NO813455L - Glue on the basis of PVAC EMULSION AND PROCEDURE FOR ITS MANUFACTURING - Google Patents

Description

The present invention relates to an adhesive based on a

aqueous latex of plasticized vinyl acetate polymer, containing at least ehpolyvinyl alcohol as a protective colloid,

and the peculiarity of the adhesive according to the invention is that the dry matter concentration in the latex is between 50 and 70% by weight, the dimensions of the particles of vinyl acetate polymer with molecular weight from 10,000 to 300,000 are between 0.1 and 3 micrometers,

the polyvinyl alcohol(s) used make up 0.5 to 3% by weight of the polymer and any plasticizer makes up 0 to 30% by weight of the polymer and the curing time is less than 10 sec.

The invention also includes a method for production

of the adhesive in question, where an aqueous emulsion of vinyl acetate either alone or with at least one copolymerizable monomer is polymerized in the presence of at least one polyvinyl alcohol, then optionally at least one plasticizer is added to the latex formed, and the peculiarity of the method according to the invention is that the polymerization mixture with pH between 2.5 and 6 contains water, 40 to 65% by weight of the mixture of vinyl acetate or a mixture of vinyl acetate and copolymerizable monomer, 1 to 10% by weight of the monomer or monomers of at least a chain transfer agent and 0.5 to 3% by weight of the mixture of monomer or monomers and chain transfer agent of at least one polyvinyl alcohol and that the plasticizer constitutes 0 to 30% by weight of the polymer formed.

These and other features of the invention appear from the patent claims.

Adhesives for porous materials are known based on aqueous latex of vinyl acetate polymer containing polyvinyl alcohol as a protective colloid, and internal or external softeners,

but these types of glue have a far too long curing time to be used on current automatic machines.

On these machines, glue of the hot melt type is usually used, i.e. mixtures of resins which are applied to the porous materials in a molten state. However, such adhesive types require storage at an elevated temperature which can lead to degradation during storage and their use under the influence of heat necessitates their melting and treatment, which can be dangerous and entail the risk of molten material being ejected.

The glue which is the subject of the present invention does not present these disadvantages, and can be used on relevant automatic machines, as it is not in a molten state and thus does not require any precautions during storage and there is no danger during handling.

In these latexes which form the basis of the adhesive, the dry matter concentration is between 50 and 70% by weight and preferably between 55 and 65% by weight and the copolymer particles have "an average diameter between 0.1 and 3 micrometers with a grain size distribution which can be wide or narrow depending on the polymerization conditions used.

By vinyl acetate polymer is meant here homopolymers as well as copolymers of the mentioned monomer with at least one copolymerisable monomer selected from alkyl esters of unsaturated mono- or dicarboxylic acids with 3 to 6 carbon atoms and with 1 to 10 carbon atoms in the alkyl group, such as acrylates, methacrylates, maleates, fumarates of methyl, ethyl, butyl, ethylhexyl, etc

vinyl esters of saturated monocarboxylic acids with 3 to 15 carbon atoms such as vinyl pivalate vinyl laurate, olefins with 2 to 5

carbon atoms such as ethylene, propylene, butenes, vinyl chloride and vinylidene chloride. In the copolymer, the copolymerizable monomer can constitute 1 to 70% by weight and preferably 5 to 50% by weight.

Some of the aforementioned copolymerizable monomers have a softening ability for polyvinyl acetate, i.e. they give copolymers a glass transition temperature lower than the glass transition temperature for polyvinyl acetate. They are consequently internal plasticizers that allow limiting the amount of plasticizer added to the latex obtained and even omitting this addition. This offers the advantage that migration of the plasticizer in the glue is avoided and allows the use of this glue for food packaging.

The polyvinyl alcohol or alcohols present in the latex in an amount: between 0.3 and 3% by weight and preferably 0.75 and 1.5

% by weight in relation to the polymer and is selected from polyvinyl alcohols with a viscosity measured in an aqueous 4% by weight solution of 2 to 50 Mpas and an ester index of 80 to 180

and preferably 100 to 150.

As regards the plasticizer, which constitutes 0 to 30% by weight and preferably 2" to 20% by weight of the polymer, this is used alone or in a mixture and is chosen from among plasticizers and classical coalescing agents for polyvinyl acetate, such as optionally halogenated 4 to 6C alkyl phthalates, such as dibutyl phthalate, diethyl phthalate, benzyl butyl phthalate, trichloroethyl phthalate, phthalate, adipate and dibenzoate of ethylene glycol, acetate of butyl carbitol, butyl glycolate, glycerol triacetyl, dipropyl or diisobutyl succinates, glutarate and adipates, tri-cresyl and triphenyl phosphates.

This plasticizer is present in the latex when the polymer

is a homopolymer of vinyl acetate or a copolymer in which the copolymerizable monomer has no softening ability or an insufficient softening ability, or is not used in a sufficient amount to soften the copolymer.

The polymerization is carried out in emulsion in a known manner,

in the presence of at least one initiator and possibly one or more emulsifiers and/or pH regulators.

The monomers that are copolymerizable with vinyl acetate are represented by alkyl esters of unsaturated mono- or dicarboxylic acids with 3 to 6 carbon atoms and 1 to 10 carbon atoms in the alkyl group, such as acrylates, methacrylates, maleates, fumarates of methyl, ethyl, butyl, ethylhexyl, vinyl esters of saturated monocarboxylic acids with 3 to 15 carbon atoms such as vinyl pivalate or vinyl laurate, olefins with 2 to 5 carbon atoms such as ethylene, propylene and butenes, further vinyl chloride and vinylidene chloride. These monomers are used alone or in a mixture in proportions between 1 and 70% by weight and preferably between 5 and 50% by weight of the mixture of vinyl acetate and copolymerizable monomer.

The vinyl acetate and the co-monomer or co-monomers are introduced

in the polymerization mixture alone or in a mixture either entirely before the polymerization or during the polymerization in step fractions or continuously, or partially before polymerization and partially during the polymerization in step fractions or continuously, under pressure if the comonomer is gaseous.

The chain transfer agent is represented, among other things, by halogenated hydrocarbons, such as ethylene chloride, chloroform, carbon tetrachloride, bromoform, carbon tetrabromide, di chloro tan.y. trichloroethane and preferably of mercaptans such as lauryl mercaptan, dodecyl mercaptan, aminophenyl mercaptan. It is introduced alone or in a mixture in a manner known per se, such as e.g. simultaneously with the monomer or the mixture of monomers or simultaneously and especially in solution in the monomers or one of the monomers.

The polyvinyl alcohol is used in an amount of 0.5 to 3% by weight and preferably 0.75 to 1.5% by weight in relation to the mixture of monomer or monomers and chain transfer agent, as a protective colloid, which affects the stability of the emulsion. It has a viscosity measured in a 4% by weight aqueous solution of between 52 Mpas and an ester index between 80 and 180 and preferably between 100 and 150. Any ordinary polyvinyl alcohol corresponding to these properties can be used alone or in admixture with another polyvinyl alcohol with different properties but within the above limits.

Alkali metal persulfates, water-soluble diazo compounds or redox systems based on aqueous hydrogen peroxide, organic peroxides or hydroperoxides are preferably used as initiators, alone or in a mixture, in proportions of approximately 0.05 to 4.5% by weight and preferably 0.1 to 2% by weight

of mononerehe. It is introduced into the polymerization mixture in its entirety before the polymerization or during the polymerization in stepwise fractions or continuously, or also partially before the polymerization, the other part being introduced during the polymerization in stepwise fractions or continuously, especially when the useful life of the initiator at the polymerization temperature is short.

The emulsifier or agents, which ensure the stability of the reaction mixture and the latex obtained, can be anionic and/or nonionic and are classic products of polymerization in emulsion.

As anionic emulsifiers, mention may be made of fatty acid salts, alkyl sulfates, alkyl sulfonates, alkyl aryl sulfonates, alkyl sulfosuccinates, alkali metal alkyl phosphates, alkyl sulfosuccinates, sulfonates of alkylphenol polyglycol ethers, the salts of esters of alkyl sulfo-polycarboxylic acids, condensation products of fatty acids with oxy- and amino-alkanesulfonic acids, sulfated derivatives of polyglycol ethers, sulfated esters of fatty acids and polyglycols and sulfated alkanolamides of fatty acids.

Fatty acid esters can be mentioned as non-ionic emulsifiers

of polyalcohols, alkahol amides of fatty acids, copolyoxides of ethylene and propylene, oxyethylenated alkylphenols and sulfated oxyethylenated alkylphenols.

The amount of emulsifier used or agents which an-

is turned is 0 to 2% by weight in relation to monomer or monomers and the introduction is carried out either in its entirety before the polymerization or partially before the polymerization, the remaining part being added to the reaction mixture during the polymerization in step fractions or continuously, or in its entirety during

the polymerization in step fractions or continuously, depending on the average particle diameter of the latex that is produced.

The pH regulator which keeps the polymerization mixture at pH 2.5 to 6 is constituted in particular by a base such as sodium hydroxide or ammonia and/or a buffer such as sodium acetate or sodium bicarbonate and is added alone or in admixture, either completely or partially before the polymerization, the remaining part is added during the polymerization in step fractions or continuously, or in its entirety during the polymerization in step fractions or continuously.■

The polymerization temperature depends on the initiator used and the polymer to be produced and is usually

o

between 2 5 and 90 C.

When the polymerization is finished, optionally, if necessary, a plasticizer is added to the formed latex in an amount not exceeding 30% by weight and preferably in an amount of 2 to 20% by weight of the polymer, to obtain an adhesive. This plasticizer, which is used alone or in a mixture, is selected from active agents and classic coalescing agents for polyvinyl acetate, such as 4 to 6c alkyl phthalates which are optionally halogenated, such as dibutyl phthalate, diethyl phthalate, butyl benzyl phthalate, trichloroethyl phthalate, phthalate, adipate and dibenzoate of ethylene glycol, butyl carbitol acetate , butyl glycolate, glycerol triacetin, succinates, glutarate, dipropyl adipate or diisobutyl adipate, tricresyl phosphates and triphenyl phosphates.

It is clear that common additives such as volatile solvents such as methylene chloride, fillers such as alkali metal carbonates, biocides, antifoam agents, etc. can be added to the glue.

The glues based on the aqueous latex of polyvinyl acetate can be used on all common machines for gluing at high speed and allow the treatment of porous materials such as wood, paper and cardboard, and the glues can be used especially within the packaging industry.

In what follows, the invention will be illustrated in more detail

by means of embodiment examples in which:

- the percentages are based on weight

- the viscosity of the polyvinyl alcohol is measured by flow through a capillary tube of an aqueous solution with a concentration of 4% by weight at 20°C. -the viscosity of the latex is measured at 23°C on the Brookfield viscosity with a revolution speed of 50 revolutions/minute,

-the molecular weight of the polymer is measured by chromatography on

gel or by viscometry

- the curing time of the glue under a load of 20 g/cm is the time required for 2 pieces of cardboard with a surface weight of 280 g/m<2> and a COBB index (30 sec.) of 71 g/m 2 which is glued together by depositing 30 to 35 g of glue/m 2 of the cardboard, with an opening time of approximately 3/10 sec. and an adhesive force of 400 g/linear cm no longer separate when subjected to a load of

20 g/cm at 20°C at 65% relative humidity.

EXAMPLE 1

In a 4 liter flask equipped with a stirrer and cooling attachment, introduce in order:

-900 g demineralised water

-53 g of an aqueous solution of 13% polyvinyl alcohol with viscosity 4 mpas and ester index 125 (a) -14 g of an aqueous solution of 12% polyvinyl alcohol with viscosity 25 mpas and ester index 140 (b) -16.5 g of an aqueous solution of 25% oxyethylenated and sulfated alkylphenol

-2 g of sodium bicarbonate

The resulting mixture is then heated at 80°C and this temperature is maintained throughout the polymerization. Before the mixture reaches 80°c, 1.7 g of ammonium persulphate dissolved in

3

10 cm of water.

A mixture is formed from 1700 g of vinyl acetate and 85 g of lauryl mercaptan and a solution of 1.7 g of potassium persulphate in 100 cm 3 of water is simultaneously introduced continuously over the course of 5 hours and 30 minutes.

The reaction mixture is kept for 1 hour at 80°C and then cooled.

2,830 g of a polyvinyl acetate latex with the following properties is obtained:

This latex is divided into 4 equal portions to each of which different amounts of dibutyl phthalate are added to obtain glue where the curing times are measured and the following results are obtained:

EXAMPLE 2

Example 1 is repeated with.:.

•SBSO and demineralized water

-106g of solution (a) of polyvinyl alcohol instead of 53 g -28g of solution (b) of polyvinyl alcohol instead of 14 g.

2900 g of latex with the following properties is obtained:

Addition of different amounts of dimethyl phthalate gives glue where the curing time is as follows:

For comparative purposes, the same experiment is carried out without lauryl mercaptan and this gives a latex with properties:

Without dibutyl phthalate and with 16% dimethyl phthalate the curing time is

for the obtained glue more than 30 seconds.

EXAMPLE 3

One proceeds in the same way as in example 2, but with 51 g of lauryl mercaptan instead of 85 g, a latex with the following properties is obtained:

Addition of a plasticizer gives glue with the following curing times:

EXAMPLE 4

Example 1 is repeated with:

-710 g demineralized water instead of 900 g

-212 g solution (a) of polyvinyl alcohol instead of 53 g -56 g of solution (b) of polyvinyl alcohol instead of 14 g

-34 g of lauryl mercaptan instead of 85 g

The properties of the latex are the following:

By adding dibutyl phthalate, glue is obtained with the following curing times:

EXAMPLE 5

Example 2 is repeated while replacing solutions (a) and (b) with 134 g of a solution of 13% polyvinyl alcohol with a viscosity of 25 mpas and an ester index of 100.

The addition of 7% dibutyl phthalate gives an adhesive with a curing time of 9.5 seconds, while without phthalate the curing time is 14.4 seconds.

EXAMPLE 6

Example 2 is repeated with:

-42.5 g of lauryl mercaptan instead of 85 g

The properties of the latex are the following:

Addition of different plasticizers in amounts of 10% in relation to the polymer gives:

EXAMPLE 7

In a 4-liter flask equipped with a stirrer and cooling apparatus, introduce in order:

- 830 g demineralized water

-116 g of an aqueous solution of 13% polyvinyl alcohol with a viscosity of 4 mpas and an ester index of 125 (a) -29 g of an aqueous solution of 12% polyvinyl alcohol with a viscosity of 25 mpas and an ester index of 140 (b) -16.5 g of an aqueous solution of 25% oxyethylenated and sulfated alkylphenol

-3 g of sodium bicarbonate

The resulting mixture is heated to 80°C and this temperature is maintained throughout the polymerization process. Before the mixture is at 80°C, 2.5 ammonium persulfate is added up to

3

dissolved in 10 cm of water.

A mixture consisting of 1360 g of vinyl acetate, 340 g of butyl maleate and 85 g of lauryl mercaptan and a solution of 4 g of potassium persulfate in 100 cm 3 of water is simultaneously introduced continuously over the course of 6 hours.

The reaction mixture is kept for a further 1 hour at 80°C and then cooled.

2,780 g of a vinyl acetate/butyl maleate copolymer latex 80/20 with the following properties is obtained:

The copolymer is softened with butyl maleate and the latex then gives an adhesive with a curing time of 7 seconds.

EXAMPLE 8

Example 7 is repeated with a mixture of 275 g of vinyl acetate instead of 1360 g and 425 g of butyl maleate instead of 340 g.

2,780 g of vinyl acetate/butyl maleate copolymer 75/25 latex with the following properties is obtained:

EXAMPLE 9

In a 4 liter flask equipped with a stirrer and cooling attachment, introduce in order:

- 830 g demineralized water

-116 g of an aqueous solution of 13% polyvinyl alcohol with viscosity 4 mpas and ester index 125 (a) -29 g of an aqueous solution of 12% polyvinyl alcohol with viscosity 25 mpas and ester index 140 (b) -16.5 g of an aqueous solution of 25% oxyethylenated and sulfated alkylphenol

-2 g of sodium bicarbonate.

The resulting mixture is then heated at 80°C and this temperature is maintained throughout the polymerization process. Before the mixture reaches a temperature of 80°C, 1.7 g of ammonium persulphate dissolved in 10 cm 3 of water is added.

The resulting mixture of 1530 g of vinyl acetate, 170 g of butyl acrylate and 85 g of lauryl mercaptan and a solution of 3.4 g of potassium persulphate in 100 cm of water is introduced simultaneously, continuously over a period of 5 hours and 30 minutes.

The reaction mixture is then kept at 80°C for one hour and then cooled.

2780 g of a vinyl acetate/butyl acrylate copolymer latex 90/10 with the following properties is obtained:

The addition of 5% dibutyl phthalate relative to the copolymer gives an adhesive with a curing time of 5 seconds.

EXAMPLE HO

Example 9 is repeated with 1360 g of vinyl acetate instead of 1530 g and 340 g of butyl acrylate instead of 170 g.

2780].g of a vinyl acetate/butyl acrylate/copolymer latex 80/20 is obtained with the following properties:

EXAMPLE 11

In a 4 liter autoclave equipped with a stirrer, introduce in order:

-893 g demineralized water

-77 g of an aqueous solution of 20% polyvinyl alcohol with a viscosity of 4 mpas and an ester index of 125 (a) -32 g of an aqueous solution of 12% polyvinyl alcohol with a viscosity of 25 mpas and an ester index of 140 (b) -18 g of an aqueous solution of 25% oxyethylenated and sulfated alkylphenol

-2 g of sodium bicarbonate

After placing the autoclave under vacuum for degassing, ethylene is introduced up to a pressure of 20 bar in the autoclave and this pressure is maintained constant during the polymerization process by adding ethylene.

The resulting mixture is heated at 80°C and this temperature is maintained throughout the polymerization.

Before the mixture reaches 80°C, 2 g of ammonium persulphate are added

3

dissolved in 100 cm water.

A mixture consisting of 165 3 g of vinyl acetate and 54 g of lauryl mercaptan and a solution of 4 g of potassium persulfate in 100 cm 3 of water is introduced simultaneously and continuously over the course of 5 hours.

The introduction of ethylene is interrupted and the reaction mixture is kept for a further 1 hour at 80°C and then cooled.

3080 g of a vinyl acetate/ethylene copolymer 90/10 with the following properties is obtained:

EXAMPLE 12

Example 11 is repeated with 1672 g of vinyl acetate instead of 1653 g and with an ethylene pressure in the autoclave of 13 bar instead of 20 bar.

3070 g of a vinyl acetate/ethylene copolymer latex 92/8 with the following properties is obtained:

Addition of 3% dibutyl phthalate relative to the copolymer gives an adhesive with a curing time of 7 seconds.

Claims (9)

1. Glue based on aqueous latex of softened polyvinyl acetate, containing at least one polyvinyl alcohol as a protective colloid, characterized in that the concentration of dry matter in the latex is between 50 and 70% by weight, the size of the particles of polyvinyl acetate with a molecular weight of 10,000 to 300,000 is between 0.1 and 3 micrometres, the polyvinyl alcohol or alcohols make up 0.5 to 3% by weight of the polymer and any plasticizer make up 0 to 30% by weight of the polymer, and the glue's curing time is less than 10 seconds. 2. ■■! Glue as specified in claim 1, characterized in that the polyvinyl acetate et a homopolymer. 3. Glue as specified in claim 1, characterized in that the polyvinyl acetate is a copolymer of the aforementioned monomer with a copolymerizable monomer represented by alkyl esters with unsaturated mono- or dicarboxylic acids (3-6c) and with 1 to 10 carbon atoms in the alkyl group, vinyl esters of unsaturated monocarboxylic acids (3-15c), olefins ( 2-5c), vinyl chloride and vinylidene chloride. 4. Glue as specified in requirements 1-3, characterized in that the polyvinyl alcohol or alcohols have a viscosity between 2 and 50 mpas. and an ester index between 80 and 180. 5. Glue as specified in requirements 1-4, characterized in that the plasticizer, alone or in a mixture, selected from alkyl (4-6c) phthalates, possibly halogenated, ethylene glycol phthalate, adipate, dibenzoate, butyl carbitol acetate, butyl glycolate, glyceryl triacetate, dipropyl or diisobutyl succinates, glutarate and adipates, tricresyl and triphenyl phosphates. 6. Method for producing the adhesive specified in claim 1, where vinyl acetate is polymerized in an aqueous emulsion alone or together with at least one copolymerizable monomer in the presence of at least one polyvinyl alcohol, after which at least one plasticizer is optionally added to the latex formed, characterized in that the polymerization mixture, where the pH is kept between 2.5 and 6, contains water, 40 to 65% by weight vinyl acetate or a mixture of vinyl acetate/copolymerizable monomer, 1-10% by weight of the monomer or monomers of at least one chain transfer agent and 0.5 to 3% by weight of the mixture of monomer or monomers and chain transfer agent of at least one polyvinyl alcohol, the plasticizer constituting 0 to 30% by weight of the polymer formed. 7. Method as stated in claim 6, characterized in that a halogenated hydrocarbon or a mercaptan is used as chain transfer agent. 8. Method as stated in claim 6 or 7, characterized in that the polymerization is carried out in the presence of at least one initiator and possibly one or more emulsifiers and/or one or more pH regulators. 9. Method as stated in claims 6 to 8, characterized in that the polymerization temperature is kept between 25 and 90°C.