Views:9 Author:Site Editor Publish Time: 2019-04-20 Origin:Site
EVA hot melt adhesive
EVA hot melt adhesive is a solid, fusible polymer that does not require solvent and does not contain moisture. The main component consists of basic resin, tackifier, plasticizer, filler, antioxidant and viscosity adjustment. The EVA hot melt adhesive is solid at normal temperature, and the colloid after heating and melting is a light brown translucent liquid.
EVA hot melt adhesive has the following characteristics: light brown:
First, the hot melt adhesive is a 100% solid at normal temperature. When heated to a certain temperature, it becomes a liquid, and once cooled below the melting point, it quickly becomes a solid. It has a melting point of 800 ° C, a release point of 7-13 seconds, a cure point of 7-14 seconds, and a cooling point of 2-3 minutes.
Second, it has the characteristics of fast curing, low pollution, and strong adhesion. The rubber layer has both flexibility and hardness.
Third, there is re-adhesion. After it is cooled and solidified on the adherend, it can be reheated and melted and reused.
Fourth, it is easy to use. As long as the EVA hot melt adhesive is heated and melted into a liquid, it can be applied to the adherend, and after pressing and cooling for a few seconds, the need for complete curing can be achieved.
EVA series hot melt adhesive is green adhesive, non-toxic and solvent-free. Since its successful development in the country in the 1970s, it has formed a series of products for packaging, positioning, speaker-specific, bookbinding and refrigerator heat sealing. Products have been widely used in bookbinding, all kinds of packaging, home appliances without device assembly and positioning, cigarette packaging and filters, material composite, hot melt glazing.
Because the affinity of hot melt adhesives is different from that of different materials to be bonded, in order to make the hot melt adhesives more "sticky", the following factors should be carefully considered when selecting hot melt adhesives:
First, the color. Due to the different colors of the substrates, the color requirements of the hot melt adhesive should be different.
Second, the surface of the substrate is treated. The surface treatment of the hot melt adhesive is not as strict as the other adhesives, but the dust and oil on the surface of the adhesive should be properly treated to make the hot melt adhesive better.
Third, the operation time. Fast work is a major feature of hot melt adhesives. The working time of hot melt adhesives is generally about 15 seconds. With the wide application of modern production methods--pipeline, the working time requirements for hot melt adhesives are getting shorter and shorter.
Fourth, temperature resistance. Hot melt adhesives are sensitive to temperature. When the temperature reaches a certain level, the hot melt adhesive begins to soften. Below a certain temperature, the hot melt adhesive will become brittle, so the choice of hot melt adhesive must fully consider the temperature change of the environment in which the product is located.
Five, sticky. The viscosity of hot melt adhesives is divided into early tack and late tack. Only the early viscosity and the late viscosity are consistent, so that the hot melt adhesive and the adherend remain stable. The viscosity of the hot melt adhesive varies depending on the material of the adhesive. Therefore, different hot melt adhesives should be selected according to different materials.
First, what is EVA hot melt adhesive
EVA hot melt adhesive is a solid fusible polymer that does not require solvent and contains 100% moisture; it is solid at normal temperature, and is heated and melted to a certain temperature to become a liquid with a certain viscosity. The molten EVA hot melt adhesive is light brown or white (added titanium dioxide). EVA hot melt adhesive consists of basic resin, tackifier, viscosity modifier and antioxidant.
1 basic resin
The basic resin of hot melt adhesive is ethylene and vinyl acetate copolymerized under high temperature and high pressure, namely EVA resin. This resin is the main component of the hot melt adhesive, accounting for more than 50% of its ingredients. The proportion and quality of the basic resin determine the basic properties of the hot melt, such as the bonding ability of the glue, the melting temperature and the choice of additives. Therefore, the EVA hot melt adhesive for binding paper used for binding should be selected from the varieties with appropriate ratio of ethylene and vinyl acetate, and having certain flexibility, elasticity, adhesion and deformation.
Tackifiers are one of the main additives for EVA hot melt adhesives. If the adhesive force at a certain temperature is only melted by the base resin, when the temperature is lowered, it is difficult to wet and penetrate the paper, and the bonding ability is lost, and the bonding effect cannot be achieved; the tackifier can be added. Improve the fluidity of the colloid and the wettability of the adherend, improve the bonding performance, and achieve the desired bond strength.
3 viscosity modifier
Viscosity modifiers are also one of the main additives for hot melt adhesives. Its function is to increase the fluidity of the colloid and adjust the solidification speed to achieve the purpose of fast bonding. Otherwise, the viscosity of the hot melt adhesive is too large, unable or difficult to flow, and it is difficult to penetrate into the signature, and it cannot be bonded. Firm. By adding a viscosity modifier having a low softening point, it is possible to achieve good penetration and adhesion when bonding.
An appropriate amount of antioxidant is added to prevent premature aging of the EVA hot melt adhesive. Because the colloid is oxidatively decomposed at a high temperature during melting, the addition of an antioxidant ensures that the bonding properties do not change under high temperature conditions.
In addition to the above raw materials, it can also be equipped with some cold-resistant agents suitable for cold-band temperature or heat-resistant agents suitable for tropical temperatures according to the temperature and regional differences.
Characteristics of two EVA hot melt adhesives
EVA hot melt adhesive has been chosen by the majority of users, and the amount is still increasing, because it has the following characteristics:
1 It is usually a solid at room temperature. When it is heated to a certain extent, it melts into a liquid. Once cooled to below the melting point, it quickly becomes solid (ie, hardens to a solid state) and is easily stored.
2 EVA hot melt adhesive has fast curing, strong adhesive force and low pollution. The adhesive layer has certain flexibility, toughness and certain hardness. It is very suitable for the bonding of books and magazines.
3 When the glue is applied to the adherend, and the adhesive layer is cured or hardened, it can be heated and melted and softened to become a glue liquid and re-bonded. For example, when the book is stuck (unstick, sticky, etc.), the cover can be reheated and re-corrected to be a good product, that is, it has a certain re-stickiness.
4 In use, as long as the hot melt adhesive is melted into a liquid adhesive in a hot melt adhesive pot and applied to the object to be adhered, after being pressed and pressed, the adhesive curing can be completed within a few seconds. The degree of hardening cooling and drying can be achieved within 2 to 3 minutes.
Use of three EVA hot melt adhesives
EVA hot melt adhesives used in China are suitable for binding. They are generally divided into high-speed adhesives and low-speed adhesives. The high-speed adhesives have a slightly faster curing speed, and the low-speed adhesives cure slowly. The adhesives are also slightly different depending on the material to be bonded. , coated paper with glue; and there are adhesive (backing glue) and side glue (adhesive on the adhesive) to meet the needs of different bond strength. The use of EVA hot melt adhesives must be prepared before use, such as feeding, preheating, and correct temperature adjustment.
1 plus compound
EVA hot melt adhesive should be added with pre-heating before use. When adding rubber, it is necessary to determine the amount of glue according to the quantity of the processed material or the length of use. Do not add too much material, causing multiple heating of the rubber. Aging, too little feed and material breakage will affect normal production. An approximation should be made before calculation, that is, for every 1000 doses or for each amount of paper.
2 EVA hot melt preheating
Before the EVA hot melt adhesive is used, the solid colloid is first preheated and melted. There are two methods for preheating: one is preheating with oil melting, that is, preheating with a jacketed crucible; the other is preheating with electric panels, that is, directly preheating in a preheating pot with a hot plate device. . The preheating time is generally 2 hours, which is subject to the time when the colloid reaches the desired temperature and has good fluidity. After the preheating is passed, the glue is released through a constant temperature pipe to a working glue pot having a temperature of 160 ° C to 200 ° C.
3 EVA hot melt adhesive adhesion and adaptability
The adhesive force of the hot melt adhesive, in the actual production process, will vary with the temperature of the hot melt adhesive, the difference of the material to be bonded, the depth of the milling back, the height of the rubberizing wheel, and the running speed of the binding machine. Different and different.
1) Hot melt adhesive heating temperature
The softening point (also called melting point) of the hot melt adhesive after heating is generally above 80 ° C, that is to say, when the colloid is heated above 80 ° C, it will soften and begin to melt. This temperature is only the melting temperature of the glue to the extent that it can be bonded to the book, and the heating temperature is raised to 130 ° C ~ 180 ° C before use. The gel at this temperature is suitable for the bonding of books in this book, regardless of viscosity or fluidity.
According to foreign data, when applying glue on ordinary book paper, when the glue temperature is 170 °C, the tensile test value of hot melt adhesive can reach 8.83±0.44N/cm; when the glue temperature rises to 180 °C, hot melt adhesive The tensile test value dropped to 7.33 ± 0.33 N / cm. On the contrary, when the temperature of the glue drops to 155 ° C, the tensile test value is only 5.22 ± 0.25 N / cm. It can be seen that the temperature at which the hot melt adhesive is heated and melted should not be too high or too low. If the temperature of the glue is too high, although the fluidity and permeability of the glue increase, the viscosity and the bond strength decrease. The temperature of the glue is too low. Although the viscosity of the gel rises, the gelatin is thick, but it affects. The fluidity of the glue and the wettability and permeability of the book back coating also reduce the tension and toughness of the glue, and even the phenomenon that the cover and the back of the book cannot be bonded after the glue is applied. Therefore, the heating temperature of the hot melt adhesive is relatively strict and must be controlled within the optimum temperature range. In foreign countries, the temperature control of hot melt adhesives is more stringent (mainly the difference between the use conditions and the environment), and the temperature range is generally controlled between ±3 and 5 °C.
2) The relationship between the paper texture and the glue temperature in the book
When the type of paper and the texture of the book are different, the temperature of the glue should be different. Because this is not only the difference in paper fibers, but also the difference in the thermal conductivity and cooling rate of the paper due to the difference in paper quality. Taking the thermal conductivity of coated paper (also known as coated paper) and letterpress paper (non-coated paper) as an example, the former cools the glue faster than the latter because the inorganic matter contained in the coated paper is better than the relief paper and newsprint. The height is about 10 times. The inorganic material has good thermal conductivity, which can accelerate the cooling rate of the hot melt adhesive.
If the sizing temperature is also 170 ° C, let us look at the tensile test value of the hot melt adhesive. The letterpress paper can reach the above-mentioned tensile force value, and the tensile test value of the coated paper can only reach 1.86±0.11 N/cm (65 g/m2) and 1.46±0.11 N/cm (100 g/m2). The pull value of the coated paper after hot-melt adhesive is so low that it is obviously not ideal. In order to increase the tensile strength of the coated paper, it is necessary to increase the temperature of the coating (enhance the penetration) and increase the strength of the glue. If the temperature of the glue is around 190 °C, the tensile strength of the hot melt can reach 4.1 to 3.9 N/cm. It can be seen that the temperature of the glue used for the hot melt adhesive should vary depending on the texture of the book paper material.
3) The relationship between the opening time of EVA hot melt adhesive and the running speed of production equipment
The wireless adhesive is set in the process, and there are three times when the hot melt adhesive is used, which should be strictly controlled and mastered. One is the open time, the second is the curing time, and the third is the cooling hardening (drying) time.
The opening time refers to the time when the glue is applied to the back of the book, the cover is wrapped, and the setting is clamped; the curing time is the time when the cover of the clamped shape is adhered to the back of the book and the glue is solidified. The cooling hardening time is the time during which the booklet that covers the cover is solidified and the glue is cooled and hardened to be cut. Only after the processing of these three times as required, the book can be shaped, and the desired adhesive effect can be achieved after cutting.
The use of hot melt adhesives is closely related to the speed of the equipment. For example, the opening time of EVA hot melt adhesives is generally 7 to 13 seconds. At this time, the perfect binder is finished from the beginning of coating. , that is, the application of a single glue → secondary glue → uniform adhesive cover → clamping and shaping work process. That is to say, if the above work process is completed within this time, the use of hot melt adhesive can obtain a good bonding effect; on the contrary, the effect of hot melt adhesive bonding is certainly not ideal, and the bond may not be firm and stick to it. Problems such as dropping pages after sticking. Therefore, when selecting the model of hot melt adhesive, it is necessary to consider whether the opening time matches the running speed of the perfect binding machine. The curing time of the hot melt adhesive is basically the same as the open time, generally 7 to 14 seconds. The opening time is slightly longer and the curing time is slightly shorter, which is more conducive to the bonding of books. In particular, the glue is used in the production line of the perfect binding, because the production line is a line operation from the beginning of the collating machine to the cutting of the finished product, and the various parts are coordinated according to the movement of the beat, especially on the bag. The time for the cover to be sent to the cutting part of the book must be guaranteed according to certain rules and corresponding time, in order to achieve the desired effect after the book is cut. To be precise, the time for the delivery of the book should be such that when the book reaches the cutting machine, it has reached the level of cooling and hardening of the book back, so that the quality of the bookbinding can be guaranteed after the book is cut. This process should be completed in 2 to 3 minutes, otherwise it will cause deformation of the back of the book, wrinkles, unstable size, and sticky knife. Therefore, the length of the book delivery device (conveyor belt) of the linkage production line needs to be selected according to the operating speed of the equipment. Generally, the length of the common conveying device is 35m to 45m, that is, it is necessary to ensure that the book with the cover is naturally cooled for more than 2 minutes during the movement on the conveying device.
Fourth, the environment and conditions of using EVA hot melt adhesive
Nowadays, EVA hot melt adhesives are used for the process of wireless binding processing. This book is becoming more and more popular. There are almost all wireless binding equipment in large, medium and small processing factories nationwide. However, due to the rush to launch, to strive for more activities, more processing and increase efficiency, and neglect the scientific nature of the environment and conditions of using EVA hot melt adhesive, the management department also lacks guidance in this aspect, so there are many unsatisfactory in processing. Unresolved quality problems, often blame this strange can not find the real reason. Here are some suggestions for the use of the unit.
1 Temperature and humidity of the production plant
EVA hot melt adhesive is a hot melt adhesive that is affected by room temperature and humidity during the open time after application. In general, the temperature in the indoor (ie, in the production workshop) should be maintained between 15 and 27 ° C (foreign as France requires 21 to 25 ° C) and the humidity should be maintained at around 50%. However, it is understood that the use of hot melt adhesives in the country can meet the standard requirements very little, so in some areas when using hot melt adhesives, summer (when the temperature is high) with too much bubble, hard to solidify and harden the cooling, cut book stick knife Such problems; in the winter (low temperature), the openness of the adhesive, curing, hardening and cooling time is shortened, the stickiness is not strong or sticky, and the book pages are broken after sticking. In other areas, the humidity is too large, the book is not fixed after the cover, and the finished product cannot be cut. These phenomena are directly related to the temperature and humidity of the work building. So ask:
1 Conditional units, it is best to install constant temperature and humidity equipment in the workshop using wireless binding equipment to ensure that the temperature and humidity are within the standard range, which is also the requirement for standardized production.
2 Unconditional units must strive to create conditions and educate scientific and standardized production management; if there are no conditions temporarily, we should also think of some remedies, such as high temperature in summer (high workshop temperature), temperature used by hot melt adhesive. It can be lowered by 10 °C to accelerate its curing speed; when the temperature is low in winter (low workshop temperature), the temperature of the glue is increased by 5 to 10 °C, so that the opening and curing time of the glue is slower and meets reasonable requirements. But this method of treatment is a timely and not a reliable and permanent method.
3 The finished books of wireless adhesive binding shall be stored in a warehouse or factory building at a temperature of between 1 and 40 ° C. It is strictly forbidden to accumulate for a long time on the wall, by heating (winter), by the window and in the open air. In order to avoid the book being damp or heated, the paper is deformed and the adhesive changes, resulting in irreparable damage, because this situation has appeared in many countries and suffered great losses. Modern post-press processing equipment, materials, and processes have changed a lot. It has been very different from the past few decades. It is not "a place where you can bind". It needs a modern environment and conditions to adapt to new processes. , the need for new materials, new equipment production. The management and technical personnel engaged in this profession must update their understanding and correct some prejudice against post-press binding processing.
5. Matters needing attention when using EVA hot melt adhesive
EVA hot melt adhesive material is a thermoplastic glue, which is different from ordinary cold glue. According to its characteristics, the following points must be mastered and paid attention to in order to achieve good results.
1 To understand and master the technical performance (technical parameters) of various types of EVA hot melt adhesives. Different types of hot melt adhesives have different opening time, curing time and hardening cooling time. In particular, it is necessary to strictly distinguish the use period of summer rubber and winter glue due to different regions; when the temperature is different, the opening and curing time will also change and cause adhesion. not effectively.
2 Use EVA hot melt adhesive, avoid direct heating with open flame, be sure to use a spacer oil bath to heat, or use a sealed electric heating plate heating device.
3 Solid EVA hot melt adhesive must be preheated by preheating device before use, and then placed in the working glue box of the glue application. The preheating time is usually 2 hours. Do not put solid rubber blocks (pre-heated glue) directly into the working plastic box to avoid uneven gelatin temperature, poor fluidity or the gel that is not completely melted on the back of the book, so that the glue is uneven and sticky. The difficulty of the knot affects the fastness and appearance quality of the book.
4 The amount of glue in the preheating pot should be properly controlled, not too much or too little. If the amount is too much, the colloids will melt and accelerate the aging and reduce the viscosity, which will affect the adhesion; however, if the amount is too small, it will affect the production.
5 Use EVA hot melt adhesive to complete the bonding process during its opening time. In the event of a downtime, the book block that is being glued in the book holder or that has been glued on the coating wheel should be removed immediately.
6 Use the perfect binding equipment to close the pre-glue and working glue pot during the long-term repair period to prevent the gel from aging and deterioration. It is better to have a separate line or plug hot glue.
7 The temperature of the molten colloid should be strictly controlled within the specified range.
8 Preheating the glue pot and the working glue pot should be cleaned regularly to prevent the accumulation of impurities in the glue liquid and affect the accuracy of the glue temperature control. Even the malfunction of the thermostat causes the glue to smoke and burn. In normal production conditions, the preheated rubber pot should be cleaned every three months. The working glue pot (for glue application) should be cleaned once every half month. The system for cleaning the glue pot should be determined and strictly enforced.