Analysis of the reasons for the bad peeling degree

2022-10-21
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Analysis of the reasons for the reduced adhesive force and poor peel strength of the composite film

the reduced adhesive force and poor peel strength of the finished composite film are related to many factors. Such as: the influence of adhesive, unsatisfactory surface tension value of composite substrate, affecting peel strength, non-standard operation process, the influence of drying temperature, improper temperature of hot steel roller, and the influence of film substrate additives, etc. Now it is analyzed separately and found appropriate solutions to reduce the failure phenomenon of poor peel strength to the lowest point

the variety and quality of adhesive do not adapt to the substrate to be compounded, which affects the peel strength.

for composite films of different purposes, appropriate substrates and adhesives should be selected. For example, when there is no aluminum foil to participate in the composite, use a general-purpose adhesive. If there is aluminum foil compounding, and the end use is to package sour and spicy foods containing liquids (such as mustard, fruit juice, soy sauce, peanuts and other foods), special adhesives for aluminum foil with anti sour and spicy substances should be selected. When choosing special adhesives for aluminum foil, priority should also be given to adhesives with slightly higher molecular weight, relatively uniform molecular weight distribution, good solvent release and good coating performance. Although the adhesive with small molecular weight has good coating performance, it has strong molecular activity and will pass through the extremely thin aluminum layer, resulting in the decrease of peel strength and adhesive force. If the composite bag is to undergo high-temperature cooking and sterilization, the high-temperature resistant (121 ℃ or 135 ℃) cooking adhesive should be selected, and the general adhesive must not be used. The general adhesive is not temperature resistant, and the composite film will usually be layered under 80 ℃, which can not meet the packaging requirements for peel strength, colorless transparent liquid. Our company often uses pu1750 and pu1875 adhesives produced by Huaguang resin company of Zhejiang New Oriental ink group for packaging of high-temperature cooking and sterilization. The effect is good. It can reach n/15mm in pet/cpp structure and n/15mm in pet/al and ny/al structure

for 15 μ PA/70 μ The composite structure of mldpe does not use 300 pu-1875 polyurethane adhesive, and the effect is good. There are several points to pay attention to when using this adhesive: 1) the surface after corona treatment of the film should reach 3.8 × ten ˉ 2n/m or more, the ideal bonding effect can be obtained; 2) The diluent usually adopts ethyl acetate or ethyl acetate, in which the water content shall not exceed 3/10000 and the alcohol content shall not exceed 2/10000; 3) Do not mix solvents containing active hydrogen into the glue solution. Such as: water, alcohol, amines; 4) Pu-1875 adhesive has the best performance when the ratio of main agent: curing agent: ethyl acetate =1:0.2:1.8 (weight ratio)

poor penetration of the adhesive into the ink, floating on the surface of the ink, and poor adhesion fastness between the ink and the substrate will also lead to delamination of the composite film, which is manifested in places with ink, especially in multicolor overprint areas. The ink is pulled down by the adhesive. Use high solid content adhesive to have enough time to penetrate into the ink layer and reach the surface of substrate. Properly increasing the amount of glue is conducive to improving the composite fastness. Selecting appropriate ink and improving the surface tension of substrate to improve the fastness of ink adhesion are also one of the ways to solve the problem. In the process of compounding, it is required that the adhesive has good fluidity and flattening. If the adhesive is deteriorated, muddy and white, it can no longer be used if it is emulsified. Therefore, when preparing the adhesive, it must be prepared appropriately according to the needs

insufficient glue amount and uneven coating will directly affect the adhesive force and peel strength

insufficient adhesive coating amount and uneven coating will also lead to reduced peel strength and adhesive force, which is the most common in the use of one component hot-melt adhesives and cannot be ignored. When using one component hot-melt adhesives, the concentration of main glue will directly affect the peel strength. We note that bopp/opp, bopp/vmopp In bopp/opp composite film, if the inner layer thickness is more than 30 μ M, the peel strength is the easiest to decline. If one component adhesive is used, a small section of composite finished products should be taken for Peel test during the compounding process, and corresponding records should be made at the same time. Generally, the ratio of main adhesive: ethyl ester is 50:50, and the effect is good. The amount of glue applied is determined by the cavity volume of the roller and is closely related to the operation concentration. If the adhesive ratio concentration is high, Ji Gaofang et al. Discussed the use of PMMA artificial eye tablets in the beauty of acquired eyeball loss caused by eye trauma, eye tumor and other reasons. The results showed that 1155 cases of artificial eyes made of PMMA materials have no crowding reaction, and can be comparable with healthy eyes in color and transparency. Combined with hydroxyapatite artificial eye platform implantation, it can achieve the effect of simulation activities. The material tension value is appropriate, and the amount of glue is also moderate, If the peel strength of the composite film is still not ideal, it should be considered to replace the corrugated roller to increase the amount of glue. The general specification of the corrugated roller is 80 μ m、100 μ m、120 μ m、140 μ M, adjusted or selected according to the actual compound

if the purity of diluent is not high enough, it will affect the composite peel strength

the function of diluent is to increase the fluidity of adhesive, improve the spreadability, better coat evenly, and make its glue better infiltrate with the substrate. If the purity of diluent is not high, containing water, alcohol and other active substances, it will consume part of the curing agent, resulting in the actual proportion imbalance between the main agent and the curing agent in the adhesive, and the bonding force will be reduced. When selecting solvent, There are three points worth learning from peers: 1) regular and quality guaranteed manufacturers must be selected for purchase; 2) Sampling inspection of each barrel after purchase. It is found that it contains water or alcohol active substances, which must not be used. Only the solvent with high purity is used, it is estimated that the composite membrane can have strong adhesion; 3) Before use, the solvent must be clean. If there is dirt and other phenomena, it is best to filter or treat it separately to avoid affecting the coating effect and peeling strength

influence of drying temperature

in the composite process, the temperature of the hot pressing roller in the drying channel should be adjusted according to the actual situation. Generally, the temperature of the hot pressing roller should be controlled at ℃. The more complete the volatilization of the solvent is required in the drying device, the higher the peel strength will be. The temperature out of control will also affect the peel strength, and the adhesive force will also be reduced. Generally, the temperature of the inlet and dryer should be 60 ℃, and the temperature of zone 2 and zone 3 should be increased accordingly. If the temperature of the inlet and dryer is too high, only the surface of the adhesive film can be dried, and the inner layer cannot be dried, which will not only affect the peel strength, but also produce peculiar smell

insufficient corona treatment of plastic film will affect the peel strength

poor corona treatment of plastic film surface and low surface tension will lead to low ink layer adhesion fastness and low bonding strength of composite film. Before the film is put into operation, it should be carefully tested, and its surface tension must be increased to 3.8 × ten ˉ More than 2n/m, preferably 4 two × ten ˉ 2n/m, because 3.8 × ten ˉ 2n/m is only the minimum requirement, and the surface tension value is lower than 3.8 × ten ˉ 2n/m film can't completely spread the ink and adhesive at all, and the composite finished product certainly can't meet the requirements of peel strength. There are usually two methods to detect the surface tension of the film: 1) dyne pen test. The pen liquid of dyne pen is usually red, and the specification is 3.8 × ten ˉ 2N/m、4.0 × ten ˉ 2N/m、4.2 × ten ˉ 2N/m、4.4 × ten ˉ 2n/m and 4.8 × ten ˉ 2n/m, if the pen solution on the film with dyne pen does not shrink, is uniform, and there is no fault, it indicates that the surface tension of the film has reached the use requirements. On the contrary, if the pen solution shrinks, disappears, is uneven, and is discontinuous, it indicates that the treatment is not enough; 2) Test with BOPP single-sided adhesive tape. Stick the BOPP single-sided adhesive tape on the surface of the film to be tested and then tear it. The corona treated film usually has low peeling sound and is firmly pasted. On the contrary, it is not firmly pasted and easy to peel. This test method depends on experience and is not suitable for testing pet, PA and other films. The base material that does not meet the requirements of corona treatment must not be compounded, because after compounding, it will certainly not meet the peel strength requirements of packaged products. The surface tension value of common substrates is: bopp3.8 × ten ˉ 2N/m、PET5.0 × ten ˉ 2N/m、PA5.2 × ten ˉ 2N/m。

too much residual solvent will affect the peel strength and adhesion

too much residual solvent will form many tiny bubbles after compounding, making the adjacent composite substrate separate, layered, and the more bubbles, the lower the peel strength. To improve the peel strength, we must reduce the generation of bubbles. The generation of bubbles is related to many factors, such as uneven glue application, low temperature of drying channel, low temperature of hot pressing roller and inappropriate indoor temperature and humidity. Generally, the indoor temperature should be controlled at ℃, and the relative humidity should be controlled at 50% - 60%. In addition, avoiding the use of high boiling point solvents can also reduce the generation of bubbles. In short, in order to improve the peel strength and adhesive force, the residual solvent should be reduced as much as possible

aging does not completely affect the peel strength

if a two-component reactive adhesive is used, it needs to be cured (also known as aging) after compounding to meet the peel strength requirements. If the ripening is not complete, the peel strength will also be reduced. Incomplete ripening has two meanings: 1) the ripening temperature is low; 2) The ripening time is not enough. Generally speaking, the composite finished products should be ripened in an environment of ℃ for more than 48 hours, and some even take longer to achieve satisfactory results. We noticed that no matter how long the low-temperature storage time is, the final peel strength of the composite film cannot reach 3.5n/15m. If the ambient temperature rises to 55 ℃, the peel strength can be as high as 6n/15mm after the same storage for 4 days

effect of additives in plastic film

additives in plastic film will also affect the bonding fastness, and this effect will not appear until a certain time, generally after 7 days, and there is a gradual downward trend. When pelleting or making polyethylene, polypropylene and other films, most of them need to add some auxiliary agents, such as antioxidant, stabilizer, anti adhesion agent, opening agent, etc. These additives are low molecular substances, which will gradually penetrate from the interior of the film to the surface over time. When carefully observed, a thin layer of powder or paraffin substances can be found, which will stick to the hand when touched by hand, slippery and white. If you wipe it with a cloth soaked in ethyl acetate, it will be wiped off. Through observation, we found that the amount of additives migrated from the newly compounded film in a short time is not large enough to cause the decline of bond fastness, but over time, the migrated additives isolate the adhesive film from the base film. It destroys the original bonding state and reduces the composite fastness. To solve this problem, we should check the feeding, choose raw materials that do not use additives or use less additives, and do not add opening agents suitable for plastic plates, pipes and profiled materials when processing and making films. There was such a failure. The processed detergent packaging bag did not have poor bonding fastness at that time. However, after the finished bag was loaded with detergent, the phenomenon of lamination of printing substrate and composite substrate occurred after storage for a period of time, and even the heat seal was broken, causing the leakage of detergent. The packaged washing powder mainly becomes anionic surfactant, clothing fluorescent agent, non-ionic surfactant, alkaline buffer, water softener and high-efficiency stain suspending agent. After analyzing the cause of the fault, the technology department believes that; PET12 μ/LDPE80 μ M composite structure is in line with the requirements. According to the composition of washing powder, it is decided to solve the problem from the ink first. Therefore, special pet printing ink was selected for printing. Then, starting with the adhesive, it was recombined and cured again, and then the peel strength was tested. Then it was loaded into this kind of washing powder for storage and extrusion test. As a result, the fault was eliminated, the packaging bag was no longer layered, and the peel strength met the requirements. It can be seen that according to different contents

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