JP2007000167A - Tennis ball and manufacturing method of tennis ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tennis ball excellent in peel strength of a core and a felt part, repulsion characteristics and a ball hitting feeling, and a manufacturing method of the tennis ball capable of joining the core and the felt part by uniformly forming an adhesive layer having a prescribed thickness with excellent workability in the state that an infiltration degree to the felt part is appropriate without using a solvent. <P>SOLUTION: The tennis ball 1 is provided with the core 2, the adhesive layer 10 and a jacket 3. The jacket 3 is composed of a melton part 4 and a seam 5. The adhesive layer 10 is formed by uniformly applying a water-based adhesive material containing sodium polyacrylate for ≥0.2 mass% and ≤5.0 mass% as a thickener to the melton by a prescribed film thickness by a knife coating method in the state that the infiltration degree to the melton is appropriate, drying it, then sticking the melton part 4 to the core 2 and volcanizing it. For the tennis ball 1, the peel strength of the core 2 and the melton part 4 is excellent and the repulsion characteristics and the ball hitting feeling are excellent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tennis ball used for hard tennis and a method for manufacturing the same.

  A tennis ball is composed of a rubber core made of a hollow sphere and an outer skin covering the surface of the core. The outer skin contributes to protecting the core, stabilizing the flight of the tennis ball by optimizing the air resistance, improving the appearance, and improving the feeling of touch. Further, the outer skin determines basic performance such as durability and feel at impact.

  For the outer skin, a woven felt (hereinafter referred to as "melton") is often used. Melton is composed of warp and weft yarns. In general meltons, spun yarns in which nylon fibers and wool are mixed are used as weft yarns, and cotton yarns are used as warp yarns. When a melton is manufactured, first, weft and warp yarns are woven to obtain an original fabric. Usually, the original fabric is woven by a special method called satin weaving. The raw fabric is brushed and fluff is scraped from the weft yarn. Furthermore, the raw fabric is shrunk, and the fluffs are entangled and hardened densely. In this way, a thick melton having a good texture can be obtained.

JP-A-2004-89613, JP-hull warp and weft have been used is Melton constructed in woven, basis weight of the Melton is at 660 g / ^{m 2} or more 790 g / ^{m 2} or less, The density of the weft yarn is 100/10 cm or more and 160/10 cm or less, and the weft yarn is a spun yarn in which a chemical fiber and wool are mixed, and the mass ratio of the chemical fiber and wool is 0.65 / 1. The invention of the tennis ball that is 0.85 / 1 or less is disclosed.

  By the way, as a method of bonding the core and the melton, a method in which a solid rubber sheet is sandwiched between them and heat and pressure are applied, or an adhesive prepared by dissolving the solid rubber in an organic solvent is applied to the adhesive surface of the melton. There is a method in which after applying and drying the solvent, this is bonded to the core and heat and pressure are applied. In the former method, since the desired solid rubber sheet is very thin, it is difficult to produce the sheet uniformly, and the latter method is usually employed.

  As a specific method, a core coated with an adhesive containing a crosslinking agent is coated with another adhesive containing a vulcanization accelerator and coated with melton, and an adhesive is coated on the melton adhesive surface. Thereafter, there is a method of applying heat and pressure by pasting together with a core coated with another adhesive beforehand. In the latter method, the bonded state is satisfactorily maintained by the other adhesive, and therefore the latter method is usually used.

Examples of coating methods include spray coating, spray coating, spread coating such as film coating, knife coating, etc. Spraying often clogs the nozzle, and film transfer is a great way to create a film with a uniform thickness. Since a large-scale facility is required, a knife coating method that is simple and easy to manage is usually used. The knife coating method is a spread coating that applies adhesive to the adhesive surface and applies the adhesive, and then applies a knife (blade) such as a doctor knife to the adhesive surface to apply the adhesive. It is a method to do.
JP 2004-89613 A

  In recent years, the influence of solvents on human health and the environment has become a problem, and it is required to use solvents as little as possible. If no solvent is used, solid rubber will be used in bulk or water-based adhesive dissolved in water will be used, but solid rubber will be used in bulk as described above. It is difficult to produce a sheet, and it is inappropriate because a large-scale facility is required to make the film uniform.

  The aqueous adhesive is applied by the aforementioned knife coating method. In this case, it is necessary to add additives to control the degree of penetration into Melton and the amount of adhesion. Conventionally, methylcellulose, sodium carboxymethylcellulose and xanthan gum are used as thickeners, and their viscosity and solid content ratio The degree of penetration and the amount of adhesion are controlled only by controlling the amount of water. However, there is a problem that an adhesive containing these is likely to penetrate into the Melton adhesive surface as compared with the solvent-based adhesive, and cannot be controlled to satisfy both the penetration degree and the adhesion amount. That is, when the viscosity has an appropriate degree of penetration, the amount of adhesion decreases and the peel strength decreases. When the viscosity is suitable for the adhesion amount, the penetration amount is too large, the flexibility of the melton is lost, and the rebound characteristics and the feel at impact are deteriorated.

  Also, at the time of application, it is necessary to supply a sufficient amount of adhesive stably and uniformly to the blade edge of the knife. In the case of a solvent-based adhesive, the adhesive itself is dragged in the transport direction of the melton. A sufficient amount of adhesive is supplied stably and uniformly. When the viscosity of the aqueous adhesive using the thickener is lowered, a sufficient amount of adhesive is supplied to the blade edge, but the penetration degree is too high. If the viscosity is increased, the adhesive attached to the blade of the knife will not move to the cutting edge, the amount of adhesive supplied to the cutting edge will be insufficient, and it will be necessary to replace or clean the blade frequently. There's a problem. In this case, it is difficult to produce an apparatus for feeding the adhesive to the blade edge, and it is expensive, so it is difficult to use this adhesive industrially. Therefore, when the water-based adhesive containing the thickener is used, there is a problem that an adhesive layer having a predetermined thickness cannot be uniformly formed with good workability.

  The above problems also occur when a needle felt obtained by repeatedly piercing and fluffing a nonwoven fabric with a needle is used as the outer skin of a tennis ball.

  The object of the present invention is that the penetration degree to the felt part is appropriate and the adhesive layer having a predetermined thickness is interposed between the core and the felt part of the outer skin, so that the peel strength, the resilience characteristic and the shot feeling are good. Without using a tennis ball and a solvent, an adhesive layer having a predetermined thickness is uniformly formed with good workability and the core and the felt part are joined with an appropriate degree of penetration into the felt part. To provide a method for manufacturing tennis balls that can be used.

The tennis ball according to the present invention is:
(1) a hollow core,
(2) a felt part covering the core, and (3) an adhesive layer interposed between the felt part and the core,
The adhesive layer is formed by applying an aqueous composition containing 0.2 mass% or more and 5.0 mass% or less of a polyacrylic acid metal salt to the felt part.

  Preferably, the aqueous adhesive contains latex. Here, latex refers to an emulsion in which natural rubber or synthetic rubber is dispersed in an aqueous solution.

A method for manufacturing a tennis ball according to the present invention includes:
(1) forming a core;
(2) An application step of spreading and applying an adhesive composed of an aqueous composition containing 0.2% by mass or more and 5.0% by mass or less of a polyacrylic acid metal salt on the back surface of the felt part;
(3) drying the spread adhesive,
(4) The process of bonding the felt part dried with the adhesive to the core, and (5) The core bonded with the felt part is put into a mold, and the core and the felt part are pressed and heated. The process of joining.

  Preferably, in the coating step, an adhesive composed of an aqueous composition containing latex and a polyacrylic acid metal salt of 0.2% by mass or more and 5.0% by mass or less is spread and coated on the back surface of the felt part. It is a process.

  Preferably, the coating step is a step of spreading and applying an adhesive composed of an aqueous composition containing 0.2 wt% to 5.0 wt% of a polyacrylic acid metal salt on the back surface of the felt portion by a knife coat method. It is.

  Preferably, the coating step is a step of spreading and coating an adhesive made of an aqueous composition containing 0.2% by mass or more and 5.0% by mass or less of sodium polyacrylate on the felt back surface.

A method for manufacturing a tennis ball according to the present invention includes:
(1) forming a core;
(2) A step of applying an adhesive containing a crosslinking agent to the core,
(3) An adhesive made of an aqueous composition containing latex, a metal salt of a polyacrylic acid of 0.2% by mass or more and 5.0% by mass or less, and a vulcanization accelerator is spread on the back surface of the felt part. The process of
(4) A step of drying the spread adhesive.
(5) The process of bonding the felt part which dried the adhesive agent to the core, and (6) The core which bonded the felt part is thrown into a shaping | molding die, and this core is pressurized and heated, and a core, a felt part, The process of joining.

  In the tennis ball of the present invention, the adhesive layer interposed between the core and the felt part has a uniform and uniform thickness, and the penetration degree to the felt part is appropriate. Good strength, rebound characteristics and feel at impact.

  In the method for manufacturing a tennis ball of the present invention, the felt part has an application step of spreading and applying a water-based adhesive containing 0.2 to 5.0% by mass of a polyacrylic acid metal salt. Without use, the adhesive layer can be formed on the felt part with good workability in a state where the penetration degree into the felt part is appropriate and the thickness is uniformly predetermined.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a partially cutaway sectional view showing a tennis ball 1 according to an embodiment of the present invention. The tennis ball 1 includes a core 2, an adhesive layer 10 and an outer skin 3. The core 2 is a hollow sphere and is formed from a crosslinked rubber (that is, an elastic material). The thickness of the core 2 is usually 3 mm to 4 mm. An internal pressure of about 80 KPa is applied to the core 2 with respect to the atmospheric pressure. Thereby, the resilience performance is imparted to the tennis ball 1. The outer skin 3 includes a melton portion 4 and a seam 5 as felt portions, and covers almost the entire surface of the core 2. The outer skin 3 is fixed to the surface of the core 2 by an adhesive layer 10.

  FIG. 2 is a plan view showing the melton part 4 used in the outer skin 3 of the tennis ball 1 of FIG. The melton part 4 has a substantially eyebrows shape. The melton portions 4 are curved so that the end portions face each other, and the two melton portions 4 are alternately combined and attached to the surface of the core 2. A seam 5 is formed at a joint portion between the two melton portions 4.

  The core 2 is formed by crosslinking a rubber composition. Suitable base rubbers include natural rubber, polybutadiene, polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polychloroprene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, isobutylene. -Isoprene copolymer and acrylic rubber are exemplified. Two or more of these rubbers may be used in combination. Preferred base rubbers are natural rubber, polybutadiene and styrene-butadiene copolymers. From the viewpoint of resilience performance, strength and cost, natural rubber is particularly preferable.

  The form of crosslinking of the rubber composition is not particularly limited, but usually sulfur crosslinking is employed. The compounding amount of sulfur is preferably 0.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of rubber. When the blending amount is less than the above range, the strength of the core 2 may be insufficient. In this respect, the amount to be blended is more preferably equal to or greater than 1.0 part by weight, and particularly preferably equal to or greater than 1.5 parts by weight. When the amount exceeds the above range, the feel at impact of the tennis ball 1 may be impaired. In this respect, the amount to be blended is more preferably equal to or less than 4.5 parts by weight, still more preferably equal to or less than 4.0 parts by weight, and particularly preferably equal to or less than 3.5 parts by weight.

  A filler may be blended in the rubber composition for the purpose of improving the strength and adjusting the specific gravity. Suitable fillers include zinc oxide, clay, calcium carbonate, magnesium carbonate, silica and carbon black.

  The rubber composition may be blended with a vulcanization accelerator, a crosslinking aid, a softening agent, a reinforcing agent, an anti-aging agent, a coloring agent, a processing aid, and the like, if necessary.

  FIG. 3 is a schematic enlarged cross-sectional view showing the melton part 4 of FIG. In this figure, the upper side is the front side of the melton part 4, and the lower side is the back side of the melton part 4 (the side that comes into contact with the core 2 when attached to the core 2). The melton part 4 is configured by weaving warp yarn 6 and weft yarn 7. The weaving structure is usually 8 satin weaves. Of course, weaving structures such as four satin weaves, five satin weaves, six satin weaves, and seven satin weaves may be used. For the warp yarn 6, cotton yarn is used. For the weft yarn 7, a spun yarn in which a chemical fiber and wool are mixed is used. Fluff 8 is generated on the weft 7 by raising.

Examples of the chemical fibers used for the weft yarn 7 include nylon fibers, polyester fibers such as polyethylene terephthalate fibers, and rayon fibers. Two or more chemical fibers may be used in combination. Nylon fiber is particularly preferable from the viewpoint that it has appropriate strength and can be obtained at low cost. The basis weight of the melton part 4 is determined in the range of 450 g / m ^{2 to} 900 g / m ² in accordance with the desired tennis ball life.

  The adhesive layer 10 is formed by drying and vulcanizing an aqueous adhesive containing a latex, a thickener, a vulcanization accelerator, and a vulcanization aid. As the latex, natural rubber latex is preferable from the viewpoint of securing strength after bonding. The latex preferably contains a rubber solid content of 30% by mass or more and 70% by mass or less. Specific examples of the natural rubber latex include trade name “UNIMAC LATEX LA” produced by UNIMAC Co., Ltd. in Thailand.

  The water-based adhesive contains a polyacrylic acid metal salt as a thickener. The polyacrylic acid metal salt is a metal salt of a polymer of acrylic acid. Examples of the polyacrylic acid metal salt include a sodium salt and a potassium salt. The sodium salt is preferable because it rolls appropriately when the water-based adhesive is applied to the melton by the knife coat method. Specific examples of sodium polyacrylate include trade names “AQUALIC DL series”, “AQUALIC H series IH”, “AQUALIC H series FH” and “AQUALIC H series MH” of Nippon Shokubai Co., Ltd. Is mentioned. From the viewpoint of obtaining an appropriate viscosity, “AQUALIC H Series FH” is preferable.

  Content of polyacrylic acid metal salt shall be 0.2 mass% or more and 5.0 mass% or less with respect to the whole aqueous adhesive. The lower limit of the content of the polyacrylic acid metal salt is preferably 0.4% by mass, more preferably 0.6% by mass, and the upper limit is preferably 4.0% by mass, more preferably 3.5% by mass. It is.

  When the content of the polyacrylic acid metal salt is less than 0.2% by mass, when the aqueous adhesive is applied to the melton by the knife coating method, the penetration amount of the aqueous adhesive into the melton increases, and the knife edge The amount of the water-based adhesive supplied to the film becomes insufficient, resulting in poor film formation. Water-based adhesives containing polyacrylic acid metal salts have a “repelling” property for a short time, and the water-based adhesive is dried before the water-based adhesive soaks into the melton. By setting, the “repelling” property can be used, but when the content of the polyacrylic acid metal salt is less than 0.2% by mass, the “repelling” property is poor and the amount of penetration into the melton increases. . If the amount of penetration into the melton is large, the amount of lubricant present between the knife and the melton will be small, and it will be difficult to form a film.

  On the other hand, if the content of the polyacrylic acid metal salt exceeds 5.0% by mass, the “repelling” property increases, the amount of penetration into the melton decreases, and the peel strength decreases.

  You may decide to mix | blend methylcellulose, sodium carboxymethylcellulose, and a xanthan gum with a water-system adhesive agent, and to adjust a penetration degree and the adhesion amount. Specific examples of methylcellulose include the trade name “Metroze 90SH100000” of Shin-Etsu Chemical Co., Ltd., and specific examples of sodium carboxymethylcellulose include the trade name “Sunrose F1400MC” of Nippon Paper Chemicals Co., Ltd.

  The vulcanization accelerator is preferably a dithiocarbamate salt from the viewpoint of strength and scorch, and EZ (zinc diethyldithiocarbamate) is particularly preferable. As a specific example, there is a trade name “Noxeller EZ” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. The vulcanization accelerator is preferably added in an amount of 0.5 to 4.0 parts by mass with respect to 100 parts by mass of the rubber component (solid content).

  Zinc oxide is preferred as the vulcanization aid. The vulcanization aid is preferably added in an amount of 1.0 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component.

  A filler may be added to the water-based adhesive for the purpose of adjusting specific gravity and the like. Examples of the filler include calcium carbonate and silica. The filler is preferably added in an amount of 20% by mass or less based on 100 parts by mass of the rubber component.

  The vulcanizing agent is not necessary when an adhesive containing sulfur as a vulcanizing agent is applied to the core 2 side, but may be added when the adhesive is applied to the core 2 side. When added, it is preferable to add 0.2 parts by weight or more and 3.0 parts by weight or less with respect to 100 parts by weight of the rubber component.

  Below, the manufacturing method of the tennis ball 1 is demonstrated. First, the rubber composition for the core 2 is blended, kneaded, and extruded by an extruder, and the strand is cut for each desired mass to obtain a plug. This plug is put into a half shell mold composed of a convex part and a concave part. The plug is pressurized and heated in the mold to obtain a bowl-shaped half shell.

  The obtained half shell is polished at the edge and the polishing powder is removed, and then an adhesive prepared by dissolving the rubber composition in a solvent is applied. Two half shells are bonded to one half shell in a state where tablets of ammonium chloride and sodium nitrite and water are charged. This is put into a core mold and vulcanized to obtain the core 2. During the vulcanization, the tablet and water are heated, and a chemical reaction occurs between ammonium chloride and sodium nitrite. Nitrogen gas is generated by this chemical reaction, and an internal pressure is applied to the core 2. The internal pressure may be applied by other means. The difference between the internal pressure of the core 2 and the atmospheric pressure at the new product stage is usually 60 KPa or more and 120 KPa or less. The internal pressure at the new stage means the internal pressure of the tennis ball 1 immediately after the container is opened after being stored in a pressurized container and sold through a normal distribution channel.

  The core 2 is usually coated with an adhesive containing natural rubber latex, sulfur and zinc oxide after the surface is polished. This adhesive may not be applied. However, it is preferable to apply it because sulfur in the adhesive reacts with the vulcanization accelerator in the aqueous adhesive and crosslinks, and the core 2 and the melton part 4 are firmly joined.

  On the other hand, the water-based adhesive is applied to the back surface of the melton by a knife coat method. FIG. 4 is a partially enlarged cross-sectional view showing a state where the water-based adhesive 12 is applied to the melton 11. In FIG. 4, a doctor knife 13 is pressed against the sheet-like melton 11. The water-based adhesive 12 is supplied before the cutting edge of the doctor knife 13 that is the transport destination of the melton 11 and is smoothed by the doctor knife 13. Since the aqueous solution of polyacrylic acid metal salt has stringiness, the aqueous adhesive 12 has stringiness. When the aqueous adhesive 12 is applied to the melton 11, the aqueous adhesive 12 is difficult to break, It tends to be a film. The water-based adhesive 12 flows into the blade edge of the doctor knife 13 and rolls smoothly and without staying partially. In the present embodiment, the water-based adhesive 12 has stringiness and is supplied uniformly and sufficiently to the cutting edge of the doctor knife 13, so that the penetration of the water-based adhesive 12 into the melton 11 is appropriate. Thus, the water-based adhesive 12 is applied to the melton 11 with a predetermined amount of thickness uniformly without breaking. The tennis ball 1 thus obtained has a uniform hardness under the outer skin 3.

  The water-based adhesive 12 is dried before it soaks into the melton 11, and moisture is evaporated. Thereafter, the melton 11 is cut into eyebrows to form the melton portion 4. The size and shape of the melton part 4 are appropriately selected. After the white rubber as the seam adhesive is applied to the side surface (cut section) of the melton part 4, the two melton parts 4 are bonded to the core 2. This is put into a tennis ball mold, heated and pressurized to obtain the tennis ball 1. In addition, after the melton 11 is cut into eyebrows and the melton portion 4 is formed, the water-based adhesive 12 may be applied to the back surface thereof. In the seam adhesive, a rubber composition adjusted to a predetermined color by a colorant is dissolved in an organic solvent such as naphtha, and a melton part 4 in which a large number of sheets are superimposed is immersed in the seam adhesive. It may be attached to the side surface of.

  Hereinafter, the effects of the present invention will be clarified based on examples, but the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by weight of natural rubber, 60 parts by weight of clay, 5 parts by weight of zinc oxide (trade name “Zinc Hana 1” from Mitsui Kinzoku Kogyo Co., Ltd.), 1 part by weight of stearic acid, 1 part by weight of sulfur and a vulcanization accelerator Kneaded a rubber composition consisting of 1 part by weight of zinc diethyldithiocarbamate (trade name “Noxeller EZ” of Ouchi Shinsei Chemical Co., Ltd.), extruded by an extruder, and cut for each desired mass, Got a plug. This plug was put into a half shell mold and vulcanized at 150 ° C. for 2 minutes to obtain a half shell.

  The obtained half shell was coated with an adhesive prepared by dissolving the rubber composition in a solvent after polishing the edge and removing the polishing powder. And two half shells were bonded together in the state by which the said tablet and water were thrown into one half shell. This was put into a core mold having a diameter of 60 mm and vulcanized at 150 ° C. for 7 minutes to obtain a core. After polishing the surface of the core, 160 parts by mass of natural rubber latex (100 parts by mass in terms of solid content), 1 part by mass of sulfur, and zinc oxide (trade name “Zinc Hana 1” from Mitsui Kinzoku Co., Ltd.) An adhesive composed of 3 parts by mass of the composition was applied.

  Natural rubber latex (trade name “UNIMAC LATEX LA” of UNIMAC Corporation: solid content 62.5 parts by mass), 160 parts by mass of sodium polyacrylate (trade name “AQUALIC H series FH” of Nippon Shokubai Co., Ltd.) 1 part by mass, 5 parts by mass of methyl cellulose (trade name “Metros 90SH10000D” from Shin-Etsu Chemical Co., Ltd.), 420 parts by mass of water, 3 parts by mass of zinc oxide (trade name “Zinc Hana 1” from Mitsui Kinzoku Co., Ltd.) And an aqueous adhesive having the composition shown in Table 1 below, consisting of 2 parts by mass of zinc diethyldithiocarbamate (trade name “Noxeller EZ” from Ouchi Shinsei Chemical Co., Ltd.) as a vulcanization accelerator. This aqueous adhesive was applied to Melton twice by a knife coating method. Next, after the melton was punched out into an eyebrow-shaped melton as shown in FIG. 2, white rubber was applied to the side surface of the melton, and the two meltons were bonded to the surface of the core by an automatic laminating machine. . This was vulcanized in a tennis ball mold at 135 ° C. for 10 minutes to obtain a tennis ball of Example 1.

[Examples 2 to 20 and Comparative Examples 1 to 4]
The tennis balls of Examples 2 to 14 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the composition of the aqueous adhesive was as shown in Table 1 and Tables 2 and 3 below. It was.

[Comparative Example 5]
100 parts by mass of natural rubber (solid), 420 parts by mass of volatile rubber oil, 5 parts by mass of zinc oxide (trade name “Zinc Hana 1” from Mitsui Kinzoku Kogyo Co., Ltd.), and zinc diethyldithiocarbamate as a vulcanization accelerator (Trade name “Noxeller EZ” from Ouchi Shinsei Chemical Co., Ltd.) A solvent-based adhesive consisting of 2 parts by mass was prepared, and this solvent-based adhesive was applied to Melton in the same manner as in Example 1. A tennis ball of Comparative Example 5 was obtained.

[Measurement of penetration degree]
The penetration degree was determined by applying a water-based adhesive or a solvent-based adhesive, cutting the dried melton, and observing the cut surface with a microscope to measure the depth. The results are shown in Tables 1, 2 and 3 above.

[Measurement of peel strength]
When a tennis ball is disassembled and cut into a 25 mm wide and 100 mm long test piece, the ends of the melton and core are peeled off by hand, and each end is gripped and pulled by a tensile tester chuck. The strength of was measured. The average value of the upper peak average value and the lower peak average value of the stress-strain curve obtained by the measurement was adopted as the peel strength. The results are shown in Tables 1, 2 and 3 above.

[Evaluation of feel at impact]
Ten players were allowed to hit a tennis ball to evaluate the hit feeling. “A” was assigned when the number of players who answered “good hitting feeling” was 8 or more, “B” when 4 or more and 7 or less, and “C” when 3 or less. “A good feel at impact” specifically refers to a state of “good separation” and “good bounce”. The results are shown in Tables 1, 2 and 3 above.

  Since the tennis ball of Comparative Example 1 has a low content of sodium polyacrylate in the water-based adhesive, the degree of penetration is greater than that of the Examples and the feel at impact is inferior. Since the tennis ball of Comparative Example 2 has a high content of sodium polyacrylate, the water-based adhesive is repelled from the melton portion, the degree of penetration is reduced, and the peel strength is inferior. Further, the amount of adhesion is small and the feel at impact is poor. In the tennis balls of Comparative Example 3 and Comparative Example 4, since the aqueous adhesive does not contain sodium polyacrylate, the amount of adhesion increases and the degree of penetration also increases in order to uniformly apply the adhesive without breaking. That is why the shot feeling is inferior. When the penetration degree of the water-based adhesive is large, the melton part is stiff like FRR and does not bounce, resulting in a heavy shot feeling. And since this water-based adhesive penetrates into the inside of the melton part and the amount interposed between the melton part and the core is small, the peel strength becomes small. The tennis ball of each example is excellent in all evaluation items. Although the evaluation content of the tennis ball of Comparative Example 5 is the same as that of the example, since the adhesive contains a solvent, it is inappropriate to use it because of the influence on human health and the environment.

  The present invention can be applied to a tennis ball using a needle felt, and can also be applied to a case where an aqueous adhesive is applied to a felt by spread coating with a roller, a spatula, or the like.

FIG. 1 is a partially cutaway sectional view showing a tennis ball according to an embodiment of the present invention. FIG. 2 is a plan view showing a melton portion of the outer skin of the tennis ball of FIG. FIG. 3 is a schematic enlarged sectional view showing the melton of FIG. FIG. 4 is a partially enlarged cross-sectional view showing a state in which the water-based adhesive is applied to the melton.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Tennis ball 2 ... Core 3 ... Outer skin 4 ... Melton part 5 ... Seam 6 ... Warp yarn 7 ... Weft yarn 8 ... Fluff 10 ... Adhesive layer 11 ... Melton 12 ... Water-based adhesive 13 ... Doctor knife

Claims (7)

A hollow core, a felt part covering the core, and an adhesive layer interposed between the felt part and the core,
The adhesive layer is a tennis ball formed by applying an aqueous composition containing a polyacrylic acid metal salt in an amount of 0.2% by mass or more and 5.0% by mass or less to a felt part.   The tennis ball according to claim 1, wherein the aqueous composition contains latex. Forming a core;
On the back surface of the felt part, an application step of spreading and applying an adhesive composed of an aqueous composition containing 0.2% by mass or more and 5.0% by mass or less of a metal polyacrylate,
Drying the spread adhesive, and
Bonding the felt part dried with the adhesive to the core;
A method for manufacturing a tennis ball, comprising: a step of putting a core bonded with the felt part into a mold and pressurizing and heating the core to join the core and the felt part.   The coating step is a step of spreading and applying an adhesive composed of an aqueous composition containing latex and a metal salt of a polyacrylic acid metal of 0.2% by mass or more and 5.0% by mass or less on the back surface of the felt part. The method for manufacturing a tennis ball according to claim 3.   The coating step is a step in which an adhesive composed of an aqueous composition containing 0.2 mass% or more and 5.0 mass% or less of a polyacrylic acid metal salt is spread-coated on the back surface of the felt portion by a knife coating method. Item 5. A method for manufacturing a tennis ball according to Item 3 or 4.   The coating step is a step of spreading and applying an adhesive composed of an aqueous composition containing 0.2% by mass or more and 5.0% by mass or less of sodium polyacrylate on the back surface of the felt part. The manufacturing method of the tennis ball in any one. Forming a core;
Applying an adhesive containing a crosslinking agent to the core;
A step of spreading and applying an adhesive composed of an aqueous composition containing latex, a metal salt of polyacrylic acid of 0.2% by mass or more and 5.0% by mass or less, and a vulcanization accelerator on the back surface of the felt part; ,
Drying the spread adhesive, and
Bonding the felt part dried with the adhesive to the core;
A method for manufacturing a tennis ball, comprising: a step of putting a core bonded with the felt part into a mold and pressurizing and heating the core to join the core and the felt part.

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