JPS601272A - Adhesive composition - Google Patents

Abstract

PURPOSE:To provide an adhesive compsn. for paper having a high solid content, a relatively low viscosity and excellent initial adhesion properties, consisting mainly of a vinyl ester resin emulsion wherein a polyvinyl alcohol polymer with a low degree of polymerization is used as protective colloid. CONSTITUTION:The adhesive compsn. consists mainly of a resin emulsion obtained by emulsion polymerizing vinyl acetate by use of a polyvinyl alcohol with a low degree of polymerization as protective colloid or by emulsion copolymerizing vinyl acetate with a copolymerizable unsatd. compd. (e.g. ethylene). The polyvinyl alcohol has an average degree of polymerization of 20-300 and is shown by the formula. It is prepd. by polymerizing a vinyl ester (e.g. vinyl acetate) in the presence of a mercaptan of formula, R-SH (where R is 1-20C alkyl, hydroxyalkyl or alkyl with a carboxyl group) and saponifying the resultant polyvinyl acetate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive composition, and more particularly to a paper adhesive composition containing a vinyl ester resin emulsion as a main component.

Vinyl ester resin emulsion for paper tubes, bag making,
It is widely used as a paper adhesive for bonding cardboard sheets together. However, in recent years, there has been a strong demand for increased lamination speed, and machine speeds have become much faster.

For this reason, the initial adhesion performance of conventional adhesives is insufficient, and there is a strong desire for an adhesive with excellent initial adhesion performance.

One way to improve initial adhesion is to increase the resin concentration of the adhesive. However, polyvinyl alcohol (hereinafter referred to as P
Most of them are mainly composed of vinyl ester resin emulsions using VA (abbreviated as VA) as a protective colloid, and in this case, increasing the resin concentration significantly increases the viscosity, so industrially it is necessary to manufacture highly concentrated emulsions. It was difficult.

The present inventors have discovered that by emulsion polymerizing a vinyl ester monomer as a fully protective colloid, a low polymerization degree PVA with a polymerization degree of 20 to 300 is used instead of the conventionally used Hatake polymerization degree PVA. The inventors have discovered that an emulsion with a high solid content and a relatively low viscosity can be obtained, and that this emulsion has excellent initial adhesion when laminating paper sheets together, and has thus arrived at the present invention.

The degree of polymerization of PVA used in the present invention is preferably in the range of 20 to 300, and the degree of polymerization is determined by acenalizing the PVA and converting it into PV.
After soaking with Ac, the viscosity was measured in acetone and the medium-knit type [
It is determined by Hanao Nakajima: Kobunshi-6451 (1949), 1. An emulsion obtained by emulsion polymerization mainly composed of vinyl acetate and using PVA with a low degree of polymerization as a protective colloid has a higher solid content than an emulsion obtained in the same way using ordinary high-11-coated PVA. The viscosity is much lower, and the solids concentration is lower than the conventional 40~
It is possible to further increase the value from around 50% (weight) @,
This makes it possible to achieve 55% or more, especially 60 inches or more. In order to maintain this effect, the PVA used in the present invention must have an average degree of polymerization of 20 to 301), preferably 50 to 200, and a degree of saponification of 70 to 99 mol, as described above. Among these PVAs, from the viewpoint of the desired viscosity reduction effect of the emulsion and the stability during emulsion polymerization, in particular, those with the general formula (+)
[However, R represents an alkyl group having 1 to 20 carbon atoms, a hydroxyalkyl group, or an alkyl group having a carboxyl group, and S represents a sulfur atom. It is preferable to use PVA with a low degree of polymerization having an average degree of polymerization of 20 to 300. If the degree of polymerization is less than 20, the stability of the emulsion will be insufficient, and if the degree of polymerization exceeds 300, the viscosity reducing effect will be reduced.

Specific examples of the alkyl group having 1 to 20 carbon atoms, hydroxyalkyl group, or alkyl group having a carboxyl group for R in the general formula (1) include methyl group, ethyl, n
-propyl, n-7', t-phthyl, n-hexyl, n-hephthyl, 2-ethylhexyl, n-dodecyl, hydroxyethyl.

Examples include 2.3-dihydroxypropyl, carboxymethyl, and carboxyether, which have such a terminal group at the end of the molecule and have an average degree of polymerization of 20 to 300 (
D Low li Combined W P V A u Example j'-tf R
- When polymerizing vinyl esters, including vinyl acetate, in the presence of mercaptans represented by S H (R is the same as above), strictly control the method of adding the mercaptans to the polymerization system. It can be obtained by saccharifying the polyvinyl acetate obtained by the conventional method. Among these, PVA in which R is an alkyl group having 8 to 20 carbon atoms is particularly preferred because it has a large stabilizing effect.

The above low degree of polymerization P in the emulsion used in the present invention
The blending amount of VA is 1 to 30% by weight, preferably 2 to 20% by weight, based on the vinyl ester resin, and in combination with the above-mentioned low polymerization degree PVA, within a range that does not impair the effects of the present invention,
Protective colloids such as normal PVA with a high degree of polymerization, modified PVA, methylcellulose, hydroxyethylcellulose, etc. can be used, and conventionally known surfactants can also be used in combination within a range that does not impede adhesive performance. The vinyl ester resin emulsion, which is the main component of the adhesive composition of the invention, is vinyl acetate alone mixed with the aforementioned low polymerization degree PV.
Those obtained by emulsion polymerization using A, or polymerizable unsaturated compounds copolymerizable with vinyl acetate, such as acrylic esters such as methyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, and methyl methacrylate. , methacrylic acid esters such as ethyl methacrylate and butyl methacrylate, α-olefins such as ethylene and imbutylene, diptyl maleate, dioctyl maleate, vinyl chloride, unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, etc. Emulsification of 111 or 2 or more types of monomers such as acids, vinyl esters of carboxylic acids having 3 to 12 carbon atoms such as N-methylolacrylamide, vinyl pukopionate, vinyl versatate (rVeova-10J, trade name of Shell Chemical), etc. It is obtained by copolymerization. Among these, acrylic esters, ethylene, and carbon i3 that effectively internally plasticize vinyl acetate resin.
A copolymerized emulsion with a vinyl ester of a carboxylic acid of 1 to 12 is preferably used. Especially when the ethylene content is 10~
A 40% by weight ethylene-vinyl acetate copolymer emulsion exhibits good adhesion to water-repellent paper and plastic-laminated so-called hydrophobic paper, and is therefore preferably used.

Furthermore, it is effective that the emulsion used in the present invention has a solid content concentration of 55% by weight or more, preferably 60% or more; anything less than 55% has poor initial adhesion. In addition, there is no particular upper limit on the solid content concentration, but
It is approximately 70% by weight.

In the adhesive composition of the present invention, necessary additives such as a plasticizer, a fungicide, an antifoaming agent, and a thickener are added to the emulsion according to the individual purpose.

The present invention will be explained in more detail with reference to Examples below.
These examples do not limit the invention in any way. In the examples, parts and parts are based on weight unless otherwise specified.

Example 1 Two parts of PVA having a hydroxyethyl tail group at one end and having a degree of polymerization of 120 and a degree of saponification of 87.5 molar were charged into a reactor equipped with a stirrer, a reflux condenser, and a nitrogen inlet tube.
After nitrogen substitution, 35 parts of ion-exchanged water was added, and the mixture was heated and stirred at 80°C.

After PVA was completely dissolved, the mixture was cooled to room temperature under a nitrogen stream, 7.5 parts of vinyl acetate monomer was added, and the temperature was raised to 70° C. with stirring. After the internal temperature reached 70° C., continuous addition of 3.5 parts of a 1% aqueous hydrogen peroxide solution and 2 parts of a 5% Rongalite aqueous solution was started to initiate polymerization. After starting Shigetani, 92.5 parts of vinyl acetate monomer was uniformly added over 2 hours. During this time, 6 parts of the above PVA was dissolved in 14 parts of ion-exchanged water that had been replaced with nitrogen.
was added continuously. After adding vinyl acetate monomer,
The temperature was raised to 80°C and maintained for 1 hour to complete polymerization.

The obtained polyvinyl acetate emulsion had a solid content concentration of 65
7%, and the viscosity was 6,500 mPa5-8 (30'CB type viscometer). 5 parts of dibutyl phthalate (DBP) was added to 100 parts of the solid content of this emulsion, and the initial adhesion was evaluated by the Tappi method described below. The results are shown in Table 1, and as is clear from the comparative examples described later, it is recognized that the initial adhesiveness is significantly improved compared to the conventional emulsion using PVA with a high degree of polymerization.

[Initial adhesion test]

Tappi Milumi Monograph Series 74 pages (196
3) The method described. Liner paper (basis weight 20
Apply adhesive to (1/rn'), stick together, and immediately
80 Time (seconds) for paper tear rate to exceed 50% after peeling
It was expressed as

Example 2 The same reactor as in Example 1 was used, and the kP V used in Example 1 was
The same operation as in Example 1 was carried out except that PVA having a degree of polymerization of 50 and a degree of saponification of 89.0 mol at one end of HOOC-CH2-CH2-8- was used. The obtained polyvinyl acetate emulsion had a solid content concentration of 1i64.8% and a viscosity of 5,800 mPa5-s (30
℃). 5 parts of DBP was added to 100 parts of the solid content of this emulsion, and the initial adhesion was evaluated. The results are shown in Table 1.Comparative Example 1 In place of PVA in Example 1, polymerization degree was 500 and saponification degree was 88.
．． Polymerization was attempted in the same manner as in Example M using 0 molar normal PVA. However, if the concentration of the PVA aqueous solution added sequentially during the polymerization was 30%, the viscosity would be too high and it could not be added, so a 20% PVA aqueous solution was used to obtain an emulsion with the same solid content concentration as in Example 1. Therefore, the amount of ion-exchanged water at the initial stage of polymerization was reduced to 25 parts. After the polymerization started, acetic acid and nyl monomer were added, but 62 of the 92.5 parts
．． When 5 parts were added, the viscosity increased significantly, resulting in poor stirring and a large number of aggregates.

Comparative Example 2 Using the same reactor as in Example 1, 8 parts of ordinary PVA with an average degree of polymerization of 1750 and a degree of saponification of 87.5 mol% and 98 parts of ion-exchanged water were added and dissolved by heating, and then vinyl acetate monomer was dissolved. Added 10 parts. The temperature was then raised to 70°C, and polymerization was carried out with 3 parts of a 1% aqueous hydrogen peroxide solution and 2 parts of an aqueous solution of 5-thiartaric acid.

After the start of polymerization, 90 parts of vinyl acetate monomer was added uniformly over 2 hours, and after the addition was completed, the mixture was maintained at 80° C. for 1 hour. The obtained polyvinyl acetate emulsion had a solid content concentration of 50.
4%, and the viscosity was 34.500 mPa5-s (30°C). DBP5 per 100 parts of solid content of the emulsion
part was added to evaluate the initial adhesion. The results are shown in Table-1.

Example 3 A pressure-resistant autoclave equipped with a repellent stirrer, a nitrogen inlet tube, and various drug injection pumps, has an n-dodecylthiyl group at one end of the molecule, and has a polymerization degree of 1101 and a saponification degree of 90.2 mol%.
After heating and dissolving 4.5 parts of low polymerization degree PVA with 60 parts of ion-exchanged water, 10' parts of vinyl acetate monomer was added, and after purging with nitrogen, the temperature was raised to 60''C, and ethylene was dissolved at 45 k4/
It was press-fitted to CD. Polymerization was carried out using a 1T hydrogen peroxide aqueous solution and a 5% Rongalite aqueous solution. After initiation of polymerization, acetic acid and 90 parts of nil monomer were continuously added over 3 hours.

The obtained ethylene-vinyl acetate copolymer emulsion had a solid content concentration of 66.3% and a viscosity of 3,800 mPa5-8 (
(30°C), ethylene content: 1 g, 5%.

Table 1 shows the results of initial adhesion using this emulsion.

Comparative Example 3 Polymerization was carried out in the same manner as in Example 3, except that ordinary PVA1 with a degree of 1 degree of 500 degrees and a degree of saponification of 87.5 mol% was used in place of the PVA used in Example 3, and 70 parts of vinyl acetate monomer was added. By the way, stirring became impossible due to the increase in viscosity.

Comparative Example 4 Amount of ion-exchanged water in Comparative Example 3? ! : An ethylene-vinyl acetate copolymer was polymerized in the same manner as in Comparative Example 3 except that the amount was changed to 90 parts, and the solid content concentration was 56.0%, the viscosity was 3,500 mPa5-s (30°C), and the ethylene content was 1 s, o%. I got an emulsion. The results of the initial adhesion of this emulsion are shown below.
Shown in 1.

Table-1

Claims (1)

Scope of Claims: (1) An adhesive composition comprising, as a main component, a vinyl ester resin emulsion in which a low polymerization degree polyvinyl alcohol polymer having an average degree of polymerization of 20 to 300 is used as a protective colloid. (2) The adhesive composition according to claim 1, wherein the low degree of polymerization polyvinyl alcohol polymer is polyvinyl alcohol represented by the general formula (1). [However, R represents an alkyl group having 1 to 20 carbon atoms, a hydroxyalkyl group, or an alkyl group having a carboxyl group, and represents a sFi sulfur atom. (8) The adhesive composition according to claim 1, wherein the vinyl ester resin emulsion is a homopolymer of vinyl acetate or a copolymer emulsion of vinyl acetate and a polymerizable unsaturated compound. (4) The polymerizable unsaturated compound is ethylene, carbon number 3 ~]2
The adhesive composition according to claim 3, which is a vinyl ester or an acrylic ester. (5) Claim 4, wherein the copolymer emulsion of vinyl acetate and a polymerizable unsaturated compound is an ethylene-vinyl acetate copolymer, and the ethylene content of the copolymer is 10 to 40 wt%. adhesive composition. (6) The adhesive composition according to claim 1, wherein the solid content concentration of the vinyl ester resin emulsion is 55 or more.