JP7741015B2 - Resin laminate - Google Patents

Description

The present invention relates to a resin laminate.

Polypropylene resin sheets are easy to mold and have low raw material costs, resulting in low manufacturing costs. Their low density also makes them easy to handle and reduces transportation costs, making them widely used for thermoforming to produce various containers, trays, and other items.

Patent Document 1 discloses a polypropylene resin for extrusion foaming that prevents drawdown during molding by adjusting the relationship between melt tension (MT) and melt flow rate (MFR).

Patent Document 2 also discloses a thermoforming sheet that contains a polypropylene resin with specific properties, a thermoplastic elastomer, and a filler, and that minimizes sagging during molding, has good moldability, and produces molded articles with minimal thickness deviation.

Japanese Patent Application Publication No. 11-80262 JP 2017-71767 A

In both Patent Documents 1 and 2, sheets with a thickness of 1 mm or more are used, particularly to suppress thickness variations. However, when using such thick sheets for thermoforming, it is difficult to accurately form intricate shapes, such as trays used to separate, store, and transport small items like cosmetics, or even smaller items like electronic components.

Furthermore, the sheet described in Patent Document 1 is a foamed sheet, and thermoformed articles formed using the foamed sheet tend to have insufficient mechanical strength and durability, and are poorly processable into complex and fine shapes.

The present invention relates to a resin laminate that has a thin film thickness suitable for molding complex shapes using thermoforming methods such as vacuum molding, pressure molding, and vacuum-pressure molding, and that has minimal drawdown or thickness deviation during molding.

As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, it was found that by forming a resin laminate in which an unstretched layer (A) and a stretched layer (B) containing a specific resin are laminated together, it is possible to obtain a resin laminate having a thin film thickness suitable for molding into a complex shape by thermoforming such as vacuum molding, pressure molding, and vacuum pressure molding, and which has little drawdown or thickness deviation during molding, and thus the present invention was completed.
That is, the present invention is as follows.

[1]
A resin laminate having a thickness of 300 to 600 μm, comprising: an unstretched layer (A); and an oriented layer (B) laminated on either or both sides of the unstretched layer (A) directly or via another layer;
the unstretched layer (A) is non-porous and contains a polyolefin resin (A-1) having a branched structure and a strain hardening coefficient (λmax(1.0)) of 6.0 or more as measured by elongational viscosity at a strain rate of ^1.0 s-1, and a polypropylene (A-2) having a strain hardening coefficient (λmax(1.0)) of less than 6.0;
the stretched layer (B) contains 50% by mass or more of polypropylene (B-1),
However, the polypropylene (A-2) and the polypropylene (B-1) may be the same or different.
[2]
The resin laminate according to [1], wherein the polypropylene (A-2) has a melt flow rate of 5.0 g/10 min or less.
[3]
The resin laminate according to [1] or [2], wherein the content of the polyolefin resin (A-1) relative to the total amount of the polypropylene (A-2) and the polyolefin resin (A-1) is 10 to 50 mass%.
[4]
[4] The resin laminate according to any one of [1] to [3], which has an antistatic layer (C) on one or both surfaces of the resin laminate.
[5]
The resin laminate according to [4], wherein the antistatic layer (C) is a coating layer containing an antistatic agent.
[6]
[6] The resin laminate according to [5], wherein the antistatic agent comprises a cationic polymer antistatic agent.

The present invention makes it possible to provide a resin laminate having a non-stretched layer and a stretched layer, with a thin film thickness suitable for molding into complex shapes by thermoforming such as vacuum molding, pressure molding, and vacuum-pressure molding, and with minimal drawdown or thickness deviation during molding.

FIG. 1 is an overall view showing a tray molded for measuring thickness deviation in the examples. FIG. 2 is a bottom view of a tray for schematically showing the measurement points of thickness deviation in the examples. FIG. 3 is a diagram schematically showing a cross section taken along line XX in FIG. FIG. 4 is a side view of a tray for schematically showing the measurement points of the thickness deviation amount in the example.

The resin laminate of the present invention will be described in detail below. The following is an example (typical example) of the present invention, and the present invention is not limited thereto.
In this specification, the numerical range "A to B" indicates "A or more and B or less."

The present invention relates to a resin laminate having a thickness of 300 to 600 μm, which comprises an unstretched layer (A) and an oriented layer (B) laminated on one or both sides of the unstretched layer (A) directly or via another layer, wherein the unstretched layer (A) is non-porous and contains a polyolefin resin (A-1) having a branched structure and a strain hardening coefficient (λmax(1.0)) of 6.0 or more as measured by extensional viscosity at a strain rate of 1.0 s ^-1 , and a polypropylene (A-2) having the strain hardening coefficient (λmax(1.0)) of less than 6.0, and the oriented layer (B) contains 50 mass% or more of polypropylene (B-1), with the proviso that the polypropylene (A-2) and the polypropylene (B-1) may be the same or different.
By forming a resin laminate in which an unstretched layer (A) and a stretched layer (B) containing a specific resin are laminated, it is possible to obtain a resin laminate having a thin film thickness suitable for molding into a complex shape by thermoforming such as vacuum molding, pressure molding, and vacuum pressure molding, and which has little drawdown or thickness deviation during molding.

[Resin laminate]
The thickness of the resin laminate is 300 to 600 μm, preferably 400 to 500 μm. By making the resin laminate have a thickness in this range, it is possible to accurately form complex shapes such as trays and containers that can be used for separating and storing and transporting small items such as cosmetics, and even smaller items such as electronic components.
If the thickness of the resin laminate is less than 300 μm, the molding window during vacuum molding may be narrow, resulting in poor productivity, or the vacuum molded product may be weak and difficult to handle.If the thickness of the resin laminate is more than 600 μm, the heating time during vacuum molding may be increased, resulting in poor productivity, or the product may be difficult to follow the mold, resulting in poor shaping.

Normally, when a thermoformable sheet is made thinner, it tends to be more prone to thickness variations and drawdown. However, the resin laminate of the present invention has an unstretched layer (A) and an oriented layer (B) laminated directly or via another layer on either or both sides of the unstretched layer (A), allowing it to have good thermoformability even when thin.

[Non-stretched layer (A)]
The unstretched layer (A) is non-porous and contains a polyolefin resin (A-1) having a branched structure and a strain hardening coefficient (λmax(1.0)) of 6.0 or more as measured by elongational viscosity at a strain rate of ^1.0 s-1, and a polypropylene (A-2) having the strain hardening coefficient (λmax(1.0)) of less than 6.0.

The non-stretched layer (A) is non-porous, which provides the following advantages over thermoforming sheets that use a foam as a layer corresponding to the non-stretched layer (A) (for example, thermoforming sheets described in JP-A Nos. 11-80262 and 8-318602):
The thermoformed articles obtained have high mechanical strength and excellent durability.
- Deep-draw moldings with more complex shapes can be formed compared to thermoforming sheets of the same thickness.
- When heating before molding, heat is easily transferred to the inside of the substrate, allowing for consistent production of high-quality molded products and excellent productivity.

In this specification, "non-porous" means that the porosity is 5% or less. Here, "porosity" refers to the ratio (volume ratio) of the volume occupied by pores in a target layer to the total volume of the target layer. The porosity can be obtained as the area ratio of pores on the cross section, calculated by observing the cross section of the target layer using a scanning electron microscope, importing the observed image into an image analyzer, and performing image analysis on the observed area.

The melt tension of the unstretched layer (A) is preferably 30 to 250 mN, and more preferably 35 to 200 mN. A melt tension of 30 mN or more for the unstretched layer is preferred because it reduces the amount of drawdown during thermoforming of a resin laminate containing the unstretched layer. Furthermore, a melt tension of 250 mN or less is preferred because it makes the molten resin sheet less likely to tear during sheet molding and easier to mold.

The unstretched layer (A) may be a single layer or a multilayer.

The thickness of the unstretched layer (A) is preferably 200 to 595 μm, and more preferably 300 to 495 μm. A thickness of 200 μm or more is preferred because it is less likely to cause uneven thickness and makes it easier to obtain high-quality molded products. Furthermore, a thickness of 595 μm or less is preferred because it allows for the formation of deep-draw molded products with more complex shapes and shortens the molding time.

(Polyolefin Resin (A-1))
The non-stretched layer (A) contains a polyolefin resin (A-1) having a branched structure and a strain hardening coefficient (λmax(1.0)) of 6.0 or more as measured by elongational viscosity at a strain rate of 1.0 s ⁻¹ .

Here, the strain hardening coefficient (λmax(1.0)) is an index representing the strength when melted, and a large value of this coefficient has the effect of improving the melt tension. As a result, even in molded articles with complex shapes, the defect phenomenon of excessive thickness deviations being formed can be prevented during thermoforming, contributing to improving the physical properties of the molded article and also to reducing the thickness of the raw sheet (gauge down), making it possible to suitably mold, for example, various containers, trays, etc. If the strain hardening coefficient of the polyolefin resin (A-1) is less than 6.0, thickness deviations may occur during thermoforming, or moldability may be reduced.
The strain hardening coefficient of the polyolefin resin (A-1) is preferably 8.0 or more, more preferably 12.0 or more, and from the viewpoint of shapeability during thermoforming, the strain hardening coefficient is more preferably 17.0 or less.

The method for calculating the strain hardening coefficient λmax(1.0) in the measurement of the extensional viscosity at a strain rate of 1.0 s ⁻¹ is described below.
The extensional viscosity at a temperature of 180°C and a strain rate of 1.0 s ^-1 is plotted on a double logarithmic graph with time t (seconds) on the horizontal axis and extensional viscosity ηE (Pa·seconds) on the vertical axis. The relationship between the time and viscosity immediately before strain hardening occurs on the double logarithmic graph is approximated by a straight line to obtain an approximate straight line.
Specifically, first, the slope at each time point when the extensional viscosity is plotted against time is determined, and in doing so, various averaging methods are used, taking into account that the extensional viscosity measurement data is discrete. For example, one method is to determine the slope of each adjacent data point and take the moving average of several surrounding points.
In the low strain range, the extensional viscosity is a simple increasing function that gradually approaches a constant value. In the absence of strain hardening, it coincides with the Trouton viscosity after a sufficient amount of time has passed. However, in the presence of strain hardening, the extensional viscosity generally begins to increase with time from a strain (= strain rate x time) of approximately 1. That is, the slope tends to decrease with time in the low strain range, but begins to increase from a strain of approximately 1, and an inflection point is present on the curve when the extensional viscosity is plotted against time. Therefore, within the strain range of approximately 0.1 to 2.5, the point where the slope at each time obtained above is at its minimum value is determined, a tangent is drawn at that point, and a straight line is extrapolated until the strain reaches 4.0. The maximum value (ηmax) of the extensional viscosity ηE until the strain reaches 4.0 and the time at which this maximum value is reached are determined, and the viscosity on the approximate straight line at that time is defined as ηlin. ηmax/ηlin is defined as λmax(1.0).

Examples of polyolefin resin (A-1) include polyethylene or polypropylene having a long-chain branched structure.

The melt tension of the polyolefin resin (A-1) is preferably 75 to 600 mN, and more preferably 100 to 500 mN.
A melt tension of 75 mN or more is preferred because it can impart a desired melt tension to the resin laminate and easily improve drawdown. A melt tension of 600 mN or less is preferred because it improves compatibility with the polypropylene (A-2) described below. If the melt tension is too high, the sheet may be easily torn during sheet molding, making sheet molding difficult.
The melt tension is a value measured at a take-up speed of 10 mm/min and 190°C.

The melt flow rate of the polyolefin resin (A-1) is preferably 0.5 to 10 g/10 min, and more preferably 1.0 to 8.0 g/10 min.
A melt flow rate of 0.5 g/10 min or more is preferable because it improves sheet formability, and a melt flow rate of 10 g/10 min or less is preferable because it suppresses necking during sheet forming and makes it easier to obtain a sheet of uniform thickness.
The melt flow rate in this specification refers to a value measured by an appropriate method depending on the type of monomer component that is most abundant in the resin. For example, in the case of propylene, the value measured at 230°C under a load of 2.16 kg in accordance with JIS K7210 was used, and in the case of polyethylene, the value measured at 190°C under a load of 2.16 kg in accordance with JIS K6922-2 was used.

(Polypropylene (A-2))
The non-stretched layer (A) contains polypropylene (A-2) having a strain hardening coefficient (λmax(1.0)) of less than 6.0 as measured by elongational viscosity at a strain rate of 1.0 s ⁻¹ .

The polypropylene (A-2) may be a propylene homopolymer, random polypropylene, or block polypropylene, or a combination of these. As the propylene homopolymer, isotactic or syndiotactic polypropylenes and polypropylenes exhibiting various stereoregularities can be used.

As polypropylene (A-2), a resin with a low melt flow rate is preferred, as this increases the melt tension and suppresses drawdown during thermoforming. The melt flow rate of polypropylene (A-2) is preferably 5.0 g/10 min or less, more preferably 3.0 g/10 min or less, and even more preferably 2.0 g/10 min or less.

(Contents of Polypropylene (A-2) and Polyolefin Resin (A-1))
The total amount of the polypropylene (A-2) and the polyolefin resin (A-1) in the non-stretched layer (A) is preferably 70% by mass or more based on the total mass of all components constituting the non-stretched layer (A), and more preferably 100% by mass when the non-stretched layer (A) does not contain the inorganic filler (A-3) described below.
The total amount of polypropylene (A-2) and polyolefin resin (A-1) is preferably 70% by mass or more, since the excellent thermoformability, which is an effect of the present invention, can be fully exhibited.

The content of the polyolefin resin (A-1) relative to the total amount of the polypropylene (A-2) and the polyolefin resin (A-1) is preferably from 10 to 50% by mass, more preferably from 20 to 40% by mass.
By setting the content of the polyolefin resin (A-1) to 10% by mass or more relative to the total amount of the polypropylene (A-2) and the polyolefin resin (A-1), a decrease in strain hardening of the resin composition, a decrease in moldability due to the occurrence of thickness deviation, and an increase in the amount of drawdown tend to be suppressed, which is preferable. Also, by setting the content to 50% by mass or less, an unnecessary increase in melt tension is suppressed, which tends to reduce the possibility that the raw sheet will be easily torn during sheet molding and the possibility that the strain hardening will be too high during vacuum molding, which is preferable.

(Inorganic filler (A-3))
The non-stretched layer (A) may contain an inorganic filler (A-3). The inclusion of the inorganic filler (A-3) is preferred because it improves the mechanical strength of the molded article. Examples of the inorganic filler (A-3) include inorganic fine powders such as calcium carbonate, calcined clay, silica, diatomaceous earth, talc, titanium oxide, barium sulfate, and alumina. The average primary particle size of the inorganic fine powder is preferably 0.01 to 15 μm.
It is preferable that the inorganic fine powder has an average primary particle size of 0.01 μm or more, since this prevents the generation of secondary coarse particles due to aggregation of the inorganic fine powder during melt extrusion. Also, it is preferable that the inorganic fine powder has an average primary particle size of 15 μm or less, since this prevents the inorganic fine powder from protruding from the sheet surface and thus prevents defects from appearing on the outermost surface.
The average primary particle size (D50) is measured by a laser light diffraction/scattering method using, for example, a Microtrac MT3300EXII (manufactured by Microtrac Bell).

When the non-stretched layer (A) contains the inorganic filler (A-3), the content of the inorganic filler relative to the total mass of all components constituting the non-stretched layer (A) is preferably 15 to 30 mass%, and more preferably 18 to 27 mass%. By containing the inorganic filler (A-3) in the non-stretched layer (A), the amount of resin contained in the molded article is reduced, which is preferable from the viewpoint of reducing the environmental load caused by the resin.
The content of the inorganic filler (A-3) is preferably 15% by mass or more, since this improves the mechanical strength of the molded article. Furthermore, the content of the inorganic filler (A-3) is preferably 30% by mass or less, since this suppresses an increase in the amount of drawdown due to an increase in specific gravity and also prevents a risk of deterioration in moldability due to an excessively low relative resin amount. When the non-stretched layer (A) contains the inorganic filler (A-3), the total amount of the polypropylene (A-2) and the polyolefin resin (A-1) contained in the layer is preferably 70 to 85% by mass, more preferably 73 to 82% by mass.

(Other optional ingredients)
The unstretched layer (A) may further contain, as necessary, a stabilizer, a light stabilizer, a dispersant, a lubricant, etc. For example, 0.001 to 1 mass % of a sterically hindered phenol-based, phosphorus-based, amine-based, or other stabilizer may be blended as the stabilizer, 0.001 to 1 mass % of a sterically hindered amine, benzotriazole-based, benzophenone-based, or other light stabilizer may be blended as the light stabilizer, and 0.01 to 4 mass % of a silane coupling agent, a higher fatty acid such as oleic acid or stearic acid, a metal soap, or the like may be blended as a dispersant for the inorganic filler.

The unstretched layer (A) may contain polyolefin resins other than the polyolefin resin (A-1) and polypropylene (A-2), or other thermoplastic resins, as long as the effects of the present invention are not impaired.

[Stretched layer (B)]
The stretched layer (B) contains 50% by mass or more of polypropylene (B-1).

By laminating the stretched layer (B) directly or via another layer on both sides or one side of the unstretched layer (A), drawdown can be suppressed. More specifically, the heat generated during thermoforming using the resin laminate causes the surface stretched layer (B) to shrink, thereby suppressing drawdown of the unstretched layer (A).

The stretched layer (B) may be single-layer or multi-layer.

The thickness of the stretched layer (B) is preferably 20 to 100 μm, more preferably 40 to 80 μm. A thickness of 20 μm or more for the stretched layer (B) is preferred because it prevents excessive shrinkage of the stretched layer during heating in thermoforming. Furthermore, a thickness of 100 μm or less for the stretched layer (B) is preferred because it reduces uneven heating of the unstretched layer (A) during thermoforming.

The stretched layer (B) may be laminated on only one side of the unstretched layer (A) or on both sides thereof. When laminated on both sides, the two stretched layers (B) may be the same or different.
From the viewpoint of production costs, it is preferable that the stretched layer (B) is laminated on only one side of the non-stretched layer (A), and from the viewpoint of suppressing curling of the laminate, it is preferable that the stretched layer (B) is laminated on both sides of the non-stretched layer (A).

The oriented layer (B) may be a uniaxially oriented layer, a biaxially oriented layer, or a combination thereof.
By forming the stretched layer (B) as a biaxially stretched layer, shrinkage of the stretched layer (B) due to heat during thermoforming using the resin laminate occurs in biaxial directions, which further suppresses drawdown, and is therefore preferred.

When the stretched layer (B) has a multilayer structure, the number of stretching axes of each layer may be the same or different. By combining layers with different numbers of stretching axes, it is possible to design a stretched layer (B) that has the advantages of both uniaxial stretching and biaxial stretching. Examples of the number of stretching axes of each layer include uniaxial/uniaxial, uniaxial/biaxial, biaxial/uniaxial, uniaxial/uniaxial/biaxial, uniaxial/biaxial/uniaxial, biaxial/uniaxial/uniaxial, uniaxial/biaxial/biaxial, biaxial/biaxial/uniaxial, or biaxial/biaxial/biaxial.

When the stretched layer (B) is laminated on both sides or one side of the unstretched layer (A) via another layer, examples of the other layer include other unstretched layers described below under [Other Layers].

(Polypropylene (B-1))
The stretched layer (B) contains 50% by mass or more of polypropylene (B-1), preferably 60% by mass or more, and more preferably 70% by mass or more of polypropylene (B-1). There is no particular upper limit to the content of polypropylene (B-1) in the stretched layer (B), and it may be 100% by mass.
When the content of polypropylene (B-1) in the stretched layer (B) is less than 50% by mass, if the remainder is mostly an organic filler and/or an inorganic filler described below, breakage during sheet molding or molding defects in the vacuum molded product may occur. If the remainder is mostly other resins, this is not preferable from the viewpoint of recyclability of the molded product.

The polypropylene (B-1) may be the same as or different from the polypropylene (A-2).

Examples of the polypropylene (B-1) include the same resins as those exemplified as the polypropylene (A-2).
When the polypropylene (B-1) is the same as the polypropylene (A-2), the stretched layer (B) contains, as a main component, the same polypropylene as the unstretched layer (A). This is preferable because it improves the recyclability of the resin laminate and molded articles produced using the same, and it also makes it easier to adjust the melt viscosities of the resin compositions constituting the unstretched layer (A) and the stretched layer (B) to be approximately the same during shaping, making it easier to stably obtain molded articles.

When polypropylene (B-1) is different from polypropylene (A-2), examples of polypropylene (B-1) include resins that differ from polypropylene (A-2) in the type of monomer copolymerized with propylene, copolymerization ratio, molecular weight, etc.

The melt flow rate of the polypropylene (B-1) is preferably 0.5 to 15 g/10 min, more preferably 3.0 to 10 g/10 min, and even more preferably 3.0 to 8.0 g/10 min.
A melt flow rate of 0.5 g/10 min or more is preferable because sheet moldability is good, and a melt flow rate of 15 g/10 min or less is preferable because the melt tension of the resin composition forming the stretched layer (B) is high, making it easier to ensure thermoformability such as vacuum molding.

(Other thermoplastic resins)
The stretched layer (B) may contain a thermoplastic resin other than polypropylene (B-1) to the extent that the effects of the present invention are not impaired. Examples of such thermoplastic resins include ethylene-based resins such as high-density polyethylene and medium-density polyethylene, and polyolefin-based resins such as propylene-based resins that are copolymers of propylene as a main component with α-olefins such as ethylene, butene-1, hexene-1, and heptene-1,4-methylpentene-1; polymethyl-1-pentene; ethylene-cyclic olefin copolymers; polyamide-based resins such as nylon-6, nylon-6,6, nylon-6,10, and nylon-6,12; thermoplastic polyester-based resins such as polyethylene terephthalate and its copolymers, polyethylene naphthalate, and aliphatic polyesters; polycarbonate; atactic polystyrene; syndiotactic polystyrene; and polyphenylene sulfide. These may also be used in combination of two or more. Among these, propylene-based resins and high-density polyethylene are preferably selected from the standpoints of cost, water resistance, and chemical resistance.

(Other optional ingredients)
The stretched layer (B) may further contain an inorganic filler and/or an organic filler, if necessary.

Examples of inorganic fillers that may be contained in the stretched layer (B) include the same examples as the inorganic filler (A-3) listed as an optional component of the non-stretched layer (A). When both the non-stretched layer (A) and the stretched layer (B) contain inorganic fillers, the inorganic filler contained in the stretched layer (B) may be the same as or different from the inorganic filler contained in the non-stretched layer (A).

The organic filler that may be contained in the stretched layer (B) can be an organic fine powder with a melting point or glass transition temperature higher than the melting point of the polypropylene (B-1) contained in the stretched layer (B) and the melting points of the other thermoplastic resins mentioned above. When the main component of the stretched layer (B) is an olefin-based resin, examples of the organic fine powder that can be used include polyethylene terephthalate, polybutylene terephthalate, polycarbonate, nylon-6, nylon-6,6, homopolymers of cyclic olefins, and copolymers of cyclic olefins and ethylene, etc., which have a melting point of 120 to 300°C or a glass transition temperature of 120 to 280°C.

The content of inorganic filler and/or organic filler in the stretched layer (B) is preferably 0.5 to 60% by mass, and more preferably 3 to 50% by mass. A content of inorganic filler and/or organic filler of 0.5% by mass or more is preferred because it improves moldability. Furthermore, a content of 60% by mass or less is preferred because it makes the stretched layer (B) less likely to break during stretching.

The stretched layer (B) may further contain stabilizers, light stabilizers, UV absorbers, dispersants, lubricants, etc., as needed. For example, 0.001 to 1 mass% of a sterically hindered phenol-based, phosphorus-based, or amine-based stabilizer may be blended as the stabilizer; 0.001 to 1 mass% of a sterically hindered amine, benzotriazole-based, or benzophenone-based light stabilizer may be blended as the light stabilizer; and 0.01 to 4 mass% of a silane coupling agent, higher fatty acid such as oleic acid or stearic acid, or metal soap may be blended as a dispersant for inorganic fine powders.

[Method of Laminating Unstretched Layer (A) and Stretched Layer (B)]
There are various methods for laminating the stretched layer (B) integrally to one or both surfaces of the unstretched layer (A). For example, the following methods (A) to (C) are preferred.
(a) A thermal lamination method in which a resin composition for the unstretched layer (A) is melt-kneaded in an extruder, and then extruded from a co-extrusion die. While the resin composition is still in a molten state, the heat is utilized to pressure-weld the stretched layer (B) to one side of the extruded layer using a metal roll or rubber roll.
(a) A method in which the unstretched layer (A) and the stretched layer (B) are bonded together with a hot melt adhesive or a solvent adhesive.
(c) In the case of (a), a known adhesive hot-melt adhesive layer is provided on the unstretched layer (A) by co-extrusion, or a stretched layer (B) provided with a hot-melt adhesive layer is used.

As described below, when the non-stretched layer (A) has another non-stretched layer on one or both sides thereof, the resin laminate of the present invention may be produced by indirectly laminating the non-stretched layer (A) and the stretched layer (B) in a manner such that "non-stretched layer (A)" in the above explanations (a) to (c) is replaced with "non-stretched sheet (A)" comprising the non-stretched layer (A) and the other non-stretched layer.

(adhesion)
Examples of hot melt adhesives used when integrally laminating the stretched layer (B) to one or both sides of the unstretched layer (A) include low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer (preferably an ethylene-vinyl acetate copolymer having a vinyl acetate content of 12% by mass or less), ethylene-acrylic acid copolymer (preferably an ethylene-acrylic acid copolymer having an ethylene content of 65 to 94% by mass), ethylene-methacrylic acid alkyl ester copolymer, ionomer (metal salt of ethylene-acrylic acid copolymer or metal salt of ethylene-methacrylic acid copolymer), ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, vinyl chloride-vinyl acetate copolymer, etc. Two or more of these may be used in combination.

Examples of solvent-based adhesives include polyether polyol-polyisocyanate adhesives and polyester polyol-polyisocyanate adhesives. Two or more of these may be used in combination. The thickness of such adhesive layers is generally 1 to 30 μm, preferably 1 to 20 μm. Specifically, coating-type adhesives are applied in an amount of 1 to 20 g/m ² , preferably 2 to 8 g/m ² . Hot-melt-type adhesives are melt-extrusion laminated and heat-sealed to a thickness of 6 to 30 μm, preferably 8 to 20 μm.

[Antistatic layer (C)]
The resin laminate may have an antistatic layer (C) on both sides or on one side as the outermost layer.
The antistatic layer (C) may be provided on the surface of either the oriented layer (B) or the unoriented layer (A), provided that it is the outermost layer of the resin laminate.

When the molded article is a container or tray, friction with the articles stored therein may cause the molded article itself or the stored articles to become charged. To prevent this, it is preferable to use an antistatic agent in the moldable resin laminate.
In the field of resin molding, kneaded-in antistatic agents are widely used, but kneading an antistatic agent into a resin composition for layer formation can sometimes cause a decrease in the viscosity of the resin composition. Therefore, from the viewpoint of drawdown resistance, it is preferable to form an antistatic layer containing an antistatic agent on the outermost surface of a resin laminate, rather than using a kneaded-in antistatic agent.
That is, it is preferable that the antistatic agent be contained in the resin laminate by providing an antistatic layer containing the antistatic agent, preferably a coating layer containing the antistatic agent provided by coating.

Furthermore, when molded products are crushed, melted, and kneaded for reuse in molding, resin compositions containing antistatic agents are prone to resin degradation due to re-melting and kneading. Generally, when using kneaded-in antistatic agents, a larger amount of antistatic agent is required to achieve the desired antistatic properties than when an antistatic layer is applied by coating, increasing the risk of resin degradation during reuse. On the other hand, when an antistatic layer is applied to the surface of a resin laminate by coating, a high antistatic effect is achieved with a smaller amount and a thinner layer, making resin degradation less likely during reuse and preferable from the perspective of recyclability.

The thickness of the antistatic layer (C) is preferably 0.001 to 10 μm, and more preferably 0.005 to 0.1 μm. By making the thickness of the antistatic layer (C) 0.001 μm or more, the desired antistatic properties can be achieved, which is preferable. Furthermore, by making the thickness of the antistatic layer (C) 10 μm or less, the end product is more recyclable and has cost benefits, which is preferable.

(Antistatic Agent)
The antistatic agent contained in the antistatic layer (C) is preferably one that does not bleed out from the surface of the resin laminate during thermoforming and does not pose a risk of contaminating articles that come into contact with the resulting molded article. Even in the case of an antistatic layer provided by coating, an antistatic agent that does not migrate to the surface of an article that comes into contact with the layer when the molded article is obtained is desired.
Therefore, it is preferable that the antistatic agent be one that can be applied to form a layer by coating using water, which has a low environmental impact, as a solvent or dispersion medium, and that does not migrate to the surface of the molded product during thermoforming.

Preferably, such antistatic agents are polymer-type antistatic agents. Examples of polymer-type antistatic agents include cationic, anionic, amphoteric, and nonionic antistatic agents. These can be used alone or in combination of two or more types.

Examples of cationic antistatic agents include antistatic agents having an ammonium salt structure, a phosphonium salt structure, etc. Examples of anionic antistatic agents include antistatic agents having an alkali metal salt structure (lithium salt, sodium salt, potassium salt, etc.) of sulfonic acid, phosphoric acid, carboxylic acid, etc. Anionic antistatic agents may be antistatic agents having an alkali metal salt structure of acrylic acid, methacrylic acid, maleic acid (anhydride), etc. in their molecular structure.

Examples of amphoteric antistatic agents include those containing both cationic and anionic antistatic structures in the same molecule. Examples of amphoteric antistatic agents include betaine antistatic agents. Examples of nonionic antistatic agents include ethylene oxide polymers with alkylene oxide structures and polymers with ethylene oxide polymerization components in the molecular chain. Other examples of antistatic agents include polymeric antistatic agents that have boron in their molecular structure.

Among these, as the polymer-type antistatic agent, a cationic polymer-type antistatic agent is preferred, a nitrogen-containing polymer-type antistatic agent is more preferred, a polymer-type antistatic agent having an ammonium salt structure is even more preferred, an acrylic resin having a tertiary or quaternary ammonium salt structure is particularly preferred, and an acrylic resin having a quaternary ammonium salt structure is most preferred.
As the cationic polymer antistatic agent, commercially available products such as Saftomer ST-1000, ST-1100, and ST-3200 (trade names) manufactured by Mitsubishi Chemical Corporation can be used.

(Method for forming antistatic layer (C))
The method for forming the antistatic layer (C) is not particularly limited. For example, a coating liquid is prepared by dispersing or dissolving the components of the antistatic layer in water, and the coating liquid is applied to a substrate and dried to form a print-receiving layer. For coating, a known coating device such as an air knife coater, gravure coater, blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, size press coater, gate roll coater, or bill blade coater can be used.

[Other layers]
The resin laminate of the present invention may have layers other than the non-stretched layer (A), the stretched layer (B), and the antistatic layer (C) described above, as long as the effects of the present invention are not impaired. For example, the surface of the non-stretched layer (A) may have another non-stretched layer that does not contain the polyolefin resin (A-1). In this case, the stretched layer (B) or the antistatic layer (C) may be laminated on the non-stretched layer (A) via the other non-stretched layer, and the other non-stretched layer may also function as an adhesive layer.

The resin contained in the other unstretched layer is not particularly limited as long as it is a thermoplastic resin, and examples thereof include polyolefin-based resins, polyamide-based resins, and polyester-based resins. However, polyolefin-based resins are preferred because they can be formed by co-extrusion with the unstretched layer (A) without using an adhesive. Specific examples include ethylene-based resins such as high-density polyethylene and medium-density polyethylene, as well as the polypropylenes listed above as examples of polypropylene (A-2), and propylene-based resins that contain propylene as the main component and are copolymers of this with α-olefins such as ethylene, butene-1, hexene-1, and heptene-1,4-methylpentene-1. Furthermore, various known additives may be contained as necessary.
The other non-oriented layer may be provided on both sides of the non-oriented layer (A) or on only one side thereof.

[Uses of resin laminate]
The resin laminate of the present invention can be suitably used as a thermoforming sheet for producing, for example, various containers, trays, and the like.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

[Raw materials]
In the examples and comparative examples, the raw materials used for the unstretched layer (A) are as shown in Table 1.

The melt flow rate, melt tension, and strain hardening of each raw material were measured using the following methods.

(Melt Flow Rate)
The polypropylene was measured in accordance with JIS K7210 at 230° C. under a load of 2.16 kg, and the polyethylene was measured in accordance with JIS K6922-2 at 190° C. under a load of 2.16 kg.

(Melt tension)
Measurement was performed using a Capilograph 1D manufactured by Toyo Seiki Seisaku-sho, Ltd., at a test temperature of 190° C., using a capillary having a length of 20 mm and a diameter of 2.0 mm. Data was taken at a take-up speed of 10 mm/min.

(Strain hardening degree)
Uniaxial extensional viscosity was measured using a TA Instruments ARES-G2 in uniaxial extension mode at 180°C under _N2 with a sample size of 20 mm length and 10 mm width. Melt viscosity was measured using the same instrument in shear mode at 180°C under _N2 with a parallel plate of 25 mm diameter.
Next, the extensional viscosity at a temperature of 180°C and a strain rate of 1.0 s ^-1 was plotted on a double logarithmic graph with time t (seconds) on the horizontal axis and extensional viscosity ηE (Pa seconds) on the vertical axis. On the double logarithmic graph, the relationship between the time and viscosity immediately before strain hardening occurred was obtained using an approximate line. The maximum value (ηmax) of the extensional viscosity ηE when the strain amount reached 4.0 and the time at which it reached the maximum value were determined, and the viscosity on the approximate line at that time was defined as ηlin, and ηmax/ηlin was defined as the strain hardening degree (λmax(1.0)).

[Production Example 1]
(Polymer-type antistatic agent)
Into a four-neck flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube, 35 parts by mass of dimethylaminoethyl methacrylate, 20 parts by mass of ethyl methacrylate, 20 parts by mass of cyclohexyl methacrylate, 25 parts by mass of stearyl methacrylate, 150 parts by mass of ethyl alcohol, and 1 part by mass of 2,2'-azobisisobutyronitrile were added. After the atmosphere in the system was replaced with nitrogen, a polymerization reaction was carried out under a nitrogen stream at a temperature of 80°C for 6 hours.
Next, 70 parts by mass of a 60% by mass ethyl alcohol solution of 3-chloro-2-hydroxypropylammonium chloride was added, and the mixture was further reacted at a temperature of 80° C. for 15 hours.
Next, ethyl alcohol was distilled off while adding ion-exchanged water dropwise to the reactor, to obtain an aqueous resin solution made of a methacrylic copolymer containing a quaternary ammonium salt group and having a solids concentration of 30 mass %, which was used as a polymer-type antistatic agent (abbreviated as AS).

[Reference example]
The polymer antistatic agent AS obtained in Production Example 1 and a low molecular weight antistatic agent ESR-381 (trade name: Rikemaster ESR-381, manufactured by Riken Vitamin Co., Ltd.; LDPE masterbatch containing diglycerol monolaurate and N-dodecyl-N,N-diethanolamine monostearate in a ratio of 15 mass%, diglycerol monolaurate/N-dodecyl-N,N-diethanolamine monostearate (mass ratio) = 80/20, base resin: LDPE) were used to compare bleed-out properties during thermoforming by the following method.

(bleed-out property)
First, polymer-type antistatic agent AS was diluted 50 times with water, and the diluted solution was bar-coated onto the surface of a commercially available PET film having a thickness of 100 μm at a rate of 4 mm/min using a No. 2 bar, followed by drying at 70° C. for 2 minutes (test sheet 1).

The low molecular weight antistatic agent ESR-381 was pressurized at 15 MPa at 230°C for 5 minutes, then cooled while being pressed at 15 MPa at 20°C for 1.5 minutes to produce a 500 μm thick sheet (test sheet 2).

The resulting test sheets 1 and 2 were each laminated with a commercially available transparent PET film with a thickness of 100 μm and pressed at 10 MPa at 130°C for 60 seconds. Test sheet 1 was laminated so that the surface coated with antistatic agent AS faced the transparent PET film. The transparent PET film was then peeled off, and the haze value of the transparent PET film with the antistatic agent transferred to its surface was measured using a Haze Meter NDH 2000 manufactured by Nippon Denshoku Industries Co., Ltd. The haze value obtained by subtracting the haze value of the PET film itself from the measurement results is shown in Table 2. A larger value indicates a greater amount of bleed-out. Although test samples 1 and 2 have different thicknesses, the pressure conditions were the same, so there is no effect on the evaluation results for bleed-out properties.

Table 2 shows that polymer-type antistatic agent AS bleeds out less from molded products even under heat and pressure conditions than general low-molecular-weight antistatic agents.

[Example 1]
(Production of stretched sheet B)
(1) A resin composition (b1) obtained by mixing 73.77 parts by mass of a propylene homopolymer (trade name "Novatec PP FY4", manufactured by Japan Polypropylene Corporation, melting point 164°C) having a melt flow rate (MFR (230°C)) of 5.0 g/10 min, 10 parts by mass of a high-density polyethylene (trade name "Novatec HD HJ381", manufactured by Japan Polyethylene Corporation), 16 parts by mass of heavy calcium carbonate having an average particle size of 1.5 μm (trade name "Softon 1800", manufactured by Bihoku Funka Kogyo Co., Ltd.), and 0.23 parts by mass of an antioxidant (trade name "PEP-36", manufactured by ADEKA Corporation) was kneaded in an extruder set at 250°C, extruded into a sheet, and further cooled in a cooling device to obtain an unstretched sheet. Next, this sheet was heated again to a temperature of 150° C., and then stretched 5 times in the machine direction to obtain a 5-times machine-stretched resin film.
(2) A resin composition (b2) obtained by mixing 51.77 parts by mass of a propylene homopolymer (trade name "Novatec PP FY4", manufactured by Japan Polypropylene Corporation, melting point 164°C) having an MFR of 5.0 g/10 min, 3 parts by mass of a high-density polyethylene (trade name "Novatec HD HJ381", manufactured by Japan Polyethylene Corporation), 45 parts by mass of heavy calcium carbonate having an average particle size of 1.5 μm (trade name "Softon 1800", manufactured by Bihoku Funka Kogyo Co., Ltd.), and 0.23 parts by mass of an antioxidant (trade name "PEP-36", manufactured by ADEKA Corporation) was kneaded in another extruder set at 250°C, and then extruded into a sheet. This was laminated on both sides of the 5-fold longitudinally stretched film obtained in the above step (1) to obtain a three-layer laminate film.
(3) Next, this three-layer laminate film was cooled to a temperature of 60°C, heated again to a temperature of 155°C, stretched 9.0 times in the transverse direction using a tenter, annealed at a temperature of 165°C, cooled to a temperature of 60°C, and then the edge portions were slit to obtain a three-layer (uniaxially stretched/biaxially stretched/uniaxially stretched) stretched sheet B having a thickness of 70 μm (b2/b1/b2=13 μm/44 μm/13 μm), a density (ρ) of 0.86 g/ ^cm3 , an opacity of 84%, and a whiteness of 96%. This was used as the stretched layer (B) in the present invention.

(Production of Unstretched Sheet A)
41.77 parts by mass of propylene homopolymer (abbreviation: h-PP1, trade name "Novatec PP FY4", manufactured by Japan Polypropylene Corporation) with an MFR (230°C) of 5.0 g/10 min, 23 parts by mass of calcium carbonate (abbreviation: CaCO ₃ , trade name "Softon 1800", manufactured by Bihoku Funka Kogyo Co., Ltd.) with an average particle size of 1.25 μm, 25 parts by mass of high-pressure low-density polyethylene (abbreviation: LDPE, trade name "Novatec LD LF129", manufactured by Japan Polyethylene Co., Ltd.) with an MFR (190°C) of 0.5 g/10 min, 25 parts by mass of high-density polyethylene (abbreviation: HDPE, trade name "Novatec HD an unstretched layer (A) containing 10 parts by mass of polyethylene terephthalate (HJ381, manufactured by Japan Polyethylene Corporation) and 0.23 parts by mass of an antioxidant (abbreviation: antioxidant, product name "PEP-36", manufactured by ADEKA Corporation);
Another unstretched layer (a1) containing 66.77 parts by mass of propylene homopolymer h-PP1, 23 parts by mass of calcium carbonate CaCO ₃ , 10 parts by mass of high-density polyethylene HDPE, and 0.23 parts by mass of an antioxidant;
Another unstretched layer (a2) consisting of 100 parts by mass of random polypropylene (propylene-ethylene random copolymer, trade name: Novatec PP FW4B, manufactured by Japan Polypropylene Corporation) was melt-kneaded at a temperature of 220 ° C. in separate extruders, fed into a single die, laminated in the die, and then extruded to obtain a five-layer sheet of (a2) / (a1) / (A) / (a1) / (a2). The thickness of the unstretched sheet A was 370 μm, and the thickness of each layer was 240 μm for the unstretched layer (A), 120 μm for the two-layer combined (a1), and 10 μm for the two-layer combined (a2).

(Production of resin laminate)
The stretched layer (B) was the aforementioned stretched sheet B, which was thermally laminated onto one side of the unstretched sheet A while the latter was still in a softened state, to obtain a resin laminate having a thickness of 440 μm.

The melt tension of the unstretched layer (A) was measured using the method described above.

[Examples 2 to 7]
A resin laminate was produced in the same manner as in Example 1, except that the raw materials of the unstretched layer (A) were changed as shown in Table 3. Furthermore, in the same manner as in Example 1, the melt tension of the unstretched layer (A) was also measured.

[Comparative Example 1]
Except for using h-PP1 instead of LDPE, a resin laminate was produced in the same manner as in Example 1. Furthermore, in the same manner as in Example 1, the melt tension of the non-oriented layer (A) was also measured.

[Comparative Example 2]
The stretched layer (B) was not laminated, and only the unstretched sheet (A) was used. In the same manner as in Example 1, the melt tension of the unstretched layer (A) was also measured.

(evaluation)
The resin laminates obtained in the respective Examples and Comparative Examples were evaluated as follows.

(Measurement of drawdown amount)
The obtained resin laminate was cut into a sample measuring 297 mm in length and 210 mm in width, and the drawdown amount was measured using a vacuum forming machine "FE36PH" manufactured by Sanwa Kogyo Co., Ltd. The measurement conditions were heater heating at 50% and heating for 35 seconds.
The drawdown amount is preferably 50 mm or less.

(Measurement of thickness deviation)
A tray measuring 27.5 cm in length, 21.5 cm in width, and 2.0 cm in depth was vacuum molded using a small multi-function vacuum and compressed air molding machine "FKS-0632-20" manufactured by Asano Laboratories, and the thickness of the molded product was measured using a thickness gauge manufactured by Olympus, PANAMETRICS-NDT Magna-Mike 8500. Figure 1 is a schematic overall view of the molded tray 1.

The thickness of tray 1 was measured at 25 locations on the bottom of the tray, 11 locations on the long sides, and 8 locations on the short sides, each at 4 cm intervals, as shown in Figures 2 to 4. The black circles in Figures 2 to 4 indicate the locations where the thickness was measured. In Figure 4, "..." indicates that there were multiple thickness measurement locations (black circles) along the way.
The thickness of the molded product was calculated by determining the difference between the maximum and minimum values on the long side of the side, the difference between the maximum and minimum values on the short side of the side, and the difference between the maximum and minimum values on the bottom. The largest of the differences between the maximum and minimum values calculated for the long side of the side, the short side of the side, and the bottom was determined as the thickness deviation.

As is clear from Table 3, the resin laminates obtained in the Examples have a small amount of drawdown during thermoforming, are less likely to develop thickness variations, and exhibit excellent moldability. On the other hand, the resin laminate obtained in Comparative Example 1 does not use polyolefin resin (A-1), which has a high degree of strain hardening, so it exhibits thickness variations during molding, a large amount of drawdown, and poor moldability. Comparative Example 2 does not include the stretched layer (B), so it exhibits an even larger amount of drawdown and exhibits even poorer moldability.

The resin laminate of the present invention can be suitably used, for example, as a thermoforming sheet for producing various containers, trays, etc.

1 tray

Claims (5)

A resin laminate having a thickness of 300 to 600 μm, comprising: an unstretched layer (A); and an oriented layer (B) laminated on either or both sides of the unstretched layer (A) directly or via another layer;
the unstretched layer (A) is non-porous and contains a polyolefin resin (A- ¹ ) having a branched structure and a strain hardening coefficient (λmax(1.0)) of 6.0 or more as measured by elongational viscosity measurement at a temperature of 180 °C and a strain rate of 1.0 s-1, and a polypropylene (A-2) having a strain hardening coefficient (λmax(1.0)) of less than 6.0;
the total amount of the polypropylene (A-2) and the polyolefin resin (A-1) in the unstretched layer (A) is 70% by mass or more,
the content of the polyolefin-based resin (A-1) relative to the total amount of the polypropylene (A-2) and the polyolefin-based resin (A-1) in the unstretched layer (A) is 10 to 50% by mass,
the stretched layer (B) contains 50% by mass or more of polypropylene (B-1),
However, the polypropylene (A-2) and the polypropylene (B-1) may be the same or different. The resin laminate according to claim 1, wherein the polypropylene (A-2) has a melt flow rate of 5.0 g/10 min or less. 3. The resin laminate according to claim 1, which has an antistatic layer (C) on the outermost surface of one or both surfaces. The resin laminate according to claim 3 , wherein the antistatic layer (C) is a coating layer containing an antistatic agent. The resin laminate according to claim 4 , wherein the antistatic agent comprises a cationic polymer antistatic agent.