In the packaging industry, adhesives are a very widely used material. In the corrugated boxes, folding boxes, paper pallets, paper tubes, and paper protection corners, adhesives are used, and the scope of use of the adhesives is also covered. From the papermaking to corrugated processing, paper or paperboard layer bonding, veneering, film and adhesive molding and other multiple processes. Therefore, for the packaging industry, its importance is naturally self-evident.
For a long time, due to the small proportion of the cost of the adhesive in the packaging products, it has not been given sufficient attention, so many packaging companies lack sufficient understanding of the adhesive. For this reason, this article will briefly analyze the market conditions, purchase methods and quality requirements of adhesives, in order to provide some reference for the purchasing personnel of packaging companies. Only by purchasing high-quality adhesives, can we ensure the bonding quality of the carton.
Current Market Analysis of the Adhesive Market According to statistics, the current annual growth rate of the adhesive market for domestic packaging has reached 8% to 10%. From the perspective of the development momentum of the packaging industry in China, this growth rate may continue. As the competition in the packaging industry continues to increase, packaging companies gradually move towards rationality and maturity in the procurement of adhesives, and the use of adhesives has become diversified, environmentally friendly, and low-cost.
Corrugated board processing is one of the most used adhesives in the packaging industry. Most of the adhesives currently used are self-made heat-curing starch adhesives, and a few manufacturers have insufficient equipment capacity or use cold-formed corrugating technology to use synthetic resins or Oxidized starch binders. Heat-curable starch adhesives are made by cardboard manufacturers using starch, caustic soda, and borax, and they are used to glue the adhesive to glue the cardboard.
The amount of adhesive used for covering (crepe paper) is second only to the corrugating process. At present, there are three types of brewing alkali, synthetic resin and starch binder on the market. The silicate is also called water glass, its adhesive strength is still acceptable, but there is a major shortage of synthetic resin binders such as slow drying speed, easy efflorescence, moisture absorption, and damage to carton properties. , Made of polyvinyl acetate emulsion. Due to the scarcity of materials, high costs, and high energy consumption, its market share is rapidly declining. In stark contrast to this, starch adhesives quickly occupied the market due to its many advantages such as fast initial adhesion, firm bonding, good water resistance, low cost, and environmental protection. It is foreseeable that in the coming decades, unless newer materials emerge, the water glass will be completely withdrawn from the market. Starch adhesives will occupy most of the market share. Synthetic resin will only be used as a supplement to become the adhesive market for facing materials. The inevitable trend of development.
In the past, due to limitations in drying speed and adhesive strength, the bonding of ordinary cartons, paper tubes, paper cards, and paper pallets basically used synthetic resin adhesives. With the continuous development of starch adhesive technology, many starch adhesives newly released on the market have the same drying speed and adhesive strength as synthetic resin adhesives, and the cost is much lower than that of synthetic resin adhesives.
At present, most of the adhesive products used in the market are solvent-based polyurethane adhesives. In view of the harmful effects of solvents on the human body, there are hidden dangers when using them. Some manufacturers have developed environmentally friendly, non-flammable, non-toxic, and widely adaptable environments. Waterborne polyurethane adhesive. However, its adhesive strength is lower than that of the solvent type, the drying speed is slow, the energy consumption and the cost are high, and the development prospect is not optimistic. Recently, foreign companies have also produced solvent-free polyurethane adhesive products. Solvent-free polyurethanes are environmentally friendly products in the true sense of the word. They have strong peeling power, low energy consumption, and a wide range of applications. Therefore, they must be rapidly promoted in the market.
In addition, some of the surface of the carton covered by the film, over UV treatment due to the permeability of the adhesive is particularly high, use some of the coating film, UV box adhesive products. Advice on the purchase of adhesives Packaging companies in the procurement of adhesives, in addition to the cost and characteristics of adhesives trade-offs, but also consider whether to match the company's equipment production capacity, operating methods. Otherwise, even expensive adhesive products may not meet the requirements of the company. In order to make better use of adhesives, packaging company procurement personnel should pay attention to the following aspects.
Necessity of using starch adhesive
The use of starch binders instead of synthetic resin binders will benefit cost savings. The starch adhesive has excellent characteristics such as fast drying, strong adhesive force, no pollution to the environment, and very low cost. In adhesive, ordinary carton bonding, paper tube bonding and paper pallet bonding, starch adhesives can completely replace the synthetic resin adhesive.
Advantages of hot melt adhesives
In many adhesives, the hot-melt adhesives have the shortest drying time, and hot-melt adhesives should be used for the adhesive molding processes that require instantaneous drying and curing. Hot melt adhesives are very suitable for the bonding process between plastic foams or EPE materials and paper. They not only dry quickly but also have a very strong bond. It should also be noted that although hot melt adhesives are the most widely used adhesives, they are not suitable for bonding of paper products that have been exposed to UV varnish.
Adhesion-coated products with UV varnish
Paper products with UV varnish on the surface require special attention for adhesion. At present, there are three commonly used bonding methods, one of which is to use primer oil first, then UV glazing, and then use a special UV box to glue the box glue; the other is to use a partial UV method to combine The parts are protected from UV varnish and then bonded with white latex. Third, the bonded parts are ground before bonding, and then coated with white latex. After the surface of the coated paper products, it is best to use a dedicated box glue sticky box glue.
Select adhesive according to job mode
It is also very important to select a binder with a suitable drying time depending on the mode of operation. The drying time of the adhesive can be divided into two aspects: the initial dry time and the dry time. The initial dry time is the time that the adhesive force generated after the adhesive is coated is sufficient to destroy the adherend. The initial drying time should be matched with the bonding process and bonding equipment, otherwise it will affect the bonding quality. Drying time refers to the time after a long time of drying to enter the next process. The thorough time directly affects the product delivery cycle.
Different working methods choose adhesives with different properties
According to different operating methods, the performance indicators of the adhesive used must also be different. Taking the snaking process as an example, the automatic squeegee has a high speed and therefore requires a lower viscosity of the adhesive and rapid drying. However, the manual squeezing speed is slow, and the viscosity of the adhesive is required to be slightly higher, and the drying speed cannot be too fast.
Consider the shelf life of the adhesive
When purchasing adhesives, the storage period should also be considered. Storage period refers to the time that the adhesive can maintain stable performance after storage under specified conditions. When purchasing, it is necessary to determine the minimum shelf life of the adhesive according to the production situation of the company. For general enterprises, the shelf life of adhesives should be more than one month.
Use of different state adhesives
At present, the common forms of adhesive on the market are emulsion, powder and solid. Emulsion glue can be used directly, but there are disadvantages such as high transportation cost, short storage period, and taking up storage space. Powdered and solid adhesives need to be converted into emulsions before they are used in certain ways, but they have a long storage period. Save on transportation costs and storage space. Taking starch adhesives as an example, in the Pearl River Delta region, due to the dense carton manufacturers and developed transportation, most packaging companies purchase emulsion-like starch adhesives; in most regions in the Mainland, due to the scattered and relatively small scale of carton enterprises, Use powdered starch binders. Therefore, different forms of adhesives should be selected according to the specific conditions of the company during the procurement.
Requirements for adhesives for different uses
Different uses of paper products have different requirements for adhesives. General paper containers only require sufficient adhesive strength during storage and transportation. For food, cosmetics, and pharmaceutical packaging, in addition to adhesive strength requirements, the adhesive used must be odorless, Non-toxic, in line with national safety and health regulations and environmental protection requirements. Some ingredients in the adhesive, such as accelerators, plasticizers, antioxidants, etc., may transfer to the inner surface of the packaging material and contaminate the food and must therefore be limited. In addition, the various resistances of the adhesives should also be investigated according to the specific use of the paper products, such as heat resistance, water resistance, chemical resistance, aging resistance, low temperature resistance, and the like.
Adhesive safety
The environmental protection and safety of adhesives is also one of the factors that must be considered. Solvent-based adhesives use a large amount of organic solvents, which not only seriously pollute the environment, harm human health, but also cause fires. Therefore, it should be possible to search for water-based or solvent-free adhesives.
How to judge the quality of adhesives
Determine the quality of the adhesive, generally from the adhesive strength, drying speed, viscosity, solid content, PH value and other aspects to consider.
Adhesive strength
The adhesive must first have sufficient adhesive strength to ensure that the adhesive does not affect the function of the paper product. To determine whether the bonding strength of the adhesive is acceptable, the two adhered materials can be torn along the adhesive interface. If it is found that the adhered material is damaged after tearing, it is proved that the adhesive strength is sufficient; if only the adhesive interface is separated, it indicates that Adhesive strength is insufficient. Sometimes the binder with poor performance will be debonded and the film will be brittle after being stored in high temperature or low temperature environment for a period of time. Therefore, it is necessary to perform high temperature thermal deformation and low temperature embrittlement experiments to determine whether the quality is reliable. The test method of high temperature heat change is to put the carton that has been completely cured at the bonding place in a constant temperature oven at 60° C. and bake it for 24 hours. After cooling, the hand taps the joint of the carton until it separates, and tears if adhered. It shows that the heat resistance of the adhesive is good. If the adhesive material is intact, only the bonding interface is disengaged, indicating that the heat resistance is not enough; the low-temperature embrittlement test method is to put the paperboard with the completely cured adhesive at -15°C. In the environment, it was frozen for 24 hours. The method of determination was the same as that of the high temperature thermal deformation test method.
Drying speed
When choosing an adhesive, it must be measured whether the drying speed matches the bonding process. The general hand-bonding process is slower and requires a longer initial drying time, while the machine-bonding process is faster and requires a shorter initial drying time. In terms of thorough time, the vast majority of cases require the sooner the better, so that we can enter the next process as soon as possible.
Viscosity
Viscosity is the most important factor affecting the quality of adhesives. If the viscosity is too large, the coating is thick, the amount of glue is large, drying is slowed down, and the wetting and penetration of the adhesive on the surface of the adherend are also affected, thereby directly affecting the adhesive strength; if the viscosity is too low, the coating is applied. The layers are thin, dry quickly, and are prone to problems such as poor adhesion. Therefore, packaging companies must constantly check the viscosity to ensure that the bond strength is within the desired range. The ideal viscosity range for various adhesives is not the same, such as 50 ± 15 seconds for corrugated paper board adhesive, 50 ± 10 seconds for automatic paper glue, 70 ± 15 seconds for manual paper glue, and glue for stick boxes. 4000mPa. S～7000mPa. S and so on.
Solid content
Solid content is also one of the important factors affecting the quality of the binder. The higher the solids content, the stronger the adhesion and the faster the drying speed. In particular, for the corrugated board processing technology and the affixing process, the higher the solid content of the binder, the quicker the initial dry and dry time of the cardboard and the higher the production efficiency. Cardboard with a binder with a high solid content absorbs less water, and the cardboard produced has good hardness and is not easily warped and deformed. Therefore, under the same conditions of other technical indicators, high solid content will help improve production efficiency and maintain the quality of paper products.
pH value
Synthetic resin adhesives are mostly weakly acidic and do not negatively affect the bonding process and paper products, but water glass and starch binders are more basic. The high alkalinity not only causes corrosion to workers and equipment, but also sometimes corrodes the adherends, forms marks that affect the appearance, and reduces the moisture resistance of the paper products. Therefore, the impact of pH on the product must be taken into consideration when purchasing the adhesive.
For corrugated paperboard adhesives, it is necessary to purchase starch, caustic soda, borax and other materials for self-adhesives. The quality of starch materials should be strictly controlled. The water content of starch should not be too high and should generally be maintained at 12% to 18%; the protein in starch The content should not exceed 1% of the content is better than 0.5%. At present, the most commonly used starches include corn starch and tapioca starch, corn starch binders are more prone to retrogradation, but strong adhesion; tapioca starch binders are more stable, but the adhesion is not as good as corn starch binders. In the procurement of starch, may wish to do occasional testing of starch to ensure the quality of the adhesive.