Observing the quality of binding from the dynamic change of bonding

The use of bonding technology for book binding is an old and practical technology. With the development of science and technology, natural products (bone glue, starch, etc.) have been used as adhesives and have entered a new period of development in which multi-component synthetic adhesives are composed of polymer blends and polymers. The use of wireless glue-binding to replace flat-booking has fundamentally changed the backwardness of the post-printing process and ensured the rapid development of the printing industry as a whole.

In the early stages of the renewal of the old and new technologies of wireless binding and peacemaking, some problems will inevitably arise. Mainly manifested as the use of glue bookbinding technology after the book, there are batches of pages, scattered racks, not easy to start reading, turning after the book spine deformation and other issues. Even the senior leaders were alerted to let the printing industry's veterans issue "adhesive clearance has no clearance" advice. The competent department of the industry also proposed the overall layout of the binding quality for the year 2000.

Why do these problems occur? Even the world-class Martini linkage production line is not spared?

The key lies in the unique characteristics and advantages of the adhesive (book block and cover), adhesive (glue glue), and adhesive (binder), which cannot be combined in the glue production process. New dynamic changes in production conditions restrict damage.

First, the adhesive body (book block and cover)

The rapid development of the market economy has led to the prosperity of the press and publishing industry, which has continuously created a record high in the quality and quantity of China's paper industry and its products. To improve paper quality in China, special sizing agents, dispersants, flocculants, defoamers, lubricants, adhesives, water repellents, anti-adhesives, wetting agents, release agents, softeners, anti-mould agents, retention The application of additives and fine chemicals such as filter aids has opened up a broad prospect for improving the production process and product characteristics of pulp, paper and board. Mastering the characteristics and technical requirements of large amounts of caustic soda, bleach, fillers, and coatings, and accurately controlling the amount used is an important part of a stable pulp and papermaking process.

The book blocks and cover sheets used as adhesive bookbinding adhesives have been developed toward coated paper (offset paper and coated paper), and they are still used for cover materials in a large number of printing materials for elementary and junior high school students and general books. Coated paper (off-set paper, coated paper), and paper for text (relief paper, offset paper).

The main source of material for the base paper is wood pulp fibers. The wood pulp used in the base paper includes chemical softwood pulp, chemical hardwood pulp, and mechanical wood pulp. In general, the number of fiber units per unit volume of "hardwood" is 10 times greater than that of "cork"; the fiber size of northern wood is smaller than that of southern wood; softwood fibers are longer and have better strength. However, there are wood species such as southern yellow pine of softwood fiber, western hemlock and red rubber tree of hardwood fiber, birch, white cypress, oak, beech and so on. The difference in fiber size, "fines" produced after being beaten or refined, will fill the voids in the fiber layer and determine the difference in smoothness, evenness, and opacity of the base paper.

In the chemical method, lignin and resin, etc. together with the fibers are dissolved during cooking and separated from the fibers by washing and finally bleached to obtain a bleached pulp. Alkaline systems have the feasibility of using fillers instead of fibers. The filler quantifies the paper while also reducing the paper strength.

The fibers constituting the base paper have a diameter of 20 μm to 65 μm even after the papermaking process of refining (or beating), pressing, and drying. The paper is subjected to water swelling and cellulose debonding alternately during the papermaking process. Each cycle of "a wet" and "dry" increases the roughness of the original paper surface.

In the refining process of raw paper into pulp, when the fibers are cut excessively, the result is a shorter fiber length.

The proportion of forest area in China is very small. Pulp for papermaking basically depends on imports. In order to protect forest resources and reduce papermaking costs, within 20 years before fast-growing forests were grouped out and in order to protect the eco-environment, the use of non-wood pulp for base paper, base paper coating, and raw paper coating was adopted and will continue to be adopted. The necessary ratio and technology are implemented in the paper industry in our country.

This means that in both perfect binding and binding papers, there are also defects such as rough surface, low strength, and easy to pull off the powder compared to foreign advanced countries. Under the new conditions of pre-printing electronic color separation, laser photocopying, and multi-color high-speed equipment for printing applications, the printing cycle is greatly shortened, and the requirements for binding are both good and fast. The dynamic new reaction on the adhesive body is:

1. Rough surface, low strength, easy to pull off the powder inside the core of the document, after the bookbinding machine milling back milling cutter cutting surface, not a smooth and flat interface, but the spine coating surface and the edge of the milling slot plush Velvet convex protrusions. This not only reduces the mechanical processing geometry of the bond, but also changes the state of the bonding interface, and at the same time blocks the wetting and filling of the bonding surface by the hot melt fluid within a specified time.

2. Quick-free printing has no longer time-lag interval requirements for binding processing. The water absorbed by the paper, especially the ridges of the bookbinding book, is too late to be distributed to the outside world, and the content album enters the glue-binding production line in a state of high moisture content. . There will be three new phenomena happening:

1 After the glue was booked, the moisture in the inner album was gradually evaporated, causing the paper to shrink, and the same amount of retraction as the milling groove. The separation of glue and hot-glued glue was loose and the "slotted small glue" was separated;

2 When the contact album was in contact with the adhesive hot melt adhesive, the hot melt (170oC) hot melt caused the moisture contained in the surface of the album to volatilize. At the same time, the coated hot melt adhesive is unable to press the water vapour that escapes to the surrounding atmosphere to the book bonding interface. The volatilized and contained water vapor molecules are not only a newly formed dispersion layer between the colloid and the adhesive body, but also cause gelation on the surface of the melted hot melt adhesive, and the overall fluidity is changed and destroyed. Slot infiltration and filling. In particular, it is more serious when the milling flute is blocked by the fiber fluff produced by cutting.

Second, adhesive material (adhesive hot melt adhesive)

After milling and back-slotting the surface of the back of the book block through the bookbinding machine's gluing roller, it is evenly coated with a certain thickness (width) of adhesive material - glued hot melt adhesive, and then automatically conveyed Cover bonding. Curing occurs as the adhesive spreads, rheology, penetration, combination, and temperature drop. When the distance between the macromolecules of the adhesive and the surface of the adherend is less than 5A, they will attract each other, generate van der Waals forces or form hydrogen bonds, covalent bonds, coordination bonds, ionic bonds, etc., and insert the wedge-shaped colloid into the milling groove The glue that has penetrated into the pores cures and generates numerous small “glue hooks” that complete the binding process.

Due to the objective reality of the structure and the surface state of the aforementioned adhesive, the poor weatherability of the adhesive composition, and the inevitable aging of the coating process, the peeling strength and uneven peeling of the adhesive layer are eliminated. Strength, impact strength and low temperature toughness are low. At present, the industry lacks effective pre-use non-destructive inspection methods and technical standards for the quality control of adhesives, so that binding companies can hardly distinguish between adhesives with glued hot melt adhesives. In order to verify the high cost of quality.

The composition of the adhesive is:

A component main adhesive resin 1
Primary adhesive resin 2

B component regulator 1
Conditioner 2

According to the ratio of tackifying resin and main tackifying resin in component A, the affinity of tackiness agent and tackifier is improved and improved; different regulators are used in blending component B to adjust the softening point and improve the fluidity. Increase the purpose of penetration. Add an appropriate amount of antioxidants to delay or prevent the aging of the adhesive during the synthesis and use of high temperature conditions. It should be said that the design theory of A and B components and the idea of ​​proportional adjustment are correct.

The problem lies in the synthesis and use of the production process and raw material selection and configuration.

The traditional cauldron production method can cause aging of the bonding material in the synthesis process due to the error that the temperature control and conduction cannot be accurately controlled.

The advanced rod extrusion process often produces uneven blends because of the higher viscosity and different softening points.

In order to increase the affinity with the spine after the surface treatment, the appropriate amount of tackifying resin is used to affect the impact strength and the self-ageing gene is significantly faster.

In order to guarantee the rapid and full filling of the milling groove, its fluidity must be improved. The quality and quantity of the modifier modifier used in turn adversely affect its own peel strength and low temperature toughness.

Manufacturers of hot melt adhesives with extremely different levels of technology are peddling the market at low prices and engaging in unfair competition. The binding and processing enterprises choose purchases at price rather than quality, and push glued hot melt adhesives into production errors from both supply and demand.

Third, the binder (binder)

The bookbinding process reform of 7 billion books and books (including 3.6 billion textbooks) per year has promoted the development of bookbinding machines. At present, binding companies use 480 to 600 bar/hour bar type bookbinding machines and 900 to 4,000 bar/hour in parkbooks, and most of them are not equipped with variable frequency systems. In the actual production operation process, it is difficult to ensure the consistency of the groove depth and pitch. Binding-linked thread milling cutter pallets are seriously worn during the processing of domestic-use paper prints and replaced more frequently. After the replacement, it also tends to occur before, after and left and right deviations, affecting the milling back slotting standards.

The serious problem is that the open top of the glue tank has an open structure and its volume is more than 2 hours.

Easy-to-apply, open glue tanks and revolving-rolled rubber wheels increase the contact area of ​​the hot melt adhesive with air to promote sufficient oxidation. In order to ensure even coating, a large amount of hot melt adhesive reserves, and the heating temperature that has been kept during storage, it is the root cause of rapid aging of the hot melt adhesive and reduced strength. The drawing of rubber across the entire length of the perfect binder is an indication of the aging of coated or uncoated rubber.

In addition, the error caused by the quality and sensitivity difference of the heating element itself can be higher than 100oC, which not only makes it difficult to control the aging of the colloid, but it also can not guarantee the overall good fluidity when adding the new compound.

Fourth, adapt to improvement

Based on the status quo of adhesives and the progress of printing technology, adhesives and adhesives should be adapted to the technical improvements of adhesives. Fundamentally speaking, the quality of the binding is determined by the quality of the glued hot melt adhesive and the stability of the glue production process.

1. As a bonding material, the synthesis process of glue-adhesive hot melt adhesives should be based on the improvement of the stability of the blending modification.

The selection of raw materials for the polymerization components should be based on ensuring quality. Through the use of new and superior materials, the contradictions that affect each other and influence each other, such as viscosity and strength, strength and softening point, softening point and fluidity, fluidity and toughness, are solved.

To change the design thinking that simply changes the temperature to change the fluidity and guarantee the gluing effect. Established innovative technology for the development of low-temperature (≤130oC) bottom and edge-adhesive general-purpose new-adhesive hot melt adhesives. Thoroughly solve the qualitative aging caused by melting at high temperature (≥170oC). The new glue-adhesive hot melt adhesive should also have the advantages of small specific gravity (≤0.95), dosage (low spine coating 0.5~1.3mm), and good containment and affinity with paper fiber fluff.

2. Binder's milling cutter should be replaced regularly to keep it sharp and have a good working interface.

The pallets should be grounded to ensure that the work surface is consistent.

Calibrate the accuracy of the colloid melting electric heating element, master the basic error, and change the glue tank under the premise of guaranteeing uniform coating. Minimize the amount of glue in the tank. At the same time equipped with pre-melting tank (≤ 100oC) secondary glue supply device based on coating needs quantitative supply.

Clean up the brush wiper in time, carefully maintain and inspect the suction device to ensure that the paper scraps are completely separated from the booklet album.

3. Conduct technical training for production management and operation personnel to improve their theoretical level and operating skills. Can better handle the problems that arise in the production process.

4, as soon as possible to determine the quality of the glue to ensure the "adhesive hot melt adhesive technology standards" and to facilitate the operation of the company's "hot melt adhesive quality standard inspection methods", standard hot melt adhesive production and use, to eliminate the listing and use of non-standard products .

Reprinted from: Hao Hao Printing

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