JP2001515115A - Polyethylene with high heat sealability - Google Patents

Abstract

  (57) [Summary] An improved composition comprising at least two polyethylene homopolymers, one component being a low melt index medium density polyethylene homopolymer and the other being a high melt index low density polyethylene homopolymer. Extrusion coating is described. Excellent heat seal strength is achieved with this blend.

Description

DETAILED DESCRIPTION OF THE INVENTION

CROSS REFERENCE TO RELATED APPLICATIONS This application is hereby incorporated by reference under 35 U.S.C. Ser. No. 60 / 055,770, filed Aug. 14, 1997, which is incorporated herein by reference . S. C. Claims the benefits of section 119 (e).

FIELD OF THE INVENTION [0002] The present invention relates to a composition obtained by blending two polyethylenes which strongly heat seals an extruded coated structure.

Background of the Invention Polyethylene blends according to the prior art are disclosed, for example, in US Pat. No. 4,339,5.
No. 07. The first component of the blend is a linear (linear) low density copolymer of ethylene and octene, and the second component is a low density polyethylene homopolymer. An example of such a linear low density polyethylene blend is Dow Chemical's linear low density polyethylene 3010. Such blends are typically useful as extrusion coatings on various structures, such as, for example, flexible polymer film / paper packaging for food and metallized polymer film balloons. This coating serves as a heat seal medium and as a barrier to protect the contents of the package from external contamination, or to keep the content, such as a gas such as helium, in a coated and sealed balloon. . The ethylene-octene copolymer component of the prior art binary blend is used to provide the strong seal strength required for certain extrusion coated structures.

[0004] However, these prior art blends create many problems during the extrusion coating operation. In particular, these blends require excessively high extrusion currents for extrusion, and some extruders do not allow operation at these high currents. Due to the need for such high currents, low-density polyethylene is usually combined with the copolymer in amounts of about 20% by weight to enhance processability. Also, these prior art blends exhibit high viscosities at the high shear rates associated with extrusion coating, and thus are prone to excessive melting temperatures in the screw feed section of the extruder. These high melting temperatures in the feed section
Along with melt fracture and gel formation, extruder discharge fluctuations, ie, surging, all of which result in quality defects. Also, prior art blends cause severe necking in the molten polymer web, resulting in instability of the ears. Because the melted web's ears are unstable, it is necessary to trim the ears,
The result is expensive polymer waste. These facts are discussed in a technical article entitled "Advantages, Ease of Processing, Blending LDPE in Mixtures" published in Converting Magazine in March 1997.

In the above technical paper, it is reported that “the performance potential of LDPE (low-density polyethylene) is expanded by the addition of comonomer. Vinyl acetate and methyl acrylate are two main examples”. I have. Ethylene vinyl acetate copolymer (EVA
) Allows such lower sheet seal initiation temperatures in heat sealing operations where low heat sealing temperatures are required. Ethylene methyl acrylate copolymer (EMA) exhibits strong heat sealing properties for both film and extrusion coating applications.

[0006] Ethylene and methyl acrylate copolymers containing from about 2% to about 5% by weight methyl acrylate are thermally stable. However, ethylene and octene (
Or any other alpha-olefin) and low-density copolymers of ethylene and vinyl acetate, containing from about 2% to about 18% by weight of vinyl acetate. The blend is thermally unstable. Both copolymers degrade upon prolonged residence in the heated extruder, such as during a temporary downtime. Such degradation or molecular cutting causes large defects in subsequent extrusion coatings. In most cases, the extruder operator is forced to clean the equipment before continuing production. Because of the susceptibility of these copolymers to thermal degradation, these copolymers must be purged from the extruder before stopping rotation of the extruder screw. Typically, the purge material is an inert polymer such as a low density polyethylene homopolymer. Such an inert polyethylene homopolymer can remain in the extruder until the next start of the extruder, and the heat-up cycle required for the extruder to reach the temperature required for extrusion coating of the copolymer Throughout the extruder. The need to purge this thermally labile copolymer from the extruder adds to the material cost because the purge material must be purchased and stocked at the location where the extrusion coating operation is to be performed.

In view of the problems associated with extrusion coating the two copolymers described above, a more ideal ethylene homopolymer is desired. Such polymers are inert homopolymers of ethylene, the extrusion coating of which is a linear low density copolymer of ethylene and octene (or any other α-olefin) or a low density copolymer of ethylene and vinyl acetate. It is desired to have a heat seal strength equivalent to or superior to that of the density copolymer. Such ideal homopolymers do not exhibit any such problems of linear low density polyethylene blends; that is, they do not require high extruder drive currents. desired. It should also not exhibit high viscosities even at high shear rates and consequently not generate excessive melting temperatures, melt fractures and gels. In addition, such ideal homopolymers should not have high web necking, where the web ears are unstable, requiring trimming of the ears and loss of material. Finally, it is desirable that such ideal homopolymers do not require a purge each time the operation is interrupted, and can remain in the extruder indefinitely between production starts.

SUMMARY OF THE INVENTION The present inventors have unexpectedly found an improved ethylene homopolymer composition for extrusion coating of a material comprising a binary blend of polyethylene pomopolymer. First
The component is a low melt index, medium density polyethylene that provides a strong heat seal. The second component is a high melt index, low density polyethylene that provides good wettability to the substrate, and such good wettability has good adhesion required for strong heat sealing, coating and It is essential for good adhesion between substrates.

[0009] The present invention surprisingly allows for heat seal strengths in excess of those of linear (linear) low density polyethylene compositions. In addition, the present invention relates to such linear low density copolymers with ethylene and octene (or any other α-olefin) or the thermal instability associated with low density copolymers with ethylene and vinyl acetate. It does not exhibit any of the problems of extrusion coating.

A preferred embodiment of the described U.S. Patent Nos. 5,268,230 and the No. 5,350,476, (199
Provisional Application No. 60 / 036,297 filed on Feb. 19, 7; Eastm
(Based on an Chemical No. 70537) 1998
Co-pending application Ser. No. 09 / 023,900, filed on Feb. 13, 2014;
And (provisional application number 60 / 043,222 filed on April 9, 1997).
U.S. Ser. No. 09/037, filed March 9, 1998, based on Eastman Chemical Inc.'s case reference number 70632).
No. 558 describes a method for producing a high gloss extrusion coating and a smooth paper laminate. Similarly, (provisional application number 60/043, filed on April 21, 1997).
No. 935; Case Number 70638 of Eastman Chemical Company and Provisional Application No. 60-055,7, filed on Aug. 14, 1997.
No. 68; based on Eastman Chemical Inc. Serial No. 70732), filed Mar. 26, 1998, US Ser.
No. 048,455 discloses an improved ternary blend of one linear low density polyethylene and two polyethylene homopolymers. Each of these patents and applications is incorporated herein by reference. One polyethylene contained in each of the above five documents has a melt index at 190 ° C. of 0.5 dg / min to 4 dg / min and a swell ratio of 1 dwell.
. 2 to 1.35, annealed density of about 0
. Medium density polyethylene with a narrow molecular weight distribution, having a polydispersity index of 926 g / cc and a polydispersity index of 9 or less. This same medium density polyethylene is the first component of the two-component polyethylene blend described in the present invention.

The blend of the present invention also contains a second component, which has a melt index measured at 190 ° C. ranging from 18 dg / min to 22 dg / min, an expansion ratio greater than 1.60, and a post-annealing density. Is from about 0.91 g / cc to about 0.92 g / cc and has a polydispersity greater than 9 and is a low density polyethylene with a broad molecular weight distribution.

The blend is prepared by mixing at least the two components described above in a known manner. Additional polyethylene components may be added as well as other known additives such as fillers, pigments, and the like. The first component described above is present in a major amount, for example, 50
It is preferred that it be present in an amount greater than% by weight. A further preferred blend is where the first component is present in an amount of about 80% by weight and the second component is present in an amount of about 20% by weight.
A blend present in an amount of weight percent.

Various extrusion coating methods are known in the art, such as extruding against a glossy or matte chill roll. The composition of the present invention can be used in any known extrusion method.

Experimental In the following examples, the physical properties were determined as follows: Melt index was 374 ° F. according to ASTM D1238-62T.
(190 ° C.). The swell ratio is defined in ASTM D1238-62T as the ratio of the diameter of the extrudate to the diameter of the orifice of the extrusion plastometer. The diameter of the test piece is
When the specimen comes out of the extrusion plastometer, the initial part
. Measure in the area between 952 cm. The measurement was performed by a standard method according to ASTM D374.

The post-annealing density was determined according to ASTM D1505. The polydispersity index is the ratio of the weight average molecular weight M _w to the number average molecular weight M _n . M _w and M _n are standard refractometer detectors and Viscotek 150R
Obtained by volume exclusion chromatography on Waters 150C gel permeation chromatography equipped with a differential viscometer system. The three column sets consisted of Waters 10 ³ , 10 ⁴ and linear mixed beds (10 ³ , 10 ⁴ and 1).
0 ⁵⁾ consists of Micro-Styragel HT column. The sample was
The experiment was performed at 140 ° C. as a 5% (weight / volume) o-dichlorobenzene solution. For any polyethylene sample, the data obtained was analyzed using a universal calibration curve using NBS 1475 (linear polyethylene) and NBS 1476 (branched polyethylene) using Viscotec Unique Software (V4.02). Interpreted.

[0016] Heat seal strength was measured using a Sentinel Bar Sealer Model 12 with opposite polymer-coated specimens, each 1.00 inches (2.54 cm) wide.
It is determined by heat welding using AF. Upper sealing bar only 40
Heat the lower sealing bar to 0 ° F. (205 ° C.) and protect it with Teflon tape. The opposing coating was placed between the sealing bars at 40 psi (2.82 kg /
cm ² ) for 2.0 seconds. Then, the sealed test piece was placed on 9.8 1b (4
. The seal strength is tested by pulling at a peel rate of 5.0 in / min (12.6 cm / min) on a Thwing-Albert tensile tester, model 1450-24-8, equipped with a 4 kg) load cell. Seal strength is given in grams.

[0017] As already mentioned in the description of Embodiment Example 1 The preferred embodiment, therefore, by blending the following ingredients, a 2-component polymer blends of the present invention were prepared: 1) 20 wt%, melt Polyethylene homopolymer with an index of 18 to 22 dg / min and a wide molecular weight distribution. 2) 80% by weight of a polyethylene homopolymer with a melt index of 0.5 to 4.0 dg / min and a narrow molecular weight distribution. The melt index of the resulting blend was 2.8 dg / min.

Extrusion of this formulation into a foil / polyethylene / paperboard structure having aluminum foil as its outer surface; ie, 0.000285 inch (0.00725 mm) foil / low density polyethylene / bleached mechanical gloss paper structure Coated. The foil surface was first coated with MICA A-291-C from MICA, an aqueous polymer chromium complex compound designed for aluminum foil. At a melting temperature of 580 ° F. (305 ° C.), add 0.002 inches (
The polymer was coated at an extrusion speed of 132 fpm (14 m / min), sufficient to achieve a coating thickness of 0.0508 mm).

During the extrusion process, the feed zone of the extruder, zones 1, 2 and 3 were each adjusted to 290 ° F.
(143 ° C.), 250 ° F. (121 ° C.) and 548 ° F. (287 ° C.). The heat seal strength was 9.0 1b / inch (1.65 kg / cm).

Example 2 (comparative) Dow Chemical's linear low density polyethylene blend 3010 has a low density homopolymer polyethylene of about 20% by weight and an octene content of about 7% by weight of about 80% by weight. 10% by weight of a blend with a copolymer of ethylene and octene. Having this formulation with aluminum foil as its outer surface,
Foil / polyethylene / paperboard construction; ie 0.000285 inch foil / low density polyethylene / bleached mechanical gloss paper construction was extrusion coated. The foil surface was first coated with MICA A-291-C from MICA, an aqueous polymer chromium complex compound designed for aluminum foil. A 0.002 inch (0.degree. F.) at a melting temperature of 597.degree.
. The polymer was coated at an extrusion speed of 132 fpm (14 m / min), sufficient to achieve a coating thickness of 0508 mm).

During the extrusion process, the feed zone of the extruder, zones 1, 2 and 3, were each adjusted to 397 ° F.
(202 ° C.), 497 ° F. (258 ° C.) and 568 ° F. (298 ° C.). The heat seal strength was 6.61 b / inch (1.84 kg / cm).

Example 3 (Comparative) Linear low density polyethylene, formulation STAMLEX 1066F from DSM, comprises about 20% by weight of low density homopolymer polyethylene and about 80% by weight, an octene content of about 7% by weight. 10 to 10% by weight of a blend of ethylene and octene copolymer. Having this formulation with aluminum foil as its outer surface,
Foil / polyethylene / paperboard construction; that is, 0.000285 inch foil / low density polyethylene / bleached mechanical gloss paper construction was extrusion coated. The foil surface was first coated with MICA A-291-C from MICA, an aqueous polymer chromium complex compound designed for aluminum foil. The primer coated foil is applied at a melting temperature of 600 ° F (316 ° C) at 0.002 inches (0 ° C).
. The polymer was coated at an extrusion speed of 132 fpm (14 m / min), sufficient to achieve a coating thickness of 0508 mm).

During the extrusion process, the feed zone of the extruder, zones 1, 2 and 3, were each adjusted to 398 ° F.
(204 ° C.), 498 ° F. (258 ° C.) and 571 ° F. (300 ° C.). The heat seal strength was 5.91 b / inch (1.06 kg / cm).

Example 4 (comparative) Rexene's linear low density polyethylene, formulation 2503-10, contains about 20
A blend of about 80% by weight of a low density homopolymer polyethylene and about 80% by weight of a copolymer of ethylene and octene having an octene content of about 7-10% by weight. This formulation was extrusion coated onto a foil / polyethylene / paperboard structure having aluminum foil as its outer surface; that is, a 0.000285 inch foil / low density polyethylene / bleached mechanical gloss paper structure. The foil surface was first coated with MICA A-291-C from MICA, an aqueous polymer chromium complex compound designed for aluminum foil. On the foil coated with primer,
At a melt temperature of 597 ° F (314 ° C), the polymer was applied at an extrusion speed of 132 fpm (14 m / min), sufficient to achieve a 0.002 inch (0.0508 mm) coating thickness.

During the extrusion process, the feed zone of the extruder, zones 1, 2 and 3 were each adjusted to 399 ° F.
(204 ° C), 498 ° F (258 ° C) and 569 ° F (298 ° C) equilibrium. The heat seal strength was 7.0 lb / inch (1.34 kg / cm).

Example 5 (Comparative) Millennium's formulation GA 61050 is an octene-ethylene copolymer having an octene content of 7% to 10% by weight. Rexene
The company's low density polyethylene, Formula 5050, is a polyethylene homopolymer.
These two polymers were combined at 80% by weight of Millennium GA615050 copolymer and 20% by weight of Rexene low density blend 5050 at a ratio of 20% by weight.
Tumbler blended. To enable extrusion coating, Millenni
Such dilution of the um copolymer was required. The tumbler blend was extrusion coated onto a foil / polyethylene / paperboard structure having aluminum foil as its outer surface; that is, a 0.000285 inch foil / low density polyethylene / bleached mechanical gloss paper structure. On this foil surface, MICA A, a water-based polymer chromium complex compound designed for aluminum foil, manufactured by MICA Co.
-291-C was applied first. 601 ° F (
At a melt temperature of 316 ° C.), the polymer was applied at an extrusion rate of 132 fpm (14 m / min), sufficient to achieve a coating thickness of 0.002 inches (0.0508 mm).

During the extrusion process, the feed zone of the extruder, zones 1, 2 and 3 were each adjusted to 401 ° F.
(205 ° C.), 498 ° F. (258 ° C.) and 563 ° F. (295 ° C.). The heat seal strength was 5.11 b / inch (0.90 kg / cm).

The above examples show that the present invention (Example 1) surprisingly shows that linear low density polyethylene blends (Examples 2 to 4), even as pure homopolymers of ethylene, in the absence of an α-olefin-ethylene copolymer. This indicates that stronger heat sealing is provided than 5). The absence of the copolymer in the present invention means that, unlike the example containing the copolymer, it is thermally stable and does not require an extruder purge following shutdown. Furthermore, these examples show that the invention does not accumulate excessive heat in the feed of the extruder, unlike linear low density polyethylene. Thus, the present invention solves surge, melt fracture, and gel formation problems.

Many modifications and variations are possible and, within the spirit and scope of the invention, which depart from the scope of the appended claims, which differ from those expressly set forth herein, Can be implemented. Moreover, all patents, patent applications, provisional patent applications, and references cited above are incorporated herein by reference for any disclosure that is suitable for the practice of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), CA, JP, KR, MX (72) Inventor Farnham, Diane Hines United States, Texas 75604, Longview, French Drive 3712 F-term (reference) 4F100 AK03A AK03B AK06A AK06B AK62 AK63 AL05A AL05B AR00C AR00D BA02 BA03 BA07 BA10C BA10D EH17C EJ65D JA06A JA06B JA07A JA07B JA13A JA13B JL12 YY00A YY00B 4J002 BB031 BB032 GF00

Claims (6)

[Claims] 1. A melt index at 190 ° C. of 0.5 dg / min to 4 dg / min.
min, a medium-density polyethylene having a narrow molecular weight distribution, having a swelling ratio of 1.2 to 1.35, an annealed density of about 0.926 g / cc, and a polydispersity index of 9 or less. One component; and a range of a melt index measured at 190 ° C. of 18 dg / min to 22 dg / min.
The expansion ratio is greater than 1.60 and the density after annealing is from about 0.91 g / cc to about 0.9
A second component comprising a low-density polyethylene having a broad molecular weight distribution and having a polydispersity index of greater than 9 and 2 g / cc. 2. The composition of claim 1, wherein said first component is present in an amount greater than 50% by weight, based on the weight of the composition. 3. The method of claim 1, wherein the first component is present in an amount of about 80% by weight, and
The composition of claim 1, wherein the component is present in an amount of about 20% by weight. 4. A molded article comprising a substrate and an extrusion coating, wherein the extrusion coating is the composition according to claim 1, 2, or 3. 5. A molded article according to claim 4, comprising at least one layer between said substrate and said extrusion coating. 6. The molded article according to claim 4, further comprising a primer layer between said substrate and said extrusion coating.