CA1136533A

CA1136533A - Process for producing a laminated sheet structure

Info

Publication number: CA1136533A
Application number: CA000336184A
Authority: CA
Inventors: Yoshitomo Miyazaki; Tomokazu Ninomiya; Takashi Yamanaka
Original assignee: Mitsui Petrochemical Industries Ltd
Current assignee: Mitsui Chemicals Inc
Priority date: 1979-09-24
Filing date: 1979-09-24
Publication date: 1982-11-30

Abstract

TITLE OF THE INVENTION
Process For Producing A Laminated Sheet Structure ABSTRACT OF THE DISCLOSURE
A laminated sheet structure is produced by bonding metal foils to a polyolefin sheet by means of adhesive film, and the adhesive film is laterally stretched before it is bonded to the metal foil.

Description

~13~

I BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to a process for producina a laminated sheet structure comprising metal foils and poly-S olefin sheets adhered with adhesive films.
Description of the Prior Art 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.
Pat. 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 characte-ristics and a particular composition.
An embodiment of the latter is disclosed in U.S. Pat.
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. 88884/1978 ~`

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 280C with an intervened adhesive layer which comprises 99 - 70 parts by weight of a modified polyolefin produced by grafting at least one monomer selected from un-saturated 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. Pat. 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 113~i533 1 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.

SUMMARY O~ THE INVENTION
An object of the present invention is to provide a process for producing a laminated sheet structure free from the above mentioned disadvantages.
Another object of the present invention is to provide a process for producing a laminated sheet structure having a very high adhesion between a metal foil and a polyolefin sheet.
~ A further object of the present invention is to ~ provide a process for producing a laminated sheet structure capable of being subjected to severe bending processing and drawing processing without breaking.
Still another object of the present invention is to provide a laminated structure having a surface of high smooth-ness and free from unevenness.

~13~i~33 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 com-posed of an adhesive film and the third layer being composedof 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, wherein a tension is applied to the second layer and the fourth layer to stretch the adhesive film in a transverse direction with respect to the direction of movement of the layers before the second layer is adhered to the first layer and the fourth layer is adhered to the fifth layer.

BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cross section of an embodiment of a laminated sheet structure produced by the process of the present inven-tion;
FIG. 2 shows diagrammatically an embodiment of the pro-cess of the present invention;
FIG. 3 shows a cross section of a curved roll for stretch-ing the adhesive film laterally; and 1136~33 1 FIG. 4 is a perspective view showin~ that the adhesive film passes over the curved roll.

~ DESCRIPTION GF THE PREFERRED EMBODIMENTS
5 ~ Referring is made to FIG. l, the laminated sheet structure is composed of a polyolefin sheet 3 as a core material sandwiched in between metal foils l and 5 by means of adhesive films 2 and 4.
As polyolefins which can be a material for the poly-olefin sheet and can be a starting material for a modifiedpolyolefins 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, homo-polymers of ~ -olefins such as ethylene, propylene, l-butene, l-pentene, 3-methyl-l-butene, l-hexene, 4-methyl-l-pentene and the like, copolymers of one of the above mentioned ~-olefins with less than l0 mole %, preferably less than 7 mole % of other ~ -olefin, or mixtures thereof. Further there may be mentioned copolymers of the above mentioned ~ ~-olefin with acyloxy, particularly, acetoxy substituted one such as vinyl acetate, or their saponified ones.
Amon~ them, middle or low density polyethylene, polypropylene, in particular, polyethylene having density of 0.9l0 - 0.970 g./cc. and melt index (190C1 of 0.05 - l00, are preferable.

~13fi533 1 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 N-monoethylamide, maleic acid N,N-diethylamide, maleic acid N-monobutylamide, maleic acid N-N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid N-monoethylamide, fumaric acid N,N-diethylamide, fumaric acid N-monobutylamide, fumaric acid N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate and the like.
Amona them, maleic anhydride is particularly preferable.

~13~iS33 1 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 I in the presence or absence of a solvent with or without an S ~ added radical initiator. Other vinyl monomer such as styrene may be added to the reaction system.
The amount of monomer grafted to a polyolefin ~herein-after called "degree of grafting") is preferably 10 4 - 3%
by weight.
A part or the whole of the polyolefin may be srafted.
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 non-modified 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-l-butene rubber, butyl rubber, butadiene rubber, styrene-butadiene rubber, ethylene-butadiene rubber, isoprene rubber and the like.
Among them, ethylene-propylene rubber and polyiso-butylene are particularly preferable.
To the polyolefin sheet as a core material and the adhesive film of the present invention there may be added heat 113f~S33 1 resistant stabilizer, weather resistant stabilizer, lubricant, antistatic agent, nucleating agent, pisment, dyestuff, fire retardant, blocking inhibitor, slipping agent and the like in an amount usually used.
5 ` The adhesive film is composed of 70 - 99 parts by weight, preferably 80 - 97 parts by weight of a modified polyolefin and l - 30 parts by weight, preferably 3 - 20 parts by weight of a hydrocarbon elastomer (totally lO0 parts by ~ weight). When the hydrocarbon elastomer is less than l 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 lO - lO0 microns by T-die shaping or inflation shaping. Thick adhesive sheet may be used, but it is not preferable from economical point of view.
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.

113~ 33 As the inorganic compound, there may be mentioned magnesium oxide, calcium oxide, aluminium oxide, titanium dioxide, magnes-ium sulfate, calcium sulfate, magnesium hydroxide, aluminum hy-droxide and the like.

According to the present invention, a tension is ap lied to the second layer and the fourth layer to stretch the adhesive film in a transverse direction with respect to the direction of movement 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 the disadvan-tages 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 con-tained between them. As the result, the adhesion between the metal foil and the adhesive film can be strengthened and simul-taneously 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, the ad-hesive 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 the polyolefin sheet can contact uniformly and tightly each other and thereby the resulting ....

113fi533 1 laminated sheet structure, as a whole, is of high mechanical strength.
As a method for applying a tension to the adhesive l films, i.e. the seccnd layer and the fourth layer in the , transverse direction with respect to the direction of proceed-ing 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 FIG. 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 l bearings 3. The degree of curving of the curved shaft can I be adjusted by an angle adjusting device 4. The rubber roll may be driven by a driving source, if necessary.
Now referring to FIG. 4, the adhesive film 42 passes over the curved rubber roll from side A to side B, and as Il the adhesive film proceeds over the curved roll, the friction 1, force between the surface of the rubber roll and the adhesive B film 42 causes expansion of the film 42 ~ the transverse direction.
Further, referring to FIG. 2, metal foils 1 and l' defatted and wound around rolls pass over guide rolls 3, 3', 4 and 4', are heated by preheaters 6 and 6' to 70C - 200C

113~;533 I 1 and fed to roll pairs 5 and 5'. Temperature of the roll pairs ~ 5 and 5' is preferably 100C - 150C. As preheaters 6 and ¦ 6', those of a hot air blowing type are prererable. Temperature I of the hot air is usually 100C - 300C, preferably 150C -250C. Thus the metal foils can be uniformly preheated with high heat efficiency.
The outside surface of the metal foil may be coated after defatted.
I 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 I resulting in a two-layered sheet, and if desired, the two-I layered sheets are heated by heaters 7 and 7' to a temperature of 120C - 200C so as to laminate to form two-layered laminates. According to the method shown in FIG. 2, the two-layered laminate is continuously and simultaneously formed, I but there may be also employed such a method that the two-I 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 from an extruder8 l in the molten state at a temperature of higher than the melting point and lower than 280C and fed to the nip of 113~i~33 1 pressure rolls 10 and 10'. Thickness of the molten polyolefin sheet is usually 1 - 6 mm. When temperature of the molten polyolefin sheet is lower than the melting point, it can not adhere to the adhesive film. On the contrary, when its ~ temperature is higher than 280C, the adhesion ability is rather lowered.
Temperature of pressure rolls 10 and 10' is set to a temperature of from room temperature to 300C. The above mentioned two-layered sheets are pressed onto the both surfaces I 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./cm. - 4 Kg./cm. during passing through~
l, the colling roll pairs. The laminated sheet structure thus 1 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 I (melt index: 1.5 and density: 0.965~ to which 1.0 % by I 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 /

113~533 1 20 microns thick at a resin temperature of 220C. The resulting film was used as an adhesive film. As a core material, a high density polyethylene tmelt index of 1.0, density of 0.957 and melting point of 120C) 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 FIG. ~ to produce a laminated sheet structure. Extruding temperature of the molten polyethylene sheet 9 was 250C, set temperature of pressure rolls 10, 10' was 200C, and pressure of the cooling rolls ranged from 0.1 Kg./cm2 to 4 Kg./cm.
The resulting laminated sheet structure has an even surface and is of high smoothness.
When the 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.

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 50 113~533 1 microns thick at a resin temperature of 240C. 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 165C) was used, and as a metal foil, an aluminum I 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 230C, set temperature of pressure I rolls 10, 10' was 220C, and pressure of the colling rolls ranged from 0.1 Kg./cm.2 to 4 Kg./cm.
The resulting laminated sheet structure has an even surface and is of high smoothness.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a laminated sheet structure compri-sing five layers, the first and the fifth layers being composed of a metal foil, the second and the fourth layers being com-posed 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, wherein a tension is applied to the second layer and the fourth layer to stretch the adhesive film in a transverse direction with res-pect to the direction of movement of the layers before the second layer is adhered to the first layer and the fourth layer is adhered to the fifth layer.

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 1 in which the polyolefin sheet is composed of polyethylene having density of 0.910 -0.970 g./cc. and melt index (at 190°C) of 0.05 - 100.

4. A process according to claim 2 in which the modified poly-olefin is that modified by maleic anhydride.

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

6. A process according to claim 2 in which the hydrocarbon elastomer is selected from polyisobutylene and ethylenepropy-lene rubber.

7. A process according to claim 1 in which the metal foil is an aluminum foil of 0.01 - 0.5 mm. in thickness.

8. A process according to claim 1 or 2 in which the tension is applied by passing the second layer and the fourth layer over rolls having a rotating shaft in a form of circular arc, respectively.