Common Problems and Solutions of PVC Absorption Technology

February 27, 2018

Introduction of suction process:

 

 

Plastic absorption is a kind of plastic processing technology. The main principle is that the flat plastic sheet is heated and softened, the vacuum is adsorbed on the mold surface, and formed after cooling. It is widely used in plastic packaging, lighting, advertisement, decoration and other industries.

 

Absorbent packaging products mainly include: bubble shell, tray, suction plastic box. Also called: vacuum cover. Bubble cover, etc. Plastic packaging equipment mainly package: suction molding machine, punching machine, sealing machine, high frequency machine, folding machine. Packaging products can be divided into: plug-in, suction card double bubble shell, half bubble shell, fold bubble shell, three fold bubble shell, etc.

 

The use of transparent plastic plastic process will be transparent plastic sheet made of specific convex shape of the mask on the surface of the product, to protect and beautify the role of products, the ordinary plastic yingpian stick on the surface layer of the solute material, so that the surface of the tray has a solute handle, used to improve packaging grades, with special plastic tray the process of modified material, the material surface resistance value of 11 ohm put less than 10. Mainly used for static tray electronic.IT products.

 

The mould used for suction production is the gypsum mould with the lowest cost, the second is the copper plating mould, and the most expensive mold is the aluminum mold. The mold has a hole in the hole and is used for the vacuum adsorption heat of the hard sheet to form the absorbent product.

 

As we often say, absorbent molding machine is used to adsorb the hot softening plastic hard sheet on the mold surface. After cooling, the plastic is formed in the shape of concave and convex shape.

 

Plastic cutting: plastic products formed by suction packaging, after punching, the large sheet is divided into a single product by cutting die.

 

Folding: one of the absorbent packaging products is called plug-in packaging, the three edges of the bubble shell need to be folded to the back of the folding machine, so that in the next packaging process, the paper card is inserted into the folding edge to form card cartridge packaging.

 

Thermal sealing: is a plastic absorption packaging process, with the sealing machine will be coated with absorbent oil on the surface of the paper card and bubble shell together, forming card packaging,

 

High frequency sealing: it is a kind of high cycle wave machine to produce ultrasonic wave, which binds bubble shell and bubble shell together to form double bubble shell packaging. Unlike high frequency sealing, ultrasonic wave can not only seal PVC.PET.PETG material, but also seal PET material. And packaging products with electromagnetic damage, especially suitable for electronic packaging: the disadvantage is the ultrasonic edge can only be spaced dotted, and usually only one edge at a time.

 



 

The principle of PVC plastic film:

 

The PVC film is close to MDF during heating and softening, and the air between PVC film and MDF film is removed by vacuum, and the PVC film is tightly attached to MDF by atmospheric pressure. This process is called vacuum plastic film.

 

The characteristics of PVC film:

 

The adhesive used for vacuum plastic film is vacuum absorbent adhesive, which is mainly waterborne polyurethane adhesive and mixed with other resins. In principle, hot melt adhesive and solvent-based adhesive can also be used, but water-based adhesive is non-toxic, odorless and moderate in price. Suitable for mechanized operation.

 

The biggest feature of this process is that it does not need to be sprayed with paint or paint, it is a lacquer free process, in addition, it can be coated with concave and convex grooves, curved surface edges, and hollowed-out engraving parts, which can not be compared with other processes.

 

Application of PVC absorbent film:

 

Vacuum plastic film coating technology is widely used in the manufacture of computer platform, loudspeaker board, cabinet, door and furniture, and a large number of applications in the processing and manufacturing of automotive interior accessories.

 

Vacuum plastic absorption processing is developing rapidly, and the medium density fiberboard (MDF) of 45% in Japan is covered with vacuum plastic film, and the MDF processed by PVC in China has reached 30 million m, and has been increasing at a rate of more than 8% per year.

 

Performance requirements of vacuum absorbent adhesive:

 

Vacuum absorbent adopts spray sizing, so it is required that the viscosity of vacuum absorbent adhesive is moderate, which can adapt to the change of winter and summer weather, and can realize spray atomization. In addition, vacuum absorbent adhesive also has the following characteristics:

 

1) good flowability and clean surface after suction.

 

(2) high solid content, fast drying.

 

3) good initial adhesion, in the grooves, the edge of the special requirements for the initial adhesion of plastic.

 

(4) the heat-resistant aging property is good, at least at 60 ℃, after 24 hours baking, the film does not curl, shrink, and foaming.

 

(5) the activation temperature is low, the activation temperature must be one when using waterborne polyurethane adhesive, the activation temperature must be in the range of 55 ~ 65 ℃, the temperature is too high and the PVC membrane is easy to perforate.

 

Common problems and Solutions in PVC suction process

 

Phenomenon 1: groove foaming

 

Cause analysis:

 

1. If the temperature or pressure does not meet the requirements, resulting in false aspiration;

 

2.The quantity of glue is not enough, the quantity of spraying is less or the plate is permeated with glue;

 

3. Not enough preheating (softening PVC film) or absorbing time (molding time);

 

4. After plastic forming, the pressure is removed before the temperature is dropped.

 

5.The heat resistance of the glue itself is not enough.

 

Solutions:

 

1. Increase in temperature or vacuum;

 

2. Increase the sizing quantity and select the good quality plate;

 

3. Increase preheating or molding time;

 

4. After plastic molding, the temperature is cooled to room temperature or slightly higher before withdrawing from the vacuum.

 

5 . The curing agent is used .

Phenomenon II: local foaming

 

Cause analysis:

 

1. Uneven spray of glue, resulting in a small amount of local adhesive, resulting in a decrease in bond strength;

 

2. PVC membrane contains plasticizer. Under the condition of aging or heating, plasticizer is easy to migrate to the surface, which affects the bond strength.

 

3. The heating pipe in the suction machine has a problem, resulting in uneven temperature.

 

Solutions:

 

1. As far as possible, the amount of glue sprayed evenly;

 

2.Use PVC film of good quality;

 

3. Timely maintenance of equipment.

 

Phenomenon 3: the edge cannot be sucked or contracted

 

Cause analysis:

 

1. The side temperature is low or the vacuum degree is not enough when the plastic is sucked;

 

2.The heat resistance of glue is not enough;

 

3.After the suction molding, the pressure is removed before the temperature is dropped.

 

Solutions:

 

1. Increase in temperature or vacuum;

 

2. Use of curing agent;

 

3. After suction molding, the temperature is cooled to room temperature or slightly higher before withdrawing from the vacuum.

 

Phenomenon 4: the surface of the product that absorbs plastic has the black spot

 

Cause analysis:

 

1. The size of the glue is large, the use of thin PVC film, easy to produce pockmarked spots, such as the characteristics of uniform dispersion;

 

2.When the curing agent is used, the curing agent is not completely dispersed.

 

3. The surface of the plate is not treated clean, or after spraying glue, the workshop is dusty, glued up, this kind of dotted is very uneven, and the size is different;

 

4. The viscosity of the glue is too large and the dispersion is uneven;

 

5. The viscosity of glue is too small or the content of solid is low, which causes the plate to be fluffed.

 

6. Air pressure is not enough and atomization is not good.

 

7. Glue is not filtered (in this case, a bucket of glue is used in the end, if it falls into stolen goods or has conjunctival formation, it should be filtered with a filter.

 

Solutions:

 

1. Choosing the glue with small particle size;

 

2.When the curing agent is mixed, the stirring time is prolonged, so that the curing agent can be completely dispersed;

 

3. Clean the surface of the plate before spraying glue, spray the workshop to separate;

 

4. Choose the glue with the proper viscosity or the glue with high solid content;

 

5.After the glue is dried, fine sandpaper can be used to polish;

 

6. Increase the vacuum degree and adjust the atomization effect;

 

7. Filter with filter when using.

 

Phenomenon five: local production of orange peel

 

Cause analysis:

 

1. Excessive spraying of local glue;

 

2. The surface of the plate has oil stain, which makes the glue produce shrinkage hole;

 

3. The curing agent is not completely dispersed and produces shrinkage.

 

Solutions:

 

1. Spray glue evenly;

 

2. Keep the surface of the sheet clean;

 

3. fully stir the curing agent to make it dispersed evenly.

 

Phenomenon six: fold

 

Cause analysis:

 

(1) the distance between narrow and long workpieces is too small;

 

(2) the edges around the upper surface of the pad are not chamfered;

 

3) the horizontal and longitudinal spacing of the workpiece is not in a straight line, which increases the resistance of the air flow.

 

(4) the set temperature is too high;

 

5) the time to reach the set pressure is too long.

 

Phenomenon 7: PVC surface whitening

 

Cause analysis:

 

(1) the set temperature is too high;

 

(2) the time of reaching the set pressure is too long;

 

The line type is not suitable.

 

Phenomenon 8: edge unglued

 

Cause analysis:

 

(1) the quality of glue is not good;

 

(2) the activation temperature of the adhesive is too high;

 

(3) the temperature of the equipment is not up to the activation temperature required by the edge of the workpiece;

 

4) workpiece pad is not suitable;

 

The property of PVC back adhesive is poor or no back glue;

 

( 6 ) The adhesive has expired or stored in conformity with the requirements ;

 

No. 7) improper method of leaking glue or spraying glue.

 

Phenomenon 9: breaking edges and falling corners

 

Generally such problems occur, the temperature is too high or low, the time or the length of the problem, the adjustment of temperature and time will be improved.

 

When there is a quality problem in PVC film, the process or parameters should be adjusted one by one for the reasons mentioned above and a good record should be made. It is not necessary to adjust many technical parameters or processes at the same time, otherwise, it is difficult to identify the real cause of the quality problem. At the same time, it is difficult to establish and adjust the production environment process standards to provide objective basis.

 

Phenomenon X: poor adsorption

The coating is too thin, the coating is uneven. B. the printing substrate is rough, the absorption is too strong. Insufficient absorbability. D. insufficient temperature during heating and welding sealing. Effect of crystallization of ink layer. F. too long storage time of absorbent oil has gone bad. Solution: A. adjust roller and coating amount. B. replace printing substrate or first bottom oil. C. change suction. Plastic oil or increase the amount of coating. D. Increase the temperature of the welding seal. E. wipe the surface of the printed matter or add 5% lactic acid dilution. F. replace the absorbent oil

 

Phenomenon Eleven: the gloss of the surface of the mill

 

The reason is that the absorbent oil is too thin, the coating is too thin, b. Dilute too much, the non-reaction solvent is too many. C. the viscosity is too high, the flow adjustment is. D., the drying temperature is low, the film forming quality is poor. Solve the problem of: A. increase the coating amount. B. try not to add the dilution as far as possible. Use raw liquid. C. Reduce coating amount. D. Properly raise drying temperature.

 

Post printing processing: a series of processing processes for the substrate after printing in order to meet the requirements of use and improve the appearance quality. 2. Glazing: strip mark theory, The essence of the glazing of printed matter is that the glazing coating flattens the surface of the printed matter and changes the glossy physical properties of the paper surface through the leveling of the coating. 3. Coating: the polymer film is covered on the surface of the printed matter and heated with binder. Process of pressing to bind it together. 4. Foil ironing: process of hot pressing transfer to the surface of a printed or other article using metal or pigment foils as raw materials. 5 Die cutting: the process of arranging a steel knife blade into a die or frame (or engraving a steel plate as a model, rolling a printed sheet of paper into a certain shape on a die cutting machine. 6. Indentation: using steel wire, by impressing, stamping marks on a piece of paper or print, 7. Indentation: use of a negative (concave, positive (convex) die, mechanical application of pressure exceeding the elastic limit of a printed material, The process of forming a solid effect of printing. 8. edition center: the book into the page to remove the surrounding white edge, the rest of the text and picture section is the plate center, plate center is the effective area to accommodate the text and picture. 9. Books: the folded book according to the order of the distribution, semi-finished products order. 10.: (two spine and back edges connected) is connected at the surface of the core and the back of the book, is a hardcover shell and back before and after the junction of the 11.. Back: also known as back flush as part of paste with the need to stick with. After a 12. mouth: cover out more than the book called the mouth. 13. tailband: also known as block cloth, rope or flower cloth, which is made by processing the lines with cloth. The 14. day: the upper blank book format called the head 15.. Anchor: the lower blank book layout is 16 feet. Front mouth: also known as a slot or edge, refers to the position of the reading edge of the mouth opposite the sewn edge of the book.17. bookend: a blank near the binding of a book is called a bookend; The other side is called incision. 18. Book seal processing: open-press-add-cut page-brush paste book shell paper-shell enveloping angle-pressure increase-natural drying-hot stamping. 19. Set processing: brushing-cover-case-sweeping-flattening-back-grooves-finished product inspection.

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