JP7558756B2 - Manufacturing method of resin laminate and manufacturing method of packaging container - Google Patents

Description

The present invention relates to a resin laminate, a packaging container, a method for manufacturing a resin laminate, and a method for manufacturing a packaging container.

Laminates of two or more types of resins (resin laminates) are used as materials for packaging containers for various liquid products, such as liquid seasonings, liquid detergents, and liquid cosmetics.

Conventionally, the resin laminate described above is a laminate in which two or more types of resin films are bonded together via an adhesive or an anchor coating agent. Resin laminates manufactured using an adhesive or an anchor coating agent can achieve sufficiently high peel strength between the resin films. However, when an adhesive or an anchor coating agent is used, VOCs (volatile organic compounds) are generated during the manufacturing process of the resin laminate.

In response to this, in recent years, from the standpoint of preserving the working environment and protecting the environment, technology has been developed to manufacture resin laminates without emitting VOCs while ensuring peel strength. For example, when manufacturing a laminate of a polyamide resin film and a polyester resin film, a manufacturing method is known in which at least one of the opposing surfaces of the two films is irradiated with an electron beam to bond them together, thereby bonding them together without using an adhesive (see, for example, Patent Document 1).

JP 2012-254594 A

Patent document 1 does not state any criteria for the level of modification required for a film surface modified by electron beams to exhibit sufficient peel strength.

The present invention has been made in consideration of these circumstances, and aims to provide a resin laminate that exhibits sufficient peel strength without using adhesives or anchor coating agents. Another aim is to provide a packaging container made from such a resin laminate. Another aim is to provide a manufacturing method for a resin laminate that produces a resin laminate while ensuring peel strength and suppressing the generation of VOCs. Another aim is to provide a manufacturing method for a packaging container that produces a packaging container while ensuring peel strength and suppressing the generation of VOCs.

To solve the above problems, one aspect of the present invention includes the following aspects.

[1] A resin laminate having at least a first layer made of polyester and a second layer made of polyolefin, the first layer and the second layer being laminated in direct contact with each other, and the surface of the first layer that contacts the second layer has a C-N bond strength derived from an aromatic amine of 0.03 or more as measured by sum frequency generation spectroscopy.

[2] A packaging container made from the resin laminate described in [1].

[3] A method for producing a resin laminate, comprising at least a step of modifying the surface of a first layer made of polyester, and a step of directly laminating and bonding a second layer made of polyolefin to the modified surface, in which the surface is modified in the modification step until the strength of the C-N bond derived from aromatic amines, as determined by measurement using sum frequency generation spectroscopy, is 0.03 or more.

[4] A method for manufacturing a packaging container, comprising the steps of: manufacturing a resin laminate by the method for manufacturing a resin laminate described in [3]; and molding the resin laminate into a container shape with the second layer of the resin laminate on the inside.

According to the present invention, it is possible to provide a resin laminate that exhibits sufficient peel strength without using an adhesive or anchor coating agent. It is also possible to provide a packaging container made from such a resin laminate. It is also possible to provide a method for producing a resin laminate that ensures peel strength and does not generate VOCs. It is also possible to produce a packaging container that ensures peel strength and suppresses VOC emissions.

FIG. 1 is a schematic cross-sectional view showing a resin laminate 1 of the present embodiment. FIG. 2 is a schematic diagram showing a packaging container 50 formed using the resin laminate 1. As shown in FIG. FIG. 3 is a process diagram showing a method for producing the resin laminate 1 of the embodiment.

Figure 1 is a schematic cross-sectional view showing a resin laminate 1 of this embodiment. The resin laminate 1 has a first layer 11 and a second layer 12. Furthermore, the resin laminate 1 may have a printed layer 14 and an intermediate layer 15. The combined structure of the first layer 11, the printed layer 14, and the intermediate layer 15 may be referred to as the substrate 10.

The first layer 11 is laminated in direct contact with the second layer 12. "Direct" means that there is no adhesive or anchor coating agent between the first layer 11 and the second layer 12, and "in direct contact" means that the first layer 11 and the second layer 12 are in contact with each other without the intervention of an adhesive or anchor coating agent.

(First layer)
The first layer 11 is made of a thermoplastic resin.
The thermoplastic resin is preferably a polyester, such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate, etc., with polyethylene terephthalate being preferred.

The first layer 11 may contain optional components such as biodegradable resins and components derived from biomass in addition to polyester, as long as the effects of the invention are not impaired.

Biodegradable resins include polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (PHBH).

The thickness of the first layer 11 is preferably 5 μm or more and 100 μm or less.

One surface 11a of the first layer 11 has been subjected to a modification treatment described below in a nitrogen atmosphere. Surface 11a is the surface of the first layer 11 that comes into contact with the second layer 12. When surface 11a is modified in a nitrogen atmosphere, nitrogen molecules (N ₂ ) in the atmosphere react with the thermoplastic resin exposed on surface 11a to form new C—N bonds.

The fact that surface 11a has been modified can be confirmed by sum frequency generation spectroscopy (SFG spectroscopy). Specifically, the strength of the C-N bond derived from the aromatic amine on surface 11a, as measured using SFG spectroscopy, is 0.03 or more. Also, the strength of the C-N bond derived from the aromatic amine is 0.5 or less.

Specifically, SFG spectroscopy is performed under the following conditions. In this embodiment, the strength of the C-N bond derived from the aromatic amine measured using SFG spectroscopy is the value measured under the following conditions.

(Method of measuring C—N bond strength)
The narrowband visible light _ω1 used in the measurement is adjusted using a Spitfire ProXP (Spectra Physics, 3.5 W, 1 kHz) as an excitation light source and a _ω1 filter (center wavelength 795 nm, bandwidth 1.5 nm).

The broadband infrared light _ω2 used in the measurement is adjusted using a Spitfire ProXP as an excitation light source and an _ω2 filter (Spectra-Physics, TOPAS C and DFG1).

The infrared laser intensity of the light source is 3.6 mW for both the narrowband visible light ω ₁ and the broadband infrared light ω _2. The narrowband visible light ω ₁ is s-polarized light, and the broadband infrared light ω ₂ is p-polarized light.

A sample film is irradiated with narrowband visible light _ω1 and broadband infrared light _ω2 , and a sum frequency _ω3 is generated from the sample film. The sum frequency _ω3 is s-polarized light.

The sum frequency generated by the above operation is detected by the detection unit. The detection unit uses an HR320 (Jobin Yvon) spectrometer and a Spec10 (Princeton Instrument) CCD.

The above method provides a sum frequency spectrum of the sample film, which shows the relationship between the sum frequency wave number (cm ⁻¹ ) and the sum frequency intensity (au).

In addition, no sample is placed at the sample film installation position, and the above operation is carried out for the background of the measuring device, and the sum frequency is measured once.
Furthermore, the above operation is carried out on the gold mirror instead of the sample film, and the sum frequency is measured once.

The background sum frequency spectrum is subtracted from the sum frequency spectrum of the sample film, and the resulting spectrum is smoothed using the Savitzky-Golay transform. The resulting spectrum is called processed spectrum 1.

Similarly, the background sum frequency spectrum is subtracted from the gold mirror sum frequency spectrum, and the resulting spectrum is smoothed using the Savitzky-Golay transform. The resulting spectrum is called processed spectrum 2.

Then, at each wavelength, the intensity of the sum frequency of processed spectrum 1 is divided by the intensity of the sum frequency of processed spectrum 2 to normalize the intensity of the sum frequency of processed spectrum 1 with the intensity of the sum frequency of processed spectrum 2, thereby obtaining a new spectrum. Peak fitting is performed on the obtained spectrum using a Lorentz function to obtain the peak intensity "around 1286 ^cm " assigned to the C-N bond derived from the aromatic amine.

The above operation is carried out on the sample film at 10 points at 0.5 mm intervals, and the peak intensity "around 1286 ^cm " is determined for each. The data for the highest intensity among the 10 peak intensities obtained is used as the data for the sample film.

In the resin laminate 1, the surface 11a has been modified to such an extent that the strength of the C-N bond derived from aromatic amines measured using SFG spectroscopy is 0.03 or more. The resin laminate 1 exhibits sufficient peel strength at the interface between the first layer 11 and the second layer 12 because the strength of the C-N bond derived from aromatic amines measured using SFG spectroscopy for the surface 11a of the first layer 11 is 0.03 or more.

Peel strength (unit: N/inch) can be measured according to the measurement method specified in JIS K 6854-1 "Adhesives - Peel adhesion strength test method, Part 1: 90 degree peel."

The first layer 11 may have a metal vapor deposition layer on the other surface 11b. Surface 11b is the surface of the first layer 11 opposite to the surface that contacts the second layer 12. The metal vapor deposition layer may be, for example, an aluminum vapor deposition layer.

(Second layer)
The second layer 12 is mainly made of polyolefin and may function as a sealant layer or an adhesive layer when the resin laminate 1 is bonded to another member (including another resin laminate 1).

The manufacturing method will be described later, but the second layer 12 may be a polyolefin film or an extruded polyolefin resin layer.

Polyolefins include polyethylene, polypropylene, and cyclic polyolefins.

The second layer 12 may contain optional components such as biodegradable resins and components derived from biomass in addition to polyolefin, as long as the effects of the invention are not impaired.

Biodegradable resins include polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (PHBH).

The thickness of the second layer 12 is preferably 10 μm or more and 500 μm or less.

(Printing layer)
The printed layer 14 is a layer on which characters and designs are printed using printing ink, a laser, or the like on a surface 14a of a film made of a thermoplastic resin.

The printing ink used to print the letters and patterns in the printing layer 14 may contain various ink binder resins such as thermoplastic resins, urethane resins, and acrylic resins as binder resins. The printing ink further contains additives such as various pigments, drying agents, and stabilizers.

In the printing layer 14, the letters and patterns are formed by known printing methods such as offset printing, gravure printing, and screen printing. The thickness of the part that constitutes the letters and patterns can usually be about 0.05 μm or more and 2.0 μm or less.

The thickness of the printing layer 14 is preferably 5 μm or more and 100 μm or less.

Surface 14a of printing layer 14 may be subjected to an oxidation treatment. The fact that surface 14a has been oxidized can be confirmed by sum frequency generation spectroscopy. In other words, surface 14a may be oxidized to a degree that can be confirmed by sum frequency generation spectroscopy. The oxidation treatment may be performed using the known methods described above.

(Middle class)
The intermediate layer 15 is in contact with the surface 11 b of the first layer 11 and the surface 14 a of the printed layer 14 , and is laminated with the first layer 11 and the printed layer 14 .

The intermediate layer 15 may be made of polyethylene. The polyethylene may be composed of only one type of polyethylene, or may be a mixture of two or more types of polyethylene.

The thickness of the intermediate layer 15 is preferably 10 μm or more and 500 μm or less.

Surface 15a of intermediate layer 15 facing printed layer 14 has been subjected to an oxidation treatment, typically ozone treatment. The fact that surface 15a has been oxidized can be confirmed by sum frequency generation spectroscopy. In other words, surface 15a has been oxidized to a degree that can be confirmed by sum frequency generation spectroscopy.

(Packaging container)
2 is a schematic diagram showing a packaging container 50 formed using the above-mentioned resin laminate 1. In the packaging container 50, the second layer 12 of the resin laminate 1 faces the inside of the container, and the printed layer 14 is exposed to the outside of the container.

The packaging container 50 is obtained by stacking two resin laminates 1 cut to a specified size with their second layers 12 facing each other and heat sealing three sides. In Figure 2, the heat-sealed portion is indicated by the symbol A.

The packaging container 50 may also be a free-standing pouch manufactured by a known method.

(Method for producing resin laminate)
The method for producing the resin laminate of this embodiment includes at least a step of modifying the surface of a first layer made of polyester under a nitrogen atmosphere, and a step of directly laminating and bonding a second layer made of polyolefin to the modified surface of the first layer.
The following explains each in order.

(Modifying step)
The first layer to be treated in the modification step is made of polyester, and a resin film made of polyester can be suitably used for the first layer.

The method for modifying the surface of the first layer may be plasma treatment or corona treatment. The modification process is carried out until the strength of the C-N bond derived from the aromatic amine is 0.03 or more when the surface of the first layer is measured using sum frequency generation spectroscopy. In addition, the modification method is not limited to plasma treatment or corona treatment as long as the same result is obtained.

When the above-mentioned modification treatment is performed in a nitrogen atmosphere, some of the nitrogen molecules in the atmosphere react with the main chains and side chains of the polymer on the surface of the first layer through a plasma state. As a result, it is believed that nitrogen atoms derived from the nitrogen molecules in the atmosphere are introduced into the polymer on the surface of the first layer, and C-N bonds are generated. Since C-N bonds are polarized, it is expected that the polarity of the surface of the first layer after the above-mentioned modification treatment will be higher than that before the treatment.
Furthermore, when the polyester contains an aromatic ring, it is believed that the aromatic ring reacts with a nitrogen atom to easily form an aromatic amine.

In the modification process, in order not to inhibit the formation of C-N bonds, the oxygen gas concentration in the atmosphere is preferably 2% or less by volume, and more preferably 50 ppm or less by volume.

It is also preferable not to introduce a gas containing oxygen atoms into the atmosphere. Examples of the "gas containing oxygen atoms" include _CO2 and _N2O .

(Laminating process)
The second layer used in the lamination step is made of polyolefin as a forming material. Either a resin film made of polyolefin as a forming material or a molten resin film obtained by melting polyolefin in an extrusion molding machine and extruding it into a film shape from a T-die can be used for the second layer.

When the resin laminate produced is to be used as a packaging material, the material for the second layer is preferably a heat-sealable polyolefin or polypropylene that can be used as a sealant layer.

When a resin film is used as the second layer, the second layer is overlaid on the surface of the modified first layer, and the laminate of the first and second layers is heated and pressed between two rolls, a heating roll and a pinch roll, to obtain a resin laminate.

When the second layer is a molten resin film, the second layer is melt-extruded and laminated onto the surface of the modified first layer. The laminate of the first and second layers is pressed while being cooled between two rolls, a cooling roll and a pinch roll, to obtain a resin laminate.

A multi-layer laminate in which a second layer is layered on the surface of a first layer, and another resin film is layered on the surface of the second layer, may be compressed while being cooled between two rolls, a cooling roll and a pinch roll, to produce a resin laminate. In this case, the second layer will adhere to the first layer as well as to the other resin film.

It is preferable that the surface of the second layer that comes into contact with the first layer is ozone treated. If the second layer is a molten resin film, it is preferable that the surface of the molten resin film that comes into contact with the first layer is ozone treated before the molten resin film is superimposed on the modified surface of the first layer.

Ozone treatment is an oxidation treatment of the surface of the molten resin film using ozone. It is recommended that an ozone generator be installed downstream in the MD direction of the molten resin film discharged from the T-die, and that the ozone treatment be carried out before the molten resin film comes into contact with the first layer.

There are no particular limitations on the method for generating ozone, but it is preferable to perform UV/ozone treatment by irradiating with ultraviolet light in the air.

In UV/ozone treatment, the surface of the second layer is irradiated with ultraviolet light using a light source that generates ultraviolet light, such as a low-pressure mercury lamp or a Xe excimer lamp. This breaks down the bonds in the polymer on the surface of the second layer. In addition, oxygen breaks down due to the ultraviolet light irradiation, generating ozone, which then oxidizes the surface of the second layer.

By subjecting the surface of the second layer to ozone treatment, the polymer on the surface is oxidized, and oxygen functional groups such as carbonyl groups and carboxy groups are generated on the surface of the second layer. These groups have high polarity, so they are strongly electrostatically attracted to the surface of the first layer that has been subjected to the above-mentioned modification treatment, allowing the first and second layers to be bonded together in an optimal manner.

Figure 3 is a process diagram showing the manufacturing method of the resin laminate 1 of this embodiment. In the process diagram shown in Figure 3, a plasma treatment is performed as the modification treatment.

The resin laminate 1 described above is manufactured by laminating a first film and a second film without using an adhesive or an anchor coating agent. The first film corresponds to the "first layer" in the manufacturing method of the present invention, and the second film corresponds to the "second layer" in the manufacturing method of the present invention.

The base film 10F is a laminate of a first film 11F formed in a strip shape, which is made of the same material as the first layer 11, a printed layer 14F formed in a strip shape, which has the same configuration as the printed layer 14, and an intermediate layer 15F formed in a strip shape, which has the same configuration as the intermediate layer 15. When the base film 10F is cut into sheets, it becomes the above-mentioned base material 10.

The substrate film 10F is sequentially unwound from the unwinding roll 10L, which is wound into a roll, and is transported to the plasma processing device 110 via the transport roll 101.

The plasma processing device 110 has a chamber 111, a roll 112, a plasma generating device 113, and transport rolls 114 and 115. The chamber 111 houses the roll 112, the plasma generating device 113, and the transport rolls 114 and 115.

The substrate film 10F that is brought into the plasma processing device 110 is wound around the roll 112 via the transport roll 114. Inside the chamber 111, an atmosphere suitable for the conditions to generate plasma is created.

The plasma generator 113 is disposed opposite the roll 112 and generates plasma in the space between the plasma generator 113 and the roll 112. One side of the base film 10F (one side 11a of the first film 11F) is plasma-treated by the generated plasma.

The plasma treatment is carried out under atmospheric pressure conditions using nitrogen (N ₂ ) as the atmospheric gas until the strength of the C—N bond derived from the aromatic amine becomes 0.03 or more when the surface 11 a of the first layer 11 of the base film 10F is measured by SFG spectroscopy.

It is advisable to confirm and determine in a preliminary experiment the processing conditions such as the output of the plasma generator 113 and the transport speed of the base film 10F such that the strength of the C-N bond derived from the aromatic amine is 0.03 or more.

The substrate film 10F, one side 11a of which has been plasma-treated, is transported out of the plasma processing device 110 via the transport roll 115.

The plasma treatment of one surface 11a of the base film 10F may be performed continuously during the transport process as described above, or may be performed in advance.

The base film 10F is fed via the transport roll 102 between the heating roll 104 and the backup roll 105, which are maintained at a predetermined temperature.

On the other hand, the second film 12F is made of the same material as the second layer 12 and is formed in a strip shape. The second film 12F is preferably one selected from the group consisting of unstretched polyethylene resin film, unstretched polypropylene resin film, cyclic polyolefin resin film, and co-extruded film of unstretched polyethylene and unstretched polypropylene.

The second film 12F is continuously unwound from the unwinding roll 12L, which is wound into a roll, and is supplied between the heating roll 104 and the backup roll 105 via the transport roll 103.

The heating roll 104 is set to a heating temperature higher than the melting point of the second film 12F. The base film 10F and the second film 12F are continuously bonded together by passing between the heating roll 104 and the backup roll 105 without applying either adhesive or anchor coating agent to the interface. This results in the raw roll 1F of the resin laminate 1 described above.

The raw web 1F is conveyed while being sandwiched between cooling rolls 106 and 107 and cooled. The raw web 1F is conveyed to the winding roll 1L and wound into a roll.

The original roll 1F is cut into appropriate sheets to form the above-mentioned resin laminate 1. The original roll 1F may also be cut downstream in the process without being wound into a roll.

In this embodiment, the resin laminate 1 is obtained as described above.

(Manufacturing method of packaging container)
The method for manufacturing a packaging container of this embodiment includes a step of manufacturing a resin laminate by the above-mentioned method for manufacturing a resin laminate, and a step of molding the resin laminate into a container shape with the second layer of the resin laminate on the inside.

One example of the process for molding the resin laminate into a container is to stack two sheets of the resin laminate cut to a specified size with their second layers facing each other, and then heat seal the three sides. In the container obtained in this way, the second layer becomes the inside of the container.

The container is then filled with the contents and the remaining side is sealed by heat sealing or the like to produce a packaged container filled with the contents.

The resin laminate 1 configured as described above can provide a resin laminate that exhibits sufficient peel strength without using adhesives or anchor coating agents.

In addition, the packaging container configured as described above uses the resin laminate as a material, resulting in a packaging container that exhibits sufficient peel strength and suppresses VOC emissions.

In addition, the method for producing a resin laminate as described above makes it possible to produce a resin laminate while ensuring peel strength and suppressing VOC emissions.

In addition, the above-mentioned method for manufacturing packaging containers makes it possible to manufacture packaging containers while ensuring peel strength and suppressing VOC emissions.

The above describes preferred embodiments of the present invention with reference to the attached drawings, but the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Method of measuring C—N bond strength)
The C--N bond strength of the plasma-treated surface was measured by the method described above in (Method of measuring C--N bond strength).

Example 1
An aluminum-deposited polyethylene terephthalate film (thickness 12 μm) was used as the first layer. The surface on which the polyethylene terephthalate was exposed was subjected to plasma treatment (modification treatment) in an atmosphere filled with nitrogen gas. The intensity of the plasma treatment was 31.3 Wmin/ ^m2 .

A polyethylene molten resin film (temperature 300°C, 20 μm) was used as the second layer. The surface of the second layer that was to be bonded to the first layer was ozone treated.

The modified surface of the first layer was laminated with the ozone-treated surface of the second layer, and a polyethylene film (thickness 105 μm) was laminated on the surface of the second layer opposite the surface in contact with the second layer to create a resin laminate.

The modified surface of the first layer was irradiated from the polyethylene film side with a laser beam used for measurement to measure the C-N bond strength, which was 0.178. Note that narrowband visible light _ω1 was irradiated at an incident angle of 38°, and broadband infrared light _ω2 was irradiated at an incident angle of 46°.

Example 2
A resin laminate was produced in the same manner as in Example 1 above, except that the plasma treatment intensity was set to 60.0 Wmin/ ^m2 .
The C--N bond strength of the modified surface of the first layer was measured and found to be 0.034.

Example 3
A resin laminate was prepared in the same manner as in Example 1 above, except that the plasma treatment intensity was 90.0 Wmin/ ^m2 .
The C--N bond strength of the modified surface of the first layer was measured and found to be 0.099.

Example 4
A resin laminate was prepared in the same manner as in Example 1 above, except that the plasma treatment intensity was 120.0 Wmin/ ^m2 .
The C--N bond strength of the modified surface of the first layer was measured and found to be 0.155.

<Comparative Example 1>
A resin laminate was produced in the same manner as in Example 1 above, except that the plasma treatment was not carried out.
The strength of the C--N bond on the modified surface of the first layer was measured and found to be below the detection limit.

(Peel test)
The peel strength of the interface between the first layer and the second layer was measured in accordance with the measurement method specified in JIS K 6854-1 "Adhesives - Peel adhesion strength test method, Part 1: 90 degree peel".

The state (peel mode) when the first layer and the second layer were peeled off was evaluated as follows.
Material failure: peeling of the test piece was not localized at the interface between the first and second layers, and was accompanied by breakage of either or both of the first and second layers.
Interface: delamination of the test specimen occurred at the interface between the first and second layers.

The evaluation results are shown in Table 1.

The above results prove that the resin laminate of the embodiment has sufficient peel strength without the use of adhesives or anchor coating agents.

These results confirm that the present invention is useful.

1...resin laminate, 11...first layer, 11a...surface in contact with second layer, 11F...first film (first layer), 12...second layer, 12F...second film (second layer), 50...packaging container

Claims (2)

modifying the surface of the first layer made of polyester;
and directly laminating and bonding a second layer made of a polyolefin material to the modified surface.
Prior to the modifying step, a preliminary experiment step is included in which a treatment condition for modifying the surface is determined until a strength of a C—N bond derived from an aromatic amine, as determined by a measurement using sum frequency generation spectroscopy, is 0.03 or more;
A method for producing a resin laminate , wherein in the modifying step, the surface is modified based on the treatment conditions determined in the preliminary experiment step . A step of producing a resin laminate by the method for producing a resin laminate according to claim 1 ;
and molding the resin laminate into a container shape with the second layer of the resin laminate facing inside.

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