GB2059340A - Process for producing a laminated sheet structure - Google Patents

Abstract

A laminated sheet structure is produced by continuously bonding metal foils 1, 5 to a polyolefin sheet 3 by means of adhesive films 2, 4, the adhesive films being transversely tensioned before they are is bonded to the metal foil, and the polyolefine sheet in molten form being then bonded to the films. The films may each be tensioned by passage over a curved roller. <IMAGE>

Description

SPECIFICATION Process for producing a laminated sheet structure BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a process for producing a laminated sheet structure comprising metal foils and polyolefin sheets adhered with adhesive films.

Description of the PriorArt Heretofore there have been known various methods for improving the adhesive strength between polyolefin sheets and metal foils of a laminated sheet comprising metal foils and a polyolefin sheet. An example of the methods is that an adhesive film is inserted between the metal foil and the polyolefin sheet and the composition of the adhesive film is improved. Another example is to control appropriately the conditions under which the laminated sheet is produced.

An embodiment of the former is disclosed in U.S.

Patent No. 3,616,019, that is, thin outer plies of metal are adhered to a relatively thick inner ply of thermoplastic with an adhesive film having particular physical characteristics and a particularcomposition.

An embodiment of the latter is disclosed in U.S.

Patent No. 3,634,166, that is, thin adhesion promoting interlayers are adhered to both sides of a polyethylene sheeting and then metal sheetings are adhered to the adhesion promoting interlayers by using rollers under pressure.

Further, Japanese Patent Laid Open No. 888841 1978 discloses a process for preparing a laminated sheet comprising a polyolefin layer having a metal foil on each of the both side. A metal foil is adhered under pressure, to each of both sides of a molten polyolefin sheet having a melting point of not higher than 2800with an intervened adhesive layer which comprises 99 - 70 parts by weight of a modified polyolefin produced by grafting at least one monomer selected from unsaturated carboxylic acids and derivatives thereof to a part or the whole of polyolefin and 1 - 30 parts by weight of a hydrocarbon elastomer.

However, U.S. Patent No.3,616,019 does not clearly disclose the actual and detailed procedure of producing the laminated sheets. According to the invention of U.S. Patent No.3,634,166, upon adhering thin films to both sides of a polyethylene sheet, the films can not be uniformly contacted with the polyethylene sheet by simply pressing the film to the polyethylene sheet by using rolls because the films are not self-supportable, and therefore a sufficient adhesion strength can not be obtained and the resulting laminated sheets do not have a smooth surface and are not suitable for shaping and working.

The invention of Japanese Patent Laid Open No.

88884/1978 can not give uniform close contact between the adhesive film and the metal foil and a good adhesion therebetween can not be produced.

Therefore, gaps are present between the metal foil and the polyolefin sheet of the resulting laminated sheet and the surface of the resulting laminated sheet is uneven and of less smoothness.

As mentioned above, breaking-away between the metal foil and the polyolefin sheet of conventional laminated sheets often occurs at the portion subjected to a processing when the laminated sheets are processed to a particular shape by bending with a small radius or drawing. Such breaking-away often causes destruction of the product thus shaped while it is in use.

The invention is aimed at providing a process for producing a laminated sheet structure free from the above mentioned disadvantages.

According to the present invention there is provided a process for producing a laminated sheet structure comprising five layers, the first and the fifth layers being composed of a metal foil, the second and the fourth layers being composed of an adhesive film and the third layer being composed of a polyolefin sheet which comprises adhering the first layer to the second layer, adhering the fifth layer to the fourth layer, and then adhering the second layer to one side of a molten polyolefin sheet and adhering the fourth layer to the other side of the molten polyolefin sheet under pressure, characterized in that tension is applied to the second and fourth layers respectively in directions transverse to directions in which the respective layers are travelling before they are adhered respectively to the first and fifth layers.

Sheets made by the preferred process to be described have very high adhesion between exterior metal foils and a central polyolefin sheet.

Such products are capable of being subjected to severe processing by bending and drawing without breaking, and have very smooth surfaces.

An embodiment of the invention is hereafter described with reference to the accompanying drawings, in which the reference numerals are individual to each figure. In the drawings: Figure 1 is a cross section of an embodiment of a laminated sheet structure produced by the process of the present invention; Figure 2 shows diagrammatically an embodiment of the process of the present invention; Figure 3 shows a cross section of a curved roll for stretching the adhesive film laterally; and Figure 4 is a perspective view showing that the adhesive film passes over the curved roll.

Description of the Preferred Embodiments Referring to Figure 1, the laminated sheet structure is composed of a polyolefin sheet 3 as a core material sandwiched in between metal foils 1 and 5 by means of adhesive films 2 and 4.

As polyolefins which can be a material for the polyolefin sheet and can be a starting material for a modified polyolefins as used for adhesive film layers 2 and 4, there may be mentioned polymers having degree of crystallization of at least 25% when measured by X-ray, for example, homopolymers of a-olefins such as ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1- pentene and the like, copolymers of one of the above mentioned a-olefins with less than 10 mole %, preferably less than 7 mole % of other a-olefin, or mixtures thereof. Furtherthere may be mentioned copolymers of the above mentioned a-olefin with acyloxy, particularly, acetoxy substituted one such as vinyl acetate, or their saponified ones.

Among them, middle or low density polyethylene, polypropylene, in particular, polyethylene having density of 0.910 - 0.970 g./cc. and melt index (190 C) of 0.05 - 100, are preferable.

Modified polyolefins used as an adhesive film may be produced by grafting unsaturated carboxylic acid or its derivative to a part or the whole of the above mentioned polyolefins.

As the unsaturated carboxylic acid, there may be mentioned acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid and the like.

As the derivatives of unsaturated acids, there may be mentioned acid anhydrides, esters, amides, imides, metal salts and the like. For example, there are maleic anhydride, citraconic anhydride, itaconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, diethyl maleate, monomethyl fumarate, dimethyl fumarate, monomethyl itaconate, diethyl itaconate, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid Nmonoethylamide, maleic acid N,N-diethylamide, maleic acid N-monobutylamide, maleic acid N-Ndibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid N-monoethylamide, fumaric acid N,N-diethylamide, fumaric acid Nmonobutylamide, fumaric acid N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate and the like.

Among them, maleic anhydride is particularly preferable.

There are various known methods for grafting the above mentioned monomer to polyolefins. For example, a polyolefin and a monomer for grafting are reacted at elevated temperatures in the presence or absence of a solvent with or without an added radical initiator. Other vinyl monomer such as styrene may be added to the reaction system.

The amount of monomer grafted to a polyolefin (hereinafter called "degree of grafting") is preferably 10-4-3% by weight.

A part or the whole of the polyolefin may be grafted. However, from industrial production point of view, it is desirable that a modified polyolefin of degree of grafting of 10-2 - 6% by weight is preliminarily prepared and then mixed with nonmodified polyolefin because the concentration of the grafting monomer in the composition can be appropriately adjusted by such procedure.

As hydrocarbon elastomers, one component of the adhesive film, there may be mentioned polyisobutylene, ethylene-propylene rubber, ethylene-1 - butene rubber, butyl rubber, butadiene rubber, styrene-butadiene rubber, ethylene-butadiene rubber, isoprene rubber and the like.

Among them, ethylene-propylene rubber and polyisobutylene are particularly preferable.

To the polyolefin sheet as a core material and the adhesive film of the present invention there may be added heat resistant stabilizer, weather resistant stabilizer, lubricant, antistatic agent, nucleating agent, pigment, dyestuff, fire retardant, blocking inhibitor, slipping agent and the like in an amount usually used.

The adhesive film is composed of 70 - 99 parts by weight, preferably 80 - 97 parts by weight of a modified polyolefin and 1 - 30 parts by weight, preferably 3 - 20 parts by weight of a hydrocarbon elastomer (totally 100 parts by weight). When the hydrocarbon elastomer is less than 1 part by weight, the adhesion strength is not improved. When it is more than 30 parts by weight, film shapeability of the adhesive film is not good.

The adhesive film is usually prepared in a form of film having thickness of 10 - 100 microns by T-die shaping or inflation shaping. Thick adhesive sheet may be used, but it is not preferable from economic al pointofview.

As the metal foil of the laminated sheet structure, there may be mentioned metals such as aluminum, iron, copper, tin, nickel and the like, and alloys containing one or more of such metals, for example, stainless steels. Among them, aluminum. The metal foil is usually 0.01 - 0.5 mm, thick and is usually defatted for use.

For the purpose of improving adhesivity, a very small amount of inorganic compounds such as lubricant, fillers and the like may be added to the adhesive film.

As the inorganic compound, there may be mentioned magnesium oxide, calcium oxide, aluminum oxide, titanium dioxide, magensium sulfate, calcium sulfate, magnesium hydroxide, aluminum hydroxide and the like.

According to the present invention, a tension is applied to the second layer and the fourth layer in the transverse direction with respect to the direction of proceeding of the layers before the second layer is adhered to the first layer and the fourth layer is adhered to the fifth layer. By such procedure, there can be prevented various disadvantages that creases of the adhesive film are formed upon bonding the adhesive film to the metal foil and the adhesive film does not uniformly contact the metal foil and thereby air is contained between them. As the result, the adhesion between the metal foil and the adhesive film can be strengthened and simultaneously the adhesion between the metal foil and the polyolefin sheet is increased. Therefore, the resulting laminated sheet structure is free from breaking-away between the metal foil and the adhesive film caused by bending processing and drawing with a small radius.

According to the process of the present invention, and adhesive film is backed with and supported by the metal foil before bonding the adhesive film to the polyolefin sheet so that the adhesive film and the polyolefin sheet can contact uniformly and tightly each other and thereby the resulting laminated sheet structure, as a whole, is of high mechanical strength.

As a method for applying a tension to the adhesive films, i.e. the second layer and the fourth layer in the transverse direction with respect to the direction of proceeding of the adhesive layers, there are known various methods. One of them is passing the adhesive film over a curved roll which shaft is in a form of circular arc. It is preferable to use a curved roll having a rubber material of a high coefficient of friction on the surface.

An example of such curved roll is shown in Figure 3. A flexible curved shaft 1 is fixed in a curved form.

Around the shaft 1 a rubber roll 2 is rotated by way of special bearings 3. The degree of curving of the curved shaft can be adjusted by an angle adjusting device 4. The rubber roll may be driven by a driving source, if necessary.

Now referring to Figure 4, the adhesive film 42 passes over the curved rubber roll from side A to side B, and as the adhesive film proceeds over the curved roll, the friction force between the surface of the rubber roll and the adhesive film 42 causes expansion of the film 42 to the transverse direction.

Further, referring to Figure 2, metal foils 1 and 1' defatted and wound around rolls pass over guide rolls 3,3', 4 and 4', are heated by preheaters 6 and 6' to 700C - 2000C and fed to roll pairs 5 and 5'.

Temperature of the roll pairs 5 and 5' is preferably 1000C - 150 C. As preheaters 6 and 6', those of a hot air blowing type are preferable. Temperature of the hot air is usually 1000C - 300"C, preferably 1500C 250 C. Thus the metal foils can be uniformly preheated with high heat efficiency.

The outside surface of the metal foil may be coated after defatted.

Thin films, preliminarily prepared as an adhesive film, 2, 2' are fed to expanding rolls 20 and 20' where the adhesive films 2, 2' are stretched in the transverse direction with respect to the direction of proceeding of the film, and then fed to roll pairs, 5 and 5' to be bonded to the metal foil reslting in a two-layered sheet, and if desired, the two-layered sheets are heated by heaters 7 and 7' to a temperature of 120 C - 200 C so as to laminate to form two-layered laminates.According to the method shown in Figure 2, the two-layered laminate is continuously and simultaneously formed, but there may be also employed such a method that the two-layered laminate is preliminarily prepared at the other place and then is directly fed on a molten polyolefin sheet 9, and in such case, heaters 7 and 7' are not necessary.

The polyolefin sheet 9 is extruded rom an extruder 8 in the molten state at a temperature of higher than the melting point and lower than 2800C and fed to the nip of pressure rolls 10 to 10'. Thickness of the molten polyolefin sheet is usually 1 - 6 mm. When temperature of the molten polylolefin sheet is lower than the melting point, it can not adhere to the adhesive film. On the contary, when its temperature is higher than 280 C, the adhesion ability is rather lowered.

Temperature of pressure rolls 10 and 10' is set to a temperature of from room temperature to 300 C. The above mentioned two-layered sheets are pressed onto the both surfaces of the molten polyolefin sheet and then fed to plural pairs of cooling rolls 11,11'.

The resulting laminated sheet structure 12 is cooled at the cooling rolls and also pressed at a pressure of 0.1 Kg./cm2 - 4 Kg.lcm? during passing through the colling roll pairs. The laminated sheet structure thus sufficiently pressed is drawn away by the drawing device 13 and then cut into products.

Example 1 10 parts by weight of high density polyethylene (melt index: 1.5 and density: 0.965) to which 1.0 /O by weight of maleic anhydride is grafted and 90 parts by weight of middle density polyethylene (melt index: 4.0 and density: 0.925) were mixed to prepare a modified polyethylene.

A composition composed of 90 parts by weight of the resulting modified polyethylene and 10 parts by weight of polyisobutylene (PIB) was shaped into an inflation film of 20 microns thick at a resin temperature of 220 C. The resulting film was used as an adhesive film. As a core material, a high density polyethylene (melt index of 1.0, density of 0.957 and melting point of 120"C) was used, and as a metal foil, an aluminum foil of 0.2 mm. thick was used. The above mentioned materials were fed to the apparatus of Figure 2 to produce a laminated sheet structure. Extruding temperature of the molten polyethylene sheet 9 was 250"C, set temperature of pressure rolls 10, 10' was 200"C, and pressure ofthe cooling rolls ranged from 0.1 Kg./cm? to 4 Kg./cm? The resulting laminated sheet structure has an even surface and is of high smoothness.

When laminated sheet structure was subjected to bending processing, any breaking-away between the.

metal foil and the polyethylene sheet did not occur and the laminated sheet structure was not broken.

Example 2 10 parts by weight of polypropylene (melt index: 7.0 and density: 0.91) to which 1.0% by weight of maleic anhydride is grafted and 90 parts by weight of polypropylene (melt index: 6.5 and density: 0.91) were mixed to prepare a modified polypropylene.

A composition composed of 90 parts by weight of the resulting modified polypropylene and 10 parts by weight of polyisobutylene (PIB) was shaped into a T-die film of 50 microns thick at a resin temperature of 240 C. The resulting film was used as an adhesive film. As a core material, polypropylene (melt index of 1.5, density of 0.91 and melting point of 165 C) was used, and as a metal foil, an aluminum foil of 0.2 mm. thick was used. The above mentioned materials were laminated to form a laminated sheet structure following the procedure of Example 1. Extruding temperature of the polypropylene sheet was 230 C, set temperature of pressure rolls 10, 10' was 220 C, and pressure of the colling rolls ranged from 0.1 Kg.Icm2. to 4 Kg/cm2 The resulting laminated sheet structure has an even surface and is of high smoothness.

Claims (11)

1. A process for producing a laminated sheet structure comprising five layers, the first and the fifth layers being composed of a metal foil, the second and the fourth layers being composed of an adhesive film and the third layer being composed of a polyolefin sheet which comprises adhering the first layer to the second layer, adhering the fifth layer to the fourth layer, and then adhering the second layer to one side of a molten polyolefin sheet and adhering the fourth layer to the other side of the molten polyolefin sheet under pressure, characterized in that tension is applied to the second and fourth layers respectively in directions transverse to directions in which the respective layers are travelling before they are adhered respectively to the first and fifth layers.

2. A process according to claim 1 in which the second and the fourth layers are adhesive films composed of 70 -99 parts by weight of a modified polyolefin produced by grafting at least one monomer selected from unsaturated carboxylic acids and derivatives thereof to a part or the whole of polyolefin and 1-30 parts by weight of a hydrocarbon elastomer.

3. A process according to claim 2 in which the modified polyolefin is that modified by maleic anhydride.

4. A process according to claim 2 or claim 3 in which the degree of grafting of the unsaturated carboxylic acids or derivatives thereof to the polyolefin ranges from 10-4to 3% by weight.

5. A process according to any of claims 2 to 4 in which the hydrocarbon elastomer is selected from polyisobutylene and ethylenepropylene rubber.

6. A process according to any preceding claim in which the polyelfin sheet is composed of polyethylene having density of 0.910 - 0.970 g./cc.

and melt index (at 190 C) of 0.05 - 100.

7. A process according to any preceding claim in which the metal foil is an aluminum foil of 0.01 - 0.5 mm. in thickness.

8. A process according to any preceding claim in which the tension is applied by passing the second layer and the fourth layer over respective rolls having a rotating shaft in a form of circular arc.

9. A process according to any preceding claim wherein the process is carried out in one continuous operation.

10. A process according to claim 1 substantially as described herein with reference to the accompanying drawings.

11. A laminated sheet structure prepared by a process according to any preceding claim.