HK40096723B - Method and a thermoplastic film for use in a printed packaging of absorbent hygienic articles - Google Patents

Description

Methods for printing and packaging absorbent sanitary products and thermoplastic films

Technical Field

This disclosure relates to a method for establishing the printability of a thermoplastic film for packaging absorbent hygiene articles, the thermoplastic film comprising at least 30% recycled polymer material. This disclosure also relates to a method for forming a thermoplastic film for packaging, and packaging for absorbent hygiene articles comprising the thermoplastic film.

Background Technology

Absorbent hygiene products, such as diapers, feminine hygiene products, incontinence products, toilet paper, and napkins, are typically stored, distributed, and sold in packages containing multiple items. Some items may also be offered in single-use packages containing only one item. These packages are usually disposable, meaning they are used only once and then discarded. Such packages can traditionally be made of or contain thermoplastic film.

In the field of packaging for absorbent hygiene products, there is a need to improve sustainability. Therefore, it is desirable to use, at least in part, recycled polymer materials to form thermoplastic films for packaging.

However, the problem is that recycled polymer materials often come from unknown sources and may include a wide variety of different polymers. Therefore, thermoplastic films made using recycled polymer materials, or those incorporating recycled polymer materials, may exhibit very different properties depending on the batch of recycled materials used in the manufacturing process. To enable the use of such thermoplastic films in large-scale production, it is necessary to be able to quickly and accurately determine which thermoplastic films meet the requirements of their intended end use and which do not.

Thermoplastic films used for packaging absorbent hygiene products are typically between 20 and 100 μm thick. To be suitable for use as packaging, thermoplastic films should possess a range of properties depending on specific packaging requirements. For example, thermoplastic films may need to have a certain level of tensile strength and/or drape.

If thermoplastic film is printed before or after forming packaging for absorbent hygiene products, certain considerations are necessary. Visual irregularities in the thermoplastic film can impair the visual quality of the printing. While irregularities in the thermoplastic film may be visually identifiable before printing, their impact on the overall quality of the print may not become apparent until after printing is complete. Therefore, after manual visual inspection, printed film or entire packages of printed film may have to be discarded due to unmet aesthetic requirements. Discarding printed thermoplastic film material results in material waste. This waste is particularly troublesome because it only becomes apparent after film printing.

Sometimes, the thermoplastic film is visually inspected (e.g., using a microscope) to assess the amount of irregularities in the film in order to evaluate its quality before printing. However, such methods often yield subjective results and/or are relatively time-consuming, which is unsatisfactory when the increased need for film quality assessment arises due to the use of recycled materials.

Therefore, it is necessary to determine the printability of thermoplastic films, including recycled materials, for packaging of absorbent hygiene products. Furthermore, there is a need for printed packaging of absorbent hygiene products that incorporates recycled materials and provides satisfactory print quality.

Summary of the Invention

At least one of the above requirements is achieved by the following method, which is used to determine the printability of a thermoplastic film for packaging of absorbent hygiene products, the thermoplastic film comprising at least 30% recycled polymer material.

The method includes:

- Provide a sample of the thermoplastic film, preferably with a size of 10cm × 10cm;

- Scan the sample to provide a pixelated image of the sample;

- Use a thresholding method to analyze the pixelated image using a computer to convert it into a binary image.

Like, where each pixel is determined to be either dark or light;

- Each group of adjacent pixels that will be identified as dark will be defined as a gel point;

- Define the size of each gel dot as a circle representing the pixel area of that gel dot, etc.

Effective diameter;

- Determine the amount of gel points, which indicates the presence of gel points greater than or equal to 150 μm in the sample.

The number of gel dots of different sizes; and

- The relative coverage area of gel dots is determined using the equivalent diameter of a circle, indicating the relative area of the sample covered by gel dots with a size greater than or equal to 150 μm; and

-If the amount of gel points is less than or equal to the first threshold and relative to the area covered by the gel points

If the value is less than or equal to the second threshold, then the thermoplastic film is determined to be suitable for printing; and

- If the amount of gel points is greater than a first threshold and/or the relative gel point coverage area is greater than a second threshold, then the thermoplastic film is determined to be unsuitable for printing.

In this disclosure, the term "gel point" is used to describe visual defects in a membrane. Such defects may originate, for example, from non-polymeric substances (such as wood fibers, paper fibers, or other materials) in a mixture of recycled materials, polymeric materials with melting points different from the main residues, or polymeric materials that are molten or unevenly distributed. The term "gel point" is used herein to describe any such visual defects in a membrane, regardless of their origin. The number, size, and distribution of gel points in thermoplastic films made at least partially of recycled polymeric materials can vary considerably depending on the material from which the recycled polymeric material originates.

Using the method described above, the relative gel point coverage area of the relative regions covered by gel points in an indicator film sample is used, along with the amount of gel points, to distinguish between thermoplastic films suitable for printing and those unsuitable for printing. This method considers gel points with a size greater than or equal to 150 μm, measured by the method disclosed herein.

The use of this method enables non-manual evaluation of thermoplastic films containing at least 30% recycled polymer material, which can be performed before printing, and thus contributes to more efficient manufacturing and reduced material waste.

This method involves providing a sample of a thermoplastic film. Optionally, the sample may be a selected sample area of a larger sheet or roll of thermoplastic film. Optionally, the sample may be cut from the thermoplastic film, which may be suitable because the sample can then be conveniently taken to a separate scanner for evaluation.

The sample size can be selected to ensure that relevant measurements of the relative gel point coverage area can be achieved. This may depend on the evaluation distribution of the gel points over the area of the thermoplastic film. For example, a sample size of 10 × 10 cm might be suitable.

A sample is scanned to provide a pixelated image of the sample. Suitable scanners for performing such scans and providing scan results in a form suitable for computer analysis are known in the art.

As is known in the art, a sample can be scanned multiple times to provide multiple images, from which an average can be formed to provide the most accurate results possible. For example, a sample can be scanned three times, and an average can be formed from the three scans to provide a pixelated image of the sample.

The pixelation resolution should be sufficient to identify gel dots with a size greater than or equal to 150 μm. For example, the pixelation resolution can be at least 1700 dpi (dots per inch). Alternatively, the pixelation resolution can be at least 2400 dpi (dots per inch), for example, 2400 dpi.

The sample was scanned three times, and the resulting images were merged before proceeding with image analysis.

The scanning device may introduce some brightness variations. To account for these variations, normalization can be performed on the pixelated image, where the pixel value is the average of Px = ((Px – Avg(ROI)/Std(ROI)) in two vertical directions, see Figure 6.

The pixelated image obtained from the scan is subjected to computer analysis using a thresholding method to provide a binary image, in which each pixel is determined to be either dark or light.

For example, a fixed grayscale threshold method can be used for computer analysis of pixelated images. An appropriate fixed grayscale threshold can be determined, for example, by comparison with a reference sample for which the presence of gel points is manually assessed.

Each pair of adjacent pixels that are considered dark in a binary image is defined as a gel point.

For example, a binary image can be formed using the lighter components of the RGB spectrum.

For each gel point, the gel point size is defined as the circle equivalent diameter of the pixel area of that gel point.

The number of gel spots in the sample with a size greater than or equal to 150 μm is calculated and determined as the amount of gel spots.

In addition, the relative gel point coverage area is determined using the circle equivalent diameter, which indicates the relative area of the sample covered by gel points with a gel point size greater than or equal to 150 μm.

According to the method disclosed here, if the amount of gel points is less than or equal to a first threshold and the relative gel point coverage area is less than or equal to a second threshold, the thermoplastic film is determined to be suitable for printing.

The first threshold indicates a limit on the number of gel points in the film, while the second threshold indicates a limit on the proportion of the film area covered by the gel points. Therefore, thermoplastic films can be evaluated by considering both measurements simultaneously.

The first and second thresholds can be set based on the printing requirements to be applied to the thermoplastic film. For example, detailed printing of small text may require a relatively low threshold to provide the desired printing accuracy. However, large areas covered in monochrome may require a relatively low threshold because gel spots on large monochrome areas will be very noticeable and easily detected. To set the thresholds, the acceptable packaging printing quality in the user's view can be investigated.

In addition to the steps described above, other steps can be applied, such as those used to eliminate clusters of adjacent pixels that are unlikely to be gel points and are considered dark. For example, the method may include a step of evaluating the solidity of each group of adjacent pixels identified as dark. This step may include comparing the solidity of each group of adjacent pixels identified as dark to a solidity requirement threshold.

Furthermore, the method may include, for example, a step of removing small groups of pixels from the pixelated image before determining the gel dot size and the amount of gel dots. For instance, only pixel groups with a size greater than a threshold number of pixels are analyzed to determine the gel dot size and the amount of gel dots, wherein the threshold number of pixels may be set to remove pixel groups that may never reach the limit of a gel dot size greater than or equal to 150 μm.

Optionally, the first threshold is less than or equal to 450 samples per 100 ^cm² , for example, less than or equal to 300 samples per 100 ^cm² .

Optionally, the second threshold is less than or equal to 20%, for example, less than or equal to 12%.

This method can be used for membranes whose transparency allows for scanning and identification of any gel points. For example, it can be used for membranes with an opacity of 70% or less.

Optionally, the membrane includes a colored pigment in the membrane resin. This colored pigment provides a uniform color to the thermoplastic membrane, which in itself does not interfere with the determination of the gel point.

Optionally, the thickness of the membrane is between 20 and 70 μm.

Optionally, the membrane comprises less than 80% recycled polymer material.

Optionally, the membrane includes:

a. The total phthalates are in the range of 0.05 to 250 mg/kg (ppm), for example 0.05 to 100 mg/kg (ppm) or for example 0.05 to 20 mg/kg (ppm); and/or

b. The total amount of organotin compounds is in the range of 0.0003 to 0.5 mg/kg (ppm), for example 0.0003 to 0.1 mg/kg (ppm) or for example 0.0003 to 0.02 mg/kg (ppm); and/or

c. The total heavy metal concentration is in the range of 0.1 to 100 mg/kg (ppm), for example, 0.1 to 60 mg/kg (ppm) or 0.1 to 30 mg/kg (ppm); and/or

d. The total amount of bisphenol A is in the range of 0.05 to 20 mg/kg (ppm), for example, 0.05 to 10 mg/kg (ppm) or 0.05 to 5 mg/kg (ppm).

Preferably, the total amount of each group of chemicals, such as phthalates, organotin compounds, heavy metals, and/or bisphenol A, in the membrane can be analyzed on the recycled resin material before membrane formation. Alternatively, the total amount of each group of chemicals on the membrane can be analyzed during membrane preparation. The total amount of these substances is related to the suitability of the membrane for use in forming packaging for hygiene products.

Organotin compounds include at least TBT and TPhT. Heavy metals include at least Pb, Hg, Cd, and hexavalent Cr. Phthalate salts include at least DINP, DEHP, DNOP, DIDP, BBP, DBP, DIBP, DPHP, and DCHP. (DINP = diisononyl phthalate, DEHP = di-(2-ethylhexyl) phthalate, DNOP = n-octyl phthalate, DIDP = diisodecyl phthalate, BBP = benzyl butyl phthalate, DBP = dibutyl phthalate, DIBP = diisobutyl phthalate, DPHP = di(2-propylheptyl) phthalate, DCHP = dicyclohexyl phthalate).

Alternatively, the film is a transparent, glossy film, and its haze can be determined.

Optionally, the method includes determining the haze of the thermoplastic film, and

If the haze is within the specified range, then the film is deemed suitable for printing and for use in the packaging of absorbent hygiene products.

If the haze level is outside the specified haze range, the film is deemed unsuitable for printing and for use in the packaging of absorbent hygiene products.

The haze range is less than 25%, for example, less than 20%, or 4% to 18%.

Haze is measured as the percentage of incident light that is scattered at an angle greater than 2.5° through a plastic film. Several factors contribute to light scattering, including impurities contained in the thermoplastic film. Haze is another factor related to the suitability of film printing.

Haze can be measured according to ASTM D1003.

Optionally, the method includes:

Determine the MD force at 5% elongation in the direction of the membrane machine, and

If the MD force at 5% elongation is within the MD force range at 5% elongation, then the film is deemed suitable for printing and for packaging of hygienic absorbent articles.

If the MD force at 5% elongation is outside the range of MD forces at 5% elongation, then the film is determined to be unsuitable for printing and for packaging of hygienic absorbent articles.

The MD force range at 5% elongation is greater than or equal to 3 N/15 mm, and optionally from 4 to 9 N/15 mm.

Optionally, the method includes:

Determine the CD force at 5% transverse elongation of the membrane, and

If the CD force at 5% elongation is within the range of the CD force at 5% elongation, then the film is deemed suitable for printing and for packaging of hygienic absorbent articles.

If the CD force at 5% elongation is outside the range of the CD force at 5% elongation, then the film is determined to be unsuitable for printing and for packaging of hygienic absorbent articles.

The CD force range at 5% elongation is greater than or equal to 3 N/15 mm, and optionally from 4 to 9 N/15 mm.

The MD and/or CD tension of a thermoplastic film at 5% elongation may be relevant to its suitability for use as packaging for hygiene products. The MD and/or CD tension at 5% elongation can be determined according to DIN EN ISO 527.

Optionally, the method includes:

Determine the 2% secant modulus (CD) of the film in the transverse direction. If the 2% secant modulus is within the range specified, then the film is deemed suitable for printing and for packaging sanitary absorbent articles.

If the CD 2% secant modulus is outside the range of CD 2% secant modulus, then the film is determined to be unsuitable for printing and for packaging of sanitary absorbent articles.

The secant modulus of CD 2% ranges from 200 to 600.

Optionally, the method includes:

Determine the MD2% secant modulus of the film in the machine direction. If the MD2% secant modulus is within the MD2% secant modulus range, then the film is suitable for printing and for packaging hygienic absorbent articles.

If the MD 2% secant modulus is outside the range of the MD 2% secant modulus, then the film is determined to be unsuitable for printing and for packaging of sanitary absorbent articles.

The 2% secant modulus of MD ranges from 200 to 550.

The modulus of a material is expressed as the applied stress divided by the resulting strain, which can be represented by a stress-strain curve. The 2% secant modulus is represented by a straight line drawn from the origin to a specific point on the stress-strain curve representing 2%.

The MD and/or CD 2% secant modulus of a thermoplastic film may be relevant to its suitability for forming packaging for hygiene articles. The MD and/or CD 2% secant modulus can be determined according to DIN EN ISO 527.

Optionally, the method includes determining the dynamic friction coefficient of the membrane.

If the dynamic coefficient of friction is within the range of the coefficient of friction, then the film is suitable for printing and for use in the packaging of hygienic absorbent articles.

If the dynamic coefficient of friction is outside the range specified in the coefficient of friction description, then the film is deemed unsuitable for printing and for packaging of sanitary absorbent articles.

The coefficient of friction is greater than or equal to 0.1, optionally less than or equal to 0.4, and optionally between 0.1 and 0.4.

The dynamic coefficient of friction can be determined according to DIN EN ISO 8295.

In a second aspect, a method for forming packaging for an absorbent article is provided, comprising:

- Provide a printed thermoplastic film material suitable for packaging of sanitary absorbent articles, determined according to any of the above options; and

- To form a package of hygienic absorbent articles comprising the thermoplastic film.

Optionally, the method further includes printing at least a portion of the film.

Optionally, the step of forming the packaging includes forming the thermoplastic film packaging such that the thermoplastic film forms the outer surface of the packaging.

Optionally, the packaging includes the thermoplastic film as a co-extruded single-layer film.

Optionally, the packaging forming step includes folding the thermoplastic film to form a pocket or bag.

Optionally, the method includes filling the package with absorbent sanitary articles.

Optionally, the absorbent hygiene item is a hygiene item such as diapers, feminine towels, underwear pads and/or incontinence products or clothing.

Optionally, the absorbent article includes absorbent paper towels or nonwoven fabrics, such as napkins, tissues, toilet paper, or household paper. The absorbent article can be folded, such as a folded napkin or tissue, or unfolded. Optionally, the absorbent article can be rolled up, such as an absorbent paper towel roll, or a household paper or toilet paper roll.

Optionally, the absorbent articles are arranged in the package as a stack of hygienic articles. Optionally, the method includes filling the package with the stack of hygienic articles.

Optionally, the method includes filling the package with a single absorbent sanitary article, thereby providing a package containing only a single article. Optionally, the single absorbent sanitary article is a sanitary article.

Optionally, the method includes forming a packaging array of the film, the array comprising at least 1,000 packages, for example at least 10,000 packages.

In the third aspect, packaging for absorbent articles made according to the method of the second aspect is provided.

In a fourth aspect, a package for an absorbent article is provided, comprising a thermoplastic film, wherein the thermoplastic film comprises at least 30% to 80% recycled polymer by weight, and the thermoplastic film has a continuous non-printed area of at least 10 × 10 cm, wherein the amount of gel points of the thermoplastic film is less than or equal to 450, and the relative coverage area of the gel points is less than or equal to 20%, according to a specific gel point evaluation method described in the detailed section below of this application.

Optionally, the thermoplastic film has a printed area outside the continuous non-printed area.

Optionally, the thermoplastic film is transparent, at least in the non-printed areas.

Optionally, the thermoplastic film contains coloring pigments in the film resin.

Optionally, the film thickness is between 20 and 70 μm.

Optionally, the membrane comprises less than 80% recycled polymer material.

Optionally, the membrane comprises:

a. The total amount of phthalates is in the range of 0.05 to 250 mg/kg (ppm), for example 0.05 to 100 mg/kg (ppm) or for example 0.05 to 20 mg/kg (ppm); and/or

b. The total amount of organotin compounds is in the range of 0.0003 to 0.5 mg/kg (ppm), for example 0.0003 to 0.1 mg/kg (ppm) or for example 0.0003 to 0.02 mg/kg (ppm); and/or

c. The total amount of heavy metals is in the range of 0.1 to 100 mg/kg (ppm), for example, 0.1 to 60 mg/kg (ppm) or 0.1 to 30 mg/kg (ppm); and/or

d. The total amount of bisphenol A is in the range of 0.05 to 20 mg/kg (ppm), for example, 0.05 to 10 mg/kg (ppm) or 0.05 to 5 mg/kg (ppm).

Optionally, the membrane has a haze of less than 25%, for example less than 20%, or 4% to 18%.

Optionally, the membrane has a MD force at 5% elongation along the membrane machine direction.

The MD force range at 5% elongation is greater than or equal to 3 N/15 mm, and optionally from 4 to 9 N/15 mm.

Optionally, the membrane has a CD force of 5% elongation in the transverse direction greater than or equal to 3 N/15 mm, and optionally 4 to 9 N/15 mm.

Optionally, the membrane has a CD 2% secant modulus along the transverse direction of the membrane.

The secant modulus of CD 2% is between 200 and 600 MPa.

Optionally, the MD 2% secant modulus of the membrane in the membrane processing direction is between 200 and 550 MPa.

Optionally, the dynamic friction coefficient of the membrane is greater than or equal to 0.1, optionally less than or equal to 0.4, and optionally between 0.1 and 0.4.

In the fifth aspect, an array of at least 1,000 packages according to the fourth aspect, as described above, is provided, the packages having similar appearance and contents.

The explanations and measurement methods described above in one aspect of this disclosure can be similarly applied to other aspects of this disclosure.

Attached Figure Description

Referring to the accompanying drawings, the following is a more detailed description of variations of the methods and apparatus disclosed in this application, which are cited as examples.

Figure 1 is a flowchart schematically illustrating a method for determining the printability of thermoplastic films for packaging of absorbent hygiene articles;

Figure 2a is an example of a scanned image from a thermoplastic film sample;

Figure 2b is a histogram of the gel point size distribution in Figure 2a;

Figure 3 is a flowchart schematically illustrating a method for forming packaging of absorbent hygiene articles using thermoplastic film;

Figure 4 shows a variation of the packaging including absorbent hygiene products;

Figure 5 shows another variation of packaging that includes absorbent hygiene products;

Figure 6 shows the standardization of the scanned image.

Detailed Implementation

Figure 1 is a flowchart schematically illustrating a method for determining the printability of a thermoplastic film for packaging of absorbent hygiene articles, the thermoplastic film comprising at least 30% recycled polymer material, the method comprising:

- Provide a sample of the thermoplastic film, preferably with a size of 10cm × 10cm (S100);

- Scan the sample to provide a pixelated image of the sample (S200);

- The pixelated image is analyzed by a computer using a thresholding method to convert the image into a binary image, wherein each pixel is determined to be either dark or light (S300);

- Define each group of adjacent pixels that are considered dark as gel points (S400);

- Define the gel dot size of each gel dot as the circle equivalent diameter of the pixel area of that gel dot (S500);

- Determine the amount of gel points (S600) indicating the number of gel points in the sample with a gel point size greater than or equal to 150 μm; and

- The relative gel point coverage area (S700) is determined using the circle equivalent diameter, indicating the relative area of the sample covered by gel points with a gel point size greater than or equal to 150 μm; and

- If the amount of gel points is less than or equal to a first threshold and the relative gel point coverage area is less than or equal to a second threshold, then the thermoplastic film is determined to be suitable for printing (S800); and

- If the amount of gel dots is greater than a first threshold and/or the relative gel dot coverage area is greater than a second threshold, then the thermoplastic film is determined to be unsuitable for printing (S800').

This method can use the RGB color model (RGB red, green, blue) to analyze pixelated images using computers.

Thresholding methods that convert an image into a binary image can include grayscale thresholding.

Next, a specific gel point evaluation method is described. While more general methods are disclosed in this application, it should be understood that this disclosure also relates to this specific gel point evaluation method itself. In particular, this disclosure also relates to packaging made from a film showing a gel point amount determined according to the specific gel point estimation method of less than or equal to 300 (e.g., less than or equal to 400) and a relative gel point coverage area of less than or equal to 12% (e.g., less than or equal to 20%). Furthermore, this disclosure also relates to packaging comprising a film having a non-printed area, wherein in the non-printed area, the film shows a gel point amount determined according to the specific gel point evaluation method of less than or equal to 300 (e.g., less than or equal to 400) and a relative gel point coverage area of less than or equal to 12% (e.g., less than or equal to 20%).

Description of gel point assessment method

The sample area with a size of 100×100mm is scanned in the membrane.

To provide a thermoplastic film sample (S100), a 110×110 mm sample is cut from the film. A frame defining an opening area of 100×100 mm is placed on the sample to define the area to be scanned.

To perform the step of scanning the sample to provide a pixelated image of the sample (S200), the frame and sample are positioned such that the film side faces the scanner glass. The sample should be flat, loose, and wrinkle-free. The scanner is then started.

The scanner used is an Epson Perfection V750Pro, and the settings are as follows:

Document type: Film (film face down)

Film type: Positive film

Image type: 24-bit color

Resolution: 2400

Calibration: Off

Configuration: No color correction

The sample was scanned three times without moving the sample or the frame during the scanning process.

The scanned images are provided to a computer, where they are analyzed as pixelated images.

To perform the step (S300) of computer analysis of a pixelated image using RGB spectrum (red, green, blue), Matlab is used.

The image is formed using the RGB spectrum.

Initially, the R, G, and B channels of each pixel in all three images are averaged to form a composite image.

The light components of the combined image can be normalized as described above and with reference to Figure 6 to account for any brightness variations.

The normalized image is then converted to a binary image, where each pixel is determined to be either dark or light. All pixels above a fixed grayscale threshold are classified as gel point pixels. The fixed grayscale threshold is a constant value applied after the image is normalized. For example, the fixed grayscale threshold can be determined by optimizing the threshold using the number of gel points in a manually counted sample as a reference. The grayscale threshold used in this example method is -4.05.

Each group of adjacent gel point pixels is defined as a single gel point.

The gel dot size of each gel dot is defined as the circle equivalent diameter of the pixel area of that gel dot (S500), and the amount of gel dots in the sample indicating the number of gel dots with a gel dot size greater than or equal to 150 μm is determined (S600), and the relative gel dot coverage area indicating the relative area of the sample covered by gel dots with a gel dot size greater than or equal to 150 μm is determined using the circle equivalent diameter (S700); using Matlab functions.

The equivalent diameter of a circle can be calculated as sqrt(4 * (pixel area) / π). If the gel point is circular and its area is the same as the pixel area of the gel point, then the equivalent diameter of the circle corresponds to the diameter (μm) that the gel point will have.

An image is resized by using a Matlab algorithm called bwareopen(image, p, conn) to remove small clusters of neighboring pixels, where p = the size of the clusters to be automatically removed. P is set to 15, and conn is set to 4. "P" represents the size of the clusters to be automatically removed, and "conn" represents the concatenation.

In addition, the solidity assessment (gel point pixels) of each group of adjacent pixels identified as dark is used to determine which groups are true gel points.

Solidity compares the pixel area of a group of gel dots to the area of the smallest possible rectangle that can enclose that group of gel dots. Solidity is defined as (gel dot pixel area) / (area of the smallest possible rectangle that can enclose that group of pixels). In this case, the solidity requirement is set to 0.3, meaning that adjacent pixel groups with a solidity less than 0.3 are considered non-gel dots.

The results of the Matlab computer analysis will be expressed as the amount of gel points and the relative area covered by the gel points.

In this example, the first threshold is set to 300 samples per 100 ^cm² , and the second threshold is set to 12%. Therefore, if the number of gel points is less than or equal to 300 and the relative gel point coverage area is less than or equal to 12%, the thermoplastic film is determined to be suitable for printing (S800).

Films deemed suitable for printing may optionally undergo further evaluation for the additional parameters mentioned in the overview section above.

The following describes various parameters measured on three different thermoplastic film samples. Sample 01 is a thermoplastic film made from virgin material and therefore does not include recycled polymer material. In this case, the virgin material is polyethylene, i.e., a fossil-based polymer. Therefore, Sample 01 is not a sample included in this disclosure but constitutes only a reference example for comparison. Sample 02 is a thermoplastic film comprising 33% recycled polymer material (PCR), with the remainder being the same virgin material as Sample 01. Sample 03 is a thermoplastic film comprising 55% recycled polymer material (PCR), with the remainder being the same virgin material as Sample 01.

The recycled polymer materials in Samples 02 and 03 comprise an unknown mixture of recycled polymer materials. The recycled polymer materials in Samples 02 and 03 originated from the same source of recycled materials.

All three samples, 01, 02, and 03, are single-layer extruded films.

All three samples were evaluated using the gel counting method described above to determine the amount of gel points and the relative gel point area, and several additional parameters shown in the table were also measured. As shown in the table below, for all three samples, the amount of gel points was less than or equal to 300, and the relative gel point coverage area was less than or equal to 12%. Several additional properties of the thermoplastic film material were also measured, as shown in the table.

The measurement parameters shown in the table above can be compared with the expected ranges described in the overview section above. Therefore, it was found that both Sample 02, with 33% recycled material, and Sample 03, with 55% recycled material, exhibit characteristics that make the material suitable for printing and use as packaging material for hygiene products.

Figures 2a and 2b are examples of scanned images from a sample, showing the distribution of gel dots on the thermoplastic film. Figure 2a is an example of a scanned image of the thermoplastic film, in this case one of three images taken from sample 02. Some gel dots may be perceived as darker spots in the image. Figure 2b is a histogram showing the distribution of gel dots in the image of Figure 2a. In this histogram, the first bar from the left represents the amount of gel dots with a size in the range of 150 to 300 μm, the second bar represents the amount of gel dots with a size in the range of 300 to 500 μm, and the third bar represents the amount of gel dots with a size greater than 500 μm.

As shown in Figure 2b, in this example histogram, the number of gel points for gel points with a size between 150 and 300 μm is approximately 190, the number of gel points for gel points with a size between 300 and 500 μm is approximately 10, and the number of gel points for gel points with a size greater than 500 μm is significantly less than 10. Therefore, this example histogram illustrates an example where the total number of gel points is less than 300.

As described in the specific gel point counting method example above, it is recommended that the first threshold be set to 300 (the amount of gel points is less than or equal to 300) and the second threshold be set to 12% (the relative gel point coverage area is less than or equal to 12%) in the overall method. These thresholds have been found to result in acceptable print quality of the thermoplastic film upon visual inspection after printing. Therefore, the method proposed herein offers advantages over previous processes for assessing the suitability of thermoplastic films for printing and packaging of hygiene products. These processes may involve, for example, manually assessing the presence of gel points by visually inspecting film samples under a microscope. In contrast, the method proposed herein offers greater reliability and efficiency.

Figure 3 is a flowchart of a method for forming packaging for absorbent sanitary articles, including:

- Provide a printed thermoplastic film material (S10) that is determined to be suitable for use in packaging of sanitary absorbent articles by any method disclosed in this application; and

- Forming a package of absorbent hygiene articles comprising the thermoplastic film (S20).

The method may include at least a portion of the printing film, taking advantage of the fact that the film has indeed been determined to be suitable for printing.

The packaging can be formed using any desired method for forming the packaging of absorbent hygiene articles, including thermoplastic films.

Specifically, the packaging forming step may include forming the thermoplastic film packaging such that the thermoplastic film forms the outer surface of the packaging.

Optionally, the packaging comprises the thermoplastic film as a co-extruded single-layer film.

Optionally, the step of forming the packaging includes folding the thermoplastic film to form a pocket or bag. Furthermore, the method may include filling the packaging with one or more absorbent hygiene items. For example, the absorbent items may be in the form of a stack of hygiene items.

Figure 4 shows a package 1 formed from a thermoplastic film 2. The film 2 forms the exterior of the package 1, and the exterior is at least partially printed with a pattern. The package 1 includes absorbent hygiene items 3, in this example, a stack of absorbent hygiene items 3.

Film 2 can be printed using any conventional thermoplastic film printing technique used for packaging absorbent hygiene products. Alternatively, the film can be printed using flexographic printing.

Optionally, and as shown in Figure 4, the film is printed such that the packaging displays a non-printed area 4 and a printed area 5. When the packaging 1 includes a non-printed area 4 having a size of at least 10 × 10 cm, the amount of gel dots and the relative gel dot coverage area can be measured in the non-printed area 4 of the packaging.

Figure 5 shows another package 1 formed from a thermoplastic film 2. The film 2 is folded to form a bag-shaped package 1. In this example, the package 1 includes a single absorbent hygiene item 3. However, it will be understood that the package 1 with the packaging shape shown in Figure 4 or the bag-shaped package 1 shown in Figure 5 may include one or more absorbent hygiene items 3. Furthermore, multiple individually packaged absorbent hygiene items 3 may be packaged in an outer package.

In other examples not shown, packaging may be provided for absorbent items such as absorbent paper towels or nonwoven fabrics.

Once the printability of a thermoplastic film for packaging absorbent hygiene products has been determined, it is conceivable that no further evaluation of the thermoplastic film is necessary. Therefore, packaging arrays can be formed from this thermoplastic film, for example, arrays comprising at least 1000 packages, or arrays comprising at least 10,000 packages. Thus, large quantities of packaging can be formed without needing to re-verify the film's suitability for printing and for packaging absorbent hygiene products.

However, since the use of recycled polymer materials inevitably means that the properties of the thermoplastic film will change each time a new source or batch of recycled polymer material is used, it is necessary to determine the printability of the thermoplastic film for the packaging of absorbent hygiene products for each new source or batch.

Claims (44)

1. A method for determining the printability of a thermoplastic film for packaging absorbent hygiene articles, said thermoplastic film comprising at least 30% recycled polymer material, said method comprising: - Provide a sample of the thermoplastic film (S100); - Scan the sample to provide a pixelated image of the sample (S200); - The pixelated image is analyzed by a computer using a thresholding method to convert the image into a binary image, wherein each pixel is determined to be either dark or light (S300); - Define each group of adjacent pixels that are determined to be dark as gel points (S400); - Define the gel dot size of each gel dot as the circle equivalent diameter of the pixel area of that gel dot (S500); - Determine the amount of gel points (S600) indicating the number of gel points in the sample having a gel point size greater than or equal to 150 μm; and - The relative gel point coverage area (S700) is determined using the equivalent diameter of the circle, indicating the relative area of the sample covered by gel points with a gel point size greater than or equal to 150 μm; and - If the amount of gel points is less than or equal to a first threshold and the relative gel point coverage area is less than or equal to a second threshold, then the thermoplastic film is determined to be suitable for printing (S800); and - If the amount of gel dots is greater than the first threshold and/or the relative gel dot coverage area is greater than the second threshold, then the thermoplastic film is determined to be unsuitable for printing (S800'). 2. The method according to claim 1, wherein the sample is 10cm × 10cm. 3. The method according to claim 1, wherein the first threshold is less than or equal to 450 samples per 100 ^cm² . 4. The method according to claim 3, wherein the first threshold is less than or equal to 300 samples per 100 ^cm² . 5. The method according to any one of claims 1-4, wherein the second threshold is less than or equal to 20%. 6. The method of claim 5, wherein the second threshold is less than or equal to 12%. 7. The method according to any one of claims 1-4, wherein the membrane comprises a coloring pigment in a membrane resin. 8. The method according to any one of claims 1-4, wherein the thickness of the membrane is between 20-70 μm. 9. The method according to any one of claims 1-4, wherein the membrane comprises less than 80% recycled polymer material. 10. The method according to any one of claims 1-4, wherein the membrane comprises: a. Total phthalate levels are in the range of 0.05 to 250 mg/kg (ppm); and/or b. The total amount of organotin compounds is in the range of 0.0003 to 0.5 mg/kg (ppm); and/or c. Total heavy metal content is in the range of 0.1 to 100 mg/kg (ppm); and/or d. The total amount of bisphenol A is in the range of 0.05 to 20 mg/kg (ppm). 11. The method of claim 10, wherein: The total amount of phthalates is in the range of 0.05 to 100 mg/kg (ppm). 12. The method according to claim 10, wherein: The total amount of phthalates is in the range of 0.05 to 20 mg/kg (ppm). 13. The method of claim 10, wherein: The total amount of organotin compounds ranged from 0.0003 to 0.1 mg/kg (ppm). 14. The method of claim 10, wherein: The total amount of organotin compounds ranged from 0.0003 to 0.02 mg/kg (ppm). 15. The method of claim 10, wherein: The total amount of heavy metals ranges from 0.1 to 60 mg/kg (ppm). 16. The method of claim 10, wherein: The total amount of heavy metals ranges from 0.1 to 30 mg/kg (ppm). 17. The method of claim 10, wherein: The total amount of bisphenol A is in the range of 0.05 to 10 mg/kg (ppm). 18. The method of claim 10, wherein: The total amount of bisphenol A is in the range of 0.05 to 5 mg/kg (ppm). 19. The method according to any one of claims 1-4, wherein the method comprises determining the haze of the thermoplastic film, and If the haze is within the haze range, then the film is determined to be suitable for printing and for packaging absorbent hygiene products. If the haze level is outside the specified haze range, then the film is determined to be unsuitable for printing and for packaging absorbent hygiene products. The haze range is less than 25%, and The haze is measured as the percentage of incident light that is scattered at a rate greater than 2.5° through the membrane. 20. The method of claim 19, wherein The haze range is less than 20%. 21. The method of claim 19, wherein The haze range is 4% to 18%. 22. The method according to any one of claims 1-4, wherein the method comprises: Determine the MD force along the machine direction of the membrane at 5% elongation, and If the MD force at 5% elongation is within the MD force range at 5% elongation, then the film is determined to be suitable for printing and for packaging of hygienic absorbent articles. If the MD force at 5% elongation is outside the range of MD forces at 5% elongation, then the film is determined to be unsuitable for printing and for packaging of hygienic absorbent articles. The MD force range at 5% elongation is greater than or equal to 3N/15mm. 23. The method of claim 22, wherein the MD force at 5% elongation ranges from 4 to 9 N/15 mm. 24. The method according to any one of claims 1-4, wherein the method comprises: Determine the CD force along the transverse direction of the membrane at 5% elongation, and If the CD force at 5% elongation is within the range of CD forces at 5% elongation, then the film is determined to be suitable for printing and for packaging of hygienic absorbent articles. If the CD force at 5% elongation is outside the range of CD forces at 5% elongation, then the film is determined to be unsuitable for printing and for packaging of hygienic absorbent articles. The CD force range at 5% elongation is greater than or equal to 3N/15mm. 25. The method of claim 24, wherein the CD force at 5% elongation ranges from 4 to 9 N/15 mm. 26. The method according to any one of claims 1-4, wherein the method further comprises: Determine the CD2% secant modulus along the transverse direction of the film. If the CD2% secant modulus is within the CD2% secant modulus range, then the film is determined to be suitable for printing and for packaging of sanitary absorbent articles. If the CD 2% secant modulus is outside the range of CD 2% secant modulus, then the film is determined to be unsuitable for printing and for packaging of sanitary absorbent articles. The CD 2% secant modulus ranges from 200 to 600 MPa. 27. The method according to any one of claims 1-4, wherein the method further comprises: Determine the MD2% secant modulus along the machine direction of the film. If the MD2% secant modulus is within the MD2% secant modulus range, then the film is determined to be suitable for printing and for packaging sanitary absorbent articles. If the MD 2% secant modulus is outside the MD 2% secant modulus range, then the film is determined to be unsuitable for printing and for packaging of sanitary absorbent articles. The MD 2% secant modulus ranges from 200 to 550 MPa. 28. A method of forming packaging for an absorbent article, comprising: -Provide thermoplastic film materials; - Determining the thermoplastic film to be suitable for printing for packaging of sanitary absorbent articles by performing the method according to any one of claims 1-27 (S10); and - Forming a package of a hygienic absorbent article comprising the thermoplastic film (S20). 29. The method of claim 28, comprising: - Print at least a portion of the film. 30. The method of claim 28 or 29, wherein the step of forming the packaging comprises forming the thermoplastic film packaging such that the thermoplastic film forms the outer surface of the packaging. 31. The method according to claim 28 or 29, wherein the packaging comprises the thermoplastic film as a co-extruded single-layer film. 32. The method of claim 28 or 29, wherein the step of forming the packaging comprises folding the thermoplastic film to form a pocket or bag. 33. The method of claim 28 or 29, comprising filling the package with absorbent sanitary articles. 34. The method of claim 33, wherein the absorbent article is a stack of sanitary articles. 35. The method of claim 33, wherein the absorbent article comprises absorbent paper towels or nonwoven fabric. 36. The method of claim 28 or 29, further comprising forming an array of packages of the film, the array comprising at least 1,000 packages. 37. The method of claim 36, wherein the array comprises at least 10,000 packages. 38. Packaging of an absorbent article made by the method according to any one of claims 28-37. 39. The packaging of claim 38, wherein the thermoplastic film comprises at least 30% to 80% recycled polymer by weight, and the thermoplastic film has a continuous non-printed area (4) of at least 10 × 10 cm, wherein, as determined by the method of any one of claims 1-27, the thermoplastic film has a gel point quantity of less than or equal to 450 per 100 ^cm² sample, and the relative coverage area of the gel points is less than or equal to 20%. 40. The packaging according to claim 39, wherein the thermoplastic film has a printed area (5) outside the continuous non-printed area (4) in the packaging. 41. The packaging according to claim 40, wherein the thermoplastic film is transparent, at least in the non-printed area. 42. The packaging according to claim 38 or 39, wherein the thermoplastic film comprises a coloring pigment in a film resin. 43. The packaging according to claim 38 or 39, comprising absorbent sanitary articles. 44. An array of at least 1,000 packages according to any one of claims 38-43, the packages having similar appearance and contents.