GB2392914A - Adhesive for water-soluble packagings - Google Patents

Abstract

Hot-melt adhesives for gluing water-soluble packagings comprise polyvinyl alcohol and plasticizer and at least one particulate additive selected from porous substances with a BET surface area (multiple point determination of the BET surface area by means of N2 adsorption in accordance with DIN 66131) above 50 m<2>/g and/or substances with a water uptake capacity above 0.02 g/g. The plasticizer may be selected from water, glycerol, ethylene glycol, sorbitol, mannitol and mixtures thereof. Examples of the particulate additive may be pyrogenic silica, homo-and/or copolymers of acrylic acid and one or more cross-linked, swellable polymers (superabsurbes). Also shown is a process for the preparation of hot-melt adhesives.

Description

23929 1 4

5 Adhesive for water-soluble packagings This invention relates to a polyvinyl alcohol composition which is either soluble or dispersible in water and which has hot-melt properties. The present invention furthermore 10 relates to a hot-melt adhesive which comprises the composition and to a process for gluing water-soluble packagings. Compared with other adhesives, hot-melt adhesives are 15 advantageous in as much as they can be used in a wide range of substances to be glued, are characterized by a very high speed of adhesion and are of low intoxication and low hazard potential and are more economical. They can therefore be used in such applications as book-binding, 20 packagings, carpentry, shoe production, gluing of fabrics etc. Moreover, on account of their water-solubility or water-dispersibility, they are outstandingly suitable for the preparation of water-soluble packagings, in particular in the consumer sector, such as packaging of plant 25 protection agents, detergents or cleaning compositions etc Hot-melt adhesives have to fulfil several use requirements, such as adhesive strength, meltability, heat resistance, resistance to low temperatures and elasticity. The base 30 polymers which are used for such hot-melt adhesives are in general ethylene/vinyl acetate copolymers and polyethylene, polypropylene, polyamide and polyester resins. Hot-melt adhesives based on polyvinyl alcohol are widely used for water-soluble or water-dispersible applications.

However, since the vinyl alcohol resin is high-melting and has a high melt viscosity at a low temperature, this resin by itself is not suitable for use as a hot-melt adhesive.

An amount of plasticizer, such as glycerol, ethylene glycol 5 or the like, is therefore added to the resin. However, mere addition of a plasticizer is not sufficient to lower the melting point and the melt viscosity to the necessary level. For this reason, hot-melt adhesives based on polyvinyl alcohol require high temperatures (not less than 10 180 C) during use. However, the use of such a high temperature leads to thermal degradation of the polyvinyl alcohol resin and reduction in the compatibility of the resin with other constituents.

15 Since the polyvinyl alcohol resin additionally has the property of becoming brittle at a low temperature, the products assembled with a hotmelt adhesive based on PVA are susceptible to deterioration at the joining sites, in particular in cold regions, and are therefore of low market 20 value. This problem manifests itself in particular in the gluing of water-soluble packagings with such PVA-based adhesives. The leakage rate is particularly high here.

The problem arises to an increased extent with water-

soluble packagings filled with aqueous compositions.

Furthermore, PVA-based adhesives absorb moisture in a high-

humidity environment, compared with the more conventional hot-melt adhesives, whereby the adhesive strength and sliding ability may deteriorate.

BE 351 114 Al discloses hot-melt adhesives for cellulose materials which comprise 2 to 35 wt.% polyvinyl alcohol, 10

to 80 wt.% urea (or its solid alkyl derivatives) and 5 to 80 wt.% viscosity modifiers (water, liquid polyhydroxy compounds, liquid alkylureas, liquid aliphatic amides or dimethyleulfoxide). Adhesive compositions for gluing polyvinyl alcohol are disclosed in JP 03-039381-A (Derwent abstract). They comprise polyvinyl alcohol, glycerol, ethylene glycol or water and optionally PEG.

Melt mixtures of polyvinyl alcohol and alkylene glycols, sorbitol, pentaerythritol, glycerol, urea, ethylurea etc. are described in J5 1387542 (Derwent abstract). These mixtures are said to be suitable as a hotmelt adhesive for 15 paper, fibres, films and wood.

German Patent Specification DE 44 05 572 C2 discloses

polyvinyl acetate resin compositions which comprise 100 parts by weight of a polyvinyl alcohol, 5 to 100 parts by 20 weight of a hydroxy-fatty acid compound having not less than 6 carbon atoms and 5 to 50 parts by weight of a plasticizer (glycerol, diglycerol, pentaerythritol, ethylene glycol, diethylene glycol, sorbitol, mannitol etc.). These hot-melt adhesives are distinguished by a low 25 melting temperature and a low viscosity at temperatures just above the melting temperature. Furthermore, the brittleness is said to be reduced and the adhesive strength increased. 30 The present invention was based on the object of providing an adhesive for water-soluble packagings, in particular for packagings of polyvinyl alcohol, which is distinguished by

improved physical properties. In particular, the processability (ease of metering without drawing threads, swelling or thermal degradation, subsequently rapid curing) and the reprocessability (stability towards melting several 5 times, re-meltability) should be improved here. In addition, the adhesive bond should be stable in the long term but readily soluble under use conditions.

It has now been found that the addition of particular 10 compounds to systems of polyvinyl alcohols and plasticizers significantly improves the physical properties thereof.

The present invention relates to a hot-melt adhesive for gluing watersoluble packagings, comprising polyvinyl 15 alcohol and plasticizer, wherein the adhesive further comprises at least one particulate additive selected from: a) porous substances with a BET surface area (multiple point determination of the BET surface area by means of N2 adsorption in accordance with DIN 66131) above 50 20 m2/g; and/or b) substances with a water uptake capacity above 0.02 gig.

According to the invention, the hot-melt adhesives comprise 25 at least one substance from group a) (i.e. a substance with a high BET surface area) and/or one substance from group b) (i.e. a substance with a high water uptake capacity).

The BET method is based on the determination of the amount 30 of adsorbate or of adsorptive consumed which is necessary in order to cover the outer surface and the accessible inner pore surface of a solid with a complete monolayer of

adsorbate. This so-called monolayer capacity is calculated from the adsorption isotherms with the aid of the BET equation. Adsorptives which are used are gases, which are adsorbed on to the surface of the solid by physisorption 5 with weak interaction forces (van der Waals forces) and are rapidly desorbed by lowering the pressure (as a rule nitrogen at its boiling point, i.e. 77.3 K). If the absolute surface area is so small that the sensitivity of the measuring instrument is not sufficient if nitrogen is 10 used, krypton (also at 77.3 K) is employed. For volumetric static measurement of the adsorption isotherms, gaseous adsorptive is fed stepwise to the specimen, which has been thoroughly dried beforehand and degassed by thorough heating in vacuo, in the specimen holder, which is kept at 15 a constant temperature. The amounts of gas na (unit: molly) adsorbed on to the specimen in equilibrium under the gas pressure of the adsorptive are determined from the particular difference between the metering and the equilibrium pressure in each metering step and plotted 20 against the relative pressure p/pO as adsorption isotherms.

For the evaluation (multiple point variant), for the isotherm points falling in the relative pressure interval from 0.05 to 0.3 a specific plot of the amounts adsorbed na in the form of the BET coefficient: y= PIP, n,, (I - pl pO) as the ordinate against the particular relative pressure x = p/pO as the abscissa is established. From the BET equation on which the calculation is based, a linear 30 relationship y = a + bx is assumed. The intercept on the

ordinate a and the gradient b are determined via a linear regression method, and from these the monolayer capacity nm (unit mol/g) can be calculated from nm = 1/(a+b). Finally, the specific surface area is obtained from this by 5 incorporation of the space requirement am for one adsorptive molecule in the monolayer as Sm = nm am À NA! wherein NA is Avogadro's constant. In accordance with the IUPAC Recommendations 1984 and DIN 66131, the value am = 0.162 nm2 is used here for nitrogen and am = 0.202 nm2 for krypton.

The hot-melt adhesive according to the invention preferably comprises the additive or additives in amounts above 0.1 and below 20 wt.%, in each case based on the hot-melt adhesive. Hot-melt adhesives according to the invention 15 which comprise the particulate additive(s) in amounts of O.l to 20 wt.%, preferably 0.5 to 10 wt.%, particularly preferably 1 to 8 wt. %, and in particular 2 to 6 wt.\, in each case based on the hot-melt adhesive, are preferred.

20 Preferred particulate additives from group a) have a relatively high BET surface area. Hot-melt adhesives according to the invention which are characterized in that they comprise as the particulate additive a substance with a BET surface area (multiple point determination of the BET 25 surface area by means of N2 adsorption in accordance with DIN 66131) of 50 to 400 m2/g, preferably 75 to 350 m2/g particularly preferably 100 to 300 m2/g, and in particular 120 to 250 m2/g, are preferred here.

30 In the case of particulate additives from group b), substances which have a high water uptake capacity are also preferred. Preferred hot-melt adhesives according to the

invention here are characterized in that they comprise, as the particulate additive, a substance with a water uptake capacity above 0.2 gig, preferably above 0.5 gig, particularly preferably above 1 gig, and in particular 5 above 1.5 gig.

Substances which have the BET surface areas or water uptake capacities mentioned can originate from various classes of substances and can be either "inorganic" or "organic" in 10 nature. Of the "inorganic" substances, silicates, zeolites, silicas etc. have proved to be preferred particulate additives.

Particularly preferred particulate additives for hot-melt 15 adhesives according to the invention are silicas, pyrogenic silicas having a particular importance. The name Aerosil has become established in the case of pyrogenic silicas.

Aerosil is obtained as the raw material with more than 20 99.8% SiO2 by flame hydrolysis of silicon tetrachloride by combustion in an oxyhydrogen flame. By choosing the flame conditions the particle fineness can be varied and as a result the specific surface area can be adjusted in the range from about 50 to 400 m2/g (e.g. Aerosil3-200 with a 25 specific surface area of 200 m2/g). Prosily is built up from amorphous particles which have a diameter of 10-20 nm and contain silanol groups on the surface. In the case of hydrophobic polymers, the hydrophilicity which thereby results often leads to difficulties during incorporation 30 and incompatibility with the polymer matrix, which not only impairs the effects sought but also results in migration phenomena. On the other hand, in the case of hydrophilic

polymers, such as the polyvinyl alcohol contained according to the invention in the hot-melt adhesive, the hydrophilicity of pyrogenic silica is of advantage.

Surface energies and electrical interactions play a large 5 role for homogeneous distribution in the matrix.

In the context of the present invention, preferred hot-melt adhesives are characterized in that they comprise, as the particulate additive, pyrogenic silica, preferably with 10 particle sizes of 5 to 50 nm, particularly preferably 10 to 30 nm, and in particular 10 to 20 nm.

Of the "organic" substances, homo- and/or copolymers based on acrylic acid and/or methacrylic acid, for example those 15 with a relative molecular weight of 500 to 70,000 g/mol, have proved advantageous in particular. In addition to polyacrylic acid and/or water-soluble salts thereof and polymethacrylic acid and/or water-soluble salts thereof, copolymers of acrylic acid and methacrylic acid, water 20 soluble salts of these copolymers, copolymers of acrylic acid and/or methacrylic acid with other unsaturated carboxylic acids, such as, maleic acid may be used.

The molecular weights stated for polymeric polycarboxylates 25 in the context of this specification are weight-average

molecular weights Mw of the particular acid form which have been determined in principle by means of gel permeation chromatography (GPC), a W detector having been employed.

The measurement was made here against an external 30 polyacrylic acid standard, which provides realistic molecular weight values because it is structurally related to the polymers investigated. These data deviate

significantly from the molecular weight data in which polystyrenesulfonic acids are employed as the standard.

The molecular weights measured against polystyrenesulfonic acids are as a rule significantly higher than the molecular 5 weights stated in this specification.

Suitable polymers are, in particular, polyacrylates, which preferably have a molecular weight of 1,000 to 20,000 g/mol. On account of their superior Volubility, 10 from this group the short-chain polyacrylates which have molecular weights of 1,000 to 10,000 g/mol, and particularly preferably 1,200 to 8,000 g/mol, for example 4,500 or 8,000, are preferred.

15 Both polyacrylates and copolymers of unsaturated carboxylic acids, monomers containing sulfonic acid groups and optionally further ionic or nonionic monomers are particularly preferably employed in the hot-melt adhesives according to the present invention.

Copolymeric polycarboxylates, in particular those of acrylic acid with methacrylic acid and of acrylic acid or methacrylic acid with maleic acid, are also suitable.

Copolymers of acrylic acid with maleic acid which contain 25 50 to 90 wt. % acrylic acid and 50 to 10 wt.% maleic acid have proved to be particularly suitable. Their relative molecular weight, based on the free acids, is in general 2,000 to 100,000 g/mol, preferably 20,000 to 90,000 g/mol, and most preferably 30,000 to 80,000 g/mol.

To improve the water-solubility, the polymers can also comprise allylsulfonic acids, such as

allyloxybenzenesulfonic acid and methallyleulfonic acid, as a monomer.

Biodegradable polymers of more than two different monomer 5 units, for example those which comprise as monomers salts of acrylic acid and of maleic acid and vinyl alcohol or vinyl alcohol derivatives or which comprise as monomers salts of acrylic acid and of 2-alkylallyleulfonic acid and sugar derivatives, are also particularly preferred.

10 Further preferred copolymers preferably contain as monomers acrolein and acrylic acid/acrylic acid salts or acrolein and vinyl acetate.

Hot-melt adhesives which are preferred according to the 15 present invention comprise, as the particulate additive, homo- and/or copolymers of acrylic acid and/or methacrylic acid. A further class of polymers which can be employed as the 20 additive in the hot-melt adhesives according to the invention with particular advantage are the so-called "superabsorbers", which are distinguished by a high water uptake capacity. Hot-melt adhesives according to the present invention which comprise, as the particulate 25 additive, one or more crosslinked, swellable polymer(s) (superabsorber(s)) are accordingly preferred.

The hot-melt adhesive of the present invention comprises at least one polyvinyl alcohol, hot-melt adhesives according 30 to the present invention which comprise 30 to 90 wt., preferably 35 to 80 wt.%, and most preferably 40 to 75 wt.%

polyvinyl alcohol, in each case based on the hot-melt adhesive, being preferred.

"Polyvinyl alcohols" (abbreviation PVA, occasionally also 5 PVOH) is the term here for polymers of the general structure -CH2-CH-CH2 CH

1 1 OH OH which also contain structural units of the type -CH2-ICH-ICHCH2

OH OH in small amounts (approx. 2%).

Commercially available polyvinyl alcohols, which are 15 available as yellowish-white powders or granules with degrees of polymerization in the range of from about 100 to 2,500 (molecular weights of about 4,000 to 100, 000 g/mol), have degrees of hydrolysis of 98-99 or 87-89 mol%, i.e. still containing a residual content of acetyl groups. The 20 polyvinyl alcohols are characterized by the manufacturers by stating the degree of polymerization of the starting polymer, the degree of hydrolysis, the saponification number or the solution viscosity.

25 Depending of the degree of hydrolysis, polyvinyl alcohols are soluble in water and a few strongly polar organic solvents (formamide, dimethylformamide, dimethylsulfoxide); they are not attacked by (chlorinated) hydrocarbons, esters, fats and oils. Polyvinyl alcohols are classified

as toxicologically acceptable and are at least partly biodegradable. The solubility in water can be reduced by after-treatment with aldehydes (acetalization), by complexing with salts of Ni or Cu or by treatment with 5 dichromates, boric acid or borax. Polyvinyl alcohol is largely impermeable to gases such as oxygen, nitrogen, helium, hydrogen, carbon dioxide, but allows water vapour pass through.

10 Hot-melt adhesives which are preferred in the context of the present invention comprise polyvinyl alcohols and/or PVA copolymers, the degree of hydrolysis of which is 70 to 100 mol%, preferably 80 to 90 mol%, particularly preferably 81 to 89 mol%, and in particular 82 to 88 mol%.

Polyvinyl alcohols of a particular molecular weight range are preferably employed, hot-melt adhesives according to the invention which comprise polyvinyl alcohols and/or PVA copolymers of which the molecular weight is from 3,500 to 20 100,000 gmol1, preferably 10,000 to 90,000 gmol1, more preferably 12,000 to 80,000 gmoll, and most preferably 13,000 to 70,000 gmol1, being preferred.

The degree of polymerization of such preferred polyvinyl 25 alcohols is from about 200 to about 2,100, preferably from about 220 to about 1,890, more preferably from about 240 to about 1, 680, and most preferably from about 260 to about 1,500.

30 Hot-melt adhesives which are preferred according to the invention are characterized in that they comprise polyvinyl alcohols and/or PVA copolymers of which the average degree

of polymerization is from 80 to 700, preferably from 150 to 400, most preferably from 180 to 300, and/or of which the molecular weight ratio MW(50%) to MW(90%) is from 0.3 to 1, preferably from 0.4 to 0.8, and most preferably from 0.45 5 to 0.6.

The polyvinyl alcohols described above are widely available commercially, for example under the trade name Mowiol (Clariant). Polyvinyl alcohols which are particularly 10 suitable in the context of the present invention are, for example, Mowiol 3-83, Mowiol 4-88, Mowiol 5-88 and Mowiol 8-88.

Further polyvinyl alcohols which are particularly suitable 15 for the hotmelt adhesives according to the present invention can be seen from the following table: Name Degree of Molecular Melting hydrolysis [%] weight [kDa] point [ C] Airvol 205 88 15 - 27 230 Vines 2019 88 15 - 27 170 Vines 2144 88 44 - 65 205 Vines 1025 99 15 - 27 170 Vines 2025 88 25 - 45 192 _ Gohsefimer 5407 30 - 28 23,600 100 Gohsefimer LL02 41 - 51 1 17, 700 100 Further polyvinyl alcohols which are suitable for the hot 20 melt adhesives wrapping are ELVANOL 51-05, 52-22, 50-42, 85-82, 75-15, T-25, T66, 90-50 (trade name of DuPont),

ALCOTEX 72.5, 78, B72, F80/40, F88/4, F88/26, F88/40,

F88/47 (trade name of Harlow Chemical Co.), Goheenol NK 05, A-300, AH-22, C-500, GH-20, GL-03, GM-14L, KA-20, KA

500, KH-20, KP-06, N-300, NH-26, NMllQ, KZ-06 (trade name 5 of Nippon Goheei K.K.). ERROL types from Wacker are also suitable.

The term "polyvinyl alcohol" is also understood as meaning, in the context of the present invention, polyvinyl acetates 10 which have been rendered soluble or dispersible in water by partial saponification or introduction of hydrophilic

groups. Such hydrophilic polyvinyl acetate resins are preferably 15 partially saponified polyvinyl acetate resins with an average degree of saponification of 30-85 mol% and an average degree of polymerization of 50-700, which can alternatively contain a monomer unit containing hydrophilic groups, or polyvinyl acetate resins with an average degree 20 of saponification of 0-30 mold and an average degree of polymerization of 50-700, which can contain 0.1-30 mol% of a monomer unit containing hydrophilic groups. The monomer unit containing hydrophilic groups, which is necessarily contained either in the polyvinyl acetate resin mentioned 25 first or in the polyvinyl acetate resin mentioned last, is preferably a monomer unit with a sulfonic acid group or an oxyalkylene group.

The abovementioned polyvinyl acetate resin includes not 30 only saponified vinyl acetate polymers, but also saponified copolymers of vinyl acetate with other monomers, such as olefins, for example ethylene, propylene, isobutylene, a

octene, a-dodecene, a-octadecene etc., including unsaturated acids, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid etc., including their salts, mono- or dialkyl esters; 5 nitrites, such as acrylonitrile, methacrylonitrile etc., amides, such as acrylamide, methacrylamide etc.; olefinsulfonic acids, such as ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid etc., including salts thereof; alkyl vinyl ethers; N-acrylamidotrimethyl LO ammonium chloride, allyltrimethylammonium chloride; dimethyldiallylvinyl ketone; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride; polyoxyalkylene (meth)allyl ethers, such as polyoxyethylene (meth)allyl ether, polyoxypropylene (meth)allyl ether etc.; polyoxyalkylene 15 (meth) acrylates, such as polyoxyethylene (meth)acrylate, polyoxypropylene (meth) acrylate etc.; polyoxyalkylene-

(meth)acrylamides, such as polyoxyethylene-

(meth)acrylamide, polyoxypropylene-(meth)acrylamide etc.; polyoxyethylene (1-(meth)acrylamido-1,1-dimethylpropyl) 20 ester; polyoxyethylene vinyl ether, polyoxypropylene vinyl ether; polyoxyethylene-allylamine, polyoxypropylene-

allylamine, polyoxyethylene-vinylamine, polyoxypropylene-

vinylamine etc. Among the abovementioned comonomers, monomers with a sulfonic acid group and those with an 25 oxyalkylene group are typical monomers containing hydrophilic groups.

The polyvinyl acetate resin preferably has an average degree of saponification preferably from 30 to 85 mol%, and 30 for even better results 45-70 mol%, and an average degree of polymerization preferably from 50 to 700, and for even better results 100-500. If the average degree of

saponification is below 30 mol%, the resin shows a high tendency towards blocking and is not soluble in water. On the other hand, the resin will have a high melting point if it exceeds 85 mol%. If the average degree of 5 polymerization is less than 50, the adhesive strength is not high enough. If it exceeds 700, the resin has a high melt viscosity.

The polyvinyl acetate resin can also be provided by 10 copolymerization of vinyl acetate as the main monomer with one or more monomers which contain hydrophilic groups and which can be copolymerized with this. The monomer containing the hydrophilic groups includes monomers containing sulfonic acid groups, monomers containing 15 carboxyl groups, monomers containing oxyalkylene groups etc. Monomers containing sulfonic acid groups and monomers containing oxyalkylene groups are particularly preferred.

The aforementioned monomers containing sulfonic acid groups 20 include (meth)allyleulfonic acid, ethylenesulfonic acid, 2-

(meth)acrylamido-2-methylpropanesulfonic acid, 2-

acrylamido-1-methylpropanesulfonic acid, sodium (meth)allyleulfonate, sodium ethylenesulfonate, sulfoalkyl maleate, such as sodium monosulfoalkyl maleate, sodium 25 disulfoalkyl maleate etc.; sodium 2(meth)acrylamido-2-

methylpropanesulfonate, sodium 2-(meth)acrylamido-1-

methylpropanesulfonate etc. The aforementioned monomers containing carboxyl groups 30 include (meth)acrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid etc., including sodium salts, potassium salts and partial esters thereof.

The monomers containing oxyalkylene groups include, inter alla: polyoxyalkylene (meth)allyl ethers, polyoxyalkylene (meth)acrylates, polyoxyalkylene-(meth)acrylamides, 5 polyoxyalkylene (1-(meth)acrylamido1,1-dimethylpropyl) esters, polyoxyalkylene vinyl ethers, polyoxyalkylene-

allylamines and polyoxyalkylene-vinylamines. The degree of condensation of the polyoxyalkylene is preferably 1-300, and for even better results 350.

The polyvinyl acetate resin which contains monomers with water-soluble groups does not have to be saponified.

However, it can be saponified to the extent of less than 30 mol%. The average degree of polymerization of the 15 polyvinyl acetate resin (A2) is preferably 50-700, and for even better results 100-500. If the average degree of polymerization is below 50, the adhesive strength is not adequate. If it exceeds 700, the melt viscosity increases.

The copolymerization ratio of the monomer containing 20 hydrophilic groups is preferably 0.1-30 mol%, and for even better results 1-20 mol%. If the copolymerization ratio of the monomer containing hydrophilic groups is less than 0.1 mol%, the water-solubility/-dispersibility is not adequate. If it exceeds 30 mol%, the adhesive strength is 25 not adequate.

The hot-melt adhesives according to the present invention preferably comprise, in addition to polyvinyl alcohol and the particulate additive(s) , further constituents, in 30 particular plasticizers. Plasticizers which can be employed in the hot-melt adhesives according to the invention are, in particular, hydrophilic, high-boiling

liquids, it optionally also being possible to employ substances which are solid at room temperature, as a solution, dispersion or melt. Particularly preferred hot-

melt adhesives according to the present invention are 5 characterized in that they comprise as plasticizers one or more materials from the group consisting of glycol, di-, trim, tetra-, penta-, hexa-, hepta-, octa-, none-, deca-, undeca-, dodecaethylene glycol, glycerol, neopentylglycol, trimethylolpropane, pentaerythritol, mono-, di-, 10 triglycerides, surfactants, in particular nonionic surfactants, and mixtures thereof.

Ethylene glycol (1,2-ethanediol, "glycol") is a colourless, viscous, sweet-tasting, highly hydroscopic liquid which is 15 miscible with water, alcohols and acetone and has a density of 1.113. The solidification point of ethylene glycol is -11.5 C and the liquid boils at 198 C. Ethylene glycol is obtained industrially from ethylene oxide by heating with water under pressure. Promising preparation processes can 20 also be based on the acetoxylation of ethylene and subsequent hydrolysis or on synthesis gas reactions.

Diethylene glycol (2,2'-oxydiethanol, Digol), HO-(CH2)2-O (CH2)2-OH, is a colourless, viscous, hydroscopic, sweetish 25 tasting liquid of density 1. 12 which melts at -6 C and boils at 245 C. Diglycol is miscible with water, alcohols, glycol ethers, ketones, esters, chloroform in all proportions, but is not miscible with hydrocarbons and oils. Diethylene glycol, which is usually called diglycol 30 for short in practice, is prepared from ethylene oxide and ethylene glycol (ethoxylation), and is thus practically the starting member of the polyethylene glycol (see above).

Glycerol is a colourless, clear, poorly mobile, odourless sweet-tasting hydroscopic liquid of density 1.261 which solidifies at 18.2 C. Glycerol was originally only a by 5 product of fat saponification, but is now synthesized industrially in large amounts. Most industrial processes are based on propene, which is processed to glycerol via the intermediate stages of allyl chloride and epichlorohydrin. Another industrial process is the 10 hydroxylation of allyl alcohol with hydrogen peroxide on a WO3 contact via the stage of glycidol.

Trimethylolpropane [TMP, etriol, ettriol, 1,1,1-

tris(hydroxymethyl)propane] is called in chemically exact 15 terms 2ethyl-2-hydroxymethyl-1,3-propanediol and is marketed in the form of colourless, hydroscopic masses with a melting point of 57-59 C and aboiling point of 160 C (7 hPa). It is soluble in water, alcohol, acetone but insoluble in aliphatic and aromatic hydrocarbons. It is 20 prepared by reaction of formaldehyde with butyraldehyde in the presence of alkalis.

Pentaerythritol [2,2-bis(hydroxymethyl)-1,3-propanediol, penta, PE] is a white, crystalline powder with a sweetish 25 taste which is not hydroscopic and combustible and has a density of 1.399, a melting point of 262 C and a boiling point of 276C (40 hPa). Pentaerythritol is readily soluble in boiling water, not very soluble in alcohol and insoluble in benzene, carbon tetrachloride, ether, 30 petroleum ether. Pentaerythritol is prepared industrially be reaction of formaldehyde with acetaldehyde in an aqueous solution of Ca(OH) 2 or also NaOH at 15-45 C. A mixed aldol

reaction first takes place here, in which formaldehyde reacts as the carbonyl component and acetaldehyde as the methylene component. Because of the high carbonyl activity of the formaldehyde, the reaction of acetaldehyde with 5 itself almost does not start at all. Finally, the tris(hydroxymethyl)acetaldebyde formed in this way is converted into pentaerythritol and formate with formaldehyde in a crossed Cannizzaro reaction.

10 Mono-, di-, triglycerides are esters of fatty acids, preferably longerchain fatty acids, with glycerol, one, two or three OH groups of the glycerol being esterified, depending on the glyceride type. As acid components with which the glycerol can be esterified into mono-, di- or IS triglycerides which can be employed according to the present invention as plasticizers are, for example, hexanoic acid (caproic acid), heptanoic acid (enanthic acid), octanoic acid (caprylic acid), nonanoic acid (pelargonic acid), decanoic acid (capric acid), undecanoic 20 acid etc. In the context of the present invention, the use of fatty acids, such as dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), hexadecanoic acid (palmitic acid), octadecanoic acid (stearic acid), eicosanoic acid (arachic acid), docosanoic acid (behenic 25 acid), tetracosanoic acid (lignoceric acid), hexacosanoic acid (cerotic acid), triacotanoic acid (melissic acid) and the unsaturated species 9chexadecenoic acid (palmitoleic acid), 6c-octadecenoic acid (petroselic acid), 6t-

octadecenoic acid (petroselaidic acid), 9c-octadecenoic 30 acid (oleic acid), 9t-octadecenoic acid ((elaidic acid), 9c,12c-octadecadienoic acid (linoleic acid), 9t,12t-

octadecadienoic acid (linolaidic acid) and 9c,12c,15c

octadecatrienoic acid (linolenic acid). For cost reasons, the native fatty substances (triglycerides) or the modified native fatty substances (partly hydrolysed fats and oils) can also be employed directly. Alternatively, fatty acid 5 mixtures can also be prepared by cleavage of native fats and oils and then separated, the purified fractions later being reacted in turn to give mono-, di- or triglycerides.

Acids which may be esterified with the glycerol are, in particular, coconut oil fatty acid (about 6 wt.% C8, 6 wt.% 10 C10, 48 wt. % C12, 18 wt.% C14, 10 wt.% C16, 2 wt.% C1B, 8 wt.% C1B', 1 wt.% Cls), palm kernel oil fatty acid (about 4 wt.% Ca, 5 wt.% C1O, 50 wt.% C12, 15 wt.% C14, 7 wt.% C16, 2 wt.% C18, 15 wt.% C18., 1 wt.% C18), tallow fatty acid (about 3 wt.% C14, 26 wt.% C16, 2 wt. % C16 ', 2 wt.% C17, 17 wt.% C18, 44 15 wt. % C18, 3 wt.% C18, 1 wt.% C18), hydrogenated tallow fatty acid (about 2 wt. % C14, 28 wt. % C16, 2 wt.% C17, 63 wt.% C18, 1 wt.% C18), technicalgrade oleic acid (about 1 wt.% Cl2, 3 wt.% C14, 5 wt.% Cl6, 6 wt.% Cl6, 1 wt. % C17, 2 wt.% C18, 70 wt.% C18,, 10 wt.% C18,,, 0.5 wt.% C1B.), 20 technical-grade palmitic/stearic acid (about 1 wt.% C12, 2 wt. % C14, 4 5 wt.% C16, 2 wt. % C17, 4 7 wt.% C1B, 1 wt.% C1B ') and soya bean oil fatty acid (about 2 wt.% C14, 15 wt.% C16, 5 wt.% C18, 25 wt. % C18', 4 5 wt% C18,,, 7 wt.% C1B) 25 Possible further plasticizers are also surfactants, in particular nonionic surfactants. Nonionic surfactants which are employed are preferably alkoxylated, advantageously ethoxylated, in particular primary alcohols having preferably 8 to 18 C atoms and on average 1 to 30 12 mol of ethylene oxide (EO) per mol of alcohol, in which the alcohol radical can be linear or, preferably, methyl-

branched in the 2-position, or can contain linear and

methyl-branched radicals as a mixture, such as are conventionally present in oxo alcohol radicals. In particular, however, alcohol ethoxylates with linear radicals from alcohols of native origin having 12 to 18 C 5 atoms, e.g. from coconut, palm, tallow fatty or oleyl alcohol, and on average 2 to 8 EO per mol of alcohol are preferred. The preferred ethoxylated alcohols include, for example, Cl2l4-alcohols with 3 EO or 4 EO, C'llalcohol with 7 EO, Cl3ls-alcohols with 3 EO, 5 EO, 7 EO or 8 EO, Cl2l8 10 alcohols with 3 EO, 5 EO or 7 EO and mixtures of these, such as mixtures of Cl2l4-alcohol with 3 EO and Cl2l8-alcohol with 5 EO. The degrees of ethoxylation stated are statistical means which can be an integer or a fraction for a specific product. Preferred alcohol ethoxylates have a 15 restricted distribution of homologues (narrow range ethoxylates, NRE). In addition to these nonionic surfactants, fatty alcohols with more than 12 EO can also be employed. Examples of these are tallow fatty alcohol with 14 EO, 25 EO, 30 EO or 40 EO.

Nonionic surfactants which have a melting point above room temperature are employed with particular advantage in the hot-melt adhesives according to the invention.

Accordingly, preferred hot-melt adhesives are characterized 25 in that they comprise, as plasticizers, nonionic surfactant(s) having a melting point above 20 C, preferably above 25 C, more preferably from 25 to 60 C, and most preferably from 26.6 to 43.3 C.

30 Suitable nonionic surfactants which have melting or softening points in the temperature range mentioned are, for example, low-foaming nonionic surfactants, which can be

solid or highly viscous at room temperature. If nonionic surfactants which are highly viscous at room temperature are employed, it is preferable for these to have a viscosity above 20 Pas, preferably above 35 Pas, and most 5 preferably above 40 Pas. Nonionic surfactants which have a wax-like consistency at room temperature are also preferred. Nonionic surfactants which are solid at room temperature 10 and are preferably to be employed originate from the groups consisting of alkoxylated nonionic surfactants, in particular ethoxylated primary alcohols, and mixtures of these surfactants with surfactants based on a more complicated structure, such as 15 polyoxypropylene/polyoxyethylene/polyoxypropylene (PO/ED/PO) surfactants.

In a preferred embodiment of the present invention, the nonionic surfactant with a melting point above room 20 temperature is an ethoxylated nonionic surfactant which has originated from the reaction of a monohydroxyalkanol or alkylphenol having 6 to 20 C atoms with preferably at least 12 mol. more preferably at least 15 mol. most preferably at least 20 mol of ethylene oxide per mol of alcohol or 25 alkylphenol.

A particularly preferred nonionic surfactant which is solid at room temperature and is to be employed is obtained from a straight-chain fatty alcohol having 16 to 20 carbon atoms 30 (Cl620-alcohol), preferably a C1alcohol, and at least 12 mol. preferably at least 15 mol. and in particular at least 20 mol of ethylene oxide. Among these, the so-called

"narrow range ethoxylates" (see above) are particularly preferred. Ethoxylated nonionic surfactant(s) which has/have been 5 obtained from C620-monohydroxyalkanols or C620-alkylphenols or C1620-fatty alcohols and more than 12 mol. preferably more than 15 mol. and most preferably more than 20 mol of ethylene oxide per mol of alcohol is/are accordingly employed in particularly preferred hot-melt adhesives 10 according to the present invention.

The nonionic surfactant preferably additionally has propylene oxide units in the molecule. Preferably, such PO units make up a proportion of up to 25 wt.%, more 15 preferably up to 20 wt.%, and most preferably up to 15 wt.% of the total molecular weight of the nonionic surfactant.

Particularly preferred nonionic surfactants are ethoxylated monohydroxyalkanols or alkylphenols which additionally have polyoxyethylene-polyoxypropylene block copolymer units.

20 The alcohol or alkylphenol part of such nonionic surfactant molecules preferably makes up more than 30 wt.%, more preferably more than 50 wt.%, and most preferably more than 70 wt.% of the total molecular weight of such nonionic surfactants. Further nonionic surfactants with melting points above room temperature which are particularly preferably to be employed comprise 40 to 70 wt.% of a polyoxypropylene/polyoxyethylene/polyoxypropylene block 30 polymer blended with 75 wt.% of a reverse block copolymer of polyoxyethylene and polyoxypropylene with 17 mol of ethylene oxide and 44 mol of propylene oxide and 25 wt.% of

a block copolymer of polyoxyethylene and polyoxypropylene, initiated with trimethylolpropane and containing 24 mol of ethylene oxide and 99 mol of propylene oxide per mol of trimethylolpropane. Nonionic surfactants which can be employed with particular advantage are obtainable, for example, under the name Poly Tergent SLF-18 from Olin Chemicals.

10 Nonionic surfactants which are also preferred have the formula RIO [CH2CH (CH3) O] X [CH2CH2O] y [CH2CH (OH) R2], 15 in which R1 represents a linear or branched aliphatic hydrocarbon radical having 4 to 18 carbon atoms or mixtures thereof, R2 represents a linear or branched hydrocarbon radical having 2 to 26 carbon atoms or mixtures thereof and x represents values from 0.5 to 1.5 and y represents a 20 value of at least 15.

Further nonionic surfactants which can preferably be employed are the poly(oxyalkylated) nonionic surfactants, with closed end groups, of the formula RIO [CH2CH (R3) O] X [CH2] kCH (OH) [CH2] joR2 in which R1 and R2 represent linear or branched, saturated or unsaturated, aliphatic or aromatic hydrocarbon radicals 30 having 1 to 30 carbon atoms, R3 represents H or a methyl, ethyl, n-propyl, iso-propyl, n-butyl, 2-butyl, or 2-methyl-

2-butyl radical, x represents values from 1 to 30, k and j

represent values from 1 to 12, preferably from 1 to 5. If the value x is 2 2, each R3 in the above formula can be different. R1 and R2 are preferably linear or branched, saturated or unsaturated, aliphatic or aromatic hydrocarbon 5 radicals having 6 to 22 carbon atoms, radicals having 8 to 18 C atoms being particularly preferred. H. -CH3 or -CH2CH3 are particularly preferred for the radical R3. More preferred values for x are from 1 to 20, most preferably 6 to 15.

As described above, each R3 in the above formula can be different, if x is 2 2. As a result, the alkylene oxide unit in square brackets can be varied. For example, if x represents 3, the radical R3 can be chosen in order to form 15 ethylene oxide (R3 = H) or propylene oxide (R3 = CH3) units, which can be joined to one another in any sequence, for example (EO) (PO) (EO), (EO) (EO) (PO), (EO) (EO) (EO), (PO) (EO) (PO), (PO) (PO) (EO) and (PO)(PO)(PO). The value 3 for x has been chosen here by way of example and can 20 certainly be greater, the range of variation increasing as the x values increase and including, for example, a large number of (EO) groups, combined with a small number of (PO) groups, or vice versa.

25 Particularly preferred poly(oxyalkylated) alcohols with closed end groups, of the above formula, have values of k 1 and j = 1, so that the above formula is simplified to RIO [CH2CH (R3) O] XCH2CH (OH) CH2OR2

In the formula mentioned last, R1, R2 and R3 are as defined above and x represents numbers from 1 to 30, preferably 1

to 20, and most preferably 6 to 18. Surfactants in which the radicals R1 and R2 contain 9 to 14 C atoms, R3 represents H and x assumes values from 6 to 15 are particularly preferred.

Glycerol carbonate, propylene glycol and propylene carbonate can be further substances which are preferably to be employed as plasticizers.

10 Glycerol carbonate is accessible by transesterification of ethylene carbonate or dimethyl carbonate with glycerol, ethylene glycol or methanol being obtained respectively as by-products. Another synthesis route starts from glycidol (2,3-epoxy-1-propanol), which is reacted with CO2 under 15 pressure in the presence of catalysts to give glycerol carbonate. Glycerol carbonate is a clear, readily mobile liquid with a density of 1.398 Acme, which boils at 125-

130 C (0.15 mbar).

20 Two isomers of propylene glycol exist, 1,3-propanediol and 1,2propanediol. 1,3-Propanediol (trimethylene glycol) is a neutral, colourless and odourless, sweet-tasting liquid of density 1.0597, which solidifies at -32 C and boils at 214 C. 1.3-Propanediol is prepared from acrolein and water 25 with subsequent catalytic hydrogenation.

1,2-Propanediol (propylene glycol), which is an oily, colourless, almost odourless liquid of density 1.0381 which solidifies at -60 C and boils at 188 C, is far more 30 important industrially. 1,2-Propanediol is prepared from propylene oxide by adding on water.

Propylene carbonate is a water-clear, readily mobile liquid with a density of 1.21 acme, the melting point is -49 C and the boiling point 242 C. Propylene carbonate is also accessible on a large industrial scale by reaction of 5 propylene oxide and CO2 at 200 C under 80 bar.

Preferred hot-melt adhesives according to the present invention comprise plasticizers in amounts of 5 to 50 wt.%, preferably 10 to 45 wt.%, and most preferably 15 to 35 10 wt.%, in each case based on the hot-melt adhesive, preferred plasticizers being substances selected from water, glycerol, diglycerol, pentaerythritol, ethylene glycol, diethylene glycol, polyethylene glycols (PEG), sorbitol, mannitol and mixtures thereof.

The present invention also provides a process for the preparation of hotmelt adhesives as defined herein, wherein the plasticizer(s) are heated, polyvinyl alcohol is added and the particulate additive(s) are incorporated into 20 the homogeneous melt.

The hot-melt adhesives according to the invention are particularly suitable for gluing water-soluble polymers, preferably water-soluble packagings of polyvinyl alcohol.

25 The present invention therefore also provides the use of hot-melt adhesives according to the present invention for gluing packagings of water-soluble material, preferably water-soluble packagings for detergents or cleaning compositions, in particular packagings of polyvinyl 30 alcohol.

In this use according to the present invention, the hot-

melt adhesives according to the present invention are distinguished in that the processability and the reprocessability are significantly improved. The hot-melt 5 adhesive can be metered without drawing threads, does not swell, is stable to heat and cures rapidly. Furthermore, it can also be melted again several times without a loss in quality. If packagings of polyvinyl alcohol are glued with the hot-melt adhesives according to the present invention 10 in the use according to the present invention, the glued join is distinguished by a particular stability, which is significantly improved compared with conventional hot-melt adhesives, in particular under climatically adverse conditions. The advantages mentioned manifest themselves particularly clearly if the packagings of water-soluble material in turn are filled with a medium which is not water-free, i.e. if they contain liquids which contain a significant water 20 content, for example above 5 wt.%, based on the solution.

Preferred uses according to the present invention are therefore characterized in that the packagings of water-

soluble material which are to be glued are filled with water-containing solutions.

The packaging parts to be glued according to the present invention can be, for example, blow moulded, injection moulded, thermoformed or calendered. Suitable blow moulding processes include extrusion blow moulding, 30 coextrusion blow moulding, injection stretch blow moulding and dip blow moulding. Injection moulding is carried out by procedures known per se under high pressures and

temperatures with the steps of closing of the mould connected to the extruder for injection moulding, injection of the polymer at a high temperature under a high pressure, cooling of the injection-moulded moulding, opening of the 5 mould and removal of the moulded blank. Further optional steps, such as application of release agents, removal from the mould etc., are known to the skilled person and can be carried out by technology which is known per se.

10 The present invention also provides a process for gluing water-soluble packagings, wherein a molten hot-melt adhesive according to the present invention is applied to parts of the packagings and the packaging is closed.

15 Particularly preferred processing temperatures for the hot-

melt adhesives according to the present invention are below 300 C, so that preferred processes are characterized in that the application temperature of the hot-melt adhesive is 30 to 250OC, more preferably 80 to 200 C, and most 20 preferably 100 to 165 C.

Examples:

52 g Glycerol were heated to 180 C, 144 g polyvinyl alcohol (Mowiol 3-83 from Clariant GmbH) being added in portions 5 during the heating-up operation, while stirring. The mixture was stirred for 10 minutes at 180 C and 4 g Aerosil 200 (pyrogenic silica, specific surface area of 200 m2/g) were subsequently added. The mixture was then stirred for a further 10 minutes.

This hot-melt adhesive was applied to packagings of polyvinyl alcohol. In this procedure, in a first test Injection-moulded components of PVA (wall thickness 0.55 mm) were glued to one another, and in a second test a 15 PVA film (thickness: 200 m) was glued together to form bags. For comparison, the same bodies and films were glued with an adhesive of 75 wt.% polyvinyl alcohol (same type as above) and 25 wt.% glycerol. 12 glued joins were stored at 30 C and 80% relative atmospheric humidity for 12 weeks and 20 stored under the same conditions in a PE bag and the strength of the gluing was tested. The following table shows the results: Injection-moulded Injection-moulded components which components in the have fallen apart PE bag which have fallen apart Adhesive according O O to the invention Comparison example 12 12

The example clearly shows the superiority of the hot-melt adhesive according to the present invention during storage under demanding conditions.

5 34 g glycerol and 1 g water were heated to 160 C, 45 g polyvinyl alcohol (Mowiol 3-83 from Clariant GmbH) being added in portions during the heating-up operation, while stirring. The mixture was stirred for 10 minutes at 160 C and 20 g Cabloc 5066 (superadsorber from Stockhausen) were 10 then added in portions. The mixture was then stirred for a further 10 minutes.

Points of adhesive with an area of 4 cm2 and a thickness of 1 mm were produced from this hot-melt adhesive. For 15 comparison, the points of adhesive were produced with an adhesive of 75 wt.% polyvinyl alcohol (same type as above) and 25 wt.% glycerol. The two mixtures were stirred with 100 ml water in a glass beaker at 25 C until the point of adhesive was dissolved. The mixture with the superadsorber 20 showed a rate of dissolution which was improved by 45%.

In addition, this hot-melt adhesive was applied to packagings of polyvinyl alcohol. In this procedure, in a first test injection-moulded components of PVA (wall 25 thickness 0.55 mm) were glued to one another, and in a second test a PVA film (thickness: 200 m) was glued together to form bags. For comparison, the same bodies and films were glued with an adhesive of 75 wt.% polyvinyl alcohol (same type as above) and 25 wt.% glycerol. 3 30 adhesive joins were stored at 30 C at 80% relative atmospheric humidity for 2 weeks and stored under the same

conditions in a PE bag and the strength of the gluing was tested. The following table shows the results: Injection-moulded Injection-moulded components which components in the have fallen apart PE bag which have fallen apart l Adhesive according O to the invention _ Comparison example 3 3 5 The example clearly shows the superiority of the hot-melt adhesive according to the present invention during storage under demanding conditions.

Claims (14)

Patent claims

1. A hot-melt adhesive for gluing water-soluble packagings, comprising polyvinyl alcohol and 5 plasticizer, wherein the adhesive further comprises at least one particulate additive selected from: a) porous substances with a BET surface area (multiple point determination of the BET surface area by means of N2 adsorption in accordance with DIN 66131) above 10 50 m2/g; and/or b) substances with a water uptake capacity above 0.02 gig.

2. A hot-melt adhesive according to claim 1, wherein the 15 particulate additive(s) are present in amounts of 0.1 to 20 wt.%, preferably 0.5 to 10 wt.%, more preferably 1 to 8 wt.%, and most preferably 2 to 6 wt.%, in each case based on the hot-melt adhesive.

20

3. A hot-melt adhesive according to claims 1 or 2, comprising, as the particulate additive, 50 to 400 m2/g, preferably 75 to 350 m2/g, more preferably 100 to 300 m2/g, and most preferably 120 to 250 m2/g of a substance with a BET surface area (multiple point 25 determination of the BET surface area by means of N2 adsorption in accordance with DIN 66131).

4. A hot-melt adhesive according to any one of claims 1 to 3, comprising, as the particulate additive, a 30 substance with a water uptake capacity above 0.2 gig, preferably above 0.5 gig, more preferably above 1 gig, and most preferably above 1.5 gig.

5. A hot-melt adhesive according to any one of claims 1 to 4, comprising, as the particulate additive, pyrogenic silica, preferably with particle sizes of 5 5 to 50 nm, more preferably 10 to 30 nm, and most preferably 10 to 20 nm.

6. A hot-melt adhesive according to any one of claims 1 to 5, comprising, as the particulate additive, homo 10 and/or copolymers of acrylic acid and/or methacrylic acid.

7. A hot-melt adhesive according to any one of claims 1 to 6, comprising, as the particulate additive, one or 15 more crosslinked, swellable polymer(s) (superabsorber(s)).

8. A hot-melt adhesive according to any one of claims 1 to 7, comprising 30 to 90 wt.%, preferably 35 to 80 20 wt.%, and most preferably 40 to 75 wt.% polyvinyl alcohol, in each case based on the hot-melt adhesive.

9. A hot-melt adhesive according to any one of claims 1 to 8, comprising plasticizers in amounts of 5 to 50 25 wt.%, preferably 10 to 45 wt.%, and most preferably 15 to 35 wt.%, in each case based on the hot-melt adhesive, preferred plasticizers being substances selected from water, glycerol, diglycerol, pentaerythritol, ethylene glycol, diethylene glycol, 30 polyethylene glycols (PEG), sorbitol, mannitol and mixtures thereof.

10. A process for the preparation of hot-melt adhesives according to any one of claims 1 to 9, wherein the plasticizer(s) are heated, polyvinyl alcohol is added and the particulate additive(s) are incorporated into 5 the homogeneous melt.

11. Use of hot-melt adhesives according to any one of claims 1 to 9 for gluing packagings of water-soluble material, preferably water-soluble packagings for 10 detergents or cleaning compositions, in particular packagings of polyvinyl alcohol.

12. Use according to claim 11, wherein the packagings of water-soluble material which are to be glued are 15 filled with water-containing solutions.

13. A process for gluing water-soluble packagings, wherein a molten hotmelt adhesive according to any one of claims 1 to 9 is applied to parts of the packagings 20 and the packaging is closed.

14. A process according to claim 13, wherein the application temperature of the hot-melt adhesive is 30 to 250 C, preferably 80 to 200 C, and most preferably 25 100 to 165 C.