GB2250513A - Film- or sheet-form adhesive material - Google Patents

Abstract

An adhesive material comprises a film or sheet of a heat-activatable adhesive containing a heat-expanding agent, said adhesive having a dynamic viscosity in the range of from 3 x 10<4> to 4 x 10<4> poises as measured at 100 DEG C. The adhesive preferably comprises a styrene-butadiene-styrene block copolymer or a chloroprene. The heat-expanding agent preferably comprises microcapsules having a shell of thermoplastic resin and a gaseous substance, e.g. butane or propane gas, encased therein. The microcapsules having a particle diameter of 1 to 50 mu m and a specific gravity of 1.0 to 1.15.

Description

FIT.6 OR SHEET-FORM ADHESIVE MATERIAL FIELD OF THE INVENTION The present invention relates to a film-or sheet-form heat-activatable adhesive material for strongly bonding an article to a surface of an adherend.

BACKGROUND OF THE INVENTION In general, heat-activatable adhesives which show their adhesive properties upon heating are used in the case where articles having large surface roughnesses such as woven or nonwoven fabrics and nets are adhered and fixed to surfaces of adherends such as apparatuses, structures, etc., or in the case where articles are bonded to surfaces of adherends comprising materials having large surfaceroughnesses.

Such an adhesive has normally been shaped beforehand into a film or sheet form, and the film or sheet form adhesive is used by placing it between an article to be adhered and a surface of an adherend, heating the adhesive to melt or soften it, and allowing the melted or softened adhesive to penetrate into recessed portions or pores of the article or adhered surface thereby to exhibit a strong adhesive strength.

However, adhesion with such the adhesive material is defective in that,because of the surface gloss of the adhesive material after adhesion and solidification thereof, the presence of the adhesive material is noticed by the viewer and the beauty of the bonded article is impaired. In particular, in the case where a net-Lke or porous article having a relatively large pore diameter is adhered, the surface gloss of the adhesive material is undesirable since it mars the image of the product, if beautiful appearance becomes important as in television sets and audio equipment.

SUMMARY OF THE INVENTION In view of the above-described problems of conventional heat-activatable adhesive materials, the present invention has been completed.

Accordingly, an object of the present invention is to provide a novel adhesive material which, when used to adhere articles, no longer has a surface gloss after solidification and, hence, does never impair the beauty of the articles.

The filmy or sheet- form heat-activatable adhesive material in accordance with the present invention comprises a film or sheet of a heat-activatable adhesive containing a heat-expanding agent, the heat-activatable adhesive having a dynamic viscosity in the range of from 3 x 104 to 4 x 105 poises as measured at 1000C.

DETAILED DESCRIPTION OF THE INVENTION The base material component of the heat-activatable adhesive used in the adhesive material of the present invention is a polymeric material capable of being activated upon heating, such as a nitrile rubber, a styrene-butadiene-styrene block copolymer, a chloroprene rubber, or the like. Of those, the styrene-butadiene-styrene block copolymer or the chloroprene rubber is particularly preferred from the standpoints of heat capacity at the time of adhering to an adhered surface and reliability of adhesion.

If required and necessary, additives such as a tackifier, a softener, an anti-oxidant, a filler, a plasticizer, a stabilizer, a pigment, a crosslinking agent, and the like can be added to the base material component in appropriate amounts.

The viscosity of the heat-activatable adhesive comprising the above-described components is an important factor in the present invention, but this will be described later.

The heat-expanding agent contained in the abovedescribed heat-activatable adhesive is not particularly limited, provided that it expands upon heating. However, a heat-foamable material which foams upon heating is especially preferred, and examples thereof include microcapsules which expand on heating.

The heat-expandable microcapsule comprises a shell and a heat-expandable substance encased therein. The shell is made preferably of a thermoplastic resin, and the examples thereof include an acrylonitrile copolymer, a vinylidene chloride-methyl methacrylate copolymer, or the like. The heatexpandable substance is a substance which expands 20 to 70 times, preferably 25 to 45 times, upon heating to 90 to 1500C, and the preferred examples thereof include a gaseous substance such as butane gas or propane gas.

When the adhesive material is heat-treated, the microcapsules contained therein expandroad collapse after expansion. The heat-expandable microcapsules are microspheres having a particle diameter of from 1 to 50 Wm, and preferably from 10 to 20 jim, and a specific gravity of from 1.0 to 1.15.

Specific examples thereof include commercially available products such as "Matsumoto Microsphere" manufactured by Matsumoto Yushi Seiyaku Co., Ltd., Japan.

The amount of the heat-expanding agent added to the heat-activatable adhesive can be appropriately determined according to the kind of the expanding agent used and conditions for heat adhesion. However, the heat-expanding agent is generally added in an amount of from 0.5 to 20 parts by weight, preferably 3 to 10 parts by weight, per 100 parts by weight, on a solid basis, of the heat-activatable adhesive, if the specific gravity of the heat-expanding agent is within the above-specified range.

The expanding temperature (foaming temperature) for the heat-expanding agent can be appropriately determined according to the heat resistance of the article to be adhered and the temperature at which the heat-activatable adhesive is activated. However, the preferred range of the foaming temperature is from 90 to 1400C.

Further, the degree of expansion (degree of foaming) is generally from about 1.5 to 10 times.

The heat-activatable adhesive composition constituted as described above is formed into a film or sheet by, for example, dissolving the adhesive composition in a solvent, uniformly dispersing the above-described heat-expanding agent into the resulting heat-activatable adhesive solution, coating the resulting dispersion on a release liner, and then drying the coating at a temperature below the expanding temperature of the heat-expanding agent.

When the thus-obtained film or sheet form adhesive material is used in heat adhesion, the adhesive material melts or softens and, at the same time, the heat-expanding agent exerts its expanding action. Because of this, even in the case where either the article or the adherend has a relatively large surface roughness, the adhesive layer formed can have a large contact area with the rough surface even at a relatively low adhesion temperature, thereby attaining a strong adhesion and fixation.

The above-described heat-activatable adhesive used in the adhesive material of the present invention is formulated so as to have a dynamic viscosity as measured at 1000C of from 3 x 104 to 4 x 105 poises, and preferably from 5 x 104 to 3 x 105 poises. If a heat-activatable adhesive having a dynamic viscosity below 3 x 104 poises at 100"C is used to produce a film or sheet form adhesive material, use of such the adhesive material in heat adhesion results in formation of an adhesive layer having a surface gloss because the fine roughness which is formed on the surface of the adhesive material as a result of the expansion thereof upon the heating disappears simultaneously with the formation thereof due to the flow of the adhesive material. Thus, the object of the present invention cannot be attained.On the other hand, if the dynamic viscosity thereof at 1000C exceeds 4 x 105 poises, the adhesive cannot sufficiently contact the rough surface of the adherend even if the adhesive softens during heat-expansion, and hence the effect of the addition of the heat-expanding agent is difficult to exhibit.

The dynamic viscosity n is obtained using the following equation.

Loss shear modulus G" (dyne/cm2) 9 (poise) =-- Frequency W (rad/sec) Further, it is preferred that the dynamic viscosity at ordinary temperature (23"C) of the heat-activatable adhesive is 5 x 105 poises or more, because the film or sheet form adhesive material using such the heat-activatable adhesive is free from tackiness and therefore has good handling properties when used in application operations, etc. Accordingly, the film or sheet form adhesive material of the present invention is characterized in that the dynamic viscosity of the adhesive is high at ordinary temperature, and decrease thereof is small even when the adhesive material is heat expanded.

According to operation conditions for adhesion and the condition of the surface of the adherend to which an article is bonded or according to the pre-processing conditions of the film or sheet form adhesive material, etc., a reinforcement in a sheet or film form such as a nonwoven fabric woven fabric, plastic film, or the like may be used in the sheet or film form adhesive material. Moreover, a pressure-sensitive adhesive layer may further be separately formed on the film or sheet form adhesive material of the present invention.

As described above, use of the heat-activatable adhesive material of the present invention in heat adhesion is advantageous in that the heat-expanding agent expands upon heating to roughen the surface of the adhesive material and this roughness can be maintained without disappearing because the heat-activatable adhesive as the base material component has a dynamic viscosity in the specific range. Therefore, the adhesive material after adhesion can retain its reduced surface gloss over a prolonged period of time and, hence, the presence of the adhesive material will not be noticed. Accordingly, the heat-activatable adhesive material of the present invention is effective in providing beautiful appearances of adhered articles even in adhesion applications where beautiful appearance is important.

The present invention will be explained in more detail by reference to the following examples, which should not be construed as limiting the scope of the invention. In these examples, all parts are by weight.

EXAMPLE 1 Formulation (A) having the following ingredients was dissolved in toluene to form an adhesive solution having a solid content of 30% by weight.

Formulation (A): Chloroprene rubber 100 parts Modified rosin resin 20 parts Terpene phenol resin 15 parts To this adhesive solution was added Matsumoto Microsphere F30D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., Japan; specific gravity 1.13) in an amount of 7 parts per 100 parts of the solid components of the adhesive solution.

The resulting mixture was stirred to obtain a heat-activatable adhesive composition.

This composition was then coated on a release paper at a thickness of 50 Wm in a dry basis, and the coating was dried at 850C for 10 minutes, thereby obtaining a film form adhesive material having slight tackiness at ordinary temperature.

EXAMPLE 2 Formulation (B) having the following ingredients was dissolved in toluene to form an adhesive solution having a solid content of 50% by weight.

Formulation (B): Styrene-butadiene-styrene block 100 parts copolymer (weight ratio of styrene/butadiene = 30/70) Coumarone-indene resin 30 parts Phenolic type anti-oxidant 2 parts To this adhesive solution was added Matsumoto Microsphere F30D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.; specific gravity 1.13) in an amount of 3 parts per 100 parts of the solid components of the adhesive solution. The resulting mixture was stirred to obtain a heat-activatable adhesive composition.

This composition was then coated on a release paper at a thickness of 50 pm in a dry basis, and the coating was dried at 80"C for 10 minutes. The resulting adhesive film was laminated to a 50 zm-thick nonwoven rayon cloth on both sides thereof by means of laminating rolls at a laminating speed of 5 m/min at 800C, thereby obtaining a film form adhesive material containing a reinforcement.

COMPARATIVE EXAMPLE To a 40 wt% toluene solution of an acrylic polymer (weight ratio of 2-ethylhexyl acrylate:vinyl acetate:acrylic acid = 100:20:5) having a weight average molecular weight of 400,000 were added 10 parts of a rosin resin and 4 parts of an isocyanate-type crosslinking agent per 100 parts of the solid component of the polymer solution. To the solution was further added Matsumoto Microsphere F30D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.; specific gravity 1.13) in an amount of 5 parts per 100 parts of the acrylic polymer.

The resulting composition was then coated on a release paper at a thickness of 50 Rm in a dry basis, and the coating was dried at 800C for 10 minutes. The resulting adhesive film was laminated to a 50 Wm-thick nonwoven rayon cloth on both sides thereof by means of laminating rolls at a laminating speed of 5 m/min at 800C, thereby obtaining a film form adhesive material containing a reinforcement.

Each of the adhesive materials obtained in the above Examples and Comparative Example was subjected to measurements of dynamic viscosity at ordinary temperature (23"C) and 100"C, adhesion strength, and glossiness according to the methods described below.

The results obtained are shown in Table 1.

[Dynamic viscosity] Using a viscoelastic spectrometer, the heat-activatable adhesive is forced to vibrate at a constant frequency of 1 Hz.

The dynamic viscosity n (poise) of the adhesive is calculated using the equation given hereinabove.

adhesive strength] The film form adhesive material is laminated beforehand to a 25 Rm-thick polyester film by means of rolls heated to 85 0C at a laminating speed of 1 m/min. This laminate is adhered to a perforated sheet as an adherend which is obtained by perforating a 1 mm thick rigid PVC sheet at a perforation diameter of 0.8 mm and a perforating degree of 50%, by pressing the laminate and the perforated sheet under conditions of 1000C, 1 min, and 4 kg/cm2, thereby to prepare test pieces. The adhesive strength of the test pieces is measured by a 1800 peeling test (peeling speed 300 mm/min) in an atmosphere of 230C and 65% RH.

[Glossiness] The film form adhesive material is placed in an oven at 1000C for 60 minutes, subsequently allowed to stand at ordinary temperature for 7 days, and then subjected to a surface glossiness measurement in accordance with JIS Z-8741.

Table 1 Dynamic viscosity Adhesive (poise) strength Ordinary (g per 20 mm Temperature 100do width) Glossiness Example 1 8.1 x 105 3 x 105 2,750 1.0 Example 2 6.3 x 105 3.5 x 104 2,520 1.0 Comparative 4.4 x 104 1.0 x 104 1,100 19 Example While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims (9)

CLAIMS:

1. A film- or sheet-form heat-activatable adhesive material comprising a film or sheet of a heat activatable adhesive containing a heat-expanding agent, said heatactivatable adhesive having a dynamic viscosity in the range of from 3 x 104 to 4 x 105 poises as measured at 100"C.

2. An adhesive material as claimed in claim 1, wherein the dynamic viscosity of said heat-activatable adhesive at ordinary temperature (23"C) is 5 x 105 poises or more.

3. An adhesive material as claimed in claim 1 or 2, wherein said heat-activatable adhesive comprises a styrene-butadiene-styrene block copolymer or a chloroprene.

4. An adhesive material as claimed in claim 1, 2 or 3, wherein said heat-activatable adhesive has a dynamic viscosity as measured at 100 C of from 5 x 104 to 3 x 105 poises.

5. An adhesive material as claimed in claim 1, 2, 3 or 4, wherein said heat-expanding agent is a heat-expandable microcapsule.

6. An adhesive material as claimed in claim 5, wherein said microcapsule comprises a thermoplastic resin as a shell and a gaseous substance encased therein.

7. An adhesive material as claimed in any preceding claim, wherein the amount of the heat-expanding agent is 0.5 to 20 parts by weight per 100 parts by weight of the solid component of the heat activatable adhesive.

8. An adhesive material as claimed in claim 1, substantially as hereinbefore described in Example 1 or 2.

9. An article when bonded to a substrate by an adhesive material as claimed in any preceding claim.