In recent years, with the rapid development of the pharmaceutical and pharmaceutical packaging industries, especially the market for pharmaceuticals such as proprietary Chinese medicines, granules, and powders, flexible packaging bags have become more and more popular in the field of pharmaceuticals due to their good barrier properties. proportion. Due to the high barrier requirements of some PTP blister packs, some medicines need to add a composite film flexible packaging bag to the outside of the package after using the blister package to enhance the protection function of the medicine and prevent water vapor and light. And other external factors damage the drug efficacy of the drug in the package. This paper mainly elaborates and studies some main process parameters in the bag making process and some problems that often occur in the actual production process.
At present, heat sealing is a kind of bag making method which is widely used in composite packaging materials. It utilizes various external conditions (such as electric heating, high-frequency voltage and ultrasonic waves) to change the sealing portion of the plastic film into a viscous flow state, and fuses the two films into one body by a certain pressure, and maintains the strength after cooling. There are many types of heat sealing methods, such as fuse sealing, ultrasonic sealing, high frequency sealing, hot air sealing, rod heat sealing and the like. According to the characteristics and requirements of pharmaceutical packaging, most of the medical flexible packaging bags are made of rod heat sealing, which is also a common heat sealing method in the whole packaging industry. This heat sealing method is mainly to coordinate the heating rod temperature, the heat sealing time, and the pressure between the heating rod and the silica gel plate, and the Zui finally achieves a satisfactory sealing effect. In general, a good sealing effect depends on whether it has good heat seal strength and a good appearance.
First, the three elements of heat sealing bags
Habitually, we call the heat sealing temperature, heat sealing time, and heat sealing pressure as the three elements of heat sealing bags.
Heat sealing temperature
The function of the heat sealing temperature is to heat the adhesive film layer to a relatively ideal viscous flow state.
Since the polymer has no defined melting point, it is a melting temperature range, that is, a temperature region between the solid phase and the liquid phase, and when heated to the temperature region, the film enters a molten state. The viscous flow temperature and decomposition temperature of the polymer are the lower and upper limits of the heat seal, respectively, and the difference between the viscous flow temperature and the decomposition temperature is an important factor for measuring the difficulty of heat sealing.
The heat sealing temperature is set according to the characteristics of the heat sealing material, the thickness of the film, the number of times of heat sealing and the size of the heat sealing area. The number of hot pressing times in the same part increases, and the temperature can be appropriately lowered. When the heat sealing area is large, the temperature can be slightly higher.
In the process of heat sealing composite bag making, the effect of heat sealing temperature on the heat sealing strength is direct, and the melting temperature of various materials directly determines the low heat sealing temperature of the composite bag. In the actual production process, the heat sealing temperature is affected by factors such as heat sealing pressure, bag making speed and thickness of the composite substrate, so the actual heat sealing temperature is often higher than the melting temperature of the heat sealing material. If the heat sealing temperature is lower than the softening point of the heat sealing material, the heat sealing layer cannot be completely sealed regardless of how the pressure is increased or the heat sealing time is extended. In general, as the heat seal temperature increases, the heat seal strength also increases, but after a certain temperature, the strength does not increase (see Figure 1 for the relationship between heat seal strength and temperature). If the heat sealing temperature is too high, it is easy to damage the heat sealing material at the welding place, and the melt extrusion produces a "root cutting" phenomenon, which greatly reduces the heat sealing strength of the sealing and the impact resistance of the composite bag.
2. Heat sealing time
Heat sealing time refers to the time the film stays under the hot knife, and it is also a key factor affecting the strength and appearance of the heat seal. The same heat sealing temperature and pressure, the heat sealing time is long, the heat sealing layer is more fully fused, and the bonding is stronger. However, the heat sealing time is too long, which is likely to cause wrinkling deformation at the heat seal weld, which affects the flatness and appearance. At the same time, the heat sealing time is too long, which may cause decomposition of macromolecules and deteriorate the sealing performance of the sealing interface.
Generally, the heat sealing time is mainly determined by the speed of the bag making machine. In the old-style bag making machine, the heat sealing time was adjusted only by changing the speed of the bag making machine. To extend the heat sealing time, it was necessary to sacrifice production efficiency. In recent years, domestic and foreign bag making machine manufacturers use independent variable frequency motor technology to control the heat sealing knife to drop and feed, so that the bag making machine can independently adjust the heat sealing time or control the heat sealing time without changing the bag making speed. Independently adjusting the bag making speed under constant conditions greatly facilitates the operation and quality control of the bag making machine and improves the production efficiency of the bag making machine.
3. Heat sealing pressure
The function of the heat sealing pressure is to cause the high molecular weight resin film which has been in the viscous flow state to generate effective molecular mutual penetration and diffusion between the heat sealing interfaces, thereby achieving a certain heat sealing effect.
To achieve the desired heat seal strength, appropriate pressure must be applied. For general thin and light medical packaging bags, the heat sealing pressure should be at least 20 N/cm2, and as the total thickness of the composite film increases or the heat sealing width increases, the required pressure should also increase accordingly. If the heat sealing pressure is insufficient, it is difficult to achieve true bonding and mutual fusion between the two layers of plastic film heat sealing materials, resulting in partial heat sealing, or difficulty in eliminating air in the heat sealing layer, resulting in a virtual seal or unevenness.
However, when the heat sealing pressure is too large, the molten material is extruded, and part of the heat sealing material is squeezed out, so that the weld bead is formed in a semi-cut state, and the weld is brittle, which affects the heat sealing effect and reduces the heat seal. strength. After heat sealing, the strength loss of the sealing part should not exceed 10% to 15%.
Changes in pressure can change the heat seal characteristics. Obviously, the higher the pressure, the lower the heat seal time or the heat seal temperature can be, but the heat seal range will be narrower. In actual operation, the pressure can be adjusted. The higher operating temperature is used to shorten the heat sealing time to increase the output. However, the operation control is difficult, and special care must be taken to avoid negative effects.
Second, the factors of the composite membrane material itself
In addition to the influence of the three parameters of the heat-sealing bag on the bag making process, the performance of the composite material is also one of the important factors that directly affect the performance indexes of the heat-sealed bag and the operating parameters of the bag during the bag making process.
1. Type and thickness of composite film heat sealing material
The general medical composite film packaging heat sealing materials are LDPE, CPP, EVA, VC hot melt adhesive and other ionic resins, otherwise co-extruded or modified PE, PP and other films. Under the same circumstances, the CPP heat seal strength of the retort pouch packaging is stronger than that of the general LDPE, and the modified film has higher strength than the unmodified film. The thickness of the heat sealing material is generally 20 to 80 μm, and some special requirements (such as a retort pouch) also reach 100 to 120 μm. With the same heat sealing material, the heat seal strength increases as the heat seal thickness increases.
In addition, the total thickness, uniformity, and flatness of the material are also important parameter indicators. Poor uniformity and flatness will make the heat sealing pressure and temperature not be uniformly transmitted to the heat sealing area of ​​the film, so that the viscous flow state of the polymer in the direction of the heat sealing tool is not uniform and cannot be ensured. The interface is closed.
2. Composite film composite strength
The composite film is formed by extrusion and dry lamination of the non-heat seal layer and the heat seal layer. The practical meaning is lamination, which is not a complex composite concept of composite materials. The interlaminar composite strength of the inner seal layer (polyethylene, etc.) and the sub-internal substrate has a great influence on the heat seal quality. Other substrates combined with the inner sealing layer play a reinforcing role for the inner layer heat sealing. Most of the composite film heat sealing damage occurs between the layers of the composite film or brittle fracture. Generally, the heat sealing strength is required. Far greater than the composite strength. For products with low composite peel strength, the tensile strength, elastic modulus and elongation of the base film and the surface film (including the inner layer) are very different, and the heat seal is often used under the action of tension. The composite film layer is first peeled off, so that the inner layer is independently subjected to the breaking tensile force, and the other layer materials lose the reinforcing effect, and the quality index such as the heat sealing strength is greatly reduced. Moreover, at the same time of heat sealing, the composite strength of the heat-sealed portion itself will decrease to some extent, so it is a prerequisite to obtain sufficient heat-sealing strength to have a fairly good composite strength between the inner sealing layer and the secondary inner sealing layer. .
3. Composite film surface material
The heat resistance of the printed substrate and other composite layer substrates has an important influence on the flatness of the composite bag. In general, the better the heat resistance of the surface material, the better the appearance properties of the bag, such as the flatness of the bag, so the surface material of the composite film often limits the heat sealing temperature of the bag making machine. According to practical experience, when the surface layer is generally high temperature resistant substrate such as PET or PA, the speed of bag making can be accelerated by increasing the heat sealing temperature in the production process without affecting the appearance of the bag; the surface material is BOPP, etc. When the substrate with poor temperature resistance is used, try to use a lower heat sealing temperature. The heat seal strength and appearance are ensured by improving the heat seal pressure and prolonging the heat seal time, and the heat seal temperature is not increased in order to speed up the production.
Third, analysis of common problems in bag making
1. The edge banding has spots, bubbles
1 material factor. For example, absorbing materials such as PT and NY are easy to absorb moisture during storage, and bubbles and spots are easily generated when bag is formed at high temperature. In addition, since the composite adhesive is not completely cured, the temperature resistance is insufficient at the high temperature heat sealing, the peel strength is poor, and the gas plaque is easily delaminated.
2 When the heat sealing part is wide, it is easy to produce air spots. The pressure should be adjusted, the gap should be adjusted, and the air is squeezed out. When the film moves, there will be fluctuations that will be trapped in the air. It should be cleaned before entering the knife. The front plate should be properly clamped before entering the heat seal.
3 The bag is not properly controlled, such as the deformation of the silicone rubber sheet for a long time, the damage of the high temperature cloth, and the dirt on the heat sealing knife. Inappropriate and uncoordinated process parameters such as bag speed, temperature, and pressure can also cause spotting.
2. Heat seal strength difference
The difference in heat seal strength is a difficult problem often encountered in the bag making process.
1 heat sealing material impact
Different types of heat sealing materials, different heat sealing strength, such as PP, PE, EVA heat sealing strength is inconsistent; the same film different polymerization methods of products, heat sealing strength is different; material thickness, uniformity, etc. will also affect the heat seal strength Different processing methods of the heat seal layer, such as blow molding, cast film, etc., all affect the heat seal strength. The storage time of the film is too long, and the precipitates are increased, and the heat seal strength is poor after corona treatment. The hygroscopic material absorbs moisture, the hot cover is delaminated, and the peel strength is lowered.
2The effect of composite film processing technology
The printing ink has poor temperature resistance or improper additives in the ink. At the high temperature of the bag, the printed layer is delaminated and the heat seal strength is lowered. Heat sealing should be designed to be as unpatterned as possible. The choice of binder in the composite process is also very important, and the reasonableness of the ratio of the binder, viscosity, etc. will affect the seal strength. In the extrusion compounding or coating process, the processing temperature is high, the degree of oxidation of the surface of the material is large, and the amount of carboxyl groups is increased, which is disadvantageous for heat sealing.
3 bag making process
The sealing of the seal after heat sealing is not enough, the shaping is insufficient, the internal stress cannot be eliminated, the strength and appearance are affected, and the cooling water circulation system should be inspected in time. The more heat seals, the higher the heat seal strength. The number of longitudinal heat seals depends on the ratio of the effective length of the longitudinal weld to the length of the bag; the number of transverse heat seals is determined by the number of combinations of the machine's transverse heat seals. Good heat sealing requires at least two heat seals.
3. Sealing film wrinkles, warping
1 heat seal temperature, causing uneven shrinkage.
2 The heat sealing time is too long, which indirectly leads to temperature accumulation and overheats the surface of the film.
3 improper control of bag tension, affecting the flatness of the film and destroying the balance of gap feeding.
4 The gap is too large, and the Zui is well controlled between 1 and 1.5 mm.
4. The cutting line is not flush with the horizontal edge
1 The lower edge of the cutting knife is too low.
2 The guide comb is bent under the cutter, which is higher than the lower knife position.
3 The cutter base is not flush.
5. The upper and lower pieces are not allowed
1 The thickness of the material is uneven and there is slack.
2 The tension roller tension is too small.
3 Some rollers rotate unbalanced during operation.
At present, heat sealing is a kind of bag making method which is widely used in composite packaging materials. It utilizes various external conditions (such as electric heating, high-frequency voltage and ultrasonic waves) to change the sealing portion of the plastic film into a viscous flow state, and fuses the two films into one body by a certain pressure, and maintains the strength after cooling. There are many types of heat sealing methods, such as fuse sealing, ultrasonic sealing, high frequency sealing, hot air sealing, rod heat sealing and the like. According to the characteristics and requirements of pharmaceutical packaging, most of the medical flexible packaging bags are made of rod heat sealing, which is also a common heat sealing method in the whole packaging industry. This heat sealing method is mainly to coordinate the heating rod temperature, the heat sealing time, and the pressure between the heating rod and the silica gel plate, and the Zui finally achieves a satisfactory sealing effect. In general, a good sealing effect depends on whether it has good heat seal strength and a good appearance.
First, the three elements of heat sealing bags
Habitually, we call the heat sealing temperature, heat sealing time, and heat sealing pressure as the three elements of heat sealing bags.
Heat sealing temperature
The function of the heat sealing temperature is to heat the adhesive film layer to a relatively ideal viscous flow state.
Since the polymer has no defined melting point, it is a melting temperature range, that is, a temperature region between the solid phase and the liquid phase, and when heated to the temperature region, the film enters a molten state. The viscous flow temperature and decomposition temperature of the polymer are the lower and upper limits of the heat seal, respectively, and the difference between the viscous flow temperature and the decomposition temperature is an important factor for measuring the difficulty of heat sealing.
The heat sealing temperature is set according to the characteristics of the heat sealing material, the thickness of the film, the number of times of heat sealing and the size of the heat sealing area. The number of hot pressing times in the same part increases, and the temperature can be appropriately lowered. When the heat sealing area is large, the temperature can be slightly higher.
In the process of heat sealing composite bag making, the effect of heat sealing temperature on the heat sealing strength is direct, and the melting temperature of various materials directly determines the low heat sealing temperature of the composite bag. In the actual production process, the heat sealing temperature is affected by factors such as heat sealing pressure, bag making speed and thickness of the composite substrate, so the actual heat sealing temperature is often higher than the melting temperature of the heat sealing material. If the heat sealing temperature is lower than the softening point of the heat sealing material, the heat sealing layer cannot be completely sealed regardless of how the pressure is increased or the heat sealing time is extended. In general, as the heat seal temperature increases, the heat seal strength also increases, but after a certain temperature, the strength does not increase (see Figure 1 for the relationship between heat seal strength and temperature). If the heat sealing temperature is too high, it is easy to damage the heat sealing material at the welding place, and the melt extrusion produces a "root cutting" phenomenon, which greatly reduces the heat sealing strength of the sealing and the impact resistance of the composite bag.
2. Heat sealing time
Heat sealing time refers to the time the film stays under the hot knife, and it is also a key factor affecting the strength and appearance of the heat seal. The same heat sealing temperature and pressure, the heat sealing time is long, the heat sealing layer is more fully fused, and the bonding is stronger. However, the heat sealing time is too long, which is likely to cause wrinkling deformation at the heat seal weld, which affects the flatness and appearance. At the same time, the heat sealing time is too long, which may cause decomposition of macromolecules and deteriorate the sealing performance of the sealing interface.
Generally, the heat sealing time is mainly determined by the speed of the bag making machine. In the old-style bag making machine, the heat sealing time was adjusted only by changing the speed of the bag making machine. To extend the heat sealing time, it was necessary to sacrifice production efficiency. In recent years, domestic and foreign bag making machine manufacturers use independent variable frequency motor technology to control the heat sealing knife to drop and feed, so that the bag making machine can independently adjust the heat sealing time or control the heat sealing time without changing the bag making speed. Independently adjusting the bag making speed under constant conditions greatly facilitates the operation and quality control of the bag making machine and improves the production efficiency of the bag making machine.
3. Heat sealing pressure
The function of the heat sealing pressure is to cause the high molecular weight resin film which has been in the viscous flow state to generate effective molecular mutual penetration and diffusion between the heat sealing interfaces, thereby achieving a certain heat sealing effect.
To achieve the desired heat seal strength, appropriate pressure must be applied. For general thin and light medical packaging bags, the heat sealing pressure should be at least 20 N/cm2, and as the total thickness of the composite film increases or the heat sealing width increases, the required pressure should also increase accordingly. If the heat sealing pressure is insufficient, it is difficult to achieve true bonding and mutual fusion between the two layers of plastic film heat sealing materials, resulting in partial heat sealing, or difficulty in eliminating air in the heat sealing layer, resulting in a virtual seal or unevenness.
However, when the heat sealing pressure is too large, the molten material is extruded, and part of the heat sealing material is squeezed out, so that the weld bead is formed in a semi-cut state, and the weld is brittle, which affects the heat sealing effect and reduces the heat seal. strength. After heat sealing, the strength loss of the sealing part should not exceed 10% to 15%.
Changes in pressure can change the heat seal characteristics. Obviously, the higher the pressure, the lower the heat seal time or the heat seal temperature can be, but the heat seal range will be narrower. In actual operation, the pressure can be adjusted. The higher operating temperature is used to shorten the heat sealing time to increase the output. However, the operation control is difficult, and special care must be taken to avoid negative effects.
Second, the factors of the composite membrane material itself
In addition to the influence of the three parameters of the heat-sealing bag on the bag making process, the performance of the composite material is also one of the important factors that directly affect the performance indexes of the heat-sealed bag and the operating parameters of the bag during the bag making process.
1. Type and thickness of composite film heat sealing material
The general medical composite film packaging heat sealing materials are LDPE, CPP, EVA, VC hot melt adhesive and other ionic resins, otherwise co-extruded or modified PE, PP and other films. Under the same circumstances, the CPP heat seal strength of the retort pouch packaging is stronger than that of the general LDPE, and the modified film has higher strength than the unmodified film. The thickness of the heat sealing material is generally 20 to 80 μm, and some special requirements (such as a retort pouch) also reach 100 to 120 μm. With the same heat sealing material, the heat seal strength increases as the heat seal thickness increases.
In addition, the total thickness, uniformity, and flatness of the material are also important parameter indicators. Poor uniformity and flatness will make the heat sealing pressure and temperature not be uniformly transmitted to the heat sealing area of ​​the film, so that the viscous flow state of the polymer in the direction of the heat sealing tool is not uniform and cannot be ensured. The interface is closed.
2. Composite film composite strength
The composite film is formed by extrusion and dry lamination of the non-heat seal layer and the heat seal layer. The practical meaning is lamination, which is not a complex composite concept of composite materials. The interlaminar composite strength of the inner seal layer (polyethylene, etc.) and the sub-internal substrate has a great influence on the heat seal quality. Other substrates combined with the inner sealing layer play a reinforcing role for the inner layer heat sealing. Most of the composite film heat sealing damage occurs between the layers of the composite film or brittle fracture. Generally, the heat sealing strength is required. Far greater than the composite strength. For products with low composite peel strength, the tensile strength, elastic modulus and elongation of the base film and the surface film (including the inner layer) are very different, and the heat seal is often used under the action of tension. The composite film layer is first peeled off, so that the inner layer is independently subjected to the breaking tensile force, and the other layer materials lose the reinforcing effect, and the quality index such as the heat sealing strength is greatly reduced. Moreover, at the same time of heat sealing, the composite strength of the heat-sealed portion itself will decrease to some extent, so it is a prerequisite to obtain sufficient heat-sealing strength to have a fairly good composite strength between the inner sealing layer and the secondary inner sealing layer. .
3. Composite film surface material
The heat resistance of the printed substrate and other composite layer substrates has an important influence on the flatness of the composite bag. In general, the better the heat resistance of the surface material, the better the appearance properties of the bag, such as the flatness of the bag, so the surface material of the composite film often limits the heat sealing temperature of the bag making machine. According to practical experience, when the surface layer is generally high temperature resistant substrate such as PET or PA, the speed of bag making can be accelerated by increasing the heat sealing temperature in the production process without affecting the appearance of the bag; the surface material is BOPP, etc. When the substrate with poor temperature resistance is used, try to use a lower heat sealing temperature. The heat seal strength and appearance are ensured by improving the heat seal pressure and prolonging the heat seal time, and the heat seal temperature is not increased in order to speed up the production.
Third, analysis of common problems in bag making
1. The edge banding has spots, bubbles
1 material factor. For example, absorbing materials such as PT and NY are easy to absorb moisture during storage, and bubbles and spots are easily generated when bag is formed at high temperature. In addition, since the composite adhesive is not completely cured, the temperature resistance is insufficient at the high temperature heat sealing, the peel strength is poor, and the gas plaque is easily delaminated.
2 When the heat sealing part is wide, it is easy to produce air spots. The pressure should be adjusted, the gap should be adjusted, and the air is squeezed out. When the film moves, there will be fluctuations that will be trapped in the air. It should be cleaned before entering the knife. The front plate should be properly clamped before entering the heat seal.
3 The bag is not properly controlled, such as the deformation of the silicone rubber sheet for a long time, the damage of the high temperature cloth, and the dirt on the heat sealing knife. Inappropriate and uncoordinated process parameters such as bag speed, temperature, and pressure can also cause spotting.
2. Heat seal strength difference
The difference in heat seal strength is a difficult problem often encountered in the bag making process.
1 heat sealing material impact
Different types of heat sealing materials, different heat sealing strength, such as PP, PE, EVA heat sealing strength is inconsistent; the same film different polymerization methods of products, heat sealing strength is different; material thickness, uniformity, etc. will also affect the heat seal strength Different processing methods of the heat seal layer, such as blow molding, cast film, etc., all affect the heat seal strength. The storage time of the film is too long, and the precipitates are increased, and the heat seal strength is poor after corona treatment. The hygroscopic material absorbs moisture, the hot cover is delaminated, and the peel strength is lowered.
2The effect of composite film processing technology
The printing ink has poor temperature resistance or improper additives in the ink. At the high temperature of the bag, the printed layer is delaminated and the heat seal strength is lowered. Heat sealing should be designed to be as unpatterned as possible. The choice of binder in the composite process is also very important, and the reasonableness of the ratio of the binder, viscosity, etc. will affect the seal strength. In the extrusion compounding or coating process, the processing temperature is high, the degree of oxidation of the surface of the material is large, and the amount of carboxyl groups is increased, which is disadvantageous for heat sealing.
3 bag making process
The sealing of the seal after heat sealing is not enough, the shaping is insufficient, the internal stress cannot be eliminated, the strength and appearance are affected, and the cooling water circulation system should be inspected in time. The more heat seals, the higher the heat seal strength. The number of longitudinal heat seals depends on the ratio of the effective length of the longitudinal weld to the length of the bag; the number of transverse heat seals is determined by the number of combinations of the machine's transverse heat seals. Good heat sealing requires at least two heat seals.
3. Sealing film wrinkles, warping
1 heat seal temperature, causing uneven shrinkage.
2 The heat sealing time is too long, which indirectly leads to temperature accumulation and overheats the surface of the film.
3 improper control of bag tension, affecting the flatness of the film and destroying the balance of gap feeding.
4 The gap is too large, and the Zui is well controlled between 1 and 1.5 mm.
4. The cutting line is not flush with the horizontal edge
1 The lower edge of the cutting knife is too low.
2 The guide comb is bent under the cutter, which is higher than the lower knife position.
3 The cutter base is not flush.
5. The upper and lower pieces are not allowed
1 The thickness of the material is uneven and there is slack.
2 The tension roller tension is too small.
3 Some rollers rotate unbalanced during operation.
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