INK OCCLUSION MATERIAL FOR WRITING UTENSILS

Abstract: The ink occlusion material for writing utensils according to the present invention comprises a fiber bundle of a mixture of an acrylic synthetic fiber and at least one hydrophobic fiber selected from the group consisting of polyester fibers and poly-­ propylene fibers in a weight ratio of 20 to 70 : 80 to 30. The two fibers are drawn so as to show a sea-island form in the cross section of said fiber bundle and spot-adhered by the partial melt-­ adhesion of the acrylic synthetic fiber and the fiber bundle is twisted at a rate of 1 to 30 T/M.

Description: BACKGROUND OF THE INVENTION The present invention relates to an ink occlusion material for writing instruments, and particularly to an aqueous-ink occlusion material and to a method for the preparation thereof. Heretofore, as an ink occlusion material for writing instruments, there has been known a material prepared by impregnating a precondensate of a thermosetting resin such as melamine, epoxy or phenol resin into a bundle of synthetic fibres such as polyester, nylon, acrylic, vinylon or polyethylene fibres, and compressing and heating the bundle to adhere the fibres together and to shape the bundle. However, it is necessary that ink should be able to flow out smoothly from the occlusion material but the thermosetting resin hardly adheres uniformly to the fibre bundle so that the capillary structure useful for ink flow and ink occlusion is incomplete and fluctuations in ink flow become high. To mitigate such disadvantages, Japanese Patent Publication No. 37571 of 1975 discloses a method in which a mixed sliver of fibres having different melting points is covered with a resin film having an approximately the same melting point as the fibres to effect hot melt adhesion. However, this method has a disadvantage in that the ink utilization ration is lowered because the resin absorbs ink. As an alternative method, Japanese Patent Publication No. 16963 of 1970 discloses a method in which the fibres are arranged mutually parallel to form a continuous fibre bundle, the bundle is treated with an adhesive solution and then squeezed and solvent is removed by drying to adhere and fix the fibres, and then finally the periphery of the fibre bundle is covered with a polymer film to prepare an ink occlusion material. However, this method has defects in that the step of adhering the film at an overlapping portion after covering the bundle with the polymer film cannot be speeded up and the proportion of defects is high and consequently the method is uneconomic. The present inventors have already proposed, in Japanese Laid-open Patent Publication No. 199698 of 1982, a method in which crimped acrylic fibres are arranged mutually parallel to form a bundle and an organic solvent which can dissolve the fibres is applied on the bundle and the bundle is heated to melt-adhere at least a portion of the fibres. However, this method, has defects in that the fibres partially fall out in a squeezing guide of the organic solvent and during the drying procedure and the adhered spots are few unless the heating is carried out under compression. Also as acrylic fibre is more hydrophilic than polyester fibre, polyethylene fibre and polypropylene fibre, the ink occlusion material retains much ink when an aqueous ink is used and thus the ink utilization ration of the material is low. Furthermore, Japanese Laid-Open Patent Publication No. 60774 of 1986 discloses a method in which a fibre of low hydrophilicity such as polyester fibre is mixed in the fibre bundle to solve the problem of the above-mentioned Japanese Laid-Open Patent Publication No. 199698 of 1982. However, when polyester fibre or other fibre of low hydrophilicity is mixed uniformly, the ink utilization ratio can be somewhat improved but the ink retainability is thereby lowered and the problem of fibre escape remains. An object of the present invention is to provide an ink occlusion material which has the same ink retention as in the case of using an acrylic fibre alone and yet shows a high ink utilization ratio and gives no problem of fibre escape and thus can be easily handled. Another object of the present invention is to provide a method for the preparation of such an easily handled ink occlusion material, which method can be carried out on a commercial scale at a low price. Summary of the Invention The ink occlusion material for writing instruments according to the present invention comprises a bundle of a mixture of acrylic synthetic fibre and at least one hydrophobic fibre selected from polyester fibres and polypropylene fibres in a weight ration of 20 to 70 : 80 to 30. The two types of fibres are drawn so as to present a sea-island form in the cross section of the bundle and spot-adhered by partial melt adhesion of the acrylic synthetic fibre and the bundle is twisted by an amount of 1 to 30 T/m. Detailed Description of the Invention The inventors have found that the objects of the invention can be attained by arranging acrylic fibres and polyester fibres or polypropylene fibres in a specified silver form to give a bundle and providing proper adhesion and twist whereby the two types of fibres exhibit a synergistic effect. In the ink occlusion material according to the present invention, the acrylic fibres, high in ink retainability, and the hydrophobic fibres, enhancing ink utilization ratio, are scattered in sea-island form as fibre groups or slivers, in the fibre bundle, and thereby sufficient ink retainability can be attained and in use ink can flow out smoothly through the hydrophobic fibre groups adjacent to the acrylic fibre groups to ensure good ink utilization. In this specification, reference to sea-island form means that the acrylic synthetic fibre or the hydrophobic fibre of the ink occlusion material presents, in the cross section of the fibre bundle an island form in which a group of 3 to 20 fibres can be counted. In a fibre bundle having such a sea-island cross section, spot-melt adhesion of acrylic fibre can be attained. since, in carrying out the method according to the present invention, the melt adhesion is effected with the fibre bundle having been twisted by an amount of 1 to 30 T/m, escape of fibres does not occur during the cutting of the fibre bundle and insertion of the cut bundle into a writing instrument and the resulting product is of high quality. The ink occlusion material of the present invention can be prepared by a procedure in which a crimped acrylic fibre is mixed with a crimped hydrophobic fibre selected from polyester fibre and polypropylene fibre in a weight ratio of 20 to 70 : 80 to 30 and to form a bundle wherein the mixed fibres are arranged parallel to a fibre axis direction so that said two types of fibre show a sea-island form in the cross section of the bundle and the mixed fibres are then twisted by an amount of 1 to 30 T/m and an organic solvent which can dissolve the acrylic fibre is applied to the bundle and the bundle is dried and then heat treated at a temperature not lower than the activation temperature of said organic solvent to melt-adhere a portion of said acrylic fibres. Any commercially available crimped acrylic fibre can be used in the present invention and, for example, one prepared by a procedure in which an acrylic polymer prepared by a copolymerization of a monomer composition containing 50 weight % or more (preferably 80 weight % or more) of acrylonitrile and, optionally, further containing acrylic acid derivatives such as methyl acrylate or methyl methacrylate, or a sulfonic acid group containing monomer is spun and crimped, can be used. Further, any commercially available polyester fibre can be used in the present invention. It is preferred to use 5 to 30 weight % of a low-melting polyester fibre having a melting point of 100 to 150°C in combination with a common polyester fibre. As the polypropylene fibre, any commercially available polypropylene fibre also can be used. It is preferred to use 5 to 30 weight % of a low-melting polypropylene fibre having a melting point of 100 to 150 °C in combination with a general polypropylene fibre. The acrylic fibre may be used to account for 20 to 70 weight % based on the total amount of the fibre bundle. It is especially preferred to account for 40 to 70 weight %. Although polyester fibre and polypropylene fibre may be used in combination as the hydrophobic fibres, it is not necessarily to use them in combination. Usually, one of them is used together with acrylic fibre. The preferred number of crimps of these fibres is 5 to 20 per inch, preferably 6 to 14 per inch. The fineness is usually 1 to 20 deniers, preferably 2 to 10 deniers. It is required that the ink occlusion material prepared according to the present invention has an almost uniform capillary structure so that the distance between the fibres is almost uniform and is neither too large nor too small and it is required to avoid tight adhesion between fibres. When a fibre with no crimp is used, partial tight adhesion tends to occur between fibres and an appropriate distance between the fibres to provide a satisfactory capillary structure cannot be attained. Thus, a crimped fibre should be used. When a crimped fibre is used, tight adhesion between fibres is generally avoided and a product of excellent ink occlusion and high ink fluidity can be obtained. The crimp may be provided physically or mechanically in the later stage of a spinning process, or it may be structurally obtained by using a latent shrinkage force of the fibre. In the present invention, cut stock of 30 to 200 mm length is worsted and drawn and then arranged mutually parallel to an axis direction and the sliver thus formed is combined for use. As the form of worsting and drawing for sliver formation, a short spinning such as 2 inch spinning, 3 inch spinning or the like and a long spinning such as worsted spinning, semi-worsted spinning or the like can be used in accordance with the fibre length. In general, a worsted sliver prepared by using fibres of 75 to 130 mm length is most preferred. The fibre bundle is formed with such slivers. The grain of the sliver can be appropriately decided according to the type of the objective ink occlusion material and is usually 1 to 100 g/m. According to the present invention, the slivers thus prepared are arranged mutually parallel to form a fibre bundle having a cross section of sea-island form. For the purpose, it is preferred that plural slivers of acrylic fibre and plural slivers of hydrophobic fibre are used in combination, preferably in a ratio of 2 ∼ 6 : 2 ∼ 6 and are drawn with small degree of doubling such, as not more than 3 times, preferably once or twice. Then, a twist of 1 to 30 T/m is provided to the fibre bundle thus prepared. The twist is preferably 3 to 20 T/m. A twist of less than 1 T/m causes escape of fibre in the squeeze guide of the organic solvent bath in the succeeding step and in the drying step and decreases the melt adhesion points, while a twist of more than 30 T/m increases distortion of the product and lowers ink occlusion. The slivers thus prepared are arranged mutually parallel and twisted and an organic solvent having dissolution ability for the acrylic fibre is applied between the fibres of the bundle by impregnation or the like to dissolve partially the acrylic fibre and to adhere it and to shape the bundle. As the organic solvents used in the present invention, there are exemplified many compounds such as amide type, nitrile type, sulfone type, sulfoxide type, nitro type and carbonate type compounds. For example, the amide type compounds include dimethylformamide and dimethylacetamide, the nitrile compounds include succinonitrile and malononitrile, the sulfone compounds include tetramethylene sulfone and ethyl methyl sulfone, the sulfoxide compounds include dimethyl sulfoxide, the nitro compounds include nitromethane, and the carbonate compounds include λ-butyrolactone and ethylene carbonate. These solvents may be used as a solution such as a mixed solution, an aqueous solution or an acetone comprising solution. The dissolution behaviours of these solvents on acrylic fibre are not necessarily the same as each other and are affected by their chemical characteristics, and their temperature dependencies and solubilization temperatures are diverse. Accordingly, any of these organic solvents can be used in the present invention if appropriate conditions are selected. However, it is essential that the chemical characteristics, especially the temperature dependence, of the organic solvent on acrylic fibre, are taken in consideration and that the temperature of the impregnation bath is selected so that the fibre does not swell at such a temperature. Accordingly, for the fixing and drying after impregnation and squeezing, the fibre is exposed to an atmosphere of higher temperature. A temperature at which the organic solvent starts to swell and dissolve the fibre is selected as the drying and fixing temperature. As the solvent used in the present invention, tetramethylene sulfone is especially preferred because of the workability and the product quality it provides. The amount of the organic solvent used should be appropriately decided according to the hardness of the ink occlusion material. The hardness is related to the size of the instrument, that is the thickness of the occlusion material, the type of connection to a pen point and the viscosity and fluidity of the ink used. The pick-up of the organic solvent on the fibre is selected usually to be in the range of from 1 to 30 weight % according to the required hardness. The range of 7 to 15 weight % is most preferred. When the solvent is used in solution, the concentration of the organic solvent in the solution can be selected according to the squeezing rate of succeeding squeezing equipment. If required, the concentration of the organic solvent in the solution can be adjusted so that the amount of the organic solvent adhered on the fibre after squeezing is 1 to 30 weight %, preferably 7 to 15 weight % based on the fibre weight. The fibre bundle, to which the organic solvent has been applied, is then heated and dried and further heat treated at a temperature higher than the activation temperature of the organic solvent and thus melt-adhered. The heating and drying can be carried out at a relatively low temperature. For example, the temperature may be 80 to 100°C in the case of an acetone/tetramethylene sulfone (85/15 weight/weight) solution. Then, the bundle is heat-treated to spot adhere the fibres. This treatment is usually carried out in as a short contact period as 0.05 to 0.3 sec. at a temperature in the range of 200 to 350°C. a contact period of 0.1 to 0.2 sec. and a treating temperature of 250 to 280°C are preferred. In the case of the above-mentioned example, the desired occlusion material can be prepared by passing it through an atmosphere at 200°C. Neither the polyester fibre nor the polypropylene fibre melt-adheres to the acrylic fibre during the heat treatment following the drying, but they are present within the spot-adhered net of the acrylic fibres. If a higher hardness is required, it is preferred to use a low-melting polyester fibre and/or a low-melting polypropylene copolymer fibre and, in this case, it is preferred that the polyester fibres and/or polypropylene fibres are spot-adhered by a heat treatment process before the organic solvent is evaporated. The hard coated layer on the periphery of the resultant ink occlusion material forms a small space between the main body of the writing instrument and the ink occlusion material when the ink occlusion material is subsequently inserted into the cylindrical main body of the instrument. The space serves to provide a path for air to be displaced by injected ink in an ink-injecting process and also as the path for air to replace by the ink flow onto the paper during writing with the completed instrument. An ink occlusion material having an equilibrium moisture regain of 0.75 to 1.6% at 20°C and 95% RH can be prepared according to the present invention. An equilibrium moisture regain of higher than 1.6% improves the ink retention but decreases the ink utility markedly, while that of lower than 0.75% lowers the ink retention. Thus, both are unsatisfactory. Brief Description of the Drawings Fig. 1 shows a cross section of the fibre bundle No. 8 in Example 1 in which two types of fibre present a sea-island form. Fig. 2 shows a cross section of the fibre bundle No. 3 in Example 1 in which two types of fibre are almost uniformly mixed. Fig. 3 shows a cross section of the fibre bundle No. 4 in Example 1 in which two types of fibre are uniformly mixed. Detailed Description of the preferred Embodiment The present invention will be illustrated by Examples in more detail as follows. Example 1 A bias-cut acrylic synthetic fibre having a fineness of 3 deniers and a cut length of 102 mm was carded and gilled or drawing in the same manner as in a conventional worsted spinning process to prepare a sliver (A) of 40 g/m. In the same manner, a bias-cut polyester fibre having a fineness of 3 deniers and a cut length of 102 mm was carded and gilled or drawn to prepare a sliver (B) of 40 g/m. The slivers (A) and (B) were mixed together by gilling or drawing as shown in Table 1 and the resultant sliver of 40 g/m was twisted (5 times/m) and then immersed in a 20% acetone solution of tetramethylene sulfone and squeezed with a rubber roller (to 50% pick-up) and passed through an air circulating oven at 90°C to remove acetone and then passed through a far-infrared drier held at 200°C to remove tetramethylene sulfone and at the same time to spot-adhere the acrylic synthetic fibres. Finally, the bundle was passed through a cutter to prepare a 100 mm length of cylindrical ink occlusion material. The length of ink occlusion material was inserted into a cylindrical body of a writing instrument (inner diameter of 16 mm) in the form of a pen. The ink used comprised aqueous pigments. In accordance with the above-described procedures, twelve fibre bundles were prepared, the sliver mixing condition, that is, the number of slivers (A) and (B) or the degree of doubling, and the number of sliver mixing process being varied as shown in Table 1 and the lengths of ink occlusion material were inserted into the body of a writing instrument. Properties, such as ink retainability and ink utilization ratio, of thus of thus obtained writing instruments were determined. The results are shown in Table 1. From the result of Table, 1, it can be seen that the products prepared by using two types of fibre in a ratio specified by the present invention to give sea-island form cross section of fibre bundle (Nos. 1, 2 and 8 to 10) are excellent in the ink retainability and ink utilization ratio, but the products with a different mixing ratio of fibres (Nos. 6 and 11) and the products in which the fibres are uniformly mixed (Nos. 3 and 4) give unsatisfactory results. Example 2 A bias-cut acrylic synthetic fibre having a fineness of 3 deniers and a cut length of 102 mm was carded and gilled or drawn in a same manner as in conventional worsted spinning to prepare a sliver (A) of 40 g/m. In a same manner, a mixed stock of bias-cut polyester fibre having a fineness of 3 deniers and a cut length of 102 mm and 80.2 weight % of a low-melting polyester fibre having the same denier and the same cut length as above was carded and gilled or drawn to prepare a sliver (B) of 40 g/m. 5 of the sliver (A) and 3 of the sliver (B) were mixed together twice by gilling or drawing and the resultant sliver of 40 g/m was twisted as shown in Table 2 and then immersed in a 20% acetone solution of tetramethylene sulfone and squeezed with a rubber roller (to 50% pick-up) and passed through an air circulating oven at 90°C to remove acetone and then passed through a far-infrared drier held at 200°C to remove tetramethylene sulfone and at the same time to spot adhere the acrylic synthetic fibres and the polyester fibres. Finally, the bundle was passed through a cutter to prepare a 100 mm length of cylindrical ink occlusion material. The length of ink occlusion material was inserted into a cylindrical main body of a writing instrument (inner diameter of 16 mm) and ink retention was determined using an aqueous ink. The results are shown in Table 2 together with the frequency of fibre escape from the sliver (frequency of troubling) in the series of processes after twisting. No. Number of twist T/m Frequency of troubling times/3hrs. Ink retainability 13 0 10 o ○ 14 1 1 o ○ 15 5 0 o ○ 16 10 0 o ○ 17 15 0 ○ 18 30 0 ○ 19 60 0 X From the results shown in Table 2, it can be seen that the products twisted according to the present invention show no fibre escape or substantially no fibre escape from the sliver, can be easily handled and have excellent ink retention. As described above, the present invention can provide reliably an ink occlusion material without trouble such as fibre escape from the sliver and is excellent in both ink retainability and ink utilization ratio. Further, since the ink occlusion material of the present invention is prepared by swelling and/or dissolving a part of the fibres to spot-adhere them with no use of a thermosetting resin, no unreacted residue of a curing agent, a treating agent and the like deposits on the fibres and adhesion between the fibres is uniform. Furthermore, neither deterioration of the ink due to chemical reaction nor poor writing caused by the clogging of ink due to the unevenness of pores as the result of uneven adhesion occurs and thus the liquid ink can be reliably supplied.

Claims: An ink occlusion material for writing instruments, in which said material comprises a bundle of a mixture of an acrylic synthetic fibre, as one type of fibre, with at least one hydrophobic fibre, as another type of fibre, selected from polyester fibres and polypropylene fibres in a weight ration of 20 to 70 : 80 to 30, the two types of fibres are drawn so as to present a sea-island form in the cross section of said bundle and spot-adhered by partial melt-adhesion of said acrylic synthetic fibre and said bundle is twisted by an amount of 1 to 30 T/m. A method for the preparation of an ink occlusion material for writing instruments, in which a crimped acrylic fibre, as one type of fibre, is mixed with at least one crimped hydrophobic fibre, as another type of fibre, selected from polyester fibres and polypropylene fibres in a weight ratio of 20 to 70 : 80 to 30 to form a bundle wherein the mixed fibres are arranged parallel to a fibre axis direction so that the two type fibres present a sea-island form in the cross section of the bundle and the mixed fibres are then twisted by an amount of 1 to 30 T/m and an organic solvent which can dissolve said acrylic fibre is applied to the fibre bundle and the bundle is dried and then heat-treated at a temperature not lower than the activation temperature of said organic solvent to melt-adhere a portion of said acrylic fibres.

Inventors: ARAI, KENJI, KOMIYA, KUNIHIKO, YAMAMOTO, TOSHIHIRO
Applicants: KANEBO LTD.
Application year: 1989
Main classification: B43K1
IPC codes: B43K5, B43K1, B43K8, D02G3, C09D11