DE2951138A1 - IRRADIATED LAYER FILM WITH HOT SEAL PROPERTIES - Google Patents

Description

The present invention relates to crosslinked layered films with heat sealing properties, especially those with coextruded polymeric multilayer structure, which in addition to an improved heat sealability have the advantage that the crosslinking is brought about by suitable irradiation leaves.

It is already known to be heat-shrinkable thermoplastic To use foils as packaging material in many fields. Usually a product is made into one of these Foil wrapped, the foil sealed and heated, so that it fits tightly to the product by shrinking. One of the most suitable and satisfactory thermoplastic materials is polyethylene. A number of methods are known to make polyethylene in to convert suitable heat-shrinkable packaging films. One such method is disclosed in U.S. Patent 2,855,517 (W.C. Ranier et al.) and another method is disclosed in U.S. Patent 3,022 (W.G. Baird, Jr. et al.). The latter patent specification describes a process by which polyethylene is continuously extruded and drawn in the form of a tube is, whereby the crosslinking of the polyethylene molecules through Electron irradiation occurs, whereupon the polyethylene is heated and stretched by putting on the tube

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pressure from the inside The film obtained by this process has very desirable heat shrinkable properties Properties.

It is well known that polymers and copolymers of olefins, particularly polyethylene, are thermosetting if they are treated with a sufficient dose of radiation. Because of this, it is common to have items before an intended irradiation to shape in order to have the properties undesirable for the shaping, the occur in the transition from thermoplastic to thermosetting material. This transition one Article from a thermoplastic to a thermosetting one Condition is also characterized by a progressive decrease in the ability of such an object of olefin polymers for heat sealing to themselves or Accompanied by other objects, to the extent that the radiation dose is increased. The film manufacturer have therefore generally recognized that highly irradiated polyethylene films do not have the ability to form reliable high strength heat seals. In the known method one must therefore, in order to films with acceptable heat sealing properties, either rely on low radiation dose or use a second layer or laminate with desirable heat seal properties, this layer or this laminate is applied to the irradiated layer some time after the irradiation.

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The object of the present invention is to create a layered film which has the desired properties possesses and can be crosslinked by irradiation so that the irradiated product has heat sealing properties, which are similar to those of non-irradiated objects.

Another object of the present invention is to provide a method for producing such a layered film to accomplish.

Another and more specific object of this invention is to provide a coextruded film, having a layer has been crosslinked by irradiation, while an other layer is the same minimally cross-linked, so that the heat sealing properties of this other layer are not adversely affected.

According to the invention, this object is achieved by a coextruded polymeric multilayer structure, which is characterized in that it has a crosslinked layer with a the crosslinking by radiation enhancing radiation enhancer and a heat sealable layer contains.

It has been found that by introducing a radiation intensifier into a crosslinkable layer, the Crosslinking effect of those used in the irradiation stage

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Can amplify radiation to such an extent that the layer containing the amplifier with a minimal amount of radiation is crosslinked and that the layer containing no enhancer is subject to only minimal crosslinking, and although to an extent that is insufficient, the heat sealing properties adversely affecting this layer.

It was therefore surprisingly found that it is possible to produce a coextruded laminate film which is crosslinked by irradiation while the desired heat sealing properties are retained with a practically non-crosslinked outer layer of the laminate are connected. This desired combination of properties is achieved by incorporating a radiation enhancer for crosslinking into the one laminate layer causes the crosslinking effect of the in the irradiation stage radiation used is greatly improved. By the presence of the radiation intensifier the required radiation dose is reduced so far that the heat-sealing properties of the heat-sealable Layer is not adversely affected by the incident radiation.

In the following, the term “polymer” includes all polymeric substances including homopolymers, copolymers, terpolymers and the like. With the term "Ver

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wetting "is the union of polymer molecules through understood a mechanism by which primary chemical bonds bind a polymer into a single Network effect so that functionally different molecules are linked together to form a single molecule will. In the case of polymers made from monoolefins, in particular of polymers and copolymers of ethylene, the crosslinking can be reduced by an increase in the amount remaining Detect residue if the sample is treated with toluene under reflux for about 2 days. This is done in usually referred to as the gel content. In this way, the crosslinking is caused by an increase in the gel content of the crosslinked sample, compared to a non-crosslinked or less crosslinked sample detected.

Under an "irradiation enhancer for crosslinking" (Irradiation Crosslinking Enhancer) is here a chemical Composition understood that when mixed with a polymer in a molten state, a material results that is crosslinked to a greater extent than the same polymer by a given dose of radiation without such an addition of radiation intensifier. This is shown by the fact that one with such a radiation intensifier provided polymer a product crosslinked by this irradiation with the same irradiation dose with a higher gel content than the same polymer without this addition.

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The laminate according to the invention exists in the broadest sense a core layer and a heat-sealable layer, both of which go through a crosslinking stage together, in which the core layer is crosslinked to a high degree due to the existing radiation intensifier for crosslinking will. The "core layer" here refers to the layer which is the essential layer in the inventive Laminate is crosslinkable, the term "core layer" not referring to a middle or innermost layer should restrict. However, the laminate may have additional layers, such as additional heat sealable layers or a layer that prevents the passage of gaseous or liquid substances such as oxygen or moisture, contain.

The core layer of the laminate according to the invention consists made of a polymer that can be crosslinked by irradiation and thereby enhances its crosslinking ability can be that it can be used according to the invention with a radiation intensifier mixed for networking. Crosslinking by irradiation can be done using various methods be performed. Electron and X-rays as well as actinic radiation such as UV light can be used for this with a wavelength above about 200 nm and below about 270 nm can be used. Preferably, however Electrons with an energy of at least 10 eV applied. The radiation source can be electron accelerators,

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ζ. B. a Van der Graaf! "- electron accelerator, with an operating voltage of 2 MV with an output power of about 5 to 10 kW. Preferably, however, is the Electron source an electron accelerator operated by an isolated core transformer with an accelerating voltage is fed from about 300 to 3000 kV.

The radiation absorbed by the core layer is referred to by the term "wheel", where wheel is defined than the amount of energy of 100 erg / g generated by the ionizing radiation on the irradiated material at the relevant Place occurs. According to the invention, the material for the core layer, d. H. for the polymer to which the radiation intensifier has been added, one is used, that is sufficient after mixing with the enhancer at an exposure dose in the range of about 0.1 to 5 MRads is crosslinked so that its gel content is increased.

The polymeric material which is mixed with a radiation intensifier and which is the core layer of the invention Laminate can be selected from a large number of materials that will crosslink when they are intended to form a laminate be subjected to irradiation. Even if polymers and copolymers of ethylene are preferred according to the invention The invention can generally also represent material with polymers of other polyolefins, in particular of 1-alkenes and their copolymers are carried out. In particular

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the invention can be carried out with polymers of propylene, butylene, pentene and hexene. Furthermore can the invention can also be carried out with polymers and copolymers of vinyl chloride. In particular, can Copolymers of ethylene and vinyl esters, e.g. B. vinyl acetate can be used. Any ethylene polymer such as high pressure and low pressure ethylene polymers and their mixtures are suitable for the purpose of the invention.

Numerous radiation enhancers for crosslinking are known. Any of these amplifiers can be used for the core layer of the laminate according to the invention can be used. For example, radiation enhancers are as follows listed compound classes are suitable:

Dialkyl maleate and fumarates, in which the alkyl group Contains 4 or more (generally 4 to 20) carbon atoms;

Vinyl esters of fatty acids in which the fatty acid

Contains 3 or more (generally 3 to 20) carbon atoms;

Vinyl alkyl ethers in which the alkyl group contains 18 or more (usually 18 to 30) carbon atoms;

Alkyl acrylates in which the alkyl group contains 1 or more (usually 1 to 20) carbon atoms; and

Alkyl methacrylates in which the alkyl group is 3 or contains more (usually 3 to 20) carbon atoms.

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According to the invention, allyl methacrylate and allyl acrylate are particularly preferred radiation intensifiers for crosslinking and diallyl maleate are used. The radiation intensifier for the crosslinking can be done with the help of various conventional techniques, e.g. B. by mixing the materials in powder form, adding the enhancer to the Polymers in the molten state or by diffusion of the radiation intensifier in gaseous or liquid Form in the solid polymer to be incorporated into the core layer. However, it is preferred before melting the core layer premix and before the melt extrusion first the radiation intensifier is mixed in in powder form. The radiation enhancer does not cause crosslinking in the solid polymer until the layer, as above discussed, is exposed to a radiation source. The radiation enhancer is usually used in small amounts From about 0.05 to 10% by weight, based on the total composition of the core layer, is used, however, the amount in any case should be sufficient to increase the gel content in the core layer.

The heat-sealable layer of the laminate according to the invention, which is coextruded simultaneously with the core layer can be made of any material that is suitable for its heat sealability used conventionally. Appropriate

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Materials can usually be with themselves heat seal at temperatures ranging from 70 to 150 ° C under a pressure of about 35 kPa to 350 kPa. These Materials have a peel strength greater than 17.9 kg / m, preferably greater than about 179 kg / m, measured according to the ASTM D-903 method.

Among the substances used as the heat-sealable layer of the invention Laminates that can be used include high pressure and low pressure polyethylene, polypropylene and other polymers of the 1-monoolefins. Particularly effective Heat sealable materials are unsaturated ester polymers such as ethylene / unsaturated ester copolymers, e.g. B. ethylene / vinyl acetate, Ethylene / vinyl propionate, ethylene / ethyl methacrylate, ethylene / ethyl acrylate, ethylene / isobutyl acrylate and the like, copolymers of unsaturated carboxylic acids such as ethylene / unsaturated carboxylic acid copolymers, e.g. B. ethylene / acrylic acid, Ethylene / methacrylic acid, ethylene / maleic acid, Ethylene / fumaric acid, ethylene / itaconic acid and the like. The carboxyl groups in the copolymers can be wholly or partially neutralized to form what is commonly referred to as an ionomer Form product.

Particularly preferred heat sealable materials are copolymers of ethylene and vinyl acetate with a content from about 5 to 40 weight percent vinyl acetate.

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This listing of fabrics used as a heat sealable layer for the laminates of the invention However, it is not complete, but merely serves for exemplary explanation. These These substances tend to weaken their heat sealability when exposed to radiation sufficient to crosslink a layer containing no radiation intensifier. Used however, if a core layer is covered with a radiation intensifier, then the required radiation dose is sufficient does not affect the heat-sealability of the heat-sealable layer in its also exposed to radiation Significantly affect quality.

After the laminate film according to the invention in conventional Way has been coextruded, it is irradiated with a dose sufficient to protect the mechanical and to strengthen the chemical properties of the core layer, without adversely affecting the quality of the heat-sealability of the heat-sealable layer. Preferably the irradiation is carried out at a dose of about 0.1 to 4 MRad. This dose is enough to bring about the desired crosslinking within the core layer without affecting the heat sealability of the heat sealable Layer is adversely affected.

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An essential reason for carrying out the crosslinking reaction is to give the core layer a better orientation process subject to heat shrinkable film. According to the present In the invention, however, it is not necessary to carry out an orientation process since the method of irradiation crosslinking other desirable properties of the laminate film are reinforced than those that affect the orientation enable. However, it is advantageous that the laminate film made according to this invention can be made by conventional means Techniques is oriented in order to obtain a film with shrink properties. In particular, will preferred that this shrinkage at a temperature at or below the boiling point of water, ie at or below 100 ° C. The laminate according to the invention can be biaxially oriented if there is a free shrinkage of at least 10% in both longitudinal and longitudinal directions at 96 ° C also has in the transverse direction.

The invention also relates to a method for producing the laminates according to the invention. The inventive Process for the production of a coextruded polymeric multilayer structure with heat sealing properties characterized by the following process steps: a) Production of a multi-layer structure, which is a crosslinkable Contains a radiation enhancer layer and a heat sealable layer, and

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b) irradiating the multilayer structure with an irradiation dose, which is sufficient to crosslink the crosslinkable layer without having an adverse effect exerts the heat sealing properties of the heat sealable layer.

The laminate according to the invention is preferably by Coextruded the materials in tubular form as generally described in U.S. Patent 3,874,967 (H.G. Schirmer) has been described.

The inventive method is based on the figure, which shows a schematic representation of the method, explained in more detail.

The two extruders 2 and 3 supply the nozzle 4 for coextrusion with the different layer materials, of which the laminate according to the invention is composed shall be. For example, the extruder 2 can contain the core layer polymer including radiation intensifiers included for the crosslinking and the extruder 3 be supplied with the heat-sealable layer material. The extruder supply the coextrusion nozzle 4 for the production of a tubular or tubular film 6. The nozzle is like this arranged that the hose down into a cooling bath of water or other inert liquid, the kept at a temperature between -18 ° and + 21 ° C

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is extruded. The cooled and flattened one Hose 16 is fed via feed rollers 18 into an irradiation chamber 20 which contains an electron source 22. After the irradiation, the flattened tubular band is over feed rollers 28 in a hot bath 30 in the Stretching tank ("racking tank") 46 carried the water or other liquid opposite to the polymer layers is inert, contains. This liquid is kept at a temperature sufficient to maintain the Maintain tape at a desired temperature for orientation of the core layer. This temperature can vary depending on The composition of the core layer may vary slightly. However, stretching techniques are well known and whichever one is desired Orientation temperature can easily be determined for a specific film material. For example lets A crosslinked high density polyethylene will easily orientate themselves at a temperature of about 88 to 102 ° C. The preferred temperature, however, is around 96 C. Air or other gases are introduced into the heated belt. a bubble between the surface of the hot bath and the top air squeeze rollers 34 forms. The amount of inflation should preferably be sufficient to provide an expansion of from about 3: 1 to about 8: 1 in effect any direction.

Although the above description relates specifically to a coextruded laminate with only two layers,

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it is apparent that other materials can be coextruded along with the two essential layers. The most easily extrudable layer is an additional heat sealable layer which is compositionally identical to the first heat sealable layer, thereby providing a three layer laminate with the core layer between these two layers. However, other materials such as layers for preventing oxygen permeation can also be bonded together with the core layer and the heat-sealable layer or the heat-sealable layers.

The invention is further illustrated by the following examples.

example 1

Several samples were produced using a core layer into which a radiation enhancer for crosslinking was incorporated according to the invention. Laminates of three concentrically arranged layers were coextruded from a 10.16 cm die using a mixture of equal weight amounts of high pressure and low pressure polyethylene. However, the central layer of the multilayer construction contained a small amount of

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Diallyl maleate as a radiation enhancer. All samples were blown using the "Bubble Technique" oriented at a temperature of about 121 C, with an elongation of about 5: 1 in both the longitudinal and was also achieved in the transverse direction. Immediately after orientation, the samples were cooled. Every sample had a thickness of about 25 µm after stretching. The structure and properties of each sample are in the Table I below compiled.

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TABLE I.

Sample layer radiation diallyl no. thickness-dose maleate ratio (MRad) (wt.%) shrinkage stress (kg / cm)
transversal longitudinal

at
93.3 ⁰ C 149 ^{0 0} 93.3 C C 149 ° C

free shrinkage (in %) longitudinally transversely

at
93.3 ° C 149 ⁰ C 93.3 ° C 149 ⁰ C.

1 1/2/1 2 0.3 30.86 21.09 13.29 17.51 6th 83 12th 78 2 1/1/1 3 0.2 26.50 27.28 17.01 22.92 8th 82 12th 79 3 1/1/1 3.5 0.3 33.82 25.10 12.16 19.26 6th 82 12th 80 4th 1/1/1 4th 0.3 23.34 29.18 22.78 23.97 8th 81 10 78

K)

CD

cn

OJ CO

Example 2

Two samples were made using a core layer which, according to the invention, is a radiation intensifier for containing the crosslinking. The two laminates were made of the same material and essentially in prepared in the same way as described in Example 1. Further samples 3 and 4 were made from polyethylene blends which were composed similarly to the mixtures used for samples 1 and 2 but with the difference that they did not contain any radiation enhancer for crosslinking and consisted of a single layer with a layer thickness comparable to that of samples 1 and 2. All Samples were about 19 µm in total thickness. The coextruded Laminates had layers of the same layer thickness.

The gel content of each sample was determined in the manner that the samples were refluxed with toluene for 21 hours to ensure that all soluble Shares had completely gone into solution. The results obtained are shown in Table II. The outer layers of the samples that did not contain any radiation enhancer for crosslinking, showed no gel, while the radiation intensifier core layer had a gel content higher than

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Xh-

Sample 3, which did not contain any radiation enhancer. Samples 1 through 4 were taking for seal strength Tested using ASTM standard method F 88-68 for both lap and edge sealing ("Trim Seal") at different electrical currents inside the heating element. The overlap seal was made using a nickel-chromium heating tape coated with a polytetrafluoroethylene film was made. The heating tape was in the manner of a pulse generator with each heating and Cooling cycle operated. The edge seals were made using a continuously heated one Heating wire made from the same alloy, which is inserted at 6-second intervals worked. The results are shown in Tables III and IV. It can be seen that the The sealing strength of the heavily irradiated samples 3 and 4 is considerably lower at a comparable current strength than that of the less irradiated samples that have a core layer with an irradiation enhancer for the Networking included.

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TABLE II

sample rf Layer structure Radiation dose 2 Diallyl % Gel in % Gel in the • No. (MRad) 3 maleate the total Outside core ⁴² < ⁶ a 5 (Wt.%) structure layer layer * - 1 1/1/1 0.2 3.8 0 12th 2 1/1/1 0.3 5.4 0 16 3 I each one 0 5.4 5.4 only one 10 I shift with J one shift 4th thickness of 0 42.6 J 19.5 / µm.

TABLE III

sample layer Rays Diallyl No. construction dose maleate (MRad) (Wt.%) 1 1/1/1 2 0.2

Seal strength (lap seal)

1/1/1

10

Amperage (A) 22nd 24.2 25.3 25.7 26.3 27.8 28, 7th strength (G) 190.5 394.6 503.5 966.2 1365.3 1093.2 1460, 5 Amperage (A) 21.9 24.4 25.2 26.5 27.5 strength (S) 158.8 517.1 1474.2 Amperage (A) 22.5 23.5 752.9 902.6 28 strength (R) 326.6 263.1 1460, 5 Amperage (A) 23 strength (G) 335.7 _{- p}

CT'O NJ CD

TABLE IV

Sample Radiation Dose Edge Seal Strength
No. (MRad)

Amperage (A) - 7.3 8, C) 8, 8

Firmness ( _G _ , 9 2567, 3 2331 , 5 1329 , 0 Amperage ( 6th , 7 7, 6th 8th , 3 Firmness ( .G 2612 , 7 2485, 7th 1950 , 4 - Amperage ( 6th 7, 4th 8th ,1 , 0 Firmness ( ^ g 2531 2177, 2 1573 , 9 - Amperage ( 8th , 3 9 ,1 Strength ι (G - - 784 , 7 748 , 4 y— A) ) A) ) A) ;)

From the examples it can be seen that the invention Laminates with a multi-layer structure have all the desired attributes of a networked structure without the otherwise occurring ones have adverse effects on the heat-sealing properties

sy: where

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Claims (15)

UEXKÜLL & SiOLBcHG PATENTANWÄLTE HttffavÜC S-I. ppohlssionai rlphi si ntative oil F ORE THl FUSOI1EAN PAHNl OFFlCE dr j d frhb by uexkull DR ULRICH GRAF STOLBERO DIPL ING JÜRGEN SUCHANTKE DIPL ING ARNULF HUBER DR ALLARD BY W. KAMEKE DR KARL HEINR. SCHULME Grace & Co. Grace Plaza, 1114 Avenue of the Americas, New York, New York 10036 V.St.A. (Prio .: December 28, 1978 US 973 850 - 16155) Hamburg, December 1979 Irradiated layer film with heat sealing properties. PATENT CLAIMS 1. Coextruded polymeric multilayer structure, characterized in that it has a crosslinked layer with a the crosslinking by radiation enhancing radiation enhancer and a heat sealable layer contains. 2. Multi-layer structure according to claim 1, characterized in that the crosslinked layer by irradiation at a dose of 0.1 to 4 MRads. 030029/061? ORIGINAL INSPECTED 3. Multi-layer structure according to claims 1 and 2, characterized in that the heat-sealable layer in the has substantially similar heat sealing properties as a non-irradiated layer of the same Material. 4. Multi-layer structure according to claim 1, characterized in that the crosslinked layer consists of the polymer an αί.-monoolefin consists. 5. Multi-layer structure according to claim 4, characterized in that the radiation intensifier is a dialkyl maleate, Dialkyl fumarate, fatty acid vinyl ester, vinyl alkyl ether, Is alkyl acrylate and / or alkyl methacrylate. 6. Multi-layer structure according to claim 5, characterized in that the radiation intensifier is an allyl methacrylate, Is allyl acrylate and / or diallyl maleate. 7. Multi-layer structure according to claim 1, characterized in that the heat-sealable layer at heat seal at a temperature in the range of 70 to 150 ° C and at a pressure of about 0.35 to 3.52 kg / cm leaves, whereby a closure is obtained, 03002 9/0617 which has a peel strength greater than 0.179 kg / cm width. 8. Multi-layer structure according to claim 1, characterized in that it is in the biaxially oriented state is present. 9. Multi-layer structure according to claim 8, characterized in that it has a free shrinkage of at least 10 % both in the axial and in the transverse direction at 96 ° C. 10. Process for the production of a coextruded polymeric multilayer structure with heat sealing properties, characterized by the following process steps: a) Production of a multilayer structure, which has a crosslinkable layer with an irradiation intensifier and contains a heat sealable layer, and b) irradiating the multilayer structure with an irradiation dose that is sufficient to reduce the crosslinkable Layer to crosslink without having an adverse effect on the heat sealing properties the heat sealable layer. 11. The method according to claim 10, characterized in that the irradiation with a dose in the range of 0.1 to about 4 MRad is performed. 030029/0617 12. The method according to claim 10, characterized in that a polymer as a crosslinkable layer ct monoolefins is used. 13. The method according to claim 10, characterized in that the radiation intensifier is a dialkyl maleate, Dialkyl fumarate, fatty acid vinyl ester, vinyl alkyl ether, Alkyl acrylate and / or alkyl methacrylate is used. 14. The method according to claim 13, characterized in that an allyl methacrylate, Allyl acrylate and / or diallyl maleate is used. 15. The method according to claim 10, characterized in that the multilayer structure in a further Process step oriented. 030029/0 6 17