JP2023172715A - Laminate sheet, and food packaging container - Google Patents

Abstract

To provide a calcium carbonate particle-containing laminate sheet in which nonuniformity of appearance and mechanical characteristics is suppressed.SOLUTION: There is provided a laminate sheet of three layers, wherein the laminate sheet includes an inner layer, and a first outer layer and a second outer layer stacked on the surface of the inner layer, the inner layer contains calcium carbonate particles satisfying a predetermined requirement, and a thermoplastic resin, the first outer layer and the second outer layer each contain a thermoplastic resin, and each ratio in thicknesses of the first outer layer and the second outer layer to the total thickness of the laminate sheet is 2.0% or more and 20.0% or less.SELECTED DRAWING: None

Description

The present invention relates to a laminated sheet and a food packaging container.

In recent years, attempts have been made to reduce the content of resin components in various resin products from the viewpoint of environmental protection.
One such attempt is to increase the amount of inorganic substances (calcium carbonate, etc.) contained in resin products (for example, Patent Document 1).

Patent No. 6857428

Here, in Patent Document 1, in a thermoplastic resin-containing laminate comprising an inner layer and a pair of outer layers laminated on both surfaces of the inner layer, calcium carbonate particles having a maximum particle size of 20 μm or less are blended in the inner layer. It is stated that

However, as a result of studies by the present inventors, when only calcium carbonate particles with a small particle size as described above are blended into a resin composition, uneven distribution of calcium carbonate particles occurs due to poor dispersibility during kneading. I found out what I got.
Uneven distribution of calcium carbonate particles in the resin composition may result in nonuniform appearance, mechanical properties, etc. in the resulting laminate or molded product thereof.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminated sheet containing calcium carbonate particles in which non-uniformity in appearance and mechanical properties is suppressed.

The present inventors have discovered that the above problem can be solved by blending two types of calcium carbonate particle groups having a predetermined average particle size or particle size distribution in a predetermined ratio in the inner layer of a three-layer laminated sheet, The present invention has now been completed. More specifically, the invention provides:

(1) A three-layer laminated sheet,
The laminated sheet includes an inner layer, a first outer layer and a second outer layer laminated on the surface of the inner layer,
The inner layer includes calcium carbonate particles and a thermoplastic resin,
The first outer layer and the second outer layer each contain a thermoplastic resin,
The content of the calcium carbonate particles is 40.0% by mass or more and 80.0% by mass or less with respect to the inner layer,
The calcium carbonate particles include at least a first calcium carbonate particle group and a second calcium carbonate particle group,
The first calcium carbonate particle group has an average particle diameter of 0.7 μm or more and 6.0 μm or less, based on an air permeation method according to JIS M-8511;
Particle size distribution D97 in the second group of calcium carbonate particles is 20.1 μm or more and 40.0 μm or less,
The mass ratio of the first calcium carbonate particle group and the second calcium carbonate particle group in the inner layer is 99.95:0.05 to 99.99:0.01,
The ratio of the thickness of the first outer layer and the second outer layer is 2.0% or more and 20.0% or less, respectively, with respect to the total thickness of the laminated sheet.
Laminated sheet.

(2) The laminate sheet according to (1), wherein the thermoplastic resin in the inner layer, the first outer layer, and the second outer layer contains a polypropylene resin and/or a polyethylene resin.

(3) the polyethylene resin includes high density polyethylene and linear low density polyethylene,
The MFR (190°C, 21.6 kg) of the high-density polyethylene according to JIS K 6922-1 (ISO1133) is 5 g/10 minutes or more and 15 g/10 minutes or less,
The linear low density polyethylene has an MFR (190°C, 2.16 kg) according to JIS K 6922-1 (ISO1133) of 0.5 g/10 minutes or more and 1.5 g/10 minutes or less,
The laminate sheet according to (2), wherein the mass ratio of the high-density polyethylene to the linear low-density polyethylene is 90:10 to 50:50.

(4) The laminate sheet according to (2), wherein the polypropylene resin is a polypropylene homopolymer and/or a polypropylene block polymer.

(5) The laminated sheet according to (1), wherein the calcium carbonate particles are heavy calcium carbonate particles.

(6) The average particle diameter of the first calcium carbonate particle group based on an air permeation method according to JIS M-8511 is 1.0 μm or more and 3.0 μm or less,
The laminated sheet according to (1), wherein the second calcium carbonate particle group has a particle size distribution D97 of 20.1 μm or more and 35.0 μm or less.

(7) The ratio of the thickness of the first outer layer and the second outer layer is 2.0% or more and 10.0% or less of the total thickness of the laminated sheet, (1) The laminated sheet described in .

(8) The laminated sheet according to any one of (1) to (7), wherein the laminated sheet is a laminated sheet for vacuum forming.

(9) A food packaging container formed from the laminated sheet of (8).

According to the present invention, a calcium carbonate particle-containing laminate sheet with suppressed non-uniformity in appearance and mechanical properties is provided.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

<Laminated sheet>
The laminated sheet of the present invention has a three-layer structure (that is, an inner layer, a first outer layer and a second outer layer laminated on the surface of the inner layer), and satisfies all of the following requirements.
(Requirement 1) The inner layer contains calcium carbonate particles and a thermoplastic resin.
(Requirement 2) The first outer layer and the second outer layer each contain a thermoplastic resin.
(Requirement 3) The content of calcium carbonate particles is 40.0% by mass or more and 80.0% by mass or less with respect to the inner layer.
(Requirement 4) The calcium carbonate particles in the inner layer include at least a first calcium carbonate particle group and a second calcium carbonate particle group.
(Requirement 5) The average particle diameter of the first calcium carbonate particle group based on the air permeation method according to JIS M-8511 is 0.7 μm or more and 6.0 μm or less.
(Requirement 6) Particle size distribution D97 in the second calcium carbonate particle group is 20.1 μm or more and 40.0 μm or less.
(Requirement 7) The mass ratio of the first calcium carbonate particle group to the second calcium carbonate particle group in the inner layer is 99.95:0.05 to 99.99:0.01.
(Requirement 8) The ratio of the thickness of the first outer layer and the second outer layer is 2.0% or more and 20.0% or less, respectively, with respect to the total thickness of the laminated sheet.

The main technical feature of the laminated sheet of the present invention is the composition of its inner layer.
Specifically, the calcium carbonate particles that are the main component of the inner layer are composed of at least two groups of calcium carbonate particles (i.e., a first group of calcium carbonate particles and a second group of calcium carbonate particles) having a predetermined average particle size or particle size distribution. particles) in a predetermined ratio (requirements 3 to 7).
The present inventors have surprisingly found that when such calcium carbonate particles are blended, the appearance and mechanical properties tend to be more uniform than when only calcium carbonate particles with a uniform average particle size are blended. I found out.

Generally, the smaller the average particle diameter of the calcium carbonate particles added to the resin composition, the better the appearance of the molded article, but the higher the viscosity during kneading and the lower the moldability.
On the other hand, the larger the average particle diameter of the calcium carbonate particles blended into the resin composition, the easier the kneading becomes, but the uneven distribution of particles in the resin composition tends to occur, and the appearance of the molded product becomes worse. tends to be uneven.

Therefore, the present inventors developed a calcium carbonate particle group (first calcium carbonate particle group) with a small particle size that satisfies (requirement 5) and a calcium carbonate particle group (second calcium carbonate particle group) that has a large particle size that satisfies (requirement 6). It has been found that by using calcium carbonate particles (calcium carbonate particles) in combination, non-uniformity in appearance can be suppressed without impairing moldability.

Furthermore, the present inventor surprisingly achieved uniform mechanical properties by adjusting the blending ratio of the first calcium carbonate particle group and the second calcium carbonate particle group to a low value (requirement 7). It was also found that sex increased.
Such an effect cannot be obtained when only the first calcium carbonate particle group or only the second calcium carbonate particle group is blended into the inner layer, or even if they are used together, (requirement 7) is not satisfied. It was difficult to play.

The inner layer in the laminated sheet of the present invention may have a structure in which the first calcium carbonate particle group densely fills the space between the second calcium carbonate particle group and the thermoplastic resin.
It is presumed that such a structure suppresses uneven distribution of calcium carbonate particles in the inner layer and improves the uniformity of mechanical properties, despite the high content of calcium carbonate particles.

In the present invention, "the appearance of the laminated sheet" includes the surface condition of the laminated sheet.
In the present invention, "heterogeneity in the appearance of the laminated sheet is suppressed" includes that almost no unevenness, deformation, tearing, etc. are observed on the entire surface condition of the laminated sheet, or no irregularities are observed at all. do.

The appearance of the laminated sheet can be evaluated by the method shown in the Examples.

In the present invention, the "mechanical properties of the laminated sheet" includes the tensile strength of the laminated sheet.
In the present invention, "heterogeneity of the mechanical properties of the laminated sheet is suppressed" includes small variations in the tensile strength of the laminated sheet.

The mechanical properties of the laminated sheet can be evaluated by the method shown in the Examples.

In the present invention, the "average particle diameter of a group of calcium carbonate particles" means a value calculated from the results of measuring the specific surface area by an air permeation method according to JIS M-8511. As the measuring device, for example, a specific surface area measuring device model SS-100 manufactured by Shimadzu Corporation can be preferably used.

In the present invention, "the particle size distribution D97 of the calcium carbonate particle group is 20.1 μm or more and 40.0 μm or less" means that 97% of all particles constituting the calcium carbonate particle group have a particle size distribution D97 of 20.1 μm or more and 40.0 μm or less. It means having a diameter (longest diameter) within a range. As a device for measuring the particle size distribution D97 and the diameter of calcium carbonate particles, for example, a laser diffraction type particle size distribution measuring device can be preferably used.

Hereinafter, the structure of the laminated sheet of the present invention will be explained in detail.

(1) Inner layer The inner layer contains calcium carbonate particles and a thermoplastic resin.

(Calcium carbonate particles blended into the inner layer)
The content of calcium carbonate particles (total amount of calcium carbonate particles) with respect to the inner layer is 40.0% by mass or more and 80.0% by mass or less.

[Type of calcium carbonate particles blended into the inner layer]
The calcium carbonate particles contained in the inner layer may be either heavy calcium carbonate or light calcium carbonate.

From the viewpoint of having more contact interfaces with the thermoplastic resin and easily improving the mechanical properties of the laminated sheet, it is preferable that the inner layer contains heavy calcium carbonate. More preferably, the calcium particles are made of ground calcium carbonate.

"Heavy calcium carbonate" is calcium carbonate obtained by mechanically pulverizing (dry method, wet method, etc.) natural raw materials (limestone, etc.) containing CaCO ₃ as a main component.
"Light calcium carbonate" is calcium carbonate prepared by a synthetic method (chemical precipitation reaction, etc.).
Therefore, heavy calcium carbonate and light calcium carbonate are clearly distinguished from each other.

The calcium carbonate particles contained in the inner layer may or may not be surface-modified.
Examples of the surface modification method include methods that can improve the dispersibility of calcium carbonate particles in the thermoplastic resin. Specifically, physical methods (plasma treatment, etc.) and chemical methods (methods using coupling agents or surfactants) can be mentioned.

[First calcium carbonate particle group and second calcium carbonate particle group]
The calcium carbonate particles contained in the inner layer include at least a first calcium carbonate particle group and a second calcium carbonate particle group.
The calcium carbonate particles contained in the inner layer include the first calcium carbonate particle group and the second calcium carbonate particle group in a mass ratio of 99.95:0.05 to 99.99:0.01.

The average particle diameter of the first calcium carbonate particle group based on an air permeation method according to JIS M-8511 is 0.7 μm or more and 6.0 μm or less.

The lower limit of the average particle diameter of the first calcium carbonate particle group based on the air permeation method according to JIS M-8511 is 0.7 μm or more, but it is preferable from the viewpoint of easily suppressing the increase in viscosity during molding. is 1.0 μm or more, more preferably 1.2 μm or more.

The upper limit of the average particle diameter of the first calcium carbonate particle group based on the air permeation method according to JIS M-8511 is 6.0 μm or less, but the diameter of the particles constituting the second calcium carbonate particle group is From the viewpoint that the effect of the present invention is more likely to be exhibited as the difference is larger, it is preferably 3.0 μm or less, more preferably 2.8 μm or less.

Particle size distribution D97 in the second calcium carbonate particle group is 20.1 μm or more and 40.0 μm or less.

The lower limit of particle size distribution D97 in the second calcium carbonate particle group is 20.1 μm or more, but the larger the difference from the average particle diameter of the first calcium carbonate particle group, the easier it is to achieve the effects of the present invention. , preferably 20.3 μm or more, more preferably 20.5 μm or more.

The upper limit of the particle size distribution D97 in the second calcium carbonate particle group is 40.0 μm or less, but from the viewpoint of easily suppressing the uneven distribution of calcium carbonate particles in the inner layer, it is preferably 35.0 μm or less, more preferably 32 μm or less. .0 μm or less.

The inner layer includes one or more groups of calcium carbonate particles (for example, a third group of calcium carbonate particles) having a different average particle size and particle size distribution from the first group of calcium carbonate particles and the second group of calcium carbonate particles. It may be included or it may not be included.
However, from the viewpoint that the effects of the present invention can be easily achieved, it is preferable that the calcium carbonate particles contained in the inner layer consist of a first calcium carbonate particle group and a second calcium carbonate particle group.

Preferred embodiments of the present invention include embodiments in which the inner layer does not substantially contain calcium carbonate particles having a particle size of more than 50.0 μm, from the viewpoint of easily suppressing uneven distribution of calcium carbonate particles.
Preferred embodiments of the present invention include embodiments in which the inner layer does not substantially contain calcium carbonate particles having a particle size of less than 0.3 μm, from the viewpoint of easily suppressing an increase in viscosity during molding.
In the present invention, "the inner layer does not substantially contain a component" refers to an embodiment in which the content of the component is less than 0.1% by mass relative to the inner layer, more preferably 0.01% by mass or less. It includes certain embodiments, and more preferably embodiments that do not contain it at all.

[Ratio of calcium carbonate particles blended into the inner layer]

The lower limit of the content of calcium carbonate particles (total amount of calcium carbonate particles) contained in the inner layer is 40.0 mass or more relative to the inner layer, but from the viewpoint of imparting sufficient mechanical properties to the laminated sheet, On the other hand, it is preferably 42.0% by mass or more, more preferably 44.0% by mass or more.

The upper limit of the content of calcium carbonate particles (total amount of calcium carbonate particles) contained in the inner layer is 80.0% by mass or less with respect to the inner layer. From the viewpoint of easily suppressing the uneven distribution of particles, the amount is 80.0% by mass or less, preferably 75.0% by mass or less, and more preferably 70.0% by mass or less, based on the inner layer.

The mass ratio of the first calcium carbonate particle group and the second calcium carbonate particle group (first calcium carbonate particle group: second calcium carbonate particle group) in the inner layer is 99.95:0.05~ 99.99:0.01.
From the viewpoint of easily improving the uniformity of mechanical properties while suppressing uneven distribution of calcium carbonate particles in the inner layer, the mass ratio (first calcium carbonate particle group: second calcium carbonate particle group) is preferably 99.96:0.04 to 99.99:0.01, more preferably 99.97:0.03 to 99.99:0.01.

(Thermoplastic resin blended into the inner layer)
As the thermoplastic resin blended into the inner layer, any resin that can be normally blended into a resin sheet can be employed. The thermoplastic resin blended into the inner layer can be used singly or in combination of two or more.

Examples of the thermoplastic resin include polyolefin resins, polyester resins, polystyrene resins, and the like. Among these, polyolefin resins are preferred from the viewpoint of moldability and the like.

In the present invention, the term "polyolefin resin" refers to a polyolefin resin whose main component is an olefin component unit.
"Mainly composed of olefin component units" means that the olefin component units are present in the polyolefin resin in an amount of 50% by mass or more (preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more). It means to be included.
The method for producing the polyolefin resin used in the present invention is not particularly limited, and any method using a Ziegler-Natta catalyst, a metallocene catalyst, a radical initiator (oxygen, peroxide, etc.), etc. may be used. .

Examples of the polyolefin resin include polypropylene resin, polyethylene resin, and the like.
The thermoplastic resin preferably contains a polypropylene resin and/or a polyethylene resin, from the viewpoint of easily achieving a good appearance and further suppressing non-uniformity of mechanical properties. Or, it is more preferable to consist only of polyethylene resin.

[Polypropylene resin]
The polypropylene resin in the present invention includes a resin in which the propylene component unit is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, most preferably 80% by mass or more.

Examples of the polypropylene resin include polypropylene homopolymers (propylene homopolymers), copolymers of propylene and other α-olefins (those copolymerizable with propylene), and the like.
Examples of "other α-olefins" include α-olefins having 4 to 10 carbon atoms (ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4- dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, etc.).

The propylene homopolymer includes linear or branched polypropylene exhibiting various stereoregularities (isotactic, syndiotactic, atactic, hemiisotactic, etc.).

The propylene copolymer may be any of a polypropylene random copolymer (random copolymer), a polypropylene block copolymer (block copolymer), a binary copolymer, a ternary copolymer, and the like. Specific examples include ethylene-propylene random copolymer, butene-1-propylene random copolymer, ethylene-butene-1-propylene random terpolymer, ethylene-propylene block copolymer, and the like.

Among the above polypropylene resins, resins containing one or more of polypropylene homopolymers and polypropylene block polymers are preferred, and resins containing only one or more of polypropylene homopolymers and polypropylene block polymers are more preferred.

[Polyethylene resin]
The polyethylene resin in the present invention includes a resin in which the ethylene component unit is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, most preferably 80% by mass or more.

Examples of polyethylene resins include high-density polyethylene (HDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer, and ethylene-propylene copolymer. Copolymer, ethylene-propylene-butene 1 copolymer, ethylene-butene 1 copolymer, ethylene-hexene 1 copolymer, ethylene-4 methylpentene 1 copolymer, ethylene-octene 1 copolymer, and the like.

As the polyethylene resin, a resin containing high-density polyethylene and linear low-density polyethylene is preferable, and a resin consisting only of high-density polyethylene and linear low-density polyethylene is more preferable.

The high-density polyethylene preferably has an MFR (190°C, 21.6 kg) according to JIS K 6922-1 (ISO1133) of 5 g/10 minutes or more and 15 g/10 minutes or less, and 7 g/10 minutes or more and 13 g/10 minutes. The following are more preferable.

The linear low density polyethylene preferably has an MFR (190°C, 2.16 kg) according to JIS K 6922-1 (ISO1133) of 0.5 g/10 minutes or more and 1.5 g/10 minutes or less, and 0.5 g/10 minutes or more and 1.5 g/10 minutes or less. More preferably, it is 7 g/10 minutes or more and 1.3 g/10 minutes or less.

In resins containing high-density polyethylene and linear low-density polyethylene, the mass ratio of both (high-density polyethylene: linear low-density polyethylene) is preferably 90:10 to 50:50, more preferably 92:8 to The ratio is 50:50, more preferably 94:6 to 50:50.

In a preferred embodiment of the present invention, the polyethylene resin includes high density polyethylene and linear low density polyethylene,
The MFR (190°C, 21.6 kg) of high-density polyethylene according to JIS K 6922-1 (ISO1133) is 5 g/10 minutes or more and 15 g/10 minutes or less,
The MFR (190°C, 2.16 kg) of linear low density polyethylene according to JIS K 6922-1 (ISO1133) is 0.5 g/10 minutes or more and 1.5 g/10 minutes or less,
The mass ratio of high density polyethylene to linear low density polyethylene is 90:10 to 50:50.

[Ratio of thermoplastic resin blended in the inner layer]
The proportion of the thermoplastic resin blended into the inner layer is not particularly limited as long as a sufficient amount of calcium carbonate can be blended.

The lower limit of the thermoplastic resin content is preferably 20.0% by mass or more, more preferably 22.0% by mass or more, still more preferably 24.0% by mass or more, based on the inner layer.

The upper limit of the content of the thermoplastic resin is preferably 60.0% by mass or less, more preferably 58.0% by mass or less, still more preferably 56.0% by mass or less, based on the inner layer.

(Other ingredients blended into the inner layer)
The inner layer may or may not contain calcium carbonate particles and other components other than the thermoplastic resin within a range that does not impede the effects of the present invention.

As other components, any component that can be normally blended into the resin sheet can be used.
Such components include inorganic fillers other than calcium carbonate particles (clay, kaolin, mica, calcium sulfate, barium sulfate, zinc oxide, silica, talc, titanium dioxide, silicon dioxide, bentonite, etc.), lubricants, dispersants, Examples include antistatic agents, antioxidants, heat stabilizers, and ultraviolet absorbers.
The types and amounts of these components can be appropriately set depending on the desired effect.

A preferred embodiment of the present invention includes a laminated sheet in which the inner layer is composed only of calcium carbonate particles and a thermoplastic resin.

(2) Outer layer The outer layer is a pair of layers laminated on the two surfaces of the inner layer (that is, in the laminated sheet of the present invention, two outer layers are formed so as to sandwich the inner layer).
In the present invention, the pair of layers are referred to as a first outer layer and a second outer layer.

The structures of the first outer layer and the second outer layer may be the same or different. However, the first outer layer and the second outer layer each contain a thermoplastic resin.

Preferred embodiments of the present invention include embodiments in which the first outer layer and the second outer layer have the same structure (composition, thickness, shape, etc.).

(Thermoplastic resin blended into the outer layer)
As the thermoplastic resin blended into the outer layer, any resin that can be normally blended into the resin sheet can be employed. The thermoplastic resin blended in the outer layer can be used singly or in combination of two or more.

As the thermoplastic resin blended in the outer layer, resins similar to those listed above (thermoplastic resin blended in the inner layer) can be employed.
However, in the laminated sheet of the present invention, the thermoplastic resin blended in the outer layer and the thermoplastic resin blended in the inner layer may be the same or different.

Preferred embodiments of the present invention include all of the following embodiments.
(Aspect 1) Aspect in which the thermoplastic resin blended in the outer layer and the thermoplastic resin blended in the inner layer are all the same (Aspect 2) The thermoplastic resin blended in the first outer layer and the thermoplastic resin blended in the second outer layer Embodiment in which the thermoplastic resin blended in the first outer layer and the thermoplastic resin blended in the inner layer are all different (Aspect 3) The thermoplastic resin blended in the first outer layer, the thermoplastic resin blended in the second outer layer, and an embodiment in which only two of the thermoplastic resins blended in the inner layer are the same.

Among the above embodiments, embodiment 3 is preferable from the viewpoint that the effects of the present invention can be easily achieved.

In the above (aspect 3), from the viewpoint that the effects of the present invention are easily achieved, the thermoplastic resin blended in the first outer layer and the thermoplastic resin blended in the second outer layer are the same (i.e. , embodiments in which only the thermoplastic resin blended in the inner layer differs) are preferred.

The thermoplastic resin in the first outer layer and the second outer layer is preferably a resin containing a polypropylene resin and/or a polyethylene resin, and more preferably a resin consisting only of a polypropylene resin and/or a polyethylene resin.

The proportion of the thermoplastic resin blended into the outer layer is not particularly limited as long as the resin sheet can be molded.

The lower limit of the thermoplastic resin content is preferably 80.0% by mass or more, more preferably 90.0% by mass or more, even more preferably 99.0% by mass or more, based on the outer layer.

The content of the thermoplastic resin is preferably 100.0% by mass based on the outer layer.

(Other ingredients added to the outer layer)
The outer layer may or may not contain other components other than the thermoplastic resin within a range that does not impede the effects of the present invention.

As other components, any component that can be normally blended into the resin sheet can be used.
Such ingredients include inorganic fillers (calcium carbonate, clay, kaolin, mica, calcium sulfate, barium sulfate, zinc oxide, silica, talc, titanium dioxide, silicon dioxide, bentonite, etc.), lubricants, dispersants, electrostatic Examples include inhibitors, antioxidants, heat stabilizers, ultraviolet absorbers, and the like.
The types and amounts of these components can be appropriately set depending on the desired effect.

A preferred embodiment of the present invention includes a laminated sheet in which the outer layer is made only of thermoplastic resin.

(3) Thickness of each layer of the laminated sheet, etc. In the laminated sheet of the present invention, the ratio of the thickness of the first outer layer and the second outer layer is 2.0%, respectively, to the total thickness of the laminated sheet. 20.0% or less. That is, in the laminated sheet of the present invention, the total thickness of the outer layer (the sum of the thicknesses of the first outer layer and the second outer layer) is 4.0% or more of the total thickness of the laminated sheet. It is 0% or less.
By making the thickness of the outer layer thinner than the thickness of the inner layer, the laminated sheet of the present invention can exhibit excellent mechanical properties exhibited by the inner layer while exhibiting a good appearance.

The lower limit of the ratio of the thickness of the first outer layer and the second outer layer is 2.0% or more, preferably 2.5%, respectively, based on the total thickness of the laminated sheet, from the viewpoint that the appearance is likely to be good. % or more, more preferably 3.0% or more.

The upper limit of the ratio of the thickness of the first outer layer and the second outer layer is 20.0% or less, preferably 18% or less of the total thickness of the laminated sheet, from the viewpoint of facilitating the effect of the inner layer. 0% or less, more preferably 16.0% or less.

In the laminated sheet of the present invention, the ratio of the thickness of the inner layer is adjusted according to the thickness of the outer layer, and is 60.0% or more and 96.0% or less with respect to the total thickness of the laminated sheet.

The lower limit of the thickness of the first outer layer and the second outer layer is preferably 5.0 μm or more, more preferably 10.0 μm or more, from the viewpoint of easily obtaining a good appearance.

The upper limit of the thickness of the first outer layer and the second outer layer is preferably 50.0 μm or less, more preferably 45.0 μm or less, from the viewpoint of moldability and the like.

The lower limit of the thickness of the inner layer is preferably 50.0 μm or more, more preferably 100.0 μm or more, from the viewpoint of easily obtaining good mechanical properties.

The upper limit of the thickness of the inner layer is preferably 950.0 μm or less, more preferably 900.0 μm or less, from the viewpoint of moldability and the like.

The lower limit of the total thickness of the laminated sheet is adjusted depending on the thickness of the outer layer and the inner layer, and is preferably 100.0 μm or more, more preferably 150.0 μm or more.

The upper limit of the total thickness of the laminated sheet is adjusted depending on the thickness of the outer layer and the inner layer, and is preferably 990.0 μm or less, more preferably 700.0 μm or less.

The density of the laminated sheet is not particularly limited.

(4) Method for manufacturing a laminate sheet The method for manufacturing a laminate sheet of the present invention is not particularly limited, and conventionally known methods for manufacturing multilayer sheets and laminates can be employed.

Examples of methods for manufacturing the laminated sheet include the following methods.
・Method of laminating the inner and outer layers formed into sheets using a calendar roll ・Method of coextruding the inner and outer layers Method of performing co-extrusion molding in the same process ・Extrusion inflation method using multiple annular dies

The laminated sheet may be stretched as necessary.

(5) Applications of laminated sheet The laminated sheet of the present invention can be employed in any application for ordinary resin sheets.

The method for forming the laminated sheet of the present invention is not particularly limited, and examples thereof include vacuum forming, pressure forming, match molding, and the like.
Among these, vacuum forming is preferred from the viewpoint of ease of forming. Therefore, the laminate sheet of the present invention includes an embodiment that is a laminate sheet for vacuum forming.

Suitable uses for the laminated sheet of the present invention include materials for packaging containers.
Therefore, the present invention includes packaging containers, particularly food packaging containers, formed from the laminated sheet of the present invention.

Food packaging containers include any containers, including trays, cups, lids of various containers, bags, and the like.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

<Preparation and evaluation of laminated sheet>
A laminated sheet was produced and evaluated using the following method.

(1) Preparation of materials Materials for each layer were prepared as follows.

(calcium carbonate particle group)
Calcium carbonate particle group-1: Heavy calcium carbonate particle group (average particle size = 0.3 μm, particle size distribution D97 = 2.5 μm, no surface treatment)
Calcium carbonate particle group-2: Heavy calcium carbonate particle group (average particle size = 1.2 μm, particle size distribution D97 = 4.0 μm, no surface treatment)
Calcium carbonate particle group-3: Heavy calcium carbonate particle group (average particle size = 5.0 μm, particle size distribution D97 = 9.5 μm, no surface treatment)
Calcium carbonate particle group-4: Heavy calcium carbonate particle group (average particle size = 10.0 μm, particle size distribution D97 = 14.5 μm, no surface treatment)
Calcium carbonate particle group-5: Heavy calcium carbonate particle group (average particle size = 17.0 μm, particle size distribution D97 = 21.0 μm, no surface treatment)
Calcium carbonate particle group-6: Heavy calcium carbonate particle group (average particle size = 28.0 μm, particle size distribution D97 = 36.0 μm, no surface treatment)
Calcium carbonate particle group-7: Heavy calcium carbonate particle group (average particle size 50.0 μm, particle size distribution D97 = 65.0 μm, no surface treatment)

Among the calcium carbonate particle groups, "calcium carbonate particle group-2" and "calcium carbonate particle group-3" correspond to the "first calcium carbonate particle group".
Among the calcium carbonate particle groups, "calcium carbonate particle group-5" and "calcium carbonate particle group-6" correspond to the "second calcium carbonate particle group".

The average particle size of the calcium carbonate particle group is a value specified based on the air permeation method according to JIS M-8511.

Particle size distribution D97 of the calcium carbonate particle group is a value measured by a laser diffraction type particle size distribution measuring device.

In the table, in the "inner layer" section, in cases where a plurality of types of calcium carbonate particle groups are combined, the mass ratio of the calcium carbonate particle groups is written in parentheses.
For example, in "Example 1-1", "49.985% by mass" of "calcium carbonate particle group-2" is blended into the inner layer, and "0.985% by mass" of "calcium carbonate particle group-5" is blended into the inner layer. 015% by mass” and the mass ratio of “calcium carbonate particle group-2” to “calcium carbonate particle group-5” is “9997:3”.

(Thermoplastic resin)
Polypropylene resin-1 (PP-1): Polypropylene homopolymer (polypropylene homopolymer, melting point 160°C)
Polypropylene resin-2 (PP-2): Polypropylene block copolymer (melting point 160°C)
Polyethylene resin (PE): blend of HDPE and LLDPE (HDPE:LLDPE (mass ratio) = 70:30)
Note that the MFR (190° C., 21.6 kg) of the above HDPE according to JIS K 6922-1 (ISO1133) is 7.5 g/10 minutes.
The MFR (190° C., 2.16 kg) of the above LLDPE according to JIS K 6922-1 (ISO1133) is 0.8 g/10 minutes.

(2) Preparation of laminated sheet A three-layer laminated sheet was prepared using the materials shown in the table by the multilayer T-die method.
The total thickness of the laminated sheet was set to 300.0 μm.
The thickness of the inner layer was set to 270 μm (90% of the total thickness of the laminated sheet).
Outer layers (first outer layer and second outer layer) were provided on both sides of the inner layer, and the thickness of each outer layer was set to 15 μm (5% of the total thickness of the laminated sheet).

(3) Evaluation of laminated sheet The appearance and mechanical properties of the laminated sheet were evaluated using the following methods. The results are shown in the "Evaluation" section of the table.

(exterior)
The appearance of the molded product obtained from the laminated sheet was evaluated by the following method.

[Appearance evaluation method]
After preheating the laminated sheet with a far-infrared heater, it was formed into a tray-shaped container with a bottom diameter of 50 mm, an opening diameter of 50 mm, a height of 30 mm, and a flange width of 5 mm using a vacuum forming machine.
The appearance of the obtained container was visually observed and evaluated based on the following criteria.

[Appearance evaluation criteria]
A: The overall surface condition was very good (no unevenness, deformation, tearing, etc. occurred at all).
B: The overall surface condition is good (some unevenness, deformation, or tearing occurred).
C: The overall surface condition is poor (unevenness, deformation, tearing, etc. clearly occurred).

(mechanical properties)
The mechanical properties (tensile strength) of the laminated sheet were evaluated by the following method.

[Method for evaluating mechanical properties]
The tensile strength of each laminated sheet was measured according to JIS K 7161-2:2014 under conditions of 23° C. and 50% RH using Autograph AG-100kNXplus (Shimadzu Corporation).
A sample (dumbbell shape) cut out from each laminated sheet was used as the test piece. The stretching speed was set at 50 mm/min.

[Evaluation criteria for mechanical properties]
A: Tensile strength was 13 MPa or more.
B: Tensile strength was 10 MPa or more and less than 13 MPa.
C: Tensile strength was less than 10 MPa.

As shown in the table, the laminate sheet satisfying the requirements of the present invention had good appearance of the obtained molded product and good mechanical properties of the laminate sheet.
Regarding the mechanical properties, the test was conducted multiple times and it was also confirmed that the variation in the tensile strength values of the laminated sheets satisfying the requirements of the present invention was small.

Although data is not shown, the laminated sheets that met the requirements of the present invention had good surface conditions regardless of whether they were molded or not.

Claims (9)

A three-layer laminated sheet,
The laminated sheet includes an inner layer, a first outer layer and a second outer layer laminated on the surface of the inner layer,
The inner layer includes calcium carbonate particles and a thermoplastic resin,
The first outer layer and the second outer layer each contain a thermoplastic resin,
The content of the calcium carbonate particles is 40.0% by mass or more and 80.0% by mass or less with respect to the inner layer,
The calcium carbonate particles include at least a first calcium carbonate particle group and a second calcium carbonate particle group,
The first calcium carbonate particle group has an average particle diameter of 0.7 μm or more and 6.0 μm or less, based on an air permeation method according to JIS M-8511;
Particle size distribution D97 in the second group of calcium carbonate particles is 20.1 μm or more and 40.0 μm or less,
The mass ratio of the first calcium carbonate particle group and the second calcium carbonate particle group in the inner layer is 99.95:0.05 to 99.99:0.01,
The ratio of the thickness of the first outer layer and the second outer layer is 2.0% or more and 20.0% or less, respectively, with respect to the total thickness of the laminated sheet.
Laminated sheet. The laminate sheet according to claim 1, wherein the thermoplastic resin in the inner layer, the first outer layer, and the second outer layer contains a polypropylene resin and/or a polyethylene resin. The polyethylene resin includes high density polyethylene and linear low density polyethylene,
The MFR (190°C, 21.6 kg) of the high-density polyethylene according to JIS K 6922-1 (ISO1133) is 5 g/10 minutes or more and 15 g/10 minutes or less,
The linear low density polyethylene has an MFR (190°C, 2.16 kg) according to JIS K 6922-1 (ISO1133) of 0.5 g/10 minutes or more and 1.5 g/10 minutes or less,
The laminate sheet according to claim 2, wherein the mass ratio of the high-density polyethylene to the linear low-density polyethylene is 90:10 to 50:50. The laminate sheet according to claim 2, wherein the polypropylene resin is a polypropylene homopolymer and/or a polypropylene block polymer. The laminated sheet according to claim 1, wherein the calcium carbonate particles are heavy calcium carbonate particles. The average particle diameter of the first calcium carbonate particle group based on an air permeation method according to JIS M-8511 is 1.0 μm or more and 3.0 μm or less,
The laminated sheet according to claim 1, wherein the second calcium carbonate particle group has a particle size distribution D97 of 20.1 μm or more and 35.0 μm or less. The thickness ratio of the first outer layer and the second outer layer is 2.0% or more and 10.0% or less with respect to the total thickness of the laminated sheet, respectively, according to claim 1. Laminated sheet. The laminated sheet according to any one of claims 1 to 7, wherein the laminated sheet is a laminated sheet for vacuum forming. A food packaging container formed from the laminated sheet according to claim 8.