Residuelessly redetachable contact-adhesive sheetlike structures

Abstract

Residuelessly redetachable contact-adhesive sheet-like structures wherein are provided approximately calotte-shaped bonding sites which are up to about 600 μm in diameter at the base where the calottes stick to the sheet-like structure and which are produced by screen or gravure printing using high-solids dispersion of adhesive substance.

Description

EXAMPLE 1

A 15-liter-capacity polymerization apparatus equipped with a stirrer, a reflux condenser, a temperature sensor, a nitrogen inlet tube and a metering device is charged, with the oxygen of the air has been displaced by N₂ with 3.00 kg of 2-ethylhexyl acrylate, 0.134 kg of acrylic acid, 0.120 kg of butanediol monoacrylate, 0. 100 kg of butanediol diacrylate, 0.020 kg of tetrabromomethane, 0.050 kg of anionic emulsifier (the sodium salt of an ethoxylated and sulfonated nonylphenol) and 5.00 kg of deionized water. The contents are heated with stirring to 76°C C. 10 g of ammonium peroxodisulfate dissolved in 50 g of H₂O are then metered in. After the polymerization has started the reaction material is held at a temperature of 84°C-86°C C. After the exothermic reaction has died down the temperature is adjusted to 80°C C.

After a reaction time of 40 minutes, 125 g of 25% strength aqueous ammonia solution, 2.5 kg of 2-ethylhexyl acrylate and a further 10 g of ammonium peroxodisulfate are added.

The polymerization is complete after a total reaction time of 6 hours.

The resultant polymer dispersion has the following data:

	Solids content:	54%	Viscosity
		Shear stress T
	Viscosity at 25°C C.:	$\left(\frac{\mathrm{dvn}.}{{\mathrm{cm}}^2}\right)$	$\left(\frac{\mathrm{dvn}.\⁢\sec .}{{\mathrm{cm}}^2}\right)$
		2.2 × 103	1.3 × 105
		2.5 × 103	2.8 × 104
		4.0 × 103	9.4 × 103
	Surface tension:	55 dyn/cm 25°C C.

A contact -adhesive sheetlike structure having calottes of the type defined is prepared as follows:

This acrylate dispersion is applied in a continuous manner in a film thickness of 1-20 g/cm², based on dry substance, to paper (or a nonwoven or a plastics sheet) by gravure or screen printing.

Technical conditions:
	Carrier web speed	about	10-100	m/min
	Screen geometry	about	40-100	mesh
	Blade setting	about	1.5-30	min
	Blade thickness	about	150-300	μm
	Contact	about	2-6	(mm)

The coat of adhesive is subsequently dried in a convection drying duct of conventional design to such an extent that it can be wound into the form of a roll without problems.

Claims

1. A residuelessly redetachable contact-adhesive sheetlike structure wherein are provided approximately calotte-shaped bonding sites which are up to about 600 μm in diameter at the base where the calottes stick, to a surface of the sheetlike structure and wherein the sites are completely isolated from each other on the surface and which are produced by screen or gravure printing using high-solids dispersions of adhesive substances.

2. A contact-adhesive sheetlike structure as claimed in claim 1 wherein the adhesive used has high surface tension, adhesivity, film-forming properties and elastomeric properties.

3. A contact-adhesive sheetlike structure as claimed in claims 1 and 2 wherein the adhesive used is based on (meth)acrylic acid esters with or without small proportions of other monomer units.

4. A contact-adhesive sheetlike structure as claimed in any one of claims 1-3 claim 1 wherein the dispersions used are aqueous dispersions, or organosols or plastisols.

5. A contact-adhesive sheetlike structure as claimed in claim 4 wherein the aqueous dispersions used are concentrated thixotropic contact-adhesive dispersions having a solids content of 55-65% by weight.

6. A contact-adhesive sheetlike structure as claimed in any one of claims 1-5 claim 1 wherein the base diameter of the calotte-shaped bonding sites is 80-500, in particular 100-400 μm.

7. A contact-adhesive sheetlike structure as claimed in any one of claims 1-6 claim 1-6 wherein the bonding sites are subsequently crosslinked.

8. A contact-adhesive sheetlike structure as claimed in claim 7 wherein the bonding sites are subsequently cross linked by electron beam.

9. A contact-adhesive sheetlike structure as claimed in any one of claims 1-8 claim 1 which has the most suitable geometric arrangement and number (per unit area) of bonding sites for the proposed adhesive attachment.

10. A residuelessly redetachable adhesive article comprising a substrate bearing a plurality of mechanically applied approximately calotte-shaped adhesive sites, each site having a base in direct contact with a surface of the substrate and which is up to 600 μm in cross-base dimension and wherein the sites are completely isolated form each other on the surface of the substrate.

11. The article according to claim 10, wherein each base is from 80 to 500 μm in cross-base dimension.

12. The article according to claim 11, wherein each base is from 100 to 400 μm in cross-base dimension.

13. The article according to claim 10, wherein the height of each site is from about 30 to 600 μm.

14. The article according to claim 10, wherein each base is from about 30 to 600 μm in cross-base dimension.

15. A method of making a residuelessly redetachable adhesive article, comprising the steps of providing a substrate and mechanically applying a plurality of approximately calotte-shaped adhesive sites on a surface of the substrate each site having a base up to 600 μm in cross-base dimension and wherein the sites are completely isolated from each other on the surface of the substrate.

16. The method according to claim 15, wherein the step of mechanically applying comprises applying a high-solids dispersion of contact adhesives and drying.

17. The method according to claim 16, wherein the step of mechanically applying comprises gravure printing.

18. The method according to claim 16, wherein the step of mechanically applying comprises screen printing.

19. The method according to claim 15, wherein the step of mechanically applying a high solids dispersion comprises applying concentrated thixotropic contact-adhesive aqueous dispersions having a solids content of 55 to 65% by weight.

20. The method according to claim 15, wherein each site is applied with a base from about 30 to 600 μm in cross-base dimension.