WO2016062684A1

WO2016062684A1 - Polyolefin-containing composition with anti-fog properties

Info

Publication number: WO2016062684A1
Application number: PCT/EP2015/074207
Authority: WO
Inventors: Geesje Klasina Spijkerman; Ted Henri Wilfred Cornelius KAMPEN; Auke Gerardus Talma
Original assignee: Akzo Nobel Chemicals International B.V.
Priority date: 2014-10-23
Filing date: 2015-10-20
Publication date: 2016-04-28
Also published as: CA2962831A1; IL251231A0; AR102909A1; TW201623563A

Abstract

Agricultural film having a visible light transmission of at least 50%, said film comprising a polyolefin-containing composition that is essentially free of plasticizer and comprises a polyolefin having dispersed therein one or more glycerol esters of saturated fatty acid with 12-22 carbon atoms, said esters having been ethoxylated to an average degree of 1.0 to below 5.0 moles of ethylene oxide groups per mole of glycerol ester.

Description

POLYOLEFIN-CONTAINING COMPOSITION WITH ANTI-FOG PROPERTIES

This invention relates to the prevention of fogging on the surface of agricultural films.

Polyolefins, such as polyethylene, are used in various agricultural applications, such as greenhouse covers and energy screens. Polyolefins have a high resistance to moisture vapour transmission and high transparency, which is evidently essential for agricultural applications.

However, due to temperature changes, any water that evaporates from the soil or plants starts to condense on the inner surface of the polyolefin film. The water droplets form a fogged surface, thereby reducing the visual transparency of the film. This effect is generally called "fogging" or "clouding". Fogging leads to reduced light transmission, which negatively affects the growth of crops covered by said film.

In order to reduce fogging of polyolefin films, so-called antifog agents can be added to the polyolefin. These antifog agents can be coated on the polyolefin film, or they can be incorporated in the polyolefin film. Incorporation in the film is generally preferred over coating on the film because of the lower processing costs, the lower environmental impact (i.e. no coating solvents required), and the absence of a separate layer that can be wiped or washed off the surface. Examples of known antifog agents for incorporation in polyolefin films are monoglycerol esters of fatty acids, sorbitan esters of fatty acids, and combinations thereof.

The antifog action of the incorporated antifog agents is most likely due to the migration of the antifog agent to the film's surface, thereby enhancing the hydrophilicity of the surface and decreasing the surface tension of the water, which causes the water to form a continuous, visually clear film instead of a fogged surface comprising individual droplets of water.

Fogging may occur under relatively cold conditions (below ambient temperature, i.e. cold outside conditions) and relatively warm conditions (above ambient temperature, e.g. in warm humid outside conditions). The first are called cold fog conditions; the second are called hot fog conditions.

WO 84/03296 discloses the use as antifog agent in low density polyethylene of a fatty acid ester alkoxylated with 10-55 ethylene oxide groups.

JP-A 62-04 240 discloses a polyethylene film with antifog properties which contains a surface active agent with a crystallization temperature of 23°C or more, a glycerol or sorbitan ester of an unsaturated fatty acid with a crystallization temperature of 23°C or less, and a plasticizer.

As surface active agent with a crystallization temperature of 23°C or more, sorbitan or glycerol esters optionally alkoxylated with 0.5-5.0 ethylene oxide or propylene oxide groups are mentioned. In the examples of this document, non- alkoxylated sorbitan sesquipalmitate and non-alkoxylated diglycerol distearate were used.

As plasticizer, di-2-ethylhexyl phthalate and tricresyl phosphate are indicated as preferred.

The plasticizer in this prior art composition is essential for obtaining sufficient antifog properties. The plasticizer, however, weakens the film to such an extent that its mechanical properties are insufficient for agricultural applications. Furthermore, plasticizers such as phthalates and phosphates are known to be toxic to humans, but also exhibit phytotoxicity, and their presence in agricultural films is also undesired from that perspective. It is therefore an object of the present invention to provide an agricultural film that is not phytotoxic, has good hot fog behaviour, and a high mechanical strength. That is: a mechanical strength which allows the composition to be applicable for agricultural applications.

In addition, it should have sufficient light transmission to allow any crops covered by it to catch sufficient visible light.

This object has been met by using a polyolefin-containing composition comprising, as antifog agent, one or more ethoxyiated glycerol esters of saturated fatty acids. In addition, the composition should be substantially deficient of plasticizer. Furthermore, the ester(s) should have a molar average degree of ethoxylation in the range of 1 .0 to below 5.0.

In a preferred embodiment, the esters have an average degree of ethoxylation in the range 1 .0-4.0, more preferably 1 .0-3.0, and most preferably 2.0-3.0.

The present invention therefore relates to an agricultural film having a visible light transmission of at least 50%, said film comprising a polyolefin-containing composition that is essentially free of plasticizer and comprises a polyolefin having dispersed therein one or more glycerol esters of saturated fatty acid with 12-22 carbon atoms, said ester(s) having been ethoxyiated to an average degree of 1 .0 to below 5.0 moles of ethylene oxide groups per mole of glycerol ester.

The agricultural film according to the present invention should have a visible light transmission of at least 50%, more preferably 60%, even more preferably at least 75%, and most preferably at least 80%.

Visible light is defined as light with a wavelength in the range 380-770 nm. The visible light transmission of the film is determined by spectrophotometry. The glycerol ester that serves as antifog agent has been ethoxylated. Ethoxylation processes are well known to those skilled in the art and preferably involve the treatment of molten ester with ethylene oxide under high pressure and temperature in the presence of a base catalyst. During this process, initial mono-glycerol esters may react to form di- and tri-glycerol esters and glycerol. Likewise, di-glycerol esters may react to form mono- and tri-glycerol esters and glycerol, etc. Essentially all these components will be ethoxylated during the process.

The average degree of ethoxylation of the resulting material can be controlled by the amount ethylene oxide, as is also well known by the skilled person.

Hence, the one or more glycerol esters generally will consist of a mixture of glycerol esters, which mixture has been ethoxylated to an average degree of ethoxylation of 1 .0 to less than 5.0.

The average degree of ethoxylation of the glycerol ester(s) is in the range of 1 .0 to below 5.0, which means that the product obtained by the ethoxylation reaction contains, on average, 1 .0 to less than 5.0 mole of ethylene oxide per mole of initial glycerol ester. This average degree of ethoxylation can be determined by determining the hydroxyl value of the material. This value can be determined by a titration method. According to this method, a solution of phthalic anhydride in pyridine is added to a sample of ethoxylated glycerol ester. Hydroxyl groups in the sample react under enhanced temperature with phthalic anhydride. The reaction is catalysed by 4-dimethyl-aminopyridine. The phthalic anhydride that has not been consumed by the sample and the acid that has formed are determined by titration with alkali. Also the total added amount of phthalic anhydride in a blank solution is determined in this way. The results allow the calculation of free OH-functionalities in the sample, from which the number of moles of ethoxylated product can be calculated. With the sample weight one can calculate the average molecular weight and, hence, the average number of moles of ethylene oxide groups per mole of initial glycerol ester.

It is noted that JP-A 02-163188 discloses the use of fatty acid esters alkoxylated with 3-8 ethylene oxide groups as antifog and antifrost agent in PVC. PVC, however, is much more polar than polyolefins. As a result, the migration behaviour of the antifog agent in these polymers will greatly differ. In addition, PVC and polyolefins also differ in crystallization behaviour; a property that also affects the migration of the antifog agent. Hence, the fact that a particular compound is able to perform well as antifog agent in PVC does not predict its suitability in polyolefins.

The glycerol esters to be ethoxylated can be prepared by known procedures, such as the giycerolysis of natural oils or fats, which are generally mixtures of various fatty acid triglycerides. This process leads to a complex mixture of alpha- and beta-monoglycerides, diglycerides, traces of triglycerides, and free fatty acids. The components of such mixtures can be separated by suitable distillation procedures.

Suitable oils and fats are beef tallow, mutton tallow, butter fat, coconut oil, corn oil, cotton seed oil, lard oil, olive oil, peanut oil, palm oil, soy bean oil, sesame oil, sunflower oil, rapeseed oil, and their partial or fully hydrogenated derivatives. Commercially available glycerol mono-esters generally contain traces of preservatives, free glycerol, free fatty acids, and glycerol di- and tri-esters. The saturated fatty acid-originating part of the glycerol ester has 12 to 22 carbon atoms, preferably 14 to 20 carbon atoms, and most preferably 16 to 18 carbon atoms. The fatty acid may be substituted by hydroxy groups. Examples of saturated fatty acids with 12 to 22 carbon atoms are lauric acid (C12), myristic acid (C14), palmitic acid (C16), stearic acid (C18), hydrogenated ricinoleic acid (C18), arachidic acid (C20), and behenic acid (C22). The glycerol esters to be ethoxyalated can be esters of monoglycerol, diglycerol, and polyglycerol. It may also be mixtures of glycerol esters of different saturated fatty acids, e.g. fatty acids with 16 and with 18 carbon atoms. The glycerol esters to be ethoxyalated can be mono-esters, di-esters, tri-esters, and mixtures thereof. In a preferred embodiment, a mixture of mono-esters, di- esters, and tri-esters is used, a large part - i.e. 20-90 wt%, more preferably 30- 80 wt%, even more preferably 40-70 wt%, and most preferably 40-60 wt% - of which consists of mono-esters.

In addition to the one or more ethoxylated saturated fatty acid esters, the composition may contain ethoxylated unsaturated fatty acid esters. An example thereof is ethoxylated glycerol mono-oleate. If such ethoxylated unsaturated fatty acid ester is present in the polyolefin-containing composition, it is preferably present in an amount of less than 70 wt%, more preferably less than 60 wt%, and most preferably less than 50 wt%, meaning that at least 30 wt%, more preferably at least 40 wt%, and most preferably at least 50 wt% of the ethoxylated fatty acid esters in the composition consist of ethoxylated saturated fatty acid esters.

The polyolefin-containing composition is essentially free of plasticizer. "Essentially free" in this respect means: an amount that does not affect the mechanical properties of the resulting agricultural film. Most preferably, the composition is free of plasticizer.

Examples of plasticizers are phosphates and phthalates, such as tricresyl phosphate and di-2-ethylhexyl phthalate.

Preferably, the polyolefin-containing composition is also free of lubricants. Lubricants make the surface of the polymer more hydrophobic, due to their hydrophobic tail. When present in a polyolefin-composition, lubricants tend to form a double layer that migrates to the polymer's surface, sticking its apolar tails out of the polymer surface. This decreases the surface tension of the polymer and therefore counteracts the effect of antifog agents. The ethoxylated glycerol ester can be incorporated in the polyolefin by mixing it into molten polyolefin using conventional techniques, such as extrusion, roll- milling or mixing it in a Banbury mixer. The ester may be added to the polyolefin before or after said polyolefin has been melted. The ethoxylated glycerol ester may be added as such, or in the form of a masterbatch in a polyolefin.

The resulting mixture is then solidified by cooling and then comminuted to a particle size satisfactory for further form shaping processes like blown film extrusion, cast film extrusion, hot melt extrusion, or equivalent heat-shaping operations.

It is also possible to incorporate this composition into a multi-layer system. Such a multi-layer system will contain at least one layer made from this composition. Other layers of such a multi-layer system may be based on, for instance, polyamide (e.g. nylon) and/or polyester (e.g. polyethylene terephthalate).

Multi-layer systems can be prepared by co-extrusion or lamination. Suitable polyolefins for use in the present invention include polyethylene, polypropylene (PP), random- and block-copolymers of ethylene and propylene, ethylene vinyl acetate copolymer (EVA), and polymers obtained from ethylene or propylene copolymerized with minimal amounts of other mono-olefinic monomers such as butene, isobutylene, acrylic acids, esters of acrylic acids, styrene or combinations thereof.

Polyethylenes include high density polyethylene (HDPE; defined by a density of greater or equal to 0.941 g/cm³), medium density polyethylene (MDPE; defined by a density range of 0.926-0.940 g/cm³), linear low density polyethylene (LLDPE; defined by a density range of 0.915-0.925 g/cm³), low density polyethylene (LDPE; defined by a density range of 0.910-0.940 g/cm³), very low density polyethylene (VLDPE; defined by a density range of 0.880-0.915 g/cm³), and blends thereof.

Suitable polyethylenes can be made by radical polymerisation or by metallocene or Ziegler Natta-catalysed polymerisation and also includes blends of such differently polymerised polyethylenes.

Preferred polyolefins are LDPE, EVA, and polymer blends containing LDPE and/or EVA.

The ethoxylated glycerol ester is incorporated in the polyolefin in an amount sufficient to impart fog resistance to the agricultural film. If an excess amount of antifog agent is incorporated in the polyolefin, the polyolefin tends to be tacky and has a greasy feel. The blocking and slip properties of the resulting agricultural film may also be adversely affected. Moreover, an excess of antifog agent in the film adversely affects the adhesion of inks thereto.

The ethoxylated glycerol ester is therefore incorporated in the polyolefin- containing composition in an amount of 0.2-6 wt%, more preferably 1 -5 wt%, and most preferably 2-4 wt%, based on the weight of the polyolefin-containing composition. In addition to the ethoxylated glycerol ester, the polyolefin film may contain various conventional additives, such as anti-static agents, anti-oxidants, anti- ozonants, slip agents, anti-block agents, light stabilizers (e.g. HALS), UV stabilizers, colorants, tackifiers, and the like, if so desired.

The polyolefin-containing composition should, however, be essentially free of compounds that severely hinder the transmission of visible light through the resulting film. Examples of such compounds are carbon black and other carbon- based materials.

The agricultural film according to the present invention can be used for various agricultural applications, such as energy screens and greenhouse covers. EXAMPLES

Test methods

Hot fog test:

Beakers of 600 ml (high model, 150 mm, 80 mm ø, without spout) were filled with 350 ml of tap water. Films prepared according to the Examples below were cut and placed on the beaker and fixed with a rubber band. The beakers were placed in a water bath at 40°C and fog was determined visually after 5, 10, 15 and 30 minutes and after 1 , 2 and 5 hours on the first day; and once a day thereafter.

The Fog Score is the best result obtained over time. It was scored according to the following system:

A: Opaque layer of small fog droplets

B: Opaque layer of large droplets

C: Complete layer of large transparent drops

D: Randomly scattered or only large transparent droplet(s)/ discontinue film of water

E: Transparent film having no visible water

Hot fog durability is defined as the time until the film started to form droplets and the Fog Score dropped below D.

Example 1

To an ethylene-vinyl acetate copolymer (EVA, 7.5 wt% vinyl acetate, MFI= 3 g/10 min), 5 wt% of glycerol monostearate (GMS) ethoxylated to an average degree of ethoxylation of 2.5 was added using a 16 mm twin screw extruder. The so formed 5 wt% masterbatch was dry blended with the same EVA polymer as mentioned above to form a composition comprising a 1 wt% ethoxylated glycerol monostearate in EVA. This composition was shaped to form a film using film blowing equipment. The visible light transmission of the resulting film more than 80%.

The antifog performance of this film is listed in Table 1 . Comparative Example A

Example 1 was repeated, except that glycerol monostearate with an average degree of ethoxylation of 5.0 was used. The antifog performance of this film is listed in Table 1 . Comparative Example B

Example 1 was repeated, except that glycerol monostearate with an average degree of ethoxylation of 10.0 was used. The antifog performance of this film is listed in Table 1 . Comparative Example C

Example 1 was repeated, except that glycerol monostearate with an average degree of ethoxylation of 30.0 was used. The antifog performance of this film is listed in Table 1 . Comparative Example D

Example 1 was repeated, except that propoxylated glycerol monostearate with an average degree of propoxylation of 2.5 was used.

The antifog performance of this film is listed in Table 1 . Comparative Example E

Example 1 was repeated, except that ethoxylated glycerol mono-oleate (GMO) with an average degree of ethoxylation of 5.0 was used. The antifog performance of this film is listed in Table 1 . Example 2

Example 1 was repeated, except that instead of 1 wt%, 1 .5 wt% of glycerol monostearate ethoxylated to an average degree of ethoxylation of 2.5 was present in the final film.

The antifog performance of this film is listed in Table 1 .

Example 3

Example 2 was repeated, except that the film contained an additional amount of 1 .5 wt% of ethoxylated glycerol mono-oleate with an average degree of ethoxylation of 5.0.

The antifog performance of this film is listed in Table 1 .

Comparative Example F

Example 3 was repeated, except that the film contained an additional amount of 1 .5 wt% 2-ethyl-hexyl phthalate (a plasticizer).

The antifog performance of this film is listed in Table 1 .

Table 1 - EVA films

These examples show that the antifog score and especially the durability thereof strongly depend on the degree of ethoxylation. A degree of ethoxylation below 5.0 gives the best results. Propoxylation does not result in a suitable durability.

The examples also show that the saturated fatty acid ester GMS gives much better results than the unsaturated fatty acid ester GMO. The tensile strength of several of these films was determined according to ISO 37-2 using a Zwick Z010 tensile tester at a test speed of 100 mm/min. The results are listed in Table 2 and show that the plasticizer that is present in the film of Comparative Example E negatively affects the mechanical strength of the film. Table 2

Example 4

Example 1 was repeated, except that LDPE (MFI= 3 gr/ 10 min) instead of EVA was used, for preparing both the masterbatch and the film.

The antifog performance of this film is listed in Table 3.

Comparative Example G

Example 4 was repeated, except that glycerol monostearate with an average degree of ethoxylation of 10.0 was used. The antifog performance of this film is listed in Table 3.

Comparative Example H

Example 4 was repeated, except that that glycerol monostearate with an average degree of ethoxylation of 30.0 was used. The antifog performance of this film is listed in Table 3.

Table 3 - LDPE films

These results show that the antifog score and durability in LDPE are also strongly dependent on the degree of ethoxylation.

Claims

Agricultural film having a visible light transmission of at least 50%, said film comprising a polyolefin-containing composition that is essentially free of plasticizer and comprises a polyolefin having dispersed therein one or more glycerol esters of saturated fatty acid with 12-22 carbon atoms, said esters having been ethoxylated to an average degree of 1 .0 to below 5.0 moles of ethylene oxide groups per mole of glycerol ester.

Agricultural film according to claim 1 wherein the polyolefin-containing composition is free of plasticizer.

Agricultural film according to claim 1 or 2 wherein a mixture of glycerol esters of saturated fatty acid with 12-22 carbon atoms that has been ethoxylated to an average degree of 1 .0 to below 5.0 moles of ethylene oxide groups per mole of glycerol ester is dispersed in the polyolefin.

Agricultural film according to any one of the preceding claims wherein the one or more glycerol esters have been ethoxylated to an average degree of 1 .0-3.0 moles of ethylene oxide groups per mole of glycerol ester.

Agricultural film according to any one of the preceding claims wherein the one or more glycerol esters is a mixture of glycerol mono-, di-, and tristearate.

Agricultural film according to any one of the preceding claims wherein at least 20 wt% of the total amount of ethoxylated glycerol ester in the polyolefin-containing composition is an ethoxylated glycerol mono-ester.

7. Agricultural film according to any one of the preceding claims wherein the polyolefin-containing composition comprises 0.5-5 wt% of ethoxylated glycerol ester, based on the weight of composition.

8. Agricultural film according to any one of the preceding claims wherein the polyolefin is selected from the group consisting of low density polyethylene and ethylene vinyl acetate copolymer.

9. Agricultural film according to any one of the preceding claims wherein said film contains several layers, at least one of said layers comprising the polyolefin-containing composition.

10. Use of the agricultural film according to any one of the preceding claims as energy screen.

1 1 . Use of the agricultural film according to any one of claims 1 -9 as greenhouse cover.