JP2017178332A - Multilayer film before foaming and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film before foaming which is unfoamed or partially foamed in a state of a container before foaming laminated on the surface of the container and which can be actually foamed by heating the container before foaming.SOLUTION: In a multilayer film before foaming constituting a container before foaming by being laminated on the surface of the container and capable of forming a foamed layer by the heating of the container before foaming: each layer is constituted by a polyolefin-based resin; a core layer containing a foaming agent of 5 mass% or more and a skin layer being disposed at the outermost surfaces of both surface sides of the core layer and not containing the foaming agent are possessed; and total light transmittance measured based on JIS K7361-1 is 60% or more. The multilayer film before foaming is preferably molded by an inflation method.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multilayer film before foaming that can be foamed by heating after being laminated in an unfoamed or partially foamed state on the surface of a paper container or the like, and a method for producing the same.

  Conventionally, for example, in foam containers such as paper cups and cup noodles, a foam layer is formed on the surface of a paper base material constituting the foam container body in order to provide heat insulation when a high-temperature liquid is added as the contents. Has been made to form.

  As a method for forming a foamed layer, it is known to use a foaming agent that foams by heating. For example, Patent Document 1 below includes a foamed resin layer in which sodium hydrogen carbonate is kneaded, and foamed resin by heating. An insulating container (foaming container) for foaming the layer is disclosed.

Japanese Patent Application Laid-Open No. 2015-051777

  When forming the foamed layer by foaming the foaming agent in the foamed resin layer by heating as in Patent Document 1, it is necessary to form the foamed layer through a heating foaming process without foaming at the stage of the pre-foaming container. .

  However, in the first place, since the foaming agent has a property of foaming by heating, this control is very difficult. For example, when a foaming agent that foams at a low temperature is used, foaming may occur due to heat during film formation when the foamed resin layer is formed even in the pre-foaming container stage (overfoaming). Conversely, when a foaming agent that foams at a high temperature is used, foaming may not occur or foaming may be insufficient even after a heating foaming step.

  In view of the above problems, the present invention provides a pre-foamed multilayer film that is unfoamed or partially foamed in the state of a pre-foaming container laminated on the surface of the container, and can be foamed through a heating foaming process of the pre-foaming container. The purpose is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors include a core layer containing a predetermined amount of a foaming agent, and a skin layer that is disposed on both sides of the core layer and does not contain a foaming agent. The present inventors have found that the above-described problems can be solved if the pre-foaming multilayer film has a total light transmittance of a predetermined value or more, and the present invention has been completed.

(1) It is a multilayer film before foaming which is laminated on the surface of the container to constitute the container before foaming,
Each layer is made of polyolefin resin,
A core layer containing 5% by mass or more of a foaming agent;
A skin layer that is disposed on the outermost surfaces on both sides of the core layer and does not contain the foaming agent;
The multilayer film before foaming whose total light transmittance measured based on JISK7361-1 is 60% or more.

  (2) The pre-foaming multilayer film according to (1), wherein the foaming agent is a combined use of an organic foaming agent and an inorganic foaming agent.

  (3) The multilayer film before foaming as described in (1) or (2), wherein the polyolefin resin is a vinyl polymer or a vinyl copolymer.

  (4) A pre-foaming container in which the pre-foaming multilayer film according to any one of (1) to (3) is laminated on the surface of the container.

  (5) A method for producing a multilayer film before foaming, wherein the multilayer film before foaming according to any one of (1) to (3) is formed by an inflation method.

(6) A method for producing a foamed container comprising the following steps 1 to 3,
Step 1: A step of obtaining a pre-foaming laminate by laminating a pre-foaming multilayer film and a substrate Step 2: a step of forming a pre-foaming container using the pre-foaming laminate Step 3: heating and foaming the pre-foaming vessel The step of the multilayer film before foaming,
Each layer is made of polyolefin resin,
A core layer containing 5% by mass or more of a foaming agent;
A skin layer that is disposed on the outermost surfaces on both sides of the core layer and does not contain the foaming agent;
The manufacturing method of a foaming container whose total light transmittance measured based on JISK7361-1 is 60% or more.

  (7) The method for manufacturing a foam container according to (6), wherein the multilayer film before foaming is formed by an inflation method.

  The multilayer film before foaming of the present invention is unfoamed or partially foamed in the state of the container before foaming laminated on the surface of the container, and can be subjected to main foaming through a heating foaming process of the container before foaming.

It is sectional drawing which shows one Embodiment of the multilayer film before foaming of this invention. It is sectional drawing which shows one Embodiment of the laminated body before foaming of this invention. It is sectional drawing which shows one Embodiment of the laminated body after foaming which comprises the foaming container obtained by the manufacturing method of this invention. 1 is a cross-sectional view of a multilayer film before foaming of Example 1. FIG. 4 is a cross-sectional view of a multilayer film before foaming of Example 2. FIG. It is sectional drawing of the multilayer film before foaming of the comparative example 3. 1 is a cross-sectional view of a pre-foamed laminate of Example 1. FIG. It is sectional drawing of the laminated body before foaming of the comparative example 7.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

<Method for producing foamed container (laminated body after foaming)>
The foam container of this embodiment can be manufactured by the following steps 1 to 3.
Step 1: A step of obtaining a pre-foaming laminate by laminating a pre-foaming multilayer film and a substrate Step 2: a step of forming a pre-foaming container using the pre-foaming laminate Step 3: heating and foaming the pre-foaming vessel Step of Performing First, the pre-foaming multilayer film and the pre-foaming laminate using the same in step 1 will be described first.

<Multi-layer film before foaming>
As shown in FIG. 1, the multilayer film 1 before foaming of this embodiment is disposed on both sides of a core layer 12 containing 5% by mass or more, preferably 5% by mass or more and 30% by mass or less of a foaming agent. And a skin layer 11 containing no foaming agent. As in steps 1 to 3, the pre-foaming multilayer film 1 is laminated on a base material such as paper to form a pre-foaming laminate (step 1), and then foamed with the pre-foaming laminate. It becomes a front container (step 2) and further becomes a foamed container through a heating foaming step (step 3).

  In the present invention, “before foaming” means a state before the foaming process in which the pre-foaming container is heated to foam the core layer 12, and “after foaming” is the original foaming process. (Main foaming) means a state in which closed cells are formed through a heating foaming step. “Before foaming” means that the foaming agent is partially foamed as well as the foaming agent is not foamed.

  Each layer (core layer and skin layer) constituting the multilayer film 1 before foaming is made of, for example, a polyolefin resin such as a polyethylene resin. As the olefin resin, it is possible to use a vinyl monomer co-polymer other than a low density polyethylene (LDPE), a medium density polyethylene (MDPE), and a high density polyethylene (HDPE), which are homopolymers of vinyl monomers. it can. Examples of vinyl homopolymers include linear low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), and ethylene-methyl methacrylate copolymer (EMMA), which are ethylene-α olefin copolymers. , Ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene- (meth) acrylic acid copolymer (EMAA), polyethylene resins such as ionomers, polypropylene (PP) and polypropylene Polypropylene resins such as copolymers can be used alone or in admixture of two or more.

  The MFR of the polyolefin resin is preferably 1 g / 10 min or more and 30 g / 10 min or less, more preferably 1 g / 10 min or more and 20 g / 10 min or less, and further preferably 1 g / 10 min or more and 10 g / 10 min or less. By adopting MFR within this range, the film forming property by the inflation method is improved. In addition, MFR of this specification including an Example is the value measured by the test method of JISK7210 (The flow test method of thermoplastics). The test conditions are those in “190 ° C., 21.18 N (2.16 kgf)” described in JIS K 6760.

  In the multilayer film 1 before foaming, the core layer 12 contains a foaming agent, and the skin layer 11 does not contain a foaming agent. When the pre-foaming multilayer film 1 includes the skin layer 11, it is possible to protect the tearing of bubbles due to foaming of the core layer 12, and to smooth the surface of the pre-foaming multilayer film 1.

  The foaming agent in the core layer 12 is unfoamed or partially foamed, and many partial foam marks 12a are observed in a cross-sectional view. This point will be described later.

  The foaming agent contained in the core layer 12 is preferably a pyrolytic foaming agent. In this case, the core layer 12 generates bubbles by heating and becomes a foamed layer. The pyrolytic foaming agent can be selected from known foaming agents, and any of organic, inorganic, and microcapsules can be selected. Moreover, it is preferable that the foaming agent used for the multilayer film before foaming of this invention is combined use of an organic type foaming agent and an inorganic type foaming agent. The foaming agent can increase the amount of gas generated by the combined use of an organic foaming agent and an inorganic foaming agent, and can adjust the foaming temperature.

  Specifically, sodium bicarbonate (sodium hydrogen carbonate) or the like is preferably used as the inorganic foaming agent, and citric acid, azodicarbonamide, p, p′-oxybisbenzenesulfonylhydrazide is used as the organic foaming agent. Dinitrosopentamethylenetetramine, hydrazodicarbonamide and the like are preferably used. As the microcapsules, those containing liquid hydrocarbons in the inside and using vinylidene chloride, acrylonitrile copolymer or the like in the outer shell are preferably used.

  The foaming agent contained in the core layer 12 is 5% by mass or more, preferably 5% by mass or more and 30% by mass or less, and preferably 10% by mass or more and 20% by mass with respect to 100 parts by mass of the resin component of the core layer. % Or less is more preferable. By containing 5% by mass or more of the foaming agent, it is possible to form a closed cell after foaming produced using the pre-foaming multilayer film and to have a sufficient heat insulating effect as a foaming container. By containing the foaming agent in an amount of 30% by mass or less, it is possible to stably form a multilayer film before foaming and prevent foam breakage due to over-foaming before the heating foaming process.

  The foaming agent contained in the core layer 12 is preferably a dry foaming agent (a foaming agent that does not contain moisture). When water is contained in the foaming agent, foaming becomes unstable at the time of film formation, and overfoaming tends to occur. For this reason, it is preferable to dry a foaming agent or a foaming agent masterbatch (MB) previously by heating. Specifically, it can be dried at a temperature of 60 ° C. or higher and 80 ° C. or lower for 360 minutes or longer.

  The skin layer 11 of the multilayer film 1 before foaming of the present embodiment may use the same resin as the olefin resin of the core layer, or may be different from the olefin resin of the core layer. The thickness ratio between the core layer and the skin layer can be appropriately set, for example, in the range of 10: 1 to 10:10, and preferably in the range of 10: 1 to 10: 5. In addition, as a laminated structure of the multilayer film before foaming of this invention, if a skin layer is a structure arrange | positioned on the both sides of a core layer, for example, 3 layer structure of a skin layer, a core layer, and a skin layer, or 4 layers The above configuration may be used and is not particularly limited.

  For example, an adhesive resin layer may be interposed between the core layer 12 and the skin layer 11 to form a five-layer structure. Examples of the adhesive resin layer include low density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene- A thermoplastic resin layer such as polyethylene resin such as methyl acrylate copolymer (EMA), ethylene- (meth) acrylic acid copolymer (EMAA), or ionomer is preferably used. The thickness of the adhesive resin layer can be, for example, 5 μm or more and 30 μm or less.

  The total thickness of the multilayer film before foaming is preferably 30 μm or more and 200 μm or less, and more preferably 70 μm or more and 150 μm or less.

The thickness of the skin layer 11 is preferably, for example, 5 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less.

  In the core layer 12 or the skin layer 11, conventionally known nucleating agents, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, pigments, dyes, and the like, as long as the object of the present invention is not impaired. , Antibacterial agents, antifungal agents, antistatic agents, foaming aids, fillers, crosslinking aids, lubricants, dispersants, inorganic fillers, neutralizing agents, metal deactivators, slip agents, antiblocking agents, etc. can be added However, in food applications, it is preferable not to contain a crosslinking aid, some foaming aids, some inorganic fillers, and metal deactivators because their use is restricted.

<Method for producing multilayer film before foaming>
The pre-foaming multilayer film 1 can be formed by a conventionally known film forming method such as an inflation method or a T-die method. In order to produce a multilayer film before foaming having a total light transmittance of 60% or more, the temperature during film formation is also important. The temperature during film formation is preferably 140 ° C. or lower, more preferably 135 ° C. or lower. In addition, in order to prevent foaming of the multilayer film before foaming, it is preferable to use an inflation method capable of forming a film at a lower temperature.

<Total light transmittance of multilayer film before foaming>
The total light transmittance of the multilayer film 1 before foaming is 60% or more, preferably 70% or more. The upper limit is preferably 90% or less, preferably 80% or less. Further, the difference in total light transmittance between the pre-foamed multilayer film and the multilayer film (base film) containing no foaming agent in the core layer is preferably within 30%, and more preferably within 20%.

  The haze value of the pre-foamed multilayer film 1 is preferably 97% or less, more preferably 95% or less, and still more preferably 92% or less.

  As shown in an example of FIG. 4 described later, the core layer 12 has a plurality of partial foaming marks 12a in which a foaming agent is partially foamed. In addition, there is also a horizontally elongated over-foaming mark 12b. This partial foaming mark 12a is considered to grow into an overfoaming mark 12b as the degree of foaming increases. Thus, although the partial foaming mark 12a and the overfoaming mark 12b are mixed as the foaming mark, the ratio (area and number) of the overfoaming mark 12b is small in FIG. The total light transmittance of the film 1 is 60% or more. On the other hand, as shown in the comparative example of FIG. 6, when the ratio (area or number) of the excessive foaming marks 12b is increased, the total light transmittance is less than 60%. In this case, the total light transmittance is lowered, the skin layer is broken and bubbles are broken, and the film-forming property becomes unstable, and the film is likely to be broken. In addition, the film thickness of the multilayer film before foaming increases and the film thickness variation increases, and the foamed container finally subjected to the heat foaming process is inferior in printability and design.

<Laminated body before foaming>
As shown in FIG. 2, the pre-foaming laminate 10 of the present embodiment is a laminate in which the pre-foaming multilayer film 1 and a substrate 3 such as paper are laminated. The lamination of the pre-foaming multilayer film 1 and the substrate 3 can be carried out by using a conventionally known melt extrusion method, dry laminating method, heat pressing method, or the like as appropriate. For example, low density polyethylene melted as an adhesive layer (LDPE) can be used for lamination by melt extrusion lamination methods such as so-called sandwich lamination.

When the base material 3 is paper, those having formability, bending resistance, rigidity, waist, strength and the like can be used. As the paper, it is possible to use, for example, a strongly sized bleached or unbleached paper base, or various paper bases such as pure white roll paper, kraft paper, paperboard, processed paper, and milk base paper. The base material may be a laminate of these paper layers. The paper has a basis weight of 80 g / m ² or more and 600 g / m ² or less, preferably a basis weight of 100 g / m ² or more and 450 g / m ² or less, and a thickness of 110 μm or more and 860 μm or less, preferably 140 μm or more and 640 μm or less. Can be used.

  The pre-foaming laminate 10 of the present embodiment may include a display layer 2 for imparting product information, aesthetics, and the like. The display layer 2 is a layer in which letters, numbers, pictures, figures, irregularities, and the like are formed by a conventionally known printing method or embossing method, and is not particularly limited. The display layer 2 is formed on the entire substrate 3. Or may be formed in part.

  The pre-foamed laminate 10 of this embodiment may include a clay layer 4. The clay layer 4 is an example of the water vapor migration preventing layer in the present invention, and when the pre-foaming laminate 10 is heated to melt the outermost skin layer 11 in the step of forming the pre-foaming container, the paper base is formed. This is a layer that is formed in order to prevent moisture in the material 3 from moving to the core layer 12 side and becoming uncontrollable foaming. The clay layer 4 allows moisture in the paper substrate 3 to escape to the display layer side. In the present invention, the water vapor migration preventing layer is not limited to the clay layer 4 but may be a resin layer such as an olefin resin having a predetermined thickness.

  The clay is not particularly limited as long as it is generally called clay, but kaolin, talc, bentonite, smectite, vermiculite, mica, chlorite, Kibushi clay, gairom clay, halloysite, mica, etc. are used. It is done. Of these, kaolin and talc are preferably used as the clay. Kaolin has excellent concealability and water absorption, and talc has low hardness (Mohs hardness 1) and excellent heat resistance. Improvement in dimensional stability can be expected.

Although the coating amount and thickness of the clay layer 4 are not particularly limited, the basis weight after drying is usually 5 g / m ² or more and 40 g / m ² or less, preferably 10 g / m ² or more and 40 g / m ² or less. It is. If the basis weight after drying is less than 5 g / m ² , moisture in the paper moves to the foamed resin layer 60 side and foams, resulting in uncontrollable foaming. If the basis weight after drying exceeds 40 g / m ² , the pre-foamed laminate 10 may become too thick, and the production suitability may deteriorate.

  The adhesive layer 5 serves as an adhesive layer for laminating the laminate 10 before foaming, and is a conventionally known adhesive or resin layer. Specifically, as the resin layer, for example, low density polyethylene (LDPE), Ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene- (meth) acryl A thermoplastic resin layer such as an acid copolymer (EMAA) or a polyethylene resin such as an ionomer is preferably used.

  In the present invention, as shown in FIG. 2, when the display layer 2 is on the outer surface side of the container, a smoothing layer may be provided between the display layer 2 and the paper substrate 3. As the smoothing layer, a white ink layer, an anchor coat layer, an overprint varnish layer, a UV curable resin layer, a press coat layer that is hot-pressed after printing, a resin layer, and the like are used in addition to the above clay layer. Can do. The surface of the paper base 3 can be smoothed by this smoothing layer, and the designability (printability) of the display layer 2 can be improved.

  Moreover, you may provide polyolefin resin layers (not shown), such as low density polyethylene (LDPE), in the surface on the opposite side to the multilayer film 1 before foaming of the paper base material 3 as needed.

<Foaming container (laminated body after foaming)>
In step 2, the pre-foaming laminate 10 is used to form a pre-foaming container, and in step 3, the pre-foaming container is heated and foamed to obtain a foaming container. FIG. 3 is a schematic cross-sectional view of the post-foaming laminate 100 constituting the foaming container. By using the laminate 10 before foaming, a container before foaming can be formed (not shown). Then, the foam layer (not shown) can be manufactured by foaming the core layer 12 to form a foam layer 12A by a heat foaming process. In the foam layer 12 </ b> A, a plurality of closed cells 6 are formed between the resins 7, thereby providing heat insulation. FIG. 3 shows an example in which the pre-foaming laminate 10 is laminated on the inner surface side of the pre-foaming container, but the present invention is not limited to this, and it may be laminated on the outer surface side of the pre-foaming container.

  The heating conditions in the heating and foaming step are not limited as long as the foamed resin layer is formed by the decomposition of the foaming agent. For example, when the laminate 10 before foaming is 100 mm × 100 m, the heating temperature is preferably 150 ° C. or higher and 300 ° C. or lower, and more preferably 180 ° C. or higher and 230 ° C. or lower. For example, when the pre-foamed laminate 10 is 100 mm × 100 m, the heating time is preferably 10 seconds or more and 180 seconds or less, and more preferably 30 seconds or more and 90 seconds or less.

  The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

<Manufacture of multilayer film before foaming>
Under the conditions shown in Table 1, using a three-layer / three-layer inflation film forming machine, the thickness setting value is 20 μm for the skin layer, 90 μm for the core layer, and the skin layer, the core layer, and the skin layer are in this order. The multilayer film before foaming of the Example and the comparative example which were laminated | stacked was manufactured. The extrusion conditions were such that the resin temperature of the core layer was the temperature shown in Table 1 (130 ° C. to 170 ° C.) and the skin layer was 130 ° C. The material composition of each layer is as follows.

Skin layer: low density polyethylene resin (LDPE), density 0.918 g / cm ³ , melting point 103 ° C., MFR 8.0 g / 10 min)
Core layer: Low density polyethylene resin (LDPE) density 0.923 g / cm ³ , melting point 109 ° C., MFR 3.7 g / 10 85 parts by weight, blowing agent (soda: organic acid salt = 5: 5) 15 Contains part by mass (containing 15% by mass of a foaming agent in the core layer). The foaming agent was kneaded with the LDPE as a master batch (MB) using the same LDPE as the LDPE used as the base resin of the core layer.

  In Table 1, “normal” means that the foaming agent MB was kneaded without drying, and “drying” means that the foaming agent MB was kneaded after drying at 60 ° C. for 12 hours. The “humidification” means that the foaming agent MB is humidified under the condition of storage at 40 ° C. and 90% for 1 hour.

  4 to 6 show cross-sectional views of the multilayer film before foaming of Example 1, Example 2, and Comparative Example 3, respectively.

<Measurement of total light transmittance>
The total light transmittance was measured for the pre-foamed multilayer films of Examples and Comparative Examples. The total light transmittance was measured based on JIS K 7361-1, and the haze was measured using a haze meter (manufactured by Murakami Color Research Laboratory, product number: HM-150) based on JIS K 7136. In the multilayer film before foaming, the multilayer film (base film) containing no foaming agent in the core layer had a total light transmittance of 89.6% and a haze value of 19.5%.

<Appearance test>
About the Example and the comparative example, the presence or absence of the bubble breakage of the multilayer film before foaming was confirmed visually.
[Evaluation criteria]
○: Bubble breakage occurred ×: Bubble breakage did not occur

<Thickness>
About the Example and the comparative example, the total thickness of the multilayer film (3 layers) before foaming was measured (it describes with the film total thickness in Table 1). In addition, about the multilayer film before foaming which the bubble breakage generate | occur | produced, the thickness of places other than the location where the bubble breakage occurred was measured. In addition, about the thickness of the location other than the location where the total thickness of the multilayer film (3 layers) before foaming or bubble breakage occurred, it measured using the thickness measuring device (the product made by PEACOCK, MODEL.G). If the thickness is as set, the total thickness of the laminated film before foaming is 130 μm. However, in the examples, the core layer is partially foamed, and in the comparative example, the core layer is overfoamed. The thickness is larger than 130 μm.

  From Table 1, the multilayer film before foaming of the present invention having a total light transmittance of 60% or more did not break before the heating foaming process, and foamed normally by the subsequent heating foaming process. On the other hand, the multilayer film before foaming of the comparative example having a total light transmittance of less than 60% had already broken bubbles before the heating foaming process, and had poor film forming properties.

<Manufacture of laminate before foaming>
A clay layer made of a clay layer coating solution containing kaolin clay and calcium carbonate was formed on one surface of a base material made of a base paper having a basis weight of 260 g / m ² by an air knife coating method. The clay layer had a basis weight of 20 g / m ² .

On the surface side of the base material on which the clay layer was formed, the multilayer films before foaming of the examples and comparative examples were fused with 20 μm thick LDPE (density 0.923 g / cm ³ , melting point 111 ° C., MFR ³ for the adhesive layer). .6 g / 10 min) to obtain a laminate before foaming. Thus, from the outside, the paper substrate 260 (g / m ² ), the clay layer 20 (g / m ² ), the adhesive layer (20 μm), and the multilayer film before foaming were laminated in this order, and A pre-foam laminate for the comparative example was produced.

  7 and 8 show cross-sectional views of the pre-foamed laminates of Example 1 and Comparative Example 7. FIG. The cross-sectional views of FIGS. 7 and 8 were measured using a TDM100-IW manufactured by Yamato Scientific Co., Ltd. with a tube voltage of 35 kV, a tube current of 23 μA, and an enlarged axis of 10 mm. In Example 1, the surface on the multilayer film side before foaming is smooth, whereas in Comparative Example 7, the surface on the multilayer film side before foaming is uneven.

<Manufacture of laminate before foaming (foaming container)>
Then, using this pre-foamed laminate for the body part, a pre-foaming container composed of a paper cup was formed so that the pre-foaming multilayer film was disposed on the content surface side of the foaming container with respect to the paper substrate (caliber) 100mm, height 109.5mm).

  Finally, by heating the pre-foaming container of Example 1 and Example 2 at 230 ° C. for 60 seconds (heating foaming step), the core layer of the pre-foaming multilayer film is foamed to form a foamed film after foaming. A foam container was manufactured.

  Table 2 shows a value obtained by dividing the thickness of the foam layer of the foam container and the foaming ratio of the bubbles in the foam layer (the thickness of the foam layer (μm) divided by 90 μm, which is the setting value of the core layer of the multilayer film before foaming). ) Is measured. The thickness (μm) of the foamed layer was measured using a TDM100-IW manufactured by Yamato Scientific Co., Ltd. as a tube voltage of 35 kV, a tube current of 23 μA, and an enlarged axis of 52 mm. An area within a width of 5 mm in the left-right direction in FIG. 3 was divided into 6 equal parts, and an average value of 7 points was measured. In addition, since "-" of Comparative Examples 1 to 7 in Table 2 could not convey the multilayer film before foaming, the laminate before foaming could not be produced. For this reason, the thickness of the foamed layer and the foaming magnification are not measured.

  About the foaming container of Example 1 and Example 2, the state which foamed normally was confirmed as typically shown in FIG. In FIG. 3, 11A and 12A are a skin layer and a core layer after the heating and foaming step, respectively, and the core layer 12 is foamed to form closed cells between the resins 7 to form a foamed layer 12A.

DESCRIPTION OF SYMBOLS 1 Multi-layer film before foaming 1A Multi-layer film after foaming 11, 11A Skin layer 12 Core layer 12A Core layer (foamed layer)
12a Partial foaming trace in which foaming agent is partially foamed 12b Overfoaming trace in which foaming agent is overfoamed 10 Laminated body before foaming 100 Laminated body after foaming 2 Display layer 3 Base material 4 Clay layer 5 Adhesive layer 6 Closed cell 7 Resin 20 Non-foaming Part

Claims (7)

A multilayer film before foaming that is laminated on the surface of the container to constitute a container before foaming,
Each layer is made of polyolefin resin,
A core layer containing 5% by mass or more of a foaming agent;
A skin layer that is disposed on the outermost surfaces on both sides of the core layer and does not contain the foaming agent;
The multilayer film before foaming whose total light transmittance measured based on JISK7361-1 is 60% or more.   The multilayer film before foaming according to claim 1, wherein the foaming agent is a combined use of an organic foaming agent and an inorganic foaming agent.   The multilayer film before foaming according to claim 1 or 2, wherein the polyolefin resin is a vinyl polymer or a vinyl copolymer.   A pre-foaming container in which the pre-foaming multilayer film according to claim 1 is laminated on the surface of the container.   The manufacturing method of the multilayer film before foaming which forms the multilayer film before foaming in any one of Claim 1 to 3 by an inflation method. It is a manufacturing method of a foaming container provided with the following process 1 to process 3,
Step 1: A step of obtaining a pre-foaming laminate by laminating a pre-foaming multilayer film and a substrate Step 2: a step of forming a pre-foaming container using the pre-foaming laminate Step 3: heating and foaming the pre-foaming vessel The step of the multilayer film before foaming,
Each layer is made of polyolefin resin,
A core layer containing 5% by mass or more of a foaming agent;
A skin layer that is disposed on the outermost surfaces on both sides of the core layer and does not contain the foaming agent;
The manufacturing method of a foaming container whose total light transmittance measured based on JISK7361-1 is 60% or more.   The method for manufacturing a foam container according to claim 6, wherein the pre-foam multilayer film is formed by an inflation method.