JP5190349B2 - Polyethylene resin for extrusion molding, method for producing the same, and obtained extrusion molded product - Google Patents

Description

  The present invention relates to a polyethylene-based resin for extrusion molding, a method for producing the same, and an obtained extrusion-molded product. More specifically, the present invention relates to a high-pressure radical polymerization low-density polyethylene (LDPE) that is widely used in extrusion coating molding. The present invention relates to a polyethylene-based resin for extrusion molding that exhibits excellent molding processability and excellent mechanical properties, a method for producing the same, and an extrusion-molded product obtained.

As long known, LDPE has many long chain branches (LCB), has a high melt tension for its viscosity, and exhibits strain-hardening properties for extension viscosity, and is therefore an excellent material for molding processability. . In particular, in the field of T-die cast film and extrusion coating, a material having a small neck-in is desired, and LDPE is a useful resin in this field.
In order to reduce the neck-in, it is necessary to increase the melt tension of the resin as much as possible, and in order to increase the melt tension, it is necessary to increase the molecular weight. However, when the molecular weight is increased, the melt viscosity may remarkably increase and molding may become difficult, and a material having a moldable melt viscosity and a melt tension as high as possible is required.

  Also, in fields other than T-die cast film and extrusion coating, for example, high melt tension and elongation to prevent parison sag in hollow molding, bubble stability of inflation film, and uniformity of foam cells in foam molding Resins that exhibit strain-curing properties of viscosity are desirable, and LDPE is widely used in these fields.

  On the other hand, LDPE generates many short chain branches (SCB) in the polymerization process, which causes a decrease in density and mechanical properties such as strength and elongation. In particular, an SCB having 3 or less carbon atoms is considered to be a cause of inferior crystal strength compared to an SCB having 4 or more carbon atoms. When compared at the same density, LDPE uses 1-hexene or 1-octene as a comonomer. It is said that the mechanical properties are inferior to the produced linear low density polyethylene (LLDPE).

  Blends of high-density polyethylene (HDPE), LLDPE, and LDPE with LDPE have been proposed in various fields in order to achieve both molding processability and mechanical properties, but basically the mechanical properties according to the blending amount of LDPE A decline is inevitable.

In recent years, research and development of LCB-polyethylene (m-LCBPE) using a metallocene catalyst has been performed in order to improve the molding processability of HDPE and LLDPE.
As a result, for example, JP-A-2-276807 (Patent Document 1) discloses an ethylene polymer obtained by solution polymerization in the presence of a catalyst composed of ethylenebis (indenyl) hafnium dichloride and methylalumoxane. Is disclosed.

  Japanese Patent Laid-Open No. 4-213309 (Patent Document 2) discloses an ethylene heavy polymer obtained by gas phase polymerization in the presence of a catalyst comprising ethylenebis (indenyl) zirconium dichloride and methylalumoxane supported on silica. Coalescence is disclosed.

  WO 93/08221 International Publication Pamphlet (Patent Document 3) discloses an ethylene polymer obtained by solution polymerization in the presence of a constrained geometric catalyst.

Furthermore, in JP-A-8-311260 (Patent Document 4), in the presence of a catalyst comprising a racemic and meso isomer of Me ₂ Si (2-Me-Ind) ₂ supported on silica and methylalumoxane, An ethylene polymer obtained by gas phase polymerization is disclosed.

  These LCBPEs have improved melt tension and improved neck-in compared to LLDPE without long chain branching. However, the effect of improving the neck-in is still small compared with a composition using LDPE.

Some m-LCBPEs have a very high value of melt tension. For example, Japanese Patent Application Laid-Open No. 2006-233206 (Patent Document 5) has a strain rate curability of elongational viscosity, and a neck-in. A polymer having a small size and good moldability is disclosed.
However, the polymer disclosed in Patent Document 5 does not always suppress the generation of draw resonance as much as LDPE. In order to ensure stability in actual molding by strain rate curability, the melt tension, which is the resistance force when the resin is actually stretched, needs to be small at low speed take-up and high at high speed take-up. This is because it is considered to be.

In general, a resin exhibiting strain rate curability is said to have good stability during high-speed stretching (for example, “Journal of the Fiber Society”, 41, T-1 (1986)). On the other hand, draw resonance and take-up surging are likely to occur when the elongation speed is increased, but it is considered that if the elongation viscosity of the resin is large, the fluctuation is suppressed against minute fluctuations during molding.
Since the elongation deformation is the smallest immediately after the resin exits the T-die and the largest immediately before the take-up roll, the variation in the deformation amount due to the fluctuation in the elongation speed is the most severe in the immediate vicinity of the take-up roll. Therefore, it is considered that the smaller the stretching speed in the immediate vicinity of the take-up roll, the more stable the molding is possible. The final deformation amount (stretching ratio) is determined by the extrusion speed of the T-die and the rotational speed of the roll. In order to reduce the speed, it is desirable to increase the extension speed in the vicinity of the T die, that is, in the initial stage of extension as much as possible. For this reason, in order to improve the stability at high speed molding, it is not sufficient that the elongation viscosity at a high elongation speed is high, and at the same time, the elongation viscosity at a low elongation speed must be low.

  Under such circumstances, it is difficult to say that the above-mentioned m-LCBPE or the like has stability at the time of neck-in and high-speed molding at the level of LDPE, particularly in extrusion coating molding. Even if LCB is introduced to reduce neck-in and melt elasticity is increased, take-up surging or draw resonance is still likely to occur when the molding speed is high, and molding processability equal to or better than LDPE has not necessarily been realized. Absent.

On the other hand, attempts have been made to improve the melt properties of polyethylene using organic peroxides. In particular, methods for improving the melt tension include, for example, JP-A-57-38837 (Patent Document 6), JP-A-58-71904 (Patent Document 7), JP-A-59-89341 (Patent Document). 8), and JP-A-7-173218 (Patent Document 9). However, these are all cross-linked at a level at which the molecular weight hardly changes, and have not yet reached a level at which the molecular weight is further increased and a performance excellent in melting characteristics and the like is exhibited.
JP-A-2-276807 JP-A-4-213309 WO93 / 08221 international publication pamphlet JP-A-8-311260 JP 2006-233206 A JP 57-38837 A JP 58-71904 A JP 59-89341 A JP-A-7-173218 Toshitaka Kanai, Akira Funaki, Journal of Textile Society, 41, T-1 (1986)

  In view of such circumstances, the object of the present invention is to exhibit molding processability equal to or higher than that of the high-pressure radical polymerization low-density polyethylene (LDPE) currently widely used in extrusion coating molding, and excellent in mechanical properties. An object of the present invention is to provide a polyethylene-based resin for extrusion molding, a production method thereof, and an extrusion-molded product obtained.

  In order to solve the above problems, the present inventors have intensively studied aiming to provide an ethylene resin for extrusion molding capable of achieving the expression of excellent mechanical strength and molding processability. As a result, with a specific MFR and density, By the polyethylene-based resin in which the number of short chain branches having 3 or less carbon atoms is not more than a specific value, and the ratio of the melt tension at a take-up speed of 12 m / min to the melt tension at a take-up speed of 3 m / min is not less than a specific value, The present inventors have found that the problem can be solved and have completed the present invention.

That is, according to the first invention of the present invention, there is provided a polyethylene resin for extrusion molding characterized by having the following properties (1) to (4).
Characteristic (1): Melt flow rate (MFR) at 190 ° C. and 2.16 kg load is 0.1 g / 10 min or more and 100 g / 10 min or less Characteristic (2): Density is 0.900 g / cm ³ or more and 0.960 g / Characteristic of cm ³ or less (3): Number of short-chain branches having 3 or less carbon atoms is 1 or less per 1000 carbons Characteristic (4): Melt tension at take-up speed of 12 m / min is MT (12), take-up speed is 3 m / min The melt tension ratio MT (12) / MT (3) when the melt tension is MT (3) is 2.0 or more, and MT (12) is 0.01N or more.

According to a second aspect of the present invention, the extrusion according to the first aspect is characterized in that a polyethylene wax having a number average molecular weight of 8,000 or less is heat-kneaded in the presence of an organic peroxide. A method for producing a polyethylene resin for molding is provided.
According to the third invention of the present invention, in the second invention, when the number average molecular weight of the polyethylene wax is M ₀ and the number average molecular weight of the polyethylene resin is M, it is calculated by the formula (1). A method for producing a polyethylene resin for extrusion molding is provided, wherein the degree of crosslinking X is 1 to 3.
X = (14,000 / M ₀ ) − (14,000 / M) Formula (1)

  According to a fourth aspect of the present invention, there is provided an extruded product according to the first aspect, which is formed by molding the above-described polyethylene resin for extrusion molding.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the polyethylene-type resin for extrusion molding (henceforth only a polyethylene-type resin) which has the moldability peculiar to LDPE, and was excellent in the mechanical physical property. Further, in extrusion lamination molding, a molded body having good stability during high-speed molding, less variation in the film thickness of the laminate film, and improved mechanical strength, preferably a laminate molded film, a conventionally known resin, etc. It can be molded with superior processability compared to.

The polyethylene resin for extrusion molding of the present invention is a polyethylene resin having the following properties (1) to (4).
Characteristic (1) Melt flow rate (MFR) at 190 ° C. and 2.16 kg load is 0.1 g / 10 min or more and 100 g / 10 min or less Characteristic (1): Melt flow rate (MFR) at 190 ° C. and 2.16 kg load There 0.1 g / 10 min or more 100 g / 10 minutes or less characteristic (2): density of 0.900 g / cm ³ or more 0.960 g / cm ³ or less characteristic (3): the number of short chain branches having 3 or less carbon atoms 1 or less per 1000 carbons (4): ratio of melt tension MT (12) when melt tension at take-up speed 12 m / min is MT (12) and melt tension at take-up speed 3 m / min is MT (3) / MT (3) is 2.0 or more and MT (12) is 0.01N or more Each characteristic of the polyethylene resin for extrusion molding of the present invention will be described in detail.

1. MFR
The polyethylene resin of the present invention has a melt flow rate (MFR) at 190 ° C. and a load of 2.16 kg of 0.1 g / 10 min to 100 g / 10 min. Preferably they are 1.0 g / 10min or more and 30 g / 10min or less, More preferably, they are 2.0g / 10min or more and 20g / 10min or less. MFR is measured under the conditions of 190 ° C. and 21.58 N based on JIS K7210 (1999). When the MFR is less than 0.1 g / 10 minutes, extrusion during molding becomes difficult. When the MFR exceeds 100 g / 10 minutes, the melt tension becomes insufficient and film molding and blow molding become unstable.
The polyethylene resin of the present invention is obtained by heat-kneading low molecular weight polyethylene having a molecular weight of 8,000 or less in the presence of an organic peroxide, for example, while stirring and kneading with an internal mixer. can do.
The MFR can be reduced by increasing the heat treatment time while watching the increase in the kneading torque of the mixer. The MFR can be controlled by the amount of the organic peroxide used, and the MFR can be reduced by increasing the amount of the organic peroxide. The temperature of the heat-kneading treatment is suitably in the range of 1 minute half-life temperature of the organic peroxide used to plus or minus 5 ° C. Furthermore, the temperature when only the polyethylene wax is melted and when the organic peroxide is added is preferably lower by 20 ° C. or more than the temperature during the heat-kneading process. In addition, the low molecular weight polyethylene to be used should have as few unnecessary low molecular weight components and high molecular weight components as possible, and preferably has a narrow molecular weight distribution. Among them, polyethylene wax produced with a single site catalyst is preferably used.

2. Density polyethylene resin of the present invention is less 0.900 g / cm ³ or more 0.960 g / cm ^3, preferably 0.910 g / cm ³ or more 0.935 g / cm ³ or less, more preferably 0.915 g / It is cm ³ or more and 0.930 g / cm ³ or less. The density is measured based on JIS K7112 (1999). If the density is less than 0.900 g / cm ³ , the advantage of high strength is lost due to the small SCB. When the density exceeds 0.960 g / cm ³ , the production is substantially difficult.
The density of the polyethylene resin of the present invention can be controlled by selecting the density of the low molecular weight polyethylene wax used. According to the above production method, it is estimated that cross-linking of molecular chains is caused by the heat-kneading process, and the density may be reduced by about 0.002 on average, and SCB is generated by the heat-kneading process compared to the cross-linking. The SCB having a real carbon number of 3 or less hardly increases.
As the low molecular weight polyethylene having a molecular weight of 8,000 or less, basically any density polyethylene can be used, and a blend of two or more kinds of polyethylene wax is also possible. However, those having a density of 0.930 g / cm ³ or less and containing many branches having 1 to 3 carbon atoms are not preferred. When a relatively low density polyethylene wax is used, it is desirable to select a polyethylene having an α-olefin having 6 or more carbon atoms as a comonomer.

3. Short chain branch having 3 or less carbon atoms In the polyethylene resin of the present invention, the number of short chain branches having 3 or less carbon atoms is 1 or less per 1000 carbons, preferably 0.5 or less, more preferably 0.1 or less. It is. The number of short chain branches having 3 or less carbon atoms is measured by ¹³ C-NMR spectrum.
Specifically, the ¹³ C-NMR spectrum measurement is performed under the following conditions using an NMR measuring apparatus JNM-GSX400 type and C-10 type probe manufactured by JEOL.
Solution and internal standard: 1,2,4-trichlorobenzene / benzene-d ₆ / hexamethyldisiloxane (mixing weight ratio 30: 10: 1)
Measurement temperature: 120 ° C
Sample concentration: 0.3 g / ml
Pulse width: 8.0 μs (Flip angle 40 °)
Pulse repetition time: 5 seconds Integration frequency: 5,000 times or more The obtained spectrum is, for example, Eric T. Hsieh & James C.H. Randall, Macromolecules Vol. 15, 353-360 (1982), Eric T. et al. Hsieh & James C.H. Randall, Macromolecules Vol. 15, 1402-1406 (1982), and an SCB number having 3 or less carbon atoms can be obtained.
When the number of short chain branches having 3 or less carbon atoms exceeds 1 per 1000 carbons, mechanical properties such as a decrease in density, strength, and elongation tend to decrease.
In order to reduce the number of short chain branches having 3 or less carbon atoms to 1 or less per 1000 carbons, short chain branches having 3 or less carbon atoms can be achieved by crosslinking polyethylene wax having 1 or less carbon atoms per 1000 carbons.

4). Melt tension (MT) and ratio of melt tension (MTR)
The polyethylene-based resin of the present invention has a melt tension ratio MT (12) / MT (when the melt tension at a take-up speed of 12 m / min is MT (12) and the melt tension at a take-up speed of 3 m / min is MT (3). 3) is 2.0 or more, preferably 2.2 or more, more preferably 2.5 or more. Although there is no restriction | limiting in particular in an upper limit, Usually, it is 3.0 or less. If the melt tension ratio MT (12) / MT (3) is less than 2, the stability during high-speed molding in T-die cast film molding or extrusion laminate molding is reduced, and a phenomenon called draw resonance or take-up surging occurs during high-speed molding. It will occur and molding will be difficult.
The melt tension at a take-up speed of 12 m / min is MT (12) and the melt tension at a take-up speed of 3 m / min is the melt tension at a take-up speed of 12 m / min and a take-up speed of 3 m / min at a temperature of 190 ° C. . Specifically, a capillary rheometer manufactured by Toyo Seiki Seisakusho Co., Ltd., Capillograph 1-B, temperature 190 ° C., barrel diameter of resin is 9.55 mm, plunger-lowering speed is 15 mm / min, 2.095 mmφ × A melt strand extruded from a nozzle with an 8 mm inflow angle of 180 ° is taken up through a pulley installed 50 cm below, and the tension applied to the pulley is measured. The take-up speed is measured in the range from 2 m / min to 20 m / min, increasing from low to high sequentially, and the melt tension values at 3 m / min and 12 m / min are determined from the plot of take-up dependence of melt tension. Let them be MT (3) and MT (12), respectively. When the strand breaks before the take-up speed reaches 12 m / min, the maximum value of the measured melt tension is defined as MT (12).
In the measurement of the melt tension, when the take-up speed of the melt strand is low, the MT is small, and when the take-up speed is fast, the MT is high and the MTR is large. LDPE is also considered to have a large MTR value by the same mechanism. In the present invention, an MTR equivalent to LDPE can be obtained by setting the crosslinking degree X described later to 1 to 3 / 1,000 methylene groups.

Further, in the present invention, MT (12) is 0.01N or more, preferably 0.015N or more, more preferably 0.02N or more. Although there is no restriction | limiting in particular in an upper limit, Usually, it is 0.06N or less. When MT (12) is less than 0.01 N, stability during high-speed molding in T-die cast film molding or extrusion laminate molding is reduced, and tension is insufficient, resulting in a large neck-in.
The polyethylene resin of the present invention satisfies the conditions that MT (12) / MT (3) is 2.0 or more and MT (12) is 0.01 N or more, so that it is neck-in and high-speed drawing in extrusion laminate molding. Time stability can be improved. Resins that satisfy the conditions are usually LDPE or a blend of LDPE, but other resins are hardly known as a single resin and are highly industrially useful. Is.

5. Production method of polyethylene resin The polyethylene resin of the present invention is produced by heat-kneading polyethylene wax having a number average molecular weight of 8,000 or less in the presence of an organic peroxide. The low molecular weight polyethylene to be used should have as few unnecessary low molecular weight components and high molecular weight components as possible, and preferably has a narrow molecular weight distribution. Among them, polyethylene wax produced with a single site catalyst is preferably used.
The polyethylene wax in the present invention is a known catalyst such as a Ziegler catalyst, a metallocene catalyst, or a Phillips catalyst, for example, a transition metal compound such as titanium or zirconium, a Ziegler catalyst comprising a magnesium compound, zirconium, hafnium, or titanium. It is obtained by mainly polymerizing ethylene using a transition metal compound such as a metallocene catalyst having at least one cyclopentadienyl group or a substituted cyclopentadienyl group and a Philips catalyst containing a chromium compound as a polymerization catalyst.
Any polyethylene wax having a number average molecular weight of 8,000 or less can be used, preferably 6,000 or less, more preferably 5,000 or less. When the number average molecular weight exceeds 8,000, the viscosity becomes too high. Further, the polyethylene wax having a number average molecular weight of 8,000 or less should have a narrow molecular weight distribution, and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 4.0 or less. More preferred is 3.0 or less.
The density can be controlled by selecting the density of the polyethylene wax used. It is presumed that cross-linking of molecular chains is caused by the heat-kneading treatment, and the density may decrease by about 0.002 on average. Compared with the cross-linking, the probability that SCB is generated by the heat-kneading treatment is low, and the substantial carbon The SCB of the number 3 or less hardly increases. Furthermore, a polyethylene-based resin with a low SCB can be obtained by selecting and heat-kneading a polyethylene wax that originally has a low SCB that adversely affects mechanical properties, and has a molding processing characteristic essentially equivalent to that of LDPE. Is obtained.

The following are mentioned as an organic peroxide used when obtaining the polyethylene-type resin of this invention.
(I) hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide,
(Ii) ketone peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, acetylacetone peroxide, cyclohexanone peroxide,
(Iii) Diacyl peroxides such as isobutyryl peroxide, diisobutanoyl peroxide, lauroyl peroxide, dilauroyl peroxide, benzoyl peroxide,
(Iv) Dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2 , 5-di- (t-butylhexyne) -3, dialkyl peroxides such as di-t-amyl peroxide,
(V) peroxyketals such as 2,2-di- (t-butylperoxy) butane,
(Vi) t-hexyl peroxypivalate, t-butyl peroxypivalate, t-amyl peroxy 2-ethylhexanoate, t-butyl peroxy 2-ethylhexanoate, t-butyl peroxyisobuty Alkyl peresters such as Rate, t-butyl peroxybenzoate, 2,4,4-trimethylpentyl-2-peroxyneodecanoate,
(Vii) percarbonates such as bis (4-t-butylcyclohexyl) peroxydicarbonate, di-isopropylperoxydicarbonate, t-amylperoxyisopropylcarbonate,
(Viii) cyclic organic peroxides such as 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
Among them, those having a 1-minute half-life temperature of 150 ° C. to 230 ° C. are preferable, and diisobutanoyl peroxide, dilauroyl peroxide, 2,4,4-trimethylpentyl-2-peroxyneodecanoate and the like are preferably used. It is done.

In the present invention, the heat-kneading treatment is usually performed by melting polyethylene wax at a temperature lower than the decomposition temperature of the organic peroxide using an internal mixer or the like, so that the organic peroxide is 0.3 to 5.0% by weight, preferably 0. It is carried out by adding 0.5 to 4.0% by weight, more preferably 0.6 to 3.0% by weight, particularly preferably 0.7 to 2.0% by weight and stirring. Subsequently, the polyethylene resin of the present invention can be obtained by raising the temperature to the decomposition temperature of the organic peroxide or higher and controlling the kneading time or the kneading torque of the mixer.
If the amount of the organic peroxide used is less than 0.3% by weight, the MFR does not decrease, and if it exceeds 5.0% by weight, the MFR may decrease excessively. MFR can be controlled by the amount of organic peroxide used, and MFR can be reduced by increasing the amount of organic peroxide. Further, MFR can be reduced by increasing the heat treatment time while observing the increase in the kneading torque of the mixer.
The temperature of the heat-kneading treatment is preferably selected from the range of a temperature 10 ° C. lower than the 1 minute half-life temperature of the organic peroxide used to a temperature 10 ° C. higher than the 1-minute half-life temperature, more preferably A temperature selected from the range of 5 ° C. lower than the 1 minute half-life temperature of the organic peroxide used to 5 ° C. higher than the 1 minute half-life temperature is suitable. If it is out of the range, it becomes difficult to obtain a target MFR resin. The time for heating and kneading can be appropriately selected, but is 1 to 120 minutes, preferably 3 to 60 minutes, and more preferably 6 to 30 minutes. If it is out of the range, it becomes difficult to obtain a target MFR resin. Furthermore, the temperature when only the polyethylene wax is melted and when the organic peroxide is added is preferably lower by 20 ° C. or more than the temperature during the heat-kneading process.

6). Crosslinking degree (X)
The polyethylene resin of the present invention obtained by the above production method has a crosslinking degree X calculated by the formula (1) of 1 when the number average molecular weight of the polyethylene wax is M ₀ and the number average molecular weight of the polyethylene resin is M. It is preferably ~ 3.
X = (14,000 / M ₀ ) − (14,000 / M) Formula (1)
In the present invention, it is presumed that a compound having a highly crosslinked structure can be obtained by heat-kneading polyethylene wax having a low molecular weight.
According to the formula (1), when the number average molecular weight M ₀ of the polyethylene wax before cross-linking is 14,000 and X = 1, the number average molecular weight M of the polyethylene-based resin after cross-linking becomes infinite in calculation. The number average molecular weight M ₀ of the polyethylene wax is preferably smaller than 14,000. Since the number average molecular weight of a polyethylene resin having an MFR of 0.1 g / 10 min or more is usually 60,000 or less, when M = 60,000 and X = 1, the number average molecular weight M ₀ of the polyethylene wax is Preferably it is less than 11,000. Similarly, when M = 60,000 and X = 3, the number average molecular weight M ₀ of the polyethylene wax is preferably smaller than 4,300. Thus, in order to increase the degree of crosslinking and to obtain the desired MFR, it is preferable that the number average molecular weight of the polyethylene wax before crosslinking is sufficiently small.

The degree of crosslinking X is 1 to 3 per 1,000 methylene groups. If the cross-linking degree X is 1 to 3 / 1,000 methylene groups, the average molecular weight from the end to the cross-linking point can be close to the critical molecular weight of polyethylene. Can be compatible. If X is less than 1, it is difficult to increase the MTR. On the other hand, when X exceeds 3, the LCB becomes too short and the melt tension becomes insufficient.
The crosslinked product formed by melt-kneading in the presence of an organic peroxide is considered to be a trifunctional random branched structure or a tetrafunctional random branched structure. When the molecular weight of the polyethylene-based resin after crosslinking is M, in the case of a trifunctional random branched structure, the number of branch points per molecule is x, and the average molecular weight between branch points is a.
M = a × (2x + 1) Equation (2)
X = xx (14,000 / M) Formula (3)
Here, for example, a cross-linked product having M of 14,000 has a = 4,700 when the cross-linking degree X = 1, and a = 2,000 when the cross-linking degree X = 3. The average molecular weight a between the branch points is the molecular weight between the crosslinking points, and is the average length of the LCB. This length is close to the critical molecular weight of polyethylene and is the limit length that functions as an LCB, so that a high melt tension is expressed, but the entanglement of molecular chains is quickly relaxed. For this reason, when the stretching speed is low, the entanglement is relaxed and does not exhibit strain hardening of the stretching viscosity, but exhibits a phenomenon called so-called “strain rate curability” that exhibits strain hardening when the stretching speed is increased.
Since the polymer relaxes from the end, the more ends, the easier the relaxation and the lower the viscosity. However, the number of ends of ordinary linear molecules and comb LCB polymers decreases in inverse proportion to the number average molecular weight. In these resins, when the molecular weight is increased to increase the melt tension, the viscosity is remarkably increased. On the other hand, in the present invention, since the probability of cross-linking between molecular ends is low, even if the molecular weight is increased by cross-linking, the number of polymer ends does not decrease. And excellent workability.

Various known additives, fillers, and the like can be added to the polyethylene resin of the present invention in appropriate amounts within a range that does not significantly impair the effects of the present invention. Examples of the additive include one or two antioxidants (phenolic, phosphorus, sulfur), lubricants, antistatic agents, light stabilizers, colorants, pigments, dyes, ultraviolet absorbers, compatibilizers, and the like. More than one species can be used together as appropriate. As the filler, for example, talc or mica can be used.
In addition, the resin composition containing the polyethylene resin of the present invention includes a thermoplastic resin and rubber, a nucleating agent, a neutralizing agent, an anti-blocking agent, a dispersant, and fluidity as long as the effects of the present invention are not impaired. An improver, a plasticizer, a release agent, a flame retardant, a colorant, a filler, a compatibilizer, an adhesive, and the like may be added.

7). Extrusion molded product The thermoplastic resin composition containing the polyethylene resin of the present invention is excellent in moldability. By processing this, various molded products excellent in mechanical strength, preferably films, more preferably. Provides a laminate film comprising the film.
The polyethylene resin of the present invention is processed by general film molding, sheet molding , and extrusion molding to obtain various molded products. Among them, an extrusion molded product is preferable. Examples of film molding include extrusion laminate molding and T-die film molding, and the film can be used as a single layer or multiple layers. In the case of multilayer molding, for example, a coextrusion method can be mentioned. On the other hand, lamination with paper and barrier films (aluminum foil, vapor deposition film, coating film, etc.) that are difficult to co-extrusion is possible by methods such as extrusion lamination molding and dry lamination molding.

Examples of the molded article obtained by processing the thermoplastic resin composition containing the polyethylene resin of the present invention include films, sheets , extruded tubes, pipes, caps, and the like. Packaging bags, liquid packaging bags, liquid paper containers, laminating fabrics, standing pouches, standard bags, heavy bags, wrap films, sugar bags, oil packaging bags, food packaging packaging films, protective films, infusion bags, Suitable for applications such as agricultural materials. It can also be used as a multilayer film by laminating with a base material such as nylon, polyester or polyolefin film.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.
In addition, the physical property of resin was measured with the following method and various evaluation was performed.

(1) Melt flow rate (MFR) at 190 ° C. and 2.16 kg load
Based on JIS K7210 (1999), the measurement was performed under the conditions of 190 ° C. and 21.58 N.
(2) Density The density was measured based on JIS K7112 (1999).
(3) Short-chain branch having 3 or less carbon atoms Measurement was performed under the following conditions using an NMR measuring apparatus JNM-GSX400 type and C-10 type probe manufactured by JEOL.
Solution and internal standard: 1,2,4-trichlorobenzene / benzene-d ₆ / hexamethyldisiloxane (mixing weight ratio 30: 10: 1)
Measurement temperature: 120 ° C
Sample concentration: 0.3 g / ml
Pulse width: 8.0 μs (Flip angle 40 °)
Pulse repetition time: 5 seconds Integration count: 5,000 times or more Hsieh & James C.H. Randall, Macromolecules Vol. 15, 353-360 (1982), Eric T. et al. Hsieh & James C.H. Randall, Macromolecules Vol. 15, 1402-1406 (1982), and the number of SCBs having 3 or less carbon atoms was determined.

(4) Molecular weight (number average molecular weight, weight average molecular weight)
Using a GPC manufactured by Waters, Model 150C, measurement was performed under the following conditions to obtain molecular weight and molecular weight distribution.
Column: Showdex HT-G and HT-806M × 2 Solvent: 1,2,4-trichlorobenzene Temperature: 140 ° C.
Flow rate: 1.0 ml / min The column was calibrated with monodisperse polystyrene manufactured by Showa Denko. (S-7300, S-3900, S-1950, S-1460, S-1010, S-565, S-152, S-66.0, S-25.5, S-55.5 each 2 mg / ml solution)
n-eicosane and n-tetracontane were measured, and the logarithmic values of elution time and molecular weight were approximated by a quartic equation. In addition, the following formula was used for conversion of the molecular weight of polystyrene and polyethylene.
M _PE = 0.468 × M _PS

(5) Tensile impact strength (TIS)
It was measured by A method of JIS K7105 (1981). The shape of the test piece was a 4 type test piece.
(6) Melt tension A capillary rheometer manufactured by Toyo Seiki Seisakusho Co., Ltd., Capillograph 1-B, temperature 190 ° C., barrel diameter of resin is 9.55 mm, plunger-lowering speed is 15 mm / min, 2.095 mmφ × The melt strand extruded from a nozzle with an 8 mm inflow angle of 180 ° was taken up through a pulley installed 50 cm below, and the tension applied to the pulley was measured. The take-up speed is measured in the range from 2 m / min to 20 m / min in order from the lower one to the higher one, and the melt tension values at 3 m / min and 12 m / min are obtained from the plot of take-up dependence of the melt tension. MT (3) and MT (12) were used respectively. In addition, when the strand was cut before the take-up speed reached 12 m / min, the maximum value of the measured melt tension was defined as MT (12).
(7) High-speed stretching stability A D2025 type single screw extruder and a slit die (width 15 cm x thickness 1 mm) are attached to a laboratory plus mill manufactured by Toyo Seiki Co., Ltd. The air gap was set to 20 cm, and a nip roll and an air knife were not installed. At that time, when it was stable visually, it was evaluated as “◯”, and when surging (draw resonance) occurred, when taking over became unstable, or when film breakage occurred, it was marked as “x”.

Example 1
375 g of polyethylene wax (molecular weight 3,600, density 0.920 g / cm ³ ) was charged into a roller mixer R500 attached to a laboratory plast mill manufactured by Toyo Seiki Co., Ltd., dissolved at 120 ° C., and kneaded at 100 rpm with nitrogen gas. After adding 0.5 g of Ciba Specialty Chemicals Irganox 1010 and 0.5 g of Ciba Specialty Chemicals Irgafos 168 as antioxidants from the substituted opening, the organic peroxide chemical Akzo 12.5 ml (10.9 g) of Kayahexa AD (2,5-dimethyl-2,5-di (t-butylperoxy) hexane) was added. Thereafter, the rotational speed was 40 rpm, the temperature was raised to 180 ° C. and kneaded for 10 minutes. When the decomposition gas was almost removed, the pressing plate was lowered, kneaded for 15 minutes and heat-treated, and the MFR was 15 g / 10 minutes. A polyethylene resin having a density of 0.917 g / cm ³ was obtained.
The obtained polyethylene resin was measured for short chain branching having 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

(Example 2)
The same procedure as in Example 1 was carried out except that the amount of Kayahexa AD manufactured by Kayaku Akzo Corporation was changed to 11.5 ml (10.0 g), polyethylene having an MFR of 20 g / 10 min and a density of 0.918 g / cm ³ . A system resin was obtained.
The obtained polyethylene resin was measured for short chain branching having 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

(Example 3 )
This powder polyethylene having a number average molecular weight of 6,000 and a density of 0.930 g / cm ³ obtained by continuous gas phase polymerization using the catalyst disclosed in JP-A-9-071614 375 g was put into a roller mixer R500 attached to a lab plast mill manufactured by Toyo Seiki Co., Ltd., dissolved at 130 ° C., kneaded at 100 rpm, and manufactured by Ciba Specialty Chemicals as an antioxidant from the opening replaced with nitrogen gas. After adding 0.5 g of Irganox 1010 and 0.5 g of Irgafos 168 manufactured by Ciba Specialty Chemicals, Trigonox 301 (3, 6, 9-triethyl-3, 6, 15.0 ml (13.1 g) of 9-trimethyl-1,4,7-triperoxonane) ) Added. Thereafter, the number of revolutions is 40 rpm, the temperature is raised to 170 ° C. and kneaded for 10 minutes. When the decomposition gas is almost eliminated, the pressing plate is lowered, kneaded for 10 minutes and heat-treated, and the MFR is 2.6 g / 10. And a polyethylene resin having a density of 0.927 g / cm ³ was obtained.
The obtained polyethylene resin was measured for short chain branching having 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

(Comparative Example 1)
Powdered polyethylene having a number average molecular weight of 15,000, an MFR of 40 g / 10 min, and a density of 0.917 g / cm ³ , obtained by continuous gas phase polymerization using the catalyst disclosed in JP-A-9-071614 (M-LCBPE), 0.1% by weight of the antioxidant Ciba Specialty Chemicals Irganox 1010 and 0.1% by weight of Ciba Specialty Chemicals Irgafos 168 are added to the polyethylene powder. 5,000 ppm of Trigonox 301 (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane) manufactured by Akzo Co., a peroxide compound, manufactured by Toyo Seiki Co., Ltd. Granulated at 40 ° C for 5 minutes at 200 ° C using a D2025 type single screw extruder attached to a lab plast mill. / 10 minutes, a polyethylene resin having a density of 0.930 g / cm ³ was obtained.
The obtained polyethylene resin was measured for short chain branching having 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

(Comparative Example 2)
200 ppm of trigonox 301 made by Akzo Co., an organic peroxide, is mixed with polyethylene resin Harmolex, NW564N (molecular weight 30,000 , density 0.918 g / cm ³ ) manufactured by Nippon Polyethylene Co., Ltd. using a 30 mmφ extruder. Granulation was performed in 5 minutes to obtain a polyethylene resin having an MFR of 2.2 g / 10 minutes and a density of 0.918 g / cm ³ .
The obtained polyethylene resin was measured for short chain branching having 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

(Comparative Example 3)
Polyethylene resin Novatec LDPE, LC600A (Molecular weight 19,700, MFR 7 g / 10 min, density 0.918 g / cm ³ ) manufactured by Nippon Polyethylene Co., Ltd. was evaluated as it was.
The polyethylene resin was measured for short chain branching of 3 or less carbon atoms, molecular weight, tensile impact strength, melt tension, and high-speed stretching stability. The results are shown in Table 1.

"Evaluation"
From the results of Table 1, Examples 1 to 3 show that the polyethylene-based resin satisfies MFR, density, short chain branching with 3 or less carbon atoms, and melt tension, which are the characteristics of the present invention. High-speed stretching stability is excellent. On the other hand, in Comparative Examples 1 and 2, since the melt tension of the polyethylene resin deviates from the characteristics of the present invention, the high-speed stretching stability is unstable. Comparative Example 3 is LDPE, and the short chain branching of the polyethylene resin having 3 or less carbon atoms deviates from the characteristics of the present invention, so that the tensile impact strength is inferior.

  Molded products obtained from the polyethylene-based resin of the present invention have an excellent balance between moldability and mechanical properties, in particular, excellent extrudability, can produce high-quality molded products efficiently, and are very useful industrially. Is high.

Claims (4)

A polyethylene resin for extrusion molding having the following characteristics (1) to (4).
Characteristic (1): Melt flow rate (MFR) at 190 ° C. and 2.16 kg load is 0.1 g / 10 min or more and 100 g / 10 min or less Characteristic (2): Density is 0.900 g / cm ³ or more and 0.960 g / Characteristic of cm ³ or less (3): Number of short-chain branches having 3 or less carbon atoms is 1 or less per 1000 carbons Characteristic (4): Melt tension at take-up speed of 12 m / min is MT (12), take-up speed is 3 m / min The melt tension ratio MT (12) / MT (3) when the melt tension is MT (3) is 2.0 or more, and MT (12) is 0.01N or more.   The method for producing a polyethylene resin for extrusion molding according to claim 1, wherein a polyethylene wax having a number average molecular weight of 8,000 or less is heat-kneaded in the presence of an organic peroxide. The cross-linking degree X calculated by the formula (1) is 1 to 3, where the number average molecular weight of the polyethylene wax is M ₀ and the number average molecular weight of the polyethylene resin is M. 3. A method for producing a polyethylene resin for extrusion molding.
X = (14,000 / M ₀ ) − (14,000 / M) Formula (1)   An extruded product obtained by molding the polyethylene resin for extrusion molding according to claim 1.