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Guangdong Open University: Development and Application of Slip and Anti-blocking Masterbatch for PET Sheets

Engineering plastics applications 2025-03-04 10:28:28
Abstract: Polyethylene terephthalate (PET) sheets have a high coefficient of friction on their surface, leading to adhesion phenomena when the material comes into contact with equipment surfaces. This is not conducive to the production, secondary processing, downstream packaging, storage, and use of PET sheets. To address this issue, the effects of slip and anti-blocking masterbatch on the frictional properties, thermoforming performance, and optical properties of PET sheets were studied. Anti-blocking particles can make the sheet surface protrude, reducing the contact area. Slip agents can reduce the coefficient of friction. As an inorganic anti-blocking agent, silica can form a stable anti-blocking effect on the sheets. Composite wax (containing several waxes with different melting points) can create a slip gradient within the sheet, effectively lowering the coefficient of friction. A high-performance slip and anti-blocking masterbatch was developed using silica and composite wax as the main components. Test results show that adding the self-made slip and anti-blocking masterbatch significantly reduces the coefficient of friction of PET sheets, demonstrating excellent sliding performance. In further thermoforming processes, the self-made slip and anti-blocking masterbatch significantly improved the anti-blocking effect of PET sheets, allowing the thermoformed cups to exhibit excellent stacking and removal performance. Optical property tests indicate that the self-made slip and anti-blocking masterbatch can enhance the slip and anti-blocking properties of PET sheets while minimizing the negative impact on their optical properties. The performance of the self-made slip and anti-blocking masterbatch meets or exceeds that of high-quality imported masterbatches.
Abstract: Polyethylene terephthalate (PET) sheets have a high coefficient of friction on their surface, leading to adhesion phenomena when the material comes into contact with equipment surfaces. This is not conducive to the production, secondary processing, downstream packaging, storage, and use of PET sheets. To address this issue, the effects of slip and anti-blocking masterbatch on the frictional properties, thermoforming performance, and optical properties of PET sheets were studied. Anti-blocking particles can make the sheet surface protrude, reducing the contact area. Slip agents can reduce the coefficient of friction. As an inorganic anti-blocking agent, silica can form a stable anti-blocking effect on the sheets. Composite wax (containing several waxes with different melting points) can create a slip gradient within the sheet, effectively lowering the coefficient of friction. A high-performance slip and anti-blocking masterbatch was developed using silica and composite wax as the main components. Test results show that adding the self-made slip and anti-blocking masterbatch significantly reduces the coefficient of friction of PET sheets, demonstrating excellent sliding performance. In further thermoforming processes, the self-made slip and anti-blocking masterbatch significantly improved the anti-blocking effect of PET sheets, allowing the thermoformed cups to exhibit excellent stacking and removal performance. Optical property tests indicate that the self-made slip and anti-blocking masterbatch can enhance the slip and anti-blocking properties of PET sheets while minimizing the negative impact on their optical properties. The performance of the self-made slip and anti-blocking masterbatch meets or exceeds that of high-quality imported masterbatches.
Abstract: Polyethylene terephthalate (PET) sheet has a high coefficient of friction on its surface, which leads to the material easily adhering to the equipment surface, causing sticking phenomena. This is not conducive to the production, secondary processing, downstream packaging, storage, and use of PET sheets. To address this issue, the effect of slip and anti-blocking masterbatch on the friction properties, thermoforming performance, and optical properties of PET sheets was studied. Anti-blocking particles can make the sheet surface protrude, reducing the contact area. Slip agents can lower the coefficient of friction. As an inorganic anti-blocking agent, silica can create a stable anti-blocking effect on the sheets. Composite wax (containing several waxes with different melting points) can form a slip gradient in the sheets, effectively reducing the coefficient of friction. A high-performance slip and anti-blocking masterbatch was developed using silica and composite wax as the main components. Test results showed that adding the self-made slip and anti-blocking masterbatch significantly reduced the coefficient of friction of PET sheets, demonstrating excellent sliding performance. In further thermoforming processes, the self-made slip and anti-blocking masterbatch significantly improved the anti-blocking effect of PET sheets, allowing the cups after thermoforming to exhibit excellent stacking and removal performance. Optical property tests indicated that the self-made slip and anti-blocking masterbatch could enhance the slip and anti-blocking properties of PET sheets while minimizing the negative impact on their optical properties. The performance of the self-made slip and anti-blocking masterbatch reached or exceeded that of similar high-quality imported masterbatches.
Polyethylene terephthalate (PET) is an engineering plastic with excellent comprehensive properties, featuring colorless, transparent, odorless, tasteless, non-toxic, superior mechanical properties, and recyclability. It is widely used in the packaging of food, beverages, cosmetics, pharmaceuticals, and electronic products [1-4]. Among various packaging forms, thermoforming packaging is one of the important application areas for PET. Thermoforming packaging primarily uses PET sheets as the molding object [2]. Due to the high coefficient of friction on the surface of PET sheets, they tend to have high adhesion, leading to sticking phenomena on the equipment surface, which is not conducive to the production, secondary processing, downstream packaging, storage, and use of PET sheets [2-4]. To solve this problem, adding slip and anti-blocking agents to PET sheets can make the surface slippery and reduce the coefficient of friction, effectively preventing sticking [3-4]. For convenience, slip and anti-blocking agents are usually made into slip and anti-blocking masterbatches, which are then added to PET sheets [4]. In this study, targeting PET sheets, and referring to the S-589 type slip and anti-blocking masterbatch produced by Swiss company SUKANO (mainly composed of silica and stearic acid ester), we innovatively used composite wax in the masterbatch to develop a new type of slip and anti-blocking masterbatch. By incorporating several waxes with different melting points, a slip gradient is formed, which can effectively reduce the coefficient of friction of the sheets.
Polyethylene terephthalate (PET) is an engineering plastic with excellent overall performance, characterized by being colorless, transparent, odorless, tasteless, non-toxic, and having superior mechanical properties as well as the characteristic of being recyclable and reusable. It is widely used in the packaging fields of food, beverages, cosmetics, pharmaceuticals, electronic products, etc. [1-4]. Among various forms of packaging, blister packaging is one of the important application areas for PET. Blister packaging mainly uses PET sheets as the forming material [2]. Due to the high surface friction coefficient of PET sheets themselves, it leads to a significant adhesion on the surface, causing sticking phenomena when they adhere to the equipment surface, which is not conducive to the production, secondary processing, downstream packaging, storage, and use of PET sheets [2-4]. To solve this problem, adding slip agents and anti-blocking agents to PET sheets can make the surface slippery and reduce the surface friction coefficient, effectively preventing the sticking phenomenon [3-4]. For ease of use, slip agents and anti-blocking agents are typically made into slip and anti-blocking masterbatches and then added to PET sheets [4]. The author, targeting PET sheets and referring to the S-589 type slip and anti-blocking masterbatch produced by Swiss company SUKANO (main components are silica and stearic acid esters), innovatively adopted a composite wax in the masterbatch to develop a new type of slip and anti-blocking masterbatch. By including several waxes with different melting points, a slip gradient is formed, which can effectively reduce the friction coefficient of the sheets.

1 Experimental Section

1.1 Main Raw Materials

PET pellets: intrinsic viscosity of 0.7~0.9 dL/g, Sinopec Yizheng Chemical Fiber Co., Ltd.;
Silica: SYLOBLOC, Grace Company, USA;
Composite wax: formulated from fatty acid esters with different alkyl chain lengths, Glycolube VL, LONZA Company, USA;
Imported high-quality slip and anti-blocking masterbatch: S-589, mainly composed of silica and stearic acid ester, SUKANO Company, Switzerland.

1.2 Main Equipment and Instruments

PET sheet extrusion production line: GW120-GF1200, GPM Machinery (Shanghai) Co., Ltd.;
Cup-shaped thermoforming machine: self-made;
Field emission scanning electron microscope (FESEM): JSM-7800 F, JEOL Ltd., Japan;
Friction coefficient/peel strength tester: PFT-F1, Labthink Instruments Co., Ltd., Jinan;
Topsizer laser particle size analyzer: OMEC Instruments Co., Ltd., Zhuhai;
Transmittance/haze meter: WGT-S, Labthink Instruments Co., Ltd., Jinan.

1.3 Preparation of PET Slip and Anti-blocking Masterbatch

The main components of the slip and anti-blocking masterbatch are silica (particle size 3~10 μm, mass fraction 5%~10%) and composite wax (mass fraction 5%~10%), using PET chips as the carrier resin. By adjusting the ratios of each component and the particle size of the anti-blocking agent (synthetic high-purity silica), self-made slip and anti-blocking masterbatches 1#, 2#, and 3# were obtained. See Table 1 for details.

Table 1 Formulations of self-made slipping and anti-blocking masterbatchTab. 1 Formulations of self-made slipping and anti-blocking masterbatch

 

1.3 Preparation of PET Slip and Anti-blocking Masterbatch

1.3 Preparation of PET Slip and Anti-blocking Masterbatch

1.3 Preparation of PET Slip and Anti-blocking Masterbatch
The main components of the slip and anti-blocking masterbatch are silica (particle size 3~10 μm, mass fraction 5%~10%) and composite wax (mass fraction 5%~10%). The carrier resin used is PET chips. By adjusting the ratios of each component and the particle size of the anti-blocking agent (synthetic high-purity silica), self-made slip and anti-blocking masterbatches 1#, 2#, and 3# were obtained, as detailed in Table 1.

Table 1 Formulations of self-made slipping and anti-blocking masterbatch

 

Table 1 Formulations of self-made slipping and anti-blocking masterbatch

 

 

1.4 Preparation of PET Sheets

To track and compare the impact of self-made slip and anti-blocking masterbatch on the performance of PET sheets, imported high-quality slip and anti-blocking masterbatch was chosen as the comparison standard. Five PET sheets of the same thickness were prepared: #1, #2, and #3 sheets added with self-made slip and anti-blocking masterbatches #1, #2, and #3 respectively; #4 sheet added with imported high-quality slip and anti-blocking masterbatch; and #5 sheet without any slip and anti-blocking masterbatch. Additionally, to facilitate the evaluation of the performance of each slip and anti-blocking masterbatch, the mass fraction of the masterbatch added during the routine production of PET sheets by the enterprise, which is 1%, was used.
The preparation of PET sheets mainly includes the following process flows and parameters. (1) Raw material crystallization and drying. Heat the PET granules for crystallization, controlling the time at 3.5 to 4.5 hours, with a temperature of 160 to 170 °C. During crystallization, dry the PET material to ensure a moisture content of less than 0.005%. (2) Melt extrusion. Melt the PET material and extrude it into sheets using an extruder, with the temperature controlled between 240 and 275 °C. (3) Cooling and shaping. Rapidly cool or slice the extruded PET sheets through a three-roll calender, with the top roll set at 30°C, the middle roll at 45°C, and the bottom roll at 60°C. (4) Winding of the product. The thickness of the PET sheets is 0.24 mm. The slip and anti-blocking masterbatch is directly added from the side feeding port in a separate manner.

1.4 Preparation of PET Sheets

1.4 Preparation of PET Sheets

1.4 Preparation of PET Sheets
To track and compare the impact of self-made slip and anti-blocking masterbatch on the performance of PET sheets, imported high-quality slip and anti-blocking masterbatch was chosen as the comparison standard. Five PET sheets of the same thickness were prepared: #1, #2, and #3 sheets added with self-made slip and anti-blocking masterbatches #1, #2, and #3 respectively; #4 sheet added with imported high-quality slip and anti-blocking masterbatch; and #5 sheet without any slip and anti-blocking masterbatch. Additionally, to facilitate the evaluation of the performance of each slip and anti-blocking masterbatch, the mass fraction of the masterbatch added during the routine production of PET sheets by the enterprise, which is 1%, was used.
To track and compare the performance impact of self-made slip and anti-blocking masterbatch on PET sheets, an imported high-quality slip and anti-blocking masterbatch was chosen as the benchmark. Five PET sheets of the same thickness were prepared: Sheets 1#, 2#, and 3# were added with self-made slip and anti-blocking masterbatches 1#, 2#, and 3# respectively; Sheet 4# was added with the imported high-quality slip and anti-blocking masterbatch; and Sheet 5# did not contain any slip and anti-blocking masterbatch. Additionally, to facilitate the evaluation of the performance of each slip and anti-blocking masterbatch, the mass fraction of the masterbatch added during the routine production of PET sheets by the enterprise, i.e., 1%, was used.
The preparation of PET sheets mainly includes the following process flows and parameters. (1) Raw material crystallization and drying. Heat the PET pellets for crystallization, controlling the time between 3.5 to 4.5 hours, at a temperature of 160 to 170 ℃. Dry the PET material simultaneously, ensuring the moisture content is less than 0.005%. (2) Melting and extrusion. Melt the PET material and extrude it into sheets using an extruder, with the temperature controlled between 240 to 275 ℃. (3) Cooling and setting. Rapidly cool or slice the extruded PET sheet through a three-roll calender, where the top roll temperature is set to 30℃, the middle roll to 45℃, and the bottom roll to 60℃. (4) Winding of the product. The thickness of the PET sheet is 0.24 mm. The slip and anti-blocking masterbatch is directly added via a side feeding method, separately from the feeding port.

1.5 Performance Testing

(1) Coefficient of friction is tested according to GB/T 10006-2021.
(2) Transmittance and haze are tested according to GB/T 2410-2008.

1.5 Performance Testing

1.5 Performance Testing

1.5 Performance Testing
(1) Coefficient of friction is tested according to GB/T 10006-2021.
(1) Coefficient of friction is tested according to GB/T 10006-2021.
(2) Transmittance and haze are tested according to GB/T 2410-2008.
(2) Transmittance and haze are tested according to GB/T 2410-2008.

 

2 Results and Analysis

2.1 Selection of Slip and Anti-blocking Agents and Surface Treatment

The mechanism of slip and anti-blocking is that the anti-blocking agent particles cause protrusions on the sheet surface, reducing the contact area, while the slip agent reduces the coefficient of friction. The anti-blocking agent forms sub-microscopic protrusions and depressions on the PET sheet surface, reducing the contact area and decreasing the adhesion between sheets [5-6]. This helps to improve the surface properties of the film, reducing the blocking phenomenon during use and processing, making it easier to peel or slide vertically or horizontally, and facilitating demolding in the thermoforming process. When selecting an anti-blocking agent, multiple factors need to be considered, including cost, effectiveness, particle size, hardness, safety, impurity content, and interactions with other additives [7-9]. Commonly used anti-blocking agents include inorganic and organic types. Among them, inorganic anti-blocking agents are cheaper and more practical, and are also more widely used [9]. After adding the slip agent to the PET sheet, it migrates from the interior of the product to the surface during processing. This migration process allows the slip agent to form a uniform thin coating on the surface of the product, which has a lubricating effect, thereby reducing the coefficient of friction on the surface of the product [5-6]. When the surface of the product comes into contact with other surfaces, the friction force between them is significantly reduced due to the presence of the coating. However, if the slip agent is used improperly or in excess, it can increase the haze of the sheet, leading to the migration of white fog-like substances, which negatively affects the optical properties of the sheet [6-7].
To achieve the optimal balance between the sliding performance and anti-blocking of PET sheets, anti-blocking agents and slip agents are usually used in combination [9-10]. The surface structure formed by the anti-blocking agent can reduce the actual contact surface area, thus providing a certain degree of slip effect. However, when the amount of anti-blocking agent added is too large, it can have the opposite effect, increasing the coefficient of friction of the PET sheet, deteriorating optical performance, increasing haze, and reducing transparency [9-10]. Therefore, when selecting and using anti-blocking agents, it is necessary to carefully control the amount added to ensure the best balance between the sliding performance, anti-blocking, and optical performance of the PET sheet.
The author chose and used inorganic anti-blocking agent—silica, mainly based on the following considerations: Firstly, high-purity silica was preferred because its refractive index is similar to that of PET; secondly, the particle size and quantity of silica play a decisive role in the anti-blocking effect; furthermore, the particle size distribution (i.e., particle size) also significantly affects the anti-blocking effect. A narrow particle size distribution, with good particle uniformity, and a particle size of about 5 μm is the best, to fully utilize the effective anti-blocking effect at this particle size. The particle size distribution of silica is shown in Figure 1.

Figure 1 Particle Size Distribution of Silica

2.1 Selection and Surface Treatment of Slip and Anti-blocking Agents

2.1 Selection and Surface Treatment of Slip and Anti-blocking Agents

2.1 Selection and Surface Treatment of Slip and Anti-blocking Agents
The mechanism of slip and anti-blocking is that the particles of the anti-blocking agent cause protrusions on the surface of the sheet, reducing the contact area, while the slip agent reduces the coefficient of friction. The anti-blocking agent forms sub-microscopic protrusions and depressions on the surface of the PET sheet, reducing the contact area and decreasing the adhesion between sheets [5-6]. This helps to improve the surface properties of the film, reducing the sticking phenomenon during use and processing, making it easier for the sheets to be peeled off vertically or slide horizontally, and facilitating demolding in the thermoforming process. When selecting an anti-blocking agent, multiple factors need to be considered, including cost, effectiveness, particle size, hardness, safety, impurity content, and interactions with other additives [7-9]. Commonly used anti-blocking agents include inorganic and organic types. Among them, inorganic anti-blocking agents are cheaper and more practical, and are also more widely used [9]. After adding a slip agent to the PET sheet, it will migrate from the interior of the product to the surface during processing. This migration process allows the slip agent to form a uniform thin coating on the surface of the product, which has a lubricating effect and reduces the coefficient of friction on the surface of the product [5-6]. When the surface of the product comes into contact with the surface of another object, the friction between them is significantly reduced due to the presence of the coating. However, if the slip agent is used improperly or in excess, it can increase the haze of the sheet, leading to the migration of white fog-like substances, thereby having a negative impact on the optical properties of the sheet [6-7].
The mechanism of slip and anti-blocking is that the particles of the anti-blocking agent cause protrusions on the surface of the sheet, reducing the contact area, while the slip agent reduces the coefficient of friction. The anti-blocking agent forms sub-microscopic protrusions and depressions on the surface of the PET sheet, reducing the contact area and decreasing the adhesion between sheets [5-6], which helps to improve the surface properties of the film, reducing the sticking phenomenon during use and processing, making it easier for the sheets to be peeled off vertically or slide horizontally, and facilitating demolding in the thermoforming process. When selecting an anti-blocking agent, multiple factors need to be considered, including cost, effectiveness, particle size, hardness, safety, impurity content, and interactions with other additives [7-9]. Commonly used anti-blocking agents include inorganic and organic types. Among them, inorganic anti-blocking agents are cheaper and more practical, and are also more widely used [9]. After adding a slip agent to the PET sheet, it will migrate from the interior of the product to the surface during processing. This migration process allows the slip agent to form a uniform thin coating on the surface of the product, which has a lubricating effect and reduces the coefficient of friction on the surface of the product [5-6]. When the surface of the product comes into contact with the surface of another object, the friction between them is significantly reduced due to the presence of the coating. However, if the slip agent is used improperly or in excess, it can increase the haze of the sheet, leading to the migration of white fog-like substances, thereby having a negative impact on the optical properties of the sheet [6-7].
To achieve the optimal balance between the sliding performance and anti-blocking of PET sheets, it is common to use a combination of anti-blocking agents and slip agents [9-10]. The surface structure formed by the anti-blocking agent can reduce the actual contact surface area, thereby serving as a slip agent to some extent. However, when the amount of the anti-blocking agent added is too large, it may have the opposite effect, increasing the coefficient of friction of the PET sheet, worsening optical properties, increasing haze, and reducing transparency [9-10]. Therefore, when selecting and using anti-blocking agents, it is necessary to carefully control the amount added to ensure the best balance between the sliding performance, anti-blocking, and optical properties of the PET sheet.
The author chose and used inorganic anti-blocking agents—silica, mainly based on the following considerations: Firstly, high-purity silica was preferred because its refractive index is close to that of PET; secondly, the particle size and number of silica particles play a decisive role in the anti-blocking effect; additionally, the distribution of particle sizes (i.e., particle size) also significantly affects the anti-blocking effect. A narrow particle size distribution with good uniformity, especially around 5 μm, is optimal, allowing for the full utilization of the effective anti-blocking effect at this particle size. The particle size distribution of silica is shown in Figure 1.

Figure 1   Particle size distribution of silicon dioxide

Figure 1   Particle size distribution of silicon dioxide
Finally, by coating the surface of silica particles with an ester material, secondary agglomeration of the particles can be prevented. After the particle surface is organically modified, the surface becomes blurred, improving compatibility with the PET matrix. Figure 2 shows the morphology of silica particles after surface treatment, magnified 1,000 times. As can be seen from Figure 2, the treated particle surface exhibits optical characteristics that are isotropic in all directions with the base PET, ensuring a smooth and anti-blocking effect while reducing the impact on the optical properties of the sheet.

Figure 2   Morphology of silicon dioxide particles after surface treatment (×1,000)

Figure 2 Morphology of silicon dioxide particles after surface treatment (×1 000)
Selecting and using composite wax as a slip agent. Composite wax, formulated with fatty acid esters of different alkyl chain lengths and several waxes with different melting points, can form a slip gradient, thereby effectively reducing the coefficient of friction of the sheet.
Selecting and using composite wax as a slip agent. Composite wax, formulated with fatty acid esters of different alkyl chain lengths and several waxes with different melting points, can form a slip gradient, thereby effectively reducing the coefficient of friction of the sheet.

2.2 Friction Properties of PET Sheets

The friction coefficient of PET sheets is an important indicator for evaluating their surface sliding performance, including static friction coefficient and dynamic friction coefficient [11]. According to GB/T 10006-2021, the static friction coefficient is the ratio of the static friction force to the normal force, reflecting the initial resistance of the PET sheet surface; the dynamic friction coefficient is the ratio of the dynamic friction force to the normal force, reflecting the sliding performance of the PET sheet surface [10-11]. In the production and use of PET sheets, the friction coefficient is directly related to the sliding performance of the sheets, the operating speed of automated production equipment, the operability and demolding performance in processes such as thermoforming, as well as the forming efficiency and quality [10-11]. Generally, a friction coefficient below 0.2 indicates that the PET sheet has high sliding performance; above 0.4 indicates low sliding performance; and between the two indicates medium sliding performance [10-11].
After preparing five types of PET sheets (1#~5#) with the same thickness, their static and dynamic friction coefficients were tested, and the results are shown in Table 2. The 1#~4# PET sheets all contained slip and anti-blocking masterbatch, thus allowing the measurement of the friction coefficients; however, the 5# sheet, without the addition of slip and anti-blocking masterbatch, had too high a friction coefficient to be measured. This shows that the slip and anti-blocking masterbatch can effectively reduce the friction coefficient of PET sheets.

Table 2 Comparison of Friction Coefficient of PET Sheets Tab. 2 Comparison of friction coefficient of PET sheets

 

The 1#~3# PET sheets were respectively added with self-made slip and anti-blocking masterbatches 1#, 2#, and 3#, while the 4# sheet was added with imported high-quality slip and anti-blocking masterbatch. Comparing the friction coefficients, it can be seen that the 1#~4# sheets all have lower friction coefficients, with the 2# sheet, which contains the 2# self-made slip and anti-blocking masterbatch, having the lowest static and dynamic friction coefficients, below 0.2, indicating high sliding performance. From the perspective of the impact on the friction coefficient of PET sheets, the 2# self-made slip and anti-blocking masterbatch outperforms the imported high-quality slip and anti-blocking masterbatch.
The particle size and quantity of silica in the slip and anti-blocking masterbatch significantly affect the properties of the sheets. If the particle size is too small, it is difficult to produce effective protrusions; if the particle size is too large, it can easily cause pitting on the appearance of the PET sheet, and even lead to easy detachment. Under the same proportion of masterbatch addition, a larger particle size will also result in a decrease in the number of particles, negatively impacting the anti-blocking performance of the sheets. The 5 μm particles

2.2 Friction Properties of PET Sheets

2.2 Friction Properties of PET Sheets

2.2 Friction Properties of PET Sheets
The coefficient of friction of PET sheets is an important indicator for evaluating their surface sliding performance, including static and dynamic coefficients of friction [11]. According to GB/T 10006-2021, the static coefficient of friction refers to the ratio of static friction force to normal force, reflecting the initial resistance of the PET sheet's surface; the dynamic coefficient of friction refers to the ratio of dynamic friction force to normal force, reflecting the sliding performance of the PET sheet's surface [10-11]. During the production and use of PET sheets, the coefficient of friction directly affects the sliding performance of the sheets, the operating speed of automated production equipment, the operability and demolding performance in processes such as thermoforming, and the efficiency and quality of molding [10-11]. Generally, a coefficient of friction below 0.2 indicates that the PET sheet has high sliding performance; above 0.4 indicates low sliding performance; and between the two indicates medium sliding performance [10-11].
The coefficient of friction of PET sheets is an important indicator for evaluating their surface sliding performance, including static and dynamic coefficients of friction [11]. According to GB/T 10006-2021, the static coefficient of friction refers to the ratio of static friction force to normal force, reflecting the initial resistance of the PET sheet's surface; the dynamic coefficient of friction refers to the ratio of dynamic friction force to normal force, reflecting the sliding performance of the PET sheet's surface [10-11]. During the production and use of PET sheets, the coefficient of friction directly affects the sliding performance of the sheets, the operating speed of automated production equipment, the operability and demolding performance in processes such as thermoforming, and the efficiency and quality of molding [10-11]. Generally, a coefficient of friction below 0.2 indicates that the PET sheet has high sliding performance; above 0.4 indicates low sliding performance; and between the two indicates medium sliding performance [10-11].
After preparing five PET sheets (No. 1-5) of the same thickness, their static and dynamic coefficients of friction were tested, with the results shown in Table 2. The PET sheets No. 1-4 all contained slip and anti-blocking masterbatch, allowing for the measurement of the coefficient of friction; however, the coefficient of friction for sheet No. 5 was too high to measure due to the absence of slip and anti-blocking masterbatch. This indicates that the slip and anti-blocking masterbatch can effectively reduce the coefficient of friction of PET sheets.
After preparing five PET sheets (No. 1-5) of the same thickness, their static and dynamic coefficients of friction were tested, with the results shown in Table 2. The PET sheets No. 1-4 all contained slip and anti-blocking masterbatch, allowing for the measurement of the coefficient of friction; however, the coefficient of friction for sheet No. 5 was too high to measure due to the absence of slip and anti-blocking masterbatch. This indicates that the slip and anti-blocking masterbatch can effectively reduce the coefficient of friction of PET sheets.

Table 2   Comparison of friction coefficient of PET sheets Tab. 2   Comparison of friction coefficient of PET sheets

 

Table 2   Comparison of friction coefficient of PET sheets Tab. 2   Comparison of friction coefficient of PET sheets

Table 2   Comparison of friction coefficient of PET sheets Tab. 2   Comparison of friction coefficient of PET sheets

 

 
PET sheets No.1 to No.3 were respectively added with self-made slip and anti-blocking masterbatches No.1, No.2, and No.3, while sheet No.4 was added with imported high-quality slip and anti-blocking masterbatch. Comparing the friction coefficients, it can be seen that all the friction coefficients of sheets No.1 to No.4 are relatively low, among which, the static and dynamic friction coefficients of sheet No.2, which was added with self-made slip and anti-blocking masterbatch No.2, are the lowest, below 0.2, indicating a high sliding performance on the surface. From the perspective of the influence on the friction coefficient of PET sheets, the self-made slip and anti-blocking masterbatch No.2 is superior to the imported high-quality slip and anti-blocking masterbatch.
1#~3# PET sheets were respectively added with self-made slip and anti-blocking masterbatches #1, #2, and #3, while sheet #4 was added with imported high-quality slip and anti-blocking masterbatch. By comparing the friction coefficients, it can be seen that the friction coefficients of sheets #1 to #4 are all relatively low, among which the static and dynamic friction coefficients of sheet #2, which contains self-made slip and anti-blocking masterbatch #2, are the lowest, below 0.2, indicating a high sliding performance on its surface. From the perspective of the impact of the slip and anti-blocking masterbatch on the friction coefficient of PET sheets, self-made slip and anti-blocking masterbatch #2 is superior to the imported high-quality slip and anti-blocking masterbatch.
The particle size and quantity of silica in the slip and anti-blocking masterbatch significantly affect the properties of the sheet. If the particle size is too small, it is difficult to produce effective protrusions; if the particle size is too large, it can easily cause pitting on the appearance of the PET sheet, or even lead to easy detachment. Under the same proportion of masterbatch addition, an overly large particle size will also result in a reduced number of particles, negatively impacting the sheet's anti-blocking performance. A particle size of 5 μm, however, can both produce effective protrusions without leading to detachment and ensure a sufficient number of particles under the same proportion of masterbatch addition. Therefore, the frictional performance of the sheet added with self-made slip and anti-blocking masterbatch #2 is superior to other products.
The particle size and quantity of silica in the slip and anti-blocking masterbatch significantly affect the properties of the sheet. If the particle size is too small, it is difficult to produce effective protrusions; if the particle size is too large, it can easily cause pitting on the appearance of the PET sheet, or even lead to easy detachment. Under the same proportion of masterbatch addition, an overly large particle size will also result in a reduced number of particles, negatively impacting the sheet's anti-blocking performance. A particle size of 5 μm, however, can both produce effective protrusions without leading to detachment and ensure a sufficient number of particles under the same proportion of masterbatch addition. Therefore, the frictional performance of the sheet added with self-made slip and anti-blocking masterbatch #2 is superior to other products.

2.3 The Impact of Slip and Anti-blocking Performance on the Thermoforming Process of PET Sheets

PET sheets are widely used in thermoformed packaging. As one of the commonly adopted thermal forming technologies in packaging, thermoforming is characterized by its environmental friendliness, low cost, high efficiency, and suitability for automated production [2]. Thermoformed packaging primarily uses PET sheets as the forming material, which, after being heated and softened, undergoes surface stretching to form the desired shape on the mold contour [2]. Following this, through processes such as cooling, setting, edge cutting, and trimming, the final product, such as a plastic cup, is obtained [2].
The sliding performance of PET sheets directly affects the friction coefficient between the sheet and the mold during the thermoforming process, thereby impacting the forming speed and quality [12]. Generally, the better the sliding performance, the smaller the friction coefficient, making it easier for the PET sheet to be released from the mold, thus improving production efficiency and achieving better forming results. Additionally, reducing friction resistance can also decrease energy consumption.
The anti-blocking performance of PET sheets determines the degree of adhesion to the mold during the thermoforming process, affecting the ease of forming and the smoothness of demolding [13]. Generally, the better the anti-blocking performance, the lower the degree of adhesion, making the thermoforming process easier and the demolding more smooth.
Five types of PET sheets (No. 1~5) with the same thickness were prepared, processed into cups using the thermoforming process, and stretched ten times. The effect of stacking and taking out after thermoforming was compared, as detailed in Table 3. No. 1~4 sheets all contained slip and anti-blocking masterbatch, resulting in good stacking and taking out effects after thermoforming; however, since No. 5 did not contain the slip and anti-blocking masterbatch, the sheets could not be separated. This indicates that the slip and anti-blocking performance of PET sheets is a critical factor in the thermoforming process. After thermoforming, the stacking and taking out effects of the cups made from sheets No. 2 and No. 4 were comparable and better than those of No. 1, and significantly better than those of No. 3. From the perspective of the stacking and taking out effect of the thermoformed PET products, it can be seen that the homemade slip and anti-blocking masterbatch (No. 2) performs as well as the imported high-quality slip and anti-blocking masterbatch (No. 4).

Table 3 Comparison of the Effect of Product Stacking and Taking Out After Thermoforming of PET Sheets Tab. 3 Comparison of the Effect of Product Stacking and Taking Out After Thermoforming of PET Sheets

 

2.3 The Impact of Slip and Anti-blocking Properties on the Thermoforming Process of PET Sheets

2.3 The Impact of Slip and Anti-blocking Properties on the Thermoforming Process of PET Sheets

2.3 The Impact of Slip and Anti-blocking Properties on the Thermoforming Process of PET Sheets
PET sheets are widely used in thermoformed packaging. As one of the extensively adopted thermal forming technologies in packaging, the thermoforming process is characterized by its environmental friendliness, low cost, high efficiency, and suitability for automated production [2]. In the thermoforming of packaging, PET sheets are primarily the object of formation. After being heated and softened, the sheets undergo surface stretching to form the desired shape on the mold contour [2]. Subsequently, through processes such as cooling, shaping, edge cutting, and trimming, the final product, such as a plastic cup, is obtained [2].
PET sheets are widely used in thermoformed packaging. As one of the extensively adopted thermal forming technologies in packaging, the thermoforming process is characterized by its environmental friendliness, low cost, high efficiency, and suitability for automated production [2]. In the thermoforming of packaging, PET sheets are primarily the object of formation. After being heated and softened, the sheets undergo surface stretching to form the desired shape on the mold contour [2]. Subsequently, through processes such as cooling, shaping, edge cutting, and trimming, the final product, such as a plastic cup, is obtained [2].
The slip properties of PET sheets directly affect the coefficient of friction between the sheet and the mold during the thermoforming process, thereby influencing the forming speed and quality [12]. Generally, the better the slip properties, the lower the coefficient of friction, making it easier for the PET sheet to be released from the mold, thus improving production efficiency and achieving better forming results. Additionally, reducing frictional resistance can also decrease energy consumption.
The slip properties of PET sheets directly affect the coefficient of friction between the sheet and the mold during the thermoforming process, thereby influencing the forming speed and quality [12]. Generally, the better the slip properties, the lower the coefficient of friction, making it easier for the PET sheet to be released from the mold, thus improving production efficiency and achieving better forming results. Additionally, reducing frictional resistance can also decrease energy consumption.
The anti-blocking properties of PET sheets determine the degree of adhesion between the sheet and the mold during the thermoforming process, which in turn affects the ease of forming and the smoothness of demolding [13]. Generally, the better the anti-blocking properties, the lower the degree of adhesion, making the thermoforming process easier and the demolding more smooth.
The anti-blocking properties of PET sheets determine the degree of adhesion between the sheet and the mold during the thermoforming process, which in turn affects the ease of forming and the smoothness of demolding [13]. Generally, the better the anti-blocking properties, the lower the degree of adhesion, making the thermoforming process easier and the demolding more smooth.
Five types of PET sheets, 1# to 5#, with the same thickness were prepared and processed into cups through the vacuum forming process. The 1# to 5# PET sheets were stretched ten times during molding, and their effects after stacking and removal following the vacuum forming process were compared. See Table 3 for details. Sheets 1# to 4# all contained slip and anti-blocking masterbatch, which resulted in good stacking and removal effects after vacuum forming; however, since 5# did not contain slip and anti-blocking masterbatch, the sheets could not be separated. This indicates that the slip and anti-blocking performance of PET sheets is an important factor affecting the vacuum forming process. After vacuum forming, the stacking and removal effect of the cups made from sheet 2# and sheet 4# was comparable, and better than that of sheet 1#, and significantly better than that of sheet 3#. From the perspective of the stacking and removal effect of vacuum-formed PET products, it can be seen that the homemade slip and anti-blocking masterbatch 2# performs as well as the imported high-quality slip and anti-blocking masterbatch.

Table 3 Comparison of the effect of product stacking and taking out after plastic molding of PET sheets Tab. 3 Comparison of effect of product stacking and taking out after plastic molding of PET sheets

 

Table 3 Comparison of the effect of product stacking and taking out after plastic molding of PET sheets Tab. 3 Comparison of effect of product stacking and taking out after plastic molding of PET sheets

Table 3 Comparison of the effect of product stacking and taking out after plastic molding of PET sheets Tab. 3 Comparison of effect of product stacking and taking out after plastic molding of PET sheets

 

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2.4 Optical Properties of PET Sheets

The optical properties of PET are typically characterized by transmittance and haze [14]. According to GB/T 2410-2008, transmittance refers to the ratio of the light flux passing through the sample to the light flux incident on the sample, and its value is directly proportional to the optical performance of the PET sheet; haze, on the other hand, is the ratio of the scattered light flux deviating from the direction of the incident light to the transmitted light flux, and its value is inversely proportional to the optical performance of the PET sheet [15]. The slip and anti-blocking properties of PET sheets and their optical properties are contradictory [14-15]. To develop PET sheets with superior optical properties, it is first necessary to ensure that the basic requirements for slip and anti-blocking properties are met.
Five types of PET sheets (No. 1~5) with the same thickness were prepared, and a vacuum forming process was used to stretch the PET sheets tenfold. The transmittance before and after vacuum forming was compared, as detailed in Table 4. From Table 4, it can be seen that, except for Sheet No. 1 and No. 2, the transmittance of the other three sheets decreased after vacuum forming. The transmittance of Sheet No. 1 and No. 2 reached 100% after vacuum forming, indicating excellent transparency. Sheet No. 5, which did not contain any masterbatch, showed little change in transmittance before and after vacuum forming. Comparing the results, the difference in transmittance among Sheets No. 1~4 before vacuum forming was not significant, but after vacuum forming, the transmittance of Sheets No. 1 and No. 2 was higher than that of Sheets No. 3 and No. 4. From the perspective of transmittance after vacuum forming, the self-made slip and anti-blocking masterbatches in Sheets No. 1 and No. 2 improved the transmittance of the PET sheets.

Table 4   Comparison of Transmittance of PET Sheets Before and After Thermoforming

 

The haze of Sheets No. 1~5 before and after vacuum forming was compared, as detailed in Table 5. From Table 5, it can be seen that since Sheets No. 1~4 all contained slip and anti-blocking masterbatch, their haze values were greater than 0%; however, the haze value of Sheet No. 5, which did not contain the slip and anti-blocking masterbatch, was 0%. This indicates that the slip and anti-blocking masterbatch has a negative impact on the optical properties of PET sheets. Before vacuum forming, among the sheets containing the slip and anti-blocking masterbatch, Sheet No. 4 had the lowest haze value; after vacuum forming, the haze of Sheets No. 1~4 increased, with Sheet No. 2 having the lowest haze value. From the perspective of haze before and after vacuum forming, the self-made slip and anti-blocking masterbatch in Sheet No. 2 had a lesser negative impact on the optical properties of the PET sheets.

2.4 Optical Properties of PET Sheet

2.4 Optical Properties of PET Sheet

2.4 Optical Properties of PET Sheet
The optical properties of PET are typically characterized by transmittance and haze [14]. According to GB/T 2410-2008, transmittance refers to the ratio of the light flux passing through the sample to the light flux incident on the sample, and its value is directly proportional to the optical performance of the PET sheet; haze is the ratio of the scattered light flux that deviates from the direction of the incident light to the transmitted light flux, and its value is inversely proportional to the optical performance of the PET sheet [15]. The slip and anti-blocking properties of PET sheets are contradictory to their optical properties [14-15]. To develop PET sheets with superior optical properties, it is first necessary to ensure that the basic requirements for slip and anti-blocking properties are met.
The optical properties of PET are typically characterized by transmittance and haze [14]. According to GB/T 2410-2008, transmittance refers to the ratio of the light flux passing through the sample to the light flux incident on the sample, and its value is directly proportional to the optical performance of the PET sheet; haze is the ratio of the scattered light flux that deviates from the direction of the incident light to the transmitted light flux, and its value is inversely proportional to the optical performance of the PET sheet [15]. The slip and anti-blocking properties of PET sheets are contradictory to their optical properties [14-15]. To develop PET sheets with superior optical properties, it is first necessary to ensure that the basic requirements for slip and anti-blocking properties are met.
Five types of PET sheets (1#~5#) with the same thickness were prepared, and a vacuum forming process was used to stretch the PET sheets ten times. Their transmittance before and after vacuum stretching was compared, as shown in Table 4. As can be seen from Table 4, except for sheets 1# and 2#, the other three sheets showed a decrease in transmittance after vacuum stretching. Sheets 1# and 2# both achieved 100% transmittance after vacuum stretching, indicating excellent transparency. Sheet 5# is a PET sheet without any masterbatch added, and its transmittance did not change much before and after vacuum stretching. By comparison, it was found that the transmittance of sheets 1#~4# was similar before vacuum stretching, but after vacuum stretching, the transmittance of sheets 1# and 2# was higher than that of sheets 3# and 4#. From the perspective of the transmittance of PET sheets after vacuum stretching, the self-made slip and anti-blocking masterbatches 1# and 2# improved the transmittance of the PET sheets.
Five types of PET sheets (1#~5#) with the same thickness were prepared, and a vacuum forming process was used to stretch the PET sheets ten times. Their transmittance before and after vacuum stretching was compared, as shown in Table 4. As can be seen from Table 4, except for sheets 1# and 2#, the other three sheets showed a decrease in transmittance after vacuum stretching. Sheets 1# and 2# both achieved 100% transmittance after vacuum stretching, indicating excellent transparency. Sheet 5# is a PET sheet without any masterbatch added, and its transmittance did not change much before and after vacuum stretching. By comparison, it was found that the transmittance of sheets 1#~4# was similar before vacuum stretching, but after vacuum stretching, the transmittance of sheets 1# and 2# was higher than that of sheets 3# and 4#. From the perspective of the transmittance of PET sheets after vacuum stretching, the self-made slip and anti-blocking masterbatches 1# and 2# improved the transmittance of the PET sheets.

Table 4 Comparison of transmittance of PET sheets before and after thermoforming Tab. 4 Comparison of transmittance of PET sheets before and after thermoforming

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