GB1595106A

GB1595106A - Foam plastic film of polyolefin material

Info

Publication number: GB1595106A
Application number: GB45176/77A
Authority: GB
Original assignee: HOECHST HOLLAND NV
Current assignee: HOECHST HOLLAND NV
Priority date: 1977-10-31
Filing date: 1977-10-31
Publication date: 1981-08-05

Description

(54) FOAM PLASTIC FILM OF POLYOLEFIN MATERIAL (71) We, HOECHST HOLLAND N.V., a Netherlands limited liability company, of Sara Burgerhartstraat 25, Amsterdam, the Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us, and method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a substantially closed-cell foam plastic film formed from a polymer mixture of lowdensity polyolefin and crystalline polyolefin, particularly for the manufacture of printed wall or ceiling coverings, and to a method of manufacturing such a foam plastic film.

Foam plastic films formed from lowdensity polyethylene or foamed highdensity polyethylene, which films may be used for the manufacture of wall coverings, are known in the art.

Thereby it has been ascertained that, as a result of the high-density of 400 kg/m3 and of the coarse cell structure (cells of 1 mm), the abrasion resistance of foamed lowdensity polyethylene is not sufficient for making durable wall coverings, whereas high-density foamed polyethylene or other crystalline polyolefines do possess a sufficiently high abrasion resistance but their capacity of absorbing colouring matter is so slight that the prints may be easily rubbed off such coverings, whilst these films moreover possess a high stiffness.

It has been tried to overcome these drawbacks by making use of a polymer mixture of 60 to 90% by weight of lowdensity polyethylene and 40 to 10% by weight of a crystalline polyolefin consisting preferably of high-density polyethylene.

This known foam plastic film with an open cell structure has, however, the drawback that for obtaining a foamed product a high amount of blowing agent is required, the mechanical properties are insufficient and moreover, the film is greatly inclined to roll up which, particularly if the film is used as a wall covering, is most disadvantageous.

The present invention in one aspect provides a substantially closed-cell foam plastic- film manufactured from a polymer mixture of low-density polyolefin and crystalline polyolefin, wherein the mixture comprises 90.599.9% by weight of lowdensity polyethylene and 9.50.1% by weight of crystalline polyolefin.

The invention in another aspect provides a method of manufacturing a substantially closed-cell foam plastic film from a polymer mixture of low-density polyolefin and crystalline polyolefin, by injecting a blowing agent into the plasticized polymer mixture and extruding the same to form a closed-cell foam plastic film, wherein the mixture comprises 90.599.9% by weight of lowdensity polyethylene and 9.50.1% by weight of crystalline polyolefin.

In this specification by a low-density polyethylene is meant a polyethylene having a density of up to 0.93 g/cm3, in contrast to a high density polyethylene which is a polyethylene having a density of more than 0.93 g/cm3. The crystalline polyolefin utilized in the present invention is a highdensity polyolefin.

Advantageously the polymer mixture comprises 90.5 to 95% by weight of lowdensity polyethylene and 9.5 to 5% by weight of high-density polyethylene.

Preferably the polyethylene mixture may contain 0.3 to 4% by weight, more preferably 1% by weight, of an ionomer.

Use of a polymer mixture according to the invention presents the following advantages: 1. a film with completely closed cells provides important advantages in further treatment, more particularly in manufacturing wall coverings, especially in printing the film; 2. the film possesses a smoother surface attended by a better adsorption of the printing pattern; 3. the film presents a less creased surface which improves or increases the surface structure and the printability; 4. the film possesses a greater strength due to the closed cell structure; 5. due to the greater stiffness of the plastic film it is better suitable for manufacturing so-called heavier types of wall coverings; 6. the plastic film may be obtained with a smaller amount of blowing agent due to a better compatibility of polymer mixture and blowing agent.

As indicated above, a low-density polyethylene means a polyethylene having a density of up to 0.93 g/cm3, preferably with not more than 20% by weight of monomers copolymerizable with ethylene, whilst a high-density polyethylene has a density of more than 0.93, for instance 0.94 to 0.97, g/cm3.

The crystalline polyolefin may be such a high-density polyethylene, a polypropylene or a propylene/ethylene copolymer.

In order to make the films opaque and to give them a matt appearance, it is advisable to include in the films a filler which reduces the ~ transparency of one film, advantageously a whitening filler in an amount of 1 to 40% by weight, preferably 1 to 20% by weight of titanium dioxide.

For obtaining a foam plastic film suitable for wall coverings at least the surface of the film to be printed is submitted to an electric (corona) discharge treatment or a coating with a layer of a polar polymer as such a physical treatment also contributes to an increase of the abrasion resistance of printing.

Also both faces of the film may be subjected to a corona-discharge treatment thus improving the adherence to a wall.

Preferably both surfaces of the film, the surface side to be printed and the surface side to be fixed to the wall, are subjected to a corona discharge treatment.

Also, only the surface side to be printed may be subjected to such a coronadischarge treatment as this treatment has a certain effect on the back side of the film and improves the adhesion between the covering and the wall, but only to such a degree that the film generally in dry condition may be removed from the wall when a normal wall covering adhesive is applied. For such a film treatment reference may be made to the periodical "Plastics and Polymers", April 1969.

In the method of the invention, the mixture with blowing agent may be pressed through a ring-shaped or slot-shaped nozzle, preferably a ring-shaped nozzle, after which the extruded tube is inflated.

For foaming the mixture any blowing agent producing a gas upon extrusion for foaming the mixture may be applied. Thus, the blowing agent may be liquid which produces the gas by evaporation. The extrusion temperature is preferably between 70 and 1900C, more preferably between 100 and 1200C, still more preferably between 105 and 115"C. The pressure lust before the extrusion preferably amounts to 60 to 120 kg/cm2, more preferably 60 to 80 kg/cm2.

Preferably the polymer mixture is molten in the extruder whereafter the blowing agent is injected, and then extrusion via the nozzle takes place. It has been found that the best foaming occurs when the distance from the extruder to the atmosphere is as small as possible so that a short nozzle is applied.

The blowing agent is chosen such that under the conditions of temperature and pressure in the extruder it is inert with respect to the polymer mixture and shows a good compatability with the polymer. The blowing agent may be a solid, a liquid or a gas, but it should possess a boiling temperature which is below the temperature of the homogeneous mixture when leaving the extruder under the pressure of the zone which the mixture enters when leaving the extruder, so that at this temperature foaming may take place.

In the method according to the invention, preferably a liquid blowing agent having a boiling temperature under atmospheric pressure of at least 100C below the temperature of the homogeneous mixture at the ~ extrusion is utilized. Examples of blowing agents are: pentane, hexane, heptane, oxtane, methylpentane or dimethylpentane, unsaturated hydrocarbons such as pentene, 4-methyl pentene, hexene, fractions of petroleum ether and halogenated hydrocarbons such as, for instance, tetrachloromethane, chloroform, ethylene dichloride, methylene chloride, 1,1,2 - trichloro - 1,2,2 - trifluoro ethane, difluorodi-chloromethane or monofluorotrichloromethane. A preferred blowing agent is pentane 1,1,2-trichloro1,2,2-trifluoroethane, hexane or petroleumether (boiling point 40--60 or 60--80"C) or methylene-chloride or a mixture thereof.

For manufacturing light foamed materials with a closed cell structure of a density of 0.1 to 0.4 g/cm3, the concentration of the blowing medium should- be less than 20% since over 20% a closed cell structure is no longer obtained.

In the manufacture of the film from 1 to 20% by weight, more preferably 2 to 15% by weight, of a blowing agent is preferably used.

Printed or structured wall coverings made from the films possess an excellent abrasion resistance to removal of colours.

The invention will now be explained with reference to a number of examples.

In these examples the foam plastic films were obtained by mixing a mixture of lowdensity polyethylene and high-density polyethylene and nucleating agents such as citric acid (e.g. 0.1%) and bicarbonde (e.g.

0.1%), talc, silicon dioxide, silicate and/or carbonate. The high-density polyethylene constitutes the crystalline polyolefin utilized in the invention. These nucleating agents are well known in the art. After addition of 20% of titanium dioxide, this mixture is plasticized and homogenized in an extruder and, after injection of blowing agents (10 parts by weight of Freon (Registered Trade Mark) 11 and 12 in a proportion of 1:1) mixed in a separate zone, after which the mass of polymer and blowing agent is extruded at the desired extrusion temperature of 90 to 1700C under an extrusion pressure just before extrusion takes place of 60 to 120 kg/cm2, by means of a ring-shaped nozzle. The ring-shaped nozzle has a diameter of 70 to 300 mm and a slot width of preferably 0.5 mm. The extruded tube is inflated under an air pressure of 25 to 50 mm of water overpressure in the interior of the tube, so that it obtains a diameter of 140--1200 mm.

The tube is folded, cut to a flat film, and the flattened film is withdrawn, submitted to a corona discharge, and reeled up.

For modifying the static properties of the surface, the film is subjected to a corona discharge treatment, the film being conveyed via a metallic roller at a speed of 15 m/min. prior to reeling up. A highfrequency potential of about 10,000 volts is supplied to an electrode system at a distance of 1.5 mm from the surface of the roller. Both surfaces are submitted to the corona treatment providing a very good surface structure for mounting the film and, on the other hand, a very good structure for applying dye material is obtained. The abrasion resistance of the film was determined by sticking the film to a flat base and by moving a tool to-and-fro on the film surface. The tool has a weight of 400 g and a width of 12.7 mm. The reciprocating movements take place on a length of 76 mm at a frequency of 40 cycles per minute. The abrasion resistance was determined by the number of passes of the tool before breaking up of the surface occurs. The abrasion resistance of the printed film was determined in the same manner.

The abrasion resistance of the printing of a wet film was determined by flooding the surface of the film and an aqueous solution containing one-percent surface active material and rubbing it with a sponge on the surface. The sponge was moved in a circle with a diameter of 63 mm at 60 rpm. under a load of 160 g. As a measure for the abrasion resistance to removing the dye from the film, the number of revolutions of the sponge for removing the dye was determined.

EXAMPLE I A mixture of 95 parts by weight of lowdensity polyethylene (0.922 g/cm3) and 5 parts by weight of high-density polyethylene (0.96 g/cm3) also containing well known nucleating agents, the density of which exceeds, 0.93 g/cm3), was extruded as a tubular film by using 10 parts by weight of Freon 11 and 12 in a proportion of 50:50, as a blowing agent, at an extrusion temperature of 110"C and pressure just before the extrusion takes place of 100 kg/cm2. The film consists substantially of closed cells. The transmission of water vapour according to DIN 53122 amounted to 2 g/cm2/day.

For comparison purposes a film of a mixture of 90% by weight of low-density polyethylene and 10% by weight of highdensity polyethylene with an open cell structure was used. The transmission of water vapour through the foil amounted to 150 g/cm2/day.

It has been found that for economically obtaining a foam plastic film of the same density 20 to 30% of blowing agent may be utilized.

EXAMPLE II A foam plastic film according to Example I was manufactured from a mixture of 91 parts by weight of low-density polyethylene (density less than 0.93 g/cm3), 8 parts by weight of high-density polyethylene and 1 part by weight of ionomer (Surlyn A, Dupont). The extrusion temperature was llO"C and the pressure just before extrusion was 100 kg/cm2. "Suryln" is a Registered Trade Mark.

With respect to a mixture of 92 parts by weight of low-density polyethylene and 8 parts by weight of high-density polyethylene, a foam plastic film of a finer cell structure and, consequently, a better surface structure is obtained. Moreover, the amount of blowing agent may be economically reduced.

Both films according to Example I and Example II comprise 99% of closed cells so that the transmission of water vapour only amounts to 3 g/cm2/day.

A film with an open cell structure obtained from 80 parts by weight of lowdensity polyethylene and 20 parts by weight of high-density polyethylene comprised 30% of open cells.

For manufacturing a wall covering the surface of the film to be printed is subjected to the aforementioned corona-discharge.

EXAMPLE III A polymer mixture of 94 parts by weight of low-density polyethylene (0.93 g/cm3), 5 parts by weight of high-density polyethylene (density 0.96 g/cm3) and 1 part by weight of ionomer (Surlyn A, Dupont) was extruded in the same way as in Example II. The extrusion temperature was 110 C and the pressure just before extrusion takes place was 100 kg/cm2.

For making a wall covering both sides of the film were subjected to the aforementioned corona-discharge treatment. Moreover, a mixture of 85 parts by weight of low-density polyethylene and 15 parts by weight of high-density polyethylene was extruded, thus forming a film with an open cell structure.

If the same amount of blowing agent (a mixture of equal parts of Freon 11 and 12) is applied, the first product possesses a density which is about 20% lower, while, moreover, the surface is smoother as a result of which printing is facilitated.

The inclination to rolling of the foam plastic film according to the invention is about 30% lower than that of the known product, the same percentage applying with respect to the fissure effect.

Instead of subjecting the film to a discharge treatment it may be coated with a saturated solution of chlorinated polyethylene in methylene chloride.

WHAT WE CLAIM IS: 1. A substantially closed-cell foam plastic film manufactured from a polymer mixture of low-density polyolefin and crystalline polyolefin, wherein the mixture comprises 90.599.9% by weight of low-density polyethylene and 9.5 ).1% by weight of crystalline polyolefin.

2. A foam plastic film as claimed in Claim 1, wherein the crystalline polyolefin is highdensity polyethylene.

3. A foam plastic film as claimed in Claim 2, wherein the mixture comprises 90.595% by weight of low-density polyethylene and 9.55% by weight of high-density polyethylene.

4. A foam plastic film as claimed in any of Claims 1 to 3, wherein at least one surface of the foam plastic film has been subjected to a physical treatment for improving the bonding properties of the surface.

5. A foam plastic film as claimed in Claim 4, wherein at least one surface of the foam plastic film has been subjected to an electrical discharge treatment or a coating with a layer of a polar polymer.

6. A foam plastic film as claimed in any of Claims 1 to 5, wherein the polymer mixture contains an ionomer.

7. A foam plastic film as claimed in claim 6, wherein the mixture contains 0.3% by weight of ionomer.

8. A foam plastic film as claimed in any of Claims 1 to 7, wherein the foam plastic film contains I40% by weight of a filler which reduces the transparency of the film.

9. A foam plastic film as claimed in Claim 8, wherein the said filler is a whitening filler.

10. A foam plastic film as claimed in Claim 9, wherein the film contains 220% by weight of a whitening filler.

11. A foam plastic film as claimed in Claim 9 or 10, wherein the whitening filler is titanium dioxide.

12. A foam plastic film as claimed in any of Claims 1 to 11, which has a density of 0.1.4 g/cm3.

13. A foam plastic film as claimed in Claim 12, which has closed cells of a size of 0.05.4 mm.

14. A foam plastic film as claimed in Claim 13, which has closed cells of a size of 0.10.30 mm.

15. A foam plastic film according to Claim 1, substantially as herein described in any of the foregoing Examples.

16. A method of manufacturing a substantially closed-cell foam plastic film from a polymer mixture of low-density polyolefin and crystalline polyolefin, by injecting a blowing agent into the plasticized polymer mixture and extruding the same to form a closed-cell foam plastic film, wherein the mixture comprises 90.599.9% by weight of low-density polyethylene and 9.50.1% by weight of crystalline polyolefin.

17. A method as claimed in Claim 16, wherein 1-20% by weight of blowing agent is applied.

18. A method as claimed in Claim 17, wherein 215% by weight of blowing agent is applied.

19. A method as claimed in any of Claims 16 to 18, wherein the extrusion is performed at a temperature of 70 to 1900C.

20. A method as claimed in Claim 19, wherein the extrusion is performed at a temperature of 100 to 1200C.

21. A method as claimed in Claim 20, wherein the extrusion is performed at a temperature of 105--1150C.

22. A method as claimed in any of Claims 16 to 21, wherein the pressure just before the extrusion is 6120 kg/cm2.

23. A method as claimed in any of Claims 16 to 22, wherein under atmospheric pressure the blowing agent has a boiling point of at least 100C below the temperature of the homogeneous mixture upon extrusion.

24. A method as claimed in any of Claims

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Claims

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surface of the film to be printed is subjected to the aforementioned corona-discharge.

EXAMPLE III A polymer mixture of 94 parts by weight of low-density polyethylene (0.93 g/cm3), 5 parts by weight of high-density polyethylene (density 0.96 g/cm3) and 1 part by weight of ionomer (Surlyn A, Dupont) was extruded in the same way as in Example II. The extrusion temperature was 110 C and the pressure just before extrusion takes place was 100 kg/cm2.

For making a wall covering both sides of the film were subjected to the aforementioned corona-discharge treatment. Moreover, a mixture of 85 parts by weight of low-density polyethylene and

15 parts by weight of high-density polyethylene was extruded, thus forming a film with an open cell structure.

If the same amount of blowing agent (a mixture of equal parts of Freon 11 and 12) is applied, the first product possesses a density which is about 20% lower, while, moreover, the surface is smoother as a result of which printing is facilitated.

The inclination to rolling of the foam plastic film according to the invention is about 30% lower than that of the known product, the same percentage applying with respect to the fissure effect.

Instead of subjecting the film to a discharge treatment it may be coated with a saturated solution of chlorinated polyethylene in methylene chloride.

WHAT WE CLAIM IS: 1. A substantially closed-cell foam plastic film manufactured from a polymer mixture of low-density polyolefin and crystalline polyolefin, wherein the mixture comprises 90.599.9% by weight of low-density polyethylene and 9.5 ).1% by weight of crystalline polyolefin.
2. A foam plastic film as claimed in Claim 1, wherein the crystalline polyolefin is highdensity polyethylene.
3. A foam plastic film as claimed in Claim 2, wherein the mixture comprises 90.595% by weight of low-density polyethylene and 9.55% by weight of high-density polyethylene.
4. A foam plastic film as claimed in any of Claims 1 to 3, wherein at least one surface of the foam plastic film has been subjected to a physical treatment for improving the bonding properties of the surface.
5. A foam plastic film as claimed in Claim 4, wherein at least one surface of the foam plastic film has been subjected to an electrical discharge treatment or a coating with a layer of a polar polymer.
6. A foam plastic film as claimed in any of Claims 1 to 5, wherein the polymer mixture contains an ionomer.
7. A foam plastic film as claimed in claim 6, wherein the mixture contains 0.3% by weight of ionomer.
8. A foam plastic film as claimed in any of Claims 1 to 7, wherein the foam plastic film contains I40% by weight of a filler which reduces the transparency of the film.
9. A foam plastic film as claimed in Claim 8, wherein the said filler is a whitening filler.
10. A foam plastic film as claimed in Claim 9, wherein the film contains 220% by weight of a whitening filler.
11. A foam plastic film as claimed in Claim 9 or 10, wherein the whitening filler is titanium dioxide.
12. A foam plastic film as claimed in any of Claims 1 to 11, which has a density of 0.1.4 g/cm3.
13. A foam plastic film as claimed in Claim 12, which has closed cells of a size of 0.05.4 mm.
14. A foam plastic film as claimed in Claim 13, which has closed cells of a size of 0.10.30 mm.
15. A foam plastic film according to Claim 1, substantially as herein described in any of the foregoing Examples.
16. A method of manufacturing a substantially closed-cell foam plastic film from a polymer mixture of low-density polyolefin and crystalline polyolefin, by injecting a blowing agent into the plasticized polymer mixture and extruding the same to form a closed-cell foam plastic film, wherein the mixture comprises 90.599.9% by weight of low-density polyethylene and 9.50.1% by weight of crystalline polyolefin.
17. A method as claimed in Claim 16, wherein 1-20% by weight of blowing agent is applied.
18. A method as claimed in Claim 17, wherein 215% by weight of blowing agent is applied.
19. A method as claimed in any of Claims 16 to 18, wherein the extrusion is performed at a temperature of 70 to 1900C.
20. A method as claimed in Claim 19, wherein the extrusion is performed at a temperature of 100 to 1200C.
21. A method as claimed in Claim 20, wherein the extrusion is performed at a temperature of 105--1150C.
22. A method as claimed in any of Claims 16 to 21, wherein the pressure just before the extrusion is 6120 kg/cm2.
23. A method as claimed in any of Claims 16 to 22, wherein under atmospheric pressure the blowing agent has a boiling point of at least 100C below the temperature of the homogeneous mixture upon extrusion.
24. A method as claimed in any of Claims

16 to 23 wherein a film of a density of 30400 kg/cm3 is extruded.
25. A method as claimed in Claim 24, wherein a film of a density of 100--250 kg/m3 is extruded.
26. A method as claimed in Claim 25, wherein a film of a density of 15-225 kg/m3 is extruded.
27. A method as claimed in any of Claims 16 to 26, wherein a film with closed cells having a size of 0.05-0.4 mm is extruded.
28. A method as claimed in Claim 27, wherein a film with closed cells having a size of 0.100.30 mm is extruded.
29. A method as claimed in Claim 28, wherein a film with closed cells having a size of 0.25 mm is extruded.
30. A method as claimed in any of Claims 16 to 29, wherein at least one nucleating agent is added to the mixture to be extruded.
31. A method as claimed in Claim 30, wherein the nucleating agent is citric acid; bicarbonate, talc, silicon dioxide, silicate and/or carbonate.
32. A method as claimed in any of Claims 16 to 31, wherein the crystalline polyolefin is high-density polyethylene.
33. A method as claimed in any of (2laims 16 to 32, wherein the mixture contains 90.595% by weight of low-density polyethylene.
34. A method as claimed in any of Claims 16 to 33, wherein at least one surface of the foam plastic film is subjected to a physical treatment for improving the bonding properties of the surface.
35. A method as claimed in Claim 34, wherein at least one surface of the foam plastic film is subjected to an electrical discharge treatment or a coating with a layer of a polar polymer.
36. A method as claimed in any Claims 16 to 35, wherein an ionomer is added to the polymer mixture.
37. A method as claimed in Claim 36, wherein 0.3 1% by weight of ionomer is added to the polymer mixture.
38. A method according to Claim 16 of manufacturing a foam plastic film, substantially as herein described in any of the foregoing Examples.
39. A foam plastic film manufactured by a method according to any of claims 16 to 38.
40. A wall or ceiling covering comprising a foam plastic film according to any of Claims 1 to 15 or claim 39.