JP3108380B2 - Reactive hot melt adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-melt adhesive composition which can have a higher degree of polymerization or form a crosslinked structure by reaction with moisture.

[0002]

2. Description of the Related Art A hot-melt adhesive is a type of adhesive in which adherends are adhered to each other in a heated and molten state, and exhibit adhesive strength when cooled and solidified. It has characteristics such as no solvent and no solvent, and has been widely used for various bonding applications.

[0003] The hot-melt adhesive is mainly composed of a thermoplastic resin having a linear chemical structure because it needs to be melted by heating. For this reason, there is no problem with the adherence of adherends whose materials themselves are not so strong, such as paper, but the adhesive strength is not sufficient for applications requiring high strength such as structural adhesives. However, when processing involving heat generation such as cutting is performed, there is a problem that peeling occurs. For this purpose, reactive isocyanate groups (NCO
Polyurethane-based hot melt adhesives using a polyurethane resin having a base group) are used.

The above-mentioned conventional polyurethane hot-melt adhesive composition has a high melt viscosity and requires high-temperature heating to reduce the viscosity. As a result, the reaction of the NCO group proceeds and the stability is not sufficient. Did not. Furthermore, when a thermoplastic resin having a low softening temperature is used as the adherend, the adherend may be deformed by the heat of the applied adhesive.

[0005] In order to solve this problem, there is provided a polyurethane-based reactive hot melt adhesive composition containing diphenylmethane diisocyanate (MDI) as an isocyanate component, wherein 2,4'-diphenylmethane diisocyanate (2,4 ' -MDI) 70% by weight
The ones used above are disclosed (JP-A-8-601).
No. 29).

Further, as a reactive hot melt adhesive which is stable in a heated and molten state and promotes curing after cooling, a reactive hot melt adhesive using a special catalyst has been disclosed (JP-A-7-258620). Gazette).

[0007]

However, Japanese Patent Laid-Open No. 8-6 / 1996
According to the technology described in Japanese Patent No. 0129, the NCO group at the 2-position in MDI has a relatively low reactivity, so that the viscosity of the composition can be reduced, but the reaction after cooling is slow. , 70% by weight of 2,4′-isomer
Those containing the above components have a practical problem since the progress of the reaction is slow.

On the other hand, according to the technique described in Japanese Patent Application Laid-Open No. 7-258620, a hot-melt adhesive based on polyurethane using an aromatic isocyanate compound disclosed in the publication is 2,4'- MDI is not used and any NCO like 4,4'-MDI
Diisocyanates are also disclosed whose groups are also highly reactive.
Therefore, when a polyurethane prepolymer is synthesized at a preferable synthesis temperature of 100 ° C. to 120 ° C., the temperature in the reaction vessel rises to near 160 ° C., and allophanate bonds and the like are generated. It is difficult.

Further, a hot melt adhesive based on a polyurethane using an aliphatic isocyanate compound described in JP-A-7-258620 has low reactivity of NCO groups and is easy to adjust the reaction temperature. Melt viscosity during production can be kept low in comparison with hot-melt adhesives based on polyurethanes using aromatic isocyanate compounds, but the physical strength of the adhesive itself is low even after curing. Therefore, the adhesive strength is limited and the cost is high.

An object of the present invention is to have a low melt viscosity and to stably adjust the melt viscosity to a low level even during production, while setting a relatively fast curing speed and increasing the physical strength of the adhesive. Another object of the present invention is to provide a reactive hot melt adhesive composition which is inexpensive and inexpensive.

[0011]

The present invention is directed to a reactive hot melt adhesive composition containing a reactive urethane prepolymer having an isocyanate group end as a component, wherein the reactive urethane prepolymer is 2,4 '. A polyisocyanate component containing 35% to 65% by weight of diphenylmethane diisocyanate (2,4′-MDI), and 2,2′-dimorpholinoethyl ether, bis (2,6-dimethylmorpholino) (Ethyl) ether is contained in the composition in an amount of 0.05 to 6% by weight.

With this configuration, the reactive hot melt adhesive, which is the object of the present invention, can be obtained. When the abundance of the 2,4′-isomer in the MDI used is 35% by weight or less, the content ratio of the highly reactive 4,4′-MDI increases, and the melt viscosity of the hot melt adhesive composition decreases. As well as insufficient stability. Also 2, 4 '
-When the abundance of the isomers is 65% by weight or more, the curing rate is not desirable even if the catalyst is added.

When the amount of the catalyst component is 0.05% by weight or less, the curing speed is not in the desired range. The chemical structure of the catalyst is 2,
2′-Dimorpholinoethyl ether (DMDEE) is shown in (Formula 1) (a), and bis (2,6-dimethylmorpholinoethyl) ether is shown in (Formula 1) (b).

[0014]

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These catalysts promote the reaction between NCO groups and moisture contained in the air or wood, thereby increasing the reaction speed of the polyurethane prepolymer and improving the adhesive strength. . Other catalysts, such as dibutyltin dilaurate, promote the reaction of NCO groups with water and improve the adhesive properties, but also promote the formation of allophanate bonds and burette bonds, and the stability and dispersion of melt viscosity in the manufacturing process. It is difficult to achieve the suppression.

Even if the 2,4'-isomer is contained in an amount of 35 to 65% by weight, it is an aromatic isocyanate compound, and a hot melt adhesive having high polyurethane strength and excellent adhesive strength can be obtained.

The reactive hot melt adhesive of the present invention preferably further contains a low molecular weight polymer of an ethylenically unsaturated monomer.

When only the polyurethane prepolymer is used as the resin component, when the NCO group reacts and cures, the molecular weight increases and sufficient adhesive strength is exhibited, but in the prepolymer state, the initial adhesive strength is insufficient depending on the application. There is also.
If the degree of polymerization of the polyurethane prepolymer is increased, the melt viscosity becomes higher, and it becomes difficult to use it as a hot melt adhesive. Low molecular weight polymer of ethylenically unsaturated monomer improves initial adhesion in such applications, and adhesion to PET resin, polyvinyl chloride resin, aluminum substrate, etc., which is difficult to adhere with polyurethane prepolymer alone It has the effect of improving and the like.

The low molecular weight polymer of the ethylenically unsaturated monomer may be added in a weight ratio of polyurethane prepolymer / low molecular weight polymer of the ethylenically unsaturated monomer of 5/95 to 5/95.
It is preferably in the range of 90/10. When the amount of the low molecular weight polymer of the ethylenically unsaturated monomer (hereinafter, simply referred to as “oligomer”) is 95 or more, the ratio of the polyurethane prepolymer having an NCO group becomes small, and the adhesive force is improved by a curing reaction. Becomes insufficient. When the addition ratio of the oligomer is 10 or less, the above-mentioned effect is not sufficiently exerted.

The reactive hot melt adhesive composition of the present invention preferably further contains a thermoplastic block copolymer having two or more polystyrene blocks and an elastic polymer block.

A thermoplastic block copolymer having two or more polystyrene blocks and an elastic polymer block has a function of immediately exerting an initial adhesive force when the adhesive is cooled and solidified, and has various adherends. (Substrate) has the effect of improving wettability and improving adhesiveness.

The amount of the thermoplastic block copolymer is from 1 to 2 parts by weight based on 100 parts by weight of the polyurethane prepolymer.
It is preferably in the range of 00 parts by weight. If it is 1 part by weight or less, the properties are not different from those of the prepolymer alone.
If it is added in an amount of 200 parts by weight or more, the content ratio of the polyurethane prepolymer becomes small, and the improvement of the adhesive force by the curing reaction becomes insufficient.

[0023]

DETAILED DESCRIPTION OF THE INVENTION The polyurethane prepolymer used as a component of the reactive hot melt adhesive of the present invention is a compound having an NCO group which is a reactive functional group, and a polyol which is an oligomer having a hydroxyl group. NCO / OH> 1 in equivalent ratio of polyisocyanate compound
The reaction can be performed under the following conditions. Preferably N
The CO / OH equivalent ratio ranges from 1.2 to 2.5. 1.
If it is less than 2, the concentration of the NCO group is too low.
If it exceeds 5, a large amount of MDI monomer remains, which is not preferable.

The polyol component used as a raw material of the above-mentioned polyurethane prepolymer has an average number of functional groups (average number of hydroxyl groups in one molecule) of 1.9 to 2.2,
It is preferable to use a polyol having a hydroxyl value of 15 to 150 (KOH mg / g). If the average number of functional groups is less than 1.9, the chain length does not sufficiently extend even by reaction with moisture, and the polyurethane does not have physical properties unique to polyurethane.
The properties of the hot melt adhesive are not satisfactory. When a polyol having a functional group number of 2.2 or more is used, a gel component is easily generated in the adhesive composition.

If the hydroxyl value of the polyol is 15 or less, the relative concentration of the reactive NCO group in the polyurethane prepolymer decreases, resulting in insufficient crosslinking effect. Conversely, when a polyol having a hydroxyl value of 150 or more is used, the concentration of NCO groups in the polyurethane prepolymer becomes too high.

By setting the hydroxyl value of the polyol and the NCO / OH equivalent ratio during the synthesis of the prepolymer in the above ranges, the concentration of the NCO groups in the polyurethane prepolymer is from 0.25 to 25% by weight, preferably from 0.5 to 25% by weight. -10% by weight, most preferably 1.5-5% by weight, and the free polyisocyanate component in the final composition is reduced to 4% by weight.
% By weight or less.

As the polyol used in the present invention, a compound having at least two or more active hydrogen atoms in a molecule and usually used when synthesizing a polyurethane is used. Specifically, polyols classified into ether-based, ester-based, polycarbonate-based, polydiene-based, and the like can be used, and are appropriately selected according to the intended use.
More than one species are used together. Examples of ether polyols include polyoxytetramethylene polyol (PTMG) and polyoxypropylene polyol (PPG), and ester polyols include polyethylene adipate (PE).
A), polybutylene adipate (PBA), polycaprolactone polyol (PCL) and the like. Also,
These copolymers, for example, a block copolymer of PTMG and caprolactone, a copolymer of polyester polyol and polyether polyol, and the like can also be used. These copolymers can be synthesized by, for example, a method of ring-opening copolymerizing PTMG with ε-caprolactone, or a method of ring-opening copolymerizing polyesterpolyol with tetrahydrofuran, ethylene oxide, or propylene oxide. The above-mentioned polyol is preferably mainly bifunctional, that is, one having two hydroxyl groups in one molecule. If necessary, a polyfunctional polyol having three or more hydroxyl groups in one molecule is used in combination. It is also possible.

As a raw material of the polyurethane prepolymer used in the present invention, in addition to the above-mentioned polyol, a low molecular weight polyfunctional alcohol or other active hydrogen-containing compound, that is, a chain extender may be used. Such a chain extender can exert the effect of improving the physical properties of the polyurethane and increasing the adhesive strength.

Specific examples of the chain extender include polyhydric alcohols such as ethylene glycol, 1,4-butanediol, neopentyl glycol, xylylene glycol, and trimethylolpropane; 4,4'-diaminodiphenylmethane; Amines such as isophorone diamine, N-
Examples thereof include amino alcohols such as methyldiethanolamine, and one or more of these are used.

The isocyanate component of the polyurethane prepolymer of the present invention is MDI as described above,
35 to 65% by weight of the 2,4'-isomer (the balance is 4,4 '
-Body) Use what is contained.

However, if necessary, other polyisocyanates may be used in order to improve the properties as long as the object of the present invention is not impaired. As such polyisocyanates, aromatic polyisocyanates such as naphthylene diisocyanate and toluene diisocyanate,
Examples thereof include aliphatic polyisocyanates such as isophorone diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and hydrogenated MDI.

The low molecular weight polymer (oligomer) of the ethylenically unsaturated monomer suitably used in the hot melt adhesive composition of the present invention has a weight average molecular weight of 10,000.
~ 30000 polymers are preferred. Such oligomers also preferably contain a reactive silyl group, particularly an alkoxysilyl group or an isocyanate group. The reactive silyl group reacts with moisture in the air to contribute to the crosslinking of molecules, and when the adherend is glass or metal oxide, it also contributes to improvement in adhesiveness.

As the ethylenically unsaturated monomer constituting the oligomer, acrylic acid and methacrylic acid having 1 carbon atom
To 12, alkyl esters, vinyl esters such as vinyl acetate, vinyl ethers, aromatic monomers such as styrene, vinyl chloride, acrylonitrile, maleic esters, fumaric esters, and the like. The above is selectively used.

As the compound used to introduce a reactive silyl group into the oligomer, an ethylenically unsaturated monomer having a reactive silyl group can be used, and vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxy Silane, vinyltris (2-methoxyethoxy) silane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltris (2-methoxyethoxy) silane, vinyltriacetoxysilane,
-(3-trimethoxysilylpropyl-benzyl) styrene sulfonate, 3-acryloxypropyltrimethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, vinylmethyldiacetoxysilane, Examples thereof include 3-methylacryloxypropylmethyl-diethoxysilane and 3-acryloxypropyldimethylmethoxysilane.

A monomer having a hydroxyl group or a monomer having an isocyanate group may be copolymerized as a component of the above oligomer. Specific examples of the monomer having such a functional group include a hydroxyl group. Examples of the monomer include hydroxyethyl acrylate and hydroxyethyl methacrylate, and examples of the monomer having an isocyanate group include isocyanate ethyl methacrylate and m-isopropenyl-γ, γ-dimethylbenzyl isocyanate.

As a method of adding the above oligomer to the reactive hot melt adhesive composition of the present invention, for example, the following method is possible. A method in which an oligomer is produced independently and added during the production of a reactive hot melt adhesive composition. The oligomer is manufactured independently and added to the polyurethane prepolymer. An ethylenically unsaturated monomer is dissolved in a polyol as a raw material of a polyurethane prepolymer, and an oligomer is formed by radical polymerization in the polyol using a chain transfer agent such as n-dodecyl mercaptan, if necessary. An ethylenically unsaturated monomer is dissolved in a polyurethane prepolymer, and an oligomer is formed by radical polymerization in a polyol using a chain transfer agent such as n-dodecyl mercaptan, if necessary. (In the case of a monomer having no hydroxyl group, such a method is also possible.)

The elastic polymer block of the thermoplastic block copolymer having two or more polystyrene blocks and the elastic polymer block according to claim 3 of the present invention includes:
A polymer block using at least one diene monomer such as butadiene and polyisoprene, or a hydrogenated polymer block thereof is preferred. When the polystyrene block is A and the elastic polymer block is B, the thermoplastic block copolymer is ABA, A- (B-
A) _n , having a structure expressed as A- (BA) _n -B. Here, n is an integer of 2 to 50.
Further, not only linear molecules but also those having a structure like a star polymer may be used. Specific examples of such a thermoplastic resin include SBS, SIS, and SEBS.

If necessary, other additives may be added to the reactive hot melt adhesive of the present invention. Examples of such additives include a plasticizer, a viscosity modifier (viscosity improver), and an oxidizer. Examples include an inhibitor, a pigment, and a stabilizer.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below (based on drawings and experimental examples). The raw materials used are as follows. -Dynacoll 7380: crystalline polyester polyol (manufactured by Huls). -Low Tg polyester polyol: 1,6-hexanediol-neopentyl glycol / adipate. Hydroxyl value = 110 (KOHmg / g). -High Tg polyester polyol: neopentyl glycol / isophthalic acid / terephthalic acid ester. Hydroxyl value 30, Tg = 50 ° C.

The above raw materials and the blending of MDI and the like are shown in Table 1.
Are shown together in the upper row. The production of the reactive hot melt adhesive composition is performed by a method well known to those skilled in the art,
An example is as follows.

The polyol is charged into a four-necked flask equipped with a thermometer, a stirrer, and a nitrogen gas inlet tube, heated to 80 ° C., and reduced in pressure to remove water. Next, a predetermined MDI is charged, and the mixture is heated to 100 to 120 ° C. and reacted for 1 hour.
A prepolymer having NCO group ends is synthesized. Further, a viscosity improver and a catalyst were added to obtain a hot melt adhesive composition. The catalyst may be added before the prepolymer is synthesized.

[0042]

[Table 1]

(Evaluation) (1) Measurement of Melt Viscosity The hot melt adhesive was heated and melted, and the viscosity at 120 ° C. was measured with a Brookfield thermocell viscometer. The melt stability was evaluated by measuring the increase in viscosity when maintained at 120 ° C. The display of the evaluation result is as follows. A: Almost no increase in viscosity occurred. ：: The viscosity is slightly increased. Δ: The viscosity clearly increased, and there was a problem with long-term use. X: The viscosity rise is large and not practical.

(2) PVC Coatability A flexible PVC sheet having a thickness of 150 μm is used as a base material, and after heating this PVC sheet to 40 ° C., a hot-melt adhesive which is heated and melted to a temperature at which it can be applied is used with an applicator. And width 100mm, thickness 100μm
And cooled to room temperature, and the condition of the hot melt adhesive applied to the substrate was visually observed and evaluated.
The results were judged according to the following criteria. ：: No defects such as waviness and elongation were observed on the sheet. Δ: The sheet has waving and elongation.

(3) Initial setting property A wood board (MDF) and a PVC sheet (150 μm in thickness) are bonded with a hot melt adhesive having a coating thickness of 100 μm.
After leaving at 20 ° C. for 30 minutes, a load of 500 g / 25 mm was applied, and 90 ° creep after 1 hour was measured. As a result of the evaluation, the initial setting property was good for both the examples and comparative examples, and no creep was observed.

(4) Reaction curing rate An adhesive film having a thickness of about 50 μm was prepared using an applicator, and then transferred to a wood board (MDF).
Cured under 0% RH environment, after 4 hours, 24 hours,
After 48 hours, the infrared absorption spectrum was measured, and the reaction rate was determined from the change in the absorption intensity based on the NCO group observed near 2270 cm ^-1 . The results were displayed as follows. ◎: Time required to reach a reaction rate of 80% was within 4 hours. ：: The time required to reach a reaction rate of 80% was within 24 hours. X: The time required to reach a reaction rate of 80% is 48 hours or more.

(5) PVC Adhesion A PVC sheet and an MDF were adhered under the same conditions as in the method for evaluating coatability described in the above (2), and the temperature was 20 ° C.
After curing for 48 hours in a 0% RH environment, the PVC sheet and the MDF were peeled off by hand, and the state of the peeling was visually evaluated. The results of the evaluation are indicated as follows. ：: MDF material destruction was observed. ×: Interfacial peeling on the PVC sheet surface was observed.

[0048]

As described above, according to the present invention, the present invention can be applied to the bonding of resin materials such as PVC, which have a low melt viscosity and therefore do not have high heat resistance, and have good thermal stability in a molten state. And a reactive hot melt adhesive that cures at the desired rate after bonding is obtained.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-258620 (JP, A) JP-A-8-60129 (JP, A) JP-A 64-54087 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) C09J 175/04-175/12 C09J 153/02 C08G 18 / 10,18 / 76

Claims (3)

(57) [Claims] 1. A reactive hot melt adhesive composition containing a reactive urethane prepolymer having an isocyanate group end as a component, wherein the reactive urethane prepolymer contains 35% by weight of 2,4′-diphenylmethane diisocyanate. A polyisocyanate component containing 65% by weight is used,
A reactive hot melt adhesive composition containing 0.05 to 6% by weight of at least one of 2,2'-dimorpholinoethyl ether and bis (2,6-dimethylmorpholinoethyl) ether in the composition. 2. The reactive hot melt adhesive composition according to claim 1, further comprising a low molecular weight polymer of an ethylenically unsaturated monomer. 3. The reactive hot melt adhesive composition according to claim 1, further comprising a thermoplastic block copolymer having two or more polystyrene blocks and one or more elastic polymer blocks.