阅读说明：本技术 发泡聚乙烯制品 (Foamed polyethylene articles ) 是由 丹尼尔·范·霍克 尼莎·安东尼 罗文德·辛格 智·雄 彼得·马尔姆洛斯 翁·张·坤 段欣 于 2018-11-06 设计创作，主要内容包括：一种聚合物组合物,基于聚合物组合物的总量(100wt％),其包含35至89.9wt％的MFR<Sub>21</Sub>MFR<Sub>2</Sub>为50至200的多峰线性低密度聚乙烯(LLDPE),10至50wt％的低密度聚乙烯(LDPE)和0.1至15.0wt％的发泡剂组分。(A polymer composition comprising a MFR of 35 to 89.9 wt. -%, based on the total amount of the polymer composition (100 wt. -%) 21 MFR 2 A multimodal Linear Low Density Polyethylene (LLDPE) of 50 to 200, 10 to 50 wt% of a Low Density Polyethylene (LDPE) and 0.1 to 15.0 wt% of a blowing agent component.)

1. A polymer composition comprising a MFR of 35 to 89.9 wt. -%, based on the total polymer composition (100 wt. -%)₂₁/MFR₂A multimodal Linear Low Density Polyethylene (LLDPE) of 50 to 200, 10 to 50 wt% of a Low Density Polyethylene (LDPE) and 0.1 to 15.0 wt% of a blowing agent component.

2. The polymer composition of any of the preceding claims, wherein the polymer composition is a polymer compositionSaid multimodal LLDPE having a density of 915 to 935kg/m³。

3. The polymer composition of claim 1 or 2, wherein the blowing agent component comprises sodium borohydride, ammonium carbonate, sodium bicarbonate and modified sodium bicarbonate, for example sodium bicarbonate modified with a proton donor such as citric acid.

4. The polymer composition of any of the preceding claims, wherein the MFR of the multimodal LLDPE₂Is 0.01 to 20g/10 min.

5. The polymer composition of any of the preceding claims, wherein the multimodal LLDPE has a Mw/Mn of 10 or more, such as 10 to 30.

6. The polymer composition of any of the preceding claims, wherein the MFR of the LDPE₂Is 0.1-20g/10 min.

7. The polymer composition of any of the preceding claims, wherein the LDPE has a density of 915 to 935kg/m³。

8. The polymer composition of any of the preceding claims, wherein the MFR of the multimodal LLDPE₂₁Is 10 to 200g/10 min.

9. The polymer composition of any of the preceding claims, comprising a MFR of 50 to 74.9 wt%₂₁/MFR₂A multimodal linear low density polyethylene of from 50 to 200, from 25 to 49.9 wt% of a low density polyethylene and from 0.1 to 15 wt% of a blowing agent component.

10. A foamed article comprising a composition comprising 35 to 90 wt% of MFR, based on the total amount of polymer composition (100 wt%)₂₁/MFR₂Is 50 to200 multimodal linear low density polyethylene, and 10 to 50 wt% LDPE.

11. A foamed layer element comprising a MFR of 35 to 90 wt%₂₁/MFR₂A multimodal linear low density polyethylene of from 50 to 200, and 10 to 50 wt% of LDPE.

12. The foamed layer member according to claim 11, wherein the foamed layer member is a foamed layer of a foamed single layer film or sheet, or a multi-layer film or sheet.

13. The foamed layer element according to claims 11 to 12, wherein the foamed layer element has a final density of 600 to 800kg/m³。

14. The foamed layer element according to claims 11 to 13, wherein the foamed layer element is foamed by 10 to 30 wt.%.

15. A foamed layer element according to claims 11 to 14, characterized in that said multimodal LLDPE has a density of 915 to 935kg/m³。

16. The foamed layer element of claims 11-15, wherein the MFR of the multimodal LLDPE₂Is 0.01 to 20g/10 min.

17. A foamed layer element according to claims 11 to 16, wherein said multimodal LLDPE has a Mw/Mn of 10 or more, such as 10 to 30.

18. The foamed layer element of claims 11-17, wherein said LLDPE has an MFR₂Is 0.01 to 20g/10 min.

19. Foamed layer element according to claims 11 to 18, characterized in that the density of the LDPE is from 915 to 935kg/m³。

20. The foamed layer element of claims 11-19, wherein the MFR of the multimodal LLDPE₂₁Is 0.01 to 20g/10 min.

21. Multilayer film or sheet comprising at least 3 layers, i.e. two outer layers and a core layer, characterized in that the core layer is foamed and comprises an MFR of 35 to 90 wt. -%₂₁/MFR₂A multimodal linear low density polyethylene of from 50 to 200, and 10 to 50 wt% of LDPE.

22. A foamed monolayer film or sheet comprising an MFR of 35 to 90 wt%₂₁/MFR₂A multimodal linear low density polyethylene of from 50 to 200, and 10 to 50 wt% of LDPE.

23. A film or sheet according to claim 21 or 22, having a thickness of from 50 to 1000 μm.

Technical Field

The present invention relates to foamed polyethylene articles, such as foamed films or sheets. In particular, the present invention relates to the use of multimodal Linear Low Density Polyethylene (LLDPE) with a broad molecular weight distribution in combination with Low Density Polyethylene (LDPE) for the preparation of foamed articles, such as foamed films or sheets, or foamed layers in films of sheets. This combination of polymers results in a foamed article having the desired properties.

Background

Foaming is a known technique which is first carried out in moulding, in which the thickness of the object is sufficiently high to allow foaming. Foaming is an interesting alternative for polymer manufacturers, as foamed articles can reduce cost, reduce weight, improve insulation, shorten injection cycles, and have other advantages.

Polyethylene foams can be prepared by extruding molten polyethylene with a blowing agent. The blowing agent may be a gas or a product that decomposes at a given temperature and releases a gas. At sufficiently high temperatures and pressures, the blowing agent will dissolve and disperse in the molten polymer. At the die (die) exit, when the pressure drops, the incompatibility of the gases in the polymer will create bubbles called cells. When the polymer cools to the solid phase, cell growth is limited.

During foaming, cells are generated and grow to a size determined by the equilibrium relationship between the pressure of the propellant and the strength of the melt contained in the polymer, thereby forming a porous polymer structure.

Foaming has also been used to make polyolefin films. This allows for a reduction in the density of the film, thus allowing less plastic to be used for a given packaging scheme. However, foaming is more challenging than molding in terms of film preparation, as no mold (mould) is present to accommodate the extruded melt and ensure a smooth surface. The use of a casting mold helps to keep the surface of the article smooth despite the presence of air bubbles in the polymer.

In film and sheet applications, foaming faces a number of difficulties associated with the rough surface formed. This is commonly referred to as the "orange peel" effect. This is a particular problem in packaging solutions where the film is printed, and this effect can lead to poor clarity of the picture or text.

Another problem with foamed films and sheets is that the small thickness compared to molding results in a severe reduction of mechanical properties. Processability is also challenging. Conventional foamed films generally do not have good enough appearance and mechanical properties to stand up to the market.

Regarding foaming itself, the dispersion of cells and the size of cells are important to limit the above disadvantages. The uniform distribution of cells and the small size of each cell may reduce the orange peel effect and minimize the degradation of mechanical properties. The control of these parameters will depend on several characteristics, including the polymer containing the blowing agent, the blowing agent itself and the process conditions.

To date, many foamed polyethylene products have failed to meet the minimum requirements of the packaging market.

In order for the foaming process to produce valuable articles such as films and sheets, the polymer bubbles formed during foaming must be stretchable but limited in size. Thus, it is clear that there is a need for polymers having excellent melt strength to allow the formation of stretchable cells that can adopt a uniform size distribution.

Disclosure of Invention

The present inventors have now found that multimodal Linear Low Density Polyethylene (LLDPE) with broad molecular weight distribution in combination with Low Density Polyethylene (LDPE) can provide desirable foamed compositions.

The multimodal LLDPE/LDPE composition provides melt strength and drawability so that the composition can be foamed without breaking to form a foamed film or sheet. The composition allows the formation of cells with a uniform structure and foamed articles, such as the foamed sheets and films of the present invention, have sufficient mechanical properties to be used in the foamed packaging market. In addition, the polymer composition of the present invention is excellent in processability during foaming.

Without wishing to be bound by theory, it is believed that blending multimodal LLDPE with broad molecular weight distribution with LDPE has a synergistic effect on cell structure and foam quality. While these examples focus on the use of chemical blowing agents, it is expected that the results will extend to other foaming techniques, such as physical foaming (using gaseous blowing agents).

Thus, viewed from one aspect the invention provides a polymer composition comprising an MFR of 35 to 89.9 wt%, based on the total amount of polymer composition (100 wt%), based on the total weight of the polymer composition (100 wt%)₂₁/MFR₂A multimodal Linear Low Density Polyethylene (LLDPE) of 50 to 200 and/or Mw/Mn of at least 10, 10 to 50 wt% of a Low Density Polyethylene (LDPE); and 0.1 to 15.0 wt% of a blowing agent component.

The present invention also provides a polymer composition comprising:

(I) a first composition comprising a MFR of 35 to 90 wt. -%, based on the total amount of the polymer composition (100 wt. -%)₂₁/MFR₂A multimodal linear low density polyethylene having a Mw/Mn of at least 10 and 50 to 200, and 10 to 50 wt% LDPE; and

(II) 0.1 to 15.0 wt% of a blowing agent component, based on the weight of the first composition.

In a preferred embodiment of the invention, the polymer of the polymer composition is selected from the group consisting of said multimodal LLDPE and LDPE. I.e. preferably the multimodal LLDPE and LDPE are the only polymer components present in the polymer composition.

Optionally, and preferably, the polymer composition may comprise additives, typically conventional additives, used in conventional amounts. The additive may comprise 0 to 10 wt%, for example 0 to 5 wt%, preferably 0.01 to 5 wt% of the polymer composition. Some of the optional additives may be in the form of well-known masterbatches and may be carried on a polymeric carrier. Any polymeric carrier is not included in the above-described polymeric components, but rather forms part of the additive package.

Viewed from another aspect, the invention provides a foamed article. In particular, the present invention provides a foamed article comprising, for example consisting of, a polymer composition comprising, based on the total amount of polymer composition (100 wt%), a MFR of 35 to 90 wt%₂₁/MFR₂Multimodal linear low density polyethylene having a Mw/Mn of at least 10 and 50 to 200, 10 to 50 wt% of LDPE, and 0 to 10 wt% of optional additives.

Viewed from another aspect the invention provides a foamed layer element comprising a MFR of 35 to 90 wt%₂₁/MFR₂Multimodal linear low density polyethylene having a Mw/Mn of at least 10 of from 50 to 200 and/or from 10 to 50 wt% of a Low Density Polyethylene (LDPE). As noted above, optional additives may also be present in amounts of 0 to 10 wt%.

The foamed layer element may be a foamed monolayer film or sheet, or one or more foamed layers of a multilayer film or sheet.

Viewed from another aspect the invention provides a monolayer foamed film or sheet comprising an MFR of from 35 to 90 wt%₂₁/MFR₂Multimodal linear low density polyethylene having a Mw/Mn of at least 10 of from 50 to 200 and/or from 10 to 50 wt% of LDPE. As noted above, optional additives may also be present in amounts of 0 to 10 wt%.

From another aspectViewed from the above, the invention provides a multilayer film or sheet wherein at least one layer of said film or sheet is foamed and wherein said foamed layer comprises a MFR of 35 to 90 wt%₂₁/MFR₂Multimodal linear low density polyethylene having a Mw/Mn of at least 10 of from 50 to 200 and/or from 10 to 50 wt% of LDPE. As noted above, optional additives may also be present in amounts of 0 to 10 wt%.

As noted above, any of the polymer compositions, articles, components, films or sheets of the present invention may contain conventional polymer additives in addition to the blowing agent component. Alternatively, the blowing agent component and some or all of these additives may be supported on a support medium (i.e., carrier), which may be a polymer as is well known in the art. Any optional carrier polymer for such additives is not included in the calculation of wt% of multimodal LLDPE or LDPE, but should be considered to be present as part of the additive package.

In another aspect, the present invention provides a multilayer film or sheet, wherein at least one layer of the film or sheet is foamed, and wherein the foamed layer consists of a polymer composition comprising 35 to 90 wt% of MFR, based on the total amount of polymer composition (100 wt%) (₂₁/MFR₂A multimodal linear low density polyethylene of 50 to 200 and/or a Mw/Mn of at least 10, and 10 to 50 wt% of LDPE.

In an alternative embodiment, the instant invention provides a monolayer foamed film or sheet consisting of a composition comprising 35 to 90 wt% of MFR, based on the total amount of polymer composition (100 wt%), based on the total weight of the polymer composition (100 wt%)₂₁/MFR₂A multimodal linear low density polyethylene of 50 to 200 and/or a Mw/Mn of at least 10, and 10 to 50 wt% of LDPE.

Viewed from another aspect, the present invention provides a method of making a foamed article comprising:

providing a first composition comprising a MFR of 35 to 90 wt. -%, based on the total amount of the first composition (100 wt. -%)₂₁/MFR₂A multimodal linear low density polyethylene having a Mw/Mn of at least 10 and 50 to 200, and 10 to 50 wt% LDPE;

adding 0.1 to 15 wt% of a blowing agent component to the first composition, based on the weight of the first composition, to form a second composition;

processing the second composition by passing the second composition through an extruder and a die to form a foamed article.

Viewed from another aspect, the present invention provides a method of making a foamed layer element comprising:

providing a first composition comprising a MFR of 35 to 90 wt%₂₁/MFR₂A multimodal linear low density polyethylene having a Mw/Mn of at least 10 and 50 to 200, and 10 to 50 wt% LDPE;

adding 0.1 to 15 wt% of a blowing agent component to the first composition, based on the weight of the first composition, to form a second composition;

the second composition is processed by passing the second composition through an extruder and die to form a foamed layer member.

Viewed from another aspect, the present invention provides a method of preparing a foamed film or sheet comprising:

providing a first polymer composition comprising an MFR of 35 to 90 wt%₂₁/MFR₂A multimodal linear low density polyethylene having a Mw/Mn of at least 10 and 50 to 200, and 10 to 50 wt% LDPE;

adding 0.1 to 15 wt% of a blowing agent component to the first composition, based on the weight of the first composition, to form a second composition;

the second composition is processed by passing it through an extruder and die to form a foamed sheet or film.

Detailed Description

The present invention relates to the formation of foamed articles, preferably foamed films or sheets comprising a foamed blend of multimodal LLDPE and LDPE. The film of the present invention is preferably a blown film made using conventional film blowing techniques.

The foamed layer of the foamed article is produced in the presence of a blowing agent to introduce gas into the extruded polymer melt and thus introduce cells into the final foamed article. Hair-like deviceThe foamed article will have a lower density than a corresponding unfoamed article. The reduction in density is desirably at least 50kg/m³E.g. at least 100kg/m³。

Although the invention will be described primarily with respect to films, it should be understood that the following preferred embodiments are also generally applicable to the sheet aspects or articles of the invention.

Multimodal LLDPE

The article or polymer composition of the invention comprises a multimodal LLDPE. The term "multimodal" means multimodal with respect to the molecular weight distribution and includes bimodal polymers, if not otherwise stated.

Generally, a polyethylene is said to be "multimodal" if it comprises at least two polyethylene fractions which are produced under different polymerization conditions, resulting in different (weight average) molecular weights and molecular weight distributions. The prefix "multi" relates to the number of different polymer fractions present in the polymer. Thus, for example, multimodal polymers include so-called "bimodal" polymers consisting of two fractions. The form of the molecular weight distribution curve, i.e. the appearance of the graph of the polymer weight fraction of a multimodal polymer (e.g. LLDPE) as a function of its molecular weight, will show two or more peaks, or at least be distinctly broadened compared with the curves for the individual fractions. For example, if in a continuous multi-stage process, a polymer is produced using reactors connected in series and using different conditions in each reactor, the polymer fractions it produces in the different reactors will each have its own molecular weight distribution and weight average molecular weight. When the molecular weight distribution curve of such a polymer is recorded, the individual curves from these fractions are superimposed into the molecular weight distribution curve of the total resulting polymer product, typically resulting in a curve having two or more distinct peaks.

In any multimodal LLDPE, it is defined to have a lower molecular weight component (LMW) and a higher molecular weight component (HMW). The LMW component has a lower molecular weight than the high molecular weight. Typically, the difference is at least 5000 g/mol. However, the difference in Mw can be more easily observed by analyzing the MFR of the components.

In the multimodal LLDPE of use in the invention, at least one of the LMW and HMW components is an ethylene copolymer. Preferably, at least the HMW component is an ethylene copolymer. The Low Molecular Weight (LMW) component may also be an ethylene copolymer. Alternatively, if one of the components is a homopolymer, the LMW is preferably a homopolymer. The combination of LMW homopolymer and HMW ethylene copolymer is particularly preferred.

The multimodal LLDPE may comprise up to 5.0 wt% of a well known polyethylene prepolymer (obtainable from a prepolymerization step well known in the art). In the case of such prepolymers, the prepolymer component is contained in one of the LMW and HMW components as defined above, preferably in the LMW component.

As used herein, the term "ethylene copolymer" is intended to encompass a copolymer comprising at least one C derived from ethylene and at least one other C_3-12α repeating units of an olefin monomer ethylene obviously forms the predominant monomer unit present preferred copolymers are binary and comprise a single comonomer, or are terpolymers and comprise two or three comonomers preferably one comonomer is present in the multimodal LLDPE of the invention.

The density of the multimodal LLDPE may be between 905 and 940kg/m³For example 915-³。

Melt flow Rate MFR of multimodal LLDPE₂Preferably in the range of 0.01 to 20g/10min, for example 0.05 to 10g/10min, preferably 0.1 to 6.0g/10 min.

MFR of multimodal LLDPE₂₁May be in the range of 5 to 500g/10min, preferably 10 to 200g/10 min. The Mw of the multimodal LLDPE may be in the range of 100,000 to 300,000, preferably in the range of 150,000 to 270,000.

An important feature is that the multimodal LLDPE of the invention has a broad molecular weight distribution. High MFR₂₁/MFR₂Values or high Mw/Mn values may indicate this.

MFR of multimodal LLDPE₂₁/MFR₂Preferably from 50 to 200, for example from 60 to 150, especially from 70 to 120. This high value reflects the breadth of the molecular weight distribution.

The Mw/Mn value of the multimodal LLDPE of the invention is preferably 10 or more, for example from 10 to 50, especially the Mw/Mn value of the LLDPE may be in the range from 10 to 30, preferably from 10 to 25. It is envisaged that the use of multimodal LLDPE with a broad molecular weight distribution during foaming provides additional melt strength and drawability and therefore can form foamed articles, such as foamed films or sheets, with a well-dispersed cell structure, the cell size of which is limited and which comprises predominantly closed cells. The combination of multimodal LLDPE and LDPE with a broad Mw/Mn has a synergistic effect, which results in an improved, e.g. uniform, cell structure after foaming.

In the foamed layer of the present invention, the length of the cells is preferably 200 to 1500 micrometers, preferably 200 to 1000 micrometers. The length/width ratio of the cells may fluctuate between 1 and 10 and may be partly adjusted by processing parameters such as speed and blow-up ratio. The length/width ratio is preferably between 1.5 and 5.

The thickness of the cells will not exceed the thickness of the foamed layer and will generally be less than the other two dimensions. On average, the 3 cell sizes will depend primarily on the composition of the foamed layer, including the selected blowing agent itself and the processing conditions.

Multimodal LLDPE can be formed from ethylene and at least one C_3-12α an olefin comonomer, such as 1-butene, 1-hexene or 1-octene preferably the multimodal LLDPE is a binary copolymer, i.e. the polymer comprises ethylene and one comonomer, or a terpolymer, i.e. the polymer comprises ethylene and two or three comonomers.

Alternatively, the comonomer content present in the multimodal LLDPE may be from 1.5 to 10 wt%, especially from 2 to 8 wt%. The content of the copolymer monomers can be determined after the basic standard peak by quantitative 13C Nuclear Magnetic Resonance (NMR) spectroscopy (J.Randall JMS-Rev.Macromol.chem.Phys., C29(2&3),201-317 (1989).

As mentioned above, multimodal LLDPE comprises at least one LMW component and one HMW component.

MFR of LMW component of multimodal LLDPE₂Preferably at least 50g/10min, preferably from 50 to 3000g/10min, more preferably from 100 to 500g/10 min. The molecular weight of the low molecular weight component should preferably be in the range of 20,000 to 50,000, for example, preferably 25,000 to 40,000.

The density of the low molecular weight component, for the copolymer, may be in the range 930 to 980kg/m³In the range of, for example, preferably 940 to 970kg/m³More preferably from 945 to 955kg/m³For the homopolymer, 940 to 975kg/m³In particular 960 to 972kg/m³。

The lower molecular weight component preferably forms 30 to 70 wt%, for example 40 to 60 wt% of the multimodal LLDPE, with the higher molecular weight component forming 70 to 30 wt%, for example 40 to 60 wt%.

The high molecular weight component has a lower MFR than the low molecular weight component₂And a lower density.

MFR of the high molecular weight component₂Preferably less than 1.0g/10min, preferably less than 0.5g/10min, in particular less than 0.2g/10 min. The density of which may be less than 915kg/m³E.g. less than 910kg/m³Preferably less than 905kg/m³. The Mw of the high molecular weight component may be from 100,000 to 1,000,000, preferably from 250,000 to 500,000.

In any of the copolymerized HMW components, at least 0.25 mol-%, preferably at least 0.5 mol-%, such as at least 1-mol-%, such as at most 10 mol-%, of repeat units are derived from the comonomer. This value can be determined or calculated. Ethylene constitutes the major component of HMW.

It is preferred if the multimodal LLDPE of the invention is made using a Ziegler Natta catalyst. The multimodal LLDPE, preferably film/sheet, used for the foamed articles of the invention is not new and can be purchased from polyolefin suppliers, such as, for example, bosu (Borouge), nordic chemical (Borealis), Exxon (Exxon), Basell (Basell), Dow (Dow), etc.

LDPE

The articles, preferably films/sheets, of the present invention further comprise low density polyethylene. The term low density polyethylene is a term of art and defines polyethylene polymers that are typically prepared using free radical initiators (e.g., peroxides) in high pressure processes, as is well known in the art. As is well known to those skilled in the art, LDPE polymers and LLDPE polymers differ.

The LDPE used in the present invention may be a LDPE copolymer or a LDPE homopolymer. Preferably, it is an LDPE homopolymer.

MFR of LDPE₂Preferably 0.1 to 20g/10min, more preferably 0.3 to 10g/10min, still more preferably 0.5 to 5.0g/10 min. The density of the LDPE is preferably 905-940kg/m³More preferably 910-³E.g. 915 to 935kg/m³。

The LDPE used in the present invention is not new and may be purchased from polyolefin suppliers such as Borre (Borough), Nordic chemical (Borealis), Exxon Mobil (Exxon), Basell (Basell), Dow (Dow) and the like.

In foamed articles, the LDPE in the foamed layer element of the invention, e.g. in any foamed film or sheet of the invention, or in the polymer composition of the invention, may be at least 10 wt%, e.g. 10 to 50 wt%, preferably 15 to 45 wt%, especially 18 to 42 wt%. In one embodiment, in the polymer composition of the present invention, the LDPE may be in the range of from 10 to 49.9 wt%, preferably in the range of from 15 to 44.9 wt%, especially in the range of from 18 to 41.9 wt%. In one embodiment, the polymer composition comprises 25 to 49.9 wt%.

In a foamed article, e.g. a foamed layer element of the invention, e.g. in any foamed film or sheet of the invention, the multimodal LLDPE may be at least 35 wt%, e.g. 35 to 90 wt%, preferably 40 to 90 wt%, e.g. 45-90 wt%, preferably 50-90 wt%. In a more preferred embodiment the multimodal LLDPE is 55 to 85 wt%, especially 58 to 72 wt%. In one embodiment, the multimodal LLDPE may be 50 to 75 wt%.

In the polymer composition of the present invention the multimodal LLDPE may be at least 35 wt%, such as 35 to 89.9 wt%, preferably 40 to 89.9 wt%, such as 45 to 89.9 wt%, preferably 50 to 89.9 wt%. In a more preferred embodiment, the multimodal LLDPE is 55 to 85 wt%, especially 58 to 72 wt%. In one embodiment, the multimodal LLDPE may be 50 to 75 wt%.

Note that the foamed article, or the polymer composition, may include other components, such as additives, decomposition products, and the like.

Preparation of polymers

Multimodal LLDPE can be a commercially available product or can be produced in a known manner according to or similar to conventional polymerization processes described in the polymer chemistry literature.

Multimodal (e.g. bimodal) polymers can be prepared by mechanically blending two or more separately prepared polymer components or, preferably, in situ blending in a multi-step polymerization process during the preparation of the polymer components. Both mechanical blending and in situ blending are well known in the art.

Thus, preferred multimodal LLDPE polymers are prepared by in-situ blending in a multi-step (i.e. two or more) polymerization or by using two or more different polymerization catalysts (including multi-or dual-site catalysts) in a single polymerization step.

Preferably, the multimodal LLDPE is produced in at least two polymerization steps using the same catalyst, e.g. a Ziegler-Natta catalyst. Thus, for example, two slurry reactors or two gas phase reactors, or any combination thereof, in any order may be employed. Preferably, however, the multimodal polymer, for example LLDPE, is prepared using slurry polymerisation in a loop reactor followed by gas phase polymerisation in a gas phase reactor.

Northern european chemical (Borealis) loop reactor-gas phase reactor systems are sold as BORSTAR reactor systems. Any multimodal LLDPE is preferably formed in a two-step process comprising a first slurry loop polymerization followed by a gas phase polymerization.

The conditions used in such processes are well known. For slurry reactors, the reaction temperature will typically be in the range of 60 to 110 ℃ (e.g. 85-110 ℃), the reactor pressure will typically be in the range of 5 to 80bar (e.g. 50-65bar), and the residence time will typically be in the range of 0.3 to 5 hours (e.g. 0.5 to 2 hours). The diluent used is generally an aliphatic hydrocarbon having a boiling point in the range from-70 to +100 ℃. In such a reactor, the polymerization can be carried out under supercritical conditions, if desired. Slurry polymerization can also be carried out in bulk, wherein the reaction medium is formed from the monomers being polymerized.

For gas phase reactors, the reaction temperature used will generally be in the range of 60 to 115 ℃ (e.g., 70 to 110 ℃), the reactor pressure will generally be in the range of 10 to 25bar, and the residence time will generally be in the range of 1 to 8 hours. The gas used is generally a non-reactive gas, such as nitrogen or a low boiling hydrocarbon, such as propane, together with the monomer (e.g. ethylene).

Preferably, the low molecular weight polymer fraction is produced in a continuously operated loop reactor, wherein ethylene is polymerized in the presence of a polymerization catalyst as described above and a chain transfer agent (such as hydrogen). The diluent is typically an inert aliphatic hydrocarbon, preferably isobutane or propane.

The same catalyst can then be used to form the high molecular weight component in the gas phase reactor.

In the case of preparing a high molecular weight component in the second step of a multi-step polymerization, it is impossible to directly measure its properties. However, one skilled in the art can use the Kim McAuley equation to determine the density, MFR, of the high molecular weight component₂And the like. Thus, density and MFR₂Both can be determined using k.k.mcauley and j.f.mcgregor: on-line interference of Polymer Properties in an Industrial Polyethylene Reactor, AIChE Journal, June 1991, Vol.37, No,6, pages 825 835-.

Multimodal LLDPE can be made using any conventional catalyst well known in the art, such as chromium, single site catalysts, including metallocenes and non-metallocenes. Preferably, a Ziegler-Natta catalyst is used.

Preferred Ziegler-Natta catalysts comprise a transition metal component and an activator. The transition metal component includes a metal of group 4 or group 5 of the periodic table (IUPAC) as an active metal. In addition, it may contain other metals or elements, such as elements of groups 2, 13 and 17. Preferably, the transition metal component is a solid. More preferably, it is supported on a support material, such as an inorganic oxide support or a magnesium halide. Examples of such catalysts are given in WO 95/35323, WO 01/55230, WO 2004/000933, EP 810235 and WO 99/51646.

Conventional cocatalysts, supports (supports), electron donors and the like may be used.

LDPE can be prepared according to any conventional high pressure polymerization (HP) process using free radical formation in a tubular or autoclave reactor. Such HP processes are well known in the polymer chemistry art and are described in the literature.

Blowing agent component

In order to prepare foamed articles such as foamed films or sheets or foamed layers within films or sheets, a blowing agent component is required. The blowing agent may be a gas or a chemical that releases a gas during extrusion.

The advantages of the proposed composition apply to all foaming techniques, for example:

1) physical foaming, using a gas to convert the particles into a foamed film or sheet;

2) chemical foaming, the particles can be converted into foamed films or sheets using a gas-releasing chemical.

Thus, in one embodiment, the blowing agent is simply a gas, typically an inert gas, which is added to the composition prior to extrusion. The blowing agent (or blowing agent) is preferably chemical and is in solid or liquid form, preferably in solid form. It is added to the polymer composition prior to the extrusion process. It will be appreciated that when the pressure drops, such blowing agents decompose to release gas which will dissolve inside the molten polymer and expand at the die outlet. Thus, in the final foamed article, the blowing agent is no longer present (other than potential degradation products, carriers, etc.). However, prior to the manufacture of foamed articles, such as films or sheets, there is a polymer composition comprising multimodal LLDPE, LDPE and a blowing agent component, which constitutes a further aspect of the invention.

Viewed from another aspect the invention provides a polymer composition comprising from 35 to 89.9 wt% ofMFR₂₁/MFR₂A multimodal linear low density polyethylene of 50 to 200 and/or a Mw/Mn of at least 10, 10 to 50 wt% of LDPE and 0.1 to 15 wt% of a blowing agent component. As noted above, optional additives may also be present in amounts of 0 to 10 wt%.

The preferred percentages of LLDPE and LDPE, as well as the content of blowing agent component, are also applicable to this embodiment of the invention. Thus, the preferred amount of multimodal LLDPE is from 35 to 89.9 wt%, preferably from 40 to 89.9 wt%, from 45 to 89.9 wt%, preferably from 50 to 89.9 wt%.

The term blowing agent component will be used herein to define the supply form of the blowing agent, including components on which the blowing agent itself may be carried. In particular, the blowing agent component may be in the form of a masterbatch and may be carried on a carrier, such as a polymeric carrier. As previously mentioned, if the carrier is a polymer, the polymer carrier is not included in the polymer composition (LLDPE/LDPE) as a weight percentage of the polymer, but is considered to be part of the blowing agent component. Furthermore, the blowing agent itself may form 100% of the blowing agent component, but typically it may form 10 to 70 wt%, for example 15 to 50 wt% of the blowing agent component. Blowing agent components are typically purchased from commercial suppliers. The data table will generally indicate the actual blowing agent content in the blowing agent component.

Suitable chemical blowing agents may be any known organic or inorganic compound that decomposes at elevated temperatures to release a gas such as air, nitrogen, carbon dioxide, carbon monoxide or other hydrocarbons. Suitable organic blowing agents useful in the present invention include sulfonyl hydrazide, 5-phenyltetrazole, azodicarbonamide, citric acid, and modified azodicarbonamides, as known in the art, such as azodicarbonamide modified with zinc oxide, calcium carbonate, and the like.

Suitable inorganic blowing agents include sodium borohydride, ammonium carbonate, sodium bicarbonate and modified sodium bicarbonate, i.e., sodium bicarbonate modified with a proton donor such as citric acid. Other options as particularly advantageous blowing agents are azodicarbonamide and sodium bicarbonate blowing agents, such as modified azodicarbonamide and modified sodium bicarbonate. Most preferred inorganic blowing agents include sodium borohydride, ammonium carbonate, sodium bicarbonate and modified sodium bicarbonate, i.e., sodium bicarbonate modified with a proton donor such as citric acid. When the product comprises a modifier, the modifier is considered to be part of the blowing agent, for example in order to promote gas release during foaming.

The amount added may range from 0.2 to 15.0 wt%, such as from 0.5 to 10.0 wt%, especially from 1.0 to 5.0 wt%, such as from 1.0 to 3.0 wt%, based on the weight of the LLDPE/LDPE mixture, taking into account the supplied blowing agent components (i.e. including any carriers etc.).

In another aspect, the polymer composition may comprise 0.2 to 15.0 wt%, especially 0.5 to 10.0 wt%, for example 1.0 to 5.0 wt%, especially 1.0 to 3.0 wt% of the blowing agent component. The weight percentages of the LLDPE and/or LDPE components can be adjusted down to accommodate these percentages.

Decomposition products of the blowing agent that form the gas phase or cell pores of the foamed polyolefin include air, nitrogen, carbon dioxide, carbon monoxide and other hydrocarbons. Azodicarbonamide primarily generates nitrogen into the melt; the modified bicarbonate primarily generates carbon dioxide gas into the melt. Eventually, these gases disappear after extrusion and are replaced by air in the film.

Articles, e.g. films or sheets

The article of the present invention is a foamed article, and preferably a foamed film or sheet. The foamed film or sheet of the present invention may be a single layer or a multilayer structure. The foamed film or sheet of the present invention preferably comprises one layer, for example 2 layers or at least 3 layers, for example 3 or 5 layers.

Particularly preferred multilayer films or sheets comprise at least three layers (e.g. 3 layers) in the following order:

(i) a layer (A) comprising a polymer,

(ii) layer (B) and

(iii) a layer (C).

Preferably, layers a and C are outer layers. Layer B is the core layer. The polymer composition of layer (a) and the polymer composition of layer (C) may be the same or different. The inner layer (C) is usually designed as a sealing layer and has good sliding properties. The outer layer (a) is usually used for lamination. (B) The layer preferably comprises the foamed layer of the present invention.

The foaming composition of the present invention may be present in any layer of the film or sheet of the present invention. Preferably, however, the foaming composition of the present invention is present in the core layer (B) of the multilayer film or sheet. However, the foaming composition may also be present in the (a) and/or (C) layer. However, this is not preferred. Preferably, layers (A) and (C) are not foamed, whereas layer (B) is foamed.

The layer not comprising the foaming composition of the invention, for example the (a) or (C) layer, may comprise any other polymer, in particular other polyethylene. The polyethylene used is preferably LLDPE and LDPE.

Preferably, layers (a) and/or (C) comprise a multimodal LLDPE. In particular, the multimodal LLDPE in layers (a) and/or (C) may be the same polymer used in the composition of the invention.

Alternatively, layer (a) and/or layer (C) may comprise the composition of the present invention, but not the blowing agent. Thus, the (A) and/or (C) layer may comprise a MFR of 35 to 9 wt%₂₁/MFR₂A multimodal linear low density polyethylene of 50 to 200 and/or a Mw/Mn of at least 10, and 10 to 50 wt% of LDPE. Conveniently, the layer composition used in layer (a) and/or (C) is the same as that used in the foamed layer.

Other options include (A) a layer comprising a MFR of 35 to 90 wt%₂₁/MFR₂A multimodal linear low density polyethylene having a value of from 50 to 200 or a Mw/Mn value of at least 10, and from 10 to 50 wt% of LDPE, and (C) a layer comprising, e.g. consisting of, the multimodal linear low density polyethylene(s) (and vice versa).

Another option is a layer (a) and/or (C) comprising a blend of LLDPEs, for example a multimodal LLDPE and a unimodal LLDPE. In general, the polymer of the outer layer may be selected widely depending on the final desired properties, such as mechanical, surface, sealing, lamination.

In a highly preferred embodiment, layer (a) and/or layer (C) is a LLDPE, in particular a single-site LLDPE (mlldpe), i.e. a LLDPE prepared using a single-site catalyst such as a metallocene. Such mLLDPE may be multimodal or unimodal. Preferably, the mLLDPE may have a Mw/Mn of from 2 to 10, for example from 2 to 4.

In a multilayer film, one layer is foamed as defined herein. Some or all of the other layers may be foamed, but this is not preferred. Preferably only one layer, i.e. the layer comprising the composition of the invention, especially the core layer, is foamed. Therefore, it is preferable that the other layers are not foamed. In a single layer structure, it is obviously necessary to foam the single layer.

Any film layer may be "composed of polyolefin as defined", i.e. composed of LDPE and multimodal LLDPE. The term "consisting of" as used in relation to the film layer material is meant to exclude the presence of other polyolefin components only. Thus, the term does not exclude the presence of additives. Some of these additives may be masterbatches and thus may be carried on a polymeric carrier. Such masterbatches are not excluded.

Any film or sheet may contain standard additives such as antioxidants, uv stabilizers, acid scavengers, nucleating agents, antiblocking agents, slip agents, and the like, as well as Polymer Processing Agents (PPA). In one embodiment, talc is not present in any foamed layer of the present invention.

The film or sheet of the present invention may comprise one or more barrier layers, as is known in the art. For example, for certain applications, it may be desirable to incorporate a barrier layer, i.e., a layer that is impermeable to air and water, into the film structure. This can be achieved using conventional lamination techniques or by co-extrusion.

In the film or sheet comprising or preferably consisting of layers (a), (B) and (C), layer (a) preferably forms 10 to 35% of the film thickness, layer (B) forms 30 to 80% of the film thickness and layer (C) preferably forms 10 to 35% of the film thickness. In such a film, layer (a) and layer (C), if present, may have equal thicknesses. Therefore, the film thickness distribution (%) of the ABC layer is preferably 10-35%/30-80%/10-35% of the total film thickness (100%) after foaming.

The films/sheets of the present invention exhibit significant properties.

In the film or sheet of the present invention, the final density of a single layer film or sheet or the density of a foamed layer of a multilayer film or sheet is from 600 to 800kg/m³。

The thickness of any film or sheet of the invention may be from 50 to 1000 μm, preferably from 50 to 200 μm for a film. The thickness of any foamed layer within such a film or sheet may be from 50 to 500 μm, preferably from 50 to 200 μm for a film.

The foamed layer of the film or sheet is preferably foamed by at least 10 wt%, for example at least 12 wt%. The maximum foaming may be 30 wt%, for example 25 wt%. The percent foaming was determined by comparing the foamed density to the pre-foamed density of the blend.

Film/sheet preparation

For film or sheet formation using polymer blends, the different polymer components (e.g. in layers (a), (B) and optionally (C)) are typically intimately mixed prior to extrusion, as is well known in the art. It is particularly preferred to thoroughly mix the components prior to extrusion, for example using a twin screw extruder, preferably a counter-rotating extruder.

With respect to the first step of the manufacturing process, the layered structure of the film/sheet of the present invention may be prepared by any conventional forming method including extrusion procedures. A monolayer film can be produced by extruding the same mixture in all 3 layers of the coextrusion. The film may be prepared by a cast film or blown film process.

The compositions of the present invention may be prepared by conventional mixing and addition of the blowing agent component. It may be passed to an extruder. The extruder melts the composition of the present invention to a suitable viscosity so that it can absorb the gas generated by the blowing agent. The extruder also mixes all the components thoroughly and holds the composition of the invention under sufficient pressure so that the gases produced by the decomposition of the blowing agent remain in solution in the mixture until the mixture is extruded.

Although the gas released by the blowing agent will plasticize the melt, the general extrusion parameters of the foamed composition will not change relative to standard non-foamed compositions. Thus, suitable pressures for the extrusion process are from about 30bar to about 300 bar. Suitable temperatures for the extrusion process are from about 170 ℃ to about 230 ℃.

Particularly preferably, the multilayer film of layers (a), (B) and (C) is formed by blown film extrusion, more preferably by a blown film coextrusion process. Typically, the composition providing layers (a), (B) and (C) is blow (co) extruded at a temperature in the range of 160 ℃ to 240 ℃ and cooled by blowing a gas, typically air, at a temperature in the range of 10 ℃ to 50 ℃ so that the height of the frost line is 1 or 2 to 8 times the diameter of the die. The blow-up ratio should generally be in the range of 1.2 to 6, preferably 1.5 to 4.

Accordingly, the present invention provides a method of making a foamed article, the method comprising:

providing a composition comprising an MFR of 35 to 89.9 wt%, based on the weight of the composition₂₁/MFR₂A multimodal linear low density polyethylene of 50 to 200 and/or a Mw/Mn of at least 10, and 10 to 50 wt% of LDPE and 0.1 to 15.0 wt% of a blowing agent component;

the composition mixture is processed by passing the composition mixture through an extruder and a die to form a foamed article, such as a film or sheet.

In one embodiment, the sheet is a multilayer sheet and the invention includes coextrusion of the composition to form the core layer B of the ABC sheet.

The present invention also provides a method of making a foamed film comprising:

a composition is provided comprising an MFR of 35 to 89.9 wt%, based on the weight of the composition₂₁/MFR₂A multimodal linear low density polyethylene having a Mw/Mn of at least 10 in the range of from 50 to 200, and 10 to 50 wt% of LDPE, and 0.1 to 15.0 wt% of a blowing agent component;

the composition mixture is processed by passing the composition mixture through an extruder and a die to form a foamed article, such as a film or sheet.

In one embodiment, the film is a multilayer film and the invention includes the coextrusion of the compositions to form the core layer B of the ABC film.

The films/sheets obtained by the process of the invention can be used in known manner for packaging applications, such as sacks or bags. Alternatively, the film may be further processed into a tubular film, which may be used directly in conventional vertical or horizontal form-fill-seal machines known in the art, or made into a tubular film by conventional tube making machines, and then used for packaging. This can be done on-line or off-line during film production by conventional techniques. The tubular film may then be fed into a form, fill and seal (FFS) machine for packaging.

The film or sheet of the present invention can be prepared by flat die extrusion or blown film extrusion. Films prepared by flat die extrusion are useful for food packaging and vertical bagging. Flat die extruded sheet is a desirable choice for thermoforming, such as trays. Circular die films are also used in food packaging and bag erecting applications. Sheets made by circular die punching are ideal for membranes such as geomembranes and roofing membranes.

The invention will now be described with reference to the following non-limiting examples and figures.

Fig. 1 is a photomicrograph of sample IE2 of the example.

Measurement method

Melt flow rate

Melt Flow Rate (MFR) is determined according to ASTM D1238 and is expressed in g/10 min. MFR is an indication of the melt viscosity of the polymer. The MFR of the polyethylene was determined at 190 ℃. The load determining the melt flow rate is generally indicated by a subscript, e.g.MFR₂MFR measured under a load of 2.16kg₅Measured under a load of 5kg or MFR₂₁Measured under a 21.6kg load. MFR_21/2Is MFR₂₁/MFR₂The ratio of (a) to (b). This is also known as FRR_21/2。

Density of

The density of the polymer is according to ISO 1183-1: 2004 method A measured on compression molded samples prepared according to EN ISO 1872-2(2 months 2007) in kg/m 3.

Percent foaming is obtained by dividing the density on the foamed film by the density on the unfoamed film.

Foaming ratio (%): (d)_i–d_f)/d_ix 100 (representing the reduction in weight density)

Wherein d is_iIs the initial density, d_fIs a foamed sealingAnd (4) degree.

To determine the foaming density, a piece of film was cut along the width of the reel.

The film was folded to stack 12 equal sized layers.

A series of 12 discs were obtained by cutting through 12 layers at a time, thus obtaining 12 different discs along the width of the film. The disc diameter was 24.9 mm.

The 4 best disks are selected from the 12 disks, typically in the middle of the stack.

The volume of each of the 4 discs was determined by multiplying the diameter by the measured thickness of each disc.

Each disc was weighed and the volumetric mass of each disc was the weight (gr) divided by the volume (cm)³) The result of (1).

Divide the mass of each disc by the volumetric mass of water (1 gr/cm)³) We obtained the density of each disc.

The density of the sample was determined from the average of the densities of the 4 discs.

Molecular weight

Mw, Mn and MWD were measured by Gel Permeation Chromatography (GPC) according to the following method:

the weight average molecular weight Mw and the molecular weight distribution (MWD ═ Mw/Mn, where Mn is the number average molecular weight and Mw is the weight average molecular weight) were measured according to ISO 16014-4:2003 and ASTM D6474-99. A Waters GPCV2000 instrument equipped with a refractive index detector and an online viscometer was used, the gel columns were 2 XGMHXL-HT and 1x G7000HXL-HT TSK-gel columns from Tosoh Bioscience, the solvent was 1,2, 4-trichlorobenzene (TCB, 2, 4-di-tert-butyl-4-methyl-phenol stabilized at 250 mg/L), the temperature was 140 ℃ and the constant flow rate was 1 mL/min. 209.5 μ L of sample solution was injected for each analysis. The columns were calibrated using a universal calibration (according to ISO 16014-2:2003) using at least 15 narrow MWD Polystyrene (PS) standards in the range of 1kg/mol to 12000 kg/mol. Mark Houwink constants as given in ASTM D6474-99 were used.

All samples were prepared by dissolving 0.5-4.0mg of polymer in 4mL (at 140 ℃) of stable TCB (same as mobile phase), continuously shaking gently for up to 3 hours at a maximum temperature of 160 ℃ before introduction into the GPC instrument.

As known in the art, if the molecular weights of the components of the polymer composition are known, the weight average molecular weight of the polymer composition can be calculated from:

wherein Mw_bIs the weight average molecular weight of the polymer composition,

w_iis the weight fraction of component "i" in the polymer composition, and

Mw_iis the weight average molecular weight of component "i".

The number average molecular weight can be calculated using well known mixing rules:

wherein Mn_bIs the number average molecular weight of the polymer composition,

w_iis the weight fraction of component "i" in the polymer composition, and

Mn_iis the number average molecular weight of component "i".