Sealing lacquer for application in a printing process

Abstract

Sealing lacquer for application in a printing process, in particular for sealing packaging parts which can be peeled off from one another. The sealing lacquer has in particular a) 40 to 65 wt % solvent, b) 0 to 10 wt % styrene butadiene block copolymer, c) 8 to 12 wt % styrene alpha methylstyrene, d) 6 to 12 wt % linear and/or radial Tri-block (SBS) block, e) 0 to 10 wt % linear Di-Block (SB) block, f) 15 to 30 wt % polyester, and g) up to 3 wt % antioxidant. The sealing lacquer provides a seal that, whether the seal is opened by peeling, or the packaging is push-through packaging, provides a holding force exhibiting a strength until cohesion failure that is determined by the pressures and temperatures used during sealing.

Claims

1. A sealing lacquer for application in a printing process for sealing packaging parts which can be peeled off from one another, the sealing lacquer containing: a) 40 to 65 wt.-% of a solvent, b) 0 to 10 wt.-% of a styrene-butadiene block copolymer, c) 8 to 12 wt.-% of a styrene-alpha-methyl-styrene, d) 6 to 12 wt.-% of a linear and/or radial tri-block (SBS)-block, e) 0 to 10 wt.-% of a linear di-block (SBS)-block, f) 15 to 30 wt.-% of a polyester, and g) up to 3 wt.-% of a antioxidant.

2. The sealing lacquer according to claim 1, wherein 2-butanone and/or cyclohexanone is used as the solvent.

3. The sealing lacquer according to claim 1, wherein the sealing lacquer contains a statistical styrene-butadiene random block polymer ((SB)n-block).

4. The sealing lacquer according to claim 1, wherein the styrene-alpha-methyl-styrene copolymer of the sealing lacquer includes a random styrene-alpha-methyl-styrene copolymer.

5. The sealing lacquer according to claim 1, wherein the tri-block (SBS)-block is linear or radial.

6. The sealing lacquer according to claim 5, wherein the tri-block is supplied in each case alone or as a mixture, and that the tri-block includes parts of di-block and tri-block, wherein a tri-block proportion is greater than a di-block proportion.

7. The sealing lacquer according to claim 1, wherein the di-block is linear and includes parts of di-block and tri-block, wherein a di-block proportion is greater than a tri-block proportion.

8. The sealing lacquer according to claim 1, wherein the polyester has a glass transition temperature between 50 C. and +80 C.

9. The sealing lacquer according to claim 1, wherein the lacquer contains up to 3% by weight of phenolic antioxidant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The results obtained are shown graphically in the drawing.

(2) FIG. 1 shows the seal seam strengths [N/15 mm] of Formulation 1 from Table 1 or Example 1 from the text, applied to substrates 1), 3), 4), 6), and 7) from Table 2 versus PS over the sealing temperature in [ C.],

(3) FIG. 2 shows the seal seam strengths [N/15 mm] of Formulation 1 from Table 1 or Example 1 from the text, applied to substrates 1), 3), 4), 6), and 7) from Table 2 versus APET over the sealing temperature in [ C.],

(4) FIG. 3 shows the seal seam strengths [N/15 mm] of the comparative example (Example 2 of Table 3; Degalan VP 4311 E from Evonik Rhm) on A115/PET12 substrate and metPET 36 m, applied on the PET side, versus PS and APET over the sealing temperature in [ C.], and

(5) FIG. 4 shows the seal seam strengths [N/15 mm] of the comparative example (Example 3 of Table 3; Degalan VP 4322 E from Evonik Rhm) on A115/PET12 substrate and metPET 36 m, applied on the PET side, versus PS and APET over the sealing temperature in [ C.], and

(6) The seal strengths shown in the figures show that with the heat sealing lacquers according to the invention, good or better seal seam strengths can be achieved at lower sealing temperatures compared to those of the prior art. However, the sealing lacquers in FIGS. 1 and 2 have more desirable mechanical properties than the adhesive or partially adhesive fracture of the sealing lacquers shown in FIGS. 3 and 4 due to the cohesive fracture that occurs. Furthermore, it can be seen from Tables 2 and 3 that all comparative examples have a poorer adhesive strength and a poorer hot seam strength compared to the sealing lacquers according to the invention, which, due to the increased internal pressure from heating during sealing, is desired for the sealing. The goal according to the invention of a high seal seam strength with concurrent good peeling ability of the plate from the base, in conjunction with improved process properties, is thus fulfilled.

(7) The other lacquers according to the invention provide similar results to those of the lacquers according to the invention. The other comparative examples mentioned in the text even show inferior seal seam strengths. The best standard example was used for comparison.

(8) The terms used are:

(9) Solvent:

(10) As indicated in the example, non-polar and/or dipolar/aprotic solvents may be used. Applicable examples of inventively usable nonpolar solvents are liquid hydrocarbons such as n-pentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, iso-octane, special gasoline 80/110, with a disperse share of between 16 and 19 and a dipolar share near 0 and whose boiling range is between 60 C. and 110 C.

(11) Applicable examples of inventively usable dipolar/aprotic solvents are liquid esters or ketones such as ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, with a disperse share of between 15 and 17 and a dipolar share between 3 and 10 and whose boiling range is between 60 C. and 110 C.

(12) Styrene-Butadiene Block Copolymer/Styrene-Alpha-Methyl-Styrene:

(13) Copolymers of styrene, and -methyl-styrene and styrene-butadiene block copolymers.

(14) Inventively usable for the lacquer composition, are used as constituents B for sealing against polyolefinic containers, mainly unsaturated styrene-butadiene block copolymers and random styrene-butadiene copolymers. Styrene-butadiene block copolymers contain two different types of blocks or phases: The middle block is typically an olefinic or hydrogenated olefinic block, which preferably increases hot tack and adhesion. The two polystyrene end blocks form a phase which reduces the viscosity of the heat-sealing lacquer while increasing the stiffness of the heat-sealing lacquer upon cooling. The concentration and rheology of the styrene phase cause the cohesive properties of the heat-sealing lacquer, the heat resistance and the sealing temperature. The addition of high diblock styrene-butadiene block copolymers, i.e. styrene end phase and an olefinic end phase, together with the mid phase styrene-butadiene block-phase copolymers, increase internal adhesion and sealing against polyolefinic substrates.

(15) Linear and/or Radial Tri-Block/Linear Di-Block (SB)-Block/Di-Block/Tri-Block:

(16) Linear in the sense of the description and the Claims means that the co-monomers are arranged in a line. When using the term radial i.e. there, the comonomers are arranged branched in the chemical sense. The terms tri-block and di-block are to be understood as follows. Tri-block polymers consist of two endblocks (e.g., styrene) and a midblock (e.g., butadiene). Polymers of generally di-block character each consist of two units of an endblock (e.g., styrene) and an endblock (e.g., butadiene). Due to the polymerization process, both phases always occur next to one another in the case of the binders according to the invention.

(17) Polyester:

(18) The first high molecular weight, saturated, linear co-polyester CI which can be used according to the invention for the lacquer composition is a condensation product of aromatic dicarboxylic acids and non-branched short-chain aliphatic diols, but with neopentyl glycol as comonomer. However, this co-polyester is not suitable for alcoholic contents. The glass transition temperature (Tg) is 67 C. and the softening point is 155 C. The acid number is <3 mgKOH/g according to DIN EN ISO 3682 and the hydroxyl value is <9 mgKOH/g according to DIN 53 240. The average molecular weight (Mw) is about 20,000 g/mol.

(19) The second high molecular weight, saturated, slightly branched co-polyester C2 which can be used according to the invention for the lacquer composition is a condensation product of aromatic dicarboxylic acids and slightly branched long-chain aliphatic diols, without neopentyl glycol of high flexibility and adhesion. The advantage of this co-polyester is the use for alcoholic contents, e.g. wet hygienic towels. The glass transition temperature (Tg) is 40 C. and the softening point is 130 C. The acid number is <3 mgKOH/g according to DIN EN ISO 3682 and the hydroxyl value is <9 mgKOH/g according to DIN 53 240. The average molecular weight (Mw) is about 15,000 g/mol.

(20) Antioxidant:

(21) Effective antioxidants for the lacquer composition according to the invention may be selected from the family of substituted phenols. Which, provided with substituents that are large, voluminous in volume and not freely movable such as a tert. Butyl group, substituted benzotriazoles and substituted phosphates. E is an additive, an effective primary antioxidant from the group of sterically hindered phenols having a molecular weight of 531 g/mol and a melting range of 50-55 C. The density is 1.02 g/cm.sup.3.

(22) Statistics:

(23) Styrene moeties. These may be statistical, i.e. arranged in random order, or in blocks, i.r. arranged in 2 or 3 blocks in order.

(24) Suitable Stirrer:

(25) This selection is not critical; for the preparation of the base lacquer a mixing vessel with agitator is used, the agitator consisting of two geometric mixing elements, a shear element and a stirring element. The mixing vessel is not heated.

(26) Medium Speed/Elevated Speed:

(27) Slow stirring about 50 rpm, medium speed about 100 rpm, elevated speed about 150 rpm.

(28) High Molecular Weight and Partially Crystalline:

(29) High molecular weight, in a chemical sense, means an average molecular weight (Mw) of greater than 10,000 g/mol based on the respective polymer; a solid containing both crystalline and amorphous regions (domains) is referred to as partially crystalline. In the example of a co-polyester, the term high molecular weight means an average molecular weight of >15,000 g/mol and partially crystalline a degree of crystallization of 20-40%. Both terms are always to be regarded depending on the particular polymer and can change accordingly.

(30) TABLE-US-00002 TABLE 1 Various formulations of HSL in wt. % including sealing seam strengths against PS and APET (substrate AL15/PET12) Styrene- Di- alpha- Tri-Block Block Application Seal Strength (SB)n- methyl- Linear/Radial (SB)- Co- Amount Seal Strength PS APET Example Solvent Block styrene (SBS)-Block Block Polyester Antioxidant (g/m.sup.2) 160/180/200 C. 160/180/200 C. Formulation 1 43 5 10 8 (linear) 8 25 1 4 10/9/9 7.5/10/9 Formulation 2 60 0 10 10 (linear) 0 19 1 4 4/4.5/5 11/11/10 Formulation 3 60 0 10 10 (radial) 0 19 1 4 7/7.7/7.7 8/9/7 Formulation 4 45 0 10 8 (linear) 0 28 1 4 6/6/6.5 7.5/8/8 8 (radial) Formulation 5 43 5 10 8 (linear) 0 25 1 4 7/7/7.5 8/8.5/8 8 (radial)

(31) TABLE-US-00003 TABLE 2 Various substrates coated with HSL 1 from Table 1 and test results. In each case, the lacquer was applied to the polyester side. HF to Warm seam strength, Warm seam strength, substrate SNF vs. PS SNF vs. APET Fracture meas. as burst pressure meas. as burst pressure Films Formulation [N/15 mm] [0 N/15 mm] [0 N/15 mm] Pattern vs. PS cup [0 mbar] vs. APET cup [0 mbar] 1) A115/PET12 1 >10 8.0 7.6 cohesive 700 610 2) Transp. PET 1 >7 6.4 6.1 cohesive 590 600 23 m 3) Met. PET 23 m 1 >7 6.6 6.2 cohesive 590 670- 4) Transp. PET 36 m 1 >9 7.4 6.7 cohesive 590 590 5) Met. PET 1 >9 7.1 7.0 cohesive 560 560 36 m 6) Wite PET 1 >5 4.1 3.9 cohesive 490 500 50 m 7) Transp. PET 1 >5 4.0 3.8 cohesive 480 490 50 m

(32) TABLE-US-00004 TABLE 3 Test results with standard HSL materials. In each case, the heat-seal lacquers were applied to the polyester side. SNF vs. Warm seam strength, Warm seam strength, meas. as Standard HF to SNF vs. PS APET Fracture meas. as burst pressure burst pressure vs. APET cup Films Materials substrate [0 N/15 mm] [0 N/15 mm] Pattern vs. PS cup [0 mbar] [0 mbar] A115/PET12 1 >7 7.0 6.9 adhesive 560 540 Met. PET 36 m 1 >7 6.8 7.1 adhesive 530 570 A115/PET12 2 >4 4.0 4.0 partially 500 400- adhesive Met. PET 36 m 2 >4 4.0 4.0 adhesive 360 340 A115/PET12 3 >4 8.7 8.9 adhesive 520 430 Met. PET 36 m 3 >4 8.8 9.7 adhesive 340 240 Transp. 3 >4 9.4 9.3 adhesive 350 330 PET 50 n A115/PET12 4 >6 6.2 6.0 adhesive 460 480 A115/PET12 5 >6 8.1 8.0 partially 500 480 adhesive A115/PET12 6 >6 8.4 8.0 adhesive 450 450