Common faults and causes of the hottest paper plas

Common faults and causes of paper plastic composite

release date: Source: China paper

paper plastic composite products are required to be firmly bonded, with a clean, flat, smooth surface, no blistering, curling, no film loss, film release, etc. There are many factors affecting the composite quality, both objective and subjective. It involves the environmental factors of the operation site (indoor temperature, humidity, dust, etc.), as well as the factors of the product itself (the ink used, the type of paper, the printing method, etc.), and is closely related to the adhesive, film and process conditions used in the paper plastic composite, the operation method, the structure and technical performance of the laminating machine, which requires comprehensive analysis

I. bonding fastness of composites

the factors that affect the bonding fastness of composites are: the bonding strength of the glue itself, the affinity between the glue and the film, paper and ink layer, the condition of the glue layer, and the operating process conditions

1. The adhesive force of glue depends on the raw material and production process formula of glue and the solid content of laminating glue. Some products have good adhesion after compounding, and after being put for a period of time, the film is separated from the paper, which is separated by gently peeling it with your hand. Even scratch the film surface with your fingernail, and the film is separated from the paper surface at the crease, or fold the composite to the film surface, and the film is separated from the paper surface at the crease, or curl the composite to the film surface, which also causes the film to be separated from the paper surface. These phenomena prove that the adhesive force fails due to the influence of external natural conditions

2. The influence of the affinity between glue and membrane on the composite fastness

the chemical structure of polypropylene membrane used for composite has no active genes, which is a non-polar substance with poor affinity to glue, causing difficulties in surface adhesion. Therefore, corona treatment should be carried out on the film to make its surface products unsaturated double bond and carbon base, so that its surface energy has active genes. As a result, the surface roughness of the film is increased, which is conducive to the coating of glue. After corona treatment, the properties of the membrane surface change from non-polar substances to polar substances, which is conducive to improving the affinity between the adhesive and the membrane. However, there is a time limit for the film after corona treatment, and it will subside after a long time. The information is introduced as 6 months. The surface tension of the failed film decreased, and the data introduction was less than 39 dyne/cm2. How to identify the corona inside the membrane and whether the corona treatment is invalid? Here are two methods

(1) write or scribe on the film surface with a fountain pen, and the side easy to be stained with ink is the corona treatment surface. If the water does not shrink or form beads, and it is not easy to wipe off, it indicates that the corona treatment surface has not failed

(2) use 38mn/m surface tension indicator: 54 grams of formamide and 46 grams of ethylene glycol ether, and then test. If the indicator does not shrink within two seconds, it is considered that the corona treatment is qualified

3. The influence of the affinity between glue and paper on the composite fastness

paper is a porous material interwoven with plant fibers. It can be used to fill the holes and improve the water resistance of the paper by sizing, so as to make up for the hollows on the surface. In order to improve the flatness and smoothness of the surface, the paper is coated with a layer of paint, which is made by calendering or super calendering

there are many kinds of paper used for printing, and the printing materials used for laminating generally include white paperboard, copper plate paper with low noise during working hours, glass paperboard and other printing materials. Classify them. One is that the paper structure is relatively tight and the surface is relatively flat, such as coated paper and cellophane. The other is paper with loose structure and rough surface, such as whiteboard. Its internal structure is similar to the first type, and its surface condition is similar to the first type. When the adhesive layer is compressed and condensed with the paper, the composite fastness of the paper with poor surface flatness is poor. The high point of the paper is bonded with glue, while the low-lying part is not bonded with glue, and the glue layer is bonded with the paper in the form of point contact. For paper with high surface flatness, the composite fastness is higher. The adhesive layer is basically combined with the paper surface in the form of point contact, and more adhesive is in contact with the paper surface. For the paper with loose structural adhesive, the paper wool is easy to be taken away by the adhesive layer after stripping. Therefore, in the process of use, the size of the glue should be adjusted according to the paper to fill the uneven surface of the paper and improve the bonding fastness

4. The influence of the affinity between glue and ink on the composite fastness

the water-based laminating adhesive should not only adhere to the film, but also to the paper and ink layer. The adhesive should adapt to these three different materials at the same time, so that the film can be well combined with the paper and ink layer

the affinity between glue and ink layer is more complex than that between glue and film, glue and paper. At present, the ink used is basically resin type. Ink is a complex mixture, which is made up of pigments, connecting materials, inconvenient oiling and auxiliary materials to improve the inkability to meet the printing requirements. Lithographic products are generally printed with spot color ink. The colors of prints are juxtaposed and overlapped, and the ink layer is thin, while the colors of embossed products are printed after mixing and blending with various colors and inks, and the ink layer is thick. From the perspective of ink layer structure, embossing is more complex than lithography. Some manufacturers of printing ink layer also use the internal structure of cast iron, that is, the chemical characteristics of the ink are mainly related to the foaming phenomenon of the film. The black surface condition is related to the affinity of the adhesive, which is related to the fastness of bonding, as can be seen from the following points

(1) the particles of the ink are large, that is, the nominal composition of the pigment is Ti (6) al (2) 5Mo⑴. 5cr-0.5fe-0.3si particles are large, and the annual reasonable difference between glue and ink layer is poor. For example, silver ink and gold ink, the particles of aluminum powder and copper powder are larger, which are much larger than those of general inks. It is attached to the surface of the ink layer in granular form and emits silver or gold light through the oblique light. The adhesive layer is bonded with silver ink and gold ink layer in the form of point contact, resulting in poor adhesion fastness and easy peeling. Domestic silver ink and gold ink particles are larger than imported ones, which is more obvious. At the same time, for the combination of gold and silver ink, water-based laminating adhesive belongs to permeable bonding, which has a wetting effect on the ink and will reflect the background color. Therefore, the background color of the product should be taken into consideration when restoring the gold and silver film

(2) for printing materials with poor paper flatness, the surface of the ink layer is uneven because a thin layer of ink cannot fill the depressions of the paper. The ink layer of lithography is thinner than that of embossing, and the unevenness of the ink layer surface is more obvious. The adhesive fastness of this composite to the ink layer will be worse

(3) the high surface smoothness of the ink layer is not conducive to the firm adhesion between the adhesive and the ink layer. Some printed matter will crystallize on the surface of the film layer due to long storage time, forming a layer of glass, which is hard and smooth. The glue and it cannot be wetted and attached to each other, resulting in poor adhesion. In serious cases, it will be separated with a gentle peel

(4) for pictures with large ink layer, the affinity between the upper glue layer and the ink layer is slightly worse than that of paper, which will also affect the fastness of adhesion. For some full-size or dotted pictures, the adhesive layer is all in contact with the ink layer. When encountering printing materials with large ink particles and uneven ink layer, the adhesion fastness is even worse. Therefore, when there is a full-size printed matter composite, we must ensure the solid content of the adhesive layer and appropriately increase the thickness of the adhesive layer

5. Influence of adhesive layer condition on composite fastness

adhesive layer condition refers to the thickness and uniformity of adhesive layer. Obviously, the thickness of the adhesive layer is conducive to the fastness of bonding. In operation, the uniformity of the adhesive layer should be maintained, and the thickness of the adhesive layer should be controlled according to the actual situation. In principle, the thinnest adhesive layer shall be controlled on the premise that the composite is firmly bonded

(1) the effect of the thickness of the adhesive layer on the composite

when the viscosity of the adhesive is constant, the thicker the adhesive layer and the more solid content, the higher the adhesion, but not the thicker the better. When the glue is too thick, the effective components in the glue can not play normally, which is easy to cause poor affinity between paper and ink, resulting in poor ink lifting effect

(2) the influence of the uniformity of the adhesive layer on the composite fastness

if the adhesive layer is uneven, the thickness is inconsistent, and there will be differences in the adhesion fastness. In the case of uneven adhesive layer with little difference, the adhesion fastness of thin adhesive is poor, and that of thick adhesive is relatively good. In the case of uneven adhesive layer with great difference, the paper and ink will separate at the thin adhesive

(3) reasons affecting uneven glue layer

a: whether the adjustment of the parts of the glue dispenser is correct

b: whether the gluing mechanism is damaged

c: whether the running speed of the machine is uniform

II. There are "snowflakes"

water-based laminating machine and oil-based laminating machine on the surface of the composite, and their working principles are different. The water-based laminating machine belongs to low temperature and pressure resistance (generally, the lamination is recommended to have no blistering on the surface of the composite), while the oil-based laminating machine belongs to high temperature and high pressure

1. As the printed matter becomes more and more exquisite, some designers design novel printing publicity, resulting in the thick ink layer of the printed matter when the printed matter is full page or multiple spot color printing. In order to prevent the printing surface from sticking, or shorten the curing time of the film, the printer operators use fast drying oil, or increase the ink mixing oil, drying oil, and powder spraying amount. It brings great difficulties to lamination. Thus, there are snowflakes after the lamination of the printed matter. In case of lamination, it is required to wipe the surface of the printed matter with powder or alcohol on the towel

2. The glue amount is too small to cover the places with thick powder on the surface of the printed matter

3. The pressure of the laminating roller of the laminating machine is too small, resulting in the print and glue can not be completely combined

III. uneven curl of composite products

1. Excessive membrane tension. The tension is too large during production, and the stress recovers after slitting, resulting in shrinkage

2. The paper is too wet, and the paper density is not enough

3. The film will be stretched and deformed due to excessive winding tension

4. The storage time is too long after reeling, and the curing time of the glue solution is too long after the film and paper are combined

IV. the spacing distance at the lap of the laminated paperboard is large

1. The winding tension is too large, and the film is deformed

2. The pressure of the press roll is too small

3. The paperboard is not dense enough to deform after moisture absorption

4. The speed of the press roll is inconsistent with the speed of the transfer paperboard

5. The unwinding device of the membrane is too tight, and the tension of the membrane is too large

v. composite products change color after mounting

1. The amount of glue on the tile mounting glue is too large

2. The pH value of tile mounting adhesive is alkaline

3. The moisture absorption of tile mounting adhesive leads to chemical reaction discoloration, and it will fall off in serious cases

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