JP6942971B2 - Inspection method for resin members with a multi-layer structure - Google Patents

Description

The present invention relates to a method for inspecting a resin member having a multi-layer structure in which an intermediate layer is formed between inner and outer layers, particularly a resin member having a highly transparent multi-layer structure.

Resin containers typified by PET (polyethylene terephthalate) bottles are widely used because of their light weight and resistance to breakage as compared with glass and metal containers. However, since the single-layer resin container is inferior in the permeability of oxygen and water vapor as compared with glass and metal, a single-layer resin container having a multi-layer structure provided with an intermediate layer having a gas barrier property has been put into practical use. .. As the composition of the intermediate layer, a polyamide resin (main material) using a polyamide resin, so-called nylon, is known, and among them, a xylylene group-containing polyamide is used. Further, as an oxidizable organic component, a polymer derived from polyene, for example, polybutadiene, etc. is added.

A resin container having such an intermediate layer is usually manufactured by forming a bottomed cylindrical preform, and then forming the preform into a predetermined shape such as a bottle by stretch blow molding or the like. .. In order for the molded plastic container to have a multi-layer structure, it must already have a multi-layer structure at the stage of a precursor such as a preform.

The molding of the precursor of the multi-layer structure is performed by a molding method such as injection molding. For example, in order to efficiently form a preform, it is manufactured by co-injection molding in which the resin of each layer is injected from a plurality of injection machines. ing. For this reason, in preforms by co-injection molding, it is important to confirm that the intermediate layer is surely inserted on the downstream side. Further, in containers such as cups and pouches, a sheet is formed into a multi-layer structure as a precursor by an inflation method, a casting method, or the like, but even in that case, it is necessary that the intermediate layer is uniformly formed.

Conventionally, various methods for non-destructively inspecting the state of the intermediate layer have been proposed. As non-destructive inspection, optical means and physical means such as ultrasonic waves are known, but optical means having a relatively short inspection time are exclusively used. As optical means, a method of irradiating the inspection body with a laser beam to grasp the presence or absence of an intermediate layer from a change in the amount of transmitted light (Patent Document 1), a method of irradiating the inspection body with a laser beam and irradiating the inspection body with the reflected light of the layer. Laser reflection method for grasping the state (presence or absence and thickness) (Patent Documents 2 to 3), method for irradiating a multilayer preform with striped illumination from the back and grasping the presence or absence of an intermediate layer from the difference in the hue of transmitted light (Patent). Document 4) and the like are known. There is also an IR method in which the presence or absence of an intermediate layer is grasped from the absorption wavelength of infrared rays based on the difference in the components of the layer material.

Japanese Unexamined Patent Publication No. 2004-117028 Japanese Unexamined Patent Publication No. 2005-49258 Japanese Unexamined Patent Publication No. 2005-49259 Japanese Unexamined Patent Publication No. 2013-134163

When a barrier resin containing an oxidizable organic component such as polybutadiene stays in the injection molding machine, heat-deteriorated substances (koge, etc.) are generated or adhere to the flow path. In addition to the defect that this heat-deteriorated product is mixed as a foreign substance, when the barrier resin passes through the flow path partially blocked by the heat-degraded product, the amount of resin in the blocked portion becomes insufficient. , There is a risk of partial thinning of the barrier resin and material shortage. Therefore, there is a demand for forming an intermediate layer without adding an oxidizable organic component.

However, the intermediate layer to which such an oxidizable organic component is not added has high transparency even at the preform stage, and it is difficult to confirm the existence of the intermediate layer by conventional optical means. In addition, the IR method is not suitable for 100% inspection because it takes time and measurement variation occurs. And opaque containers could not be the subject of inspection by conventional optical means.

An object of the present invention is to provide an inspection method capable of accurately confirming the presence or absence of an intermediate layer in a resin member having a multi-layer structure.

According to one aspect of the invention
A method for inspecting a resin member having a multi-layer structure in which an intermediate layer is formed between inner and outer layers.
By optical interference tomography, a tomographic image of the resin member is imaged in a region where the presence or absence of the intermediate layer needs to be confirmed, and the image pattern due to the interference between the reflected light from the intermediate layer and the reference light is used to obtain the image pattern of the intermediate layer. It confirms the existence ,
An inspection method is provided, wherein the reflected light from the intermediate layer includes scattered reflection due to a dispersed component in the intermediate layer.

In the inspection method according to the present invention, the presence or absence of an intermediate layer in a resin member having a multi-layer structure, particularly a resin member having a highly transparent multi-layer structure can be confirmed with high accuracy.

The figure which shows the outline of the OCT apparatus. FIG. 6A is a schematic view of the multilayer preform and a partial cross-sectional view thereof (b) is shown. An electron micrograph showing the sea-island structure of the middle layer. A multi-layer preform tomographic photograph taken by OCT technology.

The inspection method according to the present invention is based on optical coherence tomography (OCT) using the principle of Michelson interferometer, and photographs the internal structure of a sample with high resolution and high speed by utilizing the coherence of light. It is a technology. OCT technology is currently used for intraocular tomography in the medical field, especially in ophthalmology. In OCT, time domain OCT (Time Domain OCT: TD-OCT), which obtains information in the depth direction by sweeping the reference mirror over time, and Fourier transform instead of mirror sweep, obtain information in the depth direction. There is a Fourier domain OCT (Fourier Domain OCT: FD-OCT). FD-OCT further includes a spectral region OCT (Spectral Domine OCT: SD-OCT) that decomposes interfering light into a spectrum with a spectroscope and a frequency scanning OCT (Swept Source OCT: SS-OCT), and has measurable depth and spectroscopy. SS-OCT has come to be widely used in terms of the sensitivity of the vessel.

In the present invention, by non-destructively measuring the cross section of a resin member having a multi-layer structure by this OCT technique, the existence or nonexistence of an intermediate layer in the resin member having a multi-layer structure and the thickness of each layer can be accurately grasped. Can be done.

FIG. 1 is a diagram showing an outline of an apparatus 100 for confirming the existence and film thickness of an intermediate layer of a multi-layered resin member using SS-OCT. The light from the tunable light source 101 is branched into reference light and irradiation light by the half mirror 102. The reference light is reflected by the fixed reference mirror 103, and the irradiation light is incident on the multi-layer sample 104 to be reflected at the interface of each layer and scattered and reflected by the dispersed components in the layers. The reflected reference light and the reflected light from the sample are combined by the half mirror 102, and at this time, an interference phenomenon occurs due to the difference in the optical path length between the reflected reference light and the reflected light on the sample side, and the light detecting means 105 such as a CCD has an interference phenomenon. It receives the interference light and converts it into an interference signal. When there is one reflecting surface, the interference signal changes with a sine wave, and the frequency of the interference signal increases as the reflecting surface becomes deeper. Further, the stronger the reflection intensity, the larger the amplitude of the sine wave. By Fourier transforming the interference signal, the overlap of the interference signal can be decomposed, and the reflectance is obtained as a function of the depth distance, which is visualized by expressing it by the shading of the image. In the case of a multi-layer sample, the reflection at each layer interface (including the interface with air such as the surface) is displayed as a white image, and the brightness decreases toward the back (inner layer). Further, when the second component dispersed in the layer is present, the entire layer is displayed whitish.

The wavelength of light used in SS-OCT is in the near-infrared region (780 to 3000 nm), and even if the laminate is opaque in the visible light region, reflection at the layer interface may be confirmed. As the light source to be used, a light source having a variable width of about 30 nm such as 1040-1070 nm, 1045-1075 nm, 1290-1320 nm, 1300-1330 nm, 1315-1340 nm can be used.

As described above, in the OCT inspection, a tomographic photograph of the laminated body can be taken, and in the present invention, when this is used for inspection of a resin member having a multilayer structure in which an intermediate layer is formed between inner and outer layers, a resin is used. The tomographic image of the member is imaged in the area where the existence of the intermediate layer needs to be confirmed, and the existence of the intermediate layer is confirmed from the image pattern due to the interference between the reflected light from the intermediate layer and the reference light. If the tomographic image is clear, the thickness of each layer can be measured.

Examples of the resin member having a multi-layer structure targeted by the inspection method of the present invention include a resin container having a multi-layer structure such as a bottle, a cup, and a pouch. These are containers having a multi-layer structure including a water vapor barrier layer and an oxygen barrier layer as an intermediate layer as a whole or a part thereof, and examples thereof include transparent containers in which the contents can be confirmed. The term "transparent" as defined in the present invention means that the contents can be confirmed without visually recognizing the existence of the intermediate layer.
Further, the measurement target may be a preform or a sheet which is a precursor of these molded products. Especially for a member having a multi-layer structure, it is confirmed whether or not an intermediate layer exists in a necessary part.

Hereinafter, the bottle and its preform will be described as a resin member having a multi-layer structure, but the present invention is not limited thereto.

2A and 2B show an example of a multilayer preform 200 to be inspected in the present invention, where FIG. 2A shows a schematic external view and FIG. 2B shows a partial cross-sectional view. The multi-layer preform 200 is roughly divided into a mouth neck 201, a body 202, and a bottom 203. The mouth neck 201 is usually formed with a male screw that engages with a cap (not shown), but is omitted here. A neck ring 205 is formed at the boundary between the mouth neck 201 and the body 202. At the tip of the bottom portion 203, a runner portion 204 that serves as a resin injection portion during molding remains.

The multi-layer structure in this multi-layer preform is based on a three-layer structure in which an intermediate layer 200b is arranged between an outer layer 200a and an inner layer 200c. Another layer may be present between the outer layer 200a and the intermediate layer 200b, and between the inner layer 200c and the intermediate layer 200b.

In the OCT examination, in order to confirm the presence or absence of the intermediate layer at least in the body portion 202 in which the multilayer structure is formed, for example, an OCT image in the direction from the bottom portion 203 to the mouth and neck portion 201 (A direction) is acquired. It is also preferable to acquire an image of the body portion 202 in the circumferential direction (B direction) in order to confirm the film thickness and its uniformity. By scanning the region to be confirmed for the presence or absence of the intermediate layer and irradiating it with light, a tomographic image of that region can be obtained. The light can be scanned by either a method of scanning the irradiation light or a method of fixing the irradiation position and moving or rotating the preform to scan. In addition, the angle at which the irradiation light is applied to the preform is the angle at which specular reflection occurs (orthogonal to the surface), and the amount of reflected light is the strongest. It is preferable to tilt to. By increasing the scanning area, the state of the intermediate layer can be grasped in more detail. The number of scans may be appropriately set according to the purpose.

When performing a 100% inspection, the preform can be moved, rotated and scanned, and the obtained tomographic image can be compared with a preset pattern to determine the quality of the product. At that time, by automating the transfer, movement, and rotation of the preform and making the pattern comparison correspond, 100% inspection becomes possible.

In the inspection method of the present invention, in order to improve the accuracy of the OCT inspection, it is preferable to add a small amount of the second thermoplastic resin which is incompatible with the first thermoplastic resin which is the main material in the intermediate layer. As a result, a sea-island structure in which the second thermoplastic resin of the island phase is arranged in the sea phase of the first thermoplastic resin is obtained, and the blending amount of the second thermoplastic resin is set to 10% by mass or less. It is particularly useful for inspecting the presence or absence of an intermediate layer of a resin member having a multi-layer structure.

FIG. 3 shows a plate-shaped blend of polymethoxylylen adipamide (MXD6) as a gas barrier resin as the first thermoplastic resin of the intermediate layer and 10% by mass of PET resin as the second thermoplastic resin. It is a scanning electron microscope observation photograph of what was injection-molded. From FIG. 3, it can be seen that the PET resin 302 is dispersed as an island phase in the sea phase of the gas barrier resin 301. When the intermediate layer having such a sea-island structure is measured by the inspection method according to the present invention, the entire intermediate layer is displayed whitish, and the presence or absence of the intermediate layer can be easily confirmed.

The resin member having a multi-layer structure, which is the target of the inspection method of the present invention described above, can be subjected to film molding such as a molding method, a casting method, an inflation method, etc., which is known per se, coextrusion molding, etc. It can be molded by known means such as co-injection molding and compression molding. A cup-shaped, tray-shaped, or bottle-shaped container is formed by molding a preform in the form of a sheet, a pipe, a test tubular, or the like by the above molding method, and then performing secondary molding such as vacuum forming or blow molding. Can be.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

1. 1. Materials The materials used in the examples are shown.
(1) Ethylene terephthalate polyester resin PET: Isophthalic acid (copolymerization ratio = 1.8 mol%), diethylene glycol (copolymerization ratio = 2.3 mol%) Copolymerized polyethylene terephthalate resin (trade name: SHINPET 5015w: made of new photosynthetic fiber , IV = 0.83)

(2) Low-crystalline ethylene terephthalate polyester resin PET-G: Cyclohexanedimethanol (copolymerization ratio = 30 mol%), diethylene glycol (copolymerization ratio = 2.3 mol%) copolymerized polyethylene terephthalate resin (trade name: SKYGREEN PETG S2008) : Made by SK Chemical, IV = 0.78)

(3) Aromatic polyamide MXD6: Polymethaxylylene adipamide resin (trade name: S6007: manufactured by Mitsubishi Gas Chemical Company, Inc.)

(4) Transition metal catalyst Co: Cobalt neodecanoate (400 ppm of cobalt was added to MXD6).

(5) Oxidable organic component PB: Maleic acid-modified polybutadiene (3% by mass was added to MXD6).

2. Molding of multi-layer preforms Using a co-injection molding machine, multi-layer preforms having a layer structure of 2 types and 3 layers (PET / intermediate layer / PET) were molded. Dried PET is used for the injection molding machine hopper for the inner and outer PET layers, dried gas barrier resin and transition metal catalyst (MXD6 / Co) are used for the injection molding machine hopper for the intermediate layer, and PET or PET-G or PG is used as an additive. A dry blend containing the above in a predetermined ratio was added, and co-injection molding was performed so as to account for 5% by mass of the entire preform. The set temperature of the inner and outer PET layers was set to 290 ° C, and the molding temperature of the intermediate layer was set to 270 ° C.
The weight of the preform was 21 g.

3. 3. Molding of a multi-layer bottle After heating the body of the multi-layer preform from the outside with an infrared heater to a surface temperature of 100 ° C., a stretch rod is used to mechanically stretch the bottle in the axial direction, and blow air is introduced. By biaxial stretching blow, a stretching blow bottle having a capacity of 350 ml was formed in which the approximate stretching ratio in the body portion was 3 times in length, 3 times in width, and 9 times in area. The mold temperature was set to 60 ° C., and high-pressure air at room temperature (20 ° C.) of 3.5 MPa was introduced into the blow air.

OCT inspection Using an SS-OCT device (light source area: 1290-1320 nm), as shown in FIG. 2, one line of the trunk and the trunk in the direction from the bottom of the multilayer preform toward the mouth and neck (arrow A). The OCT inspection was performed on one line in the circumferential direction (arrow B) in the middle of the section. FIG. 4 shows the inspection results in Example 1. In FIG. 4, the entire intermediate layer is displayed whitish, and the other interfaces (outer layer surface, inner layer surface) are displayed as white lines. In addition, the thickness of each layer could be confirmed from the reflection intensity. The degree of recognition of each layer interface was evaluated in the following three stages.
A: As shown in FIG. 4, the entire intermediate layer was displayed whitish, and the thickness of each layer could be confirmed.
B: It was possible to confirm the existence of the intermediate layer in a slightly blurred state, but it was difficult to accurately grasp the thickness.
C: The layer interface position can be partially confirmed, but it is difficult to confirm the entire scanning range.

-Visual confirmation The white turbidity of the multi-layer preform was visually confirmed. It was evaluated whether the presence or absence of the intermediate layer was visible.

-Measurement of haze on the bottle body The haze was measured by cutting out the multi-layer bottle body and using a haze meter (trade name "NDH4000": Nippon Denshoku Kogyo Co., Ltd.). The measured value was the average value of any three points.

-Measurement of oxygen permeability The oxygen permeability of the bottle was measured for an empty bottle under the conditions of 23 ° C., 50% RH and normal pressure using an OX-TRAN (registered trademark) device manufactured by MOCON.

-Heat deterioration The dry blend used for the intermediate layer was heated on a hot plate at 270 ° C. for up to 50 minutes, and the hue was visually confirmed every 10 minutes during heating. The evaluation was based on Comparative Example 1, and a relative evaluation was performed between the Examples, which was OK if they were equivalent and NG if the coloring was stronger than the standard.
The results are shown in Table 1 below.

As shown in Table 1, in Comparative Example 1, it was difficult to confirm the intermediate layer with the OCT apparatus used. In Examples 1 to 6 to which PET was added, the presence or absence of the intermediate layer could be confirmed by OCT inspection, and in Examples 1 to 4, the film thickness could also be confirmed. However, as the amount of PET added decreased, the transparency of the bottle decreased and the oxygen permeability also increased. With the addition of PET-G, the presence or absence of the intermediate layer could be confirmed with a smaller amount than with the addition of PET. However, it can be seen that PET-G has a greater effect on the transparency and oxygen permeability of the bottle than PET. Example 10 is a conventional PET bottle, and the OCT inspection itself can be performed on a visually observable opaque resin member without any problem, and the oxygen permeability is suppressed to a low level. However, it has a greater effect on bottle transparency than other additives, and thermal deterioration during retention in the injection molding machine is expected.

From the above, the effectiveness of the inspection method according to the present invention was confirmed. Furthermore, it was confirmed that the addition of the second thermoplastic resin to the intermediate layer is useful for improving the accuracy in the OCT inspection.

100 OCT device 101 Light source 102 Half mirror 103 Reference mirror 104 Sample 105 Photodetector

Claims (3)

A method for inspecting a resin member having a multi-layer structure in which an intermediate layer is formed between inner and outer layers.
By optical interference tomography, a tomographic image of the resin member is imaged in a region where the presence or absence of the intermediate layer needs to be confirmed, and the image pattern due to the interference between the reflected light from the intermediate layer and the reference light is used to obtain the image pattern of the intermediate layer. It confirms the existence ,
An inspection method characterized in that the reflected light from the intermediate layer includes scattered reflection due to a dispersed component in the intermediate layer. The intermediate layer contains a first thermoplastic resin as a main material and a second thermoplastic resin that is incompatible with the first thermoplastic resin, and contains 1 to 10 mass of the second thermoplastic resin. The inspection method according to claim 1, further comprising a sea-island structure in which the first thermoplastic resin is the sea phase and the second thermoplastic resin is the island phase. The inspection method according to claim 1 or 2, wherein the resin member is a resin container of any of a bottle, a cup, and a pouch, or a preform or a sheet that is a precursor of the resin container.

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