JP2005314530A - Alkali-removed type protective coating for plastic and plastic molded article in which protective film is formed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkali-removed type protective coating for plastic excellent in water resistance of a coated film and adhesiveness to a substrate, having a protective function of a printed film and capable of removing the coated film with a weakly alkaline water even when stain is attached onto the coated film. <P>SOLUTION: The alkali-removed type protective coating for plastics comprises (A) an acrylic polymer having 5,000-50,000 number-average molecular weight, 10-80°C Tg and 30-100 acid value, (B) a maleic acid-modified polypropylene resin having 20,000-200,000 weight average molecular weight and (C) an organosilane compound having a functional group capable of reacting with a carboxy group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention protects the surface of the polyolefin-based plastic base material, and when dirt adheres to the coating film, quickly dissolves and removes the coating film using an alkaline solution to remove the dirt, and then repaints, The present invention relates to a protective coating for an alkali-removable plastic capable of protecting the surface, and a polyolefin resin plastic molded product coated with the coating.

  Conventionally, plastic molded products such as plastic containers and plastic pallets have been used for transportation and storage of various articles such as foods, beverages, and industrial materials. These plastic molded products are made of polyolefin resin such as polyethylene or polypropylene, and are collected and used repeatedly in the market, and their lifetime is considered to be more than 10 years.

  Plastic containers and plastic pallets that are used repeatedly over a long period of time are used for transportation and storage both indoors and outdoors, so that dirt such as dust adheres over time and tack seals used for display labels are not marked. The appearance defect such as remaining is caused, and the solution has been desired.

  In general, the company name, product name, product name, number, and the like are printed on these plastic containers and plastic pallets using epoxy-based or urethane-based ink according to the purpose of use.

  However, as described above, when used outdoors for a long period of time, this printing surface deteriorates, causing choking, and the printed film becomes powdery and easily peels off, causing poor appearance or handling workers' clothing. There were problems such as fouling.

  As a protective coating for solving these problems, a protective coating combining polyvinyl alcohol, paraffin wax, and ethylene-acrylic acid copolymer resin has been proposed (see, for example, Patent Document 1). However, since polyvinyl alcohol is a water-soluble polymer, the durability of the coating film was insufficient due to poor water resistance.

  In addition, alkali-soluble acrylic resin-based plastic paints with improved water resistance have been proposed (for example, see Patent Document 2). However, the water resistance is not always sufficient, and the adhesiveness to the base plastic is inferior.

Japanese Patent No. 2524923 JP-A-10-158571

  The problem of the present invention is that the water resistance of the coating film and the adhesion to the plastic substrate are good and have a protective function of the printed film, and even if dirt such as dust adheres to the coating film, An object of the present invention is to provide a protective coating for alkali-removable plastics that retains commercial value by protecting the printed film by removing the coating film quickly using weak alkaline water, removing the dirt, and repainting.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that an alkali-removable plastic protective coating comprising an acrylic copolymer, a maleic anhydride-modified polypropylene resin, and an organosilane compound that are specified in the present invention as essential components. The present inventors have found that the above problems can be achieved advantageously, and have completed the present invention.

  The present invention provides moderate alkali removability by using a specific acrylic polymer, improves adhesion with a base material by using a maleic anhydride-modified polypropylene resin, and is further water-resistant by using in combination with an organosilane compound. It is intended to improve the performance.

  That is, the present invention firstly includes an acrylic polymer (A) having a number average molecular weight of 5,000 to 50,000, a glass transition temperature of 10 to 80 ° C., and an acid value of 30 to 100, and a weight average molecular weight of 20,000 to 200. It is an object of the present invention to provide a protective coating for alkali-removable plastics containing a maleic anhydride-modified polypropylene resin (B) of 1,000,000 and an organosilane compound (C) having a functional group capable of reacting with a carboxyl group.

  A second object of the present invention is to provide a polyolefin resin-made plastic molded product coated with the above-described alkali-removable plastic protective coating.

  According to the protective coating for alkali-removable plastic of the present invention, it is possible to form a coating film having good adhesion and water resistance to a polyolefin-based substrate, particularly a polypropylene substrate. Moreover, it has an excellent surface protection function, and the coating film can be easily removed with alkali together with dirt, and repainting can be performed without any problem.

  The protective coating for alkali-removable plastic of the present invention will be described in detail. First, the acrylic polymer (A) used in the present invention will be described.

  The acrylic polymer (A) used for the protective coating for alkali-removable plastic of the present invention is an acrylic polymer having a number average molecular weight of 5,000 to 50,000, a glass transition temperature of 10 to 80 ° C., and an acid value of 30 to 100 ( A).

  There is no restriction | limiting in the polymerization method in the case of manufacturing an acrylic polymer (A), a block radical polymerization method, a solution radical polymerization method, a non-aqueous dispersion radical polymerization method, a suspension polymerization method in an aqueous medium, Various known polymerization methods such as emulsion polymerization can be applied. Of these, the radical polymerization method in an organic solvent is particularly convenient and preferable.

  When applying the radical polymerization method in an organic solvent, it is possible to obtain an acrylic polymer (A) dissolved and / or dispersed in water by neutralizing with an amine such as ammonia or triethylamine after radical polymerization. it can. Moreover, it is also possible to distill off the organic solvent used for superposition | polymerization by vacuum distillation etc. as needed.

  In applying the radical polymerization method in an organic solvent, various known and commonly used compounds can be used as the polymerization initiator. Typical examples include 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2,4-dimethylbutyronitrile), 2,2′-azobis (2-methylbutyronitrile). ) And the like; tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxide, cumene hydroperoxide, diisopropyl Examples thereof include peroxides such as peroxycarbonate.

  In applying the radical polymerization method in an organic solvent, various known and commonly used compounds can be used as the organic solvent. Preferably, it is a water-soluble or water-soluble solvent, for example, alcohols such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, iso-butanol, tert-butanol; ethylene glycol monomethyl Examples include cellosolves such as ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether; propylene glycol ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether and propylene glycol monopropyl ether. These compounds may be used alone or in combination of two or more.

  The monomer component constituting the acrylic polymer (A) used in the present invention includes an α, β-ethylenically unsaturated carboxylic acid monomer (a-1) and an α, β-ethylenic monomer copolymerizable therewith. It is comprised from a saturated monomer (a-2).

  Examples of the α, β-ethylenically unsaturated carboxylic acid monomer (a-1) include acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, acrylic acid dimer, And monohydroxyethyl (meth) acrylate phthalate.

Α, β-ethylenically unsaturated monomer (a-2) copolymerizable with the above (a-1)
(Methyl) (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylate 2-ethylhexyl (meth) ) Acrylic acid alkyl esters; (meth) acrylate-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; acrylamide, methacrylamide Amide compounds such as N-methylolacrylamide, N-methoxymethylacrylamide, N-butoxymethylacrylamide; cyano group-containing vinyl compounds such as acrylonitrile and methacrylonitrile; aromatic vinyl compounds such as styrene and vinyltoluene; methyl vinyl ether Vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether; vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, Examples thereof include vinyl esters such as vinyl stearate, vinyl cyclohexanecarboxylate, vinyl pivalate, vinyl octylate, vinyl benzoate and vinyl cinnamate.

  The acrylic polymer (A) has a number average molecular weight in the range of 5,000 to 50,000, preferably in the range of 10,000 to 30,000. If it is less than 5,000, water resistance will be inferior, and if it exceeds 50,000, alkali removability will become inferior.

  The glass transition temperature of the acrylic polymer (A) described above is in the range of 10 to 80 ° C, preferably in the range of 20 to 60 ° C. If it is less than 10 degreeC, a coating film becomes easy to be damaged, and when it exceeds 80 degreeC, adhesiveness will become inferior.

The above-mentioned acrylic polymer (A) has an acid value in the range of 30 to 100, preferably 30.
It is in the range of ~ 80. If it is less than 30, alkali removal becomes difficult, and if it exceeds 100, water resistance becomes poor.

  The maleic anhydride-modified polypropylene resin (B) used in the protective coating for alkali-removable plastics of the present invention includes maleic anhydride-modified polypropylene, maleic anhydride acrylic modified polypropylene, maleic anhydride modified chlorinated polypropylene, and maleic anhydride acrylic. Modified chlorinated polypropylene can be used.

  The aforementioned maleic anhydride-modified polypropylene resin (B) has a weight average molecular weight in the range of 20,000 to 200,000, preferably in the range of 30,000 to 100,000. If it is outside this range, it may be difficult to obtain a predetermined effect such as improvement in adhesion.

  As the organosilane compound (C) used in the protective coating for alkali-removable plastics of the present invention, those having a functional group capable of reacting with a carboxyl group can be used. The organosilane compound contributes to improving the water resistance of the coating film by reacting with the carboxyl group of the acrylic polymer. Examples of the functional group capable of reacting with a carboxyl group include a glycidoxy group having an epoxy ring and an epoxycyclohexyl group.

  For example, those having a glycidoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane Examples of those having an epoxy cyclohexyl group include 2- (3,4 epoxy cyclohexyl) ethyl trimethoxy silane and 2- (3,4 epoxy cyclohexyl) ethyl triethoxy silane. Moreover, the hydrolyzate of these organosilane compounds and the condensate of this organosilane can also be used, and 1 type or 2 types or more can be used in combination suitably from these.

  In the protective coating for alkali-removable plastic of the present invention, the ratio (A) :( B) of the acrylic polymer (A) and the maleic anhydride-modified polypropylene resin (B) is in the range of 60:40 to 90:10. Is more preferable, and the range of 70:30 to 85:15 is more preferable. When the amount of the maleic anhydride-modified polypropylene resin (B) is larger than this range, the alkali removability tends to be inferior, and when the amount of the maleic anhydride-modified polypropylene resin (B) is smaller than this range, the adhesion to the substrate tends to be lowered. is there.

  The equivalent ratio (c) / (a) of the functional group (c) capable of reacting with the carboxyl group (a) of the acrylic polymer (A) and the carboxyl group of the organosilane compound (C) is 0.1. It is preferably in the range of -0.7, and more preferably in the range of 0.3-0.6. When the equivalent ratio is smaller than this range, the water resistance tends to be inferior, and when the equivalent ratio is larger than this range, the alkali removability tends to be inferior.

  Further, in the protective coating for alkali-removable plastics of the present invention, known paint additives can be used as necessary. For example, adding inorganic pigments, organic pigments, extender pigments, clay minerals, lubricants, thickeners, surfactants, antifoaming agents, leveling agents, antifungal agents, antibacterial agents, antistatic agents, UV absorbers, etc. Can do.

  The protective coating for alkali-removable plastics of the present invention can be used by mixing various known and conventional resins within the scope of achieving the object of the present invention. For example, an acrylic polymer (A ), And vinyl resins other than maleic anhydride-modified polypropylene resin (B), polyester resins, polyurethane resins, epoxy resins, epoxy ester resins, acrylic resins, phenol resins, petroleum resins, ketone resins, or modified resins thereof. Can be mentioned.

  The protective coating for alkali-removable plastics according to the present invention is, for example, a solution and / or dispersion of an acrylic copolymer (A), a dispersion of a maleic anhydride-modified polypropylene resin (B), and a functional group capable of reacting with a carboxyl group. It can manufacture by the method of adding and stirring the organosilane compound (C) which has group.

  As the polyolefin-based resin used as a base material as an object to be coated with the protective coating for alkali-removable plastic of the present invention, known resins can be appropriately used. Examples thereof include polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymer. These may be used alone or in combination of two or more.

  There is no restriction | limiting in particular in the shape of an above described base material, A sheet form, plate shape, and what was shape | molded previously may be sufficient.

  In addition, for the base material, known antistatic agents, antifogging agents, antiblocking agents, antioxidants, light stabilizers, crystal nucleating agents, lubricants, etc., as required, as long as the effects of the present invention are not impaired. These additives may be blended.

  Furthermore, the substrate can be subjected to a known surface treatment for further improving the adhesion of the protective coating for alkali-removable plastic of the present invention. For example, a degreasing treatment with a solvent, a corona discharge treatment, a plasma treatment, a flame plasma treatment, an electron beam irradiation treatment, an ultraviolet ray irradiation treatment and the like may be mentioned, and a treatment combining one or more of these may be performed.

  The method of applying the alkali-removable plastic protective coating of the present invention to the surface of the base material is not particularly limited as long as the object of the present invention is not impaired. For example, dip coating, spray coating, brush coating, roller coating Known methods such as a method, an electrostatic coating method, and a centrifugal coating method can be used. Spray coating is preferred for application to the molded product. The application may be performed once, or may be performed in two or more stages. Furthermore, either one side or both sides of the substrate may be used. After coating, for example, it is dried at room temperature, or at a temperature at which the molded product is not deformed by heat, for example, in the range of 40 to 120 ° C., preferably in the range of 50 to 100 ° C., preferably 10 seconds to 30 minutes, preferably What is necessary is just to dry for 1 minute-15 minutes.

  The dry film thickness of the protective coating for alkali-removable plastic of the present invention on the substrate is not particularly limited, but is usually in the range of 0.1 to 20 μm, preferably in the range of 0.5 to 10 μm.

  After applying the coating of the present invention on the substrate as described above, the molded article having the cured film of the present invention can be obtained by drying at room temperature or heating.

  Hereinafter, in order to facilitate understanding of the present invention, the present invention will be specifically described by way of examples. However, the present invention is not limited to the examples. In addition, the part and% in each example are based on a mass reference | standard.

(Example 1)
To 400 parts of acrylic resin A-1 (solid content: 20%, acid value: 40, Tg: 40 ° C., number average molecular weight: 7 × 10 ³ ), 450 parts of ion-exchanged water is added and stirred and mixed with a dispersion stirrer. Then, 67 parts of maleic anhydride acrylic-modified polypropylene resin B-1 (solid content: 30%, weight average molecular weight: 6 × 10 ⁴ ; trade name: Auroren AE-201, Nippon Paper Chemicals Co., Ltd.) was added. And stirred until uniform. Furthermore, 5.4 parts of organosilane compound C-1 (3-glycidoxypropyltrimethoxysilane; trade name A-187 manufactured by Nippon Unicar Co., Ltd.), 5 parts of nonionic surfactant, silicone slip agent 0. After adding 5 parts and sufficiently stirring, the solid content was adjusted to 10% with ion-exchanged water to obtain a protective coating for alkali-removable plastic.

(Examples 2-18, Comparative Examples 1-7)
In the same manner as in Example 1, alkali-removable plastic protective coatings having the compositions shown in Table 1 and Tables 2 to 5 were prepared.

Mn shown in Table 1 represents the number average molecular weight.
The followings were used for the maleic anhydride-modified polypropylene resins shown in Tables 2 to 5. In the table, the formulation indicates the solid content ratio.
(B-1): Maleic anhydride / acrylic modified polypropylene (trade name: Auroren AE-201, manufactured by Nippon Paper Chemicals Co., Ltd., solid content 30%, weight average molecular weight 60,000).
(B-2): Maleic anhydride-modified chlorinated polypropylene (trade name; Supercron E-603, manufactured by Nippon Paper Chemicals Co., Ltd., solid content 30%, weight average molecular weight 55,000).
(B-3): Maleic anhydride-modified chlorinated polypropylene (trade name: CP310W, manufactured by Eastman Chemical Japan, solid content 30%, weight average molecular weight 60,000).

The following organosilane compounds shown in Tables 2 to 5 were used. In the table, the formulation indicates the solid content ratio.
(C-1): 3-glycidoxypropyltrimethoxysilane (trade name; A-187, manufactured by Nihon Unicar).
(C-2): 3-glycidoxypropyltriethoxysilane (trade name: KBE-403, manufactured by Shin-Etsu Chemical Co., Ltd.).
(C-3): β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (trade name: KBM-303, manufactured by Shin-Etsu Chemical Co., Ltd.).
(C-4): β- (3,4-epoxycyclohexyl) ethyltriethoxysilane (trade name; Coat OSil 1770, manufactured by Nihon Unicar).

(Evaluation)
The protective coatings for alkali-removable plastics obtained in Examples 1 to 18 and Comparative Examples 1 to 7 were tested for adhesion to a substrate, water resistance, and alkali removability. The coating film for testing and the testing method are as follows.

(Create coating film for test)
After spray coating the degreased polypropylene plate using an air-type hand gun, the polypropylene plate was dried in a dryer at 80 ° C. for 10 minutes. The coating thickness at this time was applied so as to be 3 μm.

(Adhesion)
After creating a grid pattern (100 squares in 1 cm × 1 cm) using a cutter knife, a peel test was performed using a cellophane adhesive tape. Judgment was made based on the number of remaining cells in the 100 cells. Judgment criteria were ◎ for those with 95 or more remaining cells, ◯ for 80-94, Δ for 50-79, and x for 49 or less.

(water resistant)
The change of the coating film after visual immersion in tap water at 25 ° C. for 24 hours was visually judged. Judgment criteria were as follows: ◎ when there was no change, ◯ when there was slight whitening but disappearing immediately at room temperature, Δ when whitening was observed, and × when the coating film was dissolved or swollen. Moreover, the external appearance after being immersed in 40 degreeC warm water for 10 minutes was determined similarly.

(Alkali removal)
The coated panel was immersed for 3 minutes in a bathtub maintained at 60 ° C. with a 1% aqueous solution of caustic soda and then washed with tap water to visually determine the extent of the coating film remaining. The case where the coating film was completely removed was evaluated as ◎, the case where the coating film remained slightly was evaluated as ○, and the case where the coating film remained was determined as ×.

  About the said Example and a comparative example, the evaluation result of each cured film is shown in Tables 6-9.

(Example 19)
The protective coating for alkali-removable plastic obtained in Example 4 was spray-coated on the outside of a polypropylene container using an air-type hand gun, and then dried at 80 ° C. for 10 minutes with a dryer. The coating thickness at this time was applied so as to be 3 μm. The coated container was left outdoors for 3 months to allow dirt and other dirt to adhere thereto, and then the alkali removal test was conducted in the same manner as in Example 1. Dirt was removed along with the coating.

  Further, the container was again spray-coated with an air-type hand gun on the outside, and then dried at 80 ° C. for 10 minutes with a dryer. The coating thickness at this time was applied so as to be 3 μm. At this time, the appearance of the coating film had no problem with no occurrence of repellency or the like.

(Example 20)
After spray-coating the protective coating for alkali-removable plastic obtained in Example 5 on a polypropylene beer container (where the screen-printed film deteriorates over time and choking) using an air-type hand gun, it is brought to room temperature. Left for 12 hours. The coating thickness at this time was applied so as to be 3 μm. When this surface was rubbed with a paper towel to confirm the presence or absence of color fading, no color fading was observed.

(Example 21)
The protective coating for alkali-removable plastic obtained in Example 8 was spray-coated using a pneumatic hand gun on the outside of the polyolefin resin pallet, and then allowed to stand at room temperature for 12 hours. The coating thickness at this time was applied so as to be 3 μm. The coated pallet was left outdoors for 3 months to allow dirt and other dirt to adhere thereto, and then the alkali removal test was conducted in the same manner as in Example 1. Dirt was removed along with the coating.

The protective coating for alkali-removable plastic of the present invention is suitably applied to molded products that are used and distributed mainly for a long time outdoors, such as plastic containers and plastic pallets. The protective coating film has a protective function of the printed film, and even if dirt such as dust adheres to the coating film, the coating film is quickly removed using weak alkaline water to remove the dirt, By re-coating, the printed film can be protected, which can contribute to maintaining the commercial value.

Claims (7)

Acrylic polymer (A) having a number average molecular weight of 5,000 to 50,000, a glass transition temperature of 10 to 80 ° C., an acid value of 30 to 100, and a maleic anhydride-modified polypropylene having a weight average molecular weight of 20,000 to 200,000 A protective coating for an alkali-removable plastic comprising a resin (B) and an organosilane compound (C) having a functional group capable of reacting with a carboxyl group. The protective coating for alkali-removable plastics according to claim 1, wherein the organosilane compound (C) is at least one selected from hydrolyzate of organosilane or condensate of organosilane. The alkali removal according to claim 1 or 2, wherein the ratio (A) :( B) of the acrylic polymer (A) and the maleic anhydride-modified polypropylene resin (B) is 60:40 to 90:10. Protective coating for mold plastics. The equivalent ratio (c) / (a) of the functional group (c) capable of reacting with the carboxyl group (a) of the acrylic polymer (A) and the carboxyl group of the organosilane compound (C) is 0.1 to 0.1. It is 0.7, The protective coating for alkali removal type plastics in any one of Claims 1-3. A polyolefin resin-made plastic molded product, wherein the surface of the molded product is coated with the protective coating for alkali-removable plastic according to any one of claims 1 to 4. The polyolefin resin-made plastic molded product according to claim 5, wherein the plastic molded product is a polyolefin-based resin container. The polyolefin resin plastic molded product according to claim 5, wherein the plastic molded product is a polyolefin resin pallet.