DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0019] Referring to FIGS. 1 to 4, there is illustrated one exemplary mode of trim cover assembly (T) in accordance with the present invention, which is to undergo a subsequent foaming process.

[0020] As can be seen from the cross-sectional view of FIG. 1, the trim cover assembly (T) is formed by sewing together a plurality of separate cover materials (A) into the illustrative three-dimensional configuration. Designations (A1) denote sewn connection corner portions of the thus-formed trim cover assembly. As far as the present embodiment is concerned, the trim cover assembly (T) is of such a generally cubic shape conforming to a predetermined outer shape of a headrest, by way of example, and has an injection hole (A2) formed in one wall of the trim cover assembly (T) in order to allow insertion of an injection nozzle therethrough as will be explained later.

[0021] FIG. 1 shows, in cross-section, a first foaming die (40) and a second foaming die (41), which are fit engageable with each other so as to receive the foregoing trim cover assembly (T) therein for a subsequent foaming process.

[0022] In accordance with the present invention, each cover material (A) of the trim cover assembly (T) is comprised of a top cover layer (1) and a slab foam wadding layer (2) laminated to the reverse side of the top cover layer (1).

[0023] The top cover layer (1) is such a known air-permeable material as a woven material, non-woven fabric, a leather material or any other proper air-permeable cover material normally used for a vehicle seat, headrest, armrest or other interior items in a vehicle or automobile.

[0024] But, the slab foam wadding layer (2) in the present invention is formed from a soft urethane foam material with a continuous cellular structure. As will be elaborated, its thickness is preferably 3 mm to 8 mm, and an air permeability of that foam wadding layer (2) is preset within the range from 0.2 cc/cm²/sec. to 1 cc/cm²/sec.

[0025] Now, a description will be made of a foaming operation to subject the above-described trim cover assembly (T) to foaming in the dies (40) (41) on the understanding that a resulting foamed product or a resulting headrest (P) is to be formed thereby for instance.

[0026] At first, a preformed three-dimensional trim cover assembly (T) with the above-discussed two-layer and air-permeable structure is provided. A pair of suitable first and second die elements (40) (41) are also provided, which each has a predetermined shape of inner die surface conforming to a half of the outer shape of the trim cover assembly (T). Designation (42) denotes a through-hole formed in the mating boundaries respective of the first and second die elements (40) (41), which is adapted for allowing insertion of an injection nozzle (N) therethrough. Although not shown, the injection nozzle (N) is operatively connected with a suitable supply device for supplying a liquid foam agent thereto, so that, in operation, a certain amount of the liquid foam agent (L) is injected from the nozzle (N) in such a manner as seen in FIG. 1.

[0027] Then, as shown in FIG. 1, an entirety of the trim cover assembly (T) is placed in position within the mated first and second die elements (40) (41), while disposing a headrest frame (C) centrally of the two die elements, such that the injection hole (A2) of the trim cover assembly is aligned with the through-hole (42) of the die elements (40) (41). Under such state, the injection nozzle (N) is inserted through those two aligned holes (A2) (42) and then a predetermined amount of the liquid foam agent (L) is injected from the nozzle (N) into the inside of the trim cover assembly (T).

[0028] At this stage, it is important to preset the amount of the liquid foam agent (L) to be injected in the trim cover assembly (T), because it is a factor for determining the degree of foaming pressure as known in the art. Thus, a proper amount of the liquid foaming agent (L) is injected in the trim cover assembly (T) in order to impregnate that particular liquid foam agent in a predetermined depth of the slab foam wadding layer (2) and thereby form an appropriate impregnation ratio (at l2, say, about 30% to 40%, for instance) of cured foaming agent or an impermeable film, as indicated by (20), relative to a whole thickness (l1) of the slab foam wadding layer (2). That is, it is an essential aspect of the present invention to avoid full occupation of such film (20) in the slab foam wadding layer (2) and also to prevent that film (20) from reaching the top cover layer (1), as shown in FIG. 4. Preferably, the liquid foaming agent (L) should be impregnated in at most half of the thickness of the slab foam wadding layer (2).

[0029] For that purpose, for example, suppose that the thickness of the slab foam wadding layer (2) is 5 mm, it is found optimal to set the foregoing degree of foaming pressure to approximately 0.1 kg in order to successfully maintain the above-noted impregnation proportion of the liquid foaming agent (L) in the 5 mm thickness of slab foam wadding layer (2), which substantially corresponds to the designation (l2) shown in FIG. 4. This was confirmed by experiments conducted on a number of different sample cover materials each of this kind of two-layer structure having such air permeable top cover layer and slab foam wadding layer with different sizes and scales.

[0030] Now, in practice, a foaming is effected to an entirety of the trim cover assembly (T), frame (C) and injected liquid foaming agent (L) within the tightly engaged dies (40, 41) under the following conditions:

[0031] a) The air permeability of the slab foam wadding layer (2) is set to be 0.2 cc/cm²/sec.,

[0032] b) The degree of foaming pressure is set to be approximately 0.1 kg, and

[0033] c) The thickness of the slab foam wadding layer (2) is 5 mm.

[0034] Note: As known in the art, the degree of foaming pressure depends on an amount of liquid foaming agent to be injected in the trim cove assembly with respect to an inner volume defined in the dies (40) (41).

[0035] As a result thereof, there was produced a resulting headrest body (P) as shown in FIG. 3, in which a mass of foam padding or foam cushion member (B) created from the liquid foaming agent (L) is filled within the trim cover assembly (T) together with the headrest frame (C). It is therefore observed and appreciated that:

[0036] (i) The liquid foaming agent (L) is impregnated evenly in the slab foam wadding layer (2) at a proper ratio of impregnation, i.e. approx. 2 mm, relative to a whole thickness, i.e. 5 mm, of that slab foam wadding layer (2), and cured therein to form approx. 2 mm thickness of an impermeable film layer (20) between the top cover layer (1) and a foam cushion member (B) being created from the liquid foaming agent (L), as in FIG. 4. Accordingly, such film layer (20) serves to enclose a whole inner space of trim cover assembly (T) and prevent escape of air therethrough, thereby allowing an increasing foamed mass of liquid foaming agent, or an outwardly increasing foaming pressure, to be applied evenly to all the inner walls of trim cover assembly (T) during foaming process, so that the outer surfaces of trim cover assembly (T) are in an optimum stretched state. In addition thereto, an outward pressure given from the increased mass of foam cushion member (B) created from the liquid foaming agent (L) effectively brings each of the cover materials (A) or the trim cover assembly (T) to pressed contact with the inner die surfaces of the dies (40, 41) in conformity therewith. Thus, it is practically possible to attain a neatly finished and desired outer appearance of resulting headrest body (P) without any crease and slack portion therein.

[0037] Also, the liquid foaming agent (L) is impregnated and cured in the sewn connection portions (A1), and particularly filing seam or needle holes therealong (not shown), thereby insuring to prevent leakage of the liquid foaming agent (L) itself from the seam or needle holes.

[0038] In this context, experiments show that use of slab foam wadding layer (2) with the air permeability of over 1 cc/cm²/sec. results in undesired penetration of liquid foaming agent (L) past through that slab foam wadding layer (20) to reach the top cover layer (1). In that instance, a substantive area of the top cover layer (1) becomes hardened to lose its stretchable property, as a result of which, the outer surfaces of trim cover assembly (T) are not uniformly stretched, with a plenty of objectionable creases and slack portions caused therein. On the other hand, experiments show that use of slab foam wadding layer (2) with the air permeability of less than 0.1 cc/cm²/sec. results in reducing air escape therethrough and thus an excessive exertion of foaming pressure upon the trim cover assembly (T) to the degree of causing the liquid foaming agent (L) to leak outwardly through the seam or needle holes of the sewn connection portions (A1).

[0039] (ii) Even if an air is trapped in the boundary between the liquid foaming agent (L) and slab foam wadding layer (2) during the foaming process, the air permeability of top cover layer (1) and the non-excessive impregnation of the liquid foaming agent (L) in the slab foam wadding layer (2) are effective in not only forcing such trapped air into the slab foam wadding layer (2), but also causing the air to flow therethrough and escape through the permeable top cover layer (1) to the outside of the trim cover assembly (T). This prevents creation of any trapped air region in local areas of trim cover assembly (T) which are adjacent to the outer surfaces of the resultant headrest (P), thus avoiding such unpleasant seating touch and problems as stated in the description of prior art.

[0040] (iii) As stated above, the liquid foaming agent (L) is impregnated in the slab foam wadding layer (2) at a small proportion relative to the whole thickness of the latter (2). Therefore, the liquid foaming agent (L) is not impregnated outwardly through the slab foam wadding layer (2) and does not reach the top cover layer (1), neither, so that the cured layer of the foaming agent (L), i.e. the film (20), is not formed beneath the top cover layer (1), thus giving an original soft cushiony touch of the hardest body (P) to a passenger.

[0041] While having described the present invention, it should be understood that the invention is not limited to the illustrated embodiment, but other modification, replacement, and addition may be applied thereto without departing from the scopes of the appended claims.