AN AQUEOUS POLYMER DISPERSION FOR ADHESIVES

Abstract

The invention relates to aqueous polymer dispersions obtained by emulsion polymerization in the presence of a stabilizing 4system containing polyvinyl alcohols (PVOH). More specifically, the invention relates to adhesive formulations containing aqueous polymer dispersions, and to the use of said adhesive formulations as adhesives for cigarette making and packaging.

Claims

1. An aqueous polymer dispersion for use in mechanical adhesive applications, comprising: a monomer mixture comprising: a vinyl ester, a stabilizing system comprising polyvinyl alcohols and a free radical redox polymerization initiator system, wherein the amount of polyvinyl alcohols in said dispersion is between 6.6 wt. %-35 wt. % based on all the monomers in the dispersion, wherein said aqueous polymer dispersion is obtained by emulsion copolymerization of the monomer mixture, wherein said aqueous polymer dispersion further comprises copolymers, including: a vinyl acetate in an amount of between 50 wt % to 90 wt % of copolymers; and an ethylene in an amount from 1 wt % to 40 wt % of the total monomers.

2. The dispersion of claim 1, the dispersion has a solid content greater than or equal to 58 wt % based on said dispersion.

3. The dispersion of claim 1, wherein the dispersion has a viscosity that keeps greater than or equal to 2,000 mPa.Math.s as the shear rate increases continuously evenly from 0 to 800 s.sup.1 during the time from 0 to 300 s according to DIN 53019.

4. The dispersion of claim 1, wherein the Brookfield viscosity of the dispersion, measured at 25 C. using Brookfield viscometer RVDV-II+P with spindle #4 at 20 rpm, is greater than or equal to 2,000 mPa.Math.s.

5. The dispersion of claim 1, wherein greater than or equal to 48 wt % of said polyvinyl alcohols, baaed on the total amount of polyvinyl alcohols, are added in an initial feeding step and/or during a polymerizing process.

6. The dispersion of claim 5, wherein 100 wt. % of said polyvinyl alcohols, based on the total amount of polyvinyl alcohols, are added in the initial feeding step and/or the polymerizing process.

7. The dispersion of claim 1, wherein said dispersion is a copolymer of vinyl esters/ethylene dispersion.

8. The dispersion of claim 1, wherein said dispersion further comprises: 1) one or more low molecular weight partially hydrolyzed polyvinyl alcohol having a degree of hydrolysis of 85-95 mol % and a Hoeppler viscosity of 3-6 mPa.Math.s at a concentration of 4% by weight at 25 C.; and 2) one or more medium to high molecular weight partially hydrolyzed polyvinyl alcohols having a degree of hydrolysis of 85-95 mol % and a Hoeppler viscosity of 10-33 mPa.Math.s at a concentration of 4% by weight at 25 C. wherein the mass ratio of the low molecular w eight polyvinyl alcohols to the medium to high molecular weight polyvinyl alcohols is greater than or equal to 6.5.

9. The dispersion of claim 1, wherein dried portions of said aqueous polymer dispersion have a Tg of 12 C.18.5 C.

10. An adhesive according to claim 1, wherein said adhesive is used in the manufacturing of cigarettes.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0074] Test Methods

Solids Content

[0075] Solids content is measured by drying 1-2 g of the aqueous polymer dispersion at 105 C. for 1 hour, and got by using the weight of the dried substance divided by the weight of the dispersion.

[0076] Brookfield Viscosity

BFV 4#/20 rpm/25 C.

[0077] Glass Transition Temperature

[0078] The glass transition temperature (Tg) is determined according to ASTM E1356, by differential scanning calorimetry (DSC), using Mettler DSC820 with a liquid N.sub.2 cooling system. The test range is 80 C.130 C. at a heating rate of 10 C./min. The Tg value herein is the mid-point of the Tg measured of the dried substance of aqueous polymer dispersions.

[0079] HAAKE rheological curve

[0080] Equipment used: Thermo HAAKE, RheoStress 600;

[0081] Rotor type: Rotor C35/2, #222-1269, Cone with d-35 mm, angle 2 DEG;

[0082] Test temperature: 25 C.;

[0083] Test range: shear rate from 0 to 800 s.sup.1;

[0084] Shear rate change: the shear rate increases continuously linearly from 0 to 800 s.sup.1 during the time from 0 to 300 s, and by then decreases from 800 s.sup.1 to 0 in the same trend.

EXAMPLES

[0085] Preparation of Vinyl Acetate/Ethylene Copolymer Dispersions

Example 1

[0086] 735.91 g of a 20% aqueous solution of polyvinyl alcohol (BP 04/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 4-5 mPa.Math.s at a concentration of 4% at 20 C. and 119.04 g of a 10.3% aqueous solution of polyvinyl alcohol (BP 17/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 21-26 mPa.Math.s at a concentrations of 4% at 20 C. were added to water while stirring. And then formic acid was added to adjust the pH to approx.4.0, and 4.30 g of 1% aqueous solution of ammonium ferrous sulfate was further added and stirred well to get an initial aqueous solution.

[0087] The prepared initial solution and 1906.00 g of vinyl acetate are added into the reactor. After heated, 156.92 g of ethylene was added.

[0088] The initiators is added by dropping, wherein the oxidizer was 10% aqueous solution of t-butyl hydroperoxide, and the reducing agent was 5% aqueous solution of sodium ascorbate. The temperature in the reactor was gradually increased to 90 C.

[0089] 124.45 g ethylene and 476.50 g of vinyl acetate was added during heating. 227.27 g of a 13.3% aqueous solution of BP 04/88 were added. Redox was added after the complete of mononers and PVOH until the pressure was lower than 15 bar. After the reaction completed, the product was cooled down, mixed with bactericide and conditioning water before discharged.

Example 2

[0090] 127.68 g of a 20% aqueous solution of polyvinyl alcohol (BP 04/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 4-5 mPa.Math.s at a concentration of 4% at 20 C. and 703.38 g of a 10.3% aqueous solution of polyvinyl alcohol (BP 17/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 21-26 mPa.Math.s at a concentrations of 4% at 20 C. were added to water while stirring. And then formic acid was added to adjust the pH to approx. 4.0, and 7.98 g of 1% aqueous solution of ammonium ferrous sulfate was further added and stirred well to get an initial aqueous solution.

[0091] The prepared initial solution and 1704.30 g of vinyl acetate are added in the reactor. The reactor was heated, and 328.30 g of ethylene was added.

[0092] The initiators is added by dropping, wherein the oxidizer was 10% aqueous solution of t-butyl hydroperoxide, and the reducing agent was 5% aqueous solution of disodium hydroxysulfinoacetate (Bruggolite FF6M, purchased from Brggemann Chemical Incorporates). And the temperature in the reactor was gradually increased to 85 C.

[0093] With a controlled reactor pressure of 65 bar, 130.50 g ethylene and 495.90 g of vinyl acetate was added. After the reaction was completed, 884.70 g of a 35% aqueous solution of BP 04/88 was added at 50 C. When cooling down, the product is mixed with bactericide and conditioning water before discharged.

Example 3

[0094] Except for the change of the polyvinyl alcohol added after polymerization to 884.70 g of a 15% aqueous solution of BP 17/88, the aqueous polymer dispersion of Example 3 was prepared in accordance with the procedures of Example 2.

Example 4

[0095] Except for the omission of polyvinyl alcohol BP 17/88, and the change of BP 04/88 to a polyvinyl alcohol (BP 05/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 5-6 mPa.Math.s of at a concentration of 4% at 20 C. in the initial aqueous solution with the deionized water being reduced to 890.12 g; and the change of the main reactive functional solution to a 13.3% aqueous solution of BP 05/88, the aqueous polymer dispersion of Example 4 was prepared in accordance with the procedures of Example 1.

Example 5

[0096] Except for the change of BP 04/88 to a polyvinyl alcohol (BP 05/88, purchased from ChangChun PetroChemical, Co. Ltd.) having a degree of hydrolysis of about 86-89 mol % and a Hoppler viscosity of about 5-6 mPa.Math.s of at a concentration of 4% at 20 C. in the initial aqueous solution with the deionized water being reduced to 761.55 g, and the change of the main reactive functional solution to 302.26 g of a 10% aqueous solution of BP 05/88, the aqueous polymer dispersion of Example 5 was prepared in accordance with the procedures of Example 1.

Example 6

[0097] Except for the change of the polyvinyl alcohols to 674.60 g of a 20% aqueous solution of BP 04/88 and 238.09 g of a 10.3% aqueous solution of BP 17/88 in the initial aqueous solution with deionized water being reduced to 728.82 g, the aqueous polymer dispersion of Example 6 was prepared in accordance with the procedures of Example 1.

Comparative Example 1

[0098] Mainly Prepared According to Ex.2 with Much Lower PVOH dosage.

[0099] The additions of ingredients and the characteristics of corresponding aqueous polymer dispersions of Examples 1-6 are presented in Table 1:

TABLE-US-00001 TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 C. Ex. 1 Initial feeding BP 04/88 (g) 147.18 25.54 25.54 134.92 BP 05/88 (g) 147 147.18 BP 17/88 (g) 12.26 72.45 72.45 12.26 24.52 Polymerizing BP 04/88 (g) 30.23 30.23 BP 05/88 (g) 30.23 30.23 After BP 04/88 (g) 309.25 Polymerized BP 17/88 (g) 132.71 Tg ( C.) 15.0 2.4 3.3 15.3 15.1 18.5 1.6 Solids content (%) 59.85 51.09 52.43 59.69 59.43 59.74 55.33 Brookfield viscosity 3,450 4,570 3,720 2,385 3,570 3,980 5,200 (mPa .Math. s) (BVF, 4#/20 rpm/25 C.) Low molecular 14.40 4.60 0.12 Infinity 14.40 6.74 0.70 weight PVOHs/ med-high molecular weight PVOHs Total amount of 7.12 15.33 8.68 6.60 7.12 7.12 3.60 PVOHs/total amount of monomers (%)

[0100] HAAKE rheological curves of the aqueous polymer dispersions of Examples 1-6 and Comparative Example 1 can be seen from the FIG. 1.

[0101] in the rheological curve of Example 5, as the shear rate increases continuously from 789.2 s.sup.1 to 799.3 s.sup.1, the viscosities at the endpoints are respectively 2,186 mPa.Math.s and 2,091 mPa.Math.s, based on which the absolute value of the average rate of change in the viscosity of the aqueous polymer dispersion is 9.5;

[0102] in the rheological curve of Example 4, as the shear rate increases continuously from 708.1 5.sup.1 to 719.3 s.sup.1, the viscosities at the endpoints are respectively 2,620 mPa.Math.s and 2,453 mPa.Math.s, based on which the absolute value of the average rate of change in the viscosity of the aqueous polymer dispersion is 15;

[0103] in the rheological curve of Example 4, as the shear rate increases continuously from 791.4 s.sup.1 to 797.5 s.sup.1, the viscosities at the endpoints are respectively 2,456 mPa.Math.s and 2,281 mPa.Math.s, based on which the absolute value of the average rate of change in the viscosity of the aqueous polymer dispersion is 29.

[0104] Accordingly, it is believed that when the shear rate increases continuously from 600 s.sup.1 to 8005.sup.1 and the absolute value of the average rate of change of viscosity is less than or equal to 50, preferably, less than or equal to 30, the rheological curve of the aqueous polymer dispersion is relatively flat, and the viscosity of said aqueous polymer dispersion is relatively stable.

APPLICATION EXAMPLES

[0105] A combination for cigarette adhesives, which can be used in high speed tipping adhesives in the roller process to hold together the filter tip and one end of a paper-wrapped cylindrical cigarette rod.

[0106] Prepare an adhesive combination with the following composition and features:

TABLE-US-00002 Components Part by weight Aqueous polymer dispersions of Example 1 100 and Comparative Example 1 Antifoam agent 0.1 Plasticizer 2~3 PVOH, 20 wt. % aqueous solution (BP 17/88) 20 Water ~2 Solids content: ~50% Viscosity: ~5,000 mPa .Math. s (BFV 4#/20 rpm/25 C.)

[0107] Cigarette machines using cigarette adhesives containing the aqueous polymer dispersion of Comparative Example 1 can run at a maximum speed of only 8,000-9,000 cigarettes/min. There is splashing of adhesives when the speed is raised in a higher level.

[0108] Cigarette adhesives containing the aqueous polymer dispersion of Example 1 could be used on new high speed cigarette making machines, the run speed of which can reach up to 10,000-16,000 cigarettes/min. The quality of products is very good.

[0109] Meanwhile, the quality of products in cigarette cutting step is also good when using the cigarette adhesive containing Ex. 1, which might be the result of higher Tg of the dispersion in Ex. 1. Fewer products adhere to cutting blades.