KR960006149B1 - Resin composition for extrusion coating - Google Patents

Abstract

The resin compound is composed of 40-60% tubular low density polyethylene, whose melting index is 1-7g/10min., ratio of expansion is 35-60% and melting tension is 1-10gf, and 60-40% linear low density polyethylene, whose melting index is 10-60g/10min., ratio of expansion is below 30% and melting tension is below 2.0gf. The resin has high expansion ratio and melting tension.

Description

Extrusion coating resin composition

FIG. 1 is a graph showing the expansion ratio and the melt tension according to the weight fractions of the pneumatic tube-type low density polyethylene and the melt index 22 having a melt index of 2.2, an expansion ratio of 51.6%, and an application tension of 4.3 g.

The present invention relates to a resin composition for compression coating having excellent physical properties and processability. More specifically, it is composed of high-pressure method low density polyethylene (hereinafter referred to as tubular low density polyethylene) and linear low density polyethylene, so that the expansion ratio and the melt tension are designed for the extrusion coating process, and are characterized by excellent processability and product characteristics. It relates to a dose resin composition.

Polyethylenes require different characteristics depending on the molding method and use, and various characteristics including the molecular structure are designed according to the characteristics. Polyethylene resin for double extrusion coating (hereinafter referred to as resin for extrusion coating) is thin film processing at high processing temperature of around 300 ℃, unlike general processing methods of polyethylene such as film, injection, foaming, blow molding and wire coating. The demanding characteristics are very demanding. This is because the properties of the extrusion coating resin greatly affect the processing characteristics and the end-use of the extrusion coating.

Extrusion coating resins require the following characteristics in their manufacture. In other words, it is a neck-in phenomenon where the width of the coating decreases rather than the width of the die when the resin is extruded. Neck-in is caused by a combination of expansion, surface tension and elastic recovery effects that occur when the resin is extruded through a die. If the neck-in becomes severe during processing, the narrowed portion at a constant extrusion amount causes wrinkles at the end of the molten film, and this wrinkle becomes an important problem in processing because a thickening phenomenon occurs at the coated edge.

The other is adhesion to various substrates used when the resin is extruded and coated with a thin film. The adhesion between the substrate and the resin can be divided into physical and chemical factors, and the physical factors are caused by adhesion or osmosis with the surface of the substrate due to the flow of the resin melted at a high temperature. The chemical factor is that the carbonyl group (-C = 0) produced by oxidizing the surface while the resin extruded from the T-die is exposed to the air creates a covalent or hydrogen bond by chemical reaction. Poor adhesion to the substrate is an important drawback that the substrate and the coated resin separate and lose high functionality.

One last property is called pullability, high-speed processing, and draw-down property, which is a measure of how thinly the film web melted from the die can be pulled out. It is in line with the question of how fast the processing speed can be. That is, when the drawing is carried out at a processing speed higher than the pullability of the extrusion coating resin, the molten web becomes unstable at the edges, resulting in uneven thickness of the coated web or even destruction of the molten web.

The important requirements required for the extrusion coating process are largely determined by the melt index (MT), the mill, the Sell Ratio (SR) and the melt tension (MT), which are the basic properties of the resin. The main factors that determine the molecular structure of the extruded coating resins that are affected and correlated with them are four factors: average molecular weight, molecular weight distribution, short chain branch (SCB) and long chain branch (LCB). to be. The melt index is a measure of the average molecular weight of resins by measuring the flowability when a low load (2.10 kg) is applied in a molten state at 190 ° C. For example, if the melt index is 7.0, the number average molecular weight (Mn) of the resin is about 30,000, and at 0.7, about 40,000, but it may vary depending on the overall conditions. Therefore, the larger the melt index is relatively less molecular weight, the smaller the melt viscosity under the same conditions. The molecular weight distribution of polyethylene is characterized by being relatively wider than other polyolefin resins, and the value of the molecular weight distribution represented by the weight average molecular weight / number average molecular weight (Mw / Mn) is usually about 3 to 13. In the case of low density polyethylene, which is widely used for extrusion coating, since it is radical polymerization, it is difficult to control the molecular weight distribution, and there are some differences depending on the autoclave and the tubular reactor, which are the forms of the conventional high pressure polymerization polymerizer. In general, when the melt index is large, the pulling property is improved during extrusion coating molding, so that the high-speed thinning is better, but the neck-in becomes large. Moreover, since the flowability of resin improves, permeability to a base material improves and adhesiveness improves.

The density is related to the melting and crystallization temperature and the physical properties of the polyethylene resin and is determined by the side chain of the polyethylene resin. Polyethylene resin is basically a polymer having a simple structure called (CH2-CH2) n, but in reality, short chain branches such as methyl, ethyl, and butyl groups, and especially low-density polyethylene resins have long chains of up to several hundred carbon atoms. Because it contains branches, it greatly affects the density. Generally, in the case of polyethylene resin, a branch exists, and since this branch interferes with the crystallization of resin, the more branches, the lower the density whose crystallinity falls. The lower the density, the better the adhesion since it promotes surface oxidation in the air. In addition, density affects the crystallization temperature (Tc). In other words, when the crystallization temperature is high, the cooling and solidification of the molten web is relatively fast, so that the width of the web is fixed quickly, so that the neck-in is small, but the effect of density is very small compared to other factors.

The expansion ratio is a value obtained by dividing the diameter of the resin obtained by measuring the melt index by the diameter of the orifice and is one of the most important factors in the design of the resin for extrusion coating as an index of melt elasticity of the resin. The expansion ratio is closely related to the molecular weight of the resin, the molecular weight distribution, and the number and distribution of long chain branches. In general, as the molecular weight increases, the swelling phenomenon of the polyethylene resin chains increases, and the expansion ratio increases, and the molecular weight distribution increases. In addition, the presence of long chain branching is a decisive factor for the expansion ratio, and the more long branching is increased. In the case of having the same long-chain index, having a uniform distribution increases the expansion ratio. If the expansion ratio is large, the neck-in decreases because the expansion force is increased when the polyethylene resin is extruded.

However, if the expansion ratio is large, the drawability of the resin is reduced, which is a barrier to the speed of extrusion coating speed. In addition, since the flowability of the resin is poor and the elasticity is large, the adhesive strength to the substrate is adversely affected. Although the expansion ratio of general polyethylene resin is about 1.15-1.85, the expansion ratio of resin suitable for extrusion coating is about 1.45-1.78. However, this expansion ratio depends on the polymerization conditions of ethylene, the type of reactor, and the characteristics of the resin for extrusion coating.

The melt tension (mt) is an important factor in determining the properties of the extrusion coating resin along with the expansion ratio, which can be measured together with the relative force required to draw the melt web. In other words, the higher the welding tension is required to take more force when taken under the same processing conditions, which means that the melt viscosity is large. Melt tension is affected by the expansion ratio and melt index of the resin, which can be regarded as fundamentally affected by molecular weight, molecular weight distribution and long chain branching. In other words, the melt tension is proportional to the expansion ratio but inversely proportional to the melt index.

Also, even with polyethylene having the same expansion ratio, the lower the melt index, the greater the melt tension. Therefore, in view of the relationship between the expansion ratio of the melt tension and the melt index, the molecular weight is large and the molecular weight distribution is wide, and the longer the chain length, the higher the melt tension. If the melt tension is large, the neck-in decreases during extrusion coating, but the pullability decreases and it is an obstacle to increasing the processing speed. In particular, when the melt tension is not uniform, the stretching of the molten web becomes unstable when the resin discharged from the extruder outlet is taken out during the extrusion coating process, and when the threshold of the feed rate is exceeded, periodic relief of the extrudate dimensions occurs. In addition, severe stretching waves can lead to severe conditions that may break the web extruded from the T-die, resulting in an interruption of the extrusion coating process.

As described above, the low-density polyethylene resin having a long chain branch and suitable melt tension is most commonly used for extrusion coating resin due to the characteristics of processes and products. However, even among low density extrusion coatings, autoclave type low density polyethylene resins with large expansion ratios and melt indexes are most commonly used because of the long chain branching and uniform distribution of long chain branches in the same molecular weight range. Coming. On the other hand, in the case of tubular low density extruded coating resin made of a tubular reactor, the molecular weight distribution is small, the long chain branch is small, the distribution of the long chain branch index is not uniform, and the expansion ratio and the melt index are low, so that the neck-in during extrusion coating process is low. It is so severe that it is rarely used in extrusion coating processes.

Accordingly, an object of the present invention is to supply an extrusion coating resin comprising such high pressure tubular low density polyethylene as a component.

On the other hand, linear low density polyethylene has a very small expansion ratio and melt tension as compared with high pressure polyethylene. Compared to low-density polyethylene, the molecular weight distribution is narrower and there is little long-chain branching. Therefore, the linear low density polyethylene has a low melt tension, so bubbles are unstable at the time of inflation film forming, and it is difficult to form a thick film. Particularly, when linear low density polyethylene is applied to the extrusion coating process, the neck-in is severe, and there are workability defects in which dimension irregularities occur in the edges. Surging phenomena that cause waves in the air cause significant defects in machinability.

Since the viscosity of linear low density polyethylene is linear, the molecular behavior at the time of melting shows melting behavior closer to high density polyethylene than to high pressure low density polyethylene. That is, compared with high pressure low density polyethylene having the same melt index, the viscosity is low at low shear rates and high at high shear rates. This causes a large motor load of the extruder at the time of extrusion coating molding and causes a large heat generation in the molding machine, and there are few examples of the use of linear low density polyethylene for extrusion coating. For the purpose of utilizing linear low density polyethylene resins as extrusion coating resins, Korean Patent Publication No. 89-466, filed with the United States of America, is applied for extrusion coating composition, substrate extrusion coating method and coating products. As in], a method of using a part or a plurality of low density polyethylene resins is adopted. However, the properties of the product specified in the above patents are known facts that have a composition of an autoclave-type low density polyethylene resin having excellent extrusion coating properties, but there are few choices of composition resins, and the composition ratio is large. .

Accordingly, an object of the present invention is to solve the above-mentioned drawbacks, and to prepare an excellent composition having improved processability and product characteristics, which are composed of tubular low density polyethylene and linear low density polyethylene, which are not adopted as extrusion coating resins, as mentioned above. It is.

It is another object of the present invention to provide a linear low density polyethylene resin mixture having a uniform thickness of the substrate or coated product in the extrusion coating process, excellent adhesion, and low neck-in.

More specifically, the expansion ratio and melt tension of the tubular low density polyethylene and linear low density polyethylene, which are difficult to use as extrusion coating resins because they have less expansion ratio and melt resin than autoclave type low density polyethylene resin, Synergistic effect is obtained to obtain a composition having an appropriate expansion ratio and melt tension. That is, the composition consisting of the tubular low-density polyethylene (A) and linear low-density polyethylene (B) of the present invention has a mixing ratio of 40% or more and less than 60%, preferably 45% or more and less than 55%. A polyethylene composition.

Wherein (A) is an ethylene homopolymer having a density of 0.90 to 0.92, the melt index is between 1.0 and 7.0, preferably 2.0 to 5.0. If the melt index is too low, the dispersibility of the resin is poor due to nonuniform kneading due to the molecular weight difference with the above (B), the pinholes are generated a lot, and the gel is severely generated, which may cause breakage of the molten web.

The expansion ratio of the tubular low density polyethylene according to the invention is at least 35%, preferably at least 45%. However, in the case of tubular low density polyethylene, it is usually about 30 to 60%. If the expansion ratio is too low, the desired effect cannot be achieved because the synergy effect with (B) composition is low.

Since the melt tension of (B) is very low, it is advantageous to have high melt tension as much as possible to reduce the neck-in, but too high may affect the pulling property and the kneading of the composition. In addition, if too low, the melt tension of the composition itself is too low, there is a fear that draw resonance (Draw-Resonance) phenomenon, such as uneven amount of extrusion of the resin discharged from the surging or extruder, resulting in poor processing of the product. Therefore, the appropriate melt tension is 1.0 to 10.0, preferably 3.0 to 5.0.

In the present invention, (B) is a copolymer of ethylene or butene, hexene, octene having a density of 0.91 to 0.93, the melt index is 10 to 60, preferably 20 to 30, the expansion ratio is 10% or more, preferably More than 20% is used. In general, linear low density polyethylenes have an expansion ratio of up to 30%. The melt tension depends on the melt index of (B) but is usually less than 2.0 and preferably less than 1.5.

According to the present invention, there is obtained a polyethylene composition having an expansion ratio and high melt tension adjusted to have an industrially wide application range, a low neck-in, excellent workability, and excellent adhesion and drawability.

Accordingly, the composition of the present invention has excellent adhesion to the substrate, low permeability, no pinholes in the molten web and the extruded coated product, and is easy to process at a speed much faster than that obtained in each single component. The industrial value is very large.

In the present invention, the mixing ratio of (A) to (B) is in the range of 40 to 60, preferably 45 to 55 and 55 to 45. When (A) is less than 45% or (B) is less than 55%, the excellent workability for which this invention aims is not obtained. This is because the composition of the present invention has a melt index of 5.5 to 80, an expansion ratio of 55 to 63%, and a melt tension of 1.5 to 2.5 within the range of this composition ratio, thereby obtaining the excellent effect aimed at by the present invention.

The mixing of (A) and (B) can be carried out by various mixing techniques which are usually used, and the resin to be mixed can be in any form as long as it can be injected into the hopper of an extruder such as pellets or powder. It is of course also possible to mix the usual stabilizers, lubricants, antistatic agents and inorganic organic fillers in the composition. Examples of these include calcium stearate, zinc stearate, erucamide, and the like, in addition to antioxidants such as Iganox 1076, 1010 and BHT of Ciba-Geigy Corporation.

The following examples are set forth to illustrate the methods and compositions of the present invention and their practical applicability, and are not intended to limit the scope of the present invention. Low-density polyethylene and linear low-density polyethylene resins described in the examples are commercial products that can be sold by Hanyang Chemical Co., Ltd. in Janggyo-dong, Jung-gu, Seoul, Korea.

In the Example and the comparison was measured according to the following conditions.

(1) Melt index: Melt index (MI) is indicated and measured under the conditions of 190 ℃, 2.16kg load by ASTM D 1238.

(2) Density: Measured using density gradient tube, detailed test method was according to ASTM D 1505.

(3) Expansion ratio: indicates die expansion, Die SwelI or Swell Ratio (SR), and measures the diameter of 1.5 ~ 3mm from the end of the resin that began to be extruded when measuring the melt index. Calculate the average value measured by rotating (measured up to 0.002mm). The expansion ratio is obtained by dividing the average value by 2,096mm, the orifice diameter of the melt index gauge.

(4) Melt Tension: Display Melt Tension (MT) and measure by attaching a series of accessories to the melt index gauge. In the measuring method, the melt tension is defined as the value of the straight line passing through the center of the wavelength appearing on the recording apparatus by hanging the resin extruded during the melt index measurement.

(5) Neck-in: One half of the value obtained by subtracting the width of the extruded resin from the width of the T-die to be extruded is to be one neck-in.

(6) Adhesiveness: Adhesiveness is measured according to the usual practice of adhesive tape. A 6 cm wide tape is attached to the coated surface in the transverse direction of the coating, and then lifted at room temperature to form a mark. When peeling off the adhesive tape, if the marks remain on the coating surface or the coating surface is torn, the adhesion is poor.

(7) Heat sealability: It is called heat seal phase. The extruded coated product is made into a test piece having a width of 15 mm and a length of 20 cm. The test piece is sealed at 160 ° C., 2 kg / cm² and 1 second using a thermal inclination tester. If peeling occurs in the extrusion coating surface, the heat sealability is good.

(8) Dispersibility: A small round material that is not mixed with the resin appearing in the cross-section of the pigment masterbatch and extruded. Visual inspection is also acceptable, and 30 rounds of 0.8 mm or less per square meter are acceptable.

(Examples 1 to 5)

(A) (A to D), which is a pellet composition composition, and linear low density polyethylene (E, F) copolymerized with ethylene and butene-1 are necessary combinations for the composition of the present invention. It is put into a mixer for about 10 minutes by rotation mixing to prepare a uniform composition suitable for the composition for extrusion coating. The production amount was set to 200kg each to be sufficient for the extrusion coating experiment. The composition ratios of the prepared compositions and the values of the main factors necessary for extrusion coating are shown in Table 2. Among the resins used, various additives such as antioxidants, etc. required for its use are prescribed by Hanyang Chemical Co., Ltd., Janggyo-dong, Seoul, Korea.

TABLE 1

TABLE 2

In Table 2, the composition ratio is the weight composition ratio of the tubular low density polyethylene from A to D in the composition of the present invention, and thus the composition ratio of the linear low density polyethylene to be mixed represents the remaining weight fraction excluding the composition ratio of the tubular low density polyethylene of the total weight. As is apparent from Table 1 and Table 2, when tubular low density polyethylene is mixed with linear low density polyethylene, the expansion ratio and melt tension, which are the main required characteristics of the extrusion coating resin, have a synergistic effect, depending on the composition ratio and the product. Able to know.

This effect appears to be due to the broadening of the molecular weight distribution by mixing low molecular weight polyethylene and high molecular weight polyethylene with each other, but there is no established theory. In Korea Patent Publication No. 83-259 [Applied by Polyethylene Resin Composition], high molecular weight polyethylene and low molecular weight polyethylene are mixed to improve processability and environmental stress crack resistance of injection molded products. There are attempts to increase diewell or die expansion thereby.

(Examples 6-9)

According to Table 2, a composition having an appropriate expansion ratio, melt tension, and melt index was selected and mixed, followed by a direct extrusion coating process using an extrusion coating apparatus. The compositions and properties of the resins of Examples 6 to 9 are shown in Table 3.

TABLE 3

The extrusion coating used used a single extruder of 28/1 and 32/1 in the ratio of screw length and diameter of the extruder. The extrusion coating machine is an extrusion coating apparatus used in the production of commercial products having a width of about 197 cm and a die spacing of about 0.03 to 0.07 cm, in which the molten web of the extrusion coating is extruded. The extrusion amount and the extrusion speed are adjusted by the screw speed of the extruder, and the coating thickness is adjusted by adjusting the extrusion coating processing speed under a constant extrusion amount. In addition, the extrusion coating conditions were carried out in the same manner in all the examples and extruders, and the coating substrate was a woven wind made by weaving yarn made of high density polyethylene. Detailed test conditions and evaluation results are shown in Table 4.

TABLE 4

The conditions shown in Table 4 are somewhat different depending on the condition and performance of the extruder to be used, but the level that can affect the processability and product properties other than the properties of the composition of the present invention.

The processing speed was evaluated by changing the speed on the basis of the indicated speed for comparative evaluation of the neck-in formation, adhesive force, and the dispersibility of the constituent components of the composition and the pigment master match.

Table 5 shows the evaluation results related to the processability and product characteristics of the evaluation products from Examples 6 to 9.

Example 6,7 could not measure the exact neck-in because it was ripe and writhing without having a constant width of the composition to be extruded at the edge at a processing speed of 150m / min. In addition, although it depends on the thickness to be coated, Examples 6 and 7 show good neck-in, adhesiveness and heat sealability based on the normal processing speed of 110 m / min, but the dispersibility between the pigment masterbatch and the composition components is poor. The use as a commercial product is meaningless. As mentioned above, the difference in flow characteristics with linear low density polyethylene is large because the melt index of the low density polyethylene component to be mixed is too low.

Therefore, as can be seen clearly in Tables 3, 4 and 5, in the case of the products applied in Examples 8 and 9, the industrial application is made by appropriately combining the tubular low density polyethylene and the linear low density polyethylene which cannot be used alone for extrusion coating. It can be seen that a composition of very high value can be obtained. In particular, in the case of Example 8 product having a composition ratio of the tubular low density polyethylene of 50%, it can be seen that the neck-in is extremely excellent and its commercial value is very high.

TABLE 5

Claims (10)

A resin composition for extrusion coating, comprising a high pressure tubular low density polyethylene and a linear low density polyethylene. The resin composition according to claim 1, wherein a melt index of the high pressure tubular low density polyethylene resin is 1.0 to 7.0 g / 10 minutes. The resin composition according to claim 1, wherein an expansion ratio of the high pressure tubular low density polyethylene resin is 35 to 60%. The melt composition of the said high pressure tubular low density polyethylene resin is 1.0-10.0 g *, The resin composition of Claim 1 characterized by the above-mentioned. The resin composition according to claim 2, 3 or 4, wherein the melt index is 5.5 to 8.0 g / 10 minutes, the expansion ratio is 55 to 63%, and the melt tension is 1.5 to 2.4 g ·. The resin composition according to claim 1, wherein a melt index of the linear low density polyethylene resin is 10 to 60 g / 10 minutes. The resin composition according to claim 1, wherein the expansion ratio of the linear low density polyethylene resin is less than 30%. The melt composition of the said linear low density polyethylene resin is less than 2.0 g *, The resin composition of Claim 1 characterized by the above-mentioned. The resin composition according to claim 1, wherein the composition ratio of the high pressure tubular low density polyethylene resin to the linear low density polyethylene resin is 40 to 60%: 60 to 40%. The resin composition according to claim 9, wherein the composition ratio of the high pressure tubular low density polyethylene resin to the linear low density polyethylene resin is 45 to 55%: 55 to 45%.