JPH0772099A - Inspecting method for defect in opaque film - Google Patents

Abstract

PURPOSE:To provide a method for inspecting an opaque film which can accurately detect a defect of the film even when color of a base of the film is of a similar shade to that of the defect or when an oil adheres to the film. CONSTITUTION:According to the inspecting method, light is cast on the surface of a to-be-inspected opaque film 5 from light sources 1, 2, and the light reflected at the film surface 5 is detected and converted into an image signal by a solid- state image pickup device 3. The obtained image signal is processed by a signal processing device 4 to judge the presence/absence of a defect in the film 5. The light having a maximum wavelength in a 350-450nm band is cast on the film from the light source 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting defects (defects) on a sheet surface which occur during the production of an opaque film or sheet.

[0002]

2. Description of the Related Art At present, films and sheets of polyester, polypropylene and the like (hereinafter referred to as films) are widely used as, for example, packaging materials, industrial materials and the like. In the manufacturing process of these films, various defects (defects) may occur on the film surface.
For example, black spots due to resin carbide or foreign matter contamination, foreign matter, machine oil, oil stains due to oil content contained in film additives, white stains due to transfer of oil on rolls, resin adhesion due to resin leakage, insufficient heating, etc. There are defects such as defective film thickness, non-stretching such as unevenness, fish eyes due to defective thickness in the film composition, and holes in the film. Since these defects pose a quality problem depending on the use of the film, the film surface is inspected for defects.

There are mainly two types of such a film inspection system: a solid-state image pickup device camera system and a laser system. In either method, the light source and the optical system that highlight the defects on the film surface are important factors.

When the film to be inspected is transparent or translucent, it is irradiated with light from a light source arranged below the film and transmitted through the film by a solid-state image pickup device such as a CCD camera arranged above the film. The method of detecting the emitted light is generally used. If there are defects in the film, changes in the light transmitted through the film will occur,
By detecting the change with a solid-state imaging device,
Confirm the existence of defects.

Further, when the film to be inspected is opaque due to coloring by various additives and the like, light cannot pass through the film, so that the above detection cannot be performed. Therefore, in this case, generally, a method of irradiating light from a light source arranged above the film and detecting light reflected on the film surface by a solid-state imaging device arranged above the film is performed. There is.

A white fluorescent lamp or an incandescent lamp is generally used as the light source. The white fluorescent lamp is used because the spectral energy distribution of the white fluorescent lamp is very close to the photoelectric conversion characteristic of the CCD element and the signal conversion efficiency is high.

[0007]

However, when a white fluorescent lamp is used as a light source in the defect inspection of an opaque film, the base color (back color) of the opaque film and the defect color are similar colors (for example, In the case where the defect is brown compared to the brown film), there is a problem that the detection capability of the defect is reduced and it is difficult to determine the presence or absence of the defect. In addition, oil is a drawback that is generally difficult to detect.

The object of the present invention is to solve the above-mentioned problems of the prior art and to detect a defect with high accuracy even when the base color of the opaque film and the color of the defect are similar colors, or even when oil is attached. The object of the present invention is to provide a defect inspection method for an opaque film.

[0009]

A method for inspecting a defect of an opaque film surface according to the present invention includes irradiating light from at least one light source onto an opaque film surface of a subject, and receiving light reflected by the film surface by a solid-state imaging device. And convert it to a video signal,
A method for inspecting a defect of an opaque film, which comprises processing the obtained video signal with a signal processing device to determine the presence or absence of a defect of the film, and applying 280 to 280
It is characterized by irradiating light having a maximum wavelength at 450 nm. In the present invention, the preferable range of the maximum wavelength is 350 to 450 nm.

In the present invention, from the light source 280 to 450
To irradiate light having a maximum wavelength of nm, for example, a blue fluorescent lamp may be used as a light source, or another light source may be used, and a color filter may be provided between the light source and the subject film to provide a light source of 280 to 280. You may make it selectively irradiate the to-be-tested film with the light of the wavelength range of 450 nm.

In the present invention, when a blue fluorescent lamp is used as the light source, the blue fluorescent lamp has no luminous flux power and the amount of light is insufficient. Therefore, in order to compensate for this, the white fluorescent lamp (maximum at 550 to 570 nm) is used. (Having a wavelength) is preferably used in combination.

In the present invention, the solid-state image pickup device is
For example, CCD type device, MOS type device, CID
Type device.

[0013]

According to the opaque film defect inspection method of the present invention, since light having a maximum wavelength of 280 to 450 nm is emitted from at least one light source, the following effects are obtained.

If the defect is oil adhesion, 280-45
The oil fluoresces upon irradiation with 0 nm light. As a result, a significant difference occurs between the video signals of the normal portion and the defective portion of the film.

Further, when the base color of the film and the color of the defect are similar colors, for example, even if the defect is brown like oil for a brown film, a hue difference occurs between the base color of the film and the defect color. , Contrast difference is obtained. as a result,
A significant difference occurs between the video signals of the normal part and the defective part of the film.

[0016]

EXAMPLES Next, the present invention will be described in detail with reference to examples. In the description of the drawings, the upper side of FIG. 1 is referred to as the upper side, the lower side is referred to as the lower side, the left side is referred to as the left side, and the right side is referred to as the right side.

FIG. 1 is a diagram showing the outline of the structure of an inspection apparatus used in the defect inspection method of the present invention. First, the outline of the apparatus will be described.

In FIG. 1, the sample film (5) is an opaque film whose base color is brown. Subject film
The base roll (6a) and the winding roll (6
b) are installed horizontally at the same height. The midpoint in the left-right direction between the rolls (6a) and (6b) is the film (5).
It is said to be the inspection position (A).

The light source (1) is a white fluorescent lamp (550 to 570).
has a maximum wavelength in nm) and is 50 mm to the left from the inspection position (A) and the distance from the film (5) above the film.
(L2) It is provided at a position of 50 mm. Also the light source (2)
Is a blue fluorescent lamp (having a maximum wavelength in 350 to 450 nm), which is located 50 mm to the right from the inspection position (A) and is a light source.
It is installed at the same height as (1). Both of these light sources
(1) and (2) are respectively directed so that the irradiation light enters the inspection position (A) on the film (5) surface. That is, the incident angle (θ) of the irradiation light from the light sources (1) and (2) on the film (5) surface is set to 45 °. The CCD line sensor (3) has a distance (L3) 73 above the film inspection position (A).
It is installed at the position of 0 mm. CCD line sensor
When the width of the sample film (5) is large, it is preferable that a plurality of (3) are installed in the film width direction in order to improve the inspection capability. The signal processing device (4) is connected to the output of the CCD line sensor (3). The distances such as (L2) and (L3) shown here are examples, and the width of the subject film (5) and the CCD line sensor
It is a value that changes depending on the number of installed units in (3) (that is, how many film widths are inspected per CCD line sensor).

Next, the inspection method will be described. In the above device configuration, the film (5) is transferred from the base roll (6a) side to the take-up roll (6b) side at a constant speed. As shown by the broken line in FIG. 1, light is emitted from both light sources (1) and (2) toward the inspection position (A) of the film (5). The energy distribution of the light emitted from both light sources (1) and (2) at this time is shown in FIG. Depending on the hue and surface condition of the film (5), a certain amount of the emitted light is reflected and the CCD line sensor
Light is received at (3). If there is some defect in the film (5), the reflected light changes, and the change is observed by the CCD line sensor (3). CCD line sensor (3)
Then, the received reflected light is converted into a video signal (voltage signal) and output to the signal processing device (4).

In the signal processing device (4), as shown in FIG. 3, first, the video AGC circuit performs the level correction process of the video signal, and then the differential emphasis process is performed, and the determination circuit determines whether there is a defect. Make a distinction. In the AGC circuit, the current video signal level is compared with the video signal level of the previous cycle in a constant cycle to continuously perform the correction. The level correction process is performed in this way because the signal from the CCD line sensor (3) has variations due to the elements, and the object film (5)
This is because the transmissivity differs depending on the signal level. In the differential emphasizing circuit, the change of the video signal due to the defect of the film (5) is minute, so the differential emphasizing of the change of the video signal is carried out, and the judging circuit judges the defect.

Next, with reference to FIGS. 4 and 5, the determination of defects in the determination circuit will be described in detail. Since the voltage of the differential signal obtained by the differential emphasizing circuit and the defect size are generally directly proportional to each other, the threshold voltage is set in advance for a defect larger than the size to be detected. Then, the threshold voltage is compared with the voltage of the differential signal. Differentiated signals above the threshold voltage are identified as defects. The differential signal having a voltage equal to or higher than the threshold voltage is binarized in synchronization with the clock pulse, and the width of the defect is determined based on the number of bits (FIG. 4). In addition, the length of the defect is determined from the duration of the binarized signal (FIG. 5). As described above, the determination circuit can determine not only the presence of a defect but also the width and length of the defect.

In this embodiment, the light source (2) is 350-4.
Since light having a maximum wavelength of 50 nm is irradiated, if oil adheres to the film (5), the oil will generate fluorescence, and the difference between the image signals of the normal part and the defective part of the film (5) will occur. Remarkably occurs. Further, even if the defect is a brown color similar to the film base color, a hue difference occurs between the film base color and the brown color of the defect, and a contrast difference is obtained.
There is a significant difference between the video signals of the normal part and the defective part in (5).
As a result, the defect detection performance of the opaque analyte film (5) was improved as compared with the conventional method.

[0024]

According to the defect inspection method of the present invention, as described above, when the defect is the adhesion of oil, the oil emits fluorescence and when the color of the defect is similar to the film base color. In addition, since the contrast difference is obtained, the difference between the image signals of the normal portion and the defective portion of the film is remarkably generated. as a result,
The detection performance of defects of the opaque film is improved.

The method of the present invention is particularly excellent in detection performance when oil adheres to a brown film.

Further, since oil has a function of generating fluorescence upon irradiation with light of 280 to 450 nm, the feature of the present invention of irradiating light having a maximum wavelength from 280 to 450 nm from a light source is an opaque film. Not only that, it is also very effective for defect inspection of transparent films.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus of the present invention.

FIG. 2 is a diagram showing an example of energy distribution of irradiation light in the present invention.

FIG. 3 is a diagram showing an outline of a signal processing device according to the present invention.

FIG. 4 is a diagram showing a defect determination method according to the present invention.

FIG. 5 is a diagram showing a defect determination method according to the present invention.

[Explanation of symbols]

 (1) (2) ... light source (3) ... solid-state imaging device (4) ... signal processing device (5) ... specimen film (6a) (6b) ... transfer means

Claims (1)

[Claims] 1. A film (5) is produced by irradiating a surface of an opaque film (5) of an object with light from at least one light source (1) (2).
The light reflected by the surface is received by the solid-state imaging device (3) and converted into a video signal, and the obtained video signal is processed by the signal processing device (4) to determine the presence or absence of defects in the film (5). A method for inspecting defects of an opaque film comprising at least 1
A defect inspection method for an opaque film, which comprises irradiating light having a maximum wavelength of 280 to 450 nm from two light sources (2).