WO2023190679A1

WO2023190679A1 - Extrusion-foamed sheet, and inspection method and inspection device for extrusion-foamed sheet

Info

Publication number: WO2023190679A1
Application number: PCT/JP2023/012787
Authority: WO
Inventors: 正浩阿部; 聡生谷口; 敦遊佐; 智史山本; 敏晴後藤; 圭水谷
Original assignee: マクセル株式会社
Priority date: 2022-03-31
Filing date: 2023-03-29
Publication date: 2023-10-05

Abstract

Provided are an extrusion-foamed sheet whereby excellent vacuum-moldability can be obtained, and an inspection method and an inspection device for the extrusion-foamed sheet. In a state in which the extrusion-foamed sheet 1 is irradiated with light from below, the extrusion-foamed sheet 1 and a ruler 10 are simultaneously imaged from above to obtain an image 21. The image 21 is subjected to edge processing to obtain an image 22. The image 22 is subjected to a two-dimensional discrete Fourier transform to obtain an image 23. The image 23 shows a frequency distribution of luminance in the image 22. The ruler 10 is removed from the image 21 to obtain an image 24. The image 24 is subjected to the two-dimensional discrete Fourier transform to obtain an image 25. When the image 23 is represented by a two-dimensional spectrum, a primary peak P1, a secondary peak P2, and a tertiary peak P3 appearing according to a 1 mm interval scale of the ruler are extracted. When the image 25 is represented by a two-dimensional spectrum, a difference Δ between a value of the luminance at the position corresponding to the central peak P0 and a value of the luminance at the position corresponding to the tertiary peak P3 is less than 25 when expressed by 256 gradations.

Description

Extruded foam sheet and inspection method and apparatus for extruded foam sheet

The present disclosure relates to an extruded foam sheet containing a polycarbonate resin, and an inspection method and apparatus for the extruded foam sheet.

In recent years, foamed resins have attracted attention as they can increase convenience by reducing the weight of resin molded bodies and reduce carbon dioxide emissions. Molding methods for foamed resin include physical foaming and chemical foaming. The chemical foam molding method uses a chemical foaming agent as a foaming agent. Chemical blowing agents have a high environmental impact and are not preferred from the perspective of protecting the global environment. On the other hand, the physical foaming method uses a physical foaming agent such as nitrogen or carbon dioxide as a foaming agent. Physical foaming agents have a small environmental impact and are therefore preferable from the perspective of protecting the global environment. The physical foam molding method includes a method of foaming highly heat-resistant engineering plastics and super engineering plastics by shearing and kneading the molten resin of engineering plastics and super engineering plastics with high-pressure supercritical fluid. .

Patent No. 6139038 (Patent Document 1) discloses a method for manufacturing a foam molded body using a relatively low pressure physical foaming agent such as nitrogen or carbon dioxide instead of a high pressure supercritical fluid. According to this method, fine foam cells can be formed in a resin molded body by a relatively simple process using a low-pressure physical foaming agent without using a special high-pressure device. Further, Patent Document 1 discloses a method of molding a foam molded article by injection molding and extrusion molding.

The injection molding method can produce foam molded products with complex shapes. However, the surface layer of the molten resin flows inside the mold while being cooled and solidified. At this time, a relatively thin non-foamed skin layer is formed on the surface layer of the foamed molded product. On the other hand, the extrusion molding method has fewer restrictions on the size and load of the mold than the injection molding method, and is suitable for continuously producing foam molded products of a single shape and a single thickness. Further, the sheet-like foamed product obtained by extrusion molding can be shaped into a somewhat complicated shape or a relatively large size by applying vacuum forming or the like. However, in the extrusion molding method, when the molten resin is discharged from the die outlet and cooled and solidified, it is difficult to form a skin layer on the surface layer of the foam molded product.

Patent Document 1 does not consider a foamed molded product made of polycarbonate resin made of a non-crystalline resin that can be vacuum formed, and cracks in the foamed molded product when heated at a temperature exceeding the glass transition temperature of the polycarbonate resin are not considered. Not considered. Here, in the case of a non-foamed resin, even if the crystalline resin is heated at a temperature higher than the glass transition temperature, it is unlikely to be significantly deformed if heated at a temperature lower than the melting point. However, in the case of non-foamed resins, amorphous resins tend to be thermally deformed when heated at temperatures higher than the glass transition temperature (the glass transition temperature of polycarbonate resin is about 145° C.). In view of this, when a foamed molded product containing amorphous resin (polycarbonate resin) is heated at a temperature higher than the glass transition temperature, it is more difficult to suppress its deformation and the cracking that accompanies the deformation. Become. Note that the glass transition temperature is a second-order transition point observed by differential scanning calorimetry (DSC).

Additionally, foamed molded products made of foamed resin have a problem in that mechanical strength decreases due to lower density aimed at improving lightweight properties. In particular, a foamed molded article made of polycarbonate resin that requires mechanical strength has a problem in that its mechanical strength is significantly lower than that of a resin molded article made of a non-foamed resin.

JP-A-8-174780 (Patent Document 2) discloses a polycarbonate extruded resin foam laminate sheet with a high expansion ratio manufactured by a coextrusion method. Polycarbonate extruded resin foam laminate sheets have excellent heat processability, particularly deep drawing processability, and are also excellent in appearance design and mechanical strength. Patent Document 2 discloses a heating dimensional change when a polycarbonate extruded resin foam laminate sheet is heated in a relatively low temperature atmosphere of 170°C.

JP 2020-006588A (Patent Document 3) discloses a resin plate. Resin plates can be used as decorative plates with excellent design by configuring the air bubbles contained in the resin plate in a predetermined manner. Light can be spread to such an extent that the bubbles can be highlighted.

Patent No. 6139038 Japanese Patent Application Publication No. 8-174780 JP2020-006588A

In recent years, when extruded foam sheets are thermally shaped into a desired shape by vacuum forming, etc., from the perspective of improving productivity, heating temperatures of relatively high temperatures of 200°C or higher and drawdown (a phenomenon in which molten resin sag due to its own weight) are required. It is required that molding can be done in a short time. However, when an extruded foam sheet having a core layer made of a foamed resin and a skin layer made of a non-foamed resin laminated on the main surface of the core layer is heated at a high temperature of 200°C or higher, the inside of the core layer covered by the skin layer The bubbles expand thermally and become more likely to coalesce. As a result, there have been problems in that the skin layer bulges out from the main surface of the extruded foam sheet, cracks occur in the core layer, etc., and proper vacuum forming cannot be performed.

Patent Document 2 discloses a method to prevent the skin layer from bulging out from the main surface of the extruded foam sheet and cracks in the core layer during vacuum forming due to unevenness of air bubbles contained in a polycarbonate resin laminated foam resin sheet. I am not proposing to do so.

Patent Document 3 does not propose improving the vacuum formability of a resin plate.

Furthermore, when heat shaping an extruded foam sheet into a desired shape, it is important to predict in advance whether heat shaping can be performed appropriately. Patent Documents 1 to 3 do not discuss methods for testing whether or not heat shaping can be performed appropriately.

An object of the present disclosure is to provide an extruded foam sheet with excellent vacuum formability, and an extruded foam sheet inspection device and inspection method for pre-inspecting whether it can be properly vacuum formed.

In order to solve the above problems, the present disclosure takes the following solutions. That is, the extruded foam sheet according to the present disclosure may include polycarbonate resin. A first image is obtained by simultaneously photographing the extruded foam sheet and a ruler having scales at 1 mm intervals from above while irradiating light from below the extruded foam sheet. A third image obtained by performing a two-dimensional discrete Fourier transform on a second image obtained by performing edge detection processing on the first image, and a third image obtained by performing a two-dimensional discrete Fourier transform on a fourth image obtained by removing the ruler from the first image. 5 images, the third image shows the frequency distribution of brightness in the second image, and the fifth image shows the frequency distribution of brightness in the fourth image. When a luminance profile is taken in the direction along the ruler from the center of the third image and expressed as a two-dimensional spectrum, the plurality of frequency components appearing by the scales of the ruler at 1 mm intervals are sequentially divided into primary peaks from the center position of the third image. , a secondary peak and a tertiary peak. When the distance between the primary peak and the center position of the third image is L, the brightness is the highest between a position at a distance of L/5 and a position at a distance of L/2 from the center position of the third image. The high frequency component is the central peak. When the brightness profile is drawn linearly from the center of the fifth image in a direction of relatively high brightness and expressed as a two-dimensional spectrum, the difference between the brightness at the position corresponding to the central peak and the brightness at the position corresponding to the tertiary peak. may be less than 25 when expressed in 256 tones.

A method for inspecting an extruded foam sheet according to the present disclosure involves simultaneously photographing the extruded foam sheet and a ruler having equidistant scales from above while irradiating the extruded foam sheet containing polycarbonate resin with light from below. obtaining an image; obtaining a second image by performing edge processing on the first image; obtaining a third image showing a frequency distribution of brightness in the second image by performing two-dimensional discrete Fourier transform on the second image; obtaining a fourth image by removing the ruler from the first image; obtaining a fifth image showing a frequency distribution of brightness in the fourth image by performing two-dimensional discrete Fourier transform on the fourth image; and brightness in the second image. measuring the difference in brightness between the third image and the fifth image based on the frequency distribution of the brightness in the fourth image and the frequency distribution of the brightness in the fourth image; and determining that the method is moldable.

The extruded foam sheet inspection device according to the present disclosure is an extruded foam sheet that is obtained by simultaneously photographing the extruded foam sheet and a ruler having equidistant scales from above while irradiating light from below the extruded foam sheet containing a polycarbonate resin. The image receiving unit may include an image receiving unit that receives the first image, and an image processing unit that processes the first image received by the first image receiving unit. The image processing unit includes an edge processing unit that performs edge processing on the first image to obtain a second image, and an edge processing unit that performs two-dimensional discrete Fourier transform on the second image to obtain a third image that indicates the frequency distribution of brightness in the second image. a first Fourier transform unit for performing a two-dimensional discrete Fourier transform on a fourth image obtained by removing the ruler from the first image to obtain a fifth image showing a frequency distribution of brightness in the fourth image; , a measurement unit that measures the difference in brightness between the third image and the fifth image based on the frequency distribution of brightness in the second image and the frequency distribution of brightness in the fourth image; and a determination unit that determines that the foam sheet can be vacuum formed.

According to the present disclosure, it is possible to provide an extruded foam sheet with excellent vacuum formability, and an extruded foam sheet inspection device and inspection method for pre-inspecting whether it can be properly vacuum formed.

FIG. 1 is a perspective view showing an extruded foam sheet according to an embodiment of the present disclosure. FIG. 2 is a photograph showing a cross section of the extruded foam sheet shown in FIG. FIG. 3 is a diagram showing how the extruded foam sheet shown in FIG. 1 is photographed. FIG. 4 is an image taken of the extruded foam sheet shown in FIG. FIG. 5 is a photograph showing a ruler. FIG. 6 is an image obtained by performing edge processing on the image shown in FIG. 4. FIG. 7 is an image obtained by performing two-dimensional discrete Fourier transform on the image shown in FIG. FIG. 8 is a graph representing the image shown in FIG. 7 as a two-dimensional spectrum. FIG. 9 is an image obtained by removing the ruler from the image shown in FIG. FIG. 10 is an image obtained by performing two-dimensional discrete Fourier transform on the image shown in FIG. FIG. 11 is a graph representing the image shown in FIG. 10 as a two-dimensional spectrum. FIG. 12 is a cross-sectional view of the extruded foam sheet shown in FIG. 1. FIG. 13 is a perspective view showing a modified extruded foam sheet. FIG. 14 is a flowchart showing a method for inspecting an extruded foam sheet. FIG. 15 is a block diagram showing an inspection device for extruded foam sheets. FIG. 16 is a perspective view showing a vacuum forming mold.

As a result of extensive studies, the present inventors have determined that the unevenness of the large number of bubbles contained in the extruded foam sheet can be suppressed, and that if the uneven brightness that appears in the image when photographing the main surface of the extruded foam sheet satisfies predetermined conditions. It has been found that during vacuum forming, it is possible to prevent the skin layer from peeling off from the core layer and cause it to bulge, and to prevent the core layer from cracking, that is, it is possible to obtain excellent vacuum formability. The present invention has been made based on such knowledge.

The extruded foam sheet according to this embodiment may contain polycarbonate resin. A first image is obtained by simultaneously photographing the extruded foam sheet and a ruler having scales at 1 mm intervals from above while irradiating light from below the extruded foam sheet. A third image obtained by performing two-dimensional discrete Fourier transform on the second image obtained by edge processing the first image, and a fifth image obtained by performing two-dimensional discrete Fourier transform on the fourth image obtained by removing the ruler from the first image. In the images, the third image shows the frequency distribution of brightness in the second image, and the fifth image shows the frequency distribution of brightness in the fourth image. When a luminance profile is taken in the direction along the ruler from the center of the third image and expressed as a two-dimensional spectrum, the plurality of frequency components appearing by the scales of the ruler at 1 mm intervals are sequentially divided into primary peaks from the center position of the third image. , a secondary peak and a tertiary peak. When the distance between the primary peak and the center position of the third image is L, the brightness is the highest between a position at a distance of L/5 and a position at a distance of L/2 from the center position of the third image. The high frequency component is the central peak. When the brightness profile is drawn linearly from the center of the fifth image in a direction of relatively high brightness and expressed as a two-dimensional spectrum, the difference between the brightness at the position corresponding to the central peak and the brightness at the position corresponding to the tertiary peak. may be less than 25 when expressed in 256 tones.

Thereby, excellent vacuum formability can be obtained.

The extruded foam sheet may contain 50% by weight or more of polycarbonate resin. Thereby, it is possible to improve the strength.

The extruded foam sheet may have a thickness of 1 to 5 mm.

The extruded foam sheet has a core layer made of a foamed resin, a first skin layer made of a non-foamed resin and laminated on one main surface of the core layer, and a second skin layer laminated on the other main surface of the core layer. It may include a layer. At least one of the first and second skin layers may be made of polycarbonate resin.

The extruded foam sheet may satisfy the following formula (1).
0.10≦(t1+t2)/T≦0.5 (1)
In formula (1), t1 represents the thickness of the first skin layer, t2 represents the thickness of the second skin layer, and T represents the thickness of the extruded foam sheet. Thereby, better vacuum formability can be obtained.

The polycarbonate resin contained in either the first or second skin layer may have a melt volume rate of 1.0 to 5 times that of the polycarbonate resin contained in the core layer. Thereby, even more excellent vacuum formability can be obtained.

The extruded foam sheet may have a length of 1000 mm or more in the extrusion direction, and a length of 1000 mm or more in the width direction perpendicular to the extrusion direction in plan view. Even with relatively large extruded foam sheets, excellent vacuum formability can be obtained.

The difference in brightness may be 20 or less when expressed in 256 tones. Thereby, better vacuum formability can be obtained.

The difference in brightness may be 15 or less when expressed in 256 tones. Thereby, even more excellent vacuum formability can be obtained.

The extruded foam sheet inspection method according to the present embodiment involves simultaneously photographing the extruded foam sheet and a ruler having equidistant scales from above while irradiating the extruded foam sheet containing polycarbonate resin with light from below. obtaining a second image by performing edge processing on the first image; obtaining a third image showing a frequency distribution of brightness in the second image by performing two-dimensional discrete Fourier transform on the second image; , obtaining a fourth image by removing the ruler from the first image; obtaining a fifth image showing the frequency distribution of brightness in the fourth image by performing two-dimensional discrete Fourier transform on the fourth image; a step of measuring the difference in brightness between the third image and the fifth image based on the frequency distribution of brightness and the frequency distribution of brightness in the fourth image; The method may include a step of determining that vacuum forming is possible. Thereby, before actually vacuum forming the extruded foam sheet, it is possible to test in advance whether or not the extruded foam sheet can be properly vacuum formed.

The step of measuring the difference in brightness between the third image and the fifth image is based on equally spaced scales on the ruler when the brightness profile is taken from the center of the third image in the direction along the ruler and expressed as a two-dimensional spectrum. The multiple frequency components that appear are defined as a primary peak, a secondary peak, and a tertiary peak in order from the center position of the third image, and when the distance between the primary peak and the center position of the third image is L, the third The frequency component with the highest brightness between the position at a distance of L/5 and the position at a distance of L/2 from the center position of the image is set as the central peak, and a straight line is formed from the center of the fifth image in the direction of relatively high brightness. When a luminance profile is taken and expressed as a two-dimensional spectrum, the difference between the luminance at the position corresponding to the central peak and the luminance at the position corresponding to the tertiary peak may be measured. In the step of determining that the extruded foam sheet can be vacuum formed, the extruded foam sheet may be determined to be vacuum formed when the difference in brightness is less than 25 expressed in 256 gradations. Thereby, before actually vacuum forming the extruded foam sheet, it is possible to test in advance whether or not the extruded foam sheet can be properly vacuum formed.

The extruded foam sheet inspection device according to the present embodiment is obtained by simultaneously photographing the extruded foam sheet and a ruler having equidistant scales from above while irradiating the extruded foam sheet containing polycarbonate resin with light from below. The image receiving unit may include an image receiving unit that receives the first image received by the first image receiving unit, and an image processing unit that processes the first image received by the first image receiving unit. The image processing unit includes an edge processing unit that performs edge processing on the first image to obtain a second image, and an edge processing unit that performs two-dimensional discrete Fourier transform on the second image to obtain a third image that indicates the frequency distribution of brightness in the second image. a first Fourier transform unit for performing a two-dimensional discrete Fourier transform on a fourth image obtained by removing the ruler from the first image to obtain a fifth image showing a frequency distribution of brightness in the fourth image; , a measurement unit that measures the difference in brightness between the third image and the fifth image based on the frequency distribution of brightness in the second image and the frequency distribution of brightness in the fourth image; and a determination unit that determines that the foam sheet can be vacuum formed. You may do so. Thereby, before actually vacuum forming the extruded foam sheet, it is possible to test in advance whether or not the extruded foam sheet can be properly vacuum formed.

The measuring unit is configured to measure a plurality of frequency components appearing by equidistant scales of the ruler from the center position of the third image when a luminance profile is taken in a direction along the ruler from the center of the third image and expressed as a two-dimensional spectrum. The primary peak, secondary peak, and tertiary peak in this order, and when the distance between the primary peak and the center position of the third image is L, the position at a distance of L/5 from the center position of the third image. When the frequency component with the highest brightness between the position at a distance of L/2 is taken as the central peak, a two-dimensional spectrum is obtained by taking a straight line of brightness profile from the center of the fifth image in a direction of relatively high brightness. When expressed as , the difference between the brightness at the position corresponding to the central peak and the brightness at the position corresponding to the tertiary peak may be measured. The determination unit may determine that the extruded foam sheet can be vacuum-formed when the difference in brightness is less than 25 expressed in 256 gradations. Thereby, before actually vacuum forming the extruded foam sheet, it is possible to test in advance whether or not the extruded foam sheet can be properly vacuum formed.

Hereinafter, embodiments of the extruded foam sheet 1 of the present disclosure will be specifically described using FIGS. 1 to 13. In addition, the same reference numerals are attached to the same or corresponding components in the figures, and the same explanations will not be repeated. Note that, in order to make the explanation easier to understand, in the drawings referred to below, the configuration is shown in a simplified or schematic manner, and some structural members are omitted.

The extruded foam sheet 1 contains polycarbonate resin. The extruded foam sheet 1 contains 50% by weight or more of polycarbonate resin. The extruded foam sheet 1 has a sheet shape. The extruded foam sheet 1 is formed by extrusion foam molding a molten polycarbonate resin. The resin used in the present disclosure may be other engineering plastics or super engineering plastics as long as they include polycarbonate resin. Engineering plastics are thermoplastic resins that have a deflection temperature under load of 100°C or higher. Examples of engineering plastics include polycarbonate resin (PC), modified polyphenylene ether (m-PPE), and syndiotactic polystyrene (SPS). Super engineering plastics are thermoplastic resins with a deflection temperature under load of 150°C or higher. Super engineering plastics include, for example, polyphenylene sulfide (PPS), polysulfone (PSF), polyether sulfone (PES), polyarylate (PAR), polyamideimide (PAI), thermoplastic polyimide (PI), and polyetherimide (PEI). , liquid crystal polymer (LCP), etc. The thermoplastic resin used in the extruded foam sheet 1 of the present disclosure can include at least one selected from the group consisting of these engineering plastics and super engineering plastics. Note that any thermoplastic resin that can be extruded can be used as the resin material of the present disclosure. However, by using the above-mentioned engineering plastics and super engineering plastics, the strength can be improved. Moreover, an ultraviolet absorber, an anti-aging agent, etc. may be added to the resin material of the extruded foam sheet 1.

The extruded foam sheet 1 can contain a foaming aid during foam molding. The foaming aid is added to increase the number of cells contained in the extruded foam sheet 1 or to increase the melt tension of the molten resin during extrusion molding to make the cells finer. Examples of the foaming aid include a bubble generating nucleating agent.

As shown in FIG. 1, the extruded foam sheet 1 includes a core layer 2, a skin layer 3 laminated on one main surface of the core layer 2, and a skin layer 4 laminated on the other main surface of the core layer 2. It has

The core layer 2 is made of foamed resin. The core layer 2 can be formed by foam-molding molten polycarbonate resin. That is, the core layer 2 has many air bubbles 2a. As shown in FIG. 2, the large number of bubbles 2a are formed relatively uniformly in a cross section cut in the thickness direction along the width direction orthogonal to the extrusion direction. That is, the large number of cells in the extruded foam sheet 1 has small unevenness in the cross section in the width direction. Note that the large number of bubbles 2a often have a substantially elliptical shape extending in the extrusion direction in a cross-sectional view cut in the thickness direction in a direction along the extrusion direction during extrusion molding. Among the large number of bubbles 2a included in the core layer 2, the bubbles included near the center in the thickness direction of the core layer 2 tend to have a larger bubble diameter than the bubbles 2a included near the ends of the core layer 2 in the thickness direction. It is in. The diameter of the large number of bubbles 2a tends to gradually become smaller from the center in the thickness direction of the core layer 2 toward the ends in the thickness direction.

The skin layer 3 is made of non-foamed resin. That is, the skin layer 3 is not foam-molded. The skin layer 3 is extruded from the die outlet in an unfoamed state by a coextrusion method, and is laminated integrally with the core layer 2.

For the skin layer 3, a thermoplastic resin that can be well bonded to the core layer 2 may be used. More specifically, it is particularly preferable that the resin material of the skin layer 3 is the same resin material as the core layer 2. Further, the skin layer 3 can be made of a reinforced resin containing an inorganic filler in order to strengthen the skin layer 3. With such a structure of the skin layer 3, the extruded foam sheet 1 can efficiently improve the strength while reducing the weight and improving the strength. Examples of the inorganic filler include glass fiber, carbon fiber, aramid fiber, talc, and mica.

The skin layer 4 is the same as the skin layer 3 except that it is laminated on the other main surface of the core layer 2. Therefore, a detailed explanation of the skin layer 4 will be omitted.

As described above, the core layer 2 has a large number of bubbles 2a with small unevenness in a cross-sectional view along the width direction. Thereby, excellent vacuum formability can be obtained.

The unevenness of a large number of bubbles can be measured as follows. First, as shown in FIG. 3, an extruded foam sheet 1 with a thickness of 3 mm is placed on the top surface of the light box 100, and the extruded foam sheet 1 is irradiated with a brightness of 1400 cd/m ² from below. The main surface of the extruded foam sheet 1 is photographed using the camera 200. At this time, the extruded foam sheet 1 and the ruler 10 (see FIG. 4) are also photographed at the same time. At the time of photographing, the ruler 10 is placed adjacent to the extruded foam sheet 1. At this time, the image is photographed in full color at a specific resolution (2016 x 1512 pixels) without any color tone correction or the like. Further, the distance between the camera lens and the extruded foam sheet 1 is set to 20 cm, and photography is performed so that the optical axis of the camera lens and the top surface of the light box 100 intersect perpendicularly.

Then, as shown in FIG. 4, since the light transmittance changes due to the unevenness of the large number of bubbles 2a, it is possible to obtain an image 21 in which unevenness in brightness appears. The main surface of the extruded foam sheet 1 is shown in the upper part of the illustrated image 21, and the relatively black part shown in the lower part of the image 21 is the ruler 10. The photographing range of the extruded foam sheet 1 in the image 21 has a length of 10 cm in the width direction TD and a length of 15.6 cm in the extrusion direction MD. The photographing range of the image 21 is preferably set so that the length in the width direction TD is 10 cm to 20 cm and the length in the extrusion direction MD is 15 cm to 25 cm. However, if the vacuum formability of the extruded foam sheet 1 can be confirmed. It is not necessarily limited to this range. Further, the resolution of the image 21 is set to be 300 dpi or more when enlarged to the actual size.

As shown in FIG. 5, the ruler 10 is a 15 cm ruler, and scales are displayed at 1 mm intervals. The scale of the ruler 10 is used to calibrate the distance in the image. The selection criteria for the ruler 10 will be described later.

Next, the image 21 is subjected to edge processing. Then, as shown in FIG. 6, an image 22 can be obtained. As a result, each scale displayed on the ruler 10 stands out. That is, the image 22 only needs to be able to make the scale of the ruler 10 stand out, and edge processing is performed so that the SN ratio, which will be described later, becomes 2 or more. For edge processing of the image 21, for example, image processing software "ImageJ 1.53k" can be used.

Next, the image 22 is subjected to a two-dimensional discrete Fourier transform. For the two-dimensional discrete Fourier transform of the image 22, for example, image processing software "ImageJ 1.53k" or the like can be used. Thereby, an image 23 after two-dimensional discrete Fourier transformation can be obtained. As shown in FIG. 7, the image 23 shows the frequency distribution of brightness in the image 22. At the center of the image 23 in the vertical direction (vertical direction in the figure), there are linear, slightly white components displayed at approximately equal intervals along the horizontal direction (horizontal direction in the figure). This is the frequency component of the scale of the ruler 10 at 1 mm intervals.

The two-dimensional discrete Fourier transform can be expressed by the following formula.

In the formula, f(x, y) indicates an image before two-dimensional discrete Fourier transform, and F(u, v) indicates an image after two-dimensional discrete Fourier transform.

A power spectrum is used when displaying an image after two-dimensional discrete Fourier transformation. That is, a function expressed by the following equation is displayed as an image after two-dimensional discrete Fourier transformation.

The horizontal profile at the vertical center of the image 23 is expressed as a two-dimensional spectrum as shown in the graph of FIG. The horizontal direction is the direction in which the scales of the ruler 10 are arranged in the image 22, that is, the longitudinal direction of the ruler 10, and can also be said to be the direction along the ruler 10. Note that when creating the horizontal profile, the profile was created by integrating 10 pixels in the vertical direction orthogonal to the horizontal profile. The vertical axis of the graph indicates the brightness (Gray Value), and the horizontal axis of the graph indicates the number of pixels in the horizontal direction of the image 23. Note that the pixels on the horizontal axis indicate 1000 pixels from the 508th pixel to the 1508th pixel in the image 23. The smaller the unevenness of the brightness of the image 22 is, the gentler the slope of the obtained graph becomes, and the larger the unevenness of the brightness of the image 22 is, the steeper the slope of the graph becomes. Also, at this time, a plurality of frequency components appear outward in the left-right direction from the horizontal axis center C of the graph (the center of the image 23), according to the scales of the ruler 10 at 1 mm intervals. These frequency components are defined as a primary peak P1, a secondary peak P2, and a tertiary peak P3 in order from the center position C of the image 23 toward the outside, as shown in FIG. In order to clearly identify the peak positions of these primary peaks P1, secondary peaks P2, and tertiary peaks P3, the ruler 10 is selected so that the S/N ratio of the primary peak P1 is 2 or more, and Perform edge processing. If a periodic pattern other than a scale is displayed on the ruler 10 by printing or the like, it is difficult to determine the peak positions corresponding to 1 mm intervals. Therefore, it is best to select a ruler 10 that is as simple as possible, displaying only scales at 1 mm intervals. Note that if it is difficult to specify the peak position of the primary peak P1, the peak position of the primary peak P1 can be clearly specified by further peak fitting using a Gaussian distribution function.

Here, the highest peak appearing near the center position C (median value) of the horizontal axis (pixel) is considered to be noise and is removed from the analysis range. More specifically, when L is the distance from the center position C of the horizontal axis (pixel) to the pixel position of the primary peak P1, the distance from the center of the horizontal axis (center position C of image 22) to L/5 is Remove range from analysis range. Then, the range from this pixel median value to L/5 to the outside and the pixel position of the tertiary peak P3 is defined as the analysis range. Further, within the range from the L/5 position to the L/2 position described above, the position with the highest luminance is defined as the central peak P0.

Next, the ruler 10 is removed from the image 21. Thereby, an image 24 can be obtained as shown in FIG. This image 24 is subjected to a two-dimensional discrete Fourier transform in the same manner as the image 22. Thereby, an image 25 after two-dimensional discrete Fourier transformation can be obtained. As shown in FIG. 10, the image 25 shows the frequency distribution of brightness in the image 24. In image 25, a line with relatively high brightness is observed in the vertical direction at the center of the image. Therefore, a linear profile is created from the center of the image 25 along this relatively high brightness direction. That is, in the image 25, the profile in the vertical direction at the center in the horizontal direction is represented by a two-dimensional spectrum as shown in the graph of FIG. The smaller the unevenness of the brightness of the image 24 is, the gentler the slope of the obtained graph becomes, and the larger the unevenness of the brightness of the image 24 is, the steeper the slope of the graph becomes. Note that, as described above, in the graph of FIG. 8, the horizontal axis indicates 1000 pixels from the 508th pixel to the 1508th pixel of the image 23. Therefore, the 1008th pixel on the horizontal axis in the graph of FIG. 11 corresponds to the 500th pixel among 0 to 100 on the horizontal axis of the graph of FIG.

When the image 25 is represented by a two-dimensional spectrum, as shown in FIG. 11, the brightness value at the position (pixel) corresponding to the above-mentioned central peak P0 and the brightness value at the position (pixel) corresponding to the above-mentioned tertiary peak P3. The difference Δ from the value of is less than 25 when expressed in 256 tones. The brightness difference Δ is preferably 20 or less, more preferably 15 or less. This reduces the unevenness of air bubbles in the cross section along the width direction in the extruded foam sheet 1, and prevents skin layer 3 or skin layer 4 from peeling off from core layer 2 and bulging during vacuum forming, or causing cracks in core layer 2. This allows excellent vacuum formability to be obtained. Note that the brightness value at the position corresponding to the central peak P0 and the brightness value at the position corresponding to the tertiary peak P3 are the average value of the brightness of 20 pixels before and after each peak position. In general, when the thickness of the extruded foam sheet 1 becomes smaller, the vacuum formability decreases even if the foamed state of the core layer 2 is the same. In other words, even if there is a change in the thickness of the extruded foam sheet 1, if light is irradiated at a brightness of 1400 cd/ ^m2 , the brightness value at the position corresponding to the central peak P0 and the brightness value at the position corresponding to the tertiary peak P3 will change. It is considered that the difference Δ from the value is detected in the same way. In addition, in this embodiment, in the graph of FIG. 11, the difference Δ between the luminance value at a position corresponding to the central peak P0 to the left from the center position C of the image 25 and the luminance value at a position corresponding to the tertiary peak P3 However, the difference Δ between the brightness value at the position corresponding to the central peak P0 on the right side and the brightness value at the position corresponding to the tertiary peak P3 may also be measured in the same way, at least on either the left or right side. It suffices if the luminance difference Δ is less than 25.

The extruded foam sheet 1 is formed into various shapes by vacuum forming. In vacuum forming, the extruded foam sheet 1 is heated to about 200° C. or higher to begin drawdown, and then applied to a mold or the like and vacuum-suctioned to form the sheet. When trying to shape the extruded foam sheet 1 into a more complicated shape, it is also possible to use a relatively large extruded foam having a length of 1000 mm or more in the extrusion direction and a length of 1000 mm or more in the width direction. When attempting to shape the sheet 1, the heating temperature during vacuum forming tends to be as high as 200° or more. According to the extruded foam sheet 1, by setting the difference Δ between the brightness value at the position corresponding to the central peak P0 and the brightness value at the position corresponding to the tertiary peak P3 to be less than 25, the heating temperature during vacuum forming can be adjusted. Even if the temperature increases, it is possible to prevent the

skin layer

3 or 4 from peeling off from the core layer 2 and bulging out, or from causing cracks in the core layer 2.

In addition, if the skin layer 3 and the skin layer 4 are colored or a decorative sheet or the like is pasted on the surface of the skin layer 3 and the skin layer 4, it is necessary to check the exact brightness unevenness as described above. cannot be measured. Therefore, for example, the skin layer 3 and the skin layer 4 or the decorative sheet are removed from the extruded foam sheet 1 by polishing using a table-top wrapping device (such as EJ200IN manufactured by Nihon Engis Co., Ltd.), and the skin layer 3 and the skin layer 4 or the decorative sheet are removed from the extruded foam sheet 1. It is sufficient to measure the uneven brightness after drying after sonic cleaning. Note that the method is not particularly limited as long as the skin layer 3 and the skin layer 4 or the decorative sheet can be removed from the extruded foam sheet 1. In addition, on the production line of the extruded foam sheet 1, if a light source that emits light perpendicularly to the extruded foam sheet 1 and a camera located on the opposite side of the extruded foam sheet 1 from the light source are placed, in-line It is possible to inspect the extruded foam sheet 1 at .

Furthermore, as described above, in order to obtain uneven brightness of the extruded foam sheet 1 by photographing, the total light transmittance of the extruded foam sheet 1 is preferably 10% to 60%. The total light transmittance is a value measured by ASTM D1003 (method A).

Next, the thickness of the extruded foam sheet 1 and the thickness of each layer of the skin layer 3 and the skin layer 4 will be explained. As shown in FIG. 12, the extruded foam sheet 1 has a thickness T of 1 to 5 mm. The skin layer 3 has a thickness t1. The skin layer 4 has a thickness t2.

The thickness t1 of the skin layer 3 and the thickness t2 of the skin layer 4 are measured as follows. A cross section of the extruded foam sheet 1 cut in the thickness direction along the width direction is observed using a microscope. In this disclosure, a KEYENCE model number VHX-60000 is used as a microscope. The magnification of the microscope may be such that the diameter of the bubbles at the interface between the skin layer 3 and the core layer 2 of the extruded foam sheet 1 can be confirmed. In the cross-sectional view of the extruded foam sheet 1, among the large number of bubbles, 15 are the bubbles close to the surface of the extruded foam sheet 1 on each virtual boundary line when the cross section of the extruded foam sheet 1 is divided into 16 equal parts in the width direction. Among them, the one closest to the surface of the extruded foam sheet 1 is confirmed. Draw an imaginary line passing through the top of the nearest bubble and perpendicular to the thickness direction. The inner layer in the thickness direction of the imaginary line was defined as the core layer 2, and the outer layer in the thickness direction was defined as the skin layer 3. The boundary between the core layer 2 and the skin layer 4 was similarly defined, and the thickness t1 of the skin layer 3 and the thickness t2 of the skin layer 4 were measured. Note that the thickness t1 of the skin layer 3 and the thickness t2 of the skin layer 4 are each preferably 0.050 mm or more from the viewpoint of making the thickness T of the extruded foam sheet 1 as uniform as possible during coextrusion molding.

The total thickness of the skin layer, which is the sum of the thickness t1 of the skin layer 3 and the thickness t2 of the skin layer 4, is preferably 0.10 to 0.5 with respect to the thickness T of the extruded foam sheet 1. That is, the extruded foam sheet 1 satisfies the following formula (1).

0.10≦(t1+t2)/T≦0.5 (1)

If the thickness (t1+t2) of the entire skin layer is less than 0.10 with respect to the thickness T of the extruded foam sheet 1, it is difficult to obtain the mechanical strength reinforcing effect by the non-foamed resin of the skin layer, and the specific flexural modulus etc. mechanical strength decreases. On the other hand, when the thickness (t1+t2) of the entire skin layer becomes larger than 0.5 with respect to the thickness T of the extruded foam sheet 1, the density of the extruded foam sheet 1 increases. As a result, the extruded foam sheet 1 loses its lightweight properties due to foaming. The ratio of the total thickness of the skin layer (t1+t2) to the thickness T of the extruded foam sheet 1 is preferably in the range of 0.15 to 0.45, more preferably in the range of 0.2 to 0.4. It is better. By setting the ratio of the thickness (t1+t2) of the entire skin layer to the thickness T of the extruded foam sheet 1 within this range, the specific flexural modulus can be improved while reducing the weight by reducing the density. In addition, by setting the ratio of the thickness of the entire skin layer (t1+t2) to the thickness T of the extruded foam sheet 1 in the range of 0.2 to 0.4, the thickness of the core layer 2 is ensured to make the bubble unevenness uniform. While achieving this, it is possible to improve secondary processability such as vacuum forming. Note that the specific flexural modulus is a value obtained by dividing the flexural modulus of the extruded foam sheet 1 by the density of the extruded foam sheet 1. That is, it can be said that the larger the specific flexural modulus, the more excellent the lightness and mechanical strength. The bending elastic modulus is measured by a three-point bending test (according to ISO178 or JIS7171). At this time, the flexural modulus is measured in the atmosphere. The test speed is 10 mm/min.

In this way, by controlling the density of the extruded foam sheet 1 and the thickness (t1+t2) of the skin layer 3 and the skin layer 4 with respect to the thickness T of the extruded foam sheet 1, the surface generated during heat forming such as vacuum forming can be reduced. Blistering and cracking can be suppressed, and excellent mechanical strength can be obtained.

The melt volume rate (hereinafter referred to as MVR) of the polycarbonate resin contained in the skin layer 3 is the same as the MVR of the polycarbonate resin contained in the core layer 2, or higher than the MVR of the polycarbonate resin contained in the core layer 2. . The MVR of the polycarbonate resin contained in the skin layer 3 is 1.0 to 5 times, preferably 1.5 to 3 times, the MVR of the polycarbonate resin contained in the core layer 2. .

By making the MVR of the resin contained in the skin layer 3 the same as the MVR of the resin contained in the core layer 2 or higher than the MVR of the resin contained in the core layer 2, the resin can be discharged from the die outlet during extrusion molding. Immediately after the skin layer 3 is formed, the temperature of the resin forming the skin layer 3 can be lowered as much as possible. As a result, the viscosity of the skin layer 3 immediately after being discharged from the die outlet can be reduced, so that swelling or tearing of the surface of the skin layer 3 caused by foaming of the resin contained in the core layer 2 can be suppressed. . That is, if the MVR ratio of the resin contained in the skin layer 3 is smaller than 1.0 times, it becomes difficult to lower the resin temperature, and it becomes difficult to suppress the swelling or tearing of the surface of the skin layer 3. Furthermore, when the MVR ratio of the resin contained in the skin layer 3 is 1.5 times or more, it becomes easier to suppress the swelling or swelling of the surface of the skin layer 3 during extrusion molding, and the preheating time during vacuum molding is reduced. It is possible to shorten the time and improve productivity. On the other hand, if the MVR ratio of the resin contained in the skin layer 3 is larger than 5 times, when trying to properly flow the resin forming the skin layer 3 in the die during extrusion molding, the resin forming the core layer 2 It is necessary to extremely lower MVR. Furthermore, when the MVR ratio of the resin contained in the skin layer 3 is 3 times or less, the area on the surface of the extruded foam sheet 1 with excellent appearance design increases. Therefore, the air bubbles tend to be uniform, and the secondary processability of the extruded foam sheet 1, such as vacuum forming, can be improved. Therefore, consideration must be given to ensuring appropriate fluidity of the resin forming the core layer 2 and skin layer 3 during extrusion molding, and controlling the viscosity to suppress swelling or tearing of the surface of the skin layer 3. For example, the MVR of the polycarbonate resin contained in the skin layer 3 is 1.0 to 5 times, preferably 1.5 to 3 times, the MVR of the polycarbonate resin contained in the core layer 2. Good. This also applies to the skin layer 4 and the core layer 2.

Incidentally, the MVR of the resin contained in the skin layer 3 and the core layer 2 is measured by a plastic flow characteristic test (based on JISK7199 and ISO11443) using a capillary rheometer and a slit die rheometer. In the present disclosure, the length of the capillary die is 5 mm, the inner diameter is 1 mm, and the measurement temperature is 300°C.

Note that, as disclosed in the above-mentioned Patent Document 1, the core layer 2 of the present disclosure is preferably foam-molded using a physical foaming agent such as nitrogen or carbon dioxide, which has a relatively low pressure. is more preferable. As a result, the pressure of the physical blowing agent can be set at a relatively low level of 1 to 6 MPa, and a large number of fine bubbles can be formed. Thereby, the appearance design of the extruded foam sheet 1 can be improved, and bulges and the like when heated at high temperatures during vacuum forming can be more reliably suppressed. The average cell diameter of the bubbles is preferably 0.1 mm or more, and 1.0 mm or less, preferably 0.3 mm or less.

The extruded foam sheet 1 may contain a large number of scale-like fillers. The scaly filler is, for example, an inorganic filler such as talc, calcium carbonate, mica, clay, boron nitride, clastonite, potassium titanate, or glass flakes. The scale-like filler may be surface-treated with a silane coupling agent, a titanate coupling agent, a phosphate coupling agent, a fatty acid coupling agent, or the like. The scaly filler has an aspect ratio of 5 or more. The aspect ratio is calculated by dividing the average particle size of the scaly filler by the average thickness (average particle size/average thickness). If the aspect ratio of the scaly filler becomes too small, it becomes difficult to exhibit excellent surface smoothness. Therefore, the aspect ratio of the scaly filler is preferably 10 or more, more preferably 30 or more. However, if the aspect ratio becomes too large, it will not be easy to control the flow rate of the mixed molten resin inside the die in the manufacturing process described below, and the surface smoothness may deteriorate. Further, the viscosity of the mixed molten resin increases significantly during extrusion molding, and heat generation within the extrusion molding apparatus described below may cause thermal deterioration of the thermoplastic resin. Therefore, the aspect ratio of the scaly filler is preferably less than 50. The specific surface area of the scaly filler is preferably 5 to 20 m ² /g. If the specific surface area of the scaly filler becomes too small, surface smoothness will be difficult to develop due to the scaly filler sliding on the surface, and if the specific surface area becomes too large, the resistance of the scaly filler in the molten resin will increase. As a result, it becomes difficult to orient the scaly filler appropriately.

The core layer 2 may include a scale-like filler oriented substantially parallel to the interface between the core layer 2 and the skin layer 3 in a region near the boundary with the skin layer 3. The neighboring region is a region positioned in the thickness direction of the core layer 2 in a range from the interface between the core layer 2 and the skin layer 3 to a thickness of 5% of the core layer thickness. Moreover, the bubbles contained in the core layer 2 have a shape extending along the extrusion direction during extrusion molding. The scale-like filler is also oriented substantially parallel to the cell walls of the cells extending in the stretching direction, so that the strength of the cell walls can be improved. As a result, tearing of the extruded foam sheet 1 along the extrusion direction can be suppressed. In addition, when the scale-like filler is approximately parallel, it means that the scale-like filler is located at the boundary between the core layer 2 and the skin layer 3 in a cross section of the extruded foam sheet 1 cut in the thickness direction in the direction along the extrusion direction during extrusion molding. It means having an inclination of 0° or more and less than 5° with respect to the plane. In other words, it refers to a state in which the surface (principal surface) of the scale-like filler and the boundary surface between the core layer 2 and the skin layer 3 are opposed to each other so as to be substantially parallel to each other. The same applies to the scale-like filler oriented in the core layer 2 near the boundary between the core layer 2 and the skin layer 4.

The orientation state of a large number of scale-like fillers included in the region near the boundary between the core layer 2 and the skin layer 3 was calculated as follows. First, in a cross section in the thickness direction along the extrusion direction during extrusion molding, 50 electron micrographs of 150 × 150 μm are taken at equal intervals from the tip to the rear end in the extrusion direction in the nearby area and at the center in the thickness direction. . Among all the scaly fillers included in these 50 electron micrographs, the scaly fillers oriented substantially parallel to the interface between the core layer 2 and the skin layer 3 are confirmed. Thereby, the proportion of the scale-like fillers oriented substantially in parallel among the large number of scale-like fillers included in the neighboring region is calculated.

The core layer 2 may include a scale-like filler oriented at an angle of 5° to 90° with respect to the surface of the extruded foam sheet 1 in the central region of the core layer 2 in the thickness direction. The central region refers to a region having a thickness of 25% from the center in the thickness direction toward the interface between the core layer 2 and the skin layer 3, assuming that the thickness of the core layer 2 is 100%. It is preferable that 40% or more of the scale-like fillers included in the central region are oriented at an angle of 5° to 90° with respect to the surface S of the extruded foam sheet 1. Thereby, the moldability of the extruded foam sheet 1 can be improved. More preferably, 60% or more, and even more preferably 80% or more of the scale-like filler is oriented at an angle of 5° to 90° with respect to the surface. Thereby, the moldability of the extruded foam sheet 1 can be further improved. The bubbles contained in the central region of the core layer 2 tend to become larger during extrusion molding compared to the above-mentioned neighboring region. This is because the central region is less likely to be cooled after extrusion than the neighboring regions. If the bubbles become too large, they may cause damage to the extruded foam sheet 1. As described above, by tilting the scale-like filler in the central region and arranging it randomly between the bubbles, it is possible to suppress the growth of the bubbles in all directions. Thereby, the strength of the extruded foam sheet 1 or the strength during molding, that is, the moldability can be improved. As a result, when a foamed resin molded product is produced by vacuum forming the extruded foamed sheet 1 as a material, it is possible to suppress the bubbles contained in the extruded foamed sheet 1 from bursting or damage to the extruded foamed sheet 1.

The orientation state of the large number of scale-like fillers included in the central region of the core layer 2 can be calculated as follows. First, as in the case of the neighboring region, 50 microscopic photographs are taken at equal intervals at the center of the core layer 2 in the thickness direction. Among all the scale-like fillers included in these 50 electron micrographs, scale-like fillers oriented at an angle of 5° to 90° with respect to the surface of the extruded foam sheet 1 are confirmed. Accordingly, the proportion of the scale-like fillers that are oriented at an angle of 5° to 90° with respect to the surface of the extruded foam sheet 1 among the large number of scale-like fillers included in the central region is calculated.

Next, a method for manufacturing the extruded foam sheet 1 will be explained (not shown). First, resin pellets as a resin material are charged into the screw cylinder of the main extruder. The resin material is polycarbonate resin. The resin pellets are heated in a screw cylinder to produce molten resin. Next, a blowing agent is injected into the molten resin from a blowing agent injection cylinder attached to the screw cylinder of the main extruder. The blowing agent is dissolved in the molten resin by the above-mentioned screw cylinder and kneaded to be uniformly dispersed. In this way, a mixed molten resin is produced. The mixed molten resin is discharged from the die outlet to form the core layer 2 . At the same time, resin pellets serving as a resin material are placed in each of the screw cylinders of the two sub-extruders, and are heated and melted to produce two molten resins. One of the two molten resins is discharged from the die outlet to form the skin layer 3, and the other is discharged from the die outlet to form the skin layer 4. The mixed molten resin and the two molten resins are combined in a die from each extruder, and a skin layer 3 is laminated on one of the main surfaces of the core layer 2, and a skin layer 4 is laminated on the other main surface of the core layer 2. are discharged from the die outlet so that they are stacked. The mixed molten resin foams when it is extruded from the die outlet into the atmosphere. In this way, the extruded foam sheet 1 is manufactured. Note that the foaming method is a physical foaming method using an inert gas such as nitrogen and carbon dioxide gas as a foaming agent. The extruded foam sheet 1 extruded in this manner is transported to a cutting machine by a take-up machine. The cutting machine cuts the extruded foam sheet 1 into a desired shape.

The extruded foam sheet 1 manufactured in this way can be used in the following applications by shaping it into a desired shape by vacuum forming or the like. For example, products and parts that require relatively high strength such as signboards or mobility materials such as automobile exterior materials, products and parts that require heat resistance such as batteries or trays for heat generating parts used in manufacturing processes that involve heating processes. , or products and parts that require weight reduction. The extruded foam sheet 1 contains a polycarbonate resin and is foam-molded by a coextrusion method, so that it is suitable as a material for molding these products and parts.

Products, parts, etc. made using the extruded foam sheet 1 can reduce the amount of resin used. As a result, the extruded foam sheet 1 according to the present embodiment can contribute to improving resource utilization efficiency, reducing transportation burden, reducing energy consumption, and reducing CO ₂ emissions. By providing extruded foam sheet 1 to society, we will help achieve Goal 7 (Affordable and Clean Energy) and Goal 9 (Industry and Technology) of the 17 Sustainable Development Goals (SDGs) established by the United Nations. We can contribute to the achievement of Goal 11 (Building sustainable cities), Goal 12 (Responsible consumption and production), and Goal 13 (Take concrete measures to combat climate change).

(Modified example)
In the embodiment described above, the skin layer 3 was formed on one main surface of the core layer 2 and the skin layer 4 was formed on the other main surface, but in the extruded foam sheet 1, the skin layer 3 was formed on one main surface of the core layer 2. Only the skin layer 3 may be provided. Further, as shown in FIG. 13, the extruded foam sheet 1 may be composed of a single layer of the core layer 2 without providing the skin layer 3 and the skin layer 4. That is, the extruded foam sheet 1 may be an extruded foam sheet 1 made of foamed resin. In addition, as mentioned above, when the heating temperature during vacuum forming is made relatively high, it is preferable that the extruded foam sheet 1 has the skin layer 3 and the skin layer 4.

Next, a method for inspecting the extruded foam sheet 1 of the present disclosure will be specifically described using FIG. 14. Note that the methods for acquiring the images 21 to 25 and measuring the brightness difference Δ are as described above, so detailed explanations will be omitted.

(Step S1)
First, the extruded foam sheet 1 is placed on the upper surface of the light box 100, and the main surface of the extruded foam sheet 1 is photographed from above the extruded foam sheet 1 using the camera 200 together with the ruler 10. As a result, an image 21 is obtained. At this time, the scales of the ruler 10 are not limited to 1 mm intervals, but may be provided at equal intervals.

(Step S2)
Next, the image 21 is subjected to edge processing to obtain an image 22.

(Step S3)
Next, the image 22 is subjected to a two-dimensional discrete Fourier transform to obtain an image 23 showing the frequency distribution of brightness in the image 22.

(Step S4)
On the other hand, the ruler 10 is removed from the image 21 and an image 24 is obtained.

(Step S5)
Next, the image 24 is subjected to a two-dimensional discrete Fourier transform to obtain an image 25 showing the frequency distribution of brightness in the image 24.

(Step S6)
Thereafter, the difference Δ in brightness between the image 23 and the image 25 is measured based on the frequency distribution of brightness in the image 22 and the frequency distribution of brightness in the image 24.

(Step S7)
Finally, it is determined whether the brightness difference Δ is less than a predetermined threshold. If the brightness difference Δ is less than a predetermined threshold, it is determined that the extruded foam sheet 1 can be appropriately vacuum formed, and if it is greater than the predetermined threshold, it is determined that the extruded foam sheet 1 can be appropriately vacuum formed. It is determined that it is not possible to do so.

More specifically, the above step S6 represents the horizontal profile at the vertical center of the image 23 as a two-dimensional spectrum as shown in the graph of FIG. 8, as described above. A plurality of frequency components appear outward from the center C of the horizontal axis of the graph (the center of the image 23) in the left-right direction, according to the equally spaced scales (for example, 1 mm intervals) of the ruler 10. As shown in FIG. 8, these frequency components are defined as a primary peak P1, a secondary peak P2, and a tertiary peak P3 in order from the center position C of the image 23 toward the outside. When the distance from the center position C of the horizontal axis (pixel) to the pixel position of the primary peak P1 is L, the range from the center of the horizontal axis (center position C of image 22) to L/5 is removed from the analysis range. . Then, the range from this pixel median value to L/5 to the outside and the pixel position of the tertiary peak P3 is defined as the analysis range. Furthermore, within the range from the L/5 position to the L/2 position described above, the position with the highest luminance is defined as the central peak P0. Furthermore, the vertical profile at the horizontal center of the image 25 is expressed as a two-dimensional spectrum as shown in the graph of FIG. When the image 25 is represented by a two-dimensional spectrum, as shown in FIG. 11, the luminance value at the position (pixel) corresponding to the above-mentioned central peak P0 and the position (pixel) corresponding to the above-mentioned tertiary peak P3. The difference Δ between these brightness values is measured.

In step S7 described above, more specifically, when the brightness difference Δ is expressed in 256 gradations, the predetermined threshold value of the brightness difference Δ can be set to 25. That is, when the brightness difference Δ is less than 25, it is possible to prevent the

skin layer

3 or 4 from peeling off from the core layer 2 and bulging during vacuum forming, or from causing cracks in the core layer 2. It is determined that the extruded foam sheet 1 can be appropriately vacuum formed. On the other hand, if the brightness difference Δ is 25 or more, it is determined that the extruded foam sheet 1 cannot be appropriately vacuum formed.

As described above, according to the method for inspecting the extruded foam sheet 1, it is possible to test in advance whether or not the extruded foam sheet 1 can be appropriately vacuum-formed without actually performing vacuum forming. Note that, as described above, the threshold value of the brightness difference Δ can be preferably set to 20, more preferably 15. That is, when the difference Δ in brightness is 20 or less, or 15 or less, it can be determined that the extruded foam sheet 1 can be vacuum-formed more appropriately.

Next, the inspection device 1000 for the extruded foam sheet 1 of the present disclosure will be specifically described using FIG. 15. Inspection apparatus 1000 includes an image receiving section 1010 and an image processing section 1020. Note that, as described above, the camera 200 in the figure photographs the main surface of the extruded foam sheet 1 along with the ruler 10 from above the extruded foam sheet 1 placed on the top surface of the light box 100. Camera 200 has an image transmitter (not shown). The image transmitting unit transmits an image 21 of the extruded foam sheet 1 and the ruler 10 to the inspection device 1000. Note that the scales of the ruler 10 are not limited to 1 mm intervals, but may be provided at equal intervals.

The image receiving unit 1010 receives the image 21 transmitted from the image transmitting unit. Note that the camera 200 and the inspection device 1000 are not particularly limited as long as they are connected via the Internet line, other wireless line, or wired line and can transmit and receive the image 21.

The image processing unit 1020 processes the image 21 received by the image receiving unit 1010 so that it can be inspected to see whether the extruded foam sheet 1 can be appropriately vacuum formed. The image processing unit 1020 includes an edge processing unit 1021, a first Fourier transform unit 1022, a second Fourier transform unit 1023, a measurement unit 1024, and a determination unit 1025. Note that the method for acquiring images 21 to 25 and measuring the brightness difference Δ in image processing is as described above, and therefore detailed explanation will be omitted.

The edge processing unit 1021 performs edge processing on the image 21 as described above. As a result, an edge-processed image 22 can be obtained.

The first Fourier transform unit 1022 performs two-dimensional discrete Fourier transform on the edge-processed image 22. As a result, an image 23 showing the frequency distribution of the brightness of the image 22 can be obtained.

The second Fourier transform unit 1023 performs a two-dimensional discrete Fourier transform on the image 24 obtained by removing the ruler 10 from the image 21. As a result, an image 25 showing the frequency distribution of the brightness of the image 24 can be obtained. Note that the image 24 may be obtained by manually removing the ruler 10 from the image 21, or by having the inspection device 1000 detect the ruler 10 in the image 21 and automatically removing the ruler 10 from the image 21. It may be obtained by removing . The image 24 is input to the second Fourier transform unit 1023 and subjected to two-dimensional discrete Fourier transform.

The measurement unit 1024 measures the difference Δ in brightness between the image 23 and the image 25 based on the frequency distribution of brightness in the image 22 and the frequency distribution of brightness in the image 24. More specifically, as described above, the horizontal profile at the vertical center of the image 23 is represented by a two-dimensional spectrum as shown in the graph of FIG. A plurality of frequency components appear outward from the center C of the horizontal axis of the graph (the center of the image 23) in the left-right direction, according to the equally spaced scales (for example, 1 mm intervals) of the ruler 10. As shown in FIG. 8, these frequency components are defined as a primary peak P1, a secondary peak P2, and a tertiary peak P3 in order from the center position C of the image 23 toward the outside. When the distance from the center position C of the horizontal axis (pixel) to the pixel position of the primary peak P1 is L, the range from the center of the horizontal axis (center position C of image 22) to L/5 is removed from the analysis range. . Then, the range from this pixel median value to L/5 to the outside and the pixel position of the tertiary peak P3 is defined as the analysis range. Furthermore, within the range from the L/5 position to the L/2 position described above, the position with the highest luminance is defined as the central peak P0. Furthermore, the vertical profile at the horizontal center of the image 25 is expressed as a two-dimensional spectrum as shown in the graph of FIG. When the image 25 is represented by a two-dimensional spectrum, as shown in FIG. 11, the luminance value at the position (pixel) corresponding to the above-mentioned central peak P0 and the position (pixel) corresponding to the above-mentioned tertiary peak P3. The difference Δ between these brightness values is measured.

The determination unit 1025 determines whether the brightness difference Δ is less than a predetermined threshold. If the brightness difference Δ is less than a predetermined threshold, it is determined that the extruded foam sheet 1 can be appropriately vacuum formed, and if it is greater than the predetermined threshold, it is determined that the extruded foam sheet 1 can be appropriately vacuum formed. It is determined that it is not possible to do so. More specifically, when the brightness difference Δ is expressed in 256 gradations, the predetermined threshold value of the brightness difference Δ can be set to 25. That is, when the brightness difference Δ is less than 25, it is possible to prevent the

skin layer

3 or 4 from peeling off from the core layer 2 and bulging during vacuum forming, or from causing cracks in the core layer 2. It is determined that the extruded foam sheet 1 can be appropriately vacuum formed. On the other hand, if the brightness difference Δ is 25 or more, it is determined that the extruded foam sheet 1 cannot be appropriately vacuum formed. Note that, as described above, the threshold value of the brightness difference Δ can be preferably set to 20, more preferably 15. That is, when the difference Δ in brightness is 20 or less, or 15 or less, it can be determined that the extruded foam sheet 1 can be vacuum-formed more appropriately.

In this way, according to the extruded foam sheet 1 inspection apparatus 1000, it is possible to test in advance whether or not the extruded foam sheet 1 can be appropriately vacuum formed without actually performing vacuum forming.

Note that the inspection device 1000 can include a photography instruction section (not shown) that instructs photography by the camera 200. For example, on the production line of the extruded foam sheet 1, the camera 200 and the inspection device 1000 described above are installed in a process after the extruded foam sheet 1 is produced. When the extruded foam sheet 1 being conveyed on the production line is detected by a sensor and the inspection apparatus 1000 receives the detection information transmitted from the sensor, the photographing instruction section may issue a photographing instruction to the camera 200. The camera 200 can photograph the extruded foam sheet 1 being conveyed from above and inspect the extruded foam sheet 1 using the above-mentioned functions. Thereby, the extruded foam sheet 1 can be inspected on the production line.

The inspection device 1000 is configured by a computer. A computer has a processor and memory. Each of the above-mentioned functions can be realized by the processor executing processing according to a program recorded in the memory. A program for causing a computer to function as the inspection device 1000 or a non-transitory recording medium recording the program may also be included in embodiments of the present disclosure. Note that the inspection device 1000 may be configured with two or more computers or one or more applications installed on the computers.

Although the embodiments have been described above, the present disclosure is not limited to the above embodiments, and various changes can be made without departing from the spirit thereof.

(Example)
As shown in Table 1 below, sample bodies (sheets) of Examples 1 to 9 and Comparative Examples 1 to 5 were prepared. The resin materials used for these samples are polycarbonate resins, and the specific details are as shown in Table 1. 1300Y" or "T2854" which is a mixed resin of polycarbonate resin and ABS, and polycarbonate resin "S-2000" or "S-3000" manufactured by Mitsubishi Engineering Plastics Corporation. Note that "L11225Z" refers to polycarbonate resin "L1225Z100" manufactured by Teijin Ltd. As the foaming aid shown in Table 1, "Metablene (registered trademark) A-3800" manufactured by Mitsubishi Chemical Corporation was used. Note that the present disclosure is not limited to these examples.

(Method for measuring bubble unevenness)
Based on the above method for measuring bubble unevenness, each sample was placed on the top of a light box "NEW5000" manufactured by Fuji Film Co., Ltd., and photographed at a brightness of 1400 cd/m ² . At this time, the main surface of each sample was photographed in 24-bit full color at a resolution of 2016 x 1512 pixels without performing any color correction. As described above, each sample was subjected to image processing and their profiles were determined. In Table 1, "brightness difference" indicates the difference between the above-mentioned central peak brightness value and the tertiary peak brightness value. When the difference in brightness was 15 or less, it was designated as "A," when it was less than 25, it was designated as "B," and when it was 25 or more, it was designated as "C." The total light transmittance of the test specimens of Examples 1 to 9 and Comparative Examples 1 to 5 was within the range of 10% to 60%.

(Evaluation results of bubble unevenness)
The sample of Example 1 was evaluated as "B", and Examples 2 to 5 were evaluated as "A". On the other hand, Comparative Examples 1 to 4 were rated "C".

(Evaluation method of vacuum formability)
First, a mold for vacuum forming was prepared. As shown in FIG. 16, the vacuum forming mold 300 had a recess 301 depressed from its upper surface, and the recess 301 had a substantially rectangular shape in plan view. The corners of the recess 301 are rounded with a radius of curvature of 15 mm, the distance between the opposing short sides of the substantially rectangular shape is 200 mm, the distance between the opposing long sides is 80 mm, and the depth of the recess 301 is was 30 mm. Using this vacuum forming mold, vacuum forming was performed on the sample bodies of Examples 1 to 5 and Comparative Examples 1 to 4, respectively. As the vacuum forming apparatus, "CFP-65P model" manufactured by Wakisaka Engineering Co., Ltd. was used. After vacuum forming, if the skin layer and core layer separate at the corner portions mentioned above, resulting in bulges in the skin layer or cracks in the core layer, the vacuum formability is considered to be poor and the core layer is evaluated as "C". If no cracks occur in the layer but the bubble diameter in the core layer exceeds 2 mm after vacuum forming, the vacuum formability is evaluated as "B", and the core layer has no cracks and the bubble diameter is noticeable. Those in which there was no change were evaluated as "A" because the vacuum formability was better.

(Evaluation results of vacuum formability)
The sample of Example 1 was evaluated as "B", and Examples 2 to 5 were evaluated as "A". On the other hand, Comparative Examples 1 to 4 were rated "C". In this way, it was confirmed that the smaller the difference in brightness, the better the vacuum formability.

Next, regarding the ratio of the thickness of the entire skin layer (t1+t2) to the thickness T of the sample, in comparison with Examples 1 to 9, the thickness ratio {(t1+t2)/T} is 0.10 to 0. .5, an evaluation of "B" or higher was obtained in both the brightness difference and vacuum formability. In particular, when the thickness ratio was between 0.20 and 0.40, the brightness difference and vacuum formability tended to be rated "A" in many specimens. That is, when the thickness ratio was 0.10 to 0.5, the difference in brightness could be made relatively small, and accordingly, excellent vacuum formability could be obtained. Further, when the thickness ratio was 0.20 to 0.40, the difference in brightness could be made smaller and better vacuum formability could be obtained. Note that the thickness ratio of Comparative Example 5 is 0.032, which is smaller than Comparative Examples 1 to 4. Therefore, although Comparative Example 5 has the same evaluation of "C" in brightness difference and vacuum formability as Comparative Examples 1 to 4, it is actually worse than Comparative Examples 1 to 4 in terms of brightness difference and vacuum formability. It is thought that he did.

Next, the difference in brightness and evaluation of vacuum formability were confirmed using the MVR magnification of the sample. In comparison with Examples 1 to 9, when the MVR magnification was 1.0 to 5 times, evaluations of "B" or higher were obtained for both the difference in brightness and vacuum formability. In particular, when the MVR magnification was 1.0 to 3 times, the difference in brightness and vacuum formability tended to be rated "A" in many specimens. That is, when the MVR magnification was 1.0 to 5 times, the difference in brightness could be made relatively small, and accordingly, excellent vacuum formability could be obtained. Further, when the MVR magnification was 1.0 to 3 times, the difference in brightness could be made smaller and better vacuum formability could be obtained. Note that the MVR magnification of Comparative Example 5 is 0.7, which is smaller than Comparative Examples 1 to 4. Therefore, although Comparative Example 5 has the same evaluation of "C" in brightness difference and vacuum formability as Comparative Examples 1 to 4, it is actually worse than Comparative Examples 1 to 4 in terms of brightness difference and vacuum formability. It is thought that he did.

Reference Signs List 1 extruded foam sheet, 2 core layer, 3 skin layer, 4 skin layer, 21 image, 22 image, 23 image, 24 image, 25 image, 1000 inspection device, 1010 image receiving section, 1020 image processing section, 1021 edge processing section , 1022 first Fourier transform unit, 1023 second Fourier transform unit, 1024 measurement unit, 1025 determination unit, P1 primary peak, P2 secondary peak, P3 tertiary peak, P0 central peak, Δ difference in brightness, L distance, T thickness, t1 thickness, t2 thickness

Claims

An extruded foam sheet containing polycarbonate resin,
A first image is obtained by simultaneously photographing the extruded foam sheet and a ruler having scales at 1 mm intervals while irradiating light from below the extruded foam sheet. A third image obtained by performing a two-dimensional discrete Fourier transform on two images, and a fifth image obtained by performing a two-dimensional discrete Fourier transform on a fourth image obtained by removing the ruler from the first image,
The third image shows the frequency distribution of brightness in the second image, the fifth image shows the frequency distribution of brightness in the fourth image,
When a luminance profile is taken from the center of the third image in a direction along the ruler and expressed as a two-dimensional spectrum, a plurality of frequency components appearing by the scales of the ruler at 1 mm intervals are sequentially expressed from the center position of the third image. When the primary peak, secondary peak, and tertiary peak are used, and when the distance between the primary peak and the center position of the third image is L, L/5 from the center position of the third image When the frequency component with the highest brightness between the position at a distance of and the position at a distance of L/2 is taken as the central peak,
When a luminance profile is drawn linearly from the center of the fifth image in a direction of relatively high luminance and expressed as a two-dimensional spectrum, the luminance at the position corresponding to the central peak and the luminance at the position corresponding to the tertiary peak are An extruded foam sheet in which the difference in brightness is less than 25 when expressed in 256 tones.
The extruded foam sheet according to claim 1,
The extruded foam sheet is an extruded foam sheet containing 50% by weight or more of polycarbonate resin.
The extruded foam sheet according to claim 1,
The extruded foam sheet has a thickness of 1 to 5 mm.
The extruded foam sheet according to claim 1,
The extruded foam sheet has a total light transmittance of 10% to 60%.
The extruded foam sheet according to claim 1,
A core layer made of foamed resin,
a first skin layer made of non-foamed resin and laminated on one main surface of the core layer;
a second skin layer laminated on the other main surface of the core layer,
An extruded foam sheet in which at least one of the first and second skin layers is made of polycarbonate resin.
The extruded foam sheet according to claim 5,
An extruded foam sheet that satisfies the following formula (1).
0.10≦(t1+t2)/T≦0.5 (1)
In formula (1), t1 represents the thickness of the first skin layer, t2 represents the thickness of the second skin layer, and T represents the thickness of the extruded foam sheet.
The extruded foam sheet according to claim 4,
An extruded foam sheet, wherein the polycarbonate resin contained in either one of the first and second skin layers has a melt volume rate of 1.0 to 5 times that of the polycarbonate resin contained in the core layer.
The extruded foam sheet according to claim 1,
The extruded foam sheet has a length of 1000 mm or more in the extrusion direction, and has a length of 1000 mm or more in the width direction perpendicular to the extrusion direction in plan view.
The extruded foam sheet according to claim 1,
The extruded foam sheet wherein the difference in brightness is 20 or less when expressed in 256 gradations.
The extruded foam sheet according to claim 1,
The extruded foam sheet wherein the difference in brightness is 15 or less when expressed in 256 gradations.
A method for inspecting an extruded foam sheet containing polycarbonate resin, the method comprising:
obtaining a first image by simultaneously photographing the extruded foam sheet and a ruler having equally spaced scales from above while irradiating the extruded foam sheet with light from below;
obtaining a second image by edge processing the first image;
obtaining a third image showing a frequency distribution of brightness in the second image by performing a two-dimensional discrete Fourier transform on the second image;
obtaining a fourth image by removing the ruler from the first image;
performing a two-dimensional discrete Fourier transform on the fourth image to obtain a fifth image showing a frequency distribution of brightness in the fourth image;
measuring a difference in brightness between the third image and the fifth image based on the frequency distribution of brightness in the second image and the frequency distribution of brightness in the fourth image;
A method for inspecting an extruded foam sheet, comprising the step of determining that the extruded foam sheet can be vacuum-formed if the difference in brightness is below a predetermined threshold.
The method for inspecting an extruded foam sheet according to claim 11,
The step of measuring the difference in brightness between the third image and the fifth image includes the step of measuring the difference in brightness between the third image and the fifth image, when a brightness profile is taken from the center of the third image in a direction along the ruler and expressed as a two-dimensional spectrum, the brightness difference is at equal intervals on the ruler. A plurality of frequency components appearing according to the scale are defined as a primary peak, a secondary peak, and a tertiary peak in order from the center position of the third image, and the distance between the primary peak and the center position of the third image is L. The frequency component with the highest brightness between the position at a distance of L/5 and the position at a distance of L/2 from the center position of the third image is defined as the central peak, and When a luminance profile is taken linearly in the direction of high luminance and expressed as a two-dimensional spectrum, the difference between the luminance at a position corresponding to the central peak and the luminance at a position corresponding to the tertiary peak is measured,
The step of determining that the extruded foam sheet is vacuum-formable includes determining that the extruded foam sheet is vacuum-formable when the difference in brightness is less than 25 expressed in 256 gradations. Inspection method.
An inspection device for extruded foam sheets containing polycarbonate resin,
an image receiving unit that receives a first image obtained by simultaneously photographing the extruded foam sheet and a ruler having equally spaced scales from above while irradiating the extruded foam sheet with light from below;
comprising an image processing unit that processes the first image received by the first image receiving unit,
The image processing unit includes:
an edge processing unit that performs edge processing on the first image to obtain a second image;
a first Fourier transform unit for performing two-dimensional discrete Fourier transform on the second image to obtain a third image showing a frequency distribution of brightness in the second image;
a second Fourier transform unit for performing two-dimensional discrete Fourier transform on a fourth image obtained by removing the ruler from the first image to obtain a fifth image showing a frequency distribution of brightness in the fourth image;
a measurement unit that measures a difference in brightness between the third image and the fifth image based on the frequency distribution of brightness in the second image and the frequency distribution of brightness in the fourth image;
An extruded foam sheet inspection device, comprising: a determination unit that determines that the extruded foam sheet can be vacuum formed when the difference in brightness is less than a predetermined threshold.
The extruded foam sheet inspection device according to claim 13,
The measuring unit is configured to calculate a plurality of frequency components appearing by equidistant scales of the ruler in the third image when a luminance profile is taken from the center of the third image in a direction along the ruler and expressed as a two-dimensional spectrum. A primary peak, a secondary peak, and a tertiary peak are defined in order from the center position of the third image, and when L is the distance between the primary peak and the center position of the third image, L/ When the frequency component with the highest brightness between the position at a distance of 5 and the position at a distance of L/2 is set as the central peak, the brightness increases linearly from the center of the fifth image in a direction of relatively high brightness. When the profile is taken and expressed as a two-dimensional spectrum, the difference between the brightness at a position corresponding to the central peak and the brightness at a position corresponding to the tertiary peak is measured,
The extruded foam sheet inspection device is characterized in that the determination unit determines that the extruded foam sheet can be vacuum formed when the difference in brightness is less than 25 expressed in 256 gradations.