NL9202002A - Product obtained by cross-linking a prepolymer, product in the form of a foil and method of manufacturing it. - Google Patents

Description

Product obtained by cross-linking a prepolymer, product in the form of a foil and method of manufacturing it.

The invention relates to a product obtained by cross-linking a mixture comprising a multifunctional prepolymer with at least one polyester main chain, in which at least two reactive ethylenically unsaturated groups are present. The invention relates in particular to such a product in the form of a foil, which foil is halogen-free and is suitable as a replacement for PVC casting foils.

To date, PVC cast films have been applied to cars such as "car striping", advertising, lettering and the like. The manufacture of such PVC cast films is described in Encyclopedia of PVC, vol. 3 and comprising applying a solvent-containing PVC paste to a backing material and heating it to evaporate the solvent and fuse the PVC. The cast film obtained can, for example, be printed with screen printing techniques, after which letters or shapes can be punched from the film. PVC casting films, which usually contain a number of additives, such as, for example, plasticizers, stabilizers, pigments, etc., have good strength and gloss and are resistant to weathering, making them suitable for outdoor use. However, a drawback of PVC casting films is that they are poorly resistant to solvents, such as petrol, which can penetrate through the film, which affects the adhesive layer. In addition, halogen-containing products, such as these PVC casting films, are no longer desirable, because they form an environmental burden after use. This has created a need for halogen-free films that can replace PVC cast films.

EP 0 419 862 discloses a foil of the type mentioned in the opening paragraph, which is manufactured by applying a copolyester prepolymer with terminal acrylate or methacrylate groups in a molten state to a backing material. The layer formed is cured by EB or UV with a photoinitiator. This technique cures under an inert atmosphere of nitrogen to form flat films. However, this technique is cumbersome and one would prefer thermal cure, using a thermal initiator and in a non-inert atmosphere. In addition, UV curing is a problem for colored films, because the curing is then incomplete. However, if the prepolymers of EP 0 419 862 are thermally cured, films are formed which are tacky to the surface and tend to curl after removal of the backing material. These problems are caused by oxygen inhibition, resulting in incomplete curing on the air-exposed surface. These problems are inherent in cross-linking with peroxide. It is known that oxygen inhibition can be counteracted by the addition of various additives, such as oxygen scavengers, organometallic salts and waxes. However, it has been found that when using the prepolymers as described in EP 0 419 862 and generally prepolymers as further defined below, the use of the known additives cannot or does not completely prevent oxygen inhibition. High concentrations of such oxygen scavengers adversely affect the mechanical properties of the resulting film.

It has now been found that non-sticky products and in particular flat, non-sticky films can be obtained by cross-linking a mixture which, in addition to a multifunctional prepolymer with at least one polyester main chain in which at least two reactive ethylenically unsaturated groups are present, has a cellu loose derivative.

The use of a cellulose derivative in a mixture with an unsaturated prepolymer is known from EP 0 297 686, but this concerns a cellulose derivative with an unsaturated group, which serves as a thickener in an impregnation or coating composition, and which cannot prevent oxygen inhibition sufficiently. . In addition, the prepolymer according to EP 0 297 686 consists of a polyether urethane, which, due to its poor mechanical properties, cannot be used for the manufacture of the films of the present invention.

The addition of the cellulose derivative to the crosslinkable mixture provides, besides the elimination of the oxygen inhibition problem, a number of unexpected advantages. The products obtained have good (mechanical) properties and in the case of foils they largely have the same (mechanical) properties as the known PVC foils; good tear strength and good printability with all known PVC printing techniques. In addition, the products are solvent resistant, which in the case of foil is a great advantage over the known PVC foils. Even when the products according to the invention exist as top coat, the properties thereof appear to be greatly improved by this application.

The prepolymer in the mixture for the manufacture of the products according to the invention preferably consists of a polyester urethane with (meth) -acrylate terminal groups and a molecular weight of 1000-10,000. In order to obtain good durability, aliphatic polyester urethanes are preferred.

Examples of such a prepolymer are Ebecryl® grades commercially available from UCB. Such species have a polyester backbone, which is linked to a hydroxyl-functional (meth) acrylate by means of a difunctional isocyanate. A large number of Ebecryl® types have been used in the present invention. These differ with regard to the polyester main chain, which can be made up of different monomers and in which, for example, additional urethane functions may also be present.

The cellulose derivative, which prevents oxygen inhibition in the mixture according to the invention, is preferably a cellulose ester and in particular cellulose acetate butyrate, cellulose acetate propionate or cellulose acetate succinate and is effective in an amount of 2-80 wt. % based on the prepolymer.

In order to obtain products with optimum mechanical properties, a reactive monomer can be incorporated into the mixture for the production of products according to the invention. The amount of the reactive monomer is at most 40 wt. %, based on the prepolymer. Preferably, this monomer is isobornyl acrylate.

The product according to the invention is very suitable in the form of a foil with a thickness of at most 200 µm. The cellulose derivative is preferably present in the mixture which cross-links to such a film in an amount of 5-30 wt. %, and preferably 15-25 wt. %, based on the prepolymer.

The invention also includes a method of manufacturing a film, wherein a mixture comprising a prepolymer with at least one polyester main chain, in which reactive ethylenically unsaturated groups are present, a cellulose derivative and a liquid diluent is applied as a layer to a release layer, the liquid diluent evaporates, the mixture cross-links into a foil and removes the release layer.

For the manufacture of the films according to the invention, the above-described mixture can suitably be applied to a release layer by known techniques, such as casting, spreading, etc. For this purpose, the diluent is added to the mixture.

As the diluent, a solvent, such as Dowanol PM® (propylene glycol methyl ether) or a mixture of solvents, such as, for example, Solvesso® (an aromatic distillation fraction) and butyl acetate or Solvesso and methyl ethyl ketone (MEK), may suitably be used. The mixture can be directly cross-linked or stored for some time. The shelf life of the mixture can be extended by keeping it at low temperature and / or by adding inhibitors.

The mixture can then be cross-linked (cured) by all conventional cross-linking methods, such as by irradiation with EB or UV or thermally. As indicated above, it is preferred to thermally cross-link the mixture in the presence of a peroxide initiator.

The mixture is then suitably cured at a temperature between 170 ° C and 210 ° C and for a time from 40 to 90 s. The initiator is suitably used in an amount of about 1-5% by weight, based on the prepolymer. Any conventional peroxide initiators can be used, such as bis (2-ethylhexyl) peroxydicarbonate (Perkadox® 16) or tert. butylperoxy-2-ethylhexanoate (Triganox® 21).

Commercial stabilizers may be included for high durability of the products of the present invention. The products have a high resistance to chemicals.

The invention further provides a self-adhesive foil, wherein the above-defined foil is provided with an adhesive layer.

The invention is illustrated by the following examples, which are not intended to limit the invention.

In the examples, all amounts are in parts by weight. The term pph refers to the number of parts per 100 parts of prepolymer.

example I

A mixture of 100 parts of Ebecryl 8804 (an aliphatic polyester urethane diacrylate oligomer from UCB), 28.8 parts of cellulose acetate butyrate (CAB 381.01) and 4 parts of Perkadox 16 initiator (bis (2-ethylhexyl) peroxydicarbonate) in Dowanol PM was a release layer applied in an amount of 100 g / m2 (solid content 60%). Then the solvent was evaporated at 50 ° C, after which the layer was cross-linked at 195 ° C for 60 s. This resulted in a foil with a thickness of about 60 µm. Likewise, films were made by replacing Ebecryl 8804 with Ebecryl 4835, Ebecryl RSX 89403, Ebecryl RSX 89462, Ebecryl RD 3/203, Ebecryl RD 3/204 and Ebecryl RD 5/203, respectively. The mechanical properties, elongation at break, 2% modulus, 13% modulus and tensile strength of the films obtained and of a comparative PVC film were determined and the results are shown in Table 1.

Example II

Following the same procedure as in Example 1, a mixture of 100 parts of Ebecryl 8804, 4 parts of Perkadox 16 and 20 parts of CAB 171-15 S was cured for 60 s at a temperature of 195 ° C. Likewise, films were made by replacing the CAB 171-15 S with CAB 381-01, CAB 551-001, CAB-SU 160 and CAP 482-20, respectively.

The mechanical properties of the films obtained were determined and the results are shown in Table 2.

Example III

Following the same procedure as in Example 1, a mixture of 100 parts of Ebecryl 8804, 4 parts of Perkadox 16 and three different amounts of CAB 381.01 was cured for 60 s at a temperature of 195 ° C. Likewise, films were prepared by replacing the CAB 381.01 in the above mixture with three different amounts of CAB 551.001 and CAP 482.20, respectively.

The mechanical properties of the films obtained were determined and the results are shown in Table 3.

Example IV

Following the same procedure as in Example 1, a mixture of 100 parts of Ebecryl 8804, 4 parts of Perkadox 16 and 21.8 pph CAB 381.01 was cured for 60 s at a temperature of 195 ° C. Likewise, films were prepared by adding different amounts of isobornyl acrylate to the above mixture. The mechanical properties of the films obtained were determined and the results are shown in Table 4.

Example V

Following the same procedure as in Example 1, a mixture of 100 parts of Ebecryl 8804, 21.8 parts of CAB

381.01 and 2.5 parts of Perkadox 16 cured for 60 s at a temperature of 195 ° C. Likewise, films were prepared with 2.5 parts of Perkadox R 370 (chemical composition unknown) and 2.5 parts of Triganox 21 (tert. Butylperoxy 2-ethylhexanoate), respectively. Correspondingly, films were prepared with 8.5 parts of Perkadox 16, Perkadox R 370 and Triganox 21, respectively. The mechanical properties of the films obtained were determined and the results are shown in Table 5.

Example VI

Following the same procedure as in Example 1, a mixture of 100 parts of Ebecryl 8804, 2.5 parts of Perkadox 16 and 23 parts of CAB 381.01 was cured for 40 s at a temperature of 195 ° C. Likewise, a mixture of 100 parts of Ebecryl 8804, 2.5 parts of Perkadox 16 and 28 parts of CAB 381.01 was cured for 66 s at a temperature of 195 ° C. The films obtained were provided with an acrylic adhesive to obtain self-adhesive films. A commercial transparent PVC film is included as a reference. Strips of these films with a width of 25 mm were pasted on painted panels. After 20 minutes, some of the strips were tested for adhesion to the panels by clamping them in a tensile testing machine and pulling the strips off the panels at an angle of 180 ° C at a speed of 200 mm / min. The force required for this is a measure of the adhesive strength. For determination of the resistance of the films to solvents, another portion of the strips was immersed in gasoline-like liquid containing 50 vol., 10 times for 10 s at 20-second intervals 24 hours after being pasted on the panels. % toluene, 30 vol. % iso-octane, 15 vol. % diisobutylene, 5 vol. % ethanol, and which has a temperature of 23 ° C. The strips were then rinsed with demineralized water and after 1 hour the strips were tested for adhesion to the panels in the manner described above. The force required to pull the strips from the panels before and after immersion in the gasoline-like liquid is shown in Table 6.

Example VII

According to the method as in example I, films were made from mixtures with Ebecryl 8804, Perkadox 16 and CAB 381.01. The amount of initiator was varied from 2.5 to 8.5 parts per 100 parts of Ebecryl 8804 and the amount of CAB 381.01 was varied from 23 to 33 parts per 100 parts of Ebecryl. The curing temperature was varied from 170 to 210 ° C and the curing time was varied from 40 to 90 s. The mechanical properties of the films obtained were determined and the results are shown in Table 7.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

Claims (13)

Product obtained by cross-linking a mixture comprising a multifunctional prepolymer with at least one polyester main chain, in which at least two reactive ethylenically unsaturated groups are present and a cellulose derivative. Product according to claim 1, characterized in that the prepolymer consists of a polyester urethane with terminal (meth) acrylate groups and a molecular weight of 1000-10,000. Product according to claim 1 or 2, characterized in that the cellulose derivative is a cellulose ester. The product according to claim 3, characterized in that the cellulose ester is cellulose acetate butyrate, cellulose acetate propionate or cellulose acetate succinate. Product according to any one of claims 1-4, characterized in that the cellulose derivative is present in the mixture in an amount of 2-80 wt. %, based on the prepolymer. Product according to any one of claims 1 to 5, characterized in that the mixture further contains a reactive monomer in an amount of up to 40 wt. %, based on the prepolymer. Product according to claim 6, characterized in that the reactive monomer is isobornyl acrylate. The product according to any one of claims 1 to 7, characterized in that the product is a foil with a thickness of at most 200 µm. Foil according to claim 8, characterized in that the cellulose derivative is present in an amount of 5-30 wt. %, based on the prepolymer. Film according to claim 9, characterized in that the cellulose derivative is present in an amount of 15-25 wt. %, based on the prepolymer. A method of manufacturing a film according to claim 8 or 9, wherein a mixture comprising a multifunctional prepolymer with at least one polyester main chain, in which at least two reactive ethylenically unsaturated groups are present, a cellulose derivative and a liquid diluent are coated on a release layer, the liquid diluent evaporates, the mixture cross-links into a foil, and the release layer is removed. 12. Process according to claim 11, characterized in that the mixture is cross-linked in the presence of a peroxide initiator. Self-adhesive foil consisting of a foil as defined in claim 8, 9 or 10 on which an adhesive layer is applied.