JP4001359B2 - Laminated sheet for thermoforming - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a laminated sheet for thermoforming made of polyethylene, a gas barrier resin and the like used for various packaging containers such as food packaging and pharmaceutical packaging.
[0002]
[Prior art]
Conventionally, as a resin suitable for a thermoformed container, a polystyrene resin has been often used because of good moldability, transparency, rigidity, and the like. In addition, polyolefin resins, especially polypropylene resins, also have excellent properties such as strength, rigidity, heat resistance, etc., so that the sheet is thermoformed into vacuum or compressed air to make food packaging, pharmaceutical packaging containers, etc. It is used for.
[0003]
On the other hand, in recent years, molded products such as plastic containers as food packaging materials have been required to have higher levels of required properties year by year, such as improved high-speed processability of containers and improved food storage performance. Therefore, a multilayer structure product that shares the respective functions is used, and as a typical example, the outer layer of polyolefin resin that handles strength properties and ethylene vinyl that handles oxygen barrier properties A multilayer molded article having an intermediate layer made of an alcohol copolymer (hereinafter referred to as EVOH) or the like can be given.
[0004]
[Problems to be solved by the invention]
However, although the thermoforming property of polystyrene resin is excellent, it has recently been suspected that the styrene monomer will elute and adversely affect the human body. Especially in the food packaging field, it is chemically stable and safe. There is a demand for the development of a high-polyolefin resin container.
[0005]
Polypropylene resin sheet, which is one of polyolefin resins, has a large drawdown due to heating during preheating during thermoforming, and the optimum molding temperature range during molding to obtain a good molded product is very narrow, Since advanced temperature control is required, process management is extremely difficult.
[0006]
Since there is a limit to improving the moldability of polypropylene resin alone, conventionally, attempts have been made to modify polypropylene by blending polyethylene, an inorganic filler, and a low molecular weight petroleum resin.
[0007]
For example, a method of adding high-viscosity polyethylene and hydrous magnesium silicate to high-viscosity polypropylene (JP-B-56-15744), and a method of adding polyethylene and ethylene-propylene copolymer to polypropylene (JP-B 63-29704). Gazette), a method using polypropylene and polyethylene having a narrow molecular weight distribution (Japanese Patent Publication No. 63-53213), and a method of adding petroleum resin to polypropylene (Japanese Patent Publication No. 6-89191), but the effect is limited. There is no actual satisfactory moldability yet.
[0008]
In addition, when inorganic fillers, petroleum resins, etc. are added and used, bleeding and elution of low molecular weight components occur, making it difficult to use for food packaging and pharmaceutical packaging from the viewpoint of safety. .
[0009]
On the other hand, for chemically stable and highly safe polyethylene resins, attempts have been made to develop thermoforming sheets. However, as with the above-described polypropylene resins, it is difficult to control thermoforming, especially deep drawability. However, it has not been commercialized in the past.
[0010]
By thermoforming a laminated sheet consisting of a gas barrier resin such as polyolefin for the inner and outer layers and EVOH for the intermediate layer, it is possible to provide a container that is inexpensive, excellent in safety, and excellent in storage stability. However, due to the problems of the thermoformability of polyolefin as described above, the present situation is that a satisfactory one has not yet been provided.
[0011]
The present invention was devised to solve the above-described problems in the prior art, and its problem is excellent in thermoforming, and can be used for the production of containers having high rigidity, good appearance, and excellent storage stability. An object of the present invention is to provide a laminated sheet for thermoforming.
[0012]
[Means for Solving the Problems]
In order to solve the technical problem, the means according to claim 1 comprises:
Having an outer layer made of polyethylene, an inner layer and a plurality of intermediate layers;
The intermediate layer has at least a polyethylene intermediate layer adjacent to the inner layer or the outer layer, a gas barrier resin layer, and an adhesive resin layer;
The outer layer and the inner layer are formed of polyethylene having a density of 0.940 to 0.960 g / cm ³ , an MFR of 1.0 to 10 g / 10 min, and a molecular weight distribution Mw / Mn of 13 to 50, and adjacent to the inner layer or the outer layer. polyethylene intermediate layer, the inner density is at least 0.010 g / cm ³ higher than the density of the polyethylene of the outer layer, and less than 0.970 g / cm ^3, MFR is 0.1-5 g / 10 min, a molecular weight distribution Mw / Forming with polyethylene whose Mn is 3 to 13,
It is in.
[0013]
In the first aspect, the inner and outer polyethylene layers mainly exhibit the function of thermoforming, and the polyethylene intermediate layer adjacent to the inner layer or the outer layer mainly functions as a thermoforming container such as strength and rigidity. It is configured.
[0014]
Hereinafter, the structural requirements of polyethylene and its action will be described in detail.
The inner and outer layers are formed of polyethylene having a density of 0.940 to 0.960 g / cm ³ , an MFR of 1.0 to 10 g / 10 min, and a molecular weight distribution Mw / Mn of 13 to 50.
[0015]
MFR is related to the stretchability of the polyethylene melt at the time of thermoforming. If it is too small, the stretchability will be poor, but if it is too large, drawdown will occur during preheating of thermoforming, and Mw / Mn is By using polyethylene of MFR and Mw / Mn in the above numerical ranges as inner and outer layer forming materials in consideration of balance with other properties, which is related to uneven thickness at the time of deep drawing, a laminated sheet Good thermoformability can be secured.
[0016]
When the density is 0.940 g / cm ³ or less, the rigidity of the thermoforming container is insufficient, and when it is 0.960 g / cm ³ or more, the crystallinity is high, and the viscosity changes rapidly in the vicinity of the crystal melting point. It becomes difficult to control the temperature and time of the hour.
[0017]
When the MFR is 1.0 g / 10 min or less, the extrudability at the time of molding the sheet is inferior. As a result, the surface of the sheet is roughened, and at the time of thermoforming, the viscosity is high and the stretchability is low and the depth is low. It is difficult to draw, and if it is 10 g / 10 min or more, the viscosity during thermoforming is low, drawdown occurs during preheating, and the strength of the thermoformed container is reduced, making it difficult to put to practical use. Become.
[0018]
If Mw / Mn is 13 or less, uneven thickness occurs when stretching by thermoforming, making it impossible to form a deep-drawn container, and if it is 50 or more, the gloss of the extruded sheet surface is poor and low molecular weight components are eluted. It becomes difficult to use in the food field.
[0019]
The polyethylene intermediate layer has a density at least 0.010 g / cm ³ higher than the density of the inner and outer polyethylene and less than 0.970 g / cm ³ , an MFR of 0.1 to 5 g / 10 min, and a molecular weight distribution Mw / Mn Is formed of polyethylene having 3 to 13.
[0020]
This intermediate layer is a layer mainly for exerting the rigidity and strength of the thermoformed container. From the viewpoint of rigidity, it is necessary to set the density high and from the viewpoint of strength, the MFR needs to be set low. Considering the balance with the property of the above, the above numerical range is suitable.
[0021]
In order to obtain a container having sufficient rigidity, it is necessary to increase the density, and the density of the polyethylene intermediate layer needs to be at least 0.010 g / cm ³ higher than that of the inner and outer layers of the polyethylene. When it is 970 g / cm ³ or more, the strength of the container is lowered.
[0022]
When the MFR is 0.1 g / 10 min or less, the flowability of the resin is poor, it is difficult to form a sheet, and the stretchability during thermoforming is also affected, making deep drawing difficult. If it is 5 g / 10 min or more, it becomes difficult to ensure practical strength as a container.
[0023]
If Mw / Mn is 3 or less, it is difficult to form a sheet because melt fracture occurs, and if it is 13 or more, low molecular weight components increase, so it is difficult to ensure practical strength as a container.
[0024]
As the gas barrier resin used in the present invention, for example, any known ones such as EVOH, nylon resin, polyacrylonitrile resin, polyvinylidene chloride resin, polyethylene terephthalate resin can be used.
[0025]
Further, as the adhesive resin used in the present invention, it is necessary to select a resin excellent in adhesiveness between polyethylene and gas barrier resin. For example, based on polyethylene, ethylene vinyl acetate copolymer, etc., unsaturated carboxylic acid Alternatively, a polyolefin-based adhesive resin obtained by graft polymerization of a derivative thereof such as an anhydride or ester amide is used in an amount of 0.01 to 1% by weight. Among these, a maleic anhydride-modified polyolefin-based resin is preferably used.
[0026]
The layer composition ratio of the laminated sheet depends on the required performance, but the thickness ratio is usually 2 to 20% for the gas barrier resin layer and about 1 to 10% for the adhesive resin layer. It is preferable that the inner layer or the polyethylene intermediate layer adjacent to the outer layer occupying a large component ratio that bears the performance such as the rigidity of the outer layer and the molded container.
[0027]
According to the above configuration of claim 1, the inner and outer polyethylene layers are mainly provided with thermoforming functions such as stretchability and deep drawability, and the polyethylene intermediate layer adjacent to the inner layer or the outer layer is mainly provided with the strength of the thermoforming container, The gas barrier resin layer is shared with gas barrier functions such as oxygen barrier properties, and the contents such as food are touched while the outer layer is added with other resins, low molecular weight substances, inorganic fillers, etc. Since the polyethylene resin is not used alone, it is possible to obtain a deeply molded thermoformed container having high safety, excellent storage stability, good appearance, high rigidity, and deep drawing.
[0028]
The means of the invention described in claim 2 is that, in the invention of claim 1, the gas barrier resin layer is formed of EVOH.
[0029]
EVOH is a resin having a very high gas barrier property, and can provide a container for applications that require severe storage stability, such as anti-oxidation of foods, and the layer thickness corresponding to the high barrier property. Can be made thin, and the adverse effect on the thermoformability of the entire laminated sheet can be reduced.
[0030]
In the present invention, it is preferable to use one having an ethylene content of usually 20 to 50 mol% and a saponification degree of 95% or more from the viewpoint of gas barrier properties and moldability.
[0031]
The means of the invention described in claim 3 is that, in the invention of claim 1, the gas barrier resin layer is formed of a nylon resin.
[0032]
In the present invention, for example, nylon 6, nylon 66, 6-66 nylon copolymer, nylon 12, xylylene group-containing polyamide, or the like can be used as the nylon resin.
[0033]
Nylon-based resin is not as gas barrier as EVOH, but it has superior laminate sheet formability, thermoformability, adhesion to polyethylene, and excellent puncture strength in molded containers compared to EVOH. Have.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The measurement method relating to polyethylene used in the present invention is as follows.
-Density (g / cm < ³ >): It calculated | required based on JISK6760.
-MFR (g / 10 minutes): It calculated | required based on JISK6760.
Molecular weight distribution (Mw / Mn): The weight average molecular weight (Mw) and the number average molecular weight (Mn) were determined by gel permeation chromatography (GPC), and the ratio (Mw / Mn) was determined.
[0035]
The polyethylene used in the present invention is an ethylene homopolymer or a copolymer composed of ethylene and an α-olefin having 3 to 20 carbon atoms. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene-1, 1-octene, and the like.
[0036]
In the present invention, a known additive such as an antistatic agent, an antioxidant, a lubricant, an antiblocking agent, an anti-ultraviolet agent, an inorganic pigment, a weathering agent, etc. is added to each layer as necessary within a range that does not impair the purpose. be able to.
[0037]
【Example】
A multilayer sheet for thermoforming of 4 types and 7 layers ((inner layer) PE1 / PE2 / Ad / GB / Ad / PE2 / PE1 (outer layer)) was formed by multilayer extrusion molding.
PE1; inner layer 1a, outer layer 1b
Polyethylene used; density; 0.945 g / cm ³ , MFR; 2.0 g / 10 min, Mw / Mn; 20
PE2: Polyethylene intermediate layer 2
Polyethylene used; density; 0.960 g / cm ³ , MFR; 1.0 g / 10 min, Mw / Mn; 10
Ad: Adhesive resin layer 3
Resin used: Maleic anhydride-modified polyethylene / GB; Gas barrier resin layer 4
Resin used: EVOH (ethylene content 32 mol%)
[0038]
Using the plug-assist vacuum / pressure forming machine, the laminated sheet is a rectangle having a bottom surface 6 of 6 cm in length and 8.5 cm in width, an upper end opening 9 having a rectangle of 7 cm in length and 9.5 cm in width, A container 5 having a flat flange portion 10 having a width of 5 mm and having a truncated pyramid shape (squeezing ratio 0.78) having a length of 5.5 cm and continuously provided in the shape of an outer casing at the periphery of the upper end opening 9. Thermoformed.
The bottom wall 7, the side wall 8, and the flange portion 10 constituting the container 5 have a structure of 4 types and 7 layers, and the composition ratio (thickness ratio) is PE1 14%, PE2 80%, BG 2%. , Ad 4%. (See Figure 1)
[0039]
The above sheet has good stretchability and deep drawability, and the resulting container has small distortion of shape, high uniformity of thickness, good appearance in terms of surface gloss, and sufficient tactile sensation. And had long-term food storage stability.
[0040]
In addition to the above-described embodiments, the object of the present invention can be achieved by, for example, (inner layer) PE1 / PE2 / Ad / GB / Ad / PE1 (outer layer) according to the application, and a recycled resin is used for the intermediate layer. It is also possible to provide a layer that does this.
[0041]
【The invention's effect】
Since this invention becomes the above-mentioned structure, there exists the effect shown below.
The laminated sheet for thermoforming of the present invention uses polyethylene having a thermoforming function for the inner and outer layers, and uses polyethylene having a strength and rigidity function for the intermediate layer, and further includes EVOH, nylon resin, etc. Since an intermediate layer made of a gas barrier resin is provided, the thermoformable sheet has a wide range of thermoforming and has good deep drawability. A container obtained from this sheet by thermoforming is Good appearance, sufficient rigidity, excellent storage stability for foods, etc., and the outer layer is made of chemically stable polyethylene while the contents come into contact with it. It can be used and deployed in the required fields.
[Brief description of the drawings]
FIG. 1 is an overall perspective view showing an example of a container thermoformed from a thermoformed laminated sheet of the present invention, with a part of a side wall broken and enlarged.
[Explanation of symbols]
1a; Inner layer 1b; Outer layer 2; Polyethylene intermediate layer 3; Adhesive resin layer 4; Gas barrier resin layer 5; Container 6; Bottom surface 7; Bottom wall 8; Side wall 9;

Claims (3)

The inner layer (1a), outer layer (1b) and a plurality of intermediate layers made of polyethylene, the intermediate layer is at least the inner layer (1a) or the polyethylene intermediate layer (2) adjacent to the outer layer (1b), and a gas barrier resin layer (4) and an adhesive resin layer (3), the inner layer (1a) and the outer layer (1b) have a density of 0.940 to 0.960 g / cm ³ and an MFR of 1.0 to 10 g / 10. The polyethylene intermediate layer (2) adjacent to the inner layer or outer layer is formed with polyethylene having a molecular weight distribution Mw / Mn of 13 to 50, and the density is at least 0.010 g / cm ³ higher than the density of the inner layer and outer layer polyethylene. And the laminated sheet for thermoforming formed with the polyethylene which is less than 0.970 g / cm < ³ >, MFR is 0.1-5 g / 10min, and molecular weight distribution Mw / Mn is 3-13. The laminated sheet for thermoforming according to claim 1, wherein the gas barrier resin layer (4) is formed of an ethylene vinyl alcohol copolymer. The laminated sheet for thermoforming according to claim 1, wherein the gas barrier resin layer (4) is formed of a nylon resin.

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