KR19990039402A - Modification of Linear Low Density Polyethylene Resin by Electron Beam Irradiation - Google Patents

Abstract

The present invention relates to a method for modifying a linear low density polyethylene (LLDPE) resin by electron beam irradiation. The present invention relates to a method for modifying a linear low density polyethylene resin in which a molecular structure is modified by irradiating an electron beam.

Description

Modification of Linear Low Density Polyethylene Resin by Electron Beam Irradiation

The present invention relates to a method for modifying a linear low density polyethylene (hereinafter referred to as "LLDPE") resin by electron beam irradiation, and more particularly, to modify the molecular structure by irradiating an electron beam (electron beam) LLDPE The present invention relates to a method of modifying a new type of LLDPE resin that improves optical and processing properties of a film.

LLDPE is usually produced by a medium and low pressure process using a metal catalyst, and has a linear structure without molecular chains having long chain branches in the backbone chain. In contrast, low density polyethylene (hereinafter referred to as "LDPE") is produced by a high pressure process by radical polymerization and has a molecular structure having many long chain branches in the main chain. Due to the difference in molecular structure, the film made of LLDPE has better mechanical strength than LDPE, but optical transparency is inferior, and high processing load and bubble stability are poor when blown film is formed. It has a disadvantage.

If the LLDPE film can be improved by improving the shortcomings of the LLDPE, the film can be used in a wide range of applications, such as packaging, industrial, agricultural, and film.

On the other hand, in order to improve the transparency and processability of the LLDPE film to date, 10 to 50% by weight of the LDPE produced by the high pressure method to the LLDPE 50 to 90% by blending (blending) was used. Thus, blending LDPE to LLDPE improves transparency and processability, but lowers the inherent mechanical properties of LLDPE. Therefore, the use of LLDPE alone is limited due to deterioration of transparency and inferior processability.

In order to solve this problem, in the present invention, the LLDPE resin was irradiated with an electron beam to transform the molecular structure from the linear structure to the branched structure, thereby obtaining an LLDPE film having greatly improved transparency and processability.

Accordingly, it is an object of the present invention to provide a method of modifying a new type of LLDPE resin which improves the optical and processing characteristics of the LLDPE film.

The method of the present invention for achieving the above object consists of modifying the molecular structure by irradiating 0.1-6 Mrad of electron beam to linear low density polyethylene (LLDPE) to which 400 to 2500 ppm of antioxidant and 50 to 1000 ppm of UV stabilizer are added.

Hereinafter, the method of the present invention will be described in more detail.

Modification of polymer material by electron beam irradiation is applied to all of you. In general, an electron beam causes a change in the molecular structure of a polymer by radicals formed by the electron beam emitted by an electron accelerator penetrating the polymer product. The electron beam energy irradiation unit uses a unit called "rad", and 1rad is a unit when 1g of sample absorbs 100erg of energy. When electron beams are irradiated to polyethylene for a certain intensity, crosslinking occurs, and these characteristics are used in thermosetting polyethylene products such as pipes and wires.

In the present invention, unlike the crosslinking method, the LLDPE resin to which the stabilizer is added is irradiated with a certain amount of electron beam to denature the molecular structure from the linear structure to the branched structure without generating a gel. Irradiation of electron beams to LLDPE resins without addition of antioxidants and UV stabilizers resulted in crosslinking reactions, resulting in unmelted gels during film formation, resulting in unacceptable results. That is, the radical formed by irradiating a certain level of electron beam to LLDPE to which antioxidant and UV stabilizer were added does not participate in the crosslinking reaction between molecules, but only in the reaction of transforming the molecular structure into a branched structure in the linear structure. It is to prepare the LLDPE resin.

In the present invention, the LLDPE used to improve transparency and processability in the LLDPE film has a melt flow index of 0.5 g / 10 min to 7.0 g / 10 min, preferably 1 g / 10 min to 3 g / 10 min. If the melt flow index is less than 0.5g / 10min, the processing load takes a lot when processing the film, if it exceeds 7.0g / 10min there is a disadvantage in that the stability of the bubble when the film processing falls. In addition, the density of the LLDPE is ^{0.917g / cm 3 ~0.930g / 10cm 3} , preferably ^{0.919g / cm 3 ~0.925g / 10cm 3} . If the density is 0.917g / cm ³ under poor in flexural modulus of the film, when it is more than 0.930g / 10cm ³ has a disadvantage that the impact strength of the film deteriorated.

According to the present invention, the stabilizer may be an antioxidant and an ultraviolet stabilizer, the antioxidant may be used alone or mixed with a phenol or phosphite compound, the ultraviolet stabilizer is a benzophenone-based ultraviolet absorber, and a radical terminator An amine compound with large steric hindrance can be used alone or in combination.

On the other hand, the antioxidant is 400 to 2500ppm, preferably 700 to 1200ppm, UV stabilizer 50 to 1000ppm, preferably 100 to 500ppm is used. If the antioxidant is less than 400ppm, the heat resistance of the resin is weak, if the antioxidant exceeds 2500ppm there is a disadvantage that the cost increase and yellowing of the additive appears. In addition, when the UV stabilizer is less than 50 ppm, an undesired crosslinking reaction occurs. When the UV stabilizer exceeds 1000 ppm, an increase in the cost and yellowing of the additives occur.

On the other hand, the electron beam irradiation amount using an electron accelerator is set so that the LLDPE resin thickness can permeate 4 mm, and the range of appropriate irradiation amount in air is 0.1 Mrad-6 Mrad, Preferably it is 0.3 Mrad-5 Mrad. When the electron beam irradiation amount is less than 0.1 Mrad, the degree of branching of the molecular structure of the LLDPE is low, which can improve the processability and transparency of the film.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to the following Examples.

Physical properties of the final film was measured by the following method.

-Melt Flow Index (MI, ASTM D-1238)

Tensile Strength (ASTM D-882)

Tear Strength (ASTM D-1922)

Impact Strength (ASTM D-1709)

-Gel Permeation Chromatograph

-Unmelted gel measurement

2 g of sample was sealed in a metal mesh and dissolved in 250 ml of xylene for 7 hours, and then dried in an 80 ° C. vacuum vacuum dryer. Then, the weight of the residue was measured and the unmelted gel was measured as a percentage of the initial weight.

Examples 1 to 3 and Comparative Example 1

LLDPE has a melt flow index of 2.8g / 10min and a density of 0.919g / cm ³ , 400ppm waste antioxidant (Shiba-Geigi Irganox 1010) and phosphite antioxidant (Shiba-Geigi Irgafos 168) 800ppm, And 250 ppm of an amine UV stabilizer (Cynamid UV 3346) and 250 ppm of a benzophenone UV stabilizer (Cynamid UV 531) were added in a row on a metal plate to irradiate the electron beam in the air. Melt flow index and molecular weight of the LLDPE resin were measured while increasing the amount of electron beam irradiation (see Table 1 below).

LLDPE Melt Index Flow and Molecular Weight Changes by Electron Beam Irradiation Example Comparative example One 2 3 One Electron beam dose (Mrad) 0.36 0.72 2.1 - Melt Flow Index (g / 10min) 2.3 1.6 0.3 2.8 Mw × 10 ^-3 (GPC) 215 227 250 205 Undissolved Gel (wt%) 0 0 0 0

Examples 4-5 and Comparative Examples 2-3

LLDPE having a melt flow index of 2.1 g / 10 min and a density of 0.918 g / cm ³ , 400 ppm of waste antioxidant (Ciba-Gaigi Irganox 1010) and 800 ppm of phosphite antioxidant (Shiba-Gaigi Irgafos 168), and 250 ppm of amine UV stabilizer (Cynamid UV 3346) and 250 ppm of benzophenone UV stabilizer (Cynamid UV 531) were added, and 0.5 Mrad and 1 Mrad of electron beams were irradiated to obtain a melt flow index of 1.0 g / 10 min and 0.6 g / 10 min, respectively. The processing load (torque) during film processing was compared with Comparative Example 2 and Comparative Example 3, which were not irradiated with electron beams (see Table 2 below). The processing load was measured using a laboratory extruder (brabender) in a blown manner to measure the load in 50㎛ thick film processing.

Machining Load Change by Electron Beam Irradiation Example Comparative example 4 5 2 3 Electron beam dose (Mrad) 0.5 1.0 - - Melt Flow Index (g / 10min) One 0.6 One 0.6 Machining Load (NM) 51 53 61 66

Example 6 and Comparative Example 4

In Example 6, LLDPE had a melt flow index of 2.1 g / 10 min, a density of 0.919 g / cm ³ , 400 ppm of waste phenolic antioxidant (Shiba-Geigi Irganox 1010) and a phosphite antioxidant (Shiba-Geigi Irgafos). 168) 800 ppm, and 250 ppm of the amine UV stabilizer (Cynamid UV 3346) and 250 ppm of the benzophenone UV stabilizer (Cynamid UV 531) were added, and Comparative Example 4 was prepared by applying the electron beam only to the same LLDPE as Example 6. Was investigated to form a 50 μm film in a 50 mm extruder to measure the physical properties of the film (see Table 3).

Properties of Electron Beam Irradiated LLDPE Films Example 6 Comparative Example 4 Electron Beam Dose (Mrad) 0.5 0.5 UV stabilizer (ppm) 500 - Melt Index (g / 10min) 1.0 1.0 Tensile Strength (Kg / cm ² ) 425 410 Elongation (%) 520 630 Tear strength (Kg / ㎛) 14.1 14 Impact strength (g / ㎛) 4.1 4.2 Transparency (Haze%) 13 33 Thickness (㎛) 50 50

As can be seen from Tables 1, 2 and 3, as the electron beam irradiation amount increased, the melt flow index decreased, the molecular weight increased, and no unmelted gel was generated within the range of 0.36 Mrad to 2 Mrad electron beam irradiation. In addition, the melt flow index is the same as 1g / 10min when compared to Example 4 and Comparative Example 2, but the processing load is reduced by about 20% compared to Comparative Example 2 Example 4 irradiated with an electron beam. Similarly, in Example 5 and Comparative Example 3, Example 5 irradiated with an electron beam showed lower processing load characteristics than Comparative Example 3. In addition, Example 6, in which the UV stabilizer was prescribed in transparency, which is an optical property, of the film properties, showed a very excellent transparency than Comparative Example 4, which was not prescribed.

Claims (5)

Modification of the linear low density polyethylene resin by electron beam irradiation characterized in that the linear low density polyethylene (LLDPE) to which 400 to 2500 ppm antioxidant and 50 to 1000 ppm ultraviolet stabilizer are added is irradiated with an electron beam of 0.1 to 6 Mrad to modify the molecular structure. Way. The linear low density of electron beam irradiation according to claim 1, wherein the melt flow index of the linear low density polyethylene is 0.5g / 10min to 7.0g / 10min, and the density is 0.917g / cm ^{3 to} 0.930g / cm ³ . Modification method of polyethylene resin. The method of modifying a linear low density polyethylene resin according to claim 1, wherein the antioxidant is used alone or in combination with a phenol or a phosphite compound. The method of modifying a linear low density polyethylene resin by electron beam irradiation according to claim 1, wherein the ultraviolet light stabilizer is used alone or in combination of a benzophenone series, which is an ultraviolet absorber, and a sterically hindered amine compound, which is a radical terminator. The method of modifying a linear low density polyethylene resin according to claim 1, wherein the electron beam irradiation amount is 0.3 to 5 Mrad.