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Date:2021-2-22 10:03:33 Publisher:Sumino Precision
Precautions for PET stretch film
Stretch film

Generally, the F-5 value of PET film in the longitudinal and transverse directions is 100~390MPa. However, this kind of film is not enough for long-term sound reproduction or small-sized tape base film. Because these tapes require greater film hardness. The effective hardness of the film is proportional to the film thickness 3X the film modulus. Even if the film is very thin, it should have a higher modulus. The high modulus film is obtained by increasing the molecular orientation of the film. Because the longitudinal modulus is related to the movement of the tape, and the transverse modulus is related to the contact of the magnetic head, it is required to have a high modulus in both directions. (The movement of the tape is usually evaluated by the elongation of the tape, the damage of the tape edge and the folding condition of the tape).

Some types of stretch films are listed below:

① Semi-stretched film (longitudinal F-5 value is 130~150MPa);
②Generally stretched film (the longitudinal F-5 value is 150~180MPa);
③ Over-stretched film (longitudinal F-5 value is 180~220MPa);
④ Exceeding the stretched film (the longitudinal F-5 value is 220~260MPa);
⑤ Double-sided stretched film (the longitudinal F-5 value is 150MPa; the transverse F-5 value is 140MPa).

As the stretching increases, the heat shrinkage shrinkage rate of the PET film increases, and the relationship between the heat shrinkage and the F-5 value is irreversible.

The basic process of producing stretched film is as follows:
(1) Stretching in LD direction;
(2) Stretching in TD direction;
(3) Re-stretch in LD direction;
(4) If necessary, stretch in the TD direction;
(5) Thermal curing.

Re-stretching in the LD direction is quite difficult, because the film is very thin and wide, which will cause

(1) Both sides should be formed quite thick to prevent the width from being reduced;
(2) The deviation of preheating and stretching rolls should be as small as possible;
(3) The stretching temperature should increase as the film passes through the machine.

Since the re-stretching process is usually costly, another method is proposed to reduce manufacturing costs. The characteristic of this new process is that the first stretching in the LD direction is carried out in two steps:

(1) The cast film is first stretched in the LD direction at 120~150℃, and the stretching ratio is controlled to make the birefringence value of the stretched film be between 0.005 and 0.025;

(2) Afterwards, the second stretching in the LD direction is carried out between 60~100℃;
(3) The uniaxially stretched film thus obtained is stretched in the TD direction at a stretch ratio of 4.3 or more;
(4) After obtaining the biaxially stretched film, heat curing.

According to such a processing technique, since no re-stretching process is required, the manufacturing cost of the stretched film is low. There are various methods for producing stretched films, some of which are listed below.

(1) The bi-oriented film is again synchronized biaxially stretched.

"The stretching ratios of the second simultaneous stretching are: LD direction is 1.05~1.90; TD direction is 1.0~1.9. The stretching temperature of simultaneous stretching is between (Tg+10)℃ and (Tm-40)℃ Time (Tg: glass transition temperature; Tm: melting temperature).

(2) Combination of multi-step LD direction stretching and re-stretching.

The cast film is stretched in the LD direction in a multi-step form into a single-oriented film with a birefringence value of 0.02~0.10, and then the film is stretched in the TD direction with a stretch ratio of 2.5 to 4.5, and a stretch ratio of 1.5 to 2.5 Stretch again in the LD direction. The stretch ratio of LD, TD and LD stretched products is higher than 25.

(3) Combination of multi-step LD stretching and simultaneous two-way stretching.

The cast film is stretched in the LD direction in a multi-step form into a single-oriented film with a birefringence value of 0.02~0.10. After that, the film is stretched in the TD direction with a stretch ratio higher than 2.5, and then simultaneously biaxially stretched. At this time, the stretch ratio of the two directions is 1.4~2.5, and the total stretch ratio of the product is above 27.

(4) Zone stretching accompanied by zone annealing.

Zone stretching and annealing include film stretching and annealing under tension conditions heated by pressing points. The purpose of zone stretching is to obtain higher molecular orientation while preventing crystallization. It is obtained by necking stretching of the film at approximately the Ts temperature. The purpose of zone annealing is to anneal the stretched film under a higher tension between Tc-Tm temperature to obtain crystals with elongated molecular chains. The LD direction modulus of the zone annealed film is almost twice that of the original film, although the TD direction modulus has decreased.

Nanjing Sumino Precision Machinery Co., Ltd. is a high-tech enterprise integrating scientific research, production and sales. It has always adhered to the business philosophy of integrity, equality, and customer benefits first. In order to better improve the quality of equipment, it has entered a more professional and standardized Production track. We have established independent research and development technologies for seven types of equipment including plastic sheet material, casting, bi-stretching, non-woven non-woven meltblown cloth, laminating film composite, recycled granulation environmental protection recycling system and coating machine manufacturing system. The center and production department provide a complete set of professional technical solutions to meet the special needs of each customer. Among them, the biaxially oriented film manufacturing system includes: BOPP biaxially oriented film manufacturing system, PVC biaxially oriented shrink film production line, PET biaxially oriented film production line, BOPA biaxially oriented film production line, BOPA biaxially oriented film production line, etc.

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