JP2005342907A - Method for forming coating film of pencil barrel and pencil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a surface coating film of a pencil barrel with a rubber feel showing an excellent adhesion with a wood, using an aqueous coating material resin and also a pencil with such a coating film. <P>SOLUTION: This method for forming the coating film of the pencil barrel comprises a process to apply to the surface of the pencil barrel a coating material which contains a one-pack type self-crosslinking polyurethane dispersion as an underwater dispersion of a polyurethane elastomer having a silanol group as a substituent, with a glass transition temperature (Tg) of less than 70°C and a process to vaporize the moisture content of the applied coating material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a coating film on a pencil shaft surface and a pencil having the coating film on the shaft surface.

It is common practice to coat the surface of the writing instrument, particularly the grip portion, with rubber, primarily for anti-slip purposes. For example, in the case of a writing instrument such as a ballpoint pen, the shaft member is often formed of plastic or metal. In such a case, the rubber coating as described above is particularly effective. And even if the shaft is a normal wooden pencil shaft, there are some which are covered with such rubber.
Conventionally, solvent-type paints have been used for the display of cosmetic tools and the like, and vinyl acetate resins, acrylic resins, alkyd resins, nitrified cotton, and the like have been conventionally used as paint resins. In recent years, water-based paints are often used as paints from the viewpoint of reducing environmental burden and safety of manufacturing processes. As such a water-based paint resin, a styrene acrylic emulsion resin, a vinyl acetate emulsion resin, or the like is used as shown in Patent Document 1 below.
JP-A-9-193589

The invention described in Patent Document 1 satisfies the requirement for a coating material for surface covering that it is quick-drying and anti-blocking. However, when trying to obtain a rubber feel with such a paint, in terms of performance as a coating film, it is fragile because of its low flexibility, and compared with a coating film of a conventional organic solvent-based paint, There was a problem that adhesion was inferior.
Therefore, an object of the present invention is to realize a rubber-tactile pencil shaft surface coating film excellent in adhesion to a shaft material with an aqueous coating resin, and to provide a pencil having such a coating film.

In view of the above problems, a method for forming a pencil shaft coating film according to the present invention is a one-component self-crosslinking polyurethane dispersion, which is a polyurethane elastomer-in-water dispersion having a silanol group as a substituent, and has a glass transition temperature ( It is characterized by comprising a step of applying a paint containing a Tg) of less than 70 ° C. to the surface of the pencil shaft and a step of evaporating water in the applied paint.
The “pencil” in the present invention is only a “pencil” in a narrow sense having a core mainly composed of graphite and clay and a “color pencil” having a core mainly composed of clay and pigment for the purpose of writing. In addition, not only for writing purposes, but also including a pencil-like shape formed by using cosmetics such as eyebrows and eye shadows as the core. Further, the “pencil axis” of the “pencil” is mainly made of wood or synthetic wood, but also includes a paper made material such as a so-called dermatograph.

  The “one-component self-crosslinking polyurethane dispersion” in the present invention refers to an underwater dispersion of a polyurethane elastomer having a silanol group as a substituent, as shown in the following chemical formula 1.

なお、上記化学式１中のＲは、ポリウレタン分子主鎖を意味する。このシラノール基同士が、下記化学式２に示すようにシロキサン結合により脱水縮合することで、ポリウレタン分子間の架橋構造が形成されることとなる。

In addition, R in the above chemical formula 1 means a polyurethane molecular main chain. The silanol groups are dehydrated and condensed by a siloxane bond as shown in the following chemical formula 2, whereby a crosslinked structure between polyurethane molecules is formed.

前記化学式２と同様、上記化学式２中のＲは、ポリウレタン分子主鎖を意味する。実際には、ポリウレタン分子主鎖には複数のシラノール基が結合している。このため、上記化学式２に示すような架橋構造は、２分子間で複数箇所で形成され得るし、また、複数分子間でも形成され得ることから、強固な結合が実現されることになる。この脱水縮合の実現には、鉛筆軸への塗布後、加温等により塗料中の水分を蒸発するのみで足り、特別な試薬等は不要である。また、木製又は合成木材製の鉛筆軸への密着性も良好である。
また、本発明における一液自己架橋型ポリウレタンディスパージョンは、ガラス転移温度（Ｔｇ）が７０℃未満のものである。ここで、一液自己架橋型ポリウレタンディスパージョンのガラス転移温度が低いほど、形成される塗膜が柔軟である。

As in the chemical formula 2, R in the chemical formula 2 means a polyurethane molecular main chain. Actually, a plurality of silanol groups are bonded to the polyurethane molecular main chain. For this reason, the cross-linking structure as shown in the chemical formula 2 can be formed at a plurality of positions between two molecules, and can also be formed between a plurality of molecules, so that a strong bond is realized. In order to realize this dehydration condensation, it is only necessary to evaporate the water in the paint by heating or the like after application to the pencil shaft, and no special reagent or the like is required. In addition, adhesion to a pencil shaft made of wood or synthetic wood is also good.
Further, the one-component self-crosslinking polyurethane dispersion in the present invention has a glass transition temperature (Tg) of less than 70 ° C. Here, the lower the glass transition temperature of the one-component self-crosslinking polyurethane dispersion, the softer the coating film formed.

That is, if the glass transition temperature is 70 ° C. or higher, the surface of the coating film is more robust than that of less than 70 ° C., but the surface lacks flexibility. On the other hand, if the glass transition temperature is less than 70 ° C., it is possible to obtain a rubber-like feel with a soft coating film. Therefore, depending on the purpose, which glass transition temperature to adopt is appropriately selected. In the present invention, a rubber having a glass transition temperature of less than 70 ° C. is used because the rubber tactile feel on the surface is emphasized.
Contains a one-component self-crosslinking polyurethane dispersion which is a dispersion in water of a polyurethane elastomer having a silanol group as a substituent, and has a glass transition temperature (Tg) of less than 70 ° C. It is possible to obtain a pencil characterized by having a coating film obtained by applying the paint to be applied to the surface of the pencil shaft and evaporating the water in the applied paint. In this pencil, as described above, the adhesion of the coating film surface is good and the rubber feel is excellent.

With the above configuration, the present invention has the following effects.
That is, according to the present invention, it is possible to realize a rubber-tactile pencil shaft surface coating film excellent in adhesion with a shaft material with an aqueous coating resin, and to provide a pencil having such a coating film. It was.

Hereinafter, the present invention will be described with reference to examples. The pencils of Examples 1 to 3 shown below are paints containing a one-component self-crosslinking polyurethane dispersion and having a glass transition temperature (Tg) of less than 70 ° C. The pencils of Comparative Examples 1 to 3 are paints containing a one-component self-crosslinking polyurethane dispersion and having a glass transition temperature (Tg) of 70 ° C. or higher. The pencils of Comparative Examples 4 and 5 are painted with a conventional water-based paint.
(1) Example 1
The pencil coating film of Example 1 is composed of 89.5 parts by weight of a one-component self-crosslinking polyurethane dispersion (WS-6021, Mitsui Takeda Chemical) as a resin, and polyoxyethylene urethane-modified ether (Nippon Paint) 7 as a thickener. .2 parts by weight, 2.4 parts by weight of silica C type (Nippon Paint) as a matting agent, and 0.9 parts by weight of a silica / mineral oil-based antifoaming agent (Nippon Paint) as a defoaming agent Been formed. The glass transition temperature (Tg) of this paint was −60 ° C. and 40 ° C. The viscosity of this paint was about 40,000 mPa · sec. Moreover, the coating film formed with this paint was matte and colorless.

(2) Example 2
The pencil coating film of Example 2 is 80 parts by weight of a one-component self-crosslinking polyurethane dispersion (WS-6021, Mitsui Takeda Chemical) as a resin, and 8 parts by weight of polyoxyethylene urethane-modified ether (Nippon Paint) as a thickener. And a paint having a composition comprising 12 parts by weight of carbon black as a pigment. The glass transition temperature (Tg) of this paint was −60 ° C. and 40 ° C. The viscosity of this paint was about 50,000 mPa · sec. Moreover, the coating film formed with this coating material was black.
(3) Example 3
The pencil coating film of Example 3 is composed of 28 parts by weight of one-part self-crosslinking polyurethane dispersion (WS-5000, Mitsui Takeda Chemical) as a resin and one-part self-crosslinking polyurethane dispersion (WS-6021, Mitsui Takeda Chemical). It was formed by a paint having a composition comprising 52 parts by weight, 8 parts by weight of polyoxyethylene urethane-modified ether (Nippon Paint) as a thickener, and 12 parts by weight of titanium oxide as a pigment. The glass transition temperature (Tg) of this paint was 3 ° C. and 68 ° C. The viscosity of this paint was about 35,000 mPa · sec. Moreover, the coating film formed with this coating material was white.

(4) Comparative Example 1
The pencil coating film of Comparative Example 1 is composed of 89.5 parts by weight of a one-component self-crosslinking polyurethane dispersion (WS-5100, Mitsui Takeda Chemical) as a resin, and polyoxyethylene urethane-modified ether (Nippon Paint) 7 as a thickener. .2 parts by weight, 2.4 parts by weight of silica C type (Nippon Paint) as a matting agent, and 0.9 parts by weight of a silica / mineral oil-based antifoaming agent (Nippon Paint) as a defoaming agent Been formed. The glass transition temperature (Tg) of this paint was 120 ° C. The viscosity of this paint was about 10,000 mPa · sec. Moreover, the coating film formed with this paint was matte and colorless.

(5) Comparative Example 2
The pencil coating film of Comparative Example 2 is composed of 80 parts by weight of a one-part self-crosslinking polyurethane dispersion (WS-4000, Takei Mitsui Chemicals) as a resin, and 8 parts by weight of polyoxyethylene urethane-modified ether (Nippon Paint) as a thickener. And a paint having a composition comprising 12 parts by weight of carbon black as a pigment. The glass transition temperature (Tg) of this paint was 136 ° C. The viscosity of this paint was about 20,000 mPa · sec. Moreover, the coating film formed with this coating material was black.
(6) Comparative Example 3
The pencil coating film of Comparative Example 3 has 72 parts by weight of a one-part self-crosslinking polyurethane dispersion (WS-5000, Mitsui Takeda Chemical) as a resin and a one-part self-crosslinking polyurethane dispersion (WS-5100, Mitsui Takeda Chemical). 8 parts by weight, polyoxyethylene urethane-modified ether (Nippon Paint) 8 parts by weight as a thickening agent, and 12 parts by weight of titanium oxide as a pigment were formed. The glass transition temperature (Tg) of this paint was 70 ° C. The viscosity of this paint was about 20,000 mPa · sec. Moreover, the coating film formed with this coating material was white.

(7) Comparative Example 4
The pencil coating film of Comparative Example 4 has 25.4 parts by weight of vinyl acetate emulsion (Nippon Paint) as resin and 59.3 parts by weight of styrene acrylic emulsion (Nippon Paint), and polyoxyethylene urethane-modified ether (Japan) as a thickener. Paint) 4.0 parts by weight, 2,2,4-trimethyl-1,3-pentanediol isobutyrate (texanol) 4.7 parts by weight as a thickening aid, silica C type as a matting agent (Nippon Paint) It was formed by a paint having a composition comprising 5.7 parts by weight and 0.8 part by weight of a silica / mineral oil-based antifoaming agent (Nippon Paint) as an antifoaming agent. The glass transition temperature (Tg) of this paint was 70 ° C. The viscosity of this paint was about 25,000 mPa · sec. The coating film formed with this paint was matte and colorless.

(8) Comparative Example 5
The pencil coating film of Comparative Example 5 is 89.5 parts by weight of a one-component polyurethane dispersion (W-6010, Mitsui Takeda Chemical) as a resin, and polyoxyethylene urethane-modified ether (Nippon Paint) 7.2 as a thickener. It is formed by a paint having a composition comprising 2.4 parts by weight of silica C type (Nippon Paint) as a matting agent and 0.9 parts by weight of a silica / mineral oil-based defoaming agent (Nippon Paint) as a defoaming agent. It was. The glass transition temperature (Tg) of this paint was 90 ° C. The viscosity of this paint was about 7,000 mPa · sec. The coating film formed with this paint was matte and colorless. The “one-component polyurethane dispersion” used in this example does not have a silanol group in the molecular structure and does not self-crosslink.

(9) Coating method Each of the pencils according to the above examples and comparative examples was subjected to surface coating in a coating process as shown in the schematic diagram of FIG.
In this painting process, first, the wooden pencil shaft 10 is sequentially fed into the first painting tank 21 and the second painting tank 22 containing the same paint 23 by the shaft protruding roll 20. That is, it is first fed from the shaft extruding roll 20 to the first coating tank 21 and then pushed to the next pencil shaft 10 and then fed to the second painting tank 22 and further pushed to the next pencil shaft 10 and dried. It leads to the furnace 30.

The paint 23 adheres to the surface of the pencil shaft 10 in the first painting tank 21 and the second painting tank 22. When the pencil shaft 10 is projected from the first painting tank 21 to the second painting tank and from the second painting tank 22 to the drying furnace 30, it passes through the ironing rubber dies 24 provided at the respective outlet portions, and the extra The paint 23 is removed and applied uniformly.
In the drying furnace 30, the pencil shaft 10 protruding from the second coating tank 22 falls on a conveyor 31 that moves in a direction perpendicular to the protruding direction. The conveyor 31 is configured to move in a state where the two conveyors are inclined inward to support the pencil shaft 10 at both ends. As a result, the side surface of the pencil shaft 10 to which the paint has adhered does not come into contact with the conveyor 31. The inside of the drying furnace 30 is kept at 80 ° C. or higher. The pencil shaft 10 passes through the drying furnace 30 for 30 to 40 seconds while being transported by the transport conveyor 31, so that the coated surface is dried and moisture is evaporated to form a coating film. .

(10) Evaluation method The pencils according to each Example and each Comparative Example were evaluated by the following items.
(10-1) Adhesiveness of coating film The adhesiveness of the coating film to the pencil shaft was evaluated. Specifically, cellophane tape (Nichiban) was applied to the coating film and immediately peeled off, and it was confirmed whether the coating film adhered to the cellophane tape. When it did not adhere, it was evaluated as “◯”, and when it adhered, it was evaluated as “x”.
(10-2) Rubber feel The rubber feel of the coating film was evaluated. Specifically, it was determined by a sensory test whether the coating film had a rubber touch. When the rubber feel was good, it was evaluated as “◯”, and when it was poor, it was evaluated as “x”.

(11) Evaluation results Table 1 below shows the results of the above evaluations for each of the above Examples and Comparative Examples.

上記結果によると、一液自己架橋型ポリウレタンディスパージョンを含有する塗料で塗膜を形成した実施例１から３まで及び比較例１から３までは、いずれも塗膜の密着性については、従来の水性塗料である比較例４及び５に優っていた。
そして、ラバー触感においては、ガラス転移温度（Ｔｇ）が７０℃未満である実施例１から３までに係る鉛筆の塗膜は、従来の水性塗料を用いた比較例４及び５に係る鉛筆の塗膜や、ガラス転移温度（Ｔｇ）が７０℃以上である比較例１から３までに係る鉛筆の塗膜より優れていることが判明した。

According to the above results, in Examples 1 to 3 and Comparative Examples 1 to 3 in which the coating film was formed with a paint containing a one-component self-crosslinking polyurethane dispersion, the adhesiveness of the coating film was the same as in the past. It was superior to Comparative Examples 4 and 5, which are water-based paints.
And in rubber tactile sensation, the pencil coating films according to Examples 1 to 3 having a glass transition temperature (Tg) of less than 70 ° C. are applied with the pencil coatings according to Comparative Examples 4 and 5 using conventional water-based paints. It was found that the film was superior to the pencil film according to Comparative Examples 1 to 3 having a glass transition temperature (Tg) of 70 ° C. or higher.

  In conclusion, pencils with a paint coating containing a one-component self-crosslinking polyurethane dispersion with a glass transition temperature (Tg) of less than 70 ° C have good adhesion and excellent rubber feel. There was found.

The pencil painting process which concerns on an Example and a comparative example is shown with the schematic.

Explanation of symbols

10 Pencil axis
20 Axial roll 21 First coating tank
22 Second paint tank 23 Paint
24 Ironing rubber die
30 Drying furnace 31 Conveyor

Claims (2)

A coating material containing a one-component self-crosslinking polyurethane dispersion, which is a dispersion in water of a polyurethane elastomer having a silanol group as a substituent, and has a glass transition temperature (Tg) of less than 70 ° C. is applied to the surface of the pencil shaft. Applying step;
And a step of evaporating water in the applied paint. A paint containing a one-component self-crosslinking polyurethane dispersion, which is a dispersion in water of a polyurethane elastomer having a silanol group as a substituent, and has a glass transition temperature (Tg) of less than 70 ° C. is applied to the surface of the pencil shaft. A pencil having a coating film obtained by applying and evaporating water in the applied paint.

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