NO148988B - PROCEDURE FOR THE MANUFACTURE OF COMPOSITE FILES - Google Patents

Description

The invention relates to a method for the production of composite foils using solvent-free adhesives based on multifunctional isocyanates and multifunctional reactive amines.

Composite foils are usually produced using solvent-containing casing adhesives which are applied by means of rollers to the foil web. Thereby, after evaporation of the solvent, a union with the other web takes place under short-term pressure. As adhesives in this method known as dry lamination, almost exclusively solvent-containing polyurethane systems in the form of moisture-curing isocyanate-deplaced prepolymers or two-component polyol/polyisocyanate mixtures are used. The latest limitations on solvent release into the atmosphere necessitate absorption or post-combustion of the solvent/air mixtures as cumbersome process steps.

The invention's task was to find an adhesive system for composite foil production that is solvent-free and can thereby be processed fire- or more explosion-proof and also enables a more economical method.

It was a further task for the present invention to provide a method for the production of composite foils which in a technologically simpler way leads to clear3 adhesive-resistant composite foils.

This task is solved according to the invention by

on one of the two foils to be glued together, one or more apply at least two end-positioned polyethers containing isocyanate groups, whose molecular weight is between 2000 and 5000, and on the other foil, one or more apply at least two reactive amino group-containing longer-chain compounds, the molar ratio between iso -

cyanate groups and amino groups lie between 1:1 and 5:1 and both components are present together in an amount from 0.5 to 5.0 g/m<2>

and the two foil layers are compressed for a short time.

Suitable at least bifunctional isocyanates usable for the method according to the invention can be prepared in a manner known per se by reacting anhydrous polyetherdiols with at least bifunctional isocyanates. Preferred polyetherdiols are derived from 2 to 4 carbon atom containing glycols. Consequently, we are talking about polyethylene and/or polypropylene glycol and/or polytetramethylene glycol (produced by ring-opening polymerization of tetrahydrofuran). In the first place, relatively low molecular weight diisocyanates come into consideration for reaction with polyetherdiols such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, toluylene diisocyanate (isomer mixture) and several others. For practical, especially toxicological reasons, diphenylmethane diisocyanate is preferred.

A conversion ratio of 1.8:1 to 2.2:1 (mol diisocyanate: mol diol) is preferably suitable for the formation of the isocyanate adducts. A lower turnover ratio is in principle also possible, provided that a too high viscous adduct is not thereby formed, with the use of which no more than 1 good mechanical casing is provided. A possible greater turnover ratio than 2.2:1 would in principle also be tolerable, if for toxicological reasons there were no concerns due to the high content of free diisocyanate.

It must be ensured that the isocyanate compounds formed during processing do not exceed a viscosity of approx. 10,000 cp. - Optionally, these reaction components can also be applied at elevated temperatures up to approx. 80°C. Generally, however, temperatures from 50 to 65°C will be preferred.

The case bonding which is only carried out with the at least two end-positioned isocyanate group-containing adducts as isocyanate components in combination with the below-mentioned amine compounds as amine component provides sufficient adhesive strengths. However, it has been shown that this can be increased considerably, when 0.5 to 20, preferably 1.0 to 10 percent by weight of a compound with at least three isocyanate groups is added to the -isocyanate adduct,

the amount by weight being referred to the isocyanate adduct. With those so-

modified isocyanate components are used, in particular a higher initial tackiness is achieved, but also an improved final tackiness. Reaction products of multifunctional alcohols and diisocyanates are suitable as additive compounds with at least three isocyanate groups (reaction ratio: 1 mol of diisocyanate per hydroxyl group), e.g. the turnover product of trimethylol-

propane and toluylene diisocyanate as well as reaction products of one mole of water and three moles of diisocyanate, e.g. starting from hexamethylene diisocyanate, also other aromatic triisocyanates such as M,4',V'-triisocyanatotriphenylmethane and likewise polyisocyanates such as polymethylenepolyphenylisocyanate.

In order for the resulting isocyanate mixtures to be easily applied to the foil webs by machine casing, they should be heated in the application vessel to reduce the processing viscosities. A temperature rise to a maximum of 80°C should therefore not be exceeded. Usually, it is quite sufficient with a tempera-

trip of approx. 60°C. Up to this temperature, when casing with the isocyanate components mentioned in example 1, measurements on the casing machines determined that there were no isocyanate concentrations in the workplace atmosphere that exceeded the permissible MAK value of 0.02 ppm.

The second reaction component used for the method according to the invention is an at least bifunctional amine. At least two amino groups must be present, which can be both primary and secondary. Such compounds are known resp. produced in a known manner.

A preferred basic structure for the amino compounds

are the polyetherdiols or also oligomeric glycols. According to an appropriate embodiment, the procedure is that "acrylonitrile is added to the polyetherdiols. The resulting adducts are then hydrogenated in a known manner, with the nitrile groups forming primary amino groups. Preferred for the production of the two reaction components of the solvent-free casing adhesive is oligomeric glycols or polyether glycols derived from polyethylene glycol, polypropylene glycol and polytetramethylene glycol of a molecular weight between about 200 and ^500, especially 300 and 2000.

Furthermore, it is possible to proceed from relatively low-molecular-weight diamines with a chain length of 2 to 18 carbon atoms, which may also be partially replaced with oxygen atoms, and to react these with at least two amine-reactive functional group-containing compounds (chain extension). Examples of such amines are

The functional groups of the chain extenders can thereby e.g. be epoxide or isocyanate residues or also ot,^-unsaturated esters or halogen atoms. The OH groups, secondary amino groups or urea groupings or introduced ester groupings which are formed by this reaction can in the meantime have a beneficial effect on the adhesion resp. the firmness of the adhesive connection.

In case of diepoxide or diglycidyl compound.e

in which R means an aliphatic or cycloaliphatic residue up to approx.

25 carbon atoms such as e.g. methylene, ethylene, propylene, neopentylene, hexamethylene, dodecamethylene, cyclohexylene, dicyclohexyl, methylene-dicyclohexyl or also a diethylene or triethylene glycol ether residue and the diprimary amine corresponding to the general formula f^N-IV<->NI^

in which R' means, for example, an ethylene, tetramethylene, hexamethylene, diethylene glycol ether, diisopropylen glycol ether or also triethylene glycol ether residue, two terminally placed, primary amino group-containing compounds with the general formula are obtained In case of chain extension with isocyanates such as e.g. toluylene, hexamethylene and isophorodiisocyanate gives two end-placed amino groups as well as urea group-containing compounds with the general formula

in which R' has the above meaning, while R means the remainder of the isocyanate used.

Chain extension reactions for suitable amines

is further mentioned in BRD application no. P 25 49 371.4.

In many cases, it may be appropriate to add 1 to 50 percent by weight, preferably 1 to 15 percent by weight, of water to the amino group-containing longer-chain compounds. This can cause an increase or an earlier achievement of the final strength and favorably influence the sealing ability of the composite film.

With mechanical lamination, a sufficiently high initial stickiness is spontaneously formed so that no delamination or "telescoping" of the composite foil occurs during winding. Within seven days of production, the adhesive strength reaches its final value when stored at room temperature. The adhesive films are then chemically cross-linked and show a condition that, in terms of packaging, satisfies all requirements with regard to joint bonding and heat resistance, which is a prerequisite for sealability. The finished compositions are further distinguished by very good optical properties. Thus, e.g. transparent compositions a high transparency. Incidentally, frequently occurring casing errors such as "fish-eye" or "orange-peel structure" cannot be determined on the compositions.

With the mentioned two-component casing adhesive it is possible to produce all compositions of plastic foils

such as polyethylene, polypropylene, polyester, polyvinyl chloride, polystyrene, polyamide foils, etc. It is also possible to produce composite foils using metal foils, e.g. aluminum foil or different cellular glass resp. paper.

According to the invention, the method will be explained

using the following examples. Those in eczema

Compounds designated as "aminopropylated" polypropylene glycols were prepared by addition of acrylonitrile to glycol and subsequent catalytic hydrogenation.

Example 1

Component A

2000 g isocyanate adduct of polypropylene glycol with molecular weight

2000 and diphenylmethane-4,4'-diisocyanate in a molar ratio of 1:2 and

100 g reaction product of 3 mol hexame/tylene diisocyanate and

1 mole of water.

The content of free isocyanate groups: 4.2% resp. 1.0 méquivalents/g Viscosity at 23°C: 25,000 cp

" 50°C: 8,000 cp

" 60°C: 2,500 cp

(each time Brookfield viscosity)

Component B

300 g aminopropylated polypropylene glycol (average molecular weight 400)

500 g aminopropylated polypropylene glycol (average molecular weight 2000)

Amine content: 2.5 mA/g

1.68 g/m² of component A heated to 60°C was applied to polyester foil (foil thickness 12 µm) and 0.35 g/m² of component B at room temperature on low-density polyethylene foil pretreated by corona discharge (foil thickness 50 ^im) as the application took place mechanically. The molar ratio between the isocyanate and amine component, referred to isocyanate to amino groups, was 1.9:1. The coated sides of the foil were compressed over rollers.

The adhesive film shows a high spontaneous initial tack (30 seconds after gluing, a cup tack of 30 p/15 mm was measured at a pull-off speed of 100 mm/min).

After eight hours of encapsulation, the components allowed themselves to be processed further due to the formation of a consistently high initial stickiness. Due to the increase in viscosity, the application amount of the isocyanate components increased to 1.92 g/m 2 , while the application amount of the amine components remained constant at 0.35 g/m p. This results in a molar application ratio of 2.2:1.

After seven days of storage at room temperature, a cup adhesive strength of 350 p/15 mm had been established. This value was determined both by a composite section produced at the beginning and also by one produced at the end of the eight hour casing time.

Example 2

Component A

Isocyanate adduct of polypropylene glycol (average molecular weight 2000) and diphenylmethane-4,4'-diisocyanate in a molar ratio of 1:2.

Content of free isocyanate groups: 3.4% resp. 0.8l m/equivalents/g Viscosity at 23°C: 20,000 cp.

" " 60°C: 2,000 cp

Component B

300 g aminopropylated polypropylene glycol (average molecular weight 400)

500 g aminopropylated polypropylene glycol (average molecular weight 2000)

Amine content: 2.5 mA/g

2.1 g/m^ of the 60°C heated component A was applied to aluminum foil (foil thickness 12 mm) and 0.4 g/m 2 of component B was applied to corona discharge pretreated low density polyethylene foil (foil thickness 50 pm) . The molar ratio between the components is 1.7:1 (isocyanate: amine group).

When joining the coated foil sides, a sufficiently high initial tackiness was achieved (tensile cup strength: 6p/15 mm at 100 mm/min. pull-off speed 30 seconds after production).

After seven days of storage, the final strength (250"p/ 15 mm) was achieved.

Example 3

Component A

2000 g isocyanate adduct of polypropylene glycol (average molecular weight 3000) and diphenylmethane-4,4'-diisocyanate in a molar ratio of 1:2 and

100 g reaction product of 3 mol hexamethylene diisocyanate and 1 mol water

Content of free isocyanate groups: 3.3% resp. 0.79 mA/g Viscosity at 23°C: 29-000 cp

" " 60°C: 6,000 cp

Component B

Aminopropylated polypropylene glycol (average molecular weight

400)

Amine content: 5 m equivalents/g

2.56-g/m² of the 60°C heated component A was applied to polyester foil (foil thickness 9 µm) °S 0.2 g/m pav component B was applied to aluminum foil (foil thickness 12 µm). The molar ratio between the two components, referred to the isocyanate and amino group, was therefore 2:1.

Initial tackiness (30 seconds after gluing): 15 p/15 mm

Final strength (after seven days): 300 p/15 mm.

Example 4

Component A

2000 g isocyanate adduct of polypropylene glycol (average molecular weight 2000) and diphenyl-4,4'-diisocyanate in a molar ratio of 1:2 and

100 g reaction product of 3 mol hexamethylene diisocyanate and 1 mol water

Content of free isocyanate group: 4.2% resp. 1.0 mA/g Viscosity at 23°C: 25,000 cp

" " 60°C: 2,500 cp

Component B

300 g aminopropylated polypropylene glycol (average molecular weight 400)

500 g aminopropylated polypropylene glycol (average molecular weight 2000) and

20 g of water

Amine content: 2.44 m equivalents/g

2.17 g/m^ of component A heated to 60°C was applied to polyester foil (foil thickness 12 ym) and 0.41 g/m<2> of component B was applied at room temperature by corona discharge to pre-treated polyethylene foil of low density ( foil thickness 40 ym). The molar ratio of the components is 2.2:1 (isocyanate:amine).

Initial tackiness (30 seconds after bonding):

10 p/ 15 mm

Final strength (after three days): 380 p/15 mm.

Claims (4)

1. Method for the production of composite foils using solvent-free adhesives based on isocyanate adhesives, characterized in that on one of the two foils to be glued together one or more, at least two terminally placed isocyanate group-containing polyethers are applied, whose molecular weight is between 2000 and 5000 and on the other foil, one or more, at least two reactive amino group-containing long-chain compounds are applied, the molar ratio between isocyanate groups and amino groups being between 1:1 and 5:1 and both components are present together in an amount from 0.5-5, 0 g/m 2 and the two foil surfaces formed are compressed for a short time. 2. Process according to claim 1, characterized in that 0.5-20, preferably 1-10% by weight of a compound which has at least three isocyanate groups is added to the polyether containing isocyanate groups, the amount being referred to the polyether containing isocyanate groups. 3. Method according to claims 1 and 2, characterized in that reaction products of polyethers with acrylonitrile which then became hydrogens are used as at least two reactive amino group-containing compounds. 4. Method according to claims 1-4, characterized in that the amino group-containing compound is added 1-50, preferably 1-15% by weight of water, the amount being referred to the amino group-containing compound.