Additive Technology Improves Packaging Material Quality

Packaging materials are a rapidly developing emerging industry. Compared with the traditional concept, in recent years, packaging materials have evolved from single-layer plastic films to multi-layer co-extrusion co-blowing, multi-layer composites and other functional film-based phases. There are also important changes in surface printing. From simple offset printing gradually evolved into fine dot-tone copperplate printing (or flexo printing). Even in the case of single-layer film packaging materials, it has evolved into high-quality films with high transparency, high luminance, high smoothness, high puncture resistance, and high sealing strength. The above changes have provided new service requirements for the development of various types of additives.

In terms of additives, the development trend in recent years is that a variety of high-efficiency new additives continue to emerge. In addition to functional additives, the importance of process additives has also been reflected. It can be said that high quality packaging films are difficult to produce without the use of process aids.

The relationship between the degree of dispersion of additives and efficacy

There is an important new concept in the expression of additive performance. That is, the degree of dispersion of the additive determines the performance of the additive. Compared with the traditional concept, the effectiveness of the additive no longer depends solely on the added weight, but on the effective total particulate amount and effective total surface area of ​​the additive added. Calculated as follows:

(1) The proportion of the same weight of additives dispersed to 2 micron diameter and dispersed to 8 micron diameter particles: namely: the same weight of additives, when dispersed to 2 microns in diameter, the total number of particles is dispersed Up to 64 times the diameter of 8 microns.
(2) The same weight of additive, dispersed to 2 microns in diameter, has a total surface area that is dispersed to a multiple of 8 microns in diameter:

Conclusion: The same weight of additive, dispersed to 2 micron particle diameter, has a total surface area that is 4 times the diameter of particles dispersed to 8 microns.

Based on the above calculations, it can be seen that the finer the auxiliaries are dispersed and the smaller the granules, the higher their effectiveness. This is also one of the principles of the rapid emergence of nanotechnology in the world.

Due to the fact that the vast majority of polymer melts have a relatively high viscosity, various additives (including solid, semi-solid, or liquid forms at polymer melt temperatures) are required in high-viscosity polymer melts. Dispersing to the nanoscale fineness obviously requires a great deal of functionality. For many auxiliaries, if they are dispersed nanometerly in the state of being alone, due to the huge surface area after dispersion and the energy of the compound surface, the auxiliaries dispersed to the nanometer level will be rapidly reassembled (Aggregate). ) or Agglomerate.

Therefore, in terms of the current level of technology, there is still a certain degree of difficulty in upgrading the auxiliary bio-agent process to nano-scale dispersion and large-scale production.

With the current level of technology, if we can increase the dispersion of various types of additives to the low-micron/sub-micron level, it is already a leading international production technology. For example, the dispersion of various additives can be controlled within the range of 0.6-2 microns, which has enabled the performance of the additives to be achieved, which is several times that of ordinary dispersions with particle sizes of 8-12 microns. A large number of production practices have confirmed that in terms of process additives, even if the same amount of additives is added, the performance of the additive masterbatch produced by different production plants can also be several times different. In terms of functional additives, a large number of production practices also confirmed the same difference in potency described above. For example, high-performance antioxidant masterbatches (eg, AY-3) can make PE bags stay in storage for 3 years and do not become yellow under high humidity with less added amount. . For another example: packing bags of powdered materials (eg milk powder, nutrient powders, washing powders), using an amine-free antistatic masterbatch (HAS-F-1 surface-drying antistatic agent masterbatch), When the antistatic agent is dispersed in the low-micron/sub-micron range, the blown packaging film can be made into a bag so that the packaged powder material does not stick to the wall. The above two functional additive masterbatches are very important for the market applicability of packaging materials. They have also been widely used in the production of high quality plastic packaging bags.

The relationship between process additives and the printing effect of ink

High-quality packaging materials, the printing effect is an important factor in determining the market competitiveness and price. The so-called printing effect, that is, the surface brightness of the ink, vividness, and adhesion fastness, anti-sticking and so on. The brightness and vividness of the ink surface are determined by the pigment, substrate resin, and additives of the ink itself; there is also a very important factor that has not yet been recognized by a large number of packaging material manufacturers, namely: packaging materials The microscopic smoothness of the surface affects the brightness and vividness of the ink film surface.

After the ink is dried, a very thin ink film is formed on the surface of the printed packaging material. The surface brightness of the ink is determined by the reflectance of the ink film after drying to visible light. In the ideal case, assuming that the oil film is flat, the principle of its reflection on visible light is shown in Fig.:

However, the actual situation is not the case. In the absence of PEA as a process aid, the surface of the packaging film produced by the roiling process or blown film process is not smooth. Under the microscope optical fiber side light source or dark field microscopic observation, no process aids are used, and there are a large number of tiny water ripples on the surface of the packaging film material. In contrast, a completely flat packaging film is obtained after the addition of the process aid PEA.

Therefore, when printing a film material produced with no process aids and having a large number of microscopic surface water ripples, there is also a certain degree of unevenness on the surface of the dried ink film.

In the case of printing using a photographic plate (or flexographic plate), the ink is dotted on the base film of the packaging material. Therefore, microscopically, each ink dot is actually a small visible light reflector. When the base plastic film is flat, these tiny reflections reflect in the same direction toward the visible light, so that the ink film shows high brightness. On the other hand, when the base plastic film is uneven, these minute reflections reflect irregularly and diffusely with visible light, so that the brightness of the ink film is significantly reduced.

A large number of production practices have proven to be using the same production equipment, the same raw material formulation,
With the same packaging film production process, the same ink, and the same printing plate, the packaging film material produced by adding no process additives and having a large amount of microscopic water ripples on the surface is printed, and after printing with PEA process additives The production of flat and highly smooth packaging film, after the ink dry solid surface brightness and vividness, is obviously different.

High-strength, high-quality packaging film

The strength of the packaging material is an important factor in determining the required thickness and cost control of the packaging material. For any product packaging, high-strength packaging materials are preferred. In other words, the high-strength packaging film has a market competitiveness in sales.

For PE membrane materials, the mixing of LDPE and LLDPE has certain technical significance. At present, the vast majority of PE membranes in the world use a LLDPE Melt index (Mi for short) of 2. High-strength LLDPE, which has been widely used internationally, has a melt flow index of (Mi) 1 or less and is rarely used. The reasons are nothing more than three: First, domestic petrochemical companies have not yet produced Mi LLDPE; second, very few suppliers import Mi 1 LLDPE into the domestic market for sales; and third, there is little supply of Mi 1 LLDPE in the market. A large number of packaging material manufacturers are not familiar with this material. However, in the final analysis, the problem is that without good process aids, the LLDPE with Mi 1 (or less than 1) cannot be processed well. Thus, Mi 1 (or less than 1) LLDPE flowing or blown films have a large number of melt flow patterns (or commonly known as snakeskin patterns) on the surface. At the same time, due to the large melt viscosity of Mi 1 (or less than 1) LLDPE, the screw power of general extrusion equipment cannot withstand higher torque.

In the formula, because the Mi 2 LLDPE feels sticky and has poor stiffness, most manufacturers use 33.3% LDPE / 66.7% LLDPE (ie, 1/2) as the highest ratio. If Mi 2 LLDPE is higher than 70% in the ratio, the film becomes too soft and sticky. In fact, Mi 1 LLDPE has 50% (or more) higher tensile force than Mi 2 LLDPE, and it has higher puncture resistance and tear resistance. Because Mi 1 LLDPE has better stiffness and less sticky feel, the ratio of LDPE / LLDPE can be changed to 10% / 90%. It should be noted that in the international market, LLDPE is about US$50/t lower than LDPE per ton. Therefore, after increasing the LLDPE ratio from 66.7% to 90%, the formula cost that can be saved is: (90 - 66.7) x 50 = 11.7 USD/ton. Therefore, when the process aid PEA is used, the cost of the material saved after the change in the formula per ton of raw materials can offset a considerable part of the use cost of the PEA process aid.

The relationship between the use of process aids and processing equipment

There is an important relationship between the use of process aids and equipment. Examples are as follows:

(1) Increase production capacity, save equipment power consumption, and reduce production costs. According to the results of long-term use of several hundred blown film equipment (including Hong Kong, Taiwan, China), PEA-2 and PEA-HD-2 can make the film blowing speed automatic under the same screw speed and other process conditions. Increase 7-10%. At the same time, the power consumption of the main motor does not increase under the conditions of further increasing the screw speed and increasing the production capacity.

(2) In the quality control of the film material, it is possible to produce a high-quality film material with a low-quality die, and the smoothness is even higher than that of the film material that is blown using a hard chromium plated mirror-polished die. For example, Huayi Technology Development Co., Ltd. research report: The surface smoothness microscopic photography analysis of the plastic bag confirmed that the mirror surface polishing of the die head can not replace the performance of the process additives.

(3) The use of process aids allows the temperature of the die head to be controlled within a range of 15-20° C. lower than without the process aid in the blown film. Therefore, in the summer, it can make up for the lack of cooling force of the cold wind ring, or make the cold wind ring not need to operate under extreme conditions, so that the foam body is stable and the blow film output does not decrease in the summer.

(4) In the past six years, the actual status of a large-scale plastic bag manufacturing plant with multiple households in Hong Kong has confirmed that the use of PEA as a process aid can significantly extend the service life of screws and barrels and reduce wear. Whenever the equipment is repaired and maintained, there is no accumulation in the inside of the blown film device, inside the die head, or in the concave position of the screw, and it is very clean and free of carbide dead ends. Therefore, the equipment overhaul period has been extended and the production volume has been stable and smooth.
(5) When used on imported multi-layer co-extruded equipment, the multi-layer co-extruded equipment can work stably and the interface smoothness between layers can be improved. Therefore, not only is the transparency and smoothness of the multilayer coextruded film improved, but also the quality control of the multilayer coextruded film is improved.