KR100428558B1 - A method for preparing a modified polyethyene with good adhesion and low viscosity for thermal spray - Google Patents

Abstract

A method for preparing maleic acid grafted polyethylene having an adhesive and low viscosity usable for thermal spraying, and a modified polyethylene prepared accordingly,

Polyethylene was introduced into a twin-screw extruder set at a temperature of 100 to 140 ° C., and then each component was added to an organic solvent such that 0.1-2 phr maleic anhydride, 0.01-1 phr benzoyl peroxide initiator and 0.05-1 phr dimethylformamide per 100 parts by weight of polyethylene. There is provided a method for preparing maleic acid grafted polyethylene having adhesiveness and low viscosity which can be used for thermal spraying operations by grafting maleic acid onto polyethylene by introducing the dissolved reaction solution into a twin screw extruder separately. Maleic acid grafted polyethylenes drawn by this method have reduced viscosity and improved moldability and adhesion of coatings during thermal spray coating operations.

Description

A method for producing modified polyethylene having adhesiveness and low viscosity for thermal use {A METHOD FOR PREPARING A MODIFIED POLYETHYENE WITH GOOD ADHESION AND LOW VISCOSITY FOR THERMAL SPRAY}

The present invention relates to a method for producing a high flow adhesive modified polyethylene and to a polyethylene produced accordingly, and more particularly, to a method for preparing maleic acid grafted polyethylene having adhesiveness and low viscosity that can be used for thermal spraying operations. To modified polyethylenes prepared accordingly.

Polyethylene has excellent corrosion resistance and flexibility, and has a low melt viscosity and is widely used as a protective coating material for steel and ceramics. However, polyethylene has little adhesive strength and is not suitable for use as a coating material unless the adhesive strength is given through proper modification.

As a method of increasing the adhesion of polyethylene, a method of preparing a copolymer of ethylene-acrylic acid or ethylene-maleic anhydride by polymerizing monomers such as acrylic acid and maleic anhydride together with ethylene has been used. However, this method has the disadvantage of requiring high pressure and temperature when polymerizing ethylene.

As another method, a method of mixing and using a polymer having high adhesion to the coating material and having compatibility with polyethylene or a method of preparing a copolymer in which acrylic acid or maleic anhydride is grafted to polyethylene is used. However, the method for preparing the graft copolymer is only a method for preparing modified polyethylene in a short time by a simple facility, and does not teach about providing high flexibility to polyethylene. As a method of grafting acrylic acid to polyethylene, there are Japanese Patent Laid-Open Nos. 7-3103645, 8-1123859, and German Patent No. 281403. German Patent No. 2658547 is a method of grafting maleic anhydride on polyethylene. No. 2849980, Japanese Patent Laid-Open Nos. 7-793495, 7-863492, 7-999193, 8-430841, 8-7167371, and 9-3277435.

The graft copolymer is prepared by adding a peroxide as a radical initiator to a mixture of polyethylene polymer molecules and acrylic acid or maleic anhydride, and then graft reacting at a melting temperature of polyethylene or higher. The polar groups grafted onto the polymer molecule impart adhesion at the contact interface of the metal-polymer. However, in the process of grafting maleic anhydride with peroxide, in addition to the graft reaction, side reactions crosslinked between polyethylene molecules occur, and the crosslinked portion increases the melt viscosity of the modified polyethylene.

In general, the thermal spray powder coating, in which the polymer powder is heated and liquefied while colliding with the coating material at high pressure, has a high melt viscosity (ie, a low melt index (MI)) because the heating state of the coating is not sufficient compared to that of the general powder coating. Film formability is reduced. Polyethylene suitable for thermal spray coating needs to be processed to have an adhesive force with a melt viscosity index of 20 or more.

In order to solve the problem, a method of using acrylic acid or maleic anhydride in a small amount is used in order to minimize crosslinking reaction or homopolymerization, but it has a disadvantage of insufficient adhesive strength.

As described above, the conventional polyethylene reforming method does not provide a method for simultaneously providing a sufficiently low melt viscosity, i.e., high fluidity and excellent adhesion, required for the thermal spray powder coating process.

It is an object of the present invention to provide a process for producing maleic acid grafted polyethylene having high flowability (low viscosity) and adhesion.

Another object of the present invention is to provide a maleic acid grafted polyethylene having high flowability and adhesion applicable to thermal spraying.

According to one aspect of the invention,

Polyethylene was introduced into a twin-screw extruder set at a temperature of 100 to 140 ° C., and then each component was added to an organic solvent such that 0.1-2 phr maleic anhydride, 0.01-1 phr benzoyl peroxide initiator and 0.05-1 phr dimethylformamide per 100 parts by weight of polyethylene. Provided is a method for producing maleic acid grafted polyethylene having adhesiveness and low viscosity, which can be used for thermal spraying operations comprising introducing the dissolved reaction solution into a twin-screw extruder and melt-mixing the maleic acid to polyethylene. do.

According to another aspect of the present invention,

There is provided an adhesive and low viscosity maleic acid grafted polyethylene that can be used in the thermal spraying operations produced by the process of the invention.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the method of the present invention, the crosslinking reaction between polyethylene chains is minimized by grafting maleic anhydride to polyethylene at a relatively low temperature by using a low-density polyethylene having high fluidity, at which it is decomposed at a relatively low temperature to initiate a reaction. By suppressing the increase, a modified polyethylene having low viscosity, i.e. high flowability and adhesion, suitable for the thermal spray coating process is produced.

The high flow adhesive modified polyethylene of the present invention is prepared by graft reaction of maleic anhydride to polyethylene molecules.

The modified polyethylene of the present invention is prepared by melt-mixing polyethylene and a reaction solution of a graft monomer, an initiator and a crosslinking agent dissolved in a solvent at a temperature of 100-140 ° C. to graf the graft monomer to a polyethylene resin.

Polyethylene is used as the resin, and in particular, high fluidity low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and the like may be used. Most preferred are high flow, low density polyethylene. The melting point of the raw polyethylene has a great influence on the physical properties of the modified polyethylene. If the melt index of polyethylene after reforming is lower than 10, it is not preferable to form a coating film by thermal spraying because of low fluidity, and it is not possible to form a uniform coating film. Therefore, it is recommended to use polyethylene having a melt index of 20 or more after modification. desirable.

As the monomer grafted to polyethylene, maleic anhydride is used at 0.1-2 phr, preferably 0.1-1 phr per 100 parts by weight of polyethylene, and the maleic anhydride monomer improves the adhesion of the coating film.

When maleic anhydride is used at 0.1 phr or less, the amount of maleic anhydride grafted to polyethylene is low so that the adhesive strength is not effectively given. When 2 phr or more is used, ungrafted maleic anhydride is excessively contained inside the polyethylene. It will remain and will cause a fall of adhesive force and a fall of the physical property of polyethylene.

In the graft reaction, a radical initiator which is decomposed at a relatively low temperature is used, and examples thereof include succinic peroxide, benzoyl peroxide, t-butylperoxy-2-ethyl hexanoate, p-chlorobenzoyl peroxide, t-butylperoxy isobutyrate, t-butylperoxy isopropyl carbonate, t-butylperoxylaurate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxy acetate, Di-t-butyl diperoxy phthalate, t-butylperoxy maleic acid, cyclohexanone peroxide, t-butylperoxy benzoate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane , t-butylcumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide or 2,5-dimethyl-2,5-di (t-butylperoxy) hexane-3, α, α-bis -t-butylperoxy-1,4-isopropylbenzene, with benzoyl peroxide being particularly preferred. The initiator is used in an amount of 0.01-1 phr per 100 parts by weight of polyethylene. When the initiator is used in an amount of 0.01 phr or less, the adhesive force is not secured because it is not sufficient for the graft reaction of maleic anhydride to the polyethylene chain, and an excessive amount of unreacted maleic anhydride is polyethylene depending on the amount of maleic anhydride used. It can remain in resin. In addition, when used in more than 1 phr of the graft reactant of the present invention due to the rapid increase in the melt viscosity at the composition ratio and reaction temperature conditions, the flow characteristics of the polyethylene is not suitable.

In the present invention, dimethylformamide is used as a crosslinking inhibitor to control the viscosity of maleic acid grafted polyethylene. That is, dimethylformamide inhibits the crosslinking reaction of polyethylene molecules by maleic anhydride generated in the grafting process of maleic anhydride, and consequently plays a role of suppressing an increase in melt viscosity of the modified polyethylene. Dimethylformamide remains in the modified polyethylene under the influence of high vaporization temperature (153 ° C), and the remaining dimethylformamide degrades the adhesion at the interface when the polyethylene melts and adheres to the metal surface. Such dimethylformamide should be used in an appropriate amount to inhibit the crosslinking reaction in the grafting process. Dimethylformamide is used at 0.05 to 1 phr per 100 parts by weight of polyethylene. When the amount is less than 0.05 phr, the melt viscosity is increased by crosslinking reaction, making it unsuitable for coating by thermal spraying. When the amount is more than 1 phr, it is caused by the heating process during the thermal spraying process due to excessive use of dimethylformamide. Removal is not effective, and work efficiency is reduced in the process of sorting the particle size during powder processing for thermal spraying.

Maleic acid grafted polyethylene is prepared by reacting the polyethylene and an organic solvent with a reaction solution in which maleic anhydride, an initiator, and a crosslinking inhibitor are dissolved. Acetone is used as the organic solvent, and acetone is preferably used in a small amount as much as possible, and it is particularly preferable to use acetone in an amount of 25 to 50 wt% based on the amount of maleic anhydride used. Below 25wt%, it is difficult to dissolve maleic anhydride into solution.In the case of 50wt% and above, acetone is excessively generated in the gas phase during the graft process, and the gas phase of unreacted maleic anhydride is promoted to worsen the working conditions. It can be cause.

The graft process is carried out in a continuous process in which polyethylene is first introduced into a temperature-set biaxial extruder, and then a reaction solution made of maleic anhydride, an initiator and a crosslinking inhibitor dissolved in the solvent is separately added to the twin screw extruder and melt mixed. Lose. If the set temperature of the extruder is lower than 100 ° C, the melting of polyethylene is not smooth and the graft reaction is not smooth. If the temperature is higher than 140 ° C, the degree of crosslinking reaction is increased to increase the melt viscosity of the modified polyethylene. Since it becomes a factor, it is preferable to carry out graft reaction at the temperature of 100-140 degreeC.

The maleic acid grafted polyethylene prepared by the method of the present invention has high flowability and adhesiveness and is applicable to thermal spraying operations.

Hereinafter, the present invention will be described in detail through examples. The examples are provided only to more easily understand the present invention and do not limit the present invention to the following examples.

Example 1

Linear low density polyethylene (LLDPE) was set at a temperature of 100 to 135 ° C., and was placed in a twin screw extruder rotating at a screw rotation speed of 200 rpm. The solution dissolved in acetone was dropped and extruded to form 0.6 phr of formamide to complete the polyethylene reforming process. The modified polyethylene extrudate was pulverized and sprayed to process a coating test piece. In the thermal spraying operation, the raw material supply, the film formability of the coated coating film, and the adhesion were excellent. In particular, the adhesive strength of this result was 100g / mm as a result of measuring the adhesive force by the 90 ° peel test on the coating formed on a 2mm thick hot rolled steel sheet without removing the black skin.

Example 2

Linear low density polyethylene (LLDPE) was set at a temperature of 100 to 120 ° C. and placed in a twin screw extruder rotating at a screw rotation speed of 250 rpm. A solution of acetone dissolved in 0.1 phr of formamide was dropped and extruded to complete the polyethylene reforming process. The modified polyethylene extrudate was pulverized and sprayed to process a coating test piece. In the thermal spraying operation, the raw material supply, the film formability of the coated coating film, and the adhesion were excellent. In particular, the adhesive strength of this result was 150g / mm when the adhesive force was measured by a 90 ° peel test on a coating formed on a 2mm thick hot rolled steel sheet without black skin.

Example 3

Linear low density polyethylene (LLDPE) was set at a temperature of 100 to 135 ° C., and was placed in a twin screw extruder rotating at a screw rotation speed of 200 rpm. The solution dissolved in acetone was dropped and extruded to form 0.3 phr of formamide to complete the polyethylene reforming process. The modified polyethylene extrudate was pulverized and sprayed to process a coating test piece. In the thermal spraying operation, the raw material supply, the film formability of the coated coating film, and the adhesion were excellent. In particular, the adhesive strength of this result was 150g / mm when the adhesive force was measured by a 90 ° peel test on a coating formed on a 2mm thick hot rolled steel sheet without black skin.

Example 4

Linear low density polyethylene (LLDPE) was set at a temperature of 140 to 150 ° C., and was placed in a twin screw extruder rotating at a screw rotation speed of 200 rpm. The solution dissolved in acetone was dropped and extruded to form 0.6 phr of formamide to complete the polyethylene reforming process. The modified polyethylene extrudate was pulverized and sprayed to process a coating test piece. The rapid formation of the melt viscosity during the spraying operation resulted in poor film formation of the coating film, resulting in poor coating formation.

The modified polyethylene prepared according to the method of the present invention is melt viscosity by crosslinking reaction by graft reaction of maleic acid to polyethylene near the melting temperature of polyethylene, which is a relatively low temperature by using a reaction initiator that decomposes at a relatively low temperature to initiate a reaction. This suppresses the increase in the viscosity of the polyethylene, thereby effectively reducing the formability and adhesion of the coating film during the thermal spray coating operation.

Claims (5)

Polyethylene was introduced into a twin-screw extruder set at a temperature of 100 to 140 ° C., and then each component was added to an organic solvent such that 0.1-2 phr maleic anhydride, 0.01-1 phr benzoyl peroxide initiator and 0.05-1 phr dimethylformamide per 100 parts by weight of polyethylene. A method for producing a maleic acid grafted polyethylene having adhesiveness and low viscosity, which can be used for thermal spraying operations, wherein the dissolved reaction solution is separately introduced into a twin screw extruder to melt-mix the maleic acid to polyethylene. delete The method of claim 1, wherein the polyethylene is a low density polyethylene (LDPE) or linear low density polyethylene having a melt index of 20 or more after the modification. delete The method of claim 1, wherein the organic solvent is acetone.