypropylene resin layer on the printing layer side of the polypropylene resin printing film and a homopolypropylene resin layer on the polypropylene resin foam sheet side. It is a layered structure of two or more layers in which each is arranged,
A polypropylene resin laminated foam sheet for molding, characterized in that the thickness ratio of the homopolypropylene resin layer to the modified polypropylene resin layer is (9 to 1):1 . The polypropylene resin laminated foam sheet for molding according to claim 3, characterized in that the peel strength between the polypropylene resin film and the printing layer satisfies the following (a) or (b):
(a) In accordance with JIS Z 0238, the peel strength measured using a test piece with a width of 15 mm at a peel rate of 300 mm/min and a peel angle of 180° is 1.8 N/15 mm or more;
(b) In accordance with JIS Z 0237, a peel strength of 2.6 N/25 mm or more is measured using a 25 mm wide test piece at a peel rate of 200 mm/min and a peel angle of 90°.

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