Cardboard is the main raw material for the production of corrugated cardboard boxes, cardboard boxes, and other products. Its performance directly or indirectly affects the internal quality and effectiveness of the product.
For corrugated cardboard boxes, cardboard boxes, and other packaging products, they have wear resistance, water resistance, and moisture resistance, as well as high strength and good air tightness, which are the basic quality requirements for the use characteristics of cardboard. However, ordinary cardboard produced by paper mills often does not have good wear resistance, waterproofing, and moisture resistance. The strength and airtightness of cardboard vary depending on the quality level of the cardboard. Therefore, in order to improve the performance of corrugated cardboard boxes and cardboard boxes, it is necessary to carry out necessary technological processing on the surface of the cardboard in order to fundamentally improve the performance and appearance quality of the cardboard.
1、 Polishing process of cardboard surface
Glazing is a common process for post press processing of packaging products. After the product surface is polished and coated, it can enhance the water resistance, sun resistance, friction resistance, pollution resistance and other properties of the printed products. At the same time, it can also improve the surface brightness of the product and greatly improve the product grade. The coating for glazing has various structures, including oil-based glazing oil for printing machine, water-based and oil-based glazing oil for glazing machine, solvent based glazing paint and UV coating paint. The characteristics of glossy coatings vary, and there are also certain differences in the surface processing effects of products. The same type of bright coating has differences in glossiness, wear resistance, etc. due to different material characteristics and formulations. When coated with matte coating, the surface of the printed product has almost no glossiness, but it has a certain artistic sense. Some products are coated with matte coating, and the process effect is no less than that of glossy coating. Whether it is a glossy or matte coating, the coating must have good wear resistance in order to protect the surface of the printed product.
The process characteristics of oily polishing. When using a printing machine to apply oily varnish, the thickness and dryness of the glossy coating are limited by the machine structure, and the glossiness and wear resistance of the printed surface are not as good as solvent based or water-based varnish used on the polishing machine. So, this type of polishing is generally only suitable for ordinary products with small batches and low quality requirements.
The process characteristics of solvent polishing. Products that use solvent polishing have high surface glossiness and wear resistance, but due to the use of organic solvents as diluents.
Like toluene, as the solvent evaporates, the cost of polishing coatings is also high. Solvent based glossy coatings have poor physical and chemical resistance, and the coating is prone to yellowing. Solvents with a strong odor not only easily pollute the environment, but also have a certain impact on production safety. Therefore, it is necessary to pay attention to the emission of exhaust gas at the production site. If the machine uses electric heating pipes for drying, it is important to maintain smooth transportation of the cardboard to prevent the cardboard from being skewed and blocking the drying channel, which may cause fire safety accidents.
The process characteristics of water-based polishing. Water-based glossy coatings have the advantages of colorless, odorless, non-toxic, non irritating, fast drying speed of the coating, wear resistance, high temperature resistance, non yellowing, non discoloration, and high transparency and glossiness. Therefore, this process is more suitable for surface finishing processing of food packaging. However, the solvent for water-based polishing is water, which can easily cause deformation of printed products after polishing. Its wear resistance is second only to solvent based glossy coatings. If the outer layer of the cardboard is packaged with PVC plastic film, it is easy to damage the glossy film layer and ink color of the printed product due to the surface sticking of the PVC plastic film. So, the outer packaging material is PVC plastic film, and water-based coatings should not be used for cardboard polishing. Instead, solvent based wear-resistant polishing coatings should be used for polishing.
UV coating process characteristics. UV coating is the use of UV coating oil coated on the surface of printed matter to form a high gloss film on the surface. After being irradiated by ultraviolet light, the upper layer of the coating undergoes photopolymerization and photocrosslinking reactions inside, which quickly solidify and dry, thus avoiding adhesion quality problems and ensuring the rapid operation of the subsequent process. The UV coating coating has the advantages of wear resistance, drug resistance, chemical resistance and good stability. Because UV coating oil does not have the problem of solvent volatilization, it is not like the problem of environmental pollution caused by solvent based glazing process, and its consumption is relatively small, and its production cost is far lower than that of film covering process. So, it is an ideal process to replace plastic lamination and solvent based glazing. However, in production, it should be noted that UV coatings can have a certain stimulating effect on the human skin, and direct UV light can also cause certain harm to the human body. After UV irradiation and drying, the coating will generate ozone, and the production site should have good ventilation and exhaust.
2、 Requirements for Glazing Coatings for Paper Packaging Products
As far as the use and processing characteristics of the product are concerned, the glazing coating must meet the basic requirements of safety, health and environmental protection. Therefore, the glazing oil has good flexibility, leveling, abrasion resistance, acid and alkali resistance and adaptability. In addition, the glazing oil must have high transparency and color fastness, and its surface facial mask layer should have good toughness to better protect the surface of printed products and enhance the waterproof, moisture-proof Performance such as dirt resistance and wear resistance.
The calendering process on the surface of cardboard is a deep processing process based on glazing. The production process is roughly as follows: the printed product is first polished with a polishing machine, and after the glossy film layer of the printed product is dried, it is hot pressed with a polishing machine to form a smoother and brighter mirror effect on the glossy film layer. This is a quality effect that cannot be achieved by general polishing processes, so this production process is more used for surface finishing of pre printed corrugated cardboard boxes, paper boxes, and other packaging products. Traditional calendering coatings use organic solvents such as toluene and Cyclohexanone as diluents. Not only can it easily pollute the environment and endanger human health, but it can also cause pollution to products, leaving safety hazards for product packaging. Therefore, it is not suitable for food and pharmaceutical packaging. From the perspective of packaging safety, non-toxic, odorless, and pollution-free water-based calendering oil should be used.
The waxing process on the surface of cardboard. The production process and equipment are relatively simple, and the operation is also very easy to master. This process uses a waxing machine to evenly coat the heated and melted paraffin liquid on the surface of cardboard or printed matter. After the paraffin coating on the paper surface cools down, it solidifies to form a thin and very smooth wax film, making the paper surface waterproof, moisture-proof, and moldy resistant This process is widely used for surface processing of food packaging, paper packaging, and other non moisture resistant products due to its ability to prevent dirt, rust, oil, and wear.
The spraying process on the surface of cardboard uses a film coating machine to spray a layer of polyethylene or polypropylene with a thickness of 0.01mm~0.07mm on the surface of the cardboard, which improves the airtightness and tensile strength of the cardboard. At the same time, it also greatly improves the moisture, water, oil, and dirt resistance of the cardboard. In recent years, with the continuous prosperity of the market economy, there has been an increasing demand for coated cardboard in liquid beverages, solid frozen foods, and other products, and the process technology for coating has become increasingly mature. According to the usage characteristics of the product, the coating processing of cardboard can be either single-sided or double-sided. The printing quality control of double-sided coated cardboard is 4 points important. If the process control is not appropriate, it is easy to have quality problems with excessive printing. That is to say. Ink printing on PE film without absorption performance can easily stain the back of the printed product. Therefore, when printing double-sided coated paperboard with Planographic printing printing machine without drying device, wear-resistant, strong adhesive and non absorbent ink should be selected for printing to ensure the printing quality of products.
The lamination process on the surface of paperboard is a commonly used finishing process for pre printed cardboard boxes, paper boxes, handbags, covers, and other products. After laminating, printed products can achieve waterproof, stain resistant, color fading resistant, heat resistant, light resistant, and friction resistant properties. At the same time, it can enhance the glossiness, aesthetics, puncture strength, and tensile strength of the product, improving its service life and packaging quality. The general process of film covering is: after the product is printed, the Pouch laminator is used to compound the plastic film and the surface of the printed matter into an integral structure to form a printed matter that combines paper and plastic. There are two types of lamination processes: immediate lamination and pre coated lamination; There are also differences in the process between hot and cold cladding. There are also different types of adhesives for film covering, including water-based film covering adhesive and solvent film covering adhesive. Solvent coated adhesive has high brightness, but there are environmental pollution issues. However, water is the solvent used for film coating adhesive, which has almost no pollution to the product and environment. Therefore, it is widely used for the surface finishing and processing of food packaging materials. Due to the need for classification processing when recycling film covered products, the regeneration process is complex and the production cost is high. Some packaging products are being replaced by calendering or UV coating processes.
3、 The production process of functional corrugated cardboard
Functional corrugated cardboard is a new type of packaging material, which differs from ordinary corrugated cardboard in that the original paper or cardboard box is processed through special technical processes, expanding the functionality of the cardboard box and improving the quality of the cardboard box. Increasing the added value of the product meets the personalized needs of product packaging.
From the perspective of logistics characteristics, product characteristics, and market requirements, functional corrugated cardboard is an important production technology to improve the quality of product packaging and effectively protect goods.
The production process of waterproof corrugated cardboard. The main performance of waterproof corrugated cardboard is that the surface of the cardboard is impermeable, but it cannot be soaked in water, otherwise it will also start to penetrate and break from the inner layer. The main processing process is to use a curtain coating method, where the melted synthetic resin or paraffin mixture flows down into a thin film from the hopper 13 and is coated on the horizontally running corrugated cardboard. After the surface of the cardboard is coated with a layer of resin film or wax film. This type of corrugated cardboard has good water resistance and wear resistance. It is mainly used for packaging pickled products, fruit and vegetable products, and refrigerated food. Due to the soft paraffin layer on the surface of the corrugated cardboard. It is also suitable for packaging high gloss furniture, high-end goods, or industrial instruments that are prone to scratches.
The production process of hydrophobic corrugated cardboard, also known as hydrophobic corrugated cardboard, has a high water repellency. When in contact with wet objects, rain, or splashing, the waterproof surface of the cardboard has a certain water repellency, so that water droplets do not penetrate into the cardboard fibers. The processing process is to first coat the cardboard with hydrophobic substances such as varnish, paraffin, and organic silicon.
It is best to apply a starch film layer on the surface of the cardboard before applying varnish, and wait for it to dry into a film before applying varnish. Organic silicon not only has good water repellency, but also has properties such as flame retardancy, corrosion resistance, and temperature resistance. Paraffin coating has high smoothness, good wear resistance, and water repellency. If appropriate water resistant additives such as Polyvinyl butyral and melamine formaldehyde resin are added to the hydrophobic coating, the water resistance of the coating can be improved, and the water repellency of the corrugated board surface can be better improved. Therefore, hydrophobic corrugated cardboard boxes are suitable for packaging powdery substances that are prone to clumping after moisture absorption, as well as refrigerated food, which can effectively protect products.
The production process of waterproof corrugated cardboard is different from waterproof and hydrophobic corrugated cardboard in terms of performance. When it is soaked in water for a long time, its strength will not significantly decrease. This good performance is related to its processing and processing characteristics. This production process can use a wax immersion automatic paper feeder to continuously feed corrugated cardboard into a paraffin impregnation tank at around 9O ℃, and after continuous impregnation for 6-12 seconds. Appropriate control can be made based on the quantity and number of layers of corrugated cardboard, and it is appropriate to soak the corrugated cardboard with wax solution. After the corrugated cardboard is soaked in wax solution, it can be taken out of the wax tank and excess wax solution can be removed. Then, it is slowly moved in a hot drying room at around 1O0 ℃ to further evenly penetrate the wax solution into the cardboard fibers. Simultaneously flatten the excess wax in the local area. After completing the hot drying, the waxed corrugated cardboard is cooled at room temperature or forced to solidify the wax solution. After soaking in paraffin, corrugated cardboard has achieved good water resistance. This type of cardboard box is particularly suitable for holding fresh seafood, refrigerated fruits, and other products with high moisture content. Another method of enhancing the water resistance of cardboard is to directly add a water resistant reinforcing agent to the papermaking slurry. Improve the water resistance of the cardboard and effectively prevent the surface of the cardboard from falling powder, hair, etc. The production process of fresh-keeping corrugated cardboard uses a special processing technology to make the cardboard box suitable for packaging fresh fruits and vegetables. It can reduce the water loss of the contents, inhibit the growth of bacteria, and absorb harmful gases inside the box. To achieve good preservation effects for fruits and vegetables. The general production methods for fresh-keeping corrugated cardboard include: clamp type, composite type, foaming type, and mixed type. Clamp type refers to the process of clamping the plastic film soaked in antibacterial and preservative into the corrugated cardboard, and then applying preservative inside the corrugated cardboard box. This type of corrugated cardboard box not only effectively prevents moisture evaporation, but also has the effect of regulating and controlling temperature to keep the goods inside fresh. The composite type is a combination of aluminum plated cling film and the inner surface of corrugated cardboard boxes, which enables the box to absorb ethylene gas, prevent moisture evaporation, and reflect radiant heat to prevent temperature rise inside the box. Thus, it plays a role in preserving freshness. The foaming type is the combination of foam plastic and corrugated cardboard, and its fresh-keeping effect is superior to the previous two methods. It has good performance in inhibiting water evaporation, controlling heat resistance, and air tightness. The production process of mixed corrugated cardboard involves adding porous ethylene gas absorption powder to the cardboard or coating special ceramic powder on the base paper that can emit a certain wavelength of infrared radiation. The cardboard boxes produced with this type of cardboard can activate some molecules in fruits and vegetables, enhance their function of resisting microbial erosion, and improve the process effect of fresh-keeping packaging.
In summary, surface treatment of cardboard is an important technical means to improve the added value and quality of goods, improve the packaging grade and quality of products, effectively prevent damage to packaging and goods, and enhance the market competitiveness of goods. So. A correct understanding of the production process and methods of cardboard surface treatment, and the selection of appropriate packaging processes based on the characteristics of the product, undoubtedly have a good promoting effect on improving the promotion of the product and improving the economic benefits of the enterprise.