WO2003035787A1

WO2003035787A1 - Aqueous adhesive, method of applying an adhesive to a substrate and substrate for use in packaging

Info

Publication number: WO2003035787A1
Application number: PCT/NL2002/000683
Authority: WO
Inventors: Ronaldus Josephus Marie Linssen; Gerhardus Wilhelmus WOUTERS
Original assignee: Ligra B.V.
Priority date: 2001-10-26
Filing date: 2002-10-25
Publication date: 2003-05-01
Also published as: NL1019240C2

Abstract

The invention relates to an aqueous adhesive comprising rubber, a water-miscible cellulose derivative and a water-miscible co-solvent, in which the adhesive, in addition to the substances mentioned in the introduction, also contains one or more additives which ensure that the stability and adhesive power of the adhesive will remain substantially constant in time. The invention further relates to a substrate for use in packaging, which is provided with an adhesive as indicated above.

Description

AQUEOUS ADHESIVE , METHOD OF APPLYING AN ADHESIVE TO A SUBSTRATE AND SUBSTRATE FOR USE IN PACKAGING

Description

The invention relates to an aqueous adhesive comprising rubber, a water-miscible cellulose derivative and a water-miscible co- solvent. The invention further relates to a method of applying said adhesive to a substrate by screen-printing and to the substrate for use in packaging, which is provided with said adhesive.

From EP-A-0866840 (in the name of the present applicant) there is known a method of applying an aqueous adhesive to a substrate and a blister pack comprising said substrate, in which the adhesive is applied by screen-printing. Said known adhesive contains 40-60 wt.% of rubber, 0.2-8 wt.% of a water-mi scible cellulose derivative and 4-20 wt.% of a water-miscible co-solvent, in which the adhesive is applied to the substrate by screen-printing.

In practice it has appeared that the package formed on the basis of said substrate deteriorates in quality with the passage of time. After intensive research and many practical tests it has become apparent that the adhesive power of the substrate provided with adhesive can be retained through the addition of particular substances.

Consequently, the aqueous adhesive according to the invention is characterized in that in addition to the substances mentioned in the preamble, the adhesive further contains one or more additives which ensure that the stability and adhesive power of the adhesive will remain substantially constant in time.

Within the framework of the research into the deterioration in the quality of the adhesive, a study has been made of the effect of the temperature, the effect of the oxygen, the effect of the humidity level, the interaction of the components of the glue in the long term, the effect of the pressure applied in the preparation of the pressure- sensitive layer of glue, as well as the effect of the UV light on the dry layer of glue. It has become apparent from said study that in particular the effect of UV light on the dry layer of glue is important and that it causes the quality of the package to deteriorate after a prolonged period of time.

The determination of the effect of UV light on the dry layer of glue was carried out by exposing packages and dry layers of glue to be marketed to sunlight for a few months, as well as to 3000 W UV metal halogen lamps. Upon exposure to light from a UV metal halogen lamp for six hours at a distance of 1.5 , to light from a UV daylight lamp for seven hours at a distance of 2 cm and to sunlight, the adhesive power was found to have decreased in the case of exposure at right angles. From the aforesaid tests it appeared that UV light has an adverse effect. This effect can be alleviated through the addition of substances according to the invention, viz. pigments, and through the addition of combinations of a UV inhibitor and HALS (Hindered Amine Light Stab lizers) or through the addition of said substances individually.

It may furthermore be preferable for the adhesive to comprise a pigment. The nature and the amount of the pigments to be used will be further described hereinafter.

From US patent No 6,225,384 there are known stabilised adhesive compositions in which said stabilisation can be obtained through the addition of particular substances, among which UV light-absorbing substances. Surprisingly, however, the quality of the substrate and thus of the package can be improved when using the specific adhesive according to the invention through the addition to the the known adhesive of a substance which eliminates, or at any rate reduces, the effect of ultraviolet light, whilst so many other factors as mentioned before could have had an effect. According to the invention it has appeared to be possible to make a correct selection from the large number of substances that can be used in accordance with the aforesaid US patent. In particular the harmful effect of the lateral irradiation of UV-A and UV-B light leads to a degradation of the adhesive power of the adhesive that is already present on the substrate of the package. In order to prevent the effect of the UV light, a pigment-based UV filter has been designed. It is important in this connection that the UV light- filtering effect, the colour of the glue, the compatibility of the colour system with the glue, the specific weight of the pigments or colorants in connection with sedimentation, the fineness of the pigments and the colour-fastness of the pigments be taken into account.

From the study it has appeared that in particular yellow, red and orange pigments of organic and inorganic origin can be used. Both types exhibit a UV-filtering action, providing that the fineness of the dispersed pigments in the binder does not exceed 4 μm. This degree of dispersion can be obtained by grinding the pigment in a manner which is known per se until the desired fineness has been obtained. Furthermore it is possible to disperse the pigment by means of equipment that is known for this purpose, such as an attritor or a sand mill.

Organic pigments have a comparatively low specific weight of 0.95-1.1, which equals the specific weight of the binder or of the adhesive itself. As a result, the risk of sedimentation in the long term is small, in particular if the degree of fineness is lower than 4 μm. It is preferred to use the so-called "slurry" method when processing organic pigments, in which the deposited pigment from the reaction of two or more components in the aqueous phase has the maximum degree of fineness. By using a water displacement method, in which a major part of the water is substituted for a universal binder, high-quality aqueous pigment pastes exhibiting maximum degrees of fineness of 1-2 μm are obtained, as a result of which sedimentation is minimised, also in the long term.

It is in particular preferable to colour the adhesive composition, which has been colourless so far, yellow by means of a water-soluble yellow colorant. In a practical embodiment a yellow colo- rant in slurry form of the type diarilide yellow No 14 having a fineness of 1-2 μm is used, the risk of sedimentation of which is practically excluded. The pigment has a specific weight of 1.05, and it furthermore meets the legal requirements as regards toxicity, because such a colorant may also be incorporated in toys.

Further experiments have shown that the quantity of pigment additives in the adhesives as described in EP-A- 0866840 that have been used so far amounted to 0.5-15 wt.% for organic yellow, orange, magenta and red pigments. For similar pigments of inorganic origin said amounts were 1-45 wt.%, preferably 3-40 wt.%, and for water-soluble colorants said amounts were 0.2-10 wt.%, preferably 0.5-3 wt.%.

It must be considered when using the pigments and colorants that said substances must not have a negative effect as regards the relevant properties of the adhesive, such as the adhesive power, and as regards the application of the adhesive by screen-printing.

An example of a UV inhibitor is phenol -2-(2H benzoriazol-2- yl)-4-methyl-6-dodecyl .

An example of the HALS substance is bis(l. 2. 2. 6. 6- pentamethyl-4-piperidyl) sebacate and methyl -1. 2. 2. 6. 6-pentamethyl-4- piperidyl sebacate. The two substances can be used in a proportion of 1 : 1 and they must be emulsified in the mixture to be used. Polyoxyethyl sorbitan fatty acid ester can be used as an emulsifier.

The amounts of UV inhibitor present in the emulsion and in the HALS preparation were 88 wt.% and 90 wt.%, respectively. In a 1% addition of the UV inhibitor and the HALS preparation, the UV photosensi- tivity clearly decreased, whereas an addition of 2 wt.% resulted in the preservation of the adhesive power in the long term.

The addition of a substance selected from the group consisting of pigment, UV inhibitor and HALS component has made it possible to achieve a significant improvement of the quality of the adhesive that is applied to a substrate by screen-printing, so that the quality thereof will be preserved for a longer period of time.

Claims

1. An aqueous adhesive comprising rubber, a water-mi scible cellulose derivative and a water-mi scible co-solvent, characterized in that in addition to the substances mentioned in the preamble, the adhesive further contains one or more additives which ensure that the stability and adhesive power of the adhesive will remain substantially constant in time.

2. An aqueous adhesive according to claim 1, characterized in that the additive has been selected from the group consisting of UV inhibitor and HALS (Hindered Amine Light Stabilizers), or a combination thereof.

3 An aqueous adhesive according to any one or more of the preceding claims, characterized in that said adhesive furthermore comprises a pigment and/or a colorant.

4. An aqueous adhesive according to claim 3, characterized in that said adhesive contains 1-45 wt.% of inorganic pigments.

5. An aqueous adhesive according to claim 3, characterized in that said adhesive contains 0.5-15 wt.% of organic pigments.

6. An aqueous adhesive according to claim 3, characterized in that said adhesive contains 0.2-10 wt.% of a water-soluble colorant.

7. An aqueous adhesive according to claim 3, characterized in that said pigment is present in slurry form.

8. An aqueous adhesive according to claim 2, characterized in that UV inhibitor and HALS are each present in an amount of 0.05-6.0 wt.%, based on the total amount of adhesive.

9. An aqueous adhesive according to any one or more of the preceding claims, characterized in that the amount of pigment in slurry form is 0.5-15.0 wt.%, based on the total amount of adhesive.

10. A method of applying an adhesive to a substrate by screen- printing, characterized in that an adhesive as defined in claims 1 - 9 is used.

11. A substrate for use in packaging, which substrate is provided with an adhesive, characterized in that the substrate provided with the adhesive has been obtained by using a method as defined in claim 10.