阅读说明：本技术 可热收缩的聚乙烯膜 (Heat shrinkable polyethylene film ) 是由 P-J·古森斯 T·库农 于 2020-04-15 设计创作，主要内容包括：可热收缩膜包含至少一个层,其由包含原始的第一聚合物组合物和至少20wt％的再生的第二聚合物组合物的聚合物共混物制成。所述第一聚合物组合物包含至少50wt％的乙烯和至少一种具有5-20个碳原子的α-烯烃的聚合物(a1),该聚合物(a1)的密度是0.918-0.945g/cm～(3),熔体指数是0.1-2.5g/10min,熔体指数比是25-80,组成分布宽度指数是至少70％,和平均模量(M)是20000-60000psi。所述第二聚合物组合物不同于所述第一聚合物组合物,其熔体指数(I-(2.16))是0.1-2.5g/10min和包含至少30wt％的密度为0.910-0.940g/cm～(3)的乙烯均聚物(b1)。(The heat shrinkable film comprises at least one layer made from a polymer blend comprising an original first polymer composition and at least 20 wt% of a regenerated second polymer composition. The first polymer composition comprises at least 50% by weight of a polymer (a1) of ethylene and at least one alpha-olefin having from 5 to 20 carbon atoms, the polymer (a1) having a density of from 0.918 to 0.945g/cm 3 The melt index is 0.1-2.5g/10min, the melt index ratio is 25-80, the composition distribution breadth index is at least 70%, and the average modulus (M) is 20000-. The second polymer composition is different from the first polymer composition in melt index (I) 2.16 ) Is 0.1-2.5g/10min and contains at least 30 wt% of a density of 0.910-0.940g/cm 3 The ethylene homopolymer (b 1).)

1. A heat shrinkable film comprising at least one layer made from a polymer blend comprising:

(a) at least 20 wt% of an original first polymer composition comprising at least 50 wt% of polymerization of at least one ethylene and at least one alpha-olefin having from 5 to 20 carbon atoms, based on the total weight of the polymer blendObject (a1), the polymer (a1) having a density of about 0.918g/cm³-about 0.945g/cm³Melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min, melt index ratio (I)_21.6/I_2.16) Is from about 25 to about 80, the Composition Distribution Breadth Index (CDBI), as defined herein, is at least 70%, and the average modulus (M), as defined herein, is 20000-; and

(b) at least 20 wt%, based on the total weight of the polymer blend, of a reclaimed second polymer composition, different from the first polymer composition, having a melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min and comprises at least 30 wt% of at least one material having a density of 0.910g/cm³-about 0.940g/cm³The ethylene homopolymer (b1) of (a),

wherein the film has a machine direction shrinkage of at least 70% when heated to 150 ℃.

2. The film of claim 1, wherein the relationship between M and dart impact strength in g/mil (DIS) of ethylene polymer (a1) corresponds to the formula:

3. the film of claim 1 or claim 2, wherein the ethylene polymer (a1) is produced using a metallocene catalyst.

4. The film of claim 1, claim 2 or claim 3, wherein the original first polymer composition comprises at least 60 wt%, preferably at least 80 wt%, of the ethylene polymer (a 1).

5. The film of claim 1 or any of claims 2-4, wherein the original first polymer composition further comprises up to 20 wt% of at least one ethylene polymer (a2) having a melt index (I) of_2.16) Is about 0.1g/10min to about 2.5g/10min andthe density was 0.941g/cm³-about 0.965g/cm³。

6. The film of claim 5, wherein the original first polymer composition further comprises from 1 to 10 weight percent of an ethylene polymer (a 2).

7. The film of claim 1 or any of claims 2 to 6, wherein the original first polymer composition further comprises up to 20 wt% of at least one ethylene polymer (a3), which is different from polymer (a1), and has a melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min and has a density of greater than 0.910g/cm³-about 0.930g/cm³。

8. The film of claim 7, wherein the original first polymer composition comprises 1 to 10 weight percent of the at least one ethylene polymer (a 3).

9. The film of claim 1 or any of claims 2-8, wherein the second polymer composition comprises at least 50 wt% of the ethylene polymer (b 1).

10. The film of claim 1 or any of claims 2-8, wherein the second polymer composition further comprises up to 70 wt% of at least one polymer (b2) of ethylene and at least one alpha-olefin having 5-20 carbon atoms, the polymer (b2) having a melt index (I) of_2.16) Is about 0.1g/10min to about 2.5g/10min and has a density of 0.910g/cm³-about 0.940g/cm³。

11. The film of claim 1 or any of claims 2-10, wherein the second polymer composition further comprises at least one slip agent.

12. The film of claim 1 or any of claims 2-11, wherein said one layer comprises 25 to 60 weight percent of the original first polymer composition based on the total weight of the polymer blend and 40 to 75 weight percent of the recycled second polymer composition based on the total weight of the polymer blend.

13. The film of claim 1 or any of claims 2-12, wherein the first and second polymer compositions are polymer melt compounded to produce the polymer blend prior to extruding the blend into a film.

14. The film of claim 1 or any of claims 2-13, wherein the first and second polymer composition polymers are separately fed to an extruder to produce the polymer blend during film formation.

15. The film of claim 1 or any of claims 2-14 having a cross-directional shrinkage of at least 15% when heated to 150 ℃.

16. The film of claim 1 or any of claims 2-15, consisting of a single layer made from the polymer blend.

17. The film of claim 1 or any of claims 2-16 comprising a core layer made from the polymer blend and at least one skin layer on each surface of the core layer.

FIELD

The present invention relates to a heat shrinkable film made of polyethylene resin.

Background

The term "heat shrinkable film" or simply "shrink film" refers to a plastic wrapping film that has the property of shrinking when heated to a temperature near the melting point of the film. These films are typically made from plastic resins such as polyvinyl chloride (PVC); polypropylene (PP); linear Low Density Polyethylene (LLDPE); low Density Polyethylene (LDPE); high Density Polyethylene (HDPE); copolymers of Ethylene and Vinyl Acetate (EVA); copolymers of ethylene and vinyl alcohol (EVOH); ionomers (e.g., surlyn. tm.); copolymers of vinylidene chloride (e.g. PVDC, SARAN)^TM) (ii) a Ethylene acrylic acid copolymers (EAA); polyamide (PA), and the like.

End uses for these films include food packaging (e.g., oxygen and moisture barrier bags for freezing poultry, primary cutting of meat and processed meat and cheese products to maintain freshness and hygiene) and non-food packaging (e.g., "over-wrapping" to protect goods from damage, soiling, tampering, and theft) during shipping, distribution, handling, and display. An example of an end use is retail, where the film is hermetically wrapped around a single or multiple items of compact discs, audio/video tapes, computer software cassettes, magazines, candy, boxed products, disposable bowls, and the like. Another example of an end use is that which can be used in wholesale retail, where multiple containers of bottled and canned goods (e.g., beverages, condiments, and personal hygiene products) are sold in bulk. Yet another example is that it could be used for courier shipping, where shrink wrapped sporting goods and individual items of household appliances are now safely shipped without the need for bulky protective cardboard boxes.

Collation shrink films are a particular type of shrink film. Collation shrink films are films that wrap around a number of packaging units (e.g., bottles or cans) and shrink to collectively hold the units in the package. For example, collation shrink films may be wrapped around multiple packs of beverage placed on a paperboard substrate, and the film then shrunk around the container. The wrapping process typically includes a shrink oven or shrink tunnel in which the film is heated to cause collation shrinkage to occur. Shrinkage of the plastic film causes it to collapse over multiple container cycles and hold them in place.

Certain classes of polymers, such as metallocene polyethylene (mPE) resins available from ExxonMobil Chemical Company of houston, texas, have shown particular promise for shrink film applications. Metallocene PE offers a good balance of operating stability, expanded output, versatility and higher alpha-olefin (HAO) performance, and simple resin sources. For example, International patent application publication No. WO 2017/139031 discloses a shrink film comprising a metallocene polyethylene polymer comprising at least 65 weight percent ethylene derived units and having a Melt Index (MI) of from about 0.1g/10min to about 2.0g/10min and a density of about 0.905g/cm³-about 0.920g/cm³And a melt index ratio (MFR) of about 25 to about 80, wherein the shrink film has a total shrinkage of 100% to 200%, a shrink force of 1.5N or less and a shrink force of 1.5N or less.

With rising resin costs and increasing environmental concerns, there is increasing interest in incorporating recycled resins into polyethylene shrink films. However, the penetration of recycled materials in shrink films is limited today, mainly due to the adverse effect of recycled materials on film properties (shrinkage, puncture, dart drop, stretch, optical property quality consistency). Furthermore, even when recycled material is used, it is often limited to waste from the original manufacture of shrink film. For example, U.S. patent No.5605660 discloses a method of making a multilayer crosslinked heat-shrinkable polyolefin film having at least one inner layer comprising a thermoplastic polymer sandwiched between two outer layers comprising a thermoplastic polymer different from the thermoplastic polymer of the inner layer, the method comprising the steps of: co-extruding a polymer into a tape; crosslinking the tape; and converting the crosslinked tape into a heat shrinkable film by orientation; wherein scrap generated in the manufacture of the heat shrinkable film is incorporated by recycling the film to the coextrusion step in an amount of up to 50% by weight of the total film weight.

There is still considerable interest in developing new polyethylene shrink films in which large amounts of waste resin (as opposed to being recycled directly from the production of the base film) can be incorporated without significantly degrading the overall film properties.

SUMMARY

In accordance with the present invention, it has now been found that shrink films having excellent properties can be produced using a specific mixture of virgin and recycled polyethylene even when the amount of recycled resin in the blend is 20% by weight or more.

Accordingly, in one aspect, the present invention relates to a heat shrinkable film comprising at least one layer made from a polymer blend comprising:

(a) at least 20% by weight, based on the total weight of the polymer blend, of an original first polymer composition comprising at least 50% by weight of at least one polymer (a1) of ethylene and at least one alpha-olefin having 5 to 20 carbon atoms, the polymer (a1) having a density of about 0.918g/cm³-about 0.945g/cm³Melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min, melt index ratio (I)_21.6/I_2.16) Is from about 25 to about 80, the Composition Distribution Breadth Index (CDBI), as defined herein, is at least 70%, and the average modulus (M), as defined herein, is 20000-; and

(b) at least 20 wt.%, based on the total weight of the polymer blend, of a reclaimed second polymer composition, different from the first polymer composition, having a melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min and comprises at least 30 wt% of at least one material having a density of 0.910g/cm³-about 0.940g/cm³The ethylene homopolymer (b1) of (a),

wherein the film has a machine direction shrinkage of at least 70% when heated to 150 ℃.

Brief description of the drawings

Figure 1 is a spider graph comparing selected physical properties of a3 layer heat shrinkable film produced according to example 1 (comprising 30 wt% recycled resin) with the same properties of two commercially available 3 layer heat shrinkable films (made from virgin resin only).

Figure 2 is a spider graph comparing selected physical properties of the heat shrinkable film of example 1 with those of a similar film produced according to example 2 comprising 50% by weight recycled resin.

Figure 3 is a spider graph comparing selected physical properties of a single layer heat shrinkable film produced according to example 3 (using resins blended in situ in an extruder) with those of a similar film produced according to example 4 (using previously compounded resins).

Figure 4 is a spider graph comparing selected physical properties of the 3-layer heat shrinkable film of example 1 (using resins blended in situ in the extruder) with those of the 3-layer film produced according to example 5 (using pre-compounded resins in the core layer).

Detailed description of the embodiments

Described herein are heat shrinkable films comprising at least one layer (referred to herein as a core layer) made from a polymer blend comprising at least 20% by weight of an original first polymer composition and at least 20% by weight of a recycled second polymer composition. For example, the core layer may comprise at least 25 wt%, such as at least 30 wt%, such as at least 35 wt%, such as at least 40% and in some embodiments may comprise up to 75 wt%, such as up to 70 wt%, such as up to 65 wt%, or up to 60 wt% of the reclaimed second polymer composition, with the remainder typically being the original first polymer composition. In a preferred embodiment, the core layer comprises from 25 to 60 wt% of the original first polymer composition based on the total weight of the polymer blend and from 40 to 75 wt% of the regenerated second polymer composition based on the total weight of the polymer blend.

As used herein, the term "virgin first polymeric composition" means a polymeric resin or a mixture or blend of two or more polymeric resins, wherein none of the resins has been previously formed into an industrial or consumer product. The term "regenerated second polymeric composition" means a polymeric resin or a mixture or blend of two or more polymeric resins that has been recovered from a previous industrial or consumer use. Thus, the reclaimed polymer compositions can include additives, such as slip agents, that are typically added to polymer resins to aid in their processing. The term "recycled" does not include waste material that may be generated in the manufacture of any of the virgin resins used herein or the heat shrinkable films described herein, although such waste material may of course be used as an additional component of the final film.

Virgin first polymer composition

The original first polymer composition comprises at least 50% by weight, such as at least 60% by weight, preferably at least 80% by weight, of a polymer (a1) of at least one ethylene and at least one alpha-olefin comonomer having from 5 to 20 carbon atoms, more preferably from 5 to 10 carbon atoms and most preferably from 5 to 8 carbon atoms. In one embodiment, polymer (a1) is a copolymer of ethylene with up to 15% by weight of 1-hexene. As is well known in the art, the molar ratio of ethylene to comonomer can be varied, as can the concentration of comonomer, in order to obtain the desired melt index ratio. Control of polymerization temperature and pressure can also be used to help control MI.

The density of the polymer (a1) was about 0.918g/cm³-about 0.945g/cm³E.g., about 0.918g/cm³-about 0.945g/cm³Melt index (I)_2.16) Is from about 0.1g/10min to about 2.5g/10min, e.g., from about 0.1g/10min to about 1.0g/10min, and a melt index ratio (I)_21.6/I_2.16) Is about 25 to about 80, for example about 30 to about 70g/10 min.

The Composition Distribution Breadth Index (CDBI) of polymer (a1) is at least 70%, for example at least 75%, where CDBI is determined as described in international patent publication WO 93/03093, columns 7 and 8, and Wild et al, j.poly.sci., poly.phys.ed., volume 20, page 441 (1982), and U.S. patent No.5008204, which are all incorporated herein by reference.

In addition, the average 1% secant modulus (M) of the polymer (a1) is 20000-. In embodiments, the relationship between M and Dart Impact Strength (DIS) in g/mil for polymer (a1) conforms to the following formula:

where "e" is the base of the natural logarithm, M is the average modulus psi, and DIS is determined according to ASTM D1709-91(26 inches). Typical DIS values are 120-1000g/mil, especially less than 800 and greater than 150 g/mil.

The polymer (a1) may be obtained by continuous gas phase polymerization using a supported metallocene catalyst in the substantial absence of an alkylaluminum-based quencher (e.g., Triethylaluminum (TEAL), Trimethylaluminum (TMAL), Triisobutylaluminum (TIBAL), tri-n-hexylaluminum (TNHAL), etc.). The catalyst may comprise at least one bridged biscyclopentadienyl transition metal complex and an alumoxane activator on a common or separate porous support, such as silica, and the catalyst is uniformly distributed in the silica pores. Further details of the production of polymer (a1) can be found in U.S. Pat. No.6255426, the entire contents of which are incorporated herein by reference.

Commercially available examples of polymer (a1) include Enable supplied by ExxonMobil Chemical^TMResins, e.g. Enable^TM4002MC (density 0.940 and MI 0.25g/10min) and Enable^TM2703HH (density 0.927 g/cm)³And MI was 0.3g/10 min).

In addition to polymer (a1), the virgin first polymer composition may also comprise at most 20 wt%, such as at most 15 wt%, such as at most 10 wt%, typically 1 to 10 wt% of at least one virgin high density ethylene polymer (a 2). Melt index (I) of suitable HDPE materials_2.16) Is about 0.1g/10min to about 2.5g/10min, e.g., 0.1 to 1g/10min, and has a density of about 0.941g/cm³-about 0.965g/cm³For example, about 0.955g/cm³-about 0.965g/cm³. Suitable commercially available example packages for Polymer (a2)Including ExxonMobil Chemical as HDPE HTA 108 (density of 0.961 g/cm)³And MI is 0.7g/10 min).

The original first polymer composition may also comprise at most 20 wt%, such as at most 15 wt%, such as at most 10 wt%, typically 1 to 10 wt% of at least one low density ethylene polymer (a3), which is different from polymer (a 1). Suitable LDPE polymers (a3) have a melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min, e.g., 0.1 to 1g/10min, and a density of greater than 0.910g/cm³-about 0.930g/cm³For example 0.915g/cm³-about 0.925g/cm³. Suitable commercially available examples of polymer (a3) include ExxonMobil Chemical as LDPE LD 165BW1 (density of 0.922 g/cm)³And MI is 0.33g/10 min).

Regenerated second polymer composition

The recycled second polymer composition used in the core layer of the shrinkable film of the present invention is different from the first polymer composition and has a melt index (I)_2.16) Is about 0.1g/10min to about 2.5g/10min, such as about 0.1g/10min to about 1.0g/10 min. The regenerated second polymer composition comprises at least 30% by weight, such as at least 40% by weight, and at most 90% by weight, or even 100% by weight, preferably 50-85% by weight, of at least one ethylene homopolymer (b1), having a density of 0.910g/cm³-about 0.940g/cm³. Such homopolymers are commonly referred to as low density polyethylene or LDPE and are produced by high pressure polymerization. LDPE has a high amount of long chain branching (usually 0.5 to 5 long chain branches/1000 carbon atoms).

In addition to the LDPE component (b1), the recycled second polymer composition may comprise at least 10% by weight, such as at least 20% by weight, and at most 60% by weight, such as at most 70% by weight, preferably from 20 to 65% by weight, of at least one linear low density copolymer (b2) of ethylene and at least one alpha-olefin having from 5 to 20 carbon atoms, the polymer (b2) having a density of 0.910g/cm³-about 0.940g/cm³. Such copolymers are commonly referred to as LLDPE and are produced by catalytic low pressure polymerization. LLDPE has little or no long chain branching (typically less than 0.1 long chain branches/1000 carbon atoms for LLDPE produced using metallocene catalysts).

Suitable commercially available examples of regenerated second polymer compositions include those available from Ravago Group asCR LS 5241, which has a defined Low Density Polyethylene (LDPE) content of at least 80% by weight and a Linear Low Density Polyethylene (LLDPE) content of at most 20% by weight. It may contain up to 2% polypropylene (PP) and traces (i.e. of polypropylene)<0.5%) other polymers, such as Ethyl Vinyl Alcohol (EVA), and processing additives, such as slip agents.The typical Melt Index (MI) and density values for CR LS 5241 are 1.3g/10min (tested at 2.16kg and 190 ℃ C.) and 0.925g/cm, respectively³。

Heat shrinkable film

The heat shrinkable film herein may be a monolayer film, in which case the core layer constitutes the entire film. Alternatively, the film may comprise two or more layers, with a core layer disposed on at least one major surface, or more typically both major surfaces, with one or more skin layers. Preferred multilayer films contain 3 layers and have a skin layer on each major surface of the core layer, and 5 layers and 2 skin layers on each major surface of the core layer. The skins may be the same or different from each other. Preferably, the skin layers are different from the core layer and in particular may be free of added recycled polymer. Suitable materials for use as skin layers in the films of the present invention are the ExxonMobil Chemical under the trade names Exced and Exced XP (e.g. Exced)^TM1018HA and excepted^TMXP8784) with a metallocene-catalyzed polyethylene resin, alone or with a HDPE resin (density 0.941 g/cm)³-about 0.965g/cm³) Or a combination of LDPE resins.

The heat shrinkable films herein may be produced by blowing or casting using conventional extrusion techniques. In forming the core layer, the virgin and recycled polymer compositions may be pre-blended by melt compounding prior to feeding to the extruder, or the different resin materials may be fed separately to the extruder.

Typically, the heat shrinkable films described herein comprise at least 20% and up to 60%, for example 30 to 50%, by weight of the reclaimed polymer composition, based on the total weight of the film. Even when such a large amount of regrind is present, the film has a machine direction shrinkage of at least 70% when heated to 150 ℃, and preferably a cross direction shrinkage of at least 15%.

The invention will now be described in more detail with reference to the following non-limiting examples and the accompanying drawings.

In the examples and the foregoing discussion, the various resin and film properties reported were measured using the following standard tests and modified standard tests:

density is measured according to ASTM D-1505.

Melt index is measured according to ASTM D-1238.

Haze% is measured according to ASTM D-1003.

The 1% secant modulus is measured according to ASTM D-882-91.

Elmendorf tear strength was measured according to ASTM D1922-15.

Tensile strength at break: was measured according to a test based on ASTM D882-18, and a gauge length of 50mm was used for all specimens, and initial clamp separation was always set to 50 mm.

The needle penetration resistance was measured according to the CEN 144777-2004-based test, and the specimens were conditioned at 23. + -. 2 ℃ and 50. + -. 10% RH for 40 hours before the test.

The 45 ° gloss is measured according to a test based on ASTM D-2457-13, where a background with dark green sandpaper is always used as a sample holder and the reading is only done in the MD direction, the results are reported as an average of five test specimens.

The retention force (N) was measured according to ISO 14616 using a Retratech shrink force tester.

Transparency is measured according to a test based on ASTM D-1746, and readings are taken only in the MD direction.

Dart drop impact is measured by a method consistent with ASTM D-1709-04 on dart drop impact tester model C from Davenport Lloyd Instruments, where a pneumatically operated ring clamp is used to obtain a uniform flat specimen and the dart is automatically released by an electromagnet once sufficient air pressure is reached on the ring clamp. The test measures the energy in terms of weight (mass) of a falling dart falling from a specified height, which will produce a 50% failure of the test specimen tested. Method A uses Tuflon^TM(phenolic resin) falling dart heads of 38mm diameter, which drop from a height of 660mm, impact resistance for films requiring a mass of 50g or less to 2kg to break them. Method B used a dart drop of 51mm diameter, which dropped from a height of 1524mm, and the internal diameter of the sample holder was 127mm for both methods a and B. The values given are obtained by means of a standard Staircase Testing Technique. The minimum width of the sample is 20cm and the recommended length is 10m and should be free of pinholes, wrinkles, creases or other obvious defects.

The shrinkage (Betex shrinkage) reported as a percentage was measured by cutting a circular coupon from a film sample using a 50mm die after conditioning the film sample at 23 + -2 deg.C and 50 + -10% relative humidity for at least 40 hours. The sample was then placed on a yellow copper foil and embedded in a layer of silicone oil. This assembly was heated by placing it on a 150 ℃ hot plate (Betex model) until the dimensional change ceased. The average shrinkage obtained with six samples is reported.

Example 1

Three-layer coextruded heat-sealable films were produced on a Windmoeller & Hoelscher (W & H) coextrusion line with a die gap of 1.4mm, a blow-up ratio (BUR) of 3.2 and an output of about 225 kg/H. The processing temperature was 200-210 ℃ and the total thickness of the film was 40 μm, and the relative layer thickness was 1 (skin layer): 3 (core layer): 1 (surface layer). The composition of the film was as follows:

core layer: 50 wt% Ravalene^TM CR LS 5241

40wt％Enable^TM 4002MC

5wt％HDPE HTA 108

5wt％LDPE LD 165BW1

Surface layer: 90 wt% excepted^TM 1018HA

10wt％HDPE HTA 108

The recycled resin used in the core layer is blended in situ with the original resin used in the core layer during the blow molding process. The regenerated resin constituted 30 wt% of the total film.

The resulting films were tested for performance and the results are summarized in table 1 and fig. 1 (grey area). Also summarized in table 1 and fig. 1 are the physical properties of the three-layer reference films, each measured at a BUR of 3.2, a total thickness of 40 μm and a layer distribution of 1: 3: 1, or a pharmaceutically acceptable salt thereof. The composition of the reference film (which was produced using only the original resin) was as follows:

reference film 1 (shown by solid line in FIG. 1)

Core layer: 80 wt% ExxonMobil^TM LDPE LD 159AC

20wt％HDPE HTA 108

Surface layer: 95 wt% ExxonMobil^TM LLDPE LL 1001XV

5wt％LDPE LD 165BW1

Reference film 2 (shown in FIG. 1 by a dotted line)

Core layer: 70 wt% Enable^TM 4002MC

20wt％HDPE HTA 108

10wt％LDPE LD 159AC

Surface layer: 90 wt% excepted^TM 1018HA

10wt％HDPE HTA 108

As can be seen from fig. 1 and table 1, the film of example 1 was at least on par with reference film 1 for all critical shrink film properties, although exhibiting slightly reduced secant modulus, tensile strength and holding power compared to reference film 2.

Example 2

The film of example 1 was again produced, but with Ravalene in the core layer^TMThe amount of CR LS 5241 was increased to 70 wt%, Enable^TM4002MC was reduced to 20 wt% and the layer distribution was 1: 5: 1. all other parameters remain the same.

The regenerated resin constituted 50 wt% of the total film.

The properties of the resulting films were tested and are summarized in table 1. The test results are compared in fig. 2 with those of the film of example 1, where the grey areas represent the performance of the film of example 1 and the solid lines represent the performance of the film of example 2. It can be seen that the properties of the film of example 2 are very similar to those of the film of example 1 (albeit with an increased amount of recycled resin), with a slight decrease in secant modulus, tensile strength and holding power, and a slight increase in haze.

TABLE 1

Examples 3 and 4

On a Hosokawa Alpine-2 monolayer blow molding line, a monolayer shrink film was produced with a BUR of 3.0 and a thickness of 50 μm, a die gap of 1.5mm and an output of about 120 kg/h. The processing temperature for producing the monolayer film was set at 250 ℃ to ensure optimum melting and avoid melt fracture due to the recycled/virgin polymer blend. In the case of example 3, the resin materials of the core layer in example 1 (i.e., 50 wt% Ravalene CR LS 5241+40 wt% Enable 4002MC +5 wt% HDPE HTA 108+5 wt% LDPE LD 165BW1) were fed into different hoppers of a single extruder of the film blowing line, respectively. In the case of example 4, the blend used was a resin previously compounded with the same composition as in example 3, this time fed only to the main hopper of the extruder.

The properties of the resulting films are summarized in table 2 and fig. 3 (the grey areas of fig. 3 represent the film of example 3, and the solid lines represent the film of example 4). While the pre-compounding step is expected to homogenize the final product and improve and maintain the consistency of film mechanical properties, it can be seen that no significant difference in film properties is observed between the in situ blend and the pre-compounded approach. This can be explained at least in part by the fact that in the tests, the pre-compounding was performed by blending the virgin pellets with the recycled pellets, no antioxidant was added, and a twin screw extruder was used that caused strong shear, no proper melt filtration and no degassing. If the pre-compounding step is performed in a single step (i.e., blending the raw pellets with the film scrap pieces), while adding the correct type and amount of antioxidant, and using prior art extrusion techniques and melt filtration systems and in-line degassing of volatiles, the respective film properties can be significantly improved compared to the in-situ blend.

Example 5

A three-layer shrink film was produced using the method and composition of example 1, but prior to the film blowing process, the resin material of the core layer was previously compounded. The properties of the resulting films were compared with those of example 1 in table 2 and fig. 4 (the gray areas in fig. 4 represent the film of example 1, and the solid line represents the film of example 5). Also no significant difference in film properties was observed between the in situ blend and the pre-compounded protocol.

TABLE 2

While the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For that reason, reference should therefore be made solely to the appended claims for purposes of determining the true scope of the present invention.