JP2007070618A - Photocurable composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocurable composition which has excellent initial adhesiveness and gives cured product layers excellent in transparency. <P>SOLUTION: This photocurable composition comprises (A) 40 to 70 wt.% of a urethane (meth)acrylate resin, (B) 20 to 50 wt.% of a urethane prepolymer having an isocyanate group at at least one terminal, (C) 2 to 15 wt.% of a compound having at least one polar group and at least one photopolymerizable group, and (D) 1 to 6 wt.% of a photopolymerization initiator, wherein each wt.% is a value based on the total weight of (A), (B), (C) and (D). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a photocurable composition, and in particular, relates to a photocurable composition that contains a urethane acrylate resin as a main agent, gives a cured film excellent in initial adhesiveness and transparency, and is useful for an adhesive, a paint, and the like. .

For the purpose of improving the image of products such as cosmetics, medical products, stationery, accessories, etc., an assembly container is provided that has folding ruled lines on plastic sheets such as amorphous polyethylene terephthalate (A-PET) that has good transparency and rigidity. It is used as a packaging material. As for the bonding of this assembled container, the initial appearance is such that the appearance of the product is highly transparent in terms of the nature of the product, and the process can be shifted to the inspection process of the assembled container including adhesiveness immediately after bonding. There is a demand for an adhesive having excellent adhesiveness.

A reactive hot melt adhesive composition containing an isocyanate group-terminated reactive urethane prepolymer has been disclosed for the bonding of this type of assembly container (Patent Document 1). However, until the adhesive is cured to some extent, unless the adhesive surface is kept pressed by external force for several hours (about 4 hours or more), the adhesive surface peels off and the initial adhesiveness is poor.

On the other hand, a method is known in which a layer made of amorphous polyethylene terephthalate (PET-G) is provided on the surface of a plastic sheet such as amorphous polyethylene terephthalate (A-PET) and can be easily bonded with a solvent or the like. However, since the surface layer of PET-G is clouded, the appearance of the packaging container is deteriorated.

Also known is an electron beam curable adhesive composition for laminates containing polyester (meth) acrylate or polyurethane (meth) acrylate as a curing agent and a compound having an isocyanate group (Patent Document 2). Since the composition has a high viscosity, there is a problem that, for example, it is difficult to remove bubbles once the composition is prepared. Heating to lower the viscosity of the composition so that bubbles can be easily removed, and when defoaming is performed using a vacuum pump or a centrifugal separator, thermal polymerization occurs due to heat generated by stirring or centrifugal shearing. There was a problem such as.
Japanese Patent No. 3108380 JP-A-7-310065

An object of the present invention is to provide a photocurable composition that provides a cured product layer having excellent initial adhesiveness and excellent transparency. Another object of the present invention is to provide a photocurable composition having excellent thermal stability.

That is, the present invention is as follows.
(A) Urethane (meth) acrylate resin in an amount of 40 to 70 wt%,
(B) a urethane prepolymer having an isocyanate group at at least one end in an amount of 20 to 50 wt%;
(C) a compound having at least one polar group and at least one photopolymerizable group in an amount of 2 to 15 wt%, and (D) a photopolymerization initiator in an amount of 1 to 6 wt%,
The photocurable composition to be contained, where each wt% is a value relative to the total weight of (A), (B), (C) and (D).
Moreover, this invention is the said photocurable composition which further contains the (E) at least 1 heat stabilizer chosen from a hindered phenol compound, a tocopherol, and a tocopherol derivative.

Since the composition of the present invention contains a predetermined compound having at least one polar group and at least one photopolymerizable group, it exhibits excellent initial adhesion to a plastic substrate, particularly PET. Moreover, by combining with a predetermined heat stabilizer, gelation or the like does not occur even when stored at 80 ° C. for a predetermined time.

(A) Urethane (meth) acrylate resin In the photocurable adhesive of the present invention, (A) the urethane (meth) acrylate resin has both ends of polyisocyanate obtained by addition reaction of isocyanate and diol. It is produced by adding (meth) acrylate having a group reactive with an isocyanate group to have two (meth) acryloyl groups in the molecule. In the present specification, (meth) acrylate includes both acrylate and methacrylate. Isocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and xylylene diisocyanate (XDI), and aliphatic systems such as hexamethylene diisocyanate (HDI) and trimethylhexamethylene diisocyanate (TMHMDI). Examples thereof include alicyclic diisocyanates such as diisocyanates, isophorone diisocyanate (IPDI), and methylenebis (4-cyclohexylisocyanate) (hydrogenated MDI). Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, polyethylene glycol, ethoxylated bisphenol A, ethoxylated bisphenol S, spiro glycol, caprolactone-modified diol, polycarbonate diol, and polyester diol. As the (meth) acrylate having a reactive group with an isocyanate group, hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate are used. Preferably, urethane acrylate having a polycarbonate skeleton and urethane acrylate having a polyester skeleton are preferable from the viewpoint of adhesion to a base material and cohesive strength of a cured product, and Art Resin NPC-25 and Art Resin KY-2 ( Both are manufactured by Negami Kogyo Co., Ltd.

  The (A) urethane (meth) acrylate resin has a styrene-equivalent weight average molecular weight of 3,000 to 30,000, preferably 5,000 to 20,000. The viscosity at 80 ° C. measured according to JISK-7117-1 is 10,000 to 300,000 mPa · s, preferably 50,000 to 150,000 mPa · s. When the viscosity is less than the lower limit value, the adhesive is likely to protrude during bonding. On the other hand, if the upper limit is exceeded, it may be difficult to apply uniformly and the appearance of the bonded portion may be impaired.

(B) Isocyanate group-containing urethane prepolymer (B) The urethane prepolymer is synthesized from a polyester polyol or polyether polyol and a diisocyanate, and has an isocyanate at at least one terminal. Polyester polyols include polyethylene adipate (PEA), polybutylene adipate (PBA), polycaprolactone polyol (PCL), etc., and polyether polyols include polyoxytetramethylene polyol (PTMG), polyoxypropylene polyol (PPG), etc. can give. Examples of the diisocyanate include the above-described diisocyanates such as tolylene diisocyanate (TDI). Preferably, it contains an aliphatic polyol-based NCO-terminated urethane prepolymer from the viewpoint of no yellowing after curing and flexibility.

  (B) The urethane prepolymer has a viscosity at 80 ° C. of preferably 10 to 5,000 mPa · s, more preferably 100 to 1,000 mPa · s.

(C) Compound having at least one polar group and at least one photopolymerizable group (C) Compound having at least one polar group and at least one photopolymerizable group (hereinafter referred to as “photopolymerizable compound”) It is considered that the photopolymerizable group is bonded to the cured product network structure, and the polar group interacts with the base material, particularly PET, thereby improving the initial adhesiveness of the cured product. . Examples of the polar group include a hydroxyl group, an amide, and an ester group, and the photopolymerizable group includes an ethylenically unsaturated bond. Examples of (C) photopolymerizable compounds include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, carbitol (meth) acrylate, polyethylene glycol di (meth) acrylate, and glycerin di (meth). Acrylates containing hydroxyl groups, such as acrylate, glycerin mono (meth) acrylate, pentaerythritol tri (meth) acrylate, tris (2-hydroxyethyl) isocyanurate di (meth) acrylate; dimethylacrylamide, diethylacrylamide, (meth) acryloylmorpholine N-vinylpyrrolidone and the like. Preferably, dimethyl acrylamide and diethyl acrylamide are used.

(D) Photopolymerization initiator As the photopolymerization initiator, known ones can be used, for example, benzophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2 -Methyl-1- [4- (methylnio) phenyl] -2-morpholinopropan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, and 2-hydroxy-2-methyl-1-phenyl-propane-1 -ON. By arbitrarily selecting the light absorption wavelength of the polymerization initiator, curability can be imparted over a wide wavelength range from the ultraviolet region to the visible light region. These photopolymerization initiators may be used in combination of two or more, for example, a photopolymerization initiator excellent in surface curability for thin film coating and a photopolymerization excellent in deep curability for thick coating. By combining the initiator, it is possible to impart excellent curability to the adhesive that cannot be obtained by using a single initiator. In the present invention, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-methyl-1- [4- (methylnio) are used from the viewpoint of storage stability of the blended adhesive and transparency of the adhesive. ) Phenyl] -2-morpholinopropan-1-one is preferred.

(E) Heat stabilizer Preferably, the composition of the present invention is selected from (E) hindered phenol compounds, tocopherols and tocopherol derivatives in addition to (A), (B), (C) and (D) above. At least one heat stabilizer. In general, the heat stabilizer includes quinone, amine, hindered phenol, and natural compounds such as tocopherol and ascorbic acid. Of these, hindered phenol and tocopherol are preferably used. The Examples of hindered phenol heat stabilizers include 2,6-di-t-butyl-p-cresol (BHT), 2,6-di-t-butyl-4-ethylphenol, pentaerythritol tetrakis- [methylene-3. -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate, tris (3 , 5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 4,4′-butylidenebis- (3-methyl-6-tert-butylphenol), and octadecyl 3,5-di-tert-butyl-4- And hydroxyhydrocinnamate. Examples of the tocopherol system include α-tocopherol, γ-tocopherol, and δ-tocopherol. Among these, 2,6-di-t-butyl-p-cresol (BHT), pentaerythritol tetrakis- [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate and d- and dl-α-tocopherol are preferred. Pentaerythritol tetrakis- [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] is octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinna, under the trade name Irganox 1010. The mate is commercially available from Ciba Specialty Chemicals as Irganox 1076.

  The blending ratios of the above (A) to (E) are (A) 40 to 70 wt%, preferably 45 to 60 wt%, (B) 20 to 50 wt%, preferably 30 to 45 wt%, based on the total weight of these components. (C) 2-15 wt%, preferably 6-12 wt%, (D) 1-6 wt%, preferably 2-4 wt%, (E) 0.01-3 wt%, preferably 0.05-0.3 wt% %. When (A) is less than the lower limit or exceeds the upper limit, the initial adhesiveness immediately after light irradiation tends to be weakened. When (B) is less than the lower limit, the adhesiveness over time is weakened, and when (B) exceeds the upper limit of the previous period, the initial adhesiveness immediately after light irradiation tends to be weakened. When (C) is less than the lower limit, the initial adhesiveness becomes weak, and when it exceeds the upper limit of the previous period, the adhesiveness at low temperatures tends to become weak. When (D) is less than the lower limit, the initial adhesiveness becomes weak, and when it exceeds the upper limit of the previous period, the adhesiveness at low temperatures tends to become weak. When (E) is less than the lower limit, it is difficult to obtain sufficient thermal stability, and even if it exceeds the upper limit of the previous period, an improvement in effect proportional to the amount added cannot be obtained.

  In addition to (A) to (E), a reactive diluent and various additives may be included as long as the object of the present invention is not impaired. Examples of the reactive diluent include 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate exemplified for (C), and examples of the additive include a leveling agent. Moreover, you may mix | blend a coloring agent and a pigment for a paint use. Moreover, you may add a photosensitizer, a dispersing agent, a plasticizer, a filler, an antifoamer, an antifoamer, an electroconductive filler, a polymerization inhibitor, an ultraviolet absorber etc. as needed.

The composition of the present invention is prepared by mixing (A), (B), (C) and (D), preferably (E) and other additives, using a known mixer such as a homomixer. Can be prepared. After mixing, it is preferable to perform a defoaming treatment with a planetary stirrer, a filter or the like. Further, only (D) may be mixed immediately before use.

The photocurable composition of the present invention can be cured by, for example, irradiating a high-pressure mercury lamp after being applied by a dispenser for hot melt adhesive. Typically, the curing energy is about 250 mJ / cm ² , cures immediately after light irradiation, and has excellent initial adhesiveness.

Example
Examples of the present invention will be described below, but the present invention is not limited thereto. In the examples, “parts” means parts by weight.

Examples 1-4, Comparative Examples 1 and 2
Each component shown in Table 1 was blended in the same table (wt%) in the order of (B) urethane prepolymer, (A) urethane acrylate resin, (C) photopolymerizable compound, and (D) photopolymerization initiator. The mixture was heated and mixed at 70 ° C. in a homomixer. After a uniform mixture was obtained, defoaming was performed with a planetary stirrer. Details of each component are as follows.
(A) Urethane acrylate resin: Art Resin NPC-25, manufactured by Negami Kogyo Co., Ltd.
(B) Urethane prepolymer: Takenate XA-18 (aliphatic), manufactured by Mitsui Takeda Chemical Co., Ltd.).
(C) Photopolymerizable compound: dimethylacrylamide (DMAA), manufactured by Kojin Co., Ltd.
(D) Photopolymerization initiator: Irgacure 651 (trademark), 2,2-dimethoxy-1,2-diphenylethane-1-one

The obtained composition was evaluated by the following methods.
Evaluation Method (1) A 160 cm × 170 cm × 300 μm A-PET sheet with UV ink printed on the front surface and antistatic treatment on the back surface was used as the initial adhesive substrate. Each composition is heated, applied to the end of the printed surface of the A-PET sheet with a coating air nozzle at a width of 4 mm, a length of 150 mm and a thickness of 90 μm, and the back side of the other end with a laminating machine Then, the bonded part was immediately irradiated with 250 mJ / cm ² of high pressure mercury lamp light, and an adhesive part was immediately formed. After the adhesive part was cooled to room temperature, the adhesive part was twisted by hand, and the initial adhesiveness was evaluated according to the following criteria by visual observation.
A: No peeling occurs.
B: Only the edge part of an adhesion part peels.
C: It peels entirely.

(2) Adhesion with time (1) The adhesive part obtained in (1) was stored in an environment of 23 ° C. and 50% RH for 12 hours. A T-type peel test was conducted at min, and the evaluation was made according to the following criteria from the peel strength and the state of visual peel.
A: Peel strength was 5N or more / 5mm width, and A-PET material destruction or cohesive failure of the cured product layer was observed.
B: Peel strength was less than 5N / 5mm width, and A-PET material destruction or cohesive failure of the cured product layer was observed.
C: The peel strength was less than 5 N / 5 mm width, and interfacial peeling between the cured product and A-PET was observed.

(3) The sample cured by the method of low-temperature adhesiveness (2) was subjected to a 180 ° peel test at a speed of 200 mm / min in an environment of 0 ° C., and the peel condition was visually observed and evaluated according to the following criteria.
A: Material destruction of A-PET or cohesive failure of the cured product was observed.
B: Interfacial peeling between the cured product and A-PET was observed.

(4) Pot life Each state of the composition after heating at 70 ° C. for 3 hours was visually observed and evaluated according to the following criteria.
A: Gelation hardly occurs.
B: A slight increase in viscosity was observed.
C: Clearly cured.

  As can be seen from Table 1, the composition of the present invention containing (C) is excellent in initial adhesiveness. On the other hand, the compositions of Comparative Examples 1 and 2 lacking (C) both have poor initial adhesion. Since Example 4 does not contain (B), it is slightly inferior in adhesiveness over time, but has no problem in initial adhesiveness.

Examples 5 to 9, Reference Example 2
The (A) urethane acrylate resin and (C) photopolymerizable compound shown in Table 2 were weighed in the amount (wt%) shown in the table in a plastic cup that can be sealed, and mixed at a liquid temperature of 60 ° C. After a uniform mixture is obtained, put a cup in the vacuum dryer and continue to reduce the pressure with a vacuum pump under the condition of a liquid temperature of 50 ° C. until the bubbles in the mixture are destroyed and no bubbles can be confirmed. After stopping, the cup was taken out from the vacuum dryer. In the cup taken out from the vacuum dryer, (B) urethane prepolymer, (D) polymerization initiator, and (E) heat stabilizer are weighed in the cup so as to have the mixing ratio shown in the table, and the liquid temperature is 50. Mixed at ° C.
Put the cup containing the mixture into the vacuum dryer again, depressurize the tank with a vacuum pump, and when the pressure in the tank reaches 0.067 MPa, the valve connecting the vacuum pump and the tank Was closed and the power of the vacuum pump was turned off. It was left for 1 hour while maintaining the reduced pressure of 0.067 MPa. Note that the degree of reduced pressure is a gauge pressure indicating how much the pressure in the vacuum dryer tank is reduced from the normal pressure state.
In Table 2, the details of each component are as follows.
(A) Urethane acrylate resin:
Examples 5 and 6: Art resin NPC-25, manufactured by Negami Kogyo Co., Ltd. Examples 7 to 10: Art resin KY-2, manufactured by Negami Kogyo Co., Ltd. (B) Urethane prepolymer: Takenate XA-18 (aliphatic Series), Mitsui Takeda Chemical Co., Ltd. (C) Photopolymerizable compound: Dimethylacrylamide (DMAA), Kojin Co., Ltd. (D) Photopolymerization initiator: Irgacure 651 (trademark), 2,2-dimethoxy- 1,2-diphenylethane-1-one (E) heat stabilizer Example 5: BHT (butylhydroxytoluene), mp 110-125 ° C
Example 6: Irganox 1010 ™, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]
Example 7: Irganox 1076 ™, octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate Example 8: dl-α-tocopherol Example 9: d-α-tocopherol Reference Example 2: ADK STAB HP-10, phosphorus-based, manufactured by Asahi Denka Kogyo Co., Ltd., melting point 148 ° C.

Reference example 1
(D) A composition was prepared in the same manner as in Example 5 except that the amount of the photopolymerization initiator was 3 wt% and no heat stabilizer was mixed.

Thermal stability evaluation The space inside the plastic cup containing each composition was purged with nitrogen, and then sealed with a lid. The sealed plastic cup was placed in an oven at 80 ° C. and allowed to stand for 24 hours, and then the state of the mixture was visually observed. Table 2 shows the sample with no change as A and the gelated product as B.

As can be seen from Table 2, the thermal stability is remarkably improved by blending a predetermined thermal stabilizer with the composition of the present invention. The stabilizer used in Reference Example 2 could not obtain the desired thermal stability effect.

  The photocurable composition of the present invention quickly gives a cured product having high transparency and transparency by photocuring, and is suitable for laminating transparent assembly containers, paints, and the like. Moreover, the combination with a predetermined heat stabilizer is excellent in thermal stability and does not gelate even when stored at a relatively high temperature.

Claims (9)

(A) Urethane (meth) acrylate resin in an amount of 40 to 70 wt%,
(B) a urethane prepolymer having an isocyanate group at at least one end in an amount of 20 to 50 wt%;
(C) a compound having at least one polar group and at least one photopolymerizable group in an amount of 2 to 15 wt%, and (D) a photopolymerization initiator in an amount of 1 to 6 wt%,
The photocurable composition to be contained, where each wt% is a value relative to the total weight of (A), (B), (C) and (D). (C) The photocurable composition according to claim 1, wherein the compound having at least one polar group and at least one photopolymerizable group is dimethyl (meth) acrylamide and / or diethyl (meth) acrylamide. The photocurable composition according to claim 1 or 2, wherein the (B) urethane prepolymer contains an aliphatic polyol residue. (A) Urethane (meth) acrylate resin contains a polycarbonate diol residue or a polyester diol residue, The photocurable composition of any one of Claims 1-3 characterized by the above-mentioned. (D) The photopolymerization initiator is 2,2-dimethoxy-1,2-diphenylethane-1-one and / or 2-methyl-1- [4- (methylnio) phenyl] -2-morpholinopropane-1- The photocurable composition of any one of Claims 1-4 which is ON. (E) The photocurable composition of any one of Claims 1-5 which further contains the at least 1 heat stabilizer chosen from a hindered phenol compound, a tocopherol, and a tocopherol derivative. (E) The photocurable composition of Claim 6 which contains a heat stabilizer in the quantity of 0.01-3 wt%. An adhesive comprising the composition according to claim 1. The coating material containing the composition of any one of Claims 1-7.