1. General
The new tape casting and winding packaging film is a plastic packaging material processed and produced with metallocene linear low-density polyethylene as the main raw material. It has the advantages of strong self-adhesive, excellent puncture resistance, excellent anti-aging performance and high tensile ratio. It is suitable for collective packaging of forage and can be used to store forage and keep fresh. As a forage packaging, its remarkable characteristics are: low ton cost, high packaging efficiency, less labor, and very good effect, which greatly reduces the waste of Forage Nutrition, improves the utilization rate of forage, shortens the marketing period of livestock and improves the quality of meat. On the basis of digesting and absorbing the production technology of BOPP, CPE, PVC, CPP and other packaging films, we give full play to our own industry and technical advantages, and carry out comprehensive development and innovation from raw material selection, masterbatch development, formula design to production process and control. We are familiar with the static and dynamic parameter indexes of various raw materials, production processes and equipment, analyze and study the reliability of various links, and finally determine various control indexes, production processes and implementation schemes. We have produced qualified products and met the design requirements.
2. Main equipment of production line
It is mainly composed of the following parts: raw material supply unit, extrusion unit, multi-functional feeding block and coextrusion die head, tape forming unit, thickness measurement unit, corona treatment unit, traction cooling unit, on-line Slitting unit, edge strip recovery unit, winding unit, automatic control system, etc.
The main equipment includes:
① Three extruders with models of 150 / 30d, 90 / 30d and 70 / 30d respectively.
② The multifunctional feeding block is composed of a material flow distribution selection plug, a distribution pin, a diversion wing plate and a melt channel cavity. By changing the selection plug, the hierarchical order of the film can be changed, such as bacab, bcacb, abbbc, etc; The split wing plate and distribution pin can adjust the layer thickness ratio of each layer, so that there are more choices and films with different functional layers can be produced.
③ The design of coextrusion die is flat shoulder type and single channel type. In the feeding block, the melt flow distributed according to a certain hierarchical order and hierarchical proportion is evenly superimposed here to form a coextrusion melt flow and flow out of the die lip at a constant pressure. Its advantage is that the melt pressure on the full width of the die lip is uniform,
In this way, the film quality has a good basic guarantee.
④ Extinction type casting roller: the roller is a double-layer jacket spiral channel quench roller, and the surface is subject to extinction treatment, so that the casting film has better forming, better appearance and internal quality.
⑤ Thickness gauge: use β X-ray, non-contact continuous measurement of the film, the measurement results are accurate and stable, and the thickness is controlled to make the film thickness uniform and stable.
⑥ Winder: there are three ways to choose: surface winding, center winding and surface center winding.
3. Process flow
The basic production process flow diagram is as follows:
Raw materials and auxiliary materials are transported to the intermediate hopper through the vacuum suction device, and then accurately weighed by the weighing element and added to the extruder according to the set proportion. The raw materials are melted, plasticized, mixed and compacted in the extruder, and enter the feeding block with constant pressure and output; Distribute the level and proportion of melt flow here, and then enter the die flow channel, distribute it to the full width die flow channel, and flow from the die lip to the casting roll; The average thickness of the film is determined by the ratio of the speed of the casting roller to the extrusion volume of the melt flow, and the thickness gauge measures the cross-sectional curve of the film, and the thickness curve of the film is quickly adjusted through PLC control. The film enters the winding unit under the traction of the traction device, which can cut the film into the specifications required by the user through the on-line slitting device, and cut out two edges, The edge strips are blown into the crusher by the fan, crushed into fluff and sent back to the extruder, which greatly improves the input-output ratio. The cut film is wound up on the paper core, automatically rewound according to the set length or diameter, inspected, labeled and qualified, and stored as finished products.
4. Main process parameters
After many experiments, comparison and optimization, we get the best formula and production process parameters as follows:
① Hierarchical distribution and process formula
For multilayer coextrusion film, its layer distribution and formula are very important, which fundamentally determines the performance of the film. The level distribution and process formula we selected are:
A metallocene linear low density polyethylene + tackifying masterbatch + anti-aging Masterbatch
B Metallocene Linear low density polyethylene with nano montmorillonite + tackifying masterbatch + whitening and shading masterbatch + anti-aging Masterbatch
C Metallocene Linear low density polyethylene + anti-aging Masterbatch
The purpose of adding tackifying masterbatch is to increase the surface self viscosity of the film, so as to prevent the film from being loose due to insufficient self viscosity during use, resulting in loss; The anti-aging masterbatch is used to prevent the aging of the film, enhance its weather resistance and prolong its service life; Whitening and shading masterbatch is used to reduce the light transmittance of the film, so as to prevent the forage in the bundle from rotting and deteriorating due to excessive photosynthesis; Metallocene Linear low density polyethylene with montmorillonite is used to increase the strength of the film.
② The main production process parameters are as follows:
(1) film thickness: 25 ± 2 μ m
(2) temperature control of extruder: A: 260-270 ℃, B: 260-280 ℃, C: 260-270 ℃
(3) die temperature control: 260-280 ℃
(4) casting roller temperature: 20-30 ℃
(5) main parameters of winding: traction tension 60N, s-traction tension 80N, contact roller driving tension 80N, center driving tension 85n, center driving tension slope 0, film roll pressure 2.5bar
5. Research and development of Masterbatch
PIB tackifying masterbatch was developed. Nano montmorillonite was added to Metallocene Linear low density polyethylene, which greatly increased the strength of the film.
6. Key technical problems in trial production
① Solve the problem of vacuum suction blockage
Due to the high viscosity of the tackifying masterbatch, the masterbatch is bonded to each other, which is easy to block the vacuum suction pipe, weighing device and conveying pipeline, which seriously affects the accurate measurement and feeding of the masterbatch, resulting in unstable product performance. In order to solve this problem, we have experimented many times in the plastic Research Institute and made the tackifying masterbatch with coating on the surface, so as to reduce the viscosity of surface particles, mix evenly with the raw materials in proportion, and feed through the vacuum suction pipe, so as to make the supply of raw materials smooth and accurate and ensure the stability of product performance; In addition, the proportion of tackifying masterbatch can be adjusted according to user requirements or seasonal changes. For example, the migration of tackifying agent is related to the storage temperature. Its migration and precipitation speed is fast in summer and slow in winter. Therefore, the proportion of adding tackifying masterbatch in the production of forage winding film is adjusted due to seasonal changes, that is, the amount added in winter is about 1% more than that in summer, wait; It is also possible to add tackifying masterbatch to both surface layers to obtain grass winding film with self-adhesive on both sides.
② Control the thickness of the film
The viscosity of Metallocene Linear low density polyethylene is very high, which makes the necking of the melt flow extruded in the extruder from the die lip to the back of the casting roll very large: the full width of the die lip of this production line is 2700mm, while the width of the melt flow extruded from the die lip to the back of the casting roll is only 2500mm. This makes it very difficult to control the thickness of the edge of the film, which affects the thickness curve of the film with the whole width. After many times of thinking and testing, we finally found a good solution, that is: change the position of the electrostatic blank holder on both sides and the angle between the electrostatic blank holder needle and the casting roller, so as to best stabilize the film edge, and then readjust the die head thermal expansion bolts corresponding to the edge film: completely loosen the edge bolts (five to six on each side) and then readjust, The value of the full width of the film is accurately input into the microcomputer to ensure that the thermal expansion bolt of the die corresponds to the range of the film controlled by it, so as to better control the thickness of the film, so as to ensure the uniformity of the film thickness curve.
③ Balance between shading and anti-aging performance
The forage winding film developed by US adds whitening and shading masterbatch to reduce the light transmittance of the film, so its appearance is white. However, ordinary whitening and shading masterbatch has a great impact on the strength and anti-aging performance of the film. Through the comparative analysis of rutile and anatase whitening masterbatch, we decided to use rutile whitening and shading masterbatch to solve this problem. Through many technical exchanges and investigations, we chose rutile whitening and shading masterbatch that meets the requirements, The appropriate aging resistant masterbatch was selected to enhance the anti-aging properties of the films. After many experiments, the mixing proportion of whitening shading masterbatch and anti-aging masterbatch is selected, so as to achieve the balance between shading and anti-aging performance.
④ Winding flatness
As we all know, users not only pay great attention to the internal quality of products, but also are very picky about the appearance of products. The first impression of a commodity to users is its appearance. The quality of the first impression determines the users likes and dislikes of the product to a great extent.
Because of its poor stiffness and strong self viscosity, the air involved in the winding of forage film is not easy to be discharged, and the film roll is easy to wrinkle. In addition, there are many slitting specifications, which is also very difficult for winding. There are three winding modes for this production line: surface winding, center winding, i.e. gap winding and center surface winding. Through the comparative experiment, we choose the central winding, and change the film roll pressing roller from the one with low hardness to the one with high hardness, which can greatly reduce the amount of air involved in the winding process and make the film flat. The surface winding and the central surface winding are not easy to discharge the air involved in the roll changing and winding process, resulting in serious wrinkles, which will affect the quality of the whole film roll.
7. Comparison of main technical indicators of products
The comparison of technical indicators of similar products in the world is as follows:
entry name
Index requirements
Measured results
Polyethylene forage film
EN ISO527-3
Agricultural forage film
Q/BSBCJ 02-10—2002
Industrial winding film
Q/BSBCJ 02-10—2002
Agricultural forage film
Industrial winding film
Tensile strength MPa ≥
portrait
twenty-five
twenty-eight
twenty-eight
thirty-eight
forty
transverse
twenty-three
twenty-five
twenty-five
thirty-eight
thirty-eight
Elongation at break (%)
portrait
four hundred
four hundred and fifty
four hundred and fifty
four hundred and eighty
four hundred and eighty
transverse
six hundred
five hundred
five hundred
five hundred and sixty
five hundred and sixty
Right angle tear strength
N/mm≥
portrait
eighty
eighty
one hundred and ten
ninety-two
transverse
eighty
eighty
ninety-five
ninety-eight
Puncture resistance J ≥
one point five
one point five
one point seven
one point six
Self adhesive (shear peel strength)
N/cm2≥
one point five
one point five
one point six
one point five
It can be seen from the above table that the indexes of the enterprise standard of the new co extrusion tape casting and winding film are higher than or equal to the international standards of similar products. The physical performance indexes of the new products tested by the national plastic product quality supervision and testing center exceed the requirements of the product standard.
8. Conclusion
By developing a new type of tape casting and winding packaging film, we have basically mastered the production technology of multi-layer co extrusion tape casting and winding packaging film with different properties, and found out the best process conditions for production. The new winding packaging film developed by us fills the gap of forage packaging and storage in China, and provides a better forage storage method for animal husbandry in China. At the same time, in the process of development, we have summarized the following technological innovations:
① Develop and develop a variety of functional masterbatch, and use blending technology to give full play to their comprehensive properties, such as tackifying masterbatch, nano material masterbatch, liquid additive masterbatch, metallocene resin carrier masterbatch, etc. it improves the operability and dispersion of masterbatch addition, controls the addition amount and density, and makes it evenly distributed and exuded according to the needs, Keep the product efficiency constant; It can also effectively reduce product costs, reduce useless additions, make full use of raw materials and produce the maximum benefits. Technically speaking, the masterbatch technology is the key to the success of the product development. In production, the blending technology is adopted, such as the blending of tackifying masterbatch and anti-aging masterbatch, and the blending of tackifying masterbatch, anti-aging masterbatch and whitening and shading masterbatch, which greatly improves the comprehensive properties of the film. In the future, we plan to add two or three sets of auxiliary material dispensing devices to each extruder (the original equipment has reserved space), which will make the blending of raw materials more accurate and convenient.
② The multi-functional coextrusion feeding block, the advanced technology of multi-layer coextrusion, and the blending technology and agent dispensing device are used to make different layers of the film have prominent different functions, such as excellent self-adhesive of layer a; The light shielding and anti-aging performance of layer B is strong, and the strength and puncture resistance are excellent, while the self-adhesive of layer C is relatively small, which makes the winding smooth and improves the labor efficiency. We plan to add two 50 / 30d extruders (the original equipment has reserved space). By changing the selection plug, the hierarchical order can be changed, and more than five layers of CO extruded asymmetric films can be produced, so that different products can choose the effective number of layers according to their needs, and different raw materials and different functional masterbatches can be used at different levels, which increases the selection range of raw materials, The functionality of the film is enhanced.
③ Update formulation design theory
Using the internationally advanced density control method of each layer in the production of coextrusion composite membrane, the permeability of functional masterbatch is different. Special performance masterbatch, such as PIB masterbatch, is used to realize the difference of self viscosity of the outer layer of the product, so as to facilitate different uses and packaging effects of the product.