DE2804942A1 - Crosslinked adhesive film prodn. from polymer emulsion - using water-soluble crosslinking acrylic! polymer contg. prim. hydrazone gps. - Google Patents

Abstract

This is a Patent of Addn. to DT 2634956 in which crosslinked films are prepd. by (i) mixing a polymer emulsion, yielding an adhesive film after drying on a substrate, with a water-soluble polyacrylic hydrazide as crosslinking agent, (ii) applying the mixt. to a flexible substrate, e.g. paper or a web, and (iii) crosslinking by quick heating at 60-160(80-120) degrees C. In the present Patent of Addn., the water-soluble polyacrylic hydrazide (I) is replaced, at least partly, by a water-soluble polymer (II) contg. prim. hydrazone gps. The synthesis of (II) is less troublesome than that of (I) and comprises the reaction of carbonyl gp.-contg. polymers in aq. soln., with an equiv. hydrazine hydrate quantity. (II) can be used directly, without further purificn. The Adhesive films have improved resistance to moisture.

Description

28049A2

Beiersdorf Aktiengesellschaft Hamburg

Process for the production of crosslinked pressure-sensitive adhesive films from aqueous polymer emulsions or dispersions (Addition to patent application P 26 34 956.4 (DT-PS))

The main application P 26 34 956.4 (■ = DT-PS) is a process for producing crosslinked pressure-sensitive adhesive films from aqueous polymer emulsions or dispersions, in which a polymer emulsion, which after drying results in a self-adhesive film that adheres well to the substrate, with a water-soluble one Polyacrylhydrazide added as a crosslinking agent, the mixture obtained is applied to a flexible base, which can consist, for example, of paper, fiber fleece (nonwoven fabric), a fabric or a film made of plastic or modified natural material, and applied to this by brief exposure to heat at a temperature of 60 to 160 ⁰ C, preferably at 80 to 120 ° C, is crosslinked.

This crosslinking process, which is simple and easy to carry out, is desirable for many areas of application or necessary post-crosslinking of aqueous dispersions adhesive films formed or emulsions of polymers, are crosslinked pressure-sensitive adhesive films or self-adhesive coatings with excellent adhesive properties obtained (high cohesiveness, high creep values, without significant Reduction of the bond strength and adhesion values), which also

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are not impaired or adversely affected by the long-term influence of moisture.

To achieve effective crosslinking, the amount of polyacrylhydrazide added to the polymer emulsion should be 0.5 to 10% by weight and preferably 0.5 to 2% by weight, each based on the polymer content of the emulsion.

As a polymer emulsion with self-adhesive properties that leave a mark on the base after application and subsequent drying result in a well-adhering self-adhesive film, those are preferably suitable for the crosslinking process, which consist of acrylic acid esters, Fumaric acid esters and / or vinyl compounds were prepared by emulsion polymerization and the optionally as further additives for modifying the properties of the pressure-sensitive adhesive films obtainable therewith, adhesive resins and / or May contain plasticizers.

Suitable polymer emulsions are in particular those from Homo- and copolymers of acrylic acid esters, which are at least 50 wt .-%, but preferably at least 85 wt .-% Acrylic acid alkyl esters exist, the primary or secondary alcohol component of which has 4 to 12 carbon atoms in unbranched or branched chain, and those polymerizable with it Monomers such as vinyl esters, vinyl ethers, vinyl ethers, lower acrylic acid esters with 1 to 3 carbon atoms in the alcohol residue, methacrylic acid alkyl esters, acrylonitrile, methacrylonitrile, Acrylic acid and / or methacrylic acid, can be polymerized. The acrylic acid ester copolymers should expediently in addition to a proportion of acrylic acid (up to 15% by weight), each based on the monomer mixture, up to a maximum 1% by weight of a polyfunctional acrylate, such as butanediol-1,4-bis-acrylate, Triethylene glycol dimethacrylate or tetramethylene glycol diacrylate, included in polymerized form.

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Preferably usable for the crosslinking process according to the main application are water-soluble polyacrylhydrazides, which by polymer-analogous reactions of polyacrylamides or their copolymers obtained with hydrazine hydrochloride or hydrazine sulfate can be and their amide groups to about 15 to 50 wt .-%, preferably from 25 to 40% by weight, by primary hydrazide groups are replaced.

Equally suitable for the crosslinking method of the parent application are water soluble Polyacrylhydrazide which can be prepared by polymer-analogous reactions of lower polyacrylic acid esters or copolymers thereof with hydrazine hydrate and their Estergruppen up to 100 wt .-%, preferably 25 to 95 wt .-%, are replaced by primary hydrazide groups.

Since water-soluble polyacrylic hydrazides of the type described are generally only used when a larger excess is used can be obtained on the hydrazine component are for Production and isolation of these water-soluble crosslinking agents, additional cleaning operations (precipitations) necessary, which require a certain amount of technical effort. It was therefore desirable to find similar crosslinking agents their synthesis is less expensive and in the same way for carrying out the simple crosslinking process described suitable for interparticle crosslinking of pressure-sensitive adhesive films obtained from aqueous dispersions or emulsions are.

It has now been found that water-soluble polymers which contain primary hydrazone groups can be produced without problems is, are also well suited as crosslinking agents for carrying out the crosslinking process described.

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The invention relates to a process for the production of crosslinked pressure-sensitive adhesive films from aqueous polymer emulsions or dispersions, in which a polymer emulsion, which after drying gives a self-adhesive film that adheres well to the substrate, is mixed with a water-soluble polyacrylhydrazide as crosslinking agent, and the mixture obtained is transferred to a flexible one Base applied and on this by brief exposure to heat at a temperature of 60 to 160 ⁰ C, preferably at 80 to 120 ⁰ C, crosslinked according to the patent

(Patent application P 26 34- 956.4), characterized in that ■ the water-soluble polyacrylic hydrazide is replaced in whole or in part by a water-soluble polymer with primary hydrazone groups is.

The preparation of the water-soluble polymers with primary hydrazone groups in the basic structure or on the side chains takes place according to known processes, expediently in such a way that polymers which have a sufficient number of carbonyl groups in the basic structure or contained on the side chains of the molecule, reacted in aqueous solution with an equivalent amount of hydrazine hydrate will. The reaction is rapid; an excess of hydrazine hydrate is not necessary. The manufacturing process as such is not the subject of the present invention.

As starting polymers for the preparation of the crosslinking agent according to the invention, the most varied, soluble Polymers containing carbonyl groups are used. By copolymerizing strongly polar monomers with carbonyl groups containing monomers can be water-soluble polymers for the reaction with the hydrazine compound easily obtain. Water-soluble starting polymers can e.g. by copolymerizing acrylic or methacrylic acid with acrylic acid esters, which have carbonyl groups in the alcoholic residue, by means of radical polymerization in various solutions

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means can be easily produced. By salt formation on the free carboxyl groups, these polymers can contribute to water alkaline pH values and then with an equivalent amount of hydrazine hydrate to the corresponding hydrazones implemented. Analogously to this, substituted acrylic acid amides with carbonyl groups can also be used instead of the acrylic acid esters Alkyl radical can be used. In the same way, polymers made from vinyl esters which have carbonyl groups in the alcohol residue, (Co) polymers of vinyl methyl ketone or acrolein and copolymers with fumaric acid esters which contain carbonyl groups, so that there are many possibilities for the selection of the starting polymers exist. Finally, polymers containing, for example, reactive anhydride moieties can also be used for the intended purpose contain. By reacting these anhydrides with alcohols bearing carbonyl groups and then reacting them with hydrazine hydrate it is also possible to obtain water-soluble crosslinking agents according to the invention.

Although it is preferred and desirable, it is not absolutely essential for the starting polymers to be water-soluble are. Since the conversion of the carbonyl groups to primary hydrazone groups increases the hydrophilicity of the polymers, it is in individual cases it is also possible to convert water-insoluble polymers into water-soluble polymers as a result of this reaction.

The aqueous solutions of the polymeric crosslinking agents obtained after the polymers have reacted with hydrazine hydrate according to the invention can generally be used without further cleaning operations. The polymer analog The reaction to hydrazones can also be carried out in a heterogeneous phase in organic solvents with hydrazine hydrate. The resulting water-soluble polymers can be used directly in aqueous solution after the organic phase has been separated off graze.

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As polymer emulsions with self-adhesive properties, which after application and subsequent drying on the substrate give well-adhering self-adhesive films are also preferred for the crosslinking process according to the additional patent application those suitable from acrylic acid esters, fumaric acid esters and / or vinyl compounds - especially on the way the emulsion polymerization - were prepared and optionally as further additives to modify the properties the pressure-sensitive adhesive films obtainable therewith can also contain tackifier resins and / or plasticizers. All in the main application specially named homo- and copolymers that are proposed for the process described there are also can be used without restriction for the process for the production of crosslinked pressure-sensitive adhesive films according to the additional application, in particular the above-described copolymers of acrylic acid esters with

high acrylic acid ester proportions, with keto or aldehyde groups in the polymer side chains or in the polymer structure in particular can be quickly networked.

These pressure-sensitive adhesive films obtained from dispersions or emulsions are expedient for effective post-crosslinking 0.5 to 10% by weight, and preferably 0.5 "to 3% by weight, of the water-soluble polymeric crosslinking agent containing primary hydrazone groups, based on the polymer content of the emulsion or dispersion, used.

The stability of the emulsions is determined by the post-crosslinking necessary addition of water-soluble polymeric crosslinking agent with primary hydrazone groups not significantly reduced. Even after the mixtures have been stored for a long time, they are the emulsions can be processed without any problems. There was a decrease in the effectiveness of the crosslinking agent, such as by hydrolysis not detectable.

The crosslinking takes place after the mixture has been applied to a flexible base made of paper, fiber

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fleece (nonwoven) fabric or a film can be made from short-term exposure to heat at temperatures between 60 and 16O ⁰ C, preferably in the temperature range between 80 and 120 ⁰ C, the usual drying area for pressure-sensitive adhesive polymer dispersions.

The mechanism of networking is analogous to the method described in the main application. The adhesive emulsions used also have a certain amount depending on the composition of the polymers and the type of auxiliary substances added Influence on the crosslinking reaction, which can already be seen from the examples in the main application.

The crosslinking process according to the invention is explained in more detail using examples:

Starting materials 1. Water-soluble polymers with prim. Hydrazone groups

For the crosslinking process according to the examples, the following three polymers with prim. Hydrazone groups used as crosslinking agents, which were prepared in the following way:
a) 0.63 mol of N-diacetone acrylamide were copolymerized radically together with 0.37 mol of acrylic acid in an ethanolic solution (according to a technically simplified embodiment, the polymerization can also be carried out as a precipitation polymerization in water). The polymerization reaction was carried out with exclusion of atmospheric oxygen at 70 to 80 ^° C. within three hours. The initiator used was a mixture of ammonium peroxydisulfate and sodium disulfite, which was dissolved in a small amount of water and added to the reaction mixture. At the end of the reaction time, the monomers were

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almost completely polymerized. The solids content of the ethanol polymer solution was about 33 wt .-% after the end of the polymerization. This solution became what was formed Copolymer precipitated by adding water and then dried.

Then the dried copolymer was dissolved in ammoniacal water (pH 10) and at room temperature with a equivalent amount of hydrazine (hydrate) converted (slightly exothermic reaction).

CH ₀ I ² CH-

CH-

C-NH-C-CH ₀ -C = O

I c- ι

CH-CH-

CH-

CH,

^ι 3

-C-NH-C - CH,

II ^£

CH, C -CH-, 3 H 3

NH ₂

HJi-NH,

The approximately 1% aqueous solution of the above Condensation reaction formed polymer with prim. Hydrazone group could be stored for a long time at room temperature and was used directly for mixing with pressure-sensitive adhesive emulsions.

b) According to a known method of methyl vinyl ketone was polymerized in acetone with azobisisobutyronitrile (AIBN) as initiator at 40 ⁰ C in 24 hours. The polymer was

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isolated after evaporation of the acetone (η ^ = 1.128, measured in 1% solution in acetone at 25 ° C).

The polymer was then dissolved in ethanol and hydrazine hydrate was added in a molar ratio of 1: 1. The education of the polyhydrazone took place at room temperature. The reaction mixture was then diluted with water. The received approx. 10% ethanol / aqueous solution (60% by volume / 40% by volume) of the polymer with prim. Hydrazone groups were used directly Networking used.

c) methyl vinyl ketone (50 mol%) and maleic anhydride (50 mol%) were polymerized at 40 ⁰ C with azobisisobutyronitrile (AIBN) as initiator in acetone within 24 hours. After the acetone had evaporated, the polymer was isolated (η -, = 1.105, measured in a 1% strength solution in acetone at 25 ^° C.).

The polymer was then immersed in ammoniacal water (pH 10) and dissolved at room temperature with an equivalent amount of hydrazine hydrate based on the carbonyl groups implemented. The approximately 10% strength aqueous solution of the polymer with hydrazone groups thus obtained was used immediately for crosslinking used.

2. Pressure-sensitive adhesive emulaions based on acrylic acid ester copolymers

For the blends according to the following examples, free-radical emulsion polymerization was carried out using the known methods Adhesive emulsions produced as follows:

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a) A mixture of:

93% by weight of 2-ethylhexyl acrylate 5 "acrylonitrile
2 "acrylic acid
0.1 "butanediol-i ^ -bis-acrylate and 0.1" carbon tetrabromide (Hegler)

was in deionized water, which is 1.5 wt% anionic Emulsifier (triethanolamine salt of 4-dodecylbenzoic acid) and 0.5% by weight of non-ionic emulsifier (nonylphenol polyglycol ether) contained, dispersed. The proportions by weight of organic phase to aqueous phase behaved as about 60:40. After displacing the oxygen in the air Nitrogen and heating the monomer emulsion to about 80 ° C, the polymerization was started by adding a small amount a mixture of ammonium peroxydisulphate and sodium disulphite. The reaction control for mastering the strong Exothermicity was carried out according to known processes, as are customary for such polymerizations in emulsions. After a reaction time of 2 1/2 hours, a stable, finely divided polymer emulsion was obtained. The solids content was approx. 60% by weight. The gel content of the polymer was 53.3%.

b) A mixture of:

68.5% by weight of 2-ethylhexyl acrylate 29.7 "n -butyl acrylic ester and 1.0 "acrylic acid

was dispersed in deionized water which, in addition to 4.0 wt. The proportions by weight of organic to aqueous phase were 50 '50.

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merization was carried out as described under a). The pesticide content was about 50% by weight. The gel content of the Polymer was 70%.

To test the technical adhesive properties, the polymer emulsions obtained by emulsion polymerization were treated with one of the polymeric crosslinking agents listed above with prim. Hydrazone groups in the form of a 10% aqueous solution are added with stirring and the mixture produced in this way is applied to a 25 μm thick polyethylene terephthalate (polyester) film using a conventional applicator (knife application) in a layer thickness of 50 g / m (dry weight). The wetting of the film when the mixture was applied was perfect. ^{The coatings were then heated to 120 °} C. for 5 minutes for drying and crosslinking.

Before the measurement of the technical adhesive properties, the test samples and the substrate intended for bonding were stored unglued for 48 hours in the test climate (conditioning). The following conditions were selected for this: normal test climate: 23 ° C., 52% relative humidity; humid test climate: 23 ⁰ C, 95% relative humidity.

The measurement of the bond strength (KK) and the creep values (Zstw,) were carried out according to those described in the main application application-related test methods. These understandably have a relatively large spreading error.

Example Λ

Varying amounts of the crosslinking agent Λ a were added to the pressure-sensitive adhesive emulsion 2a, and the bond strength and creep values were measured in the normal and moist test conditions of the pressure-sensitive adhesive films produced with the respective mixture.

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Networking KK Zstw. Zstw. medium 1 a (p / cm) Test climate Test climate (referring to
Solids content normal wet the polymer emulsion) (min) (min) (Wt%) 0 250 2,300 820 0.5 250 ^ 10,000 1 100 1.0 250 ^ 10,000 3 700 2.0 250 > 10,000 :> 10,000 2.5 250 > 10,000 ^ 10,000

Example 2

Changing amounts of the water-soluble polymeric hydrazone compound 1 b were mixed into the pressure-sensitive adhesive emulsion 2 a and Adhesive strength and creep values in the normal and humid test climate of the adhesive films produced with the respective mixture measured. (Layer thickness, dry: 32 g / m)

Networking KK Zstw. Zstw. medium 1 b (p / cm) Test climate Test climate (referring to
Pesticide proportions normal wet the polymer emulsion) (min) (min) (Wt%) O 230 3,000 700 1 225 > 10,000 ^ 10000 2 240 > 10,000 ^ 10000

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The pressure-sensitive adhesive emulsion 2a was mixed with different amounts of the polymeric hydrazone compound 1c and Adhesive strength and creep values in the normal and moist test climate of the adhesive produced with the respective mixture

adhesive film measured (layer thickness, dry: 30 g / m).

Networking KK Zstw. Zstw, medium 1 c (p / cm) Test climate Test climate (referring to
Solids content normal wet the polymer emulsion) (min) (min) (Wt%) 0 270 2,500 700 1 275 i * 10,000 > 10,000 2 275 > 10,000 ^ 10,000

Example 4

The pressure-sensitive adhesive emulsion 2b was mixed with varying amounts of the crosslinking agent 1b and the bond strength and creep values in the normal and humid test climate were mixed with the respective Adhesive films produced as a mixture measured (layer thickness, dry: 31 g / m)

Networking
medium 1 b
(referring to
Solids content
the polymer emulsion)
(Wt%) KK
(p / cm) Zstw.
Test climate
normal
(min) Zstw.
Test climate
wet
(min) 0 200 3,000 1,000 1 200 > 10,000 i »10,000 2 200 > 10,000 * 10,000

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From the examples it can be seen that according to the invention Crosslinking process obtained crosslinked pressure-sensitive adhesive films which, in addition to excellent cohesion and moisture resistance (high creep values under normal and humid conditions) have good adhesive strength. Despite successful networking, there are no noteworthy Adhesion values are impaired.

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Claims (3)

Claims 1. A process for producing crosslinked pressure-sensitive adhesive films from aqueous polymer emulsions or dispersions, in which a polymer emulsion, which after drying gives a self-adhesive film that adheres well to the substrate, is mixed with a water-soluble polyacrylhydrazide as a crosslinking agent, the mixture obtained is applied to a flexible base and on this by brief exposure to heat at a temperature of 60 to 160 ⁰ G, preferably at 80 to 120 ⁰ C, crosslinked is according to patent (patent application P 26 34 956.4), characterized in that the water-soluble polyacrylic hydrazide wholly or partially by a water-soluble polymer with primary hydrazone groups is replaced. 2. The method according to claim 1, characterized in that the amount of added crosslinking agent with prim. Hydrazone groups 0.5 to 10% by weight, preferably 0.5 to 3% by weight, based on the polymer content of the emulsion. 3. The method according to claim 1 or 2, characterized in that a polymer emulsion is used with self-adhesive properties is made from acrylic acid esters, ITumaric acid esters and / or Vinyl compounds and monomers copolymerizable therewith and which optionally contains adhesive resins and / or plasticizers as further additives. - 2 909833/0044 GTWMi- INSPECTED