IMPROVED HOT-MELT ADHESIVE FOR MANUFACTURING DISPOSABLE HYGIENE PRODUCTS

Abstract

1) Hot melt adhesive composition comprising: a) from 5% to 50% of a thermoplastic polymer (A) selected from styrene block copolymers and polyolefins; b) from 15% to 60% of a tackifying resin (B); c) from 5% to 30% of a plasticizer (C); and d) from 0.1% to 10% of a salt (D) of a hydroxylated fatty acid comprising from 8 to 24 carbon atoms.

2) Process of manufacturing a laminate, preferably a disposable nonwoven absorbent article, implementing the hot melt adhesive composition.

3) Process for cleaning the laminating device fouled by solid deposits of the hot melt

adhesive composition, comprising their manual removal by the operators at room temperature.

Claims

1. Hot melt adhesive composition comprising: a) from 5% to 50% by weight of at least one thermoplastic polymer (A) selected from styrene block copolymers (SBC) and polyolefins; b) from 15% to 60% by weight of at least one tackifying resin (B); c) from 5% to 30% by weight of at least one plasticizer (C) selected from a naphthenic oil, a paraffinic oils, polyisobutylene, a benzoate ester, a wax and an acrylic or carboxylic acid modified wax; and d) from 0.1% to 10% by weight of a salt (D) of a hydroxylated fatty acid comprising from 8 to 24 carbon atoms.

2. Hot melt adhesive composition according to claim 1, characterized in that the thermoplastic polymer (A) is a linear triblock styrene-butadiene-styrene copolymer (SBS).

3. Hot melt adhesive composition according to claim 1, characterized in that the thermoplastic polymer (A) is a copolymer of ethylene and α-olefin monomers.

4. Hot melt adhesive composition according to claim 1, characterized in that the tackifying resin (B) is selected among: (a) natural and modified rosins; (b) glycerol and pentaerythritol esters of natural and modified rosins; (c) polyterpene resins; (d) phenolic-modified terpene resins; (e) aliphatic petroleum hydrocarbon resins (C5) having a Ring and Ball softening point of from about 60° C. to 140° C., and the corresponding hydrogenated derivatives; (f) aromatic petroleum hydrocarbons resins (C9) having Ring and Ball softening point of from about 60° C. to 140° C., and the corresponding hydrogenated derivatives; (g) aliphatic and/or aromatic petroleum resins (C5/C9) having a Ring and Ball softening point of from about 60° C. to 140° C., and the corresponding hydrogenated derivatives.

5. Hot melt adhesive composition according to claim 1, characterized in that the softening point of the tackifying resin (B) lies in the range from 90° C. to 125° C.

6. Hot melt adhesive composition according to claim 1, characterized in that the hydroxylated fatty acid is ricinoleic acid.

7. Hot melt adhesive composition according to claim 1, characterized in that the salt (D) of hydroxylated fatty acid is a metallic salt with a melting point less than 120° C.

8. Hot melt adhesive composition according to claim 1, characterized in that the salt (D) of hydroxylated fatty acid is Zinc or Calcium ricinoleate.

9. Hot melt adhesive composition according to claim 1, characterized in that it comprises: a) from 15% to 45% by weight of the thermoplastic polymer (A); b) from 20% to 60% by weight of the tackifying resin (B); c) from 15% to 25% by weight of the plasticizer (C); and d) from 3% to 10% by weight of the salt (D) of hydroxylated fatty acid.

10. Process of manufacture of the hot melt adhesive composition such as defined in in claim 1, comprising at least a step of mixing and heating at a temperature ranging from 140° C. to 170° C. the ingredients of the hot melt adhesive composition, at least for a period of time long enough to melt the tackifying resin(s) (B) and the thermoplastic polymer(s) (A).

11. Process of manufacturing an assembly product comprising: a step (i) of heating at a temperature ranging from 130° C. to 180° C. the hot melt adhesive composition such as defined in claim 1, for at least a period of time long enough to render said hot melt adhesive composition liquid enough to be applied on a substrate, then a step (ii) of coating said composition on a first substrate, step a step (iii) of putting into contact the coated surface of the first substrate with the surface of a second substrate, so as to form an adhesive joint bonding the two substrates.

12. Process of manufacturing according to claim 11, characterized in that each substrate is chosen independently from one another among nonwoven fabric, tissue, absorbent fluff, super absorbent polymer (SAP), composite material, elastomeric or non elastomeric plastics.

13. Assembly product comprising at least two substrates bonded by at least one hotmelt adhesive composition such as defined in claim 1.

14. Assembly product according to claim 13, characterized in that it is a disposable nonwoven absorbent article.

15. Process for cleaning the metallic parts of a laminating device fouled by solid deposits of the hot melt adhesive composition such as defined in claim 1, said process comprising the manual removal of said deposits by the operators at room temperature.

Description

EXAMPLE 1 (REFERENCE)

[0223] The composition in Table 1 is prepared by simple mixing of its ingredients as pointed out above in the detailed description of the invention.

[0224] This adhesive composition is submitted to the following tests and measurements.

[0225] A. Loop Tack Test on Stainless Steel:

[0226] The loop tack of the adhesive composition is determined by the loop tack test on stainless steel described in FINAT Test Method No. 9.

[0227] A.1. Preliminary Preparation of a Support Coated by the Adhesive Composition of Example 1:

[0228] Use is made as a laminating device of a machine operating continuously at a line speed of approximately 20 m/minute, which machine is sold by ACUMETER Laboratory Inc. In this machine the coating nozzle is a slot nozzle.

[0229] The support employed is a 50 μm thick PET film (Mylar®) with a width of 15 cm.

[0230] The adhesive composition is heated in the melting pot at a temperature of 149° C., then is coated on the PET film as a 5 cm wide adhesive layer with a coating weight of 20 g/m.sup.2, which is centered on said PET film. A 15 cm wide release liner is then put into contact with the coated surface of the PET film by means of a nip roll applying a pressure of 1 bar.

[0231] A rectangular strip measuring 2.5 cm by 17.5 cm is cut out in the coated central area of the laminate, then is conditioned overnight at 23° C. and 50% relative humidity.

[0232] A2. Implementation of the FINAT Test Method No. 9:

[0233] The release liner is then removed from this strip and its two ends are joined together to form a loop, the adhesive layer of which is facing outward.

[0234] The two joined ends are placed in the movable j aw of a tensile testing machine capable of imposing a rate of displacement of 300 mm/minute along a vertical axis, with the possibility of forming a forward-and-backward movement. The lower part of the loop placed in the vertical position is firstly put into contact with a horizontal stainless steel plate measuring 2.5 cm by 3 cm over a square area measuring about 2.5 cm per side.

[0235] Once this contact has occurred, the displacement direction of the jaw is reversed.

[0236] The loop tack is the maximum value of the force needed for the loop to be completely debonded from the plate, and is measured in Newton (N).

[0237] It is reported in Table 2 below.

[0238] B. Peel Test on a Laminate Comprising a PE and a Non Woven PP:

[0239] B.1. Preliminary Preparation of a Laminate Bonded by the Adhesive Composition of Example 1:

[0240] Use is made, as a laminating device, of a machine operating continuously at a line speed of approximately 200 m/minute, which machine is sold by NORDSON under the name of Coater CTL 4400.

[0241] In this machine, the coating nozzle is a spray nozzle (NORDSON Signature™).

[0242] The two substrates employed are: [0243] a 20 μm thick PE film which has been previously laminated on a non woven sheet to give a cloth like back-sheet and which has a width of 20 cm, and [0244] a 14 g/m.sup.2 spunmelt nonwoven sheet of the same width, which is composed of fibers of polypropylene (PP).

[0245] These two substrates are packaged as a reel with a width of 20 cm.

[0246] The adhesive composition is heated in the melting pot at a temperature of 149° C.

[0247] It is then coated at 2 different coating weights of approximately 3 g/m.sup.2 and 5 g/m.sup.2 on the PE side of the cloth like back-sheet film. The coating pattern is a 2.54 cm wide non continuous layer made of adhesive fibers, which is centered on said PE film and along an axis which is perpendicular to the axis of the reel.

[0248] The nonwoven (PP) sheet is then put into contact with the coated surface of the PE film by means of a nip roll applying a pressure of 1 bar.

[0249] B.2. Peel:

[0250] The assembly obtained is then packaged as a reel and left for 24 hours at ambient temperature and at 50% relative humidity.

[0251] A rectangular strip measuring 2.54 cm by approximately 10 cm is then cut out in the coated central area of the laminate.

[0252] The two individual substrates are separated, starting from one end of the above rectangular strip (as a test specimen) and over approximately 2 cm.

The two free ends thus obtained are fixed to two clamping devices respectively connected to a stationary part and a movable part of a tensile testing device which are located on a vertical axis.

[0253] While a drive mechanism communicates, to the movable part, a uniform speed of 300 mm/minute, resulting in the separation of the two substrates, the separated ends of which are gradually displaced along a vertical axis while forming an angle of 180°, the stationary part, connected to a dynamometer, measures the force withstood by the test specimen thus held.

[0254] The result for each coating weight, corresponding to the peel after 24 hours at ambient temperature, is expressed in N.

[0255] The peel after, respectively, 1 month at ambient temperature and 1 month at a temperature of 55° C., is measured by repeating the above protocol except that the assembly obtained after lamination is left during the respective time at the corresponding temperature.

[0256] The results are reported in Table 2 below.

[0257] C. Shear Test on a Laminate Comprising 2 Non Woven PP:

[0258] The level of cohesion of the laminated assembly is also evaluated by the shear test, the principle of which consists of the determination of the force necessary for the separation by shear of two substrates bonded by the adhesive composition.

[0259] C.1. Preliminary Preparation of a Laminate Bonded by the Adhesive Composition of Example 1:

[0260] Use is made, as a laminating device, of a machine operating continuously at a line speed of approximately 200 m/minute, which machine is sold by NORDSON under the name of Coater CTL 4400.

[0261] In this machine, the coating nozzle is a slot nozzle, NORDSON Slot™.

[0262] The two substrates employed are identical and consist of a 40 g/m.sup.2 melt blown nonwoven sheet with a width of 20 cm composed of fibers of polypropylene (PP).

[0263] These two identical substrates are packaged as a reel with a width of 20 cm.

[0264] The adhesive composition is heated in the melting pot at a temperature of 149° C., then is coated on 2 cm from the right edge of the first substrate, resulting in the deposition over said edge of a continuous layer with a width of 1.5 cm corresponding to an amount of approximately 15 g/m.sup.2, which layer is positioned perpendicular to the axis of the reel.

[0265] The second substrate is then laminated over the first substrate by means of a nip roll applying a pressure of 1 bar, in such a way that the adhesive layer is 2 cm from its left edge.

[0266] C2. Shear:

[0267] The assembly obtained is then packaged as a reel and left for 24 hours at ambient temperature and at 50% relative humidity.

[0268] The laminated substrates with a total width of about 35 cm and assembled by the 1.5 cm wide coated region are then cut out in the cross direction, so as to obtain a test specimen of rectangular shape with a length of approximately 35 cm and a width of 2.54 cm

[0269] The first substrate of the specimen is then hung secure in an oven at 37.8° C., while a 500 g weight is attached to the secondary substrate.

[0270] The time after which the assembly fails, corresponding to the shear after 24 hours at ambient temperature, is recorded in minutes.

[0271] The shear after 1 month at ambient temperature is measured by repeating the above protocol except that the assembly obtained after lamination is left during the corresponding time and temperature.

[0272] The results are reported in Table 2 below.

[0273] D. Viscosity Change Test:

[0274] Initial viscosity of the adhesive composition is measured at a temperature of 149° C. in accordance with ASTM D-3236 using a Brookfield Thermosel viscometer and a number 27 spindle. The spindle speed was adjusted so that the percent torque was between 45% and 90%. The results are reported in centipoise (cP).

[0275] Then, 200 grams of the adhesive composition is placed in a 400-ml glass jar and covered by an aluminum foil.

[0276] The jar is aged at 149° C. for 72 hours, in order to simulate adhesive aging in the melting tank.

[0277] A 10 g sample of the adhesive composition is removed at various times (24 h, 48 h, 72 h) during aging and the viscosity is measured at a temperature of 149° C. using the same method as for the initial viscosity.

[0278] The viscosity change at the aged time (or Final viscosity) is calculated according to the following equation and is expressed in percent:

Viscosity change=((Final viscosity−Initial viscosity)*100/(Initial viscosity))

[0279] The result is reported in Table 2 below.

EXAMPLE 2 (ACCORDING TO THE INVENTION)

[0280] Example 1 is repeated with the composition of example 2 shown in Table 1.

[0281] The results for the loop tack test, the peel test, the shear test and viscosity change are reported in Table 2 below.

[0282] One can observe a very significant drop (by a factor 4) of the room temperature tack on stainless steel, by reference with Example 1, which shows that the hot melt adhesive composition has a strongly reduced adhesion on metallic substrates.

[0283] The results of peel and shear are comparable to those obtained for the reference example 1, showing in particular a strong adhesion on polymeric substrates.

[0284] With respect to the viscosity change, it appears that the composition of example 2 is just as stable as the composition of reference example 1, making it just as suited for remaining in a coater melting tank during up to three days.

EXAMPLE 3 (REFERENCE)

[0285] The composition in Table 1 is prepared by simple mixing of its ingredients as pointed out above in the detailed description of the invention.

[0286] This adhesive composition is submitted to the loop tack test on stainless steel, the peel test, the viscosity change test such as previously described.

[0287] The results are reported in Table 2 below.

[0288] This adhesive composition is also submitted to the following test.

[0289] E. Test of Delamination from an Aluminium Foil:

[0290] E.1. Preliminary Preparation of a Laminate Bonded by the Adhesive Composition of Example 3:

[0291] The protocol of A.1. above is repeated by simply replacing the release liner by an aluminium foil with a thickness of 20 μm.

[0292] E.2. Peel:

[0293] The peel measurement is then implemented as described above in B.2.

[0294] The result, corresponding to the delamination from aluminium foil, is expressed in N.

[0295] It is reported in Table 2 below.

EXAMPLE 4 (ACCORDING TO THE INVENTION 1)

[0296] Example 3 is repeated with the composition of example 4 shown in Table 1.

[0297] The results of the loop tack test, the delamination from aluminium foil test, the peel test and the viscosity change test are reported in Table 2 below.

[0298] One can observe for the loop tack on stainless steel a significant drop (by a factor 3), with respect to reference example 3. One can also observe a significant drop (by a factor of 2) of the force necessary to delaminate from the aluminium foil, by reference with Example 3. These two results show that the hot melt adhesive composition has a strongly reduced adhesion on metallic substrates.

[0299] The results of peel for each of the 2 coating weights are comparable to those obtained for the reference example 3, showing in particular a strong adhesion on polymeric substrates.

[0300] With respect to the viscosity change, it appears that the composition of example 4 is just as stable as the composition of reference example 3, making it just as suited for remaining

in a coater melting tank during up to three days.

TABLE-US-00001 TABLE 1 Exam- Exam- ple 1 Exam- ple 3 Exam- Ingredients (ref.) ple 2 (ref.) ple 4 (A) KRATON ® D1152 ES — — 18.7 17.8 (A) INFUSE ® 9807 11.7 11.1 — — (A) AFFINITY ® GA 1900 11   10.5 — — (B) QUINTONE ® DX390N — — 30   28.6 (B) ESCOREZ ® 5600 — — 14.2 13.5 (B) ESCOREZ ® 5400 — — 14.1 13.4 (B) SUKOREZ ® SU210 55.1 52.5 — — (C) NYFLEX ® 223 21.3 20.3 22.5 21.4 (D) Zinc ricinoleate —  4.8 —  4.8 (F) IRGANOX ® 1010  0.9  0.8  0.5  0.5

TABLE-US-00002 TABLE 2 Example 1 (ref.) Example 2 Example 3 (ref.) Example 4 Loop tack on stainless steel 8.3 2.0 22.5 6.6 (N) Delamination from NT* NT* 11.2 5.6 aluminium foil Peel (N) Coating weight 3 5 3 5 3 5 3 5 (g/m.sup.2) after 24 hours at 1.42 1.7 1.48 2.14 1.1 2.48 1.13 2.39 ambient temperature after 1 month at 1.16 2.18 1.30 2.46 NT* 2.2 NT* 2.02 ambient temperature after 1 month at 0.88 1.55 0.85 1.57 NT* NT* NT* NT* 55° C. Shear after 24 hours at 6.5 7.5 NT* NT* (minutes) ambient temperature after 1 month at 9.3 16.5 NT* NT* ambient temperature Viscosity at 24 hours −0.9 +2 −5.5 −5.7 change (%) at 48 hours +1.8 +1.4 −13 −10.7 at 72 hours +0.9 +0.85 −18 −19.2 *NT means Not Tested