JPH11253875A - Method for coating thixotropic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a coating break by actuating >=1 unit of stirring machine in such a manner that a stirrer moves back and forth in a direction approximately orthogonal with a coating direction within a coating liquid storage tank and allowing the coating liquid to flow over from a discharge port opening at the liquid level of this coating liquid storage tank. SOLUTION: The stirring machine 3 is installed just before the coating gap of coating rolls 1 and 2 and the stirrer 31 consisting of stirring fins for stirring the liquid crystal liquid in the coating liquid storage tank 5 is disposed at the stirring machine 3. The stirrer 31 in the coating liquid storage tank 5 is moved back and forth (reciprocating width; 850 mm, reciprocating speed; 20 reciprocations/min) by a reciprocative oscillation device 32 and the coating liquid is made to flow over from the discharge port 7 opened at the liquid level of the coating liquid storage tank 5. As a result, the long-term continuous operation without the occurrence of the coating break is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for applying a thixotropic composition.

[0002]

2. Description of the Related Art In recent years, as a method for producing a pressure-sensitive adhesive tape, there has been a demand for environmental protection, such as switching from a solvent-based pressure-sensitive adhesive to a water-based pressure-sensitive adhesive such as an emulsion-type pressure-sensitive adhesive, a hot-melt pressure-sensitive adhesive, an ultraviolet-curable pressure-sensitive adhesive, and the like. The conversion to a solventless manufacturing process using an adhesive tape has been started.

[0003] The solvent-free adhesive tape production process using an ultraviolet-curable pressure-sensitive adhesive or the like, in addition to the above-described environmental protection purpose, uses a conventional solvent, as described in JP-B-57-17030. The production process of adhesive tapes using mold adhesives enables highly efficient and efficient production of adhesive tapes and viscoelastic sheets with thick adhesive layers, which were low in productivity. . Furthermore,
In addition to the above, the solvent-free manufacturing process for pressure-sensitive adhesive tapes using an ultraviolet-curable pressure-sensitive adhesive, etc., after application, the monomer is polymerized by ultraviolet rays, so there is little restriction on the viscosity of the coating liquid, and the pressure-sensitive adhesive Of high molecular weight, and the production of an adhesive tape exhibiting high performance became possible.

However, the solvent-free production process of an adhesive tape using an ultraviolet-curable adhesive or the like involves coating a photopolymerizable composition containing a low-viscosity monomer as a main component. It is necessary to increase the viscosity of the coating liquid composed of the photopolymerizable composition in order to obtain a coated film having an appropriate thickness.

As a method for increasing the viscosity of the coating liquid, Japanese Patent Application Laid-Open No.
Japanese Patent No. 11684 discloses a thickening method by adding fumed silica. However, in the method of thickening the coating liquid by adding fumed silica, etc., the viscosity characteristics of the coating liquid become structural viscosity (thixotropic), and it is difficult to remove bubbles mixed during stirring or transport of the coating liquid. In addition, the appearance quality of the obtained sheet is deteriorated, and the coating liquid has a strong dependency on the shearing rate, so that it is easily affected by the coating speed, and the thickness accuracy of the coating film is reduced.

The invention of claim 10 disclosed in Japanese Patent Publication No. 3-40752 discloses (1) producing a composition which can be polymerized into a pressure-sensitive adhesive state, and (2) producing the composition. At least 15% pores by (3) coating the foam on a backing and (4) polymerizing the coated foam in situ to a pressure-sensitive adhesive state 12. A method for producing a pressure-sensitive adhesive product comprising the steps of obtaining a pressure-sensitive adhesive film having a cellular structure, comprising: a composition comprising a photoinitiator; 11. The method of claim 10, wherein (4) further comprises exposing to ultraviolet radiation.

The method for pre-thickening light disclosed in the above-mentioned Japanese Patent Publication No. 3-40752 discloses a coating liquid containing a crosslinkable monomer having two or more unsaturated double bonds when irradiating ultraviolet rays for thickening. Is gelled, so that it is necessary to carry out pre-thickening in a state where no crosslinkable monomer is contained, and then to add a crosslinkable monomer, which is a thickening method in which the process is complicated. In particular, in the case where the optical pre-thickening is continuously performed in-line, it is necessary to continuously and uniformly mix only a small amount of the low-viscosity crosslinkable monomer into the above-described photo-pre-thickened high-viscosity composition. This method leaves problems in accuracy and mixing operation itself and lacks stability in quality.

In any of the above-mentioned conventional techniques, variations in the liquid structure state occur in the coating liquid storage tank after a long-time operation. That is, the formation of the liquid structure proceeds, and a portion having a high apparent viscosity and a portion having no formation of the liquid structure and having a low apparent viscosity coexist. If this situation continues, there was a problem that the coating could not be sufficiently performed at the portion where the formation of the liquid structure had progressed, and so-called "out of coating" occurred.

The present applicant has previously proposed a method of applying a shearing force to a coating liquid by a rotating body or the like as a stable coating method in which "thickness of coating" does not occur when the thixotropic composition is applied. The present inventor has further studied diligently about a coating method that does not cause "cut-out", and reciprocates the above-mentioned rotating body in a direction perpendicular to the coating direction, thereby obtaining "thick-out" of the thixotropic composition. Are not generated and the accuracy of the thickness of the coating film is dramatically improved, and the present invention has been completed.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above facts, and an object of the present invention is to provide a "thickness of coating" when applying a thixotropic composition.
It is an object of the present invention to provide a coating method which is a stable coating method which does not cause any problem, and which can dramatically improve the accuracy of the thickness of the coating film, particularly the accuracy of the thickness of the coating film in the coating direction.

[0011]

According to the method for coating a thixotropic composition of the present invention, a coating solution comprising a thixotropic composition is sheared in a coating solution storage tank provided immediately before a gap between two coating rolls. A method for applying a thixotropic composition, which is applied by passing through the gap between the two application rolls while applying a force, wherein the means for applying a shear force to the application liquid comprises: 1 inserted in the coating solution
The stirrer is operated so that the stirrer reciprocates in a direction substantially perpendicular to the application direction in the coating liquid storage tank, and a stirrer is provided at a liquid outlet of the coating liquid storage tank. It is characterized in that the coating liquid overflows.

In the present invention, the coating liquid composed of a thixotropic composition has a property that a gel is changed into a fluid sol simply by stirring or shaking, and returns to a gel when left alone. A composition.

The coating liquid composed of the above-mentioned thixotropic composition is not particularly limited. For example, the coating liquid has a (meth) acrylate, a polar group,
A monomer copolymerizable with an acrylic ester, an aliphatic or alicyclic isocyanate group, an aziridinyl group, a crosslinking agent or a metal crosslinking agent having at least two functional groups selected from the group of epoxy groups, a photopolymerization initiator, etc. Photopolymerizable composition.

Examples of the above (meth) acrylate include n-butyl (meth) acrylate and (meth) acrylate.
2-ethylhexyl acrylate, isooctyl (meth) acrylate, n-octyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, and the like. These (meth) acrylates may be used alone or in combination of two or more. The glass transition temperature (Tg) of the homopolymer is -50 ° C or lower (meth)
An acrylic acid ester as a main component, and a (meth) acrylic acid ester of a lower alcohol such as methyl (meth) acrylate or ethyl (meth) acrylate can be used in combination from the balance of adhesiveness and cohesiveness. The content of the (meth) acrylate is 50 to 98% by weight, preferably 70 to 95% by weight.

The monomer having a polar group and copolymerizable with a (meth) acrylic acid ester includes, for example, a carboxyl group-containing monomer such as (meth) acrylic acid, maleic acid, fumaric acid and itaconic acid, or an anhydride thereof. Product, 2-hydroxyethyl (meth) acrylate, 4-acrylate
Hydroxy group-containing monomers such as hydroxybutyl, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, and modified caprolactone (meth) acrylate.

The monomer having the polar group and copolymerizable with the (meth) acrylic acid ester becomes a cross-linking point when cross-linked by reacting with a cross-linking agent after the formation of the polymer. The content of the monomer having a polar group and copolymerizable with the (meth) acrylate is 50 to 2% by weight, preferably 20% by weight.
~ 5% by weight. Further, in order to improve the cohesion, (meth) acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate,
A nitrogen-containing monomer such as dimethylaminopropylacrylamide may be copolymerized.

Crosslinking agents or metal crosslinking agents having at least two functional groups selected from the group consisting of aliphatic or alicyclic isocyanate groups, aziridinyl groups and epoxy groups include polyfunctional aliphatic isocyanate crosslinking agents such as , Trimethylhexamethylene diisocyanate,
Examples of the polyfunctional alicyclic isocyanate-based cross-linking agent include, for example, isophorone diisocyanate. Examples of the polyfunctional aziridine-based cross-linking agent include N, N′-hexamethylene-1,6-bis (1-aziridinecarboxamide). ), And as the polyfunctional epoxy crosslinking agent,
For example, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine and the like can be mentioned.
Examples of the metal crosslinking agent include chelating compounds such as aluminum, titanium, and zinc. Two or more of these crosslinking agents may be used in combination. Since the aromatic isocyanate crosslinking agent causes polymerization inhibition by radicals being captured and disappearing for a long time in the electron cloud composed of the aromatic ring and the isocyanate group, the above-mentioned photo-preliminary thickening is impossible, and in the present invention, Is not used. The cross-linking agent having at least two aliphatic or alicyclic isocyanate groups refers to a cross-linking agent having at least two or more isocyanate groups, excluding an aromatic isocyanate-based cross-linking agent from the group of cross-linking agents having at least two isocyanate groups. It indicates that the crosslinking agent is limited to a crosslinking agent having at least two or more aromatic isocyanate groups.

The content of the crosslinking agent or metal crosslinking agent having at least two functional groups selected from the group consisting of the aliphatic or alicyclic isocyanate group, aziridinyl group and epoxy group is 0.01 to 5 parts by weight, Preferably 0.02-
3 parts by weight.

A part of the monomer mixture comprising a monomer having a (meth) acrylate and a polar group and copolymerizable with the (meth) acrylate in the photopolymerizable composition is used as the (meth) acrylic ester. A monomer having an acid ester and a polar group, and copolymerizable with a monomer copolymerizable with the (meth) acrylate may be replaced with another monomer. Other monomers copolymerizable with the copolymerizable monomer include, for example, vinyl acetate, vinyl propionate, styrene, isobornyl (meth) acrylate, and the like.
The content of these monomers is preferably 30% by weight or less based on the total amount of monomers in the monomer mixture.

Examples of the photopolymerization initiator include, for example, 4-
(2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone [for example, manufactured by Ciba-Geigy,
Product name: Darocure 2959], α-hydroxy-
α, α'-dimethylacetophenone [eg, Ciba-Geigy, trade name: Darocure 1173], methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone [eg, Ciba-Geigy, trade name: Irgacure 651], 2 Acetophenone-based photopolymerization initiators such as -hydroxy-2-cyclohexylacetophenone [for example, trade name: Irgacure 184, manufactured by Ciba Geigy Co., Ltd.], ketal-based photopolymerization initiators such as benzyldimethyl ketal, halogenated ketones, acylphosphine oxides, Other photopolymerization initiators such as acylphosphonates can be exemplified.

The content of the photopolymerization initiator is 0.01 to
It is 5 parts by weight, preferably 0.05 to 3 parts by weight.

The photopolymerizable composition having the above-mentioned composition is further added with a tackifying resin (TF) or a filler in order to improve adhesion to an adherend such as a plastic having a small polarity. For the agent or polymerization, a chain transfer agent or the like may be contained. Examples of the TF include rosin-based resins, modified rosin-based resins, terpene-based resins, terpene-phenol-based resins, C5 and C9-based petroleum resins, hydrogenated products thereof, and hydrogenated products of cumarone resin. More than one species are used together. However, since these TFs usually have many phenolic or hydroquinone aromatic rings that inhibit photopolymerization, highly hydrogenated TFs are preferred.

The photopolymerizable composition to which the above additives have been added is
For adjusting the polymerization reaction, the amounts of the chain transfer agent and the cross-linking agent are appropriately adjusted as needed. The chain transfer agent is used to adjust the molecular weight of the acrylic copolymer obtained by photopolymerization, for example, n-dodecyl mercaptan,
T-dodecyl mercaptan and the like are preferably used. The amount of the chain transfer agent to be added is based on the total amount of the monomers 1
It is in the range of 0.01 to 0.1 part by weight based on 00 parts by weight. Examples of the filler include glass bubbles and plastic beads.

The method of applying the coating solution comprising the above-mentioned thixotropic composition is not particularly limited. For example, a coating method such as a roll coater, a die coater, a bar coater, a comma coater, a gravure coater and a Meyer bar coater may be used. This is performed using a processing device. Especially, the film thickness is 1m
When coating thickly to about m ~ 5mm, roll coater,
A bar coater, comma coater, die coater or the like is preferably used.

The means for applying a shearing force to the coating liquid composed of the thixotropic composition in the coating liquid storage tank provided immediately before the gap between the two coating rolls includes a stirrer for stirring the coating liquid in the coating liquid storage tank. The stirrer is operated such that the stirrer reciprocates in the coating liquid storage tank in a direction substantially perpendicular to the application direction together with the stirring operation of the stirrer. The stirrer is not particularly limited. For example, a stirrer formed of a rod-shaped body such as a triangle, a square,... A stirrer composed of a bent double rod, a stirrer composed of multiplexed rods, and these rods are used as arms, and projections such as spheres, plate-like pieces, wing-like pieces, and circular rings are formed at the ends of the arms. The stirrer provided may be a stirrer, a flat plate, a corrugated plate, or a stirrer formed of an irregular shaped plate.

The stirrer reciprocates in the coating liquid storage tank in a direction substantially perpendicular to the coating direction to apply a shearing force. The speed of the reciprocating motion is preferably 2 to 100 m
/ Min. When the speed of the reciprocating motion is less than 2 m / min,
When a sufficient shearing force cannot be applied and the speed exceeds 100 m / min, not only the liquid level of the coating liquid in the coating liquid storage tank becomes unstable but also bubbles may be generated in the coating liquid. The performance of the coating film is reduced, and the thickness accuracy is also reduced.

The reciprocating motion is performed in the coating liquid storage tank in a direction substantially perpendicular to the coating direction. However, the reciprocating movement does not need to be strictly in a direction perpendicular to the coating direction. What is necessary is just to move in the direction substantially perpendicular to the application direction, and slight meandering and course fluctuations are permissible. The width of the reciprocating motion is determined by the number and arrangement of the stirrers used, and is not particularly limited. However, the width of the reciprocating motion is uniform to the coating liquid over the entire width of the coating liquid in the coating liquid storage tank. The width of the reciprocating motion needs to be set so that a large shear force is exerted.

Means for applying a shearing force to the coating liquid comprising the thixotropic composition is such that the two coating rolls are applied so that the action is applied to the entire coating liquid 4 comprising the thixotropic composition in the coating liquid storage tank 5. It is installed just before the application gaps 1 and 2, and its output is set.

The outlet 7 is open to the liquid surface of the coating liquid storage tank 5, but the location and number of the outlets are not particularly limited. It is determined by the stirring movement speed, the reciprocating movement speed of the stirrer 31, and the like. It is preferable that the coating liquid is uniformly opened on the liquid surface of the coating liquid storage tank 5. It may be densely opened at both ends. Of course, there may be only one outlet.

As described above, the method for applying the thixotropic composition of the present invention can treat the photopolymerizable composition with one liquid,
It does not require a mixing process that has problems with the measurement accuracy and mixing operation itself, such as continuously and evenly mixing a very small amount of a low-viscosity crosslinkable monomer into a high-viscosity composition pre-thickened. In addition, a viscoelastic sheet of stable quality can be manufactured with high efficiency by a coating apparatus including a simple raw material single mixing process.

[0031]

Embodiments of the present invention will be specifically described below with reference to examples.

Example 1 Preparation of coating solution having thixotropic property 85 parts by weight of 2-ethylhexyl acrylate, 15 parts by weight of acrylic acid, 3 parts by weight of N-vinylpyrrolidone, 2,2-dimethoxy-2-phenyl Acetophenone (Ciba Geigy,
3. Product name: Irgacure 651) 1.5 parts by weight, filler (manufactured by Aerosil Co., trade name: Aerosil # 200)
A photopolymerizable composition comprising 5 parts by weight and 35 parts by weight of a filler (trade name: Miperon MX220, manufactured by Mitsui Petrochemical Co., Ltd.) is mixed according to a conventional method, and a thixotropic coating solution (using a BM type viscometer). Viscosity at 6 rpm: 456
(Viscosity at 0 cps and 60 rpm: 356 cps).

[Coating Apparatus] As shown in FIG. 1, a coating roll (comma roll: 100 mmφ, surface length 1000 mm,
Base roll: 180 mmφ, surface length: 1000 mm, roll gap: 1.56 mm) 1 and 2 and the coating roll 1
And a comma coater provided with a stirrer 3 installed immediately before the coating gap of No. 2 and a coating liquid storage tank 5 having a discharge port 7 opening on the surface of the coating liquid 4. In addition, the stirrer is used for the coating liquid storage tank 5.
Stirrer 31 composed of stirring fins for stirring the coating solution in the container
2 is reciprocated by a reciprocating rocking device 32 (reciprocating width 850) in a direction in which a stirrer 31 in a coating liquid storage tank 5 is substantially perpendicular to a coating direction, as shown in an explanatory view of FIG.
mm, and a reciprocating speed of 20 reciprocations / minute) to apply a shearing force to the coating liquid.

The thixotropic coating solution is
Using the above comma coater, 50μ of thickness released
m on a polyethylene terephthalate film having a coating width of 800 mm and a coating speed of 7 m / min so that the thickness at the end of the polymerization is 1.5 ± 0.0075 mm. The mold-treated polyethylene terephthalate film is closely adhered and coated, and the irradiation intensity on the coated film is set to 15 mW / cm ² and the irradiation time is set to 2.5 minutes using an ultraviolet irradiation device equipped with a high-pressure mercury lamp. For 24 hours. The obtained pressure-sensitive adhesive layer had no surface appearance quality defects due to wrinkles, bumps, and irregular thickness.

During the 24-hour continuous operation, the thickness of the pressure-sensitive adhesive layer was measured at substantially equal intervals 60 times within 24 hours by random sampling at 10 points in the width direction of the obtained pressure-sensitive adhesive layer. Was. Further, during the above-mentioned time, the so-called coating breakage in which the coating was interrupted due to the gelling of the coating solution did not occur at all.

(Embodiment 2) Instead of the stirrer 3 having the stirrer 31 composed of the stirring fin of the first embodiment, a stirrer having an annular ring is provided at the tip of the support arm 34 shown in FIG. A thixotropic coating solution was applied in the same manner as in Example 1 except that a stirrer provided with No. 33 was used, and the thickness quality of the obtained pressure-sensitive adhesive layer and process troubles such as application breakage were observed. Was observed.

(Example 3) [Preparation of coating solution having thixotropic property] 75 parts by weight of n-butyl acrylate, 25 parts by weight of acrylic acid, 2,2-dimethoxy-2-phenylacetophenone (trade name, manufactured by Ciba Geigy) : Irgacure 651) 2.5 parts by weight of a photopolymerizable composition composed of 2.5 parts by weight of a filler (Aerosil Co., trade name: Aerosil # 200) and 5 parts by weight according to a conventional method, and a thixotropic coating solution ( Using a BM viscometer, viscosity at 6 rpm: 2120 cps, viscosity at 60 rpm: 1
26 cps).

The above thixotropic coating solution is
Using the comma coater used in Example 1, on a 50 μm-thick polyethylene terephthalate film subjected to a release treatment, the thickness at the end of polymerization was 1.1 ± 0.0055 mm.
850 mm in width and a coating speed of 2 m / min., And the coated surface is coated with the release-treated polyethylene terephthalate film in close contact with it, using an ultraviolet irradiation device equipped with a high-pressure mercury lamp. The irradiation intensity on the coating film was 10 mW / cm ² , and the irradiation time was 4.
The continuous operation was performed for 24 hours so as to be 5 minutes. The obtained pressure-sensitive adhesive layer had no surface appearance quality defects due to wrinkles, bumps, and irregular thickness.

During the continuous operation for 24 hours, the thickness of the pressure-sensitive adhesive layer was measured at approximately equal intervals 60 times within 24 hours by random sampling at 10 points in the width direction of the obtained pressure-sensitive adhesive layer. Was. Further, during the above-mentioned time, the so-called coating breakage in which the coating was interrupted due to the gelling of the coating solution did not occur at all.

(Embodiment 4) In place of the stirrer 3 provided with the stirrer 31 composed of the stirring fin of the third embodiment, a stirrer formed of an annular ring is provided at the tip of the support arm 34 used in the second embodiment. Except for using a stirrer provided with a stirrer 33, a coating solution having the thixotropy was applied in the same manner as in Example 3 and the process quality such as the thickness quality of the obtained pressure-sensitive adhesive layer and the application cut-off. Were observed.

(Comparative Example 1) A coating solution having thixotropic properties was applied in the same manner as in Example 1 except that the stirrer of Example 1 was not used, and the thickness quality of the obtained pressure-sensitive adhesive layer was obtained. Observation of process troubles such as coating shortage and the like were performed. In addition, during the above-mentioned 24 hours, the coating was cut off 26 times. Each time, the coating apparatus was stopped and the coating liquid storage tank 5 was stopped.
After replacing the thixotropic coating solution present in the inside with a new one, the coating apparatus was restarted.

(Comparative Example 2) The coating liquid having thixotropic properties was applied in the same manner as in Example 3 except that the stirrer in Example 3 was not used, and the thickness quality of the obtained pressure-sensitive adhesive layer was obtained. Observation of process troubles such as coating shortage and the like were performed. In addition, the application was stopped 15 times during the above-mentioned 24 hours. Each time, the coating apparatus was stopped and the coating liquid storage tank 5 was stopped.
After replacing the thixotropic coating solution present in the inside with a new one, the coating apparatus was restarted.

Table 1 summarizes the thickness measurement data of the pressure-sensitive adhesive layers of the above Examples and Comparative Examples and the number of coating breaks that occurred within 24 hours of the continuous operation time.

[0044]

[Table 1]

[0045]

As described above, the method for applying a thixotropic composition of the present invention is constituted as described above. It is possible to operate continuously for a long period of time without causing problems, and it is possible to dramatically improve the accuracy of the thickness of the coating film obtained by coating, especially the accuracy of the thickness of the coating film in the coating direction. It became.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing a main part of a coating apparatus used in an example of a method for applying a thixotropic composition of the present invention.

FIG. 2 is an explanatory view of an operation state of a stirrer attached to the coating apparatus shown in FIG.

FIG. 3 is a side view showing a stirrer used in another embodiment of the method for applying the thixotropic composition of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 coating roll (metering roll) 2 coating roll (base roll) 3 stirrer 31, 33 stirrer 32 reciprocating rocking device 34 support arm 4 coating liquid 41 coating 5 coating liquid storage tank 6 surface-treated polyethylene terephthalate film 7 discharge Exit

Claims (1)

[Claims] 1. A coating liquid comprising a thixotropic composition is applied to a coating liquid storage tank provided immediately before a gap between two coating rolls by applying a shearing force to the coating liquid and passing through the gap between the two coating rolls. A method for applying a thixotropic composition, wherein the means for applying a shearing force to the coating liquid comprises one or more stirrers in which a stirrer is inserted into the coating liquid in the coating liquid storage tank. The coating liquid is operated so as to reciprocate in a direction substantially perpendicular to the coating direction in the coating liquid storage tank, and the coating liquid overflows from a discharge port opened in the liquid surface of the coating liquid storage tank. Coating method for a thixotropic composition.