AU726971B2

AU726971B2 - Use of an adhesive dispersion for gumming in inserting machines

Info

Publication number: AU726971B2
Application number: AU43013/97A
Authority: AU
Inventors: Ethel Abrahams; Hartmut Busching; Horst Buxhofer; Klaus Friedrich; Ralf Gossen; Werner Schaper
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1996-09-10
Filing date: 1997-09-04
Publication date: 2000-11-30
Anticipated expiration: 2017-09-04
Also published as: AU4301397A; WO1998011171A1; DK0925337T3; ATE212371T1; ES2171927T3; DE59706195D1; EP0925337B1; EP0925337A1; DE19739190A1

Abstract

In order to facilitate the production and improve the drying and adhesive qualities of traditional rubber polyvinyl acetate dispersion based adhesives, the concentration of protective colloids polyvinyl alcohol and starch ether is increased and no aqueous polymer solution of polyvinyl alcohol or dextrine is added.

Description

Use of an Adhesive Dispersion for Gumming in Inserting Machines This invention relates to use of an adhesive based on a polyvinyl acetate dispersion stabilised with protective colloids and to its production.

There are numerous publications relating to the production of polyvinyl acetate dispersions and their use. DE 33 23 851 describes an aqueous polymer dispersion of vinyl esters and optionally 50wt% of other ethylenically unsaturated compounds in the presence of starch ethers as protective colloid. In addition, other protective colloids, for example polyvinyl alcohol, may be added. However, these auxiliaries are preferably added, if at all, to the final dispersion on completion of the polymerisation process because, otherwise, they can often interfere undesirably with the polymerisation process or may undesirably modify the products. These known dispersions are used as such for the production of adhesives, especially for paper and films, and for the waterproof gluing of wood. However, they are preferably used for the production of redispersible polymer powders for the 15 preparation of wallpaper adhesive. There is no reference to their use as a a0 gumming adhesive.

"":Gumming is understood to be the coating of a substrate with a waterreactivatable adhesive. The substrate is generally a water-absorbing product, more particularly of paper or paperboard. It may be used, for example, as a postage 20 stamp, an envelope, a label, an adhesive strip, etc. The gumming adhesive is applied to the substrate in liquid form and then dried, losing its tackiness in the process. It is only when moistened with water that it becomes tacky again.

Gumming adhesives are normally based, for example, on gluten or starch derivatives (dextrin). However, fully synthetic polymers, for example polyvinyl alcohol and polyvinyl acetate, may also be used.

The formulation of gumming adhesives based on a polyvinyl acetate 9 dispersion is the subject of DD 275 069. According to this document, an aqueous solution of polyvinyl alcohol and, preferably, glycerol have to be added to the vinyl acetate dispersion. The remoistenable adhesive has the following composition by weight: 50 to 60% of a 20% polyvinyl alcohol solution, 40 to 50% of a polyvinyl acetate dispersion and 0 to 5% of glycerol. The glycerol acts as plasticiser while the polyvinyl alcohol improves reactivation by moisture. Accordingly, the production of a gumming adhesive is complicated because the auxiliaries are added in a separate process step. In addition, only some, but not all, of the requirements a gumming adhesive is expected to meet are satisfied to the required extent. This applies in particular to the stay-flat behaviour of the gummed paper, to its blocking resistance and to the setting time after remoistening.

Accordingly, the problem addressed by the present invention was to provide a LIC> gumming adhesive which would be easy to produce, which would dry more quickly L.fter application of its solution and which would become tacky again more quickly C04421 after moistening, but which would be largely resistant to blocking. In broad terms, the problem addressed by the invention was to provide a gumming adhesive with improved production, application and performance properties.

The solution to this problem is essentially based on the fact that, to produce the gumming adhesive, an aqueous polymer solution, especially a solution of polyvinyl alcohol and starch ether, is not added to the polyvinyl acetate dispersion, instead the polyvinyl acetate dispersion is prepared under particular conditions, among which the type and quantity of protective colloid used are of particular importance. Preparation of the polyvinyl acetate dispersion under particular conditions results in a gumming adhesive with a solids content of 50 to based on a stabilised polyvinyl acetate dispersion which is characterised by the following components: A) 35 to 45wt%, based on the adhesive, of a copolymer of vinyl acetate and 25 to based on the monomers, of at least one ester of fumaric acid, maleic acid, acrylic acid and/or methacrylic acid, the alkyl chain being linear or branched and having from 4 to 18 and, more particularly, from 4 to 8 carbon atoms, B) at least one protective colloid consisting of a) 15 to 30wt%, and, more particularly, 15 to 25wt%, based on the adhesive, of at least nonionic starch ether and b) 0 to 12wt%, more particularly 8 to 12wt% and, above all, 10.5 to 12wt% based on the adhesive, of polyvinyl alcohol.

Suitable "nonionic starch ethers" are, in particular, hydroxyalkyl ether starches, for example hydroxyethyl, hydroxypropyl and hydroxybutyl ether starches.

The alkyl chains contain from 2 to 8 carbon atoms and, more particularly, from 2 to 4 carbon atoms. Both degraded starches, for example starches degraded by acidic hydrolysis, and native starches may be used as starting products for the starches mentioned. In general, no particular requirements have to be satisfied in selecting S these starting products. Thus, virtually any starch of vegetable origin, for example corn starch, wheat starch, potato starch, tapioca starch, rice starch, sago starch and millet starch, may be used. Basically, hydroxyalkylation is a known process and, for this reason, need not be described in any further detail here. The degrees of substitution are also not crucial to the success of the process and, in many cases, degrees of substitution of about two are sufficient. Many of the starch derivatives suitable for use in accordance with the invention are commercially available.

The nonionic starch ether is preferably used as sole protective colloid in a quantity of 15 to 30wt% and, more particularly, in a quantity of 15 to s It is known that polyvinyl alcohol can be used in a quantity of about 2 to c s protective colloid in the polymerisation of polyvinyl acetate. According to the N, vention, this concentration should be increased despite the preconceived notion C04421 that this might adversely affect the properties of the polyvinyl acetate. It has surprisingly been found that reactivation of the gum after moistening takes place just as quickly when 8 to 12wt% of polyvinyl alcohol are added during the polymerisation process as when more than 10wt% of polyvinyl alcohol is subsequently added to the final polyvinyl acetate dispersion.

Accordingly, the polyvinyl alcohol content of the sodium acetate dispersion to be used in accordance with the invention is from 0 to 12wt%, based on the gumming adhesive preferably from 8 to 12wt% and more preferably from 10.5 to 12wt%. The percentage content can be larger during the polymerisation process because, after polymerisation, the final specification requirements are fulfilled by addition of water.

According to the invention, the polyvinyl acetate is a copolymer of vinyl acetate and 25 to 50wt%, based on the monomers of at least one ester of fumaric, maleic, acrylic and/or methacrylic acid, the alkyl chain either being linear or branched and having to contain from 4 to 18 and, more particularly, from 4 to 8 i carbon atoms. Preferred alkyl groups are ethyl, propyl, butyl and ethylhexyl groups.

The preferred comonomer is an alkyl ester of maleic acid.

The copolymerisation may largely be carried out by the process described in DE-OS 33 23 851, the composition of the mixture having to be such that a solids 20 content of 50 to 60wt% and, more particularly, 55 to 60wt%, based on the dispersion to be used as a gumming adhesive in accordance with the invention, is obtained. More particularly, the polyvinyl acetate may be produced by suspension or emulsion polymerisation, preferably by emulsion polymerisation. The particular S conditions of this process are generally known, cf. in particular DE 33 23 861.

The invention also provides a A process for the production of an adhesive with a solids content of 50 to 60wt%, based on the adhesive based on a stabilised p: polyvinyl acetate dispersion, characterised in that it contains the following components: A) 35 to 45wt%, based on the adhesive, of a copolymer of vinyl acetate and 25 to 50wt%, based on the monomers, of at least one ester of fumaric acid, maleic acid, acrylic acid and/or methacrylic acid, the alkyl chain being linear or branched and having from 4 to 18 carbon atoms, B) at least one protective colloid consisting of a) 15 to 30wt%, based on the adhesive, of at least nonionic starch ether and b) 0 to 12wt%, based on the adhesive, of polyvinyl alcohol; characterised in that the copolymerisation is carried out in the presence of the entire nonionic starch ether and polyvinyl alcohol.

The process for producing aqueous polymer dispersions comprises in $Li rticular polymerising vinyl esters together with 25 to 50wt%, based on the total 40 ight of the monomers, of other ethylenically unsaturated compounds with at least C04421 partly water-soluble initiators which yield free radicals at reaction temperatures of to +100C in the presence of hydroxyalkylated starch and/or the other stabiliser, polyvinyl alcohol, at most one third of the monomer total being introduced at the beginning and the rest of the monomers being added during the polymerisation reaction.

According to the invention, the above-described polyvinyl acetate dispersion may be used as such as a gumming adhesive. However, auxiliaries may also be added to meet special requirements and include, for example, dyes, fragrances, biocides, etc. Since they are only optionally present in the adhesive, they are not included in any of the quantities by weight shown which are "based on the adhesive There is no need to add an aqueous polymer solution, for example of polyvinyl alcohol or dexti'in, in order to improve activation behaviour after moistening, nor is such an addition appropriate.

The gumming adhesive according to the invention is distinguished by quick drying and by quick activation after moistening and also by a very intensive adhesive effect by comparison with known gumming adhesives. A particularly surprising feature is that, in spite of this, it still gives a high-gloss film characterised S- by high blocking resistance. Last but not least, the production of the gumming 20 adhesive according to the invention is easier because, for example, polyvinyl 9959 alcohol only has to be added once.

The invention is illustrated by the following Examples.

Example A :Production of the polyvinyl acetate dispersion a) Starch ether as protective colloid ~In a reaction vessel equipped with a stirrer, thermometer, two metering vessels and a reflux condenser, a pH buffer, 22.5kg of a modified potato starch (hydroxypropyl ether) and 0.05kg of a commercial defoamer are dissolved at in 26.275kg of deionised water. A solution of 10kg of deionised water and 0.5kg of K 2

S

2 0 8 is separately prepared at room temperature. This solution is placed in metering vessel 1. A mixture of 24.26kg of vinyl acetate and 16.165kg of dibutyl maleate is prepared at room temperature in metering vessel 2. The polymerisation reaction begins at a temperature of >650C by simultaneous introduction of the components from metering vessels 1 and 2 into the reaction vessel. After the onset of polymerisation, the continuous introduction from vessels 1 and 2 is controlled so that a reaction temperature of 80 to 850C is established.

The reaction time is about 3.5 to 4h.

L 1,4 On completion of polymerisation, the characteristic data of the dispersion are adjW ted with water to a solids content of about C04421 b) Polyvinyl alcohol as protective colloid In a reaction vessel equipped with a stirrer, thermometer, two metering vessels and a reflux condenser, a pH buffer, 210g of polyvinyl alcohol (degree of hydrolysis Ig of Na 2

S

2 0 5 and Ig of a commercial defoamer are dissolved at >85°C in 659g of deionised water. A solution of 110g of deionised water and 4g of K 2

S

2 08 is separately prepared at room temperature. This solution is placed in metering vessel 1. A mixture of 586.4g of vinyl acetate and 391.6g of dibutyl maleate is prepared at room temperature in metering vessel 2. The polymerisation reaction is initiated at a temperature of >65 0 C by the simultaneous introduction of the components from metering vessel 1 and 2 into the reaction vessel. After the onset of polymerisation, the continuous addition from vessels 1 and 2 is controlled so that a reaction temperature of 80 to 85 0 C is established. The reaction time is about to 4h.

On completion of the polymerisation reaction, the characteristic data of the dispersion are adjusted with water to a solids content of about Example B Properties The polyvinyl acetate dispersions described above were used unchanged as a gumming adhesive. The properties are set out in the following Table and were 20 determined as follows: Viscosity was determined by the Brookfield method according to ISO 2555 under the following conditions: RVT, spindle 4, 20rpm., S The solids content was determined in accordance DIN 53189, Method C, after 3h at 1050C by weighing out.

S25 To determine the drying time, a 40pm thick film of a dispersion having a solids content of 55wt% was applied using a box knife coater and was dried in noncirculated air at 230C/55% relative air humidity. The drying time (wet tack time) is S° the time elapsing from application to the moment when the coating is no longer tacky. This time was determined by different methods according to the substrates used (glass plate or 70g/m 2 writing paper according to DIN 19307, use class 4a): In the case of the glass plate, the degree of drying of an adhesive film can be visually determined by sliding a finger over the surface of that film. As drying progresses, the finger test is repeated at approximately 2 second intervals until the film surface shows no sign of damage. This time is measured in seconds and represents the drying time of an adhesive on glass.

In the case of writing paper, the time in seconds after which the surface of the adhesive is dry is determined by pressing one corner at a time of a ZK form folded 141rosswise 4 times onto the film surface with the thumb. The adhesive is dry when C04421 the paper does not lift and tear. The time measured in seconds is the drying time of an adhesive on paper.

To determine the setting time after remoistening, a dry adhesive film of a thick layer of a 55wt% dispersion on a paper (see drying time) is moistened with water using a sponge. Strips of paper (80g, wood-free) are applied to the adhesive thus reactivated. The strips are removed every half second. The time at which fibres are torn out when the strip of paper is removed counts as the end of the setting time.

In order to determine the beginning of blocking, 40pm thick films were applied to writing paper using a surface coater and dried for 24h under ambient conditions.

The paper is then cut into pieces measuring 10 x 10cm. Uncoated sheets of paper of the same type and size is placed on a coated sheet. The stack obtained should consist of 15 coated sheets and 15 uncoated sheets. Two equally large pieces of paperboard are added as top and bottom covers. The stack is then placed in a conditioning cabinet (40°C/70% relative humidity) and a weight of 1kg is attached.

The test specimen remains in this atmosphere for 48h. For inspection, the weight is removed and the stack is examined for blocking. Blocking is said to have started S when the adhesive film becomes tacky. If there is no sign of blocking, the weight is reattached to the test specimen. The relative air humidity is then increased by 20 followed by storage for another 48h. This procedure is continued until blocking occurs.

The quantity applied represents the quantity of solids per unit area.

The pH value is determined with a glass electrode in accordance with DIN t 0 53785/ISO 1148.

25 To determine gloss, an Erichsen surface coater and writing paper (70g/m 2 for example "Multi Bright", a product of Stora Fine Papier, NYMOLLA, SE) are required. A 40pm thick, 6cm wide strip of adhesive is applied by coating knife to a sheet of writing paper measuring 20 x 20cm. It is important that the strip of adhesive is applied without interruption in the direction of travel of the paper. After drying (ca. 15 minutes), the adhesive film is evaluated for gloss. The gloss is differentiated as follows: Standard very high gloss DH 4094 high gloss DH 4093 glossy DH 4084 mat A 4520 Gloss was always evaluated against one of the above standards.

To determine stay-flat behaviour, a 40pm thick, 6cm wide strip of adhesive _35(55% dispersion) is applied by coating knife to a 20 x 20cm sheet of writing paper g/m 2 wood-free). It is important that the strip of adhesive is applied without rrr ti ruption in the direction of travel of the paper. The adhesive is dried at C04421 23°C/55% relative air humidity. The stay-flat behaviour should be evaluated after ca. 5 minutes, lh and 24h. It is important to ensure that the coated papers are not exposed to circulated air. The evaluation should also include a direct comparison with a standard adhesive because the stay-flat behaviour changes as a function of ambient temperatures and atmospheric humidity. The stay-flat behaviour is differentiated according to the following criteria: paper stays flat paper curls slightly paper curls fairly sharply paper rolls up paper turns wavy paper develops folds Adhesin A 4520 of Henkel KGaA is used as a standard adhesive with very good stay-flat behaviour. The stay-flat evaluation should be carried out at the same ambient temperature and atmospheric humidity.

Other properties, such as colour and the beginning of blocking, were in a favourable range.

Table 1 Characterisation and processing and performance properties Example A a) Example A b) Characteristic data: Viscosity [mPas] 7200 9650 pH value Solids content ca. 55 55.5 Properties: Drying times [secs.] on paper ca. 70 [mins.] on glass ca. 3.45 3.45 Setting time after remoistening [secs.] ca. 2.5 3 3 Stay-flat Good/very good Good/very good Gloss evaluation Highly glossy (Highly)gloss Recommended application 15-25 15-25 Suitability for automatic inserting machines: Very good Very good 0* e*

S

SS

55

S

C04421

Claims

1. Use of an adhesive with a solids content of 50 to 60wt%, based on the adhesive based on a stabilised polyvinyl acetate dispersion, characterised in that it contains the following components: A) 35 to 45wt%, based on the adhesive, of a copolymer of vinyl acetate and 25 to based on the monomers, of at least one ester of fumaric acid, maleic acid, acrylic acid and/or methacrylic acid, the alkyl chain being linear or branched and having from 4 to 18 carbon atoms, B) at least one protective colloid consisting of a) 15 to 30wt%, based on the adhesive, of at least nonionic starch ether and b) 0 to 12wt%, based on the adhesive, of polyvinyl alcohol; for gumming.

2. Use as claimed in claim 1, characterised in that the comonomer is an alkyl ester of maleic acid containing 4 to 8 carbon atoms.

3. Use as claimed in claim 1 or 2, characterised in that the protective colloid is a nonionic starch ether from the following group: hydroxyethyl, hydroxypropyl or hydroxybutyl ether starch.

4. Use as claimed in any one of claims 1 to 3, characterised in that the nonionic starch ether makes up from 15 to 25wt% of the adhesive.

5. Use as claimed in any one of claims 1 to 4, characterised by a 20 percentage polyvinyl alcohol content of 8 to 12wt% based on the adhesive.

6. Use as claimed in claim 5, characterised by a percentage polyvinyl alcohol content of 10.5 to 12wt% based on the adhesive.

7. Use as claimed in any one of the preceding claims, characterised in that the solids content is from 55 to 60wt%, based on the adhesive. 25

8. Use of an adhesive based on a stabilised polyvinyl acetate dispersion, S: substantially as hereinbefore described with reference to any of the examples.

9. The use as claimed in any one of claims 1 to 8, in automatic inserting machines. A process for the production of an adhesive with a solids content of 50 to 60wt%, based on the adhesive based on a stabilised polyvinyl acetate dispersion, characterised in that it contains the following components: A) 35 to 45wt%, based on the adhesive, of a copolymer of vinyl acetate and 25 to based on the monomers, of at least one ester of fumaric acid, maleic acid, acrylic acid and/or methacrylic acid, the alkyl chain being linear or branched and having from 4 to 18 carbon atoms, B) at least one protective colloid consisting of a) 15 to 30wt%, based on the adhesive, of at least nonionic starch ether and b) 0 to 12wt%, based on the adhesive, of polyvinyl alcohol; Laracterised in that the copolymerisation is carried out in the presence of the 40 tire nonionic starch ether and polyvinyl alcohol.

C04421

11. A process as claimed in claim 10, characterised in that the comonomer is an alkyl ester of maleic acid containing 4 to 8 carbon atoms.

12. A process as claimed in claim 10 or 11, characterised in that the protective colloid is a nonionic starch ether from the following group: hydroxyethyl, hydroxypropyl or hydroxybutyl ether starch.

13. A process as claimed in any one of claims 10 to 12, characterised in that the nonionic starch ether makes up from 15 to 25wt% of the adhesive.

14. A process as claimed in any one of claims 10 to 13, characterised by a percentage polyvinyl alcohol content of 8 to 12wt% based on the adhesive.

15. A process as claimed in claim 5, characterised by a percentage polyvinyl alcohol content of 10.5 to 12wt% based on the adhesive.

16. A process as claimed in any one of claims 10 to 14, characterised in that the solids content is from 55 to 60wt%, based on the adhesive.

17. A process as claimed in any one of claims 10 to 16, characterised in that, on completion of the copolymerisation, no aqueous polymer solution is added to the polyvinyl acetate dispersion.

18. A process as claimed in claim 17, characterised in that, on completion of the copolymerisation, no solution of polyvinyl alcohol or dextrin is added to the polyvinyl acetate dispersion S 20

19. A process for the production of an adhesive based on a stabilised polyvinyl acetate dispersion, the process being substantially as hereinbefore described with reference to example A.

20. An adhesive based on a stabilised polyvinyl acetate dispersion prepared by the process of any one of claims 10 to 19. 25 Dated 18 September 2000 HENKEL KOMMANDITGESELLSCHAFT AUF AKTIEN Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON C04421