JPS62153374A - Production of pressure-sensitive adhesive sheet - Google Patents

Abstract

PURPOSE:To efficiently obtain a pressure-sensitive adhesive sheet which can be coated stably at a relatively low temp. and has bonding characteristics over a wide rang from firm bonding to restripping, by continuously mixing a pressure-sensitive adhesive component with a crosslinking agent just before application to a sheet applying the mixture to a sheet and irradiating it with an ionizing radiation. CONSTITUTION:A pressure-sensitive adhesive component is continuously mixed with a crosslinking agent just before the adhesive is applied to a sheet. After application, the sheet is irradiated with an ionizing radiation. Examples of the pressure-sensitive adhesive component are rubber elastomers, acrylic elestomers, etc. Examples of the crosslinking agent are pref. compds. having a radical-polymerizable double bond, which are liquid at room temp. (e.g., acrylic acid and its monoalkyl esters). Pref. 1-50pts.wt. crosslinking agent is mixed with 100pts.wt. pressure -sensitive adhesive compnent. Examples of the inonizing radiation are X-rays, alpha-rays and electron beams.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing a pressure-sensitive adhesive sheet, and in particular to a method for producing a pressure-sensitive adhesive sheet, in which a relatively small amount of ionizing radiation is used to impart high cohesive strength to the pressure-sensitive adhesive and improve its adhesive properties. The present invention relates to a method for stably producing a pressure-sensitive adhesive sheet that is easy to adjust and has a wide range of properties ranging from toughness to removability.

``Prior Art'' Adhesive sheets are generally constructed by providing an adhesive layer between a support and a release sheet, and are used for a very wide range of purposes such as commercial, office, and household uses such as labels, stickers, etc.
It is used as stickers, patches, etc.

As adhesives, solvent-type adhesives, emulsion-type adhesives, hot-melt-type adhesives, etc. are used, but each of them has drawbacks as described below.

In other words, solvent-based adhesives use large amounts of flammable and highly toxic solvents, which poses the risk of fire and explosion, as well as health and safety issues. It is time consuming and has poor water resistance. Furthermore, although hot-melt pressure-sensitive adhesives can be operated at high speeds, pressure-sensitive adhesive sheets with sufficient physical properties cannot be obtained by low-temperature coating.

In order to improve the above-mentioned drawbacks of hot-melt adhesives, ionizing radiation-curable true-melt adhesives are being studied. Adjust the viscosity so that it can be applied with
A method has been proposed in which the cohesive force of the adhesive is increased by causing polymerization and crosslinking reactions by irradiation with ionizing radiation. However, with this method, the viscosity of the coating solution increases over time, so
Only a small amount of diluent can be used, and a large amount of ionizing radiation is required to obtain sufficient cohesion. However, when the irradiation dose is increased, although the cohesive force increases, the adhesive force decreases extremely and the adhesive sheet base material also deteriorates, so that satisfactory results are not necessarily obtained.

"Problems to be Solved by the Invention" The present invention is intended to improve the above-mentioned drawbacks, and is capable of stable coating at relatively low temperatures, and is capable of producing high agglomeration in adhesives by irradiation with relatively small amounts of ionizing radiation. The present invention provides a method for efficiently producing a pressure-sensitive adhesive sheet that can be applied with force and has a wide range of adhesive properties ranging from toughness to removability.

"Means for Solving the Problem" The present invention provides a pressure-sensitive adhesive sheet characterized in that an adhesive component and a crosslinking agent are continuously mixed immediately before coating on the sheet, and irradiation with release radiation is performed after coating. This is the manufacturing method.

"Function" Examples of the adhesive component used in the present invention include rubber elastomers, acrylic elastomers, and the like.

Specific examples of rubber-based elastomers include natural comb (NR), isopropylene rubber (IR), styrene-butadiene block copolymer (SBS), styrene-isoprene block copolymer (Sts), butyl rubber, and polyisobutylene. , silicone rubber, polyvinyl isobutyl ether, chloroprene rubber, nitrile rubber, graft rubber, recycled rubber, and the like. These rubber elastomers include rosin, ester gum, ester gum H,
Polyterpene resin, C6 petroleum resin, C7 petroleum resin,
Tackifier resins such as DCPD petroleum resins, styrene resins, alkylphenol resins, terpenephenol resins; various plasticizers, polybutene, liquid tackifier resins, polyisobutylene low polymers, polyvinyl isobutyl ether low polymers, lanolin, decomposition Softeners such as polymerized rubber, process oil, and vulcanized oil; Fillers such as zinc white, titanium oxide, silica, aluminum hydroxide, calcium carbonate, barium sulfate, starch, clay, and talc; 2,6-tert-
Butyl-4-methylphenol, 2.5 tert-
Anti-aging agents such as butylhydroquinone, mercaptobenzimidazole, 1.1bis(4-hydroxyphenol)cyclohexane, phenyl-β-naphthylamine;
Furthermore, a stabilizer; a coloring agent, etc. are added as appropriate.

As an acrylic elastomer, a reactive oligomer having a double bond in the molecule is generally used, but the oligomer is generally added to an acrylic acid ester, which is an adhesive component monomer, to improve adhesive performance and polymerization performance, if necessary. It is synthesized by copolymerizing copolymer monomers for cohesive components and functional group monomers for improving adhesive performance using various polymerization methods.

Specific examples of acrylic esters include n-butyl acrylate, isoamyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, dodecyl acrylate, stearyl acrylate, etc. Butyl and 2-ethylhexyl acrylate are particularly preferably used.

Examples of monomers copolymerized with acrylic acid esters include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, vinyl acetate, vinyl ethyl ether, vinyl propyl ether, vinyl butyl ether, Vinyl compounds such as styrene, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, diaseptone acrylamide, acrylamide, N+
Examples include N tert-butylacrylamide and acrylonitrile.

When acrylic acid and methacrylic acid are copolymerized in small amounts, the peel adhesion strength improves, but when copolymerized in large amounts, flexibility decreases.
Since the adhesiveness decreases, it is preferable to copolymerize in an amount of about 30 mol% or less.

The weight average molecular weight of the acrylic elastomer is 1×103
When the weight average molecular weight of the elastomer becomes smaller, the cohesive force becomes smaller and it is necessary to increase the irradiation dose of ionizing radiation to increase the crosslinking density.On the other hand, when it becomes larger than 6X10', it becomes difficult to heat and melt the weight average molecular weight of the elastomer. is I
IO3-6X105, more preferably IX10'
It is desirable to adjust within a range of about 5XIO'.

The above-mentioned acrylic elastomer can be synthesized by any method such as bulk polymerization, solution polymerization, suspension polymerization, or emulsion method.

For example, in the bulk polymerization method, a polymerization catalyst such as an organic peroxide or an azo compound and a chain transfer agent such as lauryl mercaptan or octyl mercaptan are added to a polymer such as an acrylic ester to be polymerized, and the mixture is placed in a nitrogen atmosphere. 60~120℃
The compound is synthesized by polymerizing at a temperature of 20%, stopping the polymerization when the polymerization rate reaches 40 to 80%, and removing the remaining tumer. In addition, in solution polymerization, a polymer such as an acrylic ester to be polymerized, a polymerization catalyst such as an organic peroxide, an azo compound, and a chain transfer agent as necessary are added to a solvent such as ethyl acetate, cyclohexane, or toluene. It is synthesized by polymerizing at a temperature around the boiling point of the solvent, stopping the polymerization when the polymerization rate reaches 30 to 80%, and removing residual monomers and low molecular weight polymers.

In the method of the present invention, a crosslinking agent is continuously mixed into the pressure-sensitive adhesive component made of an elastomer as described above immediately before coating on a sheet. Compounds having a bond are preferably used.

Specific examples of compounds having radically polymerizable double bonds include acrylic acid and its monoalkyl esters, methacrylic acid and its monoalkyl esters, aromatic vinyl monomers, vinyl acetate, vinyl ether, acrylonitrile, n- N-vinylamides such as vinyl-2-pyrrolidone, n-vinyl urethanes, acrylamides such as n-methylol acrylamide, and reaction products of epoxy resin and acrylic acid have one polymerizable unsaturated bond in one molecule.
Monofunctional vinyl monomers: ethylene glycol, diethylene glycol, triethine glycol, neopentyl glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene gellicol, 1,6-hexanediol, glycerin, Di- or triester reaction products of polyhydric alcohols such as methylolethane, trimethylolpropane, and pentaerythritol with acrylic acid and/or methacrylic acid; A diesterification reaction product of a basic acid and hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate;
A reaction product of the above polybasic acid and an amine that has a polymerizable unsaturated bond; it also has an active hydrogen (hydroxyl group, carboxyl group, amino group, etc.) that polyadds with a polymerizable unsaturated bond and an isocyanate group in the same molecule. Monomers (e.g. allyl alcohol, 2-hydroxyethyl methacrylate, cinnamic alcohol, crotonyl alcohol, hydroxydicyclopentadiene, cinnamic acid, itaconic acid, N-methylol acrylamide, crotonic acid, etc.) to polyisocyanate Compounds (for example, triisocyanate consisting of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, triisocyanate with a billet bond consisting of 3 moles of hexamethylene diisocyanate and 1 mole of water, hexamethylene diisocyanate) triisocyanate consisting of 3 moles and 1 mole of trimethylolpropane,
Diphenylmethane 4.4″-diisocyanate, 4.4
′ -methylenebiscyclohexyl diisocyanate,
xylylene diisocyanate, etc.) and OH/NCO,,C
The molar ratio of 0OH/NC01NH2/NCO is 1 to 1°2
Examples include, but are not limited to, polyfunctional vinyl monomers having two or more polymerizable unsaturated bonds in one molecule, such as reaction products that do not contain free NGOs obtained by mixing in a ratio of isn't it. Moreover, two or more types of these can be used in combination as necessary.

In the method of the present invention, these crosslinking agents are continuously mixed into the adhesive component immediately before being applied onto the sheet.
The mixing ratio of the crosslinking agent is 0 with respect to 100 parts by weight of the adhesive component.
．． If it is less than 1 part by weight, the crosslinking reaction will not proceed and a high dose of ionizing radiation will be required to obtain desired adhesive and cohesive strength, resulting in poor coating suitability. However, 100
If the amount exceeds 1 part by weight, the adhesive force will be impaired by a small amount of radiation, so it is desirable to mix in an amount of 0.1 to 100 parts by weight, preferably 1 to 50 parts by weight.

There are no particular limitations on the method of continuous mixing, and various methods can be applied, but continuous mixing can be performed in a short period of time using devices such as static air letters, thermogenizers, and super nozzles that utilize the principle of a static mixer. Most preferably, a method is employed in which the coating is applied immediately from a die onto a sheet substrate.

The adhesive coating liquid is applied onto the sheet according to a conventional method at room temperature or by heating and melting the coating liquid, but there are no particular limitations on the sheet substrate to which it is applied.For example, high-quality paper, art paper, coated paper, etc. , cast-coated sheets such as pressure-sensitive recording paper, heat-sensitive recording paper, electrostatic recording paper, etc., plastic films such as polyethylene film, polypropylene film, polyvinyl chloride film, polyvinylidene chloride film, and even rayon fibers. , various sheets such as nonwoven fabrics of polyester fibers, composite sheets thereof, release sheets, etc. are exemplified.

The amount of adhesive coating liquid to be applied is adjusted as appropriate depending on the materials used, etc., but if it is less than 2 g/rrl in terms of dry weight, sufficient adhesive strength will not be obtained, and if it is more than 50 g/m, it will be ionizable. It is necessary to increase the radiation dose, which may cause deterioration of the adhesive sheet base material and decrease in operability.
g/rd, preferably within a range of about 5 to 40 g/rd.

The adhesive coating liquid applied onto the sheet is then irradiated with ionizing radiation to achieve the cohesive strength necessary for an adhesive sheet.
Adhesive properties are imparted, but the radiation dose irradiated is 0.
It is preferable to adjust within a range of about 1 to 15 Mrad.

Incidentally, if the irradiation is less than Q,l Mrad, a sufficient irradiation effect cannot be obtained, and if it is more than 15 Mrad, the adhesive strength of the adhesive may decrease or the adhesive sheet base material may deteriorate.

As the ionizing radiation, X-rays, α-rays, electron beams, etc. can be used, but electron beams, which have excellent transparency and can be processed at high speed, are most preferably used. The electron beam irradiation is suitably carried out using, for example, a scanning method, a curtain beam method, a broad beam method, etc., at an accelerating voltage of about 100 to 300 KV.

(The adhesive-coated sheet that has been irradiated with radiation can be assembled into an adhesive sheet by laminating it with a release sheet. However, if the release sheet is coated with an adhesive, it can be used as paper, plastic film, or metal foil. A pressure-sensitive adhesive sheet is constructed by laminating a suitable support such as a sheet or non-woven fabric to the pressure-sensitive adhesive coated surface.

There are no particular limitations on the release sheet.
High-density base paper such as conventionally used glassine paper;
Clay coated paper, kraft paper, high quality paper, woven fabric, non-woven fabric,
Polylaminated base paper, which is made by laminating polyethylene, polyester, polypropylene, etc. onto synthetic paper; plastic sheets such as plastic films and sheets are coated with a release agent such as silicone compounds or fluorine compounds, and subjected to heating, ionizing radiation irradiation, etc. Sheets and the like cured by a curing means are appropriately selected and used.

Note that ionizing radiation irradiation to the adhesive layer is not necessarily limited to before laminating a release sheet or a suitable support, and even after laminating these to form an adhesive sheet, the effect can be achieved by irradiation treatment. You can expect it. However, it is most preferable to directly irradiate the adhesive layer.

"Example" The present invention will be explained in more detail with reference to the following examples, but of course the present invention is not limited to these examples. It should be noted that the coating amount, number of parts, mixing ratio, etc. in the examples are all based on solid content. Indicated.

Example 1 100 parts by weight of a silicone mold release agent (trade name: KS-834, manufactured by Shin-Etsu Chemical) and 0 parts by weight of a catalyst (trade name: PL-3, manufactured by Shin-Etsu Chemical) were placed on glassine paper of 10 g'/rd. A coating liquid consisting of 1 part by weight was applied so that the dry weight was 0.8 g/d, and was heated and cured at 110° C. for 90 seconds to obtain a release sheet.

Electron beam curable acrylic elastomer (product name: X-5
85-954M, made by Seiden Chemical) IQ (1 part by weight
Immediately before heating and melting at 30°C and applying it on the release sheet using a die method, add a crosslinking agent having a radically polymerizable double bond (trade name: X-585-955M, manufactured by Saiden Chemical) 1.
0 parts by weight in a static mixer (product name: T, ni, -ROSS ISG MIXER 9), and the resulting adhesive coating liquid was placed on a release sheet with a dry weight of 20 g/, (The coating was applied so that

Next, a 50 μm thick polyethylene terephthalate film was laminated onto the adhesive layer to produce a film adhesive sheet. Continuous operation was carried out for 10 hours, and stable operation was possible without any particular changes in the conditions for feeding the adhesive coating liquid.

Example 2 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except that 15 parts by weight of the crosslinking agent was continuously mixed.

As in Example 1, stable continuous operation was possible.

Example 3 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that 30 parts by weight of the crosslinking agent was continuously mixed and 1 Mrad electron beam irradiation treatment was performed. As in Example 1, stable continuous operation was possible.

Example 4 As a rubber elastomer, 00 parts by weight of a styrene/isoprene/styrene hot melt adhesive (trade name: CH3 Toyo Toyo Sodani) was heated and melted at 180°C, and immediately before applying it on the release sheet using a die method, a radical 10 parts by weight of a crosslinking agent having a polymerizable double bond (product name: HX620. Nippon Kashu) was mixed with a static mixer (product name:
T, -ROSSISG MIXER, manufactured by Tokushu Kika Kogyo Co., Ltd.), and the obtained adhesive coating liquid was applied onto a release sheet so that the dry weight was 20 g/rrr, and the accelerating voltage was 170 KV. Electron beam irradiation treatment was performed at 2 Mrad.

Next, a high quality paper adhesive sheet having a weight of 50 g/rd was laminated onto the adhesive layer to produce a high quality paper adhesive sheet.

Comparative Example 1 In Example 1, 100 parts by weight of the electron beam-curable acrylic elastomer and 10 parts by weight of the crosslinking agent were mixed and melted at 130°C in a hot melt tank, and the dry weight was transferred onto a release sheet using a die method. Apply to 20g/d,
Electron beam irradiation treatment was performed at an acceleration voltage of 170 KV and 2 Mrad.

Hereinafter, film adhesive sheets were produced in the same manner, but 4
After continuous operation for about an hour, the melt viscosity of the adhesive coating solution increased significantly, making stable operation impossible.

Comparative Example 2 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except that 0.05 parts by weight of the crosslinking agent was continuously mixed.

Comparative Example 3 A pressure-sensitive adhesive sheet was produced in the same manner as in Comparative Example 1, except that 0.01 part by weight of the crosslinking agent was mixed and melted in a hot melt tank and subjected to electron beam irradiation treatment at 10 Mrad.

Comparative Example 4 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 4, except that the electron beam irradiation treatment was not performed.

The following quality comparison tests were conducted on the eight types of pressure-sensitive adhesive sheets thus obtained, and the results are listed in Table 1.

[Adhesive strength]

According to JIS-Z-1538, in a room at 20°C and 60% RH, the adhesive sheet was applied to a polyethylene plate by pressing it back and forth twice with a 2 kg roller, and after 2 hours, it was tested at a tensile speed of 30Q using an Instron type tensile tester. The adhesive strength was measured by peeling off at an angle of 180 degrees. (Unit: g
/ 25mm) [Cohesive force] Attach a 25mm x 25mm adhesive sheet to a stainless steel plate, press it with a 2 kgO roller, then keep the pasting surface vertical and apply a load of L kg to the adhesive sheet until the adhesive sheet falls off. It was measured at a time of .

Table 1 [Note] *: During peeling, the adhesive suffered cohesive failure and a portion of it remained on the polyethylene sheet.

Note that the melt viscosity of the adhesive coating liquid in Comparative Example 1 (130
°C) was 17,000 cps at first, but after 1 hour it was 30,000 cps, and after 10 hours it was 100,000 cps.
It rose to a certain level and turned into a gel. (The melt viscosity of the adhesive coating liquid of Example 1 was 15,000 cp after 10 hours, which was the same as that at the beginning.
It was s. ) Moreover, the pressure-sensitive adhesive sheet base material of Comparative Example 3 was extremely deteriorated by the large amount of electron beam irradiation treatment.

"Effect" As is clear from the results in Table 1, in the method of the present invention, a pressure-sensitive adhesive sheet with high cohesive strength and excellent adhesive properties can be produced by a relatively small amount of ionizing radiation treatment. It can be manufactured extremely stably and efficiently.

Claims (3)

[Claims] (1) A method for producing a pressure-sensitive adhesive sheet, which comprises continuously mixing an adhesive component and a crosslinking agent immediately before coating the sheet, and irradiating it with ionizing radiation after coating. (2) Claim No. 1 (2) where the adhesive component is an elastomer
1) A method for producing an adhesive sheet as described in section 1). (3) The method for producing a pressure-sensitive adhesive sheet according to claim (2), wherein the crosslinking agent is a compound having a radically polymerizable double bond.